bluuebunny/crossref_metadata_2025 huggingface dataset:
Interdiffusion-induced surface morphology in lead-alloy Josephson tunnel junction electrodes
Authors: Huang H.-C. W. , Schad R. G.
Published: February 2003

Surface morphology changes have been observed in both of the electrode alloys adjacent to the tunneling oxide layer in electrically shorted Pb-alloy Josephson devices. The morphology change appears to be a result of interdiffusion between the base electrode alloy (Pb-In-Au) and the counterelectrode alloy (Pb-Bi) through ruptures in the thin tunnel oxide. By using an electron microprobe, In atoms were found to have diffused into the Pb-Bi film, while Bi atoms diffused in the reverse direction into the Pb-In-Au film. Their diffusivities at 298 K were estimated from concentration profiles to be ∼1×10−10 cm2/s. Grain boundary diffusion is thought to be responsible for such rapid material transport. Morphology changes are explained as a consequence of stress relief in both electrodes, where the stress results from differences in interdiffusion flux. It appears that Bi diffusion flux into the Pb-In-Au layer is larger than the In flux diffusing into the Pb-Bi layer because of the smaller grain size of the Pb-In-Au layer. As a result, Pb-In-Au film is put into compressive stress, which is subsequently relieved by hillock formation, whereas Pb-Bi film is put into tensile stress, causing void formation and/or surface ripples. Morphology changes were also found to be strongly influenced by the nature of the surface coating on the films. Of particular interest, when the Pb-Bi film is uncoated or covered only with KMER (Kodak metal etch resist) photoresist, a set of multiple, concentric rings of voids were observed, each centered at the site of an oxide rupture. This ring formation therefore provides a unique means to locate the site of initial oxide rupture during failure analysis and to distinguish In-diffusion-induced failures from thermal-cycle-induced failures.
Microanalysis of single-crystal Si recrystallized using halogen lamps
Authors: Haond M. , Vu D. P. , Bensahel D. , Dupuy M.
Published: February 2003

Halogen lamps have been used to recrystallize polycrystalline silicon deposited on SiO2. 〈100〉 single crystals have been obtained. 100–200 μm wide subgrains are present in the recrystallized films. We present the results of a structural analysis of the defects by using essentially Transmission Electron Microscopy. We can classify the defects as follows: primary subgrain boundaries are misfit dislocations resulting from a low angle misorientation between adjacent growing regions. Secondary subgrain boundaries are related to the strain present in the films during the recrystallization. We find coherent and incoherent precipitates. Precipitates result from a segregation of impurities. Some of them are revealed as α-SiC.
Acoustic second harmonic generation in piezoelectric semiconductors: Effect of nonuniform electric field intensity
Authors: Palanichamy P. , Singh S. P.
Published: February 2003

Acoustic second harmonic generation is studied theoretically in nondegenerate piezoelectric semiconductors in the presence of dc electric field longitudinal to the direction of propagation of the acoustic wave. The static electric-field intensity and the carrier concentration inside the semiconductor are taken as nonuniform even in trap-free samples. This assumption used in our theory modifies the results obtained by the earlier theories considerably. It is also found that the power thus calculated for the second harmonic flux in terms of the power associated with the fundamental flux is enhanced. Comparison with the available experimental results shows a qualitative agreement. We have used the phenomenological theory and that restricts our analysis to the low frequency region.
The dc conductivity of polyphenylacetylene below room temperature
Authors: Bhatt A. P. , Anderson W. A. , Kang E. T. , Ehrlich P.
Published: February 2003

The temperature dependence of the dc conductivity for doped and undoped cis-polyphenylacetylene (PPA) is analyzed at temperatures of 110 to 300 K. The dc conductivity (σdc) data of arsenic pentafluoride-doped and iodine-doped samples suggest two major current conduction processes separated by a characteristic temperature (Tc) of about 257 K, which is independent of the doping level. At TTc, σdc is activated with an activation energy that, for PPA-AsF5, varies from 0.86 eV to 0.51 eV for doping levels of 2×10−3 to 7×10−2 moles dopant/moles monomer, respectively. PPA annealed at 130 °C, which is known to undergo isomerization and cyclization reactions, has a Tc of about 210 K, and σdc does not respond to doping. Possible conduction mechanisms are discussed.
Mechanism of dispersive transport in hydrogenated amorphous silicon
Authors: Shirafuji Junji , Matsui Hirosuke , Inuishi Yoshio
Published: February 2003

Temperature dependence of the electron mobility and the dispersion parameter in hydrogenated amorphous silicon films, deposited by glow-discharge decomposition and rf reactive sputtering methods, has been measured by means of time-of-flight technique. The results of the dispersion parameter are not consistent with the theoretical prediction which has been derived on the assumption of an exponential band tail. The temperature dependence of the electron mobility seems to be more likely to invoke the presence of traps located predominantly at about 0.2 eV below the conduction band. Several possibilities suitable to this situation are discussed.
A general theory of the Raman-type free-electron laser
Authors: Shiozawa T.
Published: February 2003

A general theoretical consideration is given for the stimulated Raman scattering in a finitely magnetized relativistic electron beam on which the operation of the Raman-type free-electron laser is based. After some preliminary discussion, the coupled mode equations are derived which relate the pump wave (assumed to be an electromagnetic wave), the scattered wave and the electron plasma wave (negative-energy wave). From the coupled mode equations obtained above, the linear growth rate for the scattered and electron plasma waves is found. Then, the energy relations are formulated for the three waves involved in the process of the stimulated Raman scattering, together with the discussion on the energy balance among these waves. A special attention is paid to the behavior of the scattered wave in the vicinity of the cyclotron resonance. Some of the important features brought about by the cyclotron resonance are as follows: (a) According to the conditions imposed on the frequency and wave number of the pump wave, the scattered wave becomes either the electromagnetic wave mode or the electron cyclotron wave mode, or it is not excited. (b) In the presence of a finite static magnetic field, the spatial growth rate for the electromagnetic wave mode takes a maximum value for a particular set of various parameters, and the maximum growth rate becomes one order of magnitude or more as large as the growth rate for the case that there is no static magnetic field applied.
Transport coefficients in arc plasma of SF6–N2 mixtures
Authors: Gleizes A. , Razafinimanana M. , Vacquie S.
Published: February 2003

We compute thermal and electrical conductivity coefficients as a function of temperature for different compositions of the N2–SF6 mixture. The method we used was derived from Chapman–Enskog’s. The composition of the plasma is calculated assuming the hypothesis of local thermodynamic equilibrium. Calculations were made for temperatures between 1000 and 15 000 K. We show that the densities of the compounds specifically due to the SF6–N2 mixture (i.e., NF, NS, N2F4, NF3, etc....) are negligible compared with the densities of the products due to SF6 alone and N2 alone. The characteristics of the transport coefficients of the mixture are therefore a combination (depending on the proportions in the mixture) of the characteristics of pure N2 and SF6. These theoretical values allow us to interpret the curves obtained experimentally by measuring, using laser interferometry at two wavelengths, the variation of electron number density in a decaying arc discharge in a SF6–N2 mixture. By substituting the values of the transport coefficients into an energy balance equation, we also determined, in the stationary state the profiles of the temperature and the electric field and the variation of the electron density with the discharge current.
Mode conversion and its utilization of degenerating surface wave modes on a plasma column
Authors: Nonaka S. , Akao Y.
Published: February 2003

Both mode conversion at degenerating points of dispersion relations for surface wave modes on a discharge plasma column and the methods for their detection and utilization are presented. Mode conversions at three degenerating points become observable by using a surface wave resonator when an azimuthal inhomogeneity of plasma is produced by a static magnetic field of about 1 G applied perpendicular to the column axis. Two of the three detected degenerating points can be utilized for an easy and exact determination of the electron density and its distribution in the discharge tube.
Optimization of a heat engine based on a dissipative system
Authors: Mozurkewich Michael , Berry R. Stephen
Published: February 2003

A new class of heat engine is analyzed in which the working fluid operates in a dissipative process, never in equilibrium. The conditions are found for stability and for the generation of work. Then the optimal path is found for operating the general dissipative engine by means of optimal control theory. The optimal cycle consists of arcs of constant power and of approximately instantaneous adiabats. If the heat flow is a function of temperature only, then the constant power arcs become isotherms. An upper bound is found to the power output. Two examples are worked out in detail: a light-driven dissipative engine whose absorption is a step function of temperature, and a light-driven dissipative engine whose working fluid undergoes a chemical reaction (isomerization), absorbing light in the isomeric form favored at high temperatures.
Pulsed resonant optogalvanic effect in neon discharges
Authors: Ben-Amar A. , Erez G. , Shuker R.
Published: February 2003

Pulsed resonant optogalvanic effect is investigated in a neon hollow cathode discharges utilizing a nitrogen pumped dye laser. We have studied by the pulsed technique transient effects in the discharge plasma such as fast relaxation of level population density and population inversion. The experimental results are correlated with a four states phenomenological model of the pulsed optogalvanic effect taking into account lumped relevant levels of the 3s and 3p manifolds of neon. The time integration of the pulsed optogalvanic siganls (OGS) yields the previously measured cw signals and explains their sign changes.
High electric field poling of electroded poly(vinylidene fluoride) at room temperature
Authors: Wang T. T. , von Seggern Heinz
Published: February 2003

Room temperature electrode poling is by far the simplest and the most convenient way of preparing piezoelectric films of poly(vinylidene fluoride) PVF2. A shortcoming of this poling technique is, however, the relatively low electric field (<3.5 MV/cm) that can applied to the film without incurring instantaneous flashover or arcing around the film edge. We demonstrate here that by simply adding a rubber O ring and a plastic plate to the regular electrode poling setup, it is possible to pole biaxially oriented PVF2 films with fields up to about 9 MV/cm for at least 5 s without incidence of breakdowns. The piezoelectric e31 coefficient of the poled film rises sharply with increasing field but, after reaching a value of about 21 mC/m2 (d31=7.5 pC/N) at 2.5 MV/cm, it levels off gradually to a value of about 31 mC/m2 (d31=11 pC/N) at fields above 6 MV/cm.
Analysis and filtering applications of two newly proposed waveguide-coaxial line junctions
Authors: Tomar Raghuvir S. , Das Gupta Chinmoy
Published: February 2003

The conventional rectangular waveguide-coaxial line junction has been modified for use as a basic prototype for developing narrow-band-rejection waveguide filters with full-band continuous mechanical tunability. Two types of configurations, namely the short-circuited version and the air-gap version, have been analyzed. Experimental results show that the pass-band ripples that these configurations exhibit can be brought down to an acceptable level through the use of an extremely thin probe.
Peripheral photoresponse of a p–n junction
Authors: Holloway H. , Brailsford A. D.
Published: February 2003

A quantitative theory is presented for the enhanced photoresponse of p–n junctions that arises from the lateral diffusion of photogenerated carriers. This mechanism leads to a photoactive area for a photodiode that may be much larger than its p–n junction area. The main theory pertains to the geometry that arises with mesa diodes, the results for which are also applicable to planar junctions that are shallow when compared with the minority-carrier diffusion length. The solution for infinitely deep planar junctions is obtained by separate analysis. The magnitude of the peripheral photoresponse is sensitive to geometric and physical factors such as semiconductor thickness, surface recombination, optical absorption length, and competition for photogenerated carriers by adjacent photodiodes. The dependence of the response upon all of these features is presented.
On the inherent inferiority of ZnSe:Mn in impact excited luminescence devices
Authors: Mach R. , von Kalben J. , Müller G. O. , Gericke W. , Reinsperger G. U.
Published: February 2003

A comparison of the properties of ZnSe and ZnS, both Mn-doped as the semiconductor layers in ‘‘identical’’ electroluminescent devices of MISIM (metal–insulator–semiconductor–insulator–metal) type shows smaller threshold voltage and tenfold lower saturation brightness levels for ZnSe. The reason can be shown to be a temperature quenching of the Mn2+ emission, which at 100 K leads to the same efficiencies of ZnS and ZnSe. Thus at low temperature ZnSe is even better because of the lower threshold but at room temperature even local temperature variations might badly influence brightness homogeneity.
Surface resistance dominated thermal transport in thin specimens
Authors: Dharmadurai G.
Published: February 2003

The effective thermal conductivity of a rarefied gas bounded by two solid surfaces is shown to be dominated by the two surface thermal resistances. Using an analogous picture, it is demonstrated that the thermal transport in a thin solid specimen under ballistic phonon propagation is as well dictated by the thermal boundary resistances of the relevant interfaces, resulting in an effective thermal conductivity proportional to the thickness of the specimen. The implications of the results are discussed.
Dependence of lateral energy transport on laser irradiance in laser-induced plasmas
Authors: Sharma S. , Moncef B. , Pant H. C.
Published: February 2003

An experimental study of lateral energy transport in laser-produced plasmas is presented. X-ray pinhole photography has been used for studying the variation of the plasma diameters at the target surface as a function of the laser intensity. A scaling law has been found for this variation.
Crystallographic polarity and etching of cadmium telluride
Authors: Fewster P. F. , Whiffin P. A. C.
Published: February 2003

This paper resolves the inconsistency in the literature on the determination of the polarity of CdTe and CdxHg1−xTe from their etching behavior. The etch (H2O:H2O2:HF, 2:2:3 v/v) has been shown to reveal pits on the Cd (111) A face and not on the Te (1̄1̄1̄) B face in contradiction to the previously published work of Warekois, Lavine, Mariano, and Gatos [J. Appl. Phys. 33, 690 (1962)] and Nakagawa, Maeda, and Takeuchi [Appl. Phys. Lett. 34, 574 (1979)]. This result agrees with the observations of Fewster, Cole, Willoughby, and Brown [J. Appl. Phys. 52, 4568 (1981)] for CdxHg1−xTe grown epitaxially on CdTe.
Superconducting tunnel junctions on oxidized Zr2Rh films
Authors: Levinson M. , Gurvitch M.
Published: February 2003

High quality superconducting Zr2Rh films have been produced by dc diode sputtering in Ar. Superconducting films were obtained for substrate temperatures of ∼350–650 °C, with the maximum values of TC (11.2 °K) and resistance ratio (∼26) falling in a narrower range ∼550–600 °C. Oxidations were performed without breaking vacuum. The best tunneling characteristics were obtained with 180 Torr sec oxygen exposure and pre- and postoxidation anneals. A ∼10 Å sputtered Zr overlayer yielded additional improvement.
Measurement of the temperature field in the gas of a photoacoustic cell
Authors: Lepoutre F. , Roger J. P. , Fournier D. , Boccara A. C.
Published: February 2003

This paper presents interferometric measurements of the temperature field in a gas heated periodically by a solid sample. These measurements allow a good verification of photoacoustic theories and a clear understanding of the generation of photoacoustic signals.
Structural characterization of low-defect-density silicon on sapphire
Authors: Carey Kent W. , Ponce Fernando A. , Amano Jun , Aranovich Julio
Published: February 2003

The structure of (100) silicon on (11̄02) sapphire is discussed for films grown by a special, defect-limiting process. A three-epitaxial-step technique, which utilizes both vapor phase epitaxy and solid phase epitaxy, is employed in the fabrication of low-defect-density films. The effects of different Si+ implantation energies and initial Si film thicknesses on the final structure of the film are investigated in order to optimize the electrical characteristics. The improvement in crystalline quality during the solid phase epitaxy step is due to overgrowth of the {221}-oriented microtwins by the [001) Si matrix. Both Rutherford backscattering spectroscopy and cross-sectional transmission electron microscopy are used in the analysis of the structure of these films.
Defect states in plastically deformed p-type silicon crystals investigated by the Hall effect
Authors: Ono Haruhiko , Sumino Koji
Published: February 2003

Measurements of Hall effect and dc conductivity have been conducted on plastically deformed p-type floating-zone-grown silicon crystals to investigate the energy levels of defects introduced by deformation. The temperature dependence of the carrier concentration is analyzed on the basis of the model in which electrically active centers induced by deformation are assumed to be distributed discretely in the crystal. It is shown that both acceptors and donors having deep energy levels are introduced simultaneously by deformation, the concentrations of which are proportional to the dislocation density. The concentration of the deformation-induced acceptors is found to be 6–7 times as high as that of the deformation-induced donors. The energy levels of these acceptors and donors are approximately at the same position, namely, 0.3–0.4 eV above the top of the valence band.
Electric conduction of low density polyethylene induced by high dose rate gamma rays
Authors: Mochizuki Seiji , Tamura Naoyuki , Yahagi Kichinosuke
Published: February 2003

Radiation induced conduction in low density polyethylene under gamma-ray irradiation at high dose rates, 1×103 to 1×104 Gy/h, was studied. After irradiation was initiated, the induced current quickly plateaus, but then subsequently begins to increase slowly with time until it attains an equilibrium value. The effect of the polarity and magnitude of the electric field and of the temperature upon time dependence of the induced current were investigated. The slowly increasing induced current can be explained by thermal detrapping from relatively deep traps; the trap depth is calculated to be ca. 0.8 eV. The induced current of the sample increases as its crystallinity increases. It was revealed that a sample with high crystallinity has shallow traps and consequently has many charge carriers and increases its induced current.
Effect of molecular rotation upon charge transport between disordered carbazole units
Authors: Slowik John H. , Chen Inan
Published: February 2003

A calculation of intermolecular transfer integrals J for carbazole molecules shows that J varies by orders of magnitude when the molecular planes are rotated. The angular variation of J is used to estimate the corresponding changes in the transition rates. It is suggested that in certain cases the electronic transition occurs after thermally activated hindered rotation. Furthermore, the rotational energy barrier may be a principal component of the rather large electronic transport activation energy which is observed experimentally when carriers move by hopping in certain amorphous organic materials.
Al–GaAs (001) Schottky barrier formation
Authors: Svensson S. P. , Landgren G. , Andersson T. G.
Published: February 2003

Schottky diodes have been fabricated by in situ deposition of Al on GaAs (001) grown by molecular beam epitaxy. A detailed study of the Schottky barrier height (φb ) dependence on surface geometry and composition has been undertaken. Reconstructed, as well as very As- and very Ga-rich surfaces have been prepared. For comparison also samples with a thin interfacial AlAs layer were produced. The barrier height was determined by the capacitance–voltage (C–V) and current–voltage (I–V) techniques. The quality of the material was controlled by deep level transient spectroscopy revealing a total concentration of levels in the upper part of the band gap in the mid 1012 cm−3 range. Measuring the barrier heights of different diodes across a wafer showed lateral variations which were preserved also after annealing. A number of possible explanations for these variations were investigated but none proved satisfactory. Averaging over a large number of diodes revealed no apparent reconstruction dependence of the barrier height. The two measurement techniques gave the same barrier height φb ≊0.75 eV. By defining the Auger As (MVV)/Ga(MMM) signal ratio as a measure on the surface composition it was found that reconstructed surfaces appeared in the interval 2<As/Ga<5. Going outside this interval the barrier increased for As/Ga<2 and decreased for 5<As/Ga<10. For As/Ga>10 an increase was again found. Annealing at 573 K led to a rapid initial increase of the barrier height for the samples with reconstructed GaAs surfaces followed by a slower interdiffusion related increase during prolonged annealing.
A superconducting flip-flop using two interacting weak links
Authors: Zhang Lide , Dai Yuan-Dong , Kao Y. H.
Published: February 2003

Experimental results are presented showing that two superconducting indium microbridges coupled via a resistor and a capacitor can exhibit bistable states under a constant current bias, with one bridge at a finite voltage while the other is at zero voltage. The voltage states of the two microbridges can be interchanged by applying an external trigger current to the circuit. Current–voltage characteristics are compared with analog simulation as well as numerical calculation and found in good agreement. The effect of bias current, coupling resistor, capacitor, bridge resistance, and critical current values on the circuit properties are investigated. Our estimate for the flip-flop switching time is in the neighborhood of 0.1 nsec.
Cathodoluminescence from deformed CaO
Authors: Llopis J. , Piqueras J.
Published: February 2003

The cathodoluminescence (CL) emission from deformed and undeformed CaO single crystals has been studied in the scanning electron microscope. Deformation enhances the emission which appears, in the CL image, localized in the deformed regions of the crystal. The CL spectrum depends on the kind of deformation applied to the crystal and is unstable under the electron beam. The results are discussed in terms of impurities and of vacancy defects generated during the plastic deformation.
Photoelectron energy distribution of Cs3Sb
Authors: Lee Chunghsin
Published: February 2003

Photoelectron energy distributions from semitransparent Cs3Sb photocathodes have been measured using a parallel plate analyzer. Argon–ion and helium–neon lasers are used as light sources. The energy spread, defined as the full width at half-maximum of the distribution, is found to depend on the incident photo energy Eλ according to the empirical relation, ΔE(eV)=0.25 Eλ (eV)−0.39. It is shown that the photoelectron energy distributions vary with the emitted current density.
Photolithography experiments using forced Rayleigh scattering
Authors: Levenson M. D.
Published: February 2003

Phase conjugate wavefront generation by degenerate four-wave mixing has been used to project images with spatial resolution greater than 500 line pairs per millimeter. The nonlinear medium, a solution of rhodamine 6G in acetone, produced the images by forced Rayleigh scattering. These images were bright enough to expose photoresist in 30 sec and their quality was adequate for fine-line lithography and consistent with theoretical expectations.
Longitudinal voltage distribution in transverse rf discharge waveguide lasers
Authors: He D. , Hall D. R.
Published: February 2003

The longitudinal variation in the voltage across a waveguide channel, excited by a transverse radio-frequency discharge has been analyzed in terms of simple transmission line theory. It is shown that the voltage variation follows a cosine curve for the waveguide structure in the absence of a discharge, and that this behavior is only slightly modified when a discharge is running. The voltage may exhibit variations of 30% for cases where the relevant waveguide length is only one tenth of the effective rf wavelength. However, it is shown that this variation may be reduced to below 5%, by the use of multiple feed points or by appropriate inductive termination of the line. Experimental results are in good agreement with theoretical predictions.
Effects of keV electron irradiation on the avalanche-electron generation rates of three donors on oxidized silicon
Authors: Sah Chih-Tang , Sun Jack Yuan-Chen , Tzou Joseph Jeng-Tao
Published: February 2003

After keV electron beam irradiation of oxidized silicon, the avalanche-electron-injection generation rates and densities of the bulk compensating donor, the interface states, and the turnaround trap all increase. Heating at 200 °C can anneal out these three donor-like traps, however, it cannot restore the generation rates back to their original and lower pre-keV electron irradiation values. The experimental results also indicate that all three traps may be related to the same mobile impurity species whose bonds are loosened by the keV electrons and then broken or released by the avalanche injected electrons.
Shock-induced radiation spectra of fused quartz
Authors: Kondo Ken-ichi , Ahrens Thomas J. , Sawaoka Akira
Published: February 2003

An optical multichannel analyzer is applied to observe shock-induced radiation spectra of fused quartz in the 23–31 GPa shock-pressure range. Characteristics of sample-driver interface strongly influence both intensity and profile of the observed spectra. Brightness and color temperature are determined by an integration of spectral radiance and a fit to the greybody radiation spectrum, respectively. The resultant brightness and color temperature are lower and considerably higher than those estimated by the theoretical calculation, respectively. Some broad but strong line spectra are, however, superimposed onto the continuous greybody radiation spectrum even though the influences of the interface are reduced as much as possible. The line spectra are probably caused by electroluminescence and/or triboluminescence.
Total internal reflectance optoacoustic spectroscopy
Authors: Muessig P. R. , Diebold G. J.
Published: February 2003

When radiation undergoes total internal reflection at a solid–gas interface, an exponentially decaying wave, known as the evanescent wave, propagates into the gas. If the incident radiation is amplitude modulated and the gas has an absorption at the wavelength of the radiation, the optoacoustic effect can be produced by absorption of energy from the evanescent wave. Experiments with 10.6 μ radiation internally reflected in an NaCl prism show the amplitude of the optoacoustic signal (in SF6) to be linearly proportional to the product of the square of the electric field amplitude and the penetration depth of the evanescent wave as given by Fresnel’s equations. The amplitude of the optoacoustic signal in a 100-μl detection cell is found to increase linearly with the mole fraction of SF6 in He over the range from 10−5 to 10−2.
Characterization of laser-produced plasma x-ray sources for use in x-ray radiography
Authors: Matthews D. L. , Campbell E. M. , Ceglio N. M. , Hermes G. , Kauffman R. , Koppel L. , Lee R. , Manes K. , Rupert V. , Slivinsky V. W. , Turner R. , Ze F.
Published: February 2003

We report the absolute conversion efficiency ξx from the incident laser light energy to x-ray photons for laser-produced plasmas. Potential x-ray backlighting (radiography) line sources having photon energies from 1.4 to 8.6 keV are studied as a function of laser wavelength, pulsewidth, and intensity. The laser intensity and pulsewidth range from 1014 to 1016 W/cm2, 100 ps to 2 ns and include incident wavelengths of 1.06, 0.53, and 0.35 μm. We found that K-shell x-ray line emission ξx : (1) decreases with increasing x-ray energy, (2) decreases with increasing laser intensity, (3) decreases rapidly with pulselength, and (4) moderately increases with decreasing laser wavelength. On the contrary, for Au M band emission, at a fixed laser intensity and pulsewidth, ξx significantly increases (∼25×) upon decreasing the laser wavelength from 1.06 to 0.35 μm.
Pulsed ion beam generation with cryogenic-anode diode
Authors: Takahashi T. , Horioka K. , Hijikawa M. , Urai A. , Kasuya K.
Published: February 2003

Magnetically insulated ion diodes with a cryogenically refrigerated anode are proposed and their characteristics are examined. Proton beams of 7 A/cm2 and deuteron beams of 5 A/cm2, with energy of about 80 keV are extracted from a refrigerated H2O or D2O anode with good reproducibility and reasonable repetition rate.
A high-energy, laser accelerator for electrons using the inverse Cherenkov effect
Authors: Fontana J. R. , Pantell R. H.
Published: February 2003

A laser method for accelerating electrons is described, based on the inverse Cherenkov effect in a gas. The laser fields are in the form of a cylindrical cone of plane waves on whose axis travel the electrons, with the cone angle and the gas refraction index such that each electron sees constant fields in time. Expressions are obtained relating the overall energy transfer to total laser power and wavelength, and to gas index and interaction length. With laser powers now available, energy increments of tens of GeV are possible. For comparative purposes, a related alternative scheme involving electrons in vacuum and evanescent laser fields is also analyzed. It is found that the method applies particularly well to adding energy to the electron bunches produced by large microwave accelerators, as collision effects are less troublesome at high injection energies.
Liquid phase epitaxial growth on {111}In planes of InP
Authors: Logan R. A. , Henry C. H. , Merritt F. R. , Mahajan S.
Published: February 2003

Two step, liquid phase epitaxy is a high yield process without critical steps in the AlGaAs system when used to form buried devices such as buried heterostructure lasers, but similar procedures give a low yield in the InGaAsP system with many short circuited devices. The {111}In stop-etch plane enables one to etch narrow mesas (≊1.5-μm wide) to ensure single mode laser operation but regrowth of InP on this plane has a highly nonradiative interface, a characteristic that appears unique to this plane. Studies of the growth morphology correlate the nonradiative behavior with an inability of the initial islands of nucleation to spread laterally to form a continuous layer which gives rise to melt entrapment.
The heteroepitaxy of Ge on Si(100) by vacuum evaporation
Authors: Ohmachi Yoshiro , Nishioka Takashi , Shinoda Yukinobu
Published: February 2003

High quality Ge epitaxial growth has been attained on Si(100) substrates at relatively low temperatures, 350 and 440 °C, by a vacuum evaporation technique. Electrical property and structural quality for the Ge layer were evaluated by Hall measurement, x-ray diffraction, and electron beam diffraction. It is found that the growth layers are p type and that net acceptor concentration and mobility strongly depend on the layer thickness. Of particular significance is the fact that the acceptor concentration decreases most rapidly and hole mobility remarkably increases with the Ge thickness. The acceptor concentration and the mobility at a point larger than 0.7 μm from the lattice mismatched interface are 1.6×1016 cm−3 and 1040 cm2/V sec, respectively. Hole mobility varies as a function of T3/2 and T−3/2 below and above ∼100 °K.
Determination of the pressure of the semimetal–semiconductor transition in the presence of a resonant acceptor level
Authors: de Carvalho M. M. G. , Fau C. , Averous M.
Published: February 2003

An expression relating the pressure dependences of the resistivity and the mobile electron concentration is derived and used along with Hall effect and resistivity data to determine the pressure at which the semimetal–semiconductor transition occurs in Hg1−xCdxTe for x=0.124, at low temperatures. The method is applicable in the presence of a resonant acceptor level.
Direct intersubband optical absorption of semiconducting thin wire
Authors: Lee Johnson
Published: February 2003

The optical absorption due to direct intersubband transitions and including the broadening effects has been calculated by using an electric dipole approximation for a quasi-one-dimensional semiconducting thin wire. Effective mass approximation is adopted to determine the eigen functions and energies of the conduction electrons in Schrodinger equation by assuming a two-dimensional infinite potential well. When the electromagnetic wave is polarized in a ẑ direction which possesses a size-quantization effect in the thin wire, the selection rule requires that the sum of the quantum numbers of the initial state and finial state must be odd integers. ac and dc conductivities, and the absorption line shapes due to collisions are discussed.
Selective solar absorption of chemically etched aluminum–silicon films
Authors: Niklasson G. A. , Craighead H. G.
Published: February 2003

Electron-beam evaporated aluminum-silicon composites were chemically etched in a NaOH solution. This treatment produced a textured surface with high solar absorptance and low thermal emittance. The optical properties were qualitatively described by a graded refractive index model.
Submillisecond grating diffractions in nematic liquid crystal films
Authors: Khoo I. C. , Shepard S.
Published: February 2003

We have quantitatively observed a large fast component in the laser induced thermal grating in nematic liquid crystal films. This effect can be successfully utilized in submillisecond and high spatial frequency four wave mixing processes with low power lasers.
Work function of Mo(110) in mixed cesium and cesium monoxide vapors
Authors: Desplat Jean-Louis
Published: February 2003

Electron emission measurements from a Mo(110) emitter are performed in a diode containing both cesium and cesium monoxide vapors over a temperature range from 500 to 1800 K. The vapor pressures can be varied independently within a limited range: typical values are 1×10−3 and 2×10−4 Torr for cesium and Cs2O, respectively. At temperatures above 1000 K, the electron emission is increased by several orders of magnitude over that obtainable with cesium vapor alone by the addition of Cs2O. This is believed to result from the dissociation of Cs2O molecules adsorbed on the emitter surface to form an adsorbed oxygen layer. At temperatures below 700 K, the work function decreases with temperature to as low as 1.2 eV around 500 K. This is interpreted as resulting from multilayer deposition of Cs2O. Application to thermionic converters is discussed.
The role of lattice strain in the phase equilibria of III-V ternary and quaternary semiconductors
Authors: Bhattacharya Pallab K. , Srinivasa Sobhana
Published: February 2003

Liquidus and solidus isotherms for ternary GaxIn1−xAs and AlxIn1−xAs and quaternary In1−xGaxAs1−yPy and In1−xGaxAs1−ySby alloy semiconductors have been calculated using the regular solution phase equilibria model for liquid phase epitaxial growth. The effect of lattice-mismatch strain in the growing layer has been incorporated in the model. Calculations have been made in order to make comparisons with published results of previous workers for both lattice-matched and mismatched layers. It is found that agreements are better with the inclusion of strain than with a zero-strain model.
Space-time correlation properties of the magnetization process and eddy current losses: Theory
Authors: Bertotti G.
Published: February 2003

The relationship between eddy current losses and magnetization dynamics is investigated on general bases, starting directly from Maxwell equations. The intrinsically stochastic character of the magnetization process is conveniently dealt with by describing the magnetization rate İ(r,t) as a random sequence of elementary magnetization jumps, each corresponding to a sudden and localized displacement of a domain wall segment in the material. A general equation is obtained, in which the loss is expressed in terms of the energy spectrum ‖İ(k,ω)‖2 of İ(r,t). The loss calculation is thus reduced to the statistical problem of determining the energy spectrum of the random quantity İ(r,t) as a function of the shape and correlation properties of the elementary magnetization events. It turns out that the hysteresis loss is related to the internal structure of the elementary jumps, while the dynamic and anomalous losses are instead determined by the space-time correlation properties of the jump sequence. An explicit expression for the dynamic loss is obtained in the important case where the magnetization process is described as a Markov process, leading to a clear-cut, direct link between the loss and the fundamental quantities which characterize the magnetization dynamics at a microscopic level. The model predicts the exact value of the Pry and Bean loss, as a particular case corresponding to very specialized correlation properties of the jump sequence. However, the model permits one to deal with actually more general and realistic descriptions of the domain structure dynamics. We believe that future applications to practical cases will provide a deeper understanding of the physical origin of loss anomalies.
Material nonlinear piezoelectric coefficients for quartz
Authors: Brendel R.
Published: February 2003

An electroelastic or polarizing effect can be used to obtain material nonlinear pizoelectric or electroelastic coefficients. It is shown that these material coefficients, obtained from general rotationally invariant nonlinear equations for small field superposed on a bias, differ from those obtained by using the phenomenological expansion of the effective elastic constants. The eight independent electroelastic coefficients listed here was calculated by using experimental data available in the literature.
Absorption edge of tin disulfide single crystals
Authors: George Joy , Valsala Kumari C. K. , Joseph K. S.
Published: February 2003

Absorption edge measurements in tin disulfide single crystals have been made. It is found that there is a shoulder in the absorption, just before the onset of band to band transitions, which is caused by transitions from valence band to donor levels (due to a doubly ionizable sulfur vacancy) situated 0.17 eV below the conduction band. It is also found that there are three valence bands which originate by spin-orbit interaction and crystal field splitting. At room temperaure (295 K) the fundamental absorption starts at 2.070±0.001 eV and the transition leading to this is an indirect forbidden one. The photoconductivity maxima, observed at 2.3 eV by earlier workers is here shown to be due to transitions from third valence band to conduction band.
Residual shallow acceptors in GaAs layers grown by metal-organic vapor phase epitaxy
Authors: Roth A. P. , Charbonneau S. , Goodchild R. G.
Published: February 2003

A study of the residual impurities present in GaAs layers grown by metal-organic vapor phase epitaxy has been conducted. Gallium arsenide layers were grown from three different trimethylgallium sources as a function of the substrate temperature and the arsine partial pressure which are the main factors controlling the concentration of residual impurities. A study of the low temperature photoluminescence spectra of the layers supported by preliminary secondary ion mass spectroscopy measurements shows that the major residual acceptors are carbon, magnesium, and zinc.
Silicon oxidation studies: A revised model for thermal oxidation
Authors: Irene E. A.
Published: February 2003

A number of recent experimental silicon oxidation studies has suggested that the present form of the linear-parabolic oxidation model is inadequate in explaining the results. However, the best available oxidation data are linear-parabolic in shape. The present study relieves this dilemma by revising the linear-parabolic model. The revisions are essentially twofold: a new transport flux, viz., transport in micropores is invoked and the viscoelastic properties of SiO2 are utilized. A revised linear-parabolic model is obtained which better explains high and low temperature oxidation behavior, the formation higher density SiO2, and the initial oxidation regime.
Theory of generation-recombination noise and responsitivity in overlap structure photoconductors
Authors: Smith D. L.
Published: February 2003

A rigorous theory of both responsitivity and generation-recombination noise in overlap structure photoconductors is presented. Because generation-recombination noise dominates under typical operating conditions, these results combine to give the detectivity D*. It is found that both responsivity and D* can be improved by use of the overlap structure. The dependence of the optimum device geometry on the operating conditions, such as bias conditions, and on the parameter to be maximized (e.g., responsivity or D*), is derived. Symmetric and asymmetric overlap structure are compared, and it is found that, except at very small bias fields, an asymmetric structure gives the largest improvement in both the responsivity and D*. Both responsivity and noise voltage are found to roll off at lower frequencies for the overlap structure than for the standard design, but become equal to the standard design values at high frequencies. Numerical results for x≊0.21 HgCdTe detectors are presented. Using an asymmetrical overlap structure the theory predicts that, under usual operating conditions, the responsivity can be more than doubled and simultaneously D* increased by over 15%. Under optimum conditions D* for the overlap structure photoconductor can equal the usually quote value of D*BLIP for a photovoltaic device; that is, it can exceed the usually quoted value of D*BLIP for a photoconductor by as much as a factor of .
Photoionization cross section of electron irradiation induced levels in silicon
Authors: Brotherton S. D. , Parker G. J. , Gill A.
Published: February 2003

Transient photocapacitance measurements have been made on 12-MeV electron irradiated silicon diodes. Both p- and n-type substrates were used in order to investigate the centers in both halves of the band gap. Photoionization cross sections were measured on two divacancy levels at EV+0.20 eV and Ec−0.23 eV, the A center (Ec−0.17 eV), and further levels at Ec−0.09 eV and EV+0.35 eV. The only center likely to be a useful counterdopant for a 3–5-μm extrinsic silicon imaging device is the divacancy at EV+0.20 eV.
On a point defect inside an idealized elastic sphere
Authors: Ling Chih-Bing , Houska Charles R.
Published: February 2003

This paper presents a method of solution for the displacement, stress, and strain due to a point defect located inside a sphere. The solution is represented by a Love stress function in spherical coordinates, which is biharmonic in character. Two axisymmetric types of the point defect are considered. One is treated as a center of dilatation and the other as a double force without moment, or a doublet, oriented axisymmetrically. The Love stress function for the point defect in an infinite solid is specified in each case by a single biharmonic function. The residual tractions on the surface of the sphere left by this function are annulled by superposing two series of biharmonic functions. When the Love stress function is determined, the displacement, stress, and strain can be derived straightforwardly.
Extraordinary Hall resistivity in amorphous terbium–iron thin films and its temperature dependence
Authors: Malmhäll R.
Published: February 2003

Measurements of the extraordinary Hall effect are performed as a function of temperature for amorphous Tb–Fe thin films of compositions close to 21 and 25 at. % Tb. The experimental results indicate that the Fe sublattice gives the dominant contribution to the extraordinary Hall effect.
A study of Schottky contacts on indium phosphide
Authors: Hökelek E. , Robinson G. Y.
Published: February 2003

The Schottky-barrier energy φB for Al, Ni, Pd, Co, Au, and Ag contacts on chemically etched 〈100〉 surfaces of both p- and n-type InP was measured and the metallurgical behavior of the contact structures was studied using Auger-electron spectroscopy. No simple linear relationship could be found between the measured Schottky barrier energies on InP and the work functions or the electronegativities of the contact metals. Therefore, the results could not be explained in terms of the traditional Schottky and Bardeen theories. However, a very well defined relationship was observed between the Schottky barrier energies and the heats of reaction per formula unit ΔHr for the most stable metal phosphides that could be formed between the contact metals and the InP substrate. The contact metals Au and Ag whose phosphides are less stable than InP (i.e., ΔHr >0) produced diffuse interfaces, characterized by extensive outdiffusion of In, and yielded low values of φBp, the Schottky-barrier energy on p-type InP; whereas the contact metals Al and Ni which can form compounds with phosphorus that are significantly more stable than InP (i.e., ΔHr <0) showed less In outdiffusion and produced higher values of φBp. Two distinct Fermi-level pinning positions located at 0.50±0.01 eV and 0.40±0.02 eV below the conduction band minimum of InP were found and correlated to the metallurgical state of the contact structures. The findings of the present study strongly suggest that Schottky-barrier formation on InP is controlled by chemical reaction between the contact metal and the InP substrate, with the degree of chemical reactivity appearing to determine the Fermi-level pinning position at the interface.
Persistent photoconductivity in (Al,Ga)As/GaAs modulation doped structures: Dependence on structure and growth temperature
Authors: Klem J. , Masselink W. T. , Arnold D. , Fischer R. , Drummond T. J. , Morkoç H. , Lee K. , Shur M. S.
Published: February 2003

When modulation doped (Al,Ga)As/GaAs heterostructures are exposed to light, the interface electron concentration and in most cases the mobility increases substantially for lattice temperatures below ∼100 K. A substantial part of the increase is persistent and attributed to the excitation of electrons from a donor–vacancy complex in the (Al,Ga)As. The change in the free electron concentration in the (Al,Ga)As is calculated using a recently developed model for electron transfer across a modulation doped heterojunction. The persistent increase in the free electron concentration is used as a measure of the trap concentration. The magnitude of the photoconductivity response decreased with increasing growth temperature in the range 580–750 °C. The dependence on Al mole fraction was studied for 0.16≤x≤1.0 and found to be a maximum for x∼0.3.