Bulk and interfacial structures of reline deep eutectic solvent: A molecular dynamics study.

PubMed

Kaur, Supreet; Sharma, Shobha; Kashyap, Hemant K

2017-11-21

We apply all-atom molecular dynamics simulations to describe the bulk morphology and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio, near neutral and charged graphene electrodes. For the bulk phase structural investigation, we analyze the simulated real-space radial distribution functions, X-ray/neutron scattering structure functions, and their partial components. Our study shows that both hydrogen-bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. Further, we examine the variation of number density profiles, orientational order parameters, and electrostatic potentials near the neutral and charged graphene electrodes with varying electrode charge density. The present study reveals the presence of profound structural layering of not only the ionic components of reline but also urea near the electrodes. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structures up to a distance of 1.2 nm from the respective electrodes. The observation of positive values of the surface potential at zero charge indicates the presence of significant nonelectrostatic attraction between the choline cation and graphene electrode. The computed differential capacitance (C d ) for reline exhibits an asymmetric bell-shaped curve, signifying different variation of C d with positive and negative surface potentials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-Ruiz, F. J.; Blas, F. J., E-mail: felipe@uhu.es; Moreno-Ventas Bravo, A. I.

We determine the interfacial properties of a symmetrical binary mixture of equal-sized spherical Lennard-Jones molecules, σ{sub 11} = σ{sub 22}, with the same dispersive energy between like species, ϵ{sub 11} = ϵ{sub 22}, but different dispersive energies between unlike species low enough to induce phase separation. We use the extensions of the improved version of the inhomogeneous long-range corrections of Janecek [J. Phys. Chem. B 110, 6264 (2006)], presented recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2009)] and Martínez-Ruiz et al. [J. Chem. Phys. 141, 184701 (2014)], to deal with the interaction energy and microscopic components ofmore » the pressure tensor. We perform Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of the symmetrical mixture with different cut-off distances r{sub c} and in combination with the inhomogeneous long-range corrections. The pressure tensor is obtained using the mechanical (virial) and thermodynamic route. The liquid-liquid interfacial tension is also evaluated using three different procedures, the Irving-Kirkwood method, the difference between the macroscopic components of the pressure tensor, and the test-area methodology. This allows to check the validity of the recent extensions presented to deal with the contributions due to long-range corrections for intermolecular energy and pressure tensor in the case of binary mixtures that exhibit liquid-liquid immiscibility. In addition to the pressure tensor and the surface tension, we also obtain density profiles and coexistence densities and compositions as functions of pressure, at a given temperature. According to our results, the main effect of increasing the cut-off distance r{sub c} is to sharpen the liquid-liquid interface and to increase the width of the biphasic coexistence region. Particularly interesting is the presence of a relative minimum in the total density profiles of the symmetrical mixture. This minimum is related with a desorption of the molecules at the interface, a direct consequence of a combination of the weak dispersive interactions between unlike species of the symmetrical binary mixture, and the presence of an interfacial region separating the two immiscible liquid phases in coexistence.« less

Fluids density functional theory and initializing molecular dynamics simulations of block copolymers

NASA Astrophysics Data System (ADS)

Brown, Jonathan R.; Seo, Youngmi; Maula, Tiara Ann D.; Hall, Lisa M.

2016-03-01

Classical, fluids density functional theory (fDFT), which can predict the equilibrium density profiles of polymeric systems, and coarse-grained molecular dynamics (MD) simulations, which are often used to show both structure and dynamics of soft materials, can be implemented using very similar bead-based polymer models. We aim to use fDFT and MD in tandem to examine the same system from these two points of view and take advantage of the different features of each methodology. Additionally, the density profiles resulting from fDFT calculations can be used to initialize the MD simulations in a close to equilibrated structure, speeding up the simulations. Here, we show how this method can be applied to study microphase separated states of both typical diblock and tapered diblock copolymers in which there is a region with a gradient in composition placed between the pure blocks. Both methods, applied at constant pressure, predict a decrease in total density as segregation strength or the length of the tapered region is increased. The predictions for the density profiles from fDFT and MD are similar across materials with a wide range of interfacial widths.

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.

1991-01-01

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.

1989-01-01

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Role of oxygen functional groups for structure and dynamics of interfacial water on low rank coal surface: a molecular dynamics simulation

NASA Astrophysics Data System (ADS)

You, Xiaofang; Wei, Hengbin; Zhu, Xianchang; Lyu, Xianjun; Li, Lin

2018-07-01

Molecular dynamics simulations were employed to study the effects of oxygen functional groups for structure and dynamics properties of interfacial water molecules on the subbituminous coal surface. Because of complex composition and structure, the graphite surface modified by hydroxyl, carboxyl and carbonyl groups was used to represent the surface model of subbituminous coal according to XPS results, and the composing proportion for hydroxyl, carbonyl and carboxyl is 25:3:5. The hydration energy with -386.28 kJ/mol means that the adsorption process between water and coal surface is spontaneous. Density profiles for oxygen atoms and hydrogen atoms indicate that the coal surface properties affect the structural and dynamic characteristics of the interfacial water molecules. The interfacial water exhibits much more ordering than bulk water. The results of radial distribution functions, mean square displacement and local self-diffusion coefficient for water molecule related to three oxygen moieties confirmed that the water molecules prefer to absorb with carboxylic groups, and adsorption of water molecules at the hydroxyl and carbonyl is similar.

Comparison of united-atom potentials for the simulation of vapor-liquid equilibria and interfacial properties of long-chain n-alkanes up to n-C100.

PubMed

Müller, Erich A; Mejía, Andrés

2011-11-10

Canonical ensemble molecular dynamics (MD) simulations are reported which compute both the vapor-liquid equilibrium properties (vapor pressure and liquid and vapor densities) and the interfacial properties (density profiles, interfacial tensions, entropy and enthalpy of surface formation) of four long-chained n-alkanes: n-decane (n-C(10)), n-eicosane (n-C(20)), n-hexacontane (n-C(60)), and n-decacontane (n-C(100)). Three of the most commonly employed united-atom (UA) force fields for alkanes (SKS: Smit, B.; Karaborni, S.; Siepmann, J. I. J. Chem. Phys. 1995,102, 2126-2140; J. Chem. Phys. 1998,109, 352; NERD: Nath, S. K.; Escobedo, F. A.; de Pablo, J. J. J. Chem. Phys. 1998, 108, 9905-9911; and TraPPE: Martin M. G.; Siepmann, J. I. J. Phys. Chem. B1998, 102, 2569-2577.) are critically appraised. The computed results have been compared to the available experimental data and those fitted using the square gradient theory (SGT). In the latter approach, the Lennard-Jones chain equation of state (EoS), appropriately parametrized for long hydrocarbons, is used to model the homogeneous bulk phase Helmholtz energy. The MD results for phase equilibria of n-decane and n-eicosane exhibit sensible agreement both to the experimental data and EoS correlation for all potentials tested, with the TraPPE potential showing the lowest deviations. However, as the molecular chain increases to n-hexacontane and n-decacontane, the reliability of the UA potentials decreases, showing notorious subpredictions of both saturated liquid density and vapor pressure. Based on the recommended data and EoS results for the heaviest hydrocarbons, it is possible to attest, that in this extreme, the TraPPE potential shows the lowest liquid density deviations. The low absolute values of the vapor pressure preclude the discrimination among the three UA potentials studied. On the other hand, interfacial properties are very sensitive to the type of UA potential thus allowing a differentiation of the potentials. Comparing the interfacial tension MD results to the available experimental data and SGT results, the TraPPE model exhibits the lowest deviations for all hydrocarbons.

Measuring Interfacial Tension Between Immiscible Liquids

NASA Technical Reports Server (NTRS)

Rashidnia, Nasser; Balasubramaniam, R.; Delsignore, David M.

1995-01-01

Glass capillary tube technique measures interfacial tension between two immiscible liquids. Yields useful data over fairly wide range of interfacial tensions, both for pairs of liquids having equal densities and pairs of liquids having unequal densities. Data on interfacial tensions important in diverse industrial chemical applications, including enhanced extraction of oil; printing; processing foods; and manufacture of paper, emulsions, foams, aerosols, detergents, gel encapsulants, coating materials, fertilizers, pesticides, and cosmetics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-Ruiz, F. J.; Blas, F. J., E-mail: felipe@uhu.es; Centro de Investigación de Física Teórica y Matemática, Universidad de Huelva, 21071 Huelva

We propose an extension of the improved version of the inhomogeneous long-range corrections of Janeček [J. Phys. Chem. B 110, 6264–6269 (2006)], presented recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2009)] to account for the intermolecular potential energy of spherical, rigid, and flexible molecular systems, to deal with the contributions to the microscopic components of the pressure tensor due to the dispersive long-range corrections. We have performed Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of spherical Lennard-Jones molecules with different cutoff distances, r{sub c} = 2.5, 3, 4, and 5σ. In addition,more » we have also considered cutoff distances r{sub c} = 2.5 and 3σ in combination with the inhomogeneous long-range corrections proposed in this work. The normal and tangential microscopic components of the pressure tensor are obtained using the mechanical or virial route in combination with the recipe of Irving and Kirkwood, while the macroscopic components are calculated using the Volume Perturbation thermodynamic route proposed by de Miguel and Jackson [J. Chem. Phys. 125, 164109 (2006)]. The vapour-liquid interfacial tension is evaluated using three different procedures, the Irving-Kirkwood method, the difference between the macroscopic components of the pressure tensor, and the Test-Area methodology. In addition to the pressure tensor and the surface tension, we also obtain density profiles, coexistence densities, vapour pressure, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the cutoff distance and the long-range corrections on these properties. According to our results, the main effect of increasing the cutoff distance (at fixed temperature) is to sharpen the vapour-liquid interface, to decrease the vapour pressure, and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases, the width of the tangential microscopic component of the pressure tensor profile increases, and the surface tension increases as the cutoff distance is larger. We have also checked the effect of the impulsive contribution to the pressure due to the discontinuity of the intermolecular interaction potential when it is cut. If this contribution is not accounted for in the calculation of the microscopic components of the pressure tensor, incorrect values of both components as well as a wrong structure along the vapour-liquid interface are obtained.« less

Molecular dynamics simulation of water at mineral surfaces: Structure, dynamics, energetics and hydrogen bonding

NASA Astrophysics Data System (ADS)

Kalinichev, A. G.; Wang, J.; Kirkpatrick, R.

2006-05-01

Fundamental molecular-level understanding of the properties of aqueous mineral interfaces is of great importance for many geochemical and environmental systems. Interaction between water and mineral surfaces substantially affects the properties of both phases, including the reactivity and functionality of the substrate surface, and the structure, dynamics, and energetics of the near surface aqueous phase. Experimental studies of interfacial water structure and dynamics using surface-sensitive techniques such as sum-frequency vibrational spectroscopy or X-ray and neutron reflectivity are not always possible for many practically important substrates, and their results often require interpretation concerning the atomistic mechanisms responsible for the observed behavior. Molecular computer simulations can provide new insight into the underlying molecular- level relationships between the inorganic substrate structure and composition and the structure, ordering, and dynamics of interfacial water. We have performed a series of molecular dynamics (MD) computer simulations of aqueous interfaces with several silicates (quartz, muscovite, and talc) and hydroxides (brucite, portlandite, gibbsite, Ca/Al and Mg/Al double hydroxides) to quantify the effects of the substrate mineral structure and composition on the structural, transport, and thermodynamic properties of water on these mineral surfaces. Due to the prevalent effects of the development of well-interconnected H-bonding networks across the mineral- water interfaces, all the hydroxide surfaces (including a fully hydroxylated quartz surface) show very similar H2O density profiles perpendicular to the interface. However, the predominant orientations of the interfacial H2O molecules and their detailed 2-dimensional near-surface structure and dynamics parallel to the interface are quite different reflecting the differences in the substrate structural charge distribution and the density and orientations of the surface OH groups. The H2O density profiles and other structural and dynamic characteristics of water at the two siloxane surfaces are very different from each other and from the hydroxide surfaces, since the muscovite surface is negatively charged and hydrophilic, while the talc surface is electrostatically neutral and hydrophobic. In general, at hydrophilic neutral surfaces both donating and accepting H-bonds from the H2O molecules are contributing to the development of the interfacial H-bond network, whereas at hydrophilic but charged surfaces only accepting or donating H-bonds with H2O molecules are possible. At the hydrophobic talc surface H-bonds among H2O molecules dominate the interfacial H-bond network and the water-surface interactions are very weak. The first water layer at all substrates is well ordered parallel to the surface, reflecting substrate crystal structures and indicating the reduced translational and orientational mobility of interfacial H2O molecules. At longer time scale (~100ps) their dynamics can be decomposed into a slow, virtually frozen, regime due to the substrate- bound H2O and a faster regime of almost free water reflecting the dynamics far from the surface. At shorter times (>10ps) the two dynamical regimes are superimposed. The much higher ordering of interfacial water (compared to bulk liquid) can not be adequately described as simply "ice-like". To some extent, it rather resembles the behavior of supercooled water.

Structural changes in block copolymer micelles induced by cosolvent mixtures†

PubMed Central

Kelley, Elizabeth G.; Smart, Thomas P.; Jackson, Andrew J.; Sullivan, Millicent O.

2013-01-01

We investigated the influence of tetrahydrofuran (THF) addition on the structure of poly(1,2-butadiene-b-ethylene oxide) [PB-PEO] micelles in aqueous solution. Our studies showed that while the micelles remained starlike, the micelle core-corona interfacial tension and micelle size decreased upon THF addition. The detailed effects of the reduction in interfacial tension were probed using contrast variations in small angle neutron scattering (SANS) experiments. At low THF contents (high interfacial tensions), the SANS data were fit to a micelle form factor that incorporated a radial density distribution of corona chains to account for the starlike micelle profile. However, at higher THF contents (low interfacial tensions), the presence of free chains in solution affected the scattering at high q and required the implementation of a linear combination of micelle and Gaussian coil form factors. These SANS data fits indicated that the reduction in interfacial tension led to broadening of the core-corona interface, which increased the PB chain solvent accessibility at intermediate THF solvent fractions. We also noted that the micelle cores swelled with increasing THF addition, suggesting that previous assumptions of the micelle core solvent content in cosolvent mixtures may not be accurate. Control over the size, corona thickness, and extent of solvent accessible PB in these micelles can be a powerful tool in the development of targeting delivery vehicles. PMID:24282441

Structural changes in block copolymer micelles induced by cosolvent mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kelley, Elizabeth G.; Smart, Thomas P.; Jackson, Andrew J.

2012-11-26

We investigated the influence of tetrahydrofuran (THF) addition on the structure of poly(1,2-butadiene-b-ethylene oxide) [PB-PEO] micelles in aqueous solution. Our studies showed that while the micelles remained starlike, the micelle core-corona interfacial tension and micelle size decreased upon THF addition. The detailed effects of the reduction in interfacial tension were probed using contrast variations in small angle neutron scattering (SANS) experiments. At low THF contents (high interfacial tensions), the SANS data were fit to a micelle form factor that incorporated a radial density distribution of corona chains to account for the starlike micelle profile. However, at higher THF contents (lowmore » interfacial tensions), the presence of free chains in solution affected the scattering at high q and required the implementation of a linear combination of micelle and Gaussian coil form factors. These SANS data fits indicated that the reduction in interfacial tension led to broadening of the core-corona interface, which increased the PB chain solvent accessibility at intermediate THF solvent fractions. We also noted that the micelle cores swelled with increasing THF addition, suggesting that previous assumptions of the micelle core solvent content in cosolvent mixtures may not be accurate. Control over the size, corona thickness, and extent of solvent accessible PB in these micelles can be a powerful tool in the development of targeting delivery vehicles.« less

Surface force and vibrational spectroscopic analyses of interfacial water molecules in the vicinity of methoxy-tri(ethylene glycol)-terminated monolayers: mechanisms underlying the effect of lateral packing density on bioinertness.

PubMed

Sekine, Taito; Asatyas, Syifa; Sato, Chikako; Morita, Shigeaki; Tanaka, Masaru; Hayashi, Tomohiro

Unequivocal dependence of bioinertness of self-assembled monolayers of methoxy-tri(ethylene glycol)-terminated alkanethiol (EG3-OMe SAMs) on their packing density has been a mystery for more than two decades. We tackled this long-standing question by performing surface force and surface-enhanced infrared absorption (SEIRA) spectroscopic measurements. Our surface force measurements revealed a physical barrier of interfacial water in the vicinity of the Au-supported EG3-OMe SAM (low packing density), whereas the Ag-supported one (high packing density) did not possess such interfacial water. In addition, the results of SEIRA measurements clearly exhibited that hydrogen bonding states of the interfacial water differ depending on the substrates. We also characterized the bioinertness of these SAMs by protein adsorption tests and adhesion assays of platelet and human umbilical vein endothelial cells. The hydrogen bonding states of the interfacial water and water-induced interaction clearly correlated with the bioinertness of the SAMs, suggesting that the interfacial water plays an important role determining the interaction of the SAMs with biomolecules and cells.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Zhuoyu; Yuan, Hongtao; Xie, Yanwu

Carrier density and disorder are two crucial parameters that control the properties of correlated two-dimensional electron systems. Furthermore, in order to disentangle their individual contributions to quantum phenomena, independent tuning of these two parameters is required. By utilizing a hybrid liquid/solid electric dual-gate geometry acting on the conducting LaAlO 3/SrTiO 3 heterointerface, we obtain an additional degree of freedom to strongly modify the electron confinement profile and thus the strength of interfacial scattering, independent from the carrier density. A dual-gate controlled nonlinear Hall effect is a direct manifestation of this profile, which can be quantitatively understood by a Poisson–Schrödinger sub-bandmore » model. In particular, the large nonlinear dielectric response of SrTiO 3 enables a very wide range of tunable density and disorder, far beyond that for conventional semiconductors. This study provides a broad framework for understanding various reported phenomena at the LaAlO 3/SrTiO 3 interface.« less

Dual-Gate Modulation of Carrier Density and Disorder in an Oxide Two-Dimensional Electron System

DOE PAGES

Chen, Zhuoyu; Yuan, Hongtao; Xie, Yanwu; ...

2016-09-08

Carrier density and disorder are two crucial parameters that control the properties of correlated two-dimensional electron systems. Furthermore, in order to disentangle their individual contributions to quantum phenomena, independent tuning of these two parameters is required. By utilizing a hybrid liquid/solid electric dual-gate geometry acting on the conducting LaAlO 3/SrTiO 3 heterointerface, we obtain an additional degree of freedom to strongly modify the electron confinement profile and thus the strength of interfacial scattering, independent from the carrier density. A dual-gate controlled nonlinear Hall effect is a direct manifestation of this profile, which can be quantitatively understood by a Poisson–Schrödinger sub-bandmore » model. In particular, the large nonlinear dielectric response of SrTiO 3 enables a very wide range of tunable density and disorder, far beyond that for conventional semiconductors. This study provides a broad framework for understanding various reported phenomena at the LaAlO 3/SrTiO 3 interface.« less

Unveiling structural, chemical and magnetic interfacial peculiarities in ε-Fe2O3/GaN (0001) epitaxial films.

PubMed

Ukleev, Victor; Suturin, Sergey; Nakajima, Taro; Arima, Taka-Hisa; Saerbeck, Thomas; Hanashima, Takayasu; Sitnikova, Alla; Kirilenko, Demid; Yakovlev, Nikolai; Sokolov, Nikolai

2018-06-07

The metastable ε-Fe 2 O 3 is known to be the most intriguing ferrimagnetic and multiferroic iron oxide phase exhibiting a bunch of exciting physical properties both below and above room temperature. The present paper unveils the structural and magnetic peculiarities of a few nm thick interface layer discovered in these films by a number of techniques. The polarized neutron reflectometry data suggests that the interface layer resembles GaFeO 3 in composition and density and is magnetically softer than the rest of the ε-Fe 2 O 3 film. While the in-depth density variation is in agreement with the transmission electron microscopy measurements, the layer-resolved magnetization profiles are qualitatively consistent with the unusual wasp-waist magnetization curves observed by superconducting quantum interference device magnetometry. Interestingly a noticeable Ga diffusion into the ε-Fe 2 O 3 films has been detected by secondary ion mass spectroscopy providing a clue to the mechanisms guiding the nucleation of exotic metastable epsilon ferrite phase on GaN at high growth temperature and influencing the interfacial properties of the studied films.

Microscopic image processing systems for measuring nonuniform film thickness profiles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, A.H.; Plawsky, J.L.; DasGupta, S.

1994-01-01

In very thin liquid films. transport processes are controlled by the temperature and the interfacial intermolecular force field which is a function of the film thickness profile and interfacial properties. The film thickness profile and interfacial properties can be measured most efficiently using a microscopic image processing system. IPS, to record the intensity pattern of the reflected light from the film. There are two types of IPS: an image analyzing interferometer (IAI) and/or an image scanning ellipsometer (ISE). The ISE is a novel technique to measure the two dimensional thickness profile of a nonuniform, thin film, from 1 nm upmore » to several {mu}m, in a steady state as well as in a transient state. It is a full field imaging technique which can study every point on the surface simultaneously with high spatial resolution and thickness sensitivity, i.e., it can measure and map the 2-D film thickness profile. Using the ISE, the transient thickness profile of a draining thin liquid film was measured and modeled. The interfacial conditions were determined in situ by measuring the Hamaker constant. The ISE and IAI systems are compared.« less

Shock Initiation and Equation of State of Ammonium Nitrate

NASA Astrophysics Data System (ADS)

Robbins, David; Sheffield, Steve; Dattelbaum, Dana; Chellappa, Raja; Velisavljevic, Nenad

2013-06-01

Ammonium nitrate (AN) is a widely used fertilizer and mining explosive commonly found in ammonium nitrate-fuel oil. Neat AN is a non-ideal explosive with measured detonation velocities approaching 4 km/s. Previously, we reported a thermodynamically-complete equation of state for AN based on its maximum density, and showed that near-full density AN did not initiate when subjected to shock input conditions up to 22 GPa. In this work, we extend these initial results, by presenting new Hugoniot data for intermediate density neat AN obtained from gas gun-driven plate impact experiments. AN at densities from 1.8 to 1.5 g/cm3 were impacted into LiF windows using a two-stage light gas gun. Dual VISARs were used to measure the interfacial particle velocity wave profile as a function of time following impact. The new Hugoniot data, in addition to updates to thermodynamic parameters derived from structural analysis and vibrational spectroscopy measurements in high pressure diamond anvil cell experiments, are used to refine the unreacted EOS for AN. Furthermore, shock initiation of neat AN was observed as the initial porosity increased (density decreased). Insights into the relationship(s) between initial density and shock initiation sensitivity are also presented, from evidence of shock initiation in the particle velocity profiles obtained for the lower density AN samples.

Density functional theory of gas-liquid phase separation in dilute binary mixtures

NASA Astrophysics Data System (ADS)

Okamoto, Ryuichi; Onuki, Akira

2016-06-01

We examine statics and dynamics of phase-separated states of dilute binary mixtures using density functional theory. In our systems, the difference of the solvation chemical potential between liquid and gas Δ {μ\\text{s}} (the Gibbs energy of transfer) is considerably larger than the thermal energy {{k}\\text{B}}T for each solute particle and the attractive interaction among the solute particles is weaker than that among the solvent particles. In these conditions, the saturated vapor pressure increases by {{k}\\text{B}}Tn2\\ell\\exp ≤ft(Δ {μ\\text{s}}/{{k}\\text{B}}T\\right) , where n2\\ell is the solute density added in liquid. For \\exp ≤ft(Δ {μ\\text{s}}/{{k}\\text{B}}T\\right)\\gg 1 , phase separation is induced at low solute densities in liquid and the new phase remains in gaseous states, even when the liquid pressure is outside the coexistence curve of the solvent. This explains the widely observed formation of stable nanobubbles in ambient water with a dissolved gas. We calculate the density and stress profiles across planar and spherical interfaces, where the surface tension decreases with increasing interfacial solute adsorption. We realize stable solute-rich bubbles with radius about 30 nm, which minimize the free energy functional. We then study dynamics around such a bubble after a decompression of the surrounding liquid, where the bubble undergoes a damped oscillation. In addition, we present some exact and approximate expressions for the surface tension and the interfacial stress tensor.

Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pradhan, P. C.; Majhi, A.; Nayak, M., E-mail: mnayak@rrcat.gov.in

2016-07-28

Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B{sub 4}C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusionmore » increases, the physical density of W layer decreases and that of B{sub 4}C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.« less

Interfacial Ordering and Accompanying Divergent Capacitance at Ionic Liquid-Metal Interfaces.

PubMed

Limmer, David T

2015-12-18

A theory is constructed for dense ionic solutions near charged planar walls that is valid for strong interionic correlations. This theory predicts a fluctuation-induced, first-order transition and spontaneous charge density ordering at the interface, in the presence of an otherwise disordered bulk solution. The surface ordering is driven by applied voltage and results in an anomalous differential capacitance, in agreement with recent simulation results and consistent with experimental observations of a wide array of systems. Explicit forms for the charge density profile and capacitance are given. The theory is compared with numerical results for the charge frustrated Ising model, which is also found to exhibit a voltage driven first-order transition.

Interfacial Ordering and Accompanying Divergent Capacitance at Ionic Liquid-Metal Interfaces

NASA Astrophysics Data System (ADS)

Limmer, David T.

2015-12-01

A theory is constructed for dense ionic solutions near charged planar walls that is valid for strong interionic correlations. This theory predicts a fluctuation-induced, first-order transition and spontaneous charge density ordering at the interface, in the presence of an otherwise disordered bulk solution. The surface ordering is driven by applied voltage and results in an anomalous differential capacitance, in agreement with recent simulation results and consistent with experimental observations of a wide array of systems. Explicit forms for the charge density profile and capacitance are given. The theory is compared with numerical results for the charge frustrated Ising model, which is also found to exhibit a voltage driven first-order transition.

Electrostatic Properties of Aqueous Salt Solution Interfaces: A Comparison of Polarizable and Non-Polarizable Ion Models

PubMed Central

Warren, G. Lee; Patel, Sandeep

2014-01-01

The effects of ion force field polarizability on the interfacial electrostatic properties of ~1 M aqueous solutions of NaCl, CsCl and NaI are investigated using molecular dynamics simulations employing both non-polarizable and Drude-polarizable ion sets. Differences in computed depth-dependent orientational distributions, “permanent” and induced dipole and quadrupole moment profiles, and interfacial potentials are obtained for both ion sets to further elucidate how ion polarizability affects interfacial electrostatic properties among the various salts relative to pure water. We observe that the orientations and induced dipoles of water molecules are more strongly perturbed in the presence of polarizable ions via a stronger ionic double layer effect arising from greater charge separation. Both anions and cations exhibit enhanced induced dipole moments and strong z alignment in the vicinity of the Gibbs dividing surface (GDS) with the magnitude of the anion induced dipoles being nearly an order of magnitude larger than those of the cations and directed into the vapor phase. Depth-dependent profiles for the trace and zz components of the water molecular quadrupole moment tensors reveal 40% larger quadrupole moments in the bulk phase relative to the vapor mimicking a similar observed 40% increase in the average water dipole moment. Across the GDS, the water molecular quadrupole moments increase non-monotonically (in contrast to the water dipoles) and exhibit a locally reduced contribution just below the surface due to both orientational and polarization effects. Computed interfacial potentials for the non-polarizable salts yield values 20 to 60 mV more positive than pure water and increase by an additional 30 to 100 mV when ion polarizability is included. A rigorous decomposition of the total interfacial potential into ion monopole, water and ion dipole, and water quadrupole components reveals that a very strong, positive ion monopole contribution is offset by negative contributions from all other potential sources. Water quadrupole components modulated by the water density contribute significantly to the observed interfacial potential increments and almost entirely explain observed differences in the interfacial potentials for the two chloride salts. By lumping all remaining non-quadrupole interfacial potential contributions into a single “effective” dipole potential, we observe that the ratio of quadrupole to “effective” dipole contributions range from 2:1 in CsCl to 1:1.5 in NaI suggesting that both contributions are comparably important in determining the interfacial potential increments. We also find that oscillations in the quadrupole potential in the double layer region are opposite in sign and partially cancel those of the “effective” dipole potential. PMID:18712908

Transition to turbulence in stratified shear flow: experiments in an inclined square duct

NASA Astrophysics Data System (ADS)

Meyer, Colin; Linden, Paul

2013-11-01

We describe laboratory experiments of countercurrent stratified shear flow in an inclined square duct. To achieve this, a long water tank was partitioned into regions of higher and lower density saltwater that are connected by an inclined square duct. The flow regime was characterized to be turbulent, intermittent, Holmboe or laminar as a function of the duct inclination, θ, and the density difference, Δρ , between the two reservoirs. The density difference and duct angle were systematically varied and a phase plane of flow regime was developed. The transition between the interrmittent regime and turbulence was experimentally determined to occur at θΔρ ~= 20 [degrees kg m-3]. This critical combination of parameters fits into the buoyancy-compensated Reynolds number scaling proposed by Brethouwer et al. (J. Fluid Mech., 2007). The turbulent interfacial thickness was found to be a function of the inclination angle, which can be predicted using the buoyancy lengthscale from Waite and Bartello (J. Fluid Mech., 2004) and others. Furthermore, we measured the density profiles at multiple points along the duct, and using these profiles, we modeled the entrainment at the interface. Support provided by the Winston Churchill Foundation of the United States.

On The Dynamics And Kinematics Of Two Fluid Phase Flow In Porous Media

DTIC Science & Technology

2015-06-16

fluid-fluid interfacial area density in a two-fluid-system. This dynamic equation set is unique to this work, and the importance of the modeled...saturation data intended to denote an equilibrium state is likely a sampling from a dynamic system undergoing changes of interfacial curvatures that are not... interfacial area density in a two-fluid-system. This dynamic equation set is unique to this work, and the importance of the modeled physics is shown

Passivation of GaSb using molecular beam epitaxy Y{sub 2}O{sub 3} to achieve low interfacial trap density and high-performance self-aligned inversion-channel p-metal-oxide-semiconductor field-effect-transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chu, R. L.; Chiang, T. H.; Hsueh, W. J.

2014-11-03

Molecular beam epitaxy deposited rare-earth oxide of Y{sub 2}O{sub 3} has effectively passivated GaSb, leading to low interfacial trap densities of (1–4) × 10{sup 12 }cm{sup −2} eV{sup −1} across the energy bandgap of GaSb. A high saturation drain current density of 130 μA/μm, a peak transconductance of 90 μS/μm, a low subthreshold slope of 147 mV/decade, and a peak field-effect hole mobility of 200 cm{sup 2}/V-s were obtained in 1 μm-gate-length self-aligned inversion-channel GaSb p-Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs). In this work, high-κ/GaSb interfacial properties were better in samples with a high substrate temperature of 200 °C than in those with high κ's deposited at room temperature, in terms of themore » interfacial electrical properties, particularly, the reduction of interfacial trap densities near the conduction band and the MOSFET device performance.« less

Interfacial Tension and Surface Pressure of High Density Lipoprotein, Low Density Lipoprotein, and Related Lipid Droplets

PubMed Central

Ollila, O. H. Samuli; Lamberg, Antti; Lehtivaara, Maria; Koivuniemi, Artturi; Vattulainen, Ilpo

2012-01-01

Lipid droplets play a central role in energy storage and metabolism on a cellular scale. Their core is comprised of hydrophobic lipids covered by a surface region consisting of amphiphilic lipids and proteins. For example, high and low density lipoproteins (HDL and LDL, respectively) are essentially lipid droplets surrounded by specific proteins, their main function being to transport cholesterol. Interfacial tension and surface pressure of these particles are of great interest because they are related to the shape and the stability of the droplets and to protein adsorption at the interface. Here we use coarse-grained molecular-dynamics simulations to consider a number of related issues by calculating the interfacial tension in protein-free lipid droplets, and in HDL and LDL particles mimicking physiological conditions. First, our results suggest that the curvature dependence of interfacial tension becomes significant for particles with a radius of ∼5 nm, when the area per molecule in the surface region is <1.4 nm2. Further, interfacial tensions in the used HDL and LDL models are essentially unaffected by single apo-proteins at the surface. Finally, interfacial tensions of lipoproteins are higher than in thermodynamically stable droplets, suggesting that HDL and LDL are kinetically trapped into a metastable state. PMID:22995496

Nb and Ta layer doping effects on the interfacial energetics and electronic properties of LaAlO3/SrTiO3 heterostructure: first-principles analysis.

PubMed

Nazir, Safdar; Behtash, Maziar; Cheng, Jianli; Luo, Jian; Yang, Kesong

2016-01-28

The two-dimensional electron gas (2DEG) formed at the n-type (LaO)(+1)/(TiO2)(0) interface in the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) has emerged as a prominent research area because of its great potential for nanoelectronic applications. Due to its practical implementation in devices, desired physical properties such as high charge carrier density and mobility are vital. In this respect, 4d and 5d transition metal doping near the interfacial region is expected to tailor electronic properties of the LAO/STO HS system effectively. Herein, we studied Nb and Ta-doping effects on the energetics, electronic structure, interfacial charge carrier density, magnetic moment, and the charge confinements of the 2DEG at the n-type (LaO)(+1)/(TiO2)(0) interface of LAO/STO HS using first-principles density functional theory calculations. We found that the substitutional doping of Nb(Ta) at Ti [Nb(Ta)@Ti] and Al [Nb(Ta)@Al] sites is energetically more favorable than that at La [Nb(Ta)@La] and Sr [Nb(Ta)@Sr] sites, and under appropriate thermodynamic conditions, the changes in the interfacial energy of HS systems upon Nb(Ta)@Ti and Nb(Ta)@Al doping are negative, implying that the formation of these structures is energetically favored. Our calculations also showed that Nb(Ta)@Ti and Nb(Ta)@Al doping significantly improve the interfacial charge carrier density with respect to that of the undoped system, which is because the Nb(Ta) dopant introduces excess free electrons into the system, and these free electrons reside mainly on the Nb(Ta) ions and interfacial Ti ions. Hence, along with the Ti 3d orbitals, the Nb 4d and Ta 5d orbitals also contribute to the interfacial metallic states; accordingly, the magnetic moments on the interfacial Ti ions increase significantly. As expected, the Nb@Al and Ta@Al doped LAO/STO HS systems show higher interfacial charge carrier density than the undoped and other doped systems. In contrast, Nb@Ti and Ta@Ti doped systems may show higher charge carrier mobility because of the lower electron effective mass.

Molecular dynamics simulations of n-hexane at 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lisal, Martin; Department of Physics, Faculty of Science, J. E. Purkinje University, 400 96 Usti n. Lab.; Izak, Pavel

Molecular dynamics simulations of n-hexane adsorbed onto the interface of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][Tf{sub 2}N]) are performed at three n-hexane surface densities, ranged from 0.7 to 2.3 {mu}mol/m{sup 2} at 300 K. For [bmim][Tf{sub 2}N] room-temperature ionic liquid, we use a non-polarizable all-atom force field with the partial atomic charges based on ab initio calculations for the isolated ion pair. The net charges of the ions are {+-}0.89e, which mimics the anion to cation charge transfer and polarization effects. The OPLS-AA force field is employed for modeling of n-hexane. The surface tension is computed using the mechanical route and itsmore » value decreases with increase of the n-hexane surface density. The [bmim][Tf{sub 2}N]/n-hexane interface is analyzed using the intrinsic method, and the structural and dynamic properties of the interfacial, sub-interfacial, and central layers are computed. We determine the surface roughness, global and intrinsic density profiles, and orientation ordering of the molecules to describe the structure of the interface. We further compute the survival probability, normal and lateral self-diffusion coefficients, and re-orientation correlation functions to elucidate the effects of n-hexane on dynamics of the cations and anions in the layers.« less

Molecular dynamics simulations of n-hexane at 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide interface.

PubMed

Lísal, Martin; Izák, Pavel

2013-07-07

Molecular dynamics simulations of n-hexane adsorbed onto the interface of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][Tf2N]) are performed at three n-hexane surface densities, ranged from 0.7 to 2.3 μmol/m(2) at 300 K. For [bmim][Tf2N] room-temperature ionic liquid, we use a non-polarizable all-atom force field with the partial atomic charges based on ab initio calculations for the isolated ion pair. The net charges of the ions are ±0.89e, which mimics the anion to cation charge transfer and polarization effects. The OPLS-AA force field is employed for modeling of n-hexane. The surface tension is computed using the mechanical route and its value decreases with increase of the n-hexane surface density. The [bmim][Tf2N]/n-hexane interface is analyzed using the intrinsic method, and the structural and dynamic properties of the interfacial, sub-interfacial, and central layers are computed. We determine the surface roughness, global and intrinsic density profiles, and orientation ordering of the molecules to describe the structure of the interface. We further compute the survival probability, normal and lateral self-diffusion coefficients, and re-orientation correlation functions to elucidate the effects of n-hexane on dynamics of the cations and anions in the layers.

Current-induced depairing in the Bi2Te3/FeTe interfacial superconductor

NASA Astrophysics Data System (ADS)

Kunchur, M. N.; Dean, C. L.; Moghadam, N. Shayesteh; Knight, J. M.; He, Q. L.; Liu, H.; Wang, J.; Lortz, R.; Sou, I. K.; Gurevich, A.

2015-09-01

We investigated current induced depairing in the Bi2Te3 /FeTe topological insulator-chalcogenide interface superconductor. The measured depairing current density provides information on the magnetic penetration depth and superfluid density, which in turn shed light on the nature of the normal state that underlies the interfacial superconductivity.

In Situ Neutron Depth Profiling of Lithium Metal-Garnet Interfaces for Solid State Batteries.

PubMed

Wang, Chengwei; Gong, Yunhui; Dai, Jiaqi; Zhang, Lei; Xie, Hua; Pastel, Glenn; Liu, Boyang; Wachsman, Eric; Wang, Howard; Hu, Liangbing

2017-10-11

The garnet-based solid state electrolyte (SSE) is considered a promising candidate to realize all solid state lithium (Li) metal batteries. However, critical issues require additional investigation before practical applications become possible, among which high interfacial impedance and low interfacial stability remain the most challenging. In this work, neutron depth profiling (NDP), a nondestructive and uniquely Li-sensitive technique, has been used to reveal the interfacial behavior of garnet SSE in contact with metallic Li through in situ monitoring of Li plating-stripping processes. The NDP measurement demonstrates predictive capabilities for diagnosing short-circuits in solid state batteries. Two types of cells, symmetric Li/garnet/Li (LGL) cells and asymmetric Li/garnet/carbon-nanotubes (LGC), are fabricated to emulate the behavior of Li metal and Li-free Li metal anodes, respectively. The data imply the limitation of Li-free Li metal anode in forming reliable interfacial contacts, and strategies of excessive Li and better interfacial engineering need to be investigated.

Interaction of a sodium ion with the water liquid-vapor interface

NASA Technical Reports Server (NTRS)

Wilson, M. A.; Pohorille, A.; Pratt, L. R.; MacElroy, R. D. (Principal Investigator)

1989-01-01

Molecular dynamics results are presented for the density profile of a sodium ion near the water liquid-vapor interface at 320 K. These results are compared with the predictions of a simple dielectric model for the interaction of a monovalent ion with this interface. The interfacial region described by the model profile is too narrow and the profile decreases too abruptly near the solution interface. Thus, the simple model does not provide a satisfactory description of the molecular dynamics results for ion positions within two molecular diameters from the solution interface where appreciable ion concentrations are observed. These results suggest that surfaces associated with dielectric models of ionic processes at aqueous solution interfaces should be located at least two molecular diameters inside the liquid phase. A free energy expense of about 2 kcal/mol is required to move the ion within two molecular layers of the free water liquid-vapor interface.

Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers.

PubMed

Gan, Zecheng; Xing, Xiangjun; Xu, Zhenli

2012-07-21

We investigate the effects of image charges, interfacial charge discreteness, and surface roughness on spherical electric double layer structures in electrolyte solutions with divalent counterions in the setting of the primitive model. By using Monte Carlo simulations and the image charge method, the zeta potential profile and the integrated charge distribution function are computed for varying surface charge strengths and salt concentrations. Systematic comparisons were carried out between three distinct models for interfacial charges: (1) SURF1 with uniform surface charges, (2) SURF2 with discrete point charges on the interface, and (3) SURF3 with discrete interfacial charges and finite excluded volume. By comparing the integrated charge distribution function and the zeta potential profile, we argue that the potential at the distance of one ion diameter from the macroion surface is a suitable location to define the zeta potential. In SURF2 model, we find that image charge effects strongly enhance charge inversion for monovalent interfacial charges, and strongly suppress charge inversion for multivalent interfacial charges. For SURF3, the image charge effect becomes much smaller. Finally, with image charges in action, we find that excluded volumes (in SURF3) suppress charge inversion for monovalent interfacial charges and enhance charge inversion for multivalent interfacial charges. Overall, our results demonstrate that all these aspects, i.e., image charges, interfacial charge discreteness, their excluding volumes, have significant impacts on zeta potentials of electric double layers.

Experimental study on interfacial area transport in downward two-phase flow

NASA Astrophysics Data System (ADS)

Wang, Guanyi

In view of the importance of two group interfacial area transport equations and lack of corresponding accurate downward flow database that can reveal two group interfacial area transport, a systematic database for adiabatic, air-water, vertically downward two-phase flow in a round pipe with inner diameter of 25.4 mm was collected to gain an insight of interfacial structure and provide benchmarking data for two-group interfacial area transport models. A four-sensor conductivity probe was used to measure the local two phase flow parameters and data was collected with data sampling frequency much higher than conventional data sampling frequency to ensure the accuracy. Axial development of local flow parameter profiles including void fraction, interfacial area concentration, and Sauter mean diameter were presented. Drastic inter-group transfer of void fraction and interfacial area was observed at bubbly to slug transition flow. And the wall peaked interfacial area concentration profiles were observed in churn-turbulent flow. The importance of local data about these phenomenon on flow structure prediction and interfacial area transport equation benchmark was analyzed. Bedsides, in order to investigate the effect of inlet conditions, all experiments were repeated after installing the flow straightening facility, and the results were briefly analyzed. In order to check the accuracy of current data, the experiment results were cross-checked with rotameter measurement as well as drift-flux model prediction, the averaged error is less than 15%. Current models for two-group interfacial area transport equation were evaluated using these data. The results show that two-group interfacial area transport equations with current models can predict most flow conditions with error less than 20%, except some bubbly to slug transition flow conditions and some churn-turbulent flow conditions. The disagreement between models and experiments could result from underestimate of inter-group void transfer.

Density, refractive index, interfacial tension, and viscosity of ionic liquids [EMIM][EtSO4], [EMIM][NTf2], [EMIM][N(CN)2], and [OMA][NTf2] in dependence on temperature at atmospheric pressure.

PubMed

Fröba, Andreas P; Kremer, Heiko; Leipertz, Alfred

2008-10-02

The density, refractive index, interfacial tension, and viscosity of ionic liquids (ILs) [EMIM][EtSO 4] (1-ethyl-3-methylimidazolium ethylsulfate), [EMIM][NTf 2] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), [EMIM][N(CN) 2] (1-ethyl-3-methylimidazolium dicyanimide), and [OMA][NTf 2] (trioctylmethylammonium bis(trifluoromethylsulfonyl)imide) were studied in dependence on temperature at atmospheric pressure both by conventional techniques and by surface light scattering (SLS). A vibrating tube densimeter was used for the measurement of density at temperatures from (273.15 to 363.15) K and the results have an expanded uncertainty ( k = 2) of +/-0.02%. Using an Abbe refractometer, the refractive index was measured for temperatures between (283.15 and 313.15) K with an expanded uncertainty ( k = 2) of about +/-0.0005. The interfacial tension was obtained from the pendant drop technique at a temperature of 293.15 K with an expanded uncertainty ( k = 2) of +/-1%. For higher and lower temperatures, the interfacial tension was estimated by an adequate prediction scheme based on the datum at 293.15 K and the temperature dependence of density. For the ILs studied within this work, at a first order approximation, the quantity directly accessible by the SLS technique was the ratio of surface tension to dynamic viscosity. By combining the experimental results of the SLS technique with density and interfacial tension from conventional techniques, the dynamic viscosity could be obtained for temperatures between (273.15 and 333.15) K with an estimated expanded uncertainty ( k = 2) of less than +/-3%. The measured density, refractive index, and viscosity are represented by interpolating expressions with differences between the experimental and calculated values that are comparable with but always smaller than the expanded uncertainties ( k = 2). Besides a comparison with the literature, the influence of structural variations on the thermophysical properties of the ILs is discussed in detail. The viscosities mostly agree with values reported in the literature within the combined estimated expanded uncertainties ( k = 2) of the measurements while our density and interfacial tension data differ by more than +/-1% and +/-5%.

Local epitaxial growth of ZrO2 on Ge (100) substrates by atomic layer epitaxy

NASA Astrophysics Data System (ADS)

Kim, Hyoungsub; Chui, Chi On; Saraswat, Krishna C.; McIntyre, Paul C.

2003-09-01

High-k dielectric deposition processes for gate dielectric preparation on Si surfaces usually result in the unavoidable and uncontrolled formation of a thin interfacial oxide layer. Atomic layer deposition of ˜55-Å ZrO2 film on a Ge (100) substrate using ZrCl4 and H2O at 300 °C was found to produce local epitaxial growth [(001) Ge//(001) ZrO2 and [100] Ge//[100] ZrO2] without a distinct interfacial layer, unlike the situation observed when ZrO2 is deposited using the same method on Si. Relatively large lattice mismatch (˜10%) between ZrO2 and Ge produced a high areal density of interfacial misfit dislocations. Large hysteresis (>200 mV) and high frequency dispersion were observed in capacitance-voltage measurements due to the high density of interface states. However, a low leakage current density, comparable to values obtained on Si substrates, was observed with the same capacitance density regardless of the high defect density.

Control of interfacial properties of Pr-oxide/Ge gate stack structure by introduction of nitrogen

NASA Astrophysics Data System (ADS)

Kato, Kimihiko; Kondo, Hiroki; Sakashita, Mitsuo; Nakatsuka, Osamu; Zaima, Shigeaki

2011-06-01

We have demonstrated the control of interfacial properties of Pr-oxide/Ge gate stack structure by the introduction of nitrogen. From C- V characteristics of Al/Pr-oxide/Ge 3N 4/Ge MOS capacitors, the interface state density decreases without the change of the accumulation capacitance after annealing. The TEM and TED measurements reveal that the crystallization of Pr-oxide is enhanced with annealing and the columnar structure of cubic-Pr 2O 3 is formed after annealing. From the depth profiles measured using XPS with Ar sputtering for the Pr-oxide/Ge 3N 4/Ge stack structure, the increase in the Ge component is not observed in a Pr-oxide film and near the interface between a Pr-oxide film and a Ge substrate. In addition, the N component segregates near the interface region, amorphous Pr-oxynitride (PrON) is formed at the interface. As a result, Pr-oxide/PrON/Ge stacked structure without the Ge-oxynitride interlayer is formed.

Sedimentation of a two-dimensional colloidal mixture exhibiting liquid-liquid and gas-liquid phase separation: a dynamical density functional theory study.

PubMed

Malijevský, Alexandr; Archer, Andrew J

2013-10-14

We present dynamical density functional theory results for the time evolution of the density distribution of a sedimenting model two-dimensional binary mixture of colloids. The interplay between the bulk phase behaviour of the mixture, its interfacial properties at the confining walls, and the gravitational field gives rise to a rich variety of equilibrium and non-equilibrium morphologies. In the fluid state, the system exhibits both liquid-liquid and gas-liquid phase separation. As the system sediments, the phase separation significantly affects the dynamics and we explore situations where the final state is a coexistence of up to three different phases. Solving the dynamical equations in two-dimensions, we find that in certain situations the final density profiles of the two species have a symmetry that is different from that of the external potentials, which is perhaps surprising, given the statistical mechanics origin of the theory. The paper concludes with a discussion on this.

Modeling micelle formation and interfacial properties with iSAFT classical density functional theory

NASA Astrophysics Data System (ADS)

Wang, Le; Haghmoradi, Amin; Liu, Jinlu; Xi, Shun; Hirasaki, George J.; Miller, Clarence A.; Chapman, Walter G.

2017-03-01

Surfactants reduce the interfacial tension between phases, making them an important additive in a number of industrial and commercial applications from enhanced oil recovery to personal care products (e.g., shampoo and detergents). To help obtain a better understanding of the dependence of surfactant properties on molecular structure, a classical density functional theory, also known as interfacial statistical associating fluid theory, has been applied to study the effects of surfactant architecture on micelle formation and interfacial properties for model nonionic surfactant/water/oil systems. In this approach, hydrogen bonding is explicitly included. To minimize the free energy, the system minimizes interactions between hydrophobic components and hydrophilic components with water molecules hydrating the surfactant head group. The theory predicts micellar structure, effects of surfactant architecture on critical micelle concentration, aggregation number, and interfacial tension isotherm of surfactant/water systems in qualitative agreement with experimental data. Furthermore, this model is applied to study swollen micelles and reverse swollen micelles that are necessary to understand the formation of a middle-phase microemulsion.

Lattice density functional theory for confined Ising fluids: comparison between different functional approximations in slit pore

NASA Astrophysics Data System (ADS)

Chen, Xueqian; Feng, Wei; Liu, Honglai; Hu, Ying

2016-09-01

In this paper, Lafuente and Cuesta's cluster density functional theory (CDFT) and lattice mean field approximation (LMFA) are formulated and compared within the framework of lattice density functional theory (LDFT). As a comparison, an LDFT based on our previous work on nonrandom correction to LMFA is also developed, where local density approximation is adopted on the correction. The numerical results of density distributions of an Ising fluid confined in a slit pore obtained from Monte Carlo simulation are used to check these functional approximations. Due to rational treatment on the coupling between site-excluding entropic effect and contact-attracting enthalpic effect by CDFT with Bethe-Peierls approximation (named as BPA-CDFT for short), the improvement of BPA-CDFT beyond LMFA is checked as expected. And it is interesting that our LDFT has a comparative accuracy with BPA-CDFT. Apparent differences between the profiles such as solvation force, excess adsorption quantity and interfacial tension from LMFA and non-LMFAs are found in our calculations. We also discuss some possible theoretical extensions of BPA-CDFT.

Self consistent solution of Schrödinger Poisson equations and some electronic properties of ZnMgO/ZnO hetero structures

NASA Astrophysics Data System (ADS)

Uslu, Salih; Yarar, Zeki

2017-02-01

The epitaxial growth of quantum wells composed of high quality allows the production and application to their device of new structures in low dimensions. The potential profile at the junction is determined by free carriers and by the level of doping. Therefore, the shape of potential is obtained by the electron density. Energy level determines the number of electrons that can be occupied at every level. Energy levels and electron density values of each level must be calculated self consistently. Starting with V(z) test potential, wave functions and electron densities for each energy levels can be calculated to solve Schrödinger equation. If Poisson's equation is solved with the calculated electron density, the electrostatic potential can be obtained. The new V(z) potential can be calculated with using electrostatic potential found beforehand. Thus, the obtained values are calculated self consistently to a certain error criterion. In this study, the energy levels formed in the interfacial potential, electron density in each level and the wave function dependence of material parameters were investigated self consistently.

Mechanistic study of the rubber-brass adhesion interphase

NASA Astrophysics Data System (ADS)

Ashirgade, Akshay

Brass-plated steel tire cords form an essential strengthening component of a radial automobile tire. Adhesion between rubber compound and brass-plated steel tire cord is crucial in governing the overall performance of tires. The rubber-brass interfacial adhesion is influenced by the chemical composition and thickness of the interfacial layer. It has been shown that the interfacial layer consists mainly of sulfides and oxides of copper and zinc. This thesis discusses the effect of changes in the chemical composition and the structure of the interfacial layers due to addition of adhesion promoter resins. Grazing incidence X-Ray Diffraction (GIXRD) experiments were run on sulfidized polished brass coupons previously bonded to six experimental rubber compounds. It was confirmed that heat and humidity conditions lead to physical and chemical changes of the rubber-steel tire cord interfacial layer, closely related to the degree of rubber-brass adhesion. Morphological transformation of the interfacial layer led to loss of adhesion after aging. The adhesion promoter resins inhibit unfavorable morphological changes in the interfacial layer thus stabilizing it during aging and prolonging failure. Tire cord adhesion tests illustrated that the one-component resins improved adhesion after aging using a rubber compound with lower cobalt loading. Based on the acquired diffraction profiles, these resins were also found to impede crystallization of the sulfide layer after aging leading to improved adhesion. Secondary Ion Mass Spectrometry (SIMS) depth profiles, SEM micrographs and AFM images strongly corroborated the findings from GIXRD. FTIR was utilized in a novel way to understand the degradation mechanism due to aging. A model for rubber and interfacial layer degradation is proposed to illustrate the effect of aging and the one-component resins. This interfacial analysis adds valuable new information to our understanding of the complex nature of the rubber-brass bonding mechanism.

Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

DOE PAGES

Ge, Ting; Robbins, Mark O.; Perahia, Dvora; ...

2014-07-25

Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface.more » The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is signifcantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. When the strength of the interface saturates, the number of interfacial entanglements scales with the corresponding bulk entanglement density. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.« less

Ultrathin ZnS and ZnO Interfacial Passivation Layers for Atomic-Layer-Deposited HfO2 Films on InP Substrates.

PubMed

Kim, Seung Hyun; Joo, So Yeong; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

2016-08-17

Ultrathin ZnS and ZnO films grown by atomic layer deposition (ALD) were employed as interfacial passivation layers (IPLs) for HfO2 films on InP substrates. The interfacial layer growth during the ALD of the HfO2 film was effectively suppressed by the IPLs, resulting in the decrease of electrical thickness, hysteresis, and interface state density. Compared with the ZnO IPL, the ZnS IPL was more effective in reducing the interface state density near the valence band edge. The leakage current density through the film was considerably lowered by the IPLs because the film crystallization was suppressed. Especially for the film with the ZnS IPL, the leakage current density in the low-voltage region was significantly lower than that observed for the film with the ZnO IPL, because the direct tunneling current was suppressed by the higher conduction band offset of ZnS with the InP substrate.

Effects of Interfacial Fluorination on Performance Enhancement of High-k-Based Charge Trap Flash Memory

NASA Astrophysics Data System (ADS)

Wang, Chenjie; Huo, Zongliang; Liu, Ziyu; Liu, Yu; Cui, Yanxiang; Wang, Yumei; Li, Fanghua; Liu, Ming

2013-07-01

The effects of interfacial fluorination on the metal/Al2O3/HfO2/SiO2/Si (MAHOS) memory structure have been investigated. By comparing MAHOS memories with and without interfacial fluorination, it was identified that the deterioration of the performance and reliability of MAHOS memories is mainly due to the formation of an interfacial layer that generates excess oxygen vacancies at the interface. Interfacial fluorination suppresses the growth of the interfacial layer, which is confirmed by X-ray photoelectron spectroscopy depth profile analysis, increases enhanced program/erase efficiency, and improves data retention characteristics. Moreover, it was observed that fluorination at the SiO-HfO interface achieves a more effective performance enhancement than that at the HfO-AlO interface.

Interfacial tension measurement of immiscible liq uids using a capillary tube

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Balasubramaniam, R.; Delsignore, D.

1992-01-01

The interfacial tension of immiscible liquids is an important thermophysical property that is useful in the behavior of liquids both in microgravity (Martinez et al. (1987) and Karri and Mathur (1988)) and in enhanced oil recovery processes under normal gravity (Slattery (1974)). Many techniques are available for its measurement, such as the ring method, drop weight method, spinning drop method, and capillary height method (Adamson (1960) and Miller and Neogi (1985)). Karri and Mathur mention that many of the techniques use equations that contain a density difference term and are inappropriate for equal density liquids. They reported a new method that is suitable for both equal and unequal density liquids. In their method, a capillary tube forms one of the legs of a U-tube. The interfacial tension is related to the heights of the liquids in the cups of the U-tube above the interface in the capillary. Our interest in this area arose from a need to measure small interfacial tension (around 1 mN/m) for a vegetable oil/silicon oil system that was used in a thermocapillary drop migration experiment (Rashidnia and Balasubramaniam (1991)). In our attempts to duplicate the method proposed by Karri and Mathur, we found it quite difficult to anchor the interface inside the capillary tube; small differences of the liquid heights in the cups drove the interface out of the capillary. We present an alternative method using a capillary tube to measure the interfacial tensions of liquids of equal or unequal density. The method is based on the combined capillary rises of both liquids in the tube.

Interfacial layer thickness dependent electrical characteristics of Au/(Zn-doped PVA)/n-4H-SiC (MPS) structures at room temperature

NASA Astrophysics Data System (ADS)

Lapa, Havva Elif; Kökce, Ali; Al-Dharob, Mohammed; Orak, İkram; Özdemir, Ahmet Faruk; Altındal, Semsettin

2017-10-01

Au/(Zn-doped PVA)/n-4H-SiC metal/polymer/semiconductor (MPS) structures with different interfacial layer thickness values (50, 150, 500 nm) were fabricated and their electrical characteristics were compared. Their electrical parameters (i.e. reverse-bias saturation current (Io), ideality factor (n), zero-bias barrier height (BH) (Φbo), series and shunt resistances (Rs, Rsh)) were calculated from the forward bias current-voltage (IF-VF) data whereas other parameters (i.e. Fermi energy level (EF), BH (Vb) and donor concentration (Nd)) were calculated from the linear part of C-2-V characteristics at room temperature. Obtained results confirmed that the values of n, Φbo, Rs and Rsh increase with increasing interlayer thickness, and linear correlation between n and Φbo was observed. The high values of n for three structures can be ascribed to the presence of an interlayer, surface states (Nss) and barrier inhomogeneities. The energy density distribution profile of Nss was obtained from the IF-VF data by taking into account voltage-dependent effective BH (Ve) and n for each structure. The Ri vs V plot for these structures was obtained using both Ohm's law and Nicollian-Brews method. All these experimental results show that the interfacial layer and its thickness play an important role in main electric parameters of these structures.

Coupled metal partitioning dynamics and toxicodynamics at biointerfaces: a theory beyond the biotic ligand model framework.

PubMed

Duval, Jérôme F L

2016-04-14

A mechanistic understanding of the processes governing metal toxicity to microorganisms (bacteria, algae) calls for an adequate formulation of metal partitioning at biointerfaces during cell exposure. This includes the account of metal transport dynamics from bulk solution to biomembrane and the kinetics of metal internalisation, both potentially controlling the intracellular and surface metal fractions that originate cell growth inhibition. A theoretical rationale is developed here for such coupled toxicodynamics and interfacial metal partitioning dynamics under non-complexing medium conditions with integration of the defining cell electrostatic properties. The formalism explicitly considers intertwined metal adsorption at the biointerface, intracellular metal excretion, cell growth and metal depletion from bulk solution. The theory is derived under relevant steady-state metal transport conditions on the basis of coupled Nernst-Planck equation and continuous logistic equation modified to include metal-induced cell growth inhibition and cell size changes. Computational examples are discussed to identify limitations of the classical Biotic Ligand Model (BLM) in evaluating metal toxicity over time. In particular, BLM is shown to severely underestimate metal toxicity depending on cell exposure time, metal internalisation kinetics, cell surface electrostatics and initial cell density. Analytical expressions are provided for the interfacial metal concentration profiles in the limit where cell-growth is completely inhibited. A rigorous relationship between time-dependent cell density and metal concentrations at the biosurface and in bulk solution is further provided, which unifies previous equations formulated by Best and Duval under constant cell density and cell size conditions. The theory is sufficiently flexible to adapt to toxicity scenarios with involved cell survival-death processes.

Molecular mechanics and structure of the fluid-solid interface in simple fluids

NASA Astrophysics Data System (ADS)

Wang, Gerald J.; Hadjiconstantinou, Nicolas G.

2017-09-01

Near a fluid-solid interface, the fluid spatial density profile is highly nonuniform at the molecular scale. This nonuniformity can have profound effects on the dynamical behavior of the fluid and has been shown to play an especially important role when modeling a wide variety of nanoscale heat and momentum transfer phenomena. We use molecular-mechanics arguments and molecular-dynamics (MD) simulations to develop a better understanding of the structure of the first fluid layer directly adjacent to the solid in the layering regime, as delineated by a nondimensional number that compares the effects of wall-fluid interaction to thermal energy. Using asymptotic analysis of the Nernst-Planck equation, we show that features of the fluid density profile close to the wall, such as the areal density of the first layer ΣFL (defined as the number of atoms in this layer per unit of fluid-solid interfacial area), can be expressed as polynomial functions of the fluid average density ρave. This is found to be in agreement with MD simulations, which also show that the width of the first layer hFL is a linear function of the average density and only a weak function of the temperature T . These results can be combined to show that, for system average densities corresponding to a dense fluid (ρave≥0.7 ), the ratio C ≡ΣFLρavehFL, representing a density enhancement with respect to the bulk fluid, depends only weakly on temperature and is essentially independent of density. Further MD simulations suggest that the above results, nominally valid for large systems (solid in contact with semi-infinite fluid), also describe fluid-solid interfaces under considerable nanoconfinement, provided ρave is appropriately defined.

Thermal stability of Ag, Al, Sn, Pb, and Hg films reinforced by 2D (C, Si) crystals and the formation of interfacial fluid states in them upon heating. MD experiment

NASA Astrophysics Data System (ADS)

Polukhin, V. A.; Kurbanova, E. D.

2016-02-01

Molecular dynamics simulation is used to study the thermal stability of the interfacial states of metallic Al, Ag, Sn, Pb, and Hg films (i.e., the structural elements of superconductor composites and conducting electrodes) reinforced by 2D graphene and silicene crystals upon heating up to disordering and to analyze the formation of nonautonomous fluid pseudophases in interfaces. The effect of perforation defects in reinforcing 2D-C and 2D-Si planes with passivated edge covalent bonds on the atomic dynamics is investigated. As compared to Al and Ag, the diffusion coefficients in Pd and Hg films increase monotonically with temperature during thermally activated disordering processes, the interatomic distances decrease, the sizes decrease, drops form, and their density profile grows along the normal. The coagulation of Pb and Hg drops is accompanied by a decrease in the contact angle, the reduction of the interface contact with graphene, and the enhancement of its corrugation (waviness).

Spin-orbit torque in a three-dimensional topological insulator-ferromagnet heterostructure: Crossover between bulk and surface transport

NASA Astrophysics Data System (ADS)

Ghosh, S.; Manchon, A.

2018-04-01

Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three-dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore our model accounts for the spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large dampinglike torque reported recently is more likely attributed to the Berry curvature of interfacial states, while spin Hall torque remains small even in the bulk-dominated regime.

Simulation studies of phase inversion in agitated vessels using a Monte Carlo technique.

PubMed

Yeo, Leslie Y; Matar, Omar K; Perez de Ortiz, E Susana; Hewitt, Geoffrey F

2002-04-15

A speculative study on the conditions under which phase inversion occurs in agitated liquid-liquid dispersions is conducted using a Monte Carlo technique. The simulation is based on a stochastic model, which accounts for fundamental physical processes such as drop deformation, breakup, and coalescence, and utilizes the minimization of interfacial energy as a criterion for phase inversion. Profiles of the interfacial energy indicate that a steady-state equilibrium is reached after a sufficiently large number of random moves and that predictions are insensitive to initial drop conditions. The calculated phase inversion holdup is observed to increase with increasing density and viscosity ratio, and to decrease with increasing agitation speed for a fixed viscosity ratio. It is also observed that, for a fixed viscosity ratio, the phase inversion holdup remains constant for large enough agitation speeds. The proposed model is therefore capable of achieving reasonable qualitative agreement with general experimental trends and of reproducing key features observed experimentally. The results of this investigation indicate that this simple stochastic method could be the basis upon which more advanced models for predicting phase inversion behavior can be developed.

Extracting elastic properties of an atomically thin interfacial layer by time-domain analysis of femtosecond acoustics

NASA Astrophysics Data System (ADS)

Chen, H.-Y.; Huang, Y.-R.; Shih, H.-Y.; Chen, M.-J.; Sheu, J.-K.; Sun, C.-K.

2017-11-01

Modern devices adopting denser designs and complex 3D structures have created much more interfaces than before, where atomically thin interfacial layers could form. However, fundamental information such as the elastic property of the interfacial layers is hard to measure. The elastic property of the interfacial layer is of great importance in both thermal management and nano-engineering of modern devices. Appropriate techniques to probe the elastic properties of interfacial layers as thin as only several atoms are thus critically needed. In this work, we demonstrated the feasibility of utilizing the time-resolved femtosecond acoustics technique to extract the elastic properties and mass density of a 1.85-nm-thick interfacial layer, with the aid of transmission electron microscopy. We believe that this femtosecond acoustics approach will provide a strategy to measure the absolute elastic properties of atomically thin interfacial layers.

Core–Shell Nanoparticle Coating as an Interfacial Layer for Dendrite-Free Lithium Metal Anodes

DOE PAGES

Liu, Wei; Li, Weiyang; Zhuo, Denys; ...

2017-02-08

Lithium metal based batteries represent a major challenge and opportunity in enabling a variety of devices requiring high-energy-density storage. However, dendritic lithium growth has limited the practical application of lithium metal anodes. Here we report a nanoporous, flexible and electrochemically stable coating of silica@poly(methyl methacrylate) (SiO 2@PMMA) core–shell nanospheres as an interfacial layer on lithium metal anode. This interfacial layer is capable of inhibiting Li dendrite growth while sustaining ionic flux through it, which is attributed to the nanoscaled pores formed among the nanospheres. Lastly, enhanced Coulombic efficiencies during lithium charge/discharge cycles have been achieved at various current densities andmore » areal capacities.« less

Core–Shell Nanoparticle Coating as an Interfacial Layer for Dendrite-Free Lithium Metal Anodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; Li, Weiyang; Zhuo, Denys

Lithium metal based batteries represent a major challenge and opportunity in enabling a variety of devices requiring high-energy-density storage. However, dendritic lithium growth has limited the practical application of lithium metal anodes. Here we report a nanoporous, flexible and electrochemically stable coating of silica@poly(methyl methacrylate) (SiO 2@PMMA) core–shell nanospheres as an interfacial layer on lithium metal anode. This interfacial layer is capable of inhibiting Li dendrite growth while sustaining ionic flux through it, which is attributed to the nanoscaled pores formed among the nanospheres. Lastly, enhanced Coulombic efficiencies during lithium charge/discharge cycles have been achieved at various current densities andmore » areal capacities.« less

Oxidation state and interfacial effects on oxygen vacancies in tantalum pentoxide

DOE PAGES

Bondi, Robert J.; Marinella, Matthew J.

2015-02-28

First-principles density-functional theory (DFT) calculations are used to study the atomistic structure, structural energetics, and electron density near the O monovacancy (V O n; n=0,1+,2+) in both bulk, amorphous tantalum pentoxide (a-Ta 2O 5) and also at vacuum and metallic Ta interfaces. We calculate multivariate vacancy formation energies to evaluate stability as a function of oxidation state, distance from interface plane, and Fermi energy. V O n of all oxidation states preferentially segregate at both Ta and vacuum interfaces, where the metallic interface exhibits global formation energy minima. In a-Ta 2O 5, V O 0 are characterized by structural contractionmore » and electron density localization, while V O 2+ promote structural expansion and are depleted of electron density. In contrast, interfacial V O 0 and V O 2+ show nearly indistinguishable ionic and electronic signatures indicative of a reduced V O center. Interfacial V O 2+ extract electron density from metallic Ta indicating V O 2+ is spontaneously reduced at the expense of the metal. This oxidation/reduction behavior suggests careful selection and processing of both oxide layer and metal electrodes for engineering memristor device operation.« less

Effect of urea and glycerol on the adsorption of ribonuclease A at the air-water interface.

PubMed

Hüsecken, Anne K; Evers, Florian; Czeslik, Claus; Tolan, Metin

2010-08-17

This study reports on the influence of nonionic cosolvents on the interfacial structure of ribonuclease A (RNase) adsorbed at the air-water interface. We applied X-ray reflectometry to obtain detailed volume fraction profiles of the adsorbed layers and to follow the effect of glycerol and urea on the adsorbate structure as a function of cosolvent concentration. Under all conditions studied, the adsorbed RNase layer maintains its compact shape, and the adsorbed RNase molecules adopt a flat-on orientation at the interface. Both kosmotropic glycerol and chaotropic urea exert profound effects on the adsorbate: The surface excess decreases linearly with glycerol content and is also reduced at low urea concentration. However, at high urea concentration, parts of the adsorbed layer are dehydrated and become exposed to air. The electron density and volume fraction profiles of the adsorbed protein provide clear evidence that these effects are ruled by different mechanisms.

Experimental evidence of a liquid-liquid transition in interfacial water

NASA Astrophysics Data System (ADS)

Zanotti, J.-M.; Bellissent-Funel, M.-C.; Chen, S.-H.

2005-07-01

At ambient pressure, bulk liquid water shows an anomalous increase of thermodynamic quantities and apparent divergences of dynamic properties on approaching a temperature Ts of 228 K. At normal pressure, supercooled water spontaneously freezes below the homogeneous nucleation temperature, TH = 235 K. Upon heating, the two forms of Amorphous Solid Water (ASW), LDA (Low Density Amorphous Ice) and HDA (High Density Amorphous Ice), crystallise above TX = 150 K. As a consequence, up to now no experiment has been able to explore the properties of liquid water in this very interesting temperature range between 150 and 235 K. We present nanosecond-time-scale measurements of local rotational and translational dynamics of interfacial, non-crystalline, water from 77 to 280 K. These experimental dynamic results are combined with calorimetric and diffraction data to show that after exhibiting a glass transition at 165 K, interfacial water experiences a first-order liquid-liquid transition at 240 K from a low-density to a high-density liquid. This is the first direct evidence of the existence of a liquid-liquid transition involving water.

Monte Carlo studies on the interfacial properties and interfacial structures of ternary symmetric blends with gradient copolymers.

PubMed

Sun, Dachuan; Guo, Hongxia

2012-08-09

Using Monte Carlo simulation methods, the effects of the comonomer sequence distribution on the interfacial properties (including interfacial tension, interfacial thickness, saturated interfacial area per copolymer, and bending modulus) and interfacial structures (including chain conformations and comonomer distributions of the simulated copolymers at the interfaces) of a ternary symmetric blend containing two immiscible homopolymers and one gradient copolymer are investigated. We find that copolymers with a larger composition gradient width have a broader comonomer distribution along the interface normal, and hence more pronouncedly enlarge the interfacial thickness and reduce the interfacial tension. Furthermore, the counteraction effect, which arises from the tendency of heterogeneous segments in gradient copolymers to phase separate and enter their miscible phases to reduce the local enthalpy, decreases the stretching of copolymers along the interface normal direction. As a result, copolymers with a larger width of gradient composition can occupy a larger interfacial area and form softer monolayers at saturation and are more efficient in facilitating the formation of bicontinuous microemulsions. Additionally, chain length ratio, segregation strength, and interactions between homopolymers and copolymers can alter the interfacial character of gradient copolymers. There exists a strong coupling between the comonomer sequence distribution, chain conformation, and interfacial properties. Especially, bending modulus is mainly determined by the complicated interplay of interfacial copolymer density and interfacial chain conformation.

The hydration structure at yttria-stabilized cubic zirconia (110)-water interface with sub-Ångström resolution

DOE PAGES

Hou, Binyang; Kim, Seunghyun; Kim, Taeho; ...

2016-06-15

The interfacial hydration structure of yttria-stabilized cubic zirconia (110) surface in contact with water was determined with ~0.5 Å resolution by high-resolution X-ray reflectivity measurement. The terminal layer shows a reduced electron density compared to the following substrate lattice layers, which indicates there are additional defects generated by metal depletion as well as intrinsic oxygen vacancies, both of which are apparently filled by water species. Above this top surface layer, two additional adsorbed layers are observed forming a characteristic interfacial hydration structure. The first adsorbed layer shows abnormally high density as pure water and likely includes metal species, whereas themore » second layer consists of pure water. The observed interfacial hydration structure seems responsible for local equilibration of the defective surface in water and eventually regulating the long-term degradation processes. As a result, the multitude of water interactions with the zirconia surface results in the complex but highly ordered interfacial structure constituting the reaction front.« less

Organic semiconductor density of states controls the energy level alignment at electrode interfaces

PubMed Central

Oehzelt, Martin; Koch, Norbert; Heimel, Georg

2014-01-01

Minimizing charge carrier injection barriers and extraction losses at interfaces between organic semiconductors and metallic electrodes is critical for optimizing the performance of organic (opto-) electronic devices. Here, we implement a detailed electrostatic model, capable of reproducing the alignment between the electrode Fermi energy and the transport states in the organic semiconductor both qualitatively and quantitatively. Covering the full phenomenological range of interfacial energy level alignment regimes within a single, consistent framework and continuously connecting the limiting cases described by previously proposed models allows us to resolve conflicting views in the literature. Our results highlight the density of states in the organic semiconductor as a key factor. Its shape and, in particular, the energy distribution of electronic states tailing into the fundamental gap is found to determine both the minimum value of practically achievable injection barriers as well as their spatial profile, ranging from abrupt interface dipoles to extended band-bending regions. PMID:24938867

Interfacial thermodynamics of water and six other liquid solvents.

PubMed

Pascal, Tod A; Goddard, William A

2014-06-05

We examine the thermodynamics of the liquid-vapor interface by direct calculation of the surface entropy, enthalpy, and free energy from extensive molecular dynamics simulations using the two-phase thermodynamics (2PT) method. Results for water, acetonitrile, cyclohexane, dimethyl sulfoxide, hexanol, N-methyl acetamide, and toluene are presented. We validate our approach by predicting the interfacial surface tensions (IFT--excess surface free energy per unit area) in excellent agreement with the mechanical calculations using Kirkwood-Buff theory. Additionally, we evaluate the temperature dependence of the IFT of water as described by the TIP4P/2005, SPC/Ew, TIP3P, and mW classical water models. We find that the TIP4P/2005 and SPC/Ew water models do a reasonable job of describing the interfacial thermodynamics; however, the TIP3P and mW are quite poor. We find that the underprediction of the experimental IFT at 298 K by these water models results from understructured surface molecules whose binding energies are too weak. Finally, we performed depth profiles of the interfacial thermodynamics which revealed long tails that extend far into what would be considered bulk from standard Gibbs theory. In fact, we find a nonmonotonic interfacial free energy profile for water, a unique feature that could have important consequences for the absorption of ions and other small molecules.

Atomistic simulations of bulk, surface and interfacial polymer properties

NASA Astrophysics Data System (ADS)

Natarajan, Upendra

In chapter I, quasi-static molecular mechanics based simulations are used to estimate the activation energy of phenoxy rings flips in the amorphous region of a semicrystalline polyimide. Intra and intermolecular contributions to the flip activation energy, the torsional cooperativity accompanying the flip, and the effect of the flip on the motion in the glassy bulk state, are looked at. Also, comparison of the weighted mean activation energy is made with experimental data from solid state NMR measurements; the simulated value being 17.5 kcal/mol., while the experimental value was observed to be 10.5 kcal/mol. Chapter II deals with construction of random copolymer thin films of styrene-butadiene (SB) and styrene-butadiene-acrylonitrile (SBA). The structure and properties of the free surfaces presented by these thin films are analysed by, the atom mass density profiles, backbone bond orientation function, and the spatial distribution of acrylonitrile groups and styrene rings. The surface energies of SB and SBA are calculated using an atomistic equation and are compared with experimental data in the literature. In chapter III, simulations of polymer-polymer interfaces between like and unlike polymers, specifically cis-polybutadiene (PBD) and atatic polypropylene (PP), are presented. The structure of an incompatible polymer-polymer interface, and the estimation of the thermodynamic work of adhesion and interfacial energy between different incompatible polymers, form the focus here. The work of adhesion is calculated using an atomistic equation and is further used in a macroscopic equation to estimate the interfacial energy. The interfacial energy is compared with typical values for other immiscible systems in the literature. The interfacial energy compared very well with interfacial energy values for a few other immiscible hydrocarbon pairs. In chapter IV, the study proceeds to look at the interactions between nonpolar and polar small molecules with SB and SBA thin film surfaces. Toluene, hexadecane and water molecules are separately simulated to interact with SB and SBA surfaces in vacuum. The energetics of interaction are calculated atomistically and used in the atomistic equation to calculate the interfacial energy or the interaction energy. Comparisons with experimental data are not made due to the small concentrations of the molecules on the polymer surface. However, fundamental understanding of the structure of the system and the breakup of the energetics are provided by such a study.

Linear and nonlinear instability in vertical counter-current laminar gas-liquid flows

NASA Astrophysics Data System (ADS)

Schmidt, Patrick; Ó Náraigh, Lennon; Lucquiaud, Mathieu; Valluri, Prashant

2016-04-01

We consider the genesis and dynamics of interfacial instability in vertical gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory (Orr-Sommerfeld analysis) together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. We investigate the influence of two main flow parameters on the interfacial dynamics, namely the film thickness and pressure drop applied to drive the gas stream. To make contact with existing studies in the literature, the effect of various density contrasts is also examined. Energy budget analyses based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low density contrast. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. Direct numerical simulations of the same system (low density contrast) show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. For high density contrasts, corresponding more closely to an air-water-type system, linear stability theory is also successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times. Nevertheless, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic motion. The same linear stability theory predicts when the direction of travel of the waves changes — from downwards to upwards. We outline the practical implications of this change in terms of loading and flooding. The change in direction of the wave propagation is represented graphically in terms of a flow map based on the liquid and gas flow rates and the prediction carries over to the nonlinear regime with only a small deviation.

Linear and nonlinear instability in vertical counter-current laminar gas-liquid flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Patrick; Lucquiaud, Mathieu; Valluri, Prashant, E-mail: prashant.valluri@ed.ac.uk

We consider the genesis and dynamics of interfacial instability in vertical gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory (Orr-Sommerfeld analysis) together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. We investigate the influence of two main flow parameters on the interfacial dynamics, namely the film thickness and pressure drop applied to drive the gas stream. To make contact with existing studies in the literature, the effect of various density contrasts is also examined. Energy budget analysesmore » based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low density contrast. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. Direct numerical simulations of the same system (low density contrast) show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. For high density contrasts, corresponding more closely to an air-water-type system, linear stability theory is also successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times. Nevertheless, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic motion. The same linear stability theory predicts when the direction of travel of the waves changes — from downwards to upwards. We outline the practical implications of this change in terms of loading and flooding. The change in direction of the wave propagation is represented graphically in terms of a flow map based on the liquid and gas flow rates and the prediction carries over to the nonlinear regime with only a small deviation.« less

Modeling Interfacial Thermal Boundary Conductance of Engineered Interfaces

DTIC Science & Technology

2014-08-31

melting / recrystallization of the subsurface Ag/Cu interface. Observed the formation of a novel, lattice-mismatched interfacial microstruc- ture...calculations were converged within 1 × 10−4 Ryd with respect to wave function cutoff energy, energy density cutoff, and k- point sampling. The A-EAM

On the interfacial thermodynamics of nanoscale droplets and bubbles

NASA Astrophysics Data System (ADS)

Corti, David S.; Kerr, Karl J.; Torabi, Korosh

2011-07-01

We present a new self-consistent thermodynamic formalism for the interfacial properties of nanoscale embryos whose interiors do not exhibit bulklike behavior and are in complete equilibrium with the surrounding mother phase. In contrast to the standard Gibbsian analysis, whereby a bulk reference pressure based on the same temperature and chemical potentials of the mother phase is introduced, our approach naturally incorporates the normal pressure at the center of the embryo as an appropriate reference pressure. While the interfacial properties of small embryos that follow from the use of these two reference pressures are different, both methods yield by construction the same reversible work of embryo formation as well as consistency between their respective thermodynamic and mechanical routes to the surface tension. Hence, there is no a priori reason to select one method over another. Nevertheless, we argue, and demonstrate via a density-functional theory (with the local density approximation) analysis of embryo formation in the pure component Lennard-Jones fluid, that our new method generates more physically appealing trends. For example, within the new approach the surface tension at all locations of the dividing surface vanishes at the spinodal where the density profile spanning the embryo and mother phase becomes completely uniform (only the surface tension at the Gibbs surface of tension vanishes in the Gibbsian method at this same limit). Also, for bubbles, the location of the surface of tension now diverges at the spinodal, similar to the divergent behavior exhibited by the equimolar dividing surface (in the Gibbsian method, the location of the surface of tension vanishes instead). For droplets, the new method allows for the appearance of negative surface tensions (the Gibbsian method always yields positive tensions) when the normal pressures within the interior of the embryo become less than the bulk pressure of the surrounding vapor phase. Such a prediction, which is allowed by thermodynamics, is consistent with the interpretation that the mother phase's attempted compression of the droplet is counterbalanced by the negative surface tension, or free energy cost to decrease the interfacial area. Furthermore, for these same droplets, the surface of tension can no longer be meaningfully defined (the surface of tension always remains well defined in the Gibbsian method). Within the new method, the dividing surface at which the surface tension equals zero emerges as a new lengthscale, which has various thermodynamic analogs to and similar behavior as the surface of tension.

Ultra-low thermal conductivity of high-interface density Si/Ge amorphous multilayers

NASA Astrophysics Data System (ADS)

Goto, Masahiro; Xu, Yibin; Zhan, Tianzhuo; Sasaki, Michiko; Nishimura, Chikashi; Kinoshita, Yohei; Ishikiriyama, Mamoru

2018-04-01

Owing to their phonon scattering and interfacial thermal resistance (ITR) characteristics, inorganic multilayers (MLs) have attracted considerable attention for thermal barrier applications. In this study, a-Si/a-Ge MLs with layer thicknesses ranging from 0.3 to 5 nm and different interfacial elemental mixture states were fabricated using a combinatorial sputter-coating system, and their thermal conductivities were measured via a frequency-domain thermo-reflectance method. An ultra-low thermal conductivity of κ = 0.29 ± 0.01 W K-1 m-1 was achieved for a layer thickness of 0.8 nm. The ITR was found to decrease from 8.5 × 10-9 to 3.6 × 10-9 m2 K W-1 when the interfacial density increases from 0.15 to 0.77 nm-1.

Numerical investigation of split flows by gravity currents into two-layered stratified water bodies

NASA Astrophysics Data System (ADS)

Cortés, A.; Wells, M. G.; Fringer, O. B.; Arthur, R. S.; Rueda, F. J.

2015-07-01

The behavior of a two-dimensional (2-D) gravity current impinging upon a density step in a two-layered stratified basin is analyzed using a high-resolution Reynolds-Averaged Navier-Stokes model. The gravity current splits at the density step, and the portion of the buoyancy flux becoming an interflow is largely controlled by the vertical distribution of velocity and density within the gravity current and the magnitude of the density step between the two ambient layers. This is in agreement with recent laboratory observations. The strongest changes in the ambient density profiles occur as a result of the impingement of supercritical currents with strong density contrasts, for which a large portion of the gravity current detaches from the bottom and becomes an interflow. We characterize the current partition process in the simulated experiments using the densimetric Froude number of the current (Fr) across the density step (upstream and downstream). When underflows are formed, more supercritical currents are observed downstream of the density step compared to upstream (Fru < Frd), and thus, stronger mixing of the current with the ambient water downstream. However, when split flows and interflows are formed, smaller Fr values are identified after the current crosses the density step (Fru > Frd), which indicates lower mixing between the current and ambient water after the impingement due to the significant stripping of interfacial material at the density step.

Atomic density effects on temperature characteristics and thermal transport at grain boundaries through a proper bin size selection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vo, Truong Quoc; Kim, BoHung, E-mail: muratbarisik@iyte.edu.tr, E-mail: bohungk@ulsan.ac.kr; Barisik, Murat, E-mail: muratbarisik@iyte.edu.tr, E-mail: bohungk@ulsan.ac.kr

2016-05-21

This study focuses on the proper characterization of temperature profiles across grain boundaries (GBs) in order to calculate the correct interfacial thermal resistance (ITR) and reveal the influence of GB geometries onto thermal transport. The solid-solid interfaces resulting from the orientation difference between the (001), (011), and (111) copper surfaces were investigated. Temperature discontinuities were observed at the boundary of grains due to the phonon mismatch, phonon backscattering, and atomic forces between dissimilar structures at the GBs. We observed that the temperature decreases gradually in the GB area rather than a sharp drop at the interface. As a result, threemore » distinct temperature gradients developed at the GB which were different than the one observed in the bulk solid. This behavior extends a couple molecular diameters into both sides of the interface where we defined a thickness at GB based on the measured temperature profiles for characterization. Results showed dependence on the selection of the bin size used to average the temperature data from the molecular dynamics system. The bin size on the order of the crystal layer spacing was found to present an accurate temperature profile through the GB. We further calculated the GB thickness of various cases by using potential energy (PE) distributions which showed agreement with direct measurements from the temperature profile and validated the proper binning. The variation of grain crystal orientation developed different molecular densities which were characterized by the average atomic surface density (ASD) definition. Our results revealed that the ASD is the primary factor affecting the structural disorders and heat transfer at the solid-solid interfaces. Using a system in which the planes are highly close-packed can enhance the probability of interactions and the degree of overlap between vibrational density of states (VDOS) of atoms forming at interfaces, leading to a reduced ITR. Thus, an accurate understanding of thermal characteristics at the GB can be formulated by selecting a proper bin size.« less

Atomic density effects on temperature characteristics and thermal transport at grain boundaries through a proper bin size selection

NASA Astrophysics Data System (ADS)

Vo, Truong Quoc; Barisik, Murat; Kim, BoHung

2016-05-01

This study focuses on the proper characterization of temperature profiles across grain boundaries (GBs) in order to calculate the correct interfacial thermal resistance (ITR) and reveal the influence of GB geometries onto thermal transport. The solid-solid interfaces resulting from the orientation difference between the (001), (011), and (111) copper surfaces were investigated. Temperature discontinuities were observed at the boundary of grains due to the phonon mismatch, phonon backscattering, and atomic forces between dissimilar structures at the GBs. We observed that the temperature decreases gradually in the GB area rather than a sharp drop at the interface. As a result, three distinct temperature gradients developed at the GB which were different than the one observed in the bulk solid. This behavior extends a couple molecular diameters into both sides of the interface where we defined a thickness at GB based on the measured temperature profiles for characterization. Results showed dependence on the selection of the bin size used to average the temperature data from the molecular dynamics system. The bin size on the order of the crystal layer spacing was found to present an accurate temperature profile through the GB. We further calculated the GB thickness of various cases by using potential energy (PE) distributions which showed agreement with direct measurements from the temperature profile and validated the proper binning. The variation of grain crystal orientation developed different molecular densities which were characterized by the average atomic surface density (ASD) definition. Our results revealed that the ASD is the primary factor affecting the structural disorders and heat transfer at the solid-solid interfaces. Using a system in which the planes are highly close-packed can enhance the probability of interactions and the degree of overlap between vibrational density of states (VDOS) of atoms forming at interfaces, leading to a reduced ITR. Thus, an accurate understanding of thermal characteristics at the GB can be formulated by selecting a proper bin size.

Measurement of Interfacial Profiles of Wavy Film Flow on Inclined Wall

NASA Astrophysics Data System (ADS)

Rosli, N.; Amagai, K.

2016-02-01

Falling liquid films on inclined wall present in many industrial processes such as in food processing, seawater desalination and electronic devices manufacturing industries. In order to ensure an optimal efficiency of the operation in these industries, a fundamental study on the interfacial flow profiles of the liquid film is of great importance. However, it is generally difficult to experimentally predict the interfacial profiles of liquid film flow on inclined wall due to the instable wavy flow that usually formed on the liquid film surface. In this paper, the liquid film surface velocity was measured by using a non-intrusive technique called as photochromic dye marking method. This technique utilizes the color change of liquid containing the photochromic dye when exposed to the UV light source. The movement of liquid film surface marked by the UV light was analyzed together with the wave passing over the liquid. As a result, the liquid film surface was found to slightly shrink its gradual movement when approached by the wave before gradually move again after the intersection with the wave.

Single-molecule interfacial electron transfer dynamics in solar energy conversion

NASA Astrophysics Data System (ADS)

Dhital, Bharat

This dissertation work investigated the parameters affecting the interfacial electron transfer (ET) dynamics in dye-semiconductor nanoparticles (NPs) system by using single-molecule fluorescence spectroscopy and imaging combined with electrochemistry. The influence of the molecule-substrate electronic coupling, the molecular structure, binding geometry on the surface and the molecule-attachment surface chemistry on interfacial charge transfer processes was studied on zinc porphyrin-TiO2 NP systems. The fluorescence blinking measurement on TiO2 NP demonstrated that electronic coupling regulates dynamics of charge transfer processes at the interface depending on the conformation of molecule on the surface. Moreover, semiconductor surface charge induced electronic coupling of molecule which is electrostatically adsorbed on the semiconductor surface also predominantly alters the ET dynamics. Furthermore, interfacial electric field and electron accepting state density dependent ET dynamics has been dissected in zinc porphyrin-TiO2 NP system by observing the single-molecule fluorescence blinking dynamics and fluorescence lifetime with and without applied bias. The significant difference in fluorescence fluctuation and lifetime suggested the modulation of charge transfer dynamics at the interface with external electric field perturbation. Quasi-continuous distribution of fluorescence intensity with applied negative potential was attributed to the faster charge recombination due to reduced density of electron accepting states. The driving force and electron accepting state density ET dependent dynamics has also been probed in zinc porphyrin-TiO2 NP and zinc porphyrin-indium tin oxide (ITO) systems. Study of a molecule adsorbed on two different semiconductors (ITO and TiO2), with large difference in electron densities and distinct driving forces, allows us to observe the changes in rates of back electron transfer process reflected by the suppressed fluorescence blinking of molecule on ITO surface. Finally, the electric field effect on the interface properties has been probed by using surface-enhanced Raman spectroscopy and supported by density functional theory calculations in alizarin-TiO2 system. The perturbation, created by the external potential, has been observed to cause a shift and/or splitting interfacial bond vibrational mode, typical indicator of the coupling energy changes between alizarin and TiO2. Such splitting provides evidence for electric field-dependent electronic coupling changes that have a significant impact on the interfacial electron transfer dynamics.

Characterization of interfacial failure in SiC reinforced Si3N4 matrix composite material by both fiber push-out testing and Auger electron spectroscopy

NASA Technical Reports Server (NTRS)

Eldridge, J. I.; Honecy, F. S.

1990-01-01

AES depth profiling and a fiber push-out test for interfacial shear-strength determination have been used to ascertain the mechanical/chemical properties of the fiber/matrix interface in SiC-reinforced reaction-bonded Si3N4, with attention to the weak point where interfacial failure occurs. In the cases of both composite fracture and fiber push-outs, the interfacial failure occurred either between the two C-rich coatings that are present on the double-coated SiC fibers, or between the inner C-rich coating and the SiC fiber. Interface failure occurs at points of very abrupt concentration changes.

Linear Instability Analysis of non-uniform Bubbly Mixing layer with Two-Fluid model

NASA Astrophysics Data System (ADS)

Sharma, Subash; Chetty, Krishna; Lopez de Bertodano, Martin

We examine the inviscid instability of a non-uniform adiabatic bubbly shear layer with a Two-Fluid model. The Two-Fluid model is made well-posed with the closure relations for interfacial forces. First, a characteristic analysis is carried out to study the well posedness of the model over range of void fraction with interfacial forces for virtual mass, interfacial drag, interfacial pressure. A dispersion analysis then allow us to obtain growth rate and wavelength. Then, the well-posed two-fluid model is solved using CFD to validate the results obtained with the linear stability analysis. The effect of the void fraction and the distribution profile on stability is analyzed.

Asymmetrical interfacial reactions of Ni/SAC101(NiIn)/Ni solder joint induced by current stressing

NASA Astrophysics Data System (ADS)

Lin, Chen-Yi; Chiu, Tsung-Chieh; Lin, Kwang-Lung

2018-03-01

An electric current can asymmetrically trigger either atomic migration or interfacial reactions between a cathode and an anode. The present study investigated the dissolution of metallization and formation of an interfacial intermetallic compound (IMC) in the Cu/Ni/Sn1.0Ag0.1Cu0.02Ni0.05In/Ni/Cu solder joint at various current densities in the order of 103 A/cm2 at temperatures ranging from 100 °C to 150 °C. The polarization behavior of Ni dissolution and IMC formation under current stressing were systematically investigated. The asymmetrical interfacial reactions of the solder joint were found to be greatly influenced by ambient temperature. The dissolution of Ni and its effect on interfacial IMC formation were also discussed.

Effects of Condensation on Peri-implant Bone Density and Remodeling

PubMed Central

Wang, L.; Wu, Y.; Perez, K.C.; Hyman, S.; Brunski, J.B.; Tulu, U.; Bao, C.; Salmon, B.; Helms, J.A.

2017-01-01

Bone condensation is thought to densify interfacial bone and thus improve implant primary stability, but scant data substantiate either claim. We developed a murine oral implant model to test these hypotheses. Osteotomies were created in healed maxillary extraction sites 1) by drilling or 2) by drilling followed by stepwise condensation with tapered osteotomes. Condensation increased interfacial bone density, as measured by a significant change in bone volume/total volume and trabecular spacing, but it simultaneously damaged the bone. On postimplant day 1, the condensed bone interface exhibited microfractures and osteoclast activity. Finite element modeling, mechanical testing, and immunohistochemical analyses at multiple time points throughout the osseointegration period demonstrated that condensation caused very high interfacial strains, marginal bone resorption, and no improvement in implant stability. Collectively, these multiscale analyses demonstrate that condensation does not positively contribute to implant stability. PMID:28048963

Effects of Condensation on Peri-implant Bone Density and Remodeling.

PubMed

Wang, L; Wu, Y; Perez, K C; Hyman, S; Brunski, J B; Tulu, U; Bao, C; Salmon, B; Helms, J A

2017-04-01

Bone condensation is thought to densify interfacial bone and thus improve implant primary stability, but scant data substantiate either claim. We developed a murine oral implant model to test these hypotheses. Osteotomies were created in healed maxillary extraction sites 1) by drilling or 2) by drilling followed by stepwise condensation with tapered osteotomes. Condensation increased interfacial bone density, as measured by a significant change in bone volume/total volume and trabecular spacing, but it simultaneously damaged the bone. On postimplant day 1, the condensed bone interface exhibited microfractures and osteoclast activity. Finite element modeling, mechanical testing, and immunohistochemical analyses at multiple time points throughout the osseointegration period demonstrated that condensation caused very high interfacial strains, marginal bone resorption, and no improvement in implant stability. Collectively, these multiscale analyses demonstrate that condensation does not positively contribute to implant stability.

Structure that encapsulates lithium metal for high energy density battery anode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, Yi; Yan, Kai; Chu, Steven

A battery includes 1) an anode, 2) a cathode, and 3) an electrolyte disposed between the anode and the cathode. The anode includes a current collector and an interfacial layer disposed over the current collector, and the interfacial layer includes an array of interconnected, protruding regions that define spaces.

First-passage dynamics of linear stochastic interface models: weak-noise theory and influence of boundary conditions

NASA Astrophysics Data System (ADS)

Gross, Markus

2018-03-01

We consider a one-dimensional fluctuating interfacial profile governed by the Edwards–Wilkinson or the stochastic Mullins-Herring equation for periodic, standard Dirichlet and Dirichlet no-flux boundary conditions. The minimum action path of an interfacial fluctuation conditioned to reach a given maximum height M at a finite (first-passage) time T is calculated within the weak-noise approximation. Dynamic and static scaling functions for the profile shape are obtained in the transient and the equilibrium regime, i.e. for first-passage times T smaller or larger than the characteristic relaxation time, respectively. In both regimes, the profile approaches the maximum height M with a universal algebraic time dependence characterized solely by the dynamic exponent of the model. It is shown that, in the equilibrium regime, the spatial shape of the profile depends sensitively on boundary conditions and conservation laws, but it is essentially independent of them in the transient regime.

Pair correlation functions and the wavevector-dependent surface tension in a simple density functional treatment of the liquid-vapour interface.

PubMed

Parry, A O; Rascón, C; Willis, G; Evans, R

2014-09-03

We study the density-density correlation function G(r, r') in the interfacial region of a fluid (or Ising-like magnet) with short-ranged interactions using square gradient density functional theory. Adopting a simple double parabola approximation for the bulk free-energy density, we first show that the parallel Fourier transform G(z, z'; q) and local structure factor S(z; q) separate into bulk and excess contributions. We attempt to account for both contributions by deriving an interfacial Hamiltonian, characterised by a wavevector dependent surface tension σ(q), and then reconstructing density correlations from correlations in the interface position. We show that the standard crossing criterion identification of the interface, as a surface of fixed density (or magnetization), does not explain the separation of G(z, z'; q) and the form of the excess contribution. We propose an alternative definition of the interface position based on the properties of correlations between points that 'float' with the surface and show that this describes the full q and z dependence of the excess contributions to both G and S. However, neither the 'crossing-criterion' nor the new 'floating interface' definition of σ(q) are quantities directly measurable from the total structure factor S(tot)(q) which contains additional q dependence arising from the non-local relation between fluctuations in the interfacial position and local density. Since it is the total structure factor that is measured experimentally or in simulations, our results have repercussions for earlier attempts to extract and interpret σ(q).

Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

NASA Astrophysics Data System (ADS)

Ge, Ting; Robbins, Mark O.; Perahia, Dvora; Grest, Gary S.

2014-07-01

Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface. The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is significantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.

Molecular dynamics analysis of a equilibrium nanoscale droplet on a solid surface with periodic roughness

NASA Astrophysics Data System (ADS)

Furuta, Yuma; Surblys, Donatas; Yamaguchi, Yastaka

2016-11-01

Molecular dynamics simulations of the equilibrium wetting behavior of hemi-cylindrical argon droplets on solid surfaces with a periodic roughness were carried out. The rough solid surface is located at the bottom of the calculation cell with periodic boundary conditions in surface lateral directions and mirror boundary condition at the top boundary. Similar to on a smooth surface, the change of the cosine of the droplet contact angle was linearly correlated to the potential well depth of the inter-atomic interaction between liquid and solid on a surface with a short roughness period while the correlation was deviated on one with a long roughness period. To further investigate this feature, solid-liquid, solid-vapor interfacial free energies per unit projected area of solid surface were evaluated by using the thermodynamic integration method in independent quasi-one-dimensional simulation systems with a liquid-solid interface or vapor-solid interface on various rough solid surfaces at a constant pressure. The cosine of the apparent contact angles estimated from the density profile of the droplet systems corresponded well with ones calculated from Young's equation using the interfacial energies evaluated in the quasi-one dimensional systems.

The Effect of Water and Confinement on Self-Assembly of Imidazolium Based Ionic Liquids at Mica Interfaces

PubMed Central

Cheng, H.-W.; Dienemann, J.-N.; Stock, P.; Merola, C.; Chen, Y.-J.; Valtiner, M.

2016-01-01

Tuning chemical structure and molecular layering of ionic liquids (IL) at solid interfaces offers leverage to tailor performance of ILs in applications such as super-capacitors, catalysis or lubrication. Recent experimental interpretations suggest that ILs containing cations with long hydrophobic tails form well-ordered bilayers at interfaces. Here we demonstrate that interfacial bilayer formation is not an intrinsic quality of hydrophobic ILs. In contrast, bilayer formation is triggered by boundary conditions including confinement, surface charging and humidity present in the IL. Therefore, we performed force versus distance profiles using atomic force microscopy and the surface forces apparatus. Our results support models of disperse low-density bilayer formation in confined situations, at high surface charging and/or in the presence of water. Conversely, interfacial structuring of long-chain ILs in dry environments and at low surface charging is disordered and dominated by bulk structuring. Our results demonstrate that boundary conditions such as charging, confinement and doping by impurities have decisive influence on structure formation of ILs at interfaces. As such, these results have important implications for understanding the behavior of solid/IL interfaces as they significantly extend previous interpretations. PMID:27452615

The Effect of Water and Confinement on Self-Assembly of Imidazolium Based Ionic Liquids at Mica Interfaces.

PubMed

Cheng, H-W; Dienemann, J-N; Stock, P; Merola, C; Chen, Y-J; Valtiner, M

2016-07-25

Tuning chemical structure and molecular layering of ionic liquids (IL) at solid interfaces offers leverage to tailor performance of ILs in applications such as super-capacitors, catalysis or lubrication. Recent experimental interpretations suggest that ILs containing cations with long hydrophobic tails form well-ordered bilayers at interfaces. Here we demonstrate that interfacial bilayer formation is not an intrinsic quality of hydrophobic ILs. In contrast, bilayer formation is triggered by boundary conditions including confinement, surface charging and humidity present in the IL. Therefore, we performed force versus distance profiles using atomic force microscopy and the surface forces apparatus. Our results support models of disperse low-density bilayer formation in confined situations, at high surface charging and/or in the presence of water. Conversely, interfacial structuring of long-chain ILs in dry environments and at low surface charging is disordered and dominated by bulk structuring. Our results demonstrate that boundary conditions such as charging, confinement and doping by impurities have decisive influence on structure formation of ILs at interfaces. As such, these results have important implications for understanding the behavior of solid/IL interfaces as they significantly extend previous interpretations.

Depth profile of halide anions under highly charged biological membrane

NASA Astrophysics Data System (ADS)

Sung, Woongmo; Wang, Wenjie; Lee, Jonggwan; Vaknin, David; Kim, Doseok

2015-03-01

Halide ion (Cl- and I-) distribution under a cationic Langmuir monolayer consisting of 1,2-dipalmitoyl-3 trimethylammonium-propane (DPTAP) molecules was investigated by vibrational sum-frequency generation (VSFG) and X-ray spectroscopy. From VSFG spectra, it was observed that large halide anions (I-) screen surface charge more efficiently so that interfacial water alignment becomes more randomized. On the other hand, number density of ions directly measured by X-ray fluorescence spectroscopy at grazing incidence angle reveals that the ion densities within 6 ~ 8 nm are the same for both I- and Cl-. Since the observed ion densities in both cases are almost equal to the charge density of the DPTAP monolayer, we propose that larger halide anions are attracted closer to the surface making direct binding with the charged headgroups of the molecules in the monolayer, accomplishing charge neutrality in short distance. This direct adsorption of anions also disturbs the monolayer structure both in terms of the conformation of alkyl chains and the vertical configuration of the monolayer, with iodine having the stronger effect. Our study shows that the length scale that ions neutralize a charged interface varies significantly and specifically even between monovalent ions.

Enhancement of the Mechanical Properties of Basalt Fiber-Wood-Plastic Composites via Maleic Anhydride Grafted High-Density Polyethylene (MAPE) Addition.

PubMed

Chen, Jinxiang; Wang, Yong; Gu, Chenglong; Liu, Jianxun; Liu, Yufu; Li, Min; Lu, Yun

2013-06-18

This study investigated the mechanisms, using microscopy and strength testing approaches, by which the addition of maleic anhydride grafted high-density polyethylene (MAPE) enhances the mechanical properties of basalt fiber-wood-plastic composites (BF-WPCs). The maximum values of the specific tensile and flexural strengths are achieved at a MAPE content of 5%-8%. The elongation increases rapidly at first and then continues slowly. The nearly complete integration of the wood fiber with the high-density polyethylene upon MAPE addition to WPC is examined, and two models of interfacial behavior are proposed. We examined the physical significance of both interfacial models and their ability to accurately describe the effects of MAPE addition. The mechanism of formation of the Model I interface and the integrated matrix is outlined based on the chemical reactions that may occur between the various components as a result of hydrogen bond formation or based on the principle of compatibility, resulting from similar polarity. The Model I fracture occurred on the outer surface of the interfacial layer, visually demonstrating the compatibilization effect of MAPE addition.

First-Order Interfacial Transformations with a Critical Point: Breaking the Symmetry at a Symmetric Tilt Grain Boundary

NASA Astrophysics Data System (ADS)

Yang, Shengfeng; Zhou, Naixie; Zheng, Hui; Ong, Shyue Ping; Luo, Jian

2018-02-01

First-order interfacial phaselike transformations that break the mirror symmetry of the symmetric ∑5 (210 ) tilt grain boundary (GB) are discovered by combining a modified genetic algorithm with hybrid Monte Carlo and molecular dynamics simulations. Density functional theory calculations confirm this prediction. This first-order coupled structural and adsorption transformation, which produces two variants of asymmetric bilayers, vanishes at an interfacial critical point. A GB complexion (phase) diagram is constructed via semigrand canonical ensemble atomistic simulations for the first time.

SIMS depth profiling of rubber-tyre cord bonding layers prepared using 64Zn depleted ZnO

NASA Astrophysics Data System (ADS)

Fulton, W. S.; Sykes, D. E.; Smith, G. C.

2006-07-01

Zinc oxide and copper/zinc sulphide layers are formed during vulcanisation and moulding of rubber to brass-coated steel tyre reinforcing cords. Previous studies have described how zinc diffuses through the rubber-brass interface to form zinc sulphide, and combines with oxygen to create zinc oxide during dezincification. The zinc is usually assumed to originate in the brass of the tyre cord, however, zinc oxide is also present in the rubber formulation. We reveal how zinc from these sources is distributed within the interfacial bonding layers, before and after heat and humidity ageing. Zinc oxide produced using 64Zn-isotope depleted zinc was mixed in the rubber formulation in place of the natural ZnO and the zinc isotope ratios within the interfacial layers were followed by secondary ion mass spectroscopy (SIMS) depth profiling. Variations in the relative ratios of the zinc isotopes during depth profiling were measured for unaged, heat-aged and humidity-aged wire samples and in each case a relatively large proportion of the zinc incorporated into the interfacial layer as zinc sulphide was shown to have originated from ZnO in the rubber compound.

Transforming from planar to three-dimensional lithium with flowable interphase for solid lithium metal batteries

PubMed Central

Liu, Yayuan; Lin, Dingchang; Jin, Yang; Liu, Kai; Tao, Xinyong; Zhang, Qiuhong; Zhang, Xiaokun; Cui, Yi

2017-01-01

Solid-state lithium (Li) metal batteries are prominent among next-generation energy storage technologies due to their significantly high energy density and reduced safety risks. Previously, solid electrolytes have been intensively studied and several materials with high ionic conductivity have been identified. However, there are still at least three obstacles before making the Li metal foil-based solid-state systems viable, namely, high interfacial resistance at the Li/electrolyte interface, low areal capacity, and poor power output. The problems are addressed by incorporating a flowable interfacial layer and three-dimensional Li into the system. The flowable interfacial layer can accommodate the interfacial fluctuation and guarantee excellent adhesion at all time, whereas the three-dimensional Li significantly reduces the interfacial fluctuation from the whole electrode level (tens of micrometers) to local scale (submicrometer) and also decreases the effective current density for high-capacity and high-power operations. As a consequence, both symmetric and full-cell configurations can achieve greatly improved electrochemical performances in comparison to the conventional Li foil, which are among the best reported values in the literature. Noticeably, solid-state full cells paired with high–mass loading LiFePO4 exhibited, at 80°C, a satisfactory specific capacity even at a rate of 5 C (110 mA·hour g−1) and a capacity retention of 93.6% after 300 cycles at a current density of 3 mA cm−2 using a composite solid electrolyte middle layer. In addition, when a ceramic electrolyte middle layer was adopted, stable cycling with greatly improved capacity could even be realized at room temperature. PMID:29062894

Transforming from planar to three-dimensional lithium with flowable interphase for solid lithium metal batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yayuan; Lin, Dingchang; Jin, Yang

Solid-state lithium (Li) metal batteries are prominent among next-generation energy storage technologies due to their significantly high energy density and reduced safety risks. Previously, solid electrolytes have been intensively studied and several materials with high ionic conductivity have been identified. However, there are still at least three obstacles before making the Li metal foil-based solid-state systems viable, namely, high interfacial resistance at the Li/electrolyte interface, low areal capacity, and poor power output. The problems are addressed by incorporating a flowable interfacial layer and three-dimensional Li into the system. The flowable interfacial layer can accommodate the interfacial fluctuation and guarantee excellentmore » adhesion at all time, whereas the three-dimensional Li significantly reduces the interfacial fluctuation from the whole electrode level (tens of micrometers) to local scale (submicrometer) and also decreases the effective current density for high-capacity and high-power operations. As a consequence, both symmetric and full-cell configurations can achieve greatly improved electrochemical performances in comparison to the conventional Li foil, which are among the best reported values in the literature. Noticeably, solid-state full cells paired with high–mass loading LiFePO4 exhibited, at 80°C, a satisfactory specific capacity even at a rate of 5 C (110 mA·hour g -1) and a capacity retention of 93.6% after 300 cycles at a current density of 3 mA cm -2 using a composite solid electrolyte middle layer. In addition, when a ceramic electrolyte middle layer was adopted, stable cycling with greatly improved capacity could even be realized at room temperature.« less

Transforming from planar to three-dimensional lithium with flowable interphase for solid lithium metal batteries

DOE PAGES

Liu, Yayuan; Lin, Dingchang; Jin, Yang; ...

2017-10-01

Solid-state lithium (Li) metal batteries are prominent among next-generation energy storage technologies due to their significantly high energy density and reduced safety risks. Previously, solid electrolytes have been intensively studied and several materials with high ionic conductivity have been identified. However, there are still at least three obstacles before making the Li metal foil-based solid-state systems viable, namely, high interfacial resistance at the Li/electrolyte interface, low areal capacity, and poor power output. The problems are addressed by incorporating a flowable interfacial layer and three-dimensional Li into the system. The flowable interfacial layer can accommodate the interfacial fluctuation and guarantee excellentmore » adhesion at all time, whereas the three-dimensional Li significantly reduces the interfacial fluctuation from the whole electrode level (tens of micrometers) to local scale (submicrometer) and also decreases the effective current density for high-capacity and high-power operations. As a consequence, both symmetric and full-cell configurations can achieve greatly improved electrochemical performances in comparison to the conventional Li foil, which are among the best reported values in the literature. Noticeably, solid-state full cells paired with high–mass loading LiFePO4 exhibited, at 80°C, a satisfactory specific capacity even at a rate of 5 C (110 mA·hour g -1) and a capacity retention of 93.6% after 300 cycles at a current density of 3 mA cm -2 using a composite solid electrolyte middle layer. In addition, when a ceramic electrolyte middle layer was adopted, stable cycling with greatly improved capacity could even be realized at room temperature.« less

A note on the resonant interaction between a surface wave and two interfacial waves

NASA Astrophysics Data System (ADS)

Jamali, Mirmosadegh; Lawrence, Gregory A.; Seymour, Brian

2003-09-01

Hill & Foda (1998) and Jamali (1998) have presented theoretical and experimental studies of the resonant interaction between a surface wave and two oblique interfacial waves. Despite many similarities between the findings there is one seemingly major difference. Hill & Foda's (1998) analysis indicated that there are only narrow bands of frequency, density ratio and direction angle within which growth is possible. On the other hand, Jamali (1998) predicted and observed wave growth over wide ranges of frequency and direction angle, and for all the density ratios that he investigated. We show that Hill & Foda's (1998) second-order representation of the dynamic interfacial boundary condition is missing a term proportional to the time derivative of the square of the velocity shear across the interface. When this missing term is included in the analysis, the resulting predictions are consistent with the laboratory experiments.

A Note on the Resonant Interaction of a Surface Wave With two Interfacial Waves

NASA Astrophysics Data System (ADS)

Jamali, M.; Lawrence, G. A.; Seymour, B. R.

2002-12-01

Recently Hill and Foda (1998) and Jamali (1998) have performed theoretical and experimental studies of the resonant interaction between a surface wave and two oblique interfacial waves. Despite many similarities between the findings of the two studies there is one seemingly major difference. The analysis of Hill and Foda (1998) indicated that there are only narrow bands of frequency, density ratio, and direction angle within which growth is possible. On the other hand Jamali (1998) predicted and observed wave growth over wide ranges of frequency and direction angle, and for all the density ratios that he investigated. We show that second order representation of the dynamic interfacial boundary condition of Hill and Foda (1998) is missing a term proportional to the velocity shear across the interface. When this missing term is included in the analysis the resulting predictions are consistent with the laboratory experiments.

The complex fluid dynamics of simple diffusion

NASA Astrophysics Data System (ADS)

Vold, Erik

2017-11-01

Diffusion as the mass transport process responsible for mixing fluids at the atomic level is often underestimated in its complexity. An initial discontinuity between two species of different atomic masses exhibits a mass density discontinuity under isothermal pressure equilibrium implying equal species molar densities. The self-consistent kinetic transport processes across such an interface leads to a zero sum of mass flux relative to the center of mass and so diffusion alone cannot relax an initially stationary mass discontinuity nor broaden the density profile at the interface. The diffusive mixing leads to a molar imbalance which drives a center of mass velocity which moves the heavier species toward the lighter species leading to the interfacial density relaxation. Simultaneously, the species non-zero molar flux modifies the pressure profile in a transient wave and in a local perturbation. The resulting center of mass velocity has two components; one, associated with the divergence of the flow, persists in the diffusive mixing region throughout the diffusive mixing process, and two, travelling waves at the front of the pressure perturbations propagate away from the mixing region. The momentum in these waves is necessary to maintain momentum conservation in the center of mass frame. Thus, in a number of ways, the diffusive mixing provides feedback into the small scale advective motions. Numerical methods which diffuse all species assuming P-T equilibrium may not recover the subtle dynamics of mass transport at an interface. Work performed by the LANS, LLC, under USDOE Contract No. DE-AC52-06NA25396, funded by the (ASC) Program.

Interfacial Water-Transport Effects in Proton-Exchange Membranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kienitz, Brian; Yamada, Haruhiko; Nonoyama, Nobuaki

2009-11-19

It is well known that the proton-exchange membrane is perhaps the most critical component of a polymer-electrolyte fuel cell. Typical membranes, such as Nafion(R), require hydration to conduct efficiently and are instrumental in cell water management. Recently, evidence has been shown that these membranes might have different interfacial morphology and transport properties than in the bulk. In this paper, experimental data combined with theoretical simulations will be presented that explore the existence and impact of interfacial resistance on water transport for Nafion(R) 21x membranes. A mass-transfer coefficient for the interfacial resistance is calculated from experimental data using different permeation cells.more » This coefficient is shown to depend exponentially on relative humidity or water activity. The interfacial resistance does not seem to exist for liquid/membrane or membrane/membrane interfaces. The effect of the interfacial resistance is to flatten the water-content profiles within the membrane during operation. Under typical operating conditions, the resistance is on par with the water-transport resistance of the bulk membrane. Thus, the interfacial resistance can be dominant especially in thin, dry membranes and can affect overall fuel-cell performance.« less

Enhancement of the Device Performance and the Stability with a Homojunction-structured Tungsten Indium Zinc Oxide Thin Film Transistor.

PubMed

Park, Hyun-Woo; Song, Aeran; Choi, Dukhyun; Kim, Hyung-Jun; Kwon, Jang-Yeon; Chung, Kwun-Bum

2017-09-14

Tungsten-indium-zinc-oxide thin-film transistors (WIZO-TFTs) were fabricated using a radio frequency (RF) co-sputtering system with two types of source/drain (S/D)-electrode material of conducting WIZO (homojunction structure) and the indium-tin oxide (ITO) (heterojunction structure) on the same WIZO active-channel layer. The electrical properties of the WIZO layers used in the S/D electrode and the active-channel layer were adjusted through oxygen partial pressure during the deposition process. To explain enhancements of the device performance and stability of the homojunction-structured WIZO-TFT, a systematic investigation of correlation between device performance and physical properties at the interface between the active layer and the S/D electrodes such as the contact resistance, surface/interfacial roughness, interfacial-trap density, and interfacial energy-level alignments was conducted. The homojunction-structured WIZO-TFT exhibited a lower contact resistance, smaller interfacial-trap density, and flatter interfacial roughness than the WIZO-TFT with the heterojunction structure. The 0.09 eV electron barrier of the homojunction-structured WIZO-TFT is lower than the 0.21 eV value that was obtained for the heterojunction-structured WIZO-TFT. This reduced electron barrier may be attributed to enhancements of device performance and stability, that are related to the carrier transport.

Engineering Pt/Pd Interfacial Electronic Structures for Highly Efficient Hydrogen Evolution and Alcohol Oxidation.

PubMed

Fan, Jinchang; Qi, Kun; Zhang, Lei; Zhang, Haiyan; Yu, Shansheng; Cui, Xiaoqiang

2017-05-31

Tailoring the interfacial structure of Pt-based catalysts has emerged as an effective strategy to improve catalytic activity. However, little attention has been focused on investigating the relationship between the interfacial facets and their catalytic activity. Here, we design and implement Pd-Pt interfaces with controlled heterostructure features by epitaxially growing Pt nanoparticles on Pd nanosheets. On the basis of both density functional theory calculation and experimental results, we demonstrate that charge transfer from Pd to Pt is highly dependent on the interfacial facets of Pd substrates. Therefore, the Pd-Pt heterostructure with Pd(100)-Pt interface exhibits excellent activity and long-term stability for hydrogen evolution and methanol/ethanol oxidation reactions in alkaline medium, much better than that with Pd (111)-Pt interface or commercial Pt/C. Interfacial crystal facet-dependent electronic structural modulation sheds a light on the design and investigation of new heterostructures for high-activity catalysts.

Unexpected molecular weight effect in polymer nanocomposites

DOE PAGES

Cheng, Shiwang; Holt, Adam P.; Wang, Huiqun; ...

2016-01-22

Here, the properties of the interfacial layer between the polymer matrix and nanoparticles largely determine the macroscopic properties of polymer nanocomposites (PNCs). Although the static thickness of the interfacial layer was found to increase with the molecular weight (MW), the influence of MW on segmental relaxation and the glass transition in this layer remains to be explored. In this Letter, we show an unexpected MW dependence of the interfacial properties in PNC with attractive polymer-nanoparticle interactions: the thickness of the interfacial layer with hindered segmental relaxation decreases as MW increases, in sharp constrast to theoretical predictions. Further analyses reveal amore » reduction in mass density of the interfacial layer with increasing MW, which can explain these unexpected dynamic effects. Our observations call for a significant revision of the current understandings of PNCs and suggest interesting ways to tailor their properties.« less

Quantitative assessment of interfacial interactions with rough membrane surface and its implications for membrane selection and fabrication in a MBR.

PubMed

Chen, Jianrong; Mei, Rongwu; Shen, Liguo; Ding, Linxian; He, Yiming; Lin, Hongjun; Hong, Huachang

2015-03-01

The interfacial interactions between a foulant particle and rough membrane surface in a submerged membrane bioreactor (MBR) were quantitatively assessed by using a new-developed method. It was found that the profile of total interaction versus separation distance was complicated. There were an energy barrier and two negative energy ranges in the profile. Further analysis showed that roughness scale significantly affected the strength and properties of interfacial interactions. It was revealed that there existed a critical range of roughness scale within which the total energy in the separation distance ranged from 0 to several nanometers was continually repulsive. Decrease in foulant size would increase the strength of specific interaction energy, but did not change the existence of a critical roughness scale range. These findings suggested the possibility to "tailor" membrane surface morphology for membrane fouling mitigation, and thus gave significant implications for membrane selection and fabrication in MBRs. Copyright © 2014 Elsevier Ltd. All rights reserved.

Application of nanoindentation testing to study of the interfacial transition zone in steel fiber reinforced mortar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Xiaohui; Jacobsen, Stefan; He Jianying

2009-08-15

The characteristics of the profiles of elastic modulus and hardness of the steel fiber-matrix and fiber-matrix-aggregate interfacial zones in steel fiber reinforced mortars have been investigated by using nanoindentation and Scanning Electron Microscopy (SEM), where two sets of parameters, i.e. water/binder ratio and content of silica fume were considered. Different interfacial bond conditions in the interfacial transition zones (ITZ) are discussed. For sample without silica fume, efficient interfacial bonds across the steel fiber-matrix and fiber-matrix-aggregate interfaces are shown in low water/binder ratio mortar; while in high water/binder ratio mortar, due to the discontinuous bleeding voids underneath the fiber, the fiber-matrixmore » bond is not very good. On the other hand, for sample with silica fume, the addition of 10% silica fume leads to no distinct presence of weak ITZ in the steel fiber-matrix interface; but the effect of the silica fume on the steel fiber-matrix-aggregate interfacial zone is not obvious due to voids in the vicinity of steel fiber.« less

On interfacial properties of tetrahydrofuran: Atomistic and coarse-grained models from molecular dynamics simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garrido, J. M.; Algaba, J.; Blas, F. J., E-mail: felipe@uhu.es

2016-04-14

We have determined the interfacial properties of tetrahydrofuran (THF) from direct simulation of the vapor-liquid interface. The molecules are modeled using six different molecular models, three of them based on the united-atom approach and the other three based on a coarse-grained (CG) approach. In the first case, THF is modeled using the transferable parameters potential functions approach proposed by Chandrasekhar and Jorgensen [J. Chem. Phys. 77, 5073 (1982)] and a new parametrization of the TraPPE force fields for cyclic alkanes and ethers [S. J. Keasler et al., J. Phys. Chem. B 115, 11234 (2012)]. In both cases, dispersive and coulombicmore » intermolecular interactions are explicitly taken into account. In the second case, THF is modeled as a single sphere, a diatomic molecule, and a ring formed from three Mie monomers according to the SAFT-γ Mie top-down approach [V. Papaioannou et al., J. Chem. Phys. 140, 054107 (2014)]. Simulations were performed in the molecular dynamics canonical ensemble and the vapor-liquid surface tension is evaluated from the normal and tangential components of the pressure tensor along the simulation box. In addition to the surface tension, we have also obtained density profiles, coexistence densities, critical temperature, density, and pressure, and interfacial thickness as functions of temperature, paying special attention to the comparison between the estimations obtained from different models and literature experimental data. The simulation results obtained from the three CG models as described by the SAFT-γ Mie approach are able to predict accurately the vapor-liquid phase envelope of THF, in excellent agreement with estimations obtained from TraPPE model and experimental data in the whole range of coexistence. However, Chandrasekhar and Jorgensen model presents significant deviations from experimental results. We also compare the predictions for surface tension as obtained from simulation results for all the models with experimental data. The three CG models predict reasonably well (but only qualitatively) the surface tension of THF, as a function of temperature, from the triple point to the critical temperature. On the other hand, only the TraPPE united-atoms models are able to predict accurately the experimental surface tension of the system in the whole temperature range.« less

Interfacial dynamic surface traps of lead sulfide (PbS) nanocrystals: test-platform for interfacial charge carrier traps at the organic/inorganic functional interface

NASA Astrophysics Data System (ADS)

Kim, Youngjun; Ko, Hyungduk; Park, Byoungnam

2018-04-01

Nanocrystal (NC) size and ligand dependent dynamic trap formation of lead sulfide (PbS) NCs in contact with an organic semiconductor were investigated using a pentacene/PbS field effect transistor (FET). We used a bilayer pentacene/PbS FET to extract information of the surface traps of PbS NCs at the pentacene/PbS interface through the field effect-induced charge carrier density measurement in the threshold and subthreshold regions. PbS size and ligand dependent trap properties were elucidated by the time domain and threshold voltage measurements in which threshold voltage shift occurs by carrier charging and discharging in the trap states of PbS NCs. The observed threshold voltage shift is interpreted in context of electron trapping through dynamic trap formation associated with PbS NCs. To the best of our knowledge, this is the first demonstration of the presence of interfacial dynamic trap density of PbS NC in contact with an organic semiconductor (pentacene). We found that the dynamic trap density of the PbS NC is size dependent and the carrier residence time in the specific trap sites is more sensitive to NC size variation than to NC ligand exchange. The probing method presented in the study offers a means to investigate the interfacial surface traps at the organic-inorganic hetero-junction, otherwise understanding of the buried surface traps at the functional interface would be elusive.

Multiple-relaxation-time color-gradient lattice Boltzmann model for simulating two-phase flows with high density ratio

NASA Astrophysics Data System (ADS)

Ba, Yan; Liu, Haihu; Li, Qing; Kang, Qinjun; Sun, Jinju

2016-08-01

In this paper we propose a color-gradient lattice Boltzmann (LB) model for simulating two-phase flows with high density ratio and high Reynolds number. The model applies a multirelaxation-time (MRT) collision operator to enhance the stability of the simulation. A source term, which is derived by the Chapman-Enskog analysis, is added into the MRT LB equation so that the Navier-Stokes equations can be exactly recovered. Also, a form of the equilibrium density distribution function is used to simplify the source term. To validate the proposed model, steady flows of a static droplet and the layered channel flow are first simulated with density ratios up to 1000. Small values of spurious velocities and interfacial tension errors are found in the static droplet test, and improved profiles of velocity are obtained by the present model in simulating channel flows. Then, two cases of unsteady flows, Rayleigh-Taylor instability and droplet splashing on a thin film, are simulated. In the former case, the density ratio of 3 and Reynolds numbers of 256 and 2048 are considered. The interface shapes and spike and bubble positions are in good agreement with the results of previous studies. In the latter case, the droplet spreading radius is found to obey the power law proposed in previous studies for the density ratio of 100 and Reynolds number up to 500.

Giant interfacial perpendicular magnetic anisotropy in Fe/CuIn 1 -xGaxSe2 beyond Fe/MgO

NASA Astrophysics Data System (ADS)

Masuda, Keisuke; Kasai, Shinya; Miura, Yoshio; Hono, Kazuhiro

2017-11-01

We study interfacial magnetocrystalline anisotropies in various Fe/semiconductor heterostructures by means of first-principles calculations. We find that many of those systems show perpendicular magnetic anisotropy (PMA) with a positive value of the interfacial anisotropy constant Ki. In particular, the Fe/CuInSe 2 interface has a large Ki of ˜2.3 mJ /m2 , which is about 1.6 times larger than that of Fe/MgO known as a typical system with relatively large PMA. We also find that the values of Ki in almost all the systems studied in this work follow the well-known Bruno's relation, which indicates that minority-spin states around the Fermi level provide dominant contributions to the interfacial magnetocrystalline anisotropies. Detailed analyses of the local density of states and wave-vector-resolved anisotropy energy clarify that the large Ki in Fe/CuInSe 2 is attributed to the preferable 3 d -orbital configurations around the Fermi level in the minority-spin states of the interfacial Fe atoms. Moreover, we have shown that the locations of interfacial Se atoms are the key for such orbital configurations of the interfacial Fe atoms.

Interfacial waves generated by electrowetting-driven contact line motion

NASA Astrophysics Data System (ADS)

Ha, Jonghyun; Park, Jaebum; Kim, Yunhee; Shin, Bongsu; Bae, Jungmok; Kim, Ho-Young

2016-10-01

The contact angle of a liquid-fluid interface can be effectively modulated by the electrowetting-on-dielectric (EWOD) technology. Rapid movement of the contact line can be achieved by swift changes of voltage at the electrodes, which can give rise to interfacial waves under the strong influence of surface tension. Here we experimentally demonstrate EWOD-driven interfacial waves of overlapping liquids and compare their wavelength and decay length with the theoretical results obtained by a perturbation analysis. Our theory also allows us to predict the temporal evolution of the interfacial profiles in either rectangular or cylindrical containers, as driven by slipping contact lines. This work builds a theoretical framework to understand and predict the dynamics of capillary waves of a liquid-liquid interface driven by EWOD, which has practical implications on optofluidic devices used to guide light.

Enhancement of the Mechanical Properties of Basalt Fiber-Wood-Plastic Composites via Maleic Anhydride Grafted High-Density Polyethylene (MAPE) Addition

PubMed Central

Chen, Jinxiang; Wang, Yong; Gu, Chenglong; Liu, Jianxun; Liu, Yufu; Li, Min; Lu, Yun

2013-01-01

This study investigated the mechanisms, using microscopy and strength testing approaches, by which the addition of maleic anhydride grafted high-density polyethylene (MAPE) enhances the mechanical properties of basalt fiber-wood-plastic composites (BF-WPCs). The maximum values of the specific tensile and flexural strengths areachieved at a MAPE content of 5%–8%. The elongation increases rapidly at first and then continues slowly. The nearly complete integration of the wood fiber with the high-density polyethylene upon MAPE addition to WPC is examined, and two models of interfacial behavior are proposed. We examined the physical significance of both interfacial models and their ability to accurately describe the effects of MAPE addition. The mechanism of formation of the Model I interface and the integrated matrix is outlined based on the chemical reactions that may occur between the various components as a result of hydrogen bond formation or based on the principle of compatibility, resulting from similar polarity. The Model I fracture occurred on the outer surface of the interfacial layer, visually demonstrating the compatibilization effect of MAPE addition. PMID:28809285

Solid-liquid interfacial free energy of ice Ih, ice Ic, and ice 0 within a mono-atomic model of water via the capillary wave method.

PubMed

Ambler, Michael; Vorselaars, Bart; Allen, Michael P; Quigley, David

2017-02-21

We apply the capillary wave method, based on measurements of fluctuations in a ribbon-like interfacial geometry, to determine the solid-liquid interfacial free energy for both polytypes of ice I and the recently proposed ice 0 within a mono-atomic model of water. We discuss various choices for the molecular order parameter, which distinguishes solid from liquid, and demonstrate the influence of this choice on the interfacial stiffness. We quantify the influence of discretisation error when sampling the interfacial profile and the limits on accuracy imposed by the assumption of quasi one-dimensional geometry. The interfacial free energies of the two ice I polytypes are indistinguishable to within achievable statistical error and the small ambiguity which arises from the choice of order parameter. In the case of ice 0, we find that the large surface unit cell for low index interfaces constrains the width of the interfacial ribbon such that the accuracy of results is reduced. Nevertheless, we establish that the interfacial free energy of ice 0 at its melting temperature is similar to that of ice I under the same conditions. The rationality of a core-shell model for the nucleation of ice I within ice 0 is questioned within the context of our results.

Flux-pinning-induced interfacial shearing and transverse normal stress in a superconducting coated conductor long strip

NASA Astrophysics Data System (ADS)

Jing, Ze; Yong, Huadong; Zhou, Youhe

2012-08-01

In this paper, a theoretical model is proposed to analyze the transverse normal stress and interfacial shearing stress induced by the electromagnetic force in the superconducting coated conductor. The plane strain approach is used and a singular integral equation is derived. By assuming that the critical current density is magnetic field independent and the superconducting film is infinitely thin, the interfacial shearing stress and normal stress in the film are evaluated for the coated conductor during the increasing and decreasing in the transport current, respectively. The calculation results are discussed and compared for the conductor with different substrate and geometry. The results indicate that the coated conductor with stiffer substrate and larger width experiences larger interfacial shearing stress and less normal stress in the film.

Interplay between Interfacial Structures and Device Performance in Organic Solar Cells: A Case Study with the Low Work Function Metal, Calcium.

PubMed

Ju, Huanxin; Knesting, Kristina M; Zhang, Wei; Pan, Xiao; Wang, Chia-Hsin; Yang, Yaw-Wen; Ginger, David S; Zhu, Junfa

2016-01-27

A better understanding of how interfacial structure affects charge carrier recombination would benefit the development of highly efficient organic photovoltaic (OPV) devices. In this paper, transient photovoltage (TPV) and charge extraction (CE) measurements are used in combination with synchrotron radiation photoemission spectroscopy (SRPES) to gain insight into the correlation between interfacial properties and device performance. OPV devices based on PCDTBT/PC71BM with a Ca interlayer were studied as a reference system to investigate the interfacial effects on device performance. Devices with a Ca interlayer exhibit a lower recombination than devices with only an Al cathode at a given charge carrier density (n). In addition, the interfacial band structures indicate that the strong dipole moment produced by the Ca interlayer can facilitate the extraction of electrons and drive holes away from the cathode/polymer interface, resulting in beneficial reduction in interfacial recombination losses. These results help explain the higher efficiencies of devices made with Ca interlayers compared to that without the Ca interlayer.

Auger compositional depth profiling of the metal contact-TlBr interface

NASA Astrophysics Data System (ADS)

Nelson, A. J.; Swanberg, E. L.; Voss, L. F.; Graff, R. T.; Conway, A. M.; Nikolic, R. J.; Payne, S. A.; Kim, H.; Cirignano, L.; Shah, K.

2015-08-01

Degradation of room temperature operation of TlBr radiation detectors with time is thought to be due to electromigration of Tl and Br vacancies within the crystal as well as the metal contacts migrating into the TlBr crystal itself due to electrochemical reactions at the metal/TlBr interface. Scanning Auger electron spectroscopy (AES) in combination with sputter depth profiling was used to investigate the metal contact surface/interfacial structure on TlBr devices. Device-grade TlBr was polished and subjected to a 32% HCl etch to remove surface damage and create a TlBr1-xClx surface layer prior to metal contact deposition. Auger compositional depth profiling results reveal non-equilibrium interfacial diffusion after device operation in both air and N2 at ambient temperature. These results improve our understanding of contact/device degradation versus operating environment for further enhancing radiation detector performance.

Nondestructive depth profile of the chemical state of ultrathin Al2O3/Si interface

NASA Astrophysics Data System (ADS)

Lee, Jong Cheol; Oh, S.-J.

2004-05-01

We investigated a depth profile of the chemical states of an Al2O3/Si interface using nondestructive photon energy-dependent high-resolution x-ray photoelectron spectroscopy (HRXPS). The Si 2p binding energy, attributed to the oxide interfacial layer (OIL), was found to shift from 102.1 eV to 102.9 eV as the OIL region closer to Al2O3 layer was sampled, while the Al 2p binding energy remains the same. This fact strongly suggests that the chemical state of the interfacial layer is not Al silicate as previously believed. We instead propose from the HRXPS of Al 2p and Si 2p depth-profile studies that the chemical states of the Al2O3/Si interface mainly consist of SiO2 and Si2O3.

Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements, and Crazing

DOE PAGES

Ge, Ting; Grest, Gary S.; Robbins, Mark O.

2014-09-26

Large-scale molecular simulations are performed to investigate tensile failure of polymer interfaces as a function of welding time t. Changes in the tensile stress, mode of failure and interfacial fracture energy G I are correlated to changes in the interfacial entanglements as determined from Primitive Path Analysis. Bulk polymers fail through craze formation, followed by craze breakdown through chain scission. At small t welded interfaces are not strong enough to support craze formation and fail at small strains through chain pullout at the interface. Once chains have formed an average of about one entanglement across the interface, a stable crazemore » is formed throughout the sample. The failure stress of the craze rises with welding time and the mode of craze breakdown changes from chain pullout to chain scission as the interface approaches bulk strength. The interfacial fracture energy G I is calculated by coupling the simulation results to a continuum fracture mechanics model. As in experiment, G I increases as t 1/2 before saturating at the average bulk fracture energy G b. As in previous studies of shear strength, saturation coincides with the recovery of the bulk entanglement density. Before saturation, G I is proportional to the areal density of interfacial entanglements. Immiscibiltiy limits interdiffusion and thus suppresses entanglements at the interface. Even small degrees of immisciblity reduce interfacial entanglements enough that failure occurs by chain pullout and G I << G b.« less

Grafting of polyethylenimine onto cellulose nanofibers for interfacial enhancement in their epoxy nanocomposites.

PubMed

Zhao, Jiangqi; Li, Qingye; Zhang, Xiaofang; Xiao, Meijie; Zhang, Wei; Lu, Canhui

2017-02-10

Cellulose nanofibers (CNFs) were surface-modified with polyethyleneimine (PEI), which brought plentiful amine groups on the surface of CNFs, leading to a reduced hydrogen bond density between CNFs and consequently less CNFs agglomerates. The amine groups could also react with the epoxy as an effective curing agent that could increase the interfacial crosslinking density and strengthen interfacial adhesion. The tensile strength and Young's modulus of CNFs-PEI/Epoxy nanocomposites were 88.1% and 237.6% higher than those of neat epoxy, respectively. The tensile storage modulus of the nanocomposites also increased significantly at the temperature either below or above the Tg. The coefficient of thermal expansion for the CNFs-PEI/Epoxy nanocomposites was 22.2ppmK -1 , much lower than that of the neat epoxy (88.6ppmK -1 ). In addition, the thermal conductivity of the nanocomposites was observed to increase as well. The exceptional and balanced properties may provide the nanocomposites promising applications in automotive, construction and electronic devices. Copyright © 2016 Elsevier Ltd. All rights reserved.

Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Nam-Hui; Jung, Jinyong; Cho, Jaehun

2015-10-05

We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlO{sub x} and Ta/Pt/Co/AlO{sub x} structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy are significantly improved due to the better interface between heavy metal and ferromagnetic layer. From the frequency shift between Stokes- and anti-Stokes spin-waves, we successively obtain considerably larger iDM energy densities (D{sub max} = 1.65 ± 0.13 mJ/m{sup 2} at t{sub Co} = 1.35 nm) upon adding the Ta buffer layer, despite the nominally identical interface materials. Moreover, the energy density shows an inverse proportionality with the Co layer thickness,more » which is the critical clue that the observed iDMI is indeed originating from the interface between the Pt and Co layers.« less

Analysis of nanoscale two-phase flow of argon using molecular dynamics

NASA Astrophysics Data System (ADS)

Verma, Abhishek Kumar; Kumar, Rakesh

2014-12-01

Two phase flows through micro and nanochannels have attracted a lot of attention because of their immense applicability to many advanced fields such as MEMS/NEMS, electronic cooling, bioengineering etc. In this work, a molecular dynamics simulation method is employed to study the condensation process of superheated argon vapor force driven flow through a nanochannel combining fluid flow and heat transfer. A simple and effective particle insertion method is proposed to model phase change of argon based on non-periodic boundary conditions in the simulation domain. Starting from a crystalline solid wall of channel, the condensation process evolves from a transient unsteady state where we study the influence of different wall temperatures and fluid wall interactions on interfacial and heat transport properties of two phase flows. Subsequently, we analyzed transient temperature, density and velocity fields across the channel and their dependency on varying wall temperature and fluid wall interaction, after a dynamic equilibrium is achieved in phase transition. Quasi-steady nonequilibrium temperature profile, heat flux and interfacial thermal resistance were analyzed. The results demonstrate that the molecular dynamics method, with the proposed particle insertion method, effectively solves unsteady nonequilibrium two phase flows at nanoscale resolutions whose interphase between liquid and vapor phase is typically of the order of a few molecular diameters.

Interfacial Coupling Effect on Electron Transport in MoS2/SrTiO3 Heterostructure: An Ab-initio Study.

PubMed

Bano, Amreen; Gaur, N K

2018-01-15

A variety of theoretical and experimental works have reported several potential applications of MoS 2 monolayer based heterostructures (HSs) such as light emitting diodes, photodetectors and field effect transistors etc. In the present work, we have theoretically performed as a model case study, MoS 2 monolayer deposited over insulating SrTiO 3 (001) to study the band alignment at TiO 2 termination. The interfacial characteristics are found to be highly dependent on the interface termination. With an insulating oxide material, a significant band gap (0.85eV) is found in MoS 2 /TiO 2 interface heterostructure (HS). A unique electronic band profile with an indirect band gap (0.67eV) is observed in MoS 2 monolayer when confined in a cubic environment of SrTiO 3 (STO). Adsorption analysis showed the chemisorption of MoS 2 on the surface of STO substrate with TiO 2 termination which is justified by the charge density calculations that shows the existence of covalent bonding at the interface. The fabrication of HS of such materials paves the path for developing the unprecedented 2D materials with exciting properties such as semiconducting devices, thermoelectric and optoelectronic applications.

Two-Layer Viscous Shallow-Water Equations and Conservation Laws

NASA Astrophysics Data System (ADS)

Kanayama, Hiroshi; Dan, Hiroshi

In our previous papers, the two-layer viscous shallow-water equations were derived from the three-dimensional Navier-Stokes equations under the hydrostatic assumption. Also, it was noted that the combination of upper and lower equations in the two-layer model produces the classical one-layer equations if the density of each layer is the same. Then, the two-layer equations were approximated by a finite element method which followed our numerical scheme established for the one-layer model in 1978. Also, it was numerically demonstrated that the interfacial instability generated when the densities are the same can be eliminated by providing a sufficient density difference. In this paper, we newly show that conservation laws are still valid in the two-layer model. Also, we show results of a new physical experiment for the interfacial instability.

Adsorption properties of polar/apolar inducers at a charged interface and their relevance to leukemia cell differentiation.

PubMed

Carlà, M; Cuomo, M; Arcangeli, A; Olivotto, M

1995-06-01

The interfacial adsorption properties of polar/apolar inducers of cell differentiation (PAIs) were studied on a mercury electrode. This study, on a clean and reproducible charged surface, unraveled the purely physical interactions among these compounds and the surface, apart from the complexity of the biological membrane. The interfacial behavior of two classical inducers, hexamethylenebisacetamide (HMBA) and dimethylsulfoxide, was compared with that of a typical apolar aliphatic compound, 1-octanol, that has a similar hydrophobic moiety as HMBA but a much smaller dipolar moment. Both HMBA and Octanol adsorb flat in contact with the surface because of hydrophobic forces, with a very similar free energy of adsorption. However, the ratio of polar to apolar moieties in PAIs turned out to be crucial to drive the adsorption maximum toward physiological values of surface charge density, where octanol is desorbed. The electrostatic effects in the interfacial region reflected the adsorption properties: the changes in the potential drop across the interfacial region as a function of the surface charge density, in the physiological range, were opposite in PAIs as compared with apolar aliphatic compounds, as exemplified by octanol. This peculiar electrostatic effect of PAIs has far-reaching relevance for the design of inducers with an adequate therapeutic index to be used in clinical trials.

Probing Interfacial Processes on Graphene Surface by Mass Detection

NASA Astrophysics Data System (ADS)

Kakenov, Nurbek; Kocabas, Coskun

2013-03-01

In this work we studied the mass density of graphene, probed interfacial processes on graphene surface and examined the formation of graphene oxide by mass detection. The graphene layers were synthesized by chemical vapor deposition method on copper foils and transfer-printed on a quartz crystal microbalance (QCM). The mass density of single layer graphene was measured by investigating the mechanical resonance of the QCM. Moreover, we extended the developed technique to probe the binding dynamics of proteins on the surface of graphene, were able to obtain nonspecific binding constant of BSA protein of graphene surface in aqueous solution. The time trace of resonance signal showed that the BSA molecules rapidly saturated by filling the available binding sites on graphene surface. Furthermore, we monitored oxidation of graphene surface under oxygen plasma by tracing the changes of interfacial mass of the graphene controlled by the shifts in Raman spectra. Three regimes were observed the formation of graphene oxide which increases the interfacial mass, the release of carbon dioxide and the removal of small graphene/graphene oxide flakes. Scientific and Technological Research Council of Turkey (TUBITAK) grant no. 110T304, 109T209, Marie Curie International Reintegration Grant (IRG) grant no 256458, Turkish Academy of Science (TUBA-Gebip).

Connecting Molecular Dynamics Simulations and Fluids Density Functional Theory of Block Copolymers

NASA Astrophysics Data System (ADS)

Hall, Lisa

Increased understanding and precise control over the nanoscale structure and dynamics of microphase separated block copolymers would advance development of mechanically robust but conductive materials for battery electrolytes, among other applications. Both coarse-grained molecular dynamics (MD) simulations and fluids (classical) density functional theory (fDFT) can capture the microphase separation of block copolymers, using similar monomer-based chain models and including local packing effects. Equilibrium free energies of various microphases are readily accessible from fDFT, which allows us to efficiently determine the equilibrium nanostructure over a large parameter space. Meanwhile, MD allows us to visualize specific polymer conformations in 3D over time and to calculate dynamic properties. The fDFT density profiles are used to initialize the MD simulations; this ensures the MD proceeds in the appropriate microphase separated state rather than in a metastable structure (useful especially for nonlamellar structures). The simulations equilibrate more quickly than simulations initialized with a random state, which is significant especially for long chains. We apply these methods to study the interfacial behavior and microphase separated structure of diblock and tapered block copolymers. Tapered copolymers consist of pure A and B monomer blocks on the ends separated by a tapered region that smoothly varies from A to B (or from B to A for an inverse taper). Intuitively, tapering increases the segregation strength required for the material to microphase separate and increases the width of the interfacial region. Increasing normal taper length yields a lower domain spacing and increased polymer mobility, while larger inverse tapers correspond to even lower domain spacing but decreased mobility. Thus the changes in dynamics with tapering cannot be explained by mapping to a diblock system at an adjusted effective segregation strength. This material is based upon work supported by the National Science Foundation under Grant 1454343 and the Department of Energy under Grant DE-SC0014209.

Measurements of Submicron Particle Adsorption and Particle Film Elasticity at Oil-Water Interfaces.

PubMed

Manga, Mohamed S; Hunter, Timothy N; Cayre, Olivier J; York, David W; Reichert, Matthew D; Anna, Shelly L; Walker, Lynn M; Williams, Richard A; Biggs, Simon R

2016-05-03

The influence of particle adsorption on liquid/liquid interfacial tension is not well understood, and much previous research has suggested conflicting behaviors. In this paper we investigate the surface activity and adsorption kinetics of charge stabilized and pH-responsive polymer stabilized colloids at oil/water interfaces using two tensiometry techniques: (i) pendant drop and (ii) microtensiometer. We found, using both techniques, that charge stabilized particles had little or no influence on the (dynamic) interfacial tension, although dense silica particles affected the "apparent" measured tension in the pendent drop, due to gravity driven elongation of the droplet profile. Nevertheless, this apparent change additionally allowed the study of adsorption kinetics, which was related qualitatively between particle systems by estimated diffusion coefficients. Significant and real interfacial tension responses were measured using ∼53 nm core-shell latex particles with a pH-responsive polymer stabilizer of poly(methyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (pMMA-b-pDMAEMA) diblock copolymer. At pH 2, where the polymer is strongly charged, behavior was similar to that of the bare charge-stabilized particles, showing little change in the interfacial tension. At pH 10, where the polymer is discharged and poorly soluble in water, a significant decrease in the measured interfacial tension commensurate with strong adsorption at the oil-water interface was seen, which was similar in magnitude to the surface activity of the free polymer. These results were both confirmed through droplet profile and microtensiometry experiments. Dilational elasticity measurements were also performed by oscillation of the droplet; again, changes in interfacial tension with droplet oscillation were only seen with the responsive particles at pH 10. Frequency sweeps were performed to ascertain the dilational elasticity modulus, with measured values being significantly higher than previously reported for nanoparticle and surfactant systems, and similar in magnitude to protein stabilized droplets.

Petascale Simulations of the Morphology and the Molecular Interface of Bulk Heterojunctions

DOE PAGES

Carrillo, Jan-Michael Y.; Seibers, Zach; Kumar, Rajeev; ...

2016-07-14

Understanding how additives interact and segregate within bulk heterojunction (BHJ) thin films is critical for exercising control over structure at multiple length scales and delivering improvements in photovoltaic performance. The morphological evolution of poly(3-hexylthiophene) (P3HT) and phenyl-C 61-butyric acid methyl ester (PCBM) blends that are commensurate with the size of a BHJ thin film is examined using petascale coarse-grained molecular dynamics simulations. When comparing 2 component and 3 component systems containing short P3HT chains as additives undergoing thermal annealing we demonstrate that the short chains alter the morphol- ogy in apparently useful ways: They efficiently migrate to the P3HT/PCBM interface,more » increasing the P3HT domain size and interfacial area. Simulation results agree with depth profiles determined from neutron reflectometry measurements that reveal PCBM enrichment near substrate and air interfaces, but a decrease in that PCBM enrich- ment when a small amount of short P3HT chains are integrated into the BHJ blend. Atomistic simulations of the P3HT/PCBM blend interfaces show a non-monotonic dependence of the interfacial thickness as a function of number of repeat units in the oligomeric P3HT additive, and the thiophene rings orient parallel to the interfacial plane as they approach the PCBM domain. Using the nanoscale geometries of the P3HT oligomers, LUMO and HOMO energy levels calculated by density functional theory are found to be invariant across the donor/acceptor interface. Finally, these connections between additives, processing, and morphology at all length scales are generally useful for efforts to improve device performance.« less

Effects of raw materials on the properties of wood fiber-polyethylene composites--part 3: effect of a compatibilizer and wood adhesive on the interfacial adhesion of wood/plastic composites

Treesearch

Chin-yin Hwang; Chung-yun Hse; Todd F. Shupe

2008-01-01

The objective of this study was to examine the effect of maleated polypropylene compatabilizer on the interfacial properties of wood and polyolefins. Birch wood dowels containing an adhesive applied on the surface were embedded in molten plastic matrices using specially designed jigs. The three plastics investigated included low density polyethylene (LFPE), linear low...

Mixing and Formation of Layers by Internal Wave Forcing

NASA Astrophysics Data System (ADS)

Dossmann, Yvan; Pollet, Florence; Odier, Philippe; Dauxois, Thierry

2017-12-01

The energy pathways from propagating internal waves to the scales of irreversible mixing in the ocean are not fully described. In the ocean interior, the triadic resonant instability is an intrinsic destabilization process that may enhance the energy cascade away from topographies. The present study focuses on the integrated impact of mixing processes induced by a propagative normal mode-1 over long-term experiments in an idealized setup. The internal wave dynamics and the evolution of the density profile are followed using the light attenuation technique. Diagnostics of the turbulent diffusivity KT and background potential energy BPE are provided. Mixing effects result in a partially mixed layer colocated with the region of maximum shear induced by the forcing normal mode. The maximum measured turbulent diffusivity is 250 times larger than the molecular value, showing that diapycnal mixing is largely enhanced by small-scale turbulent processes. Intermittency and reversible energy transfers are discussed to bridge the gap between the present diagnostic and the larger values measured in Dossmann et al. (). The mixing efficiency η is assessed by relating the BPE growth to the linearized KE input. One finds a value of Γ=12-19%, larger than the mixing efficiency in the case of breaking interfacial wave. After several hours of forcing, the development of staircases in the density profile is observed. This mechanism has been previously observed in experiments with weak homogeneous turbulence and explained by Phillips (1972) argument. The present experiments suggest that internal wave forcing could also induce the formation of density interfaces in the ocean.

Multiple-relaxation-time color-gradient lattice Boltzmann model for simulating two-phase flows with high density ratio

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ba, Yan; Liu, Haihu; Li, Qing

2016-08-15

In this paper, we propose a color-gradient lattice Boltzmann (LB) model for simulating two-phase flows with high density ratio and high Reynolds number. The model applies a multi-relaxation-time (MRT) collision operator to enhance the stability of the simulation. A source term, which is derived by the Chapman-Enskog analysis, is added into the MRT LB equation so that the Navier-Stokes equations can be exactly recovered. Also, a new form of the equilibrium density distribution function is used to simplify the source term. To validate the proposed model, steady flows of a static droplet and the layered channel flow are first simulatedmore » with density ratios up to 1000. Small values of spurious velocities and interfacial tension errors are found in the static droplet test, and improved profiles of velocity are obtained by the present model in simulating channel flows. Then, two cases of unsteady flows, Rayleigh-Taylor instability and droplet splashing on a thin film, are simulated. In the former case, the density ratio of 3 and Reynolds numbers of 256 and 2048 are considered. The interface shapes and spike/bubble positions are in good agreement with the results of previous studies. In the latter case, the droplet spreading radius is found to obey the power law proposed in previous studies for the density ratio of 100 and Reynolds number up to 500.« less

Enhanced interfacial deformation in a Marangoni flow: A measure of the dynamical surface tension

NASA Astrophysics Data System (ADS)

Leite Pinto, Rodrigo; Le Roux, Sébastien; Cantat, Isabelle; Saint-Jalmes, Arnaud

2018-02-01

We investigate the flows and deformations resulting from the deposition of a water soluble surfactant at a bare oil-water interface. Once the surfactant is deposited, we show that the oil-water interface is deformed with a water bump rising upward into the oil. For a given oil, the maximal deformation—located at the surfactant deposition point—decreases with the oil-layer thickness. We also observe a critical oil-layer thickness below which the deformation becomes as large as the oil layer, leading to the rupture of this layer and an oil-water dewetting. Experimentally, it is found that this critical thickness depends on the oil density and viscosity. We then provide an analytical modelization that explains quantitatively all these experimental features. In particular, our analysis allows us to derive an analytical relationship between the vertical profile of the oil-water interface and the in-plane surface tension profile. Therefore, we propose that the monitoring of the interface vertical shape can be used as a new spatially resolved tensiometry technique.

Surface tension and phase coexistence properties of the lattice fluid from a virtual site removal Monte Carlo strategy

NASA Astrophysics Data System (ADS)

Provata, Astero; Prassas, Vassilis D.; Theodorou, Doros N.

1997-10-01

A thin liquid film of lattice fluid in equilibrium with its vapor is studied in 2 and 3 dimensions with canonical Monte Carlo simulation (MC) and Self-Consistent Field Theory (SCF) in the temperature range 0.45Tc to Tc, where Tc the liquid-gas critical temperature. Extending the approach of Oates et al. [Philos. Mag. B 61, 337 (1990)] to anisotropic systems, we develop a method for the MC computation of the transverse and normal pressure profiles, hence of the surface tension, based on virtual removals of individual sites or blocks of sites from the system. Results from implementation of this new method, obtained at very modest computational cost, are in reasonable agreement with exact values and other MC estimates of the surface tension of the 2-d and 3-d model systems, respectively. SCF estimates of the interfacial density profiles, the surface tension, the vapor pressure curve and the binodal curve compare well with MC results away from Tc, but show the expected deviations at high temperatures.

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

PubMed Central

Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

2016-01-01

Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

Intermolecular and interfacial forces: Elucidating molecular mechanisms using chemical force microscopy

NASA Astrophysics Data System (ADS)

Ashby, Paul David

Investigation into the origin of forces dates to the early Greeks. Yet, only in recent decades have techniques for elucidating the molecular origin of forces been developed. Specifically, Chemical Force Microscopy uses the high precision and nanometer scale probe of Atomic Force Microscopy to measure molecular and interfacial interactions. This thesis presents the development of many novel Chemical Force Microscopy techniques for measuring equilibrium and time-dependant force profiles of molecular interactions, which led to a greater understanding of the origin of interfacial forces in solution. In chapter 2, Magnetic Feedback Chemical Force Microscopy stiffens the cantilever for measuring force profiles between self-assembled monolayer (SAM) surfaces. Hydroxyl and carboxyl terminated SAMs produce long-range interactions that extend one or three nanometers into the solvent, respectively. In chapter 3, an ultra low noise AFM is produced through multiple modifications to the optical deflection detection system and signal processing electronics. In chapter 4, Brownian Force Profile Reconstruction is developed for accurate measurement of steep attractive interactions. Molecular ordering is observed for OMCTS, 1-nonanol, and water near flat surfaces. The molecular ordering of the solvent produces structural or solvation forces, providing insight into the orientation and possible solidification of the confined solvent. Seven molecular layers of OMCTS are observed but the oil remains fluid to the last layer. 1-nonanol strongly orders near the surface and becomes quasi-crystalline with four layers. Water is oriented by the surface and symmetry requires two layers of water (3.7 A) to be removed simultaneously. In chapter 5, electronic control of the cantilever Q (Q-control) is used to obtain the highest imaging sensitivity. In chapter 6, Energy Dissipation Chemical Force Microscopy is developed to investigate the time dependence and dissipative characteristics of SAM interfacial interactions in solution. Long-range adhesive forces for hydroxyl and carboxyl terminated SAM surfaces arise from solvent, not ionic, interactions. Exclusion of the solvent and contact between the SAM surfaces leads to rearrangement of the SAM headgroups. The isolation of the chemical and physical interfacial properties from the topography by Energy Dissipation Chemical Force Microscopy produces a new quantitative high-sensitivity imaging mode.

Dependence of interfacial Dzyaloshinskii-Moriya interaction and perpendicular magnetic anisotropy on the thickness of the heavy-metal layer

NASA Astrophysics Data System (ADS)

Kim, Nam-Hui; Han, Dong-Soo; Jung, Jinyong; Park, Kwonjin; Swagten, Henk J. M.; Kim, June-Seo; You, Chun-Yeol

2017-10-01

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) and the interfacial perpendicular magnetic anisotropy (iPMA) between a heavy metal and ferromagnet are investigated by employing Brillouin light scattering. With increasing thickness of the heavy-metal (Pt) layer, the iDMI and iPMA energy densities are rapidly enhanced and they saturate for a Pt thickness of 2.4 nm. Since these two individual magnetic properties show the same Pt thickness dependence, this is evidence that the iDMI and iPMA at the interface between the heavy metal and ferromagnet, the physical origin of these phenomena, are effectively enhanced upon increasing the thickness of the heavy-metal layer.

The effect of crystallographic misorientation and interfacial separation on jump-to-contact behavior and defect generation in aluminum

NASA Astrophysics Data System (ADS)

Khajehvand, Milad; Sepehrband, Panthea

2018-07-01

The jump-to-contact (JC) phenomenon for (111)-oriented surfaces in aluminum at room temperature is studied via molecular dynamics simulations. The effect of crystallographic misorientation and interfacial distance on the JC behavior and distribution of the resultant defects at the interface is investigated. The effect of misorientation on the critical distance for JC is found to be negligible. However, when JC occurs, different distribution of defects is observed for various misorientation angles. The density of defects is shown to be a function of interfacial distance for low misorientation angles, but independent of it for misorientation angles of ∼30 ± 10°.

Deconstructing Temperature Gradients across Fluid Interfaces: The Structural Origin of the Thermal Resistance of Liquid-Vapor Interfaces

NASA Astrophysics Data System (ADS)

Muscatello, Jordan; Chacón, Enrique; Tarazona, Pedro; Bresme, Fernando

2017-07-01

The interfacial thermal resistance determines condensation-evaporation processes and thermal transport across material-fluid interfaces. Despite its importance in transport processes, the interfacial structure responsible for the thermal resistance is still unknown. By combining nonequilibrium molecular dynamics simulations and interfacial analyses that remove the interfacial thermal fluctuations we show that the thermal resistance of liquid-vapor interfaces is connected to a low density fluid layer that is adsorbed at the liquid surface. This thermal resistance layer (TRL) defines the boundary where the thermal transport mechanism changes from that of gases (ballistic) to that characteristic of dense liquids, dominated by frequent particle collisions involving very short mean free paths. We show that the thermal conductance is proportional to the number of atoms adsorbed in the TRL, and hence we explain the structural origin of the thermal resistance in liquid-vapor interfaces.

First-Principles Prediction of Liquid/Liquid Interfacial Tension.

PubMed

Andersson, M P; Bennetzen, M V; Klamt, A; Stipp, S L S

2014-08-12

The interfacial tension between two liquids is the free energy per unit surface area required to create that interface. Interfacial tension is a determining factor for two-phase liquid behavior in a wide variety of systems ranging from water flooding in oil recovery processes and remediation of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid/liquid systems of arbitrary compositions. The consistency of the predictions with experimental data is significant for binary, ternary, and multicomponent water/organic compound systems, which offers confidence in using the model to predict behavior where no data exists. The method is fast and can be used as a screening technique as well as to extend experimental data into conditions where measurements are technically too difficult, time consuming, or impossible.

Two-Fluid Models and Interfacial Area Transport in Microgravity Condition

NASA Technical Reports Server (NTRS)

Ishii, Mamoru; Sun, Xiao-Dong; Vasavada, Shilp

2004-01-01

The objective of the present study is to develop a two-fluid model formulation with interfacial area transport equation applicable for microgravity conditions. The new model is expected to make a leapfrog improvement by furnishing the constitutive relations for the interfacial interaction terms with the interfacial area transport equation, which can dynamically model the changes of the interfacial structures. In the first year of this three-year project supported by the U.S. NASA, Office of Biological and Physics Research, the primary focus is to design and construct a ground-based, microgravity two-phase flow simulation facility, in which two immiscible fluids with close density will be used. In predicting the two-phase flow behaviors in any two-phase flow system, the interfacial transfer terms are among the most essential factors in the modeling. These interfacial transfer terms in a two-fluid model specify the rate of phase change, momentum exchange, and energy transfer at the interface between the two phases. For the two-phase flow under the microgravity condition, the stability of the fluid particle interface and the interfacial structures are quite different from those under normal gravity condition. The flow structure may not reach an equilibrium condition and the two fluids may be loosely coupled such that the inertia terms of each fluid should be considered separately by use of the two-fluid model. Previous studies indicated that, unless phase-interaction terms are accurately modeled in the two-fluid model, the complex modeling does not necessarily warrant an accurate solution.

Interfacial Charge-Carrier Trapping in CH3NH3PbI3-Based Heterolayered Structures Revealed by Time-Resolved Photoluminescence Spectroscopy.

PubMed

Yamada, Yasuhiro; Yamada, Takumi; Shimazaki, Ai; Wakamiya, Atsushi; Kanemitsu, Yoshihiko

2016-06-02

The fast-decaying component of photoluminescence (PL) under very weak pulse photoexcitation is dominated by the rapid relaxation of the photoexcited carriers into a small number of carrier-trapping defect states. Here, we report the subnanosecond decay of the PL under excitation weaker than 1 nJ/cm(2) both in CH3NH3PbI3-based heterostructures and bare thin films. The trap-site density at the interface was evaluated on the basis of the fluence-dependent PL decay profiles. It was found that high-density defects determining the PL decay dynamics are formed near the interface between CH3NH3PbI3 and the hole-transporting Spiro-OMeTAD but not at the CH3NH3PbI3/TiO2 interface and the interior regions of CH3NH3PbI3 films. This finding can aid the fabrication of high-quality heterointerfaces, which are required improving the photoconversion efficiency of perovskite-based solar cells.

Interfacial welding of dynamic covalent network polymers

NASA Astrophysics Data System (ADS)

Yu, Kai; Shi, Qian; Li, Hao; Jabour, John; Yang, Hua; Dunn, Martin L.; Wang, Tiejun; Qi, H. Jerry

2016-09-01

Dynamic covalent network (or covalent adaptable network) polymers can rearrange their macromolecular chain network by bond exchange reactions (BERs) where an active unit replaces a unit in an existing bond to form a new bond. Such macromolecular events, when they occur in large amounts, can attribute to unusual properties that are not seen in conventional covalent network polymers, such as shape reforming and surface welding; the latter further enables the important attributes of material malleability and powder-based reprocessing. In this paper, a multiscale modeling framework is developed to study the surface welding of thermally induced dynamic covalent network polymers. At the macromolecular network level, a lattice model is developed to describe the chain density evolution across the interface and its connection to bulk stress relaxation due to BERs. The chain density evolution rule is then fed into a continuum level interfacial model that takes into account surface roughness and applied pressure to predict the effective elastic modulus and interfacial fracture energy of welded polymers. The model yields particularly accessible results where the moduli and interfacial strength of the welded samples as a function of temperature and pressure can be predicted with four parameters, three of which can be measured directly. The model identifies the dependency of surface welding efficiency on the applied thermal and mechanical fields: the pressure will affect the real contact area under the consideration of surface roughness of dynamic covalent network polymers; the chain density increment on the real contact area of interface is only dependent on the welding time and temperature. The modeling approach shows good agreement with experiments and can be extended to other types of dynamic covalent network polymers using different stimuli for BERs, such as light and moisture etc.

Transport properties at fluids interfaces: a molecular study for a macroscopic modelling

NASA Astrophysics Data System (ADS)

Russo, Antonio; Morciano, Matteo; Sibley, David N.; Nold, Andreas; Goddard, Benjamin D.; Asinari, Pietro; Kalliadasis, Serafim

2017-11-01

Rapid developments in the field of micro- and nano-fluidics require detailed analysis of the properties of matter at the molecular level. But despite numerous works in the literature, appropriate macroscopic relations able to integrate a microscopic description of fluid and soft matter properties at liquid-vapour and multi-fluid interfaces are missing. As a consequence, studies on interfacial phenomena and micro-device designs often rely on oversimplified assumptions, e.g. that the viscosities can be considered constant across interfaces. In our work, we present non-equilibrium MD simulations to scrutinise efficiently and systematically, through the tools of statistical mechanics, the anisotropic properties of fluids, namely density variations, stress tensor, and shear viscosity, at the fluid interfaces between liquid and vapour and between two partially miscible fluids. Our analysis has led to the formulation of a general relation between shear viscosity and density variations validated for a wide spectrum of interfacial fluid problems. In addition, it provides a rational description of other interfacial quantities of interest, including surface tension and its origins, and more generally, it offers valuable insight of molecular transport phenomena at interfaces.

A correlation between secondary structure and rheological properties of low-density lipoproteins at air/water interfaces.

PubMed

Khattari, Ziad

2017-09-01

The secondary structure of apolipoprotein B-100 is studied within the bulk phase and at the air/water interface. In these "in viro" experiments, infrared reflection absorption spectroscopy (IRRAS) study was performed at the air/water interface while circular dichroism (CD) was conducted in the bulk phase. In the bulk phase, the conformational structure containing a significant amount of β-structure, whereas varying amount of α-helix, unordered structures, and β-sheet were observed at the air/water interface depending on the low-density lipoprotein (LDL) film interfacial pressure. The present IRRAS results demonstrate the importance of interfacial pressure-induced structural conformations on the apoB-100. A correlation between the secondary structure of the apoB-100 protein and the monomolecular film elasticity at the air/water interface was also established. The orientation of apoB-100 with respect to the LDL film-normal was found to depend on the interfacial pressure exhibited by the monomolecular film. These results may shed light on LDL's pivotal role in the progression of atherosclerotic coronary artery disease as demonstrated previously by clinical trials.

Influence of physical properties and operating parameters on hydrodynamics in Centrifugal Partition Chromatography.

PubMed

Adelmann, S; Schembecker, G

2011-08-12

Besides the selection of a suitable biphasic solvent system the separation efficiency in Centrifugal Partition Chromatography (CPC) is mainly influenced by the hydrodynamics in the chambers. The flow pattern, the stationary phase retention and the interfacial area for mass transfer strongly depend on physical properties of the solvent system and operating parameters. In order to measure these parameters we visualized the hydrodynamics in a FCPC-chamber for five different solvent systems with an optical measurement system and calculated the stationary phase retention, interfacial area and the distribution of mobile phase thickness in the chamber. Although inclined chambers were used we found that the Coriolis force always deflected the mobile phase towards the chamber wall reducing the interfacial area. This effect increased for systems with low density difference. We also have shown that the stability of phase systems (stationary phase retention) and its tendency to disperse increased for smaller values of the ratio of interfacial tension and density difference. But also the viscosity ratio and the flow pattern itself had a significant effect on retention and dispersion of the mobile phase. As a result operating parameters should be chosen carefully with respect to physical properties for a CPC system. In order to reduce the effect of the Coriolis force CPC devices with greater rotor radius are desirable. Copyright © 2011 Elsevier B.V. All rights reserved.

Interfacial Engineered Polyaniline/Sulfur-Doped TiO2 Nanotube Arrays for Ultralong Cycle Lifetime Fiber-Shaped, Solid-State Supercapacitors.

PubMed

Li, Chun; Wang, Zhuanpei; Li, Shengwen; Cheng, Jianli; Zhang, Yanning; Zhou, Jingwen; Yang, Dan; Tong, Dong-Ge; Wang, Bin

2018-05-30

Fiber-shaped supercapacitors (FSCs) have great promises in wearable electronics applications. However, the limited specific surface area and inadequate structural stability caused by the weak interfacial interactions of the electrodes result in relatively low specific capacitance and unsatisfactory cycle lifetime. Herein, solid-state FSCs with high energy density and ultralong cycle lifetime based on polyaniline (PANI)/sulfur-doped TiO 2 nanotube arrays (PANI/S-TiO 2 ) are fabricated by interfacial engineering. The experimental results and ab initio calculations reveal that S doping can effectively promote the conductivity of titania nanotubes and increase the binding energy of PANI anchored on the electrode surface, leading to a much stronger binding of PANI on the surface of the electrode and excellent electrode structure stability. As a result, the FSCs using the PANI/S-TiO 2 electrodes deliver a high specific capacitance of 91.9 mF cm -2 , a capacitance retention of 93.78% after 12 000 charge-discharge cycles, and an areal energy density of 3.2 μW h cm -2 . Meanwhile, the all-solid-state FSC device retains its excellent flexibility and stable electrochemical capacitance even after bending 150 cycles. The enhanced performances of FSCs could be attributed to the large surface area, reduced ion diffusion path, improved electrical conductivity, and engineered interfacial interaction of the rationally designed electrodes.

Al atom on MoO3(010) surface: adsorption and penetration using density functional theory.

PubMed

Wu, Hong-Zhang; Bandaru, Sateesh; Wang, Da; Liu, Jin; Lau, Woon Ming; Wang, Zhenling; Li, Li-Li

2016-03-14

Interfacial issues, such as the interfacial structure and the interdiffusion of atoms at the interface, are fundamental to the understanding of the ignition and reaction mechanisms of nanothermites. This study employs first-principle density functional theory to model Al/MoO3 by placing an Al adatom onto a unit cell of a MoO3(010) slab, and to probe the initiation of interfacial interactions of Al/MoO3 nanothermite by tracking the adsorption and subsurface-penetration of the Al adatom. The calculations show that the Al adatom can spontaneously go through the topmost atomic plane (TAP) of MoO3(010) and reach the 4-fold hollow adsorption-site located below the TAP, with this subsurface adsorption configuration being the most preferred one among all plausible adsorption configurations. Two other plausible configurations place the Al adatom at two bridge sites located above the TAP of MoO3(010) but the Al adatom can easily penetrate below this TAP to a relatively more stable adsorption configuration, with a small energy barrier of merely 0.2 eV. The evidence of subsurface penetration of Al implies that Al/MoO3 likely has an interface with intermixing of Al, Mo and O atoms. These results provide new insights on the interfacial interactions of Al/MoO3 and the ignition/combustion mechanisms of Al/MoO3 nanothermites.

Quantifying Interfacial pH Variation at Molecular Length Scales Using a Concurrent Non-Faradaic Reaction.

PubMed

Ryu, Jaeyune; Wuttig, Anna; Surendranath, Yogesh

2018-05-15

We quantify changes in the interfacial pH local to the electrochemical double layer during electrocatalysis, using a concurrent non-faradaic probe reaction. In the absence of electrocatalysis, nanostructured Pt/C surfaces mediate the reaction of H2 with cis-2-butene-1,4-diol to form a mixture of 1,4-butanediol and n-butanol with a selectivity that is linearly dependent on the bulk solution pH. We show that kinetic branching occurs from a common surface-bound intermediate, ensuring that this probe reaction is uniquely sensitive to the interfacial pH within molecular length scales of the surface. We use the pH-dependent selectivity of this reaction to track changes in interfacial pH during concurrent hydrogen oxidation electrocatalysis and find that the local pH can vary dramatically, > 3 units, relative to the bulk value even at modest current densities in well-buffered electrolytes. This work highlights the key role that interfacial pH variation plays in modulating inner-sphere electrocatalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal conductance at atomically clean and disordered silicon/aluminum interfaces: A molecular dynamics simulation study

NASA Astrophysics Data System (ADS)

Ih Choi, Woon; Kim, Kwiseon; Narumanchi, Sreekant

2012-09-01

Thermal resistance between layers impedes effective heat dissipation in electronics packaging applications. Thermal conductance for clean and disordered interfaces between silicon (Si) and aluminum (Al) was computed using realistic Si/Al interfaces and classical molecular dynamics with the modified embedded atom method potential. These realistic interfaces, which include atomically clean as well as disordered interfaces, were obtained using density functional theory. At 300 K, the magnitude of interfacial conductance due to phonon-phonon scattering obtained from the classical molecular dynamics simulations was approximately five times higher than the conductance obtained using analytical elastic diffuse mismatch models. Interfacial disorder reduced the thermal conductance due to increased phonon scattering with respect to the atomically clean interface. Also, the interfacial conductance, due to electron-phonon scattering at the interface, was greater than the conductance due to phonon-phonon scattering. This indicates that phonon-phonon scattering is the bottleneck for interfacial transport at the semiconductor/metal interfaces. The molecular dynamics modeling predictions for interfacial thermal conductance for a 5-nm disordered interface between Si/Al were in-line with recent experimental data in the literature.

Tailoring the Interfacial Chemical Interaction for High-Efficiency Perovskite Solar Cells.

PubMed

Zuo, Lijian; Chen, Qi; De Marco, Nicholas; Hsieh, Yao-Tsung; Chen, Huajun; Sun, Pengyu; Chang, Sheng-Yung; Zhao, Hongxiang; Dong, Shiqi; Yang, Yang

2017-01-11

The ionic nature of perovskite photovoltaic materials makes it easy to form various chemical interactions with different functional groups. Here, we demonstrate that interfacial chemical interactions are a critical factor in determining the optoelectronic properties of perovskite solar cells. By depositing different self-assembled monolayers (SAMs), we introduce different functional groups onto the SnO 2 surface to form various chemical interactions with the perovskite layer. It is observed that the perovskite solar cell device performance shows an opposite trend to that of the energy level alignment theory, which shows that chemical interactions are the predominant factor governing the interfacial optoelectronic properties. Further analysis verifies that proper interfacial interactions can significantly reduce trap state density and facilitate the interfacial charge transfer. Through use of the 4-pyridinecarboxylic acid SAM, the resulting perovskite solar cell exhibits striking improvements to the reach the highest efficiency of 18.8%, which constitutes an ∼10% enhancement compared to those without SAMs. Our work highlights the importance of chemical interactions at perovskite/electrode interfaces and paves the way for further optimizing performances of perovskite solar cells.

Interfacial Shear Strength and Adhesive Behavior of Silk Ionomer Surfaces.

PubMed

Kim, Sunghan; Geryak, Ren D; Zhang, Shuaidi; Ma, Ruilong; Calabrese, Rossella; Kaplan, David L; Tsukruk, Vladimir V

2017-09-11

The interfacial shear strength between different layers in multilayered structures of layer-by-layer (LbL) microcapsules is a crucial mechanical property to ensure their robustness. In this work, we investigated the interfacial shear strength of modified silk fibroin ionomers utilized in LbL shells, an ionic-cationic pair with complementary ionic pairing, (SF)-poly-l-glutamic acid (Glu) and SF-poly-l-lysine (Lys), and a complementary pair with partially screened Coulombic interactions due to the presence of poly(ethylene glycol) (PEG) segments and SF-Glu/SF-Lys[PEG] pair. Shearing and adhesive behavior between these silk ionomer surfaces in the swollen state were probed at different spatial scales and pressure ranges by using functionalized atomic force microscopy (AFM) tips as well as functionalized colloidal probes. The results show that both approaches were consistent in analyzing the interfacial shear strength of LbL silk ionomers at different spatial scales from a nanoscale to a fraction of a micron. Surprisingly, the interfacial shear strength between SF-Glu and SF-Lys[PEG] pair with partially screened ionic pairing was greater than the interfacial shear strength of the SF-Glu and SF-Lys pair with a high density of complementary ionic groups. The difference in interfacial shear strength and adhesive strength is suggested to be predominantly facilitated by the interlayer hydrogen bonding of complementary amino acids and overlap of highly swollen PEG segments.

Classical density functional theory and Monte Carlo simulation study of electric double layer in the vicinity of a cylindrical electrode

NASA Astrophysics Data System (ADS)

Zhou, Shiqi; Lamperski, Stanisław; Sokołowska, Marta

2017-07-01

We have performed extensive Monte-Carlo simulations and classical density functional theory (DFT) calculations of the electrical double layer (EDL) near a cylindrical electrode in a primitive model (PM) modified by incorporating interionic dispersion interactions. It is concluded that (i) in general, an unsophisticated use of the mean field (MF) approximation for the interionic dispersion interactions does not distinctly worsen the classical DFT performance, even if the salt ions considered are highly asymmetrical in size (3:1) and charge (5:1), the bulk molar concentration considered is high up to a total bulk ion packing fraction of 0.314, and the surface charge density of up to 0.5 C m-2. (ii) More specifically, considering the possible noises in the simulation, the local volume charge density profiles are the most accurately predicted by the classical DFT in all situations, and the co- and counter-ion singlet distributions are also rather accurately predicted; whereas the mean electrostatic potential profile is relatively less accurately predicted due to an integral amplification of minor inaccuracy of the singlet distributions. (iii) It is found that the layered structure of the co-ion distribution is abnormally possible only if the surface charge density is high enough (for example 0.5 C m-2) moreover, the co-ion valence abnormally influences the peak height of the first counter-ion layer, which decreases with the former. (iv) Even if both the simulation and DFT indicate an insignificant contribution of the interionic dispersion interaction to the above three ‘local’ quantities, it is clearly shown by the classical DFT that the interionic dispersion interaction does significantly influence a ‘global’ quantity like the cylinder surface-aqueous electrolyte interfacial tension, and this may imply the role of the interionic dispersion interaction in explaining the specific Hofmeister effects. We elucidate all of the above observations based on the arguments from the liquid state theory and at the molecular scale.

Ab initio and classical molecular dynamics studies of the structural and dynamical behavior of water near a hydrophobic graphene sheet.

PubMed

Rana, Malay Kumar; Chandra, Amalendu

2013-05-28

The behavior of water near a graphene sheet is investigated by means of ab initio and classical molecular dynamics simulations. The wetting of the graphene sheet by ab initio water and the relation of such behavior to the strength of classical dispersion interaction between surface atoms and water are explored. The first principles simulations reveal a layered solvation structure around the graphene sheet with a significant water density in the interfacial region implying no drying or cavitation effect. It is found that the ab initio results of water density at interfaces can be reproduced reasonably well by classical simulations with a tuned dispersion potential between the surface and water molecules. Calculations of vibrational power spectrum from ab initio simulations reveal a shift of the intramolecular stretch modes to higher frequencies for interfacial water molecules when compared with those of the second solvation later or bulk-like water due to the presence of free OH modes near the graphene sheet. Also, a weakening of the water-water hydrogen bonds in the vicinity of the graphene surface is found in our ab initio simulations as reflected in the shift of intermolecular vibrational modes to lower frequencies for interfacial water molecules. The first principles calculations also reveal that the residence and orientational dynamics of interfacial water are somewhat slower than those of the second layer or bulk-like molecules. However, the lateral diffusion and hydrogen bond relaxation of interfacial water molecules are found to occur at a somewhat faster rate than that of the bulk-like water molecules. The classical molecular dynamics simulations with tuned Lennard-Jones surface-water interaction are found to produce dynamical results that are qualitatively similar to those of ab initio molecular dynamics simulations.

X-Ray Scattering Studies of the Liquid-Vapor Interface of Gallium.

NASA Astrophysics Data System (ADS)

Kawamoto, Eric Hitoshi

A UHV system was developed for performing X-ray scattering studies and in situ analyses of liquid metal surfaces. A nearly ideal choice for this study, gallium has a melting point just above room temperature; is amenable to handling in both air and vacuum; its surface oxides can be removed while its cleanliness is maintained and monitored. Using argon glow-discharge sputtering techniques to remove intervening surface oxides, thin wetting layers of gallium were prepared atop nonreactive substrates, to be used as samples suited for liquid surface scattering experiments. Preliminary measurements of X-ray reflectivity from the liquid-vapor interface of gallium were performed with the X-ray UHV chamber configured for use in conjunction with liquid surface spectrometers at two synchrotron beamlines. A novel technique for carrying out and interpreting scattering measurements from curved liquid surfaces was demonstrated. The energy tunability and intense focused white beam flux from a wiggler source was shown to place within reach the large values of wavevector transfer at which specular reflectivity data yield small length scale information about surface structure. Various theoretical treatments and simulations predict quasi-lamellar ordering of atoms near the free surface of metallic liquids due to energetics particular to metals (electron delocalization, the dependence of system energy on ion and electron densities, surface tension and electrostatic energy). However, the experimental data reported to date is insufficient to distinguish between a monotonic, sigmoidal electron density profile found at the free surfaces of dielectric liquids, and the damped oscillatory layer-like profiles anticipated for metallic liquids. Out to a wavevector transfer of Q = 0.55 A ^{-1}, the reflectivity data measured from a curved Ga surface is not inconsistent with what is expected for a liquid-vapor electron density profile of Gaussian width sigma = 1.3 +/- 0.2 A. Subsequent measurements roughly tripled the range of Q, but an oxidized surface led to poor data and hindered interpretation. The analysis presented is speculative at best, but within the context of the thermally excited capillary wave model of simple liquid surfaces, there seems to be no serious deviation from the simple Gaussian interfacial profile with the aforementioned roughness.

Metal-dielectric interactions

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1979-01-01

Metal direlectric surface interactions and dielectric films on metal substrates were investigated. Since interfacial interaction depends so heavily on the nature of the surfaces, analytical surface tools such as Auger emission spectroscopy, X-ray photoelectron spectroscopy and field ion microscopy were used to assist in surface and interfacial characterization. The results indicate that with metals contacting certain glasses in the clean state interfacial, bonding produces fractures in the glasses while when a film such as water is present, fractures occur in the metal near the interface. Friction forces were used to measure the interfacial bond strengths. Studies with metals contacting polymers using field ion microscopy revealed that strong bonding forces could develop being between a metal and polymer surface with polymer transferring to the metal surface in various ways depending upon the forces applied to the surface in contact. With the deposition of refractory carbides, silicides and borides onto metal and alloy substrates the presence of oxides at the interface or active gases in the deposition plasma were shown to alter interfacial properties and chemistry. Auger ion depth profile analysis indicated the chemical composition at the interface and this could be related to the mechanical, friction, and wear behavior of the coating.

Interfacial reaction dependent performance of hollow carbon nanosphere - sulfur composite as a cathode for Li-S battery

DOE PAGES

Zheng, Jianming; Yan, Pengfei; Gu, Meng; ...

2015-05-26

Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density, cost effectiveness and environmental friendliness of sulfur. However, there are still a number of challenges, such as low Coulombic efficiency and poor long-term cycling stability, impeding the commercialization of Li-S battery. The electrochemical performance of Li-S battery is closely related with the interfacial reactions occurring between hosting substrate and active sulfur species which are poorly conducting at fully oxidized and reduced states. Here, we correlate the relationship between the performance and interfacial reactions in the Li-S battery system, using a hollow carbon nanosphere (HCNS) withmore » highly graphitic character as hosting substrate for sulfur. With an appropriate amount of sulfur loading, HCNS/S composite exhibits excellent electrochemical performance because of the fast interfacial reactions between HCNS and the polysulfides. However, further increase of sulfur loading leads to increased formation of highly resistive insoluble reaction products (Li 2S 2/Li 2S) which limits the reversibility of the interfacial reactions and results in poor electrochemical performance. In conclusion, these findings demonstrate the importance of the interfacial reaction reversibility in the whole electrode system on achieving high capacity and long cycle life of sulfur cathode for Li-S batteries.« less

Electrical impedance imaging in two-phase, gas-liquid flows: 1. Initial investigation

NASA Technical Reports Server (NTRS)

Lin, J. T.; Ovacik, L.; Jones, O. C.

1991-01-01

The determination of interfacial area density in two-phase, gas-liquid flows is one of the major elements impeding significant development of predictive tools based on the two-fluid model. Currently, these models require coupling of liquid and vapor at interfaces using constitutive equations which do not exist in any but the most rudimentary form. Work described herein represents the first step towards the development of Electrical Impedance Computed Tomography (EICT) for nonintrusive determination of interfacial structure and evolution in such flows.

Li-Doped Ionic Liquid Electrolytes: From Bulk Phase to Interfacial Behavior

NASA Technical Reports Server (NTRS)

Haskins, Justin B.; Lawson, John W.

2016-01-01

Ionic liquids have been proposed as candidate electrolytes for high-energy density, rechargeable batteries. We present an extensive computational analysis supported by experimental comparisons of the bulk and interfacial properties of a representative set of these electrolytes as a function of Li-salt doping. We begin by investigating the bulk electrolyte using quantum chemistry and ab initio molecular dynamics to elucidate the solvation structure of Li(+). MD simulations using the polarizable force field of Borodin and coworkers were then performed, from which we obtain an array of thermodynamic and transport properties. Excellent agreement is found with experiments for diffusion, ionic conductivity, and viscosity. Combining MD simulations with electronic structure computations, we computed the electrochemical window of the electrolytes across a range of Li(+)-doping levels and comment on the role of the liquid environment. Finally, we performed a suite of simulations of these Li-doped electrolytes at ideal electrified interfaces to evaluate the differential capacitance and the equilibrium Li(+) distribution in the double layer. The magnitude of differential capacitance is in good agreement with our experiments and exhibits the characteristic camel-shaped profile. In addition, the simulations reveal Li(+) to be highly localized to the second molecular layer of the double layer, which is supported by additional computations that find this layer to be a free energy minimum with respect to Li(+) translation.

Orientation-dependent hydration structures at yttria-stabilized cubic zirconia surfaces

DOE PAGES

Hou, Binyang; Kim, Seunghyun; Kim, Taeho; ...

2016-11-30

Water interaction with surfaces is very important and plays key roles in many natural and technological processes. Because the experimental challenges that arise when studying the interaction water with specific crystalline surfaces, most studies on metal oxides have focused on powder samples, which averaged the interaction over different crystalline surfaces. As a result, studies on the crystal orientation-dependent interaction of water with metal oxides are rarely available in the literature. In this work, water adsorption at 8 mol % yttria-stabilized cubic single crystal zirconia (100) and (111) surfaces was studied in terms of interfacial hydration structures using high resolution X-raymore » reflectivity measurements. The interfacial electron density profiles derived from the structure factor analysis of the measured data show the existence of multiple layers of adsorbed water with additional peculiar metal adsorption near the oxide surfaces.Surface relaxation, depletion, and interaction between the adsorbed layers and bulk water are found to vary greatly between the two surfaces and are also different when compared to the previously studied (110) surface. The fractional ratio between chemisorbed and physisorbed water species were also quantitatively estimated, which turned out to vary dramatically from surface to surface. Finally, the result gives us a unique opportunity to reconsider the simplified 2:1 relation between chemisorption and physisorption, originally proposed by Morimoto et al. based on the adsorption isotherms of water on powder metal oxide samples.« less

Interface Trap Density Reduction for Al2O3/GaN (0001) Interfaces by Oxidizing Surface Preparation prior to Atomic Layer Deposition.

PubMed

Zhernokletov, Dmitry M; Negara, Muhammad A; Long, Rathnait D; Aloni, Shaul; Nordlund, Dennis; McIntyre, Paul C

2015-06-17

We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.

Plasma modification of sisal and high-density polyethylene composites : effect on mechanical properties

Treesearch

A.R. Martin; S. Manolache; L.H.C. Mattoso; R.M. Rowell; F. Denes

2000-01-01

Sisal fibers and finely powdered high-density polyethylene were surface functionalized using dichlorosilane (DS) under R-F plasma conditions to improve interfacial adhesion between the two dissimilar substrates. The functionalized polyethylene (70%) and sisal (30%) were compounded on four different ways using thermokinetic mixer and injected molded into composites...

Density gradients at hydrogel interfaces for enhanced cell penetration.

PubMed

Simona, B R; Hirt, L; Demkó, L; Zambelli, T; Vörös, J; Ehrbar, M; Milleret, V

2015-04-01

We report that stiffness gradients facilitate infiltration of cells through otherwise cell-impermeable hydrogel interfaces. By enabling the separation of hydrogel manufacturing and cell seeding, and by improving cell colonization of additively manufactured hydrogel elements, interfacial density gradients present a promising strategy to progress in the creation of 3D tissue models.

Decoupling electron and ion storage and the path from interfacial storage to artificial electrodes

NASA Astrophysics Data System (ADS)

Chen, Chia-Chin; Maier, Joachim

2018-02-01

The requirements for rechargeable batteries place high demands on the electrodes. Efficient storage means accommodating both ions and electrons, not only in substantial amounts, but also with substantial velocities. The materials' space could be largely extended by decoupling the roles of ions and electrons such that transport and accommodation of ions take place in one phase of a composite, and transport and accommodation of electrons in the other phase. Here we discuss this synergistic concept being equally applicable for positive and negative electrodes along with examples from the literature for Li-based and Ag-based cells. Not only does the concept have the potential to mitigate the trade-off between power density and energy density, it also enables a generalized view of bulk and interfacial storage as necessary for nanocrystals. It furthermore allows for testable predictions of heterogeneous storage in passivation layers, dependence of transfer resistance on the state of charge, or heterogeneous storage of hydrogen at appropriate contacts. We also present an outlook on constructing artificial mixed-conductor electrodes that have the potential to achieve both high energy density and high power density.

Mode selective generation of guided waves by systematic optimization of the interfacial shear stress profile

NASA Astrophysics Data System (ADS)

Yazdanpanah Moghadam, Peyman; Quaegebeur, Nicolas; Masson, Patrice

2015-01-01

Piezoelectric transducers are commonly used in structural health monitoring systems to generate and measure ultrasonic guided waves (GWs) by applying interfacial shear and normal stresses to the host structure. In most cases, in order to perform damage detection, advanced signal processing techniques are required, since a minimum of two dispersive modes are propagating in the host structure. In this paper, a systematic approach for mode selection is proposed by optimizing the interfacial shear stress profile applied to the host structure, representing the first step of a global optimization of selective mode actuator design. This approach has the potential of reducing the complexity of signal processing tools as the number of propagating modes could be reduced. Using the superposition principle, an analytical method is first developed for GWs excitation by a finite number of uniform segments, each contributing with a given elementary shear stress profile. Based on this, cost functions are defined in order to minimize the undesired modes and amplify the selected mode and the optimization problem is solved with a parallel genetic algorithm optimization framework. Advantages of this method over more conventional transducers tuning approaches are that (1) the shear stress can be explicitly optimized to both excite one mode and suppress other undesired modes, (2) the size of the excitation area is not constrained and mode-selective excitation is still possible even if excitation width is smaller than all excited wavelengths, and (3) the selectivity is increased and the bandwidth extended. The complexity of the optimal shear stress profile obtained is shown considering two cost functions with various optimal excitation widths and number of segments. Results illustrate that the desired mode (A0 or S0) can be excited dominantly over other modes up to a wave power ratio of 1010 using an optimal shear stress profile.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth.

PubMed

Jarisz, Tasha A; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K

2018-06-14

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth

NASA Astrophysics Data System (ADS)

Jarisz, Tasha A.; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K.

2018-06-01

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Viscoplastic sculpting in stable triple layer heavy oil transport flow

NASA Astrophysics Data System (ADS)

Sarmadi, Parisa; Hormozi, Sarah; A. Frigaard, Ian

2017-11-01

In we introduced a novel methodology for efficient transport of heavy oil via a triple layer core-annular flow. Pumping pressures are significantly reduced by concentrating high shear rates to a lubricating layer, while ideas from Visco-Plastic Lubrication are used to eliminate interfacial instabilities. We purposefully position a shaped unyielded skin of a viscoplastic fluid between the transported oil and the lubricating fluid layer to balance the density difference between the fluids. Here we address the sculpting of the shaped skin within a concentric inflow manifold. We use the quasi-steady model to provide inputs to an axisymmetric triple layer computation, showing the development of the streamwise skin profile and establishment of the flow. For this, we use a finite element discretization with the augmented-Lagrangian method to represent the yield surface behaviour accurately and a PLIC method to track the interface motion.

Boundary Waves on the Ice Surface Created by Currents

NASA Astrophysics Data System (ADS)

Naito, K.; Izumi, N.; Yokokawa, M.; Yamada, T.; de Lima, A. C.

2013-12-01

The formation of periodic boundary waves, e.g. antidunes and cyclic steps (Parker & Izumi 2000) has been known to be caused by instabilities between flow and bed (e.g. Engelund 1970), and are observed not only on river beds or ocean floors but also on ice surfaces, such as the surface of glaciers and underside of river ice (Carey 1966). In addition, owing to recent advancements of remote sensing technology, it has been found that the surfaces of the polar ice caps on Mars as well as on the Earth have step-like formations (Smith & Holt 2010) which are assumed to be boundary waves, because they are generated perpendicularly to the direction of the currents. These currents acting on the polar ice caps are density airflow, i.e. katabatic wind (Howard et al 2000). The comprehension of the formation process of the Martian polar ice caps may reveal climate changes which have occurred on Mars. Although the formation of boundary waves on river beds or ocean floors has been studied by a number of researchers, there are few works on their formation on ice surfaces. Yokokawa et al (2013) suggested that the temperature distribution of the ambient air, fluid and ice is a factor which determines the direction of migration of boundary waves formed on ice surfaces through their experiments. In this study, we propose a mathematical model in order to describe the formation process of the boundary waves and the direction of their migration. We consider that a liquid is flowing through a flume filled with a flat ice layer on the bottom. The flow is assumed to be turbulent and its temperature is assumed to merge with the ambient temperature at the flow surface and with the melting point of ice at the bottom (ice surface). The ice surface evolution is dependent on the unbalance between the interfacial heat flux of the liquid and ice, and we employ the Reynolds-averaged Navier-Stokes equation, the continuity equation, heat transfer equations for the liquid and ice, and a heat balance equation at the flow-ice interface. It is assumed that the interfacial heat fluxes of the liquid and ice are determined by the temperature profile, and the Reynolds stress and the turbulent heat flux are expressed by the eddy diffusivity of momentum and the eddy diffusivity of heat, respectively. In addition, the liquid can be divided into two layers; viscous sublayer and turbulent layer. In order to determine the velocity and temperature profile in the liquid, we employ the Prandtl-Taylor analogy which assumes that the velocity profile follows a linear law in the viscous sublayer and a logarithmic law in the turbulent layer, and the eddy diffusivity of heat is described by the eddy diffusivity of momentum and Prandtl number of the liquid. Finally, we obtain the temperature profiles (because the heat transfer equation for the ice reduces to the Laplace equation, the temperature profile in the ice can be easily estimated) and interfacial heat fluxes.

Multidimensional equilibria and their stability in copolymer-solvent mixtures

NASA Astrophysics Data System (ADS)

Glasner, Karl; Orizaga, Saulo

2018-06-01

This paper discusses localized equilibria which arise in copolymer-solvent mixtures. A free boundary problem associated with the sharp-interface limit of a density functional model is used to identify both lamellar and concentric domain patterns composed of a finite number of layers. Stability of these morphologies is studied through explicit linearization of the free boundary evolution. For the multilayered lamellar configuration, transverse instability is observed for sufficiently small dimensionless interfacial energies. Additionally, a crossover between small and large wavelength instabilities is observed depending on whether solvent-polymer or monomer-monomer interfacial energy is dominant. Concentric domain patterns resembling multilayered micelles and vesicles exhibit bifurcations wherein they only exist for sufficiently small dimensionless interfacial energies. The bifurcation of large radii vesicle solutions is studied analytically, and a crossover from a supercritical case with only one solution branch to a subcritical case with two is observed. Linearized stability of these configurations shows that azimuthal perturbation may lead to instabilities as interfacial energy is decreased.

Improved interfacial and electrical properties of GaAs metal-oxide-semiconductor capacitors with HfTiON as gate dielectric and TaON as passivation interlayer

NASA Astrophysics Data System (ADS)

Wang, L. S.; Xu, J. P.; Zhu, S. Y.; Huang, Y.; Lai, P. T.

2013-08-01

The interfacial and electrical properties of sputtered HfTiON on sulfur-passivated GaAs with or without TaON as interfacial passivation layer (IPL) are investigated. Experimental results show that the GaAs metal-oxide-semiconductor capacitor with HfTiON/TaON stacked gate dielectric annealed at 600 °C exhibits low interface-state density (1.0 × 1012 cm-2 eV-1), small gate leakage current (7.3 × 10-5 A cm-2 at Vg = Vfb + 1 V), small capacitance equivalent thickness (1.65 nm), and large equivalent dielectric constant (26.2). The involved mechanisms lie in the fact that the TaON IPL can effectively block the diffusions of Hf, Ti, and O towards GaAs surface and suppress the formation of interfacial As-As bonds, Ga-/As-oxides, thus unpinning the Femi level at the TaON/GaAs interface and improving the interface quality and electrical properties of the device.

Elucidating the influence of polymorph-dependent interfacial solvent structuring at chitin surfaces.

PubMed

Brown, Aaron H; Walsh, Tiffany R

2016-10-20

Interfacial solvent structuring is thought to be influential in mediating the adsorption of biomolecules at aqueous materials interfaces. However, despite the enormous potential for exploitation of aqueous chitin interfaces in industrial, medical and drug-delivery applications, little is known at the molecular-level about such interfacial solvent structuring for chitin. Here we use molecular simulation to predict the structure of the [100] and [010] interfaces of α-chitin and β-chitin dihydrate in contact with liquid water and saline solution. We find the α-chitin [100] interface supports lateral high-density regions in the first water layer at the interface, which are also present, but not as pronounced, for β-chitin. The lateral structuring of interfacial ions at the saline/chitin interface is also more pronounced for α-chitin compared with β-chitin. Our findings provide a foundation for the systematic design of biomolecules with selective binding affinity for different chitin polymorphs. Copyright © 2016 Elsevier Ltd. All rights reserved.

Metal/oxide interfacial effects on the selective oxidation of primary alcohols

PubMed Central

Zhao, Guofeng; Yang, Fan; Chen, Zongjia; Liu, Qingfei; Ji, Yongjun; Zhang, Yi; Niu, Zhiqiang; Mao, Junjie; Bao, Xinhe; Hu, Peijun; Li, Yadong

2017-01-01

A main obstacle in the rational development of heterogeneous catalysts is the difficulty in identifying active sites. Here we show metal/oxide interfacial sites are highly active for the oxidation of benzyl alcohol and other industrially important primary alcohols on a range of metals and oxides combinations. Scanning tunnelling microscopy together with density functional theory calculations on FeO/Pt(111) reveals that benzyl alcohol enriches preferentially at the oxygen-terminated FeO/Pt(111) interface and undergoes readily O–H and C–H dissociations with the aid of interfacial oxygen, which is also validated in the model study of Cu2O/Ag(111). We demonstrate that the interfacial effects are independent of metal or oxide sizes and the way by which the interfaces were constructed. It inspires us to inversely support nano-oxides on micro-metals to make the structure more stable against sintering while the number of active sites is not sacrificed. The catalyst lifetime, by taking the inverse design, is thereby significantly prolonged. PMID:28098146

Effects of cathode electrolyte interfacial (CEI) layer on long term cycling of all-solid-state thin-film batteries

DOE PAGES

Wang, Ziying; Lee, Jungwoo Z.; Xin, Huolin L.; ...

2016-05-30

All-solid-state lithium-ion batteries have the potential to not only push the current limits of energy density by utilizing Li metal, but also improve safety by avoiding flammable organic electrolyte. However, understanding the role of solid electrolyte – electrode interfaces will be critical to improve performance. In this paper, we conducted long term cycling on commercially available lithium cobalt oxide (LCO)/lithium phosphorus oxynitride (LiPON)/lithium (Li) cells at elevated temperature to investigate the interfacial phenomena that lead to capacity decay. STEM-EELS analysis of samples revealed a previously unreported disordered layer between the LCO cathode and LiPON electrolyte. This electrochemically inactive layer grewmore » in thickness leading to loss of capacity and increase of interfacial resistance when cycled at 80 °C. Finally, the stabilization of this layer through interfacial engineering is crucial to improve the long term performance of thin-film batteries especially under thermal stress.« less

Thickness dependence of the interfacial Dzyaloshinskii–Moriya interaction in inversion symmetry broken systems

PubMed Central

Cho, Jaehun; Kim, Nam-Hui; Lee, Sukmock; Kim, June-Seo; Lavrijsen, Reinoud; Solignac, Aurelie; Yin, Yuxiang; Han, Dong-Soo; van Hoof, Niels J. J.; Swagten, Henk J. M.; Koopmans, Bert; You, Chun-Yeol

2015-01-01

In magnetic multilayer systems, a large spin-orbit coupling at the interface between heavy metals and ferromagnets can lead to intriguing phenomena such as the perpendicular magnetic anisotropy, the spin Hall effect, the Rashba effect, and especially the interfacial Dzyaloshinskii–Moriya (IDM) interaction. This interfacial nature of the IDM interaction has been recently revisited because of its scientific and technological potential. Here we demonstrate an experimental technique to straightforwardly observe the IDM interaction, namely Brillouin light scattering. The non-reciprocal spin wave dispersions, systematically measured by Brillouin light scattering, allow not only the determination of the IDM energy densities beyond the regime of perpendicular magnetization but also the revelation of the inverse proportionality with the thickness of the magnetic layer, which is a clear signature of the interfacial nature. Altogether, our experimental and theoretical approaches involving double time Green's function methods open up possibilities for exploring magnetic hybrid structures for engineering the IDM interaction. PMID:26154986

Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer.

PubMed

Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J

2016-06-09

Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack.

Snake states and their symmetries in graphene

NASA Astrophysics Data System (ADS)

Tiwari, Rakesh; Liu, Yang; Brada, Matej; Bruder, C.; Kusmartsev, F. V.; Mele, E. J.

Snake states are open trajectories for charged particles moving in two dimensions under the influence of a spatially varying perpendicular magnetic field. They can also occur in a constant perpendicular magnetic field when the particle density is made nonuniform as realized at a pn junction in a semiconductor, or in graphene. We examine the correspondence of such trajectories in monolayer graphene in the quantum limit for two families of domain walls: (a) a uniform doped carrier density in an antisymmetric perpendicular magnetic field and (b) antisymmetric carrier density distribution in a uniform perpendicular magnetic field. Although, these families support different internal symmetries, the pattern of the boundary and interface currents is the same in both cases. We demonstrate that these two physically different situations are gauge equivalent when rewritten in a Nambu doubled formulation of the two limiting problems. Using gauge transformations in particle-hole space to connect these two problems, we map the protected interfacial modes to the Bogoliubov quasiparticles of an interfacial one-dimensional p-wave paired state.

Non-contact, non-destructive, quantitative probing of interfacial trap sites for charge carrier transport at semiconductor-insulator boundary

NASA Astrophysics Data System (ADS)

Choi, Wookjin; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori; Yokoyama, Masaaki; Seki, Shu

2014-07-01

The density of traps at semiconductor-insulator interfaces was successfully estimated using microwave dielectric loss spectroscopy with model thin-film organic field-effect transistors. The non-contact, non-destructive analysis technique is referred to as field-induced time-resolved microwave conductivity (FI-TRMC) at interfaces. Kinetic traces of FI-TRMC transients clearly distinguished the mobile charge carriers at the interfaces from the immobile charges trapped at defects, allowing both the mobility of charge carriers and the number density of trap sites to be determined at the semiconductor-insulator interfaces. The number density of defects at the interface between evaporated pentacene on a poly(methylmethacrylate) insulating layer was determined to be 1012 cm-2, and the hole mobility was up to 6.5 cm2 V-1 s-1 after filling the defects with trapped carriers. The FI-TRMC at interfaces technique has the potential to provide rapid screening for the assessment of interfacial electronic states in a variety of semiconductor devices.

Thermoelectric Properties of Complex Oxide Heterostructures

NASA Astrophysics Data System (ADS)

Cain, Tyler Andrew

Thermoelectrics are a promising energy conversion technology for power generation and cooling systems. The thermal and electrical properties of the materials at the heart of thermoelectric devices dictate conversion efficiency and technological viability. Studying the fundamental properties of potentially new thermoelectric materials is of great importance for improving device performance and understanding the electronic structure of materials systems. In this dissertation, investigations on the thermoelectric properties of a prototypical complex oxide, SrTiO3, are discussed. Hybrid molecular beam epitaxy (MBE) is used to synthesize La-doped SrTiO3 thin films, which exhibit high electron mobilities and large Seebeck coefficients resulting in large thermoelectric power factors at low temperatures. Large interfacial electron densities have been observed in SrTiO3/RTiO 3 (R=Gd,Sm) heterostructures. The thermoelectric properties of such heterostructures are investigated, including the use of a modulation doping approach to control interfacial electron densities. Low-temperature Seebeck coefficients of extreme electron-density SrTiO3 quantum wells are shown to provide insight into their electronic structure.

Optimization of the Energy Level Alignment between the Photoactive Layer and the Cathode Contact Utilizing Solution-Processed Hafnium Acetylacetonate as Buffer Layer for Efficient Polymer Solar Cells.

PubMed

Yu, Lu; Li, Qiuxiang; Shi, Zhenzhen; Liu, Hao; Wang, Yaping; Wang, Fuzhi; Zhang, Bing; Dai, Songyuan; Lin, Jun; Tan, Zhan'ao

2016-01-13

The insertion of an appropriate interfacial buffer layer between the photoactive layer and the contact electrodes makes a great impact on the performance of polymer solar cells (PSCs). Ideal interfacial buffer layers could minimize the interfacial traps and the interfacial barriers caused by the incompatibility between the photoactive layer and the electrodes. In this work, we utilized solution-processed hafnium(IV) acetylacetonate (Hf(acac)4) as an effective cathode buffer layer (CBL) in PSCs to optimize the energy level alignment between the photoactive layer and the cathode contact, with the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) all simultaneously improved with Hf(acac)4 CBL, leading to enhanced power conversion efficiencies (PCEs). Ultraviolet photoemission spectroscopy (UPS) and scanning Kelvin probe microscopy (SKPM) were performed to confirm that the interfacial dipoles were formed with the same orientation direction as the built-in potential between the photoactive layer and Hf(acac)4 CBL, benefiting the exciton separation and electron transport/extraction. In addition, the optical characteristics and surface morphology of the Hf(acac)4 CBL were also investigated.

Albumin-mediated deposition of bone-like apatite onto nano-sized surfaces: Effect of surface reactivity and interfacial hydration.

PubMed

D'Elia, Noelia L; Gravina, Noel; Ruso, Juan M; Marco-Brown, Jose L; Sieben, Juan M; Messina, Paula V

2017-05-15

The bioactivity of an implant is displayed on its ability to induce heterogeneous nucleation of biogenic apatite onto its surface upon immersion in body fluids; forming, through this layer, a stable bond with the host tissue. The present article evaluates the bioactivity of different nanostructured substrates based on synthetic hydroxyapatite (HA) and titania (TiO 2 ) nanoparticles, where we extend the debate regarding the selective roles played by the presence of albumin on the biogenic apatite coating evolution. The substrates bone-bonding potential was evaluated by keeping the materials in contact with Simulated Body Fluid, while the influence of the presence of Bovine Serum Albumin in bioactivity was analyzed by a spectrophotometric technique. Our results show that materials' surface reactivity and their interfacial hydration are responsible for the bonding-site alteration and surface charge density distribution, which in turn, regulate the protein adsorption process. As a matter of fact, variations on the protein adsorbed density have a directly proportional impact on calcium binding sites, which should be responsible for the initiation of the mineralization process, disturbing the deposition of the interfacial calcium phosphate (Ca-P) mineralized coating. Copyright © 2017 Elsevier Inc. All rights reserved.

Organic heterojunctions: Contact-induced molecular reorientation, interface states, and charge re-distribution

PubMed Central

Opitz, Andreas; Wilke, Andreas; Amsalem, Patrick; Oehzelt, Martin; Blum, Ralf-Peter; Rabe, Jürgen P.; Mizokuro, Toshiko; Hörmann, Ulrich; Hansson, Rickard; Moons, Ellen; Koch, Norbert

2016-01-01

We reveal the rather complex interplay of contact-induced re-orientation and interfacial electronic structure – in the presence of Fermi-level pinning – at prototypical molecular heterojunctions comprising copper phthalocyanine (H16CuPc) and its perfluorinated analogue (F16CuPc), by employing ultraviolet photoelectron and X-ray absorption spectroscopy. For both layer sequences, we find that Fermi-level (EF) pinning of the first layer on the conductive polymer substrate modifies the work function encountered by the second layer such that it also becomes EF-pinned, however, at the interface towards the first molecular layer. This results in a charge transfer accompanied by a sheet charge density at the organic/organic interface. While molecules in the bulk of the films exhibit upright orientation, contact formation at the heterojunction results in an interfacial bilayer with lying and co-facial orientation. This interfacial layer is not EF-pinned, but provides for an additional density of states at the interface that is not present in the bulk. With reliable knowledge of the organic heterojunction’s electronic structure we can explain the poor performance of these in photovoltaic cells as well as their valuable function as charge generation layer in electronic devices. PMID:26887445

High density tape/head interface study

NASA Technical Reports Server (NTRS)

Csengery, L. C.

1983-01-01

The high energy (H sub c approximately or = to 650 oersteds) tapes and high track density (84 tracks per inch) heads investigated had, as its goal, the definition of optimum combinations of head and tape, including the control required of their interfacial dynamics that would enable the manufacture of high rate (150 Mbps) digital tape recorders for unattended space flight.

Effect of Interfacial Bonding on Interphase Properties in SiO2/Epoxy Nanocomposite: A Molecular Dynamics Simulation Study.

PubMed

Wang, Zhikun; Lv, Qiang; Chen, Shenghui; Li, Chunling; Sun, Shuangqing; Hu, Songqing

2016-03-23

Atomistic molecular dynamics simulations have been performed to explore the effect of interfacial bonding on the interphase properties of a nanocomposite system that consists of a silica nanoparticle and the highly cross-linked epoxy matrix. For the structural properties, results show that interfacial covalent bonding can broaden the interphase region by increasing the radial effect range of fluctuated mass density and oriented chains, as well as strengthen the interphase region by improving the thermal stability of interfacial van der Waals excluded volume and reducing the proportion of cis conformers of epoxy segments. The improved thermal stability of the interphase region in the covalently bonded model results in an increase of ∼21 K in the glass transition temperature (Tg) compared to that of the pure epoxy. It is also found that interfacial covalent bonding mainly restricts the volume thermal expansion of the model at temperatures near or larger than Tg. Furthermore, investigations from mean-square displacement and fraction of immobile atoms point out that interfacial covalent and noncovalent bonding induces lower and higher mobility of interphase atoms than that of the pure epoxy, respectively. The obtained critical interfacial bonding ratio when the interphase and matrix atoms have the same mobility is 5.8%. These results demonstrate that the glass transitions of the interphase and matrix will be asynchronous when the interfacial bonding ratio is not 5.8%. Specifically, the interphase region will trigger the glass transition of the matrix when the ratio is larger than 5.8%, whereas it restrains the glass transition of the matrix when the ratio is smaller than 5.8%.

Enhanced Corrosion Resistance and Interfacial Conductivity of TiC x/a-C Nanolayered Coatings via Synergy of Substrate Bias Voltage for Bipolar Plates Applications in PEMFCs.

PubMed

Yi, Peiyun; Zhang, Weixin; Bi, Feifei; Peng, Linfa; Lai, Xinmin

2018-06-06

Proton-exchange membrane fuel cells are one kind of renewable and clean energy conversion device, whose metallic bipolar plates are one of the key components. However, high interfacial contact resistance and poor corrosion resistance are still great challenges for the commercialization of metallic bipolar plates. In this study, we demonstrated a novel strategy for depositing TiC x /amorphous carbon (a-C) nanolayered coatings by synergy of 60 and 300 V bias voltage to enhance corrosion resistance and interfacial conductivity. The synergistic effects of bias voltage on the composition, microstructure, surface roughness, electrochemical corrosion behaviors, and interfacial conductivity of TiC x /a-C coatings were explored. The results revealed that the columnar structures in the inner layer were suppressed and the surface became rougher with the 300 V a-C layer outside. The composition analysis indicated that the sp 2 content increased with an increase of 300 V sputtering time. Due to the synergy strategy of bias voltage, lower corrosion current densities were achieved both in potentiostatic polarization (1.6 V vs standard hydrogen electrode) and potentiodynamic polarization. With the increase of 300 V sputtering time, the interfacial conductivity was improved. The enhanced corrosion resistance and interfacial conductivity of the TiC x /a-C coatings would provide new opportunities for commercial bipolar plates.

Mechanical properties of protein adsorption layers at the air/water and oil/water interface: a comparison in light of the thermodynamical stability of proteins.

PubMed

Mitropoulos, Varvara; Mütze, Annekathrin; Fischer, Peter

2014-04-01

Over the last decades numerous studies on the interfacial rheological response of protein adsorption layers have been published. The comparison of these studies and the retrieval of a common parameter to compare protein interfacial activity are hampered by the fact that different boundary conditions (e.g. physico-chemical, instrumental, interfacial) were used. In the present work we review previous studies and attempt a unifying approach for the comparison between bulk protein properties and their adsorption films. Among many common food grade proteins we chose bovine serum albumin, β-lactoglobulin and lysozyme for their difference in thermodynamic stability and studied their adsorption at the air/water and limonene/water interface. In order to achieve this we have i) systematically analyzed protein adsorption kinetics in terms of surface pressure rise using a drop profile analysis tensiometer and ii) we addressed the interfacial layer properties under shear stress using an interfacial shear rheometer under the same experimental conditions. We could show that thermodynamically less stable proteins adsorb generally faster and yield films with higher shear rheological properties at air/water interface. The same proteins showed an analog behavior when adsorbing at the limonene/water interface but at slower rates. Copyright © 2013 Elsevier B.V. All rights reserved.

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei

In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

DOE PAGES

Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; ...

2016-09-02

In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

A molecular dynamics study on the interaction between epoxy and functionalized graphene sheets

NASA Astrophysics Data System (ADS)

Melro, L. S.; Pyrz, R.; Jensen, L. R.

2016-07-01

The interaction between graphene and epoxy resin was studied using molecular dynamics simulations. The interfacial shear strength and pull out force were calculated for functionalised graphene layers (carboxyl, carbonyl, and hydroxyl) and epoxy composites interfaces. The influence of functional groups, as well as their distribution and coverage density on the graphene sheets were also analysed through the determination of the Young's modulus. Functionalisation proved to be detrimental to the mechanical properties, nonetheless according to interfacial studies the interaction between graphene and epoxy resin increases.

Defect-driven interfacial electronic structures at an organic/metal-oxide semiconductor heterojunction.

PubMed

Winget, Paul; Schirra, Laura K; Cornil, David; Li, Hong; Coropceanu, Veaceslav; Ndione, Paul F; Sigdel, Ajaya K; Ginley, David S; Berry, Joseph J; Shim, Jaewon; Kim, Hyungchui; Kippelen, Bernard; Brédas, Jean-Luc; Monti, Oliver L A

2014-07-16

The electronic structure of the hybrid interface between ZnO and the prototypical organic semiconductor PTCDI is investigated via a combination of ultraviolet and X-ray photoelectron spectroscopy (UPS/XPS) and density functional theory (DFT) calculations. The interfacial electronic interactions lead to a large interface dipole due to substantial charge transfer from ZnO to 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which can be properly described only when accounting for surface defects that confer ZnO its n-type properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gold-film coating assisted femtosecond laser fabrication of large-area, uniform periodic surface structures.

PubMed

Feng, Pin; Jiang, Lan; Li, Xin; Rong, Wenlong; Zhang, Kaihu; Cao, Qiang

2015-02-20

A simple, repeatable approach is proposed to fabricate large-area, uniform periodic surface structures by a femtosecond laser. 20 nm gold films are coated on semiconductor surfaces on which large-area, uniform structures are fabricated. In the case study of silicon, cross-links and broken structures of laser induced periodic surface structures (LIPSSs) are significantly reduced on Au-coated silicon. The good consistency between the scanning lines facilitates the formation of large-area, uniform LIPSSs. The diffusion of hot electrons in the Au films increases the interfacial carrier densities, which significantly enhances interfacial electron-phonon coupling. High and uniform electron density suppresses the influence of defects on the silicon and further makes the coupling field more uniform and thus reduces the impact of laser energy fluctuations, which homogenizes and stabilizes large-area LIPSSs.

Monte-Carlo modelling of nano-material photocatalysis: bridging photocatalytic activity and microscopic charge kinetics.

PubMed

Liu, Baoshun

2016-04-28

In photocatalysis, it is known that light intensity, organic concentration, and temperature affect the photocatalytic activity by changing the microscopic kinetics of holes and electrons. However, how the microscopic kinetics of holes and electrons relates to the photocatalytic activity was not well known. In the present research, we developed a Monte-Carlo random walking model that involved all of the charge kinetics, including the photo-generation, the recombination, the transport, and the interfacial transfer of holes and electrons, to simulate the overall photocatalytic reaction, which we called a "computer experiment" of photocatalysis. By using this model, we simulated the effect of light intensity, temperature, and organic surface coverage on the photocatalytic activity and the density of the free electrons that accumulate in the simulated system. It was seen that the increase of light intensity increases the electron density and its mobility, which increases the probability for a hole/electron to find an electron/hole for recombination, and consequently led to an apparent kinetics that the quantum yield (QY) decreases with the increase of light intensity. It was also seen that the increase of organic surface coverage could increase the rate of hole interfacial transfer and result in the decrease of the probability for an electron to recombine with a hole. Moreover, the increase of organic coverage on the nano-material surface can also increase the accumulation of electrons, which enhances the mobility for electrons to undergo interfacial transfer, and finally leads to the increase of photocatalytic activity. The simulation showed that the temperature had a more complicated effect, as it can simultaneously change the activation of electrons, the interfacial transfer of holes, and the interfacial transfer of electrons. It was shown that the interfacial transfer of holes might play a main role at low temperature, with the temperature-dependence of QY conforming to the Arrhenius model. The activation of electrons from the traps to the conduction band might become important at high temperature, which accelerates the electron movement for recombination and leads to a temperature dependence of QY that deviates from the Arrhenius model.

Influence of the insertion of a nano-oxide layer on the interfacial magnetism of FeMn /NiFe/Cu/NiFe spin valves

NASA Astrophysics Data System (ADS)

Tafur, Miguel; Alayo, W.; Munayco, P.; Baggio-Saitovitch, E.; Nascimento, V. P.; Alvarenga, A. D.; Brewer, W. D.

2007-05-01

We have studied the influence of an inserted nano-oxide layer (NOL) on the interfacial magnetism in spin-valve systems showing the giant magnetoresistance effect. Specifically, we performed a magnetic depth profile of these structures with and without a NOL, using the x-ray magnetic circular dichroism technique. We found that insertion of a NOL into the spin-valve structure is correlated with a stronger reduction of the magnetic moments at the ferromagnetic (FM)/NOL/FM interface in comparison with a spin valve without NOL.

On electrical and interfacial properties of iron and platinum Schottky barrier diodes on (111) n-type Si0.65Ge0.35

NASA Astrophysics Data System (ADS)

Hamri, D.; Teffahi, A.; Djeghlouf, A.; Chalabi, D.; Saidane, A.

2018-04-01

Current-voltage (I-V), capacitance-voltage-frequency (C-V-f) and conductance-voltage-frequency (G/ω-V-f) characteristics of Molecular Beam Epitaxy (MBE)-deposited Fe/n-Si0.65Ge0.35 (FM1) and Pt/n-Si0.65Ge0.35(PM2) (111) orientated Schottky barrier diodes (SBDs) have been investigated at room-temperature. Barrier height (ΦB0), ideality factor (n) and series resistance (RS) were extracted. Dominant current conduction mechanisms were determined. They revealed that Poole-Frenkel-type conduction mechanism dominated reverse current. Differences in shunt resistance confirmed the difference found in leakage current. Under forward bias, quasi-ohmic conduction is found at low voltage regions and space charge-limited conduction (SCLC) at higher voltage regions for both SBDs. Density of interface states (NSS) indicated a difference in interface reactivity. Distribution profiles of series resistance (RS) with bias gives a peak in depletion region at low-frequencies that disappears with increasing frequencies. These results show that interface states density and series resistance of Schottky diodes are important parameters that strongly influence electrical properties of FM1 and PM2 structures.

Nanosecond pulsed electric field induced changes in cell surface charge density.

PubMed

Dutta, Diganta; Palmer, Xavier-Lewis; Asmar, Anthony; Stacey, Michael; Qian, Shizhi

2017-09-01

This study reports that the surface charge density changes in Jurkat cells with the application of single 60 nanosecond pulse electric fields, using atomic force microscopy. Using an atomic force microscope tip and Jurkat cells on silica in a 0.01M KCl ionic concentration, we were able to measure the interfacial forces, while also predicting surface charge densities of both Jurkat cell and silica surfaces. The most important finding is that the pulsing conditions varyingly reduced the cells' surface charge density. This offers a novel way in which to examine cellular effects of pulsed electric fields that may lead to the identification of unique mechanical responses. Compared to a single low field strength NsPEF (15kV/cm) application, exposure of Jurkat cells to a single high field strength NsPEF (60kV/cm) resulted in a further reduction in charge density and major morphological changes. The structural, physical, and chemical properties of biological cells immensely influence their electrostatic force; we were able to investigate this through the use of atomic force microscopy by measuring the surface forces between the AFM's tip and the Jurkat cells under different pulsing conditions as well as the interfacial forces in ionic concentrations. Copyright © 2017 Elsevier Ltd. All rights reserved.

Optimal contant time injection policy for enhanced oil recovery and characterization of optimal viscous profiles

NASA Astrophysics Data System (ADS)

Daripa, Prabir

2011-11-01

We numerically investigate the optimal viscous profile in constant time injection policy of enhanced oil recovery. In particular, we investigate the effect of a combination of interfacial and layer instabilities in three-layer porous media flow on the overall growth of instabilities and thereby characterize the optimal viscous profile. Results based on monotonic and non-monotonic viscous profiles will be presented. Time permitting. we will also present results on multi-layer porous media flows for Newtonian and non-Newtonian fluids and compare the results. The support of Qatar National Fund under a QNRF Grant is acknowledged.

Ductile failure initiation and evolution in porous polycrystalline aggregates due to interfacial effects

NASA Astrophysics Data System (ADS)

Ashmawi, Waeil Muhammad Al-Anwar

New analytical and computational formulations have been developed for the investigation of micro structurally induced ductile failure mechanisms in porous polycrystalline aggregates with low and high (CSL) angle grain-boundaries (GBs). A multiple-slip rate-dependent crystalline constitutive formulation that is coupled to the evolution of mobile and immobile dislocation densities, a new internal porosity formulation for void nucleation and growth, and specialized computational schemes have been developed to obtain a detailed understanding of the multi-scale interrelated physical mechanisms that result in ductile failure in polycrystalline materials. Comprehensive transmission and pile-up mechanisms have also been introduced to investigate dislocation-density impedance and slip-rate incompatibility at the GBs. The interrelated effects of GB orientation, mobile and immobile dislocation densities, strain hardening, geometrical softening, localized plastic strains, and dislocation-density transmission and blockage on void growth, interaction, and coalescence have been studied. Criteria have been developed to identify and monitor the initiation and development of potential dislocation-density activity sites adjacent to GB regions. These interactions play an important role in the formation of GB pile-up and transmission regions. The effects of GB structure and orientation on ductile failure have been accounted for by the development of GB interfacial kinematic conditions that account for a multitude of dislocation-density interactions with GBs, such as full and partial transmission, impedance, blockage, and absorption. Pile-ups and transmission regions are identified and monitored as the deformation and failure evolve. These kinematic conditions are linked to the initiation and evolution of failure modes by the development of a new internal porosity evolution formulation that accounts for void nucleation and growth. The internal porosity relation is coupled with the proposed dislocation-density based crystalline constitutive formulation, the interfacial GB dislocation-density interaction models, and the specialized computational schemes to obtain detailed predictions of the behavior of aggregates with explicit voids that have different orientations and combinations of sizes, shapes, and spacings. Results from the present study indicate that material failure is a competition between different interrelated effects, such as stress triaxiality, accumulated plastic shear strain, temperature, dislocation density concentration, and grain and GB crystallographic orientations. For all void arrangements, as the void size is increased, specimen necking is diffuse and failure is concentrated in the ligament regions. Furthermore, there are more dislocation-density activity sites for potential transmission and pile-ups at the GBs. Failure is concentrated along the void peripheries and within intervoid ligaments. It has been shown that the evolution of the mobile dislocation density saturation curves, and their saturation rate are directly related to the aggregate response. Nucleation and growth for all void distributions have occurred in regions of maximum dislocation density and along preferred crystallographic orientations. Spatial distributions of porosity, accumulated plastic strains, and pressure have been obtained to further elucidate how these parameters evolve and affect void to void interaction in critical ligament and localized regions as a function of intervoid spacing and nominal strains. These failure predictions can be also used to identify intergranular and transgranular failure propagation. The present study underscores the importance of using dislocation-density based multiple-slip crystalline constitutive formulations and GB interfacial mechanisms that are consistent with experimental observations and results to accurately characterize the microstructural evolution of deformation and failure modes on a length scale that is commensurate with the material competition between the inherent strengthening and softening mechanisms of crystalline systems.

Interfacial strain effects on lithium diffusion pathways in the spinel solid electrolyte Li-doped MgAl2O4

NASA Astrophysics Data System (ADS)

O'Rourke, Conn; Morgan, Benjamin J.

2018-04-01

The (Li,Al)-codoped magnesium spinel (LixMg1 -2 xAl2 +xO4 ) is a solid lithium-ion electrolyte with potential use in all-solid-state lithium-ion batteries. The spinel structure means that interfaces with spinel electrodes, such as LiyMn2O4 and Li4 +3 zTi5O12 , may be lattice matched, with potentially low interfacial resistances. Small lattice parameter differences across a lattice-matched interface are unavoidable, causing residual epitaxial strain. This strain potentially modifies lithium diffusion near the electrolyte-electrode interface, contributing to interfacial resistance. Here, we report a density functional theory study of strain effects on lithium diffusion pathways for (Li,Al)-codoped magnesium spinel, for xLi=0.25 and xLi=0.5 . We have calculated diffusion profiles for the unstrained materials, and for isotropic and biaxial tensile strains of up to 6 % , corresponding to {100 } epitaxial interfaces with LiyMn2O4 and Li4 +3 zTi5O12 . We find that isotropic tensile strain reduces lithium diffusion barriers by as much as 0.32 eV , with typical barriers reduced by ˜0.1 eV. This effect is associated with increased volumes of transitional octahedral sites, and broadly follows qualitative changes in local electrostatic potentials. For biaxial (epitaxial) strain, which more closely approximates strain at a lattice-matched electrolyte-electrode interface, changes in octahedral site volumes and in lithium diffusion barriers are much smaller than under isotropic strain. Typical barriers are reduced by only ˜0.05 eV. Individual effects, however, depend on the pathway considered and the relative strain orientation. These results predict that isotropic strain strongly affects ionic conductivities in (Li,Al)-codoped magnesium spinel electrolytes, and that tensile strain is a potential route to enhanced lithium transport. For a lattice-matched interface with candidate spinel-structured electrodes, however, epitaxial strain has a small, but complex, effect on lithium diffusion barriers.

On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

NASA Astrophysics Data System (ADS)

Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

2016-05-01

The dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. The fluid in basic state is prescribed to rotate with a Keplerian profile ? modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabiliser irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non-Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density In addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect. Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

Infiltration sintering properties of Ni-4B-4Si(wt.%) alloy powders

NASA Astrophysics Data System (ADS)

Yang, Q.; Zhang, X. C.; Wang, F. L.; Zou, J. T.

2018-01-01

The Ni-4B-4Si(wt.%) alloy powders were infiltrated into the nickel skeletons, the effects of sintering temperatures (1050-1150 °C) and skeletons (loose and compact nickel powders) on the microstructures and hardness of the sintered alloys were investigated. The Ni-B-Si alloy sintered at 1100 °C consisted of γ-Ni and Ni3B, and Si mainly solid soluted in the γ-Ni. The loose nickel powders favored to the infiltration of Ni-B-Si liquid alloy into the nickel skeletons, the sintered alloys exhibited dense microstructures and good interfacial bonding with Ni substrates. The interfacial hardness was equal to that of the sintered alloys and Ni substrates. Loose nickel powders ensured the density and interfacial bonding of the sintered alloys, the infiltration sintering process can be simplified and easily applied to practice.

Theoretical prediction of crystallization kinetics of a supercooled Lennard-Jones fluid

NASA Astrophysics Data System (ADS)

Gunawardana, K. G. S. H.; Song, Xueyu

2018-05-01

The first order curvature correction to the crystal-liquid interfacial free energy is calculated using a theoretical model based on the interfacial excess thermodynamic properties. The correction parameter (δ), which is analogous to the Tolman length at a liquid-vapor interface, is found to be 0.48 ± 0.05 for a Lennard-Jones (LJ) fluid. We show that this curvature correction is crucial in predicting the nucleation barrier when the size of the crystal nucleus is small. The thermodynamic driving force (Δμ) corresponding to available simulated nucleation conditions is also calculated by combining the simulated data with a classical density functional theory. In this paper, we show that the classical nucleation theory is capable of predicting the nucleation barrier with excellent agreement to the simulated results when the curvature correction to the interfacial free energy is accounted for.

Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer

PubMed Central

Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J.

2016-01-01

Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack. PMID:27279454

Low temperature thermal ALD of a SiNx interfacial diffusion barrier and interface passivation layer on SixGe1- x(001) and SixGe1- x(110)

NASA Astrophysics Data System (ADS)

Edmonds, Mary; Sardashti, Kasra; Wolf, Steven; Chagarov, Evgueni; Clemons, Max; Kent, Tyler; Park, Jun Hong; Tang, Kechao; McIntyre, Paul C.; Yoshida, Naomi; Dong, Lin; Holmes, Russell; Alvarez, Daniel; Kummel, Andrew C.

2017-02-01

Atomic layer deposition of a silicon rich SiNx layer on Si0.7Ge0.3(001), Si0.5Ge0.5(001), and Si0.5Ge0.5(110) surfaces has been achieved by sequential pulsing of Si2Cl6 and N2H4 precursors at a substrate temperature of 285 °C. XPS spectra show a higher binding energy shoulder peak on Si 2p indicative of SiOxNyClz bonding while Ge 2p and Ge 3d peaks show only a small amount of higher binding energy components consistent with only interfacial bonds, indicating the growth of SiOxNy on the SiGe surface with negligible subsurface reactions. Scanning tunneling spectroscopy measurements confirm that the SiNx interfacial layer forms an electrically passive surface on p-type Si0.70Ge0.30(001), Si0.50Ge0.50(110), and Si0.50Ge0.50(001) substrates as the surface Fermi level is unpinned and the electronic structure is free of states in the band gap. DFT calculations show that a Si rich a-SiO0.4N0,4 interlayer can produce lower interfacial defect density than stoichiometric a-SiO0.8N0.8, substoichiometric a-Si3N2, or stoichiometric a-Si3N4 interlayers by minimizing strain and bond breaking in the SiGe by the interlayer. Metal-oxide-semiconductor capacitors devices were fabricated on p-type Si0.7Ge0.3(001) and Si0.5Ge0.5(001) substrates with and without the insertion of an ALD SiOxNy interfacial layer, and the SiOxNy layer resulted in a decrease in interface state density near midgap with a comparable Cmax value.

High On/Off Ratio Memristive Switching of Manganite/Cuprate Bilayer by Interfacial Magnetoelectricity

DOE PAGES

Shen, Xiao; Pennycook, Timothy J.; Hernandez-Martin, David; ...

2016-05-27

Memristive switching serves as the basis for a new generation of electronic devices. Conventional memristors are two-terminal devices in which the current is turned on and off by redistributing point defects, e.g., vacancies. Memristors based on alternative mechanisms have been explored, but achieving both high on/off ratio and low switching energy, as needed in applications, remains a challenge. This paper reports memristive switching in La 0.7Ca 0.3MnO 3/PrBa 2Cu 3O 7 bilayers with an on/off ratio greater than 103 and results of density functional theory calculations in terms of which it is concluded that the phenomenon is likely the resultmore » of a new type of interfacial magnetoelectricity. More specifically, this study shows that an external electric field induces subtle displacements of the interfacial Mn ions, which switches on/off an interfacial magnetic “dead layer”, resulting in memristive behavior for spin-polarized electron transport across the bilayer. The interfacial nature of the switching entails low energy cost, about of a tenth of atto Joule for writing/erasing a “bit”. To conclude, the results indicate new opportunities for manganite/cuprate systems and other transition metal oxide junctions in memristive applications.« less

Effect of a surface tension gradient on the slip flow along a superhydrophobic air-water interface

NASA Astrophysics Data System (ADS)

Song, Dong; Song, Baowei; Hu, Haibao; Du, Xiaosong; Du, Peng; Choi, Chang-Hwan; Rothstein, Jonathan P.

2018-03-01

Superhydrophobic surfaces have been shown to produce significant drag reduction in both laminar and turbulent flows by introducing an apparent slip velocity along an air-water interface trapped within the surface roughness. In the experiments presented within this study, we demonstrate the existence of a surface tension gradient associated with the resultant Marangoni flow along an air-water interface that causes the slip velocity and slip length to be significantly reduced. In this study, the slip velocity along a millimeter-sized air-water interface was investigated experimentally. This large-scale air-water interface facilitated a detailed investigation of the interfacial velocity profiles as the flow rate, interfacial curvature, and interface geometry were varied. For the air-water interfaces supported above continuous grooves (concentric rings within a torsional shear flow) where no surface tension gradient exists, a slip velocity as high as 30% of the bulk velocity was observed. However, for the air-water interfaces supported above discontinuous grooves (rectangular channels in a Poiseuille flow), the presence of a surface tension gradient reduced the slip velocity and in some cases resulted in an interfacial velocity that was opposite to the main flow direction. The curvature of the air-water interface in the spanwise direction was found to dictate the details of the interfacial flow profile with reverse flow in the center of the interface for concave surfaces and along the outside of the interface for convex surfaces. The deflection of the air-water interface was also found to greatly affect the magnitude of the slip. Numerical simulations imposed with a relatively small surface tension gradient along the air-water interface were able to predict both the reduced slip velocity and back flow along the air-water interface.

Modeling of Interfacial Modification Effects on Thermal Conductivity of Carbon Nanotube Composites

NASA Technical Reports Server (NTRS)

Clancy, Thomas C.; Gates, Thomas S.

2006-01-01

The effect of functionalization of carbon nanotubes on the thermal conductivity of nanocomposites has been studied using a multi-scale modeling approach. These results predict that grafting linear hydrocarbon chains to the surface of a single wall carbon nanotube with covalent chemical bonds should result in a significant increase in the thermal conductivity of these nanocomposites. This is due to the decrease in the interfacial thermal (Kapitza) resistance between the single wall carbon nanotube and the surrounding polymer matrix upon chemical functionalization. The nanocomposites studied here consist of single wall carbon nanotubes in a bulk poly(ethylene vinyl acetate) matrix. The nanotubes are functionalized by end-grafting linear hydrocarbon chains of varying length to the surface of the nanotube. The effect which this functionalization has on the interfacial thermal resistance is studied by molecular dynamics simulation. Interfacial thermal resistance values are calculated for a range of chemical grafting densities and with several chain lengths. These results are subsequently used in an analytical model to predict the resulting effect on the bulk thermal conductivity of the nanocomposite.

Nanoparticle motion on the surface of drying droplets

NASA Astrophysics Data System (ADS)

Zhao, Mingfei; Yong, Xin

2018-03-01

Advances in solution-based printing and surface patterning techniques for additive manufacturing demand a clear understanding of particle dynamics in drying colloidal droplets and its relationship with deposit structure. Although the evaporation-driven deposition has been studied thoroughly for the particles dispersed in the bulk of the droplet, few investigations have focused on the particles strongly adsorbed to the droplet surface. We modeled the assembly and deposition of the surface-active particles in a drying sessile droplet with a pinned contact line by the multiphase lattice Boltzmann-Brownian dynamics method. The particle trajectory and its area density profile characterize the assembly dynamics and deposition pattern development during evaporation. While the bulk-dispersed particles continuously move to the contact line, forming the typical "coffee-ring" deposit, the interface-bound particles migrate first toward the apex and then to the contact line as the droplet dries out. To understand this unexpected behavior, we resolve the droplet velocity field both in the bulk and within the interfacial region. The simulation results agree well with the analytical solution for the Stokes flow inside an evaporating droplet. At different stages of evaporation, our study reveals that the competition between the tangential surface flow and the downward motion of the evaporating liquid-vapor interface governs the dynamics of the interface-bound particles. In particular, the interface displacement contributes to the particle motion toward the droplet apex in a short phase, while the outward advective flow prevails at the late stage of drying and carries the particles to the contact line. The final deposit of the surface-adsorbed particles exhibits a density enhancement at the center, in addition to a coffee ring. Despite its small influence on the final deposit in the present study, the distinct dynamics of surface-active particles due to the interfacial confinement could offer a new route to deposition control when combined with Marangoni effects.

Calculation of surface potentials at the silica–water interface using molecular dynamics: Challenges and opportunities

NASA Astrophysics Data System (ADS)

Lowe, Benjamin M.; Skylaris, Chris-Kriton; Green, Nicolas G.; Shibuta, Yasushi; Sakata, Toshiya

2018-04-01

Continuum-based methods are important in calculating electrostatic properties of interfacial systems such as the electric field and surface potential but are incapable of providing sufficient insight into a range of fundamentally and technologically important phenomena which occur at atomistic length-scales. In this work a molecular dynamics methodology is presented for interfacial electric field and potential calculations. The silica–water interface was chosen as an example system, which is highly relevant for understanding the response of field-effect transistors sensors (FET sensors). Detailed validation work is presented, followed by the simulated surface charge/surface potential relationship. This showed good agreement with experiment at low surface charge density but at high surface charge density the results highlighted challenges presented by an atomistic definition of the surface potential. This methodology will be used to investigate the effect of surface morphology and biomolecule addition; both factors which are challenging using conventional continuum models.

Graphene-induced band gap renormalization in polythiophene: a many-body perturbation study

NASA Astrophysics Data System (ADS)

Marsusi, F.; Fedorov, I. A.; Gerivani, S.

2018-01-01

Density functional theory and many-body perturbation theory at the G0W0 level are employed to study the electronic properties of polythiophene (PT) adsorbed on the graphene surface. Analysis of the charge density difference shows that substrate-adsorbate interaction leads to a strong physisorption and interfacial electric dipole moment formation. The electrostatic potential displays a  -0.19 eV shift in the graphene work function from its initial value of 4.53 eV, as the result of the interaction. The LDA band gap of the polymer does not show any change. However, the band structure exhibits weak orbital hybridizations resulting from slight overlapping between the polymer and graphene states wave functions. The interfacial polarization effects on the band gap and levels alignment are investigated at the G0W0 level and show a notable reduction of PT band gap compared to that of the isolated chain.

Quality improvements of ZnxCdyMg1-x-ySe layers grown on InP substrates by a thin ZnCdSe interfacial layer

NASA Astrophysics Data System (ADS)

Zeng, L.; Yang, B. X.; Tamargo, M. C.; Snoeks, E.; Zhao, L.

1998-03-01

The quality of lattice-matched ZnxCdyMg1-x-ySe epitaxial layers grown on (001) InP substrates with a III-V buffer layer has been improved by initially growing a ZnCdSe interfacial layer (50 Å) at low temperature. The widths of double crystal x-ray rocking curves for ZnxCdyMg1-x-ySe epilayers with band gaps as high as 3.05 eV were reduced to about 70 arcsec. The defect density evaluated from etch pit density and plan-view transmission electron microscopy measurements was reduced by two orders of magnitude, to 106-107cm-2. The photoluminescence band edge emission became more symmetric and slightly narrower. It is proposed that an initial two-dimensional growth mode has been achieved by incorporating such a lattice-matched ZnCdSe layer.

Role of scaffold network in controlling strain and functionalities of nanocomposite films

DOE PAGES

Chen, Aiping; Hu, Jia -Mian; Lu, Ping; ...

2016-06-10

One novel approach to manipulating functionalities in correlated complex oxides is strain. However, significant epitaxial strain can only be achieved in ultrathin layers. We show that, under direct lattice matching framework, large and uniform vertical strain up to 2% can be achieved to significantly modify the magnetic anisotropy, magnetism, and magnetotransport properties in heteroepitaxial nanoscaffold films, over a few hundred nanometers in thickness. Comprehensive designing principles of large vertical strain have been proposed. Phase-field simulations not only reveal the strain distribution but also suggest that the ultimate strain is related to the vertical interfacial area and interfacial dislocation density. Moreover,more » by changing the nanoscaffold density and dimension, the strain and the magnetic properties can be tuned. The established correlation among the vertical interface—strain—properties in nanoscaffold films can consequently be used to tune other functionalities in a broad range of complex oxide films far beyond critical thickness.« less

The ordering of symmetric diblock copolymers: A comparison of self-consistent-field and density functional approaches

NASA Astrophysics Data System (ADS)

Nath, Shyamal K.; McCoy, John D.; Curro, John G.; Saunders, Randall S.

1997-02-01

Polymer reference interaction site model (PRISM) based density functional (DF) theory is used to evaluate the structure and thermodynamics of structurally symmetric, freely jointed, diblock chains with 0.50 volume fraction. These results are compared to the results of self-consistent-field (SCF) theory. Agreement between the predictions of the SCF and DF theories is found for the lamella spacing well above the order-disorder transition (ODT) and for the qualitative behavior of the interfacial thickness as a function of both chain length and Flory-Huggins χ parameter. Disagreement is found for the magnitude of the interfacial thickness where DF theory indicates that the thickness is 1.7±0.2 times larger than that predicted by SCF theory. It appears that behavior on the monomer length scale is sensitive to system specific details which are neglected by SCF theory.

The Study of Interpenetration Length between dPS Films and PS-grafted Layers

NASA Astrophysics Data System (ADS)

Lee, Hoyeon; Jo, Seongjun; Hirata, Toyoaki; Yamada, Norifumi L.; Tanaka, Keiji; Ryu, Du Yeol

In polymer thin film system, the type of interfacial interaction is a critical parameter to determining the thermal and physical properties of polymer films. Interestingly, the interfacial energy of grafted substrates with polymer chains is remarkably altered by simply controlling grafting density, which has been referred to as autophobicity. In this study, we investigated the interpenetrating interfaces between deuterated polystyrene (dPS) and grafted substrates with the same chemical identity. PS-grafted substrates were prepared using a grafting-to approach with hydroxyl end-functionalized polystyrene (PSOH) in a dry brush regime, where the brush thickness and grafting density were determined based on the chain length (or molecular weight, Mn) of PSOHs. The interpenetration lengths (ξ) at interfaces between dPS and PS-grafted layers were characterized using neutron reflectivity (NR) measurements (performed at the SOFIA beam-line at J-PARC, Japan). Academic adviser.

Role of scaffold network in controlling strain and functionalities of nanocomposite films

PubMed Central

Chen, Aiping; Hu, Jia-Mian; Lu, Ping; Yang, Tiannan; Zhang, Wenrui; Li, Leigang; Ahmed, Towfiq; Enriquez, Erik; Weigand, Marcus; Su, Qing; Wang, Haiyan; Zhu, Jian-Xin; MacManus-Driscoll, Judith L.; Chen, Long-Qing; Yarotski, Dmitry; Jia, Quanxi

2016-01-01

Strain is a novel approach to manipulating functionalities in correlated complex oxides. However, significant epitaxial strain can only be achieved in ultrathin layers. We show that, under direct lattice matching framework, large and uniform vertical strain up to 2% can be achieved to significantly modify the magnetic anisotropy, magnetism, and magnetotransport properties in heteroepitaxial nanoscaffold films, over a few hundred nanometers in thickness. Comprehensive designing principles of large vertical strain have been proposed. Phase-field simulations not only reveal the strain distribution but also suggest that the ultimate strain is related to the vertical interfacial area and interfacial dislocation density. By changing the nanoscaffold density and dimension, the strain and the magnetic properties can be tuned. The established correlation among the vertical interface—strain—properties in nanoscaffold films can consequently be used to tune other functionalities in a broad range of complex oxide films far beyond critical thickness. PMID:27386578

Oscillatory interfacial instability between miscible fluids

NASA Astrophysics Data System (ADS)

Shevtsova, Valentina; Gaponenko, Yuri; Mialdun, Aliaksandr; Torregrosa, Marita; Yasnou, Viktar

Interfacial instabilities occurring between two fluids are of fundamental interest in fluid dynamics, biological systems and engineering applications such as liquid storage, solvent extraction, oil recovery and mixing. Horizontal vibrations applied to stratified layers of immiscible liquids may generate spatially periodic waving of the interface, stationary in the reference frame of the vibrated cell, referred to as a "frozen wave". We present experimental evidence that frozen wave instability exists between two ordinary miscible liquids of similar densities and viscosities. At the experiments and at the numerical model, two superimposed layers of ordinary liquids, water-alcohol of different concentrations, are placed in a closed cavity in a gravitationally stable configuration. The density and viscosity of these fluids are somewhat similar. Similar to the immiscible fluids this instability has a threshold. When the value of forcing is increased the amplitudes of perturbations grow continuously displaying a saw-tooth structure. The decrease of gravity drastically changes the structure of frozen waves.

Non-contact, non-destructive, quantitative probing of interfacial trap sites for charge carrier transport at semiconductor-insulator boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Wookjin; Miyakai, Tomoyo; Sakurai, Tsuneaki

The density of traps at semiconductor–insulator interfaces was successfully estimated using microwave dielectric loss spectroscopy with model thin-film organic field-effect transistors. The non-contact, non-destructive analysis technique is referred to as field-induced time-resolved microwave conductivity (FI-TRMC) at interfaces. Kinetic traces of FI-TRMC transients clearly distinguished the mobile charge carriers at the interfaces from the immobile charges trapped at defects, allowing both the mobility of charge carriers and the number density of trap sites to be determined at the semiconductor-insulator interfaces. The number density of defects at the interface between evaporated pentacene on a poly(methylmethacrylate) insulating layer was determined to be 10{supmore » 12 }cm{sup −2}, and the hole mobility was up to 6.5 cm{sup 2} V{sup −1} s{sup −1} after filling the defects with trapped carriers. The FI-TRMC at interfaces technique has the potential to provide rapid screening for the assessment of interfacial electronic states in a variety of semiconductor devices.« less

High-Current-Density Vertical-Tunneling Transistors from Graphene/Highly Doped Silicon Heterostructures.

PubMed

Liu, Yuan; Sheng, Jiming; Wu, Hao; He, Qiyuan; Cheng, Hung-Chieh; Shakir, Muhammad Imran; Huang, Yu; Duan, Xiangfeng

2016-06-01

Scalable fabrication of vertical-tunneling transistors is presented based on heterostructures formed between graphene, highly doped silicon, and its native oxide. Benefiting from the large density of states of highly doped silicon, the tunneling transistors can deliver a current density over 20 A cm(-2) . This study demonstrates that the interfacial native oxide plays a crucial role in governing the carrier transport in graphene-silicon heterostructures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomic-scale compensation phenomena at polar interfaces.

PubMed

Chisholm, Matthew F; Luo, Weidong; Oxley, Mark P; Pantelides, Sokrates T; Lee, Ho Nyung

2010-11-05

The interfacial screening charge that arises to compensate electric fields of dielectric or ferroelectric thin films is now recognized as the most important factor in determining the capacitance or polarization of ultrathin ferroelectrics. Here we investigate using aberration-corrected electron microscopy and density-functional theory to show how interfaces cope with the need to terminate ferroelectric polarization. In one case, we show evidence for ionic screening, which has been predicted by theory but never observed. For a ferroelectric film on an insulating substrate, we found that compensation can be mediated by an interfacial charge generated, for example, by oxygen vacancies.

Accurate determination of interfacial protein secondary structure by combining interfacial-sensitive amide I and amide III spectral signals.

PubMed

Ye, Shuji; Li, Hongchun; Yang, Weilai; Luo, Yi

2014-01-29

Accurate determination of protein structures at the interface is essential to understand the nature of interfacial protein interactions, but it can only be done with a few, very limited experimental methods. Here, we demonstrate for the first time that sum frequency generation vibrational spectroscopy can unambiguously differentiate the interfacial protein secondary structures by combining surface-sensitive amide I and amide III spectral signals. This combination offers a powerful tool to directly distinguish random-coil (disordered) and α-helical structures in proteins. From a systematic study on the interactions between several antimicrobial peptides (including LKα14, mastoparan X, cecropin P1, melittin, and pardaxin) and lipid bilayers, it is found that the spectral profiles of the random-coil and α-helical structures are well separated in the amide III spectra, appearing below and above 1260 cm(-1), respectively. For the peptides with a straight backbone chain, the strength ratio for the peaks of the random-coil and α-helical structures shows a distinct linear relationship with the fraction of the disordered structure deduced from independent NMR experiments reported in the literature. It is revealed that increasing the fraction of negatively charged lipids can induce a conformational change of pardaxin from random-coil to α-helical structures. This experimental protocol can be employed for determining the interfacial protein secondary structures and dynamics in situ and in real time without extraneous labels.

Nanoscale morphology of Ni{sub 50}Ti{sub 45}Cu{sub 5} nanoglass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Śniadecki, Z., E-mail: sniadecki@ifmpan.poznan.pl; Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen; Wang, D.

2016-03-15

Nanoglasses are noncrystalline solids with a granular nano-/microstructure. In contrast to their nanocrystalline analogs, typically constituted of grains and grain boundaries, nanoglasses consist of glassy regions with a structure corresponding to melt-quenched glasses and amorphous interfaces characterized by a reduced density. Their unique properties can be controlled by modifying size and chemical composition of the granular and interfacial regions. Ni{sub 50}Ti{sub 45}Cu{sub 5} amorphous films were obtained by magnetron sputtering and analyzed to determine their nanoscale morphology and the formation mechanisms. The nanoglasses were noted to have a hierarchical nano-columnar structure with the smallest Ni-rich (Ni:Ti ratio of ca. 5:3)more » amorphous columns with diameters of about 8 nm and Ti-rich glassy interfacial regions with a substantially lower density. The results were obtained utilizing X-ray diffraction and different microscopic methods, e.g., atomic force microscopy and transmission electron microscopy. A detailed analysis indicates the complexity of the formation mechanisms of topologically and chemically distinguishable structural units with curvature driven surface diffusion, surface mobility, self-shadowing and internal stresses as the most important parameters. Common and simple synthesis method and the possibility for easy modification of the morphology and, consequently, the physical properties offer an opportunity for intensive studies of this new class of materials, opening the way towards possible applications. - Highlights: • Ni{sub 50}Ti{sub 45}Cu{sub 5} thin film nanoglasses were synthesized by magnetron sputtering. • Ti amorphous interfacial phase with reduced density is observed. • Stabilization of interfaces by specific local thermodynamic conditions.« less

Poly(vinylidene fluoride) Flexible Nanocomposite Films with Dopamine-Coated Giant Dielectric Ceramic Nanopowders, Ba(Fe0.5Ta0.5)O3, for High Energy-Storage Density at Low Electric Field.

PubMed

Wang, Zhuo; Wang, Tian; Wang, Chun; Xiao, Yujia; Jing, Panpan; Cui, Yongfei; Pu, Yongping

2017-08-30

Ba(Fe 0.5 Ta 0.5 )O 3 /poly(vinylidene fluoride) (BFT/PVDF) flexible nanocomposite films are fabricated by tape casting using dopamine (DA)-modified BFT nanopowders and PVDF as a matrix polymer. After a surface modification of installing a DA layer with a thickness of 5 nm, the interfacial couple interaction between BFT and PVDF is enhanced, resulting in less hole defects at the interface. Then the dielectric constant (ε'), loss tangent (tan δ), and AC conductivity of nanocomposite films are reduced. Meanwhile, the value of the reduced dielectric constant (Δε') and the strength of interfacial polarization (k) are introduced to illustrate the effect of DA on the dielectric behavior of nanocomposite films. Δε' can be used to calculate the magnitude of interfacial polarization, and the strength of the dielectric constant contributed by the interface can be expressed as k. Most importantly, the energy-storage density and energy-storage efficiency of nanocomposite films with a small BFT@DA filler content of 1 vol % at a low electric field of 150 MV/m are enhanced by about 15% and 120%, respectively, after DA modification. The high energy-storage density of 1.81 J/cm 3 is obtained in the sample. This value is much larger than the reported polymer-based nanocomposite films. In addition, the outstanding cycle and bending stability of the nanocomposite films make it a promising candidate for future flexible portable energy devices.

Residual stress within nanoscale metallic multilayer systems during thermal cycling

DOE PAGES

Economy, David Ross; Cordill, Megan Jo; Payzant, E. Andrew; ...

2015-09-21

Projected applications for nanoscale metallic multilayers will include wide temperature ranges. Since film residual stress has been known to alter system reliability, stress development within new film structures with high interfacial densities should be characterized to identify potential long-term performance barriers. To understand factors contributing to thermal stress evolution within nanoscale metallic multilayers, stress in Cu/Nb systems adhered to Si substrates was calculated from curvature measurements collected during cycling between 25 °C and 400 °C. Additionally, stress within each type of component layers was calculated from shifts in the primary peak position from in-situ heated X-ray diffraction. The effects ofmore » both film architecture (layer thickness) and layer order in metallic multilayers were tracked and compared with monolithic Cu and Nb films. Analysis indicated that the thermoelastic slope of nanoscale metallic multilayer films depends on thermal expansion mismatch, elastic modulus of the components, and also interfacial density. The layer thickness (i.e. interfacial density) affected thermoelastic slope magnitude while layer order had minimal impact on stress responses after the initial thermal cycle. When comparing stress responses of monolithic Cu and Nb films to those of the Cu/Nb systems, the nanoscale metallic multilayers show a similar increase in stress above 200 °C to the Nb monolithic films, indicating that Nb components play a larger role in stress development than Cu. Local stress calculations from X-ray diffraction peak shifts collected during heating reveal that the component layers within a multilayer film respond similarly to their monolithic counterparts.« less

TiN/Al2O3/ZnO gate stack engineering for top-gate thin film transistors by combination of post oxidation and annealing

NASA Astrophysics Data System (ADS)

Kato, Kimihiko; Matsui, Hiroaki; Tabata, Hitoshi; Takenaka, Mitsuru; Takagi, Shinichi

2018-04-01

Control of fabrication processes for a gate stack structure with a ZnO thin channel layer and an Al2O3 gate insulator has been examined for enhancing the performance of a top-gate ZnO thin film transistor (TFT). The Al2O3/ZnO interface and the ZnO layer are defective just after the Al2O3 layer formation by atomic layer deposition. Post treatments such as plasma oxidation, annealing after the Al2O3 deposition, and gate metal formation (PMA) are promising to improve the interfacial and channel layer qualities drastically. Post-plasma oxidation effectively reduces the interfacial defect density and eliminates Fermi level pinning at the Al2O3/ZnO interface, which is essential for improving the cut-off of the drain current of TFTs. A thermal effect of post-Al2O3 deposition annealing at 350 °C can improve the crystalline quality of the ZnO layer, enhancing the mobility. On the other hand, impacts of post-Al2O3 deposition annealing and PMA need to be optimized because the annealing can also accompany the increase in the shallow-level defect density and the resulting electron concentration, in addition to the reduction in the deep-level defect density. The development of the interfacial control technique has realized the excellent TFT performance with a large ON/OFF ratio, steep subthreshold characteristics, and high field-effect mobility.

Graphene-enhanced intermolecular interaction at interface between copper- and cobalt-phthalocyanines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dou, Wei-Dong; Center of Super-Diamond and Advanced Films; Huang, Shu-Ping

2015-10-07

Interfacial electronic structures of copper-phthalocyanine (CuPc), cobalt-phthalocyanine (CoPc), and graphene were investigated experimentally by using photoelectron spectroscopy. While the CuPc/graphene interface shows flat band structure and negligible interfacial dipole indicating quite weak molecule-substrate interaction, the CuPc/CoPc/graphene interface shows a large interfacial dipole and obvious energy level bending. Controlled experiments ruled out possible influences from the change in film structure of CuPc and pure π–π interaction between CoPc and CuPc. Analysis based on X-ray photoelectron spectroscopy and density functional theory reveals that the decrease in the work function for the CuPc/CoPc/graphene system is induced by the intermolecular interaction between CuPc andmore » CoPc which is enhanced owning to the peculiar electronic properties at the CoPc-graphene interface.« less

The effects of interfacial recombination and injection barrier on the electrical characteristics of perovskite solar cells

NASA Astrophysics Data System (ADS)

Shi, Lin Xing; Wang, Zi Shuai; Huang, Zengguang; Sha, Wei E. I.; Wang, Haoran; Zhou, Zhen

2018-02-01

Charge carrier recombination in the perovskite solar cells (PSCs) has a deep influence on the electrical performance, such as open circuit voltage, short circuit current, fill factor and ultimately power conversion efficiency. The impacts of injection barrier, recombination channels, doping properties of carrier transport layers and light intensity on the performance of PSCs are theoretically investigated by drift-diffusion model in this work. The results indicate that due to the injection barrier at the interfaces of perovskite and carrier transport layer, the accumulated carriers modify the electric field distribution throughout the PSCs. Thus, a zero electric field is generated at a specific applied voltage, with greatly increases the interfacial recombination, resulting in a local kink of current density-voltage (J-V) curve. This work provides an effective strategy to improve the efficiency of PSCs by pertinently reducing both the injection barrier and interfacial recombination.

Improved interfacial and electrical properties of atomic layer deposition HfO2 films on Ge with La2O3 passivation

NASA Astrophysics Data System (ADS)

Li, Xue-Fei; Liu, Xiao-Jie; Cao, Yan-Qiang; Li, Ai-Dong; Li, Hui; Wu, Di

2013-01-01

We report the characteristics of HfO2 films deposited on Ge substrates with and without La2O3 passivation at 250 °C by atomic layer deposition (ALD) using La[N(SiMe3)2]3 and Hf[N(CH3)(C2H5)]4 as the precursors. The HfO2 is observed to form defective HfGeOx at its interface during 500 °C postdeposition annealing. The insertion of an ultrathin La2O3 interfacial passivation layer effectively prevents the Ge outdiffusion and improves interfacial and electrical properties. Capacitance equivalent thickness (CET) of 1.35 nm with leakage current density JA of 8.3 × 10-4 A/cm2 at Vg = 1 V is achieved for the HfO2/La2O3 gate stacks on Ge substrates.

Nitride passivation reduces interfacial traps in atomic-layer-deposited Al2O3/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Aoki, T.; Fukuhara, N.; Osada, T.; Sazawa, H.; Hata, M.; Inoue, T.

2014-07-01

Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C-V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C-V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm-2eV-1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Ziying; Lee, Jungwoo Z.; Xin, Huolin L.

All-solid-state lithium-ion batteries have the potential to not only push the current limits of energy density by utilizing Li metal, but also improve safety by avoiding flammable organic electrolyte. However, understanding the role of solid electrolyte – electrode interfaces will be critical to improve performance. In this paper, we conducted long term cycling on commercially available lithium cobalt oxide (LCO)/lithium phosphorus oxynitride (LiPON)/lithium (Li) cells at elevated temperature to investigate the interfacial phenomena that lead to capacity decay. STEM-EELS analysis of samples revealed a previously unreported disordered layer between the LCO cathode and LiPON electrolyte. This electrochemically inactive layer grewmore » in thickness leading to loss of capacity and increase of interfacial resistance when cycled at 80 °C. Finally, the stabilization of this layer through interfacial engineering is crucial to improve the long term performance of thin-film batteries especially under thermal stress.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donald, Scott B.; Siekhaus, Wigbert J.; Nelson, Art J.

X-ray photoelectron spectroscopy in combination with secondary ion mass spectrometry depth profiling were used to investigate the surface and interfacial chemistry of C + ion implanted polycrystalline uranium subsequently oxidized in air for over 10 years at ambient temperature. The original implantation of 33 keV C + ions into U 238 with a dose of 4.3 × 10 17 cm –3 produced a physically and chemically modified surface layer that was characterized and shown to initially prevent air oxidation and corrosion of the uranium after 1 year in air at ambient temperature. The aging of the surface and interfacial layersmore » were examined by using the chemical shift of the U 4f, C 1s, and O 1s photoelectron lines. In addition, valence band spectra were used to explore the electronic structure of the aged carbide surface and interface layer. Moreover, the time-of-flight secondary ion mass spectrometry depth profiling results for the aged sample confirmed an oxidized uranium carbide layer over the carbide layer/U metal interface.« less

Effect of Pr Valence State on Interfacial Structure and Electrical Properties of Pr Oxide/PrON/Ge Gate Stack Structure

NASA Astrophysics Data System (ADS)

Kato, Kimihiko; Sakashita, Mitsuo; Takeuchi, Wakana; Kondo, Hiroki; Nakatsuka, Osamu; Zaima, Shigeaki

2011-04-01

In this study, we investigated the valence state and chemical bonding state of Pr in a Pr oxide/PrON/Ge structure. We clarified the relationship between the valence state of Pr and the Pr oxide/Ge interfacial reaction using Pr oxide/Ge and Pr oxide/PrON/Ge samples. We found the formation of three Pr oxide phases in Pr oxide films; hexagonal Pr2O3 (h-Pr2O3) (Pr3+), cubic Pr2O3 (c-Pr2O3) (Pr3+), and c-PrO2 (Pr4+). We also investigated the effect of a nitride interlayer on the interfacial reaction in Pr oxide/Ge gate stacks. In a sample with a nitride interlayer (Pr oxide/PrON/Ge), metallic Pr-Pr bonds are also formed in the c-Pr2O3 film. After annealing in H2 ambient, the diffusion of Ge into Pr oxide is not observed in this sample. Pr-Pr bonds probably prevent the interfacial reaction and Ge oxide formation, considering that the oxygen chemical potential of this film is lower than that of a GeO2/Ge system. On the other hand, the rapid thermal oxidation (RTO) treatment terminates the O vacancies and defects in c-Pr2O3. As a result, c-PrO2 with tetravalent Pr is formed in the Pr oxide/PrON/Ge sample with RTO. In this sample, the leakage current density is effectively decreased in comparison with the sample without RTO. Hydrogen termination works effectively in Pr oxide/PrON/Ge samples with and without RTO, and we can achieve an interface state density of as low as 4 ×1011 eV-1·cm-2.

Experiences on Cryogenic Injection under Supercritical Condition

DTIC Science & Technology

2000-05-22

and Roshko [2] for incompressible but variable-density gaseous turbulent mixing layers. Fractal analysis of the jet boundary also shows a similarity to...spreading angle versus the chamber-to-injectant density ratio.(* refers to data taken at AFRL. - FRACTAL ANALYSIS OF THE JET RaLhtINRECDPSUE *This appeared to...be a suitable analysis method to investigate the morphology of the interfacial phenomena and in recent years a number of applications of fractal

An Nmr Study of Supercooled Water Under Nanoconfinement by Hydrophobic Surfaces

NASA Astrophysics Data System (ADS)

Ling, Yan-Chun

The main focus of this dissertation is studying the properties of bulk water, confined water, and interfacial water. The thermodynamics, dynamics and state of water are investigated by DSC and 1H NMR methods. Hydrophobic slit-shaped pores with tunable pore size from 0.5 nm to 1.6 nm are applied as confinement media in our experiments. By confining water in nanopores, we are able to cool the water lower than its homogeneous nucleation temperature 235 K at ambient pressure and access the "no man's land". Both experimental and simulation results show water has heterogeneity property, with two "phases", one is high-density liquid (HDL) "phase" which has dense-packing structure, the other is low-density liquid (LDL) "phase" which has more tetrahedral structure. At room temperature, HDL and LDL two "phases" can coexist in millisecond time scale and 10 nanometer length scale. The room temperature water structure is dominated by HDL structure. By decreasing the temperature, HDL could convert to LDL gradually. At 200 K, LDL dominates the liquid state of water. It is of importance to emphasis, for water confined in nanopores there is no crystallization above 200 K. A dynamic crossover at 225 K in the liquid state is observed in our hydrophobic system, similar to that observed in hydrophilic system. This proves such dynamic crossover is not induced by crystallization or surface effect, but originally from the intrinsic properties of water. At 190 K, we find a second change of rotational correlation time, which resembles the glassification process of supercooled confined water, suggesting a higher rotational glass transition temperature for bulk water. In the lower temperature range 145 K water. In the lower temperature range 145 K < T < 165 K, the interfacial water induced glass transition is observed. At sufficient low temperature, confinement plays an important role for the induced glass transition. We also study the properties of interfacial water by confining water in smaller hydrophobic pores. It shows the interfacial water remains liquid state at 140 K. There is an Arrhenius to Arrhenius dynamic crossover at 170 K due to the rotational motion slowing down. Comparing to bulk water, interfacial water has fast rotation but effectively immobile. Our studies thus provide a complete picture for the rather controversial supercooled region and also differentiate the properties of bulk water, confined water and interfacial water using different techniques.

Asymmetric orientation of toluene molecules at oil-silica interfaces

NASA Astrophysics Data System (ADS)

Ledyastuti, Mia; Liang, Yunfeng; Kunieda, Makoto; Matsuoka, Toshifumi

2012-08-01

The interfacial structure of heptane and toluene at oil-silica interfaces has previously been studied by sum frequency generation [Z. Yang et al., J. Phys. Chem. C. 113, 20355 (2009)], 10.1021/jp9043122. It was found that the toluene molecule is almost perpendicular to the silica surface with a tilt angle of about 25°. Here, we have investigated the structural properties of toluene and heptane at oil-silica interfaces using molecular dynamics simulations for two different surfaces: the oxygen-bridging (hydrophobic) and hydroxyl-terminated (hydrophilic) surfaces of quartz (silica). Based on the density profile, it was found that both heptane and toluene oscillate on silica surfaces, with heptane showing more oscillation peaks. Furthermore, the toluene molecules of the first layer were found to have an asymmetric distribution of orientations, with more CH3 groups pointed away from the silica surface than towards the silica surface. These findings are generally consistent with previous experiments, and reveal enhanced molecular structures of liquids at oil-silica interfaces.

Asymmetric orientation of toluene molecules at oil-silica interfaces.

PubMed

Ledyastuti, Mia; Liang, Yunfeng; Kunieda, Makoto; Matsuoka, Toshifumi

2012-08-14

The interfacial structure of heptane and toluene at oil-silica interfaces has previously been studied by sum frequency generation [Z. Yang et al., J. Phys. Chem. C. 113, 20355 (2009)]. It was found that the toluene molecule is almost perpendicular to the silica surface with a tilt angle of about 25°. Here, we have investigated the structural properties of toluene and heptane at oil-silica interfaces using molecular dynamics simulations for two different surfaces: the oxygen-bridging (hydrophobic) and hydroxyl-terminated (hydrophilic) surfaces of quartz (silica). Based on the density profile, it was found that both heptane and toluene oscillate on silica surfaces, with heptane showing more oscillation peaks. Furthermore, the toluene molecules of the first layer were found to have an asymmetric distribution of orientations, with more CH(3) groups pointed away from the silica surface than towards the silica surface. These findings are generally consistent with previous experiments, and reveal enhanced molecular structures of liquids at oil-silica interfaces.

The Lγ Phase of Pulmonary Surfactant.

PubMed

Kumar, Kamlesh; Chavarha, Mariya; Loney, Ryan W; Weiss, Thomas M; Rananavare, Shankar B; Hall, Stephen B

2018-06-05

To determine how different components affect the structure of pulmonary surfactant, we measured X-ray scattering by samples derived from calf surfactant. The surfactant phospholipids demonstrated the essential characteristics of the L γ phase: a unit cell with a lattice constant appropriate for two bilayers, and crystalline chains detected by wide-angle X-ray scattering (WAXS). The electron density profile, obtained from scattering by oriented films at different relative humidities (70-97%), showed that the two bilayers, arranged as mirror images, each contain two distinct leaflets with different thicknesses and profiles. The detailed structures suggest one ordered leaflet that would contain crystalline chains and one disordered monolayer likely to contain the anionic compounds, which constitute ∼10% of the surfactant phospholipids. The spacing and temperature dependence detected by WAXS fit with an ordered leaflet composed of dipalmitoyl phosphatidylcholine. Physiological levels of cholesterol had no effect on this structure. Removing the anionic phospholipids prevented formation of the L γ phase. The cationic surfactant proteins inhibited L γ structures, but at levels unlikely related to charge. Because the L γ phase, if arranged properly, could produce a self-assembled ordered interfacial monolayer, the structure could have important functional consequences. Physiological levels of the proteins, however, inhibit formation of the L γ structures at high relative humidities, making their physiological significance uncertain.

3D printed Ti6Al4V implant surface promotes bone maturation and retains a higher density of less aged osteocytes at the bone-implant interface.

PubMed

Shah, Furqan A; Snis, Anders; Matic, Aleksandar; Thomsen, Peter; Palmquist, Anders

2016-01-01

For load-bearing orthopaedic applications, metal implants having an interconnected pore structure exhibit the potential to facilitate bone ingrowth and the possibility for reducing the stiffness mismatch between the implant and bone, thus eliminating stress-shielding effects. 3D printed solid and macro-porous Ti6Al4V implants were evaluated after six-months healing in adult sheep femora. The ultrastructural composition of the bone-implant interface was investigated using Raman spectroscopy and electron microscopy, in a correlative manner. The mineral crystallinity and the mineral-to-matrix ratios of the interfacial tissue and the native bone were found to be similar. However, lower Ca/P ratios, lower carbonate content, but higher proline, phenylalanine and tyrosine levels indicated that the interfacial tissue remained less mature. Bone healing was more advanced at the porous implant surface (vs. the solid implant surface) based on the interfacial tissue ν1 CO3(2-)/ν2 PO4(3-) ratio, phenylalanine and tyrosine levels approaching those of the native bone. The mechanosensing infrastructure in bone, the osteocyte lacuno-canalicular network, retained ∼40% more canaliculi per osteocyte lacuna, i.e., a 'less aged' morphology at the interface. The osteocyte density per mineralised surface area was ∼36-71% higher at the interface after extended healing periods. In osseointegration research, the success of an implant surface or design is commonly determined by quantifying the amount of new bone, rather than its maturation, composition and structure. This work describes a novel correlative methodology to investigate the ultrastructure and composition of bone formed around and within 3D printed Ti6Al4V implants having an interconnected open-pore structure. Raman spectroscopy demonstrates that the molecular composition of the interfacial tissue at different implant surfaces may vary, suggesting differences in the extent to which bone maturation occurs even after long-term healing. Bone maturation corresponded well with the structural parameters associated with remodelling kinetics, for example, the osteocyte density and the average number of canaliculi per osteocyte lacuna. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Liquid-vapor equilibrium and interfacial properties of square wells in two dimensions

NASA Astrophysics Data System (ADS)

Armas-Pérez, Julio C.; Quintana-H, Jacqueline; Chapela, Gustavo A.

2013-01-01

Liquid-vapor coexistence and interfacial properties of square wells in two dimensions are calculated. Orthobaric densities, vapor pressures, surface tensions, and interfacial thicknesses are reported. Results are presented for a series of potential widths λ* = 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5, where λ* is given in units of the hard core diameter σ. Critical and triple points are explored. No critical point was found for λ* < 1.4. Corresponding states principle analysis is performed for the whole series. For λ* = 1.4 and 1.5 evidence is presented that at an intermediate temperature between the critical and the triple point temperatures the liquid branch becomes an amorphous solid. This point is recognized in Armas-Pérez et al. [unpublished] as a hexatic phase transition. It is located at reduced temperatures T* = 0.47 and 0.35 for λ* = 1.4 and 1.5, respectively. Properties such as the surface tension, vapor pressure, and interfacial thickness do not present any discontinuity at these points. This amorphous solid branch does not follow the corresponding state principle, which is only applied to liquids and gases.

Investigation on Surface Polarization of Al2O3-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray Photoelectron Spectroscopy.

PubMed

Duan, Tian Li; Pan, Ji Sheng; Wang, Ning; Cheng, Kai; Yu, Hong Yu

2017-08-17

The surface polarization of Ga-face gallium nitride (GaN) (2 nm)/AlGaN (22 nm)/GaN channel (150 nm)/buffer/Si with Al 2 O 3 capping layer is investigated by angle-resolved X-ray photoelectron spectroscopy (ARXPS). It is found that the energy band varies from upward bending to downward bending in the interface region, which is believed to be corresponding to the polarization variation. An interfacial layer is formed between top GaN and Al 2 O 3 due to the occurrence of Ga-N bond break and Ga-O bond forming during Al 2 O 3 deposition via the atomic layer deposition (ALD). This interfacial layer is believed to eliminate the GaN polarization, thus reducing the polarization-induced negative charges. Furthermore, this interfacial layer plays a key role for the introduction of the positive charges which lead the energy band downward. Finally, a N 2 annealing at 400 °C is observed to enhance the interfacial layer growth thus increasing the density of positive charges.

A Novel Charged Medium Consisting of Gas-Liquid Interfacial Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaneko, Toshiro; Hatakeyama, Rikizo

Due to the unique properties of ionic liquids such as their extremely low vapor pressure and high heat capacity, we succeed in creating the reactive gas (plasmas)--liquid (ionic liquids) interfacial field under a low gas pressure condition, where the plasma ion behavior can be controlled. The effects of the plasma ion irradiation on the liquid medium are quantitatively revealed for the first time. In connection with the plasma ion irradiation, the potential structure and optical emission properties of the gas-liquid interfacial plasma are investigated by changing a polarity of the electrode in the liquid to evaluate the plasma-liquid interactions. Thesemore » results would contribute to synthesizing the metal nanoparticles with carbon nanotubes as a template in the ionic liquid. It is found that the high density, mono-dispersed, and isolated metal nanoparticles are synthesized between or inside the carbon nanotubes by controlling the gas-liquid interfacial plasmas. Furthermore, we can form novel nano-bio composite materials, such as DNA encapsulated carbon nanotubes using the plasma ion irradiation method in an electrolyte plasma with DNA, and demonstrate modifications of the electrical properties of the carbon nanotubes depending on the kinds of encapsulated DNA for the first time.« less

Effect of van der Waals forces on thermal conductance at the interface of a single-wall carbon nanotube array and silicon

NASA Astrophysics Data System (ADS)

Feng, Ya; Zhu, Jie; Tang, Dawei

2014-12-01

Molecular dynamics simulations are performed to evaluate the effect of van der Waals forces among single-wall carbon nanotubes (SWNTs) on the interfacial thermal conductance between a SWNT array and silicon substrate. First, samples of SWNTs vertically aligned on silicon substrate are simulated, where both the number and arrangement of SWNTs are varied. Results reveal that the interfacial thermal conductance of a SWNT array/Si with van der Waals forces present is higher than when they are absent. To better understand how van der Waals forces affect heat transfer through the interface between SWNTs and silicon, further constructs of one SWNT surrounded by different numbers of other ones are studied, and the results show that the interfacial thermal conductance of the central SWNT increases with increasing van der Waals forces. Through analysis of the covalent bonds and vibrational density of states at the interface, we find that heat transfer across the interface is enhanced with a greater number of chemical bonds and that improved vibrational coupling of the two sides of the interface results in higher interfacial thermal conductance. Van der Waals forces stimulate heat transfer at the interface.

Interfacial structure and electrical properties of ultrathin HfO2 dielectric films on Si substrates by surface sol-gel method

NASA Astrophysics Data System (ADS)

Gong, You-Pin; Li, Ai-Dong; Qian, Xu; Zhao, Chao; Wu, Di

2009-01-01

Ultrathin HfO2 films with about ~3 nm thickness were deposited on n-type (1 0 0) silicon substrates using hafnium chloride (HfCl4) source by the surface sol-gel method and post-deposition annealing (PDA). The interfacial structure and electrical properties of ultrathin HfO2 films were investigated. The HfO2 films show amorphous structures and smooth surface morphologies with a very thin interfacial oxide layer of ~0.5 nm and small surface roughness (~0.45 nm). The 500 °C PDA treatment forms stronger Hf-O bonds, leading to passivated traps, and the interfacial layer is mainly Hf silicate (HfxSiyOz). Equivalent oxide thickness of around 0.84 nm of HfO2/Si has been obtained with a leakage current density of 0.7 A cm-2 at Vfb + 1 V after 500 °C PDA. It was found that the current conduction mechanism of HfO2/Si varied from Schottky-Richardson emission to Fowler-Nordheim tunnelling at an applied higher positive voltage due to the activated partial traps remaining in the ultrathin HfO2 films.

Electric Field Control of the Ferromagnetic CaRuO3 /CaMnO3 Interface

NASA Astrophysics Data System (ADS)

Grutter, Alexander; Kirby, Brian; Gray, Matthew; Flint, Charles; Suzuki, Yuri; Borchers, Julie

2015-03-01

Electric field control of magnetism has been recognized as one of the most important goals in nanoscale magnetics research. The most popular routes towards achieving magnetoelectric (ME) coupling have focused on heterostructures incorporating multiferroics or ferroelectrics. Such studies often rely on voltage induced distortion to induce strain in the magnetic film and alter the magnetic properties. However, successful attempts to induce ME coupling without multiferroicity or magnetoelasticity remain relatively rare. The ferromagnetic interface between the antiferromagnetic insulator CaMnO3 and the paramagnetic metal CaRuO3 is a promising candidate for direct magnetization control. This interfacial ferroagnetism is stabilized through the competition between interfacial double exchange and antiferromagnetic superexchange between adjacent Mn4+ so that the system is expected to be very sensitive to small changes in interfacial carrier density. Using polarized neutron reflectometry, we have probed the electric field dependence of the interfacial magnetization of CaRuO3/CaMnO3 bilayers deposited on SrTiO3. We find that electric fields of +/-8 kV/m are sufficient to switch the interfaces from largely ferromagnetic to completely antiferromagnetic.

Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO 3-buffered ferroelectric BaTiO 3 film on GaAs

DOE PAGES

Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; ...

2015-11-16

The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO 3 thin filmsgrown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO 3 grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. We also use a combination of aberration-corrected scanning transmission electron microscopy andmore » first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectricpolarization of a BaTiO 3 thin filmgrown on GaAs. Moreover, we demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO 3), and propose that the presence of surface charge screening allows the formation of switchable domains.« less

Interfacial interaction track of amorphous solid dispersions established by water-soluble polymer and indometacin.

PubMed

Li, Jing; Fan, Na; Wang, Xin; Li, Chang; Sun, Mengchi; Wang, Jian; Fu, Qiang; He, Zhonggui

2017-08-30

The present work studied interfacial interactions of amorphous solid dispersions matrix of indometacin (IMC) that established using PVP K30 (PVP) and PEG 6000 (PEG) by focusing on their interaction forces and wetting process. Infrared spectroscopy (IR), raman spectroscopy, X-ray photoelectron spectra and contact angle instrument were used throughout the study. Hydrogen bond energy formed between PEG and IMC were stronger than that of PVP and IMC evidenced by molecular modeling measurement. The blue shift of raman spectroscopy confirmed that hydrogen bonding forces were formed between IMC and two polymers. The contact angle study can be used as an easy method to determine the dissolution mechanism of amorphous solid dispersions through fitting the profile of contact angle of water on a series of tablets. It is believed that the track of interfacial interactions will certainly become powerful tools to for designing and evaluating amorphous solid dispersions. Copyright © 2017 Elsevier B.V. All rights reserved.

Sinusoidal Forcing of Interfacial Films

NASA Astrophysics Data System (ADS)

Rasheed, Fayaz; Raghunandan, Aditya; Hirsa, Amir; Lopez, Juan

2015-11-01

Fluid transport, in vivo, is accomplished via pumping mechanisms of the heart and lungs, which results in biological fluids being subjected to oscillatory shear. Flow is known to influence biological macromolecules, but predicting the effect of shear is incomplete without also accounting for the influence of complex interfaces ubiquitous throughout the body. Here, we investigated the oscillatory response of the structure of aqueous interfacial films using a cylindrical knife edge viscometer. Vitamin K1 was used as a model monolayer because its behaviour has been thoroughly quantified and it doesn't show any measurable hysteresis. The monolayer was subjected to sinusoidal forcing under varied conditions of surface concentrations, periodic frequencies, and knife edge amplitudes. Particle Image Velocimetry(PIV) data was collected using Brewster Angle Microscopy(BAM), revealing the influence of oscillatory interfacial shear stress on the monolayer. Insights were gained as to how the velocity profile dampens at specific distances from the knife edge contact depending on the amplitude, frequency, and concentration of Vitamin K1. Supported by NNX13AQ22G, National Aeronautics and Space Administration.

Thermodynamics, interfacial pressure isotherms and dilational rheology of mixed protein-surfactant adsorption layers.

PubMed

Fainerman, V B; Aksenenko, E V; Krägel, J; Miller, R

2016-07-01

Proteins and their mixtures with surfactants are widely used in many applications. The knowledge of their solution bulk behavior and its impact on the properties of interfacial layers made great progress in the recent years. Different mechanisms apply to the formation process of protein/surfactant complexes for ionic and non-ionic surfactants, which are governed mainly by electrostatic and hydrophobic interactions. The surface activity of these complexes is often remarkably different from that of the individual protein and has to be considered in respective theoretical models. At very low protein concentration, small amounts of added surfactants can change the surface activity of proteins remarkably, even though no strongly interfacial active complexes are observed. Also small added amounts of non-ionic surfactants change the surface activity of proteins in the range of small bulk concentrations or surface coverages. The modeling of the equilibrium adsorption behavior of proteins and their mixtures with surfactants has reached a rather high level. These models are suitable also to describe the high frequency limits of the dilational viscoelasticity of the interfacial layers. Depending on the nature of the protein/surfactant interactions and the changes in the interfacial layer composition rather complex dilational viscoelasticities can be observed and described by the available models. The differences in the interfacial behavior, often observed in literature for studies using different experimental methods, are at least partially explained by a depletion of proteins, surfactants and their complexes in the range of low concentrations. A correction of these depletion effects typically provides good agreement between the data obtained with different methods, such as drop and bubble profile tensiometry. Copyright © 2015 Elsevier B.V. All rights reserved.

Interfacial Structure and Chemistry of GaN on Ge(111)

NASA Astrophysics Data System (ADS)

Zhang, Siyuan; Zhang, Yucheng; Cui, Ying; Freysoldt, Christoph; Neugebauer, Jörg; Lieten, Ruben R.; Barnard, Jonathan S.; Humphreys, Colin J.

2013-12-01

The interface of GaN grown on Ge(111) by plasma-assisted molecular beam epitaxy is resolved by aberration corrected scanning transmission electron microscopy. A novel interfacial structure with a 5∶4 closely spaced atomic bilayer is observed that explains why the interface is flat, crystalline, and free of GeNx. Density functional theory based total energy calculations show that the interface bilayer contains Ge and Ga atoms, with no N atoms. The 5∶4 bilayer at the interface has a lower energy than a direct stacking of GaN on Ge(111) and enables the 5∶4 lattice-matching growth of GaN.

Hierarchically Porous N-Doped Carbon Nanotubes/Reduced Graphene Oxide Composite for Promoting Flavin-Based Interfacial Electron Transfer in Microbial Fuel Cells.

PubMed

Wu, Xiaoshuai; Qiao, Yan; Shi, Zhuanzhuan; Tang, Wei; Li, Chang Ming

2018-04-11

Interfacial electron transfer between an electroactive biofilm and an electrode is a crucial step for microbial fuel cells (MFCs) and other bio-electrochemical systems. Here, a hierarchically porous nitrogen-doped carbon nanotubes (CNTs)/reduced graphene oxide (rGO) composite with polyaniline as the nitrogen source has been developed for the MFC anode. This composite possesses a nitrogen atom-doped surface for improved flavin redox reaction and a three-dimensional hierarchically porous structure for rich bacterial biofilm growth. The maximum power density achieved with the N-CNTs/rGO anode in S. putrefaciens CN32 MFCs is 1137 mW m -2 , which is 8.9 times compared with that of the carbon cloth anode and also higher than those of N-CNTs (731.17 mW m -2 ), N-rGO (442.26 mW m -2 ), and the CNTs/rGO (779.9 mW m -2 ) composite without nitrogen doping. The greatly improved bio-electrocatalysis could be attributed to the enhanced adsorption of flavins on the N-doped surface and the high density of biofilm adhesion for fast interfacial electron transfer. This work reveals a synergistic effect from pore structure tailoring and surface chemistry designing to boost both the bio- and electrocatalysis in MFCs, which also provide insights for the bioelectrode design in other bio-electrochemical systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Gui -Liang; Amine, Rachid; Xu, Yue -Feng

Cathode materials are critical to the energy density, power density and safety of sodium-ion batteries (SIBs). Herein, we performed a comprehensive study to elucidate and exemplify the interplay mechanism between phase structures, interfacial microstrain and electrochemical properties of layered-structured Na xNi 1/3Co 1/3Mn 1/3O 2 cathode materials for high voltage SIBs. The electrochemical test results showed that Na xNi 1/3Co 1/3Mn 1/3O 2 with an intergrowth P2/O3/O1 structure demonstrates better electrochemical performance and better thermal stability than Na xNi 1/3Co 1/3Mn 1/3O 2 with P2/O3 binary-phase integration and Na xNi 1/3Co 1/3Mn 1/3O 2 where only the P phase ismore » dominant. This result is caused by the distinct interfacial microstrain development during the synthesis and cycling of the P2/O3/O1 phase. In operando high energy X-ray diffraction further revealed that the intergrowth P2/O1/O3 cathode can inhibit the irreversible P2–O2 phase transformation and simultaneously improve the structure stability of the O3 and O1 phases during cycling. Here, we believe that interfacial microstrain can serve as an indispensable bridge to guide future design and synthesis of high performance SIB cathode materials and other high energy battery materials.« less

Mean-time-to-failure study of flip chip solder joints on Cu/Ni(V)/Al thin-film under-bump-metallization

NASA Astrophysics Data System (ADS)

Choi, W. J.; Yeh, E. C. C.; Tu, K. N.

2003-11-01

Electromigration of eutectic SnPb flip chip solder joints and their mean-time-to-failure (MTTF) have been studied in the temperature range of 100 to 140 °C with current densities of 1.9 to 2.75×104 A/cm2. In these joints, the under-bump-metallization (UBM) on the chip side is a multilayer thin film of Al/Ni(V)/Cu, and the metallic bond-pad on the substrate side is a very thick, electroless Ni layer covered with 30 nm of Au. When stressed at the higher current densities, the MTTF was found to decrease much faster than what is expected from the published Black's equation. The failure occurred by interfacial void propagation at the cathode side, and it is due to current crowding near the contact interface between the solder bump and the thin-film UBM. The current crowding is confirmed by a simulation of current distribution in the solder joint. Besides the interfacial void formation, the intermetallic compounds formed on the UBM as well as the Ni(V) film in the UBM have been found to dissolve completely into the solder bump during electromigration. Therefore, the electromigation failure is a combination of the interfacial void formation and the loss of UBM. Similar findings in eutectic SnAgCu flip chip solder joints have also been obtained and compared.

Interfacial development of electrophoretically deposited graphene oxide films on Al alloys

DOE PAGES

Jin, Sumin; Dickerson, James H.; Pham, Viet Hung; ...

2015-07-28

Adhesion between film and substrate is critical for electronic device and coating applications. Interfacial development between electrophoretically deposited graphene oxide films on Al 1100 and Al 5052 alloys were investigated using FT-IR and XPS depth profiling techniques. Obtained results suggest metal ion permeation from the substrates into deposited graphene oxide films. The interface between the films and the substrates were primarily composed of Al-O-C bonds from oxygenated defects on graphene oxide plane rather than expected Al-C formation. Films heat treated at 150 °C had change in microstructure and peak shifts in XPS spectra suggesting change in chemical structure of bondsmore » between the films and the substrates.« less

Molecular simulation of thermodynamic and transport properties for the H{sub 2}O+NaCl system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orozco, Gustavo A.; Jiang, Hao; Panagiotopoulos, Athanassios Z., E-mail: azp@princeton.edu

Molecular dynamics and Monte Carlo simulations have been carried out to obtain thermodynamic and transport properties of the binary mixture H{sub 2}O+NaCl at temperatures from T = 298 to 473 K. In particular, vapor pressures, liquid densities, viscosities, and vapor-liquid interfacial tensions have been obtained as functions of pressure and salt concentration. Several previously proposed fixed-point-charge models that include either Lennard-Jones (LJ) 12-6 or exponential-6 (Exp6) functional forms to describe non-Coulombic interactions were studied. In particular, for water we used the SPC and SPC/E (LJ) models in their rigid forms, a semiflexible version of the SPC/E (LJ) model, and themore » Errington-Panagiotopoulos Exp6 model; for NaCl, we used the Smith-Dang and Joung-Cheatham (LJ) parameterizations as well as the Tosi-Fumi (Exp6) model. While none of the model combinations are able to reproduce simultaneously all target properties, vapor pressures are well represented using the SPC plus Joung-Cheathem model combination, and all LJ models do well for the liquid density, with the semiflexible SPC/E plus Joung-Cheatham combination being the most accurate. For viscosities, the combination of rigid SPC/E plus Smith-Dang is the best alternative. For interfacial tensions, the combination of the semiflexible SPC/E plus Smith-Dang or Joung-Cheatham gives the best results. Inclusion of water flexibility improves the mixture densities and interfacial tensions, at the cost of larger deviations for the vapor pressures and viscosities. The Exp6 water plus Tosi-Fumi salt model combination was found to perform poorly for most of the properties of interest, in particular being unable to describe the experimental trend for the vapor pressure as a function of salt concentration.« less

Enhanced dielectric properties due to space charge-induced interfacial polarization in multilayer polymer films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xinyue; Tseng, Jung-Kai; Treufeld, Imre

We report that with the recent advancement of power electronics, polymer film capacitors have become increasingly important. However, the low temperature rating (up to 85 °C) and low energy density (5 J cm -3 at breakdown) of state-of-the-art biaxially oriented polypropylene (BOPP) films have been limiting factors for advanced power electronics. Based on our recent work, multilayer films (MLFs), which consist of a high energy density polymer [e.g., poly(vinylidene fluoride) (PVDF)] and a high breakdown/low loss polymer [e.g., polycarbonate (PC)], have shown potential to achieve high energy density (13–17 J cm -3), enhanced breakdown strength, high temperature tolerance, and lowmore » loss simultaneously. In this study, the dielectric properties of PC/PVDF 50/50 32- and 256-layer (32L and 256L) films were investigated. The breakdown strength of the 32L film was as high as 800 MV m -1 at room temperature, as compared to 600 MV m -1 of PVDF and 750 MV m-1 of PC. The temperature rating of the 32L film reached 120 °C, higher than that of BOPP. In addition, it was observed that the 32L film with thicker PC layers exhibited a higher breakdown strength and a lower DC conductivity than the 256L film with thinner PC layers at elevated temperatures. These differences were attributed to the difference in the interfacial polarization of space charges, which was further verified by thermally stimulated depolarization current spectroscopy. In conclusion, we conclude that interfacial polarization endows MLFs with the desirable dielectric properties for next generation film capacitors.« less

Enhanced dielectric properties due to space charge-induced interfacial polarization in multilayer polymer films

DOE PAGES

Chen, Xinyue; Tseng, Jung-Kai; Treufeld, Imre; ...

2017-09-15

We report that with the recent advancement of power electronics, polymer film capacitors have become increasingly important. However, the low temperature rating (up to 85 °C) and low energy density (5 J cm -3 at breakdown) of state-of-the-art biaxially oriented polypropylene (BOPP) films have been limiting factors for advanced power electronics. Based on our recent work, multilayer films (MLFs), which consist of a high energy density polymer [e.g., poly(vinylidene fluoride) (PVDF)] and a high breakdown/low loss polymer [e.g., polycarbonate (PC)], have shown potential to achieve high energy density (13–17 J cm -3), enhanced breakdown strength, high temperature tolerance, and lowmore » loss simultaneously. In this study, the dielectric properties of PC/PVDF 50/50 32- and 256-layer (32L and 256L) films were investigated. The breakdown strength of the 32L film was as high as 800 MV m -1 at room temperature, as compared to 600 MV m -1 of PVDF and 750 MV m-1 of PC. The temperature rating of the 32L film reached 120 °C, higher than that of BOPP. In addition, it was observed that the 32L film with thicker PC layers exhibited a higher breakdown strength and a lower DC conductivity than the 256L film with thinner PC layers at elevated temperatures. These differences were attributed to the difference in the interfacial polarization of space charges, which was further verified by thermally stimulated depolarization current spectroscopy. In conclusion, we conclude that interfacial polarization endows MLFs with the desirable dielectric properties for next generation film capacitors.« less

Trapping effects in irradiated and avalanche-injected MOS capacitors

NASA Technical Reports Server (NTRS)

Bakowski, M.; Cockrum, R. H.; Zamani, N.; Maserjian, J.; Viswanathan, C. R.

1978-01-01

The trapping parameters for holes, and for electrons in the presence of trapped holes, have been measured from a set of wafers with different oxide thickness processed under controlled conditions. The trap cross-sections and densities indicate at least three trap species, including an interfacial species, a dominant bulk species which is determined to tail off from the silicon interface, and a third, lower density bulk species that is distributed throughout the oxide.

Mechanism of CO 2 hydrogenation over Cu/ZrO 2(2̅12) interface from first-principles kinetics Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Hong, Qi-Jun; Liu, Zhi-Pan

2010-10-01

It has been a goal consistently pursued by chemists to understand and control the catalytic process over composite materials. In order to provide deeper insight on complex interfacial catalysis at the experimental conditions, we performed an extensive analysis on CO 2 hydrogenation over a Cu/ZrO 2 model catalyst by employing density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations based on the continuous stirred tank model. The free energy profiles are determined for the reaction at the oxygen-rich Cu/m-ZrO 2 (2̅12) interface, where all interfacial Zr are six-coordinated since the interface accumulates oxidative species at the reaction conditions. We show that not only methanol but also CO are produced through the formate pathway dominantly, whilst the reverse-water-gas-shift (RWGS) channel has only a minor contribution. H 2CO is a key intermediate species in the reaction pathway, the hydrogenation of which dictates the high temperature of CO 2 hydrogenation. The kinetics simulation shows that the CO 2 conversion is 1.20%, the selectivity towards methanol is 68% at 500 K and the activation energies for methanol and CO formation are 0.79 and 1.79 eV, respectively. The secondary reactions due to the product readsorption lower the overall turnover frequency (TOF) but increase the selectivity towards methanol by 16%. We also show that kMC is a more reliable tool for simulating heterogeneous catalytic processes compared to the microkinetics approach.

Structure and Mechanical Properties of Polybutadiene Thin Films Bound to Surface-Modified Carbon Interface.

PubMed

Hori, Koichiro; Yamada, Norifumi L; Fujii, Yoshihisa; Masui, Tomomi; Kishimoto, Hiroyuki; Seto, Hideki

2017-09-12

The structure and mechanical properties of polybutadiene (PB) films on bare and surface-modified carbon films were examined. There was an interfacial layer of PB near the carbon layer whose density was higher (lower) than that of the bulk material on the hydrophobic (hydrophilic) carbon surface. To glean information about the structure and mechanical properties of PB at the carbon interface, a residual layer (RL) adhering to the carbon surface, which was considered to be a model of "bound rubber layer", was obtained by rinsing the PB film with toluene. The density and thickness of the RLs were identical to those of the interfacial layer of the PB film. In accordance with the change in the density, normal stress of the RLs evaluated by atomic force microscopy was also dependent on the surface free energy: the RLs on the hydrophobic carbon were hard like glass, whereas those on the hydrophilic carbon were soft like rubber. Similarly, the wear test revealed that the RLs on the hydrophilic carbon could be peeled off by scratching under a certain stress, whereas the RLs on the hydrophobic carbons were resistant to scratching.

Nucleation and growth kinetics during metal-induced layer exchange crystallization of Ge thin films at low temperatures

NASA Astrophysics Data System (ADS)

Hu, Shu; McIntyre, Paul C.

2012-02-01

The kinetics of Al-catalyzed layer exchange crystallization of amorphous germanium (Ge) thin films at low temperatures is reported. Observation of Ge mass transport from an underlying amorphous Ge layer to the Al film surface through an interposed sub-nanometer GeOx interfacial layer allows independent measurement of the areal density and average area of crystalline Ge islands formed on the film surface. We show that bias-voltage stressing of the interfacial layer can be used to control the areal density of nucleated Ge islands. Based on experimental observations, the Johnson-Mehl-Avrami-Kolmogorov phase transformation theory is used to model nanoscale nucleation and growth of Ge islands in two dimensions. Ge island nucleation kinetics follows an exponentially decaying nucleation rate with time. Ge island growth kinetics switches from linear growth at a constant growth velocity to diffusion-limited growth as the growth front advances. The transition point between these two regimes depends on the Ge nucleation site density and the annealing temperature. Knowledge of the kinetics of low-temperature crystallization is important in achieving textured polycrystalline Ge thin films with large grains for applications in large-area electronics and solar energy conversion.

Second-Order Vibrational Lineshapes from the Air/Water Interface.

PubMed

Ohno, Paul E; Wang, Hong-Fei; Paesani, Francesco; Skinner, James L; Geiger, Franz M

2018-05-10

We explore by means of modeling how absorptive-dispersive mixing between the second- and third-order terms modifies the imaginary χ total (2) responses from air/water interfaces under conditions of varying charge densities and ionic strength. To do so, we use published Im(χ (2) ) and χ (3) spectra of the neat air/water interface that were obtained either from computations or experiments. We find that the χ total (2) spectral lineshapes corresponding to experimentally measured spectra contain significant contributions from both interfacial χ (2) and bulk χ (3) terms at interfacial charge densities equivalent to less than 0.005% of a monolayer of water molecules, especially in the 3100 to 3300 cm -1 frequency region. Additionally, the role of short-range static dipole potentials is examined under conditions mimicking brine. Our results indicate that surface potentials, if indeed present at the air/water interface, manifest themselves spectroscopically in the tightly bonded H-bond network observable in the 3200 cm -1 frequency range.

Half-metallicity at the (110) interface between a full Heusler alloy and GaAs

NASA Astrophysics Data System (ADS)

Nagao, Kazutaka; Miura, Yoshio; Shirai, Masafumi

2006-03-01

The electronic properties of Co2CrAl/GaAs interfaces are investigated by using first-principles calculations with density functional theory. It is found that spin polarization tends to remain relatively high at the (110) interface and reaches almost unity for a specific (110) interfacial structure. Furthermore, the nearly-half-metallic interface turns out to be the most stable of the (110) interfacial structures studied here. Spin polarization calculated only from the sp -projected density of states is also examined in order to eliminate the effects stemming from the localized d components. The analysis shows that the high spin polarization at the (110) interface owes little to the localized d component and, therefore, is expected to be fairly relevant to transport properties. Co2CrSi/GaAs , Co2MnSi/GaAs , and Co2MnGe/GaAs heterostructures are also investigated, and similar half-metal-like behavior at (110) interface is observed for all of them.

Double-plasma enhanced carbon shield for spatial/interfacial controlled electrodes in lithium ion batteries via micro-sized silicon from wafer waste

NASA Astrophysics Data System (ADS)

Chen, Bing-Hong; Chuang, Shang-I.; Duh, Jenq-Gong

2016-11-01

Using spatial and interfacial control, the micro-sized silicon waste from wafer slurry could greatly increase its retention potential as a green resource for silicon-based anode in lithium ion batteries. Through step by step spatial and interfacial control for electrode, the cyclability of recycled waste gains potential performance from its original poor retention property. In the stages of spatial control, the electrode stabilizers of active, inactive and conductive additives were mixed into slurries for maintaining architecture and conductivity of electrode. In addition, a fusion electrode modification of interfacial control combines electrolyte additive, technique of double-plasma enhanced carbon shield (D-PECS) to convert the chemical bond states and to alter the formation of solid electrolyte interphases (SEIs) in the first cycle. The depth profiles of chemical composition from external into internal electrode illustrate that the fusion electrode modification not only forms a boundary to balance the interface between internal and external electrodes but also stabilizes the SEIs formation and soothe the expansion of micro-sized electrode. Through these effect approaches, the performance of micro-sized Si waste electrode can be boosted from its serious capacity degradation to potential retention (200 cycles, 1100 mAh/g) and better meet the requirements for facile and cost-effective in industrial production.

Wettability of AFM tip influences the profile of interfacial nanobubbles

NASA Astrophysics Data System (ADS)

Teshima, Hideaki; Takahashi, Koji; Takata, Yasuyuki; Nishiyama, Takashi

2018-02-01

To accurately characterize the shape of interfacial nanobubbles using atomic force microscopy (AFM), we investigated the effect of wettability of the AFM tip while operating in the peak force tapping (PFT) mode. The AFM tips were made hydrophobic and hydrophilic by Teflon AF coating and oxygen plasma treatment, respectively. It was found that the measured base radius of nanobubbles differed between AFM height images and adhesion images, and that this difference depended on the tip wettability. The force curves obtained during the measurements were also different depending on the wettability, especially in the range of the tip/nanobubble interaction and in the magnitude of the maximum attractive force in the retraction period. The difference suggests that hydrophobic tips penetrate the gas/liquid interface of the nanobubbles, with the three phase contact line being pinned on the tip surface; hydrophilic tips on the other hand do not penetrate the interface. We then quantitatively estimated the pinning position and recalculated the true profiles of the nanobubbles by comparing the height images and adhesion images. As the AFM tip was made more hydrophilic, the penetration depth decreased and eventually approached zero. This result suggests that the PFT measurement using a hydrophilic tip is vital for the acquisition of reliable nanobubble profiles.

Interfacial Structures of Trihexyltetradecylphosphonium-bis(mandelato)borate Ionic Liquid Confined between Gold Electrodes.

PubMed

Wang, Yong-Lei; Golets, Mikhail; Li, Bin; Sarman, Sten; Laaksonen, Aatto

2017-02-08

Atomistic molecular dynamics simulations have been performed to study microscopic the interfacial ionic structures, molecular arrangements, and orientational preferences of trihexyltetradecylphosphonium-bis(mandelato)borate ([P 6,6,6,14 ][BMB]) ionic liquid confined between neutral and charged gold electrodes. It was found that both [P 6,6,6,14 ] cations and [BMB] anions are coabsorbed onto neutral electrodes at different temperatures. The hexyl and tetradecyl chains in [P 6,6,6,14 ] cations lie preferentially flat on neutral electrodes. The oxalato and phenyl rings in [BMB] anions are characterized by alternative parallel-perpendicular orientations in the mixed innermost ionic layer adjacent to neutral electrodes. An increase in temperature has a marginal effect on the interfacial ionic structures and molecular orientations of [P 6,6,6,14 ][BMB] ionic species in a confined environment. Electrifying gold electrodes leads to peculiar changes in the interfacial ionic structures and molecular orientational arrangements of [P 6,6,6,14 ] cations and [BMB] anions in negatively and positively charged gold electrodes, respectively. As surface charge density increases (but lower than 20 μC/cm 2 ), the layer thickness of the mixed innermost interfacial layer gradually increases due to a consecutive accumulation of [P 6,6,6,14 ] cations and [BMB] anions at negatively and positively charged electrodes, respectively, before the formation of distinct cationic and anionic innermost layers. Meanwhile, the molecular orientations of two oxalato rings in the same [BMB] anions change gradually from a parallel-perpendicular feature to being partially characterized by a tilted arrangement at an angle of 45° from the electrodes and finally to a dominant parallel coordination pattern along positively charged electrodes. Distinctive interfacial distribution patterns are also observed accordingly for phenyl rings that are directly connected to neighboring oxalato rings in [BMB] anions.

A nanoscale study of charge extraction in organic solar cells: the impact of interfacial molecular configurations.

PubMed

Tang, Fu-Ching; Wu, Fu-Chiao; Yen, Chia-Te; Chang, Jay; Chou, Wei-Yang; Gilbert Chang, Shih-Hui; Cheng, Horng-Long

2015-01-07

In the optimization of organic solar cells (OSCs), a key problem lies in the maximization of charge carriers from the active layer to the electrodes. Hence, this study focused on the interfacial molecular configurations in efficient OSC charge extraction by theoretical investigations and experiments, including small molecule-based bilayer-heterojunction (sm-BLHJ) and polymer-based bulk-heterojunction (p-BHJ) OSCs. We first examined a well-defined sm-BLHJ model system of OSC composed of p-type pentacene, an n-type perylene derivative, and a nanogroove-structured poly(3,4-ethylenedioxythiophene) (NS-PEDOT) hole extraction layer. The OSC with NS-PEDOT shows a 230% increment in the short circuit current density compared with that of the conventional planar PEDOT layer. Our theoretical calculations indicated that small variations in the microscopic intermolecular interaction among these interfacial configurations could induce significant differences in charge extraction efficiency. Experimentally, different interfacial configurations were generated between the photo-active layer and the nanostructured charge extraction layer with periodic nanogroove structures. In addition to pentacene, poly(3-hexylthiophene), the most commonly used electron-donor material system in p-BHJ OSCs was also explored in terms of its possible use as a photo-active layer. Local conductive atomic force microscopy was used to measure the nanoscale charge extraction efficiency at different locations within the nanogroove, thus highlighting the importance of interfacial molecular configurations in efficient charge extraction. This study enriches understanding regarding the optimization of the photovoltaic properties of several types of OSCs by conducting appropriate interfacial engineering based on organic/polymer molecular orientations. The ultimate power conversion efficiency beyond at least 15% is highly expected when the best state-of-the-art p-BHJ OSCs are combined with present arguments.

Fracture of coherent interfaces between an fcc metal matrix and the Cr23C6 carbide precipitate from first principles

NASA Astrophysics Data System (ADS)

Barbé, Elric; Fu, Chu-Chun; Sauzay, Maxime

2018-02-01

It is known that microcrack initiation in metallic alloys containing second-phase particles may be caused by either an interfacial or an intraprecipitate fracture. So far, the dependence of these features on properties of the precipitate and the interface is not clearly known. The present study aims to determine the key properties of carbide-metal interfaces controlling the energy and critical stress of fracture, based on density functional theory (DFT) calculations. We address coherent interfaces between a fcc iron or nickel matrix and a frequently observed carbide, the M23C6 , for which a simplified chemical composition Cr23C6 is assumed. The interfacial properties such as the formation and Griffith energies, and the effective Young's modulus are analyzed as functions of the magnetic state of the metal lattice, including the paramagnetic phase of iron. Interestingly, a simpler antiferromagnetic phase is found to exhibit similar interfacial mechanical behavior to the paramagnetic phase. A linear dependence is determined between the surface (and interface) energy and the variation of the number of chemical bonds weighted by the respective bond strength, which can be used to predict the relative formation energy for the surface and interface with various chemical terminations. Finally, the critical stresses of both intraprecipitate and interfacial fractures due to a tensile loading are estimated via the universal binding energy relation (UBER) model, parametrized on the DFT data. The validity of this model is verified in the case of intraprecipitate fracture, against results from DFT tensile test simulations. In agreement with experimental evidences, we predict a much stronger tendency for an interfacial fracture for this carbide. In addition, the calculated interfacial critical stresses are fully compatible with available experimental data in steels, where the interfacial carbide-matrix fracture is only observed at incoherent interfaces.

Effects of nitrogen incorporation in HfO(2) grown on InP by atomic layer deposition: an evolution in structural, chemical, and electrical characteristics.

PubMed

Kang, Yu-Seon; Kim, Dae-Kyoung; Kang, Hang-Kyu; Jeong, Kwang-Sik; Cho, Mann-Ho; Ko, Dae-Hong; Kim, Hyoungsub; Seo, Jung-Hye; Kim, Dong-Chan

2014-03-26

We investigated the effects of postnitridation on the structural characteristics and interfacial reactions of HfO2 thin films grown on InP by atomic layer deposition (ALD) as a function of film thickness. By postdeposition annealing under NH3 vapor (PDN) at 600 °C, an InN layer formed at the HfO2/InP interface, and ionized NHx was incorporated in the HfO2 film. We demonstrate that structural changes resulting from nitridation of HfO2/InP depend on the film thickness (i.e., a single-crystal interfacial layer of h-InN formed at thin (2 nm) HfO2/InP interfaces, whereas an amorphous InN layer formed at thick (>6 nm) HfO2/InP interfaces). Consequently, the tetragonal structure of HfO2 transformed into a mixture structure of tetragonal and monoclinic because the interfacial InN layer relieved interfacial strain between HfO2 and InP. During postdeposition annealing (PDA) in HfO2/InP at 600 °C, large numbers of oxidation states were generated as a result of interfacial reactions between interdiffused oxygen impurities and out-diffused InP substrate elements. However, in the case of the PDN of HfO2/InP structures at 600 °C, nitrogen incorporation in the HfO2 film effectively blocked the out-diffusion of atomic In and P, thus suppressing the formation of oxidation states. Accordingly, the number of interfacial defect states (Dit) within the band gap of InP was significantly reduced, which was also supported by DFT calculations. Interfacial InN in HfO2/InP increased the electron-barrier height to ∼0.6 eV, which led to low-leakage-current density in the gate voltage region over 2 V.

Investigating the properties and interaction mechanism of nano-silica in polyvinyl alcohol/polyacrylamide blends at an atomic level.

PubMed

Wei, Qinghua; Wang, Yanen; Wang, Shuzhi; Zhang, Yingfeng; Chen, Xiongbiao

2017-11-01

The nano-silica can be incorporated into polymers for improved mechanical properties. Notably, the interaction between nano-silica and polymer is of a microscopic phenomenon and thus, hard to observe and study by using experimental methods. Based on molecular dynamics, this paper presents a study on the properties and the interaction mechanism of nano-silica in the polyvinyl alcohol (PVA)/polyacrylamide (PAM) blends at an atomic level. Specifically, six blends of PVA/PAM with varying concentrations of nano-silica (0-13wt%) and two interfacial interaction models of polymers on the silica surface were designed and analyzed at an atomic level in terms of concentration profile, mechanical properties, fractional free volume (FFV), dynamic properties of polymers and X-ray diffraction patterns. The concentration profile results and micromorphologies of equilibrium models suggest PAM molecular chains are easier to be adsorbed on the silica surface than PVA molecular chains in blends. The incorporation of nano-silica into the PVA/PAM blends can increase the blend mechanical properties, densities, and semicrystalline character. Meanwhile, the FFV and the mobility of polymer chain decrease with the silica concentration, which agrees with the results of mechanical properties, densities, and semicrystalline character. Our results also illustrate that an analysis of binding energies and pair correlation functions (PCF) allows for the discovery of the interaction mechanism of nano-silica in PVA/PAM blends; and that hydrogen bond interactions between polar functional groups of polymer molecular chains and the hydroxyl groups of the silica surface are involved in adsorption of the polymers on the silica surface, thus affecting the interaction mechanism of nano-silica in PVA/PAM blend systems. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effects of wettability and interfacial nanobubbles on flow through structured nanochannels: an investigation of molecular dynamics

NASA Astrophysics Data System (ADS)

Yen, Tsu-Hsu

2015-12-01

Solid-fluid boundary conditions are strongly influenced by a number of factors, including the intrinsic properties of the solid/fluid materials, surface roughness, wettability, and the presence of interfacial nanobubbles (INBs). The interconnected nature of these factors means that they should be considered jointly. This paper employs molecular dynamics (MD) simulation in a series of studies aimed at elucidating the influence of wettability in boundary behaviour and the accumulation of interfacial gas. Specifically, we examined the relationship between effective slip length, the morphology of nanobubbles, and wettability. Two methods were employed for the promotion of hydrophobicity between two structured substrates with similar intrinsic contact angles. We also compared anisotropic and isotropic atomic arrangements in the form of graphite and Si(100), respectively. A physical method was employed to deal with variations in surface roughness, whereas a chemical method was used to adjust the wall-fluid interaction energy (ɛwf). We first compared the characteristic properties of wettability, including contact angle and fluid density within the cavity. We then investigated the means by which variations in solid-fluid interfacial wettability affect interfacial gas molecules. Our results reveal that the morphology of INB on a patterned substrate is determined by wettability as well as the methods employed for the promotion of hydrophobicity. The present study also illustrates the means by which the multiple effects of the atomic arrangement of solids, surface roughness, wettability and INB influence effective slip length.

Formation of periodic interfacial misfit dislocation array at the InSb/GaAs interface via surface anion exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai

The relationship between growth temperature and the formation of periodic interfacial misfit (IMF) dislocations via the anion exchange process in InSb/GaAs heteroepitaxy was systematically investigated. The microstructural and electrical properties of the epitaxial layer were characterized using atomic force microscope, high-resolution x-ray diffraction, transmission electron microscopy, and Hall resistance measurement. The formation of interfacial misfit (IMF) dislocation arrays depended on growth temperature. A uniformly distributed IMF array was found in a sample grown at 310 °C, which also exhibited the lowest threading dislocation density. The analysis suggested that an incomplete As-for-Sb anion exchange process impeded the formation of IMF on samplemore » grown above 310 °C. At growth temperature below 310 °C, island coalescence led to the formation of 60° dislocations and the disruption of periodic IMF array. All samples showed higher electron mobility at 300 K than at 77 K.« less

Influence of Sulphur Impurities on the Interfacial Tension between Aluminium and Cryolite Alumina Melts

NASA Astrophysics Data System (ADS)

Korenko, Michal

2007-06-01

The interfacial tension (IFT) between aluminium and cryolite melts containing different salt additions (AlF3, NaF,Na2SO4) has been measured during electrolysis by the capillary depression method. The technique is based on the measurement of the capillary depression occurring when a capillary, which is moved vertically down through the molten salt layer, passes through the metal/salt interface. The depression is measured by simultaneous video recording of the immersion height of the alumina capillary. The interfacial tension is strongly dependent on the n(NaF)/n(AlF3) ratio. The addition of Na2SO4 decreases the IFT of the aluminium/electrolyte interface. We also found the different influence of the conditions of electrolysis on the IFT in systems with and without Na2SO4. In systems without Na2SO4 the IFT decreases with increasing current density, and in systems with Na2SO4 it increases.

Improvement in the breakdown endurance of high-κ dielectric by utilizing stacking technology and adding sufficient interfacial layer.

PubMed

Pang, Chin-Sheng; Hwu, Jenn-Gwo

2014-01-01

Improvement in the time-zero dielectric breakdown (TZDB) endurance of metal-oxide-semiconductor (MOS) capacitor with stacking structure of Al/HfO2/SiO2/Si is demonstrated in this work. The misalignment of the conduction paths between two stacking layers is believed to be effective to increase the breakdown field of the devices. Meanwhile, the resistance of the dielectric after breakdown for device with stacking structure would be less than that of without stacking structure due to a higher breakdown field and larger breakdown power. In addition, the role of interfacial layer (IL) in the control of the interface trap density (D it) and device reliability is also analyzed. Device with a thicker IL introduces a higher breakdown field and also a lower D it. High-resolution transmission electron microscopy (HRTEM) of the samples with different IL thicknesses is provided to confirm that IL is needed for good interfacial property.

Exploring parameter space effects on structure-property relationships of surfactants at liquid-liquid interfaces.

PubMed

Emborsky, Christopher P; Cox, Kenneth R; Chapman, Walter G

2011-08-28

The ubiquitous use of surfactants in commercial and industrial applications has led to many experimental, theoretical, and simulation based studies. These efforts seek to provide a molecular level understanding of the effects on structuring behavior and the corresponding impacts on observable properties (e.g., interfacial tension). With such physical detail, targeted system design can be improved over typical techniques of observational trends and phenomenological correlations by taking advantage of predictive system response. This research provides a systematic study of part of the broad parameter space effects on equilibrium microstructure and interfacial properties of amphiphiles at a liquid-liquid interface using the interfacial statistical associating fluid theory density functional theory as a molecular model for the system from the bulk to the interface. Insights into the molecular level physics and thermodynamics governing the system behavior are discussed as they relate to both predictions qualitatively consistent with experimental observations and extensions beyond currently available studies. © 2011 American Institute of Physics

Accessing the bottleneck in all-solid state batteries, lithium-ion transport over the solid-electrolyte-electrode interface.

PubMed

Yu, Chuang; Ganapathy, Swapna; Eck, Ernst R H van; Wang, Heng; Basak, Shibabrata; Li, Zhaolong; Wagemaker, Marnix

2017-10-20

Solid-state batteries potentially offer increased lithium-ion battery energy density and safety as required for large-scale production of electrical vehicles. One of the key challenges toward high-performance solid-state batteries is the large impedance posed by the electrode-electrolyte interface. However, direct assessment of the lithium-ion transport across realistic electrode-electrolyte interfaces is tedious. Here we report two-dimensional lithium-ion exchange NMR accessing the spontaneous lithium-ion transport, providing insight on the influence of electrode preparation and battery cycling on the lithium-ion transport over the interface between an argyrodite solid-electrolyte and a sulfide electrode. Interfacial conductivity is shown to depend strongly on the preparation method and demonstrated to drop dramatically after a few electrochemical (dis)charge cycles due to both losses in interfacial contact and increased diffusional barriers. The reported exchange NMR facilitates non-invasive and selective measurement of lithium-ion interfacial transport, providing insight that can guide the electrolyte-electrode interface design for future all-solid-state batteries.

A quantitative study of factors influencing lamellar eutectic morphology during solidification

NASA Technical Reports Server (NTRS)

Kaukler, W. F. S.

1981-01-01

The factors that influence the shape of the solid-liquid interface of a lamellar binary eutectic alloy are evaluated. Alloys of carbon tetrabromide and hexachloroethane which serve as a transparent analogue of lamellar metallic eutectics are used. The observed interface shapes are analyzed by computer-aided methods. The solid-liquid interfacial free energies of each of the individual phases comprising the eutectic system are measured as a function of composition using a 'grain boundary groove' technique. The solid-liquid interfacial free energy of the two phases are evaluated directly from the eutectic interface. The phase diagram for the system, the heat of fusion as a function of composition, and the density as a function of composition are measured. The shape of the eutectic interface is controlled mainly by the solid-liquid and solid-solid interfacial free energy relationships at the interface and by the temperature gradient present, rather than by interlamellar diffusion in the liquid at the interface, over the range of growth rates studied.

Interfacial behaviours between lithium ion conductors and electrode materials in various battery systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Bingbin; Wang, Shanyu; Evans IV, Willie J.

In recent years room temperature Li+ ion conductors have been intensively revisited in order to develop safe lithium ion (Li-ion) batteries and beyond that can be deployed in the electrical vehicles. Through careful modification on materials synthesis, promising solid Li+ conductors with high ionic conductivity, competitve with liquid electrolytes, have been demonstrated. However, the integration of those highly conductive solid electrolytes into the whole system is still very challenging mainly due to the high impedance existing in the different interfaces throughout the entire battery structure. Herein , this review paper focuses on the overview of the interfacial behaviors between Li+more » conductors and cathode/anode materials. The origin, evolution and potential solutions to reuce these interfacial impedances are reviewed for various battery systems spanning from Li-ion, lithium sulfur (Li-S), lithium oxygen (Li-O2) batteries to lithium metal protection. The predicted gravimetric and volumetric energy densities at different scenarios are also discussed along with the prospectives for further development of solid state batteries.« less

Cell Partition in Two Polymer Aqueous Phases

NASA Technical Reports Server (NTRS)

Brooks, D. E.

1985-01-01

In a reduced gravity environment the two polymer phases will not separate via density driven settling in an acceptably short length of time. It is to be expected that a certain amount of phase separation will take place, however, driven by the reduction in free energy gained when the interfacial area is reduced. This stage of separation process will therefore depend directly on the magnitude of the interfacial tension between the phases. In order to induce complete phase separation in a short time, electric field-induced separation which occurs because the droplets of one phase in the other have high electrophoretic mobilities which increase with droplet size was investigated. These mobilities are significant only in the presence of certain salts, particularly phosphates. The presence of such salts, in turn has a strong effect on the cell partition behavior in dextran-poly (ethylene glycol) (PEG) systems. The addition of the salts necessary to produce phase drop mobilities has a large effect on the interfacial tensions in the systems.

Systematic Approach to Electrostatically Induced 2D Crystallization of Nanoparticles at Liquid Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuto, M.; Kewalramani, S.; Wang, S.

2011-02-07

We report an experimental demonstration of a strategy for inducing two-dimensional (2D) crystallization of charged nanoparticles on oppositely charged fluid interfaces. This strategy aims to maximize the interfacial adsorption of nanoparticles, and hence their lateral packing density, by utilizing a combination of weakly charged particles and a high surface charge density on the planar interface. In order to test this approach, we investigated the assembly of cowpea mosaic virus (CPMV) on positively charged lipid monolayers at the aqueous solution surface, by means of in situ X-ray scattering measurements at the liquid-vapor interface. The assembly was studied as a function ofmore » the solution pH, which was used to vary the charge on CPMV, and of the mole fraction of the cationic lipid in the binary lipid monolayer, which set the interface charge density. The 2D crystallization of CPMV occurred in a narrow pH range just above the particle's isoelectric point, where the particle charge was weakly negative, and only when the cationic-lipid fraction in the monolayer exceeded a threshold. The observed 2D crystals exhibited nearly the same packing density as the densest lattice plane within the known 3D crystals of CPMV. The above electrostatic approach of maximizing interfacial adsorption may provide an efficient route to the crystallization of nanoparticles at aqueous interfaces.« less

Tunable Interfacial Thermal Conductance by Molecular Dynamics

NASA Astrophysics Data System (ADS)

Shen, Meng

We study the mechanism of tunable heat transfer through interfaces between solids using a combination of non-equilibrium molecular dynamics simulation (NEMD), vibrational mode analysis and wave packet simulation. We investigate how heat transfer through interfaces is affected by factors including pressure, interfacial modulus, contact area and interfacial layer thickness, with an overreaching goal of developing fundamental knowledge that will allow one to tailor thermal properties of interfacial materials. The role of pressure and interfacial stiffness is unraveled by our studies on an epitaxial interface between two Lennard-Jones (LJ) crystals. The interfacial stiffness is varied by two different methods: (i) indirectly by applying pressure which due to anharmonic nature of bonding, increases interfacial stiffness, and (ii) directly by changing the interfacial bonding strength by varying the depth of the potential well of the LJ potential. When the interfacial bonding strength is low, quantitatively similar behavior to pressure tuning is observed when the interfacial thermal conductance is increased by directly varying the potential-well depth parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent, and even slightly decreases with increasing pressure. This decrease can be explained by the change in overlap between the vibrational densities of states of the two crystalline materials. The role of contact area is studied by modeling structures comprised of Van der Waals junctions between single-walled nanotubes (SWCNT). Interfacial thermal conductance between SWCNTs is obtained from NEMD simulation as a function of crossing angle. In this case the junction conductance per unit area is essentially a constant. By contrast, interfacial thermal conductance between multiwalled carbon nanotubes (MWCNTs) is shown to increase with diameter of the nanotubes by recent experimental studies [1]. To elucidate this behavior we studied a simplified model comprised of an interface between two stacks of graphene ribbons to mimic the contact between multiwalled nanotubes. Our results, in agreement with experiment, show that the interfacial thermal conductance indeed increases with the number of graphene layers, corresponding to larger diameter and larger number of walls in MWCNT. The role of interfacial layer thickness is investigated by modeling a system of a few layers of graphene sandwiched between two silicon slabs. We show, by wave packet simulation and by theoretical calculation of a spring-mass model, that the transmission coefficient of individual vibrational modes is strongly dependent on the frequency and the number of graphene layers due to coherent interference effects; by contrast, the interfacial thermal conductance obtained in NEMD simulation, which represents an integral over all phonons, is essentially independent of the number of graphene layers, in agreement with recent experiments. Furthermore, when we heat one atomic layer of graphene directly, the effective interfacial conductance associated with heat dissipation to the silicon substrate is very small. We attribute this to the resistance associated with heat transfer between high and low frequency phonon modes within graphene. Finally, we also replaced graphene layers by a few WSe2 sheets and observed that interfacial thermal resistance of a Si/n-WSe2/Si structure increases linearly with interface thickness at least for 1 < n <= 20, indicating diffusive heat transfer mechanism, in contrast to ballistic behavior of a few graphene layers. The corresponding thermal conductivity (0.048 W m-1 K-1) of a few WSe2 layers is rather small. By comparing phonon dispersion of graphene layers and WSe2 sheets, we attribute the diffusive behavior of a few WSe2 sheets to abundant optical phonons at low and medium frequencies leading to very short mean free path. Our computational studies of effects of pressure and structural properties on interfacial thermal conductance provide fundamental insights for tunable heat transfer in nanostructures. [1] Professor D. Y. Li from University of Vanderbilt, private communication (Nov. 14, 2011).

Giant magneto-impedance and stress-impedance effects of microwire composites for sensing applications

NASA Astrophysics Data System (ADS)

Qin, F. X.; Peng, H. X.; Popov, V. V.; Phan, M. H.

2011-02-01

Composites consisting of glass-coated amorphous microwire Co 68.59Fe 4.84Si 12.41B 14.16 and 913 E-glass prepregs were designed and fabricated. The influences of tensile stress, annealing and number of composite layers on the giant magneto-impedance (GMI) and giant stress-impedance (GSI) effects in these composites were investigated systematically. It was found that the application of tensile stress along the microwire axis or an increase in the number of composite layers reduced the GMI effect and increased the circular anisotropy field, while the annealing treatment had a reverse effect. The value of matrix-wire interfacial stress calculated via the GMI profiles coincided with the value of the applied effective tensile stress to yield similar GMI profiles. Enhancement of the GSI effect was achieved in the composites relative to their single microwire inclusion. These findings are important for the development of functional microwire-based composites for magnetic- and stress-sensing applications. They also open up a new route for probing the interfacial stress in fibre-reinforced polymer (FRP) composites.

XPS and SIMS study of the surface and interface of aged C + implanted uranium

DOE PAGES

Donald, Scott B.; Siekhaus, Wigbert J.; Nelson, Art J.

2016-09-08

X-ray photoelectron spectroscopy in combination with secondary ion mass spectrometry depth profiling were used to investigate the surface and interfacial chemistry of C + ion implanted polycrystalline uranium subsequently oxidized in air for over 10 years at ambient temperature. The original implantation of 33 keV C + ions into U 238 with a dose of 4.3 × 10 17 cm –3 produced a physically and chemically modified surface layer that was characterized and shown to initially prevent air oxidation and corrosion of the uranium after 1 year in air at ambient temperature. The aging of the surface and interfacial layersmore » were examined by using the chemical shift of the U 4f, C 1s, and O 1s photoelectron lines. In addition, valence band spectra were used to explore the electronic structure of the aged carbide surface and interface layer. Moreover, the time-of-flight secondary ion mass spectrometry depth profiling results for the aged sample confirmed an oxidized uranium carbide layer over the carbide layer/U metal interface.« less

In-Situ Quantification of the Interfacial Rheological Response of Bacterial Biofilms to Environmental Stimuli

PubMed Central

Rühs, Patrick A.; Böni, Lukas; Fuller, Gerald G.; Inglis, R. Fredrik; Fischer, Peter

2013-01-01

Understanding the numerous factors that can affect biofilm formation and stability remain poorly understood. One of the major limitations is the accurate measurement of biofilm stability and cohesiveness in real-time when exposed to changing environmental conditions. Here we present a novel method to measure biofilm strength: interfacial rheology. By culturing a range of bacterial biofilms on an air-liquid interface we were able to measure their viscoelastic growth profile during and after biofilm formation and subsequently alter growth conditions by adding surfactants or changing the nutrient composition of the growth medium. We found that different bacterial species had unique viscoelastic growth profiles, which was also highly dependent on the growth media used. We also found that we could reduce biofilm formation by the addition of surfactants or changing the pH, thereby altering the viscoelastic properties of the biofilm. Using this technique we were able to monitor changes in viscosity, elasticity and surface tension online, under constant and varying environmental conditions, thereby providing a complementary method to better understand the dynamics of both biofilm formation and dispersal. PMID:24244319

Defensive Armor of Potato Tubers: Nonpolar Metabolite Profiling, Antioxidant Assessment, and Solid-State NMR Compositional Analysis of Suberin-Enriched Wound-Healing Tissues

PubMed Central

Dastmalchi, Keyvan; Kallash, Linda; Wang, Isabel; Phan, Van C.; Huang, Wenlin; Serra, Olga; Stark, Ruth E.

2016-01-01

The cultivation, storage, and distribution of potato tubers are compromised by mechanical damage and suboptimal healing. To investigate wound-healing progress in cultivars with contrasting russeting patterns, metabolite profiles reported previously for polar tissue extracts were complemented by GC/MS measurements for nonpolar extracts and quantitative 13C NMR of interfacial solid suspensions. Potential marker compounds that distinguish cultivar type and wound-healing time point included fatty acids, fatty alcohols, alkanes, glyceryl esters, α,ω-fatty diacids, and hydroxyfatty acids. The abundant long-chain fatty acids in nonpolar extracts and solids from the smooth-skinned Yukon Gold cultivar suggested extensive suberin biopolymer formation; this hypothesis was supported by high proportions of arenes, alkenes, and carbonyl groups in the solid and among the polar markers. The absence of many potential marker classes in nonpolar Atlantic extracts and interfacial solids suggested a limited extent of suberization. Modest scavenging activities of all nonpolar extracts indicate that the majority of antioxidants produced in response to wounding are polar. PMID:26166447

Defensive Armor of Potato Tubers: Nonpolar Metabolite Profiling, Antioxidant Assessment, and Solid-State NMR Compositional Analysis of Suberin-Enriched Wound-Healing Tissues.

PubMed

Dastmalchi, Keyvan; Kallash, Linda; Wang, Isabel; Phan, Van C; Huang, Wenlin; Serra, Olga; Stark, Ruth E

2015-08-05

The cultivation, storage, and distribution of potato tubers are compromised by mechanical damage and suboptimal healing. To investigate wound-healing progress in cultivars with contrasting russeting patterns, metabolite profiles reported previously for polar tissue extracts were complemented by GC/MS measurements for nonpolar extracts and quantitative (13)C NMR of interfacial solid suspensions. Potential marker compounds that distinguish cultivar type and wound-healing time point included fatty acids, fatty alcohols, alkanes, glyceryl esters, α,ω-fatty diacids, and hydroxyfatty acids. The abundant long-chain fatty acids in nonpolar extracts and solids from the smooth-skinned Yukon Gold cultivar suggested extensive suberin biopolymer formation; this hypothesis was supported by high proportions of arenes, alkenes, and carbonyl groups in the solid and among the polar markers. The absence of many potential marker classes in nonpolar Atlantic extracts and interfacial solids suggested a limited extent of suberization. Modest scavenging activities of all nonpolar extracts indicate that the majority of antioxidants produced in response to wounding are polar.

Effect of Various Material Properties on the Adhesive Stage of Fretting

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1974-01-01

Various properties of metals and alloys were studied with respect to their effect on the initial stage of the fretting process, namely adhesion. Crystallographic orientation, crystal structure, interfacial binding energies of dissimiliar metal, segregation of alloy constituents and the nature and structure of surface films were found to influence adhesion. High atomic density, low surface energy grain orientations exhibited lower adhesion than other orientations. Knowledge of interfacial surface binding energies assists in predicting adhesive transfer and wear. Selective surface segregation of alloy constituents accomplishes both a reduction in adhesion and improved surface oxidation characteristics. Equivalent surface coverages of various adsorbed species indicate that some are markedly more effective in inhibiting adhesion than others.

Atomic layer deposition of insulating nitride interfacial layers for germanium metal oxide semiconductor field effect transistors with high-κ oxide/tungsten nitride gate stacks

NASA Astrophysics Data System (ADS)

Kim, Kyoung H.; Gordon, Roy G.; Ritenour, Andrew; Antoniadis, Dimitri A.

2007-05-01

Atomic layer deposition (ALD) was used to deposit passivating interfacial nitride layers between Ge and high-κ oxides. High-κ oxides on Ge surfaces passivated by ultrathin (1-2nm) ALD Hf3N4 or AlN layers exhibited well-behaved C-V characteristics with an equivalent oxide thickness as low as 0.8nm, no significant flatband voltage shifts, and midgap density of interface states values of 2×1012cm-1eV-1. Functional n-channel and p-channel Ge field effect transistors with nitride interlayer/high-κ oxide/metal gate stacks are demonstrated.

Adsorption of organic molecules on mineral surfaces studied by first-principle calculations: A review.

PubMed

Zhao, Hongxia; Yang, Yong; Shu, Xin; Wang, Yanwei; Ran, Qianping

2018-04-09

First-principle calculations, especially by the density functional theory (DFT) methods, are becoming a power technique to study molecular structure and properties of organic/inorganic interfaces. This review introduces some recent examples on the study of adsorption models of organic molecules or oligomers on mineral surfaces and interfacial properties obtained from first-principles calculations. The aim of this contribution is to inspire scientists to benefit from first-principle calculations and to apply the similar strategies when studying and tailoring interfacial properties at the atomistic scale, especially for those interested in the design and development of new molecules and new products. Copyright © 2017. Published by Elsevier B.V.

Role of mixed boundaries on flow in open capillary channels with curved air-water interfaces.

PubMed

Zheng, Wenjuan; Wang, Lian-Ping; Or, Dani; Lazouskaya, Volha; Jin, Yan

2012-09-04

Flow in unsaturated porous media or in engineered microfluidic systems is dominated by capillary and viscous forces. Consequently, flow regimes may differ markedly from conventional flows, reflecting strong interfacial influences on small bodies of flowing liquids. In this work, we visualized liquid transport patterns in open capillary channels with a range of opening sizes from 0.6 to 5.0 mm using laser scanning confocal microscopy combined with fluorescent latex particles (1.0 μm) as tracers at a mean velocity of ∼0.50 mm s(-1). The observed velocity profiles indicate limited mobility at the air-water interface. The application of the Stokes equation with mixed boundary conditions (i.e., no slip on the channel walls and partial slip or shear stress at the air-water interface) clearly illustrates the increasing importance of interfacial shear stress with decreasing channel size. Interfacial shear stress emerges from the velocity gradient from the adjoining no-slip walls to the center where flow is trapped in a region in which capillary forces dominate. In addition, the increased contribution of capillary forces (relative to viscous forces) to flow on the microscale leads to increased interfacial curvature, which, together with interfacial shear stress, affects the velocity distribution and flow pattern (e.g., reverse flow in the contact line region). We found that partial slip, rather than the commonly used stress-free condition, provided a more accurate description of the boundary condition at the confined air-water interface, reflecting the key role that surface/interface effects play in controlling flow behavior on the nanoscale and microscale.

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

DOE PAGES

Hernandez-Alvarado, Freddy; Kalaga, Dinesh V.; Turney, Damon; ...

2017-05-06

Micro-bubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a down-flow bubble column reactor with micro-bubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fractionmore » and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal measurements are discussed and compared for a bubble column reactor with dispersed micro-bubbles. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1,000 to 4,500 m 2/m 3) with sub-millimeter bubbles (500 to 900 µm) and high overall void fractions (10% – 60%) in comparison with previous bubble column reactor designs. The void fraction data was analyzed using slip velocity model and empirical correlation has been proposed to predict the Sauter mean bubble diameter.« less

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez-Alvarado, Freddy; Kalaga, Dinesh V.; Turney, Damon

Micro-bubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a down-flow bubble column reactor with micro-bubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fractionmore » and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal measurements are discussed and compared for a bubble column reactor with dispersed micro-bubbles. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1,000 to 4,500 m 2/m 3) with sub-millimeter bubbles (500 to 900 µm) and high overall void fractions (10% – 60%) in comparison with previous bubble column reactor designs. The void fraction data was analyzed using slip velocity model and empirical correlation has been proposed to predict the Sauter mean bubble diameter.« less

Influence of alkyl chain length and anion species on ionic liquid structure at the graphite interface as a function of applied potential

NASA Astrophysics Data System (ADS)

Li, Hua; Wood, Ross J.; Endres, Frank; Atkin, Rob

2014-07-01

Atomic force microscopy (AFM) force measurements elucidate the effect of cation alkyl chain length and the anion species on ionic liquid (IL) interfacial structure at highly ordered pyrolytic graphite (HOPG) surfaces as a function of potential. Three ILs are examined: 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP), 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] TFSA). The step-wise force-distance profiles indicate the ILs adopt a multilayered morphology near the surface. When the surface is biased positively or negatively versus Pt quasireference electrode, both the number of steps, and the force required to rupture each step increase, indicating stronger interfacial structure. At all potentials, push-through forces for [HMIM] FAP are the highest, because the long alkyl chain results in strong cohesive interactions between cations, leading to well-formed layers that resist the AFM tip. The most layers are observed for [EMIM] FAP, because the C2 chains are relatively rigid and the dimensions of the cation and anion are similar, facilitating neat packing. [EMIM] TFSA has the smallest push-through forces and fewest layers, and thus the weakest interfacial structure. Surface-tip attractive forces are measured for all ILs. At the same potential, the attractions are the strongest for [EMIM] TFSA and the weakest for [HMIM] FAP because the interfacial layers are better formed for the longer alkyl chain cation. This means interfacial forces are stronger, which masks the weak attractive forces.

In Situ Visualization of the Growth and Fluctuations of Nanoparticle Superlattice in Liquids

NASA Astrophysics Data System (ADS)

Ou, Zihao; Shen, Bonan; Chen, Qian

We use liquid phase transmission electron microscopy to image and understand the crystal growth front and interfacial fluctuation of a nanoparticle superlattice. With single particle resolution and hundreds of nanoscale building blocks in view, we are able to identify the interface between ordered lattice and disordered structure and visualize the kinetics of single building block attachment at the lattice growth front. The spatial interfacial fluctuation profiles support the capillary wave theory, from which we derive a surface stiffness value consistent with scaling analysis. Our experiments demonstrate the potential of extending model study on collective systems to nanoscale with single particle resolution and testing fundamental theories of condensed matter at a length scale linking atoms and micron-sized colloids.

Pseudopotential Computations for Metal/Alumina Interfaces

NASA Astrophysics Data System (ADS)

Zhang, Wenqing

2003-03-01

Metal/alumina interfaces are found, for example, in electronic devices, as thermal barrier coatings in gas turbines, and in coatings to inhibit corrosion and wear. Of particular importance to their performance is their adhesion. Ultrasoft pseudopotentials combined with plane wave methods and density-functional theory have been employed to compute the properties of these relatively complex interfaces, including effects of impurity segregation. Interfacial stoichiometry and impurity content affect interfacial properties importantly. Thermodynamic links between our first principles results and metallurgical variables such as oxygen activity and oxygen partial pressure are established. This allows for a comparison between theoretical predictions and experimental measurements. Good agreement is obtained for predicted interfacial variables such as atomic structure and adhesive bond strengths on comparison with results of sessile drop, fracture, and other experiments on interfaces of Ni, Cu, Al, and Ag with alumina [1-3], including effects of water and sulfur interfacial impurities. Understanding of the nature of the adhesive bonding at the atomic level is obtained by the pseudopotential first principles approach. [1] W.Zhang, and J.R.Smith, and A.G.Evans, Acta Mater., 50,3803(2002). [2] W.Zhang, and J.R.Smith, Phys. Rev. Lett. 85, 3225(2000). [3] W.Zhang, and J.R.Smith, Phys. Rev. B61, 16883(2000).

Capacitive charge storage at an electrified interface investigated via direct first-principles simulations

NASA Astrophysics Data System (ADS)

Radin, Maxwell D.; Ogitsu, Tadashi; Biener, Juergen; Otani, Minoru; Wood, Brandon C.

2015-03-01

Understanding the impact of interfacial electric fields on electronic structure is crucial to improving the performance of materials in applications based on charged interfaces. Supercapacitors store energy directly in the strong interfacial field between a solid electrode and a liquid electrolyte; however, the complex interplay between the two is often poorly understood, particularly for emerging low-dimensional electrode materials that possess unconventional electronic structure. Typical descriptions tend to neglect the specific electrode-electrolyte interaction, approximating the intrinsic "quantum capacitance" of the electrode in terms of a fixed electronic density of states. Instead, we introduce a more accurate first-principles approach for directly simulating charge storage in model capacitors using the effective screening medium method, which implicitly accounts for the presence of the interfacial electric field. Applying this approach to graphene supercapacitor electrodes, we find that results differ significantly from the predictions of fixed-band models, leading to improved consistency with experimentally reported capacitive behavior. The differences are traced to two key factors: the inhomogeneous distribution of stored charge due to poor electronic screening and interfacial contributions from the specific interaction with the electrolyte. Our results are used to revise the conventional definition of quantum capacitance and to provide general strategies for improving electrochemical charge storage, particularly in graphene and similar low-dimensional materials.

Reduced Capillary Length Scale in the Application of Ostwald Ripening Theory to the Coarsening of Charged Colloidal Crystals in Electrolyte Solutions

NASA Astrophysics Data System (ADS)

Rowe, Jeffrey D.; Baird, James K.

2007-06-01

A colloidal crystal suspended in an electrolyte solution will ordinarily exchange ions with the surrounding solution and develop a net surface charge density and a corresponding double layer. The interfacial tension of the charged surface has contributions arising from: (a) background interfacial tension of the uncharged surface, (b) the entropy associated with the adsorption of ions on the surface, and (c) the polarizing effect of the electrostatic field within the double layer. The adsorption and polarization effects make negative contributions to the surface free energy and serve to reduce the interfacial tension below the value to be expected for the uncharged surface. The diminished interfacial tension leads to a reduced capillary length scale. According to the Ostwald ripening theory of particle coarsening, the reduced capillary length will cause the solute supersaturation to decay more rapidly and the colloidal particles to be smaller in size and greater in number than in the absence of the double layer. Although the length scale for coarsening should be little affected in the case of inorganic colloids, such as AgI, it should be greatly reduced in the case of suspensions of protein crystals, such as apoferritin, catalase, and thaumatin.

Capsaicin Interaction with TRPV1 Channels in a Lipid Bilayer: Molecular Dynamics Simulation

PubMed Central

Hanson, Sonya M.; Newstead, Simon; Swartz, Kenton J.; Sansom, Mark S.P.

2015-01-01

Transient receptor potential vanilloid subtype 1 (TRPV1) is a heat-sensitive ion channel also involved in pain sensation, and is the receptor for capsaicin, the active ingredient of hot chili peppers. The recent structures of TRPV1 revealed putative ligand density within the S1 to S4 voltage-sensor-like domain of the protein. However, questions remain regarding the dynamic role of the lipid bilayer in ligand binding to TRPV1. Molecular dynamics simulations were used to explore behavior of capsaicin in a 1-palmitoyl-2-oleoyl phosphatidylcholine bilayer and with the target S1–S4 transmembrane helices of TRPV1. Equilibrium simulations reveal a preferred interfacial localization for capsaicin. We also observed a capsaicin molecule flipping from the extracellular to the intracellular leaflet, and subsequently able to access the intracellular TRPV1 binding site. Calculation of the potential of mean force (i.e., free energy profile) of capsaicin along the bilayer normal confirms that it prefers an interfacial localization. The free energy profile indicates that there is a nontrivial but surmountable barrier to the flipping of capsaicin between opposing leaflets of the bilayer. Molecular dynamics of the S1–S4 transmembrane helices of the TRPV1 in a lipid bilayer confirm that Y511, known to be crucial to capsaicin binding, has a distribution along the bilayer normal similar to that of the aromatic group of capsaicin. Simulations were conducted of the TRPV1 S1–S4 transmembrane helices in the presence of capsaicin placed in the aqueous phase, in the lipid, or docked to the protein. No stable interaction between ligand and protein was seen for simulations initiated with capsaicin in the bilayer. However, interactions were seen between TRPV1 and capsaicin starting from the cytosolic aqueous phase, and capsaicin remained stable in the majority of simulations from the docked pose. We discuss the significance of capsaicin flipping from the extracellular to the intracellular leaflet and mechanisms of binding site access by capsaicin. PMID:25809255

Atomic-scale structural and electronic properties of SrTiO3/GaAs interfaces: A combined STEM-EELS and first-principles study

NASA Astrophysics Data System (ADS)

Hong, Liang; Bhatnagar, Kunal; Droopad, Ravi; Klie, Robert F.; Öǧüt, Serdar

2017-07-01

The electronic properties of epitaxial oxide thin films grown on compound semiconductors are largely determined by the interfacial atomic structure, as well as the thermodynamic conditions during synthesis. Ferroelectric polarization and Fermi-level pinning in SrTiO3 films have been attributed to the presence of oxygen vacancies at the oxide/semiconductor interface. Here, we present scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy analyses of GaAs films grown on SrTiO3 combined with first-principles calculations to determine the atomic and electronic structures of the SrTiO3/GaAs interfaces. An atomically abrupt SrO/As interface is observed and the interfacial SrO layer is found to be O-deficient. First-principles density functional theory (DFT) calculations show SrO/Ga and Sr/As interfaces are favorable under O-rich and O-poor conditions, respectively. The SrO/Ga interface is reconstructed via the formation of Ga-Ga dimers while the Sr/As interface is abrupt and consistent with the experiment. DFT calculations further reveal that intrinsic two-dimensional electron gas (2DEG) forms in both SrO/Ga and Sr/As interfaces, and the Fermi level is pinned to the localized 2DEG states. Interfacial O vacancies can enhance the 2DEG density while it is possible for Ga/As vacancies to unpin the Fermi level from the 2DEG states.

Insights into the structural effects of layered cathode materials for high voltage sodium-ion batteries

DOE PAGES

Xu, Gui -Liang; Amine, Rachid; Xu, Yue -Feng; ...

2017-06-08

Cathode materials are critical to the energy density, power density and safety of sodium-ion batteries (SIBs). Herein, we performed a comprehensive study to elucidate and exemplify the interplay mechanism between phase structures, interfacial microstrain and electrochemical properties of layered-structured Na xNi 1/3Co 1/3Mn 1/3O 2 cathode materials for high voltage SIBs. The electrochemical test results showed that Na xNi 1/3Co 1/3Mn 1/3O 2 with an intergrowth P2/O3/O1 structure demonstrates better electrochemical performance and better thermal stability than Na xNi 1/3Co 1/3Mn 1/3O 2 with P2/O3 binary-phase integration and Na xNi 1/3Co 1/3Mn 1/3O 2 where only the P phase ismore » dominant. This result is caused by the distinct interfacial microstrain development during the synthesis and cycling of the P2/O3/O1 phase. In operando high energy X-ray diffraction further revealed that the intergrowth P2/O1/O3 cathode can inhibit the irreversible P2–O2 phase transformation and simultaneously improve the structure stability of the O3 and O1 phases during cycling. Here, we believe that interfacial microstrain can serve as an indispensable bridge to guide future design and synthesis of high performance SIB cathode materials and other high energy battery materials.« less

The interfacial-organized monolayer water film (MWF) induced ``two-step'' aggregation of nanographene: both in stacking and sliding assembly pathways

NASA Astrophysics Data System (ADS)

Lv, Wenping; Wu, Ren'an

2013-03-01

A computational investigation was carried out to understand the aggregation of nanoscale graphene with two typical pathways of stacking assembly and sliding assembly in water. The interfacial-organized monolayer water film (MWF) induced ``two-step'' aggregation of nanographene in both stacking and sliding assembly pathways was reported for the first time. By means of potential mean forces (PMFs) calculation, no energy barrier was observed during the sliding assembly of two graphene nanosheets, while the PMF profiles could be impacted by the contact forms of nanographene and the MWF within the interplate of two graphene nanosheets. To explore the potential physical basis of the ``hindering role'' of self-organized interfacial water, the dynamical and structural properties as well as the status of hydrogen bonds (H-bonds) for interfacial water were investigated. We found that the compact, ordered structure and abundant H-bonds of the MWF could be taken as the fundamental aspects of the ``hindering role'' of interfacial water for the hydrophobic assembly of nanographene. These findings are displaying a potential to further understand the hydrophobic assembly which mostly dominate the behaviors of nanomaterials, proteins etc. in aqueous solutions.A computational investigation was carried out to understand the aggregation of nanoscale graphene with two typical pathways of stacking assembly and sliding assembly in water. The interfacial-organized monolayer water film (MWF) induced ``two-step'' aggregation of nanographene in both stacking and sliding assembly pathways was reported for the first time. By means of potential mean forces (PMFs) calculation, no energy barrier was observed during the sliding assembly of two graphene nanosheets, while the PMF profiles could be impacted by the contact forms of nanographene and the MWF within the interplate of two graphene nanosheets. To explore the potential physical basis of the ``hindering role'' of self-organized interfacial water, the dynamical and structural properties as well as the status of hydrogen bonds (H-bonds) for interfacial water were investigated. We found that the compact, ordered structure and abundant H-bonds of the MWF could be taken as the fundamental aspects of the ``hindering role'' of interfacial water for the hydrophobic assembly of nanographene. These findings are displaying a potential to further understand the hydrophobic assembly which mostly dominate the behaviors of nanomaterials, proteins etc. in aqueous solutions. Electronic supplementary information (ESI) available: The evolution of interaction energy for two graphene nanosheets assembly in stacking (a) and sliding (b) pathway was plotted in Fig. S1. The time evolution of three dimension distance for stacking assembly of two graphene nanosheets with the edge-edge orientation of 45° was plotted in Fig. S2. The initial orientations of graphene nanosheets in three simulations (edge-edge distance in x-direction (dx) was 0.3 nm, but in z-direction (dz) was 0.0 nm, 0.4 nm and 0.7 nm, respectively) were shown in Fig. S3. The snapshots of the evolution of hydration shells during the sliding assembly of nanographene were shown in Fig. S4, with the separation of two graphene nanosheets in z-direction is (a) 0 nm and (b) 0.7 nm, respectively. The process of two graphene nanosheets assembly in stacking pathway was shown in Movie S1 as video. The process of two graphene nanosheets (with a separation of 0.7 nm in normal direction) assembly in sliding pathway was shown in Movie S2 as video. The dynamical evolution of interfacial water during the sliding assembly of nanographene was shown in Movie S3 as video. The process of extruding the monolayer water film (MWF) out of the interplate of two graphene nanosheets was shown in Movie S4 as video. Movie S5 displays that the graphene-water-graphene sandwiched structure was successfully maintained during a 10 ns MD simulation. See DOI: 10.1039/c3nr33447c

Effects of interfacial interaction on the properties of poly(vinyl chloride)/styrene-butadiene rubber blends

NASA Astrophysics Data System (ADS)

Zhu, Shuihan

PVC/SBR blends---new thermoplastic elastomer material---were developed. They have potential applications due to low costs and low-temperature elasticity. A unique compatibilization method was employed to enhance the mechanical properties of the materials a compatibilizer miscible with one of the blend components can react chemically with the other component(s). Improvements in tensile and impact behavior were observed as a result of the compatibilization. A novel characterization technique to study the interface of PVC/SBR blends was developed. This technique involves the observation of the unstained sample under electron beam irradiation by a transmission electron microscope (TEM). An enrichment of rubber at the interface between PVC and SBR was detected in the compatiblized PVC/SBR blends. Magnetic relaxation measurements show that the rubber concentration in the proximity of PVC increases with the degree of covulcanization between NBR and SBR. The interface development and the rheological effect during processing were investigated. The interfacial concentration profile and the interfacial thickness were obtained by grayscale measurements on TEM micrographs, evaluation of SIMS images, and measurements of micromechanical properties.

Interfacial interactions between plastic particles in plastics flotation.

PubMed

Wang, Chong-qing; Wang, Hui; Gu, Guo-hua; Fu, Jian-gang; Lin, Qing-quan; Liu, You-nian

2015-12-01

Plastics flotation used for recycling of plastic wastes receives increasing attention for its industrial application. In order to study the mechanism of plastics flotation, the interfacial interactions between plastic particles in flotation system were investigated through calculation of Lifshitz-van der Waals (LW) function, Lewis acid-base (AB) Gibbs function, and the extended Derjaguin-Landau-Verwey-Overbeek potential energy profiles. The results showed that van der Waals force between plastic particles is attraction force in flotation system. The large hydrophobic attraction, caused by the AB Gibbs function, is the dominant interparticle force. Wetting agents present significant effects on the interfacial interactions between plastic particles. It is found that adsorption of wetting agents promotes dispersion of plastic particles and decreases the floatability. Pneumatic flotation may improve the recovery and purity of separated plastics through selective adsorption of wetting agents on plastic surface. The relationships between hydrophobic attraction and surface properties were also examined. It is revealed that there exists a three-order polynomial relationship between the AB Gibbs function and Lewis base component. Our finding provides some insights into mechanism of plastics flotation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Research on c-HfO2 (0 0 1)/α -Al2O3 (1 -1 0 2) interface in CTM devices based on first principle theory

NASA Astrophysics Data System (ADS)

Lu, Wenjuan; Dai, Yuehua; Wang, Feifei; Yang, Fei; Ma, Chengzhi; Zhang, Xu; Jiang, Xianwei

2017-12-01

With the growing application of high-k dielectrics, the interface between HfO2 and Al2O3 play a crucial role in CTM devices. To clearly understand the interaction of the HfO-AlO interface at the atomic and electronic scale, the bonding feature, electronic properties and charge localized character of c- HfO2 (0 0 1)/α-Al2O3 (1 -1 0 2) interface has been investigated by first principle calculations. The c- HfO2 (0 0 1)/α-Al2O3 (1 -1 0 2) interface has adhesive energy about -1.754 J/m2, suggesting that this interface can exist stably. Through analysis of Bader charge and charge density difference, the intrinsic interfacial gap states are mainly originated from the OII and OIII types oxygen atoms at the interface, and only OIII type oxygen atoms can localized electrons effectively and are provided with good reliability during P/E cycles, which theoretically validate the experimental results that HfO2/Al2O3 multi-layered charge trapping layer can generate more effective traps in memory device. Furthermore, the influence of interfacial gap states during P/E cycles in the defective interface system have also been studied, and the results imply that defective system displays the degradation on the reliability during P/E cycles, while, the charge localized ability of interfacial states is stronger than intrinsic oxygen vacancy in the trapping layer. Besides, these charge localized characters are further explained by the analysis of the density of states correspondingly. In sum, our results compare well with similar experimental observations in other literatures, and the study of the interfacial gap states in this work would facilitate further development of interface passivation.

A high density two-dimensional electron gas in an oxide heterostructure on Si (001)

NASA Astrophysics Data System (ADS)

Jin, E. N.; Kornblum, L.; Kumah, D. P.; Zou, K.; Broadbridge, C. C.; Ngai, J. H.; Ahn, C. H.; Walker, F. J.

2014-11-01

We present the growth and characterization of layered heterostructures comprised of LaTiO3 and SrTiO3 epitaxially grown on Si (001). Magnetotransport measurements show that the sheet carrier densities of the heterostructures scale with the number of LaTiO3/SrTiO3 interfaces, consistent with the presence of an interfacial 2-dimensional electron gas (2DEG) at each interface. Sheet carrier densities of 8.9 × 1014 cm-2 per interface are observed. Integration of such high density oxide 2DEGs on silicon provides a bridge between the exceptional properties and functionalities of oxide 2DEGs and microelectronic technologies.

Engineering the surface of LiCoO 2 electrodes using atomic layer deposition for stable high-voltage lithium ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Jin; Zhao, Jie; Liu, Yayuan

Here, developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important, owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles. Here, we deposited chemically inert and ionically conductive LiAlO 2 interfacial layers on LiCoO 2 electrodes using the atomic layer deposition technique. During prolonged cycling at high-voltage, the LiAlO 2 coating not only prevented interfacial reactions between the LiCoO 2 electrode and electrolyte, as confirmed by electrochemical impedance spectroscopy and Raman characterizations, but also allowed lithium ions to freely diffuse into LiCoOmore » 2 without sacrificing the power density. As a result, a capacity value close to 200 mA·h·g –1 was achieved for the LiCoO 2 electrodes with commercial level loading densities, cycled at the cut-off potential of 4.6 V vs. Li +/Li for 50 stable cycles; this represents a 40% capacity gain, compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs. Li +/Li.« less

Interfacial band-edge engineered TiO2 protection layer on Cu2O photocathodes for efficient water reduction reaction

NASA Astrophysics Data System (ADS)

Choi, Jaesuk; Song, Jun Tae; Jang, Ho Seong; Choi, Min-Jae; Sim, Dong Min; Yim, Soonmin; Lim, Hunhee; Jung, Yeon Sik; Oh, Jihun

2017-01-01

Photoelectrochemical (PEC) water splitting has emerged as a potential pathway to produce sustainable and renewable chemical fuels. Here, we present a highly active Cu2O/TiO2 photocathode for H2 production by enhancing the interfacial band-edge energetics of the TiO2 layer, which is realized by controlling the fixed charge density of the TiO2 protection layer. The band-edge engineered Cu2O/TiO2 (where TiO2 was grown at 80 °C via atomic layer deposition) enhances the photocurrent density up to -2.04 mA/cm2 at 0 V vs. RHE under 1 sun illumination, corresponding to about a 1,200% enhancement compared to the photocurrent density of the photocathode protected with TiO2 grown at 150 °C. Moreover, band-edge engineering of the TiO2 protection layer prevents electron accumulation at the TiO2 layer and enhances both the Faraday efficiency and the stability for hydrogen production during the PEC water reduction reaction. This facile control over the TiO2/electrolyte interface will also provide new insight for designing highly efficient and stable protection layers for various other photoelectrodes such as Si, InP, and GaAs. [Figure not available: see fulltext.

Atomic force microscopy evaluation of aqueous interfaces of immobilized hyaluronan.

PubMed

Morra, Marco; Cassinelli, Clara; Pavesio, Alessandra; Renier, Davide

2003-03-15

Hyaluronan (HA) was immobilized on aminated glass surfaces in three different ways: by simple ionic interaction and by covalent linking at low density and at full density. In agreement with previous reports, in vitro experiments show that the outcome of fibroblast adhesion tests is markedly affected by the details of the coupling procedure, suggesting that different interfacial forces are operating at the aqueous/HA interface in the three cases investigated. The interfacial properties of the HA-coated surfaces were probed by force-distance curves obtained with the atomic force microscope (AFM). This approach readily shows significant differences among the tested samples, which are directly related to the coupling strategy and to results of cell adhesion tests. In particular, the range of interaction between the tip and the surface is much lower when HA is covalently linked than when it is ionically coupled, suggesting a more compact surface structure in the former case. Increasing HA surface density minimizes the interaction force between the surface and the AFM tip, likely reflecting more complete shielding by the HA chains of the underlying substrate. In summary, these measurements clearly show the different nature of the aqueous interfaces tested, and underline the role of this analytical approach in the development and control of finely tuned biomaterial surfaces.

Engineering the surface of LiCoO 2 electrodes using atomic layer deposition for stable high-voltage lithium ion batteries

DOE PAGES

Xie, Jin; Zhao, Jie; Liu, Yayuan; ...

2017-07-25

Here, developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important, owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles. Here, we deposited chemically inert and ionically conductive LiAlO 2 interfacial layers on LiCoO 2 electrodes using the atomic layer deposition technique. During prolonged cycling at high-voltage, the LiAlO 2 coating not only prevented interfacial reactions between the LiCoO 2 electrode and electrolyte, as confirmed by electrochemical impedance spectroscopy and Raman characterizations, but also allowed lithium ions to freely diffuse into LiCoOmore » 2 without sacrificing the power density. As a result, a capacity value close to 200 mA·h·g –1 was achieved for the LiCoO 2 electrodes with commercial level loading densities, cycled at the cut-off potential of 4.6 V vs. Li +/Li for 50 stable cycles; this represents a 40% capacity gain, compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs. Li +/Li.« less

Determination of pseudogap state density and carrier mobility in rf sputtered amorphous silicon. Quarterly technical progress report, January-March 31, 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paul, W

1980-06-01

The effect of a variety of plasma cleaning procedures on the level of bulk and interfacial contaminants in the films is analyzed by secondary ion mass spectrometry. Bulk levels of 0 have been reduced considerably by N/sub 2/ plasma cleaning, but no reproducible reductions in interfacial contamination have been achieved. A method is described of determining the gap state density N(epsilon) of a-Si:H from field effect, in which no assumptions are made about the form of the band bending in the semiconductor. The problem is reduced to three successive integrals over an assumed N(epsilon) by change of variable from distancemore » to applied voltage and the best fit to the experimental data is obtained by iteration of the assumed state density. The method is shown to be no less rigorous and considerably more economical than the recent analysis of Goodman, Fritzsche and Ozaki. In addition, an experimental means of determining the flat-band voltage to within 5% of the maximum gate voltage V/sub g/ used is demonstrated, by finding the value of V/sub g/ for which (kT/e)dlog I/sub SD//dV/sub g/ is independent of temperature.« less

Spectroscopic ellipsometry analysis of a thin film composite membrane consisting of polysulfone on a porous α-alumina support.

PubMed

Ogieglo, Wojciech; Wormeester, Herbert; Wessling, Matthias; Benes, Nieck E

2012-02-01

Exposure of a thin polymer film to a fluid can affect properties of the film such as the density and thickness. In particular in membrane technology, these changes can have important implications for membrane performance. Spectroscopic ellipsometry is a convenient technique for in situ studies of thin films, because of its noninvasive character and very high precision. The applicability of spectroscopic ellipsometry is usually limited to samples with well-defined interfacial regions, whereas in typical composite membranes, often substantial and irregular intrusion of the thin film into the pores of a support exists. In this work, we provide a detailed characterization of a polished porous alumina membrane support, using variable-angle spectroscopic ellipsometry in combination with atomic force microscopy and mercury porosimetry. Two Spectroscopic ellipsometry optical models are presented that can adequately describe the surface roughness of the support. These models consider the surface roughness as a distinct layer in which the porosity gradually increases toward the outer ambient interface. The first model considers the porosity profile to be linear; the second model assumes an exponential profile. It is shown that the models can be extended to account for a composite membrane geometry, by deposition of a thin polysulfone film onto the support. The developed method facilitates practicability for in situ spectroscopic ellipsometry studies of nonequilibrium systems, i.e., membranes under actual permeation conditions.

High efficiency, low cost, thin film silicon solar cell design and method for making

DOEpatents

Sopori, Bhushan L.

2001-01-01

A semiconductor device having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer.

High efficiency low cost thin film silicon solar cell design and method for making

DOEpatents

Sopori, Bhushan L.

1999-01-01

A semiconductor device having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer.

A CSF-SPH method for simulating drainage and imbibition at pore-scale resolution while tracking interfacial areas

NASA Astrophysics Data System (ADS)

Sivanesapillai, Rakulan; Falkner, Nadine; Hartmaier, Alexander; Steeb, Holger

2016-09-01

We present a conservative smoothed particle hydrodynamics (SPH) model to study the flow of multiple, immiscible fluid phases in porous media using direct pore-scale simulations. Particular focus is put on continuously tracking the evolution of interfacial areas, which are considered to be important morphological quantities affecting multiphase transport in porous media. In addition to solving the Navier-Stokes equations, the model accounts for the effects of capillarity at interfaces and contact lines. This is done by means of incorporating the governing interfacial mass and momentum balances using the continuum surface force (CSF) method, thus rendering model calibration routines unnecessary and minimizing the set of constitutive and kinematic assumptions. We address the application of boundary conditions at rigid solid surfaces and study the predictive capability of the model as well as optimal choices for numerical parameters using an extensive model validation procedure. We demonstrate the applicability of the model to simulate multiphase flows involving partial wettability, dynamic effects, large density ratios (up to 1000), large viscosity ratios (up to 100), as well as fragmentation and coalescence of fluid phases. The model is used to study the evolution of fluid-fluid interfacial areas during saturation-controlled primary drainage and main imbibition of heterogeneous pore spaces at low capillary numbers. A variety of pore-scale effects, such as wetting phase entrapment and fragmentation due to snap-off, are observed. Specific fluid-fluid interfacial area is observed to monotonically increase during primary drainage and hysteretic effects are apparent during main imbibition.

Interfacial layers from the protein HFBII hydrophobin: dynamic surface tension, dilatational elasticity and relaxation times.

PubMed

Alexandrov, Nikola A; Marinova, Krastanka G; Gurkov, Theodor D; Danov, Krassimir D; Kralchevsky, Peter A; Stoyanov, Simeon D; Blijdenstein, Theodorus B J; Arnaudov, Luben N; Pelan, Eddie G; Lips, Alex

2012-06-15

The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins. Copyright © 2012 Elsevier Inc. All rights reserved.

The energetics of adhesion in composite materials

NASA Astrophysics Data System (ADS)

Harding, Philip Hiram

Composite materials are used throughout modern society, and often the most important parameter in determining their properties is the adhesion at material interfaces within the composite. A broad investigation is completed, the global objective of which is to develop understanding of the role of adhesion in composite materials. The scope of this study ranges from macroscopic effects of adhesion on filled polymer composites to microscopic adhesion measurements with engineered interfaces. The surface of a filler material is systematically modified and surface characterization techniques are used to quantify the influence of the surface treatments on surface energetics and wetting properties. Filled polymer composites are prepared and composite mechanical properties determined with beam deflection tests. Filler surface treatments significantly alter the composite yield stress for composites which fail interfacially and are observed to increase or decrease mechanical strength, depending on the chemical nature of the modification. Thermodynamic adhesion mechanisms active at the filler-matrix interfaces are then explored by making direct interfacial strength measurements whereby a single spherical particle is introduced into the polymeric matrix. Interfacial strength is determined by submitting the single-particle composite (SPC) to uni-axial tension and relating the macroscopic stress at interfacial failure to that experienced at the interface. The technique provides a measurement of interfacial strength between two elastic materials, one unaffected by frictional forces, viscoelasticity, and thermal stresses. The SPC measurements are used to verify proposed adhesion mechanisms at the various filler-polymer interfaces and establish the role of adhesion in the filled polymer composites. The SPC technique is then used to investigate the adhesion promotion mechanism of organofunctional silanes, which are shown to be controlled by the compatibility and penetration of the silane organofunctional group. The effects of thermal residual stresses on interfacial strength are also investigated using the SPC technique. Processing conditions, i.e., time-temperature profiles, are used to systematically vary the thermal residual stresses within the polymeric matrix. The interfaces studied are deleteriously affected by increases in thermal residual stresses.

Digital model for X-ray diffraction with application to composition and strain determination in strained InAs/GaSb superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Yifei; Kim, Honggyu; Zuo, Jian-Min

2014-07-07

We propose a digital model for high quality superlattices by including fluctuations in the superlattice periods. The composition and strain profiles are assumed to be coherent and persist throughout the superlattice. Using this model, we have significantly improved the fit with experimental X-ray diffraction data recorded from the nominal InAs/GaSb superlattice. The lattice spacing of individual layers inside the superlattice and the extent of interfacial intermixing are refined by including both (002) and (004) and their satellite peaks in the fitting. For the InAs/GaSb strained layer superlattice, results show: (i) the GaSb-on-InAs interface is chemically sharper than the InAs-on-GaSb interface,more » (ii) the GaSb layers experience compressive strain with In incorporation, (iii) there are interfacial strain associated with InSb-like bonds in GaSb and GaAs-like bonds in InAs, (iv) Sb substitutes a significant amount of In inside InAs layer near the InAs-on-GaSb interface. For support, we show that the composition profiles determined by X-ray diffraction are in good agreement with those obtained from atom probe tomography measurement. Comparison with the kinetic growth model shows a good agreement in terms of the composition profiles of anions, while the kinetic model underestimates the intermixing of cations.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Predota, Milan; Machesky, Michael L.; Wesolowski, David J.

The zeta potential (ZP) is an oft-reported measure of the macroscopic charge state of solid surfaces and colloidal particles in contact with solvents. However, the origin of this readily measurable parameter has remained divorced from the molecular-level processes governing the underlying electrokinetic phenomena, which limits its usefulness. Here, we connect the macroscopic measure to the microscopic realm through nonequilibrium molecular dynamics simulations of electroosmotic flow between parallel slabs of the hydroxylated (110) rutile (TiO 2) surface. These simulations provided streaming mobilities, which were converted to ZP via the commonly used Helmholtz-Smoluchowski equation. A range of rutile surface charge densities (0.1more » to –0.4 C/m 2), corresponding to pH values between about 2.8 and 9.4, in RbCl, NaCl, and SrCl 2 aqueous solutions, were modeled and compared to experimental ZPs for TiO 2 particle suspensions. Simulated ZPs qualitatively agree with experiment and show that “anomalous” ZP values and inequalities between the point of zero charge derived from electrokinetic versus pH titration measurements both arise from differing co- and counterion sorption affinities. We show that at the molecular level the ZP arises from the delicate interplay of spatially varying dynamics, structure, and electrostatics in a narrow interfacial region within about 15 Å of the surface, even in dilute salt solutions. This contrasts fundamentally with continuum descriptions of such interfaces, which predict the ZP response region to be inversely related to ionic strength. In reality the properties of this interfacial region are dominated by relatively immobile and structured water. Furthermore, viscosity values are substantially greater than in the bulk, and electrostatic potential profiles are oscillatory in nature.« less

Molecular origins of the zeta potential

DOE PAGES

Predota, Milan; Machesky, Michael L.; Wesolowski, David J.

2016-09-19

The zeta potential (ZP) is an oft-reported measure of the macroscopic charge state of solid surfaces and colloidal particles in contact with solvents. However, the origin of this readily measurable parameter has remained divorced from the molecular-level processes governing the underlying electrokinetic phenomena, which limits its usefulness. Here, we connect the macroscopic measure to the microscopic realm through nonequilibrium molecular dynamics simulations of electroosmotic flow between parallel slabs of the hydroxylated (110) rutile (TiO 2) surface. These simulations provided streaming mobilities, which were converted to ZP via the commonly used Helmholtz-Smoluchowski equation. A range of rutile surface charge densities (0.1more » to –0.4 C/m 2), corresponding to pH values between about 2.8 and 9.4, in RbCl, NaCl, and SrCl 2 aqueous solutions, were modeled and compared to experimental ZPs for TiO 2 particle suspensions. Simulated ZPs qualitatively agree with experiment and show that “anomalous” ZP values and inequalities between the point of zero charge derived from electrokinetic versus pH titration measurements both arise from differing co- and counterion sorption affinities. We show that at the molecular level the ZP arises from the delicate interplay of spatially varying dynamics, structure, and electrostatics in a narrow interfacial region within about 15 Å of the surface, even in dilute salt solutions. This contrasts fundamentally with continuum descriptions of such interfaces, which predict the ZP response region to be inversely related to ionic strength. In reality the properties of this interfacial region are dominated by relatively immobile and structured water. Furthermore, viscosity values are substantially greater than in the bulk, and electrostatic potential profiles are oscillatory in nature.« less

Fast Low-Current Spin-Orbit-Torque Switching of Magnetic Tunnel Junctions through Atomic Modifications of the Free-Layer Interfaces

NASA Astrophysics Data System (ADS)

Shi, Shengjie; Ou, Yongxi; Aradhya, S. V.; Ralph, D. C.; Buhrman, R. A.

2018-01-01

Future applications of spin-orbit torque will require new mechanisms to improve the efficiency of switching nanoscale magnetic tunnel junctions (MTJs), while also controlling the magnetic dynamics to achieve fast nanosecond-scale performance with low-write-error rates. Here, we demonstrate a strategy to simultaneously enhance the interfacial magnetic anisotropy energy and suppress interfacial spin-memory loss by introducing subatomic and monatomic layers of Hf at the top and bottom interfaces of the ferromagnetic free layer of an in-plane magnetized three-terminal MTJ device. When combined with a β -W spin Hall channel that generates spin-orbit torque, the cumulative effect is a switching current density of 5.4 ×106 A /cm2 .

Molecularly "engineered" anode adsorbates for probing OLED interfacial structure-charge injection/luminance relationships: large, structure-dependent effects.

PubMed

Huang, Qinglan; Evmenenko, Guennadi; Dutta, Pulak; Marks, Tobin J

2003-12-03

Molecule-scale structure effects at organic light-emitting diodes (OLED) anode-organic transport layer interfaces are probed via a self-assembly approach. A series of ITO anode-linked silyltriarylamine molecules differing in aryl group and linker density are synthesized for this purpose and used to probe the relationship between nanoscale interfacial chemical structure, charge injection and electroluminescence properties. Dramatic variations in hole injection magnitude and OLED performance can be correlated with the molecular structures and electrochemically derived heterogeneous electron-transfer rates of such triarylamine fragments, placed precisely at the anode-hole transport layer interface. Very bright and efficient ( approximately 70 000 cd/m2 and approximately 2.5% forward external quantum efficiency) OLEDs have thereby been fabricated.

Schottky barrier at graphene/metal oxide interfaces: insight from first-principles calculations

NASA Astrophysics Data System (ADS)

Cheng, Kai; Han, Nannan; Su, Yan; Zhang, Junfeng; Zhao, Jijun

2017-02-01

Anode materials play an important role in determining the performance of lithium ion batteries. In experiment, graphene (GR)/metal oxide (MO) composites possess excellent electrochemical properties and are promising anode materials. Here we perform density functional theory calculations to explore the interfacial interaction between GR and MO. Our result reveals generally weak physical interactions between GR and several MOs (including Cu2O, NiO). The Schottky barrier height (SBH) in these metal/semiconductor heterostructures are computed using the macroscopically averaged electrostatic potential method, and the role of interfacial dipole is discussed. The calculated SBHs below 1 eV suggest low contact resistance; thus these GR/MO composites are favorable anode materials for better lithium ion batteries.

Schottky barrier at graphene/metal oxide interfaces: insight from first-principles calculations.

PubMed

Cheng, Kai; Han, Nannan; Su, Yan; Zhang, Junfeng; Zhao, Jijun

2017-02-06

Anode materials play an important role in determining the performance of lithium ion batteries. In experiment, graphene (GR)/metal oxide (MO) composites possess excellent electrochemical properties and are promising anode materials. Here we perform density functional theory calculations to explore the interfacial interaction between GR and MO. Our result reveals generally weak physical interactions between GR and several MOs (including Cu2O, NiO). The Schottky barrier height (SBH) in these metal/semiconductor heterostructures are computed using the macroscopically averaged electrostatic potential method, and the role of interfacial dipole is discussed. The calculated SBHs below 1 eV suggest low contact resistance; thus these GR/MO composites are favorable anode materials for better lithium ion batteries.

A density functional theory study of the role of functionalized graphene particles as effective additives in power cable insulation

PubMed Central

Song, Shuwei; Zhao, Hong; Zheng, Xiaonan; Zhang, Hui; Wang, Ying; Han, Baozhong

2018-01-01

The role of a series of functionalized graphene additives in power cable insulation in suppressing the growth of electrical treeing and preventing the degradation of the polymer matrix has been investigated by density functional theory calculations. Bader charge analysis indicates that pristine, doped or defect graphene could effectively capture hot electrons to block their attack on cross-linked polyethylene (XLPE) because of the π–π conjugated unsaturated structures. Further exploration of the electronic properties in the interfacial region between the additives and XLPE shows that N-doped single-vacancy graphene, graphene oxide and B-, N-, Si- or P-doped graphene oxide have relatively strong physical interaction with XLPE to restrict its mobility and rather weak chemical activity to prevent the cleavage of the C–H or C–C bond, suggesting that they are all potential candidates as effective additives. The understanding of the features of functionalized graphene additives in trapping electrons and interfacial interaction will assist in the screening of promising additives as voltage stabilizers in power cables. PMID:29515821

A density functional theory study of the role of functionalized graphene particles as effective additives in power cable insulation.

PubMed

Song, Shuwei; Zhao, Hong; Zheng, Xiaonan; Zhang, Hui; Liu, Yang; Wang, Ying; Han, Baozhong

2018-02-01

The role of a series of functionalized graphene additives in power cable insulation in suppressing the growth of electrical treeing and preventing the degradation of the polymer matrix has been investigated by density functional theory calculations. Bader charge analysis indicates that pristine, doped or defect graphene could effectively capture hot electrons to block their attack on cross-linked polyethylene (XLPE) because of the π-π conjugated unsaturated structures. Further exploration of the electronic properties in the interfacial region between the additives and XLPE shows that N-doped single-vacancy graphene, graphene oxide and B-, N-, Si- or P-doped graphene oxide have relatively strong physical interaction with XLPE to restrict its mobility and rather weak chemical activity to prevent the cleavage of the C-H or C-C bond, suggesting that they are all potential candidates as effective additives. The understanding of the features of functionalized graphene additives in trapping electrons and interfacial interaction will assist in the screening of promising additives as voltage stabilizers in power cables.

A New Self-Consistent Field Model of Polymer/Nanoparticle Mixture

NASA Astrophysics Data System (ADS)

Chen, Kang; Li, Hui-Shu; Zhang, Bo-Kai; Li, Jian; Tian, Wen-De

2016-02-01

Field-theoretical method is efficient in predicting assembling structures of polymeric systems. However, it’s challenging to generalize this method to study the polymer/nanoparticle mixture due to its multi-scale nature. Here, we develop a new field-based model which unifies the nanoparticle description with the polymer field within the self-consistent field theory. Instead of being “ensemble-averaged” continuous distribution, the particle density in the final morphology can represent individual particles located at preferred positions. The discreteness of particle density allows our model to properly address the polymer-particle interface and the excluded-volume interaction. We use this model to study the simplest system of nanoparticles immersed in the dense homopolymer solution. The flexibility of tuning the interfacial details allows our model to capture the rich phenomena such as bridging aggregation and depletion attraction. Insights are obtained on the enthalpic and/or entropic origin of the structural variation due to the competition between depletion and interfacial interaction. This approach is readily extendable to the study of more complex polymer-based nanocomposites or biology-related systems, such as dendrimer/drug encapsulation and membrane/particle assembly.

Interfacial structure, bonding and composition of InAs and GaSb thin films determined using coherent Bragg rod analysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cionca, C.; Walko, D. A.; Yacoby, Y.

2007-01-01

We have used Bragg rod x-ray diffraction combined with a direct method of phase retrieval to extract atomic resolution electron-density maps of a complementary series of heteroepitaxial III-V semiconductor samples. From the three-dimensional electron-density maps we derive the monolayer spacings, the chemical compositions, and the characteristics of the bonding for all atomic planes in the film and across the film-substrate interface. InAs films grown on GaSb(001) under two different As conditions (using dimer or tetramer forms) both showed conformal roughness and mixed GaAs/InSb interfacial bonding character. The As tetramer conditions favored InSb bonding at the interface while, in the casemore » of the dimer, the percentages corresponding to GaAs and InSb bonding were equal within the experimental error. The GaSb film grown on InAs(001) displayed significant In and As interdiffusion and had a relatively large fraction of GaAs-like bonds at the interface.« less

Evaluation of physics-based numerical modelling for diverse design architecture of perovskite solar cells

NASA Astrophysics Data System (ADS)

Mishra, A. K.; Catalan, Jorge; Camacho, Diana; Martinez, Miguel; Hodges, D.

2017-08-01

Solution processed organic-inorganic metal halide perovskite based solar cells are emerging as a new cost effective photovoltaic technology. In the context of increasing the power conversion efficiency (PCE) and sustainability of perovskite solar cells (PSC) devices, we comprehensively analyzed a physics-based numerical modelling for doped and un-doped PSC devices. Our analytics emphasized the role of different charge carrier layers from the view point of interfacial adhesion and its influence on charge extraction rate and charge recombination mechanism. Morphological and charge transport properties of perovskite thin film as a function of device architecture are also considered to investigate the photovoltaic properties of PSC. We observed that photocurrent is dominantly influenced by interfacial recombination process and photovoltage has functional relationship with defect density of perovskite absorption layer. A novel contour mapping method to understand the characteristics of current density-voltage (J-V) curves for each device as a function of perovskite layer thickness provide an important insight about the distribution spectrum of photovoltaic properties. Functional relationship of device efficiency and fill factor with absorption layer thickness are also discussed.

On the nonlinear interfacial instability of rotating core-annular flow

NASA Technical Reports Server (NTRS)

Coward, Aidrian V.; Hall, Philip

1993-01-01

The interfacial stability of rotating core-annular flows is investigated. The linear and nonlinear effects are considered for the case when the annular region is very thin. Both asymptotic and numerical methods are used to solve the flow in the core and film regions which are coupled by a difference in viscosity and density. The long-term behavior of the fluid-fluid interface is determined by deriving its nonlinear evolution in the form of a modified Kuramoto-Sivashinsky equation. We obtain a generalization of this equation to three dimensions. The flows considered are applicable to a wide array of physical problems where liquid films are used to lubricate higher or lower viscosity core fluids, for which a concentric arrangement is desired. Linearized solutions show that the effects of density and viscosity stratification are crucial to the stability of the interface. Rotation generally destabilizes non-axisymmetric disturbances to the interface, whereas the centripetal forces tend to stabilize flows in which the film contains the heavier fluid. Nonlinear affects allow finite amplitude helically travelling waves to exist when the fluids have different viscosities.

Profiling the Local Seebeck Coefficient of InAs-GaAs Quantum Dots Using Scanning Thermoelectric Microscopy

NASA Astrophysics Data System (ADS)

Lin, Yen-Hsiang; Walrath, Jenna; Huang, Simon; Goldman, Rachel

2014-03-01

Thermoelectric (TE) devices offer a method of recovering waste heat through solid state conversion of heat to electricity. However, the typical efficiencies of TE devices are 5-10% which constitutes a barrier to wide spread use. There have recently been a number of reports of an increase in the bulk thermopower due to nanostructuring. In addition to our recent report of enhanced thermopower for GaAs embedded with indium nanocrystals, a theoretical study by Mahan and Sofo suggested that the best thermoelectric materials have a delta function density of states. Quantum dots fit ideally into such a picture. To date, the influence of nanostructuring on the electronic LDOS and thermopower has been studied using spatially averaged measurements; a nanoscale investigation of the effects of nanostructures on thermopower has yet to be presented. To investigate the link between dimensionality and TE properties, we are examining structures ranging from QDs to bulk-like layers, comparing SThEM measurements of the local Seebeck coefficient, S, with STS measurements of the local density of states (LDOS). STM, STS, and SThEM performed on InAs quantum dots (QDs) grown on GaAs. SThEM reveals enhanced S-values near the QD edge; STS reveals band-bending at the QD/GaAs interface, suggesting that the S enhancement is due to interfacial charge accumulation.

Interactions of anesthetics with the water-hexane interface. A molecular dynamics study

NASA Technical Reports Server (NTRS)

Chipot, C.; Wilson, M. A.; Pohorille, A.

1997-01-01

The free energy profiles characterizing the transfer of nine solutes across the liquid-vapor interfaces of water and hexane and across the water-hexane interface were calculated from molecular dynamics simulations. Among the solutes were n-butane and three of its halogenated derivatives, as well as three halogenated cyclobutanes. The two remaining molecules, dichlorodifluoromethane and 1,2-dichloroperfluoroethane, belong to series of halo-substituted methanes and ethanes, described in previous studies (J. Chem. Phys. 1996, 104, 3760; Chem. Phys. 1996, 204, 337). Each series of molecules contains structurally similar compounds that differ greatly in anesthetic potency. The accuracy of the simulations was tested by comparing the calculated and the experimental free energies of solvation of all nine compounds in water and in hexane. In addition. the calculated and the measured surface excess concentrations of n-butane at the water liquid-vapor interface were compared. In all cases, good agreement with experimental results was found. At the water-hexane interface, the free energy profiles for polar molecules exhibited significant interfacial minima, whereas the profiles for nonpolar molecules did not. The existence of these minima was interpreted in terms of a balance between the free energy contribution arising from solute-solvent interactions and the work to form a cavity that accommodates the solute. These two contributions change monotonically, but oppositely, across the interface. The interfacial solubilities of the solutes, obtained from the free energy profiles, correlate very well with their anesthetic potencies. This is the case even when the Meyer-Overton hypothesis, which predicts a correlation between anesthetic potency and solubility in oil, fails.

Polysaccharide/Surfactant complexes at the air-water interface - effect of the charge density on interfacial and foaming behaviors.

PubMed

Ropers, M H; Novales, B; Boué, F; Axelos, M A V

2008-11-18

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide. Besides classical methods to investigate polymer/surfactant systems, we applied, for the first time concerning these systems, the analogy between the small angle neutron scattering by foams and the neutron reflectivity of films to measure in situ film thicknesses of foams. CTAB/pectin foam films are much thicker than the pure surfactant foam film but similar for high- and low-charged pectin/CTAB systems despite the difference in structure of complexes at interfaces. The improvement of the foam properties of CTAB bound to pectin is shown to be directly related to the formation of pectin-CTAB complexes at the air-water interface. However, in opposition to surface activity, there is no specific behavior for the highly charged pectin: foam properties depend mainly upon the bulk charge concentration, while the interfacial behavior is mainly governed by the charge density of pectin. For the highly charged pectin, specific cooperative effects between neighboring charged sites along the chain are thought to be involved in the higher surface activity of pectin/CTAB complexes. A more general behavior can be obtained at lower charge density either by using a low-charged pectin or by neutralizing the highly charged pectin in decreasing pH.

Interfacial properties in a discrete model for tumor growth

NASA Astrophysics Data System (ADS)

Moglia, Belén; Guisoni, Nara; Albano, Ezequiel V.

2013-03-01

We propose and study, by means of Monte Carlo numerical simulations, a minimal discrete model for avascular tumor growth, which can also be applied for the description of cell cultures in vitro. The interface of the tumor is self-affine and its width can be characterized by the following exponents: (i) the growth exponent β=0.32(2) that governs the early time regime, (ii) the roughness exponent α=0.49(2) related to the fluctuations in the stationary regime, and (iii) the dynamic exponent z=α/β≃1.49(2), which measures the propagation of correlations in the direction parallel to the interface, e.g., ξ∝t1/z, where ξ is the parallel correlation length. Therefore, the interface belongs to the Kardar-Parisi-Zhang universality class, in agreement with recent experiments of cell cultures in vitro. Furthermore, density profiles of the growing cells are rationalized in terms of traveling waves that are solutions of the Fisher-Kolmogorov equation. In this way, we achieved excellent agreement between the simulation results of the discrete model and the continuous description of the growth front of the culture or tumor.

Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerr, A. J.; Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093; Chagarov, E.

2014-09-14

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al{sub 2}O{sub 3} gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge.more » These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001)« less

Simulations of Precipitate Microstructure Evolution during Heat Treatment

NASA Astrophysics Data System (ADS)

Wu, Kaisheng; Sterner, Gustaf; Chen, Qing; Jou, Herng-Jeng; Jeppsson, Johan; Bratberg, Johan; Engström, Anders; Mason, Paul

Precipitation, a major solid state phase transformation during heat treatment processes, has for more than one century been intensively employed to improve the strength and toughness of various high performance alloys. Recently, sophisticated precipitation reaction models, in assistance with well-developed CALPHAD databases, provide an efficient and cost-effective way to tailor precipitate microstructures that maximize the strengthening effect via the optimization of alloy chemistries and heat treatment schedules. In this presentation, we focus on simulating precipitate microstructure evolution in Nickel-base superalloys under arbitrary heat treatment conditions. The newly-developed TC-PRISMA program has been used for these simulations, with models refined especially for non-isothermal conditions. The effect of different cooling profiles on the formation of multimodal microstructures has been thoroughly examined in order to understand the underlying thermodynamics and kinetics. Meanwhile, validations against several experimental results have been carried out. Practical issues that are critical to the accuracy and applicability of the current simulations, such as modifications that overcome mean-field approximations, compatibility between CALPHAD databases, selection of key parameters (particularly interfacial energy and nucleation site densities), etc., are also addressed.

Interfacial Alloy Hydride Destabilization in Mg/Pd Thin Films

NASA Astrophysics Data System (ADS)

Chung, C.-J.; Lee, Sang-Chul; Groves, James R.; Brower, Edwin N.; Sinclair, Robert; Clemens, Bruce M.

2012-03-01

Recently, a large increase in the equilibrium hydrogen pressure has been reported for MG thin films capped with a Pd layer. We show that this increase is due to intermixing of Mg and Pd, as opposed to a strain effect as previously claimed. Transmission electron microscopy and depth profiling x-ray photoemission spectroscopy are used to directly measure interfacial intermixing between Mg and Pd, and we find that intermixing and equilibrium hydrogen pressure both increase with annealing. We present a thermodynamic model of the effect of alloying on equilibrium pressure, and find that the observed equilibrium pressure increase is consistent with the observed thickness of the intermixed region, which is of the order of a few nm. We also show that stress measured during hydrogenation corresponds to a negligible increase in equilibrium pressure.

Grain-boundary free energy in an assembly of elastic disks.

PubMed

Lusk, Mark T; Beale, Paul D

2004-02-01

Grain-boundary free energy is estimated as a function of misoriention for symmetric tilt boundaries in an assembly of nearly hard disks. Fluctuating cell theory is used to accomplish this since the most common techniques for calculating interfacial free energy cannot be applied to such assemblies. The results are analogous to those obtained using a Leonard-Jones potential, but in this case the interfacial energy is dominated by an entropic contribution. Disk assemblies colorized with free and specific volume elucidate differences between these two characteristics of boundary structure. Profiles are also provided of the Helmholtz and Gibbs free energies as a function of distance from the grain boundaries. Low angle grain boundaries are shown to follow the classical relationship between dislocation orientation/spacing and misorientation angle.

Positron Annihilation Spectroscopy as a Novel Interfacial Probe for Thin Polymeric Films and Nano-Composites

NASA Astrophysics Data System (ADS)

Awad, Somia; Chen, Hongmin; Maina, Grace; Lee, L. James; Gu, Xiaohong; Jean, Y. C.

2010-03-01

Positron annihilation spectroscopy (PAS) has been developed as a novel probe to characterize the sub-nanometer defect, free volume, profile from the surface, interfaces, and to the bulk in polymeric materials when a variable mono-energy slow positron beam is used. Free-volume hole sizes, fractions, and distributions are measurable as a function of depth at the high precision. PAS has been successfully used to study the interfacial properties of polymeric nanocomposites at different chemical bonding. In nano-scale thin polymeric films, such as in PS/SiO2, and PU/ZnO, significant variations of Tg as a function of depth and of wt% oxide are observed. Variations of Tg are dependent on strong or weak interactions between polymers and nano-scale oxides surfaces.

Effects of post-deposition annealing ambient on band alignment of RF magnetron-sputtered Y2O3 film on gallium nitride

PubMed Central

2013-01-01

The effects of different post-deposition annealing ambients (oxygen, argon, forming gas (95% N2 + 5% H2), and nitrogen) on radio frequency magnetron-sputtered yttrium oxide (Y2O3) films on n-type gallium nitride (GaN) substrate were studied in this work. X-ray photoelectron spectroscopy was utilized to extract the bandgap of Y2O3 and interfacial layer as well as establishing the energy band alignment of Y2O3/interfacial layer/GaN structure. Three different structures of energy band alignment were obtained, and the change of band alignment influenced leakage current density-electrical breakdown field characteristics of the samples subjected to different post-deposition annealing ambients. Of these investigated samples, ability of the sample annealed in O2 ambient to withstand the highest electric breakdown field (approximately 6.6 MV/cm) at 10−6 A/cm2 was related to the largest conduction band offset of interfacial layer/GaN (3.77 eV) and barrier height (3.72 eV). PMID:23360596

Nitride passivation reduces interfacial traps in atomic-layer-deposited Al{sub 2}O{sub 3}/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aoki, T., E-mail: aokit@sc.sumitomo-chem.co.jp; Fukuhara, N.; Osada, T.

2014-07-21

Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al{sub 2}O{sub 3}. This AlN passivation incorporated nitrogen at the Al{sub 2}O{sub 3}/GaAs interface, improving the capacitance-voltage (C–V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C–V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (D{sub it}). The D{sub it} was reduced over the entire GaAs band gap. In particular, these devices exhibited D{sub it} around the midgap ofmore » less than 4 × 10{sup 12} cm{sup −2}eV{sup −1}, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.« less

Electrostatic Self-Assembly Enabling Integrated Bulk and Interfacial Sodium Storage in 3D Titania-Graphene Hybrid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Gui-Liang; Xiao, Lisong; Sheng, Tian

Room temperature sodium-ion batteries have attracted increased attention for energy storage due to the natural abundance of sodium. However, it remains a huge challenge to develop versatile electrode materials with favorable properties, which requires smart structure design and good mechanistic understanding. Herein, we reported a general and scalable approach to synthesize 3D titania-graphene hybrid via electrostatic-interaction-induced self-assembly. Synchrotron X-ray probe, transmission electron microscopy and computational modeling revealed that the strong interaction between Titania and graphene through comparably strong van-der-Waals forces not only facilitates bulk Na+ intercalation but also enhances the interfacial sodium storage. As a result, the titania-graphene hybrid exhibitsmore » exceptional long-term cycle stability up to 5000 cycles, and ultrahigh rate capability up to 20 C for sodium storage. Furthermore, density function theory calculation indicated that the interfacial Li+, K+, Mg2+ and Al3+ storage can be enhanced as well. The proposed general strategy opens up new avenues to create versatile materials for advanced battery systems.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Javaid, Saqib; National Centre of Physics, Islamabad 45320; Javed Akhtar, M., E-mail: javedakhtar6@gmail.com

Recently, experimental results have shown that photovoltaic properties of Fullerene (C60)/Phthalocyanine based devices improve considerably as molecular orientation is changed from edge-on to face-on. In this work, we have studied the impact of molecular orientation on C60/ZnPc interfacial properties, particularly focusing on experimentally observed face-on and edge-on configuration, using density functional theory based simulations. The results show that the interfacial electronic properties are strongly anisotropic: direction of charge transfer and interface dipole fluctuates as molecular orientation is switched. As a result of orientation dependant interface dipole, difference between acceptor LUMO and donor HOMO increases as the orientation is changed frommore » edge-on to face-on, suggesting a consequent increase in open circuit voltage (V{sub OC}). Moreover, adsorption and electronic properties indicate that the interfacial interactions are much stronger in the face-on configuration which should further facilitate the charge-separation process. These findings elucidate the energy level alignment at C60/ZnPc interface and help to identify interface dipole as the origin of the orientation dependence of V{sub OC}.« less

Electrostatic Self-Assembly Enabling Integrated Bulk and Interfacial Sodium Storage in 3D Titania-Graphene Hybrid.

PubMed

Xu, Gui-Liang; Xiao, Lisong; Sheng, Tian; Liu, Jianzhao; Hu, Yi-Xin; Ma, Tianyuan; Amine, Rachid; Xie, Yingying; Zhang, Xiaoyi; Liu, Yuzi; Ren, Yang; Sun, Cheng-Jun; Heald, Steve M; Kovacevic, Jasmina; Sehlleier, Yee Hwa; Schulz, Christof; Mattis, Wenjuan Liu; Sun, Shi-Gang; Wiggers, Hartmut; Chen, Zonghai; Amine, Khalil

2018-01-10

Room-temperature sodium-ion batteries have attracted increased attention for energy storage due to the natural abundance of sodium. However, it remains a huge challenge to develop versatile electrode materials with favorable properties, which requires smart structure design and good mechanistic understanding. Herein, we reported a general and scalable approach to synthesize three-dimensional (3D) titania-graphene hybrid via electrostatic-interaction-induced self-assembly. Synchrotron X-ray probe, transmission electron microscopy, and computational modeling revealed that the strong interaction between titania and graphene through comparably strong van der Waals forces not only facilitates bulk Na + intercalation but also enhances the interfacial sodium storage. As a result, the titania-graphene hybrid exhibits exceptional long-term cycle stability up to 5000 cycles, and ultrahigh rate capability up to 20 C for sodium storage. Furthermore, density function theory calculation indicated that the interfacial Li + , K + , Mg 2+, and Al 3+ storage can be enhanced as well. The proposed general strategy opens up new avenues to create versatile materials for advanced battery systems.

Spontaneous Self-Formation of 3D Plasmonic Optical Structures.

PubMed

Choi, Inhee; Shin, Yonghee; Song, Jihwan; Hong, SoonGweon; Park, Younggeun; Kim, Dongchoul; Kang, Taewook; Lee, Luke P

2016-08-23

Self-formation of colloidal oil droplets in water or water droplets in oil not only has been regarded as fascinating fundamental science but also has been utilized in an enormous number of applications in everyday life. However, the creation of three-dimensional (3D) architectures by a liquid droplet and an immiscible liquid interface has been less investigated than other applications. Here, we report interfacial energy-driven spontaneous self-formation of a 3D plasmonic optical structure at room temperature without an external force. Based on the densities and interfacial energies of two liquids, we simulated the spontaneous formation of a plasmonic optical structure when a water droplet containing metal ions meets an immiscible liquid polydimethylsiloxane (PDMS) interface. At the interface, the metal ions in the droplet are automatically reduced to form an interfacial plasmonic layer as the liquid PDMS cures. The self-formation of both an optical cavity and integrated plasmonic nanostructure significantly enhances the fluorescence by a magnitude of 1000. Our findings will have a huge impact on the development of various photonic and plasmonic materials as well as metamaterials and devices.

Improvement in interfacial characteristics of low-voltage carbon nanotube thin-film transistors with solution-processed boron nitride thin films

NASA Astrophysics Data System (ADS)

Jeon, Jun-Young; Ha, Tae-Jun

2017-08-01

In this article, we demonstrate the potential of solution-processed boron nitride (BN) thin films for high performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with low-voltage operation. The use of BN thin films between solution-processed high-k dielectric layers improved the interfacial characteristics of metal-insulator-metal devices, thereby reducing the current density by three orders of magnitude. We also investigated the origin of improved device performance in SWCNT-TFTs by employing solution-processed BN thin films as an encapsulation layer. The BN encapsulation layer improves the electrical characteristics of SWCNT-TFTs, which includes the device key metrics of linear field-effect mobility, sub-threshold swing, and threshold voltage as well as the long-term stability against the aging effect in air. Such improvements can be achieved by reduced interaction of interfacial localized states with charge carriers. We believe that this work can open up a promising route to demonstrate the potential of solution-processed BN thin films on nanoelectronics.

Interfacial engineering of microstructured materials

NASA Astrophysics Data System (ADS)

Poda, Aimee

The tribological behavior of octadecyltrichlorosilane self assembled monolayers (OTS-SAMs) has been successfully exploited to reduce energy losses and to produce adequate adhesion barrier properties on many MEMS surfaces. Unfortunately, performance discrepancies are reported in the literature between films produced on smooth surfaces as compared to typical MEMS surfaces maintaining topographical roughness. Rational explanations in terms of reproducibility issues, production considerations, and the scale of measurement technique have been introduced to account for some of the variation. The tribological phenomena at the micro-scale are complicated by the fact that rather than inertial effects, the forces associated with the surface become dominant factors influencing the mechanical behavior of contacting components. In MEMS, real mechanical contacts typically consist of a few nanometer scale asperities. Furthermore, various surface topographies exist for MEMS device fabrication and their corresponding asperity profiles can vary drastically based on the production process. This dissertation presents research focusing on the influence of topographical asperities on OTS film properties of relevance for efficient tribological improvement. A fundamental approach has been taken to carefully examine the factors that contribute to high quality film formation, specifically formation temperature and the role of interfacial water layer associated with the sample surface. As evidenced on smooth surfaces, the characteristics for successful tribological performance of OTS films are strongly dependent on the lateral packing density and molecular orientation of the monolayer. Limited information is available on how monolayers associate on topographical asperities and whether these topographical asperities influence the interfacial reactivity of MEMS surfaces. A silica film produced from a low temperature, vapor-phase hydrolysis of tetrachlorosilane with a tunable topography is introduced and leveraged as a novel investigative platform for advanced analytical investigations often restricted to use on smooth surfaces. This tunable surface allows intellectual insight into the nature of surface properties associated with silica surfaces, the uptake of interfacial water and the subsequent influence of surface morphology on OTS film formation. FTIR analysis was utilized for an examination of interfacial properties on both smooth Si(100) surfaces and on the tunable MVD topography in combination with an investigation of OTS film formation mechanism. A dilute etchant technique is developed to provide topographic contrast for AFM imaging to allow direct examination of film packing characteristics in relation to surface asperities. A relationship between monolayer adsorption characteristics and topographical asperities with observed variations in monolayer order resultant from surface roughness has been elucidated. Results show that the packing structure of OTS monolayers is dependent on the local asperity curvature which is qualitatively different from that observed on flat surfaces. In addition, a difference in surface reactivity is observed as a result of different surface topographies with thicker silica layers maintaining a thicker interfacial water layer resulting in a higher coverage of OTS monolayers at similar reaction times and conditions. This work shows changes in surface reactivity as a consequence of different morphological surface characteristics and preparation procedures. Additional research is presented on a new class of SAM, namely octadecylphoshonic acid and its monolayer formation mechanism and properties are compared to conventional OTS monolayers. This monolayer is translated to investigative probes based on Aluminum oxide specifically tailored for a tribological comparison across multi-scale friction regimes.

Liquid-Vapor Interfacial Properties of Aqueous Solutions of Guanidinium and Methyl Guanidinium Chloride: Influence of Molecular Orientation on Interface Fluctuations

PubMed Central

Ou, Shuching; Cui, Di; Patel, Sandeep

2014-01-01

The guanidinium cation (C(NH2)3+) is a highly stable cation in aqueous solution due to its efficient solvation by water molecules and resonance stabilization of the charge. Its salts increase the solubility of nonpolar molecules (”salting-in”) and decrease the ordering of water. It is one of the strongest denaturants used in biophysical studies of protein folding. We investigate the behavior of guanidinium and its derivative, methyl guanidinium (an amino acid analogue) at the air-water surface, using atomistic molecular dynamics (MD) simulations and calculation of potentials of mean force. Methyl guanidinium cation is less excluded from the air-water surface than guanidinium cation, but both cations show orientational dependence of surface affinity. Parallel orientations of the guanidinium ring (relative to the Gibbs dividing surface) show pronounced free energy minima in the interfacial region, while ring orientations perpendicular to the GDS exhibit no discernible surface stability. Calculations of surface fluctuations demonstrate that near the air-water surface, the parallel-oriented cations generate significantly greater interfacial fluctuations compared to other orientations, which induces more long-ranged perturbations and solvent density redistribution. Our results suggest a strong correlation with induced interfacial fluctuations and ion surface stability. These results have implications for interpreting molecular-level, mechanistic action of this osmolyte’s interaction with hydrophobic interfaces as they impact protein denaturation (solubilization). PMID:23937431

Mechanically Enhanced Liquid Interfaces at Human Body Temperature Using Thermosensitive Methylated Nanocrystalline Cellulose.

PubMed

Scheuble, N; Geue, T; Kuster, S; Adamcik, J; Mezzenga, R; Windhab, E J; Fischer, P

2016-02-09

The mechanical performance of materials at oil/water interfaces after consumption is a key factor affecting hydrophobic drug release. In this study, we methylated the surface of nanocrystalline cellulose (NCC) by mercerization and dimethyl sulfate exposure to produce thermosensitive biopolymers. These methylated NCC (metNCC) were used to investigate interfacial thermogelation at air/water and medium-chain triglyceride (MCT)/water interfaces at body temperature. In contrast to bulk fluid dynamics, elastic layers were formed at room temperature, and elasticity increased significantly at body temperature, which was measured by interfacial shear and dilatational rheology in situ. This unique phenomenon depends on solvent quality, temperature, and polymer concentration at interfaces. Thus, by adjusting the degree of hydrophobicity of metNCC, the interfacial elasticity and thermogelation of the interfaces could be varied. In general, these new materials (metNCC) formed more brittle interfacial layers compared to commercial methylcellulose (MC A15). Thermogelation of methylcellulose promotes attractive intermolecular forces, which were reflected in a change in self-assembly of metNCC at the interface. As a consequence, layer thickness and density increased as a function of temperature. These effects were measured by atomic force microscopy (AFM) images of the displaced interface and confirmed by neutron reflection. The substantial structural and mechanical change of methylcellulose interfaces at body temperature represents a controllable encapsulation parameter allowing optimization of lipid-based drug formulations.

Capacitive charge storage at an electrified interface investigated via direct first-principles simulations [Direct Simulation of Capacitive Charging of Graphene and Implications for Supercapacitor Design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radin, Maxwell D.; Ogitsu, Tadashi; Biener, Juergen

Understanding the impact of interfacial electric fields on electronic structure is crucial to improving the performance of materials in applications based on charged interfaces. Supercapacitors store energy directly in the strong interfacial field between a solid electrode and a liquid electrolyte; however, the complex interplay between the two is often poorly understood, particularly for emerging low-dimensional electrode materials that possess unconventional electronic structure. Typical descriptions tend to neglect the specific electrode-electrolyte interaction, approximating the intrinsic “quantum capacitance” of the electrode in terms of a fixed electronic density of states. Instead, we introduce a more accurate first-principles approach for directly simulatingmore » charge storage in model capacitors using the effective screening medium method, which implicitly accounts for the presence of the interfacial electric field. Applying this approach to graphene supercapacitor electrodes, we find that results differ significantly from the predictions of fixed-band models, leading to improved consistency with experimentally reported capacitive behavior. The differences are traced to two key factors: the inhomogeneous distribution of stored charge due to poor electronic screening and interfacial contributions from the specific interaction with the electrolyte. Lastly, our results are used to revise the conventional definition of quantum capacitance and to provide general strategies for improving electrochemical charge storage, particularly in graphene and similar low-dimensional materials.« less

Capacitive charge storage at an electrified interface investigated via direct first-principles simulations [Direct Simulation of Capacitive Charging of Graphene and Implications for Supercapacitor Design

DOE PAGES

Radin, Maxwell D.; Ogitsu, Tadashi; Biener, Juergen; ...

2015-03-11

Understanding the impact of interfacial electric fields on electronic structure is crucial to improving the performance of materials in applications based on charged interfaces. Supercapacitors store energy directly in the strong interfacial field between a solid electrode and a liquid electrolyte; however, the complex interplay between the two is often poorly understood, particularly for emerging low-dimensional electrode materials that possess unconventional electronic structure. Typical descriptions tend to neglect the specific electrode-electrolyte interaction, approximating the intrinsic “quantum capacitance” of the electrode in terms of a fixed electronic density of states. Instead, we introduce a more accurate first-principles approach for directly simulatingmore » charge storage in model capacitors using the effective screening medium method, which implicitly accounts for the presence of the interfacial electric field. Applying this approach to graphene supercapacitor electrodes, we find that results differ significantly from the predictions of fixed-band models, leading to improved consistency with experimentally reported capacitive behavior. The differences are traced to two key factors: the inhomogeneous distribution of stored charge due to poor electronic screening and interfacial contributions from the specific interaction with the electrolyte. Lastly, our results are used to revise the conventional definition of quantum capacitance and to provide general strategies for improving electrochemical charge storage, particularly in graphene and similar low-dimensional materials.« less

First principles study on electrochemical and chemical stability of solid electrolyte–electrode interfaces in all-solid-state Li-ion batteries

DOE PAGES

Zhu, Yizhou; He, Xingfeng; Mo, Yifei

2015-12-11

All-solid-state Li-ion batteries based on ceramic solid electrolyte materials are a promising next-generation energy storage technology with high energy density and enhanced cycle life. The poor interfacial conductance is one of the key limitations in enabling all-solid-state Li-ion batteries. However, the origin of this poor conductance has not been understood, and there is limited knowledge about the solid electrolyte–electrode interfaces in all-solid-state Li-ion batteries. In this paper, we performed first principles calculations to evaluate the thermodynamics of the interfaces between solid electrolyte and electrode materials and to identify the chemical and electrochemical stabilities of these interfaces. Our computation results revealmore » that many solid electrolyte–electrode interfaces have limited chemical and electrochemical stability, and that the formation of interphase layers is thermodynamically favorable at these interfaces. These formed interphase layers with different properties significantly affect the electrochemical performance of all-solid-state Li-ion batteries. The mechanisms of applying interfacial coating layers to stabilize the interface and to reduce interfacial resistance are illustrated by our computation. This study demonstrates a computational scheme to evaluate the chemical and electrochemical stability of heterogeneous solid interfaces. Finally, the enhanced understanding of the interfacial phenomena provides the strategies of interface engineering to improve performances of all-solid-state Li-ion batteries.« less

Energy storage in ferroelectric polymer nanocomposites filled with core-shell structured polymer@BaTiO3 nanoparticles: understanding the role of polymer shells in the interfacial regions.

PubMed

Zhu, Ming; Huang, Xingyi; Yang, Ke; Zhai, Xing; Zhang, Jun; He, Jinliang; Jiang, Pingkai

2014-11-26

The interfacial region plays a critical role in determining the electrical properties and energy storage density of dielectric polymer nanocomposites. However, we still know a little about the effects of electrical properties of the interfacial regions on the electrical properties and energy storage of dielectric polymer nanocomposites. In this work, three types of core-shell structured polymer@BaTiO3 nanoparticles with polymer shells having different electrical properties were used as fillers to prepare ferroelectric polymer nanocomposites. All the polymer@BaTiO3 nanoparticles were prepared by surface-initiated reversible-addition-fragmentation chain transfer (RAFT) polymerization, and the polymer shells were controlled to have the same thickness. The morphology, crystal structure, frequency-dependent dielectric properties, breakdown strength, leakage currents, energy storage capability, and energy storage efficiency of the polymer nanocomposites were investigated. On the other hand, the pure polymers having the same molecular structure as the shells of polymer@BaTiO3 nanoparticles were also prepared by RAFT polymerization, and their electrical properties were provided. Our results show that, to achieve nanocomposites with high discharged energy density, the core-shell nanoparticle filler should simultaneously have high dielectric constant and low electrical conductivity. On the other hand, the breakdown strength of the polymer@BaTiO3-based nanocomposites is highly affected by the electrical properties of the polymer shells. It is believed that the electrical conductivity of the polymer shells should be as low as possible to achieve nanocomposites with high breakdown strength.

Capillary-wave dynamics and interface structure modulation in binary Bose-Einstein condensate mixtures

NASA Astrophysics Data System (ADS)

Indekeu, Joseph O.; Van Thu, Nguyen; Lin, Chang-You; Phat, Tran Huu

2018-04-01

The localized low-energy interfacial excitations, or interfacial Nambu-Goldstone modes, of phase-segregated binary mixtures of Bose-Einstein condensates are investigated analytically. To this end a double-parabola approximation (DPA) is performed on the Lagrangian density in Gross-Pitaevskii theory for a system in a uniform potential. This DPA entails a model in which analytic expressions are obtained for the excitations underlying capillary waves or ripplons for arbitrary strength K (>1 ) of the phase segregation. The dispersion relation ω (k ) ∝k3 /2 is derived directly from the Bogoliubov-de Gennes equations in the limit that the wavelength 2 π /k is much larger than the interface width. The proportionality constant in the dispersion relation provides the static interfacial tension. A correction term in ω (k ) of order k5 /2 is calculated analytically within the DPA model. The combined result is tested against numerical diagonalization of the exact Bogoliubov-de Gennes equations. Satisfactory agreement is obtained in the range of physically relevant wavelengths. The ripplon dispersion relation is relevant to state-of-the-art experiments using (quasi)uniform optical-box traps. Furthermore, within the DPA model explicit expressions are obtained for the structural deformation of the interface due to the passing of the capillary wave. It is found that the amplitude of the wave is enhanced by an amount that is quadratic in the ratio of the phase velocity ω /k to the sound velocity c . For generic mixtures consisting of condensates with unequal healing lengths, an additional modulation is predicted of the common value of the condensate densities at the interface.

Effect of Surface Oxidation on Interfacial Water Structure at a Pyrite (100) Surface as Studied by Molecular Dynamics Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Jiaqi; Miller, Jan D.; Dang, Liem X.

2015-06-01

In the first part of this paper, a Scanning Electron Microscopy and contact angle study of a pyrite surface (100) is reported describing the relationship between surface oxidation and the hydrophilic surface state. In addition to these experimental results, the following simulated surface states were examined using Molecular Dynamics Simulation (MDS): fresh unoxidized (100) surface; polysulfide at the (100) surface; elemental sulfur at the (100) surface. Crystal structures for the polysulfide and elemental sulfur at the (100) surface were simulated using Density Functional Theory (DFT) quantum chemical calculations. The well known oxidation mechanism which involves formation of a metal deficientmore » layer was also described with DFT. Our MDS results of the behavior of interfacial water at the fresh and oxidized pyrite (100) surfaces without/with the presence of ferric hydroxide include simulated contact angles, number density distribution for water, water dipole orientation, water residence time, and hydrogen-bonding considerations. The significance of the formation of ferric hydroxide islands in accounting for the corresponding hydrophilic surface state is revealed not only from experimental contact angle measurements but also from simulated contact angle measurements using MDS. The hydrophilic surface state developed at oxidized pyrite surfaces has been described by MDS, on which basis the surface state is explained based on interfacial water structure. The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences (BES), of the DOE funded work performed by Liem X. Dang. Battelle operates the Pacific Northwest National Laboratory for DOE. The calculations were carried out using computer resources provided by BES.« less

Atomic-layer-deposited Al2O3 and HfO2 on InAlAs: A comparative study of interfacial and electrical characteristics

NASA Astrophysics Data System (ADS)

Wu, Li-Fan; Zhang, Yu-Ming; Lv, Hong-Liang; Zhang, Yi-Men

2016-10-01

Al2O3 and HfO2 thin films are separately deposited on n-type InAlAs epitaxial layers by using atomic layer deposition (ALD). The interfacial properties are revealed by angle-resolved x-ray photoelectron spectroscopy (AR-XPS). It is demonstrated that the Al2O3 layer can reduce interfacial oxidation and trap charge formation. The gate leakage current densities are 1.37 × 10-6 A/cm2 and 3.22 × 10-6 A/cm2 at +1 V for the Al2O3/InAlAs and HfO2/InAlAs MOS capacitors respectively. Compared with the HfO2/InAlAs metal-oxide-semiconductor (MOS) capacitor, the Al2O3/InAlAs MOS capacitor exhibits good electrical properties in reducing gate leakage current, narrowing down the hysteresis loop, shrinking stretch-out of the C-V characteristics, and significantly reducing the oxide trapped charge (Q ot) value and the interface state density (D it). Project supported by the National Basic Research Program of China (Grant No. 2010CB327505), the Advanced Research Foundation of China (Grant No. 914xxx803-051xxx111), the National Defense Advance Research Project, China (Grant No. 513xxxxx306), the National Natural Science Foundation of China (Grant No. 51302215), the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 14JK1656), and the Science and Technology Project of Shaanxi Province, China (Grant No. 2016KRM029).

Interfacial Properties of High-Density Lipoprotein-like Lipid Droplets with Different Lipid and Apolipoprotein A-I Compositions

PubMed Central

Koivuniemi, Artturi; Sysi-Aho, Marko; Orešič, Matej; Ollila, Samuli

2013-01-01

The surface properties of high-density lipoproteins (HDLs) are important because different enzymes bind and carry out their functions at the surface of HDL particles during metabolic processes. However, the surface properties of HDL and other lipoproteins are poorly known because they cannot be directly measured for nanoscale particles with contemporary experimental methods. In this work, we carried out coarse-grained molecular dynamics simulations to study the concentration of core lipids in the surface monolayer and the interfacial tension of droplets resembling HDL particles. We simulated lipid droplets composed of different amounts of phospholipids, cholesterol esters (CEs), triglycerides (TGs), and apolipoprotein A-Is. Our results reveal that the amount of TGs in the vicinity of water molecules in the phospholipid monolayer is 25–50% higher compared to the amount of CEs in a lipid droplet with a mixed core of an equal amount of TG and CE. In addition, the correlation time for the exchange of molecules between the core and the monolayer is significantly longer for TGs compared to CEs. This suggests that the chemical potential of TG is lower in the vicinity of aqueous phase but the free-energy barrier for the translocation between the monolayer and the core is higher compared to CEs. From the point of view of enzymatic modification, this indicates that TG molecules are more accessible from the aqueous phase. Further, our results point out that CE molecules decrease the interfacial tension of HDL-like lipid droplets whereas TG keeps it constant while the amount of phospholipids varies. PMID:23708359

Real-time feedback control of the plasma density profile on ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Mlynek, A.; Reich, M.; Giannone, L.; Treutterer, W.; Behler, K.; Blank, H.; Buhler, A.; Cole, R.; Eixenberger, H.; Fischer, R.; Lohs, A.; Lüddecke, K.; Merkel, R.; Neu, G.; Ryter, F.; Zasche, D.; ASDEX Upgrade Team

2011-04-01

The spatial distribution of density in a fusion experiment is of significant importance as it enters in numerous analyses and contributes to the fusion performance. The reconstruction of the density profile is therefore commonly done in offline data analysis. In this paper, we present an algorithm which allows for density profile reconstruction from the data of the submillimetre interferometer and the magnetic equilibrium in real-time. We compare the obtained results to the profiles yielded by a numerically more complex offline algorithm. Furthermore, we present recent ASDEX Upgrade experiments in which we used the real-time density profile for active feedback control of the shape of the density profile.

Shear strength of metal - SiO2 contacts

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1978-01-01

The strength of the bond between metals and SiO2 is studied by measuring the static coefficient of friction of metals contacting alpha-quartz in ultrahigh vacuum. It was found that copper with either chemisorbed oxygen, nitrogen or sulphur exhibited higher contact strength on stoichiometric SiO2 than did clean copper. Since the surface density of states induced by these species on copper is similar, it appears that the strength of the interfacial bond can be related to the density of states on the metal surface.

Shear strength of metal - SiO2 contacts

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1978-01-01

The strength of the bond between metals and SiO2 was studied by measuring the static coefficient of friction of metals contacting alpha-quartz in ultrahigh vacuum. It was found that copper with either chemisorbed oxygen, nitrogen, or sulphur exhibited higher contact strength on stoichiometric SiO2 than did clean copper. Since the surface density of states induced by these species on copper is similar, it appears that the strength of the interfacial bond can be related to the density of states on the metal surface.

Charge Equilibration Force Fields for Lipid Environments: Applications to Fully Hydrated DPPC Bilayers and DMPC-Embedded Gramicidin A

PubMed Central

Davis, Joseph E.; Patel, Sandeep

2009-01-01

Polarizable force fields for lipid and solvent environments are used for molecular dynamics simulations of a fully hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer and gramicidin A (gA) dimer embedded in a dimyristoylphosphatidylcholine (DMPC) bilayer. The lipid bilayer is modelled using the CHARMM charge equilibration (CHEQ) polarizable force field for lipids and the TIP4P-FQ force field to represent solvent. For the DPPC bilayer system, results are compared to the same system simulated using the nonpolarizable CHARMM27r (C27r) force field and TIP3P water. Calculated atomic and electron density profiles, headgroup orientations as measured by the phosphorus-nitrogen vector orientation, and deuterium order parameters are found to be consistent with previous simulations and with experiment. The CHEQ model exhibits greater water penetration into the bilayer interior, as demonstrated by the potential of mean force calculated from the water density profile. This is a result of the variation of the water molecular dipole from 2.55 D in the bulk to 1.88 D in the interior. We discuss this finding in the context of previous studies (both simulation and experiment) that have investigated the extent of penetration of water into DPPC bilayers. We also discuss the effects of including explicit polarization on the water dipole moment variation as a function of distance from the bilayer. We show distributions of atomic charges over the course of the simulation, since the CHEQ model allows the charges to fluctuate. We have calculated the interfacial dipole potential, which the CHEQ model predicts to be 0.95 V compared to 0.86 V as predicted by the C27r model. We also discuss dielectric permittivity profiles and the differences arising between the two models. We obtain bulk values of 72.77 for the CHEQ model (TIP4P-FQ water) and 91.22 for C27r (TIP3P), and values approaching unity in the membrane interior. Finally, we present results of simulations of gA embedded in a DMPC bilayer using the CHEQ model and discuss structural properties. PMID:19526999

Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements

NASA Astrophysics Data System (ADS)

Gadag, Shiva P.; Patra, Susant

2000-12-01

Solder joint interconnects are mechanical means of structural support for bridging the various electronic components and providing electrical contacts and a thermal path for heat dissipation. The functionality of the electronic device often relies on the structural integrity of the solder. The dimensional stability of solder joints is numerically predicted based on their mechanical properties. Algorithms to model the kinetics of dissolution and subsequent growth of intermetallic from the complete knowledge of a single history of time-temperature-reflow profile, by considering equivalent isothermal time intervals, have been developed. The information for dissolution is derived during the heating cycle of reflow and for the growth process from cooling curve of reflow profile. A simple and quick analysis tool to derive tensile stress-strain maps as a function of the reflow temperature of solder and strain rate has been developed by numerical program. The tensile properties are used in modeling thermal strain, thermal fatigue and to predict the overall fatigue life of solder joints. The numerical analysis of the tensile properties as affected by their composition and rate of testing, has been compiled in this paper. A numerical model using constitutive equation has been developed to evaluate the interfacial fatigue crack growth rate. The model can assess the effect of cooling rate, which depends on the level of strain energy release rate. Increasing cooling rate from normalizing to water-quenching, enhanced the fatigue resistance to interfacial crack growth by up to 50% at low strain energy release rate. The increased cooling rates enhanced the fatigue crack growth resistance by surface roughening at the interface of solder joint. This paper highlights salient features of process modeling. Interfacial intermetallic microstructure is affected by cooling rate and thereby affects the mechanical properties.

Interface Engineering of Garnet Solid Electrolytes

NASA Astrophysics Data System (ADS)

Cheng, Lei

Solid lithium ion conductors represent a promising class of materials for next generation high energy density batteries, with the potential for enabling use of high capacity Li metal anodes and providing opportunities for novel lithium-free cathode materials. However, highly resistive interfaces stymie their practical use. This urgent scientific challenge requires mechanistic understanding of ion transport at interfaces, as well as development of novel processes to achieve low interfacial resistances. The goal of this PhD dissertation was to generate fundamental understandings of garnet-structured Al substituted Li7La3Zr2O 12 (LLZO) electrolyte surfaces and interfaces with lithium metal electrodes. Specifically in this research, the topmost surface microstructure, local chemical environment, and surface chemistry were carefully studied. The ceramic processing of garnet is discussed and ways to control the sintering behavior and microstructures were explored and successfully demonstrated. Factors contributing to high interfacial resistance were systematically studied. The source of the high interfacial impedance has been traced to the presence of Li2CO 3 on pellet surfaces resulting from air exposure after processing. In addition, it was discovered that surface grain boundaries are surprisingly fast ion transport pathways and surface microstructure is critically important to lithium ion transport at interfaces. Complex homo- and heterostructured LLZO solid electrolytes with controllable surface and bulk microstructures were successfully fabricated, which allowed the comparison and separation of the contribution from the surface and the bulk. Engineered pellet surfaces allowed us to achieve the lowest interfacial resistance ever reported for this composition, resulting in significantly improved cycling behavior. Lastly, it was found that LLZO surfaces can be effectively stabilized under air exposure conditions, preventing Li2CO3 formation and maintaining low interfacial resistances. This opens new opportunities for garnet solid electrolyte in practical applications.

Wettability of supercritical carbon dioxide/water/quartz systems: simultaneous measurement of contact angle and interfacial tension at reservoir conditions.

PubMed

Saraji, Soheil; Goual, Lamia; Piri, Mohammad; Plancher, Henry

2013-06-11

Injection of carbon dioxide in deep saline aquifers is considered as a method of carbon sequestration. The efficiency of this process is dependent on the fluid-fluid and rock-fluid interactions inside the porous media. For instance, the final storage capacity and total amount of capillary-trapped CO2 inside an aquifer are affected by the interfacial tension between the fluids and the contact angle between the fluids and the rock mineral surface. A thorough study of these parameters and their variations with temperature and pressure will provide a better understanding of the carbon sequestration process and thus improve predictions of the sequestration efficiency. In this study, the controversial concept of wettability alteration of quartz surfaces in the presence of supercritical carbon dioxide (sc-CO2) was investigated. A novel apparatus for measuring interfacial tension and contact angle at high temperatures and pressures based on Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method was developed and validated with a simple system. Densities, interfacial tensions, and dynamic contact angles of CO2/water/quartz systems were determined for a wide range of pressures and temperatures relevant to geological sequestration of CO2 in the subcritical and supercritical states. Image analysis was performed with ADSA-NA method that allows the determination of both interfacial tensions and contact angles with high accuracy. The results show that supercritical CO2 alters the wettability of quartz surface toward less water-wet conditions compared to subcritical CO2. Also we observed an increase in the water advancing contact angles with increasing temperature indicating less water-wet quartz surfaces at higher temperatures.

Interfacial Interactions in Monolayer and Few-Layer SnS/CH3 NH3 PbI3 Perovskite van der Waals Heterostructures and Their Effects on Electronic and Optical Properties.

PubMed

Li, Jian-Cai; Wei, Zeng-Xi; Huang, Wei-Qing; Ma, Li-Li; Hu, Wangyu; Peng, Ping; Huang, Gui-Fang

2018-02-05

A high light-absorption coefficient and long-range hot-carrier transport of hybrid organic-inorganic perovskites give huge potential to their composites in solar energy conversion and environmental protection. Understanding interfacial interactions and their effects are paramount for designing perovskite-based heterostructures with desirable properties. Herein, we systematically investigated the interfacial interactions in monolayer and few-layer SnS/CH 3 NH 3 PbI 3 heterostructures and their effects on the electronic and optical properties of these structures by density functional theory. It was found that the interfacial interactions in SnS/CH 3 NH 3 PbI 3 heterostructures were van der Waals (vdW) interactions, and they were found to be insensitive to the layer number of 2D SnS sheets. Interestingly, although their band gap decreased upon increasing the layer number of SnS, the near-gap electronic states and optical absorption spectra of these heterostructures were found to be strikingly similar. This feature was determined to be critical for the design of 2D layered SnS-based heterostructures. Strong absorption in the ultraviolet and visible-light regions, type II staggered band alignment at the interface, and few-layer SnS as an active co-catalyst make 2D SnS/CH 3 NH 3 PbI 3 heterostructures promising candidates for photocatalysis, photodetectors, and solar energy harvesting and conversion. These results provide first insight into the nature of interfacial interactions and are useful for designing hybrid organic-inorganic perovskite-based devices with novel properties. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

An insight into intrinsic interfacial properties between Li metals and Li10GeP2S12 solid electrolytes.

PubMed

Chen, Bingbing; Ju, Jiangwei; Ma, Jun; Zhang, Jianjun; Xiao, Ruijuan; Cui, Guanglei; Chen, Liquan

2017-11-29

Density functional theory simulations and experimental studies were performed to investigate the interfacial properties, including lithium ion migration kinetics, between lithium metal anode and solid electrolyte Li 10 GeP 2 S 12 (LGPS). The LGPS[001] plane was chosen as the studied surface because the easiest Li + migration pathway is along this direction. The electronic structure of the surface states indicated that the electrochemical stability was reduced at both the PS 4 - and GeS 4 -teminated surfaces. For the interface cases, the equilibrium interfacial structures of lithium metal against the PS 4 -terminated LGPS[001] surface (Li/PS 4 -LGPS) and the GeS 4 -terminated LGPS[001] surface (Li/GeS 4 -LGPS) were revealed based on the structural relaxation and adhesion energy analysis. Solid electrolyte interphases were expected to be formed at both Li/PS 4 -LGPS and Li/GeS 4 -LGPS interfaces, resulting in an unstable state of interface and large interfacial resistance, which was verified by the EIS results of the Li/LGPS/Li cell. In addition, the simulations of the migration kinetics show that the energy barriers for Li + crossing the Li/GeS 4 -LGPS interface were relatively low compared with the Li/PS 4 -LGPS interface. This may contribute to the formation of Ge-rich phases at the Li/LGPS interface, which can tune the interfacial structures to improve the ionic conductivity for future all-solid-state batteries. This work will offer a thorough understanding of the Li/LGPS interface, including local structures, electronic states and Li + diffusion behaviors in all-solid-state batteries.

Pinning effects from substrate and AFM tip surfaces on interfacial nanobubbles

NASA Astrophysics Data System (ADS)

Teshima, Hideaki; Takahashi, Koji; Takata, Yasuyuki; Nishiyama, Takashi

2017-11-01

Measurement accuracy of atomic force microscopy (AFM) is vital to understand the mechanism of interfacial nanobubbles. In this study, we report the influence of pinning derived from both substrate and AFM tip surfaces on the measured shape of interfacial nanobubbles in peak force tapping mode. First, we pushed the nanobubbles using the AFM tip with high peak force setpoint. As a result, the deformed nanobubbles kept their flat shape for several tens of minutes. We quantitatively discuss the pinning force from substrate surface, which retains the flat shape enhancing the stability of nanobubbles. Next, we prepared three AFM tips with different wettability and measured the nanobubbles with an identical setpoint. By comparing the force curves obtained during the measurements, it seems that the (middle-)hydrophobic tips penetrated the liquid/gas interface and received repulsive force resulting from positive meniscus formed by pinning at the tip surface. In contrast, hydrophilic tip didn't penetrate the interface and received the force from the deformation of the interface of the nanobubbles. In addition, the measurements using the (middle-)hydrophobic tips led to the underestimation of the nanobubbles profile corresponding to the pinning position at the tip surfaces.

A Study of the Stability Mechanism of the Dispersed Particle Gel Three-Phase Foam Using the Interfacial Dilational Rheology Method.

PubMed

Yao, Xue; Yi, Ping; Zhao, Guang; Sun, Xin; Dai, Caili

2018-04-28

The dispersed particle gel (DPG) three-phase foam is a novel profile control and flooding system. The stability mechanism of the DPG three-phase foam was studied using an interfacial dilational rheology method. The results show that the elastic modulus of the DPG three-phase foam is up to 14 mN/m, which is much higher than the traditional foam. The increase in interface elasticity produces significantly positive effects on foam stability. Emphasis is given to the influences of frequency, temperature, pressure, and concentration on the viscoelasticity and interfacial adsorption of DPG particles, which change the modules of the foam interface and have a significant effect on foam stability. In addition, the microstructure of the DPG three-phase foam was observed. A viscoelastic shell is formed by the aggregation of the DPG particles on the interface. The irreversible adsorption gives the interface high elasticity and mechanical strength. The electrostatic repulsion between particles increases the spacing between bubbles. The combined effects of these factors give the interface higher mechanical strength, slow down the film drainage, effectively prevent gas permeation, and significantly improve the foam stability.

A Study of the Stability Mechanism of the Dispersed Particle Gel Three-Phase Foam Using the Interfacial Dilational Rheology Method

PubMed Central

Yi, Ping; Zhao, Guang; Sun, Xin; Dai, Caili

2018-01-01

The dispersed particle gel (DPG) three-phase foam is a novel profile control and flooding system. The stability mechanism of the DPG three-phase foam was studied using an interfacial dilational rheology method. The results show that the elastic modulus of the DPG three-phase foam is up to 14 mN/m, which is much higher than the traditional foam. The increase in interface elasticity produces significantly positive effects on foam stability. Emphasis is given to the influences of frequency, temperature, pressure, and concentration on the viscoelasticity and interfacial adsorption of DPG particles, which change the modules of the foam interface and have a significant effect on foam stability. In addition, the microstructure of the DPG three-phase foam was observed. A viscoelastic shell is formed by the aggregation of the DPG particles on the interface. The irreversible adsorption gives the interface high elasticity and mechanical strength. The electrostatic repulsion between particles increases the spacing between bubbles. The combined effects of these factors give the interface higher mechanical strength, slow down the film drainage, effectively prevent gas permeation, and significantly improve the foam stability. PMID:29710805

Flow-induced 2D protein crystallization: characterization of the coupled interfacial and bulk flows.

PubMed

Young, James E; Posada, David; Lopez, Juan M; Hirsa, Amir H

2015-05-14

Two-dimensional crystallization of the protein streptavidin, crystallizing below a biotinylated lipid film spread on a quiescent air-water interface is a well studied phenomenon. More recently, 2D crystallization induced by a shearing interfacial flow has been observed at film surface pressures significantly lower than those required in a quiescent system. Here, we quantify the interfacial and bulk flow associated with 2D protein crystallization through numerical modeling of the flow along with a Newtonian surface model. Experiments were conducted over a wide range of conditions resulting in a state diagram delineating the flow strength required to induce crystals for various surface pressures. Through measurements of the velocity profile at the air-water interface, we found that even in the cases where crystals are formed, the macroscopic flow at the interface is well described by the Newtonian model. However, the results show that even in the absence of any protein in the system, the viscous response of the biotinylated lipid film is complicated and strongly dependent on the strength of the flow. This observation suggests that the insoluble lipid film plays a key role in flow-induced 2D protein crystallization.

Molecular simulation of fluid mixtures in bulk and at solid-liquid interfaces

NASA Astrophysics Data System (ADS)

Kern, Jesse L.

The properties of a diverse range of mixture systems at interfaces are investigated using a variety of computational techniques. Molecular simulation is used to examine the thermodynamic, structural, and transport properties of heterogeneous systems of theoretical and practical importance. The study of binary hard-sphere mixtures at a hard wall demonstrates the high accuracy of recently developed classical-density functionals. The study of aluminum--gallium solid--liquid heterogeneous interfaces predicts a significant amount of prefreezing of the liquid by adopting the structure of the solid surface. The study of ethylene-expanded methanol within model silica mesopores shows the effect of confinement and surface functionalzation on the mixture composition and transport inside of the pores. From our molecular-dynamics study of binary hard-sphere fluid mixtures at a hard wall, we obtained high-precision calculations of the wall-fluid interfacial free energies, gamma. We have considered mixtures of varying diameter ratio, alpha = 0.7,0.8,0.9; mole fraction, x 1 = 0.25,0.50,0.75; and packing fraction, eta < 0.50. Using Gibbs-Cahn Integration, gamma is calculated from the system pressure, chemical potentials, and density profiles. Recent classical density-functional theory predictions agree very well with our results. Structural, thermodynamic, and transport properties of the aluminum--gallium solid--liquid interface at 368 K are obtained for the (100), (110), and (111) orientations using molecular dynamics. Density, potential energy, stress, and diffusion profiles perpendicular to the interface are calculated. The layers of Ga that form on the Al surface are strongly adsorbed and take the in-plane structure of the underlying crystal layers for all orientations, which results in significant compressive stress on the Ga atoms. Bulk methanol--ethylene mixtures under vapor-liquid equilibrium conditions have been characterized using Monte Carlo and molecular dynamics. The simulated vapor-liquid coexistence curves for the pure-component and binary mixtures agree well with experiment, as do the mixture volumetric expansion results. Using chemical potentials obtained from the bulk simulations, the filling of a number of model silica mesopores with ethylene and methanol is simulated. We report the compositions of the confined fluid mixtures over a range of pressures and for three degrees of nominal pore hydrophobicity.

Structural modifications due to interface chemistry at metal-nitride interfaces

DOE PAGES

Yadav, S. K.; Shao, S.; Wang, J.; ...

2015-11-27

Based on accurate first principles density functional theory (DFT) calculations, an unusual phenomenon of interfacial structural modifications, due to the interface chemistry influence is identified at two metal-nitride interfaces with strong metal-nitrogen affinity, Al/TiN {111} and Al/VN {111} interfaces. It is shown that at such interfaces, a faulted stacking structure is energetically preferred on the Al side of the interface. And both intrinsic and extrinsic stacking fault energies in the vicinity Al layers are negligibly small. However, such phenomenon does not occur in Pt/TiN and Pt/VN interfaces because of the weak Pt-N affinity. As a result, corresponding to structural energiesmore » of metal-nitride interfaces, the linear elasticity analysis predicts characteristics of interfacial misfit dislocations at metal-nitride interfaces.« less

Liquid behavior of cross-linked actin bundles.

PubMed

Weirich, Kimberly L; Banerjee, Shiladitya; Dasbiswas, Kinjal; Witten, Thomas A; Vaikuntanathan, Suriyanarayanan; Gardel, Margaret L

2017-02-28

The actin cytoskeleton is a critical regulator of cytoplasmic architecture and mechanics, essential in a myriad of physiological processes. Here we demonstrate a liquid phase of actin filaments in the presence of the physiological cross-linker, filamin. Filamin condenses short actin filaments into spindle-shaped droplets, or tactoids, with shape dynamics consistent with a continuum model of anisotropic liquids. We find that cross-linker density controls the droplet shape and deformation timescales, consistent with a variable interfacial tension and viscosity. Near the liquid-solid transition, cross-linked actin bundles show behaviors reminiscent of fluid threads, including capillary instabilities and contraction. These data reveal a liquid droplet phase of actin, demixed from the surrounding solution and dominated by interfacial tension. These results suggest a mechanism to control organization, morphology, and dynamics of the actin cytoskeleton.

Structural modifications due to interface chemistry at metal-nitride interfaces

PubMed Central

Yadav, S. K.; Shao, S.; Wang, J.; Liu, X.-Y.

2015-01-01

Based on accurate first principles density functional theory (DFT) calculations, an unusual phenomenon of interfacial structural modifications, due to the interface chemistry influence is identified at two metal-nitride interfaces with strong metal-nitrogen affinity, Al/TiN {111} and Al/VN {111} interfaces. It is shown that at such interfaces, a faulted stacking structure is energetically preferred on the Al side of the interface. And both intrinsic and extrinsic stacking fault energies in the vicinity Al layers are negligibly small. However, such phenomenon does not occur in Pt/TiN and Pt/VN interfaces because of the weak Pt-N affinity. Corresponding to structural energies of metal-nitride interfaces, the linear elasticity analysis predicts characteristics of interfacial misfit dislocations at metal-nitride interfaces. PMID:26611639

Simulating the Effect of Contact Atomic Structure on the Spin-Dependent Transport Properties of Gold Nanowires

NASA Astrophysics Data System (ADS)

Ansarino, Masoud; Ravan, Bahram Abedi

Some experimental research works report on the superb magnetoresistance properties of magnetically contacted gold nanowires. With the intention of trying to understand the spin-dependent transport mechanism of these structures, in this work we have used first-principles density functional theory methods to investigate effects of interface structure on the spintronic characteristics of Au nanowires. Monatomic chains of gold are sandwiched between two ferromagnetic electrodes of Fe and by substituting the interfacial Fe atoms with some other transition metal elements (including Cr, Mn, Co and Ni) the occurrence of possible enhancement in the electronic conductance and magnetoresistance characteristics of the device are investigated. It is observed that replacing the interfacial atoms with Ni raises the junction’s magnetoresistance ratio to as high as 2000%.

Hafnium oxide films for application as gate dielectrics

NASA Astrophysics Data System (ADS)

Hsu, Shuo-Lin

The deposition and characterization of HfO2 films for potential application as a high-kappa gate dielectric in MOS devices has been investigated. DC magnetron reactive sputtering was utilized to prepare the HfO2 films. Structural, chemical, and electrical analyses were performed to characterize the various physical, chemical and electrical properties of the sputtered HfO2 films. The sputtered HfO2 films were annealed to simulate the dopant activation process used in semiconductor processing, and to study the thermal stability of the high-kappa, films. The changes in the film properties due to the annealing are also discussed in this work. Glancing angle XRD was used to analyse the atomic scale structure of the films. The as deposited films exhibit an amorphous, regardless of the film thickness. During post-deposition annealing, the thicker films crystallized at lower temperature (< 600°C), and ultra-thin (5.8 nm) film crystallized at higher temperature (600--720°C). The crystalline phase which formed depended on the thickness of the films. The low temperature phase (monoclinic) formed in the 10--20 nm annealed films, and high temperature phase (tetragonal) formed in the ultra-thin annealed HfO2 film. TEM cross-section studies of as deposited samples show that an interfacial layer (< 1nm) exists between HfO2/Si for all film thicknesses. The interfacial layer grows thicker during heat treatment, and grows more rapidly when grain boundaries are present. XPS surface analysis shows the as deposited films are fully oxidized with an excess of oxygen. Interfacial chemistry analysis indicated that the interfacial layer is a silicon-rich silicate layer, which tends to transform to silica-like layer during heat treatment. I-V measurements show the leakage current density of the Al/as deposited-HfO 2/Si MOS diode is of the order of 10-3 A/cm 2, two orders of magnitude lower than that of a ZrO2 film with similar physical thickness. Carrier transport is dominated by Schottky emission at lower electric fields, and by Frenkel-Poole emission in the higher electric field region. After annealing, the leakage current density decreases significantly as the structure remains amorphous structure. It is suggested that this decrease is assorted with the densification and defect healing which accures when the porous as-deposited amorphous structure is annealed. The leakage current density increases of the HfO2 layer crystallizes on annealing, which is attributed to the presence of grain boundaries. C-V measurements of the as deposited film shows typical C-V characteristics, with negligible hystersis, a small flat band voltage shift, but great frequency dispersion. The relative permittivity of HfO2/interfacial layer stack obtained from the capacitance at accumulation is 15, which corresponds to an EOT (equivalent oxide thickness) = 1.66 nm. After annealing, the frequency dispersion is greatly enhanced, and the C-V curve is shifted toward the negative voltage. Reliability tests show that the HfO2 films which remain amorphous after annealing possess superior resistance to constant voltage stress and ambient aging. This study concluded that the sputtered HfO 2 films exhibit an amorphous as deposited. Postdeposition annealing alters the crystallinity, interfacial properties, and electrical characteristics. The HfO2 films which remain amorphous structure after annealing possess the best electrical properties.

Unusual dewetting of thin polymer films in liquid media containing a poor solvent and a nonsolvent.

PubMed

Xu, Lin; Sharma, Ashutosh; Joo, Sang Woo; Liu, Hui; Shi, Tongfei

2014-12-16

We investigate the control of pattern size and kinetics in spontaneous dewetting of thin polymer films (polystyrene) that are stable to thermal annealing by annealing in a poor solvent (acetone)/nonsolvent (ethanol or n-hexane) liquid mixture. Dewetting occurs by the formation and growth of circular holes that coalesce to form droplets. The influence of the nature and the volume fraction of the nonsolvents on the contact angle of polymer droplets, number density of holes, and the kinetics of holes formation and growth is studied. Addition of ethanol greatly increases the hole density and slows down the kinetics substantially, while affecting only a small change in wettability. n-Hexane addition shows an interesting nonmonotonic response in decreasing the hole density and contact angle in the volume fraction range of 0-0.3 but an opposite effect beyond that. Although the two nonsolvents chosen cannot by themselves induce dewetting, their relative affinity for the solid substrate vis-à-vis acetone can strongly influence the observed dewetting scenarios that are not understood by the existing theoretical considerations. n-Hexane, for example, has great affinity for silicon substrate. In addition to the changes in wettability, viscosity, and film interfacial tension engendered by the nonsolvents, the possibility of the formation of adsorbed liquid layers at the substrate-polymer interface, which can modify the interfacial friction and slippage, needs to be considered.

Monolayer nanoparticle-covered liquid marbles derived from a sol-gel coating

NASA Astrophysics Data System (ADS)

Li, Xiaoguang; Wang, Yiqi; Huang, Junchao; Yang, Yao; Wang, Renxian; Geng, Xingguo; Zang, Duyang

2017-12-01

A sol-gel coating consisting of hydrophobic SiO2 nanoparticles (NPs) was used to produce monolayer NP-covered (mNPc) liquid marbles. The simplest approach was rolling a droplet on this coating, and an identifiable signet allowed determination of the coverage ratio of the resulting liquid marble. Alternatively, the particles were squeezed onto a droplet surface with two such coatings, generating surface buckling from interfacial NP jamming, and then a liquid marble was produced via a jamming-relief process in which water was added into the buckled droplet. This process revealed an ˜7% reduction in particle distance after interfacial jamming. The mNPc liquid marbles obtained by the two methods were transparent with smooth profiles, as naked droplets, and could be advantageously used in fundamental and applied researches for their unique functions.

Bile salts at the air-water interface: adsorption and desorption.

PubMed

Maldonado-Valderrama, J; Muros-Cobos, J L; Holgado-Terriza, J A; Cabrerizo-Vílchez, M A

2014-08-01

Bile salts (BS) are bio-surfactants which constitute a vital component in the process of fat digestion. Despite the importance of the interfacial properties in their biological role, these have been scarcely studied in the literature. In this work, we present the adsorption-desorption profiles of two BS (NaTC and NaGDC) including dilatational rheology. Findings from this study reveal very different surface properties of NaTC and NaGDC which originate from different complexation properties relevant to the digestion process. Dynamic adsorption curves show higher adsorption rates for NaTC and suggest the existence of various conformational regimes in contrast to NaGDC which presents only one conformational regime. This is corroborated by analysis of the adsorption isotherms and more in detail by the rheological behaviour. Accordingly, the dilatational response at 1Hz displays two maxima of the dilatational modulus for NaTC as a function of bulk concentration, in contrast to NaGDC which displays only one maximum. The desorption profiles reveal that NaTC adopts an irreversibly adsorbed form at high surface coverage whereas NaGDC fully desorbs from the surface within the whole range of concentrations used. Analysis of the adsorption-desorption profiles provides new insight into the surface properties of BS, suggesting a surface complexation of NaTC. This knowledge can be useful since through interfacial engineering we might control the extent of lipolysis providing the basis for the rational design of food products with tailored digestibility. Copyright © 2014 Elsevier B.V. All rights reserved.

Effects of fiber/matrix interactions on the interfacial deformation micromechanics of cellulose-fiber/polymer composites

NASA Astrophysics Data System (ADS)

Tze, William Tai-Yin

The overall objective of this dissertation was to gain an understanding of the relationship between interfacial chemistry and the micromechanics of the cellulose-fiber/polymer composites. Regenerated cellulose (lyocell) fibers were treated with amine-, phenylamine-, phenyl-, and octadecyl-silanes, and also styrene-maleic anhydride copolymer. Inverse gas chromatography was conducted to evaluate the modified surfaces and to examine the adsorption behavior of ethylbenzene, a model compound for polystyrene, onto the fibers. Micro-composites were formed by depositing micro-droplets of polystyrene onto single fibers. The fiber was subjected to a tensile strain, and Raman spectroscopy was employed to determine the point-to-point variation of the strain- and stress-sensitive 895 cm-1 band of cellulose along the embedded region. Inverse gas chromatography studies reveal that the Ia-b values, calculated by matching the Lewis acid parameter ( KA) and basic parameter (KB) between polystyrene and different fibers, were closely correlated to the acid-base adsorption enthalpies of ethylbenzene onto the corresponding fibers. Hence, Ia-b was subsequently used as a convenient indicator for fiber/matrix acid-base interaction. The Raman micro-spectroscopic studies demonstrate that the interfacial tensile strain and stress are highest at the edge of the droplet, and these values decline from the edge region to the middle region of the embedment. The maximum of these local strains corresponds to a strain-control fracture of the matrix polymer. The minimum of the local tensile stress corresponds to the extent of fiber-to-matrix load transfer. The slope of the tensile stress profile allows for an estimation of the maximum interfacial shear stress, which is indicative of fiber/polymer (practical) adhesion. As such, a novel micro-Raman tensile technique was established for evaluating the ductile-fiber/brittle-polymer system in this study. The micro-Raman tensile technique provided maximum interfacial shear stress values of 8.0 to 13.8 MPa, ranking functional groups according to their practical adhesion to polystyrene: alkyl < untreated < phenyl = phenylamine = styrene copolymer < amine. Overall, interfacial bonding can be increased by increasing the acid-base interactions (Ia-b) or reducing the chemical incompatibility (Deltadelta) between the fibers and matrix. Therefore, interfacial chemistry can be employed to enhance and predict cellulose-fiber/polymer adhesion to better engineer composite properties and ultimately better utilize bio-resources.

Effects of Mean Flow Profiles on Instability of a Low-Density Gas Jet Injected into a High-Density Gas

NASA Technical Reports Server (NTRS)

Vedantam, Nanda Kishore

2003-01-01

The objective of this study was to investigate the effects of the mean flow profiles on the instability characteristics in the near-injector region of low-density gas jets injected into high-density ambient gas mediums. To achieve this, a linear temporal stability analysis and a spatio-temporal stability analysis of a low-density round gas jet injected vertically upwards into a high-density ambient gas were performed by assuming three different sets of mean velocity and density profiles. The flow was assumed to be isothermal and locally parallel. Viscous and diffusive effects were ignored. The mean flow parameters were represented as the sum of the mean value and a small normal-mode fluctuation. A second order differential equation governing the pressure disturbance amplitude was derived from the basic conservation equations. The first set of mean velocity and density profiles assumed were those used by Monkewitz and Sohn for investigating absolute instability in hot jets. The second set of velocity and density profiles assumed for this study were the ones used by Lawson. And the third set of mean profiles included a parabolic velocity profile and a hyperbolic tangent density profile. The effects of the inhomogeneous shear layer and the Froude number (signifying the effects of gravity) on the temporal and spatio-temporal results for each set of mean profiles were delineated. Additional information is included in the original extended abstract.

Measurement of resistance to solute transport across surfactant-laden interfaces using a Fluorescence Recovery After Photobleaching (FRAP) technique

NASA Technical Reports Server (NTRS)

Browne, Edward P.; Nivaggioli, Thierry; Hatton, T. Alan

1994-01-01

A noninvasive fluorescence recovery after photobleaching (FRAP) technique is under development to measure interfacial transport in two phase systems without disturbing the interface. The concentration profiles of a probe solute are measured in both sides of the interface by argon-ion laser, and the system relaxation is then monitored by a microscope-mounted CCD camera.

Correlation of ion and beam current densities in Kaufman thrusters.

NASA Technical Reports Server (NTRS)

Wilbur, P. J.

1973-01-01

In the absence of direct impingement erosion, electrostatic thruster accelerator grid lifetime is defined by the charge exchange erosion that occurs at peak values of the ion beam current density. In order to maximize the thrust from an engine with a specified grid lifetime, the ion beam current density profile should therefore be as flat as possible. Knauer (1970) has suggested this can be achieved by establishing a radial plasma uniformity within the thruster discharge chamber; his tests with the radial field thruster provide an example of uniform plasma properties within the chamber and a flat ion beam profile occurring together. It is shown that, in particular, the ion density profile within the chamber determines the beam current density profile, and that a uniform ion density profile at the screen grid end of the discharge chamber should lead to a flat beam current density profile.

The structural, electronic and optical properties of Au-ZnO interface structure from the first-principles calculation

NASA Astrophysics Data System (ADS)

Huo, Jin-Rong; Li, Lu; Cheng, Hai-Xia; Wang, Xiao-Xu; Zhang, Guo-Hua; Qian, Ping

2018-03-01

The interface structure, electronic and optical properties of Au-ZnO are studied using the first-principles calculation based on density functional theory (DFT). Given the interfacial distance, bonding configurations and terminated surface, we built the optimal interface structure and calculated the electronic and optical properties of the interface. The total density of states, partial electronic density of states, electric charge density and atomic populations (Mulliken) are also displayed. The results show that the electrons converge at O atoms at the interface, leading to a stronger binding of interfaces and thereby affecting the optical properties of interface structures. In addition, we present the binding energies of different interface structures. When the interface structure of Au-ZnO gets changed, furthermore, varying optical properties are exhibited.

Modeling the purging of dense fluid from a street canyon driven by an interfacial mixing flow and skimming flow

NASA Astrophysics Data System (ADS)

Baratian-Ghorghi, Z.; Kaye, N. B.

2013-07-01

An experimental study is presented to investigate the mechanism of flushing a trapped dense contaminant from a canyon by turbulent boundary layer flow. The results of a series of steady-state experiments are used to parameterize the flushing mechanisms. The steady-state experimental results for a canyon with aspect ratio one indicate that dense fluid is removed from the canyon by two different processes, skimming of dense fluid from the top of the dense layer; and by an interfacial mixing flow that mixes fresh fluid down into the dense lower layer (entrainment) while mixing dense fluid into the flow above the canyon (detrainment). A model is developed for the time varying buoyancy profile within the canyon as a function of the Richardson number which parameterizes both the interfacial mixing and skimming processes observed. The continuous release steady-state experiments allowed for the direct measurement of the skimming and interfacial mixing flow rates for any layer depth and Richardson number. Both the skimming rate and the interfacial mixing rate were found to be power-law functions of the Richardson number of the layer. The model results were compared to the results of previously published finite release experiments [Z. Baratian-Ghorghi and N. B. Kaye, Atmos. Environ. 60, 392-402 (2012)], 10.1016/j.atmosenv.2012.06.077. A high degree of consistency was found between the finite release data and the continuous release data. This agreement acts as an excellent check on the measurement techniques used, as the finite release data was based on curve fitting through buoyancy versus time data, while the continuous release data was calculated directly by measuring the rate of addition of volume and buoyancy once a steady-state was established. Finally, a system of ordinary differential equations is presented to model the removal of dense fluid from the canyon based on empirical correlations of the skimming and interfacial mixing taken form the steady-state experiments. The ODE model predicts well the time taken for a finite volume of dense fluid to be flushed from a canyon.

Fluorinated copper phthalocyanine nanowires for enhancing interfacial electron transport in organic solar cells.

PubMed

Yoon, Seok Min; Lou, Sylvia J; Loser, Stephen; Smith, Jeremy; Chen, Lin X; Facchetti, Antonio; Marks, Tobin J; Marks, Tobin

2012-12-12

Zinc oxide is a promising candidate as an interfacial layer (IFL) in inverted organic photovoltaic (OPV) cells due to the n-type semiconducting properties as well as chemical and environmental stability. Such ZnO layers collect electrons at the transparent electrode, typically indium tin oxide (ITO). However, the significant resistivity of ZnO IFLs and an energetic mismatch between the ZnO and the ITO layers hinder optimum charge collection. Here we report that inserting nanoscopic copper hexadecafluorophthalocyanine (F(16)CuPc) layers, as thin films or nanowires, between the ITO anode and the ZnO IFL increases OPV performance by enhancing interfacial electron transport. In inverted P3HT:PC(61)BM cells, insertion of F(16)CuPc nanowires increases the short circuit current density (J(sc)) versus cells with only ZnO layers, yielding an enhanced power conversion efficiency (PCE) of ∼3.6% vs ∼3.0% for a control without the nanowire layer. Similar effects are observed for inverted PTB7:PC(71)BM cells where the PCE is increased from 8.1% to 8.6%. X-ray scattering, optical, and electrical measurements indicate that the performance enhancement is ascribable to both favorable alignment of the nanowire π-π stacking axes parallel to the photocurrent flow and to the increased interfacial layer-active layer contact area. These findings identify a promising strategy to enhance inverted OPV performance by inserting anisotropic nanostructures with π-π stacking aligned in the photocurrent flow direction.

Interfacial, Electrical, and Band Alignment Characteristics of HfO2/Ge Stacks with In Situ-Formed SiO2 Interlayer by Plasma-Enhanced Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Cao, Yan-Qiang; Wu, Bing; Wu, Di; Li, Ai-Dong

2017-05-01

In situ-formed SiO2 was introduced into HfO2 gate dielectrics on Ge substrate as interlayer by plasma-enhanced atomic layer deposition (PEALD). The interfacial, electrical, and band alignment characteristics of the HfO2/SiO2 high-k gate dielectric stacks on Ge have been well investigated. It has been demonstrated that Si-O-Ge interlayer is formed on Ge surface during the in situ PEALD SiO2 deposition process. This interlayer shows fantastic thermal stability during annealing without obvious Hf-silicates formation. In addition, it can also suppress the GeO2 degradation. The electrical measurements show that capacitance equivalent thickness of 1.53 nm and a leakage current density of 2.1 × 10-3 A/cm2 at gate bias of Vfb + 1 V was obtained for the annealed sample. The conduction (valence) band offsets at the HfO2/SiO2/Ge interface with and without PDA are found to be 2.24 (2.69) and 2.48 (2.45) eV, respectively. These results indicate that in situ PEALD SiO2 may be a promising interfacial control layer for the realization of high-quality Ge-based transistor devices. Moreover, it can be demonstrated that PEALD is a much more powerful technology for ultrathin interfacial control layer deposition than MOCVD.

Interfacial, Electrical, and Band Alignment Characteristics of HfO2/Ge Stacks with In Situ-Formed SiO2 Interlayer by Plasma-Enhanced Atomic Layer Deposition.

PubMed

Cao, Yan-Qiang; Wu, Bing; Wu, Di; Li, Ai-Dong

2017-12-01

In situ-formed SiO 2 was introduced into HfO 2 gate dielectrics on Ge substrate as interlayer by plasma-enhanced atomic layer deposition (PEALD). The interfacial, electrical, and band alignment characteristics of the HfO 2 /SiO 2 high-k gate dielectric stacks on Ge have been well investigated. It has been demonstrated that Si-O-Ge interlayer is formed on Ge surface during the in situ PEALD SiO 2 deposition process. This interlayer shows fantastic thermal stability during annealing without obvious Hf-silicates formation. In addition, it can also suppress the GeO 2 degradation. The electrical measurements show that capacitance equivalent thickness of 1.53 nm and a leakage current density of 2.1 × 10 -3 A/cm 2 at gate bias of V fb  + 1 V was obtained for the annealed sample. The conduction (valence) band offsets at the HfO 2 /SiO 2 /Ge interface with and without PDA are found to be 2.24 (2.69) and 2.48 (2.45) eV, respectively. These results indicate that in situ PEALD SiO 2 may be a promising interfacial control layer for the realization of high-quality Ge-based transistor devices. Moreover, it can be demonstrated that PEALD is a much more powerful technology for ultrathin interfacial control layer deposition than MOCVD.

Silicon homo-heterojunction solar cells: A promising candidate to realize high performance more stably

NASA Astrophysics Data System (ADS)

Tan, Miao; Zhong, Sihua; Wang, Wenjie; Shen, Wenzhong

2017-08-01

We have investigated the influences of diverse physical parameters on the performances of a silicon homo-heterojunction (H-H) solar cell, which encompasses both homojunction and heterojunction, together with their underlying mechanisms by the aid of AFORS-HET simulation. It is found that the performances of H-H solar cell are less sensitive to (i) the work function of the transparent conductive oxide layer, (ii) the interfacial density of states at the front hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) interface, (iii) the peak dangling bond defect densities within the p-type a-Si:H (p-a-Si:H) layer, and (iv) the doping concentration of the p-a-Si:H layer, when compared to that of the conventional heterojunction with intrinsic thin layer (HIT) counterparts. These advantages are due to the fact that the interfacial recombination and the recombination within the a-Si:H region are less affected by all the above parameters, which fundamentally benefit from the field-effect passivation of the homojunction. Therefore, the design of H-H structure can provide an opportunity to produce high-efficiency solar cells more stably.

Preparation and Characterisation of Linear Low-Density Polyethylene / Thermoplastic Starch Blends Filled with Banana Fibre

NASA Astrophysics Data System (ADS)

Kahar, A. W. M.; Ann, L. Ju

2017-06-01

In this study, the influence of banana fibre (BF) loading using sodium hydroxide (NaOH) pre-treated and succinic anhydride-treated (SA) BF on the mechanical properties of linear low-density polyethylene (LLDPE)/thermoplastic starch (TPS) matrix is investigated. LLDPE/TPS/BF composites were developed under different BF conditions, with and without chemical modifications with the BF content ranging from 5% to 30% based on the total composite. The tensile strength showed an increase with an increase of fibre content up to 10%, thereby decreasing gradually beyond this level. NaOH pre-treated and SA treated BF added with LLDPE/TPS composite displays a higher tensile strength as compared to untreated BF in LLDPE/TPS composites. Thermal behaviour of the BF incorporated in LLDPE/TPS composite was characterised using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). This showed that SA treated BF exhibits better thermal stability, compared to other composites. This is because of the improvement in interfacial adhesion existing between both the fibre and matrix. In addition, a morphology study confirmed that pre-treated and treated BF had excellent interfacial adhesion with LLDPE/TPS matrix, leading to better mechanical properties of resultant composites.

Atomic Layer Deposition of Stable LiAlF4 Lithium Ion Conductive Interfacial Layer for Stable Cathode Cycling.

PubMed

Xie, Jin; Sendek, Austin D; Cubuk, Ekin D; Zhang, Xiaokun; Lu, Zhiyi; Gong, Yongji; Wu, Tong; Shi, Feifei; Liu, Wei; Reed, Evan J; Cui, Yi

2017-07-25

Modern lithium ion batteries are often desired to operate at a wide electrochemical window to maximize energy densities. While pushing the limit of cutoff potentials allows batteries to provide greater energy densities with enhanced specific capacities and higher voltage outputs, it raises key challenges with thermodynamic and kinetic stability in the battery. This is especially true for layered lithium transition-metal oxides, where capacities can improve but stabilities are compromised as wider electrochemical windows are applied. To overcome the above-mentioned challenges, we used atomic layer deposition to develop a LiAlF 4 solid thin film with robust stability and satisfactory ion conductivity, which is superior to commonly used LiF and AlF 3 . With a predicted stable electrochemical window of approximately 2.0 ± 0.9 to 5.7 ± 0.7 V vs Li + /Li for LiAlF 4 , excellent stability was achieved for high Ni content LiNi 0.8 Mn 0.1 Co 0.1 O 2 electrodes with LiAlF 4 interfacial layer at a wide electrochemical window of 2.75-4.50 V vs Li + /Li.

In-situ probing of coupled atomic restructuring and metallicity of oxide heterointerfaces induced by polar adsorbates

NASA Astrophysics Data System (ADS)

Ryu, S.; Zhou, H.; Paudel, T. R.; Irwin, J.; Podkaminer, J. P.; Bark, C. W.; Lee, D.; Kim, T. H.; Fong, D. D.; Rzchowski, M. S.; Tsymbal, E. Y.; Eom, C. B.

2017-10-01

Microscopic understanding of the surface-controlled conductivity of the two dimensional electron gas at complex oxide interfaces is crucial for developing functional interfaces. We observe conductivity and structural modification using in-situ synchrotron surface x-ray diffraction as the surface of a model LaAlO3/SrTiO3 (001) heterostructure is changed by polar adsorbates. We find that polar adsorbate-induced interfacial metallicity reduces polar distortions in the LaAlO3 layer. First-principles density functional theory calculations show that surface dipoles introduced by polar adsorbates lead to additional charge transfer and the reduction of polar displacements in the LaAlO3 layer, consistent with the experimental observations. Our study supports that internal structural deformations controlling functionalities can be driven without the application of direct electrical or thermal bias and offers a route to tuning interfacial properties. These results also highlight the important role of in-situ x-ray scattering with atomic resolution in capturing and exploring structural distortions and charge density changes caused by external perturbations such as chemical adsorption, redox reaction, and generation and/or annihilation of surface defects.

Building Organic/Inorganic Hybrid Interphases for Fast Interfacial Transport in Rechargeable Metal Batteries.

PubMed

Zhao, Qing; Tu, Zhengyuan; Wei, Shuya; Zhang, Kaihang; Choudhury, Snehashis; Liu, Xiaotun; Archer, Lynden A

2018-01-22

We report a facile in situ synthesis that utilizes readily accessible SiCl 4 cross-linking chemistry to create durable hybrid solid-electrolyte interphases (SEIs) on metal anodes. Such hybrid SEIs composed of Si-interlinked OOCOR molecules that host LiCl salt exhibit fast charge-transfer kinetics and as much as five-times higher exchange current densities, in comparison to their spontaneously formed analogues. Electrochemical analysis and direct optical visualization of Li and Na deposition in symmetric Li/Li and Na/Na cells show that the hybrid SEI provides excellent morphological control at high current densities (3-5 mA cm -2 ) for Li and even for notoriously unstable Na metal anodes. The fast interfacial transport attributes of the SEI are also found to be beneficial for Li-S cells and stable electrochemical cycling was achieved in galvanostatic studies at rates as high as 2 C. Our work therefore provides a promising approach towards rational design of multifunctional, elastic SEIs that overcome the most serious limitations of spontaneously formed interphases on high-capacity metal anodes. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Parameterization of an interfacial force field for accurate representation of peptide adsorption free energy on high-density polyethylene

PubMed Central

Abramyan, Tigran M.; Snyder, James A.; Yancey, Jeremy A.; Thyparambil, Aby A.; Wei, Yang; Stuart, Steven J.; Latour, Robert A.

2015-01-01

Interfacial force field (IFF) parameters for use with the CHARMM force field have been developed for interactions between peptides and high-density polyethylene (HDPE). Parameterization of the IFF was performed to achieve agreement between experimental and calculated adsorption free energies of small TGTG–X–GTGT host–guest peptides (T = threonine, G = glycine, and X = variable amino-acid residue) on HDPE, with ±0.5 kcal/mol agreement. This IFF parameter set consists of tuned nonbonded parameters (i.e., partial charges and Lennard–Jones parameters) for use with an in-house-modified CHARMM molecular dynamic program that enables the use of an independent set of force field parameters to control molecular behavior at a solid–liquid interface. The R correlation coefficient between the simulated and experimental peptide adsorption free energies increased from 0.00 for the standard CHARMM force field parameters to 0.88 for the tuned IFF parameters. Subsequent studies are planned to apply the tuned IFF parameter set for the simulation of protein adsorption behavior on an HDPE surface for comparison with experimental values of adsorbed protein orientation and conformation. PMID:25818122

A mean-density model of ionic surfactants for the dispersion of carbon nanotubes in aqueous solutions

NASA Astrophysics Data System (ADS)

Joung, Young Soo

2018-05-01

We propose a new analytical model of ionic surfactants used for the dispersion of carbon nanotubes (CNTs) in aqueous solutions. Although ionic surfactants are commonly used to facilitate the dispersion of CNTs in aqueous solutions, understanding the dispersion process is challenging and time-consuming owing to its complexity and nonlinearity. In this work, we develop a mean-density model of ionic surfactants to simplify the calculation of interaction forces between CNTs stabilized by ionic surfactants. Using this model, we can evaluate various interaction forces between the CNTs and ionic surfactants under different conditions. The dispersion mechanism is investigated by estimating the potential of mean force (PMF) as a function of van der Waals forces, electrostatic forces, interfacial tension, and osmotic pressure. To verify the proposed model, we compare the PMFs derived using our method with those derived from molecular dynamics simulations using comparable CNTs and ionic surfactants. Notably, for stable dispersions, the osmotic pressure and interfacial energy are important for long-range and short-range interactions, respectively, in comparison with the effect of electrostatic forces. Our model effectively prescribes specific surfactants and their concentrations to achieve stable aqueous suspensions of CNTs.

In-situ probing of coupled atomic restructuring and metallicity of oxide heterointerfaces induced by polar adsorbates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, S.; Zhou, H.; Paudel, T. R.

Microscopic understanding of the surface-controlled conductivity of the two dimensional electron gas at complex oxide interfaces is crucial for developing functional interfaces. We observe conductivity and structural modification using in-situ synchrotron surface x-ray diffraction as the surface of a model LaAlO3/SrTiO3 (001) heterostructure is changed by polar adsorbates. We find that polar adsorbate-induced interfacial metallicity reduces polar distortions in the LaAlO3 layer. First-principles density functional theory calculations show that surface dipoles introduced by polar adsorbates lead to additional charge transfer and the reduction of polar displacements in the LaAlO3 layer, consistent with the experimental observations. Our study supports that internalmore » structural deformations controlling functionalities can be driven without the application of direct electrical or thermal bias and offers a route to tuning interfacial properties. These results also highlight the important role of in-situ x-ray scattering with atomic resolution in capturing and exploring structural distortions and charge density changes caused by external perturbations such as chemical adsorption, redox reaction, and generation and/or annihilation of surface defects.« less

Interfacial characteristics and leakage current transfer mechanisms in organometal trihalide perovskite gate-controlled devices via doping of PCBM

NASA Astrophysics Data System (ADS)

Wang, Yucheng; Zhang, Yuming; Liu, Yintao; Pang, Tiqiang; Hu, Ziyang; Zhu, Yuejin; Luan, Suzhen; Jia, Renxu

2017-11-01

Two types of perovskite (with and without doping of PCBM) based metal-oxide-semiconductor (MOS) gate-controlled devices were fabricated and characterized. The study of the interfacial characteristics and charge transfer mechanisms by doping of PCBM were analyzed by material and electrical measurements. Doping of PCBM does not affect the size and crystallinity of perovskite films, but has an impact on carrier extraction in perovskite MOS devices. The electrical hysteresis observed in capacitance-voltage and current-voltage measurements can be alleviated by doping of PCBM. Experimental results demonstrate that extremely low trap densities are found for the perovskite device without doping, while the doped sample leads to higher density of interface state. Three mechanisms including Ohm’s law, trap-filled-limit (TFL) emission, and child’s law were used to analyze possible charge transfer mechanisms. Ohm’s law mechanism is well suitable for charge transfer of both the perovskite MOS devices under light condition at large voltage, while TFL emission well addresses the behavior of charge transfer under dark at small voltage. This change of charge transfer mechanism is attributed to the impact of the ion drift within perovskites.

High efficiency low cost thin film silicon solar cell design and method for making

DOEpatents

Sopori, B.L.

1999-04-27

A semiconductor device is described having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer. 9 figs.

Design of exceptionally strong and conductive Cu alloys beyond the conventional speculation via the interfacial energy-controlled dispersion of γ-Al2O3 nanoparticles

PubMed Central

Zeon Han, Seung; Kim, Kwang Ho; Kang, Joonhee; Joh, Hongrae; Kim, Sang Min; Ahn, Jee Hyuk; Lee, Jehyun; Lim, Sung Hwan; Han, Byungchan

2015-01-01

The development of Cu-based alloys with high-mechanical properties (strength, ductility) and electrical conductivity plays a key role over a wide range of industrial applications. Successful design of the materials, however, has been rare due to the improvement of mutually exclusive properties as conventionally speculated. In this paper, we demonstrate that these contradictory material properties can be improved simultaneously if the interfacial energies of heterogeneous interfaces are carefully controlled. We uniformly disperse γ-Al2O3 nanoparticles over Cu matrix, and then we controlled atomic level morphology of the interface γ-Al2O3//Cu by adding Ti solutes. It is shown that the Ti dramatically drives the interfacial phase transformation from very irregular to homogeneous spherical morphologies resulting in substantial enhancement of the mechanical property of Cu matrix. Furthermore, the Ti removes impurities (O and Al) in the Cu matrix by forming oxides leading to recovery of the electrical conductivity of pure Cu. We validate experimental results using TEM and EDX combined with first-principles density functional theory (DFT) calculations, which all consistently poise that our materials are suitable for industrial applications. PMID:26616045

Design of exceptionally strong and conductive Cu alloys beyond the conventional speculation via the interfacial energy-controlled dispersion of γ-Al2O3 nanoparticles.

PubMed

Han, Seung Zeon; Kim, Kwang Ho; Kang, Joonhee; Joh, Hongrae; Kim, Sang Min; Ahn, Jee Hyuk; Lee, Jehyun; Lim, Sung Hwan; Han, Byungchan

2015-11-30

The development of Cu-based alloys with high-mechanical properties (strength, ductility) and electrical conductivity plays a key role over a wide range of industrial applications. Successful design of the materials, however, has been rare due to the improvement of mutually exclusive properties as conventionally speculated. In this paper, we demonstrate that these contradictory material properties can be improved simultaneously if the interfacial energies of heterogeneous interfaces are carefully controlled. We uniformly disperse γ-Al2O3 nanoparticles over Cu matrix, and then we controlled atomic level morphology of the interface γ-Al2O3//Cu by adding Ti solutes. It is shown that the Ti dramatically drives the interfacial phase transformation from very irregular to homogeneous spherical morphologies resulting in substantial enhancement of the mechanical property of Cu matrix. Furthermore, the Ti removes impurities (O and Al) in the Cu matrix by forming oxides leading to recovery of the electrical conductivity of pure Cu. We validate experimental results using TEM and EDX combined with first-principles density functional theory (DFT) calculations, which all consistently poise that our materials are suitable for industrial applications.

Molecular-Scale Study of Aspartate Adsorption on Goethite and Competition with Phosphate.

PubMed

Yang, Yanli; Wang, Shengrui; Xu, Yisheng; Zheng, Binghui; Liu, Jingyang

2016-03-15

Knowledge of the interfacial interactions between aspartate and minerals, especially its competition with phosphate, is critical to understanding the fate and transport of amino acids in the environment. Adsorption reactions play important roles in the mobility, bioavailability, and degradation of aspartate and phosphate. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) measurements and density functional theory (DFT) calculations were used to investigate the interfacial structures and their relative contributions in single-adsorbate and competition systems. Our results suggest three dominant mechanisms for aspartate: bidentate inner-sphere coordination involving both α- and γ-COO(-), outer-sphere complexation via electrostatic attraction and H-bonding between aspartate NH2 and goethite surface hydroxyls. The interfacial aspartate is mainly governed by pH and is less sensitive to changes of ionic strength and aspartate concentration. The phosphate competition significantly reduces the adsorption capacity of aspartate on goethite. Whereas phosphate adsorption is less affected by the presence of aspartate, including the relative contributions of diprotonated monodentate, monoprotonated bidentate, and nonprotonated bidentate structures. The adsorption process facilitates the removal of bioavailable aspartate and phosphate from the soil solution as well as from the sediment pore water and the overlying water.

Nanoporous Mo2C functionalized 3D carbon architecture anode for boosting flavins mediated interfacial bioelectrocatalysis in microbial fuel cells

NASA Astrophysics Data System (ADS)

Zou, Long; Lu, Zhisong; Huang, Yunhong; Long, Zhong-er; Qiao, Yan

2017-08-01

An efficient microbial electrocatalysis in microbial fuel cells (MFCs) needs both high loading of microbes (biocatalysts) and robust interfacial electron transfer from microbes to electrode. Herein a nanoporous molybdenum carbide (Mo2C) functionalized carbon felt electrode with rich 3D hierarchical porous architecture is applied as MFC anode to achieve superior electrocatalytic performance. The nanoporous Mo2C functionalized anode exhibits strikingly improved microbial electrocatalysis in MFCs with 5-fold higher power density and long-term stability of electricity production. The great enhancement is attributed to the introduction of rough Mo2C nanostructural interface into macroporous carbon architecture for promoting microbial growth with great excretion of endogenous electron shuttles (flavins) and rich available nanopores for enlarging electrochemically active surface area. Importantly, the nanoporous Mo2C functionalized anode is revealed for the first time to have unique electrocatalytic activity towards redox reaction of flavins with more negative redox potential, indicating a more favourable thermodynamic driving force for anodic electron transfer. This work not only provides a promising electrode for high performance MFCs but also brings up a new insight into the effect of nanostructured materials on interfacial bioelectrocatalysis.

A computational DFT study of structural transitions in textured solid-fluid interfaces

NASA Astrophysics Data System (ADS)

Yatsyshin, Petr; Parry, Andrew O.; Kalliadasis, Serafim

2015-11-01

Fluids adsorbed at walls, in capillary pores and slits, and in more exotic, sculpted geometries such as grooves and wedges can exhibit many new phase transitions, including wetting, pre-wetting, capillary-condensation and filling, compared to their bulk counterparts. As well as being of fundamental interest to the modern statistical mechanical theory of inhomogeneous fluids, these are also relevant to nanofluidics, chemical- and bioengineering. In this talk we will show using a microscopic Density Functional Theory (DFT) for fluids how novel, continuous, interfacial transitions associated with the first-order prewetting line, can occur on steps, in grooves and in wedges, that are sensitive to both the range of the intermolecular forces and interfacial fluctuation effects. These transitions compete with wetting, filling and condensation producing very rich phase diagrams even for relatively simple geometries. We will also discuss practical aspects of DFT calculations, and demonstrate how this statistical-mechanical framework is capable of yielding complex fluid structure, interfacial tensions, and regions of thermodynamic stability of various fluid configurations. As a side note, this demonstrates that DFT is an excellent tool for the investigations of complex multiphase systems. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031.

Effect of surface microstructure on electrochemical performance of garnet solid electrolytes.

PubMed

Cheng, Lei; Chen, Wei; Kunz, Martin; Persson, Kristin; Tamura, Nobumichi; Chen, Guoying; Doeff, Marca

2015-01-28

Cubic garnet phases based on Al-substituted Li7La3Zr2O12 (LLZO) have high ionic conductivities and exhibit good stability versus metallic lithium, making them of particular interest for use in next-generation rechargeable battery systems. However, high interfacial impedances have precluded their successful utilization in such devices until the present. Careful engineering of the surface microstructure, especially the grain boundaries, is critical to achieving low interfacial resistances and enabling long-term stable cycling with lithium metal. This study presents the fabrication of LLZO heterostructured solid electrolytes, which allowed direct correlation of surface microstructure with the electrochemical characteristics of the interface. Grain orientations and grain boundary distributions of samples with differing microstructures were mapped using high-resolution synchrotron polychromatic X-ray Laue microdiffraction. The electrochemical characteristics are strongly dependent upon surface microstructure, with small grained samples exhibiting much lower interfacial resistances and better cycling behavior than those with larger grain sizes. Low area specific resistances of 37 Ω cm(2) were achieved; low enough to ensure stable cycling with minimal polarization losses, thus removing a significant obstacle toward practical implementation of solid electrolytes in high energy density batteries.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Jacob W.; Lam, Royce K.; Saykally, Richard J., E-mail: saykally@berkeley.edu

Nitrate and nitrite ions are of considerable interest, both for their widespread use in commercial and research contexts and because of their central role in the global nitrogen cycle. The chemistry of atmospheric aerosols, wherein nitrate is abundant, has been found to depend on the interfacial behavior of ionic species. The interfacial behavior of ions is determined largely by their hydration properties; consequently, the study of the hydration and interfacial behavior of nitrate and nitrite comprises a significant field of study. In this work, we describe the study of aqueous solutions of sodium nitrate and nitrite via X-ray absorption spectroscopymore » (XAS), interpreted in light of first-principles density functional theory electronic structure calculations. Experimental and calculated spectra of the nitrogen K-edge XA spectra of bulk solutions exhibit a large 3.7 eV shift between the XA spectra of nitrate and nitrite resulting from greater stabilization of the nitrogen 1s energy level in nitrate. A similar shift is not observed in the oxygen K-edge XA spectra of NO{sub 3}{sup −} and NO{sub 2}{sup −}. The hydration properties of nitrate and nitrite are found to be similar, with both anions exhibiting a similar propensity towards ion pairing.« less

Insights into electrode/electrolyte interfacial processes and the effect of nanostructured cobalt oxides loading on graphene-based hybrids by scanning electrochemical microscopy

NASA Astrophysics Data System (ADS)

Gupta, Sanju; Carrizosa, Sara B.

2016-12-01

Nanostructured cobalt oxide polymorphs (CoO and Co3O4) deposited via electrodeposition allowed optimal loading on supercapacitive graphene nanosheets producing a set of graphene-based hybrids namely, CoO/GO, CoO/ErGO, Co3O4/GO, Co3O4/rGO, and Co3O4/ErGO, as pseudocapacitive electrochemical electrodes. We gained fundamental insights into the complex physicochemical interfacial processes at electrode surfaces and electrode/electrolyte (or solid/liquid) interfaces by scanning electrochemical microscopy operating in the feedback probe approach and imaging modes while monitoring and mapping the redox probe (re)activity behavior. We determined the various experimental descriptors including diffusion coefficient, electron transfer rate, and electroactive site distribution on electrodes. We emphasize the interplay of (1) heterogeneous basal and edge plane active sites, (2) graphene surface functional moieties (conducting/semiconducting), and (3) crystalline spinel cobalt oxides (semiconducting/insulating) coated graphene, reinforcing the available electron density of states in the vicinity of the Fermi level contributing to higher electroactivity, faster interfacial diffusion, and shorter distances for electron transfer, facilitated through molecular and chemical bridges obtained by electrodeposition as compared with the physical deposition.

Smoothed Particle Hydrodynamics: A consistent model for interfacial multiphase fluid flow simulations

NASA Astrophysics Data System (ADS)

Krimi, Abdelkader; Rezoug, Mehdi; Khelladi, Sofiane; Nogueira, Xesús; Deligant, Michael; Ramírez, Luis

2018-04-01

In this work, a consistent Smoothed Particle Hydrodynamics (SPH) model to deal with interfacial multiphase fluid flows simulation is proposed. A modification to the Continuum Stress Surface formulation (CSS) [1] to enhance the stability near the fluid interface is developed in the framework of the SPH method. A non-conservative first-order consistency operator is used to compute the divergence of stress surface tensor. This formulation benefits of all the advantages of the one proposed by Adami et al. [2] and, in addition, it can be applied to more than two phases fluid flow simulations. Moreover, the generalized wall boundary conditions [3] are modified in order to be well adapted to multiphase fluid flows with different density and viscosity. In order to allow the application of this technique to wall-bounded multiphase flows, a modification of generalized wall boundary conditions is presented here for using the SPH method. In this work we also present a particle redistribution strategy as an extension of the damping technique presented in [3] to smooth the initial transient phase of gravitational multiphase fluid flow simulations. Several computational tests are investigated to show the accuracy, convergence and applicability of the proposed SPH interfacial multiphase model.

Topographically induced internal solitary waves in a pycnocline: Ultrasonic probes and stereo-correlation measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dossmann, Yvan, E-mail: yvan.dossmann@anu.edu.au; CNRM-GAME, UMR3589 METEO-FRANCE and CNRS, 42 avenue Gaspard Coriolis, 31057 Toulouse Cedex 01; Laboratoire d’Aérologie, 14 avenue Edouard Belin, 31400 Toulouse

Internal solitary waves (ISWs) are large amplitude stable waves propagating in regions of high density gradients such as the ocean pycnocline. Their dynamics has often been investigated in two-dimensional approaches, however, their three-dimensional evolution is still poorly known. Experiments have been conducted in the large stratified water tank of CNRM-GAME to study the generation of ISWs in two academic configurations inspired by oceanic regimes. First, ultrasonic probes are used to measure the interfacial displacement in the two configurations. In the primary generation case for which the two layers are of constant density, the generation of ISWs is investigated in twomore » series of experiments with varying amplitude and forcing frequency. In the secondary generation case for which the lower layer is stratified, the generation of ISWs from the impact of an internal wave beam on the pycnocline and their subsequent dynamics is studied. The dynamics of ISWs in these two regimes accords well with analytical approaches and numerical simulations performed in analogous configurations. Then, recent developments of a stereo correlation technique are used to describe the three-dimensional structure of propagating ISWs. In the primary generation configuration, small transverse effects are observed in the course of the ISW propagation. In the secondary generation configuration, larger transverse structures are observed in the interfacial waves dynamics. The interaction between interfacial troughs and internal waves propagating in the lower stratified layer are a possible cause for the generation of these structures. The magnitude of these transverse structures is quantified with a nondimensional parameter in the two configurations. They are twice as large in the secondary generation case as in the primary generation case.« less

Nano scale dynamics of bubble nucleation in confined liquid subjected to rapid cooling: Effect of solid-liquid interfacial wettability

NASA Astrophysics Data System (ADS)

Hasan, Mohammad Nasim; Rabbi, Kazi Fazle; Mukut, K. M.; Tamim, Saiful Islam; Faisal, A. H. M.

2017-06-01

This study focuses on the occurrence of bubble nucleation in a liquid confined in a nano scale confinement and subjected to rapid cooling at one of its wall. Due to the very small size scale of the present problem, we adopt the molecular dynamics (MD) approach. The liquid (Argon) is confined within two solid (Platinum) walls. The temperature of the upper wall of the confinement is maintained at 90 K while the lower wall is being cooled rapidly to 50 K from initial equilibrium temperature of 90 K within 0.1 ns. This results in the nucleation and formation of nanobubbles in the liquid. The pattern of bubble nucleation has been studied for three different conditions of solid-liquid interfacial wettability such as hydrophilic, hydrophobic and neutral. Behavior of bubble nucleation is significantly different in the three case of solid-liquid interfacial wettability. In case of the hydrophobic confinement (weakly adsorbing), the liquid cannot achieve deeper metastability; vapor layers appear immediately on the walls. In case of the neutral confinement (moderately adsorbing), bubble nucleation is promoted by the walls where the nucleation is heterogeneous. In case of the hydrophilic walls (strongly adsorbing) bubbles are developed inside the liquid; that is the nucleation process is homogeneous. The variation in bubble nucleation under different conditions of surface wettability has been studied by the analysis of number density distribution, spatial temperature distribution, spatial number density distribution and heat flux through the upper and lower walls of the confinement. The present study indicates that the variation of heat transfer efficiency due to different surface wettability has significant effect on the size, shape and location of bubble nucleation in case rapid cooling of liquid in nano confinement.

The Role of Interfacial Electronic Properties on Phonon Transport in Two-Dimensional MoS 2 on Metal Substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Zhequan; Chen, Liang; Yoon, Mina

2016-11-08

In this paper, we investigate the role of interfacial electronic properties on the phonon transport in two-dimensional MoS 2 adsorbed on metal substrates (Au and Sc) using first-principles density functional theory and the atomistic Green’s function method. Our study reveals that the different degree of orbital hybridization and electronic charge distribution between MoS 2 and metal substrates play a significant role in determining the overall phonon–phonon coupling and phonon transmission. The charge transfer caused by the adsorption of MoS 2 on Sc substrate can significantly weaken the Mo–S bond strength and change the phonon properties of MoS 2, which resultmore » in a significant change in thermal boundary conductance (TBC) from one lattice-stacking configuration to another for same metallic substrate. In a lattice-stacking configuration of MoS 2/Sc, weakening of the Mo–S bond strength due to charge redistribution results in decrease in the force constant between Mo and S atoms and substantial redistribution of phonon density of states to low-frequency region which affects overall phonon transmission leading to 60% decrease in TBC compared to another configuration of MoS 2/Sc. Strong chemical coupling between MoS 2 and the Sc substrate leads to a significantly (~19 times) higher TBC than that of the weakly bound MoS 2/Au system. Our findings demonstrate the inherent connection among the interfacial electronic structure, the phonon distribution, and TBC, which helps us understand the mechanism of phonon transport at the MoS 2/metal interfaces. Finally, the results provide insights for the future design of MoS 2-based electronics and a way of enhancing heat dissipation at the interfaces of MoS 2-based nanoelectronic devices.« less

DFT calculations of strain and interface effects on electronic structures and magnetic properties of L10-FePt/Ag heterojunction of GMR applications

NASA Astrophysics Data System (ADS)

Pramchu, Sittichain; Jaroenjittichai, Atchara Punya; Laosiritaworn, Yongyut

2018-03-01

In this work, density functional theory (DFT) was employed to investigate the effect of strain and interface on electronic structures and magnetic properties of L10-FePt/Ag heterojunction. Two possible interface structures of L10-FePt(001)/Ag(001), that is, interface between Fe and Ag layers (Fe/Ag) and between Pt and Ag layers (Pt/Ag), were inspected. It was found that Pt/Ag interface is more stable than Fe/Ag interface due to its lower formation energy. Further, under the lattice mismatch induced tensile strain, the enhancement of magnetism for both Fe/Ag and Pt/Ag interface structures has been found to have progressed, though the magnetic moments of "interfacial" Fe and Pt atoms have been found to have decreased. To explain this further, the local density of states (LDOS) analysis suggests that interaction between Fe (Pt) and Ag near Fe/Ag (Pt/Ag) interface leads to spin symmetry breaking of the Ag atom and hence induces magnetism magnitude. In contrast, the magnetic moments of interfacial Fe and Pt atoms reduce because of the increase in the electronic states near the Fermi level of the minority-spin electrons. In addition, the significant enhancements of the LDOS near the Fermi levels of the minority-spin electrons signify the boosting of the transport properties of the minority-spin electrons and hence the spin-dependent electron transport at this ferromagnet/metal interface. From this work, it is expected that this clarification of the interfacial magnetism may inspire new innovation on how to improve spin-dependent electron transport for enhancing the giant magnetoresistance (GMR) ratio of potential GMR-based spintronic devices.

Mechanism of phosphorus passivation of near-interface oxide traps in 4H–SiC MOS devices investigated by CCDLTS and DFT calculation

NASA Astrophysics Data System (ADS)

Jayawardena, Asanka; Shen, X.; Mooney, P. M.; Dhar, Sarit

2018-06-01

Interfacial charge trapping in 4H–SiC MOS capacitors with P doped SiO2 or phospho-silicate glass (PSG) as a gate dielectric has been investigated with temperature dependent capacitance–voltage measurements and constant capacitance deep level transient spectroscopy (CCDLTS) measurements. The measurements indicate that P doping in the dielectric results in significant reduction of near-interface electron traps that have energy levels within 0.5 eV of the 4H–SiC conduction band edge. Extracted trap densities confirm that the phosphorus induced near-interface trap reduction is significantly more effective than interfacial nitridation, which is typically used for 4H–SiC MOSFET processing. The CCDLTS measurements reveal that the two broad near-interface trap peaks, named ‘O1’ and ‘O2’, with activation energies around 0.15 eV and 0.4 eV below the 4H–SiC conduction band that are typically observed in thermal oxides on 4H–SiC, are also present in PSG devices. Previous atomic scale ab initio calculations suggested these O1 and O2 traps to be carbon dimers substituted for oxygen dimers (CO=CO) and interstitial Si (Sii) in SiO2, respectively. Theoretical considerations in this work suggest that the presence of P in the near-interfacial region reduces the stability of the CO=CO defects and reduces the density of Sii defects through the network restructuring. Qualitative comparison of results in this work and reported work suggest that the O1 and O2 traps in SiO2/4H–SiC MOS system negatively impact channel mobility in 4H–SiC MOSFETs.

Nanoscopic diffusion studies on III-V compound semiconductor structures: Experiment and theory

NASA Astrophysics Data System (ADS)

Gonzalez Debs, Mariam

The electronic structure of multilayer semiconductor heterostructures is affected by the detailed compositional profiles throughout the structure and at critical interfaces. The extent of interdiffusion across these interfaces places limits on both the processing time and temperatures for many applications based on the resultant compositional profile and associated electronic structure. Atomic and phenomenological methods were used in this work through the combination of experiment and theory to understand the nanoscopic mechanisms in complex heterostructures. Two principal studies were conducted. Tin diffusion in GaAs was studied by fitting complex experimental diffusion profiles to a phenomenological model which involved the diffusion of substitutional and interstitial dopant atoms. A methodology was developed combining both the atomistic model and the use of key features within these experimentally-obtained diffusion profiles to determine meaningful values of the transport and defect reaction rate parameters. Interdiffusion across AlSb/GaSb multi-quantum well interfaces was also studied. The chemical diffusion coefficient characterizing the AlSb/GaSb diffusion couple was quantitatively determined by fitting the observed photoluminescence (PL) peak shifts to the solution of the Schrodinger equation using a potential derived from the solution of the diffusion equation to quantify the interband transition energy shifts. First-principles calculations implementing Density Functional Theory were performed to study the thermochemistry of point defects as a function of local environment, allowing a direct comparison of interfacial and bulk diffusion phenomena within these nanoscopic structures. Significant differences were observed in the Ga and Al vacancy formation energies at the AlSb/GaSb interface when compared to bulk AlSb and GaSb with the largest change found for Al vacancies. The AlSb/GaSb structures were further studied using positron annihilation spectroscopy (PAS) to investigate the role of vacancies in the interdiffusion of Al and Ga in the superlattices. The PL and PAS experimental techniques together with the phenomenological and atomistic modeling allowed for the determination of the underlying mass transport mechanisms at the nanoscale.

Interfacial reactions and wetting in Al-Mg sintered by powder metallurgy process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faisal, Heny, E-mail: faisal@physics.its.ac.id; Darminto,; Triwikantoro,

2016-04-19

Was conducted to analyze the effect of temperature variation on the bonding interface sintered composite Al-Mg and analyze the effect of variations of the density and hardness sinter. Research carried out by the base material powders of Al, Mg powder and solvent n-butanol. The method used in this study is a powder metallurgy, with a composition of 60% volume fraction of Al - 40% Mg. Al-Mg mixing with n-butanol for 1 hour at 500 rpm. Then the emphasis (cold comression) with a size of 1.4 cm in diameter dies and height of 2.8 cm, is pressed with a force of 20 MPa and heldmore » for 15 minutes. After the sample into pellets, then sintered at various temperatures 300 °C, 350 °C, 400 °C and 450 °C. Characterization is done by using the testing green density, sintered density, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), vickers microhardness, and press test. XRD data analysis done by using X’Pert High Score Plus (HSP) to determine whether there is a new phase is formed. Test results show that the sintered density increasing sintering temperature, the resulting density is also increasing (shrinkage). However, at a temperature of 450 °C decreased (swelling). With the increased sinter density, interfacial bonding getting Kuta and more compact so that its hardness is also increased. From the test results of SEM / EDX, there Mg into Al in the border area. At temperatures of 300 °C, 350 °C, 400 °C, the phase formed is Al, Mg and MgO. While phase is formed at a temperature of 450 °C is aluminum magnesium (Al{sub 3}Mg{sub 2}), Aluminum Magnesium Zinc (AlMg{sub 2}Zn).« less

The virialization density of peaks with general density profiles under spherical collapse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rubin, Douglas; Loeb, Abraham, E-mail: dsrubin@physics.harvard.edu, E-mail: aloeb@cfa.harvard.edu

2013-12-01

We calculate the non-linear virialization density, Δ{sub c}, of halos under spherical collapse from peaks with an arbitrary initial and final density profile. This is in contrast to the standard calculation of Δ{sub c} which assumes top-hat profiles. Given our formalism, the non-linear halo density can be calculated once the shape of the initial peak's density profile and the shape of the virialized halo's profile are provided. We solve for Δ{sub c} for halos in an Einstein de-Sitter and a ΛCDM universe. As examples, we consider power-law initial profiles as well as spherically averaged peak profiles calculated from the statisticsmore » of a Gaussian random field. We find that, depending on the profiles used, Δ{sub c} is smaller by a factor of a few to as much as a factor of 10 as compared to the density given by the standard calculation ( ≈ 200). Using our results, we show that, for halo finding algorithms that identify halos through an over-density threshold, the halo mass function measured from cosmological simulations can be enhanced at all halo masses by a factor of a few. This difference could be important when using numerical simulations to assess the validity of analytic models of the halo mass function.« less

Comprehensive numerical methodology for direct numerical simulations of compressible Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reckinger, Scott James; Livescu, Daniel; Vasilyev, Oleg V.

A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.

Effects of Mean Flow Profiles on the Instability of a Low-Density Gas Jet Injected into a High-Density Gas

NASA Technical Reports Server (NTRS)

Vedantam, NandaKishore; Parthasarathy, Ramkumar N.

2004-01-01

The effects of the mean velocity profiles on the instability characteristics in the near-injector region of axisymmetric low density gas jets injected vertically upwards into a high-density gas medium were investigated using linear inviscid stability analysis. The flow was assumed to be isothermal and locally parallel. Three velocity profiles, signifying different changes in the mean velocity in the shear layer, were used in the analysis. The effects of the inhomogeneous shear layer and the Froude number (signifying the effects of gravity) on the instability for each set of mean profiles were delineated. At a large Froude number (negligible gravity), a critical density ratio was found for the three profiles at which the jet became absolutely unstable. The critical density ratio for each velocity profile was increased as the Froude number was reduced. A critical Froude number was found for the three sets of profiles, below which the jet was absolutely unstable for all the density ratios less than unity, which demarcated the jet flow into the momentum-driven regime and the buoyancy-driven regime.

Molecular Dynamics Simulations of Ion-Doped Microphase Separated Diblock Copolymers

NASA Astrophysics Data System (ADS)

Seo, Youngmi; Brown, Jonathan R.; Hall, Lisa M.

The effects of ion doping on microphase separated block copolymers are crucial to understand for transport applications such as battery electrolytes or fuel cell membranes. Prior experiments and theories have observed interesting trends, e.g. ions generally increase effective χ, broaden the domain interface at high loadings, and significantly change the order-to-disorder transition point. To provide a molecular level understanding of these trends and further information about ion dynamics, in this study, we perform molecular dynamics (MD) simulations using a generic coarse-grained model. We capture the selective ion solvation in one polymer microphase by adding an 1/r4 term to the intermolecular potential to account for the charge induced dipole effect between cations and A monomers. The model was validated by comparing with experimental domain spacing and density profile results. We find that as ions are added, the lamellar interface becomes sharper at first, then broadens with further ion loading, and finally forms a cylindrical morphology. We also observe that the interfacial broadening is retarded as the associative interaction between cations and A monomers or the ion-ion interaction strength is increased. These observations are compared to the results from fluids density functional theory (fDFT) which uses a similar model. We analyze ion dynamics in the model systems and discuss the impacts of ion selectivity and other variables on transport. This material is based upon work supported by the National Science Foundation under Grant 1454343.

Atomistic Molecular Dynamics Simulations of Charged Latex Particle Surfaces in Aqueous Solution.

PubMed

Li, Zifeng; Van Dyk, Antony K; Fitzwater, Susan J; Fichthorn, Kristen A; Milner, Scott T

2016-01-19

Charged particles in aqueous suspension form an electrical double layer at their surfaces, which plays a key role in suspension properties. For example, binder particles in latex paint remain suspended in the can because of repulsive forces between overlapping double layers. Existing models of the double layer assume sharp interfaces bearing fixed uniform charge, and so cannot describe aqueous binder particle surfaces, which are soft and diffuse, and bear mobile charge from ionic surfactants as well as grafted multivalent oligomers. To treat this industrially important system, we use atomistic molecular dynamics simulations to investigate a structurally realistic model of commercial binder particle surfaces, informed by extensive characterization of particle synthesis and surface properties. We determine the interfacial profiles of polymer, water, bound and free ions, from which the charge density and electrostatic potential can be calculated. We extend the traditional definitions of the inner and outer Helmholtz planes to our diffuse interfaces. Beyond the Stern layer, the simulated electrostatic potential is well described by the Poisson-Boltzmann equation. The potential at the outer Helmholtz plane compares well to the experimental zeta potential. We compare particle surfaces bearing two types of charge groups, ionic surfactant and multivalent oligomers, with and without added salt. Although the bare charge density of a surface bearing multivalent oligomers is much higher than that of a surfactant-bearing surface at realistic coverage, greater counterion condensation leads to similar zeta potentials for the two systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polster, C. S.; Zhang, R.; Cyb, M. T.

CO and H{sub 2} oxidation were studied over a series of Pt/CeO{sub 2} catalysts with differing Pt loadings and dispersions. Kinetic rate analysis confirms the presence of dual Langmuir-Hinshelwood (L-H) and Mars and van Krevelen (M-vK) pathways and is used to explain the loss in CO oxidation selectivity at low CO concentrations. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the strong CO coverage dependence on both CO and O{sub 2} concentrations and explains the transition from L-H to M-vK reaction character. Redox site measurements are performed on Pt/CeO{sub 2} catalysts by anaerobic titrations under conditions where themore » M-vK pathway dominates the reaction rate. Similar redox site densities per interfacial Pt atom suggest that interfacial Pt-O-Ce sites are responsible for M-vK redox activity.« less

Probing the dielectric response of the interfacial buffer layer in epitaxial graphene via optical spectroscopy

NASA Astrophysics Data System (ADS)

Hill, Heather M.; Rigosi, Albert F.; Chowdhury, Sugata; Yang, Yanfei; Nguyen, Nhan V.; Tavazza, Francesca; Elmquist, Randolph E.; Newell, David B.; Hight Walker, Angela R.

2017-11-01

Monolayer epitaxial graphene (EG) is a suitable candidate for a variety of electronic applications. One advantage of EG growth on the Si face of SiC is that it develops as a single crystal, as does the layer below, referred to as the interfacial buffer layer (IBL), whose properties include an electronic band gap. Although much research has been conducted to learn about the electrical properties of the IBL, not nearly as much work has been reported on the optical properties of the IBL. In this work, we combine measurements from Mueller matrix ellipsometry, differential reflectance contrast, atomic force microscopy, and Raman spectroscopy, as well as calculations from Kramers-Kronig analyses and density-functional theory, to determine the dielectric function of the IBL within the energy range of 1 eV to 8.5 eV.

Further studies of iron adhesion: ( 1 1 1 ) surfaces

NASA Astrophysics Data System (ADS)

Spencer, Michelle J. S.; Hung, Andrew; Snook, Ian K.; Yarovsky, Irene

2002-08-01

Adhesion between ideal bulk-terminated bcc Fe(1 1 1) match and mismatch interfaces was simulated using density functional theory (DFT) within the plane-wave pseudopotential representation. Interfaces were modelled using the supercell approach where the interfacial separation was varied by changing the size of the vacuum spacer between image cells in the z-direction. The adhesive energy values were calculated for discrete interfacial separations and the data was fitted to the universal binding energy relation (UBER) [Rose et al., Phys. Rev. B 28 (1983) 1835]. The parameters obtained from these fits allowed the work of separation ( Wsep) to be determined and a comparison to be made of the adhesion properties of the match and mismatch interfaces. The results were also compared to those obtained previously for the (1 0 0) and (1 1 0) surfaces.

Interfacial spin-filter assisted spin transfer torque effect in Co/BeO/Co magnetic tunnel junction

NASA Astrophysics Data System (ADS)

Tang, Y.-H.; Chu, F.-C.

2015-03-01

The first-principles calculation is employed to demonstrate the spin-selective transport properties and the non-collinear spin-transfer torque (STT) effect in the newly proposed Co/BeO/Co magnetic tunnel junction. The subtle spin-polarized charge transfer solely at O/Co interface gives rise to the interfacial spin-filter (ISF) effect, which can be simulated within the tight binding model to verify the general expression of STT. This allows us to predict the asymmetric bias behavior of non-collinear STT directly via the interplay between the first-principles calculated spin current densities in collinear magnetic configurations. We believe that the ISF effect, introduced by the combination between wurtzite-BeO barrier and the fcc-Co electrode, may open a new and promising route in semiconductor-based spintronics applications.

Ultralight mesoporous magnetic frameworks by interfacial assembly of Prussian blue nanocubes.

PubMed

Kong, Biao; Tang, Jing; Wu, Zhangxiong; Wei, Jing; Wu, Hao; Wang, Yongcheng; Zheng, Gengfeng; Zhao, Dongyuan

2014-03-10

A facile approach for the synthesis of ultralight iron oxide hierarchical structures with tailorable macro- and mesoporosity is reported. This method entails the growth of porous Prussian blue (PB) single crystals on the surface of a polyurethane sponge, followed by in situ thermal conversion of PB crystals into three-dimensional mesoporous iron oxide (3DMI) architectures. Compared to previously reported ultralight materials, the 3DMI architectures possess hierarchical macro- and mesoporous frameworks with multiple advantageous features, including high surface area (ca. 117 m(2) g(-1)) and ultralow density (6-11 mg cm(-3)). Furthermore, they can be synthesized on a kilogram scale. More importantly, these 3DMI structures exhibit superparamagnetism and tunable hydrophilicity/hydrophobicity, thus allowing for efficient multiphase interfacial adsorption and fast multiphase catalysis. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radical re-appraisal of water structure in hydrophilic confinement.

PubMed

Soper, Alan K

2013-12-18

The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap. The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density. There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K. The radical proposal is made here that water in hydrophilic confinement is under significant tension, around -100 MPa, inside the pore.

Application of optical 3D measurement on thin film buckling to estimate interfacial toughness

NASA Astrophysics Data System (ADS)

Jia, H. K.; Wang, S. B.; Li, L. A.; Wang, Z. Y.; Goudeau, P.

2014-03-01

The shape-from-focus (SFF) method has been widely studied as a passive depth recovery and 3D reconstruction method for digital images. An important step in SFF is the calculation of the focus level for different points in an image by using a focus measure. In this work, an image entropy-based focus measure is introduced into the SFF method to measure the 3D buckling morphology of an aluminum film on a polymethylmethacrylate (PMMA) substrate at a micro scale. Spontaneous film wrinkles and telephone-cord wrinkles are investigated after the deposition of a 300 nm thick aluminum film onto the PMMA substrate. Spontaneous buckling is driven by the highly compressive stress generated in the Al film during the deposition process. The interfacial toughness between metal films and substrates is an important parameter for the reliability of the film/substrate system. The height profiles of different sections across the telephone-cord wrinkle can be considered a straight-sided model with uniform width and height or a pinned circular model that has a delamination region characterized by a sequence of connected sectors. Furthermore, the telephone-cord geometry of the thin film can be used to calculate interfacial toughness. The instability of the finite element model is introduced to fit the buckling morphology obtained by SFF. The interfacial toughness is determined to be 0.203 J/m2 at a 70.4° phase angle from the straight-sided model and 0.105 J/m2 at 76.9° from the pinned circular model.

Scaling of confinement and profiles in the EXTRAP T2 reversed-field pinch

NASA Astrophysics Data System (ADS)

Welander, A.

1999-01-01

In the EXTRAP T2 reversed-field pinch the diagnostic techniques for the measurement of electron density and temperature include; Thomson scattering which gives values at three radial positions in the core (r/a = 0, 0.28, 0.56), Langmuir probes which give values at the edge (r/a > 0.9) and interferometry which gives a line-averaged density. The empirical scaling of electron density and temperature including profile information with global plasma parameters has been studied. The density profile is subject to large variations, with an average parabolic shape when the density is low and flatter shapes when the density is increased. The change in the profile shape can be attributed to a shift in the penetration length of neutrals from the vicinity of the wall. The temperature scales roughly as I/n1/2 where I is the plasma current and n is the density. The temperature profile is always quite flat with lower variations and there is a tendency for a flatter profile at higher temperatures.

Dielectric collapse at the LaAlO 3/SrTiO 3 (001) heterointerface under applied electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minohara, M.; Hikita, Y.; Bell, C.

The fascinating interfacial transport properties at the LaAlO 3/SrTiO 3 heterointerface have led to intense investigations of this oxide system. Exploiting the large dielectric constant of SrTiO 3 at low temperatures, tunability in the interfacial conductivity over a wide range has been demonstrated using a back-gate device geometry. In order to understand the effect of back-gating, it is crucial to assess the interface band structure and its evolution with external bias. In this study, we report measurements of the gate-bias dependent interface band alignment, especially the confining potential profile, at the conducting LaAlO 3/SrTiO 3 (001) heterointerface using soft andmore » hard x-ray photoemission spectroscopy in conjunction with detailed model simulations. Depth-profiling analysis incorporating the electric field dependent dielectric constant in SrTiO 3 reveals that a significant potential drop on the SrTiO 3 side of the interface occurs within ~2 nm of the interface under negative gate-bias. These results demonstrate gate control of the collapse of the dielectric permittivity at the interface, and explain the dramatic loss of electron mobility with back-gate depletion.« less

Dielectric collapse at the LaAlO 3/SrTiO 3 (001) heterointerface under applied electric field

DOE PAGES

Minohara, M.; Hikita, Y.; Bell, C.; ...

2017-08-25

The fascinating interfacial transport properties at the LaAlO 3/SrTiO 3 heterointerface have led to intense investigations of this oxide system. Exploiting the large dielectric constant of SrTiO 3 at low temperatures, tunability in the interfacial conductivity over a wide range has been demonstrated using a back-gate device geometry. In order to understand the effect of back-gating, it is crucial to assess the interface band structure and its evolution with external bias. In this study, we report measurements of the gate-bias dependent interface band alignment, especially the confining potential profile, at the conducting LaAlO 3/SrTiO 3 (001) heterointerface using soft andmore » hard x-ray photoemission spectroscopy in conjunction with detailed model simulations. Depth-profiling analysis incorporating the electric field dependent dielectric constant in SrTiO 3 reveals that a significant potential drop on the SrTiO 3 side of the interface occurs within ~2 nm of the interface under negative gate-bias. These results demonstrate gate control of the collapse of the dielectric permittivity at the interface, and explain the dramatic loss of electron mobility with back-gate depletion.« less

Nano-sized precipitate stability and its controlling factors in a NiAl-strengthened ferritic alloy

PubMed Central

Sun, Zhiqian; Song, Gian; Ilavsky, Jan; Ghosh, Gautam; Liaw, Peter K.

2015-01-01

Coherent B2-ordered NiAl-type precipitates have been used to reinforce solid-solution body-centered-cubic iron for high-temperature application in fossil-energy power plants. In this study, we investigate the stability of nano-sized precipitates in a NiAl-strengthened ferritic alloy at 700–950 °C using ultra-small angle X-ray scattering and electron microscopies. Here we show that the coarsening kinetics of NiAl-type precipitates is in excellent agreement with the ripening model in multicomponent alloys. We further demonstrate that the interfacial energy between the matrix and NiAl-type precipitates is strongly dependent on differences in the matrix/precipitate compositions. Our results profile the ripening process in multicomponent alloys by illustrating controlling factors of interfacial energy, diffusivities, and element partitioning. The study provides guidelines to design and develop high-temperature alloys with stable microstructures for long-term service. PMID:26537060

Characteristics of the Martian atmosphere surface layer

NASA Technical Reports Server (NTRS)

Clow, G. D.; Haberle, R. M.

1990-01-01

Elements of various terrestrial boundary layer models are extended to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface ('constant flux') layer. The atmospheric surface layer consists of an interfacial sublayer immediately adjacent to the ground and an overlying fully turbulent surface sublayer where wind-shear production of turbulence dominates buoyancy production. Within the interfacial sublayer, sensible and latent heat are transported by non-steady molecular diffusion into small-scale eddies which intermittently burst through this zone. Both the thickness of the interfacial sublayer and the characteristics of the turbulent eddies penetrating through it depend on whether airflow is aerodynamically smooth or aerodynamically rough, as determined by the Roughness Reynold's number. Within the overlying surface sublayer, similarity theory can be used to express the mean vertical windspeed, temperature, and water vapor profiles in terms of a single parameter, the Monin-Obukhov stability parameter. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed using data from the TPRC Data Series and the first-order Chapman-Cowling expressions; the required collision integrals were approximated using the Lenard-Jones potential. Parameterizations for specific heat and binary diffusivity were also determined. The Brutsart model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the definition of the Monin-Obukhov length was modified to properly account for the buoyancy forces arising from water vapor gradients in the Martian atmospheric boundary layer. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.

Effect of the Thermocouple on Measuring the Temperature Discontinuity at a Liquid-Vapor Interface.

PubMed

Kazemi, Mohammad Amin; Nobes, David S; Elliott, Janet A W

2017-07-18

The coupled heat and mass transfer that occurs in evaporation is of interest in a large number of fields such as evaporative cooling, distillation, drying, coating, printing, crystallization, welding, atmospheric processes, and pool fires. The temperature jump that occurs at an evaporating interface is of central importance to understanding this complex process. Over the past three decades, thermocouples have been widely used to measure the interfacial temperature jumps at a liquid-vapor interface during evaporation. However, the reliability of these measurements has not been investigated so far. In this study, a numerical simulation of a thermocouple when it measures the interfacial temperatures at a liquid-vapor interface is conducted to understand the possible effects of the thermocouple on the measured temperature and features in the temperature profile. The differential equations of heat transfer in the solid and fluids as well as the momentum transfer in the fluids are coupled together and solved numerically subject to appropriate boundary conditions between the solid and fluids. The results of the numerical simulation showed that while thermocouples can measure the interfacial temperatures in the liquid correctly, they fail to read the actual interfacial temperatures in the vapor. As the results of our numerical study suggest, the temperature jumps at a liquid-vapor interface measured experimentally by using a thermocouple are larger than what really exists at the interface. For a typical experimental study of evaporation of water at low pressure, it was found that the temperature jumps measured by a thermocouple are overestimated by almost 50%. However, the revised temperature jumps are still in agreement with the statistical rate theory of interfacial transport. As well as addressing the specific application of the liquid-vapor temperature jump, this paper provides significant insight into the role that heat transfer plays in the operation of thermocouples in general.

Phase-Transfer Energetics of Small-Molecule Alcohols Across the Water-Hexane Interface: Molecular Dynamics Simulation Using Charge Equilibration Models

PubMed Central

Bauer, Brad A.; Zhong, Yang; Meninger, David J.; Davis, Joseph E.; Patel, Sandeep

2010-01-01

We study the water-hexane interface using molecular dynamics (MD) and polarizable charge equilibration (CHEQ) force fields. Bulk densities for TIP4P-FQ water and hexane, 1.0086±0.0002 g/cm3 and 0.6378±0.0001 g/cm3, demonstrate excellent agreement with experiment. Interfacial width and interfacial tension are consistent with previously reported values. The in-plane component of the dielectric permittivity (ε∥) for water is shown to decrease from 81.7±0.04 to unity, transitioning longitudinally from bulk water to bulk hexane. ε∥ for hexane reaches a maximum in the interface, but this term represents only a small contribution to the total dielectric constant (as expected for a non-polar species). Structurally, net orientations of the molecules arise in the interfacial region such that hexane lies slightly parallel to the interface and water reorients to maximize hydrogen bonding. Interfacial potentials due to contributions of the water and hexane are calculated to be -567.9±0.13mV and 198.7±0.01mV, respectively, giving rise to a total potential in agreement with the range of values reported from previous simulations of similar systems. Potentials of mean force (PMF) calculated for methanol, ethanol, and 1-propanol for the transfer from water to hexane indicate an interfacial free energy minimum, corresponding to the amphiphilic nature of the molecules. The magnitudes of transfer free energies were further characterized from the solvation free energies of alcohols in water and hexane using thermodynamic integration. This analysis shows that solvation free energies for alcohols in hexane are 0.2-0.3 kcal/mol too unfavorable, whereas solvation of alcohols in water is approximately 1 kcal/mol too favorable. For the pure hexane-water interfacial simulations, we observe a monotonic decrease of the water dipole moment to near-vacuum values. This suggests that the electrostatic component of the desolvation free energy is not as severe for polarizable models than for fixed-charge force fields. The implications of such behavior pertain to the modeling of polar and charged solutes in lipidic environments. PMID:21414823

Second harmonic generation study of malachite green adsorption at the interface between air and an electrolyte solution: observing the effect of excess electrical charge density at the interface.

PubMed

Song, Jinsuk; Kim, Mahn Won

2010-03-11

Understanding the differential adsorption of ions at the interface of an electrolyte solution is very important because it is closely related, not only to the fundamental aspects of biological systems, but also to many industrial applications. We have measured the excess interfacial negative charge density at air-electrolyte solution interfaces by using resonant second harmonic generation of oppositely charged probe molecules. The excess charge density increased with the square root of the bulk electrolyte concentration. A new adsorption model that includes the electrostatic interaction between adsorbed molecules is proposed to explain the measured adsorption isotherm, and it is in good agreement with the experimental results.

Density profiles around A+B→C reaction-diffusion fronts in partially miscible systems: A general classification.

PubMed

Loodts, V; Trevelyan, P M J; Rongy, L; De Wit, A

2016-10-01

Various spatial density profiles can develop in partially miscible stratifications when a phase A dissolves with a finite solubility into a host phase containing a dissolved reactant B. We investigate theoretically the impact of an A+B→C reaction on such density profiles in the host phase and classify them in a parameter space spanned by the ratios of relative contributions to density and diffusion coefficients of the chemical species. While the density profile is either monotonically increasing or decreasing in the nonreactive case, reactions combined with differential diffusivity can create eight different types of density profiles featuring up to two extrema in density, at the reaction front or below it. We use this framework to predict various possible hydrodynamic instability scenarios inducing buoyancy-driven convection around such reaction fronts when they propagate parallel to the gravity field.

Primordial inhomogeneities in the expanding universe. II - General features of spherical models at late times

NASA Technical Reports Server (NTRS)

Olson, D. W.; Silk, J.

1979-01-01

This paper studies the density profile that forms around a spherically symmetric bound central core immersed in a homogeneous-background k = 0 or k = -1 Friedmann-Robertson-Walker cosmological model, with zero pressure. Although the density profile in the linearized regime is almost arbitrary, in the nonlinear regime certain universal features of the density profile are obtained that are independent of the details of the initial conditions. The formation of 'halos' ('holes') with densities greater than (less than) the average cosmological density is discussed. It is shown that in most regions 'halos' form, and universal values are obtained for the slope of the ln (density)-ln (radius) profile in those 'halos' at late times, independently of the shape of the initial density profile. Restrictions are derived on where it is possible for 'holes' to exist at late times and on how such 'holes' must have evolved.

Reaction Dynamics at Liquid Interfaces

NASA Astrophysics Data System (ADS)

Benjamin, Ilan

2015-04-01

The liquid interface is a narrow, highly anisotropic region, characterized by rapidly varying density, polarity, and molecular structure. I review several aspects of interfacial solvation and show how these affect reactivity at liquid/liquid interfaces. I specifically consider ion transfer, electron transfer, and SN2 reactions, showing that solvent effects on these reactions can be understood by examining the unique structure and dynamics of the liquid interface region.

Tuning Interfacial Thermal Conductance of Graphene Embedded in Soft Materials by Vacancy Defects

DOE PAGES

Liu, Ying; Hu, Chongze; Huang, Jingsong; ...

2015-06-23

Nanocomposites based on graphene dispersed in matrices of soft materials are promising thermal management materials. Their effective thermal conductivity depends on both the thermal conductivity of graphene and the conductance of the thermal transport across graphene-matrix interfaces. Here we report on molecular dynamics simulations of the thermal transport across the interfaces between defected graphene and soft materials in two different modes: in the across mode, heat enters graphene from one side of its basal plane and leaves through the other side; in the non-across mode, heat enters or leaves a graphene simultaneously from both sides of its basal plane. Wemore » show that, as the density of vacancy defects in graphene increases from 0 to 8%, the conductance of the interfacial thermal transport in the across mode increases from 160.4 16 to 207.8 11 MW/m2K, while that in the non-across mode increases from 7.2 0.1 to 17.8 0.6 MW/m2K. The molecular mechanisms for these variations of thermal conductance are clarified by using the phonon density of states and structural characteristics of defected graphenes. On the basis of these results and effective medium theory, we show that it is possible to enhance the effective thermal conductivity of thermal nanocomposites by tuning the density of vacancy defects in graphene despite the fact that graphene s thermal conductivity always decreases as vacancy defects are introduced.« less

Atom-scale depth localization of biologically important chemical elements in molecular layers.

PubMed

Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

2016-08-23

In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.

Atom-scale depth localization of biologically important chemical elements in molecular layers

PubMed Central

Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

2016-01-01

In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers’ global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces. PMID:27503887

Location-Specific Measurements of The Glass Transition Temperature in Fluorescently Labeled Diblock Copolymers

NASA Astrophysics Data System (ADS)

Christie, Dane; Register, Richard; Priestley, Rodney

Block copolymers can self-assemble into periodic structures containing a high internal surface area, nanoscale domain periods, and periodically varying composition profiles. Depending on their components, block copolymers may also exhibit variations in their dynamic properties e.g., glass transition temperature (Tg) across the domain period. Measuring the variation of Tg across the domain period of block copolymers has remained a significant challenge due to the nanometer length scale of the domain period. Here we use fluorescence spectroscopy and the selective incorporation of a pyrene-containing methacrylate monomer at various positions along the chain to characterize the distribution of glass transition temperatures across the domain period of an amorphous block copolymer. The pyrene-containing monomer location is determined from the monomer segment distribution calculated using self-consistent field theory. Our model system is a lamella-forming diblock copolymer of poly(butyl methacrylate - b- methyl methacrylate). We show that Tg is asymmetrically distributed across the interface; as the interface is approached, larger gradients in Tg exist in the hard PMMA-rich domain than in the soft PBMA-rich domain. By characterizing Tg of PBMA or PMMA interfacial segments, we show that polymer dynamics at the interface are heterogeneous; there is a 15 K difference in Tg measured between PBMA interfacial segments and PMMA interfacial segments.

Density profile and fiber alignment in fiberboard from three southern hardwoods

Treesearch

George E. Woodson

1977-01-01

Density profile and fiber orientation were evaluated for their effects on selected mechanical properties of medium density fiberboard. Bending MOE and modulus of rigidity were predicted from density profiles established by x-ray radiography. Orthotropic ratios ranged from 1.19 to 2.32 for electrically aligned fiberboards from three southern hardwoods. Off-axis tensile...

High dielectric constant and energy density induced by the tunable TiO2 interfacial buffer layer in PVDF nanocomposite contained with core-shell structured TiO2@BaTiO3 nanoparticles

NASA Astrophysics Data System (ADS)

Hu, Penghao; Jia, Zhuye; Shen, Zhonghui; Wang, Peng; Liu, Xiaoru

2018-05-01

To realize application in high-capacity capacitors and portable electric devices, large energy density is eagerly desired for polymer-based nanocomposite. The core-shell structured nanofillers with inorganic buffer layer are recently supposed to be promising in improving the dielectric property of polymer nanocomposite. In this work, core-shell structured TO@BT nanoparticles with crystalline TiO2 buffer layer coated on BaTiO3 nanoparticle were fabricated via solution method and heat treatment. The thickness of the TO buffer layer can be tailored by modulating the additive amount of the titanate coupling agent in preparation process, and the apparent dielectric properties of nanocomposite are much related to the thickness of the TO layer. The relatively thin TO layer prefer to generate high polarization to increase dielectric constant while the relatively thick TO layer would rather to homogenize field to maintain breakdown strength. Simulation of electric field distribution in the interfacial region reveals the improving effect of the TO buffer layer on the dielectric properties of nanocomposite which accords with the experimental results well. The optimized nanoparticle TO@BT-2 with a mean thickness of 3-5 nm buffer layer of TO is effective in increasing both the ε and Eb in the PVDF composite film. The maximal discharged energy density of 8.78 J/cm3 with high energy efficiency above 0.6 is obtained in TO@BT-2/PVDF nanocomposite with 2.5 vol% loading close to the breakdown strength of 380 kV/mm. The present study demonstrates the approach to optimize the structure of core-shell nanoparticles by modulating buffer layer and provides a new way to further enlarge energy density in polymer nanocomposite.

Interfacial sciences in unconventional petroleum production: from fundamentals to applications.

PubMed

He, Lin; Lin, Feng; Li, Xingang; Sui, Hong; Xu, Zhenghe

2015-08-07

With the ever increasing demand for energy to meet the needs of growth in population and improvement in the living standards in particular in developing countries, the abundant unconventional oil reserves (about 70% of total world oil), such as heavy oil, oil/tar sands and shale oil, are playing an increasingly important role in securing global energy supply. Compared with the conventional reserves unconventional oil reserves are characterized by extremely high viscosity and density, combined with complex chemistry. As a result, petroleum production from unconventional oil reserves is much more difficult and costly with more serious environmental impacts. As a key underpinning science, understanding the interfacial phenomena involved in unconventional petroleum production, such as oil liberation from host rocks, oil-water emulsions and demulsification, is critical for developing novel processes to improve oil production while reducing GHG emission and other environmental impacts at a lower operating cost. In the past decade, significant efforts and advances have been made in applying the principles of interfacial sciences to better understand complex unconventional oil-systems, while many environmental and production challenges remain. In this critical review, the recent research findings and progress in the interfacial sciences related to unconventional petroleum production are critically reviewed. In particular, the chemistry of unconventional oils, liberation mechanisms of oil from host rocks and mechanisms of emulsion stability and destabilization in unconventional oil production systems are discussed in detail. This review also seeks to summarize the current state-of-the-art characterization techniques and brings forward the challenges and opportunities for future research in this important field of physical chemistry and petroleum.

Role of the interfacial binding domain in the oxidative susceptibility of lecithin:cholesterol acyltransferase.

PubMed Central

Wang, Kewei; Subbaiah, Papasani V

2002-01-01

We had previously shown that the cholesterol esterification activity of lecithin:cholesterol acyltransferase (LCAT) is destroyed by oxidation, but still it retains the ability to hydrolyse water-soluble substrates. This suggested that the inactivation of the enzyme is not due to its catalytic function, but due to a loss of its hydrophobic binding. Since recent studies have shown that a tryptophan residue in the putative interfacial domain (Trp(61)) is critical for the activity, we determined the possible role of this residue in the oxidative susceptibility and substrate specificity of LCAT by site-directed mutagenesis. Deletion of Trp(61) resulted in a 56% loss of cholesterol esterification (LCAT) activity, but the phospholipase A(2) (PLA(2)) and the esterase activities of the enzyme were stimulated slightly. Replacing Trp(61) with another aromatic residue [Trp(61)-->Tyr (W61Y)] resulted in an increase in all activities (14-157%), whereas replacing it with an aliphatic residue [Trp(61)-->Gly (W61G)] caused a dramatic loss of LCAT (-90%) and PLA(2) (-82%) activities, but not the esterase activity (-5%). W61Y was the most sensitive to oxidation, whereas W61G was the most resistant, with respect to the LCAT and PLA(2) activities. However, the activities which do not involve interfacial binding, namely the esterase activity and the transesterification of short-chain phospholipids, were more resistant to oxidation in all LCATs, indicating a selective loss of the interfacial binding by oxidation. Furthermore, replacing the two cysteines (Cys(31) and Cys(184)) in the Trp(61) deletion mutant caused additional resistance of the enzyme to oxidizing agents, showing that both domains of the enzyme contribute independently to its oxidative susceptibility. Since the hydrolysis of truncated phospholipids, generated during the oxidation of low-density lipoproteins, does not require the interfacial-binding domain, our results suggest that LCAT may take part in the detoxification of these compounds even after the loss of its cholesterol esterification function. PMID:11966470

Trunk density profile estimates from dual X-ray absorptiometry.

PubMed

Wicke, Jason; Dumas, Geneviève A; Costigan, Patrick A

2008-01-01

Accurate body segment parameters are necessary to estimate joint loads when using biomechanical models. Geometric methods can provide individualized data for these models but the accuracy of the geometric methods depends on accurate segment density estimates. The trunk, which is important in many biomechanical models, has the largest variability in density along its length. Therefore, the objectives of this study were to: (1) develop a new method for modeling trunk density profiles based on dual X-ray absorptiometry (DXA) and (2) develop a trunk density function for college-aged females and males that can be used in geometric methods. To this end, the density profiles of 25 females and 24 males were determined by combining the measurements from a photogrammetric method and DXA readings. A discrete Fourier transformation was then used to develop the density functions for each sex. The individual density and average density profiles compare well with the literature. There were distinct differences between the profiles of two of participants (one female and one male), and the average for their sex. It is believed that the variations in these two participants' density profiles were a result of the amount and distribution of fat they possessed. Further studies are needed to support this possibility. The new density functions eliminate the uniform density assumption associated with some geometric models thus providing more accurate trunk segment parameter estimates. In turn, more accurate moments and forces can be estimated for the kinetic analyses of certain human movements.

Fermi level pinning at epitaxial Si on GaAs(100) interfaces

NASA Astrophysics Data System (ADS)

Silberman, J. A.; de Lyon, T. J.; Woodall, J. M.

1991-12-01

GaAs Schottky barrier contacts and metal-insulator-semiconductor structures that include thin epitaxial Si interfacial layers operate in a manner consistent with an unpinned Fermi level at the GaAs interface. These findings raise the question of whether this effect is an intrinsic property of the epitaxial GaAs(100)-Si interface. We have used x-ray photoemission spectroscopy to monitor the Fermi level position during in situ growth of thin epitaxial Si layers. In particular, films formed on heavily doped n- and p-type substrates were compared so as to use the large depletion layer fields available with high impurity concentration as a field-effect probe of the interface state density. The results demonstrate that epitaxial bonding at the interface alone is insufficient to eliminate Fermi level pinning, indicating that other mechanisms affect the interfacial charge balance in the devices that utilize Si interlayers.

Preparation, co-assembling and interfacial crosslinking of photocurable and folate-conjugated amphiphilic block copolymers for controlled and targeted drug delivery: smart armored nanocarriers.

PubMed

Khoee, Sepideh; Kavand, Alireza

2014-02-12

Novel pH-sensitive, biodegradable and biocompatible copolymers based on polycaprolactone-poly(ethylene glycol) (PCL/PEG) were synthesized and further modified with folic acid and/or acryloyl chloride. The mixed polymeric micelles were formed by self-assembling of folated-copolymer and non-folated-copolymer with different compositions via nanoprecipitation method. The solubilization of quercetin as anti-cancer drug by the mixed micelle with the optimized composition (folated/non-folated 20/80) was more efficient than those made of each one alone. Nanogels with different crosslinking density were produced in the presence of ethylene glycol dimethacrylate (EGDMA) as the crosslinker via a photochemical method. Interfacial crosslinking of acrylated groups were utilized to produce a core-shell spherical nanoparticle to evaluate their in-vitro drug release and degradation rate. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

Bioactive glass coatings for orthopedic metallic implants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopez-Esteban, Sonia; Saiz, Eduardo; Fujino, Sigheru

2003-06-30

The objective of this work is to develop bioactive glass coatings for metallic orthopedic implants. A new family of glasses in the SiO2-Na2O-K2O-CaO-MgO-P2O5 system has been synthesized and characterized. The glass properties (thermal expansion, softening and transformation temperatures, density and hardness) are in line with the predictions of established empirical models. The optimized firing conditions to fabricate coatings on Ti-based and Co-Cr alloys have been determined and related to the glass properties and the interfacial reactions. Excellent adhesion to alloys has been achieved through the formation of 100-200 nm thick interfacial layers (Ti5Si3 on Ti-based alloys and CrOx on Co-Cr).more » Finally, glass coatings, approximately 100 mu m thick, have been fabricated onto commercial Ti alloy-based dental implants.« less

Coexistence and interfacial properties of a triangle-well mimicking the Lennard-Jones fluid and a comparison with noble gases.

PubMed

Bárcenas, M; Reyes, Y; Romero-Martínez, A; Odriozola, G; Orea, P

2015-02-21

Coexistence and interfacial properties of a triangle-well (TW) fluid are obtained with the aim of mimicking the Lennard-Jones (LJ) potential and approach the properties of noble gases. For this purpose, the scope of the TW is varied to match vapor-liquid densities and surface tension. Surface tension and coexistence curves of TW systems with different ranges were calculated with replica exchange Monte Carlo and compared to those data previously reported in the literature for truncated and shifted (STS), truncated (ST), and full Lennard-Jones (full-LJ) potentials. We observed that the scope of the TW potential must be increased to approach the STS, ST, and full-LJ properties. In spite of the simplicity of TW expression, a remarkable agreement is found. Furthermore, the variable scope of the TW allows for a good match of the experimental data of argon and xenon.

Enhanced magneto-optical Kerr effect at Fe/insulator interfaces

NASA Astrophysics Data System (ADS)

Gu, Bo; Takahashi, Saburo; Maekawa, Sadamichi

2017-12-01

Using density functional theory calculations, we have found an enhanced magneto-optical Kerr effect in Fe/insulator interfaces. The results of our study indicate that interfacial Fe atoms in the Fe films have a low-dimensional nature, which causes the following two effects: (i) The diagonal component σx x of the optical conductivity decreases dramatically because the hopping integral for electrons between Fe atoms is suppressed by the low dimensionality. (ii) The off-diagonal component σx y of the optical conductivity does not change at low photon energies, but it is enhanced at photon energies around 2 eV, where we obtain enhanced orbital magnetic moments and spin-orbit correlations for the interfacial Fe atoms. A large Kerr angle develops in proportion to the ratio σx y/σx x . Our findings indicate an efficient way to enhance the effect of spin-orbit coupling at metal/insulator interfaces without using heavy elements.

Liquid-liquid interfacial nanoparticle assemblies

DOEpatents

Emrick, Todd S [South Deerfield, MA; Russell, Thomas P [Amherst, MA; Dinsmore, Anthony [Amherst, MA; Skaff, Habib [Amherst, MA; Lin, Yao [Amherst, MA

2008-12-30

Self-assembly of nanoparticles at the interface between two fluids, and methods to control such self-assembly process, e.g., the surface density of particles assembling at the interface; to utilize the assembled nanoparticles and their ligands in fabrication of capsules, where the elastic properties of the capsules can be varied from soft to tough; to develop capsules with well-defined porosities for ultimate use as delivery systems; and to develop chemistries whereby multiple ligands or ligands with multiple functionalities can be attached to the nanoparticles to promote the interfacial segregation and assembly of the nanoparticles. Certain embodiments use cadmium selenide (CdSe) nanoparticles, since the photoluminescence of the particles provides a convenient means by which the spatial location and organization of the particles can be probed. However, the systems and methodologies presented here are general and can, with suitable modification of the chemistries, be adapted to any type of nanoparticle.

Restorative effect of oxygen annealing on device performance in HfIZO thin-film transistors

NASA Astrophysics Data System (ADS)

Ha, Tae-Jun

2015-03-01

Metal-oxide based thin-film transistors (oxide-TFTs) are very promising for use in next generation electronics such as transparent displays requiring high switching and driving performance. In this study, we demonstrate an optimized process to secure excellent device performance with a favorable shift of the threshold voltage toward 0V in amorphous hafnium-indium-zinc-oxide (a-HfIZO) TFTs by using post-treatment with oxygen annealing. This enhancement results from the improved interfacial characteristics between gate dielectric and semiconductor layers due to the reduction in the density of interfacial states related to oxygen vacancies afforded by oxygen annealing. The device statistics confirm the improvement in the device-to-device and run-to-run uniformity. We also report on the photo-induced stability in such oxide-TFTs against long-term UV irradiation, which is significant for transparent displays.

Spin valve effect of the interfacial spin accumulation in yttrium iron garnet/platinum bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Lichuan; Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716; Zhang, Dainan

2014-09-29

We report the spin valve effect in yttrium iron garnet/platinum (YIG/Pt) bilayers. The spin Hall effect (SHE) generates spin accumulation at the YIG/Pt interface and can be opened/closed by magnetization switching in the electrical insulator YIG. The interfacial spin accumulation was measured in both YIG/Pt and YIG/Cu/Pt structures using a planar Hall configuration. The spin valve effect remained, even after a 2 nm thick Cu layer was inserted between the YIG and Pt layers, which aimed to exclude the induced magnetization at the YIG/Pt interface. The transverse Hall voltage and switching field were dependent on the applied charge current density. Themore » origin of this behavior can be explained by the SHE induced torque exerted on the domain wall, caused by the transfer of the spin angular momentum from the spin-polarized current to the YIG magnetic moment.« less

Prediction of two-dimensional electron gas mediated magnetoelectric coupling at ferroelectric PbTiO3/SrTiO3 heterostructures

NASA Astrophysics Data System (ADS)

Wei, Lan-ying; Lian, Chao; Meng, Sheng

2017-05-01

First-principles calculations predict the emergence of magnetoelectric coupling mediated by two-dimensional electron gas (2DEG) at the ferroelectric PbTiO3/SrTiO3 heterostructure. Free electrons endowed by naturally existing oxygen vacancies in SrTiO3 are driven to the heterostructure interface under the polarizing field of ferroelectric PbTiO3 to form a 2DEG. The electrons are captured by interfacial Ti atoms, which surprisingly exhibits ferromagnetism even at room temperature with a small critical density of ˜15.5 μ C /cm2 . The ferroelectricity-controlled ferromagnetism mediated by interfacial 2DEG shows strong magnetoelectric coupling strength, enabling convenient control of magnetism by electric field and vice versa. The PbTiO3/SrTiO3 heterostructure is cheap, easily grown, and controllable, promising future applications in low-cost spintronics and information storage at ambient condition.

Reprint of "Theoretical description of metal/oxide interfacial properties: The case of MgO/Ag(001)"

NASA Astrophysics Data System (ADS)

Prada, Stefano; Giordano, Livia; Pacchioni, Gianfranco; Goniakowski, Jacek

2017-02-01

We compare the performances of different DFT functionals applied to ultra-thin MgO(100) films supported on the Ag(100) surface, a prototypical system of a weakly interacting oxide/metal interface, extensively studied in the past. Beyond semi-local DFT-GGA approximation, we also use the hybrid DFT-HSE approach to improve the description of the oxide electronic structure. Moreover, to better account for the interfacial adhesion, we include the van de Waals interactions by means of either the semi-empirical force fields by Grimme (DFT-D2 and DFT-D2*) or the self-consistent density functional optB88-vdW. We compare and discuss the results on the structural, electronic, and adhesion characteristics of the interface as obtained for pristine and oxygen-deficient Ag-supported MgO films in the 1-4 ML thickness range.

Theoretical description of metal/oxide interfacial properties: The case of MgO/Ag(001)

NASA Astrophysics Data System (ADS)

Prada, Stefano; Giordano, Livia; Pacchioni, Gianfranco; Goniakowski, Jacek

2016-12-01

We compare the performances of different DFT functionals applied to ultra-thin MgO(100) films supported on the Ag(100) surface, a prototypical system of a weakly interacting oxide/metal interface, extensively studied in the past. Beyond semi-local DFT-GGA approximation, we also use the hybrid DFT-HSE approach to improve the description of the oxide electronic structure. Moreover, to better account for the interfacial adhesion, we include the van de Waals interactions by means of either the semi-empirical force fields by Grimme (DFT-D2 and DFT-D2*) or the self-consistent density functional optB88-vdW. We compare and discuss the results on the structural, electronic, and adhesion characteristics of the interface as obtained for pristine and oxygen-deficient Ag-supported MgO films in the 1-4 ML thickness range.

Structural rearrangement and dispersion of functionalized graphene sheets in aqueous solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Yun Jung; Huang, Liwei; Wang, Howard

2015-09-01

Surfactants are widely used for dispersing graphene and functionalized graphene sheets (FGS) in colloidal suspensions, but there have been few studies of the structure of the dispersed graphene-surfactant complexes in suspension and of their time evolution. Here, we combine experimental study of efficiencies of ionic surfactants/polymers in suspending FGS in water with characterization using atomic force microscopy, small angle neutron scattering, and molecular simulations to probe the detailed structures of FGSs. A systematic study of FGS dispersions using ionic surfactants with varying chain lengths revealed that the effective charge density of surfactant layer defines the concentration of dispersed FGS whilemore » the strength of interfacial binding defines the stability of graphene dispersion over long time aging. Ionic surfactants with strong interfacial binding and large molecular weight increase the dispersing power by over an order of magnitude.« less

Shell structure of natural rubber particles: evidence of chemical stratification by electrokinetics and cryo-TEM.

PubMed

Rochette, Christophe N; Crassous, Jérôme J; Drechsler, Markus; Gaboriaud, Fabien; Eloy, Marie; de Gaudemaris, Benoît; Duval, Jérôme F L

2013-11-26

The interfacial structure of natural rubber (NR) colloids is investigated by means of cryogenic transmission electron microscopy (cryo-TEM) and electrokinetics over a broad range of KNO3 electrolyte concentrations (4-300 mM) and pH values (1-8). The asymptotic plateau value reached by NR electrophoretic mobility (μ) in the thin double layer limit supports the presence of a soft (ion- and water-permeable) polyelectrolytic type of layer located at the periphery of the NR particles. This property is confirmed by the analysis of the electron density profile obtained from cryo-TEM that evidences a ∼2-4 nm thick corona surrounding the NR polyisoprene core. The dependence of μ on pH and salt concentration is further marked by a dramatic decrease of the point of zero electrophoretic mobility (PZM) from 3.6 to 0.8 with increasing electrolyte concentration in the range 4-300 mM. Using a recent theory for electrohydrodynamics of soft multilayered particles, this "anomalous" dependence of the PZM on electrolyte concentration is shown to be consistent with a radial organization of anionic and cationic groups across the peripheral NR structure. The NR electrokinetic response in the pH range 1-8 is indeed found to be equivalent to that of particles surrounded by a positively charged ∼3.5 nm thick layer (mean dissociation pK ∼ 4.2) supporting a thin and negatively charged outermost layer (0.6 nm in thickness, pK ∼ 0.7). Altogether, the strong dependence of the PZM on electrolyte concentration suggests that the electrostatic properties of the outer peripheral region of the NR shell are mediated by lipidic residues protruding from a shell containing a significant amount of protein-like charges. This proposed NR shell interfacial structure questions previously reported NR representations according to which the shell consists of either a fully mixed lipid-protein layer, or a layer of phospholipids residing exclusively beneath an outer proteic film.

Gradient Theory simulations of pure fluid interfaces using a generalized expression for influence parameters and a Helmholtz energy equation of state for fundamentally consistent two-phase calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahms, Rainer N.

2014-12-31

The fidelity of Gradient Theory simulations depends on the accuracy of saturation properties and influence parameters, and require equations of state (EoS) which exhibit a fundamentally consistent behavior in the two-phase regime. Widely applied multi-parameter EoS, however, are generally invalid inside this region. Hence, they may not be fully suitable for application in concert with Gradient Theory despite their ability to accurately predict saturation properties. The commonly assumed temperature-dependence of pure component influence parameters usually restricts their validity to subcritical temperature regimes. This may distort predictions for general multi-component interfaces where temperatures often exceed the critical temperature of vapor phasemore » components. Then, the calculation of influence parameters is not well defined. In this paper, one of the first studies is presented in which Gradient Theory is combined with a next-generation Helmholtz energy EoS which facilitates fundamentally consistent calculations over the entire two-phase regime. Illustrated on pentafluoroethane as an example, reference simulations using this method are performed. They demonstrate the significance of such high-accuracy and fundamentally consistent calculations for the computation of interfacial properties. These reference simulations are compared to corresponding results from cubic PR EoS, widely-applied in combination with Gradient Theory, and mBWR EoS. The analysis reveals that neither of those two methods succeeds to consistently capture the qualitative distribution of obtained key thermodynamic properties in Gradient Theory. Furthermore, a generalized expression of the pure component influence parameter is presented. This development is informed by its fundamental definition based on the direct correlation function of the homogeneous fluid and by presented high-fidelity simulations of interfacial density profiles. As a result, the new model preserves the accuracy of previous temperature-dependent expressions, remains well-defined at supercritical temperatures, and is fully suitable for calculations of general multi-component two-phase interfaces.« less

V/sub 3/Ga wire fabricated by the modified jelly roll technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gubser, D.U.; Francavilla, T.L.; Pande, C.S.

V/sub 3/Ga wire has been fabricated by the modified jelly roll technique for the first time. Critical current densities in magnetic fields to 22 T, critical magnetic fields, and superconducting transition temperatures are reported for this wire as a function of reaction temperature for forming the interfacial V/sub 3/Ga layer. Superconducting properties of the reacted wire are optimized for reaction temperatures between 550--580 /sup 0/C. With a reaction temperature of 580 /sup 0/C, the overall (noncopper) current density of the wire is over 10/sup 4/ amp/cm/sup 2/ at 19 T.

High power densities from high-temperature material interactions. [in thermionic energy conversion and metallic fluid heat pipes

NASA Technical Reports Server (NTRS)

Morris, J. F.

1981-01-01

Thermionic energy conversion (TEC) and metallic-fluid heat pipes (MFHPs), offering unique advantages in terrestrial and space energy processing by virtue of operating on working-fluid vaporization/condensation cycles that accept great thermal power densities at high temperatures, share complex materials problems. Simplified equations are presented that verify and solve such problems, suggesting the possibility of cost-effective applications in the near term for TEC and MFHP devices. Among the problems discussed are: the limitation of alkali-metal corrosion, protection against hot external gases, external and internal vaporization, interfacial reactions and diffusion, expansion coefficient matching, and creep deformation.

Cross-linking of sodium caseinate-structured emulsion with transglutaminase alters postprandial metabolic and appetite responses in healthy young individuals.

PubMed

Juvonen, Kristiina R; Macierzanka, Adam; Lille, Martina E; Laaksonen, David E; Mykkänen, Hannu M; Niskanen, Leo K; Pihlajamäki, Jussi; Mäkelä, Kari A; Mills, Clare E N; Mackie, Alan R; Malcolm, Paul; Herzig, Karl-Heinz; Poutanen, Kaisa S; Karhunen, Leila J

2015-08-14

The physico-chemical and interfacial properties of fat emulsions influence lipid digestion and may affect postprandial responses. The aim of the present study was to determine the effects of the modification of the interfacial layer of a fat emulsion by cross-linking on postprandial metabolic and appetite responses. A total of fifteen healthy individuals (26.5 (sem 6.9) years and BMI 21.9 (sem 2.0) kg/m2) participated in a cross-over design experiment in which they consumed two isoenergetic (1924 kJ (460 kcal)) and isovolumic (250 g) emulsions stabilised with either sodium caseinate (Cas) or transglutaminase-cross-linked sodium caseinate (Cas-TG) in a randomised order. Blood samples were collected from the individuals at baseline and for 6 h postprandially for the determination of serum TAG and plasma NEFA, cholecystokinin (CCK), glucagon-like peptide 1 (GLP-1), glucose and insulin responses. Appetite was assessed using visual analogue scales. Postprandial TAG and NEFA responses and gastric emptying (GE) rates were comparable between the emulsions. CCK increased more after the ingestion of Cas-TG than after the ingestion of Cas (P< 0.05), while GLP-1 responses did not differ between the two test emulsions. Glucose and insulin profiles were lower after consuming Cas-TG than after consuming Cas (P< 0.05). The overall insulin, glucose and CCK responses, expressed as areas above/under the curve, did not differ significantly between the Cas and Cas-TG meal conditions. Satiety ratings were reduced and hunger, desire to eat and thirst ratings increased more after the ingestion of Cas-TG than after the ingestion of Cas (P< 0.05). The present results suggest that even a subtle structural modification of the interfacial layer of a fat emulsion can alter the early postprandial profiles of glucose, insulin, CCK, appetite and satiety through decreased protein digestion without affecting significantly on GE or overall lipid digestion.

Non-stationary self-focusing of intense laser beam in plasma using ramp density profile

DOE Office of Scientific and Technical Information (OSTI.GOV)

Habibi, M.; Ghamari, F.

2011-10-15

The non-stationary self-focusing of high intense laser beam in under-dense plasma with upward increasing density ramp is investigated. The obtained results show that slowly increasing plasma density ramp is very important in enhancing laser self-focusing. Also, the spot size oscillations of laser beam in front and rear of the pulse for two different density profiles are shown. We have selected density profiles that already were used by Sadighi-Bonabi et al.[Phys. Plasmas 16, 083105 (2009)]. Ramp density profile causes the laser beam to become more focused and penetrations deeps into the plasma by reduction of diffraction effects. Our computations show moremore » reliable results in comparison to the previous works.« less

Interfacial Engineering for Low-Density Graphene Nanocomposites

DTIC Science & Technology

2014-07-23

structure of polydimethylsiloxane ( PDMS ) to contain pyrene pendant groups such that it would non-covalently bind to graphene. This would allow for...high graphene loadings and conductive strain-sensitivity in PDMS . SEM images of these composites are shown here: 2 The high level of dispersion...allowed for a pristine graphene composite conductivity of 220 S/m; this is after using a membrane to induce separation between graphene-bound PDMS

"Supersaturated" self-assembled charge-selective interfacial layers for organic solar cells.

PubMed

Song, Charles Kiseok; Luck, Kyle A; Zhou, Nanjia; Zeng, Li; Heitzer, Henry M; Manley, Eric F; Goldman, Samuel; Chen, Lin X; Ratner, Mark A; Bedzyk, Michael J; Chang, Robert P H; Hersam, Mark C; Marks, Tobin J

2014-12-24

To achieve densely packed charge-selective organosilane-based interfacial layers (IFLs) on the tin-doped indium oxide (ITO) anodes of organic photovoltaic (OPV) cells, a series of Ar2N-(CH2)n-SiCl3 precursors with Ar = 3,4-difluorophenyl, n = 3, 6, 10, and 18, was synthesized, characterized, and chemisorbed on OPV anodes to serve as IFLs. To minimize lateral nonbonded -NAr2···Ar2N- repulsions which likely limit IFL packing densities in the resulting self-assembled monolayers (SAMs), precursor mixtures having both small and large n values are simultaneously deposited. These "heterogeneous" SAMs are characterized by a battery of techniques: contact angle measurements, X-ray reflectivity, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry, and DFT computation. It is found that the headgroup densities of these "supersaturated" heterogeneous SAMs (SHSAMs) are enhanced by as much as 17% versus their homogeneous counterparts. Supersaturation significantly modifies the IFL properties including the work function (as much as 16%) and areal dipole moment (as much as 49%). Bulk-heterojunction OPV devices are fabricated with these SHSAMs: ITO/IFL/poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][2-[[(2-ethylhexyl)oxy]carbonyl]-3-fluorothieno[3,4-b]thiophenediyl

A relationship between three-dimensional surface hydration structures and force distribution measured by atomic force microscopy.

PubMed

Miyazawa, Keisuke; Kobayashi, Naritaka; Watkins, Matthew; Shluger, Alexander L; Amano, Ken-ichi; Fukuma, Takeshi

2016-04-07

Hydration plays important roles in various solid-liquid interfacial phenomena. Very recently, three-dimensional scanning force microscopy (3D-SFM) has been proposed as a tool to visualise solvated surfaces and their hydration structures with lateral and vertical (sub) molecular resolution. However, the relationship between the 3D force map obtained and the equilibrium water density, ρ(r), distribution above the surface remains an open question. Here, we investigate this relationship at an interface of an inorganic mineral, fluorite, and water. The force maps measured in pure water are directly compared to force maps generated using the solvent tip approximation (STA) model and from explicit molecular dynamics simulations. The results show that the simulated STA force map describes the major features of the experimentally obtained force image. The agreement between the STA data and the experiment establishes the correspondence between the water density used as an input to the STA model and the experimental hydration structure and thus provides a tool to bridge the experimental force data and atomistic solvation structures. Further applications of this method should improve the accuracy and reliability of both interpretation of 3D-SFM force maps and atomistic simulations in a wide range of solid-liquid interfacial phenomena.

Nucleation and growth in cluster dynamics: A quantitative test of the classical kinetic approach

NASA Astrophysics Data System (ADS)

Gránásy, László; James, Peter F.

2000-12-01

Nucleation and size dependent growth of nanometer sized crystalline particles in glassy media have been studied by numerically solving the Turnbull-Fisher master equations that describe the time evolution of cluster population. Time dependencies of the formation rate and number density are determined for large clusters (built of up to 2×105 formula units, containing 1.8×106 atoms). We demonstrate that the formation rate and number density of such clusters are well approximated by Shneidman's asymptotically exact analytical solution. A quantitative test of the kinetic Turnbull-Fisher model has been performed: Evaluating the kinetic coefficients and interfacial parameters from the transient time and steady-state nucleation rates measured on six stoichiometric oxide glass compositions (lithium-disilicate, barium-disilicate, lithium-diborate, wollastonite, 1:2:3 and 2:1:3 soda-lime-silica glass compositions), we calculated the macroscopic growth rates and compared with experiments. For wollastonite, lithium-diborate and the 1:2:3 soda-lime-silica glass, differences of 2 to 4 orders of magnitude have been observed between theory and experiment. This inadequacy of the microscopic kinetic parameters in describing macroscopic growth cannot be explained by either the curvature effect on the interfacial free energy or the self-consistency correction for the cluster free energy. The origin of the discrepancy is discussed.

“Supersaturated” Self-Assembled Charge-Selective Interfacial Layers for Organic Solar Cells

DOE PAGES

Song, Charles Kiseok; Luck, Kyle A.; Zhou, Nanjia; ...

2014-11-24

Here, to achieve densely packed charge-selective organosilane-based interfacial layers (IFLs) on the tin-doped indium oxide (ITO) anodes of organic photovoltaic (OPV) cells, a series of Ar 2N-(CH 2) n-SiCl3 precursors with Ar = 3,4-difluorophenyl, n = 3, 6, 10, and 18, was synthesized, characterized, and chemisorbed on OPV anodes to serve as IFLs. To minimize lateral nonbonded -NAr 2···Ar 2N- repulsions which likely limit IFL packing densities in the resulting self-assembled monolayers (SAMs), precursor mixtures having both small and large n values are simultaneously deposited. These “heterogeneous” SAMs are characterized by a battery of techniques: contact angle measurements, X-ray reflectivity,more » X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry, and DFT computation. It is found that the headgroup densities of these “supersaturated” heterogeneous SAMs (SHSAMs) are enhanced by as much as 17% versus their homogeneous counterparts. Supersaturation significantly modifies the IFL properties including the work function (as much as 16%) and areal dipole moment (as much as 49%). Bulk-heterojunction OPV devices are fabricated with these SHSAMs: ITO/IFL/poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5- b']dithiophene-2,6-diyl][2-[[(2-ethylhexyl)oxy]carbonyl]-3-fluorothieno[3,4-b]thiophenediyl

Atomistic Simulation of High-Density Uranium Fuels

DOE PAGES

Garcés, Jorge Eduardo; Bozzolo, Guillermo

2011-01-01

We apply an atomistic modeling approach to deal with interfacial phenomena in high-density uranium fuels. The effects of Si, as additive to Al or as U-Mo-particles coating, on the behavior of the Al/U-Mo interface is modeled by using the Bozzolo-Ferrante-Smith (BFS) method for alloys. The basic experimental features characterizing the real system are identified, via simulations and atom-by-atom analysis. These include (1) the trend indicating formation of interfacial compounds, (2) much reduced diffusion of Al into U-Mo solid solution due to the high Si concentration, (3) Si depletion in the Al matrix, (4) an unexpected interaction between Mo and Simore » which inhibits Si diffusion to deeper layers in the U-Mo solid solution, and (5) the minimum amount of Si needed to perform as an effective diffusion barrier. Simulation results related to alternatives to Si dispersed in the Al matrix, such as the use of C coating of U-Mo particles or Zr instead of the Al matrix, are also shown. Recent experimental results confirmed early theoretical proposals, along the lines of the results reported in this work, showing that atomistic computational modeling could become a valuable tool to aid the experimental work in the development of nuclear fuels.« less

What Can We Learn from Solid State NMR on the Electrode-Electrolyte Interface?

PubMed

Haber, Shira; Leskes, Michal

2018-06-11

Rechargeable battery cells are composed of two electrodes separated by an ion-conducting electrolyte. While the energy density of the cell is mostly determined by the redox potential of the electrodes and amount of charge they can store, the processes at the electrode-electrolyte interface govern the battery's lifetime and performance. Viable battery cells rely on unimpeded ion transport across this interface, which depends on its composition and structure. These properties are challenging to determine as interfacial phases are thin, disordered, heterogeneous, and can be very reactive. The recent developments and applications of solid state NMR spectroscopy in the study of interfacial phenomena in rechargeable batteries based on lithium and sodium chemistries are reviewed. The different NMR interactions are surveyed and how these are used to shed light on the chemical composition and architecture of interfacial phases as well as directly probe ion transport across them is described. By combining new methods in solid state NMR spectroscopy with other analytical tools, a holistic description of the electrode-electrolyte interface can be obtained. This will enable the design of improved interfaces for developing battery cells with high energy, high power, and longer lifetime. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrodeposition of Ni on Bi2Te3 and Interfacial Reaction Between Sn and Ni-Coated Bi2Te3

NASA Astrophysics Data System (ADS)

Tseng, Yu-Chen; Lee, Hsuan; Hau, Nga Yu; Feng, Shien-Ping; Chen, Chih-Ming

2018-01-01

Bismuth-telluride (Bi2Te3)-based compounds are common thermoelectric materials used for low-temperature applications, and nickel (Ni) is usually deposited on the Bi2Te3 substrates as a diffusion barrier. Deposition of Ni on the p-type (Sb-doped) and n-type (Se-doped) Bi2Te3 substrates using electroplating and interfacial reactions between Sn and Ni-coated Bi2Te3 substrates are investigated. Electrodeposition of Ni on different Bi2Te3 substrates is characterized based on cyclic voltammetry and Tafel measurements. Microstructural characterizations of the Ni deposition and the Sn/Ni/Bi2Te3 interfacial reactions are performed using scanning electron microscopy. A faster growth rate is observed for the Ni deposition on the n-type Bi2Te3 substrate which is attributed to a lower activation energy of reduction due to a higher density of free electrons in the n-type Bi2Te3 material. The common Ni3Sn4 phase is formed at the Sn/Ni interfaces on both the p-type and n-type Bi2Te3 substrates, while the NiTe phase is formed at a faster rate at the interface between Ni and n-type Bi2Te3 substrates.

Exploring Interfacial Events in Gold-Nanocluster-Sensitized Solar Cells: Insights into the Effects of the Cluster Size and Electrolyte on Solar Cell Performance.

PubMed

Abbas, Muhammad A; Kim, Tea-Yon; Lee, Sang Uck; Kang, Yong Soo; Bang, Jin Ho

2016-01-13

Gold nanoclusters (Au NCs) with molecule-like behavior have emerged as a new light harvester in various energy conversion systems. Despite several important strides made recently, efforts toward the utilization of NCs as a light harvester have been primarily restricted to proving their potency and feasibility. In solar cell applications, ground-breaking research with a power conversion efficiency (PCE) of more than 2% has recently been reported. Because of the lack of complete characterization of metal cluster-sensitized solar cells (MCSSCs), however, comprehensive understanding of the interfacial events and limiting factors which dictate their performance remains elusive. In this regard, we provide deep insight into MCSSCs for the first time by performing in-depth electrochemical impedance spectroscopy (EIS) analysis combined with physical characterization and density functional theory (DFT) calculations of Au NCs. In particular, we focused on the effect of the size of the Au NCs and electrolytes on the performance of MCSSCs and reveal that they are significantly influential on important solar cell characteristics such as the light absorption capability, charge injection kinetics, interfacial charge recombination, and charge transport. Besides offering comprehensive insights, this work represents an important stepping stone toward the development of MCSSCs by accomplishing a new PCE record of 3.8%.

Structure and Electronic Properties of Interface-Confined Oxide Nanostructures

DOE PAGES

Liu, Yun; Ning, Yanxiao; Yu, Liang; ...

2017-09-16

The controlled fabrication of nanostructures has often made use of a substrate template to mediate and control the growth kinetics. Electronic substrate-mediated interactions have been demonstrated to guide the assembly of organic molecules or the nucleation of metal atoms but usually at cryogenic temperatures, where the diffusion has been limited. Combining STM, STS, and DFT studies, we report that the strong electronic interaction between transition metals and oxides could indeed govern the growth of low-dimensional oxide nanostructures. As a demonstration, a series of FeO triangles, which are of the same structure and electronic properties but with different sizes (side lengthmore » >3 nm), are synthesized on Pt(111). The strong interfacial interaction confines the growth of FeO nanostructures, leading to a discrete size distribution and a uniform step structure. Given the same interfacial configuration, as-grown FeO nanostructures not only expose identical edge/surface structure but also exhibit the same electronic properties, as manifested by the local density of states and local work functions. We expect the interfacial confinement effect can be generally applied to control the growth of oxide nanostructures on transition metal surfaces. These oxide nanostructures of the same structure and electronic properties are excellent models for studies of nanoscale effects and applications.« less

High Detectivity Graphene-Silicon Heterojunction Photodetector.

PubMed

Li, Xinming; Zhu, Miao; Du, Mingde; Lv, Zheng; Zhang, Li; Li, Yuanchang; Yang, Yao; Yang, Tingting; Li, Xiao; Wang, Kunlin; Zhu, Hongwei; Fang, Ying

2016-02-03

A graphene/n-type silicon (n-Si) heterojunction has been demonstrated to exhibit strong rectifying behavior and high photoresponsivity, which can be utilized for the development of high-performance photodetectors. However, graphene/n-Si heterojunction photodetectors reported previously suffer from relatively low specific detectivity due to large dark current. Here, by introducing a thin interfacial oxide layer, the dark current of graphene/n-Si heterojunction has been reduced by two orders of magnitude at zero bias. At room temperature, the graphene/n-Si photodetector with interfacial oxide exhibits a specific detectivity up to 5.77 × 10(13) cm Hz(1/2) W(-1) at the peak wavelength of 890 nm in vacuum, which is highest reported detectivity at room temperature for planar graphene/Si heterojunction photodetectors. In addition, the improved graphene/n-Si heterojunction photodetectors possess high responsivity of 0.73 A W(-1) and high photo-to-dark current ratio of ≈10(7) . The current noise spectral density of the graphene/n-Si photodetector has been characterized under ambient and vacuum conditions, which shows that the dark current can be further suppressed in vacuum. These results demonstrate that graphene/Si heterojunction with interfacial oxide is promising for the development of high detectivity photodetectors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dynamic Stabilization of Metal Oxide–Water Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

McBriarty, Martin E.; von Rudorff, Guido Falk; Stubbs, Joanne E.

2017-02-08

The interaction of water with metal oxide surfaces plays a crucial role in the catalytic and geochemical behavior of metal oxides. In a vast majority of studies, the interfacial structure is assumed to arise from a relatively static lowest energy configuration of atoms, even at room temperature. Using hematite (α-Fe2O3) as a model oxide, we show through a direct comparison of in situ synchrotron X-ray scattering with density functional theory-based molecular dynamics simulations that the structure of the (1102) termination is dynamically stabilized by picosecond water exchange. Simulations show frequent exchanges between terminal aquo groups and adsorbed water in locationsmore » and with partial residence times consistent with experimentally determined atomic sites and fractional occupancies. Frequent water exchange occurs even for an ultrathin adsorbed water film persisting on the surface under a dry atmosphere. The resulting time-averaged interfacial structure consists of a ridged lateral arrangement of adsorbed water molecules hydrogen bonded to terminal aquo groups. Surface pKa prediction based on bond valence analysis suggests that water exchange will influence the proton-transfer reactions underlying the acid/base reactivity at the interface. Our findings provide important new insights for understanding complex interfacial chemical processes at metal oxide–water interfaces.« less

Role of the interface between distributed fibre optic strain sensor and soil in ground deformation measurement

NASA Astrophysics Data System (ADS)

Zhang, Cheng-Cheng; Zhu, Hong-Hu; Shi, Bin

2016-11-01

Recently the distributed fibre optic strain sensing (DFOSS) technique has been applied to monitor deformations of various earth structures. However, the reliability of soil deformation measurements remains unclear. Here we present an integrated DFOSS- and photogrammetry-based test study on the deformation behaviour of a soil foundation model to highlight the role of strain sensing fibre-soil interface in DFOSS-based geotechnical monitoring. Then we investigate how the fibre-soil interfacial behaviour is influenced by environmental changes, and how the strain distribution along the fibre evolves during progressive interface failure. We observe that the fibre-soil interfacial bond is tightened and the measurement range of the fibre is extended under high densities or low water contents of soil. The plastic zone gradually occupies the whole fibre length when the soil deformation accumulates. Consequently, we derive a theoretical model to simulate the fibre-soil interfacial behaviour throughout the progressive failure process, which accords well with the experimental results. On this basis, we further propose that the reliability of measured strain can be determined by estimating the stress state of the fibre-soil interface. These findings may have important implications for interpreting and evaluating fibre optic strain measurements, and implementing reliable DFOSS-based geotechnical instrumentation.

Direct spontaneous growth and interfacial structural properties of inclined GaN nanopillars on r-plane sapphire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adikimenakis, A.; Aretouli, K. E.; Tsagaraki, K.

2015-06-28

The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with increasing the duration of the nitridation process and the power applied on the radio-frequency plasma source, as well as the III/V flux ratio, while variation of the first two parameters enhanced the roughness of the substrate's surface. Transmission electron microscopy (TEM) techniques were employed to reveal the structuralmore » characteristics of the NPs and their nucleation mechanism from steps on the sapphire surface and/or interfacial semipolar GaN nanocrystals. Lattice strain measurements showed a possible Al enrichment of the first 5–6 monolayers of the NPs. By combining cross-sectional and plan-view TEM observations, the three-dimensional model of the NPs was constructed. The orientation relationship and interfacial accommodation between the NPs and the nonpolar a-plane GaN film were also elucidated. The NPs exhibited strong and narrow excitonic emission, suggesting an excellent structural quality.« less

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazioti, C.; Kehagias, Th.; Pavlidou, E.

2015-10-21

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults andmore » threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults.« less

Structure and Electronic Properties of Interface-Confined Oxide Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yun; Ning, Yanxiao; Yu, Liang

The controlled fabrication of nanostructures has often made use of a substrate template to mediate and control the growth kinetics. Electronic substrate-mediated interactions have been demonstrated to guide the assembly of organic molecules or the nucleation of metal atoms but usually at cryogenic temperatures, where the diffusion has been limited. Combining STM, STS, and DFT studies, we report that the strong electronic interaction between transition metals and oxides could indeed govern the growth of low-dimensional oxide nanostructures. As a demonstration, a series of FeO triangles, which are of the same structure and electronic properties but with different sizes (side lengthmore » >3 nm), are synthesized on Pt(111). The strong interfacial interaction confines the growth of FeO nanostructures, leading to a discrete size distribution and a uniform step structure. Given the same interfacial configuration, as-grown FeO nanostructures not only expose identical edge/surface structure but also exhibit the same electronic properties, as manifested by the local density of states and local work functions. We expect the interfacial confinement effect can be generally applied to control the growth of oxide nanostructures on transition metal surfaces. These oxide nanostructures of the same structure and electronic properties are excellent models for studies of nanoscale effects and applications.« less

Ferroelectric Polarization-Modulated Interfacial Fine Structures Involving Two-Dimensional Electron Gases in Pb(Zr,Ti)O3/LaAlO3/SrTiO3 Heterostructures.

PubMed

Wang, Shuangbao; Bai, Yuhang; Xie, Lin; Li, Chen; Key, Julian D; Wu, Di; Wang, Peng; Pan, Xiaoqing

2018-01-10

Interfacial fine structures of bare LaAlO 3 /SrTiO 3 (LAO/STO) heterostructures are compared with those of LAO/STO heterostructures capped with upward-polarized Pb(Zr 0.1 ,Ti 0.9 )O 3 (PZT up ) or downward-polarized Pb(Zr 0.5 ,Ti 0.5 )O 3 (PZT down ) overlayers by aberration-corrected scanning transmission electron microscopy experiments. By combining the acquired electron energy-loss spectroscopy mapping, we are able to directly observe electron transfer from Ti 4+ to Ti 3+ and ionic displacements at the interface of bare LAO/STO and PZT down /LAO/STO heterostructure unit cell by unit cell. No evidence of Ti 3+ is observed at the interface of the PZT up /LAO/STO samples. Furthermore, the confinement of the two-dimensional electron gas (2DEG) at the interface is determined by atomic-column spatial resolution. Compared with the bare LAO/STO interface, the 2DEG density at the LAO/STO interface is enhanced or depressed by the PZT down or PZT up overlayer, respectively. Our microscopy studies shed light on the mechanism of ferroelectric modulation of interfacial transport at polar/nonpolar oxide heterointerfaces, which may facilitate applications of these materials as nonvolatile memory.

Predicting CO2-H2O Interfacial Tension Using COSMO-RS.

PubMed

Silvestri, A; Stipp, S L S; Andersson, M P

2017-02-14

Knowledge about the interaction between fluids and solids and the interfacial tension (IFT) that results is important for predicting behavior and properties in industrial systems and in nature, such as in rock formations before, during, and after CO 2 injection for long-term storage. Many authors have studied the effect of the environmental variables on the IFT in the CO 2 -H 2 O system. However, experimental measurements above CO 2 supercritical conditions are scarce and sometimes contradictory. Molecular modeling is a valuable tool for complementing experimental IFT determination, and it can help us interpret results and gain insight under conditions where experiments are difficult or impossible. Here, we report predictions for CO 2 -water interfacial tension performed using density functional theory (DFT) combined with the COSMO-RS implicit solvent model. We predicted the IFT dependence as a function of pressure (0-50 MPa), temperature (273-383 K), and salinity (0-5 M NaCl). The results agree well with literature data, within the estimated uncertainty for experiments and for molecular dynamics (MD) simulations, suggesting that the model can be used as a fast alternative to time-consuming computational approaches for predicting the CO 2 -water IFT over a range of pressures, temperatures, and salinities.

Growth and characterization of InSb on (1 0 0) Si for mid-infrared application

NASA Astrophysics Data System (ADS)

Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

2018-05-01

Monolithic integration of InSb on (1 0 0) Si is a practical approach to realizing on-chip mid-infrared photonic devices. An InSb layer was grown on a (1 0 0) Si substrate using an AlSb/GaSb buffer containing InSb quantum dots (QDs). The growth process for the buffer involved the growth of GaSb on Si using an interfacial misfit array, followed by InSb QDs on AlSb to decrease the density of microtwins. InSb layers were separately grown on AlSb and GaSb surfaces to compare the effect of different interfacial misfit arrays. The samples were characterized using transmission electron microscopy and X-ray diffraction to determine the structural properties of the buffer and InSb layers. The InSb on the AlSb sample exhibited higher crystal quality than the InSb on GaSb sample due to a more favorable arrangement of interfacial misfit dislocations. Hall measurements of unintentionally doped InSb layers demonstrated a higher carrier mobility in the InSb on the AlSb sample than in InSb on GaSb. Growing InSb on AlSb also improved the photoresponsivity of InSb as a photoconductor on Si.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujiwara, K., E-mail: ku.fujiwara@screen.co.jp; Department of Mechanical Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871; Shibahara, M., E-mail: siba@mech.eng.osaka-u.ac.jp

A classical molecular dynamics simulation was conducted for a system composed of fluid molecules between two planar solid surfaces, and whose interactions are described by the 12-6 Lennard-Jones form. This paper presents a general description of the pressure components and interfacial tension at a fluid-solid interface obtained by the perturbative method on the basis of statistical thermodynamics, proposes a method to consider the pressure components tangential to an interface which are affected by interactions with solid atoms, and applies this method to the calculation system. The description of the perturbative method is extended to subsystems, and the local pressure componentsmore » and interfacial tension at a liquid-solid interface are obtained and examined in one- and two-dimensions. The results are compared with those obtained by two alternative methods: (a) an evaluation of the intermolecular force acting on a plane, and (b) the conventional method based on the virial expression. The accuracy of the numerical results is examined through the comparison of the results obtained by each method. The calculated local pressure components and interfacial tension of the fluid at a liquid-solid interface agreed well with the results of the two alternative methods at each local position in one dimension. In two dimensions, the results showed a characteristic profile of the tangential pressure component which depended on the direction tangential to the liquid-solid interface, which agreed with that obtained by the evaluation of the intermolecular force acting on a plane in the present study. Such good agreement suggests that the perturbative method on the basis of statistical thermodynamics used in this study is valid to obtain the local pressure components and interfacial tension at a liquid-solid interface.« less

Long-wave-instability-induced pattern formation in an evaporating sessile or pendent liquid layer

NASA Astrophysics Data System (ADS)

Wei, Tao; Duan, Fei

2018-03-01

We investigate the nonlinear dynamics and stability of an evaporating liquid layer subject to vapor recoil, capillarity, thermocapillarity, ambient cooling, viscosity, and negative or positive gravity combined with buoyancy effects in the lubrication approximation. Using linear theory, we identify the mechanisms of finite-time rupture, independent of thermocapillarity and direction of gravity, and predict the effective growth rate of an interfacial perturbation which reveals competition among the mechanisms. A stability diagram is predicted for the onset of long-wave (LW) evaporative convection. In the two-dimensional simulation, we observe well-defined capillary ridges on both sides of the valley under positive gravity and main and secondary droplets under negative gravity, while a ridge can be trapped in a large-scale drained region in both cases. Neglecting the other non-Boussinesq effects, buoyancy does not have a significant influence on interfacial evolution and rupture time but makes contributions to the evaporation-driven convection and heat transfer. The average Nusselt number is found to increase with a stronger buoyancy effect. The flow field and interface profile jointly manifest the LW Marangoni-Rayleigh-Bénard convection under positive gravity and the LW Marangoni convection under negative gravity. In the three-dimensional simulation of moderate evaporation with a random perturbation, the rupture patterns are characterized by irregular ridge networks with distinct height scales for positive and negative gravity. A variety of interfacial and internal dynamics are displayed, depending on evaporation conditions, gravity, Marangoni effect, and ambient cooling. Reasonable agreement is found between the present results and the reported experiments and simulations. The concept of dissipative compacton also sheds light on the properties of interfacial fractalization.

Variation in sensitivity, absorption and density of the central rod distribution with eccentricity.

PubMed

Tornow, R P; Stilling, R

1998-01-01

To assess the human rod photopigment distribution and sensitivity with high spatial resolution within the central +/-15 degrees and to compare the results of pigment absorption, sensitivity and rod density distribution (number of rods per square degree). Rod photopigment density distribution was measured with imaging densitometry using a modified Rodenstock scanning laser ophthalmoscope. Dark-adapted sensitivity profiles were measured with green stimuli (17' arc diameter, 1 degrees spacing) using a T ubingen manual perimeter. Sensitivity profiles were plotted on a linear scale and rod photopigment optical density distribution profiles were converted to absorption profiles of the rod photopigment layer. Both the absorption profile of the rod photopigment and the linear sensitivity profile for green stimuli show a minimum at the foveal center and increase steeply with eccentricity. The variation with eccentricity corresponds to the rod density distribution. Rod photopigment absorption profiles, retinal sensitivity profiles, and the rod density distribution are linearly related within the central +/-15 degrees. This is in agreement with theoretical considerations. Both methods, imaging retinal densitometry using a scanning laser ophthalmoscope and dark-adapted perimetry with small green stimuli, are useful for assessing the central rod distribution and sensitivity. However, at present, both methods have limitations. Suggestions for improving the reliability of both methods are given.

Controlled growth of heteroepitaxial zinc oxide nanostructures on gallium nitride.

PubMed

Kong, Bo Hyun; Kim, Dong Chan; Mohanta, Sanjay Kumar; Han, Won Suk; Cho, Hyung Koun; Hong, Chang-Hee; Kim, Hyung Gu

2009-07-01

ZnO epitaxial layers were grown on GaN underlying films by metalorganic chemical vapor deposition at various temperatures. An increase in growth temperature led to morphological changes from a smooth film with hexagonal-shaped surface pits to honeycomb-like nanostructures with deep hollow, and additionally resulted in a decrease in dislocation density in the interfacial layers. The reduced dislocation density at the higher growth temperature was attributed to an increase in the size of the critical nucleus and the low nucleation density at the initial stage. The shifts in the peak positions in the X-ray diffraction and photoluminescence were also observed in the samples grown at different temperatures, and were caused by the variation of residual strains after the complete coalescence of the nuclei.

Band-gap corrected density functional theory calculations for InAs/GaSb type II superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jianwei; Zhang, Yong

2014-12-07

We performed pseudopotential based density functional theory (DFT) calculations for GaSb/InAs type II superlattices (T2SLs), with bandgap errors from the local density approximation mitigated by applying an empirical method to correct the bulk bandgaps. Specifically, this work (1) compared the calculated bandgaps with experimental data and non-self-consistent atomistic methods; (2) calculated the T2SL band structures with varying structural parameters; (3) investigated the interfacial effects associated with the no-common-atom heterostructure; and (4) studied the strain effect due to lattice mismatch between the two components. This work demonstrates the feasibility of applying the DFT method to more exotic heterostructures and defect problemsmore » related to this material system.« less

Molecular Dynamics of a Water-Lipid Bilayer Interface

NASA Technical Reports Server (NTRS)

Wilson, Michael A.; Pohorille, Andrew

1994-01-01

We present results of molecular dynamics simulations of a glycerol 1-monooleate bilayer in water. The total length of analyzed trajectories is 5ns. The calculated width of the bilayer agrees well with the experimentally measured value. The interior of the membrane is in a highly disordered fluid state. Atomic density profile, orientational and conformational distribution functions, and order parameters indicate that disorder increases toward the center of the bilayer. Analysis of out-of-plane thermal fluctuations of the bilayer surfaces occurring at the time scale of the present calculations reveals that the distribution of modes agrees with predictions of the capillary wave model. Fluctuations of both bilayer surfaces are uncorrelated, yielding Gaussian distribution of instantaneous widths of the membrane. Fluctuations of the width produce transient thinning defects in the bilayer which occasionally span almost half of the membrane. The leading mechanism of these fluctuations is the orientational and conformational motion of head groups rather than vertical motion of the whole molecules. Water considerably penetrates the head group region of the bilayer but not its hydrocarbon core. The total net excess dipole moment of the interfacial water points toward the aqueous phase, but the water polarization profile is non-monotonic. Both water and head groups significantly contribute to the surface potential across the interface. The calculated sign of the surface potential is in agreement with that from experimental measurements, but the value is markedly overestimated. The structural and electrical properties of the water-bilayer system are discussed in relation to membrane functions, in particular transport of ions and nonelectrolytes across membranes.