Search NASA⌕ Search

SEARCH · Search NASA

Results for “surface structure”

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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Functional properties of Yttrium Iron Garnett thin films on graphene-coated Gd 3 Ga 5 O 12 for remote epitaxial transfer

Remote epitaxial growth via a graphene interlayer and subsequent mechanical exfoliation of a free-standing membrane is a recently developed technique used to transfer complex oxide thin films onto non-native substrates to form heterogeneously integrated structures for various device applications. One such oxide is Yttrium Iron Garnet (YIG), a material of choice for a wide range of magnetoelectric and spintronic devices owing to its strong magnetic properties and low microwave losses. YIG is predominantly grown on lattice matched Gadolinium Gallium Garnet (GGG) substrates, but by utilizing the remote epitaxy technique, high quality YIG films can be transferred from GGG onto another substrate such as piezoelectric Lithium Niobate (LN). Mechanical strain coupling between the layers and magnetostrictive nature of YIG would allow for the investigation of the interplay in YIG/LN structures leading to the design of novel frequency agile magneto-acoustic devices. In this study functional properties of a YIG film grown using PLD on graphene-coated GGG substrate were investigated and compared to traditional YIG on GGG. Both materials were characterized in terms of crystal structure, surface morphology, FMR and Gilbert damping, and Raman and XAS spectroscopy. Further, it was found that YIG on graphene-coated GGG exhibits significantly higher microwave losses than standard YIG on GGG (FMR linewidth 30.9 vs 2.1 Oe at 10 GHz, and Gilbert damping coefficient 15.4x10 -4 vs 3.4x10 -4 respectively), which was attributed to increased concentration of Fe 2+ cations in YIG/Graphene/GGG. While the damping is higher in these studied films compared to YIG grown directly on GGG, the resulting properties are still very favorable compared to many other competing materials which can be grown without the need for lattice matched substrates, such as metallic ferromagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Heterometallic metal-organic framework-templated synthesis of porous Co{sub 3}O{sub 4}/ZnO nanocage catalysts for the carbonylation of glycerol

The efficient synthesis of glycerol carbonate (GLC) has recently received great attention due to its significance in reducing excess glycerol in biodiesel production as well as its promising applications in several industrial fields. However, the achievement of high conversion and high selectivity of GLC from glycerol in heterogeneous catalytic processes remains a challenge due to the absence of high-performance solid catalysts. Herein, highly porous nanocage catalysts composed of well-mixed Co{sub 3}O{sub 4} and ZnO nanocrystals were successfully fabricated via a facile heterometallic metal-organic framework (MOF)-templated synthetic route. Benefiting from a high porosity and the synergistic effect between Co{sub 3}O{sub 4} and ZnO, the as-prepared composite catalysts exhibited a significantly enhanced production efficiency of GLC in the carbonylation reaction of glycerol with urea compared to the single-component counterparts. The yield of GLC over the Co{sub 50}Zn{sub 50}-350 catalyst reached 85.2%, with 93.3% conversion and near 91% GLC selectivity, and this catalytic performance was superior to that over most heterogeneous catalysts. More importantly, the proposed templated synthetic strategy of heterometallic MOFs facilitates the regulation of catalyst composition and surface structure and can therefore be potentially extended in the tailoring of other metal oxide composite catalysts. - Graphical abstract: Highly porous Co{sub 3}O{sub 4}/ZnO nanocages were fabricated via a heterometallic MOF-templated route and exhibited a significantly enhanced photocatalytic performance in the production of glycerol carbonate. Display Omitted - Highlights: • Porous Co{sub 3}O{sub 4}/ZnO nanocages were synthesized by a facile thermolysis route of heterometallic MOFs. • The as-prepared nanocages possessed massive pores and Co{sub 3}O{sub 4}/ZnO heterojunctions. • The Co{sub 3}O{sub 4}/ZnO ratio in the composites was easily adjusted by tuning the Co/Zn ratio in the precursors. • The composite catalysts exhibited a significantly enhanced production efficiency of glycerol carbonate in the carbonylation reaction of glycerol with urea.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

A facile approach to prepare graphene via solvothermal reduction of graphite oxide

Highlights: • Graphene was prepared via a novel and facile solvothermal reduction method for graphite oxide. • Most of the oxygen functional groups of graphite oxide were removed. • The reduced graphene oxide obtained was featured with bilayer nanosheets. - Abstract: In this work, a facile reduction strategy is reported for the fabrication of graphene. Graphite oxide (GO) is reduced via a novel solvothermal reaction in a mixed solution of acetone and sodium hypochlorite (NaClO). The structure, surface chemistry, morphology and thermal stability of the as-prepared reduced graphene oxide (RGO) are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results indicate that most of the oxygenated groups in GO are effectively removed in this solvothermal reaction. The novel reduction method provides a simple, cost-effective and efficient strategy for the fabrication of graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural and vibrational investigations of Nb-doped TiO{sub 2} thin films

Highlights: • We studied the evolutions of structure for TiO{sub 2} thin film as changes with Nb doping and temperatures. • Up to 800 °C, the grain size of Nb{sub 0.1}Ti{sub 0.9}O{sub 2} is smaller than for pure TiO{sub 2} because doped Nb hinders the growth of the TiO{sub 2} grains. • There was no formation of the rutile phase at high temperature. • Nb doped TiO{sub 2} films have high electron densities at 400–700 °C. • Nb dope extends the absorbance spectra of TiO{sub 2} which leads to the band gap reduce. - Abstract: Acid-catalyzed sol–gel and spin-coating methods were used to prepare Nb-doped TiO{sub 2} thin film. In this work, we studied the effect of niobium doping on the structure, surface, and absorption properties of TiO{sub 2} by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectometry (XRR), X-ray photoelectron spectroscopy (XPS), Raman, and UV–vis absorption spectroscopy at various annealing temperatures. EDX spectra show that the Nb:Ti atomic ratios of the niobium-doped titania films are in good agreement with the nominal values (5 and 10%). XPS results suggest that charge compensation is achieved by the formation of Ti vacancies. Specific niobium phases are not observed, thus confirming that niobium is well incorporated into the titania crystal lattice. Thin films are amorphous at room temperature and the formation of anatase phase appeared at an annealing temperature close to 400 °C. The rutile phase was not observed even at 900 °C (XRD and Raman spectroscopy). Grain sizes and electron densities increased when the temperature was raised. Nb-doped films have higher electron densities and lower grain sizes due to niobium doping. Grain size inhibition can be explained by lattice stress induced by the incorporation of larger Nb{sup 5+} ions into the lattice. The band gap energy of indirect transition of the TiO{sub 2} thin films was calculated to be about 3.03 eV. After niobium doping, it decreased to 2.40 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Control synthesis of bismuth sulphide films and their application for laser detectors

Highlights: • Bi{sub 2}S{sub 3} films have been synthesized via a facile hydrothermal process. • We fabricated Bi{sub 2}S{sub 3} films-based laser detectors successfully. • The photoelectric properties were studied upon 450 nm, 650 nm and 850 nm laser beam. • The laser detectors exhibit excellent photoconductive performance. • We found Prolonging the reaction time was beneficial for the photoelectric performance. - Abstract: Herein, we utilize a facile hydrothermal process for the synthesis of Bi{sub 2}S{sub 3} films on the SnO{sub 2}: F films (FTO) substrate. The structure, surface morphology and thickness of the samples were characterized by variously analysis method. The Bi{sub 2}S{sub 3} films-based laser detectors exhibit excellent linear photocurrent characteristics, good sensitivity to 450 nm, 650 nm and 850 nm laser beam. Prolonging the reaction time was beneficial for the photoelectric performance of the Bi{sub 2}S{sub 3} films-based laser detectors. The photoelectric conversion properties can be improved by optimizing the thickness of the films. The experimental results of this work can provide an additional opportunity for fabricating excellent photoconductive performance laser detectors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Manipulation of an ionic and electronic conductive interface for highly-stable high-voltage cathodes

A stable and conductive interface is one of the decisive factors in manipulating the performance of high voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode for Li-ion batteries. Herein, a hybrid Li 3 PO 4 -TiO 2 coating layer is designed as an interfacial material via controllable atomic layer deposition (ALD) on LNMO. The coating acts not just as a physical barrier to prevent the side-reactions between cathode and electrolyte at high voltage, more importantly, the hybrid coating material improves both interfacial ionic and electronic conductivities to build facile Li-ion and electron diffusion pathways for LNMO. The optimized LNMO demonstrates improved rate capability and long-life stability. The capacity retention is 81.2% comparing with 47.4% of bare LNMO at 0.5C after 300 cycles. Detailed surface structural evolution is studied via X-ray absorption near edge spectroscopy and transmission electron microscopy. Furthermore, this work provides new insights of hybrid interfacial design via ALD and promotes novel electrode architectures for batteries.

25 ENERGY STORAGE↗
DOE OSTI2025

Fundamental flow characterization for LiCl–KCl molten salt natural circulation closed loop

Molten salt flow characterization presents numerous challenges due to the hostile environments that cause corrosion and erosion of instrumentation and structural components. To support future molten salt flow characterization under natural convection conditions, a LiCl–KCl eutectic molten salt loop was designed and constructed. The primary objective of this loop is to facilitate natural convection as the principal cooling mechanism, enabling insights into the physics behind natural convection in closed loops and serving as a baseline for loop dimensional and non-dimensional analyses. Here, this study summarizes the fundamental functions employed for flow characterization and introduces a model to estimate flow rate when intrusive instrumentation is unavailable. The approach relies solely on structural surface measurements to avoid flow disturbances. Furthermore, a comprehensive thermal–hydraulic analysis is included to deepen understanding of the system’s behavior.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Interactions in misaligned layered materials

The deliberate introduction of stacking faults has been found to induce properties markedly distinct from those of perfectly stacked particles or sheets, with even minute deviations leading to significant alterations in material characteristics. In this review article, we discuss the effects of stacking faults – both linear and rotational – on surface structures influencing ion adsorption, particle–particle affinity governing crystal growth, friction, and electronic properties. In conclusion, our comprehensive overview sheds light on the multifaceted impact of stacking faults on these phenomena, offering insights that bridge multiple disciplines, and provides numerous interdisciplinary research questions, paving the way for future innovations.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In-situ and In-operando Cobalt Oxidation Studied by Atom Probe Tomography

Heterogeneous catalysis is one of the pillars of the chemical industry and the “green chemistry” concept. However, the sparse understanding of surface mechanisms at molecular scale impedes development of high-performance catalysts and requires development of new tools and methodologies. Cobalt is notably able to dissociate CO 2 into CO(g) and O 2 (g), allowing further conversion to higher value compounds such as long-chain hydrocarbons. Such application leads inevitably to Co surface oxidation. Finally, from its pure form (Co(0)) to oxidized ones (CoO and Co 3 O 4 ) the formation mechanism remains unclear as well as the surface structure evolution and its influence on the chemical reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Growth Mode Transition in Complex Oxide Heteroepitaxy: Atomically Resolved Studies

Here we performed investigations of the atomic-scale surface structure of epitaxial La 5/8 Ca 3/8 MnO 3 thin films as a model system dependent on growth conditions in pulsed laser deposition with emphasis on film growth kinetics. Postdeposition in situ scanning tunneling microscopy was combined with in operando reflective high-energy electron diffraction to monitor the film growth and ex situ X-ray diffraction for structural analysis. We find a correlation between the out-of-plane lattice parameter and both adspecies mobility and height of the Ehrlich–Schwoebel barrier, with mobility of adatoms greater over the cationically stoichiometric terminations. We find that the data suggest that the out-of-plane lattice parameter is dependent on the mechanism of epitaxial strain relaxation, which is controlled by the oxidative power of the deposition environment.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Variable Surface Termination and Ligand Passivation of Lead Sulfide Nanocrystals Synthesized with Excess Lead Chloride

The surface termination and ligand passivation of semiconducting nanocrystals (NCs) impact the stability, optical properties, and self-assembly of NCs. In this work, we definitively characterize the surface of lead sulfide (PbS) NCs synthesized from excess PbCl 2 . With a combination of small-angle neutron scattering (SANS), photoluminescence, and 1D and 2D NMR experiments, we show that the surface termination of PbS NCs depends on the presence of PbCl 2 during ligand exchange. When excess PbCl 2 is removed prior to ligand exchange, PbS[RNH 3 + Cl – ] NCs are obtained, which are terminated by a monolayer of PbCl x on the {100} PbS facet and passivated by oleylammonium chloride ligands. On the other hand, when excess PbCl 2 remains in solution during ligand exchange, lead oleate forms and attaches to the {111} PbS facets of PbS[RNH 3 + Cl – ] NCs, creating PbS@PbCl x NCs. PbS@PbCl x NCs are coated in an epitaxial layer of PbCl x on both the {100} PbS and {111} PbS facets, making them 0.3–0.4 nm larger on average than PbS[RNH 3 + Cl – ] NCs with identical absorption wavelengths. Additionally, PbS@PbCl x NCs have a consistently higher photoluminescence quantum yield and longer photoluminescence lifetimes than PbS[RNH 3 + Cl – ] NCs. This study clarifies the surface structure of PbS NCs synthesized from excess PbCl 2 , highlighting ligand exchange strategies and reconciling observations from across the literature.

Anions↗
DOE OSTI2026

Bifunctional Electrocatalysts with High-Entropy Alloys: Bridging Hydrogen Evolution and Oxygen Reduction

High-entropy alloys (HEAs) have emerged as a promising class of bifunctional electrocatalysts capable of simultaneously driving the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) with high activity and durability. Their near-equiatomic multicomponent compositions give rise to unique physicochemical characteristics, including lattice distortion, sluggish diffusion, high-entropy stabilization, and pronounced electronic heterogeneity, that collectively generate diverse and synergistic active sites inaccessible in conventional alloys. This review summarizes recent progress in HEA-based bifunctional electrocatalysis, with a focus on the fundamental mechanisms governing HER and ORR activity, stability, and selectivity. We discuss advances in synthesis strategies, ranging from confined growth and step-alloying to scalable continuous-flow methods, that enable precise control over composition, size, and surface structure. Complementary computational and data-driven approaches, including density functional theory, machine-learning-assisted screening, and descriptor development, are highlighted as essential tools for navigating the vast HEA design space and establishing structure−property relationships. Particular attention is paid to adsorption-energy distributions, multisite cooperativity, and environmental effects under realistic electrochemical conditions. Finally, we outline current challenges and future opportunities for integrating mechanistic understanding with AI-guided, closed-loop design frameworks to accelerate the discovery of next-generation HEA bifunctional electrocatalysts for sustainable energy conversion.

Alloys↗
DOE OSTI2017

Competitive Adsorption-Assisted Formation of One-Dimensional Cobalt Nanochains with High CO Hydrogenation Activity

In the present work, cobalt nanochains have been successfully synthesized by a novel co assisted self-assembling formation strategy. A dramatic morphology transformation from cobalt nanoparticles to nanochains are observed when co molecules were introduced into the synthetic system. DFT calculations further confirm that competitive co-adsorbed co and oleylamine over the cobalt nanoparticles facilitates the formation of cobalt nanochains, which show higher co hydrogenation performance. The present work provides a new strategic and promising method for controllable synthesis of catalyst nanomaterials with the preferred surface structure and morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Single-Nanoflake Photo-Electrochemistry Reveals Champion and Spectator Flakes in Exfoliated MoSe 2 Films

Semiconducting transition-metal dichalcogenide (TMD) nanoflake thin films are promising large-area electrodes for photo-electrochemical solar energy conversion applications. However, their energy conversion efficiencies are typically much lower than those of bulk electrodes. It is unclear to what extent this efficiency gap stems from differences among nanoflakes (e.g., area, thickness, and surface structural features). It is also unclear whether individual exfoliated nanoflakes can achieve energy conversion efficiencies similar to those of bulk crystals. Here, we use a single-nanoflake photo-electrochemical approach to show that there are both highly active and completely inactive nanoflakes within a film. For the exfoliated MoSe 2 samples studied herein, 7% of nanoflakes are highly active champions, whose photocurrent efficiency exceeds that of the bulk crystal. However, 66% of nanoflakes are inactive spectators, which are mostly responsible for the overall lower photocurrent efficiency compared to the bulk crystal. The photocurrent collection efficiency increases with nanoflake area and decreases more at perimeter edges than at interior step edges. These observations, which are hidden in ensemble-level measurements, reveal the underlying performance issues of exfoliated TMD electrodes for photo-electrochemical energy conversion applications.

14 SOLAR ENERGY↗
DOE OSTI2018

Understanding Chemical Bonding in Alloys and the Representation in Atomistic Simulations

Alloys are widely used in catalysts and structural materials. The nature of chemical bonding and the origin of alloy formation energies, defect energies, and interfacial properties have not been well understood to date but are critical to material performance. In this contribution, we explain the polar nature of chemical bonding and an implementation in classical and reactive atomistic simulations to understand such properties more quantitatively. Electronegativity differences between metal atoms lead to polar bonding, and exothermic alloy formation energies are related to charge transfer between the different elements. These differences can be quantified by atomic charges using pairwise charge increments, determined by matching the computed alloy formation energy to experimentally measured alloy formation energies using pair potentials for the pure metals. The polar character of alloys is comparable to organic molecules and partially ionic minerals, for example, AlNi and AlNi3 alloys assume significant atomic charges of ±0.40e and +0.60e/–0.20e, respectively. The subsequent analysis of defect sites and defect energies using force-field-based calculations shows excellent agreement with calculations using density functional theory and embedded atom models (EAM). The formation of vacancy and antisite defects is characterized by a redistribution of charge in the first shell of neighbor atoms in the classical models whereby electroneutrality is maintained and charge increments correlate with differences in electronegativity. The proposed atomic charges represent internal dipole and multipole moments, consistent with existing definitions for organic and inorganic compounds and with the extended Born model (Heinz, H.; Suter, U. W. J. Phys. Chem. B2004,108 (47), 18341–18352). The method can be applied to any alloy and has a reproducibility of ±10%. In contrast, quantum mechanical charge schemes remain associated with deviations exceeding ±100%. The atomic charges for alloys provide a simple initial measure for the internal electronic structure, surface adsorption of molecules, and reactivity in catalysis and corrosion. The models are compatible with the Interface force field (IFF), CHARMM, AMBER, OPLS-AA, PCFF, CVFF, and GROMOS for reliable atomistic simulations of alloys and their interfaces with minerals and electrolytes from the nanometer scale to the micrometer scale.

Chemistry↗
DOE OSTI2024

Black Phosphorus for Mid-Infrared Optoelectronics: Photophysics, Scalable Processing, and Device Applications

High efficiency mid-infrared (λ = 3-8 μm) light emitters and photodetectors are pivotal for advancing next-generation optoelectronics. However, narrow-bandgap semiconductors face fundamental challenges such as pronounced nonradiative carrier recombination and thermally generated noise, which impede device performance. Recently, two-dimensional layered black phosphorus (BP) and its alloys have attracted substantial interest for mid-infrared device applications, demonstrating superior performance relative to conventional III-V and II-VI semiconductors with similar bandgaps. In this review, we discuss the optical properties of BP, contrasting these with those of covalent compounds. Owing to its inherently self-terminated surface structure and reduced nonradiative recombination, BP exhibits high performance in light emission and photodetection at room temperature. Furthermore, this review highlights recent advances in the large-area processing of BP thin films, paving the way for practical device applications and integration. Finally, we explore ongoing challenges and emerging opportunities in the utilization of BP for functional mid-infrared devices.

Higashitarumizu, Naoki↗
DOE OSTI2020

Strain-Modulated Platinum–Palladium Nanowires for Oxygen Reduction Reaction

Electrocatalytic activity of alloy nanocatalytsts can be manipulated effectively by tuning their physical properties (ensemble, geometric, and ligand effects) to afford optimal surface structure and compositions for proton exchange membrane fuel cell (PEMFC) application. Herein, highly catalytic platinum-palladium nanowires (Pt n Pd 100-n NWs) with a subtle lattice strain and Boerdijk-Coxeter helix type morphology are synthesized through a surfactant-free, thermal single phase solvent method. X-ray diffraction results show that Pt n Pd 100-n NWs are exposed through the (111) facets and their shrinking or expanding lattice parameters can be modulated by the alloy compositions. Electrochemical results reveal that their high catalytic activity correlates with the lattice shrinking, facets, and bimetallic compositions, showing higher activity when the ratio of Pt and Pd is similar to ~78:22, which is further supported by DFT results. Compared to the nanoparticle type platinum-palladium alloyed catalysts with similar metal compositions (Pt n Pd 100-n NPs), the Pt n Pd 100-n NWs exhibit significantly improved electrocatalytic activity and stability for the oxygen reduction reaction. Our findings open new strategies to design the highly active and stable alloy nanocatalysts with controllable compositions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Effects of Ball Milling on the Electrochemical Capacity and Interfacial Stability of Li 2 MnO 3 Cathode Materials

The cycling mechanism of Li 2 MnO 3 cathode materials synthesized by conventional solid-state methods at high temperatures (800-900 °C) has been intensively investigated. Previous studies showed that CO 2 and O 2 gas evolution accounts for most of the charge capacity, followed by some Mn reduction during discharge. In this work, we analyze the effects of ball milling on the structure, surface contaminant, and electrochemical capacity of Li 2 MnO 3 cathode material, with or without a graphitic fluoride (C-F) additive. At the same time, C-F is added to form a protective coating layer that reduces unwanted reactions with the electrolyte during later electrochemical cycling. We find that the C-F ball-milled material shows Li 2 MnO 3 /LiMnO 2 composite phases, while the purely ball-milled material shows a single Li 2 MnO 3 phase. Furthermore, we characterize surface species and gas evolution during the first cycle, which reveals the decomposition of Li 2 CO 3 and the carbonate electrolyte during the first charge, especially during the high potential region (>4.4 V), and the electrochemical reduction of only a small fraction of the evolved gas on the first discharge (<2.75 V). The appearance further demonstrates the repetitive nature of this process during charge and disappearance during discharge of Mn 2p 3/2 X-ray photoelectron spectroscopy (XPS) spectra signals during the first two cycles. These processes result in first discharge specific capacities of only 155 and 170 mAh/g after first charge specific capacities of 210 and 320 mAh/g for the pure ball-milled and ball-milled with C-F materials, respectively. These studies demonstrate the interfacial instability introduced by ball milling. However, the electrochemical capacity is significantly increased, necessitating further investigation to determine whether ball milling can activate Mn-containing cathode materials.

25 ENERGY STORAGE↗