bluuebunny/crossref_metadata_2025 huggingface dataset:
Prebaking and silicon epitaxial growth enhanced by UV radiation
Authors: Ishitani A. , Ohshita Y. , Tanigaki K. , Takada K. , Itoh S.
Published: July 2002

UV light irradiation effects on prebaking and silicon epitaxial growth is studied. An ArF excimer laser, a KrF excimer laser, and a Hg-Xe lamp are used as light sources. The epitaxial growth is carried out using a SiH2Cl2/H2 system under reduced pressure. ArF radiation and Hg-Xe radiation are found to be effective for volatilizing native SiO2 on silicon-substrate surfaces even at low temperatures. When a substrate surface is irradiated with these UV radiations during prebaking and epitaxial growth, epilayer surface morphology and crystalline quality are much improved. Furthermore, the epitaxial growth rate seems to be enhanced photothermally by excimer laser radiations, and photochemically by Hg-Xe radiation.
Different ‘‘single grain junctions’’ within a ZnO varistor
Authors: Tao M. , Ai Bui , Dorlanne O. , Loubiere A.
Published: July 2002

The experimental part of this work describes a new method to determine the electrical characteristics of a single ZnO varistor grain-to-grain junction. The experimental results are described in statistical terms because each single barrier has been found to present its own electrical characteristics. There are ‘‘good’’ and ‘‘bad’’ barriers. On the basis of our experimental observations, we present an original approach to describing the current-voltage characteristics of ZnO varistors from the characteristics of individual junctions (series or parallel models). Finally, this work demonstrates that a ZnO sample having a low thickness and a large nonlinear coefficient value requires only ‘‘good’’ junctions.
Rapid thermal annealing of Be+-implanted In0.52Al0.48As
Authors: Lee Wai , Fonstad Clifton G.
Published: July 2002

A capless rapid thermal annealing method has been used to activate Be atoms implanted into n-In0.52Al0.48As. The dependence of electrical activation upon various annealing conditions has been investigated. Annealing at 800–850 °C for 2–3 s yields high electrical activation. Activation efficiencies of 76% and 49% are achieved on InAlAs layers with implant doses of 2×1013 and 2×1014 cm−2, respectively. The lowest sheet resistivity obtained was 2.2 kΩ/⧠ at an implant dose of 1.5×1014 cm−2. Electrical characteristics of Be-implanted p+-n InAlAs diodes are also presented. The forward diode currents were dominated by recombination current components at room temperature. The reverse leakage currents increase with increasing implant doses. Diodes annealed at 800 °C for 2–3 s have the lowest reverse leakage currents.
Experimental study of microwave magnetostatic waves in thin-film yttrium-iron-garnet with a new magnetic-induction probe
Authors: Vlannes Nickolas P.
Published: July 2002

A new high spatial-resolution magnetic-induction probe that measures microwave magnetic field patterns of magnetostatic waves in ferrite thin films has been developed. The probe’s sensing element is either a strand of 25.4-μm-diam gold wire wrapped around a plastic support or an aluminum rectangular loop photolithographically fabricated on glass. The gold wire method yielded a smallest size of 120 μm, and the aluminum loops achieved a highest resolution of 45 μm. The probe is designed for studies of amplitude profiles, dispersion relations, and phase-propagation direction. Investigations of magnetostatic surface waves (MSSW) and backward volume waves (MSBVW) propagating in liquid-phase epitaxially (LPE) grown yttrium-iron-garnet (YIG) were conducted. The LPE-YIG sample used was 4.5 μm thick with the [111] direction perpendicular to the surface of the sample. MSSW and MSBVW of 2–4 GHz microwave frequency were launched in the LPE-YIG, 4.1° from the [01̄1] direction. Studies of MSSW were done under uniform and nonuniform in-plane magnetic bias fields. When contrasted to expected spreading due to diffraction, MSSW in uniform bias fields were found to ‘‘focus’’ as the wave propagated. The ‘‘focusing’’ effect was determined by measurement of the microwave magnetic field profile, transverse to the phase-propagation direction, as a function of propagation distance. As the MSSW propagated, the peak value of the profile increased while the profile width decreased until a maximum profile amplitude occurred, after which the MSSW decreased in amplitude and the width increased. With MSSW and MSBVW in constant uniform bias fields, direct measure of the wavelengths at various microwave frequencies yielded the dispersion relation for each type of wave. Determination of the dispersion relation of MSBVW confirmed the backward nature of these waves.
Investigation of crystalline and optical properties of Al0.48In0.52As grown by molecular-beam expitaxy
Authors: Praseuth J. P. , Goldstein L. , Hénoc P. , Primot J. , Danan G.
Published: July 2002

An investigation of the crystalline and optical properties of AlInAs as a function of the molecular-beam epitaxial growth conditions is reported. The surface reconstruction phases diagram has been established. We show the possibility of growing this material with smooth surface under (Al-In)-stabilized (4×2) reconstructed surface. Such layers present a specific photoluminescence behavior; transmission electron microscopy observations suggest the existence of spinodal decomposition. Films grown under usual (2×4) surface show 2-K photoluminescence peak as narrow as 16 meV (FWHM), but we found that no correlation may be established a priori between the optical and crystalline properties. A high silicon doping study is also reported. We show the segregation and accumulation of Si toward the surface at high level.
The design and simulation of high-voltage Applied-B ion diodes for inertial confinement fusion
Authors: Slutz S. A. , Seidel D. B. , Coats R. S.
Published: July 2002

We present the design of the high-voltage (30 MV) Applied-B ion diode that is now being tested on the PBFA-II accelerator at Sandia National Laboratories. This diode design is the first application of a new set of numerical design tools that have been developed over the past several years. Furthermore, this design represents significant departures from previous designs due to much higher voltage and the use of a nonprotonic ion, Li+. The higher voltage increases the magnetic field strength required to insulate the diode from 1 to 2 T of previous diodes to 3–7 T. This represents a very large increase in the magnetic field energy and the magnetic forces exerted on the field-coil structures. Our new design incorporates changes in the field-coil locations to significantly reduce the field energy and the forces on the field-coil structures. The use of nonprotonic ions introduces a new complication in that these ions will be stripped when they penetrate material, i.e., the gas cell membrane. The importance of current neutralization, charge-exchange reactions, and the conservation of canonical angular momentum are discussed in the context of designing light ion diodes suitable as drivers for inertial confinement fusion. We have simulated the performance of this diode design using the electromagnetic particle-in-cell code, magic. We find that the most sensitive point in the power flow is the transition from the self-magnetically insulated transmission line to the applied field region of the diode.
Ferrimagnetic resonance in garnet films at large precession angles
Authors: Gnatzig K. , Dötsch H. , Ye M. , Brockmeyer A.
Published: July 2002

Perpendicular ferrimagnetic resonance in (111) oriented epitaxial garnet films is excited by strong rf drive fields causing large foldover effects. The precession angle of the magnetization is derived from the measured change of Faraday rotation of linearly polarized light passing through the films. Precession angles of over 60° have been observed. Measurements of the steady-state precession angles are in good agreement with calculations on the basis of Gilbert equations. The transient behavior of the precession, however, is slower than calculated. Conditions to achieve large precession angles are given.
Raman scattering evaluation of lattice damage and electrical activity in Be-implanted GaAs
Authors: Gargouri M. , Prevot B. , Schwab C.
Published: July 2002

Systematic Raman scattering experiments were carried out on [001] GaAs implanted with 70-keV Be+ ions both after implantation for samples subjected to fluences spanning the 1013–1015 cm−2 range and after successive isochronal thermal annealing steps performed between 200 and 900 °C for a selected series of Be doses. The implantation-induced damages were observed via the modifications with increasing fluence, of the first-order Raman line parameters (mainly for the LO peak) classified in terms of mode energy softening and linewidth increase. These modifications were quantitatively accounted for within the spatial coherence-length reduction formalism, which makes it possible to evaluate the mean size of unperturbed regions in as-implanted GaAs. Upon successive thermal treatments, the implanted layers were found to recover their crystalline perfection at a temperature as low as 500 °C. Above this temperature the Be electrical activation is evidenced by the sudden and drastic modification of only the ‘‘longitudinal’’ response, which is interpreted as due to the coupling between the LO phonon and an overdamped plasmon. The detailed analysis of the coupled-mode behavior is presented in the case of p-doped GaAs. From the Raman line-shape analysis, including a near-surface free-carrier depleted zone, we have obtained information about the electrical properties of the layer in terms of carrier density and mobility. It is further shown that in the case of strong damping, the ratio ω2p/Γp, where ωp and Γp are, respectively, the plasmon frequency and damping, is a pertinent quantity since it is proportional to the electrical conductivity. All the reported Raman conclusions agree well with results found in the literature that were obtained from direct electrical techniques. Possible mechanisms involved in the electrical activation of Be in GaAs are briefly discussed.
The fabrication of single heterojunction AlGaAs/InGaP electroluminescent diodes
Authors: Su Y. K. , Wu M. C. , Chang C. Y. , Cheng K. Y.
Published: July 2002

High quality GaAs/AlxGa1−xAs/In0.5Ga0.5P single heterostructure electroluminescent devices have been fabricated by liquid-phase epitaxy. Three different compositions (x=0.45, 0.58, and 0.85) of AlxGa1−xAs layers were made to compare their properties. Diodes fabricated from these heterostructures have been characterized by electron beam induced current, electroluminescence, quantum efficiency, output power, and current-voltage measurements. Emission peak wavelengths and full width at half maximum values of the light emitting diodes are, respectively, 652.5, 654.4, and 652.8 nm, and 67, 67, and 75 meV. The peak wavelengths of the light emitting diode shift 6 meV towards the lower-energy side compared to the photoluminescent peak wavelength of the same electron concentration in the Te-doped In0.5Ga0.5P layer. For most light emitting diodes, output powers and efficiency are in the range of 50–100 μW and 0.062%–0.1%, respectively.
A columnar-growth mode in strained compositionally modulated Cu-Ni: Cross-sectional electron microscopy
Authors: Flevaris N. K. , Karakostas Th.
Published: July 2002

A columnar structure and a toothlike surface morphology were observed for a compositionally modulated Cu6.8-Ni7.0 film by cross-sectional transmission electron microscopy (XTEM). The surface facets were found to be nearly crystallographic planes. The coherency strains are considered, in discussing these XTEM observations, in conjunction with the nonequilibrium growth conditions, x-ray diffraction data, and characteristics of Cu and Ni. Their importance in the growth as well as in determining physical properties of such systems is also discussed.
Growth dynamics of aluminum nitride and aluminum oxide thin films synthesized by ion-assisted deposition
Authors: Netterfield R. P. , Müller K.-H. , McKenzie D. R. , Goonan M. J. , Martin P. J.
Published: July 2002

Some aspects of the dynamics of thin-film synthesis of aluminum nitride and aluminum oxide produced by ion-assisted deposition have been deduced from in situ measurements by ellipsometry, photometry, and ion scattering spectroscopy. Measurements obtained during the etching of aluminum films by nitrogen and oxygen ion beams have established the thickness of the synthesized layer and the rate of compound formation. Some of these measurements have been compared with a theoretical model which predicts the time evolution of the synthesized surface layer as well as the steady-state layer thickness. The breakdown voltage and variation of capacitance with applied voltage of aluminum oxide films prepared by ion-assisted deposition are also presented. Furthermore, the optical properties of ion-assisted AlN and Al2O3 in the visible region are given.
Power transmission capacity of As-S glass fiber on CO laser delivery
Authors: Arai Tsunenori , Kikuchi Makoto , Saito Mitsunori , Takizawa Masaya
Published: July 2002

In this paper we describe the performance of CO laser power delivery over an As-S glass fiber, which has a fluorinated ethylene propylene resin (Teflon FEP) cladding, as well as kinetics of melting break off of the fiber on power delivery. The maximum fiber power output of 15.3 W with an intensity of 12.2 kW/cm2 was obtained by using a fiber whose core diameter was 400 μm and which was not forced cooled. Maximum transmission power was restricted by the thermal damage occurring at the end of the fiber. Kinetics of this thermal damage were investigated by measuring the temperature on the cladding surface and by estimating temperature distribution in the fiber through calculations. The localized heat input at the end of the fiber was estimated at approximately ten times higher than other portions of the fiber.
Particulate metallic glass composite magnetostrictors for interferometric magnetometry
Authors: Brugel D. , Gibbs M. R. J. , Squire P. T.
Published: July 2002

The design of sensor heads for fiber optic interferometric magnetometers is critical when sub-nano-Tesla fields are to be measured. Magnetically soft metallic glasses can exhibit large magnetostrictions and are candidates as materials for this application. However, their usefulness is limited at high frequencies through eddy current losses in bulk materials. This paper discusses the use of particulate metallic glasses in an inert binder. Measurements are presented on magnetization and magnetostriction of these composite materials in the quasi-dc regime. Their dynamic behavior when used as magnetic field sensors is also described.
The Faraday dark space of a He glow discharge
Authors: Kagan Yu. M. , Cohen C. , Avivi P.
Published: July 2002

The axial distribution of the plasma parameters in the Faraday dark space (FDS) was measured in the direction moving from the negative glow to the positive column (PC). The axial electric field and the electron temperature increases, whereas the concentration of electrons decreases. The flow of electrons in the FDS consists of a drift flow, diffusion flow, and thermal diffusion flow. Both the diffusion and the thermal diffusion are individually large but as they are in opposite direction their influence on the current is small. The ratio of the anysotropic part f1 in the velocity distribution function of the electrons to the isotropic part f0 is much higher in the FDS than in the PC. This is due to the gradients of the concentration and temperature of electrons in the FDS.
The diffusion of elements implanted in films of cobalt disilicide
Authors: Thomas O. , Gas P. , Charai A. , LeGoues F. K. , Michel A. , Scilla G. , d’Heurle F. M.
Published: July 2002

The diffusion of several elements implanted into layers of CoSi2 with a nominal thickness of 800 nm, grown by metal-silicon reaction, has been studied by secondary ion mass spectroscopy. Boron has by far the highest mobility. It is totally homogenized by heat treatment for 0.5 h at 800 °C; it displays evidence of grain-boundary diffusion at 400 °C and of lattice diffusion at 450 °C. The next group of elements, gallium, phosphorus, and germanium (used as a tracer in lieu of a silicon isotope) diffuse distinctly less rapidly, and remain nonhomogenized after annealing at 800 °C. The lattice diffusion of arsenic and antimony is not detectable (by the means presently used), even after heat treatment at the same relatively high temperature. Low-temperature effects, and effects far away from the implanted region, are dominated by grain-boundary diffusion. The lattice diffusion increases from boron to phosphorus and germanium, with activation energies determined to be 2.0 and 2.7 eV for boron and phosphorus, respectively. The results are discussed by comparison with those previously obtained with TiSi2.
Hydrogen-induced contamination of III-V compound surfaces
Authors: Proix F. , Sébenne C. A. , Cherchour M. , M’hamedi O. , Lacharme J. P.
Published: July 2002

Specific examples are reported from the study of H/GaAs(110), H2+/GaAs(110), and H/InP(110) systems in which the initially clean surfaces, prepared by cleavage in ultrahigh vacuum, became contaminated through enhanced or displacive reactions involving excited hydrogen. They show that elements forming volatile hydrides can be displaced by atomic or ionized hydrogen onto the sample surface from those parts of the ultrahigh vacuum chamber (walls, equipments) on which they are present. The surface electronic properties were followed by photoemission yield spectroscopy. Comparison with the clean systems shows that the main effects of contamination on these properties concern (i) an irreproducible variation of the ionization energy during the adsorption stage at the lower exposures, and (ii) the nonobservation of the yield quenching phenomenon which appears during the dissociation stage upon heavy hydrogenation in the clean cases.
Collective effects in electronic sputtering of organic molecular ions by fast incident cluster ions
Authors: Salehpour Mehran , Fishel Derry L. , Hunt Jerry E.
Published: July 2002

The collective sputtering effect of fast primary cluster ions on the yield of secondary molecular ions has been demonstrated for the first time. Results show that the sputtering yield of valine negative molecular ions per incident carbon atom, in a C+n incident cluster ion, increases with increasing n. The yield results are interpreted as a direct effect of the enhancement in the electronic stopping power per atom in cluster ions compared to atomic ions.
Modeling of charge-injection effects in metal-oxide-semiconductor structures
Authors: Avni E. , Shappir J.
Published: July 2002

A recently published dynamic balance model which describes gate-oxide degradation following prolonged charge injection is modified. This modification replaces the average electric field in the oxide with the electric field spatial distribution. It is shown that a very close interchangeable relationship exists between the electric field spatial distribution and the spatial distributions of the trapped charge and generated trapping sites. The validity of the new modified model is confirmed for different oxide thicknesses (130–720 Å), injection techniques (hot-electron injection and constant current-tunneling injection), and gate electrode material (aluminum versus polycrystalline silicon). The most attractive feature of the modified dynamic balance model is its ability to describe the steady-state occupation level changes for any given electric field following any oxide stress injection. Furthermore, the modified model is used to propose a new breakdown model which is described in a companion paper.
Diffusion of ion-implanted gold in p-type silicon
Authors: Coffa S. , Calcagno L. , Campisano S. U. , Calleri G. , Ferla G.
Published: July 2002

We report detailed measurements of gold concentration profiles in 〈100〉, p-type silicon. The gold has been introduced by ion implantation and diffused in the temperature range 1073–1473 K and for times ranging from 60 s to 100 h. The resistivity profiles have been converted into gold concentration profiles by using the recently measured value of the entropy factor for the ionization of the gold donor level. The measured profiles and their time dependence can be accounted for by the kick-out diffusion mechanism. The activation energies for the effective diffusion coefficient and for the gold substitutional concentration are 1.7±0.1 and 1.6±0.1 eV, respectively. The resulting flux of silicon self-interstitials is thus described by an activation energy of 3.3±0.1 eV.
Calculation of the traversal time in resonant tunneling devices
Authors: Anwar A. F. M. , Khondker A. N. , Khan M. Rezwan
Published: July 2002

Transmission line techniques are used to calculate the traversal time of electrons in resonant tunneling structures. It is suggested that the real part of the quantum-mechanical wave impedance Re[(2ℏ/m*)ψ′/ψ], at resonance, can be used to calculate the electron traversal time. Furthermore, it is shown that for symmetric structures the lifetime and evolution time of electrons are the same. The sum of the lifetime and the evolution time equals the electron traversal time. Traversal time variations for the asymmetric well are discussed.
Optically detected magnetic resonance studies of donor-double-acceptor recombination processes in n-type GaP crystals
Authors: Ishikawa Yukari , Hayashi Yoshikazu , Itoh Noriaki
Published: July 2002

We have studied luminescence and optically detected magnetic resonance (ODMR) of n-type GaP crystals. Two luminescence bands at 1.5 and 1.7 eV, among which the 1.7 eV one decays faster than the other, are observed in the temperature range between 4.2 and 77 K. An ODMR signal, which shows the same photon-energy dependence as the 1.5-eV luminescence band, is found to have the characteristics of the electrons trapped by shallow donors. We suggest that the two luminescence bands arise from electron transitions from shallow donors to the same double acceptors: the 1.7 eV luminescence is to the doubly occupied acceptors and the 1.5 eV luminescence is to those half-occupied.
On the determination of the density of states in inhomogeneous samples from steady-state space-charge-limited currents
Authors: Sworakowski J. , Nešpůrek S.
Published: July 2002

The reliability of the determination of the density of local states in inhomogeneous samples from space-charge-limited current-voltage characteristics is examined. It is shown that the densities of states may be determined with an error as large as several orders of magnitude, depending on spatial distributions of the states. The energies of the local states may be determined to within a few kT. The equations derived in the paper are applied to experimental results on a-Si:H reported in the literature allowing for a reconstruction of the spatial distribution of local states.
Native acceptor levels in Ga-rich GaAs
Authors: Bugajski M. , Ko K. H. , Lagowski J. , Gatos H. C.
Published: July 2002

A photoluminescence, photocapacitance, and thermal annealing study of Ga-rich GaAs has revealed the complex behavior of acceptor levels at 68–77 and 200 meV above the valence band. The concentration of all levels is enhanced by Ga-rich growth conditions, however, only the 77- and 200-meV levels formed preferably in n-type GaAs are consistent with a double-acceptor model of the gallium antisite defect. In p-type GaAs the 68-meV level associated with a different single-acceptor defect is dominant. It is argued that the inhibited formation of double-acceptor GaAs defects in p-type crystals is caused by the Fermi-energy control of the defect formation.
Spatial distribution of residual shallow acceptors in undoped semi-insulating GaAs
Authors: Wagner J. , Wettling W. , Windscheif J. , Rothemund W.
Published: July 2002

The spatial distribution of residual shallow acceptors in undoped semi-insulating GaAs has been studied quantitatively by electronic Raman scattering with a spatial resolution of ∼50 μm. This acceptor distribution has been correlated with the spatial distribution of the compensating EL2 donor in its neutral charge state measured by near-IR absorption topography. An enhanced acceptor concentration is found in regions which show high-IR absorption: From the comparison with low-temperature cathodoluminescence results, it is found that the intensity of the band-to-acceptor recombination normalized to the band-to-band luminescence intensity reproduces the acceptor distribution measured by Raman scattering. Implications of the present result on the compensation model for undoped semi-insulating GaAs are discussed.
Picosecond relaxation mechanisms in highly excited GaInAsP
Authors: Fox A. M. , Manning R. J. , Miller A.
Published: July 2002

We have investigated the relaxation dynamics of highly excited GaxIn1−xAsyP1−y/InP with 5-ps resolution using a mode-locked 1.054-μm Nd:glass laser. Two samples with band gaps of 1.49 and 1.24 μm were studied at room temperature by the time-resolved nonlinear transmission and transient grating techniques. At excited carrier densities ≳5×1018 cm−3 carrier relaxation times as short as 6 ps have been measured. The results are consistent with ultrafast decay by stimulated radiative recombination, and time-integrated luminescence measurements support this interpretation. We find no evidence for plasma expansion. At lower densities the carrier relaxation is determined by Auger and bimolecular recombination, and longer decay constants in the range 100–500 ps are measured.
Preferred orientation in experimentally deformed YBa2Cu3O6+x
Authors: Wenk Hans-Rudolf , Pannetier Jean , Bussod Gilles , Pechenik Alexander
Published: July 2002

Neutron diffraction data document that [001] axes of YBa2Cu3O6+x in an experimentally deformed polycrystalline aggregate are preferentially aligned parallel to the compression direction. Preferred crystallographic orientation strongly affects oxygen stoichiometry results determined by structure refinement analysis of neutron diffraction data and appropriate corrections are necessary.
Two-dimensional analysis of electrical breakdown in a nonuniform gap between a wire and a plane
Authors: Ramakrishna K. , Cohen I. M. , Ayyaswamy P. S.
Published: July 2002

Electrical breakdown of a gap between a wire (modeled as a hyperboloid) and a plane has been investigated numerically by solving the two-dimensional form of the diffusion flux equations for the charged particle number densities and Poisson’s equation for the self-consistent electric field. Electron impact ionization, thermal ionization, and three-body recombination have been considered as the charged particle production and loss mechanisms. The electrode surfaces are considered to be absorbing and the initial density of the particles is small, but nonzero. A gap length of 0.5 mm is investigated and the gas medium is air or argon at atmospheric pressure. The temporal development of the profiles of ion and electron number densities, potential and electric field, and current growth on both the electrodes are presented when the applied voltage is 1500 and 2500 V for both positive and negative wires. When the wire is negatively biased, the peaks in the radial distribution of both of the charged particle densities near the wire occur off the axis except during the very early part of the breakdown. With positive polarity, the electron density maximum always occurs on the discharge axis, while for ions it moves away from the axis, later in the transient, due to the reverse particle drift in the electric field from the negative polarity case. The discharge spreads farther out into the ambient (almost two times the gap length) when the wire is negatively biased than with positive polarity. The effect of charge separation on the externally applied electric field is significant at voltages 2500 V and higher. Ionization is greater in argon than in air for a fixed potential difference between the electrodes.
Degradation of doped Si regions contacted with transition-metal silicides due to metal-dopant compound formation
Authors: Maex K. , De Keersmaecker R. F. , Ghosh G. , Delaey L. , Probst V.
Published: July 2002

The stability of doped Si with respect to a contacting silicide is investigated for TiSi2, VSi2, CoSi2, ZrSi2, MoSi2, TaSi2, WSi2, and PtSi on As- and B-doped Si by calculation of the critical portion of the ternary diagram. From the thermodynamic calculations it is shown that high B concentrations in Si will be unstable underneath an overlaying TiSi2, TaSi2, and ZrSi2 film. In the case of As-doped Si, high concentrations in Si are unstable with respect to an overlaying TiSi2, TaSi2, ZrSi2, and PtSi film. The effect of metal-dopant compound formation is not expected to occur in the case of VSi2, MoSi2, and CoSi2, and probably also not for WSi2, on B-doped Si. It is similarly not expected to occur in the case of VSi2, CoSi2, MoSi2, and WSi2 on As-doped Si. The relevance of these thermodynamic predictions for technological applications is illustrated by experimental results on the diffusion of B and As from various implanted silicide layers. From comparison of thermodynamic properties of M-P and M-As compounds, it was shown that no advantage is expected from P over As as far as metal-dopant compound formation is concerned.
Two-dimensional diffraction catastrophe on an anisotropic substrate
Authors: Fang Song-Ru , Zhang Shu-Yi , Lu Zheng-Feng
Published: July 2002

The two-dimensional diffraction catastrophe forms on an anisotropic substrate are studied. According to the catastrophe theory, they separately belong to fold caustics and cusp ones. The acoustic fields associated with these caustics are also classified into two categories, and can be expressed by the Airy function and the Pearcy function, respectively. The forms of these two kinds of caustics have been determined by these expressions of the acoustic fields. The experimental verifications have been provided by the surface acoustic wave (SAW) field excited by a circular arc interdigital transducer on YZ-LiNbO3. By means of the dark-field method, we have obtained photographs of SAW caustics. The experimental results agree with our theoretical calculations. We have concluded that it is the velocity anisotropy of the substrate that causes these two kinds of caustics.
Magnetic viscosity in Ni/Cu compositionally modulated alloys
Authors: Bennett L. H. , Swartzendruber L. J. , Ettedgui H. , Atzmony U. , Lashmore D. S. , Watson R. E.
Published: July 2002

The existence of a magnetic aftereffect (magnetic viscosity) in Ni/Cu multilayered alloys was established using a vibrating sample magnetometer at room temperature and at 86 K. It was shown that the effect is strongly dependent on the step field H2 (i.e., the value the field is reduced to after the magnetic moment has been aligned in high field) and exhibits a maximum relaxation rate for values of H2 around the reverse coercive field −Hc. Aftereffect behavior of this type has been observed in other materials, although most often for systems composed of superparamagnetic particles, where the relaxation freezes out at low temperatures. In contrast, the relaxation in the CMA was shown to be enhanced at 86 K over its value at room temperature. New measurements over a wider temperature range show that the enhancement in this sample reaches a maximum near 120 K, but below that temperature the relaxation does freeze out. The temperature of maximum enhancement varies from sample to sample.
Origin of orbital momentum and magnetic anisotropy in transition metals
Authors: Jansen H. J. F.
Published: July 2002

Orbital angular momentum is necessary in order to have magnetic anisotropy. In a magnetic system, orbital angular momentum is caused by spin-orbit coupling as well as by many-body correlation effects. Standard band-structure calculations only include the first of these two contributions. In this paper it is argued that, even in transition metals, the second contribution is probably more important.
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u patterned laser deposition of high-T
c Y-Ba-Cu-O superconducting thin films
Authors: Singh R. K. , Narayan J. , Singh A. K. , Lee C. B.
Published: July 2002

Reliable critical current density measurements have been sucessfully carried out on superconducting thin films which were in situ patterned during the laser deposition process. This method does not require cumbersome wet etching or post-ion-implantation patterning steps for measuring transport critical current densities of thin films. Epitaxial films of YBa2Cu3O7 on (100) SrTiO3 and (100)yttria-stabilized ZrO2 (YSZ) were fabricated at low processing temperatures (500–650 °C) by the excimer laser ablation technique in an oxygen ambient coupled with a dc bias voltage of +300 V on an interposing ring between the substrate and the target. Steel masks of various lateral dimensions were placed close to the substrate to generate various patterns. The superconducting properties obtained at the masked and unmasked areas of the film were similar and reproducible. The thickness and width of the mask have been found to be critical in controlling the superconducting properties of the patterned thin films. Excellent quality superconducting thin films were obtained in the patterned areas. The critical temperature of the films was found to lie in the range of 88–90 K, and the best critical current density values (at 77 K and zero magnetic field) of 1.0×106, 5.0×106, and 6.5×106 A/cm2 were obtained for films deposited on (100) YSZ, (100) SrTiO3 , and (100) LaAlO3 , respectively.
Conductivity tensor of anisotropic composite media from the microstructure
Authors: Torquato S. , Sen Asok K.
Published: July 2002

Perturbation expansions and rigorous bounds on the effective conductivity tensor σe of d-dimensional anisotropic two-phase composite media of arbitrary topology have recently been shown by the authors to depend upon the set of n-point probability functions S(i)1,..., S(i)n. S(i)n gives the probability of simultaneously finding n points in phase i (i=1,2). Here we describe a means of representing these statistical quantities for distributions of identical, oriented inclusions of arbitrary shape. Our results are applied by computing second-order perturbation expansions and bounds for a certain distribution of oriented cylinders with a finite aspect ratio. We examine both cases of conducting cylindrical inclusions in an insulating matrix and of insulating cracks or voids in a conducting matrix.
The spontaneous resistive anisotropy in amorphous and hydrogenated FeZr
Authors: Ma H. , Wang Z. , Kunkel H. P. , Williams Gwyn , Ryan D. H.
Published: July 2002

Measurements of the spontaneous resistive anisotropy(SRA)—basically the difference between the longitudinal and transverse magnetoresistance extrapolated to zero induction—in amorphous FeZr as a function of field (0–1 T) and temperature (1.5–300 K) are presented. The Fe concentrations investigated range from 89 to 92 at. % and the effects of hydrogenation have also been studied. For the hydrogen-free samples a nonzero SRA develops at the ferromagnetic ordering (Curie) temperature Tc and persists to the lowest attainable temperature, with no obvious anomaly in the vicinity of the proposed transverse-spin freezing temperature Txy. With the inclusion of hydrogen, both Tc and the magnitude of the SRA increase, and attempts are made to correlate such increases with the changes in band structure and mean iron moment.
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u measurement of stress in Co/Cu, Co/Pd, and Co/Au compositionally modulated multilayer films
Authors: Awano H. , Suzuki Y. , Katayama T. , Itoh A.
Published: July 2002

Temporal changes of sign and magnitude of the intrinsic stress during ultra-high vacuum deposition of Co/Cu, Co/Pd, and Co/Au compositionally modulated multilayer films (CMF’s) were investigated by means of a cantilever technique. The intrinsic stress corresponding to monatomic layers could be detected during deposition. The intrinsic stress in Co layers deposited on Cu, Pd, and Au layers is tensile and the stress of Cu, Pd, and Au layers on Co is compressive. The intrinsic stress of a Co layer on Cu in Co/Cu CMF approaches near to the ideal critical shear stress of the perfect crystal, 1×1011 dyn/cm2.
Experimental study of the electron density and discharge dynamics in a XeCl excimer laser
Authors: Meyer J. , Elezzabi A. Y.
Published: July 2002

The temporal variation of the electron and current densities as well as the discharge voltage in a XeCl excimer laser discharge is studied as function of gas pressure and HCl+Xe concentration. The results show that independent of pressure and gas mix composition the electron drift velocity is a constant of vd=(1.2±0.2)×106 cm s−1. While in discharges containing only helium the current and electron density are independent of pressure P, both quantities vary as P0.6 once Xe and HCl have been added. The results are examined considering the most important atomic reaction rates.
Characteristics and thermal behavior of W/Si multilayers with well-defined interfaces
Authors: Dupuis V. , Ravet M. F. , Tête C. , Piecuch M. , Vidal B.
Published: July 2002

Multilayers consisting of alternating thin bilayers of W and Si (period: 1.5<d<9 nm) have been analyzed by x-ray scattering (absolute reflectivity, period, mosaicity, interface roughness, crystallinity, and density) and by cross-sectional transmission electron microscopy observations (periodicity, crystalline phase, and damaged area). Our purpose was to determine the thermal properties of the multilayers with respect to the period value under pulsed laser heating (with a nanosecond Nd-YAG laser at different energy densities up to 1 J/cm2 and at a wavelength λ=0.53 μm) and by furnace annealing (250<T<1000 °C under 10−7 Torr pressure). We propose that two distinct diffusion mechanisms are involved in annealings: first, interdiffusion in the amorphous phase and then crystallization into WSi2, the latter related to a period contraction of about 5–10%. The diffusion coefficients and the crystallization temperature depend drastically on the period value. Simulations of small-angle x-ray scattering curves take well into account this thermal evolution. Extinctions and modulations of the intensities of the Bragg peaks are well fitted by thickness and roughness variations.
Interstitial oxygen determination in heavily doped silicon
Authors: Borghesi A. , Geddo M. , Guizzetti G. , Geranzani P.
Published: July 2002

Systematic infrared transmission measurements have been performed on heavily Sb-doped (up to 2×1018 atoms/cm3) silicon samples. The interstitial oxygen content is obtained analyzing the optical response near the 1107-cm−1 oxygen absorption band with a new technique based on a curved baseline, accounting for free-carrier absorption. The results are discussed and compared with those obtained for the same samples by a short baseline technique and by secondary-ion mass spectroscopy (SIMS) analysis. Regression straight-line fits, relative to two lots of 16 samples each, show a good linear correlation between infrared (IR) and SIMS data, although the IR estimates are consistently lower than those obtained by SIMS.
Resist degradation under plasma exposure: Synergistic effects of ion bombardment
Authors: Joubert O. , Fiori C. , Oberlin J. C. , Paniez P. , Pelletier J. , Pons M. , Vachette T. , Weill A.
Published: July 2002

Bulk resist degradation under O2 or Ar plasma exposure is experimentally demonstrated. The degradation mechanisms are analyzed in Ar plasma and a synergistic effect of ion bombardment is presented. Mechanical effects of ion bombardment lead to a surface degradation of the resist whereas thermal effects allow the extension of the degradation to the bulk. Self-diffusion of chains is demonstrated which clearly emphasizes the role of the viscoelastic properties in polymer degradation.
Reflectance anisotropy investigation of the metalorganic chemical-vapor deposition of III-V heterojunctions
Authors: Koch Stephanie M. , Acher Olivier , Omnes Franck , Defour Martin , Drévillon B. , Razeghi Manijeh
Published: July 2002

Using reflectance anisotropy (RA), we investigated in situ the metalorganic chemical-vapor deposition of a number of III-V heterojunctions. Each type of heterojunction exhibits a characteristic RA record as a function of time, depending on the film composition, growth rate, and interface quality, as well as the light wavelength used. Signal changes occurring over different time scales are related to a number of different contributions to the optical anisotropy of the material. Changes during the first 5–10 s are due to the optical anisotropy of both the surface and heterointerface. Over a time scale of several minutes, the signal exhibits damped sinusoidal behavior; a model is proposed to account for these changes, taking into account the interference of light in the growing layer. Finally, the steady-state signal obtained after many minutes is indicative of the difference in surface optical anisotropy between the epilayer and substrate. Practical applications of RA, including heterojunction optimization, superlattice monitoring, and reactor geometry improvements, are also presented.
High power microwave generation from a tunable radially extracted vircator
Authors: Hwang C. S. , Wu M. W. , Song P. S. , Hou W. S.
Published: July 2002

High power microwaves in the dominant TE10 mode emitted from the radially extracted vircator were studied experimentally at the diode voltages from 660 kV up to 1.2 MV and at diode currents from 37 up to 88 kA. The dominant microwave source is in the region of the virtual cathode. The return-current rods on the virtual cathode side of the anode narrows the output microwave frequency. There are dominant frequencies observed in the experiments. For example, three dominant narrow-band microwave pulses were observed at 8.63±0.05, 9.75±0.03, and 10.53±0.03 GHz. They are tunable and scaled linearly with the diode current at the inflection point. All the observed dominant frequencies are in good agreement with the scaling law f=(4.77/d)ln[γ0+(γ20−1)1/2] derived either from the two-dimensional virtual-cathode oscillation or from the one-dimensional harmonic reflexing-electron oscillation. This agreement also confirms that these two oscillations in our vircator generate nearly the same frequency. The maximum observed powers are 120 MW at 8.63 GHz, 75 MW at 9.75 GHz, and 60 MW at 10.53 GHz.
Grain growth processes in ZnO varistors with various valence states of manganese and cobalt
Authors: Chen Ying-Chung , Shen Chi-Yen , Wu Long
Published: July 2002

Grain growth in ZnO ceramics with various valence states of added manganese and cobalt was studied. The results were discussed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grain growth equation: R̄n/t = Γo expR̄n/t=Γo exp( − E/RT). In this work, the grain growth kinetic exponent n was 6 and the activation energy was 301±35 kJ/mol. The grain size increased with the valence states of manganese and cobalt. The addition of CoOx affected not only the mean grain size, grain growth kinetic exponent, and activation energy, but also inhibited the effects of Bi2O3-liquid phase sintering.
Synthesis of new amorphous oxides with ferromagnetic character in iron oxide-based systems
Authors: Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2002

New amorphous oxides with ferromagnetic character have been found in the Sr-Fe-O and Bi-Fe-O systems. The compositions were 35SrO⋅65Fe2O3 (mol%) and Bi3Fe5O12, and the specimens were prepared by using the twin-roller quenching method. The ferromagnetic character was ascertained by means of magnetization measurements at room temperature. Although the magnetization tended to saturate at relatively low external fields for both systems, hyperfine structure in the Mössbauer spectra was barely observed at room temperature for Bi3Fe5O12 only. It is thought that this phenomenon is due to the superparamagnetic behavior of microcrystal-like clusters which may exist in these amorphous oxides.
Characteristics of a cylindrical Langmuir probe of finite length
Authors: Jaeger E. F. , Berry L. A. , Batchelor D. B.
Published: July 2002

The current collected by a finite-length cylindrical probe is calculated numerically from a self-consistent solution to the Poisson–Vlasov system of equations. A Boltzmann distribution is assumed for the electrons, and results are compared to the standard ‘‘orbital-motion-limited’’ theory. When the probe is very long compared to the sheath thickness and the ratio of probe radius to electron Debye length, Rp/λDe ≲ 1, the collected current agrees with the orbital-motion theory for cylindrical probes; when the probe is very short compared to the sheath thickness and Rp/λDe ≲ 1, the collected current agrees with the orbital-motion theory for spherical probes. When the probe length is comparable to the sheath thickness, there is a critical potential above which the probe behaves as a sphere and below which it behaves as a cylinder. Ion charge density, space potential, and ion particle orbits are displayed graphically in the sheath plasma surrounding the probe tip.
Annealing dependence of coercivity, anisotropy field, and resistivity for amorphous CoZrNb films deposited by dc planar magnetron sputtering
Authors: Takahashi T. , Ikeda N. , Naoe M.
Published: July 2002

Amorphous CoZrNb films have been deposited by magnetron sputtering which can greatly improve the utilization efficiency of a magnetic alloy target with high permeability. The saturation magnetization 4πMs of the CoZrNb films was about 14 kG. The easy and hard axes of magnetization of the films were orthogonal to each other in the film plane. The coercivity Hc in the easy and hard directions decreased from 0.9 to 0.2 Oe after annealing in a rotating dc magnetic field HA. However, Hc increased drastically to 20 Oe by heating at the annealing temperature TA of 400 °C. With increasing TA and HA, the anisotropy field Hk gradually decreased from 12 to 1 Oe and the resistivity ρ also decreased from 200 to 150 μΩ cm. Consequently, it was found that Hc and ρ depended strongly on TA; and that Hk had definite relationships with both TA and HA.
Effects of rapid thermal processing on molecular-beam epitaxy GaAs with SiOx encapsulation
Authors: Ito Akira , Usami Akira , Kitagawa Akio , Wada Takao , Tokuda Yutaka , Kano Hiroyuki
Published: July 2002

Variations of deep levels in Si-doped molecular-beam epitaxy (MBE) n-GaAs layers by rapid thermal processing (RTP) were investigated by deep-level transient spectroscopy. RTP was performed at 850, 910, and 1000 °C with SiOx encapsulation. Native deep levels M1 (Ec − 0.18 eV), M3 (Ec − 0.33 eV), and M4 (Ec − 0.51 eV) are annealed out by RTP at a higher temperature (1000 °C) compared with the case of capless RTP. Three electron traps NC1 (Ec − 0.36 eV), NC2 (Ec − 0.48 eV), and EL2 (Ec − 0.81 eV) are produced by RTP. After RTP at 850 and 910 °C, the concentrations of the EL2 decrease with depth from the surface and show no peculiar lateral distribution across the wafer, which is different from that of capless RTP reported previously. The formation of the EL2 is enhanced by the stoichiometry change due to the Ga outdiffusion into the SiOx film during RTP. After RTP at 1000 °C, the outdiffusion of the EL2 is observed near the surface. This result seems to be ascribed to the As loss, since it can no longer prevent the As evaporation at such high temperature. Though it has been reported previously that an N1 trap which has a broad energy level (Ec − 0.5–0.7 eV) is formed in MBE GaAs by RTP without any encapsulation, no N1 trap was observed in a SiOx-capped sample after RTP. We discuss the difference of the EL2 concentration depth profiles between SiOx-capped MBE GaAs and capless samples after RTP, considering the absence of the trap N1 in capped samples.