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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Effect of an oxide layer on high velocity impact of tantalum particles characterized using molecular dynamics

Micro-cold spray, also commonly referred to as the aerosol deposition method or vacuum kinetic spraying, is a process for depositing nanostructured films of metals and ceramics by impacting solid nanoparticles at high velocity onto a substrate at room temperature and at low pressures. Tantalum films deposited by micro-cold spray are desirable because tantalum is non-reactive to certain molten metals and can therefore serve as a non-reactive barrier coating. However, unlike most other metals deposited by micro-cold spray, tantalum quickly forms an oxide layer when exposed to air. In the deposition of films using traditional cold spray with much larger particles, native oxides must fracture for particle–substrate bonding to occur. Furthermore, the fraction of the particle that is oxidized in micro-cold spray and the strain rates experienced by the particles upon impact are both much larger than in cold spray, suggesting that the role of the oxide on film deposition may be distinct. The effect of this oxide layer on particle deformation and adherence to a substrate under high strain rates is studied using molecular dynamics simulations. The effect of oxide layer thickness, particle diameter, and impact velocity are examined.

42 ENGINEERING↗
DOE OSTI2023

HydroGEN Seedling: Monolithically Integrated Thin Film/Silicon Tandem Photoelectrodes for High-Efficiency and Stable Photoelectrochemical Water Splitting

In this project, we propose to develop monolithically integrated Si-based tandem photoelectrodes to achieve both high solar-to-hydrogen (STH) efficiency (>15%) and long-term stability (>1,000 hours) in spontaneous water splitting systems. The proposed tandem devices consist of a Ta 3 N 5 , BCTSSe, or In 0.5 Ga 0.5 N top junction, which has a bandgap of ~1.7-2.0 eV and can split the solar spectrum with the Si bottom junction. Ta 3 N 5 , BCTSSe, and InGaN will be grown/deposited on a low-resistivity nanowire tunnel junction on Si substrates using atomic layer deposition (ALD), sputtering, and molecular beam epitaxy (MBE), respectively. Both n and p-type Si solar wafers will be utilized, which can serve as the photoanode or photocathode, respectively. We will use N-rich GaN ultrathin passivation layers to protect photoelectrodes from corrosion and oxidation.

08 HYDROGEN↗
DOE OSTI2026

Materials Studies of Niobium Thin Films for Quantum Circuit Applications: Progress and Challenges

Niobium (Nb) films have emerged as a crucial material in the development of superconducting qubits, which are key components in quantum computing technology. Here, this review provides a comprehensive examination of Nb films from a materials perspective, focusing on their intrinsic properties, fabrication methods/techniques, and their influence on qubit performance, particularly through surface and interface driven loss mechanisms. We discuss the key material properties that are essential for qubit operation. Various deposition techniques for Nb thin films, such as sputtering, evaporation, molecular beam epitaxy, and atomic layer deposition, are explored, alongside their impact on film quality, uniformity, and qubit performance. Additionally, the influence of surface roughness, thin-film thickness, and substrate materials on quantum coherence is analyzed. Challenges such as defects and material degradation in Nb films are reviewed, along with strategies to mitigate these issues. Finally, we present the latest advancements and future directions in Nb film research, including potential improvements to enhance qubit coherence and scalability for large-scale quantum computing systems. Ultimately, a deeper understanding of surface and interface phenomena is essential for pushing the limits of qubit performance and realizing next-generation quantum technologies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Effect of different manufacturing methods on polyamide reverse-osmosis membranes for desalination: Insights from molecular dynamics simulations

Membranes are a key technology platform for a broad application of energy-efficient separations. To best serve the separation demands of industry, the manufacturing processes for these membranes are garnering increasing attention. In particular, for water desalination, the industry leading polyamide (PA) reverse osmosis (RO) membranes can be manufactured via molecular layer-by-layer (mLBL) deposition, interfacial polymerization (IP), and 3D-printing technique. However, the influence of different manufacturing methods on PA membrane’s properties is far from understood. Here, in this study, we present the high-pressure transport behavior of water and salt ions for PA membranes formed with IP, mLBL, and 3D-printing through non-equilibrium molecular dynamics simulations. Studies show that membranes fabricated with 3D-printing have similar performances to those manufactured using mLBL, quantified by water permeability, rejection of salt ions, structural integrity, and porosity features. However, the membranes formed with IP exhibit faster water transport, lower rejection, worse structural integrity, and more inhomogeneous network pores than those constructed using mLBL and 3D-printing. The unconnected water-accessible space governs water transport for PA membranes formed with mLBL and 3D-printing, which offers the impermanent open-closed pores that enable water to jump through PA membranes. In contrast, the permeated water-enterable space plays a prominent role in water movement across the PA membrane formed with IP, providing a continuous transport channel at high pressure. Importantly, we observe the more significant compaction features at high pressure for PA membranes formed with IP than mLBL and 3D printing. In short, these findings provide a comprehensive understanding of existing membrane preparation technologies. It also provides a guide for developing the new membrane preparation process at the molecular level.

3D-printing↗
DOE OSTI2023

Ceramic thin-film composite membranes with tunable subnanometer pores for molecular sieving

Abstract Ceramic membranes are a promising alternative to polymeric membranes for selective separations, given their ability to operate under harsh chemical conditions. However, current fabrication technologies fail to construct ceramic membranes suitable for selective molecular separations. Herein, we demonstrate a molecular-level design of ceramic thin-film composite membranes with tunable subnanometer pores for precise molecular sieving. Through burning off the distributed carbonaceous species of varied dimensions within hybrid aluminum oxide films, we created membranes with tunable molecular sieving. Specifically, the membranes created with methanol showed exceptional selectivity toward monovalent and divalent salts. We attribute this observed selectivity to the dehydration of the large divalent ions within the subnanometer pores. As a comparison, smaller monovalent ions can rapidly permeate with an intact hydration shell. Lastly, the flux of neutral solutes through each fabricated aluminum oxide membrane was measured for the demonstration of tunable separation capability. Overall, our work provides the scientific basis for the design of ceramic membranes with subnanometer pores for molecular sieving using atomic layer deposition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Atomic-Layer-Deposited Aluminum Oxide Thin Films Probed with X-ray Scattering and Compared to Molecular Dynamics and Density Functional Theory Models

A better understanding of amorphous aluminum oxide’s structure and electronic properties is obtained through combined experimental and computational approaches. Grazing incidence X-ray scattering measurements were carried out on aluminum oxide thin films grown using thermal atomic layer deposition. The corresponding pair distribution functions (PDFs) showed structures similar to previously reported PDFs of solid-state amorphous alumina and molten alumina. Structural models based on crystalline alumina polymorphs (PDFgui) and amorphous alumina (molecular dynamics, MD) were examined for structural comparisons to the experimental PDF data. Smaller MD models were optimized and verified against larger models to allow for quantum chemical electronic structure calculations. The electronic structure of the amorphous alumina models yields additional insight into the band structure and electronic defects present in amorphous alumina that are not present in crystalline samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A perspective on ordered vacancy compound and parent chalcopyrite thin film absorbers for photoelectrochemical water splitting

Chalcopyrites could fill the gap between the low-cost, poor-efficiency single junction metal oxide photoelectrochemical (PEC) water splitting cells and the high efficiency, yet costly III–V tandems. In this Perspective, we first review the key barriers that must be addressed by the community to enable economical chalcopyrite-based PEC water splitting. Then, we highlight how theoretical modeling can be used to identify promising ordered vacancy compound absorbers with improved energetics compared to their chalcopyrite parents. Finally, we describe how advanced spectroscopic analysis performed on chalcopyrite photocathodes after PEC testing uncovered a new passivation layer candidate for prolonged durability.

08 HYDROGEN↗
DOE OSTI2020

Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor

Two-dimensional nanoelectronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with ab initio calculations establish the large work function and narrow bands of α-RuCl 3 enable modulation doping of exfoliated single and bilayer graphene, chemical vapor deposition grown graphene and WSe 2 , and molecular beam epitaxy grown EuS. We further demonstrate proof of principle photovoltage devices, control via twist angle, and charge transfer through hexagonal boron nitride. Short-ranged lateral doping (≤65 nm) and high homogeneity are achieved in proximate materials with a single layer of α-RuCl 3 . Here, this leads to the best-reported monolayer graphene mobilities (4900 cm 2 /(V s)) at these high hole densities (3 × 10 13 cm -2 ) and yields larger charge transfer to bilayer graphene (6 × 10 13 cm -2 ).

2D atomic crystals↗
DOE OSTI2021

2D Mg-Cu Intermetallic Compounds with Nontrivial Band Topology and Dirac Nodal Lines

Synthesis of vertical heterostructures that include atomically thin layers of materials with topologically nontrivial energy bands is desirable for exploring exotic quantum states. In this study, the authors report on atomic-layer-by-layer deposition of magnesium on copper(111) surface by molecular beam epitaxy, monitored in situ by low-energy electron microscopy and diffraction, and modeled by ab initio theory. It is found that a 2D MgCu 2 intermetallic compound forms during initial Mg deposition and persists till a full monolayer of Mg is formed. Deposition of additional Mg triggers a phase transition from the commensurate MgCu 2 to an incommensurate Mg 2 Cu layer and enables growth of the second layer of Mg. Ab initio calculations indicate non-trivial topology of the electron bands in the interfacial Mg 2 Cu layer and the existence of Dirac nodal lines near the Fermi level. The new 2D Mg 2 Cu material emerges as a promising platform to study new topological states of matter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Multijunction organic photovoltaics incorporating solution and vacuum deposited active layers

There is disclosed an organic photovoltaic device comprising at least one first subcell comprising at least one first small molecular weight material deposited by solution processing, and at least one second subcell comprising a weight at least one second small molecular material deposited by vacuum evaporation. Also disclosed herein is a method for preparing an organic photovoltaic device comprising at least one first subcell comprising at least one first small molecular weight material and at least one second subcell comprising at least one second small molecular weight material, the method comprising depositing at least one first small weight material by solution processing; and depositing at least one second small weight material by vacuum evaporation.

Forrest, Stephen R.↗
DOE OSTI2026

Gas permeation properties of amorphous zeolitic imidazolate framework membranes made by atomic/molecular layer deposition

Amorphous metal-organic framework (MOF) membranes are desirable because they may retain some of the molecular sieving properties of their crystalline counterparts while being free of grain boundary defects, which often hinder the consistent achievement of high membrane performance. However, current methods, like melting and compression, for fabricating amorphous MOF membranes involve multi-step processes that require the formation of a crystalline membrane first, that is then amorphized, and therefore, could be challenging to scale. Here, we utilize atomic/molecular layer deposition (ALD/MLD) of diethylzinc (DEZ) and 2-methylimidazole (2mIm) to directly synthesize ultrathin amorphous zeolitic imidazolate framework (aZIF) deposits on γ-alumina-coated α-alumina supports. As the number of ALD/MLD cycles increased from 10 to 300, gas permeances decreased while ideal selectivities increased. Mixture separation factors for C3H6/C3H8, CO2/N2, and H2/C3H8 as high as 4, 37, and 194, respectively, were obtained. At 200 °C and 2.5 bar equimolar feed of H2 and C3H8, a H2/C3H8 mixture separation factor of 185 is obtained with an H2 permeance of ca. 4.15x10-8 mol/m2-s-Pa (124 GPU). Additionally, the membrane achieves a CO2/N2 mixture separation factor of 37 at 25 °C and 1 bar with a CO2 permeance of ca. 3.96x10-8 mol/m2-s-Pa (118 GPU). Considering the vast array of compositionally distinct aZIFs that can be potentially deposited by this approach, an enormously large parameter space for membrane design is emerging to be explored.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Resolving atomic transport through iron oxide under irradiation using isotopic tracers

Structural materials in nuclear environments are exposed to complex and harsh conditions, including high temperatures, corrosive solutions, and irradiation. Material stability and likewise degradation are fundamentally controlled by atomic transport mechanisms. Here, we investigate the influence of radiation-induced, non-equilibrium point defect populations on mass transport within model oxide systems using isotopic tracers and atom probe tomography. An isotopically labelled hematite (a-Fe2O3) film was synthesized with 16O- and 18O-rich layers (>30nm and 10 nm, respectively) sequentially deposited via molecular beam epitaxy. One region of the film was proton irradiated to ~0.1 dpa at 450°C, and regions outside the beam spot provided a non-irradiated control of thermal annealing only. 3D APT was used to directly visualize the elemental and O-isotopic redistribution following both thermal and combined thermal and irradiation conditions. Complementary scanning transmission electron microscopy (STEM) was also employed to study the microstructural evolution. Error function fits of the 18O-concentration profiles enabled quantification of diffusion coefficients.

isotopic tracers, diffusion, proton irradiation, h↗
DOE OSTI2021

Direct Chemical Vapor Deposition Synthesis of Porous Single-Layer Graphene Membranes with High Gas Permeances and Selectivities

Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membrane material for high-performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching-based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade-off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. Here in this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single-layer graphene membranes with the highest H 2 /CH 4 separation performances recorded to date (H 2 permeance > 4000 GPU and H 2 /CH 4 selectivity > 2000) are fabricated by manipulating growth temperature, precursor concentration, and non-covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single-layer graphene exploits its tremendous potential as high-performance gas-sieving membranes.

chemical vapor deposition↗
DOE OSTI2022

Self-healing Growth of LaNiO 3 on a Mixed-Terminated Perovskite Surface

Developing atomic-scale synthesis control is a prerequisite for understanding and engineering the exotic physics inherent to transition-metal oxide heterostructures. Thus, far, however, the number of materials systems explored has been extremely limited, particularly with regard to the crystalline substrate, which is routinely SrTiO 3 . Here, we investigate the growth of a rare-earth nickelate-LaNiO 3 -on (LaAlO 3 )(Sr 2 AlTaO 6 ) (LSAT) (001) by oxide molecular beam epitaxy (MBE). Whereas the LSAT substrates are smooth, they do not exhibit the single surface termination usually assumed necessary for control over the interface structure. Performing both nonresonant and resonant anomalous in situ synchrotron surface X-ray scattering during MBE growth, we show that reproducible heterostructures can be achieved regardless of both the mixed surface termination and the layer-by-layer deposition sequence. The rearrangement of the layers occurs dynamically during growth, resulting in the fabrication of high-quality LaNiO 3 /LSAT heterostructures with a sharp and consistent interfacial structure. This is due to the thermodynamics of the deposition window as well as the nature of the chemical species at interfaces-here, the flexible charge state of nickel at the oxide surface. This has important implications regarding the use of a wider variety of substrates for fundamental studies on complex oxide synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Bulk and Short-Circuit Anion Diffusion in Epitaxial Fe 2 O 3 Films Quantified Using Buried Isotopic Tracer Layers

Self-diffusion is a fundamental physical process that, in solid materials, is intimately correlated with both microstructure and functional properties. In this work, a universal approach is presented to precisely characterize self-diffusion in ionic solids by isotopically enriching anions and/or cations at specific locations within an epitaxial film stack, and characterize their redistribution at high spatial resolution with atom probe tomography. Nanoscale anion diffusivity is quantified in epitaxial α-Fe 2 O 3 thin films deposited by molecular beam epitaxy with a thin (10 nm) buried layer highly enriched in 18 O. The isotopic sensitivity of the atom probe allows precise measurement of 18 O distribution across the sharp interfaces between this layer and the surrounding Fe 2 O 3 after annealing. Short-circuit anion diffusion through 1D and 2D structural defects in Fe 2 O 3 are also directly visualized in 3D. This versatile approach to study precisely tailored thin film samples at high spatial and mass fidelity will facilitate a deeper understanding of atomic-scale diffusion phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Energy alignment manipulation at the C 60 /TiO 2 (110) interface using a blanket molecular dipole approach

In this work, modifying the energy alignment between the frontier levels of a chromophore and the band edges of a semiconductor substrate using a “blanket layer” of molecular dipoles is explored. The electronic structure, measured with ultraviolet and x-ray photoemission spectroscopy, of C 60 deposited directly onto the TiO 2 (110) surface is compared with that of C 60 deposited onto the surface covered by a blanket layer of the custom-designed helical peptide Z-(Aib) 6 -Ipa, which has a large dipole moment of 18.6 D oriented along its molecular axis and pointing toward the substrate. The C 60 HOMO level is shifted 600 meV to deeper binding energy in the presence of the blanket layer, in good agreement with what is expected from a simple parallel plate capacitor model. These results demonstrate a simple and versatile strategy for controlling energy level alignment at organic/inorganic interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Self-assembled nanocolumns in Bi 2 Se 3 grown by molecular beam epitaxy

Layered van der Waals (vdW) materials grown by physical vapor deposition techniques are generally assumed to have a weak interaction with the substrate during growth. This leads to films with relatively small domains that are usually triangular and a terraced morphology. In this paper, we demonstrate that Bi 2 Se 3 , a prototypical vdW material, will form a nano-column morphology when grown on GaAs(001) substrates. This morphology is explained by a relatively strong film/substrate interaction, long adatom diffusion lengths, and a high reactive selenium flux. In conclusion, this discovery paves the way toward growth of self-assembled vdW structures even in the absence of strain.

36 MATERIALS SCIENCE↗