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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Optimization of three-dimensional metamaterials for terahertz energy harvesting

This work focuses on finite element modeling (FEM) of a three-dimensional metamaterial used as an absorber for terahertz energy harvesting. The metamaterial consists of patterned pillars of an SU-8 dielectric photoresist coupled to a copper metal overlayer. Here, our study shows that the electromagnetic performance of the metamaterial is dependent on the following characteristic design parameters of the SU-8 dielectric: pillar height, bottom side length, and spacing between adjacent pillars. Using FEM, the metamaterial geometry is successfully optimized and the surface plasmon can be tuned to a peak frequency of 1.2 THz and a maximum terahertz absorption amplitude of 30%.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of processing parameters on the morphologies of complex sesquioxide thin films

Controlling and predicting the morphology of lanthanide sesquioxides in thin film form is vital to their use in current applications. In the present study, single and codeposited Sm2O3, Er2O3, and Lu2O3 thin films were grown on yttria-stabilized zirconia (8%) substrates by radio frequency magnetron sputtering at room temperature and 500 °C. The effect of two different substrate temperatures and altering the oxide cation on the structural and morphological properties of the films was analyzed. The thin films were characterized by profilometry, scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The single-component Lu2O3 and Sm2O3 films obtained were of the cubic phase, and the Er2O3 was a mix of cubic and monoclinic phases. It was observed for both the Er2O3 and Lu2O3 films that increasing the substrate temperature to 500 °C resulted in larger grained polycrystalline films. In contrast, large grained polycrystalline films were obtained at both room temperature and 500 °C for Sm2O3 and uneven granularity increased as temperature increased. Codeposition of Lu2O3 and Sm2O3, and Lu2O3 and Er2O3 resulted in a cubic bixbyite phase (the C phase of the lanthanide sesquioxide) solid solution. It was observed that the structure and morphology of the films can be controlled by manipulating deposition parameters. Both substrate temperature and altering the oxide cation contributed to changes in crystallinity and grain structure, which can modify the chemical and physical properties of the films for their applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomic layer deposition of MoO x thin films using Mo( i PrCp) 2 H 2 and O 3

Here, this work studied the growth of molybdenum oxide thin films with thermal atomic layer deposition (ALD) using Mo(iPrCp)2H2 and O3 as precursors. Growth parameters were determined by varying growth temperature and precursor dose times. ALD growth was exhibited in a temperature range of 100–200 °C. The growth per cycle ranged from 1.3 to 1.7 Å/cycle with a standard uniformity parameter of <5%. Attempts to grow films using H2O as an oxygen source showed no significant growth. Film properties were measured using spectroscopic ellipsometry, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Remote heteroepitaxy of GaN microrod heterostructures for deformable light-emitting diodes and wafer recycle

There have been rapidly increasing demands for flexible lighting apparatus, and micrometer-scale light-emitting diodes (LEDs) are regarded as one of the promising lighting sources for deformable device applications. Herein, we demonstrate a method of creating a deformable LED, based on remote heteroepitaxy of GaN microrod (MR) p - n junction arrays on c -Al 2 O 3 wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution scanning transmission electron microscopy, and the density functional theory simulations clarify how the remote heteroepitaxy is made possible through graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Knots are not for naught: Design, properties, and topology of hierarchical intertwined microarchitected materials

Lightweight and tough engineered materials are often designed with three-dimensional hierarchy and interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. We introduce a previously unexplored class of architected materials, whose components are interwoven and contain no junctions, and incorporate micro-knots as building blocks within these hierarchical networks. Tensile experiments, which show close quantitative agreements with an analytical model for overhand knots, reveal that knot topology allows a new regime of deformation capable of shape retention, leading to a ~92% increase in absorbed energy and an up to ~107% increase in failure strain compared to woven structures, along with an up to ~11% increase in specific energy density compared to topologically similar monolithic lattices. Our exploration unlocks knotting and frictional contact to create highly extensible low-density materials with tunable shape reconfiguration and energy absorption capabilities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thin film design of amorphous hafnium oxide nanocomposites enabling strong interfacial resistive switching uniformity

A design concept of phase-separated amorphous nanocomposite thin films is presented that realizes interfacial resistive switching (RS) in hafnium-oxide-based devices. The films are formed by incorporating an average of 7% Ba into hafnium oxide during pulsed laser deposition at temperatures ≤400°C. The added Ba prevents the films from crystallizing and leads to ~20-nm-thin films consisting of an amorphous HfO x host matrix interspersed with ~2-nm-wide, ~5-to-10-nm-pitch Ba-rich amorphous nanocolumns penetrating approximately two-thirds through the films. This restricts the RS to an interfacial Schottky-like energy barrier whose magnitude is tuned by ionic migration under an applied electric field. Resulting devices achieve stable cycle-to-cycle, device-to-device, and sample-to-sample reproducibility with a measured switching endurance of ≥10 4 cycles for a memory window ≥10 at switching voltages of ±2 V. Each device can be set to multiple intermediate resistance states, which enables synaptic spike-timing–dependent plasticity. The presented concept unlocks additional design variables for RS devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy’s behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m 1/2 , which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Deep Learning and Structural Imaging of Materials

Deep learning has had a transformative effect on numerous domains and is actively utilized by many scientists in data-intensive fields such as high-energy physics and cosmology. Materials science, and in particular, the structural imaging of materials with electrons and X-rays are projected to enter the age of scientific data torrents, positioning them as new application spaces for modern artificial intelligence. In this contribution, we provide a synopsis on the foundations and latest progress in deep learning and present an in-depth application of utilizing modern deep artificial neural networks in scanning transmission electron microscopy to extract structural material properties. We use this case study to expose the strengths of deep learning-based models and discuss their current limitations, in the process highlighting their potential use in other data-intensive structural imaging modalities.

Laanait, Nouamane↗
DOE OSTI2023

Engineered Wood: Sustainable Technologies and Applications

Natural wood has been used for construction, fuel, and furniture for thousands of years because of its versatility, renewability, and aesthetic appeal. However, new opportunities for wood are arising as researchers have developed ways to tune the material's optical, thermal, mechanical, and ionic transport properties by chemically and physically modifying wood's naturally porous structure and chemical composition. Such modifications can be used to produce sustainable, functional materials for various emerging applications such as automobiles, construction, energy storage, and environmental remediation. In this review, we highlight recent advancements in engineered wood for sustainable technologies, including thermal and light management, environmental remediation, nanofluidics, batteries, and structural materials with high strength-to-weight ratios. Additionally, the current challenges, opportunities, and future of wood research are discussed, providing a guideline for the further development of next-generation, sustainable wood-based materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Vertical nanoscale strain-induced electronic localization in epitaxial La2/3Sr1/3MnO3 films with ZrO2 nanopillar inclusions

Abstract Unusual electrical transport properties associated with weak or strong localization are sometimes found in disordered electronic materials. Here, we report experimental observation of a crossover of electronic behavior from weak localization to enhanced weak localization due to the spatial influence of disorder induced by ZrO 2 nanopillars in (La 2/3 Sr 1/3 MnO 3 ) 1− x :(ZrO 2 ) x ( x = 0, 0.2, and 0.3) nanocomposite films. The spatial strain regions, identified by scanning transmission electron microscopy and high-resolution x-ray diffraction, induce a coexistence of two-dimentional (2D) and three-dimentional (3D) localization and switches to typical 2D localization with increasing density of ZrO 2 pillars due to length scale confinement, which interestingly accords with enhancing vertically interfacial strain. Based on the excellent agreement of our experimental results with one-parameter scaling theory of localization, the enhanced weak localization exists in metal range close to the fixed point. These films provide a tunable experimental model for studying localization in particular the transition regime by appropriate choice of the second epitaxial phase. Graphical Abstract

36 MATERIALS SCIENCE↗
DOE OSTI2021

Topological order of the Rys F-model and its breakdown in realistic square spin ice: Topological sectors of Faraday loops

Both the Rys F-model and antiferromagnetic square ice possess the same ordered, antiferromagnetic ground state, but the ordering transition is of second order in the latter, and of infinite order in the former. To tie this difference to topological properties and their breakdown, we introduce a Faraday lines representation where loops carry the energy and magnetization of the system. Because the F-model does not admit monopoles, its Faraday loops have distinct topological properties, absent in square ice, and which allow for a natural partition of its phase space into topological sectors. Then, the Néel temperature corresponds to a transition from topologically trivial to non-trivial Faraday loops. Because magnetization is a homotopy invariant of the Faraday loops, and it is zero for topologically trivial ones, the susceptibility is zero below a critical field. In square spin ice, instead, monopoles destroy the homotopy invariance and the parity distinction among loops, thus erasing this rich topological structure. Consequently, even trivial loops can be magnetized in square ice, and their susceptibility is never zero.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Pattern formation and transport for externally driven active matter on periodic substrates (a)

Abstract We investigate the transport of interacting active run-and-tumble particles moving under an external drift force through a periodic array of obstacles for increasing drive amplitudes. For high activity where the system forms a motility-induced phase-separated state, there are several distinct dynamic phases including a low drive pinned cluster phase, an intermediate uniform fluid, and a higher drive stripe crystal state. The transitions between the phases are correlated with signatures in the transport curves, differential mobility, and power spectra of the velocity fluctuations. In contrast, in the low activity regime the transport curves and power spectra undergo little change as a function of drive. We argue that in the high activity limit, the behavior is similar to that of driven solids on periodic substrates, while in the low activity limit the system behaves like a driven fluid.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Metasurface-based varifocal Alvarez lens at microwave frequencies

Lenses with a tunable focus are highly desirable but remain a challenge. Here, we demonstrate a microwave varifocal meta-lens based on the Alvarez lens principle, consisting of two mechanically movable tri-layer metasurface phase plates with reversed cubic spatial profiles. The manufactured multilayer Alvarez meta-lens enables microwave beam collimation/focusing at frequencies centered at 7.5 GHz, and shows one octave focal length tunability when transversely translating the phase plates by 8 cm. The measurements reveal a gain enhancement up to 15 dB, 3-dB beam width down to 3.5 ∘ , and relatively broad 3-dB bandwidth of 3 GHz. These advantageous characteristics, along with its simplicity, compactness, and lightweightness, make the demonstrated flat Alvarez meta-lens suitable for deployment in many microwave systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

SCHOTT laser glass [Invited]

Laser glass is a highly engineered optical material that enables the amplification of light in laser systems. It is known for being the heart of the largest laser facilities ever built, where thousands of neodymium-doped meter-sized slabs of laser glass create intense beams of near-infrared laser radiation used to study fusion reactions. Or if doped with ytterbium and erbium, laser glass can be made into millimeter-sized components empowering range-finders and dermatological lasers. Decades of development have poised laser glass for the next challenge on the horizon: amplifying light for sustainable inertial fusion energy power plants.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optical, electrical, and EPR studies of polycrystalline Al:Cr:ZnSe gain elements

Transition metal-doped II-VI (TM:II-VI) chalcogenides are well-known laser materials for optically pumped middle-infrared lasers. Cr:ZnSe is a key representative of this class of transition metal doped II-VI gain media and is arguably considered the material of choice for optically pumped middle-infrared lasers. In addition to effective mid-IR lasing under optical excitation, these crystals, being wide-band semiconductors, hold the potential for direct electrical excitation. One way to form n-type conductivity in ZnSe crystals is by annealing them in a melt of Zn-Al alloy. However, this annealing of Cr:ZnSe crystals results in their purification and transfer of chromium to the melt of Zn-Al alloy. In this article, we report on optimizing the doping technique for providing n-type conductivity in Al:Cr:ZnSe crystals while preserving the chromium concentration. Al:Cr:ZnSe samples with resistivities ranging from 10.8 to 992 Ω-cm were fabricated. While the 2 + valence state of Cr is typically dominant in Cr:ZnSe, both Cr 2+ and Cr + were detected in Al:Cr:ZnSe samples. The maximum level of Cr + concentration was measured to be 4 × 10 18 cm -3 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mid-infrared luminescence properties of erbium and dysprosium doped lanthanum titanate glasses

Glasses of composition x RE 2 O 3 -(17− x ) La 2 O 3 -83 TiO 2 were prepared by levitation melting from x = 0.1 to 9 for RE=Er and at x =0.1 and 1 for RE=Dy. The glasses have high transition temperature, exhibit low OH, and 1 mm thick discs are transparent out to 6 μ m. Mid-infrared emission lineshapes and lifetimes are comparable to what is seen in tellurite glasses containing Er 3+ and Dy 3+ . For x fixed at 1, the Er 3+ : 4 I 11/2 → 4 I 13/2 transition at 2716 nm has a fluorescence lifetime of 254 μ s and the Dy 3+ : 6 H 13/2 → 6 H 15/2 transition at 2957 nm has a fluorescence lifetime of 9.09 μ s. The results indicate that doped lanthanum titanate glasses offer the thermal stability of a ’hard’ glass with the host properties typically associated with ’soft’ glasses. Problems with the measurement of spectral features in the mid-infrared that could erroneously be assigned as resulting from rare-earth ion emissions are presented and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-dimensional quantum key distribution using orbital angular momentum of single photons from a colloidal quantum dot at room temperature

High-dimensional quantum key distribution (HDQKD) is a promising avenue to address the inherent limitations of basic quantum key distribution (QKD) protocols. However, experimental realizations of HDQKD to date have relied on indeterministic photon sources that limit the achievable key rate. In this paper, we demonstrate a full emulation of a HDQKD system using a single colloidal giant quantum dot (gQD) as a deterministic, compact, and room-temperature single-photon source (SPS). We demonstrate a practical protocol by encoding information in a high-dimensional space (d = 3) of the orbital angular momentum of the photons. Our experimental configuration incorporates two spatial light modulators for encoding and decoding the spatial information carried by individual photons. Our experimental demonstration establishes the feasibility of utilizing high radiative quantum yield gQDs as practical SPSs for HDQKD. We also experimentally demonstrate surpassing the traditional d = 2 QKD capacity with comparable error rates, indicating a significant improvement in performance while maintaining reliability.

36 MATERIALS SCIENCE↗