UK PubMed Central (United Kingdom)

The use of sub-nanometer resolution electron density as spatial constraints for denovo and ab-initio structure prediction requires knowledge of protein boundaries...Full Text Available

Energy Technology Data Exchange (ETDEWEB)

Progress in the development of high-efficiency GaAs solar cells on low-cost, large-area, large-grain, optical-grade polycrystalline Ge substrates is described in this paper. First, we present results on the growth of specular GaAs-AlGaAs layers, across the various crystalline orientations of a polycrystalline Ge substrate, by metallorganic chemical vapor deposition (MOCVD). Second, we present the preliminary optimization of minority-carrier properties of GaAs-AlGaAs structures on poly-Ge substrates towards the improvement of GaAs solar cells. We have demonstrated comparable minority-carrier lifetimes in GaAs double-hetero structures grown on optical-grade poly-Ge substrates and electronic-grade single-crystal Ge substrates. In addition, we describe device-structure optimization that have led us to achieve a open-circuit voltage of {approximately}1 Volt in a ...

International Nuclear Information System (INIS)

A new structure of GaAs MESFET with high radiation tolerance is proposed. Changes in electrical parameters of a GaAs MESFET as a function of total #gamma#-ray dose have been found to be caused mainly by a decrease in the effective carrier concentration in an active layer. The authors have designed a new structure from a simulation based on an empirical relationship between the changes of the effective carrier concentration and the total #gamma#-ray dose. It has been successfully demonstrated by utilizing a highly-doped thin active layer (4 x 10"1"8 cm"-"3, 100 Angstrom) grown by OMVPE. This MESFET can withstand a dose ten times higher [1 x 10"9 rads(GaAs)] than a conventional one can.

Energy Technology Data Exchange (ETDEWEB)

GaAs material and device structure optimization studies on optical-grade, millimeter-and-less grain-size polycrystalline Ge substrates are presented. We discuss the growth of high-quality epitaxial layers across various crystalline orientations of a polycrystalline substrate; this is important for obtaining high-performance solar cells. The GaAs solar cell on n-type poly-Ge substrate is a p-on-n type, with an undoped spacer between the p-emitter and the n-base. An experimental study of dark currents in these junctions, with and without the spacer, as a function of temperature (77K to 288K) is presented; this study suggests that the spacer reduces the tunneling contribution to dark current. In addition, we describe device-structure optimization studies that have led us to achieve an open-circuit voltage (V{sub oc}) exceeding 1 Volt and an AM1.5 efficiency of {approximately}19{percent} for a 4-cm{sup ...

Energy Technology Data Exchange (ETDEWEB)

Quaternary semiconductor compounds are ideal candidates for use in monolithic cascade solar cells because the lattice constant and the bandgap of such compounds can be independently varied. The quaternary semiconductor compound Ga[sub 0.83]In[sub 0.17]As[sub 0.67]P[sub 0.33] not only is lattice matched to GaAs and Ge but also provides a current matched top cell for the GaInAsP/Ge monolithic cascade solar cell. Under concentration of 100 suns, the projected efficiency for such a cell is about 34%. The growth of Ga[sub 0.83]In[sub 0.17]As[sub 0.67]P[sub 0.33] lattice matched to GaAs and Ge has been demonstrated. GaInAsP solar cells have been grown on both GaAs and Ge substrates. A GaInAsP on GaAs solar cell with an active area efficiency of 23.2% for 1 sun, AM 1.5 direct illumination has been prepared. A proposed structure for the GaInAsP/Ge cascade cell is also given.

Science.gov (United States)

The use of Auger electron spectroscopy (AES) combined with in situ sputter etching for revealing the metallurgy of the metal-semiconductor interface is presented. The physical basis, measurement techniques, and data interpretation for Auger analysis of thin-film structures are briefly reviewed. Results of a detailed study of an alloyed multilayered contact (Ni/Au-Ge) on n-type epitaxial GaAs are summarized to illustrate how electrical and metallurgical contact properties can be correlated using AES. In addition, the results of a study of the growth kinetics and chemical phase identification of palladium silicide on single-crystal Si is given, as well as the initial results of a study of aluminum-palladium silicide interaction at elevated temperature. (auth)

Science.gov (United States)

The growth of an oxide interfacial layer was recently found to increase the open-circuit voltage (OCV) and efficiency by up to 60 per cent in GaAs metal-semiconductor solar cells. Details of oxidation techniques to provide the necessary oxide thickness and chemical structure and using ozone, water-vapor-saturated oxygen, or oxygen gas discharges are described, as well as apparent crystallographic orientation effects. Preliminary results of the oxide chemistry obtained from X-ray, photoelectron spectroscopy are given. Ratios of arsenic oxide to gallium oxide of unity or less seem to be preferable. Samples with the highest OVC predominantly have As(+3) in the arsenic oxide rather than As(+5). A major difficulty at this time is a reduction in OCV by 100-200 mV when the antireflection coating is vacuum deposited.

British Library Electronic Table of Contents (United Kingdom)

Epitaxial thin films of nanotwinned face-centered cubic metals such as Cu possess an unprecedented combination of high hardness and high electrical conductivity due to the unique structure of nanometer-spaced coherent twin boundaries. Recent studies of in-situ nanoindentation in a transmission electron microscope have provided new insights on the deformation behavior of nanotwins that are reviewed here. In particular, two unit processes are highlighted: first, stress-induced migration of ?3 {112} incoherent twin boundary that leads to de-twinning of nanotwins; second, twinning dislocation can be multiplied at ?3 {111} coherent twin boundary.

Energy Technology Data Exchange (ETDEWEB)

The reactions between (100) GaAs and the near-noble metals Ni, Pd, and Pt have been investigated by application of high-resolution transmission electron microscopy (TEM), energy-dispersive analysis of x rays in the scanning TEM and Rutherford backscattering spectrometry. Emphasis is placed on the evolution of the phase distributions, film compositions, and interface morphologies during annealing at temperatures up to 480 /sup 0/C. The first phase in the Ni/GaAs reaction is shown to have the nominal composition Ni/sub 3/GaAs. Ternary phases of the type Pd/sub x/GaAs are also found to be the dominant products of the Pd/GaAs reaction. Conversely, only binary phases result from the Pt/GaAs reaction. These observations are used to construct isothermal sections of the M--Ga--As thin-film phase diagrams. The behavior of a thin (1--2 nm) native oxide--hydrocarbon layer during the Ni/GaAs, Pd/GaAs, and Pt/GaAs reactions is also investigated. Only the ...

Energy Technology Data Exchange (ETDEWEB)

Y{sub 2-x}Tb{sub x}SiO{sub 5} and Y{sub 2-x}Eu{sub x}SiO{sub 5} nanophosphors with seven different kinds of silicate sources were synthesized by sol-gel method. The structures have been investigated to be composed of nanometer-size grains of 30-60 nm through X-ray diffraction (XRD) and scanning electron microscopy (SEM) was used to compare the different morphology of patterns from seven different silicon sources. The photoluminescence of Y{sub 2-x}Tb{sub x}SiO{sub 5} was investigated as a function of silicate sources and the results revealed that these nanometer materials showed the characteristic emission {sup 5}D{sub 4} {yields} {sup 7}F{sub J} (J 6, 5, 4, 3) of Tb ions. The characteristic emission {sup 5}D{sub 0} {yields} {sup 7}F{sub J} (J = 1, 2, 4) of Eu ions was also found in the materials of Y{sub 2-x}Eu{sub x}SiO{sub 5}.

International Nuclear Information System (INIS)

The possibilities to grow isolated structures of complex oxides by pulsed laser deposition through stencils were investigated. A stencil consisting of a SiN membrane with apertures of several hundred nanometers embedded in a Si chip is placed in front of a heated substrate (up to 750 degrees Celsius). Deposition through these apertures results in resistless, direct patterning by local deposition of complex oxides like ferroelectric Lead Zirconate Titanate. The created isolated structures were analyzed by AFM imaging. Under-deposition, in this work called broadening, is inevitable during stencil deposition and is depending on deposition parameters, especially pressure. Different causes of broadening are mapped and discussed.

International Nuclear Information System (INIS)

We present the results of a comprehensive study of the temperature dependences of the quantum efficiency for ultraviolet detectors based on GaAs, GaP and 4H--SiC Schottky structures, and on Si, GaAs p-n structures. For ultraviolet detectors based on Schottky structures, the quantum efficiency increases with increasing temperature for all photon energies, even including the semiconductor intrinsic absorption region. On the other hand, for ultraviolet detectors based on p-n structures, the quantum efficiency is practically temperature independent in the semiconductor intrinsic absorption region. The change in the quantum efficiency for the GaAs and Si detectors is less than 0.01% per degree. To explain the measurements, a variable trap occupancy model is presented. Subsurface imperfections of the semiconductor cause fluctuations in the profile ...

British Library Electronic Table of Contents (United Kingdom)

Novel fluoroalkyl end-capped vinyltrimethoxysilane oligomer/hydroxyapatite (HAp) nanocomposites were prepared by the reaction of calcium nitrate tetrahydrate and phosphoric acid in the presence of the corresponding oligomer. These fluorinated oligomer/HAp composites thus obtained are nanometer size-controlled fine particles (83-173 nm), and were found to exhibit good dispersibility in methanol, ethanol, and isopropyl alcohol. These fluorinated HAp nanocomposites were applied to the surface modification of glass and poly(methyl methacrylate) (PMMA) to exhibit good hydro- and oleophobic characteristics imparted by fluorine on their surface. In addition, the surface structural changes of the modified polyethylene terephtalate and PMMA films treated with these fluorinated nanocomposites before...

Energy Technology Data Exchange (ETDEWEB)

Room-temperature cw operation for InGaP/InGaAlP double heterostructure (DH) laser diodes on GaAs substrates was achieved for the first time. The DH wafers were grown by low-pressure metalorganic chemical vapor deposition using methyl metalorganics. A lasing wavelength of 679 nm and a threshold current of 109 mA at 24C were obtained for an inner stripe structure laser diode with a 250- m-long and 7- m stripe geometry. The laser operated at up to 51C. The characteristic temperature T0 was 87 K at around room temperature. The lowest threshold current density, 5.0 kA/cmS, was obtained with a 20- m stripe width laser diode under room-temperature pulsed operation.

Energy Technology Data Exchange (ETDEWEB)

No abstract prepared.

Energy Technology Data Exchange (ETDEWEB)

Solid-state nuclear magnetic resonance (NMR) has been used to explore the nanometer-scale structure of Nafion, the widely used fuel cell membrane, and its composites. We have shown that solid-state NMR can characterize chemical structure and composition, domain size and morphology, internuclear distances, molecular dynamics, etc. The newly-developed water channel model of Nafion has been confirmed, and important characteristic length-scales established. Nafion-based organic and inorganic composites with special properties have also been characterized and their structures elucidated. The morphology of Nafion varies with hydration level, and is reflected in the changes in surface-to-volume (S/V) ratio of the polymer obtained by small-angle X-ray scattering (SAXS). The S/V ratios of different Nafion models have been evaluated numerically. It has been found that only the water channel model gives the ...

Energy Technology Data Exchange (ETDEWEB)

No abstract prepared

Energy Technology Data Exchange (ETDEWEB)

Modelization of crack propagation and theoretical prediction of rupture are the two main objectives of researchers in stress corrosion cracking. Nevertheless, to reach this aim, the behavior of the passive film which appears spontaneously on the substrate in contact with an environment has to be known. This structural and mechanical characterization is all the more difficult because the number of parameters is important: crystallinity rate, defects concentration, thickness (about a few nanometers), electric field, chemical composition (a lot of oxides are present), peeling layers (atomic structure for example) and some hypothesis can be made about their multi-layer structure, their chemical composition or their epitaxial character... Passive films formed on 316L or 304L stainless steels in different aqueous solutions (in ambient air, in MgCl{sub 2} at 117 deg. C...) have been studied and some important ...

International Nuclear Information System (INIS)

Electrodeposition of semiconducting iron oxide (Fe_2O_3) thin film was carried out from an alkaline sulphate bath. A 0.1 M ferrous sulphate (FeSO_4#centre dot#7H_2O) was complexed with 0.1 M citric acid. By addition of 1 N NaOH, pH of the solution was made alkaline (pH=9) and deposition of iron oxide (Fe_2O_3) thin films was carried out potentiostatically at room temperature (300 K). From cyclic voltametry (CV), electrochemical studies were carried out for deposition of iron oxide thin films. The XRD studies reveal that Fe_2O_3 with epsilon (#epsilon#) phase having monoclinic crystal structure is formed. By observing scanning electron microscope (SEM), it is seen that iron oxide films were homogeneous, uniform and well covered to surface of the substrate. Grain size was found to be in nanometers range from XRD analysis. The optical band gap of Fe_2O_3 thin film was estimated to be 1.90 eV. Electrical resistivity was order of 10"4 #OMEGA# cm. ...

International Nuclear Information System (INIS)

The intensity of superstructure reflections and associated diffuse scattering from In_0_._5Ga_0_._5P and In_0_._5Al_0_._5P epitaxic layers grown on (001) GaAs substrates was mapped in reciprocal space. The Warren-Cowley short-range-order parameters were obtained through the usual process for evaluating Fourier coefficients. Varying values for the correlation length in different directions indicate how group III atoms stack up in ordered states. The resultant structure with long-range order confirms the hypothesis made on the basis of electron diffraction and high-resolution transmission electron microscopy studies. (orig.).

British Library Electronic Table of Contents (United Kingdom)

Isosteric heats and adsorption isotherms of methane on nanometer active carbon were measured at supercritical temperature (273-373 K) and pressure from 0 to 10 MPa. The measured data agreed well with Dubinin-Astakhov (DA) model at lower pressure but failed when pressure exceeded a special range. General Freundlich (GF) equation was used to modify the DA equation at high pressure and thus formed a combined bisection model GFDA. The adsorption mechanism of methane on nanometer active carbon was raised according to GFDA model and the heterogeneous energy distribution of the adsorbent was analyzed.

Energy Technology Data Exchange (ETDEWEB)

The research supported by this Department of Energy contract has primarily been devoted to the study of the electronic properties of surfaces with sub-micron size. In previous years, we have studied the photoexcitation of electrons from field emission tips by a focussed Argon-ion laser beam tuned to operate at specific photon energy. The photoexcited electrons escape into the vacuum by tunneling through a surface potential barrier which is distorted by the application of a strong electric field. The interest in these experiments lies in a better understanding of the photoexcitation process at low photon energies. The techniques that have been developed directly measure the excited state energy distribution of electrons emitted through the surface potential barrier. The basic information gained from this research is relevant to opto-electronic devices which rely on photoexcitation of electrons in the presence of strong interfacial electric fields for their operation. In addition, the ...

International Nuclear Information System (INIS)

Reactive milling of NiO + Al powder mixture resulted in the formation of NiAl-Al_2O_3 nanocomposite powders, with a crystallite size of about 20 nm. The Hall-Williamson analysis revealed that NiAl showed an orientation dependent crystallite size after short processing time and orientation dependent internal strain after long milling time. Both anisotropies were removed by heating the powders in the differential scanning calorimetry. Calorimetric studies showed one exothermic effect attributed to the reduction reaction of NiO and endothermic one associated with melting of Al. Two methods were applied for powders compaction: resistance sintering and pulse electric discharge. In both cases the densities of abut 90% of the theoretical value were achieved. A significant increase in average NiAl crystallites size in compacted samples was observed, up to several hundreds of nanometers.(author)

Energy Technology Data Exchange (ETDEWEB)

A modulation transfer function (MTF) calibration method based on binary pseudo-random (BPR) gratings and arrays [Proc. SPIE 7077-7 (2007), Opt. Eng. 47, 073602 (2008)] has been proven to be an effective MTF calibration method for a number of interferometric microscopes and a scatterometer [Nucl. Instr. and Meth. A616, 172 (2010)]. Here we report on a further expansion of the application range of the method. We describe the MTF calibration of a 6 inch phase shifting Fizeau interferometer. Beyond providing a direct measurement of the interferometer's MTF, tests with a BPR array surface have revealed an asymmetry in the instrument's data processing algorithm that fundamentally limits its bandwidth. Moreover, the tests have illustrated the effects of the instrument's detrending and filtering procedures on power spectral density measurements. The details of the development of a BPR test sample suitable for calibration of scanning and transmission electron ...

Energy Technology Data Exchange (ETDEWEB)

The research supported by this Department of Energy contract has primarily been devoted to the study of the electronic properties of surfaces with sub-micron size. In previous years, we have studied the photoexcitation of electrons from field emission tips by a focussed Argon-ion laser beam tuned to operate at specific photon energy. The photoexcited electrons escape into the vacuum by tunneling through a surface potential barrier which is distorted by the application of a strong electric field. The interest in these experiments lies in a better understanding of the photoexcitation process at low photon energies. The techniques that have been developed directly measure the excited state energy distribution of electrons emitted through the surface potential barrier. The basic information gained from this research is relevant to opto-electronic devices which rely on photoexcitation of electrons in the presence of strong interfacial electric fields for their operation. In addition, the ...

Energy Technology Data Exchange (ETDEWEB)

No abstract prepared.

International Nuclear Information System (INIS)

We report on the transport properties of a high mobility two-dimensional hole system (2DHS) confined in GaAs/AlGaAs quantum wells grown by molecular-beam epitaxy on the (100) surface of GaAs. The quantum wells are modulation doped with carbon utilizing a resistive filament source. At T=0.3 K and carrier density p=1x10"1"1 cm"-"2, a mobility of 10"6 cm"2/Vs is achieved. At fixed carrier density p=10"1"1 cm"-"2, the mobility is found to be a nonmonotonic function of the quantum well width. The mobility peaks at 10"6 cm"2/Vs for a 15-nm well and is reduced for both smaller and larger well widths for these (100) samples. The mobility anisotropy is found to be small. Mobility along [011] is approximately 20% higher than along the [011] direction. In addition, the low-temperature carrier density is found to have low sensitivity to light. The hole density increases by only #approx#10% after exposure to red light at T=4.2 K. In structures designed for ...

Energy Technology Data Exchange (ETDEWEB)

Computation of effective flow properties of fluids in porous media based on three dimensional (3D) pore structure information has become more successful in the last few years, due to both improvements in the input data and the network models. Computed X-ray microtomography has been successful in 3D pore imaging at micron scale, which is adequate for many sandstones. For other rocks of economic interest, such as chalk and diatomite, submicron resolution is needed in order to resolve the 3D-pore structure. To achieve submicron resolution, a new method of sample serial sectioning and imaging using Focused Ion Beam (FIB) technology has been developed and 3D pore images of the pore system for diatomite and chalk have been obtained. FIB was used in the milling of layers as wide as 50 micrometers and as thin as 100 nanometers by sputtering of atoms from the sample surface. The focused ion beam, consisting of gallium ions (Ga+) ...

International Nuclear Information System (INIS)

This thesis is devoted to the study and development of Heterojunction Bipolar Transistors (HBTs) designed for high voltage operation. The work concentrates on the use of wide bandgap III-V semiconductor materials as the collector material and their associated properties influencing breakdown, such as impact ionisation coefficients. The work deals with issues related to incorporating a wide bandgap collector into double heterojunction structures such as conduction band discontinuities at the base-collector junction and results are presented which detail, a number of methods designed to eliminate the effects of such discontinuities. In particular the use of AlGaAs as the base material has been successful in eliminating the conduction band spike at this interface. A method of electrically injecting electrons into the collector has been employed to investigate impact ionisation in GaAs, GaInP and AlInP which has used the intrinsic gain of the ...

International Nuclear Information System (INIS)

The DLTS technique was employed to study deep defect centers in Si doped epitaxial layers of Al_0_._3_7Ga_0_._1_6In_0_._4_7P grown by MOCVD as a part of epitaxial structure GaAs/AlGaInP/GaAs on GaAs substrates. A high concentration of DX centers located in a region near the inverted interface GaAs/Al_0_._3_7Ga_0_._1_6In_0_._4_7P was found. The width of this region with the maximum DX center concentration ranges from 5 to 20 nm. By filling the DX centers in the whole region, the activation energy for electron emission was found to be 0.48 eV. However, it is shown for the first time, that the activation energy of the DX center increases with increasing the distance from the GaAs/Al_0_._3_7Ga_0_._1_6In_0_._4_7P inverted interface. A nonuniform of the DX center concentration on the wafers is also observed. The concentration varies in the range of 1#centre dot#10"1"7 cm"-"3 - 10"1"8 cm"-"3. (author)

Energy Technology Data Exchange (ETDEWEB)

High-purity and doped GaAs films have been grown by Liquid-phase epitaxy (LPE) for development of a blocked impurity band (BIB) detector for far-infrared radiation. The film growth process developed has resulted in the capability to grow GaAs with a net active impurity concentration below 1 x 10{sup 13} cm{sup -3}, ideal for the blocking layer of the BIB detector. The growth of n-type LPE GaAs films with donor concentrations below the metal-insulator transition, as required for the absorbing layer of a BIB detector, has been achieved. The control of the donor concentration, however, was found to be insufficient for detector production. The growth by LPE of a high-purity film onto a commercially grown vapor-phase epitaxial (VPE) n-type GaAs doped absorbing layer resulted in a BIB device that showed a significant reduction in the low-temperature dark current compared to the absorbing layer only. Extended ...

Science.gov (United States)

The zinc-blende (ZB) and wurtzite (W) structures are the most common crystal forms of binary octet semiconductors. In this work we have developed a simple scaling that systematizes the {ital T}=0 energy difference {Delta}{ital E}{sub W{minus}ZB} between W and ZB for all simple binary semiconductors. We have first calculated the energy difference {Delta}{ital E}{sub W{minus}ZB}{sup LDF}({ital AB}) for AlN, GaN, InN, AlP, AlAs, GaP, GaAs, ZnS, ZnSe, ZnTe, CdS, C, and Si using a numerically precise implementation of the first-principles local-density formalism (LDF), including structural relaxations. We then find a {ital linear} scaling between {Delta}{ital E}{sub W{minus}ZB}{sup LDF}({ital AB}) and an atomistic orbital-radii coordinate {ital {tilde R}}({ital A},{ital B}) that depends only on the properties of the free atoms {ital A} and {ital B} making up the binary compound {ital AB}. Unlike classical ...

Energy Technology Data Exchange (ETDEWEB)

The various factors that affect the open-circuit voltage ([ital V][sub oc]) of a two-terminal GaInP[sub 2]/GaAs tandem cell are examined. These include a) an anomalous problem associated with the GaAs bottom cell and b) back surface passivation of the thin GaInP[sub 2] top cell. Solutions to these problems are presented and yield tandem [ital V][sub oc]s close to the practical theoretical limits.

International Nuclear Information System (INIS)

This paper discusses the structural and compositional changes at the nanometer scale associated with the nucleation and growth of #alpha# precipitates in the #beta# titanium alloy Ti-5553 (Ti-5Al-5Mo-5 V-3Cr-0.5Fe) with #omega# precipitates acting as heterogeneous nucleation sites. The microstructural evolution in this alloy, during #beta#-solutionizing, quenching and aging type heat-treatments, has been investigated by combining results from scanning electron microscopy, orientation imaging microscopy, transmission electron microscopy, high-resolution TEM and three-dimensional atom probe (3DAP) tomography. Athermal #omega# precipitates form in this alloy on quenching from above the #beta# transus temperature. On isothermal annealing at low temperatures, these #omega# precipitates coarsen to form chemically ordered #omega# precipitates, accompanied by the nucleation of the stable #alpha# phase. Annealing at higher temperatures leads to ...

Energy Technology Data Exchange (ETDEWEB)

The magnetic susceptibility of GaAs samples containing a large concentration of native defects was investigated by dc magnetization measurements. Thin GaAs films grown by molecular-beam epitaxy at very low temperatures and bulk GaAs:S samples irradiated with fast neutrons have been studied. For all samples, the susceptibility follows a Curie-Weiss law, indicating the presence of localized magnetic moments. These moments are attributed to unpaired spins located at the native defects. Negative Curie-Weiss temperatures found for both neutron-irradiated and low-temperature-grown GaAs is a clear manifestation of an antiferromagnetic interaction between the moments. The presence of a highly inhomogeneous distribution of native defects has to be assumed to account for the observed antiferromagnetic ordering.

UK PubMed Central (United Kingdom)

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems...Full Text Available

UK PubMed Central (United Kingdom)

Inhibition of photosynthesis by ultraviolet-A radiation (UV-A, 315-380 nanometers) was examined in three marine angiosperms: Halophila engelmannii Aschers, Halodule wrightii...Full Text Available

Energy Technology Data Exchange (ETDEWEB)

The properties of Mn-doped GaAs layers grown by laser deposition were investigated with measurements of Hall effect and magneto-optical Kerr effect (MOKE). The electrical and magnetic parameters of the layers were defined by growth temperature and quantity of sputtered Mn. It was shown that room-temperature ferromagnetism is revealed by MOKE and, after ruby laser 25 ns pulse annealing, by Hall effect measurements.

Science.gov (United States)

By using a model dielectric matrix in electron self-energy evaluations the computational effort of a quasiparticle band-structure calculation for a semiconductor is greatly reduced. Applications to various systems with or without inversion symmetry, having narrow or wide band gaps, and semiconductor alloys demonstrate the reliability and accuracy of the method. Calculations have been performed for thirteen semiconducting or insulating materials: Si, LiCl, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, and the Al{sub 0.5}Ga{sub 0.5}As and In{sub 0.53}Ga{sub 0.47}As alloys. Excellent agreement with experimental results is obtained for the quasiparticle energies for these materials. The only three exceptions, {ital E}({Gamma}{sub 1{ital c}}) of AlP, {ital E}({ital L}{sub 1{ital c}}) of AlAs, and {ital E}({ital L}{sub 1{ital c}}) of AlSb are discussed and attributed to various experimental uncertainties. Several other ...

Science.gov (United States)

We present results from the first studies of electric-field effects on optical transitions in visible-band-gap InGaP/InAlGaP multiple-quantum-well (MQW) structures. These structures, grown at 775 [degree]C by metalorganic vapor phase epitaxy on (100) GaAs substrates misoriented 6[degree] towards P(111)[r angle][l angle]111[r angle]A, consist of nominally undoped MQWs surrounded by doped In[sub 0.49]Al[sub 0.51]P cladding layers to form [ital p]-[ital i]-[ital n] diodes. The Stark shifts of various allowed and forbidden quantum-well transitions were observed in bias-dependent electroreflectance spectra of In[sub 0.49]Ga[sub 0.51]P/In[sub 0.49](Al[sub 0.5]Ga[sub 0.5])[sub 0.51]P MQW samples with 10-nm-thick layers. We find the magnitude of these shifts to depend on the details of the Mg doping profile, confirming the importance of Mg diffusion and unintentional background doping in these materials. Our results show that ...

Science.gov (United States)

The authors present electric-field dependent electroreflectance and photocurrent spectra of visible-bandgap In{sub x}(Al{sub y}Ga{sub 1{minus}y}){sub 1{minus}x}P/In{sub x{prime}}(Al{sub y{prime}}Ga{sub 1{minus}y{prime}}){sub 1{minus}x{prime}}P multiple-quantum-well (MQW) structures. These structures, grown by metal-organic vapor phase epitaxy on 6{degrees}-misoriented (100) GaAs substrates, have undoped MQWs sandwiched between doped In{sub 0.5}Al{sub 0.5}P layers, forming p-i-n diodes. Quantum-well compositions in the range 0.46{le}x{le}0.52 and 0{le}y{le}0.4, corresponding to bandgaps in the red to yellow-green range, were used. The Stark shifts in these various samples were measured and found to depend on the details of the Mg p-type doping profile, confirming important diffusion effects, in agreement with secondary ion mass spectrometry and capacitance-voltage data. The results show that these new materials are promising ...

Energy Technology Data Exchange (ETDEWEB)

The utilization of GaAs in photovoltaic (PV) applications has been hindered by the cost of substrates and processing. This paper examines the cost effectiveness of GaAs cells for use in concentrator modules when produced at the 10 to 50 MW level per year. Information on costs associated with substrates, epitaxial processing, and subsequent device fabrication will be compared to allowable costs as projected by the US Department of Energy (DOE). The high cot of GaAs solar cells can be mitigated by use of low-cost substrates or high-concentration systems. The costs then can be accommodated when the production level is sufficiently high to take advantage of economies of scale in device processing and substrate price benefits when procured at high volumes. We have found that development of processing equipment, both for the epitaxial growth and device processing, is the key to obtaining production costs consistent with DOE ...

International Nuclear Information System (INIS)

A systematic study for the materials design of III-V and II-VI compound-based ferromagnetic diluted magnetic semiconductors is given based on ab initio calculations within the local spin density approximation. The electronic structures of 3d-transition-metal-atom-doped GaN and Mn-doped InN, InP, InAs, InSb, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs and AlSb were calculated by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation. It is found that the ferromagnetic ground states are readily achievable in V-, Cr- or Mn-doped GaN without any additional carrier doping treatments, and that InN is the most promising candidate for high-T_C ferromagnet. A simple explanation of the systematic behavior of the magnetic states in III-V and II-VI compound-based diluted magnetic semiconductors is also given. It is also shown that V or Cr-doped ZnS, ZnSe, and ZnTe are ferromagnetic without p- or n-type doping treatment. However, Mn-, ...

Energy Technology Data Exchange (ETDEWEB)

The paper reports on the results of a study of the synthesis conditions effects on magnetic and transport properties of nanosized layers of high-T{sub c} diluted magnetic semiconductors (DMS), such as Ge:Mn, Si:Mn and Si:Fe, fabricated by laser-plasma deposition over a wide range of the growth temperature, T{sub g}=(20-550) deg. C on single-crystal GaAs or Al{sub 2}O{sub 3} substrates. Ferromagnetism of the layers was detected by measurement data of the magneto-optical Kerr effect, anomalous Hall effect, negative magnetoresistance and ferromagnetic resonance (FMR) at 5-500 K. The optimum growth temperature, T{sub g}, for Si:Mn/GaAs layers with T{sub c}{approx}400 K is shown to be about 400 deg. C. The Si:Mn/Al{sub 2}O{sub 3} layers with 35% of Mn have the metal-type of conductivity with manifestation of magnetization up to room temperature. Different types of uniformly doped structures and digital alloys have been investigated. In contrast to ...

Energy Technology Data Exchange (ETDEWEB)

The strongly localized one-electron (D{sup 0}) and two-electron (D{sup -}) donor states are considered with the lattice deformation around the donor center taken into account. For GaAs, donor energy levels have been calculated as functions of the hydrostatic pressure. The calculated energy positions and pressure coefficients agree with the experimental data. It is shown that the interaction with phonons reduces the probability of radiative transitions between the states of different localization and leads to the metastability of shallow-level donor states with respect to the D{sup -} state in GaAs and both the states (D{sup 0} and D{sup -}) in CdF{sub 2}. (author) 7 refs, 1 fig

Science.gov (United States)

A 5 GHz GaAs monolithic astable multivibrator-type voltage-controlled oscillator has been developed. The monolithic oscillator uses 2 micron long self-aligned TiW-silicide gate MESFETs as well as GaAs Schottky diodes for capacitance. Good agreement between the experiment and calculations for oscillation frequency characteristics versus control voltage is obtained by assuming donor density in the FET active layer to be a Gaussian distribution. This oscillator is useful for monolithic front ends and phase-locked oscillators used in microwave signal processing. X-band oscillation frequency can be obtained with 1 micron long gate FET and low loss resonance inductors.

Science.gov (United States)

Direct coupljng between Al and Au metal]jzations can result in an increase in gate resistance due to a metallurgical reaction. (purple plague). An RF life test on ...

Energy Technology Data Exchange (ETDEWEB)

In the last two years, rapid progress has been made in the energy conversion efficiencies of GaAs solar cells fabricated from molecular beam epitaxy (MBE) material. The efficiencies of cells fabricated from MBE material are now comparable with those fabricated from metal-organic chemical vapor deposition material, even for cells of dimension 2 cmx4 cm. This paper reviews the progress in MBE cell efficiencies. Also discussed is the role oval defects play in GaAs diode and solar cell performance. (orig.).

Science.gov (United States)

We report the first visible (657 nm) vertical-cavity surface-emitting laser. The photopumped undoped structure was grown using low-pressure metalorganic vapor-phase epitaxy in a single-growth sequence on misoriented GaAs substrates. The optical cavity consists of an In{sub 0.54}Ga{sub 0.46}P/In{sub 0.48}(Al{sub 0.7}Ga{sub 0.3}){sub 0.52} P strained quantum-well active region and a lattice-matched In{sub 0.48}(Al{sub {ital y}}Ga{sub 1{minus}{ital y}}){sub 0.52} P (0.7{le}{ital y}{le}1.0) graded spacer region, while the distributed Bragg reflectors are composed of Al{sub 0.5}Ga{sub 0.5}As/AlAs quarter-wave stacks. Room-temperature optically pumped lasing was achieved with a very low-threshold power, clearly demonstrating the viability of this new technology. These results provide the foundation for visible semiconductor laser-diode arrays for a number of applications including laser projection displays, holographic memories, and plastic fiber ...

Science.gov (United States)

The (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P material system, lattice matched to GaAs substrates, is useful for visible laser diodes. Here, low pressure organometallic vapor phase epitaxial growth of Ga/sub 0.5/In/sub 0.5/P and (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P is examined. Epitaxial layers of bulk materials are characterized using photoluminescence, electroreflectance, Raman scattering spectroscopy, and surface morphology studies to determine lattice match and optimum growth conditions. Lattice matching at the growth temperature produces featureless growth surfaces, while lattice matching at room temperatures results in minimum photoluminescence linewidth but cracked surface due to tensile strain during growth. Raman scattering spectra of the quaternary reveal a three-mode structure, with spectral peaks due to GaP-like, in P-like, and AIP-like LO phonons. Additionally, (Al/sub x/Ga/sub 1-x/)/sub 0.5/In/sub 0.5/P/Ga/sub 0.5/In/sub ...

Energy Technology Data Exchange (ETDEWEB)

New techniques were developed to construct Schottky barrier and homojunction solar cells on GaAs substrates. Schottky barrier metal-semiconductor solar cells were produced for the first time on p-type GaAs substrate using a sputter-deposition method to form the barrier. The sputter deposition of gold or gold/palladium is the key to the method since normal thermal evaporation of gold onto p-type GaAs produces ohmic contacts. The results of this investigation are consistent with the idea that sputter damage produces donor type surface states on GaAs. Barrier heights were measured for both p-type sputtered and n-type thermally evaporated diodes using current-voltage and capacitance-voltage methods. Deep-level transient spectroscopy was used to identify the trap center concentration and energy levels for both diodes in an effort to explain the relatively large dark current in the p-type sputtered diodes. ...

Energy Technology Data Exchange (ETDEWEB)

The observed strength of the carbon dioxide absorption bands recorded on spectrobolograms of the transparency of the earth's atmosphere between wavelengths 300 and 2500 nanometers as part of the Smithsonian Solar Constant Program were used to extract the abundance of carbon dioxide in the atmosphere. The details of the analysis and the sources of error are discussed. 11 references, 5 figures, 1 table. (ACR)

International Nuclear Information System (INIS)

Nanocrystalline materials can exhibit properties which are considerably different from their coarse-grained counterparts, making them unique for basic or applied research and also very promising for potential applications. The topics which are addressed in the present paper are magnetic properties and magnetic correlations on the nanometer scale, mechanical properties, in particular the influence of grain boundaries on the elastic and plastic behaviour, and vibration models of grain boundary atoms in nanostructured materials. (author)

CERN Document Server

We explore a planar GaAs/AlAs photonic microcavity using pump-probe spectroscopy. Free carriers are excited in the GaAs with short pump pulses. The time-resolved reflectivity is spectrally resolved short probe pulses. We show experimentally that the cavity resonance and its width depend on the dynamic refractive index of both the lambda-slab and the lambda/4 GaAs mirrors. We clearly observe a double exponential relaxation of both the the cavity resonance and its width, which is due to the different recombination timescales in the lambda-slab and the mirrors. In particular, the relaxation time due to the GaAs mirrors approaches the photon storage time of the cavity, a regime for which nonlinear effects have been predicted. The strongly non-single exponential behavior of the resonance and the width is in excellent agreement to a transfer-matrix model taking into account two recombination times. The change in width leads to a ...

Science.gov (United States)

Data are presented on the insulating properties and capacitance-voltage (CV) characteristics of metal-oxide-semiconductor (MOS) device-thickness (below approx. 100 nm) native oxides formed by wet thermal oxidation of thin InAlP epilayers lattice matched to GaAs. Low leakage current densities of J=1.4 x 10-9 A/cm2 and J=8.7 x 10-11 A/cm2 are observed at an applied field of 1 MV/cm for MOS capacitors fabricated with 17 nm and 48 nm oxides, respectively. TEM images show that the In-rich interfacial particles which exist in 110 nm oxides are absent in 17 nm oxide films. Quasi-static capacitance-voltage measurements of MOS capacitors fabricated on both n-type and p-type GaAs show that the InAlP oxide-GaAs interface is sufficiently free of traps to support inversion, indicating an unpinned Fermi level. These data suggest that InAlP native oxides may be a viable insulator for GaAs MOS device applications.

Energy Technology Data Exchange (ETDEWEB)

In this work, we describe the fabrication and operating characteristics of GaAs/AlGaAs thin film solar cells processed by the epitaxial liftoff (ELO) technique. This technique allows the transfer of these cells onto glass substrates. The performance of the lifted-off solar cell is demonstrated by means of electrical measurements under both dark and illuminated conditions. We have also optimized the light trapping conditions in this direct-gap material. The results show that good solar absorption is possible in active layers as thin as 0.32 {mu}m. In such a thin solar cell, the open circuit voltage would be enhanced. We believe that the combination of an epitaxial liftoff thin GaAs film, and nano-texturing can lead to record breaking performance. {copyright} {ital 1997 American Institute of Physics.}

Energy Technology Data Exchange (ETDEWEB)

Today TBP and TBAs are the compounds which have the highest potential to replace the hydrides arsine and phosphine in the MOVPE process. The authors have demonstrated the entire material system Ga-In-As-P can be grown without any loss of quality using TBP and TBAs not only in one reactor, but in a complete family of reactors. These reactors range from small-scale single wafer R and D reactors to multiwafer Planetary Reactor systems. Both InP based and GaAs based materials could be grown with an excellent quality. Thus all growth processes for III-V devices--long and short wavelength lasers, LEDs, high speed transistors, etc.--can be switched to TBP and TBAs. This will drastically reduce safety hazards and lead to processes that have advantages both from the ecological and economical point of view.

International Nuclear Information System (INIS)

Conventional interconnect and switching technology is rapidly becoming a critical issue in the realization of systems using high speed silicon and GaAs based technologies. In recent years clock speeds and on-chip density for VLSI/VHSIC technology has made packaging these high speed chips extremely difficult. A strong case can be made for using optical interconnects for on-chip/on-wafer, chip-to-chip and board-to-board high speed communications. GaAs integrated optoelectronic circuits (IOC's) are being developed in a number of laboratories for performing Input/Output functions at all levels. In this paper integrated optoelectronic materials, electronics and optoelectronic devices are presented. IOC's are examined from the standpoint of what it takes to fabricate the devices and what performance can be expected.

Energy Technology Data Exchange (ETDEWEB)

Pattern formation on GaAs by Ga{sup +} focused-ion-beam (FIB) irradiation and subsequent Cl{sub 2} gas etching was carried out. A higher etch rate at the FIB-irradiated area compared with that not irradiated under Cl{sub 2} gas allows pattern construction without a mask process. The degree of residual crystal damage was evaluated using photoluminescence (PL) intensity measurements. The PL intensity in the etched region was one order of magnitude stronger than that of FIB sputtering, and was several times stronger than that of Ga{sup +} FIB-assisted Cl{sub 2} etching. Etch depths of the order of 100 nm, which is five times deeper than that obtained by FIB sputtering, were efficiently performed using moderate Ga{sup +}-ion doses.

International Nuclear Information System (INIS)

Deep level effects in GaAs MOSFET have been characterised in the ohmic channel using DLTS, low frequency excess noise and dispersion technique. An isothermal multi exponential curve fitting method has been devised and implanted into the DLTS system. Multi exponential curve fitting method used to decompose a multi exponential transient into its constituents so that the peak signature can be better characterised for the case whereas several peaks are closely spaced. Low frequency excess noise and dispersion techniques also confirm the trap in signature of the same traps observed in the DLTS measurements. (author)

International Nuclear Information System (INIS)

Electron probe microanalysis (EPMA) offers high sensitivity and high accuracy in quantitative measurements of chemical compositions and mass coverages. Owing to the low detection limits of the wavelength-dispersive technique, monolayers with mass coverages of about 0.05 pg cm z can be detected. Assuming a density of 5 g cm--3 this corresponds to a thickness of 0.1 nm. With these advantages in mind, EPMA was extended to depth profile analysis in the sub-micron range using a surface removal technique. The present paper shows how depth profile analysis can be improved by combining EPMA and the focused ion beam (FIB) technique. The focused ion beam system uses a Ga+ ion beam. The ion beam allows the milling of defined geometries on the nanometer scale, so that very shallow bevels with exactly defined angles in relation to the surface can be obtained. Low surface damage is expected due to low sputtering effects. Calibrated WDX measurements along the bevel deliver ...

Energy Technology Data Exchange (ETDEWEB)

The primary objective is to perform a fundamental study of filtration of nanoparticles, and to obtain filtration knowledge necessary to design particle collection devices/systems for nanoparticle processing and for preventing nanoparticle emissions into the environment. The research covered a wide area relevant to nanoparticle filtration, under these main topics: (1) nanoparticle filtration and molecular dynamics simulation, (2) nanoparticle virtual impactor, (3) particle transport under low pressure, and (4) development of a high-throughput nanoparticle generator. A number of novel tools and numerical models have been developed under the DOE support.

International Nuclear Information System (INIS)

A new polarized electron gun for use on the SLC at SLAC has been built and tested. It is a diode gun with a laser driven GaAs photocathode. It is designed to provide short (2ns) pulses of 10 A at 160 kV at 120 Hz. The design features of the gun and results from a testing program on a new and dedicated beam line are presented. Early results from operation on the SLC will also be shown.

Energy Technology Data Exchange (ETDEWEB)

As the only non-polar plane the (110) surface has a unique role in GaAs. Together with Silicon as a dopant it is an important substrate orientation for the growth of n-type or p-type heterostructures. As a consequence, this thesis will concentrate on growth and research on that surface. In the course of this work we were able to realize two-dimensional electron systems with the highest mobilities reported so far on this orientation. Therefore, we review the necessary growth conditions and the accompanying molecular process. The two-dimensional electron systems allowed the study of a new, intriguing transport anisotropy not explained by current theory. Moreover, we were the first growing a two-dimensional hole gas on (110) GaAs with Si as dopant. For this purpose we invented a new growth modulation technique necessary to retrieve high mobility systems. In addition, we discovered and studied the metal-insulator transition in thin bulk p-type ...

Energy Technology Data Exchange (ETDEWEB)

Two window layer materials, Al{sub 0.51}In{sub 0.49}P (E{sub g} = 2.3 eV) and Ga{sub 0.51}In{sub 0.49}P (E{sub g} = 1.88 eV) were compared for gas-source and solid-source MBE grown GaAs and Ga{sub 0.84}In{sub 0.16}As{sub 0.68}P{sub 0.32} (E{sub g} = 1.55 eV) solar cells. Due to the wider band-gap of Al{sub 0.51}In{sub 0.49}P, the increased spectral response was observed for both GaAs and Ga{sub 0.84}In{sub 0.16}As{sub 0.68}P{sub 0.32} material based solar cells. In the case of the GaAs cells, the short-circuit current density was observed to increase from 32.5 mA/cm{sup 2} to 34.4 mA/cm{sup 2} with the Al{sub 0.51}In{sub 0.49}P window layer at AM0. Similar improvement was observed for the Ga{sub 0.84}In{sub 0.16}As{sub 0.68}P{sub 0.32} solar cells.

Energy Technology Data Exchange (ETDEWEB)

Since information has been regarded os a physical entity, the field of quantum information theory has blossomed. This brings novel applications, such as quantum computation. This field has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineering, to the physical sciences. Thus, we now have an interdisciplinary field where great efforts are being made in order to build devices that should allow for the processing of information at a quantum level, and also in the understanding of the complex structure of some physical processes at a more basic level. This thesis is devoted to the theoretical study of structures at the nanometer-scale, 'nanostructures', through physical processes that mainly involve the solid-state and quantum optics, in order to propose reliable schemes for the processing of quantum information. Initially, the main results ...

Energy Technology Data Exchange (ETDEWEB)

III-V semiconductors, GaAs and in particular InGaP, are used in many different electronic applications, such as high power and high frequency devices, laser diodes and high brightness LED. Their direct bandgap and high reliability make them ideal candidates for the realisation of high efficiency solar cells: in the past years they have been successfully used as power sources for satellites in space, where they are able to produce electricity from sunlight with an overall efficiency of around 30%. Nowadays, the use of arsenides and phosphides as photovoltaic (PV) devices is confined only to space applications since their price is much higher than conventional Si flat panel modules, the leading PV market technology. But with the introduction of multijunction solar cells capable of operating in high concentration solar light, the area and, therefore, the cost of these cells can be reduced and will eventually find an application and market also on Earth. This article ...

Science.gov (United States)

Surface scientists argue about the fundamental nature of Schottky barriers, or more precisely what determines the location of the Fermi level at semiconductor surfaces and interfaces. Electrical and materials engineers worry about how to make Schottky barrier diodes and gates to field effect transistors and the control of barrier heights. There is some interesting middle ground in which the location of the surface and interface Fermi level can, for example, determine semiconductor doping characteristics during crystal growth. The authors will discuss several interesting and well known examples of doping characteristics which are still somewhat mysterious. Specifically, they address the following question: (1) why is Ge doped GaAs p type when grown from Ga melts but n type when grown from Au melts (2) why is low resistivity p type ZnSe, AlAs, and AlGaInP hard to make, and more importantly, how can the problem be fixed. In addition they describe how this concept ...

Energy Technology Data Exchange (ETDEWEB)

The optoelectronic compounds of GaAs and ZnSe are difficult to analyze by PIXE (particle-induced X-ray emission) due to the strong absorption of the As and Se K{sub {alpha}} X-rays. As part of a program to investigate optoelectronic materials using ion beam techniques, we have explored the possibility of using the high sensitivity of PIXE to check these materials for stoichiometry and dopant concentrations. The K{sub {alpha}} X-ray intensity ratios of Ga to As and Zn to Se have been investigated using H beams of 0.5 to 2.5 MeV and He beams of 1.0 to 2.5 MeV. The variation in the X-ray intensity ratio with beam energy and target thickness is modelled in terms of the cross section for X-ray production and the absorption coefficients of the X-rays in the target. The results of this model show the experimental conditions that must be satisfied in order that the X-ray intensity ratios are not strongly affected by X-ray absorption; and therefore, the conditions necessary ...

Energy Technology Data Exchange (ETDEWEB)

Undoped Al /SUB 0.5/ In /SUB 0.5/ P-Ga /SUB 0.5/ In /SUB 0.5/ P double heterostructure was grown on (100) GaAs by metalorganic chemical-vapor deposition for the first time. A mirror-like grown surface was obtained. Over ten-times stronger photoluminescence-intensity was gained from the sandwiched Ga /SUB 0.5/ In /SUB 0.5/ P-layer, than that from a single epitaxially-grown Ga /SUB 0.5/ In /SUB 0.5/ P-layer on (100) GaAs, indicating that high-quality Al /SUB 0.5/ In /SUB 0.5/ P-Ga /SUB 0.5/ In /SUB 0.5/ P heterointerfaces are formed in the double heterostructure. A lasing action by optical pumping with an argon ion laser was observed in the double heterostructure at 90 K. The observed stimulated emission wavelength was 6470 A.

International Nuclear Information System (INIS)

Using the ammonia (NH3) plasma generated by a helical antenna surrounded by two magnetic coils, the transition of the discharge mode from low-density plasma to high-density one was observed. At the transition, the emission intensities from the H atoms and NH radicals especially increased in the optical emission spectroscopy, while the intensities of the other emission lines also increased abruptly. The nitridation of gallium arsenide (GaAs) surface was performed using the high-density NH3 plasma, and the properties of the nitrided surface layer were compared with those nitrided by high-density N2 plasma using the same apparatus. From the spectroscopic ellipsometry measurements, the thickness of the nitrided layer was estimated to be 16-18 nm, while that by N2 was 3-4 nm. From the Ga 3d spectra, the contamination with oxygen in the nitridation layer by NH3 plasma was less than that by N2 plasma.

Energy Technology Data Exchange (ETDEWEB)

To attain reproducible and stable contacts to compound semiconductor devices, it is necessary to achieve thermodynamically stable phases after the reaction of metals with the compound semiconductor. In this study, the final phases produced by the reactions between GaAs and thin metal films of Co, Rh, Ir, Ni, Pd, and Pt have been investigated. They are identified as MGa for M = Co, Rh, Ni, Pd, and Pt, monoarsenides of Co and Ni, diarsenides of Rh, Ir, Pd, and Pt, and Ir/sub 3/Ga/sub 5/. These phases, if deposited directly onto GaAs, will produce thermally stable contacts. In addition to the identification of these stable phases, analyses of the products of thin-film M/GaAs reactions by transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectrometry reveal the distribution, grain size, and crystallographic texture of these end phases. Trends in these observations across the six metal/GaAs reactions studied are ...

Energy Technology Data Exchange (ETDEWEB)

This dissertation deals with both the theoretical and the technological aspects of monolithic tunable lasers, and the experimental techniques for opto-electronic integration. In the theoretical part, the principles and limitations of wavelength tuning and spectral linewidth reduction in monolithic semiconductor lasers are described, with coupled distributed feedback-Fabry Perot (DFB-FP) lasers and long DFB lasers as examples. Stepwise tuning of wavelength over tens of nanometers and continuous tuning over the range of a mode spacing are shown to be possible. Spatial hole burning is found to affect the spectral linewidth of lasers involving strong active gratings. On the technological side, one of the major issues is the fabrication of flexible gratings. Direct-writing techniques, such as focused ion beam (FIB) implantation and e-beam lithography, provide the resolution, flexibility and accuracy that conventional holographic lithography lacks. The parasitic ...

International Nuclear Information System (INIS)

Inorganic nanoparticles are indispensable for science and technology as materials, pigments and cosmetics products. Improving the dispersion stability of nanoparticles in various liquids is essential for those applications. In this review, we discuss why it is difficult to control the stability of nanoparticles in liquids. We also overview the role of surface interaction between nanoparticles in their dispersion and characterization, e.g. by colloid probe atomic force microscopy (CP-AFM). Two types of surface modification concepts, post-synthesis and in situ modification, were investigated in many previous studies. Here, we focus on post-synthesis modification using adsorption of various kinds of polymer dispersants and surfactants on the particle surface, as well as surface chemical reactions of silane coupling agents. We discuss CP-AFM as a technique to analyze the surface interaction between nanoparticles and the effect of surface modification on the nanoparticle dispersion in ...

International Nuclear Information System (INIS)

Macroparticle acceleration driven by low current, high voltage cathode spots has been investigated for potential applications ranging from micrometeoroid simulation to nanoparticle deposition/implantation. Acceleration by this process was observed to occur when nanometer and micrometer-sized particles were exposed to a high voltage pulse in the presence of a plasma discharge. The applied negative voltage pulse initiates the formation of multiple, high voltage, low current cathode spots which provide the mechanism of actual acceleration of the charged dust particles. Dust streams generated by this process were detected using laser scattering techniques. Cathode spot behavior was also documented. The particle impact craters observed at the surface of downstream witness badges were documented using scanning electron microscopy and light microscopy. The observed impacts suggest the presence of energetic macroparticles formed during this process.

International Nuclear Information System (INIS)

Analytical TEM and high resolution TEM were used in the microstructural characterization of hot-press sintered Si_3N_4-SiC platelets composites. The quantity of sintering additives, Er_2O_3 and AlN, was varied to produce different matrices, e. g. Si_3N_4, #beta#'+#alpha#'-Sialon and #alpha#'-Sialon. Detailed analysis of platelet-sialon matrix interfaces revealed the presence of AlN polytypoids. The polytypoids nucleate preferentially onto the (0001) plane of SiC and growth epitaxially in several ten nanometer layers contributing in this way to crystallize, partially, the matrix intergranular glass pockets contacting the platelets. Possible applications of the phenomena to microstructural control, grain boundary phase control and enhanced creep resistance are discussed. (orig.).

British Library Electronic Table of Contents (United Kingdom)

The author analyzes conference materials, emphasizing the studies and latest developments useful for industrial heterogeneous catalysis in view of the requirements of green chemistry. Industrial catalysts is developing along a nanometer scale, so especial attention is devoted to analyzing the reports in the Nanochemistry section on the creation of nanocatalysts, the production of active phase nanoparticles, and the formation of new synthesized material properties. The catalysts developed earlier by Russian research in cooperation with Belarusian scientists are considered, and it is shown that not only are expensive nanocontacts extremely promising for industry, but the efficient and economic low-percentage new generation of nanocatalysts synthesized by wet chemistry and containing nanopart...

Energy Technology Data Exchange (ETDEWEB)

A method of patterning n-type GaAs, InP, InGaAs, and InGaAsP by photoelectrochemical (PEC) etching in conjunction with a submicron focused ion beam (FIB) at low dose is described. The ion beam is used to produce damage in a desired pattern in the material. Subsequent PEC etching of the material reveals the ion induced features in relief. The procedure is highly sensitive, requiring a dose of only 5 x 10/sup 9/ ions/cm/sup 2/ for the differential etch to become apparent. The sensitivity allows rapid pattern generation in our FIB system.

Energy Technology Data Exchange (ETDEWEB)

A local Heine-Abarenkov model potential is proposed for zinc blende-type crystals. The potential parameters are determined by satisfying the zero pressure condition and the first zero of the empirical pseudopotential interpolated from band calculations. Two sets of parameters are presented for thirteen tetrahedral compounds such as AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, and CdTe.

Science.gov (United States)

In an earlier paper (Phys. Rev. Lett. 66, 41 (1991)), we calculated both the dielectric constant ({epsilon}{sub {infinity}}) and the nonlinear optical susceptibilities for second-harmonic generation ({chi}{sup (2)}) in the static limit for AlP, AlAs, GaP, and GaAs in the local-density approximation with and without a self-energy correction in the form of a scissors operator,'' including local-field effects. In this paper, we expand our presentation of this calculation. Agreement with experiment to within 15% for the nonlinear susceptibility is demonstrated where experiments are available (GaP and GaAs); the dielectric constants are in no worse than 4% agreement with experiment. The virtual hole'' contributions are reformulated to avoid large numerical cancellations in the case of near degeneracies. The virtual electron'' terms dominate over the virtual hole'' terms ...

Energy Technology Data Exchange (ETDEWEB)

This thesis details the first direct ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples over a wide range of temperatures. By utilizing a 90 fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion due to heating and subsequent contraction caused by cooling provided the dominant influence on the probe. At room temperature a rise due to thermal expansion was observed, corresponding to a maximum net displacement of {approximately} 1 {Angstrom} at 32 ps. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, thus allowing a determination of the rate of expansion as well as the surface thermal diffusivity, ...

Energy Technology Data Exchange (ETDEWEB)

This article considers the fundamentals of what happens in asolid when it is impacted with a medium energy gallium ion. The study ofthe ion/sample interaction at the nanometer scale is applicable to mostfocused ion beam (FIB) based work even if the FIB/sample interaction isonly a step in the process, e.g., micromachining or microelectronicdevice processing. Whereas the objective in other articles in this issueis to use the FIB tool to characterize a material or to machine a deviceor transmission electron microscopy (TEM) sample, the goal of the FIB inthis article is to have the FIB/sample interaction itself become theproduct. To that end, the FIB/sample interaction is considered in threecategories according to geometry: below, at, and above the surface.First, the FIB ions can penetrate the top atom layer(s) and interactbelow the surface. Ion implantation and ion damage on flat surfaces havebeen comprehensively examined; however, FIB applications require thefurther ...

Energy Technology Data Exchange (ETDEWEB)

The theoretical performance of ideal single- and multijunction cells are compared at 100xconcentration under a range of cloudless-sky conditions. The sensitivities of device performance to cell temperature and spectral variations are shown to depend on the number of junctions (one, two or three), the way in which the junctions are connected (series, parallel or independent), and the band gaps of the devices. The average performances of all of the multijunction devices surpass that of a single-junction GaAs device, but the inconsistency in performance of some of the multijunction devices is significant for large variations in cell temperature and incident spectrum. The choice of band gap and connection scheme is more important than the number of junctions in determining the consistency of device performance. (orig.).

Energy Technology Data Exchange (ETDEWEB)

The current status of non-silicon photovoltaic solar cells is discussed including the identification of current technical and economic issues and future research directions for potential high efficiency low cost technologies. This review covers such advanced materials as CdS/Cu/sub 2/S, CdS/CuInSe/sub 2/, and GaAs homojunction and heterojunction devices; such emerging materials as InP, Zn/sub 3/P/sub 2/ and CdTe; and liquid junction electrochemical photovoltaic cells. An attempt is made to compare the current relative status of these various technologies and to indicate their near term potential where possible. 105 refs.

International Nuclear Information System (INIS)

We provide a brief review of our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in two most important dilute nitride systems-Ga(In)NAs grown on GaAs substrates and Ga(Al,In)NP grown on Si and GaP substrates. These results have led to the identification of defect complexes in the alloys, involving intrinsic defects such as As_G_a antisites and Ga_i self-interstitials. They have also shed light on formation mechanisms of the defects and on their role in non-radiative carrier recombination that is harmful to the performance of potential optoelectronic and photonic devices based on these dilute nitrides.

Energy Technology Data Exchange (ETDEWEB)

This report describes progress during the first year of a three-year project. The objective of the research is to examine new design approaches for achieving very high conversion efficiencies. The program is divided into two areas. The first centers on exploring new thin-film approaches specifically designed for III-V semiconductors. The second area centers on exploring design approaches for achieving high conversion efficiencies without requiring extremely high quality material. Research activities consisted of an experimental study of minority carrier recombination in n-type, metal-organic chemical vapor deposition (MOCVD)-deposited GaAs, an assessment of the minority carrier lifetimes in n-GaAs grown by molecular beam epitaxy, and developing a high-efficiency cell fabrication process.

International Nuclear Information System (INIS)

The highest equilibrium free-carrier doping concentration possible in a given material is limited by the ''pinning energy'' which shows a remarkable universal alignment in each class of semiconductors. Our first-principles total energy calculations reveal that equilibrium n -type doping is ultimately limited by the spontaneous formation of close-shell acceptor defects: the 3- -charged cation vacancy in AlN, GaN, InP, and GaAs and the 1- -charged DX center in AlAs, AlP, and GaP. This explains the alignment of the pinning energies and predicts the maximum equilibrium doping levels in different materials. (c) 2000 The American Physical Society

British Library Electronic Table of Contents (United Kingdom)

Within the framework of the effective-mass approximation, using a variational method, we have calculated the effect of intense laser radiation on the binding energy of the shallow-donor impurities in a Ga1- x In x N y As1- y /GaAs single quantum well for different nitrogen and indium mole concentrations. Our numerical results show that the binding energy strongly depends on the laser intensity and frequency (via the laser dressing parameter) and it also depends on the nitrogen and indium concentrations. Impurity binding energy under intense laser fields can be tuned by changing the nitrogen and indium mole fraction.

Science.gov (United States)

A general model for the analysis of metal-semiconductor solar cells is presented. The model takes into account the cell optical properties, carrier recombination effects, semiconductor minority-carrier properties, series resistance, cell thickness, and active surface area. Numerical methods are used to solve the appropriate continuity equations and hence compute the photocurrent density under AMO conditions. The operation of the model is demonstrated using p- and n-type Si and GaAs with Au being taken as the barrier metal. Calculations are presented showing the effect on solar energy conversion efficiency of surface recombination velocity, barrier height, minority-carrier lifetime, barrier metal thickness, collecting grid configuration, and cell thickness. A comparison of practical and computed data for the Au/n-GaAs system yields good agreement. (AIP)

Energy Technology Data Exchange (ETDEWEB)

Abstract: We report for the selective-area chemical synthesis of semiconductor single-crystal organic nanowires of silver-tetracyanoquinodimethane (Ag-TCNQ). Straight and smooth Ag-TCNQ nanowires can be produced and patterned on micrometer and nanometer scale on silicon substrates covered with a thin layer of Ag film through the reaction of TCNQ and Ag in a simple gas-solid chemical reaction process. Ag-TCNQ nanowires are characterized by UV-vis, IR and Raman spectroscopy, respectively. The Ag-TCNQ nanowires grows preferentially along the [100] direction of strong - stacking of Ag-TCNQ molecules. Nanodevices based on these nanowires are fabricated using focus ion beam (FIB) technique. Electrical properties are characterized and I-V hysteresis is observed, which shows memory effect with electrical switching of three orders on-off ratio. These nanowires could be potential for use in optical storage, ultrahigh-density nanoscale memory and logic devices.

Energy Technology Data Exchange (ETDEWEB)

A method to control charge transfer reaction in DNA using hybrid nanometer-sized TiO{sub 2} nanoparticles was developed. In this system extended charge separation reflects the sequence of DNA and was measured using metallic silver deposition or by photocurrent response. Light-induced extended charge separation in these systems was found to be dependent on the DNA-bridge length and sequence. The yield of photocatalytic deposition of silver was studied in systems having GG accepting sites imbedded in AT runs at varying distances from the TiO{sub 2} nanoparticle surface. Weak distance dependence of charge separation indicative of a hole hopping through mediating adenine (A) sites was found. The quantum yield of silver deposition in the system having a GG accepting site placed 8.5 {angstrom} from the nanoparticle surface was found to be {Phi} = 0.70 (70%) and {Phi} = 0.56 (56%) for (A){sub n} and (AT){sub n/2} bridge, respectively. Hole injection to GG trapping sites ...

British Library Electronic Table of Contents (United Kingdom)

Ultra fine tungsten carbide and cobalt powders were milled by high energy planetary ball mill at different ball to powder weight ratios (BPR) to produce particles of WC-10wt%Co hard metal in nanometer scale size. Microstructural characterizations by TEM show that the particle size of tungsten carbide was achieved to 32nm after milling at 15 BPR during 10h. In order to reduce the WC grain growth during the sintering process, tantalum carbide was added to the hard metal as a WC grain growth inhibitor. The nano hard metal powders were compacted at 200MPa pressure and sintered at 1370-1450degreeC temperatures in a high purity hydrogen atmosphere. The results show that the addition of 0.6wt% of TaC improves the hardness and fracture toughness from 1493 HV30 and 11.8MPam (for TaC free sample) to...

CERN Document Server

Cell membranes are studded with protrusions that were thoroughly analyzed with electron microscopy. However, the nanometer-scale three-dimensional motions generated by cell membranes to fit the topography of foreign surfaces and initiate adhesion remain poorly understood. Here, we describe the dynamics of surface deformations displayed by monocytic cells bumping against fibronectin-coated surfaces. We observed membrane undulations with typically 5 nm amplitude and 5-10 second lifetime. Cell membranes behaved as independent units of micrometer size. Cells detected the presence of foreign surfaces at 50 nm separation, resulting in time-dependent amplification of membrane undulations. Molecular contact then ensued with apparent cell-membrane separation of 30-40 nm, and this distance steadily decreased during the following tens of seconds. Contact maturation was associated with in-plane egress of bulky molecules and robust membrane fluctuations. Thus, membrane ...

Energy Technology Data Exchange (ETDEWEB)

Lubricant additives have been known to affect rolling element bearing surface durability for many years. Tapered roller bearings were used in fatigue testing of lubricants formulated with gear oil type additive systems. These systems have sulfur- and phosphoruscontaining compounds used for gear protection as well as bearing lubrication. Several variations of a commercially available base additive formulation were tested having modified sulfur components. The variations represent a range of ''active'' extreme pressure (EP) chemistries. The bearing fatigue test results were compared with respect to EP formulation and test conditions. Inner ring near-surface material in selected test bearings was evaluated on two scales: the micrometer scale using optical metallography and the nanometer scale using transmission electron microscopy (TEM). Focused-ion beam (FIB) techniques were used for TEM specimen preparation. Imaging and chemical ...

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Using a 47 GeV electron beam, the Final Focus Test Beam (FFTB) produces vertical spot sizes around 70 nm. These small beam sizes introduce an excellent opportunity to develop and test high resolution Radio Frequency Beam Position Monitors (RF-BPMs). These BPMs are designed to measure pulse to pulse beam motion (jitter) at a theoretical resolution of approximately 1 nm. The beam induces a TM{sub 110} mode with an amplitude linearly proportional to its charge and displacement from the BPM's (cylindrical cavity) axis. The C-band (5,712 MHz) TM{sub 110} signal is processed and converted into beam position for use by the Stanford Linear Collider (SLC) control system. Presented are the experimental procedures, acquisition, and analysis of data demonstrating resolution of jitter near 25 nm. With the design of future e{sup +}e{sup -} linear colliders requiring spot sizes close to 3 nm, understanding and developing RF-BPMs will be essential in resolving and controlling jitter.

Science.gov (United States)

A post-accident-heat-removal structural effects analysis for the steel liner in the FFTF concrete containment structure is presented. (JWR)

Science.gov (United States)

An interest in electronic materials has led me to investigate new synthetic approaches to III-V' type semiconducting (13-15, current IUPAC designation for B and N groups in the Periodic Table) and magnetic (3-15) compounds. It is now possible to prepare binary (GaAs and GdP) and ternary mixed-metal (Al[sub x]Ga[sub 1-x]As) and mixed-pnictide (GaP[sub x]As[sub 1-x]) compounds in seconds from rapid, low-temperature-initiated metathesis reactions between a metal (III) trihalide and a trisodium pnictide, exemplified by MX[sub 3] + Na[sub 3]Pn [yields] MPn + 3 NaX, where M is Al, Ga, In, (Al,Ga), or a lanthanide; X is F, Cl, or I; and Pn is P, As, Sb, or (P,As). The precursors are mixed together in a dry box and ignited by light grinding with a mortar and pestle, or by brief, local heating from a hot filament. These reactions are very exothermic (calculated [Delta]H[sub rxn] (GaAs) = 138 kcal/mol) and typically reach temperatures in excess ...

Energy Technology Data Exchange (ETDEWEB)

GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias ...

Science.gov (United States)

Another difference lies in the speed of star evolution. 2. Computation of Stellar Structure and Their Evolution. The structure of stars at certain instants ...

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The B-Factory which is constructed by National Laboratory for High Energy Physics is the device for elucidating the breakdown of symmetry of matter and antimatter by studying the behavior of B mesons which are generated in large quantity when the electrons and the positrons which are accelerated to light velocity level are collided. In order to maintain electron beam-positron beam bunch circling the ring at light velocity stably, the instability of the coupled bunch must be overcome. For this purpose, the ultrahigh speed beam position digital feedback control system was developed. This system is composed of the high speed input-output substrate using GaAs LSI, the feedback computation substrate using complementary metal oxide semiconductor and the memory mounted on it, and the real time operation device. The development of both substrates and their functions are explained. The real time data collection and the change of computation parameters for specific bunch in ...

International Nuclear Information System (INIS)

Electron spin polarization in excess of 70% has been observed in photoemission from a 0.1 #mu#m-thick epitaxial layer of In_xGa_1_-_xAs with x #approx# 0.13 grown on a GaAs substrate. Under these conditions, the epitaxial layer is expected to be highly strained by the 0.9% lattice mismatch, as confirmed by x-ray diffractometer measurements of the lattice parameter. The electron polarization and the quantum efficiency have been measured as a function of the excitation photon energy from 1.25 to 2.0 eV. A significant enhancement of the electron polarization occurs in the vicinity of 1.33 eV where the expected strain-induced level splitting permits optical excitation of a single band transition. Measurements made on a control sample of 1.14 #mu#m thickness, significantly larger than the critical thickness for pseudomorphic strain, show no polarization enhancement. These measurements represent the first observation of strain-enhanced electron spin polarization for ...

International Nuclear Information System (INIS)

Thinning specimens to electron transparency for electron microscopy analysis can be done by conventional (2-4 kV) argon ion milling or focused ion beam (FIB) lift-out techniques. Both these methods tend to leave 'mottling' visible on thin specimen areas, and this is believed to be surface damage caused by ion implantation and amorphisation. A low energy (250-500 V) Argon ion polish has been shown to greatly improve specimen quality for crystalline silicon samples. Here we investigate the preparation of technologically important materials for nanoanalysis using conventional and lift-out methods followed by a low energy polish in a GentleMill"T"M low energy ion mill. We use a low energy, low angle (6-8 deg.) ion beam to remove the surface damage from previous processing steps. We assess this method for the preparation of technologically important materials, such as steel, silicon and GaAs. For these materials the ability to create specimens from specific sites, and ...

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(Al{sub y}Ga{sub 1{minus}y}){sup 1{minus}x}In{sub x}P semiconductor alloys lattice-matched to GaAs are widely used in visible optoelectronic devices. One of the most recent developments in this area is the AlGaInP-based red vertical cavity surface emitting laser (VCSEL). These lasers, which employ AlGaInP active regions and AlGaAs distributed Bragg reflectors (DBRs), have demonstrated continuous-wave (CW) lasing over the 630--690 nm region of the spectrum. Applications for these lasers include plastic fiber data communications, laser printing and bar code scanning. In this paper, the authors present an overview of recent developments in the processing and performance of AlGaInP based VCSELs. This overview will include a review of the general heterostructure designs that have been employed, as well as the performance of lasers fabricated by both ion implantation and selective oxidation.

Science.gov (United States)

The specification describes a semiconductor solar cell and fabrication process therefor wherein a thin N-type gallium arsenide layer is deposited on a larger P-type substrate layer which is selected from the group of III-V ternary compounds consisting of aluminum phosphide antimonide, AlPSb, and aluminum indium phosphide, AlInP. P-type impurities are diffused from the substrate layer into a portion of the thin N-type gallium arsenide layer to form P-type region wherein which defines a PN junction in the thin gallium arsenide layer. Thus, the quantity of gallium arsenide required to provide this PN photovoltaic junction layer in the cell is minimized, and th P-type substrate serves as a high bandgap window layer for the cell. Such high bandgap of this window material is especially well suited for efficiently transmitting the blue spectrum of sunlight to the PN junction, thus enhancing the power conversion efficiency of the solar cell.

International Nuclear Information System (INIS)

Focused ion beam (FIB) processes have been developed for Y--Ba--Cu--O superconductor films. A Y--Cu liquid metal ion source has been fabricated, using a Y_6_7 --Cu_3_3 eutectic alloy as the ion source. As-sputtered Y--Ba--Cu--O film etch rate ratios to GaAs(100) and Si(100) substrates are 0.28 and 1.4 for 130-keV Au"+ FIB ion etching, respectively. Y--Ba--Cu--O submicron patterns have been demonstrated by using FIB lithography and Cl_2 reactive ion beam etching. Moreover, a Y--Ba--Cu--O superconducting line with 4-#mu#m linewidth has been fabricated by annealing an as-sputtered Y--Ba--Cu--O line pattern. T/sub c/ control of Y--Ba--Cu--O film has been achieved by 200-keV Ne"+, using conventional ion implantation and 300 keV Si"+"+ FIB ion implantation.

Energy Technology Data Exchange (ETDEWEB)

The transient enhanced diffusion of low and high dose implanted beryllium in undoped gallium arsenide during post-implant rapid thermal annealing in the temperature range of 700-900 C for 60-240 s has been studied and successfully simulated by the kick-out diffusion model, involving singly positively charged Be interstitials and doubly positively charged Ga self-interstitials. Using the ''plus one'' approach for Ga interstitial generation after implantation with the local Ga interstitial sink concept as well as the appropriate initial and boundary conditions for involved mobile species, and taking into account Fermi-level and built-in electric field effects, the obtained partial differential equations have been solved numerically by means of an explicit finite difference method. The thermal equilibrium concentrations and the diffusivities of Be and Ga interstitials, all as a function of temperature, have been deduced from the fits of the experimental ...

International Nuclear Information System (INIS)

The characteristics of defects induced by Si and Ga focused ion beam (FIB) implantation in n-GaAs have been investigated by means of deep-level transient spectroscopy (DLTS), C--V carrier profiling, and resistance measurements. The DLTS spectra of Si and Ga FIB implanted samples annealed at temperatures up to 500 "0C are apparently identical to one another and show three different electron traps with an activation energy between 0.25 and 0.6 eV. The resistance increases by more than five orders of magnitude by Si and Ga FIB implantation due to the induced defects. However, it is restored to initial values after annealing at 600 "0C, except for a sample of Ga implantation with a dose higher than 10"1"4 cm"2 . For annealing of induced defects, there are no intrinsic problems for FIB implantation with a dose lower than 10"1"3 cm"2.

International Nuclear Information System (INIS)

Using standard microfabrication techniques, it is now possible to construct devices that appear to reliably manipulate electrons one at a time. These devices have potential use as building blocks in quantum computing devices, or as a standard of electrical current derived only from a frequency and the fundamental charge. To date, the error rate in semiconductor 'tuneable-barrier' pump devices, those which show most promise for high-frequency operation, have not been tested in detail. We present high-accuracy measurements of the current from an etched GaAs quantum dot pump, operated at zero source-drain bias voltage with a single ac-modulated gate at 340 MHz driving the pump cycle. By comparison with a reference current derived from primary standards, we show that the electron transfer accuracy is better than 15 parts per million. High-resolution studies of the dependence of the pump current on the quantum dot tuning parameters also reveal possible deviations from a ...

International Nuclear Information System (INIS)

We theoretically model a nuclear-state preparation scheme that increases the coherence time of a two-spin qubit in a double quantum dot. The two-electron system is tuned repeatedly across a singlet-triplet level-anticrossing with alternating slow and rapid sweeps of an external bias voltage. Using a Landau-Zener-Stueckelberg model, we find that in addition to a small nuclear polarization that weakly affects the electron spin coherence, the slow sweeps are only partially adiabatic and lead to a weak nuclear spin measurement and a nuclear-state narrowing which prolongs the electron spin coherence. This resolves some open problems brought up by a recent experiment. We also show that the electronic two-spin states singlet and triplet T_+ are promising candidates for the implementation of a qubit in GaAs double quantum dots (DQD). A coherent superposition of the two-spin states is obtained by finite time Landau-Zener-Stueckelberg interferometry and the single qubit ...

International Nuclear Information System (INIS)

Low-energy focused ion beam (FIB) is a useful tool for shallow doping, gas-assisted etching, and other uses to minimize substrate damage in semiconductor device fabrication. The possibility to form a finely FIB of low energy under 1 keV was suggested in the investigations on the retarding mode in electron optical systems. The abilities of the simplest type of retarding mode FIB column are examined here. The optical properties are calculated for the corresponding model and some images are observed with Ga"+ ion beams <0.3 #mu#m in diameter for beam energies, 10, 5, and 1 keV, using a retarding mode one-lens FIB system. 1-keV and 100-eV Ga"+ FIB was implanted to Ga/As substrate, and the defects are analyzed by deep-level transient spectroscopy. The defect concentration for 100 eV was < (1)/(5) that for 1000 keV.

UK PubMed Central (United Kingdom)

Studies of the antigenic structure of the polysaccharide component of gonococcal lipopolysaccaride (LPS) indicated that the non-serogroup antigen structure is antigenically heterogeneous. Immunodiffusion...Full Text Available

Energy Technology Data Exchange (ETDEWEB)

This paper reviews our simulation study by numerical calculation based on two-, three- and multi-grain-size models on WC grain growth in fine grained WC-Co hardmetal doped with VC. The study aimed to presume or predict the following: (1) the cause and conditions for the abnormal grain growth which occurs in some cases in the fine grained hardmetal prepared from fine WC powders with mean grain size below about 0.2{mu}m, and (2) how the mean grain size of the hardmetal varies with decreasing mean grain size of the WC starting powder to 0.1 pm or nano-meter size. The calculation results by these three kinds of models suggested the following, respectively: (1) the occurrence of the abnormal grain growth is generally substantial for WC starting powder with bimodal size-distribution and mean gram size below 0.1 - 0.2{mu}m, and not due to the non-uniform distribution of the grain growth inhibitor, (2) the introduction of middle grains caused the disappearance of small ...

International Nuclear Information System (INIS)

A novel pseudo-morphotactic transformation route was developed to synthesize polycrystalline ?-W2N nanoplates by thermally treating tungstate-based inorganic-organic hybrid nanobelts with a lamellar microstructure in an NH3 flow. The tungstate-based hybrid nanobelts were formed in a water-in-oil-microemulsion-like 'commercial H2WO4 powders/n-octylamine/heptane' reaction system. The as-obtained hybrid nanobelts were thermally treated in an NH3 atmosphere at 650-800 oC for 2 h to form cubic ?-W2N nanoplates. XRD, SEM, TEM, FT-IR and TG-DTA were used to characterize the precursors and their final products. The polycrystalline ?-W2N nanoplates derived from hybrid nanobelts, with side lengths of several hundred nanometers, consist of small nanocrystals with an average grain size of 3.2 nm. The formation of ?-W2N nanoplates involved two steps: decomposing tungstate-based hybrid nanobelts into WOy and W species and then nitridizing the active W-containing species to ?-W2N ...

Energy Technology Data Exchange (ETDEWEB)

Based on their interesting properties, metal nanoparticles show the potential as an analytical tool in electronic (Burmeister et al. 2004), optical (Yguerabide and Yguerabide 1998), and catalytic applications (Liu 2006). Their characteristics depend on the composition, shape, and size of the single particles. These various properties are utilized in many different approaches such as optics, magnetics (Lang et al. 2007), and laser technology (Csaki et al. 2007). We investigated an alternative method for the synthesis of nanoparticles. In this case, an enzyme, horseradish peroxidase, induces a silver deposition and replaces a metal nanoparticle as the reaction seed. Depending on the reaction time, we could obtain particles in a range of few nanometers up to more than 250 nm. For a better understanding of the enzymatic silver deposition process, the silver particles produced by this process were analyzed by SEM, TEM, and atomic force microscopy (AFM) on a single ...

Science.gov (United States)

Natural bone consists of hard nanostructured hydroxyapatite (HA) in a nanostructured protein-based soft hydrogel template (ie, mostly collagen). For this reason, nanostructured HA has been an intriguing coating material on traditionally used titanium for improving orthopedic applications. In addition, helical rosette nanotubes (HRNs), newly developed materials which form through the self-assembly process of DNA base pair building blocks in body solutions, are soft nanotubes with a helical architecture that mimics natural collagen. Thus, the objective of this in vitro study was for the first time to combine the promising attributes of HRNs and nanocrystalline HA on titanium and assess osteoblast (bone-forming cell) functions. Different sizes of nanocrystalline HA were synthesized in this study through a wet chemical precipitation process following either hydrothermal treatment or sintering. Transmission electron microscopy images showed that HRNs aligned with nanocrystalline HA, which ...

Energy Technology Data Exchange (ETDEWEB)

Various methods for storing hydrogen have been examined in an effort to find ways to store hydrogen in increasingly smaller volumes with decreasing weight of the whole hydrogen storage system. Metal hydrides, in which hydrogen is chemically bound to a metal atom, are considered to be very promising candidates for hydrogen storage because they have high gravimetric and volumetric storage capacities. This study investigated the effect of different magnesium (Mg) and aluminium (Al) ratios on the absorption and desorption properties of thin films. Neutron reflectometry (NR) was used in this study to better understand the absorption and desorption properties of commercially promising hydrogen storage materials. The large negative scattering length of hydrogen atoms changes the reflectivity curve substantially, so that NR can determine the total amount of stored hydrogen as well as the hydrogen distribution along the film normal, with nanometer resolution. In order to ...

Energy Technology Data Exchange (ETDEWEB)

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Energy Technology Data Exchange (ETDEWEB)

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Science.gov (United States)

... Accession Number : AD0618975. Title : STRUCTURE OF LIQUID NITROGEN,. Corporate Author : CALIFORNIA INST OF TECH PASADENA. ...

International Nuclear Information System (INIS)

English 2006 [1 p.] Germany Lenk, Andreas Institute of Structure Physics,

Energy Technology Data Exchange (ETDEWEB)

We summarize the Hopf algebra structure on Feynman diagrams and emphasize the interest in further algebraic structures hidden in Feynman graphs.

Energy Technology Data Exchange (ETDEWEB)

Much research has been carried out in order to manage structured documents such as SGML documents and to provide powerful query facilities which exploit document structures as well as document contents. In order to perform structure queries efficiently in a structured document management system, an index structure which supports fast document element access must be provided. However, there has been little research on the index structures for structured documents. In this paper, we propose various kinds of new inverted indexing schemes and signature file schemes for efficient structure query processing. We evaluate the storage requirements and disk access time of our schemes and present the analytical and experimental results.

Energy Technology Data Exchange (ETDEWEB)

In order to perform the structural analysis and stress evaluation for frame structures in the nuclear power plants, ADAMS (AIJ Design Analysis and Modules System) has been developed by the addition of the following functions to the ICES-STRUDL system. 1. Load combination and stress evaluation on the basis of specifications for designing steel structure (issued by the Architecture Institute of Japan). 2. Combination of load and stress evaluation of piping support on the basis of the regulations of Ministry of International Trade and Industry. 3. Addition of other functions than that described above. ADAMS enables structural analysis and stress evaluation exactly and efficiently not only for a large scale structure such as the pipe whip protection structure installed inside of the primary containment vessel for many loading cases but also for a large number of ...

International Nuclear Information System (INIS)

The aim of the paper is to define and study algebraic operations closely related to the group structure on the homotopy groups of topological spaces. These are certain many-place operations on the homotopy groups. The family of these operations induces an algebraic structure on the homotopy groups, which is called an A?-group structure by analogy with the A?-structures introduced by Stasheff.

International Nuclear Information System (INIS)

It is shown that the available data on x, Q"2, and A dependence of nuclear structure functions and for their ratios (EMS effect) can be described in terms of the flucton model with rescaling of parton distributions in nuclei. The x, Q"2 and A dependence of nuclear structure functions in the cumulative range (x >1) is predicted.

UK PubMed Central (United Kingdom)

Emphasis was put on the comparative quantitative structure-activity approaches to the exploration of action mechanisms of structurally different classes of compounds showing the same type of activity...Full Text Available

UK PubMed Central (United Kingdom)

AbstractX-ray diffraction analysis of pressure-induced structural changes in the Aequorea yellow fluorescent protein Citrine reveals the structural basis for the continuous...Full Text Available

UK PubMed Central (United Kingdom)

BackgroundStructured noncoding RNAs perform many functions that are essential for protein synthesis, RNA processing, and gene regulation. Structured RNAs can be detected by comparative...Full Text Available

British Library Electronic Table of Contents (United Kingdom)

The present paper considers the evaluation of timber structures with the focus on robustness due to connection ductility. The robustness analysis is based on the structural reliability framework applied to a simplified mechanical system. The structural timber system is depicted as a parallel system. An evaluation method of the ductile behaviour is introduced. For different ductile behaviours, the system reliability is estimated based on Monte Carlo simulation. A correlation between the strength of the structural elements is introduced. The results indicate that the reliability of a structural timber system can be significantly increased due to the ductile behavior.

British Library Electronic Table of Contents (United Kingdom)

Major similarities between robustness assessment and seismic design exist, and significant information can be brought from seismic design to robustness design. As will be discussed, although some methods and limitations considered in seismic design can improve robustness, the capacity of the structure to sustain limited damage without disproportionate effects is significantly more complex. In fact, seismic design can either improve or reduce the resistance of structures to unforeseeable events, depending on the structural type, triggering event, structural material, among others. Based on a case study, the influence of redundancy and ductility on the seismic behavior and robustness of a long-span timber structure is assessed.

Science.gov (United States)

Data are presented demonstrating short-wavelength (approx. <6400 A) continuous (cw) laser operation of p-n diode In/sub 0.5/(Al/sub x/Ga/sub 1-//sub x/)/sub 0.5/P multiple quantum well heterostructure (QWH) lasers grown lattice matched on GaAs substrates using metalorganic chemical vapor deposition. In the range from -30 /sup 0/C to room temperature (RTapprox. =300 K, lambdaapprox. =6395 A) the threshold current density changes from 2.3 x 10/sup 3/ A/cm/sup 2/ (-30 /sup 0/C) to 3.7 x 10/sup 3/ A/cm/sup 2/ (RT, 300 K). The cw 300 K photopumped laser operation of the same quaternary QWH crystal is an order of magnitude lower in threshold (7 x 10/sup 3/ W/cm/sup 2/, J/sub eq/approx.2.9 x 10/sup 3/ A/cm/sup 2/) than previously reported for this crystal system, and agrees with the successful demonstration of cw 300 K laser diodes at this short wavelength.

Science.gov (United States)

The photopumped phonon-assisted laser operation (612 nm, 77 K) of a high-gapIn/sub 1/minus//ital y//(Al/sub /ital x//Ga/sub 1/minus//ital x//)/sub /ital y//P quantum wellheterostructure (QWH) lattice matched to GaAs (/ital y/approx.0.5) is identified usinga single rectangular sample that is shifted in its heat sinking from (a) low/ital Q/ when clamped onto Au (bare edges) to (b) high /ital Q/ when furthercompressed into Au with all four edges reflecting. For the low-/ital Q/ QWH samplephotopumped in a spot (partially photopumped), phonon-assisted laser operation(abrupt threshold, narrow spectrum) is observed on closely spaced end-to-endlaser modes ..delta../ital E/=/h bar/..omega../sub LO/approx.45--47 meV below the lowestconfined-particle transitions. For the /ital same/ sample shifted tohigh /ital Q/, edge-to-edge laser operation across the sample on confined-particletransitions is ''turned on'' also, thus providing an ...

Energy Technology Data Exchange (ETDEWEB)

The dependence of the photoluminescent properties of In{sub 0.48}(Al{sub {ital y}}Ga{sub 1{minus}{ital y}}){sub 0.52}P alloys (0{le}{ital y}{le}0.5) on growth temperature and substrate misorientation off GaAs(100) has been studied. Samples were grown using low-pressure metalorganic vapor phase epitaxy. By studying the dependence of ordering behavior in InGaP as a function of substrate misorientation and growth temperature simultaneously, a very large range in low-temperature photoluminescence emission energy---135 meV---has been obtained. The photoluminescence linewidth exhibits a strong, continuous dependence on the extent of atomic ordering (the emission energy) in the alloys. The results indicate that inhomogeneity in the microstructure of the material (i.e., between ordered'' domains and the disordered'' matrix) is the dominant photoluminescence broadening mechanism. This investigation has allowed a significant optimization ...

Energy Technology Data Exchange (ETDEWEB)

Using conventional deep level transient spectroscopy (DLTS), we have characterized the defects introduced in OMVPE n-GaAs at 15 K by 5.4 MeV alpha particle irradiation from an americium 241 radio-nuclide. After this low temperature irradiation two new defects not yet reported for alpha irradiated GaAs before, E[alpha]7 and E[alpha]9, were detected 0.07 eV and 0.19 eV below the conduction band, respectively. The introduction rates of E[alpha]7 and E[alpha]9 are calculated to be 41 cm[sup -1] and 187 cm[sup -1] respectively. It was observed that both defects obeyed first order annealing kinetics, with E[alpha]9 being removed at 225 K and E[alpha]7 at 245 K corresponding to the well known stage I annealing region. The annealing rate of E[alpha]7 corresponds to an activation energy of 0.86 eV, with a pre-exponential factor of 1.0 x 10[sup 15]s[sup -1]; and the removal of E[alpha]9 has an activation energy of 0.88 eV and a pre-exponential factor of 1.7 x 10[sup 17]s[sup ...

Science.gov (United States)

Ultimate Compressive Strength = 3000.0 psi. 3.0 Failure Criteria. The structural criteria used to evaluate the combustor components was chosen ...

UK PubMed Central (United Kingdom)

The molecular structure, chemical properties, and biological function of the xyloglucan polysaccharide isolated from cell walls of suspension-cultured sycamore (Acer pseudoplatanus)...Full Text Available

Science.gov (United States)

Robert A. Martock. Cleveland State University, Cleveland, Ohio. Synthesis and Structural Characterization of a. Novel Indium Mercapto Derivative. [Clln(SCH. 2 ...

Energy Technology Data Exchange (ETDEWEB)

Morphological and structural changes of nylon 66 were evaluated during a continuous heat-draw process. Results are discussed.

UK PubMed Central (United Kingdom)

Prokaryotic genomes can be annotated based on their structural, operational, and functional properties. These annotations provide the pivotal scaffold for understanding cellular functions on a genome-scale,...Full Text Available

British Library Electronic Table of Contents (United Kingdom)

Design rules for robustness require insensitivity to local failure and the prevention of progressive collapse. This is often verified by applying the load case ''removal of a limited part of the structure''. This paper will evaluate typical structural systems for large-span timber roof structures against these requirements, comparing the results against typical reasons for damages and failures. Applying the finding that most failures of timber structures are not caused by random occurrences or local defects, but by global (repetitive) defects (e.g. from systematic mistakes), it is shown that the objective of load transfer-often mentioned as preferable-should be critically analysed for such structures. Based on these findings, proposals for structural systems and details towards a robust de...

International Nuclear Information System (INIS)

The A-dependence of the nuclear structure functions is described rather well within the framework of the quark-parton-flucton model of nucleus. 16 refs. (author).

CERN Document Server

In undirected graphical models, learning the graph structure and learning the functions that relate the predictive variables (features) to the responses given the structure are two topics that have been widely investigated in machine learning and statistics. Learning graphical models in two stages will have problems because graph structure may change after considering the features. The main contribution of this paper is the proposed method that learns the graph structure and functions on the graph at the same time. General graphical models with binary outcomes conditioned on predictive variables are proved to be equivalent to multivariate Bernoulli model. The reparameterization of the potential functions in graphical model by conditional log odds ratios in multivariate Bernoulli model offers advantage in the representation of the conditional independence structure in the model. ...

International Nuclear Information System (INIS)

Augmented plane wave calculation of gadolinium electronic structure crystallized in a hexagonal close-packed lattice is carried out.

International Nuclear Information System (INIS)

... structure crystal-phase transformations fluorescence fluorescence spectroscopy

UK PubMed Central (United Kingdom)

Acquisition of detailed knowledge of the structure and evolution of Trypanosoma cruzi populations is essential for control of Chagas disease....Full Text Available

UK PubMed Central (United Kingdom)

The organizational structure of medical record departments in Iran is not appropriate for the efficient management of healthcare information. In addition, there is no strong information management division...Full Text Available

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KoreaScience (Korea)

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Energy Technology Data Exchange (ETDEWEB)

HANARO fuel test loop will be equipped in HANARO to obtain the development betterment of advanced fuel and materials through the irradiation test. The object of this study is to evaluate the structural integrity of FTL in-pool piping by investigating a dynamic analysis of the loop containing a postulated rupture section. The method to perform the dynamic analysis and structural integrity evaluation caused by the pipe whip in water environment can be a reference for a similar structural integrity evaluation. (author). 7 refs., 39 tabs., 34 figs.

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KoreaScience (Korea)

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Energy Technology Data Exchange (ETDEWEB)

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Energy Technology Data Exchange (ETDEWEB)

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DEFF Research Database (Denmark)

Udgivelsesdato: null-null

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International Science & Technology Center (ISTC)

Multi-functional Bioactive Nano-structured Coatings for Load-Bearing Implants

KoreaScience (Korea)

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KoreaScience (Korea)

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Energy Technology Data Exchange (ETDEWEB)

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International Nuclear Information System (INIS)

Germanium coordination compounds (GCC) with oxiethilidendyphosphonic acid (Ge-Oedph) film structures electrophysical, optical, structural and adsorptive properties investigation results are represented. This structure concerns to a new perspective class of functional materials. The mechanism GCC films electric conductivity is investigated and explained. GCC possible application fields are specified.

KoreaScience (Korea)

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Energy Technology Data Exchange (ETDEWEB)

Short communication.

KoreaScience (Korea)

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CERN Document Server

Neutrinoless Double Beta Decay ($0\

KoreaScience (Korea)

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KoreaScience (Korea)

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KoreaScience (Korea)

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KoreaScience (Korea)

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KoreaScience (Korea)

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International Nuclear Information System (INIS)

The Structural Aging (SAG) Program is carried out by the Oak Ridge National Laboratory (ORNL) under sponsorship of the United States Nuclear Regulatory Commission (USNRC). The Program has evolved from preliminary studies conducted to evaluate the long-term environmental challenges to light-water reactor safety-related concrete civil structures. An important conclusion of these studies was that a damage methodology, which can provide a quantitative measure of a concrete structure's durability with respect to potential future requirements, needs to be developed. Under the SAG Program, this issue is being addressed through: establishment of a structural materials information center, evaluation of structural component assessment and repair technologies, and development of a quantitative methodology for structural aging determinations. Progress to date of each of ...

Energy Technology Data Exchange (ETDEWEB)

This paper states the concept of a heat-resistant structure of the HOPE airframe having a 10 ton weight when lifting off and also the research situation of heat-resistant structural materials. To study the structure, established are design conditions for lift-off, reentry to the atmosphere and landing. As to the load condition, the load at the time of lift-off is most critical. Relating to the temperature environment condition, thermal analysis is made of the time when a HOPE is on the orbit (low-temperature range) and reenters the atmosphere (high-temperature range), when the temperature environment is critical. The analysis shows that the temrerature environment is in a {minus}80-1700{degree}C (range). The heat-resistant structural materials are developed so as to meet these conditions. The paper describes distribution of the airframe surface temperature by aerodynamic heating at the reentry, ...

Energy Technology Data Exchange (ETDEWEB)

Here we present evidence that in water/acetonitrile solvent detailed structural and dynamic information can be obtained for important proteins that are naturally present as oligomers under native conditions. An NMR-derived human insulin monomer structure in H{sub 2}O/CD{sub 3}CN, 65/35 vol%, pH 3.6 is presented and compared with the available X-ray structure of a monomer that forms part of a hexamer (Acta Crystallogr. 2003 Sec. D59, 474) and with NMR structures in water and organic cosolvent. Detailed analysis using PFGSE NMR, temperature-dependent NMR, dilution experiments and CSI proves that the structure is monomeric in the concentration and temperature ranges 0.1-3 mM and 10-30 deg. C, respectively. The presence of long-range interstrand NOEs, as found in the crystal structure of the monomer, provides the evidence for conservation of the tertiary ...

Energy Technology Data Exchange (ETDEWEB)

For a wider application of GaAs single crystals for semiconductor devices a cheaper process to grow crystals with high purity and low dislocation density is required. According to todays knowledge the Czochralski method with a hot wall vessel should be the choice. The temperature of the vessel has to be 700deg C to avoid condensation of arsenic which vapourizes from the 1240deg C hot melt. Arsenic vapour is very agressive against all metals. Therefore the corrosion resistance of metals and alloys with a high melting point and also ceramics has been tested. All the alloys under investigation are corroded severely so that they have to be excluded as a material for the vessel. The metals tantalum, molybdenum and tungsten are more resistent, titanium forms initially a thick protection layer and further corrosion is greatly reduced. The ceramics investigated (TiB{sub 2}; ALN; Makor; BN) are not attacked by arsenic though they may store some arsenic. (orig./MM). ...

Science.gov (United States)

Reciprocity is one of the defining features of social exchange and social life, yet exchange theorists have tended to take it for granted. Drawing on work from a decade-long theoretical research program, I argue that reciprocity is structured and variable across different forms of exchange, that these variations in the structure of reciprocity have profound effects on the emergence of integrative bonds of trust and solidarity, and that these effects are explained and mediated by a set of risk- and conflict-based processes. I discuss the consequences of this work for organizational theories of embeddedness and the production of social capital through network ties. Finally, I ask how the structure of networks and the structure of reciprocity are related to one another, and explore possible implications of the structure of reciprocity for exchange theorists' assumptions about actor ...

British Library Electronic Table of Contents (United Kingdom)

Summary: Protein features are often displayed along the linear sequence of amino acids that make up that protein, but in reality these features occupy a position in the folded proteins 3D space. Mapping sequence features to known or predicted protein structures is useful when trying to deduce the function of those features and when evaluating sequence or structural predictions. To facilitate this goal, we developed PDBpaint, a simple tool that displays protein sequence features gathered from bioinformatics resources on top of protein structures, which are displayed in an interactive window (using the Jmol Java viewer). PDBpaint can be used either with existing protein structures or with novel structures provided by the user. The current version of PDBpaint allows the visualization of annot...

Energy Technology Data Exchange (ETDEWEB)

Study of glacial geology, stream drainage, bedrock topography, and subsurface structure maps in Isabella, Midland, Arenac, Gladwin, Clare, Ogemaw, Iosco, Mecosta, and Montcalm counties in Michigan revealed distinct correlations between patterns and types of glacial deposits and subsurface structures. Anticlinal structures associated with the Mt. Pleasant, North Buckeye, and South Buckeye, Hamilton, Deep River, Clayton, Logan, Six Lakes, and West Branch oil and gas fields occur along areas where northeast-trending glacial moraines and truncated, attenuated, or deviated. Furthermore, these anticlinal structures are associated with lacustrine sands and gravels and glacial outwash deposits nearly surrounded by glacial tills or lacustrine sands and clays. All of the anticlinal structures are associated with bedrock topography highs and alignment of streams parallel to the trends of the ...

UK PubMed Central (United Kingdom)

AbstractThe structural integrity of striated muscle is determined by extra-sarcomere cytoskeleton that includes structures that connect the Z-disks and M-bands of a sarcomere to sarcomeres...Full Text Available

UK PubMed Central (United Kingdom)

The structure of the skin in the epauletted fruit bat (Epomophorus wahlbergi) wing and body trunk was studied with a view to understanding possible adaptations for gas metabolism and...Full Text Available

International Nuclear Information System (INIS)

1973. 27 p. United States American Society of Mechanical Engineers.;

UK PubMed Central (United Kingdom)

The quantitative experimental uncertainty in the structure of fully hydrated, biologically relevant, fluid (L_α) phase lipid bilayers has been too large to...Full Text Available

Science.gov (United States)

Several central results of the method of structural formulae for some classes of analytic functions, which were known before for a disc and an annulus, are generalized to analytic functions in a finitely connected circular domain.

UK PubMed Central (United Kingdom)

Although deep-sea cephalopods are key marine organims, their feeding ecology remains essentially unknown. Here, we report for the first time the trophic structure of an assemblage of these animals (19...Full Text Available