bluuebunny/crossref_metadata_2025 huggingface dataset:
Susceptibility of Si:P across the metal-insulator transition (abstract)
Authors: Roy A. , Sarachik M. P.
Published: July 2002

We have made static susceptibility measurements at temperatures down to 1.25 K on samples of phosphorus doped silicon with dopant concentrations in the range 0.75<n/nc<1.25, where nc is the critical concentration for the metal-insulator transition. We find that a quantitative knowledge of the diamagnetism associated with the phosphorus dopants is a necessary prerequisite for any quantitative analysis of the paramagnetism in this narrow range of concentration. The data at high temperatures (> 70 K) indicate that the diamagnetic susceptibility in this concentration range is approximately proportional to the concentration, on the basis of which we find it possible to make an estimate of the diamagnetism associated with each dopant. Using this estimate, we show that the paramagnetism at low temperatures (1.25–10 K) exhibits no qualitative change in behavior as one crosses the metal-insulator transition.
Spin rotation in R2Fe14BHx
Authors: Regnard J.-R. , Yaouanc A. , Fruchart D. , Le Roux D. , L’Héritier Ph. , Coey J. M. D. , Gavigan J. P.
Published: July 2002

We have studied by 57Fe Mössbauer spectroscopy and low field magnetization on oriented powders the temperature and hydrogen dependence of the magnetic structure of R2Fe14B compounds with R=Dy, Ho, and Y. We show that the iron sublattice may be canted by an angle ≂15° at high temperature. Hydrogen increases this canting at low temperature. It increases the spin reorientation temperature measured by bulk magnetization for Ho2Fe14B and induces a spin reorientation in the Dy alloys. These effects show that the strength of the crystal field terms of fourth (and maybe sixth) order compared to the terms of second order is increased by hydrogen.
Magnetic excitations in Fe-doped Mn3Si
Authors: Cowley E. R. , Tomiyoshi S. , Yamaguchi Y. , Ohashi M. , Shirane G.
Published: July 2002

Inelastic scattering of neutrons has been used to study the magnetic excitations in Fe-doped Mn3Si at 7 K. Mn3Si is an incommensurate antiferromagnet with magnetic Bragg points of the form (h,k,l)±(δ,δ,δ) with δ=0.425. Its magnetic excitations are qualitatively similar to those of the γ-Mn alloys, or of the itinerant antiferromagnet, chromium. The addition of 5 at. % of iron causes the value of δ to change to 1/2, so that the material becomes a commensurate antiferromagnet, greatly simplifying the shape of the excitation spectrum. In addition the low Néel temperature (23 K) permits measurements to be extended to energies of several times kTN. Constant energy scans through a magnetic Bragg point are qualitatively consistent with the spin-wave dispersion relation forming a ‘‘cone’’ around the magnetic Bragg point. Low-energy scans (1 meV≤ΔE≤4 meV) are centered on the Bragg point and flat-topped, while at higher energies (5 meV≤ΔE≤15 meV) the peak is clearly resolved as double. A fit using a damped-harmonic oscillator cross section suggests that the slope of the dispersion relation increases with energy, and that the excitations are highly damped.
Penetration depths of antiferromagnetic superconductors: NdRh4B4 and SmR4B4 (abstract)
Authors: Hou M. K. , Huang C. Y. , Maple M. B. , Torikachvili M. S. , Kozlowski G.
Published: July 2002

We have investigated two antiferromagnetic superconductors, NdRh4B4 and SmRh4B4, which exhibit two quite different temperature dependencies of the upper critical field arising from two different mechanisms1 of the modification of superconductivity by the presence of antiferromagnetism. In order to further study these mechanisms, we have investigated the electromagnetic properties and have measured the penetration depths λ(T) of NdRh4B4 (Tc=5.45 K, TN1=1.31 K, and TN2=0.89 K) and SmRh4 B4 (Tc=2.2 K, TN=0.9 K), employing a tunnel diode oscillator at ∼30 MHz. Above the antiferromagnetic transition temperature (TN1 for NdRh4B4 and TN for SmRh4B4), the temperature dependencies of the penetration depths of these two superconductors fit the BCS theory well. We have found λ(0)=2170 and 980 Å for NdRh4B4 and SmRh4B4, respectively. However, as temperature is lowered, λ(T) for NdRh4B4 increases near TN1 and then saturates near TN2, presumably owing to the molecular field effect.2 The spin-fluctuation effects,2 expected to be significant near TN2 for NdRh4B4 and TN for SmRh4B4, have not been observed within our experimental accuracy.
Reply to ‘‘Comment on ‘Small-angle neutron scattering evidence for the absence of long-range magnetic order in amorphous Fe91Zr9’ ’’ [J. Appl. Phys. 5
7, 3407 (1985)]
Authors: Fish G. E. , Rhyne J. J.
Published: July 2002

Experimental evidence is presented and reviewed that amorphous Fe91Zr9 does not exhibit conventional long-range ordered ferromagnetism below its Tc=210 K, but rather enters a state characteristic of a strongly exchange-frustrated system in which the ferromagnetic correlations are quite short range (less than 30 Å) as determined by small-angle neutron scattering (SANS). At a lower temperature the SANS develops a Lorentzian-squared component to the line shape which is evidence of cluster spin freezing. Inelastic scattering data show no resolvable spin-wave peaks and place an upper limit of 12–15 meV Å2 on the spin stiffness D. The anomalously small ratio of D/Tc is further evidence of a system near a multicritical point concentration.
Explosive-driven magnetic flux cumulation by the propagation of shock-compressed conductive region in highly porous metal powders
Authors: Nagayama Kunihito , Mashimo Tsutomu
Published: July 2002

The explosive-driven magnetic flux cumulation process by the convergence of high-pressure shock waves in highly porous metal powders has been studied experimentally. The field-multiplication ratio depends mainly on the initial density of powder, although the flux compression signal has been detected for all the powders tested. Extremely light aluminum powders of initial density, of about 0.41 g/cm3 is shown to be the most promising within this experiment. The time evolution of flux density, i.e., B(t) for the case of light metal powders (Al and Mg), can be well approximated by the inverse power law. The results are explained by the magnetohydrodynamic theory.
Aging kinetics of magnetic losses in annealed Fe78B13Si9 amorphous-metallic alloy
Authors: Liebermann H. H.
Published: July 2002

The stability of magnetic properties is of critical importance in the acceptance of amorphous-metallic alloys for use in various applications. The change in magnetic losses after isothermal high-temperature aging is shown to follow first-order kinetics. The temperature dependence of the first-order rate constant is well described by a simple Arrhenius relation. Empirical equations are established and extrapolated to predict long-time, low-temperature stability of magnetic losses. Aging kinetics of magnetic losses are shown to be faster than crystallization kinetics for the particular experimental data considered. As magnetic-loss stability is expected to increase to that of stability against crystallization, provided that appropriate aging environmental precautions are taken, it appears that neither bulk crystallization nor environmentally induced magnetic-property degradation are expected at typical transformer-operating temperature and life.
Magnetic phase transitions in nanocrystalline erbium
Authors: Cowen J. A. , Stolzman Barry , Averback R. S. , Hahn H.
Published: July 2002

Nanocrystalline samples of 99.9% pure erbium with particle sizes between 10 and 70 nm have been produced by the inert gas condensation technique. Magnetic susceptibility measurements on samples compacted to between 50% and 75% of bulk density indicate a modification in the high-temperature phases and superparamagnetic behavior at low temperatures. ESR signals near g=10 are probably due to Er compounds which may form during the production process.
Residual magnetism effects on the eddy current nondestructive test signal
Authors: Palanisamy R.
Published: July 2002

Nondestructive test techniques based on the principle of eddy currents are being widely used in manufacturing industries to assure internal and surface qualities of materials and components. A problem often encountered in the nondestructive testing of ferrous products is the residual magnetism introduced by some manufacturing processes prior to the testing. Existing industrial specifications on the acceptable level of residual magnetism prior to eddy current testing are considered too conservative. The purpose of this investigation was to determine experimentally the change in eddy current flaw signal amplitude as a function of residual magnetic field intensity in ferrous products. Specimens having artificial flaws of known dimensions were eddy current tested at different frequencies and at different residual magnetic field intensities. Results of these experiments are discussed in this paper.
Automated magnetization measurements
Authors: Barlow R. D. , D’Agostino M. , Hill E. W. , Jones M. R. B. , Pointon A. J. , Whall T. E.
Published: July 2002

An automated vibrating sample magnetometer (VSM) has been constructed in order to facilitate measurements of the magnetization of conducting samples of different fields and temperatures over a period of time. The principal features of the VSM are large amplitude oscillations, low-frequency, stable horizontal sinusoidal motion, a 12-coil detection system to allow compensation for image effects, and a state-of-the-art automated detection system.
Magnetic microstructure of amorphous alloys studied using scanning electron microscopy with polarization analysis (abstract)
Authors: Unguris J. , Hembree G. G. , Celotta R. J. , Pierce D. T. , Aroca C.
Published: July 2002

The recent development of scanning electron microscopy with polarization analysis (SEMPA) has made the direct measurement of magnetic structures with submicron spatial resolution possible.1,2 Because the secondary electron spin polarization is proportional to the magnetization in the area probed by the incident electron beam, the magnetization is measured directly, independent of topographic contrast. Topographic images are measured simultaneously, however, permitting comparisons between magnetic and structural properties. In addition the use of multiple, orthogonal detectors permits measurement of the magnetization magnitude and direction. We have recently used this technique to look at various Fe-rich amorphous ferromagnetic alloys. In particular SEMPA was used to examine the rotation of the magnetization within domain walls and to study changes in magnetic microstructure due to Ar ion bombardment and annealing.
Polymorphism of amorphous pure iron
Authors: Xiao Gang , Chien C. L.
Published: July 2002

We investigate the state of amorphous pure Fe by utilizing various Fe-based amorphous alloy systems having stable amorphous phases up to very high Fe concentrations and extrapolating the properties toward those of amorphous pure Fe. Concentration dependence of hyperfine interaction parameters of Fe-early transition metal (Ti, Zr, Hf, Nb, Ta, and Mo) and Fe-metalloid (B, Sb, Si, and Ge) reveals the polymorphism of amorphous Fe.
Direction of the easy axis in amorphous Tb-Fe (abstract)
Authors: Hellman F. , van Dover R. B. , Gyorgy E. M.
Published: July 2002

Detailed examination of the angle of the effective easy axis in dual-gun cosputtered amorphous Tb-Fe shows an unexpected small deviation from the normal to the film. In other respects, the magnetic properties of films prepared by codeposition are quite comparable to those prepared by other means.1 The easy axis is tilted in the plane normal to the film and parallel to the line connecting the two sources during deposition. The tilt angle is a strong function of film thickness, composition, deposition temperature, and the incident angles of the Tb and Fe vapor beams. The most peculiar result found is a large jump in the angle at the compensation composition for thick (5000-Å) samples grown at room temperature. Bright-field transmission electron microscope (TEM) images of the films show them to be smooth and featureless. A comparison of x-ray, TEM, and magnetic measurements on films prepared under a variety of conditions show the relationship between the microstructure and the tilted easy axis.
Resistivity effects in the Ce(Pd,Rh)3B1 and Ce(Rh,Ru)3B2 system
Authors: Perez I. , Croft M. , Liang G. , Zhou J. B. , Shaheen S. A. , Jhans H.
Published: July 2002

We report Ce-L3-valence state and temperature-dependent resistivity results on two pseudoternary alloy series: CeT3Bn where n=1 with T=(Pd, Rh) and where n=2 with T=(Rh,Ru). Our results indicate that both series pass continuously from a Kondo local-moment regime to a mixed valent regime to a saturated valence regime with decreasing 4d electron concentration on the T sublattice. We correlate the temperature-dependent resistivity results with the Ce-L3-valence variation for both series. For the n=1 series, Kondo-type behavior appears in the local-moment regime, while for the n=2 series, ferromagnetism appears in the local-moment regime. We also note that in the mixed valence regime, for both series, the absolute value of the resistance drops rapidly, indicating a loss of magnetic scattering.
Neutron scattering study of the spin ordering in amorphous Tb45Fe55 and Tb25Fe75
Authors: Spano M. L. , Rhyne J. J.
Published: July 2002

Small-angle neutron scattering measurements (SANS) have been made on Tb45Fe55 and Tb25Fe75 as a function of temperature. The SANS results show that long-range ferromagnetic order is quenched in these alloys and is replaced by a spin-glass-like state. For T>Tc, where Tc is the transition temperature, both samples exhibit a conventional Lorentzian line shape (in q), but they depart from this form below Tc. We have fitted the low-temperature line shapes with the Lorentzian plus Lorentzian-squared form appropriate for random field systems. As the temperature of the Tb45Fe55 alloy is lowered, the correlation length ξ rises to a rounded maximum of about 80 Å at 250 K (Tc =298 K) and decreases to about 60 Å at 5 K. In contrast, ξ in the Tb25Fe75 alloy exhibits a cusplike form reaching a resolution limited value between 400 and 410 K before declining slowly to 55 Å at low T. In both alloys the coefficient of the Lorentzian term rises sharply as T→0, whereas the Lorentzian-squared coefficient follows approximately the square of the order parameter divided by the correlation length. Both systems thus lend support to the suppression of long-range order by the random anisotropy field.
Evidence for weak link and anisotropy limitations on the transport critical current in bulk polycrystalline Y1Ba2Cu3Ox
Authors: Ekin J. W. , Braginski A. I. , Panson A. J. , Janocko M. A. , Capone D. W. , Zaluzec N. J. , Flandermeyer B. , de Lima O. F. , Hong M. , Kwo J. , Liou S. H.
Published: July 2002

Measurements of the transport critical-current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak-link regions between high Jc regions. The weak-link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain-boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 Å). The effect of intrinsic conduction anisotropy is discussed. A current-transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.
Interferometric determination of the refractive index of optical fiber cladding and an examination of its homogeneity
Authors: El-Hennawi H. A. , El-Diasty F. , Meshrif O.
Published: July 2002

The refractive index of optical fiber cladding has been measured to an accuracy of 1×10−4 using multiple-beam Fizeau fringes. The interferometric method has been also used as a control on the process of cladding production by examining the homogeneity of fiber cladding.
Enhanced elimination of implantation damage upon exceeding the solid solubility
Authors: Jones Kevin S. , Prussin S. , Weber E. R.
Published: July 2002

Implantation of silicon wafers with Ga and P, under specific conditions, results in enhanced category-II (end of range) dislocation loop elimination after short thermal cycling. Comparison of these results with transmission electron microscopy studies of Si-, Ge-, As-, Al-, and Sb-implanted samples indicate that the enhanced elimination process occurs only when the peak of the impurity concentration exceeds the solid solubility of the impurity in silicon at the annealing temperature and the resulting precipitates are dissolving. The activation energy for enhanced elimination of these extrinsic catetory-II dislocation loops is shown to be 5±0.5 eV. It is proposed that vacancy emission by the dissolving precipitates is responsible for the enhanced elimination.
Multilayers of HgTe-CdTe grown by low-temperature metalorganic chemical vapor deposition
Authors: Williams L. M. , Lu P.-Y. , Chu S. N. G. , Wang C.-H.
Published: July 2002

This paper describes the growth of multilayers of HgTe-CdTe on cadmium telluride substrates using metalorganic chemical vapor deposition. These structures were grown using a novel precracking technique that allows growth of the multilayers at low temperatures from the source gases dimethylmercury, dimethylcadmium, and diethyltelluride. Cross sections of several samples were examined using scanning electron microscopy and transmission electron microscopy; these samples were found to have sharp interfaces. The structures for this study are the most sophisticated multilayers of HgTe-CdTe ever grown by metalorganic chemical vapor deposition.
Negative-resistance characteristics of polycrystalline silicon resistors
Authors: Ramkumar K. , Satyam M.
Published: July 2002

This paper presents a theoretical analysis to explain the origin of the observed negative-resistance characteristics of polycrystalline silicon resistors. This analysis is based on the effects of self-heating of the resistor on the transportation of carriers across the grain-boundary barrier.
Depth profiling by particle-induced x-ray emission analysis using a parameter-fitting technique
Authors: Yamada Kenichi , Kido Yoshiaki
Published: July 2002

A parameter-fitting technique has been developed to draw depth information by particle-induced x-ray emission analysis with 0.5–3.0-MeV He+ beams. In principle, it is possible to determine a depth profile of a target element of interest whose distribution is defined by n parameters (aj), if the x-ray yields are measured for different n incident energies Ei(i=1,2,...,n). In this case, one can calculate the x-ray yield Y(Ei) and get such combinations (aj) that give the x-ray yield coinciding with the measured one. Thus, one obtains n coupled equations, Y(Ei)=Fi(aj), which can be solved graphically as the crossing point in the n-dimension space of (aj). This technique is applied to analysis of the target structures which can be defined by one or two parameters such as multielemental and multilayered structures and interdiffusion and range profiles.
Carrier dynamics in quantum wells behaving as giant traps
Authors: Debbar Nacer , Bhattacharya Pallab
Published: July 2002

An Arrhenius-type of expression is derived for the emission rate of electrons from a quantum well on the basis of detailed balance principles. The formulation is applied to a 150-Å In0.2Ga0.8As/Al0.16Ga0.84As strained single quantum well grown by molecular beam epitaxy. From an analysis of the data it is possible to estimate the conduction band offset ΔEc, which may be extremely useful for strained systems.
Photoluminescence in strained InGaAs-GaAs heterostructures
Authors: Gal M. , Taylor P. C. , Usher B. F. , Orders P. J.
Published: July 2002

Photoluminescence in strained InxGa1−xAs-GaAs single heterostructures, grown by molecular-beam epitaxy, is studied, and the critical layer thickness is determined for a range of In mole fractions. The critical thicknesses are compared with similar values measured on the same layers by double-crystal x-ray diffraction. Both techniques give essentially the same results. The photoluminescence line shapes are discussed for layer thicknesses below and above the critical thickness.
Polybenzimidazole as a thermally stable Langmuir–Blodgett film insulator in InP metal-insulator-semiconductor devices
Authors: Fowler M. T. , Suzuki M. , Engel A. K. , Asano K. , Itoh T.
Published: July 2002

In order to fabricate metal-insulator-semiconductor (MIS) devices on III-V semiconductors it is often necessary to use deposited insulators, since these semiconductors do not form native oxides of the quality found with the Si/SiO2 system. Langmuir–Blodgett (LB) organic thin films have previously been investigated as such insulators. Unfortunately, conventional LB films have too low a melting point (about 70 °C) for practical applications. We have studied films which are spread as a monomer, then polymerize on the water surface to form poly [1,4-phenylene-5,5′(6,6′)-bibenzimidazole-2,2′-diyl] (PBI). We show that deposited films of PBI have the repeatable and finely controllable thickness of conventional LB films, but remain fairly stable when subjected to temperatures up to 400 °C. Using PBI LB films as a gate insulator we have fabricated working depletion mode MISFET structures on n-type indium phosphide with gate lengths down to 1.2 μm.
Rapid thermal annealing of InP using GaAs and InP proximity caps
Authors: del Alamo Jesús A. , Mizutani Takashi
Published: July 2002

Rapid thermal annealing of InP in an inert atmosphere is demonstrated using face-to-face GaAs and InP proximity caps to protect the active surface from decomposition. No surface damage of any kind is detected by optical microscopy, photoluminescence spectroscopy, or Raman scattering on samples annealed for 4 s at temperatures up to 850 °C. As application, the rapid thermal annealing of Si-implanted InP samples is carried out. Full activation of the implanted species is obtained at annealing temperatures of 850 °C. Rapid thermal annealing of InP using a GaAs proximity cap promises to be a practical technology for the fabrication of semiconductor devices based on InP.
Study of induced uniaxial anisotropy in magnetic thin films by transverse susceptibility
Authors: Le Dang K. , Veillet P. , Suran G. , Ounadjela K.
Published: July 2002

The transverse susceptibility was measured in Co86Ti14 ferromagnetic thin films which possess an induced in-plane uniaxial anisotropy, as a function of a dc magnetic field H applied parallel to the hard axis. The susceptibility reaches a sharp maximum when H is close to the value of the anisotropy field HK previously determined. A theoretical model based upon a small deviation of H from the hard axis is developed to evaluate the angular dispersion of HK.
Effects of tunneling on a-Si:H Schottky barriers
Authors: Mariucci L. , Gislon P. , Coluzza C. , Frova A.
Published: July 2002

Schottky diodes have been prepared by depositing semitransparent metallic films (Pd, Cr, and Au) onto hydrogenated amorphous silicon (a-Si:H) grown by the glow-discharge method. The a-Si:H was n doped and undoped presenting different densities of gap states (Ns). Barrier heights Φb were measured by internal photoemission and correlated to Ns. The activation energies were also determined. The results are understood in terms of both thermionic-field-emission tunneling and resonant tunneling through localized states of the conduction-band tail. It is found that the latter tunneling effect has a remarkable influence on the experimentally determined value of Φb.
Bipolar junction formation in the case of molecular materials
Authors: Simon J. , Tournilhac F. , André J.-J.
Published: July 2002

The standard model of junction formation based on delocalized electronic levels is highly inappropriate in the case of molecular materials that are constituted of individual molecular units subsequently condensed into a material. A model is proposed to describe the electrical characteristics arising at interfaces between p- and n-doped molecular materials. Two antagonistic forces will govern the amount of charge transfer giving rise to the space-charge region (i) the driving force is given by the difference in redox potentials between the electron donor and the electron acceptor (ii) the opposite force is due to ion-ion repulsions between ionized impurities. A numerical calculation permits the estimation of the characteristics of the space-charge region and demonstrates that minute amounts of impurities must be present within the materials; doped insulators, therefore, cannot lead to well-behaved devices.
Study of the dislocation mechanism responsible for the Bordoni relaxation in aluminum by the two-wave acoustic coupling method
Authors: Bujard M. , Gremaud G. , Benoit W.
Published: July 2002

The most realistic model for the interpretation of the Bordoni relaxation observed by internal friction experiments is the mechanism of kink pair formation (KPF) on the dislocations. However, according to this model, high values of the critical resolved shear stress should also be measured at low temperature in face-centered-cubic (fcc) metals, but this has never been observed. Using the newly developed two-wave acoustic coupling method, we have studied the reality of the KPF model as an explanation for the Bordoni relaxation in aluminum. The results are in very good agreement with the predictions of the KPF model and thus confirm this model. On the other hand, experimental evidence that the kink mobility is very high in aluminum have been found. Therefore, the diffusion time of the kinks is negligibly small for the KPF process in fcc metals. Values of the internal stress field in cold-worked samples have also been obtained using the two-wave acoustic coupling approach. A description of the experimental method and the theoretical approach for the interpretation of the results will also be given in this paper.
Fractal aspects of the dielectric response of charge carriers in disordered materials
Authors: Niklasson G. A.
Published: July 2002

We put forward a fractal model for the anomalous low-frequency dispersion in the dielectric properties of materials. This dispersion consists of two fractional power laws in the frequency domain. We review the theory of the dielectric response due to fractal time processes and conduction on fractal structures. A fractal time process can arise from multiple trapping and trap-controlled hopping. The most studied fractal structure is percolation clusters. The anomalous low-frequency dispersion can be modeled by considering a combination of a fractal time process and a fractal structure. The power law at low frequencies is due to the fractal time process, while the high-frequency power law depends on both the conduction on the fractal structure and the fractal time process. The crossover between the two power laws corresponds to the correlation length of the material. We have compared this model to available experimental data. Experiments show the qualitative features predicted by the fractal model, but quantitative agreement is lacking in many cases. Even for percolation systems at the percolation threshold, discrepancies are apparent. This points to the need for further refinements of the theory. Some possible reasons for the discrepancies are pointed out.
Silicon-on-insulator material formed by oxygen implantation and high-temperature annealing: Carrier transport, oxygen activity, and interface properties
Authors: Cristoloveanu S. , Gardner S. , Jaussaud C. , Margail J. , Auberton-Hervé A. J. , Bruel M.
Published: July 2002

The crucial roles of high-temperature annealing (1300–1340 °C) and ambient gas are emphasized by the electrical properties of structure fabricated on silicon-on-insulator by deep oxygen implantation. Hall-effect measurements down to 77 K, as well as the characteristics of front channel and back channel transistors, show that the silicon overlay is quasihomogeneous, as a consequence of drastic improvement of the buried interface region. This is illustrated by the high carrier mobilities (1250 cm2 V−1 s−1 for electrons at 300 K), the dominance of acoustic phonon scattering, and the interface parameters that are more favorable than after low-temperature anneals and similar to those of bulk Si. The properties and the temperature behavior of oxygen-related donors are also investigated via the Hall effect. About 1015 cm−3 thermal donors are generated around 450–550 °C, while 1017 cm−3 new donors are formed at 750 °C. New donors presumably originate from the interface states of SiOx precipitates.
Hybrid modes in a circular waveguide with an impedance wall
Authors: Elsherbeni A. Z. , Hamid M.
Published: July 2002

A general characteristic equation is derived in order to determine the propagating modes inside a circular waveguide with an impedance wall. Furthermore, corrections to the eigenvalues reported by Mohsen and Hamid are also presented.
Aerosol generators for singlet oxygen production
Authors: Blauer Jay A. , Munjee S. A. , Truesdell K. A. , Curtis E. C. , Sullivan J. F.
Published: July 2002

Two aerosol generators for O2(a1Δ) production were designed, fabricated, and tested over a wide range of operating conditions. Each generator consisted of an injector assembly, a reaction chamber, and a nonmoving centrifugal phase separator, and differed from the other principally in the number of individual injector elements incorporated into the design (1 vs 5). A one-dimensional engineering model of two-phase reacting flow was developed and compared to the experimental aerosol performance data. Similar comparisons were also made with available data regarding the performance of generators based upon the sparger and wet wall concepts. These comparisons indicated that quenching losses in regions of two-phase flow were heavily influenced by surface effects. The data indicated a collisional probability for quenching of O2(a1Δ) at the gas-basic H2O2 interface in the vicinity of 2±1×10−3. The implications of the results of data correlations given herein relative to the design of compact, high energy density generators are discussed.
Investigation of OH-H2 and OH-CO reactions using argon-sensitized pulse radiolysis
Authors: Bera Ranajit K. , Hanrahan Robert J.
Published: July 2002

Gas-phase OH radical reactions with H2 and CO were studied using pulse radiolysis absorption spectroscopy in Ar-H2O-H2 and Ar-H2O-CO systems. Computer simulation was used to examine the contribution of various reactions involved in OH decay and to confirm the experimentally measured bimolecular rate constants of OH+H2 and OH+CO reactions. In the hydrogen-argon-water system, it was found that the OH+H reaction makes a substantial contribution to OH decay in competition with the process OH+H2. The value of the OH+H2 abstraction rate constant, (3.2±0.7)×10−15 cm3 molecules−1 s−1, obtained empirically from a plot of the pseudo-first-order rate constant for OH consumption versus H2 pressure was about 50% lower than most literature values, but proved to be acceptable in the dynamic simulations. Although some 30 reactions are needed to describe the Ar-H2O-CO system, the OH concentration decreases almost exponentially, mostly by the OH+CO addition reaction, with small contributions by other processes. The empirically determined OH+CO bimolecular rate constant of (1.55±0.13)×10−13 cm3 molecule−1 s−1 agreed well with literature values determined in the presence of Ar buffer gas and also led to consistent predictions in the computer simulation work.
Analytic parametrization of transport coefficients of Lennard–Jones (n,6) fluids
Authors: Vicharelli P. A.
Published: July 2002

Simple, easy to use analytic formulas for the calculation of neutral-gas transport properties such as viscosity, thermal conductivity, and diffusion coefficients are presented. The formulas are based on least-squares parametrizations of accurate numerical calculations of collision integrals for Lennard–Jones (n,6) fluids with n=9, 12, and 18. The accuracy of these formulas is shown to be of the order of 1%–2% for a wide range of fluid conditions. Analytic formulas for reduced transport coefficients are also proposed. The simplicity and accuracy of these results allow the inclusion of reliable neutral-gas transport properties in the computer modeling of high-pressure discharges, e.g., arc lamps, without the penalty of large increases in execution times.
Impurity states in Sb-doped amorphous semiconductors
Authors: Gosain D. P. , Bhatia K. L. , Parthasarathy G. , Gopal E. S. R.
Published: July 2002

A systematic investigation of the effects of antimony dopant on the electronic transport properties of amorphous (GeSe3.5)100−xSbx under high pressure (up to 120 kbar) has been carried out down to liquid-nitrogen temperature for the first time. Differential thermal analysis and x-ray diffraction methods were used for the characterization of freshly prepared and pressure-quenched materials which indicated the presence of structural phase transition in both GeSe3.5 and (GeSe3.5)100−xSbx around 105 kbar pressure. Electrical transport data revealed the strong compositional dependence of the electronic conduction process. A distinct kink in the conductivity temperature plot at pressures>15 kbar was observed in the Sb-doped compositions indicating the presence of different conduction processes. An attempt has been made to interpret the pressure-induced effect in the transport properties of these glasses considering the possible presence of both thermally activated conduction in the extended states and hopping process in the localized tail states. However, the interpretation of the transport data is not straightforward and the pressure dependence of the thermoelectric power will be needed to complete the picture.
Theoretical investigations on the dynamical behavior of a Josephson sampling gate with a balance comparator
Authors: Heinemann S. , Semenov V. K.
Published: July 2002

The dynamical behavior of a balance sampling gate, consisting of two directly serially connected Josephson junctions and a common shunt resistor, has been investigated by numerical simulations and approximated equations of the resistive shunted junction model. A reduced damping parameter has been found which determines the sampler behavior alone and enables an optimization. A 2.4-ps rise time of the response to a step-function signal predicted by the approximated theory has been verified by numerical simulations. The sampling gate can be driven directly by a room-temperature generator with a rise time of a few hundred picoseconds.
GaAs tunnel junction grown by metalorganic vapor-phase epitaxy for multigap cascade solar cells
Authors: Basmaji P. , Guittard M. , Rudra A. , Carlin J. F. , Gibart P.
Published: July 2002

GaAs tunnel p-n junctions with peak current densities up to 45 A cm−2 were grown by metallorganic vapor-phase epitaxy. These tunnel diodes are suitable for intercell ohmic contacts between the case of integrated tandem photovoltaic subcells in solar cells based on GaAs. The peak current is high enough for concentration up to C=1000.
Voltage-charge relation in small tunnel junctions
Authors: Tamura Hirotaka , Hasuo Shinya , Okabe Yoichi
Published: July 2002

A tunnel junction with a small capacitance behaves as a nonlinear capacitor with a periodic voltage-charge relation if kT≪e2/2C. The static voltage-charge relation in the junction is calculated taking into account the charge quantization in units of electrons. The response of the junction to dc and ac signal is obtained. When an ac signal is applied to the junction, the I-V characteristics of the junction show voltage steps with currents proportional to the frequency of the signal.
Defect site competition for metal atoms in intrinsically gettered silicon: Numerical model
Authors: Lavine J. P.
Published: July 2002

Intrinsic gettering of silicon immobilizes metal atoms at oxide precipitates and other crystal defects in the bulk of a wafer. The competition for metal atoms between these bulk gettering sites and near-surface defect sites is investigated with simple models. Metal-decorated near-surface defect sites lead to dark or leakage currents that limit semiconductor-device performance. The calculations indicate the circumstances under which bulk gettering sites are predicted to be successful in competing for metal atoms. Numerical results are shown for variations in the number of near-surface sites, the metal atom capacity of a bulk site, and the number of initial metal atoms. Predicted profiles of free and trapped metal atoms are presented.
Optical characterizations of undoped GaAs crystals grown by reduced pressure metalorganic vapor-phase epitaxy
Authors: Kusano Junichi , Segawa Yusaburo , Iwai Sohachi , Aoyagi Yoshinobu , Namba Susumu
Published: July 2002

Undoped gallium arsenide crystals were successfully grown by the reduced pressure metalorganic vapor-phase epitaxy technique using the (AsH3)/[Ga(CH3)3] mole ratio ranging from 10 to 128. The photoluminescence of the free exciton and sharp emission peaks due to the radiative recombination of bound excitons at 1.8 K indicated that this series of samples were high-purity epitaxial layers. In particular, by using a picosecond pulsed laser and a decay measuring system, the radiative lifetime of the photoexcited carrier at 77 K was determined for various samples. The maximum decay time was found to be 2.8 ns at the (V/III) ratio of 32. The relationship between the radiative and nonradiative transition probabilities at 77 K was qualitatively estimated from the measurement of the photoluminescence intensity and the decay time. The nonradiative process, which consists of the deep impurity level, strongly depends on the (V/III) ratio. At the (V/III) ratio of between 32 and 45, the nonradiative transition probability has the minimum value and the emission efficiency has the maximum.
Formation mechanism of drawing-induced peroxy radicals in pure silica optical fibers
Authors: Hibino Yoshinori , Hanafusa Hiroaki
Published: July 2002

Drawing condition dependencies of peroxy radicals (PRs) in as-drawn pure silica optical fibers have been investigated using an electron-spin-resonance technique. The PRs increase in concentration with decreasing drawing temperature and velocity. A model of thermally activated transition between the precursor and PRs is applied to the formation of the PRs in the drawing process. The analysis indicates that the PR is more stable in silica glass than the precursor, and shows that the precursor concentration has linear relationships to the reciprocals of the drawing temperature and velocity, respectively.
Surface plasmon dispersion analysis in the metal-oxide-metal tunnel diode
Authors: Donohue J. F. , Wang E. Y.
Published: July 2002

Three peaks corresponding to the ultraviolet, visible, and near infrared were recently observed in the light emission spectra of a metal-oxide-metal (MOM) tunnel diode. This was the first time UV emission was reported at room temperature with a MOM diode, and it was associated with the radiative surface plasmon. Simple dielectric theory predicts the location of the UV peak as well as the others, but is unable to give a complete description of the spectral output. To gain a clearer understanding of the spectral emission, a more comprehensive detailed model of surface plasmon dispersion in the MOM system is presented. The model is very general and includes the effects that different oxides, metals, and their thicknesses have on the dispersion curves. When applied to simpler systems, the model agrees well with the theoretical work of others. Also, associated with the cathode-oxide interface is a nonradiative mode that is found to play a major role in the transition from the visible to UV peaks in the diode’s spectra.
Spreading of Au dots on InP surfaces
Authors: Elias K. R. , Mahajan S. , Bauer C. L. , Milnes A. G. , Bonner W. A.
Published: July 2002

Circular gold dots, measuring about 200 μm in diameter and either 150 or 300 nm in thickness, have been produced on {100}, {110}, and {111} substrates of indium phosphide by a combination of vapor deposition and photolithographic processing, annealed at temperatures ranging from 420–460 °C, and subsequently examined by optical microscopy. During annealing, a reaction product, bounded by well-defined crystallographic planes of the substrate, forms, expands parabolically with annealing time, and eventually saturates due to the limited supply of gold. Generally, reactions proceed at least three times faster at {100} and {110} planes than at {111}In planes, in which reactions proceed about three times faster than at {111}P planes. Analysis of concomitant reaction kinetics yields an activation energy of 8.6±3.0 eV for reactions at {111}In planes. Results are interpreted in terms of a preferential interfacial reaction at {111}In planes, which is controlled by solid-state diffusion and eventual escape of phosphorus.
Investigations of dynamical changes in metal/silicon and ion-implanted silicon thin films by cross-sectional transmission electron microscopy with intermittent annealings in N2 ambient
Authors: Lu S. W. , Nieh C. W. , Chen L. J.
Published: July 2002

The feasibility of studying dynamical changes in metal/silicon and ion-implanted silicon thin films by cross-sectional transmission electron microscopy with intermittent annealings in N2 ambient up to 900 °C is demonstrated. Interactions of nickel thin films with oxidation-induced stacking faults and fluorine bubbles, the evolution of microstructural defects and solid-phase epitaxial growth in BF+2 -implanted silicon are provided as examples. The technique may be applied to clarify a number of important issues encountered in the study of the reactions and diffusion of thin films and obtain information otherwise unattainable.
Properties of zinc phosphide (Zn3P2) thin films prepared by hot-wall technique under high Sb vapor pressure
Authors: Fuke Shunro , Imai Tetsuji , Okuyama Shinobu , Kuwahara Kazuhiro
Published: July 2002

Zinc phosphide thin films have been deposited by a hot-wall deposition technique under high antimony vapor pressures. It is observed that the Sb-rich films retain the Zn3P2 crystal structure with a larger c axis. The Sb atoms, with a larger atomic radius than P atoms, are incorporated into the P sublattice of Zn3P2 yielding the mixed crystal Zn3P2(1−x)Sb2x . The films have lower band-gap energy and resistivity than undoped Zn3P2 films.
Plane crystalline films of stearic acid and ω-heptadecenoic acid as electron-beam resist
Authors: Tawata Masahiro , Morita Shinzo , Hattori Shuzo
Published: July 2002

Plane crystalline films of stearic acid and ω-heptadecenoic acid were formed by annealing evaporated microcrystalline films and evaluated as an electron-beam resist. The stearic acid film showed positive patterns at doses higher than 100 μC/cm2. For the ω-heptadecenoic acid film exposed at a minimum dose of 7 μC/cm2, negative patterns were developed by heating in a vacuum. Positive patterns were also formed at doses higher than 100 μC/cm2.
Operation of a 120-MW ion beam source using an Applied-Bθ ion diode
Authors: Lockner T. R. , Poukey J. W. , Stygar W. , Humphries S. , Kraybill D. M.
Published: July 2002

The operation of an Applied-Bθ ion diode has been studied at voltages up to 1.8 MV and diode currents of 250 kA. Peak ion currents up to 80 kA were observed at diode current efficiencies of up to 33% during the 60 ns power pulse. Ion and electron flow patterns have been carefully measured which indicate electron loss at locations far removed from the anode-cathode gap and ion current density enhancement at the inner anode radius due to motion of the cathode electron sheath. Numerical simulations performed with particle-in-cell codes agree well with the experimentally determined diode parameters including electron dynamics and ion and electron fluxes.
Influence of highly charged impurities on ion temperatures measured with active-beam plasma diagnostics
Authors: Donné A. J. H. , de Heer F. J.
Published: July 2002

The presence of highly charged impurity ions in a (tokamak) plasma can be very disturbing if one wants to apply active-beam scattering diagnostics, for instance, for the measurement of the local ion temperature, since it is nearly impossible to separate particles scattered by the main plasma constituent from those scattered by the impurity ions. In this work it is shown, by making use of already published theoretical results of the electron-loss probability as a function of impact parameter, that not only for H, but also for He injected neutrals, the effect of impurity ions on the relevant energy distribution of scattered neutrals is negligible.
Antireflection coating for ZnIn2S4 single crystals
Authors: Vigil O. , Lopez S. , Morris E. , Leccabue F.
Published: July 2002

Single- and double-layer thin-film antireflection coatings have been computer designed for ZnIn2S4 single crystals. The parameters of the thin-film layers, i.e., optimal thickness and refractive index, were determined. SiOx thin films, as antireflection coatings, have been deposited by reactive sputtering in order to reduce the average reflectance and to increase the photocurrent of the ZnIn2S4 single crystal.
Growth and characterization of InGaAs/GaAsP strained layer superlattices
Authors: Katsuyama T. , Bedair S. M. , Giles N. C. , Burns R. P. , Schetzina J. F.
Published: July 2002

InGaAs/GaAsP strained layer superlattices have been grown by metalorganic chemical vapor deposition on (100) GaAs at 630 °C. The superlattices consist of 5–45 periods of alternate InGaAs and GaAsP layers with equal and opposite lattice mismatch up to 1.1% with respect to the GaAs substrate. Thus, their lattice constant as a whole will be matched to that of GaAs. Cross-sectional transmission electron microscopy and x-ray diffraction measurements indicate that the superlattices have high structural quality with no misfit dislocations at the interface between the superlattice and the substrate. A very intense and sharp photoluminescence spectrum (linewidth=4 meV) at 4.5 K suggests that the interface abruptness is less than two monolayers. Photoluminescence measurements along the beveled surface of the superlattice also indicate a high optical quality within the superlattice as well as at the superlattice/substrate interface.
Ion range distributions in multilayered structures: Bi in Si/Ge
Authors: Tsao J. Y. , Picraux S. T. , Brice D. K. , Wright A. F.
Published: July 2002

Bismuth-ion range distributions have been measured in Si/Ge multilayered structures by glancing-angle Rutherford-backscattering spectrometry. The structures were formed by ultrahigh vacuum deposition of various combinations of Si and Ge layers, with thicknesses ranging from 25 to 60 nm, and then implanted with Bi ions at energies ranging from 70 to 385 keV. The measured distributions exhibit, as expected, discontinuities at the Si/Ge interfaces and depend markedly both on the exact sequencing and thicknesses of the layers, as well as on the range-to-layer–thickness ratio. The measured distributions are compared to those calculated by a recently developed approximate method for determining such distributions, the method of equivalent atomic stopping (MEAS). The overall agreement is good and illustrates the usefulness of MEAS in predicting implant distributions in multilayers not yet studied experimentally.