Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Film microstructures”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Dependence of Andreev reflection and Schottky barriers on GaMnAs/Nb interface treatment

We studied the interfacial contact between GaMnAs and superconducting Nb micro-structures both with and without removing the native GaMnAs surface oxide. Our results show that a strong Schottky barrier forms at the interface when the oxide layer is left between Nb and GaMnAs. This barrier can be confused for Andreev Reflection and erroneously used to extract spin polarization. A simple acid etch is shown to remove the oxide film, thus decreasing the interface resistance, removing the Schottky barrier, and causing a clear Andreev reflection effect. One key recommendation for point contact Andreev reflection studies is to push the tip hard enough into contact and verify that the total resistance is not too high.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1992

Effects of space environment on structural materials

A preliminary study of materials exposed in space in a low Earth orbit for nearly six years has revealed a wide range of micrometeorite or microparticle impact craters ranging in size from 1 to 1000 micron in diameter, debris particles from adjacent and distant materials systems, reaction products, and other growth features on the specimen surfaces, and related phenomena. The exposed surface features included fine grained and nearly amorphous materials as well as a large array of single crystal particles. A replication type, lift off technique was developed to remove reaction products and debris from the specimen surfaces in order to isolate them from the background substrate without creating microchemical or microstructural artifacts or alterations. This resulted in surface features resting on a carbon support film which was virtually invisible to observation by electron microscopy and nondispersive x ray analysis. Some evidence for blisters on leading edge aluminum alloy surfaces and a high surface region concentration of oxygen determined by Auger electron spectrometry suggests oxygen effects where fluences exceed 10(exp 21) atoms/sq cm.

Miglionico, C.↗
DOE OSTI2016

Kinetics of photo-activated charge carriers in Sn:CdS

Kinetics of the photo-activated charge carriers has been investigated in Tin substituted Cadmium Sulphide, Cd{sub 1-x}Sn{sub x}S (x=0, 0.05, 0.10 and 0.15), thin films prepared by spray pyrolysis. X-Ray Diffraction shows an increase in strain that resulted in the decreased crystallite size upon Sn substitution. At the first sight, the photo current characteristics show a quenching effect on Sn substitution. However, survival of persistent photocurrents is seen even up to 15% of Sn substitution. Transient photo current decay could be explained with a 2τ relaxation model. CdS normally has an n-type character and the Sn doping expected to inject hole carriers. The two fold increase in τ{sub 1}, increase in activation energy and the decrease in photocurrents upon Sn substitution point towards a band gap cleaning scenario that include compensation and associated carrier injection dynamics. In addition Atomic Force Microscopy shows a drastic change in microstructure that modulates the carrier dynamics as a whole.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Hydroxyapatite coating on biodegradable AZ31 and Mg-Ca alloys prepared by RF-magnetron sputtering

A thin film of hydroxyapatite (HA) was deposited on AZ31 and Mg-Ca alloys by using radio frequency (RF) magnetron sputtering. The thickness of the HA coating was determined to be 750 nm. The phase composition, microstructure, and surface morphology of the HA coatings were investigated using X-ray diffraction and scanning electron microscopy. In vitro degradation behaviour of the HA coated alloys was evaluated in simulated body fluid (SBF) and 3.5wt.% NaCl solution using electrochemical method. The coatings homogeneously covered the entire surface of the substrates. The coating structure corresponded to a nanostructured HA. The ultrathin coating significantly improved the degradation resistance of the alloy. Nanocrystalline HA coating significantly improved the corrosion resistance of the Mg-Ca and AZ31 magnesium alloys. The polarization resistance (Rp) of the coated Mg-Ca alloy was more than two-order of magnitude higher and the corrosion current density I{sub corr} reduced by ∼ 98% as compared to the base alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Fabrication of Polymer Membrane-Suspended Microstructures on Printed Circuit Boards

When microelectromechanical systems are manufactured in high densities, the necessary routing layer structures can become complex and thus expensive if executed in silicon technology. If, additionally, the microstructures are also to be fabricated suspended on membranes, complex thinning processes become necessary to form these often rather fragile membranes. Here, a novel fabrication concept is demonstrated that allows for the fabrication of membrane-suspended microstructures using standard microfabrication techniques directly integrated with printed circuit boards (PCB) by laminating polyimide (PI) films over cavities in the PCB. This results in cost-effective routing layer fabrication and direct compatibility with common electronic component standards such as SMT (surface-mount technology) and THT (through-hole technology). To illustrate the capabilities of the fabrication process, we fabricated an array of membrane suspended microheaters. Individual platinum microheater elements are suspended on PI membranes that are 25 μm thick and 500 μm in diameter. The fabricated PCB carries a 10x10 array of suspended microheaters on an area of 26,mm x 26,mm. Here, the characterization of the microheater array shows that a yield of 86% functional microheaters was achieved. An individual microheater shows an almost linear heating characteristic at least up to 200°C demonstrating the viability of the technique for creating functional membrane-suspended microstructures on a PCB. [2021-0226]

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Chapter 6: Luminescence and Thermal Imaging of Thin-Film Photovoltaic Materials, Devices, and Modules

In this chapter, we describe luminescence and thermal imaging in the context of thin-film PV devices. First, we discuss both traditional and developing experimental designs, including dark LIT (DLIT), illuminated LIT, PL using different illumination configurations, traditional EL performed under forward -bias current injection, and contactless EL induced with sub -cell illumination patterns. Next, we provide some brief theoretical background to highlight relationships between fundamental materials properties and the resulting luminescence and thermal images. Finally, we give examples of thin-film PV PL, EL, and LIT images to demonstrate the utility of these imaging methods ranging from understanding the microstructure of active layers to managing the quality and reliability of full PV modules.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2017

CeB{sub 6} thin films produced on different substrates by electron-beam deposition

Films of cerium hexaboride, a material promising for use in thermoelectric devices at liquidhelium temperatures, are produced by electron-beam deposition. Deposition is carried out from ceramic targets onto insulator, semiconductor, and metal substrates at different temperatures. The microstructure, the elemental and phase compositions, the temperature dependences of the resistivity and the Seebeck coefficient are thoroughly studied. CaB{sub 6}-structured films, for which the structure is characteristic of cerium hexaboride and the elemental composition is close to the stoichiometric composition, are obtained. At low temperatures, the resistivity of the films is somewhat higher than that of single-crystal samples, and the Seebeck coefficient is close to the corresponding coefficient for single-crystal samples. The main cause of the difference between the resistance values is a high concentration of oxygen impurity detected in the films.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Room temperature photoluminescence from In{sub x}Al{sub (1−x)}N films deposited by plasma-assisted molecular beam epitaxy

InAlN films deposited by plasma-assisted molecular beam epitaxy exhibited a lateral composition modulation characterized by 10–12 nm diameter, honeycomb-shaped, columnar domains with Al-rich cores and In-rich boundaries. To ascertain the effect of this microstructure on its optical properties, room temperature absorption and photoluminescence characteristics of In{sub x}Al{sub (1−x)}N were comparatively investigated for indium compositions ranging from x = 0.092 to 0.235, including x = 0.166 lattice matched to GaN. The Stokes shift of the emission was significantly greater than reported for films grown by metalorganic chemical vapor deposition, possibly due to the phase separation in these nanocolumnar domains. The room temperature photoluminescence also provided evidence of carrier transfer from the InAlN film to the GaN template.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Fabrication and characterization of high energy density lithium-rich nickel manganese cobalt oxide cathode thin films

This paper reports a method to prepare Li-rich NMC (Li1.2Mn0.55Ni0.15Co0.1O2) thin film cathodes for Li-ion batteries using magnetron sputtering and post-annealing in O2. The use of thin films with no binder and conductive additives enables to study in detail the surface reaction chemistry upon cycling as well as the microstructural changes in the bulk. We show that it is essential to control the deposition pressure to obtain the expected layered(R-3m)-layered(C2/m) structure, thus providing large reversible capacities up to 270 mAh g-1 and voltage profiles close to those expected. This is substantiated by TEM/SAED results showing that the films consist of a layered structure with trigonal symmetry in which Li/TM ordering is achieved. The study of various XPS core levels determines that the surface is comprised of Mn4+, Co3+ and Ni2+ cations inside an O2- framework. The losses mechanisms are studied during long cycling. After 184 cycles, the microstructure does not reveal the presence of Li/TM ordering, which supports that Li2MnO3 conversion is irreversible. In addition, we characterize that the surface chemistry evolves significantly upon cycling. The surface of cycled discharged electrodes is mostly made of inorganic species (LiF, Lix POy Fz , LixPFy), along with small amounts of organic species with C-O and O-C=O groups such as PEO, LiOR and LiCO2R. Moreover, the results support that Ni and Co migrate into the bulk whereas Mn is enriched at the surface. In the case of Mn, the reduction of Mn4+ into Mn3+ is clearly evidenced, as expected from the activation of Li2MnO3 domains.

Baggetto, Loic↗
DOE OSTI2015

Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 0.72}Ti{sub 0.28}O{sub 3} substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Preparing magnetic yttrium iron garnet nanodot arrays by ultrathin anodic alumina template on silicon substrate

Ultrahigh density periodically ordered magnetic yttrium iron garnet (Y{sub 3}Fe{sub 5}O{sub 12}, YIG) nanodot arrays have been prepared by pulsed laser deposition through an ultrathin alumina mask (UTAM). UTAM having periodically ordered circularly shaped holes with 350 nm in diameter, 450 nm in inter-pore distance, and 700 nm in height has been prepared on silicon substrate. Furthermore, the microstructure and magnetic properties of YIG nanodot arrays have been characterized. Nanodot arrays with a sharp distribution in diameter centered at 340 nm with standard deviation of 10 nm have been fabricated. Moreover, typical hysteresis loops and ferromagnetic resonance spectra in in-plane and out-of-plane revealed that this unique structure greatly influences the magnetics properties of YIG. First, coercivity of YIG nanodot arrays in in-plane was increased about from 15 Oe of YIG films to 500 Oe. Then, the degree of uniformity about nanodot height decided that two or more resonance peaks in out-of-plane were detected in the spectra. The peak-to-peak linewidth values were about 94 Oe and 40 Oe in the parallel and perpendicular directions, respectively, which indicated that the values were larger by the two-magnon scattering. Consequently, this pattering method creates opportunities for studying physics in oxide nanomagnets and may be applied in spin-wave devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Bismuth-Based Perovskite-Inspired Solar Cells: In Situ Diagnostics Reveal Similarities and Differences in the Film Formation of Bismuth- and Lead-Based Films

Organic–inorganic lead-based halide perovskite compounds currently yield thin film solar cells with a power conversion efficiency (PCE) of >23%. However, replacing the lead with less-toxic elements while maintaining a high PCE remains a challenge. For this reason, there has been significant effort to develop Pb-free compounds, including methylammonium bismuth iodide (MA 3 Bi 2 I 9 ), but such systems severely underperform when compared with the prototypical Pb-based methylammonium lead iodide (MAPbI 3 ). For the latter, it is known that lead complexes with polar solvents, such as dimethyl sulfoxide (DMSO) and dimethylformamide (DMF), to form iodoplumbates which can co-crystallize into solvated phases. Herein, the solidification and growth behaviors of Bi- and Pb-based films is investigated using multi-probe in situ characterization methods. It is shown that the Bi-based compound crystallizes directly and rapidly into a textured polycrystalline microstructure from a precursor solution without evolving through intermediate crystalline solvated phases, in contrast to MAPbI 3 . This solidification process produces isolated crystals and challenges the growth of continuous and crystalline films required for solar cells. Further, it is revealed that solvent engineering with antisolvent dripping is crucial to enable the formation of continuous polycrystalline films of MA 3 Bi 2 I 9 and functional solar cells thereof.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ferroelectric polymer-ceramic composite thick films for energy storage applications

We have successfully fabricated large area free standing polyvinylidene fluoride -Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3} (PVDF-PZT) ferroelectric polymer-ceramic composite (wt% 80–20, respectively) thick films with an average diameter (d) ∼0.1 meter and thickness (t) ∼50 μm. Inclusion of PZT in PVDF matrix significantly enhanced dielectric constant (from 10 to 25 at 5 kHz) and energy storage capacity (from 11 to 14 J/cm{sup 3}, using polarization loops), respectively, and almost similar leakage current and mechanical strength. Microstructural analysis revealed the presence of α and β crystalline phases and homogeneous distribution of PZT crystals in PVDF matrix. It was also found that apart from the microcrystals, well defined naturally developed PZT nanocrystals were embedded in PVDF matrix. The observed energy density indicates immense potential in PVDF-PZT composites for possible applications as green energy and power density electronic elements.

36 MATERIALS SCIENCE↗
NASA NTRS2015

Techniques for Achieving Zero Stress in Thin Films of Iridium, Chromium, and Nickel

We examine techniques for achieving zero intrinsic stress in thin films of iridium, chromium, and nickel deposited by magnetron sputter deposition. The intrinsic stress is further correlated to the microstructural features and physical properties such as surface roughness and optical density at a scale appropriate to soft X-ray wavelengths. The examination of the stress in these materials is motivated by efforts to advance the optical performance of light-weight X-ray space telescopes into the regime of sub-arcsecond resolution through various deposition techniques that rely on control of the film stress to values within 10-100 MPa. A characteristic feature of the intrinsic stress behavior in chromium and nickel is their sensitivity to the magnitude and sign of the intrinsic stress with argon gas pressure and deposition rate, including the existence of a critical argon process pressure that results in zero film stress which scales linearly with the atomic mass of the sputtered species. While the effect of stress reversal with argon pressure has been previously reported by Hoffman and others for nickel and chromium, we report this effect for iridium. In addition to stress reversal, we identify zero stress in the optical functioning iridium layer shortly after island coalescence for low process pressures at a film thickness of approximately 35nm. The measurement of the low values of stress during deposition was achieved with the aid of a sensitive in-situ instrument capable of a minimum detectable level of stress, assuming a 35nm thick film, in the range of 0.40-6.0 MPa for <111> oriented crystalline silicon substrate thicknesses of 70-280 microns, respectively.

X-ray optical thin films↗
DOE OSTI2026

Distribution of 7 Li implants in Nb films for a sterile neutrino search

The Beryllium-7 Electron capture in Superconducting Tunnel junctions (BeEST) experiment searches for sub-MeV sterile neutrinos by measuring the 7 Li recoil spectrum from 7 Be decay in Ta-based superconducting quantum sensors. Its sensitivity is limited by spectral broadening from interactions between 7 Be/ 7 Li and the Ta host material. This study investigates Nb as an alternative sensor material using scanning transmission electron microscopy (STEM) and atom probe tomography (APT) on 7 Li-implanted Nb films (∼0.5 at. %). STEM shows no 7 Li cluster formation and no implantation-induced microstructural degradation, while APT reveals some limited 7 Li segregation to grain boundaries. Although this segregation may slightly influence binding energies, it is unlikely to affect the broadening of the recoil spectrum significantly. These findings support Nb as a viable sensor material for future phases of the BeEST experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Combinatorial Deposition of Ultrathick Ta-W-Au-Bi High-Entropy Alloys for Next-Generation Hohlraums by Direct-Current Magnetron Sputtering

Hohlraum temperature calculations with the model by J. H. Hammer and M. D. Rosen predict a higher X-ray drive from Ta-W-Au-Bi high-entropy alloys compared to pure Au and recently developed Ta 4 Au and Au-Bi hohlraums. Here, we study the microstructure and properties of 25-75−µm-thick Ta-W-Au-Bi alloy films deposited via combinatorial direct-current magnetron sputtering. All of the films have promising physical properties, including high electrical resistivity, that satisfy the requirements for magnetically assisted inertial confinement fusion experiments. While porosity tends to increase with increasing Bi content, we also found that films with Bi content > 44 at. % exhibited densification close to the substrate/film interface and formed a single-phase alloy. In conclusion, these findings provide a potential path forward for the development of Ta-W-Au-Bi alloys for next-generation hohlraum materials.

Magnetron sputtering↗
DOE OSTI2025

Three-dimensional nucleation and growth of deformation twins in magnesium

At two-thirds the weight of aluminum, magnesium alloys have the potential to reduce the fuel consumption of transportation vehicles. These advancements depend on our ability to optimize the desirable versus undesirable effects of deformation twins, which are three-dimensional (3D) microstructural domains that form under mechanical stresses. Previously only characterized through surface or thin-film measurements, we here present 3D in situ characterization of deformation twinning inside an embedded grain over mesoscopic fields of view using dark-field x-ray microscopy supported by crystal plasticity finite element analysis. The results revealed the role of triple junctions on twin nucleation and the sequence and irregularity of twin growth and showed that twin-grain junctions, twin-twin junctions, and twin boundaries were the sites of localized dislocation accumulation.

Lee, Sangwon [Univ. of Michigan, Ann Arbor, MI (Un↗
DOE OSTI2018

Short-Range Order in Amorphous and Crystalline Ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2}

The microstructures of amorphous and polycrystalline ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO{sub 2} and ZrO{sub 2}. After rapid thermal annealing, the mixed Hf{sub 0.5}Zr{sub 0.5}O{sub 2} oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO{sub 2} and ZrO{sub 2}. The presence of the HfO{sub 2} and ZrO{sub 2} phases in the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films is also detected by ellipsometry.

36 MATERIALS SCIENCE↗