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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Visible light-induced photocatalytic properties of WO{sub 3} films deposited by dc reactive magnetron sputtering

The authors examined the photocatalytic activity of WO{sub 3} films (thickness 500-600 nm) deposited on a fused quartz substrate heated at 350-800 deg. C by dc reactive magnetron sputtering using a W metal target under the O{sub 2} gas pressure from 1.0 to 5.0 Pa. Films deposited at 800 deg. C under 5.0 Pa have excellent crystallinity of triclinic, P1(1) structure and a large surface area, as confirmed by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Exposure of acetaldehyde (CH{sub 3}CHO) adsorbed onto the film surface to ultraviolet, visible, or standard fluorescence light induces oxidative photocatalytic decomposition indicated by a decrease in CH{sub 3}CHO concentration and generation of CO{sub 2} gas. For all three types of irradiation, concentration ratio of decreased CH{sub 3}CHO to increased CO{sub 2} is about 1:1, suggesting the possible presence of intermediates. The sputter-deposited WO{sub 3} film can be a good candidate as a visible light-responsive photocatalyst.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Colour centres and nanostructures on the surface of laser crystals

This paper presents a study of structural and radiationinduced colour centres in the bulk and ordered nanostructures on the surface of doped laser crystals: sapphire, yttrium aluminium garnet and strontium titanate. The influence of thermal annealing, ionising radiation and plasma exposure on the spectroscopic properties of high-purity materials and crystals containing Ti, V and Cr impurities is examined. Colour centres resulting from changes in the electronic state of impurities and plasma-induced surface modification of the crystals are studied by optical, EPR and X-ray spectroscopies, scanning electron microscopy and atomic force microscopy. X-ray line valence shift measurements are used to assess changes in the electronic state of some impurity and host ions in the bulk and on the surface of oxide crystals. Conditions are examined for the formation of one- and two-level arrays of ordered crystallites 10{sup -10} to 10{sup -7} m in size on the surface of crystals doped with irongroup and lanthanoid ions. The spectroscopic properties of the crystals are analysed using ab initio self-consistent field calculations for Me{sup n+} : [O{sup 2-}]{sub k} clusters. (interaction of laser radiation with matter. laser plasma)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Structural, Morphological and Optical properties of Sputtered Nickel oxide Thin Films

Nickel oxide (NiO) thin films have been deposited by dc reactive magnetron sputtering technique on glass substrates at various substrate temperatures in the range of 303 to 723 K. The influence of substrate temperature on structural, morphological, compositional and optical properties was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and spectrophotometer studies. The structural properties of the films were strongly influenced by the substrate temperature. From the microstructural studies, fine and uniform grains were grown with RMS roughness of 9.4 nm at substrate temperature of 523 K. The optical results indicated that the optical transmittance of the films increases with increasing substrate temperature up to 523 K, thereafter decreases. The optical band of the films increases with substrate temperature initially, thereafter decreased at higher temperatures. The Highest optical transmittance of 60 % and optical band gap of 3.82 eV was observed in the present study.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Mechanosynthesis, deposition and characterization of CZTS and CZTSe materials for solar cell applications

Mechanosynthesis of nanocrystalline powders of CZTS and CZTSe by ball milling technique and the physical properties of thermally evaporated CZTS and CZTSe thin films as a function of substrate temperature are investigated. Nanocrystalline Cu–Zn–Tin–Sulphide (CZTS) and Cu–Zn–Tin–Selenide (CZTSe) powders synthesized by ball milling at different milling time using the source materials of Cu, Zn, Sn, S (or) Se in the ratio 2:1:1:4 are investigated. The above synthesized powder was thermally evaporated on glass substrate kept at room temperature and 673 K under a vacuum of 10{sup −6} mbar to prepare quaternary compound semiconducting thin films in a single step process. The synthesized powder and deposited CZTS and CZTSe thin films belong to tetragonal crystal system. Raman spectra reveal that the synthesized nanocrystals are pure without any secondary phases. A gradual reduction in optical bandgap of films was observed with increasing substrate temperature due to increased crystallinity of the films. The changes in surface morphology of the films with respect to substrate temperature were studied by scanning electron microscopy and atomic force microscopy. Electrical studies indicate that the deposited films have p-type conductivity. - Highlights: • Nanocrystalline powders of CZTS and CZTSe are synthesized by ball milling technique. • The ball milled powder was thermally evaporated on glass at room temperature and 673 K. • Raman spectroscopy reveals that the synthesized nanocrystals are pure without any secondary phases. • SEM and AFM micrographs illustrate the granular type of growth and the roughness and particle sizes obtained at the substrate temperature of 673 K are higher than those obtained in the room temperature. • Hall coefficient obtained for the film confirms the p-type conductivity. • A gradual reduction in optical bandgap was observed with increasing substrate temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Morphology dependent electrochemical performance of sputter deposited Sn thin films

Graphical abstract: Smooth homogenous anode surface results in better electrochemical performance in terms of capacity and cycle life. Highlights: ► Controlling rate of deposition of Sn thin films for different surface morphology. ► Higher deposition rate results in poor capacity retention. ► Lower deposition rate of 0.25 nm s{sup −1} helps in higher capacity retention. ► Electrochemical performance correlated homogeneity and interparticle contact area. -- Abstract: This study deals with tailoring of the surface morphology, microstructure, and electrochemical properties of Sn thin films deposited by magnetron sputtering with different deposition rates. Scanning electron microscopy and atomic force microscopy are used to characterize the film surface morphology. Electrochemical properties of Sn thin film are measured and compared by cyclic voltammetry and charge–discharge cycle data at a constant current density. Sn thin film fabricated with a higher deposition rate exhibited an initial discharge capacity of 798 mAh g{sup −1} but reduced to 94 mAh g{sup −1} at 30th cycle. Film deposited with lower deposition rate delivered 770 mAh g{sup −1} during 1st cycle with improved capacity retention of 521 mAh g{sup −1} on 30th cycle. Comparison of electrochemical performances of these films has revealed important distinctions, which are associated with the surface morphology and hence on rate of deposition.

36 MATERIALS SCIENCE↗
DOE OSTI2010

InP substrate evaluation by MOVPE growth of lattice matched epitaxial layers.

InP substrates form the starting point for a wide variety of semiconductor devices. The surface morphology produced during epitaxy depends critically on the starting substrate. We evaluated (1 0 0)-oriented InP wafers from three different vendors by growing thick (5 mu m) lattice-matched epilayers of InP, Gain As, and AlInAs. We assessed the surfaces with differential interference contrast microscopy and atomic force microscopy. Wafers with near singular (1 0 0) orientations produced inferior surfaces in general. Vicinal substrates with small misorientations improved the epitaxial surface for InP dramatically, reducing the density of macroscopic defects while maintaining a low RMS roughness. GaInAs and AlInAs epitaxy step-bunched forming undulations along the miscut direction. Sulfur-doped wafers were considered for singular (1 0 0) and for 0.2 degrees misorientation toward (1 1 0). We found that mound defects observed for InP and GaInAs layers on iron-doped singular wafers were absent for singular sulfur-doped wafers. These observations support the conclusion that dislocation termination at the surface and expansion of the step spiral lead to the macroscopic defects observed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

High-quality graphene grown on polycrystalline PtRh{sub 20} alloy foils by low pressure chemical vapor deposition and its electrical transport properties

High-quality continuous uniform monolayer graphene was grown on polycrystalline PtRh{sub 20} alloy foils by low pressure chemical vapor deposition. The morphology of graphene was investigated by Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. Analysis results confirm that high quality single-layer graphene was fabricated on PtRh{sub 20} foil at 1050 °C using a lower flux of methane under low pressure. Graphene films were transferred onto the SiO{sub 2}/Si substrate by the bubbling transfer method. The mobility of a test field effect transistor made of the graphene grown on PtRh{sub 20} was measured and reckoned at room temperature, showing that the carrier mobility was about 4000 cm{sup 2} V{sup −1} s{sup −1}. The results indicate that desired quality of single-layer graphene grown on PtRh{sub 20} foils can be obtained by tuning reaction conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Highly textured growth of AlN films on sapphire by magnetron sputtering for high temperature surface acoustic wave applications

Piezoelectric aluminum nitride films were deposited onto 3 in. [0001] sapphire substrates by reactive magnetron sputtering to explore the possibility of making highly (002)-textured AlN films to be used in surface acoustic wave (SAW) devices for high temperature applications. The synthesized films, typically 1 {mu}m thick, exhibited a columnar microstructure and a high c-axis texture. The relationship between the microstructures and process conditions was examined by x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscopy analyses. The authors found that highly (002)-textured AlN films with a full width at half maximum of the rocking curve of less than 0.3 deg. can be achieved under high nitrogen concentration and moderate growth temperature, i.e., 250 deg. C. The phi-scan XRD reveals the high in-plane texture of deposited AlN films. The SAW devices, based on the optimized AlN films on sapphire substrate, were characterized before and after an air annealing process at 800 deg. C for 90 min. The frequency response, recorded after the annealing process, confirmed that the thin films were still strong in a high temperature environment and that they had retained their piezoelectric properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanofabrication of silicon surfaces for reduced virus adhesion

Nanofabrication is a remarkably effective technique to create desirable nanoscale patterns. Here, the effect of surface nanofabrication on altering virus adhesion to the substrates was examined. Arrays of nanoholes, 50 nm in diameter, 22 nm deep, and 100 nm in pitch distance, were created on silicon (Si) wafers by electron-beam lithography and reactive ion etching. MS2 coliphage, which is 26 ± 2 nm in diameter and is frequently used as a surrogate for human viruses, was applied to investigate the interaction between the virions and smooth or nanostructured Si surfaces. Scanning electron microscopy and atomic force microscopy along with surface wettability analyses revealed that the nanofabrication had the effect of reducing not only the number of viruses attached but also the strength of virus adhesion. These effects were ascribed to the presence of nanoholes, which were inaccessible to the virions due to the unique surface topographical parameters and the surface chemistry, resulting in the decrease of the overall solid contact area for MS2 attachment. The periodic spacing of the nanoholes also limited the unit landing area for MS2 particles, restricting the formation of MS2 aggregates and leading to the reduced amount of MS2 attachment. We anticipate that smart design of a surface’s chemical composition and nanostructure will offer a feasible solution to improve mitigations for controlling viral adhesion and transmission to and from food contact surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Initial formation stage and succedent biomineralization of pearls

The initial formation stage and succedent biomineralization of pearls were studied using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy and atomic force microscopy. A new initial formation phase with needle-like structure which is found to be nanocrystallites of aragonite was discovered. As a result, two possible formation modes are proposed to describe the initial formation stage of pearls. As for the succedent mineralization of “brick and mortar” structure, nanostripes were first discovered inside the “brick” (aragonite platelet), compared with the foregoing finding of nanograins. The various nanostructures of aragonite platelet allow us to reconsider the role of the inter- and intracrystalline organic material surrounding CaCO{sub 3}, and a possible biomineralization mechanism was proposed. - Highlights: • A new initial formation mineral phase was discovered in pearl. • Nanograins and nanostripes inside aragonite platelets were found in pearl. • Two possible initial formation stages were proposed for pearl. • A possible biomineralization mechanism of nacre in pearl was proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Modified chemical synthesis of porous α-Sm{sub 2}S{sub 3} thin films

Highlights: • A novel chemical route to prepare α-Sm{sub 2}S{sub 3} thin films. • A porous honeycomb like morphology of the α-Sm{sub 2}S{sub 3} thin film. • An application of α-Sm{sub 2}S{sub 3} thin film toward its supercapacitive behaviour. - Abstract: The paper reports synthesis of porous α-Sm{sub 2}S{sub 3} thin films using modified chemical synthesis, also known as successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), wettability and ultraviolet–visible spectroscopy (UV–vis) techniques are used for the study of structural, elemental, morphological and optical properties of α-Sm{sub 2}S{sub 3} films. An orthorhombic crystal structure of α-Sm{sub 2}S{sub 3} is resulted from XRD study. The SEM and AFM observations showed highly porous α-Sm{sub 2}S{sub 3} film surface. An optical band gap of 2.50 eV is estimated from optical absorption spectrum. The porous α-Sm{sub 2}S{sub 3} thin film tuned for supercapacitive behaviour using cyclic voltammetry and galvanostatic charge discharge showed a specific capacitance and energy density of 294 Fg{sup –1} and 48.9 kW kg{sup –1}, respectively in 1 M LiClO{sub 4}–propylene carbonate electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microscopic Examination of the Silicon Surface Subjected to High-Dose Silver Implantation

Low-energy (E = 30 keV) Ag{sup +} ions have been implanted into single-crystalline Si wafers (c-Si) with an implantation dose varying from 1.25 × 10{sup 15} to 1.5 × 10{sup 17} ions cm{sup –2} and an ion beam current density varying from 2 to 15 μA/cm{sup 2}. The surface morphology of implanted wafers has been examined using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy, and their structure has been studied by means of reflection high-energy electron diffraction and elemental microanalysis. It has been shown that for minimal irradiation doses used in experiments, the surface layer of c-Si experiences amorphization. It has been found that when the implantation dose is in excess of the threshold value (~3.1 × 10{sup 15} ions cm{sup –2}), Ag nanoparticles uniformly distributed over the Si surface arise in the irradiated Si layer. At a dose exceeding 10{sup 17} ions cm{sup –2}, a porous Si structure is observed. In this case, the Ag nanoparticle size distribution becomes bimodal with coarse particles localized at the walls of Si pores.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Few-Layers Graphene Film and Copper Surface Morphology for Improved Corrosion Protection of Copper

Graphene has shown excellent corrosion protection of copper (Cu). The corrosion protection of Cu is governed by the characteristics of the deposited graphene and Cu surface morphology underneath. In this work, graphene films (1-2, 4-5 layers) were deposited on Cu using a chemical vapor deposition by changing hydrogen (H{sub 2}) concentration during the annealing stage. The chemical structure and surface microstructural features of graphene/Cu were inspected by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The electrochemical corrosion performance of graphene/Cu was studied in 0.5 M sodium chloride solution using potentiodynamic polarization and electrochemical impedance spectroscopic measurements. The 1-2 layers of graphene and rough Cu surface were obtained for low H{sub 2} concentrations (0 and 2.5%), whereas high H{sub 2} concentrations, 20 and 50%, resulted in a smooth Cu surface and 4-5 layers of graphene. Our results showed that Cu with a smooth surface and multilayer graphene film exhibited the best corrosion resistance against electrochemical degradation. Tafel analysis revealed that Cu with 4-5 layers of graphene coating corroded nearly three orders of magnitude slower than the annealed Cu, without graphene coating. The results of this study can be useful for several applications where Cu is in close contact with salt species.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synchronous RNA conformational changes trigger ordered phase transitions in crystals

Time-resolved studies of biomacromolecular crystals have been limited to systems involving only minute conformational changes within the same lattice. Ligand-induced changes greater than several angstroms, however, are likely to result in solid-solid phase transitions, which require a detailed understanding of the mechanistic interplay between conformational and lattice transitions. Here we report the synchronous behavior of the adenine riboswitch aptamer RNA in crystal during ligand-triggered isothermal phase transitions. Direct visualization using polarized video microscopy and atomic force microscopy shows that the RNA molecules undergo cooperative rearrangements that maintain lattice order, whose cell parameters change distinctly as a function of time. The bulk lattice order throughout the transition is further supported by time-resolved diffraction data from crystals using an X-ray free electron laser. The synchronous molecular rearrangements in crystal provide the physical basis for studying large conformational changes using time-resolved crystallography and micro/nanocrystals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Growth and characterization of thin oriented Co{sub 3}O{sub 4} (111) films obtained by decomposition of layered cobaltates Na{sub x}CoO{sub 2}

The formation and structural characterization of highly (111)-oriented Co{sub 3}O{sub 4} films prepared by a novel procedure from weakly (001)-oriented Na{sub x}CoO{sub 2} is reported. The Na{sub x}CoO{sub 2} films were deposited on both single crystal and amorphous substrates by chemical solution deposition (CSD) method and crystallized at 700 °C. Subsequently they were transformed into (111)-oriented Co{sub 3}O{sub 4} phase during post-growth annealing at 900 °C. The degree of preferred orientation in Co{sub 3}O{sub 4}, which was determined by phi-scan and pole figure measurements, depends on the content of Na in the starting Na{sub x}CoO{sub 2} phase. Surface morphology of the films was investigated using electron microscopy and atomic force microscopy. - Graphical abstract: Structure of growth twins and possible O{sup 2−} stacking sequences in (111)-oriented Co{sub 3}O{sub 4} thin films on α-Al{sub 2}O{sub 3}(001) prepared by chemical solution deposition through the transformation of (001)-oriented Na{sub x}CoO{sub 2} thin film. - Highlights: • Single phase Co{sub 3}O{sub 4} thin films was prepared by means of chemical solution deposition. • Conditions for γ-Na{sub x}CoO{sub 2} to Co{sub 3}O{sub 4} transformation were optimized. • Growth twinning of Co{sub 3}O{sub 4} films due to two possible O{sup 2−} stacking sequences. • Growth with (pseudo)epitaxial relation Co{sub 3}O{sub 4} (111)[−121]//α-Al{sub 2}O{sub 3} (001)[10−10].

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Photo-crystallization in a-Se layer structures: Effects of film-substrate interface-rigidity

Amorphous selenium (a-Se) films deposited on rigid substrates can undergo photo-induced crystallization (PC) even at temperatures (T) well below the glass transition, T{sub g} ∼ 313 K. Substrate-generated shear strain is known to promote the PC process. In the present work, we explore the influence of different substrates (Si and glass), and different film-layer-substrate combinations, on the PC in a variety of a-Se films and film-structures. The intermediate layers (indium tin oxide and polyimide) are chosen to promote conductivity and/or to be a buffer against interface strain in structures of interest for digital imaging applications. The PC characteristics in these samples are evaluated and compared using optical microscopy, atomic-force microscopy, Raman mapping, and T-dependent Raman spectroscopy. Both the presence of a soft intermediate layer, and the thermal softening that occurs for T increasing through T{sub g}, inhibit the tendency for the onset of PC. The extensive PC mapping results in the wide range of samples studied here, as well as the suppression of PC near T{sub g} in this array of samples, strongly support the generality of this behavior. As a consequence, one may expect that the stability of a-Se films against PC can be enhanced by decreasing the rigidity of the film-substrate interface. In this regard, advanced film structures that employ flexible substrates, soft intermediate layers, and/or are designed to be operated near T{sub g} should be explored.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Surface Treatment of Carbon Fibers by Continuous Gaseous System

The mechanical performance of carbon fiber-polymer composites strongly depends on interfacial adhesion, which is function of types of carbon fiber, surface chemistry, physical and chemical interactions, and mechanical interlocking. Untreated and unsized high strength carbon fibers were oxidized by continuous thermochemical and atmospheric plasma treatment. Surface properties were investigated before and after treatment (chemistry, topography), as well as their mechanical properties. X-ray photoelectron spectroscopy revealed a significant increase of the oxygen atomic content from 3% to around 20% and the analysis of the carbon peak showed that carboxylic acid functionalities and hydroxyl groups were generated. An observation of the fiber surface by scanning electron microscopy and atomic force microscopy did not show any dramatic change of the fiber morphology and surface topography. A Raman spectroscopy analysis exhibited that the weak boundary layers and debris remaining at the surface of untreated fibers were removed. No significant damage of the mechanical properties (tensile strength) was noticed. The influence of the changes of the surface properties on interfacial adhesion of carbon fiber-epoxy and -vinyl ester matrix was evaluated using 90 flexural and short beam shear tests with unidirectional coupons. A significant increase of the 90 flexural and short beam shear strength showed that the interfacial adhesion between carbon fibers and epoxy resins was improved. The observation of the fracture profile by scanning electron microcopy confirmed those results, as the rupture of the coupons after surface treatment was more cohesive.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Investigation of high hole mobility In{sub 0.41}Ga{sub 0.59}Sb/Al{sub 0.91}Ga{sub 0.09}Sb quantum well structures grown by molecular beam epitaxy

Modulation-doped In{sub 0.41}Ga{sub 0.59}Sb/Al{sub 0.91}Ga{sub 0.09}Sb quantum-well (QW) structures were grown by molecular beam epitaxy. Cross-sectional transmission electron microscopy and atomic force microscopy studies show high crystalline quality and smooth surface morphology. X-ray diffraction investigations confirm 1.94% compressive strain within In{sub 0.41}Ga{sub 0.59}Sb channel. High room temperature hole mobility with high sheet density of 1000 cm{sup 2}/Vs, 0.877 × 10{sup 12}/cm{sup 2}, and 965 cm{sup 2}/Vs, 1.112 × 10{sup 12}/cm{sup 2} were obtained with different doping concentrations. Temperature dependent Hall measurements show different scattering mechanisms on hole mobility at different temperature range. The sheet hole density keeps almost constantly from 300 K to 77 K. This study shows great potential of In{sub 0.41}Ga{sub 0.59}Sb/Al{sub 0.91}Ga{sub 0.09}Sb QW for high-hole-mobility device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗