General contraction of Gaussian basis sets. II - Atomic natural orbitals and the calculation of atomic and molecular properties

NASA Technical Reports Server (NTRS)

Almlof, Jan; Taylor, Peter R.

1990-01-01

A recently proposed scheme for using natural orbitals from atomic configuration interaction wave functions as a basis set for linear combination of atomic orbitals (LCAO) calculations is extended for the calculation of molecular properties. For one-electron properties like multipole moments, which are determined largely by the outermost regions of the molecular wave function, it is necessary to increase the flexibility of the basis in these regions. This is most easily done by uncontracting the outermost Gaussian primitives, and/or by adding diffuse primitives. A similar approach can be employed for the calculation of polarizabilities. Properties which are not dominated by the long-range part of the wave function, such as spectroscopic constants or electric field gradients at the nucleus, can generally be treated satisfactorily with the original atomic natural orbital sets.

Controlling the surface termination of NdGaO3 (110): the role of the gas atmosphere.

PubMed

Cavallaro, Andrea; Harrington, George F; Skinner, Stephen J; Kilner, John A

2014-07-07

In this work the effect of gas atmosphere on the surface termination reconstruction of single crystal NdGaO3 (110) (NGO) during thermal annealing was analyzed. Using Low Energy Ion Scattering (LEIS) it has been possible to study the chemical composition of the first atomic layer of treated NGO single crystal samples. NGO has been analyzed both as-received and after a specific thermal treatment at 1000 °C under different gas fluxes (argon, nitrogen, static air, synthetic air, nitrogen plus 5% hydrogen and wet synthetic air respectively). Thermal annealing of perovskite single crystals, as already reported in the literature, is used to obtain a fully A-cation surface termination. Nevertheless the effect of the gas-atmosphere on this process has not been previously reported. By the use of sequential low energy Ar(+) sputtering combined with the primary ion LEIS analysis, the reconstruction of the outermost atomic layers has allowed the clarification of the mechanism of NGO neodymium surface enrichment. It is proposed that the gallium at the surface is submitted to a reduction/evaporation mechanism caused by low oxygen partial pressure and/or high water pressure in the vector gas. Below the first surface atomic layers of an as-received NGO single-crystal a gallium-rich phase has also been observed.

Ab initio molecular dynamics study of thermite reaction at Al and CuO nano-interfaces at different temperatures

NASA Astrophysics Data System (ADS)

Tang, Cui-Ming; Chen, Xiao-Xu; Cheng, Xin-Lu; Zhang, Chao-Yang; Lu, Zhi-Peng

2018-05-01

The thermite reaction at Al/CuO nano-interfaces is investigated with ab initio molecular dynamics calculations in canonical ensemble at 500 K, 800 K, 1200 K and 1500 K, respectively. The reaction process and reaction products are analyzed in terms of chemical bonds, average charge, time constants and total potential energy. The activity of the reactants enhances with increasing temperature, which induces a faster thermite reaction. The alloy reaction obviously expands outward at Cu-rich interface of Al/CuO system, and the reaction between Al and O atoms obviously expands outward at O-rich interface as temperature increases. Different reaction products are found at the outermost layer of different interfaces in the Al/CuO system. In generally, the average charge of the outer layer aluminum atoms (i.e., Al1, Al2, Al5 and Al6) increases with temperature. The potential energy of Al/CuO system decreases significantly, which indicates that drastic exothermic reaction occurs at the Al/CuO system. This research enhances fundamental understanding in temperature effect on the thermite reaction at atomic level, which can potentially open new possibilities for its industrial application.

Glomus drummondii and G. walkeri, two new species of arbuscular mycorrhizal fungi (Glomeromycota).

PubMed

Błaszkowski, Janusz; Renker, Carsten; Buscot, François

2006-05-01

Two new ectocarpic arbuscular mycorrhizal fungal species, Glomus drummondii and G. walkeri (Glomeromycota), found in maritime sand dunes of northern Poland and those adjacent to the Mediterranean Sea are described and illustrated. Mature spores of G. drummondii are pastel yellow to maize yellow, globose to subglobose, (58-)71(-85) micromdiam, or ovoid, 50-80x63-98 microm. Their wall consists of three layers: an evanescent, hyaline, short-lived outermost layer, a laminate, smooth, pastel yellow to maize yellow middle layer, and a flexible, smooth, hyaline innermost layer. Spores of G. walkeri are white to pale yellow, globose to subglobose, (55-)81(-95) micromdiam, or ovoid, 60-90x75-115 microm, and have a spore wall composed of three layers: a semi-permanent, hyaline outermost layer, a laminate, smooth, white to pale yellow middle layer, and a flexible, smooth, hyaline innermost layer. In Melzer's reagent, only the inner- and outermost layers stain reddish white to greyish rose in G. drummondii and G. walkeri, respectively. Both species form vesicular-arbuscular mycorrhizae in one-species cultures with Plantago lanceolata as the host plant. Phylogenetic analyses of the ITS and parts of the LSU of the nrDNA of spores placed both species in Glomus Group B sensu Schüssler et al. [Schüssler A, Schwarzott D, Walker C, 2001. A new fungal phylum, the Glomeromycota: phylogeny and evolution. Mycolological Research 105: 1413-1421.].

High-Performance Rh 2 P Electrocatalyst for Efficient Water Splitting

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

Duan, Haohong; Li, Dongguo; Tang, Yan

2017-04-05

Search for active, stable and cost-efficient electrocatalysts for hydrogen production via water splitting could make substantial impact to the energy technologies that do not rely on fossil fuels. Here we report the synthesis of rhodium phosphide electrocatalyst with low metal loading in the form of nanocubes (NCs) dispersed in high surface area carbon (Rh2P/C) by a facile solvo-thermal approach. The Rh2P/C NCs exhibit remarkable performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) compared to Rh/C and Pt/C catalysts. The atomic structure of the rhodium phosphide nanocubes was directly observed by annular dark-field scanning transmission electron microscopy (ADF-STEM),more » which revealed phosphorous-rich outermost atomic layer. Combined experimental and computational studies suggest that surface phosphorous plays crucial role in determining the robust catalyst properties.« less

In situ ceramic layer growth on coated fuel particles dispersed in a zirconium metal matrix

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

Terrani, Kurt A; Silva, G W Chinthaka M; Kiggans, Jim

2013-01-01

The extent and nature of the chemical interaction between the outermost coating layer of coated fuel particles embedded in zirconium metal during fabrication of metal matrix microencapsulated fuels was examined. Various particles with outermost coating layers of pyrocarbon, SiC, and ZrC have been investigated in this study. ZrC-Zr interaction was least substantial while PyC-Zr reaction can be exploited to produce a ZrC layer at the interface in an in situ manner. The thickness of the ZrC layer in the latter case can be controlled by adjusting the time and temperature during processing. The kinetics of ZrC layer growth is significantlymore » faster from what is predicted using literature carbon diffusivity data in ZrC. SiC-Zr interaction is more complex and results in formation of various chemical phases in a layered aggregate morphology at the interface.« less

Effect of cathodic polarization on coating doxycycline on titanium surfaces.

PubMed

Geißler, Sebastian; Tiainen, Hanna; Haugen, Håvard J

2016-06-01

Cathodic polarization has been reported to enhance the ability of titanium based implant materials to interact with biomolecules by forming titanium hydride at the outermost surface layer. Although this hydride layer has recently been suggested to allow the immobilization of the broad spectrum antibiotic doxycycline on titanium surfaces, the involvement of hydride in binding the biomolecule onto titanium remains poorly understood. To gain better understanding of the influence this immobilization process has on titanium surfaces, mirror-polished commercially pure titanium surfaces were cathodically polarized in the presence of doxycycline and the modified surfaces were thoroughly characterized using atomic force microscopy, electron microscopy, secondary ion mass spectrometry, and angle-resolved X-ray spectroscopy. We demonstrated that no hydride was created during the polarization process. Doxycycline was found to be attached to an oxide layer that was modified during the electrochemical process. A bacterial assay using bioluminescent Staphylococcus epidermidis Xen43 showed the ability of the coating to reduce bacterial colonization and planktonic bacterial growth. Copyright © 2016 Elsevier B.V. All rights reserved.

Structural analysis of the outermost hair surface using TOF-SIMS with gas cluster ion beam sputtering.

PubMed

Lshikawa, Kazutaka; Okamoto, Masayuki; Aoyagi, Satoka

2016-06-28

A hair cuticle, which consists of flat overlapping scales that surround the hair fiber, protects inner tissues against external stimuli. The outermost surface of the cuticle is covered with a thin membrane containing proteins and lipids called the epicuticle. In a previous study, the authors conducted a depth profile analysis of a hair cuticle's amino acid composition to characterize its multilayer structure. Time-of-flight secondary ion mass spectrometry with a bismuth primary ion source was used in combination with the C60 sputtering technique for the analysis. It was confirmed that the lipids and cysteine-rich layer exist on the outermost cuticle surface, which is considered to be the epicuticle, though the detailed structure of the epicuticle has not been clarified. In this study, depth profile analysis of the cuticle surface was conducted using the argon gas cluster ion beam (Ar-GCIB) sputtering technique, in order to characterize the structure of the epicuticle. The shallow depth profile of the cuticle surface was investigated using an Ar-GCIB impact energy of 5 keV. Compared to the other amino acid peaks rich in the epicuticle, the decay of 18-methyleicosanic acid (18-MEA) thiolate peak was the fastest. This result suggests that the outermost surface of the hair is rich in 18-MEA. In conclusion, our results indicate that the outermost surfaces of cuticles have a multilayer (lipid and protein layers), which is consistent with the previously proposed structure.

Duplex aluminized coatings

NASA Technical Reports Server (NTRS)

Gedwill, M. A.; Grisaffe, S. J. (Inventor)

1975-01-01

The surface of a metallic base system is initially coated with a metallic alloy layer that is ductile and oxidation resistant. An aluminide coating is then applied to the metallic alloy layer. The chemistry of the metallic alloy layer is such that the oxidation resistance of the subsequently aluminized outermost layer is not seriously degraded.

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol

NASA Astrophysics Data System (ADS)

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-07-01

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03894h

Scanning probe microscopy for the analysis of composite Ti/hydrocarbon plasma polymer thin films

NASA Astrophysics Data System (ADS)

Choukourov, A.; Grinevich, A.; Slavinska, D.; Biederman, H.; Saito, N.; Takai, O.

2008-03-01

Composite Ti/hydrocarbon plasma polymer films with different Ti concentration were deposited on silicon by dc magnetron sputtering of titanium in an atmosphere of argon and hexane. As measured by Kelvin force microscopy and visco-elastic atomic force microscopy, respectively, surface potential and hardness increase with increasing Ti content. Adhesion force to silicon and to fibrinogen molecules was stronger for the Ti-rich films as evaluated from the AFM force-distance curves. Fibrinogen forms a very soft layer on these composites with part of the protein molecules embedded in the outermost region of the plasma polymer. An increase of the surface charge due to fibrinogen adsorption has been observed and attributed to positively charged αC domains of fibrinogen molecule.

Liquid Adsorption of Organic Compounds on Hematite α-Fe2O3 Using ReaxFF.

PubMed

Chia, Chung-Lim; Avendaño, Carlos; Siperstein, Flor R; Filip, Sorin

2017-10-24

ReaxFF-based molecular dynamics simulations are used in this work to study the effect of the polarity of adsorbed molecules in the liquid phase on the structure and polarization of hematite (α-Fe 2 O 3 ). We compared the adsorption of organic molecules with different polarities on a rigid hematite surface and on a flexible and polarizable surface. We show that the displacements of surface atoms and surface polarization in a flexible hematite model are proportional to the adsorbed molecule's polarity. The increase in electrostatic interactions resulting from charge transfer in the outermost solid atoms in a flexible hematite model results in better-defined adsorbed layers that are less ordered than those obtained assuming a rigid solid. These results suggest that care must be taken when parametrizing empirical transferable force fields because the calculated charges on a solid slab in vacuum may not be representative of a real system, especially when the solid is in contact with a polar liquid.

Novel application of polyelectrolyte multilayers as nanoscopic closures with hermetic sealing.

PubMed

Marcott, Stephanie A; Ada, Sena; Gibson, Phillip; Camesano, Terri A; Nagarajan, R

2012-03-01

Closure systems for personnel protection applications, such as protective clothing or respirator face seals, should provide effective permeation barrier to toxic gases. Currently available mechanical closure systems based on the hook and loop types (example, Velcro) do not provide adequate barrier to gas permeation. To achieve hermetic sealing, we propose a nonmechanical, nanoscopic molecular closure system based on complementary polyelectrolyte multilayers, one with a polycation outermost layer and the other with a polyanion outermost layer. The closure surfaces were prepared by depositing polyelectrolyte multilayers under a variety of deposition conditions, on conformable polymer substrates (thin films of polyethylene teraphthalate, PET or polyimide, PI). The hermetic sealing property of the closures was evaluated by measuring the air flow resistance using the dynamic moisture permeation cell (DMPC) at different humidity conditions. The DMPC measurements show that the polyelectrolyte multilayer closures provide significantly large resistance to air flow, approximately 20-800 times larger than that possible with conventional hook and loop type closure systems, at all humidity levels (from 5 to 95% relative humidity). Hence, from the point of view of providing a hermetic seal against toxic gas permeation, the polyelectrolyte multilayer closures are viable candidates for further engineering development. However, the adhesive strength of the multilayer closures measured by atomic force microscopy suggests that the magnitude of adhesion is much smaller than what is possible with mechanical closures. Therefore, we envisage the development of a composite closure system combining the mechanical closure to provide strong adhesion and the multilayer closure to provide hermetic sealing. © 2012 American Chemical Society

Buffer layer for thin film structures

DOEpatents

Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

2006-10-31

A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

Buffer layer for thin film structures

DOEpatents

Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

2010-06-15

A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

Method of protecting the surface of a substrate. [by applying aluminide coating

NASA Technical Reports Server (NTRS)

Gedwill, M. A. (Inventor); Grisaffe, S. J.

1974-01-01

The surface of a metallic base system is initially coated with a metallic alloy layer that is ductile and oxidation resistant. An aluminide coating is then applied to the metallic alloy layer. The chemistry of the metallic alloy layer is such that the oxidation resistance of the subsequently aluminized outermost layer is not seriously degraded.

Space Station WP-2 application of LDEF MLI results

NASA Technical Reports Server (NTRS)

Smith, Charles A.; Hasegawa, Mark M.; Jones, Cherie A.

1993-01-01

The Cascaded Variable Conductance Heat Pipe Experiment, which was developed by Michael Grote of McDonnell Douglas Electronic Systems Company, was located in Tray F-9 of the Long Duration Exposure Facility (LDEF), where it received atomic oxygen almost normal to its surface. The majority of the tray was covered by aluminized Kapton polyimide multilayer insulation (MLI), which showed substantial changes from atomic oxygen erosion. Most of the outermost Kapton layer of the MLI and the polyester scrim cloth under it were lost, and there was evidence of contaminant deposition which discolored the edges of the MLI blanket. Micrometeoroid and orbital debris (MM/OD) hits caused small rips in the MLI layers, and in some cases left cloudy areas where the vapor plume caused by a hit condensed on the next layer. The MLI was bent gradually through 90 deg at the edges to enclose the experiment, and the Kapton that survived along the curved portion showed the effects of atomic oxygen erosion at oblique angles. In spite of space environment effects over the period of the LDEF mission, the MLI blanket remained functional. The results of the analysis of LDEF MLI were used in developing the standard MLI blanket for Space Station Work Package-2 (WP-2). This blanket is expected to last 30 years when exposed to the low Earth orbit (LEO) environment constituents of atomic oxygen and MM/OD, which are the most damaging to MLI materials. The WP-2 standard blanket consists of an outer cover made from Beta-cloth glass fiber fabric which is aluminized on the interior surface, and an inner cover of 0.076-mm (0.003-in) double-side-aluminized perforated Kapton. The inner reflector layers are 0.0076-mm (0.0003-in) double-side aluminized, perforated Kapton separated by layers of Dacron polyester fabric. The outer cover was selected to be resistant to the LEO environment and durable enough to survive in orbit for 30 years. This paper describes the analyses of the LDEF MLI results, and how these results contributed to the selection of the WP-2 MLI blanket materials and configuration.

Protein Sensors Based on Optical Ring Resonators

NASA Technical Reports Server (NTRS)

Lin, Ying; Ksendzov, Alexander

2006-01-01

Prototype transducers based on integrated optical ring resonators have been demonstrated to be useful for detecting the protein avidin in extremely dilute solutions. In an experiment, one of the transducers proved to be capable of indicating the presence of avidin at a concentration of as little as 300 pM in a buffer solution a detection sensitivity comparable to that achievable by previously reported protein-detection techniques. These transducers are serving as models for the further development of integrated-optics sensors for detecting small quantities of other proteins and protein-like substances. The basic principle of these transducers was described in Chemical Sensors Based on Optical Ring Resonators (NPO-40601), NASA Tech Briefs, Vol. 29, No. 10 (October 2005), page 32. The differences between the present transducers and the ones described in the cited prior article lie in details of implementation of the basic principle. As before, the resonator in a transducer of the present type is a closed-circuit dielectric optical waveguide. The outermost layer of this waveguide, analogous to the optical cladding layer on an optical fiber, consists of a layer comprising sublayers having indices of refraction lower than that of the waveguide core. The outermost sublayer absorbs the chemical of interest (in this case, avidin). The index of refraction of the outermost sublayer changes with the concentration of absorbed avidin. The resonator is designed to operate with relatively strong evanescent-wave coupling between the outer sublayer and the electromagnetic field propagating along the waveguide core. By virtue of this coupling, the chemically induced change in the index of refraction of the outermost sublayer causes a measurable change in the spectrum of the resonator output.

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

Tougaard, Sven

The author reports a systematic study of the range of validity of a previously developed algorithm for automated x-ray photoelectron spectroscopy analysis, which takes into account the variation in both peak intensity and the intensity in the background of inelastically scattered electrons. This test was done by first simulating spectra for the Au4d peak with gold atoms distributed in the form of a wide range of nanostructures, which includes overlayers with varying thickness, a 5 A layer of atoms buried at varying depths and a substrate covered with an overlayer of varying thickness. Next, the algorithm was applied to analyzemore » these spectra. The algorithm determines the number of atoms within the outermost 3 {lambda} of the surface. This amount of substance is denoted AOS{sub 3{lambda}} (where {lambda} is the electron inelastic mean free path). In general the determined AOS{sub 3{lambda}} is found to be accurate to within {approx}10-20% depending on the depth distribution of the atoms. The algorithm also determines a characteristic length L, which was found to give unambiguous information on the depth distribution of the atoms for practically all studied cases. A set of rules for this parameter, which relates the value of L to the depths where the atoms are distributed, was tested, and these rules were found to be generally valid with only a few exceptions. The results were found to be rather independent of the spectral energy range (from 20 to 40 eV below the peak energy) used in the analysis.« less

Influence of salt and rinsing protocol on the structure of PAH/PSS polyelectrolyte multilayers.

PubMed

Feldötö, Zsombor; Varga, Imre; Blomberg, Eva

2010-11-16

A quartz crystal microbalance (QCM) and dual polarization interferometry (DPI) have been utilized to study how the structure of poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers is affected by the rinsing method (i.e., the termination of polyelectrolyte adsorption). The effect of the type of counterions used in the deposition solution was also investigated, and the polyelectrolyte multilayers were formed in a 0.5 M electrolyte solution (NaCl and KBr). From the measurements, it was observed that thicker layers were obtained when using KBr in the deposition solution than when using NaCl. Three different rinsing protocols have been studied: (i) the same electrolyte solution as used during multilayer formation, (ii) pure water, and (iii) first a salt solution (0.5 M) and then pure water. When the multilayer with PAH as the outermost layer was exposed to pure water, an interesting phenomenon was discovered: a large change in the energy dissipation was measured with the QCM. This could be attributed to the swelling of the layer, and from both QCM and DPI it is obvious that only the outermost PAH layer swells (to a thickness of 25-30 nm) because of a decrease in ionic strength and hence an increase in intra- and interchain repulsion, whereas the underlying layers retain a very rigid and compact structure with a low water content. Interestingly, the outermost PAH layer seems to obtain very similar thicknesses in water independent of the electrolyte used for the multilayer buildup. Another interesting aspect was that the measured thickness with the DPI evaluated by a single-layer model did not correlate with the estimated thickness from the model calculations performed on the QCM-D data. Thus, we applied a two-layer model to evaluate the DPI data and the results were in excellent agreement with the QCM-D results. To our knowledge, this evaluation of DPI data has not been done previously.

Evaluation of alternative cleaners for solder flux and mold release removal

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

Lopez, E.P.; Peebles, D.E.; Reich, J.E.

1991-01-01

As part of a solvent substitution program, an evaluation of selected alternative cleaners for solder flux and mold release removal has been performed. Six cleaners were evaluated for their efficiency in removing a rosin mildly activated flux and a silicone mold release from copper, 17-4PH stainless steel, polyimide quartz glass and tin-lead surfaces. A parallel effort also studied deionized water removal of organic acid fluxes. Auger electron spectroscopy and X-ray photoelectron spectroscopy were used to determine relative elemental cleanliness of the outermost atomic layers. An Omega Meter Test was used to measure residual ionic contamination. Water drop contact angles weremore » used to measure the effectiveness of silicone removal from Cu substrates. In most cases, the cleanliness levels were good to excellent. 10 refs., 8 figs., 19 tabs.« less

The surface properties of Shewanella putrefaciens 200 and S. oneidensis MR-1: the effect of pH and terminal electron acceptors.

PubMed

Furukawa, Yoko; Dale, Jason R

2013-04-08

We investigated the surface characteristics of two strains of Shewanella sp., S. oneidensis MR-1 and S. putrefaciens 200, that were grown under aerobic conditions as well as under anaerobic conditions with trimethylamine oxide (TMAO) as the electron acceptor. The investigation focused on the experimental determination of electrophoretic mobility (EPM) under a range of pH and ionic strength, as well as by subsequent modeling in which Shewanella cells were considered to be soft particles with water- and ion-permeable outermost layers. The soft layer of p200 is significantly more highly charged (i.e., more negative) than that of MR-1. The effect of electron acceptor on the soft particle characteristics of Shewanella sp. is complex. The fixed charge density, which is a measure of the deionized and deprotonated functional groups in the soft layer polymers, is slightly greater (i.e., more negative) for aerobically grown p200 than for p200 grown with TMAO. On the other hand, the fixed charge density of aerobically grown MR1 is slightly less than that of p200 grown with TMAO. The effect of pH on the soft particle characteristics is also complex, and does not exhibit a clear pH-dependent trend. The Shewanella surface characteristics were attributed to the nature of the outermost soft layer, the extracellular polymeric substances (EPS) in case of p200 and lypopolysaccharides (LPS) in case of MR1 which generally lacks EPS. The growth conditions (i.e., aerobic vs. anaerobic TMAO) have an influence on the soft layer characteristics of Shewanella sp. cells. Meanwhile, the clear pH dependency of the mechanical and morphological characteristics of EPS and LPS layers, observed in previous studies through atomic force microscopy, adhesion tests and spectroscopies, cannot be corroborated by the electrohydrodynamics-based soft particle characteristics which does not exhibited a clear pH dependency in this study. While the electrohydrodynamics-based soft-particle model is a useful tool in understanding bacteria's surface properties, it needs to be supplemented with other characterization methods and models (e.g., chemical and micromechanical) in order to comprehensively address all of the surface-related characteristics important in environmental and other aqueous processes.

Theoretical model of the helium zone plate microscope

NASA Astrophysics Data System (ADS)

Salvador Palau, Adrià; Bracco, Gianangelo; Holst, Bodil

2017-01-01

Neutral helium microscopy is a new technique currently under development. Its advantages are the low energy, charge neutrality, and inertness of the helium atoms, a potential large depth of field, and the fact that at thermal energies the helium atoms do not penetrate into any solid material. This opens the possibility, among others, for the creation of an instrument that can measure surface topology on the nanoscale, even on surfaces with high aspect ratios. One of the most promising designs for helium microscopy is the zone plate microscope. It consists of a supersonic expansion helium beam collimated by an aperture (skimmer) focused by a Fresnel zone plate onto a sample. The resolution is determined by the focal spot size, which depends on the size of the skimmer, the optics of the system, and the velocity spread of the beam through the chromatic aberrations of the zone plate. An important factor for the optics of the zone plate is the width of the outermost zone, corresponding to the smallest opening in the zone plate. The width of the outermost zone is fabrication limited to around 10 nm with present-day state-of-the-art technology. Due to the high ionization potential of neutral helium atoms, it is difficult to build efficient helium detectors. Therefore, it is crucial to optimize the microscope design to maximize the intensity for a given resolution and width of the outermost zone. Here we present an optimization model for the helium zone plate microscope. Assuming constant resolution and width of the outermost zone, we are able to reduce the problem to a two-variable problem (zone plate radius and object distance) and we show that for a given beam temperature and pressure, there is always a single intensity maximum. We compare our model with the highest-resolution zone plate focusing images published and show that the intensity can be increased seven times. Reducing the width of the outermost zone to 10 nm leads to an increase in intensity of more than 8000 times. Finally, we show that with present-day state-of-the-art detector technology (ionization efficiency 1 ×10-3 ), a resolution of the order of 10 nm is possible. In order to make this quantification, we have assumed a Lambertian reflecting surface and calculated the beam spot size that gives a signal 100 cts/s within a solid angle of 0.02 sr, following an existing helium microscope design.

The impact of atomization on the surface composition of spray-dried milk droplets.

PubMed

Foerster, Martin; Gengenbach, Thomas; Woo, Meng Wai; Selomulya, Cordelia

2016-04-01

The dominant presence of fat at the surface of spray-dried milk powders has been widely reported in the literature and described as resulting in unfavourable powder properties. The mechanism(s) causing this phenomenon are yet to be clearly identified. A systematic investigation of the component distribution in atomized droplets and spray-dried particles consisting of model milk systems with different fat contents demonstrated that atomization strongly influences the final surface composition. Cryogenic flash-freezing of uniform droplets from a microfluidic jet nozzle directly after atomization helped to distinguish the influence of the atomization stage from the drying stage. It was confirmed that the overrepresentation of fat on the surface is independent of the atomization technique, including a pressure-swirl single-fluid spray nozzle and a pilot-scale rotary disk spray dryer commonly used in industry. It is proposed that during the atomization stage a disintegration mechanism along the oil-water interface of the fat globules causes the surface predominance of fat. X-ray photoelectron spectroscopic measurements detected the outermost fat layer and some adjacent protein present on both atomized droplets and spray-dried particles. Confocal laser scanning microscopy gave a qualitative insight into the protein and fat distribution throughout the cross-sections, and confirmed the presence of a fat film along the particle surface. The film remained on the surface in the subsequent drying stage, while protein accumulated underneath, driven by diffusion. The results demonstrated that atomization induces component segregation and fat-rich surfaces in spray-dried milk powders, and thus these cannot be prevented by adjusting the spray drying conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

First-principles density functional theory (DFT) study of gold nanorod and its interaction with alkanethiol ligands.

PubMed

Hu, Hang; Reven, Linda; Rey, Alejandro

2013-10-17

The structure and mechanical properties of gold nanorods and their interactions with alkenthiolate self-assembled monolayers have been determined using a novel first-principle density functional theory simulation approach. The multifaceted, 1-dimensional, octagonal nanorod has alternate Au100 and Au110 surfaces. The structural optimization of the gold nanorods was performed with a mixed basis: the outermost layer of gold atoms used double-ζ plus polarization (DZP), the layer below used double-ζ (DZ), and the inner layers used single-ζ (SZ). The final structure compares favorably with simulations using DZP for all atoms. Phonon dispersion calculations and ab initio molecular dynamics (AIMD) were used to establish the dynamic and thermal stability of the system. From the AIMD simulations it was found that the nanorod system will undergo significant surface reconstruction at 300 K. In addition, when subjected to mechanical stress in the axial direction, the nanorod responds as an orthotropic material, with uniform expansion along the radial direction. The Young's moduli are 207 kbar in the axial direction and 631 kbar in the radial direction. The binding of alkanethiolates, ranging from methanethiol to pentanethiol, caused formation of surface point defects on the Au110 surfaces. On the Au100 surfaces, the defects occurred in the inner layer, creating a small surface island. These defects make positive and negative concavities on the gold nanorod surface, which helps the ligand to achieve a more stable state. The simulation results narrowed significant knowledge gaps on the alkanethiolate adsorption process and on their mutual interactions on gold nanorods. The mechanical characterization offers a new dimension to understand the physical chemistry of these complex nanoparticles.

High temperature gas nitriding and tempering in 17Cr-1Ni-0.5C-0.4V steel

NASA Astrophysics Data System (ADS)

Kong, J. H.; Lee, D. J.; On, H. Y.; Park, S. J.; Kim, S. K.; Kang, C. Y.; Sung, J. H.; Lee, H. W.

2010-12-01

High temperature gas nitriding (HTGN) at 1050 °C and tempering of a 17Cr-1Ni-0.5C-0.4V (CNV) steel were experimentally investigated. The phases appearing in the surface layer of the HTGN-treated steel were martensite and austenite with mostly Cr2N precipitates that were formed by permeated nitrogen, and a small amount of Cr23C6 and VN precipitates. The reverse migration of carbon hindered the diffusion of nitrogen when nitrogen permeated from the surface to the interior, which resulted in the accumulation of nitrogen on the outermost surface. The strong affinity between nitrogen and chromium atoms induced the diffusion of chromium from the interior to the surface, leading to the substitution of Cr23C6 for Cr2N. After tempering the HTGN-treated steel at 500 °C, the dense precipitates of Cr2N and the increased martensite phase in the surface layer led to secondary hardening, which increased the hardness value up to 901 Hv.

Using the Hilbert uniqueness method in a reconstruction algorithm for electrical impedance tomography.

PubMed

Dai, W W; Marsili, P M; Martinez, E; Morucci, J P

1994-05-01

This paper presents a new version of the layer stripping algorithm in the sense that it works essentially by repeatedly stripping away the outermost layer of the medium after having determined the conductivity value in this layer. In order to stabilize the ill posed boundary value problem related to each layer, we base our algorithm on the Hilbert uniqueness method (HUM) and implement it with the boundary element method (BEM).

Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice

PubMed Central

Sánchez, M. Alejandra; Kling, Tanja; Ishiyama, Tatsuya; van Zadel, Marc-Jan; Mezger, Markus; Jochum, Mara N.; Cyran, Jenée D.; Smit, Wilbert J.; Bakker, Huib J.; Shultz, Mary Jane; Morita, Akihiro; Donadio, Davide; Nagata, Yuki; Bonn, Mischa; Backus, Ellen H. G.

2017-01-01

On the surface of water ice, a quasi-liquid layer (QLL) has been extensively reported at temperatures below its bulk melting point at 273 K. Approaching the bulk melting temperature from below, the thickness of the QLL is known to increase. To elucidate the precise temperature variation of the QLL, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surface-specific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice faces at different temperatures. For the basal face, a stepwise, sudden weakening of the hydrogen-bonded structure of the outermost water layers occurs at 257 K. The spectral calculations from the molecular dynamics simulations reproduce the experimental findings; this allows us to interpret our experimental findings in terms of a stepwise change from one to two molten bilayers at the transition temperature. PMID:27956637

Novel water filtration of saline water in the outermost layer of mangrove roots.

PubMed

Kim, Kiwoong; Seo, Eunseok; Chang, Suk-Kyu; Park, Tae Jung; Lee, Sang Joon

2016-02-05

The scarcity of fresh water is a global challenge faced at present. Several desalination methods have been suggested to secure fresh water from sea water. However, conventional methods suffer from technical limitations, such as high power consumption, expensive operating costs, and limited system durability. In this study, we examined the feasibility of using halophytes as a novel technology of desalinating high-concentration saline water for long periods. This study investigated the biophysical characteristics of sea water filtration in the roots of the mangrove Rhizophora stylosa from a plant hydrodynamic point of view. R. stylosa can grow even in saline water, and the salt level in its roots is regulated within a certain threshold value through filtration. The root possesses a hierarchical, triple layered pore structure in the epidermis, and most Na(+) ions are filtered at the first sublayer of the outermost layer. The high blockage of Na(+) ions is attributed to the high surface zeta potential of the first layer. The second layer, which is composed of macroporous structures, also facilitates Na(+) ion filtration. This study provides insights into the mechanism underlying water filtration through halophyte roots and serves as a basis for the development of a novel bio-inspired desalination method.

Direct quantitative measurement of the C═O⋅⋅⋅H–C bond by atomic force microscopy

PubMed Central

Kawai, Shigeki; Nishiuchi, Tomohiko; Kodama, Takuya; Spijker, Peter; Pawlak, Rémy; Meier, Tobias; Tracey, John; Kubo, Takashi; Meyer, Ernst; Foster, Adam S.

2017-01-01

The hydrogen atom—the smallest and most abundant atom—is of utmost importance in physics and chemistry. Although many analysis methods have been applied to its study, direct observation of hydrogen atoms in a single molecule remains largely unexplored. We use atomic force microscopy (AFM) to resolve the outermost hydrogen atoms of propellane molecules via very weak C═O⋅⋅⋅H–C hydrogen bonding just before the onset of Pauli repulsion. The direct measurement of the interaction with a hydrogen atom paves the way for the identification of three-dimensional molecules such as DNAs and polymers, building the capabilities of AFM toward quantitative probing of local chemical reactivity. PMID:28508080

Platinized tin oxide catalysts for CO2 lasers: Effects of pretreatment

NASA Technical Reports Server (NTRS)

Gardner, Steven D.; Hoflund, Gar B.; Schryer, David R.; Upchurch, Billy T.

1990-01-01

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as PtO2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Platinized tin oxide catalysts for CO2 lasers - Effects of pretreatment

NASA Technical Reports Server (NTRS)

Gardner, Steven D.; Hoflund, Gar B.; Schryer, David R.; Upchurch, Billy T.

1989-01-01

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as Pto2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Wheel-type magnetic refrigerator

DOEpatents

Barclay, John A.

1983-01-01

The disclosure is directed to a wheel-type magnetic refrigerator capable of cooling over a large temperature range. Ferromagnetic or paramagnetic porous materials are layered circumferentially according to their Curie temperature. The innermost layer has the lowest Curie temperature and the outermost layer has the highest Curie temperature. The wheel is rotated through a magnetic field perpendicular to the axis of the wheel and parallel to its direction of rotation. A fluid is pumped through portions of the layers using inner and outer manifolds to achieve refrigeration of a thermal load.

Wheel-type magnetic refrigerator

DOEpatents

Barclay, J.A.

1982-01-20

The disclosure is directed to a wheel-type magnetic refrigerator capable of cooling over a large temperature range. Ferromagnetic or paramagnetic porous materials are layered circumferentially according to their Curie temperature. The innermost layer has the lowest Curie temperature and the outermost layer has the highest Curie temperature. The wheel is rotated through a magnetic field perpendicular to the axis of the wheel and parallel to its direction of rotation. A fluid is pumped through portions of the layers using inner and outer manifolds to achieve refrigeration of a thermal load.

Preparation of Water-Repellent Glass by Sol-Gel Process Using Perfluoroalkylsilane and Tetraethoxysilane.

PubMed

Jeong, Hye-Jeong; Kim, Dong-Kwon; Lee, Soo-Bok; Kwon, Soo-Han; Kadono, Kohei

2001-03-01

Coating films on glass substrate were prepared by sol-gel process using alkoxide solutions containing perfluoroalkylsilane (PFAS) and tetraethoxysilane (TEOS). The physical properties of the coating films were characterized by SEM, FT-IR, and XRD. And their surface properties were investigated by measuring contact angles and atomic compositions. Transparent coating films with smooth surface and uniform thickness could be obtained. The contact angles of the coating films for water and methylene iodide are extremely high, at 118 degrees and 97 degrees, respectively, and their surface free energies are about 9.7 dyn/cm. It was found that the water-repellent glass prepared is very hydrophobic and exhibits excellent water-repellency. Hydrophobic perfluoroalkyl groups are preferentially enriched to the outermost layer at the coating film-air interface, and two layers probably exist in the coating film. The upper layer oriented toward the air is composed of mainly perfluoroalkyl groups originating from PFAS, and the lower layer is composed of mainly -OSiO- groups originating from TEOS. The heat treatment after drying step cannot influence the surface enrichment of the perfluoroalkyl group. The hydrolysis reaction should be more completely done before the dip coating step to obtain lower surface free energy. The burning temperature should be less than 300 degrees C because the perfluoroalkyl group begins to decompose from this temperature. Copyright 2001 Academic Press.

Genetics Home Reference: keratitis-ichthyosis-deafness syndrome

MedlinePlus

... outermost layer of skin (the epidermis ). The GJB2 gene mutations that cause KID syndrome change single protein building ... in KID syndrome. It is unclear how GJB2 gene mutations affect the eye. Because at least one of ...

Tuning the synthesis of platinum-copper nanoparticles with a hollow core and porous shell for the selective hydrogenation of furfural to furfuryl alcohol.

PubMed

Huang, Shuangshuang; Yang, Nating; Wang, Shibin; Sun, Yuhan; Zhu, Yan

2016-08-07

Pt-Cu nanoparticles constructed with a hollow core and porous shell have been synthesized in which Pt-Cu cages with multiporous outermost shells are formed at the initial stage and then the Pt and Cu atoms in solution continuously fed these hollow-core of cages by passing through the porous tunnels of the outermost shells, finally leading to the formation of hollow structures with different sizes. Furthermore, these hollow-core Pt-Cu nanoparticles are more effective than the solid-core Pt-Cu nanoparticles for the catalytic hydrogenation of furfural toward furfuryl alcohol. The former can achieve almost 100% conversion of furfural with 100% selectivity toward the alcohol.

Energy filtering transmission electron microscopy immunocytochemistry and antigen retrieval of surface layer proteins from Tannerella forsythensis using microwave or autoclave heating with citraconic anhydride

PubMed Central

2012-01-01

Tannerella forsythensis (Bacteroides forsythus), an anaerobic Gram-negative species of bacteria that plays a role in the progression of periodontal disease, has a unique bacterial protein profile. It is characterized by two unique protein bands with molecular weights of more than 200 kDa. It also is known to have a typical surface layer (S-layer) consisting of regularly arrayed subunits outside the outer membrane. We examined the relationship between high molecular weight proteins and the S-layer using electron microscopic immunolabeling with chemical fixation and an antigen retrieval procedure consisting of heating in a microwave oven or autoclave with citraconic anhydride. Immunogold particles were localized clearly at the outermost cell surface. We also used energy-filtering transmission electron microscopy (EFTEM) to visualize 3, 3′-diaminobenzidine tetrahydrochloride (DAB) reaction products after microwave antigen retrieval with 1% citraconic anhydride. The three-window method for electron spectroscopic images (ESI) of nitrogen by the EFTEM reflected the presence of moieties demonstrated by the DAB reaction with horseradish peroxidase (HRP)-conjugated secondary antibodies instead of immunogold particles. The mapping patterns of net nitrogen were restricted to the outermost cell surface. PMID:22984898

Energy filtering transmission electron microscopy immunocytochemistry and antigen retrieval of surface layer proteins from Tannerella forsythensis using microwave or autoclave heating with citraconic anhydride.

PubMed

Moriguchi, K; Mitamura, Y; Iwami, J; Hasegawa, Y; Higuchi, N; Murakami, Y; Maeda, H; Yoshimura, F; Nakamura, H; Ohno, N

2012-11-01

Tannerella forsythensis (Bacteroides forsythus), an anaerobic Gram-negative species of bacteria that plays a role in the progression of periodontal disease, has a unique bacterial protein profile. It is characterized by two unique protein bands with molecular weights of more than 200 kDa. It also is known to have a typical surface layer (S-layer) consisting of regularly arrayed subunits outside the outer membrane. We examined the relationship between high molecular weight proteins and the S-layer using electron microscopic immunolabeling with chemical fixation and an antigen retrieval procedure consisting of heating in a microwave oven or autoclave with citraconic anhydride. Immunogold particles were localized clearly at the outermost cell surface. We also used energy-filtering transmission electron microscopy (EFTEM) to visualize 3, 3'-diaminobenzidine tetrahydrochloride (DAB) reaction products after microwave antigen retrieval with 1% citraconic anhydride. The three-window method for electron spectroscopic images (ESI) of nitrogen by the EFTEM reflected the presence of moieties demonstrated by the DAB reaction with horseradish peroxidase (HRP)-conjugated secondary antibodies instead of immunogold particles. The mapping patterns of net nitrogen were restricted to the outermost cell surface.

Single-molecule conductance through multiple π-π-stacked benzene rings determined with direct electrode-to-benzene ring connections.

PubMed

Schneebeli, Severin T; Kamenetska, Maria; Cheng, Zhanling; Skouta, Rachid; Friesner, Richard A; Venkataraman, Latha; Breslow, Ronald

2011-02-23

Understanding electron transport across π-π-stacked systems will help to answer fundamental questions about biochemical redox processes and benefit the design of new materials and molecular devices. Herein we employed the STM break-junction technique to measure the single-molecule conductance of multiple π-π-stacked aromatic rings. We studied electron transport through up to four stacked benzene rings held together in an eclipsed fashion via a paracyclophane scaffold. We found that the strained hydrocarbons studied herein couple directly to gold electrodes during the measurements; hence, we did not require any heteroatom binding groups as electrical contacts. Density functional theory-based calculations suggest that the gold atoms of the electrodes bind to two neighboring carbon atoms of the outermost cyclophane benzene rings in η(2) fashion. Our measurements show an exponential decay of the conductance with an increasing number of stacked benzene rings, indicating a nonresonant tunneling mechanism. Furthermore, STM tip-substrate displacement data provide additional evidence that the electrodes bind to the outermost benzene rings of the π-π-stacked molecular wires.

Atomic radii for atoms with the 6s shell outermost: The effective atomic radius and the van der Waals radius from {sub 55}Cs to {sub 80}Hg

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

Tatewaki, Hiroshi, E-mail: htatewak@nsc.nagoya-cu.ac.jp; Institute of Advanced Studies in Artificial Intelligence, Chukyo University, Toyota, Aichi 470-0393; Hatano, Yasuyo

We consider, for atoms from {sub 55}Cs to {sub 80}Hg, the effective atomic radius (r{sub ear}), which is defined as the distance from the nucleus at which the magnitude of the electric field is equal to that in He at one half of the equilibrium bond length of He{sub 2}. The values of r{sub ear} are about 50% larger than the mean radius of the outermost occupied orbital of 6s, . The value of r{sub ear} decreases from {sub 55}Cs to {sub 56}Ba and undergoes increases and decreases with rising nuclear charge from {sub 57}La to {sub 70}Y b. Inmore » fact r{sub ear} is understood as comprising two interlaced sequences; one consists of {sub 57}La, {sub 58}Ce, and {sub 64}Gd, which have electronic configuration (4f{sup n−1})(5d{sup 1})(6s{sup 2}), and the remaining atoms have configuration (4f{sup n})(6s{sup 2}). The sphere defined by r{sub ear} contains 85%–90% of the 6s electrons. From {sub 71}Lu to {sub 80}Hg the radius r{sub ear} also involves two sequences, corresponding to the two configurations 5d{sup n+1}6s{sup 1} and 5d{sup n}6s{sup 2}. The radius r{sub ear} according to the present methodology is considerably larger than r{sub vdW} obtained by other investigators, some of who have found values of r{sub vdW} close to .« less

The c-axis charge traveling wave in a coupled system of Josephson junctions

NASA Astrophysics Data System (ADS)

Shukrinov, Yu. M.; Hamdipour, M.

2012-05-01

We demonstrate a manifestation of the charge traveling wave along the c axis (TW) in current voltage characteristics of coupled Josephson junctions in high- T c superconductors. The branches related to the TW with different wavelengths are found for the stacks with different number of Josephson junctions at different values of system's parameters. Transitions between the TW branches and the outermost branch are observed. The electric charge in the superconducting layers and charge-charge correlation functions for TW and outermost branches show different behavior with bias current. We propose an experimental testing of the TW branching by microwave irradiation.

Wheel-type magnetic refrigerator

DOEpatents

Barclay, J.A.

1983-10-11

The disclosure is directed to a wheel-type magnetic refrigerator capable of cooling over a large temperature range. Ferromagnetic or paramagnetic porous materials are layered circumferentially according to their Curie temperature. The innermost layer has the lowest Curie temperature and the outermost layer has the highest Curie temperature. The wheel is rotated through a magnetic field perpendicular to the axis of the wheel and parallel to its direction of rotation. A fluid is pumped through portions of the layers using inner and outer manifolds to achieve refrigeration of a thermal load. 7 figs.

Method of controllong the deposition of hydrogenated amorphous silicon and apparatus therefor

DOEpatents

Hanak, Joseph J.

1985-06-25

An improved method and apparatus for the controlled deposition of a layer of hydrogenated amorphous silicon on a substrate. Means is provided for the illumination of the coated surface of the substrate and measurement of the resulting photovoltage at the outermost layer of the coating. Means is further provided for admixing amounts of p type and n type dopants to the reactant gas in response to the measured photovoltage to achieve a desired level and type of doping of the deposited layer.

Distribution of strontium-90 in a 1959 wheat sample.

PubMed

RIVERA, J

1961-03-17

At least 22 percent of the strontium-90 found in a sample of wheat harvested in 1959 was due to direct deposition. Twenty-seven percent of the total strontium-90 content of this wheat sample was contained in the outermost bran layer.

16 CFR 1632.1 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-01-01

... which contain upholstery material between the ticking and the mattress core, and any detachable... which do not contain upholstery material between the ticking and the mattress core, upholstered... outermost layer of fabric or related material that encloses the core and upholstery materials of a mattress...

Obsidian hydration profiles measured by sputter-induced optical emission.

PubMed

Tsong, I S; Houser, C A; Yusef, N A; Messier, R F; White, W B; Michels, J W

1978-07-28

The variation of concentrations of hydrogen, sodium, potassium, lithium, calcium, magnesium, silicon, and aluminum as a function of depth in the hydration layer of obsidian artifacts has been determined by sputter-induced optical emission. The surface hydration is accompanied by dealkalization, and there is a buildup of alkaline earths, calcium and magnesium in the outermost layers. These results have clarified the phenomena underlying the obsidian hydration dating technique.

Keratinocyte differentiation is regulated by the Rho and ROCK signaling pathway.

PubMed

McMullan, Rachel; Lax, Siân; Robertson, Vicki H; Radford, David J; Broad, Simon; Watt, Fiona M; Rowles, Alison; Croft, Daniel R; Olson, Michael F; Hotchin, Neil A

2003-12-16

The epidermis comprises multiple layers of specialized epithelial cells called keratinocytes. As cells are lost from the outermost epidermal layers, they are replaced through terminal differentiation, in which keratinocytes of the basal layer cease proliferating, migrate upwards, and eventually reach the outermost cornified layers. Normal homeostasis of the epidermis requires that the balance between proliferation and differentiation be tightly regulated. The GTP binding protein RhoA plays a fundamental role in the regulation of the actin cytoskeleton and in the adhesion events that are critically important to normal tissue homeostasis. Two central mediators of the signals from RhoA are the ROCK serine/threonine kinases ROCK-I and ROCK-II. We have analyzed ROCK's role in the regulation of epidermal keratinocyte function by using a pharmacological inhibitor and expressing conditionally active or inactive forms of ROCK-II in primary human keratinocytes. We report that blocking ROCK function results in inhibition of keratinocyte terminal differentiation and an increase in cell proliferation. In contrast, activation of ROCK-II in keratinocytes results in cell cycle arrest and an increase in the expression of a number of genes associated with terminal differentiation. Thus, these results indicate that ROCK plays a critical role in regulating the balance between proliferation and differentiation in human keratinocytes.

Processing of hydroxylapatite coatings on titanium alloy bone prostheses

DOEpatents

Nastasi, M.A.; Levine, T.E.; Mayer, J.W.; Pizziconi, V.B.

1998-10-06

Processing of hydroxylapatite sol-gel films on titanium alloy bone prostheses. A method utilizing non-line-of-sight ion beam implantation and/or rapid thermal processing to provide improved bonding of layers of hydroxylapatite to titanium alloy substrates while encouraging bone ingrowth into the hydroxylapatite layers located away from the substrate, is described for the fabrication of prostheses. The first layer of hydroxylapatite is mixed into the substrate by the ions or rapidly thermally annealed, while subsequent layers are heat treated or densified using ion implantation to form layers of decreasing density and larger crystallization, with the outermost layers being suitable for bone ingrowth.

Processing of hydroxylapatite coatings on titanium alloy bone prostheses

DOEpatents

Nastasi, Michael A.; Levine, Timothy E.; Mayer, James W.; Pizziconi, Vincent B.

1998-01-01

Processing of hydroxylapatite sol-gel films on titanium alloy bone prostheses. A method utilizing non-line-of-sight ion beam implantation and/or rapid thermal processing to provide improved bonding of layers of hydroxylapatite to titanium alloy substrates while encouraging bone ingrowth into the hydroxylapatite layers located away from the substrate, is described for the fabrication of prostheses. The first layer of hydroxylapatite is mixed into the substrate by the ions or rapidly thermally annealed, while subsequent layers are heat treated or densified using ion implantation to form layers of decreasing density and larger crystallization, with the outermost layers being suitable for bone ingrowth.

Surface Chemistry of La0.99Sr0.01NbO4-d and Its Implication for Proton Conduction.

PubMed

Li, Cheng; Pramana, Stevin S; Ni, Na; Kilner, John; Skinner, Stephen J

2017-09-06

Acceptor-doped LaNbO 4 is a promising electrolyte material for proton-conducting fuel cell (PCFC) applications. As charge transfer processes govern device performance, the outermost surface of acceptor-doped LaNbO 4 will play an important role in determining the overall cell performance. However, the surface composition is poorly characterized, and the understanding of its impact on the proton exchange process is rudimentary. In this work, the surface chemistry of 1 atom % Sr-doped LaNbO 4 (La 0.99 Sr 0.01 NbO 4-d , denoted as LSNO) proton conductor is characterized using LEIS and SIMS. The implication of a surface layer on proton transport is studied using the isotopic exchange technique. It has shown that a Sr-enriched but La-deficient surface layer of about 6-7 nm thick forms after annealing the sample under static air at 1000 °C for 10 h. The onset of segregation is found to be between 600 and 800 °C, and an equilibrium surface layer forms after 10 h annealing. A phase separation mechanism, due to the low solubility of Sr in LaNbO 4 , has been proposed to explain the observed segregation behavior. The surface layer was concluded to impede the water incorporation process, leading to a reduced isotopic fraction after the D 2 16 O wet exchange process, highlighting the impact of surface chemistry on the proton exchange process.

Structural morphology of YBa 2Cu 3O 7- x

NASA Astrophysics Data System (ADS)

Sun, B. N.; Hartman, P.; Woensdregt, C. F.; Schmid, H.

1990-03-01

The structural morphology of YBa 2Cu 3O 7- x (YBCO) has been investigated by application of the periodic bond chain (PBC) theory. For x=1, the F forms were found to be {001}, {011}, {013}, {112} and {114}. Attachment energies have been calculated in broken bond model and in an electrostatic point charge model. For x=1 the theoretical growth habit is tabular to platy {001} with {011} as side faces. For x=0 {010} also becomes an F form. The habit is isometric with large {001} and {011} and small {010} faces. The outermost layer of {001} contains half of the Cu + ( x=1) or Cu 3+ and O 2- ( x=0) ions in an ordered arrangement based on a c(2x2) quadratic lattice. For the outermost layer of (010) ( x=0) an ordering scheme of the copper and oxygen ions is proposed. The occurrence of {010} rather than {011} on grown crystals has to be ascribed to external factors.

A new series of two-dimensional silicon crystals with versatile electronic properties

NASA Astrophysics Data System (ADS)

Chae, Kisung; Kim, Duck Young; Son, Young-Woo

2018-04-01

Silicon (Si) is one of the most extensively studied materials owing to its significance to semiconductor science and technology. While efforts to find a new three-dimensional (3D) Si crystal with unusual properties have made some progress, its two-dimensional (2D) phases have not yet been explored as much. Here, based on a newly developed systematic ab initio materials searching strategy, we report a series of novel 2D Si crystals with unprecedented structural and electronic properties. The new structures exhibit perfectly planar outermost surface layers of a distorted hexagonal network with their thicknesses varying with the atomic arrangement inside. Dramatic changes in electronic properties ranging from semimetal to semiconducting with indirect energy gaps and even to one with direct energy gaps are realized by varying thickness as well as by surface oxidation. Our predicted 2D Si crystals with flat surfaces and tunable electronic properties will shed light on the development of silicon-based 2D electronics technology.

Metallic MoN layer and its application as anode for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Zhang, Qiaoxuan; Ma, Jiachen; Lei, Ming; Quhe, Ruge

2018-04-01

Recently, two-dimensional (2D) metallic MoN was manufactured successfully in experiment. Its intrinsic properties remain to be explored theoretically, in depth. The intrinsic properties of a MoN monolayer are investigated by first-principles calculations. The distinct geometric properties of the outermost Mo and N surfaces are discovered. We predict an extremely high work function of 6.3 eV of the N surface, which indicates the great value of the 2D MoN for application in the semiconductor industry. We further explore the potential of 2D MoN as anode material for lithium-ion batteries. It is found that the adsorption energy of a single Li atom on an MoN surface can be as low as -4.04 eV. The small diffusion barriers (0.41 eV) and high theoretical maximum capacity (406 mAh · g-1 with the inclusion of multilayer adsorption) all imply an outstanding lithium-ion battery performance by 2D MoN.

Thermogravimetric analysis of the interaction of ferromagnetic metal atom and multiwalled carbon nanotubes.

PubMed

Rawat, Naveen; Gudyaka, Russel; Kumar, Mohit; Joshi, Bharat; Santhanam, Kalathur S V

2008-04-01

This paper describes the thermal oxidative behavior of atomized iron or atomized cobalt in the presence of multiwalled carbon nanotubes (MWCNT). The thermogravimetric analysis shows the atomized iron thermal oxidation starts at about 500 degrees C that is absent when the atomized iron is sintered with multiwalled carbon naonotubes. The thermal oxidation of iron in the sintered samples requires the collapse of the multiwalled carbon nanotubes. A similar behavior is observed with atomized cobalt when its oxidation requires the collapse of the nanotubes. This thermal oxidative shift is interpreted as due to the atomized iron or atomized cobalt atom experiencing extensive overlap and confinement effect with multiwalled carbon nanotubes causing a spin transfer. This confinement effect is suggested to produce a transformation of iron from the outermost electronic distribution of 3d64s2 to an effective configuration of 3d84s0 and for cobalt 3d74s2 to 3d94s0 producing spintronics effect.

Imaging Cell Wall Architecture in Single Zinnia elegans Tracheary Elements1[OA

PubMed Central

Lacayo, Catherine I.; Malkin, Alexander J.; Holman, Hoi-Ying N.; Chen, Liang; Ding, Shi-You; Hwang, Mona S.; Thelen, Michael P.

2010-01-01

The chemical and structural organization of the plant cell wall was examined in Zinnia elegans tracheary elements (TEs), which specialize by developing prominent secondary wall thickenings underlying the primary wall during xylogenesis in vitro. Three imaging platforms were used in conjunction with chemical extraction of wall components to investigate the composition and structure of single Zinnia TEs. Using fluorescence microscopy with a green fluorescent protein-tagged Clostridium thermocellum family 3 carbohydrate-binding module specific for crystalline cellulose, we found that cellulose accessibility and binding in TEs increased significantly following an acidified chlorite treatment. Examination of chemical composition by synchrotron radiation-based Fourier-transform infrared spectromicroscopy indicated a loss of lignin and a modest loss of other polysaccharides in treated TEs. Atomic force microscopy was used to extensively characterize the topography of cell wall surfaces in TEs, revealing an outer granular matrix covering the underlying meshwork of cellulose fibrils. The internal organization of TEs was determined using secondary wall fragments generated by sonication. Atomic force microscopy revealed that the resulting rings, spirals, and reticulate structures were composed of fibrils arranged in parallel. Based on these combined results, we generated an architectural model of Zinnia TEs composed of three layers: an outermost granular layer, a middle primary wall composed of a meshwork of cellulose fibrils, and inner secondary wall thickenings containing parallel cellulose fibrils. In addition to insights in plant biology, studies using Zinnia TEs could prove especially productive in assessing cell wall responses to enzymatic and microbial degradation, thus aiding current efforts in lignocellulosic biofuel production. PMID:20592039

Proscene: A feature-rich framework for interactive environments

NASA Astrophysics Data System (ADS)

Charalambos, Jean Pierre

We introduce Proscene, a feature-rich, open-source framework for interactive environments. The design of Proscene comprises a three-layered onion-like software architecture, promoting different possible development scenarios. The framework innermost layer decouples user gesture parsing from user-defined actions. The in-between layer implements a feature-rich set of widely-used motion actions allowing the selection and manipulation of objects, including the scene viewpoint. The outermost layer exposes those features as a Processing library. The results have shown the feasibility of our approach together with the simplicity and flexibility of the Proscene framework API.

Array analyses of SmKS waves and the stratification of Earth's outermost core

NASA Astrophysics Data System (ADS)

Kaneshima, Satoshi

2018-03-01

We perform array analyses of SmKS waves in order to investigate the Vp structure of the Earth's outermost core. For earthquakes recorded by broadband seismometer networks in the world, we measure differential travel times between S3KS and S2KS, between S4KS and S3KS, and between S5KS and S3KS by array techniques. The differential times are well fit by a Vp model of the Earth's outermost core, KHOMC (Kaneshima and Helffrich, 2013). Differential slownesses of S4KS and S2KS relative to S2KS are also measured for the highest quality data. The measured slownesses, with unique sensitivity to the outer core 200-400 km below the CMB, are matched by KHOMC. These observations consolidate the evidence for the presence at the top of the outer core of a layer that has a distinctively steeper Vp gradient than the bulk of the outer core. We invert new SmKS differential time data set by a tau-p method and attempt to refine the Vp profile of KHOMC. The essential features of KHOMC are preserved after the model refinement. However, the newly estimated layer thickness is nearly 450 km, which is thicker than that of KHOMC. The Vp anomalies relative to PREM for the depths 400-800 km below the CMB are less than 0.03 km/s, consistent with the degree of agreement between different Vp models for the depth range.

Aeroelastic Scaling of a Joined Wing Aircraft Concept

DTIC Science & Technology

2010-01-11

waxed and then peel ply is laid down, next the layers of fabric are laid down (outermost first) with an outer layer of light glass scrim used as the...A parametric model is developed using Phoenix Integration’s Model Center Software (MC). This model includes the vortex lattice software, AVL that...piece of real-time footage taken from the on-board, gimbaled camera. 2009 Progress Report 27 Figure 35 – initial Autonomous Flight After

Architecture and assembly of the Bacillus subtilis spore coat.

PubMed

Plomp, Marco; Carroll, Alicia Monroe; Setlow, Peter; Malkin, Alexander J

2014-01-01

Bacillus spores are encased in a multilayer, proteinaceous self-assembled coat structure that assists in protecting the bacterial genome from stresses and consists of at least 70 proteins. The elucidation of Bacillus spore coat assembly, architecture, and function is critical to determining mechanisms of spore pathogenesis, environmental resistance, immune response, and physicochemical properties. Recently, genetic, biochemical and microscopy methods have provided new insight into spore coat architecture, assembly, structure and function. However, detailed spore coat architecture and assembly, comprehensive understanding of the proteomic composition of coat layers, and specific roles of coat proteins in coat assembly and their precise localization within the coat remain in question. In this study, atomic force microscopy was used to probe the coat structure of Bacillus subtilis wild type and cotA, cotB, safA, cotH, cotO, cotE, gerE, and cotE gerE spores. This approach provided high-resolution visualization of the various spore coat structures, new insight into the function of specific coat proteins, and enabled the development of a detailed model of spore coat architecture. This model is consistent with a recently reported four-layer coat assembly and further adds several coat layers not reported previously. The coat is organized starting from the outside into an outermost amorphous (crust) layer, a rodlet layer, a honeycomb layer, a fibrous layer, a layer of "nanodot" particles, a multilayer assembly, and finally the undercoat/basement layer. We propose that the assembly of the previously unreported fibrous layer, which we link to the darkly stained outer coat seen by electron microscopy, and the nanodot layer are cotH- and cotE- dependent and cotE-specific respectively. We further propose that the inner coat multilayer structure is crystalline with its apparent two-dimensional (2D) nuclei being the first example of a non-mineral 2D nucleation crystallization pattern in a biological organism.

Architecture and Assembly of the Bacillus subtilis Spore Coat

PubMed Central

Plomp, Marco; Carroll, Alicia Monroe; Setlow, Peter; Malkin, Alexander J.

2014-01-01

Bacillus spores are encased in a multilayer, proteinaceous self-assembled coat structure that assists in protecting the bacterial genome from stresses and consists of at least 70 proteins. The elucidation of Bacillus spore coat assembly, architecture, and function is critical to determining mechanisms of spore pathogenesis, environmental resistance, immune response, and physicochemical properties. Recently, genetic, biochemical and microscopy methods have provided new insight into spore coat architecture, assembly, structure and function. However, detailed spore coat architecture and assembly, comprehensive understanding of the proteomic composition of coat layers, and specific roles of coat proteins in coat assembly and their precise localization within the coat remain in question. In this study, atomic force microscopy was used to probe the coat structure of Bacillus subtilis wild type and cotA, cotB, safA, cotH, cotO, cotE, gerE, and cotE gerE spores. This approach provided high-resolution visualization of the various spore coat structures, new insight into the function of specific coat proteins, and enabled the development of a detailed model of spore coat architecture. This model is consistent with a recently reported four-layer coat assembly and further adds several coat layers not reported previously. The coat is organized starting from the outside into an outermost amorphous (crust) layer, a rodlet layer, a honeycomb layer, a fibrous layer, a layer of “nanodot” particles, a multilayer assembly, and finally the undercoat/basement layer. We propose that the assembly of the previously unreported fibrous layer, which we link to the darkly stained outer coat seen by electron microscopy, and the nanodot layer are cotH- and cotE- dependent and cotE-specific respectively. We further propose that the inner coat multilayer structure is crystalline with its apparent two-dimensional (2D) nuclei being the first example of a non-mineral 2D nucleation crystallization pattern in a biological organism. PMID:25259857

Sequential magnetic switching in Fe/MgO(001) superlattices

NASA Astrophysics Data System (ADS)

Magnus, F.; Warnatz, T.; Palsson, G. K.; Devishvili, A.; Ukleev, V.; Palisaitis, J.; Persson, P. O. Å.; Hjörvarsson, B.

2018-05-01

Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchange coupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90∘ periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the top layer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180∘ periodic alignment is obtained at remanence and with increasing applied field the layer switching starts from the two outermost layers and proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensional magnetic structures with a predefined discrete switching sequence.

S-layer fusion proteins — construction principles and applications

PubMed Central

Ilk, Nicola; Egelseer, Eva M; Sleytr, Uwe B

2011-01-01

Crystalline bacterial cell surface layers (S-layers) are the outermost cell envelope component of many bacteria and archaea. S-layers are monomolecular arrays composed of a single protein or glycoprotein species and represent the simplest biological membrane developed during evolution. The wealth of information available on the structure, chemistry, genetics and assembly of S-layers revealed a broad spectrum of applications in nanobiotechnology and biomimetics. By genetic engineering techniques, specific functional domains can be incorporated in S-layer proteins while maintaining the self-assembly capability. These techniques have led to new types of affinity structures, microcarriers, enzyme membranes, diagnostic devices, biosensors, vaccines, as well as targeting, delivery and encapsulation systems. PMID:21696943

Optimized Granularity Analysis of Maximum Power Point Trackers in Low Power Applications

DTIC Science & Technology

2017-06-01

Second Reader: Robert Ashton THIS PAGE INTENTIONALLY LEFT BLANK i REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704–0188 Public reporting...Unclassified 19. SECURITY CLASSIFICATION OF ABSTRACT Unclassified 20. LIMITATION OF ABSTRACT UU NSN 7540–01-280-5500 Standard Form 298 (Rev...5  Figure 2.  Germanium Atoms Sharing Outermost Shell Electrons That Form Covalent Bonds. Source: [6

pH dependent growth of poly( L-lysine)/poly( L-glutamic) acid multilayer films and their cell adhesion properties

NASA Astrophysics Data System (ADS)

Richert, Ludovic; Arntz, Youri; Schaaf, Pierre; Voegel, Jean-Claude; Picart, Catherine

2004-10-01

The short-term interaction of chondrosarcoma cells with (PGA/PLL) polyelectrolyte multilayers was investigated in a serum-containing medium for films built at different pHs and subsequently exposed to the culture medium. The buildup of the films and their stability was first investigated by means of optical waveguide lightmode spectroscopy, quartz crystal microbalance, streaming potential measurements and atomic force microscopy. While film growth is linear at all pHs, after a few layers have been deposited the growth is much larger for the films built at basic pH and even more pronounced for those built at acidic pH. However, these latter films remain stable in the culture medium only if they have been crosslinked prior to the ionic strength and pH jumps. The films built at acidic pH were found to swell in water by about 200% whereas those built at other pHs did not swell in a physiological buffer. For thin films (≈20 nm) built at pH = 7.4, the detachment forces were dependent on the outermost layer, the forces being significantly higher on PLL-ending films than on PGA-ending ones. In contrast, for the thick films built at pH = 4.4 and at pH = 10.4 (thickness of the order of few hundred of nanometers), the detachment forces were independent of the outermost layer of the film. The films built at pH = 10.4, which shrink in contact with salt containing solutions, were highly cell adhesive whereas those built at acidic pH were highly cell resistant. Protein adsorption and film roughness (as measured by AFM) could not explain these striking differences. The high adhesion observed on the film built at pH 10.4 may rather be related to the secondary structure of the film and to its relatively low swellability in water, whereas the cell resistance of the films built at pH 4.4 may be linked to their high swellability. Therefore, for the PGA/PLL films, the cell adhesion properties can be tuned depending on the deposition pH of the polyelectrolyte solutions. This study reveals the importance of the multilayer structure and architecture to control the detachment force of cells onto such films.

General contraction of Gaussian basis sets. Part 2: Atomic natural orbitals and the calculation of atomic and molecular properties

NASA Technical Reports Server (NTRS)

Almloef, Jan; Taylor, Peter R.

1989-01-01

A recently proposed scheme for using natural orbitals from atomic configuration interaction (CI) wave functions as a basis set for linear combination of atomic orbitals (LCAO) calculations is extended for the calculation of molecular properties. For one-electron properties like multipole moments, which are determined largely by the outermost regions of the molecular wave function, it is necessary to increase the flexibility of the basis in these regions. This is most easily done by uncontracting the outmost Gaussian primitives, and/or by adding diffuse primitives. A similar approach can be employed for the calculation of polarizabilities. Properties which are not dominated by the long-range part of the wave function, such as spectroscopic constants or electric field gradients at the nucleus, can generally be treated satisfactorily with the original atomic natural orbital (ANO) sets.

Researches on tungsten carbide

NASA Astrophysics Data System (ADS)

1994-11-01

This paper summarizes results of the researches on tungsten carbide (WC), carried out in the 5-year period starting 1989 by the Science and Technology Agency's National Institute for Researches in Inorganic Materials. The high-frequency heating, floating zone technique, generally suited for growth of large-size, single crystals of high melting materials, is inapplicable to the hexagonal WC system, which is decomposed. This problem has been solved by adding boron to the system, to allow it to exist with the W-C-B melt at an equilibrium. The computer-aided control techniques have enabled automatic growth of the single crystals of carbides and borides. The de Haas-Van Alphen effect of the single WC crystals has been observed, to establish the Fermi surface model. The single crystals of transition metal carbides, such as WC, have been coated with the monolayer of graphite at high repeatability, to create the surface layer materials. An attempt has been done to produce the halite type structure by substituting Ti as the atom in the outermost layer of TiC by W. The new method, based on the low-speed deuterium ion scattering, has been developed to analyze the surface bonding conditions, clarifying the conditions of alkalis adsorbed on and bonded to metallic surfaces, and their surface reactivities.

Composite armor, armor system and vehicle including armor system

DOEpatents

Chu, Henry S.; Jones, Warren F.; Lacy, Jeffrey M.; Thinnes, Gary L.

2013-01-01

Composite armor panels are disclosed. Each panel comprises a plurality of functional layers comprising at least an outermost layer, an intermediate layer and a base layer. An armor system incorporating armor panels is also disclosed. Armor panels are mounted on carriages movably secured to adjacent rails of a rail system. Each panel may be moved on its associated rail and into partially overlapping relationship with another panel on an adjacent rail for protection against incoming ordnance from various directions. The rail system may be configured as at least a part of a ring, and be disposed about a hatch on a vehicle. Vehicles including an armor system are also disclosed.

Analytical pyrolysis and stable isotope analyses reveal past environmental changes in coralloid speleothems from Easter Island (Chile).

PubMed

Miller, Ana Z; De la Rosa, José M; Jiménez-Morillo, Nicasio T; Pereira, Manuel F C; González-Pérez, José A; Calaforra, José M; Saiz-Jimenez, Cesareo

2016-08-26

This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey-brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for δ(15)N values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk δ(13)C values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The δ(13)C values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

Overexpression of transcription factor OsWR2 1 regulates wax/cutin biosynthesis and enhances drought tolerance in rice

USDA-ARS?s Scientific Manuscript database

Drought is the major abiotic stress limiting crop production. Plant cuticle represents the outer-most layer of the epidermis and previous studies demonstrate its association with plant response to climatological drought. We report here the functional characterization of the rice ((Oryza sativa L.) W...

The Effects of the Location of Au Additives on Combustion-generated SnO2 Nanopowders for CO Gas Sensing

PubMed Central

Bakrania, Smitesh D.; Wooldridge, Margaret S.

2010-01-01

The current work presents the results of an experimental study of the effects of the location of gold additives on the performance of combustion-generated tin dioxide (SnO2) nanopowders in solid state gas sensors. The time response and sensor response to 500 ppm carbon monoxide is reported for a range of gold additive/SnO2 film architectures including the use of colloidal, sputtered, and combustion-generated Au additives. The opportunities afforded by combustion synthesis to affect the SnO2/additive morphology are demonstrated. The best sensor performance in terms of sensor response (S) and time response (τ) was observed when the Au additives were restricted to the outermost layer of the gas-sensing film. Further improvement was observed in the sensor response and time response when the Au additives were dispersed throughout the outermost layer of the film, where S = 11.3 and τ = 51 s, as opposed to Au localized at the surface, where S = 6.1 and τ = 60 s. PMID:22163586

Micro-arc oxidation as a tool to develop multifunctional calcium-rich surfaces for dental implant applications.

PubMed

Ribeiro, A R; Oliveira, F; Boldrini, L C; Leite, P E; Falagan-Lotsch, P; Linhares, A B R; Zambuzzi, W F; Fragneaud, B; Campos, A P C; Gouvêa, C P; Archanjo, B S; Achete, C A; Marcantonio, E; Rocha, L A; Granjeiro, J M

2015-09-01

Titanium (Ti) is commonly used in dental implant applications. Surface modification strategies are being followed in last years in order to build Ti oxide-based surfaces that can fulfill, simultaneously, the following requirements: induced cell attachment and adhesion, while providing a superior corrosion and tribocorrosion performance. In this work micro-arc oxidation (MAO) was used as a tool for the growth of a nanostructured bioactive titanium oxide layer aimed to enhance cell attachment and adhesion for dental implant applications. Characterization of the surfaces was performed, in terms of morphology, topography, chemical composition and crystalline structure. Primary human osteoblast adhesion on the developed surfaces was investigated in detail by electronic and atomic force microscopy as well as immunocytochemistry. Also an investigation on the early cytokine production was performed. Results show that a relatively thick hybrid and graded oxide layer was produced on the Ti surface, being constituted by a mixture of anatase, rutile and amorphous phases where calcium (Ca) and phosphorous (P) were incorporated. An outermost nanometric-thick amorphous oxide layer rich in Ca was present in the film. This amorphous layer, rich in Ca, improved fibroblast viability and metabolic activity as well as osteoblast adhesion. High-resolution techniques allowed to understand that osteoblasts adhered less in the crystalline-rich regions while they preferentially adhere and spread over in the Ca-rich amorphous oxide layer. Also, these surfaces induce higher amounts of IFN-γ cytokine secretion, which is known to regulate inflammatory responses, bone microarchitecture as well as cytoskeleton reorganization and cellular spreading. These surfaces are promising in the context of dental implants, since they might lead to faster osseointegration. Copyright © 2015 Elsevier B.V. All rights reserved.

Tumor-free distance from outermost layer of cervix is of prognostic value in surgically treated cervical cancer patients: a multicenter study.

PubMed

Saatli, Bahadir; Olgan, Safak; Gorken, Iknur B; Uslu, Turhan; Saygili, Ugur; Dicle, Nilgun; Cingillioglu, Basak; Gumurdulu, Derya; Guzel, Ahmet Baris; Koyuncuoglu, Meral

2014-06-01

This study aimed at determining if tumor-free distance (TFD) from outermost layer of cervix predicts surgicopathologic factors and outcome in surgically treated cervical cancer patients. One hundred sixteen surgically treated cervical squamous cell carcinomas between 1991 and 2010 with FIGO stage IB/2A were identified and re-evaluated histologically regarding the TFD. TFD was defined as the distance between outermost layer of cervix and deepest cervical stromal invasion. Depth of invasion (DOI) and TFD were expressed as continuous variables and compared with traditional surgicopathologic variables and survival to determine their prognostic significance. The mean DOI was 10.3 mm and the mean TFD was 4.2 mm. The most common stage was IB1 (60 patients, 51.7 %). The mean number of removed pelvic lymph nodes was 32.2 (median 30; range 8-78). Positive pelvic lymph nodes were found in 27 (23 %) of the patients. Sixty-eight patients had lymphovascular space involvement (LVSI). Sixty-eight patients (59 %) received postoperative radiotherapy where the following items were present: tumor diameter >4 cm, positive lymph nodes, LVSI and positive surgical margins. With the median follow-up of 53 months (3-219 months); 14 patients had local and 13 patients had distant metastases (5 of the patients had both at the time of recurrence). With logistic regression analysis, TFD was a predictor of pelvic lymph involvement (p = 0.028) and LVSI (p = 0.008) while DOI was a predictor of LVSI (p = 0.044). In Cox regression analysis, increased TFD was associated with improved disease-free survival (DFS) (p = 0.007). DFS curves (for TFD cut off value 2.5 mm) according to Kaplan-Meier were found to be statistically significant (log rank test = 0.002). The results indicate that TFD is predictive of pelvic lymph node involvement, LVSI and patient outcome in surgically treated cervical cancer patients. However, prospective measurement of TFD is still necessary to determine its value in clinical practice.

Surface modification of nitrogen-doped carbon nanotubes by ozone via atomic layer deposition

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

Lushington, Andrew; Liu, Jian; Tang, Yongji

The use of ozone as an oxidizing agent for atomic layer deposition (ALD) processes is rapidly growing due to its strong oxidizing capabilities. However, the effect of ozone on nanostructured substrates such as nitrogen-doped multiwalled carbon nanotubes (NCNTs) and pristine multiwalled carbon nanotubes (PCNTs) are not very well understood and may provide an avenue toward functionalizing the carbon nanotube surface prior to deposition. The effects of ALD ozone treatment on NCNTs and PCNTs using 10 wt. % ozone at temperatures of 150, 250, and 300 °C are studied. The effect of ozone pulse time and ALD cycle number on NCNTs and PCNTsmore » was also investigated. Morphological changes to the substrate were observed by scanning electron microscopy and high resolution transmission electron microscopy. Brunauer-Emmett-Teller measurements were also conducted to determine surface area, pore size, and pore size distribution following ozone treatment. The graphitic nature of both NCNTs and PCNTs was determined using Raman analysis while x-ray photoelectron spectroscopy (XPS) was employed to probe the chemical nature of NCNTs. It was found that O{sub 3} attack occurs preferentially to the outermost geometric surface of NCNTs. Our research also revealed that the deleterious effects of ozone are found only on NCNTs while little or no damage occurs on PCNTs. Furthermore, XPS analysis indicated that ALD ozone treatment on NCNTs, at elevated temperatures, results in loss of nitrogen content. Our studies demonstrate that ALD ozone treatment is an effective avenue toward creating low nitrogen content, defect rich substrates for use in electrochemical applications and ALD of various metal/metal oxides.« less

Electron solvation by polar molecules: the interaction of Na atoms with solid methanol films studied with MIES and density functional theory calculations.

PubMed

Borodin, A; Höfft, O; Kahnert, U; Kempter, V; Ferro, Y; Allouche, A

2004-05-08

The interaction of Na atoms with CH(3)OH films was studied with metastable impact electron spectroscopy (MIES) under UHV conditions. The films were grown at 90(+/-10) K on tungsten substrates and exposed to Na. Na-induced formation of methoxy (CH(3)O) species takes place, and Na atoms become ionized. At small Na exposures the outermost solvent layer remains largely intact as concluded from the absence of MIES signals caused by the reaction products. However, emission from CH(3)O, located at the film surface, occurs at larger exposures. In the same exposure range also Na species can be detected at the surface. The spectral feature from 3s Na ionization occurs at an energetic position different from that found for metals or semiconductors. The results are compared with density functional theory calculations [see Y. Ferro, A. Allouche, and V. Kempter, J. Chem. Phys. 120, 8683 (2004), preceding paper]. Experiment and theory agree in the energetic positions of the main spectral features from the methanol and sodium ionization. The calculations suggest that the 3s Na emission observed experimentally originates from solvated 3s electrons which are located far from the Na core and become stabilized by solvent molecules. The simultaneous emergence of emission from CH(3)O and from solvated 3s electrons suggests that the delocalization and, consequently, the solvation play an important role in the Na-induced formation of CH(3)O from CH(3)OH. (c) 2004 American Institute of Physics.

Organ fusion and defective cuticle function in a lacs1 lacs2 double mutant of Arabidopsis

USDA-ARS?s Scientific Manuscript database

As the outermost layer on aerial tissues of the primary plant body, the cuticle plays important roles in plant development and physiology. The major components of the cuticle are cutin and cuticular wax, both of which are composed primarily of fatty acid derivatives synthesized in the epidermal cell...

Subsurface segregation of yttria in yttria stabilized zirconia

NASA Astrophysics Data System (ADS)

de Ridder, M.; van Welzenis, R. G.; van der Gon, A. W. Denier; Brongersma, H. H.; Wulff, S.; Chu, W.-F.; Weppner, W.

2002-09-01

The segregation behavior in 3 and 10 mol % polycrystalline yttria stabilized zirconia (YSZ), calcined at temperatures ranging from 300 to 1600 degC, is characterized using low-energy ion scattering (LEIS). In order to be able to separate the Y and Zr LEIS signals, YSZ samples have been prepared using isotopically enriched 94ZrO2 instead of natural zirconia. The samples are made via a special precipitation method at a low temperature. The segregation to the outermost surface layer is dominated by impurities. The increased impurity levels are restricted to this first layer, which underlines the importance of the use of LEIS for this study. For temperatures of 1000 degC and higher, the oxides of the impurities Na, Si, and Ca even cover the surface completely. The performance of a device like the solid oxide fuel cell which has an YSZ electrolyte and a working temperature around 1000 degC, will, therefore, be strongly hampered by these impurities. The reduction of impurities, to prevent accumulation at the surface, will only be effective if the total impurity bulk concentration can be reduced below the 10 ppm level. Due to the presence of the impurities, yttria cannot accumulate in the outermost layer. It does so, in contrast to the general belief, in the subsurface layer and to much higher concentrations than the values reported previously. The difference in the interfacial free energies of Y2O3 and ZrO2 is determined to be -21plus-or-minus3 kJ/mol.

Response of the Shockley surface state to an external electrical field: A density-functional theory study of Cu(111)

NASA Astrophysics Data System (ADS)

Berland, K.; Einstein, T. L.; Hyldgaard, P.

2012-01-01

The response of the Cu(111) Shockley surface state to an external electrical field is characterized by combining a density-functional theory calculation for a slab geometry with an analysis of the Kohn-Sham wave functions. Our analysis is facilitated by a decoupling of the Kohn-Sham states via a rotation in Hilbert space. We find that the surface state displays isotropic dispersion, quadratic until the Fermi wave vector but with a significant quartic contribution beyond. We calculate the shift in energetic position and effective mass of the surface state for an electrical field perpendicular to the Cu(111) surface; the response is linear over a broad range of field strengths. We find that charge transfer occurs beyond the outermost copper atoms and that accumulation of electrons is responsible for a quarter of the screening of the electrical field. This allows us to provide well converged determinations of the field-induced changes in the surface state for a moderate number of layers in the slab geometry.

Low-Noise Large-Area Photoreceivers with Low Capacitance Photodiodes

NASA Technical Reports Server (NTRS)

Joshi, Abhay M. (Inventor); Datta, Shubhashish (Inventor)

2013-01-01

A quad photoreceiver includes a low capacitance quad InGaAs p-i-n photodiode structure formed on an InP (100) substrate. The photodiode includes a substrate providing a buffer layer having a metal contact on its bottom portion serving as a common cathode for receiving a bias voltage, and successive layers deposited on its top portion, the first layer being drift layer, the second being an absorption layer, the third being a cap layer divided into four quarter pie shaped sections spaced apart, with metal contacts being deposited on outermost top portions of each section to provide output terminals, the top portions being active regions for detecting light. Four transimpedance amplifiers have input terminals electrically connected to individual output terminals of each p-i-n photodiode.

Ultrasonic measurements of surface defects on flexible circuits using high-frequency focused polymer transducers

NASA Astrophysics Data System (ADS)

Wagle, Sanat; Habib, Anowarul; Melandsø, Frank

2017-07-01

High-frequency transducers made from a layer-by-layer deposition method are investigated as transducers for ultrasonic imaging. Prototypes of adhesive-free transducers with four active elements were made on a high-performance poly(ether imide) substrate with precision milled spherical cavities used to produce focused ultrasonic beams. The transducer prototypes were characterized using a pulse-echo experimental setup in a water tank using a glass plate as a reflector. Then, transducer was used in a three-dimensional ultrasonic scanning tank, to produce high-resolution ultrasonic images of flexible electronic circuits with the aim to detect defects in the outermost cover layer.

Armor structures

DOEpatents

Chu, Henry Shiu-Hung [Idaho Falls, ID; Lacy, Jeffrey M [Idaho Falls, ID

2008-04-01

An armor structure includes first and second layers individually containing a plurality of i-beams. Individual i-beams have a pair of longitudinal flanges interconnected by a longitudinal crosspiece and defining opposing longitudinal channels between the pair of flanges. The i-beams within individual of the first and second layers run parallel. The laterally outermost faces of the flanges of adjacent i-beams face one another. One of the longitudinal channels in each of the first and second layers faces one of the longitudinal channels in the other of the first and second layers. The channels of the first layer run parallel with the channels of the second layer. The flanges of the first and second layers overlap with the crosspieces of the other of the first and second layers, and portions of said flanges are received within the facing channels of the i-beams of the other of the first and second layers.

Effect of physisorbed molecules and an external external fields on the metallic Shockley surface state of Cu(111): A density functional theory study

NASA Astrophysics Data System (ADS)

Berland, Kristian; Einstein, T. L.; Hyldgaard, Per

2012-02-01

To manipulate the Cu(111) partially-filled Shockley surface state, we study its response to an external fieldootnotetextKB, TLE, PH; arXiv 1109:6706 E and physisorbed PAHs and quinone molecules. We use density-functional theory calculations with periodic-boundary conditions. The van der Waals density functional version vdW-DF2 accounts for the molecular adsorption. The issue that the Kohn-Sham wave functions couple to both sides of the Cu slab is handled with a decoupling scheme based on a rotation in Hilbert space. A convergence study reveals that to obtain a proper Shockley surface state, 6 Cu layers is sufficient, while 15 is optimal. We use 6 layers for the response to the molecules and 15 to external field. We find that the surface state displays isotropic dispersion (up to order k^6), free-electron like until the Fermi wave vector but with a significant quartic component beyond. The shift in band minimum and effective mass depend linearly on E, with a smaller fractional change in the latter. Charge transfer occurs beyond the outermost copper atoms, and most of the screening is due to bulk electrons. We find that the molecular physisorption increases the band minimum, with the effect the of a quinone being much stronger than the corresponding PAH.

Effect of Initial Iron Content in a Zinc Bath on the Dissolution Rate of Iron During a Hot Dip Galvanizing Process

NASA Astrophysics Data System (ADS)

Lee, Sang Myung; Lee, Suk Kyu; Paik, Doo-Jin; Park, Joo Hyun

2017-04-01

The mechanism of iron dissolution and the effect of initial Fe content in a Zn bath on the dissolution rate of iron were investigated using a finger rotating method (FRM). When the initial iron content, [Fe]°, in the zinc bath was less than the solubility limit, the iron content in the zinc bath showed a rapid increase, whereas a moderate increase was observed when [Fe]° was close to the solubility limit. Based on Eisenberg's kinetic model, the mass transfer coefficient of iron in the present experimental condition was calculated to be k M = 1.2 × 10-5 m/s, which was similar to the results derived by Giorgi et al. under industrial practice conditions. A dissolution of iron occurred even when the initial iron content in the zinc bath was greater than the solubility limit, which was explained by the interfacial thermodynamics in conjunction with the morphology of the surface coating layer. By analyzing the diffraction patterns using TEM, the outermost dendritic-structured coating layer was confirmed as FeZn13 ( ζ). In order to satisfy the local equilibrium based on the Gibbs-Thomson equation, iron in the dendrite-structured phase spontaneously dissolved into the zinc bath, resulting in the enrichment of iron in front of the dendrite tip. Through the diffusion boundary layer in front of the dendritic-structured layer, dissolved Fe atoms diffused out and reacted with Zn and small amounts of Al, resulting in the formation of dross particles such as FeZn10Al x ( δ). It was experimentally confirmed that the smaller the difference between the initial iron content in the zinc bath and the iron solubility limit at a given temperature, the lower the number of formed dross particles.

Migration and site selection of Ornithodiplostomum ptychocheilus (Trematoda: Digenea) metacercariae in the brain of fathead minnows ( Pimephales promelas).

PubMed

Matisz, Chelsea E; Goater, Cameron P; Bray, Douglas

2010-04-01

The migration of subadult parasites to preferred sites within final hosts is well characterized. In contrast, the migration of larval stages of trematodes to specific sites within their second intermediate hosts is poorly understood. We used a serial necropsy approach to characterize the migration of Ornithodiplostomum ptychocheilus diplostomules from the point of cercarial penetration, to encystment within the outermost tissues of the brain of fathead minnows. Diplostomules utilized peripheral nerves to access the central nerve cord, or they used specific cranial nerves to directly access the brain. Within 3 h of exposure to cercariae, 46% of all diplostomules were observed within the medulla of the brain. Diplostomules subsequently utilized specific neural tracts to reach lateral regions of the outermost tissue layer of the optic lobes, the stratum marginale. Diplostomules remained in this layer during their 4-week growth phase, then shifted site to the adjacent meninges for encystment. Characterization of a habitat shift for developing versus encysted metacercariae helps explain the results of previous ecological studies that document transient changes in the effects of metacercariae on the surivival, behaviour, and anti-parasite defences of infected fish.

High precision position sensor based on CPA in a composite multi-layered system.

PubMed

Dey, Sanjeeb; Singh, Suneel; Rao, Desai Narayana

2018-04-16

We propose a scheme for high precision position sensing based on coherent perfect absorption (CPA) in a five-layered structure comprising three layers of metal-dielectric composites and two spacer (air) layers. Both the outermost interfaces of the five layered medium are irradiated by two identical coherent light waves at the same angle of incidence. We first investigate the occurrence of CPA in a symmetric layered structure as a function of different system parameters for oblique incidence. Thereafter, by shifting the middle layer, beginning from one end of the structure to the other, we observe the periodic occurrence of extremely narrow CPA resonances at several positions of the middle layer. Moreover this phenomenon is seen to recur even at many other wavelengths. We discuss how the position sensitivity of this phenomenon can be utilized for designing a CPA based high precision position sensing device.

The feasibility of assessing the diets of minke whale ( Balaenoptera acutorostrata) in the East Sea through fatty acid composition in blubber and stable isotopic ratio of skin

NASA Astrophysics Data System (ADS)

Ko, Ah-Ra; Ju, Se-Jong; Choi, Seok-Gwan; Shin, Kyung-Hoon

2016-09-01

To track the diet of minke whale ( Balaenoptera acutorostrata) in the East Sea (Japan Sea), a conjoint analysis of fatty acids and C and N stable isotopes was performed on blubber and skin from the whale and its potential prey. The total lipid content in the blubber of minke whales ranged from 37.9% to 82.7% of wet mass (mean ± SD, 63.1 ± 17.2%), with triacylglycerols being the dominant lipids (96.9%-99.2% of total lipids). The lipid and fatty acid (FA) contents were systematically stratified throughout the depth of the blubber layers; contents of the dominant monounsaturated FAs (MUFAs), including 18:1ω9 and 16:1ω7, increased from the innermost layer to the outermost layer, whereas contents of saturated FAs (SFAs) and polyunsaturated FAs (PUFAs) were higher in the innermost layer than in the outermost layer. This stratification is related to the different physiological roles of the blubber layers; e.g., thermoregulation, streaming, and buoyancy. A comparison of the FA compositions of the innermost layer of minke whales with those of potential prey indicates that FA compositions in the whales are similar to those of Pacific herring. In addition, stable isotope ratios (δ13C and δ15N) suggest that minke whale and Pacific herring have the same or similar diets. Therefore, the diets of minke whale from the East Sea (Japan Sea) could be inferred from information on the diet of the Pacific herring, although FA compositions and stable isotope ratios for Pacific herring would not exactly reflect the whale's diet. Although the very limited number of samples was used in this study, our preliminary findings are very promising to help understand the feeding ecology of minke whales in the East Sea (Japan Sea).

Functional Layer-by-Layer Thin Films of Inducible Nitric Oxide (NO) Synthase Oxygenase and Polyethylenimine: Modulation of Enzyme Loading and NO-Release Activity.

PubMed

Gunasekera, Bhagya; Abou Diwan, Charbel; Altawallbeh, Ghaith; Kalil, Haitham; Maher, Shaimaa; Xu, Song; Bayachou, Mekki

2018-03-07

Nitric oxide (NO) release counteracts platelet aggregation and prevents the thrombosis cascade in the inner walls of blood vessels. NO-release coatings also prevent thrombus formation on the surface of blood-contacting medical devices. Our previous work has shown that inducible nitric oxide synthase (iNOS) films release NO fluxes upon enzymatic conversion of the substrate l-arginine. In this work, we report on the modulation of enzyme loading in layer-by-layer (LbL) thin films of inducible nitric oxide synthase oxygenase (iNOSoxy) on polyethylenimine (PEI). The layer of iNOSoxy is electrostatically adsorbed onto the PEI layer. The pH of the iNOSoxy solution affects the amount of enzyme adsorbed. The overall negative surface charge of iNOSoxy in solution depends on the pH and hence determines the density of adsorbed protein on the positively charged PEI layer. We used buffered iNOSoxy solutions adjusted to pHs 8.6 and 7.0, while saline PEI solution was used at pH 7.0. Atomic force microscopy imaging of the outermost layer shows higher protein adsorption with iNOSoxy at pH 8.6 than with a solution of iNOSoxy at pH 7.0. Graphite electrodes with PEI/iNOSoxy films show higher catalytic currents for nitric oxide reduction mediated by iNOSoxy. The higher enzyme loading translates into higher NO flux when the enzyme-modified surface is exposed to a solution containing the substrate and a source of electrons. Spectrophotometric assays showed higher NO fluxes with iNOSoxy/PEI films built at pH 8.6 than with films built at pH 7.0. Fourier transform infrared analysis of iNOSoxy adsorbed on PEI at pH 8.6 and 7.0 shows structural differences of iNOSoxy in films, which explains the observed changes in enzymatic activity. Our findings show that pH provides a strategy to optimize the NOS loading and enzyme activity in NOS-based LbL thin films, which enables improved NO release with minimum layers of PEI/NOS.

Ti/Al multilayer zone plate and Bragg-Fresnel lens.

PubMed

Koike, M; Suzuki, I H; Komiya, S; Amemiya, Y

1998-05-01

By using a helicon plasma sputtering technique, a one-dimensional Ti/Al multilayer zone plate with an outermost layer width of 76 nm has been successfully fabricated. A Bragg-Fresnel lens has been made by combining this zone plate with a Ge(422) crystal. Comparison of the Ti/Al multilayer zone plate with the Ag/Al zone plate is discussed in terms of focusing efficiency.

Relationships between surface free energy, surface texture parameters and controlled drug release in hydrophilic matrices.

PubMed

Saurí, J; Suñé-Negre, J M; Díaz-Marcos, J; Vilana, J; Millán, D; Ticó, J R; Miñarro, M; Pérez-Lozano, P; García-Montoya, E

2015-01-15

The study of controlled release and drug release devices has been dominated by considerations of the bulk or average properties of material or devices. Yet the outermost surface atoms play a central role in their performance. The objective of this article has been to characterize the surface of hydrophilic matrix tablets using the contact angle (CA) method to ascertain the surface free energy, and atomic force microscopy (AFM) and confocal microscopy (CM) for the physical characterization of the surface of the hydrophilic matrix. The surface free energy results obtained show that hydroxypropylmethylcellulose K15M hinders the spreading of water on the surface of the tablet, such that the concentration of HPMC K15M increases the reaction rate of the hydrophobic interactions between the chains of HPMC K15M which increases with respect to the rate of penetration of water into the tablet. In this study, we developed a new method to characterize the swelling of the tablets and established a relationship between the new method based on microswelling and the swelling ratio parameter. The surface texture parameters have been determined and the morphology of the tablets of the different formulations and the evolution of the surface morphology after interacting with the water, swelling and forming a gel layer were characterized. This work represents significant progress in the characterization of matrix tablets. Copyright © 2014 Elsevier B.V. All rights reserved.

Band bending at magnetic Ni/Ge(001) interface investigated by X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Bocîrnea, Amelia Elena; Tănase, Liviu Cristian; Costescu, Ruxandra Maria; Apostol, Nicoleta Georgiana; Teodorescu, Cristian Mihail

2017-12-01

We report the molecular beam epitaxy growth of Ni on a clean Ge(001) surface with an intermediate NiGe layer forming at the interface at room temperature. The crystallinity of the substrate is lost after the deposition of more than 2 Ni monolayers. The Schottky barrier formation is investigated by X-ray photoelectron spectroscopy. The method allows us to infer a 0.39-0.45 eV band bending at the interface between the compound and Ge(001). Magneto-optical Kerr effect measurements were conclusive in detecting the ferromagnetic ordering of Ni outermost layers.

Use of separate ZnTe interface layers to form ohmic contacts to p-CdTe films

DOEpatents

Gessert, T.A.

1999-06-01

A method of is disclosed improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurium-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact. 11 figs.

Use of separate ZnTe interface layers to form OHMIC contacts to p-CdTe films

DOEpatents

Gessert, Timothy A.

1999-01-01

A method of improving electrical contact to a thin film of a p-type tellurium-containing II-VI semiconductor comprising: depositing a first undoped layer of ZnTe on a thin film of p-type tellurium containing II-VI semiconductor with material properties selected to limit the formation of potential barriers at the interface between the p-CdTe and the undoped layer, to a thickness sufficient to control diffusion of the metallic-doped ZnTe into the p-type tellurim-containing II-VI semiconductor, but thin enough to minimize affects of series resistance; depositing a second heavy doped p-type ZnTe layer to the first layer using an appropriate dopant; and depositing an appropriate metal onto the outer-most surface of the doped ZnTe layer for connecting an external electrical conductor to an ohmic contact.

Spider Silk Spun and Integrated into Composites

DTIC Science & Technology

2009-02-20

and elongation of sericin is lower than those of fibroin and, finally, (0 local shear damage is dominant in damaged sericin between fibres, while the... sericin at fibre-joint often shows microflow. These analytical studies are presently being expanded to include synthetic composites made of both...with sericin . Such a cocoon consists of three main parts: an outermost loose mesh structure, the middle shell layers and the innermost tetelette; all

Positrons in surface physics

NASA Astrophysics Data System (ADS)

Hugenschmidt, Christoph

2016-12-01

Within the last decade powerful methods have been developed to study surfaces using bright low-energy positron beams. These novel analysis tools exploit the unique properties of positron interaction with surfaces, which comprise the absence of exchange interaction, repulsive crystal potential and positron trapping in delocalized surface states at low energies. By applying reflection high-energy positron diffraction (RHEPD) one can benefit from the phenomenon of total reflection below a critical angle that is not present in electron surface diffraction. Therefore, RHEPD allows the determination of the atom positions of (reconstructed) surfaces with outstanding accuracy. The main advantages of positron annihilation induced Auger-electron spectroscopy (PAES) are the missing secondary electron background in the energy region of Auger-transitions and its topmost layer sensitivity for elemental analysis. In order to enable the investigation of the electron polarization at surfaces low-energy spin-polarized positrons are used to probe the outermost electrons of the surface. Furthermore, in fundamental research the preparation of well defined surfaces tailored for the production of bound leptonic systems plays an outstanding role. In this report, it is envisaged to cover both the fundamental aspects of positron surface interaction and the present status of surface studies using modern positron beam techniques.

Fine structure of the dorsal lingual epithelium of the juvenile hawksbill turtle, Eretmochelys imbricata bissa.

PubMed

Iwasaki, S; Asami, T; Wanichanon, C

1996-04-01

Various species of turtles are adapted to different environments, such as freshwater, seawater, and terrestrial habitats. Comparisons of histological and ultrastructural features of the tongue of the juvenile Hawksbill turtle, Eretmochelys imbricata bissa, with those of freshwater turtles should reveal some aspects of the relationship between the structure of the lingual epithelium and the environment. The light microscope, scanning electron microscope and transmission electron microscope were used. Light microscopy revealed that the mucosal epithelium of the tongue was of the keratinized, stratified squamous type. Under the scanning electron microscope, no lingual papillae were visible on the dorsal surface of the tongue. Micropits and the thickening of cell margins were clearly seen on the surface of cells located on the outermost side. The transmission electron microscope revealed that the cells in the intermediate layer were gradually flattened from the basal side to the surface side, as were their nuclei. In the shallow intermediate layer, the cells were significantly flattened, and their nuclei were condensed or had disappeared. The cytoplasm contained keratohyalin granules, tonofibrils, free ribosomes, mitochondria, and rough endoplasmic reticulum. Numerous free ribosomes were attached to the surface of small keratohyalin granules. The cells of the keratinized layer were significantly flattened, and their nuclei had completely disappeared. Most of cytoplasm was filled with keratin fibers of high electron density. Keratin fibers of the shedding cells, which were located on the outermost side of the keratinized layer, appeared looser, and each fiber, which was somewhat thicker than the tonofibrils and tonofilaments, was clearly distinguishable. The lingual epithelium of the juvenile Hawksbill turtle differs significantly from that of the adult freshwater turtle, in spite of the similarity in gross morphology of the tongues of these species.

Bioactivity and cytocompatibility of zirconia (ZrO(2)) films fabricated by cathodic arc deposition.

PubMed

Liu, Xuanyong; Huang, Anping; Ding, Chuanxian; Chu, Paul K

2006-07-01

Zirconium oxide thin films were fabricated on silicon wafers using a filtered cathodic arc system in concert with oxygen plasma. The structure and phase composition of the zirconium oxide thin films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). The bioactivity was assessed by investigating the formation of apatite on the film surface after soaking in simulated body fluids. Bone marrow mesenchymal stem cells (BMMSC) were used to further evaluate the cytocompatibility of the materials. The results indicate that the films are composed of stoichiometric ZrO(2) and the composition is quite uniform throughout the thickness. Bone-like apatite can be formed on the surface of the ZrO(2) thin film in our SBF immersion experiments, suggesting that the surface is bioactive. The outermost layer of the ZrO(2) thin film comprises nano-sized particles that can be identified by AFM images taken on the thin film surface and TEM micrographs obtained from the interface between the ZrO(2) thin film and apatite layer. The nanostructured surface is believed to be the key factor that apatite is induced to precipitate on the surface. Bone marrow mesenchymal stem cells are observed to grow and proliferate in good states on the film surface. Our results show that ZrO(2) thin films fabricated by cathodic arc deposition exhibit favorable bioactivity and cytocompatibility.

Condensing Heat Exchanger with Hydrophilic Antimicrobial Coating

NASA Technical Reports Server (NTRS)

Thomas, Christopher M. (Inventor); Ma, Yonghui (Inventor)

2014-01-01

A multi-layer antimicrobial hydrophilic coating is applied to a substrate of anodized aluminum, although other materials may form the substrate. A silver layer is sputtered onto a thoroughly clean anodized surface of the aluminum to about 400 nm thickness. A layer of crosslinked, silicon-based macromolecular structure about 10 nm thickness overlies the silver layer, and the outermost surface of the layer of crosslinked, silicon-based macromolecular structure is hydroxide terminated to produce a hydrophilic surface with a water drop contact angle of less than 10.degree.. The coated substrate may be one of multiple fins in a condensing heat exchanger for use in the microgravity of space, which has narrow channels defined between angled fins such that the surface tension of condensed water moves water by capillary flow to a central location where it is pumped to storage. The antimicrobial coating prevents obstruction of the capillary passages.

Hemocompatibility Improvement of Chromium-Bearing Bare-Metal Stent Platform After Magnetoelectropolishing

NASA Astrophysics Data System (ADS)

Rokicki, Ryszard; Haider, Waseem; Maffi, Shivani Kaushal

2015-01-01

Research was undertaken to determine the influence of the increased content of chromium in the outermost passive layer of magneto-electrochemically refined Co-Cr alloy L-605 surface on its hemocompatibility. The chemistry, roughness, surface energy, and wettability of conventionally electropolished (EP) and magnetoelectropolished (MEP) samples were studied with x-ray photoelectron spectroscopy (XPS), open circuit potential, atomic force microscopy, and contact angle meter. In vitro hemocompatibility of tested material surfaces was assessed using two important indicators of vascular responses to biomaterial, namely endothelialization and platelets adhesion. The endothelialization was assessed by seeding and incubating samples with human umbilical vein endothelial cells (HUVEC) for 3 days before counting and observing them under a fluorescent microscope. The platelet (rich plasma blood) adhesion and activation test on EP and MEP L-605 alloy surfaces was assessed using a laser scanning confocal microscope. The XPS analysis of MEP samples showed significant enrichment of the passive layer with Cr and O when compared with the EP one. The amount of other elements in the passive layer did not show a significant difference between EP and MEP treatments. The adhesion of HUVEC cells shows remarkable affinity to surfaces enriched in Cr (MEP) with almost 100% confluency. In addition, the number of platelets that adhered to standard EP surfaces was higher compared to the MEP surface. The present study shows that the chromium-enriched surface of cobalt-chromium alloy L-605 by the magnetoelectropolishing process tremendously improves surface hemocompatibility with regard to stent functionality by enhanced endothelialization and lower platelet adhesion and should be taken under consideration as an alternative surface of biodegradable polymer drug-eluting stents, polymer-free drug-eluting stents as well as bare-metal stents.

Roles of the Bacillus anthracis Spore Protein ExsK in Exosporium Maturation and Germination

DTIC Science & Technology

2009-12-01

exosporium maturation and assembly and suggest a novel role for the exosporium in germination. During starvation, bacteria of the genus Bacillus...Bacillus subtilis, the outermost struc- ture is a protective layer called the coat, which guards the spore against reactive small molecules, degradative ...analysis. Generation of anti-ExsK antibodies. Recombinant ExsK was generated and purified using the pET expression system (Novagen) according to the

Nuclear fuel particles and method of making nuclear fuel compacts therefrom

DOEpatents

DeVelasco, Rubin I.; Adams, Charles C.

1991-01-01

Methods for making nuclear fuel compacts exhibiting low heavy metal contamination and fewer defective coatings following compact fabrication from a mixture of hardenable binder, such as petroleum pitch, and nuclear fuel particles having multiple layer fission-product-retentive coatings, with the dense outermost layer of the fission-product-retentive coating being surrounded by a protective overcoating, e.g., pyrocarbon having a density between about 1 and 1.3 g/cm.sup.3. Such particles can be pre-compacted in molds under relatively high pressures and then combined with a fluid binder which is ultimately carbonized to produce carbonaceous nuclear fuel compacts having relatively high fuel loadings.

Blubber-depth distribution and bioaccumulation of PCBs and organochlorine pesticides in Arctic-invading killer whales.

PubMed

Pedro, Sara; Boba, Conor; Dietz, Rune; Sonne, Christian; Rosing-Asvid, Aqqalu; Hansen, Martin; Provatas, Anthony; McKinney, Melissa A

2017-12-01

Sightings of killer whales (Orcinus orca) in Greenland have increased in recent years, coincident with sea ice loss. These killer whales are likely from fish-feeding North Atlantic populations, but may have access to marine mammal prey in Greenlandic waters, which could lead to increased exposures to biomagnifying contaminants. Most studies on polychlorinated biphenyl (PCB) and organochlorine (OC) contaminants in killer whales have used biopsies which may not be representative of contaminant concentrations through the entire blubber depth. Here, we measured PCB and OC concentrations in 10 equal-length blubber sections of 18 killer whales harvested in southeast Greenland (2012-2014), and 3 stranded in the Faroe Islands (2008) and Denmark (2005). Overall, very high concentrations of ΣPCB, Σchlordanes (ΣCHL), and Σdichlorodiphenyltrichloroethane (ΣDDT) were found in the southeast Greenland and Denmark individuals (means of ~40 to 70mgkg -1 lipid weight). These concentrations were higher than in the Faroe Island individuals (means of ~2 to 5mgkg -1 lipid weight) and above those previously reported for other fish-feeding killer whales in the North Atlantic, likely in part due to additional feeding on marine mammals. On a wet weight basis, concentrations of all contaminants were significantly lower in the outermost blubber layer (0.15-0.65cm) compared to all other layers (p<0.01), except for Σhexachlorocyclohexanes. However, after lipid correction, no variation was found for ΣCHL and Σchlorobenzene concentrations, while the outermost layer(s) still showed significantly lower ΣPCB, ΣDDT, Σmirex, Σendosulfan, and dieldrin concentrations than one or more of the inner layers. Yet, the magnitude of these differences was low (up to 2-fold) suggesting that a typical biopsy may be a reasonable representation of the PCB and OC concentrations reported in killer whales, at least on a lipid weight basis. Copyright © 2017 Elsevier B.V. All rights reserved.

Ceres’ impact craters: probes of near-surface internal structure and composition

NASA Astrophysics Data System (ADS)

Bland, Michael T.; Raymond, Carol; Park, Ryan; Schenk, Paul; McCord, Tom; Reddy, Vishnu; King, Scott; Sykes, Mark; Russell, Chris

2015-11-01

Dawn Framing Camera images of Ceres have revealed the existence of a heavily cratered surface. Shape models derived from these images indicate that most (though not all) large craters are quite deep: up to 6 km for craters larger than 100 km in diameter. The retention of deep craters is not consistent with a simple differentiated internal structure consisting of an outer layer composed solely of pure water ice (covered with a rocky lag) overlying a rocky core. Here we use finite element simulations to show that, for Ceres’ relatively warm surface temperatures, the timescale required to completely flatten a crater 60-km in diameter (or greater) is less than 100 Myr, assuming a relatively pure outer ice layer (for ice grain sizes ≤ 1 cm). Preserving substantial topography requires that the viscosity of Ceres’ outer-most layer (25-50 km thick) is substantially greater than that of pure water ice. A factor of ten increase in viscosity can be achieved by assuming the layer is a 50/50 ice-rock mixture by volume; however, our simulations show that such an increase is insufficient to prevent substantial relaxation over timescales of 1 Gyr. Only particulate volume fractions greater than 50% provide an increase in viscosity sufficient to prevent large-scale, rapid relaxation. Such volume fractions suggest an outer layer composed of frozen soil/regolith (i.e., more rock than ice by volume), a very salt-rich layer, or both. Notably, while most basins appear quite deep, a few relatively shallow basins have been observed (e.g., Coniraya), suggesting that relaxation may be occurring over very long timescales (e.g., 4 Ga), that Ceres’ interior is compositionally and spatial heterogeneous, and/or that temporal evolution of the interior structure and composition has occurred. If these shallow basins are in fact the result of relaxation, it places an upper limit on the viscosity of Ceres’ outer-most interior layer, implying at least some low-viscosity material is present and likely eliminating the possibility of a purely rocky (homogeneous, low density, high porosity) interior.

Confocal Raman spectroscopy: In vivo biochemical changes in the human skin by topical formulations under UV radiation.

PubMed

Tosato, M G; Orallo, D E; Ali, S M; Churio, M S; Martin, A A; Dicelio, L

2015-12-01

A new approach to the study of the effects on human skin of mycosporine-like amino acids (MAAs) and gadusol (Gad) incorporated in polymer gel is proposed in this work. The depth profile and photoprotector effects of Pluronic F127® gels containing each of the natural actives were evaluated by in vivo confocal Raman spectroscopy aiming at the analysis of the biochemical changes on human skin. Hierarchical cluster analysis (HCA) showed that the data corresponding to different depths of the skin, from surface to 4 μm, and from 6 to 16 μm, remained in the same cluster. In vivo Raman spectra, classified into five different layers of epidermis according to their similarities, indicated that the amount of Gad gel increased by about 26% in the outermost layer of the stratum corneum (SC) and that MAAs gel at 2 μm depth was 103.4% higher than in the outermost layer of the SC. Variations in the SC of urocanic acid at 1490-1515 cm(-1) and 1652 cm(-1) and histidine at 1318 cm(-1) were calculated, before and after UV exposure with or without gels. With the application of gels the vibrational modes that correspond to lipids in trans conformation (1063 and 1128 cm(-1)) increased with respect to normal skin, whereas gauche conformation (1085 cm(-1)) disappeared. Our studies suggest that gels protected the skin against the stress of the natural defense mechanism caused by high levels of UV exposure. Copyright © 2015 Elsevier B.V. All rights reserved.

Geobacter Dominates the Inner Layers of a Stratified Biofilm on a Fluidized Anode During Brewery Wastewater Treatment

PubMed Central

Tejedor-Sanz, Sara; Fernández-Labrador, Patricia; Hart, Steven; Torres, Cesar I.; Esteve-Núñez, Abraham

2018-01-01

In this study, we designed a microbial electrochemical fluidized bed reactor (ME-FBR), with an electroconductive anodic bed made of activated carbon particles for treating a brewery wastewater. Under a batch operating mode, acetate and propionate consumption rates were 13-fold and 2.4-fold higher, respectively, when the fluidized anode was polarized (0.2 V) with respect to open circuit conditions. Operating in a continuous mode, this system could effectively treat the brewery effluent at organic loading rates (OLR) over 1.7 kg m-3NRV d-1 and with removal efficiencies of 95 ± 1.4% (hydraulic retention time of 1 day and an influent of 1.7 g-COD L-1). The coulombic efficiency values highly depended upon the OLR applied, and varied from a 56 ± 15% to 10 ± 1%. Fluorescence in situ hybridization (FISH) analysis revealed a relative high abundance of Geobacter species (ca. 20%), and clearly showed a natural microbial stratification. Interestingly, the Geobacter cluster was highly enriched in the innermost layers of the biofilm (thickness of 10 μm), which were in contact with the electroconductive particles of bed, whereas the rest of bacteria were located in the outermost layers. To our knowledge, this is the first time that such a clear microbial stratification has been observed on an anode-respiring biofilm. Our results revealed the relevant role of Geobacter in switching between the electrode and other microbial communities performing metabolic reactions in the outermost environment of the biofilm. PMID:29568284

Insight into the product film formed on Ni-advanced weathering steel in a tropical marine atmosphere

NASA Astrophysics Data System (ADS)

Wu, Wei; Cheng, Xuequn; Hou, Huaxing; Liu, Bo; Li, Xiaogang

2018-04-01

The product film formed on Ni-advanced weathering steel in a tropical marine environment was investigated in detail through outdoor exposure by using diverse surface analysis techniques combined with electrochemical impedance spectroscopy and scanning kelvin probe measurements. The results showed that the product film was mainly composed of nanophasic goethite in the inner layer and maghemite, akaganeite, and hematite in the outer layer. Moreover, the resistance to atmospheric corrosion gradually increased from the outermost product film to the innermost film. Ni was significantly enriched in the inner layer in the form of the spinel phase NiFe2O4, which transformed lepidocrocite to fine-grained goethite, withstood the invasion of chloridion, and improved the corrosion potential of the product film in a tropical marine atmosphere.

Asymptotic theory of intermediate- and high-degree solar acoustic oscillations

NASA Technical Reports Server (NTRS)

Brodsky, M.; Vorontsov, S. V.

1993-01-01

A second-order asymptotic approximation is developed for adiabatic nonradial p-modes of a spherically symmetric star. The exact solutions of adiabatic oscillations are assumed in the outermost layers, where the asymptotic description becomes invalid, which results in a eigenfrequency equation with model-dependent surface phase shift. For lower degree modes, the phase shift is a function of frequency alone; for high-degree modes, its dependence on the degree is explicitly taken into account.

Seismic Wave Velocity in Earth's Shallow Core

NASA Astrophysics Data System (ADS)

Alexandrakis, C.; Eaton, D. W.

2008-12-01

Studies of the outer core indicate that it is composed of liquid Fe and Ni alloyed with a ~10% fraction of light elements such as O, S or Si. Recently, unusual features, such as sediment accumulation, immiscible fluid layers or stagnant convection, have been predicted in the shallow core region. Secular cooling and compositional buoyancy drive vigorous convection that sustains the geodynamo, although critical details of light-element composition and thermal regime remain uncertain. Seismic velocity models can provide important constraints on the light element composition, however global reference models, such as Preliminary Reference Earth Model (PREM), IASP91 and AK135 vary significantly in the 200 km below the core-mantle boundary. Past studies of the outermost core velocity structure have been hampered by traveltime uncertainties due to lowermost mantle heterogeneities. The recently published Empirical Transfer Function (ETF) method has been shown to reduce the uncertainty using a waveform stacking approach to improve global observations of SmKS teleseismic waves. Here, we apply the ETF method to achieve a precise top-of-core velocity measurement of 8.05 ± 0.03 km/s. This new model accords well with PREM. Since PREM is based on the adiabatic form of the Adams-Williamson equation, it assumes a well mixed (i.e. homogeneous) composition. This result suggests a lack of heterogeneity in the outermost core due to layering or stagnant convection.

Wet-chemical dissolution of TRISO-coated simulated high-temperature-reactor fuel particles

NASA Astrophysics Data System (ADS)

Skolo, K. P.; Jacobs, P.; Venter, J. H.; Klopper, W.; Crouse, P. L.

2012-01-01

Chemical etching with different mixtures of acidic solutions has been investigated to disintegrate the two outermost coatings from tri-structural isotropic coated particles containing zirconia kernels, which are used in simulated particles instead of uranium dioxide. A scanning electron microscope (SEM) was used to study the morphology of the particles after the first etching step as well as at different stages of the second etching step. SEM examination shows that the outer carbon layer can be readily removed with a CrO 3-HNO 3/H 2SO 4 solution. This finding was verified by energy dispersive spectroscopy (EDS) analysis. Etching of the silicon carbide layer in a hydrofluoric-nitric solution yielded partial removal of the coating and localized attack of the underlying coating layers. The SEM results provide evidence that the etching of the silicon carbide layer is strongly influenced by its microstructure.

Transient analysis for alternating over-current characteristics of HTSC power transmission cable

NASA Astrophysics Data System (ADS)

Lim, S. H.; Hwang, S. D.

2006-10-01

In this paper, the transient analysis for the alternating over-current distribution in case that the over-current was applied for a high-TC superconducting (HTSC) power transmission cable was performed. The transient analysis for the alternating over-current characteristics of HTSC power transmission cable with multi-layer is required to estimate the redistribution of the over-current between its conducting layers and to protect the cable system from the over-current in case that the quench in one or two layers of the HTSC power cable happens. For its transient analysis, the resistance generation of the conducting layers for the alternating over-current was reflected on its equivalent circuit, based on the resistance equation obtained by applying discrete Fourier transform (DFT) for the voltage and the current waveforms of the HTSC tape, which comprises each layer of the HTSC power transmission cable. It was confirmed through the numerical analysis on its equivalent circuit that after the current redistribution from the outermost layer into the inner layers first happened, the fast current redistribution between the inner layers developed as the amplitude of the alternating over-current increased.

Effect of Space Radiation Processing on Lunar Soil Surface Chemistry: X-Ray Photoelectron Spectroscopy Studies

NASA Technical Reports Server (NTRS)

Dukes, C.; Loeffler, M.J.; Baragiola, R.; Christoffersen, R.; Keller, J.

2009-01-01

Current understanding of the chemistry and microstructure of the surfaces of lunar soil grains is dominated by a reference frame derived mainly from electron microscopy observations [e.g. 1,2]. These studies have shown that the outermost 10-100 nm of grain surfaces in mature lunar soil finest fractions have been modified by the combined effects of solar wind exposure, surface deposition of vapors and accretion of impact melt products [1,2]. These processes produce surface-correlated nanophase Feo, host grain amorphization, formation of surface patinas and other complex changes [1,2]. What is less well understood is how these changes are reflected directly at the surface, defined as the outermost 1-5 atomic monolayers, a region not easily chemically characterized by TEM. We are currently employing X-ray Photoelectron Spectroscopy (XPS) to study the surface chemistry of lunar soil samples that have been previously studied by TEM. This work includes modification of the grain surfaces by in situ irradiation with ions at solar wind energies to better understand how irradiated surfaces in lunar grains change their chemistry once exposed to ambient conditions on earth.

Influence of the chemical surface structure on the nanoscale friction in plasma nitrided and post-oxidized ferrous alloy

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

Freislebem, Márcia; Menezes, Caren M.; Cemin, Felipe

2014-09-15

Friction is a ubiquitous phenomenon in everyday activities spanning from vehicles where efficient brakes are mandatory up to mechanical devices where its minimum effects are pursued for energy efficiency issues. Recently, theoretical models succeed correlating the friction behavior with energy transference via phonons between sliding surfaces. Therefore, considering that the energy losses by friction are prompted through phonons, the chemical surface structure between sliding surfaces is very important to determine the friction phenomenon. In this work, we address the issue of friction between a conical diamond tip sliding on different functionalized flat steel surfaces by focusing the influence of themore » chemical bonds in the outermost layers on the sliding resistance. This geometry allows probing the coupling of the sharp tip with terminator species on the top and underneath material surface at in-depth friction measurements from 20 to 200 nm. Experimentally, the friction coefficient decreases when nitrogen atoms are substituted for oxygen in the iron network. This effect is interpreted as due to energy losses through phonons whilst lower vibrational frequency excitation modes imply lower friction coefficients and a more accurate adjustment is obtained when a theoretical model with longitudinal adsorbate vibration is used.« less

40th Anniversary of Voyager

NASA Image and Video Library

2017-09-05

On September 5, 1977, Voyager 1 was launched on a mission to explore where nothing had flown before. First on its journey were Jupiter and Saturn and it is currently exploring interstellar space. Its twin spacecraft, Voyager 2, visited Uranus and Neptune and is now in the outermost layer of the heliosphere, called the heliosheath. Forty years later, both spacecraft continue to send back data and are searching for the heliopause, the region where the Sun’s influence wanes, which has never been reached by any spacecraft.

CRUSTAL FAILURE DURING BINARY INSPIRAL

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

Penner, A. J.; Andersson, N.; Jones, D. I.

2012-04-20

We present the first fully relativistic calculations of the crustal strain induced in a neutron star by a binary companion at the late stages of inspiral, employing realistic equations of state for the fluid core and the solid crust. We show that while the deep crust is likely to fail only shortly before coalescence, there is a large variation in elastic strain, with the outermost layers failing relatively early on in the inspiral. We discuss the significance of the results for both electromagnetic and gravitational-wave astronomy.

S-layer and cytoplasmic membrane - exceptions from the typical archaeal cell wall with a focus on double membranes.

PubMed

Klingl, Andreas

2014-01-01

The common idea of typical cell wall architecture in archaea consists of a pseudo-crystalline proteinaceous surface layer (S-layer), situated upon the cytoplasmic membrane. This is true for the majority of described archaea, hitherto. Within the crenarchaea, the S-layer often represents the only cell wall component, but there are various exceptions from this wall architecture. Beside (glycosylated) S-layers in (hyper)thermophilic cren- and euryarchaea as well as halophilic archaea, one can find a great variety of other cell wall structures like proteoglycan-like S-layers (Halobacteria), glutaminylglycan (Natronococci), methanochondroitin (Methanosarcina) or double layered cell walls with pseudomurein (Methanothermus and Methanopyrus). The presence of an outermost cellular membrane in the crenarchaeal species Ignicoccus hospitalis already gave indications for an outer membrane similar to Gram-negative bacteria. Although there is just limited data concerning their biochemistry and ultrastructure, recent studies on the euryarchaeal methanogen Methanomassiliicoccus luminyensis, cells of the ARMAN group, and the SM1 euryarchaeon delivered further examples for this exceptional cell envelope type consisting of two membranes.

Hazards protection for space suits and spacecraft

NASA Technical Reports Server (NTRS)

Kosmo, Joseph J. (Inventor); Dawn, Frederic S. (Inventor)

1990-01-01

A flexible multi-layered covering article for protection against the hazards of exposure to the environment of outer space is disclosed. The covering includes an outer layer section comprising an outermost lamina of woven expanded tetrafluoroethylene yarns (Gore Tex) for protecting against abrasion and tearing, an underlying weave of meta-aramid yarns (Nomex) and para-aramid yarns (Kevlar) for particle impart protection, and electrostatic charge dissipation and control system incorporated therein, and a chemical contaminants control barrier applied as a coating. A middle section includes a succession of thermal insulating layers of polymeric thermoplastic or thermoforming material, each of which is coated with a metal deposit of high infra-red emissivity and low solar radiation absorption characteristics and separated from adjacent insulating layers by a low thermal conductance material. The covering further includes a radiation attenuating layer of a tungsten-loaded polymeric elastomer binder for protecting against bremsstrahlung radiation and an inner layer of rip-stop polyester material for abrasion protection. A chloroprene coating may be supplied the polyester-material for added micrometeroid protection. Securing means of low heat conductance material secures the multi-layers together as a laminar composite.

Vertical distribution of overpotentials and irreversible charge losses in lithium ion battery electrodes.

PubMed

Klink, Stefan; Schuhmann, Wolfgang; La Mantia, Fabio

2014-08-01

Porous lithium ion battery electrodes are characterized using a vertical distribution of cross-currents. In an appropriate simplification, this distribution can be described by a transmission line model (TLM) consisting of infinitely thin electrode layers. To investigate the vertical distribution of currents, overpotentials, and irreversible charge losses in a porous graphite electrode in situ, a multi-layered working electrode (MWE) was developed as the experimental analogue of a TLM. In this MWE, each layer is in ionic contact but electrically insulated from the other layers by a porous separator. It was found that the negative graphite electrodes get lithiated and delithiated stage-by-stage and layer-by-layer. Several mass-transport- as well as non-mass-transport-limited processes could be identified. Local current densities can reach double the average, especially on the outermost layer at the beginning of each intercalation stage. Furthermore, graphite particles close to the counter electrode act as "electrochemical sieve" reducing the impurities present in the electrolyte such as water. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the distribution of Na+ pump sites in the frog skin

PubMed Central

Mills, JW; DiBona, DR

1977-01-01

Exposure of the outside of the isolated frog skin to a Ringer's solution, made hypertonic by the addition of mannitol, causes a rapid and sustained increase in transepithelial permeability through a structural distortion-a focal blistering-of the "tight" junctions of the outermost living cell layer. [(3)H]ouabain, used as an autoradiographic marker for the Na+-pump (Na+-K+-adenosine triphosphatase), is usually unable to penetrate the frog skin from the outside solution, but when added to a hypertonic mannitol- Ringer's solution in the outside bath it readily penetrates the epithelium, presumably through the opened shunt pathway. Radioautographic analysis of [(3)H]ouabain binding sites revealed that most of ouabain enters from the outside solution binds to the sites on the cell membranes of the stratum spinosum, as was the case when it was applied from the inside bath in an earlier study. The outer living cell layer, the first to be exposed to ouabain, does not appear to be the major site for the Na+-pump, and therefore, is not likely to be responsible for most of the active pumping of Na+. This result demonstrates that previous failure to show a high density of Na+-pump sites on the cells of the outermost layer, when [(3)H]ouabain was applied from the inside solution, was not due to the inability of the marker to reach these cells at a sufficient concentration to reveal all pump sites. These results provide further support for a model of Na+-transport across the frog skin which distributes the active pump step on the inward facing membranes of all living cells. PMID:144738

Functional Analysis of an S-Layer-Associated Fibronectin-Binding Protein in Lactobacillus acidophilus NCFM

PubMed Central

Hymes, Jeffrey P.; Johnson, Brant R.; Barrangou, Rodolphe

2016-01-01

Bacterial surface layers (S-layers) are crystalline arrays of self-assembling proteinaceous subunits called S-layer proteins (Slps) that comprise the outermost layer of the cell envelope. Many additional proteins that are associated with or embedded within the S-layer have been identified in Lactobacillus acidophilus NCFM, an S-layer-forming bacterium that is widely used in fermented dairy products and probiotic supplements. One putative S-layer-associated protein (SLAP), LBA0191, was predicted to mediate adhesion to fibronectin based on the in silico detection of a fibronectin-binding domain. Fibronectin is a major component of the extracellular matrix (ECM) of intestinal epithelial cells. Adhesion to intestinal epithelial cells is considered an important trait for probiotic microorganisms during transit and potential association with the intestinal mucosa. To investigate the functional role of LBA0191 (designated FbpB) in L. acidophilus NCFM, an fbpB-deficient strain was constructed. The L. acidophilus mutant with a deletion of fbpB lost the ability to adhere to mucin and fibronectin in vitro. Homologues of fbpB were identified in five additional putative S-layer-forming species, but no homologues were detected in species outside the L. acidophilus homology group. PMID:26921419

Reassembly of S-layer proteins

NASA Astrophysics Data System (ADS)

Pum, Dietmar; Sleytr, Uwe B.

2014-08-01

Crystalline bacterial cell surface layers (S-layers) represent the outermost cell envelope component in a broad range of bacteria and archaea. They are monomolecular arrays composed of a single protein or glycoprotein species and represent the simplest biological membranes developed during evolution. They are highly porous protein mesh works with unit cell sizes in the range of 3 to 30 nm, and pore sizes of 2 to 8 nm. S-layers are usually 5 to 20 nm thick (in archaea, up to 70 nm). S-layer proteins are one of the most abundant biopolymers on earth. One of their key features, and the focus of this review, is the intrinsic capability of isolated native and recombinant S-layer proteins to form self-assembled mono- or double layers in suspension, at solid supports, the air-water interface, planar lipid films, liposomes, nanocapsules, and nanoparticles. The reassembly is entropy-driven and a fascinating example of matrix assembly following a multistage, non-classical pathway in which the process of S-layer protein folding is directly linked with assembly into extended clusters. Moreover, basic research on the structure, synthesis, genetics, assembly, and function of S-layer proteins laid the foundation for their application in novel approaches in biotechnology, biomimetics, synthetic biology, and nanotechnology.

Broad-band emission properties of central engine powered supernova ejecta interacting with a circumstellar medium

NASA Astrophysics Data System (ADS)

Suzuki, Akihiro; Maeda, Keiichi

2018-04-01

We investigate broad-band emission from supernova ejecta powered by a relativistic wind from a central compact object. A recent two-dimensional hydrodynamic simulation studying the dynamical evolution of supernova ejecta with a central energy source has revealed that outermost layers of the ejecta are accelerated to mildly relativistic velocities because of the breakout of a hot bubble driven by the energy injection. The outermost layers decelerate as they sweep a circumstellar medium surrounding the ejecta, leading to the formation of the forward and reverse shocks propagating in the circumstellar medium and the ejecta. While the ejecta continue to release the internal energy as thermal emission from the photosphere, the energy dissipation at the forward and reverse shock fronts gives rise to non-thermal emission. We calculate light curves and spectral energy distributions of thermal and non-thermal emission from central engine powered supernova ejecta embedded in a steady stellar wind with typical mass loss rates for massive stars. The light curves are compared with currently available radio and X-ray observations of hydrogen-poor superluminous supernovae, as well as the two well-studied broad-lined Ic supernovae, 1998bw and 2009bb, which exhibit bright radio emission indicating central engine activities. We point out that upper limits on radio luminosities of nearby superluminous supernovae may indicate the injected energy is mainly converted to thermal radiation rather than creating mildly relativistic flows owing to photon diffusion time scales comparable to the injection time scale.

Nanomanufacturing of silicon surface with a single atomic layer precision via mechanochemical reactions.

PubMed

Chen, Lei; Wen, Jialin; Zhang, Peng; Yu, Bingjun; Chen, Cheng; Ma, Tianbao; Lu, Xinchun; Kim, Seong H; Qian, Linmao

2018-04-18

Topographic nanomanufacturing with a depth precision down to atomic dimension is of importance for advancement of nanoelectronics with new functionalities. Here we demonstrate a mask-less and chemical-free nanolithography process for regio-specific removal of atomic layers on a single crystalline silicon surface via shear-induced mechanochemical reactions. Since chemical reactions involve only the topmost atomic layer exposed at the interface, the removal of a single atomic layer is possible and the crystalline lattice beneath the processed area remains intact without subsurface structural damages. Molecular dynamics simulations depict the atom-by-atom removal process, where the first atomic layer is removed preferentially through the formation and dissociation of interfacial bridge bonds. Based on the parametric thresholds needed for single atomic layer removal, the critical energy barrier for water-assisted mechanochemical dissociation of Si-Si bonds was determined. The mechanochemical nanolithography method demonstrated here could be extended to nanofabrication of other crystalline materials.

Distribution of rock, metals, and ices in Callisto.

PubMed

Anderson, J D; Schubert, G; Jacobson, R A; Lau, E L; Moore, W B; Sjogren, W L

1998-06-05

Radio Doppler data from a single encounter (C3) of the Galileo spacecraft with Callisto, the outermost Galilean moon of Jupiter, indicated that Callisto was probably undifferentiated. Now, similar data from a second encounter (C9) corroborate this conclusion, but more accurate data from a third encounter (C10) indicate that the rock and ice within Callisto have partially, but not completely, separated. Callisto may be differentiated into a rock-metal core less than 25 percent of Callisto's radius, an outer layer of clean ice less than 350 km thick, and a middle layer of mixed rock and ice. Models in which ice and rock are mixed all the way to the center of Callisto are also consistent with the data.

Disentangling atomic-layer-specific x-ray absorption spectra by Auger electron diffraction spectroscopy

NASA Astrophysics Data System (ADS)

Matsui, Fumihiko; Matsushita, Tomohiro; Kato, Yukako; Hashimoto, Mie; Daimon, Hiroshi

2009-11-01

In order to investigate the electronic and magnetic structures of each atomic layer at subsurface, we have proposed a new method, Auger electron diffraction spectroscopy, which is the combination of x-ray absorption spectroscopy (XAS) and Auger electron diffraction (AED) techniques. We have measured a series of Ni LMM AED patterns of the Ni film grown on Cu(001) surface for various thicknesses. Then we deduced a set of atomic-layer-specific AED patterns in a numerical way. Furthermore, we developed an algorithm to disentangle XANES spectra from different atomic layers using these atomic-layer-specific AED patterns. Surface and subsurface core level shift were determined for each atomic layer.

Transfer of a weakly bound electron in collisions of Rydberg atoms with neutral particles. II. Ion-pair formation and resonant quenching of the Rb(nl) and Ne(nl) States by Ca, Sr, and Ba atoms

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

Narits, A. A.; Mironchuk, E. S.; Lebedev, V. S., E-mail: vlebedev@sci.lebedev.ru

2013-10-15

Electron-transfer processes are studied in thermal collisions of Rydberg atoms with alkaline-earth Ca(4s{sup 2}), Sr(5s{sup 2}), and Ba(6s{sup 2}) atoms capable of forming negative ions with a weakly bound outermost p-electron. We consider the ion-pair formation and resonant quenching of highly excited atomic states caused by transitions between Rydberg covalent and ionic terms of a quasi-molecule produced in collisions of particles. The contributions of these reaction channels to the total depopulation cross section of Rydberg states of Rb(nl) and Ne(nl) atoms as functions of the principal quantum number n are compared for selectively excited nl-levels with l Much-Less-Than n andmore » for states with large orbital quantum numbers l = n - 1, n - 2. It is shown that the contribution from resonant quenching dominates at small values of n, and the ion-pair formation process begins to dominate with increasing n. The values and positions of the maxima of cross sections for both processes strongly depend on the electron affinity of an alkaline-earth atom and on the orbital angular momentum l of a highly excited atom. It is shown that in the case of Rydberg atoms in states with large l {approx} n - 1, the rate constants of ion-pair formation and collisional quenching are considerably lower than those for nl-levels with l Much-Less-Than n.« less

Degradation processes of reinforced concretes by combined sulfate–phosphate attack

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

Secco, Michele, E-mail: michele.secco@unipd.it; Department of Civil, Environmental and Architectural Engineering; Lampronti, Giulio Isacco, E-mail: gil21@cam.ac.uk

2015-02-15

A novel form of alteration due to the interaction between hydrated cement phases and sulfate and phosphate-based pollutants is described, through the characterization of concrete samples from an industrial reinforced concrete building. Decalcification of the cement matrices was observed, with secondary sulfate and phosphate-based mineral formation, according to a marked mineralogical and textural zoning. Five alteration layers may be detected: the two outermost layers are characterized by the presence of gypsum–brushite solid solution phases associated with anhydrous calcium sulfates and phosphates, respectively, while a progressive increase in apatite and ammonium magnesium phosphates is observable in the three innermost layers, associatedmore » with specific apatite precursors (brushite, octacalcium phosphate and amorphous calcium phosphate, respectively). The heterogeneous microstructural development of secondary phases is related to the chemical, pH and thermal gradients in the attacked cementitious systems, caused by different sources of pollutants and the exposure to the sun's radiation.« less

Depth profiling the solid electrolyte interphase on lithium titanate (Li4Ti5O12) using synchrotron-based photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Nordh, Tim; Younesi, Reza; Brandell, Daniel; Edström, Kristina

2015-10-01

The presence of a surface layer on lithium titanate (Li4Ti5O12, LTO) anodes, which has been a topic of debate in scientific literature, is here investigated with tunable high surface sensitive synchrotron-based photoelectron spectroscopy (PES) to obtain a reliable depth profile of the interphase. Li||LTO cells with electrolytes consisting of 1 M lithium hexafluorophosphate dissolved in ethylene carbonate:diethyl carbonate (LiPF6 in EC:DEC) were cycled in two different voltage windows of 1.0-2.0 V and 1.4-2.0 V. LTO electrodes were characterized after 5 and 100 cycles. Also the pristine electrode as such, and an electrode soaked in the electrolyte were analyzed by varying the photon energies enabling depth profiling of the outermost surface layer. The main components of the surface layer were found to be ethers, P-O containing compounds, and lithium fluoride.

Isotope effect on blob-statistics in gyrofluid simulations of scrape-off layer turbulence

NASA Astrophysics Data System (ADS)

Meyer, O. H. H.; Kendl, A.

2017-12-01

In this contribution we apply a recently established stochastic model for scrape-off layer fluctuations to long time series obtained from gyrofluid simulations of fusion edge plasma turbulence. Characteristic parameters are estimated for different fusion relevant isotopic compositions (protium, deuterium, tritium and singly charged helium) by means of conditional averaging. It is shown that large amplitude fluctuations associated with radially propagating filaments in the scrape-off layer feature double-exponential wave-forms. We find increased pulse duration and longer waiting times between peaks for heavier ions, while the amplitudes are similar. The associated radial blob velocity is shown to be reduced for heavier ions. A parabolic relation between skewness and kurtosis of density fluctuations seems to be present. Improved particle confinement in terms of reduced mean value close to the outermost radial boundary and blob characteristics for heavier plasmas is presented.

Fuel and oxygen addition for metal smelting or refining process

DOEpatents

Schlichting, Mark R.

1994-01-01

A furnace 10 for smelting iron ore and/or refining molten iron 20 is equipped with an overhead pneumatic lance 40, through which a center stream of particulate coal 53 is ejected at high velocity into a slag layer 30. An annular stream of nitrogen or argon 51 enshrouds the coal stream. Oxygen 52 is simultaneously ejected in an annular stream encircling the inert gas stream 51. The interposition of the inert gas stream between the coal and oxygen streams prevents the volatile matter in the coal from combusting before it reaches the slag layer. Heat of combustion is thus more efficiently delivered to the slag, where it is needed to sustain the desired reactions occurring there. A second stream of lower velocity oxygen can be delivered through an outermost annulus 84 to react with carbon monoxide gas rising from slag layer 30, thereby adding still more heat to the furnace.

Fuel and oxygen addition for metal smelting or refining process

DOEpatents

Schlichting, M.R.

1994-11-22

A furnace for smelting iron ore and/or refining molten iron is equipped with an overhead pneumatic lance, through which a center stream of particulate coal is ejected at high velocity into a slag layer. An annular stream of nitrogen or argon enshrouds the coal stream. Oxygen is simultaneously ejected in an annular stream encircling the inert gas stream. The interposition of the inert gas stream between the coal and oxygen streams prevents the volatile matter in the coal from combusting before it reaches the slag layer. Heat of combustion is thus more efficiently delivered to the slag, where it is needed to sustain the desired reactions occurring there. A second stream of lower velocity oxygen can be delivered through an outermost annulus to react with carbon monoxide gas rising from slag layer, thereby adding still more heat to the furnace. 7 figs.

Lance for fuel and oxygen injection into smelting or refining furnace

DOEpatents

Schlichting, Mark R.

1994-01-01

A furnace 10 for smelting iron ore and/or refining molten iron 20 is equipped with an overhead pneumatic lance 40, through which a center stream of particulate coal 53 is ejected at high velocity into a slag layer 30. An annular stream of nitrogen or argon 51 enshrouds the coal stream. Oxygen 52 is simultaneously ejected in an annular stream encircling the inert gas stream 51. The interposition of the inert gas stream between the coal and oxygen streams prevents the volatile matter in the coal from combusting before it reaches the slag layer. Heat of combustion is thus more efficiently delivered to the slag, where it is needed to sustain the desired reactions occurring there. A second stream of lower velocity oxygen can be delivered through an outermost annulus 84 to react with carbon monoxide gas rising from slag layer 30, thereby adding still more heat to the furnace.

Lance for fuel and oxygen injection into smelting or refining furnace

DOEpatents

Schlichting, M.R.

1994-12-20

A furnace for smelting iron ore and/or refining molten iron is equipped with an overhead pneumatic lance, through which a center stream of particulate coal is ejected at high velocity into a slag layer. An annular stream of nitrogen or argon enshrouds the coal stream. Oxygen is simultaneously ejected in an annular stream encircling the inert gas stream. The interposition of the inert gas stream between the coal and oxygen streams prevents the volatile matter in the coal from combusting before it reaches the slag layer. Heat of combustion is thus more efficiently delivered to the slag, where it is needed to sustain the desired reactions occurring there. A second stream of lower velocity oxygen can be delivered through an outermost annulus to react with carbon monoxide gas rising from slag layer, thereby adding still more heat to the furnace. 7 figures.

Interaction of lysozyme with a tear film lipid layer model: A molecular dynamics simulation study.

PubMed

Wizert, Alicja; Iskander, D Robert; Cwiklik, Lukasz

2017-12-01

The tear film is a thin multilayered structure covering the cornea. Its outermost layer is a lipid film underneath of which resides on an aqueous layer. This tear film lipid layer (TFLL) is itself a complex structure, formed by both polar and nonpolar lipids. It was recently suggested that due to tear film dynamics, TFLL contains inhomogeneities in the form of polar lipid aggregates. The aqueous phase of tear film contains lachrymal-origin proteins, whereby lysozyme is the most abundant. These proteins can alter TFLL properties, mainly by reducing its surface tension. However, a detailed nature of protein-lipid interactions in tear film is not known. We investigate the interactions of lysozyme with TFLL in molecular details by employing coarse-grained molecular dynamics simulations. We demonstrate that lysozyme, due to lateral restructuring of TFLL, is able to penetrate the tear lipid film embedded in inverse micellar aggregates. Copyright © 2017 Elsevier B.V. All rights reserved.

Behavior of sphingomyelin and ceramide in a tear film lipid layer model.

PubMed

Olżyńska, Agnieszka; Cwiklik, Lukasz

2017-03-01

Tear film lipid layer is a complex lipid mixture forming the outermost interface between eye and environment. Its key characteristics, such as surface tension and structural stability, are governed by the presence of polar lipids. The origin of these lipids and exact composition of the mixture are still elusive. We focus on two minor polar lipid components of the tear film lipid later: sphingomyelin and ceramide. By employing coarse grain molecular dynamics in silico simulations accompanied by Langmuir balance experiments we provide molecular-level insight into behavior of these two lipids in a tear film lipid layer model. Sphingomyelin headgroups are significantly exposed at the water-lipids boundary while ceramide molecules are incorporated between other lipids frequently interacting with nonpolar lipids. Even though these two lipids increase surface tension of the film, their molecular-level behavior suggests that they have a stabilizing effect on the tear film lipid layer. Copyright © 2016 Elsevier GmbH. All rights reserved.

A bio-ballistic micro-jet for drug injection into animal skin using a Nd:YAG laser

NASA Astrophysics Data System (ADS)

Yoh, J. J.; Jang, H.; Park, M.; Han, T.; Hah, J.

2016-01-01

Imaging of the abdominal skin of a guinea pig after injecting a fluorescent probe and biotin via the laser-induced ballistic technique revealed the epidermal and dermal layers which were stained well below 60 \\upmu m underneath the outer layer of the skin. An extensive network of cells was evident in the deeper layer of the stained dermis as the distributed fluorescein isothiocyanate dose was administered by repeated injection using a laser-based micro-jet. We performed optically controlled release of the drug by breaching the guinea pig's skin tissue targeting the region 10-400 \\upmu m beneath the outermost layer. Tissue damage was minimized by reducing the injection volume to approximately 100 nl per pulse. This was done using a micro-jet diameter equal to half of that of a conventional 200 \\upmu m syringe needle. Thus, the optimally controlled delivery of liquid drugs using an irradiated laser pulse was shown to be possible.

Applications of AFM for atomic manipulation and spectroscopy

NASA Astrophysics Data System (ADS)

Custance, Oscar

2009-03-01

Since the first demonstration of atom-by-atom assembly [1], atomic manipulation with scanning tunneling microscopy has yielded stunning realizations in nanoscience. A new exciting panorama has been recently opened with the possibility of manipulating atoms at surfaces using atomic force microscopy (AFM) [2-5]. In this talk, we will present two different approaches that enable patterning structures at semiconductor surfaces by manipulating individual atoms with AFM and at room temperature [2, 3]. We will discuss the physics behind each protocol through the analysis of the measured forces associated with these manipulations [3-5]. Another challenging issue in scanning probe microscopy is the ability to disclose the local chemical composition of a multi-element system at atomic level. Here, we will introduce a single-atom chemical identification method, which is based on detecting the forces between the outermost atom of the AFM tip and the atoms at a surface [6]. We demonstrate this identification procedure on a particularly challenging system, where any discrimination attempt based solely on topographic measurements would be impossible to achieve. [4pt] References: [0pt] [1] D. M. Eigler and E. K. Schweizer, Nature 344, 524 (1990); [0pt] [2] Y. Sugimoto, M. Abe, S. Hirayama, N. Oyabu, O. Custance and S. Morita, Nature Materials 4, 156 (2005); [0pt] [3] Y. Sugimoto, P. Pou, O. Custance, P. Jelinek, M. Abe, R. Perez and S. Morita, Science 322, 413 (2008); [0pt] [4] Y. Sugimoto, P. Jelinek, P. Pou, M. Abe, S. Morita, R. Perez and O. Custance, Phys. Rev. Lett. 98, 106104 (2007); [0pt] [5] M. Ternes, C. P. Lutz, C. F. Hirjibehedin, F. J. Giessibl and A. J. Heinrich, Science 319, 1066 (2008); [0pt] [6] Y. Sugimoto, P. Pou, M. Abe, P. Jelinek, R. Perez, S. Morita, and O. Custance, Nature 446, 64 (2007)

Observation of impulsive acoustic events and the excitation of solar oscillations. Annual report, 1 November 1991-31 October 1992

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

Restaino, S.R.; Stebbins, R.T.; Goode, P.R.

1992-12-04

The five-minute solar oscillation has been exploited in numerous seismic studies in which internal properties of the Sun have been inferred. It is generally regarded that these modes are excited by turbulent convection in the Sun's outermost layers. We observe the oscillatory wakes caused by impulsive events, matching those described by Lamb (1909). These correspond to the events modeled by Goode, et al., which they associate with excitation of the global five-minute oscillations.... Sun: Oscillations, Sun: Atmospheric motions, Sun: Atmosphere.

Gene expression and morphogenesis during the deposition of Drosophila wing cuticle

PubMed Central

Adler, Paul N.

2017-01-01

ABSTRACT The exoskeleton of insects and other arthropods is a very versatile material that is characterized by a complex multilayer structure. In Sobala and Adler (2016) we analyzed the process of wing cuticle deposition by RNAseq and electron microscopy. In this extra view we discuss the unique aspects of the envelope the first and most outermost layer and the gene expression program seen at the end of cuticle deposition. We discussed the role of undulae in the deposition of cuticle and how the hydrophobicity of wing cuticle arises. PMID:28631994

Gene expression and morphogenesis during the deposition of Drosophila wing cuticle.

PubMed

Adler, Paul N

2017-07-03

The exoskeleton of insects and other arthropods is a very versatile material that is characterized by a complex multilayer structure. In Sobala and Adler (2016) we analyzed the process of wing cuticle deposition by RNAseq and electron microscopy. In this extra view we discuss the unique aspects of the envelope the first and most outermost layer and the gene expression program seen at the end of cuticle deposition. We discussed the role of undulae in the deposition of cuticle and how the hydrophobicity of wing cuticle arises.

Movement of endogenous calcium in the elongating zone of graviresponding roots of Zea mays

NASA Technical Reports Server (NTRS)

Moore, R.; Cameron, I. L.; Smith, N. K.

1989-01-01

Endogenous calcium (Ca) accumulates along the lower side of the elongating zone of horizontally oriented roots of Zea mays cv. Yellow Dent. This accumulation of Ca correlates positively with the onset of gravicurvature, and occurs in the cytoplasm, cell walls and mucilage of epidermal cells. Corresponding changes in endogenous Ca do not occur in cortical cells of the elongating zone of intact roots. These results indicate that the calcium asymmetries associated with root gravicurvature occur in the outermost layers of the root.

Interfacial and topological effects on the glass transition in free-standing polystyrene films

NASA Astrophysics Data System (ADS)

Lyulin, Alexey V.; Balabaev, Nikolay K.; Baljon, Arlette R. C.; Mendoza, Gerardo; Frank, Curtis W.; Yoon, Do Y.

2017-05-01

United-atom molecular-dynamics computer simulations of atactic polystyrene (PS) were performed for the bulk and free-standing films of 2 nm-20 nm thickness, for both linear and cyclic polymers comprised of 80 monomers. Simulated volumetric glass-transition temperatures (Tg) show a strong dependence on the film thickness below 10 nm. The glass-transition temperature of linear PS is 13% lower than that of the bulk for 2.5 nm-thick films, as compared to less than 1% lower for 20 nm films. Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approximately 1 nm below the surface than it is in the bulk. The enhanced population of the end groups is expected to result in a more mobile interfacial layer and the consequent dependence of Tg on the film thickness. In addition, the simulations show an enrichment of backbone aliphatic carbons and concomitant deficit of phenyl aromatic carbons in the interfacial film layer. This deficit would weaken the strong phenyl-phenyl aromatic (π -π ) interactions and, hence, lead to a lower film-averaged Tg in thin films, as compared to the bulk sample. To investigate the relative importance of the two possible mechanisms (increased chain ends at the surface or weakened π -π interactions in the interfacial region), the data for linear PS are compared with those for cyclic PS. For the cyclic PS, the reduction of the glass-transition temperature is also significant in thin films, albeit not as much as for linear PS. Moreover, the deficit of phenyl carbons in the film interface is comparable to that observed for linear PS. Therefore, chain-end effects alone cannot explain the observed pronounced Tg dependence on the thickness of thin PS films; the weakened phenyl-phenyl interactions in the interfacial region seems to be an important cause as well.

Measurement and Control of In-plane Surface Chemistry at the Silicon/Silicon Dioxide Interface

NASA Astrophysics Data System (ADS)

Gokce, Bilal

In-plane directional control of surface chemistry during interface formation can lead to new opportunities regarding device structures and applications. Control of this type requires techniques that can probe and hence provide feedback on the chemical reactivity of bonds not only in specific directions but also in real time. In this thesis work, I demonstrate both control and measurement of the oxidation of H-terminated Si(111). The nonlinear optical tool of Second-Harmonic-Generation (SHG) is used to show that Si oxidation in air is a two-stage process where the H of the "up" bonds of the outermost Si layer is replaced by OH, followed by O insertion into the "back" bonds. Detailed information about both stages is revealed by investigating the effect of uniaxial strain and carrier concentration on this chemical reaction. It is shown that even small amounts of strain manipulate the reaction kinetics of surface bonds significantly, with tensile strain enhancing oxidation and compressive strain retarding it. This dramatic change suggests a strain-driven charge transfer mechanism between Si--H up bonds and Si--Si back bonds in the outer layer of Si atoms. Data on differently doped samples reveal that high concentrations of electrons increase the chemical reactivity of the outer-layer Si--Si back bonds relative to the Si--H up bonds while high concentrations of holes cause a greater increase in the reactivity of the Si--H up bonds than that of the Si--Si back bonds. However, the thicknesses of the natural oxides of all samples follow the same path and stabilize near 1 nm at room temperature, regardless of the chemical kinetics of the different bonds, as determined by spectroscopic ellipsometry. Real-time measurement during SHG experiments is achieved by analyzing SHG anisotropy data with the anisotropic bond-charge model of nonlinear optics where peaks in the SHG spectrum are correlated with the near alignment of bonds to the direction of the excitation field.

Polyelectrolyte multi-layers assembly of SiCHA nanopowders and collagen type I on aminolysed PLA films to enhance cell-material interactions.

PubMed

Baba Ismail, Yanny Marliana; Ferreira, Ana Marina; Bretcanu, Oana; Dalgarno, Kenneth; El Haj, Alicia J

2017-11-01

This paper presents a new approach in assembling bone extracellular matrix components onto PLA films, and investigates the most favourable environment which can be created using the technique for cell-material interactions. Poly (lactic acid) (PLA) films were chemically modified by covalently binding the poly(ethylene imine) (PEI) as to prepare the substrate for immobilization of polyelectrolyte multilayers (PEMs) coating. Negatively charged polyelectrolyte consists of well-dispersed silicon-carbonated hydroxyapatite (SiCHA) nanopowders in hyaluronic acid (Hya) was deposited onto the modified PLA films followed by SiCHA in collagen type I as the positively charged polyelectrolyte. The outermost layer was finally cross-linked by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrocholoride and N-hydroxysulfosuccinimide sodium salt (EDC/NHS) solutions. The physicochemical features of the coated PLA films were monitored via X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscope (AFM). The amounts of calcium and collagen deposited on the surface were qualitatively and quantitatively determined. The surface characterizations suggested that 5-BL has the optimum surface roughness and highest amounts of calcium and collagen depositions among tested films. In vitro human mesenchymal stem cells (hMSCs) cultured on the coated PLA films confirmed that the coating materials greatly improved cell attachment and survival compared to unmodified PLA films. The cell viability, cell proliferation and Alkaline Phosphatase (ALP) expression on 5-BL were found to be the most favourable of the tested films. Hence, this newly developed coating materials assembly could contribute to the improvement of the bioactivity of polymeric materials and structures aimed to bone tissue engineering applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Analytic Expressions for the Inner-rim Structure of Passively Heated Protoplanetary Disks

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

Ueda, Takahiro; Okuzumi, Satoshi; Flock, Mario, E-mail: t_ueda@geo.titech.ac.jp

We analytically derive the expressions for the structure of the inner region of protoplanetary disks based on the results from the recent hydrodynamical simulations. The inner part of a disk can be divided into four regions: a dust-free region with a gas temperature in the optically thin limit, an optically thin dust halo, an optically thick condensation front, and the classical, optically thick region, in order from the innermost to the outermost. We derive the dust-to-gas mass ratio profile in the dust halo using the fact that partial dust condensation regulates the temperature relative to the dust evaporation temperature. Beyondmore » the dust halo, there is an optically thick condensation front where all the available silicate gas condenses out. The curvature of the condensation surface is determined by the condition that the surface temperature must be nearly equal to the characteristic temperature ∼1200 K. We derive the midplane temperature in the outer two regions using the two-layer approximation, with the additional heating by the condensation front for the outermost region. As a result, the overall temperature profile is step-like, with steep gradients at the borders between the outer three regions. The borders might act as planet traps where the inward migration of planets due to gravitational interaction with the gas disk stops. The temperature at the border between the two outermost regions coincides with the temperature needed to activate magnetorotational instability, suggesting that the inner edge of the dead zone must lie at this border. The radius of the dead zone inner edge predicted from our solution is ∼2–3 times larger than that expected from the classical optically thick temperature.« less

Analytic Expressions for the Inner-rim Structure of Passively Heated Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Ueda, Takahiro; Okuzumi, Satoshi; Flock, Mario

2017-07-01

We analytically derive the expressions for the structure of the inner region of protoplanetary disks based on the results from the recent hydrodynamical simulations. The inner part of a disk can be divided into four regions: a dust-free region with a gas temperature in the optically thin limit, an optically thin dust halo, an optically thick condensation front, and the classical, optically thick region, in order from the innermost to the outermost. We derive the dust-to-gas mass ratio profile in the dust halo using the fact that partial dust condensation regulates the temperature relative to the dust evaporation temperature. Beyond the dust halo, there is an optically thick condensation front where all the available silicate gas condenses out. The curvature of the condensation surface is determined by the condition that the surface temperature must be nearly equal to the characteristic temperature ˜1200 K. We derive the midplane temperature in the outer two regions using the two-layer approximation, with the additional heating by the condensation front for the outermost region. As a result, the overall temperature profile is step-like, with steep gradients at the borders between the outer three regions. The borders might act as planet traps where the inward migration of planets due to gravitational interaction with the gas disk stops. The temperature at the border between the two outermost regions coincides with the temperature needed to activate magnetorotational instability, suggesting that the inner edge of the dead zone must lie at this border. The radius of the dead zone inner edge predicted from our solution is ˜2-3 times larger than that expected from the classical optically thick temperature.

Functional Analysis of an S-Layer-Associated Fibronectin-Binding Protein in Lactobacillus acidophilus NCFM.

PubMed

Hymes, Jeffrey P; Johnson, Brant R; Barrangou, Rodolphe; Klaenhammer, Todd R

2016-05-01

Bacterial surface layers (S-layers) are crystalline arrays of self-assembling proteinaceous subunits called S-layer proteins (Slps) that comprise the outermost layer of the cell envelope. Many additional proteins that are associated with or embedded within the S-layer have been identified in Lactobacillus acidophilus NCFM, an S-layer-forming bacterium that is widely used in fermented dairy products and probiotic supplements. One putative S-layer-associated protein (SLAP), LBA0191, was predicted to mediate adhesion to fibronectin based on the in silico detection of a fibronectin-binding domain. Fibronectin is a major component of the extracellular matrix (ECM) of intestinal epithelial cells. Adhesion to intestinal epithelial cells is considered an important trait for probiotic microorganisms during transit and potential association with the intestinal mucosa. To investigate the functional role of LBA0191 (designated FbpB) in L. acidophilus NCFM, an fbpB-deficient strain was constructed. The L. acidophilus mutant with a deletion off bpB lost the ability to adhere to mucin and fibronectin in vitro Homologues off bpB were identified in five additional putative S-layer-forming species, but no homologues were detected in species outside theL. acidophilus homology group. Copyright © 2016 Hymes et al.

Self-limited growth of Si on B atomic-layer formed Ge(1 0 0) by ultraclean low-pressure CVD system

NASA Astrophysics Data System (ADS)

Yokogawa, Takashi; Ishibashi, Kiyohisa; Sakuraba, Masao; Murota, Junichi; Inokuchi, Yasuhiro; Kunii, Yasuo; Kurokawa, Harushige

2008-07-01

Utilizing BCl 3 reaction on Ge(1 0 0) and subsequent Si epitaxial growth by SiH 4 reaction at 300 °C, B atomic-layer doping in Si/Ge(1 0 0) heterostructure was investigated. Cl atoms on the B atomic-layer formed Ge(1 0 0) scarcely affect upon the SiH 4 reaction. It is also found that Si atom amount deposited by SiH 4 reaction on Ge(1 0 0) is effectively enhanced by the existence of B atomic layer and the deposition rate tends to decrease at around 2-3 atomic layers which is three times larger than that in the case without B. The results of angle-resolved X-ray photoelectron spectroscopy show that most B atoms are incorporated at the heterointerface between the Si and Ge.

Epitaxial Growth of Rhenium with Sputtering

DTIC Science & Technology

2016-05-06

corresponds to two atomic Re layers , considering that the c-axis lattice constant of the tri- atomic layered hcp Re unit cell is ~4.5 Å. Frequently, two...Å) corresponds to two Re atomic layers since the c-axis lattice constant of hcp Re, which is composed of three Re atomic layers , is ~4.5 Å...The growth starts in a three dimensional mode but transforms into two dimensional mode as the film gets thicker. With a thin (~2 nm) seed layer

Affinities and architecture of Devonian trunks of Prototaxites loganii.

PubMed

Retallack, G J; Landing, Ed

2014-01-01

Devonian fossil logs of Prototaxites loganii have been considered kelp-like aquatic algae, rolled up carpets of liverworts, enormous saprophytic fungal fruiting bodies or giant lichens. Algae and rolled liverwort models cannot explain the proportions and branching described here of a complete fossil of Prototaxites loganii from the Middle Devonian (386 Ma) Bellvale Sandstone on Schunnemunk Mountain, eastern New York. The "Schunnemunk tree" was 8.83 m long and had six branches, each about 1 m long and 9 cm diam, on the upper 1.2 m of the main axis. The coalified outermost layer of the Schunnemunk trunk and branches have isotopic compositions (δ(13)CPDB) of -25.03 ± 0.13‰ and -26.17 ± 0.69‰, respectively. The outermost part of the trunk has poorly preserved invaginations above cortical nests of coccoid cells embraced by much-branched tubular cells. This histology is unlike algae, liverworts or vascular plants and most like lichen with coccoid chlorophyte phycobionts. Prototaxites has been placed within Basidiomycota but lacks clear dikaryan features. Prototaxites and its extinct order Nematophytales may belong within Mucoromycotina or Glomeromycota. © 2014 by The Mycological Society of America.

Autonomic innervation of the muscles in the wall of the bladder and proximal urethra of male rats.

PubMed Central

Watanabe, H; Yamamoto, T Y

1979-01-01

The muscular coat of the body of the rat bladder is innervated almost exclusively by cholinergic endings:adrenergic endings are rare. In the inner longitudinal muscle layer of the proximal urethra, 53% of 310 autonomic nerve endings observed in close relation to the smooth muscle cells were adrenergic and the remaining 47% cholinergic. The middle circular muscle layer of the proximal urethra was innervated predominantly by adrenergic endings: in this layer 86% of the total of 335 endings examined wre regarded as adrenergic. A similar predominantly adrenergic innervation was noted in the outer longitudinal layer of the proximal urethra. A number of striated muscle fibres arose from the outermost striated muscle layer of the proximal urethra and intruded deeply into the outer and middle smooth muscle layers. These intruding striated muscle fibres also received direct autonomic (mostly adrenergic) innervation. The significance of these findings in relation to the physiology of the lower urinary tracts is discussed. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 13 Fig. 14 Fig. 15 Fig. 16 PMID:489473

Skin permeation and antioxidant efficacy of topically applied resveratrol.

PubMed

Alonso, Cristina; Martí, M; Barba, C; Carrer, V; Rubio, L; Coderch, L

2017-08-01

The permeation of resveratrol was assessed by in vitro and in vivo experiments 24 h after topical administration. The in vitro profile of resveratrol was assessed by Raman spectroscopy. Human skin permeation was analysed in vivo by the tape stripping method with the progressive removal of the stratum corneum layers using adhesive tape strips. Moreover, the free radical scavenging activity of resveratrol after its topical application was determined using the DPPH assay. The Raman spectra indicated that the topically applied resveratrol penetrates deep into the skin. The results showed high amounts of resveratrol in the different stratum corneum layers close to the surface and a constant lower amount in the upper layers of the viable epidermis. The concentration of resveratrol present in the outermost stratum corneum layers was obtained by tape stripping after in vivo application. The results demonstrated that resveratrol mainly remained in the human stratum corneum layers. After topical application, resveratrol maintained its antiradical activity. The antioxidant efficacy of the compound was higher in the inner layers of the stratum corneum. As these results have demonstrated, topically applied resveratrol reinforces the antioxidant system of the stratum corneum and provides an efficient means of increasing the tissue levels of antioxidants in the human epidermis.

Direct observation of nanowire growth and decomposition.

PubMed

Rackauskas, Simas; Shandakov, Sergey D; Jiang, Hua; Wagner, Jakob B; Nasibulin, Albert G

2017-09-26

Fundamental concepts of the crystal formation suggest that the growth and decomposition are determined by simultaneous embedding and removal of the atoms. Apparently, by changing the crystal formation conditions one can switch the regimes from the growth to decomposition. To the best of our knowledge, so far this has been only postulated, but never observed at the atomic level. By means of in situ environmental transmission electron microscopy we monitored and examined the atomic layer transformation at the conditions of the crystal growth and its decomposition using CuO nanowires selected as a model object. The atomic layer growth/decomposition was studied by varying an O 2 partial pressure. Three distinct regimes of the atomic layer evolution were experimentally observed: growth, transition and decomposition. The transition regime, at which atomic layer growth/decomposition switch takes place, is characterised by random nucleation of the atomic layers on the growing {111} surface. The decomposition starts on the side of the nanowire by removing the atomic layers without altering the overall crystal structure, which besides the fundamental importance offers new possibilities for the nanowire manipulation. Understanding of the crystal growth kinetics and nucleation at the atomic level is essential for the precise control of 1D crystal formation.

Characterization and use of crystalline bacterial cell surface layers

NASA Astrophysics Data System (ADS)

Sleytr, Uwe B.; Sára, Margit; Pum, Dietmar; Schuster, Bernhard

2001-10-01

Crystalline bacterial cell surface layers (S-layers) are one of the most common outermost cell envelope components of prokaryotic organisms (archaea and bacteria). S-layers are monomolecular arrays composed of a single protein or glycoprotein species and represent the simplest biological membranes developed during evolution. S-layers as the most abundant of prokaryotic cellular proteins are appealing model systems for studying the structure, synthesis, genetics, assembly and function of proteinaceous supramolecular structures. The wealth of information existing on the general principle of S-layers have revealed a broad application potential. The most relevant features exploited in applied S-layer research are: (i) pores passing through S-layers show identical size and morphology and are in the range of ultrafiltration membranes; (ii) functional groups on the surface and in the pores are aligned in well-defined positions and orientations and accessible for chemical modifications and binding functional molecules in very precise fashion; (iii) isolated S-layer subunits from a variety of organisms are capable of recrystallizing as closed monolayers onto solid supports (e.g., metals, polymers, silicon wafers) at the air-water interface, on lipid films or onto the surface of liposomes; (iv) functional domains can be incorporated in S-layer proteins by genetic engineering. Thus, S-layer technologies particularly provide new approaches for biotechnology, biomimetics, molecular nanotechnology, nanopatterning of surfaces and formation of ordered arrays of metal clusters or nanoparticles as required for nanoelectronics.

Facile large-scale synthesis of brain-like mesoporous silica nanocomposites via a selective etching process

NASA Astrophysics Data System (ADS)

Chen, Yu; Wang, Qihua; Wang, Tingmei

2015-10-01

The core-shell structured mesoporous silica nanomaterials (MSNs) are experiencing rapid development in many applications such as heterogeneous catalysis, bio-imaging and drug delivery wherein a large pore volume is desirable. We develop a one-pot method for large-scale synthesis of brain-like mesoporous silica nanocomposites based on the reasonable change of the intrinsic nature of the -Si-O-Si- framework of silica nanoparticles together with a selective etching strategy. The as-synthesized products show good monodispersion and a large pore volume of 1.0 cm3 g-1. The novelty of this approach lies in the use of an inorganic-organic hybrid layer to assist the creation of large-pore morphology on the outermost shell thereby promoting efficient mass transfer or storage. Importantly, the method is reliable and grams of products can be easily prepared. The morphology on the outermost silica shell can be controlled by simply adjusting the VTES-to-TEOS molar ratio (VTES: triethoxyvinylsilane, TEOS: tetraethyl orthosilicate) as well as the etching time. The as-synthesized products exhibit fluorescence performance by incorporating rhodamine B isothiocyanate (RITC) covalently into the inner silica walls, which provide potential application in bioimaging. We also demonstrate the applications of as-synthesized large-pore structured nanocomposites in drug delivery systems and stimuli-responsive nanoreactors for heterogeneous catalysis.The core-shell structured mesoporous silica nanomaterials (MSNs) are experiencing rapid development in many applications such as heterogeneous catalysis, bio-imaging and drug delivery wherein a large pore volume is desirable. We develop a one-pot method for large-scale synthesis of brain-like mesoporous silica nanocomposites based on the reasonable change of the intrinsic nature of the -Si-O-Si- framework of silica nanoparticles together with a selective etching strategy. The as-synthesized products show good monodispersion and a large pore volume of 1.0 cm3 g-1. The novelty of this approach lies in the use of an inorganic-organic hybrid layer to assist the creation of large-pore morphology on the outermost shell thereby promoting efficient mass transfer or storage. Importantly, the method is reliable and grams of products can be easily prepared. The morphology on the outermost silica shell can be controlled by simply adjusting the VTES-to-TEOS molar ratio (VTES: triethoxyvinylsilane, TEOS: tetraethyl orthosilicate) as well as the etching time. The as-synthesized products exhibit fluorescence performance by incorporating rhodamine B isothiocyanate (RITC) covalently into the inner silica walls, which provide potential application in bioimaging. We also demonstrate the applications of as-synthesized large-pore structured nanocomposites in drug delivery systems and stimuli-responsive nanoreactors for heterogeneous catalysis. Electronic supplementary information (ESI) available: The average particle size distribution of LPASN-1, LPASN-2 and LPASN-3; the wide-angle XRD pattern of LPASN-2/LPASN-3/LPASN-4; the catalytic properties of LPASN-PNIPAM at different temperatures (15 °C and 33 °C). See DOI: 10.1039/c5nr04123f

Grand Canonical Investigation of the Quasi Liquid Layer of Ice: Is It Liquid?

PubMed

Pickering, Ignacio; Paleico, Martin; Sirkin, Yamila A Perez; Scherlis, Damian A; Factorovich, Matías H

2018-05-10

In this study, the solid-vapor equilibrium and the quasi liquid layer (QLL) of ice Ih exposing the basal and primary prismatic faces were explored by means of grand canonical molecular dynamics simulations with the monatomic mW potential. For this model, the solid-vapor equilibrium was found to follow the Clausius-Clapeyron relation in the range examined, from 250 to 270 K, with a Δ H sub of 50 kJ/mol in excellent agreement with the experimental value. The phase diagram of the mW model was constructed for the low pressure region around the triple point. The analysis of the crystallization dynamics during condensation and evaporation revealed that, for the basal face, both processes are highly activated, and in particular cubic ice is formed during condensation, producing stacking-disordered ice. The basal and primary prismatic surfaces of ice Ih were investigated at different temperatures and at their corresponding equilibrium vapor pressures. Our results show that the region known as QLL can be interpreted as the outermost layers of the solid where a partial melting takes place. Solid islands in the nanometer length scale are surrounded by interconnected liquid areas, generating a bidimensional nanophase segregation that spans throughout the entire width of the outermost layer even at 250 K. Two approaches were adopted to quantify the QLL and discussed in light of their ability to reflect this nanophase segregation phenomena. Our results in the μVT ensemble were compared with NPT and NVT simulations for two system sizes. No significant differences were found between the results as a consequence of model system size or of the working ensemble. Nevertheless, certain advantages of performing μVT simulations in order to reproduce the experimental situation are highlighted. On the one hand, the QLL thickness measured out of equilibrium might be affected because of crystallization being slower than condensation. On the other, preliminary simulations of AFM indentation experiments show that the tip can induce capillary condensation over the ice surface, enlarging the apparent QLL.

Photometric and Spectroscopic Observations of SN 2012dn, a Super-Chandra Candidate Type-Ia Supernova

NASA Astrophysics Data System (ADS)

Parrent, Jerod T.; Transient Factory, Palomar; Cumbres Observatory Global Telescope Network, Las

2013-01-01

Currently, there is no singular standard model picture of type-Ia supernovae (SNe Ia) with a parameter-space of predictions that overlap the observed, diverse array of SN Ia properties. The same can be said for the super-luminous versions of SNe Ia, those thought to originate from up to 2.4 solar mass progenitor systems. To make matters worse, we remain in the dark-ages of astronomy regarding the interpretation of their observed spectra. In short, line-blending due to resonant line-scattering alone prevents making clear the compositional makeup of the outermost ejected layers. Since simulations of violent merger and single degenerate scenarios are both able to roughly reproduce spectroscopic observations, the direct mapping of the ejecta via spectrum synthesis measurements is of high importance. For example, with the closest SN Ia to date, SN 2011fe, we were able to map (in velocity space) the composition of the outer layers of ejecta. We did this by evolving simple P-Cygni-blends of synthetic spectra over the course of the first month (post-explosion), with an average of 1.8 days between observations by which to compare. As a result, SN 2011fe gave a clearer picture of the compositional structure of a ''normal'' SN Ia. We now have another chance to put this measure of SN Ia diversity into practice with the discovery of a brighter than normal southern hemisphere object, SN 2012dn. Here we present g-, r-, and i-band photometric observations obtained at Faulkes Telescope South, as well as optical time-series spectra from Gemini-North, Gemini-South, SALT, and MMT facilities. With 19 spectroscopic observations spanning its first month, post-explosion, we are able to measure the relative velocities of the periodic table in the outermost layers of ejected material. This serves as a means for distinguishing the origin of SNe Ia and their various forms.

Apparatus for producing diamond-like carbon flakes

NASA Technical Reports Server (NTRS)

Banks, Bruce A. (Inventor)

1986-01-01

A vacuum arc from a spot at the face of a graphite cathode to a graphite anode produces a beam of carbon ions and atoms. A carbon coating from this beam is deposited on an ion beam sputtered target to produce diamond-like carbon flakes. A graphite tube encloses the cathode, and electrical isolation is provided by an insulating sleeve. The tube forces the vacuum arc spot to be confined to the surface on the outermost end of the cathode. Without the tube the arc spot will wander to the side of the cathode. This spot movement results in low rates of carbon deposition, and the properties of the deposited flakes are more graphite-like than diamond-like.

Effect of Elastic Strain Fluctuation on Atomic Layer Growth of Epitaxial Silicide in Si Nanowires by Point Contact Reactions.

PubMed

Chou, Yi-Chia; Tang, Wei; Chiou, Chien-Jyun; Chen, Kai; Minor, Andrew M; Tu, K N

2015-06-10

Effects of strain impact a range of applications involving mobility change in field-effect-transistors. We report the effect of strain fluctuation on epitaxial growth of NiSi2 in a Si nanowire via point contact and atomic layer reactions, and we discuss the thermodynamic, kinetic, and mechanical implications. The generation and relaxation of strain shown by in situ TEM is periodic and in synchronization with the atomic layer reaction. The Si lattice at the epitaxial interface is under tensile strain, which enables a high solubility of supersaturated interstitial Ni atoms for homogeneous nucleation of an epitaxial atomic layer of the disilicide phase. The tensile strain is reduced locally during the incubation period of nucleation by the dissolution of supersaturated Ni atoms in the Si lattice but the strained-Si state returns once the atomic layer epitaxial growth of NiSi2 occurs by consuming the supersaturated Ni.

Atomic-Layer-Deposited Transparent Electrodes for Silicon Heterojunction Solar Cells

DOE PAGES

Demaurex, Benedicte; Seif, Johannes P.; Smit, Sjoerd; ...

2014-11-01

We examine damage-free transparent-electrode deposition to fabricate high-efficiency amorphous silicon/crystalline silicon heterojunction solar cells. Such solar cells usually feature sputtered transparent electrodes, the deposition of which may damage the layers underneath. Using atomic layer deposition, we insert thin protective films between the amorphous silicon layers and sputtered contacts and investigate their effect on device operation. We find that a 20-nm-thick protective layer suffices to preserve, unchanged, the amorphous silicon layers beneath. Insertion of such protective atomic-layer-deposited layers yields slightly higher internal voltages at low carrier injection levels. However, we identify the presence of a silicon oxide layer, formed during processing,more » between the amorphous silicon and the atomic-layer-deposited transparent electrode that acts as a barrier, impeding hole and electron collection.« less

Electron Pair Repulsion Responsible for the Peculiar Edge Effects and Surface Chemistry of Black Phosphorus.

PubMed

Kong, Xiang-Peng; Shen, Xiaomei; Jang, Joonkyung; Gao, Xingfa

2018-03-01

The electronic and optical properties of black phosphorus (black-P) are significantly modulated by fabricating the edges of this two-dimensional material. Electron lone pairs (ELPs) are ubiquitous in black-P, but their role in creating the edge effects of black-P is poorly understood. Using first-principle calculations, we report ELPs of black-P experience severe Coulomb repulsion and play a central role in creating the edge effects of black-P. We discover the outermost P atoms of the zigzag edges of black-PQDs are free of the Coulomb repulsion, but the P atoms of the armchair edges do experience the Coulomb repulsion. The Coulomb repulsion serves as a new chemical driving force to make electron donor-acceptor bonds with chemical groups bearing vacant orbitals. Our results provide insights into the mechanism responsible for the peculiar edge effects of black-P and highlight the opportunity to use the ELPs of black-P for their damage-free surface functionalization.

Mitigating leaks in membranes

DOEpatents

Karnik, Rohit N.; Bose, Suman; Boutilier, Michael S.H.; Hadjiconstantinou, Nicolas G.; Jain, Tarun Kumar; O'Hern, Sean C.; Laoui, Tahar; Atieh, Muataz A.; Jang, Doojoon

2018-02-27

Two-dimensional material based filters, their method of manufacture, and their use are disclosed. In one embodiment, a membrane may include an active layer including a plurality of defects and a deposited material associated with the plurality of defects may reduce flow therethrough. Additionally, a majority of the active layer may be free from the material. In another embodiment, a membrane may include a porous substrate and an atomic layer deposited material disposed on a surface of the porous substrate. The atomic layer deposited material may be less hydrophilic than the porous substrate and an atomically thin active layer may be disposed on the atomic layer deposited material.

Influence of trace elements on dental enamel properties: A review.

PubMed

Qamar, Zeeshan; Haji Abdul Rahim, Zubaidah Binti; Chew, Hooi Pin; Fatima, Tayyaba

2017-01-01

Dental enamel, an avascular, irreparable, outermost and protective layer of the human clinical crown has a potential to withstand the physico-chemical effects and forces. These properties are being regulated by a unique association among elements occurring in the crystallites setup of human dental enamel. Calcium and phosphate are the major components (hydroxyapatite) in addition to some trace elements which have a profound effect on enamel. The current review was planned to determine the aptitude of various trace elements to substitute and their influence on human dental enamel in terms of physical and chemical properties.

Chemical shielding properties for BN, BP, AlN, and AlP nanocones: DFT studies

NASA Astrophysics Data System (ADS)

Mirzaei, Mahmoud; Yousefi, Mohammad; Meskinfam, Masoumeh

2012-06-01

The properties of boron nitride (BN), boron phosphide (BP), aluminum nitride (AlN), and aluminum phosphide (AlP) nanocones were investigated by density functional theory (DFT) calculations. The investigated structures were optimized and chemical shielding (CS) properties including isotropic and anisotropic CS parameters were calculated for the atoms of the optimized structures. The magnitudes of CS parameters were observed to be mainly dependent on the bond lengths of considered atoms. The results indicated that the atoms could be divided into atomic layers due to the similarities of their CS properties for the atoms of each layer. The trend means that the atoms of each layer detect almost similar electronic environments. Moreover, the atoms at the apex and mouth of nanocones exhibit different properties with respect to the other atomic layers.

Disorders of metal metabolism

PubMed Central

Ferreira, Carlos R.; Gahl, William A.

2017-01-01

Trace elements are chemical elements needed in minute amounts for normal physiology. Some of the physiologically relevant trace elements include iodine, copper, iron, manganese, zinc, selenium, cobalt and molybdenum. Of these, some are metals, and in particular, transition metals. The different electron shells of an atom carry different energy levels, with those closest to the nucleus being lowest in energy. The number of electrons in the outermost shell determines the reactivity of such an atom. The electron shells are divided in sub-shells, and in particular the third shell has s, p and d sub-shells. Transition metals are strictly defined as elements whose atom has an incomplete d sub-shell. This incomplete d sub-shell makes them prone to chemical reactions, particularly redox reactions. Transition metals of biologic importance include copper, iron, manganese, cobalt and molybdenum. Zinc is not a transition metal, since it has a complete d sub-shell. Selenium, on the other hand, is strictly speaking a nonmetal, although given its chemical properties between those of metals and nonmetals, it is sometimes considered a metalloid. In this review, we summarize the current knowledge on the inborn errors of metal and metalloid metabolism. PMID:29354481

Model potentials for main group elements Li through Rn

NASA Astrophysics Data System (ADS)

Sakai, Yoshiko; Miyoshi, Eisaku; Klobukowski, Mariusz; Huzinaga, Sigeru

1997-05-01

Model potential (MP) parameters and valence basis sets were systematically determined for the main group elements Li through Rn. For alkali and alkaline-earth metal atoms, the outermost core (n-1)p electrons were treated explicitly together with the ns valence electrons. For the remaining atoms, only the valence ns and np electrons were treated explicitly. The major relativistic effects at the level of Cowan and Griffin's quasi-relativistic Hartree-Fock method (QRHF) were incorporated in the MPs for all atoms heavier than Kr. The valence orbitals thus obtained have inner nodal structure. The reliability of the MP method was tested in calculations for X-, X, and X+ (X=Br, I, and At) at the SCF level and the results were compared with the corresponding values given by the numerical HF (or QRHF) calculations. Calculations that include electron correlation were done for X-, X, and X+ (X=Cl and Br) at the SDCI level and for As2 at the CASSCF and MRSDCI levels. These results were compared with those of all-electron (AE) calculations using the well-tempered basis sets. Close agreement between the MP and AE results was obtained at all levels of the treatment.

A laser syringe aimed at delivering drug into the outer layer of human skin

NASA Astrophysics Data System (ADS)

Yoh, Jack J.; Jang, Hun-jae; Park, Mi-ae; Han, Tae-hee; Hah, Jung-moo

2012-07-01

A desire to eliminate hypodermic needle in transdermal drug delivery may now be realized. Imaging of the skin after injection of fluorescent probe and biotin via the bio-ballistic technique revealed the epidermal and dermal layers which were stained well below 60 μm underneath the abdominal skin of the guinea-pig. An extensive network of cells are shown in the deeper layer of the stained dermis as the distributed fluorescein isothiocyanate (FITC) dose is administered by repeated injection via the laser-based microjet. Here, we show our method of laser-based microjet drug delivery is capable of breaching guinea-pig's skin tissue and then delivering controlled dose of drug to the targeted region between 10 to 400 μm underneath the outermost layer of the skin. While minimizing pain and tissue damage by reducing the injection volume to ˜100 nl per pulse and the microjet diameter of half the conventional syringe needle in 100 μm, the optimally controlled delivery of liquid drug by the irradiated laser pulse is shown possible.

Science and Emerging Technology of 2D Atomic Layered Materials and Devices

DTIC Science & Technology

2017-09-09

AFRL-AFOSR-JP-TR-2017-0067 Science & Emerging Technology of 2D Atomic Layered Materials and Devices Angel Rubio UNIVERSIDAD DEL PAIS VASCO - EUSKAL...Emerging Technology of 2D Atomic Layered Materials and Devices 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-15-1-0006 5c.  PROGRAM ELEMENT NUMBER...reporting documents for AOARD project 144088, “2D Materials and Devices Beyond Graphene Science & Emerging Technology of 2D Atomic Layered Materials and

Tear Film Dynamics: the roles of complex structure and rheology

NASA Astrophysics Data System (ADS)

Dey, Mohar; Feng, James; Vivek, Atul S.; Dixit, Harish N.; Richhariya, Ashutosh

2016-11-01

Ocular surface infections such as microbial and fungal keratitis are among leading causes of blindness in the world. A thorough understanding of the pre-corneal tear film dynamics is essential to comprehend the role of various tear layer components in the escalation of such ocular infections. The pre-corneal tear film comprises of three layers of complex fluids, viz. the innermost mucin layer, a hydrophilic protective cover over the sensitive corneal epithelium, the intermediate aqueous layer that forms the bulk of the tear film and is often embedded with large number of bio-polymers either in the form of soluble mucins or pathogens, and finally the outermost lipid layer that stabilizes the film by decreasing the air/tear film interfacial tension. We have developed a comprehensive mathematical model to describe such a film by incorporating the effects of the non-uniform mucin distribution along with the complex rheology of the aqueous layer with/without pathogens, Marangoni effects from the lipid layer and the slip effects at the base of the tear film. A detailed linear stability analysis and a fully non-linear solution determine the break up time (BUT) of such a tear film. We also probe the role of the various components of the pre-corneal tear film in the dynamics of rupture.

Partially Oxidized SnS2 Atomic Layers Achieving Efficient Visible-Light-Driven CO2 Reduction.

PubMed

Jiao, Xingchen; Li, Xiaodong; Jin, Xiuyu; Sun, Yongfu; Xu, Jiaqi; Liang, Liang; Ju, Huanxin; Zhu, Junfa; Pan, Yang; Yan, Wensheng; Lin, Yue; Xie, Yi

2017-12-13

Unraveling the role of surface oxide on affecting its native metal disulfide's CO 2 photoreduction remains a grand challenge. Herein, we initially construct metal disulfide atomic layers and hence deliberately create oxidized domains on their surfaces. As an example, SnS 2 atomic layers with different oxidation degrees are successfully synthesized. In situ Fourier transform infrared spectroscopy spectra disclose the COOH* radical is the main intermediate, whereas density-functional-theory calculations reveal the COOH* formation is the rate-limiting step. The locally oxidized domains could serve as the highly catalytically active sites, which not only benefit for charge-carrier separation kinetics, verified by surface photovoltage spectra, but also result in electron localization on Sn atoms near the O atoms, thus lowering the activation energy barrier through stabilizing the COOH* intermediates. As a result, the mildly oxidized SnS 2 atomic layers exhibit the carbon monoxide formation rate of 12.28 μmol g -1 h -1 , roughly 2.3 and 2.6 times higher than those of the poorly oxidized SnS 2 atomic layers and the SnS 2 atomic layers under visible-light illumination. This work uncovers atomic-level insights into the correlation between oxidized sulfides and CO 2 reduction property, paving a new way for obtaining high-efficiency CO 2 photoreduction performances.

Surface functionalization of WS2 fullerene-like nanoparticles.

PubMed

Shahar, Chen; Zbaida, David; Rapoport, Lev; Cohen, Hagai; Bendikov, Tatyana; Tannous, Johny; Dassenoy, Fabrice; Tenne, Reshef

2010-03-16

WS(2) belongs to a family of layered metal dichalcogenide compounds that are known to form cylindrical (inorganic nanotubes-INT) and polyhedral nanostructures--onion or nested fullerene-like (IF) particles. The outermost layers of these IF nanoparticles can be peeled under shear stress, thus IF nanoparticles have been studied for their use as solid lubricants. However, the IF nanoparticles tend to agglomerate, presumably because of surface structural defects induced by elastic strain and curvature, a fact that has a deleterious effect on their tribological properties. In the present work, chemical modification of the IF-WS(2) surface with alkyl-silane molecules is reported. The surface-modified IF nanoparticles display improved dispersion in oil-based suspensions. The alkyl-silane coating reduces the IF-WS(2) nanoparticles' tendency to agglomerate and consequently improves the long-term tribological behavior of oil formulated with the IF additive.

Ultrasound-induced cavitation damage to external epithelia of fish skin.

PubMed

Frenkel, V; Kimmel, E; Iger, Y

1999-10-01

Transmission electron microscopy was used to show the effects of therapeutic ultrasound (< or = 1.0 W/cm2, 1 MHz) on the external epithelia of fish skin. Exposures of up to 90 s produced damage to 5 to 6 of the outermost layers. Negligible temperature elevations and lack of damage observed when using degassed water indicated that the effects were due to cavitation. The minimal intensity was determined for inducing cellular damage, where the extent and depth of damage to the tissues was correlated to the exposure duration. The results may be interpreted as a damage front, advancing slowly from the outer cells inward, presumably in association with the slow replacement of the perforated cell contents with the surrounding water. This study illustrates that a controlled level of microdamage may be induced to the outer layers of the tissues.

Charge creation and nucleation of the longitudinal plasma wave in coupled Josephson junctions

NASA Astrophysics Data System (ADS)

Shukrinov, Yu. M.; Hamdipour, M.

2010-11-01

We study the phase dynamics in coupled Josephson junctions described by a system of nonlinear differential equations. Results of detailed numerical simulations of charge creation in the superconducting layers and the longitudinal plasma wave (LPW) nucleation are presented. We demonstrate the different time stages in the development of the LPW and present the results of FFT analysis at different values of bias current. The correspondence between the breakpoint position on the outermost branch of current voltage characteristics (CVC) and the growing region in time dependence of the electric charge in the superconducting layer is established. The effects of noise in the bias current and the external microwave radiation on the charge dynamics of the coupled Josephson junctions are found. These effects introduce a way to regulate the process of LPW nucleation in the stack of IJJ.

Characterization on White Etching Layer Formed During Ceramic Milling of Inconel 718

NASA Astrophysics Data System (ADS)

Kruk, A.; Wusatowska-Sarnek, A. M.; Ziętara, M.; Jemielniak, K.; Siemiątkowski, Z.; Czyrska-Filemonowicz, A.

2018-03-01

A comprehensive characterization of the near surface formed during the interrupted high-speed dry ceramic milling of IN718 was performed using light imaging, SEM/EDX, TEM and nano-hardness methods. It was found out that even an initial cut by a fresh tool creates a sub-surface alteration roughly 20 µm deep. The depth of altered sub-surface progressively changed to a roughly 40 µm when the tool reached an approximately half of its life, and almost 60 µm at the tool's end of the life. In the last two cases, the visible WEL (utilizing a light microscope) of the thickness roughly 6 and 15 µm was created, respectively. The outermost layer of the deformed subsurface was found to be for all three cases approximately 1.5 µm thick and composed of dynamically recrystallized γ phase grains with the average diameter of approximately 150 nm. This layer was free of δ phase and γ' or γ″ precipitates. It was followed by a plastically deformed zone.

Enhancing the Oxidation Performance of Wrought Ni-Base Superalloy by Minor Additions of Active Elements

NASA Astrophysics Data System (ADS)

Tawancy, H. M.

2016-12-01

We show that the oxidation performance of Cr2O3-forming superalloy based upon the Ni-Cr-W system is significantly improved by the presence of minor concentrations of La, Si and Mn, which outweigh the detrimental effect of high W concentration in the alloy. Although Cr2O3 is known to transform into volatile CrO3 at temperatures ≥950 °C, the respective protection is extended to temperatures reaching 1150 °C, which has also been correlated with the beneficial effects of La, Si and Mn. During high-temperature oxidation, an inner protective La- and Si-modified layer of α-Cr2O3 in contact with the superalloy substrate is developed and shielded by an outermost layer of MnCr2O4. The distribution of La and Si in the inner oxide layer has been characterized down to the scale of transmission electron microscopy, and the possible mechanisms underlying their beneficial effects are elucidated.

Theoretical study for heterojunction surface of NEA GaN photocathode dispensed with Cs activation

NASA Astrophysics Data System (ADS)

Xia, Sihao; Liu, Lei; Wang, Honggang; Wang, Meishan; Kong, Yike

2016-09-01

For the disadvantages of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, new-type NEA GaN photocathodes with heterojunction surface dispensed with Cs activation are investigated based on first-principle study with density functional theory. Through the growth of an ultrathin n-type GaN cap layer on p-type GaN emission layer, a p-n heterojunction is formed on the surface. According to the calculation results, it is found that Si atoms tend to replace Ga atoms to result in an n-type doped cap layer which contributes to the decreasing of work function. After the growth of n-type GaN cap layer, the atom structure near the p-type emission layer is changed while that away from the surface has no obvious variations. By analyzing the E-Mulliken charge distribution of emission surface with and without cap layer, it is found that the positive charge of Ga and Mg atoms in the emission layer decrease caused by the cap layer, while the negative charge of N atom increases. The conduction band moves downwards after the growth of cap layer. Si atom produces donor levels around the valence band maximum. The absorption coefficient of GaN emission layer decreases and the reflectivity increases caused by n-type GaN cap layer.

Compositional modulated atomic layer stacking and uniaxial magnetocrystalline anisotropy of CoPt alloy sputtered films with close-packed plane orientation

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

Saito, Shin, E-mail: ssaito@ecei.tohoku.ac.jp; Nozawa, Naoki; Hinata, Shintaro

An atomic layer stacking structure in hexagonal close packed (hcp) Co{sub 100−x}Pt{sub x} alloy films with c-plane sheet texture was directly observed by a high-angle annular dark-field imaging scanning transmission electron microscopy. The analysis of sequential and/or compositional atomic layer stacking structure and uniaxial magnetocrystalline anisotropy (K{sub u} = K{sub u1} + K{sub u2}) revealed that (1) integrated intensity of the superlattice diffraction takes the maximum at x = 20 at. % and shows broadening feature against x for the film fabricated under the substrate temperature (T{sub sub}) of 400 °C. (2) Compositional separation structure in atomic layers is formed for the films fabricated under T{sub sub} = 400 °C.more » A sequential alternative stacking of atomic layers with different compositions is hardly formed in the film with x = 50 at. %, whereas easily formed in the film with x = 20 at. %. This peculiar atomic layer stacking structure consists of in-plane-disordered Pt-rich and Pt-poor layers, which is completely different from the so-called atomic site ordered structure. (3) A face centered cubic atomic layer stacking as faults appeared in the host hcp atomic layer stacking exists in accompanies with irregularities for the periodicity of the compositional modulation atomic layers. (4) K{sub u1} takes the maximum of 1.4 × 10{sup 7 }erg/cm{sup 3} at around x = 20 at. %, whereas K{sub u2} takes the maximum of 0.7 × 10{sup 7 }erg/cm{sup 3} at around x = 40 at. %, which results in the maximum of 1.8 × 10{sup 7 }erg/cm{sup 3} of K{sub u} at x = 30 at. % and a shoulder in compositional dependence of K{sub u} in the range of x = 30–60 at. %. Not only compositional separation of atomic layers but also sequential alternative stacking of different compositional layers is quite important to improve essential uniaxial magnetocrystalline anisotropy.« less

Boundary-field-driven control of discontinuous phase transitions on hyperbolic lattices

NASA Astrophysics Data System (ADS)

Lee, Yoju; Verstraete, Frank; Gendiar, Andrej

2016-08-01

The multistate Potts models on two-dimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the so-called bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the second-order phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the first-order (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field.

Synthesis and structure of cesium complexes of nitrilotris(methylenephosphonic) acid [Cs-μ6-NH(CH2PO3)3H4] and [Cs2-μ10-NH(CH2PO3H)3] · H2O

NASA Astrophysics Data System (ADS)

Somov, N. V.; Chausov, F. F.; Zakirov, R. M.

2017-07-01

3D coordination polymers cesium nitrilotris(methylenephosphonate) and dicesium nitrilotris( methylenephosphonate) are synthesized and their crystal structure is determined. In the crystal of [Cs-μ6-NH(CH2PO3)3H4] (space group P, Z = 2), cesium atoms occupy two crystallographically inequivalent positions with c.n. = 10 and c.n. = 14. The phosphonate ligand plays the bridging function; its denticity is nine. The crystal packing consists of alternating layers of Cs atoms in different environments with layers of ligand molecules between them. A ligand is bound to three Cs atoms of one layer and three Cs atoms of another layer. In the crystal of [Cs2-μ10-NH(CH2PO3H)3] · H2O (space group P, Z = 2), the complex has a dimeric structure: the bridging phosphonate ligand coordinates Cs to form a three-dimensional Cs4O6 cluster. The denticity of the ligand is equal to nine; the coordination numbers of cesium atoms are seven and nine. Two-dimensional corrugated layers of Cs4O6 clusters lie in the (002) plane, and layers of ligand molecules are located between them. Each ligand molecule coordinates eight Cs atoms of one layer and two Cs atoms of the neighboring layer.

A complete study of the precision of the concentric MacLaurin spheroid method to calculate Jupiter's gravitational moments

NASA Astrophysics Data System (ADS)

Debras, F.; Chabrier, G.

2018-01-01

A few years ago, Hubbard (2012, ApJ, 756, L15; 2013, ApJ, 768, 43) presented an elegant, non-perturbative method, called concentric MacLaurin spheroid (CMS), to calculate with very high accuracy the gravitational moments of a rotating fluid body following a barotropic pressure-density relationship. Having such an accurate method is of great importance for taking full advantage of the Juno mission, and its extremely precise determination of Jupiter gravitational moments, to better constrain the internal structure of the planet. Recently, several authors have applied this method to the Juno mission with 512 spheroids linearly spaced in altitude. We demonstrate in this paper that such calculations lead to errors larger than Juno's error bars, invalidating the aforederived Jupiter models at the level required by Juno's precision. We show that, in order to fulfill Juno's observational constraints, at least 1500 spheroids must be used with a cubic, square or exponential repartition, the most reliable solutions. When using a realistic equation of state instead of a polytrope, we highlight the necessity to properly describe the outermost layers to derive an accurate boundary condition, excluding in particular a zero pressure outer condition. Providing all these constraints are fulfilled, the CMS method can indeed be used to derive Jupiter models within Juno's present observational constraints. However, we show that the treatment of the outermost layers leads to irreducible errors in the calculation of the gravitational moments and thus on the inferred physical quantities for the planet. We have quantified these errors and evaluated the maximum precision that can be reached with the CMS method in the present and future exploitation of Juno's data.

Environment modelling in near Earth space: Preliminary LDEF results

NASA Technical Reports Server (NTRS)

Coombs, C. R.; Atkinson, D. R.; Wagner, J. D.; Crowell, L. B.; Allbrooks, M.; Watts, A. J.

1992-01-01

Hypervelocity impacts by space debris cause not only local cratering or penetrations, but also cause large areas of damage in coated, painted or laminated surfaces. Features examined in these analyses display interesting morphological characteristics, commonly exhibiting a concentric ringed appearance. Virtually all features greater than 0.2 mm in diameter possess a spall zone in which all of the paint was removed from the aluminum surface. These spall zones vary in size from approximately 2 - 5 crater diameters. The actual craters in the aluminum substrate vary from central pits without raised rims, to morphologies more typical of craters formed in aluminum under hypervelocity laboratory conditions for the larger features. Most features also possess what is referred to as a 'shock zone' as well. These zones vary in size from approximately 1 - 20 crater diameters. In most cases, only the outer-most layer of paint was affected by this impact related phenomenon. Several impacts possess ridge-like structures encircling the area in which this outer-most paint layer was removed. In many ways, such features resemble the lunar impact basins, but on an extremely reduced scale. Overall, there were no noticeable penetrations, bulges or spallation features on the backside of the tray. On Row 12, approximately 85 degrees from the leading edge (RAM direction), there was approximately one impact per 15 cm(exp 2). On the trailing edge, there was approximately one impact per 72 cm(exp 2). Currently, craters on four aluminum experiment trays from Bay E09, directly on the leading edge are being measured and analyzed. Preliminary results have produced more than 2200 craters on approximately 1500 cm(exp 2) - or approximately 1 impact per 0.7 cm(exp 2).

Conserved S-Layer-Associated Proteins Revealed by Exoproteomic Survey of S-Layer-Forming Lactobacilli

PubMed Central

Johnson, Brant R.; Hymes, Jeffrey; Sanozky-Dawes, Rosemary; Henriksen, Emily DeCrescenzo

2015-01-01

The Lactobacillus acidophilus homology group comprises Gram-positive species that include L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii. While these bacteria are closely related, they have varied ecological lifestyles as dairy and food fermenters, allochthonous probiotics, or autochthonous commensals of the host gastrointestinal tract. Bacterial cell surface components play a critical role in the molecular dialogue between bacteria and interaction signaling with the intestinal mucosa. Notably, the L. acidophilus complex is distinguished in two clades by the presence or absence of S-layers, which are semiporous crystalline arrays of self-assembling proteinaceous subunits found as the outermost layer of the bacterial cell wall. In this study, S-layer-associated proteins (SLAPs) in the exoproteomes of various S-layer-forming Lactobacillus species were proteomically identified, genomically compared, and transcriptionally analyzed. Four gene regions encoding six putative SLAPs were conserved in the S-layer-forming Lactobacillus species but not identified in the extracts of the closely related progenitor, L. delbrueckii subsp. bulgaricus, which does not produce an S-layer. Therefore, the presence or absence of an S-layer has a clear impact on the exoproteomic composition of Lactobacillus species. This proteomic complexity and differences in the cell surface properties between S-layer- and non-S-layer-forming lactobacilli reveal the potential for SLAPs to mediate intimate probiotic interactions and signaling with the host intestinal mucosa. PMID:26475115

Focal high cell density generates a gradient of patterns in self-organizing vascular mesenchymal cells.

PubMed

Cheng, Henry; Reddy, Aneela; Sage, Andrew; Lu, Jinxiu; Garfinkel, Alan; Tintut, Yin; Demer, Linda L

2012-01-01

In embryogenesis, structural patterns, such as vascular branching, may form via a reaction-diffusion mechanism in which activator and inhibitor morphogens guide cells into periodic aggregates. We previously found that vascular mesenchymal cells (VMCs) spontaneously aggregate into nodular structures and that morphogen pairs regulate the aggregation into patterns of spots and stripes. To test the effect of a focal change in activator morphogen on VMC pattern formation, we created a focal zone of high cell density by plating a second VMC layer within a cloning ring over a confluent monolayer. After 24 h, the ring was removed and pattern formation monitored by phase-contrast microscopy. At days 2-8, the patterns progressed from uniform distributions to swirl, labyrinthine and spot patterns. Within the focal high-density zone (HDZ) and a narrow halo zone, cells aggregated into spot patterns, whilst in the outermost zone of the plate, cells formed a labyrinthine pattern. The area occupied by aggregates was significantly greater in the outermost zone than in the HDZ or halo. The rate of pattern progression within the HDZ increased as a function of its plating density. Thus, focal differences in cell density may drive pattern formation gradients in tissue architecture, such as vascular branching. Copyright © 2012 S. Karger AG, Basel.

Evidence of a molecular boundary lubricant at snakeskin surfaces

PubMed Central

Spinner, Marlene; Jaye, Cherno; Fischer, Daniel A.; Gorb, Stanislav N.; Weidner, Tobias

2015-01-01

During slithering locomotion the ventral scales at a snake's belly are in direct mechanical interaction with the environment, while the dorsal scales provide optical camouflage and thermoregulation. Recent work has demonstrated that compared to dorsal scales, ventral scales provide improved lubrication and wear protection. While biomechanic adaption of snake motion is of growing interest in the fields of material science and robotics, the mechanism for how ventral scales influence the friction between the snake and substrate, at the molecular level, is unknown. In this study, we characterize the outermost surface of snake scales using sum frequency generation (SFG) spectra and near-edge X-ray absorption fine structure (NEXAFS) images collected from recently shed California kingsnake (Lampropeltis californiae) epidermis. SFG's nonlinear optical selection rules provide information about the outermost surface of materials; NEXAFS takes advantage of the shallow escape depth of the electrons to probe the molecular structure of surfaces. Our analysis of the data revealed the existence of a previously unknown lipid coating on both the ventral and dorsal scales. Additionally, the molecular structure of this lipid coating closely aligns to the biological function: lipids on ventral scales form a highly ordered layer which provides both lubrication and wear protection at the snake's ventral surface. PMID:26655468

Evidence of a molecular boundary lubricant at snakeskin surfaces.

PubMed

Baio, Joe E; Spinner, Marlene; Jaye, Cherno; Fischer, Daniel A; Gorb, Stanislav N; Weidner, Tobias

2015-12-06

During slithering locomotion the ventral scales at a snake's belly are in direct mechanical interaction with the environment, while the dorsal scales provide optical camouflage and thermoregulation. Recent work has demonstrated that compared to dorsal scales, ventral scales provide improved lubrication and wear protection. While biomechanic adaption of snake motion is of growing interest in the fields of material science and robotics, the mechanism for how ventral scales influence the friction between the snake and substrate, at the molecular level, is unknown. In this study, we characterize the outermost surface of snake scales using sum frequency generation (SFG) spectra and near-edge X-ray absorption fine structure (NEXAFS) images collected from recently shed California kingsnake (Lampropeltis californiae) epidermis. SFG's nonlinear optical selection rules provide information about the outermost surface of materials; NEXAFS takes advantage of the shallow escape depth of the electrons to probe the molecular structure of surfaces. Our analysis of the data revealed the existence of a previously unknown lipid coating on both the ventral and dorsal scales. Additionally, the molecular structure of this lipid coating closely aligns to the biological function: lipids on ventral scales form a highly ordered layer which provides both lubrication and wear protection at the snake's ventral surface. © 2015 The Author(s).

A review of atomic clock technology, the performance capability of present spaceborne and terrestrial atomic clocks, and a look toward the future

NASA Technical Reports Server (NTRS)

Vessot, Robert F. C.

1989-01-01

Clocks have played a strong role in the development of general relativity. The concept of the proper clock is presently best realized by atomic clocks, whose development as precision instruments has evolved very rapidly in the last decades. To put a historical prospective on this progress since the year AD 1000, the time stability of various clocks expressed in terms of seconds of time error over one day of operation is shown. This stability of operation must not be confused with accuracy. Stability refers to the constancy of a clock operation as compared to that of some other clocks that serve as time references. Accuracy, on the other hand, is the ability to reproduce a previously defined frequency. The issues are outlined that must be considered when accuracy and stability of clocks and oscillators are studied. In general, the most widely used resonances result from the hyperfine interaction of the nuclear magnetic dipole moment and that of the outermost electron, which is characteristic of hydrogen and the alkali atoms. During the past decade hyperfine resonances of ions have also been used. The principal reason for both the accuracy and the stability of atomic clocks is the ability of obtaining very narrow hyperfine transition resonances by isolating the atom in some way so that only the applied stimulating microwave magnetic field is a significant source of perturbation. It is also important to make resonance transitions among hyperfine magnetic sublevels where separation is independent, at least to first order, of the magnetic field. In the case of ions stored in traps operating at high magnetic fields, one selects the trapping field to be consistent with a field-independent transition of the trapped atoms.

Multidimensional indexing structure for use with linear optimization queries

NASA Technical Reports Server (NTRS)

Bergman, Lawrence David (Inventor); Castelli, Vittorio (Inventor); Chang, Yuan-Chi (Inventor); Li, Chung-Sheng (Inventor); Smith, John Richard (Inventor)

2002-01-01

Linear optimization queries, which usually arise in various decision support and resource planning applications, are queries that retrieve top N data records (where N is an integer greater than zero) which satisfy a specific optimization criterion. The optimization criterion is to either maximize or minimize a linear equation. The coefficients of the linear equation are given at query time. Methods and apparatus are disclosed for constructing, maintaining and utilizing a multidimensional indexing structure of database records to improve the execution speed of linear optimization queries. Database records with numerical attributes are organized into a number of layers and each layer represents a geometric structure called convex hull. Such linear optimization queries are processed by searching from the outer-most layer of this multi-layer indexing structure inwards. At least one record per layer will satisfy the query criterion and the number of layers needed to be searched depends on the spatial distribution of records, the query-issued linear coefficients, and N, the number of records to be returned. When N is small compared to the total size of the database, answering the query typically requires searching only a small fraction of all relevant records, resulting in a tremendous speedup as compared to linearly scanning the entire dataset.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing.

PubMed

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-03

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing

PubMed Central

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-01

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future. PMID:28045075

SELMA mission: How do airless bodies interact with space environment? The Moon as an accessible laboratory

NASA Astrophysics Data System (ADS)

Futaana, Yoshifumi; Barabash, Stas; Wieser, Martin; Wurz, Peter; Hurley, Dana; Horányi, Mihaly; Mall, Urs; Andre, Nicolas; Ivchenko, Nickolay; Oberst, Jürgen; Retherford, Kurt; Coates, Andrew; Masters, Adam; Wahlund, Jan-Erik; Kallio, Esa; SELMA Proposal Team

2018-07-01

The Moon is an archetypal atmosphere-less celestial body in the Solar System. For such bodies, the environments are characterized by complex interaction among the space plasma, tenuous neutral gas, dust and the outermost layer of the surface. Here we propose the SELMA mission (Surface, Environment, and Lunar Magnetic Anomalies) to study how airless bodies interact with space environment. SELMA uses a unique combination of remote sensing via ultraviolet and infrared wavelengths, and energetic neutral atom imaging, as well as in situ measurements of exospheric gas, plasma, and dust at the Moon. After observations in a lunar orbit for one year, SELMA will conduct an impact experiment to investigate volatile content in the soil of the permanently shadowed area of the Shackleton crater. SELMA also carries an impact probe to sound the Reiner-Gamma mini-magnetosphere and its interaction with the lunar regolith from the SELMA orbit down to the surface. SELMA was proposed to the European Space Agency as a medium-class mission (M5) in October 2016. Research on the SELMA scientific themes is of importance for fundamental planetary sciences and for our general understanding of how the Solar System works. In addition, SELMA outcomes will contribute to future lunar explorations through qualitative characterization of the lunar environment and, in particular, investigation of the presence of water in the lunar soil, as a valuable resource to harvest from the lunar regolith.

Tracking solvents in the skin through atomically resolved measurements of molecular mobility in intact stratum corneum

PubMed Central

Topgaard, Daniel; Sparr, Emma

2017-01-01

Solvents are commonly used in pharmaceutical and cosmetic formulations and sanitary products and cleansers. The uptake of solvent into the skin may change the molecular organization of skin lipids and proteins, which may in turn alter the protective skin barrier function. We herein examine the molecular effects of 10 different solvents on the outermost layer of skin, the stratum corneum (SC), using polarization transfer solid-state NMR on natural abundance 13C in intact SC. With this approach it is possible to characterize the molecular dynamics of solvent molecules when present inside intact SC and to simultaneously monitor the effects caused by the added solvent on SC lipids and protein components. All solvents investigated cause an increased fluidity of SC lipids, with the most prominent effects shown for the apolar hydrocarbon solvents and 2-propanol. However, no solvent other than water shows the ability to fluidize amino acids in the keratin filaments. The solvent molecules themselves show reduced molecular mobility when incorporated in the SC matrix. Changes in the molecular properties of the SC, and in particular alternation in the balance between solid and fluid SC components, may have significant influences on the macroscopic SC barrier properties as well as mechanical properties of the skin. Deepened understanding of molecular effects of foreign compounds in SC fluidity can therefore have strong impact on the development of skin products in pharmaceutical, cosmetic, and sanitary applications. PMID:28028209

Characterization of poly(Sodium Styrene Sulfonate) Thin Films Grafted from Functionalized Titanium Surfaces

PubMed Central

Zorn, Gilad; Baio, Joe E.; Weidner, Tobias; Migonney, Veronique; Castner, David G.

2011-01-01

Biointegration of titanium implants in the body is controlled by their surface properties. Improving surface properties by coating with a bioactive polymer is a promising approach to improve the biological performance of titanium implants. To optimize the grafting processes, it is important to fully understand the composition and structure of the modified surfaces. The main focus of this study is to provide a detailed, multi-technique characterization of a bioactive poly(sodium styrene sulfonate) (pNaSS) thin film grafted from titanium surfaces via a two-step procedure. Thin titanium films (~50 nm thick with an average surface roughness of 0.9±0.2nm) prepared by evaporation onto silicon wafers were used as smooth model substrates. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed that the titanium film was covered with a TiO2 layer that was at least 10nm thick and contained hydroxyl groups present at the outermost surface. These hydroxyl groups were first modified with a 3-methacryloxypropyltrimethoxysilane (MPS) cross linker. XPS and ToF-SIMS showed that a monolayer of the MPS molecules were successfully attached onto the titanium surfaces. The pNaSS film was grafted from the MPS modified titanium through atom transfer radical polymerization. Again, XPS and ToF-SIMS were used to verify that the pNaSS molecules were successfully grafted onto the modified surfaces. Atomic force microscopy analysis showed that the film was smooth and uniformly covered the surface. Fourier transform infrared spectroscopy indicated an ordered array of grafted NaSS molecules were present on the titanium surfaces. Sum frequency generation vibration spectroscopy and near edge X-ray absorption fine structure spectroscopy illustrated that the NaSS molecules were grafted onto the titanium surface with a substantial degree of orientational order in the styrene rings. PMID:21892821

Patterned growth of p-type MoS 2 atomic layers using sol-gel as precursor

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

Zheng, Wei; Lin, Junhao; Feng, Wei

2D layered MoS 2 has drawn intense attention for its applications in flexible electronic, optoelectronic, and spintronic devices. Most of the MoS 2 atomic layers grown by conventional chemical vapor deposition techniques are n-type due to the abundant sulfur vacancies. Facile production of MoS 2 atomic layers with p-type behavior, however, remains challenging. Here, a novel one-step growth has been developed to attain p-type MoS 2 layers in large scale by using Mo-containing sol–gel, including 1% tungsten (W). Atomic-resolution electron microscopy characterization reveals that small tungsten oxide clusters are commonly present on the as-grown MoS 2 film due to themore » incomplete reduction of W precursor at the reaction temperature. These omnipresent small tungsten oxide clusters contribute to the p-type behavior, as verified by density functional theory calculations, while preserving the crystallinity of the MoS 2 atomic layers. The Mo containing sol–gel precursor is compatible with the soft-lithography techniques, which enables patterned growth of p-type MoS 2 atomic layers into regular arrays with different shapes, holding great promise for highly integrated device applications. Lastly, an atomically thin p–n junction is fabricated by the as-prepared MoS 2, which shows strong rectifying behavior.« less

Patterned growth of p-type MoS 2 atomic layers using sol-gel as precursor

DOE PAGES

Zheng, Wei; Lin, Junhao; Feng, Wei; ...

2016-07-19

2D layered MoS 2 has drawn intense attention for its applications in flexible electronic, optoelectronic, and spintronic devices. Most of the MoS 2 atomic layers grown by conventional chemical vapor deposition techniques are n-type due to the abundant sulfur vacancies. Facile production of MoS 2 atomic layers with p-type behavior, however, remains challenging. Here, a novel one-step growth has been developed to attain p-type MoS 2 layers in large scale by using Mo-containing sol–gel, including 1% tungsten (W). Atomic-resolution electron microscopy characterization reveals that small tungsten oxide clusters are commonly present on the as-grown MoS 2 film due to themore » incomplete reduction of W precursor at the reaction temperature. These omnipresent small tungsten oxide clusters contribute to the p-type behavior, as verified by density functional theory calculations, while preserving the crystallinity of the MoS 2 atomic layers. The Mo containing sol–gel precursor is compatible with the soft-lithography techniques, which enables patterned growth of p-type MoS 2 atomic layers into regular arrays with different shapes, holding great promise for highly integrated device applications. Lastly, an atomically thin p–n junction is fabricated by the as-prepared MoS 2, which shows strong rectifying behavior.« less

Gravitational effects on planetary neutron flux spectra

NASA Astrophysics Data System (ADS)

Feldman, W. C.; Drake, D. M.; O'dell, R. D.; Brinkley, F. W.; Anderson, R. C.

1989-01-01

The effects of gravity on the planetary neutron flux spectra for planet Mars, and the lifetime of the neutron, were investigated using a modified one-dimensional diffusion accelerated neutral-particle transport code, coupled with a multigroup cross-section library tailored specifically for Mars. The results showed the presence of a qualitatively new feature in planetary neutron leakage spectra in the form of a component of returning neutrons with kinetic energies less than the gravitational binding energy (0.132 eV for Mars). The net effect is an enhancement in flux at the lowest energies that is largest at and above the outermost layer of planetary matter.

Effects of various vehicles on skin hydration in vivo.

PubMed

Wiedersberg, S; Leopold, C S; Guy, R H

2009-01-01

The stratum corneum, the outermost layer of the skin, regulates the passive loss of water to the environment. Furthermore, it is well accepted that drug penetration is influenced by skin hydration, which may be manipulated by the application of moisturizing or oleaginous vehicles. Measurements of transepidermal water loss (TEWL), and of skin hydration using a corneometer, were used to assess the effect of different vehicles on stratum corneum barrier function in vivo in human volunteers. A microemulsion significantly increased skin hydration relative to a reference vehicle based on medium chain triglycerides; in contrast, Transcutol(R) lowered skin hydration. TEWL measurements confirmed these observations. Copyright 2009 S. Karger AG, Basel.

Integrated carbon fiber electrodes within hollow polymer microneedles for transdermal electrochemical sensing

PubMed Central

Miller, Philip R.; Gittard, Shaun D.; Edwards, Thayne L.; Lopez, DeAnna M.; Xiao, Xiaoyin; Wheeler, David R.; Monteiro-Riviere, Nancy A.; Brozik, Susan M.; Polsky, Ronen; Narayan, Roger J.

2011-01-01

In this study, carbon fiber electrodes were incorporated within a hollow microneedle array, which was fabricated using a digital micromirror device-based stereolithography instrument. Cell proliferation on the acrylate-based polymer used in microneedle fabrication was examined with human dermal fibroblasts and neonatal human epidermal keratinocytes. Studies involving full-thickness cadaveric porcine skin and trypan blue dye demonstrated that the hollow microneedles remained intact after puncturing the outermost layer of cadaveric porcine skin. The carbon fibers underwent chemical modification in order to enable detection of hydrogen peroxide and ascorbic acid; electrochemical measurements were demonstrated using integrated electrode-hollow microneedle devices. PMID:21522504

Fourier transform Raman spectroscopic studies of human and animal skins

NASA Astrophysics Data System (ADS)

Barry, Brian W.; Edwards, Howell G.; Williams, Adrian C.

1994-01-01

The stratum corneum is the outermost layer of the skin and provides the principal barrier for the ingress of chemicals and environmental toxins into human and animal tissues. However, human skin has several advantages for the administration of therapeutic agents (transdermal drug delivery), but problems occur with the supply, storage, and biohazardous nature of human tissue. Hence, alternative animal tissues have been prepared to model drug diffusion across human skin but the molecular basis for comparison is lacking. Here, FT-Raman spectra of mammalian (human and pig) and reptilian (snake) skins have been obtained and the structural dissimilarities are correlated with drug diffusion studies across the tissues.

Graphite based Schottky diodes formed semiconducting substrates

NASA Astrophysics Data System (ADS)

Schumann, Todd; Tongay, Sefaattin; Hebard, Arthur

2010-03-01

We demonstrate the formation of semimetal graphite/semiconductor Schottky barriers where the semiconductor is either silicon (Si), gallium arsenide (GaAs) or 4H-silicon carbide (4H-SiC). The fabrication can be as easy as allowing a dab of graphite paint to air dry on any one of the investigated semiconductors. Near room temperature, the forward-bias diode characteristics are well described by thermionic emission, and the extracted barrier heights, which are confirmed by capacitance voltage measurements, roughly follow the Schottky-Mott relation. Since the outermost layer of the graphite electrode is a single graphene sheet, we expect that graphene/semiconductor barriers will manifest similar behavior.

Synthesis of Pd₃Co₁@Pt/C core-shell catalysts for methanol-tolerant cathodes of direct methanol fuel cells.

PubMed

Aricò, Antonino S; Stassi, Alessandro; D'Urso, Claudia; Sebastián, David; Baglio, Vincenzo

2014-08-18

A composite Pd-based electrocatalyst consisting of a surface layer of Pt (5 wt.%) supported on a core Pd3Co1 alloy (95 wt.%) and dispersed as nanoparticles on a carbon black support (50 wt.% metal content) was prepared by using a sulphite-complex route. The structure, composition, morphology, and surface properties of the catalyst were investigated by XRD, XRF, TEM, XPS and low-energy ion scattering spectroscopy (LE-ISS). The catalyst showed an enrichment of Pt on the surface and a smaller content of Co in the outermost layers. These characteristics allow a decrease the Pt content in direct methanol fuel cell cathode electrodes (from 1 to 0.06 mg cm(-2)) without significant decay in performance, due also to a better tolerance to methanol permeated through the polymer electrolyte membrane. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Triangular lattice atomic layer of Sn(1 × 1) at graphene/SiC(0001) interface

NASA Astrophysics Data System (ADS)

Hayashi, Shingo; Visikovskiy, Anton; Kajiwara, Takashi; Iimori, Takushi; Shirasawa, Tetsuroh; Nakastuji, Kan; Miyamachi, Toshio; Nakashima, Shuhei; Yaji, Koichiro; Mase, Kazuhiko; Komori, Fumio; Tanaka, Satoru

2018-01-01

Sn atomic layers attract considerable interest owing to their spin-related physical properties caused by their strong spin-orbit interactions. We performed Sn intercalation into the graphene/SiC(0001) interface and found a new type of Sn atomic layer. Sn atoms occupy on-top sites of Si-terminated SiC(0001) with in-plane Sn-Sn bondings, resulting in a triangular lattice. Angle-resolved photoemission spectroscopy revealed characteristic dispersions at \\bar{\\text{K}} and \\bar{\\text{M}} points, which agreed well with density functional theory calculations. The Sn triangular lattice atomic layer at the interface showed no oxidation upon exposure to air, which is useful for characterization and device fabrication ex situ.

Coated armor system and process for making the same

DOEpatents

Chu, Henry S.; Lillo, Thomas M.; McHugh, Kevin M.

2010-11-23

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

Armor systems including coated core materials

DOEpatents

Chu, Henry S [Idaho Falls, ID; Lillo, Thomas M [Idaho Falls, ID; McHugh, Kevin M [Idaho Falls, ID

2012-07-31

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

Armor systems including coated core materials

DOEpatents

Chu, Henry S; Lillo, Thomas M; McHugh, Kevin M

2013-10-08

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

Atomic Resolution of Calcium and Oxygen Sublattices of Calcite in Ambient Conditions by Atomic Force Microscopy Using qPlus Sensors with Sapphire Tips.

PubMed

Wastl, Daniel S; Judmann, Michael; Weymouth, Alfred J; Giessibl, Franz J

2015-01-01

Characterization and imaging at the atomic scale with atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomically resolved imaging of the calcite (101̅4) surface plane using stiff quartz cantilevers ("qPlus sensors", stiffness k = 1280 N/m) equipped with sapphire tips in ambient conditions without any surface preparation. With 10 atoms in one surface unit cell, calcite has a highly complex surface structure comprising three different chemical elements (Ca, C, and O). We obtain true atomic resolution of calcite in air at relative humidity ranging from 20% to 40%, imaging atomic steps and single atomic defects. We observe a great durability of sapphire tips with their Mohs hardness of 9, only one step below diamond. Depending on the state of the sapphire tip, we resolve either the calcium or the oxygen sublattice. We determine the tip termination by comparing the experimental images with simulations and discuss the possibility of chemical tip identification in air. The main challenges for imaging arise from the presence of water layers, which form on almost all surfaces and have the potential to dissolve the crystal surface. Frequency shift versus distance spectra show the presence of at least three ordered hydration layers. The measured height of the first hydration layer corresponds well to X-ray diffraction data and molecular dynamic simulations, namely, ∼220 pm. For the following hydration layers we measure ∼380 pm for the second and third layer, ending up in a total hydration layer thickness of at least 1 nm. Understanding the influence of water layers and their structure is important for surface segregation, surface reactions including reconstructions, healing of defects, and corrosion.

In situ monitoring of atomic layer epitaxy via optical ellipsometry

NASA Astrophysics Data System (ADS)

Lyzwa, F.; Marsik, P.; Roddatis, V.; Bernhard, C.; Jungbauer, M.; Moshnyaga, V.

2018-03-01

We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity. Ruddlesden-Popper thin films of SrO(SrTiO3) n=4 were grown by means of metalorganic aerosol deposition in the atomic layer epitaxy mode on SrTiO3(1 0 0), LSAT(1 0 0) and DyScO3(1 1 0) substrates. The measured time dependences of ellipsometric angles, Δ(t) and Ψ(t), were described by using a simple optical model, considering the sequence of atomic layers SrO and TiO2 with corresponding bulk refractive indices. As a result, valuable online information on the atomic layer epitaxy process was obtained. Ex situ characterization techniques, i.e. transmission electron microscopy, x-ray diffraction and x-ray reflectometry verify the crystal structure and confirm the predictions of optical ellipsometry.

Atom Probe Tomography Analysis of Ag Doping in 2D Layered Material (PbSe) 5(Bi 2Se 3) 3

DOE PAGES

Ren, Xiaochen; Singh, Arunima K.; Fang, Lei; ...

2016-09-07

Impurity doping in two-dimensional (2D) materials can provide a route to tuning electronic properties, so it is important to be able to determine the distribution of dopant atoms within and between layers. Here we report the totnographic mapping of dopants in layered 2D materials with atomic sensitivity and subnanometer spatial resolution using atom, probe tomography (APT). Also, APT analysis shows that Ag dopes both Bi 2Se 3 and PbSe layers in (PbSe) 5(Bi 2Se 3) 3, and correlations :in the position of Ag atoms suggest a pairing across neighboring Bi 2Se 3 and PbSe layers. Finally, density functional theory (DFT)more » calculations confirm the favorability of substitutional-doping for both Pb and Bi and provide insights into the,observed spatial correlations in dopant locations.« less

Atomic Oxygen Durability of Second Surface Silver Microsheet Glass Concentrators

NASA Technical Reports Server (NTRS)

deGroh, Kim K.; Jaworske, Donald A.; Smith, Daniela C.; Mroz, Thaddeus S.

1996-01-01

Second surface silver microsheet glass concentrators are being developed for potential use in future solar dynamic space power systems. Traditional concentrators are aluminum honeycomb sandwich composites with either aluminum or graphite epoxy face sheets, where a reflective aluminum layer is deposited onto an organic leveling layer on the face sheet. To protect the underlying layers, a SiO2 layer is applied on top of the aluminum reflective layer. These concentrators may be vulnerable to atomic oxygen degradation due to possible atomic oxygen attack of the organic layers at defect sites in the protective and reflective coatings. A second surface microsheet glass concentrator would be inherently more atomic oxygen durable than these first surface concentrators. In addition, a second surface microsheet glass concentrator design provides a smooth optical surface and allows for silver to be used as a reflective layer, which would improve the reflectivity of the concentrator and the performance of the system. A potential threat to the performance of second surface microsheet glass concentrators is atomic oxygen attack of the underlying silver at seams and edges or at micrometeoroid and debris (MMD) impacts sites. Second surface silver microsheet glass concentrator samples were fabricated and tested for atomic oxygen durability. The samples were iteratively exposed to an atomic oxygen environment in a plasma asher. Samples were evaluated for potential degradation at fabrication seams, simulated MMD impact sites, and edges. Optical microscopy was used to evaluate atomic oxygen degradation. Reflectance was obtained for an impacted sample prior to and after atomic oxygen exposure. After an initial atomic oxygen exposure to an effective fluence of approx. 1 x 10(exp 21) atoms/cm(exp 2), oxidation of the silver at defect sites and edges was observed. Exposure to an additional approx. 1 x 10(exp 21) atoms/cm(exp 2) caused no observed increase in oxidation. Oxidation at an impact site caused negligible changes in reflectance. In all cases oxidation was found to be confined to the vicinity of the seams, impact sites, edges or defect sites. Asher to in-space atomic oxygen correlation issues will be addressed.

Surface passivation investigation on ultra-thin atomic layer deposited aluminum oxide layers for their potential application to form tunnel layer passivated contacts

NASA Astrophysics Data System (ADS)

Xin, Zheng; Ling, Zhi Peng; Nandakumar, Naomi; Kaur, Gurleen; Ke, Cangming; Liao, Baochen; Aberle, Armin G.; Stangl, Rolf

2017-08-01

The surface passivation performance of atomic layer deposited ultra-thin aluminium oxide layers with different thickness in the tunnel layer regime, i.e., ranging from one atomic cycle (∼0.13 nm) to 11 atomic cycles (∼1.5 nm) on n-type silicon wafers is studied. The effect of thickness and thermal activation on passivation performance is investigated with corona-voltage metrology to measure the interface defect density D it(E) and the total interface charge Q tot. Furthermore, the bonding configuration variation of the AlO x films under various post-deposition thermal activation conditions is analyzed by Fourier transform infrared spectroscopy. Additionally, poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) is used as capping layer on ultra-thin AlO x tunneling layers to further reduce the surface recombination current density to values as low as 42 fA/cm2. This work is a useful reference for using ultra-thin ALD AlO x layers as tunnel layers in order to form hole selective passivated contacts for silicon solar cells.

Multi-ported, internally recuperated burners for direct flame impingement heating applications

DOEpatents

Abbasi, Hamid A.; Kurek, Harry; Chudnovsky, Yaroslav; Lisienko, Vladimir G.; Malikov, German K.

2010-08-03

A direct flame impingement method and apparatus employing at least one multi-ported, internally recuperated burner. The burner includes an innermost coaxial conduit having a first fluid inlet end and a first fluid outlet end, an outermost coaxial conduit disposed around the innermost coaxial conduit and having a combustion products outlet end proximate the first fluid inlet end of the innermost coaxial conduit and a combustion products inlet end proximate the first fluid outlet end of the innermost coaxial conduit, and a coaxial intermediate conduit disposed between the innermost coaxial conduit and the outermost coaxial conduit, whereby a second fluid annular region is formed between the innermost coaxial conduit and the intermediate coaxial conduit and a combustion products annular region is formed between the intermediate coaxial conduit and the outermost coaxial conduit. The intermediate coaxial conduit has a second fluid inlet end proximate the first fluid inlet end of the innermost coaxial conduit and a second fluid outlet end proximate the combustion products inlet end of the outermost coaxial conduit.

Vertical distribution of lipids, fatty acids and organochlorine contaminants in the blubber of southern hemisphere humpback whales (Megaptera novaeangliae).

PubMed

Waugh, Courtney A; Nichols, Peter D; Schlabach, Martin; Noad, Michael; Bengtson Nash, Susan

2014-03-01

Persistent organic pollutants (POPs), such as toxic lipophilic organochlorine (OC) compounds, accumulate in the blubber tissue of marine mammals. Toxicological sampling methods most frequently target only the superficial blubber layer. Vertical distribution of these contaminants through the blubber mantle may, however, not be homogenous and could reflect any dissemination of lipids and fatty acids (FAs). It is therefore critical to assess stratification patterns in a species of interest as a quality control measure for interpretation of toxicological data. Here, we analysed and compared the distribution of lipids, FAs, and OCs in the outermost and innermost blubber layer of southern hemisphere humpback whales. FA stratification was evident for short-chain (≤18) monounsaturated fatty acids (SC-MUFA), which were concentrated in the outer layer, consistent with the thermoregulatory role of this blubber layer. This stratification was, however, not reflected in OC distribution, which was similar in the inner and outer blubber layers of male humpback whales. By comparison, a noticeable gradient in total blubber lipid from the outer to the inner layer was observed in two lactating females, which coincided with higher lipid normalised contaminant levels in the inner layer. This study contains the most comprehensive assessment of humpback whale blubber stratification to date, however, further investigation of biological and ecological influencing factors is required. Copyright © 2013 Elsevier Ltd. All rights reserved.

Atomic hydrogen storage method and apparatus

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1978-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Atomic hydrogen storage method and apparatus

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1980-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compounds maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Atomic hydrogen storage. [cryotrapping and magnetic field strength

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1980-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Superconducting and Magnetic Properties of Vanadium/iron Superlattices.

NASA Astrophysics Data System (ADS)

Wong, Hong-Kuen

A novel ultrahigh vacuum evaporator was constructed for the preparation of superlattice samples. The thickness control was much better than an atomic plane. With this evaporator we prepared V/Fe superlattice samples on (0001) sapphire substrates with different thicknesses. All samples showed a good bcc(110) structure. Mossbauer experiments showed that the interface mixing extended a distance of about one atomic plane indicating an almost rectangular composition profile. Because of this we were able to prepare samples with layer thickness approaching one atomic plane. Even with ultrathin Fe layers, the samples are ferromagnetic, at least at lower temperatures. Superparamagnetism and spin glass states were not seen. In the absence of an external field, the magnetic moments lie close to the film plane. In addition to this shape anisotropy, there is some uniaxial anisotropy. No magnetic dead layers have been observed. The magnetic moments within the Fe layers vary little with the distance from the interfaces. At the interfaces the Fe moment is reduced and an antiparallel moment is induced on the vanadium atoms. It is observed that ultrathin Fe layers behave in a 2D fashion when isolated by sufficiently thick vanadium layers; however, on thinning the vanadium layers, a magnetic coupling between the Fe layers has been observed. We also studied the superconducting properties of V/Fe sandwiches and superlattices. In both cases, the Fe layer, a strong pair-breaker, suppresses the superconducting transition temperature consistent with the current knowledge of the magnetic proximity effect. For the sandwiches with thin (thick) vanadium layers, the temperature dependence of the upper critical fields is consistent with the simple theory for a 2D (3D) superconductor. For the superlattices, when the vanadium layer is on the order of the BCS coherence length and the Fe layer is only a few atomic planes thick, a 2D-3D crossover has been observed in the temperature dependence of the parallel upper critical field. This implies the coexistence of superconductivity and ferromagnetism. We observe three dimensional behavior for thinner Fe layers ((TURN)1 atomic plane) and two dimensional behavior for thicker Fe layers (greater than 10 atomic planes).

Crystalline boron nitride aerogels

DOEpatents

Zettl, Alexander K.; Rousseas, Michael; Goldstein, Anna P.; Mickelson, William; Worsley, Marcus A.; Woo, Leta

2017-04-04

This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.

Organization of Lipids in the Tear Film: A Molecular-Level View

PubMed Central

Wizert, Alicja; Iskander, D. Robert; Cwiklik, Lukasz

2014-01-01

Biophysical properties of the tear film lipid layer are studied at the molecular level employing coarse grain molecular dynamics (MD) simulations with a realistic model of the human tear film. In this model, polar lipids are chosen to reflect the current knowledge on the lipidome of the tear film whereas typical Meibomian-origin lipids are included in the thick non-polar lipids subphase. Simulation conditions mimic those experienced by the real human tear film during blinks. Namely, thermodynamic equilibrium simulations at different lateral compressions are performed to model varying surface pressure, and the dynamics of the system during a blink is studied by non-equilibrium MD simulations. Polar lipids separate their non-polar counterparts from water by forming a monomolecular layer whereas the non-polar molecules establish a thick outermost lipid layer. Under lateral compression, the polar layer undulates and a sorting of polar lipids occurs. Moreover, formation of three-dimensional aggregates of polar lipids in both non-polar and water subphases is observed. We suggest that these three-dimensional structures are abundant under dynamic conditions caused by the action of eye lids and that they act as reservoirs of polar lipids, thus increasing stability of the tear film. PMID:24651175

Microsurgical removal of epidermal and cortical cells: evidence that the gravitropic signal moves through the outer cell layers in primary roots of maize

NASA Technical Reports Server (NTRS)

Yang, R. L.; Evans, M. L.; Moore, R.

1990-01-01

There is general agreement that during root gravitropism some sort of growth-modifying signal moves from the cap to the elongation zone and that this signal ultimately induces the curvature that leads to reorientation of the root. However, there is disagreement regarding both the nature of the signal and the pathway of its movement from the root cap to the elongation zone. We examined the pathway of movement by testing gravitropism in primary roots of maize (Zea mays L.) from which narrow (0.5 mm) rings of epidermal and cortical tissue were surgically removed from various positions within the elongation zone. When roots were girdled in the apical part of the elongation zone gravitropic curvature occurred apical to the girdle but not basal to the girdle. Filling the girdle with agar allowed curvature basal to the girdle to occur. Shallow girdles, in which only two or three cell layers (epidermis plus one or two cortical cell layers) were removed, prevented or greatly delayed gravitropic curvature basal to the girdle. The results indicate that the gravitropic signal moves basipetally through the outermost cell layers, perhaps through the epidermis itself.

A hierarchical model of metabolic machinery based on the kcore decomposition of plant metabolic networks.

PubMed

Filho, Humberto A; Machicao, Jeaneth; Bruno, Odemir M

2018-01-01

Modeling the basic structure of metabolic machinery is a challenge for modern biology. Some models based on complex networks have provided important information regarding this machinery. In this paper, we constructed metabolic networks of 17 plants covering unicellular organisms to more complex dicotyledonous plants. The metabolic networks were built based on the substrate-product model and a topological percolation was performed using the kcore decomposition. The distribution of metabolites across the percolation layers showed correlations between the metabolic integration hierarchy and the network topology. We show that metabolites concentrated in the internal network (maximum kcore) only comprise molecules of the primary basal metabolism. Moreover, we found a high proportion of a set of common metabolites, among the 17 plants, centered at the inner kcore layers. Meanwhile, the metabolites recognized as participants in the secondary metabolism of plants are concentrated in the outermost layers of the network. This data suggests that the metabolites in the central layer form a basic molecular module in which the whole plant metabolism is anchored. The elements from this central core participate in almost all plant metabolic reactions, which suggests that plant metabolic networks follows a centralized topology.

A hierarchical model of metabolic machinery based on the kcore decomposition of plant metabolic networks

PubMed Central

Filho, Humberto A.; Machicao, Jeaneth

2018-01-01

Modeling the basic structure of metabolic machinery is a challenge for modern biology. Some models based on complex networks have provided important information regarding this machinery. In this paper, we constructed metabolic networks of 17 plants covering unicellular organisms to more complex dicotyledonous plants. The metabolic networks were built based on the substrate-product model and a topological percolation was performed using the kcore decomposition. The distribution of metabolites across the percolation layers showed correlations between the metabolic integration hierarchy and the network topology. We show that metabolites concentrated in the internal network (maximum kcore) only comprise molecules of the primary basal metabolism. Moreover, we found a high proportion of a set of common metabolites, among the 17 plants, centered at the inner kcore layers. Meanwhile, the metabolites recognized as participants in the secondary metabolism of plants are concentrated in the outermost layers of the network. This data suggests that the metabolites in the central layer form a basic molecular module in which the whole plant metabolism is anchored. The elements from this central core participate in almost all plant metabolic reactions, which suggests that plant metabolic networks follows a centralized topology. PMID:29734359

The big lobe of 67P/Churyumov-Gerasimenko comet: morphological and spectrophotometric evidences of layering as from OSIRIS data

NASA Astrophysics Data System (ADS)

Ferrari, Sabrina; Penasa, L.; La Forgia, F.; Massironi, M.; Naletto, G.; Lazzarin, M.; Fornasier, S.; Hasselmann, P. H.; Lucchetti, A.; Pajola, M.; Ferri, F.; Cambianica, P.; Oklay, N.; Tubiana, C.; Sierks, H.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Davidsson, B.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Deller, J.; Franceschi, M.; Frattin, E.; Fulle, M.; Groussin, O.; Gutiérrez, P. J.; Güttler, C.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Keller, H. U.; Knollenberg, J.; Kührt, E.; Küppers, M.; Lara, L. M.; López-Moreno, J. J.; Marzari, F.; Shi, X.; Simioni, E.; Thomas, N.; Vincent, J.-B.

2018-06-01

Between 2014 and 2016, ESA's Rosetta OSIRIS cameras acquired multiple-filters images of the layered nucleus of comet 67P/Churyumov-Gerasimenko, ranging from ultraviolet to near-infrared wavelengths. No correlation between layers disposition and surface spectral variegation has been observed so far. This paper investigates possible spectral differences among decametre-thickness outcropping layers of the biggest lobe of the comet by means of OSIRIS image dataset. A two-classes Maximum Likelihood classification was applied on consolidated outcrops and relative deposits identified on post-perihelion multispectral images of the big lobe. We distinguished multispectral data on the basis of the structural elevation of the onion-shell Ellipsoidal Model of 67P. The spatial distribution of the two classes displays a clear dependence on the structural elevation, with the innermost class resulting over 50% brighter that the outermost one. Consolidated cometary materials located at different structural levels are characterized by different brightness and revealed due to the selective removal of large volumes. This variegation can be attributed to a different texture of the outcrop surface and/or to a different content of refractory materials.

Atomic-Layer-Confined Doping for Atomic-Level Insights into Visible-Light Water Splitting.

PubMed

Lei, Fengcai; Zhang, Lei; Sun, Yongfu; Liang, Liang; Liu, Katong; Xu, Jiaqi; Zhang, Qun; Pan, Bicai; Luo, Yi; Xie, Yi

2015-08-03

A model of doping confined in atomic layers is proposed for atomic-level insights into the effect of doping on photocatalysis. Co doping confined in three atomic layers of In2S3 was implemented with a lamellar hybrid intermediate strategy. Density functional calculations reveal that the introduction of Co ions brings about several new energy levels and increased density of states at the conduction band minimum, leading to sharply increased visible-light absorption and three times higher carrier concentration. Ultrafast transient absorption spectroscopy reveals that the electron transfer time of about 1.6 ps from the valence band to newly formed localized states is due to Co doping. The 25-fold increase in average recovery lifetime is believed to be responsible for the increased of electron-hole separation. The synthesized Co-doped In2S3 (three atomic layers) yield a photocurrent of 1.17 mA cm(-2) at 1.5 V vs. RHE, nearly 10 and 17 times higher than that of the perfect In2S3 (three atomic layers) and the bulk counterpart, respectively. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An Introduction to Atomic Layer Deposition

NASA Technical Reports Server (NTRS)

Dwivedi, Vivek H.

2017-01-01

Atomic Layer Deposition has been instrumental in providing a deposition method for multiple space flight applications. It is well known that ALD is a cost effective nanoadditive-manufacturing technique that allows for the conformal coating of substrates with atomic control in a benign temperature and pressure environment. Through the introduction of paired precursor gases, thin films can be deposited on a myriad of substrates from flat surfaces to those with significant topography. By providing atomic layer control, where single layers of atoms can be deposited, the fabrication of metal transparent films, precise nano-laminates, and coatings of nano-channels, pores and particles is achievable. The feasibility of this technology for NASA line of business applications range from thermal systems, optics, sensors, to environmental protection. An overview of this technology will be presented.

Adsorption, hydrogenation and dehydrogenation of C2H on a CoCu bimetallic layer

NASA Astrophysics Data System (ADS)

Wu, Donghai; Yuan, Jinyun; Yang, Baocheng; Chen, Houyang

2018-05-01

In this paper, adsorption, hydrogenation and dehydrogenation of C2H on a single atomic layer of bimetallic CoCu were investigated using first-principles calculations. The CoCu bimetallic layer is formed by Cu replacement of partial Co atoms on the top layer of a Co(111) surface. Our adsorption and reaction results showed those sites, which have stronger adsorption energy of C2H, possess higher reactivity. The bimetallic layer possesses higher reactivity than either of the pure monometallic layer. A mechanism of higher reactivity of the bimetallic layer is proposed and identified, i.e. in the bimetallic catalyst, the catalytic performance of one component is promoted by the second component, and in our work, the catalytic performance of Co atoms in the bimetallic layer are improved by introducing Cu atoms, lowing the activation barrier of the reaction of C2H. The bimetallic layer could tune adsorption and reaction of C2H by modulating the ratio of Co and Cu. Results of adsorption energies and adsorption configurations reveal that C2H prefers to be adsorbed in parallel on both the pure Co metallic and CoCu bimetallic layers, and Co atoms in subsurface which support the metallic or bimetallic layer have little effect on C2H adsorption. For hydrogenation reactions, the products greatly depend on the concentration and initial positions of hydrogen atoms, and the C2H hydrogenation forming acetylene is more favorable than forming vinylidene in both thermodynamics and kinetics. This study would provide fundamental guidance for hydrocarbon reactions on Co-based and/or Cu-based bimetallic surface chemistry and for development of new bimetallic catalysts.

Effects of two kinds of underwear on thermophysiological responses and clothing microclimate during 30 min walking and 60 min recovery in the cold.

PubMed

Ha, M; Tokura, H; Tanaka, Y; Holmér, I

1996-01-01

Thermophysiological responses and clothing microclimate under the influences of different underwear materials were compared during walking and recovery in the cold. Two kinds of underwear were used: two layers of cotton underwear with two-piece long-sleeved shirt and long-legged trousers (C), two layers of polypropylene underwear with two-piece long-sleeved shirt and long-legged trousers (P). In addition, the subject put on a two-piece ski suit of 100% polyester including 100% polyester padding. Seven adult females served as subjects in this study. The test was done in a climatic chamber at an ambient air temperature of 2 degrees C, a relative humidity of 65% and an air velocity of 0.14 m.s-1. The subject walked on a motor-driven treadmill with a 6 km/h speed for 30 min followed by 60 min recovery. Rectal temperature, skin temperatures, clothing microclimate (temperature, humidity), metabolic heat production and heart rate were measured. Furthermore, subjective ratings on thermal sensation, sweating/shivering sensation, clothing wettedness sensation and skin wettedness sensation for whole body were asked. The major findings are summarized as follows: 1) Mean skin temperature was not significantly different during walking, but it was significantly higher in P than in C during the recovery. 2) The absolute humidity of innermost layer and outermost layer were not significantly different during walking, but it was significantly higher in P than in C during the recovery. 3) Clothing microclimate temperature of innermost was not significantly different during the first half of walking, but it was significantly higher in C than in P during the second half of walking and significantly lower in C than in P during the recovery. Clothing microclimate temperature of outermost was not significantly different during walking, but it was significantly higher in P than in C during the recovery. 4) Metabolic heat production for the last 10 min during recovery tended to be higher in P. 5) The degree of skin wettedness sensation and clothing wettedness sensation for whole body was significantly higher in P during walking and recovery. Thus, it was concluded that two kinds of underwear with different properties to moisture could influence, not only clothing microclimate, but also physiological parameters like skin temperatures and metabolic heat production in the cold differently.

Methods of producing armor systems, and armor systems produced using such methods

DOEpatents

Chu, Henry S; Lillo, Thomas M; McHugh, Kevin M

2013-02-19

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

Measurement of the first ionization potential of lawrencium, element 103.

PubMed

Sato, T K; Asai, M; Borschevsky, A; Stora, T; Sato, N; Kaneya, Y; Tsukada, K; Düllmann, Ch E; Eberhardt, K; Eliav, E; Ichikawa, S; Kaldor, U; Kratz, J V; Miyashita, S; Nagame, Y; Ooe, K; Osa, A; Renisch, D; Runke, J; Schädel, M; Thörle-Pospiech, P; Toyoshima, A; Trautmann, N

2015-04-09

The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row--including the actinides--even affecting ground-state configurations. Atomic s and p1/2 orbitals are stabilized by relativistic effects, whereas p3/2, d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP1) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by the difficulty in obtaining the heaviest elements on scales of more than one atom at a time. Here we report that the experimentally obtained IP1 of the heaviest actinide, lawrencium (Lr, atomic number 103), is 4.96(+0.08)(-0.07) electronvolts. The IP1 of Lr was measured with (256)Lr (half-life 27 seconds) using an efficient surface ion-source and a radioisotope detection system coupled to a mass separator. The measured IP1 is in excellent agreement with the value of 4.963(15) electronvolts predicted here by state-of-the-art relativistic calculations. The present work provides a reliable benchmark for theoretical calculations and also opens the way for IP1 measurements of superheavy elements (that is, transactinides) on an atom-at-a-time scale.

Properties of Surface-Modification Layer Generated by Atomic Hydrogen Annealing on Poly(ethylene naphthalate) Substrate

NASA Astrophysics Data System (ADS)

Heya, Akira; Matsuo, Naoto

2008-01-01

The surface of a poly(ethylene naphthalate) (PEN) substrate was modified by atomic hydrogen annealing (AHA). In this method, a PEN substrate was exposed to atomic hydrogen generated by cracking hydrogen molecules on heated tungsten wire. The properties of the surface-modification layer by AHA were evaluated by spectroscopic ellipsometry. It is found that the thickness of the modified layer was 5 nm and that the modification layer has a low refractive index compared with the PEN substrate. The modification layer relates to the reduction reaction of the PEN substrate by AHA.

Atomic-order thermal nitridation of group IV semiconductors for ultra-large-scale integration

NASA Astrophysics Data System (ADS)

Murota, Junichi; Le Thanh, Vinh

2015-03-01

One of the main requirements for ultra-large-scale integration (ULSI) is atomic-order control of process technology. Our concept of atomically controlled processing for group IV semiconductors is based on atomic-order surface reaction control in Si-based CVD epitaxial growth. On the atomic-order surface nitridation of a few nm-thick Ge/about 4 nm-thick Si0.5Ge0.5/Si(100) by NH3, it is found that N atoms diffuse through nm-order thick Ge layer into Si0.5Ge0.5/Si(100) substrate and form Si nitride, even at 500 °C. By subsequent H2 heat treatment, although N atomic amount in Ge layer is reduced drastically, the reduction of the Si nitride is slight. It is suggested that N diffusion in Ge layer is suppressed by the formation of Si nitride and that Ge/atomic-order N layer/Si1-xGex/Si (100) heterostructure is formed. These results demonstrate the capability of CVD technology for atomically controlled nitridation of group IV semiconductors for ultra-large-scale integration. Invited talk at the 7th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2014, 2-6 November, 2014, Ha Long, Vietnam.

Proteins in the Cocoon of Silkworm Inhibit the Growth of Beauveria bassiana

PubMed Central

Zhang, Yan; Li, Youshan; Liu, Huawei; Xia, Qingyou; Zhao, Ping

2016-01-01

Silk cocoons are composed of fiber proteins (fibroins) and adhesive glue proteins (sericins), which provide a physical barrier to protect the inside pupa. Moreover, other proteins were identified in the cocoon silk, many of which are immune related proteins. In this study, we extracted proteins from the silkworm cocoon by Tris-HCl buffer (pH7.5), and found that they had a strong inhibitory activity against fungal proteases and they had higher abundance in the outer cocoon layers than in the inner cocoon layers. Moreover, we found that extracted cocoon proteins can inhibit the germination of Beauveria bassiana spores. Consistent with the distribution of protease inhibitors, we found that proteins from the outer cocoon layers showed better inhibitory effects against B. bassiana spores than proteins from the inner layers. Liquid chromatography-tandem mass spectrometry was used to reveal the extracted components in the scaffold silk, the outermost cocoon layer. A total of 129 proteins were identified, 30 of which were annotated as protease inhibitors. Protease inhibitors accounted for 89.1% in abundance among extracted proteins. These protease inhibitors have many intramolecular disulfide bonds to maintain their stable structure, and remained active after being boiled. This study added a new understanding to the antimicrobial function of the cocoon. PMID:27032085

Thermal Convection in High-Pressure Ice Layers Beneath a Buried Ocean within Titan and Ganymede

NASA Astrophysics Data System (ADS)

Tobie, G.; Choblet, G.; Dumont, M.

2014-12-01

Deep interiors of large icy satellites such as Titan and Ganymede probably harbor a buried ocean sandwiched between low pressure ice and high-pressure ice layers. The nature and location of the lower interface of the ocean involves equilibration of heat and melt transfer in the HP ices and is ultimately controlled by the amount heat transferred through the surface ice Ih layer. Here, we perform 3D simulations of thermal convection, using the OEDIPUS numerical tool (Choblet et al. GJI 2007), to determine the efficiency of heat and mass transfer through these HP ice mantles. In a first series of simulations with no melting, we show that a significant fraction of the HP layer reaches the melting point. Using a simple description of water production and transport, our simulations demonstrate that the melt generation in the outermost part of the HP ice layer and its extraction to the overlying ocean increase the efficiency of heat transfer and reduce strongly the internal temperature. structure and the efficiency of the heat transfer. Scaling relationships are proposed to describe the cooling effect of melt production/extraction and used to investigate the consequences of internal melting on the thermal history of Titan and Ganymede's interior.

A study of the thermal denaturation of the S-layer protein from Lactobacillus salivarius

NASA Astrophysics Data System (ADS)

Lighezan, Liliana; Georgieva, Ralitsa; Neagu, Adrian

2012-09-01

Surface layer (S-layer) proteins display an intrinsic self-assembly property, forming monomolecular crystalline arrays, identified in outermost structures of the cell envelope in many organisms, such as bacteria and archaea. Isolated S-layer proteins also possess the ability to recrystallize into regular lattices, being used in biotechnological applications, such as controlling the architecture of biomimetic surfaces. To this end, the stability of the S-layer proteins under high-temperature conditions is very important. In this study, the S-layer protein has been isolated from Lactobacillus salivarius 16 strain of human origin, and purified by cation-exchange chromatography. Using circular dichroism (CD) spectroscopy, we have investigated the thermal denaturation of the S-layer protein. The far- and near-UV CD spectra have been collected, and the temperature dependence of the CD signal in these spectral domains has been analyzed. The variable temperature results show that the secondary and tertiary structures of the S-layer protein change irreversibly due to the heating of the sample. After the cooling of the heated protein, the secondary and tertiary structures are partially recovered. The denaturation curves show that the protein unfolding depends on the sample concentration and on the heating rate. The secondary and tertiary structures of the protein suffer changes in the same temperature range. We have also detected an intermediate state in the protein denaturation pathway. Our results on the thermal behavior of the S-layer protein may be important for the use of S-layer proteins in biotechnological applications, as well as for a better understanding of the structure and function of S-layer proteins.

Atomic Structures of Silicene Layers Grown on Ag(111): Scanning Tunneling Microscopy and Noncontact Atomic Force Microscopy Observations

PubMed Central

Resta, Andrea; Leoni, Thomas; Barth, Clemens; Ranguis, Alain; Becker, Conrad; Bruhn, Thomas; Vogt, Patrick; Le Lay, Guy

2013-01-01

Silicene, the considered equivalent of graphene for silicon, has been recently synthesized on Ag(111) surfaces. Following the tremendous success of graphene, silicene might further widen the horizon of two-dimensional materials with new allotropes artificially created. Due to stronger spin-orbit coupling, lower group symmetry and different chemistry compared to graphene, silicene presents many new interesting features. Here, we focus on very important aspects of silicene layers on Ag(111): First, we present scanning tunneling microscopy (STM) and non-contact Atomic Force Microscopy (nc-AFM) observations of the major structures of single layer and bi-layer silicene in epitaxy with Ag(111). For the (3 × 3) reconstructed first silicene layer nc-AFM represents the same lateral arrangement of silicene atoms as STM and therefore provides a timely experimental confirmation of the current picture of the atomic silicene structure. Furthermore, both nc-AFM and STM give a unifying interpretation of the second layer (√3 × √3)R ± 30° structure. Finally, we give support to the conjectured possible existence of less stable, ~2% stressed, (√7 × √7)R ± 19.1° rotated silicene domains in the first layer. PMID:23928998

Kinetics of the maintenance of the epidermis

NASA Astrophysics Data System (ADS)

Zhdanov, Vladimir P.; Cho, Nam-Joon

2013-08-01

The epidermis is the outermost layer of skin. It is comprised of keratin-containing cells called keratinocytes. Functionally, the epidermis serves as a physical barrier that can prevent infection and regulate body hydration. Maintenance and repair of the epidermis are important for human health. Mechanistically, these processes occur primarily via proliferation and differentiation of stem cells located in the basal monolayer. These processes are believed to depend on cell-cell communication and spatial constraints but existing kinetic models focus mainly on proliferation and differentiation. To address this issue, we present a mean-field kinetic model that takes these additional factors into account and describes the epidermis at a biosystem level. The corresponding equations operate with the populations of stem cells and differentiated cells in the basal layer. The keratinocytes located above the basal layer are treated at a more coarse-grained level by considering the thickness of the epidermis. The model clarifies the likely role of various negative feedbacks that may control the epidermis and, accordingly, provides insight into the cellular mechanisms underlying complex biological phenomena such as wound healing.

The cuticle modulates ultraviolet reflectance of avian eggshells

PubMed Central

Fecheyr-Lippens, Daphne C.; Igic, Branislav; D'Alba, Liliana; Hanley, Daniel; Verdes, Aida; Holford, Mande; Waterhouse, Geoffrey I. N.; Grim, Tomas; Hauber, Mark E.; Shawkey, Matthew D.

2015-01-01

ABSTRACT Avian eggshells are variedly coloured, yet only two pigments, biliverdin and protoporphyrin IX, are known to contribute to the dramatic diversity of their colours. By contrast, the contributions of structural or other chemical components of the eggshell are poorly understood. For example, unpigmented eggshells, which appear white to the human eye, vary in their ultraviolet (UV) reflectance, which may be detectable by birds. We investigated the proximate mechanisms for the variation in UV-reflectance of unpigmented bird eggshells using spectrophotometry, electron microscopy, chemical analyses, and experimental manipulations. We specifically tested how UV-reflectance is affected by the eggshell cuticle, the outermost layer of most avian eggshells. The chemical dissolution of the outer eggshell layers, including the cuticle, increased UV-reflectance for only eggshells that contained a cuticle. Our findings demonstrate that the outer eggshell layers, including the cuticle, absorb UV-light, probably because they contain higher levels of organic components and other chemicals, such as calcium phosphates, compared to the predominantly calcite-based eggshell matrix. These data highlight the need to examine factors other than the known pigments in studies of avian eggshell colour. PMID:25964661

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lei, Qingyu; Golalikhani, Maryam; Davidson, Bruce A.; Liu, Guozhen; Schlom, Darrell G.; Qiao, Qiao; Zhu, Yimei; Chandrasena, Ravini U.; Yang, Weibing; Gray, Alexander X.; Arenholz, Elke; Farrar, Andrew K.; Tenne, Dmitri A.; Hu, Minhui; Guo, Jiandong; Singh, Rakesh K.; Xi, Xiaoxing

2017-12-01

Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive molecular-beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr1+xTi1-xO3+δ, Ruddlesden-Popper phase Lan+1NinO3n+1 (n = 4), and LaAl1+yO3(1+0.5y)/SrTiO3 interfaces, that atomic layer-by-layer laser molecular-beam epitaxy significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With atomic layer-by-layer laser molecular-beam epitaxy we have produced conducting LaAlO3/SrTiO3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism.

Structural properties and diffusion processes of the Cu 3Au (0 0 1) surface

NASA Astrophysics Data System (ADS)

Wang, Fang; Zhang, Jian-Min; Zhang, Yan; Ji, Vincent

2010-09-01

The surface relaxation and surface energy of both the mixed AuCu and pure Cu terminated Cu 3Au (0 0 1) surfaces are simulated and calculated by using the modified analytical embedded-atom method. We find that the mixed AuCu termination is energetically preferred over the pure Cu termination thereby the mono-vacancy diffusion is also investigated in the topmost few layers of the mixed AuCu terminated Cu 3Au (0 0 1) surface. In the mixed AuCu terminated surface the relaxed Au atoms are raised above Cu atoms for 0.13 Å in the topmost layer. All the surface atoms displace outwards, this effect occurs in the first three layers and changes the first two inter-layer spacing. For mono-vacancy migration in the first layer, the migration energies of Au and Cu mono-vacancy via two-type in-plane displace: the nearest neighbor jump (NNJ) and the second nearest neighbor jump (2NNJ), are calculated and the results show that the NNJ requires a much lower energy than 2NNJ. For the evolution of the energy requirements for successive nearest neighbor jumps (SNNJ) along three different paths: circularity, zigzag and beeline, we find that the circularity path is preferred over the other two paths due to its minimum energy barriers and final energies. In the second layer, the NN jumps in intra- and inter-layer of the Cu mono-vacancy are investigated. The calculated energy barriers and final energies show that the vacancy prefer jump up to a proximate Cu site. This replacement between the Cu vacancy in the second layer and Cu atom in the first layer is remunerative for the Au atoms enrichment in the topmost layer.

A basin-hopping Monte Carlo investigation of the structural and energetic properties of 55- and 561-atom bimetallic nanoclusters: the examples of the ZrCu, ZrAl, and CuAl systems.

PubMed

De Souza, Douglas G; Cezar, Henrique M; Rondina, Gustavo G; de Oliveira, Marcelo F; Da Silva, Juarez L F

2016-05-05

We report a basin-hopping Monte Carlo investigation within the embedded-atom method of the structural and energetic properties of bimetallic ZrCu, ZrAl, and CuAl nanoclusters with 55 and 561 atoms. We found that unary Zr55, Zr561, Cu55, Cu561, Al55, and Al561 systems adopt the well known compact icosahedron (ICO) structure. The excess energy is negative for all systems and compositions, which indicates an energetic preference for the mixing of both chemical species. The ICO structure is preserved if a few atoms of the host system are replaced by different species, however, the composition limit in which the ICO structure is preserved depends on both the host and new chemical species. Using several structural analyses, three classes of structures, namely ideal ICO, nearly ICO, and distorted ICO structures, were identified. As the amounts of both chemical species change towards a more balanced composition, configurations far from the ICO structure arise and the dominant structures are nearly spherical, which indicates a strong minimization of the surface energy by decreasing the number of atoms with lower coordination on the surface. The average bond lengths follow Vegard's law almost exactly for ZrCu and ZrAl, however, this is not the case for CuAl. Furthermore, the radial distribution allowed us to identify the presence of an onion-like behavior in the surface of the 561-atom CuAl nanocluster with the Al atoms located in the outermost surface shell, which can be explained by the lower surface energies of the Al surfaces compared with the Cu surfaces. In ZrCu and ZrAl the radial distribution indicates a nearly homogeneous distribution for the chemical species, however, with a slightly higher concentration of Al atoms on the ZrAl surface, which can also be explained by the lower surface energy.

Fabricating Large-Area Sheets of Single-Layer Graphene by CVD

NASA Technical Reports Server (NTRS)

Bronikowski, Michael; Manohara, Harish

2008-01-01

This innovation consists of a set of methodologies for preparing large area (greater than 1 cm(exp 2)) domains of single-atomic-layer graphite, also called graphene, in single (two-dimensional) crystal form. To fabricate a single graphene layer using chemical vapor deposition (CVD), the process begins with an atomically flat surface of an appropriate substrate and an appropriate precursor molecule containing carbon atoms attached to substituent atoms or groups. These molecules will be brought into contact with the substrate surface by being flowed over, or sprayed onto, the substrate, under CVD conditions of low pressure and elevated temperature. Upon contact with the surface, the precursor molecules will decompose. The substituent groups detach from the carbon atoms and form gas-phase species, leaving the unfunctionalized carbon atoms attached to the substrate surface. These carbon atoms will diffuse upon this surface and encounter and bond to other carbon atoms. If conditions are chosen carefully, the surface carbon atoms will arrange to form the lowest energy single-layer structure available, which is the graphene lattice that is sought. Another method for creating the graphene lattice includes metal-catalyzed CVD, in which the decomposition of the precursor molecules is initiated by the catalytic action of a catalytic metal upon the substrate surface. Another type of metal-catalyzed CVD has the entire substrate composed of catalytic metal, or other material, either as a bulk crystal or as a think layer of catalyst deposited upon another surface. In this case, the precursor molecules decompose directly upon contact with the substrate, releasing their atoms and forming the graphene sheet. Atomic layer deposition (ALD) can also be used. In this method, a substrate surface at low temperature is covered with exactly one monolayer of precursor molecules (which may be of more than one type). This is heated up so that the precursor molecules decompose and form one monolayer of the target material.

An Energy-Dispersive X-Ray Fluorescence Spectrometry and Monte Carlo simulation study of Iron-Age Nuragic small bronzes ("Navicelle") from Sardinia, Italy

NASA Astrophysics Data System (ADS)

Schiavon, Nick; de Palmas, Anna; Bulla, Claudio; Piga, Giampaolo; Brunetti, Antonio

2016-09-01

A spectrometric protocol combining Energy Dispersive X-Ray Fluorescence Spectrometry with Monte Carlo simulations of experimental spectra using the XRMC code package has been applied for the first time to characterize the elemental composition of a series of famous Iron Age small scale archaeological bronze replicas of ships (known as the ;Navicelle;) from the Nuragic civilization in Sardinia, Italy. The proposed protocol is a useful, nondestructive and fast analytical tool for Cultural Heritage sample. In Monte Carlo simulations, each sample was modeled as a multilayered object composed by two or three layers depending on the sample: when all present, the three layers are the original bronze substrate, the surface corrosion patina and an outermost protective layer (Paraloid) applied during past restorations. Monte Carlo simulations were able to account for the presence of the patina/corrosion layer as well as the presence of the Paraloid protective layer. It also accounted for the roughness effect commonly found at the surface of corroded metal archaeological artifacts. In this respect, the Monte Carlo simulation approach adopted here was, to the best of our knowledge, unique and enabled to determine the bronze alloy composition together with the thickness of the surface layers without the need for previously removing the surface patinas, a process potentially threatening preservation of precious archaeological/artistic artifacts for future generations.

Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges.

PubMed

Duan, Xidong; Wang, Chen; Pan, Anlian; Yu, Ruqin; Duan, Xiangfeng

2015-12-21

The discovery of graphene has ignited intensive interest in two-dimensional layered materials (2DLMs). These 2DLMs represent a new class of nearly ideal 2D material systems for exploring fundamental chemistry and physics at the limit of single-atom thickness, and have the potential to open up totally new technological opportunities beyond the reach of existing materials. In general, there are a wide range of 2DLMs in which the atomic layers are weakly bonded together by van der Waals interactions and can be isolated into single or few-layer nanosheets. The van der Waals interactions between neighboring atomic layers could allow much more flexible integration of distinct materials to nearly arbitrarily combine and control different properties at the atomic scale. The transition metal dichalcogenides (TMDs) (e.g., MoS2, WSe2) represent a large family of layered materials, many of which exhibit tunable band gaps that can undergo a transition from an indirect band gap in bulk crystals to a direct band gap in monolayer nanosheets. These 2D-TMDs have thus emerged as an exciting class of atomically thin semiconductors for a new generation of electronic and optoelectronic devices. Recent studies have shown exciting potential of these atomically thin semiconductors, including the demonstration of atomically thin transistors, a new design of vertical transistors, as well as new types of optoelectronic devices such as tunable photovoltaic devices and light emitting devices. In parallel, there have also been considerable efforts in developing diverse synthetic approaches for the rational growth of various forms of 2D materials with precisely controlled chemical composition, physical dimension, and heterostructure interface. Here we review the recent efforts, progress, opportunities and challenges in exploring the layered TMDs as a new class of atomically thin semiconductors.

Three-dimensional atom probe tomography of oxide, anion, and alkanethiolate coatings on gold.

PubMed

Zhang, Yi; Hillier, Andrew C

2010-07-15

We have used three-dimensional atom probe tomography to analyze several nanometer-thick and monomolecular films on gold surfaces. High-purity gold wire was etched by electropolishing to create a sharp tip suitable for field evaporation with a radius of curvature of <100 nm. The near-surface region of a freshly etched gold tip was examined with the atom probe at subnanometer spatial resolution and with atom-level composition accuracy. A thin contaminant layer, primarily consisting of water and atmospheric gases, was observed on a fresh tip. This sample exhibited crystalline lattice spacings consistent with the interlayer spacing of {200} lattice planes of bulk gold. A thin oxide layer was created on the gold surface via plasma oxidation, and the thickness and composition of this layer was measured. Clear evidence of a nanometer-thick oxide layer was seen coating the gold tip, and the atomic composition of the oxide layer was consistent with the expected stoichiometry for gold oxide. Monomolecular anions layers of Br(-) and I(-) were created via adsorption from aqueous solutions onto the gold. Atom probe data verified the presence of the monomolecular anion layers on the gold surface, with ion density values consistent with literature values. A hexanethiolate monolayer was coated onto the gold tip, and atom probe analysis revealed a thin film whose ion fragments were consistent with the molecular composition of the monolayer and a surface coverage similar to that expected from literature. Details of the various coating compositions and structures are presented, along with discussion of the reconstruction issues associated with properly analyzing these thin-film systems.

Initial evaluation and comparison of plasma damage to atomic layer carbon materials using conventional and low T{sub e} plasma sources

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

Jagtiani, Ashish V.; Miyazoe, Hiroyuki; Chang, Josephine

2016-01-15

The ability to achieve atomic layer precision is the utmost goal in the implementation of atomic layer etch technology. Carbon-based materials such as carbon nanotubes (CNTs) and graphene are single atomic layers of carbon with unique properties and, as such, represent the ultimate candidates to study the ability to process with atomic layer precision and assess impact of plasma damage to atomic layer materials. In this work, the authors use these materials to evaluate the atomic layer processing capabilities of electron beam generated plasmas. First, the authors evaluate damage to semiconducting CNTs when exposed to beam-generated plasmas and compare thesemore » results against the results using typical plasma used in semiconductor processing. The authors find that the beam generated plasma resulted in significantly lower current degradation in comparison to typical plasmas. Next, the authors evaluated the use of electron beam generated plasmas to process graphene-based devices by functionalizing graphene with fluorine, nitrogen, or oxygen to facilitate atomic layer deposition (ALD). The authors found that all adsorbed species resulted in successful ALD with varying impact on the transconductance of the graphene. Furthermore, the authors compare the ability of both beam generated plasma as well as a conventional low ion energy inductively coupled plasma (ICP) to remove silicon nitride (SiN) deposited on top of the graphene films. Our results indicate that, while both systems can remove SiN, an increase in the D/G ratio from 0.08 for unprocessed graphene to 0.22 to 0.26 for the beam generated plasma, while the ICP yielded values from 0.52 to 1.78. Generally, while some plasma-induced damage was seen for both plasma sources, a much wider process window as well as far less damage to CNTs and graphene was observed when using electron beam generated plasmas.« less

Quantitative Raman spectrum and reliable thickness identification for atomic layers on insulating substrates.

PubMed

Li, Song-Lin; Miyazaki, Hisao; Song, Haisheng; Kuramochi, Hiromi; Nakaharai, Shu; Tsukagoshi, Kazuhito

2012-08-28

We demonstrate the possibility in quantifying the Raman intensities for both specimen and substrate layers in a common stacked experimental configuration and, consequently, propose a general and rapid thickness identification technique for atomic-scale layers on dielectric substrates. Unprecedentedly wide-range Raman data for atomically flat MoS(2) flakes are collected to compare with theoretical models. We reveal that all intensity features can be accurately captured when including optical interference effect. Surprisingly, we find that even freely suspended chalcogenide few-layer flakes have a stronger Raman response than that from the bulk phase. Importantly, despite the oscillating intensity of specimen spectrum versus thickness, the substrate weighted spectral intensity becomes monotonic. Combined with its sensitivity to specimen thickness, we suggest this quantity can be used to rapidly determine the accurate thickness for atomic layers.

Dopant Distribution in Atomic Layer Deposited ZnO:Al Films Visualized by Transmission Electron Microscopy and Atom Probe Tomography.

PubMed

Wu, Yizhi; Giddings, A Devin; Verheijen, Marcel A; Macco, Bart; Prosa, Ty J; Larson, David J; Roozeboom, Fred; Kessels, Wilhelmus M M

2018-02-27

The maximum conductivity achievable in Al-doped ZnO thin films prepared by atomic layer deposition (ALD) is limited by the low doping efficiency of Al. To better understand the limiting factors for the doping efficiency, the three-dimensional distribution of Al atoms in the ZnO host material matrix has been examined on the atomic scale using a combination of high-resolution transmission electron microscopy (TEM) and atom probe tomography (APT). Although the Al distribution in ZnO films prepared by so-called "ALD supercycles" is often presented as atomically flat δ-doped layers, in reality a broadening of the Al-dopant layers is observed with a full-width-half-maximum of ∼2 nm. In addition, an enrichment of the Al at grain boundaries is observed. The low doping efficiency for local Al densities > ∼1 nm -3 can be ascribed to the Al solubility limit in ZnO and to the suppression of the ionization of Al dopants from adjacent Al donors.

Dopant Distribution in Atomic Layer Deposited ZnO:Al Films Visualized by Transmission Electron Microscopy and Atom Probe Tomography

PubMed Central

2018-01-01

The maximum conductivity achievable in Al-doped ZnO thin films prepared by atomic layer deposition (ALD) is limited by the low doping efficiency of Al. To better understand the limiting factors for the doping efficiency, the three-dimensional distribution of Al atoms in the ZnO host material matrix has been examined on the atomic scale using a combination of high-resolution transmission electron microscopy (TEM) and atom probe tomography (APT). Although the Al distribution in ZnO films prepared by so-called “ALD supercycles” is often presented as atomically flat δ-doped layers, in reality a broadening of the Al-dopant layers is observed with a full-width–half-maximum of ∼2 nm. In addition, an enrichment of the Al at grain boundaries is observed. The low doping efficiency for local Al densities > ∼1 nm–3 can be ascribed to the Al solubility limit in ZnO and to the suppression of the ionization of Al dopants from adjacent Al donors. PMID:29515290

Scalable quantum computer architecture with coupled donor-quantum dot qubits

DOEpatents

Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

2014-08-26

A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

Chemical Sensors Based on Optical Ring Resonators

NASA Technical Reports Server (NTRS)

Homer, Margie; Manfreda, Allison; Mansour, Kamjou; Lin, Ying; Ksendzov, Alexander

2005-01-01

Chemical sensors based on optical ring resonators are undergoing development. A ring resonator according to this concept is a closed-circuit dielectric optical waveguide. The outermost layer of this waveguide, analogous to the optical cladding layer on an optical fiber, is a made of a polymer that (1) has an index of refraction lower than that of the waveguide core and (2) absorbs chemicals from the surrounding air. The index of refraction of the polymer changes with the concentration of absorbed chemical( s). The resonator is designed to operate with relatively strong evanescent-wave coupling between the outer polymer layer and the electromagnetic field propagating along the waveguide core. By virtue of this coupling, the chemically induced change in index of refraction of the polymer causes a measurable shift in the resonance peaks of the ring. In a prototype that has been used to demonstrate the feasibility of this sensor concept, the ring resonator is a dielectric optical waveguide laid out along a closed path resembling a racetrack (see Figure 1). The prototype was fabricated on a silicon substrate by use of standard techniques of thermal oxidation, chemical vapor deposition, photolithography, etching, and spin coating. The prototype resonator waveguide features an inner cladding of SiO2, a core of SixNy, and a chemical-sensing outer cladding of ethyl cellulose. In addition to the ring Chemical sensors based on optical ring resonators are undergoing development. A ring resonator according to this concept is a closed-circuit dielectric optical waveguide. The outermost layer of this waveguide, analogous to the optical cladding layer on an optical fiber, is a made of a polymer that (1) has an index of refraction lower than that of the waveguide core and (2) absorbs chemicals from the surrounding air. The index of refraction of the polymer changes with the concentration of absorbed chemical( s). The resonator is designed to operate with relatively strong evanescent-wave coupling between the outer polymer layer and the electromagnetic field propagating along the waveguide core. By virtue of this coupling, the chemically induced change in index of refraction of the polymer causes a measurable shift in the resonance peaks of the ring. In a prototype that has been used to demonstrate the feasibility of this sensor concept, the ring resonator is a dielectric optical waveguide laid out along a closed path resembling a racetrack (see Figure 1). The prototype was fabricated on a silicon substrate by use of standard techniques of thermal oxidation, chemical vapor deposition, photolithography, etching, and spin coating. The prototype resonator waveguide features an inner cladding of SiO2, a core of SixNy, and a chemical-sensing outer cladding of ethyl cellulose. In addition to the ring res

Simulated hail impact testing of photovoltaic solar panels

NASA Technical Reports Server (NTRS)

Moore, D.; Wilson, A.; Ross, R.

1978-01-01

Techniques used to simulate and study the effect of hail on photovoltaic solar panels are described. Simulated hail stones (frozen ice spheres projected at terminal velocity) or steel balls were applied by air guns, gravity drop, or static loading. Tests with simulated hail and steel balls yielded different results. The impact strength of 10 commercially available flat-plate photovoltaic modules was tested. It was found that none of the six panel designs incorporating clear potting silicone material as the outermost layer remained undamaged by 1-in. simulated hailstones, while a photovoltaic module equipped with a 0.188-in.-thick acrylic cover sheet would be able to withstand the impact of a 2-in.-diameter hailstone.

Design and Characteristics of the Anticoincidence Detector for the GLAST Large Area Telescope

NASA Technical Reports Server (NTRS)

Moiseev, A. A.; Hartman, R. C.; Johnson, T. E.; Ormes, J. F.; Thompson, D. J.

2005-01-01

The Anti-Coincidence Detector (ACD) is the outermost detector layer in the GLAST Large Area Telescope (LAT), surrounding the top and sides of the tracker. The purpose of the ACD is to detect and veto incident cosmic ray charged particles, which outnumber cosmic gamma rays by 3-4 orders of magnitude. The challenge in ACD design is that it must have high (0.9997) detection efficiency for singly charged relativistic particles, but must also have low sensitivity to backsplash particles. These are products of high- energy interactions in the LAT calorimeter. They can cause a veto signal in the ACD, resulting in loss of good gamma-ray events.

Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling.

PubMed

Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

2016-01-07

Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.

A two-dimensional organic–inorganic hybrid compound, poly[(ethylenediamine)tri-μ-oxido-oxidocopper(II)molybdenum(VI)

PubMed Central

Gun, Ozgul; VanDerveer, Don; Emirdag-Eanes, Mehtap

2008-01-01

A new organic–inorganic two-dimensional hybrid compound, [CuMoO4(C2H8N2)], has been hydro­thermally synthesized at 443 K. The unit cell contains layers composed of CuN2O4 octa­hedra and MoO4 tetra­hedra. Corner-sharing MoO4 and CuN2O4 polyhedra form CuMoO4 bimetallic sites that are joined together through O atoms, forming an edge-sharing Cu2Mo2O4 chain along the c axis. The one-dimensional chains are further linked through bridging O atoms that join the Cu and Mo atoms into respective chains along the b axis, thus establishing layers in the bc plane. The ethyl­enediamine ligand is coordinated to the Cu atom through its two N atoms and is oriented perpendicularly to the two-dimensional –Cu—O—Mo– layers. The average distance between adjacent layers, as calculated by consideration of the closest and furthest distances between two layers, is 8.7 Å. The oxidation states of the Mo and Cu atoms of VI and II, respectively, were confirmed by bond-valence sum calculations. PMID:21200997

Enhancement of resistive switching properties in Al2O3 bilayer-based atomic switches: multilevel resistive switching

NASA Astrophysics Data System (ADS)

Vishwanath, Sujaya Kumar; Woo, Hyunsuk; Jeon, Sanghun

2018-06-01

Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (105) with better endurance (∼2000 cycles) and longer data retention (104 s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.

Implementation of atomic layer etching of silicon: Scaling parameters, feasibility, and profile control

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

Ranjan, Alok, E-mail: alok.ranjan@us.tel.com; Wang, Mingmei; Sherpa, Sonam D.

2016-05-15

Atomic or layer by layer etching of silicon exploits temporally segregated self-limiting adsorption and material removal steps to mitigate the problems associated with continuous or quasicontinuous (pulsed) plasma processes: selectivity loss, damage, and profile control. Successful implementation of atomic layer etching requires careful choice of the plasma parameters for adsorption and desorption steps. This paper illustrates how process parameters can be arrived at through basic scaling exercises, modeling and simulation, and fundamental experimental tests of their predictions. Using chlorine and argon plasma in a radial line slot antenna plasma source as a platform, the authors illustrate how cycle time, ionmore » energy, and radical to ion ratio can be manipulated to manage the deviation from ideality when cycle times are shortened or purges are incomplete. Cell based Monte Carlo feature scale modeling is used to illustrate profile outcomes. Experimental results of atomic layer etching processes are illustrated on silicon line and space structures such that iso-dense bias and aspect ratio dependent free profiles are produced. Experimental results also illustrate the profile control margin as processes move from atomic layer to multilayer by layer etching. The consequence of not controlling contamination (e.g., oxygen) is shown to result in deposition and roughness generation.« less

Prenucleation Induced by Crystalline Substrates

NASA Astrophysics Data System (ADS)

Men, H.; Fan, Z.

2018-04-01

Prenucleation refers to the phenomenon of atomic ordering in the liquid adjacent to the substrate/liquid interface at temperatures above the liquidus. In this paper, we have systematically investigated and holistically quantified the prenucleation phenomenon as a function of temperature and the lattice misfit between the substrate and the solid, using molecular dynamics (MD) simulations. Our results have confirmed that at temperatures above the liquidus, the atoms in the liquid at the interface may exhibit pronounced atomic ordering, manifested by atomic layering normal to the interface, in-plane atomic ordering parallel to the interface, and the formation of a 2-dimensional (2D) ordered structure (a few atomic layers in thickness) on the substrate surface. Holistic quantification of such atomic ordering at the interface has revealed that the atomic layering is independent of lattice misfit and is only slightly enhanced by reducing temperature while both in-plane atomic ordering and the formation of the 2D ordered structure are significantly enhanced by reducing the lattice misfit and/or temperature. This substrate-induced atomic ordering in the liquid may have a significant influence on the subsequent heterogeneous nucleation process.

Phase transitions and kinetic properties of gold nanoparticles confined between two-layer graphene nanosheets

NASA Astrophysics Data System (ADS)

Wang, Gang; Wu, Nanhua; Chen, Jionghua; Wang, Jinjian; Shao, Jingling; Zhu, Xiaolei; Lu, Xiaohua; Guo, Lucun

2016-11-01

The thermodynamic and kinetic behaviors of gold nanoparticles confined between two-layer graphene nanosheets (two-layer-GNSs) are examined and investigated during heating and cooling processes via molecular dynamics (MD) simulation technique. An EAM potential is applied to represent the gold-gold interactions while a Lennard-Jones (L-J) potential is used to describe the gold-GNS interactions. The MD melting temperature of 1345 K for bulk gold is close to the experimental value (1337 K), confirming that the EAM potential used to describe gold-gold interactions is reliable. On the other hand, the melting temperatures of gold clusters supported on graphite bilayer are corrected to the corresponding experimental values by adjusting the εAu-C value. Therefore, the subsequent results from current work are reliable. The gold nanoparticles confined within two-layer GNSs exhibit face center cubic structures, which is similar to those of free gold clusters and bulk gold. The melting points, heats of fusion, and heat capacities of the confined gold nanoparticles are predicted based on the plots of total energies against temperature. The density distribution perpendicular to GNS suggests that the freezing of confined gold nanoparticles starts from outermost layers. The confined gold clusters exhibit layering phenomenon even in liquid state. The transition of order-disorder in each layer is an essential characteristic in structure for the freezing phase transition of the confined gold clusters. Additionally, some vital kinetic data are obtained in terms of classical nucleation theory.

ELECTRON MICROSCOPE STUDY OF MYCOBACTERIUM LEPRAE AND ITS ENVIRONMENT IN A VESICULAR LEPROUS LESION

PubMed Central

Imaeda, Tamotsu; Convit, Jacinto

1962-01-01

Imaeda, Tamotsu (Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela) and Jacinto Convit. Electron microscope study of Mycobacterium leprae and its environment in a vesicular leprous lesion. J. Bacteriol. 83:43–52. 1962.—Biopsied specimens of a borderline leprosy lesion were observed with the electron microscope. In this lesion, the majority of Mycobacterium leprae were laden with cytoplasmic components. The bacilli were separated from the cytoplasm of host cells by an enclosing membrane, thus differing from the environment of well-developed lepra cells in lepromatous lesions. The cell wall is composed of a moderately dense layer. A diffuse layer is discernible outside the cell wall, separated from it by a low density space. It is suggested that the cell wall is further coated by a low density layer, although the nature of the outermost diffuse layer has not yet been determined. The plasma membrane consists of a double layer, i.e., dense inner and outer layers separated by a low density space. The outer layer is closely adjacent to the cell wall. In the region where the outer layer of the plasma membrane enters the cytoplasm and is transformed into a complex membranous structure, the inner layer encloses this membranous configuration. Together they form the intracytoplasmic membrane system. In the bacterial cytoplasm, moderately dense, presumably polyphosphate bodies are apparent. As neither these bodies nor the intracytoplasmic membrane system are visible in the degenerating bacilli, it seems probable that these two components represent indicators of the state of bacillary activity. Images PMID:16561926

Atomic and electronic structure of the CdTe(111)B–(2√3 × 4) orthogonal surface

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

Bekenev, V. L., E-mail: bekenev@ipms.kiev.ua; Zubkova, S. M.

2017-01-15

The atomic and electronic structure of four variants of Te-terminated CdTe(111)B–(2√3 × 4) orthogonal polar surface (ideal, relaxed, reconstructed, and reconstructed with subsequent relaxation) are calculated ab initio for the first time. The surface is modeled by a film composed of 12 atomic layers with a vacuum gap of ~16 Å in the layered superlattice approximation. To close Cd dangling bonds on the opposite side of the film, 24 fictitious hydrogen atoms with a charge of 1.5 electrons each are added. Ab initio calculations are performed using the Quantum Espresso program based on density functional theory. It is demonstrated thatmore » relaxation leads to splitting of the four upper layers. The band energy structures and total and layer-by-layer densities of electronic states for the four surface variants are calculated and analyzed.« less

The General Penrose Inequality: Lessons from Numerical Evidence

NASA Astrophysics Data System (ADS)

Karkowski, J.; Malec, E.

2005-01-01

Formulation of the Penrose inequality becomes ambiguous when the past and future apparent horizons do cross. We test numerically several natural possibilities of stating the inequality in punctured and boosted single- and double-black holes, in a Dain--Friedrich class of initial data and in conformally flat spheroidal data. The Penrose inequality holds true in vacuum configurations for the outermost element amongst the set of disjoint future and past apparent horizons (as expected) and (unexpectedly) for each of the outermost past and future apparent horizons, whenever these two bifurcate from an outermost minimal surface, regardless of whether they intersect or remain disjoint. In systems with matter the conjecture breaks down only if matter does not obey the dominant energy condition.

Superconducting ferecrystals: turbostratically disordered atomic-scale layered (PbSe)1.14(NbSe2)n thin films.

PubMed

Grosse, Corinna; Alemayehu, Matti B; Falmbigl, Matthias; Mogilatenko, Anna; Chiatti, Olivio; Johnson, David C; Fischer, Saskia F

2016-09-16

Hybrid electronic heterostructure films of semi- and superconducting layers possess very different properties from their bulk counterparts. Here, we demonstrate superconductivity in ferecrystals: turbostratically disordered atomic-scale layered structures of single-, bi- and trilayers of NbSe2 separated by PbSe layers. The turbostratic (orientation) disorder between individual layers does not destroy superconductivity. Our method of fabricating artificial sequences of atomic-scale 2D layers, structurally independent of their neighbours in the growth direction, opens up new possibilities of stacking arbitrary numbers of hybrid layers which are not available otherwise, because epitaxial strain is avoided. The observation of superconductivity and systematic Tc changes with nanostructure make this synthesis approach of particular interest for realizing hybrid systems in the search of 2D superconductivity and the design of novel electronic heterostructures.

High-aspect ratio zone plate fabrication for hard x-ray nanoimaging

NASA Astrophysics Data System (ADS)

Parfeniukas, Karolis; Giakoumidis, Stylianos; Akan, Rabia; Vogt, Ulrich

2017-08-01

We present our results in fabricating Fresnel zone plate optics for the NanoMAX beamline at the fourth-generation synchrotron radiation facility MAX IV, to be used in the energy range of 6-10 keV. The results and challenges of tungsten nanofabrication are discussed, and an alternative approach using metal-assisted chemical etching (MACE) of silicon is showcased. We successfully manufactured diffraction-limited zone plates in tungsten with 30 nm outermost zone width and an aspect ratio of 21:1. These optics were used for nanoimaging experiments at NanoMAX. However, we found it challenging to further improve resolution and diffraction efficiency using tungsten. High efficiency is desirable to fully utilize the advantage of increased coherence on the optics at MAX IV. Therefore, we started to investigate MACE of silicon for the nanofabrication of high-resolution and high-efficiency zone plates. The first type of structures we propose use the silicon directly as the phase-shifting material. We have achieved 6 μm deep dense vertical structures with 100 nm linewidth. The second type of optics use iridium as the phase material. The structures in the silicon substrate act as a mold for iridium coating via atomic layer deposition (ALD). A semi-dense pattern is used with line-to-space ratio of 1:3 for a so-called frequency-doubled zone plate. This way, it is possible to produce smaller structures with the tradeoff of the additional ALD step. We have fabricated 45 nm-wide and 3.6 μm-tall silicon/iridium structures.

High-resolution high-efficiency multilayer Fresnel zone plates for soft and hard x-rays

NASA Astrophysics Data System (ADS)

Sanli, Umut T.; Keskinbora, Kahraman; Gregorczyk, Keith; Leister, Jonas; Teeny, Nicolas; Grévent, Corinne; Knez, Mato; Schütz, Gisela

2015-09-01

X-ray microscopy enables high spatial resolutions, high penetration depths and characterization of a broad range of materials. Calculations show that nanometer range resolution is achievable in the hard X-ray regime by using Fresnel zone plates (FZPs) if certain conditions are satisfied. However, this requires, among other things, aspect ratios of several thousands. The multilayer (ML) type FZPs, having virtually unlimited aspect ratios, are strong candidates to achieve single nanometer resolutions. Our research is focused on the fabrication of ML-FZPs which encompasses deposition of multilayers over a glass fiber via the atomic layer deposition (ALD), which is subsequently sliced in the optimum thickness for the X-ray energy by a focused ion beam (FIB). We recently achieved aberration free imaging by resolving 21 nm features with an efficiency of up to 12.5 %, the highest imaging resolution achieved by an ML-FZP. We also showed efficient focusing of 7.9 keV X-rays down to 30 nm focal spot size (FWHM). For resolutions below ~10 nm, efficiencies would decrease significantly due to wave coupling effects. To compensate this effect high efficiency, low stress materials have to be researched, as lower intrinsic stresses will allow fabrication of larger FZPs with higher number of zones, leading to high light intensity at the focus. As a first step we fabricated an ML-FZP with a diameter of 62 μm, an outermost zone width of 12 nm and 452 active zones. Further strategies for fabrication of high resolution high efficiency multilayer FZPs will also be discussed.

Surface-structure sensitivity of CeO 2 nanocrystals in photocatalysis and enhancing the reactivity with nanogold

DOE PAGES

Lei, Wanying; Zhang, Tingting; Gu, Lin; ...

2015-06-19

Structure–function correlations are a central theme in heterogeneous (photo)catalysis. In this research, using aberration-corrected scanning transmission electron microscopy (STEM), the atomic surface structures of well-defined one-dimensional (1D) CeO 2 nanorods (NRs) and 3D nanocubes (NCs) are directly visualized at subangstrom resolution. CeO 2 NCs predominantly expose the {100} facet, with {110} and {111} as minor cutoff facets at the respective edges and corners. Notably, the outermost surface layer of the {100} facet is nearly O-terminated. Neither surface relaxations nor reconstructions on {100} are observed, indicating unusual polarity compensation, which is primarily mediated by near-surface oxygen vacancies. The surface of CeOmore » 2 NRs is highly stepped, with the enclosed {110} facet exposing Ce cations and O anions on terraces. On the basis of STEM profile-view imaging and electronic structure analysis, the photoreactivity of CeO2 nanocrystals toward aqueous methyl orange degradation under UV is revealed to be surface-structure-sensitive, following the order: {110} >> {100}. The underlying surface-structure sensitivity can be attributed to the variation in low-coordinate surface cerium cations between {110} and {100} facets. To further enhance light absorption, Au nanoparticles (NPs) are deposited on CeO 2 NRs to form Au/CeO 2 plasmonic nanocomposites, which dramatically promotes the photoreactivity that is Au particle size- and excitation light wavelength-dependent. The mechanisms responsible for the enhancement of photocatalytic activity are discussed, highlighting the crucial role of photoexcited charge carrier transfer.« less

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

Ganesh, Panchapakesan; Kent, Paul R; Mochalin, Vadym N

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbon nanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core ofmore » the nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbon nanostructure appears, with a shell-shell spacing of about {approx}3.4 {angstrom} for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large ({approx}29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.« less

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

Ren, Xiaochen; Singh, Arunima K.; Fang, Lei

Impurity doping in two-dimensional (2D) materials can provide a route to tuning electronic properties, so it is important to be able to determine the distribution of dopant atoms within and between layers. Here we report the totnographic mapping of dopants in layered 2D materials with atomic sensitivity and subnanometer spatial resolution using atom, probe tomography (APT). Also, APT analysis shows that Ag dopes both Bi 2Se 3 and PbSe layers in (PbSe) 5(Bi 2Se 3) 3, and correlations :in the position of Ag atoms suggest a pairing across neighboring Bi 2Se 3 and PbSe layers. Finally, density functional theory (DFT)more » calculations confirm the favorability of substitutional-doping for both Pb and Bi and provide insights into the,observed spatial correlations in dopant locations.« less

Alkali (Li, K and Na) and alkali-earth (Be, Ca and Mg) adatoms on SiC single layer

NASA Astrophysics Data System (ADS)

Baierle, Rogério J.; Rupp, Caroline J.; Anversa, Jonas

2018-03-01

First-principles calculations within the density functional theory (DFT) have been addressed to study the energetic stability, and electronic properties of alkali and alkali-earth atoms adsorbed on a silicon carbide (SiC) single layer. We observe that all atoms are most stable (higher binding energy) on the top of a Si atom, which moves out of the plane (in the opposite direction to the adsorbed atom). Alkali atoms adsorbed give raise to two spin unpaired electronic levels inside the band gap leading the SiC single layer to exhibit n-type semiconductor properties. For alkaline atoms adsorbed there is a deep occupied spin paired electronic level inside the band gap. These finding suggest that the adsorption of alkaline and alkali-earth atoms on SiC layer is a powerful feature to functionalize two dimensional SiC structures, which can be used to produce new electronic, magnetic and optical devices as well for hydrogen and oxygen evolution reaction (HER and OER, respectively). Furthermore, we observe that the adsorption of H2 is ruled by dispersive forces (van der Waals interactions) while the O2 molecule is strongly adsorbed on the functionalized system.

Migration and Differentiation of GFP-transplanted Bone Marrow-derived Cells into Experimentally Induced Periodontal Polyp in Mice.

PubMed

Matsuda, Saeka; Shoumura, Masahito; Osuga, Naoto; Tsujigiwa, Hidetsugu; Nakano, Keisuke; Okafuji, Norimasa; Ochiai, Takanaga; Hasegawa, Hiromasa; Kawakami, Toshiyuki

2016-01-01

Perforation of floor of the dental pulp is often encountered during root canal treatment in routine clinical practice of dental caries. If perforation were large, granulation tissue would grow to form periodontal polyp. Granulation tissue consists of proliferating cells however their origin is not clear. It was shown that the cells in granulation tissue are mainly from migration of undifferentiated mesenchymal cells of the bone marrow. Hence, this study utilized GFP bone marrow transplantation mouse model. The floor of the pulp chamber in maxillary first molar was perforated using ½ dental round bur. Morphological assessment was carried out by micro CT and microscopy and GFP cell mechanism was further assessed by immunohistochemistry using double fluorescent staining with GFP-S100A4; GFP-Runx2 and GFP-CD31. Results of micro CT revealed alveolar bone resorption and widening of periodontal ligament. Histopathological examination showed proliferation of fibroblasts with some round cells and blood vessels in the granulation tissue. At 2 weeks, the outermost layer of the granulation tissue was lined by squamous cells with distinct intercellular bridges. At 4 weeks, the granulation tissue became larger than the perforation and the outermost layer was lined by relatively typical stratified squamous epithelium. Double immunofluorescent staining of GFP and Runx2 revealed that both proteins were expressed in spindle-shaped cells. Double immunofluorescent staining of GFP and CD31 revealed that both proteins were expressed in vascular endothelial cells in morphologically distinct vessels. The results suggest that fibroblasts, periodontal ligament fibroblasts and blood vessels in granulation tissue were derived from transplanted-bone marrow cells. Thus, essential growth of granulation tissue in periodontal polyp was caused by the migration of undifferentiated mesenchymal cells derived from bone marrow, which differentiated into fibroblasts and later on differentiated into other cells in response to injury.

RUTI: a new chance to shorten the treatment of latent tuberculosis infection.

PubMed

Cardona, Pere-Joan

2006-01-01

Treatment of latent tuberculosis infection (LTBI) requires a long period of chemotherapy (9 months), which makes treatment-compliance extremely difficult. Current knowledge of latent bacilli and of the lesions with which they are associated suggests that these bacilli survive in granulomas with a central necrotic core and an outermost layer of foamy macrophages (FM) that represent an important immunosuppressive barrier. The presence of FM, which is especially strong in mice, explains not only the kinetics of the drainage of dead bacilli, debris and surfactant, but also how latent bacilli can escape from the granuloma and re-grow in the periphery, particularly in the alveolar spaces where they can disseminate easily. RUTI, a therapeutic vaccine made of detoxified, fragmented Mycobacterium tuberculosis cells, delivered in liposomes, was used to assess its effectiveness in a short period of chemotherapy (1 month). The rationale of this therapy was first to take advantage of the bactericidal properties of chemotherapy to kill active growing bacilli, eliminate the outermost layer of FM and reduce local inflammatory responses so as to avoid the predictable Koch phenomenon caused by M. tuberculosis antigens when given therapeutically. After chemotherapy, RUTI can be inoculated to reduce the probability of regrowth of the remaining latent bacilli. RUTI has already demonstrated its efficacy in controlling LTBI in experimental models of mice and guinea-pigs after a short period of chemotherapy; these experiments in animals showed the induction of a mixed Th1/Th2/Th3, polyantigenic response with no local or systemic toxicity. Local accumulation of specific CD8 T cells and a strong humoral response are characteristic features of RUTI that explain its protective properties; these are particular improvements when compared with BCG, although the regulatory response to RUTI may also be an important advantage. Further experiments using bigger animals (goats and mini-pigs) will provide more data on the efficacy of RUTI before starting phase I clinical trials.

Origins of Moiré Patterns in CVD-grown MoS2 Bilayer Structures at the Atomic Scales.

PubMed

Wang, Jin; Namburu, Raju; Dubey, Madan; Dongare, Avinash M

2018-06-21

The chemical vapor deposition (CVD)-grown two-dimensional molybdenum disulfide (MoS 2 ) structures comprise of flakes of few layers with different dimensions. The top layers are relatively smaller in size than the bottom layers, resulting in the formation of edges/steps across adjacent layers. The strain response of such few-layer terraced structures is therefore likely to be different from exfoliated few-layered structures with similar dimensions without any terraces. In this study, the strain response of CVD-grown few-layered MoS 2 terraced structures is investigated at the atomic scales using classic molecular dynamics (MD) simulations. MD simulations suggest that the strain relaxation of CVD-grown triangular terraced structures is observed in the vertical displacement of the atoms across the layers that results in the formation of Moiré patterns. The Moiré islands are observed to nucleate at the corners or edges of the few-layered structure and propagate inwards under both tensile and compressive strains. The nucleation of these islands is observed to happen at tensile strains of ~ 2% and at compressive strains of ~2.5%. The vertical displacements of the atoms and the dimensions of the Moiré islands predicted using the MD simulation are in excellent agreement with that observed experimentally.

Rydberg States of Alkali Metal Atoms on Superfluid Helium Droplets - Theoretical Considerations

NASA Astrophysics Data System (ADS)

Pototschnig, Johann V.; Lackner, Florian; Hauser, Andreas W.; Ernst, Wolfgang E.

2017-06-01

The bound states of electrons on the surface of superfluid helium have been a research topic for several decades. One of the first systems treated was an electron bound to an ionized helium cluster. Here, a similar system is considered, which consists of a helium droplet with an ionized dopant inside and an orbiting electron on the outside. In our theoretical investigation we select alkali metal atoms (AK) as central ions, stimulated by recent experimental studies of Rydberg states for Na, Rb, and Cs attached to superfluid helium nanodroplets. Experimental spectra , obtained by electronic excitation and subsequent ionization, showed blueshifts for low lying electronic states and redshifts for Rydberg states. In our theoretical treatment the diatomic AK^+-He potential energy curves are first computed with ab initio methods. These potentials are then used to calculate the solvation energy of the ion in a helium droplet as a function of the number of atoms. Additional potential terms, derived from the obtained helium density distribution, are added to the undisturbed atomic pseudopotential in order to simulate a 'modified' potential felt by the outermost electron. This allows us to compute a new set of eigenstates and eigenenergies, which we compare to the experimentally observed energy shifts for highly excited alkali metal atoms on helium nanodroplets. A. Golov and S. Sekatskii, Physica B, 1994, 194, 555-556 E. Loginov, C. Callegari, F. Ancilotto, and M. Drabbels, J. Phys. Chem. A, 2011, 115, 6779-6788 F. Lackner, G. Krois, M. Koch, and W. E. Ernst, J. Phys. Chem. Lett., 2012, 3, 1404-1408 F. Lackner, G. Krois, M. Theisen, M. Koch, and W. E. Ernst, Phys. Chem. Chem. Phys., 2011, 13, 18781-18788

Possible Charge-Exchange X-Ray Emission in the Cygnus Loop Detected with Suzaku

NASA Technical Reports Server (NTRS)

Katsuda, Satoru; Tsunemi, Hiroshi; Mori, Koji; Uchida, Hiroyuki; Kosugi, Hiroko; Kimura, Masashi; Nakajima, Hiroshi; Takakura, Satoru; Petre, Robert; Hewitt. John W.;

Polymerization of a divalent/tetravalent metal-storing atom-mimicking dendrimer.

PubMed

Albrecht, Ken; Hirabayashi, Yuki; Otake, Masaya; Mendori, Shin; Tobari, Yuta; Azuma, Yasuo; Majima, Yutaka; Yamamoto, Kimihisa

2016-12-01

The phenylazomethine dendrimer (DPA) has a layer-by-layer electron density gradient that is an analog of the Bohr atom (atom mimicry). In combination with electron pair mimicry, the polymerization of this atom-mimicking dendrimer was achieved. The valency of the mimicked atom was controlled by changing the chemical structure of the dendrimer. By mimicking a divalent atom, a one-dimensional (1D) polymer was obtained, and by using a planar tetravalent atom mimic, a 2D polymer was obtained. These poly(dendrimer) polymers could store Lewis acids (SnCl 2 ) in their unoccupied orbitals, thus indicating that these poly(dendrimer) polymers consist of a series of nanocontainers.

Origin of the DA and non-DA white dwarf stars

NASA Technical Reports Server (NTRS)

Shipman, Harry L.

1989-01-01

Various proposals for the bifurcation of the white dwarf cooling sequence are reviewed. 'Primordial' theories, in which the basic bifurcation of the white dwarf sequence is rooted in events predating the white dwarf stage of stellar evolution, are discussed, along with the competing 'mixing' theories in which processes occurring during the white dwarf stage are responsible for the existence of DA or non-DA stars. A new proposal is suggested, representing a two-channel scenario. In the DA channel, some process reduces the hydrogen layer mass to the value of less than 10 to the -7th. The non-DA channel is similar to that in the primordial scenario. These considerations suggest that some mechanism operates in both channels to reduce the thickness of the outermost layer of the white dwarf. It is also noted that accretion from the interstellar medium has little to do with whether a particular white dwarf becomes a DA or a non-DA star.

Marginally outer trapped surfaces and symmetries

NASA Astrophysics Data System (ADS)

Carrasco, Alberto; Mars, Marc

2009-05-01

We study properties of outermost marginally outer trapped surfaces in slices of space-times possessing certain symmetries, like isometries, homotheties or conformal Killings. In particular, we find restrictions on these surfaces for the vector field generating the symmetry. As an application we give a result of non-existence of outermost marginally outer trapped surfaces in accelerated Friedmann-Lemaître-Roberson-Walker spacetimes.

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

DOE PAGES

Celik, Fuat E.; Mavrikakis, Manos

2015-01-12

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While themore » metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.« less

Stability of Surface and Subsurface Hydrogen on and in Au/Ni Near-Surface Alloys

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

Celik, Fuat E.; Mavrikakis, Manos

2015-10-01

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While themore » metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.« less

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

NASA Astrophysics Data System (ADS)

Celik, Fuat E.; Mavrikakis, Manos

2015-10-01

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While the metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.

Assembly of the outermost spore layer: pieces of the puzzle are coming together.

PubMed

Stewart, George C

2017-05-01

Certain endospore-forming soil dwelling bacteria are important human, animal or insect pathogens. These organisms produce spores containing an outer layer, the exosporium. The exosporium is the site of interactions between the spore and the soil environment and between the spore and the infected host during the initial stages of infection. The composition and assembly process of the exosporium are poorly understood. This is partly due to the extreme stability of the exosporium that has proven to be refractive to existing methods to deconstruct the intact structure into its component parts. Although more than 20 proteins have been identified as exosporium-associated, their abundance, relationship to other proteins and the processes by which they are assembled to create the exosporium are largely unknown. In this issue of Molecular Microbiology, Terry, Jiang, and colleagues in Per Bullough's laboratory show that the ExsY protein is a major structural protein of the exosporium basal layer of B. cereus family spores and that it can self-assemble into complex structures that possess many of the structural features characteristic of the exosporium basal layer. The authors refined a model for exosporium assembly. Their findings may have implications for exosporium formation in other spore forming bacteria, including Clostridium species. © 2017 John Wiley & Sons Ltd.

Characterization of a yeast sporulation-specific P450 family protein, Dit2, using an in vitro assay to crosslink formyl tyrosine.

PubMed

Bemena, Leo D; Mukama, Omar; Wang, Ning; Gao, Xiao-Dong; Nakanishi, Hideki

2018-02-01

The outermost layer of the yeast Saccharomyces cerevisiae spore, termed the dityrosine layer, is primarily composed of bisformyl dityrosine. Bisformyl dityrosine is produced in the spore cytosol by crosslinking of two formyl tyrosine molecules, after which it is transported to the nascent spore wall and assembled into the dityrosine layer by an unknown mechanism. A P450 family protein, Dit2, is believed to mediate the crosslinking of bisformyl dityrosine molecules. To characterize Dit2 and gain insight into the biological process of dityrosine layer formation, we performed an in vitro assay to crosslink formyl tyrosine with using permeabilized cells. For an unknown reason, the production of bisformyl dityrosine could not be confirmed under our experimental conditions, but dityrosine was detected in acid hydrolysates of the reaction mixtures in a Dit2 dependent manner. Thus, Dit2 mediated the crosslinking of formyl tyrosine in vitro. Dityrosine was detected when formyl tyrosine, but not tyrosine, was used as a substrate and the reaction required NADPH as a cofactor. Intriguingly, apart from Dit2, we found that the spore wall, but not the vegetative cell wall, contains bisformyl dityrosine crosslinking activity. This activity may be involved in the assembly of the dityrosine layer. © The Authors 2017. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

Investigations into the impact of various substrates and ZnO ultra thin seed layers prepared by atomic layer deposition on growth of ZnO nanowire array

PubMed Central

2012-01-01

The impact of various substrates and zinc oxide (ZnO) ultra thin seed layers prepared by atomic layer deposition on the geometric morphology of subsequent ZnO nanowire arrays (NWs) fabricated by the hydrothermal method was investigated. The investigated substrates included B-doped ZnO films, indium tin oxide films, single crystal silicon (111), and glass sheets. Scanning electron microscopy and X-ray diffraction measurements revealed that the geometry and aligment of the NWs were controlled by surface topography of the substrates and thickness of the ZnO seed layers, respectively. According to atomic force microscopy data, we suggest that the substrate, fluctuate amplitude and fluctuate frequency of roughness on ZnO seed layers have a great impact on the alignment of the resulting NWs, whereas the influence of the seed layers' texture was negligible. PMID:22759838

STM/STS Study of the Sb (111) Surface

NASA Astrophysics Data System (ADS)

Chekmazov, S. V.; Bozhko, S. I.; Smirnov, A. A.; Ionov, A. M.; Kapustin, A. A.

An Sb crystal is a Peierls insulator. Formation of double layers in the Sb structure is due to the shift of atomic planes (111) next but one along the C3 axis. Atomic layers inside the double layer are connected by covalent bonds. The interaction between double layers is determined mainly by Van der Waals forces. The cleave of an Sb single crystal used to be via break of Van der Waals bonds. However, using scanning tunneling microscopy (STM) and spectroscopy (STS) we demonstrated that apart from islands equal in thickness to the double layer, steps of one atomic layer in height also exist on the cleaved Sb (111) surface. Formation of "unpaired" (111) planes on the surface leads to a local break of conditions of Peierls transition. STS experiment reveals higher local density of states (LDOS) measured for "unpaired" (111) planes in comparison with those for the double layer.

Persistent mobility edges and anomalous quantum diffusion in order-disorder separated quantum films

NASA Astrophysics Data System (ADS)

Zhong, Jianxin; Stocks, G. Malcolm

2007-01-01

A concept of order-disorder separated quantum films is proposed for the design of ultrathin quantum films of a few atomic layers thick with unconventional transport properties. The concept is demonstrated through studying an atomic bilayer comprised of an ordered layer and a disordered layer. Without the disordered layer or the ordered layer, the system is a conducting two-dimensional (2D) crystal or an insulating disordered 2D electron system. Without the order-disorder phase separation, a disordered bilayer is insulating under large disorder. In an order-disorder separated atomic bilayer, however, we show that the system behaves remarkably different from conventional ordered or disordered electron systems, exhibiting metal-insulator transitions with persistent mobility edges and superdiffusive anomalous quantum diffusion.

Dynamics behavior of lithium in graphite lattice: MD calculation approach

NASA Astrophysics Data System (ADS)

Shimizu, A.; Tachikawa, H.

2000-12-01

In order to investigate the diffusion process of Li atom in graphite, molecular dynamics simulation was achieved on the basis of molecular mechanics 2 (MM2) method using four layers cluster model one of which is composed of C150H30 with terminating hydrogen atoms. According to the simulations at 500 K, Li atom stabilizes initially around the center of mass, gets out of the graphite layers after 3.0 ps through diffusion, which is different from the movement of Li+ ion captured by the dangling bonds of the edge carbon atoms. The diffusion process of Li atom is found to be composed of following four steps in series: (1) vibration around the stabilization point; (2) bulk diffusion; (3) vibration under influence of the dangling bonds of edge carbon atoms; and (4) escape from the graphite layers. The diffusivity for step (3) is smaller than that for step (2).

Growth of germanium on Au(111): formation of germanene or intermixing of Au and Ge atoms?

PubMed

Cantero, Esteban D; Solis, Lara M; Tong, Yongfeng; Fuhr, Javier D; Martiarena, María Luz; Grizzi, Oscar; Sánchez, Esteban A

2017-07-19

We studied the growth of Ge layers on Au(111) under ultra-high vacuum conditions from the submonolayer regime up to a few layers with Scanning Tunneling Microscopy (STM), Direct Recoiling Spectroscopy (DRS) and Low Energy Electron Diffraction (LEED). Most STM images for the thicker layers are consistent with a commensurate 5 × 8 arrangement. The high surface sensitivity of TOF-DRS allows us to confirm the coexistence of Au and Ge atoms in the top layer for all stages of growth. An estimation of the Au to Ge ratio at the surface of the thick layer gives about 1 Au atom per 2 Ge ones. When the growth is carried out at sample temperatures higher than about 420 K, a fraction of the deposited Ge atoms migrate into the bulk of Au. This incorporation of Ge into the bulk reduces the growth rate of the Ge films, making it more difficult to obtain films thicker than a few layers. After sputtering the Ge/Au surface, the segregation of bulk Ge atoms to the surface occurs for temperatures ≥600 K. The surface obtained after segregation of Ge reaches a stable condition (saturation) with an n × n symmetry with n on the order of 14.

The fabrication of a double-layer atom chip with through silicon vias for an ultra-high-vacuum cell

NASA Astrophysics Data System (ADS)

Chuang, Ho-Chiao; Lin, Yun-Siang; Lin, Yu-Hsin; Huang, Chi-Sheng

2014-04-01

This study presents a double-layer atom chip that provides users with increased diversity in the design of the wire patterns and flexibility in the design of the magnetic field. It is more convenient for use in atomic physics experiments. A negative photoresist, SU-8, was used as the insulating layer between the upper and bottom copper wires. The electrical measurement results show that the upper and bottom wires with a width of 100 µm can sustain a 6 A current without burnout. Another focus of this study is the double-layer atom chips integrated with the through silicon via (TSV) technique, and anodically bonded to a Pyrex glass cell, which makes it a desired vacuum chamber for atomic physics experiments. Thus, the bonded glass cell not only significantly reduces the overall size of the ultra-high-vacuum (UHV) chamber but also conducts the high current from the backside to the front side of the atom chip via the TSV under UHV (9.5 × 10-10 Torr). The TSVs with a diameter of 70 µm were etched through by the inductively coupled plasma ion etching and filled by the bottom-up copper electroplating method. During the anodic bonding process, the electroplated copper wires and TSVs on atom chips also need to pass the examination of the required bonding temperature of 250 °C, under an applied voltage of 1000 V. Finally, the UHV test of the double-layer atom chips with TSVs at room temperature can be reached at 9.5 × 10-10 Torr, thus satisfying the requirements of atomic physics experiments under an UHV environment.

Nano-decoration of the Hemagglutinating Virus of Japan envelope (HVJ-E) using a layer-by-layer assembly technique.

PubMed

Okada, Takaharu; Uto, Koichiro; Sasai, Masao; Lee, Chun Man; Ebara, Mitsuhiro; Aoyagi, Takao

2013-06-18

In this study, we created a nanoscale layer of hyaluronic acid (HA) on the inactivated Hemagglutinating Virus of Japan envelope (HVJ-E) via a layer-by-layer (LbL) assembly technique for CD-44 targeted delivery. HVJ-E was selected as the template virus because it has shown a tumor-suppressing ability by eliciting inflammatory cytokine production in dendritic cells. Although it has been required to increase the tumor-targeting ability and reduce nonspecific binding because HVJ-E fuses with virtually all cells and induces hemagglutination in the bloodstream, complete modifications of single-envelope-type viruses with HA have been difficult. Therefore, we studied the surface ζ potential of HVJ-E at different pH values and carefully examined the deposition conditions for the first layer using three cationic polymers: poly-L-lysine (PLL), chitosan (CH), and glycol chitosan (GC). GC-coated HVJ-E particles showed the highest disperse ability under physiological pH and salt conditions without aggregation. An HA layer was then prepared via alternating deposition of HA and GC. The successive decoration of multilayers on HVJ-E has been confirmed by dynamic light scattering (DLS), ζ potentials, and transmission electron microscopy (TEM). An enzymatic degradation assay revealed that only the outermost HA layer was selectively degraded by hyaluronidase. However, entire layers were destabilized at lower pH. Therefore, the HA/GC-coated HVJ-E describe here can be thought of as a potential bomb for cancer immunotherapy because of the ability of targeting CD44 as well as the explosion of nanodecorated HA/GC layers at endosomal pH while preventing nonspecific binding at physiological pH and salt conditions such as in the bloodstream or normal tissues.

Enhancement of resistive switching properties in Al2O3 bilayer-based atomic switches: multilevel resistive switching.

PubMed

Vishwanath, Sujaya Kumar; Woo, Hyunsuk; Jeon, Sanghun

2018-06-08

Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (10 5 ) with better endurance (∼2000 cycles) and longer data retention (10 4 s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.

Stratification of earth's outermost core inferred from SmKS array data

NASA Astrophysics Data System (ADS)

Kaneshima, Satoshi; Matsuzawa, Takanori

2015-12-01

S mKS arrivals recorded by large-scale broadband seismometer arrays are analyzed to investigate the depth profile of P wave speed ( V p ) in the outermost core. The V p structure of the upper 700 km of the outer core has been determined using S mKS waves of Fiji-Tonga events recorded at stations in Europe. According to a recent outer core model (KHOMC), the V p value is 0.45 % slower at the core mantle boundary (CMB) than produced by the Preliminary Reference Earth Model (PREM), and the slow anomaly gradually diminishes to insignificant values at ˜300 km below the CMB. In this study, after verifying these KHOMC features, we show that the differential travel times measured for S mKS waves that are recorded by other large-scale arrays sampling laterally different regions are well matched by KHOMC. We also show that KHOMC precisely fits the observed relative slowness values between S2KS, S3KS, and S4KS (S mKS waves with m= 2, 3, and 4). Based on these observations, we conclude that S mKS predominantly reflect the outer core structure. Then we evaluate biases of secondary importance which may be caused by mantle heterogeneity. The KHOMC V p profile can be characterized by a significant difference in the radial V p gradient between the shallower 300 km and the deeper part of the upper 700 km of the core. The shallower part has a V p gradient of -0.0018 s -1, which is steeper by 0.0001 s -1 when compared to the deeper core presented by PREM. The steeper V p gradient anomaly of the uppermost core corresponds to a radial variation in the pressure derivative of the bulk modulus, K '= d K/ d P. The K ' value is 3.7, which is larger by about 0.2 than that of the deeper core. The radial variation in K ' is too large to have a purely thermal origin, according to recent ab initio calculations on liquid iron alloys, and thus requires a thick and compositionally stratified layering at the outermost outer core.

Microporous structure with layered interstitial surface treatment, and method and apparatus for preparation thereof

NASA Technical Reports Server (NTRS)

Koontz, Steven L. (Inventor)

1994-01-01

A microporous structure with layered interstitial surface treatments, and method and apparatus for preparation thereof is presented. The structure is prepared by sequentially subjecting a uniformly surface-treated structure to atomic oxygen treatment to remove an outer layer of surface treatment to a generally uniform depth, and then surface treating the so exposed layer with another surface treating agent. The atomic oxygen/surface treatment steps may optionally be repeated, each successive time to a lesser depth, to produce a microporous structure having multilayered surface treatments. The apparatus employs at least one side arm from a main atomic oxygen-containing chamber. The side arm has characteristic relaxation times such that a uniform atomic oxygen dose rate is delivered to a specimen positioned transversely in the side arm spaced from the main gas chamber.

Modulating drug release from gastric-floating microcapsules through spray-coating layers.

PubMed

Lee, Wei Li; Tan, Jun Wei Melvin; Tan, Chaoyang Nicholas; Loo, Say Chye Joachim

2014-01-01

Floating dosage forms with prolonged gastric residence time have garnered much interest in the field of oral delivery. However, studies had shown that slow and incomplete release of hydrophobic drugs during gastric residence period would reduce drug absorption and cause drug wastage. Herein, a spray-coated floating microcapsule system was developed to encapsulate fenofibrate and piroxicam, as model hydrophobic drugs, into the coating layers with the aim of enhancing and tuning drug release rates. Incorporating fenofibrate into rubbery poly(caprolactone) (PCL) coating layer resulted in a complete and sustained release for up to 8 h, with outermost non-drug-holding PCL coating layer serving as a rate-controlling membrane. To realize a multidrug-loaded system, both hydrophilic metformin HCl and hydrophobic fenofibrate were simultaneously incorporated into these spray-coated microcapsules, with metformin HCl and fenofibrate localized within the hollow cavity of the capsule and coating layer, respectively. Both drugs were observed to be completely released from these coated microcapsules in a sustained manner. Through specific tailoring of coating polymers and their configurations, piroxicam loaded in both the outer polyethylene glycol and inner PCL coating layers was released in a double-profile manner (i.e. an immediate burst release as the loading dose, followed by a sustained release as the maintenance dose). The fabricated microcapsules exhibited excellent buoyancy in simulated gastric fluid, and provided controlled and sustained release, thus revealing its potential as a rate-controlled oral drug delivery system.

Atomically thin gallium layers from solid-melt exfoliation

PubMed Central

Kochat, Vidya; Samanta, Atanu; Zhang, Yuan; Bhowmick, Sanjit; Manimunda, Praveena; Asif, Syed Asif S.; Stender, Anthony S.; Vajtai, Robert; Singh, Abhishek K.; Tiwary, Chandra S.; Ajayan, Pulickel M.

2018-01-01

Among the large number of promising two-dimensional (2D) atomic layer crystals, true metallic layers are rare. Using combined theoretical and experimental approaches, we report on the stability and successful exfoliation of atomically thin “gallenene” sheets on a silicon substrate, which has two distinct atomic arrangements along crystallographic twin directions of the parent α-gallium. With a weak interface between solid and molten phases of gallium, a solid-melt interface exfoliation technique is developed to extract these layers. Phonon dispersion calculations show that gallenene can be stabilized with bulk gallium lattice parameters. The electronic band structure of gallenene shows a combination of partially filled Dirac cone and the nonlinear dispersive band near the Fermi level, suggesting that gallenene should behave as a metallic layer. Furthermore, it is observed that the strong interaction of gallenene with other 2D semiconductors induces semiconducting to metallic phase transitions in the latter, paving the way for using gallenene as promising metallic contacts in 2D devices. PMID:29536039

Atomic Layer Deposition of Titanium Oxide on Single-Layer Graphene: An Atomic-Scale Study toward Understanding Nucleation and Growth

PubMed Central

2017-01-01

Controlled synthesis of a hybrid nanomaterial based on titanium oxide and single-layer graphene (SLG) using atomic layer deposition (ALD) is reported here. The morphology and crystallinity of the oxide layer on SLG can be tuned mainly with the deposition temperature, achieving either a uniform amorphous layer at 60 °C or ∼2 nm individual nanocrystals on the SLG at 200 °C after only 20 ALD cycles. A continuous and uniform amorphous layer formed on the SLG after 180 cycles at 60 °C can be converted to a polycrystalline layer containing domains of anatase TiO2 after a postdeposition annealing at 400 °C under vacuum. Using aberration-corrected transmission electron microscopy (AC-TEM), characterization of the structure and chemistry was performed on an atomic scale and provided insight into understanding the nucleation and growth. AC-TEM imaging and electron energy loss spectroscopy revealed that rocksalt TiO nanocrystals were occasionally formed at the early stage of nucleation after only 20 ALD cycles. Understanding and controlling nucleation and growth of the hybrid nanomaterial are crucial to achieving novel properties and enhanced performance for a wide range of applications that exploit the synergetic functionalities of the ensemble. PMID:28356613

Double-atomic layer of Tl on Si(111): Atomic arrangement and electronic properties

NASA Astrophysics Data System (ADS)

Mihalyuk, Alexey N.; Bondarenko, Leonid V.; Tupchaya, Alexandra Y.; Gruznev, Dimitry V.; Chou, Jyh-Pin; Hsing, Cheng-Rong; Wei, Ching-Ming; Zotov, Andrey V.; Saranin, Alexander A.

2018-02-01

Metastable double-atomic layer of Tl on Si(111) has recently been found to display interesting electric properties, namely superconductivity below 0.96 K and magnetic-field-induced transition into an insulating phase intermediated by a quantum metal state. In the present work, using a set of experimental techniques, including low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, in a combination with density-functional-theory calculations, we have characterized atomic and electronic properties of the Tl double layer on Si(111). The double Tl layer has been concluded to contain ∼ 2.4 monolayer of Tl. A top Tl layer has a '1 × 1' basic structure and displays 6 × 6 moiré pattern which originates from various residence sites of Tl atoms. Upon cooling below ∼ 140 K, the 6 × 6 moiré pattern changes to that having a 6√{ 3} × 6√{ 3} periodicity. However, the experimentally determined electron band dispersions show a 1 × 1 periodicity. The calculated band structure unfolded into the 1 × 1 surface Brillouin zone reproduces well the main features of the photoelectron spectra.

Enhanced Kinetics of Electrochemical Hydrogen Uptake and Release by Palladium Powders Modified by Electrochemical Atomic Layer Deposition

DOE PAGES

Benson, David M.; Tsang, Chu F.; Sugar, Joshua Daniel; ...

2017-04-28

One method for the formation of nanofilms of materials, is Electrochemical atomic layer deposition (E-ALD), one atomic layer at a time. It uses the galvanic exchange of a less noble metal, deposited using underpotential deposition (UPD), to produce an atomic layer of a more noble element by reduction of its ions. This process is referred to as surface limited redox replacement and can be repeated in a cycle to grow thicker deposits. Previously, we performed it on nanoparticles and planar substrates. In the present report, E-ALD is applied for coating a submicron-sized powder substrate, making use of a new flowmore » cell design. E-ALD is used to coat a Pd powder substrate with different thicknesses of Rh by exchanging it for Cu UPD. Furthermore, cyclic voltammetry and X-ray photoelectron spectroscopy indicate an increasing Rh coverage with increasing numbers of deposition cycles performed, in a manner consistent with the atomic layer deposition (ALD) mechanism. Cyclic voltammetry also indicated increased kinetics of H sorption and desorption in and out of the Pd powder with Rh present, relative to unmodified Pd.« less

Establishment of a Novel Lingual Organoid Culture System: Generation of Organoids Having Mature Keratinized Epithelium from Adult Epithelial Stem Cells

NASA Astrophysics Data System (ADS)

Hisha, Hiroko; Tanaka, Toshihiro; Kanno, Shohei; Tokuyama, Yoko; Komai, Yoshihiro; Ohe, Shuichi; Yanai, Hirotsugu; Omachi, Taichi; Ueno, Hiroo

2013-11-01

Despite the strong need for the establishment of a lingual epithelial cell culture system, a simple and convenient culture method has not yet been established. Here, we report the establishment of a novel lingual epithelium organoid culture system using a three-dimensional matrix and growth factors. Histological analyses showed that the generated organoids had both a stratified squamous epithelial cell layer and a stratum corneum. Very recently, we showed via a multicolor lineage tracing method that Bmi1-positive stem cells exist at the base of the epithelial basal layer in the interpapillary pit. Using our new culture system, we found that organoids could be generated by single Bmi1-positive stem cells and that in the established organoids, multiple Bmi1-positive stem cells were generated at the outermost layer. Moreover, we observed that organoids harvested at an early point in culture could be engrafted and maturate in the tongue of recipient mice and that the organoids generated from carcinogen-treated mice had an abnormal morphology. Thus, this culture system presents valuable settings for studying not only the regulatory mechanisms of lingual epithelium but also lingual regeneration and carcinogenesis.

Purification of Lactobacillus acidophilus surface-layer protein and its immunomodulatory effects on RAW264.7 cells.

PubMed

Zhang, Dandan; Wu, Mengting; Guo, Yuxing; Xun, Mingyue; Wang, Wenwen; Wu, Zhen; Pan, Daodong

2017-09-01

Surface-layer proteins (SLP) have been found in the outermost layer of the cell wall in many types of lactobacillus are considered to be an important factor with respect to intestinal immunity. The present study compared the effects of SLP extracted by different concentrations of LiCl and carbamide, and subsequently identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism and differential scanning calorimetry. Furthermore, RAW 264.7 cells were used to evaluate the immunomodulatory effects of SLP. SLP were derived from Lactobacillus acidophilus CICC6074 with a molecular weight of 46 kDa, and consisted of 16.9% α-helix, 42.3% β-sheet, 20.8% β-turns and 22.5% random coils. SLP promoted NO secretion and higher quantities of NO were produced as the SLP concentrations increased. SLP concentrations over 50 µg mL -1 significantly decreased the amount of tumor necrosis factor-α secreted by RAW264.7 cells. SLP can trigger immunomodulatory effects in RAW 264.7 cells. This provides crucial information that will enable the further use of L. acidophilus in food, medicine and other products. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Initial development of the endocarp in Lithraea brasiliensis Marchand (Anacardiaceae): with taxonomic notes.

PubMed

De Oliveira, João M S; Mariath, Jorge E A

2015-09-01

Investigation into the initial developmental stages of a given structure is fundamental for precise characterization as well as for comparative analysis in relation to other taxa when homologies are established. For the Anacardiaceae family, investigations of the initial development of the pericarp or its basic histological sites, the epicarp, mesocarp and endocarp, are relevant since these regions are of taxonomic and phylogenetic importance. The initial stages of endocarp development in Lithraea brasiliensis were studied using light microscopy. In L. brasiliensis, the fruits are of the drupe type. The endocarp originates exclusively in the epidermis of the locular cavity and is composed of only three strata. The crystalliferous layer, typical in fruits of the Anacardiaceae family, originates in the carpelar mesophyll and runs adjacent to the outermost layer of the endocarp. The endocarp in Lithraea brasiliensis is of the Anacardium type. The results of the present study are important for the identification of the Lithraea species that occur in the state of Rio Grande do Sul. In L. molleoides, the crystalliferous layer was shown to originate from the locular epidermis and this developmental aspect enables it to be differentiated from L. brasiliensis and demonstrates that there is variability of endocarp development in Lithraea.

Carbon Displacement-Induced Single Carbon Atomic Chain Formation and its Effects on Sliding of SiC Fibers in SiC/graphene/SiC Composite

DOE PAGES

Wallace, Joseph B.; Chen, Di; Shao, Lin

2015-11-03

Understanding radiation effects on the mechanical properties of SiC composites is important to their application in advanced reactor designs. By means of molecular dynamics simulations, we found that due to strong interface bonding between the graphene layers and SiC, the sliding friction of SiC fibers is largely determined by the frictional behavior between graphene layers. Upon sliding, carbon displacements between graphene layers can act as seed atoms to induce the formation of single carbon atomic chains (SCACs) by pulling carbon atoms from the neighboring graphene planes. The formation, growth, and breaking of SCACs determine the frictional response to irradiation.

Research on information security system of waste terminal disposal process

NASA Astrophysics Data System (ADS)

Zhou, Chao; Wang, Ziying; Guo, Jing; Guo, Yajuan; Huang, Wei

2017-05-01

Informatization has penetrated the whole process of production and operation of electric power enterprises. It not only improves the level of lean management and quality service, but also faces severe security risks. The internal network terminal is the outermost layer and the most vulnerable node of the inner network boundary. It has the characteristics of wide distribution, long depth and large quantity. The user and operation and maintenance personnel technical level and security awareness is uneven, which led to the internal network terminal is the weakest link in information security. Through the implementation of security of management, technology and physics, we should establish an internal network terminal security protection system, so as to fully protect the internal network terminal information security.

Peeling the onion: the outer layers of Cryptococcus neoformans.

PubMed

Agustinho, Daniel P; Miller, Liza C; Li, Lucy X; Doering, Tamara L

2018-01-01

Cryptococcus neoformans is an opportunistic fungal pathogen that is ubiquitous in the environment. It causes a deadly meningitis that is responsible for over 180,000 deaths worldwide each year, including 15% of all AIDS-related deaths. The high mortality rates for this infection, even with treatment, suggest a need for improved therapy. Unique characteristics of C. neoformans may suggest directions for drug discovery. These include features of three structures that surround the cell: the plasma membrane, the cell wall around it, and the outermost polysaccharide capsule. We review current knowledge of the fundamental biology of these fascinating structures and highlight open questions in the field, with the goal of stimulating further investigation that will advance basic knowledge and human health.

Application of optical coherence tomography for assessment of transcutaneous vaccine delivery

NASA Astrophysics Data System (ADS)

Kamali, T.; Rattanapak, T.; Hook, S.; Meglinski, I.

2012-03-01

Immunization is one of the most efficient and cost-effective means for the prevention of diseases, but most vaccines have to be administered invasively. A novel strategy of inducing an immune response is topical application of vaccines to intact skin. Apart from being a non-invasive route of drug delivery, skin delivery also offers an advantageous mode of immunization due to the ability of skin immune cells to present antigens to the immune system. Topical vaccine penetration through the outermost layers of skin is based on the percutaneous diffusion of lipid-based nano-particles. In the current study we investigate the applicability of Optical Coherence Tomography for monitoring transcutaneous delivery of a peptide vaccine into the skin in vivo.

Effects of microgravity on epidermal development in the rat

NASA Technical Reports Server (NTRS)

Hoath, Steven B.

1995-01-01

The overall goal of this project was to investigate the effects of prolonged weightlessness on the development of the skin in the fetal and newborn rat. Specifically, we used the NASA microgravitational rat model to test the following hypotheses: (1) Exposure of the pregnant rat to microscopy during late gestation will diminish the transport of calcium across the placenta from the mother to the fetus leading to decreases in total epidermal and dermal calcium content; (2) Microgravity will lead to slowing of body growth and diminish the rate of formation of the outermost layer of the epidermis and the stratum corneum; and (3) Microgravity will lead to formation of a stratum corneum with decreased DC electrical resistance and increased permeability to tritiated water.

Peeling the onion: the outer layers of Cryptococcus neoformans

PubMed Central

Agustinho, Daniel P; Miller, Liza C; Li, Lucy X; Doering, Tamara L

2018-01-01

Cryptococcus neoformans is an opportunistic fungal pathogen that is ubiquitous in the environment. It causes a deadly meningitis that is responsible for over 180,000 deaths worldwide each year, including 15% of all AIDS-related deaths. The high mortality rates for this infection, even with treatment, suggest a need for improved therapy. Unique characteristics of C. neoformans may suggest directions for drug discovery. These include features of three structures that surround the cell: the plasma membrane, the cell wall around it, and the outermost polysaccharide capsule. We review current knowledge of the fundamental biology of these fascinating structures and highlight open questions in the field, with the goal of stimulating further investigation that will advance basic knowledge and human health. PMID:29742198

The Polyketide Components of Waxes and the Cer-cqu Gene Cluster Encoding a Novel Polyketide Synthase, the β-Diketone Synthase, DKS.

PubMed

von Wettstein-Knowles, Penny

2017-07-10

The primary function of the outermost, lipophilic layer of plant aerial surfaces, called the cuticle, is preventing non-stomatal water loss. Its exterior surface is often decorated with wax crystals, imparting a blue-grey color. Identification of the barley Cer-c , -q and -u genes forming the 101 kb Cer-cqu gene cluster encoding a novel polyketide synthase-the β-diketone synthase (DKS), a lipase/carboxyl transferase, and a P450 hydroxylase, respectively, establishes a new, major pathway for the synthesis of plant waxes. The major product is a β-diketone (14,16-hentriacontane) aliphatic that forms long, thin crystalline tubes. A pathway branch leads to the formation of esterified alkan-2-ols.

Atomic layer epitaxy of YBaCuO for optoelectronic applications

NASA Technical Reports Server (NTRS)

Skogman, R. A.; Khan, M. A.; Van Hove, J. M.; Bhattarai, A.; Boord, W. T.

1992-01-01

An MOCVD-based atomic-layer epitaxy process is being developed as a potential solution to the problems of film-thickness and interface-abruptness control which are encountered when fabricating superconductor-insulator-superconductor devices using YBa2Cu3O(7-x). In initial studies, the atomic-layer MOCVD process yields superconducting YBa2Cu3O(7-x) films with substrate temperatures of 605 C during film growth, and no postdeposition anneal. The low temperature process yields a smooth film surface and can reduce interface degradation due to diffusion.

Materials Design Through Chemical Control of Precursors

DTIC Science & Technology

2008-08-22

Ligand Sets,” H. M. El-Kaderi, M.J. Heeg, and C.H. Winter, Polyhedron 2006, 25, 224-234. 7. “Atomic Layer Deposition of Ga2O3 Films from a...poster presentation. 4. “Atomic Layer Deposition (ALD) of High Quality Ga2O3 Thin Films from a Dimeric Dialkylamido-Bridged Gallium Complex,” C. L...growth of Ga2O3 films from a new metalorganic precursor (“Atomic Layer Deposition of Ga2O3 Films from a 4 Dialkylamido-Based Precursor,” C. L

Extended X-ray absorption fine structure investigation of Sn local environment in strained and relaxed epitaxial Ge{sub 1−x}Sn{sub x} films

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

Gencarelli, F., E-mail: federica.gencarelli@imec.be; Heyns, M.; Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, B-3001 Leuven

2015-03-07

We present an extended X-ray absorption fine structure investigation of the local environment of Sn atoms in strained and relaxed Ge{sub 1−x}Sn{sub x} layers with different compositions. We show that the preferred configuration for the incorporation of Sn atoms in these Ge{sub 1−x}Sn{sub x} layers is that of a α-Sn defect, with each Sn atom covalently bonded to four Ge atoms in a classic tetrahedral configuration. Sn interstitials, Sn-split vacancy complexes, or Sn dimers, if present at all, are not expected to involve more than 2.5% of the total Sn atoms. This finding, along with a relative increase of Snmore » atoms in the second atomic shell around a central Sn atom in Ge{sub 1−x}Sn{sub x} layers with increasing Sn concentrations, suggests that the investigated materials are homogeneous random substitutional alloys. Within the accuracy of the measurements, the degree of strain relaxation of the Ge{sub 1−x}Sn{sub x} layers does not have a significant impact on the local atomic surrounding of the Sn atoms. Finally, the calculated topological rigidity parameter a** = 0.69 ± 0.29 indicates that the strain due to alloying in Ge{sub 1−x}Sn{sub x} is accommodated via bond stretching and bond bending, with a slight predominance of the latter, in agreement with ab initio calculations reported in literature.« less

Electrochemical monitoring of native catalase activity in skin using skin covered oxygen electrode.

PubMed

Nocchi, Sarah; Björklund, Sebastian; Svensson, Birgitta; Engblom, Johan; Ruzgas, Tautgirdas

2017-07-15

A skin covered oxygen electrode, SCOE, was constructed with the aim to study the enzyme catalase, which is part of the biological antioxidative system present in skin. The electrode was exposed to different concentrations of H 2 O 2 and the amperometric current response was recorded. The observed current is due to H 2 O 2 penetration through the outermost skin barrier (referred to as the stratum corneum, SC) and subsequent catalytic generation of O 2 by catalase present in the underlying viable epidermis and dermis. By tape-stripping the outermost skin layers we demonstrate that SC is a considerable diffusion barrier for H 2 O 2 penetration. Our experiments also indicate that skin contains a substantial amount of catalase, which is sufficient to detoxify H 2 O 2 that reaches the viable epidermis after exposure of skin to high concentrations of peroxide (0.5-1mM H 2 O 2 ). Further, we demonstrate that the catalase activity is reduced at acidic pH, as compared with the activity at pH 7.4. Finally, experiments with often used penetration enhancer thymol shows that this compound interferes with the catalase reaction. Health aspect of this is briefly discussed. Summarizing, the results of this work show that the SCOE can be utilized to study a broad spectrum of issues involving the function of skin catalase in particular, and the native biological antioxidative system in skin in general. Copyright © 2017 Elsevier B.V. All rights reserved.

The influence of radiation-induced vacancy on the formation of thin-film of compound layer during a reactive diffusion process

NASA Astrophysics Data System (ADS)

Akintunde, S. O.; Selyshchev, P. A.

2016-05-01

A theoretical approach is developed that describes the formation of a thin-film of AB-compound layer under the influence of radiation-induced vacancy. The AB-compound layer is formed as a result of a chemical reaction between the atomic species of A and B immiscible layers. The two layers are irradiated with a beam of energetic particles and this process leads to several vacant lattice sites creation in both layers due to the displacement of lattice atoms by irradiating particles. A- and B-atoms diffuse via these lattice sites by means of a vacancy mechanism in considerable amount to reaction interfaces A/AB and AB/B. The reaction interfaces increase in thickness as a result of chemical transformation between the diffusing species and surface atoms (near both layers). The compound layer formation occurs in two stages. The first stage begins as an interfacial reaction controlled process, and the second as a diffusion controlled process. The critical thickness and time are determined at a transition point between the two stages. The influence of radiation-induced vacancy on layer thickness, speed of growth, and reaction rate is investigated under irradiation within the framework of the model presented here. The result obtained shows that the layer thickness, speed of growth, and reaction rate increase strongly as the defect generation rate rises in the irradiated layers. It also shows the feasibility of producing a compound layer (especially in near-noble metal silicide considered in this study) at a temperature below their normal formation temperature under the influence of radiation.

Atomic layer deposition of a high-k dielectric on MoS2 using trimethylaluminum and ozone.

PubMed

Cheng, Lanxia; Qin, Xiaoye; Lucero, Antonio T; Azcatl, Angelica; Huang, Jie; Wallace, Robert M; Cho, Kyeongjae; Kim, Jiyoung

2014-08-13

We present an Al2O3 dielectric layer on molybdenum disulfide (MoS2), deposited using atomic layer deposition (ALD) with ozone/trimethylaluminum (TMA) and water/TMA as precursors. The results of atomic force microscopy and low-energy ion scattering spectroscopy show that using TMA and ozone as precursors leads to the formation of uniform Al2O3 layers, in contrast to the incomplete coverage we observe when using TMA/H2O as precursors. Our Raman and X-ray photoelectron spectroscopy measurements indicate minimal variations in the MoS2 structure after ozone treatment at 200 °C, suggesting its excellent chemical resistance to ozone.

Rational design of atomic-layer-deposited LiFePO4 as a high-performance cathode for lithium-ion batteries.

PubMed

Liu, Jian; Banis, Mohammad N; Sun, Qian; Lushington, Andrew; Li, Ruying; Sham, Tsun-Kong; Sun, Xueliang

2014-10-08

Atomic layer deposition is successfully applied to synthesize lithium iron phosphate in a layer-by-layer manner by using self-limiting surface reactions. The lithium iron phosphate exhibits high power density, excellent rate capability, and ultra-long lifetime, showing great potential for vehicular lithium batteries and 3D all-solid-state microbatteries. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomically thin transition metal layers: Atomic layer stabilization and metal-semiconductor transition

NASA Astrophysics Data System (ADS)

Hwang, Jeongwoon; Oh, Young Jun; Kim, Jiyoung; Sung, Myung Mo; Cho, Kyeongjae

2018-04-01

We have performed first-principle calculations to explore the possibility of synthesizing atomically thin transition metal (TM) layers. Buckled structures as well as planar structures of elemental 2D TM layers result in significantly higher formation energies compared with sp-bonded elemental 2D materials with similar structures, such as silicene and phosphorene. It is shown that the TM layers can be stabilized by surface passivation with HS, C6H5S2, or O, and O passivation is most effective. The surface oxygen passivation can improve stability leading to thermodynamically stable TM monolayers except Au, which is the most non-reactive metal element. Such stabilized TM monolayers also show an electronic structure transition from metallic state of free-standing TM layer to semiconducting O-passivated Mo and W monolayers with band gaps of 0.20-1.38 eV.

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides.

PubMed

Jood, Priyanka; Ohta, Michihiro

2015-03-16

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS₂-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS₂ sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor.

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides

PubMed Central

Jood, Priyanka; Ohta, Michihiro

2015-01-01

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS2-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS2 sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor. PMID:28787992

The S-layer Associated Serine Protease Homolog PrtX Impacts Cell Surface-Mediated Microbe-Host Interactions of Lactobacillus acidophilus NCFM

PubMed Central

Johnson, Brant R.; O’Flaherty, Sarah; Goh, Yong Jun; Carroll, Ian; Barrangou, Rodolphe; Klaenhammer, Todd R.

2017-01-01

Health-promoting aspects attributed to probiotic microorganisms, including adhesion to intestinal epithelia and modulation of the host mucosal immune system, are mediated by proteins found on the bacterial cell surface. Notably, certain probiotic and commensal bacteria contain a surface (S-) layer as the outermost stratum of the cell wall. S-layers are non-covalently bound semi-porous, crystalline arrays of self-assembling, proteinaceous subunits called S-layer proteins (SLPs). Recent evidence has shown that multiple proteins are non-covalently co-localized within the S-layer, designated S-layer associated proteins (SLAPs). In Lactobacillus acidophilus NCFM, SLP and SLAPs have been implicated in both mucosal immunomodulation and adhesion to the host intestinal epithelium. In this study, a S-layer associated serine protease homolog, PrtX (prtX, lba1578), was deleted from the chromosome of L. acidophilus NCFM. Compared to the parent strain, the PrtX-deficient strain (ΔprtX) demonstrated increased autoaggregation, an altered cellular morphology, and pleiotropic increases in adhesion to mucin and fibronectin, in vitro. Furthermore, ΔprtX demonstrated increased in vitro immune stimulation of IL-6, IL-12, and IL-10 compared to wild-type, when exposed to mouse dendritic cells. Finally, in vivo colonization of germ-free mice with ΔprtX led to an increase in epithelial barrier integrity. The absence of PrtX within the exoproteome of a ΔprtX strain caused morphological changes, resulting in a pleiotropic increase of the organisms’ immunomodulatory properties and interactions with some intestinal epithelial cell components. PMID:28713337

Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures

NASA Astrophysics Data System (ADS)

Kang, Kibum; Lee, Kan-Heng; Han, Yimo; Gao, Hui; Xie, Saien; Muller, David A.; Park, Jiwoong

2017-10-01

High-performance semiconductor films with vertical compositions that are designed to atomic-scale precision provide the foundation for modern integrated circuitry and novel materials discovery. One approach to realizing such films is sequential layer-by-layer assembly, whereby atomically thin two-dimensional building blocks are vertically stacked, and held together by van der Waals interactions. With this approach, graphene and transition-metal dichalcogenides--which represent one- and three-atom-thick two-dimensional building blocks, respectively--have been used to realize previously inaccessible heterostructures with interesting physical properties. However, no large-scale assembly method exists at present that maintains the intrinsic properties of these two-dimensional building blocks while producing pristine interlayer interfaces, thus limiting the layer-by-layer assembly method to small-scale proof-of-concept demonstrations. Here we report the generation of wafer-scale semiconductor films with a very high level of spatial uniformity and pristine interfaces. The vertical composition and properties of these films are designed at the atomic scale using layer-by-layer assembly of two-dimensional building blocks under vacuum. We fabricate several large-scale, high-quality heterostructure films and devices, including superlattice films with vertical compositions designed layer-by-layer, batch-fabricated tunnel device arrays with resistances that can be tuned over four orders of magnitude, band-engineered heterostructure tunnel diodes, and millimetre-scale ultrathin membranes and windows. The stacked films are detachable, suspendable and compatible with water or plastic surfaces, which will enable their integration with advanced optical and mechanical systems.

Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructures.

PubMed

Kang, Kibum; Lee, Kan-Heng; Han, Yimo; Gao, Hui; Xie, Saien; Muller, David A; Park, Jiwoong

2017-10-12

High-performance semiconductor films with vertical compositions that are designed to atomic-scale precision provide the foundation for modern integrated circuitry and novel materials discovery. One approach to realizing such films is sequential layer-by-layer assembly, whereby atomically thin two-dimensional building blocks are vertically stacked, and held together by van der Waals interactions. With this approach, graphene and transition-metal dichalcogenides-which represent one- and three-atom-thick two-dimensional building blocks, respectively-have been used to realize previously inaccessible heterostructures with interesting physical properties. However, no large-scale assembly method exists at present that maintains the intrinsic properties of these two-dimensional building blocks while producing pristine interlayer interfaces, thus limiting the layer-by-layer assembly method to small-scale proof-of-concept demonstrations. Here we report the generation of wafer-scale semiconductor films with a very high level of spatial uniformity and pristine interfaces. The vertical composition and properties of these films are designed at the atomic scale using layer-by-layer assembly of two-dimensional building blocks under vacuum. We fabricate several large-scale, high-quality heterostructure films and devices, including superlattice films with vertical compositions designed layer-by-layer, batch-fabricated tunnel device arrays with resistances that can be tuned over four orders of magnitude, band-engineered heterostructure tunnel diodes, and millimetre-scale ultrathin membranes and windows. The stacked films are detachable, suspendable and compatible with water or plastic surfaces, which will enable their integration with advanced optical and mechanical systems.

Atomic-layer soft plasma etching of MoS2

PubMed Central

Xiao, Shaoqing; Xiao, Peng; Zhang, Xuecheng; Yan, Dawei; Gu, Xiaofeng; Qin, Fang; Ni, Zhenhua; Han, Zhao Jun; Ostrikov, Kostya (Ken)

2016-01-01

Transition from multi-layer to monolayer and sub-monolayer thickness leads to the many exotic properties and distinctive applications of two-dimensional (2D) MoS2. This transition requires atomic-layer-precision thinning of bulk MoS2 without damaging the remaining layers, which presently remains elusive. Here we report a soft, selective and high-throughput atomic-layer-precision etching of MoS2 in SF6 + N2 plasmas with low-energy (<0.4 eV) electrons and minimized ion-bombardment-related damage. Equal numbers of MoS2 layers are removed uniformly across domains with vastly different initial thickness, without affecting the underlying SiO2 substrate and the remaining MoS2 layers. The etching rates can be tuned to achieve complete MoS2 removal and any desired number of MoS2 layers including monolayer. Layer-dependent vibrational and photoluminescence spectra of the etched MoS2 are also demonstrated. This soft plasma etching technique is versatile, scalable, compatible with the semiconductor manufacturing processes, and may be applicable for a broader range of 2D materials and intended device applications. PMID:26813335

Relationships between Liquid Atomization and Solid Fragmentation

DTIC Science & Technology

2016-03-01

Sallam, C. Aalburg, G.M. Faeth, K.-C. Lin, C.D. Carter, and T.A. Jackson, Primary Breakup of Aerated- Liquid Jets in Supersonic Crossflows, Atomization...Wu, L.-K. Tseng, and G. M. Faeth, Primary Breakup in Gas / Liquid Mixing Layers for Turbulent Liquids , Atomization and Sprays, 295-317, 1992 P.-K...Wu, G. A. Ruff, and G. M. Faeth, Primary Breakup in Liquid - Gas Mixing Layers, Atomization and Sprays, 1, 421-440, 1991 P.-K. Wu and G. M. Faeth

Photographer : JPL Range : 7 million kilometers (5 million miles) Callisto is the outermost Galilean

NASA Technical Reports Server (NTRS)

1979-01-01

Photographer : JPL Range : 7 million kilometers (5 million miles) Callisto is the outermost Galilean satellite of Jupiter and the darkest of the four, but still twice as bright as Earth's Moon. Mottled appearance from bright and dark patches; bright ones look like rayed or brite craters on our Moon. This face of Callisto is always turned toward Jupiter. Photo taken through violet filter.

[Morphological changes on cochlear hair cells of rats in simulated weightlessness and inboard noise].

PubMed

2017-06-18

To observe the morphological changes on cochlear hair cells of rats in simulated weightlessness and inboard noise and to investigate the different changes in three turns of hair cells. Thirty-two healthy SD rats, all males, were randomly divided into four groups: control group, weightlessness group, noise group and weightlessness+noise groups (n=8). Then rats were exposed to -30° head down tilt as simulated weightlessness and inboard noise including steady-state noise which was (72±2) dB SPL and impulse noise up to 160 dB SPL in spaceship environment. The control group was kept in normal condition for 8 weeks. Bilateral auditory brainstem response (ABR) thresholds were tested before and after exposure respectively, and immunofluorescence staining and scanning electron microscopy (SEMs) of basilar membrane were applied after exposure. ABR threshold shifts of each group were higher after exposure. There was difference between ABRs of the experiment groups before and after exposure (P<0.05). IF showed that the inner hair cells (IHCs) missing was the main damage in the basal turn of weightlessness group, the hair cells in the middle turn were swell and in the top turn, the hair cells were not clear. In noise group, the main loss happened in the outer hair cells (OHCs) of the outermost layer. In weightlessness+noise group, the nuclear missing in the basal turn was apparent, and mainly happened at the outermost layer. Meanwhile, the missing of hair cells in the middle turn and top turn was seen at the innermost layer. SEM showed that the cilia in the basal turn of weightlessness group were serious lodging, and occasional absence. Furthermore, the basal cilia in noise group became lodged and absent, and the other two turns were seriously missing. And in weightlessness+noise group, the cilia missing in the basal turn was apparently seen. The damage degree of the four groups: weightlessness+noise group>noise group>weightlessness group>control group and the damage degree of the four turns of hair cells: basal turn>mid turn>top turn. The rats exposed to the above environment for 2 weeks displayed obvious changes in cochlea morphology, and the weightlessness +noise group had the most obvious damage.

Functionalized graphene-Pt composites for fuel cells and photoelectrochemical cells

DOEpatents

Diankov, Georgi; An, Jihwan; Park, Joonsuk; Goldhaber, David J. K.; Prinz, Friedrich B.

2017-08-29

A method of growing crystals on two-dimensional layered material is provided that includes reversibly hydrogenating a two-dimensional layered material, using a controlled radio-frequency hydrogen plasma, depositing Pt atoms on the reversibly hydrogenated two-dimensional layered material, using Atomic Layer Deposition (ALD), where the reversibly hydrogenated two-dimensional layered material promotes loss of methyl groups in an ALD Pt precursor, and forming Pt-O on the reversibly hydrogenated two-dimensional layered material, using combustion by O.sub.2, where the Pt-O is used for subsequent Pt half-cycles of the ALD process, where growth of Pt crystals occurs.

Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

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

Hultqvist, Adam; Bent, Stacey F.; Li, Jian V.

2015-07-20

Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystallinemore » II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

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

Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius

2015-07-20

Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II-VImore » systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

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

Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius

2015-07-20

Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VImore » systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Atomically Thin Al2O3 Films for Tunnel Junctions

NASA Astrophysics Data System (ADS)

Wilt, Jamie; Gong, Youpin; Gong, Ming; Su, Feifan; Xu, Huikai; Sakidja, Ridwan; Elliot, Alan; Lu, Rongtao; Zhao, Shiping; Han, Siyuan; Wu, Judy Z.

2017-06-01

Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard AlOx tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin Al2O3 tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial H2O pulse hydroxylated the Al surface and enabled the creation of an atomically thin Al2O3 tunnel barrier with a high-quality M -I interface and a significantly enhanced barrier height compared to thermal AlOx . These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition Al2O3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions.

Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

PubMed Central

Matsui, Fumihiko; Eguchi, Ritsuko; Nishiyama, Saki; Izumi, Masanari; Uesugi, Eri; Goto, Hidenori; Matsushita, Tomohiro; Sugita, Kenji; Daimon, Hiroshi; Hamamoto, Yuji; Hamada, Ikutaro; Morikawa, Yoshitada; Kubozono, Yoshihiro

2016-01-01

From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K)C8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3 Å and 5.7 Å above the photoelectron emitter C atom and the stacking structures were determined as AB- and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2 × 2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K)C8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms. PMID:27811975

Electroless atomic layer deposition

DOEpatents

Robinson, David Bruce; Cappillino, Patrick J.; Sheridan, Leah B.; Stickney, John L.; Benson, David M.

2017-10-31

A method of electroless atomic layer deposition is described. The method electrolessly generates a layer of sacrificial material on a surface of a first material. The method adds doses of a solution of a second material to the substrate. The method performs a galvanic exchange reaction to oxidize away the layer of the sacrificial material and deposit a layer of the second material on the surface of the first material. The method can be repeated for a plurality of iterations in order to deposit a desired thickness of the second material on the surface of the first material.

Surface Phenomena During Plasma-Assisted Atomic Layer Etching of SiO2.

PubMed

Gasvoda, Ryan J; van de Steeg, Alex W; Bhowmick, Ranadeep; Hudson, Eric A; Agarwal, Sumit

2017-09-13

Surface phenomena during atomic layer etching (ALE) of SiO 2 were studied during sequential half-cycles of plasma-assisted fluorocarbon (CF x ) film deposition and Ar plasma activation of the CF x film using in situ surface infrared spectroscopy and ellipsometry. Infrared spectra of the surface after the CF x deposition half-cycle from a C 4 F 8 /Ar plasma show that an atomically thin mixing layer is formed between the deposited CF x layer and the underlying SiO 2 film. Etching during the Ar plasma cycle is activated by Ar + bombardment of the CF x layer, which results in the simultaneous removal of surface CF x and the underlying SiO 2 film. The interfacial mixing layer in ALE is atomically thin due to the low ion energy during CF x deposition, which combined with an ultrathin CF x layer ensures an etch rate of a few monolayers per cycle. In situ ellipsometry shows that for a ∼4 Å thick CF x film, ∼3-4 Å of SiO 2 was etched per cycle. However, during the Ar plasma half-cycle, etching proceeds beyond complete removal of the surface CF x layer as F-containing radicals are slowly released into the plasma from the reactor walls. Buildup of CF x on reactor walls leads to a gradual increase in the etch per cycle.

Quantitative Subsurface Atomic Structure Fingerprint for 2D Materials and Heterostructures by First-Principles-Calibrated Contact-Resonance Atomic Force Microscopy.

PubMed

Tu, Qing; Lange, Björn; Parlak, Zehra; Lopes, Joao Marcelo J; Blum, Volker; Zauscher, Stefan

2016-07-26

Interfaces and subsurface layers are critical for the performance of devices made of 2D materials and heterostructures. Facile, nondestructive, and quantitative ways to characterize the structure of atomically thin, layered materials are thus essential to ensure control of the resultant properties. Here, we show that contact-resonance atomic force microscopy-which is exquisitely sensitive to stiffness changes that arise from even a single atomic layer of a van der Waals-adhered material-is a powerful experimental tool to address this challenge. A combined density functional theory and continuum modeling approach is introduced that yields sub-surface-sensitive, nanomechanical fingerprints associated with specific, well-defined structure models of individual surface domains. Where such models are known, this information can be correlated with experimentally obtained contact-resonance frequency maps to reveal the (sub)surface structure of different domains on the sample.

Vector dissipative solitons in graphene mode locked fiber lasers

NASA Astrophysics Data System (ADS)

Zhang, Han; Tang, Dingyuan; Zhao, Luming; Bao, Qiaoliang; Loh, Kian Ping

2010-09-01

Vector soliton operation of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated. Either the polarization rotation or polarization locked vector dissipative solitons were experimentally obtained in a dispersion-managed cavity fiber laser with large net cavity dispersion, while in the anomalous dispersion cavity fiber laser, the phase locked nonlinear Schrödinger equation (NLSE) solitons and induced NLSE soliton were experimentally observed. The vector soliton operation of the fiber lasers unambiguously confirms the polarization insensitive saturable absorption of the atomic layer graphene when the light is incident perpendicular to its 2-dimentional (2D) atomic layer.

Influence of the "surface effect" on the segregation parameters of S in Fe(100): A multi-scale modelling and Auger Electron Spectroscopy study

NASA Astrophysics Data System (ADS)

Barnard, P. E.; Terblans, J. J.; Swart, H. C.

2015-12-01

The article takes a new look at the process of atomic segregation by considering the influence of surface relaxation on the segregation parameters; the activation energy (Q), segregation energy (ΔG), interaction parameter (Ω) and the pre-exponential factor (D0). Computational modelling, namely Density Functional Theory (DFT) and the Modified Darken Model (MDM) in conjunction with Auger Electron Spectroscopy (AES) was utilized to study the variation of the segregation parameters for S in the surface region of Fe(100). Results indicate a variation in each of the segregation parameters as a function of the atomic layer under consideration. Values of the segregation parameters varied more dramatically as the surface layer is approached, with atomic layer 2 having the largest deviations in comparison to the bulk values. This atomic layer had the highest Q value and formed the rate limiting step for the segregation of S towards the Fe(100) surface. It was found that the segregation process is influenced by two sets of segregation parameters, those of the surface region formed by atomic layer 2, and those in the bulk material. This article is the first to conduct a full scale investigation on the influence of surface relaxation on segregation and labelled it the "surface effect".

Atomic layer deposition-based functionalization of materials for medical and environmental health applications

PubMed Central

Narayan, Roger J.; Adiga, Shashishekar P.; Pellin, Michael J.; Curtiss, Larry A.; Hryn, Alexander J.; Stafslien, Shane; Chisholm, Bret; Shih, Chun-Che; Shih, Chun-Ming; Lin, Shing-Jong; Su, Yea-Yang; Jin, Chunming; Zhang, Junping; Monteiro-Riviere, Nancy A.; Elam, Jeffrey W.

2010-01-01

Nanoporous alumina membranes exhibit high pore densities, well-controlled and uniform pore sizes, as well as straight pores. Owing to these unusual properties, nanoporous alumina membranes are currently being considered for use in implantable sensor membranes and water purification membranes. Atomic layer deposition is a thin-film growth process that may be used to modify the pore size in a nanoporous alumina membrane while retaining a narrow pore distribution. In addition, films deposited by means of atomic layer deposition may impart improved biological functionality to nanoporous alumina membranes. In this study, zinc oxide coatings and platinum coatings were deposited on nanoporous alumina membranes by means of atomic layer deposition. PEGylated nanoporous alumina membranes were prepared by self-assembly of 1-mercaptoundec-11-yl hexa(ethylene glycol) on platinum-coated nanoporous alumina membranes. The pores of the PEGylated nanoporous alumina membranes remained free of fouling after exposure to human platelet-rich plasma; protein adsorption, fibrin networks and platelet aggregation were not observed on the coated membrane surface. Zinc oxide-coated nanoporous alumina membranes demonstrated activity against two waterborne pathogens, Escherichia coli and Staphylococcus aureus. The results of this work indicate that nanoporous alumina membranes may be modified using atomic layer deposition for use in a variety of medical and environmental health applications. PMID:20308114

Diffusion induced atomic islands on the surface of Ni/Cu nanolayers

NASA Astrophysics Data System (ADS)

Takáts, Viktor; Csik, Attila; Hakl, József; Vad, Kálmán

2018-05-01

Surface islands formed by grain-boundary diffusion has been studied in Ni/Cu nanolayers by in-situ low energy ion scattering spectroscopy, X-ray photoelectron spectroscopy, scanning probe microscopy and ex-situ depth profiling based on ion sputtering. In this paper a new experimental approach of measurement of grain-boundary diffusion coefficients is presented. Appearing time of copper atoms diffused through a few nanometer thick nickel layer has been detected by low energy ion scattering spectroscopy with high sensitivity. The grain-boundary diffusion coefficient can be directly calculated from this appearing time without using segregation factors in calculations. The temperature range of 423-463 K insures the pure C-type diffusion kinetic regime. The most important result is that surface coverage of Ni layer by Cu atoms reaches a maximum during annealing and stays constant if the annealing procedure is continued. Scanning probe microscopy measurements show a Volmer-Weber type layer growth of Cu layer on the Ni surface in the form of Cu atomic islands. Depth distribution of Cu in Ni layer has been determined by depth profile analysis.

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

NASA Astrophysics Data System (ADS)

Jamil, Rabia; Ali, Abu Bakar; Abbas, Muqaddar; Badshah, Fazal; Qamar, Sajid

2017-08-01

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom-field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.

Quantum state engineering with ultra-short-period (AlN)m/(GaN)n superlattices for narrowband deep-ultraviolet detection.

PubMed

Gao, Na; Lin, Wei; Chen, Xue; Huang, Kai; Li, Shuping; Li, Jinchai; Chen, Hangyang; Yang, Xu; Ji, Li; Yu, Edward T; Kang, Junyong

2014-12-21

Ultra-short-period (AlN)m/(GaN)n superlattices with tunable well and barrier atomic layer numbers were grown by metal-organic vapour phase epitaxy, and employed to demonstrate narrowband deep ultraviolet photodetection. High-resolution transmission electron microscopy and X-ray reciprocal space mapping confirm that superlattices containing well-defined, coherently strained GaN and AlN layers as thin as two atomic layers (∼ 0.5 nm) were grown. Theoretical and experimental results demonstrate that an optical absorption band as narrow as 9 nm (210 meV) at deep-ultraviolet wavelengths can be produced, and is attributable to interband transitions between quantum states along the [0001] direction in ultrathin GaN atomic layers isolated by AlN barriers. The absorption wavelength can be precisely engineered by adjusting the thickness of the GaN atomic layers because of the quantum confinement effect. These results represent a major advance towards the realization of wavelength selectable and narrowband photodetectors in the deep-ultraviolet region without any additional optical filters.

Atomically thick bismuth selenide freestanding single layers achieving enhanced thermoelectric energy harvesting.

PubMed

Sun, Yongfu; Cheng, Hao; Gao, Shan; Liu, Qinghua; Sun, Zhihu; Xiao, Chong; Wu, Changzheng; Wei, Shiqiang; Xie, Yi

2012-12-19

Thermoelectric materials can realize significant energy savings by generating electricity from untapped waste heat. However, the coupling of the thermoelectric parameters unfortunately limits their efficiency and practical applications. Here, a single-layer-based (SLB) composite fabricated from atomically thick single layers was proposed to optimize the thermoelectric parameters fully. Freestanding five-atom-thick Bi(2)Se(3) single layers were first synthesized via a scalable interaction/exfoliation strategy. As revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, surface distortion gives them excellent structural stability and a much increased density of states, resulting in a 2-fold higher electrical conductivity relative to the bulk material. Also, the surface disorder and numerous interfaces in the Bi(2)Se(3) SLB composite allow for effective phonon scattering and decreased thermal conductivity, while the 2D electron gas and energy filtering effect increase the Seebeck coefficient, resulting in an 8-fold higher figure of merit (ZT) relative to the bulk material. This work develops a facile strategy for synthesizing atomically thick single layers and demonstrates their superior ability to optimize the thermoelectric energy harvesting.

Triply responsive films in bioelectrocatalysis with a binary architecture: combined layer-by-layer assembly and hydrogel polymerization.

PubMed

Yao, Huiqin; Hu, Naifei

2011-05-26

In this work, triply responsive films with a specific binary architecture combining layer-by-layer assembly (LbL) and hydrogel polymerization were successfully prepared. First, concanavalin A (Con A) and dextran (Dex) were assembled into {Con A/Dex}(5) LbL layers on electrode surface by the lectin-sugar biospecific interaction between them. The poly(N,N-diethylacrylamide) (PDEA) hydrogels with entrapped horseradish peroxidase (HRP) were then synthesized by polymerization on the surface of LbL inner layers, forming {Con A/Dex}(5)-(PDEA-HRP) films. The films demonstrated reversible pH-, thermo-, and salt-responsive on-off behavior toward electroactive probe Fe(CN)(6)(3-) in its cyclic voltammetric responses. This multiple stimuli-responsive films could be further used to realize triply switchable electrochemical reduction of H(2)O(2) catalyzed by HRP immobilized in the films and mediated by Fe(CN)(6)(3-) in solution. The responsive mechanism of the films was explored and discussed. The pH-sensitive property of the system was attributed to the electrostatic interaction between the {Con A/Dex}(5) inner layers and the probe at different pH, and the thermo- and salt-responsive behaviors should be ascribed to the structure change of PDEA hydrogels for the PDEA-HRP outermost layers under different conditions. The concept of binary architecture was also used to fabricate {Con A/Dex}(5)-(PDEA-GOD) films on electrodes, where GOD = glucose oxidase, which was applied to realize the triply switchable bioelectrocatalysis of glucose by GOD in the films with ferrocenedicarboxylic acid as the mediator in solution. This film system with the unique binary architecture may establish a foundation for fabricating a novel type of multicontrollable biosensors based on bioelectrocatalysis with immobilized enzymes.

A new Pb{sup II}(ethylenediaminetetraacetate) coordination polymer with a two-dimensional layer structure

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

Zhao, D., E-mail: iamzd@hpu.edu.cn; Zhang, R. H.; Li, F. F.

2016-12-15

A new Pb{sup II}−edta{sup 4–} coordination polymer, Pb{sub 2}(edta)(H{sub 2}O){sub 0.76} (edta{sup 4–} = ethylenediaminetetraacetate) was synthesized under hydrothermal condition. Single crystal X-ray analysis reveals that it represents a novel two-dimensional (2D) Pb{sup 2+}–edta{sup 4–} layer structure with a (4,8{sup 2})-topology. Each edta{sup 4–} ligand employs its four carboxylate O and two N atoms to chelate one Pb{sup II} atom (hexa-coordinated) and connects five Pb{sup II} atoms (ennea-coordinated) via its four carboxylate groups to form 2D layer framework. Adjacent layers are packed into the overall structure through vander Waals interactions.

Hexadecapolar Colloids

DOE PAGES

Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; ...

2016-02-11

Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Becausemore » of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.« less

Positron-Electron Annihilation Process in (2,2)-Difluoropropane Molecule

NASA Astrophysics Data System (ADS)

Liu, Yang; Ma, Xiao-Guang; Zhu, Ying-Hao

2016-04-01

The positron-electron annihilation process in (2,2)-difluoropropane molecule and the corresponding gamma-ray spectra are studied by quantum chemistry method. The positrophilic electrons in (2,2)-difluoropropane molecule are found for the first time. The theoretical predictions show that the outermost 2s electrons of fluoride atoms play an important role in positron-electron annihilation process of (2,2)-difiuoropropane. In the present scheme, the correlation coefficient between the theoretical gamma-ray spectra and the experiments can be 99%. The present study gives an alternative annihilation model for positron-electron pair in larger molecules. Supported by the National Natural Science Foundation of China under Grant No. 11347011 and the Natural Science Foundation Project of Shandong Province under Grant No. ZR2011AM010 and 2014 Technology Innovation Fund of Ludong University under Grant Nos. 1d151007 and ld15l016

Atomic and molecular layer deposition for surface modification

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

Vähä-Nissi, Mika, E-mail: mika.vaha-nissi@vtt.fi; Sievänen, Jenni; Salo, Erkki

2014-06-01

Atomic and molecular layer deposition (ALD and MLD, respectively) techniques are based on repeated cycles of gas–solid surface reactions. A partial monolayer of atoms or molecules is deposited to the surface during a single deposition cycle, enabling tailored film composition in principle down to molecular resolution on ideal surfaces. Typically ALD/MLD has been used for applications where uniform and pinhole free thin film is a necessity even on 3D surfaces. However, thin – even non-uniform – atomic and molecular deposited layers can also be used to tailor the surface characteristics of different non-ideal substrates. For example, print quality of inkjetmore » printing on polymer films and penetration of water into porous nonwovens can be adjusted with low-temperature deposited metal oxide. In addition, adhesion of extrusion coated biopolymer to inorganic oxides can be improved with a hybrid layer based on lactic acid. - Graphical abstract: Print quality of a polylactide film surface modified with atomic layer deposition prior to inkjet printing (360 dpi) with an aqueous ink. Number of printed dots illustrated as a function of 0, 5, 15 and 25 deposition cycles of trimethylaluminum and water. - Highlights: • ALD/MLD can be used to adjust surface characteristics of films and fiber materials. • Hydrophobicity after few deposition cycles of Al{sub 2}O{sub 3} due to e.g. complex formation. • Same effect on cellulosic fabrics observed with low temperature deposited TiO{sub 2}. • Different film growth and oxidation potential with different precursors. • Hybrid layer on inorganic layer can be used to improve adhesion of polymer melt.« less

Radial cold trap

DOEpatents

Grundy, Brian R.

1981-01-01

The radial cold trap comprises a housing having a plurality of mesh bands disposed therein. The mesh bands comprise concentrically arranged bands of mesh with the mesh specific surface area of each band increasing from the outermost mesh band to the innermost mesh band. An inlet nozzle is attached to the outside section of the housing while an outlet nozzle is attached to the inner portion of the housing so as to be concentrically connected to the innermost mesh band. An inlet baffle having orifices therein may be disposed around the outermost mesh band and within the housing for directing the flow of the fluid from the inlet nozzle to the outermost mesh band in a uniform manner. The flow of fluid passes through each consecutive mesh band and into the outlet nozzle. The circular pattern of the symmetrically arranged mesh packing allows for better utilization of the entire cold trap volume.

Radial cold trap

DOEpatents

Grundy, B.R.

1981-09-29

The radial cold trap comprises a housing having a plurality of mesh bands disposed therein. The mesh bands comprise concentrically arranged bands of mesh with the mesh specific surface area of each band increasing from the outermost mesh band to the innermost mesh band. An inlet nozzle is attached to the outside section of the housing while an outlet nozzle is attached to the inner portion of the housing so as to be concentrically connected to the innermost mesh band. An inlet baffle having orifices therein may be disposed around the outermost mesh band and within the housing for directing the flow of the fluid from the inlet nozzle to the outermost mesh band in a uniform manner. The flow of fluid passes through each consecutive mesh band and into the outlet nozzle. The circular pattern of the symmetrically arranged mesh packing allows for better utilization of the entire cold trap volume. 2 figs.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-05-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

PubMed Central

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-01-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

First-principles study on silicon atom doped monolayer graphene

NASA Astrophysics Data System (ADS)

Rafique, Muhammad; Shuai, Yong; Hussain, Nayyar

2018-01-01

This paper illustrates the structural, electronic and optical properties of individual silicon (Si) atom-doped single layer graphene using density functional theory method. Si atom forms tight bonding with graphene layer. The effect of doping has been investigated by varying the concentration of Si atoms from 3.125% to 9.37% (i.e. From one to three Si atoms in 4 × 4 pure graphene supercell containing 32 carbon atoms), respectively. Electronic structure, partial density of states (PDOS) and optical properties of pure and Si atom-doped graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with Si atom doped graphene. It is revealed that upon Si doping in graphene, a finite band gap appears at the high symmetric K-point, thereby making graphene a direct band gap semiconductor. Moreover, the band gap value is directly proportional to the concentration of impurity Si atoms present in graphene lattice. Upon analyzing the optical properties of Si atom-doped graphene structures, it is found that, there is significant change in the refractive index of the graphene after Si atom substitution in graphene. In addition, the overall absorption spectrum of graphene is decreased after Si atom doping. Although a significant red shift in absorption is found to occur towards visible range of radiation when Si atom is substituted in its lattice. The reflectivity of graphene improves in low energy region after Si atom substitution in graphene. These results can be useful for tuning the electronic structure and to manipulate the optical properties of graphene layer in the visible region.

Au/Ti resistors used for Nb/Pb-alloy Josephson junctions. II. Thermal stability

NASA Astrophysics Data System (ADS)

Murakami, Masanori; Kim, K. K.

1984-10-01

In the preceding paper bilayered Au/Ti resistors were found to have excellent electrical stability during storage at room temperature after preannealing at an elevated temperature, which is essential to design logic and memory circuits of Nb/Pb-alloy Josephson junction devices. The resistors could contact directly with the Pb-alloy control lines in which Pb and In atoms which are known to intermix easily with Au atoms are contained. Since Pb and In atoms in the control lines are separated from Au atoms of the resistors by thin Ti layers, thermal stability at the contacts is a major concern for use of the Au/Ti resistor material in the Josephson devices. In the present study, surface morphology change and diffusion mechanism at the resistor/control-line contacts were studied using x-ray diffraction and scanning electron microscopy for square-shaped Au/Ti resistors covered by Pb-In layers. The samples were isothermally annealed at temperatures ranging from 353 to 423 K. The diffusion did not occur immediately after annealing at these temperatures. After the incubation period, the interdiffusion was observed to initiate at the edges of the resistors facing to the center of the cathode. Significant amounts of the In atoms in the Pb-In layers were observed to diffuse into the Au layers of the resistors, forming AuIn2 compounds under the Ti layers. By measuring growth rates of the AuIn2 layers, the diffusion coefficients and the activation energy for the layer growth were determined. Also, by analyzing changes in the In concentration in the Pb-In layers during annealing, interdiffusion coefficients of In atoms in the Pb-In layers were determined using a computer simulation technique. The activation energy was about 1.1 eV. Since these diffusion coefficients were found to be very close to those determined previously in bulk materials, the diffusion kinetics is believed to be controlled by the lattice diffusion. Based on the present results, several methods to reduce the interdiffusion between Pb-alloy and Au/Ti resistors were proposed.

An Introduction to Atomic Layer Deposition with Thermal Applications

NASA Technical Reports Server (NTRS)

Dwivedi, Vivek H.

2015-01-01

Atomic Layer Deposition (ALD) is a cost effective nano-manufacturing technique that allows for the conformal coating of substrates with atomic control in a benign temperature and pressure environment. Through the introduction of paired precursor gases thin films can be deposited on a myriad of substrates ranging from glass, polymers, aerogels, and metals to high aspect ratio geometries. This talk will focus on the utilization of ALD for engineering applications.

Horizontal gene transfer contributed to the evolution of extracellular surface structures: the freshwater polyp Hydra is covered by a complex fibrous cuticle containing glycosaminoglycans and proteins of the PPOD and SWT (sweet tooth) families.

PubMed

Böttger, Angelika; Doxey, Andrew C; Hess, Michael W; Pfaller, Kristian; Salvenmoser, Willi; Deutzmann, Rainer; Geissner, Andreas; Pauly, Barbara; Altstätter, Johannes; Münder, Sandra; Heim, Astrid; Gabius, Hans-Joachim; McConkey, Brendan J; David, Charles N

2012-01-01

The single-cell layered ectoderm of the fresh water polyp Hydra fulfills the function of an epidermis by protecting the animals from the surrounding medium. Its outer surface is covered by a fibrous structure termed the cuticle layer, with similarity to the extracellular surface coats of mammalian epithelia. In this paper we have identified molecular components of the cuticle. We show that its outermost layer contains glycoproteins and glycosaminoglycans and we have identified chondroitin and chondroitin-6-sulfate chains. In a search for proteins that could be involved in organising this structure we found PPOD proteins and several members of a protein family containing only SWT (sweet tooth) domains. Structural analyses indicate that PPODs consist of two tandem β-trefoil domains with similarity to carbohydrate-binding sites found in lectins. Experimental evidence confirmed that PPODs can bind sulfated glycans and are secreted into the cuticle layer from granules localized under the apical surface of the ectodermal epithelial cells. PPODs are taxon-specific proteins which appear to have entered the Hydra genome by horizontal gene transfer from bacteria. Their acquisition at the time Hydra evolved from a marine ancestor may have been critical for the transition to the freshwater environment.

Horizontal Gene Transfer Contributed to the Evolution of Extracellular Surface Structures: The Freshwater Polyp Hydra Is Covered by a Complex Fibrous Cuticle Containing Glycosaminoglycans and Proteins of the PPOD and SWT (Sweet Tooth) Families

PubMed Central

Böttger, Angelika; Doxey, Andrew C.; Hess, Michael W.; Pfaller, Kristian; Salvenmoser, Willi; Deutzmann, Rainer; Geissner, Andreas; Pauly, Barbara; Altstätter, Johannes; Münder, Sandra; Heim, Astrid; Gabius, Hans-Joachim; McConkey, Brendan J.; David, Charles N.

2012-01-01

The single-cell layered ectoderm of the fresh water polyp Hydra fulfills the function of an epidermis by protecting the animals from the surrounding medium. Its outer surface is covered by a fibrous structure termed the cuticle layer, with similarity to the extracellular surface coats of mammalian epithelia. In this paper we have identified molecular components of the cuticle. We show that its outermost layer contains glycoproteins and glycosaminoglycans and we have identified chondroitin and chondroitin-6-sulfate chains. In a search for proteins that could be involved in organising this structure we found PPOD proteins and several members of a protein family containing only SWT (sweet tooth) domains. Structural analyses indicate that PPODs consist of two tandem β-trefoil domains with similarity to carbohydrate-binding sites found in lectins. Experimental evidence confirmed that PPODs can bind sulfated glycans and are secreted into the cuticle layer from granules localized under the apical surface of the ectodermal epithelial cells. PPODs are taxon-specific proteins which appear to have entered the Hydra genome by horizontal gene transfer from bacteria. Their acquisition at the time Hydra evolved from a marine ancestor may have been critical for the transition to the freshwater environment. PMID:23300632

Ablation plume structure and dynamics in ambient gas observed by laser-induced fluorescence imaging spectroscopy

NASA Astrophysics Data System (ADS)

Miyabe, M.; Oba, M.; Iimura, H.; Akaoka, K.; Khumaeni, A.; Kato, M.; Wakaida, I.

2015-08-01

The dynamic behavior of an ablation plume in ambient gas has been investigated by laser-induced fluorescence imaging spectroscopy. The second harmonic beam from an Nd:YAG laser (0.5-6 J/cm2) was focused on a sintered oxide pellet or a metal chip of gadolinium. The produced plume was subsequently intersected with a sheet-shaped UV beam from a dye laser so that time-resolved fluorescence images were acquired with an intensified CCD camera at various delay times. The obtained cross-sectional images of the plume indicate that the ablated ground state atoms and ions of gadolinium accumulate in a hemispherical contact layer between the plume and the ambient gas, and a cavity containing a smaller density of ablated species is formed near the center of the plume. At earlier expansion stage, another luminous component also expands in the cavity so that it coalesces into the hemispherical layer. The splitting and coalescence for atomic plume occur later than those for ionic plume. Furthermore, the hemispherical layer of neutral atoms appears later than that of ions; however, the locations of the layers are nearly identical. This coincidence of the appearance locations of the layers strongly suggests that the neutral atoms in the hemispherical layer are produced as a consequence of three-body recombination of ions through collisions with gas atoms. The obtained knowledge regarding plume expansion dynamics and detailed plume structure is useful for optimizing the experimental conditions for ablation-based spectroscopic analysis.

Formation, characterization, and dynamics of onion-like carbon structures for electrical energy storage from nanodiamonds using reactive force fields

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

Ganesh, P.; Kent, P. R. C.; Mochalin, V.

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbonnanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core of themore » nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbonnanostructure appears, with a shell-shell spacing of about ~3.4 Å for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large (~29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.« less

Formation, characterization and dynamics of onion like carbon structures from nanodiamonds using reactive force-fields for electrical energy storage

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

Kent, Paul R

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbon nanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core ofmore » the nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbon nanostructure appears, with a shell-shell spacing of about {approx}3.4 {angstrom} for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large ({approx}29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.« less

Insertion of Ag atoms into layered MoO{sub 3} via a template route

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

Shao, Ke, E-mail: shaoke@szu.edu.cn; Wang, Hao

2012-11-15

Graphical abstract: PVP–Ag{sup +} complex self-assembled with inorganic (Mo{sub x}O{sub y}){sub ∞}{sup n−} chains into a layered hybrid, in which the PVP–Ag complex was intercalated between the (Mo{sub x}O{sub y}){sub ∞}{sup n−} layers. Calcinations of this hybrid at 500 °C lead to formation of Ag/MoO{sub 3} nanohybrid. By this method we have successfully inserted Ag atoms into the semiconductor MoO{sub 3} lattice. Display Omitted Highlights: ► We fabricated a PVP–Ag/polyoxomolybdate layered hybrid via in situ self-assembly. ► The PVP–Ag complex has been inserted between the molybdenum oxide layers. ► This layered hybrid transformed into Ag/MoO{sub 3} nanocomposite after calcinations. ►more » HR-TEM images show that Ag atoms of about 1 nm have been inserted in the MoO{sub 3} layers. -- Abstract: We report insertion of Ag atoms into layered MoO{sub 3} via an in situ template route. PVP–Ag{sup +} complex self-assembled with inorganic (Mo{sub x}O{sub y}){sub ∞}{sup n−} chains into a layered hybrid, in which the PVP–Ag complex was intercalated between the (Mo{sub x}O{sub y}){sub ∞}{sup n−} layers. Calcinations of this hybrid at 500 °C lead to formation of Ag/MoO{sub 3} hybrid, in which Ag nanoparticles of about 1 nm have been inserted between the MoO{sub 3} layers. By this method pillared MoO{sub 3} has been obtained very easily. We believe that this research opens new routes to fabricate novel intercalation compounds and metal/semiconductor nanohybrids via an efficient and green route.« less

Two-band induced superconductivity in single-layer graphene and topological insulator bismuth selenide

NASA Astrophysics Data System (ADS)

Talantsev, E. F.; Crump, W. P.; Tallon, J. L.

2018-01-01

Proximity-induced superconductivity in single-layer graphene (SLG) and in topological insulators represent almost ideal examples of superconductivity in two dimensions. Fundamental mechanisms governing superconductivity in the 2D limit are of central interest for modern condensed-matter physics. To deduce fundamental parameters of superconductor/graphene/superconductor and superconductor/bismuth selenide/superconductor junctions we investigate the self-field critical currents in these devices using the formalism of the Ambegaokar-Baratoff model. Our central finding is that the induced superconducting state in SLG and bismuth selenide each exhibits gapping on two superconducting bands. Based on recent results obtained on ultra-thin films of natural superconductors, including single-atomic layer of iron selenide, double and triple atomic layers of gallium, and several atomic layer tantalum disulphide, we conclude that a two-band induced superconducting state in SLG and bismuth selenide is part of a wider, more general multiple-band phenomenology of currently unknown origin.

Permeability of Iris germanica’s multiseriate exodermis to water, NaCl, and ethanol

PubMed Central

Meyer, Chris J.; Steudle, Ernst

2011-01-01

The exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature exodermis) and on air-gap-exposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5×10−8 to 3.9×10−8 m s−1 MPa−1. Puncturing the MEX increased Lppc to 19×10−8 m s−1 MPa−1, indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress. PMID:21131546

Fabrication of Nanolaminates with Ultrathin Nanolayers Using Atomic Layer Deposition: Nucleation & Growth Issues

DTIC Science & Technology

2009-02-01

Tecnologia de Superficies y Materiales (SMCTSM), XXVII Congreso Nacional, Oaxaca, Oaxaca, Mexico, September 26, 2007. 26. "Atomic Layer Deposition of...Nanolaminates: Fabrication and Properties" (Plenary Lecture), Sociedad Mexicana de Ciencia y Tecnologia de Superficies y Materiales (SMCTSM), XXVII

Single-Layer Limit of Metallic Indium Overlayers on Si(111).

PubMed

Park, Jae Whan; Kang, Myung Ho

2016-09-09

Density-functional calculations are used to identify one-atom-thick metallic In phases grown on the Si(111) surface, which have long been sought in quest of the ultimate two-dimensional (2D) limit of metallic properties. We predict two metastable single-layer In phases, one sqrt[7]×sqrt[3] phase with a coverage of 1.4 monolayer (ML; here 1 ML refers to one In atom per top Si atom) and the other sqrt[7]×sqrt[7] phase with 1.43 ML, which indeed agree with experimental evidences. Both phases reveal quasi-1D arrangements of protruded In atoms, leading to 2D-metallic but anisotropic band structures and Fermi surfaces. This directional feature contrasts with the free-electron-like In-overlayer properties that are known to persist up to the double-layer thickness, implying that the ultimate 2D limit of In overlayers may have been achieved in previous studies of double-layer In phases.

In-plane heterostructures of graphene and hexagonal boron nitride with controlled domain sizes

NASA Astrophysics Data System (ADS)

Liu, Zheng; Ma, Lulu; Shi, Gang; Zhou, Wu; Gong, Yongji; Lei, Sidong; Yang, Xuebei; Zhang, Jiangnan; Yu, Jingjiang; Hackenberg, Ken P.; Babakhani, Aydin; Idrobo, Juan-Carlos; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M.

2013-02-01

Graphene and hexagonal boron nitride (h-BN) have similar crystal structures with a lattice constant difference of only 2%. However, graphene is a zero-bandgap semiconductor with remarkably high carrier mobility at room temperature, whereas an atomically thin layer of h-BN is a dielectric with a wide bandgap of ~5.9 eV. Accordingly, if precise two-dimensional domains of graphene and h-BN can be seamlessly stitched together, hybrid atomic layers with interesting electronic applications could be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically patterned h-BN atomic layers. Our approach can create periodic arrangements of domains with size ranging from tens of nanometres to millimetres. The resulting graphene/h-BN atomic layers can be peeled off the growth substrate and transferred to various platforms including flexible substrates. We also show that the technique can be used to fabricate two-dimensional devices, such as a split closed-loop resonator that works as a bandpass filter.

Effect of additional elements on compositional modulated atomic layered structure of hexagonal Co{sub 80}Pt{sub 20} alloy films with superlattice diffraction

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

Hinata, Shintaro; Research Fellowship Division Japan Society for the Promotion of Science; Yamane, Akira

2016-05-15

The effect of additional element on compositionally modulated atomic layered structure of hexagonal Co{sub 80}Pt{sub 20} alloy films with superlattice diffraction was investigated. In this study it is found that the addition of Cr or W element to Co{sub 80}Pt{sub 20} alloy film shows less deterioration of hcp stacking structure and compositionally modulated atomic layer stacking structure as compared to Si or Zr or Ti with K{sub u} of around 1.4 or 1.0 × 10{sup 7} erg/cm{sup 3} at 5 at.% addition. Furthermore, for O{sub 2} addition of O{sub 2} ≥ 5.0 × 10{sup −3} Pa to CoPt alloy, compositionallymore » modulated atomic layer stacking structure will be deteriorated with enhancement of formation of hcp stacking structure which leads higher K{sub u} of 1.0 × 10{sup 7} erg/cm{sup 3}.« less

Biological fabrication of cellulose fibers with tailored properties

NASA Astrophysics Data System (ADS)

Natalio, Filipe; Fuchs, Regina; Cohen, Sidney R.; Leitus, Gregory; Fritz-Popovski, Gerhard; Paris, Oskar; Kappl, Michael; Butt, Hans-Jürgen

2017-09-01

Cotton is a promising basis for wearable smart textiles. Current approaches that rely on fiber coatings suffer from function loss during wear. We present an approach that allows biological incorporation of exogenous molecules into cotton fibers to tailor the material’s functionality. In vitro model cultures of upland cotton (Gossypium hirsutum) are incubated with 6-carboxyfluorescein-glucose and dysprosium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-glucose, where the glucose moiety acts as a carrier capable of traveling from the vascular connection to the outermost cell layer of the ovule epidermis, becoming incorporated into the cellulose fibers. This yields fibers with unnatural properties such as fluorescence or magnetism. Combining biological systems with the appropriate molecular design offers numerous possibilities to grow functional composite materials and implements a material-farming concept.

Oxidative stress in entomopathogenic fungi grown on insect-like hydrocarbons.

PubMed

Huarte-Bonnet, Carla; Juárez, M Patricia; Pedrini, Nicolás

2015-08-01

Entomopathogenic fungi mostly attack their insect hosts by penetration through the cuticle. The outermost insect surface is covered by a lipid-rich layer, usually composed of very long chain hydrocarbons. These fungi are apt to grow on straight chain hydrocarbons (alkanes) as the sole carbon source. Insect-like hydrocarbons are first hydroxylated by a microsomal P450 monooxygenase system, and then fully catabolized by peroxisomal β-oxidation reactions in Beauveria bassiana. In this review, we will discuss lipid metabolism adaptations in alkane-grown fungi, and how an oxidative stress scenario is established under these conditions. Fungi have to pay a high cost for hydrocarbon utilization; high levels of reactive oxygen species are produced and a concomitant antioxidant response is triggered in fungal cells to cope with this drawback.

The Polyketide Components of Waxes and the Cer-cqu Gene Cluster Encoding a Novel Polyketide Synthase, the β-Diketone Synthase, DKS

PubMed Central

von Wettstein-Knowles, Penny

2017-01-01

The primary function of the outermost, lipophilic layer of plant aerial surfaces, called the cuticle, is preventing non-stomatal water loss. Its exterior surface is often decorated with wax crystals, imparting a blue–grey color. Identification of the barley Cer-c, -q and -u genes forming the 101 kb Cer-cqu gene cluster encoding a novel polyketide synthase—the β-diketone synthase (DKS), a lipase/carboxyl transferase, and a P450 hydroxylase, respectively, establishes a new, major pathway for the synthesis of plant waxes. The major product is a β-diketone (14,16-hentriacontane) aliphatic that forms long, thin crystalline tubes. A pathway branch leads to the formation of esterified alkan-2-ols. PMID:28698520

CVD synthesis of large-area, highly crystalline MoSe2 atomic layers on diverse substrates and application to photodetectors.

PubMed

Xia, Jing; Huang, Xing; Liu, Ling-Zhi; Wang, Meng; Wang, Lei; Huang, Ben; Zhu, Dan-Dan; Li, Jun-Jie; Gu, Chang-Zhi; Meng, Xiang-Min

2014-08-07

Synthesis of large-area, atomically thin transition metal dichalcogenides (TMDs) on diverse substrates is of central importance for the large-scale fabrication of flexible devices and heterojunction-based devices. In this work, we successfully synthesized a large area of highly-crystalline MoSe2 atomic layers on SiO2/Si, mica and Si substrates using a simple chemical vapour deposition (CVD) method at atmospheric pressure. Atomic force microscopy (AFM) and Raman spectroscopy reveal that the as-grown ultrathin MoSe2 layers change from a single layer to a few layers. Photoluminescence (PL) spectroscopy demonstrates that while the multi-layer MoSe2 shows weak emission peaks, the monolayer has a much stronger emission peak at ∼ 1.56 eV, indicating the transition from an indirect to a direct bandgap. Transmission electron microscopy (TEM) analysis confirms the single-crystallinity of MoSe2 layers with a hexagonal structure. In addition, the photoresponse performance of photodetectors based on MoSe2 monolayer was studied for the first time. The devices exhibit a rapid response of ∼ 60 ms and a good photoresponsivity of ∼ 13 mA/W (using a 532 nm laser at an intensity of 1 mW mm(-2) and a bias of 10 V), suggesting that MoSe2 monolayer is a promising material for photodetection applications.

Atomic Precision Plasma Processing - Modeling Investigations

NASA Astrophysics Data System (ADS)

Rauf, Shahid

2016-09-01

Sub-nanometer precision is increasingly being required of many critical plasma processes in the semiconductor industry. Some of these critical processes include atomic layer etch and plasma enhanced atomic layer deposition. Accurate control over ion energy and ion / radical composition is needed during plasma processing to meet the demanding atomic-precision requirements. While improvements in mainstream inductively and capacitively coupled plasmas can help achieve some of these goals, newer plasma technologies can expand the breadth of problems addressable by plasma processing. Computational modeling is used to examine issues relevant to atomic precision plasma processing in this paper. First, a molecular dynamics model is used to investigate atomic layer etch of Si and SiO2 in Cl2 and fluorocarbon plasmas. Both planar surfaces and nanoscale structures are considered. It is shown that accurate control of ion energy in the sub-50 eV range is necessary for atomic scale precision. In particular, if the ion energy is greater than 10 eV during plasma processing, several atomic layers get damaged near the surface. Low electron temperature (Te) plasmas are particularly attractive for atomic precision plasma processing due to their low plasma potential. One of the most attractive options in this regard is energetic-electron beam generated plasma, where Te <0.5 eV has been achieved in plasmas of molecular gases. These low Te plasmas are computationally examined in this paper using a hybrid fluid-kinetic model. It is shown that such plasmas not only allow for sub-5 eV ion energies, but also enable wider range of ion / radical composition. Coauthors: Jun-Chieh Wang, Jason Kenney, Ankur Agarwal, Leonid Dorf, and Ken Collins.

China’s Historic Rights in the South China Sea: A Time for Reconsideration and Pacific Settlement

DTIC Science & Technology

2014-05-18

jurisdiction over internal waters as they do over land territory. 34 In the case of an archipelagic state (a state constituted wholly by one or...more archipelagos), the state “may draw straight archipelagic baseslines joining the outermost points of the outermost islands and drying reefs of the...archipelago”. 35 The territorial sea, contiguous zone, exclusive economic zone and continental shelf are measured from the archipelagic baseline

Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers

DOE PAGES

Anasori, Babak; Shi, Chenyang; Moon, Eun Ju; ...

2016-02-24

In this paper, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M 3C 2 and M 4C 3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX] nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M' 2M"C 2 and M' 2M" 2C 3 – where M' and M" are two different earlymore » transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M' atoms only occupy the outer layers and the M" atoms fill the middle layers. In other words, M' atomic layers sandwich the middle M"–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo 2TiC 2 and Mo 2Ti 2C 3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC] nM structures. The electronic properties of these Mo-containing MXenes are compared with their Ti 3C 2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo 2TiC 2T x exhibits semiconductor-like transport behavior, while Ti 3C 2T x is a metal. Finally, this finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.« less

Improvement of light extraction of LYSO scintillator by using a combination of self-assembly of nanospheres and atomic layer deposition.

PubMed

Zhu, Zhichao; Liu, Bo; Zhang, Haifeng; Ren, Weina; Cheng, Chuanwei; Wu, Shuang; Gu, Mu; Chen, Hong

2015-03-23

The self-assembled monolayer periodic array of polystyrene spheres conformally coated with TiO₂ layer using atomic layer deposition is designed to obtain a further enhancement of light extraction for LYSO scintillator. The maximum enhancement is 149% for the sample with polystyrene spheres conformally coated with TiO₂ layer, while the enhancement is only 76% for the sample with only polystyrene spheres. Such further enhancement could be contributed from the additional modes forming by TiO₂ layer due to its high refractive index, which can be approved by the simulation of electric field distribution. The experimental results are agreement with the simulated results. Furthermore, the prepared structured layer exhibits an excellent combination with the surface of scintillator, which is in favor of the practical application. Therefore, it is safely concluded that the combination of self-assembly method and atomic layer deposition is a promising approach to obtain a significant enhancement of light extraction for a large area. This method can be extended to many other luminescent materials and devices.

Secondary ion emission from phosphatidic acid sandwich films under atomic and molecular primary ion bombardment

NASA Astrophysics Data System (ADS)

Stapel, D.; Benninghoven, A.

2001-11-01

Secondary ion yields increase considerably when changing from atomic to molecular primary ions. Since secondary ion emission from deeper layers could result in a pronounced yield increase, the secondary ion emission depth of molecular fragments was investigated. A phosphatidic acid Langmuir-Blodgett (LB) sandwich system was applied. The well-defined layer structure of the applied sample allows the assignment of different depths of origin to the selected fragment ions. At least 93% of the detected characteristic molecular fragment ions originate from the first and second layers. This holds true for all applied atomic and molecular primary ions.

Mid-latitude empirical model of the height distribution of atomic oxygen in the MLT region for different solar and geophysical conditions

NASA Astrophysics Data System (ADS)

Semenov, A.; Shefov, N.; Fadel, Kh.

The model of altitude distributions of atomic oxygen in the region of the mesopause and lower thermosphere (MLT) is constructed on the basis of empirical models of variations of the intensities, temperatures and altitudes of maximum of the layers of the emissions of atomic oxygen at 557.7 nm, hydroxyl and Atmospheric system of molecular oxygen. An altitude concentration distribution of neutral components is determined on the basis of systematization of the long-term data of temperature of the middle atmosphere from rocket, nightglow and ionospheric measurements at heights of 30-110 km in middle latitudes. They include dependence on a season, solar activity and a long-term trend. Examples of results of calculation for different months of year for conditions of the lower and higher solar activity are presented. With increasing of solar activity, the height of a layer of a maximum of atomic oxygen becomes lower, and the thickness of the layer increases. There is a high correlation between characteristics of a layer of atomic oxygen and a maximum of temperature at heights of the mesopause and lower thermosphere. This work is supported by grant of ISTC No. 2274.

Dynamical screening of the van der Waals interaction between graphene layers.

PubMed

Dappe, Y J; Bolcatto, P G; Ortega, J; Flores, F

2012-10-24

The interaction between graphene layers is analyzed combining local orbital DFT and second order perturbation theory. For this purpose we use the linear combination of atomic orbitals-orbital occupancy (LCAO-OO) formalism, that allows us to separate the interaction energy as the sum of a weak chemical interaction between graphene layers plus the van der Waals interaction (Dappe et al 2006 Phys. Rev. B 74 205434). In this work, the weak chemical interaction is calculated by means of corrected-LDA calculations using an atomic-like sp(3)d(5) basis set. The van der Waals interaction is calculated by means of second order perturbation theory using an atom-atom interaction approximation and the atomic-like-orbital occupancies. We also analyze the effect of dynamical screening in the van der Waals interaction using a simple model. We find that this dynamical screening reduces by 40% the van der Waals interaction. Taking this effect into account, we obtain a graphene-graphene interaction energy of 70 ± 5 meV/atom in reasonable agreement with the experimental evidence.

Scaffolding proteins in the development and maintenance of the epidermal permeability barrier.

PubMed

Crawford, Melissa; Dagnino, Lina

2017-10-02

The skin of mammals and other terrestrial vertebrates protects the organism against the external environment, preventing heat, water and electrolyte loss, as well as entry of chemicals and pathogens. Impairments in the epidermal permeability barrier function are associated with the genesis and/or progression of a variety of pathological conditions, including genetic inflammatory diseases, microbial and viral infections, and photodamage induced by UV radiation. In mammals, the outside-in epidermal permeability barrier is provided by the joint action of the outermost cornified layer, together with assembled tight junctions in granular keratinocytes found in the layers underneath. Tight junctions serve as both outside-in and inside-out barriers, and impede paracellular movements of ions, water, macromolecules and microorganisms. At the molecular level, tight junctions consist of integral membrane proteins that form an extracellular seal between adjacent cells, and associate with cytoplasmic scaffold proteins that serve as links with the actin cytoskeleton. In this review, we address the roles that scaffold proteins play specifically in the establishment and maintenance of the epidermal permeability barrier, and how various pathologies alter or impair their functions.

On the wetting properties of human stratum corneum epidermidis surface exposed to cold atmospheric-pressure pulsed plasma

NASA Astrophysics Data System (ADS)

Athanasopoulos, D.; Svarnas, P.; Ladas, S.; Kennou, S.; Koutsoukos, P.

2018-05-01

The Stratum corneum is the outermost layer of the skin, acting as a protective barrier of the epidermis, and its surface properties are directly related to the spreading of topically applied drugs and cosmetics. Numerous works have been devoted to the wettability of this layer over the past 70 years, but, despite the extensive application of atmospheric-pressure plasmas to dermatology, stratum corneum wettability with respect to plasma-induced species has never been considered. The present report assesses the treatment of human stratum corneum epidermidis by atmospheric-pressure pulsed cold plasma-jets for various time intervals and both chemical and morphological modifications are probed. The increase and saturation of the surface free energy due to functionalization are demonstrated, whereas prolonged treatment leads to tissue local disruption (tissue integrity is lost, and stratum corneum looks exfoliated, porous, and even thermally damaged). The latter point arises skepticism about the common practice of contacting atmospheric-pressure plasmas with skin without any previous precautions since the lost skin surface integrity may allow the penetration of pathogenic microorganisms.

Diffuse reflectance spectroscopy and optical polarization imaging of in-vivo biological tissue

NASA Astrophysics Data System (ADS)

Mora-Núñez, A.; Castillejos, Y.; García-Torales, G.; Martínez-Ponce, G.

2013-11-01

A number of optical techniques have been reported in the scientific literature as accomplishable methodologies to diagnose diseases in biological tissue, for instance, diffuse reflectance spectroscopy (DRS) and optical polarization imaging (OPI). The skin is the largest organ in the body and consists of three primary layers, namely, the epidermis (the outermost layer exposed to the world), the dermis, and the hypodermis. The epidermis changes from to site to site, mainly because of difference in hydration. A lower water content increase light scattering and reduce the penetration depth of radiation. In this work, two hairless mice have been selected to evaluate their skin features by using DRS and OPI. Four areas of the specimen body were chosen to realize the comparison: back, abdomen, tail, and head. From DRS, it was possible to distinguish the skin nature because of different blood irrigation at dermis. In the other hand, OPI shows pseudo-depolarizing regions in the measured Mueller images related to a spatially varying propagation of the scattered light. This provides information about the cell size in the irradiated skin.

Paradigm shift regarding the transversalis fascia, preperitoneal space, and Retzius' space.

PubMed

Asakage, N

2018-06-01

There has been confusion in the anatomical recognition when performing inguinal hernia operations in Japan. From now on, a paradigm shift from the concept of two-dimensional layer structure to the three-dimensional space recognition is necessary to promote an understanding of anatomy. Along with the formation of the abdominal wall, the extraperitoneal space is formed by the transversalis fascia and preperitoneal space. The transversalis fascia is a somatic vascular fascia originating from an arteriovenous fascia. It is a dense areolar tissue layer at the outermost of the extraperitoneal space that runs under the diaphragm and widely lines the body wall muscle. The umbilical funiculus is taken into the abdominal wall and transformed into the preperitoneal space that is a local three-dimensional cavity enveloping preperitoneal fasciae composed of the renal fascia, vesicohypogastric fascia, and testiculoeferential fascia. The Retzius' space is an artificial cavity formed at the boundary between the transversalis fascia and preperitoneal space. In the underlay mesh repair, the mesh expands in the range spanning across the Retzius' space and preperitoneal space.

Nuclear fuel elements and method of making same

DOEpatents

Schweitzer, Donald G.

1992-01-01

A nuclear fuel element for a high temperature gas nuclear reactor that has an average operating temperature in excess of 2000.degree. C., and a method of making such a fuel element. The fuel element is characterized by having fissionable fuel material localized and stabilized within pores of a carbon or graphite member by melting the fissionable material to cause it to chemically react with the carbon walls of the pores. The fissionable fuel material is further stabilized and localized within the pores of the graphite member by providing one or more coatings of pyrolytic carbon or diamond surrounding the porous graphite member so that each layer defines a successive barrier against migration of the fissionable fuel from the pores, and so that the outermost layer of pyrolytic carbon or diamond forms a barrier between the fissionable material and the moderating gases used in an associated high temperature gas reactor. The method of the invention provides for making such new elements either as generally spherically elements, or as flexible filaments, or as other relatively small-sized fuel elements that are particularly suited for use in high temperature gas reactors.

Excellent Resistive Switching Performance of Cu-Se-Based Atomic Switch Using Lanthanide Metal Nanolayer at the Cu-Se/Al2O3 Interface.

PubMed

Woo, Hyunsuk; Vishwanath, Sujaya Kumar; Jeon, Sanghun

2018-03-07

The next-generation electronic society is dependent on the performance of nonvolatile memory devices, which has been continuously improving. In the last few years, many memory devices have been introduced. However, atomic switches are considered to be a simple and reliable basis for next-generation nonvolatile devices. In general, atomic switch-based resistive switching is controlled by electrochemical metallization. However, excess ion injection from the entire area of the active electrode into the switching layer causes device nonuniformity and degradation of reliability. Here, we propose the fabrication of a high-performance atomic switch based on Cu x -Se 1- x by inserting lanthanide (Ln) metal buffer layers such as neodymium (Nd), samarium (Sm), dysprosium (Dy), or lutetium (Lu) between the active metal layer and the electrolyte. Current-atomic force microscopy results confirm that Cu ions penetrate through the Ln-buffer layer and form thin conductive filaments inside the switching layer. Compared with the Pt/Cu x -Se 1- x /Al 2 O 3 /Pt device, the optimized Pt/Cu x -Se 1- x /Ln/Al 2 O 3 /Pt devices show improvement in the on/off resistance ratio (10 2 -10 7 ), retention (10 years/85 °C), endurance (∼10 000 cycles), and uniform resistance state distribution.

Effects of alterations of the E. coli lipopolysaccharide layer on membrane permeabilization events induced by Cecropin A.

PubMed

Agrawal, Anurag; Weisshaar, James C

2018-04-22

The outermost layer of Gram negative bacteria is composed of a lipopolysaccharide (LPS) network that forms a dense protective hydrophilic barrier against entry of hydrophobic drugs. At low μM concentrations, a large family of cationic polypeptides known as antimicrobial peptides (AMPs) are able to penetrate the LPS layer and permeabilize the outer membrane (OM) and the cytoplasmic membrane (CM), causing cell death. Cecropin A is a well-studied cationic AMP from moth. Here a battery of time-resolved, single-cell microscopy experiments explores how deletion of sugar layers and/or phosphoryl negative charges from the core oligosaccharide layer (core OS) of K12 E. coli alters the timing of OM and CM permeabilization induced by Cecropin A. Deletion of sugar layers, or phosphoryl charges, or both from the core OS shortens the time to the onset of OM permeabilization to periplasmic GFP and also the lag time between OM permeabilization and CM permeabilization. Meanwhile, the 12-h minimum inhibitory concentration (MIC) changes only twofold with core OS alterations. The results suggest a two-step model in which the core oligosaccharide layers act as a kinetic barrier to penetration of Cecropin A to the lipid A outer leaflet of the OM. Once a threshold concentration has built up at the lipid A leaflet, nucleation occurs and the OM is locally permeabilized to GFP and, by inference, to Cecropin A. Whenever Cecropin A permeabilizes the OM, CM permeabilization always follows, and cell growth subsequently halts and never recovers on the 45 min observation timescale. Copyright © 2018 Elsevier B.V. All rights reserved.

Atomic Resolution Structural and Chemical Imaging Revealing the Sequential Migration of Ni, Co, and Mn upon the Battery Cycling of Layered Cathode

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

Yan, Pengfei; Zheng, Jianming; Zhang, Ji-Guang

Layered lithium transition metal oxides (LTMO) are promising candidate cathode materials for next generation high energy density lithium ion battery. The challenge for using this category of cathode is the capacity and voltage fading, which is believed to be associated with the layered structure disordering, a process that is initiated from the surface or solid-electrolyte interface and facilitated by transition metal (TM) reduction and oxygen vacancy formation. However, the atomic level dynamic mechanism of such a layered structure disordering is still not fully clear. In this work, utilizing atomic resolution electron energy loss spectroscopy (EELS), we map, for the firstmore » time at atomic scale, the spatial evolution of Ni, Co and Mn in a cycled LiNi1/3M1/3Co1/3O2 layered cathode. In combination with atomic level structural imaging, we discovered the direct correlation of TM ions migration behavior with lattice disordering, featuring the residing of TM ions in the tetrahedral site and a sequential migration of Ni, Co, and Mn upon the increased lattice disordering of the layered structure. This work highlights that Ni ions, though acting as the dominant redox species in many LTMO, are labile to migrate to cause lattice disordering upon battery cycling; while the Mn ions are more stable as compared with Ni and Co and can act as pillar to stabilize layered structure. Direct visualization of the behavior of TM ions during the battery cycling provides insight for designing of cathode with structural stability and correspondingly a superior performance.« less

Strain-Tuning Atomic Substitution in Two-Dimensional Atomic Crystals.

PubMed

Li, Honglai; Liu, Hongjun; Zhou, Linwei; Wu, Xueping; Pan, Yuhao; Ji, Wei; Zheng, Biyuan; Zhang, Qinglin; Zhuang, Xiujuan; Zhu, Xiaoli; Wang, Xiao; Duan, Xiangfeng; Pan, Anlian

2018-05-22

Atomic substitution offers an important route to achieve compositionally engineered two-dimensional nanostructures and their heterostructures. Despite the recent research progress, the fundamental understanding of the reaction mechanism has still remained unclear. Here, we reveal the atomic substitution mechanism of two-dimensional atomic layered materials. We found that the atomic substitution process depends on the varying lattice constant (strain) in monolayer crystals, dominated by two strain-tuning (self-promoted and self-limited) mechanisms using density functional theory calculations. These mechanisms were experimentally confirmed by the controllable realization of a graded substitution ratio in the monolayers by controlling the substitution temperature and time and further theoretically verified by kinetic Monte Carlo simulations. The strain-tuning atomic substitution processes are of general importance to other two-dimensional layered materials, which offers an interesting route for tailoring electronic and optical properties of these materials.

Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

DOE PAGES

Xie, Shuifen; Choi, Sang -Il; Lu, Ning; ...

2014-05-05

Here, an effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the depositedmore » Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@Pt nL (n = 1–6) core–shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt 2–3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt 1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.« less

Broadband atomic-layer MoS₂ optical modulators for ultrafast pulse generations in the visible range.

PubMed

Zhang, Yuxia; Yu, Haohai; Zhang, Rui; Zhao, Gang; Zhang, Huaijin; Chen, Yanxue; Mei, Liangmo; Tonelli, Mauro; Wang, Jiyang

2017-02-01

Visible lasers are a fascinating regime, and their significance is illustrated by the 2014 Noble prizes in physics and chemistry. With the development of blue laser diodes (LDs), the LD-pumped solid-state visible lasers become a burgeoning direction today. Constrained by the scarce visible optical modulators, the solid-state ultrafast visible lasers are rarely realized. Based on the bandgap structure and optoelectronic properties of atomic-layer MoS₂, it can be proposed that MoS₂ has the potential as a visible optical modulator. Here, by originally revealing layer-dependent nonlinear absorption of the atomic-layer MoS₂ in the visible range, broadband atomic-layer MoS₂ optical modulators for the visible ultrafast pulse generation are developed and selected based on the proposed design criteria for novel two-dimensional (2D) optical modulators. By applying the selected MoS₂ optical modulators in the solid-state praseodymium lasers, broadband mode-locked ultrafast lasers from 522 to 639 nm are originally realized. We believe that this Letter should promote the development of visible ultrafast photonics and further applications of 2D optoelectronic materials.

The role of Ag buffer layer in Fe islands growth on Ge (111) surfaces

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

Fu, Tsu-Yi, E-mail: phtifu@phy.ntnu.edu.tw; Wu, Jia-Yuan; Jhou, Ming-Kuan

2015-05-07

Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kindsmore » of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed.« less

A combined scanning tunneling microscope-atomic layer deposition tool.

PubMed

Mack, James F; Van Stockum, Philip B; Iwadate, Hitoshi; Prinz, Fritz B

2011-12-01

We have built a combined scanning tunneling microscope-atomic layer deposition (STM-ALD) tool that performs in situ imaging of deposition. It operates from room temperature up to 200 °C, and at pressures from 1 × 10(-6) Torr to 1 × 10(-2) Torr. The STM-ALD system has a complete passive vibration isolation system that counteracts both seismic and acoustic excitations. The instrument can be used as an observation tool to monitor the initial growth phases of ALD in situ, as well as a nanofabrication tool by applying an electric field with the tip to laterally pattern deposition. In this paper, we describe the design of the tool and demonstrate its capability for atomic resolution STM imaging, atomic layer deposition, and the combination of the two techniques for in situ characterization of deposition.

Atomic layer deposition of ultrathin blocking layer for low-temperature solid oxide fuel cell on nanoporous substrate

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

Yu, Wonjong; Cho, Gu Young; Noh, Seungtak

2015-01-15

An ultrathin yttria-stabilized zirconia (YSZ) blocking layer deposited by atomic layer deposition (ALD) was utilized for improving the performance and reliability of low-temperature solid oxide fuel cells (SOFCs) supported by an anodic aluminum oxide substrate. Physical vapor-deposited YSZ and gadolinia-doped ceria (GDC) electrolyte layers were deposited by a sputtering method. The ultrathin ALD YSZ blocking layer was inserted between the YSZ and GDC sputtered layers. To investigate the effects of an inserted ultrathin ALD blocking layer, SOFCs with and without an ultrathin ALD blocking layer were electrochemically characterized. The open circuit voltage (1.14 V) of the ALD blocking-layered SOFC was visiblymore » higher than that (1.05 V) of the other cell. Furthermore, the ALD blocking layer augmented the power density and improved the reproducibility.« less

Atomic Layer Deposition of Electron Selective SnOx and ZnO Films on Mixed Halide Perovskite: Compatibility and Performance.

PubMed

Hultqvist, Adam; Aitola, Kerttu; Sveinbjörnsson, Kári; Saki, Zahra; Larsson, Fredrik; Törndahl, Tobias; Johansson, Erik; Boschloo, Gerrit; Edoff, Marika

2017-09-06

The compatibility of atomic layer deposition directly onto the mixed halide perovskite formamidinium lead iodide:methylammonium lead bromide (CH(NH 2 ) 2 , CH 3 NH 3 )Pb(I,Br) 3 (FAPbI 3 :MAPbBr 3 ) perovskite films is investigated by exposing the perovskite films to the full or partial atomic layer deposition processes for the electron selective layer candidates ZnO and SnO x . Exposing the samples to the heat, the vacuum, and even the counter reactant of H 2 O of the atomic layer deposition processes does not appear to alter the perovskite films in terms of crystallinity, but the choice of metal precursor is found to be critical. The Zn precursor Zn(C 2 H 5 ) 2 either by itself or in combination with H 2 O during the ZnO atomic layer deposition (ALD) process is found to enhance the decomposition of the bulk of the perovskite film into PbI 2 without even forming ZnO. In contrast, the Sn precursor Sn(N(CH 3 ) 2 ) 4 does not seem to degrade the bulk of the perovskite film, and conformal SnO x films can successfully be grown on top of it using atomic layer deposition. Using this SnO x film as the electron selective layer in inverted perovskite solar cells results in a lower power conversion efficiency of 3.4% than the 8.4% for the reference devices using phenyl-C 70 -butyric acid methyl ester. However, the devices with SnO x show strong hysteresis and can be pushed to an efficiency of 7.8% after biasing treatments. Still, these cells lacks both open circuit voltage and fill factor compared to the references, especially when thicker SnO x films are used. Upon further investigation, a possible cause of these losses could be that the perovskite/SnO x interface is not ideal and more specifically found to be rich in Sn, O, and halides, which is probably a result of the nucleation during the SnO x growth and which might introduce barriers or alter the band alignment for the transport of charge carriers.

Atomic study on the ordered structure in Al melts induced by liquid/substrate interface with Ti solute

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

Zhang, H. L.; Han, Y. F., E-mail: yfhan@sjtu.edu.cn, E-mail: bdsun@sjtu.edu.cn; Zhou, W.

2015-01-26

Atomic ordering in Al melts induced by liquid/substrate interface with Ti solute was investigated by ab initio molecular dynamics simulations and in-situ synchrotron X-ray diffraction. It is predicted that deformed nanoscale ordering Al layers with a rhombohedral-centered hexagonal structure (R3{sup ¯}m space group) instead of the intrinsic fcc structure (Fm3{sup ¯}m space group) form on substrate at temperature above Al liquids. With Al atoms stacking away from the interface, the ordering structure reaches a critical thickness, which inhibits the consecutive stacking of Al atoms on substrates. The locally stacking reconstruction induced by Ti atom relieves the accumulated elastic strain energymore » in ordered Al layers, facilitating fully heterogeneous nucleation on substrate beyond the deformed ordering Al layer around the melting point. The roles of liquid/substrate interface with Ti solute in the physical behavior of heterogeneous nucleation on substrate were discussed.« less

Atomic Layer Engineering of High-κ Ferroelectricity in 2D Perovskites.

PubMed

Li, Bao-Wen; Osada, Minoru; Kim, Yoon-Hyun; Ebina, Yasuo; Akatsuka, Kosho; Sasaki, Takayoshi

2017-08-09

Complex perovskite oxides offer tremendous potential for controlling their rich variety of electronic properties, including high-T C superconductivity, high-κ ferroelectricity, and quantum magnetism. Atomic-scale control of these intriguing properties in ultrathin perovskites is an important challenge for exploring new physics and device functionality at atomic dimensions. Here, we demonstrate atomic-scale engineering of dielectric responses using two-dimensional (2D) homologous perovskite nanosheets (Ca 2 Na m-3 Nb m O 3m+1 ; m = 3-6). In this homologous 2D material, the thickness of the perovskite layers can be incrementally controlled by changing m, and such atomic layer engineering enhances the high-κ dielectric response and local ferroelectric instability. The end member (m = 6) attains a high dielectric constant of ∼470, which is the highest among all known dielectrics in the ultrathin region (<10 nm). These results provide a new strategy for achieving high-κ ferroelectrics for use in ultrascaled high-density capacitors and post-graphene technology.

Atomic intercalation to measure adhesion of graphene on graphite

PubMed Central

Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; Belianinov, Alexei; Kalinin, Sergei V.; Baddorf, Arthur P.; Maksymovych, Petro

2016-01-01

The interest in mechanical properties of two-dimensional materials has emerged in light of new device concepts taking advantage of flexing, adhesion and friction. Here we demonstrate an effective method to measure adhesion of graphene atop highly ordered pyrolytic graphite, utilizing atomic-scale ‘blisters' created in the top layer by neon atom intercalates. Detailed analysis of scanning tunnelling microscopy images is used to reconstruct atomic positions and the strain map within the deformed graphene layer, and demonstrate the tip-induced subsurface translation of neon atoms. We invoke an analytical model, originally devised for graphene macroscopic deformations, to determine the graphite adhesion energy of 0.221±0.011 J m−2. This value is in excellent agreement with reported macroscopic values and our atomistic simulations. This implies mechanical properties of graphene scale down to a few-nanometre length. The simplicity of our method provides a unique opportunity to investigate the local variability of nanomechanical properties in layered materials. PMID:27796294

Atomistics of Ge deposition on Si(100) by atomic layer epitaxy.

PubMed

Lin, D S; Wu, J L; Pan, S Y; Chiang, T C

2003-01-31

Chlorine termination of mixed Ge/Si(100) surfaces substantially enhances the contrast between Ge and Si sites in scanning tunneling microscopy observations. This finding enables a detailed investigation of the spatial distribution of Ge atoms deposited on Si(100) by atomic layer epitaxy. The results are corroborated by photoemission measurements aided by an unusually large chemical shift between Cl adsorbed on Si and Ge. Adsorbate-substrate atomic exchange during growth is shown to be important. The resulting interface is thus graded, but characterized by a very short length scale of about one monolayer.

76 FR 15945 - Application(s) for Duty-Free Entry of Scientific Instruments

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-22

.... 9700 South Cass Ave., Lemont, IL 60439. Instrument: TFS500 Atomic Layer Deposition System. Manufacturer: Beneq OY, Finland. Intended Use: The instrument will be used in experiments on atomic layer deposition... and precursor combinations. For the research the instrument is required to have a modular deposition...

Fermi level de-pinning of aluminium contacts to n-type germanium using thin atomic layer deposited layers

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

Gajula, D. R., E-mail: dgajula01@qub.ac.uk; Baine, P.; Armstrong, B. M.

Fermi-level pinning of aluminium on n-type germanium (n-Ge) was reduced by insertion of a thin interfacial dielectric by atomic layer deposition. The barrier height for aluminium contacts on n-Ge was reduced from 0.7 eV to a value of 0.28 eV for a thin Al{sub 2}O{sub 3} interfacial layer (∼2.8 nm). For diodes with an Al{sub 2}O{sub 3} interfacial layer, the contact resistance started to increase for layer thicknesses above 2.8 nm. For diodes with a HfO{sub 2} interfacial layer, the barrier height was also reduced but the contact resistance increased dramatically for layer thicknesses above 1.5 nm.

Fabrication of low-temperature solid oxide fuel cells with a nanothin protective layer by atomic layer deposition

PubMed Central

2013-01-01

Anode aluminum oxide-supported thin-film fuel cells having a sub-500-nm-thick bilayered electrolyte comprising a gadolinium-doped ceria (GDC) layer and an yttria-stabilized zirconia (YSZ) layer were fabricated and electrochemically characterized in order to investigate the effect of the YSZ protective layer. The highly dense and thin YSZ layer acted as a blockage against electron and oxygen permeation between the anode and GDC electrolyte. Dense GDC and YSZ thin films were fabricated using radio frequency sputtering and atomic layer deposition techniques, respectively. The resulting bilayered thin-film fuel cell generated a significantly higher open circuit voltage of approximately 1.07 V compared with a thin-film fuel cell with a single-layered GDC electrolyte (approximately 0.3 V). PMID:23342963

Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane

PubMed Central

Zhao, Yan; Liu, Huimin; Tang, Kaini; Jin, Yali; Pan, Jiefeng; der Bruggen, Bart Van; Shen, Jiangnan; Gao, Congjie

2016-01-01

A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes (AEMs). Three-layer architecture was developed by deposition of polydopamine (PDA) and electro-deposition of N-O-sulfonic acid benzyl chitosan (NSBC). The innermost and outermost layers were PDA with different deposition time. The middle layer was prepared by NSBC. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs. The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes. A series of electrodialysis experiments in which Cl−/SO42− separation was studied, demonstrating the monovalent anion selectivity of the samples. The Cl−/SO42− permselectivity of the modified membranes can reach up to 2.20, higher than that of the commercial membrane (only 0.78) during 90 minutes in electrodialysis (ED). The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties. Sodium dodecyl benzene sulfonate (SDBS) was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 Ωcm2 30 minutes later. PMID:27853255

Water-induced polaron formation at the pentacene surface: Quantum mechanical molecular mechanics simulations

NASA Astrophysics Data System (ADS)

Cramer, Tobias; Steinbrecher, Thomas; Koslowski, Thorsten; Case, David A.; Biscarini, Fabio; Zerbetto, Francesco

2009-04-01

Water is an omnipresent polar impurity that is expected to be the origin of many electric degradation phenomena observed in organic semiconductors. Here, we describe a microscopic model for polaron formation in the outermost layer of a pentacene crystal due to the polarization of a nearby water layer. The efficient coupling of a classical force field that describes the liquid with a tight-binding model that represents the π system of the organic layer permits the calculation of nanosecond length trajectories. The model predicts that the reorientation of water dipoles stabilizes positive charge carriers on average by 0.6 eV and thus leads to a polaron trap state at the liquid interface. Thermal fluctuations of the water molecules provoke two-dimensional diffusive hopping of the charge carrier parallel to the interface with mobilities of up to 0.6cm2s-1V-1 and lead to an amorphous broadening of the valence-band tail. As a consequence, water-filled nanocavities act as trapping sites in pentacene transistors. Instead, a complete wetting of the organic film is expected to result in fast thermally activated hopping transport. Polaron trapping is thus not expected to be a limiting factor for transistor-based sensors that operate under water.

Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane.

PubMed

Zhao, Yan; Liu, Huimin; Tang, Kaini; Jin, Yali; Pan, Jiefeng; der Bruggen, Bart Van; Shen, Jiangnan; Gao, Congjie

2016-11-17

A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes (AEMs). Three-layer architecture was developed by deposition of polydopamine (PDA) and electro-deposition of N-O-sulfonic acid benzyl chitosan (NSBC). The innermost and outermost layers were PDA with different deposition time. The middle layer was prepared by NSBC. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs. The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes. A series of electrodialysis experiments in which Cl - /SO 4 2- separation was studied, demonstrating the monovalent anion selectivity of the samples. The Cl - /SO 4 2- permselectivity of the modified membranes can reach up to 2.20, higher than that of the commercial membrane (only 0.78) during 90 minutes in electrodialysis (ED). The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties. Sodium dodecyl benzene sulfonate (SDBS) was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 Ωcm 2 30 minutes later.

UV fluorescence excitation spectroscopy as a non-invasive predictor of epidermal proliferation and clinical performance of cosmetic formulations

NASA Astrophysics Data System (ADS)

Maidhof, Robert; Liebel, Frank; Hwang, Cheng; Ruvolo, Eduardo; Lyga, John

2017-02-01

The epidermis is the outermost layer of skin and is composed of cells primarily containing keratin. It consists of about ten layers of living cells (keratinocytes) and ten layers of dead cells (corneocytes). These cells are continually shed from the outside and replaced from the inside in a process called desquamation which is controlled by two biological events - proliferation and differentiation. One method to non-invasively study biological changes in the skin is using fluorescence excitation spectroscopy. Several characteristic excitation-emission peaks occur in skin that have been related to the epidermal and dermal composition. The magnitude of the peak that occurs at 295nm excitation (F295) has been linked to changes in skin proliferation, cell turnover, epidermal thickening, and skin aging. We hypothesize that changes in this fluorescent signal could be used to assess the potential activity of cosmetic anti-aging compounds to deliver a benefit to skin. Previous work with retinol and glycolic acid, two commonly used actives that effect epidermal proliferation and exfoliation, has demonstrated an increase in F295 (attributed to tryptophan excitation fluorescence). In this study we present the results of a placebo controlled study that aims to correlate changes in F295 with biological performance (epidermal thickening and Ki67 expression).

Mimicking the cell membrane: bio-inspired simultaneous functions with monovalent anion selectivity and antifouling properties of anion exchange membrane

NASA Astrophysics Data System (ADS)

Zhao, Yan; Liu, Huimin; Tang, Kaini; Jin, Yali; Pan, Jiefeng; der Bruggen, Bart Van; Shen, Jiangnan; Gao, Congjie

2016-11-01

A new bio-inspired method was applied in this study to simultaneously improve the monovalent anion selectivity and antifouling properties of anion exchange membranes (AEMs). Three-layer architecture was developed by deposition of polydopamine (PDA) and electro-deposition of N-O-sulfonic acid benzyl chitosan (NSBC). The innermost and outermost layers were PDA with different deposition time. The middle layer was prepared by NSBC. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that PDA and NSBC were successfully modified on the surfaces of AEMs. The contact angle of the membranes indicated an improved hydrophilicity of the modified membranes. A series of electrodialysis experiments in which Cl-/SO42- separation was studied, demonstrating the monovalent anion selectivity of the samples. The Cl-/SO42- permselectivity of the modified membranes can reach up to 2.20, higher than that of the commercial membrane (only 0.78) during 90 minutes in electrodialysis (ED). The increase value of the resistance of the membranes was also measured to evaluate the antifouling properties. Sodium dodecyl benzene sulfonate (SDBS) was used as the fouling material in the ED process and the membrane area resistance of modified membrane increase value of was only 0.08 Ωcm2 30 minutes later.

Thickness determination of few-layer hexagonal boron nitride films by scanning electron microscopy and Auger electron spectroscopy

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

Sutter, P., E-mail: psutter@bnl.gov; Sutter, E.

2014-09-01

We assess scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) for thickness measurements on few-layer hexagonal boron nitride (h-BN), the layered dielectric of choice for integration with graphene and other two-dimensional materials. Observations on h-BN islands with large, atomically flat terraces show that the secondary electron intensity in SEM reflects monolayer height changes in films up to least 10 atomic layers thickness. From a quantitative analysis of AES data, the energy-dependent electron escape depth in h-BN films is deduced. The results show that AES is suitable for absolute thickness measurements of few-layer h-BN of 1 to 6 layers.

Understanding metallic bonding: Structure, process and interaction by Rasch analysis

NASA Astrophysics Data System (ADS)

Cheng, Maurice M. W.; Oon, Pey-Tee

2016-08-01

This paper reports the results of a survey of 3006 Year 10-12 students on their understandings of metallic bonding. The instrument was developed based on Chi's ontological categories of scientific concepts and students' understanding of metallic bonding as reported in the literature. The instrument has two parts. Part one probed into students' understanding of metallic bonding as (a) a submicro structure of metals, (b) a process in which individual metal atoms lose their outermost shell electrons to form a 'sea of electrons' and octet metal cations or (c) an all-directional electrostatic force between delocalized electrons and metal cations, that is, an interaction. Part two assessed students' explanation of malleability of metals, for example (a) as a submicro structural rearrangement of metal atoms/cations or (b) based on all-directional electrostatic force. The instrument was validated by the Rasch Model. Psychometric assessment showed that the instrument possessed reasonably good properties of measurement. Results revealed that it was reliable and valid for measuring students' understanding of metallic bonding. Analysis revealed that the structure, process and interaction understandings were unidimensional and in an increasing order of difficulty. Implications for the teaching of metallic bonding, particular through the use of diagrams, critiques and model-based learning, are discussed.

Transparent Oxide TFTs Fabricated by Atomic Layer Deposition

DTIC Science & Technology

2014-04-17

Transparent Oxide TFTs Fabricated by Atomic Layer Deposition(FA2386-11-1-114052) Yukiharu Uraoka, Nara Institute of Science and Technology Term...2011.5.1-2012.4.30 Purpose and Background: In recent years, the application of zinc oxide (ZnO) thin films as an active channel layer in TFTs has...or other flexible substrates. Higher field-effect mobility of ZnO TFTs than a-Si:H TFTs has been recently demonstrated. However, reliability for

Quaternary Chalcogenide-Based Misfit Nanotubes LnS(Se)-TaS(Se)2 (Ln = La, Ce, Nd, and Ho): Synthesis and Atomic Structural Studies.

PubMed

Lajaunie, Luc; Radovsky, Gal; Tenne, Reshef; Arenal, Raul

2018-01-16

We have synthesized quaternary chalcogenide-based misfit nanotubes LnS(Se)-TaS 2 (Se) (Ln = La, Ce, Nd, and Ho). None of the compounds described here were reported in the literature as a bulk compound. The characterization of these nanotubes, at the atomic level, has been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy. In particular, quantification at sub-nanometer scale was achieved by acquiring high-quality electron energy-loss spectra at high energy (∼between 1000 and 2500 eV). Remarkably, the sulfur was found to reside primarily in the distorted rocksalt LnS lattice, while the Se is associated with the hexagonal TaSe 2 site. Consequently, these quaternary misfit layered compounds in the form of nanostructures possess a double superstructure of La/Ta and S/Se with the same periodicity. In addition, the interlayer spacing between the layers and the interatomic distances within the layer vary systematically in the nanotubes, showing clear reduction when going from the lightest (La atom) to the heaviest (Ho) atom. Amorphous layers, of different nature, were observed at the surface of the nanotubes. For La-based NTs, the thin external amorphous layer (inferior to 10 nm) can be ascribed to a Se deficiency. Contrarily, for Ho-based NTs, the thick amorphous layer (between 10 and 20 nm) is clearly ascribed to oxidation. All of these findings helped us to understand the atomic structure of these new compounds and nanotubes thereof.

Protection of Polymers from the Space Environment by Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Lindholm, Ned F.; Zhang, Jianming; Minton, Timothy K.; O'Patchen, Jennifer; George, Steven M.; Groner, Markus D.

2009-01-01

Polymers in space may be subjected to a barrage of incident atoms, photons, and/or ions. For example, oxygen atoms can etch and oxidize these materials. Photons may act either alone or in combination with oxygen atoms to degrade polymers and paints and thus limit their usefulness. Colors fade under the intense vacuum ultraviolet (VUV) solar radiation. Ions can lead to the build-up of static charge on polymers. Atomic layer deposition (ALD) techniques can provide coatings that could mitigate many challenges for polymers in space. ALD is a gas-phase technique based on two sequential, self-limiting surface reactions, and it can deposit very uniform, conformal, and pinhole-free films with atomic layer control. We have studied the efficacy of various ALD coatings to protect Kapton® polyimide, FEP Teflon®, and poly(methyl methacrylate) films from atomic-oxygen and VUV attack. Atomic-oxygen and VUV studies were conducted with the use of a laser-breakdown source for hyperthermal O atoms and a D2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al2O3 ALD coatings applied to polyimide and FEP Teflon® films protected the underlying substrates from O-atom attack, and ZnO coatings protected the poly(methyl methacrylate) substrate from VUV-induced damage.

The properties of plasma-enhanced atomic layer deposition (ALD) ZnO thin films and comparison with thermal ALD

NASA Astrophysics Data System (ADS)

Kim, Doyoung; Kang, Hyemin; Kim, Jae-Min; Kim, Hyungjun

2011-02-01

Zinc oxide (ZnO) thin films were prepared by plasma-enhanced atomic layer deposition (PE-ALD) using oxygen plasma as a reactant and the properties were compared with those of thermal atomic layer deposition (TH-ALD) ZnO thin films. While hexagonal wurzite phase with preferential (0 0 2) orientation was obtained for both cases, significant differences were observed in various aspects of film properties including resistivity values between these two techniques. Photoluminescence (PL) measurements have shown that high resistivity of PE-ALD ZnO thin films is due to the oxygen interstitials at low growth temperature of 200 °C, whose amount decreases with increasing growth temperature. Thin film transistors (TFT) using TH- and PE-ALD ZnO as an active layer were also fabricated and the device properties were evaluated comparatively.

Protection layers on a superconducting microwave resonator toward a hybrid quantum system

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

Lee, Jongmin, E-mail: jongmin.lee@sandia.gov; Sandia National Laboratories, Albuquerque, New Mexico 87123; Park, Dong Hun, E-mail: leomac@umd.edu

2015-10-07

We propose a protection scheme of a superconducting microwave resonator to realize a hybrid quantum system, where cold neutral atoms are coupled with a single microwave photon through magnetic dipole interaction at an interface inductor. The evanescent field atom trap, such as a waveguide/nanofiber atom trap, brings both surface-scattered photons and absorption-induced broadband blackbody radiation which result in quasiparticles and a low quality factor at the resonator. A proposed multiband protection layer consists of pairs of two dielectric layers and a thin nanogrid conductive dielectric layer above the interface inductor. We show numerical simulations of quality factors and reflection/absorption spectra,more » indicating that the proposed multilayer structure can protect a lumped-element microwave resonator from optical photons and blackbody radiation while maintaining a reasonably high quality factor.« less

Microporous structure with layered interstitial surface treatment, and method and apparatus for preparation thereof

NASA Technical Reports Server (NTRS)

Koontz, Steven L. (Inventor)

1992-01-01

A microporous structure with layered interstitial surface treatments, and the method and apparatus for its preparation are disclosed. The structure is prepared by sequentially subjecting a uniformly surface treated structure to atomic oxygen treatment to remove an outer layer of surface treatment to a generally uniform depth, and then surface treating the so exposed layer with another surface treating agent. The atomic oxygen/surface treatment steps may optionally be repeated, each successive time to a lesser depth, to produce a microporous structure having multilayered surface treatments. The apparatus employs at least one side arm from a main oxygen-containing chamber. The side arm has characteristic relaxation times such that a uniform atomic oxygen dose rate is delivered to a specimen positioned transversely in the side arm spaced from the main gas chamber.

Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

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

Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

Atomic layer deposition synthesized TiO{sub x} thin films and their application as microbolometer active materials

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

Tanrikulu, Mahmud Yusuf, E-mail: mytanrikulu@adanabtu.edu.tr; Rasouli, Hamid Reza; Ghaffari, Mohammad

2016-05-15

This paper demonstrates the possible usage of TiO{sub x} thin films synthesized by atomic layer deposition as a microbolometer active material. Thin film electrical resistance is investigated as a function of thermal annealing. It is found that the temperature coefficient of resistance values can be controlled by coating/annealing processes, and the value as high as −9%/K near room temperature is obtained. The noise properties of TiO{sub x} films are characterized. It is shown that TiO{sub x} films grown by atomic layer deposition technique could have a significant potential to be used as a new active material for microbolometer-based applications.

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

Anasori, Babak; Shi, Chenyang; Moon, Eun Ju

In this paper, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M 3C 2 and M 4C 3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX] nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M' 2M"C 2 and M' 2M" 2C 3 – where M' and M" are two different earlymore » transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M' atoms only occupy the outer layers and the M" atoms fill the middle layers. In other words, M' atomic layers sandwich the middle M"–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo 2TiC 2 and Mo 2Ti 2C 3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC] nM structures. The electronic properties of these Mo-containing MXenes are compared with their Ti 3C 2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo 2TiC 2T x exhibits semiconductor-like transport behavior, while Ti 3C 2T x is a metal. Finally, this finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.« less

Controlling surface-segregation of a polymer to display carboxy groups on an outermost surface using perfluoroacyl groups.

PubMed

Nishimori, Keisuke; Kitahata, Shigeru; Nishino, Takashi; Maruyama, Tatsuo

2018-05-10

Controlling the surface properties of solid polymers is important for practical applications. We here succeeded in controlling the surface segregation of polymers to display carboxy groups on an outermost surface, which allowed the covalent immobilization of functional molecules via the carboxy groups on a substrate surface. Random methacrylate-based copolymers containing carboxy groups, in which carboxy groups were protected with perfluoroacyl (Rf) groups, were dip-coated on acrylic substrate surfaces. X-ray photoelectron spectroscopy and contact-angle measurements revealed that the Rf groups were segregated to the outermost surface of the dip-coated substrates. The Rf groups were removed by hydrolysis of the Rf esters in the copolymers, resulting in the display of carboxy groups on the surface. The quantification of carboxy groups on a surface revealed that the carboxy groups were reactive to a water-soluble solute in aqueous solution. The surface segregation was affected by the molecular structure of the copolymer used for dip-coating.

Reusable crucible for containing corrosive liquids

DOEpatents

de Pruneda, Jean A. H.

1995-01-01

A reusable, non-wetting, corrosion-resistant material suitable for containment of corrosive liquids is formed of a tantalum or tantalum alloy substrate that is permeated with carbon atoms. The substrate is carburized to form surface layers of TaC and Ta.sub.2 C, and then is heated at high temperature under vacuum until the carbon atoms in the carbide layers diffuse throughout the substrate to form a solid solution of carbon atoms randomly interspersed in the tantalum or tantalum alloy lattice.

Reusable crucible for containing corrosive liquids

DOEpatents

Pruneda, J.A.H. de.

1995-01-24

A reusable, non-wetting, corrosion-resistant material suitable for containment of corrosive liquids is formed of a tantalum or tantalum alloy substrate that is permeated with carbon atoms. The substrate is carburized to form surface layers of TaC and Ta[sub 2]C, and then is heated at high temperature under vacuum until the carbon atoms in the carbide layers diffuse throughout the substrate to form a solid solution of carbon atoms randomly interspersed in the tantalum or tantalum alloy lattice. 10 figures.

Interaction between antimony atoms and micropores in silicon

NASA Astrophysics Data System (ADS)

Odzhaev, V. B.; Petlitskii, A. N.; Plebanovich, V. I.; Sadovskii, P. K.; Tarasik, M. I.; Chelyadinskii, A. R.

2018-01-01

The interaction between Sb atoms and micropores of a getter layer in silicon is studied. The getter layer was obtained via implantation of Sb+ ions into silicon and subsequent heat treatment processes. The antimony atoms located in the vicinity of micropores are captured by micropores during gettering annealing and lose its electrical activity. The activation energy of capture process to the pores for antimony is lower than that of antimony diffusion in silicon deformation fields around microvoids on the diffusion process.

Ultrafast atomic layer-by-layer oxygen vacancy-exchange diffusion in double-perovskite LnBaCo2O5.5+δ thin films.

PubMed

Bao, Shanyong; Ma, Chunrui; Chen, Garry; Xu, Xing; Enriquez, Erik; Chen, Chonglin; Zhang, Yamei; Bettis, Jerry L; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qingyu

2014-04-22

Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln = Er, Pr; -0.5 < δ < 0.5) by carefully monitoring the resistance changes under a switching flow of oxidizing gas (O2) and reducing gas (H2) in the temperature range of 250 ~ 800 °C. A giant resistance change ΔR by three to four orders of magnitude in less than 0.1 s was found with a fast oscillation behavior in the resistance change rates in the ΔR vs. t plots, suggesting that the oxygen vacancy exchange diffusion with oxygen/hydrogen atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism. The first principles density functional theory calculations indicate that hydrogen atoms are present in LnBCO as bound to oxygen forming O-H bonds. This unprecedented oscillation phenomenon provides the first direct experimental evidence of the layer by layer oxygen vacancy exchange diffusion mechanism.

Young Investigator Proposal, Research Area 7.4 Reactive Chemical Systems: Multifunctional, Bimetallic Nanomaterials Prepared by Atomic Layer Electroless Deposition

DTIC Science & Technology

2017-09-30

Report: Young Investigator Proposal, Research Area 7.4 Reactive Chemical Systems: Multifunctional, Bimetallic Nanomaterials Prepared by Atomic Layer...ES) U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER...Number: W911NF-16-1-0438 Organization: University of Massachusetts - North Dartmouth Title: Young Investigator Proposal, Research Area 7.4 Reactive

Synthesis of selenium nano-composite (t-Se@PS) by surface initiated atom transfer radical polymerization.

PubMed

Wang, Michael C P; Gates, Byron D

2012-09-04

Selenium nanostructures, which are otherwise susceptible to oxidative damage, were encapsulated with a thin layer of polystyrene. The thin layer of polystyrene was grafted onto the surfaces of selenium by a surface initiated atom transfer radical polymerization reaction. These encapsulated nanostructures demonstrate an enhanced resistance towards corrosion.

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

Benson, David M.; Tsang, Chu F.; Sugar, Joshua Daniel

One method for the formation of nanofilms of materials, is Electrochemical atomic layer deposition (E-ALD), one atomic layer at a time. It uses the galvanic exchange of a less noble metal, deposited using underpotential deposition (UPD), to produce an atomic layer of a more noble element by reduction of its ions. This process is referred to as surface limited redox replacement and can be repeated in a cycle to grow thicker deposits. Previously, we performed it on nanoparticles and planar substrates. In the present report, E-ALD is applied for coating a submicron-sized powder substrate, making use of a new flowmore » cell design. E-ALD is used to coat a Pd powder substrate with different thicknesses of Rh by exchanging it for Cu UPD. Furthermore, cyclic voltammetry and X-ray photoelectron spectroscopy indicate an increasing Rh coverage with increasing numbers of deposition cycles performed, in a manner consistent with the atomic layer deposition (ALD) mechanism. Cyclic voltammetry also indicated increased kinetics of H sorption and desorption in and out of the Pd powder with Rh present, relative to unmodified Pd.« less

Atomic layer confined vacancies for atomic-level insights into carbon dioxide electroreduction

NASA Astrophysics Data System (ADS)

Gao, Shan; Sun, Zhongti; Liu, Wei; Jiao, Xingchen; Zu, Xiaolong; Hu, Qitao; Sun, Yongfu; Yao, Tao; Zhang, Wenhua; Wei, Shiqiang; Xie, Yi

2017-02-01

The role of oxygen vacancies in carbon dioxide electroreduction remains somewhat unclear. Here we construct a model of oxygen vacancies confined in atomic layer, taking the synthetic oxygen-deficient cobalt oxide single-unit-cell layers as an example. Density functional theory calculations demonstrate the main defect is the oxygen(II) vacancy, while X-ray absorption fine structure spectroscopy reveals their distinct oxygen vacancy concentrations. Proton transfer is theoretically/experimentally demonstrated to be a rate-limiting step, while energy calculations unveil that the presence of oxygen(II) vacancies lower the rate-limiting activation barrier from 0.51 to 0.40 eV via stabilizing the formate anion radical intermediate, confirmed by the lowered onset potential from 0.81 to 0.78 V and decreased Tafel slope from 48 to 37 mV dec-1. Hence, vacancy-rich cobalt oxide single-unit-cell layers exhibit current densities of 2.7 mA cm-2 with ca. 85% formate selectivity during 40-h tests. This work establishes a clear atomic-level correlation between oxygen vacancies and carbon dioxide electroreduction.

Two-dimensional ferroelectric topological insulators in functionalized atomically thin bismuth layers

NASA Astrophysics Data System (ADS)

Kou, Liangzhi; Fu, Huixia; Ma, Yandong; Yan, Binghai; Liao, Ting; Du, Aijun; Chen, Changfeng

2018-02-01

We introduce a class of two-dimensional (2D) materials that possess coexisting ferroelectric and topologically insulating orders. Such ferroelectric topological insulators (FETIs) occur in noncentrosymmetric atomic layer structures with strong spin-orbit coupling (SOC). We showcase a prototype 2D FETI in an atomically thin bismuth layer functionalized by C H2OH , which exhibits a large ferroelectric polarization that is switchable by a ligand molecule rotation mechanism and a strong SOC that drives a band inversion leading to the topologically insulating state. An external electric field that switches the ferroelectric polarization also tunes the spin texture in the underlying atomic lattice. Moreover, the functionalized bismuth layer exhibits an additional quantum order driven by the valley splitting at the K and K' points in the Brillouin zone stemming from the symmetry breaking and strong SOC in the system, resulting in a remarkable state of matter with the simultaneous presence of the quantum spin Hall and quantum valley Hall effect. These phenomena are predicted to exist in other similarly constructed 2D FETIs, thereby offering a unique quantum material platform for discovering novel physics and exploring innovative applications.

Quantitative analysis of hydrogen in SiO{sub 2}/SiN/SiO{sub 2} stacks using atom probe tomography

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

Kunimune, Yorinobu, E-mail: yorinobu.kunimune.vz@renesas.com; Shimada, Yasuhiro; Sakurai, Yusuke

2016-04-15

We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO{sub 2}/SiN/SiO{sub 2} (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actualmore » hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.« less

Atomic scale imaging of competing polar states in a Ruddlesden-Popper layered oxide.

PubMed

Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J; Schlom, Darrell G; Alem, Nasim; Gopalan, Venkatraman

2016-08-31

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

PubMed Central

Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

2016-01-01

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden–Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure. PMID:27578622

Interfacial structure of two-dimensional epitaxial Er silicide on Si(111)

NASA Astrophysics Data System (ADS)

Tuilier, M. H.; Wetzel, P.; Pirri, C.; Bolmont, D.; Gewinner, G.

1994-07-01

Auger-electron diffraction (AED) and surface-extended x-ray-absorption fine structure (SEXAFS) have been used to obtain a complete description of the atomic structure of a two-dimensional epitaxial Er silicide layer on Si(111). AED reveals that a monolayer of Er is located underneath a buckled Si double layer. The relevant Er-Si interlayer spacings are determined by means of single scattering cluster simulations and a R-factor analysis to be 1.92+/-0.05 Å to the first and 2.70+/-0.05 Å to the second Si top layer. Er near-neighbor bond lengths and coordination numbers are obtained independently from polarization-dependent SEXAFS. The SEXAFS data, when combined with the Si top-layer geometry inferred from AED, permit the determination of the atomic positions at the silicide/Si(111) interface. The Er is found to reside in relaxed T4 sites of Si(111) with a single Er-Si distance of 3.09+/-0.04 Å to the first- and second-layer Si atoms of the substrate.

Comparison of the Results of MISSE 6 Atomic Oxygen Erosion Yields of Layered Kapton H Films with Monte Carlo Computational Predictions

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Groh, Kim De; Kneubel, Christian A.

2014-01-01

A space experiment flown as part of the Materials International Space Station Experiment 6B (MISSE 6B) was designed to compare the atomic oxygen erosion yield (Ey) of layers of Kapton H polyimide with no spacers between layers with that of layers of Kapton H with spacers between layers. The results were compared to a solid Kapton H (DuPont, Wilmington, DE) sample. Monte Carlo computational modeling was performed to optimize atomic oxygen interaction parameter values to match the results of both the MISSE 6B multilayer experiment and the undercut erosion profile from a crack defect in an aluminized Kapton H sample flown on the Long Duration Exposure Facility (LDEF). The Monte Carlo modeling produced credible agreement with space results of increased Ey for all samples with spacers as well as predicting the space-observed enhancement in erosion near the edges of samples due to scattering from the beveled edges of the sample holders.

Atomic scale imaging of competing polar states in a Ruddlesden-Popper layered oxide

NASA Astrophysics Data System (ADS)

Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

2016-08-01

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

Low-frequency Raman fingerprints of two-dimensional metal dichalcogenide layer stacking configurations

DOE PAGES

Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; ...

2015-05-12

In this study, stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks, however fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe 2 and WSe 2 crystals synthesized by chemical vapor deposition we show that the generally unexplored low frequency (LF) Raman modes (< 50more » cm -1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.« less

Solute segregation and deviation from bulk thermodynamics at nanoscale crystalline defects.

PubMed

Titus, Michael S; Rhein, Robert K; Wells, Peter B; Dodge, Philip C; Viswanathan, Gopal Babu; Mills, Michael J; Van der Ven, Anton; Pollock, Tresa M

2016-12-01

It has long been known that solute segregation at crystalline defects can have profound effects on material properties. Nevertheless, quantifying the extent of solute segregation at nanoscale defects has proven challenging due to experimental limitations. A combined experimental and first-principles approach has been used to study solute segregation at extended intermetallic phases ranging from 4 to 35 atomic layers in thickness. Chemical mapping by both atom probe tomography and high-resolution scanning transmission electron microscopy demonstrates a markedly different composition for the 4-atomic-layer-thick phase, where segregation has occurred, compared to the approximately 35-atomic-layer-thick bulk phase of the same crystal structure. First-principles predictions of bulk free energies in conjunction with direct atomistic simulations of the intermetallic structure and chemistry demonstrate the breakdown of bulk thermodynamics at nanometer dimensions and highlight the importance of symmetry breaking due to the proximity of interfaces in determining equilibrium properties.

Potassium 4-azidobenzene­sulfonate1

PubMed Central

Biesemeier, Frank; Geiseler, Gertraud; Harms, Klaus; Müller, Ulrich

2014-01-01

In, K+·SO3–p-C6H4–N3 −, the conformation angle of the azido group with respect to the benzene ring is 19.1 (3)°, so that the anion is chiral within the crystal structure. In addition, the crystal structure is also chiral (Sohncke space group). The potassium ion is coordinated by three closer O atoms from three different sulfonyl groups [K⋯O 2.6486 (17) to 2.7787 (17) Å], three more distant O atoms [K⋯O 2.959 (2) to 3.206 (2) Å] and three N atoms at 3.073 (2) to 3.268 (2) Å. The anions are packed into layers perpendicular to b, only O and N atoms being at the surface of the layers. The K+ ions are located between the layers. PMID:25249882

Synthesis, crystal structure and electronic structure of the binary phase Rh2Cd5

NASA Astrophysics Data System (ADS)

Koley, Biplab; Chatterjee, S.; Jana, Partha P.

2017-02-01

A new phase in the Rh-Cd binary system - Rh2Cd5 has been identified and characterized by single crystal X-ray diffraction and Energy dispersive X-ray analysis. The stoichiometric compound Rh2Cd5 crystallizes with a unit cell containing 14 atoms, in the orthorhombic space group Pbam (55). The crystal structure of Rh2Cd5 can be described as a defect form of the In3Pd5 structure with ordered vacancies, formed of two 2D atomic layers with the stacking sequence: ABAB. The A type layers consist of (3.6.3.6)-Kagomé nets of Cd atoms while the B type layers consist of (35) (37)- nets of both Cd and Rh atoms. The stability of this line phase is investigated by first principle electronic structure calculations on the model of ordered Rh2Cd5.

A neutral molecular-based layered magnet [Fe(C2O4)(CH3OH)]n exhibiting magnetic ordering at TN approximately 23 K.

PubMed

Zhang, Bin; Zhang, Yan; Zhang, Jinbiao; Li, Junchao; Zhu, Daoben

2008-10-07

Solvothermal synthesis of FeCl(2).4H2O and H2C2O(4).2H2O in methanol at 120 degrees C yielded yellow plate-like crystals of [Fe(C2O4)(CH3OH)]n. Each iron atom is in a distorted octahedral environment, being bonded to four oxygen atoms from two bisbidentate oxalate anions, one O atom of a chelating oxalate anion and one O atom from a methanol molecule as an oxalate group bridging ligand in a five-coordination mode. The neutral layer of [Fe(C2O4)(CH3OH)]n with a [4,4] net along the ac plane. There is no interaction between layers. A long range magnetic ordering with spin canting at TN approximately 23 K was observed and confirmed by AC susceptibility measurements.

Observation of hidden atomic order at the interface between Fe and topological insulator Bi2Te3.

PubMed

Sánchez-Barriga, Jaime; Ogorodnikov, Ilya I; Kuznetsov, Mikhail V; Volykhov, Andrey A; Matsui, Fumihiko; Callaert, Carolien; Hadermann, Joke; Verbitskiy, Nikolay I; Koch, Roland J; Varykhalov, Andrei; Rader, Oliver; Yashina, Lada V

2017-11-22

To realize spintronic devices based on topological insulators (TIs), well-defined interfaces between magnetic metals and TIs are required. Here, we characterize atomically precisely the interface between the 3d transition metal Fe and the TI Bi 2 Te 3 at different stages of its formation. Using photoelectron diffraction and holography, we show that after deposition of up to 3 monolayers Fe on Bi 2 Te 3 at room temperature, the Fe atoms are ordered at the interface despite the surface disorder revealed by our scanning-tunneling microscopy images. We find that Fe occupies two different sites: a hollow adatom deeply relaxed into the Bi 2 Te 3 quintuple layers and an interstitial atom between the third (Te) and fourth (Bi) atomic layers. For both sites, our core-level photoemission spectra and density-functional theory calculations demonstrate simultaneous chemical bonding of Fe to both Te and Bi atoms. We further show that upon deposition of Fe up to a thickness of 20 nm, the Fe atoms penetrate deeper into the bulk forming a 2-5 nm interface layer containing FeTe. In addition, excessive Bi is pushed down into the bulk of Bi 2 Te 3 leading to the formation of septuple layers of Bi 3 Te 4 within a distance of ∼25 nm from the interface. Controlling the magnetic properties of the complex interface structures revealed by our work will be of critical importance when optimizing the efficiency of spin injection in TI-based devices.

Adsorbate-induced reconstruction in the phase 1 × 2-3H/Rh(110)

NASA Astrophysics Data System (ADS)

Michl, M.; Nichtl-Pecher, W.; Oed, W.; Landskron, H.; Heinz, K.; Müller, K.

1989-10-01

The 1 × 2-3H superstructure of hydrogen on Rh(110) at coverage θ = {3}/{2} is analysed by low energy electron diffraction at 90 K. The spectra of eight beams are recorded with a computer-controlled TV measurement technique which yields low noise data even for weak superstructure spots by multiple averaging. Comparison to full dynamical calculations shows that a kinematic treatment of the hydrogen layer diffraction coupled to the full dynamical diffraction of the substrate is a very good approximation. Spectra computed in this way are compared with experimental data by R-factor evaluation. The three non-equivalent hydrogen atoms are found to adsorb in quasi-three-fold coordinated adsorption sites with slightly different local configurations and with H-Rh bond lengths between 1.87 and 1.93 Å to the first-layer rhodium atoms. Interaction between the adatoms seems to weaken the bonding to the adjacent atom in the second layer, so that H-Rh bond lengths larger than 2.17 Å result. A slight reconstruction of the substrate is necessary to bring superstructure spot intensities near the experimentally observed level. Rhodium atoms bonded to two hydrogen atoms are moved out of the surface by 0.03 ± 0.02 Å relative to Rh atoms bonded to only a single H atom. The relaxation of the first Rh layer spacing is determined to be {d 12}/{d 0} = -3.8 ± 1% and {d 22}/{d 0} = 0 ± 1% . The best fit Pendry R-factor is 0.33.

Bi-layer Channel AZO/ZnO Thin Film Transistors Fabricated by Atomic Layer Deposition Technique

NASA Astrophysics Data System (ADS)

Li, Huijin; Han, Dedong; Liu, Liqiao; Dong, Junchen; Cui, Guodong; Zhang, Shengdong; Zhang, Xing; Wang, Yi

2017-03-01

This letter demonstrates bi-layer channel Al-doped ZnO/ZnO thin film transistors (AZO/ZnO TFTs) via atomic layer deposition process at a relatively low temperature. The effects of annealing in oxygen atmosphere at different temperatures have also been investigated. The ALD bi-layer channel AZO/ZnO TFTs annealed in dry O2 at 300 °C exhibit a low leakage current of 2.5 × 10-13A, I on/ I off ratio of 1.4 × 107, subthreshold swing (SS) of 0.23 V/decade, and high transmittance. The enhanced performance obtained from the bi-layer channel AZO/ZnO TFT devices is explained by the inserted AZO front channel layer playing the role of the mobility booster.

On seismic resolution of lateral heterogeneity in the Earth's outermost core

NASA Astrophysics Data System (ADS)

Garnero, Edward J.; Helmberger, Donald V.

1995-03-01

Issues concerning resolution of seismically determined outermost core properties are presented with an example from three earthquakes in the Fiji-Tonga region. Travel time behavior of the commonly used family of S mKS waves, which travel as S in the mantle, P in the core, reflecting m - 1 times at the underside of the core-mantle boundary (CMB), are analyzed over a large distance range (125-165°). Data having wavepaths through an area of known D″ heterogeneity (±2%) exhibit systematic anomalies in S mKS differential times. Two-dimensional wave propagation experiments demonstrate how large-scale lower-mantle velocity perturbations can explain long-wavelength behavior of such anomalous S mKS times, though heterogeneity on smaller scales may be responsible for the observed scatter about these trends. If lower-mantle heterogeneity is not properly accounted for in deriving a core model, misfit of the mantle model maps directly into core structure. The existence of outermost core heterogeneity is difficult to resolve at present, owing to uncertainties in global lower-mantle structure. Resolving a one-dimensional chemically stratified outermost core also remains difficult, owing to the same uncertainties. Inclusion of the slowly accruing broadband data should help in this regard. Restricting study to higher multiples of S mKS ( m = 2, 3, 4) can help reduce the effect of mantle heterogeneity, because of the closeness of the mantle legs of the wavepaths. S mKS waves are ideal in providing additional information on the details of lower-mantle heterogeneity.

The role of charge transfer in the oxidation state change of Ce atoms in the TM13-CeO2(111) systems (TM = Pd, Ag, Pt, Au): a DFT + U investigation.

PubMed

Tereshchuk, Polina; Freire, Rafael L H; Ungureanu, Crina G; Seminovski, Yohanna; Kiejna, Adam; Da Silva, Juarez L F

2015-05-28

Despite extensive studies of transition metal (TM) clusters supported on ceria (CeO2), fundamental issues such as the role of the TM atoms in the change in the oxidation state of Ce atoms are still not well understood. In this work, we report a theoretical investigation based on static and ab initio molecular dynamics density functional theory calculations of the interaction of 13-atom TM clusters (TM = Pd, Ag, Pt, Au) with the unreduced CeO2(111) surface represented by a large surface unit cell and employing Hubbard corrections for the strong on-site Coulomb correlation in the Ce f-electrons. We found that the TM13 clusters form pyramidal-like structures on CeO2(111) in the lowest energy configurations with the following stacking sequence, TM/TM4/TM8/CeO2(111), while TM13 adopts two-dimensional structures at high energy structures. TM13 induces a change in the oxidation state of few Ce atoms (3 of 16) located in the topmost Ce layer from Ce(IV) (itinerant Ce f-states) to Ce(III) (localized Ce f-states). There is a charge flow from the TM atoms to the CeO2(111) surface, which can be explained by the electronegativity difference between the TM (Pd, Ag, Pt, Au) and O atoms, however, the charge is not uniformly distributed on the topmost O layer due to the pressure induced by the TM13 clusters on the underlying O ions, which yields a decrease in the ionic charge of the O ions located below the cluster and an increase in the remaining O ions. Due to the charge flow mainly from the TM8-layer to the topmost O-layer, the charge cannot flow from the Ce(IV) atoms to the O atoms with the same magnitude as in the clean CeO2(111) surface. Consequently, the effective cationic charge decreases mainly for the Ce atoms that have a bond with the O atoms not located below the cluster, and hence, those Ce atoms change their oxidation state from IV to III. This increases the size of the Ce(III) compared with the Ce(IV) cations, which builds-in a strain within the topmost Ce layer, and hence, also affecting the location of the Ce(III) cations and the structure of the TM13 clusters.

Highly structured and surface modified poly(epsilon-caprolactone) scaffolds derived from co-continuous polymer blends for bone tissue engineering

NASA Astrophysics Data System (ADS)

Mehr, Nima Ghavidel

Chitosan, an important member of the polysaccharide family was used to alter the chemistry of PCL scaffolds and bring hydrophilicity to the surface. The deposition of a homogeneous chitosan layer on the surface of the PCL scaffolds was carried out using a Layer-by-Layer (LbL) selfassembly of poly(dialyldemethylammunium chloride) (PDADMAC) as cationic and poly(sodium 4-styrenesulfonate) (PSS) as anionic polyelectrolytes. The final negatively charged PSS layer allows for the addition of the positively charged chitosan as the outermost layer. Gravimetric measurements revealed that the addition of up to 3 layers leads to the formation of interdiffusing polyelectrolyte layers which do not allow for the formation of defined positive or negative charges. By increasing the number of polyelectrolyte layers with alternating charges, more welldefined layers are formed. Detailed analyses of O/C, N/C and S/C ratios by X-ray photoelectron spectroscopy (XPS) show that the PSS molecule dominates the surface as the last deposited polyelectrolyte layer at higher number of depositions (n=8), which can later be the surface for the deposition of chitosan. The LbL deposition of the chitosan layer on the LbL coating was then shown to be locally homogeneous at different depths within the scaffolds which also clarified that the LbL method is superior to the dip coating strategy. SEM analysis showed that there is a rough chitosan surface on the 2D solid PCL constructs whose thickness ranges from 550-700 nanometers. These results demonstrate that the application of LbL self-assembly of polyelectrolytes followed by the addition of chitosan as the outermost layer provides a route towards stable and homogeneous surface modification and has the potential to transform a classic fully interconnected porous synthetic polymer material to one with essentially complete chitosanlike surface characteristics. The osteogenic potential of PCL scaffolds with a chitosan coating using Layer-by-Layer (LbL) surface modification has never been evaluated before. This part of the study tests the hypothesis that in vitro osteogenesis can be achieved in 3D PCL scaffolds with fully interconnected pores of 84 im or 141 im average diameter and biomineralization can be enhanced when pore surfaces are coated with chitosan adsorbed to LbL deposited polyelectrolytes. In order to reduce the errors originating from cell infiltration inefficiencies, the most competent cell seeding protocol has to be defined. Among classical cell seeding at 37°C, 2-step seeding at 37°C and cold seeding at 4°C in a medium containing 2% FBS, the last strategy proved to yield the best population of freshly trypsinized hBMSCs at all depths of the 1mm-thick scaffolds. hBMSCs cold-seeded in PCL scaffolds with or without an LbL-chitosan coating were cultured for 10 days in proliferation medium, followed by 21 days in osteogenic medium. At day 2, MSCs formed sparse monolayers with rounded cell morphologies with thin filopodia anchored to the unmodified PCL, as compared to more spread cells on chitosan-coated pore surfaces. At day 10, cells proliferated as an external layer, and migrated onto secreted collagen networks that filled the interpore spaces of all scaffolds, but only adhered to chitosan-coated pore surfaces. At day 31, similar levels of tissue formed in scaffolds with and without chitosan, but more tissue was deposited in the outer pores than the inner pores. Furthermore, more biomineralized matrix was observed in the inner 84 im chitosan-coated pores (p<0.05). In the PCL-only samples, haphazard mineral deposits were observed in highly colonized outer layers and in the inner 141 im pores. MSCs cultured on chitosan-coated 2D control surfaces show higher alkaline phosphatase staining but negligible mineralization. This study showed that hBMSCs survive, proliferate, and attach to fibrotic matrix rather than the PCL-only scaffold pore surfaces. LbL-chitosan-coated scaffolds showed more biomineralization in 3D inner 84 im pores, a cell response that may be related to surface curvature in addition to improved surface hydrophilicity. (Abstract shortened by UMI.).

Uncertainty Analysis of Air Radiation for Lunar Return Shock Layers

NASA Technical Reports Server (NTRS)

Kleb, Bil; Johnston, Christopher O.

2008-01-01

By leveraging a new uncertainty markup technique, two risk analysis methods are used to compute the uncertainty of lunar-return shock layer radiation predicted by the High temperature Aerothermodynamic Radiation Algorithm (HARA). The effects of epistemic uncertainty, or uncertainty due to a lack of knowledge, is considered for the following modeling parameters: atomic line oscillator strengths, atomic line Stark broadening widths, atomic photoionization cross sections, negative ion photodetachment cross sections, molecular bands oscillator strengths, and electron impact excitation rates. First, a simplified shock layer problem consisting of two constant-property equilibrium layers is considered. The results of this simplified problem show that the atomic nitrogen oscillator strengths and Stark broadening widths in both the vacuum ultraviolet and infrared spectral regions, along with the negative ion continuum, are the dominant uncertainty contributors. Next, three variable property stagnation-line shock layer cases are analyzed: a typical lunar return case and two Fire II cases. For the near-equilibrium lunar return and Fire 1643-second cases, the resulting uncertainties are very similar to the simplified case. Conversely, the relatively nonequilibrium 1636-second case shows significantly larger influence from electron impact excitation rates of both atoms and molecules. For all cases, the total uncertainty in radiative heat flux to the wall due to epistemic uncertainty in modeling parameters is 30% as opposed to the erroneously-small uncertainty levels (plus or minus 6%) found when treating model parameter uncertainties as aleatory (due to chance) instead of epistemic (due to lack of knowledge).

A study of the possible characteristics of a low-altitude electron layer in the Martian atmosphere

NASA Technical Reports Server (NTRS)

Wallio, H. A.

1974-01-01

The apparent diurnal Martian surface pressure variations, as deduced from radio occultation experiments, is discussed and explained as possibly arising from the effect of a low-altitude electron layer. Possible source and loss mechanisms for the low altitude electron layer are presented and discussed. Time dependent differential equations describing the electron layer are derived, and then integrated to investigate the electron distribution resulting from several processes that might occur in the atmosphere. It is concluded that the source mechanism is the sublimation of alkali atoms from a permanent dust layer, and that the dominant loss process must involve CO2 clustering about the alkali atoms. An electron layer is developed which explains the apparent diurnal surface pressure variation.

Exposure of LDEF materials to atomic oxygen: Results of EOIM 3

NASA Technical Reports Server (NTRS)

Jaggers, C. H.; Meshishnek, M. J.

1995-01-01

The third Effects of Oxygen Atom Interaction with Materials (EOIM 3) experiment flew on STS-46 from July 31 to August 8, 1992. The EOIM-3 sample tray was exposed to the low-earth orbit space environment for 58.55 hours at an altitude of 124 nautical miles resulting in a calculated total atomic oxygen (AO) fluence of 1.99 x 10(exp 20) atoms/sq cm. Five samples previously flown on the Long Duration Exposure Facility (LDEF) Experiment M0003 were included on the Aerospace EOIM 3 experimental tray: (1) Chemglaze A276 white thermal control paint from the LDEF trailing edge (TE); (2) S13GLO white thermal control paint from the LDEF TE; (3) S13GLO from the LDEF leading edge (LE) with a visible contamination layer from the LDEF mission; (4) Z306 black thermal control paint from the LDEF TE with a contamination layer from the LDEF mission; and (5) anodized aluminum from the LDEF TE with a contamination layer from the LDEF mission. The purpose of this experiment was twofold: (l) investigate the response of trailing edge LDEF materials to atomic oxygen exposure, thereby simulating LDEF leading edge phenomena; (2) investigate the response of contaminated LDEF samples to atomic oxygen in attempts to understand LDEF contamination-atomic oxygen interactions. This paper describes the response of these materials to atomic oxygen exposure, and compares the results of the EOIM 3 experiment to the LDEF mission and to ground-based atomic oxygen exposure studies.

Hydrothermal syntheses, characterizations and crystal structures of a new lead(II) carboxylate-phosphonate with a double layer structure and a new nickel(II) carboxylate-phosphonate containing a hydrogen-bonded 2D layer with intercalation of ethylenediamines

NASA Astrophysics Data System (ADS)

Song, Jun-Ling; Mao, Jiang-Gao; Sun, Yan-Qiong; Zeng, Hui-Yi; Kremer, Reinhard K.; Clearfield, Abraham

2004-03-01

Hydrothermal reactions of N, N-bis(phosphonomethyl)aminoacetic acid (HO 2CCH 2N(CH 2PO 3H 2) 2) with metal(II) salts afforded two new metal carboxylate-phosphonates, namely, Pb 2[O 2CCH 2N(CH 2PO 3)(CH 2PO 3H)]·H 2O ( 1) and {NH 3CH 2CH 2NH 3}{Ni[O 2CCH 2N(CH 2PO 3H) 2](H 2O) 2} 2 ( 2). Among two unique lead(II) ions in the asymmetric unit of complex 1, one is five coordinated by five phosphonate oxygen atoms from 5 ligands, whereas the other one is five-coordinated by a tridentate chelating ligand (1 N and 2 phosphonate O atoms) and two phosphonate oxygen atoms from two other ligands. The carboxylate group of the ligand remains non-coordinated. The bridging of above two types of lead(II) ions through phosphonate groups resulted in a <002> double layer with the carboxylate group of the ligand as a pendant group. These double layers are further interlinked via hydrogen bonds between the carboxylate groups into a 3D network. The nickel(II) ion in complex 2 is octahedrally coordinated by a tetradentate chelating ligand (two phosphonate oxygen atoms, one nitrogen and one carboxylate oxygen atoms) and two aqua ligands. These {Ni[O 2CCH 2N(CH 2PO 3H) 2][H 2O] 2} - anions are further interlinked via hydrogen bonds between non-coordinated phosphonate oxygen atoms to form a <800> hydrogen bonded 2D layer. The 2H-protonated ethylenediamine cations are intercalated between two layers, forming hydrogen bonds with the non-coordinated carboxylate oxygen atoms. Results of magnetic measurements for complex 2 indicate that there is weak Curie-Weiss behavior with θ=-4.4 K indicating predominant antiferromagnetic interaction between the Ni(II) ions. Indication for magnetic low-dimension magnetism could not be detected.

Atomic-scale analysis of cation ordering in reduced calcium titanate.

PubMed

Li, Luying; Hu, Xiaokang; Jiang, Fan; Jing, Wenkui; Guo, Cong; Jia, Shuangfeng; Gao, Yihua; Wang, Jianbo

2017-11-03

The phenomenon of cation ordering is closely related to certain physical properties of complex oxides, which necessitates the search of underlying structure-property relationship at atomic resolution. Here we study the superlattices within reduced calcium titanate single crystal micro-pillars, which are unexpected from the originally proposed atomic model. Bright and dark contrasts at alternating Ti double layers perpendicular to b axis are clearly observed, but show no signs in corresponding image simulations based on the proposed atomic model. The multi-dimensional chemical analyses at atomic resolution reveal periodic lower Ti concentrations at alternating Ti double layers perpendicular to b axis. The following in-situ heating experiment shows no phase transition at the reported T c and temperature independence of the superlattices. The dimerization of the Ti-Ti bonds at neighboring double rutile-type chains within Ti puckered sheets are directly observed, which is found to be not disturbed by the cation ordering at alternating Ti double layers. The characterization of cation ordering of complex oxides from chemical and structural point of view at atomic resolution, and its reaction to temperature variations are important for further understanding their basic physical properties and exploiting potential applications.

Synthesis of two-dimensional TlxBi1−x compounds and Archimedean encoding of their atomic structure

PubMed Central

Gruznev, Dimitry V.; Bondarenko, Leonid V.; Matetskiy, Andrey V.; Mihalyuk, Alexey N.; Tupchaya, Alexandra Y.; Utas, Oleg A.; Eremeev, Sergey V.; Hsing, Cheng-Rong; Chou, Jyh-Pin; Wei, Ching-Ming; Zotov, Andrey V.; Saranin, Alexander A.

2016-01-01

Crystalline atomic layers on solid surfaces are composed of a single building block, unit cell, that is copied and stacked together to form the entire two-dimensional crystal structure. However, it appears that this is not an unique possibility. We report here on synthesis and characterization of the one-atomic-layer-thick TlxBi1−x compounds which display quite a different arrangement. It represents a quasi-periodic tiling structures that are built by a set of tiling elements as building blocks. Though the layer is lacking strict periodicity, it shows up as an ideally-packed tiling of basic elements without any skips or halting. The two-dimensional TlxBi1−x compounds were formed by depositing Bi onto the Tl-covered Si(111) surface where Bi atoms substitute appropriate amount of Tl atoms. Atomic structure of each tiling element as well as arrangement of TlxBi1−x compounds were established in a detail. Electronic properties and spin texture of the selected compounds having periodic structures were characterized. The shown example demonstrates possibility for the formation of the exotic low-dimensional materials via unusual growth mechanisms. PMID:26781340

Atomic Layer Epitaxy of Aluminum Nitride: Unraveling the Connection between Hydrogen Plasma and Carbon Contamination.

PubMed

Erwin, Steven C; Lyons, John L

2018-06-13

Atomistic control over the growth of semiconductor thin films, such as aluminum nitride, is a long-sought goal in materials physics. One promising approach is plasma-assisted atomic layer epitaxy, in which separate reactant precursors are employed to grow the cation and anion layers in alternating deposition steps. The use of a plasma during the growth-most often a hydrogen plasma-is now routine and generally considered critical, but the precise role of the plasma is not well-understood. We propose a theoretical atomistic model and elucidate its consequences using analytical rate equations, density functional theory, and kinetic Monte Carlo statistical simulations. We show that using a plasma has two important consequences, one beneficial and one detrimental. The plasma produces atomic hydrogen in the gas phase, which is important for removing methyl radicals left over from the aluminum precursor molecules. However, atomic hydrogen also leads to atomic carbon on the surface and, moreover, opens a channel for trapping these carbon atoms as impurities in the subsurface region, where they remain as unwanted contaminants. Understanding this dual role leads us to propose a solution for the carbon contamination problem which leaves the main benefit of the plasma largely unaffected.

First Principles Study of Adsorption of Hydrogen on Typical Alloying Elements and Inclusions in Molten 2219 Al Alloy.

PubMed

Liu, Yu; Huang, Yuanchun; Xiao, Zhengbing; Jia, Guangze

2017-07-19

To better understand the effect of the components of molten 2219 Al alloy on the hydrogen content dissolved in it, the H adsorption on various positions of alloying element clusters of Cu, Mn and Al, as well as the inclusion of Al₂O₃, MgO and Al₄C₃, were investigated by means of first principles calculation, and the thermodynamic stability of H adsorbed on each possible site was also studied on the basis of formation energy. Results show that the interaction between Al, MgO, Al₄C₃ and H atoms is mainly repulsive and energetically unfavorable; a favorable interaction between Cu, Mn, Al₂O₃ and H atoms was determined, with H being more likely to be adsorbed on the top of the third atomic layer of Cu(111), the second atomic layer of Mn(111), and the O atom in the third atomic layer of Al₂O₃, compared with other sites. It was found that alloying elements Cu and Mn and including Al₂O₃ may increase the hydrogen adsorption in the molten 2219 Al alloy with Al₂O₃ being the most sensitive component in this regard.

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

Polyakova, I. N., E-mail: polyakova@igic.ras.ru; Poznyak, A. L.; Sergienko, V. S.

Four Cu(II) complexes with the RR,SS-Edds{sup 4-} and SS-HEdds{sup 3-} anions are synthesized, and their crystal structures are studied. In the compounds [Cu2(RR,SS-Edds)] . 6H{sub 2}O (I) and Ba2[Cu(RR,SS-Edds)](ClO{sub 4}){sub 2} . 8H{sub 2}O (II), the ligand forms hexacoordinate chelate [Cu(Edds)]{sup 2-} complexes with the N atoms and O atoms of the propionate groups in the equatorial positions and the O atoms of the acetate groups in the axial vertices. In the compounds Ba[Cu(SS-HEdds)]ClO{sub 4} . 2H{sub 2}O (III) and Ba3[Cu2(RR,SS-Edds){sub 2}](ClO{sub 4}){sub 2} . 6H{sub 2}O (IV), one of the propionate arms, the protonated arm in III and themore » deprotonated arm in IV, does not enter into the coordination sphere of the Cu atom. An acetate arm moves to its position in the equatorial plane, and the free axial vertex is occupied by an O atom of the perchlorate ion. In I-IV, the lengths of the equatorial Cu-N and Cu-O bonds fall in the ranges 1.970-2.014 and 1.921-1.970 A, respectively. The axial Cu-O bonds with the acetate groups and ClO{sub 4}{sup -} anions are elongated to 2.293-2.500 and 2.727-2.992 A, respectively. In structure I, the second Cu atom acts as a counterion forming bonds with the O atoms of two water molecules and three O atoms of the Edds ligands. In II-IV, the Ba{sup 2+} cations are hydrated and bound to the O atoms of the anionic complexes and (except for one of the cations in IV) ClO{sub 4}{sup -} anions. The coordination number of the Ba cations is nine. The structural units in I-IV are connected into layers. In I, an extended system of hydrogen bonds links the layers into a framework. In II and III, the layers are linked only by weak hydrogen bonds, one bond per structural unit. In IV, ClO{sub 4}{sup -} anions are bound to the Ba and Cu atoms of neighboring layers, thus serving as bridges between the layers.« less

Atomic migration of carbon in hard turned layers of carburized bearing steel

DOE PAGES

Bedekar, Vikram; Poplawsky, Jonathan D.; Guo, Wei; ...

2016-01-01

In grain finement and non-equilibrium there is carbon segregation within grain boundaries alters the mechanical performance of hard turning layers in carburized bearing steel. Moreover, an atom probe tomography (APT) study on the nanostructured hard turning layers reveals carbon migration to grain boundaries as a result of carbide decomposition during severe plastic deformation. In addition, samples exposed to different cutting speeds show that the carbon migration rate increases with the cutting speed. For these two effects lead to an ultrafine carbon network structure resulting in increased hardness and thermal stability in the severely deformed surface layer.

Atomic Scale Study on Growth and Heteroepitaxy of ZnO Monolayer on Graphene.

PubMed

Hong, Hyo-Ki; Jo, Junhyeon; Hwang, Daeyeon; Lee, Jongyeong; Kim, Na Yeon; Son, Seungwoo; Kim, Jung Hwa; Jin, Mi-Jin; Jun, Young Chul; Erni, Rolf; Kwak, Sang Kyu; Yoo, Jung-Woo; Lee, Zonghoon

2017-01-11

Atomically thin semiconducting oxide on graphene carries a unique combination of wide band gap, high charge carrier mobility, and optical transparency, which can be widely applied for optoelectronics. However, study on the epitaxial formation and properties of oxide monolayer on graphene remains unexplored due to hydrophobic graphene surface and limits of conventional bulk deposition technique. Here, we report atomic scale study of heteroepitaxial growth and relationship of a single-atom-thick ZnO layer on graphene using atomic layer deposition. We demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation. We experimentally determine that the thinnest ZnO monolayer has a wide band gap (up to 4.0 eV), due to quantum confinement and graphene-like structure, and high optical transparency. This study can lead to a new class of atomically thin two-dimensional heterostructures of semiconducting oxides formed by highly controlled epitaxial growth.

Optimization of Al2O3/TiO2 nanolaminate thin films prepared with different oxide ratios, for use in organic light-emitting diode encapsulation, via plasma-enhanced atomic layer deposition.

PubMed

Kim, Lae Ho; Jeong, Yong Jin; An, Tae Kyu; Park, Seonuk; Jang, Jin Hyuk; Nam, Sooji; Jang, Jaeyoung; Kim, Se Hyun; Park, Chan Eon

2016-01-14

Encapsulation is essential for protecting the air-sensitive components of organic light-emitting diodes (OLEDs), such as the active layers and cathode electrodes. Thin film encapsulation approaches based on an oxide layer are suitable for flexible electronics, including OLEDs, because they provide mechanical flexibility, the layers are thin, and they are easy to prepare. This study examined the effects of the oxide ratio on the water permeation barrier properties of Al2O3/TiO2 nanolaminate films prepared by plasma-enhanced atomic layer deposition. We found that the Al2O3/TiO2 nanolaminate film exhibited optimal properties for a 1 : 1 atomic ratio of Al2O3/TiO2 with the lowest water vapor transmission rate of 9.16 × 10(-5) g m(-2) day(-1) at 60 °C and 90% RH. OLED devices that incorporated Al2O3/TiO2 nanolaminate films prepared with a 1 : 1 atomic ratio showed the longest shelf-life, in excess of 2000 hours under 60 °C and 90% RH conditions, without forming dark spots or displaying edge shrinkage.

Structural modifications of graphyne layers consisting of carbon atoms in the sp- and sp{sup 2}-hybridized states

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

Belenkov, E. A., E-mail: belenkov@csu.ru; Mavrinskii, V. V.; Belenkova, T. E.

2015-05-15

A model scheme is proposed for obtaining layered compounds consisting of carbon atoms in the sp- and (vnsp){sup 2}-hybridized states. This model is used to find the possibility of existing the following seven basic structural modifications of graphyne: α-, β1-, β2-, β3-, γ1-, γ2-, and γ3-graphyne. Polymorphic modifications β3 graphyne and γ3 graphyne are described. The basic structural modifications of graphyne contain diatomic polyyne chains and consist only of carbon atoms in two different crystallographically equivalent states. Other nonbasic structural modifications of graphyne can be formed via the elongation of the carbyne chains that connect three-coordinated carbon atoms and viamore » the formation of graphyne layers with a mixed structure consisting of basic layer fragments, such as α-β-graphyne, α-γ-graphyne, and β-γ-graphyne. The semiempirical quantum-mechanical MNDO, AM1, and PM3 methods and ab initio STO6-31G basis calculations are used to find geometrically optimized structures of the basic graphyne layers, their structural parameters, and energies of their sublimation. The energy of sublimation is found to be maximal for γ2-graphyne, which should be the most stable structural modification of graphyne.« less

Complexation of Uranium by Cells and S-Layer Sheets of Bacillus sphaericus JG-A12

PubMed Central

Merroun, Mohamed L.; Raff, Johannes; Rossberg, André; Hennig, Christoph; Reich, Tobias; Selenska-Pobell, Sonja

2005-01-01

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) possessing an ability to bind uranium and other heavy metals. Purified and recrystallized S-layer proteins were shown to be phosphorylated by phosphoprotein-specific staining, inductive coupled plasma mass spectrometry analysis, and a colorimetric method. We used extended X-ray absorption fine-structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, we investigated the complexation of uranium by the vegetative bacterial cells. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission electron microscopy showed that the uranium accumulated by the cells of this strain is located in dense deposits at the cell surface. PMID:16151146

Rich interfacial chemistry and properties of carbon-doped hexagonal boron nitride nanosheets revealed by electronic structure calculations

NASA Astrophysics Data System (ADS)

Xie, Wei; Tamura, Takahiro; Yanase, Takashi; Nagahama, Taro; Shimada, Toshihiro

2018-04-01

The effect of C doping to hexagonal boron nitride (h-BN) to its electronic structure is examined by first principles calculations using the association from π-electron systems of organic molecules embedded in a two-dimensional insulator. In a monolayered carbon-doped structure, odd-number doping with carbon atoms confers metallic properties with different work functions. Various electronic interactions occur between two layers with odd-number carbon substitution. A direct sp3 covalent chemical bond is formed when C replaces adjacent B and N in different layers. A charge transfer complex between layers is found when C replaces B and N in the next-neighboring region, which results in narrower band gaps (e.g., 0.37 eV). Direct bonding between C and B atoms is found when two C atoms in different layers are at a certain distance.

New twinning route in face-centered cubic nanocrystalline metals.

PubMed

Wang, Lihua; Guan, Pengfei; Teng, Jiao; Liu, Pan; Chen, Dengke; Xie, Weiyu; Kong, Deli; Zhang, Shengbai; Zhu, Ting; Zhang, Ze; Ma, Evan; Chen, Mingwei; Han, Xiaodong

2017-12-15

Twin nucleation in a face-centered cubic crystal is believed to be accomplished through the formation of twinning partial dislocations on consecutive atomic planes. Twinning should thus be highly unfavorable in face-centered cubic metals with high twin-fault energy barriers, such as Al, Ni, and Pt, but instead is often observed. Here, we report an in situ atomic-scale observation of twin nucleation in nanocrystalline Pt. Unlike the classical twinning route, deformation twinning initiated through the formation of two stacking faults separated by a single atomic layer, and proceeded with the emission of a partial dislocation in between these two stacking faults. Through this route, a three-layer twin was nucleated without a mandatory layer-by-layer twinning process. This route is facilitated by grain boundaries, abundant in nanocrystalline metals, that promote the nucleation of separated but closely spaced partial dislocations, thus enabling an effective bypassing of the high twin-fault energy barrier.

Ultraviolet electroluminescence from nitrogen-doped ZnO-based heterojuntion light-emitting diodes prepared by remote plasma in situ atomic layer-doping technique.

PubMed

Chien, Jui-Fen; Liao, Hua-Yang; Yu, Sheng-Fu; Lin, Ray-Ming; Shiojiri, Makoto; Shyue, Jing-Jong; Chen, Miin-Jang

2013-01-23

Remote plasma in situ atomic layer doping technique was applied to prepare an n-type nitrogen-doped ZnO (n-ZnO:N) layer upon p-type magnesium-doped GaN (p-GaN:Mg) to fabricate the n-ZnO:N/p-GaN:Mg heterojuntion light-emitting diodes. The room-temperature electroluminescence exhibits a dominant ultraviolet peak at λ ≈ 370 nm from ZnO band-edge emission and suppressed luminescence from GaN, as a result of the decrease in electron concentration in ZnO and reduced electron injection from n-ZnO:N to p-GaN:Mg because of the nitrogen incorporation. The result indicates that the in situ atomic layer doping technique is an effective approach to tailoring the electrical properties of materials in device applications.

Ion blocking dip shape analysis around a LaAlO3/SrTiO3 interface

NASA Astrophysics Data System (ADS)

Jalabert, D.; Zaid, H.; Berger, M. H.; Fongkaew, I.; Lambrecht, W. R. L.; Sehirlioglu, A.

2018-05-01

We present an analysis of the widths of the blocking dips obtained in MEIS ion blocking experiments of two LaAlO3/SrTiO3 heterostructures differing in their LaAlO3 layer thicknesses. In the LaAlO3 layers, the observed blocking dips are larger than expected. This enlargement is the result of the superposition of individual dips at slightly different angular positions revealing a local disorder in the atomic alignment, i.e., layer buckling. By contrast, in the SrTiO3 substrate, just below the interface, the obtained blocking dips are thinner than expected. This thinning indicates that the blocking atoms stand at a larger distance from the scattering center than expected. This is attributed to an accumulation of Sr vacancies at the layer/substrate interface which induces lattice distortions shifting the atoms off the scattering plane.

Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

DOE PAGES

Song, Tiancheng; Cai, Xinghan; Tu, Matisse Wei-Yuan; ...

2018-05-03

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI 3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI 3. In conclusion, ourmore » work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI 3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.« less

Giant tunneling magnetoresistance in spin-filter van der Waals heterostructures

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

Song, Tiancheng; Cai, Xinghan; Tu, Matisse Wei-Yuan

Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here, we report multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI 3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI 3. In conclusion, ourmore » work reveals the possibility to push magnetic information storage to the atomically thin limit and highlights CrI 3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.« less

Electrical Investigation of Metal-Olivine Systems and Application to the Deep Interior of Mercury

NASA Astrophysics Data System (ADS)

Zhang, Zhou; Pommier, Anne

2017-12-01

We report electrical conductivity measurements on metal-olivine systems at about 5 and 6 GPa and up to 1,675°C in order to investigate the electrical properties of core-mantle boundary (CMB) systems. Electrical experiments were conducted in the multianvil apparatus using the impedance spectroscopy technique. The samples are composed of one metal layer (Fe, FeS, FeSi2, or Fe-Ni-S-Si) and one polycrystalline olivine layer, with the metal:olivine ratio ranging from 1:0.7 to 1:9.2. For all samples, we observe that the bulk electrical conductivity increases with temperature from 10-2.5 to 101.8 S/m, which is higher than the conductivity of polycrystalline olivine but lower than the conductivity of the pure metal phase at similar conditions. In some experiments, a conductivity jump is observed at the temperature corresponding to the melting temperature of the metallic phase. Both the metal:olivine ratio and the metal phase geometry control the electrical conductivity of the two-layer samples. By combining electrical results, textural analyses of the samples, and previous studies of the structure and composition of Mercury's interior, we propose an electrical profile of the deep interior of the planet that accounts for a layered CMB-outer core structure. The electrical model agrees with existing conductivity estimates of Mercury's lower mantle and CMB using magnetic observations and thermodynamic calculations, and thus, supports the hypothesis of a layered CMB-outermost core structure in the present-day interior of Mercury. We propose that the layered CMB-outer core structure is possibly electrically insulating, which may influence the planet's structure and cooling history.

Measuring the Density of States of the Inner and Outer Wall of Double-Walled Carbon Nanotubes.

PubMed

Chambers, Benjamin A; Shearer, Cameron J; Yu, LePing; Gibson, Christopher T; Andersson, Gunther G

2018-06-19

The combination of ultraviolet photoelectron spectroscopy and metastable helium induced electron spectroscopy is used to determine the density of states of the inner and outer coaxial carbon nanotubes. Ultraviolet photoelectron spectroscopy typically measures the density of states across the entire carbon nanotube, while metastable helium induced electron spectroscopy measures the density of states of the outermost layer alone. The use of double-walled carbon nanotubes in electronic devices allows for the outer wall to be functionalised whilst the inner wall remains defect free and the density of states is kept intact for electron transport. Separating the information of the inner and outer walls enables development of double-walled carbon nanotubes to be independent, such that the charge transport of the inner wall is maintained and confirmed whilst the outer wall is modified for functional purposes.

Keratin film ablation for the fabrication of brick and mortar skin structure using femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Haq, Bibi Safia; Khan, Hidayat Ullah; Dou, Yuehua; Alam, Khan; Attaullah, Shehnaz; Zari, Islam

2015-09-01

The patterning of thin keratin films has been explored to manufacture model skin surfaces based on the "bricks and mortar" view of the relationship between keratin and lipids. It has been demonstrated that laser light is capable of preparing keratin-based "bricks and mortar" wall structure as in epidermis, the outermost layer of the human skin. "Bricks and mortar" pattern in keratin films has been fabricated using an ArF excimer laser (193 nm wavelength) and femtosecond laser (800 and 400 nm wavelength). Due to the very low ablation threshold of keratin, femtosecond laser systems are practical for laser processing of proteins. These model skin structures are fabricated for the first time that will help to produce potentially effective moisturizing products for the protection of skin from dryness, diseases and wrinkles.

Structure of Mycobacterium tuberculosis mtFabD, a malonyl-CoA:acyl carrier protein transacylase (MCAT).

PubMed

Ghadbane, Hemza; Brown, Alistair K; Kremer, Laurent; Besra, Gurdyal S; Fütterer, Klaus

2007-10-01

Mycobacteria display a unique and unusual cell-wall architecture, central to which is the membrane-proximal mycolyl-arabinogalactan-peptidoglycan core (mAGP). The biosynthesis of mycolic acids, which form the outermost layer of the mAGP core, involves malonyl-CoA:acyl carrier protein transacylase (MCAT). This essential enzyme catalyses the transfer of malonyl from coenzyme A to acyl carrier protein AcpM, thus feeding these two-carbon units into the chain-elongation cycle of the type II fatty-acid synthase. The crystal structure of M. tuberculosis mtFabD, the mycobacterial MCAT, has been determined to 3.0 A resolution by multi-wavelength anomalous dispersion. Phasing was facilitated by Ni2+ ions bound to the 20-residue N-terminal affinity tag, which packed between the two independent copies of mtFabD.

A numerical analysis of the British Experimental Rotor Program blade

NASA Technical Reports Server (NTRS)

Duque, Earl P. N.

1989-01-01

Two Computational Fluid Dynamic codes which solve the compressible full-potential and the Reynolds-Averaged Thin-Layer Navier-Stokes equations were used to analyze the nonrotating aerodynamic characteristics of the British Experimental Rotor Program (BERP) helicopter blade at three flow regimes: low angle of attack, high angle of attack and transonic. Excellent agreement was found between the numerical results and experiment. In the low angle of attack regime, the BERP had less induced drag than a comparable aspect ratio rectangular planform wing. At high angle of attack, the blade attained high-lift by maintaining attached flow at the outermost spanwise locations. In the transonic regime, the BERP design reduces the shock strength at the outer spanwise locations which affects wave drag and shock-induced separation. Overall, the BERP blade exhibited many favorable aerodynamic characteristics in comparison to conventional helicopter rotor blades.

[Recent studies on corneal epithelial barrier function].

PubMed

Liu, F F; Li, W; Liu, Z G; Chen, W S

2016-08-01

Corneal epithelium, the outermost layer of eyeball, is the main route for foreign materials to enter the eye. Under physiological conditions, the corneal epithelial superficial cells form a functionally selective permeability barrier. Integral corneal epithelial barrier function not only ensures the enrolling of nutrients which is required for regular metabolism, but also prevents foreign bodies, or disease-causing microorganism invasion. Recently, a large number of clinical and experimental studies have shown that abnormal corneal epithelial barrier function is the pathological basis for many ocular diseases. In addition, some study found that corneal epithelial barrier constitutes a variety of proteins involved in cell proliferation, differentiation, apoptosis, and a series of physiological and pathological processes. This paper reviewed recent studies specifically on the corneal epithelial barrier, highlights of its structure, function and influence factors. (Chin J Ophthalmol, 2016, 52: 631-635).

Application of Fourier transform-second-harmonic generation imaging to the rat cervix.

PubMed

Lau, T Y; Sangha, H K; Chien, E K; McFarlin, B L; Wagoner Johnson, A J; Toussaint, K C

2013-07-01

We present the application of Fourier transform-second-harmonic generation (FT-SHG) imaging to evaluate the arrangement of collagen fibers in five nonpregnant rat cervices. Tissue slices from the mid-cervix and near the external orifice of the cervix were analyzed in both two-dimensions (2D) and three-dimensions (3D). We validate that the cervical microstructure can be quantitatively assessed in three dimensions using FT-SHG imaging and observe collagen fibers oriented both in and out-of-plane in the outermost and the innermost layers, which cannot be observed using 2D FT-SHG analysis alone. This approach has the potential to be a clinically applicable method for measuring progressive changes in collagen organization during cervical remodeling in humans. © 2013 The Authors Journal of Microscopy © 2013 Royal Microscopical Society.

Electron Microscopy Abrasion Analysis of Candidate Fabrics for Planetary Space Suit Protective Overgarment Application

NASA Technical Reports Server (NTRS)

Hennessy, Mary J.

1992-01-01

The Electron Microscopy Abrasion Analysis of Candidate Fabrics for Planetary Space Suit Protective Overgarment Application is in support of the Abrasion Resistance Materials Screening Test. The fundamental assumption made for the SEM abrasion analysis was that woven fabrics to be used as the outermost layer of the protective overgarment in the design of the future, planetary space suits perform best when new. It is the goal of this study to determine which of the candidate fabrics was abraded the least in the tumble test. The sample that was abraded the least will be identified at the end of the report as the primary candidate fabric for further investigation. In addition, this analysis will determine if the abrasion seen by the laboratory tumbled samples is representative of actual EVA Apollo abrasion.

Mechanics, morphology, and mobility in stratum corneum membranes

NASA Astrophysics Data System (ADS)

Olmsted, Peter; Das, Chinmay; Noro, Massimo

2012-02-01

The stratum corneum is the outermost layer of skin, and serves as a protective barrier against external agents, and to control moisture. It comprises keratin bodies (corneocytes) embedded in a matrix of lipid bilayers. Unlike the more widely studied phospholipid bilayers, the SC bilayers are typically in a gel-like state. Moreover, the SC membrane composition is radically different from more fluid counterparts: it comprises single tailed fatty acids, ceramides, and cholesterol; with many distinct ceramides possessing different lengths of tails, and always with two tails of different lengths. I will present insight from computer simulations into the morphology, mechanical properties, and diffusion (barrier) properties of these highly heterogeneous membranes. Our results provide some clue as to the design principles for the SC membrane, and is an excellent example of the use of wide polydispersity by natural systems.

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.

High Performance and Highly Reliable ZnO Thin Film Transistor Fabricated by Atomic Layer Deposition for Next Generation Displays

DTIC Science & Technology

2011-08-19

zinc oxide ( ZnO ) thin film as an active channel layer in TFT has become of great interest owing to their specific...630-0192 Japan Phone: +81-743-72-6060 Fax: +81-743-72-6069 E-mail: uraoka@ms.naist.jp Keywords: zinc oxide , thin film transistors , atomic layer...deposition Symposium topic: Transparent Semiconductors Oxides [Abstract] In this study, we fabricated TFTs using ZnO thin film as the

Quorum-Quenching and Matrix-Degrading Enzymes in Multilayer Coatings Synergistically Prevent Bacterial Biofilm Formation on Urinary Catheters.

PubMed

Ivanova, Kristina; Fernandes, Margarida M; Francesko, Antonio; Mendoza, Ernest; Guezguez, Jamil; Burnet, Michael; Tzanov, Tzanko

2015-12-16

Bacteria often colonize in-dwelling medical devices and grow as complex biofilm communities of cells embedded in a self-produced extracellular polymeric matrix, which increases their resistance to antibiotics and the host immune system. During biofilm growth, bacterial cells cooperate through specific quorum-sensing (QS) signals. Taking advantage of this mechanism of biofilm formation, we hypothesized that interrupting the communication among bacteria and simultaneously degrading the extracellular matrix would inhibit biofilm growth. To this end, coatings composed of the enzymes acylase and α-amylase, able to degrade bacterial QS molecules and polysaccharides, respectively, were built on silicone urinary catheters using a layer-by-layer deposition technique. Multilayer coatings of either acylase or amylase alone suppressed the biofilm formation of corresponding Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Further assembly of both enzymes in hybrid nanocoatings resulted in stronger biofilm inhibition as a function of acylase or amylase position in the layers. Hybrid coatings, with the QS-signal-degrading acylase as outermost layer, demonstrated 30% higher antibiofilm efficiency against medically relevant Gram-negative bacteria compared to that of the other assemblies. These nanocoatings significantly reduced the occurrence of single-species (P. aeruginosa) and mixed-species (P. aeruginosa and Escherichia coli) biofilms on silicone catheters under both static and dynamic conditions. Moreover, in an in vivo animal model, the quorum quenching and matrix degrading enzyme assemblies delayed the biofilm growth up to 7 days.

Nanoscale Probing of Electrical Signals in Biological Systems

DTIC Science & Technology

2012-03-18

Membranes Anodized aluminum oxide ( AAO ) is an ideal prototype substrate for studying ion transport through nanoporous membranes . For optimal...electrochemical microscopy, scanning ion conductance microscopy, nanoporous membranes , anodized aluminum oxide , atomic layer deposition, focused ion beam...capacity. This approach utilizes atomic layer deposition (ALD) of a thin conformal Ir film into a nanoporous anodized aluminum oxide (

Antimonide-Based Compound Semiconductors for Low-Power Electronics

DTIC Science & Technology

2013-01-01

A, Madan HS, Kirk AP, Zhao DA, Mourey DA, Hudait MK, et al. Fermi level unpinning of GaSb (100) using plasma enhanced atomic layer deposition of...et al. Atomic layer deposition of Al2O3 on GaSb using in situ hydrogen plasma exposure. Appl Phys Lett. 2012;101: 231601. [18] Ali A, Madan H

Cost-Effective Systems for Atomic Layer Deposition

ERIC Educational Resources Information Center

Lubitz, Michael; Medina, Phillip A., IV; Antic, Aleks; Rosin, Joseph T.; Fahlman, Bradley D.

2014-01-01

Herein, we describe the design and testing of two different home-built atomic layer deposition (ALD) systems for the growth of thin films with sub-monolayer control over film thickness. The first reactor is a horizontally aligned hot-walled reactor with a vacuum purging system. The second reactor is a vertically aligned cold-walled reactor with a…

Nano-soldering to single atomic layer

DOEpatents

Girit, Caglar O [Berkeley, CA; Zettl, Alexander K [Kensington, CA

2011-10-11

A simple technique to solder submicron sized, ohmic contacts to nanostructures has been disclosed. The technique has several advantages over standard electron beam lithography methods, which are complex, costly, and can contaminate samples. To demonstrate the soldering technique graphene, a single atomic layer of carbon, has been contacted, and low- and high-field electronic transport properties have been measured.

Electronic structure studies of a clock-reconstructed Al/Pd(1 0 0) surface alloy

NASA Astrophysics Data System (ADS)

Kirsch, Janet E.; Tainter, Craig J.

We have employed solid-state Fenske-Hall band structure calculations to examine the electronic structure of Al/Pd(1 0 0), a surface alloy that undergoes a reconstruction, or rearrangement, of the atoms in the top few surface layers. Surface alloys are materials that consist primarily of a single elemental metal, but which have a bimetallic surface composition that is only a few atomic layers in thickness. The results of this study indicate that reconstruction into a clock configuration simultaneously optimizes the intralayer bonding within the surface plane and the bonding between the first and second atomic layers. These results also allow us to examine the fundamental relationship between the electronic and physical structures of this reconstructed surface alloy.

Comparison of trimethylgallium and triethylgallium as “Ga” source materials for the growth of ultrathin GaN films on Si (100) substrates via hollow-cathode plasma-assisted atomic layer deposition

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

Alevli, Mustafa, E-mail: mustafaalevli@marmara.edu.tr; Haider, Ali; Kizir, Seda

2016-01-15

GaN films grown by hollow cathode plasma-assisted atomic layer deposition using trimethylgallium (TMG) and triethylgallium (TEG) as gallium precursors are compared. Optimized and saturated TMG/TEG pulse widths were used in order to study the effect of group-III precursors. The films were characterized by grazing incidence x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Refractive index follows the same trend of crystalline quality, mean grain, and crystallite sizes. GaN layers grown using TMG precursor exhibited improved structural and optical properties when compared to GaN films grown with TEG precursor.

Strong Fermi-Level Pinning at Metal/n-Si(001) Interface Ensured by Forming an Intact Schottky Contact with a Graphene Insertion Layer.

PubMed

Yoon, Hoon Hahn; Jung, Sungchul; Choi, Gahyun; Kim, Junhyung; Jeon, Youngeun; Kim, Yong Soo; Jeong, Hu Young; Kim, Kwanpyo; Kwon, Soon-Yong; Park, Kibog

2017-01-11

We report the systematic experimental studies demonstrating that a graphene layer inserted at metal/n-Si(001) interface is efficient to explore interface Fermi-level pinning effect. It is confirmed that an inserted graphene layer prevents atomic interdiffusion to form an atomically abrupt Schottky contact. The Schottky barriers of metal/graphene/n-Si(001) junctions show a very weak dependence on metal work-function, implying that the metal Fermi-level is almost completely pinned at charge neutrality level close to the valence band edge of Si. The atomically impermeable and electronically transparent properties of graphene can be used generally to form an intact Schottky contact for all semiconductors.

Surface structure and chemistry of Pt/Cu/Pt(1 1 1) near surface alloy model catalyst in CO

NASA Astrophysics Data System (ADS)

Zeng, Shibi; Nguyen, Luan; Cheng, Fang; Liu, Lacheng; Yu, Ying; Tao, Franklin (Feng)

2014-11-01

Near surface alloy (NSA) model catalyst Pt/Cu/Pt(1 1 1) was prepared on Pt(1 1 1) through a controlled vapor deposition of Cu atoms. Different coordination environments of Pt atoms of the topmost Pt layer with the underneath Cu atoms in the subsurface result in different local electronic structures of surface Pt atoms. Surface structure and chemistry of the NAS model catalyst in Torr pressure of CO were studied with high pressure scanning tunneling microscopy (HP-STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In Torr pressure of CO, the topmost Pt layer of Pt/Cu/Pt(1 1 1) is restructured to thin nanoclusters with size of about 1 nm. Photoemission feature of O 1s of CO on Pt/Cu/Pt(1 1 1) suggests CO adsorbed on both edge and surface of these formed nanoclusters. This surface is active for CO oxidation. Atomic layers of carbon are formed on Pt/Cu/Pt(1 1 1) at 573 K in 2 Torr of CO.

C 60 -induced Devil's Staircase transformation on a Pb/Si(111) wetting layer

DOE PAGES

Wang, Lin -Lin; Johnson, Duane D.; Tringides, Michael C.

2015-12-03

Density functional theory is used to study structural energetics of Pb vacancy cluster formation on C 60/Pb/Si(111) to explain the unusually fast and error-free transformations between the “Devil's Staircase” (DS) phases on the Pb/Si(111) wetting layer at low temperature (~110K). The formation energies of vacancy clusters are calculated in C 60/Pb/Si(111) as Pb atoms are progressively ejected from the initial dense Pb wetting layer. Vacancy clusters larger than five Pb atoms are found to be stable with seven being the most stable, while vacancy clusters smaller than five are highly unstable, which agrees well with the observed ejection rate ofmore » ~5 Pb atoms per C 60. Furthermore, the high energy cost (~0.8 eV) for the small vacancy clusters to form indicates convincingly that the unusually fast transformation observed experimentally between the DS phases, upon C 60 adsorption at low temperature, cannot be the result of single-atom random walk diffusion but of correlated multi-atom processes.« less

Enhanced electrical properties of dual-layer channel ZnO thin film transistors prepared by atomic layer deposition

NASA Astrophysics Data System (ADS)

Li, Huijin; Han, Dedong; Dong, Junchen; Yu, Wen; Liang, Yi; Luo, Zhen; Zhang, Shengdong; Zhang, Xing; Wang, Yi

2018-05-01

The thin film transistors (TFTs) with a dual-layer channel structure combing ZnO thin layer grown at 200 °C and ZnO film grown at 120 °C by atomic layer deposition are fabricated. The dual-layer channel TFT exhibits a low leakage current of 2.8 × 10-13 A, Ion/Ioff ratio of 3.4 × 109, saturation mobility μsat of 12 cm2 V-1 s-1, subthreshold swing (SS) of 0.25 V/decade. The SS value decreases to 0.18 V/decade after the annealing treatment in O2 due to the reduction of the trap states at the channel/dielectric interface and in the bulk channel layer. The enhanced performance obtained from the dual-layer channel TFTs is due to the ability of maintaining high mobility and suppressing the increase in the off-current at the same time.

Hybrid inorganic–organic superlattice structures with atomic layer deposition/molecular layer deposition

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

Tynell, Tommi; Yamauchi, Hisao; Karppinen, Maarit, E-mail: maarit.karppinen@aalto.fi

2014-01-15

A combination of the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques is successfully employed to fabricate thin films incorporating superlattice structures that consist of single layers of organic molecules between thicker layers of ZnO. Diethyl zinc and water are used as precursors for the deposition of ZnO by ALD, while three different organic precursors are investigated for the MLD part: hydroquinone, 4-aminophenol and 4,4′-oxydianiline. The successful superlattice formation with all the organic precursors is verified through x-ray reflectivity studies. The effects of the interspersed organic layers/superlattice structure on the electrical and thermoelectric properties of ZnO are investigatedmore » through resistivity and Seebeck coefficient measurements at room temperature. The results suggest an increase in carrier concentration for small concentrations of organic layers, while higher concentrations seem to lead to rather large reductions in carrier concentration.« less

Bi-layer Channel AZO/ZnO Thin Film Transistors Fabricated by Atomic Layer Deposition Technique.

PubMed

Li, Huijin; Han, Dedong; Liu, Liqiao; Dong, Junchen; Cui, Guodong; Zhang, Shengdong; Zhang, Xing; Wang, Yi

2017-12-01

This letter demonstrates bi-layer channel Al-doped ZnO/ZnO thin film transistors (AZO/ZnO TFTs) via atomic layer deposition process at a relatively low temperature. The effects of annealing in oxygen atmosphere at different temperatures have also been investigated. The ALD bi-layer channel AZO/ZnO TFTs annealed in dry O 2 at 300 °C exhibit a low leakage current of 2.5 × 10 -13 A, I on /I off ratio of 1.4 × 10 7 , subthreshold swing (SS) of 0.23 V/decade, and high transmittance. The enhanced performance obtained from the bi-layer channel AZO/ZnO TFT devices is explained by the inserted AZO front channel layer playing the role of the mobility booster.