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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The effect of Ta interface on the crystallization of amorphous phase change material thin films

The crystallization of amorphous GeTe and Ge{sub 2}Sb{sub 2}Te{sub 5} phase change material films, with thickness between 10 and 100 nm, sandwiched between either Ta or SiO{sub 2} layers, was investigated by optical reflectivity. Ta cladding layers were found to increase the crystallization temperature, even for films as thick as 100 nm. X-Ray diffraction investigations of crystallized GeTe films showed a very weak texture in Ta cladded films, in contrast with the strong texture observed for SiO{sub 2} cladding layers. This study shows that crystallization mechanism of phase change materials can be highly impacted by interface effects, even for relatively thick films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

In situ monitoring of structure formation in the active layer of polymer solar cells during roll-to-roll coating

The active layer crystallization during roll-to-roll coating of organic solar cells is studied in situ. We developed an X-ray setup where the coater unit is an integrated part of the small angle X-ray scattering instrument, making it possible to control the coating process while recording scattering measurements in situ, enabling us to follow the crystal formation during drying. By varying the distance between the coating head and the point where the X-ray beam hits the film, we obtained measurements of 4 different stages of drying. For each of those stages, the scattering from as long a foil as possible is summed together, with the distance from coating head to scattering point kept constant. The results are average crystallographic properties for the active layer coated on a 30 m long foil. With this insight into the dynamics of crystallization in a roll-coated polymer film, we find that the formation of textured and untextured crystallites seems uncorrelated, and happens at widely different rates. Untextured P3HT crystallites form later in the drying process than expected which may explain previous studies speculating that untextured crystallization depends on concentration. Textured crystallites, however, begin forming much earlier and steadily increases as the film dries, showing a development similar to other in situ studies of these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Enhanced magnetostrictive effect in epoxy-bonded Tb{sub x}Dy{sub 0.9−x}Nd{sub 0.1}(Fe{sub 0.8}Co{sub 0.2}){sub 1.93} pseudo 1–3 particulate composites

The spin configuration and spontaneous magnetostriction λ{sub 111} of Tb{sub x}Dy{sub 0.9−x}Nd{sub 0.1}(Fe{sub 0.8}Co{sub 0.2}){sub 1.93} (0.20 ≤ x ≤ 0.60) alloys have been investigated. The easy magnetization direction (EMD) at room temperature was observed towards the 〈111〉 axis when 0.40 ≤ x ≤ 0.60, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ{sub 111}, which increases from 1640 ppm for x = 0.40 to 1900 ppm for x = 0.60. The strong 〈111〉-oriented pseudo 1–3 particulate composite was fabricated by embedding and aligning particles in a passive epoxy matrix under an applied magnetic field. An enhanced magnetostrictive effect, the large low-field magnetostriction, λ{sub a}, as high as 480 ppm at 3 kOe, was obtained for the sample of x = 0.40, in an excess of 75% of its polycrystalline alloy although it only contains 27 vol. % alloy particles. This enhanced effect can be attributed to its low magnetic anisotropy, anisotropic magnetostrictive nature (e.g., λ{sub 111} ≠ λ{sub 100,} 〈111〉EMD), chain structure, and the 〈111〉-textured orientation. In addition, we give a direct experimental support that the 〈111〉EMD of particle and the strong 〈111〉-textured orientation are the crucial factors to realize the enhanced magnetostrictive effect in 1–3 particulate composites.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Performance improvements of wavelength-shifting-fiber neutron detectors using high-resolution positioning algorithms

On the basis of FluoroBancroft linear-algebraic method [S.B. Andersson, Opt. Exp. 16, 18714 (2008)] three highly-resolved positioning methods were proposed for wavelength-shifting fiber (WLSF) neutron detectors. Using a Gaussian or exponential-decay light-response function (LRF), the non-linear relation of photon-number profiles vs. x-pixels was linearized and neutron positions were determined. The proposed algorithms give an average 0.03-0.08 pixel position error, much smaller than that (0.29 pixel) from a traditional maximum photon algorithm (MPA). The new algorithms result in better detector uniformity, less position misassignment (ghosting), better spatial resolution, and an equivalent or better instrument resolution in powder diffraction than the MPA. Moreover, these characters will facilitate broader applications of WLSF detectors at time-of-flight neutron powder diffraction beamlines, including single-crystal diffraction and texture analysis.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Formation of (111) orientation-controlled ferroelectric orthorhombic HfO{sub 2} thin films from solid phase via annealing

0.07YO{sub 1.5}-0.93HfO{sub 2} (YHO7) films were prepared on various substrates by pulse laser deposition at room temperature and subsequent heat treatment to enable a solid phase reaction. (111)-oriented 10 wt. % Sn-doped In{sub 2}O{sub 3}(ITO)//(111) yttria-stabilized zirconia, (111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrates, and (111)ITO/(111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrates were employed for film growth. In this study, X-ray diffraction measurements including θ–2θ measurements, reciprocal space mappings, and pole figure measurements were used to study the films. The film on (111)ITO//(111)yttria-stabilized zirconia was an (111)-orientated epitaxial film with ferroelectric orthorhombic phase; the film on (111)ITO/(111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si was an (111)-oriented uniaxial textured film with ferroelectric orthorhombic phase; and no preferred orientation was observed for the film on the (111)Pt/TiO{sub x}/SiO{sub 2}/(001)Si substrate, which does not contain ITO. Polarization–hysteresis measurements confirmed that the films on ITO covered substrates had saturated ferroelectric hysteresis loops. A remanent polarization (P{sub r}) of 9.6 and 10.8 μC/cm{sup 2} and coercive fields (E{sub c}) of 1.9 and 2.0 MV/cm were obtained for the (111)-oriented epitaxial and uniaxial textured YHO7 films, respectively. These results demonstrate that the (111)-oriented ITO bottom electrodes play a key role in controlling the orientation and ferroelectricity of the phase formation of the solid films deposited at room temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Enhanced dielectric and piezoelectric responses in Zn 1 -x Mg x O thin films near the phase separation boundary

Dielectric and piezoelectric properties for Zn 1-x Mg x O (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn 1-x Mg x O (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane ( d 33,f ) and in-plane ( e 31,f ) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. As a result, the enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn 1-x Mg x O an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2017

In-situ synchrotron x-ray characterization of K 2 CsSb photocathode grown by ternary co-evaporation

K2CsSb is a promising photocathode candidate to serve as an electron source in next-generation light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). As the traditional recipe for creation of K2CsSb photocathodes typically results in a rough surface that deteriorates electron beam quality, significant effort has been made to explore novel growth methods for K2CsSb photocathodes. In this paper, a method of ternary co-evaporation of K, Cs, and Sb is described. By using in-situ synchrotron X-ray techniques, the quality of the photocathode is characterized during and after the growth. K2CsSb photocathodes grown by this method on Si (100) and MgO (001) substrates show strong (222) texture, and the two photocathodes exhibit 1.7% and 3.4% quantum efficiencies at a wavelength of 530 nm, with a rms surface roughness of about 2-4 nm. This represents an order of magnitude reduction in roughness compared to typical sequential deposition and should result in a significant improvement in the brightness of the generated electron beam.

Ding, Z.↗
DOE OSTI2017

Relationship between electrical properties and crystallization of indium oxide thin films using ex-situ grazing-incidence wide-angle x-ray scattering

Grazing-incidence, wide-angle x-ray scattering measurements were conducted on indium oxide thin films grown on silica substrates via pulsed laser deposition. Growth temperatures (T G ) in this study ranged from -50 °C to 600 °C, in order to investigate the thermal effects on the film structure and its spatial homogeneity, as well as their relationship to electrical properties. Films grown below room temperature were amorphous, while films prepared at T G = 25 °C and above crystallized in the cubic bixbyite structure, and their crystalline fraction increased with deposition temperature. The electrical conductivity (σ) and electrical mobility (μ) were strongly enhanced at low deposition temperatures. For T G = 25 °C and 50 °C, a strong < 100 > preferred orientation (texture) occurred, but it decreased as the deposition temperature, and consequential crystallinity, increased. Higher variations in texture coefficients and in lattice parameters were measured at the film surface compared to the interior of the film, indicating strong microstructural gradients. At low crystallinity, the in-plane lattice spacing expanded, while the out-of-plane spacing contracted, and those values merged at T G = 400 °C, where high μ was measured. This directional difference in lattice spacing, or deviatoric strain, was linear as a function of both deposition temperature and the degree of crystallinity. The crystalline sample with T G = 100 °C had the lowest mobility, as well as film diffraction peaks which split into doublets. The deviatoric strains from these doublet peaks differ by a factor of four, supporting the presence of both a microstructure and strain gradient in this film. More isotropic films exhibit larger l values, indicating that the microstructure directly correlates with electrical properties. Lastly, these results provide valuable insights that can help to improve the desirable properties of indium oxide, as well as other transparent conducting oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Topological spin dynamics in cubic FeGe near room temperature

Understanding spin-wave dynamics in chiral magnets is a key step for the development of high-speed, spin-wave based spintronic devices that take advantage of chiral and topological spin textures for their operation. Here, we present an experimental and theoretical study of spin-wave dynamics in a cubic B20 FeGe single crystal. Using the combination of waveguide microwave absorption spectroscopy (MAS), micromagnetic simulations, and analytical theory, we identify the resonance dynamics in all magnetic phases (field polarized, conical, helical, and skyrmion phases). Finally, because the resonance frequencies of specific chiral spin textures are unique, a quantitative agreement between our theoretical predictions and experimental findings for all resonance frequencies and spin wave modes enables us to unambiguously identify chiral magnetic phases and to demonstrate that MAS is a powerful tool to efficiently extract a magnetic phase diagram.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Patterning of graphene oxide with optoelectronic tweezers

Optoelectronic tweezers (OET) offer a means for parallel trapping and dynamic manipulation of micro-scale particles using low-intensity light. Such capabilities can facilitate the formation of bulk materials with a precisely tailored microstructure. Here, we report the use of OET to vertically align, trap, and reposition sheets of graphene oxide (GO) in liquids, paving the way for textured and patterned graphene macroassemblies that could offer superior performance for applications in energy storage, catalysis, and electronic devices. Trapping can be achieved with low-power light from inexpensive digital projectors and diode lasers, making it simple for users to create and apply patterns while avoiding undesirable photothermal heating effects. To give users a quantitative idea of trap stiffness, we also present a theoretical framework for predicting the maximum achievable speed of a GO platelet in an OET trap.

Lim, Matthew B. (ORCID:0000000161299876)↗
DOE OSTI2018

Time and frequency dependent mechanical properties of LaCoO 3 -based perovskites: Neutron diffraction and domain mobility

The study of domain wall movement and texture formation in ferroelastic LaCoO 3 perovskite under constant applied compressive stress has been performed using in situ neutron diffraction. Additionally, it was established that under constant applied compressive stress the domain walls show mobility that may lead both to the shrinkage (creep strain) and to the expansion (negative creep strain) of LaCoO 3 perovskite. The domain wall movement and texture formation can be explained by the availability, mobility, and interaction of twins, stacking faults, antiphase boundaries, dislocations, and point defects, such as oxygen vacancies and their complexes as well as impurity atoms. Lastly, the equation of motion was used to describe the possible mechanisms of domain wall movement under applied stress, and it was determined that the available solutions of this equation allow both for the shrinkage (creep strain) and for the expansion (negative creep strain) of LaCoO 3 perovskite to occur.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Quantification of MagLIF morphology using the Mallat scattering transformation

The morphology of the stagnated plasma resulting from magnetized liner inertial fusion is measured by imaging the self-emission x rays coming from the multi-keV plasma. Equivalent diagnostic responses can be generated by integrated radiation-magnetohydrodynamic (rad-MHD) simulations from programs such as HYDRA and GORGON. There have been only limited quantitative ways to compare the image morphology, that is the texture, of simulations and experiments. We have developed a metric of image morphology based on the Mallat scattering transformation (MST), a transformation that has proved to be effective at distinguishing textures, sounds, and written characters. This metric is designed, demonstrated, and refined by classifying ensembles (i.e., classes) of synthetic stagnation images and by regressing an ensemble of synthetic stagnation images to the morphology (i.e., model) parameters used to generate the synthetic images. We use this metric to quantitatively compare simulations to experimental images, experimental images to each other, and to estimate the morphological parameters of the experimental images with uncertainty. This coordinate space has proved to be very adept at doing a sophisticated relative background subtraction in the MST space. This was needed to compare the experimental self-emission images to the rad-MHD simulation images.

Glinsky, Michael E. (ORCID:0000000324933326)↗
DOE OSTI2020

Magnetic droplet solitons

Magnetic droplet solitons are dynamical magnetic textures that form due to an attractive interaction between spin waves in thin films with perpendicular magnetic anisotropy. Spin currents and the spin torques associated with these currents enable their formation as they provide a means to excite non-equilibrium spin-wave populations and compensate their decay. Recent years have seen rapid advances in experiments that realize and study magnetic droplets. Important advances include the first direct x-ray images of droplets, determination of their threshold and sustaining currents, measurement of their generation and annihilation time, and evidence for drift instabilities, which can limit their lifetime. This perspective discusses these studies and contrasts these solitons to other types of spin-current excitations, such as spin-wave bullets, and static magnetic textures, including magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as current controlled microwave frequency oscillators with potential applications in neuromorphic chips as nonlinear oscillators with memory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Yield strength of CeO 2 measured from static compression in a radial diamond anvil cell

Cerium oxide (ceria, CeO 2 ) is frequently used as a standard in applications such as synchrotron and x-ray free electron lasers for calibrating x-ray wavelengths and offers the potential for understanding the high pressure properties and deformation mechanisms in a wide range of similar face centered cubic (fcc) materials. In this study, the pressure dependence of the strength of ceria was investigated up to 38 GPa using angle dispersive x-ray diffraction in a radial geometry in a diamond anvil cell. In this experiment, the difference in the stress along the axis of compression and perpendicular to the direction of compression can be determined, giving a quantity known as the differential stress. It was found that the differential stress (t), a measure of the lower bound for yield strength, initially increases rapidly from 0.35 ± 0.06 GPa to 2.2 ± 0.4 GPa at pressures of 1.8 and 3.8 GPa, respectively. Above 4 GPa, t increases more slowly to 13.8 ± 2.6 GPa at a pressure of 38 GPa. The changes in the preferred orientation (texture) of CeO 2 with pressure were also measured, allowing for the determination of active deformation mechanisms using an elasto-viscoplastic self-consistent model (EVPSC). It was found that as pressure increased, the [001] direction had a slight preferred orientation along the axis of compression. Our EVPSC model of experimental fiber (cylindrically symmetric) textures and lattice strains were most consistent with dominant slip activity along ${111}$ $\langle$$1\bar10$$\rangle$.

36 MATERIALS SCIENCE↗
DOE OSTI2022

From vertices to vortices in magnetic nanoislands

We report recent studies in magnetic nanoarrays show that a variety of complex magnetic states and textures emerge as a function of a single magnetic nanoisland's aspect ratio. We propose a model that, in addition to fitting experiments, predicts magnetic states with continuous symmetry at particular aspect ratios and reveals a duality between vortex and vertex states. Our model opens new means of engineering novel types of artificial spin systems, and their application to complex magnetic textures in devices and computing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

New dynamic diamond anvil cell for time-resolved radial x-ray diffraction

The dynamic diamond anvil cell (dDAC) is a recently developed experimental platform that has shown promise for studying the behavior of materials at strain rates ranging from intermediate to quasi-static and shock compression regimes. Combining dDAC with time-resolved x-ray diffraction (XRD) in the radial geometry (i.e., with incident x-rays perpendicular to the axis of compression) enables the study of material properties such as strength, texture evolution, and deformation mechanisms. This work describes a radial XRD dDAC setup at beamline P02.2 (Extreme Conditions Beamline) at DESY’s PETRA III synchrotron. Time-resolved radial XRD data are collected for titanium, zirconium, and zircon samples, demonstrating the ability to study the strength and texture of materials at compression rates above 300 GPa/s. In addition, the simultaneous optical imaging of the DAC sample chamber is demonstrated. The ability to conduct simultaneous radial XRD and optical imaging provides the opportunity to characterize plastic strain and deviatoric strain rates in the DAC at intermediate rates, exploring the strength and deformation mechanisms of materials in this regime.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Tailoring additive manufacturing to optimize dynamic properties in 316L stainless steel

With the advent of additive manufacturing, manipulation of typical microstructural elements such as grain size, texture, and defect densities is now possible at a faster time scale. While the processing–structure–property relationship in additive manufactured metals has been well studied over the past decade, little work has been done in understanding how this process affects the dynamic behavior of materials. We postulate that additive manufacturing can be used to alter the material microstructure and used to enhance its dynamic strength. In this work, 316L stainless steel (SS) was manufactured via selected laser melting and its microstructure was altered through changing build parameters like laser power, speed, and hatch spacing systematically. These samples were then subjected to spall recovery experiments to measure the spall strength and quantify the amount of damage as a function of build parameters. By mapping the spall strength as a function of build parameters, this work demonstrated that indeed additive manufacturing can be used to tailor the spall strength of 316L SS. This work also determined the optimum build parameters (laser power=195W; scanning speed=1083mm/s; hatch spacing=0.09mm; layer thickness=0.02mm) to obtain the highest spall strength and the least amount of total damage in 316L SS. Microstructural characterization of the pre- and post-mortem samples revealed that increased grain average misorientation and textural index were the main driving force behind this higher spall strength. This work aims to enhance microstructural engineering techniques to design materials with greater resistance to dynamic shock loading.

36 MATERIALS SCIENCE↗