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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Current advances on Talbot–Lau x-ray imaging diagnostics for high energy density experiments (invited)

Talbot–Lau x-ray interferometry is a refraction-based diagnostic that can map electron density gradients through phase-contrast methods. The Talbot–Lau x-ray deflectometry (TXD) diagnostics have been deployed in several high energy density experiments. To improve diagnostic performance, a monochromatic TXD was implemented on the Multi-Tera Watt (MTW) laser using 8 keV multilayer mirrors (Δθ/θ = 4.5%-5.6%). Copper foil and wire targets were irradiated at 10 14 –10 15 W/cm 2 . Laser pulse length (~10 to 80 ps) and backlighter target configurations were explored in the context of Moiré fringe contrast and spatial resolution. Foil and wire targets delivered increased contrast <30%. The best spatial resolution (<6 μm) was measured for foils irradiated 80° from the surface. Further TXD diagnostic capability enhancement was achieved through the development of advanced data postprocessing tools. The Talbot Interferometry Analysis (TIA) code enabled x-ray refraction measurements from the MTW monochromatic TXD. Additionally, phase, attenuation, and dark-field maps of an ablating x-pinch load were retrieved through TXD. The images show a dense wire core of ~60 μm diameter surrounded by low-density material of ~40 μm thickness with an outer diameter ratio of ~2.3. Attenuation at 8 keV was measured at ~20% for the dense core and ~10% for the low-density material. Instrumental and experimental limitations for monochromatic TXD diagnostics are presented. Enhanced postprocessing capabilities enabled by TIA are demonstrated in the context of high-intensity laser and pulsed power experimental data analysis. Significant advances in TXD diagnostic capabilities are presented. Furthermore, these results inform future diagnostic technique upgrades that will improve the accuracy of plasma characterization through TXD.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Tunable Magnetic and Optical Anisotropy in ZrO 2 ‐Co Vertically Aligned Nanocomposites

Abstract Metamaterials have gained great research interest in recent years owing to their potential for property tunability, multifunctionality, and property coupling. As a new group of self‐assembled thin films, vertically aligned nanocomposite (VAN)‐based hybrid metamaterials have been demonstrated with significant anisotropic physical properties and a broad range of property tailorability, such as optical anisotropy, magnetic anisotropy, hyperbolic dispersion, and enhanced second harmonic generation properties. Herein, self‐assembled ZrO 2 ‐Co nanocomposite films, with high epitaxial quality and ultra‐fine vertically aligned Co nanopillars (with an average diameter of ≈2 nm) embedded in a ZrO 2 matrix, are fabricated using a pulsed laser deposition (PLD) method. The Co pillar density can be effectively tuned by varying the Co concentration in the target, which results in tunable optical properties and magnetic properties. Specifically, a high saturation magnetization of 100 emu cm −3 , strong out‐of‐plane magnetic anisotropy and tailorable magnetization properties are achieved via tuning the Co nanopillar density. Coupled with hyperbolic dispersion of dielectric constant from 950 to 1500 nm in wavelength, plasmonic Co metal nanopillars, and the unique dielectric ZrO 2 matrix, this new nanoscale hybrid metamaterial shows great potential for future integrated optical and magnetic device designs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Novel Poly-Si:Ga/SiOx Passivating Contacts through Non-Equilibrium Doping

Poly-Si/SiOx passivating contacts are one of the key enablers for high-efficiency, low-cost c-Si solar cells. In recent years, record devices have reached efficiencies of 26% in the laboratory and 25% in the industry. The current cell structure utilizing a tunneling oxide passivating contact structure with a back phosphorus-doped poly- Si/SiOx passivating contact and a front boron diffused emitter suffers from large emitter recombination. Thus, replacing the front B diffused emitter with a p-type passivating contact is a route to overcome this deficiency. This gives rise to front/back poly-Si based passivating contacts. To address the low passivation performance of the B-doped poly-Si passivating contacts, we replace B with Ga as a novel p-type dopant to avoid dopant accumulation in the tunneling oxide, which is known to lead to large degradation loss in passivation quality. Here, we introduce a non-equilibrium method via pulsed laser melting to thermally melt and recrystallize the poly-Si and redistribute the dopants, achieving doping concentrations above the solid solubility limit (~4E19 cm-3). We demonstrate a good passivation quality with an iVoc of 721 mV with an active Ga doping concentration in poly-Si >1020 cm-3. Furthermore, we show a low contact resistivity of 33.2 +/- 9.3 mO cm2 using a diode model calculation. Finally, cross-section scanning spreading resistance microscopy was performed to determine the resistance profile across the non-homogeneously doped poly-Si layer.

c-Si↗
DOE OSTI2024

Nanoporous Carbon Coatings Direct Li Electrodeposition Morphology and Performance in Li Metal Anode Batteries

Li metal anodes could significantly improve battery energy density. However, Li generally electrodeposits in poorly controlled morphology, leading to safety and performance problems. One factor that controls Li anode performance and electrodeposition morphology is the nature of the electrolyte–current collector interface. Herein, we modify the Cu current collector interface by depositing precisely controlled nanoporous carbon (NPC) coatings using pulsed laser deposition to develop an understanding of how NPC coating density and thickness impact Li electrodeposition. We find that NPC density and thickness guide Li morphological evolution differently and dictate whether Li deposits at the NPC-Cu or NPC-electrolyte interface. NPC coatings generally lower overpotential for Li electrodeposition, though thicker NPC coatings limit kinetics when cycling at a high rate. Lower-density NPC enables the highest Coulombic efficiency (CE) during calendar aging tests, and higher-density NPC enables the highest CE during cycling tests.

25 ENERGY STORAGE↗
NASA NTRS1974

Analytical studies of ultrashort optical pulse propagation in a resonant absorbing medium

Resonant absorption in a laser pulse can be reduced to zero if the trailing part induces stimulated emission and returns the absorbed energy back to the pulse. This kind of effect is called Self-Induced Transparency (SIT). Analytic descriptions of short pulse propagation in a resonant medium, based on Slowly Varying Envelope Approximation (SVEA) and in linear media, have been extended in studies of SIT along two principal directions: First, to improve the SVEA by introducing Short Pulse Approximation (SPA); and second, to consider the effect of nonlinear refractive index.

Lee, C. T.↗
NASA NTRS1975

Satellite laser ranging work at the Goddard Space Flight Center

The pulsed-laser satellite ranging systems presently being operated by the Goddard Space Flight Center are described along with their range and accuracy capabilities. The major subsystems are outlined, operation of the fixed system and the two mobile systems is discussed, and the performance of all three systems is evaluated. It is noted that these systems have an accuracy of better than 10 cm on a carefully surveyed range as well as in regular satellite ranging operations and are capable of ranging to all currently launched retroreflector-equipped satellites with the exception of Timation III. Future improvements discussed include a third mobile system which will be able to range distant satellites, such as Timation III, with an accuracy of better than 5 cm and the use of a frequency-doubled Nd:YAG laser in place of the ruby lasers now being employed.

Mcgunigal, T. E.↗
NASA NTRS1988

Laser action in chromium-doped forsterite

This paper reports on pulsed laser operation obtained in chromium-activated forsterite Cr(3+):Mg2SiO4 at room temperature. The spectrum of the free-running laser peaks at 1235 nm and a bandwidth of about 22 nm. The spectral range of the laser emission is expected to extend from 850 to 1300, provided the parasitic impurity absorption may be minimized by improved crystal growth techique.

Petricevic, V.↗
DOE OSTI2020

Epitaxial stabilization of ultra thin films of high entropy perovskite

High entropy oxides (HEOs) are a class of materials, containing equimolar portions of five or more transition metal and/or rare-earth elements. We report here about the layer-by-layer growth of HEO [(La 0.2 Pr 0.2 Nd 0.2 Sm 0.2 Eu 0.2 )NiO 3 ] thin films on NdGaO 3 substrates by pulsed laser deposition. The combined characterizations with in situ reflection high energy electron diffraction, atomic force microscopy, and x-ray diffraction affirm the single crystalline nature of the film with smooth surface morphology. The desired +3 oxidation of Ni has been confirmed by an element sensitive x-ray absorption spectroscopy measurement. Temperature dependent electrical transport measurements revealed a first order metal-insulator transition with the transition temperature very similar to the undoped NdNiO 3 . Furthermore, since both these systems have a comparable tolerance factor, this work demonstrates that the electronic behaviors of A-site disordered perovskite-HEOs are primarily controlled by the average tolerance factor.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanoporous Titanium (Oxy)nitride Films as Broadband Solar Absorbers

Broadband absorption of solar light is a key aspect in many applications that involve an efficient conversion of solar energy to heat. Titanium nitride (TiN)-based materials, in the form of periodic arrays of nanostructures or multilayers, can promote significant heat generation upon illumination thanks to their efficient light absorption and refractory character. In this work, pulsed laser deposition was chosen as a synthesis technique to shift metallic bulk-like TiN to nanoparticle-assembled hierarchical oxynitride (TiO x N y ) films by increasing the background gas deposition pressure. The nanoporous hierarchical films exhibit a tree-like morphology, a strong broadband solar absorption (~90% from the UV to the near-infrared range), and could generate temperatures of ~475 °C under moderate light concentration (17 Suns). The high heat generation achieved by treelike films is ascribed to their porous morphology, nanocrystalline structure, and oxynitride composition, which overall contribute to a superior light trapping and dissipation to heat. These properties pave the way for the implementation of such films as solar absorber structures.

14 SOLAR ENERGY↗
DOE OSTI2021

Effects of Sn substitution in SrRuO 3 epitaxial films

Epitaxial SrRu 1–x Sn x O 3 (0 ≤ x ≤ 1) thin films were deposited on SrTiO 3 (001) substrates by sequential two-target synthesis using pulsed laser deposition to achieve stable phases in this family of quaternary perovskites. The SrRu 1–x Sn x O 3 films exhibit a good crystalline quality, a sharp interface between film and substrate, and an atomically smooth surface. A gradual expansion of the c-axis lattice parameter was observed with Sn doping serving as a means to tune chemical pressure and magnetism. With an increase in Sn doping, the resistivity of the film increased, and the ferromagnetism decreased. These results illustrate use of lattice engineering, e.g., tuning of c-axis lattice parameter with chemical doping, to control electronic and magnetic properties of epitaxial thin films for applications in oxide electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Many routes to ferroelectric HfO 2 : A review of current deposition methods

Although 10 years have passed since the initial report of ferroelectricity in hafnia (HfO 2 ), researchers are still intensely fascinated by this material system and the promise it holds for future applications. A wide variety of deposition methods have been deployed to create ferroelectric HfO 2 thin films such as atomic layer deposition, chemical solution deposition, and physical vapor deposition methods such as sputtering and pulsed laser deposition. Process and design parameters such as deposition temperature, precursor choice, target source, vacuum level, reactive gases, substrate strain, and many others are often integral in stabilizing the polar orthorhombic phase and ferroelectricity. We examine processing parameters across four main different deposition methods and their effect on film microstructure, phase evolution, defect concentration, and resultant electrical properties. The goal of this review is to integrate the process knowledge collected over the past 10 years in the field of ferroelectric HfO 2 into a single comprehensive guide for the design of future HfO 2 -based ferroelectric materials and devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Aspects of the synthesis of thin film superconducting infinite-layer nickelates

The recent observation of superconductivity in Nd 0.8 Sr 0.2 NiO 2 calls for further investigation and optimization of the synthesis of this infinite-layer nickelate structure. Here, we present our current understanding of important aspects of the growth of the parent perovskite compound via pulsed laser deposition on SrTiO 3 (001) substrates and the subsequent topotactic reduction. We find that to achieve single-crystalline, single-phase superconducting Nd 0.8 Sr 0.2 NiO 2 , it is essential that the precursor perovskite Nd 0.8 Sr 0.2 NiO 3 thin film is stabilized with no visible impurity phases; in particular, a Ruddlesden–Popper-type secondary phase is often observed. We have further investigated the evolution of the soft-chemistry topotactic reduction conditions to realize full transformation to the infinite-layer structure with no film decomposition or formation of other phases. We find that capping the nickelate film with a subsequent SrTiO 3 layer provides an epitaxial template to the top region of the nickelate film, much like the substrate. Thus, for currently optimized growth conditions, we can stabilize superconducting single-phase Nd 0.8 Sr 0.2 NiO 2 (001) epitaxial thin films up to ~10 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Vertically Aligned Single-Crystalline CoFe 2 O 4 Nanobrush Architectures with High Magnetization and Tailored Magnetic Anisotropy

Micrometer-tall vertically aligned single-crystalline CoFe 2 O 4 nanobrush architectures with extraordinarily large aspect ratio have been achieved by the precise control of a kinetic and thermodynamic non-equilibrium pulsed laser epitaxy process. Direct observations by scanning transmission electron microscopy reveal that the nanobrush crystal is mostly defect-free by nature, and epitaxially connected to the substrate through a continuous 2D interface layer. In contrast, periodic dislocations and lattice defects such as anti-phase boundaries and twin boundaries are frequently observed in the 2D interface layer, suggesting that interface misfit strain relaxation under a non-equilibrium growth condition plays a critical role in the self-assembly of such artificial architectures. Further, magnetic property measurements have found that the nanobrushes exhibit a saturation magnetization value of 6.16 μB/f.u., which is much higher than the bulk value. The discovery not only enables insights into an effective route for fabricating unconventional high-quality nanostructures, but also demonstrates a novel magnetic architecture with potential applications in nanomagnetic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Epitaxial Stabilization and Oxygen Evolution Reaction Activity of Metastable Columbite Iridium Oxide

Non-rutile polymorphs of binary iridium oxide such as columbite IrO 2 (α-IrO 2 ) are promising candidates for highly active acid-stable oxygen evolution reaction (OER) catalysts, yet their synthesis has been challenging due to the dominant thermodynamic stability of rutile IrO 2 (R-IrO 2 ). Here, we report the growth of α-IrO 2 via epitaxial thin films using pulsed laser deposition. We observe that, in competition with R-IrO 2 (100), the films can be optimized to be predominantly (100)-oriented α-IrO 2 . Surprisingly, the activity of α-IrO 2 shows a large discrepancy of ~0.2 V in the overpotential compared to its predicted activity, which is resolved via theoretical calculations to be a crystal orientation effect. This demonstrates that the electrocatalytic activity can be significantly varied upon crystal orientation, a parameter that is difficult to control in conventional polycrystalline systems but accessible in epitaxial thin films. In total, this study demonstrates epitaxial thin film growth as a powerful technique, which can overcome large energetic instabilities on the order of ~300 meV to stabilize metastable material structures inaccessible by bulk synthesis. As a result, this provides unique opportunities to effectively identify the atomic structure of active catalysts by combining investigations of metastable materials with theoretical predictions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Unravelling the room temperature growth of two-dimensional h-BN nanosheets for multifunctional applications

The room temperature growth of two-dimensional van der Waals (2D-vdW) materials is indispensable for state-of-the-art nanotechnology. Low temperature growth supersedes the requirement of elevated growth temperatures accompanied with high thermal budgets. Moreover, for electronic applications, low or room temperature growth reduces the possibility of intrinsic film-substrate interfacial thermal diffusion related deterioration of the functional properties and the consequent deterioration of the device performance. Here, we demonstrated the growth of ultrawide-bandgap boron nitride (BN) at room temperature by using the pulsed laser deposition (PLD) process, which exhibited various functional properties for potential applications. Comprehensive chemical, spectroscopic and microscopic characterizations confirmed the growth of ordered nanosheet-like hexagonal BN (h-BN). Functionally, the nanosheets show hydrophobicity, high lubricity (low coefficient of friction), and a low refractive index within the visible to near-infrared wavelength range, and room temperature single-photon quantum emission. In conclusion, our work unveils an important step that brings a plethora of potential applications for these room temperature grown h-BN nanosheets as the synthesis can be feasible on any given substrate, thus creating a scenario for “h-BN on demand” under a frugal thermal budget.

2D h-BN↗
DOE OSTI2025

Online Bayesian State Estimation for Real-Time Monitoring of Growth Kinetics in Thin Film Synthesis

Rapid validation of newly predicted materials through autonomous synthesis requires real-time adaptive control methods that exploit physics knowledge, a capability that is lacking in most systems. Here, in this study, we demonstrate an approach to enable real-time control of thin film synthesis by combining in situ optical diagnostics with a Bayesian state estimation method. We developed a physical model for film growth and applied the direct filter (DF) method for real-time estimation of nucleation and growth rates during pulsed laser deposition (PLD). We validated the approach using simulated and experimental reflectivity data for WSe 2 growth and ultimately deployed the algorithm on an autonomous PLD system during the growth of 1T'-MoTe 2 . The DF robustly estimates growth parameters in real time at early stages of growth, down to 15% monolayer area coverage. This fusion of in situ diagnostics, data assimilation, and physical modeling opens new opportunities in adaptive control of synthesis trajectories toward desired material states.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Low Energy Implantation into Transition-Metal Dichalcogenide Monolayers to Form Janus Structures

Atomically-thin two-dimensional (2D) materials face significant energy barriers for synthesis and processing into functional metastable phases such as Janus structures. Here, in this study, the controllable implantation of hyperthermal species from pulsed laser deposition (PLD) plasmas is introduced as a top-down method to compositionally engineer 2D monolayers. The kinetic energies of Se clusters impinging on suspended monolayer WS 2 crystals were controlled in the <10 eV/atom range with in situ plasma diagnostics to determine the thresholds for selective top layer replacement of sulfur by selenium for the formation of high quality WSSe Janus monolayers at low (300 °C) temperatures, and bottom layer replacement for complete conversion to WSe 2 . Atomic-resolution electron microscopy and spectroscopy in tilted geometry confirm the WSSe Janus monolayer. Molecular dynamics simulations reveal that Se clusters implant to form disordered metastable alloy regions, which then recrystallize to form highly ordered structures, opening the door for low-energy implantation by PLD as a novel method to explore the synthesis of 2D Janus layers and alloys of variable composition.

2D materials↗