Structure Formation of Ultrathin PEO Films at Solid Interfaces—Complex Pattern Formation by Dewetting and Crystallization

PubMed Central

Braun, Hans-Georg; Meyer, Evelyn

2013-01-01

The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups. PMID:23385233

Optical bandgap of single- and multi-layered amorphous germanium ultra-thin films

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

Liu, Pei; Zaslavsky, Alexander; Longo, Paolo

2016-01-07

Accurate optical methods are required to determine the energy bandgap of amorphous semiconductors and elucidate the role of quantum confinement in nanometer-scale, ultra-thin absorbing layers. Here, we provide a critical comparison between well-established methods that are generally employed to determine the optical bandgap of thin-film amorphous semiconductors, starting from normal-incidence reflectance and transmittance measurements. First, we demonstrate that a more accurate estimate of the optical bandgap can be achieved by using a multiple-reflection interference model. We show that this model generates more reliable results compared to the widely accepted single-pass absorption method. Second, we compare two most representative methods (Taucmore » and Cody plots) that are extensively used to determine the optical bandgap of thin-film amorphous semiconductors starting from the extracted absorption coefficient. Analysis of the experimental absorption data acquired for ultra-thin amorphous germanium (a-Ge) layers demonstrates that the Cody model is able to provide a less ambiguous energy bandgap value. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO{sub 2} superlattices with single and multiple a-Ge layers down to 2 nm thickness.« less

Collective Behavior of Amoebae in Thin Films

NASA Astrophysics Data System (ADS)

Bae, Albert

2005-03-01

We have discovered new aspects of social behavior in Dictyostelium discoideum by culturing high density colonies in liquid media depleted of nutrients in confined geometries by using three different preparations: I. thin (15-40um thick) and II. ultrathin (<3um) films of liquid media with a mineral oil overlayer, and III. microfluidic chambers fabricated in PDMS (˜7um tall). We find greatly reduced, if not eliminated, cell on cell layering in the microfluidic system when compared to the wetting layer preparations. The ultrathin films reveal robust behavior of cells despite flattening that increased their areas by over an order of magnitude. We also observed that the earliest synchronized response of cells following the onset of starvation, a precursor to aggregation, was hastened by reducing the thickness of the aqueous culture layer. We were surprised to find that the threshold concentration for aggregation was raised by thin film confinement when compared to bulk behavior. Finally, both the ultra thin and microfluidic preparations reveal, with new clarity, vortex states of aggregation.

Controllable fabrication of ultrathin free-standing graphene films

PubMed Central

Chen, Jianyi; Guo, Yunlong; Huang, Liping; Xue, Yunzhou; Geng, Dechao; Liu, Hongtao; Wu, Bin; Yu, Gui; Hu, Wenping; Liu, Yunqi; Zhu, Daoben

2014-01-01

Graphene free-standing film-like or paper-like materials have attracted great attention due to their intriguing electronic, optical and mechanical properties and potential application in chemical filters, molecular storage and supercapacitors. Although significant progress has been made in fabricating graphene films or paper, there is still no effective method targeting ultrathin free-standing graphene films (UFGFs). Here, we present a modified filtration assembly method to prepare these ultrathin films. With this approach, we have fabricated a series of ultrathin free-standing graphene oxide films and UFGFs, up to 40 mm in diameter, with controllable thickness from micrometre to nanoscale (approx. 40 nm) dimensions. This method can be easily scaled up and the films display excellent optical, electrical and electrochemical properties. The ability to produce UFGFs from graphene oxide with a scalable, low-cost approach should take us a step closer to real-world applications of graphene. PMID:24615152

Trends in the thermodynamic stability of ultrathin supported oxide films

DOE PAGES

Plessow, Philipp N.; Bajdich, Michal; Greene, Joshua; ...

2016-05-05

The formation of thin oxide films on metal supports is an important phenomenon, especially in the context of strong metal support interaction (SMSI). Computational predictions of the stability of these films are hampered by their structural complexity and a varying lattice mismatch with different supports. In this study, we report a large combination of supports and ultrathin oxide films studied with density functional theory (DFT). Trends in stability are investigated through a descriptor-based analysis. Since the studied films are bound to the support exclusively through metal–metal interaction, the adsorption energy of the oxide-constituting metal atom can be expected to bemore » a reasonable descriptor for the stability of the overlayers. If the same supercell is used for all supports, the overlayers experience different amounts of stress. Using supercells with small lattice mismatch for each system leads to significantly improved scaling relations for the stability of the overlayers. Finally, this approach works well for the studied systems and therefore allows the descriptor-based exploration of the thermodynamic stability of supported thin oxide layers.« less

Designing metal hemispheres on silicon ultrathin film solar cells for plasmonic light trapping.

PubMed

Gao, Tongchuan; Stevens, Erica; Lee, Jung-kun; Leu, Paul W

2014-08-15

We systematically investigate the design of two-dimensional silver (Ag) hemisphere arrays on crystalline silicon (c-Si) ultrathin film solar cells for plasmonic light trapping. The absorption in ultrathin films is governed by the excitation of Fabry-Perot TEMm modes. We demonstrate that metal hemispheres can enhance absorption in the films by (1) coupling light to c-Si film waveguide modes and (2) exciting localized surface plasmon resonances (LSPRs). We show that hemisphere arrays allow light to couple to fundamental TEm and TMm waveguide modes in c-Si film as well as higher-order versions of these modes. The near-field light concentration of LSPRs also may increase absorption in the c-Si film, though these resonances are associated with significant parasitic absorption in the metal. We illustrate how Ag plasmonic hemispheres may be utilized for light trapping with 22% enhancement in short-circuit current density compared with that of a bare 100 nm thick c-Si ultrathin film solar cell.

Fabrication of Large-area Free-standing Ultrathin Polymer Films

PubMed Central

Stadermann, Michael; Baxamusa, Salmaan H.; Aracne-Ruddle, Chantel; Chea, Maverick; Li, Shuaili; Youngblood, Kelly; Suratwala, Tayyab

2015-01-01

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described. PMID:26066738

Single crystalline silicene consist of various superstructures using a flexible ultrathin Ag(111) template on Si(111)

NASA Astrophysics Data System (ADS)

Hsu, Hung-Chang; Lu, Yi-Hung; Su, Tai-Lung; Lin, Wen-Chin; Fu, Tsu-Yi

2018-07-01

Using scanning tunneling microscopy, we studied the formation of silicene on an ultrathin Ag(111) film with a thickness of 6–12 monolayers, which was prepared on a Si(111) substrate. A low-energy electron diffraction pattern with an oval spot indicated that the ultrathin Ag(111) film is more disordered than the single-crystal Ag(111). After Si epitaxy growth, we still measured the classical 4 × 4, √13 × √13, and 2√3 × 2√3 silicene superstructures, which are the same as the silicene superstructure on single-crystal Ag(111). Growing silicene on a single-crystal Ag(111) bulk usually results in the formation of a defect boundary due to the inconsistent orientation of various superstructures. By comparing the angles and boundary conditions between various silicene superstructures on the ultrathin film and single-crystal Ag(111), we discovered that a consistent orientation of various superstructures without obvious boundary defects formed on the ultrathin Ag(111) film. The results indicated single crystalline silicene formation, which was attributed to the domain rotation and lateral shift of the disordered ultrathin Ag(111) film.

TOPICAL REVIEW: Ultra-thin film encapsulation processes for micro-electro-mechanical devices and systems

NASA Astrophysics Data System (ADS)

Stoldt, Conrad R.; Bright, Victor M.

2006-05-01

A range of physical properties can be achieved in micro-electro-mechanical systems (MEMS) through their encapsulation with solid-state, ultra-thin coatings. This paper reviews the application of single source chemical vapour deposition and atomic layer deposition (ALD) in the growth of submicron films on polycrystalline silicon microstructures for the improvement of microscale reliability and performance. In particular, microstructure encapsulation with silicon carbide, tungsten, alumina and alumina-zinc oxide alloy ultra-thin films is highlighted, and the mechanical, electrical, tribological and chemical impact of these overlayers is detailed. The potential use of solid-state, ultra-thin coatings in commercial microsystems is explored using radio frequency MEMS as a case study for the ALD alloy alumina-zinc oxide thin film.

Effects of different wetting layers on the growth of smooth ultra-thin silver thin films

NASA Astrophysics Data System (ADS)

Ni, Chuan; Shah, Piyush; Sarangan, Andrew M.

2014-09-01

Ultrathin silver films (thickness below 10 nm) are of great interest as optical coatings on windows and plasmonic devices. However, producing these films has been a continuing challenge because of their tendency to form clusters or islands rather than smooth contiguous thin films. In this work we have studied the effect of Cu, Ge and ZnS as wetting layers (1.0 nm) to achieve ultrasmooth thin silver films. The silver films (5 nm) were grown by RF sputter deposition on silicon and glass substrates using a few monolayers of the different wetting materials. SEM imaging was used to characterize the surface properties such as island formation and roughness. Also the optical properties were measured to identify the optical impact of the different wetting layers. Finally, a multi-layer silver based structure is designed and fabricated, and its performance is evaluated. The comparison between the samples with different wetting layers show that the designs with wetting layers which have similar optical properties to silver produce the best overall performance. In the absence of a wetting layer, the measured optical spectra show a significant departure from the model predictions, which we attribute primarily to the formation of clusters.

Influence of Thickness on the Electrical Transport Properties of Exfoliated Bi2Te3 Ultrathin Films

NASA Astrophysics Data System (ADS)

Mo, D. L.; Wang, W. B.; Cai, Q.

2016-08-01

In this work, the mechanical exfoliation method has been utilized to fabricate Bi2Te3 ultrathin films. The thickness of the ultrathin films is revealed to be several tens of nanometers. Weak antilocalization effects and Shubnikov de Haas oscillations have been observed in the magneto-transport measurements on individual films with different thickness, and the two-dimensional surface conduction plays a dominant role. The Fermi level is found to be 81 meV above the Dirac point, and the carrier mobility can reach ~6030 cm2/(Vs) for the 10-nm film. When the film thickness decreases from 30 to 10 nm, the Fermi level will move 8 meV far from the bulk valence band. The coefficient α in the Hikami-Larkin-Nagaoka equation is shown to be ~0.5, manifesting that only the bottom surface of the Bi2Te3 ultrathin films takes part in transport conductions. These will pave the way for understanding thoroughly the surface transport properties of topological insulators.

Structural phase diagram for ultra-thin epitaxial Fe 3O 4 / MgO(0 01) films: thickness and oxygen pressure dependence

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

Alraddadi, S.; Hines, W.; Yilmaz, T.

2016-02-19

A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe 3O 4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10 -7 torr to 1 × 10 -5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED)more » and x-ray photoemission spectroscopy (XPS), respectively. Moreover, the quality of the epitaxial Fe 3O 4 ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe 3O 4 phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe 3O 4 films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.« less

Using Ultrathin Parylene Films as an Organic Gate Insulator in Nanowire Field-Effect Transistors.

PubMed

Gluschke, J G; Seidl, J; Lyttleton, R W; Carrad, D J; Cochrane, J W; Lehmann, S; Samuelson, L; Micolich, A P

2018-06-27

We report the development of nanowire field-effect transistors featuring an ultrathin parylene film as a polymer gate insulator. The room temperature, gas-phase deposition of parylene is an attractive alternative to oxide insulators prepared at high temperatures using atomic layer deposition. We discuss our custom-built parylene deposition system, which is designed for reliable and controlled deposition of <100 nm thick parylene films on III-V nanowires standing vertically on a growth substrate or horizontally on a device substrate. The former case gives conformally coated nanowires, which we used to produce functional Ω-gate and gate-all-around structures. These give subthreshold swings as low as 140 mV/dec and on/off ratios exceeding 10 3 at room temperature. For the gate-all-around structure, we developed a novel fabrication strategy that overcomes some of the limitations with previous lateral wrap-gate nanowire transistors. Finally, we show that parylene can be deposited over chemically treated nanowire surfaces, a feature generally not possible with oxides produced by atomic layer deposition due to the surface "self-cleaning" effect. Our results highlight the potential for parylene as an alternative ultrathin insulator in nanoscale electronic devices more broadly, with potential applications extending into nanobioelectronics due to parylene's well-established biocompatible properties.

A repeated halving approach to fabricate ultrathin single-walled carbon nanotube films for transparent supercapacitors.

PubMed

Niu, Zhiqiang; Zhou, Weiya; Chen, Jun; Feng, Guoxing; Li, Hong; Hu, Yongsheng; Ma, Wenjun; Dong, Haibo; Li, Jinzhu; Xie, Sishen

2013-02-25

Ultrathin SWCNT transparent and conductive films on flexible and transparent substrates are prepared via repeatedly halving the directly grown SWCNT films and flexible and transparent supercapacitors with excellent performance were fabricated. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 films

NASA Astrophysics Data System (ADS)

Moyer, J. A.; Vaz, C. A. F.; Kumah, D. P.; Arena, D. A.; Henrich, V. E.

2012-11-01

The effect of film thickness on the magnetic properties of ultrathin Fe-doped cobalt ferrite (Co1-xFe2+xO4) grown on MgO (001) substrates is investigated by superconducting quantum interference device magnetometry and x-ray magnetic linear dichroism, while the distribution of the Co2+ cations between the octahedral and tetrahedral lattice sites is studied with x-ray absorption spectroscopy. For films thinner than 10 nm, there is a large enhancement of the magnetic moment; conversely, the remanent magnetization and coercive fields both decrease, while the magnetic spin axes of all the cations become less aligned with the [001] crystal direction. In particular, at 300 K the coercive fields of the thinnest films vanish. The spectroscopy data show that no changes occur in the cation distribution as a function of film thickness, ruling this out as the origin of the enhanced magnetic moment. However, the magnetic measurements all support the possibility that these ultrathin Fe-doped CoFe2O4 films are transitioning into a superparamagnetic state, as has been seen in ultrathin Fe3O4. A weakening of the magnetic interactions at the antiphase boundaries, leading to magnetically independent domains within the film, could explain the enhanced magnetic moment in ultrathin Fe-doped CoFe2O4 and the onset of superparamagnetism at room temperature.

Physicochemically functional ultrathin films by interfacial polymerization

DOEpatents

Lonsdale, Harold K.; Babcock, Walter C.; Friensen, Dwayne T.; Smith, Kelly L.; Johnson, Bruce M.; Wamser, Carl C.

1990-01-01

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

Molecular Imaging of Ultrathin Pentacene Films: Evidence for Homoepitaxy

NASA Astrophysics Data System (ADS)

Wu, Yanfei; Haugstad, Greg; Frisbie, C. Daniel

2013-03-01

Ultrathin polycrystalline films of organic semiconductors have received intensive investigations due to the critical role they play in governing the performance of organic thin film transistors. In this work, a variety of scanning probe microscopy (SPM) techniques have been employed to investigate ultrathin polycrystalline films (1-3 nm) of the benchmark organic semiconductor pentacene. By using spatially resolved Friction Force Microscopy (FFM), Kelvin Probe Force Microscopy (KFM) and Electrostatic Force Microscopy (EFM), an interesting multi-domain structure is revealed within the second layer of the films, characterized as two distinct friction and surface potential domains correlating with each other. The existence of multiple homoepitaxial modes within the films is thus proposed and examined. By employing lattice-revolved imaging using contact mode SPM, direct molecular evidence for the unusual homoepitaxy is obtained.

Method for laser welding ultra-thin metal foils

DOEpatents

Pernicka, J.C.; Benson, D.K.; Tracy, C.E.

1996-03-26

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld. 5 figs.

Method for laser welding ultra-thin metal foils

DOEpatents

Pernicka, John C.; Benson, David K.; Tracy, C. Edwin

1996-01-01

A method for simultaneously cutting and welding ultra-thin foils having a thickness of less than 0.002 inches wherein two ultra-thin films are stacked and clamped together. A pulsed laser such as of the Neodymium: YAG type is provided and the beam of the laser is directed onto the stacked films to cut a channel through the films. The laser is moved relative to the stacked foils to cut the stacked foils at successive locations and to form a plurality of connected weld beads to form a continuous weld.

Thickness-dependence of optical constants for Ta2O5 ultrathin films

NASA Astrophysics Data System (ADS)

Zhang, Dong-Xu; Zheng, Yu-Xiang; Cai, Qing-Yuan; Lin, Wei; Wu, Kang-Ning; Mao, Peng-Hui; Zhang, Rong-Jun; Zhao, Hai-bin; Chen, Liang-Yao

2012-09-01

An effective method for determining the optical constants of Ta2O5 thin films deposited on crystal silicon (c-Si) using spectroscopic ellipsometry (SE) measurement with a two-film model (ambient-oxide-interlayer-substrate) was presented. Ta2O5 thin films with thickness range of 1-400 nm have been prepared by the electron beam evaporation (EBE) method. We find that the refractive indices of Ta2O5 ultrathin films less than 40 nm drop with the decreasing thickness, while the other ones are close to those of bulk Ta2O5. This phenomenon was due to the existence of an interfacial oxide region and the surface roughness of the film, which was confirmed by the measurement of atomic force microscopy (AFM). Optical properties of ultrathin film varying with the thickness are useful for the design and manufacture of nano-scaled thin-film devices.

Physicochemically functional ultrathin films by interfacial polymerization

DOEpatents

Lonsdale, H.K.; Babcock, W.C.; Friensen, D.T.; Smith, K.L.; Johnson, B.M.; Wamser, C.C.

1990-08-14

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclosed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers. 3 figs.

Coulomb gap: how a metal film becomes an insulator

PubMed

Butko; DiTusa; Adams

2000-02-14

Electron tunneling measurements of the density of states (DOS) in ultrathin Be films reveal that a correlation gap mediates their insulating behavior. In films with sheet resistance R<5000 Omega the correlation singularity appears as the usual perturbative ln(V) zero bias anomaly (ZBA) in the DOS. As R is increased further, however, the ZBA grows and begins to dominate the DOS spectrum. This evolution continues until a nonperturbative |V| Efros-Shklovskii Coulomb gap spectrum finally emerges in the highest R films. Transport measurements of films which display this gap are well described by a universal variable range hopping law R(T) = (h/2e(2))exp(T0/T)(1/2).

Synthesis of Ultrathin ta-C Films by Twist-Filtered Cathodic Arc Carbon Plasmas

DTIC Science & Technology

2001-04-01

system. Ultrathin tetrahedral amorphous carbon (ta-C) films have been deposited on 6 inch wafers. Film properties have been investigated with respect to...Diamondlike films are characterized by an outstanding combination of advantageous properties : they can be very hard, tough, super-smooth, chemically...5 nm) hard carbon films are being used as protective overcoats on hard disks and read-write heads. The tribological properties of the head-disk

Room Temperature Ferroelectricity in Ultrathin SnTe Films

NASA Astrophysics Data System (ADS)

Chang, Kai; Liu, Junwei; Lin, Haicheng; Zhao, Kun; Zhong, Yong; Ji, Shuai-Hua; He, Ke; Wang, Lili; Ma, Xucun; Fu, Liang; Chen, Xi; Xue, Qi-Kun

2015-03-01

The ultrathin SnTe films with several unit cell thickness grown on graphitized SiC(0001) surface have been studied by the scanning tunneling microscopy and spectroscopy (STM/S). The domain structures, local lattice distortion and the electronic band bending at film edges induced by the in-plane spontaneous polarization along < 110 > have been revealed at atomic scale. The experiments at variant temperature show that the Curie temperature Tc of the one unit cell thick (two atomic layers) SnTe film is as high as 280K, much higher than that of the bulk counterpart (~100K) and the 2-4 unit cell thick films even indicate robust ferroelectricity at room temperature. This Tc enhancement is attributed to the stress-free interface, larger electronic band gap and greatly reduced Sn vacancy concentration in the ultrathin films. The lateral domain size varies from several tens to several hundreds of nanometers, and the spontaneous polarization direction could be modified by STM tip. Those properties of ultrathin SnTe films show the potential application on ferroelectric devices. The work was financially supported by Ministry of Science and Technology of China, National Science Foundation and Ministry of Education of China.

Suppression of superconductivity in epitaxial MgB2 ultrathin films

NASA Astrophysics Data System (ADS)

Zhang, Chen; Wang, Yue; Wang, Da; Zhang, Yan; Liu, Zheng-Hao; Feng, Qing-Rong; Gan, Zi-Zhao

2013-07-01

MgB2 ultrathin films have potential to make sensitive superconducting devices such as superconducting single-photon detectors working at relatively high temperatures. We have grown epitaxial MgB2 films in thicknesses ranging from about 40 nm to 6 nm by using the hybrid physical-chemical vapor deposition method and performed electrical transport measurements to study the thickness dependence of the superconducting critical temperature Tc. With reducing film thickness d, although a weak depression of the Tc has been observed, which could be attributed to an increase of disorder (interband impurity scattering) in the film, the Tc retains close to the bulk value of MgB2 (39 K), being about 35 K in the film of 6 nm thick. We show that this result, beneficial to the application of MgB2 ultrathin films and in accordance with recent theoretical calculations, is in contrast to previous findings in MgB2 films prepared by other methods such as co-evaporation and molecular-beam epitaxy, where a severe Tc suppression has been observed with Tc about one third of the bulk value in films of ˜5 nm thick. We discuss this apparent discrepancy in experiments and suggest that, towards the ultrathin limit, the different degrees of Tc suppression displayed in currently obtained MgB2 films by various techniques may arise from the different levels of disorder present in the film or different extents of proximity effect at the film surface or film-substrate interface.

Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

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

Schumann, F.O.; Willis, R.F.; Goodman, K.W.

1997-04-01

The authors have studied the magnetic structure of ultrathin Fe-Ni alloy films as a function of Fe concentration by measuring the linear dichroism of the 3p-core levels in angle-resolved photoemission spectroscopy. The alloy films, grown by molecular-beam epitaxy on Cu(001) surfaces, were fcc and approximately four monolayers thick. The intensity of the Fe dichroism varied with Fe concentration, with larger dichroisms at lower Fe concentrations. The implication of these results to an ultrathin film analogue of the bulk Invar effect in Fe-Ni alloys will be discussed. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Lightmore » Source.« less

Coupling of microphase separation and dewetting in weakly segregated diblock co-polymer ultrathin films.

PubMed

Yan, Derong; Huang, Haiying; He, Tianbai; Zhang, Fajun

2011-10-04

We have studied the coupling behavior of microphase separation and autophobic dewetting in weakly segregated poly(ε-caprolactone)-block-poly(L-lactide) (PCL-b-PLLA) diblock co-polymer ultrathin films on carbon-coated mica substrates. At temperatures higher than the melting point of the PLLA block, the co-polymer forms a lamellar structure in bulk with a long period of L ∼ 20 nm, as determined using small-angle X-ray scattering. The relaxation procedure of ultrathin films with an initial film thickness of h = 10 nm during annealing has been followed by atomic force microscopy (AFM). In the experimental temperature range (100-140 °C), the co-polymer dewets to an ultrathin film of itself at about 5 nm because of the strong attraction of both blocks with the substrate. Moreover, the dewetting velocity increases with decreasing annealing temperatures. This novel dewetting kinetics can be explained by a competition effect of the composition fluctuation driven by the microphase separation with the dominated dewetting process during the early stage of the annealing process. While dewetting dominates the relaxation procedure and leads to the rupture of the ultrathin films, the composition fluctuation induced by the microphase separation attempts to stabilize them because of the matching of h to the long period (h ∼ 1/2L). The temperature dependence of these two processes leads to this novel relaxation kinetics of co-polymer thin films. © 2011 American Chemical Society

Dynamic response of ultrathin highly dense ZIF-8 nanofilms.

PubMed

Cookney, Joanna; Ogieglo, Wojciech; Hrabanek, Pavel; Vankelecom, Ivo; Fila, Vlastimil; Benes, Nieck E

2014-10-11

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for non-equilibrium organic polymers.

Skyrmion morphology in ultrathin magnetic films

NASA Astrophysics Data System (ADS)

Gross, I.; Akhtar, W.; Hrabec, A.; Sampaio, J.; Martínez, L. J.; Chouaieb, S.; Shields, B. J.; Maletinsky, P.; Thiaville, A.; Rohart, S.; Jacques, V.

2018-02-01

Nitrogen-vacancy magnetic microscopy is employed in the quenching mode as a noninvasive, high-resolution tool to investigate the morphology of isolated skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to be strongly affected by local pinning effects and magnetic field history. Micromagnetic simulations including a static disorder, based on the physical model of grain-to-grain thickness variations, reproduce all experimental observations and reveal the key role of disorder and magnetic history in the stabilization of skyrmions in ultrathin magnetic films. This work opens the way to an in-depth understanding of skyrmion dynamics in real, disordered media.

Extraordinary optical transmission in nanopatterned ultrathin metal films without holes

DOE PAGES

Peer, Akshit; Biswas, Rana

2016-02-01

In this study, we experimentally and theoretically demonstrate that a continuous gold film on a periodically textured substrate exhibits extraordinary optical transmission, even though no holes were etched in the film. Our film synthesis started by nanoimprinting a periodic array of nanocups with a period of ~750 nm on a polystyrene film over a glass substrate. A thin non-conformal gold film was sputter-deposited on the polystyrene by angle-directed deposition. The gold film was continuous with spatial thickness variation, the film being thinnest at the bottom of the nanocup. Measurements revealed an extraordinary transmission peak at a wavelength just smaller thanmore » the period, with an enhancement of ~2.5 compared to the classically expected value. Scattering matrix simulations model well the transmission and reflectance measurements when an ultrathin gold layer (~5 nm), smaller than the skin depth is retained at the bottom of the nanocups. Electric field intensities are enhanced by >100 within the nanocup, and ~40 in the ultrathin gold layer causing transmission through it. We show a wavelength red-shift of ~30 nm in the extraordinary transmission peak when the nanocups are coated with a thin film of a few nanometers, which can be utilized for biosensing. The continuous corrugated metal films are far simpler structures to observe extraordinary transmission, circumventing the difficult process of etching the metal film. Such continuous metal films with ultrathin regions are simple platforms for non-linear optics, plasmonics, and biological and chemical sensing.« less

Growth of highly strained CeO 2 ultrathin films

DOE PAGES

Shi, Yezhou; Lee, Sang Chul; Monti, Matteo; ...

2016-11-07

Large biaxial strain is a promising route to tune the functionalities of oxide thin films. However, large strain is often not fully realized due to the formation of misfit dislocations at the film/substrate interface. In this work, we examine the growth of strained ceria (CeO 2) thin films on (001)-oriented single crystal yttria-stabilized zirconia (YSZ) via pulsed-laser deposition. By varying the film thickness systematically between 1 and 430 nm, we demonstrate that ultrathin ceria films are coherently strained to the YSZ substrate for thicknesses up to 2.7 nm, despite the large lattice mismatch (~5%). The coherency is confirmed by bothmore » X-ray diffraction and high-resolution transmission electron microscopy. This thickness is several times greater than the predicted equilibrium critical thickness. Partial strain relaxation is achieved by forming semirelaxed surface islands rather than by directly nucleating dislocations. In situ reflective high-energy electron diffraction during growth confirms the transition from 2-D (layer-by-layer) to 3-D (island) at a film thickness of ~1 nm, which is further supported by atomic force microscopy. We propose that dislocations likely nucleate near the surface islands and glide to the film/substrate interface, as evidenced by the presence of 60° dislocations. Finally, an improved understanding of growing oxide thin films with a large misfit lays the foundation to systematically explore the impact of strain and dislocations on properties such as ionic transport and redox chemistry.« less

Preparation and characterization of the nanoporous ultrathin multilayer films based on molybdenum polyoxometalate (Mo 38) n

NASA Astrophysics Data System (ADS)

Wang, L.; Jiang, M.; Wang, E. B.; Duan, L. Y.; Hao, N.; Lan, Y.; Xu, L.; Li, Z.

2003-11-01

Ultrathin multilayer films of the wheel-shaped molybdenum polyoxometalate cluster (Mo 38) n and poly(allylamine hydrochloride)(PAH) have been prepared by the layer-by-layer (LbL) self-assembly method. The ((Mo 38) n/PAH) m multilayer films have been characterized by X-ray photoelectron spectra (XPS) and atomic force microscopy (AFM). UV-VIS measurements reveal regular film growth with each (Mo 38) n adsorption. The electrochemistry behavior of the film at room temperature was investigated.

Dissolvable Films of Silk Fibroin for Ultrathin Conformal Bio-Integrated Electronics

DTIC Science & Technology

2010-06-01

the systems described in the following, ultrathin, spin- cast films of polyimide (PI) served as a support for arrays of electrodes designed for...micropatterning of optically transparent, mechanically robust, biocompatible silk fibroin films. Adv. Mater. 20, 3070–3072 (2008). 20. Murphy, A. R., John, P. S...analysis of induced colour change on periodically nanopatterned silk films. Opt. Express 17, 21271–21279 (2009). 25. Parker, S. T. et al. Biocompatible

Growth and characterization of few unit-cell NbN superconducting films on 3C-SiC/Si substrate

NASA Astrophysics Data System (ADS)

Chang, H. W.; Wang, C. L.; Huang, Y. R.; Chen, T. J.; Wang, M. J.

2017-11-01

Superconducting δ-NbN ultrathin film has become a key element in extremely sensitive detector applications in recent decades because of its excellent electronic properties. We have realized the epitaxial growth of ultrathin δ-NbN films on (100)-oriented 3C-SiC/Si substrates by dc reactive magnetron sputtering at 760 °C with a deposition rate of 0.054 nm s-1. High-resolution transmission electron microscope images confirm the excellent epitaxy of these films. Even with a thickness of 1.3 nm (˜3 unit cells), the δ-NbN film shows a superconducting transition above 8 K. Furthermore, our ultrathin δ-NbN films demonstrate a long Ginzburg-Landau superconducting coherent length ({ξ }{{G}{{L}}}(0)> 5 {{nm}}) with a critical current density of about 2.2 MA cm-2, and good stability in an ambient environment.

Temporally and Spatially Resolved Plasma Spectroscopy in Pulsed Laser Deposition of Ultra-Thin Boron Nitride Films (Postprint)

DTIC Science & Technology

2015-04-24

AFRL-RX-WP-JA-2016-0196 TEMPORALLY AND SPATIALLY RESOLVED PLASMA SPECTROSCOPY IN PULSED LASER DEPOSITION OF ULTRA-THIN BORON NITRIDE...AND SPATIALLY RESOLVED PLASMA SPECTROSCOPY IN PULSED LASER DEPOSITION OF ULTRA-THIN BORON NITRIDE FILMS (POSTPRINT) 5a. CONTRACT NUMBER FA8650...distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas were investigated

Subatomic deformation driven by vertical piezoelectricity from CdS ultrathin films.

PubMed

Wang, Xuewen; He, Xuexia; Zhu, Hongfei; Sun, Linfeng; Fu, Wei; Wang, Xingli; Hoong, Lai Chee; Wang, Hong; Zeng, Qingsheng; Zhao, Wu; Wei, Jun; Jin, Zhong; Shen, Zexiang; Liu, Jie; Zhang, Ting; Liu, Zheng

2016-07-01

Driven by the development of high-performance piezoelectric materials, actuators become an important tool for positioning objects with high accuracy down to nanometer scale, and have been used for a wide variety of equipment, such as atomic force microscopy and scanning tunneling microscopy. However, positioning at the subatomic scale is still a great challenge. Ultrathin piezoelectric materials may pave the way to positioning an object with extreme precision. Using ultrathin CdS thin films, we demonstrate vertical piezoelectricity in atomic scale (three to five space lattices). With an in situ scanning Kelvin force microscopy and single and dual ac resonance tracking piezoelectric force microscopy, the vertical piezoelectric coefficient (d 33) up to 33 pm·V(-1) was determined for the CdS ultrathin films. These findings shed light on the design of next-generation sensors and microelectromechanical devices.

Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors.

PubMed

Khim, Dongyoon; Ryu, Gi-Seong; Park, Won-Tae; Kim, Hyunchul; Lee, Myungwon; Noh, Yong-Young

2016-04-13

A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Real-Time Deposition Monitor for Ultrathin Conductive Films

NASA Technical Reports Server (NTRS)

Hines, Jacqueline

2011-01-01

A device has been developed that can be used for the real-time monitoring of ultrathin (2 or more) conductive films. The device responds in less than two microseconds, and can be used to monitor film depositions up to about 60 thick. Actual thickness monitoring capability will vary based on properties of the film being deposited. This is a single-use device, which, due to the very low device cost, can be disposable. Conventional quartz/crystal microbalance devices have proven inadequate to monitor the thickness of Pd films during deposition of ultrathin films for hydrogen sensor devices. When the deposited film is less than 100 , the QCM measurements are inadequate to allow monitoring of the ultrathin films being developed. Thus, an improved, high-sensitivity, real-time deposition monitor was needed to continue Pd film deposition development. The new deposition monitor utilizes a surface acoustic wave (SAW) device in a differential delay-line configuration to produce both a reference response and a response for the portion of the device on which the film is being deposited. Both responses are monitored simultaneously during deposition. The reference response remains unchanged, while the attenuation of the sensing path (where the film is being deposited) varies as the film thickness increases. This device utilizes the fact that on high-coupling piezoelectric substrates, the attenuation of an SAW undergoes a transition from low to very high, and back to low as the conductivity of a film on the device surface goes from nonconductive to highly conductive. Thus, the sensing path response starts with a low insertion loss, and as a conductive film is deposited, the film conductivity increases, causing the device insertion loss to increase dramatically (by up to 80 dB or more), and then with continued film thickness increases (and the corresponding conductivity increases), the device insertion loss goes back down to the low level at which it started. This provides a continuous, real-time monitoring of film deposition. For use with different films, the device would need to be calibrated to provide an understanding of how film thickness is related to film conductivity, as the device is responding primarily to conductivity effects (and not to mass loading effects) in this ultrathin film regime.

Ultrathin Lutetium Oxide Film as an Epitaxial Hole-Blocking Layer for Crystalline Bismuth Vanadate Water Splitting Photoanodes

DOE PAGES

Zhang, Wenrui; Yan, Danhua; Tong, Xiao; ...

2018-01-08

Here a novel ultrathin lutetium oxide (Lu 2O 3) interlayer is integrated with crystalline bismuth vanadate (BiVO4) thin film photoanodes to facilitate carrier transport through atomic-scale interface control. The epitaxial Lu 2O 32O 3

Modeling the mechanical properties of ultra-thin polymer films [Structural modeling of films of atomic scale thickness

DOE PAGES

Espinosa-Loza, Francisco; Stadermann, Michael; Aracne-Ruddle, Chantel; ...

2017-11-16

A modeling method to extract the mechanical properties of ultra-thin films (10–100 nm thick) from experimental data generated by indentation of freestanding circular films using a spherical indenter is presented. The relationship between the mechanical properties of the film and experimental parameters including load, and deflection are discussed in the context of a constitutive material model, test variables, and analytical approaches. As a result, elastic and plastic regimes are identified by comparison of finite element simulation and experimental data.

Modeling the mechanical properties of ultra-thin polymer films [Structural modeling of films of atomic scale thickness

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

Espinosa-Loza, Francisco; Stadermann, Michael; Aracne-Ruddle, Chantel

A modeling method to extract the mechanical properties of ultra-thin films (10–100 nm thick) from experimental data generated by indentation of freestanding circular films using a spherical indenter is presented. The relationship between the mechanical properties of the film and experimental parameters including load, and deflection are discussed in the context of a constitutive material model, test variables, and analytical approaches. As a result, elastic and plastic regimes are identified by comparison of finite element simulation and experimental data.

Nanoscale interfacial heat transport of ultrathin epitaxial hetero films: Few monolayer Pb(111) on Si(111)

NASA Astrophysics Data System (ADS)

Witte, T.; Frigge, T.; Hafke, B.; Krenzer, B.; Horn-von Hoegen, M.

2017-06-01

We studied the phononic heat transport from ultrathin epitaxial Pb(111) films across the heterointerface into a Si(111) substrate by means of ultrafast electron diffraction. The thickness of the Pb films was varied from 15 to 4 monolayers. It was found that the thermal boundary conductance σTBC of the heterointerface is independent of the film thickness. We have no evidence for finite size effects: the continuum description of heat transport is still valid, even for the thinnest films of only 4 monolayer thickness.

Subatomic deformation driven by vertical piezoelectricity from CdS ultrathin films

PubMed Central

Wang, Xuewen; He, Xuexia; Zhu, Hongfei; Sun, Linfeng; Fu, Wei; Wang, Xingli; Hoong, Lai Chee; Wang, Hong; Zeng, Qingsheng; Zhao, Wu; Wei, Jun; Jin, Zhong; Shen, Zexiang; Liu, Jie; Zhang, Ting; Liu, Zheng

2016-01-01

Driven by the development of high-performance piezoelectric materials, actuators become an important tool for positioning objects with high accuracy down to nanometer scale, and have been used for a wide variety of equipment, such as atomic force microscopy and scanning tunneling microscopy. However, positioning at the subatomic scale is still a great challenge. Ultrathin piezoelectric materials may pave the way to positioning an object with extreme precision. Using ultrathin CdS thin films, we demonstrate vertical piezoelectricity in atomic scale (three to five space lattices). With an in situ scanning Kelvin force microscopy and single and dual ac resonance tracking piezoelectric force microscopy, the vertical piezoelectric coefficient (d33) up to 33 pm·V−1 was determined for the CdS ultrathin films. These findings shed light on the design of next-generation sensors and microelectromechanical devices. PMID:27419234

Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions.

PubMed

Zhou, Wenjun; Mandia, David J; Barry, Seán T; Albert, Jacques

2014-12-29

The optical properties of an ultrathin discontinuous gold film in different dielectric surroundings are investigated experimentally by measuring the polarization-dependent wavelength shifts and amplitudes of the cladding mode resonances of a tilted fiber Bragg grating. The gold film was prepared by electron-beam evaporation and had an average thickness of 5.5 nm ( ± 1 nm). Scanning electron imaging was used to determine that the film is actually formed of individual particles with average lateral dimensions of 28 nm ( ± 8 nm). The complex refractive indices of the equivalent uniform film in air at a wavelength of 1570 nm were calculated from the measurements to be 4.84-i0.74 and 3.97-i0.85 for TM and TE polarizations respectively (compared to the value for bulk gold: 0.54-i10.9). Additionally, changes in the birefringence and dichroism of the films were measured as a function of the surrounding medium, in air, water and a saturated NaCl (salt) solution. These results show that the film has stronger dielectric behavior for TM light than for TE, a trend that increases with increasing surrounding index. Finally, the experimental results are compared to predictions from two widely used effective medium approximations, the generalized Maxwell-Garnett and Bruggeman theories for gold particles in a surrounding matrix. It is found that both of these methods fail to predict the observed behavior for the film considered.

Development of an ultra-thin film comprised of a graphene membrane and carbon nanotube vein support.

PubMed

Lin, Xiaoyang; Liu, Peng; Wei, Yang; Li, Qunqing; Wang, Jiaping; Wu, Yang; Feng, Chen; Zhang, Lina; Fan, Shoushan; Jiang, Kaili

2013-01-01

Graphene, exhibiting superior mechanical, thermal, optical and electronic properties, has attracted great interest. Considering it being one-atom-thick, and the reduced mechanical strength at grain boundaries, the fabrication of large-area suspended chemical vapour deposition graphene remains a challenge. Here we report the fabrication of an ultra-thin free-standing carbon nanotube/graphene hybrid film, inspired by the vein-membrane structure found in nature. Such a square-centimetre-sized hybrid film can realize the overlaying of large-area single-layer chemical vapour deposition graphene on to a porous vein-like carbon nanotube network. The vein-membrane-like hybrid film, with graphene suspended on the carbon nanotube meshes, possesses excellent mechanical performance, optical transparency and good electrical conductivity. The ultra-thin hybrid film features an electron transparency close to 90%, which makes it an ideal gate electrode in vacuum electronics and a high-performance sample support in transmission electron microscopy.

Robust Polymer Films: Nanoscale Stiffening as a Route to Strong Materials

DTIC Science & Technology

2011-10-20

Rheological Methods," Drexel University, Philadelphia, PA, March 4, 2011. S.Xu, "Geometry and molecular architecture effects in nanobubble inflation...2007. G.B. McKenna, "The viscoelastic properties of ultrathin polymer films as measured with a novel nanobubble inflation technique.” March Meeting of...mechanical response of ultrathin polymer films using the Texas Tech nanobubble inflation technique as the means to determine the viscoelastic

Fabrication of ultrathin MIL-96(Al) films and study of CO2 adsorption/desorption processes using quartz crystal microbalance.

PubMed

Andrés, Miguel A; Benzaqui, M; Serre, C; Steunou, N; Gascón, I

2018-06-01

This contribution reports the fabrication and characterization of ultrathin films of nanoparticles of the water stable microporous Al tricarboxylate metal organic framework MIL-96(Al). The preparation of MOF dispersions in chloroform has been optimized to obtain dense monolayer films of good quality, without nanoparticle agglomeration, at the air-water interface that can be deposited onto solid substrates of different nature without any previous substrate functionalization. The MOF studied shows great interest for CO 2 capture because it presents Al 3+ Lewis centers and hydroxyl groups that strongly interact with CO 2 molecules. A comparative CO 2 adsorption study on drop-cast, Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) films using a Quartz Crystal Microbalance-based setup (QCM) has revealed that the CO 2 uptake depends strongly on the film fabrication procedure and the storage conditions. Noteworthy the CO 2 adsorption capacity of LB films is increased by 30% using a simple and green treatment (immersion of the film into water during 12 h just after film preparation). Finally, the stability of LB MOF monolayers upon several CO 2 adsorption/desorption cycles has been demonstrated, showing that CO 2 can be easily desorbed from the films at 303 K by flowing an inert gas (He). These results show that MOF LB monolayers can be of great interest for the development of MOF-based devices that require the use of very small MOF quantities, especially gas sensors. Copyright © 2018 Elsevier Inc. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2009-01-01

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

"Self-Peel-Off" Transfer Produces Ultrathin Polyvinylidene-Fluoride-Based Flexible Nanodevices.

PubMed

Tai, Yanlong; Lubineau, Gilles

2017-04-01

Here, a new strategy, self-peel-off transfer, for the preparation of ultrathin flexible nanodevices made from polyvinylidene-fluoride (PVDF) is reported. In this process, a functional pattern of nanoparticles is transferred via peeling from a temporary substrate to the final PVDF film. This peeling process takes advantage of the differences in the work of adhesion between the various layers (the PVDF layer, the nanoparticle-pattern layer and the substrate layer) and of the high stresses generated by the differential thermal expansion of the layers. The work of adhesion is mainly guided by the basic physical/chemical properties of these layers and is highly sensitive to variations in temperature and moisture in the environment. The peeling technique is tested on a variety of PVDF-based functional films using gold/palladium nanoparticles, carbon nanotubes, graphene oxide, and lithium iron phosphate. Several PVDF-based flexible nanodevices are prepared, including a single-sided wireless flexible humidity sensor in which PVDF is used as the substrate and a double-sided flexible capacitor in which PVDF is used as the ferroelectric layer and the carrier layer. Results show that the nanodevices perform with high repeatability and stability. Self-peel-off transfer is a viable preparation strategy for the design and fabrication of flexible, ultrathin, and light-weight nanodevices.

Coexistence of colossal stress and texture gradients in sputter deposited nanocrystalline ultra-thin metal films

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

Kuru, Yener; Welzel, Udo; Mittemeijer, Eric J.

2014-12-01

This paper demonstrates experimentally that ultra-thin, nanocrystalline films can exhibit coexisting colossal stress and texture depth gradients. Their quantitative determination is possible by X-ray diffraction experiments. Whereas a uniform texture by itself is known to generally cause curvature in so-called sin{sup 2}ψ plots, it is shown that the combined action of texture and stress gradients provides a separate source of curvature in sin{sup 2}ψ plots (i.e., even in cases where a uniform texture does not induce such curvature). On this basis, the texture and stress depth profiles of a nanocrystalline, ultra-thin (50 nm) tungsten film could be determined.

The influence of the surface parameter changes onto the phonon states in ultrathin crystalline films

NASA Astrophysics Data System (ADS)

Šetrajčić, Jovan P.; Ilić, Dušan I.; Jaćimovski, Stevo K.

2018-04-01

In this paper, we have analytically investigated how the changes in boundary surface parameters influence the phonon dispersion law in ultrathin films of the simple cubic crystalline structure. Spectra of possible phonon states are analyzed using the method of two-time dependent Green's functions and for the diverse combination of boundary surface parameters, this problem was presented numerically and graphically. It turns out that for certain values and combinations of parameters, displacement of dispersion branches outside of bulk zone occurs, leading to the creation of localized phonon states. This fact is of great importance for the heat removal, electrical conductivity and superconducting properties of ultrathin films.

Ultrathin planar hematite film for solar photoelectrochemical water splitting

DOE PAGES

Liu, Dong; Bierman, David M.; Lenert, Andrej; ...

2015-10-08

Hematite holds promise for photoelectrochemical (PEC) water splitting due to its stability, low-cost, abundance and appropriate bandgap. However, it suffers from a mismatch between the hole diffusion length and light penetration length. We have theoretically designed and characterized an ultrathin planar hematite/silver nanohole array/silver substrate photoanode. Due to the supported destructive interference and surface plasmon resonance, photons are efficiently absorbed in an ultrathin hematite film. In conclusion, compared with ultrathin hematite photoanodes with nanophotonic structures, this photoanode has comparable photon absorption but with intrinsically lower recombination losses due to its planar structure and promises to exceed the state-of-the-art photocurrent ofmore » hematite photoanodes.« less

Effective passivation of silicon surfaces by ultrathin atomic-layer deposited niobium oxide

NASA Astrophysics Data System (ADS)

Macco, B.; Bivour, M.; Deijkers, J. H.; Basuvalingam, S. B.; Black, L. E.; Melskens, J.; van de Loo, B. W. H.; Berghuis, W. J. H.; Hermle, M.; Kessels, W. M. M. Erwin

2018-06-01

This letter reports on effective surface passivation of n-type crystalline silicon by ultrathin niobium oxide (Nb2O5) films prepared by atomic layer deposition (ALD) and subjected to a forming gas anneal at 300 °C. A champion recombination parameter J0 of 20 fA/cm2 and a surface recombination velocity Seff of 4.8 cm/s have been achieved for ultrathin films of 1 nm. The surface pretreatment was found to have a strong impact on the passivation. Good passivation can be achieved on both HF-treated c-Si surfaces and c-Si surfaces with a wet-chemically grown interfacial silicon oxide layer. On HF-treated surfaces, a minimum film thickness of 3 nm is required to achieve a high level of surface passivation, whereas the use of a wet chemically-grown interfacial oxide enables excellent passivation even for Nb2O5 films of only 1 nm. This discrepancy in passivation between both surface types is attributed to differences in the formation and stoichiometry of interfacial silicon oxide, resulting in different levels of chemical passivation. On both surface types, the high level of passivation of ALD Nb2O5 is aided by field-effect passivation originating from a high fixed negative charge density of 1-2 × 1012 cm-3. Furthermore, it is demonstrated that the passivation level provided by 1 nm of Nb2O5 can be further enhanced through light-soaking. Finally, initial explorations show that a low contact resistivity can be obtained using Nb2O5-based contacts. Together, these properties make ALD Nb2O5 a highly interesting building block for high-efficiency c-Si solar cells.

A molecular dynamics analysis of ion irradiation of ultrathin amorphous carbon films

NASA Astrophysics Data System (ADS)

Qi, J.; Komvopoulos, K.

2016-09-01

Molecular dynamics (MD) simulations provide insight into nanoscale problems where continuum description breaks down, such as the modeling of ultrathin films. Amorphous carbon (a-C) films are commonly used as protective overcoats in various contemporary technologies, including microelectromechanical systems, bio-implantable devices, optical lenses, and hard-disk drives. In all of these technologies, the protective a-C film must be continuous and very thin. For example, to achieve high storage densities (e.g., on the order of 1 Tb/in.2) in magnetic recording, the thickness of the a-C film used to protect the magnetic media and the recording head against mechanical wear and corrosion must be 2-3 nm. Inert ion irradiation is an effective post-deposition method for reducing the film thickness, while preserving the mechanical and chemical characteristics. In this study, MD simulations of Ar+ ion irradiated a-C films were performed to elucidate the effects of the ion incidence angle and ion kinetic energy on the film thickness and structure. The MD results reveal that the film etching rate exhibits a strong dependence on the ion kinetic energy and ion incidence angle, with a maximum etching rate corresponding to an ion incidence angle of ˜20°. It is also shown that Ar+ ion irradiation mainly affects the structure of the upper half of the ultrathin a-C film and that carbon atom hybridization is a strong function of the ion kinetic energy and ion incidence angle. The results of this study elucidate the effects of important ion irradiation parameters on the structure and thickness of ultrathin films and provide fundamental insight into the physics of dry etching.

Transport in ultrathin gold films decorated with magnetic Gd atoms

NASA Astrophysics Data System (ADS)

Alemani, Micol; Helgren, Erik; Hugel, Addison; Hellman, Frances

2008-03-01

We have performed four-probe transport measurements of ultrathin Au films decorated with Gd ad-atoms. The samples were prepared by quench condensation, i.e., sequential evaporation on a cryogenically cooled substrate under UHV conditions while monitoring the film thickness and resistance. Electrically continuous Au films at thickness of about 2 mono-layers of material are grown on an amorphous Ge wetting layer. The quench condensation method provides a sensitive control on the sample growth process, allowing us to tune the morphological and electrical configuration of the system. The ultrathin gold films develop from an insulating to a metallic state as a function of film thickness. The temperature dependence of the Au conductivity for different thickness is studied. It evolves from hopping transport for the insulating films, to a ln T dependence for thicker films. For gold films in the insulating regime we found a decreasing resistance by adding Gd. This is in agreement with a decreasing tunneling barrier height between metallic atoms. The Gd magnetic moments are randomly oriented for isolated atoms. This magnetic disorder leads to scattering of the charge carriers and a reduced conductivity compared to nonmagnetic materials.

Superstable Ultrathin Water Film Confined in a Hydrophilized Carbon Nanotube.

PubMed

Tomo, Yoko; Askounis, Alexandros; Ikuta, Tatsuya; Takata, Yasuyuki; Sefiane, Khellil; Takahashi, Koji

2018-03-14

Fluids confined in a nanoscale space behave differently than in the bulk due to strong interactions between fluid molecules and solid atoms. Here, we observed water confined inside "open" hydrophilized carbon nanotubes (CNT), with diameter of tens of nanometers, using transmission electron microscopy (TEM). A 1-7 nm water film adhering to most of the inner wall surface was observed and remained stable in the high vacuum (order of 10 -5 Pa) of the TEM. The superstability of this film was attributed to a combination of curvature, nanoroughness, and confinement resulting in a lower vapor pressure for water and hence inhibiting its vaporization. Occasional, suspended ultrathin water film with thickness of 3-20 nm were found and remained stable inside the CNT. This film thickness is 1 order of magnitude smaller than the critical film thickness (about 40 nm) reported by the Derjaguin-Landau-Verwey-Overbeek theory and previous experimental investigations. The stability of the suspended ultrathin water film is attributed to the additional molecular interactions due to the extended water meniscus, which balances the rest of the disjoining pressures.

Ultrathin Shape Change Smart Materials.

PubMed

Xu, Weinan; Kwok, Kam Sang; Gracias, David H

2018-02-20

With the discovery of graphene, significant research has focused on the synthesis, characterization, and applications of ultrathin materials. Graphene has also brought into focus other ultrathin materials composed of organics, polymers, inorganics, and their hybrids. Together, these ultrathin materials have unique properties of broad significance. For example, ultrathin materials have a large surface area and high flexibility which can enhance conformal contact in wearables and sensors leading to improved sensitivity. When porous, the short transverse diffusion length in these materials allows rapid mass transport. Alternatively, when impermeable, these materials behave as an ultrathin barrier. Such controlled permeability is critical in the design of encapsulation and drug delivery systems. Finally, ultrathin materials often feature defect-free and single-crystal-like two-dimensional atomic structures resulting in superior mechanical, optical, and electrical properties. A unique property of ultrathin materials is their low bending rigidity, which suggests that they could easily be bent, curved, or folded into 3D shapes. In this Account, we review the emerging field of 2D to 3D shape transformations of ultrathin materials. We broadly define ultrathin to include materials with a thickness below 100 nm and composed of a range of organic, inorganic, and hybrid compositions. This topic is important for both fundamental and applied reasons. Fundamentally, bending and curving of ultrathin films can cause atomistic and molecular strain which can alter their physical and chemical properties and lead to new 3D forms of matter which behave very differently from their planar precursors. Shape change can also lead to new 3D architectures with significantly smaller form factors. For example, 3D ultrathin materials would occupy a smaller space in on-chip devices or could permeate through tortuous media which is important for miniaturized robots and smart dust applications. Our Account highlights several differences between ultrathin and traditional shape change materials. The latter is typically associated with hydrogels, liquid crystals, or shape memory elastomers. As compared to bulk materials, ultrathin materials can much more easily bend and fold due to the significantly reduced bending modulus. Consequently, it takes much less energy to alter the shape of ultrathin materials, and even small environmental stimuli can trigger a large response. Further, the energy barriers between different configurations are small which allow a variety of conformations and enhances programmability. Finally, due to their ultrathin nature, the shape changes are typically not slowed down by sluggish mass or thermal transport, and thus, responses can be much faster than those of bulk materials. The latter point is important in the design of high-speed actuators. Consequently, ultrathin materials could enable low-power, rapid, programmable, and complex shape transformations in response to a broad range of stimuli such as pH, temperature, electromagnetic fields, or chemical environments. The Account also includes a discussion of applications, important challenges, and future directions.

Nanoparticles in Mesostructured Polymers: Stabilizations and Morphology Selection

NASA Astrophysics Data System (ADS)

Kim, Jaeup; O'Shaughnessy, Ben

2002-03-01

A major challenge in the rapidly developing field of nano-materials is finding ways to create delicate spatial arrangements of nano-sized particles. Nanostructured polymer phases and ultrathin polymer films offer potential templates to spontaneously generate this spatial organization. Here we present theory of such systems. Our conclusions are as follows. (1) Nanoparticles tending to aggregate into clusters under van der Waals attractions may be stabilized in a stretched polymer environment as offered by tethered thin film brushes or lamellar diblock phases. By extending the hydrodynamic analogy of Williams and Pincus to the real case of the end-annealed Semenov brush, we show cluster formation is strongly influenced: disc-shaped clusters are suppressed in favor of extended cylindrical forms. (2) The final morphology of extended nanoparticle aggregates depends on the polymer environment. If the nanoparticle/air/polymer surface tensions and the degree of chain stretching satisfy certain conditions, the polymer media selects the length scale of nanoparticle clusters. This offers the possibility of tuning nanoparticle aggregate morphology by suitable choice of polymeric media. Our predictions are consistent with experiments at Columbia by Levicky, Durning, Cerise and Liu demonstrating nanoparticle stabilization and morphology selection in ultrathin end-tethered polymer films.

Ultrathin phase-change coatings on metals for electrothermally tunable colors

NASA Astrophysics Data System (ADS)

Bakan, Gokhan; Ayas, Sencer; Saidzoda, Tohir; Celebi, Kemal; Dana, Aykutlu

2016-08-01

Metal surfaces coated with ultrathin lossy dielectrics enable color generation through strong interferences in the visible spectrum. Using a phase-change thin film as the coating layer offers tuning the generated color by crystallization or re-amorphization. Here, we study the optical response of surfaces consisting of thin (5-40 nm) phase-changing Ge2Sb2Te5 (GST) films on metal, primarily Al, layers. A color scale ranging from yellow to red to blue that is obtained using different thicknesses of as-deposited amorphous GST layers turns dim gray upon annealing-induced crystallization of the GST. Moreover, when a relatively thick (>100 nm) and lossless dielectric film is introduced between the GST and Al layers, optical cavity modes are observed, offering a rich color gamut at the expense of the angle independent optical response. Finally, a color pixel structure is proposed for ultrahigh resolution (pixel size: 5 × 5 μm2), non-volatile displays, where the metal layer acting like a mirror is used as a heater element. The electrothermal simulations of such a pixel structure suggest that crystallization and re-amorphization of the GST layer using electrical pulses are possible for electrothermal color tuning.

Aerosol-assisted chemical vapor deposition of ultra-thin CuOx films as hole transport material for planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Zhang, Zhixin; Chen, Shuqun; Li, Pingping; Li, Hongyi; Wu, Junshu; Hu, Peng; Wang, Jinshu

This paper reports on the fabrication of CuOx films to be used as hole transporting layer (HTL) in CH3NH3PbI3 perovskite solar cells (PSCs). Ultra-thin CuOx coatings were grown onto FTO substrates for the first time via aerosol-assisted chemical vapor deposition (AACVD) of copper acetylacetonate in methanol. After incorporating into the PSCs prepared at ambient air, a highest power conversion efficiency (PCE) of 8.26% with HTL and of 3.34% without HTL were achieved. Our work represents an important step in the development of low-cost CVD technique for fabricating ultra-thin metal oxide functional layers in thin film photovoltaics.

Spin fluctuation induced linear magnetoresistance in ultrathin superconducting FeSe films

DOE PAGES

Wang, Qingyan; Zhang, Wenhao; Chen, Weiwei; ...

2017-07-21

The discovery of high-temperature superconductivity in FeSe/STO has trigged great research interest to reveal a range of exotic physical phenomena in this novel material. Here we present a temperature dependent magnetotransport measurement for ultrathin FeSe/STO films with different thickness and protection layers. Remarkably, a surprising linear magnetoresistance (LMR) is observed around the superconducting transition temperatures but absent otherwise. The experimental LMR can be reproduced by magnetotransport calculations based on a model of magnetic field dependent disorder induced by spin fluctuation. Thus, the observed LMR in coexistence with superconductivity provides the first magnetotransport signature for spin fluctuation around the superconducting transitionmore » region in ultrathin FeSe/STO films.« less

High-Performance Ultrathin Active Chiral Metamaterials.

PubMed

Wu, Zilong; Chen, Xiaodong; Wang, Mingsong; Dong, Jianwen; Zheng, Yuebing

2018-05-22

Ultrathin active chiral metamaterials with dynamically tunable and responsive optical chirality enable new optical sensors, modulators, and switches. Herein, we develop ultrathin active chiral metamaterials of highly tunable chiroptical responses by inducing tunable near-field coupling in the metamaterials and exploit the metamaterials as ultrasensitive sensors to detect trace amounts of solvent impurities. To demonstrate the active chiral metamaterials mediated by tunable near-field coupling, we design moiré chiral metamaterials (MCMs) as model metamaterials, which consist of two layers of identical Au nanohole arrays stacked upon one another in moiré patterns with a dielectric spacer layer between the Au layers. Our simulations, analytical fittings, and experiments reveal that spacer-dependent near-field coupling exists in the MCMs, which significantly enhances the spectral shift and line shape change of the circular dichroism (CD) spectra of the MCMs. Furthermore, we use a silk fibroin thin film as the spacer layer in the MCM. With the solvent-controllable swelling of the silk fibroin thin films, we demonstrate actively tunable near-field coupling and chiroptical responses of the silk-MCMs. Impressively, we have achieved the spectral shift over a wavelength range that is more than one full width at half-maximum and the sign inversion of the CD spectra in a single ultrathin (1/5 of wavelength in thickness) MCM. Finally, we apply the silk-MCMs as ultrasensitive sensors to detect trace amounts of solvent impurities down to 200 ppm, corresponding to an ultrahigh sensitivity of >10 5 nm/refractive index unit (RIU) and a figure of merit of 10 5 /RIU.

Supramolecular architectures of iron phthalocyanine Langmuir-Blodgett films: The role played by the solution solvents

NASA Astrophysics Data System (ADS)

Rubira, Rafael Jesus Gonçalves; Aoki, Pedro Henrique Benites; Constantino, Carlos José Leopoldo; Alessio, Priscila

2017-09-01

The developing of organic-based devices has been widely explored using ultrathin films as the transducer element, whose supramolecular architecture plays a central role in the device performance. Here, Langmuir and Langmuir-Blodgett (LB) ultrathin films were fabricated from iron phthalocyanine (FePc) solutions in chloroform (CHCl3), dichloromethane (CH2Cl2), dimethylformamide (DMF), and tetrahydrofuran (THF) to determine the influence of different solvents on the supramolecular architecture of the ultrathin films. The UV-vis absorption spectroscopy shows a strong dependence of the FePc aggregation on these solvents. As a consequence, the surface pressure vs. mean molecular area (π-A) isotherms and Brewster angle microscopy (BAM) reveal a more homogeneous (surface morphology) Langmuir film at the air/water interface for FePc in DMF. The same morphological pattern observed for the Langmuir films is preserved upon LB deposition onto solid substrates. The Raman and FTIR analyses indicate the DMF-FePc interaction relies on coordination bonds between N atom (from DMF) and Fe atom (from FePc). Besides, the FePc molecular organization was also found to be affected by the DMF-FePc chemical interaction. It is interesting to note that, if the DMF-FePc leads to less aggregated FePc either in solution or ultrathin films (Langmuir and LB), with time (one week) the opposite trend is found. Taking into account the N-Fe interaction, the performance of the FePc ultrathin films with distinct supramolecular architectures composing sensing units was explored as proof-of-principle in the detection of trace amounts of atrazine herbicide in water using impedance spectroscopy. Further statistical and computational analysis reveal not only the role played by FePc supramolecular architecture but also the sensitivity of the system to detect atrazine solutions down to 10-10 mol/L, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations.

Effect of processing parameters on microstructure of MoS{sub 2} ultra-thin films synthesized by chemical vapor deposition method

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

Song, Yang; You, Suping; Sun, Kewei

2015-06-15

MoS{sub 2} ultra-thin layers are synthesized using a chemical vapor deposition method based on the sulfurization of molybdenum trioxide (MoO{sub 3}). The ultra-thin layers are characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy and atomic force microscope (AFM). Based on our experimental results, all the processing parameters, such as the tilt angle of substrate, applied voltage, heating time and the weight of source materials have effect on the microstructures of the layers. In this paper, the effects of such processing parameters on the crystal structures and morphologies of the as-grown layers are studied. It is found that the film obtainedmore » with the tilt angle of 0.06° is more uniform. A larger applied voltage is preferred to the growth of MoS{sub 2} thin films at a certain heating time. In order to obtain the ultra-thin layers of MoS{sub 2}, the weight of 0.003 g of source materials is preferred. Under our optimal experimental conditions, the surface of the film is smooth and composed of many uniformly distributed and aggregated particles, and the ultra-thin MoS{sub 2} atomic layers (1∼10 layers) covers an area of more than 2 mm×2 mm.« less

Out-of-plane chiral domain wall spin-structures in ultrathin in-plane magnets

DOE PAGES

Chen, Gong; Kang, Sang Pyo; Ophus, Colin; ...

2017-05-19

Chiral spin textures in ultrathin films, such as skyrmions or chiral domain walls, are believed to offer large performance advantages in the development of novel spintronics technologies. While in-plane magnetized films have been studied extensively as media for current- and field-driven domain wall dynamics with applications in memory or logic devices, the stabilization of chiral spin textures in in-plane magnetized films has remained rare. Here we report a phase of spin structures in an in-plane magnetized ultrathin film system where out-of-plane spin orientations within domain walls are stable. Moreover, while domain walls in in-plane films are generally expected to bemore » non-chiral, we show that right-handed spin rotations are strongly favoured in this system, due to the presence of the interfacial Dzyaloshinskii-Moriya interaction. These results constitute a platform to explore unconventional spin dynamics and topological phenomena that may enable high-performance in-plane spin-orbitronics devices.« less

Ultralight shape-recovering plate mechanical metamaterials

NASA Astrophysics Data System (ADS)

Davami, Keivan; Zhao, Lin; Lu, Eric; Cortes, John; Lin, Chen; Lilley, Drew E.; Purohit, Prashant K.; Bargatin, Igor

2015-12-01

Unusual mechanical properties of mechanical metamaterials are determined by their carefully designed and tightly controlled geometry at the macro- or nanoscale. We introduce a class of nanoscale mechanical metamaterials created by forming continuous corrugated plates out of ultrathin films. Using a periodic three-dimensional architecture characteristic of mechanical metamaterials, we fabricate free-standing plates up to 2 cm in size out of aluminium oxide films as thin as 25 nm. The plates are formed by atomic layer deposition of ultrathin alumina films on a lithographically patterned silicon wafer, followed by complete removal of the silicon substrate. Unlike unpatterned ultrathin films, which tend to warp or even roll up because of residual stress gradients, our plate metamaterials can be engineered to be extremely flat. They weigh as little as 0.1 g cm-2 and have the ability to `pop-back' to their original shape without damage even after undergoing multiple sharp bends of more than 90°.

Nonbolometric bottleneck in electron-phonon relaxation in ultrathin WSi films

NASA Astrophysics Data System (ADS)

Sidorova, Mariia V.; Kozorezov, A. G.; Semenov, A. V.; Korneeva, Yu. P.; Mikhailov, M. Yu.; Devizenko, A. Yu.; Korneev, A. A.; Chulkova, G. M.; Goltsman, G. N.

2018-05-01

We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in τe -ph˜14 0 -19 0 ps at TC=3.4 K , supporting the results of earlier measurements by independent techniques.

Unique system of FE/PD for magneto-optical recording and magnetic switching devices

DOEpatents

Liu, Chian Q.; Bader, Samuel D.

1992-01-01

A high density magneto-optical information storage medium utilizing the properties of an ultrathin iron film on a palladium substrate. The present invention comprises a magneto-optical medium capable of thermal and magnetic stability and capable of possessing a vertical orientation of the magnetization vector for the magnetic material. Data storage relies on the temperature dependence of the coercivity of the ultrathin film. Data retrieval derives from the Kerr effect which describes the direction of rotation of a plane of polarized light traversing the ultrathin magnetic material as a function of the orientation of the magnetization vector.

Patterned FePt nanostructures using ultrathin self-organized templates

NASA Astrophysics Data System (ADS)

Deng, Chen Hua; Zhang, Min; Wang, Fang; Xu, Xiao Hong

2018-02-01

Patterned magnetic thin films are both scientifically interesting and technologically useful. Ultrathin self-organized anodic aluminum oxide (AAO) template can be used to fabricate large area nanodot and antidot arrays. The magnetic properties of these nanostructures may be tuned by the morphology of the AAO template, which in turn can be controlled by synthetic parameters. In this work, ultrathin AAO templates were used as etching masks for the fabrication of both FePt nanodot and antidot arrays with high areal density. The perpendicular magnetic anisotropy of L10 FePt thin films are preserved in the nanostructures.

Thermally generated metals for plasmonic coloring and surface-enhanced Raman sensing

NASA Astrophysics Data System (ADS)

Huang, Zhenping; Chen, Jian; Liu, Guiqiang; Wang, Yan; Liu, Yi; Tang, Li; Liu, Zhengqi

2018-03-01

Spectral coloring glass and its application on the surface-enhanced Raman scattering are demonstrated experimentally via a simple and moderate heat-treating of the top ultrathin gold film to create discrete nanoparticles, which can produce localized surface plasmon resonances and strong plasmonic near-field coupling effects. Ultrathin metal films with a wide range of thicknesses are investigated by different heat-treatment processes. The annealed metal films have been demonstrated with a series of spectral coloring responses. Moreover, the microscopy images of the metal film structures confirm the formation of distinct geometry features in these operation procedures. Densely packed nanoparticles are observed for the ultrathin metal film with the single-digit level of thickness. With increasing the film thickness over 10 nm, metallic clusters and porous morphologies can be obtained. Importantly, the metallic resonators can provide enhanced Raman scattering with the detection limit down to 10 - 7 molL - 1 of Rhodamine 6G molecules due to the excitation of plasmon resonances and strong near-field coupling effects. These features hold great potential for large-scale and low-cost production of colored glass and Raman substrate.

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films

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

Liu, Xiaojie; Wang, Cai -Zhuang

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. Furthermore, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films

DOE PAGES

Liu, Xiaojie; Wang, Cai -Zhuang

2017-04-03

Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. Furthermore, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.

Skin dose for head and neck cancer patients treated with intensity-modulated radiation therapy(IMRT)

NASA Astrophysics Data System (ADS)

Fu, Hsiao-Ju; Li, Chi-Wei; Tsai, Wei-Ta; Chang, Chih-Chia; Tsang, Yuk-Wah

2017-11-01

The reliability of thermoluminescent dosimeters (ultrathin TLD) and ISP Gafchromic EBT2 film to measure the surface dose in phantom and the skin dose in head-and-neck patients treated with intensity-modulated radiation therapy technique(IMRT) is the research focus. Seven-field treatment plans with prescribed dose of 180 cGy were performed on Eclipse treatment planning system which utilized pencil beam calculation algorithm(PBC). In calibration tests, the variance coefficient of the ultrathin TLDs were within 3%. The points on the calibration curve of the Gafchromic film was within 1% variation. Five measurements were taken on phantom using ultrathin TLD and EBT2 film respectively. The measured mean surface doses between ultrathin TLD or EBT2 film were within 5% deviation. Skin doses of 6 patients were measured for initial 5 fractions and the mean dose per-fraction was calculated. If the extrapolated doses for 30 fractions were below 4000 cGy, the skin reaction grading observed according to Radiation Therapy Oncology Group (RTOG) was either grade 1 or grade 2. If surface dose exceeded 5000 cGy in 32 fractions, then grade 3 skin reactions were observed.

FABRICATION AND OPTOELECTRONIC PROPERTIES OF MgxZn1-xO ULTRATHIN FILMS BY LANGMUIR-BLODGETT TECHNOLOGY

NASA Astrophysics Data System (ADS)

Tang, Dongyan; Feng, Qian; Jiang, Enying; He, Baozhu

2012-08-01

By transferring MgxZn1-xO sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir-Blodgett (LB) multilayers of MgxZn1-xO (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, MgxZn1-xO ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with MgxZn1-xO sols under Π-A isotherms inferred the interaction of stearic acid with MgxZn1-xO sols during the formation of monolayer at air-water interface. X-ray diffraction (XRD) was used to determine the crystal structures of MgxZn1-xO nanoparticles and ultrathin films. The surface morphologies of MgxZn1-xO ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of MgxZn1-xO were detected and discussed based on photoluminescence (PL) spectra.

Electrical transport of spin-polarized carriers in disordered ultrathin films.

PubMed

Hernandez, L M; Bhattacharya, A; Parendo, Kevin A; Goldman, A M

2003-09-19

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of a collective state that forms when the carriers are spin polarized at low temperatures and in high magnetic fields.

SERS Taper-Fiber Nanoprobe Modified by Gold Nanoparticles Wrapped with Ultrathin Alumina Film by Atomic Layer Deposition

PubMed Central

Xu, Wenjie; Chen, Zhenyi; Chen, Na; Zhang, Heng; Liu, Shupeng; Hu, Xinmao; Wen, Jianxiang; Wang, Tingyun

2017-01-01

A taper-fiber SERS nanoprobe modified by gold nanoparticles (Au-NPs) with ultrathin alumina layers was fabricated and its ability to perform remote Raman detection was demonstrated. The taper-fiber nanoprobe (TFNP) with a nanoscale tip size under 80 nm was made by heated pulling combined with the chemical etching method. The Au-NPs were deposited on the TFNP surface with the electrostatic self-assembly technology, and then the TFNP was wrapped with ultrathin alumina layers by the atomic layer deposition (ALD) technique. The results told us that with the increasing thickness of the alumina film, the Raman signals decreased. With approximately 1 nm alumina film, the remote detection limit for R6G aqueous solution reached 10−6 mol/L. PMID:28245618

High-mobility ultrathin semiconducting films prepared by spin coating.

PubMed

Mitzi, David B; Kosbar, Laura L; Murray, Conal E; Copel, Matthew; Afzali, Ali

2004-03-18

The ability to deposit and tailor reliable semiconducting films (with a particular recent emphasis on ultrathin systems) is indispensable for contemporary solid-state electronics. The search for thin-film semiconductors that provide simultaneously high carrier mobility and convenient solution-based deposition is also an important research direction, with the resulting expectations of new technologies (such as flexible or wearable computers, large-area high-resolution displays and electronic paper) and lower-cost device fabrication. Here we demonstrate a technique for spin coating ultrathin (approximately 50 A), crystalline and continuous metal chalcogenide films, based on the low-temperature decomposition of highly soluble hydrazinium precursors. We fabricate thin-film field-effect transistors (TFTs) based on semiconducting SnS(2-x)Se(x) films, which exhibit n-type transport, large current densities (>10(5) A cm(-2)) and mobilities greater than 10 cm2 V(-1) s(-1)--an order of magnitude higher than previously reported values for spin-coated semiconductors. The spin-coating technique is expected to be applicable to a range of metal chalcogenides, particularly those based on main group metals, as well as for the fabrication of a variety of thin-film-based devices (for example, solar cells, thermoelectrics and memory devices).

High-mobility ultrathin semiconducting films prepared by spin coating

NASA Astrophysics Data System (ADS)

Mitzi, David B.; Kosbar, Laura L.; Murray, Conal E.; Copel, Matthew; Afzali, Ali

2004-03-01

The ability to deposit and tailor reliable semiconducting films (with a particular recent emphasis on ultrathin systems) is indispensable for contemporary solid-state electronics. The search for thin-film semiconductors that provide simultaneously high carrier mobility and convenient solution-based deposition is also an important research direction, with the resulting expectations of new technologies (such as flexible or wearable computers, large-area high-resolution displays and electronic paper) and lower-cost device fabrication. Here we demonstrate a technique for spin coating ultrathin (~50Å), crystalline and continuous metal chalcogenide films, based on the low-temperature decomposition of highly soluble hydrazinium precursors. We fabricate thin-film field-effect transistors (TFTs) based on semiconducting SnS2-xSex films, which exhibit n-type transport, large current densities (>105Acm-2) and mobilities greater than 10cm2V-1s-1-an order of magnitude higher than previously reported values for spin-coated semiconductors. The spin-coating technique is expected to be applicable to a range of metal chalcogenides, particularly those based on main group metals, as well as for the fabrication of a variety of thin-film-based devices (for example, solar cells, thermoelectrics and memory devices).

Influence of interface layer on optical properties of sub-20 nm-thick TiO2 films

NASA Astrophysics Data System (ADS)

Shi, Yue-Jie; Zhang, Rong-Jun; Li, Da-Hai; Zhan, Yi-Qiang; Lu, Hong-Liang; Jiang, An-Quan; Chen, Xin; Liu, Juan; Zheng, Yu-Xiang; Wang, Song-You; Chen, Liang-Yao

2018-02-01

The sub-20 nm ultrathin titanium dioxide (TiO2) films with tunable thickness were deposited on Si substrates by atomic layer deposition (ALD). The structural and optical properties were acquired by transmission electron microscopy, atomic force microscopy and spectroscopic ellipsometry. Afterwards, a constructive and effective method of analyzing interfaces by applying two different optical models consisting of air/TiO2/Ti x Si y O2/Si and air/effective TiO2 layer/Si, respectively, was proposed to investigate the influence of interface layer (IL) on the analysis of optical constants and the determination of band gap of TiO2 ultrathin films. It was found that two factors including optical constants and changing components of the nonstoichiometric IL could contribute to the extent of the influence. Furthermore, the investigated TiO2 ultrathin films of 600 ALD cycles were selected and then annealed at the temperature range of 400-900 °C by rapid thermal annealing. Thicker IL and phase transition cause the variation of optical properties of TiO2 films after annealing and a shorter electron relaxation time reveals the strengthened electron-electron and electron-phonon interactions in the TiO2 ultrathin films at high temperature. The as-obtained results in this paper will play a role in other studies of high dielectric constants materials grown on Si substrates and in the applications of next generation metal-oxide-semiconductor devices.

Identification of O-rich structures on platinum(111)-supported ultrathin iron oxide films

DOE PAGES

Merte, Lindsay R.; Bai, Yunhai; Zeuthen, Helene; ...

2016-01-06

Using high-resolution scanning tunneling microscopy (STM) we have studied the oxidation of ultrathin FeO films grown on Pt(111). At the initial stage of the FeO film oxidation by atomic oxygen exposure, we identified three distinct types of line defects, all of which form boundaries between FeO domains of opposite orientation. Two types of line defects appearing bright ( type-i) and dark ( type-ii) in the STM images at typical scanning parameters are “metallic”, whereas the third line defect exhibits nonmetallic behavior ( type-iii). Atomic-scale structure models of these line defects are proposed, with type-i defects exhibiting 4-fold coordinated Fe atoms,more » type-ii exhibiting 2-fold coordinated O atoms, and type-iii exhibiting tetrahedrally-coordinated Fe atoms. In addition, FeO 2 trilayer islands are formed upon oxidation, which appear at FCC-type domains of the moiré structure. At high scanning bias, distinct protrusions on the trilayer islands are observed over surface O ions, which are assigned to H adatoms. The experimental data are supported by density functional theory (DFT) calculations, in which bare and hydroxylated FeO 2 trilayer islands are compared. Finally, we compare the formation of O-rich features on continuous FeO films using atomic oxygen with the oxidation of Pt(111)-supported FeO islands accomplished by O 2 exposure.« less

Bottom Extreme-Ultraviolet-Sensitive Coating for Evaluation of the Absorption Coefficient of Ultrathin Film

NASA Astrophysics Data System (ADS)

Hijikata, Hayato; Kozawa, Takahiro; Tagawa, Seiichi; Takei, Satoshi

2009-06-01

A bottom extreme-ultraviolet-sensitive coating (BESC) for evaluation of the absorption coefficients of ultrathin films such as extreme ultraviolet (EUV) resists was developed. This coating consists of a polymer, crosslinker, acid generator, and acid-responsive chromic dye and is formed by a conventional spin-coating method. By heating the film after spin-coating, a crosslinking reaction is induced and the coating becomes insoluble. A typical resist solution can be spin-coated on a substrate covered with the coating film. The evaluation of the linear absorption coefficients of polymer films was demonstrated by measuring the EUV absorption of BESC substrates on which various polymers were spin-coated.

Equilibrium oxygen storage capacity of ultrathin CeO 2-δ depends non-monotonically on large biaxial strain

DOE PAGES

Gopal, Chirranjeevi Balaji; Garcia-Melchor, Max; Lee, Sang Chul; ...

2017-05-18

Elastic strain is being increasingly employed to enhance the catalytic properties of mixed ion–electron conducting oxides. However, its effect on oxygen storage capacity is not well established. Here, we fabricate ultrathin, coherently strained films of CeO 2-δ between 5.6% biaxial compression and 2.1% tension. In situ ambient pressure X-ray photoelectron spectroscopy reveals up to a fourfold enhancement in equilibrium oxygen storage capacity under both compression and tension. This non-monotonic variation with strain departs from the conventional wisdom based on a chemical expansion dominated behaviour. Through depth profiling, film thickness variations and a coupled photoemission–thermodynamic analysis of space-charge effects, we showmore » that the enhanced reducibility is not dominated by interfacial effects. On the basis of ab initio calculations of oxygen vacancy formation incorporating defect interactions and vibrational contributions, we suggest that the non-monotonicity arises from the tetragonal distortion under large biaxial strain. Finally, these results may guide the rational engineering of multilayer and core–shell oxide nanomaterials.« less

The impact of ultra-thin titania interlayers on open circuit voltage and carrier lifetime in thin film solar cells

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

Moerman, David; Colbert, Adam E.; Ginger, David S., E-mail: ginger@chem.washington.edu

We study the effects of modifying indium tin oxide electrodes with ultrathin titania (TiO{sub 2}) layers grown via plasma-enhanced atomic layer deposition (PE-ALD). We find an optimal thickness of PE-ALD-grown titania by tracking performance, which initially increases, peaks, and eventually decreases with increasing TiO{sub 2} thickness. We use scanning Kelvin probe microscopy (SKPM) to measure both the local work function and its distribution as a function of TiO{sub 2} thickness. We find that the variance in contact potential difference across the surface of the film is related to either the amorphous or anatase TiO{sub 2} form. Finally, we use localmore » SKPM recombination rate experiments, supported by bulk transient photovoltage and charge extraction measurements. We show that the optimum TiO{sub 2} thickness is the one for which the carrier lifetime is the longest and the charge carrier density is the highest, when the TiO{sub 2} is amorphous, in agreement with the device measurements.« less

Enhancement of absorption and color contrast in ultra-thin highly absorbing optical coatings

NASA Astrophysics Data System (ADS)

Kats, Mikhail A.; Byrnes, Steven J.; Blanchard, Romain; Kolle, Mathias; Genevet, Patrice; Aizenberg, Joanna; Capasso, Federico

2013-09-01

Recently a new class of optical interference coatings was introduced which comprises ultra-thin, highly absorbing dielectric layers on metal substrates. We show that these lossy coatings can be augmented by an additional transparent subwavelength layer. We fabricated a sample comprising a gold substrate, an ultra-thin film of germanium with a thickness gradient, and several alumina films. The experimental reflectivity spectra showed that the additional alumina layer increases the color range that can be obtained, in agreement with calculations. More generally, this transparent layer can be used to enhance optical absorption, protect against erosion, or as a transparent electrode for optoelectronic devices.

Electric field effect on exchange interaction in ultrathin Co films with ionic liquids

NASA Astrophysics Data System (ADS)

Ishibashi, Mio; Yamada, Kihiro T.; Shiota, Yoichi; Ando, Fuyuki; Koyama, Tomohiro; Kakizakai, Haruka; Mizuno, Hayato; Miwa, Kazumoto; Ono, Shimpei; Moriyama, Takahiro; Chiba, Daichi; Ono, Teruo

2018-06-01

Electric-field modulations of magnetic properties have been extensively studied not only for practical applications but also for fundamental interest. In this study, we investigated the electric field effect on the exchange interaction in ultrathin Co films with ionic liquids. The exchange coupling J was characterized from the direct magnetization measurement as a function of temperature using Pt/ultrathin Co/MgO structures. The trend of the electric field effect on J is in good agreement with that of the theoretical prediction, and a large change in J by applying a gate voltage was observed by forming an electric double layer using ionic liquids.

Theoretical requirements for broadband perfect absorption of acoustic waves by ultra-thin elastic meta-films

PubMed Central

Duan, Yuetao; Luo, Jie; Wang, Guanghao; Hang, Zhi Hong; Hou, Bo; Li, Jensen; Sheng, Ping; Lai, Yun

2015-01-01

We derive and numerically demonstrate that perfect absorption of elastic waves can be achieved in two types of ultra-thin elastic meta-films: one requires a large value of almost pure imaginary effective mass density and a free space boundary, while the other requires a small value of almost pure imaginary effective modulus and a hard wall boundary. When the pure imaginary density or modulus exhibits certain frequency dispersions, the perfect absorption effect becomes broadband, even in the low frequency regime. Through a model analysis, we find that such almost pure imaginary effective mass density with required dispersion for perfect absorption can be achieved by elastic metamaterials with large damping. Our work provides a feasible approach to realize broadband perfect absorption of elastic waves in ultra-thin films. PMID:26184117

Determination of magnetic anisotropy constants in Fe ultrathin film on vicinal Si(111) by anisotropic magnetoresistance

PubMed Central

Ye, Jun; He, Wei; Wu, Qiong; Liu, Hao-Liang; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

2013-01-01

The epitaxial growth of ultrathin Fe film on Si(111) surface provides an excellent opportunity to investigate the contribution of magnetic anisotropy to magnetic behavior. Here, we present the anisotropic magnetoresistance (AMR) effect of Fe single crystal film on vicinal Si(111) substrate with atomically flat ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the tiny misorientation from Fe(111) plane, the symmetry of magnetocrystalline anisotropy energy changes from the six-fold to a superposition of six-fold, four-fold and a weakly uniaxial contribution. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from torque curves on the basis of AMR results. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of various magnetic anisotropy constants. PMID:23828508

Study of anisotropy, magnetization reversal and damping in ultrathin Co films on MgO (0 0 1) substrate

NASA Astrophysics Data System (ADS)

Mallik, Srijani; Bedanta, Subhankar

2018-01-01

Ultrathin Co films of 3 nm thickness have been prepared on MgO (0 0 1) substrate in presence or absence of substrate pre-annealing. Uniaxial anisotropy is induced in the samples due to the deposition under oblique angle of incidence. Along with the oblique deposition induced anisotropy, another uniaxial anisotropy contribution has been observed due to pre-annealing. However, no cubic anisotropy has been observed here as compared to the thicker films. Angle dependent ferromagnetic resonance (FMR) measurement confirms the presence of two anisotropies in the pre-annealed sample with ∼18° misalignment with each other. The two anisotropy constants were calculated from both superconducting quantum interference device (SQUID) magnetometry and FMR spectroscopy. The magnetization reversal is governed by nucleation dominated aftereffect followed by domain wall motion for the pre-annealed sample. Branched domains are observed for the sample prepared without pre-annealing which indicates grain disorientation of Co. However, in the thicker (25 nm) Co films ripple domains were observed in contrary to ultrathin (3 nm) films.

Ultrathin nanofibrous films prepared from cadmium hydroxide nanostrands and anionic surfactants.

PubMed

Peng, Xinsheng; Karan, Santanu; Ichinose, Izumi

2009-08-04

We developed a simple fabrication method of ultrathin nanofibrous films from the dispersion of cadmium hydroxide nanostrands and anionic surfactants. The nanostrands were prepared in a dilute aqueous solution of cadmium chloride by using 2-aminoethanol. They were highly positively charged and gave bundlelike fibers upon mixing an aqueous solution of anionic surfactant. The nanostrand/surfactant composite fibers were filtered on an inorganic membrane filter. The resultant nanofibrous film was very uniform in the area of a few centimeters square when the thickness was not less than 60 nm. The films obtained with sodium tetradecyl sulfate (STS) had a composition close to the electroneutral complex, [Cd37(OH)68(H2O)n] x 6(STS), as confirmed by energy dispersive X-ray analysis. They were water-repellent with a contact angle of 117 degrees, and the value slightly decreased with the alkyl chain length of anionic surfactants. Ultrathin nanofibrous films were stable enough to be used for ultrafiltration at pressure difference of 90 kPa. We could effectively separate Au nanoparticles of 40 nm at an extremely high filtration rate of 14000 L/(h m2 bar).

Polarity compensation in ultra-thin films of complex oxides: The case of a perovskite nickelate

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

Middey, S.; Rivero, P.; Meyers, D.

2014-10-29

In this study, we address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO 3 on the band insulator SrTiO 3 along the pseudo cubic [111] direction. While in general the metallic LaNiO 3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, andmore » synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La 2Ni 2O 5 (Ni 2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO 3/SrTiO 3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.« less

Tg and Structural Recovery of Single Ultrathin Films

NASA Astrophysics Data System (ADS)

Simon, Sindee

The behavior of materials confined at the nanoscale has been of considerable interest over the past two decades. Here, the focus is on recent results for single polystyrene ultrathin films studied with ultrafast scanning chip calorimetry. The Tg depression of a 20 nm-thick high-molecular-weight polystyrene film is found to be a function of cooling rate, decreasing with increasing cooling rate; whereas, at high enough cooling rates (e.g., 1000 K/s), Tg is the same as the bulk within the error of the measurements. Structural recovery is also performed with chip calorimetry as a function of aging time and temperature, and the evolution of the fictive temperature is followed. The advantages of the Flash DSC include sufficient sensitivity to measure enthalpy recovery for a single 20 nm-thick film, as well as extension of the measurements to aging temperatures as high as 15 K above nominal Tg and to aging times as short as 0.01 s. The aging behavior and relaxation time-temperature map for single ultrathin films are compared to those for bulk material. Comparison to behavior in other geometries will also be discussed.

Three-configurational surface magneto-optical Kerr effect measurement system for an ultrahigh vacuum in situ study of ultrathin magnetic films

NASA Astrophysics Data System (ADS)

Lee, J.-W.; Jeong, J.-R.; Kim, D.-H.; Ahn, J. S.; Kim, J.; Shin, S.-C.

2000-10-01

We have constructed a three-configurational surface magneto-optical Kerr effect system, which provides the simultaneous measurements of the "polar," "longitudinal," and "transverse" Kerr hysteresis loops at the position where deposition is carried out in an ultrahigh vacuum growth chamber. The present system enables in situ three-dimensional vectorial studies of ultrathin film magnetism with a submonolayer sensitivity. We present three-configurational hysteresis loops measured during the growth of Co films on Pd(111), glass, and Pd/glass substrates.

Ferroelectric ultrathin perovskite films

DOEpatents

Rappe, Andrew M; Kolpak, Alexie Michelle

2013-12-10

Disclosed herein are perovskite ferroelectric thin-film. Also disclosed are methods of controlling the properties of ferroelectric thin films. These films can be used in a variety materials and devices, such as catalysts and storage media, respectively.

Understanding Metal-Insulator transitions in ultra-thin films of LaNiO3

NASA Astrophysics Data System (ADS)

Ravichandran, Jayakanth; King, Philip D. C.; Schlom, Darrell G.; Shen, Kyle M.; Kim, Philip

2014-03-01

LaNiO3 (LNO) is a bulk paramagnetic metal and a member of the family of RENiO3 Nickelates (RE = Rare Earth Metals), which is on the verge of the metal-insulator transition. Ultra-thin films of LNO has been studied extensively in the past and due to its sensitivity to disorder, the true nature of the metal-insulator transition in these films have been hard to decipher. We grow high quality ultra-thin films of LNO using reactive molecular beam epitaxy (MBE) and use a combination of ionic liquid gating and magneto-transport measurements to understand the nature and tunability of metal-insulator transition as a function of thickness for LNO. The underlying mechanisms for the transition are discussed in the framework of standard transport models. These results are discussed in the light of other Mott insulators such as Sr2IrO4, where we have performed similar measurements around the insulating state.

Chemical surface deposition of ultra-thin semiconductors

DOEpatents

McCandless, Brian E.; Shafarman, William N.

2003-03-25

A chemical surface deposition process for forming an ultra-thin semiconducting film of Group IIB-VIA compounds onto a substrate. This process eliminates particulates formed by homogeneous reactions in bath, dramatically increases the utilization of Group IIB species, and results in the formation of a dense, adherent film for thin film solar cells. The process involves applying a pre-mixed liquid coating composition containing Group IIB and Group VIA ionic species onto a preheated substrate. Heat from the substrate causes a heterogeneous reaction between the Group IIB and VIA ionic species of the liquid coating composition, thus forming a solid reaction product film on the substrate surface.

Novel self-organization mechanism in ultrathin liquid films: theory and experiment.

PubMed

Trice, Justin; Favazza, Christopher; Thomas, Dennis; Garcia, Hernando; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2008-07-04

When an ultrathin metal film of thickness h (<20 nm) is melted by a nanosecond pulsed laser, the film temperature is a nonmonotonic function of h and achieves its maximum at a certain thickness h*. This is a consequence of the h and time dependence of energy absorption and heat flow. Linear stability analysis and nonlinear dynamical simulations that incorporate such intrinsic interfacial thermal gradients predict a characteristic pattern length scale Lambda that decreases for h>h*, in contrast to the classical spinodal dewetting behavior where Lambda increases monotonically as h2. These predictions agree well with experimental observations for Co and Fe films on SiO2.

An easily accessible carbon material derived from carbonization of polyacrylonitrile ultrathin films: ambipolar transport properties and application in a CMOS-like inverter.

PubMed

Jiao, Fei; Zhang, Fengjiao; Zang, Yaping; Zou, Ye; Di, Chong'an; Xu, Wei; Zhu, Daoben

2014-03-04

Ultrathin carbon films were prepared by carbonization of a solution processed polyacrylonitrile (PAN) film in a moderate temperature range (500-700 °C). The films displayed balanced hole (0.50 cm(2) V(-1) s(-1)) and electron mobilities (0.20 cm(2) V(-1) s(-1)) under ambient conditions. Spectral characterization revealed that the electrical transport is due to the formation of sp(2) hybridized carbon during the carbonization process. A CMOS-like inverter demonstrated the potential application of this material in the area of carbon electronics, considering its processability and low-cost.

Solution-processed ultrathin chemically derived graphene films as soft top contacts for solid-state molecular electronic junctions.

PubMed

Li, Tao; Hauptmann, Jonas Rahlf; Wei, Zhongming; Petersen, Søren; Bovet, Nicolas; Vosch, Tom; Nygård, Jesper; Hu, Wenping; Liu, Yunqi; Bjørnholm, Thomas; Nørgaard, Kasper; Laursen, Bo W

2012-03-08

A novel method using solution-processed ultrathin chemically derived graphene films as soft top contacts for the non-destructive fabrication of molecular junctions is demonstrated. We believe this protocol will greatly enrich the solid-state test beds for molecular electronics due to its low-cost, easy-processing and flexible nature. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrathin Carbon Film Protected Silver Nanostructures for Surface-Enhanced Raman Scattering.

PubMed

Peng, Yinshan; Zheng, Xianliang; Tian, Hongwei; Cui, Xiaoqiang; Chen, Hong; Zheng, Weitao

2016-06-23

In this article, ultrathin carbon film protected silver substrate (Ag/C) was prepared via a plasma-enhanced chemical vapor deposition (PECVD) method. The morphological evolution of silver nanostructures underneath, as well as the surface-enhanced Raman scattering (SERS) activity of Ag/C hybrid can be tuned by controlling the deposition time. The stability and reproducibility of the as-prepared hybrid were also studied. © The Author(s) 2016.

Archetypal structure of ultrathin alumina films: Grazing-incidence x-ray diffraction on Ni(111)

NASA Astrophysics Data System (ADS)

Prévot, G.; Le Moal, S.; Bernard, R.; Croset, B.; Lazzari, R.; Schmaus, D.

2012-05-01

We have studied by grazing-incidence x-ray diffraction the atomic structure of an ultrathin alumina film grown on Ni(111). We show that, since there is neither registry between the film and the substrate nor induced Ni relaxations, this system appears to be a prototypical freestanding oxide layer. We have been able to unambiguously determine the three-dimensional structure of the film, which consists of a substrate/Al16/O24/Al24/O28 stacking within a (18.23 × 10.53 Å) R0° unit cell. From the different Al coordinations (3/4/5) in the layer and from the precise determination of the Al-O interatomic distances, we conclude that the film structure presents some similarities with the η phase of bulk alumina, which also has a high surface/bulk ratio. The precise comparison between these two structures allows us to explain that the perfect 3 ratio between the two sides of the mesh of the film is governed by the stacking of the two central planes, combining oxygen close-packed atoms below Al atoms in tetrahedral or pyramidal positions. Moreover, Al atoms at the interface plane of the ultrathin film adopt a quasitrihedral configuration, which confirms that, in the alumina η phase, Al atoms with such a coordination are located near the surface of the nanocrystals. The atomic structure is also very close to the one first proposed by Kresse [G. Kresse, M. Schmid, E. Napetschnig, M. Shishkin, L. Köhler, and P. Varga, ScienceSCIEAS0036-807510.1126/science.1107783 308, 1440 (2005)] for alumina films on NiAl(110). This strongly suggests that this atomic model, within small variations, can be extended to ultrathin alumina film on numerous other metal substrates and may be quasi-intrinsic to a freestanding layer rather than governed by the interactions between the film and the substrate.

Electrical properties of spin coated ultrathin titanium oxide films on GaAs

NASA Astrophysics Data System (ADS)

Dutta, Shankar; Pal, Ramjay; Chatterjee, Ratnamala

2015-04-01

In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (˜10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10-20 nm with thickness around 10-12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be -0.1 V to -0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10-4 A cm-2 at 3 V) compared to the unpassivated film (1.8 × 10-3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm-1 and 7.2 MV cm-1 respectively.

Simultaneous determination of the residual stress, elastic modulus, density and thickness of ultrathin film utilizing vibrating doubly clamped micro-/nanobeams

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

Stachiv, Ivo, E-mail: stachiv@fzu.cz; Institute of Physics, Czech Academy of Sciences, Prague; Kuo, Chih-Yun

2016-04-15

Measurement of ultrathin film thickness and its basic properties can be highly challenging and time consuming due to necessity of using several very sophisticated devices. Here, we report an easy accessible resonant based method capable to simultaneously determinate the residual stress, elastic modulus, density and thickness of ultrathin film coated on doubly clamped micro-/nanobeam. We show that a general dependency of the resonant frequencies on the axial load is also valid for in-plane vibrations, and the one depends only on the considered vibrational mode. As a result, we found that the film elastic modulus, density and thickness can be evaluatedmore » from two measured in-plane and out-plane fundamental resonant frequencies of micro-/nanobeam with and without film under different prestress forces. Whereas, the residual stress can be determined from two out-plane (in-plane) measured consecutive resonant frequencies of beam with film under different prestress forces without necessity of knowing film and substrate properties and dimensions. Moreover, we also reveal that the common uncertainties in force (and thickness) determination have a negligible (and minor) impact on the determined film properties. The application potential of the present method is illustrated on the beam made of silicon and SiO{sub 2} with deposited 20 nm thick AlN and 40 nm thick Au thin films, respectively.« less

Magnetic properties influenced by interfaces in ultrathin Co/Ge(1 0 0) and Co/Ge(1 1 1) films

NASA Astrophysics Data System (ADS)

Tsay, J. S.; Yao, Y. D.; Cheng, W. C.; Tseng, T. K.; Wang, K. C.; Yang, C. S.

2003-10-01

Magnetic properties influenced by interfaces in ultrathin Co/Ge(1 0 0) and Co/Ge(1 1 1) films with thickness below 28 monolayers (ML) have been studied using the surface magneto-optic Kerr effect (SMOKE) technique. In both systems, the nonferromagnetic layer, as an interface between Co and Ge, plays an important role during annealing. In general, ultrathin Co films with fixed total thickness but fabricated at different temperatures on the same substrate, their Kerr hysteresis loops disappear roughly at the same temperature. This suggests that the thickness of the interfacial layer could inversely prevent the diffusion between Co and Ge substrate. From the annealing studies for both systems with total film thickness of 28 monolayers, we have found that Kerr signal disappears at 375 K for Co/Ge(1 1 1) and 425 K for Co/Ge(1 0 0) films. This suggests that Co/Ge(1 1 1) films possess a lower thermal stability than that of the Co/Ge(1 0 0) films. Our experimental data could be explained by different interfacial condition between Ge(1 0 0) and Ge(1 1 1), the different onset of interdiffusion, and the surface structure condition of Ge(1 0 0) and Ge(1 1 1).

Ultrathin free-standing graphene oxide film based flexible touchless sensor

NASA Astrophysics Data System (ADS)

Liu, Lin; Wang, Yingyi; Li, Guanghui; Qin, Sujie; Zhang, Ting

2018-01-01

Ultrathin free-standing graphene oxide (GO) films were fabricated by vacuum filtration method assisted with Ni(OH)2 nanosheets as the sacrifice layer. The surface of the obtained GO film is very clean as the Ni(OH)2 nanosheets can be thoroughly etched by HCl. The thickness of the GO films can be well-controlled by changing the volume of GO dispersion, and the thinnest GO film reached ~12 nm. As a novel and transparent dielectric material, the GO film has been applied as the dielectric layer for the flexible touchless capacitive sensor which can effectively distinguish the approaching of an insulator or a conductor. Project supported by the National Natural Science Foundation of China (No. 61574163) and the Foundation Research Project of Jiangsu Province (Nos. BK20160392, BK20170008).

The Role of Partial Surface Charge Compensation in the Properties of Ferroelectric and Antiferroelectric Thin Films

NASA Astrophysics Data System (ADS)

Swedberg, Elena

Ferroelectric and antiferroelectric ultrathin films have attracted a lot of attention recently due to their remarkable properties and their potential to allow for device miniaturization in numerous applications. However, when the ferroelectric films are scaled down, it brings about an unavoidable depolarizing field. A partial surface charge compensation allows to control the residual depolarizing field and manipulate the properties of ultrathin ferroelectric films. In this dissertation we take advantage of atomistic first-principles-based simulations to expand our understanding of the role of the partial surface charge compensation in the properties of ferroelectric and antiferroelectric ultrathin films. The application of our computational methodology to study the effect of the partial surface charge compensation in ferroelectric ultrathin films led to the prediction that, depending on the quality of the surface charge compensation, ferroelectric thin films respond to an electric field in a qualitatively different manner. They can be tuned to behave like a linear dielectric, a ferroelectric or even an antiferroelectric. This effect was shown to exist in films with different mechanical boundary conditions and different crystal symmetries. There are a number of potential applications where such properties of ferroelectric thin films can be used. One of these potential applications is energy storage. We will show that, in the antiferroelectric regime, ferroelectric thin films exhibit drastic enhancement of energy storage density which is a desirable property. One of the most promising applications of ferroelectric ultrathin films that emerged only recently is the harvesting of the giant electrocaloric effect. Interestingly, despite numerous studies of the electrocaloric effect in ferroelectric thin films, it is presently unknown how a residual depolarizing field affects the electrocaloric properties of such films. Application of state-of-the-art computational methods to investigate the electrocaloric effect in ferroelectric films with partial surface charge compensation led to the prediction that the residual depolarizing field can perform a dual role in the electrocaloric effect in these films. When the depolarizing field creates competition between the monodomain and nanodomain states, we predict an enhancement of the electrocaloric effect due to the frustration that increases the entropy of the state and therefore the electrocaloric temperature change. On the other hand, when the depolarizing field leads to a formation of nanodomains, thin films either exhibit a small electrocaloric effect or lose their electrocaloric properties altogether to the irreversible nanodomain motion. When the residual depolarizing field is weak enough to permit the formation of monodomain phases, the electrocaloric effect is significantly reduced as compared to bulk. We believe that our findings could potentially reveal additional opportunities to optimize solid state cooling technology. While the electrocaloric effect has been a popular topic of interest in recent years [12], there still exists numerous gaps in the fundamental understanding of the effect. In particular, it is presently unknown whether the scaling laws, known to exist for magnetocaloric materials, can be applied to ferroelectric and antiferroelectric electrocalorics. We predict the existence of scaling laws for low-field electrocaloric temperature change in antiferroelectric and ferroelectric materials. With the help of first-principles-based simulations, we showed computationally that the scaling laws exist for antiferroelectric PbZrO3 along with ferroelectrics PbTiO3, BaTiO 3 and KNbO3. Additional evidence of the scaling laws existence are provided using experimental data from the literature. Interestingly, our studies on ferroelectric films predicted the existence of antiferroelectric behavior in ultrathin films with partial surface charge compensation. One may wonder whether it is possible to stabilize the ferroelectric phase in antiferroelectric films and what role the surface charge screening would play in such a transition. Motivated to address these fundamental questions, we used computational experiments to study antiferroelectric ultrathin films with a residual depolarizing field. Our studies led to the following predictions. We found that PbZrO3 thin films exhibit the ferroelectric phase upon scaling down and under the condition of efficient surface charge compensation. We also found a strong competition between the antiferroelectric and ferroelectric phases for the thin films of the critical size associated with antiferroelectric-ferroelectric phase transition. This finding motivated us to study the electrocaloric effect in PbZrO3 thin films with antiferroelectric-ferroelectric phase competition. We found that high tunability of the phase transition by the electric field leads to a wide range of temperatures associated with a strong electrocaloric effect. In addition, we found that epitaxial strain provides further tunability to the electrocaloric properties. In summary, our studies led to a broader and deeper understanding of the abundantly many roles surface charge compensation plays in ultrathin ferroelectrics and antiferroelectrics.

In situ monitoring of thermal crystallization of ultrathin tris(8-hydroxyquinoline) aluminum films using surface-enhanced Raman scattering.

PubMed

Muraki, Naoki

2014-01-01

Thermal crystallization of 3, 10, and 60 nm-thick tris(8-hydroxyquinoline)aluminum (Alq3) films is studied using surface-enhanced Raman scattering with a constant heating rate. An abrupt higher frequency shift of the quinoline-stretching mode is found to be an indication of a phase transition of Alq3 molecules from amorphous to crystalline. While the 60 nm-thick film shows the same crystallization temperature as a bulk sample, the thinner films were found to have a lower crystallization temperature and slower rate of crystallization. Non-isothermal kinetics analysis is performed to quantify kinetic properties such as the Avrami exponent constants and crystallization rates of ultrathin Alq3 films.

Magnetic and structural characterization of ultra-thin Fe (222) films

NASA Astrophysics Data System (ADS)

Loving, Melissa G.; Brown, Emily E.; Rizzo, Nicholas D.; Ambrose, Thomas F.

2018-05-01

Varied thickness body centered cubic (BCC) ultrathin Fe films (10-50Å) have been sputter deposited onto Si (111) substrates. BCC Fe with the novel (222) texture was obtained by H- terminating the Si (111) starting substrate then immediately depositing the magnetic films. Structural results derived from grazing incidence x-ray diffraction and x-ray reflectivity confirm the crystallographic texture, film thickness, and interface roughness. Magnetic results indicate that Fe (222) exhibits soft magnetic switching (easy axis), high anisotropy (hard axis), which is maintained across the thickness range, and a positive magnetostriction (for the thicker film layers). The observed soft magnetic switching in this system makes it an ideal candidate for future magnetic memory development as well as other microelectronics applications that utilize magnetic materials.

Negative differential resistance in electron tunneling in ultrathin films near the two-dimensional limit

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

Batabyal, R.; Abdul Wasey, A. H. M.; Mahato, J. C.

We report on our observation of negative differential resistance (NDR) in electron tunneling conductance in atomic-scale ultrathin Ag films on Si(111) substrates. NDR was observed by scanning tunneling spectroscopy measurements. The tunneling conductance depends on the electronic local density of states (LDOS) of the sample. We show that the sample bias voltage, at which negative differential resistance and peak negative conductance occur, depends on the film thickness. This can be understood from the variation in the LDOS of the Ag films as a function of film thickness down to the two-dimensional limit of one atomic layer. First principles density functionalmore » theory calculations have been used to explain the results.« less

Formation and prevention of fractures in sol-gel-derived thin films.

PubMed

Kappert, Emiel J; Pavlenko, Denys; Malzbender, Jürgen; Nijmeijer, Arian; Benes, Nieck E; Tsai, Peichun Amy

2015-02-07

Sol-gel-derived thin films play an important role as the functional coatings for various applications that require crack-free films to fully function. However, the fast drying process of a standard sol-gel coating often induces mechanical stresses, which may fracture the thin films. An experimental study on the crack formation in sol-gel-derived silica and organosilica ultrathin (submicron) films is presented. The relationships among the crack density, inter-crack spacing, and film thickness were investigated by combining direct micrograph analysis with spectroscopic ellipsometry. It is found that silica thin films are more prone to fracturing than organosilica films and have a critical film thickness of 300 nm, above which the film fractures. In contrast, the organosilica films can be formed without cracks in the experimentally explored regime of film thickness up to at least 1250 nm. These results confirm that ultrathin organosilica coatings are a robust silica substitute for a wide range of applications.

New possibilities for tuning ultrathin cobalt film magnetic properties by a noble metal overlayer.

PubMed

Kisielewski, M; Maziewski, A; Tekielak, M; Wawro, A; Baczewski, L T

2002-08-19

Complementary multiscale magneto-optical studies based on the polar Kerr effect are carried out on an ultrathin cobalt wedge covered with a silver wedge and subsequently with the Au thick layer. A few monolayers of Ag are found to have a substantial effect on magnetic anisotropy, the coercivity field, and Kerr rotation. The silver overlayer thickness-driven magnetic reorientation from easy axis to easy plane generates a new type of 90 degrees magnetic wall for cobalt thicknesses between 1.3 and 1.8 nm. The tuning of the wall width in a wide range is possible. Tailoring of the overlayer structure can be used for ultrathin film magnetic patterning.

In situ study of the electronic structure of atomic layer deposited oxide ultrathin films upon oxygen adsorption using ambient pressure XPS

DOE PAGES

Mao, Bao-Hua; Crumlin, Ethan; Tyo, Eric C.; ...

2016-07-21

In this work, ambient pressure X-ray photoelectron spectroscopy (APXPS) was used to investigate the effect of oxygen adsorption on the band bending and electron affinity of Al 2O 3, ZnO and TiO 2 ultrathin films (~1 nm in thickness) deposited on a Si substrate by atomic layer deposition (ALD). Upon exposure to oxygen at room temperature (RT), upward band bending was observed on all three samples, and a decrease in electron affinity was observed on Al 2O 3 and ZnO ultrathin films at RT. At 80°C, the magnitude of the upward band bending decreased, and the change in the electronmore » affinity vanished. These results indicate the existence of two surface oxygen species: a negatively charged species that is strongly adsorbed and responsible for the observed upward band bending, and a weakly adsorbed species that is polarized, lowering the electron affinity. Based on the extent of upward band bending on the three samples, the surface coverage of the strongly adsorbed species exhibits the following order: Al 2O 3 > ZnO > TiO 2. This finding is in stark contrast to the trend expected on the surface of these bulk oxides, and highlights the unique surface activity of ultrathin oxide films with important implications, for example, in oxidation reactions taking place on these films or in catalyst systems where such oxides are used as a support material.« less

Time-resolved atomic force microscopy imaging studies of asymmetric PS-b-PMMA ultrathin films: Dislocation and disclination transformations, defect mobility, and evolution of nanoscale morphology

NASA Astrophysics Data System (ADS)

Hahm, J.; Sibener, S. J.

2001-03-01

Time-sequenced atomic force microscopy (AFM) studies of ultrathin films of cylinder-forming polystyrene-block-polymethylmethacrylate (PS-b-PMMA) copolymer are presented which delineate thin film mobility kinetics and the morphological changes which occur in microphase-separated films as a function of annealing temperature. Of particular interest are defect mobilities in the single layer (L thick) region, as well as the interfacial morphological changes which occur between L thick and adjacent 3L/2 thick layers, i.e., structural changes which occur during multilayer evolution. These measurements have revealed the dominant pathways by which disclinations and dislocations transform, annihilate, and topologically evolve during thermal annealing of such films. Mathematical combining equations are given to better explain such defect transformations and show the topological outcomes which result from defect-defect encounters. We also report a collective, Arrhenius-type flow of defects in localized L thick regions of the film; these are characterized by an activation energy of 377 kJ/mol. These measurements represent the first direct investigation of time-lapse interfacial morphological changes including associated defect evolution pathways for polymeric ultrathin films. Such observations will facilitate a more thorough and predictive understanding of diblock copolymer thin film dynamics, which in turn will further enable the utilization of these nanoscale phase-separated materials in a range of physical and chemical applications.

'One-component' ultrathin multilayer films based on poly(vinyl alcohol) as stabilizing coating for phenytoin-loaded liposomes.

PubMed

Zasada, Katarzyna; Łukasiewicz-Atanasov, Magdalena; Kłysik, Katarzyna; Lewandowska-Łańcucka, Joanna; Gzyl-Malcher, Barbara; Puciul-Malinowska, Agnieszka; Karewicz, Anna; Nowakowska, Maria

2015-11-01

Ultrathin "one-component" multilayer polymeric films for potential biomedical applications were designed based on polyvinyl alcohol,-a non-toxic, fully degradable synthetic polymer. Good uniformity of the obtained film and adequate adsorption properties of the polymeric layers were achieved by functional modification of the polymer, which involved synthesis of cationic and anionic derivatives. Synthesized polymers were characterized by FTIR, NMR spectroscopy, dynamic light scattering measurements and elemental analysis. The layer by layer assembly technique was used to build up a multilayer film and this process was followed using UV-Vis spectroscopy and ellipsometry. The morphology and thickness of the obtained multilayered film material was evaluated by atomic force microscopy (AFM). Preliminary studies on the application of the obtained multilayer film for coating of liposomal nanocarriers containing phenytoin, an antiarrhythmic drug, were performed. The coating effectively stabilizes liposomes and the effect increases with an increasing number of deposited layers until the polymeric film reaches the optimal thickness. The obtained release profiles suggest that bilayer-coated liposomes release phenytoin less rapidly than uncoated ones. The cytotoxicity studies performed for all obtained nanocarriers confirmed that none of them has negative effect on cell viability. All of the performed experiments suggest that liposomes coated with ultrathin film obtained from PVA derivatives can be attractive drug nanocarriers. Copyright © 2015 Elsevier B.V. All rights reserved.

Camphor-Enabled Transfer and Mechanical Testing of Centimeter-Scale Ultrathin Films.

PubMed

Wang, Bin; Luo, Da; Li, Zhancheng; Kwon, Youngwoo; Wang, Meihui; Goo, Min; Jin, Sunghwan; Huang, Ming; Shen, Yongtao; Shi, Haofei; Ding, Feng; Ruoff, Rodney S

2018-05-21

Camphor is used to transfer centimeter-scale ultrathin films onto custom-designed substrates for mechanical (tensile) testing. Compared to traditional transfer methods using dissolving/peeling to remove the support-layers, camphor is sublimed away in air at low temperature, thereby avoiding additional stress on the as-transferred films. Large-area ultrathin films can be transferred onto hollow substrates without damage by this method. Tensile measurements are made on centimeter-scale 300 nm-thick graphene oxide film specimens, much thinner than the ≈2 μm minimum thickness of macroscale graphene-oxide films previously reported. Tensile tests were also done on two different types of large-area samples of adlayer free CVD-grown single-layer graphene supported by a ≈100 nm thick polycarbonate film; graphene stiffens this sample significantly, thus the intrinsic mechanical response of the graphene can be extracted. This is the first tensile measurement of centimeter-scale monolayer graphene films. The Young's modulus of polycrystalline graphene ranges from 637 to 793 GPa, while for near single-crystal graphene, it ranges from 728 to 908 GPa (folds parallel to the tensile loading direction) and from 683 to 775 GPa (folds orthogonal to the tensile loading direction), demonstrating the mechanical performance of large-area graphene in a size scale relevant to many applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal Adatoms and Clusters on Ultrathin Zirconia Films

PubMed Central

2016-01-01

Nucleation and growth of transition metals on zirconia has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Since STM requires electrical conductivity, ultrathin ZrO2 films grown by oxidation of Pt3Zr(0001) and Pd3Zr(0001) were used as model systems. DFT studies were performed for single metal adatoms on supported ZrO2 films as well as the (1̅11) surface of monoclinic ZrO2. STM shows decreasing cluster size, indicative of increasing metal–oxide interaction, in the sequence Ag < Pd ≈ Au < Ni ≈ Fe. Ag and Pd nucleate mostly at steps and domain boundaries of ZrO2/Pt3Zr(0001) and form three-dimensional clusters. Deposition of low coverages of Ni and Fe at room temperature leads to a high density of few-atom clusters on the oxide terraces. Weak bonding of Ag to the oxide is demonstrated by removing Ag clusters with the STM tip. DFT calculations for single adatoms show that the metal–oxide interaction strength increases in the sequence Ag < Au < Pd < Ni on monoclinic ZrO2, and Ag ≈ Au < Pd < Ni on the supported ultrathin ZrO2 film. With the exception of Au, metal nucleation and growth on ultrathin zirconia films follow the usual rules: More reactive (more electropositive) metals result in a higher cluster density and wet the surface more strongly than more noble metals. These bind mainly to the oxygen anions of the oxide. Au is an exception because it can bind strongly to the Zr cations. Au diffusion may be impeded by changing its charge state between −1 and +1. We discuss differences between the supported ultrathin zirconia films and the surfaces of bulk ZrO2, such as the possibility of charge transfer to the substrate of the films. Due to their large in-plane lattice constant and the variety of adsorption sites, ZrO2{111} surfaces are more reactive than many other oxygen-terminated oxide surfaces. PMID:27213024

Superstructures and Electronic Properties of Manganese-Phthalocyanine Molecules on Au(110) from Submonolayer Coverage to Ultrathin Molecular Films.

PubMed

Topyła, M; Néel, N; Kröger, J

2016-07-12

The adsorption of manganese-phthalocyanine molecules on Au(110) was investigated using a low-temperature scanning tunneling microscope. A rich variety of commensurate superstructures was observed upon increasing the molecule coverage from submonolayers to ultrathin films. All structures were associated with reconstructions of the Au(110) substrate. Molecules adsorbed in the second molecular layer exhibited negative differential conductance occurring symmetrically around zero bias voltage. A double-barrier tunneling model rationalized this observation in terms of a peaked molecular resonance at the Fermi energy together with a voltage drop across the molecular film.

Ultrathin Polymer Films, Patterned Arrays, and Microwells

NASA Astrophysics Data System (ADS)

Yan, Mingdi

2002-05-01

The ability to control and tailor the surface and interface properties of materials is important in microelectronics, cell growth control, and lab-on-a-chip devices. Modification of material surfaces with ultrathin polymer films is attractive due to the availability of a variety of polymers either commercially or by synthesis. We have developed two approaches to the attachment of ultrathin polymer films on solid substrates. In the first method, a silane-functionalized perfluorophenyl azide (PFPA-silane) was synthesized and used to covalently immobilize polymer thin films on silicon wafers. Silanization of the wafer surface with the PFPA-silane introduced a monolayer of azido groups which in turn covalently attached the polymer film by way of photochemically initiated insertion reactions. The thickness of the film could be adjusted by the type and the molecular weight of the polymer. The method is versatile due to the general C-H and/or N-H insertion reactions of crosslinker; and therefore, no specific reactive functional groups on the polymers are required. Using this method, a new type of microwell array was fabricated from covalently immobilized polymer thin films on flat substrates. The arrays were characterized with AFM, XPS, and TOF-SIMS. The second method describes the attachment of polymer thin films on solid substrates via UV irradiation. The procedure consisted of spin-coating a polymer film and irradiating the film with UV light. Following solvent extraction, a thin film remained. The thickness of the film, from a few to over a hundred nanometers, was controlled by varying solution concentration and the molecular weight of the polymer.

Multiscale Relaxation Dynamics in Ultrathin Metallic Glass-Forming Films

NASA Astrophysics Data System (ADS)

Bi, Q. L.; Lü, Y. J.; Wang, W. H.

2018-04-01

The density layering phenomenon originating from a free surface gives rise to the layerlike dynamics and stress heterogeneity in ultrathin Cu-Zr glassy films, which facilitates the occurrence of multistep relaxations in the timescale of computer simulations. Taking advantage of this condition, we trace the relaxation decoupling and evolution with temperature simply via the intermediate scattering function. We show that the β relaxation hierarchically follows fast and slow modes in films, and there is a β -relaxation transition as the film is cooled close to the glass transition. We provide the direct observation of particle motions responsible for the β relaxation and reveal the dominant mechanism varying from the thermal activated to the cooperative jumps across the transition.

Resistive switching of organic–inorganic hybrid devices of conductive polymer and permeable ultra-thin SiO2 films

NASA Astrophysics Data System (ADS)

Yamamoto, Shunsuke; Kitanaka, Takahisa; Miyashita, Tokuji; Mitsuishi, Masaya

2018-06-01

We propose a resistive switching device composed of conductive polymer (PEDOT:PSS) and SiO2 ultra-thin films. The SiO2 film was fabricated from silsesquioxane polymer nanosheets as a resistive switching layer. Devices with metal (Ag or Au)∣SiO2∣PEDOT:PSS architecture show good resistive switching performance with set–reset voltages as low as several hundred millivolts. The device properties and the working mechanism were investigated by varying the electrode material, surrounding atmosphere, and SiO2 film thickness. Results show that resistive switching is based on water and ion migration at the PEDOT:PSS∣SiO2 interface.

Surface Acoustic Wave Monitor for Deposition and Analysis of Ultra-Thin Films

NASA Technical Reports Server (NTRS)

Hines, Jacqueline H. (Inventor)

2015-01-01

A surface acoustic wave (SAW) based thin film deposition monitor device and system for monitoring the deposition of ultra-thin films and nanomaterials and the analysis thereof is characterized by acoustic wave device embodiments that include differential delay line device designs, and which can optionally have integral reference devices fabricated on the same substrate as the sensing device, or on a separate device in thermal contact with the film monitoring/analysis device, in order to provide inherently temperature compensated measurements. These deposition monitor and analysis devices can include inherent temperature compensation, higher sensitivity to surface interactions than quartz crystal microbalance (QCM) devices, and the ability to operate at extreme temperatures.

Resistive switching of organic-inorganic hybrid devices of conductive polymer and permeable ultra-thin SiO2 films.

PubMed

Yamamoto, Shunsuke; Kitanaka, Takahisa; Miyashita, Tokuji; Mitsuishi, Masaya

2018-06-29

We propose a resistive switching device composed of conductive polymer (PEDOT:PSS) and SiO 2 ultra-thin films. The SiO 2 film was fabricated from silsesquioxane polymer nanosheets as a resistive switching layer. Devices with metal (Ag or Au)∣SiO 2 ∣PEDOT:PSS architecture show good resistive switching performance with set-reset voltages as low as several hundred millivolts. The device properties and the working mechanism were investigated by varying the electrode material, surrounding atmosphere, and SiO 2 film thickness. Results show that resistive switching is based on water and ion migration at the PEDOT:PSS∣SiO 2 interface.

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

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

Flötotto, D., E-mail: d.floetotto@is.mpg.de; Wang, Z. M.; Jeurgens, L. P. H.

2014-03-03

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al{sub 2}O{sub 3} films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively.

Enhanced Hydrogen Transport over Palladium Ultrathin Films through Surface Nanostructure Engineering.

PubMed

Abate, Salvatore; Giorgianni, Gianfranco; Gentiluomo, Serena; Centi, Gabriele; Perathoner, Siglinda

2015-11-01

Palladium ultrathin films (around 2 μm) with different surface nanostructures are characterized by TEM, SEM, AFM, and temperature programmed reduction (TPR), and evaluated in terms of H2 permeability and H2-N2 separation. A change in the characteristics of Pd seeds by controlled oxidation-reduction treatments produces films with the same thickness, but different surface and bulk nanostructure. In particular, the films have finer and more homogeneous Pd grains, which results in lower surface roughness. Although all samples show high permeo-selectivity to H2 , the samples with finer grains exhibit enhanced permeance and lower activation energy for H2 transport. The analysis of the data suggests that grain boundaries between the Pd grains at the surface favor H2 transfer from surface to subsurface. Thus, the surface nanostructure plays a relevant role in enhancing the transport of H2 over the Pd ultrathin film, which is an important aspect to develop improved membranes that function at low temperatures and toward new integrated process architectures in H2 and syngas production with enhanced sustainability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of nanoconfinement on the sputter yield in ultrathin polymeric films: Experiments and model

NASA Astrophysics Data System (ADS)

Cristaudo, Vanina; Poleunis, Claude; Delcorte, Arnaud

2018-06-01

This fundamental contribution on secondary ion mass spectrometry (SIMS) polymer depth-profiling by large argon clusters investigates the dependence of the sputter yield volume (Y) on the thickness (d) of ultrathin films as a function of the substrate nature, i.e. hard vs soft. For this purpose, thin films of polystyrene (PS) oligomers (∼4,000 amu) are spin-coated, respectively, onto silicon and poly (methyl methacrylate) supports and, then, bombarded by 10 keV Ar3000+ ions. The investigated thickness ranges from 15 to 230 nm. Additionally, the influence of the polymer molecular weight on Y(d) for PS thin films on Si is explored. The sputtering efficiency is found to be strongly dependent on the overlayer thickness, only in the case of the silicon substrate. A simple phenomenological model is proposed for the description of the thickness influence on the sputtering yield. Molecular dynamics (MD) simulations conducted on amorphous films of polyethylene-like oligomers of increasing thickness (from 2 to 20 nm), under comparable cluster bombardment conditions, predict a significant increase of the sputtering yield for ultrathin layers on hard substrates, induced by energy confinement in the polymer, and support our phenomenological model.

Layered ultra-thin coherent structures used as electrical resistors having low-temperature coefficient of resistivity

DOEpatents

Werner, T.R.; Falco, C.M.; Schuller, I.K.

1982-08-31

A thin film resistor having a controlled temperature coefficient of resistance (TCR) ranging from negative to positive degrees kelvin and having relatively high resistivity. The resistor is a multilayer superlattice crystal containing a plurality of alternating, ultra-thin layers of two different metals. TCR is varied by controlling the thickness of the individual layers. The resistor can be readily prepared by methods compatible with thin film circuitry manufacturing techniques.

Magneto-optical Kerr rotation and color in ultrathin lossy dielectric

NASA Astrophysics Data System (ADS)

Zhang, Jing; Wang, Hai; Qu, Xin; Zhou, Yun song; Li, Li na

2017-05-01

Ultra-thin optical coating comprising nanometer-thick silicon absorbing films on iron substrates can display strong optical interference effects. A resonance peak of ∼1.6^\\circ longitudinal Kerr rotation with the silicon thickness of ∼47 \\text{nm} was found at the wavelength of 660 nm. The optical properties of silicon thin films were well controlled by the sputtering power. Non-iridescence color exhibition and Kerr rotation enhancement can be manipulated and encoded individually.

Multi-Layer Coating of Ultrathin Polymer Films on Nanoparticles of Alumina by a Plasma Treatment

DTIC Science & Technology

2001-01-01

Proc. Vol. 635 © 2001 Materials Research Society Multi-Layer Coating of Ultrathin Polymer Films on Nanoparticles of Alumina by a Plasma Treatment Donglu...interconnected organic and inorganic networks results in coatings with a very low permeability for gases and liquids. Hybrid materials are very suitable for... materials consist of a clear alcoholic solution that can easily be processed by classical application techniques such as dipping, spraying, or spin coating

Optimization of ion-atomic beam source for deposition of GaN ultrathin films.

PubMed

Mach, Jindřich; Šamořil, Tomáš; Kolíbal, Miroslav; Zlámal, Jakub; Voborny, Stanislav; Bartošík, Miroslav; Šikola, Tomáš

2014-08-01

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Ultra-thin passivating film induced by vinylene carbonate on highly oriented pyrolytic graphite negative electrode in lithium-ion cell

NASA Astrophysics Data System (ADS)

Matsuoka, O.; Hiwara, A.; Omi, T.; Toriida, M.; Hayashi, T.; Tanaka, C.; Saito, Y.; Ishida, T.; Tan, H.; Ono, S. S.; Yamamoto, S.

We investigated the influence of vinylene carbonate, as an additive molecule, on the decomposition phenomena of electrolyte solution [ethylene carbonate (EC)—ethyl methyl carbonate (EMC) (1:2 by volume) containing 1 M LiPF 6] on a highly oriented pyrolytic graphite (HOPG) negative electrode by using cyclic voltammetry (CV) and atomic force microscopy (AFM). Vinylene carbonate deactivated reactive sites (e.g. radicals and oxides at the defects and the edge of carbon layer) on the cleaved surface of the HOPG negative electrode, and prevented further decomposition of the other solvents there. Further, vinylene carbonate induced an ultra-thin film (less than 1.0 nm in thickness) on the terrace of the basal plane of the HOPG negative electrode, and this film suppressed the decomposition of electrolyte solution on the terraces of the basal plane. We consider that this ultra-thin passivating film is composed of a reduction product of vinylene carbonate (VC), and might have a polymer structure. These induced effects might explain how VC improves the life performance of lithium-ion cells.

Naturally formed ultrathin V2O5 heteroepitaxial layer on VO2/sapphire(001) film

NASA Astrophysics Data System (ADS)

Littlejohn, Aaron J.; Yang, Yunbo; Lu, Zonghuan; Shin, Eunsung; Pan, KuanChang; Subramanyam, Guru; Vasilyev, Vladimir; Leedy, Kevin; Quach, Tony; Lu, Toh-Ming; Wang, Gwo-Ching

2017-10-01

Vanadium dioxide (VO2) and vanadium pentoxide (V2O5) thin films change their properties in response to external stimuli such as photons, temperature, electric field and magnetic field and have applications in electronics, optical devices, and sensors. Due to the multiple valence states of V and non-stoichiometry in thin films, it is challenging to grow epitaxial, single-phase V-oxide on a substrate, or a heterostructure of two epitaxial V-oxides. We report the formation of a heterostructure consisting of a few nm thick ultrathin V2O5 epitaxial layer on pulsed laser deposited tens of nm thick epitaxial VO2 thin films grown on single crystal Al2O3(001) substrates without post annealing of the VO2 film. The simultaneous observation of the ultrathin epitaxial V2O5 layer and VO2 epitaxial film is only possible by our unique reflection high energy electron diffraction pole figure analysis. The out-of-plane and in-plane epitaxial relationships are V2O5[100]||VO2[010]||Al2O3[001] and V2O5[03 2 bar ]||VO2[100]||Al2O3[1 1 bar 0], respectively. The existence of the V2O5 layer on the surface of the VO2 film is also supported by X-ray photoelectron spectroscopy and Raman spectroscopy.

A general strategy for hybrid thin film fabrication and transfer onto arbitrary substrates.

PubMed

Zhang, Yong; Magan, John J; Blau, Werner J

2014-04-28

The development of thin film-based structures/devices often requires thin films to be transferred onto arbitrary substrates/surfaces. Controllable and non-destructive transfer method, although highly desired, remains quite challenging. Here we report a general method for fabrication and transfer of hybrid (ultra)thin films. The proposed solution-based in-situ transfer method shows not only its robust ability for thin film transfer onto arbitrary substrates but also its highly controlled and non-destructive characteristic. With a hole structure as the support, fully-stretched free-standing thin film is prepared. The successful transfer to a curved surface demonstrates the possibility for production of thin film-coated complex optical components. Ultrathin (35 nm) hybrid film transferred onto PET (50 μm thick) shows high transparency (>90% in visible range), conductivity (1.54 × 10(4) S/m), and flexibility (radius of curvature down to mm scale). The reported transfer method would provide a powerful route towards complex thin film-based structures/devices.

A General Strategy for Hybrid Thin Film Fabrication and Transfer onto Arbitrary Substrates

PubMed Central

Zhang, Yong; Magan, John J.; Blau, Werner J.

2014-01-01

The development of thin film-based structures/devices often requires thin films to be transferred onto arbitrary substrates/surfaces. Controllable and non-destructive transfer method, although highly desired, remains quite challenging. Here we report a general method for fabrication and transfer of hybrid (ultra)thin films. The proposed solution-based in-situ transfer method shows not only its robust ability for thin film transfer onto arbitrary substrates but also its highly controlled and non-destructive characteristic. With a hole structure as the support, fully-stretched free-standing thin film is prepared. The successful transfer to a curved surface demonstrates the possibility for production of thin film-coated complex optical components. Ultrathin (35 nm) hybrid film transferred onto PET (50 μm thick) shows high transparency (>90% in visible range), conductivity (1.54 × 104 S/m), and flexibility (radius of curvature down to mm scale). The reported transfer method would provide a powerful route towards complex thin film-based structures/devices. PMID:24769689

Probing of the interfacial Heisenberg and Dzyaloshinskii-Moriya exchange interaction by magnon spectroscopy.

PubMed

Zakeri, Khalil

2017-01-11

This Topical Review presents an overview of the recent experimental results on the quantitative determination of the magnetic exchange parameters in ultrathin magnetic films and multilayers grown on different substrates. The experimental approaches for probing both the symmetric Heisenberg and the antisymmetric Dzyaloshinskii-Moriya exchange interaction in ultrathin magnetic films and at interfaces are discussed in detail. It is explained how the experimental spectrum of magnetic excitations can be used to quantify the strength of these interactions.

The Ultrathin Limit and Dead-layer Effects in Local Polarization Switching of BiFeO3

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

Maksymovych, Petro; Huijben, Mark; Pan, Minghu

Using piezoresponse force microscopy in ultra-high vacuum, polarization switching has been detected and quantified in epitaxial BiFeO3 films from 200 down to ~ 4 unit cells. Local remnant piezoresponse was used to infer the applied electric field inside the ferroelectric volume, and account for the elusive effect of dead-layers in ultrathin films. The dead-layer manifested itself in the slower than anticipated decrease of the switching bias with film thickness, yielding apparent Kay-Dunn scaling of the switching field, while the statistical analysis of hysteresis loops revealed lateral variation of the dead-layer with sub-10 nm resolution.

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

PubMed

Huang, Lizhen; Hu, Xiaorong; Chi, Lifeng

2015-09-15

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

320-nm Flexible Solution-Processed 2,7-dioctyl[1] benzothieno[3,2-b]benzothiophene Transistors.

PubMed

Ren, Hang; Tang, Qingxin; Tong, Yanhong; Liu, Yichun

2017-08-09

Flexible organic thin-film transistors (OTFTs) have received extensive attention due to their outstanding advantages such as light weight, low cost, flexibility, large-area fabrication, and compatibility with solution-processed techniques. However, compared with a rigid substrate, it still remains a challenge to obtain good device performance by directly depositing solution-processed organic semiconductors onto an ultrathin plastic substrate. In this work, ultrathin flexible OTFTs are successfully fabricated based on spin-coated 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) films. The resulting device thickness is only ~320 nm, so the device has the ability to adhere well to a three-dimension curved surface. The ultrathin C8-BTBT OTFTs exhibit a mobility as high as 4.36 cm² V -1 s -1 and an on/off current ratio of over 10⁶. These results indicate the substantial promise of our ultrathin flexible C8-BTBT OTFTs for next-generation flexible and conformal electronic devices.

320-nm Flexible Solution-Processed 2,7-dioctyl[1] benzothieno[3,2-b]benzothiophene Transistors

PubMed Central

Ren, Hang; Tang, Qingxin; Tong, Yanhong; Liu, Yichun

2017-01-01

Flexible organic thin-film transistors (OTFTs) have received extensive attention due to their outstanding advantages such as light weight, low cost, flexibility, large-area fabrication, and compatibility with solution-processed techniques. However, compared with a rigid substrate, it still remains a challenge to obtain good device performance by directly depositing solution-processed organic semiconductors onto an ultrathin plastic substrate. In this work, ultrathin flexible OTFTs are successfully fabricated based on spin-coated 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) films. The resulting device thickness is only ~320 nm, so the device has the ability to adhere well to a three-dimension curved surface. The ultrathin C8-BTBT OTFTs exhibit a mobility as high as 4.36 cm2 V−1 s−1 and an on/off current ratio of over 106. These results indicate the substantial promise of our ultrathin flexible C8-BTBT OTFTs for next-generation flexible and conformal electronic devices. PMID:28792438

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of ultrathin block copolymer films.

PubMed

Huang, Changchun; Wen, Gangyao; Li, Jingdan; Wu, Tao; Wang, Lina; Xue, Feifei; Li, Hongfei; Shi, Tongfei

2016-09-15

Effects of copolymer composition, film thickness, and solvent vapor annealing time on dewetting of spin-coated polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films (<20nm thick) were mainly investigated by atomic force microscopy. Surface chemical analysis of the ultrathin films annealed for different times were performed using X-ray photoelectron spectroscopy and contact angle measurement. With the annealing of acetone vapor, dewetting of the films with different thicknesses occur via the spinodal dewetting and the nucleation and growth mechanisms, respectively. The PS-b-PMMA films rupture into droplets which first coalesce into large ones to reduce the surface free energy. Then the large droplets rupture into small ones to increase the contact area between PMMA blocks and acetone molecules resulting from ultimate migration of PMMA blocks to droplet surface, which is a novel dewetting process observed in spin-coated films for the first time. Copyright © 2016 Elsevier Inc. All rights reserved.

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

PubMed

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

2016-08-17

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

Confined Transformation Derived Ultrathin Titanate Nanosheets/ Graphene Films for Excellent Na/K Ion Storage.

PubMed

Zeng, Cheng; Xie, Fangxi; Yang, Xianfeng; Jaroniec, Mietek; Zhang, Lei; Qiao, Shizhang

2018-05-02

Confined transformation of assembled two-dimensional MXene (titanium carbide) and reduced graphene oxide (rGO) nanosheets was employed to prepare the free-standing films of the integrated ultrathin sodium titanate (NTO)/potassium titanate (KTO) nanosheets sandwiched between graphene layers. The ultrathin Ti-based nanosheets reduce the diffusion distance while rGO layers enhance conductivity. Incorporation of graphene into the titanate films produced efficient binder-free anodes for ion storage. The resulting NTO/rGO electrode for sodium ion batteries exhibited an excellent rate performance and long cycling stability characterized by reversible capacity of 72 mA h g-1 at 5 A g-1 after 10000 cycles. Moreover, flexible KTO/rGO electrode for potassium ion batteries maintained a reversible capacity of 75 mA h g-1 after 700 cycles at 2 A g-1. These results demonstrate the superiority of the unique sandwich-type electrodes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Restoring the magnetism of ultrathin LaMn O3 films by surface symmetry engineering

NASA Astrophysics Data System (ADS)

Peng, J. J.; Song, C.; Li, F.; Gu, Y. D.; Wang, G. Y.; Pan, F.

2016-12-01

The frustration of magnetization and conductivity properties of ultrathin manganite is detrimental to their device performance, preventing their scaling down process. Here we demonstrate that the magnetism of ultrathin LaMn O3 films can be restored by a SrTi O3 capping layer, which engineers the surface from a symmetry breaking induced out-of-plane orbital occupancy to the recovered in-plane orbital occupancy. The stabilized in-plane orbital occupancy would strengthen the intralayer double exchange and thus recovers the robust magnetism. This method is proved to be effective for films as thin as 2 unit cells, greatly shrinking the critical thickness of 6 unit cells for ferromagnetic LaMn O3 as demonstrated previously [Wang et al., Science 349, 716 (2015), 10.1126/science.aaa5198]. The achievement made in this work opens up new perspectives to an active control of surface states and thereby tailors the surface functional properties of transition metal oxides.

Chain and mirophase-separated structures of ultrathin polyurethane films

NASA Astrophysics Data System (ADS)

Kojio, Ken; Uchiba, Yusuke; Yamamoto, Yasunori; Motokucho, Suguru; Furukawa, Mutsuhisa

2009-08-01

Measurements are presented how chain and microphase-separated structures of ultrathin polyurethane (PU) films are controlled by the thickness. The film thickness is varied by a solution concentration for spin coating. The systems are PUs prepared from commercial raw materials. Fourier-transform infrared spectroscopic measurement revealed that the degree of hydrogen bonding among hard segment chains decreased and increased with decreasing film thickness for strong and weak microphase separation systems, respectively. The microphase-separated structure, which is formed from hard segment domains and a surrounding soft segment matrix, were observed by atomic force microscopy. The size of hard segment domains decreased with decreasing film thickness, and possibility of specific orientation of the hard segment chains was exhibited for both systems. These results are due to decreasing space for the formation of the microphase-separated structure.

Improved metal-insulator-transition characteristics of ultrathin VO2 epitaxial films by optimized surface preparation of rutile TiO2 substrates

NASA Astrophysics Data System (ADS)

Martens, Koen; Aetukuri, Nagaphani; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.

2014-02-01

Key to the growth of epitaxial, atomically thin films is the preparation of the substrates on which they are deposited. Here, we report the growth of atomically smooth, ultrathin films of VO2 (001), only ˜2 nm thick, which exhibit pronounced metal-insulator transitions, with a change in resistivity of ˜500 times, at a temperature that is close to that of films five times thicker. These films were prepared by pulsed laser deposition on single crystalline TiO2(001) substrates that were treated by dipping in acetone, HCl and HF in successive order, followed by an anneal at 700-750 °C in flowing oxygen. This pretreatment removes surface contaminants, TiO2 defects, and provides a terraced, atomically smooth surface.

On the persistence of polar domains in ultrathin ferroelectric capacitors.

PubMed

Zubko, Pavlo; Lu, Haidong; Bark, Chung-Wung; Martí, Xavi; Santiso, José; Eom, Chang-Beom; Catalan, Gustau; Gruverman, Alexei

2017-07-19

The instability of ferroelectric ordering in ultra-thin films is one of the most important fundamental issues pertaining realization of a number of electronic devices with enhanced functionality, such as ferroelectric and multiferroic tunnel junctions or ferroelectric field effect transistors. In this paper, we investigate the polarization state of archetypal ultrathin (several nanometres) ferroelectric heterostructures: epitaxial single-crystalline BaTiO 3 films sandwiched between the most habitual perovskite electrodes, SrRuO 3 , on top of the most used perovskite substrate, SrTiO 3 . We use a combination of piezoresponse force microscopy, dielectric measurements and structural characterization to provide conclusive evidence for the ferroelectric nature of the relaxed polarization state in ultrathin BaTiO 3 capacitors. We show that even the high screening efficiency of SrRuO 3 electrodes is still insufficient to stabilize polarization in SrRuO 3 /BaTiO 3 /SrRuO 3 heterostructures at room temperature. We identify the key role of domain wall motion in determining the macroscopic electrical properties of ultrathin capacitors and discuss their dielectric response in the light of the recent interest in negative capacitance behaviour.

Ultrathin Composite Polymeric Membranes for CO2 /N2 Separation with Minimum Thickness and High CO2 Permeance.

PubMed

Benito, Javier; Sánchez-Laínez, Javier; Zornoza, Beatriz; Martín, Santiago; Carta, Mariolino; Malpass-Evans, Richard; Téllez, Carlos; McKeown, Neil B; Coronas, Joaquín; Gascón, Ignacio

2017-10-23

The use of ultrathin films as selective layers in composite membranes offers significant advantages in gas separation for increasing productivity while reducing the membrane size and energy costs. In this contribution, composite membranes have been obtained by the successive deposition of approximately 1 nm thick monolayers of a polymer of intrinsic microporosity (PIM) on top of dense membranes of the ultra-permeable poly[1-(trimethylsilyl)-1-propyne] (PTMSP). The ultrathin PIM films (30 nm in thickness) demonstrate CO 2 permeance up to seven times higher than dense PIM membranes using only 0.04 % of the mass of PIM without a significant decrease in CO 2 /N 2 selectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High resolution electron energy loss spectroscopy of spin waves in ultra-thin film - The return of the adiabatic approximation?

NASA Astrophysics Data System (ADS)

Ibach, Harald

2014-12-01

The paper reports on recent considerable improvements in electron energy loss spectroscopy (EELS) of spin waves in ultra-thin films. Spin wave spectra with 4 meV resolution are shown. The high energy resolution enables the observation of standing modes in ultra-thin films in the wave vector range of 0.15 Å- 1 < q|| < 0.3 Å- 1. In this range, Landau damping is comparatively small and standing spin wave modes are well-defined Lorentzians for which the adiabatic approximation is well suited, an approximation which was rightly dismissed by Mills and collaborators for spin waves near the Brillouin zone boundary. With the help of published exchange coupling constants, the Heisenberg model, and a simple model for the spectral response function, experimental spectra for Co-films on Cu(100) as well as for Co films capped with further copper layers are successfully simulated. It is shown that, depending on the wave vector and film thickness, the most prominent contribution to the spin wave spectrum may come from the first standing mode, not from the so-called surface mode. In general, the peak position of a low-resolution spin wave spectrum does not correspond to a single mode. A discussion of spin waves based on the "dispersion" of the peak positions in low resolution spectra is therefore subject to errors.

Combined three-axis surface magneto-optical Kerr effects in the study of surface and ultrathin-film magnetism

NASA Astrophysics Data System (ADS)

Yang, Z. J.; Scheinfein, M. R.

1993-12-01

Surface and ultrathin-film magnetocrystalline anisotropy in epitaxial fcc Fe thin films grown on room-temperature Cu(100) single crystals has been investigated, in situ, by the combined surface magneto-optical Kerr effects (SMOKE). In polar, longitudinal, and transverse Kerr effects, the direction of the applied magnetic field must be distinguished from the direction of magnetization during the switching process. For arbitrary orientations of the magnetization and field axis relative to the optical scattering plane, any of the three Kerr effects may contribute to the detected signal. A general expression for the normalized light intensity sensed by a photodiode detector, involving all three combined Kerr effects, is obtained both in the ultrathin-film limit and for bulk, at general oblique incidence angles and with different orientations of the polarizer, modulator, and analyzer. This expression is used to interpret the results of fcc Fe/Cu(100) SMOKE measurements. For films grown at room temperature, polar and longitudinal Kerr-effect magnetization loops show that the easy axis of magnetization rotates from the (canted) out-of-plane direction to the in-plane direction at a thickness of about 4.7 monolayers. Transverse Kerr-effect measurements indicate that the in-plane easy axes are biaxial.

Scaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures

NASA Astrophysics Data System (ADS)

Nagarajan, V.; Junquera, J.; He, J. Q.; Jia, C. L.; Waser, R.; Lee, K.; Kim, Y. K.; Baik, S.; Zhao, T.; Ramesh, R.; Ghosez, Ph.; Rabe, K. M.

2006-09-01

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c /a˜1.058) is maintained down to 50Å thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (ΔP) using a pulsed probe setup and the out-of-plane piezoelectric response (d33) revealed a systematic drop from ˜140μC/cm2 and 60pm/V for a 150Å thick film to 11μC/cm2 and 7pm/V for a 50Å thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180° polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity.

Ultrathin Nanocrystalline Diamond Films with Silicon Vacancy Color Centers via Seeding by 2 nm Detonation Nanodiamonds.

PubMed

Stehlik, Stepan; Varga, Marian; Stenclova, Pavla; Ondic, Lukas; Ledinsky, Martin; Pangrac, Jiri; Vanek, Ondrej; Lipov, Jan; Kromka, Alexander; Rezek, Bohuslav

2017-11-08

Color centers in diamonds have shown excellent potential for applications in quantum information processing, photonics, and biology. Here we report chemical vapor deposition (CVD) growth of nanocrystalline diamond (NCD) films as thin as 5-6 nm with photoluminescence (PL) from silicon-vacancy (SiV) centers at 739 nm. Instead of conventional 4-6 nm detonation nanodiamonds (DNDs), we prepared and employed hydrogenated 2 nm DNDs (zeta potential = +36 mV) to form extremely dense (∼1.3 × 10 13 cm -2 ), thin (2 ± 1 nm), and smooth (RMS roughness < 0.8 nm) nucleation layers on an Si/SiO x substrate, which enabled the CVD growth of such ultrathin NCD films in two different and complementary microwave (MW) CVD systems: (i) focused MW plasma with an ellipsoidal cavity resonator and (ii) pulsed MW plasma with a linear antenna arrangement. Analytical ultracentrifuge, infrared and Raman spectroscopies, atomic force microscopy, and scanning electron microscopy are used for detailed characterization of the 2 nm H-DNDs and the nucleation layer as well as the ultrathin NCD films. We also demonstrate on/off switching of the SiV center PL in the NCD films thinner than 10 nm, which is achieved by changing their surface chemistry.

Enhanced light absorption in an ultrathin silicon solar cell utilizing plasmonic nanostructures

NASA Astrophysics Data System (ADS)

Xiao, Sanshui; Mortensen, Niels A.

2012-10-01

Nowadays, bringing photovoltaics to the market is mainly limited by high cost of electricity produced by the photovoltaic solar cell. Thin-film photovoltaics offers the potential for a significant cost reduction compared to traditional photovoltaics. However, the performance of thin-film solar cells is generally limited by poor light absorption. We propose an ultrathin-film silicon solar cell configuration based on SOI structure, where the light absorption is enhanced by use of plasmonic nanostructures. By placing a one-dimensional plasmonic nanograting on the bottom of the solar cell, the generated photocurrent for a 200 nm-thickness crystalline silicon solar cell can be enhanced by 90% in the considered wavelength range. These results are paving a promising way for the realization of high-efficiency thin-film solar cells.

Local variation of fragility and glass transition temperature of ultra-thin supported polymer films.

PubMed

Hanakata, Paul Z; Douglas, Jack F; Starr, Francis W

2012-12-28

Despite extensive efforts, a definitive picture of the glass transition of ultra-thin polymer films has yet to emerge. The effect of film thickness h on the glass transition temperature T(g) has been widely examined, but this characterization does not account for the fragility of glass-formation, which quantifies how rapidly relaxation times vary with temperature T. Accordingly, we simulate supported polymer films of a bead-spring model and determine both T(g) and fragility, both as a function of h and film depth. We contrast changes in the relaxation dynamics with density ρ and demonstrate the limitations of the commonly invoked free-volume layer model. As opposed to bulk polymer materials, we find that the fragility and T(g) do not generally vary proportionately. Consequently, the determination of the fragility profile--both locally and for the film as a whole--is essential for the characterization of changes in film dynamics with confinement.

Stability of Polymer Ultrathin Films (<7 nm) Made by a Top-Down Approach.

PubMed

Bal, Jayanta Kumar; Beuvier, Thomas; Unni, Aparna Beena; Chavez Panduro, Elvia Anabela; Vignaud, Guillaume; Delorme, Nicolas; Chebil, Mohamed Souheib; Grohens, Yves; Gibaud, Alain

2015-08-25

In polymer physics, the dewetting of spin-coated polystyrene ultrathin films on silicon remains mysterious. By adopting a simple top-down method based on good solvent rinsing, we are able to prepare flat polystyrene films with a controlled thickness ranging from 1.3 to 7.0 nm. Their stability was scrutinized after a classical annealing procedure above the glass transition temperature. Films were found to be stable on oxide-free silicon irrespective of film thickness, while they were unstable (<2.9 nm) and metastable (>2.9 nm) on 2 nm oxide-covered silicon substrates. The Lifshitz-van der Waals intermolecular theory that predicts the domains of stability as a function of the film thickness and of the substrate nature is now fully reconciled with our experimental observations. We surmise that this reconciliation is due to the good solvent rinsing procedure that removes the residual stress and/or the density variation of the polystyrene films inhibiting thermodynamically the dewetting on oxide-free silicon.

Rutherford forward scattering and elastic recoil detection (RFSERD) as a method for characterizing ultra-thin films

DOE PAGES

Lohn, Andrew J.; Doyle, Barney L.; Stein, Gregory J.; ...

2014-04-03

We present a novel ion beam analysis technique combining Rutherford forward scattering and elastic recoil detection (RFSERD) and demonstrate its ability to increase efficiency in determining stoichiometry in ultrathin (5-50 nm) films as compared to Rutherford backscattering. In the conventional forward geometries, scattering from the substrate overwhelms the signal from light atoms but in RFSERD, scattered ions from the substrate are ranged out while forward scattered ions and recoiled atoms from the thin film are simultaneously detected in a single detector. Lastly, the technique is applied to tantalum oxide memristors but can be extended to a wide range of materialsmore » systems.« less

Insulator at the ultrathin limit: MgO on Ag(001).

PubMed

Schintke, S; Messerli, S; Pivetta, M; Patthey, F; Libioulle, L; Stengel, M; De Vita, A; Schneider, W D

2001-12-31

The electronic structure and morphology of ultrathin MgO films epitaxially grown on Ag(001) were investigated using low-temperature scanning tunneling spectroscopy and scanning tunneling microscopy. Layer-resolved differential conductance (dI/dU) measurements reveal that, even at a film thickness of three monolayers, a band gap of about 6 eV is formed corresponding to that of the MgO(001) single-crystal surface. This finding is confirmed by layer-resolved calculations of the local density of states based on density functional theory.

Nanopatterning of magnetic domains: Fe coverage of self-assembled alumina nanostructure

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

Wu, Qibin; Wang, Bo -Yao; Lin, Wen -Chin

2015-08-19

Nanosized ultrathin magnetic films were prepared by controlling the deposition of Fe onto an oxidized NiAl(001) surface with an alumina nanostructure on it. Because the ultrathin ferromagnetic Fe films on the bare NiAl(001) surface are separated by paramagnetic Fe nanoparticles on the alumina stripes, as determined by scanning electron microscopy with spin analysis, they form rectangular domains with sizes ranging from tens of nanometer to larger than a micrometer. Furthermore, magnetic domain patterning can thus be achieved by controlling the Fe coverage and nanostructured template.

Formation of ultrathin Ni germanides: solid-phase reaction, morphology and texture

NASA Astrophysics Data System (ADS)

van Stiphout, K.; Geenen, F. A.; De Schutter, B.; Santos, N. M.; Miranda, S. M. C.; Joly, V.; Detavernier, C.; Pereira, L. M. C.; Temst, K.; Vantomme, A.

2017-11-01

The solid-phase reaction of ultrathin (⩽10 nm) Ni films with different Ge substrates (single-crystalline (1 0 0), polycrystalline, and amorphous) was studied. As thickness goes down, thin film texture becomes a dominant factor in both the film’s phase formation and morphological evolution. As a consequence, certain metastable microstructures are epitaxially stabilized on crystalline substrates, such as the ɛ-Ni5Ge3 phase or a strained NiGe crystal structure on the single-crystalline substrates. Similarly, the destabilizing effect of axiotaxial texture on the film’s morphology becomes more pronounced as film thicknesses become smaller. These effects are contrasted by the evolution of germanide films on amorphous substrates, on which neither epitaxy nor axiotaxy can form, i.e. none of the (de)stabilizing effects of texture are observed. The crystallization of such amorphous substrates however, drives the film breakup.

Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

DOE PAGES

Wang, Siming; Antonakos, C.; Bordel, C.; ...

2016-11-07

Here, a fabrication process has been developed for high energy ion beam assisted deposition (IBAD) biaxial texturing of ultrathin (~1 nm) MgO films, using a high ion-to-atom ratio and post-deposition annealing instead of a homoepitaxial MgO layer. These films serve as the seed layer for epitaxial growth of materials on amorphous substrates such as electron/X-ray transparent membranes or nanocalorimetry devices. Stress measurements and atomic force microscopy of the MgO films reveal decreased stress and surface roughness, while X-ray diffraction of epitaxial overlayers demonstrates the improved crystal quality of films grown epitaxially on IBAD MgO. The process simplifies the synthesis ofmore » IBAD MgO, fundamentally solves the “wrinkle” issue induced by the homoepitaxial layer on sub-50 nm membranes, and enables studies of epitaxial materials in electron/X-ray transmission and nanocalorimetry.« less

Increased magnetic damping in ultrathin films of Co2FeAl with perpendicular anisotropy

NASA Astrophysics Data System (ADS)

Takahashi, Y. K.; Miura, Y.; Choi, R.; Ohkubo, T.; Wen, Z. C.; Ishioka, K.; Mandal, R.; Medapalli, R.; Sukegawa, H.; Mitani, S.; Fullerton, E. E.; Hono, K.

2017-06-01

We estimated the magnetic damping constant α of Co2FeAl (CFA) Heusler alloy films of different thicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect and ferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibited perpendicular magnetic anisotropy arising from the presence of the interface with MgO. While α increased gradually with decreasing CFA film thickness down to 1.2 nm, it was increased substantially when the thickness was reduced further to 1.0 nm. Based on the microstructure analyses and first-principles calculations, we attributed the origin of the large α in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereby in the scatterings of their spins.

Fabrication and stability investigation of ultra-thin transparent and flexible Cu-Ag-Au tri-layer film on PET

NASA Astrophysics Data System (ADS)

Prakasarao, Ch Surya; D'souza, Slavia Deeksha; Hazarika, Pratim; Karthiselva N., S.; Ramesh Babu, R.; Kovendhan, M.; Kumar, R. Arockia; Joseph, D. Paul

2018-04-01

The need for transparent conducting electrodes with high transmittance, low sheet resistance and flexibility to replace Indium Tin Oxide is ever growing. We have deposited and studied the performance of ultra-thin Cu-Ag-Au tri-layer films over a flexible poly-ethylene terephthalate substrate. Scotch tape test showed good adhesion of the metallic film. Transmittance of the tri-layer was around 40 % in visible region. Optical profiler measurements were done to study the surface features. The XRD pattern revealed that film was amorphous. Sheet resistance measured by four probe technique was around 7.7 Ohm/Δ and was stable up to 423 K. The transport parameters by Hall effect showed high conductivity and carrier concentration with a mobility of 5.58 cm2/Vs. Tests performed in an indigenously designed bending unit indicated the films to be stable both mechanically and electrically even after 50,000 bending cycles.

Composite membranes from photochemical synthesis of ultrathin polymer films

NASA Astrophysics Data System (ADS)

Liu, Chao; Martin, Charles R.

1991-07-01

THERE has recently been a resurgence of interest in synthetic membranes and membrane-based processes1-12. This is motivated by a wide variety of technological applications, such as chemical separations1-7, bioreactors and sensors8,9, energy conversion10,11 and drug-delivery systems12. Many of these technologies require the ability to prepare extremely thin, defect-free synthetic (generally polymeric) films, which are supported on microporous supports to form composite membranes. Here we describe a method for producing composite membranes of this sort that incorporate high-quality polymer films less than 50-nm thick. The method involves interfacial photopolymerization of a thin polymer film on the surface of the microporous substrate. We have been able to use this technique to synthesize a variety of functionalized ultrathin films based on electroactive, photoactive and ion-exchange polymers. We demonstrate the method here with composite membranes that show exceptional gas-transport properties.

Image potential states at transition metal oxide surfaces: A time-resolved two-photon photoemission study on ultrathin NiO films

NASA Astrophysics Data System (ADS)

Gillmeister, K.; Kiel, M.; Widdra, W.

2018-02-01

For well-ordered ultrathin films of NiO(001) on Ag(001), a series of unoccupied states below the vacuum level has been found. The states show a nearly free electron dispersion and binding energies which are typical for image potential states. By time-resolved two-photon photoemission (2PPE), the lifetimes of the first three states and their dependence on oxide film thickness are determined. For NiO film thicknesses between 2 and 4 monolayers (ML), the lifetime of the first state is in the range of 28-42 fs and shows an oscillatory behavior with increasing thickness. The values for the second state decrease monotonically from 88 fs for 2 ML to 33 fs for 4 ML. These differences are discussed in terms of coupling of the unoccupied states to the layer-dependent electronic structure of the growing NiO film.

CdO nanosheet film with a (200)-preferred orientation with sensitivity to liquefied petroleum gas (LPG) at low-temperatures.

PubMed

Cui, Guangliang; Li, Zimeng; Gao, Liang; Zhang, Mingzhe

2012-12-21

CdO nanosheet film can be synthesized by electrochemical deposition in an ultra-thin liquid layer by using Cd(NO(3))(2) and HNO(3) as source materials for Cd and oxygen respectively. HNO(3) is also used to adjust the pH of the electrolyte. Studies on the detailed structure indicate that the synthesized CdO nanosheet film has a face-centered cubic structure with (200)-preferred orientation. The response of the CdO nanosheet film to liquefied petroleum gas (LPG) at low temperature has been significantly improved by the novel structure of film. It has exhibited excellent sensitivity and selectivity to LPG at low temperature. A new growth mechanism of electrochemical deposition has been proposed to elaborate the formation of nanosheet in an ultra-thin liquid layer. The self-oscillation of potential in the growth interface and intermediate hydroxide are responsible for the formation of nanosheets.

Appearance and disappearance of ferromagnetism in ultrathin LaMnO3 on SrTiO3 substrate: A viewpoint from first principles

NASA Astrophysics Data System (ADS)

An, Ming; Weng, Yakui; Zhang, Huimin; Zhang, Jun-Jie; Zhang, Yang; Dong, Shuai

2017-12-01

The intrinsic magnetic state (ferromagnetic or antiferromagnetic) of ultrathin LaMnO3 films on the most commonly used SrTiO3 substrate is a long-existing question under debate. Either strain effect or nonstoichiometry was argued to be responsible for the experimental ferromagnetism. In a recent experiment [X. R. Wang, C. J. Li, W. M. Lü, T. R. Paudel, D. P. Leusink, M. Hoek, N. Poccia, A. Vailionis, T. Venkatesan, J. M. D. Coey, E. Y. Tsymbal, Ariando, and H. Hilgenkamp, Science 349, 716 (2015), 10.1126/science.aaa5198], one more mechanism, namely, the self-doping due to polar discontinuity, was argued to be the driving force of ferromagnetism beyond the critical thickness. Here systematic first-principles calculations have been performed to check these mechanisms in ultrathin LaMnO3 films as well as superlattices. Starting from the very precise descriptions of both LaMnO3 and SrTiO3, it is found that the compressive strain is the dominant force for the appearance of ferromagnetism, while the open surface with oxygen vacancies leads to the suppression of ferromagnetism. Within LaMnO3 layers, the charge reconstructions involve many competitive factors and certainly go beyond the intuitive polar catastrophe model established for LaAlO3/SrTiO3 heterostructures. Our paper not only explains the long-term puzzle regarding the magnetism of ultrathin LaMnO3 films but also sheds light on how to overcome the notorious magnetic dead layer in ultrathin manganites.

Large Optoelectronic Enhancement of Light-Harvesting Polymers by Chain Confinement and Charge Percolation for LEDs and Photocells Based on Ultrathin Films and CNT Nanocomposites

DTIC Science & Technology

2010-09-30

as determined by TEM. The monomers, reactants, and solvents, 2,2-bis(3amino- 4 - aminophenol )hexafluoropropane (BisAPAF), 4,6-diaminoresorcinal... aminophenol ) hexafluoropropane (BisAPAF) (377.58 mg, 1mmole), into anhydrous NMP ( 4 ml) with anhydrous pyridine (162.89 mg, 2mmole) in a dry 25ml glass...1. REPORT DATE 16 NOV 2010 2. REPORT TYPE FInal 3. DATES COVERED 07-07-2009 to 06-08-2010 4 . TITLE AND SUBTITLE Large Optoelectronic

Highly efficient ultrathin-film amorphous silicon solar cells on top of imprinted periodic nanodot arrays

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

Yan, Wensheng, E-mail: yws118@gmail.com; Gu, Min, E-mail: mgu@swin.edu.au; Tao, Zhikuo

2015-03-02

The addressing of the light absorption and conversion efficiency is critical to the ultrathin-film hydrogenated amorphous silicon (a-Si:H) solar cells. We systematically investigate ultrathin a-Si:H solar cells with a 100 nm absorber on top of imprinted hexagonal nanodot arrays. Experimental evidences are demonstrated for not only notable silver nanodot arrays but also lower-cost ITO and Al:ZnO nanodot arrays. The measured external quantum efficiency is explained by the simulation results. The J{sub sc} values are 12.1, 13.0, and 14.3 mA/cm{sup 2} and efficiencies are 6.6%, 7.5%, and 8.3% for ITO, Al:ZnO, and silver nanodot arrays, respectively. Simulated optical absorption distribution shows high lightmore » trapping within amorphous silicon layer.« less

Large-area synthesis of WSe2 from WO3 by selenium-oxygen ion exchange

NASA Astrophysics Data System (ADS)

Browning, Paul; Eichfeld, Sarah; Zhang, Kehao; Hossain, Lorraine; Lin, Yu-Chuan; Wang, Ke; Lu, Ning; Waite, A. R.; Voevodin, A. A.; Kim, Moon; Robinson, Joshua A.

2015-03-01

Few-layer tungsten diselenide (WSe2) is attractive as a next-generation electronic material as it exhibits modest carrier mobilities and energy band gap in the visible spectra, making it appealing for photovoltaic and low-powered electronic applications. Here we demonstrate the scalable synthesis of large-area, few-layer WSe2 via replacement of oxygen in hexagonally stabilized tungsten oxide films using dimethyl selenium. Cross-sectional transmission electron microscopy reveals successful control of the final WSe2 film thickness through control of initial tungsten oxide thickness, as well as development of layered films with grain sizes up to several hundred nanometers. Raman spectroscopy and atomic force microscopy confirms high crystal uniformity of the converted WSe2, and time domain thermo-reflectance provide evidence that near record low thermal conductivity is achievable in ultra-thin WSe2 using this method.

Ultrathin Au film on polymer surface for surface plasmon polariton waveguide application

NASA Astrophysics Data System (ADS)

Liu, Tong; Ji, Lanting; He, Guobing; Sun, Xiaoqiang; Wang, Fei; Zhang, Daming

2017-11-01

Formation of laterally continuous ultrathin gold films on polymer substrates is a technological challenge. In this work, the vacuum thermal evaporation method is adopted to form continuous Au films in the thickness range of 7-17 nm on polymers of Poly(methyl-methacrylate-glycidly-methacrylate) and SU-8 film surface without using the adhesion or metallic seeding layers. Absorption spectrum, scanning electron microscope and atomic force microscope images are used to characterize the Au film thickness, roughness and optical loss. The result shows that molecular-scale structure, surface energy and electronegativity have impacts on the Au film morphology on polymers. Wet chemical etching is used to fabricate 7-nm thick Au stripes embedded in polymer claddings. These long-range surface plasmon polariton waveguides demonstrate the favorable morphological configurations and cross-sectional states. Through the end-fire excitation method, propagation losses of 6-μm wide Au stripes are compared to theoretical values and analyzed from practical film status. The smooth, patternable gold films on polymer provide potential applications to plasmonic waveguides, biosensing, metamaterials and optical antennas.

Computational Study of In-Plane Phonon Transport in Si Thin Films

PubMed Central

Wang, Xinjiang; Huang, Baoling

2014-01-01

We have systematically investigated the in-plane thermal transport in Si thin films using an approach based on the first-principles calculations and lattice dynamics. The effects of phonon mode depletion induced by the phonon confinement and the corresponding variation in interphonon scattering, which may be important for the thermal conductivities of ultra-thin films but are often neglected in precedent studies, are considered in this study. The in-plane thermal conductivities of Si thin films with different thicknesses have been predicted over a temperature range from 80 K to 800 K and excellent agreements with experimental results are found. The validities of adopting the bulk phonon properties and gray approximation of surface specularity in thin film studies have been clarified. It is found that in ultra-thin films, while the phonon depletion will reduce the thermal conductivity of Si thin films, its effect is largely offset by the reduction in the interphonon scattering rate. The contributions of different phonon modes to the thermal transport and isotope effects in Si films with different thicknesses under various temperatures are also analyzed. PMID:25228061

Transport properties of ultrathin BaFe1.84Co0.16As2 superconducting nanowires

NASA Astrophysics Data System (ADS)

Yuan, Pusheng; Xu, Zhongtang; Li, Chen; Quan, Baogang; Li, Junjie; Gu, Changzhi; Ma, Yanwei

2018-07-01

Superconducting nanowire single-photon detectors (SNSPDs) have an absolute advantage over other types of single-photon detectors, except for the low operating temperature. Therefore, much effort has been devoted to finding high-temperature superconducting materials that are suitable for preparing SNSPDs. Copper-based and MgB2 ultrathin superconducting nanowires have already been reported. However, the transport properties of iron-based ultrathin superconducting nanowires have not been studied. In this work, a 10 nm thick × 200 nm wide × 30 μm long high-quality superconducting nanowire was fabricated from ultrathin BaFe1.84Co0.16As2 films by a lift-off process. The precursor BaFe1.84Co0.16As2 film with a thickness of 10 nm and root-mean-square roughness of 1 nm was grown on CaF2 substrates by pulsed laser deposition. The nanowire shows a high superconducting critical temperature {T}{{c}}{{zero}} = 20 K with a narrow transition width of ΔT = 2.5 K and exhibits a high critical current density J c of 1.8 × 107 A cm-2 at 10 K. These results of ultrathin BaFe1.84Co0.16As2 nanowire will attract interest in electronic applications, including SNSPDs.

Stabilization of ultrathin (hydroxy)oxide films on transition metal substrates for electrochemical energy conversion

NASA Astrophysics Data System (ADS)

Zeng, Zhenhua; Chang, Kee-Chul; Kubal, Joseph; Markovic, Nenad M.; Greeley, Jeffrey

2017-06-01

Design of cost-effective electrocatalysts with enhanced stability and activity is of paramount importance for the next generation of energy conversion systems, including fuel cells and electrolysers. However, electrocatalytic materials generally improve one of these properties at the expense of the other. Here, using density functional theory calculations and electrochemical surface science measurements, we explore atomic-level features of ultrathin (hydroxy)oxide films on transition metal substrates and demonstrate that these films exhibit both excellent stability and activity for electrocatalytic applications. The films adopt structures with stabilities that significantly exceed bulk Pourbaix limits, including stoichiometries not found in bulk and properties that are tunable by controlling voltage, film composition, and substrate identity. Using nickel (hydroxy)oxide/Pt(111) as an example, we further show how the films enhance activity for hydrogen evolution through a bifunctional effect. The results suggest design principles for this class of electrocatalysts with simultaneously enhanced stability and activity for energy conversion.

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

Plessow, Philipp N.; Bajdich, Michal; Greene, Joshua

The formation of thin oxide films on metal supports is an important phenomenon, especially in the context of strong metal support interaction (SMSI). Computational predictions of the stability of these films are hampered by their structural complexity and a varying lattice mismatch with different supports. In this study, we report a large combination of supports and ultrathin oxide films studied with density functional theory (DFT). Trends in stability are investigated through a descriptor-based analysis. Since the studied films are bound to the support exclusively through metal–metal interaction, the adsorption energy of the oxide-constituting metal atom can be expected to bemore » a reasonable descriptor for the stability of the overlayers. If the same supercell is used for all supports, the overlayers experience different amounts of stress. Using supercells with small lattice mismatch for each system leads to significantly improved scaling relations for the stability of the overlayers. Finally, this approach works well for the studied systems and therefore allows the descriptor-based exploration of the thermodynamic stability of supported thin oxide layers.« less

Palladium-directed self-assembly of multi-titanium(IV)-porphyrin arrays on the substrate surface as sensitive ultrathin films for hydrogen peroxide sensing, photocurrent generation, and photochromism of viologen

NASA Astrophysics Data System (ADS)

He, Wen-Li; Fang, Fang; Ma, Dong-Mei; Chen, Meng; Qian, Dong-Jin; Liu, Minghua

2018-01-01

Multiporphyrin arrays are large, π-conjugated chromophores with high absorption efficiency and strong chemical stability that play an important role in supramolecular and advanced material sciences. Palladium-directed self-assembly of multiporphyrin array ultrathin films was achieved on substrate surfaces using oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium (IV) complex [TiO(TPyP)] as a linker and sodium tetrachloropalladate (Na2PdCl4) as a connector. The Pd-TiOTPyP films as prepared were characterized by using UV-vis absorption and X-ray photoelectron spectroscopy, as well as by atomic force and scanning electron microscopy. The Soret absorption band of TiOTPyP was observed to red shift by 6 nm when the Pd-TiOTPyP multilayer-modified quartz substrate was immersed in an aqueous solution containing hydrogen peroxide. This was attributed to the formation of a TiO2TPyP monoperoxo complex. This oxidation reaction could be accelerated in an acidic solution. Furthermore, the immobilized Pd-TiOTPyP multilayers could act as light-harvesting units for photocurrent generation and photochromism of viologens, with strong stability, reproducibility, and recyclability. The photocurrent density could be enhanced in electrolyte solutions containing electron donors such as triethanolamine, or electron acceptors such as viologens. Finally, photoinduced reduction (photochromism) of viologens was investigated using the Pd-TiOTPyP multilayers as light sensitizers and EDTA as the electron donors.

Transport properties of ultra-thin VO2 films on (001) TiO2 grown by reactive molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Paik, Hanjong; Moyer, Jarrett A.; Spila, Timothy; Tashman, Joshua W.; Mundy, Julia A.; Freeman, Eugene; Shukla, Nikhil; Lapano, Jason M.; Engel-Herbert, Roman; Zander, Willi; Schubert, Jürgen; Muller, David A.; Datta, Suman; Schiffer, Peter; Schlom, Darrell G.

2015-10-01

We report the growth of (001)-oriented VO2 films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2 substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2 films with abrupt MIT behavior.

Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O

DOE PAGES

Cockayne, Eric; Mihalkovič, Marek; Henley, Christopher L.

2016-01-07

Here, we model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO 3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti 7O 7, pores. The quasicrystal structue is a simple decoration of three types of tiles: square, triangle and 30° rhombus, with edge lengths 6.85 Å, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, andmore » identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.« less

Ultrathin pyrolytic carbon films on a magnetic substrate

NASA Astrophysics Data System (ADS)

Umair, Ahmad; Raza, Tehseen Z.; Raza, Hassan

2016-07-01

We report the growth of ultrathin pyrolytic carbon (PyC) films on nickel substrate by using chemical vapor deposition at 1000 °C under methane ambience. We find that the ultra-fast cooling is crucial for PyC film uniformity by controlling the segregation of carbon on nickel. We characterize the in-plane crystal size of the PyC film by using Raman spectroscopy. The Raman peaks at ˜1354 and ˜1584 cm-1 wavenumbers are used to extract the D and G bands. The corresponding peak intensities are then used in an excitation energy dependent equation to calculate the in-plane crystal size. Using Raman area mapping, the mean value of in-plane crystal size over an area of 100 μm × 100 μm is about 22.9 nm with a standard deviation of about 2.4 nm.

Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1.

PubMed

Ogieglo, Wojciech; Furchner, Andreas; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, Matthias

2017-11-02

Mixed-penetrant sorption into ultrathin films of a superglassy polymer of intrinsic microporosity (PIM-1) was studied for the first time by using interference-enhanced in situ spectroscopic ellipsometry. PIM-1 swelling and the concurrent changes in its refractive index were determined in ultrathin (12-14 nm) films exposed to pure and mixed penetrants. The penetrants included water, n-hexane, and ethanol and were chosen on the basis of their significantly different penetrant-penetrant and penetrant-polymer affinities. This allowed studying microporous polymer responses at diverse ternary compositions and revealed effects such as competition for the sorption sites (for water/n-hexane or ethanol/n-hexane) or enhancement in sorption of typically weakly sorbing water in the presence of more highly sorbing ethanol. The results reveal details of the mutual sorption effects which often complicate comprehension of glassy polymers' behavior in applications such as high-performance membranes, adsorbents, or catalysts. Mixed-penetrant effects are typically very challenging to study directly, and their understanding is necessary owing to a broadly recognized inadequacy of simple extrapolations from measurements in a pure component environment.

Numerical experiments on evaporation and explosive boiling of ultra-thin liquid argon film on aluminum nanostructure substrate

NASA Astrophysics Data System (ADS)

Wang, Weidong; Zhang, Haiyan; Tian, Conghui; Meng, Xiaojie

2015-04-01

Evaporation and explosive boiling of ultra-thin liquid film are of great significant fundamental importance for both science and engineering applications. The evaporation and explosive boiling of ultra-thin liquid film absorbed on an aluminum nanostructure solid wall are investigated by means of molecular dynamics simulations. The simulated system consists of three regions: liquid argon, vapor argon, and an aluminum substrate decorated with nanostructures of different heights. Those simulations begin with an initial configuration for the complex liquid-vapor-solid system, followed by an equilibrating system at 90 K, and conclude with two different jump temperatures, including 150 and 310 K which are far beyond the critical temperature. The space and time dependences of temperature, pressure, density number, and net evaporation rate are monitored to investigate the phase transition process on a flat surface with and without nanostructures. The simulation results reveal that the nanostructures are of great help to raise the heat transfer efficiency and that evaporation rate increases with the nanostructures' height in a certain range.

Numerical experiments on evaporation and explosive boiling of ultra-thin liquid argon film on aluminum nanostructure substrate.

PubMed

Wang, Weidong; Zhang, Haiyan; Tian, Conghui; Meng, Xiaojie

2015-01-01

Evaporation and explosive boiling of ultra-thin liquid film are of great significant fundamental importance for both science and engineering applications. The evaporation and explosive boiling of ultra-thin liquid film absorbed on an aluminum nanostructure solid wall are investigated by means of molecular dynamics simulations. The simulated system consists of three regions: liquid argon, vapor argon, and an aluminum substrate decorated with nanostructures of different heights. Those simulations begin with an initial configuration for the complex liquid-vapor-solid system, followed by an equilibrating system at 90 K, and conclude with two different jump temperatures, including 150 and 310 K which are far beyond the critical temperature. The space and time dependences of temperature, pressure, density number, and net evaporation rate are monitored to investigate the phase transition process on a flat surface with and without nanostructures. The simulation results reveal that the nanostructures are of great help to raise the heat transfer efficiency and that evaporation rate increases with the nanostructures' height in a certain range.

Electronic-Reconstruction-Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films.

PubMed

Wang, Lingfei; Kim, Rokyeon; Kim, Yoonkoo; Kim, Choong H; Hwang, Sangwoon; Cho, Myung Rae; Shin, Yeong Jae; Das, Saikat; Kim, Jeong Rae; Kalinin, Sergei V; Kim, Miyoung; Yang, Sang Mo; Noh, Tae Won

2017-11-01

Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic-device applications. In the few-nanometers-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO 3 films as a model system, an intrinsic tunneling-conductance enhancement is reported near the terrace edges. Scanning-probe-microscopy results demonstrate the existence of highly conductive regions (tens of nanometers wide) near the terrace edges. First-principles calculations suggest that the terrace-edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling-conductance enhancement can be discovered in other transition metal oxides and controlled by surface-termination engineering. The controllable electronic reconstruction can facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

"Un-annealed and Annealed Pd Ultra-Thin Film on SiC Characterized by Scanning Probe Microscopy and X-ray Photoelectron Spectroscopy"

NASA Technical Reports Server (NTRS)

Lu, W. J.; Shi, D. T.; Elshot, K.; Bryant, E.; Lafate, K.; Chen, H.; Burger, A.; Collins, W. E.

1998-01-01

Pd/SiC has been used as a hydrogen and a hydrocarbon gas sensor operated at high temperature. UHV (Ultra High Vacuum)-Scanning Tunneling Microscopy (STM), Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) techniques were applied to study the relationship between the morphology and chemical compositions for Pd ultra-thin films on SiC (less than 30 angstroms) at different annealing temperatures. Pd ultra-thin film on 6H-SiC was prepared by the RF sputtering method. The morphology from UHV-STM and AFM shows that the Pd thin film was well deposited on SiC substrate, and the Pd was partially aggregated to round shaped participates at an annealing temperature of 300 C. At 400 C, the amount of surface participates decreases, and some strap shape participates appear. From XPS, Pd2Si was formed on the surface after annealing at 300 C, and all Pd reacted with SiC to form Pd2Si after annealing at 400 C. The intensity of the XPS Pd peak decreases enormously at 400 C. The Pd film diffused into SiC, and the Schottky barrier height has almost no changes. The work shows the Pd sicilides/SiC have the same electronic properties with Pd/SiC, and explains why the Pd/SiC sensor still responds to hydrogen at high operating temperatures.

Periodically pulsed wet annealing approach for low-temperature processable amorphous InGaZnO thin film transistors with high electrical performance and ultrathin thickness

PubMed Central

Kim, Ye Kyun; Ahn, Cheol Hyoun; Yun, Myeong Gu; Cho, Sung Woon; Kang, Won Jun; Cho, Hyung Koun

2016-01-01

In this paper, a simple and controllable “wet pulse annealing” technique for the fabrication of flexible amorphous InGaZnO thin film transistors (a-IGZO TFTs) processed at low temperature (150 °C) by using scalable vacuum deposition is proposed. This method entailed the quick injection of water vapor for 0.1 s and purge treatment in dry ambient in one cycle; the supply content of water vapor was simply controlled by the number of pulse repetitions. The electrical transport characteristics revealed a remarkable performance of the a-IGZO TFTs prepared at the maximum process temperature of 150 °C (field-effect mobility of 13.3 cm2 V−1 s−1; Ion/Ioff ratio ≈ 108; reduced I-V hysteresis), comparable to that of a-IGZO TFTs annealed at 350 °C in dry ambient. Upon analysis of the angle-resolved x-ray photoelectron spectroscopy, the good performance was attributed to the effective suppression of the formation of hydroxide and oxygen-related defects. Finally, by using the wet pulse annealing process, we fabricated, on a plastic substrate, an ultrathin flexible a-IGZO TFT with good electrical and bending performances. PMID:27198067

Periodically pulsed wet annealing approach for low-temperature processable amorphous InGaZnO thin film transistors with high electrical performance and ultrathin thickness.

PubMed

Kim, Ye Kyun; Ahn, Cheol Hyoun; Yun, Myeong Gu; Cho, Sung Woon; Kang, Won Jun; Cho, Hyung Koun

2016-05-20

In this paper, a simple and controllable "wet pulse annealing" technique for the fabrication of flexible amorphous InGaZnO thin film transistors (a-IGZO TFTs) processed at low temperature (150 °C) by using scalable vacuum deposition is proposed. This method entailed the quick injection of water vapor for 0.1 s and purge treatment in dry ambient in one cycle; the supply content of water vapor was simply controlled by the number of pulse repetitions. The electrical transport characteristics revealed a remarkable performance of the a-IGZO TFTs prepared at the maximum process temperature of 150 °C (field-effect mobility of 13.3 cm(2) V(-1) s(-1); Ion/Ioff ratio ≈ 10(8); reduced I-V hysteresis), comparable to that of a-IGZO TFTs annealed at 350 °C in dry ambient. Upon analysis of the angle-resolved x-ray photoelectron spectroscopy, the good performance was attributed to the effective suppression of the formation of hydroxide and oxygen-related defects. Finally, by using the wet pulse annealing process, we fabricated, on a plastic substrate, an ultrathin flexible a-IGZO TFT with good electrical and bending performances.

Selection and Manufacturing of Membrane Materials for Solar Sails

NASA Technical Reports Server (NTRS)

Bryant, Robert G.; Seaman, Shane T.; Wilkie, W. Keats; Miyaucchi, Masahiko; Working, Dennis C.

2013-01-01

Commercial metallized polyimide or polyester films and hand-assembly techniques are acceptable for small solar sail technology demonstrations, although scaling this approach to large sail areas is impractical. Opportunities now exist to use new polymeric materials specifically designed for solar sailing applications, and take advantage of integrated sail manufacturing to enable large-scale solar sail construction. This approach has, in part, been demonstrated on the JAXA IKAROS solar sail demonstrator, and NASA Langley Research Center is now developing capabilities to produce ultrathin membranes for solar sails by integrating resin synthesis with film forming and sail manufacturing processes. This paper will discuss the selection and development of polymer material systems for space, and these new processes for producing ultrathin high-performance solar sail membrane films.

Fabrication of ultrathin film capacitors by chemical solution deposition

DOE PAGES

Brennecka, Geoff L.; Tuttle, Bruce A.

2007-10-01

We present that a facile solution-based processing route using standard spin-coating deposition techniques has been developed for the production of reliable capacitors based on lead lanthanum zirconate titanate (PLZT) with active areas of ≥1 mm 2 and dielectric layer thicknesses down to 50 nm. With careful control of the dielectric phase development through improved processing, ultrathin capacitors exhibited slim ferroelectric hysteresis loops and dielectric constants of >1000, similar to those of much thicker films. Furthermore, it has been demonstrated that chemical solution deposition is a viable route to the production of capacitor films which are as thin as 50 nmmore » but are still macroscopically addressable with specific capacitance values >160 nF/mm 2.« less

Silicon nanomembranes as a means to evaluate stress evolution in deposited thin films

Treesearch

Anna M. Clausen; Deborah M. Paskiewicz; Alireza Sadeghirad; Joseph Jakes; Donald E. Savage; Donald S. Stone; Feng Liu; Max G. Lagally

2014-01-01

Thin-film deposition on ultra-thin substrates poses unique challenges because of the potential for a dynamic response to the film stress during deposition. While theoretical studies have investigated film stress related changes in bulk substrates, little has been done to learn how stress might evolve in a film growing on a compliant substrate. We use silicon...

Vanadium dioxide film protected with an atomic-layer-deposited Al{sub 2}O{sub 3} thin film

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

Wang, Xiao; Cao, Yunzhen, E-mail: yzhcao@mail.sic.ac.cn; Yang, Chao

2016-01-15

A VO{sub 2} film exposed to ambient air is prone to oxidation, which will degrade its thermochromic properties. In this work, the authors deposited an ultrathin Al{sub 2}O{sub 3} film with atomic layer deposition (ALD) to protect the underlying VO{sub 2} film from degradation, and then studied the morphology and crystalline structure of the films. To assess the protectiveness of the Al{sub 2}O{sub 3} capping layer, the authors performed a heating test and a damp heating test. An ultrathin 5-nm-thick ALD Al{sub 2}O{sub 3} film was sufficient to protect the underlying VO{sub 2} film heated at 350 °C. However, in amore » humid environment at prolonged durations, a thicker ALD Al{sub 2}O{sub 3} film (15 nm) was required to protect the VO{sub 2}. The authors also deposited and studied a TiO{sub 2}/Al{sub 2}O{sub 3} bilayer, which significantly improved the protectiveness of the Al{sub 2}O{sub 3} film in a humid environment.« less

How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?

PubMed

Ogieglo, Wojciech; Rahimi, Khosorov; Rauer, Sebastian Bernhard; Ghanem, Bader; Ma, Xiaohua; Pinnau, Ingo; Wessling, Matthias

2017-07-27

Dynamic sorption of ethanol and toluene vapor into ultrathin supported films of polymer of intrinsic microporosity PIM-1 down to a thickness of 6 nm are studied with a combination of in situ spectroscopic ellipsometry and in situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphology. For ethanol below 20 nm, three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to that of thicker films. Second, at low penetrant activities (below 0.3p/p 0 ), films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite a similar swelling magnitude. Third, for the ultrathin films, the onset of the dynamic penetrant-induced glass transition P g has been found to shift to higher values, indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the superglassy PIM-1 at the substrate surface leads to an arrested, even more rigid, and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics, and two distinct penetrant-induced relaxation phenomena, probably associated with the film outer surface and the bulk, are detected. Following the direction of the penetrant's diffusion, the surface seems to plasticize earlier than the bulk, and the two relaxations remain well separated down to 6 nm film thickness, where they remarkably merge to form just a single relaxation.

A novel interferometric method for the study of the viscoelastic properties of ultra-thin polymer films determined from nanobubble inflation

NASA Astrophysics Data System (ADS)

Chapuis, P.; Montgomery, P. C.; Anstotz, F.; Leong-Hoï, A.; Gauthier, C.; Baschnagel, J.; Reiter, G.; McKenna, G. B.; Rubin, A.

2017-09-01

Glass formation and glassy behavior remain as the important areas of investigation in soft matter physics with many aspects which are still not completely understood, especially at the nanometer size-scale. In the present work, we show an extension of the "nanobubble inflation" method developed by O'Connell and McKenna [Rev. Sci. Instrum. 78, 013901 (2007)] which uses an interferometric method to measure the topography of a large array of 5 μ m sized nanometer thick films subjected to constant inflation pressures during which the bubbles grow or creep with time. The interferometric method offers the possibility of making measurements on multiple bubbles at once as well as having the advantage over the AFM methods of O'Connell and McKenna of being a true non-contact method. Here we demonstrate the method using ultra-thin films of both poly(vinyl acetate) (PVAc) and polystyrene (PS) and discuss the capabilities of the method relative to the AFM method, its advantages and disadvantages. Furthermore we show that the results from experiments on PVAc are consistent with the prior work on PVAc, while high stress results with PS show signs of a new non-linear response regime that may be related to the plasticity of the ultra-thin film.

Operando SXRD of E-ALD deposited sulphides ultra-thin films: Crystallite strain and size

NASA Astrophysics Data System (ADS)

Giaccherini, Andrea; Russo, Francesca; Carlà, Francesco; Guerri, Annalisa; Picca, Rosaria Anna; Cioffi, Nicola; Cinotti, Serena; Montegrossi, Giordano; Passaponti, Maurizio; Di Benedetto, Francesco; Felici, Roberto; Innocenti, Massimo

2018-02-01

Electrochemical Atomic Layer Deposition (E-ALD), exploiting surface limited electrodeposition of atomic layers, can easily grow highly ordered ultra-thin films and 2D structures. Among other compounds CuxZnyS grown by means of E-ALD on Ag(111) has been found particularly suitable for the solar energy conversion due to its band gap (1.61 eV). However its growth seems to be characterized by a micrometric thread-like structure, probably overgrowing a smooth ultra-thin films. On this ground, a SXRD investigation has been performed, to address the open questions about the structure and the growth of CuxZnyS by means of E-ALD. The experiment shows a pseudo single crystal pattern as well as a powder pattern, confirming that part of the sample grows epitaxially on the Ag(111) substrate. The growth of the film was monitored by following the evolution of the Bragg peaks and Debye rings during the E-ALD steps. Breadth and profile analysis of the Bragg peaks lead to a qualitative interpretation of the growth mechanism. This study confirms that Zn lead to the growth of a strained Cu2S-like structure, while the growth of the thread-like structure is probably driven by the release of the stress from the epitaxial phase.

Omnidirectional, broadband light absorption using large-area, ultrathin lossy metallic film coatings

NASA Astrophysics Data System (ADS)

Li, Zhongyang; Palacios, Edgar; Butun, Serkan; Kocer, Hasan; Aydin, Koray

2015-10-01

Resonant absorbers based on nanostructured materials are promising for variety of applications including optical filters, thermophotovoltaics, thermal emitters, and hot-electron collection. One of the significant challenges for such micro/nanoscale featured medium or surface, however, is costly lithographic processes for structural patterning which restricted from industrial production of complex designs. Here, we demonstrate lithography-free, broadband, polarization-independent optical absorbers based on a three-layer ultrathin film composed of subwavelength chromium (Cr) and oxide film coatings. We have measured almost perfect absorption as high as 99.5% across the entire visible regime and beyond (400-800 nm). In addition to near-ideal absorption, our absorbers exhibit omnidirectional independence for incidence angle over ±60 degrees. Broadband absorbers introduced in this study perform better than nanostructured plasmonic absorber counterparts in terms of bandwidth, polarization and angle independence. Improvements of such “blackbody” samples based on uniform thin-film coatings is attributed to extremely low quality factor of asymmetric highly-lossy Fabry-Perot cavities. Such broadband absorber designs are ultrathin compared to carbon nanotube based black materials, and does not require lithographic processes. This demonstration redirects the broadband super absorber design to extreme simplicity, higher performance and cost effective manufacturing convenience for practical industrial production.

Rapid amperometric detection of trace metals by inhibition of an ultrathin polypyrrole-based glucose biosensor.

PubMed

Ayenimo, Joseph G; Adeloju, Samuel B

2016-02-01

A sensitive and reliable inhibitive amperometric glucose biosensor is described for rapid trace metal determination. The biosensor utilises a conductive ultrathin (55 nm thick) polypyrrole (PPy) film for entrapment of glucose oxidase (GOx) to permit rapid inhibition of GOx activity in the ultrathin film upon exposure to trace metals, resulting in reduced glucose amperometric response. The biosensor demonstrates a relatively fast response time of 20s and does not require incubation. Furthermore, a complete recovery of GOx activity in the ultrathin PPy-GOx biosensor is quickly achieved by washing in 2mM EDTA for only 10s. The minimum detectable concentrations achieved with the biosensor for Hg(2+), Cu(2+), Pb(2+) and Cd(2+) by inhibitive amperometric detection are 0.48, 1.5, 1.6 and 4.0 µM, respectively. Also, suitable linear concentration ranges were achieved from 0.48-3.3 µM for Hg(2+), 1.5-10 µM for Cu(2+), 1.6-7.7 µM for Pb(2+) and 4-26 µM for Cd(2+). The use of Dixon and Cornish-Bowden plots revealed that the suppressive effects observed with Hg(2+) and Cu(2+) were via non-competitive inhibition, while those of Pb(2+) and Cd(2+) were due to mixed and competitive inhibition. The stronger inhibition exhibited by the trace metals on GOx activity in the ultrathin PPy-GOx film was also confirmed by the low inhibition constant obtained from this analysis. The biosensor was successfully applied to the determination of trace metals in tap water samples. Copyright © 2015 Elsevier B.V. All rights reserved.

High electron mobility and quantum oscillations in non-encapsulated ultrathin semiconducting Bi2O2Se

NASA Astrophysics Data System (ADS)

Wu, Jinxiong; Yuan, Hongtao; Meng, Mengmeng; Chen, Cheng; Sun, Yan; Chen, Zhuoyu; Dang, Wenhui; Tan, Congwei; Liu, Yujing; Yin, Jianbo; Zhou, Yubing; Huang, Shaoyun; Xu, H. Q.; Cui, Yi; Hwang, Harold Y.; Liu, Zhongfan; Chen, Yulin; Yan, Binghai; Peng, Hailin

2017-07-01

High-mobility semiconducting ultrathin films form the basis of modern electronics, and may lead to the scalable fabrication of highly performing devices. Because the ultrathin limit cannot be reached for traditional semiconductors, identifying new two-dimensional materials with both high carrier mobility and a large electronic bandgap is a pivotal goal of fundamental research. However, air-stable ultrathin semiconducting materials with superior performances remain elusive at present. Here, we report ultrathin films of non-encapsulated layered Bi2O2Se, grown by chemical vapour deposition, which demonstrate excellent air stability and high-mobility semiconducting behaviour. We observe bandgap values of ˜0.8 eV, which are strongly dependent on the film thickness due to quantum-confinement effects. An ultrahigh Hall mobility value of >20,000 cm2 V-1 s-1 is measured in as-grown Bi2O2Se nanoflakes at low temperatures. This value is comparable to what is observed in graphene grown by chemical vapour deposition and at the LaAlO3-SrTiO3 interface, making the detection of Shubnikov-de Haas quantum oscillations possible. Top-gated field-effect transistors based on Bi2O2Se crystals down to the bilayer limit exhibit high Hall mobility values (up to 450 cm2 V-1 s-1), large current on/off ratios (>106) and near-ideal subthreshold swing values (˜65 mV dec-1) at room temperature. Our results make Bi2O2Se a promising candidate for future high-speed and low-power electronic applications.

Seeds screening aqueous synthesis, multiphase interfacial separation and in situ optical characterization of invisible ultrathin silver nanowires.

PubMed

Zhang, Xiao-Yang; Xue, Xiao-Mei; Zhou, Huan-Li; Zhao, Ning; Shan, Feng; Su, Dan; Liu, Yi-Ran; Zhang, Tong

2018-06-21

We report a multi-step synthetic method to obtain ultrathin silver nanowires (Ag NWs) from an aqueous solution with a ∼17 nm diameter average, and where some of them decreased down to 9 nm. Carefully designed seed screening processes including LED irradiation at high temperature for a short time, and then continuous H2O2 etching, and relative growth mechanisms of high-yield five-twinned pentagonal seeds and ultrathin Ag NWs in aqueous environment are detailed. Then, a rapid and simple multiphase interfacial assembly method particularly suitable for the separation of ultrathin Ag NWs from various by-products was demonstrated with a clear mechanism explanation. Next, a unique optical interaction between light and individual AG NWs, as well as feature structures in the AG NWs film, was investigated by a micro-domain optical confocal microscope measurement in situ together with a theoretical explanation using modal transmission theory. That revealed that the haze problem of AG NWs films was not only arising from the interaction between light and individual or crossed Ag NWs but was also greatly dependent on a weak coupling effect of leaky modes supported by adjacent Ag NWs with large distances which had not been considered before. We then provided direct experimental evidence and concluded how to obtain haze-free films with 100% transparency in the whole visible range based on ultrathin Ag NWs. This breakthrough in diameter confinement and purification of Ag NWs is a highly expected step to overcome the well-focused light diffusion and absorption problems of Ag NWs-based devices applied in various fields such as flexible electronics, high-clarity displays, visible transparent heaters, photovoltaics and various optoelectronic technologies.

EDMOS in ultrathin FDSOI: Impact of the drift region properties

NASA Astrophysics Data System (ADS)

Litty, Antoine; Ortolland, Sylvie; Golanski, Dominique; Dutto, Christian; Cristoloveanu, Sorin

2016-11-01

The development of high-voltage MOSFET (HVMOS) is necessary for including power management or radiofrequency functionalities in CMOS technology. In this paper, we investigate the fabrication and optimization of an Extended Drain MOSFET (EDMOS) directly integrated in the ultra-thin SOI film (7 nm) of the 28 nm FDSOI CMOS technology node. Thanks to TCAD simulations, we analyse in detail the device behaviour as a function of the doping level and length of the drift region. The influence of the back-plane doping type and of the back-biasing schemes is discussed. DC measurements of fabricated EDMOS samples reveal promising performances in particular in terms of specific on-resistance versus breakdown voltage trade-off. The experimental results indicate that, even in an ultrathin film, the engineering of the drift region could be a lever to obtain integrated HVMOS (3.3-5 V).

Spatially and momentum resolved energy electron loss spectra from an ultra-thin PrNiO{sub 3} layer

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

Kinyanjui, M. K., E-mail: michael.kinyanjui@uni-ulm.de; Kaiser, U.; Benner, G.

2015-05-18

We present an experimental approach which allows for the acquisition of spectra from ultra-thin films at high spatial, momentum, and energy resolutions. Spatially and momentum (q) resolved electron energy loss spectra have been obtained from a 12 nm ultra-thin PrNiO{sub 3} layer using a nano-beam electron diffraction based approach which enabled the acquisition of momentum resolved spectra from individual, differently oriented nano-domains and at different positions of the PrNiO{sub 3} thin layer. The spatial and wavelength dependence of the spectral excitations are obtained and characterized after the analysis of the experimental spectra using calculated dielectric and energy loss functions. The presentedmore » approach makes a contribution towards obtaining momentum-resolved spectra from nanostructures, thin film, heterostructures, surfaces, and interfaces.« less

Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

DOE PAGES

Emmez, Emre; Anibal Boscoboinik, J.; Tenney, Samuel; ...

2015-06-30

Bilayer silicate films grown on metal substrates are weakly bound to the metal surfaces, which allows ambient gas molecules to intercalate the oxide/metal interface. In this work, we studied the interaction of oxygen with Ru(0001) supported ultrathin silicate and aluminosilicate films at elevated O 2 pressures (10 -5–10 mbar) and temperatures (450–923 K). The results show that the silicate films stay essentially intact under these conditions, and oxygen in the film does not exchange with oxygen in the ambient. O 2 molecules readily penetrate the film and dissociate on the underlying Ru surface underneath. Also, the silicate layer does howevermore » strongly passivate the Ru surface towards RuO 2(110) oxide formation that readily occurs on bare Ru(0001) under the same conditions. Lastly, the results indicate considerable spatial effects for oxidation reactions on metal surfaces in the confined space at the interface. Moreover, the aluminosilicate films completely suppress the Ru oxidation, providing some rationale for using crystalline aluminosilicates in anti-corrosion coatings.« less

Characterization of ultrathin SOI film and application to short channel MOSFETs.

PubMed

Tang, Xiaohui; Reckinger, Nicolas; Larrieu, Guilhem; Dubois, Emmanuel; Flandre, Denis; Raskin, Jean-Pierre; Nysten, Bernard; Jonas, Alain M; Bayot, Vincent

2008-04-23

In this study, a very dilute solution (NH(4)OH:H(2)O(2):H(2)O 1:8:64 mixture) was employed to reduce the thickness of commercially available SOI wafers down to 3 nm. The etch rate is precisely controlled at 0.11 Å s(-1) based on the self-limited etching speed of the solution. The thickness uniformity of the thin film, evaluated by spectroscopic ellipsometry and by high-resolution x-ray reflectivity, remains constant through the thinning process. Moreover, the film roughness, analyzed by atomic force microscopy, slightly improves during the thinning process. The residual stress in the thin film is much smaller than that obtained by sacrificial oxidation. Mobility, measured by means of a bridge-type Hall bar on 15 nm film, is not significantly reduced compared to the value of bulk silicon. Finally, the thinned SOI wafers were used to fabricate Schottky-barrier metal-oxide-semiconductor field-effect transistors with a gate length down to 30 nm, featuring state-of-the-art current drive performance.

Structural, electronic and chemical properties of metal/oxide and oxide/oxide interfaces and thin film structures

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

Lad, Robert J.

1999-12-14

This project focused on three different aspects of oxide thin film systems: (1) Model metal/oxide and oxide/oxide interface studies were carried out by depositing ultra-thin metal (Al, K, Mg) and oxide (MgO, AlO{sub x}) films on TiO{sub 2}, NiO and {alpha}-Al{sub 2}O{sub 3} single crystal oxide substrates. (2) Electron cyclotron resonance (ECR) oxygen plasma deposition was used to fabricate AlO{sub 3} and ZrO{sub 2} films on sapphire substrates, and film growth mechanisms and structural characteristics were investigated. (3) The friction and wear characteristics of ZrO{sub 2} films on sapphire substrates in unlubricated sliding contact were studied and correlated with filmmore » microstructure. In these studies, thin film and interfacial regions were characterized using diffraction (RHEED, LEED, XRD), electron spectroscopies (XPS, UPS, AES), microscopy (AFM) and tribology instruments (pin-on-disk, friction microprobe, and scratch tester). By precise control of thin film microstructure, an increased understanding of the structural and chemical stability of interface regions and tribological performance of ultra-thin oxide films was achieved in these important ceramic systems.« less

Injection doping of ultrathin microcrystalline silicon films prepared by CC-CVD

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

Koynov, S.; Grebner, S.; Schwarz, R.

1997-07-01

Recently, the authors have proposed a cyclic method, referred to as Closed Chamber CVD (CC-CVD), for the preparation of {micro}c-Si films of high crystalline fraction at increased deposition rates. In this work, they first report new process conditions of CC-CVD, which result in growth of highly crystalline films with a sharp interface on a foreign substrate. Then these conditions are further used together with a pulsed injection of B{sub 2}H{sub 6} in an appropriate moment of each cycle, so that the disturbance of the crystallization process is prevented. A series of ultrathin {micro}c-Si films, doped by this technique, is characterizedmore » by conductivity measurements, SEM, Raman Scattering, optical transmission and UV reflection. A strong reduction of the transient interface layer is achieved and conductivity as high as 2 S/cm with an activation energy of 27 meV is reached.« less

Acoustic Phonons and Mechanical Properties of Ultra-Thin Porous Low-k Films: A Surface Brillouin Scattering Study

NASA Astrophysics Data System (ADS)

Zizka, J.; King, S.; Every, A.; Sooryakumar, R.

2018-04-01

To reduce the RC (resistance-capacitance) time delay of interconnects, a key development of the past 20 years has been the introduction of porous low-k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low-k materials have reached thicknesses below 100 nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson's ratio, and Young's modulus of these porous low-k SiOC:H films (˜ 25-250 nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.

Conformal surface plasmons propagating on ultrathin and flexible films

PubMed Central

Shen, Xiaopeng; Cui, Tie Jun; Martin-Cano, Diego; Garcia-Vidal, Francisco J.

2013-01-01

Surface plasmon polaritons (SPPs) are localized surface electromagnetic waves that propagate along the interface between a metal and a dielectric. Owing to their inherent subwavelength confinement, SPPs have a strong potential to become building blocks of a type of photonic circuitry built up on 2D metal surfaces; however, SPPs are difficult to control on curved surfaces conformably and flexibly to produce advanced functional devices. Here we propose the concept of conformal surface plasmons (CSPs), surface plasmon waves that can propagate on ultrathin and flexible films to long distances in a wide broadband range from microwave to mid-infrared frequencies. We present the experimental realization of these CSPs in the microwave regime on paper-like dielectric films with a thickness 600-fold smaller than the operating wavelength. The flexible paper-like films can be bent, folded, and even twisted to mold the flow of CSPs. PMID:23248311

Water Vapor Uptake of Ultrathin Films of Biologically Derived Nanocrystals: Quantitative Assessment with Quartz Crystal Microbalance and Spectroscopic Ellipsometry.

PubMed

Niinivaara, Elina; Faustini, Marco; Tammelin, Tekla; Kontturi, Eero

2015-11-10

Despite the relevance of water interactions, explicit analysis of vapor adsorption on biologically derived surfaces is often difficult. Here, a system was introduced to study the vapor uptake on a native polysaccharide surface; namely, cellulose nanocrystal (CNC) ultrathin films were examined with a quartz crystal microbalance with dissipation monitoring (QCM-D) and spectroscopic ellipsometry (SE). A significant mass uptake of water vapor by the CNC films was detected using the QCM-D upon increasing relative humidity. In addition, thickness changes proportional to changes in relative humidity were detected using SE. Quantitative analysis of the results attained indicated that in preference to being soaked by water at the point of hydration each individual CNC in the film became enveloped by a 1 nm thick layer of adsorbed water vapor, resulting in the detected thickness response.

Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-Layer-Induced Octahedral Distortion

DOE PAGES

Thomas, S.; Kuiper, B.; Hu, J.; ...

2017-10-27

With reduced dimensionality, it is often easier to modify the properties of ultrathin films than their bulk counterparts. Strain engineering, usually achieved by choosing appropriate substrates, has been proven effective in controlling the properties of perovskite oxide films. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. Here we report the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO 3 films by the deposition of a SrTiO 3 capping layer, which can be lithographically patterned to achieve local control. Here, using a scanning Sagnac magnetic microscope, we show an increasemore » in the Curie temperature of SrRuO 3 due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. Lastly, this capping-layer-based technique may open new possibilities for developing functional oxide materials.« less

Transport properties of ultra-thin VO{sub 2} films on (001) TiO{sub 2} grown by reactive molecular-beam epitaxy

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

Paik, Hanjong; Tashman, Joshua W.; Moyer, Jarrett A.

2015-10-19

We report the growth of (001)-oriented VO{sub 2} films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO{sub 2} surface. Another key limitation is interdiffusion with the (001) TiO{sub 2} substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion bymore » using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO{sub 2} films with abrupt MIT behavior.« less

Plasma-enhanced pulsed-laser deposition of single-crystalline M o2C ultrathin superconducting films

NASA Astrophysics Data System (ADS)

Zhang, Fan; Zhang, Zhi; Wang, Huichao; Chan, Cheuk Ho; Chan, Ngai Yui; Chen, Xin Xin; Dai, Ji-Yan

2017-08-01

Transition-metal carbides (TMCs) possess many intriguing properties and inspiring application potentials, and recently the study of a two-dimensional form of TMCs has attracted great attention. Herein, we report successful fabrication of continuous M o2C ultrathin single-crystalline films at 700 ∘C with an approach of plasma-enhanced pulsed-laser deposition. By sophisticated structural analyses, the M o2C films are characterized as single crystal with a rarely reported face-centered cubic structure. In further electrical transport measurements, superconductivity observed in the M o2C films demonstrates a typical two-dimensional feature, which is consistent with Berezinskii-Kosterlitz-Thouless transitions. Besides, large upper critical magnetic fields are discovered in this system. Our work offers an approach to grow large-area and high-quality TMCs at relatively low temperatures. This study may stimulate more related investigations on the synthesis, characterizations, and applications of two-dimensional TMCs.

Modeling of UV laser-induced patterning of ultrathin Co films on bulk SiO2: verification of short- and long-range ordering mechanisms

NASA Astrophysics Data System (ADS)

Trice, Justin; Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, R.

2006-03-01

Irradiating ultrathin Co films (1 to 10 nm) by a short-pulsed UV laser leads to pattern formation with both short- and long-range order (SRO, LRO). Single beam irradiation produces SRO, while two-beam interference irradiation produces a quasi-2D arrangement of nanoparticles with LRO and SRO. The pattern formation primarily occurs in the molten phase. An estimate of the thermal behavior of the film/substrate composite following a laser pulse is presented. The thermal behavior includes the lifetime of the liquid phase and the thermal gradient during interference heating. Based on this evidence, the SRO is attributed to spinodal dewetting of the film while surface tension gradients induced by the laser interference pattern appear to influence LRO [1]. [1] C.Favazza, J.Trice, H.Krishna, R.Sureshkumar, and R.Kalyanaraman, unpublished.

Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-Layer-Induced Octahedral Distortion.

PubMed

Thomas, S; Kuiper, B; Hu, J; Smit, J; Liao, Z; Zhong, Z; Rijnders, G; Vailionis, A; Wu, R; Koster, G; Xia, J

2017-10-27

With reduced dimensionality, it is often easier to modify the properties of ultrathin films than their bulk counterparts. Strain engineering, usually achieved by choosing appropriate substrates, has been proven effective in controlling the properties of perovskite oxide films. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. Here we report the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO_{3} films by the deposition of a SrTiO_{3} capping layer, which can be lithographically patterned to achieve local control. Using a scanning Sagnac magnetic microscope, we show an increase in the Curie temperature of SrRuO_{3} due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. This capping-layer-based technique may open new possibilities for developing functional oxide materials.

Acoustic Phonons and Mechanical Properties of Ultra-Thin Porous Low- k Films: A Surface Brillouin Scattering Study

NASA Astrophysics Data System (ADS)

Zizka, J.; King, S.; Every, A.; Sooryakumar, R.

2018-07-01

To reduce the RC (resistance-capacitance) time delay of interconnects, a key development of the past 20 years has been the introduction of porous low- k dielectrics to replace the traditional use of SiO2. Moreover, in keeping pace with concomitant reduction in technology nodes, these low- k materials have reached thicknesses below 100 nm wherein the porosity becomes a significant fraction of the film volume. The large degree of porosity not only reduces mechanical strength of the dielectric layer but also renders a need for non-destructive approaches to measure the mechanical properties of such ultra-thin films within device configurations. In this study, surface Brillouin scattering (SBS) is utilized to determine the elastic constants, Poisson's ratio, and Young's modulus of these porous low- k SiOC:H films (˜ 25-250 nm thick) grown on Si substrates by probing surface acoustic phonons and their dispersions.

Clay induced aggregation of a tetra-cationic metalloporphyrin in Layer by Layer self assembled film

NASA Astrophysics Data System (ADS)

Banik, Soma; Bhattacharjee, J.; Hussain, S. A.; Bhattacharjee, D.

2015-12-01

Porphyrins have a general tendency to form aggregates in ultrathin films. Also electrostatic adsorption of cationic porphyrins onto anionic nano clay platelets results in the flattening of porphyrin moieties. The flattening is evidenced by the red-shifting of Soret band with respect to the aqueous solution. In the present communication, we have studied the clay induced aggregation behaviour of a tetra-cationic metalloporphyrin Manganese (III) 5, 10, 15, 20-tetra (4 pyridyl)-21 H, 23 H-porphine chloride tetrakis (methochloride) (MnTMPyP) in Layer-by-Layer (LbL) self assembled film. The adsorption of dye molecules onto nano clay platelets resulted in the flattening of the meso substituent groups of the dye chromophore. In Layer-by-Layer ultrathin film, the flattened porphyrin molecules tagged nano clay platelets were further associated to form porphyrin aggregates. This has been clearly demonstrated from the UV-vis absorption spectroscopic studies. Atomic Force Microscopic (AFM) studies gave visual evidence of the association of organo-clay hybrid molecules in the LbL film.

Tunable magnetic properties by interfacial manipulation of L1(0)-FePt perpendicular ultrathin film with island-like structures.

PubMed

Feng, C; Wang, S G; Yang, M Y; Zhang, E; Zhan, Q; Jiang, Y; Li, B H; Yu, G H

2012-02-01

Based on interfacial manipulation of the MgO single crystal substrate and non-magnetic AIN compound, a L1(0)-FePt perpendicular ultrathin film with the structure of MgO/FePt-AIN/Ta was designed, prepared, and investigated. The film is comprised of L1(0)-FePt "magnetic islands," which exhibits a perpendicular magnetic anisotropy (PMA), tunable coercivity (Hc), and interparticle exchange coupling (IEC). The MgO substrate promotes PMA of the film because of interfacial control of the FePt lattice orientation. The AIN compound is doped to increase the difference of surface energy between FePt layer and MgO substrate and to suppress the growth of FePt grains, which takes control of island growth mode of FePt atoms. The AIN compound also acts as isolator of L1(0)-FePt islands to pin the sites of FePt domains, resulting in the tunability of Hc and IEC of the films.

Chemical vapor deposition of anisotropic ultrathin gold films on optical fibers: real-time sensing by tilted fiber Bragg gratings and use of a dielectric pre-coating

NASA Astrophysics Data System (ADS)

Mandia, David J.; Zhou, Wenjun; Ward, Matthew J.; Joress, Howie; Giorgi, Javier B.; Gordon, Peter; Albert, Jacques; Barry, Seán. T.

2014-09-01

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

High-Pressure CO2 Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film Confinement.

PubMed

Ogieglo, Wojciech; Ghanem, Bader; Ma, Xiaohua; Wessling, Matthias; Pinnau, Ingo

2018-04-04

Ultrathin microporous polymer films are pertinent to the development and further spread of nanotechnology with very promising potential applications in molecular separations, sensors, catalysis, or batteries. Here, we report high-pressure CO 2 sorption in ultrathin films of several chemically different polymers of intrinsic microporosity (PIMs), including the prototypical PIM-1. Films with thicknesses down to 7 nm were studied using interference-enhanced in situ spectroscopic ellipsometry. It was found that all PIMs swell much more than non-microporous polystyrene and other high-performance glassy polymers reported previously. Furthermore, chemical modifications of the parent PIM-1 strongly affected the swelling magnitude. By investigating the behavior of relative refractive index, n rel , it was possible to study the interplay between micropores filling and matrix expansion. Remarkably, all studied PIMs showed a maximum in n rel at swelling of 2-2.5% indicating a threshold point above which the dissolution in the dense matrix started to dominate over sorption in the micropores. At pressures above 25 bar, all PIMs significantly plasticized in compressed CO 2 and for the ones with the highest affinity to the penetrant, a liquidlike mixing typical for rubbery polymers was observed. Reduction of film thickness below 100 nm revealed pronounced nanoconfinement effects and resulted in a large swelling enhancement and a quick loss of the ultrarigid character. On the basis of the partial molar volumes of the dissolved CO 2 , the effective reduction of the T g was estimated to be ∼200 °C going from 128 to 7 nm films.

Dynamics of ultra-thin polystyrene with and without a (artificial) dead layer studied by resonance enhanced dynamic light scattering

NASA Astrophysics Data System (ADS)

Vianna, S. D. B.; Lin, F. Y.; Plum, M. A.; Duran, H.; Steffen, W.

2017-05-01

Using non-invasive, marker-free resonance enhanced dynamic light scattering, the dynamics of capillary waves on ultrathin polystyrene films' coupling to the viscoelastic and mechanical properties have been studied. The dynamics of ultrathin polymer films is still debated. In particular the question of what influence either the solid substrate and/or the fluid-gas interface has on the dynamics and the mechanical properties of films of glass forming liquids as polymers is in the focus of the present research. As a consequence, e.g., viscosity close to interfaces and thus the average viscosity of very thin films are prone to change. This study is focused on atactic, non-entangled polystyrene thin films on the gold surface. A slow dynamic mode was observed with Vogel-Fulcher-Tammann temperature dependence, slowing down with decreasing film thickness. We tentatively attribute this relaxation mode to overdamped capillary waves because of its temperature dependence and the dispersion with a wave vector which was found. No signs of a more mobile layer at the air/polymer interface or of a "dead layer" at the solid/polymer interface were found. Therefore we investigated the influence of an artificially created dead layer on the capillary wave dynamics by introducing covalently bound polystyrene polymer brushes as anchors. The dynamics was slowed down to a degree more than expected from theoretical work on the increase of density close to the solid liquid interface—instead of a "dead layer" of 2 nm, the interaction seems to extend more than 10 nm into the polymer.

Bias current dependence of resistivity in Co0.4Fe0.4B0.2 ultrathin film prepared by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Mandal, Snehal; Mazumdar, Dipak; Das, I.

2018-04-01

Ultrathin film of Co0.4Fe0.4B0.2 was prepared on p-type Si (100) substrate by RF magnetron sputtering. X-Ray Reflectivity and Atomic Force Microscopy measurements were performed to estimate the thickness and surface roughness of the film. Electrical transport measurements were performed by four-probe method in a current-in-plane (CIP) geometry. Presence of non-linearity in the current-voltage (I-V) characteristics was observed at higher current range. The electrical resistivity was found to change by several orders of magnitude (105) by changing the bias current from nano-ampere (nA) to milli-ampere (mA) range. This bias current dependence of the resistivity has been explained by different transport mechanisms.

Formation of silicon nanodots via ion beam sputtering of ultrathin gold thin film coatings on Si

PubMed Central

2011-01-01

Ion beam sputtering of ultrathin film Au coatings used as a physical catalyst for self-organization of Si nanostructures has been achieved by tuning the incident particle energy. This approach holds promise as a scalable nanomanufacturing parallel processing alternative to candidate nanolithography techniques. Structures of 11- to 14-nm Si nanodots are formed with normal incidence low-energy Ar ions of 200 eV and fluences above 2 × 1017 cm-2. In situ surface characterization during ion irradiation elucidates early stage ion mixing migration mechanism for nanodot self-organization. In particular, the evolution from gold film islands to the formation of ion-induced metastable gold silicide followed by pure Si nanodots formed with no need for impurity seeding. PMID:21711934

Quantum-Fluctuation Effects in the Transport Properties of Ultrathin Films of Disordered Superconductors above the Paramagnetic Limit

NASA Astrophysics Data System (ADS)

Khodas, M.; Levchenko, A.; Catelani, G.

2012-06-01

We study the transport in ultrathin disordered film near the quantum critical point induced by the Zeeman field. We calculate corrections to the normal state conductivity due to quantum pairing fluctuations. The fluctuation-induced transport is mediated by virtual rather than real quasiparticle excitations. We find that at zero temperature, where the corrections come from purely quantum fluctuations, the Aslamazov-Larkin paraconductivity term, the Maki-Thompson interference contribution, and the density of states effects are all of the same order. The total correction leads to the negative magnetoresistance. This result is in qualitative agreement with the recent transport observations in the parallel magnetic field of the homogeneously disordered amorphous films and superconducting two-dimensional electron gas realized at the oxide interfaces.

Ultrathin NiGe films prepared via catalytic solid-vapor reaction of Ni with GeH(4).

PubMed

Peter, Antony P; Opsomer, Karl; Adelmann, Christoph; Schaekers, Marc; Meersschaut, Johan; Richard, Olivier; Vaesen, Inge; Moussa, Alain; Franquet, Alexis; Zsolt, Tokei; Van Elshocht, Sven

2013-10-09

A low-temperature (225-300 °C) solid-vapor reaction process is reported for the synthesis of ultrathin NiGe films (∼6-23 nm) on 300 mm Si wafers covered with thermal oxide. The films were prepared via catalytic chemical vapor reaction of germane (GeH4) gas with physical vapor deposited (PVD) Ni films of different thickness (2-10 nm). The process optimization by investigating GeH4 partial pressure, reaction temperature, and time shows that low resistive, stoichiometric, and phase pure NiGe films can be formed within a broad window. NiGe films crystallized in an orthorhombic structure and were found to exhibit a smooth morphology with homogeneous composition as evidenced by glancing angle X-ray diffraction (GIXRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Rutherford back-scattering (RBS) analysis. Transmission electron microscopy (TEM) analysis shows that the NiGe layers exhibit a good adhesion without voids and a sharp interface on the thermal oxide. The NiGe films were found to be morphologically and structurally stable up to 500 °C and exhibit a resistivity value of 29 μΩ cm for 10 nm NiGe films.

Interparticle coupling effect of silver-gold heterodimer to enhance light harvesting in ultrathin perovskite solar cell

NASA Astrophysics Data System (ADS)

Hu, Zhaosheng; Ma, Tingli; Hayase, Shuzi

2018-01-01

Thin perovskite solar cells are under intensive interest since they reduce the amount of absorber layer, especially toxic lead in methylammonium lead iodide (MAPbI3) devices and have wide application in semitransparent and tandem solar cells. However, due to the decrease of the layer thickness, thin perovskite devices with weak light-harvesting have poor performance. Moreover, the performance of plasmonic thin perovskite devices by incorporating noncoupling metal NPs cannot give comparable performance with normal devices. In this perspective, we discuss the implication of employing random silver-gold heterodimers in MAPbI3 solar cells with the aim of establishing some guidelines for the efficient ultrathin perovskite solar cells. This method induces an extraordinarily high light-harvesting for ultrathin perovskite film. And the underlying physical mechanism behind the enhanced absorption is deeply investigated by plasmon hybridization, dipolar-dipolar coupling method and FDTD simulation. We notice that perovskite embedded silver-gold heterodimer overcomes the vanished antibonding plasmon resononse (σ * ) in nonjunction area of gold/silver homodimer. A 150-nm perovskite film with embedded random silver-gold heterodimers with 80 nm size and 25 nm gap distance processes 28.15% absorption enhancement compared to the reference film, which is higher than the reported 10% for gold homodimers. And we also predict a realistic solution-processed, easy, and low-cost fabrication method, which provide a means to realize highly efficient ultrathin perovskite solar cell including other absorber-based photovoltaics.

A cost-effective nanoporous ultrathin film electrode based on nanoporous gold/IrO2 composite for proton exchange membrane water electrolysis

NASA Astrophysics Data System (ADS)

Zeng, Yachao; Guo, Xiaoqian; Shao, Zhigang; Yu, Hongmei; Song, Wei; Wang, Zhiqiang; Zhang, Hongjie; Yi, Baolian

2017-02-01

A cost-effective nanoporous ultrathin film (NPUF) electrode based on nanoporous gold (NPG)/IrO2 composite has been constructed for proton exchange membrane (PEM) water electrolysis. The electrode was fabricated by integrating IrO2 nanoparticles into NPG through a facile dealloying and thermal decomposition method. The NPUF electrode is featured in its 3D interconnected nanoporosity and ultrathin thickness. The nanoporous ultrathin architecture is binder-free and beneficial for improving electrochemical active surface area, enhancing mass transport and facilitating releasing of oxygen produced during water electrolysis. Serving as anode, a single cell performance of 1.728 V (@ 2 A cm-2) has been achieved by NPUF electrode with a loading of IrO2 and Au at 86.43 and 100.0 μg cm-2 respectively, the electrolysis voltage is 58 mV lower than that of conventional electrode with an Ir loading an order of magnitude higher. The electrolysis voltage kept relatively constant up to 300 h (@250 mA cm-2) during the course of durability test, manifesting that NPUF electrode is promising for gas evolution.

Classical And Quantum Rainbow Scattering From Surfaces

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

Winter, H.; Schueller, A.; Busch, M.

2011-06-01

The structure of clean and adsorbate covered surfaces as well as of ultrathin films can be investigated by grazing scattering of fast atoms. We present two recent experimental techniques which allow one to study the structure of ordered arrangements of surface atoms in detail. (1) Rainbow scattering under axial surface channeling conditions, and (2) fast atom diffraction. Our examples demonstrate the attractive features of grazing fast atom scattering as a powerful analytical tool in studies on the structure of surfaces. We will concentrate our discussion on the structure of ultrathin silica films on a Mo(112) surface and of adsorbed oxygenmore » atoms on a Fe(110) surface.« less

Gigantic Dzyaloshinskii-Moriya interaction in the MnBi ultrathin films

NASA Astrophysics Data System (ADS)

Yu, Jie-Xiang; Zang, Jiadong; Zang's Team

The magnetic skyrmion, a swirling-like spin texture with nontrivial topology, is driven by strong Dzyaloshinskii-Moriya (DM) interaction originated from the spin-orbit coupling in inversion symmetry breaking systems. Here, based on first-principles calculations, we predict a new material, MnBi ultrathin film, with gigantic DM interactions. The ratio of the DM interaction to the Heisenberg exchange is about 0.3, exceeding any values reported so far. Its high Curie temperature, high coercivity, and large perpendicular magnetoanisotropy make MnBi a good candidate for future spintronics studies. Topologically nontrivial spin textures are emergent in this system. We expect further experimental efforts will be devoted into this systems.

Ultrathin (<1 μm) Substrate-Free Flexible Photodetector on Quantum Dot-Nanocellulose Paper

PubMed Central

Wu, Jingda; Lin, Lih Y.

2017-01-01

Conventional approaches to flexible optoelectronic devices typically require depositing the active materials on external substrates. This is mostly due to the weak bonding between individual molecules or nanocrystals in the active materials, which prevents sustaining a freestanding thin film. Herein we demonstrate an ultrathin freestanding ZnO quantum dot (QD) active layer with nanocellulose structuring, and its corresponding device fabrication method to achieve substrate-free flexible optoelectronic devices. The ultrathin ZnO QD-nanocellulose composite is obtained by hydrogel transfer printing and solvent-exchange processes to overcome the water capillary force which is detrimental to achieving freestanding thin films. We achieved an active nanocellulose paper with ~550 nm thickness, and >91% transparency in the visible wavelength range. The film retains the photoconductive and photoluminescent properties of ZnO QDs and is applied towards substrate-free Schottky photodetector applications. The device has an overall thickness of ~670 nm, which is the thinnest freestanding optoelectronic device to date, to the best of our knowledge, and functions as a self-powered visible-blind ultraviolet photodetector. This platform can be readily applied to other nano materials as well as other optoelectronic device applications. PMID:28266651

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

Ultrathin free-standing close-packed gold nanoparticle films: conductivity and Raman scattering enhancement.

PubMed

Yu, Qing; Huang, Hongwen; Peng, Xinsheng; Ye, Zhizhen

2011-09-01

A simple filtration technique was developed to prepare large scale free-standing close-packed gold nanoparticle ultrathin films using metal hydroxide nanostrands as both barrier layer and sacrificial layer. As thin as 70 nm, centimeter scale robust free-standing gold nanoparticle thin film was obtained. The thickness of the films could be easily tuned by the filtration volumes. The electronic conductivities of these films varied with the size of the gold nanoparticles, post-treatment temperature, and thickness, respectively. The conductivity of the film prepared from 20 nm gold nanoparticles is higher than that of the film prepared from 40 nm gold nanoparticle by filtering the same filtration volume of their solution, respectively. Their conductivities are comparable to that of the 220 nm thick ITO film. Furthermore, these films demonstrated an average surface Raman scattering enhancement up to 6.59 × 10(5) for Rhodamine 6 G molecules on the film prepared from 40 nm gold nanoparticles. Due to a lot of nano interspaces generated from the close-packed structures, two abnormal enhancements and relative stronger intensities of the asymmetrical vibrations at 1534 and 1594 cm(-1) of R6G were observed, respectively. These robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and hold the potential application for electrodes and surface enhanced Raman detectors. This method is applicable for preparation of other nanoparticle free-standing thin films.

Three-Component Integrated Ultrathin Organic Photosensors for Plastic Optoelectronics.

PubMed

Wang, Hanlin; Liu, Hongtao; Zhao, Qiang; Cheng, Cheng; Hu, Wenping; Liu, Yunqi

2016-01-27

By three-component integration, an integrated organic photosensor is presented using common organic dyes as building blocks. Gray-scale photosensing and signal amplification are achieved in the device within a wide range of light intensities. Moreover, with ultrathin film techniques, 470 nm thick devices are realized and continue to work when harshly bent. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

MnO2 ultrathin films deposited by means of magnetron sputtering: Relationships between process conditions, structural properties and performance in transparent supercapacitors

NASA Astrophysics Data System (ADS)

Borysiewicz, Michał A.; Wzorek, Marek; Myśliwiec, Marcin; Kaczmarski, Jakub; Ekielski, Marek

2016-12-01

This study focuses on the relationships between the process parameters during magnetron sputter deposition of MnO2 and the resulting film properties. Three MnO2 phases were identified - γ, β and λ and the dependence of MnO2 phase presence on the oxygen content in the sputtering atmosphere was found. Selected MnO2 phases were subsequently applied as ultrathin coatings on top of nanostructured ZnO electrodes for transparent supercapacitors with LiCl-based gel electrolyte. The films containing λ-MnO2 exhibited both the highest optical transparency of 62% at 550 nm as well as the highest specific capacitance in the supercapacitor structure, equal to 73.1 μF/cm2. Initially lower, the capacitance was elevated by charge-discharge conditioning.

Kelvin–Helmholtz instability in an ultrathin air film causes drop splashing on smooth surfaces

PubMed Central

Liu, Yuan; Tan, Peng; Xu, Lei

2015-01-01

When a fast-moving drop impacts onto a smooth substrate, splashing will be produced at the edge of the expanding liquid sheet. This ubiquitous phenomenon lacks a fundamental understanding. Combining experiment with model, we illustrate that the ultrathin air film trapped under the expanding liquid front triggers splashing. Because this film is thinner than the mean free path of air molecules, the interior airflow transfers momentum with an unusually high velocity comparable to the speed of sound and generates a stress 10 times stronger than the airflow in common situations. Such a large stress initiates Kelvin–Helmholtz instabilities at small length scales and effectively produces splashing. Our model agrees quantitatively with experimental verifications and brings a fundamental understanding to the ubiquitous phenomenon of drop splashing on smooth surfaces. PMID:25713350

Corrosion-resistant metal surfaces

DOEpatents

Sugama, Toshifumi [Wading River, NY

2009-03-24

The present invention relates to metal surfaces having thereon an ultrathin (e.g., less than ten nanometer thickness) corrosion-resistant film, thereby rendering the metal surfaces corrosion-resistant. The corrosion-resistant film includes an at least partially crosslinked amido-functionalized silanol component in combination with rare-earth metal oxide nanoparticles. The invention also relates to methods for producing such corrosion-resistant films.

Transport properties of ultrathin YBa2Cu3O7 -δ nanowires: A route to single-photon detection

NASA Astrophysics Data System (ADS)

Arpaia, Riccardo; Golubev, Dmitri; Baghdadi, Reza; Ciancio, Regina; Dražić, Goran; Orgiani, Pasquale; Montemurro, Domenico; Bauch, Thilo; Lombardi, Floriana

2017-08-01

We report on the growth and characterization of ultrathin YBa2Cu3O7 -δ (YBCO) films on MgO (110) substrates, which exhibit superconducting properties at thicknesses down to 3 nm. YBCO nanowires, with thicknesses down to 10 nm and widths down to 65 nm, have also been successfully fabricated. The nanowires protected by a Au capping layer show superconducting properties close to the as-grown films and critical current densities, which are limited by only vortex dynamics. The 10-nm-thick YBCO nanowires without the Au capping present hysteretic current-voltage characteristics, characterized by a voltage switch which drives the nanowires directly from the superconducting to the normal state. We associate such bistability to the presence of localized normal domains within the superconductor. The presence of the voltage switch in ultrathin YBCO nanostructures, characterized by high sheet resistance values and high critical current values, makes our nanowires very attractive devices to engineer single-photon detectors.

Flexible, Low-Power Thin-Film Transistors Made of Vapor-Phase Synthesized High-k, Ultrathin Polymer Gate Dielectrics.

PubMed

Choi, Junhwan; Joo, Munkyu; Seong, Hyejeong; Pak, Kwanyong; Park, Hongkeun; Park, Chan Woo; Im, Sung Gap

2017-06-21

A series of high-k, ultrathin copolymer gate dielectrics were synthesized from 2-cyanoethyl acrylate (CEA) and di(ethylene glycol) divinyl ether (DEGDVE) monomers by a free radical polymerization via a one-step, vapor-phase, initiated chemical vapor deposition (iCVD) method. The chemical composition of the copolymers was systematically optimized by tuning the input ratio of the vaporized CEA and DEGDVE monomers to achieve a high dielectric constant (k) as well as excellent dielectric strength. Interestingly, DEGDVE was nonhomopolymerizable but it was able to form a copolymer with other kinds of monomers. Utilizing this interesting property of the DEGDVE cross-linker, the dielectric constant of the copolymer film could be maximized with minimum incorporation of the cross-linker moiety. To our knowledge, this is the first report on the synthesis of a cyanide-containing polymer in the vapor phase, where a high-purity polymer film with a maximized dielectric constant was achieved. The dielectric film with the optimized composition showed a dielectric constant greater than 6 and extremely low leakage current densities (<3 × 10 -8 A/cm 2 in the range of ±2 MV/cm), with a thickness of only 20 nm, which is an outstanding thickness for down-scalable cyanide polymer dielectrics. With this high-k dielectric layer, organic thin-film transistors (OTFTs) and oxide TFTs were fabricated, which showed hysteresis-free transfer characteristics with an operating voltage of less than 3 V. Furthermore, the flexible OTFTs retained their low gate leakage current and ideal TFT characteristics even under 2% applied tensile strain, which makes them some of the most flexible OTFTs reported to date. We believe that these ultrathin, high-k organic dielectric films with excellent mechanical flexibility will play a crucial role in future soft electronics.

Fabrication and characterization of NiO based metal-insulator-metal diode using Langmuir-Blodgett method for high frequency rectification

NASA Astrophysics Data System (ADS)

Azad, Ibrahim; Ram, Manoj K.; Goswami, D. Yogi; Stefanakos, Elias

2018-04-01

Thin film metal-insulator-metal (MIM) diodes have attracted significant attention for use in infrared energy harvesting and detection applications. As demonstrated over the past decades, MIM or metal-insulator-insulator-metal (MIIM) diodes can operate at the THz frequencies range by quantum tunneling of electrons. The aim of this work is to synthesize required ultra-thin insulating layers and fabricate MIM diodes using the Langmuir-Blodgett (LB) technique. The nickel stearate (NiSt) LB precursor film was deposited on glass, silicon (Si), ITO glass and gold coated silicon substrates. The photodesorption (UV exposure) and the thermodesorption (annealing at 100 °C and 350 °C) methods were used to remove organic components from the NiSt LB film and to achieve a uniform homogenous nickel oxide (NiO) film. These ultrathin NiO films were characterized by EDS, AFM, FTIR and cyclic voltammetry methods, respectively. The MIM diode was fabricated by depositing nickel (Ni) on the NiO film, all on a gold (Au) plated silicon (Si) substrate. The current (I)-voltage (V) characteristics of the fabricated diode were studied to understand the conduction mechanism assumed to be tunneling of electron through the ultra-thin insulating layer. The sensitivity of the diode was measured to be as high as 35 V-1. The diode resistance was ˜100 ohms (at a bias voltage of 0.60 V), and the rectification ratio was about 22 (for a signal voltage of ±200 mV). At the bias point, the diode response demonstrated significant non-linearity and high asymmetry, which are very desirable characteristics for applications in infrared detection and harvesting.

Electronic Disorder in Organic Semiconducting Films Observed with Kelvin Probe Force Microscopy

NASA Astrophysics Data System (ADS)

Hoffman, Benjamin Carl

This work is a study into electronic disorder within organic semiconducting (OSC) films from a scan-probe perspective. Organic electronics are an exciting technology poised for use in next generation devices with unique applications such as transparent displays and ultrathin flexible solar cells. Understanding and mapping electronic disorder in OSC has a high degree of relevance towards recognizing the properties of charge trapping that hinders transport and diminishes device performance. Evidence of surface potential inhomogeneity is identified by using Kelvin probe force microscopy (KPFM) to measure the contact potential difference (CPD) between probe and sample. OSC films are grown via organic molecular beam deposition (OMBD) to create well-ordered crystals with precise control of nominal thickness. Further research methods involve the study of diffraction peaks from grazing-incidence wide-angle x-ray scattering (GIWAXS) for crystallographic analysis as well as use of a probe station for transfer characteristics of fabricated thin film transistors. Initial research into this subject involved thin films of the novel organic molecule 2,8- diflouro-5,11-bis(triethylsilylethynyl)-anthradithiophene (diF-TES-ADT) that were grown on silicon substrates with a native oxide layer and analyzed with GIWAXS and KPFM. The crystallography of the films is that of a uniform (001) orientation. Variations in surface potential in diF-TES-ADT crystallites are observed to be unique from variations in the substrate. Nevertheless, surface potential variations in thick films are influenced by chemical passivation of the substrate and so the source of CPD variations are assigned to be intrinsic defects. Chemical treatment and processing methods control the growth kinetics which are linked to charge traps locally distorting the surface potential in OSC films. To continue the research into identifying charge trapping in ultra-thin films, 1.5 monolayer thick films of alpha-sexithiophene (6T) were grown on silicon substrates with a thick oxide layer to compare the surface potential of the first monolayer with that of the bilayer. The temperature of the substrate during film growth was varied and found to influence the interlayer surface potential contrast. Higher temperature samples have a bilayer with CPD above that of the monolayer, while lower temperature samples have a bilayer with CPD below that of the monolayer. GIWAXS data collected shows that the lower temperature sample has no observed out-of-plane order which we identify as the source of interlayer trapping formed between the first and second monolayers of the 6T films. The final project into the specifics of disorder involves using ultrathin films of 6T in an operational transistor with grounded source-drain electrodes to study the influence of gate bias on surface potential. Using the mean and standard deviation of CPD for a series of gate biases, the trap density of states (DOS) is calculated directly while allowing for the quantification of spatial variations. CPD histograms from the series of images illustrate the screening of deep traps as the transistor is turned on. While in the 'off' regime the images are electrostatic, after transitioning to the 'on' state the images show instability after threshold voltage. This dynamic 'on' state offers a unique view of shallow trap states being filled and then thermally released.

Optical Properties of Al-Doped ZnO Films in the Infrared Region and Their Absorption Applications

NASA Astrophysics Data System (ADS)

Zheng, Hua; Zhang, Rong-Jun; Li, Da-Hai; Chen, Xin; Wang, Song-You; Zheng, Yu-Xiang; Li, Meng-Jiao; Hu, Zhi-Gao; Dai, Ning; Chen, Liang-Yao

2018-05-01

The optical properties of aluminum-doped zinc oxide (AZO) thin films were calculated rapidly and accurately by point-by-point analysis from spectroscopic ellipsometry (SE) data. It was demonstrated that there were two different physical mechanisms, i.e., the interfacial effect and crystallinity, for the thickness-dependent permittivity in the visible and infrared regions. In addition, there was a blue shift for the effective plasma frequency of AZO when the thickness increased, and the effective plasma frequency did not exist for AZO ultrathin films (< 25 nm) in the infrared region, which demonstrated that AZO ultrathin films could not be used as a negative index metamaterial. Based on detailed permittivity research, we designed a near-perfect absorber at 2-5 μm by etching AZO-ZnO alternative layers. The alternative layers matched the phase of reflected light, and the void cylinder arrays extended the high absorption range. Moreover, the AZO absorber demonstrated feasibility and applicability on different substrates.

Evaluating nanoscale ultra-thin metal films by means of lateral photovoltaic effect in metal-semiconductor structure.

PubMed

Zheng, Diyuan; Yu, Chongqi; Zhang, Qian; Wang, Hui

2017-12-15

Nanoscale metal-semiconductor (MS) structure materials occupy an important position in semiconductor and microelectronic field due to their abundant physical phenomena and effects. The thickness of metal films is a critical factor in determining characteristics of MS devices. How to detect or evaluate the metal thickness is always a key issue for realizing high performance MS devices. In this work, we propose a direct surface detection by use of the lateral photovoltaic effect (LPE) in MS structure, which can not only measure nanoscale thickness, but also detect the fluctuation of metal films. This method is based on the fact that the output of lateral photovoltaic voltage (LPV) is closely linked with the metal thickness at the laser spot. We believe this laser-based contact-free detection is a useful supplement to the traditional methods, such as AFM, SEM, TEM or step profiler. This is because these traditional methods are always incapable of directly detecting ultra-thin metal films in MS structure materials.

Formation and investigation of ultrathin layers of Co2FeSi ferromagnetic alloy synthesized on silicon covered with a CaF2 barrier layer

NASA Astrophysics Data System (ADS)

Grebenyuk, G. S.; Gomoyunova, M. V.; Pronin, I. I.; Vyalikh, D. V.; Molodtsov, S. L.

2016-03-01

Ultrathin (∼2 nm) films of Co2FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ. Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3p and Co 3p electrons. The study shows that the synthesis of the Co2FeSi ferromagnetic alloy occurs in the temperature range of 200-400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

Probing nanoscale ion dynamics in ultrathin films of polymerized ionic liquids by broadband dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Sangoro, Joshua; Heres, Maximilian; Cosby, Tyler

Continuous progress in energy storage and conversion technologies necessitates novel experimental approaches that can provide fundamental insights regarding the impact of reduced dimensions on the functional properties of materials. In this talk, a nondestructive experimental approach to probe nanoscale ion dynamics in ultrathin films of polymerized ionic liquids over a broad frequency range spanning over six orders of magnitude by broadband dielectric spectroscopy will be presented. The approach involves using an electrode configuration with lithographically patterned silica nanostructures, which allow for an air gap between the confined ion conductor and one of the electrodes. It is observed that the characteristic ion dynamics rates significantly slow down with decreasing film thicknesses above the calorimetric glass transition of the bulk polymer. However, the mean rates remain bulk-like at lower temperatures. These results highlight the increasing influence of the polymer/substrate interactions with decreasing film thickness on ion dynamics. The authors gratefully acknowledge the National Science Foundation for financial support through the Polymers Program award DMR-1508394.

Broadband photocarrier dynamics and nonlinear absorption of PLD-grown WTe2 semimetal films

NASA Astrophysics Data System (ADS)

Gao, Wenbin; Huang, Lei; Xu, Jinlong; Chen, Yequan; Zhu, Chunhui; Nie, Zhonghui; Li, Yao; Wang, Xuefeng; Xie, Zhenda; Zhu, Shining; Xu, Jun; Wan, Xiangang; Zhang, Chao; Xu, Yongbing; Shi, Yi; Wang, Fengqiu

2018-04-01

WTe2 is a unique material in the family of transition metal dichalcogenides and it has been proposed as a candidate for type-II Weyl semimetals. However, thus far, studies on the optical properties of this emerging material have been significantly hindered by the lack of large-area, high-quality WTe2 materials. Here, we grow a centimeter-scale, highly crystalline WTe2 ultrathin film (˜35 nm) by a pulsed laser deposition technique. Broadband pump-probe spectroscopy (1.2-2.5 μm) reveals a peculiar ultrafast optical response where an initial photo-bleaching signal (lasting ˜3 ps) is followed by a long-lived photoinduced absorption signature. Nonlinear absorption characterization using femtosecond pulses confirms the saturable absorption response of the WTe2 ultrathin films, and we further demonstrated a mode-locked Thulium fiber laser using a WTe2 absorber. Our work provides important insights into linear and nonlinear optical responses of WTe2 thin films.

Evaluating nanoscale ultra-thin metal films by means of lateral photovoltaic effect in metal-semiconductor structure

NASA Astrophysics Data System (ADS)

Zheng, Diyuan; Yu, Chongqi; Zhang, Qian; Wang, Hui

2017-12-01

Nanoscale metal-semiconductor (MS) structure materials occupy an important position in semiconductor and microelectronic field due to their abundant physical phenomena and effects. The thickness of metal films is a critical factor in determining characteristics of MS devices. How to detect or evaluate the metal thickness is always a key issue for realizing high performance MS devices. In this work, we propose a direct surface detection by use of the lateral photovoltaic effect (LPE) in MS structure, which can not only measure nanoscale thickness, but also detect the fluctuation of metal films. This method is based on the fact that the output of lateral photovoltaic voltage (LPV) is closely linked with the metal thickness at the laser spot. We believe this laser-based contact-free detection is a useful supplement to the traditional methods, such as AFM, SEM, TEM or step profiler. This is because these traditional methods are always incapable of directly detecting ultra-thin metal films in MS structure materials.

Switching characteristics for ferroelectric random access memory based on RC model in poly(vinylidene fluoride-trifluoroethylene) ultrathin films

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

Liu, ChangLi; Complex and Intelligent System Research Center, East China University of Science and Technology, Shanghai 200237; Wang, XueJun

2016-05-15

The switching characteristic of the poly(vinylidene fluoride-trifluoroethlene) (P(VDF-TrFE)) films have been studied at different ranges of applied electric field. It is suggest that the increase of the switching speed upon nucleation protocol and the deceleration of switching could be related to the presence of a non-ferroelectric layer. Remarkably, a capacitor and resistor (RC) links model plays significant roles in the polarization switching dynamics of the thin films. For P(VDF-TrFE) ultrathin films with electroactive interlayer, it is found that the switching dynamic characteristics are strongly affected by the contributions of resistor and non-ferroelectric (non-FE) interface factors. A corresponding experiment is designedmore » using poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic) (PEDOT-PSSH) as interlayer with different proton concentrations, and the testing results show that the robust switching is determined by the proton concentration in interlayer and lower leakage current in circuit to reliable applications of such polymer films. These findings provide a new feasible method to enhance the polarization switching for the ferroelectric random access memory.« less

Surface structural reconstruction of SrVO3 thin films on SrTiO3 (001)

NASA Astrophysics Data System (ADS)

Wang, Gaomin; Saghayezhian, Mohammad; Chen, Lina; Guo, Hangwen; Zhang, Jiandi

Paramagnetic metallic oxide SrVO3>(SVO) is an itinerant system known to undergo thickness-induced metal-insulator-transition (MIT) in ultrathin film form, which makes it a prototype system for the study of the mechanism behind metal-insulator-transition like structure distortion, electron correlations and disorder-induced localization. We have grown SrVO3 thin film with atomically flat surface through the layer-by-layer deposition by laser Molecular Beam Epitaxy (laser-MBE) on SrTiO3 (001) surface. Low Energy Electron Diffraction (LEED) measurements reveal that there is a (√2X √2) R45°surface reconstruction independent of film thickness. By using LEED-I(V) structure refinement, we determine the surface structure. In combination with X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM), we discuss the implication on the MIT in ultrathin films below 2-3 unit cell thickness. This work is supported by the National Science Foundation under the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

Influence of hydrogen on the structure and stability of ultra-thin ZnO on metal substrates

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

Bieniek, Bjoern; Hofmann, Oliver T.; Institut für Festkörperphysik, TU Graz, 8010 Graz

2015-03-30

We investigate the atomic and electronic structure of ultra-thin ZnO films (1 to 4 layers) on the (111) surfaces of Ag, Cu, Pd, Pt, Ni, and Rh by means of density-functional theory. The ZnO monolayer is found to adopt an α-BN structure on the metal substrates with coincidence structures in good agreement with experiment. Thicker ZnO layers change into a wurtzite structure. The films exhibit a strong corrugation, which can be smoothed by hydrogen (H) adsorption. An H over-layer with 50% coverage is formed at chemical potentials that range from low to ultra-high vacuum H{sub 2} pressures. For the Agmore » substrate, both α-BN and wurtzite ZnO films are accessible in this pressure range, while for Cu, Pd, Pt, Rh, and Ni wurtzite films are favored. The surface structure and the density of states of these H passivated ZnO thin films agree well with those of the bulk ZnO(0001{sup ¯})-2×1-H surface.« less

Corrosion Protection of Copper Using Al2O3, TiO2, ZnO, HfO2, and ZrO2 Atomic Layer Deposition.

PubMed

Daubert, James S; Hill, Grant T; Gotsch, Hannah N; Gremaud, Antoine P; Ovental, Jennifer S; Williams, Philip S; Oldham, Christopher J; Parsons, Gregory N

2017-02-01

Atomic layer deposition (ALD) is a viable means to add corrosion protection to copper metal. Ultrathin films of Al 2 O 3 , TiO 2 , ZnO, HfO 2 , and ZrO 2 were deposited on copper metal using ALD, and their corrosion protection properties were measured using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). Analysis of ∼50 nm thick films of each metal oxide demonstrated low electrochemical porosity and provided enhanced corrosion protection from aqueous NaCl solution. The surface pretreatment and roughness was found to affect the extent of the corrosion protection. Films of Al 2 O 3 or HfO 2 provided the highest level of initial corrosion protection, but films of HfO 2 exhibited the best coating quality after extended exposure. This is the first reported instance of using ultrathin films of HfO 2 or ZrO 2 produced with ALD for corrosion protection, and both are promising materials for corrosion protection.

NOL specular spin-valve heads using an ultrathin CoFe free layer

NASA Astrophysics Data System (ADS)

Fukuzawa, Hideaki; Koi, Katsuhiko; Tomita, Hiroshi; Fuke, Hiromi Niu; Kamiguchi, Yuzo; Iwasaki, Hitoshi; Sahashi, Masashi

2001-10-01

This paper reports the film and head performance of specular spin valves with nano-oxide layer (NOL-SPSV). A large MR ratio of 17% was obtained by using an ultrathin CoFe free layer with a high conductance Cu layer, which decreases the sense current field of a free layer and brings good soft magnetic characteristics. Prototype heads with a read track width of 0.47-0.61 μm were fabricated by using NOL-SPSV films with an MR ratio of 14-15%, Hua˜400 Oe, and Hc˜5 Oe. High output signal voltage of 8-11 mV/μm was realized in the NOL-SPSV heads.

BIMOS transistor solutions for ESD protection in FD-SOI UTBB CMOS technology

NASA Astrophysics Data System (ADS)

Galy, Philippe; Athanasiou, S.; Cristoloveanu, S.

2016-01-01

We evaluate the Electro-Static Discharge (ESD) protection capability of BIpolar MOS (BIMOS) transistors integrated in ultrathin silicon film for 28 nm Fully Depleted SOI (FD-SOI) Ultra Thin Body and BOX (UTBB) high-k metal gate technology. Using as a reference our measurements in hybrid bulk-SOI structures, we extend the BIMOS design towards the ultrathin silicon film. Detailed study and pragmatic evaluations are done based on 3D TCAD simulation with standard physical models using Average Current Slope (ACS) method and quasi-static DC stress (Average Voltage Slope AVS method). These preliminary 3D TACD results are very encouraging in terms of ESD protection efficiency in advanced FD-SOI CMOS.

Electrolyte-Sensing Transistor Decals Enabled by Ultrathin Microbial Nanocellulose

PubMed Central

Yuen, Jonathan D.; Walper, Scott A.; Melde, Brian J.; Daniele, Michael A.; Stenger, David A.

2017-01-01

We report an ultra-thin electronic decal that can simultaneously collect, transmit and interrogate a bio-fluid. The described technology effectively integrates a thin-film organic electrochemical transistor (sensing component) with an ultrathin microbial nanocellulose wicking membrane (sample handling component). As far as we are aware, OECTs have not been integrated in thin, permeable membrane substrates for epidermal electronics. The design of the biocompatible decal allows for the physical isolation of the electronics from the human body while enabling efficient bio-fluid delivery to the transistor via vertical wicking. High currents and ON-OFF ratios were achieved, with sensitivity as low as 1 mg·L−1. PMID:28102316

Electrolyte-Sensing Transistor Decals Enabled by Ultrathin Microbial Nanocellulose

NASA Astrophysics Data System (ADS)

Yuen, Jonathan D.; Walper, Scott A.; Melde, Brian J.; Daniele, Michael A.; Stenger, David A.

2017-01-01

We report an ultra-thin electronic decal that can simultaneously collect, transmit and interrogate a bio-fluid. The described technology effectively integrates a thin-film organic electrochemical transistor (sensing component) with an ultrathin microbial nanocellulose wicking membrane (sample handling component). As far as we are aware, OECTs have not been integrated in thin, permeable membrane substrates for epidermal electronics. The design of the biocompatible decal allows for the physical isolation of the electronics from the human body while enabling efficient bio-fluid delivery to the transistor via vertical wicking. High currents and ON-OFF ratios were achieved, with sensitivity as low as 1 mg·L-1.

Spin accumulation in disordered topological insulator ultrathin films

NASA Astrophysics Data System (ADS)

Siu, Zhuo Bin; Ho, Cong Son; Tan, Seng Ghee; Jalil, Mansoor B. A.

2017-08-01

Topological insulator (TI) ultrathin films differ from the more commonly studied semi-infinite bulk TIs in that the former possess both top and bottom surfaces where the surface states localized at different surfaces can couple to one another across the finite thickness of the film. In the presence of an in-plane magnetization, the TI thin films display two distinct phases depending on which of the inter-surface coupling or the magnetization is stronger. In this work, we consider a Bi2Se3 TI thin film system with an in-plane magnetization and numerically calculate the resulting spin accumulation on both surfaces of the film due to an in-plane electric field to linear order. We describe a numerical scheme for performing the Kubo formula calculation in which we include impurity scattering and vertex corrections. We find that the sums of the spin accumulation over the two surfaces in the in-plane direction perpendicular to the magnetization and in the out of plane direction are antisymmetric in Fermi energy around the charge neutrality point and are non-vanishing only when the symmetry between the top and bottom TI surfaces is broken. The impurity scattering, in general, diminishes the magnitude of the spin accumulation.

Photochemistry on ultrathin metal films: Strongly enhanced cross sections for NO2 on Ag /Si(100)

NASA Astrophysics Data System (ADS)

Wesenberg, Claudia; Autzen, Olaf; Hasselbrink, Eckart

2006-12-01

The surface photochemistry of NO2 on ultrathin Ag(111) films (5-60nm ) on Si(100) substrates has been studied. NO2, forming N2O4 on the surface, dissociates to release NO and NO2 into the gas phase with translational energies exceeding the equivalent of the sample temperature. An increase of the photodesorption cross section is observed for 266nm light when the film thickness is decreased below 30nm despite the fact that the optical absorptivity decreases. For 4.4nm film thickness this increase is about threefold. The data are consistent with a similar effect for 355nm light. The reduced film thickness has no significant influence on the average translation energy of the desorbing molecules or the branching into the different channels. The increased photodesorption cross section is interpreted to result from photon absorption in the Si substrate producing electrons with no or little momenta parallel to the surface at energies where this is not allowed in Ag. It is suggested that these electrons penetrate through the Ag film despite the gap in the surface projected band structure.

Graphene-Based Environmental Barriers

PubMed Central

Guo, Fei; Silverberg, Gregory; Bowers, Shin; Kim, Sang-Pil; Datta, Dibakar; Shenoy, Vivek; Hurt, Robert H.

2012-01-01

Many environmental technologies rely on containment by engineered barriers that inhibit the release or transport of toxicants. Graphene is a new, atomically thin, two-dimensional sheet material, whose aspect ratio, chemical resistance, flexibility, and impermeability make it a promising candidate for inclusion in a next generation of engineered barriers. Here we show that ultrathin graphene oxide (GO) films can serve as effective barriers for both liquid and vapor permeants. First, GO deposition on porous substrates is shown to block convective flow at much lower mass loadings than other carbon nanomaterials, and can achieve hydraulic conductivities of 5×10−12 cm/s or lower. Second we show that ultrathin GO films of only 20 nm thickness coated on polyethylene films reduce their vapor permeability by 90% using elemental mercury as a model vapor toxicant. The barrier performance of GO in this thin-film configuration is much better than the Nielsen model limit, which describes ideal behavior of flake-like fillers uniformly imbedded in a polymer. The Hg barrier performance of GO films is found to be sensitive to residual water in the films, which is consistent with molecular dynamics (MD) simulations that show lateral diffusion of Hg atoms in graphene interlayer spaces that have been expanded by hydration. PMID:22717015

Critical current enhancement driven by suppression of superconducting fluctuation in ion-gated ultrathin FeSe

NASA Astrophysics Data System (ADS)

Harada, T.; Shiogai, J.; Miyakawa, T.; Nojima, T.; Tsukazaki, A.

2018-05-01

The framework of phase transition, such as superconducting transition, occasionally depends on the dimensionality of materials. Superconductivity is often weakened in the experimental conditions of two-dimensional thin films due to the fragile superconducting state against defects and interfacial effects. In contrast to this general trend, superconductivity in the thin limit of FeSe exhibits an opposite trend, such as an increase in critical temperature (T c) and the superconducting gap exceeding the bulk values; however, the dominant mechanism is still under debate. Here, we measured thickness-dependent electrical transport properties of the ion-gated FeSe thin films to evaluate the superconducting critical current (I c) in the ultrathin FeSe. Upon systematically decreasing the FeSe thickness by the electrochemical etching technique in the Hall bar-shaped electric double-layer transistors, we observed a dramatic enhancement of I c reaching about 10 mA and corresponding to about 107 A cm‑2 in the thinnest condition. By analyzing the transition behavior, we clarify that the suppressed superconducting fluctuation is one of the origins of the large I c in the ion-gated ultrathin FeSe films. These results indicate the existence of a robust superconducting state possibly with dense Cooper pairs at the thin limit of FeSe.

Fabrication of superconducting nanowires from ultrathin MgB2 films via focused ion beam milling

NASA Astrophysics Data System (ADS)

Zhang, Chen; Wang, Da; Liu, Zheng-Hao; Zhang, Yan; Ma, Ping; Feng, Qing-Rong; Wang, Yue; Gan, Zi-Zhao

2015-02-01

High quality superconducting nanowires were fabricated from ultrathin MgB2 films by a focused ion beam milling technique. The precursor MgB2 films in 10 nm thick were grown on MgO substrates by using a hybrid physical-chemical vapor deposition method. The nanowires, in widths of about 300-600 nm and lengths of 1 or 10 μm, showed high superconducting critical temperatures (Tc's) above 34 K and narrow superconducting transition widths (ΔTc's) of 1-3 K. The superconducting critical current density Jc of the nanowires was above 5 × 107 A/cm2 at 20 K. The high Tc, narrow ΔTc, and high Jc of the nanowires offered the possibility of making MgB2-based nano-devices such as hot-electron bolometers and superconducting nanowire single-photon detectors with high operating temperatures at 15-20 K.

Verwey transition in a magnetite ultrathin film by resonant x-ray scattering

NASA Astrophysics Data System (ADS)

Grenier, S.; Bailly, A.; Ramos, A. Y.; De Santis, M.; Joly, Y.; Lorenzo, J. E.; Garaudée, S.; Frericks, M.; Arnaud, S.; Blanc, N.; Boudet, N.

2018-03-01

We report a detailed study of the Verwey transition in a magnetite ultrathin film (UTF) grown on Ag(001) using resonant x-ray scattering (RXS). RXS was measured at the Fe K-edge on the crystal truncation rod of the substrate, increasing the sensitivity to the film thanks to the cross-interference, thereby obtaining an x-ray phase-shift reference and a polarization analyzer. The spectra were interpreted with ad hoc calculations based on density functional theory within a surface-scattering formalism. We observed that the UTF has a relatively sharp transition temperature TV=120 K and is remarkably close to the bulk temperature for such thickness. We determined the specific Fe stacking at the interface with the substrate below TV, and detected a spectroscopic signal evolving with temperature from TV up to at least TV+80 K, hinting that the RT crystallographic structure does not set at TV in the UTF.

Ultra thin metallic coatings to control near field radiative heat transfer

NASA Astrophysics Data System (ADS)

Esquivel-Sirvent, R.

2016-09-01

We present a theoretical calculation of the changes in the near field radiative heat transfer between two surfaces due to the presence of ultra thin metallic coatings on semiconductors. Depending on the substrates, the radiative heat transfer is modulated by the thickness of the ultra thin film. In particular we consider gold thin films with thicknesses varying from 4 to 20 nm. The ultra-thin film has an insulator-conductor transition close to a critical thickness of dc = 6.4 nm and there is an increase in the near field spectral heat transfer just before the percolation transition. Depending on the substrates (Si or SiC) and the thickness of the metallic coatings we show how the near field heat transfer can be increased or decreased as a function of the metallic coating thickness. The calculations are based on available experimental data for the optical properties of ultrathin coatings.

A method to monitor the quality of ultra-thin nitride for trench DRAM with a buried strap structure

NASA Astrophysics Data System (ADS)

Wu, Yung-Hsien; Wang, Chun-Yao; Chang, Ian; Kao, Chien-Kang; Kuo, Chia-Ming; Ku, Alex

2007-02-01

A new approach to monitor the quality of an ultra-thin nitride film has been proposed. The nitride quality is monitored by observing the oxide thickness for the nitride film after wet oxidation since the resistance to oxidation strongly depends on its quality. To obtain a stable oxide thickness without interference from extrinsic factors for process monitoring, monitor wafers without dilute HF solution clean are suggested because the native-oxide containing surface is less sensitive to oxygen and therefore forms the nitride film with stable quality. In addition, the correlation between variable retention time (VRT) performance of a real dynamic random access memory (DRAM) product and oxide thickness from different nitride process temperatures can be successfully explained and this correlation can also be used to establish the appropriate oxide thickness range for process monitoring.

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model.

PubMed

Currie, Marc; Mastro, Michael A; Wheeler, Virginia D

2018-05-23

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 °C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (≤150 °C) growth of ultrathin films (100-1000 Å) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10 -4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films' optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Facile fabrication of ultrathin Pt overlayers onto nanoporous metal membranes via repeated Cu UPD and in situ redox replacement reaction.

PubMed

Liu, Pengpeng; Ge, Xingbo; Wang, Rongyue; Ma, Houyi; Ding, Yi

2009-01-06

Ultrathin Pt films from one to several atomic layers are successfully decorated onto nanoporous gold (NPG) membranes by utilizing under potential deposition (UPD) of Cu onto Au or Pt surfaces, followed by in situ redox replacement reaction (RRR) of UPD Cu by Pt. The thickness of Pt layers can be controlled precisely by repeating the Cu-UPD-RRR cycles. TEM observations coupled with electrochemical testing suggest that the morphology of Pt overlayers changes from an ultrathin epitaxial film in the case of one or two atomic layers to well-dispersed nanoislands in the case of four and more atomic layers. Electron diffraction (ED) patterns confirm that the as-prepared NPG-Pt membranes maintain a single-crystalline structure, even though the thickness of Pt films reaches six atomic layers, indicating the decorated Pt films hold the same crystallographic relationship to the NPG substrate during the entire fabrication process. Due to the regular modulation of Pt utilization, the electrocatalytic activity of NPG-Pt exhibits interesting surface structure dependence in methanol, ethanol, and CO electrooxidation reactions. These novel bimetallic nanocatalysts show excellent electrocatalytic activity and much enhanced poison tolerance as compared to the commercial Pt/C catalysts. The success in the fabrication of NPG-Pt-type materials provides a new path to prepare electrocatalysts with ultralow Pt loading and high Pt utilization, which is of great significance in energy-related applications, such as direct alcohol fuel cells (DAFCs).

Anatase TiO2 ultrathin nanobelts derived from room-temperature-synthesized titanates for fast and safe lithium storage

PubMed Central

Wen, Wei; Wu, Jin-ming; Jiang, Yin-zhu; Yu, Sheng-lan; Bai, Jun-qiang; Cao, Min-hua; Cui, Jie

2015-01-01

Lithium-ion batteries (LIBs) are promising energy storage devices for portable electronics, electric vehicles, and power-grid applications. It is highly desirable yet challenging to develop a simple and scalable method for constructions of sustainable materials for fast and safe LIBs. Herein, we exploit a novel and scalable route to synthesize ultrathin nanobelts of anatase TiO2, which is resource abundant and is eligible for safe anodes in LIBs. The achieved ultrathin nanobelts demonstrate outstanding performances for lithium storage because of the unique nanoarchitecture and appropriate composition. Unlike conventional alkali-hydrothermal approaches to hydrogen titanates, the present room temperature alkaline-free wet chemistry strategy guarantees the ultrathin thickness for the resultant titanate nanobelts. The anatase TiO2 ultrathin nanobelts were achieved simply by a subsequent calcination in air. The synthesis route is convenient for metal decoration and also for fabricating thin films of one/three dimensional arrays on various substrates at low temperatures, in absence of any seed layers. PMID:26133276

Dissolvable Films of Silk Fibroin for Ultrathin Conformal Bio-integrated Electronics

DTIC Science & Technology

2010-01-01

spin- cast films of polyimide (PI) served as a support for arrays of electrodes designed for passive neural recording. Control devices consisted of...optically transparent, mechanically robust, biocompatible silk fibroin films. Adv. Mater. 20, 3070–3072 (2008). 20. Murphy, A. R., John, P. S. & Kaplan, D...induced colour change on periodically nanopatterned silk films. Opt. Express 17, 21271–21279 (2009). 25. Parker, S. T. et al. Biocompatible silk printed

Diffusion of phonons through (along and across) the ultrathin crystalline films

NASA Astrophysics Data System (ADS)

Šetrajčić, J. P.; Jaćimovski, S. K.; Vučenović, S. M.

2017-11-01

Instead of usual approach, applying displacement-displacement Green's functions, the momentum-momentum Green's functions will be used to calculate the diffusion tensor. With this type of Green's function we have calculated and analyzed dispersion law in film-structures. A small number of phonon energy levels along the direction of boundary surfaces joint of the film are discrete-ones and in this case standing waves could occur. This is consequence of quantum size effects. These Green's functions enter into Kubo's formula defining diffusion properties of the system and possible heat transfer direction through observed structures. Calculation of the diffusion tensor for phonons in film-structure requires solving of the system of difference equations. Boundary conditions are included into mentioned system through the Hamiltonian of the film-structure. It has been shown that the diagonal elements of the diffusion tensor express discrete behavior of the dispersion law of elementary excitations. More important result is-that they are temperature independent and that their values are much higher comparing with bulk structures. This result favors better heat conduction of the film, but in direction which is perpendicular to boundary film surface. In the same time this significantly favors appearance 2D superconducting surfaces inside the ultra-thin crystal structure, which are parallel to the boundary surface.

Electrical and optical properties of sub-10 nm nickel silicide films for silicon solar cells

NASA Astrophysics Data System (ADS)

Brahmi, Hatem; Ravipati, Srikanth; Yarali, Milad; Shervin, Shahab; Wang, Weijie; Ryou, Jae-Hyun; Mavrokefalos, Anastassios

2017-01-01

Highly conductive and transparent films of ultra-thin p-type nickel silicide films have been prepared by RF magnetron sputtering of nickel on silicon substrates followed by rapid thermal annealing in an inert environment in the temperature range 400-600 °C. The films are uniform throughout the wafer with thicknesses in the range of 3-6 nm. The electrical and optical properties are presented for nickel silicide films with varying thickness. The Drude-Lorentz model and Fresnel equations were used to calculate the dielectric properties, sheet resistance, absorption and transmission of the films. These ultrathin nickel silicide films have excellent optoelectronic properties for p-type contacts with optical transparencies up to 80% and sheet resistance as low as ~0.15 µΩ cm. Furthermore, it was shown that the use of a simple anti-reflection (AR) coating can recover most of the reflected light approaching the values of a standard Si solar cell with the same AR coating. Overall, the combination of ultra-low thickness, high transmittance, low sheet resistance and ability to recover the reflected light by utilizing standard AR coating makes them ideal for utilization in silicon based photovoltaic technologies as a p-type transparent conductor.

Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films.

PubMed

Krishna, H; Sachan, R; Strader, J; Favazza, C; Khenner, M; Kalyanaraman, R

2010-04-16

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is dependent on film thickness. For films with thickness h of 2 nm < or = h < or = 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films with 11.5 nm < or = h < or = 20 nm, the intermediate stages consisted of regularly sized holes. Measurement of the characteristic length scales for different stages of dewetting as a function of film thickness showed a systematic increase, which is consistent with the spinodal dewetting instability over the entire thickness range investigated. This change in morphology with thickness is consistent with observations made previously for polymer films (Sharma and Khanna 1998 Phys. Rev. Lett. 81 3463-6; Seemann et al 2001 J. Phys.: Condens. Matter 13 4925-38). Based on the behavior of free energy curvature that incorporates intermolecular forces, we have estimated the morphological transition thickness for the intermolecular forces for Ag on SiO2. The theory predictions agree well with observations for Ag. These results show that it is possible to form a variety of complex Ag nanomorphologies in a consistent manner, which could be useful in optical applications of Ag surfaces, such as in surface enhanced Raman sensing.

Theoretical and empirical investigations of KCl:Eu2+ for nearly water-equivalent radiotherapy dosimetry

PubMed Central

Zheng, Yuanshui; Han, Zhaohui; Driewer, Joseph P.; Low, Daniel A.; Li, H. Harold

2010-01-01

Purpose: The low effective atomic number, reusability, and other computed radiography-related advantages make europium doped potassium chloride (KCl:Eu2+) a promising dosimetry material. The purpose of this study is to model KCl:Eu2+ point dosimeters with a Monte Carlo (MC) method and, using this model, to investigate the dose responses of two-dimensional (2D) KCl:Eu2+ storage phosphor films (SPFs). Methods: KCl:Eu2+ point dosimeters were irradiated using a 6 MV beam at four depths (5–20 cm) for each of five square field sizes (5×5–25×25 cm2). The dose measured by KCl:Eu2+ was compared to that measured by an ionization chamber to obtain the magnitude of energy dependent dose measurement artifact. The measurements were simulated using DOSXYZnrc with phase space files generated by BEAMnrcMP. Simulations were also performed for KCl:Eu2+ films with thicknesses ranging from 1 μm to 1 mm. The work function of the prototype KCl:Eu2+ material was determined by comparing the sensitivity of a 150 μm thick KCl:Eu2+ film to a commercial BaFBr0.85I0.15:Eu2+-based SPF with a known work function. The work function was then used to estimate the sensitivity of a 1 μm thick KCl:Eu2+ film. Results: The simulated dose responses of prototype KCl:Eu2+ point dosimeters agree well with measurement data acquired by irradiating the dosimeters in the 6 MV beam with varying field size and depth. Furthermore, simulations with films demonstrate that an ultrathin KCl:Eu2+ film with thickness of the order of 1 μm would have nearly water-equivalent dose response. The simulation results can be understood using classic cavity theories. Finally, preliminary experiments and theoretical calculations show that ultrathin KCl:Eu2+ film could provide excellent signal in a 1 cGy dose-to-water irradiation. Conclusions: In conclusion, the authors demonstrate that KCl:Eu2+-based dosimeters can be accurately modeled by a MC method and that 2D KCl:Eu2+ films of the order of 1 μm thick would have minimal energy dependence. The data support the future research and development of a KCl:Eu2+ storage phosphor-based system for quantitative, high-resolution multidimensional radiation therapy dosimetry. PMID:20175476

A Ga2O3 underlayer as an isomorphic template for ultrathin hematite films toward efficient photoelectrochemical water splitting.

PubMed

Hisatomi, Takashi; Brillet, Jérémie; Cornuz, Maurin; Le Formal, Florian; Tétreault, Nicolas; Sivula, Kevin; Grätzel, Michael

2012-01-01

Hematite photoanodes for photoelectrochemical (PEC) water splitting are often fabricated as extremely-thin films to minimize charge recombination because of the short diffusion lengths of photoexcited carriers. However, poor crystallinity caused by structural interaction with a substrate negates the potential of ultrathin hematite photoanodes. This study demonstrates that ultrathin Ga2O3 underlayers, which were deposited on conducting substrates prior to hematite layers by atomic layer deposition, served as an isomorphic (corundum-type) structural template for ultrathin hematite and improved the photocurrent onset of PEC water splitting by 0.2 V. The benefit from Ga2O3 underlayers was most pronounced when the thickness of the underlayer was approximately 2 nm. Thinner underlayers did not work effectively as a template presumably because of insufficient crystallinity of the underlayer, while thicker ones diminished the PEC performance of hematite because the underlayer prevented electron injection from hematite to a conductive substrate due to the large conduction band offset. The enhancement of PEC performance by a Ga2O3 underlayer was more significant for thinner hematite layers owing to greater margins for improving the crystallinity of ultrathin hematite. It was confirmed that a Ga2O3 underlayer was applicable to a rough conducting substrate loaded with Sb-doped SnO2 nanoparticles, improving the photocurrent by a factor of 1.4. Accordingly, a Ga2O3 underlayer could push forward the development of host-guest-type nanocomposites consisting of highly-rough substrates and extremely-thin hematite absorbers.

Molecular dynamics simulation on adsorption of pyrene-polyethylene onto ultrathin single-walled carbon nanotube

NASA Astrophysics Data System (ADS)

Cai, Lu; Lv, Wenzhen; Zhu, Hong; Xu, Qun

2016-07-01

The mechanism of the adsorption of pyrene-polyethylene (Py-PE) onto ultrathin single-walled carbon nanotube (SWNT) was studied by using all-atom molecular dynamics (MD) simulations. We found that solvent polarity and pyrene group are two critical factors in the Py-PE decoration on ultrathin SWNT. Combined MD simulations with free energy calculations, our results indicate that larger solvent polarity can decrease the contribution of conformation entropy, but contributes little to the interaction energy, moreover, larger SWNT diameter can decrease the contribution of conformation entropy but lead to the increasing of the interaction energy. In polar organic solvent (N, N-Dimethylacetamide), the pyrene group plays a key role in the adsorption of Py-PE onto ultrathin SWNT, not only facilitates the spontaneous adsorption of Py-PE onto ultrathin SWNT, but also helps to form compact structure between themselves in the final adsorption states. While in aqueous solution, pyrene group no longer works as an anchor, but still affects a lot to the final adsorption conformation. Our present work provides detailed theoretical clue to understand the noncovalent interaction between aromatic segment appended polymer and ultrathin SWNT, and helps to explore the potential application of ultrathin SWNT in the fields of hybrid material, biomedical and electronic materials.

Investigations into the formation of nanocrystalline quantum dot thin films by mist deposition process

NASA Astrophysics Data System (ADS)

Kshirsagar, Aditya

Semiconductor nanocrystalline quantum dots (NQDs) have material properties remarkably different compared to bulk semiconductors with the same material composition. These NQDs have various novel applications in the electronic and photonic industry, such as light emitting diodes (LEDs) and flat-panel displays. In these applications, ultra-thin films of NQDs in the monolayer regime are needed to ensure optimal current transport properties and device efficiency. There is ongoing search to find a suitable method to deposit and pattern such ultra-thin films of quantum dots with few monolayer thicknesses. Several competing approaches are available, each with its pros and cons. This study explores mist deposition as the technique to fill this void. In this study, ultra-thin films of quantum dots are deposited on diverse substrates and are characterized to understand the mechanics of mist deposition. Various applications of blanket deposited and patterned quantum dot films are studied. The results discussed here include atomic force microscopy analysis of the films to study surface morphology, fluorescence microscopy to study light emission and optical microscope images to study patterning techniques. These results demonstrate the ability of mist deposition to form 1-4 monolayers thick, uniform, defect-free patterned films with root mean square (RMS) surface roughness less than 2 nm. LEDs fabricated using mist deposition show a peak luminescence greater than 500 cd/m2 for matched red, yellow and green devices using Alq3 as the electron transport layer, and over 9000 cd/m2 for red devices using ZnO as the electron transport layer, respectively. In addition to the experimental approach to study the process and explore potential applications, simulation and modeling are carried out to understand the various aspects of mist deposition. A mathematical model is presented which discusses the atomization process of the precursor solution, the physics involved during the deposition process, and the mechanics of film formation. Results of film morphology simulation using Monte Carlo techniques and process simulation using multi-physics approach are discussed. Problems in pattern transfer due to electrostatic effects when using shadow masks are presented in a separate chapter.

Electric field mediated breakdown of thin liquid films separating microscopic emulsion droplets

NASA Astrophysics Data System (ADS)

Mostowfi, Farshid; Khristov, Khristo; Czarnecki, Jan; Masliyah, Jacob; Bhattacharjee, Subir

2007-04-01

The authors present a microfluidic technique for electrically induced breakup of thin films formed between microscopic emulsion droplets. The method involves creating a stationary film at the intersection of two microchannels etched onto a glass substrate. After stabilizing the film, a ramped potential is applied across it. The electrical stresses developed at the film interfaces lead to its rupture above a threshold potential. The potential difference at which the film ruptures assesses the film stability. This approach is employed to demonstrate how surfactant (lecithin) adsorption imparts stability to an ultrathin oil film formed between two water droplets.

Patchwork Coating of Fragmented Ultra-Thin Films and Their Biomedical Applications in Burn Therapy and Antithrombotic Coating

PubMed Central

Okamura, Yosuke; Nagase, Yu; Takeoka, Shinji

2015-01-01

We have proposed free-standing centimeter-sized ultra-thin films (nanosheets) for biomedical applications. Such nanosheets exhibit unique properties such as transparency, flexibility, and good adhesiveness. However, they are only easily adhered to broad and flat surfaces due to their dimensions. To this end, we recently proposed an innovative nanomaterial: the nanosheets fragmented into submillimeter-size pieces. Intriguingly, such fragmented nanosheets could be adhered to uneven and irregular surfaces in addition to flat surfaces in a spread-out “patchwork” manner. We herein review the fabrication procedure and characterization of fragmented nanosheets composed of biodegradable polyesters and thermostable bio-friendly polymers, and their biomedical applications in burn therapy and antithrombotic coating using a “patchwork coating”. PMID:28793663

Patchwork Coating of Fragmented Ultra-Thin Films and Their Biomedical Applications in Burn Therapy and Antithrombotic Coating.

PubMed

Okamura, Yosuke; Nagase, Yu; Takeoka, Shinji

2015-11-11

We have proposed free-standing centimeter-sized ultra-thin films (nanosheets) for biomedical applications. Such nanosheets exhibit unique properties such as transparency, flexibility, and good adhesiveness. However, they are only easily adhered to broad and flat surfaces due to their dimensions. To this end, we recently proposed an innovative nanomaterial: the nanosheets fragmented into submillimeter-size pieces. Intriguingly, such fragmented nanosheets could be adhered to uneven and irregular surfaces in addition to flat surfaces in a spread-out "patchwork" manner. We herein review the fabrication procedure and characterization of fragmented nanosheets composed of biodegradable polyesters and thermostable bio-friendly polymers, and their biomedical applications in burn therapy and antithrombotic coating using a "patchwork coating".

GaAs shallow-homojunction solar cells

NASA Technical Reports Server (NTRS)

Fan, J. C. C.

1981-01-01

The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

Connecting quantum dots and bionanoparticles in hybrid nanoscale ultra-thin films

NASA Astrophysics Data System (ADS)

Tangirala, Ravisubhash; Hu, Yunxia; Zhang, Qingling; He, Jinbo; Russell, Thomas; Emrick, Todd

2008-03-01

Aldehyde-functionalized CdSe quantum dots and nanorods, and horse spleen ferritin bionanoparticles, were co-assembled at an oil-water interface. Reaction of the aldehydes with the surface-available amines on the ferritin particles enabled cross-linking at the interface, converting the assembled nanoparticles into robust ultra-thin films. The cross-linked capsules and sheets thus made by aldehyde-amine conjugation could be disrupted by addition of acid. Reductive amination chemistry could be performed to convert these degradable capsules and sheets into structures with irreversible cross-linking. Fluorescence confocal microscopy, scanning force microscopy and pendant drop tensiometry were used to characterize these hybrid nanoparticle-based materials, and transmission electron microscopy (TEM) confirmed the presence of both the synthetic and naturally derived nanoparticles.

Measurement of conformability and adhesion energy of polymeric ultrathin film to skin model

NASA Astrophysics Data System (ADS)

Sugano, Junki; Fujie, Toshinori; Iwata, Hiroyasu; Iwase, Eiji

2018-06-01

We measured the conformability and adhesion energy of a polymeric ultrathin film “nanosheet” with hundreds of nanometer thickness to a skin model with epidermal depressions. To compare the confirmability of the nanosheets with different thicknesses and/or under different attaching conditions, we proposed a measurement method using skin models with the same surface profile and defined the surface strain εS as the quantified value of the conformability. Then, we measured the adhesion energy of the nanosheet at each conformability through a vertical tensile test. Experimental results indicate that the adhesion energy does not depend on the liquid used in wetting the nanosheet before attaching to the skin model and increases monotonously as the surface strain εS increases.

Structure of a zinc oxide ultra-thin film on Rh(100)

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

Yuhara, J.; Kato, D.; Matsui, T.

The structural parameters of ultra-thin zinc oxide films on Rh(100) are investigated using low-energy electron diffraction intensity (LEED I–V) curves, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations. From the analysis of LEED I–V curves and DFT calculations, two optimized models A and B are determined. Their structures are basically similar to the planer h-BN ZnO(0001) structure, although some oxygen atoms protrude from the surface, associated with an in-plane shift of Zn atoms. From a comparison of experimental STM images and simulated STM images, majority and minority structures observed in the STM images represent the two optimizedmore » models A and B, respectively.« less

Tunneling interferometry and measurement of the thickness of ultrathin metallic Pb(111) films

NASA Astrophysics Data System (ADS)

Ustavshchikov, S. S.; Putilov, A. V.; Aladyshkin, A. Yu.

2017-10-01

Spectra of the differential tunneling conductivity for ultrathin lead films grown on Si(111) 7 × 7 single crystals with a thickness of 9 to 50 ML have been studied by low-temperature scanning tunneling microscopy and spectroscopy. The presence of local maxima of the tunneling conductivity is characteristic of such systems. The energies of maxima of the differential conductivity are determined by the spectrum of quantum-confined states of electrons in a metallic layer and, consequently, the local thickness of the layer. It has been shown that features of the microstructure of substrates, such as steps of monatomic height, structural defects, and inclusions of other materials covered with a lead layer, can be visualized by bias-modulation scanning tunneling spectroscopy.

An Atomic-Scale X-ray View of Functional Oxide Films

NASA Astrophysics Data System (ADS)

Tung, I.-Cheng

Complex oxides are a class of materials that exhibit a wide variety of physical functionalities, such as ferroelectricity, colossal magnetoresistance, mulitferroicity and superconductivity, with outstanding potential for meeting many of our technological demands. The primary objective of this dissertation is to understand the structural and electronic behavior of complex oxide ultrathin films subjected to confinement, lattice misfit and broken symmetry at the interface. In complex oxide ultrathin films, heteroepitaxial synthesis has evolved into a reliable strategy to engineer orbital-lattice interactions in correlated materials and led to new and entirely unexpected phenomena at their interfaces. I experimentally demonstrated that the bulk crystal symmetry directs the atomic and orbital responses adopted by coherently strained ultrathin films of RNiO3 (R = La, Nd) with detailed X-ray scattering, polarization-dependent X-ray absorption spectroscopy (XAS) and supported by a mathematical point group symmetry analysis, found that strain-stabilized phases maintain a ``memory'' of their bulk state. This topic, however, touched only upon the properties of such films. A fundamental challenge in this research area occurs before this and centers around the understanding of how to create high-quality films with arbitrary configurations. A longstanding challenge in the oxide thin film community has been the growth of An+1BnO3 n+1 Ruddlesden-Popper (RP) compounds. To understand this problem, we have utilized a newly constructed oxide MBE with in situ synchrotron X-ray scattering capability to study the initial growth of such layered oxides and track the dynamic evolution. X-ray results are supported by theoretical calculations that demonstrated the layered oxide films dynamically rearrange during growth, leading to structures that are highly unexpected, and suggest a general approach that may be essential for the construction of metastable RP phases with performing the first atomically controlled synthesis of single-crystalline La3Ni2O7. By building upon this knowledge, I have completed the first to date study of in situ surface X-ray scattering during homoepitaxial MBE growth of SrTiO3, which demonstrates codeposition is consistent with a 2D island growth mode with SrTiO3 islands, but shuttered deposition proceeds by the growth of SrO islands which then restructure into atomically flat SrTiO3 layer during the deposition of the TiO2. From this point, we have conducted a detailed microscopic study of epitaxial LaNiO3 ultrathin films grown on SrTiO3 (001) by using reactive MBE with in situ surface X-ray diffraction and ex situ soft XAS to explore the influence of polar mismatch on the resulting structural and electronic properties. Overall, this thesis highlights the power of artificial confinement to harness control over competing phases in complex oxides with atomic-scale precision.

Giant Ferroelectric Polarization in Ultrathin Ferroelectrics via Boundary-Condition Engineering.

PubMed

Xie, Lin; Li, Linze; Heikes, Colin A; Zhang, Yi; Hong, Zijian; Gao, Peng; Nelson, Christopher T; Xue, Fei; Kioupakis, Emmanouil; Chen, Longqing; Schlom, Darrel G; Wang, Peng; Pan, Xiaoqing

2017-08-01

Tailoring and enhancing the functional properties of materials at reduced dimension is critical for continuous advancement of modern electronic devices. Here, the discovery of local surface induced giant spontaneous polarization in ultrathin BiFeO 3 ferroelectric films is reported. Using aberration-corrected scanning transmission electron microscopy, it is found that the spontaneous polarization in a 2 nm-thick ultrathin BiFeO 3 film is abnormally increased up to ≈90-100 µC cm -2 in the out-of-plane direction and a peculiar rumpled nanodomain structure with very large variation in c/a ratios, which is analogous to morphotropic phase boundaries (MPBs), is formed. By a combination of density functional theory and phase-field calculations, it is shown that it is the unique single atomic Bi 2 O 3 - x layer at the surface that leads to the enhanced polarization and appearance of the MPB-like nanodomain structure. This finding clearly demonstrates a novel route to the enhanced functional properties in the material system with reduced dimension via engineering the surface boundary conditions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Employing Synergetic Effect of Doping and Thin Film Coating to Boost the Performance of Lithium-Ion Battery Cathode Particles

PubMed Central

Patel, Rajankumar L.; Jiang, Ying-Bing; Choudhury, Amitava; Liang, Xinhua

2016-01-01

Atomic layer deposition (ALD) has evolved as an important technique to coat conformal protective thin films on cathode and anode particles of lithium ion batteries to enhance their electrochemical performance. Coating a conformal, conductive and optimal ultrathin film on cathode particles has significantly increased the capacity retention and cycle life as demonstrated in our previous work. In this work, we have unearthed the synergetic effect of electrochemically active iron oxide films coating and partial doping of iron on LiMn1.5Ni0.5O4 (LMNO) particles. The ionic Fe penetrates into the lattice structure of LMNO during the ALD process. After the structural defects were saturated, the iron started participating in formation of ultrathin oxide films on LMNO particle surface. Owing to the conductive nature of iron oxide films, with an optimal film thickness of ~0.6 nm, the initial capacity improved by ~25% at room temperature and by ~26% at an elevated temperature of 55 °C at a 1C cycling rate. The synergy of doping of LMNO with iron combined with the conductive and protective nature of the optimal iron oxide film led to a high capacity retention (~93% at room temperature and ~91% at 55 °C) even after 1,000 cycles at a 1C cycling rate. PMID:27142704

Comparison of molecular orientation and phase transition behaviors in the two kinds of ordered ultrathin films of reversed duckweed polymer ES-3 studied by infrared grazing reflection-absorption spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Qiang; Xu, Weiqing; Zhao, Bing

2003-03-01

A multilayer LB film and a casting film of reversed duckweed polymer ES-3 on Au-evaporated glass slides were investigated by Fourier Transform infrared grazing reflection-absorption spectroscopy. It is found that the two kinds of ordered ultrathin films have different orientation of alkyl chains, nearly perpendicular to the substrate surface for the LB film while rather tilted for the casting film. The studies on their thermal transition behaviors indicate that both of the films have three phase transition processes, respectively, occurring near 65, 105 and 140 °C for the former while near 80, 105 and 140 °C for the latter, but show different transition behavior in the each corresponding transition process. It is referred that at room temperature there are island-like domain structures formed in the LB film, but no ones in the casting film; however, the latter can form the domain structures between the first two transition points due to the desorption of solvents. The formation of domain structure seems to play two important roles, one of which is to make alkyl chains more perpendicular to the substrate surface, and the other to make alkyl chains more packed closely. Thermal cyclic experiments reveal that neither of the films could return to its original state after thermal cyclic treatment up to the temperature, which is above the third transition point, although its alkyl chain becomes highly ordered again.

Ultrathin dendrimer-graphene oxide composite film for stable cycling lithium-sulfur batteries.

PubMed

Liu, Wen; Jiang, Jianbing; Yang, Ke R; Mi, Yingying; Kumaravadivel, Piranavan; Zhong, Yiren; Fan, Qi; Weng, Zhe; Wu, Zishan; Cha, Judy J; Zhou, Henghui; Batista, Victor S; Brudvig, Gary W; Wang, Hailiang

2017-04-04

Lithium-sulfur batteries (Li-S batteries) have attracted intense interest because of their high specific capacity and low cost, although they are still hindered by severe capacity loss upon cycling caused by the soluble lithium polysulfide intermediates. Although many structure innovations at the material and device levels have been explored for the ultimate goal of realizing long cycle life of Li-S batteries, it remains a major challenge to achieve stable cycling while avoiding energy and power density compromises caused by the introduction of significant dead weight/volume and increased electrochemical resistance. Here we introduce an ultrathin composite film consisting of naphthalimide-functionalized poly(amidoamine) dendrimers and graphene oxide nanosheets as a cycling stabilizer. Combining the dendrimer structure that can confine polysulfide intermediates chemically and physically together with the graphene oxide that renders the film robust and thin (<1% of the thickness of the active sulfur layer), the composite film is designed to enable stable cycling of sulfur cathodes without compromising the energy and power densities. Our sulfur electrodes coated with the composite film exhibit very good cycling stability, together with high sulfur content, large areal capacity, and improved power rate.

Highly conductive ultrathin Co films by high-power impulse magnetron sputtering

NASA Astrophysics Data System (ADS)

Jablonka, L.; Riekehr, L.; Zhang, Z.; Zhang, S.-L.; Kubart, T.

2018-01-01

Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 µΩ cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 µΩ cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.

Growth, stability and decomposition of Mg2Si ultra-thin films on Si (100)

NASA Astrophysics Data System (ADS)

Sarpi, B.; Zirmi, R.; Putero, M.; Bouslama, M.; Hemeryck, A.; Vizzini, S.

2018-01-01

Using Auger Electron Spectroscopy (AES), Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Low Energy Electron Diffraction (LEED), we report an in-situ study of amorphous magnesium silicide (Mg2Si) ultra-thin films grown by thermally enhanced solid-phase reaction of few Mg monolayers deposited at room temperature (RT) on a Si(100) surface. Silicidation of magnesium films can be achieved in the nanometric thickness range with high chemical purity and a high thermal stability after annealing at 150 °C, before reaching a regime of magnesium desorption for temperatures higher than 350 °C. The thermally enhanced reaction of one Mg monolayer (ML) results in the appearance of Mg2Si nanometric crystallites leaving the silicon surface partially uncovered. For thicker Mg deposition nevertheless, continuous 2D silicide films are formed with a volcano shape surface topography characteristic up to 4 Mg MLs. Due to high reactivity between magnesium and oxygen species, the thermal oxidation process in which a thin Mg2Si film is fully decomposed (0.75 eV band gap) into a magnesium oxide layer (6-8 eV band gap) is also reported.

Surface chemical reactivity of ultrathin Pd(111) films on Ru(0001): Importance of orbital symmetry in the application of the d-band model

DOE PAGES

Yin, Xiangshi; Cooper, Valentino R.; Weitering, Hanno H.; ...

2015-09-22

The chemical bonding of adsorbate molecules on transition-metal surfaces is strongly influenced by the hybridization between the molecular orbitals and the metal d-band. The strength of this interaction is often correlated with the location of the metal d-band center relative to the Fermi level. Here, we exploit finite size effects in the electronic structure of ultrathin Pd(111) films grown on Ru(0001) to tune their reactivity by changing the film thickness one atom layer at a time, while keeping all other variables unchanged. Interestingly, while bulk Pd(111) is reactive toward oxygen, Pd(111) films below five monolayers are surprisingly inert. This observationmore » is fully in line with the d-band model prediction when applied to the orbitals involved in the bonding. The shift of the d-band center with film thickness is primarily attributed to shifts in the partial density of states associated with the 4d xz and 4d yz orbitals. This study provides an in-depth look into the orbital specific contributions to the surface chemical reactivity, providing new insights that could be useful in surface catalysis.« less

Brillouin light scattering studies of the mechanical properties of ultrathin low-k dielectric films

NASA Astrophysics Data System (ADS)

Link, A.; Sooryakumar, R.; Bandhu, R. S.; Antonelli, G. A.

2006-07-01

In an effort to reduce RC time delays that accompany decreasing feature sizes, low-k dielectric films are rapidly emerging as potential replacements for silicon dioxide (SiO2) at the interconnect level in integrated circuits. The main challenge in low-k materials is their substantially weaker mechanical properties that accompany the increasing pore volume content needed to reduce k. We show that Brillouin light scattering is an excellent nondestructive technique to monitor and characterize the mechanical properties of these porous films at thicknesses well below 200nm that are pertinent to present applications. Observation of longitudinal and transverse standing wave acoustic resonances and the dispersion that accompany their transformation into traveling waves with finite in-plane wave vectors provides for a direct measure of the principal elastic constants that completely characterize the mechanical properties of these ultrathin films. The mode amplitudes of the standing waves, their variation within the film, and the calculated Brillouin intensities account for most aspects of the spectra. We further show that the values obtained by this method agree well with other experimental techniques such as nanoindentation and picosecond laser ultrasonics.

Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

NASA Astrophysics Data System (ADS)

Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

2007-11-01

A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO2). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer etal . [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-film boundary conditions result in qualitatively different dispersion relationships especially in the limit as kho≪1, where k is the wavenumber of the perturbation and ho is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface deformation. Hence, surface deformation caused by liquid phase instabilities is rapidly quenched-in during the cooling phase. This deformed state is further evolved by subsequent laser pulses. These results have implications to developing accurate computer simulations of thin-film dewetting by energetic beams aimed at the manufacturing of optically active nanoscale materials for applications including information processing, optical devices, and solar energy harvesting.

Tunable broadband near-infrared absorber based on ultrathin phase-change material

NASA Astrophysics Data System (ADS)

Hu, Er-Tao; Gu, Tong; Guo, Shuai; Zang, Kai-Yan; Tu, Hua-Tian; Yu, Ke-Han; Wei, Wei; Zheng, Yu-Xiang; Wang, Song-You; Zhang, Rong-Jun; Lee, Young-Pak; Chen, Liang-Yao

2017-11-01

In this work, a tunable broadband near-infrared light absorber was designed and fabricated with a simple and lithography free approach by introducing an ultrathin phase-change material Ge2Sb2Te5 (GST) layer into the metal-dielectric multilayered film structure with the structure parameters as that: SiO2 (72.7 nm)/Ge2Sb2Te5 (6.0 nm)/SiO2 (70.2 nm)/Cu (>100.0 nm). The film structure exhibits a modulation depth of ∼72.6% and an extinction ratio of ∼8.8 dB at the wavelength of 1410 nm. The high light absorption (95%) of the proposed film structure at the wavelength of 450 nm in both of the amorphous and crystalline phase of GST, indicates that the intensity of the reflectance in the infrared region can be rapidly tuned by the blue laser pulses. The proposed planar layered film structure with layer thickness as the only controllable parameter and large reflectivity tuning range shows the potential for practical applications in near-infrared light modulation and absorption.

In-situ observation of equilibrium transitions in Ni films; agglomeration and impurity effects.

PubMed

Thron, Andrew M; Greene, Peter; Liu, Kai; van Benthem, Klaus

2014-02-01

Dewetting of ultra-thin Ni films deposited on SiO2 layers was observed, in cross-section, by in situ scanning transmission electron microscopy. Holes were observed to nucleate by voids which formed at the Ni/SiO2 interface rather than at triple junctions at the free surface of the Ni film. Ni islands were observed to retract, in attempt to reach equilibrium on the SiO2 layer. SiO2 layers with 120 nm thickness were found to limit in situ heating experiments due to poor thermal conductivity of SiO2. The formation of graphite was observed during the agglomeration of ultra-thin Ni films. Graphite was observed to wet both the free surface and the Ni/SiO2 interface of the Ni islands. Cr forms surface oxide layers on the free surface of the SiO2 layer and the Ni islands. Cr does not prevent the dewetting of Ni, however it will likely alter the equilibrium shape of the Ni islands. © 2013 Published by Elsevier B.V.

Dynamics of metal-induced crystallization of ultrathin Ge films by rapid thermal annealing

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

Liao, Yuanxun; Huang, Shujuan; Shrestha, Santosh

2015-12-07

Though Ge crystallization has been widely studied, few works investigate metal-induced crystallization of ultrathin Ge films. For 2 nm Ge films in oxide matrix, crystallization becomes challenging due to easy oxidation and low mobility of Ge atoms. Introducing metal atoms may alleviate these problems, but the functions and the behaviours of metal atoms need to be clarified. This paper investigates the crystallization dynamics of a multilayer structure 1.9 nm Ge/0.5 nm Al/1.5 nm Al{sub 2}O{sub 3} under rapid thermal annealing (RTA). The functions of metal atoms, like effective anti-oxidation, downshifting Raman peaks, and incapability to decrease crystallization temperature, are found and explained. The metalmore » behaviours, such as inter-diffusion and defect generation, are supported with direct evidences, Al-Ge nanobicrystals, and Al cluster in Ge atoms. With these understandings, a two-step RTA process achieves high-quality 2 nm nanocrystal Ge films with Raman peak at 298 cm{sup −1} of FWHM 10.3 cm{sup −1} and atomic smooth interfaces.« less

Dynamics of laser ablation at the early stage during and after ultrashort pulse

NASA Astrophysics Data System (ADS)

Ilnitsky, D. K.; Khokhlov, V. A.; Zhakhovsky, V. V.; Petrov, Yu V.; Migdal, K. P.; Inogamov, N. A.

2016-11-01

Study of material flow in two-temperature states is needed for a fundamental understanding the physics of femtosecond laser ablation. To explore phenomena at a very early stage of laser action on a metallic target our in-house two-temperature hydrodynamics code is used here. The early stage covers duration of laser pulse with next first few picoseconds. We draw attention to the difference in behavior at this stage between the cases: (i) of an ultrathin film (thickness of order of skin depth d skin or less), (ii) thin films (thickness of a film is 4-7 of d skin for gold), and (iii) bulk targets (more than 10d skin for gold). We demonstrate that these differences follow from a competition among conductive cooling of laser excited electrons in a skin layer, electron-ion coupling, and hydrodynamics of unloading caused by excess of pressure of excited free electrons. Conductive cooling of the skin needs a heat sink, which is performed by the cold material outside the skin. Such sink is unavailable in the ultrathin films.

Magneto-optical properties of CoFeB ultrathin films: Effect of Ta buffer and capping layer

NASA Astrophysics Data System (ADS)

Husain, Sajid; Gupta, Nanhe Kumar; Barwal, Vineet; Chaudhary, Sujeet

2018-05-01

The effect of adding Ta as a capping and buffer layer on ultrathin CFB(Co60Fe20B20) thin films has been investigated by magneto-optical Kerr effect. A large difference in the coercivity and saturation field is observed between the single layer CFB(2nm) and Ta(5nm)/CFB(2nm)/Ta(2nm) trilayer structure. In particular, the in-plane anisotropy energy is found to be 90kJ/m3 on CFB(2nm) and 2.22kJ/m3 for Ta(5nm)/CFB(2nm)/Ta(2nm) thin films. Anisotropy energy further reduced to 0.93kJ/m3 on increasing the CFB thinness in trilayer structure i.e., Ta(5nm)/CFB(4nm)/Ta(2nm). Using VSM measurement, the saturation magnetization is found to be 1230±50 kA/m. Low coercivity and anisotropy energy in capped and buffer layer thin films envisage the potential of employing CFB for low field switching applications of the spintronic devices.

Domain growth of carbon nanotubes assisted by dewetting of thin catalyst precursor films

NASA Astrophysics Data System (ADS)

Srivastava, Alok Kumar; Sachan, Priyanka; Samanta, Chandan; Mukhopadhyay, Kingsuk; Sharma, Ashutosh

2014-01-01

We explore self-organized dewetting of ultrathin films of a novel metal complex as a one step surface patterning method to create nanoislands of iron, using which spatially separated carbon nanostructures were synthesized. Dewetting of ultrathin metal complex films was induced by two different methods: liquid solvent exposure and thermal annealing to engender surface patterning. For thermal dewetting, thin films of the iron oleate complex were dewetted at high temperature. In the case of liquid solvent assisted dewetting, the metal complex, mixed with a sacrificial polymer (polystyrene) was spin coated as thin films (<40 nm) and then dewetted under an optimal solution mixture consisting of methyl ethyl ketone, acetone and water. The carrier polymer was then selectively removed to produce the iron metal islands. These metal islands were used for selective growth of discrete patches of multiwall CNTs and CNFs by a chemical vapor deposition (CVD) process. Solvent induced dewetting showed clear advantages over thermal dewetting owing to reduced size of catalyst domains formed by dewetting, an improved control over CNT growth as well as in its ability to immobilize the seed particles. The generic solution mediated dewetting and pattern generation in thin films of various catalytic precursors can thus be a powerful method for selective domain growth of a variety of functional nanomaterials.

Stepwise crystallization and the layered distribution in crystallization kinetics of ultra-thin poly(ethylene terephthalate) film

NASA Astrophysics Data System (ADS)

Zuo, Biao; Xu, Jianquan; Sun, Shuzheng; Liu, Yue; Yang, Juping; Zhang, Li; Wang, Xinping

2016-06-01

Crystallization is an important property of polymeric materials. In conventional viewpoint, the transformation of disordered chains into crystals is usually a spatially homogeneous process (i.e., it occurs simultaneously throughout the sample), that is, the crystallization rate at each local position within the sample is almost the same. Here, we show that crystallization of ultra-thin poly(ethylene terephthalate) (PET) films can occur in the heterogeneous way, exhibiting a stepwise crystallization process. We found that the layered distribution of glass transition dynamics of thin film modifies the corresponding crystallization behavior, giving rise to the layered distribution of the crystallization kinetics of PET films, with an 11-nm-thick surface layer having faster crystallization rate and the underlying layer showing bulk-like behavior. The layered distribution in crystallization kinetics results in a particular stepwise crystallization behavior during heating the sample, with the two cold-crystallization temperatures separated by up to 20 K. Meanwhile, interfacial interaction is crucial for the occurrence of the heterogeneous crystallization, as the thin film crystallizes simultaneously if the interfacial interaction is relatively strong. We anticipate that this mechanism of stepwise crystallization of thin polymeric films will allow new insight into the chain organization in confined environments and permit independent manipulation of localized properties of nanomaterials.

Stepwise crystallization and the layered distribution in crystallization kinetics of ultra-thin poly(ethylene terephthalate) film

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

Zuo, Biao, E-mail: chemizuo@zstu.edu.cn, E-mail: wxinping@yahoo.com; Xu, Jianquan; Sun, Shuzheng

2016-06-21

Crystallization is an important property of polymeric materials. In conventional viewpoint, the transformation of disordered chains into crystals is usually a spatially homogeneous process (i.e., it occurs simultaneously throughout the sample), that is, the crystallization rate at each local position within the sample is almost the same. Here, we show that crystallization of ultra-thin poly(ethylene terephthalate) (PET) films can occur in the heterogeneous way, exhibiting a stepwise crystallization process. We found that the layered distribution of glass transition dynamics of thin film modifies the corresponding crystallization behavior, giving rise to the layered distribution of the crystallization kinetics of PET films,more » with an 11-nm-thick surface layer having faster crystallization rate and the underlying layer showing bulk-like behavior. The layered distribution in crystallization kinetics results in a particular stepwise crystallization behavior during heating the sample, with the two cold-crystallization temperatures separated by up to 20 K. Meanwhile, interfacial interaction is crucial for the occurrence of the heterogeneous crystallization, as the thin film crystallizes simultaneously if the interfacial interaction is relatively strong. We anticipate that this mechanism of stepwise crystallization of thin polymeric films will allow new insight into the chain organization in confined environments and permit independent manipulation of localized properties of nanomaterials.« less

Investigation of amorphous RuMoC alloy films as a seedless diffusion barrier for Cu/ p-SiOC:H ultralow- k dielectric integration

NASA Astrophysics Data System (ADS)

Jiao, Guohua; Liu, Bo; Li, Qiran

2015-08-01

Ultrathin RuMoC amorphous films prepared by magnetron co-sputtering with Ru and MoC targets in a sandwiched scheme Si/ p-SiOC:H/RuMoC/Cu were investigated as barrier in copper metallization. The evolution of final microstructure of RuMoC alloy films show sensitive correlation with the content of doped Mo and C elements and can be easily controlled by adjusting the sputtering power of the MoC target. There was no signal of interdiffusion between the Cu and SiOC:H layer in the sample of Cu/RuMoC/ p-SiOC:H/Si, even annealing up to 500 °C. Very weak signal of oxygen have been confirmed in the RuMoC barrier layer both as-deposited and after being annealed, and a good performance on preventing oxygen diffusion has been proved. Leakage current and resistivity evaluations also reveal the excellent thermal reliability of this Si/ p-SiOC:H/RuMoC/Cu film stack at the temperatures up to 500 °C, indicating its potential application in the advanced barrierless Cu metallization.

Phase-field modeling of chemical control of polarization stability and switching dynamics in ferroelectric thin films

DOE PAGES

Cao, Ye; Kalinin, Sergei V.

2016-12-15

Phase-field simulation (PFS) has revolutionized the understanding of domain structure and switching behavior in ferroelectric thin films and ceramics. Generally, PFS is based on the solution of (a set of) Landau-Ginzburg-Devonshire equations for a defined order parameter field(s) under physical boundary conditions (BCs) of fixed potential or charge. While well matched to the interfaces in bulk materials and devices, these BCs are generally not applicable to free ferroelectric surfaces. Here, we developed a self-consistent phase-field model with BCs based on electrochemical equilibria. We chose Pb(Zr 0.2Ti 0.8)O 3 ultrathin film consisting of (001) oriented single tetragonal domain ( Pz) asmore » a model system and systematically studied the effects of oxygen partial pressure, temperature, and surface ions on the ferroelectric state and compared it with the case of complete screening. We have further explored the polarization switching induced by the oxygen partial pressure and observed pronounced size effect induced by chemical screening. Finally, our paper thus helps to understand the emergent phenomena in ferroelectric thin films brought about by the electrochemical ionic surface compensations.« less

Phase-field modeling of chemical control of polarization stability and switching dynamics in ferroelectric thin films

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

Cao, Ye; Kalinin, Sergei V.

Phase-field simulation (PFS) has revolutionized the understanding of domain structure and switching behavior in ferroelectric thin films and ceramics. Generally, PFS is based on the solution of (a set of) Landau-Ginzburg-Devonshire equations for a defined order parameter field(s) under physical boundary conditions (BCs) of fixed potential or charge. While well matched to the interfaces in bulk materials and devices, these BCs are generally not applicable to free ferroelectric surfaces. Here, we developed a self-consistent phase-field model with BCs based on electrochemical equilibria. We chose Pb(Zr 0.2Ti 0.8)O 3 ultrathin film consisting of (001) oriented single tetragonal domain ( Pz) asmore » a model system and systematically studied the effects of oxygen partial pressure, temperature, and surface ions on the ferroelectric state and compared it with the case of complete screening. We have further explored the polarization switching induced by the oxygen partial pressure and observed pronounced size effect induced by chemical screening. Finally, our paper thus helps to understand the emergent phenomena in ferroelectric thin films brought about by the electrochemical ionic surface compensations.« less

Anionic poly(p-phenylenevinylene)/layered double hydroxide ordered ultrathin films with multiple quantum well structure: a combined experimental and theoretical study.

PubMed

Yan, Dongpeng; Lu, Jun; Ma, Jing; Wei, Min; Wang, Xinrui; Evans, David G; Duan, Xue

2010-05-18

The sulfonated phenylenevinylene polyanion derivate (APPV) and exfoliated Mg-Al-layered double hydroxide (LDH) monolayers were alternatively assembled into ordered ultrathin films (UTFs) employing a layer-by-layer method, which shows uniform yellow luminescence. UV-vis absorption and fluorescence spectroscopy present a stepwise and regular growth of the UTFs upon increasing deposited cycles. X-ray diffraction, atomic force microscopy, and scanning electron microscopy demonstrate that the UTFs are orderly periodical layered structure with a thickness of 3.3-3.5 nm per bilayer. The APPV/LDH UTFs exhibit well-defined polarized photoemission characteristic with the maximum luminescence anisotropy of approximately 0.3. Moreover, the UTF exhibit longer fluorescence lifetime (3-3.85-fold) and higher photostability than the drop-casting APPV film under UV irradiation, suggesting that the existence of a LDH monolayer enhances the optical performance of the APPV polyanion. A combination study of electrochemistry and periodic density functional theory was used to investigate the electronic structure of the APPV/LDH system, illustrating that the APPV/LDH UTF is a kind of organic-inorganic hybrid multiple quantum well (MQW) structure with a low band energy of 1.7-1.8 eV, where the valence electrons of APPV can be confined into the energy wells formed by the LDH monolayers effectively. Therefore, this work not only gives a feasible method for fabricating a luminescence ultrathin film but also provides a detailed understanding of the geometric and electronic structures of photoactive polyanions confined between the LDH monolayers.

Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics.

PubMed

Hutchins, Daniel O; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E; Castner, David G; Ma, Hong; Jen, Alex K-Y

2012-11-15

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlO x (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10 -8 A cm -2 and capacitance density of 0.62 µF cm -2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm 2 V -1 s -1 .

Atomic Scale Control of Competing Electronic Phases in Ultrathin Correlated Oxides

NASA Astrophysics Data System (ADS)

Shen, Kyle

2015-03-01

Ultrathin epitaxial thin films offer a number of unique advantages for engineering the electronic properties of correlated transition metal oxides. For example, atomically thin films can be synthesized to artificially confine electrons in two dimensions. Furthermore, using a substrate with a mismatched lattice constant can impose large biaxial strains of larger than 3% (Δa / a), much larger than can achieved in bulk single crystals. Since these dimensionally confined or strained systems may necessarily be less than a few unit cells thick, investigating their properties and electronic structure can be particularly challenging. We employ a combination of reactive oxide molecular beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES) to investigate how dimensional confinement and epitaxial strain can be used to manipulate electronic properties and structure in correlated transition metal oxide thin films. We describe some of our recent work manipulating and studying the electronic structure of ultrathin LaNiO3 through a thickness-driven metal-insulator transition between three and two unit cells (Nature Nanotechnology 9, 443, 2014), where coherent Fermi liquid-like quasiparticles are suppressed at the metal-insulator transition observed in transport. We also will describe some recent unpublished work using epitaxial strain to drive a Lifshitz transition in atomically thin films of the spin-triplet ruthenate superconductor Sr2RuO4, where we also can dramatically alter the quasiparticle scattering rates and drive the system towards non-Fermi liquid behavior near the critical point (B. Burganov, C. Adamo, in preparation). Funding provided by the Office of Naval Research and Air Force Office of Scientific Research.

Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics

PubMed Central

Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.

2013-01-01

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlOx (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10−8 A cm−2 and capacitance density of 0.62 µF cm−2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm2 V−1 s−1. PMID:24288423

First-principles studies of hydrogen interaction with ultrathin Mg and Mg-based alloy films

NASA Astrophysics Data System (ADS)

Yoon, Mina; Weitering, Hanno H.; Zhang, Zhenyu

2011-01-01

The search for technologically and economically viable storage solutions for hydrogen fuel would benefit greatly from research strategies that involve systematic property tuning of potential storage materials via atomic-level modification. Here, we use first-principles density-functional theory to investigate theoretically the structural and electronic properties of ultrathin Mg films and Mg-based alloy films and their interaction with atomic hydrogen. Additional delocalized charges are distributed over the Mg films upon alloying them with 11.1% of Al or Na atoms. These extra charges contribute to enhance the hydrogen binding strength to the films. We calculated the chemical potential of hydrogen in Mg films for different dopant species and film thickness, and we included the vibrational degrees of freedom. By comparing the chemical potential with that of free hydrogen gas at finite temperature (T) and pressure (P), we construct a hydrogenation phase diagram and identify the conditions for hydrogen absorption or desorption. The formation enthalpies of metal hydrides are greatly increased in thin films, and in stark contrast to its bulk phase, the hydride state can only be stabilized at high P and T (where the chemical potential of free H2 is very high). Metal doping increases the thermodynamic stabilities of the hydride films and thus significantly helps to reduce the required pressure condition for hydrogen absorption from H2 gas. In particular, with Na alloying, hydrogen can be absorbed and/or desorbed at experimentally accessible T and P conditions.

Method for fabricating thin films of pyrolytic carbon

DOEpatents

Brassell, G.W.; Lewis, J. Jr.; Weber, G.W.

1980-03-13

The present invention relates to a method for fabricating ultrathin films of pyrolytic carbon. Pyrolytic carbon is vapor deposited onto a concave surface of a heated substrate to a total uniform thickness in the range of about 0.1 to 1.0 micrometer. The carbon film on the substrate is provided with a layer of adherent polymeric resin. The resulting composite film of pyrolytic carbon and polymeric resin is then easily separated from the substrate by shrinking the 10 polymeric resin coating with thermally induced forces.

Method for fabricating thin films of pyrolytic carbon

DOEpatents

Brassell, Gilbert W.; Lewis, Jr., John; Weber, Gary W.

1982-01-01

The present invention relates to a method for fabricating ultra-thin films of pyrolytic carbon. Pyrolytic carbon is vapor deposited onto a concave surface of a heated substrate to a total uniform thickness in the range of about 0.1 to 1.0 micrometer. The carbon film on the substrate is provided with a layer of adherent polymeric resin. The resulting composite film of pyrolytic carbon and polymeric resin is then easily separated from the substrate by shrinking the polymeric resin coating with thermally induced forces.

Development of Membrane Process for Carbon Dioxide Separation from Diving Atmosphere

DTIC Science & Technology

1990-05-01

backing, or support layer, as is shown in Figure 17b. The ultrathin film and backing of this composite membrane, which is sometimes called a " thin - film ...As a result, the properties and performance of a thin - film laminate can be better controlled, in principle, than those of a "skinned" membrane...method of preparing an asymmetric membrane is by coating a thin nonporous film directly on the surface of a suitable microporous t __ .. NEW DEVELOPMEN"TS

Time-dependent changes in the growth of ultrathin ionic liquid films on Ag(111).

PubMed

Lexow, Matthias; Talwar, Timo; Heller, Bettina S J; May, Benjamin; Bhuin, Radha G; Maier, Florian; Steinrück, Hans-Peter

2018-05-09

Various amounts of the ionic liquids (ILs) [C1C1Im][Tf2N] and [C8C1Im][Tf2N] were deposited in vacuo by physical vapour deposition (PVD) on single crystalline Ag(111) at room temperature and subsequently monitored by angle-resolved X-ray photoelectron spectroscopy (ARXPS) as a function of time. For very low coverages of up to one closed molecular layer, an initial wetting layer was rapidly formed for both ILs. Deposition of higher amounts of [C1C1Im][Tf2N] revealed an initial three-dimensional film morphology. On the time scale of hours, characteristic changes of the XPS signals were observed. These are interpreted as island spreading and a transformation towards a nearly two dimensional [C1C1Im][Tf2N] film as the final state. In contrast, a film morphology close to 2D was found from the very beginning for [C8C1Im][Tf2N] deposited on Ag(111) demonstrating the influence of the alkyl chain length on the growth kinetics. These studies also highlight the suitability of time-resolved ARXPS for the investigation of IL/solid interfaces, which play a crucial role in IL thin film applications such as in catalysis, sensor, lubrication, and coating technologies.

Nanowire decorated, ultra-thin, single crystalline silicon for photovoltaic devices.

PubMed

Aurang, Pantea; Turan, Rasit; Unalan, Husnu Emrah

2017-10-06

Reducing silicon (Si) wafer thickness in the photovoltaic industry has always been demanded for lowering the overall cost. Further benefits such as short collection lengths and improved open circuit voltages can also be achieved by Si thickness reduction. However, the problem with thin films is poor light absorption. One way to decrease optical losses in photovoltaic devices is to minimize the front side reflection. This approach can be applied to front contacted ultra-thin crystalline Si solar cells to increase the light absorption. In this work, homojunction solar cells were fabricated using ultra-thin and flexible single crystal Si wafers. A metal assisted chemical etching method was used for the nanowire (NW) texturization of ultra-thin Si wafers to compensate weak light absorption. A relative improvement of 56% in the reflectivity was observed for ultra-thin Si wafers with the thickness of 20 ± 0.2 μm upon NW texturization. NW length and top contact optimization resulted in a relative enhancement of 23% ± 5% in photovoltaic conversion efficiency.

Manipulation of Spin-Torque Generation Using Ultrathin Au

NASA Astrophysics Data System (ADS)

An, Hongyu; Haku, Satoshi; Kanno, Yusuke; Nakayama, Hiroyasu; Maki, Hideyuki; Shi, Ji; Ando, Kazuya

2018-06-01

The generation and the manipulation of current-induced spin-orbit torques are of essential interest in spintronics. However, in spite of the vital progress in spin orbitronics, electric control of the spin-torque generation still remains elusive and challenging. We report on electric control of the spin-torque generation using ionic-liquid gating of ultrathin Au. We show that by simply depositing a SiO2 capping layer on an ultrathin-Au /Ni81Fe19 bilayer, the spin-torque generation efficiency is drastically enhanced by a maximum of 7 times. This enhancement is verified to be originated from the rough ultrathin-Au /Ni81Fe19 interface induced by the SiO2 deposition, which results in the enhancement of the interface spin-orbit scattering. We further show that the spin-torque generation efficiency from the ultrathin Au film can be reversibly manipulated by a factor of 2 using the ionic gating with an external electric field within a small range of 1 V. These results pave a way towards the efficient control of the spin-torque generation in spintronic applications.

Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au.

PubMed

Capelli, R; Mahne, N; Koshmak, K; Giglia, A; Doyle, B P; Mukherjee, S; Nannarone, S; Pasquali, L

2016-07-14

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.

Enhanced Self-Organized Dewetting of Ultrathin Polymer Blend Film for Large-Area Fabrication of SERS Substrate.

PubMed

Zhang, Huanhuan; Xu, Lin; Xu, Yabo; Huang, Gang; Zhao, Xueyu; Lai, Yuqing; Shi, Tongfei

2016-12-06

We study the enhanced dewetting of ultrathin Polystyrene (PS)/Poly (methyl methacrylate) (PMMA) blend films in a mixed solution, and reveal the dewetting can act as a simple and effective method to fabricate large-area surface-enhanced Raman scattering (SERS) substrate. A bilayer structure consisting of under PMMA layer and upper PS layer forms due to vertical phase separation of immiscible PS/PMMA during the spin-coating process. The thicker layer of the bilayer structure dominates the dewetting structures of PS/PMMA blend films. The diameter and diameter distribution of droplets, and the average separation spacing between the droplets can be precisely controlled via the change of blend ratio and film thickness. The dewetting structure of 8 nm PS/PMMA (1:1 wt%) blend film is proved to successfully fabricate large-area (3.5 cm × 3.5 cm) universal SERS substrate via deposited a silver layer on the dewetting structure. The SERS substrate shows good SERS-signal reproducibility (RSD < 7.2%) and high enhancement factor (2.5 × 10 7 ). The enhanced dewetting of polymer blend films broadens the application of dewetting of polymer films, especially in the nanotechnology, and may open a new approach for the fabrication of large-area SERS substrate to promote the application of SERS substrate in the rapid sensitive detection of trace molecules.

Enhanced Self-Organized Dewetting of Ultrathin Polymer Blend Film for Large-Area Fabrication of SERS Substrate

PubMed Central

Zhang, Huanhuan; Xu, Lin; Xu, Yabo; Huang, Gang; Zhao, Xueyu; Lai, Yuqing; Shi, Tongfei

2016-01-01

We study the enhanced dewetting of ultrathin Polystyrene (PS)/Poly (methyl methacrylate) (PMMA) blend films in a mixed solution, and reveal the dewetting can act as a simple and effective method to fabricate large-area surface-enhanced Raman scattering (SERS) substrate. A bilayer structure consisting of under PMMA layer and upper PS layer forms due to vertical phase separation of immiscible PS/PMMA during the spin-coating process. The thicker layer of the bilayer structure dominates the dewetting structures of PS/PMMA blend films. The diameter and diameter distribution of droplets, and the average separation spacing between the droplets can be precisely controlled via the change of blend ratio and film thickness. The dewetting structure of 8 nm PS/PMMA (1:1 wt%) blend film is proved to successfully fabricate large-area (3.5 cm × 3.5 cm) universal SERS substrate via deposited a silver layer on the dewetting structure. The SERS substrate shows good SERS-signal reproducibility (RSD < 7.2%) and high enhancement factor (2.5 × 107). The enhanced dewetting of polymer blend films broadens the application of dewetting of polymer films, especially in the nanotechnology, and may open a new approach for the fabrication of large-area SERS substrate to promote the application of SERS substrate in the rapid sensitive detection of trace molecules. PMID:27922062

Omnidirectional and broadband absorption enhancement from trapezoidal Mie resonators in semiconductor metasurfaces

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

Pala, Ragip A.; Butun, Serkan; Aydin, Koray

2016-09-19

Light trapping in planar ultrathin-film solar cells is limited due to a small number of optical modes available in the thin-film slab. A nanostructured thin-film design could surpass this limit by providing broadband increase in the local density of states in a subwavelength volume and maintaining efficient coupling of light. Here we report a broadband metasurface design, enabling efficient and broadband absorption enhancement by direct coupling of incoming light to resonant modes of subwavelength scale Mie nanoresonators defined in the thin-film active layer. Absorption was investigated both theoretically and experimentally in prototypes consisting of lithographically patterned, two-dimensional periodic arrays ofmore » silicon nanoresonators on silica substrates. A crossed trapezoid resonator shape of rectangular cross section is used to excite broadband Mie resonances across visible and near-IR spectra. Our numerical simulations, optical absorption measurements and photocurrent spectral response measurements demonstrate that crossed trapezoidal Mie resonant structures enable angle-insensitive, broadband absorption. A short circuit current density of 12.0 mA/cm 2 is achieved in 210 nm thick patterned Si films, yielding a 4-fold increase compared to planar films of the same thickness. As a result, it is suggested that silicon metasurfaces with Mie resonator arrays can provide useful insights to guide future ultrathin-film solar cell designs incorporating nanostructured thin active layers.« less

Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au

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

Capelli, R.; Koshmak, K.; Giglia, A.

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of themore » film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.« less

Zeroth order Fabry-Perot resonance enabled ultra-thin perfect light absorber using percolation aluminum and silicon nanofilms

DOE PAGES

Mirshafieyan, Seyed Sadreddin; Luk, Ting S.; Guo, Junpeng

2016-03-04

Here, we demonstrated perfect light absorption in optical nanocavities made of ultra-thin percolation aluminum and silicon films deposited on an aluminum surface. The total layer thickness of the aluminum and silicon films is one order of magnitude less than perfect absorption wavelength in the visible spectral range. The ratio of silicon cavity layer thickness to perfect absorption wavelength decreases as wavelength decreases due to the increased phase delays at silicon-aluminum boundaries at shorter wavelengths. It is explained that perfect light absorption is due to critical coupling of incident wave to the fundamental Fabry-Perot resonance mode of the structure where themore » round trip phase delay is zero. Simulations were performed and the results agree well with the measurement results.« less

Anomalously deep polarization in SrTiO3 (001) interfaced with an epitaxial ultrathin manganite film

DOE PAGES

Wang, Zhen; Tao, Jing; Yu, Liping; ...

2016-10-17

Using atomically-resolved imaging and spectroscopy, we reveal a remarkably deep polarization in non-ferroelectric SrTiO 3 near its interface with an ultrathin nonmetallic film of La 2/3Sr 1/3MnO 3. Electron holography shows an electric field near the interface in SrTiO 3, yielding a surprising spontaneous polarization density of ~ 21 μC/cm 2. Combining the experimental results with first principles calculations, we propose that the observed deep polarization is induced by the electric field originating from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties ofmore » transition metal oxides.« less

Dynamics of ultrathin metal films on amorphous substrates under fast thermal processing

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

Favazza, Christopher; Kalyanaraman, Ramki; Sureshkumar, Radhakrishna

A mathematical model is developed to analyze the growth/decay rate of surface perturbations of an ultrathin metal film on an amorphous substrate (SiO{sub 2}). The formulation combines the approach of Mullins [W. W. Mullins, J. Appl. Phys. 30, 77 (1959)] for bulk surfaces, in which curvature-driven mass transport and surface deformation can occur by surface/volume diffusion and evaporation-condensation processes, with that of Spencer et al. [B. J. Spencer, P. W. Voorhees, and S. H. Davis, Phys. Rev. Lett. 67, 26 (1991)] to describe solid-state transport in thin films under epitaxial strain. Modifications of the Mullins model to account for thin-filmmore » boundary conditions result in qualitatively different dispersion relationships especially in the limit as kh{sub o}<<1, where k is the wavenumber of the perturbation and h{sub o} is the unperturbed film height. The model is applied to study the relative rate of solid-state mass transport as compared to that of liquid phase dewetting in a thin film subjected to a fast thermal pulse. Specifically, we have recently shown that multiple cycles of nanosecond (ns) pulsed laser melting and resolidification of ultrathin metal films on amorphous substrates can lead to the formation of various types of spatially ordered nanostructures [J. Trice, D. Thomas, C. Favazza, R. Sureshkumar, and R. Kalyanaraman, Phys. Rev. B 75, 235439 (2007)]. The pattern formation has been attributed to the dewetting of the thin film by a hydrodynamic instability. In such experiments the film is in the solid state during a substantial fraction of each thermal cycle. However, results of a linear stability analysis based on the aforementioned model suggest that solid-state mass transport has a negligible effect on morphological changes of the surface. Further, a qualitative analysis of the effect of thermoelastic stress, induced by the rapid temperature changes in the film-substrate bilayer, suggests that stress relaxation does not appreciably contribute to surface deformation. Hence, surface deformation caused by liquid phase instabilities is rapidly quenched-in during the cooling phase. This deformed state is further evolved by subsequent laser pulses. These results have implications to developing accurate computer simulations of thin-film dewetting by energetic beams aimed at the manufacturing of optically active nanoscale materials for applications including information processing, optical devices, and solar energy harvesting.« less

Angularly resolved characterization of ion beams from laser-ultrathin foil interactions

NASA Astrophysics Data System (ADS)

Scullion, C.; Doria, D.; Romagnani, L.; Ahmed, H.; Alejo, A.; Ettlinger, O. C.; Gray, R. J.; Green, J.; Hicks, G. S.; Jung, D.; Naughton, K.; Padda, H.; Poder, K.; Scott, G. G.; Symes, D. R.; Kar, S.; McKenna, P.; Najmudin, Z.; Neely, D.; Zepf, M.; Borghesi, M.

2016-09-01

Methods and techniques used to capture and analyze beam profiles produced from the interaction of intense, ultrashort laser pulses and ultrathin foil targets using stacks of Radiochromic Film (RCF) and Columbia Resin #39 (CR-39) are presented. The identification of structure in the beam is particularly important in this regime, as it may be indicative of the dominance of specific acceleration mechanisms. Additionally, RCF can be used to deconvolve proton spectra with coarse energy resolution while mantaining angular information across the whole beam.

Universal depinning transition of domain walls in ultrathin ferromagnets

NASA Astrophysics Data System (ADS)

Diaz Pardo, R.; Savero Torres, W.; Kolton, A. B.; Bustingorry, S.; Jeudy, V.

2017-05-01

We present a quantitative and comparative study of magnetic-field-driven domain-wall depinning transition in different ferromagnetic ultrathin films over a wide range of temperature. We reveal a universal scaling function accounting for both drive and thermal effects on the depinning transition, including critical exponents. The consistent description we obtain for both the depinning and subthreshold thermally activated creep motion should shed light on the universal glassy dynamics of thermally fluctuating elastic objects pinned by disordered energy landscapes.

Dynamic XPS measurements of ultrathin polyelectrolyte films containing antibacterial Ag–Cu nanoparticles

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

Taner-Camcı, Merve; Suzer, Sefik, E-mail: suzer@fen.bilkent.edu.tr

Ultrathin films consisting of polyelectrolyte layers prepared by layer-by-layer deposition technique and containing also Ag and Cu nanoparticles exhibit superior antibacterial activity toward Escherichia coli. These films have been investigated with XPS measurements under square wave excitation at two different frequencies, in order to further our understanding about the chemical/physical nature of the nanoparticles. Dubbed as dynamical XPS, such measurements bring out similarities and differences among the surface structures by correlating the binding energy shifts of the corresponding XPS peaks. Accordingly, it is observed that the Cu2p, Ag3d of the metal nanoparticles, and S2p of cysteine, the stabilizer and themore » capping agent, exhibit similar shifts. On the other hand, the C1s, N1s, and S2p peaks of the polyelectrolyte layers shift differently. This finding leads us the claim that the Ag and Cu atoms are in a nanoalloy structure, capped with cystein, as opposed to phase separated entities.« less

Control of magnetism in Co by an electric field

NASA Astrophysics Data System (ADS)

Chiba, D.; Ono, T.

2013-05-01

In this paper, we review the recent experimental developments on electric-field switching of ferromagnetism in ultra-thin Co films. The application of an electric field changes the electron density at the surface of the Co film, which results in modulation of its Curie temperature. A capacitor structure consisting of a gate electrode, a solid-state dielectric insulator and a Co bottom electrode is used to observe the effect. To obtain a larger change in the electron density, we also fabricated an electric double-layer capacitor structure using an ionic liquid. A large change in the Curie temperature of ∼100 K across room temperature is achieved with this structure. The application of the electric field influences not only the Curie temperature but also the domain-wall motion. A change in the velocity of a domain wall prepared in a Co micro-wire of more than one order of magnitude is observed. Possible mechanisms to explain the above-mentioned electric-field effects in Co ultra-thin films are discussed.

Improved hole-injection and power efficiency of organic light-emitting diodes using an ultrathin cerium fluoride buffer layer

NASA Astrophysics Data System (ADS)

Lu, Hsin-Wei; Kao, Po-Ching; Chu, Sheng-Yuan

2016-09-01

In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3 film as an ultra-thin buffer layer between the ITO and NPB hole transport layer, with the structure configuration ITO/CeF3 (1 nm)/NPB (40 nm)/Alq3 (60 nm)/LiF (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The work function increased from 4.8 eV (standard ITO electrode) to 5.2 eV (1-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The turn-on voltage decreased from 4.2 V to 4.0 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 10820 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.5 cd/A when the 1-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

Electrical properties of epitaxial yttrium iron garnet ultrathin films at high temperatures

NASA Astrophysics Data System (ADS)

Thiery, N.; Naletov, V. V.; Vila, L.; Marty, A.; Brenac, A.; Jacquot, J.-F.; de Loubens, G.; Viret, M.; Anane, A.; Cros, V.; Ben Youssef, J.; Beaulieu, N.; Demidov, V. E.; Divinskiy, B.; Demokritov, S. O.; Klein, O.

2018-02-01

We report a study on the electrical properties of 19-nm-thick yttrium iron garnet (YIG) films grown by liquid phase epitaxy on gadolinium gallium garnet single crystal. The electrical conductivity and Hall coefficient are measured in the high-temperature range [300,400] K using a Van der Pauw four-point probe technique. We find that the electrical resistivity decreases exponentially with increasing temperature following an activated behavior corresponding to a band gap of Eg≈2 eV. It drops to values about 5 ×103Ω cm at T =400 K, thus indicating that epitaxial YIG ultrathin films behave as large gap semiconductors. We also infer the Hall mobility, which is found to be positive (p type) at 5 cm2V-1sec-1 and almost independent of temperature. We discuss the consequence for nonlocal spin transport experiments performed on YIG at room temperature and demonstrate the existence of electrical offset voltages to be disentangled from pure spin effects.

An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic-inorganic hybrid perovskite solar cells.

PubMed

Seo, Seongrok; Park, Ik Jae; Kim, Myungjun; Lee, Seonhee; Bae, Changdeuck; Jung, Hyun Suk; Park, Nam-Gyu; Kim, Jin Young; Shin, Hyunjung

2016-06-02

NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5-7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1-2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current-voltage hysteresis.

Transparent 'solution' of ultrathin magnesium hydroxide nanocrystals for flexible and transparent nanocomposite films.

PubMed

Wang, Jie-Xin; Sun, Qian; Chen, Bo; Wu, Xi; Zeng, Xiao-Fei; Zhang, Cong; Zou, Hai-Kui; Chen, Jian-Feng

2015-05-15

Transparent solutions of nanocrystals exhibit many unique properties, and are thus attractive materials for numerous applications. However, the synthesis of transparent nanocrystal solutions of magnesium hydroxide (MH) with wide applications is yet to be realized. Here, we report a facile two-step process, which includes a direct reactive precipitation in alcohol phase instead of aqueous phase combined with a successive surface modification, to prepare transparent alcohol solutions containing lamellar MH nanocrystals with an average size of 52 nm and an ultrathin thickness of 1-2 nm, which is the thinnest MH nanoplatelet reported in the literatures. Further, highly flexible and transparent nanocomposite films are fabricated with a solution mixing method by adding the transparent MH nanocrystal solutions into PVB solution. Considering the simplicity of the fabrication process, high transparency and good flexibility, this MH/polymer nanocomposite film is promising for flame-resistant applications in plastic electronics and optical devices with high transparency, such as flexible displays, optical filters, and flexible solar cells.

Fluctuation conductance and the Berezinskii-Kosterlitz-Thouless transition in two dimensional epitaxial NbTiN ultra-thin films

NASA Astrophysics Data System (ADS)

K, Makise; H, Terai; T, Yamashita; S, Miki; Z, Wang; Uzawa Y, Y.; S, Ezaki; T, Odou; B, Shinozaki

2012-12-01

We study on the electric transport properties of epitaxial NbTiN ultrathin films in a range from 2 to 8nm. The films with 4 nm thick shows superconductivity of which mean-field superconducting transition temperature is TC0 = 9.43 K The excess conductance due to superconducting fluctuations was measured at temperatures above TC0. The paraconductivity shows a two-dimensional like behaviour at close to TC0. Experimental results are in good agreement with the sum of Aslamazov - Larkin and Maki - Thompson term for superconducting fluctuation theory. Decreasing temperature below TC0, the current-voltage characteristic shows a crossover from linear to nonlinear behaviour. The exponent α of current-voltage relation, V ~ Iα showed universal jump at TCBKT = 9.33 K As results, we find that there is a consistency between the parametrization of the2D characteristics of fluctuation paraconductivity above TC0 and Berezinskii-Kosterlitz-Thouless type behaviour below TC0.

Nanoporous Ni(OH)2 thin film on 3D Ultrathin-graphite foam for asymmetric supercapacitor.

PubMed

Ji, Junyi; Zhang, Li Li; Ji, Hengxing; Li, Yang; Zhao, Xin; Bai, Xin; Fan, Xiaobin; Zhang, Fengbao; Ruoff, Rodney S

2013-07-23

Nanoporous nickel hydroxide (Ni(OH)2) thin film was grown on the surface of ultrathin-graphite foam (UGF) via a hydrothermal reaction. The resulting free-standing Ni(OH)2/UGF composite was used as the electrode in a supercapacitor without the need for addition of either binder or metal-based current collector. The highly conductive 3D UGF network facilitates electron transport and the porous Ni(OH)2 thin film structure shortens ion diffusion paths and facilitates the rapid migration of electrolyte ions. An asymmetric supercapacitor was also made and studied with Ni(OH)2/UGF as the positive electrode and activated microwave exfoliated graphite oxide ('a-MEGO') as the negative electrode. The highest power density of the fully packaged asymmetric cell (44.0 kW/kg) was much higher (2-27 times higher), while the energy density was comparable to or higher, than high-end commercially available supercapacitors. This asymmetric supercapacitor had a capacitance retention of 63.2% after 10,000 cycles.

Ultrathin gas permeable oxide membranes for chemical sensing: Nanoporous Ta 2O 5 test study

DOE PAGES

Imbault, Alexander; Wang, Yue; Kruse, Peter; ...

2015-09-25

Conductometric gas sensors made of gas permeable metal oxide ultrathin membranes can combine the functions of a selective filter, preconcentrator, and sensing element and thus can be particularly promising for the active sampling of diluted analytes. Here we report a case study of the electron transport and gas sensing properties of such a membrane made of nanoporous Ta 2O 5. These membranes demonstrated a noticeable chemical sensitivity toward ammonia, ethanol, and acetone at high temperatures above 400 °C. Furthermore, different from traditional thin films, such gas permeable, ultrathin gas sensing elements can be made suspended enabling advanced architectures of ultrasensitivemore » analytical systems operating at high temperatures and in harsh environments.« less

Growth of beta-MnO2 Films on TiO2(110) by Oxygen-Plasma-Assisted Molecular Beam Epitaxy

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

Chambers, Scott A.; Liang, Yong

Discusses the essential need to understand the heterogeneous chemistry of mineral surfaces at a molecular level for accurate modeling of surface complexion processes in natural environments. Describes the first MBE growth and characterization of ultrathin films of B-MnO2 on TiO2 (110).

Enabling High Performance Instruments for Astronomy and Space Exploration and ALD

NASA Technical Reports Server (NTRS)

Greer, Frank; Lee, M. C.; Hoenk, M. E.; Jones, T. J.; Jacquot, B. C.; Dickie, M.; Monacos, S.; Nikzad, S.; Day, P.; Leduc, R.;

Structure and morphology of magnetron sputter deposited ultrathin ZnO films on confined polymeric template

NASA Astrophysics Data System (ADS)

Singh, Ajaib; Schipmann, Susanne; Mathur, Aakash; Pal, Dipayan; Sengupta, Amartya; Klemradt, Uwe; Chattopadhyay, Sudeshna

2017-08-01

The structure and morphology of ultra-thin zinc oxide (ZnO) films with different film thicknesses on confined polymer template were studied through X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS). Using magnetron sputter deposition technique ZnO thin films with different film thicknesses (<10 nm) were grown on confined polystyrene with ∼2Rg film thickness, where Rg ∼ 20 nm (Rg is the unperturbed radius of gyration of polystyrene, defined by Rg = 0.272 √M0, and M0 is the molecular weight of polystyrene). The detailed internal structure, along the surface/interfaces and the growth direction of the system were explored in this study, which provides insight into the growth procedure of ZnO on confined polymer and reveals that a thin layer of ZnO, with very low surface and interface roughness, can be grown by DC magnetron sputtering technique, with approximately full coverage (with bulk like electron density) even in nm order of thickness, in 2-7 nm range on confined polymer template, without disturbing the structure of the underneath template. The resulting ZnO-polystyrene hybrid systems show strong ZnO near band edge (NBE) and deep-level (DLE) emissions in their room temperature photoluminescence spectra, where the contribution of DLE gets relatively stronger with decreasing ZnO film thickness, indicating a significant enhancement of surface defects because of the greater surface to volume ratio in thinner films.

High-temperature superconductivity: A conventional conundrum

DOE PAGES

Božović, Ivan

2016-01-07

High-temperature superconductivity in ultrathin films of iron selenide deposited on strontium titanate has been attributed to various exotic mechanisms, and new experiments indicate that it may be conventional, with broader implications.

Surface profiles and modulation of ultra-thin perfluoropolyether lubricant in contact sliding

NASA Astrophysics Data System (ADS)

Sinha, S. K.; Kawaguchi, M.; Kato, T.

2004-08-01

Deformation in shear and associated tribological behaviours of ultra-thin lubricants are of significant importance for the lubrication of magnetic hard disks and for other applications such as micro-electromechanical systems, nano-fluidics and nanotechnology. This paper presents the characteristics of the perfluoropolyether ultra-thin lubricant, in terms of its surface profiles when subjected to a contact sliding test. The results indicate that for a several-monolayers thick (~4.0-4.5 nm) lubricant film, sliding produces a considerable amount of surface roughness due to peaks of lubricant that persist during sliding; however, it can flow back or return to a smooth profile after a lapse of time when the sliding is stopped. For a monolayer-thin (~1.4-1.57 nm) film, the lubricant flow is restricted, and the rough profile created due to sliding persists and almost becomes permanent on the wear track. During sliding, due to high shear stress, a characteristic feature of lubricant profile modulation is observed. This modulation, or waviness, is due to the accumulation of lubricant in piles or islands, giving certain amplitudes and frequencies, which themselves depend upon the percentage of lubricant molecules that are chemically bonded to the substrate and the lubricant thickness. The results indicate that ultra-thin lubricants (monolayer and thicker) behave more like a semi-solid (having some sliding characteristics similar to those of rubbers) than a liquid when subjected to a high shear rate during contact sliding.

Pathways from disordered to ordered nanostructures from defect guided dewetting of ultrathin bilayers.

PubMed

Hens, Abhiram; Mondal, Kartick; Biswas, Gautam; Bandyopadhyay, Dipankar

2016-03-01

Transitions from spinodal to pattern-guided dewetting of a bilayer of ultrathin films (<10nm) confined between a pair of patterned surfaces have been explored employing molecular dynamic (MD) simulations. The physical or chemical defects of different sizes and shapes are decorated on the confining substrates by either removal or addition of multiple layers of similar or dissimilar atoms. The simulations are performed to identify the transition from spinodal pathway to the heterogeneous nucleation route, with the variation in the size of the substrate patterns. The MD simulations reveal the limits beyond which the defects can guide the dewetting to generate ordered patterns of nanoscopic size and periodicity. Comparing the results obtained from the MD simulations with the more widely employed continuum dynamics approach highlights the importance of the MD approach in quantitatively analyzing the dynamics of the dewetting of ultrathin films. The study demonstrates that the pattern-guided dewetting of confined bilayers can lead to ordered holes, droplets, and stripes with size and periodicity less than 10nm, which are yet to be realized experimentally and can be of significance for a number of future applications. Copyright © 2015 Elsevier Inc. All rights reserved.

Ultra-thin and -broadband microwave magnetic absorber enhanced by phase gradient metasurface incorporation

NASA Astrophysics Data System (ADS)

Fan, Ya; Wang, Jiafu; Li, Yongfeng; Pang, Yongqiang; Zheng, Lin; Xiang, Jiayu; Zhang, Jieqiu; Qu, Shaobo

2018-05-01

Based on the effect of anomalous reflection and refraction caused by the circularly cross-polarized phase gradient metasurface (PGM), an ultra-thin and -broadband composite absorber composed of metasurface and conventional magnetic absorbing film is proposed and demonstrated in this paper. In the case of keeping nearly the same thickness of absorbing layer, the equivalent thickness of magnetic absorbing film is enlarged by the effect of anomalous reflection and refraction, resulting in the expansion and improvement of the absorbing bandwidth and efficiency in low microwave frequency. A biarc metallic sub-cell for circularly crossed polarization is adopted to form a broadband phase gradient, by the means of rotating the Pancharatnam–Berry phases. As indicated in the experimental results, the fabricated 3.6 mm-thick absorber can averagely absorb microwave energy with the specular reflection below  ‑10 dB in the frequency interval of 2–12 GHz, which shows a good match with simulated results. Due to ultra-thin thickness and ultra-wide operating bandwidth, the proposed application of PGM in absorbing can provide an alternative way to enhance the absorbing property of current absorbing materials.

Parameter Space of Atomic Layer Deposition of Ultrathin Oxides on Graphene

PubMed Central

2016-01-01

Atomic layer deposition (ALD) of ultrathin aluminum oxide (AlOx) films was systematically studied on supported chemical vapor deposition (CVD) graphene. We show that by extending the precursor residence time, using either a multiple-pulse sequence or a soaking period, ultrathin continuous AlOx films can be achieved directly on graphene using standard H2O and trimethylaluminum (TMA) precursors even at a high deposition temperature of 200 °C, without the use of surfactants or other additional graphene surface modifications. To obtain conformal nucleation, a precursor residence time of >2s is needed, which is not prohibitively long but sufficient to account for the slow adsorption kinetics of the graphene surface. In contrast, a shorter residence time results in heterogeneous nucleation that is preferential to defect/selective sites on the graphene. These findings demonstrate that careful control of the ALD parameter space is imperative in governing the nucleation behavior of AlOx on CVD graphene. We consider our results to have model system character for rational two-dimensional (2D)/non-2D material process integration, relevant also to the interfacing and device integration of the many other emerging 2D materials. PMID:27723305

Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition

PubMed Central

Liao, Yu-Kuang; Liu, Yung-Tsung; Hsieh, Dan-Hua; Shen, Tien-Lin; Hsieh, Ming-Yang; Tzou, An-Jye; Chen, Shih-Chen; Tsai, Yu-Lin; Lin, Wei-Sheng; Chan, Sheng-Wen; Shen, Yen-Ping; Cheng, Shun-Jen; Chen, Chyong-Hua; Wu, Kaung-Hsiung; Chen, Hao-Ming; Kuo, Shou-Yi; Charlton, Martin D. B.; Hsieh, Tung-Po; Kuo, Hao-Chung

2017-01-01

Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin films with the thickness of a few nanometers on rough surfaces. We present a new ”paradigm shift” non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In,Ga)Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase. PMID:28383488

Influence of C or In buffer layer on photoluminescence behaviour of ultrathin ZnO film

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

Saravanan, K., E-mail: saravanan@igcar.gov.in; Jayalakshmi, G.; Krishnan, R.

We study the effect of the indium or carbon buffer layer on the photoluminescence (PL) property of ZnO ultrathin films deposited on a Si(100) substrate. The surface morphology of the films obtained using scanning tunnelling microscopy shows spherical shaped ZnO nanoparticles of size ∼8 nm in ZnO/C/Si and ∼22 nm in ZnO/Si samples, while the ZnO/In/Si sample shows elliptical shaped ZnO particles. Further, the ZnO/C/Si sample shows densely packed ZnO nanoparticles in comparison with other samples. Strong band edge emission has been observed in the presence of In or C buffer layer, whereas the ZnO/Si sample exhibits poor PL emission. The influencemore » of C and In buffer layers on the PL behaviour of ZnO films is studied in detail using temperature dependent PL measurements in the range of 4 K–300 K. The ZnO/C/Si sample exhibits a multi-fold enhancement in the PL emission intensity with well-resolved free and bound exciton emission lines. Our experimental results imply that the ZnO films deposited on the C buffer layer showed higher particle density and better exciton emission desired for optoelectronic applications.« less

Enhanced electrical stability of nitrate ligand-based hexaaqua complexes solution-processed ultrathin a-IGZO transistors

NASA Astrophysics Data System (ADS)

Choi, C.; Baek, Y.; Lee, B. M.; Kim, K. H.; Rim, Y. S.

2017-12-01

We report solution-processed, amorphous indium-gallium-zinc-oxide-based (a-IGZO-based) thin-film transistors (TFTs). Our proposed solution-processed a-IGZO films, using a simple spin-coating method, were formed through nitrate ligand-based metal complexes, and they were annealed at low temperature (250 °C) to achieve high-quality oxide films and devices. We investigated solution-processed a-IGZO TFTs with various thicknesses, ranging from 4 to 16 nm. The 4 nm-thick TFT films had smooth morphology and high-density, and they exhibited excellent performance, i.e. a high saturation mobility of 7.73  ±  0.44 cm2 V-1 s-1, a sub-threshold swing of 0.27 V dec-1, an on/off ratio of ~108, and a low threshold voltage of 3.10  ±  0.30 V. However, the performance of the TFTs degraded as the film thickness was increased. We further performed positive and negative bias stress tests to examine their electrical stability, and it was noted that the operating behavior of the devices was highly stable. Despite a small number of free charges, the high performance of the ultrathin a-IGZO TFTs was attributed to the small effect of the thickness of the channel, low bulk resistance, the quality of the a-IGZO/SiO2 interface, and high film density.

Optimizing ultrathin Ag films for high performance oxide-metal-oxide flexible transparent electrodes through surface energy modulation and template-stripping procedures

PubMed Central

Yang, Xi; Gao, Pingqi; Yang, Zhenhai; Zhu, Juye; Huang, Feng; Ye, Jichun

2017-01-01

Among new flexible transparent conductive electrode (TCE) candidates, ultrathin Ag film (UTAF) is attractive for its extremely low resistance and relatively high transparency. However, the performances of UTAF based TCEs critically depend on the threshold thickness for growth of continuous Ag films and the film morphologies. Here, we demonstrate that these two parameters could be strongly altered through the modulation of substrate surface energy. By minimizing the surface energy difference between the Ag film and substrate, a 9 nm UTAF with a sheet resistance down to 6.9 Ω sq−1 can be obtained using an electron-beam evaporation process. The resultant UTAF is completely continuous and exhibits smoother morphologies and smaller optical absorbances in comparison to the counterpart of granular-type Ag film at the same thickness without surface modulation. Template-stripping procedure is further developed to transfer the UTAFs to flexible polymer matrixes and construct Al2O3/Ag/MoOx (AAM) electrodes with excellent surface morphology as well as optical and electronic characteristics, including a root-mean-square roughness below 0.21 nm, a transparency up to 93.85% at 550 nm and a sheet resistance as low as 7.39 Ω sq−1. These AAM based electrodes also show superiority in mechanical robustness, thermal oxidation stability and shape memory property. PMID:28291229

Optimizing ultrathin Ag films for high performance oxide-metal-oxide flexible transparent electrodes through surface energy modulation and template-stripping procedures

NASA Astrophysics Data System (ADS)

Yang, Xi; Gao, Pingqi; Yang, Zhenhai; Zhu, Juye; Huang, Feng; Ye, Jichun

2017-03-01

Among new flexible transparent conductive electrode (TCE) candidates, ultrathin Ag film (UTAF) is attractive for its extremely low resistance and relatively high transparency. However, the performances of UTAF based TCEs critically depend on the threshold thickness for growth of continuous Ag films and the film morphologies. Here, we demonstrate that these two parameters could be strongly altered through the modulation of substrate surface energy. By minimizing the surface energy difference between the Ag film and substrate, a 9 nm UTAF with a sheet resistance down to 6.9 Ω sq-1 can be obtained using an electron-beam evaporation process. The resultant UTAF is completely continuous and exhibits smoother morphologies and smaller optical absorbances in comparison to the counterpart of granular-type Ag film at the same thickness without surface modulation. Template-stripping procedure is further developed to transfer the UTAFs to flexible polymer matrixes and construct Al2O3/Ag/MoOx (AAM) electrodes with excellent surface morphology as well as optical and electronic characteristics, including a root-mean-square roughness below 0.21 nm, a transparency up to 93.85% at 550 nm and a sheet resistance as low as 7.39 Ω sq-1. These AAM based electrodes also show superiority in mechanical robustness, thermal oxidation stability and shape memory property.

Structure and strain relaxation mechanisms of ultrathin epitaxial Pr2O3 films on Si(111)

NASA Astrophysics Data System (ADS)

Schroeder, T.; Lee, T.-L.; Libralesso, L.; Joumard, I.; Zegenhagen, J.; Zaumseil, P.; Wenger, C.; Lupina, G.; Lippert, G.; Dabrowski, J.; Müssig, H.-J.

2005-04-01

The structure of ultrathin epitaxial Pr2O3 films on Si(111) was studied by synchrotron radiation-grazing incidence x-ray diffraction. The oxide film grows as hexagonal Pr2O3 phase with its (0001) plane attached to the Si(111) substrate. The hexagonal (0001) Pr2O3 plane matches the in-plane symmetry of the hexagonal Si(111) surface unit cell by aligning the ⟨101¯0⟩Pr2O3 along the ⟨112¯⟩ Si directions. The small lattice mismatch of 0.5% results in the growth of pseudomorphic oxide films of high crystalline quality with an average domain size of about 50 nm. The critical thickness tc for pseudomorphic growth amounts to 3.0±0.5nm. The relaxation of the oxide film from pseudomorphism to bulk behavior beyond tc causes the introduction of misfit dislocations, the formation of an in-plane small angle mosaicity structure, and the occurence of a phase transition towards a (111) oriented cubic Pr2O3 film structure. The observed phase transition highlights the influence of the epitaxial interface energy on the stability of Pr2O3 phases on Si(111). A mechanism is proposed which transforms the hexagonal (0001) into the cubic (111) Pr2O3 epilayer structure by rearranging the oxygen network but leaving the Pr sublattice almost unmodified.

A method to investigate the electron scattering characteristics of ultrathin metallic films by in situ electrical resistance measurements.

PubMed

Trindade, I G; Fermento, R; Leitão, D; Sousa, J B

2009-07-01

In this article, a method to measure the electrical resistivity/conductivity of metallic thin films during layer growth on specific underlayers is described. The in situ monitoring of an underlayer electrical resistance, its change upon the incoming of new material atoms/molecules, and the growth of a new layer are presented. The method is easy to implement and allows obtaining in situ experimental curves of electrical resistivity dependence upon film thickness with a subatomic resolution, providing insight in film growth microstructure characteristics, specular/diffuse electron scattering surfaces, and optimum film thicknesses.

Magnetron sputtered boron films and TI/B multilayer structures

DOEpatents

Makowiecki, Daniel M.; Jankowski, Alan F.

1993-01-01

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for ultra-thin band pass filters as well as the low Z element in low Z/high Z mirrors which enhance reflectivity from grazing to normal incidence.

Magnetron sputtered boron films and Ti/B multilayer structures

DOEpatents

Makowiecki, Daniel M.; Jankowski, Alan F.

1995-01-01

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for ultra-thin band pass filters as well as the low Z element in low Z/high Z mirrors which enhance reflectivity from grazing to normal incidence.

Magnetron sputtered boron films and TI/B multilayer structures

DOEpatents

Makowiecki, D.M.; Jankowski, A.F.

1993-04-20

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for ultra-thin band pass filters as well as the low Z element in low Z/high Z mirrors which enhance reflectivity from grazing to normal incidence.

Magnetron sputtered boron films and Ti/B multilayer structures

DOEpatents

Makowiecki, D.M.; Jankowski, A.F.

1995-02-14

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for ultra-thin band pass filters as well as the low Z element in low Z/high Z mirrors which enhance reflectivity from grazing to normal incidence. 6 figs.

Heterogeneity in ultrathin films simulated by Monte Carlo method

NASA Astrophysics Data System (ADS)

Sun, Jiebing; Hannon, James B.; Kellogg, Gary L.; Pohl, Karsten

2007-03-01

The 3D composition profile of ultra-thin Pd films on Cu(001) has been experimentally determined using low energy electron microscopy (LEEM).^[1] Quantitative measurements of the alloy concentration profile near steps show that the Pd distribution in the 3^rd layer is heterogeneous due to step overgrowth during Pd deposition. Interestingly, the Pd distribution in the 2^nd layer is also heterogeneous, and appears to be correlated with the distribution in the 1^st layer. We describe Monte Carlo simulations that show that correlation is due to Cu-Pd attraction, and that the 2^nd layer Pd is, in fact, laterally equilibrated. By comparing measured and simulated concentration profiles, we can estimate this attraction within a simple bond counting model. [1] J. B. Hannon, J. Sun, K. Pohl, G. L. Kellogg, Phys. Rev. Lett. 96, 246103 (2006)

Wrapping with a splash: High-speed encapsulation with ultrathin sheets

NASA Astrophysics Data System (ADS)

Kumar, Deepak; Paulsen, Joseph D.; Russell, Thomas P.; Menon, Narayanan

2018-02-01

Many complex fluids rely on surfactants to contain, protect, or isolate liquid drops in an immiscible continuous phase. Thin elastic sheets can wrap liquid drops in a spontaneous process driven by capillary forces. For encapsulation by sheets to be practically viable, a rapid, continuous, and scalable process is essential. We exploit the fast dynamics of droplet impact to achieve wrapping of oil droplets by ultrathin polymer films in a water phase. Despite the violence of splashing events, the process robustly yields wrappings that are optimally shaped to maximize the enclosed fluid volume and have near-perfect seams. We achieve wrappings of targeted three-dimensional (3D) shapes by tailoring the 2D boundary of the films and show the generality of the technique by producing both oil-in-water and water-in-oil wrappings.

Mesoporous polyaniline film on ultra-thin graphene sheets for high performance supercapacitors

NASA Astrophysics Data System (ADS)

Wang, Qian; Yan, Jun; Fan, Zhuangjun; Wei, Tong; Zhang, Milin; Jing, Xiaoyan

2014-02-01

A facile approach has been developed to fabricate mesoporous PANI film on ultra-thin graphene nanosheet (G-mPANI) hybrid by in situ polymerization using graphene-mesoporous silica composite as template. Due to its mesoporous structure, over-all conductive network, G-mPANI electrode displays a specific capacitance of 749 F g-1 at 0.5 A g-1 with excellent rate capability (remains 73% even at 5.0 A g-1), much higher than that of pristine PANI electrode (315 F g-1 at 0.5 A g-1, 39% retention at 5.0 A g-1) in 1 mol L-1 H2SO4 aqueous solution. More interestingly, the G-mPANI hybrid can maintain 88% of its initial capacitance compared to 45% for pristine PANI after 1000 cycles, suggesting a superior electrochemical cyclic stability.

Polarity-driven oxygen vacancy formation in ultrathin LaNiO 3 films on SrTiO 3

DOE PAGES

Tung, I-Cheng; Luo, Guangfu; Lee, June Hyuk; ...

2017-10-18

Oxide heterostructures offer a pathway to control emergent phases in complex oxides, but their creation often leads to boundaries that have a polar discontinuity. In order to fabricate atomic-scale arrangements of dissimilar materials, we need a clear understanding of the pathways by which materials resolve polarity issues. By examining the real-time lattice structure in-situ during growth for the case of polar LaNiO 3 synthesized on non-polar SrTiO 3 (001), we demonstrate how films in ultra-thin limit form as LaNiO 2.5 and then evolve into LaNiO 3 as the thickness increases. Theory explains how the polar energetics drives the formation ofmore » oxygen vacancies and the stability of these phases with thickness and structure.« less

Freestanding palladium nanosheets with plasmonic and catalytic properties

NASA Astrophysics Data System (ADS)

Huang, Xiaoqing; Tang, Shaoheng; Mu, Xiaoliang; Dai, Yan; Chen, Guangxu; Zhou, Zhiyou; Ruan, Fangxiong; Yang, Zhilin; Zheng, Nanfeng

2011-01-01

Ultrathin metal films can exhibit quantum size and surface effects that give rise to unique physical and chemical properties. Metal films containing just a few layers of atoms can be fabricated on substrates using deposition techniques, but the production of freestanding ultrathin structures remains a significant challenge. Here we report the facile synthesis of freestanding hexagonal palladium nanosheets that are less than 10 atomic layers thick, using carbon monoxide as a surface confining agent. The as-prepared nanosheets are blue in colour and exhibit a well-defined but tunable surface plasmon resonance peak in the near-infrared region. The combination of photothermal stability and biocompatibility makes palladium nanosheets promising candidates for photothermal therapy. The nanosheets also exhibit electrocatalytic activity for the oxidation of formic acid that is 2.5 times greater than that of commercial palladium black catalyst.

Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

PubMed

Park, Daesung; Herpers, Anja; Menke, Tobias; Heidelmann, Markus; Houben, Lothar; Dittmann, Regina; Mayer, Joachim

2014-06-01

Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

Effect of structure on the tribology of ultrathin graphene and graphene oxide films.

PubMed

Chen, Hang; Filleter, Tobin

2015-03-27

The friction and wear properties of graphene and graphene oxide (GO) with varying C/O ratio were investigated using friction force microscopy. When applied as solid lubricants between a sliding contact of a silicon (Si) tip and a SiO2/Si substrate, graphene and ultrathin GO films (as thin as 1-2 atomic layers) were found to reduce friction by ∼6 times and ∼2 times respectively as compared to the unlubricated contact. The differences in measured friction were attributed to different interfacial shear strengths. Ultrathin films of GO with a low C/O ratio of ∼2 were found to wear easily under small normal load. The onset of wear, and the location of wear initiation, is attributed to differences in the local shear strength of the sliding interface as a result of the non-homogeneous surface structure of GO. While the exhibited low friction of GO as compared to SiO2 makes it an economically viable coating for micro/nano-electro-mechanical systems with the potential to extend the lifetime of devices, its higher propensity for wear may limit its usefulness. To address this limitation, the wear resistance of GO samples with a higher C/O ratio (∼4) was also studied. The higher C/O ratio GO was found to exhibit much improved wear resistance which approached that of the graphene samples. This demonstrates the potential of tailoring the structure of GO to achieve graphene-like tribological properties.

On the role of ultra-thin oxide cathode synthesis on the functionality of micro-solid oxide fuel cells: Structure, stress engineering and in situ observation of fuel cell membranes during operation

NASA Astrophysics Data System (ADS)

Lai, Bo-Kuai; Kerman, Kian; Ramanathan, Shriram

Microstructure and stresses in dense La 0.6Sr 0.4Co 0.8Fe 0.2O 3 (LSCF) ultra-thin films have been investigated to increase the physical thickness of crack-free cathodes and active area of thermo-mechanically robust micro-solid oxide fuel cell (μSOFC) membranes. Processing protocols employ low deposition rates to create a highly granular nanocrystalline microstructure in LSCF thin films and high substrate temperatures to produce linear temperature-dependent stress evolution that is dominated by compressive stresses in μSOFC membranes. Insight and trade-off on the synthesis are revealed by probing microstructure evolution and electrical conductivity in LSCF thin films, in addition to in situ monitoring of membrane deformation while measuring μSOFC performance at varying temperatures. From these studies, we were able to successfully fabricate failure-resistant square μSOFC (LSCF/YSZ/Pt) membranes with width of 250 μm and crack-free cathodes with thickness of ∼70 nm. Peak power density of ∼120 mW cm -2 and open circuit voltage of ∼0.6 V at 560 °C were achieved on a μSOFC array chip containing ten such membranes. Mechanisms affecting fuel cell performance are discussed. Our results provide fundamental insight to pathways of microstructure and stress engineering of ultra-thin, dense oxide cathodes and μSOFC membranes.

Optical properties of thin gold films applied to Schottky barrier solar cells

NASA Technical Reports Server (NTRS)

YEH Y. M.

1974-01-01

The Schottky barrier solar cell is considered a possible candidate for converting solar to electrical energy both for space and terrestrial applications. Knowledge of the optical constants of the ultrathin metal film used in the cell is essential for analyzing and designing higher efficiency Schottky barrier cells. The optical constants of 7.5 -nm (75-A) gold films on gallium arsenide have been obtained. In addition, the absolute collection efficiency of Schottky barrier solar cells has been determined from measured spectral response and optical constants of the gold film.

Accelerated aging in ultrathin films of a molecular glass former.

PubMed

Sepúlveda, A; Leon-Gutierrez, E; Gonzalez-Silveira, M; Rodríguez-Tinoco, C; Clavaguera-Mora, M T; Rodríguez-Viejo, J

2011-07-08

We report the thermodynamic measurement of the enthalpy released during the aging of supported films of a molecular glass former, toluene, at temperatures well below the glass transition temperature. By using microfabricated devices with very short equilibration times (below 1 s), we evidence a remarkable variation of the relaxation rate on decreasing film thickness from 100 nm down to a 7 nm thick film. Our results demonstrate that surface atoms are more efficient than bulk atoms in attaining low energy configurations within the potential energy landscape.

Thin Films of Novel Linear-Dendritic Diblock Copolymers

NASA Astrophysics Data System (ADS)

Iyer, Jyotsna; Hammond, Paula

1998-03-01

A series of diblock copolymers with one linear block and one dendrimeric block have been synthesized with the objective of forming ultrathin film nanoporous membranes. Polyethyleneoxide serves as the linear hydrophilic portion of the diblock copolymer. The hyperbranched dendrimeric block consists of polyamidoamine with functional end groups. Thin films of these materials made by spin casting and the Langmuir-Blodgett techniques are being studied. The effect of the polyethylene oxide block size and the number and chemical nature of the dendrimer end group on the nature and stability of the films formed willbe discussed.

Cap-Induced Magnetic Anisotropy in Ultra-thin Fe/MgO(001) Films

NASA Astrophysics Data System (ADS)

Brown-Heft, Tobias; Pendharkar, Mihir; Lee, Elizabeth; Palmstrom, Chris

Magnetic anisotropy plays an important role in the design of spintronic devices. Perpendicular magnetic anisotropy (PMA) is preferred for magnetic tunnel junctions because the resulting energy barrier between magnetization states can be very high and this allows enhanced device scalability suitable for magnetic random access memory applications. Interface induced anisotropy is often used to control magnetic easy axes. For example, the Fe/MgO(001) system has been predicted to exhibit PMA in the ultrathin Fe limit. We have used in-situ magneto optic Kerr effect and ex-situ SQUID to study the changes in anisotropy constants between bare Fe/MgO(001) films and those capped with MgO, Pt, and Ta. In some cases in-plane anisotropy terms reverse sign after capping. We also observe transitions from superparamagnetic to ferromagnetic behavior induced by capping layers. Perpendicular anisotropy is observed for Pt/Fe/MgO(001) films after annealing to 300°C. These effects are characterized and incorporated into a magnetic simulation that accurately reproduces the behavior of the films. This work was supported in part by the Semiconductor Research Corporation programs (1) MSR-Intel, and (2) C-SPIN.

Spatiospectral Analysis of Accelerated Protons from Sub-Micron Liquid Crystal Films

NASA Astrophysics Data System (ADS)

Willis, Christopher; Poole, Patrick; Cochran, Ginevra; van Woerkom, Linn; Schumacher, Douglass

2017-10-01

Recent studies on ion acceleration have trended towards ultra-thin (<1 μm) targets due to improved ion energies and yields from these targets. As discussed here, ultra-thin targets may exhibit unusual spatial distributions in the accelerated ions, such that ion spectrometer data may not be representative of the overall distribution. More complete characterization of the ions requires spectral unfolding of radiochromic film (RCF) data, yielding spatially dependent spectra. Spatiospectral data will be presented from several experiments using sub-micron liquid crystal film targets at the Scarlet (OSU), Texas Petawatt (UT, Austin) and PHELIX (GSI, Darmstadt) laser facilities, including evidence of >75 MeV protons from 300 nm films at PHELIX. Analysis of RCF data is supported by Monte-Carlo modeling of RCF response to ions and electrons using FLUKA. Trends in the resulting ion distributions will be discussed including spatially varying slope temperature and observation of annular ring features at moderate ion energies on many shots. This material is based upon work supported by the AFOSR under award FA9550-14-1-0085, by the DARPA PULSE program through a Grant from AMRDEC, and by the NNSA under contract DE-NA0003107.

Nano-structured variable capacitor based on P(VDF-TrFE) copolymer and carbon nanotubes

NASA Astrophysics Data System (ADS)

Lakbita, I.; El-Hami, K.

2018-02-01

A newly organic capacitor was conceived with a variable capacitance using the inverse piezoelectric effect. The device consists of two parallel plates of carbon nanotubes (CNTs), known for their large surface area, high sensitivity and high electric conductivity, separated by a thin film of a dielectric layer of Polyinylidene fluoride and trifluoroehtylene (P(VDF-TrFE)) promising material for piezoelectric and ferroelectric properties. The obtained architecture is the CNT/PVDF-TrFE/CNT capacitor device. In this study, an ultra-thin film of P(VDF-TrFE) (54/46) with thickness of 20 nm was elaborated on highly oriented pyrolytic graphite (HOPG) by spin-coating. The morphology of the ultra-thin film and the mechanical behavior of CNT/P(VDF-TrFE)/CNT system were studied using the atomic force microscopy (AFM) combined with a lock-in amplifier in contact mode. All changes in applied voltage induce a change in thin film thickness according to the inverse piezoelectric effect that affect, consequently the capacitance. The results showed that the ratio of capacitance change ΔC to initial capacitance C0 is ΔC/C0=5%. This value is sufficient to use P(VDF-TrFE) as variable organic capacitor.

Strain stabilization and thickness dependence of magnetism in epitaxial transition metal monosilicide thin films on Si(111)

NASA Astrophysics Data System (ADS)

Geisler, Benjamin; Kratzer, Peter

2013-09-01

We present a comprehensive study of different 3d transition metal monosilicides in their ground state crystal structure (B20), ranging from equilibrium bulk over biaxially strained bulk to epitaxial thin films on Si(111), by means of density functional theory. The magnetic properties of MnSi and FeSi films are found to be considerably modified due to the epitaxial strain induced by the substrate. In MnSi bulk material, which can be seen as a limit of thick films, we find a strain-induced volume expansion, an increase of the magnetic moments, and a significant rise of the energy difference between different spin configurations. The latter can be associated with an increase of the Curie temperature, which is in accordance with recent experimental results. While a ferromagnetic spin alignment is found to be the ground state also for ultrathin films, we show that for films of intermediate thickness a partially compensating magnetic ordering is more favorable; however, the films retain a net magnetic moment. Furthermore, we analyze the orbital structure in FeSi around the band gap, which can be located somewhere in the density of states for all studied B20 transition metal monosilicides, and find that FeSi becomes metallic and ferromagnetic under epitaxial strain. Finally, the influence of on-site electronic correlation and the reliability of ab initio calculations for 3d transition metal monosilicides are discussed.

An Investigation into III-V Compounds to Reach 20% Efficiency with Minimum Cell Thickness in Ultrathin-Film Solar Cells

NASA Astrophysics Data System (ADS)

Haque, K. A. S. M. Ehteshamul; Galib, Md. Mehedi Hassan

2013-10-01

III-V single-junction solar cells have already achieved very high efficiency levels. However, their use in terrestrial applications is limited by the high fabrication cost. High-efficiency, ultrathin-film solar cells can effectively solve this problem, as their material requirement is minimum. This work presents a comparison among several III-V compounds that have high optical absorption capability as well as optimum bandgap (around 1.4 eV) for use as solar cell absorbers. The aim is to observe and compare the ability of these materials to reach a target efficiency level of 20% with minimum possible cell thickness. The solar cell considered has an n-type ZnSe window layer, an n-type Al0.1Ga0.9As emitter layer, and a p-type Ga0.5In0.5P back surface field (BSF) layer. Ge is used as the substrate. In the initial design, a p-type InP base was sandwiched between the emitter and the BSF layer, and the design parameters for the device were optimized by analyzing the simulation outcomes with ADEPT/F, a one-dimensional (1D) simulation tool. Then, the minimum cell thickness that achieves 20% efficiency was determined by observing the efficiency variation with cell thickness. Afterwards, the base material was changed to a few other selected III-V compounds, and for each case, the minimum cell thickness was determined in a similar manner. Finally, these cell thickness values were compared and analyzed to identify more effective base layer materials for III-V single-junction solar cells.

Demonstration of thin film pair distribution function analysis (tfPDF) for the study of local structure in amorphous and crystalline thin films

DOE PAGES

Jensen, K. M.Ø.; Blichfeld, A. B.; Bauers, S. R.; ...

2015-07-05

By means of normal incidence, high flux and high energy x-rays, we have obtained total scattering data for Pair Distribution Function (PDF) analysis from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. We illustrate the ‘tfPDF’ method through studies of as depositedmore » (i.e. amorphous) and crystalline FeSb 3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb 3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb 3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb 6 octahedra with motifs highly resembling the local structure in crystalline FeSb 3. Analysis of the amorphous structure allows predicting whether the final crystalline product will form the FeSb 3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films.« less

Demonstration of thin film pair distribution function analysis (tfPDF) for the study of local structure in amorphous and crystalline thin films

PubMed Central

Jensen, Kirsten M. Ø.; Blichfeld, Anders B.; Bauers, Sage R.; Wood, Suzannah R.; Dooryhée, Eric; Johnson, David C.; Iversen, Bo B.; Billinge, Simon J. L.

2015-01-01

By means of normal-incidence, high-flux and high-energy X-rays, total scattering data for pair distribution function (PDF) analysis have been obtained from thin films (tf), suitable for local structure analysis. By using amorphous substrates as support for the films, the standard Rapid Acquisition PDF setup can be applied and the scattering signal from the film can be isolated from the total scattering data through subtraction of an independently measured background signal. No angular corrections to the data are needed, as would be the case for grazing incidence measurements. The ‘tfPDF’ method is illustrated through studies of as-deposited (i.e. amorphous) and crystalline FeSb3 films, where the local structure analysis gives insight into the stabilization of the metastable skutterudite FeSb3 phase. The films were prepared by depositing ultra-thin alternating layers of Fe and Sb, which interdiffuse and after annealing crystallize to form the FeSb3 structure. The tfPDF data show that the amorphous precursor phase consists of corner-sharing FeSb6 octahedra with motifs highly resembling the local structure in crystalline FeSb3. Analysis of the amorphous structure allows the prediction of whether the final crystalline product will form the FeSb3 phase with or without excess Sb present. The study thus illustrates how analysis of the local structure in amorphous precursor films can help to understand crystallization processes of metastable phases and opens for a range of new local structure studies of thin films. PMID:26306190

Sorption Behavior of Compressed CO2 and CH4 on Ultrathin Hybrid Poly(POSS-imide) Layers.

PubMed

Raaijmakers, Michiel J T; Ogieglo, Wojciech; Wiese, Martin; Wessling, Matthias; Nijmeijer, Arian; Benes, Nieck E

2015-12-09

Sorption of compressed gases into thin polymeric films is essential for applications including gas sensors and membrane based gas separation. For glassy polymers, the sorption behavior is dependent on the nonequilibrium status of the polymer. The uptake of molecules by a polymer is generally accompanied by dilation, or swelling, of the polymer material. In turn, this dilation can result in penetrant induced plasticization and physical aging that affect the nonequilibrium status of the polymer. Here, we investigate the dilation and sorption behavior of ultrathin membrane layers of a hybrid inorganic-organic network material that consists of alternating polyhedral oligomeric silsesquioxane and imide groups, upon exposure to compressed carbon dioxide and methane. The imide precursor contains fluoroalkene groups that provide affinity toward carbon dioxide, while the octa-functionalized silsesquioxane provides a high degree of cross-linking. This combination allows for extremely high sorption capacities, while structural rearrangements of the network are hindered. We study the simultaneous uptake of gases and dilation of the thin films at high pressures using spectroscopic ellipsometry measurements. Ellipsometry provides the changes in both the refractive index and the film thickness, and allows for accurate quantification of sorption and swelling. In contrast, gravimetric and volumetric measurements only provide a single parameter; this does not allow an accurate correction for, for instance, the changes in buoyancy because of the extensive geometrical changes of highly swelling films. The sorption behavior of the ultrathin hybrid layers depends on the fluoroalkene group content. At low pressure, the apparent molar volume of the gases is low compared to the liquid molar volume of carbon dioxide and methane, respectively. At high gas concentrations in the polymer film, the apparent molar volume of carbon dioxide and methane exceeds that of the liquid molar volume, and approaches that of the gas phase. The high sorption capacity and reversible dilation characteristics of the presented materials provide new directions for applications including gas sensors and gas separation membranes.

In Situ Ramp Anneal X-ray Diffraction Study of Atomic Layer Deposited Ultrathin TaN and Ta 1-x Al x N y Films for Cu Diffusion Barrier Applications

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

Consiglio, S.; Dey, S.; Yu, K.

2016-01-01

Ultrathin TaN and Ta 1-xAl xN y films with x = 0.21 to 0.88 were deposited by atomic layer deposition (ALD) and evaluated for Cu diffusion barrier effectiveness compared to physical vapor deposition (PVD) grown TaN. Cu diffusion barrier effectiveness was investigated using in-situ ramp anneal synchrotron X-ray diffraction (XRD) on Cu/1.8 nm barrier/Si stacks. A Kissinger-like analysis was used to assess the kinetics of Cu 3Si formation and determine the effective activation energy (E a) for Cu silicidation. Compared to the stack with a PVD TaN barrier, the stacks with the ALD films exhibited a higher crystallization temperature (Tmore » c) for Cu silicidation. The Ea values of Cu 3Si formation for stacks with the ALD films were close to the reported value for grain boundary diffusion of Cu whereas the Ea of Cu 3Si formation for the stack with PVD TaN is closer to the reported value for lattice diffusion. For 3 nm films, grazing incidence in-plane XRD showed evidence of nanocrystallites in an amorphous matrix with broad peaks corresponding to high density cubic phase for the ALD grown films and lower density hexagonal phase for the PVD grown film further elucidating the difference in initial failure mechanisms due to differences in barrier crystallinity and associated phase.« less

Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability

PubMed Central

Zhao, Wenchao; Ye, Long; Zhang, Shaoqing; Fan, Bin; Sun, Mingliang; Hou, Jianhui

2014-01-01

Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function. PMID:25300365

Directed ordering of phase separated domains and dewetting of thin polymer blend films on a topographically patterned substrate.

PubMed

Bhandaru, Nandini; Karim, Alamgir; Mukherjee, Rabibrata

2017-07-21

Substrate pattern guided self-organization of ultrathin and confined polymeric films on a topographically patterned substrate is a useful approach for obtaining ordered meso and nano structures over large areas, particularly if the ordering is achieved during film preparation itself, eliminating any post-processing such as thermal or solvent vapor annealing. By casting a dilute solution of two immiscible polymers, polystyrene (PS) and polymethylmethacrylate (PMMA), from a common solvent (toluene) on a topographically patterned substrate with a grating geometry, we show the formation of self-organized meso patterns with various degrees of ordering. The morphology depends on both the concentration of the dispensed solution (C n ) and the blend composition (R B ). Depending on the extent of dewetting during spin coating, the final morphologies can be classified into three distinct categories. At a very low C n the solution dewets fully, resulting in isolated polymer droplets aligned along substrate grooves (Type 1). Type 2 structures comprising isolated threads with aligned phase separated domains along each substrate groove are observed at intermediate C n . A continuous film (Type 3) is obtained above a critical concentration (C n *) that depends on R B . While the extent of ordering of the domains gradually diminishes with an increase in film thickness for Type 3 patterns, the size of the domains remains much smaller than that on a flat substrate, resulting in significant downsizing of the features due to the lateral confinement imposed on the phase separation process by the topographic patterns. Finally, we show that some of these structures exhibit excellent broadband anti-reflection (AR) properties.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants.

PubMed

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-08-07

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

NASA Astrophysics Data System (ADS)

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-08-01

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

PubMed Central

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-01-01

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry. PMID:26249536

Large-Scale Precise Printing of Ultrathin Sol-Gel Oxide Dielectrics for Directly Patterned Solution-Processed Metal Oxide Transistor Arrays.

PubMed

Lee, Won-June; Park, Won-Tae; Park, Sungjun; Sung, Sujin; Noh, Yong-Young; Yoon, Myung-Han

2015-09-09

Ultrathin and dense metal oxide gate di-electric layers are reported by a simple printing of AlOx and HfOx sol-gel precursors. Large-area printed indium gallium zinc oxide (IGZO) thin-film transistor arrays, which exhibit mobilities >5 cm(2) V(-1) s(-1) and gate leakage current of 10(-9) A cm(-2) at a very low operation voltage of 2 V, are demonstrated by continuous simple bar-coated processes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrathin free-standing close-packed gold nanoparticle films: Conductivity and Raman scattering enhancement

NASA Astrophysics Data System (ADS)

Yu, Qing; Huang, Hongwen; Peng, Xinsheng; Ye, Zhizhen

2011-09-01

A simple filtration technique was developed to prepare large scale free-standing close-packed gold nanoparticle ultrathin films using metal hydroxide nanostrands as both barrier layer and sacrificial layer. As thin as 70 nm, centimeter scale robust free-standing gold nanoparticle thin film was obtained. The thickness of the films could be easily tuned by the filtration volumes. The electronic conductivities of these films varied with the size of the gold nanoparticles, post-treatment temperature, and thickness, respectively. The conductivity of the film prepared from 20 nm gold nanoparticles is higher than that of the film prepared from 40 nm gold nanoparticle by filtering the same filtration volume of their solution, respectively. Their conductivities are comparable to that of the 220 nm thick ITO film. Furthermore, these films demonstrated an average surface Raman scattering enhancement up to 6.59 × 105 for Rhodamine 6 G molecules on the film prepared from 40 nm gold nanoparticles. Due to a lot of nano interspaces generated from the close-packed structures, two abnormal enhancements and relative stronger intensities of the asymmetrical vibrations at 1534 and 1594 cm-1 of R6G were observed, respectively. These robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and hold the potential application for electrodes and surface enhanced Raman detectors. This method is applicable for preparation of other nanoparticle free-standing thin films.A simple filtration technique was developed to prepare large scale free-standing close-packed gold nanoparticle ultrathin films using metal hydroxide nanostrands as both barrier layer and sacrificial layer. As thin as 70 nm, centimeter scale robust free-standing gold nanoparticle thin film was obtained. The thickness of the films could be easily tuned by the filtration volumes. The electronic conductivities of these films varied with the size of the gold nanoparticles, post-treatment temperature, and thickness, respectively. The conductivity of the film prepared from 20 nm gold nanoparticles is higher than that of the film prepared from 40 nm gold nanoparticle by filtering the same filtration volume of their solution, respectively. Their conductivities are comparable to that of the 220 nm thick ITO film. Furthermore, these films demonstrated an average surface Raman scattering enhancement up to 6.59 × 105 for Rhodamine 6 G molecules on the film prepared from 40 nm gold nanoparticles. Due to a lot of nano interspaces generated from the close-packed structures, two abnormal enhancements and relative stronger intensities of the asymmetrical vibrations at 1534 and 1594 cm-1 of R6G were observed, respectively. These robust free-standing gold nanoparticle films could be easily transferred onto various solid substrates and hold the potential application for electrodes and surface enhanced Raman detectors. This method is applicable for preparation of other nanoparticle free-standing thin films. Electronic supplementary information (ESI) available: Figure S1, the SEM images and photograph of the films prepared from 10 ml, 20 nm gold nanoparticles. Scheme S1, the vibrations of 1534 and 1594 cm-1 of R6G. See DOI: 10.1039/c1nr10578g

A Program of Research on Microfabrication Techniques for VLSI Magnetic Devices.

DTIC Science & Technology

1982-11-30

epitaxial ( LPE ) garnet films have been investigated by transmission electron microscopy B. A special technique involving physical polishing and ion milling...was used for producing ultra-thin cross-sections of the LPE garnet films . To our knowledge no one else has such capabilities. It was found that the...Materials and the Effects of Ion Implantation on them 3 2.1 The Effects of Deuterium and Oxygen Implantation on the Magnetic 3 Parameters of Garnet Films 2.2

Size Dependent Mechanical Behavior of Free-Standing Glassy Polymer Thin Films

DTIC Science & Technology

2014-08-31

thickness is less than 20 ( ) 1 ( / ) bulk film E EE h hδ = + 14 nm using the liquid dewetting method. Additionally, earlier studies by McKenna’s group and...coated substrates: Rupture, dewetting , and drop formation. J. Colloid Interface Sci. 178(2), 383 (1996). 8. C.B. Roth and J.R. Dutcher: Glass transition...Phys. J. E. 20(2), 143 (2006). 31. J. Wang and G.B. McKenna: Viscoelastic and Glass Transition Properties of Ultrathin Polystyrene Films by Dewetting

Facile fabrication of network film electrodes with ultrathin Au nanowires for nonenzymatic glucose sensing and glucose/O2 fuel cell.

PubMed

Yang, Lu; Zhang, Yijia; Chu, Mi; Deng, Wenfang; Tan, Yueming; Ma, Ming; Su, Xiaoli; Xie, Qingji; Yao, Shuozhuo

2014-02-15

We report here on the facile fabrication of network film electrodes with ultrathin Au nanowires (AuNWs) and their electrochemical applications for high-performance nonenzymatic glucose sensing and glucose/O2 fuel cell under physiological conditions (pH 7.4, containing 0.15M Cl(-)). AuNWs with an average diameter of ~7 or 2 nm were prepared and can self-assemble into robust network films on common electrodes. The network film electrode fabricated with 2-nm AuNWs exhibits high sensitivity (56.0 μA cm(-2)mM(-1)), low detection limit (20 μM), short response time (within 10s), excellent selectivity, and good storage stability for nonenzymatic glucose sensing. Glucose/O2 fuel cells were constructed using network film electrodes as the anode and commercial Pt/C catalyst modified glassy carbon electrode as cathode. The glucose/O2 fuel cell using 2-nm AuNWs as anode catalyst output a maximum power density of is 126 μW cm(-2), an open-circuit cell voltage of 0.425 V, and a short-circuit current density of 1.34 mA cm(-2), respectively. Due to the higher specific electroactive surface area of 2-nm AuNWs, the network film electrode fabricated with 2-nm AuNWs exhibited higher electrocatalytic activity toward glucose oxidation than the network film electrode fabricated with 7-nm AuNWs. The network film electrode exhibits high electrocatalytic activity toward glucose oxidation under physiological conditions, which is helpful for constructing implantable electronic devices. © 2013 Elsevier B.V. All rights reserved.

Highly stable, protein resistant thin films on SiC-modified silicon substrates.

PubMed

Qin, Guoting; Zhang, Rui; Makarenko, Boris; Kumar, Amit; Rabalais, Wayne; López Romero, J Manuel; Rico, Rodrigo; Cai, Chengzhi

2010-05-21

Thin films terminated with oligo(ethylene glycol) (OEG) could be photochemically grafted onto ultrathin silicon carbide layers that were generated on silicon substrates via carbonization with acetylene at 820 degrees C. The OEG coating reduced the non-specific adsorption of fibrinogen on the substrates by 99.5% and remained resistant after storage in PBS for 4 weeks at 37 degrees C.

Control of Reaction Surface in Low Temperature CVD to Enhance Nucleation and Conformal Coverage

ERIC Educational Resources Information Center

Kumar, Navneet

2009-01-01

The Holy Grail in CVD community is to find precursors that can afford the following: good nucleation on a desired substrate and conformal deposition in high AR features. Good nucleation is not only necessary for getting ultra-thin films at low thicknesses; it also offers films that are smooth at higher thickness values. On the other hand,…

Origins of the two simultaneous mechanisms causing glass transition temperature reductions in high molecular weight freestanding polymer films.

PubMed

Prevosto, Daniele; Capaccioli, Simone; Ngai, K L

2014-02-21

From ellipsometry measurements, Pye and Roth [Phys. Rev. Lett. 107, 235701 (2011)] presented evidence of the presence of two glass transitions originating from two distinctly different and simultaneous mechanisms to reduce the glass transition temperature within freestanding polystyrene films with thickness less than 70 nm. The upper transition temperature T(u)(g)(h) is higher than the lower transition temperature T(l)(g)(h) in the ultrathin films. After comparing their data with the findings of others, using the same or different techniques, they concluded that new theoretical interpretation is needed to explain the two transitions and the different dependences of T(u)(g)(h) and T(l)(g)(h) on film thickness and molecular weight. We address the problem based on advance in delineating the different viscoelastic mechanisms in the glass-rubber transition zone of polymers. Theoretical considerations as well as experiments have shown in time-scales immediately following the segmental α-relaxation are the sub-Rouse modes with longer length scale but shorter than that of the Rouse modes. The existence of the sub-Rouse modes in various polymers including polystyrene has been repeatedly confirmed by experiments. We show that the sub-Rouse modes can account for the upper transition and the properties observed. The segmental α-relaxation is responsible for the lower transition. This is supported by the fact that the segmental α-relaxation in ultrathin freestanding PS films had been observed by dielectric relaxation measurements and photon correlation spectroscopy. Utilizing the temperature dependence of the segmental relaxation times from these experiments, the glass transition temperature T(α)(g)associated with the segmental relaxation in the ultrathin film is determined. It turns out that T(α)(g) is nearly the same as T(l)(g)(h) of the lower transition, and hence definitely segmental α-relaxation is the mechanism for the lower transition. Since it is unlikely that the segmental α-relaxation can give rise to two very different transitions simultaneously, a new mechanism for the upper transition is needed, and the sub-Rouse modes provide the mechanism.

UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

2016-08-01

In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent conducting oxides.

Selective, ultrathin membrane skins prepared by deposition of novel polymer films on porous alumina supports

NASA Astrophysics Data System (ADS)

Balachandra, Anagi Manjula

Membrane-based separations are attractive in industrial processes because of their low energy costs and simple operation. However, low permeabilities often make membrane processes uneconomical. Since flux is inversely proportional to membrane thickness, composite membranes consisting of ultrathin, selective skins on highly permeable supports are required to simultaneously achieve high throughput and high selectivity. However, the synthesis of defect-free skins with thicknesses less than 50 nm is difficult, and thus flux is often limited. Layer-by-layer deposition of oppositely charged polyelectrolytes on porous supports is an attractive method to synthesize ultrathin ion-separation membranes with high flux and high selectivity. The ion-transport selectivity of multilayer polyelectrolyte membranes (MPMs) is primarily due to Donnan exclusion; therefore increase in fixed charge density should yield high selectivity. However, control over charge density in MPMs is difficult because charges on polycations are electrostatically compensated by charges on polyanions, and the net charge in the bulk of these films is small. To overcome this problem, we introduced a templating method to create ion-exchange sites in the bulk of the membrane. This strategy involves alternating deposition of a Cu2+-poly(acrylic acid) complex and poly(allylamine hydrochloride) on a porous alumina support followed by removal of Cu2+ and deprotonation to yield free -COO- ion-exchange sites. Diffusion dialysis studies showed that the Cl-/SO42-. Selectivity of Cu2+-templated membranes is 4-fold higher than that of membranes prepared in the absence of Cu2+. Post-deposition cross-linking of these membranes by heat-induced amide bond formation further increased Cl-/SO42- selectivity to values as high as 600. Room-temperature, surface-initiated atom transfer radical polymerization (ATRP) provides another convenient method for formation of ultrathin polymer skins. This process involves attachment of polymerization initiators to a porous alumina support and subsequent polymerization from these initiators. Because ATRP is a controlled polymerization technique, it yields well-defined polymer films with low polydispersity indices (narrow molecular weight distributions). Additionally, this method is attractive because film thickness can be easily controlled by adjusting polymerization time. Gas-permeability data showed that grafted poly(ethylene glycol dimethacrylate) membranes have a CO 2/CH4 selectivity of 20, whereas poly(2-hydroxyethyl methacrylate) (PHEMA) films grown from a surface have negligible selectivity. However, derivatization of PHEMA with pentadecafluorooctanoyl chloride increases the solubility of CO2 in the membrane and results in a CO2/CH4 selectivity of 9. Although composite PHEMA membranes have no significant gas-transport selectivity, diffusion dialysis studies with PHEMA membranes showed moderate ion-transport selectivities. Cross-linking of PHEMA membranes by reaction with succinyl chloride greatly enhanced anion-transport selectivities while maintaining reasonable flux. The selectivities of these systems demonstrate that alternating polyelectrolyte deposition and surface-initiated ATRP are indeed capable of forming ultrathin, defect-free membrane skins that can potentially be modified for specific separations.

Low voltage operation of IGZO thin film transistors enabled by ultrathin Al2O3 gate dielectric

NASA Astrophysics Data System (ADS)

Ma, Pengfei; Du, Lulu; Wang, Yiming; Jiang, Ran; Xin, Qian; Li, Yuxiang; Song, Aimin

2018-01-01

An ultrathin, 5 nm, Al2O3 film grown by atomic-layer deposition was used as a gate dielectric for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The Al2O3 layer showed a low surface roughness of 0.15 nm, a low leakage current, and a high breakdown voltage of 6 V. In particular, a very high gate capacitance of 720 nF/cm2 was achieved, making it possible for the a-IGZO TFTs to not only operate at a low voltage of 1 V but also exhibit desirable properties including a low threshold voltage of 0.3 V, a small subthreshold swing of 100 mV/decade, and a high on/off current ratio of 1.2 × 107. Furthermore, even under an ultralow operation voltage of 0.6 V, well-behaved transistor characteristics were still observed with an on/off ratio as high as 3 × 106. The electron transport through the Al2O3 layer has also been analyzed, indicating the Fowler-Nordheim tunneling mechanism.

Flexible Mixed-Potential-Type (MPT) NO₂ Sensor Based on An Ultra-Thin Ceramic Film.

PubMed

You, Rui; Jing, Gaoshan; Yu, Hongyan; Cui, Tianhong

2017-07-29

A novel flexible mixed-potential-type (MPT) sensor was designed and fabricated for NO₂ detection from 0 to 500 ppm at 200 °C. An ultra-thin Y₂O₃-doped ZrO₂ (YSZ) ceramic film 20 µm thick was sandwiched between a heating electrode and reference/sensing electrodes. The heating electrode was fabricated by a conventional lift-off process, while the porous reference and the sensing electrodes were fabricated by a two-step patterning method using shadow masks. The sensor's sensitivity is achieved as 58.4 mV/decade at the working temperature of 200 °C, as well as a detection limit of 26.7 ppm and small response time of less than 10 s at 200 ppm. Additionally, the flexible MPT sensor demonstrates superior mechanical stability after bending over 50 times due to the mechanical stability of the YSZ ceramic film. This simply structured, but highly reliable flexible MPT NO₂ sensor may lead to wide application in the automobile industry for vehicle emission systems to reduce NO₂ emissions and improve fuel efficiency.

Superabsorbing, Artificial Metal Films Constructed from Semiconductor Nanoantennas.

PubMed

Kim, Soo Jin; Park, Junghyun; Esfandyarpour, Majid; Pecora, Emanuele F; Kik, Pieter G; Brongersma, Mark L

2016-06-08

In 1934, Wilhelm Woltersdorff demonstrated that the absorption of light in an ultrathin, freestanding film is fundamentally limited to 50%. He concluded that reaching this limit would require a film with a real-valued sheet resistance that is exactly equal to R = η/2 ≈ 188.5Ω/□, where [Formula: see text] is the impedance of free space. This condition can be closely approximated over a wide frequency range in metals that feature a large imaginary relative permittivity εr″, that is, a real-valued conductivity σ = ε0εr″ω. A thin, continuous sheet of semiconductor material does not facilitate such strong absorption as its complex-valued permittivity with both large real and imaginary components preclude effective impedance matching. In this work, we show how a semiconductor metafilm constructed from optically resonant semiconductor nanostructures can be created whose optical response mimics that of a metallic sheet. For this reason, the fundamental absorption limit mentioned above can also be reached with semiconductor materials, opening up new opportunities for the design of ultrathin optoelectronic and light harvesting devices.

Gate-Variable Mid-Infrared Optical Transitions in a (Bi1-xSbx)2Te3 Topological Insulator.

PubMed

Whitney, William S; Brar, Victor W; Ou, Yunbo; Shao, Yinming; Davoyan, Artur R; Basov, D N; He, Ke; Xue, Qi-Kun; Atwater, Harry A

2017-01-11

We report mid-infrared spectroscopy measurements of ultrathin, electrostatically gated (Bi 1-x Sb x ) 2 Te 3 topological insulator films in which we observe several percent modulation of transmittance and reflectance as gating shifts the Fermi level. Infrared transmittance measurements of gated films were enabled by use of an epitaxial lift-off method for large-area transfer of topological insulator films from infrared-absorbing SrTiO 3 growth substrates to thermal oxidized silicon substrates. We combine these optical experiments with transport measurements and angle-resolved photoemission spectroscopy to identify the observed spectral modulation as a gate-driven transfer of spectral weight between both bulk and 2D topological surface channels and interband and intraband channels. We develop a model for the complex permittivity of gated (Bi 1-x Sb x ) 2 Te 3 and find a good match to our experimental data. These results open the path for layered topological insulator materials as a new candidate for tunable, ultrathin infrared optics and highlight the possibility of switching topological optoelectronic phenomena between bulk and spin-polarized surface regimes.

Flexible Mixed-Potential-Type (MPT) NO2 Sensor Based on An Ultra-Thin Ceramic Film

PubMed Central

You, Rui; Jing, Gaoshan; Yu, Hongyan; Cui, Tianhong

2017-01-01

A novel flexible mixed-potential-type (MPT) sensor was designed and fabricated for NO2 detection from 0 to 500 ppm at 200 °C. An ultra-thin Y2O3-doped ZrO2 (YSZ) ceramic film 20 µm thick was sandwiched between a heating electrode and reference/sensing electrodes. The heating electrode was fabricated by a conventional lift-off process, while the porous reference and the sensing electrodes were fabricated by a two-step patterning method using shadow masks. The sensor’s sensitivity is achieved as 58.4 mV/decade at the working temperature of 200 °C, as well as a detection limit of 26.7 ppm and small response time of less than 10 s at 200 ppm. Additionally, the flexible MPT sensor demonstrates superior mechanical stability after bending over 50 times due to the mechanical stability of the YSZ ceramic film. This simply structured, but highly reliable flexible MPT NO2 sensor may lead to wide application in the automobile industry for vehicle emission systems to reduce NO2 emissions and improve fuel efficiency. PMID:28758933

Oxygen-enabled control of Dzyaloshinskii-Moriya Interaction in ultra-thin magnetic films.

PubMed

Belabbes, Abderrezak; Bihlmayer, Gustav; Blügel, Stefan; Manchon, Aurélien

2016-04-22

The search for chiral magnetic textures in systems lacking spatial inversion symmetry has attracted a massive amount of interest in the recent years with the real space observation of novel exotic magnetic phases such as skyrmions lattices, but also domain walls and spin spirals with a defined chirality. The electrical control of these textures offers thrilling perspectives in terms of fast and robust ultrahigh density data manipulation. A powerful ingredient commonly used to stabilize chiral magnetic states is the so-called Dzyaloshinskii-Moriya interaction (DMI) arising from spin-orbit coupling in inversion asymmetric magnets. Such a large antisymmetric exchange has been obtained at interfaces between heavy metals and transition metal ferromagnets, resulting in spin spirals and nanoskyrmion lattices. Here, using relativistic first-principles calculations, we demonstrate that the magnitude and sign of DMI can be entirely controlled by tuning the oxygen coverage of the magnetic film, therefore enabling the smart design of chiral magnetism in ultra-thin films. We anticipate that these results extend to other electronegative ions and suggest the possibility of electrical tuning of exotic magnetic phases.

Oxygen-enabled control of Dzyaloshinskii-Moriya Interaction in ultra-thin magnetic films

PubMed Central

Belabbes, Abderrezak; Bihlmayer, Gustav; Blügel, Stefan; Manchon, Aurélien

2016-01-01

The search for chiral magnetic textures in systems lacking spatial inversion symmetry has attracted a massive amount of interest in the recent years with the real space observation of novel exotic magnetic phases such as skyrmions lattices, but also domain walls and spin spirals with a defined chirality. The electrical control of these textures offers thrilling perspectives in terms of fast and robust ultrahigh density data manipulation. A powerful ingredient commonly used to stabilize chiral magnetic states is the so-called Dzyaloshinskii-Moriya interaction (DMI) arising from spin-orbit coupling in inversion asymmetric magnets. Such a large antisymmetric exchange has been obtained at interfaces between heavy metals and transition metal ferromagnets, resulting in spin spirals and nanoskyrmion lattices. Here, using relativistic first-principles calculations, we demonstrate that the magnitude and sign of DMI can be entirely controlled by tuning the oxygen coverage of the magnetic film, therefore enabling the smart design of chiral magnetism in ultra-thin films. We anticipate that these results extend to other electronegative ions and suggest the possibility of electrical tuning of exotic magnetic phases. PMID:27103448

Semi-crystalline morphologies of linear and cyclic poly(ɛ-caprolactones) in the diffusion-limited film thickness regime

NASA Astrophysics Data System (ADS)

Kelly, Giovanni; Bergeson, Amelia; Haque, Farihah; Grayson, Scott; Albert, Julie

Thin and ultrathin films of semi-crystalline polymers have been studied for decades due to their far-reaching applications including opto-electronic materials and biological studies of drug delivery and cell adhesion. This body of work has focused on every aspect of crystallization, from the fundamental thermodynamics and kinetics of crystal growth to methods for affecting crystalline morphologies via blending with other polymers. Due to significant synthetic challenges, one area where progress has lagged behind is the study of non-linear architectures, especially ring polymers. However, pioneering work by polymer chemists around the world has closed that gap, and we are beginning to observe important differences between ring and linear polymers in bulk materials. As a complement to those advances, this work aims to compare the morphologies of linear and cyclic poly(ɛ-caprolactones) (PCL) observed in heavily-confined ultrathin films where crystal growth is diffusion-limited. Understanding how confinement effects alter morphology will provide invaluable insight into differences in crystal growth as a function of molecular architecture.

Thickness-dependent appearance of ferromagnetism in Pd(100) ultrathin films

NASA Astrophysics Data System (ADS)

Sakuragi, S.; Sakai, T.; Urata, S.; Aihara, S.; Shinto, A.; Kageshima, H.; Sawada, M.; Namatame, H.; Taniguchi, M.; Sato, T.

2014-08-01

We report the appearance of ferromagnetism in thin films of Pd(100), which depends on film thickness in the range of 3-5 nm on SrTiO3(100) substrates. X-ray magnetic circular dichroism measurement shows the intrinsic nature of ferromagnetism in Pd(100) films. The spontaneous magnetization in Pd(100) films, corresponding to is 0.61μB/atom, is comparable to Ni, and it changes in an oscillatory manner depending on film thickness, where the period quantitatively agrees with the theoretical prediction based on the two-dimensional quantum well in the film. This indicates that the discrete electronic states in the quantum well shift to Fermi energy to satisfy the condition for ferromagnetism (Stoner criterion) at a specific film thickness.

Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices.

PubMed

George, J P; Smet, P F; Botterman, J; Bliznuk, V; Woestenborghs, W; Van Thourhout, D; Neyts, K; Beeckman, J

2015-06-24

The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5-15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln2O2CO3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 μC/cm(2), and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices.

Long-wave dynamics of an elastic sheet lubricated by a thin liquid film on a wetting substrate

NASA Astrophysics Data System (ADS)

Young, Y.-N.; Stone, H. A.

2017-06-01

The dynamics of an elastic sheet lubricated by a thin liquid film on a wetting solid substrate is examined using both numerical simulations of a long-wave lubrication equation and a quasistatic model. Interactions between the liquid and the wetting substrate are modeled by a disjoining pressure that gives rise to an ultrathin (precursor) film. For a fluid interface without elastic bending stiffness, a flat precursor film may be linearly unstable and evolve towards an equilibrium of a single "drop" connected to a flat ultrathin film. Similar behavior is found when the thin film is covered by an elastic sheet: The sheet deforms, rearranging the thin liquid film, and contributes regulating surface forces such as a bending resistance and/or a tensile force, which may arise from interactions between the sheet and liquid or inextensibility of the sheet. Glasner's quasistatic model [Phys. Fluids 15, 1837 (2003), 10.1063/1.1578076], developed for a liquid film, is adopted to investigate the combined effects of elastic and tensile forces in the sheet on the thin film dynamics. The equilibrium height of the drop is found to vary inversely with the bending rigidity. When the elastic sheet is inextensible (such as a lipid bilayer membrane), a compressive tensile force may occur and the equilibrium film height is dependent less on the bending rigidity and more on the excess area of the membrane. Analyses of the lubrication equation also show that the precursor film transitions monotonically to the core film for tension-dominated dynamics. In contrast, for elasticity-dominated dynamics, a spatial oscillation of film height in the contact line region is found. In addition, elasticity in the sheet causes a sliding motion of the thin film: the contact angle is rendered zero by elasticity, and the contact line moves at a finite speed.

Evidence for stable grain boundary melt films in experimentally deformed olivine-orthopyroxene rocks

NASA Astrophysics Data System (ADS)

de Kloe, R.; Drury, M. R.; van Roermund, H. L. M.

The microstructure of olivine-olivine grain boundaries has been studied in experimentally deformed (1200-1227°C, 300MPa) partially molten olivine and olivine-orthopyroxene rocks. In-situ melting produced 1vol% melt in all samples studied. Grain boundary analyses were carried out using a number of transmission electron microscopy techniques. The grain boundary chemistry in undeformed olivine-orthopyroxene starting material showed evidence for the presence of an intergranular phase along some, but not all, of the olivine-olivine boundaries. In the deformed samples, ultrathin Si-rich, Al- and Ca-bearing amorphous films have been observed along all investigated olivine-olivine grain boundaries. The chemistry of the grain boundaries, which is considered to be indicative for the presence of a thin film, was measured with energy-dispersive X-ray spectroscopy (EDX) and energy-filtering imaging. The amorphous nature of the films was confirmed with diffuse dark field imaging, Fresnel fringe imaging, and high-resolution electron microscopy. The films range in thickness from 0.6 to 3.0nm, and EDX analyses show that the presence of Al and Ca is restricted to this ultrathin film along the grain boundaries. Because thin melt films have been observed in all the samples, they are thought to be stable features of the melt microstructure in deformed partially molten rocks. The transition from the occasional presence of films in the undeformed starting material to the general occurrence of the films in deformed materials suggests that deformation promotes the formation and distribution of the films. Alternatively, hot-pressing may be too short for films to develop along all grain boundaries. A difference in creep strength between the studied samples could not be attributed to grain boundary melt films, as these have been found in all deformed samples. However, a weakening effect of grain boundary melt films on olivine rheology could not be ruled out due to the lack of confirmed melt-film free experiments.

Response of cells on surface-induced nanopatterns: fibroblasts and mesenchymal progenitor cells.

PubMed

Khor, Hwei Ling; Kuan, Yujun; Kukula, Hildegard; Tamada, Kaoru; Knoll, Wolfgang; Moeller, Martin; Hutmacher, Dietmar W

2007-05-01

Ultrathin films of a poly(styrene)-block-poly(2-vinylpyrindine) diblock copolymer (PS-b-P2VP) and poly(styrene)-block-poly(4-vinylpyrindine) diblock copolymer (PS-b-P4VP) were used to form surface-induced nanopattern (SINPAT) on mica. Surface interaction controlled microphase separation led to the formation of chemically heterogeneous surface nanopatterns on dry ultrathin films. Two distinct nanopatterned surfaces, namely, wormlike and dotlike patterns, were used to investigate the influence of topography in the nanometer range on cell adhesion, proliferation, and migration. Atomic force microscopy was used to confirm that SINPAT was stable under cell culture conditions. Fibroblasts and mesenchymal progenitor cells were cultured on the nanopatterned surfaces. Phase contrast and confocal laser microscopy showed that fibroblasts and mesenchymal progenitor cells preferred the densely spaced wormlike patterns. Atomic force microscopy showed that the cells remodelled the extracellular matrix differently as they migrate over the two distinctly different nanopatterns.

Structure, magnetic ordering, and spin filtering efficiency of NiFe{sub 2}O{sub 4}(111) ultrathin films

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

Matzen, S.; Moussy, J.-B., E-mail: jean-baptiste.moussy@cea.fr; Wei, P.

2014-05-05

NiFe{sub 2}O{sub 4}(111) ultrathin films (3–5 nm) have been grown by oxygen-assisted molecular beam epitaxy and integrated as effective spin-filter barriers. Structural and magnetic characterizations have been performed in order to investigate the presence of defects that could limit the spin filtering efficiency. These analyses have revealed the full strain relaxation of the layers with a cationic order in agreement with the inverse spinel structure but also the presence of antiphase boundaries. A spin-polarization up to +25% has been directly measured by the Meservey-Tedrow technique in Pt(111)/NiFe{sub 2}O{sub 4}(111)/γ-Al{sub 2}O{sub 3}(111)/Al tunnel junctions. The unexpected positive sign and relatively small valuemore » of the spin-polarization are discussed, in comparison with predictions and previous indirect tunnelling magnetoresistance measurements.« less

Probing the thermal decomposition behaviors of ultrathin HfO2 films by an in situ high temperature scanning tunneling microscope.

PubMed

Xue, Kun; Wang, Lei; An, Jin; Xu, Jianbin

2011-05-13

The thermal decomposition of ultrathin HfO(2) films (∼0.6-1.2 nm) on Si by ultrahigh vacuum annealing (25-800 °C) is investigated in situ in real time by scanning tunneling microscopy. Two distinct thickness-dependent decomposition behaviors are observed. When the HfO(2) thickness is ∼ 0.6 nm, no discernible morphological changes are found below ∼ 700 °C. Then an abrupt reaction occurs at 750 °C with crystalline hafnium silicide nanostructures formed instantaneously. However, when the thickness is about 1.2 nm, the decomposition proceeds gradually with the creation and growth of two-dimensional voids at 800 °C. The observed thickness-dependent behavior is closely related to the SiO desorption, which is believed to be the rate-limiting step of the decomposition process.

Dynamics and morphology of chiral magnetic bubbles in perpendicularly magnetized ultra-thin films

NASA Astrophysics Data System (ADS)

Sarma, Bhaskarjyoti; Garcia-Sanchez, Felipe; Nasseri, S. Ali; Casiraghi, Arianna; Durin, Gianfranco

2018-06-01

We study bubble domain wall dynamics using micromagnetic simulations in perpendicularly magnetized ultra-thin films with disorder and Dzyaloshinskii-Moriya interaction. Disorder is incorporated into the material as grains with randomly distributed sizes and varying exchange constant at the edges. As expected, magnetic bubbles expand asymmetrically along the axis of the in-plane field under the simultaneous application of out-of-plane and in-plane fields. Remarkably, the shape of the bubble has a ripple-like part which causes a kink-like (steep decrease) feature in the velocity versus in-plane field curve. We show that these ripples originate due to the nucleation and interaction of vertical Bloch lines. Furthermore, we show that the Dzyaloshinskii-Moriya interaction field is not constant but rather depends on the in-plane field. We also extend the collective coordinate model for domain wall motion to a magnetic bubble and compare it with the results of micromagnetic simulations.

Strain-induced oxygen vacancies in ultrathin epitaxial CaMnO3 films

NASA Astrophysics Data System (ADS)

Chandrasena, Ravini; Yang, Weibing; Lei, Qingyu; Delgado-Jaime, Mario; de Groot, Frank; Arenholz, Elke; Kobayashi, Keisuke; Aschauer, Ulrich; Spaldin, Nicola; Xi, Xiaoxing; Gray, Alexander

Dynamic control of strain-induced ionic defects in transition-metal oxides is considered to be an exciting new avenue towards creating materials with novel electronic, magnetic and structural properties. Here we use atomic layer-by-layer laser molecular beam epitaxy to synthesize high-quality ultrathin single-crystalline CaMnO3 films with systematically varying coherent tensile strain. We then utilize a combination of high-resolution soft x-ray absorption spectroscopy and bulk-sensitive hard x-ray photoemission spectroscopy in conjunction with first-principles theory and core-hole multiplet calculations to establish a direct link between the coherent in-plane strain and the oxygen-vacancy content. We show that the oxygen vacancies are highly mobile, which necessitates an in-situ-grown capping layer in order to preserve the original strain-induced oxygen-vacancy content. Our findings open the door for designing and controlling new ionically active properties in strongly-correlated transition-metal oxides.

Magnetron sputtered boron films

DOEpatents

Makowiecki, Daniel M.; Jankowski, Alan F.

1998-01-01

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for producing hardened surfaces, surfacing machine tools, etc. and for ultra-thin band pass filters as well as the low Z element in low Z/high Z optical components, such as mirrors which enhance reflectivity from grazing to normal incidence.

Magnetron sputtered boron films

DOEpatents

Makowiecki, D.M.; Jankowski, A.F.

1998-06-16

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for producing hardened surfaces, surfacing machine tools, etc. and for ultra-thin band pass filters as well as the low Z element in low Z/high Z optical components, such as mirrors which enhance reflectivity from grazing to normal incidence. 8 figs.

Narrow-band tunable terahertz emission from ferrimagnetic Mn{sub 3-x}Ga thin films

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

Awari, N.; University of Groningen, 9747 AG Groningen; Kovalev, S., E-mail: s.kovalev@hzdr.de, E-mail: c.fowley@hzdr.de, E-mail: rodek@tcd.ie

2016-07-18

Narrow-band terahertz emission from coherently excited spin precession in metallic ferrimagnetic Mn{sub 3-x}Ga Heusler alloy nanofilms has been observed. The efficiency of the emission, per nanometer film thickness, is comparable or higher than that of classical laser-driven terahertz sources based on optical rectification. The center frequency of the emission from the films can be tuned precisely via the film composition in the range of 0.20–0.35 THz, making this type of metallic film a candidate for efficient on-chip terahertz emitters. Terahertz emission spectroscopy is furthermore shown to be a sensitive probe of magnetic properties of ultra-thin films.

High-speed growth of TiO2 nanotube arrays with gradient pore diameter and ultrathin tube wall under high-field anodization

NASA Astrophysics Data System (ADS)

Yuan, Xiaoliang; Zheng, Maojun; Ma, Li; Shen, Wenzhong

2010-10-01

Highly ordered TiO2 nanotubular arrays have been prepared by two-step anodization under high field. The high anodizing current densities lead to a high-speed film growth (0.40-1.00 µm min - 1), which is nearly 16 times faster than traditional fabrication of TiO2 at low field. It was found that an annealing process of Ti foil is an effective approach to get a monodisperse and double-pass TiO2 nanotubular layer with a gradient pore diameter and ultrathin tube wall (nearly 10 nm). A higher anodic voltage and longer anodization time are beneficial to the formation of ultrathin tube walls. This approach is simple and cost-effective in fabricating high-quality ordered TiO2 nanotubular arrays for practical applications.

High-speed growth of TiO2 nanotube arrays with gradient pore diameter and ultrathin tube wall under high-field anodization.

PubMed

Yuan, Xiaoliang; Zheng, Maojun; Ma, Li; Shen, Wenzhong

2010-10-08

Highly ordered TiO(2) nanotubular arrays have been prepared by two-step anodization under high field. The high anodizing current densities lead to a high-speed film growth (0.40-1.00 microm min(-1)), which is nearly 16 times faster than traditional fabrication of TiO(2) at low field. It was found that an annealing process of Ti foil is an effective approach to get a monodisperse and double-pass TiO(2) nanotubular layer with a gradient pore diameter and ultrathin tube wall (nearly 10 nm). A higher anodic voltage and longer anodization time are beneficial to the formation of ultrathin tube walls. This approach is simple and cost-effective in fabricating high-quality ordered TiO(2) nanotubular arrays for practical applications.

Reflow dynamics of thin patterned viscous films

NASA Astrophysics Data System (ADS)

Leveder, T.; Landis, S.; Davoust, L.

2008-01-01

This letter presents a study of viscous smoothening dynamics of a nanopatterned thin film. Ultrathin film manufacturing processes appearing to be a key point of nanotechnology engineering and numerous studies have been recently led in order to exhibit driving parameters of this transient surface motion, focusing on time scale accuracy method. Based on nanomechanical analysis, this letter shows that controlled shape measurements provided much more detailed information about reflow mechanism. Control of reflow process of any complex surface shape, or measurement of material parameter as thin film viscosity, free surface energy, or even Hamaker constant are therefore possible.

Thin-film X-ray filters on microstructured substrates and their thermophysical properties

NASA Astrophysics Data System (ADS)

Mitrofanov, A. V.

2018-02-01

It is shown that structured substrates having micron- or submicron-sized through holes and coated with an ultrathin organic film can be used for the fabrication of thin-film X-ray filters via direct growth of functional layers on a substrate by sputter deposition, without additional complex processing steps. An optimised process is considered for the fabrication of X-ray filters on support structures in the form of electroplated fine nickel grids and on track-etched polymer membranes with micron- and submicrondiameter through pores. 'Optimisation' is here taken to mean matching the sputter deposition conditions with the properties of substrates so as to avoid overheating. The filters in question are intended for both imaging and single-channel detectors operating in the soft X-ray and vacuum UV spectral regions, at wavelengths from 10 to 60 nm. Thermal calculations are presented for the heating of ultrathin layers of organic films and thin-film support substrates during the sputter deposition of aluminium or other functional materials. The paper discusses approaches for cooling thinfilm composites during the sputter deposition process and the service of the filters in experiments and gives a brief overview of the works that utilised filters produced by the described technique on microstructured substrates, including orbital solar X-ray research in the framework of the CORONAS programme and laboratory laser plasma experiments.

Preparation of c-axis perpendicularly oriented ultra-thin L10-FePt films on MgO and VN underlayers

NASA Astrophysics Data System (ADS)

Futamoto, Masaaki; Shimizu, Tomoki; Ohtake, Mitsuru

2018-05-01

Ultra-thin L10-FePt films of 2 nm average thickness are prepared on (001) oriented MgO and VN underlayers epitaxially grown on base substrate of SrTiO3(001) single crystal. Detailed cross-sectional structures are observed by high-resolution transmission electron microscopy. Continuous L10-FePt(001) thin films with very flat surface are prepared on VN(001) underlayer whereas the films prepared on MgO(001) underlayer consist of isolated L10-FePt(001) crystal islands. Presence of misfit dislocation and lattice bending in L10-FePt material is reducing the effective lattice mismatch with respect to the underlayer to be less than 0.5 %. Formation of very flat and continuous FePt layer on VN underlayer is due to the large surface energy of VN material where de-wetting of FePt material at high temperature annealing process is suppressed under a force balance between the surface and interface energies of FePt and VN materials. An employment of underlayer or substrate material with the lattice constant and the surface energy larger than those of L10-FePt is important for the preparation of very thin FePt epitaxial thin continuous film with the c-axis controlled to be perpendicular to the substrate surface.

High efficient light absorption and nanostructure-dependent birefringence of a metal-dielectric symmetrical layered structure

NASA Astrophysics Data System (ADS)

Jen, Yi-Jun; Jhang, Yi-Ciang; Liu, Wei-Chih

2017-08-01

A multilayer that comprises ultra-thin metal and dielectric films has been investigated and applied as a layered metamaterial. By arranging metal and dielectric films alternatively and symmetrically, the equivalent admittance and refractive index can be tailored separately. The tailored admittance and refractive index enable us to design optical filters with more flexibility. The admittance matching is achieved via the admittance tracing in the normalized admittance diagram. In this work, an ultra-thin light absorber is designed as a multilayer composed of one or several cells. Each cell is a seven-layered film stack here. The design concept is to have the extinction as large as possible under the condition of admittance matching. For a seven-layered symmetrical film stack arranged as Ta2O5 (45 nm)/ a-Si (17 nm)/ Cr (30 nm)/ Al (30 nm)/ Cr (30 nm)/ a-Si (17 nm)/ Ta2O5 (45 nm), its mean equivalent admittance and extinction coefficient over the visible regime is 1.4+0.2i and 2.15, respectively. The unit cell on a transparent BK7 glass substrate absorbs 99% of normally incident light energy for the incident medium is glass. On the other hand, a transmission-induced metal-dielectric film stack is investigated by using the admittance matching method. The equivalent anisotropic property of the metal-dielectric multilayer varied with wavelength and nanostructure are investigated here.

Improved Stability and Performance of Visible Photoelectrochemical Water Splitting on Solution-Processed Organic Semiconductor Thin Films by Ultrathin Metal Oxide Passivation

DOE PAGES

Wang, Lei; Yan, Danhua; Shaffer, David W.; ...

2017-12-27

Solution-processable organic semiconductors have potentials as visible photoelectrochemical (PEC) water splitting photoelectrodes due to their tunable small band gap and electronic energy levels, but they are typically limited by poor stability and photocatalytic activity. In this study, we demonstrate the direct visible PEC water oxidation on solution-processed organic semiconductor thin films with improved stability and performance by ultrathin metal oxide passivation layers. N-type fullerene-derivative thin films passivated by sub-2 nm ZnO via atomic layer deposition enabled the visible PEC water oxidation at wavelengths longer than 600 nm in harsh alkaline electrolyte environments with up to 30 μA/cm 2 photocurrents atmore » the thermodynamic water-oxidation equilibrium potential and the photoanode half-lifetime extended to ~1000 s. The systematic investigation reveals the enhanced water oxidation catalytic activity afforded by ZnO passivation and the charge tunneling governing the hole transfer through passivation layers. Further enhanced PEC performances were realized by improving the bottom ohmic contact to the organic semiconductor, achieving ~60 μA/cm 2 water oxidation photocurrent at the equilibrium potential, the highest values reported for organic semiconductor thin films to our knowledge. The improved stability and performance of passivated organic photoelectrodes and discovered design rationales provide useful guidelines for realizing the stable visible solar PEC water splitting based on organic semiconductor thin films.« less

Improved Stability and Performance of Visible Photoelectrochemical Water Splitting on Solution-Processed Organic Semiconductor Thin Films by Ultrathin Metal Oxide Passivation

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

Wang, Lei; Yan, Danhua; Shaffer, David W.

Solution-processable organic semiconductors have potentials as visible photoelectrochemical (PEC) water splitting photoelectrodes due to their tunable small band gap and electronic energy levels, but they are typically limited by poor stability and photocatalytic activity. In this study, we demonstrate the direct visible PEC water oxidation on solution-processed organic semiconductor thin films with improved stability and performance by ultrathin metal oxide passivation layers. N-type fullerene-derivative thin films passivated by sub-2 nm ZnO via atomic layer deposition enabled the visible PEC water oxidation at wavelengths longer than 600 nm in harsh alkaline electrolyte environments with up to 30 μA/cm 2 photocurrents atmore » the thermodynamic water-oxidation equilibrium potential and the photoanode half-lifetime extended to ~1000 s. The systematic investigation reveals the enhanced water oxidation catalytic activity afforded by ZnO passivation and the charge tunneling governing the hole transfer through passivation layers. Further enhanced PEC performances were realized by improving the bottom ohmic contact to the organic semiconductor, achieving ~60 μA/cm 2 water oxidation photocurrent at the equilibrium potential, the highest values reported for organic semiconductor thin films to our knowledge. The improved stability and performance of passivated organic photoelectrodes and discovered design rationales provide useful guidelines for realizing the stable visible solar PEC water splitting based on organic semiconductor thin films.« less

Symmetry of Epitaxial BiFeO3 Films in the Ultrathin Regime

NASA Astrophysics Data System (ADS)

Yang, Yongsoo; Schlep&üTz, Christian; Adamo, Carolina; Schlom, Darrell; Clarke, Roy

2013-03-01

BiFeO3 (BFO) films grown on SrTiO3 (STO) with a SrRuO3 buffer layer exhibit a monoclinic structure at thicknesses greater than 40 nm, but higher structural symmetry can be observed for thinner films [Phys. Rev. B 81, 144115 (2010)]. We report a structural phase transition from monoclinic to tetragonal in ultra-thin BFO films grown directly on (100)-oriented STO. X-ray diffraction measurements of 3-dimensional reciprocal space maps reveal half-integer order peaks due to oxygen octahedral tilting. When the film thickness is decreased below 20 unit cells, the integer-order Bragg peak splitting associated with the presence of multiple domains of the monoclinic phase disappears. Instead, a single peak that is commensurate with the STO substrate lattice appears. The diffraction pattern has four-fold symmetry, ruling out the presence of a single monoclinic domain in favor of a tetragonal film structure. The evolution of the oxygen octahedra tilt pattern inferred from the intensities of half-order peaks suggests that this transition originates from the corner-connectivity of oxygen atoms at the interface between BFO and STO, and also strongly supports this monoclinic to tetragonal transition. Supported in part by the U.S. Department of Energy (DE-FG02-06ER46273). Measurements performed at Sectors 13-BMC, 33-IDD, 33-BMC of the Advanced Photon Source, Argonne National Laboratory, USA (DOE contract No. DE-AC02-06CH11357).

Confinement induced densification in supported unentangled polymer films

NASA Astrophysics Data System (ADS)

Pradipkanti, L.; Satapathy, Dillip K.

2017-05-01

We report the densification phenomena inunentangled and low-molecular weight polystyrene (PS) thin films supported on solid substrates having thickness from 25 nm to 230 nm. The mass density of the thin polymer films were extracted from X-ray reflectivity profiles and also from the refractive index by using Clausius and Mossotti equation. The mass densityof polymeris found to increasesignificantly with decrease in film thickness below ten times the radius of gyration of the polymer. The net increase in mass density of the polymer film upon reduction in thickness is discussed in terms of three-layer model and the presence of unentangled polymer chains. We conjecture that, the densification of ultra-thin polymer films can strongly alter the polymer conformations at film/substrate interface.

Chiral magnetic conductivity and surface states of Weyl semimetals in topological insulator ultra-thin film multilayer.

PubMed

Owerre, S A

2016-06-15

We investigate an ultra-thin film of topological insulator (TI) multilayer as a model for a three-dimensional (3D) Weyl semimetal. We introduce tunneling parameters t S, [Formula: see text], and t D, where the former two parameters couple layers of the same thin film at small and large momenta, and the latter parameter couples neighbouring thin film layers along the z-direction. The Chern number is computed in each topological phase of the system and we find that for [Formula: see text], the tunneling parameter [Formula: see text] changes from positive to negative as the system transits from Weyl semi-metallic phase to insulating phases. We further study the chiral magnetic effect (CME) of the system in the presence of a time dependent magnetic field. We compute the low-temperature dependence of the chiral magnetic conductivity and show that it captures three distinct phases of the system separated by plateaus. Furthermore, we propose and study a 3D lattice model of Porphyrin thin film, an organic material known to support topological Frenkel exciton edge states. We show that this model exhibits a 3D Weyl semi-metallic phase and also supports a 2D Weyl semi-metallic phase. We further show that this model recovers that of 3D Weyl semimetal in topological insulator thin film multilayer. Thus, paving the way for simulating a 3D Weyl semimetal in topological insulator thin film multilayer. We obtain the surface states (Fermi arcs) in the 3D model and the chiral edge states in the 2D model and analyze their topological properties.

Enhanced Electroluminescence from Silicon Quantum Dots Embedded in Silicon Nitride Thin Films Coupled with Gold Nanoparticles in Light Emitting Devices

PubMed Central

Muñoz-Rosas, Ana Luz; Alonso-Huitrón, Juan Carlos

2018-01-01

Nowadays, the use of plasmonic metal layers to improve the photonic emission characteristics of several semiconductor quantum dots is a booming tool. In this work, we report the use of silicon quantum dots (SiQDs) embedded in a silicon nitride thin film coupled with an ultra-thin gold film (AuNPs) to fabricate light emitting devices. We used the remote plasma enhanced chemical vapor deposition technique (RPECVD) in order to grow two types of silicon nitride thin films. One with an almost stoichiometric composition, acting as non-radiative spacer; the other one, with a silicon excess in its chemical composition, which causes the formation of silicon quantum dots imbibed in the silicon nitride thin film. The ultra-thin gold film was deposited by the direct current (DC)-sputtering technique, and an aluminum doped zinc oxide thin film (AZO) which was deposited by means of ultrasonic spray pyrolysis, plays the role of the ohmic metal-like electrode. We found that there is a maximum electroluminescence (EL) enhancement when the appropriate AuNPs-spacer-SiQDs configuration is used. This EL is achieved at a moderate turn-on voltage of 11 V, and the EL enhancement is around four times bigger than the photoluminescence (PL) enhancement of the same AuNPs-spacer-SiQDs configuration. From our experimental results, we surmise that EL enhancement may indeed be due to a plasmonic coupling. This kind of silicon-based LEDs has the potential for technology transfer. PMID:29565267

Novel processing to produce polymer/ceramic nanocomposites by atomic layer deposition

NASA Astrophysics Data System (ADS)

Liang, Xinhua

Polymeric materials can be greatly influenced by nanoscale inclusions of inorganic materials. The main goal of this thesis is to fabricate novel polymer/ceramic composite materials for two different applications using atomic layer deposition (ALD) or molecular layer deposition (MLD) methods. One is to produce well-dispersed polymer/ceramic nanocomposites with improved barrier properties for packaging applications. The other is to produce porous polymer/ceramic composites with improved bioactivity for tissue engineering applications. ALD has been successfully utilized for the conformal and uniform deposition of ultra-thin alumina and titania films on primary micron-sized polymer particles. The mechanism to initiate alumina and titania ALD on polymer particles without chemical functional groups was confirmed. A nucleation period was needed for both alumina and titania ALD on high density polyethylene (HDPE) particles and no nucleation period was needed for alumina ALD on polymethyl methacrylate particles. Titania ALD films deposited at low temperatures had an amorphous structure and showed much weaker photoactivity than common pigment-grade anatase TiO2 particles. Highly uniform and conformal ultra-thin aluminum alkoxide (alucone) polymer films were deposited on primary silica and titania nanoparticles using MLD in a fluidized bed reactor. The deposition chemistry and properties of alucone MLD films were investigated. The photoactivity of pigment-grade TiO2 particles was quenched after 20 cycles of an alucone MLD film, but the films shrank and decomposed in the presence of water, which decreased the passivation effect of the photoactivity of TiO2 particles. Well-dispersed polymer/ceramic nanocomposites were obtained by extruding alumina ALD coated HDPE particles. The diffusion coefficient of the fabricated nanocomposite membranes can be reduced by half with the inclusion of 7.3 vol.% alumina flakes. However, a corresponding increase in permeability was also observed due to the voids formed at or near the interface of the polymer and alumina flakes during the extrusion process. Efforts to improve the barrier properties of the membranes included 3-aminopropyltriethoxysilane treatment and coating alucone MLD films on alumina coated particles prior to extrusion. The porous polymer/ceramic particles were synthesized by depositing ultra-thin alumina or titania films on highly porous poly(styrene-divinylbenzene) particles using a low-temperature ALD process. Analytical characterization revealed that conformal alumina and titania films were grown on internal and external polymer particle surfaces, and the pore filling mechanism was a uniform coating of the pore walls. The ALD layers can improve the bioactivity and protein adsorption of the polymer substrates.

Layer-by-layer assembled heteroatom-doped graphene films with ultrahigh volumetric capacitance and rate capability for micro-supercapacitors.

PubMed

Wu, Zhong-Shuai; Parvez, Khaled; Winter, Andreas; Vieker, Henning; Liu, Xianjie; Han, Sheng; Turchanin, Andrey; Feng, Xinliang; Müllen, Klaus

2014-07-09

Highly uniform, ultrathin, layer-by-layer heteroatom (N, B) co-doped graphene films are fabricated for high-performance on-chip planar micro-supercapacitors with an ultrahigh volumetric capacitance of ∼488 F cm(-3) and excellent rate capability due to the synergistic effect of nitrogen and boron co-doping. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly Robust Neutral Plane Oxide TFTs Withstanding 0.25 mm Bending Radius for Stretchable Electronics

PubMed Central

Kim, Yong-Hwan; Lee, Eunji; Um, Jae Gwang; Mativenga, Mallory; Jang, Jin

2016-01-01

Advancements in thin-film transistor (TFT) technology have extended to electronics that can withstand extreme bending or even folding. Although the use of ultrathin plastic substrates has achieved considerable advancement towards this end, free-standing ultrathin plastics inevitably suffer from mechanical instability and are very difficult to handle during TFT fabrication. Here, in addition to the use of a 1.5 μm-thick polyimide (PI) substrate, a 1.5 μm-thick PI film is also deposited on top of the TFT devices to ensure that the devices are located at the neutral plane of the two PI films for high folding stability. For mechanical support during TFT fabrication up to the deposition of the top PI film, the PI substrate is spin coated on top of a carrier glass that is coated with a mixture of carbon nanotubes (CNTs) and graphene oxide (GO). The mixture of CNT and GO facilitates mechanical detachment of the neutral plane (NP) TFTs from the carrier glass before they are transferred to a polydimethylsiloxane (PDMS) substrate as islands. Being located in the neutral bending plane, the NP TFT can be transferred to the PDMS without performance degradation and exhibit excellent mechanical stability after stretching the PDMS substrate up to a 25% elastic elongation. PMID:27165715

Impact of Ultrathin C60 on Perovskite Photovoltaic Devices.

PubMed

Liu, Dianyi; Wang, Qiong; Traverse, Christopher J; Yang, Chenchen; Young, Margaret; Kuttipillai, Padmanaban S; Lunt, Sophia Y; Hamann, Thomas W; Lunt, Richard R

2018-01-23

Halide perovskite solar cells have seen dramatic progress in performance over the past several years. Certified efficiencies of inverted structure (p-i-n) devices have now exceeded 20%. In these p-i-n devices, fullerene compounds are the most popular electron-transfer materials. However, the full function of fullerenes in perovskite solar cells is still under investigation, and the mechanism of photocurrent hysteresis suppression by fullerene remains unclear. In previous reports, thick fullerene layers (>20 nm) were necessary to fully cover the perovskite film surface to make good contact with perovskite film and avoid large leakage currents. In addition, the solution-processed fullerene layer has been broadly thought to infiltrate into the perovskite film to passivate traps on grain boundary surfaces, causing suppressed photocurrent hysteresis. In this work, we demonstrate an efficient perovskite photovoltaic device with only 1 nm C 60 deposited by vapor deposition as the electron-selective material. Utilizing a combination of fluorescence microscopy and impedance spectroscopy, we show that the ultrathin C 60 predominately acts to extract electrons from the perovskite film while concomitantly suppressing the photocurrent hysteresis by reducing space charge accumulation at the interface. This work ultimately helps to clarify the dominant role of fullerenes in perovskite solar cells while simplifying perovskite solar cell design to reduce manufacturing costs.

X-Ray Spectroscopy of Ultra-Thin Oxide/Oxide Heteroepitaxial Films: A Case Study of Single-Nanometer VO2/TiO2.

PubMed

Quackenbush, Nicholas F; Paik, Hanjong; Woicik, Joseph C; Arena, Dario A; Schlom, Darrell G; Piper, Louis F J

2015-08-21

Epitaxial ultra-thin oxide films can support large percent level strains well beyond their bulk counterparts, thereby enabling strain-engineering in oxides that can tailor various phenomena. At these reduced dimensions (typically < 10 nm), contributions from the substrate can dwarf the signal from the epilayer, making it difficult to distinguish the properties of the epilayer from the bulk. This is especially true for oxide on oxide systems. Here, we have employed a combination of hard X-ray photoelectron spectroscopy (HAXPES) and angular soft X-ray absorption spectroscopy (XAS) to study epitaxial VO2/TiO2 (100) films ranging from 7.5 to 1 nm. We observe a low-temperature (300 K) insulating phase with evidence of vanadium-vanadium (V-V) dimers and a high-temperature (400 K) metallic phase absent of V-V dimers irrespective of film thickness. Our results confirm that the metal insulator transition can exist at atomic dimensions and that biaxial strain can still be used to control the temperature of its transition when the interfaces are atomically sharp. More generally, our case study highlights the benefits of using non-destructive XAS and HAXPES to extract out information regarding the interfacial quality of the epilayers and spectroscopic signatures associated with exotic phenomena at these dimensions.

Temperature Controlled Electrostatic Disorder and Polymorphism in Ultrathin Films of α-Sexithiophene

NASA Astrophysics Data System (ADS)

Hoffman, Benjamin; Jafari, Sara; McAfee, Terry; Apperson, Aubrey; O'Connor, Brendan; Dougherty, Daniel

Competing phases in well-ordered alpha-sexithiophene (α-6T) are shown to contribute to electrostatic disorder observed by differences in surface potential between mono- and bi-layer crystallites. Ultrathin films are of key importance to devices in which charge transport occurs in the first several monolayers nearest to a dielectric interface (e.g. thin film transistors) and complex structures in this regime impact the general electrostatic landscape. This study is comprised of 1.5 ML sample crystals grown via organic molecular beam deposition onto a temperature controlled hexamethyldisilazane (HMDS) passivated SiO2 substrate to produce well-ordered layer-by-layer type growth. Sample topography and surface potential were characterized simultaneously using Kelvin Probe Force Microscopy to then isolate contact potential differences by first and second layer α-6T regions. Films grown on 70° C, 120° C substrates are observed to have a bilayer with lower, higher potential than the monolayer, respectively. Resulting interlayer potential differences are a clear source of electrostatic disorder and are explained as subtle shifts in tilt-angles between layers relative to the substrate. These empirical results continue our understanding of how co-existing orientations contribute to the complex electrostatics influencing charge transport. NSF CAREER award DMR-1056861.

CH3Br adsorption on MgO/Mo ultrathin films: A DFT study

NASA Astrophysics Data System (ADS)

Cipriano, Luis A.; Tosoni, Sergio; Pacchioni, Gianfranco

2018-06-01

The adsorption of methyl bromide on MgO ultrathin films supported on Mo(100) was studied by means of density functional theory calculations, in comparison to the MgO(100) and Mo(100) surfaces. The adsorption energy and geometry were shown to depend on the thickness of the supported oxide film. MgO films as thick as 2ML (or more) display adsorptive properties similar to MgO(100), i.e. the adsorption of CH3Br is mostly due to dispersion and the molecule lies in a tilted geometry almost parallel to the surface. The CH3Br HOMO-LUMO gap is almost unaltered with respect to the gas phase. On metallic Mo(100) surfaces the bonding is completely different with the CH3Br molecule strongly bound and the C-Br bond axis almost vertical with respect to the metal surface. The MgO monolayer supported on Mo exhibits somehow intermediate properties: the tilt angle is larger and the bonding is stronger than on MgO(100), due to the effect of the supporting metal. In this case, a small reduction of the HOMO-LUMO gap of the adsorbed molecule is reported. The results help to rationalize the observed behavior in photodissociation of CH3Br supported on different substrates.

High spin-polarization in ultrathin Co2MnSi/CoPd multilayers

NASA Astrophysics Data System (ADS)

Galanakis, I.

2015-03-01

Half-metallic Co2MnSi finds a broad spectrum of applications in spintronic devices either in the form of thin films or as spacer in multilayers. Using state-of-the-art ab-initio electronic structure calculations we exploit the electronic and magnetic properties of ultrathin Co2MnSi/CoPd multilayers. We show that these heterostructures combine high values of spin-polarization at the Co2MnSi spacer with the perpendicular magnetic anisotropy of binary compounds such as CoPd. Thus they could find application in spintronic/magnetoelectronic devices.

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.

Microwave Characterization of Ba-Substituted PZT and ZnO Thin Films.

PubMed

Tierno, Davide; Dekkers, Matthijn; Wittendorp, Paul; Sun, Xiao; Bayer, Samuel C; King, Seth T; Van Elshocht, Sven; Heyns, Marc; Radu, Iuliana P; Adelmann, Christoph

2018-05-01

The microwave dielectric properties of (Ba 0.1 Pb 0.9 )(Zr 0.52 Ti 0.48 )O 3 (BPZT) and ZnO thin films with thicknesses below were investigated. No significant dielectric relaxation was observed for both BPZT and ZnO up to 30 GHz. The intrinsic dielectric constant of BPZT was as high as 980 at 30 GHz. The absence of strong dielectric dispersion and loss peaks in the studied frequency range can be linked to the small grain diameters in these ultrathin films.

Structural Stability of Diffusion Barriers in Cu/Ru/MgO/Ta/Si

PubMed Central

Hsieh, Shu-Huei; Chen, Wen Jauh; Chien, Chu-Mo

2015-01-01

Various structures of Cu (50 nm)/Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm)/Si were prepared by sputtering and electroplating techniques, in which the ultra-thin trilayer of Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm) is used as the diffusion barrier against the interdiffusion between Cu film and Si substrate. The various structures of Cu/Ru/MgO/Ta/Si were characterized by four-point probes for their sheet resistances, by X-ray diffractometers for their crystal structures, by scanning electron microscopes for their surface morphologies, and by transmission electron microscopes for their cross-section and high resolution views. The results showed that the ultra-thin tri-layer of Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm) is an effective diffusion barrier against the interdiffusion between Cu film and Si substrate. The MgO, and Ta layers as deposited are amorphous. The mechanism for the failure of the diffusion barrier is that the Ru layer first became discontinuous at a high temperature and the Ta layer sequentially become discontinuous at a higher temperature, the Cu atoms then diffuse through the MgO layer and to the substrate at the discontinuities, and the Cu3Si phases finally form. The maximum temperature at which the structures of Cu (50 nm)/Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm)/Si are annealed and still have low sheet resistance is from 550 to 750 °C for the annealing time of 5 min and from 500 to 700 °C for the annealing time of 30 min. PMID:28347099

Carrier mobility degradation due to high dose implantation in ultrathin unstrained and strained silicon-on-insulator films

NASA Astrophysics Data System (ADS)

Dupré, C.; Ernst, T.; Hartmann, J.-M.; Andrieu, F.; Barnes, J.-P.; Rivallin, P.; Faynot, O.; Deleonibus, S.; Fazzini, P. F.; Claverie, A.; Cristoloveanu, S.; Ghibaudo, G.; Cristiano, F.

2007-11-01

Based on electrical measurements and transmission electron microscopy (TEM) imaging, we propose an explanation for the electron and hole mobility degradation with gate length reduction in metal-oxide-semiconductor field effect transistors (MOSFETs). We demonstrate that ion implantation, normally used for source/drain doping, is responsible for transport degradation for short-channel devices. Implantation impact on electrons and holes mobility was investigated both on silicon-on-insulator (SOI) and tensile strained silicon-on-insulator (sSOI) substrates. Wafers with ultrathin Si films (from 8 to 35 nm) were Ge implanted at 3 keV and various concentrations (from 5×1014 to 2×1015 atoms cm-2), then annealed at 600 °C for 1 h. Secondary ion mass spectrometry enabled us to quantify the Ge-implanted atoms concentrations. The end-of-range defects impact on mobility was investigated with the pseudo-MOSFET technique. Measurements showed a mobility decrease as the implantation dose increased. We demonstrated that sSOI mobility is more sensitive to implantation than SOI mobility, without any implantation-induced strain relaxation in sSOI (checked using the ultraviolet Raman technique). A 36% (25%) holes (electrons) mobility degradation was measured for sSOI, while SOI presented a 21% mobility degradation for holes and 5% for electrons. Finally, the electrical results were compared with morphological studies. Plan-view TEM showed the presence of interstitial defects formed during ion implantation and annealing. The defect density was estimated to be two times higher in sSOI than in SOI, which is in full agreement with electrical results mentioned before. The results are relevant for the optimization of the source and drain regions of advanced nanoscale SOI and sSOI transistors.

Low-Dimensional Nanomaterials as Active Layer Components in Thin-Film Photovoltaics

NASA Astrophysics Data System (ADS)

Shastry, Tejas Attreya

Thin-film photovoltaics offer the promise of cost-effective and scalable solar energy conversion, particularly for applications of semi-transparent solar cells where the poor absorption of commercially-available silicon is inadequate. Applications ranging from roof coatings that capture solar energy to semi-transparent windows that harvest the immense amount of incident sunlight on buildings could be realized with efficient and stable thin-film solar cells. However, the lifetime and efficiency of thin-film solar cells continue to trail their inorganic silicon counterparts. Low-dimensional nanomaterials, such as carbon nanotubes and two-dimensional metal dichalcogenides, have recently been explored as materials in thin-film solar cells due to their exceptional optoelectronic properties, solution-processability, and chemical inertness. Thus far, issues with the processing of these materials has held back their implementation in efficient photovoltaics. This dissertation reports processing advances that enable demonstrations of low-dimensional nanomaterials in thin-film solar cells. These low-dimensional photovoltaics show enhanced photovoltaic efficiency and environmental stability in comparison to previous devices, with a focus on semiconducting single-walled carbon nanotubes as an active layer component. The introduction summarizes recent advances in the processing of carbon nanotubes and their implementation through the thin-film photovoltaic architecture, as well as the use of two-dimensional metal dichalcogenides in photovoltaic applications and potential future directions for all-nanomaterial solar cells. The following chapter reports a study of the interaction between carbon nanotubes and surfactants that enables them to be sorted by electronic type via density gradient ultracentrifugation. These insights are utilized to construct of a broad distribution of carbon nanotubes that absorb throughout the solar spectrum. This polychiral distribution is then shown to result in record breaking performance in a carbon nanotube solar cell, and subsequent chapters study the mechanisms behind charge transfer in the polychiral carbon nanotube / fullerene solar cell. Further processing advances, chiral distribution tailoring, and solvent additives are shown to enable more uniform and larger area carbon nanotube solar cells while maintaining record-breaking performance. In order to increase overall photovoltaic performance of a carbon nanotube active layer solar cell, this dissertation also demonstrates a ternary polymer-carbon nanotube-small molecule photovoltaic with high efficiency and stability enabled by the nanomaterial. Finally, the use of the two-dimensional metal dichalcogenide molybdenum disulfide as a photovoltaic material is explored in an ultrathin solar cell with higher efficiency per thickness than leading organic and inorganic thin-film photovoltaics. Overall, this work demonstrates breakthroughs in utilizing low-dimensional nanomaterials as active layer components in photovoltaics and will inform ongoing research in making ultrathin, stable, efficient solar cells.

Magnetron sputtered boron films for increasing hardness of a metal surface

DOEpatents

Makowiecki, Daniel M [Livermore, CA; Jankowski, Alan F [Livermore, CA

2003-05-27

A method is described for the production of thin boron and titanium/boron films by magnetron sputter deposition. The amorphous boron films contain no morphological growth features, unlike those found when thin films are prepared by various physical vapor deposition processes. Magnetron sputter deposition method requires the use of a high density crystalline boron sputter target which is prepared by hot isostatic pressing. Thin boron films prepared by this method are useful for producing hardened surfaces, surfacing machine tools, etc. and for ultra-thin band pass filters as well as the low Z element in low Z/high Z optical components, such as mirrors which enhance reflectivity from grazing to normal incidence.

Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics.

PubMed

Kim, Dae-Hyeong; Viventi, Jonathan; Amsden, Jason J; Xiao, Jianliang; Vigeland, Leif; Kim, Yun-Soung; Blanco, Justin A; Panilaitis, Bruce; Frechette, Eric S; Contreras, Diego; Kaplan, David L; Omenetto, Fiorenzo G; Huang, Yonggang; Hwang, Keh-Chih; Zakin, Mitchell R; Litt, Brian; Rogers, John A

2010-06-01

Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain/machine interfaces. This article describes a material strategy for a type of bio-interfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal models illustrate one mode of use for this class of technology. These concepts provide new capabilities for implantable and surgical devices.

Dissolvable Films of Silk Fibroin for Ultrathin, Conformal Bio-Integrated Electronics

PubMed Central

Kim, Dae-Hyeong; Viventi, Jonathan; Amsden, Jason J.; Xiao, Jianliang; Vigeland, Leif; Kim, Yun-Soung; Blanco, Justin A.; Panilaitis, Bruce; Frechette, Eric S.; Contreras, Diego; Kaplan, David L.; Omenetto, Fiorenzo G.; Huang, Yonggang; Hwang, Keh-Chih; Zakin, Mitchell R.; Litt, Brian; Rogers, John A.

2011-01-01

Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain-machine interfaces. This paper describes a material strategy for a type of bio-interfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal models illustrate one mode of use for this class of technology. These concepts provide new capabilities for implantable or surgical devices. PMID:20400953

Ultra-thin alumina and silicon nitride MEMS fabricated membranes for the electron multiplication

NASA Astrophysics Data System (ADS)

Prodanović, V.; Chan, H. W.; Graaf, H. V. D.; Sarro, P. M.

2018-04-01

In this paper we demonstrate the fabrication of large arrays of ultrathin freestanding membranes (tynodes) for application in a timed photon counter (TiPC), a novel photomultiplier for single electron detection. Low pressure chemical vapour deposited silicon nitride (Si x N y ) and atomic layer deposited alumina (Al2O3) with thicknesses down to only 5 nm are employed for the membrane fabrication. Detailed characterization of structural, mechanical and chemical properties of the utilized films is carried out for different process conditions and thicknesses. Furthermore, the performance of the tynodes is investigated in terms of secondary electron emission, a fundamental attribute that determines their applicability in TiPC. Studied features and presented fabrication methods may be of interest for other MEMS application of alumina and silicon nitride as well, in particular where strong ultra-thin membranes are required.

Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics

NASA Astrophysics Data System (ADS)

Kim, Dae-Hyeong; Viventi, Jonathan; Amsden, Jason J.; Xiao, Jianliang; Vigeland, Leif; Kim, Yun-Soung; Blanco, Justin A.; Panilaitis, Bruce; Frechette, Eric S.; Contreras, Diego; Kaplan, David L.; Omenetto, Fiorenzo G.; Huang, Yonggang; Hwang, Keh-Chih; Zakin, Mitchell R.; Litt, Brian; Rogers, John A.

2010-06-01

Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain/machine interfaces. This article describes a material strategy for a type of bio-interfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal models illustrate one mode of use for this class of technology. These concepts provide new capabilities for implantable and surgical devices.

Atomic Layer Deposition of Metastable β-Fe 2 O 3 via Isomorphic Epitaxy for Photoassisted Water Oxidation

DOE PAGES

Emery, Jonathan D.; Schlepütz, Christian M.; Guo, Peijun; ...

2014-12-09

Here, we report the growth and photoelectrochemical (PEC) characterization of the uncommon bibyite phase of iron(III) oxide (β-Fe 2O 3) epitaxially stabilized via atomic layer deposition on an conductive, transparent, and isomorphic template (Sn-doped In 2O 3). Furthermore, as a photoanode, unoptimized β-Fe 2O 3 ultrathin films perform similarly to their ubiquitous α-phase (hematite) counterpart, but reveal a more ideal bandgap (1.8 eV), a ~0.1 V improved photocurrent onset potential, and longer wavelength (>600 nm) spectral response. Finally, stable operation under basic water oxidation justifies further exploration of this atypical phase and motivates the investigation of other unexplored metastable phasesmore » as new PEC materials.« less

Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces

PubMed Central

Syurik, Julia; Siddique, Radwanul Hasan; Dollmann, Antje; Gomard, Guillaume; Schneider, Marc; Worgull, Matthias; Wiegand, Gabriele; Hölscher, Hendrik

2017-01-01

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications. PMID:28429805

Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces

NASA Astrophysics Data System (ADS)

Syurik, Julia; Siddique, Radwanul Hasan; Dollmann, Antje; Gomard, Guillaume; Schneider, Marc; Worgull, Matthias; Wiegand, Gabriele; Hölscher, Hendrik

2017-04-01

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications.

Responsive Plasma Polymerized Ultrathin Nanocomposite Films

DTIC Science & Technology

2012-01-01

29 74 32 75 Ab so rb an ce (a .u .) Wavenumber, cm-1 pNIPAAM A B C D E Fig . 2. FTIR spectra of A) NIPAAM monomer B) Spun- cast P-NIPAAM film and...self- actuating response to specific stimuli are desirable in a wide range of applications including thermalandchemical sensing, tunableoptics...targeteddrug delivery, switchable surfaces and micro actuators [1e6]. Designing materials which are capable of generating a response from the stim- ulus

Enhanced Atom Mobility on the Surface of a Metastable Film

NASA Astrophysics Data System (ADS)

Picone, A.; Riva, M.; Fratesi, G.; Brambilla, A.; Bussetti, G.; Finazzi, M.; Duò, L.; Ciccacci, F.

2014-07-01

A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.

Enhanced atom mobility on the surface of a metastable film.

PubMed

Picone, A; Riva, M; Fratesi, G; Brambilla, A; Bussetti, G; Finazzi, M; Duò, L; Ciccacci, F

2014-07-25

A remarkable enhancement of atomic diffusion is highlighted by scanning tunneling microscopy performed on ultrathin metastable body-centered tetragonal Co films grown on Fe(001). The films follow a nearly perfect layer-by-layer growth mode with a saturation island density strongly dependent on the layer on which the nucleation occurs, indicating a lowering of the diffusion barrier. Density functional theory calculations reveal that this phenomenon is driven by the increasing capability of the film to accommodate large deformations as the thickness approaches the limit at which a structural transition occurs. These results disclose the possibility of tuning surface diffusion dynamics and controlling cluster nucleation and self-organization.

High performance top-gated ferroelectric field effect transistors based on two-dimensional ZnO nanosheets

NASA Astrophysics Data System (ADS)

Tian, Hongzheng; Wang, Xudong; Zhu, Yuankun; Liao, Lei; Wang, Xianying; Wang, Jianlu; Hu, Weida

2017-01-01

High quality ultrathin two-dimensional zinc oxide (ZnO) nanosheets (NSs) are synthesized, and the ZnO NS ferroelectric field effect transistors (FeFETs) are demonstrated based on the P(VDF-TrFE) polymer film used as the top gate insulating layer. The ZnO NSs exhibit a maximum field effect mobility of 588.9 cm2/Vs and a large transconductance of 2.5 μS due to their high crystalline quality and ultrathin two-dimensional structure. The polarization property of the P(VDF-TrFE) film is studied, and a remnant polarization of >100 μC/cm2 is achieved with a P(VDF-TrFE) thickness of 300 nm. Because of the ultrahigh remnant polarization field generated in the P(VDF-TrFE) film, the FeFETs show a large memory window of 16.9 V and a high source-drain on/off current ratio of more than 107 at zero gate voltage and a source-drain bias of 0.1 V. Furthermore, a retention time of >3000 s of the polarization state is obtained, inspiring a promising candidate for applications in data storage with non-volatile features.

Brillouin light scattering investigation of interfacial Dzyaloshinskii–Moriya interaction in ultrathin Co/Pt nanostripe arrays

NASA Astrophysics Data System (ADS)

Bouloussa, H.; Yu, J.; Roussigné, Y.; Belmeguenai, M.; Stashkevitch, A.; Yang, H.; Chérif, S. M.

2018-06-01

Interface Dzyaloshinskii–Moriya interaction (iDMI) is known to induce spinwaves non-reciprocity in ultrathin films. Indeed, Brillouin light scattering has been used to investigate how the lateral size reduction can affect the iDMI constant in Pt (6 nm)/Co (3 nm) based-nanostripe arrays. For this, 100 and 300 nm-width nanostripes have been fabricated using e-beam lithography and ion etching, and their behaviour has then been compared to the reference continuous film. The experimental data showed that the measured iDMI induced non-reciprocity is slightly different for the 100 nm-width nanostripes with respect to the other samples. This suggests that the width of the nanostripes can influence the strength of the apparent iDMI if this dimension is comparable to the spin waves attenuation length propagating within the nanostripes. Indeed, in contrast to the other samples, the linear frequency difference (non-reciprocity) behaviour versus wavenumber for the 100 nm-width nanostripes has been analysed and discussed through two approaches: either a different iDMI constant or an iDMI constant similar to one of the continuous films with a non-zero intercept for a zero wavenumber.

Bayesian inference of metal oxide ultrathin film structure based on crystal truncation rod measurements

PubMed Central

Anada, Masato; Nakanishi-Ohno, Yoshinori; Okada, Masato; Kimura, Tsuyoshi; Wakabayashi, Yusuke

2017-01-01

Monte Carlo (MC)-based refinement software to analyze the atomic arrangements of perovskite oxide ultrathin films from the crystal truncation rod intensity is developed on the basis of Bayesian inference. The advantages of the MC approach are (i) it is applicable to multi-domain structures, (ii) it provides the posterior probability of structures through Bayes’ theorem, which allows one to evaluate the uncertainty of estimated structural parameters, and (iii) one can involve any information provided by other experiments and theories. The simulated annealing procedure efficiently searches for the optimum model owing to its stochastic updates, regardless of the initial values, without being trapped by local optima. The performance of the software is examined with a five-unit-cell-thick LaAlO3 film fabricated on top of SrTiO3. The software successfully found the global optima from an initial model prepared by a small grid search calculation. The standard deviations of the atomic positions derived from a dataset taken at a second-generation synchrotron are ±0.02 Å for metal sites and ±0.03 Å for oxygen sites. PMID:29217989

Unexpected behavior of ultra-thin films of blends of polystyrene/poly(vinyl methyl ether) studied by specific heat spectroscopy

NASA Astrophysics Data System (ADS)

Madkour, Sherif; Szymoniak, Paulina; Schick, Christoph; Schönhals, Andreas

2017-05-01

Specific heat spectroscopy (SHS) employing AC nanochip calorimetry was used to investigate the glassy dynamics of ultra-thin films (thicknesses: 10 nm-340 nm) of a polymer blend, which is miscible in the bulk. In detail, a Poly(vinyl methyl ether) (PVME)/Polystyrene (PS) blend with the composition of 25/75 wt. % was studied. The film thickness was controlled by ellipsometry while the film topography was checked by atomic force microscopy. The results are discussed in the framework of the balance between an adsorbed and a free surface layer on the glassy dynamics. By a self-assembling process, a layer with a reduced mobility is irreversibly adsorbed at the polymer/substrate interface. This layer is discussed employing two different scenarios. In the first approach, it is assumed that a PS-rich layer is adsorbed at the substrate. Whereas in the second approach, a PVME-rich layer is suggested to be formed at the SiO2 substrate. Further, due to the lower surface tension of PVME, with respect to air, a nanometer thick PVME-rich surface layer, with higher molecular mobility, is formed at the polymer/air interface. By measuring the glassy dynamics of the thin films of PVME/PS in dependence on the film thickness, it was shown that down to 30 nm thicknesses, the dynamic Tg of the whole film was strongly influenced by the adsorbed layer yielding a systematic increase in the dynamic Tg with decreasing the film thickness. However, at a thickness of ca. 30 nm, the influence of the mobile surface layer becomes more pronounced. This results in a systematic decrease in Tg with the further decrease of the film thickness, below 30 nm. These results were discussed with respect to thin films of PVME/PS blend with a composition of 50/50 wt. % as well as literature results.

The effects of ultra-thin cerium fluoride film as the anode buffer layer on the electrical characteristics of organic light emitting diodes

NASA Astrophysics Data System (ADS)

Lu, Hsin-Wei; Tsai, Cheng-Che; Hong, Cheng-Shong; Kao, Po-Ching; Juang, Yung-Der; Chu, Sheng-Yuan

2016-11-01

In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3film as an ultra-thin buffer layer between the indium tin oxide (ITO) electrode and α-naphthylphenylbiphenyldiamine (NPB) hole transport layer, with the structure configuration ITO/CeF3 (0.5, 1, and 1.5 nm)/α-naphthylphenylbiphenyl diamine (NPB) (40 nm)/tris(8-hydroxyquinoline) aluminum (Alq3) (60 nm)/lithium fluoride (LiF) (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results revealed the formation of the UV-ozone treated CeF3 film. The work function increased from 4.8 eV (standard ITO electrode) to 5.22 eV (0.5-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The surface roughness of the UV-ozone treated CeF3 film was smoother than that of the standard ITO electrode. Further, the UV-ozone treated CeF3 film increased both the surface energy and polarity, as determined from contact angle measurements. In addition, admittance spectroscopy measurements showed an increased capacitance and conductance of the OLEDs. Accordingly, the turn-on voltage decreased from 4.2 V to 3.6 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 24760 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.8 cd/A when the 0.5-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

Variations in interface compound nucleation for Ti-Al ultrathin films on Si substrates

NASA Astrophysics Data System (ADS)

Han, C. C.; Bené, R. W.

1985-11-01

We have determined the structures of compounds nucleated in a series of sequentially sputtered thin bilayer films of Al and Ti on Si substrates for a range of metal thicknesses and for both (100) and (111) substrates. The compound structures were determined by transmission electron microscopy and diffraction, augmented by Auger electron spectroscopy. An annealing temperature of about 380 °C for 30 min was required to produce compound nucleation. For the Ti/Al/Si(100) system it was found that the phases which were nucleated for samples with 30-min, 380 °C anneals varied from TiAl3 to Ti8Al24 to an unknown compound of tetragonal structure (a=b=5.782 Å, c=6.713 Å) as the Al intermediate layer thickness is changed from 200 to 60 to 40 Å. TiAl3 was the compound nucleated at 380 °C for all other cases. Finally, 410 °C annealing of the Al/Ti/Si(100) samples for 30 min resulted in formation of an apparently Al-altered form of TiSi2.

Two-dimensional limit of crystalline order in perovskite membrane films

DOE PAGES

Hong, Seung Sae; Yu, Jung Ho; Lu, Di; ...

2017-11-17

Long-range order and phase transitions in two-dimensional (2D) systems—such as magnetism, superconductivity, and crystallinity—have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO 3, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO 3 membrane lattice collapsesmore » below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. Finally, the transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices.« less

APCVD hexagonal boron nitride thin films for passive near-junction thermal management of electronics

NASA Astrophysics Data System (ADS)

KC, Pratik; Rai, Amit; Ashton, Taylor S.; Moore, Arden L.

2017-12-01

The ability of graphene to serve as an ultrathin heat spreader has been previously demonstrated with impressive results. However, graphene is electrically conductive, making its use in contact with electronic devices problematic from a reliability and integration perspective. As an alternative, hexagonal boron nitride (h-BN) is a similarly structured material with large in-plane thermal conductivity but which possesses a wide band gap, thereby giving it potential to be utilized for directing contact, near-junction thermal management of electronics without shorting or the need for an insulating intermediate layer. In this work, the viability of using large area, continuous h-BN thin films as direct contact, near-junction heat spreaders for electronic devices is experimentally evaluated. Thin films of h-BN several square millimeters in size were synthesized via an atmospheric pressure chemical vapor deposition (APCVD) method that is both simple and scalable. These were subsequently transferred onto a microfabricated test device that simulated a multigate transistor while also allowing for measurements of the device temperature at various locations via precision resistance thermometry. Results showed that these large-area h-BN films with thicknesses of 77-125 nm are indeed capable of significantly lowering microdevice temperatures, with the best sample showing the presence of the h-BN thin film reduced the effective thermal resistance by 15.9% ± 4.6% compared to a bare microdevice at the same power density. Finally, finite element simulations of these experiments were utilized to estimate the thermal conductivity of the h-BN thin films and identify means by which further heat spreading performance gains could be attained.

Atomic layer deposition and post-growth thermal annealing of ultrathin MoO3 layers on silicon substrates: Formation of surface nanostructures

NASA Astrophysics Data System (ADS)

Liu, Hongfei; Yang, Ren Bin; Yang, Weifeng; Jin, Yunjiang; Lee, Coryl J. J.

2018-05-01

Ultrathin MoO3 layers have been grown on Si substrates at 120 °C by atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo(CO)6] and ozone (O3) as the Mo- and O-source precursors, respectively. The ultrathin films were further annealed in air at Tann = 550-750 °C for 15 min. Scanning-electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy have been employed to evaluate the morphological and elemental properties as well as their evolutions upon annealing of the thin films. They revealed an interfacial SiOx layer in between the MoO3 layer and the Si substrate; this SiOx layer converted into SiO2 during the annealing; and the equivalent thickness of the MoO3 (SiO2) layer decreased (increased) with the increase in Tann. Particles with diameters smaller than 50 nm emerged at Tann = 550 °C and their sizes (density) were reduced (increased) by increasing Tann to 650 °C. A further increase of Tann to 750 °C resulted in telephone-cord-like MoO3 structures, initiated from isolated particles on the surface. These observations have been discussed and interpreted based on temperature-dependent atomic interdiffusions, surface evaporations, and/or melting of MoO3, which shed new light on ALD MoO3 towards its electronic applications.

New ultrathin film heterostructure for low-e application by sputtering technique: a theoretical and experimental study

NASA Astrophysics Data System (ADS)

Ruíz-Robles, M. A.; Abundiz-Cisneros, N.; Bender-Pérez, C. E.; Gutiérrez-Lazos, C. D.; Fundora-Cruz, A.; Solís-Pomar, F.; Pérez-Tijerina, E.

2018-03-01

The design and optical characterization by UV–vis transmittance of ultrathin low-emissivity (low-e) windows by reactive sputtering are reported. Two heterostructures on a glass substrate were considered for the low-e windows. The first heterostructure is Si3N4/TiO2/ZnO/Ag/SnO2/Si3N4 and the second is Si3N4/Ag/Si3N4. The transmittance and reflectance of these heterostructures were simulated to determine the required thickness of each layer. The first heterostructure exhibited maximum transmittance of 85% at 550 nm, slightly higher than the one determined by simulation and less than 50% transmittance in the near-infrared region (900 nm). The second heterostructure exhibited transmittance greater than 86% at 550 nm and <50% transmittance in the near-infrared region. In addition, we found that the bandwidth and maximum position of the transmittance depend on the Si3N4 layer thickness. Specifically, the thickness of the first Si3N4 layer allows the modulation of the transmittance bandwidth and the thickness of the second Si3N4 layer allows the modulation of the maximum position. The low-e windows were protected by the deposition of an ultrathin film of NiCr alloy (Ni 80%, Cr 20%) that preserved the optical characteristics and decreased the maximum of the transmittance only by 3%.

Origins of the two simultaneous mechanisms causing glass transition temperature reductions in high molecular weight freestanding polymer films

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

Prevosto, Daniele, E-mail: ngai@df.unipi.it, E-mail: Prevosto@df.unipi.it; Capaccioli, Simone; Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa

2014-02-21

From ellipsometry measurements, Pye and Roth [Phys. Rev. Lett. 107, 235701 (2011)] presented evidence of the presence of two glass transitions originating from two distinctly different and simultaneous mechanisms to reduce the glass transition temperature within freestanding polystyrene films with thickness less than 70 nm. The upper transition temperature T{sub g}{sup u}(h) is higher than the lower transition temperature T{sub g}{sup l}(h) in the ultrathin films. After comparing their data with the findings of others, using the same or different techniques, they concluded that new theoretical interpretation is needed to explain the two transitions and the different dependences of T{submore » g}{sup u}(h) and T{sub g}{sup l}(h) on film thickness and molecular weight. We address the problem based on advance in delineating the different viscoelastic mechanisms in the glass-rubber transition zone of polymers. Theoretical considerations as well as experiments have shown in time-scales immediately following the segmental α-relaxation are the sub-Rouse modes with longer length scale but shorter than that of the Rouse modes. The existence of the sub-Rouse modes in various polymers including polystyrene has been repeatedly confirmed by experiments. We show that the sub-Rouse modes can account for the upper transition and the properties observed. The segmental α-relaxation is responsible for the lower transition. This is supported by the fact that the segmental α-relaxation in ultrathin freestanding PS films had been observed by dielectric relaxation measurements and photon correlation spectroscopy. Utilizing the temperature dependence of the segmental relaxation times from these experiments, the glass transition temperature T{sub g}{sup α} associated with the segmental relaxation in the ultrathin film is determined. It turns out that T{sub g}{sup α} is nearly the same as T{sub g}{sup l}(h) of the lower transition, and hence definitely segmental α-relaxation is the mechanism for the lower transition. Since it is unlikely that the segmental α-relaxation can give rise to two very different transitions simultaneously, a new mechanism for the upper transition is needed, and the sub-Rouse modes provide the mechanism.« less

Vanadium dioxide as a material to control light polarization in the visible and near infrared

NASA Astrophysics Data System (ADS)

Cormier, Patrick; Son, Tran Vinh; Thibodeau, Jacques; Doucet, Alexandre; Truong, Vo-Van; Haché, Alain

2017-01-01

We report on the possible use of vanadium dioxide to produce ultrathin (<100 nm) adjustable phase retarders working over a wide spectral range. The refractive index of vanadium dioxide undergoes large changes when the material undergoes a phase transition from semiconductor to metal at a temperature of 68 °C. In a thin film, the resulting optical phase shift is different for s- and p-polarizations in both reflection and transmission, and under certain conditions the polarization state changes between linear or circular or between linear polarizations oriented differently when the material phase transitions. Specific ultrathin modulators are proposed based on the results.

Atomic Layer Deposition in Bio-Nanotechnology: A Brief Overview.

PubMed

Bishal, Arghya K; Butt, Arman; Selvaraj, Sathees K; Joshi, Bela; Patel, Sweetu B; Huang, Su; Yang, Bin; Shukohfar, Tolou; Sukotjo, Cortino; Takoudis, Christos G

2015-01-01

Atomic layer deposition (ALD) is a technique increasingly used in nanotechnology and ultrathin film deposition; it is ideal for films in the nanometer and Angstrom length scales. ALD can effectively be used to modify the surface chemistry and functionalization of engineering-related and biologically important surfaces. It can also be used to alter the mechanical, electrical, chemical, and other properties of materials that are increasingly used in biomedical engineering and biological sciences. ALD is a relatively new technique for optimizing materials for use in bio-nanotechnology. Here, after a brief review of the more widely used modes of ALD and a few of its applications in biotechnology, selected results that show the potential of ALD in bio-nanotechnology are presented. ALD seems to be a promising means for tuning the hydrophilicity/hydrophobicity characteristics of biomedical surfaces, forming conformal ultrathin coatings with desirable properties on biomedical substrates with a high aspect ratio, tuning the antibacterial properties of substrate surfaces of interest, and yielding multifunctional biomaterials for medical implants and other devices.

Evidence of a Transition Layer between the Free Surface and the Bulk.

PubMed

Ogieglo, Wojciech; Tempelman, Kristianne; Napolitano, Simone; Benes, Nieck E

2018-03-15

The free surface, a very thin layer at the interface between polymer and air, is considered the main source of the perturbations in the properties of ultrathin polymer films, i.e., nanoconfinement effects. The structural relaxation of such a layer is decoupled from the molecular dynamics of the bulk. The free surface is, in fact, able to stay liquid even below the temperature where the polymer resides in the glassy state. Importantly, this surface layer is expected to have a very sharp interface with the underlying bulk. Here, by analyzing the penetration of n-hexane into polystyrene films, we report on the existence of a transition region, not observed by previous investigations, extending for 12 nm below the free surface. The presence of such a layer permits reconciling the behavior of interfacial layers with current models and has profound implications on the performance of ultrathin membranes. We show that the expected increase in the flux of the permeating species is actually overruled by nanoconfinement.

Transparent and Flexible Capacitors with an Ultrathin Structure by Using Graphene as Bottom Electrodes.

PubMed

Guo, Tao; Zhang, Guozhen; Su, Xi; Zhang, Heng; Wan, Jiaxian; Chen, Xue; Wu, Hao; Liu, Chang

2017-11-28

Ultrathin, transparent and flexible capacitors using graphene as the bottom electrodes were directly fabricated on polyethylene naphthalate (PEN) substrates. ZrO₂ dielectric films were deposited on the treated surface of graphene by atomic layer deposition (ALD). The deposition process did not introduce any detectible defects in the graphene, as indicated by Raman measurements, guaranteeing the electrical performances of the graphene electrodes. The Aluminum-doped zinc oxide (AZO) films were prepared as the top electrodes using the ALD technique. The capacitors presented a high capacitance density (10.3 fF/μm² at 10 kHz) and a relatively low leakage current (5.3 × 10 -6 A/cm² at 1 V). Bending tests revealed that the capacitors were able to work normally at an outward bending radius of 10 mm without any deterioration of electrical properties. The capacitors exhibited an average optical transmittance of close to 70% at visible wavelengths. Thus, it opens the door to practical applications in transparent integrated circuits.

Transparent and Flexible Capacitors with an Ultrathin Structure by Using Graphene as Bottom Electrodes

PubMed Central

Guo, Tao; Zhang, Guozhen; Su, Xi; Zhang, Heng; Wan, Jiaxian; Chen, Xue; Wu, Hao; Liu, Chang

2017-01-01

Ultrathin, transparent and flexible capacitors using graphene as the bottom electrodes were directly fabricated on polyethylene naphthalate (PEN) substrates. ZrO2 dielectric films were deposited on the treated surface of graphene by atomic layer deposition (ALD). The deposition process did not introduce any detectible defects in the graphene, as indicated by Raman measurements, guaranteeing the electrical performances of the graphene electrodes. The Aluminum-doped zinc oxide (AZO) films were prepared as the top electrodes using the ALD technique. The capacitors presented a high capacitance density (10.3 fF/μm2 at 10 kHz) and a relatively low leakage current (5.3 × 10−6 A/cm2 at 1 V). Bending tests revealed that the capacitors were able to work normally at an outward bending radius of 10 mm without any deterioration of electrical properties. The capacitors exhibited an average optical transmittance of close to 70% at visible wavelengths. Thus, it opens the door to practical applications in transparent integrated circuits. PMID:29182551

Ultrathin planar graphene supercapacitors.

PubMed

Yoo, Jung Joon; Balakrishnan, Kaushik; Huang, Jingsong; Meunier, Vincent; Sumpter, Bobby G; Srivastava, Anchal; Conway, Michelle; Reddy, Arava Leela Mohana; Yu, Jin; Vajtai, Robert; Ajayan, Pulickel M

2011-04-13

With the advent of atomically thin and flat layers of conducting materials such as graphene, new designs for thin film energy storage devices with good performance have become possible. Here, we report an "in-plane" fabrication approach for ultrathin supercapacitors based on electrodes comprised of pristine graphene and multilayer reduced graphene oxide. The in-plane design is straightforward to implement and exploits efficiently the surface of each graphene layer for energy storage. The open architecture and the effect of graphene edges enable even the thinnest of devices, made from as grown 1-2 graphene layers, to reach specific capacities up to 80 μFcm(-2), while much higher (394 μFcm(-2)) specific capacities are observed multilayer reduced graphene oxide electrodes. The performances of devices with pristine as well as thicker graphene-based structures are examined using a combination of experiments and model calculations. The demonstrated all solid-state supercapacitors provide a prototype for a broad range of thin-film based energy storage devices.

The influence of nano-oxide layer on magnetostriction of sensing layer in bottom spin valves

NASA Astrophysics Data System (ADS)

Qiu, J. J.; Han, G. C.; Li, K. B.; Liu, Z. Y.; Zong, B. Y.; Wu, Y. H.

2006-05-01

The magnetostriction coefficient (λs) of ultrathin sputtered polycrystalline as-deposited and annealed Ta/Ni81Fe19(t)/Ta films was studied as a function of the thickness. λs and magnetoresistance (MR) of bottom-type spin valves (SVs) with nano-oxide layer (NOL) added in the pinned layer were investigated by using NiFe, Co90Fe10, and CoFe/NiFe/CoFe layers as free layer (FL), respectively. λs of SV with NOL increased slightly except that of CoFe FL. NOLs were added at different positions to study the effects of NOL on λs of CoFe FL. All λs of CoFe FL change from negative to positive and its absolute value also increases significantly with CoFeOx related NOL added below. Our λs and surface roughness results indicated that the structure of the film not the roughness dominates λs of ultrathin FL in SVs.

Wrapping with a splash: High-speed encapsulation with ultrathin sheets.

PubMed

Kumar, Deepak; Paulsen, Joseph D; Russell, Thomas P; Menon, Narayanan

2018-02-16

Many complex fluids rely on surfactants to contain, protect, or isolate liquid drops in an immiscible continuous phase. Thin elastic sheets can wrap liquid drops in a spontaneous process driven by capillary forces. For encapsulation by sheets to be practically viable, a rapid, continuous, and scalable process is essential. We exploit the fast dynamics of droplet impact to achieve wrapping of oil droplets by ultrathin polymer films in a water phase. Despite the violence of splashing events, the process robustly yields wrappings that are optimally shaped to maximize the enclosed fluid volume and have near-perfect seams. We achieve wrappings of targeted three-dimensional (3D) shapes by tailoring the 2D boundary of the films and show the generality of the technique by producing both oil-in-water and water-in-oil wrappings. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Thermal conductivity of ultrathin nano-crystalline diamond films determined by Raman thermography assisted by silicon nanowires

NASA Astrophysics Data System (ADS)

Anaya, Julian; Rossi, Stefano; Alomari, Mohammed; Kohn, Erhard; Tóth, Lajos; Pécz, Béla; Kuball, Martin

2015-06-01

The thermal transport in polycrystalline diamond films near its nucleation region is still not well understood. Here, a steady-state technique to determine the thermal transport within the nano-crystalline diamond present at their nucleation site has been demonstrated. Taking advantage of silicon nanowires as surface temperature nano-sensors, and using Raman Thermography, the in-plane and cross-plane components of the thermal conductivity of ultra-thin diamond layers and their thermal barrier to the Si substrate were determined. Both components of the thermal conductivity of the nano-crystalline diamond were found to be well below the values of polycrystalline bulk diamond, with a cross-plane thermal conductivity larger than the in-plane thermal conductivity. Also a depth dependence of the lateral thermal conductivity through the diamond layer was determined. The results impact the design and integration of diamond for thermal management of AlGaN/GaN high power transistors and also show the usefulness of the nanowires as accurate nano-thermometers.

Antireflective glass nanoholes on optical lenses.

PubMed

Lee, Youngseop; Bae, Sang-In; Eom, Jaehyeon; Suh, Ho-Cheol; Jeong, Ki-Hun

2018-05-28

Antireflective structures, inspired from moth eyes, are still reserved for practical use due to their large-area nanofabrication and mechanical stability. Here we report an antireflective optical lens with large-area glass nanoholes. The nanoholes increase light transmission due to the antireflective effect, depending on geometric parameters such as fill factor and height. The glass nanoholes of low effective refractive index are achieved by using solid-state dewetting of ultrathin silver film, reactive ion etching, and wet etching. An ultrathin silver film is transformed into nanoholes for an etch mask in reactive ion etching after thermal annealing at a low temperature. Unlike conventional nanopillars, nanoholes exhibit high light transmittance with enhancement of ~4% over the full visible range as well as high mechanical hardness. Also, an antireflective glass lens is achieved by directly employing nanoholes on the lens surface. Glass nanoholes of highly enhanced optical and mechanical performance can be directly utilized for commercial glass lenses in various imaging and lighting applications.

Role of an ultra-thin AlN/GaN superlattice interlayer on the strain engineering of GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy

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

Shen, X. Q.; Takahashi, T.; Matsuhata, H.

2013-12-02

We investigate the role of an ultra-thin AlN/GaN superlattice interlayer (SL-IL) on the strain engineering of the GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy. It is found that micro-cracks limitted only at the SL-IL position are naturally generated. These micro-cracks play an important role in relaxing the tensile strain caused by the difference of the coefficient of thermal expansion between GaN and Si and keeping the residual strain in the crack-free GaN epilayers resulted from the SL-IL during the growth. The mechanism understanding of the strain modulation by the SL-IL in the GaN epilayersmore » grown on Si substrates makes it possible to design new heterostructures of III-nitrides for optic and electronic device applications.« less

Role of an ultra-thin AlN/GaN superlattice interlayer on the strain engineering of GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Shen, X. Q.; Takahashi, T.; Rong, X.; Chen, G.; Wang, X. Q.; Shen, B.; Matsuhata, H.; Ide, T.; Shimizu, M.

2013-12-01

We investigate the role of an ultra-thin AlN/GaN superlattice interlayer (SL-IL) on the strain engineering of the GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy. It is found that micro-cracks limitted only at the SL-IL position are naturally generated. These micro-cracks play an important role in relaxing the tensile strain caused by the difference of the coefficient of thermal expansion between GaN and Si and keeping the residual strain in the crack-free GaN epilayers resulted from the SL-IL during the growth. The mechanism understanding of the strain modulation by the SL-IL in the GaN epilayers grown on Si substrates makes it possible to design new heterostructures of III-nitrides for optic and electronic device applications.

An Ultrathin Single Crystalline Relaxor Ferroelectric Integrated on a High Mobility Semiconductor.

PubMed

Moghadam, Reza M; Xiao, Zhiyong; Ahmadi-Majlan, Kamyar; Grimley, Everett D; Bowden, Mark; Ong, Phuong-Vu; Chambers, Scott A; Lebeau, James M; Hong, Xia; Sushko, Peter V; Ngai, Joseph H

2017-10-11

The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, the integration of gate materials that enable nonvolatile or hysteretic functionality in field-effect transistors could lead to device technologies that consume less power or allow for novel modalities in computing. Here we present electrical characterization of ultrathin single crystalline SrZr x Ti 1-x O 3 (x = 0.7) films epitaxially grown on a high mobility semiconductor, Ge. Epitaxial films of SrZr x Ti 1-x O 3 exhibit relaxor behavior, characterized by a hysteretic polarization that can modulate the surface potential of Ge. We find that gate layers as thin as 5 nm corresponding to an equivalent-oxide thickness of just 1.0 nm exhibit a ∼2 V hysteretic window in the capacitance-voltage characteristics. The development of hysteretic metal-oxide-semiconductor capacitors with nanoscale gate thicknesses opens new vistas for nanoelectronic devices.

Defect-free erbium silicide formation using an ultrathin Ni interlayer.

PubMed

Choi, Juyun; Choi, Seongheum; Kang, Yu-Seon; Na, Sekwon; Lee, Hoo-Jeong; Cho, Mann-Ho; Kim, Hyoungsub

2014-08-27

An ultrathin Ni interlayer (∼1 nm) was introduced between a TaN-capped Er film and a Si substrate to prevent the formation of surface defects during thermal Er silicidation. A nickel silicide interfacial layer formed at low temperatures and incurred uniform nucleation and the growth of a subsequently formed erbium silicide film, effectively inhibiting the generation of recessed-type surface defects and improving the surface roughness. As a side effect, the complete transformation of Er to erbium silicide was somewhat delayed, and the electrical contact property at low annealing temperatures was dominated by the nickel silicide phase with a high Schottky barrier height. After high-temperature annealing, the early-formed interfacial layer interacted with the growing erbium silicide, presumably forming an erbium silicide-rich Er-Si-Ni mixture. As a result, the electrical contact property reverted to that of the low-resistive erbium silicide/Si contact case, which warrants a promising source/drain contact application for future high-performance metal-oxide-semiconductor field-effect transistors.

Study of series-connected polymer tandem solar cells based on a highly efficient donor material of PTB7-Th

NASA Astrophysics Data System (ADS)

Zang, Yue; Gao, Xiumin; Xin, Qing; Lin, Jun; Zhao, Jufeng

2017-06-01

A highly efficient donor polymer, PTB7-Th, combined with acceptor fullerene PC71BM was introduced as the subcell in the series-connected tandem devices to achieve high-performance polymer tandem solar cells. Design of the device architecture was investigated using modeling and simulation methods to identify the optimal structure and to predict performance of the tandem cells. To address the challenge of current matching between the constituent subcells, the effect of active layer thickness, different device structure, and use of ultrathin Ag film were analyzed. It was found that the distribution of optical intensity in the tandem structure can be optimized through the optical spacer effect of interfacial layers and micro-cavity effect derived from the embedded ultrathin Ag film. Our results indicate that the efficient light utilization with appropriate subcells can allow achievement of power conversion efficiency of 12%, which can be 25% higher than that of a single cell of PTB7-Th.

Chitosan-based ultrathin films as antifouling, anticoagulant and antibacterial protective coatings.

PubMed

Bulwan, Maria; Wójcik, Kinga; Zapotoczny, Szczepan; Nowakowska, Maria

2012-01-01

Ultrathin antifouling and antibacterial protective nanocoatings were prepared from ionic derivatives of chitosan using layer-by-layer deposition methodology. The surfaces of silicon, and glass protected by these nanocoatings were resistant to non-specific adsorption of proteins disregarding their net charges at physiological conditions (positively charged TGF-β1 growth factor and negatively charged bovine serum albumin) as well as human plasma components. The coatings also preserved surfaces from the formation of bacterial (Staphylococcus aureus) biofilm as shown using microscopic studies (SEM, AFM) and the MTT viability test. Moreover, the chitosan-based films adsorbed onto glass surface demonstrated the anticoagulant activity towards the human blood. The antifouling and antibacterial actions of the coatings were correlated with their physicochemical properties. The studied biologically relevant properties were also found to be dependent on the thickness of those nanocoatings. These materials are promising for biomedical applications, e.g., as protective coatings for medical devices, anticoagulant coatings and protective layers in membranes.

Antibacterial and Barrier Properties of Gelatin Coated by Electrospun Polycaprolactone Ultrathin Fibers Containing Black Pepper Oleoresin of Interest in Active Food Biopackaging Applications

PubMed Central

Castro-Mayorga, Jinneth Lorena

2018-01-01

The present study evaluated the effect of using electrospun polycaprolactone (PCL) as a barrier coating and black pepper oleoresin (OR) as a natural extract on the morphology, thermal, mechanical, antimicrobial, oxygen, and water vapor barrier properties of solvent cast gelatin (GEL). The antimicrobial activity of the developed multilayer system obtained by the so-called electrospinning coating technique was also evaluated against Staphylococcus aureus strains for 10 days. The results showed that the multilayer system containing PCL and OR increased the thermal resistance, elongated the GEL film, and significantly diminished its permeance to water vapor. Active multilayer systems stored in hermetically closed bottles increased their antimicrobial activity after 10 days by inhibiting the growth of Staphylococcus aureus. This study demonstrates that addition of electrospun PCL ultrathin fibers and OR improved the properties of GEL films, which promoted its potential use in active food packaging applications. PMID:29597268

Magnetic Phase Transition in Ion-Irradiated Ultrathin CoN Films via Magneto-Optic Faraday Effect.

PubMed

Su, Chiung-Wu; Chang, Yen-Chu; Chang, Sheng-Chi

2013-11-15

The magnetic properties of 1 nm thick in-plane anisotropic Co ultrathin film on ZnO(0001) were investigated through successive 500 eV nitrogen-ion sputtering. Magneto-optical Faraday effects were used to observe the evolution of the ion-irradiated sample in longitudinal and perpendicular magnetic fields. The ferromagnetic phase of the initial in-plane anisotropic fcc β-Co phase transformation to β-Co(N) phase was terminated at paramagnetic CoN x phase. In-plane anisotropy with weak out-of-plane anisotropy of the Co/ZnO sample was initially observed in the as-grown condition. In the sputtering process, the N⁺ ions induced simultaneous sputtering and doping. An abrupt spin reorientation behavior from in-plane to out-of-plane was found under prolonged sputtering condition. The existence of perpendicular anisotropy measured from the out-of-plane Faraday effect may be attributed to the co-existence of residual β-Co and Co₄N exchange bonding force by the gradual depletion of Co-N thickness.

Ultrathin 2D Photocatalysts: Electronic-Structure Tailoring, Hybridization, and Applications.

PubMed

Di, Jun; Xiong, Jun; Li, Huaming; Liu, Zheng

2018-01-01

As a sustainable technology, semiconductor photocatalysis has attracted considerable interest in the past several decades owing to the potential to relieve or resolve energy and environmental-pollution issues. By virtue of their unique structural and electronic properties, emerging ultrathin 2D materials with appropriate band structure show enormous potential to achieve efficient photocatalytic performance. Here, the state-of-the-art progress on ultrathin 2D photocatalysts is reviewed and a critical appraisal of the classification, controllable synthesis, and formation mechanism of ultrathin 2D photocatalysts is presented. Then, different strategies to tailor the electronic structure of ultrathin 2D photocatalysts are summarized, including component tuning, thickness tuning, doping, and defect engineering. Hybridization with the introduction of a foreign component and maintaining the ultrathin 2D structure is presented to further boost the photocatalytic performance, such as quantum dots/2D materials, single atoms/2D materials, molecular/2D materials, and 2D-2D stacking materials. More importantly, the advancement of versatile photocatalytic applications of ultrathin 2D photocatalysts in the fields of water oxidation, hydrogen evolution, CO 2 reduction, nitrogen fixation, organic syntheses, and removal pollutants is discussed. Finally, the future opportunities and challenges regarding ultrathin 2D photocatalysts to bring about new opportunities for future research in the field of photocatalysis are also presented. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

X-Ray Spectroscopy of Ultra-Thin Oxide/Oxide Heteroepitaxial Films: A Case Study of Single-Nanometer VO2/TiO2

PubMed Central

Quackenbush, Nicholas F.; Paik, Hanjong; Woicik, Joseph C.; Arena, Dario A.; Schlom, Darrell G.; Piper, Louis F. J.

2015-01-01

Epitaxial ultra-thin oxide films can support large percent level strains well beyond their bulk counterparts, thereby enabling strain-engineering in oxides that can tailor various phenomena. At these reduced dimensions (typically < 10 nm), contributions from the substrate can dwarf the signal from the epilayer, making it difficult to distinguish the properties of the epilayer from the bulk. This is especially true for oxide on oxide systems. Here, we have employed a combination of hard X-ray photoelectron spectroscopy (HAXPES) and angular soft X-ray absorption spectroscopy (XAS) to study epitaxial VO2/TiO2 (100) films ranging from 7.5 to 1 nm. We observe a low-temperature (300 K) insulating phase with evidence of vanadium-vanadium (V-V) dimers and a high-temperature (400 K) metallic phase absent of V-V dimers irrespective of film thickness. Our results confirm that the metal insulator transition can exist at atomic dimensions and that biaxial strain can still be used to control the temperature of its transition when the interfaces are atomically sharp. More generally, our case study highlights the benefits of using non-destructive XAS and HAXPES to extract out information regarding the interfacial quality of the epilayers and spectroscopic signatures associated with exotic phenomena at these dimensions. PMID:28793516

Enhanced interfacial Dzyaloshinskii-Moriya interaction and isolated skyrmions in the inversion-symmetry-broken Ru/Co/W/Ru films

NASA Astrophysics Data System (ADS)

Samardak, Alexander; Kolesnikov, Alexander; Stebliy, Maksim; Chebotkevich, Ludmila; Sadovnikov, Alexandr; Nikitov, Sergei; Talapatra, Abhishek; Mohanty, Jyoti; Ognev, Alexey

2018-05-01

An enhancement of the spin-orbit effects arising on an interface between a ferromagnet (FM) and a heavy metal (HM) is possible through the strong breaking of the structural inversion symmetry in the layered films. Here, we show that an introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and simultaneously induce a large interfacial Dzyaloshinskii-Moriya interaction (iDMI). The study of the spin-wave propagation in the Damon-Eshbach geometry by Brillouin light scattering spectroscopy reveals the drastic increase in the iDMI value with the increase in W thickness (tW). The maximum iDMI of -3.1 erg/cm2 is observed for tW = 0.24 nm, which is 10 times larger than for the quasi-symmetrical Ru/Co/Ru films. We demonstrate the evidence of the spontaneous field-driven nucleation of isolated skyrmions supported by micromagnetic simulations. Magnetic force microscopy measurements reveal the existence of sub-100-nm skyrmions in the zero magnetic field. The ability to simultaneously control the strength of PMA and iDMI in quasi-symmetrical HM/FM/HM trilayer systems through the interface engineered inversion asymmetry at the nanoscale excites new fundamental and practical interest in ultrathin ferromagnets, which are a potential host for stable magnetic skyrmions.

X-ray Spectroscopy of Ultra-thin Oxide/oxide Heteroepitaxial Films: A Case Study of Single-nanometer VO2/TiO2

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

Quackenbush, Nicholas F.; Paik, Hanjong; Woicik, Joseph C.

2015-08-21

Epitaxial ultra-thin oxide films can support large percent level strains well beyond their bulk counterparts, thereby enabling strain-engineering in oxides that can tailor various phenomena. At these reduced dimensions (typically < 10 nm), contributions from the substrate can dwarf the signal from the epilayer, making it difficult to distinguish the properties of the epilayer from the bulk. This is especially true for oxide on oxide systems. Here, we have employed a combination of hard X-ray photoelectron spectroscopy (HAXPES) and angular soft X-ray absorption spectroscopy (XAS) to study epitaxial VO2/TiO2 (100) films ranging from 7.5 to 1 nm. We observe amore » low-temperature (300 K) insulating phase with evidence of vanadium-vanadium (V-V) dimers and a high-temperature (400 K) metallic phase absent of V-V dimers irrespective of film thickness. Results confirm that the metal insulator transition can exist at atomic dimensions and that biaxial strain can still be used to control the temperature of its transition when the interfaces are atomically sharp. Generally, our case study highlights the benefits of using non-destructive XAS and HAXPES to extract out information regarding the interfacial quality of the epilayers and spectroscopic signatures associated with exotic phenomena at these dimensions.« less

Synthesis, Characterization, and Electrochemical Properties of Polyaniline Thin Films

NASA Astrophysics Data System (ADS)

Rami, Soukaina

Conjugated polymers have been used in various applications (battery, supercapacitor, electromagnetic shielding, chemical sensor, biosensor, nanocomposite, light-emitting-diode, electrochromic display etc.) due to their excellent conductivity, electrochemical and optical properties, and low cost. Polyaniline has attracted the researchers from all disciplines of science, engineering, and industry due to its redox properties, environmental stability, conductivity, and optical properties. Moreover, it is a polymer with fast electroactive switching and reversible properties displayed at low potential, which is an important feature in many applications. The thin oriented polyaniline films have been fabricated using self-assembly, Langmuir-Blodgett, in-situ self-assembly, layer-by-layer, and electrochemical technique. The focus of this thesis is to synthesize and characterize polyaniline thin films with and without dyes. Also, the purpose of this thesis is to find the fastest electroactive switching PANI electrode in different electrolytic medium by studying their electrochemical properties. These films were fabricated using two deposition techniques: in-situ self-assembly and electrochemical deposition. The characterization of these films was done using techniques such as Fourier Transform Infrared Spectroscopy (FTIR), UV-spectroscopy, Scanning Electron Microscope (SEM), and X-Ray Diffraction (XRD). FTIR and UV-spectroscopy showed similar results in the structure of the polyaniline films. However, for the dye incorporated films, since there was an addition in the synthesis of the material, peak locations shifted, and new peaks corresponding to these materials appeared. The 1 layer PANI showed compact film morphology, comparing to other PANI films, which displayed a fiber-like structure. Finally, the electrochemical properties of these thin films were studied using cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in different scenarios. These scenarios included the study in different acid based electrolytes and different gel based electrolytes. The ultra-thin self-assembled PANI films were shown to have a faster switching time, especially for the 1 layer PANI, whereas the color contrast could be observed for the film containing the dye molecule. Also, HCl based electrolyte gave the best electrochemical reversibility compared to other acids used. For the gelatin and PVA based electrolytes, having the same concentration, the results were similar. Hence, the change in the electrolyte consistencies, from liquid to semi-solid, did not change the electrochemical properties of the films. Finally, in the EIS, it was shown that these PANI thin films exhibit a pseudo-capacitance behavior, and as the film thickness grew, the capacitance increased.

Theoretical realization of robust broadband transparency in ultrathin seamless nanostructures by dual blackbodies for near infrared light

NASA Astrophysics Data System (ADS)

Zhang, Lei; Hao, Jiaming; Ye, Huapeng; Yeo, Swee Ping; Qiu, Min; Zouhdi, Said; Qiu, Cheng-Wei

2013-03-01

We propose a counter-intuitive mechanism of constructing an ultrathin broadband transparent device with two perfect blackbodies. By introducing hybridization of plasmon modes, resonant modes with different symmetries coexist in this system. A broadband transmission spectrum in the near infrared regime is achieved through controlling their coupling strengths, which is governed by the thickness of high refractive index layer. Meanwhile, the transparency bandwidth is found to be tunable in a large range by varying the geometric dimension. More significantly, from the point view of applications, the proposed method of achieving broadband transparency can perfectly tolerate the misalignment and asymmetry of periodic nanoparticles on the top and bottom, which is empowered by the unique dual of coupling-in and coupling-out processes within the pair of blackbodies. Moreover, roughness has little influence on its transmission performance. According to the coupled mode theory, the distinguished transmittance performance is physically interpreted by the radiative decay rate of the entire system. In addition to the feature of uniquely robust broadband transparency, such a ultrathin seamless nanostructure (in the presence of a uniform silver layer) also provides polarization-independent and angle-independent operations. Therefore, it may power up a wide spectrum of exciting applications in thin film protection, touch screen techniques, absorber-emitter transformation, etc.We propose a counter-intuitive mechanism of constructing an ultrathin broadband transparent device with two perfect blackbodies. By introducing hybridization of plasmon modes, resonant modes with different symmetries coexist in this system. A broadband transmission spectrum in the near infrared regime is achieved through controlling their coupling strengths, which is governed by the thickness of high refractive index layer. Meanwhile, the transparency bandwidth is found to be tunable in a large range by varying the geometric dimension. More significantly, from the point view of applications, the proposed method of achieving broadband transparency can perfectly tolerate the misalignment and asymmetry of periodic nanoparticles on the top and bottom, which is empowered by the unique dual of coupling-in and coupling-out processes within the pair of blackbodies. Moreover, roughness has little influence on its transmission performance. According to the coupled mode theory, the distinguished transmittance performance is physically interpreted by the radiative decay rate of the entire system. In addition to the feature of uniquely robust broadband transparency, such a ultrathin seamless nanostructure (in the presence of a uniform silver layer) also provides polarization-independent and angle-independent operations. Therefore, it may power up a wide spectrum of exciting applications in thin film protection, touch screen techniques, absorber-emitter transformation, etc. Electronic supplementary information (ESI) available: Comparison of transmittance spectra between structures with and without Ag film at the middle. Transmittance spectra of structures with different thicknesses of Ag film. See DOI: 10.1039/c3nr34278f

Ab initio understanding of magnetic properties in Zn2+ substitution of Fe3O4 ultra-thin film with dilute Zn substitution

NASA Astrophysics Data System (ADS)

Huang, Zhaocong; Chen, Qian; Jiang, Sheng; Dong, Shuai; Zhai, Ya

2018-05-01

The mechanism of the magnetic properties on the Zn2+ substituted Fe3O4 film have been investigated based on first principle calculations. It is found that the surface effect plays an important role in the occupation of Zn ion, and in turn changes the magnetic moment. It may also destroy the half metallic behavior of Fe3O4 film even if the Zn2+ concentration only is one Zn2+ per unit cell (4%), which is different from that in bulk material.

Preventing kinetic roughening in physical vapor-phase-deposited films.

PubMed

Vasco, E; Polop, C; Sacedón, J L

2008-01-11

The growth kinetics of the mostly used physical vapor-phase deposition techniques -molecular beam epitaxy, sputtering, flash evaporation, and pulsed laser deposition-is investigated by rate equations with the aim of testing their suitability for the preparation of ultraflat ultrathin films. The techniques are studied in regard to the roughness and morphology during early stages of growth. We demonstrate that pulsed laser deposition is the best technique for preparing the flattest films due to two key features [use of (i) a supersaturated pulsed flux of (ii) hyperthermal species] that promote a kinetically limited Ostwald ripening mechanism.

Indigenous unit for bending and twisting tests of ultra-thin films on a flexible substrate

NASA Astrophysics Data System (ADS)

D'souza, Slavia Deeksha; Hazarika, Pratim; Prakasarao, Ch Surya; Kovendhan, M.; Kumar, R. Arockia; Joseph, D. Paul

2018-04-01

An indigenous unit is designed to test the stability of thin films deposited on to a flexible substrate by inducing a required number of bending and twisting under specific conditions. The unit is designed using aluminum and automated by sending pulse width modulated signals to servo motors using ATmega328 microcontroller. We have tested the unit by imparting stress on to a commercial ITO film deposited on a PET substrate. After a definite number of bending and twisting cycles, the electrical and surface properties are studied and the results are discussed.

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

Jung, Min-Cherl; Zhang, Dongrong; Nikiforov, Gueorgui O.

Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

In-space fabrication of thin-film structures

NASA Technical Reports Server (NTRS)

Lippman, M. E.

1972-01-01

A conceptual study of physical vapor-deposition processes for in-space fabrication of thin-film structures is presented. Potential advantages of in-space fabrication are improved structural integrity and surface reflectivity of free-standing ultra-thin films and coatings. Free-standing thin-film structures can find use as photon propulsion devices (solar sails). Other applications of the concept involve free-standing shadow shields, or thermal control coatings of spacecraft surfaces. Use of expendables (such as booster and interstage structures) as source material for the physical vapor deposition process is considered. The practicability of producing thin, textured, aluminum films by physical vapor deposition and subsequent separation from a revolving substrate is demonstrated by laboratory experiments. Heating power requirement for the evaporation process is estimated for a specific mission.

Enhanced amplified spontaneous emission using layer-by-layer assembled cowpea mosaic virus

NASA Astrophysics Data System (ADS)

Li, Na; Deng, Zhaoqi; Lin, Yuan; Zhang, Xiaojie; Geng, Yanhou; Ma, Dongge; Su, Zhaohui

2009-01-01

Layer-by-layer assembly technique was used to construct ultrathin film of cowpea mosaic virus (CPMV) by electrostatic interactions, and the film was employed as a precursor on which an OF8T2 film was deposited by spin coating. Amplified spontaneous emission (ASE) was observed and improved for the OF8T2 film. Compared with OF8T2 film on quartz, the introduction of CPMV nanoparticles reduced the threshold and loss, and remarkably increased the net gain. The threshold, loss, and gain reached 0.05 mJ/pulse, 6.9 cm-1, and 82 cm-1, respectively. CPMV nanoparticles may enormously scatter light, resulting in a positive feedback, thus the ASE is easily obtained and improved.

Numerical simulation and stability analysis of solutocapillary effect in ultrathin films

NASA Astrophysics Data System (ADS)

Gordeeva, V. Yu.; Lyushnin, A. V.

2017-04-01

Polar fluids, like water or polydimethylsiloxane, are widely used in technical and medical applications. Capillary effects arising from surface tension gradients can be significant in thin liquid films. The present paper is dedicated to investigation of capillary flow due to a surfactant added to a polar liquid under conditions when intermolecular forces and disjoining pressure play an important role. Evolution equations are formulated for a film profile and the surfactant concentration. Stability analysis shows that the Marangoni effect destabilizes the film, and oscillatory modes appear at slow evaporation rates. We find that the film has four stability modes of at slow evaporation: monotonic stable, monotonic unstable, oscillatory stable, and oscillatory unstable, depending on the wave number of disturbances.

Fabrication and Structural Characterization of an Ultrathin Film of a Two-Dimensional-Layered Metal-Organic Framework, {Fe(py)2[Ni(CN)4]} (py = pyridine).

PubMed

Sakaida, Shun; Haraguchi, Tomoyuki; Otsubo, Kazuya; Sakata, Osami; Fujiwara, Akihiko; Kitagawa, Hiroshi

2017-07-17

We report the fabrication and characterization of the first example of a tetracyanonickelate-based two-dimensional-layered metal-organic framework, {Fe(py) 2 Ni(CN) 4 } (py = pyridine), thin film. To fabricate a nanometer-sized thin film, we utilized the layer-by-layer method, whereby a substrate was alternately soaked in solutions of the structural components. Surface X-ray studies revealed that the fabricated film was crystalline with well-controlled growth directions both parallel and perpendicular to the substrate. In addition, lattice parameter analysis indicated that the crystal system is found to be close to higher symmetry by being downsized to a thin film.

Loss/gain-induced ultrathin antireflection coatings

PubMed Central

Luo, Jie; Li, Sucheng; Hou, Bo; Lai, Yun

2016-01-01

Tradional antireflection coatings composed of dielectric layers usually require the thickness to be larger than quarter wavelength. Here, we demonstrate that materials with permittivity or permeability dominated by imaginary parts, i.e. lossy or gain media, can realize non-resonant antireflection coatings in deep sub-wavelength scale. Interestingly, while the reflected waves are eliminated as in traditional dielectric antireflection coatings, the transmitted waves can be enhanced or reduced, depending on whether gain or lossy media are applied, respectively. We provide a unified theory for the design of such ultrathin antireflection coatings, showing that under different polarizations and incident angles, different types of ultrathin coatings should be applied. Especially, under transverse magnetic polarization, the requirement shows a switch between gain and lossy media at Brewster angle. As a proof of principle, by using conductive films as a special type of lossy antireflection coatings, we experimentally demonstrate the suppression of Fabry-Pérot resonances in a broad frequency range for microwaves. This valuable functionality can be applied to remove undesired resonant effects, such as the frequency-dependent side lobes induced by resonances in dielectric coverings of antennas. Our work provides a guide for the design of ultrathin antireflection coatings as well as their applications in broadband reflectionless devices. PMID:27349750

Interface science of virtual GaN substrates on Si(111) via Sc2O3/Y2O3 buffers: Experiment and theory

NASA Astrophysics Data System (ADS)

Tarnawska, L.; Dabrowski, J.; Grzela, T.; Lehmann, M.; Niermann, T.; Paszkiewicz, R.; Storck, P.; Schroeder, T.

2013-06-01

The final film quality of GaN on foreign substrates is known to crucially depend on the initial GaN interface and nucleation characteristics. To shed light on these characteristics of recently pioneered virtual, hexagonal GaN(0001) substrates on Si(111) via step graded Sc2O3(111)/Y2O3(111) buffers, a complex GaN(0001)/Sc2O3(111) interface structure model and the initial nucleation scenario is derived from a combined experimental (reflection high energy electron diffraction and X-ray photoelectron spectroscopy) and theoretical ab initio study. It is shown that the GaN/Sc2O3 interface chemistry is determined by a N-Ga-O-Sc atomic arrangement leading to N-polar GaN films. However, the atomic GaN(0001)/Sc2O3(111) interface configuration is complex and local perturbations might be at the origin of Ga-polar inversion domains in the mainly N-polar GaN films. The initial growth of GaN on Sc2O3 is characterized by an ultrathin N-Ga-O-Sc wetting layer which carries tensile strain and relaxes with increasing thickness. Further GaN deposition results in the formation of 3D islands which fully relax before island coalescence occurs. The implications of the GaN/Sc2O3 interface configuration, the 3D nucleation growth mode, and the coalescence process of misaligned islands are discussed with respect to the defect characteristics (inversion domains, cubic inclusions, threading dislocations) of the final GaN layer.