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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Temperature dependence of the anisotropy in magnetic relaxation in YBa2Cu3O(7-x) thin films

The relaxation of diamagnetic magnetization in the c-axis-aligned YBa2Cu3O(7-x) thin film is studied as a function of orientation and temperature in the range of 5-50 K at H = 0.2 T. The magnetization M(T,H) in the orientations H parallel to c and H perpendicular to c and at all the temperatures is found to decrease logarithmically with time t. The activation energy for the movement of flux lines U is found to be 30-110 meV in the range 5-50 K. For H parallel c, U increases continuously with T, whereas for H perpendicular c, U has two apparent maxima: at T = 10 K and T greater than 50 K. These results are discussed in terms of the thermally activated flux motion model.

Vitta, Satish↗
NASA NTRS1991

Microwave properties of YBa2Cu3O(7-delta) high-transition-temperature superconducting thin films measured by the power transmission method

The microwave response of YBa2Cu3O(7-delta) superconducting thin films deposited on LaAlO3, MgO, YSZ, and LaGaO3 substrates are studied. It is found that the microwave transmission properties are very weakly dependent on temperature in the normal state but change drastically upon transition to the superconducting state. In particular, the transmission decreases and there is a negative phase shift with respect to the phase at room temperature when the sample is cooled through its transition temperature. The magnetic penetration depth for all the films was determined from the surface reactance of the films. The microwave complex conductivity is determined in both the normal and the superconducting state. It is observed that both sigma1 and sigma2 increase in transition to the superconducting state. The surface resistivity is calculated for all the films.

Miranda, F. A.↗
NASA NTRS1992

Thin film growth of the 2122-phase of BCSCO superconductor with high degree of crystalline perfection

Thin films of the 80 K-phase of BiCaSrCu-oxide superconductor having the composition of Bi2Ca1.05Sr2.1Cu2.19O(x) and high degree of crystalline perfection have been grown on c-axis oriented twin free single crystal substrates of NdGaO3. This has been achieved by carefully establishing the growth conditions of the LPE experiments. The temperature regime of 850 to 830 C and quenching of the specimens on the termination of the growth period are found to be pertinent for the growth of quasi-single crystalline superconducting BCSCO films on NdGaO3 substrates. The TEM analysis reveals a single crystalline nature of these films which exhibit 100 percent reflectivity in infrared regions at liquid nitrogen temperature.

Raina, K. K.↗
NASA NTRS1993

Vapor-Exposure Cell For Testing Thin-Film Electrodes

Vapor-exposure test cell (VETC) designed to be used in testing thin-film electrodes on solid electrolytes electrochemically at high temperature. Use of VETC much simpler and less expensive than testing alkali-metal thermal-to-electric converter (AMTEC) fuel cell, electrolysis cell, or other entire device containing solid electrolyte and electrodes of material and configuration to be characterized.

Ryan, Margaret A.↗
NASA NTRS1993

Heat flux measurements on ceramics with thin film thermocouples

Two methods were devised to measure heat flux through a thick ceramic using thin film thermocouples. The thermocouples were deposited on the front and back face of a flat ceramic substrate. The heat flux was applied to the front surface of the ceramic using an arc lamp Heat Flux Calibration Facility. Silicon nitride and mullite ceramics were used; two thicknesses of each material was tested, with ceramic temperatures to 1500 C. Heat flux ranged from 0.05-2.5 MW/m2(sup 2). One method for heat flux determination used an approximation technique to calculate instantaneous values of heat flux vs time; the other method used an extrapolation technique to determine the steady state heat flux from a record of transient data. Neither method measures heat flux in real time but the techniques may easily be adapted for quasi-real time measurement. In cases where a significant portion of the transient heat flux data is available, the calculated transient heat flux is seen to approach the extrapolated steady state heat flux value as expected.

Holanda, Raymond↗
DOE OSTI2023

Light-Induced Structural Dynamics and Charge Transport in Layered Halide Perovskite Thin Films

The dynamic nature of the metal halide perovskite lattice upon photoexcitation plays a vital role in their properties. Here we report an observation of light-induced structure dynamics in quasi-2D Ruddlesden–Popper phase perovskite thin films and its impact on the carrier transport properties. By a time-resolved X-ray scattering technique, we observe a rapid lattice expansion upon photoexcitation, followed by a slow relaxation over the course of 100 ns in the dark. Theoretical modeling suggests that the expansion originates from the lattice’s thermal fluctuations caused by photon energy deposition. Power dependent optical spectroscopy and photoconductivity indicate that high laser powers triggered a strong local structural disorder, which increased the charge dissociation activation energy that results in localized transport. Finally, our study investigates the impact of laser energy deposition on the lattices and the subsequent carrier transport properties, that are relevant to device operations.

2D perovskites↗
DOE OSTI2025

Photothermoelectric effect in cadmium arsenide thin films for unbiased, mid-infrared photodetection

Mid-infrared photodetectors that can operate at room temperature are of great interest for a wide range of applications. Here, we demonstrate unbiased, mid-infrared (10.4 μm) photodetection in epitaxial thin films of the three-dimensional Dirac semimetal cadmium arsenide (Cd 3 As 2 ), which are grown on a III–V heterostructure. We show that the photocurrent response of planar metal–Cd 3 As 2 –metal devices is consistent with the photothermoelectric effect, which is due to a temperature gradient that develops under asymmetric illumination of the device. We show that the photoresponsivity of Cd 3 As 2 channel devices is an order of magnitude greater than devices with a III–V semiconductor channel, attesting to the excellent thermoelectric properties of Cd 3 As 2 and promising efficient unbiased, room-temperature mid-infrared photodetection.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Molecular beam epitaxy and crystal structure of majority a -plane-oriented and substrate-strained Mn 3 Sn thin films grown directly on sapphire (0001)

The Kagome antiferromagnet Mn 3 Sn has garnered much attention due to the presence of exciting properties such as anomalous Hall and Nernst effects. This paper discusses the synthesis of crystalline Mn 3 Sn thin films, prepared on Al 2 O 3 (0001) substrates at 453 ± 5°C using molecular beam epitaxy. The growth is monitored in situ using reflection high energy electron diffraction and measured ex situ using x-ray diffraction, Rutherford back-scattering, and cross-sectional scanning transmission electron microscopy. Our analysis shows the in-plane lattice constants of a 1,M = 4.117 ± 0.027 Å and a 2,M = 4.943 ± 0.033 Å, which is a very unexpected result when compared to the bulk a-plane Mn 3 Sn. This indicates a strain in the film and makes it challenging to provide a straightforward explanation. In an effort to explain our results, we discuss two possible orientation relationships between the Mn 3 Sn films and the sapphire substrates. Samples prepared under these conditions appear to have smooth surfaces locally, but overall the film has a 3D island morphology. First-principles calculations provide atomic models of the Mn 3 Sn (112¯0) lattice on Al 2 O 3 (0001) high symmetry sites, indicating that the L3-R90° is the most stable configuration. A detailed discussion of the experimental data and theoretical results, as well as strain effects, is provided.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Layered Sn-Au Thin Films for Increased Electrochemical ATR-SEIRAS Enhancement

Operando electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (EC ATR-SEIRAS) is a valuable method for a fundamental understanding of electrochemical interfaces under real operating conditions. The applicability of this method depends on the ability to tune the optical and catalytic properties of an electrode film, and it thus requires unique optimization for any given material. Motivated by the growing interest in Sn-based electrocatalysts for selective reduction of CO2 to formate species, we investigate several Sn thin-film synthesis routes for the resulting SEIRA signal response. We compare the SEIRA performance of thermally evaporated metallic Sn to a series of Sn-based films on top of a SEIRA-active Au substrate (metallic Sn, oxide-derived metallic Sn, and metal oxide SnOx). Using alkanethiol self-assembled monolayers as a probe, we find that electrodepositing metallic catalyst films on top of SEIRA-active Au substrates yield higher signal relative to thermal evaporation as well as higher signal than the independent SEIRA-active Au underlayer. These observations come despite the fact that thermally evaporated Sn has a significantly higher surface roughness (and thus higher adsorbate population), suggesting specific SEIRA-magnifying effects for the stacked films. Finally, we applied these films to observe the electrochemical conversion of CO2. Differences are observed in spectral features based on the composition of the electrode being either metallic or oxide-derived metallic Sn, implying differences in their respective reaction pathways.

CO2 reduction↗
DOE OSTI2022

Functional properties of Yttrium Iron Garnett thin films on graphene-coated Gd 3 Ga 5 O 12 for remote epitaxial transfer

Remote epitaxial growth via a graphene interlayer and subsequent mechanical exfoliation of a free-standing membrane is a recently developed technique used to transfer complex oxide thin films onto non-native substrates to form heterogeneously integrated structures for various device applications. One such oxide is Yttrium Iron Garnet (YIG), a material of choice for a wide range of magnetoelectric and spintronic devices owing to its strong magnetic properties and low microwave losses. YIG is predominantly grown on lattice matched Gadolinium Gallium Garnet (GGG) substrates, but by utilizing the remote epitaxy technique, high quality YIG films can be transferred from GGG onto another substrate such as piezoelectric Lithium Niobate (LN). Mechanical strain coupling between the layers and magnetostrictive nature of YIG would allow for the investigation of the interplay in YIG/LN structures leading to the design of novel frequency agile magneto-acoustic devices. In this study functional properties of a YIG film grown using PLD on graphene-coated GGG substrate were investigated and compared to traditional YIG on GGG. Both materials were characterized in terms of crystal structure, surface morphology, FMR and Gilbert damping, and Raman and XAS spectroscopy. Further, it was found that YIG on graphene-coated GGG exhibits significantly higher microwave losses than standard YIG on GGG (FMR linewidth 30.9 vs 2.1 Oe at 10 GHz, and Gilbert damping coefficient 15.4x10 -4 vs 3.4x10 -4 respectively), which was attributed to increased concentration of Fe 2+ cations in YIG/Graphene/GGG. While the damping is higher in these studied films compared to YIG grown directly on GGG, the resulting properties are still very favorable compared to many other competing materials which can be grown without the need for lattice matched substrates, such as metallic ferromagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multifunctional Metal–Oxide Nanocomposite Thin Film with Plasmonic Au Nanopillars Embedded in Magnetic La 0.67 Sr 0.33 MnO 3 Matrix

Searching for multifunctional materials with tunable magnetic and optical properties has been a critical task toward the implementation of future integrated optical devices. Vertically aligned nanocomposite (VAN) thin films provide a unique platform for multifunctional material designs. In this work, a new metal–oxide VAN has been designed with plasmonic Au nanopillars embedded in a ferromagnetic La 0.67 Sr 0.33 MnO 3 (LSMO) matrix. Such Au–LSMO nanocomposite presents intriguing plasmon resonance in the visible range and magnetic anisotropy property, which are functionalized by the Au and LSMO phase, respectively. Furthermore, the vertically aligned nanostructure of metal and dielectric oxide results in the hyperbolic property for near-field electromagnetic wave manipulation. Such optical and magnetic response could be further tailored by tuning the composition of Au and LSMO phases.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structural, optical, and thermal properties of BN thin films grown on diamond via pulsed laser deposition

Heterostructures based on ultrawide-bandgap (UWBG) semiconductors (bandgap > 4.0 eV), such as BN and diamond, hold significant importance for the development of high-power electronics in the next generation. However, achieving in situ heteroepitaxy of BN/diamond or vice versa remains exceptionally challenging due to the complex growth kinetics involved. In this work, we grew BN thin film on (100) single-crystal diamonds using pulsed laser deposition and investigated its structural, magnetic, optical, and thermal properties. Throughout this study, the structural analyses confirmed the growth of BN films, which exhibited diamagnetic behavior at room temperature. Notably, the film demonstrated anisotropic refractive index characteristics within the visible-to-near-infrared wavelength range. The room-temperature cross-plane thermal conductivity of BN is 1.53 ± 0.77 W/mK, while the thermal conductance of the BN/diamond interface is 20 ± 2 MW/m 2 ⁢K. These findings have significant implications for a range of device applications based on UWBG BN/diamond heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

In Situ Recrystallization of Co-Evaporated Cu(In,Ga)Se2 Thin Films by Copper Chloride Vapor Treatment towards Solar Cell Applications

Cu(In,Ga)Se2 (or CIGS) thin films and devices were fabricated using a modified three-stage process. Using high deposition rates and a low temperature during the process, a copper chloride vapor treatment was introduced in between the second and third stages to enhance the films properties. X-ray diffraction and scanning electron microscopy demonstrate that drastic changes occur after this recrystallization process, yielding films with much larger grains. Secondary ion mass spectrometry shows that the depth profile of many elements is not modified (such as Cu, In and Se) while others change dramatically (such as Ga and Na). Because of the competing effects of these changes, not all parameters of the solar cells are enhanced, yielding an increase of 15% in the device efficiency at the most.

14 SOLAR ENERGY↗