International Nuclear Information System (INIS)

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

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.

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Atomic layer epitaxy (ALE) was used to grow several components of the cascade solar cell structure in the AlGaAs/GaAs system. An ALE reactor was constructed for multiwafer growth with a growth rate of 0.6 {mu}m h{sup -1}. Device quality GaAs and Al{sub x}Ga{sub 1-x}As films were grown with p-type background carbon doping in the ranges 10{sup 16}-10{sup 19} cm{sup -3} and 10{sup 16}-10{sup 20} cm{sup -3} respectively. N-type films were achieved by SiH{sub 4} doping, producing carrier concentrations in the range 10{sup 16}-10{sup 18} cm{sup -3}. In addition, the potential applications of the ALE technique in the photovoltaic field are discussed. (orig.).

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).

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 ...

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 ...

Science.gov (United States)

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

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GaAs material and device structure optimization studies on optical-grade, millimeter-and-less grain-size polycrystalline Ge substrates are presented. We discuss the growth of high-quality epitaxial layers across various crystalline orientations of a polycrystalline substrate; this is important for obtaining high-performance solar cells. The GaAs solar cell on n-type poly-Ge substrate is a p-on-n type, with an undoped spacer between the p-emitter and the n-base. An experimental study of dark currents in these junctions, with and without the spacer, as a function of temperature (77K to 288K) is presented; this study suggests that the spacer reduces the tunneling contribution to dark current. In addition, we describe device-structure optimization studies that have led us to achieve an open-circuit voltage (V{sub oc}) exceeding 1 Volt and an AM1.5 efficiency of {approximately}19{percent} for a 4-cm{sup 2}-area ...

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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.

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

Science.gov (United States)

... The insu- lation between gate and nanowire is the high-k dielectric HfO2, deposited by atomic layer depo- sition (ALD). ...

International Nuclear Information System (INIS)

Striking differences in differential reflectance and carrier relaxation in In0.4Ga0.6As and In0.4Ga0.6As0.98N0.02 single quantum wells (SQWs) were studied using ultrafast time-resolved photoreflectance. Even with extremely thin SQW of only 60 A within 3000 A wide GaAs confining layers, negative and positive differential reflectance was observed for the excitation photon energy far above the bandgaps at 820 and 880 nm for both samples. Due to absorption by the GaAs confining layer, the peak differential reflectance pumped at 820 nm is an order of magnitude larger than that pumped at 880 nm; and it is larger for InGaAs SQWs than for InGaAsN SQWs. The shorter carrier lifetimes of these samples result from carrier-carrier scattering as pumped at both wavelengths. The longer carrier lifetime as pumped at 880 nm is due to hot phonon decay in InGaAs but may be due to stimulated emission in InGaAsN. The results ...

International Nuclear Information System (INIS)

Surface energy of III-V semiconductors ended by (110) clean surface and surface covered by atomic monolayer of aluminium, copper and sulfur has been calculated. We have used the Greens-function technique based on the scheme of linear muffin-tin orbitals in the atomic sphere approximation (LMTO-ASA) for the crystal potential and width the local density approximation (LDA) for electrons. Two types of coverage are considered: full monolayer with two additional atoms per two-dimensional unit cell and half monolayer with one additional atom per unit cell. Full monolayer of metallic atoms increases the surface energy. Cu atoms lead to greater destabilization than Al atoms. Sulfur atoms stabilize (110) surface for all considered compounds. (author)

CERN Document Server

Atomic pioneers

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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)

We have investigated the generation and propagation of misfit dislocations in strained In/sub y/Ga/sub 1-//sub y/As/GaAs multiquantum wells grown by molecular-beam epitaxy, with cross-sectional transmission electron microscopy. The samples are of excellent optical quality, with multiquantum wells having well widths of 100 A, being characterized by excitonic linewidths and Stokes shifts of 1.5--2.5 and 1--2 meV, respectively. We have examined the growth of 2-..mu..m-thick multiquantum-well samples grown either directly on GaAs, or with an intermediate composition buffer layer, and for the cases of small (y = 0.07) and large (y = 0.16) misfits. It is seen that for the case of quantum wells with small misfit, grown directly on GaAs, metastable growth can be achieved. This is confirmed by low-temperature absorption measurements and from transmission electron microscopy experiments performed both before and after post-growth ...

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 ...

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The temperature dependence of the spontaneous magnetization of epitaxial iron films with a thickness ranging from d=20 to 200nm has been measured. The films are grown on GaAs (100) substrates which are covered by a 150nm thick silver (100) buffer layer. For three-dimensional BCC iron it was observed already in 1929 that saturation of the spontaneous magnetization for T->0 is perfectly described by a T{sup 2} power law. On the other hand, for thin two-dimensional (2D) iron films a T{sup 3/2} law has been established in many recent experimental investigations. In our iron films grown on diamagnetic silver, this dimensionality change occurs at a thickness between d=100 and 200nm. Comparison of the here-observed T{sup 3/2} coefficients with those on iron films grown on paramagnetic tungsten (110) shows that the 2D interactions are {approx}20 times larger in the films on tungsten. Recent results on Fe films which are grown directly on ...

International Nuclear Information System (INIS)

In this work, the silicon oxynitride layer was studied as a tunneling layer for non-volatile memory application by fabricating low temperature polysilicon thin film transistors on glass. Silicon wafers were oxynitrided by only nitrous oxide plasma under different radio frequency powers and plasma treatment times. Plasma oxynitridation was performed in RF plasma using inductively coupled plasma chemical vapor deposition. The X-ray energy dispersive spectroscopy was employed to analyze the atomic concentration ratio of nitrogen/oxygen in oxynitride layer. The oxynitrided layer formed under radio frequency power of 150 W and substrate temperature of 623 K was found to contain the atomic concentration ratio of nitrogen/oxygen as high as 1.57. The advantage of high nitrogen concentration in silicon oxide layer formed by using nitrous oxide plasma ...

International Nuclear Information System (INIS)

Layer-by-layer formation for #pi#-conjugated azomethine multilayers bonded on substrates was investigated. The multilayers were synthesized using ethanol (EtOH) and dichloromethane (DCM) as reaction solvents. The multilayer characteristics were analyzed using UV-vis absorption spectroscopy, ellipsometric thickness, and atomic force microscopy. The absorption spectra and ellipsometric thicknesses of multilayers formed using EtOH and DCM were compared. The results indicate that EtOH is more suitable than DCM for such layer-by-layer formation. In addition, bandgaps estimated from the absorption edge of multilayers were investigated. The results indicate that the bandgap decreases as the number of benzene rings contained in the molecular chain of the multilayer increases. Also, a multilayer with four benzene rings bonded on a substrate had a bandgap close to that of a polymer with a similar chemical structure.

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 ...

International Nuclear Information System (INIS)

High quality graphene sheets are synthesized through efficient oxidation process followed by rapid thermal expansion and reduction by H2. The number of graphene layers is controlled by tuning the oxidation degree of GOs. The higher the oxidation degree of GOs is getting, the fewer the numbers of graphene layers can be obtained. The material is characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, atomic force microscopy, transmission electron microscopy and Fourier transform infrared spectroscopies. The obtained graphene sheets with single, triple and quintuplicate layers as anode materials exhibit a high reversible capacity of 1175, 1007, and 842 mA h g-1, respectively, which show that the graphene sheets with fewer layers have higher reversible capacity. -- Graphical abstract: The typical TEM images of the graphene sheets derived from ...

International Nuclear Information System (INIS)

Extended X-ray absorption fine structure (EXAFS) measurements of bismuth clusters in the temperature range of 23 -300 K have been performed using synchrotron radiation in order to investigate the size dependent phase transition. The inter-atomic distances around 3.0 A and 3.6 A are attributed to the nearest neighbors within the layer and between layers, respectively. EXAFS functions were analysed by the curve fitting method within a symmetric distribution approximation. The nearest neighbor distance of the 0.5 nm thick films is shorter than that of the 300 nm thick films at all the temperatures, which is related to the reduction of the inter-layer correlation.

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 ...

Energy Technology Data Exchange (ETDEWEB)

No abstract prepared

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)

A number of different theoretical approaches have been used to model to atomic structure and properties of solid-liquid interfaces. Most calculations indicate that ordering occurs in the first several layers of the liquid, adjacent to the crystal surface. In contrast to the numerous theoretical investigations, there have been no direct experimental observations of the atomic structure of a solid-liquid interface for comparison. Saka et al. examined solid-liquid interfaces in In and In-Sb at lattice-fringe resolution in the TEM, but their data do not reveal information about the atomic structure of the liquid phase. The purpose of this study is to determine the atomic structure of a solid-liquid interface using a highly viscous supercooled liquid, i.e., a crystal-amorphous interface.

British Library Electronic Table of Contents (United Kingdom)

Chitosan (Ch) microspheres have been developed by precipitation method, cross-linked with glutaraldehyde and used as a template for layer-by-layer (LBL) deposition of two natural polyelectrolytes. Using a LBL methodology, Ch microspheres were alternately coated with hyaluronic acid (HA) and Ch under mild conditions. The roughness of the Ch-based crosslinked microspheres was characterized by atomic force microscopy (AFM). Morphological characterization was performed by environmental scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and stereolight microscopy. The swelling behaviour of the microspheres demonstrated that the ones with more bilayers presented the highest water uptake and the uncoated cross-linked Ch microspheres showed the lowest uptake capability. Micros...

Science.gov (United States)

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

Energy Technology Data Exchange (ETDEWEB)

Nano-materials in which a large fraction of atoms resides within a few atomic layers near the surface can be designed to have novel properties by manipulating their surface parameters. We show that the effective elastic constants of nano-porous/cellular materials can be made to exceed those of the parent materials provided the pore surface elastic parameters satisfy certain conditions. These stiff nano-porous materials herald a radical breakthrough in sandwich-type construction.

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The growth and properties of Si{sub 1{minus}y}C{sub y} and Si{sub 1{minus}x{minus}y}Ge{sub x}C{sub y} alloys pseudomorphically strained on Si(001) will be reviewed. Although the bulk solubility of carbon in silicon is small, epitaxial layers with more than 1 at.% C can be fabricated. The relation between substitutional and interstitial carbon incorporation will be presented. Substitutionally incorporated C atoms allow strain manipulation, including the growth of strain-free or inversely strained Si{sub 1{minus}x{minus}y}Ge{sub x}C{sub y} layers. The mechanical properties, microscopic structure, thermal stability, as well as the influence of C atoms on band structure will be discussed.

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 properties of these materials, ...

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)

Homogenous Al{sub x}Ga{sub 1{minus}x}P liquid phase epitaxial layers have been obtained with the temperature difference method under controlled vapor pressure (TDM-CVP). Very clear fine structures near band edge in photoluminescence spectra have been observed at 77 K for the first time. Photoluminescence measurement results confirmed that the free exciton recombination without phonon assistance plays an important role in the luminescence at 77 K and becomes dominant at room temperature. It is considered that Zero-phonon assisted free exciton recombination is intensified by some local perturbations to electrical potentials against carriers or excitons introduced by Al atoms in Al{sub x}Ga{sub 1{minus}x}P layers, which can give momentum change necessary for recombination.

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Mechanisms and associated energetics for adatom diffusion on the (100) and (110) surfaces of Ni, Cu, Rh, Pd, and Ag are investigated. Self-diffusion was studied on (100) and (I 10) surfaces of Ni, Cu, Pd and Ag using corrected effective medium method (CEM) and approximation to CEM used for molecular dynamics and Monte Carlo studies (MD/MC-CEM). Self-diffusion on Pd(100), Ag(100), Ni(110), Cu(110), Pd(110), and Ag(110) is accomplished by classical diffusion: the adatom hops from its equilibrium adsorption site over an intervening bridge site to an adjacent equilibrium site. Self-diffusion on Ni(100) and Cu(100) proceeds by atomic-exchange diffusion: the adatom on the surface displaces an atom in the first surface layer. Aside from explicit inclusion of the kinetic-exchange-correlation energy, it is critical to include enough movable atoms in the calculation to insure correct energetics. Distortions ...

British Library Electronic Table of Contents (United Kingdom)

Deposition of CN-based films by a novel version of active screen plasma nitriding, aiming at surface modification of polymers, is reported. The approach relies on the use of pure graphite as the grid material, which was found to act both as an active screen and as a dry source of carbon atoms for the synthesis of thin films consisting mainly of a stoichiometric CN layer with columnar-type structure and dome-like nanostructured morphology.

International Nuclear Information System (INIS)

In this work we investigate an iron oxide thin film grown with atomic layer deposition for a gas sensor application. The objective is to characterize the structural, chemical, and electrical properties of the film, and to demonstrate its gas-sensitivity. The obtained scanning electron microscopy and atomic force microscopy results indicate that the film has a granular structure and that it has grown mainly on the glass substrate leaving the platinum electrodes uncovered. X-ray diffraction results show that iron oxide is in the #alpha#-Fe_2O_3 (hematite) phase. X-ray photoelectron spectra recorded at elevated temperature imply that the surface iron is mainly in the Fe"3"+ state and that oxygen has two chemical states: one corresponding to the lattice oxygen and the other to adsorbed oxygen species. Electric conductivity has an activation energy of 0.3-0.5 eV and almost Ohmic current-voltage dependency. When exposed to O_2 ...

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A set of equations describing a stress-mediated evolution of the nonequilibrium dopant-defect system has been derived and analyzed. Together with coupled diffusion of dopant atoms and point defects, we consider the drift of all mobile species in different charge states, namely vacancies, self-interstitials, and pairs 'dopant atom-point defect', in the field of stress. It has been shown that stresses may affect the diffusion of dopant atoms mainly in two ways: (1) directly, due to the drift of the pairs in the field of stress; (2) indirectly, by the formation of nonuniform defect distribution due to the drift of point defects. On this basis, various features of doping processes, such as phenomena of 'uphill' impurity diffusion near the surface (within the framework of the first or second mechanisms) and the peculiarities of high concentration phosphorus diffusion (due to the second ...

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A number of properties in steel components are detrimentally influenced when exposed to hydrogen environments. Under these conditions, atomic hydrogen is adsorbed on the steel surface, then absorbed and preferentially transported towards tri-dimensional stressed regions in the crystal lattice and into defects such as interfaces or dislocations. The hydrogen embrittlement susceptibility is strongly influenced by various microstructural parameters including the type of inclusions, steel composition and heat treating conditions. One of the alternatives employed in minimizing hydrogen embrittlement is the use of surface barriers for hydrogen permeation. In particular, the presence of surface nitride layers in steels can be considered as an effective barrier. Nitride steel surface layers can be produced by plasma nitriding with the concomitant benefits of improved surface hardness, as well as superior wear and fatigue ...

International Nuclear Information System (INIS)

Research highlights: #-># Morphological and chemical characterization at atomic scale of porous alumina layers anodised in ordered regimes. #-># Characterization based on the use of FEG-SEM, STEM-HAADF, STEM-EELS and STEM-X-EDS. #-># Nanoscale distribution of P-, C- and S-bearing species in the pore wall. - Abstract: Ordered porous alumina layers prepared by two-step anodising in phosphoric, oxalic and sulphuric acids have been characterized at sub-nanometer scale using electron microscopy techniques. FEG-SEM and STEM-HAADF images allowed estimating the pore size, cell wall and pore wall thicknesses of the layers. Nanoanalytical characterization has been performed by STEM-EELS and STEM-X-EDS. Detailed features of the spatial distribution of anions in the pore wall of the films have been obtained. Maximum concentration of P-species occurs, approximately, at the middle of the pore wall; adjacent ...

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 ...

International Nuclear Information System (INIS)

Ti and its alloys (Ti-6Al-4V) have been used in different engineering applications due to their several outstanding properties. Nevertheless, their use in practical applications is limited in many cases due to their poor tribological property. Researches are ongoing on surface modification of Ti based materials by different plasma and ion based techniques to overcome this problem. However, the conventional plasma nitriding techniques have several problems such as formation of an arc, increased possibility of surface contamination due to a comparatively higher operating pressure, production of a very thin nitrided layer after a long processing time, etc. In this present work, the possibility of a new low-pressure plasma nitriding process using a Plasma Enhanced Chemical Vapor Deposition (PECVD) based saddle field fast atom beam source on a Ti-6Al-4V alloy sample is investigated. Plasma nitriding was carried out at 900 deg. C and at a pressure ...

Energy Technology Data Exchange (ETDEWEB)

The present study is devoted to the investigation of the mechanism of aluminium nitriding by a technique that employs implantation of low-energy nitrogen ions and diffusional transport of atoms. The nitriding of aluminium is investigated, because this is a method for surface modification of aluminium and has a potential for application in a broad spectrum of fields such as automobile, marine, aviation, space technologies, etc. However, at present nitriding of aluminium does not find any large scale industrial application, due to problems in the formation of stoichiometric aluminium nitride layers with a sufficient thickness and good quality. For the purposes of this study, ion nitriding is chosen, as an ion beam method with the advantage of good and independent control over the process parameters, which thus can be related uniquely to the physical properties of the resulting layers. Moreover, ion nitriding has a close ...

Energy Technology Data Exchange (ETDEWEB)

Significant ion irradiation during film growth is required for the formation of cubic boron nitride (cBN) films. Meanwhile, a huge level of intrinsic stress possibly induced by the ion bombardment has been frequently reported to result in cracking and/or lack of adhesion of deposited cBN films. The present work has been performed to investigate the interfacial and/or the buffer layer structures with better matching to the cBN film by relaxation of the film stress using ion-beam-assisted deposition (IBAD). Boron nitride films have been synthesized on Si(100) wafer and tungsten carbide (WC) substrates by depositing boron vapor under simultaneous bombardment with nitrogen ions and nitrogen-argon mixture ions in the energy range of 0.5-10 keV. Cubic BN films with enhanced tribological properties have been explored by inserting a BN layer with various B/N compositions as a controlled buffer at the interface. Significant relaxation of the film stress ...

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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.}

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Abstract A next generation material for surface passivation of crystalline Si is Al2O3. It has been shown that both thermal and plasma-assisted (PA) atomic layer deposition (ALD) Al2O3 provide an adequate level of surface passivation for both p- and n-type Si substrates. However, conventional time-resolved ALD is limited by its low deposition rate. Therefore, an experimental high-deposition-rate prototype ALD reactor based on the spatially separated ALD principle has been developed and Al2O3 deposition rates up to 1.2-nm/s have been demonstrated. In this work, the passivation quality and uniformity of the experimental spatially separated ALD Al2O3 films are evaluated and compared to conventional temporal ALD Al2O3, by use of quasi-steady-state photo-conductance (QSSPC) and carrier density ...

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The morphological aspects of ternary phase formation during the Pd-GaAs reaction have been studied by application of transmission electron microscopy (TEM) and Rutherford backscattering (RBS) techniques. The TEM images show that the first product phase, ''phase I'', forms during deposition of Pd onto (100) GaAs and exhibits the preferred orientation (0001)/sub I/ approx. // (01 anti 1)/sub GaAs/. In the presence of unreacted Pd, the second phase, ''phase II'', nucleates at large-angle grain boundaries in the phase I film as the annealing temperature increases above approx.250C. Energy dispersive analysis of x-rays and RBS suggest the nominal compositions Pd3GaAs and Pd4GaAs for phases I and II, respectively.

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

International Nuclear Information System (INIS)

We present a high temperature heat oven with merits of conventional heat pipe oven and study ots thermal characteristics. The oven consists of stainless steel body and heating part of three layers of ceramic tubes. We obtained the maximum temperature of about 1350. deg. C at the center which was measured by thermocouple and infrared thermometer. And we compared the heating characteristics in the cases of external heating and no extent heating. It was applied to self diffraction experiment in the samarium gas which was one of the high melting point material.

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Apparent growth of amorphous layers during low temperature annealing was observed in low energy Ge"+-implanted (0 0 1)Si by high-resolution transmission electron microscopy. The occurrence of abnormal growth is due to the randomization of heavily damaged regions beneath the original amorphous/crystalline interfaces. The randomization process is attributed to the strain, incurred by the presence of a high density of large Ge atoms in the heavily damaged Si substrate, relaxation to lower the free energy of the systems. The randomization upon annealing may be fruitfully applied to minimize the transient enhanced diffusion in shallow junction formation.

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Single crystals of trigonal Cr{sub 2}Te{sub 3}, monoclinic Cr{sub 5}Te{sub 8}, and trigonal Cr{sub 5}Te{sub 8} were prepared and the single crystal structures were determined. The structures are related to the NiAs structure type by successive removal of Cr in every second metal atom layer parallel to the c axis. The strong relationship between the structures is evidenced by their very similar X-ray powder patterns. In trigonal Cr{sub 2}Te{sub 3} excess Cr occupies only one of the two possible sites. In monoclinic Cr{sub 5}Te{sub 8} the Cr atoms occupy four different crystallographic sites. The resulting ordering of the vacancies is significantly different from the hitherto reported crystal structures of transition metal chalcogenides M{sub 5}X{sub 8}. A slight increase of the tellurium content leads to an order-disorder transition from the monoclinic to a trigonal phase. The Cr atoms are located on ...

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Epitaxial CeO_2 buffer layers were fabricated by pulsed laser deposition (PLD) on r-cut sapphire substrates. An atomically flat CeO_2 surface with a high density of nanodots was formed by a self-assembly process. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy investigation showed that the nanodots were CeO_2 other than impurities. YBa_2Cu_3O_7_-_#delta# (YBCO) thin films were then grown on the annealed and the as-grown CeO_2-buffered sapphires by PLD. The transport measurement results showed that the nanodots enhanced the effective pinning potential and significantly increased critical current density (J _c). Especially, YBCO films with an annealed CeO_2 buffer layer showed a high J _c peak when the applied field was directed along the c-axis of YBCO. Cross-section transmission electron microscopy investigation revealed that the J _c peaks in YBCO with annealed CeO_2 buffer ...

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The aim of this work is to describe the processes during plasma nitriding of Nb-containing, powder metallurgy prepared (PM) tool steel. PM steel was studied containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb and 1.0% W, produced by melt atomization and hot isostatic pressing. The hardened and tempered steel was plasma nitrided at temperatures ranging from 470 to 530 deg. C. The nitriding time was 30-180 min. Optical microscopy, electron microscopy, XRD, EDS, WDS and hardness measurements were used to study the steel's properties, microstructure, phases and chemical composition. The nitriding temperature of 470 deg. C was found to be unsuitable for practical use because the layers prepared at this temperature were non-uniform. The compound layer formed by M{sub 2,3}(C,N) and M{sub 4}N was found after nitriding at temperatures of 500 and 530 deg. C for at least 60 min. The effect of niobium on the ...

International Nuclear Information System (INIS)

Aluminium nitride (AlN) is a very interesting ceramic because of its combination of properties such as high thermal stability, high hardness and an unusual combination of high thermal and low electrical conductivity. But it is very difficulty to obtain an AlN layer on the aluminium substrates by thermochemical nitriding process. Since a thin film of aluminium oxide existing on the surface of every aluminium substrate prevents the nitrogen atoms from diffusing into the aluminium lattice. However, it is possible to sputter the oxide film away from the aluminium surface in a glow discharge with the use of plasma nitriding technique and to allow the formation of AlN layer on the aluminium bulk. In the present work specimen of aluminium Al 99.5 has been plasma nitrided in a modified plasma nitriding unit, in which a diffusion pump was used to obtain an especially low partial pressure of oxygen in the vauum chamber. The ...

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 investigation has allowed a ...

International Nuclear Information System (INIS)

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

International Nuclear Information System (INIS)

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

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 for ...

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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 ...

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The transport and partitioning of {sup 129}I has been examined for a shallow groundwater flow system at Sturgeon Falls in northeastern Ontario. Recharge into a sandy surficial postglacial deltaic aquifer occurs in the vicinity of a seasonally-wet boreal forest. Concentrations of stable iodine, {sup 129}I, tritium, radiocarbon, stable isotopes and major ions were measured on samples of groundwater and precipitation. The present-day tritium profile delineates the position of the early 1960's above-ground nuclear weapons pulse at a depth of approximately 12 m. The concentrations of stable iodine for groundwaters above, near and below the above-ground nuclear weapons pulse range from 0.07 to 1.7 ppb. Over that same interval {sup 129}I concentrations decreased from 1.9 x 10{sup 6} atoms/L at 9 m, to approximately 1.9 x 10{sup 5} atoms/L in tritium-depleted waters at 35 m, below the present-day depth of the recharging above-ground nuclear ...

Science.gov (United States)

We model nongraphitized carbon black surfaces and investigate adsorption of argon on these surfaces by using the grand canonical Monte Carlo simulation. In this model, the nongraphitized surface is modeled as a stack of graphene layers with some carbon atoms of the top graphene layer being randomly removed. The percentage of the surface carbon atoms being removed and the effective size of the defect (created by the removal) are the key parameters to characterize the nongraphitized surface. The patterns of adsorption isotherm and isosteric heat are particularly studied, as a function of these surface parameters as well as pressure and temperature. It is shown that the adsorption isotherm shows a steplike behavior on a perfect graphite surface and becomes smoother on nongraphitized surfaces. Regarding the isosteric heat versus loading, we observe for the case of graphitized thermal carbon black the ...

Science.gov (United States)

A doubly Q-switched laser with both an acousto-optic (AO) modulator and a GaAs saturable absorber can obtain a more symmetric and shorter pulse with high pulse peak power, which has been experimentally proved. The key parameters of an optimally coupled doubly Q-switched laser with both an AO modulator and a GaAs saturable absorber are determined, and a group of general curves are generated for what we believe is the first time, when the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs are combined, and the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the AO Q-switch are considered. These key parameters include the optimal normalized coupling parameter, the optimal normalized GaAs saturable absorber parameters, and the normalized parameters of the AO Q-switch, which can maximize ...

British Library Electronic Table of Contents (United Kingdom)

A series of NHC silver(I), mercury(II) and palladium(II) complexes, [(1,3-diethylbimy)6Ag4I3]I (2), [(1-benzyl-3-picolylbimy)Ag2Br2]n (3), [(1-benzyl-3-picolylbimy)HgI(CH2CN)]2 (4), {[(1-picolyl-3-npropylbimy)2Hg][Hg2I6]}n (5) and [(1,3-dipicolylbimy)PdCl]Cl (6), as well as one anionic complex [1,3-diethylbimidazolium]2[HgI4] (1) (bimy=benzimidazol-2-ylidene), have been prepared and characterized. Interestingly, a wind wheel-like Ag4I3 arrangement in 2 is formed, 1D polymeric chain containing 12-membered macrometallocycles and quadrangle Ag2Br2 units in 3 is generated, and the a-carbon atom of deprotonated acetonitrile ([CH2CN]-) in 4 participates in coordination with mercury(II) atom. In the crystal packings of complexes 1-6, 2D supramolecular layers or 3D supramolecular architectures are...

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High concentrations of self-interstitials are trapped by dopant atoms during ion implantation into Si. For group V dopants, these complexes are sufficiently stable to survive solid-phase-epitaxial (SPE) growth but break up on subsequent thermal processing and cause a transient-enhanced diffusion. Dopant diffusion coefficients are enhanced by up to five orders of magnitude over tracer values and are characterized by an activation energy of approximately one half of the tracer values. In the case of group III dopants, any complexes formed during implantation do not survive SPE growth but a second source of self-interstitials becomes significant and leads to similar transient effects. This is the damaged layer underlying the original amorphous/crystalline interface. These observations provide direct evidence for long-range self-interstitial migration in Si, and we believe these are the first observations of the interstitialcy diffusion mechanism ...

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In this experiment, a Si wafer containing four lightly doped B marker layers epitaxially grown by CVD has been implanted with 100 keV Si{sup +} ions to a dose of 2 x 10{sup 14} ions/cm{sup 2} and annealed at 850 deg. C for several times in an RTA system in flowing N{sub 2}. TEM and SIMS analysis, in conjunction with a transient enhanced diffusion (TED) evaluation method based on the kick-out diffusion mechanism, have allowed us to accurately study the boron TED evolution in presence of extended defects. We show that the silicon surface plays a key role in the recombination of Si interstitial atoms by providing the first experimental evidence of the resulting Si{sub int}s supersaturation gradient between the defect region and the surface. Our results indicate an upper limit of about 200 nm for the surface recombination length of Si interstitials at 850 deg. C in a N{sub 2} ambient.

International Nuclear Information System (INIS)

The localized Pt deposition on Si by 30 keV Ga"+ focused ion beam (FIB), 10 keV electron beam (EB) or dual beams (FIB and EB) using precursor gas has been compared by analysis using a 300 keV Be"2"+ microprobe with a beam spot size of 80 nm. The distribution of deposited Pt, Ga from the ion beam itself, and C from the precursor gas was obtained at and nearby the deposited areas by micro-RBS spectra and RBS mapping. All of the beam processed areas showed a uniform Pt distribution at the deposited areas. The amount of Pt atoms increased with the increase in ion or electron dose due to the decomposition of precursor gas. The thickness of Pt layer by EB is considerably less than that by FIB due to the reduced deposition rate. Ga atoms from the center of processed areas partly redeposited at and nearby the FIB processed areas within #approx#3 #mu#m. The Ga incorporation by dual beam processing was reduced compared with that by ...

International Nuclear Information System (INIS)

With the aim of studying the magnetic properties of reduced-dimensionality magnetic systems we have patterned 250 nm- and 500 nm-size square elements on Fe/NiO layers by 30 keV Ga"+ focused ion beam (FIB) milling, varying beam current and pixel dwell time. By high resolution scanning electron microscope (SEM) imaging and atomic force microscopy (AFM) analysis we found that island size decreases from the nominal value by increasing the beam current and features sharpness improves on increasing the dwell time. The top surface of the isolated features has a pronounced edge bending which may be as high as 9 nm with respect to the flat inner area of the island and decreases as dwell time grows. By varying the ion fluence we found that such a shape is related to a surface swelling effect occurring at low ion fluence in the irradiated areas. The swelling-related damage at the edges is expected to influence the magnetic properties of the patterned ...

International Nuclear Information System (INIS)

This work estimates the power requirements for using photochemical processes driven by space nuclear power to counteract the Earth's ozone layer depletion. The total quantity of ozone (O_3) in the Earth's atmosphere is estimated to be about 4.7 x 10"3"7 molecules. The ozone production and destruction rates in the stratosphere are both on the order of 4.9 x 10"3"1 molecules/s, differing by a small fraction so that the net depletion rate is about 0.16 to 0.26% per year. The delivered optical power requirement for offsetting this depletion is estimated to be on the order of 3 GW. If the power were produced by satellite reactors at 800 km altitude (orbit decay time #approx# 300 years), some means of efficient power beaming would be needed to deliver the power to stratospheric levels (10--50 km). Ultraviolet radiation at 140--150 nm could have higher absorption rates in O_2 (leading to production of atomic oxygen, which can combine with O_2 to form ...

British Library Electronic Table of Contents (United Kingdom)

A Ni3Al coating was prepared by plasma spraying technique on the surface of titanium alloy. Ni-Al mixed powders, coatings and reaction products were investigated by scanning electron microscope, EDS, DSC and XRD. A tight bonding between the coating and the substrate was formed. The X-ray diffraction analysis of the patterns showed that the coating not only had Ni3Al phase, but also had NiO and Al2O3 phase microcontent. Comparing Ni coated Al to Ni3Al at 900^oC, the diffusion was stronger and the diffusion layer was thicker. A minute pore structure was formed at 1200^oC in the front edge of solid-state reaction layer. So Ni3Al restrained the solid-state reaction of the coating with the substrate, and as a whole weakened the entry of oxygen atoms into the substrate and quenched the out-diffu...

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

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Bilayers of pure palladium and gold films were evaporated alternatively on (100) and (111) monocrystalline silicon substrates. After annealing, in a vacuum furnace from 100 to 650degreeC during 30min, the growth sequence of the Pd2Si and PdSi phases that evolved as the result of the diffusion reaction was examined by means of Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), whereas the surface morphology was investigated by scanning electron microscopy (SEM) technique. The effect of the intermediate gold layer is investigated in order to test its effectiveness as barrier for Cu and Si atoms interdiffusion and its influence on the morphology of the formed palladium silicides. The effect of substrate orientation on the palladium silicides growth and formation was also e...

British Library Electronic Table of Contents (United Kingdom)

To investigate the variation in the fine structure of polyamide thin-film composite (TFC) membranes prepared via two different interfacial polymerization conditions (IP-I and IP-II), experiments on Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), water contact angle, and positron annihilation spectroscopy (PAS) coupled to a slow positron beam were conducted. Polyamide TFC membranes were prepared via the interfacial polymerization reaction between triethylenetetramine (TETA) and trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane. Compared with the polyamide TFC membrane prepared via IP-I, the polyamide layer prepared via IP-II showed a shorter S plateau length (thinner thickness), a higher o-Ps intensity I3 value (higher free-volume con...

CERN Document Server

substrate). Within each group of simulations, three lubricant film thicknesses are studied to examine the effect of varying lubricant thickness. Statistical data are collected from each simulation and presented in this work. Via these data, together with the evolution, of atomic and molecular configurations, a very detailed picture of the properties of this thin film interface is presented. In particular, we conclude that perfluoropolyether lubricant forms distinct molecular layers when confined between two substrates, the rate of heat generation under shearing conditions typical of those in a head-disk interface is insufficient for thermal mechanisms to result directly in lubricant degradation, and mechanical stresses attained in the head-disk interface are unlikely to result in any significant degree of lubricant degradation. This thesis examines the tribology of a head-disk interface in an operating hard disk drive via non-equilibrium ...

International Nuclear Information System (INIS)

By using megaelectronvolt "4He ion backscattering techniques and transmission electron microscopy, the authors have investigated the interactions of ion beams with thin film structures in a number of silicide-forming systems. The mixed layer was found to be an equilibrium compound for near-noble metals and an amorphous phase for refractory metals. Differences in behavior have also been observed in near-noble metal systems. For palladium, the Pd_2Si phase grew with ion dose and remained crystalline up to high dose. For nickel, the compound Ni_2Si was formed initially and became amorphous on prolonged irradiation. All the results indicate the significance of atomic mobility at target temperatures in determining the phase formation and in explaining the sensitivity of the silicides to ion bombardment. (Auth.).

British Library Electronic Table of Contents (United Kingdom)

Magnetic pulse welding is a solid state impact welding process, similar to explosive welding, which produces metallurgical bond by oblique high-speed impact between two metal bodies. This violent impact removes the metal surface oxide layers and then joins the two atomic level clean metal surfaces together by the incidental compression pressure. The impact velocity is at 200?400?m/s and the being welded metal surface undergoes severe plastic deformation with strain rate in the order of 106?107?s?1. The ultrafine-grained structure was observed on the welded interface. This article studied two types of similar material lap joint interfaces and the base metals were aluminum alloy 6061 and copper alloy 110. Nano-indentation testing shows that the welded interfaces have significantly greater ha...

International Nuclear Information System (INIS)

Accurate full-potential self-consistent linearized augmented-plane-wave (FLAPW) calculations have been carried out for hexagonal boron nitride. The resulting energy-band structure indicates that this material is an indirect-gap insulator and shows the existence of two unoccupied interlayer bands, similar to those found in graphite and graphite intercalation compounds. Chemical bonding is mainly covalent, with a small charge transfer towards the nitrogen atoms. Moreover, model-potential calculations, based on first-principles FLAPW wave functions and potentials, have been used to study slabs of thickness up to 35 layers. Contrary to the case of graphite, our results do not provide evidence of surface states associated with the interlayer bands.

International Nuclear Information System (INIS)

The formation of thin SiO_2 layers on silicon and metal silicides was studied by phase- and thickness measurements with Rutherford back-scattering of 2 MeV alfa particles. Thermal oxidation was done in steam and dry oxygen at temperatures between 750 degrees Celsius and 1 100 degrees Celsius, while SiO_2 formation at room temperature was carried out by anodic oxidation. The study of silicon oxidation was done on Si<100>, Si<111> and amorphous silicon substrates. Thermal oxidation of CoSi_2, CrSi_2, NiSi_2, PtSi and TiSi_2 was investigated. The oxidation rates of the silicides were found to be much higher than for silicon. The oxidation process is also diffusion-limited with a higher oxidation rate for steam as compared to dry oxygen. The silicide layers were found to stay intact during thermal oxidation. A certain amount of structural and chemical instability did appear. Chemical instabiliy was shown by metal oxidation which led to ...

Science.gov (United States)

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

Energy Technology Data Exchange (ETDEWEB)

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

Science.gov (United States)

... 4 Joint Committee on Atomic Energy as a Model . . . . . ... Joint Committee on Atomic Energy as a Model ...

Energy Technology Data Exchange (ETDEWEB)

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

Energy Technology Data Exchange (ETDEWEB)

Transient Enhanced Diffusion (TED) of dopants in Si is the consequence of the evolution, upon annealing, of a large supersaturation of Si self-interstitial atoms left after ion bombardment. In the case of amorphizing implants, this supersaturation is located just beneath the c/a interface and evolves through the nucleation and growth of End-Of-Range (EOR) defects. For this reason, the authors discuss here the relation between TED and EOR defects. Modelling of the behavior of these defects upon annealing allows one to understand why and how they affect dopant diffusion. This is possible through the development of the Ostwald ripening theory applied to extrinsic dislocation loops. This theory is shown to be readily able to quantitatively describe the evolution of the defect population (density, size) upon annealing and gives access to the variations of the mean supersaturation of Si self-interstitial atoms between the loops and responsible for ...

International Nuclear Information System (INIS)

Growth of Ru- and RuO_2-composite (ROC) nanodots on atomic-layer-deposited Al_2O_3 film has been studied for the first time using ion-beam sputtering followed by post-deposition annealing (PDA). X-ray photoelectron spectroscopy analyses reveal that RuO_2 and Ru co-exist before annealing, and around 10% RuO_2 is reduced to metallic Ru after PDA at 900 deg. C for 15 s. Scanning electron microscopy measurements show that well-defined spherical ROC nanodots are not formed till the PDA temperature is raised to 900 deg. C. The mean diameter of the nanodots enlarges with increasing PDA temperature whereas the nanodot density decreases, which is attributed to coalescence process between adjacent nanodots. It is further illustrated that the resulting nanodot size and density are weakly dependent on the annealing time, but are markedly influenced by the decomposition of RuO_2. In this article, the ROC nanodots with a high density of 1.6 x 10"1"1 cm"-"2, a mean diameter of 20 ...

International Nuclear Information System (INIS)

On the basis of accurate crystal structure determination, the mineral phosphuranylite corresponds to the chemical formula KCa(H_3O)_3(UO_2)_7(PO_4)_4O_4.8H_2O. Cmcm, a=15.778 (3)-15.899(2), b=13.702(2)-13.790(5), c=17.253(3)-17.330(3)A, Z=4, D_x=4.575-4.631g cm"-"3, #mu#=287.6-291.1cm"-"1. The presence of potassium (about 1.80wt%K_2O), overlooked until now, has been confirmed by microprobe analysis on samples from four different localities. The best data for structure determination have been obtained by single-crystal X-ray diffraction on specimens from Capoterra, Sardinia, and Bois Noirs, France; here 1453 and 1254 independent reflections, respectively, were used in the refinement, and the corresponding final R index is 0.036 and 0.048. The structure consists of layers of phosphate groups connected with hexagonal, pentagonal and tetragonal dipyramids centered on the U atoms. The Ca and K atoms are located within channels ...

Energy Technology Data Exchange (ETDEWEB)

Described herein are the results of the FY1994 research program for analysis and evaluation for thin film solar cells. The study on quantitative analysis of hydrogen atoms in a plasma determines quantity of hydrogen atoms in the plasma of monosilane diluted with hydrogen. It is found, contrary to expectation, that quantity of hydrogen atoms in the plasma decreases as it is more diluted with hydrogen. The study on light-induced degradation of the thin chlorine-base amorphous silicon films confirms that the plasma CVD method with 20% of dichlorosilane gas added to monosilane gas produces the thin amorphous silicon film 3 times faster than the conventional method. The thin film has essentially the same defect density as the one prepared by the conventional method, showing good photoelectric characteristics. The thin film of chlorinated amorphous silicon has a 1 digit lower defect density than the conventional one of amorphous ...

Science.gov (United States)

Deforestation in Mato Grosso, Brazil. atom_author. atom_name, Jesse Allen. atom_link. kml_href, http://earthobservatory.nasa.gov/Feeds/GoogleEarth/ ...

CERN Document Server

Individual laser cooled atoms are delivered on demand from a single atom magneto-optic trap to a high-finesse optical cavity using an atom conveyor. Strong coupling of the atom with the cavity field allows simultaneous cooling and detection of individual atoms for time scales exceeding 15 s. The single atom scatter rate is studied as a function of probe-cavity detuning and probe Rabi frequency, and the experimental results are in good agreement with theoretical predictions. We demonstrate the ability to manipulate the position of a single atom relative to the cavity mode with excellent control and reproducibility.

CERN Document Server

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

Science.gov (United States)

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

Energy Technology Data Exchange (ETDEWEB)

Austenitic stainless steels have been implanted with molybdenum ions (Mo[sup +], 100 keV, 2.5 x 10[sup 16] atoms cm[sup -2]). The implanted material has been characterized by XPS and RBS. The implanted region has a thickness of [approx] 1000 A with a maximum molybdenum concentration of [approx] 9 at.% Mo located at [approx] 210 A from the surface. The effects of implanted molybdenum on the passivation of the alloy in 0.5 M H[sub 2]SO[sub 4] have been investigated by electrochemistry and XPS. After XPS analysis the samples were transferred without exposure to air into a glove-box with an inert atmosphere. The electrochemical behaviour of the alloy is significantly modified by the implanted molybdenum. The major effect is that the activation peak disappears. A bilayer structure (outer hydroxide/inner oxide) of the passive film is observed for both the implanted and non-implanted alloys and the thicknesses of the films are similar. On the implanted alloy the outer ...

Science.gov (United States)

The DITE (Divertor Injection Tokamak Experiment) program has been undertaken to demonstrate the feasibility of impurity control by the use of a diverter in an injection-heated toroidal plasma configuration. Rather than behaving in accordance with neoclassical toroidal containment theory, the plasma is subject to various instabilities, particularly the resistive fluid MHD types, follows the empirical scaling of energy confinement time with plasma parameters observed in other plasma devices. DITE experiments have, however, extended the range of current and density. Impurities arising from plasma interactions with the vacuum vessel surface are controlled by the bundle divertor, which diverts a portion of plasma and power in the plasma scrape-off layer into a separate target chamber where impurities can be removed. Auxiliary plasma heating is provided by the injection of powerful beams of neutral hydrogen atoms produced by multi-aperture ion ...

International Nuclear Information System (INIS)

This paper deals with the characterization of passive films formed on stainless steel (26% Cr and 0 to 3%Mo). The influence of the applied passivation potential and the effect of molybdenum additions to steel upon the composition profiles of passive films formed in an aqueous NaCl solution (3.5% at pH 2.5) are studied. The technique involved is Auger electron spectroscopy combined with ion sputtering. Some electrochemical techniques have been used in conjunction. A quantitative approach of the Auger spectra during the progressive removal of the passive film is described. The peak-to-peak height of the Auger lines are treated in order to yield the atomic fraction of the various elements present in a given subsurface layer. The analytical study of the film by electron spectroscopy indicates that molybdenum plays a part at the metal-oxide interface where this element acts on the chromium diffusion process. This phenomenon, which depends on the ...

Energy Technology Data Exchange (ETDEWEB)

The diffusion of ion beam injected self-interstitials (I) and their interaction with impurities in crystalline Si has been investigated and modeled. In particular, the I-substitutional carbon (C) interactions have been studied, using a molecular-beam-epitaxy grown Si{sub 1-y}C{sub y} layer interposed between the shallow I-source and a deeper B-spike (marker for I-concentration). Substitutional C atoms are shown to trap I's, to be removed from their substitutional sites, and to form stable precipitates into the C-rich region. The I-trapping mechanism was quantitatively studied by a simulation code. The reactions causing trapping and deactivation are described. In addition, the boron markers approach was extended to the two dimensional (2D) diffusion. High resolution scanning capacitance microscopy was used for quantitative measurements of the 2D boron transient enhanced diffusion induced on a boron delta array by the I's ion ...

Energy Technology Data Exchange (ETDEWEB)

Micropatterned materials were obtained by a controlled laser ablation of a photoimmobilised homogeneous layer of hyaluronic acid (Hyal) and its sulphated derivative (HyalS). The photoimmobilisation was performed by coating the polysaccharide, adequately functionalised with a photoreactive group, on aminosilanised glass substrate and immobilising it on the surface under UV light. Hyal or HyalS photoimmobilised samples were then subjected to laser ablation with wavelengths in the UV regions in order to drill the pattern. Four different patterns with stripes of 100, 50, 25 and 10 {mu}m were generated. A chemical characterisation by attenuated total reflection/Fourier transform infrared (ATR/FT-IR) and time of flight-secondary ions mass spectrometry (TOF-SIMS) confirmed the success of the laser ablation procedure and the presence of alternating stripes of polysaccharide and native glass. The exact dimensions of the stripes were determined by atomic ...

International Nuclear Information System (INIS)

A scalar-relativistic procedure for calculating the valence-electron contribution to the total energy of bulk and thin-film solids has been developed and applied to the fcc and bcc phases of the group-VIB transition elements Cr, Mo, and W. This approach, which is based on the linear augmented-plane-wave method and local-density-functional theory, contains no shape approximations for either the charge density or potential. The formulation adopts a rigid-core approximation and incorporates an exact treatment of the core-charge tails that extend beyond the muffin-tin spheres. The application of this procedure to bcc Cr, Mo, and W yields calculated lattice parameters and bulk moduli that are in good (Cr) to excellent (Mo and W) agreement with experiment. The present calculated properties also agree quite well with the results of previous calculations involving a variety of band-structure methods. The calculated fcc-bcc energy difference for Cr, Mo, and W increases in a nearly linear manner ...

International Nuclear Information System (INIS)

This work describes the ability of ion beam analysis techniques IBA to simultaneously determine the concentration and the possible depth profile of some light elements, such as carbon, oxygen and nitrogen, in matrices of high atomic number Z, such as stainless steel materials. In fact, the nitriding process of some materials has the potential to improve their tribological and mechanical properties and to offer various advantages as compared with other methods used in the modification of surfaces. Gas and Plasma nitriding were applied to certain types of steel, such as AISI-304 and H-13 which are commonly used in the industry, in order to improve their hardness and their surface corrosion resistance. The improvement was correlated with the depth profile of N and the consequent structure variations. More specifically, non-Rutherford elastic backscattering (alpha, alpha) at 5 MeV was performed on different samples, before and after nitriding, in order to determine the ...

International Nuclear Information System (INIS)

Boron is implanted in crystalline silicon through oxide layers with different thicknesses. The implantation is carried out at various doses and energies of interest in ultra large scale integration (ULSI) application. Rapid thermal annealings (RTA) are used to obtain shallow junctions and electrical activation of the B atoms. However, transient enhanced diffusion induced by implantation damage can be observed. The boron concentration profiles before and after annealing are obtained with secondary ion mass spectrometry (SIMS). It is found that the diffusion transient in the tail region of the boron profile increases with decreasing oxide thickness. Even more, if the implantation damage concerns mostly the oxide, i.e. when the concentration peak is located in this oxide, the oxygen knocked into the silicon substrate could play this way an important role in restricting the boron diffusion, which is good to obtain very shallow junctions. On the ...

Energy Technology Data Exchange (ETDEWEB)

The electrochemical method has been used to deposit zinc oxide (ZnO) thin films from aqueous zinc nitrate solution at 80 deg. C onto fluorine doped tin oxide (FTO) coated glass substrates. ZnO thin films were grown between - 0.900 and - 1.025 V vs Ag/AgCl as established by voltammogram. Characterisation of ZnO films was carried out for both as-deposited and annealed films in order to study the effect of annealing. Structural analysis of the ZnO films was performed using X-ray diffraction, which showed polycrystalline films of hexagonal phase with (002) preferential orientation. Atomic force microscopy was used to study the surface morphology. Optical studies identified the bandgap to be {approx} 3.20 eV and refractive index to 2.35. The photoelectrochemical cell signal indicated that the films had n-type electrical conductivity and current-voltage measurements showed the glass/FTO/ZnO/Au devices exhibit rectifying properties. The thickness of the ZnO films was ...

Energy Technology Data Exchange (ETDEWEB)

Picosecond charge-collection transients measured for GaAs/AlGaAs HBTs following 3.0 MeV [alpha]-particle and 620 nm picosecond laser excitation reveal charge-collection efficiencies up to twenty-eight times smaller than for GaAs MESFETs, with [approximately]90% of the charge collected within 75 ps of the ionizing event. The small charge-collection efficiency of the HBTs is a consequence of the ultrafast charge-collection dynamics in these devices. The authors show that picosecond laser excitation reproduces nicely the ion-induced transients, providing a valuable tool for the investigation of charge-collection and SEU phenomena in these devices.

International Nuclear Information System (INIS)

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

Energy Technology Data Exchange (ETDEWEB)

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

International Nuclear Information System (INIS)

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

International Nuclear Information System (INIS)

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.

Science.gov (United States)

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International Nuclear Information System (INIS)

Transient enhanced diffusion (TED) from implantation of 5keVB_1_0H_1_4 and 0.5 keV B ions has been quantified and compared for nominal boron doses of 10"1"4 and 10"1"5cm"-"2. Boron diffusivity during annealing was extracted from secondary ion mass spectroscopy depth profiles of diffused marker layers in boron doping-superlattices and the actual implanted B dose was independently measured by nuclear reaction analysis. Comparable enhancements were observed from both ions. Transmission electron microscopy analysis revealed that both boron- and decaborane-implanted samples were amorphized at a nominal 10"1"5cm"-"2B dose. A comparison with data from low energy Si implants revealed a similar dependence of diffusivity enhancement on implant dose. These findings are consistent with the understanding that TED is caused by the interstitial supersaturation resulting from a number of excess interstitials approximately equal to the number of implanted atoms ...

International Nuclear Information System (INIS)

Reactive Magnetron Sputtering is a complex process and huge efforts are made addressing the understanding of its fundamental phenomena and the simulation of the deposition process by e.g. Particle in Cell/Monte Carlo (PIC/MC). One of the most uncertain parameters in this reactive sputtering process is the incorporation coefficient of the reactive gas in the growing layer, i.e. the real-time sticking coefficient during deposition. In this work, mass spectrometry is used to deliver more insights on this complex matter. Earlier, a method was developed to determine the incorporation coefficient of the reactive gas molecules in the growing metal film, using mass spectrometry combined with thin film analysis techniques (electron probe microanalysis and x-ray photoelectron spectroscopy). This method delivers a global, realistic incorporation coefficient which can be used in models for the reactive sputtering process. In this work, new insights have been added to the ...

International Nuclear Information System (INIS)

Ab initio total energy calculations within the framework of density functional theory have been performed for atomic hydrogen and oxygen chemisorption on the (0001) surface of double hexagonal packed (dhcp) americium using a full-potential all-electron linearized augmented plane wave plus local orbitals method. Chemisorption energies were optimized with respect to the distance of the adatom from the relaxed surface for three adsorption sites, namely top, bridge, and hollow hcp sites, the ad-layer structure corresponding to the coverage of a 0.25 monolayer in all cases. Chemisorption energies were computed at the scalar-relativistic level (no spin-orbit coupling NSOC) and at the fully relativistic level (with spin-orbit coupling SOC). The two-fold bridge adsorption site was found to be the most stable site for O at both the NSOC and SOC theoretical levels with chemisorption energies of 8.204 eV and 8.368 eV respectively, while the three-fold ...

International Nuclear Information System (INIS)

Austenitic stainless steels (304-type) have been implanted with nitrogen ions in order to investigate the effects of implanted nitrogen on their electrochemical behaviour and on the nature of the passive film formed on the steels in acid (0.5M H_2SO_4). Alloys with two nitrogen doses have been prepared (2.5x10"1"6 and 2x10"1"7 N atoms/cm"2). The implanted alloys have been characterized by "1"5N-NRA (nuclear reaction analysis) and XPS (X-ray photoelectron spectroscopy). Alloy surfaces with well-defined N concentrations were prepared, prior to the electrochemical measurements, by argon-ion sputtering of the implanted material for a fixed time in order to reach a well-defined point on the nitrogen depth profile. The samples were then transferred without exposure to air to an electrochemical cell mounted in an inert gas glove box. The implanted nitrogen modifies the electrochemical behaviour of the alloy. The anodic dissolution in the active state is enhanced, and the ...

Science.gov (United States)

For understanding on basic radiation mechanism of the high-gain FEL based on SASE, the author presents electron-crystal interpretation of FEL radiation. In the electron-crystal, electrons are localized at regularly spaced multi-layers, which represents micro-bunching, whose spacing is equal to the radiation wavelength, and the multi-layers are perpendicular to beam axis, thus, diffracted wave creates Bragg's spots in forward and backward directions. Due to the Doppler's effect, frequency of the back-scattered wave is up-converted, generates forwardly focused X-ray. The Bragg's effect contributes focusing the X-ray beam into a spot, thus peak power becomes extremely higher by factor of typically 107. This is the FEL radiation. As well known, the total numbers of scattered photons in Bragg's spots is equal to the total elastic scattering photons from the atoms contained in the crystal. ...

Energy Technology Data Exchange (ETDEWEB)

An extensive series of pulse height measurements have been performed in partially depleted Si surface barrier detectors, using various heavy ions (Li, B, C, O, Al and Cl), at energies between 5 and 70 MeV. After correcting for the small energy loss of the incident ions in traversing the gold surface barrier layer of the detector and for the residual nuclear stopping, the resulting pulse heights per MeV for the various heavy ions were found to be up to 2.5% larger than for the {sup 241}Am (5.486 MeV) alpha particle. This increase, although significant, is smaller than had been anticipated from an extrapolation of the earlier study of H, He and Li pulse heights by Lennard et al.. A new method of analysis of pulse height data, which significantly reduces the uncertainties associated with the dead layer energy loss and nuclear stopping corrections, was used in order to determine directly the variation of the average energy for electron-hole pair ...

Energy Technology Data Exchange (ETDEWEB)

In situ scanning tunneling microscopy has been used to study the nucleation and growth mechanisms and the structure of passive films formed on Cu(111) surfaces in 0.1 M borate buffer solution (pH 9.3). A surface topography characterized by terraces with monoatomic steps is obtained after potentiodynamic reduction down to {minus}1.12 V/standard hydrogen electrode (SHE), of the electropolished surface exposed to air. The formation of a single Cu{sub 2}O passive layer at 0.03 V/SHE proceeds first by a roughening of the steps assigned to a locally blocked step flow process due to a competition between dissolution and preferential nucleation of the oxide at the steps. The observed oxide nuclei are 2--3 nm wide and about one atomic plane high. This process leads to the complete coverage of the terraces by a grain-like structure of the oxide film. The initial terrace topography is completely altered. Thickening of this oxide layer ...

Energy Technology Data Exchange (ETDEWEB)

Doping of molecular organic materials is important for the functionality of organic electronic devices as e.g solar cells. We investigated the doping behaviour of the acceptor molecules Cl{sub 2}-DCNQI and F{sub 16}CuPc incorporated into a CuPc matrix. In-situ XPS/UPS measurements were performed on coevaporated films. Doping by Cl{sub 2}-DCNQI was not successful. The molecule lost its chlorine atoms during thermal evaporation. For pristine F{sub 16}CuPc layers we observe a strong broadening of the photoemission features with increasing deposition rate indicating different domains probably of different molecular structure of differing electric interface potential. F{sub 16}CuPc incorporated into CuPc shows sharp photoemission features. With increasing F{sub 16}CuPc content Fermi level shifts are observed in both phases. In CuPc the maximum shift is about 0.45 eV towards the HOMO level indicating p-doping. Simultaneously the Fermi level in F{sub ...

International Nuclear Information System (INIS)

Certain problems of gamma-absorption method of measuring the thickness of layers in multi-layer items are analyzed. Two examples of solving the above-mentioned problems have been considered. One of them deals with a two-layer item, its integral thickness being known or measured in advance, the second example is referred to a two-layer item with unknown integral value

International Nuclear Information System (INIS)

A novel sodium lead pentaborate, NaPbB5O9, has been successfully synthesized by standard solid-state reaction. The single-crystal X-ray structural analysis showed that NaPbB5O9 crystallizes in the monoclinic space group P21/c with a=6.5324(10) A, b=13.0234(2) A, c=8.5838(10) A, ?=104.971(10)o, and Z=4. The crystal structure is composed of double ring [B5O9]3- units, [PbO7] and [NaO7] polyhedra. [B5O9]3- groups connect with each other forming two-dimensional infinite ?[B5O9]3- layers, while [PbO7] and [NaO7] polyhedra are located between the layers. [PbO7] polyhedra linked together via corner-sharing O atom forming novel infinite ?[PbO6] chains along the c axis. The thermal behavior, IR spectrum and the optical diffuse reflectance spectrum of NaPbB5O9 were reported. -- Graphical abstract: A new phase, NaPbB5O9, has been discovered in the ternary M2O-PbO-B2O3 (M=alkali-metal) system. The crystal structure consists of a novel ...

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.

International Nuclear Information System (INIS)

The spontaneous evolution from ultracold Rydberg atoms to plasma is investigated in a caesium MOT by using the method of field ionization. The plasma transferred from atoms in different Rydberg states (n=22-32) are obtained experimentally. Dependence of the threshold time of evolving to plasma and the threshold number of initial Rydberg atoms on the principal quantum number of initial Rydberg states is studied. The experimental results are in agreement with hot-cold Rydberg-Rydberg atom collision ionization theory. (authors)

Energy Technology Data Exchange (ETDEWEB)

To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the Canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. Bubbles containing ...

Energy Technology Data Exchange (ETDEWEB)

Objective is to study the effects of local structure, interatomic forces, and atom size on the mobility of metal atoms in amorphous silica and at the silica surface. EXAFS studies of Zn and Pt in silica are reported. (DLC)

Energy Technology Data Exchange (ETDEWEB)

Strong-interaction effects have been observed in the x-ray spectra of atoms formed with [Sigma][sup [minus

Science.gov (United States)

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Energy Technology Data Exchange (ETDEWEB)

A summary of the basic principles of K-matrix theory and examples of its applications to atomic spectra are discussed. (AIP)

International Nuclear Information System (INIS)

The thermodynamic aspects of indium-face InN growth by radio frequency plasma-assisted molecular-beam epitaxy (rf-MBE) and the nucleation of InN on gallium-face GaN (0001) surface were investigated. The rates of InN decomposition and indium desorption from the surface were measured in situ using reflected high-energy electron diffraction and the rf-MBE 'growth window' of In-face InN (0001) was identified. It is shown that sustainable growth can be achieved only when the arrival rate of active nitrogen species on the surface is higher than the arrival rate of indium atoms. The maximum substrate temperature permitting InN growth as a function of the active nitrogen flux was determined. The growth mode of InN on Ga-face GaN (0001) surface was investigated by reflected high-energy electron diffraction and atomic force microscopy. It was found to be of the Volmer-Weber-type for substrate temperatures less than 350 deg. C and of the ...

Energy Technology Data Exchange (ETDEWEB)

This work deals with a rational vision of stratospheric ozone including the threats on ozone layer, the verifications and the fears. After a recalling on the ozone layer history, the authors treats the question of the ultraviolets particularly the beneficial effects. Then an explanation of the ozone layer decrease is given. (O.L.). 29 refs., 6 figs.

International Nuclear Information System (INIS)

Analysis of steady-state and transient photoconductivity measurements at room temperature performed on c-axis oriented GaN nanowires yielded estimates of free carrier concentration, drift mobility, surface band bending, and surface capture coefficient for electrons. Samples grown (unintentionally n-type) by nitrogen-plasma-assisted molecular beam epitaxy primarily from two separate growth runs were examined. The results revealed carrier concentration in the range of (3-6)x10"1"6 cm"-"3 for one growth run, roughly 5x10"1"4-1x10"1"5 cm"-"3 for the second, and drift mobility in the range of 500-700 cm"2/(V s) for both. Nanowires were dispersed onto insulating substrates and contacted forming single-wire, two-terminal structures with typical electrode gaps of #approx =#3-5 #mu#m. When biased at 1 V bias and illuminated at 360 nm (3.6 mW/cm"2) the thinner (#approx =#100 nm diameter) nanowires with the higher background doping showed an abrupt increase in photocurrent from 5 pA (noise level) ...

International Nuclear Information System (INIS)

Doping of manganese (Mn3+/Mn4+) into the Aurivillius phase Pb1-xBi4+xTi4-xMnxO15 was carried out using the molten salt technique for various Mn concentrations (x=0, 0.2, 0.4, 0.6, 0.8, and 1). Single phase samples could be obtained in the composition range with x up to 0.6 as confirmed by X-ray and neutron diffraction analysis. Dielectric measurements show a peak at 801, 803, 813 and 850 K for samples with x=0, 0.2, 0.4, and 0.6, respectively, related to the ferroelectric transition temperature (Tc). The main contribution of the in-plane polarization for x?0.2 which was calculated from the atomic positions obtained by the structure analysis is the dipole moment in the Ti(1)O6 layer; however, for x?0.4 the polarization originates from the dipole moment in the Ti(2)O6 layer. Mn doping in the Pb1-xBi4+xTi4-xMnxO15 does not show any long range magnetic ordering. -- Graphical abstract: The dipole moment of TiO6 dependence of x ...

International Nuclear Information System (INIS)

Empirical formulae are proposed for the description of relation between optimum energies minimizing the mean-weighted error of gamma absorption measurement of the thickness of layers in two-layer products with the thickness of every layer from 30 up to 150 mm by carbon. Error of informational parameter approximation with the application of tables does not exceed 10% in case of non-accurate assessment of layers thickness not exceeding 2.5%. Generalized equation is derived which binds main parameters of the task and permits to choose optimum energies with the accuracy sufficient for practical purposes

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).

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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.

International Nuclear Information System (INIS)

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_#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_#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 for ...

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The variations of thickness of the ozone layer over Denmark in the 1978-1994 period based on monthly figures are presented. (CLS)

International Nuclear Information System (INIS)

Silicon layered structures containing porous silicon modified with various thermal treatments and epitaxial layers deposited on porous layers were studied with a number of complementary X-ray diffraction methods using synchrotron source. The methods of characterization included recording of rocking curves for reflections with various asymmetry as well as projection, section and micro-Laue topography. It was found that oxidizing and sintering of porous silicon seriously modified the strains in the porous layer and in some cases even inverting the sense of strain with respect to that in initially formed porous layer. Consequently the deposited epitaxial layer usually was not laterally coherent with the substrate. Some of investigated layers were not stable in time and after few months period exhibited significant lost of coherence of porous ...

Science.gov (United States)

The thermodynamic characteristics of adsorption of sulfur-containing amino acids and their derivatives on the surface of graphitized thermal carbon black were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the S atom in amino acids and the graphite C atom were determined. It was shown that an intramolecular H-bond influenced the adsorption of amino acids on the surface of graphitized thermal carbon black.

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I propose that an interpretation of the interaction of noble gas atoms with metal surfaces as predominantly physisorbing provides the best explanation for the systematics of their binding energies and surface dipoles, as well as for the tendency of noble gas atoms to bind in low coordinated sites. In the present context physisorption is defined as a process driven by the overlap of the electrostatic atomic potentials of the interacting species. (orig.)

British Library Electronic Table of Contents (United Kingdom)

Henry constants for the adsorption of o- and p-phenylenediamines on the surface of graphitized thermal carbon black within the temperature range 433?479 K were calculated by the molecular statistical method. The parameters of the atom-atom potential function of intermolecular interaction between the nitrogen atom in aniline and isomeric phenylenediamines and the carbon atom of the basal face of graphite were determined. It was shown that an intramolecular H bond influenced the geometry and adsorption properties of o-phenylenediamine.

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This two-volume reference uses many equations to provide detailed information on atomic and nuclear decay phenomena.

Energy Technology Data Exchange (ETDEWEB)

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

International Nuclear Information System (INIS)

The use of workstations, controllers or embedded systems and their applications have become much more relevant than previously. PC-based systems, a cooker programmer, applications of, for example, Prolog machines, Unix and Ada papers, Robotics and Automation are typical examples of this. The three keynote addresses of this symposium have as their subjects the most spectacular microcomputer fields and are presented by leading experts. The papers presented cover most of the traditional interests of Euromicro. Special emphasis is given to contributions on the use of workstations and personal computers, on RISC and GaAs and on transputers.

CERN Document Server

Searches for permanent electric-dipole moments (EDM) of atoms provide important constraints on competing extensions to the standard model of elementary particles. Recently proposed experiment with liquid $^{129}$Xe [M.V. Romalis and M.P. Ledbetter, Phys. Rev. Lett. \\textbf{87}, 067601 (2001)] may significantly improve present limits on the EDMs. To interpret experimental data in terms of CP-violating sources, one must relate measured atomic EDM to various model interactions via electronic-structure calculations. Here we study density dependence of atomic EDMs. The analysis is carried out in the framework of the cell model of the liquid coupled with relativistic atomic-structure calculations. We find that compared to an isolated atom, the EDM of an atom of liquid Xe is suppressed by about 40%.

Energy Technology Data Exchange (ETDEWEB)

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 ...

Science.gov (United States)

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

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

International Nuclear Information System (INIS)

A method was proposed and examined to deposit thick cubic boron nitride (cBN)-rich layer of good adhesion to silicon substrate. The method combined (i) the insertion of a thick sp"2 buffer layer, and (ii) the use of an appropriate assist ion beam energy for the growth of the cBN-rich top layer. The sp"2-bonded boron nitride buffer layer was deposited under irradiation of ions with energies in the range of 200-360 eV. The buffer layer was found to contain curled graphitic basal planes, and so was supposed to be relatively deformable, and facilitate the relaxation of stresses in the cBN-rich top layer. The ion assist introduced during the growth of the cBN-rich layer was supposed to both create and annihilate defects, and so resulted in the generation and relaxation of internal stresses. Results showed that the insertion of a 492 nm sp"2 ...

Science.gov (United States)

An experimental realization of the focusing of an atomic beam by a spontaneous radiation pressure force is reported. A simple light field configuration for focusing an atomic beam is described which is formed by four divergent Gaussian laser beams propagating along the + or - x and + or - y directions of a Cartesian coordinate system. An experimental arrangement for the laser focusing is shown, and the experimental procedure is described. The resulting atomic beam profiles are shown and discussed. It is concluded that the experiments open up the possibility of gaining control over such parameters of atomic beams as their density and divergence. 7 references.

International Nuclear Information System (INIS)

Y2Te4O11:Eu3+ and Y2Te5O13:Eu3+ single crystals in sub-millimeter scale were synthesized from the binary oxides (Y2O3, Eu2O3 and TeO2) using CsCl as fluxing agent. Crystallographic structures of the undoped yttrium oxotellurates(IV) Y2Te4O11 and Y2Te5O13 have been determined and refined from single-crystal X-ray diffraction data. In Y2Te4O11, a layered structure is present where the reticulated sheets consisting of edge-sharing [YO8]13- polyhedra are interconnected by the oxotellurate(IV) units, whereas in Y2Te5O13 only double chains of condensed yttrium-oxygen polyhedra with coordination numbers of 7 and 8 are left, now linked in two crystallographic directions by the oxotellurate(IV) entities. The Eu3+ luminescence spectra and the decay time from different energy levels of the doped compounds were investigated and all detected emission levels were identified. Luminescence properties of the Eu3+ cations have been interpreted in consideration of the now accessible ...

International Nuclear Information System (INIS)

Amorphization and a dual implant technique have been used to manipulate residual defects that persist following implantation and post-implant thermal treatments. Residual defects can often be attributed to ion-induced defect excesses. A defect is considered to be excess when it occurs in a localized region at a concentration greater than its complement. Sources of excess defects include spatially separated Frenkel pairs, excess interstitials resulting from the implanted atoms, and sputtering. Preamorphizing prior to dopant implantation has been proposed to eliminate dopant broadening due to ion channeling as well as dopant diffusion during subsequent annealing. However, transient-enhanced diffusion (TED) of implanted boron has been observed in pre-amorphized Si. The defects driving this enhanced boron diffusion are thought to be the extended interstitial-type defects that form below the amorphous-crystalline interface during implantation. A dual implantation ...

Energy Technology Data Exchange (ETDEWEB)

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

Science.gov (United States)

In this paper, we studied vapor-liquid equilibria (VLE) and adsorption of ethylene on graphitized thermal carbon black and in slit pores whose walls are composed of graphene layers. Simple models of a one-center Lennard-Jones (LJ) potential and a two-center united atom (UA)-LJ potential are investigated to study the impact of the choice of potential models in the description of VLE and adsorption behavior. Here, we used a Monte Carlo simulation method with grand canonical Monte Carlo (GCMC) and Gibbs ensemble Monte Carlo ensembles. The one-center potential model cannot describe adequately the VLE over the practical range of temperature from the triple point to the critical point. On the other hand, the two-center potential model (Wick et al. J. Phys. Chem. B 2000, 104, 8008-8016) performs well in the description of VLE (saturated vapor and liquid densities and vapor pressure) over the wide range of temperature. This UA-LJ model is then used in ...

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Science.gov (United States)

... AT THE INTERFACE, A THIN OXIDE LAYER IS OBSERVED ALONG WITH POSSIBLE PALLADIUM SILICIDES. PALLADIUM ...

International Nuclear Information System (INIS)

The authors present an investigation of structural changes occurring in bilayer stacks with crystalline columnar growth when one of the layers is substituted by layers known to grow amorphous. In Co/Cu multilayers the Co layers were substituted by CoZr layers of varying Zr content and layer thickness. Structural characterization was performed by transmission electron microscopy (TEM). They show that the amorphization of the CoZr layers leading to a destruction of the columnar growth depends both on the Zr content and on the thickness of the CoZr layers. Additionally a change to textured growth with a normal to the substrate occurs with increasing Zr content. They explain their observations by a simple picture based on the hard sphere model.

International Nuclear Information System (INIS)

Reflection coefficients of electromagnetic waves in a nonuniform plasma layer with electrons, positive ions and negative ions, covering a metal surface are investigated by using the finite-difference-time-domain method. It is shown that the reflection coefficients are influenced greatly by the density gradient on the layer edge, layer thickness and electron proportion, i.e., the effect of the negative ions. It is also found that low reflection or high attenuation can be reached by properly choosing high electron proportion, thick plasma layer, and smooth density gradient in the low frequency regime, but sharp density gradient in the high frequency regime. (authors)

CERN Document Server

We study spontaneously generated entanglement (SGE) between two identical multilevel atoms in free space via vacuum-induced radiative coupling. We show that the SGE in two-atom systems may initially increase with time but eventually vanishes in the time scale determined by the excited state lifetime and radiative coupling strength between the two atoms. We demonstrate that a steady-state SGE can be established by incoherently pumping the excited states of the two-atom system. We have shown that an appropriate rate of incoherent pump can help producing optimal SGE. The multilevel systems offer us more chanel to establish entanglement. The system under consideration could be realized in a tight trap or atoms/ions doped in a solid substrate.

International Nuclear Information System (INIS)

The scattering of atoms by a resonance standing light wave is considered under conditions when the lower of two resonance levels is metastable, while the upper level rapidly decays due to mainly spontaneous radiative transitions to the nonresonance levels of an atom. The diffraction scattering regime is studied, when the Rabi frequency is sufficiently high and many diffraction maxima are formed due to scattering. The dynamics of spontaneous radiation of an atom is investigated. It is shown that scattering slows down substantially the radiative decay of the atom. The regions and characteristics of the power and exponential decay are determined. The adiabatic and nonadiabatic scattering regimes are studied. It is shown that the wave packets of atoms in the metastable and resonance excited states narrow down during scattering. A limiting (minimal) size of the wave packets is found, ...

International Nuclear Information System (INIS)

We present and characterize an experimental system in which we achieve the integration of an ultrahigh finesse optical cavity with a Bose-Einstein condensate (BEC). The conceptually novel design of the apparatus for the production of BECs features nested vacuum chambers and an in vacuo magnetic transport configuration. It grants large scale spatial access to the BEC for samples and probes via a modular and exchangeable ''science platform.'' We are able to produce 87Rb condensates of 5x106 atoms and to output couple continuous atom lasers. The cavity is mounted on the science platform on top of a vibration isolation system. The optical cavity works in the strong coupling regime of cavity quantum electrodynamics and serves as a quantum optical detector for single atoms. This system enables us to study atom optics on a single particle level and to further develop the field of quantum ...

Energy Technology Data Exchange (ETDEWEB)

An atom-by-atom understanding of life processes is emerging from a flurry of experiments fueled by synchrotron sources and DNA technology. {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}.

Energy Technology Data Exchange (ETDEWEB)

At least quinary alloys form metallic glass upon cooling below the glass transition temperature at a rate less than 10.sup.3 K/s. Such alloys comprise zirconium and/or hafnium in the range of 45 to 65 atomic percent, titanium and/or niobium in the range of 4 to 7.5 atomic percent, and aluminum and/or zinc in the range of 5 to 15 atomic percent. The balance of the alloy compositions comprise copper, iron, and cobalt and/or nickel. The composition is constrained such that the atomic percentage of iron is less than 10 percent. Further, the ratio of copper to nickel and/or cobalt is in the range of from 1:2 to 2:1. The alloy composition formula is: (Zr,Hf).sub.a (Al,Zn).sub.b (Ti,Nb).sub.c (Cu.sub.x Fe.sub.y (Ni,Co).sub.z).sub.d wherein the constraints upon the formula are: a ranges from 45 to 65 atomic percent, b ranges from 5 to 15 atomic percent, c ranges from 4 ...

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This report includes the issuances received during the specified period from the Commission (CLI), the Atomic Safety and Licensing Appeal Boards (ALAB), the Atomic Safety and Licensing Boards (LBP), the Administrative Law Judge (ALJ), the Directors' Decisions (DD), and the Denials of Petitions for Rulemaking (DPRM).

International Science & Technology Center (ISTC)

Investigation of Interaction of Laser Radiation with Radioactive Deposits on the metal Surface and Creation of Experimental Stand for Development of Laser Technology for Remote Treatment of Materials Contaminated with Radioactive Substances at the Atomic Power Plants

UK PubMed Central (United Kingdom)

We present a software system that computationally reproduces biochemical radioisotope-tracer experiments. It consists of three main components: A mapping database of substrate-product atomic correspondents...Full Text Available

International Nuclear Information System (INIS)

Aug 2010 p. 31-35 Japan Kishioka, Kazuhiko Japan Atomic Industrial Forum,

International Nuclear Information System (INIS)

English 2005 p. 52-59 International Atomic Energy Agency (IAEA) Collier,

International Nuclear Information System (INIS)

This patent describes a radioiodinated benzodiazepine derivative. It comprises a lower alkyl group with 1-4 C-atoms and a radioactive iodine.

International Nuclear Information System (INIS)

Experimental results on study of helium concentration influence on degree of molybdenum radiation hardening for various method of cyclotron doping differing in degree and damage character are presented. It is established that accumulation of helium atoms in molybdenum for simultaneous formation of radiation defects caused by low energetic primary-knocked atoms leads to higher degree of hardening than for high energetic ion irradiation. It is shown that with increase of helium atom concentration the degree of radiation hardening for the same level of damage increases. 4 refs.; 3 figs. (author).

International Nuclear Information System (INIS)

... Power Company, Tokyo (Japan) Ishida, T. Japan Atomic Power Company,

Science.gov (United States)

... US Congress, Joint Committee on Atomic Energy, Development, Use, and Control ofNuclear Energy for the Common Defense and Security and for ...

Energy Technology Data Exchange (ETDEWEB)

Nanowires, films, and membranes comprising ordered porous manganese oxide-based octahedral molecular sieves, and methods of making, are disclosed. A single crystal ultra-long nanowire includes an ordered porous manganese oxide-based octahedral molecular sieve, and has an average length greater than about 10 micrometers and an average diameter of about 5 nanometers to about 100 nanometers. A film comprises a microporous network comprising a plurality of single crystal nanowires in the form of a layer, wherein a plurality of layers is stacked on a surface of a substrate, wherein the nanowires of each layer are substantially axially aligned. A free standing membrane comprises a microporous network comprising a plurality of single crystal nanowires in the form of a layer, wherein a plurality of layers is aggregately stacked, and wherein the nanowires of each layer ...

British Library Electronic Table of Contents (United Kingdom)

In this work AISI 1045 steel were duplex treated via plasma nitriding of chromized layer. Samples were pack chromized by using a powder mixture consisting of ferrochromium, ammonium chloride and alumina at 1273K for 5h. The samples were then plasma-nitrided for 5h at 803K and 823K, in a gas mixture of 75%N2+25%H2. The treated specimens were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and Vickers micro-hardness test. The thickness of chromized layer before nitriding was about 8mm and it was increased after plasma nitriding. According to XRD analysis, the chromized layer was composed of chromium and iron carbides. Plasma nitriding of chromized layer resulted in the formation of chromium and iron nitrides and carbides. The hardness of the duplex layer...

Energy Technology Data Exchange (ETDEWEB)

We propose a scheme with potential experimental realization to generate 'polarization' entanglement between two atomic ensembles and show one of the applications - a novel secure communication allowing asymptotically key distribution and quasisecure direct communication. The scheme involves laser manipulation of atomic ensembles, adjustable quarter- and half-wave plates, beam splitters, polarizing beam splitters and single-photon detectors, and well fits the status of the current experimental technology.

International Nuclear Information System (INIS)

An apparatus allowing the photoexcitation of barium atomic beam over its whole surface is described. This photoexcitation is achieved by another barium spectrum emitted up steam of the beam by a cathodic out-flow produced at the exit oven. The fluorescence spectrum is studied in detail as well as the influence of different parameters, such as oven temperature, current intensity of the outflow, and excitation depth. A calculation shows how to determine Einstein coefficient, oscillator strengths and atomic lifetimes from our experimental measurements.

International Nuclear Information System (INIS)

A semi-empirical relation which can be used to determine the total attenuation cross sections of samples containing H, C, N and O in the energy range 145-1332 keV has been derived based on the total attenuation cross sections of several sugars, amino acids and fatty acids. The cross sections have been measured by performing transmission experiments in a narrow beam good geometry set-up by employing a high-resolution hyperpure germanium detector at seven energies of biological importance such as 145.4 keV, 279.2 keV, 514 keV, 661.6 keV, 1115.5 keV, 1173.2 keV and 1332.1 keV. The semi-empirical relation can reproduce the experimental values within 1-2%. The total attenuation cross sections of five elements carbon, aluminium, titanium, copper and zirconium measured in the same experimental set-up at the energies mentioned above have been used in a new matrix method to evaluate the effective atomic numbers and the effective electron densities of samples such as ...

International Nuclear Information System (INIS)

An 'electron-bridge' mechanism of nuclear reaction in an atom or ion by ultra-intense laser fields is presented. A preliminary estimate of the intensity dependence of the rate of disintegration reaction of deuteron nucleus in deuterium atom is made for 800 nm laser fields. For intensities below 5x1021 W/cm2, the rate of disintegration by the 'electron-bridge' mechanism is found to be small, but it rises sharply and becomes large already for ?1022 W/cm2.

Energy Technology Data Exchange (ETDEWEB)

We report measurements of the temperature dependence of the threshold current of GaAs, 1.3-..mu..m InGaAsP, and 1.5-..mu..m InGaAsP double heterostructure lasers using short electrical pulses. T/sub 0/approx.200 K is observed for all the lasers. These high T/sub 0/ values show that the carrier density at threshold does not increase rapidly with increasing temperature in any of the lasers studied and thus the observed low cw T/sub 0/ of InGaAsP lasers is primarily due to a decrease of the carrier lifetime at threshold with increasing temperature.

Energy Technology Data Exchange (ETDEWEB)

Efforts concentrated on updating of the Rockwell reference concept, definition of new system options, studies of special emphasis topics, further definition of the transportation system, and further program definition. The Rockwell reference satellite concept has a gallium arsenide (GaAs) solar cell array having flat concentrators with an effective concentration ratio of 1.83at end of life. Alternatives to this concept includes solid state power amplifiers or magnetrons for dc/RF conversion and multibandgap solar cells for solar to dc energy conversion. Two solid state concepts were studied. It was determined that the magnetron approach was the lowest mass and cost system.

Energy Technology Data Exchange (ETDEWEB)

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

International Nuclear Information System (INIS)

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

British Library Electronic Table of Contents (United Kingdom)

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

Science.gov (United States)

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

Energy Technology Data Exchange (ETDEWEB)

The proton beam has an advantage of the sharp dose falloff in dose distribution called Bragg peak while conventional radiation therapy modalities such as photons exhibit considerable amount of exit dose. To take advantage of this property it is important to know the exact location of the distal dose falloff. An error can cause overdose to the normal tissue or underdose to the tumor volume. The only way of finding out the dose distribution in-situ in particle therapy is to measure the gammas produced by nuclear reactions with tissue materials. Two kinds of gammas can be used: one is prompt gamma and the other is coincident gamma from the positron-emission isotopes. We chose to detect prompt gammas, and developed a prompt gamma scanning system (PGS). The proton beams of the proton therapy facility at National Cancer Center were used. The gamma distribution was compared to the dose distribution measured by an ionization chamber at three different energies of 100, 150, 200 MeV's. ...