bluuebunny/crossref_metadata_2025 huggingface dataset:
A constitutive relation for hysteresis in superconductors
Authors: Hodgdon Marion L.
Published: July 2002

A constitutive relation consisting of a differential equation Ḃ=α‖Ḣ‖[ f(H)−B]+Ḣg(H), where Ḣ is nonzero, and an experimentally determined condition imposed at the points where Ḣ changes sign is shown to provide a remarkably good and useful representation of hysteresis in superconductors. The solutions of the differential equation provide expressions for important hysteresis curves. From analysis based on the ideas of the Bean and Kim models, in which the critical current density is related to the width of the major loop, expressions for the major loop are used to establish a system of nonlinear equations for the critical current density, the equilibrium magnetization, and their derivatives. This system of equations can be used to evaluate free parameters in assumed forms for the critical current density. Here, the equations are used to compute values for Jc and Me directly. Sample calculations with analytic forms of f, g, and α, and data from measured hysteresis curves are presented.
A Schottky barrier study of HBr magnetron enhanced reactive ion etching damage in silicon
Authors: Nakagawa O. S. , Ashok S. , Kruger J. K.
Published: July 2002

Hydrogen bromide (HBr) magnetron enhanced reactive ion etching (MERIE) damage on crystalline silicon was investigated by studying the electrical properties of subsequently formed Schottky diodes. After removal of 4000 Å of silicon from p-type and n-type Si wafers in a MERIE system using HBr chemistry, Schottky diodes were formed on the surface and their electrical characteristics evaluated to assess the influence of ion bombardment. In p-type Si hydrogen permeation was found to be the dominant factor of the RIE damage causing deactivation of dopants and Schottky barrier height enhancement. However, such effects can be removed by anneal at 180 °C. On the other hand, no significant changes were observed in n-Si, with or without anneals at various temperatures. In both cases manifestation of ion-bombardment damage was absent, in contrast to what has generally been seen in RIE systems using conventional gas chemistry.
The use of azo-compounds as probes of carbon incorporation of nominally undoped metalorganic vapor phase epitaxy grown GaAs
Authors: Buchan N. I. , Kuech T. F. , Beach D. , Scilla G. , Cardone F.
Published: July 2002

Secondary ion mass spectroscopy has been used to quantitatively determine the carbon concentration in nominally undoped GaAs grown by metalorganic vapor phase epitaxy from TMG (13C 99%) and AsH3. Both an increase in the V/III ratio and the addition of supplemental gas phase radicals reduced the carbon incorporated from the TMG. Higher V/III ratios are proposed to increase the surface concentration of AsHx species. Supplemental gas phase t-butyl radicals, produced from the decomposition of azo-t-butane, are proposed to attack AsH3, also resulting in an increase in the surface concentration of AsHx species. Higher surface concentrations of AsHx are then proposed to reduce carbon incorporation by enhancing the desorption of carbon-containing species.
Pump polarization effects in synchronously pumped mode-locked dye lasers
Authors: Jiang S. H. , Casperson Lee W.
Published: July 2002

The effects of pump polarization on the performance of synchronously pumped mode-locked dye lasers have been investigated. A semiclassical model is derived and the numerical results are compared with experimental data. The theoretical pump polarization dependencies of the pulse shape, pulse width, peak power, and pulse delay have been determined, and experimental data obtained with an argon-pumped rhodamine 6G dye laser are in good agreement with the theory.
Population dynamics of a CO2 laser studied by coherent anti-Stokes Raman scattering
Authors: Kishimoto T. , Wenzel N. , Grosse-Wilde H.
Published: July 2002

We have studied, both in theory and experiment, the operational behavior of continuous wave CO2 lasers by monitoring the ro-vibrational state manifold of the pumping gas N2 by coherent antiStokes Raman scattering (CARS). Detailed information has been gained about the interaction between cavity photons and vibrationally excited N2(X) states for two types of sealed-off and diffusion-cooled CO2 lasers: a radiofrequency excited waveguide laser and a conventional, direct current excited version. CARS spectroscopy permits for the first time an impressive demonstration of the cooling effect of the intracavity photon flux on the vibrationally coupled v=1 state of N2 and the upper laser level involving the asymmetric stretching mode of the CO2 molecule. The kinetic model calculations indicate that the electron number density and electron temperature in the CO2 waveguide laser are higher than usually assumed in the literature.
Quasistatic fields generated by electric and magnetic dipoles located in a partially bounded space
Authors: Boridy Elie
Published: July 2002

The problems of an electric and a magnetic dipole placed at the center of an open spherical, perfectly conducting cavity are analytically investigated. Numerical applications illustrate graphically the theoretical results.
Thermal magnons in bcc cobalt-itinerancy and exchange stiffness (invited)
Authors: Karanikas J. M. , Sooryakumar R. , Prinz G. A. , Jonker B. T.
Published: July 2002

The stable hcp and the metastable bcc phases of cobalt have almost identical nearest-neighbor distances, but substantially different coordination numbers z (zbcc=8, zhcp=12). While z is central to magnetic behavior in insulating systems, these distinctive structural features of cobalt offer an opportunity to address the role of coordination in strong itinerant ferromagnets. We report a room-temperature Brillouin scattering study of surface and bulk spin waves in molecular-beam-epitaxially grown thin films of bcc cobalt. Fitting expressions for the surface and bulk magnon dispersion to the measured frequency shifts versus applied magnetic field provides values for the gyromagnetic ratio, saturation magnetization M, and the exchange stiffness constant D for bcc cobalt. Our results reveal that M is about 10% lower than that of the hcp phase, while D scales with z, a characteristic of an insulating ferromagnet.
Atomic and magnetic spatial correlations in Fe-13.5% V (abstract)
Authors: Cable J. W. , Gillon B. , Mirebeau I. , Parette G. , Nakai Y.
Published: July 2002

Recently, considerable theoretical effort has been directed toward a general understanding of the thermally induced concentration and magnetic moment fluctuations in alloys and the relationship of these fluctuations to alloy phase stability. The atom–atom, atom–moment, and moment–moment spatial correlations that are determined from neutron diffuse scattering measurements can be directly compared to those based on electronic structure calculations and thereby provide stringent tests for the theoretical approaches as well as theoretical assistance in the interpretation of experimental results. These comparisons are best made with single crystal data taken along high symmetry directions but surprisingly little of such data is available. In this paper we report the atom–atom and atom–moment correlations along the three highest symmetry directions for the ferromagnetic bcc alloy Fe-13.5% V. These are compared with and are found to be in excellent agreement with predictions from ‘‘first-principles’’ calculations1 of the same correlation functions.
Fluctuation-induced tetracritical point in the magnetic phase diagram of a quasi-two-dimensional XY antiferromagnet
Authors: Plumer M. L. , Caillé A.
Published: July 2002

Monte Carlo simulation results of the classical antiferromagnetic planar model on a stacked triangular lattice with weak interplanar exchange coupling, and an in-plane applied magnetic field, are reported. The determined field-temperature phase diagram differs significantly from the corresponding mean-field result and shows that tetracritical behavior occurs at H=0, T=TN, similar to that found previously for the cases of isotropic and quasi-one-dimensional magnetic interactions.
Magnetic phase transitions in CsCoBr3
Authors: Farkas A. , Gaulin B. D. , Tun Z. , Briat B.
Published: July 2002

Elastic neutron-scattering measurements have been performed on CsCoBr3, an Ising-like antiferromagnet on a stacked triangular lattice. Three magnetic phase transitions are seen in both zero field and a magnetic field of 2.2 T applied along the stacking direction c. The field does not qualitatively change the behavior near the phase transitions and the transition temperatures are affected only slightly. The high-temperature ordered phase is known to be partially paramagnetic and the transition from the completely paramagnetic phase to this ordered phase was carefully studied. The transition is found to be continuous and characterized by the critical exponent β=0.22±0.01, a result that disagrees with previous measurement. The disagreement can be attributed to a large amount of temperature-dependent paramagnetic scattering that exists in both the paramagnetic and the partially paramagnetic ordered phase.
Spin-phonon renormalization of the excitation energies in Heisenberg magnets
Authors: Drye T. J. , Tucker J. W.
Published: July 2002

Numerical results are presented for the damping of the phonon excitations in a Heisenberg ferromagnet for temperatures up to half the Curie temperature and across the whole Brillouin zone. The results are based on the diagrammatic theory of the influence of spin-phonon interactions in general spin Heisenberg magnets, recently reported by the authors. The results identify four different situations that can be classified according to the ratio ξ = cj/(J+a), where cj is the phonon velocity, J+ the transverse exchange interaction, and a a lattice spacing. These are the high-J+ region with ξ≪1; the equal-J+ region, 1≲ξ≲2.5; the mid-J+ region, 2.5≲ξ<2√3, and the low-J+ region with ξ ≳2√3. A number of features of the phonon damping are observed. The most interesting being the sharp peak in the equal-J+ region arising from the scattering by acoustic spin waves, the rich directional dependence in the mid-J+ region, and the sharp spike just above the onset of the phonon damping in the low-J+ region.
Calculation of hyperfine fields in binary Y-Fe compounds and in Y2Fe14B
Authors: Coehoorn R. , Denissen C. J. M. , Eppenga R.
Published: July 2002

The Fermi contact contribution to the hyperfine fields on Fe nuclei in Y2Fe17, Y6Fe23, YFe3, YFe2, and Y2Fe14B has been calculated by means of first principles self-consistent band structure calculations. The calculated and experimental hyperfine fields are strongly correlated, but, similar to results reported earlier for elemental Fe, the absolute values of all calculated hyperfine fields are systematically too small. The 4s electron contribution to the hyperfine fields is shown to result in significant deviations from a simple proportionality relation between the hyperfine fields and the local Fe moments.
Microscope textures of nematic droplets in polymer dispersed liquid crystals
Authors: Ondris-Crawford Renate , Boyko Evan P. , Wagner Brian G. , Erdmann John H. , Žumer Slobodan , Doane J. William
Published: July 2002

Computer simulations are made of polarizing microscope textures of supramicron-sized nematic droplets with director configurations which commonly occur in polymer and other dispersions. The simulations are computed from polarization rotations and phase shifts caused by nonuniform optical anisotropies of the nematic structure in liquid crystal droplets. The treatment is limited to the case of spherical droplets which are optically soft so that reflection and refraction at the droplet surface, as well as refraction on any internal structure, can be neglected. Simulated polarizing microscope textures of four different director configurations at different orientations are presented graphically. The simulated pictures are shown to compare well with observations of actual nematic droplets viewed under crossed polars.
Epitaxial growth of fcc-Sm/Yb artificial superlattices
Authors: Maeda Atsushi , Satake Tohru , Fujimori Toshinari , Kuroda Haruo
Published: July 2002

Yb metal deposited by a molecular-beam epitaxy technique was grown as an fcc single crystal on a NaCl substrate with an epitaxial relationship in which the Yb (100) [100] is parallel to the NaCl (100) [100]. An epitaxial Sm/Yb superlattice was successfully prepared on this Yb buffer layer at a growth temperature of 290 K. The Sm layers in the prepared superlattices were found to be in the fcc structure which is a new metastable phase. It was also shown that fcc-Sm can be epitaxially grown on the fcc-Yb layer up to a thickness of 3000 Å.
Elastic and thermal properties of mesotaxial CoSi2 layers on Si
Authors: Bai G. , Nicolet M-A. , Vreeland T.
Published: July 2002

Single crystalline 110 nm thick CoSi2 layers formed on both (100)- and (111)-oriented Si wafers by high dose 59Co implantation and thermal annealing were analyzed by x-ray double crystal diffractometry. The lateral mismatch of both (100)- and (111)-oriented samples are similar (∼−0.7%) at room temperature, meaning that the average spacing between misfit dislocations is roughly the same (∼30 nm). But the perpendicular mismatch differs for the two substrate orientations, reflecting the elastic anisotropy of the single-crystalline CoSi2 layers. The three elastic constants of cubic CoSi2 (C11 = 277, C12C12= 222, C44 = 100 GPa) were extracted from these lattice mismatches and the sample curvature measurements. X-ray rocking curves were also recorded up to ∼500 °C. The average spacing between the misfit dislocations remains unchanged, meaning that the misfit dislocations do not shear up to 500 °C. The linear thermal expansion coefficient of CoSi2 (9.5 × 10−6/°C) was obtained under the assumption that the elastic constants do not change with temperature.
Spatial carrier separation evaluated with a relaxation time distribution in doping-modulated amorphous silicon multilayers
Authors: Oheda Hidetoshi
Published: July 2002

The relationship between spatial carrier separation and screening depth of internal electric field in doping-modulated amorphous multilayers is discussed qualitatively based on an analysis of relaxation-time distribution. Since dominant recombination kinetics between spatially separated electrons and holes is considered to be tunneling recombination, the relaxation time is related with mutual distance between carriers. It is found that spatial carrier separation is already incomplete under a very weak excitation intensity of around 0.1 mW or very slight screening of the internal electric field. At the intermediate excitation-intensity region extending over several orders of magnitude until complete screening of the internal electric field is established, the mutual separation between carriers reduces very slowly in accordance with a very gradual increase in screening of the internal electric field. This is a characteristic feature of the doping-modulated amorphous multilayers, and may result from comparable thickness between space-charge region and unit undoped layer in the multilayer.
Stimulated emission and gain measurements in molecular-beam epitaxially grown CdTe
Authors: Hays J. M. , Song J. J. , Wu O. K.
Published: July 2002

Stimulated emission has been observed in molecular-beam epitaxially (MBE) grown films of cadmium telluride (CdTe), using a nanosecond pulsed dye laser as an excitation source. The films were 2.0–2.4 μm thick. Stimulated emission (SE) is seen to arise at several energy positions of the spectra. The different SE peaks exhibited different gain values. The gain was measured using the single beam method, by varying the length of excitation. The bulk CdTe sample studied exhibited stronger saturation effects than those seen in the MBE films.
Resonant level lifetime in GaAs-AlAs double-barrier structures including Γ-X mixing
Authors: Zheng T. F. , Cai W. , Hu P. , Lax M. , Shum Kai , Alfano R. R.
Published: July 2002

A quantitative model for calculation of the lifetime of quasibound states, including the Γ-X transfer, in a AlAs-GaAs-AlAs double-barrier structure is presented. When device is designed that a Γ-like energy level approaches to an X-like energy level, anticrossing of the Γ-X transition occurs and the lifetime of the state can be several orders larger than that of a pure Γ system.
Raman scattering studies of Cd1−xMnxTe films grown on GaAs by pulsed laser evaporation and epitaxy
Authors: Feng Z. C. , Perkowitz S. , Dubowski J. J.
Published: July 2002

We have used Raman scattering to study a series of thin (111) Cd1−xMnxTe (CMT) films grown on (111) GaAs by pulsed laser evaporation and epitaxy. We show Raman spectra of CMT with 0.059≤x≤0.70, at 80 K. Samples with x≳0.4 exhibit up to 8th order combinations of CdTe-like and MnTe-like longitudinal optical phonons, which vary with excitation energy between 2.4 and 2.7 eV. We interpret these overtones as arising from outgoing resonance with the fundamental gap, and present an equation for the mth order phonon line intensity. We confirm the dependence of phonon frequency on x(Mn), and examine the variation of the phonon mode intensities with x(Mn). We also discuss the line widths of Raman and photoluminescence spectra versus x(Mn).
Secondary ion mass spectrometry study of the thermal stability of Cu/refractory metal/Si structures
Authors: Lane L. C. , Nason T. C. , Yang G.-R. , Lu T.-M. , Bakhru H.
Published: July 2002

Evidence is presented for the blocking of Cu diffusion into SiO2 and Si by Ta and Ta/W barriers. The anneal was performed at 450 °C for 30 min. Here, W is rejected as a potential barrier for Cu technology. A Cr layer as thin as 200 Å is shown to limit diffusion into Si to ∼600 Å. The study also demonstrates the utility and versatility of secondary ion mass spectrometry for evaluating potential diffusion barriers, and the need for such corroborative characterization in light of the lesser sensitivity of Rutherford backscattering spectroscopy.
Low-loss, single-mode In0.53Ga0.47As/In0.52Al0.48As/InP optical waveguides fabricated by Zn-induced impurity-induced layer disordering
Authors: Lai R. , Pamulapati J. , Bhattacharya P. K. , Baird R. J.
Published: July 2002

We have investigated the properties of Zn diffusion in the In0.53Ga0.47As/In0.52Al0.48As superlattice and have made optical guides delineated by Zn-induced layer disordering in the multilayers. Measurements on the single-mode waveguides show loses as low as 2.3 dB/cm including coupling loss.
Tellurium and zinc doping in In0.32Ga0.68P layers grown by liquid-phase epitaxy
Authors: Chen Chyuan-Wei , Wu Meng-Chyi
Published: July 2002

In0.32Ga0.68P epitaxial layers doped with Te and Zn were grown on (100) GaAs0.61P0.39 epitaxial substrates by liquid-phase epitaxy using a supercooling method. The electrical properties of doped layers were determined by C-V measurements at 300 K. Room-temperature carrier concentrations ranging from 9×1016 to 2×1018 cm−3 for n-type and from 3×1016 to 6×1018 cm−3 for p-type dopants are obtained reproducibly. The full width at half maximum value of the 300 K photoluminescent spectrum increases with carrier concentration for Te- and Zn-doped layers. The relative intensity of 300-K photoluminescent peak presents the maximum values at 1×1018 and 6×1017 cm−3 for electron and hole concentrations, respectively. The 100-K photoluminescent spectra show three distinctive peaks and their relative intensities change with hole concentrations. Finally, the relationship between the acceptor ionization energy and hole concentration is described.
Enhancement of magneto-optical Kerr effect in Fe/PbTe and Fe/Pb bilayer films
Authors: Cai Jian-Wang , Lu Mu , Zhai Hong-Ru , Miao Yong-Zhi , Wang Hao , Xu Yong-Bing , Huang Hai-Bo
Published: July 2002

The magneto-optical polar Kerr rotation spectra and reflectivity spectra in the wavelength region 400–700 nm are studied for Fe/PbTe and Fe/Pb bilayer films. Large Kerr rotation enhancement with high reflectivity was observed. The experimental data of reflectivity are nearly consistent with theoretical calculation using Fresnel’s equations. However, the observed Kerr rotation spectra behavior is quite different from that expected by macroscopic optical theory.
Aluminum cluster ions generated by a liquid metal ion source
Authors: Sakaguchi Kenji , Mihama Kazuhiro , Saito Yahachi
Published: July 2002

Aluminum cluster ions Al+n are generated by a liquid metal ion source and observed up to n=10 using a magnetic mass analyzer. Relative integrated intensities of cluster ions as a function of n show a distinct step between n=7 and 8, which is explained by the electronic shell model. Cluster ions have lower kinetic energy compared with monomer ions which are accelerated to the full energy. Moreover, energy spread of cluster ions is larger than that of monomer ions. These results are attributed to the difference of ion formation mechanism. In addition to the fully accelerated monomer ions, at a high ion current region there also appear monomer ions with energy deficit which are formed in the same process as cluster ions.
Characterization of insulated gate Ga0.47In0.53As/Al0.48In0.52As heterojunction field-effect transistors
Authors: Leonard T. P. , Bregman J. , Pepper M. , Davies G. J. , Scott E. G.
Published: July 2002

Insulated gate Ga0.47In0.53As/Al0.48In0.52As heterojunction field-effect transistors have been prepared using SiOx and SrF2 insulation and dilute acid and O2 plasma surface cleaning. The leakage current-gate voltage characteristics at different temperatures are analyzed by thermionic and field emission theories to extract the effective barrier heights. The transistor pinch-off characteristics and effective barrier height results are compared with elemental depth profiles obtained from Auger electron spectroscopy. It is concluded that O2 plasma cleaning followed by SiOx gate insulation, is the most suitable technique for fabricating devices and leads to an effective barrier height of 0.3±0.1 V. With refinement this fabrication route should lead to satisfactory room-temperature operation.
Photoluminescence spectra in an applied magnetic field for excitons bound to ionized donors in high-purity, epitaxial GaAs
Authors: Zemon S. , Lambert G.
Published: July 2002

The magnetic-field dependence (0–6.4 T) of the photoluminescence spectra of ionized donor-bound excitons [(D+, X)] has been studied for high-purity GaAs grown by organometallic vapor phase epitaxy. Detailed data were taken on circularly polarized emission, leading to an electron-hole-coupling model which yields total angular momentum values of J=1,2. The effective magnetic-moment g values describing the substate splittings between MJ = +1 and −1 are found to be 0.86 and ≊0.5 for the J=1 and 2 states, respectively. The studies were performed on material with background, donor impurities identified as Si and Ge, yielding a chemical shift between (D+Si, X) and (D+Ge, X) of 0.15 meV at 6.4 T. Well-resolved (D+, X) features were only observed in the highest-purity material (impurity concentrations ≊ low 1014 cm−3). Some results are also reported for a layer grown by molecular-beam epitaxy whose lack of neutral-donor-related features permits the high-energy (D+, X) components to be observed at high fields.
High band-gap hydrogenated amorphous silicon-selenium alloys
Authors: Al-Dallal S. , Aljishi S. , Hammam M. , Al-Alawi S. M. , Stutzmann M. , Jin Shu , Muschik T. , Schwarz R.
Published: July 2002

Hydrogenated amorphous silicon-selenium alloy thin films were prepared by the decomposition of SiH4 and H2Se gas mixtures in a radio-frequency plasma glow discharge at a substrate temperature of 250 °C. The alloy composition was varied by changing the gas volume ratio Rv = {[H2Se]/[SiH4]}. Infrared and Raman spectroscopies were used to probe the bonding structure of the material. In addition to the hydrogen induced bands normally observed in a-Si:H, a new selenium induced band at 390 cm−1, assigned to the stretching mode of the Si—Se bond, was observed. Analysis of the vibrational SiH stretching region reveals the presence of a significant level of (Si)xSe3−xSiH and (Si)ySe2−ySiH2 configurations. Optical and electrical measurements show that increasing the selenium content results in an increase in the optical (Tauc) gap and a decrease in the dark conductivity (σD) and photoconductivity (σph). However, the photosensitivity (σph/σD) remains high for the entire composition range. The Urbach energy and defect density were obtained from subgap absorption measurements. Upon increasing the Se content, a broadening of the band tails and an increase in the defect density were observed. The photoluminescence intensity and width at half-maximum data for the alloys are consistent with the results drawn from the optical absorption measurements.
Carrier removal and changes in electrical properties of neutron irradiated GaAs
Authors: Williams J. G. , Patel J. U. , Ougouag A. M. , Yang S.-Y.
Published: July 2002

The changes in electrical properties of n-GaAs as a result of irradiations with fast neutrons have been studied. Epitaxial layers doped with Si at concentrations in the range 1.35×1015 to 1.599×1016 cm−3 were irradiated with reactor neutron fluences up to 1.31×1015 cm−2. When the changes in carrier concentration, Hall mobility, and resistivity were more than 25% of their initial values, nonlinear dependence on neutron fluence was apparent. New theory is proposed which explains the changes in electrical properties in terms of rates of trapping and release of charges. A theoretical relationship is derived for the change in carrier concentration as a function of neutron fluence and doping level. A linear relationship between neutron fluence and Fermi level shift was found to be consistent with the observed changes in carrier concentration.
Effect of void-size distribution on the Hugoniot state at low shock pressures
Authors: Griffiths David J. , Buettner Douglas J. , Tsou Peter
Published: July 2002

In most theoretical and experimental investigations into the shock response of underdense solid media, the influence of the medium’s mesostructure on the resulting pressure and degree of compaction has not been taken into account. In typical cases examined, shock pressures are well in excess of 1 GPa and this approach is clearly justified. However, at low pressures, calculations show that the distribution of void sizes can affect the final state achieved upon shocking the medium from a given initial porosity. This paper analyzes the response of porous aluminum to low pressure shocking and demonstrates a dependence of the final shocked state on the distribution of void sizes.
Viscosity of molten Pd77Cu6.5Si16.5 and the principle of corresponding states
Authors: Lee S. K. , Tsang K. H. , Kui H. W.
Published: July 2002

The viscosity of Pd77Cu6.5Si16.5 was measured from 995 to 1183 K by capillary flow method. In the experiment, fluxing of the molten specimen by boron oxide was necessary in order to inhibit the formation of crystallites at temperatures near its liquidus. It was found that the viscosity can be described very well by the following Vogel–Fulcher equation: ln η=−3.764+938.543/(T−726), where T is in K. No discontinuity in viscosity was observed at the thermodynamic melting temperature. Recently Tsao and Spaepen [Amorphous Materials: Modeling of Structure and Properties, edited by V. Vitek (The Metallurgical Society of AIME, New York, 1983), p. 323] determined the equilibrium viscosity of the same system near the glass transition temperature. It turned out that the viscosity data from the two regimes cannot be joined together by a single Vogel–Fulcher equation of constant parameters. Finally the present results were compared with those earlier viscosity data of Pd40Ni40P20 and Au77Ge13.6Si9.4 [D. E. Polk and D. Turnbull, Acta Metall. 20, 493 (1972)] to test the validity of the principle of corresponding states for atomic transport properties.
cw laser crystallization of amorphous silicon: Thermal or athermal process
Authors: Ivanda M. , Furić K. , Gamulin O. , Peršin M. , Gracin D.
Published: July 2002

Hydrogenated amorphous silicon films have been deposited by dc magnetron sputtering on different substrates with different thicknesses and hydrogen concentration. The microscopic area of amorphous layers was crystallized by the focused beam of a cw laser. The laser threshold power for transition from the amorphous to crystalline state is dependent on the radius of the laser beam, film thickness, material of the substrate, and hydrogen concentration. These experimental results show that cw laser crystallization of amorphous silicon is a thermally induced process.
The effect of edges on photothermal imaging
Authors: Friedrich Kerstin , Walther Heinz-Guenter
Published: July 2002

The photothermal edge effect was theoretically investigated under the realistic assumption of a Gaussian distributed heating beam, which is not only absorbed at the upper surface of the sample, but because of scattered light also in the vertical plane. The photothermal signal scanned over an edge strongly depends on the detector aperture and in the case of a narrow point-like detector aperture it depends also on the radius R. An explanation of elevations in the signal near the edge is given.
Plasma enhanced chemical vapor deposition and characterization of boron nitride gate insulators on InP
Authors: Bath A. , van der Put P. J. , Becht J. G. M. , Schoonman J. , Lepley B.
Published: July 2002

Thin films of boron nitride have been deposited in a plasma-enhanced chemical vapor deposition system, for use as a gate dielectric layer on InP. The InP substrates were pretreated by in situ HCl vapor etching prior to the film deposition. Borane-dimethylamine and ammonia were used as sources for boron and nitrogen. The depositions were carried out at low temperatures (320 °C), the samples being not directly exposed to the plasma which minimizes radiation damage to the substrates. The deposited films were characterized by ellipsometry, x-ray photoelectron spectroscopy, infrared and ultraviolet−visible spectroscopy. Metal-insulator-semiconductor structures were realized to evaluate the bulk dielectric and insulator−semiconductor interface properties. The growth rates are low (20 nm/h). X-ray photoelectron spectroscopy and infrared measurements showed that the layers are essentially boron nitride, with some boron excess (typically N/B≂0.8). The dielectric films were found to have an optical index n≂1.7, an optical band gap E0≂ 5.8 eV, a resistivity of about 1013 Ω cm and a dielectric constant of 3.5. Frequency dispersion, between 100 Hz and 1 MHz, of capacitance in accumulation did not exceed 10%. The interface state density was in the 1011–1012 cm−2 eV−1 range.
Spectroscopic properties, energy transfer, and laser operation of pulsed holmium lasers
Authors: Kalisky Y. , Kagan J. , Sagie D. , Brenier A. , Pedrini C. , Boulon G.
Published: July 2002

Spectroscopic studies of Er:Tm:Ho:LiYF4 (YLF) and Cr:Tm:Ho:Y3Al5O12 (YAG) crystals were performed, with a detailed analysis of the absorption spectra of Er:Tm:Ho:YLF at 4 K. The dynamics of energy transfer Cr3+→Tm3+→Ho3+ (in YAG) and Tm3+→Ho3+ (in YAG and YLF) were studied utilizing laser-induced fluorescence. Pulsed, free-running laser performance of a freon-cooled Er:Tm:Ho:YLF at −10 and −50 °C, at different current densities with maximum laser energies of 1.5 and 2.25 J/pulse, respectively, was performed.
Splitting and contrary motion of coherent bremsstrahlung peaks in strained-layer superlattices
Authors: Ashrafi S. , Sáenz A. W. , Überall H.
Published: July 2002

The peaks in the spectrum of coherent bremsstrahlung from MeV-GeV electrons in crystalline targets are split into components if the target is a strained-layer superlattice (SLS). We have studied this effect theoretically for an illustrative example; it also entails that when the crystal is rocked, a contrary motion of the split components takes place. Due to their strong dependence on beam orientation relative to a channel axis, these new predicted phenomena should provide a sensitive measure of the strains in SLS layers; but because of the broadening of the photon peaks in thin layers, good observability will be restricted to superlattice layers with a thickness of several hundred Å or more.
Surface analysis of reactive ion-etched InP
Authors: van Roijen R. , Kemp M. B. M. , Bulle-Lieuwma C. W. T. , van Ijzendoorn L. J. , Thijssen T. L. G.
Published: July 2002

A dry-etch process for InP is developed using a mixture of Cl2, Ar, CH4, and H2. This process results in a high etch rate and good anisotropy. The induced damage is investigated by surface characterization after etching, using x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, photoluminescence measurements, and transmission electron microscopy. The etch mechanism is briefly discussed.
S
0 Lamb mode pattern investigation in piezoelectric composite plates through a heterodyne laser probe
Authors: Alippi A. , Bettucci A. , Craciun F.
Published: July 2002

The S0 Lamb mode pattern on the surface of a piezoelectric composite plate is experimentally determined by a heterodyne laser probe at the resonance frequencies corresponding to the symmetrical stop-band edges. A transmission matrix model is used to calculate the surface vibration pattern and a good agreement is obtained between the theoretical and experimental results.
In0.53Ga0.47As metal-semiconductor-metal photodetector using proton bombarded p-type material
Authors: Rao Mulpuri V. , Hong W-P. , Caneau C. , Chang G-K. , Papanicolaou N. , Dietrich H. B.
Published: July 2002

Metal-semiconductor-metal (MSM) photodetectors have been fabricated using as-grown and proton-bombarded p-type In0.53Ga0.47As. Proton bombardment caused a decrease in the dark current, an increase in the breakdown voltage, and an improvement in the speed of the MSM detector. The dark current of the MSM detector with 3×1015 cm−3 proton bombardment is 10 nA at 2 V and 300 nA at 5-V bias. The dc responsivity is 0.7 A/W and impulse response full width at half maximum is 160 ps for 1.3 μm radiation at 5 V bias.
Inelastic electron tunneling spectroscopy of amorphous SiOx barriers
Authors: Mallik R. R. , Kulnis W. J. , Butler T.
Published: July 2002

Inelastic electron tunneling spectroscopy (IETS) is used to record the vibrational spectra of thin films of amorphous SiOx prepared by radio-frequency planar magnetron sputter deposition in argon. The SiOx films are incorporated as the insulating barriers in aluminium SiOx/lead tunnel junctions, with no prior or subsequent oxidation of the aluminium films. Peak assignments are presented by comparison with infrared, Raman, and neutron scattering data for bulk silica, and a plausible stoichiometry is proposed. The SiOx barriers can be considered as model glass substrates for further adsorption studies, and hence extend the analytical capabilities of IETS.
Defect reactivation and structural relaxation in deposited amorphous SiO2
Authors: Devine R. A. B.
Published: July 2002

Si dangling-bond defects present in films of amorphous SiO2 deposited by plasma-enhanced chemical vapor deposition and induced by exposure to ultraviolet radiation present in low-pressure Kr, Kr/20%F, and O2 plasmas have been studied. It is demonstrated that defects are created and self-annealing occurs during the deposition process. It is argued that low deposition rates should result in the least defective films. Exposure to ≊300-nm wavelength radiation reveals defects whereas ≤260-nm radiation bleaches them. The process of excitation-bleaching can be cycled without apparent loss in total defect density. Studies of defect revelation as a function of substrate temperature during exposure down to 80 K indicate that the process is more efficient at high temperature than at low. Thermal annealing and reactivation measurements show that irreversible annealing begins for temperatures ≳400 °C and after 800 °C no measurable densities of defects can be reactivated. This regime is demonstrated to correspond with a change in the microscopic structure of the deposited films.
An effective barrier against the interdiffusion of iron and zinc dopants in InP
Authors: Young E. W. A. , Fontijn G. M. , Vriezema C. J. , Zalm P. C.
Published: July 2002

The diffusion of iron and zinc in InP is studied with secondary-ion mass spectrometry (SIMS). Intentionally doped metalorganic-vapor-phase-epitaxy- (MOVPE-) grown layers as well as ion-implanted samples were investigated. In addition, resistivity measurements were performed on MOVPE-grown, iron-doped InP layers. The diffusion behavior of iron is strongly influenced by the presence of zinc and vice versa. In adjacent regions of iron and zinc-doped layers of InP there is a dramatic interdiffusion of both dopants. The interdiffusion process can be described with a kick-out mechanism in which iron interstitials kick out substitutional zinc. The diffusion of the iron interstitials is an extremely fast transport process in InP, but the concentration of iron interstitials remains below 5×1014 at cm−3. Due to this fast transport, the interdiffusion process proceeds even through barrier layers of (undoped) InP, while in the barrier layer itself the iron concentration remains below the SIMS detection limit (<5×1014 at cm−3). A sulphur-doped, n-type layer of InP stops the diffusion of iron. The semi-insulating properties of iron-doped layers of InP are affected by the interdiffusion process of iron and zinc. Since sulphur-doped InP inhibits the interdiffusion, such a layer can be applied as a barrier layer to separate zinc-doped and iron-doped regions in InP and thus preserve the semi-insulating character of the iron-doped InP.
Theoretical study of a supersonic high-repetition-rate H2+F2-pumped HF laser
Authors: Stricker J. , Waichman K. , Chuchem D.
Published: July 2002

A numerical model for calculating the performance of a premixed pulsed supersonic HF chemical laser, pumped by the H2+F2 chain reaction, is presented. The laser kinetic equations, which are coupled to the supersonic gas dynamics and to the chemical equations, are integrated along the flow direction. The model which has been shown to accurately predict the measured gain coefficients, the lasing induction times, and the laser power output, has been used for parametric studies leading to a better understanding of the laser operation. Conditions for maximum gain and maximum laser energy for each of the input parameters were investigated. The lasing zone length in the flow direction was studied. A comparison between the experimental and calculated results shows that the model can be used to evaluate unknown chemical and energy transfer rates.
The time dependence of the surface-force-induced contact radius between glass particles and polyurethane substrates: Effects of substrate viscoelasticity on particle adhesion
Authors: Bowen R. C. , DeMejo L. P. , Rimai D. S. , Vreeland W. B.
Published: July 2002

Glass particles having mean diameters of 20 μm were deposited onto substrates consisting of cross-linked polyurethane having Young’s moduli of 2.5 and 32 MPa. The surface-force-induced contact radii were then determined, as a function of time for periods between 20 and 3600 min, using scanning electron microscopy. No changes in the contact radius with time was found with either substrate. This suggests that the 0.75 power dependence of the contact radius on particle radius, for particles in contact with polyurethane substrates, previously reported [D. S. Rimai, L. P. DeMejo, and R. C. Bowen, J. Appl. Phys. 66, 3574 (1989)] was not caused by viscous response of the substrate.
Magnetic Co/Al multilayers prepared by planar magnetron sputtering
Authors: Cui F. Z. , Wang J. F. , Fan Y. D. , Li H. D.
Published: July 2002

Structures and magnetic properties of Co/Al multilayers prepared by means of planar magnetron sputtering were investigated. We compare the results with those of the previously reported films fabricated by electron-beam deposition. It is found that remarkable differences exist between the films synthesized by the two methods. For example, the sputtered multilayers show a transition from in-plane to out-of-plane magnetization at a crossover thickness of Co layer from 14 to 7 Å. For samples with tCo ≤ 6 Å, the Co layers were discontinuous. Formation of the CoAl compound in the samples has not been observed.
Morphology of platinum silicide films prepared by conventional and rapid thermal annealing and deep levels induced in silicon
Authors: Dimitriadis C. A. , Polychroniadis E. K. , Evangelou E. K. , Giakoumakis G. E.
Published: July 2002

Electron microscopic studies and the electrical properties of Pt contacts on n-type Si annealed by conventional furnace and rapid thermal annealing (RTA) were investigated with scanning electron microscopy, transmission electron microscopy, x-ray analysis, capacitance-voltage, and deep-level transient spectroscopy measurements. An incomplete reaction between Pt and Si is observed after furnace annealing at 550 °C due to the presence of oxygen in the ambient. An almost complete reaction between Pt and Si is achieved after silicidation by RTA at 550 °C. An acceptorlike level located 0.11 eV below the conduction-band edge with a concentration of 2×1013 cm−3 is detected only after furnace annealing at 550 °C. Silicidation by RTA at 550 °C does not introduce traps in the Si band gap.
Reaction and growth of Yb/Hg1−xCdxTe(110) interfaces
Authors: Raisanen A. , Haugstad G. , Yu X. , Franciosi A.
Published: July 2002

Detailed synchrotron radiation photoemission studies of Yb/Hg1−xCdxTe junctions as a function of Yb coverage were performed at room temperature. Photoemission from physisorbed xenon after cooling the sample to 35 K was also used to examine the local overlayer work function and the development of interface morphology. For Yb coverages less than 6 Å, the data provide evidence for the lateral growth of islands consisting of Yb-Te reaction products involving divalent Yb, and an associated Hg depletion within an 18-Å-thick near-surface layer. Upon island coalescence at an Yb coverage of 6 Å, the formation of a metallic Yb-rich layer at the surface is observed. This layer traps Hg atoms diffusing across the interface through the formation of an Yb-Hg alloy, and is responsible for the nonmonotonic behavior of the Hg interface concentration as a function of Yb coverage.
Electroreflectance and deep-level transient spectroscopy studies of metal/n-InP interfaces
Authors: Shi Z. Q. , Anderson W. A.
Published: July 2002

Electroreflectance (ER) and deep-level transient spectroscopy (DLTS) were used to study the effect of surface treatment and substrate temperature on the characteristics of metal/n-InP. The Franz–Keldysh oscillations (FKO) were observed for all samples. From the period of the FKO, the surface electric field ξ was calculated and found to be a function of reverse dc bias, Vdc, but not ac modulating voltage, Vac. Surface potential and carrier concentration were determined from the plot of ξ2 vs Vdc. The Schottky barrier height φB and surface carrier concentration were found to be 0.46 eV and 8.0×1015/cm3 for the metal-semiconductor (MS) diode deposited at room temperature (RT=300 K). With a thin layer of thermal oxide, the φB was increased to 0.70 eV. For a MS diode deposited at low temperature (LT=77 K), φB was found to be as high as 0.96 eV. DLTS studies of InP MS diodes revealed two extra interface traps on RT diodes and a much higher trap density compared with the LT diode. The results clearly show the effect of surface treatment and substrate temperature during metal deposition on the behavior of MS and metal-insulator-semiconductor interfaces. It is demonstrated that the ER technique can be utilized as an optical Mott–Schottky method. It permits an independent confirmation of surface electric field, doping concentration, and barrier height.
Cracks and critical current
Authors: Kim S. G. , Duxbury P. M.
Published: July 2002

In superconductors, cracks (of width w ≳ ξs) are effective in enhancing local supercurrent, and we calculate the size of these supercurrent hot spots as a function of the crack length a and the London penetration depth λ using the two-dimensional (2D) London theory. In the λ→∞ limit and constant injected current density, we show that this 2D solution is also exact for the current flow in a thin film containing a through crack. We argue that large local supercurrents near a surface crack nucleate vortex creation. If flux pinning is weak enough these vortices flow under the influence of the large local Lorentz force. The dissipation so produced can lead to a reduction in observed critical current. If flux pinning is moderate, the first additional vortices nucleated near the crack tip are pinned, in a region we label ρ, the flux pinning zone. In the case of a through crack in a thin film, we then argue that jc(a) reduces as jc(a)/jc(0) ∼ (ρ/a)x (for a/L≪1), where L is the film width and x =1/2 for the simplest London theory. We compare this theory with the Bean (critical state) model, which predicts that the critical current is (approximately) determined by the cross section available for supercurrent, so that in a film containing a crack, jc(a)/jc(0) ∼ 1 − a/L (ignoring self-field effects). We argue that superconductors with sufficiently weak pinning should obey the hot-spot theory, while sufficiently hard superconductors should obey the critical-state model, and suggest experiments that should illustrate these two limiting cases.
Photoacoustic signals from strongly absorbing gases in the vacuum ultraviolet
Authors: Inagaki T. , Hagihara T. , Furusawa Y. , Hieda K.
Published: July 2002

Photoacoustic (PA) measurements on some molecular gases, such as air and benzene vapor, have been performed by the microphone method in a wavelength range from 300 to 135 nm using synchrotron radiation as a light source. It was found that the amplitude signals in the region of strong absorptions exhibit the minima, instead of the maxima, corresponding to the absorption maxima. Mechanism by which the absorption maxima are inverted to the amplitude minima was found explicable in terms of the thermal diffusion model similar to one examined by Rosencwaig and Gersho [J. Appl. Phys. 47, 64 (1976)] for analysis of the PA signal from solids. The phase signals were found to yield a spectrum that approximates the absorption spectrum.
The stability of cylindrical voids and of cylinders subject to closure by viscous flow or evaporation/condensation
Authors: Shieh S.-Y. , Evans J. W.
Published: July 2002

The stability of a cylindrical pore in an infinite medium, or of an infinite cylinder, when surface energy is significant is considered. The growth of small sinusoidal perturbations by viscous flow (creeping flow) or by evaporation/condensation are examined. The principal results are the dependence of perturbation growth rate on perturbation wavelength. For the creeping flow case no maximum in perturbation growth rate appears. The results are compared with those of Lord Rayleigh [Philos. Mag. 34-207, 145 (1892)] and of Nichols and Mullins [Trans. AIME 233, 1840 (1965)].
0.4–3.0-MeV-range Be-ion implantations into InP:Fe
Authors: Nadella Ravi K. , Rao Mulpuri V. , Simons David S. , Chi Peter H.
Published: July 2002

High-energy (MeV) Be implants in the energy range 0.4–3.0 MeV and dose range 2×1013–6×1014 cm−2 were performed in InP:Fe. Phosphorus coimplantation was used at all Be implant energies and doses to minimize Be redistribution during annealing. For comparison, the Be implant alone was also performed at 1 MeV for a dose of 2×1014 cm−2. The first four moments of the Be implant depth distributions were calculated from the secondary-ion-mass spectrometry (SIMS) data on the as-implanted samples. Variable temperature/time rapid thermal annealing (RTA) cycles were used to activate the Be implant. A maximum of 94% activation was obtained for 875 °C/15-s RTA on the 2-MeV/2×1014-cm−2 Be implant. In contrast to Be-implanted samples, no in-diffusion of Be was observed in Be/P-coimplanted samples. For the annealed samples, two additional Be peaks located at 0.8Rp and 0.9Rp (range) were observed in the SIMS depth profiles.