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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Nanoscale selective area growth of thick, dense, uniform, In-rich, InGaN nanostructure arrays on GaN/sapphire template

Uniform, dense, single-phase, 150 nm thick indium gallium nitride (InGaN) nanostructure (nanorods and nanostripes) arrays have been obtained on gallium nitride templates, by metal organic chemical vapor deposition and nanoscale selective area growth on silicon dioxide patterned masks. The 150 nm thick InGaN nanorods have a perfect hexagonal pyramid shape with relatively homogenous indium concentration up to 22%, which is almost twice as high as in planar InGaN grown in the same condition, and luminesce at 535 nm. InGaN nanostripes feature c-axis oriented InGaN in the core which is covered by InGaN grown along semi-polar facets with higher In content. Transmission electron microscope and sub micron beam X-rays diffraction investigations confirm that both InGaN nanostructures are mostly defect free and monocrystalline. The ability to grow defect-free thick InGaN nanostructures with reduced polarization and high indium incorporation offers a solution to develop high efficiency InGaN-based solar cells.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Universal mechanism for ion-induced nanostructure formation on III-V compound semiconductor surfaces

We have examined the formation of nanostructures on ion-irradiated compound semiconductor surfaces. We computed the ion doses needed to fully deplete group V elements from the surfaces. These group V depletion doses are in good agreement with the measured threshold ion doses for nucleation of group III-rich nanostructures on a wide variety of III-V compound semiconductor surfaces. Since the group V depletion doses decrease with increasing sputtering yield, these results suggest a universal nanostructure formation mechanism which depends upon the total sputtering yield of each III-V compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Thermal conductivity of bulk nanostructured lead telluride

Thermal conductivity of lead telluride with embedded nanoinclusions was examined using Monte Carlo simulations with intrinsic phonon transport properties obtained from first-principles-based lattice dynamics. The nanoinclusion/matrix interfaces were set to completely reflect phonons to model the maximum interface-phonon-scattering scenario. The simulations with the geometrical cross section and volume fraction of the nanoinclusions matched to those of the experiment show that the experiment has already reached the theoretical limit of thermal conductivity. The frequency-dependent analysis additionally identifies that the thermal conductivity reduction is dominantly attributed to scattering of low frequency phonons and demonstrates mutual adaptability of nanostructuring and local disordering.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electronic structure and optical properties of CdS{sub x}Se{sub 1−x} solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

The electronic structure and optical properties of a series of iso-electronic and iso-structural CdS{sub x}Se{sub 1−x} solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electrochemical and Raman spectroscopy identification of morphological and phase transformations in nanostructured TiO 2 (B)

TiO 2 (B) exhibits unique electrochemical lithiation behavior where two closely spaced reduction and oxidation peaks, referred to as “double peaks,” are observed for 3-D forms of bulk and nanostructured TiO 2 (B) while a single broad redox peak is observed for 2-D nanosheet architectures. Here, we have used a combination of transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy and cyclic voltammetry on TiO 2 (B) nanosheets as well as a series of thermally annealed nanosheets to map the morphological and phase transformation pathways that help clarify the structure-dependent lithiation behavior. We found that the double peak redox behavior only arises once a three dimensional nanocrystalline structure of TiO 2 (B) exists by observing nanoparticle growth on the TiO 2 (B) nanosheet surface via TEM at temperatures above 150 °C. This morphological transformation was also verified by Raman spectroscopy. The appearance of low-energy torsional modes at temperatures above 150 °C which are not observed in 2-D morphologies of TiO 2 (B) agrees well with TEM evidence of 3-D nanoparticle formation. Using scan rate dependent cyclic voltammetry we also verified that all lithiation behavior associated with TiO 2 (B) (either nanosheet or nanoparticle) is due primarily to a surface redox (pseudocapacitive) mechanism. The thermal annealing study also shows the phase transformation of surface nucleated TiO 2 (B) nanoparticles to anatase nanoparticles at temperatures above 200 °C. These studies clearly show how nano-morphological control can influence electrochemical lithiation behavior and help identify a possible mechanism to explain the double peak phenomenon observed for TiO 2 (B).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Nanostructured columnar heterostructures of TiO{sub 2} and Cu{sub 2}O enabled by a thin-film self-assembly approach: Potential for photovoltaics

Graphical abstract: Display Omitted Highlights: ► Material self-assembly in phase-separated oxides is exploited. ► Three-dimensionally nanostructured epitaxial films are grown using sputtering. ► Films are composed of well-ordered oriented nanopillars of n-type TiO{sub 2} and p-type Cu{sub 2}O. ► Observed interfaces at adjacent TiO{sub 2}–Cu{sub 2}O columns are nearly atomically distinct. ► Absorption profile of the composite film captures a wide range of the solar spectrum. -- Abstract: Significant efforts are being devoted to the development of multifunctional thin-film heterostructures and nanostructured material architectures for components with novel applications of superconductivity, multiferroicity, solar photocatalysis and energy conversion. In particular, nanostructured assemblies with well-defined geometrical shapes have emerged as possible high efficiency and economically viable alternatives to planar photovoltaic thin-film architectures. By exploiting phase-separated self-assembly, here we present advances in a vertically oriented two-component system that offers potential for future development of nanostructured thin film solar cells. Through a single-step deposition by magnetron sputtering, we demonstrate growth of an epitaxial, composite film matrix formed as self-assembled, well ordered, phase segregated, and oriented nanopillars of n-type TiO{sub 2} and p-type Cu{sub 2}O. The composite films were structurally characterized to atomic resolution by a variety of analytical tools, and evaluated for preliminary optical properties using absorption measurements. We find nearly atomically distinct TiO{sub 2}–Cu{sub 2}O interfaces (i.e., needed for possible active p–n junctions), and an absorption profile that captures a wide range of the solar spectrum extending from ultraviolet to visible wavelengths. This high-quality materials system could lead to photovoltaic devices that can be optimized for both incident light absorption and carrier collection.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Shape-Controlled Narrow-Gap SnTe Nanostructures: From Nanocubes to Nanorods and Nanowires

The rational design and synthesis of narrow-gap colloidal semiconductor nanocrystals (NCs) is an important step toward the next generation of solution-processable photovoltaics, photodetectors, and thermoelectric devices. SnTe NCs are particularly attractive as a Pb-free alternative to NCs of narrow-gap lead chalcogenides. Previous synthetic efforts on SnTe NCs have focused on spherical nanoparticles. Here we report new strategies for synthesis of SnTe NCs with shapes tunable from highly monodisperse nanocubes, to nanorods (NRs) with variable aspect ratios, and finally to long, straight nanowires (NWs). Reaction at high temperature quickly forms thermodynamically favored nanocubes, but low temperatures lead to elongated particles. Transmission electron microscopy studies of reaction products at various stages of the synthesis reveal that the growth and shape-focusing of monodisperse SnTe nanocubes likely involves interparticle ripening, while directional growth of NRs and NWs may be initiated by particle dimerization via oriented attachment.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by transmission electron microscopy and electron energy loss spectroscopy

Nanoscale defect structure within the magnetic penetration depth of ∼100 nm is key to the performance limitations of niobium superconducting radio frequency cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls, we discover the existence of nanoscale hydrides in electropolished cavities limited by the high field Q slope, and show the decreased hydride formation in the electropolished cavity after 120 °C baking. Furthermore, we demonstrate that adding 800 °C hydrogen degassing followed by light buffered chemical polishing restores the hydride formation to the pre-120 °C bake level. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120 °C bake.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Insulator Nanostructure Desorption Ionization Mass Spectrometry

Surface-assisted laser desorption ionization (SALDI) is an approach for gas-phase ion generation for mass spectrometry using laser excitation on typically conductive or semiconductive nanostructures. Here, we introduce insulator nanostructure desorption ionization mass spectrometry (INDI-MS), a nanostructured polymer substrate for SALDI-MS analysis of small molecules and peptides. INDI-MS surfaces are produced through the self-assembly of a perfluoroalkyl silsesquioxane nanostructures in a single chemical vapor deposition silanization-step. We find that surfaces formed from the perfluorooctyltrichlorosilane monomer assemble semielliptical features with a 10 nm height, diameters between 10 and 50 nm, and have attomole–femtomole sensitivities for selected analytes. Surfaces prepared with silanes that either lack the trichloro or perfluoro groups, lack sensitivity. Further, we demonstrate that hydrophobic INDI regions can be micropatterned onto hydrophilic surfaces to perform on-chip self-desalting in an array format.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Sulfated glycopeptide nanostructures for multipotent protein activation

Biological systems have evolved to utilize numerous proteins with capacity to bind polysaccharides for the purpose of optimizing their function. A well-known subset of these proteins with binding domains for the highly diverse sulfated polysaccharides are important growth factors involved in biological development and tissue repair. Here, we report on supramolecular sulfated glycopeptide nanostructures, which display a trisulfated monosaccharide on their surfaces and bind five critical proteins with very different polysaccharide binding domains. Binding does not disrupt the filamentous shape of the nanostructures or their internal β-sheet backbone, but must involve accessible adaptive configurations to interact with such different proteins. The glycopeptide nanostructures amplified signaling of bone morphogenetic protein 2 significantly more than the natural sulfated polysaccharide heparin, and promoted regeneration of bone in the spine with a protein dose that is 100-fold lower than expected. These super-bioactive nanostructures may enable many therapies in the horizon involving proteins.

36 MATERIALS SCIENCE↗