bluuebunny/crossref_metadata_2025 huggingface dataset:
A practical algorithm for least-squares spline approximation of data containing noise
Authors: Thijsse Barend J. , Hollanders Mark A. , Hendrikse Jan
Published: July 2002

A simple yet robust algorithm is presented to approximate data containing noise by smooth spline functions. The method is easy to implement and fast. Experience has shown that in the great majority of cases no user decisions are required to obtain adequate approximants, which is a useful property for routine processing of experimental data. The statistical basis of the algorithm is a generalized version of the Durbin–Watson statistic, which performs well even in the presence of correlated noise. Examples are given to illustrate the power of the algorithm. © 1998 American Institute of Physics.
Properties of amorphous germanium tunnel barriers
Authors: Gibson G. A. , Meservey R.
Published: July 2002

The properties of tunnel barriers made with amorphous Ge (a-Ge) deposited at approximately 80 K were studied in Al/a-Ge/Al tunnel junctions and also in junctions where one electrode was Ni or Fe. The conduction process was shown to be tunneling for barriers less than about 100 A at liquid He temperature and consistent with Mott variable-range hopping for higher temperatures and thicknesses. Measurements were made of current density J and dynamic conductance dJ/dV as a function of voltage V, thickness s, and temperature T. The measurements were compared with available theoretical expressions for rectangular tunnel barriers based on the WKB approximation. The applicability of these expressions for barrier heights less than 100 meV was examined and a modified equation for J(V) was derived which eliminated assumptions which are inaccurate for such low barriers. The measurements were also compared to this modified equation and to numerical solutions. Values for the effective tunnel barrier height ranging from 20 to 80 meV were obtained. Theoretical expressions for J(V) could be fitted to the measurements fairly well, but not perfectly; for J(T) the fit was poor. Values of s obtained using the modified expression for J(V) tended to be 10%–20% less than those measured by a quartz-crystal thickness gauge using the bulk crystal density. The conductance peaks corresponding to the peaks in the superconducting density of states were considerably broadened over Al/Al2O3/Al junctions either because of depairing of the Al films in contact with a-Ge or from an inelastic process in the barrier. No spin polarization of the tunnel currents was observed when one of the electrodes was Ni or Fe. Some measurements were made of a-Ge barriers treated with glow discharges in N2, O2, and H2. The properties of a-Ge were very similar to those previously found for a-Si. Evidently the basic conduction process in these junctions is tunneling, but the simple tunneling model cannot entirely explain the results. Various proposals to account for these divergences from the simple tunneling model are discussed.
Electronic conduction in polyethylene naphthalate at high electric fields
Authors: Kojima Kenzo , Takai Yoshiaki , Ieda Masayuki
Published: July 2002

The electric conduction in polyethylene naphthalate film was investigated under high electric fields. The current strongly depended on the electrode materials, especially on the cathode metal. Schottky-injection current was observed in the specimen with an Al cathode at the fields less than 106 V/cm, while at higher fields (>106 V/cm) tunneling-injection current and electroluminescence were observed simultaneously, suggesting the impact ionization by electrons injected from the electrode.
Diffusion through perforated membranes
Authors: Fabrikant V. I.
Published: July 2002

The diffusion process through a thin membrane, perforated by several holes of arbitrary shape, is considered. A general theorem is established which relates the total flux through each hole with the concentration distribution of some chemical species, prescribed in the hole, by a system of linear algebraic equations. The theorem is applied to the case of arbitrarily located elliptical holes. Several specific examples are considered.
Hydrodynamical treatment of spectral broadening of turbulent plasma
Authors: Khan T. P.
Published: July 2002

A theory for the determination of intensity spectrum in plasma interacting with a laser beam is presented. The calculations have been based on hydrodynamical equations including nonlinear terms.
Spectral sensitization of amorphous silicon by bromoindium phthalocyanine
Authors: Borsenberger Paul M.
Published: July 2002

The spectral sensitization of hydrogenated amorphous silicon by surface layers of bromoindium phthalocyanine and 1,1-bis(4-di-p-tolylaminophenyl)-cyclohexane has been investigated. By this technique, the long-wavelength edge of the photoconductive action spectrum can be extended by approximately 100 nm into the near infrared. The sensitization is explained by an exciton dissociation process within the phthalocyanine, followed by hole injection into the amorphous silicon.
Effects of nonequilibrium quasiparticles on characteristics of Nb/AlOx/Nb/n-InSb triodes
Authors: Tamura Hirotaka , Hasuo Shinya
Published: July 2002

A triode with a Nb/AlOx/Nb Josephson junction emitter and an n-InSb collector was fabricated and tested. The base layer was superconducting Nb film. The collector current of the triode was controlled by the injection of low-energy quasiparticles with an energy near the gap energy of the base layer. Common-base small-signal current gain was 10−3 to about 0.1 at 1.7 K. The characteristics of the triode were calculated. The analysis used a model where the collector-base junction is treated as a tunnel junction, and the quasiparticle density was calculated by using the rate equations given by Rothwarf and Taylor [Phys. Rev. Lett. 19, 27 (1967)]. The calculated characteristics agreed qualitatively with the measured results.
A deep level transient spectroscopy study of electron traps in n-type GaAs after pulsed electron beam irradiation
Authors: Marrakchi G. , Barbier D. , Guillot G. , Nouailhat A.
Published: July 2002

Electrical and deep level transient spectroscopy measurements on Schottky barriers were performed in order to characterize electrically active defects in n-type GaAs (Bridgman substrates or liquid-phase epitaxial layers) after pulsed electron beam annealing. Both surface damage and bulk defects were observed in the Bridgman substrates depending on the pulse energy density. No electron traps were detected in the liquid-phase epitaxial layers before and after annealing for an energy density of 0.4 J/cm2. The existence of an interfacial insulating layer at the metal-semiconductor interface, associated with As out-diffusion during the pulsed electron irradiation, was revealed by the abnormally high values of the Schottky barrier diffusion potential. Moreover, two new electron traps with activation energy of 0.35 and 0.43 eV, called EP1 and EP2, were introduced in the Bridgman substrates after pulsed electron beam annealing. The presence of these traps, related to the As evaporation, was tentatively attributed to the decrease of the EL2 electron trap signal after 0.4-J/cm2 annealing. It is proposed that these new defects states are due to the decomposition of the AsGa-Asi complex recently considered as the most probable defect configuration for the dominant EL2 electron trap usually detected in as-grown GaAs substrates.
Variational and transport properties of high-pressure arc plasmas
Authors: Tsui K. H.
Published: July 2002

One-dimensional steady-state transport equations are used to describe the equilibrium state of multiple species cylindrically symmetric arc plasmas. The effects of axial and azimuthal variations are introduced through the boundary conditions at the center. It is shown that the axisymmetric case of m=0 is actually the case of large m being smoothed out by thermal fluctuations where m is the azimuthal mode number. The conservation of mass density flux gives rise to mutual diffusion and a criterion is given to predict which neutral species should concentrate at the center and vice versa. By writing the energy balance equation in the form of action integral, it is clear that the power dissipation is always a minimum, thus proving the Steenbeck’s minimum principle. A local thermal equilibrium model is used to obtain the electron density. This model is tested against the experimental results of a helium arc with copper electrodes at atmospheric pressure. The steep positive density gradient of the copper is the consequence of pressure balance with the much higher density helium, and the steepness is directly related to the disparity of the two densities.
Edge-cladding glasses for solid-state laser garnet crystals
Authors: Meissner H. E. , Toratani H. , Izumitani T. , Stokowski S. E.
Published: July 2002

A range of glass compositions has been identified in the PbO-Bi2O3-CuO-Al2O3-SiO2 system which will be applied as absorbent claddings to Nd3+ and Cr3+ co-doped gadolinium scandium gallium garnet and Nd3+-doped gadolinium gallium garnet crystal slabs for high-power laser applications. Coefficients of thermal expansion and refractive indices at 1.06 μm of the cladding match those of the crystals. Absorption coefficients are between 30 and 40 cm−1. Estimates of stress birefringence in the crystalline medium indicate that values below 10 nm/cm are achievable with cladding layers of 1 mm thickness and crystal slabs of 50–100 mm width.
Electrodynamic similitude and physical scale modeling of nondispersive targets
Authors: Schumacher Clifford R.
Published: July 2002

The predictions of electrodynamic similitude, relating scattering from scaled targets to scattering from full-size targets, have been treated completely and rigorously. The usual assumption is made that the targets are those whose conductivity, permittivity, and permeability do not change with frequency. A complete set of solutions is presented to the three general nonlinear modeling equations in six variables. For the first time, particular emphasis is given to the effects of differences between absolute, geometric, and complete scaling on the electromagnetic fields and on the radar cross section, and effects of approximations to complete scaling are analyzed. Conditions are obtained on properties of materials required for models made from these materials to accurately simulate systems. Absorption and energy balance are also treated, and the influence of finite conductivity on surface currents is shown. The claim that scaled-down models may be used to represent real targets is based on the linearity of Maxwell’s equations. Therefore, the physics involved in nonlocality and nonlinearity, its relation to the Maxwell equations in macroscopic media, and its impact on physical scale modeling are first examined. The behavior of electromagnetic fields is also treated as a function of frequency. Upper bounds on the electric conductivity and limitations on the electric and magnetic polarizability of realistic materials can have profound implications for model measurments. All the energy density in the reflected wave may be lost at higher frequencies by incomplete scaling of even apparently nonabsorptive targets. Thus, the ratio of measured radar cross sections of geometrically scaled targets to those predicted for a completely scaled model eventually approaches zero.
Pore-size distributions from nuclear magnetic resonance spin-lattice relaxation measurements of fluid-saturated porous solids. I. Theory and simulation
Authors: Davies S. , Packer K. J.
Published: July 2002

An improved model for the estimation of pore-size distributions by inversion of nuclear magnetic resonance (NMR) spin-lattice relaxation data is presented. The model is based upon the Brownstein–Tarr treatment of the spin-lattice relaxation behavior of a fluid confined within a pore. A computer program, porefit, has been written to invert the experimental relaxation data. Computer simulations show that, subject to the requirements of an adequate signal-to-noise ratio and a sufficient number of data points, the program produces realistic reconstructions of known input distributions. The technique should allow, inter alia, increased use of NMR relaxation measurements in the prediction of the petrophysical characteristics of rock samples from oil reservoirs.
Single-chamber, i
n s
i
t
u processing of superconducting YBa2Cu3O7−δ thin films on stainless steel with yttria-stabilized zirconia buffer layer
Authors: Kumar Ashok , Ganapathi L. , Kanetkar S. M. , Narayan J.
Published: July 2002

Single-chamber in situ laser processing of high-Tc YBa2Cu3O7−δ film on stainless steel (302) substrates with yttria-stabilized zirconia (YSZ) buffer layers, has been carried out using a multitarget deposition system. YSZ and YBa2Cu3O7−δ films were deposited sequentially by KrF excimer laser (λ=248 nm) at substrate temperature of 650 °C. The films were characterized by x-ray diffraction, four point probe ac electrical resistivity, scanning electron microscopy and Auger electron spectroscopy (AES) techniques. Due to the matching of the thermal expansion coefficient of YSZ with stainless steel and its diffusion barrier characteristics, good quality high-Tc films have been grown on stainless steel substrates with superconducting transition temperature, Tc (onset), of 92 K and Tco (zero resistivity temperature) of 84 K. AES depth profiling indicated little interdiffusion of Fe across the interface of YSZ and stainless steel. A laser evaporation method was used for patterning the YBa2Cu3O7−δ films and critical current density, Jc, was measured to be ∼5×104 Acm−2 at 40 K. It was observed that the zero resistivity temperature significantly changed with the variation of buffer layer thickness, buffer layer processing temperature, and ambient oxygen partial pressure during the deposition of YBa2Cu3O7−δ.
Fracture and spall ejecta mass distribution: Lognormal and multifractal distributions
Authors: Baker L. , Giancola A. J. , Allahdadi F.
Published: July 2002

Numerous distributions (Mott, exponential, bimodal) have been proposed on the basis of geometrical or semi-empirical grounds as suitable for characterizing the mass distribution from fracture or spallation. It is argued here that the lognormal distribution is particularly suitable on the basis of a number of considerations: empirical fits, the fractal character of fracture, and the geometrical arguments when carried to their logical conclusion. We explain the deviations from the lognormal distribution as due to the finite thickness of the shell, which violates the scale-independence requirement for exact fractal behavior and introduces multifractal character to the spallation process. A plausiblity argument for the observed relationship between ductility and the shape of the distribution is offered.
The capacitance-voltage characteristics and hydrogen concentration in phospho-silicate glass films: Relation to phosphorus concentration and annealing effects
Authors: Murarka S. P. , Li S. C. , Guo X. S. , Lanford W. A.
Published: July 2002

Capacitance-voltage (C-V) characteristics of the low-pressure chemical vapor deposited phospho-silicate glass (P-glass) films deposited on thin (∼250 Å) thermal SiO2 films on silicon have been investigated as a function of the phosphorus content and rapid thermal annealing in the temperature range of room temperature to 450 °C carried out in various ambients. Simultaneously, the quantitative hydrogen concentration depth profiles of both as-deposited and annealed oxide films were obtained using the nuclear reaction technique. The C-V characteristics were found to be related to the charges in the oxide. The charge density, in turn, is controlled by both the phosphorus and the hydrogen (hydrogenous species) concentration in the films. An interactive relationship that controls the C-V characteristics is postulated between the presence of phosphorus and hydrogen and their concentrations in these oxides. A schematic model is presented that also postulates that hydrogenous species of two different characters are present in these films: one that easily comes out of the film at low temperature annealing and the other that comes out at significantly higher temperatures.
Properties of Co-N, Co-Fe-N, and Co-Zr-N films prepared by rf sputtering in nitrogen-argon gas mixtures
Authors: Shih K. K. , Karasinski J.
Published: July 2002

The structure and properties of Co-N, Co-Fe-N, and Co-Zr-N films, prepared by rf reactive sputtering using nitrogen and argon gases, have been studied. The resistivity and coercivity of Co-N, Co-Fe-N, and Co-Zr-N films were determined as a function of nitrogen partial pressure. It was found that the properties of Co-N and Co-Fe-N films were very similar where the properties were determined mainly by the nitride phases in these films. The resistivity of both Co-N and Co-Fe-N films increased with the increase of nitrogen pressure. The coercivity of both films decreased with an initial increase of nitrogen pressure, then increased with a further increase of pressure so that there is a region of nitrogen pressures where the coercivity is at its lowest value. The low coercivity is attributed to the formation of the Co4N phase in Co-N films and both Co4N and Fe4N phases in Co-Fe-N films. For Co-Zr-N films, resistivity first decreased with an increase of nitrogen pressure, then increased with a further increase of pressure, indicating the presence of a Zr-N phase in these films. The coercivity increased with an increase of nitrogen pressure. The Zr-N phase was not observed in the x-ray diffraction measurements due to the low concentration of Zr in these films.
The influence of oxygen partial pressure and temperature on Bi-Pb-Sr-Ca-Cu-O 110 K superconductor phase formation and its stability
Authors: Zhu Wen , Nicholson Patrick S.
Published: July 2002

A systematic study of the influence of oxygen partial pressure on 110 K phase formation in the Bi-Pb-Sr-Ca-Cu-O system has been undertaken on the optimum nominal composition to promote the Bi2Sr2Ca2Cu3Ow (2223, 110 K) phase, i.e.; Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06Ow. The relationship between 110 K phase fraction, oxygen partial pressure, sintering temperature, and time has been mapped for this composition via experimental data. The optimum conditions for 110 K phase formation were identified as 0.01≤PO2≤0.35 atm, at 820≤T≤880 °C for ≤36 h with intermediate grinding every 6 h. The single 110 K phase stability range was determined as PO2≤0.5 atm. The variation of oxygen partial pressure during the 110 K phase formation process was monitored via a Y2O3-ZrO2 oxygen sensor and a possible mechanism for its formation and the effect of PO2 thereon is discussed.
Electrode effects in ultraviolet preionized breakdown of HN3 versus microwave excitation
Authors: Wright M. W. , Schlie L. A. , Black G.
Published: July 2002

Distinct differences in the emission spectra from the breakdown of HN3 are observed for transverse excitation of HN3 gas mixtures by ultraviolet (UV) preionization relative to pulsed microwave discharges. In the dc UV preionized discharges, electrode effects liberate metal atoms dominating the emission spectra while the NH(A-X) band emission is absent. Pulsed microwave excitation incorporating an electrodeless quartz discharge region produces the NH(A-X) emission but reduced by significant quenching.
Studies of photorefractive diffraction dynamic in paraelectric KTa1−xNbxO3 crystals
Authors: Ye Peixian , Yang Changxi , Lian Yingwu , Wang Dadi , Guan Qincai , Wang Jiyang
Published: July 2002

The dynamics of photorefractive diffraction in paraelectric KTa1−xNbxO3 crystals during writing, reading, and erasing have been studied systematically. Experimental observations related not only to the diffraction from the first-order photorefractive grating but also to that from the second-order photorefractive grating, and where a writing beam with spots smaller than, as well as larger than, the entrance surface of the crystal was used. All the complicated behaviors observed have been explained qualitatively. An electron-hole transport model and a nonequilibrium screening model have been applied, and the existence of an internal dc electric field induced during writing simultaneously by an optical field and an externally applied field has been suggested and demonstrated. The significant influence of this induced field is indicated.
Plasma-sheath approximate solutions for planar and cylindrical anodes and probes
Authors: Biblarz O. , Brown G. S.
Published: July 2002

Anode sheaths are explored in detail for collisional, identical-specie-temperature plasmas where sheath dimensions are in the micron range. The selected approach involves postulation of a specific electric field distribution with three shape factors. Previous research using this approach is verified and expanded upon using greater parameter ranges. z, a dimensionless quantity specifying plasma composition and condition, groups diverse plasmas into families exhibiting similar sheath characteristics. η, a nondimensional ratio of electrical energy to thermal energy in the sheath, allows temperature effects to be studied. This investigation focuses on plasma families that span a z range of 1.1729 to 2.1493 at η values defined by discrete plasma temperatures of 6000, 3000, and 300 K. Results indicate that at the lower temperatures, charge production in the outer sheath is somewhat generic to the electric field distribution, and that the sheaths themselves are nearly unaffected by substantial changes in temperature (i.e., η). Conversely, sheath density and extent are shown to vary significantly for differing z values. Equations governing cylindrical anodes generate sheaths that are virtually identical to corresponding planar cases. It is shown that only those anodes whose radii are comparable to the plasma’s characteristic radius (γ) must be treated with the cylindrical formulation; low- and moderate-pressure plasmas would require micron-diameter anodes to be thus affected. Finally, an analytical approach shown yields solutions that confirm the numerical results, and offers an algebraic approximation for high-η plasmas.
Raman study of the formation of tungsten silicide thin films
Authors: Vuppuladhadium Rama , Jackson Howard E. , Boyd Joseph T.
Published: July 2002

Raman scattering has been used to study the formation of tungsten silicide thin films. The tungsten films were sputter deposited on p-type <100≳ and <111≳ silicon substrates and the tungsten silicide formed by either rapid thermal annealing or laser annealing. Raman data were correlated with sheet resistance measurements and scanning electron micrographs to demonstrate that rapid thermal annealing at high temperatures for short times results in low resistance tungsten silicide thin films. All of the annealed samples forming tetragonal tungsten silicide display a sharp Raman peak around 333 cm−1 and a less intense peak around 450 cm−1. X-ray diffraction studies confirmed the formation of tetragonal tungsten silicide. Samples laser annealed at low laser powers show additional Raman peaks which suggest the formation of an intermediate WSix state. Finally, an estimate of the microcrystallite size of the tungsten silicide thin films was obtained from the Raman data for both rapid thermally annealed and laser annealed samples.
Analytical two-layer Hall analysis: Application to modulation-doped field-effect transistors
Authors: Look D. C. , Stutz C. E. , Bozada C. A.
Published: July 2002

The classical magnetic-field-dependent Hall coefficient and conductivity equations are inverted to give the mobilities μ1 and μ2 and carrier concentrations n1 (or p1) and n2 (or p2) in two degenerate bands. The two-band solution holds for arbitrary magnetic-field strength as long as quantum effects can be ignored (i.e., kT≳ℏeB/m*), and it is argued that the analysis can also be applied to two separate layers up to reasonable field strengths. The results are used to determine the two-dimensional electron gas mobility and carrier concentration in a modulation-doped field-effect transistor with a highly doped cap layer.
Study of submicron InP transferred electron devices
Authors: Wu K. F. , Czekaj J. , Shaw M. P.
Published: July 2002

We have performed an experimental and numerical investigation of near-micron, and a numerical investigation of submicron sized InP transferred electron devices (TEDs) having alloyed metal cathode ‘‘current-limiting’’ contacts. A drift and diffusion analysis utilizing a modified Schottky barrier for the cathode contact was used to model the dc characteristics of near-micron structures, while a Boltzmann transport equation moments analysis with a cathode mobility model was implemented in order to simulate the ac and dc results in general. Our theoretical study emphasized the length effect for submicron structures. A generalized ‘‘different areas rule’’ for short devices was compared with the results of our numerical analysis. Submicron InP TEDs were studied and simulated numerically in the near millimeter wave region (100–250 GHz). The static velocity-field, v(E), characteristics showed a large deviation from long device behavior (≳1.0 μm) as the device length decreased into the submicron region. The upper limit for the transit-time frequency was predicted numerically to be about 230 GHz for a 0.2-μm InP TED. The interrelated controlling parameters: device length, bias, boundary conditions, doping density, were investigated in the numerical analysis and utilized to set design rules.
Theoretical analysis of the static deflection of plates for atomic force microscope applications
Authors: Sader John Elie , White Lee
Published: July 2002

The analysis of the static deflection of cantilever plates is of fundamental importance in application to the atomic force microscope (AFM). In this paper we present a detailed theoretical study of the deflection of such cantilevers. This shall incorporate the presentation of approximate analytical methods applicable in the analysis of arbitrary cantilevers, and a discussion of their limitations and accuracies. Furthermore, we present results of a detailed finite element analysis for a current AFM cantilever, which will be of value to the users of the AFM.
Raman scattering from carbon in tungsten/carbon multilayer films
Authors: Jiang Z. , Vidal B. , Desrousseaux G. , Dupuis V. , Piecuch M. , Ravet M. F.
Published: July 2002

Period expansion after annealing in tungsten/carbon (W/C) multilayer films has been observed by several authors. Although most results have emphasized that the carbon layers play the important role in such thermal evolution, it is important to clarify the structure of the carbon atoms in those multilayers both before and after annealing in order to explain such period expansion more clearly. In this paper, Raman scattering is carried out on the W/C multilayers fabricated by various methods, all of which showed different period expansion values ranging from 0% to 20%. We show that the initial carbon in those multilayers becomes graphitized differently depending on the fabrication methods. The carbon fabricated by rf sputtering under a reactive gas has the highest amount of graphite component as compared with those prepared under a pure argon gas atmosphere. After annealing at 1000 °C, graphitization can be observed, but there are no obvious structural differences for the carbon in all the annealed W/C multilayer films. Such graphitization of the carbon layer causes a decrease in its density, and thus an increase in its thickness. Due to the different initial states of the carbon in the multilayers produced by the different methods and to the identical final state after annealing, the different carbon layer thickness expansions are expected and do agree with the small angle x-ray diffraction measurements.
Evidence of refractive index change by Ti indiffusion into LiNbO3 substrate as a result of multipulse free-running ruby laser irradiation
Authors: Dinescu Maria , Chitica N. , Timus Clementina , Mihailescu I. N. , Andrei A. , Maiello Gabriella , Schirone L. , Ferrari A. , Bertolotti M.
Published: July 2002

It is shown that the multipulse free-running ruby laser irradiation of z-cut LiNbO3 single-crystalline samples with 400 Å-thick Ti deposits results, under certain conditions, in an efficient Ti indiffusion with minimum perturbation. Implanted zones exhibit optical characteristics appropriate for the preparation of optical devices.
Effects of deposition temperature on the giant magnetoresistance of as-deposited Ag-Co thin films
Authors: Lee W. Y. , Deline V. R. , Gorman G. , Kellock A. , Miller D. , Neiman D. , Savoy R. , Vazquez J. , Beyers R.
Published: July 2002

Giant magnetoresistance (GMR) is reported in Ag1−xCox(x=0.26–0.53) films cosputtered on Si at 28–354 °C from separate Ag and Co targets. GMR ratios (10 kOe maximum field) as high as 0.55 and 0.24 at 5 and 295 K, respectively, are achieved for the Ag0.67Co0.33 films deposited at a substrate temperature, Ts, of 125 °C. The GMR ratio increases slightly when the Ts increases from 28 to ≂125 °C, and decreases substantially at Ts≳175 °C. The resistivity of these films decreases monotonically with increasing Ts and levels off to a value ≂3× of Ag at Ts≥250 °C. The films deposited at lower Ts consist of essentially a metastable Ag-Co solid solution, while those deposited at higher Ts consist of separate fcc Ag and fcc Co. The coercivity of these films increases rapidly at Ts≫125 °C, consistent with the growth of single-domain ferromagnetic Co particles in this Ts range. The Ts dependence of GMR ratios is interpreted based on spin-dependent interfacial scattering arising from the Ts dependence of the size and number of ferromagnetic Co particles within the electron mean free path.
Low temperature operation of Ge-Ag ohmic contacts to a high mobility two dimensional electron gas
Authors: Chabasseur-Molyneux V. , Frost J. E. F. , Tribble M. J. , Grimshaw M. P. , Ritchie D. A. , Churchill A. C. , Jones G. A. C. , Pepper M. , Burroughes J. H.
Published: July 2002

Ge-Ag ohmic contacts with good dimensional control to a two dimensional electron gas operating at low temperatures are demonstrated. At 4.2 K, the specific contact resistance lies in the range 2–5 Ω mm for anneals between 520 and 560 °C. The surface morphology is smooth, and the edge definition is of the order of 100 nm. Secondary ion mass spectroscopy analysis indicates that Ge diffusion is limited to within 2000 Å of the surface for a concentration of 1017 cm−3 in samples annealed at 540 °C and below.
Response to ‘‘Comment on ‘Generalized study on angular dependence of induced second-order nonlinear optical polarizations and phase matching in biaxial crystals’ ’’ [J. Appl. Phys. 74, 5916 (1993)]
Authors: Ito Hiromasa
Published: July 2002

As pointed out by the comment of J. Shi, there were several errors in our old communication [J. Appl. Phys. 40, 3992 (1975)]. Most of them were collected by other researchers in their own papers; however, this is a nice opportunity to point out all the errors in our paper.
Orientation-dependent growth of InGaAs/InP for applications in laser-diode arrays
Authors: Zwinge G. , Wehmann H.-H. , Schlachetzki A. , Hsu C. C.
Published: July 2002

Growth by metalorganic vapor-phase epitaxy is generally a process which depends on crystal orientation. Different growth rates in [001] and [111] orientation during simultaneous growth on structured InP substrates are observed. In the extreme case no growth occurs on (111) planes. This effect can be utilized for the growth of buried heterostructures with especially patterned substrates using a single growth step, provided the growth parameters are properly chosen.
Methyl- and dimethyl-associated paramagnetic centers in SiO2 thin films
Authors: Hoinkis M. , Crowder M. S. , Nguyen B. C. , Galiano M. L.
Published: July 2002

SiO2 thin films, deposited by the plasma-enhanced chemical vapor deposition technique using tetraethylorthosilicate (TEOS) and O2 as precursors, exhibit electron-paramagnetic-resonance signals that are interpreted in terms of methyl- and dimethyl-associated centers. The former are observed in as-deposited films and in films thermally treated below 500 °C while the latter are observed in films that have been thermally treated between 700 and 950 °C. These hydrocarbon-containing paramagnetic centers originate from TEOS’s ethyl constituents that are incorporated in the SiO2 film during growth.
Morphological stability of a molten pool during the radiative heating of a thin silicon film
Authors: Brush L. N.
Published: July 2002

A two-dimensional model of a laser-melted thin silicon film and surrounding solid is presented. The model is used to calculate the radius of the circular pool formed by the heat from a laser beam having a Gaussian profile. The accompanying temperature profiles throughout the liquid and the solid are also calculated as a function of the heat source strength. It is shown that for a range of parameter values, a layer of superheated solid and a layer of supercooled liquid can appear adjacent to the solid-liquid interface. This thermal profile can lead to morphological instability. The results of a morphological stability analysis of the circular liquid pool show that the mode of the perturbation appearing at the onset of instability is affected both by the surface tension and by the distance to which the regions of supercooled liquid and superheated solid extend from the solid-liquid interface into the bulk liquid and bulk solid phases, respectively. The calculations compare favorably with previously published experimental results.
Chemical model for wire chamber aging in CF4/iC4H10 gases
Authors: Wise J. , Kadyk J. A. , Hess D. W.
Published: July 2002

Aging of proportional counters in CF4/iC4H10 mixtures is studied as a function of gas composition. Anode surfaces are analyzed by Auger electron spectroscopy. Anode-wire deposits are formed from 95/5 and 90/10 mixtures of CF4/iC4H10; etching of deposits occurs in 50/50 and 80/20 mixtures of CF4/iC4H10 and in pure CF4. Gold-plated wires are resistant to aging resulting from chemical attack by CF4, but non-gold-plated wires are too reactive for use in CF4-containing gases. An apparent cathode aging process resulting in loss of gain rather than in a self-sustained discharge current is observed in CF4 and CF4-rich gases. Principles of low-pressure rf plasma chemistry are used to interpret the plasma chemistry in avalanches (≥1 atm, dc). To understand anode aging in CF4/iC4H10 gases, a four-part model is developed considering: (i) plasma polymerization of iC4H10; (ii) etching of wire deposits by CF4; (iii) deposition that occurs as a result of radical scavenging in strongly etching environments; and (iv) reactivity of the wire surface. Practical guidelines suggested by the model and application of the model to other fluorine-containing gases are discussed.
Physical damage in silicon formed by helicon wave plasma etching
Authors: Tsukada Tsutomu , Nogami Hiroshi , Hayashi Jun , Kawaguchi Kazu , Hara Tohru
Published: July 2002

Damage formed on silicon by helicon wave oxygen plasma is studied. The damage density decreases from 1.9×1016 to 9.3×1015/cm2 with an increase of helicon wave power from 0.5 to 2.0 kW in the exposure for 5 min at a rf bias power density of 0.45 W/cm2 at 1.6 MHz. This decrease is mainly due to the rapid decrease of self-bias voltage Vdc, with these power and ion current increases. This damage density variation is much different from those in other kinds of etching, such as, in an electron cyclotron resonance plasma etching. However, the damage density increases with a bias power increase. Lower damage etching, therefore, can be achieved when high helicon wave and low bias powers are supplied.
Incorporation of nitrogen in Si3N4-capped silicon by cw Ar+-laser melting
Authors: Willems G. J. , Maes H. E.
Published: July 2002

A study of the mechanisms that determine the incorporation of nitrogen in Si3N4-capped silicon by cw Ar+-laser melting is presented. A theoretical description is given of the nitride capping layer erosion by the liquid silicon in the molten zone, the segregation at the slanted solidification interface, the diffusion in the molten zone of nitrogen expelled from the solid, and the solid-state diffusion of nitrogen. This theoretical model is used to explain the shape and the dependency on laser melt conditions of the nitrogen profiles measured in Si3N4-capped bulk silicon samples after laser melting. It is shown that the freshly frozen-in nitrogen profile can be described by an exponentially decaying function of depth in the sample, which is modified by solid-state diffusion and precipitation at the sample surface. It is suggested that the nitrogen concentration measured at the melt depth is indicative of the nitrogen concentration in the bulk of the molten zone. The results also apply to impurities other than nitrogen with a segregation coefficient smaller than 1 and to other continuous energy sources applied for superficial melting.
Initial stages of InAs deposition on SrF2-coated EuBa2Cu3O7−y thin-film superconductors
Authors: Watanabe Yoshio , Maeda Fumihiko , Oshima Masaharu , Michikami Osamu
Published: July 2002

Initial stages of InAs deposition on EuBa2Cu3O7−y (EBCO) thin-film superconductors with a SrF2 interlayer are investigated by using synchrotron-radiation photoelectron spectroscopy. Core-level and valence-band spectra can give imformation on both oxidation of InAs and reduction of the underlying EBCO with a very thin surface layer. These spectral evolutions demonstrate that SrF2 does not affect the underlying EBCO, and that the two-step growth procedure, comprising the initial InAs layer growth at room temperature and the top InAs layer growth at 200 °C, is effective in suppressing the interfacial redox reactions. Furthermore, cross-sectional transmission electron microscopy and x-ray-diffraction studies comfirm that SrF2 forms a uniform layer on the EBCO surface, and that the two-step growth process can crystallize an InAs top layer, which is highly (111) oriented with a full width at half-maximum of 0.25°.
New transport phenomena in a ballistic heterostructure field-effect transistor
Authors: Kastalsky A. , Bhat R. , Cho A. Y. , Sivco D. L.
Published: July 2002

We observed new transport properties in an InGaAs/InAlAs field-effect transistor with source-drain separation of ∼40 nm. Through measurements of real-space transfer current to the gate we obtained clear evidence of ballistic electron transport in the two-dimensional channel of the device. Another important new feature is the drain current saturation at low drain biases. This effect is explained by a poor electron exchange at the interface of a two-dimensional gas with bulk at the device contacts.
Observation of surface defects in 6H-SiC wafers
Authors: Evwaraye A. O. , Smith S. R. , Skowronski M. , Mitchel W. C.
Published: July 2002

A broad peak was observed in commercially available single-crystal 6H-SiC material. The samples were nitrogen doped, n type with free carrier concentration (ND−NA) of 1.3×1018 cm−3 that was determined from capacitance-voltage (C-V) measurements. The defect concentration profile showed that the defect was spatially localized and had a maximum concentration of 2.5×1014 cm−3 at 570 Å from the semiconductor-metal interface. The activation energy varied with applied voltage from Ec−0.40 eV at VR=−7 V to Ec−0.54 eV at VR=−5 V. This can be explained qualitatively in terms of the Poole–Frenkel effect. The defect was removed by the growth and subsequent removal of an oxide layer. Therefore, we conclude that the defect was caused by residual damage from the polishing process.
Nucleation of copper on TiW and TiN during chemical vapor deposition
Authors: Kim Do-Heyoung , Wentorf Robert H. , Gill William N.
Published: July 2002

Copper grows as continuous films on various silicides and metals at substrate temperatures of 310–385 °C, total pressures of 2–10 Torr, and precursor vessel temperatures of 60–80 °C (precursor mole fractions of 0.004–0.35) with hydrogen using copper (II) hexafluoroacetylacetonate [Cu(HFA)2] as the precursor. However, on TiW, TiW:N, and TiN substrates, that were previously exposed to air, copper formed only small crystalline aggregates, not continuous films, perhaps because of a thin surface layer of oxide. This conclusion was supported by Auger electron spectroscopy and scanning electron microscopy analyses.
Effects of high field electron injection into the gate oxide of P-channel metal–oxide–semiconductor transistors
Authors: Moragues J. M. , Oualid J. , Jerisian R. , Ciantar E.
Published: July 2002

Electron injection at high field and moderate fluence into the gate oxide of P-channel metal–oxide–semiconductor transistors creates net positive charges and related interfacial states as it has often been reported. A threshold electric field at around 7.2 MV/cm is found for the generation of positive charges. For this same oxide field the interfacial state density increases abruptly. For an average oxide field in the 8–9-MV/cm range, the densities of positive charges and interfacial states increase linearly with the fluence for F<1016 e/cm2 and saturate for F≳1017 e/cm2. The positive charge density is more important near the channel edges. The interfacial state density seems to be homogeneously distributed along the channel. The density of electron traps is negligible for the studied dry gate oxide except in the overlaps above drain and source and in some cases near the channel edges. The negative space charge, resulting from electron trapping in these regions, reduces the length of the electron injection and in some cases the surface of the channel which contributes to the charge pumping current. Two types of relaxation have been observed.
Dynamical properties of Josephson junctions coupled by a transmission line
Authors: Smith H. J. T. , Blackburn James A. , Gro/nbech-Jensen Niels
Published: July 2002

A system composed of two Josephson junctions connected by a transmission line has been studied by means of electronic analog simulation. Under external current bias, the resistive component of the coupling induces frequency locking between the two junctions at commensurate ratios. The resonant modes of the transmission line give rise to steps in the I-V characteristics of the system.
Single-crystal silicon microblocks produced by a selective recrystallization technique
Authors: Hayama Hiroshi , Mukainari Masahito , Saito Takeshi
Published: July 2002

A previously reported ac magnetic-field technique has here been applied to selective recrystallization on quartz substrates of polysilicon thin films which had been patterned into specific microblock designs. With the recrystallization it has been possible to produce single-crystal silicon microblocks of a maximum size of approximately 60×40×2 μm,3 large enough for the fabrication of high-performance thin-film transistors. Microblocks used in the experiments were of two types: ‘‘network’’ rectangles, connected on the wafer two dimensionally with polysilicon paths, and ‘‘isolated’’ rectangles adjacent to the network rectangles. The surface morphology of the recrystallized silicon films was observed with scanning electron microscopy. While no grain boundaries were found on the surfaces of the recrystallized network rectangles, many grain boundaries were observed to remain on the recrystallized isolated rectangles. X-ray diffractions for the recrystallized network rectangles were measured with a microfocused x-ray beam, and the recrystallized network rectangles were confirmed to be single-crystal silicon microblocks of good crystal quality. It had been expected that network rectangles would be more greatly heated, as compared to isolated rectangles, by the eddy currents induced by the ac magnetic fields, and the observed higher quality of network-rectangle recrystallization has verified that anticipated eddy-current contribution.
Liquid phase epitaxy of n-type GaAs from Bi solution
Authors: Gladkov P. , Monova E. , Weber J.
Published: July 2002

Liquid phase epitaxy of GaAs from Bi melt was studied for growth temperatures between 670–750○C. The layers were characterized by Van der Pauw and photoluminescence measurements. All epitaxial layers were n-type and exhibit low compensation and electron mobilities up to 6×104 cm2/V s at 77 K. A gradual increase in the n-type doping was observed with growth temperature. Intentional doping of GaAs with Sn leads to a Sn distribution coefficient ∼60 times larger for the Bi melt in comparison to the Ga melt. Extremely low compensation of the Sn-doped layers (K≤0.1 for Nd=2.5×1017 cm−3) is obtained.
An efficient microwave power source: The free-electron laser afterburner
Authors: Wang Changbiao , Sessler Andrew M.
Published: July 2002

A kind of microwave power source, called a free-electron laser (FEL) afterburner, that consists of a free-electron laser buncher and a slow-wave output structure sharing a magnetic wiggler field with the buncher is proposed. The buncher and the slow-wave structure can operate in either a traveling-wave state or a standing-wave state. In the buncher, the wiggler field together with the radiation field makes an electron beam bunched, and in the slow-wave structure the wiggler field keeps the beam bunched while the bunched beam interacts strongly with the slow-wave structure and thus produces rf power. The bunching process comes from the free-electron laser mechanism, and the generating process of rf power is in a slow-wave structure. A three-dimensional, time-dependent code is used to simulate a particular standing-wave FEL afterburner and it is shown that rf power of up to 1.4 GW at 17.12 GHz, can be obtained from a 1 kA, 5 MeV electron beam with an energy spread of less than 1% and an emittance of less than 0.5×10−3 π rad m.
Steady-state gain and saturation flux measurements in a high efficiency, electron-beam-pumped, Ar-Xe laser
Authors: Perkins Thomas T.
Published: July 2002

Flat-top, Ar-Xe laser pulses at 1.73 μm have been achieved by pumping the laser medium with a constant-current electron beam for pulse durations of up to 2.5 ms. The 220 keV electron beam pumped an active volume of 50×8×6 cm3 at power loadings of 6–100 W/cm3. Small signal gain, saturation flux, and nonsaturable absorption were determined as a function of Xe concentration, total gas pressure, and pump power density by a Rigrod analysis. In the experimental regime investigated, the small signal gain increased as the total laser pressure decreased and as the partial pressure of Xe decreased. The Xe concentration was varied from 0.5% to 2.0% and the total pressure was varied from 250 to 860 Torr. The results are consistent with Xe quenching of the upper laser level being the dominant deexcitation process and with the collisional broadening dominating the linewidth. The peak intrinsic efficiency observed was 2.2%.
Difference-frequency generation of near infrared picosecond pulses by noncritical temperature tuning of LiB3O5
Authors: Seifert F. , Petrov V.
Published: July 2002

The output of a commercial picosecond Ti:sapphire laser is mixed with the 514.5 nm line of a continuous wave Ar+ laser to produce 1.4 ps pulses between 1.295 and 1.7 μm. Noncritical temperature tuning of LiB3O5 has a number of advantages over the other two applicable crystals: β-BaB2O4 and KTiOPO4. The infrared pulse durations are measured by parametric amplification in KTiOPO4.