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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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O

Here, we model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO 3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti 7 O 7 , pores. The quasicrystal structue is a simple decoration of three types of tiles: square, triangle and 30° rhombus, with edge lengths 6.85 Å, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Soft Microfluidic Assemblies of Sensors, Circuits, and Radios for the Skin

When mounted on the skin, modern sensors, circuits, radios, and power supply systems have the potential to provide clinical-quality health monitoring capabilities for continuous use, beyond the confines of traditional hospital or laboratory facilities. The most well-developed component technologies are, however, broadly available only in hard, planar formats. As a result, existing options in system design are unable to effectively accommodate integration with the soft, textured, curvilinear, and time-dynamic surfaces of the skin. Here, we describe experimental and theoretical approaches for using ideas in soft microfluidics, structured adhesive surfaces, and controlled mechanical buckling to achieve ultralow modulus, highly stretchable systems that incorporate assemblies of high-modulus, rigid, state-of-the-art functional elements. Here, the outcome is a thin, conformable device technology that can softly laminate onto the surface of the skin to enable advanced, multifunctional operation for physiological monitoring in a wireless mode.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

Ion Imaging Near a Reactive Surface

In this project, resonance enhanced multi-photon ionization followed by spatial mode ion imaging (REMPI-SMII) has been developed as a new tool for in-situ monitoring of local catalytic activity near a chemically active surface. A prototype experimental setup was developed for the demonstration, and initial results indicate this approach is feasible as a new diagnostic for online monitoring of catalytic reactions. The catalytic conversion of H 2 and D 2 to form HD over a Pt surface was carried out using a dual-molecular beam arrangement with reactant beams impinging on a structured Pt surface. The catalytic production of HD was successfully detected through the REMPI-SMII approach, and next steps were identified to improve the experimental design for better spatial resolution and mapping of catalytic surface activity.

47 OTHER INSTRUMENTATION↗
NASA NTRS2011

Effects of Solar Wind Conditions on the Plasma Wake Within a Polar Crater: Preliminary Results

As the solar wind sweeps horizontally past a shadowed lunar crater it simultaneously diffuses toward the surface through an ambipolar process, forming a plasma wake (e.g., Figure 1). Importantly, the resulting electric field structure diverts solar wind protons toward the cold crater floor where they may represent a source of surficial hydrogen. We present a handful of two-dimensional kinetic simulations exploring the range of wake structures and surface particle fluxes possible under various background plasma conditions.

Zimmerman, M. I.↗
DOE OSTI2017

Disconnecting structure and dynamics in glassy thin films

Nanometrically thin glassy films depart strikingly from the behavior of their bulk counterparts. We investigate whether the dynamical differences between a bulk and thin film polymeric glass former can be understood by differences in local microscopic structure. Machine learning methods have shown that local structure can serve as the foundation for successful, predictive models of particle rearrangement dynamics in bulk systems. By contrast, in thin glassy films, we find that particles at the center of the film and those near the surface are structurally indistinguishable despite exhibiting very different dynamics. Next, we show that structure-independent processes, already present in bulk systems and demonstrably different from simple facilitated dynamics, are crucial for understanding glassy dynamics in thin films. Our analysis suggests a picture of glassy dynamics in which two dynamical processes coexist, with relative strengths that depend on the distance from an interface. Here, one of these processes depends on local structure and is unchanged throughout most of the film, while the other is purely Arrhenius, does not depend on local structure, and is strongly enhanced near the free surface of a film.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A simple electron counting model for half-Heusler surfaces

Heusler compounds are a ripe platform for discovery and manipulation of emergent properties in topological and magnetic heterostructures. In these applications, the surfaces and interfaces are critical to performance; however, little is known about the atomic-scale structure of Heusler surfaces and interfaces or why they reconstruct. Using a combination of molecular beam epitaxy, core-level and angle-resolved photoemission, scanning tunneling microscopy, and density functional theory, we map the phase diagram and determine the atomic and electronic structures for several surface reconstructions of CoTiSb (001), a prototypical semiconducting half-Heusler. At low Sb coverage, the surface is characterized by Sb-Sb dimers and Ti vacancies, while, at high Sb coverage, an adlayer of Sb forms. The driving forces for reconstruction are charge neutrality and minimizing the number of Sb dangling bonds, which form metallic surface states within the bulk bandgap. We develop a simple electron counting model that explains the atomic and electronic structure, as benchmarked against experiments and first-principles calculations. We then apply the model to explain previous experimental observations at other half-Heusler surfaces, including the topological semimetal PtLuSb and the half-metallic ferromagnet NiMnSb. The model provides a simple framework for understanding and predicting the surface structure and properties of these novel quantum materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

First-Principles Study of Alkoxides Adsorbed on Au(111) and Au(110) Surfaces: Assessing the Roles of Noncovalent Interactions and Molecular Structures in Catalysis

Microscopic understanding of molecular adsorption on catalytic surfaces is crucial for controlling the activity and selectivity of chemical reactions. However, for complex molecules, the adsorption process is very system-specific and there is a clear need to elaborate systematic understanding of important factors that determine catalytic functionality. In this study, we investigate the binding of eight molecules, including seven alkoxides and one carboxylate, on the Au(111) and Au(110) surfaces. Our density-functional theory calculations including long-range van der Waals interactions demonstrate the significant role of these “weak” noncovalent forces on the adsorption structures, energetics, and relative adsorbate stabilities. Interestingly, the binding energy trends are insensitive to the surface structure. Instead, the adsorption stability depends strongly on the structural and chemical characteristics of the molecules: linear vs branching configurations, number of unsaturated C–C bonds, bidentate adsorption, and the presence of electronegative atoms. Finally, our calculations help establish the influence of individual and collective chemical factors that determine the catalytic selectivity of alkoxides.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Strong spin-orbit coupling and Dirac nodal lines in the three-dimensional electronic structure of metallic rutile IrO 2

Using high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we have studied the bulk and surface electronic structure of metallic rutile 5d transition metal oxide IrO 2 that harbors both edge and corner sharing Ir-O octahedrons. We observe strong modulation of the band structure by spin-orbit coupling (SOC). The measured band structure is well reproduced by our ab initio calculation without band renormalization, suggesting the absence of the SOC-enhanced correlation effect in IrO 2 . In accordance with the calculation, we visualize two types of Dirac nodal lines (DNLs) protected by mirror symmetry and nonsymmorphic crystal symmetry, respectively. SOC gaps the first type of DNLs, which may contribute largely to the strong spin Hall effect. Furthermore, the second type of DNLs at the edges of Brillouin zone, however, remain intact against SOC. Our results not only provide important insights into the exotic transport properties of IrO 2 , but also shed light on the understanding of the role of SOC in the iridate family.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

Structural design aspects of reusable surface insulation thermal protection systems.

Low density fiber ceramic materials coated with refractory ceramics meet the requirements of reusable low weight thermal protection systems. The structural characteristics of this class of material impose unique design and analysis requirements on the application to spacecraft structural elements. Finite element type stress analysis techniques are required to adequately predict the structural response of the system. Parametric analyses have been performed to determine the response of the system to variations in geometry, and to thermal and structural load conditions. Sensitivity of coating, insulation and attachment stresses are presented and critical failure modes are identified.

Michalak, R. J.↗
DOE OSTI2014

Multimetallic Core/Interlayer/Shell Nanostructures as Advanced Electrocatalysts

The fine balance between activity and durability is crucial for the development of high performance electrocatalysts. The importance of atomic structure and compositional gradients is a guiding principle in exploiting the knowledge from well-defined materials in the design of novel electrocatalysts with a Ni core, Au interlayer and PtNi shell nanostructure (Ni@Au@PtNi). This multimetallic system is found to have the optimal balance of activity and durability due to the synergy between stabilizing effect of subsurface Au and modified electronic structure of surface Pt through interaction with subsurface Ni atoms. The electrocatalysts with Ni@Au@PtNi core-interlayer-shell structure exhibit high intrinsic and mass activities as well as superior durability for the oxygen reduction reaction with less than 10% activity loss after 10,000 potential cycles between 0.6 and 1.1 V vs. the reversible hydrogen electrode.

activity↗
DOE OSTI2015

Diamond heteroepitaxial lateral overgrowth

A method of diamond heteroepitaxial lateral overgrowth is demonstrated which utilizes a photolithographic metal mask to pattern a thin (001) epitaxial diamond surface. Significant structural improvement was found, with a threading dislocation density reduced by two orders of magnitude at the top surface of a thick overgrown diamond layer. In the initial stage of overgrowth, a reduction of diamond Raman linewidth in the overgrown area was also realized. Thermally-induced stress and internal stress were determined by Raman spectroscopy of adhering and delaminated diamond films. As a result, the internal stress is found to decrease as sample thickness increases.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Reflection high-energy electron diffraction study of growth and interface formation of the Ga(1-x)In(x)Sb/InAs strained-layer superlattices

Reflection high-energy electron diffraction (RHEED) during molecular beam epitaxy is used to study the growth and interface formation of the Ga(1-x)In(x)Sb/InAs (x is not greater than 0.4) strained-layer superlattices (SLSs) on GaSb(100) substrates. A number of surface atomic structures were observed in the growth of the SLS: a (1 x 3) phase from the InAs epilayer surface, a (2 x 3) phase, a (2 x 4) phase, and diffuse (1 x 1)-like phases from the InAs epilayer surface. It is suggested that the long-range order quality of the interface of Ga(1-x)In(x)Sb on InAs may be better than that of the interface of InAs on Ga(1-x)In(x)Sb, but the abruptness of the interfaces would still be compatible. The RHEED intensity variations in the formation of the interfaces are discussed in terms of interface chemical reactions.

Fan, W. C.↗
NASA NTRS2006

Stability of Atmospheric-Pressure Plasma Induced Changes on Polycarbonate Surfaces

Polycarbonate films are subjected to plasma treatment in a number of applications such as improving adhesion between polycarbonate and silicon alloy in protective and optical coatings. The changes in surface chemistry due to plasma treatment have tendency to revert back. Thus stability of the plasma induced changes on polymer surfaces over desired time period is very important. The objective of this study was to examine the effect of ageing on atmospheric pressure helium-plasma treated polycarbonate (PC) sample as a function of treatment time. The ageing effects were studied over a period of 10 days. The samples were plasma treated for 0.5, 2, 5 and 10 minutes. Contact angle measurements were made to study surface energy changes. Modification of surface chemical structure was examined using, X-ray Photoelectron Spectroscopy (XPS). Contact angle measurements on untreated and plasma treated surfaces were made immediately, 24, 48, 72 and 96 hrs after treatment. Contact angle decreased from 93 deg for untreated sample to 30 deg for sample plasma treated for 10 minutes. After 10 days the contact angles for the 10 minute plasma treated sample increased to 67 deg, but it never reverted back to that of untreated surface. Similarly the O/C ratio increased from 0.136 for untreated sample to 0.321 for 10 minute plasma treated sample indication increase in surface energy.

Sharma, Rajesh↗
DOE OSTI2014

Physical deoxygenation of graphene oxide paper surface and facile in situ synthesis of graphene based ZnO films

In-situ sputtering ZnO films on graphene oxide (GO) paper are used to fabricate graphene based ZnO films. Crystal structure and surface chemical states are investigated. Results indicated that GO paper can be effectively deoxygenated by in-situ sputtering ZnO on them without adding any reducing agent. Based on the principle of radio frequency magnetron sputtering, we propose that during magnetron sputtering process, plasma streams contain large numbers of electrons. These electrons not only collide with argon atoms to produce secondary electrons but also they are accelerated to bombard the substrates (GO paper) resulting in effective deoxygenation of oxygen-containing functional groups. In-situ sputtering ZnO films on GO paper provide an approach to design graphene-semiconductor nanocomposites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tunable surface acoustic wave device using semiconducting MgZnO and piezoelectric NiZnO dual-layer structure on glass

Tunable surface acoustic wave (SAW) devices have attracted considerable interests due to its applications in emerging fields, such as secured wireless communication, adaptive signal processing, and smart sensing systems. We report a dual-input-voltage-controlled tunable SAW built on glass, which uses a ZnO-based dual-layer structure consisting of a piezoelectric Ni- doped ZnO (NZO) and semiconducting Mg-doped ZnO (MZO). The interdigital (IDT) electrodes are buried in the piezoelectric NZO layer to form the delay line for SAW propagation, while the semiconductor MZO layer serves as the channel of a thin film transistor (TFT) to modulate the conductivity. Results show the interface between MZO channel and SiO 2 gate dielectric layer of the TFTT significantly impacts on SAW tuning performances due to Zn diffusion from MZO into SiO 2 . The TFT-SAW device using an ultra-thin MgO layer as interface modification enables SAW frequency tuning of 0.53% under solely V gs control with 0–12 V. The required voltage range is significantly reduced compared regular MZO-NZO TFT-SAW counterpart (Δf/f c ~ 0.25%; V gs –30 to –14 V) without interface modification. With additional control of V ds , the SAW frequency tunability is further expanded from 0.46% to 0.63%. As a result, this dual-input voltage-controlled frequency tuning device on glass is promising for low-voltage, low-cost portable smart sensors and voltage-controlled reconfigurable radio-frequency identification tags.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Spontaneous Ionic Polarization in Ammonia-Based Ionic Liquid [Spontaneous Ionic Polarization in Ionic Liquid]

Ionic liquids and gels have attracted attention for a variety of energy storage applications, as well as for high performance electrolytes for batteries and super-capacitors. Although the electronic structure of ionic electrolytes in these applications is of practical importance for device design and improved performance, the understanding of the electronic structure of ionic liquids and gels is still at an early stage. Here we report soft x-ray spectroscopic measurements of the surface electronic structure of a representative ammonia-based ionic gel (DEME-TFSI with PSPMMA- PS copolymer). We observe that near the outermost surface, the area of the anion peak (1s N - core level in TFSI) is relatively larger than that of the cation peak (N + in DEME). This spontaneous ionic polarization of the electrolyte surface, which is absent for the pure ionic liquid without copolymer, can be directly tuned by the copolymer content in the ionic gel, and further results in a modulation in work function. Finally, these results shed new light on the control of surface electronic properties of ionic electrolytes, as well as a difference between their implementation in ionic liquids and gels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Genesis and Propagation of Fractal Structures During Photoelectrochemical Etching of n-Silicon

The genesis, propagation, and dimensions of fractal-etch patterns that form anodically on front- or back-illuminated n-Si(100) photoelectrodes in contact with 11.9 M NH 4 F (aqueous) have been investigated during either a linear potential sweep or a constant potential hold ( E = +6.0 V versus Ag/AgCl). Optical images collected in situ during electrochemical experiments reflected the location and underlying mechanism of initiation and propagation of the structures on the surface. X-ray photoelectron spectroscopic (XPS) data collected for samples emersed from the electrolyte at varied times provided detailed information about the chemistry of the surface during fractal etching. The fractal structure was strongly influenced by the orientation of the crystalline Si sample. Furthermore, the etch patterns were initially generated at points along the circumference of bubbles that formed upon immersion of n-Si(100) samples in the electrolyte, most likely due to the electrochemical and electronic isolation of areas beneath bubbles. XPS data showed the presence of a tensile-stressed silicon surface throughout the etching process as well as the presence of SiO x F y on the surface. The two-dimensional fractal dimension, D f,2D , of the patterns increased with etching time to a maximum observed value of D f,2D = 1.82. Promotion of fractal etching near etch masks that electrochemically and electronically isolated areas of the photoelectrode surface enabled the selective placement of highly branched structures at desired locations on an electrode surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗