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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Investigation of surface potential in the V-defect region of MBE Cd{sub x}Hg{sub 1−x}Te film

Atomic-force microscopy is used to investigate the distribution of the contact-potential difference (surface potential) in Cd{sub x}Hg{sub 1−x}Te epitaxial films grown by molecular-beam epitaxy. Modification of the solid-solution composition near the V-defect results in a variation in the contact-potential difference. It is shown that the solid-solution composition varies by ∼0.05 (2.5 at %) towards increasing mercury content in the V-defect region, and a region of mercury depletion by 0.36 at % is observed at the V-defect periphery. From analysis of the surface-potential distribution, it is shown that the Cd{sub x}Hg{sub 1−x}Te epitaxial film contains unform V-defects with a diameter less than 1 μm in addition to macroscopic V-defects.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Cd{sub 1−x}Mn{sub x}Te ultrasmall quantum dots growth in a silicate glass matrix by the fusion method

In this study, we synthesized Cd{sub 1−x}Mn{sub x}Te ultrasmall quantum dots (USQDs) in SiO{sub 2}-Na{sub 2}CO{sub 3}-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3} glass system using the fusion method. Growth of these Cd{sub 1−x}Mn{sub x}Te USQDs was confirmed by optical absorption, atomic force microscopy (AFM), magnetic force microscopy (MFM), scanning transmission electron microscopy (TEM), and electron paramagnetic resonance (EPR) measurements. The blueshift of absorption transition with increasing manganese concentration gives evidence of incorporation of manganese ions (Mn{sup 2+}) in CdTe USQDs. AFM, TEM, and MFM confirmed, respectively, the formation of high quality Cd{sub 1−x}Mn{sub x}Te USQDs with uniformly distributed size and magnetic phases. Furthermore, EPR spectra showed six lines associated to the S = 5/2 spin half-filled d-state, characteristic of Mn{sup 2+}, and confirmed that Mn{sup 2+} are located in the sites core and surface of the CdTe USQD. Therefore, synthesis of high quality Cd{sub 1−x}Mn{sub x}Te USQDs may allow the control of optical and magnetic properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Properties and device performance of BN thin films grown on GaN by pulsed laser deposition

Wide and ultrawide-bandgap semiconductors lie at the heart of next-generation high-power, high-frequency electronics. Here, in this paper, we report the growth of ultrawide-bandgap boron nitride (BN) thin films on wide-bandgap gallium nitride (GaN) by pulsed laser deposition. Comprehensive spectroscopic (core level and valence band x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman) and microscopic (atomic force microscopy and scanning transmission electron microscopy) characterizations confirm the growth of BN thin films on GaN. Optically, we observed that the BN/GaN heterostructure is second-harmonic generation active. Moreover, we fabricated the BN/GaN heterostructure-based Schottky diode that demonstrates rectifying characteristics, lower turn-on voltage, and an improved breakdown capability (~234 V) as compared to GaN (~168 V), owing to the higher breakdown electrical field of BN. Our approach is an early step toward bridging the gap between wide and ultrawide-bandgap materials for potential optoelectronics as well as next-generation high-power electronics.

42 ENGINEERING↗
DOE OSTI2023

Low temperature absolute internal quantum efficiency of InGaN-based light-emitting diodes

A method to reveal low temperature absolute internal quantum efficiency of an InGaN-based light-emitting diode (LED) is reported. Structural (via scanning electron and atomic force microscopies, x-ray diffraction, and Raman spectroscopy) and optical (via temperature- and power-dependent photoluminescence) properties of InGaN-based blue LEDs are coupled with a channel-based recombination model, which reveals the low temperature absolute internal quantum efficiency of the LED on traditional sapphire and emerging Si (111) substrates as 27.5% and 71.1%, respectively. High low-temperature absolute internal quantum efficiency of the former is attributed to its lower defect density and less strain. Furthermore, our results show assuming perfect (i.e., 100%) internal quantum efficiency in an InGaN-based LED at low temperatures could be misleading, and using negative thermal quenching properties of defect luminesce bands with a channel-based recombination model can be a method to quantify LED's less than ideal low temperature internal quantum efficiencies.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effects of magnetic flux density and substrate bias voltage on Ni films prepared on a flexible substrate material using unbalanced magnetron sputtering assisted by inductively coupled plasma

The authors fabricated Ni films on a flexible substrate material using unbalanced magnetron sputtering assisted by inductively coupled plasma. The effects of magnetic flux density B{sub C} and substrate DC bias voltage V{sub S} on the Ni film structures were investigated. For V{sub S} = −40 V, the average surface grain size D{sub G} measured by atomic force microscopy for B{sub C} = 0, 3, and 5 mT was 88.2, 95.4, and 104.4 nm, respectively. In addition, D{sub G} increased with V{sub S}. From x-ray diffraction measurements, the (111) and (200) peaks were clearly visible for the fabricated Ni films. The ratio of the integrated intensities of I(111)/I(200) increased with V{sub S}. For V{sub S} = −40 V and B{sub C} = 3 mT, a film resistivity ρ of 8.96 × 10{sup −6} Ω cm was observed, which is close to the Ni bulk value of 6.84 × 10{sup −6} Ω cm. From these results, the authors determined that the structure of the fabricated Ni films on the flexible substrate material was affected by the values of B{sub C} and V{sub S}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Effect of Ion Irradiation on Nanocrystallization and Surface Relief of a Ribbon from Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} Alloy

Using the methods of X-ray diffraction and atomic force microscopy, the process of crystallization of an amorphous Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} alloy irradiated with accelerated Ar{sup +} ions is investigated. It is found out that an irradiation by the Ar{sup +} ions with the energy 30 keV at the ion current density 300 μA/cm{sup 2} (fluence 3.75·10{sup 15} cm{sup –2}, irradiation time ~2 s, ion-beam short-duration heating up to 350°С, which is 150°С lower than the thermal crystallization threshold) results in a complete crystallization of this amorphous alloy (throughout the bulk of a 25 μm ribbon) followed by precipitation of solid solution crystals of α-Fe(Si), close in its composition to Fe{sub 80}Si{sub 20}, stable phase of Fe{sub 3}Si, and metastable hexagonal phases. By the methods of atomic force and scanning tunneling microscopy it is shown that nanocrystallization caused by ion irradiation is accompanied by surface relief changes both on the irradiated and unirradiated sides of the Fe{sub 72.5}Cu{sub 1}Nb{sub 2}Mo{sub 1.5}Si{sub 14}B{sub 9} alloy ribbon at the depth exceeding by a factor of 10{sup 3} that of the physical ion penetration for this material. The data obtained, taking into account a significant temperature decrease and multiple acceleration of the crystallization process, serve an evidence of the radiation-dynamic influence of accelerated ions on the metastable amorphous medium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Plasmon resonances in a two-dimensional lattice of metal particles in a dielectric layer: Structural and polarization properties

The results of experimental and theoretical investigation of planar two-dimensional (2D) samples of plasmon structures are presented. The samples represent a 2D lattice of gold nanoparticles embedded in a thin dielectric layer and are studied by atomic force microscopy (AFM) and optical methods. Absorption bands associated with the excitation of various surface plasmon resonances (SPR) are interpreted. It is found that the choice of the mutual orientation of the polarization plane and the edge of the unit cell of the 2D lattice determines the spectral position of the lattice surface plasmon resonance (LSPR) related to the lattice period. It is shown that the interaction of p- and s-polarized light with a 2D lattice of nanoparticles is described by the dipole–dipole interaction between nanoparticles embedded in a medium with effective permittivity. Analysis of the spectra of ellipsometric parameters allows one to determine the amplitude and phase anisotropy of transmission, which is a consequence of the imperfection of the 2D lattice of samples.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characteristics of Amorphous As{sub 2}S{sub 3} Semiconductor Films Obtained via Spin Coating

Centrifugation is used in fabricating, e.g., films with large areas and/or thicknesses of several micrometers. However, it has yet to be widely employed for chalcogenide compounds, due to their relatively weak solubility in most solvents. Determining the optimum conditions for preparing solutions of chalcogenide compounds and obtaining films via centrifugation is therefore of great interest. Specific features of amorphous arsenic sulfide (As{sub 2}S{sub 3}) films prepared via the centrifugation of solutions in n-butylamine have been studied. These films were characterized by means of X-ray diffraction analysis, IR spectroscopy, atomic-force microscopy and Raman spectroscopy. It was shown that amorphous As{sub 2}S{sub 3} films have a greater elasticity modulus than those of analogous composition produced via thermal evaporation in vacuum, or As{sub 2}S{sub 3} glass. A structural model based on arsenic sulfide clusters whose surfaces are bound by negatively and positively charged ions is used to explain the experimental results obtained in this work. DC measurements show that the amorphous films exhibit semiconductor-type conductivity. Their room temperature conductivity is ~10{sup −15} S/cm, which indicates good dielectric properties. The films are optically transparent starting from the yellow spectral range, making them promising functional materials for engineering applications in optics and photonics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Cobalt Modification of Thin Rutile Films Magnetron-Sputtered in Vacuum

Using X-ray phase analysis, atomic force microscopy, and secondary ion mass-spectrometry, the phase formation and component distribution in a Co–TiO{sub 2} film system have been investigated during magnetron sputtering of the metal on the oxide and subsequent vacuum annealing. It has been found that cobalt diffuses deep into titanium oxide to form complex oxides CoTi{sub 2}O{sub 5} and CoTiO{sub 3}. A mechanism behind their formation at grain boundaries throughout the thickness of the TiO{sub 2} film is suggested. It assumes the reactive diffusion of cobalt along grain boundaries in the oxide. A quantitative model of reactive interdiffusion in a bilayer polycrystalline metal–oxide film system with limited solubility of components has been developed. The individual diffusion coefficients of cobalt and titanium have been determined in the temperature interval 923–1073 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electrocatalysis of Hydrogen Evolution Reaction on Au(111) by Spontaneously Deposited Iridium in Acid Solution

Iridium nanoislands are spontaneously deposited on Au(111) from (1 mMIrCl(3) center dot xH(2)O + 0.5 MH2SO4) depositing solution. Atomic Force Microscopy images of the obtained Ir/Au(111) bimetallic surfaces show that gold surface is fully covered with nanosized Ir islands after only 3 min of deposition. X-Ray Photoelectron Spectroscopy analysis shows that the deposit consists of a mixture of adsorbed hydrated IrCl3 and to a lesser extent of Ir(OH)(3). Cyclic Voltammetry characterization in 0.5 M H2SO4 solution does not show clear Hupd region prior to hydrogen evolution reaction (HER). Linear Sweep Voltammetry measurements show pronounced catalysis of HER on Ir modified Au(111) surface compared to bare Au(111). With prolonged Ir deposition, the observed limited increasing activity for HER of Ir/Au(111) surfaces is in accordance with the limited Ir/Au(111) surface morphology changes. (c) The Author(s) 2018. Published by ECS.

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

The growth of GaSb/Al{sub 0.33}Ga{sub 0.67}Sb MQW on n-Silicon (1 0 0) with Al{sub 0.66}Ga{sub 0.34}Sb/AlSb SPS layers

Highlights: • GaSb/Al{sub 0.33}GaSb MQW layer was grown on Si (1 0 0) by MBE. • The effect of miscut angle of Si substrate was studied. • A lot of twins were removed by Al{sub 0.66}Ga{sub 0.34}Sb/AlSb SPS layers. • Good quality of GaSb/Al{sub 0.33}Ga{sub 0.67}Sb MQW layers were proved by PL spectra. • Optimum growth temperature of the AlSb buffer layer was studied. - Abstract: GaSb/Al{sub 0.33}Ga{sub 0.67}Sb multi-quantum well (MQW) film on n-Si (1 0 0) substrates is grown by molecular beam epitaxy. The effects of a miscut angle of the Si substrate (0°, 5°, and 7°) on the properties of an AlSb layer were also studied. The suppression of the anti-phase domains (APD) was observed at a miscut angle of 5° on Si (1 0 0). It was found that the growth temperature in the range of 510–670 °C affects the quality of AlSb layers on Si. Low root-mean-square surface (RMS) roughness values of 3–5 nm were measured by atomic force microscopy at growth temperatures ranging from 550 °C to 630 °C. In addition, Al{sub 0.66}Ga{sub 0.34}Sb/AlSb short period superlattice (SPS) layers were used to overcome problems associated with a large lattice mismatch. The RMS values of samples with a SPS were partially measured at approximately ∼1 nm, showing a larger APD surface area than samples without a SPS layer. Bright-field cross-sectional transmission electron microscopy images of the GaSb/Al{sub 0.33}Ga{sub 0.67}Sb MQW, the AlSb buffer layer and the Al{sub 0.66}Ga{sub 0.34}Sb/AlSb SPS layers show that numerous twins from the AlSb/Si interface were removed by the AlSb buffer layer and the Al{sub 0.66}Ga{sub 0.34}Sb/AlSb SPS. The GaSb/Al{sub 0.33}Ga{sub 0.67}Sb MQW PL spectra were obtained at 300 K and 10 K with a fixed excitation power of 103 mW. Emission peaks appeared at 1758 nm and 1620 nm, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Josephson Effect in the Micron and Submicron YBCO Constrictions Fabricated Using the Femtosecond Laser Technique

A femtosecond laser was used successfully to fabricate planar micron and submicron-sized constrictiontype Josephson junctions on YBa{sub 2}Cu{sub 3}O{sub 7−x} thin films. A simple program using G-code (control systems) programming language was written to control the movement of the sample stage during the etching process. The constriction’s geometry was investigated using both atomic force microscopy (AFM) and scanning electron microscopy (SEM). Electrical transport measurements were performed at different temperatures. Shapiro steps were observed and analyzed. The micron-sized constriction shows a linear relationship for the measured critical current against the temperature which is consistent with the behavior of an S–s’–Stype Josephson junction where “S” stands for a bulk superconductive material that is untouched by the laser and “s”’ is superconducting material whose critical temperature is lower than the value of “S” In the case of the narrower submicronsized constriction, the measured critical current dependence with temperature shows an exponential decay, which is consistent with the behavior of the long S–N–Stype Josephson junction where “N” stands for a normal material. A model is proposed to describe the observed behavior by considering the effect of sample heating during the constriction’s fabrication.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Importance of phospholipid bilayer integrity in the analysis of protein–lipid interactions

Highlights: • We show long-term mechanical stabilization of solid supported bilayers. • Bilayer integrity is essential for the investigation of protein–lipid interactions. • Protein adsorption to a bilayer containing defects causes membrane destruction. - Abstract: The integrity of supported phospholipid bilayer membranes is of crucial importance for the investigation of lipid–protein interactions. Therefore we recorded the formation of supported membranes on SiO{sub 2} and mica by quartz crystal microbalance and controlled the integrity by atomic force microscopy. This study aims to analyze how membrane defects affect protein–lipid interactions. The experiments focused on a lipid mixture of POPC/DOPC/Chol/POPS/PI(4,5)P{sub 2} (37:20:20:20:3) and the binding of the peripheral membrane associated protein annexin A2. We found that formation of a continuous undisturbed bilayer is an indispensable precondition for a reliable determination and quantification of lipid–protein-interactions. If membrane defects were present, protein adsorption causes membrane disruption and lipid detachment on a support thus leading to false determination of binding constants. Our results obtained for PI(4,5)P{sub 2} and cholesterol containing supported membranes yield new knowledge to construct functional surfaces that may cover nanoporous substrates, form free standing membranes or may be used for lab-on-a-chip applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Effects of hypergravity on adipose-derived stem cell morphology, mechanical property and proliferation

Alteration in specific inertial conditions can lead to changes in morphology, proliferation, mechanical properties and cytoskeleton of cells. In this report, the effects of hypergravity on morphology of Adipose-Derived Stem Cells (ADSCs) are indicated. ADSCs were repeatedly exposed to discontinuous hypergravity conditions of 10 g, 20 g, 40 g and 60 g by utilizing centrifuge (three times of 20 min exposure, with an interval of 40 min at 1 g). Cell morphology in terms of length, width and cell elongation index and cytoskeleton of actin filaments and microtubules were analyzed by image processing. Consistent changes observed in cell elongation index as morphological change. Moreover, cell proliferation was assessed and mechanical properties of cells in case of elastic modulus of cells were evaluated by Atomic Force Microscopy. Increase in proliferation and decrease in elastic modulus of cells are further results of this study. Staining ADSC was done to show changes in cytoskeleton of the cells associated to hypergravity condition specifically in microfilament and microtubule components. After exposing to hypergravity, significant changes were observed in microfilaments and microtubule density as components of cytoskeleton. It was concluded that there could be a relationship between changes in morphology and MFs as the main component of the cells. - Highlights: • Hypergravity (10 g, 20 g, 40 g and 60 g) affects on adipose derived stem cells (ADSCs). • ADSCs after exposure to the hypergravity are more slender. • The height of ADSCs increases in all test groups comparing their control group. • Hypergravity decreases ADSCs modulus of elasticity and cell actin fiber content. • Hypergravity enhances proliferation rate of ADSCs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Correlated mechanochemical maps of Arabidopsis thaliana primary cell walls using atomic force microscope infrared spectroscopy

Spatial heterogeneity in composition and organisation of the primary cell wall affects the mechanics of cellular morphogenesis. However, directly correlating cell wall composition, organisation and mechanics has been challenging. To overcome this barrier, we applied atomic force microscopy coupled with infrared (AFM-IR) spectroscopy to generate spatially correlated maps of chemical and mechanical properties for paraformaldehyde-fixed, intact Arabidopsis thaliana epidermal cell walls. AFM-IR spectra were deconvoluted by non-negative matrix factorisation (NMF) into a linear combination of IR spectral factors representing sets of chemical groups comprising different cell wall components. This approach enables quantification of chemical composition from IR spectral signatures and visualisation of chemical heterogeneity at nanometer resolution. Cross-correlation analysis of the spatial distribution of NMFs and mechanical properties suggests that the carbohydrate composition of cell wall junctions correlates with increased local stiffness. Together, our work establishes new methodology to use AFM-IR for the mechanochemical analysis of intact plant primary cell walls.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Influence of grain orientation on the incipient oxidation behavior of Haynes 230 at 900 °C

Ni-based superalloy Haynes 230 is used in many applications such as very high temperature reactor (VHTR) or solid oxide fuel cells (SOFCs) where it is exposed to high temperature service environment. In order to improve the resistance for high temperature oxidation, the effect of crystallographic orientation on the early stage oxidation was investigated. It was demonstrated that different oxide thicknesses are formed on grains having different orientations. Comparison of electron backscatter diffraction (EBSD) orientation maps before and after oxidation at 900 °C indicates that grains near (111) orientation, especially with the deviation angle from <111> that is smaller than 20°, are more oxidation resistant than grains of other orientations. Correlation between the results of electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) was used to compare the oxidation rate of grains having different crystallographic orientation. The oxidation rate was found to change with the crystallographic orientation as follows (111) < (110) < (100), also it was demonstrated that the oxidation rate changes are a nearly linear function of the angle of deviation from <111> direction. The morphology of surface oxide also depends on the orientation of grains. - Highlights: • Comparison of EBSD maps before and after oxidation allows to investigate the effect of orientation on oxidation in a more direct way; • Effect of crystallographic orientation on oxidation behavior of alloy 230 is studied by combination of EBSD and AFM; • Different thickness of oxide is formed on grain with different orientation and dependence of anisotropic oxidation behavior is discussed; • The morphology of grains is also orientation dependence.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Collapse of Langmuir monolayer at lower surface pressure: Effect of hydrophobic chain length

Long chain fatty acid molecules (e.g., stearic and behenic acids) form a monolayer on water surface in the presence of Ba{sup 2+} ions at low subphase pH (≈ 5.5) and remain as a monolayer before collapse generally occurs at higher surface pressure (π{sub c} > 50 mN/m). Monolayer formation is verified from the surface pressure vs. area per molecule (π-A) isotherms and also from the atomic force microscopy (AFM) analysis of the films deposited by single upstroke of hydrophilic Si (001) substrate through the monolayer covered water surface. At high subphase pH (≈ 9.5), barium stearate molecules form multilayer structure at lower surface pressure which is verified from the π-A isotherms and AFM analysis of the film deposited at 25 mN/m. Such monolayer to multilayer structure formation or monolayer collapse at lower surface pressure is unusual as at this surface pressure generally fatty acid salt molecules form a monolayer on the water surface. Formation of bidentate chelate coordination in the metal containing headgroups is the reason for such monolayer to multilayer transition. However, for longer chain barium behenate molecules only monolayer structure is maintained at that high subphase pH (≈ 9.5) due to the presence of relatively more tail-tail hydrophobic interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Characteristics of LaB{sub 6} thin films grown by pulsed laser deposition

LaB{sub 6} thin films were deposited at a temperature of 500 °C under vacuum or Ar atmosphere by the pulsed laser deposition technique on (100) Si substrates using a KrF laser. Grazing incidence x-ray diffraction investigations found that films were nanocrystalline, with grain size dimensions from 86 to 102 nm and exhibited microstrain values around 1.1%. Simulations of the x-ray reflectivity curves acquired from the deposited films showed that films had a density around 4.55 g/cm{sup 3}, and were very smooth, with a surface roughness root-mean-square of 1.5 nm, which was also confirmed by scanning electron and atomic force microscopy measurements. All films were covered by a ∼2 nm thick contamination layer that formed when samples were exposed to the ambient. Auger electron spectroscopy investigations found very low oxygen impurity levels below 1.5 at. % once the contamination surface layer was removed by Ar ion sputtering. Four point probe measurements showed that films were conductive, with a resistivity value around 200 μΩ cm for those deposited under Ar atmosphere and slightly higher for those deposited under vacuum. Nanoindentation and scratch investigations showed that films were rather hard, H ∼ 16 GPa, E ∼ 165 GPa, and adherent to the substrate. Thermionic emission measurements indicated a work function value of 2.66 eV, very similar to other reported values for LaB{sub 6}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗