International Nuclear Information System (INIS)

GaAs1-xPx p-n junction structures were grown on the epi-ready n-type GaAs(100) substrate by solid source MBE system for different phosphor compositions. To obtain the lattice-match sample structure was applied graded growth procedure. The structural and optical properties of the sample structures with different P concentration were investigated by using X-ray diffraction (XRD), spectroscopic ellipsometry (SE). In addition, The range of lattice parameters in the graded epilayer and phosphorous composition were determined from the HRXRD rocking curve simulation. We analyse dielectric function spectra of disordered GaAs1-xPx junction structures measured using spectroscopic ellipsometry at room temperature in the 0.6-4.7 eV photon energy region. The critical energy points such as band gap energy and spin-orbit-split energy of these structures were determined using ...

International Nuclear Information System (INIS)

The feasibility of continuous production of gallium arsenide ribbon single crystals, by passage of a molten zone through boron-oxide encapsulated GaAs feedstock, is being investigated. Polycrystalline GaAs ribbons have been grown in graphite boats by passage of a wide zone through B2O3-encapsulated feed-stock, confined by a quartz cover plate. Failure to remove the encapsulant above its glass transition temperature, however, resulted in cracking of the ribbons on cooling to room temperature. In order to study the crucial zone melting step in isolation from the encapsulation steps of the continuous process, a constrained-zone melting apparatus has been constructed in which the boron oxide serves only as a sealant to suppress arsenic vaporization. Large grained polycrystalline samples have been produced with this apparatus.

Energy Technology Data Exchange (ETDEWEB)

This paper will discuss initial studies of thin-film GaAs grown by molecular-beam epitaxy for use in developing a thin-film GaAs solar cell. Photocurrent and photoluminescence intensity are related to the material morphology as a function of growth conditions. Growth temperature and V/III ratio have a dramatic effect on the photocurrent. However, it seems likely that even after optimizing such growth parameters, it will be necessary to provide substrates that can provide templates to enhance grain size from the start of thin-film growth. {copyright} {ital 1997 American Institute of Physics.}

International Nuclear Information System (INIS)

The dependence of the photoluminescent properties of In_0_._4_8(Al_yGa_1_-_y)_0_._5_2P alloys (0#<=#y#<=#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 of the optical ...

Science.gov (United States)

By gas-source molecular-beam epitaxy, we obtained a device-quality GaInP epitaxial layer lattice matched to (100)-GaAs substrates, with a photoluminescence efficiency comparable to that of a crystal grown by liquid-phase epitaxy. A GaInP/AlInP double heterostructure laser with a GaInP active layer was fabricated, and pulsed lasing operation was achieved at room temperature for, we believe, the first time.

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.

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 ...

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.

Science.gov (United States)

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 ...

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 ...

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.

CERN Document Server

A new monolithic semi-insulating (SI) GaAs sensor design for X-ray imaging applications between 10-100keV has been proposed. Monolithic pixel detectors offer a number of advantages over hybrid bump-bonded detectors, such as high device yield, low costs and are easier to produce large scale arrays. In this thesis, an investigation is made of the use of a SI GaAs wafer as both a detector element and substrate for the epitaxially grown High Electron Mobility Transistors (HEMTs). The design of the HEMT transistors, optimised for this application, were produced with the aid of the Silvaco 'Virtual Wafer Fab' simulation package. It was determined that the device characteristics would consist of a small positive threshold voltage, a low off-state drain current and high transconductance. The final HEMT transistor design, that would be integrated to a pixel detector, had a threshold voltage of 0.17V, an off-state leakage current of ...

International Nuclear Information System (INIS)

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)right-angle left-angle 111 right-angle A, consist of nominally undoped MQWs surrounded by doped In_0_._4_9Al_0_._5_1P cladding layers to form p-i-n diodes. The Stark shifts of various allowed and forbidden quantum-well transitions were observed in bias-dependent electroreflectance spectra of In_0_._4_9Ga_0_._5_1P/In_0_._4_9(Al_0_._5Ga_0_._5)_0_._5_1P 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 (InAlGa)P materials are promising for ...

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.

Science.gov (United States)

Stresses commonly present in AlGaAs/GaAs laser heterostructures were reduced using Molecular Beam Epitaxy grown Al/sub 0.3/Ga/sub 0.7/P/sub 0.01/As/sub 0.99/ cladding layers. The Al/sub 0.3/Ga/sub 0.7/P/sub 0.01/As/sub 0.99/ alloy was grown using an incident P/sub 2/ flux of roughly-equal1 x 10/sup 14//cm/sup 2/ indicating a sticking coefficient of 0.1 at a substrate temperature of 600 /sup 0/C. X-ray automatic Bragg angle control curvature measurements were used to monitor the residual heteroepitaxial stress. Broadened double crystal x-ray linewidths indicated the occurrence of alloy grading and broadened interfaces. The effects of P concentration and film thickness on stress and on the existence of a misfit dislocation grid are discussed.

International Nuclear Information System (INIS)

Self-assembled quantum dots (QDs) are envisioned as building blocks for realization of novel nanoelectronic devices, for which the site-selective growth is highly desirable. This thesis presents a successful route toward selective positioning of self-assembled InAs QDs on patterned GaAs surface by combination of in situ focused ion beam (FIB) implantation and molecular beam epitaxy (MBE) technology. First, a buffer layer of GaAs was grown by MBE before a square array of holes with a pitch of 1-2 #mu#m was fabricated by FIB implantation of Ga and In, ions respectively. Later, an in-situ annealing step followed by InAs deposition was performed. The InAs QDs were preferentially formed in the holes generated by FIB. The influence of ion dose, annealing parameters and InAs amount was investigated in this work. With optimized parameters, more than 50 % single dot occupancy per hole is achieved. Furthermore, the photoluminescence ...

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. 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.

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 site-selective growth of InAs quantum dots (QDs) by a combined focused ion beam (FIB) and molecular beam epitaxy (MBE) process has been demonstrated. An array of FIB modified spots on MBE grown GaAs was fabricated. Thereafter, an in situ annealing step followed by InAs deposition was performed. The InAs QDs were preferentially formed in the holes generated by the FIB. The influences of ion dose, annealing parameters, and InAs amount were investigated. With optimized parameters, the authors observe more than 50% single dot occupancy per holes. Photoluminescence spectra confirm the good optical quality of the QDs.

Energy Technology Data Exchange (ETDEWEB)

In this paper, we discuss various aspects of the development of an inverted-grown AlGaAs/GaAs cascade solar cell incorporating a patterned germanium tunnel junction. Topics include the development of the Al{sub 0.37}Ga{sub 0.63}As top cell, the growth of the GaAs bottom cell over the patterned germanium tunnel junction, and a technique for selective removal of thin AlGaAs/GaAs heterostructures after lattice-matched growth on germanium substrates. The problems to be overcome for the achievement of around 30% efficiencies in the AlGaAs/GaAs cascade cell under concentrator applications are also discussed. (orig.).

Science.gov (United States)

For visible-light-emitting laser diodes, InGaAsP double heterostructures have been grown on GaAs substrates using liquid-phase epitaxy. As the growth temperature is as high as about 780 /sup 0/C, a large amount of phosphorus evaporates from the solutions for the cladding layers during the growth process. The phosphorus vapor disturbs the solution composition for the active layer, so that very thin and uniform active layers cannot be obtained. By using In-P-Sn solution and supplying the phosphorus partial pressure around the graphite boat, the influence of phosphorus vapor ambient for InGaAsP (lambda/sub P//sub L/ = 805 nm) growth is confirmed. When the phosphorus partial pressure increases, the surface of epitaxial layer becomes rough and the substrate is partly etched back. From x-ray diffraction and photoluminescence spectral measurements, the composition of the grown layer is also found to be changed. As a result of ...

Energy Technology Data Exchange (ETDEWEB)

The Heusler alloy Ni{sub 2}MnIn is a promising material as spin injector because of its predicted half-metallicity at the interface to InAs. We grow thin films of this Heusler alloy by thermal coevaporation of Nickel and the alloy MnIn. The alloy is grown on Si{sub 3}N{sub 4} membranes and amorphous carbon films for transmission-electron microscopy (TEM) as well as on Si and InAs. The degree of the transport spin polarization of the films grown on Si(100), InAs(100) and in-situ cleaved (110) surfaces of InAs is determined by point-contact Andreev reflection spectroscopy (PCAR). The almost perfect lattice match between InAs and Ni{sub 2}MnIn supports highly oriented growth, as we have proven by electron diffraction under grazing incidence. Lateral spin valves with Heusler electrodes are lithographically defined. In view of the temperature-sensitivity of the optical and electron-beam resists, the samples are ...

Energy Technology Data Exchange (ETDEWEB)

Main topic of the project was the manufacturing of highly efficient GaAs-solar cells and the fabrication of concentrator cells. During this process significant progress was made with the material preparation, the solar cell technology and the material and process characterisation. This succeeded in the following efficiencies: - GaAs solar cell made by MOVPE technology: 22.9% on 4 cm{sup 2} (AM1.5g) - GaAs solar cell made by LPE-ER process: 22.8% on 4 cm{sup 2} (AM1.5g) - GaAs concentrator solar cell made by LPE-ER process: 24.9% at C=100xAM1.5d - GaAs concentrator module with fresnel lenses: Module efficiency 20.1% (under irradiation of 793 W/m{sup 2}). Another main focus was the epitaxy of GaAs on Si substrate. Two different approaches were investigated. Together with the cooperation partner ASE, Heilbronn a selective growth technology was developed that led to a decreased crack ...

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)

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)

Data are presented demonstrating very-short-wavelength (625 nm) room-temperature (300 K) continuous (cw) photopumped laser operation of In/sub 1-//sub y/(Al/sub x/Ga/sub 1-//sub x/)/sub y/P-In/sub 1-//sub y/ (Al/sub x/Ga/sub 1-//sub x/)/sub y/P quantum well heterostructures grown lattice matched (yapprox. =0.5) on a GaAs substrate via metalorganic chemical vapor deposition. In addition, 300 K pulsed laser operation (J/sub th/approx.10/sup 4/ A/cm/sup 2/, 625 nm) of diodes fabricated from the same crystal is described.

International Nuclear Information System (INIS)

Epitaxial metastable (GaSb)/sub 1-x/Ge/sub x/ alloys with compostions across the pseudobinary phase diagram have been grown on (100) GaAs substrates by multitarget rf sputtering. An essential feature allowing the growth of these metastable materials was low-energy ion bombardment of the growing film during deposition to enhance surface diffusion, promote mixing, and preferentially sputter incipient second-phase precipitates. Annealing experiments indicated that the metastable films exhibit good high-temperature stability and that they transform through a continuous series of GaSb-rich and Ge-rich phases in which the solute concentrations decrease until the equilibrium two-phase alloy is obtained. While the calculated free-energy difference between the single-phase metastable and equilibrium states is approx.18 meV, the measured activation barrier for the transformation is approx.3 eV. All films were p-type with room-temperature hole ...

Science.gov (United States)

... The approach is to perform noise spectral density measurements and selected materials structure measurements on GaAs detector materials, with ...

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 ...

Energy Technology Data Exchange (ETDEWEB)

Short communication.

Science.gov (United States)

Photorefractives, in general, are among the most promising materials solutions to real time optical correlation. Applications include military target recognition and civilian robotic vision. Crystals of sillenite structure photorefractives, Bi12XO20, where X equals Si, Ge, or Ti, have been grown by melt techniques and in the case of bismuth silicon oxide (BSO) and bismuth titanium oxide (BTO) by the hydrothermal method of high-temperature/high-pressure solution growth. The two growth methods are discussed and crystals grown by the two methods are compared in this paper. Optical absorption and TSC studies show that hydrothermal BSO is essentially free of the native antisite Bi defect which usually acts as a donor. These studies also show that the trap density is greatly reduced in hydrothermal material. Preliminary experiments show that hydrothermal BTO crystals have improved properties over melt grown ...

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 ...

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.

British Library Electronic Table of Contents (United Kingdom)

Abstract Here we propose a software for the estimation of the occupied area and volume of fungal cultures. This software was developed using a Matlab platform and allows analysis of high-definition images from optical, electronic or atomic force microscopes. In a first step, a single hypha grown on potato dextrose agar was monitored using optical microscopy to estimate the change in occupied area and volume. Weight measurements were carried out to compare them with the estimated volume, revealing a slight difference of less than 1.5%. Similarly, samples from two different solid-state fermentation cultures were analyzed using images from a scanning electron microscope (SEM) and an environmental SEM (ESEM). Occupied area and volume were calculated for both samples, and the results obtained w...

Energy Technology Data Exchange (ETDEWEB)

The theory for the general case of solar cells operating inside integrating cavity receivers is established. This is applied to the particular case of different configurations of silicon and GaAs cells. The results of the analysis show that a composite system of silicon and GaAs cells manufactured using relatively simple technology could reach an efficiency of 34%. The optimal configuration is that in which the GaAs cells are placed in the directly illuminated area of the receiver and the silicon cells are placed in the indirectly illuminated area of the receiver. (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 ...

Energy Technology Data Exchange (ETDEWEB)

Si/Pd-based contact schemes based on the solid phase regrowth (SPR) principle have been developed to form low resistance ohmic contacts to n type Al{sub 0.5}In{sub 0.5}P and Ga{sub 0.5}In{sub 0.5}P lattice matched to GaAs grown by gas source molecular beam epitaxy (GSMBE). Lowest contact resistivities of {approximately} 6 {times} 10{sup {minus}6} {Omega}-cm{sup 2} and {approximately} 1 {times} 10{sup {minus}5} {Omega}-cm{sup 2} have been obtained on Al{sub 0.5}In{sub 0.5}P and Ga{sub 0.5}In{sub 0.5}P respectively (both doped to {approximately} 2 {times} 10{sup 18} cm{sup {minus}3}). In this article, the electrical properties and the ohmic contact formation model of the Si/Pd-based contacts to n-Al{sub 0.5}In{sub 0.5}P and n-Ga{sub 0.5}In{sub 0.5}P are presented.

Science.gov (United States)

AlGaInP double heterostructure laser diodes with a GaInP active layer constitute a basic laser structure for visible-light lasers using an AlGaInP alloy system. This paper gives a detailed description of (Al/sub x/Ga/sub 1 - x/)/sub 0.5/In/sub 0.5/P metalorganic vapor phase epitaxial growth, laser-fabrication processes, and basic device-characteristics for these lasers. The obtained pulsed-threshold-current was about 3.8 kA/cm/sup 2/(3.2 kA/cm/sup 2/ minimum) for laser diodes with an 8-10 /n//m wide and 150-300 ..mu..m long injection stripe. High characteristic-temperature T/sub o/ for the temperature dependence of pulsed threshold current was obtained and was found to be dependent on band-gap-energy differences between active layers and cladding layers. The maximum value for T/sub o/ was 222 K. The lasing wavelength of an AlGaInP double heterostructure laser diode with a GaInP active layer was found to depend on growth conditions and dopant behaviour during the growth, and it varied ...

International Nuclear Information System (INIS)

We have investigated the correlation between V-shaped defect formation and the optical properties of AlGaN/(In)GaN multiple quantum wells (MQWs) grown under different growth conditions and then demonstrated the characteristics of fabricated ultraviolet (UV) light emitting diodes (LEDs). From the temperature-dependent photoluminescence (PL) measurement, the internal quantum efficiency for 300 K was obtained as 43.6% for a sample with a low density of V-defects in a MQW and 13.7% for a sample with a high density of V-defects. The carrier lifetime based on the time resolved PL measurement at room temperature was 0.32 ns for a sample with a high density of V-defects and 1.26 ns for a sample with a low density of V-defects. And we also found that the density of V-defects affected the external quantum efficiency and wall plug efficiency of the fabricated UV LEDs. (fast track ...

Energy Technology Data Exchange (ETDEWEB)

Rice (Oryza sativa L.) was grown at 330 and 660 {mu}L CO{sub 2} L{sup {minus}1} and at 40/33/37, 34/27/31, and 28/21/25{degree}C day/night/paddy water temperatures respectively. Sucrose phosphate synthase (SPS) activity was measured at saturating substrate concentrations at 59 days after planting. SPS activity increased 2 and 3 fold with increasing CO{sub 2} at 28 and 34{degree}C air temperatures respectively. At 40{degree}C SPS activity decreased by 37% at elevated CO{sub 2} and most plants failed to reach maturity. Similar responses were found in leaf samples taken in the dark. These results indicate that SPS, an enzyme involved in the regulation of C partitioning in leaves, increases in activity at elevated CO{sub 2}. This is in contrast to previous results with soybean. The changes in SPS activity will also be discussed in relation to leaf starch/sucrose ratios.

International Nuclear Information System (INIS)

A container experiment was conducted to test the hypothesis that uncomposted wool wastes could be used as nutrient source and growth medium constituent for container-grown plants. The treatments were: (1) rate of wool-waste application (0 or unamended control, 20, 40, 80, and 120 g of wool per 8-in. pot), (2) growth medium constituents [(2.1) wool plus perlite, (2.2) wool plus peat, and (2.3) wool plus peat plus perlite], and (3) plant species (basil and Swiss chard). A single addition of 20, 40, 80, or 120 g of wool-waste to Swiss chard (Beta vulgaris L.) and basil (Ocimum basilicum L.) in pots with growth medium provided four harvests of Swiss chard and five harvests of basil. Total basil yield from the five harvests was 1.6-5 times greater than the total yield from the unamended control, while total Swiss chard yield from the four harvests was 2-5 times greater relative to the respective unamended control. The addition of wool-waste to the growth medium ...

International Nuclear Information System (INIS)

InP-quantum dots (QDs) are promising sources of single-photons and as active laser medium, emitting in the red part of the visible spectrum and thus in the range of the highest sensitivity of current silicon detectors. The self assembled QDs were grown by metal organic vapor phase epitaxy and are embedded in between distributed Bragg reflectors (DBRs), afterwards the sample was processed by a Focused Ion Beam to fabricate micro-pillars. The DBRs and the high refractive index step between pillar and air results in a three dimensional mode confinement and highly directed emission and thus higher intensity. We have investigated the mode spectra by micro-photoluminescence measurements for different pillar diameters and compared the spectra with a theoretical model showing up good consistency. Q-factors up to 3600 were achieved.

CERN Document Server

Surface compositional changes in GaAs due to RF plasmas of different gases have been investigated by XPS and etch rates were measured using AFM. Angular Resolved XPS (ARXPS) was also employed for depth analysis of the composition of the surface layers. An important role in this study was determination of oxide thickness using XPS data. The study of surface - plasma interaction was undertaken by correlating results of surface analysis with plasma diagnosis. Different experiments were designed to accurately measure the BEs associated with the Ga 3d, Ga 2p sub 3 sub / sub 2 and LMM peaks using XPS analysis and propose identification in terms of the oxides of GaAs. Along with GaAs wafers, some reference compounds such as metallic Ga and Ga sub 2 O sub 3 powder were used. A separate study aiming the identification of the GaAs surface oxides formed on the GaAs surface during and after ...

International Nuclear Information System (INIS)

We have investigated the formation and coarsening of Ga droplets on focused-ion-beam (FIB) irradiated GaAs surfaces. To separately examine formation and coarsening, Ga droplets were fabricated by Ga"+ FIB irradiation of GaAs substrates with and without pre-patterned holes. We determined the droplet growth rate and size distribution as a function of FIB energy following irradiation. The data suggest a droplet formation mechanism that involves Ga precipitation from a Ga-rich layer, followed by droplet coarsening via a combination of diffusion and Ostwald ripening or coalescence via droplet migration (dynamic coalescence).

Energy Technology Data Exchange (ETDEWEB)

This paper reports advances in the development of solar cells made from GaAs-on-Si structures prepared by metalorganic chemical vapor deposition (MOCVD). The use of concentrator cells, operating at [similar to]200 suns, has led to the efficiency achievements of 21.3% (AM1.5D) for a GaAs-on-Si solar cell, and 27.6 (AM1.5D) for a homoepitaxial GaAs cell. The development of epitaxial multilayer dielectric mirrors (Bragg reflectors), as back-surface reflectors in thin-film GaAs cells, on both Si and GaAs substrates, is shown to lead to modest efficiency increases, over that of conventional designs.

International Nuclear Information System (INIS)

We show that the morphology and the luminescence properties of ZnO layers produced by magnetron sputtering can be controlled by technological parameters of sputtering, particularly by the ratio of argon to oxygen gases in the gas flow during the growth process. Smooth and flat layers were produced with a high Ar/O ratio, while porous layers with various morphologies were obtained with a low Ar/O ratio. The layers produced with O/Ar ration equal to 10 exhibit extremely high near-bandgap luminescence intensity even higher in comparison with bulk ZnO single crystals. The free carrier density estimated from the analysis of photoluminescence spectra is also very high in these samples suggesting that these technological conditions promote both optical and electrical activation of the doping Al impurity. The samples grown with high Ar/O ratios exhibit strong visible emission which is controlled by the technological conditions.

Science.gov (United States)

An analytical method was developed for the determination of eleven agrochemicals [abamectin (as B1a), bifenazate, bifenthrin, carfentrazone-ethyl, cymoxanil, hexythiazox, imidacloprid, mefenoxam, pymetrozine, quinoxyfen, and trifloxystrobin] in dried hops. The method utilized polymeric and NH2 solid phase extraction (SPE) column cleanups and liquid chromatography with mass spectrometry (LC-MS/MS). Method validation and concurrent recoveries from untreated dried hops ranged from 71 to 126% for all compounds over three levels of fortification (0.10, 1.0, and 10.0 ppm). Commercially grown hop samples collected from several field sites had detectable residues of bifenazate, bifenthrin, hexythiazox, and quinoxyfen. The control sample used was free of contamination below the 0.050 ppm level for all agrochemicals of interest. The limit of quantitation and limit of detection for all compounds were 0.10 and 0.050 ppm, respectively. ...

International Nuclear Information System (INIS)

A wide variety of thin film coatings, deposited by different techniques and with potential applications in various important areas, have been characterised by the Phase Modulated Spectroscopic Ellipsometer, installed recently in the Spectroscopy Division, B.A.R.C. The Phase Modulated technique provides a faster and more accurate data acquisition process than the conventional ellipsometry. The measured Ellipsometry spectra are fitted with theoretical spectra generated assuming an appropriate model regarding the sample. The fittings have been done objectively by minimising the squared difference (#chi#"2) between the measured and calculated values of the ellipsometric parameters and thus accurate information have been derived regarding the thickness and optical constants (viz, the refractive index and extinction coefficient) of the different layers, the surface roughness and the inhomogeneities present in the layers. Measurements have been done on (i) ion-implanted ...

Energy Technology Data Exchange (ETDEWEB)

The aim of this thesis is to study the coherent transport in semiconducting-superconducting junctions. The SnPb-GaAs system has been studied. It has been shown that the behaviour of this junction is controlled by the disordered area induced by the annealing of the connection near the interface. For a few resistant junction, a conductance anomaly under the gap has been observed and has been explained by a mesoscopic effect in the limit of the very high disorders. The conductance of more resistant junctions has only been bound to the properties of the very disordered area of the semiconductor. The part of the electron-electron interactions on the phase coherence length and on the conductance has been studied. The evolving of the correction of the conductance due to interactions in magnetic field has been followed. The effect of the spin degeneration suppression in CdTe and the GaAs sign inversion in Shubnikov de Haas oscillations rate has been observed. At last has ...

Energy Technology Data Exchange (ETDEWEB)

The use of medicinal plants in the treatment of diseases has increased significantly in the last years, as has research concerning chemical characterization of these plants. In this study, inorganic constituents were determined in leaves and in extracts from three medicinal plant species of the Casearia genus (C. sylvestris, C. decandra and C. obliqua) collected in distinct regions of the Atlantic Forest, SP. The elemental compositions of the soils in which these plants were grown were also determined. Traditionally, these plants are used due to their antiinflammatory, antiacid, antiseptic and cicatrizing properties. The antiulcer and the antitumor activities of the Casearia genus and its capacity to neutralize snake and bee venoms, have also been scientifically confirmed. The analytical methodology used was neutron activation analysis. Long and short irradiation periods of the samples and the standards were carried out at IPEN's ...

International Nuclear Information System (INIS)

The paper generalizes some results of the United States/Moldova program on advanced composite organic and semiconductor light emitters. High density exciton system bound to N impurity superlattice grown by modern technologies and GaP:N, GaP:N:Sm nanocrystals distributed in transparent fluorine-containing polymers will be used as the base elements for new generation of optoelectronic devices. The work seeks to expand further the applications of GaP itself through the formation of nanocomposites. Classic and new methods are applied for preparation of GaP:N nanoparticles with the controlled dimensions developed clear quantum confinement effect. The long-term ordered bulk GaP crystals as well as their nanoparticles have been investigated by TEM, XRD, Raman scattering, and luminescent methods. The evolution of the Raman Light Scattering and luminescence spectra is reported from pure and doped GaP single crystals grown over 40 years ago and evaluated ...

International Nuclear Information System (INIS)

This paper reports on a series of experiments performed to examine the ability of ion beam assisted thermal deposition to produce good adhesion of Au metallization on GaAs left-angle 100 right-angle substrates. A study of the influence of Ar ion-assisted thermal deposition of the Au films as well as in situ pre-sputtering of the GaAs surface with low-energy Ar ions prior to thermal deposition, shows that strong adhesion can be achieved without resorting to chemical cleaning. The substrate temperature and the relative flux of Ar ions to incident Au atoms were varied in order to correlate these parameters with film adhesion. The interfaces of films processed under these various conditions were examined by XTEM, RBS and XPS. Orientation texture was studied by x-ray diffraction (XRD).

International Nuclear Information System (INIS)

Biaxially textured tungsten nanorods (A15 crystal structure) have been grown by oblique angle DC magnetron sputtering using a novel rotation mode called 'two-step rotation'. In this mode, the substrate is given a fast rotation through 1800 at 90 rpm and this is followed by a rest period of 30 s. These nanorods are vertically aligned and have a [100] texture normal to the substrate along with preferential in-plane texture as shown by x-ray pole figure analysis. In contrast, the tungsten nanorods obtained without substrate rotation are slanted at an angle of ?450 and have a [100] texture tilted 160 with respect to the substrate normal. The flux is incident from two diametrically opposite points on the sample at an oblique angle, averaging out the growth into vertical columns that retain the in-plane texture. Scanning electron microscopy shows that the tungsten nanorods have a mixture of {211} and {421} crystal habits; these planes are both ...

Energy Technology Data Exchange (ETDEWEB)

Recently we have found a highly effective additive for the melt growth processings attaining high critical currents in YBCO superconductor. It is platinum and it behaves as an effective grain growth inhibitor for the Y{sub 2}BaCuO{sub 5} phase. Even with less than 1 wt.% doping, Y{sub 2}BaCuO{sub 5} particles becomes less than one micron in size and distribute themselves to become homogeneously embedded in the large grown YBa{sub 2}Cu{sub 3}O{sub y} grains. The sample shows large magnetic hysteresis and a typical J{sub c} value estimated by using Bean's model critical state model is 18000 A/cm{sup 2} at 77 K and 1 T. We found that rhodium has a similar remarkable effect. (orig.).

Energy Technology Data Exchange (ETDEWEB)

We report on the elimination of defect formation which is associated with high dose indium implantations under solid phase epitaxial regrowth (SPER) annealing conditions of 650-800 deg. C. This is achieved by incorporating a layer of epitaxially grown Si{sub 1-y}C {sub y} layer, strategically located at the end-of-range (EOR) of the implant profile. An indium implant of 115 keV at 1 x 10{sup 14} cm{sup -2} was performed followed by annealing at temperature ranges of 650-800 deg. C. Samples with the Si{sub 1-y}C {sub y} layer revealed the elimination of secondary EOR defects with effectively suppressed indium transient enhanced diffusion (TED), indicating the function of carbon as an efficient sink for silicon interstitials at reduced annealing temperatures, in the SPER dopant activation regime.

UK PubMed Central (United Kingdom)

Many auxin responses are dependent on redistribution and/or polar transport of indoleacetic acid. Polar transport of auxin can be inhibited through the application of phytotropins such as 1-naphthylphthalamic...Full Text Available

Energy Technology Data Exchange (ETDEWEB)

The optically stimulated luminescence (OSL) results a highly appropriate dosimetric technique for readings of absorbed radiation 'in alive' and 'in situ', as well as in real time. The CVD diamond on the other hand presents excellent qualities like radiation reader thanks to its reproducibility, radiation resistance, biocompatibility and non toxicity. The present work studies the answer of two diamond films pure and polluted with nitrogen (750 ppm) grown by the Chemical Vapor Deposition method (CVD) on silicon substrate (001) irradiated with beta (Sr-90) in the 0.833-100 Gy interval. The optical stimulation was carried out by 40 seconds with infrared laser (830 nm, 0.36 W/cm{sup 2}) and the filter BG-39 (300-600 nm) coupled the PM. The intensity and the decay of the hyperbolic type of the LOE curves were similar in both samples, for the non doped diamond were observed trapping states in 200-380 C being ...

International Nuclear Information System (INIS)

The radiation-induced microstructural changes have been studied by cross-sectional transmission electron microscopy for single-crystal #alpha#-Al_2O_3 samples irradiated with triple ion beams (0.25 MeV H"+, 0.6 MeV He"+ and 2.4 MeV O"2"+; 'Triple (A)'), (0.33 MeV H"+, 0.45 MeV He"+ and 1.3 MeV O"+; 'Triple (B)') and three consecutive single ion beams (0.3 MeV H"+ ion followed by 0.6 MeV He"+ and then 0.8 MeV O"+ ions) at 650 C to doses in the range 0.1-8.4 dpa at the damage peak. In the specimen irradiated with Triple (A), having the same average projected range to a total peak dose of 3.7 dpa, cavities with an average diameter of 13 nm were formed between 1.2 and 1.75 #mu#m in depth causing a swelling of 0.1% at the peak, which is larger than those of the specimens irradiated with other conditions. The extent of the cavity-introduced region is some 40% smaller than observed in the damage region due to the He"+ and the O"+ ions and due to the H"+ ions in the ...

International Nuclear Information System (INIS)

Transient enhanced diffusion (TED) and dose loss (pile-up) are investigated for phosphorus-implanted samples covered with both oxide and nitride films. P ions were implanted into p-type (1 0 0) CZ-Si (dose 5x10"1"3 cm"-"3, 100 keV) through a chemical vapor deposition (CVD) Si_3N_4 film. For a half of samples, Si_3N_4 was etched off and SiO_2 films were grown by CVD. Both samples were annealed for 20-360 min at 700 deg. C. Diffusivity of P and the dose loss were estimated based on the secondary-ion mass spectrometry (SIMS) P profiles. Both Si/Si_3N_4 and Si/SiO_2 interfaces were investigated with transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). There is no significant difference in P diffusivity between the SiO_2 and Si_3N_4 films for the present annealing condition of 700 deg. C for 20-360 min. Regarding dose loss, a distinct different behavior was observed. In case ...

Environmental Research Database

DescriptionThe objective of this project is to relate the processing quality of wheat to the composition of the developing and mature grain using material grown under a range of nutrient regimes including long term organic and fertilised systems from the Rothamsted Broadbalk experiment, variety trials and organically grown wheat. Preliminary studies have indicated substantial differences in the transcriptome profiles of wheat grown with artificial fertiliser and with organic fertiliser on Broadbalk and tru [continued...

Science.gov (United States)

Metal-Semiconductor Solar Cells," J. Appl. Phys. 46,. 1286 (1975). 12) H. B. Kim , G. G. Sweeney and I. S. Heng, "Analysis of ...

UK PubMed Central (United Kingdom)

Electronic and structural properties of antiphase boundaries in group III-V semiconductor compounds have been receiving increased attention due to the potential to integration of optically-active III-V...Full Text Available

International Nuclear Information System (INIS)

Using the slow electrons spectrometer one can get information on the surface structure, its element composition, chemical bonds, adsorption phenomena, electron state density and surface oscillation. We have developed the methods and created the apparatus that makes it possible to investigate the electron backscattering by solid surface. We have studied the electron scattering by the polycrystalline and monocrystalline. GaAs surface in the energy range of 0 to 9 eV. The FWHM of electron energy distribution function was 70 meV. (author).

Energy Technology Data Exchange (ETDEWEB)

As part of a five-year-lasting open-top-chamber experiment at the `Edelmannshof` site (Welzheimer Wald) we analyzed Norway spruce trees (Picea abies (L.) Karst.) with regard to carbohydrate and energy (ATP/ADP ratio) metabolism. End products, intermediates, and a regulator of carbon allocation (starch, sucrose, hexoses, fructose-2,6-bisphosphate) as well as enzyme activities involved in sucrose metabolism (sucrose-P synthase, sucrose synthase, acid invertase) were determined in needle and trunk samples of the different treatments (charcoal-filtered, unfiltered, ambient air). Changes of these parameters were documented annually and with regard to needle development (up to 2 years after bud break), and diurnally during an ozone period in midsummer. Samples from trees grown in an unfiltered atmosphere showed relatively high sucrose and hexose contents of the needles. The capacities of sucrose-P synthase (increased; sucrose ...

UK PubMed Central (United Kingdom)

Ethane oxidation was studied in ethane-grown resting cells (mycelia) of an Acremonium sp. and in cell-free preparations of such mycelia. From resting cell experiments evidence was found for a pathway...Full Text Available

British Library Electronic Table of Contents (United Kingdom)

Single crystals of ytterbium tartrate trihydrate have been grown by gel method using silica and agar-agar gels as media of growth. The medium of growth influences the morphology of grown crystals, silica gel yielding single and polycrystalline in the form of spherulites whereas agar-agar gel leading to growth of single and twinned crystals. Materials grown as single crystals have been characterized by using optical and scanning electron microscopy (SEM), EDAX, XRD, FT-IR, CHN and thermogravimetric techniques. The stoichiometry of the grown single crystals is suggested to be Yb(C4H4O6) (C4H5O6).3H2O. The FT-IR spectrum shows the presence of singly as well as doubly ionized tartrate ligands. Results of thermal analysis indicate that the material is thermally stable up to a temperature of 200...

Science.gov (United States)

Excitonic transitions in metalorganic vapor phase epitaxially grown In[sub [ital x

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 ...

Energy Technology Data Exchange (ETDEWEB)

An updated review of the state of the art in the development of GaAs solar cells is provided, with emphasis on AlGaAs-GaAs cells suitable for space applications. A set of theoretically derived characteristics is given for this type of solar cell. Comparison of measured performance with theory shows excellent agreement. Data on the effects of radiation damage (high-energy electrons, protons, and neutrons) is also integrated into a form useful for evaluation purposes. Techniques for fabricating (AlGa)As-GaAs solar cells in quantities large enough for practical applications are discussed and are shown to have been demonstrated. The possibility of extending these techniques to the fabrication of very thin low-weight cells for space applications is also considered. Finally, the results obtained to date in the development of GaAs solar cells for applications requiring concentrated sunlight are reviewed, for terrestrial as well as for space ...

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.}

International Nuclear Information System (INIS)

Efficient, low-temperature conversion of infrared light into visible light (red, orange, green) is reported at single heterojunctions and undoped quantum wells of GaAs and ordered Al_xGa_1_-_xInP_2; an increase in photon energy of 700 meV is obtained. The signal originates from the high-band-gap layers and disappears only if the excitation energy is tuned below the GaAs band gap. The intensity of the up-converted photoluminescence (PL) is found to decrease significantly slower with increasing temperature than that of the regular PL and it remains observable up to 200 K. Interface-induced cold Auger processes along with the presence of trapped states for both electrons and holes in these ordered alloys account for this nonlinear mechanism. A colinear double-beam experiment confirms this. copyright 1996 The American Physical Society.

International Nuclear Information System (INIS)

Pattern formation on GaAs by Ga"+ focused-ion-beam (FIB) irradiation and subsequent Cl_2 gas etching was carried out. A higher etch rate at the FIB-irradiated area compared with that not irradiated under Cl_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"+ FIB-assisted Cl_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"+-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)

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.

International Nuclear Information System (INIS)

Both soil and plant samples of nine different plant species grown in soils from southeastern China contaminated with uranium mine tailings were analyzed for the plant uptake and translocation of "2"3"8U, "2"2"6Ra and "2"3"2Th. Substantial differences were observed in the soil-plant transfer factor (TF) among these radionuclides and plant species. Lupine (Lupinus albus) exhibited the highest uptake of "2"3"8U (TF value of 3.7x10"-"2), while Chinese mustard (Brassica chinensis) had the least (0.5x10"-"2). However, in the case of "2"2"6Ra and "2"3"2Th, the highest TFs were observed for white clover (Trifolium pratense) (3.4x10"-"2) and ryegrass (Lolium perenne) (2.1x10"-"3), respectively. "2"3"2Th in the tailings/soil mixture was less available for plant uptake than "2"2"6Ra or "2"3"8U, and this was especially evident for Chinese mustard and corn (Zea mays). The root/shoot (R/S) ratios obtained for different plants and radionuclides shown that ...

Energy Technology Data Exchange (ETDEWEB)

We summarize the results of point-contact Andreev-reflection (PCAR) spectroscopy in MgB{sub 2} doped by chemical substitutions, either magnetic (Mn) or non-magnetic (Al,C), obtained by us and by other groups in the last four years. Despite the variety of samples used (crystals and polycrystals of various origin) and some minor differences in the experimental techniques, these measurements have directly provided a complete and consistent picture of the effects of chemical substitutions on the gaps of MgB{sub 2} shedding light on other relevant parameters (scattering rates, DOSs) affected by doping. In Al-doped crystals and polycrystals, the gap amplitudes {delta}{sub {sigma}} and {delta}{sub {pi}} - obtained through a two-band Blonder-Tinkham-Klapwijk (BTK) fit of the Andreev-reflection conductance curves - decrease on increasing the Al content x (i.e. on decreasing the critical temperature of the contacts T{sub c}{sup A}), but remain clearly distinct with no ...

Science.gov (United States)

An x-ray diffraction approach has been developed for determination of the kinetics of growth of Pd/sub 2/Si layers. Epitaxial Pd/sub 2/Si films were grown on Si(111) substrates over a temperature range of 160-222/sup 0/C by a solid-state reaction between the substrates and the Pd overlayers. The parabolic rate equation was verified and rate constants showed Arrhenius behavior with an activation energy E/sub a/ = 1.06 eV and prefactor k/sub 0/ = 7 x 10/sup -4/ cm/sup 2//s. The low value of E/sub a/ suggests a short-circuit diffusion mechanism. It is reasonable to expect that impurities and microstructure may play important roles in the growth process. Impurity levels in the specimens were evaluated by analytic techniques suited to thin-film study: Rutherford backscattering spectrometry, secondary ion mass spectrometry, and Auger electron spectrometry. No impurities were present at concentrations approaching 1 at. %. Some O, C, and F were detected at the Pd/sub ...

International Nuclear Information System (INIS)

Arsenic was predominantly present as inorganic arsenite in the fronds of the hyperaccumulator Chinese brake. - Arsenic speciation is important not only for understanding the mechanisms of arsenic accumulation and detoxification by hyperaccumulators, but also for designing disposal options of arsenic-rich biomass. The primary objective of this research was to understand the speciation and leachability of arsenic in the fronds of Chinese brake (Pteris vittata L.), an arsenic hyperaccumulator, with an emphasis on the implications for arsenic-rich biomass disposal. Chinese brake was grown for 18 weeks in a soil spiked with 50 mg As kg"-"1 as arsenate (AsO_4"3"-), arsenite (AsO_3"3"-), dimethylarsinic acid (DMA), or methylarsonic acid (MMA). Plant samples were extracted with methanol/water (1:1) and arsenic speciation was performed using high performance liquid chromatography coupled with atomic fluorescence spectrometry. The impacts of air-drying ...

International Nuclear Information System (INIS)

Single crystals of semi-organic L-histidine hydrobromide have been grown by slow evaporation technique from a mixture of L-histidine and hydrobromic acid in aqueous solution at ambient temperature. From high-resolution X-ray diffraction analysis, the crystalline perfection of the grown crystal has been studied. Single crystal X-ray diffraction analyses, Nuclear Magnetic Resonance spectral analysis, Thermo-Gravimetry (TG), Differential Thermal Analysis (DTA) and hardness test have been employed to characterize the as-grown crystals. The UV cutoff wavelength of the grown crystal is below 300 nm and has a wide transparency window, which is suitable for second harmonic generation of laser in the blue region. Nonlinear optical characteristics have been studied using Q switched Nd:YAG laser (#lambda#=1064 nm). The second harmonic generation conversion efficiency of the grown crystals ...

Energy Technology Data Exchange (ETDEWEB)

The article is the second part of a review dealing with latest developments in the area of solar cell technologies and application. Physical principles, design and efficiency as well as advantages and disadvantages of GaAs- and CdS-solar cells are described. Power generation solar cell systems with voltage converters, combined solar cell/solar collector systems and thermoelectric solar systems are presented in the second part of the article.

British Library Electronic Table of Contents (United Kingdom)

The light-emitting properties of cubic silicon carbide films grown by vacuum vapor phase epitaxy on Si(100) and Si(111) substrates under conditions of decreased growth temperatures (T gr ? 900?700?C) have been discussed. Structural investigations have revealed a nanocrystalline structure and, simultaneously, a homogeneity of the phase composition of the grown 3C-SiC films. Photoluminescence spectra of these structures under excitation of the electronic subsystem by a helium-cadmium laser (?excit = 325 nm) are characterized by a rather intense luminescence band with the maximum shifted toward the ultraviolet (?3 eV) region of the spectral range. It has been found that the integral curve of photoluminescence at low temperatures of measurements is split into a set of Lorentzian components. Th...

Wastenet

...qualified and who were under consideration at the time, USDA Secretary Tom Vilsack chose an animal husbandry specialist employed by one of the largest organic livestock product marketers in the country. While this appointee had grown up on a conventional farm, her immediate occupation is not that of ...

UK PubMed Central (United Kingdom)

We have investigated the transport of tritiated indole-3-acetic acid (IAA) in intact, red light-grown maize (Zea mays) coleoptiles during gravitropic induction and the subsequent development...Full Text Available

UK PubMed Central (United Kingdom)

An enzyme active against carboxymethyl cellulose (CMC) was purified from the stationary-phase-culture supernatant of Clostridium josui grown in a medium containing ball-milled cellulose. The purification...Full Text Available

UK PubMed Central (United Kingdom)

Moderate doses of red (660 nanometer) irradiation cause a rapid increase in the translocation of fluorescein in dark-grown mung bean hypocotyl (Vigna radiata L.) segments. The increase...Full Text Available

UK PubMed Central (United Kingdom)

There has been great interest in understanding the methods by which collagen-based load-bearing tissue is constructed, grown and maintained in vertebrate animals. To date, the responsibility for this...Full Text Available

UK PubMed Central (United Kingdom)

Dramatic differences in the height of lima beans (Phaseolus lunatus L.) treated with two different Rhizobium strains were studied. Lima beans were grown in Perlite...Full Text Available

UK PubMed Central (United Kingdom)

Lactobacillus buchneri ST2A vigorously decarboxylates histidine to the biogenic amine histamine, which is excreted into the medium. Cells grown in the presence of histidine generate both a transmembrane...Full Text Available

UK PubMed Central (United Kingdom)

Over the last several years, as cesarean deliveries have grown increasingly common, there has been a great deal of public and professional interest in the phenomenon of women ‘choosing’...Full Text Available

UK PubMed Central (United Kingdom)

Growth of the malolactic bacterium Leuconostoc oenos was improved with respect to both the specific growth rate and the biomass yield during the fermentation of glucose-malate mixtures as compared with...Full Text Available

International Nuclear Information System (INIS)

This investigation clearly demonstrates that through partial impregnation techniques wood-polymer composites can be formed from the Pinus species grown in South Africa with a considerable saving in monomer costs without sacrificing the important physical properties of these materials.

Science.gov (United States)

Sep 28, 2011 ... Description: Four Populus clones were grown in central Missouri for 2 years at 1 x 1 m spacing to study total biomass production on floodplain ...

UK PubMed Central (United Kingdom)

Confluent monolayers of microvascular endothelial cells, derived from the rat epididymal fat pad and grown in culture, were radioiodinated by using the lactoper-oxidase method. Their radioiodinated...Full Text Available

International Nuclear Information System (INIS)

Transient, greatly enhanced diffusion has been observed on annealing solid-phase-epitaxial (SPE) grown Si-Sb alloys. This is shown to be due to a high concentration of interstitials being trapped during SPE regrowth. The migration enthalpy, for diffusion of Sb by an interstitialcy mechanism was measured as 1.8 +/- 0.2 eV. The interstitials eventually condensed into loops, marking the end of the transient. In a SPE grown Si-Bi alloy a similar transient enhanced diffusion was observed, with an activation energy of 2.0 +/- 0.2 eV, but no loops formed. 8 figures, 7 references.

Energy Technology Data Exchange (ETDEWEB)

Callus cultures derived from pith tissue of Nicotiana tobacum were grown on two media either under continuous illumination or in complete darkness. The first medium limited greening ability of callus grown in the light (3 milligrams per liter naphthalene acetic acid, 0.3 milligram per liter 2-isopentenylaminopurine, Murashige and Skoog salts, and 2% sucrose). The second medium encouraged chlorophyll synthesis (greening) though not shoot formation (0.3 milligram per liter naphthalene acetic acid; 0.3 milligrams per liter 2-isopentylaminopurine). To measure intracellular concentrations, calli were grown for 15 days on these standard media containing (U-/sup 14/C)sucrose. The dry weight proportions of the calli (as a fraction of fresh weight) and many metabolite concentrations nearly doubled in light-grown cells compared to dark-grown cells and increase 30 to 40% on low-auxin media ...

International Nuclear Information System (INIS)

We have investigated the characteristics of ion-beam-induced spontaneous etching (IBISE) of GaAs in Cl_2 ambient by using a Ga-focused ion beam (FIB) with an energy ranging from 3 to 15 keV. The etched depth of the irradiated region was more than 20 times greater than that of unirradiated region. When the sputtered depth by FIB irradiation amounted to around 8 A at each ion energy, the etched depth in Cl_2 ambient for 1 hour became saturated. The saturated etched depths were 450, 550, 750 and 800 A at the ion energy of 3, 5, 10 and 15 keV, respectively. The residual damage of the etched surface was also investigated by photoluminescence (PL) measurement. The maximal PL intensity was obtained at around the threshold dose of IBISE and increased with decreasing ion energy. The full recovery of PL intensity was observed at the ion energy of 3 keV after annealing at 400degC. (author).

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)

A p[sup +]-Al[sub 0.3]Ga[sub 0.7]As/n[sup +]-GaAs heterojunction tunnel diode was fabricated using Atomic Layer Epitaxy (ALE) growth technique. Background carbon doping of [similar to]10[sup 20] cm[sup [minus]3] was achieved in the p-side of the diode by optimizing growth conditions such as V/III ratio, exposure times to reactant gases, and growth temperature. In the n-side of the diode GaAs was doped with silane and doping concentrations as high as 7[times]10[sup 18] cm[sup [minus]3] were also achieved. The dopants are chosen to satisfy the high levels and low diffusion requirements. The diode can be used to interconnect the high and low band-gap cells in the AlGaAs/GaAs cascade solar cell structure. The reactor used in this investigation is a commercial MOCVD system which has been specially modified for dual operation of ALE and MOCVD growth modes.

Energy Technology Data Exchange (ETDEWEB)

A review is given of the state-of-the-art of single and polycrystalline solar cells, which includes a short theoretical review, laboratory achievements, and production methods. The Si single and polycrystalline cell and the amorphous Si cell are described, including material preparation, crystal and sheet growth, and cell and panel production. Promising second generation thin film solar cells including GaAs, CdS(CuInSe/sub 2/), and CdTe are briefly described. Economical aspects are discussed.

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.

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 of the conduction band and the valence band edges. In the presence of an electric ...

Energy Technology Data Exchange (ETDEWEB)

Both (001)- and (111)-oriented CeO[sub 2] thin films have been grown on amorphous fused silica (SiO[sub 2]) substrates by ion-beam assisted pulsed laser ablation of a polycrystalline CeO[sub 2] target. Using 200 eV Ar[sup +] ions incident at 55[degree] to the substrate normal, the preferred orientation for CeO[sub 2] film growth is (001) at room temperature, but changes to (111) for temperatures [ge]300 [degree]C. Furthermore, the ion-beam assisted CeO[sub 2] films exhibit strong in-plane crystallographic alignment. In contrast, CeO[sub 2] films grown without ion-beam assistance exhibit a mixture of polycrystalline orientations with the relative amounts depending on growth temperature. Under optimum conditions, off-normal-incidence Ar[sup +] ions produce a (111)-oriented crystalline CeO[sub 2] film that is aligned with respect to a single in-plane axis, on an amorphous substrate.

Energy Technology Data Exchange (ETDEWEB)

Abstract not provided

UK PubMed Central (United Kingdom)

Acquisition of three-alternative simultaneous matching-to-sample and oddity-from-sample was investigated. Five goldfish were trained on matching and five on oddity for a minimum of 70 days. Subsequently,...Full Text Available

International Nuclear Information System (INIS)

Boat sampling technique (BST) is a surface sampling technique, which has been developed for obtaining, in-situ, metal samples from the surface of an operating component without affecting its operating service life. The BST is non-destructive in nature and the sample is obtained without plastic deformation or without thermal degradation of the parent material. The shape and size of the sample depends upon the shape of the cutter and the surface geometry of the parent material. Miniature test specimens are generated from the sample and the specimens are subjected to various tests, viz. Metallurgical Evaluation, Metallographic Evaluation, Micro-hardness Evaluation, sensitisation test, small punch test etc. to confirm the integrity and assessment of safe operating life of the component. This paper highlights design objective of boat sampling ...

Science.gov (United States)

Continuous wave operation of an Al/sub 0.21/Ga/sub 0.31/In/sub 0.48/P /Ga/sub 0.52/In/sub 0.48/P /Al/sub 0.21/Ga/sub 0.31/In/sub 0.48/P double heterostructure (DH) laser diode was achieved for the first time at 77 K. The device was made from a DH wafer grown by atmospheric metalorganic chemical vapor deposition using triethyl metals and phosphine as source materials. At 77 K, the lasing wavelength was 0.653 ..mu..m and the threshold current was 55 mA for a diode with a nitride-insulated, 8-..mu..m-wide and 250-..mu..m-long stripe geometry.

Science.gov (United States)

Room-temperature continuous-wave (cw) operation of a GaInP/AlGaInP multiquantum well (MQW) laser was achieved for the first time. The threshold current was 70 mA at 22 /sup 0/C for a device with an 8-..mu..m-wide and a 250-..mu..m-long planar stripe. The emission wavelength was 668 nm. The characteristic temperature T/sub 0/ was 138 K under cw operation. The wafer with the MQW structure composed of 100-A-thick GaInP wells and 40-A-thick AlGaInP barrier layers was grown by atmospheric pressure metalorganic chemical vapor deposition.

International Nuclear Information System (INIS)

The metallo-organic chemical vapor deposition (MOCVD) process has been used with great success to grow AlGaAs-GaAs and InGaAsP-InGaAs-InP heterostructure materials for electronic and optoelectronic applications. Devices fabricated from Al/sub x/Ga/sub 1-x/As-GaAs heterostructures grown by MOCVD include bipolar transistors, field-effect transistors (FETs), high-mobility (or modulation-doped) FETs, large-area high-efficiency solar cells, low-threshold lasers, high-power lasers, quantum-well lasers, and visible lasers. The state of the art for the MOCFD growth of optoelectronic devices is reviewed in this paper, and some comments are made regarding future trends in the growth of these materials by MOCVD.

British Library Electronic Table of Contents (United Kingdom)

Pots used for experiments conducted on plants grown in them create rooting environments that are affected by limited soil volume, which can affect various physiological processes, including transpiration, and plant growth. However, the applicability of results from pot experiments to the field has received limited attention. The objective of this study was to compare the growth and transpiration of maize (Zea mays L.) and winter wheat (Triticum aestivum L.) when grown in pots and field plots under various constant water deficits. The experiments were conducted under similar environmental conditions for both pots and plots. Transpirational responses at both transient (RTTr) and daily (RDTr) time scales to a decreasing fraction of available soil water (FASW) were analyzed. For a comparable F...

Energy Technology Data Exchange (ETDEWEB)

Epitaxial films grown pseudomorphically on substrates provide a way to stabilise non-equilibrium structures of materials. Obviously, there always is a certain lattice misfit between substrate and film material in its bulk equilibrium structure. In the pseudomorphic regime, this misfit can either lead to the growth of films in a strained bulk structure or even yield structures that are not stable in the bulk. Large misfits do not necessarily imply large lateral stress. Theory can help to predict e.g. geometry, stress and magnetic properties of pseusomorphically grown metal films. In this work, we considered the fcc-bcc epitaxial Bain path of 3d, 4d, and 5d transition metals, which provides a reasonable description of tetragonally distorted films on substrates. We carried out density functional calculations in the implementation of the full potential local orbital program package FPLO. Emphasis is put on similarities among the transition metals.

International Nuclear Information System (INIS)

Lupinus albus L. plants were grown from seeds and irradiated at various stages of development with acute or chronic gamma rays. All plants were greenhouse grown (pre- and post-irradiation) and allowed to proceed through their normal growth cycle. The purpose of these experiments was to establish a Plactochron Index for Lupinus albus L. and to determine the effects of acute and chronic irradiation on development at the macro and microscopic levels. A Plastochron Index was calculated and used as an indirect time scale to evaluate the effects of gamma rays from a common base line. Acute radiation treatment lasted for a period of a few days, whereas chronic treatment was initiated at the seedling stage and lasted for the entire growth season. Vegetative plants were used to study the effects of acute radiation exposure on apical meristem morphology, Plastochron Index, phyllatoxis and gross morphology.

British Library Electronic Table of Contents (United Kingdom)

In this paper, it is shown that (In1?xAlx)2S3 thin films can be grown through the co-evaporation of elemental indium, aluminum and sulfur. It is nevertheless observed that the introduction of aluminum within the indium sulfide thin films hinders the crystallites size and even yields almost amorphous films when x is 0.2. The investigations of the optical properties of the films reveal that contrary to what could be expected, the band gap increase is low; the highest values measured do not exceed 2.2eV. However, as suggested by X-ray photoelectron spectroscopy measurements, such widening most probably affects the lower conduction band states.

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)

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

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)

Environmental Research Database

DescriptionThis cross-disciplinary project will combine chemical, ecological and modelling techniques to determine whether cabbages grown under an organic regime differ in terms of pest dynamics and plant chemistry. There is increasing pressure to de-intensify agricultural practice and organic approaches are becoming more popular and widely adopted. However, there are very few, if any, detailed scientific investigations into the claims made about improved pest control, reduced environmental impact and be [continued...

International Nuclear Information System (INIS)

Epitaxial cobalt disilicide (CoSi_2) layers are grown on n-Si_0_._8_3Ge_0_._1_7/n-Si(001) using a sacrificial Si capping layer at the growth temperature T_s=650 deg. C by reactive chemical vapor deposition using cyclopentadienyl dicarbonyl cobalt (Co(#eta#"5-C_5H_5)(CO)_2). Structural and electrical properties of epi-CoSi_2/Si_0_._8_3Ge_0_._1_7/Si(001) were measured by transmission electron microscopy, X-ray diffraction, Auger electron spectroscopy and sheet resistance measurement as a function of annealing temperature. The combined results showed that the epitaxial CoSi_2 phase by the reaction of Co with the Si capping layer was formed in the as-grown layers. Rapid thermal anneals for the investigation of thermal stability of the as-grown layers showed good thermal stability of the epitaxial CoSi_2 layers with the low sheet resistance value as low as congruent with 4.4 #OMEGA#/cm up to the annealing temperature as high as ...

Science.gov (United States)

This study investigated relationships between molecular weight distributions of unreduced grain proteins and grain, flour, and end-use quality characteristics of soft white winter wheats grown in Oregon. Absorbance area and area % values of protein fractions separated by size exclusion HPLC (SE-HPL...

Science.gov (United States)

Plant biomass, stem juice and stem sugar were determined for four sugarcane cultivars grown for three months at daytime [CO2] of 360 (ambient) and 720 (doubled) ppm and temperatures (T) of 1.5 (near-ambient) and 6.0C higher than outside ambient T. Leaf area and biomass, stem biomass, stem juice and ...

Energy Technology Data Exchange (ETDEWEB)

Structural studies of Ni/Cu multilayers grown by electro-deposition technique under different electro-chemical conditions have been carried out using specular and off-specular neutron reflectometry techniques at room temperature. The specular reflectivity measurements give values of layer thickness, density and interface roughness for these two films. The Off-specular reflectivity measurements indicate different interface morphology of the two films.

UK PubMed Central (United Kingdom)

1. A cell-free system, prepared from Pseudomonas N.C.I.B. 9340 grown on 4-chloro-2-methylphenoxyacetate (MCPA) was shown to catalyse the reaction sequence: 5-chloro-3-methylcatechol...Full Text Available

UK PubMed Central (United Kingdom)

Large (about 200 grams dry weight) and small (about 5 grams dry weight) specimens of the leaf succulent Agave vilmoriniana Berger were grown outdoors at Phoenix, Arizona. Potted plants...Full Text Available

Energy Technology Data Exchange (ETDEWEB)

In the paper, a potential of solar energy for drying of medicinal plants in Polish conditions is estimated and development of solar drying technologies is presented. The results of economic assessment of flat-plate solar collectors applied for drying of medicinal plants on a farm are promising. In some specific conditions, e.g. drying of wild grown medicinal plants in remote areas, even application of photovoltaic modules for driving of a fan of a solar dryer is a profitable option and enables easy control of the drying air temperature.

UK PubMed Central (United Kingdom)

Barley (Hordeum vulgare L. cv Golden Promise) plants were grown in a continuous culture system in which the root and shoot ammonia and amino acid levels were constant over a 6-hour...Full Text Available

Science.gov (United States)

Heterostructures based on AlGaInP alloy compounds are very attractive for visible semiconductor lasers, heterojunction bipolar transistors (HBTs), and high-electron-mobility transistors (HEMTs) lattice matched to GaAs substrates. Several wet etching solutions for AlGaP of different compositions have been studied. Al{sub 0.5}Ga{sub 0.5}P is found to etch in HF, H{sub 3}PO{sub 4}, hyphosphorous acid (HOPH{sub 2}:O), HCl, KOH, and 1% Br{sub 2}-methanol (MeOH). Etching of Al{sub 0.5}Ga{sub 0.5}P in HCl is reaction limited with an activation energy of {approximately}54.4 kJ/mol. At fixed conditions, the etch rates of Al{sub x}Ga{sub 1{minus}x}P vary exponentially with x in HF and HCl, while in 1% Br{sub 2}-MeOH and mixtures of HCl and HNO{sub 3} the etch rates follow a linear dependence on AlP mole fraction. HF has been found to be a good etchant for AlGaP over InGaP or AlInP with high selectivity, while HCl is useful for the reverse case. The use of 1% Br{sub 2}-MeOH ...

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 ...

Energy Technology Data Exchange (ETDEWEB)

This paper describes a method for preparing the sample handling and inlet system of a mass spectrometer for analysis of a subsequent sample following analysis of a previous sample comprising the flushing of the system interior with supercritical CO{sub 2} and venting the interior. The method eliminates the effect of system ``memory`` on the subsequent analysis, especially following persistent samples such as xenon and krypton.

UK PubMed Central (United Kingdom)

Feed samples from 94 cases involving fungal contamination and suspected mycotoxicosis of farm animals in western Canada were examined during 1982-1994 to assess the incidence of mycotoxins. Samples...Full Text Available

International Nuclear Information System (INIS)

The purpose of this report is to describe the sampling approaches, modifications made to the 100 Area and 300 Area component of the RCBRA Sampling and Analysis Plan, summarize validation efforts, and provide sample identification numbers.

Energy Technology Data Exchange (ETDEWEB)

The Rotary Mode Core Sample System (RMCSS) is used to obtain stratified samples of the waste deposits in single-shell and double-shell waste tanks at the Hanford Site. The samples are used to characterize the waste in support of ongoing and future waste remediation efforts. Four sampling trucks have been developed to obtain these samples. Truck I was the first in operation and is currently being used to obtain samples where the push mode is appropriate (i.e., no rotation of drill). Truck 2 is similar to truck 1, except for added safety features, and is in operation to obtain samples using either a push mode or rotary drill mode. Trucks 3 and 4 are now being fabricated to be essentially identical to truck 2.

UK PubMed Central (United Kingdom)

Rationale and ObjectivesSample-size estimation is an important consideration when planning a receiver operating characteristic (ROC) study. The aim of this work was...Full Text Available

British Library Electronic Table of Contents (United Kingdom)

The National Food and Nutrient Analysis Program (NFNAP) was implemented in 1997 to update and improve the quality of food composition data maintained by the United States Department of Agriculture (USDA). NFNAP was designed to sample and analyze frequently consumed foods in the U.S. food supply using statistically rigorous sampling plans, established sample handling procedures, and qualified analytical laboratories. Methods for careful handling of food samples from acquisition to analysis were developed to ensure the integrity of the samples and subsequent generation of accurate nutrient values. The infrastructure of NFNAP, under which over 1500 foods have been sampled, mandates tested sample handling protocols for a wide variety of foods. The majority of these foods were categorized into ...

Energy Technology Data Exchange (ETDEWEB)

Yellow-emitting pulsed laser operation of an Al/sub 0.37/Ga/sub 0.15/In/sub 0.48/P/Al/sub 0.16/Ga/sub 0.36/In/sub 0.48/P/ Al/sub 0.37/Ga/sub 0.15/In/sub 0.48/P double heterostructure laser diode was obtained at 77 K. The emission wavelength was 579 nm. The threshold current density was 5.6 kA/cm/sup 2/ for a diode with a Si/sub 3/N/sub 4/ insulated 8-..mu..m-wide and 250-..mu..m-long stripe geometry. The device was made from a DH wafer grown by conventional metalorganic chemical vapor deposition using triethyl metals and phosphine as source materials.

Energy Technology Data Exchange (ETDEWEB)

AlGaInP epitaxial layers grown at 690 {degree}C by atmospheric pressure organometallic vapor phase epitaxy are investigated by transmission electron microscopy. For the first time, compositionally modulated and ordered structures are simultaneously observed in AlGaInP alloys. The ordering is of the CuPt type with ordering along the {l brace}111{r brace} directions. The ordered regions appear as plate-like microdomains, while the composition modulation takes the form of a fine columnar constrast oriented along the growth direction. In addition, from the results of (001) plan-view diffraction contrast examination, the principal strain direction associated with the modulation structures is found to be perpendicular to the growth direction and lies in the surface plane. Thus, it is concluded that the spinodal decomposition is initiated and developed on the surface during the growth of the AlGaInP epitaxial layers and, finally, forms the columnar structure.

British Library Electronic Table of Contents (United Kingdom)

The electrical characteristics of thin TiO2 films prepared by metal?organic chemical vapor deposition grown on a p-type InP substrate were studied. For a TiO2 film of 4.7?nm on InP without and with ammonium sulfide treatment, the leakage currents are 8.8?10?2 and 1.1?10?4?A/cm2 at +2 V bias and 1.6?10?1 and 8.3?10?4?A/cm2 at ?2?V bias. The lower leakage currents of TiO2 with ammonium sulfide treatment arise from the improvement of interface quality. The dielectric constant and effective oxide charge number density are 33 and 2.5?1013?cm2, respectively. The lowest mid-gap interface state density is around 7.6?1011?cm?2?eV?1. The equivalent oxide thickness is 0.52?nm. The breakdown electric field increases with decreasing thickness in the range of 2.5 to 7.6?nm and reaches 9.3?MV/cm at 2.5?n...

Energy Technology Data Exchange (ETDEWEB)

In this study, SnO{sub 2} thin films have been grown using spray pyrolysis technique on glass substrates under a substrate temperature (T{sub s} = 440 {sup o}C). The precursors were methanol CH{sub 4}O and anhydrous tin tetrachloride. XRD analyses yielded strong (1 1 0)-(1 0 1)-(2 0 0) X-ray diffraction peaks which are characteristics to tetragonal crystals. Atomic Force Microscopy (AFM) analyses showed the existence of clusters with particular pyramidal shapes. The main part of this study concerns the optical measurements of transmittance T({lambda}) and reflectance R({lambda}) spectra inside 250-1800 nm domain. Conjoint optical and thermal properties were deduced using the Amlouk-Boubaker Opto-Thermal Expansivity {psi}{sub AB}. The obtained value: {psi}{sub AB} {approx} 23.4 m{sup 3} s{sup -1} helped situating the performance of the as-grown SnO{sub 2} compound among most known PV-T oxides like ZnO and TiO{sub 2}.

Energy Technology Data Exchange (ETDEWEB)

Continuous-wave (cw) operation at temperatures up to 23 /sup 0/C of an Al/sub 0.26/Ga/sub 0.26/In/sub 0.48/P/Ga/sub 0.52/In/sub 0.48/P/ Al/sub 0.26/Ga/sub 0.26/In/sub 0.48/P double heterostructure (DH) laser has been achieved for the first time. The threshold current was 160 mA at 20 /sup 0/C for a device with a 10-..mu..m-wide and 250-..mu..m-long ion-implanted stripe geometry. The emission wavelength was 671 nm during cw operation at 10 /sup 0/C. To reduce thermal resistance to a heat sink, a dually stacked structure made of a thin (approx.0.3 ..mu..m) p-AlGaInP layer and a p-Al/sub 0.76/Ga/sub 0.24/As layer was used as a cladding layer. The DH wafer was grown by atmospheric pressure metalorganic chemical vapor deposition.

International Nuclear Information System (INIS)

Experimental observations related to the initiation of plastic deformation in metals and alloys irradiated with fission neutrons have been analyzed. The experimental results, showing irradiation-induced increase in the upper yield stress followed by a yield drop and plastic instability, cannot be explained in terms of conventional dispersed-barrier hardening because (a) the grown-in dislocations are not free, and (b) irradiation-induced defect clusters are not rigid indestructible Orowan obstacles. A new model called 'cascade-induced source hardening' is presented where glissile loops produced directly in cascades are envisaged to decorate the grown-in dislocations so that they cannot act as dislocation sources. The upper yield stress is related to the breakaway stress which is necessary to pull the dislocation away from the clusters/loops decorating it. The magnitude of the breakaway stress has been estimated and is found to be in good ...

International Nuclear Information System (INIS)

GaN and Al_1_-_xGa_xN films were grown by the method of ECR-MBE. Absorption constants as a function of wavelength were determined from transmission measurements. Photoconducting detectors were fabricated from these films and characterized in terms of their spectral response and photoconductive gain. Mobility-lifetime products were determined from the measurement of photoconductive gain. The resistivity and mobility-lifetime products of the films were varied from 10--10"9 ohm-cm and 10"-"3--10"-"8 cm"2/V respectively by changing the microwave power in the ECR discharge from 20--60 watts. The change in the mobility-lifetime product is attributed to change in the lifetimes of the photogenerated carriers. This assumption is supported by direct measurement of detector response times. Finally, the authors report for the first time, the detection of alpha particles using GaN detectors.

International Nuclear Information System (INIS)

Reflectance anisotropy spectroscopy (RAS) has been used, together with scanning tunnelling spectroscopy (STS), to investigate the optical and electronic properties of nanodots formed by depositing Ag on the Si(111)-3 x 1-Ag surface. One-dimensional (1D) arrays of nanodots were grown on a single-domain (3 x 1)-Ag surface and the anisotropic optical response in the 0.5-5 eV range measured by RAS. Aligned, elongated Ag islands were also grown on this surface to compare their properties with those of the nanodots. STS of the Ag islands showed distinct metallic behaviour, whereas the nanodots revealed a bandgap of #approx#0.6 eV, indicating that the surface of the dots has a non-metallic character, similar to that of the Si(111)-3 x 1-Ag surface. RAS also showed substantial differences between the structures, with a large infrared anisotropy for the metallic Ag islands consistent with anisotropic Drude-like intraband transitions, whereas the ...

Science.gov (United States)

A film of GaSb grown epitaxially on a Si substrate is a direct transition semiconductor useful for application as a light source in Si photonics and channel material in next-generation field effect transistors because its energy bandgap is close to the optical fibre communication wavelength and it possesses high carrier mobility. Here, we report a novel method for heteroepitaxial growth of high-quality GaSb/Si films, despite having a lattice mismatch as large as ? 12%, using elastically strain-relaxed GaSb nanodots with ultrahigh density as seed crystals for film growth. The nanodot seed crystals were grown epitaxially by restricted contact with the Si substrate through nanowindows in an ultrathin SiO(2) film on the Si substrate. A light-emitting diode containing GaSb/Si films with a thickness of ? 90 nm fabricated by this method operated at room temperature. The growth method was also used to fabricate AlGaSb films of high quality. Our method ...

International Nuclear Information System (INIS)

A single plasma process involving three consecutive steps has been developed for producing high gas flow catalytic nanostructures on the electrodes of proton exchange membrane (PEM) fuel cells (FC). Using a high density helicon radio frequency (13.56 MHz) plasma, nickel is sputtered onto a porous carbon support. Changing the background gas from argon to methane/hydrogen allowed 2 ?m long, 37 nm diameter carbon nanofibres (CNFs) to be grown by diffusion through the nickel clusters in a 'tip growth' mechanism at the relatively low temperature of 400 deg. C. The third step involves plasma sputtering of platinum onto the CNFs, resulting in nanoclusters (3-8 nm) being formed on the periphery of the CNFs. Four FC cathodes were synthesized on carbon paper and PTFE/carbon loaded cloth (known as gas diffusion layer, GDL), both with and without CNFs, with the Pt/CNFs nanostructures grown on PTFE/carbon loaded cloth having the best FC performances. ...

Energy Technology Data Exchange (ETDEWEB)

Polycrystalline silicon films have been grown from Si{sub 2}H{sub 6} by low-pressure chemical vapour deposition at 800 K and in situ laser annealing (LA) on amorphous silicon seed layers deposited on a metallic Ti/Pd/Ag multilayer. The crystalline volume fraction in the seed layer was controlled by thermal annealing. According to the metal-induced crystallization effect, the presence of the metal induces a lower-temperature crystallization of silicon in the seed layers. X-ray diffraction and scanning electron microscopy data show that the formation of palladium silicides in the seed layer drives the growth of wire-like columns which are found to change morphology depending on the seed layer microstructure and LA parameters. It is suggested that superficial palladium was found to affect also the growth rate by enhancing the Si{sub 2}H{sub 6} dissociation.

British Library Electronic Table of Contents (United Kingdom)

Ferroelectric thin films such as BST, PZT and PLZT are extensively being studied for the fabrication of DRAMS since they have high dielectric constant. The large and reversible remnant polarization of these materials makes it attractive for nonvolatile ferroelectric RAM application. In this paper we report the characterization of Ba0.7Sr0.3TiO3 (BST) thin films grown by pulsed laser ablation on oxide electrodes. The structural and electrical properties of the fabricated devices were studied. Growth of crystalline BST films was observed on La0.5Sr0.5CoO3 (LSCO) thin film electrodes at relatively low substrate temperature compared to BST grown on PtSi substrates. Electrical characterization was carried out by fabricating PtSi/LSCO/BST/LSCO heterostructures. The leakage current of the heteros...

Environmental Research Database

ObjectivesThis working group aims to conduct an in-depth analysis and synthesis of the health risks and benefits of producing and consuming your own food in urban areas. It will have a particular focus on urban soil pollutants - including both toxic elements and persistent organic pollutants that can pass up through the food chain or be ingested in soil. It will consider pathways of pollutant transport and deposition and human uptake from urban cultivation. Against the health risks associated with expos [continued...]DescriptionIn the UK there are over 250,000 allotment holders, many in urban areas, and in many city gardens fruit and vegetables are grown, often in regions known to have a legacy of environmental pollution. The activities of cultivating and eating 'home grown' foods holds both risks and benefits, yet the balance of risk and benefits and the resulting net implications for human health have not been clearly established. This has ...

Energy Technology Data Exchange (ETDEWEB)

In the present study, the type and densities of defects in AlN crystals grown on 6H-SiC seeds by the sublimation-recombination method were assessed. The positions of the defects in AlN were first identified by defect selective etching (DSE) in molten NaOH-KOH at 400 C for 2 minutes. Etching produced pits of three different sizes: 1.77 m, 2.35 m , and 2.86 m. The etch pits were either aligned together forming a sub-grain boundary or randomly distributed. The smaller etch pits were either isolated or associated with larger etch pits. After preparing crosssections of the pits by the focused ion beam (FIB) technique, transmission electron microscopy (TEM) was performed to determine which dislocation type (edge, mixed or screw) produced a specific etch pit sizes. Preliminary TEM bright field and dark field study using different zone axes and diffraction vectors indicates an edge dislocation with a Burgers vector 1/3[1120] is associated with the smallest etch pit size.

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Surface oxide films were grown on 99.99% copper and brass (copper-zinc alloy, Cu77Zn21Al2) in 0.1 mol L{sup -1} borax solution at open circuit potential and were characterized using various experimental techniques. The composition of the passive films formed in situ on the different materials was studied using differential reflectance spectroscopy. The thickness of the oxide layers on copper and brass was compared by chronopotentiometric curves and potentiodynamic reductions. The electrical properties of each oxide were analyzed by means of electrochemical impedance spectroscopy. Their influence on the oxygen reduction reaction was also investigated using voltammetry hydrodynamic tools such as the rotating disk electrode. The results show that the incorporation of Zn to Cu in brass changes the composition and the thickness of the surface film. The films grown on brass tend to be thicker but less resistive and Zn compounds incorporate to the ...

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Room-temperature pulsed laser operation of (Al/sub 0.55/Ga/sub 0.45/)/sub 0.5/In/sub 0.5/P /(Al/sub 0.17/Ga/sub 0.83/)/sub 0.5/In/sub 0.5/P / (Al/sub 0.55/Ga/sub 0.45/)/sub 0.5/In/sub 0.5/P double heterostructure laser diodes grown by metalorganic chemical vapor deposition has been achieved. The lasing wavelength is 626.2 nm, which is the shortest ever reported for an AlGaInP double heterostructure laser. Threshold current density is 50 kA/cm/sup 2/ for a diode with a 20-..mu..m-wide and 200-..mu..m-long stripe.

International Nuclear Information System (INIS)

Single crystals of GdCl_3 doped with different concentrations of Ce"3"+ have been grown using the Bridgman-Stockbarger technique and their luminescence and scintillation properties were investigated. The luminescence spectrum of GdCl_3:Ce"3"+ is complex and consists of two bands with maxima at 350 nm and 370 nm. The maximal light yield in GdCl_3:Ce"3"+ was observed at #approx#1 mol% of Ce"3"+ (more than 38 000 ph/MeV).

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Originally designed exclusively for peak load covering, pumped storage plants are now faced with new challenges brought about by the deregulation of the electricity market and the substantial growth of wind power capacity. Today's pumped storage plants are started more frequently and often for shorter periods of time. The grid controlling tasks have increased the importance of the role played by this type of power plant and improved sales considerably. But the operational demands have grown substantially as well. This paper discusses the ensuing adaptation of power plant operation as well as options available to power plant operators. (orig.)

International Nuclear Information System (INIS)

Arrays of CdS:Mn"2"+:Cu"+ micro- and nanowires grown in polycarbonate ion-track templates exhibit photoluminescence in the spectral domain ranging from 500 to 800 nm at room temperature. A comparison with similar CdS and CdS:Mn"2"+ wire arrays is presented. The individual contributions to the emission spectra of Cu"+ and Mn"2"+ ions in the CdS matrix are explained using their energy level schemes. Also SEM, EDX and EPR data are given for these wires. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

International Nuclear Information System (INIS)

Single-crystalline CeRh_2Si_2 and CePd_2Si_2 were grown by the Czochralsky pulling method and the temperature dependence of magnetic susceptibility was investigated. The crystalline electric field (CEF) states in each compound were determined by considering the tetragonal CEF Hamiltonian with mean-field approximation. Interactions between Ce"3"+ ion and the surrounding ligands in CeRh_2Si_2 turned out to be strong and highly anisotropic in comparison to CePd_2Si_2. (orig.)

British Library Electronic Table of Contents (United Kingdom)

LUCIFER (Low-background Underground Cryogenic Installation For Elusive Rates) is a new project for the study of neutrinoless Double Beta Decay, based on the technology of scintillating bolometers. These devices promise a very efficient rejection of the alpha background, opening the way to a virtual background-free experiment if candidates with a transition energy higher than 2615 keV are investigated. The baseline candidate for LUCIFER is 82Se. This isotope will be embedded in ZnSe crystals grown with enriched selenium and operated as scintillating bolometers in a low-radioactivity underground dilution refrigerator. In this paper, the LUCIFER concept will be introduced. The sensitivity and the very promising prospects related to this project will be discussed.

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The application of medium energy ion scattering in combination with channelling and blocking to the study of the initial stages of palladium silicide formation is discussed. After a brief description of the experimental arrangement and method, the effects on the Rutherford backscattering spectra of depositing small quantities of palladium on clean Si(111) are reported. The uniformity and thermal stability of thin palladium silicide films grown at room temperature were measured. Finally, channelling and blocking results were used to carry out a structural analysis of thin epitaxial Pd_2Si layers. (Auth.).

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LaAlO{sub 3} and CeO{sub 2} films have been successfully grown using sol-gel precursors. LaAlO{sub 3} precursor solution has been prepared from a metal alkoxide route and spun-cast on a SrTiO{sub 3} (100) single crystal to yield an epitaxial film following pyrolysis at 800{degrees}C in a rapid thermal annealer. A CeO{sub 2} precursor solution has been made using both an aqueous and an alkoxide route.

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Over the past decade, the energy {open_quotes}paper{close_quotes} market has grown into one of the largest traded markets in the world providing hedging instruments for the producer as well as the enduser of energy products. Because banks, stockholders, and other financial providers rely on a borrower`s ability to generate cash flow to repay their investment, borrowers are increasingly turning to the derivatives markets to provide security against one of the most volatile markets in he world. The existence of this market has enhanced the ability of financial institutions to lend with confidence and appropriate aggressiveness to the oil and gas industry.

International Nuclear Information System (INIS)

The ZnO nanorods were used as a template to fabricate nickel nanoclusters by electrodeposition. The ZnO nanorod arrays act as a nano-semiconductor electrode for depositing metallic and magnetic nickel nanoclusters. The growth sites of Ni nanoclusters could be controlled by adjusting the applied potential. Under -1.15 V the Ni nanoclusters could be grown on the tips of ZnO nanorods. On increasing the potential to be more negative the ZnO nanorods were covered by Ni nanoclusters. The magnetic properties of the electrodeposited Ni nanoclusters also evolved with the applied potentials.

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A considerable time can elapse between initial selection of candidate plus trees and harvest of improved seed. The technique showing the greatest promise of shortening this interval is vegetative propagation. Stock plants are grown for two years from seed before the first propagation cycle begins and each plant can be bulked-up 300-500 times over two cycles. An initial stock of 2500 superior Sitka Spruce plants can be multiplied to yield between 300,000 and 750,000 rooted cuttings for forest use within four years from the start of propagation.

International Nuclear Information System (INIS)

Methanosarcina thermophila, a nonmarine methanogenic archaebacterium, can grow in a range of saline concentrations. At less than 0.4 M NaCl, Ms. thermophila accumulated glutamate in response to increasing osmotic stress. At greater than 0.4 M NaCl, this organism synthesized a modified #beta#-amino acid that was identified as N"v"a"r"-"e"p"s"i"l"o"n-acetyl-#beta#-lysine by NMR spectroscopy and ion-exchange HPLC. This #beta#-amino acid derivative accumulated to high intracellular concentrations (up to 0.6 M) in Ms. thermophila and in another methanogen examined - Methanogenium cariaci, a marine species. The compound has features that are characteristic of a compatible solute: it is neutrally charged at physiological pH and it is highly soluble. When the cells were grown in the presence of exogenous glycine betaine, a physiological pH and it is highly soluble. When the cells were grown in the presence of exogenous glycine betaine, a physiological ...

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... activation analysis biological materials bremsstrahlung environment lead lead

International Nuclear Information System (INIS)

... blood serum patients radioimmunoassay sampling tracer techniques isotope

International Nuclear Information System (INIS)

A procedure for the determination of lead in soil samples by "2"0"3Pb radioisotope dilution substoichiometric method is described. Japan NIES No.2 river clay standard sample and 83-40 Tibet soil standard sample were determined. The obtained values were in good agreement with reference values. The standard deviation of the method was less then 5%. Detection limit was about 0.1 #mu#g Pb.

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The applicability of the radionuclide X-ray fluorescence analysis (RXFA) for qualitative and quantitative evaluation of environmental plant samples is discussed and examples of determination of Mn, Fe, Ni, Cu, Zn, Pb in samples of apple trees are given. The instrumentation, the standard and sample preparation are also presented.

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 devices to extract impact ...

British Library Electronic Table of Contents (United Kingdom)

We carried out theoretical analyses based on ab initio calculations incorporates in which free energy of the vapor phase is incorporated in order to determine the initial growth kinetics of c-GaN on GaN(001)-(4x1). The feasibility of the theoretical approach had been confirmed by calculations of Ga adsorption-desorption transition temperature and transition beam equivalent pressures on the GaAs(001)-(4x2)b2 surface in our previous work [Y. Kangawa, T. Ito, A. Taguchi, K. Shiraishi, T. Ohachi, Surf. Sci. 493 (2001) 178]. The results of calculations suggest that no Ga adsorption occurs on the initial surface under typical growth conditions but that a Ga adsorption site appears after N adsorption on GaN(001)-(4x1). That is, in the initial growth stage of c-GaN on GaN(001)-(4x1), a N-adsorbed ...

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.

Science.gov (United States)

A newly developed 220 Mbps free-space 4-ary pulse position modulation (PPM) direct detection optical communication system is described. High speed GaAs integrated circuits were used to construct the PPM encoder and receiver electronic circuits. Both PPM slot and word timing recovery were provided in the PPM receiver. The optical transmitter consisted of an AlGaAs laser diode (Mitsubishi ML5702A, lambda=821nm) and a high speed driver unit. The photodetector consisted of a silicon avalanche photodiode (APD) (RCA30902S) preceded by an optical interference filter (delta lambda=10nm). Preliminary tests showed that the self-synchronized PPM receiver could achieve a receiver bit error rate of less than 10(exp -6) at 25 nW average received optical signal power or 360 photons per transmitted information bit. The relatively poor receiver sensitivity was believed to be caused by the insufficient electronic bandwidth of the APD preamplifier and the poor linearity of the ...

British Library Electronic Table of Contents (United Kingdom)

Abstract Visible blue cathodoluminescence (CL), photoluminescence (PL), x-ray excited optical luminescence (XEOL) and electroluminescence (EL) via Zf free excitonic emission have been obtained from CuBr thin films deposited on glass, Cr coated glass, GaAs and Si substrates. In addition to the Zf emission several peaks corresponding to Cu+ emissions via 3d94s - d10 transitions were observed on the AC EL spectrum at 2.10, 2.7, 3.03, 3.07 and 3.80 eV. X-ray diffraction (XRD) measurements confirmed that the vacuum evaporated CuBr thin films grow preferentially with a (111) orientation irrespective of the substrate. While the AC voltage source was found to have no detrimental effects on CuBr thin films, cathodic deposition of Cu metal via electrolytic decomposition was observed under steady sta...

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 ...

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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/sup +/ 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/sup +/ 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.

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This sampling and analysis plan (SAP) identifies characterization objectives pertaining to sample collection, laboratory analytical evaluation, and reporting requirements for vapor samples obtained during the operation of mixer pumps in tank 241-AZ-101. The primary purpose of the mixer pump test (MPT) is to demonstrate that the two 300 horsepower mixer pumps installed in tank 241-AZ-101 can mobilize the settled sludge so that it can be retrieved for treatment and vitrification. Sampling will be performed in accordance with Tank 241-AZ-101 Mixer Pump Test Data Quality Objective (Banning 1999) and Data Quality Objectives for Regulatory Requirements for Hazardous and Radioactive Air Emissions Sampling and Analysis (Mulkey 1999). The sampling will verify if current air emission estimates used in the permit application are correct and provide information for future ...

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This paper describes a novel Fourier transform infrared (FTIR) spectroscopic method that can be used to rapidly screen soil samples from potentially hazardous waste sites. Samples are heated in a thermal desorption unit and the resultant vapors are collected and analyzed in a long-path gas cell mounted in a FTIR. Laboratory analysis of a soil sample by FTIR takes approximately 10 minutes. This method has been developed to identify and quantify microgram concentrations of explosives in soil samples and is directly applicable to the detection of selected volatile organics, semivolatile organics, and pesticides.

British Library Electronic Table of Contents (United Kingdom)

Differential Scanning Calorimetry (DSC) is employed to study the changes in enthalpy of natural rubber latex samples when heated under a controlled temperature program. It is found that the mass normalized areas of the DSC curves between room temperature and 170??C for different latex samples are inversely proportional to the dry rubber content (DRC) of the samples, measured following the weighing and drying method. The changes in total enthalpy of the samples in this temperature range are interpreted as due to the variations in the quantity of water present in the samples. The measurements have been repeated by diluting selected samples with known quantities of water, and it is found that the normalized areas of the DSC curves are directly proportional to the amount of water added to the ...

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SummaryBackground The choice of sampling techniques in bronchoscopy with sampling from a visible lesion will depend on the expected diagnostic yields and the costs of the sampling techniques. Aims The aim of this study was to determine the most economical combination of sampling techniques when approaching endobronchial visible lesions. Methods A cost minimization analysis was performed. All bronchoscopies from 2003 and 2004 at Haukeland university hospital, Bergen, Norway, were reviewed retrospectively for diagnostic yields. 162 patients with endobronchial disease were included. Potential sampling techniques used were biopsy, brushing, endobronchial needle aspiration (EBNA) and washings. Costs were estimated based on registration of equipment costs and personnel costs. Sensitivity analyse...

International Nuclear Information System (INIS)

An easy and simple method for gamma assay of large multi-gamma lines samples was introduced in this work. This method performs the assay using point source calibration. The correction factors for volume and self-attenuation are experimentally deduced from the spectra of different thicknesses samples utilizing the following two simple well known facts: large and small samples of the same homogenous material have identical specific activities; the self-attenuation of gamma line decreases as its energy increases. The method was successfully applied to naturally occurring radioactive material (NORM) large samples. This method does not require complicated mathematical procedures. Neither sample matrix data nor detector unit composition is needed.

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This paperwork explain the method of water sampling to obtain the precipitate of BaCO3 solutions that will be used to analyze 13C from field work in Kelana Jaya, Selangor, Langkawi, Kedah and Taiping, Perak. The sampling involves collecting of water samples for groundwater from boreholes and surface water from canal, river, pond and ex-mining pond from several locations at the study sites. This study also elaborates the instruments and chemicals used. The main purpose of this sampling is to obtain the precipitate of BaCO3 for 13C analysis of dissolved inorganic carbon (DIC). A correct sampling method according to standard is very important to ensure an accurate and precise result. With this, the data from the laboratory analysis result can be fully utilized to make the interpretation of the pollutants movement. (Author)

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The Waste Sampling and Characterization Facility (WSCF) complex consists of the main structure (WSCF) and four support structures located in the 600 Area of the Hanford site east of the 200 West area and south of the Hanford Meterology Station. WSCF is to be used for low level sample analysis, less than 2 mRem. The Laboratory features state-of-the-art analytical and low level radiological counting equipment for gaseous, soil, and liquid sample analysis. In particular, this facility is to be used to perform Resource Conservation and Recovery Act (RCRA) of 1976 and Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980 sample analysis in accordance with U.S. Environmental Protection Agency Protocols, room air and stack monitoring sample analysis, waste water treatment process support, and contractor laboratory quality assurance checks. The ...

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Samples of nylon 66 rods were irradiated using a cobalt-60 gamma ray source at a dose rate of 0.25 Mrad h[sup -1] in air at room temperature to a maximum dose of 500 Mrad. The linear coefficient of thermal expansion ([alpha]) was measured using a three-terminal capacitance technique reported previously. The variation of [alpha] with temperature between 10 K and 340 K was investigated for an unirradiated sample and two samples irradiated to 300 Mrad and 500 Mrad. In the range 10K to 160K, [alpha] is almost invariant with radiation dose and there is little difference between the values for the unirradiated and the 300 Mrad irradiated samples above 160 K. The sample irradiated to 500 Mrad does show a 6% increase in [alpha] over the other samples in the higher temperature range. All samples show an increase overall in the value of [alpha] with ...

UK PubMed Central (United Kingdom)

ObjectiveTo compare the relations of social self-control and sensation seeking with substance use across samples of US and Russian adolescents.Full Text Available

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This report presents results from the soil inorganic analysis of the 44th set of environmental quality assessment samples, of the quality assessment program, that were received on or before June 3, 1996. The samples were analyzed for RCRA metals.

UK PubMed Central (United Kingdom)

In this paper, we report a method of precise in situ x-ray scattering measurements on protein solutions using small stationary sample cells. Although reduction in the radiation damage...Full Text Available

UK PubMed Central (United Kingdom)

Linking biological samples found at a crime scene with the actual crime event represents the most important aspect of forensic investigation, together with the identification of the sample donor. While...Full Text Available

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Adenosine triphosphate (ATP) is an indicator of living biomass in marine particulates. This report details the method used by Lawrence Berkeley Laboratory to analyze particulate ATP in samples taken from oligotrophic, tropical ocean waters. It represents a synthesis of previously published methods.

UK PubMed Central (United Kingdom)

Real-time PCR has the potential to streamline detection and identification of Cryptosporidium spp. in human clinical samples. In the present...Full Text Available

UK PubMed Central (United Kingdom)

The procedure currently used for isolating legionellae from environmental samples recommend filtration through a 0.2-microns-pore-size polycarbonate filter. In this study we evaluated the performance...Full Text Available

UK PubMed Central (United Kingdom)

The British Andrology Society guidelines for the assessment of post vasectomy semen samples recommend that initial assessment is undertaken 16 weeks post vasectomy and after the patient has produced...Full Text Available

UK PubMed Central (United Kingdom)

To diagnose asymptomatic bacterial vaginosis (BV), self-sampled vaginal smears were collected during a study of risk factors for preterm birth in African American women. More than 90% of those...Full Text Available

Science.gov (United States)

We have grown crack-free antiferroelectric (AFE) Pb{sub 0.92}La{sub 0.08}Zr{sub 0.95}Ti{sub 0.05}O{sub 3} (PLZT) films on nickel foils by chemical solution deposition. To eliminate the parasitic effect caused by the formation of a low-permittivity interfacial oxide, we applied a conductive buffer layer of lanthanum nickel oxide (LNO) on the nickel foil by chemical solution deposition prior to the PLZT deposition. Use of the LNO buffer allowed high-quality film-on-foil capacitors to be prepared at high temperatures in air. With the AFE PLZT deposited on LNO-buffered Ni foils, we observed field-induced phase transformations of AFE to ferroelectric (FE). The AFE-to-FE phase transition field, E{sub AF} = 260 kV cm{sup -1}, and the reverse phase transition field, E{sub FA} = 220 kV cm{sup -1}, were measured at room temperature on a {approx}1.15 {micro}m thick PLZT film grown on LNO-buffered Ni foils. The relative permittivities of the AFE and FE ...

International Nuclear Information System (INIS)

(1974). Hungary Kolomiytsev, MA Dundua, V.Yu. Pachulia, NV Bagdavadze,