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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Nuclear Data Sheets for A = 112

Evaluated nuclear structure and decay data for all nuclei within the A = 112 mass chain are presented. The experimental data are evaluated and best values for level and gamma-ray energies, quantum numbers, lifetimes, gamma-ray intensities, and other nuclear properties are recommended. Inconsistencies and discrepancies that exist in the literature are noted. This work supersedes the earlier evaluation by D. De Frenne and E. Jacobs (1996De55), published in Nuclear Data Sheets79, 639 (1996)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Comparative study of polar and semipolar (112⁻2) InGaN layers grown by metalorganic vapour phase epitaxy

InGaN layers were grown simultaneously on (112⁻2) GaN and (0001) GaN templates by metalorganic vapour phase epitaxy. At higher growth temperature (≥750°C), the indium content (<15%) of the (112⁻2) and (0001) InGaN layers was similar. However, for temperatures less than 750°C, the indium content of the (112⁻2) InGaN layers (15%–26%) were generally lower than those with (0001) orientation (15%–32%). The compositional deviation was attributed to the different strain relaxations between the (112⁻2) and (0001) InGaN layers. Room temperature photoluminescence measurements of the (112⁻2) InGaN layers showed an emission wavelength that shifts gradually from 380 nm to 580 nm with decreasing growth temperature (or increasing indium composition). The peak emission wavelength of the (112⁻2) InGaN layers with an indium content of more than 10% blue-shifted a constant value of ≈(50–60) nm when using higher excitation power densities. This blue-shift was attributed to band filling effects in the layers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Intentional anisotropic strain relaxation in (112{sup ¯}2) oriented Al{sub 1−x}In{sub x}N one-dimensionally lattice matched to GaN

We report on (112{sup ¯}2) oriented Al{sub 1−x}In{sub x}N grown by low pressure metal organic vapor phase epitaxy on (112{sup ¯}2) GaN templates on patterned r-plane sapphire. The indium incorporation efficiency as well as the growth rate of (112{sup ¯}2) oriented layers are similar to c-plane oriented Al{sub 1−x}In{sub x}N layers. Deposition of thick Al{sub 1−x}In{sub x}N layers does not lead to additional roughening like in case of c-plane oriented Al{sub 1−x}In{sub x}N. Independent of the thickness, the degree of relaxation of layers lattice matched in m-direction is in the range of 33%–45% in [112{sup ¯}3{sup ¯}]-direction. Associated with the relaxation in [112{sup ¯}3{sup ¯}]-direction, there is a tilt of the Al{sub 1−x}In{sub x}N layers around the [11{sup ¯}00] axis due to slip of threading dislocations on the basal (0001)-plane. Relaxation in m-direction is not observable for layers lattice matched in [112{sup ¯}3{sup ¯}] direction. The possibility to adjust the lattice parameter of AlInN in [112{sup ¯}3{sup ¯}] direction without changing the lattice parameter in m-direction by anisotropic strain relaxation opens up opportunities for subsequent growth of optically active structures. One possibility is to form relaxed buffer layers for GaInN quantum well structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Temporally and spatially resolved photoluminescence investigation of (112{sup ¯}2) semi-polar InGaN/GaN multiple quantum wells grown on nanorod templates

By means of time-resolved photoluminescence (PL) and confocal PL measurements, temporally and spatially resolved optical properties have been investigated on a number of In{sub x}Ga{sub 1−x}N/GaN multiple-quantum-well (MQW) structures with a wide range of indium content alloys from 13% to 35% on (112{sup ¯}2) semi-polar GaN with high crystal quality, obtained through overgrowth on nanorod templates. With increasing indium content, the radiative recombination lifetime initially increases as expected, but decreases if the indium content further increases to 35%, corresponding to emission in the green spectral region. The reduced radiative recombination lifetime leads to enhanced optical performance for the high indium content MQWs as a result of strong exciton localization, which is different from the behaviour of c-plane InGaN/GaN MQWs, where quantum confined Stark effect plays a dominating role in emission process.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2003

The Effect of Film Composition on the Texture and Grain Size of CuInS2 Prepared by Spray Pyrolysis

Ternary single-source precursors were used to deposit CuInS2 thin films using chemical spray pyrolysis. We investigated the effect of the film composition on texture, secondary phase formation, and grain size. As-grown films were most often In-rich. They became more (204/220)-oriented as indium concentration increased, and always contained a yet unidentified secondary phase. The (112)-prefened orientation became more pronounced as the film composition became more Cu-rich. The secondary phase was determined to be an In-rich compound based on composition analysis and Raman spectroscopy. In addition, as-grown Cu-rich (112)-oriented films did not exhibit the In-rich compound. Depositing a thin Cu layer prior to the growth of CuInS2 increased the maximum grain size from - 0.5 micron to - 1 micron, and prevented the formation of the In-rich secondary phase.

Jin, Michael H.↗
DOE OSTI2015

Mobility of indium on the ZnO(0001) surface

The mobility of indium on the Zn-polar (0001) surface of single crystal ZnO wafers was investigated using real-time x-ray photoelectron spectroscopy. A sudden transition in the wettability of the ZnO(0001) surface was observed at ∼520 °C, with indium migrating from the (0001{sup ¯}) underside of the wafer, around the non-polar (11{sup ¯}00) and (112{sup ¯}0) sidewalls, to form a uniform self-organized (∼20 Å) adlayer. The In adlayer was oxidized, in agreement with the first principles calculations of Northrup and Neugebauer that In{sub 2}O{sub 3} precipitation can only be avoided under a combination of In-rich and Zn-rich conditions. These findings suggest that unintentional In adlayers may form during the epitaxial growth of ZnO on indium-bonded substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Systems and methods for forming solar cells with CuInSe.sub.2 and Cu(In,Ga)Se.sub.2 films

Systems and methods for forming solar cells with CuInSe.sub.2 and Cu(In,Ga)Se.sub.2 films are provided. In one embodiment, a method comprises: during a first stage (220), performing a mass transport through vapor transport of an indium chloride (InCl.sub.x) vapor (143, 223) and Se vapor (121, 225) to deposit a semiconductor film (212, 232, 252) upon a substrate (114, 210, 230, 250); heating the substrate (114, 210, 230, 250) and the semiconductor film to a desired temperature (112); during a second stage (240) following the first stage (220), performing a mass transport through vapor transport of a copper chloride (CuCl.sub.x) vapor (143, 243) and Se vapor (121, 245) to the semiconductor film (212, 232, 252); and during a third stage (260) following the second stage (240), performing a mass transport through vapor transport of an indium chloride (InCl.sub.x) vapor (143, 263) and Se vapor (121, 265) to the semiconductor film (212, 232, 252).

14 SOLAR ENERGY↗
DOE OSTI2014

Photoconductivity in reactively evaporated copper indium selenide thin films

Copper indium selenide thin films of composition CuInSe{sub 2} with thickness of the order of 130 nm are deposited on glass substrate at a temperature of 423 ±5 K and pressure of 10{sup −5} mbar using reactive evaporation, a variant of Gunther's three temperature method with high purity Copper (99.999%), Indium (99.999%) and Selenium (99.99%) as the elemental starting materials. X-ray diffraction (XRD) studies shows that the films are polycrystalline in nature having preferred orientation of grains along the (112) plane. The structural type of the film is found to be tetragonal with particle size of the order of 32 nm. The structural parameters such as lattice constant, particle size, dislocation density, number of crystallites per unit area and strain in the film are also evaluated. The surface morphology of CuInSe{sub 2} films are studied using 2D and 3D atomic force microscopy to estimate the grain size and surface roughness respectively. Analysis of the absorption spectrum of the film recorded using UV-Vis-NIR Spectrophotometer in the wavelength range from 2500 nm to cutoff revealed that the film possess a direct allowed transition with a band gap of 1.05 eV and a high value of absorption coefficient (α) of 10{sup 6} cm{sup −1} at 570 nm. Photoconductivity at room temperature is measured after illuminating the film with an FSH lamp (82 V, 300 W). Optical absorption studies in conjunction with the good photoconductivity of the prepared p-type CuInSe{sub 2} thin films indicate its suitability in photovoltaic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Markedly distinct growth characteristics of semipolar (112{sup ¯}2) and (1{sup ¯}1{sup ¯}22{sup ¯}) InGaN epitaxial layers

We compare metalorganic vapor phase epitaxy of InGaN/GaN heterostructures on semipolar (112{sup ¯}2) and (1{sup ¯}1{sup ¯}22{sup ¯}) GaN bulk substrates. In incorporation efficiency is higher for (112{sup ¯}2) InGaN, which enables higher temperature growth of InGaN and is beneficial for quality improvement. InGaN/GaN quantum wells (QWs) on (112{sup ¯}2) show abrupt interfaces, but those on (1{sup ¯}1{sup ¯}22{sup ¯}) tend to form three-dimensional nanofacets. Differences in growth temperature and structures of the (112{sup ¯}2) and (1{sup ¯}1{sup ¯}22{sup ¯}) QWs cause higher internal quantum efficiencies of the (112{sup ¯}2) [(1{sup ¯}1{sup ¯}22{sup ¯})] QWs at shorter (longer) wavelengths.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (112{sup -}2) GaN templates

We present results of scanning transmission electron tomography on GaN/(In,Ga)N/GaN nanocolumns (NCs) that grew uniformly inclined towards the patterned, semi-polar GaN(112{sup -}2) substrate surface by molecular beam epitaxy. For the practical realization of the tomographic experiment, the nanocolumn axis has been aligned parallel to the rotation axis of the electron microscope goniometer. The tomographic reconstruction allows for the determination of the three-dimensional indium distribution inside the nanocolumns. This distribution is strongly interrelated with the nanocolumn morphology and faceting. The (In,Ga)N layer thickness and the indium concentration differ between crystallographically equivalent and non-equivalent facets. The largest thickness and the highest indium concentration are found at the nanocolumn apex parallel to the basal planes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Basal-plane growth of cadmium arsenide by molecular beam epitaxy

(001)-oriented thin films of the three-dimensional Dirac semimetal cadmium arsenide can realize a quantum spin Hall insulator and other kinds of topological physics, all within the flexible architecture of epitaxial heterostructures. Here, we report a method for growing (001) cadmium arsenide films using molecular beam epitaxy. The introduction of a thin indium arsenide wetting layer improves surface morphology and structural characteristics, as measured by x-ray diffraction and reflectivity, atomic force microscopy, and scanning transmission electron microscopy. The electron mobility of 50-nm-thick films is found to be 9300cm 2 /Vs at 2 K, comparable to the highest-quality films grown in the conventional (112) orientation. This work demonstrates a simple experimental framework for exploring topological phases that are predicted to exist in proximity to the three-dimensional Dirac semimetal phase.

36 MATERIALS SCIENCE↗
NASA NTRS2008

Spray Chemical Vapor Deposition of Single-Source Precursors for Chalcopyrite I-III-VI2 Thin-Film Materials

Thin-film solar cells on flexible, lightweight, space-qualified substrates provide an attractive approach to fabricating solar arrays with high mass-specific power. A polycrystalline chalcopyrite absorber layer is among the new generation of photovoltaic device technologies for thin film solar cells. At NASA Glenn Research Center we have focused on the development of new single-source precursors (SSPs) for deposition of semiconducting chalcopyrite materials onto lightweight, flexible substrates. We describe the syntheses and thermal modulation of SSPs via molecular engineering. Copper indium disulfide and related thin-film materials were deposited via aerosol-assisted chemical vapor deposition using SSPs. Processing and post-processing parameters were varied in order to modify morphology, stoichiometry, crystallography, electrical properties, and optical properties to optimize device quality. Growth at atmospheric pressure in a horizontal hotwall reactor at 395 C yielded the best device films. Placing the susceptor closer to the evaporation zone and flowing a more precursor-rich carrier gas through the reactor yielded shinier-, smoother-, and denser-looking films. Growth of (112)-oriented films yielded more Cu-rich films with fewer secondary phases than growth of (204)/(220)-oriented films. Post-deposition sulfur-vapor annealing enhanced stoichiometry and crystallinity of the films. Photoluminescence studies revealed four major emission bands and a broad band associated with deep defects. The highest device efficiency for an aerosol-assisted chemical vapor deposited cell was one percent.

Hepp, Aloysius F.↗
NASA NTRS2006

Aerosol-Assisted Chemical Vapor Deposited Thin Films for Space Photovoltaics

Copper indium disulfide thin films were deposited via aerosol-assisted chemical vapor deposition using single source precursors. Processing and post-processing parameters were varied in order to modify morphology, stoichiometry, crystallography, electrical properties, and optical properties in order to optimize device-quality material. Growth at atmospheric pressure in a horizontal hot-wall reactor at 395 C yielded best device films. Placing the susceptor closer to the evaporation zone and flowing a more precursor-rich carrier gas through the reactor yielded shinier, smoother, denser-looking films. Growth of (112)-oriented films yielded more Cu-rich films with fewer secondary phases than growth of (204)/(220)-oriented films. Post-deposition sulfur-vapor annealing enhanced stoichiometry and crystallinity of the films. Photoluminescence studies revealed four major emission bands (1.45, 1.43, 1.37, and 1.32 eV) and a broad band associated with deep defects. The highest device efficiency for an aerosol-assisted chemical vapor deposited cell was 1.03 percent.

Hepp, Aloysius F.↗
DOE OSTI2015

High-accuracy coupled cluster calculations of atomic properties

The four-component Fock-space coupled cluster and intermediate Hamiltonian methods are implemented to evaluate atomic properties. The latter include the spectra of nobelium and lawrencium (elements 102 and 103) in the range 20000-30000 cm{sup −1}, the polarizabilities of elements 112-114 and 118, required for estimating their adsorption enthalpies on surfaces used to separate them in accelerators, and the nuclear quadrupole moments of some heavy atoms. The calculations on superheavy elements are supported by the very good agreement with experiment obtained for the lighter homologues.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Fabrication and characterization of Cu(In,Ga)Se{sub 2} p-channel thin film transistors

Cu(In,Ga)Se{sub 2} thin film transistors are demonstrated with the on-off ratio of ∼10{sup 3} and the saturation hole mobility of 1.8 cm{sup 2}/V-s. Due to the high hole concentration (∼5 × 10{sup 17 }cm{sup −3}), the channel needs to be etched to turn off for the accumulation mode operation. The Cu(In,Ga)Se{sub 2} film after etching reveals a larger mobility, and a narrower (112) X-ray diffraction line than the original thick layer, indicating the better crystallinity of the initial growth as compared to the subsequent Cu(In,Ga)Se{sub 2} layer. Both the hole concentration and the saturation mobility increase with the decreasing Cu/(In + Ga) ratio probably due to the effect of Cu vacancies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The influence of Se pressure on the electronic properties of CuInSe{sub 2} grown under Cu-excess

Standard Cu-poor Cu(In,Ga)Se{sub 2} solar cell absorbers are usually prepared under high Se excess since the electronic properties of the absorbers are better if prepared under high Se pressure. However, in CuInSe{sub 2}, grown under Cu-excess, it was found that solar cell properties improve with lowering the Se pressure, mostly because of reduced tunnel contribution to the recombination path. Lower Se pressure during Cu-rich growth leads to increased (112) texture of the absorber films, to better optical film quality, as seen by increased excitonic luminescence and to lower net doping levels, which explains the reduced tunnelling effect. These findings show an opposite trend from the one observed in Cu-poor Cu(In,Ga)Se{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Observation of [VCu1–Ini2+VCu1–] Defect Triplets in Cu-Deficient CuInS2

Copper indium disulfide (CuInS2) is a semiconductor with a direct energy band gap of 1.53 eV, an optimal value for highly efficient thin-film solar cells. But it has reached only ~ 11 % power conversion efficiency, far less than the theoretically achievable value of ~ 30 %. The cause of this low performance is not understood. A single crystal grown from 1 mol% Cu-deficient melt was studied, using atomic resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and electron dispersive spectroscopy (EDS). While the bulk crystal is exactly stoichiometric CuInS2, it contains nanometer-thick, structurally coherent, Cu-deficient interphases that form along rotational twin boundaries in the {112} plane. Transition zones from bulk crystal to interphase are observed, where In is seen to move from its normal site InIn in the chalcopyrite structure to a tetrahedral interstitial site Ini, while Cu remains in its normal CuCu position. Two InIn rows of the bulk crystal merge into one row of Ini, causing excess Ini in the interphase. The concentrations of CuCu and Ini reflect a ratio of Cu vacancies, VCu, to excess Ini of ~ 2. Their relative lattice positions, and the high electrical resistivity of the crystal, suggests that VCu and excess Ini ‘precipitate’ as self-compensating, electrically neutral, [VCu1- Ini2+ VCu1-] defect triplets. This is the first atomic-level observation of the ordered defect that has been invoked as the basic structural modifier in chalcopyrite compound homologs. The interphases introduce an optical gap of 1.47 eV. Electron trapping in band tail states, evident from a photoconductivity exponent of 0.54, is the likely cause of an unusually low electron mobility of 0.1 cm2V-1s-1. The overall result is that making CuInS2 slightly copper-poor inserts nanometer-thick layers of the interphase into the bulk crystal. This study shows that apparently conflicting results of the effect of Cu deficiency on CuInS2 thin-film solar cells may be resolved by analyzing structure and composition at nanometer spatial resolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural and electronic properties of InN nanowire network grown by vapor-liquid-solid method

Growth of InN nanowires have been carried out on quartz substrates at different temperatures by vapor-liquid-solid (VLS) technique using different thicknesses of Au catalyst layer. It has been found that a narrow window of Au layer thickness and growth temperature leads to multi-nucleation, in which each site acts as the origin of several nanowires. In this multi-nucleation regime, several tens of micrometer long wires with diameter as small as 20 nm are found to grow along [112{sup -}0] direction (a-plane) to form a dense network. Structural and electronic properties of these wires are studied. As grown nanowires show degenerate n-type behavior. Furthermore, x-ray photoemission study reveals an accumulation of electrons on the surface of these nanowires. Interestingly, the wire network shows persistence of photoconductivity for several hours after switching off the photoexcitation.

36 MATERIALS SCIENCE↗