Search NASA⌕ Search

SEARCH · Search NASA

Results for “Texturing”

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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

In-situ L-TEM observations of dynamics of nanometric skyrmions and antiskyrmions

Nanometer-scale magnetic skyrmions and antiskyrmions exhibit unique dynamical behaviors in response to external stimuli, which are critical for their applications in low-power-consumption spintronic devices. This review discusses recent advancements in in-situ Lorentz transmission electron microscopy (L-TEM) observations of skyrmion and antiskyrmion dynamics, and demonstrates the manipulation and evolution of these textures in various magnetic materials under electric, magnetic, and thermal stimuli. Specifically, the motion tracking of single skyrmions and their clusters, and the deformation and transformation of skyrmions has been demonstrated in chiral helimagnets FeGe, Co 9 Zn 9 Mn 2 , and Co 10 Zn 10 with precise application of electric currents. Skyrmions can undergo dynamic transitions in current-driven skyrmion motions, from pinned states to linear flows, and even exhibit deformation into elliptical shapes, underscoring their topological robustness and dynamic flexibility. In addition, the manipulation of single antiskyrmions and antiskyrmion-lattice phases in (Fe 0.63 Ni 0.3 Pd 0.07 ) 3 P with S 4 symmetry is discussed, highlighting their high mobility and unique sliding capabilities along stripe domains at room temperature, facilitated by nanosecond pulsed electric currents. Finally, the temperature gradient-driven motion and topological transformation of elliptical skyrmions and antiskyrmions in this same material are investigated. In conclusion, the comprehensive insights gained from the L-TEM imaging technique are pivotal in advancing the design and functionality of next-generation skyrmion/antiskyrmion-based spintronic devices.

(Anti)skyrmion↗
DOE OSTI2011

Influence of nitrogen background pressure on structure of niobium nitride films grown by pulsed laser deposition

Depositions of niobium nitride thin films on Nb using pulsed laser deposition (PLD) with different nitrogen background pressures (10.7 to 66.7 Pa) have been performed. The effect of nitrogen pressure on NbN formation in this process was examined. The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), and energy dispersive X-ray (EDX) analysis. Hexagonal {beta}-Nb{sub 2}N and cubic {delta}-NbN phases resulted when growth was performed in low nitrogen background pressures. With an increase in nitrogen pressure, NbN films grew in single hexagonal {beta}-Nb{sub 2}N phase. The formation of the hexagonal texture during the film growth was studied. The c/a ratio of the hexagonal {beta}-Nb{sub 2}N unit cell parameter increases with increasing nitrogen pressure. Furthermore, the N:Nb ratio has a strong influence on the lattice parameter of the {delta}-NbN, where the highest value was achieved for this ratio was 1.19. It was found that increasing nitrogen background pressure leads to change in the phase structure of the NbN film. With increasing nitrogen pressure, the film structure changes from hexagonal to a mixed phase and then back to a hexagonal phase.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ultrasensitive Sub-monolayer Palladium Induced Chirality Switching and Topological Evolution of Skyrmions

Chiral spin textures are fundamentally interesting, with promise for device applications. Stabilizing chirality is conventionally achieved by introducing Dzyaloshinskii-Moriya interaction (DMI) in asymmetric multilayers, where the thickness of each layer is at least a few monolayers. Here we report an ultrasensitive chirality switching in (Ni/Co) n multilayer induced by capping with only 0.22 monolayer of Pd. Using spin-polarized low-energy electron microscopy, we monitor the gradual evolution of domain walls from left-handed to right-handed Néel walls and quantify the DMI induced by the Pd capping layer. We also observe the chiral evolution of a skyrmion during the DMI switching, where no significant topological protection is found as the skyrmion winding number varies. This corresponds to a minimum energy cost of <1 attojoule during the skyrmion chirality switching. Here, our results demonstrate the detailed chirality evolution within skyrmions during the DMI sign switching, which is relevant to practical applications of skyrmionic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Tunable Thermal Energy Transport across Diamond Membranes and Diamond–Si Interfaces by Nanoscale Graphoepitaxy

The development of electronic devices, especially those that involve heterogeneous integration of materials, has led to increased challenges in addressing their thermal operational temperature demands. The heat flow in these systems is significantly influenced or even dominated by thermal boundary resistance at the interface between dissimilar materials. However, controlling and tuning heat transport across an interface and in the adjacent materials has so far drawn limited attention. In this work, we grow chemical vapor-deposited diamond on silicon substrates by graphoepitaxy and experimentally demonstrate tunable thermal transport across diamond membranes and diamond–silicon interfaces. We observed the highest diamond–silicon thermal boundary conductance (TBC) measured to date and increased diamond thermal conductivity due to strong grain texturing in the diamond near the interface. Additionally, nonequilibrium molecular dynamics simulations and a Landauer approach are used to understand the diamond–silicon TBC. Further, these findings pave the way for tuning or increasing thermal conductance in heterogeneously integrated electronics that involve polycrystalline materials and will impact applications including electronics thermal management and diamond growth.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Sensitivity of Surface Flux Simulations to Hydrologic Parameters Based on an Uncertainty Quantification Framework Applied to the Community Land Model

Uncertainties in hydrologic parameters could have significant impacts on the simulated water and energy fluxes and land surface states, which will in turn affect atmospheric processes and the carbon cycle. Quantifying such uncertainties is an important step toward better understanding and quantification of uncertainty of integrated earth system models. In this paper, we introduce an uncertainty quantification (UQ) framework to analyze sensitivity of simulated surface fluxes to selected hydrologic parameters in the Community Land Model (CLM4) through forward modeling. Thirteen flux tower footprints spanning a wide range of climate and site conditions were selected to perform sensitivity analyses by perturbing the parameters identified. In the UQ framework, prior information about the parameters was used to quantify the input uncertainty using the Minimum-Relative-Entropy approach. The quasi-Monte Carlo approach was applied to generate samples of parameters on the basis of the prior pdfs. Simulations corresponding to sampled parameter sets were used to generate response curves and response surfaces and statistical tests were used to rank the significance of the parameters for output responses including latent (LH) and sensible heat (SH) fluxes. Overall, the CLM4 simulated LH and SH show the largest sensitivity to subsurface runoff generation parameters. However, study sites with deep root vegetation are also affected by surface runoff parameters, while sites with shallow root zones are also sensitive to the vadose zone soil water parameters. Generally, sites with finer soil texture and shallower rooting systems tend to have larger sensitivity of outputs to the parameters. Our results suggest the necessity of and possible ways for parameter inversion/calibration using available measurements of latent/sensible heat fluxes to obtain the optimal parameter set for CLM4. This study also provided guidance on reduction of parameter set dimensionality and parameter calibration framework design for CLM4 and other land surface models under different hydrologic and climatic regimes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Large anomalous Hall effect in the chiral-lattice antiferromagnet CoNb 3 S 6

An ordinary Hall effect in a conductor arises due to the Lorentz force acting on the charge carriers. In ferromagnets, an additional contribution to the Hall effect, the anomalous Hall effect (AHE), appears proportional to the magnetization. While the AHE is not seen in a collinear antiferromagnet, with zero net magnetization, recently it has been shown that an intrinsic AHE can be non-zero in non-collinear antiferromagnets as well as in topological materials hosting Weyl nodes near the Fermi energy. Here we report a large anomalous Hall effect with Hall conductivity of 27 Ω -1 cm -1 in a chiral-lattice antiferromagnet, CoNb 3 S 6 consisting of a small intrinsic ferromagnetic component (approximate to 0.0013 μ B per Co) along c-axis. This small moment alone cannot explain the observed size of the AHE. Finally, we attribute the AHE to either formation of a complex magnetic texture or the combined effect of the small intrinsic moment on the electronic band structure.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Titanium nitride: A new Ohmic contact material for n-type CdS

In devices based on CdS, indium is often used to make Ohmic contacts. Since indium is scarce and expensive, suitable replacement materials need to be found. In this work, we show that sputtered titanium nitride forms an Ohmic contact with n-type CdS. The CdS films, deposited with chemical bath deposition, have a hexagonal crystal structure and are polycrystalline, mostly with a (002) texture. The thickness of the films is {approx}600 nm, and the donor density is 1.9 x 10{sup 16} cm{sup -3}. The donor density increases to 1.5 x 10{sup 17} cm{sup -3} upon annealing. The contact resistivity of sputtered TiN on CdS is found to be 4.7 {+-} 0.6 {Omega} cm{sup 2}. This value is sufficiently small to avoid large resistive losses in most CdS device applications. To demonstrate the use of TiN in a CdS device, a Au/CdS/TiN Schottky diode was constructed. The diode has a potential barrier of 0.69 V and an ideality factor of 2.2.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Highest transmittance and high-mobility amorphous indium gallium zinc oxide films on flexible substrate by room-temperature deposition and post-deposition anneals

Amorphous indium gallium zinc oxide (a-IGZO) thin films of the highest transmittance reported in literature were initially deposited onto flexible polymer substrates at room temperature. The films were annealed in vacuum, air, and oxygen to enhance their electrical and optical performances. Electrical and optical characterizations were done before and after anneals. A partial reversal of the degradation in electrical properties upon annealing in oxygen was achieved by subjecting the films to subsequent vacuum anneals. A model was developed based on film texture and structural defects which showed close agreement between the measured and calculated carrier mobility values at low carrier concentrations (2-6 x 10{sup 19} cm{sup -3}).

36 MATERIALS SCIENCE↗
DOE OSTI2011

An evolutionary yield function based on Barlat 2000 yield function for the superconducting niobium sheet

Superconducting radio frequency (SRF) niobium cavities are widely used in high-energy physics to accelerate particle beams in particle accelerators. The performance of SRF cavities is affected by the microstructure and purity of the niobium sheet, surface quality, geometry, etc. Following optimum strain paths in the forming of these cavities can significantly control these parameters. To select these strain paths, however, information about the mechanical behavior, microstructure, and formability of the niobium sheet is required. In this study the Barlat 2000 yield function has been used as a yield function for high purity niobium. Results from this study showed that, due to intrinsic behavior, it is necessary to evolve the anisotropic coefficients of Barlat's yield function in order to properly model the plastic behavior of the niobium sheet. The accuracy of the newly developed evolutionary yield function was verified by applying it to the modeling of the hydrostatic bulging of the niobium sheet. Also, in a separate attempt crystal plasticity finite element method was use to model the behavior of the polycrystalline niobium sheet with a particular initial texture.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Characterization and control of crystal nucleation in amorphous electron beam evaporated silicon for thin film solar cells

The kinetics of crystal nucleation in high-rate electron beam evaporated amorphous Si for polycrystalline thin film solar cells was systematically studied on SiN and selected ZnO:Al-coated glass substrates with dissimilar surface topographies by employing Raman spectroscopy, transmission electron microscopy, and optical microscopy. The influence of the surface topography of the substrate and the disorder of the deposited amorphous Si could be correlated to the respective characteristics of the transient and steady state regime of the nucleation rate. The steady state nucleation rate I{sub ss}, its corresponding activation energy E{sub Iss}, and consequently the size of the grains in the crystallized Si were found to be governed by the interplay between the surface roughness and the deposition temperature. The steady state nucleation rate I{sub ss} increased gradually upon increasing the substrate roughness, while lowering the deposition temperature of the amorphous Si on rough textures resulted in a decline of I{sub ss}. The time-lag {tau}, which represents a distinctive parameter for the transient regime, was only slightly affected by the substrate topography. The deposition temperature, however, had a significant influence on {tau}, with {tau} increasing by a factor of 8 upon lowering the deposition temperature from 300 to 200 deg. C for all substrate topographies. These characteristics could be correlated with the increasing structural disorder of the deposited a-Si upon decreasing the deposition temperature. Based on this analysis, we could determine design rules for the controlled preparation of large-grained poly-Si in minimized processing time on any of the used substrate types by individually adjusting the deposition temperature and implementing nucleation layers.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Tunning of microstructure and thermoelectric properties of Ca{sub 3}Co{sub 4}O{sub 9} ceramics by high-magnetic-field sintering

The structural, magnetic, electrical, and thermal transport properties of Ca{sub 3}Co{sub 4}O{sub 9} ceramics sintered under high magnetic field were investigated. Crystal grain texturing and densification were achieved through cold-pressing and high-magnetic-field sintering techniques. The c-axis of the layered crystal grain was partly oriented along the c-axis of the pressed samples via a cold-pressing technique, and the degree of orientation was further increased while applying the magnetic field in the sample sintering progress. The easy magnetization axis of Ca{sub 3}Co{sub 4}O{sub 9} polycrystalline ceramics was found to be the c-axis. The room-temperature resistivity along the ab-plane of the sample sintered under 8 T magnetic field was about 30% smaller than that of the sample sintered without magnetic field, and the Seebeck coefficient of the former reached 177.7 {mu}V/K at the room temperature, which is about 50% larger than that of the latter. Consequently, for the sample sintered at 8 T magnetic field, the power factor along the ab-plane was enhanced by about 1.8 times compared to the sample without magnetic field sintering. The obtained result is suggested to originate from the variations of the carrier mobility and spin-orbital degeneracy due to high-magnetic-field sintering in the progress of the sample preparation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Well-isolated L1{sub 0} FePt-SiN{sub x}-C nanocomposite films with large coercivity and small grain size

FePt-SiN{sub x}-C films on TiN/CrRu/glass substrate with large coercivity, (001) texture, and small isolated grains were obtained by co-sputtering FePt, Si{sub 3}N{sub 4}, and C targets at 380 deg. C. It was found that when C was doped into the FePt-SiN{sub x} films, the out-of-plane coercivity increased while the small in-plane coercivity remained unchanged. Grain size decreased and grain size distribution became more uniform with increasing the C doping concentration. The x-ray photoelectron spectroscopy (XPS) depth profile showed a uniform depth distribution of Si in the FePt layer. The Si2p XPS spectrum implied the existence of Fe-Si bonds, indicating that SiN{sub x} was located at the FePt grain boundaries and was stable against diffusion to the surface, thus favoring grain isolation. Well-isolated FePt (001) granular films with coercivity higher than 21.5 kOe and an average grain size of 5.6 nm were obtained by doping 40 vol. % of SiN{sub x} and 20 vol. % of C.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Columnar grain growth of FePt(L1{sub 0}) thin films

An experimental approach for obtaining perpendicular FePt-SiOx thin films with a large height to diameter ratio FePt(L1{sub 0}) columnar grains is presented in this work. The microstructure for FePt-SiOx composite thin films as a function of oxide volume fraction, substrate temperature, and film thickness is studied by plan view and cross section TEM. The relations between processing, microstructure, epitaxial texture, and magnetic properties are discussed. By tuning the thickness of the magnetic layer and the volume fraction of oxide in the film at a sputtering temperature of 410 deg. C, a 16 nm thick perpendicular FePt film with {approx}8 nm diameter of FePt grains was obtained. The height to diameter ratio of the FePt grains was as large as 2. Ordering at lower temperature can be achieved by introducing a Ag sacrificial layer.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Observation and simulation of hard x ray photoelectron diffraction to determine polarity of polycrystalline zinc oxide films with rotation domains

X ray photoelectron diffraction (XPD) patterns of polar zinc oxide (ZnO) surfaces were investigated experimentally using hard x rays and monochromatized Cr K{alpha} radiation and theoretically using a cluster model approach and a dynamical Bloch wave approach. We focused on photoelectrons emitted from the Zn 2p{sub 3/2} and O 1s orbitals in the analysis. The obtained XPD patterns for the (0001) and (0001) surfaces of a ZnO single crystal were distinct for a given emitter and polarity. Polarity determination of c-axis-textured polycrystalline ZnO thin films was also achieved with the concept of XPD, even though the in-plane orientation of the columnar ZnO grains was random.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Tailoring interfacial exchange coupling with low-energy ion beam bombardment: Tuning the interface roughness

By ascertaining NiO surface roughness in a Ni{sub 80}Fe{sub 20}/NiO film system, we were able to correlate the effects of altered interface roughness from low-energy ion-beam bombardment of the NiO layer and the different thermal instabilities in the NiO nanocrystallites. From experiment and by modelling the temperature dependence of the exchange bias field and coercivity, we have found that reducing the interface roughness and changing the interface texture from an irregular to striped conformation enhanced the exchange coupling strength. Our results were in good agreement with recent simulations using the domain state model that incorporated interface mixing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Epitaxial growth of Ti{sub 3}SiC{sub 2} thin films with basal planes parallel or orthogonal to the surface on {alpha}-SiC

The growth of Ti{sub 3}SiC{sub 2} thin films were studied onto {alpha}-SiC substrates differently oriented by thermal annealing of TiAl layers deposited by magnetron sputtering. For any substrate's orientation, transmission electron microscopy coupled with x-ray diffraction showed the coherent epitaxial growth of Ti{sub 3}SiC{sub 2} films along basal planes of SiC. Specifically for the (1120) 4H-SiC, Ti{sub 3}SiC{sub 2} basal planes are found to be orthogonal to the surface. The continuous or textured nature of Ti{sub 3}SiC{sub 2} films does not depend of the SiC stacking sequence and is explained by a step-flow mechanism of growth mode. The ohmic character of the contact was confirmed by current-voltage measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Introduction to mathematical models and methods

Some well known mathematical models in the form of partial differential equations representing real world systems are introduced along with fundamental concepts of Image Processing. Notions such as seismic texture, seismic attributes, core data, well logging, seismic tomography and reservoirs simulation are discussed.

58 GEOSCIENCES↗
DOE OSTI2012

Enhanced thermal conductivity of polycrystalline aluminum nitride thin films by optimizing the interface structure

The growth-temperature dependency and interface structure effects on the thermal conductivity of the highly textured AlN thin films on (001) Si substrates were systematically studied by characterizing the crystal structures, surface morphologies, interface structures, chemical compositions, and thermal conductivity using x-ray diffraction analysis, atomic force microscopy, high resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and 3-omega method, respectively. By optimizing the interface microstructure and the growth temperature, thermal conductivity of polycrystalline AlN thin films can be greatly enhanced from 9.9 to 26.7 W/mK, when the growth temperature increases from 330 to 560 Degree-Sign C. This achievement is considered to be associated with the diminishment of the amorphous and disordered layer at the AlN/Si interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗