bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of ion temperatures by means of Rutherford scattering of energetic neutrals above the limiting angle
Authors: van Blokland A. A. E. , Donné A. J. H.
Published: July 2002

A technique to measure the ion temperature in a thermonuclear plasma is proposed, based on Rutherford scattering of a beam of energetic neutral particles by the plasma ions. If the mass of the beam particles, mb, is larger than the mass of the scattering ions, mp, a sharp maximum (limiting) angle θlim=sin−1(mp/mb) exists in case the thermal velocities of the plasma ions are neglected. When the scattering ions have thermal velocities, however, scattering of beam particles can occur through angles larger than θlim. Measurement of the intensity of particles above the limiting angle can be used to find the temperature of the plasma ions, with a 10% accuracy and a spatial and temporal resolution of 10 cm and a few μs, respectively, provided the ion velocity distribution is Maxwellian. A feasibility study elucidates that this method can also be used to measure the temperature of a 3He minority component.
Radiation-induced defect centers in glass ceramics
Authors: Tsai T. E. , Friebele E. J. , Griscom D. L. , Pannhorst W.
Published: July 2002

Electron spin resonance (ESR) was used to characterize the radiation-induced defect centers in low-thermal-expansion glass ceramics, including two types of Zerodur and Astrositall. The observed ESR spectra can be associated with different types of defect centers: a Zn+ center, several types of oxygen hole centers (OHCs), an aluminum-oxygen hole center (Al-OHC), an Fe3+ center, Ti3+ and Zr3+ centers, and three types of As centers. An Sb4+ center, which is not observed in Zerodur, is tentatively identified in Astrositall. From the effect of crystallization on the observed defect concentrations in Zerodur and computer simulation of the spectral lines of some of the centers, we infer that among the nine defect centers observed in the Zerodurs, the As-associated centers are located in the glassy phase and/or at the interface between the glassy and crystalline phases, Zn+ and Al-OHC are in the crystalline phase, and the rest (including most of the OHCs) are in the glassy phase. Radiation-induced compaction in these materials appears to be related to the generation of OHCs in the glass phase.
Gaussian decomposition of beams and other functions
Authors: de Wolf David A.
Published: July 2002

The Gabor expansion of a function f (x) decomposes it into a double sum over integers m and n of a product of basis functions g(x−mX) and Fourier-series exponentials exp(2πin/X) for given spacing X. The choice of basis function determines the coefficients amn of the expansion. If f (x) is band limited, the double sum can for all practical purposes be replaced by a single sum over Gaussian basis functions. This is extremely useful for expansion of multidimensional functions such as beams in phase space. Conditions of validity are given, and several examples illustrate the technique.
Effect of illumination on the tunneling conductance of high-electron-mobility structures
Authors: Hurd C. M. , McAlister S. P. , McKinnon W. R. , Day D. J.
Published: July 2002

We consider a typical unipolar GaAs/AlxGa1−xAs heterostructure with deep donors in both the AlxGa1−xAs supply layer and in the GaAs buffer, and with parallel conduction through the undepleted supply layer. We calculate the effect of steady illumination on the internal barriers that control access to the conduction channels for electrons passing between source and drain. From the barrier heights obtained, we calculate the tunneling conductances at the supply/cap and supply/buffer interfaces by treating them as back-to-back Schottky diodes. We express these conductances as light-dependent access resistances to the parallel conduction channels in the structure, taking into account the distributed resistance between the channels. Thus we extend an existing model of a unipolar heterostructure to include the effects of illumination on the current distribution between parallel channels.
Structural investigation of surfaces of blue bronze and hematite by scanning tunneling microscopy
Authors: Heil J. , Wesner J. , Lommel B. , Assmus W. , Grill W.
Published: July 2002

Images of the surfaces of cleaved crystals of K0.3MoO3 (blue bronze) and α-Fe2O3 (hematite) have been obtained in air at room temperature using a scanning tunneling microscope in the fast scanning mode. The pictures show a resolution in the range of 0.5 nm and compare well with surface structures derived from the bulk crystal parameters.
Experimental study of energy transport in thin Al and Au foils irradiated with a 263-nm laser
Authors: Tanaka K. A. , Yamauchi A. , Kodama R. , Mochizuki T. , Yabe T. , Yamanaka T. , Nakai S. , Yamanaka C.
Published: July 2002

Irradiating an ultraviolet (uv) laser on aluminum (Al) and gold (Au) thin targets, emissions from the rear side of the targets were temporally resolved. A clear difference was observed between the above two targets. Given the fact that absorbed laser energy can be converted with a very high efficiency to soft x rays in a high-Z plasma, a characteristic emission peak only observed for Au targets was attributed to the effect of soft x-ray energy transport. The observed results were compared with those computed by a one-dimensional hydrodynamic simulation himico. The ablation pressures estimated from the emissions indicate that the pressure scaling for Au is close to the one by x-ray drivers rather than by a uv laser.
Perpendicular magnetic anisotropy and magneto-optical Kerr effect of vapor-deposited Co/Pt-layered structures
Authors: Zeper W. B. , Greidanus F. J. A. M. , Carcia P. F. , Fincher C. R.
Published: July 2002

We prepared by vapor deposition at room temperature thin (500 Å) Co/Pt multilayers or layered structures directly onto glass or Si substrates. They show a preferential magnetization perpendicular to the film plane for Co thicknesses below 12 Å and a 100% perpendicular remanence for Co thicknesses below 4.5 Å. The magnetic anisotropy can be explained by an interface contribution to the anisotropy. We also investigated the magneto-optical (MO) polar Kerr effect of these multilayers. Because of their excellent magnetic properties and their potentially high oxidation and corrosion resistance, these Co/Pt-layered structures are very promising candidates for MO recording. The Kerr rotation θk at λ=820 nm for a 35×(4.0 Å Co+12.7 Å Pt)-layered structure, which has 100% magnetic remanence, is modest (−0.12°), but the reflectivity R is high (70%), which results in a respectable figure of merit Rθ2k. Furthermore, the Kerr effect increases towards shorter wavelengths and thus favors future higher-density recording.
Electronic transport investigation of arsenic-implanted silicon. I. Annealing influence on the transport coefficients
Authors: Christofides Constantinos , Jaouen Herve , Ghibaudo Gerard
Published: July 2002

ac and dc Hall-effect measurements, as a function of temperature and frequency, have been employed to characterize arsenic-implanted silicon films. A significant modification of the carrier scattering mechanism occurs for annealing temperature around 550 °C which is manifested as a drastic change in the behavior of the temperature and frequency dependence of the transport parameters. Finally, the experimental results are discussed with respect to transport models which take into account short- and long-range disorder, in order to help us understand the behavior of the implantation defects and inhomogeneities, and their thermal annihilation.
Generation-recombination-induced nonlinear characteristics of solid-state bipolar devices
Authors: Khan W. I.
Published: July 2002

Generation-recombination processes have been studied with the use of a phenomenological approach. The approach is in principle based on the combined mechanisms involved in the dominant deep-level traps and in radiative and nonradiative processes in these devices. It is possible with the use of the approach to predict different types of carrier transition phenomena under zero- and nonzero-bias conditions. Carrier phase diagrams have been produced which can depict, in classified form, all possible transitions as a function of the coefficients involved in the phenomena. Attempts have also been made to deal with the generation-recombination processes associated with the midgap single-level impurities, in line with Shockley–Hall–Read theory. The approach leads to the development of a two-root model which demonstrates the existence or nonexistence of hysteresis in the I-V characteristics of devices. Detailed mathematical results and physical modeling have been presented. Graphical representation and experimental evidence of the model have also been produced.
Accurate determination of heterojunction band discontinuities in the presence of interface traps using capacitance-voltage techniques
Authors: Leu L. Y. , Forrest S. R.
Published: July 2002

The effects that interface traps have on the determination of the heterojunction band discontinuity energies ΔEc measured via capacitance-voltage analysis are considered. We show that both the trap density σiK and conduction-band discontinuity energy ΔEcK measured using the method of Kroemer, Chien, Harris, and Edwall [Appl. Phys. Lett. 36, 295 (1980)] are functions of the heterointerface width d, the difference between the actual and the measured heterojunction positions Δxj, and the doping levels of the two contacting materials. These error sources can be corrected by using simple amended equations developed in this study. This amended technique improves the measurement accuracy of both trap density and heterojunction band discontinuity energy, is easy to use, and is relatively insensitive to variations in doping and trap density in the interface region. This technique is applied to the analysis of a vapor phase epitaxial N-n InP/In0.53 Ga0.47 As heterojunction for which we find ΔEc =(0.24±0.01) eV.
Pencil lead tips: A field ion and field electron emission microscopic study
Authors: Khairnar Rajendra S. , Dharmadhikari C. V. , Joag Dilip S.
Published: July 2002

Pencil lead tips composed of graphite flakes were subjected to field ion and field emission microscopic investigations. The ion micrographs showed elongated images of ledge atoms of the graphite flakes due to uneven magnification over the layers of the flake. The gross features of the field evaporated tip surface were observed by scanning electron microscopy. The field emission pattern showed emitting lobes which displayed intensity fluctuations consisting of a combination of emission spots turning on and off randomly and a localized flicker of individual spots. These effects gave rise to noise in the emission current involving isolated spikes of rapid rise time and trains of digital pulses of constant height. The variation of noise with residual gas pressure, emission current, and temperature has also been investigated. The results are discussed in view of the microtopography of the pencil lead tips and the nature of the emitting sites on the surface.
Conversion acceptor and its contribution to hole scattering in annealed GaAs
Authors: Choi C. T. , Kim B. H. , Jung Y. J. , Shin Y. G. , Lee B. C. , Lee K. H. , Lee H. J.
Published: July 2002

Unintentionally doped GaAs crystals grown by the horizontal Bridgman method were annealed at temperatures in the range from 700 to 910 °C under As overpressure. The n-type crystals subjected to heat treatment under As overpressure lower than the growing pressure revealed a conductivity-type conversion to p type. The electrical conductivity, Hall coefficient, and photoionization cross sections were measured on the p-type samples, and the resulting analysis indicates that the conversion center is a double acceptor, most probably associated with CuGa defect. The activation energies attributable to the singly and doubly ionized states of the acceptor were found to be ∼150 and ∼380 meV at 0 K, respectively. The doubly ionized acceptor states turned out to provide strong space-charge scattering, which plays a crucial role in determining the hole behavior in the present material at high temperatures.
Radiation losses in intersecting optical waveguides
Authors: Agrawal Niraj , McCaughan L.
Published: July 2002

A systematic theory for radiation losses in intersecting optical waveguides is presented for the first time. These losses are shown to arise from a coupling between guided and radiation fields of the individual waveguides. The existence of a doubly peaked radiation loss characteristic with respect to the intersection angle is predicted for single-Δn intersecting waveguides and verified experimentally. A method for reducing the radiation losses by a simple modification of the intersection region is also discussed.
Laser-induced ablation pressure in thin gold foils
Authors: Godwal B. K. , Shirsat T. S. , Pant H. C.
Published: July 2002

A study of the variation of the effective ablation pressure with thickness of laser irradiated thin gold foils is presented. Gold foils (2.5 and 12.0 μm thick) were irradiated by a glass laser (1.06 μm wavelength, 5-ns pulse duration) in 1011–1013 W/cm2 irradiance range. Ablation pressure and its scaling is found to be higher for the 12-μm-thick gold target. The results are consistent with other results obtained on the basis of enhanced x-ray transmission through thin gold foils. Theoretical estimates of the x-ray transport are carried out to support this.
Decay instability of an upper-hybrid wave in a plasma cylinder
Authors: Konar S. , Jain V. K. , Tripathi V. K.
Published: July 2002

A nonlocal theory of parametric decay of an upper-hybrid wave into an ion-acoustic wave and an upper-hybrid sideband reveals that an axially symmetric pump tends to excite axially symmetric modes. The growth rate falls off with the frequency ω0 of the pump and the azimuthal model number l of the decay waves. In cases where ion and electron temperatures are nearly equal the decay process goes over to nonlinear ion Landau damping; however, the behavior of the growth rate with ω0 and l remains the same. The resonant and nonresonant decay via ion-cyclotron modes also show similar behavior, although with a smaller growth rate.
Incident-angle bandwidth of surface acoustic wave acousto-optic devices using total internal reflection
Authors: Li S. W. , Bourkoff E.
Published: July 2002

For YZ-LiNbO3 acousto-optic devices that use the side entry and total internal reflection techniques, interaction efficiency is calculated using the Green’s function model and the proper expressions for the piezoelectric surface wave and Gaussian beam. This theoretical calculation taking the special interaction geometry into account shows that the incident-angle bandwidth for P-polarized light is about twice as large as that for S-polarized light for YZ-LiNbO3 devices, which agrees with previously reported experimental results.
Thermal properties of five-layer infinite plate structures with embedded heat sources
Authors: Palisoc Arthur L. , Min Y. Jay , Lee Chin C.
Published: July 2002

The analytical three-dimensional temperature solution of a five-layer anisotropic plate structure with infinite lateral boundaries and with embedded heat sources has been derived. By incorporating the method of images, this solution can be utilized to obtain the exact solution of a five-layer structure with rectangular lateral boundaries and with embedded heat sources. Consequently, this solution constitutes the most general analytical expression reported so far. The solution is in the form of a double Fourier integration. To carry out the integration effectively, the characteristics of the transformed temperature in the Fourier domain have been studied. Subsequently, an integration algorithm has been developed for the efficient numerical integration of the double Fourier inverse transform for temperature calculation. In comparison with the double Fourier series solution of rectangular structure, the solution reported here is not only much more computationally effective but also more general. Besides thermal problems, the solution also has important applications in electrostatics since the thermostatics share the same equations with electrostatics. Examples of electrostatic problems are multilayer stripline, and microstrip, multilevel interconnection of integrated circuits, and multilayer printed circuit boards.
Strain effects on superconducting properties in Nb3Al multifilamentary wires
Authors: Kuroda T. , Wada H. , Iijima Y. , Inoue K.
Published: July 2002

Critical temperatures Tc and critical currents Ic under uniaxial tensile loading have been studied on multifilamentary Nb3Al wires fabricated by a newly developed composite diffusion process. Both Tc and Ic are monotonically decreased with applied strain, showing reversible behavior up to fracture strains of the wires at about 1.3%. These characteristics may be attributed to the composite wire structure, namely to the small difference in thermal contraction between the niobium matrix and the Nb3Al filaments, as well as to the extremely small sizes of the Nb3Al filaments.
S parameter measurements on single superconducting thin-film three-terminal devices made of high-T
c and low-T
c materials
Authors: Martens J. S. , Hohenwarter G. K. G. , Beyer J. B. , Nordman J. E. , Ginley D. S.
Published: July 2002

We have investigated three-terminal single-layer thin-film superconducting devices made of YBaCuO and Nb. The devices incorporate regions of weak superconductivity in multiple parallel links that are influenced by current in a separate control line. These experiments were designed to study the possible application of this device as an rf amplifier. With the device biased, rf power was applied to the control line and the transmission coefficient, S21, was measured. The reverse transmission coefficient, S12, was also measured for comparison. Upon biasing into a flux flow state, the S21 of the device at rf frequencies was found to increase 10–15 dB over the zero bias value and over the reverse feed (S12 ) value. The device behaved linearly up to power inputs of +5 dBm (1-dB compression point). The bandwidth was limited only by the impedance transformer.
Influence of ion-bombardment cleaning on the aging rates in island copper films on fused quartz substrates
Authors: Murali Sastry M. S. , Pattabi Manjunatha
Published: July 2002

Presented in this communication are the results of aging experiments carried out on copper island films deposited on fused quartz substrates held at 380 K in a vacuum of 1×10−5 Torr. Ion-bombardment cleaning of the substrates prior to deposition of the films was found to significantly alter the aging rates in the films. The mobility coalescence model was operative during the aging process, and it is inferred from the data that adsorbed gases on the substrate surface affect the nucleation and reduce the mobility of copper islands, which reduces the aging rate. The mean island sizes were determined for some of the films from activation energy measurements.
Nonlinear conductivity of an In-Y1Ba2Cu3O7−x interface
Authors: Hui Y. C. , Hui P. M. , Lemberger T. R. , Garland J. C.
Published: July 2002

We report dynamic resistance (dV/dI) measurements of a large, macroscopic interface between In metal and polycrystalline Y1Ba2Cu3O7−x. The interface was prepared by pressing a 3-mm2 In pellet onto a freshly prepared Y1Ba2Cu3O7−x polycrystalline ceramic surface. Although this interface covered about 105 crystallites of the superconductor, the electrical characteristics were very similar to those observed in point contact measurements on both single-crystal and polycrystalline specimens. A slowly varying bias-dependent background resistivity, narrow resistance peaks, and a zero-bias resistance anomaly were all features of the dV/dI spectra. Both the temperature and magnetic field dependencies of the interface conductivity are reported.
The effects of growth temperature on the dimethyl-Cd doping of GaAs by metalorganic vapor-phase epitaxy: Evidence of impurity-induced nucleation of two-dimensional clusters
Authors: Matsumoto Koh , Hidaka Junnich , Uchida Kazuo
Published: July 2002

Dimethyl-Cd (DMCd) doping of GaAs was carried out at various growth temperatures ranging from 650 to 750 °C by atmospheric pressure metalorganic vapor-phase epitaxy MOVPE. For the samples grown at 680 °C, the acceptor concentration was proportional to DMCd flow rate, while for the samples grown at 720 °C, the acceptor concentration was proportional to the exponential of the DMCd flow rate. To explain this exponential dependency at 720 °C, the impurity-induced two-dimensional nucleation model was proposed.
Application of surface laser-light scattering spectroscopy to photoabsorbing systems: The measurement of interfacial tension and viscosity in crude oil
Authors: Dorshow Richard B. , Swofford Robert L.
Published: July 2002

We have successfully used surface laser-light scattering spectroscopy to measure the interfacial tension and viscosity in a strongly photoabsorbing crude oil system. Photothermal distortion of the sample interface was avoided by judicious choice of laser power, scattering angle, and optical configuration. Measurements were performed on a stock tank crude oil/air interface at ambient conditions for a series of incident laser powers. The measured interfacial tension was in good agreement with that obtained using the Wilhelmy plate technique. The measured viscosity was in good agreement with that obtained using low-shear viscometry. Both the interfacial tension and the liquid viscosity were independent of laser power for low incident powers. Surface laser-light scattering is now fully qualified for measurements of interfacial tension and viscosity of reservoir fluids at the elevated pressures and temperatures of an oil-field reservoir.
Volumetric stability of two-step ionization dominated discharges
Authors: Friedland L. , Jacob J. H. , Mangano J. A.
Published: July 2002

The stability of self-sustained discharges is investigated both analytically and numerically. The dominant ionization mechanism in the discharge is assumed to be two-step ionization while both electron loss mechanisms attachment and recombination are considered. It is shown that the stiff voltage source is marginally stable when the electron loss rate is due solely to electron-molecular ion recombination. In the presence of attachment the stiff voltage source is unstable and the growth rate of the instability is approximately the attachment rate. A stiff current is shown to be more stable and the discharge is stable irrespective of the loss rate. The theory is verified numerically for at atmospheric Co2 laser discharge.
Space- and time-resolved photoluminescence of In-alloyed GaAs using photoluminescence excitation correlation spectroscopy
Authors: Johnson M. B. , McGill T. C. , Hunter A. T.
Published: July 2002

Photoluminescence excitation correlation spectroscopy is used to space and time resolve photoluminescence (PL) intensity variations in the region of isolated dislocations in as-grown In-alloyed GaAs. Spatially resolved PL maps show an annulus of high intensity with an inner and outer dark background surrounding a dislocation. Typical inner and outer diameters of the annuli are about 200 and 400 μm, respectively, which is smaller than the average dislocation separation in In-alloyed GaAs. Temporal resolution of the PL measures the carrier lifetime in the bright and dark regions. These measurements show that the lifetime variation accounts for the PL intensity variation. The variation of the lifetime with temperature indicates that the defects governing the lifetimes in the bright and dark regions are different. Moreover, both defects are deep and neither defect is EL2.
Epitaxial growth of ZnTe on GaSb(100) by rf sputtering
Authors: Tokumitsu Yoji , Kawabuchi Akira , Kitayama Haruyuki , Imura Takeshi , Osaka Yukio , Nishiyama Fumitaka
Published: July 2002

Zinc telluride is deposited by rf sputtering on the clean surface of well lattice-matched GaSb(100) substrates (with mismatch about 0.1%). The surface native oxides have been etched off by H2 plasma treatment at substrate temperatures of more than 220 °C. Reflection high-energy electron diffraction patterns of ZnTe films prepared at 320 °C are streaked with (100) characteristics, which shows that the deposited layers are grown epitaxially. The crystalline quality of the ZnTe films which depends on the substrate temperature is evaluated by means of the optical reflectance. The peak height of the second-derivative reflectance spectra, a measure of the crystalline quality, steeply increases at deposition temperatures of 270–320 °C. The deposition temperature of more than 320 °C is needed for high crystalline quality. Moreover, the film prepared at 370 °C on GaSb gives a minimum aligned yield χmin of 8% in ion beam channeling experiments of Rutherford backscattering spectrometry.
Observation of a propagating normal/superconducting interface via I-V analysis in YBa2Cu3Ox
Authors: Rey C. M. , Kennedy R. J. , Boninsegni M. , Moulton W. G. , Testardi L. R.
Published: July 2002

Current-voltage (I-V) measurements for the high-temperature superconducting phase of polycrystalline YBa2 Cu3 Ox show loop behavior for temperatures below Tc . A thermal model has been constructed which shows that the loop is caused by a normal/superconducting interface, created by the heat at the solder junction, propagating down the sample. The importance of this effect to device applications and to critical current measurements is briefly discussed.
Prebreakdown characteristics of thin film-coated molybdenum electrodes
Authors: He Ping , Sinha M. K.
Published: July 2002

The effect of thin molybdenum films on molybdenum cathodes on the prebreakdown current between molybdenum electrodes in high vacuum has been studied. Films of four thicknesses: 10, 30, 100, and 300 Å were used and the Fowler–Nordheim plots were made to determine the field enhancement factor β and the electron emission area a. Maximum reduction of the prebreakdown current by a factor of 3000 was observed. The reduction in the current is a result of a decrease of both the field enhancement factor and the electron emission area of the cathode.
Comment on ‘‘Laser-induced reemission of silicon atoms implanted into quartz’’ [J. Appl. Phys. 6
4, 3663 (1988)]
Authors: Miotello A. , Checchetto R.
Published: July 2002

Recently reported experimental results concerning changes of as-implanted Si profiles into quartz, following nanosecond laser pulses, are reanalyzed in terms of Si thermal migration in a laser-induced liquid phase of SiO2. The occurrence of a liquid phase is proved by numerical integration of the heat equation including the Stefan boundary condition.
Electron paramagnetic resonance study on the p-type doping of copper indium disulfide by phosphorus implantation
Authors: Hsu Y. J , Hwang H. L.
Published: July 2002

High doping efficiencies have been observed in phosphorus-implanted CuInS2 single crystals by pulsed electron-beam annealing, which could not be achieved by the conventional furnace annealing method. This paper presents the investigations by using the electron paramagnetic resonance measurement on this p-type doping effect. The electron paramagnetic resonance signal from the phosphorus interstitials was observed in the as-implanted crystals. The same signal appeared in the subsequently thermally annealed samples but disappeared in the pulsed electron beam annealed ones. This shows the superiority of melting crystal surfaces in the pulsed electron-beam annealing on eliminating the implantation-induced defects to obtain high doping efficiencies.
Effects of rapid thermal oxidation on electrical characteristics of chemical-vapor-deposited SiO2 gate dielectrics
Authors: Ting W. , Li P. C. , Lo G. Q. , Kwong D. L. , Alvi N. S.
Published: July 2002

In this paper, effects of rapid thermal oxidation (RTO) on electrical characteristics of thin (200 Å) chemical-vapor-deposited (CVD) SiO2 have been studied. Current density-electric field (J-E) characteristics, flat-band voltage, and gate voltage shifts under constant-current stressing were also examined. Results show that RTO improves the charge trapping property of as-deposited CVD oxides. In addition, RTO of CVD oxides also increases the electron injection barrier height of the as-deposited samples at the cathode and produces devices with lower leakage current and tighter breakdown distribution.
A measurement of a minority-carrier lifetime in a p-type silicon wafer by a two-mercury probe method
Authors: Suzuki Eiichi , Hayashi Yutaka
Published: July 2002

A simple evaluation technique of a lifetime τ and diffusion coefficient D of minority carriers in a semiconductor wafer by using the newly contrived two-mercury probe method and a graphic analysis is described. The two-mercury probe method makes it possible to measure τ and D in an electrode-free wafer sample. The graphic analysis can be applied to a semiconductor wafer with a large backsurface recombination velocity for evaluation of τ and D. Using the proposed technique, the minority-carrier lifetime and diffusion coefficient have been successfully evaluated even in a p-type low-resistivity (0.2–0.5 Ω cm) silicon wafer for the first time.
Spectral dependence of photorefractive erasure in Bi12GeO20 and Bi12SiO20
Authors: Baquedano J. A. , Contreras L. , Diéguez E. , Cabrera J. M.
Published: July 2002

A holographic method similar to that previously used with LiNbO3 to study the spectral behavior of photorefractive centers has been applied to Bi12SiO20 (BSO) and Bi12GeO20 (BGO). By erasing with incoherent light a previously written grating, measurements of the grating decay constants as a function of the erasing wavelength have been carried out. The grating erasure exhibits decays made up of a sum of two exponential terms for all wavelengths between 390 and 620 nm. In terms of recent photorefractive models which use two active species, our results imply that there exist two different photorefractive centers in BGO and BSO. By numerically fitting the observed spectral dependencies of the decay constants to the model equations, the absorption bands associated to these centers have been obtained. Their peak positions and half-widths are the following: 2.7 eV (0.27 eV) and 3.1 eV (0.4 eV) for BSO; 2.8 eV (0.3 eV) and 3.1 eV (0.4 eV) for BGO.
Saturation behavior of silicon Auston switches
Authors: Dunham Mark E. , Ziemba Frank , Moross Jack
Published: July 2002

The laser-energized photoconductive switch (Auston switch) has been described previously with various applications. We report new measurements investigating the physical behavior of several types of silicon Auston switches, establishing basic quantum efficiency, charge-voltage behavior, and voltage-time response. Previously predicted nonlinear effects are observed, resulting in departures from ideal performance for most designs. However, operation in the saturated mode and a transmission line environment allows several designs to produce a step waveform that gives previously unattainable combinations of amplitude and rise time. In particular, the goal of a low aberration, 150-V, 35-ps step has been achieved, and process parameters affecting this performance are described.
Chemical vapor deposition of YBa2Cu3O7−x superconducting films
Authors: Dickinson P. H. , Geballe T. H. , Sanjurjo A. , Hildenbrand D. , Craig G. , Zisk M. , Collman J. , Banning S. A. , Sievers R. E.
Published: July 2002

Superconducting thin films of YBa2Cu3O7−x have been produced by chemical vapor deposition. Volatile coordination compound precursors of the oxide components, β-diketonates of Y, Ba, and Cu, are thermally decomposed on hot substrates to form crystalline films. The Ba compound was evaporated in the presence of externally added vapors of the β-diketonate to obtain steady evaporative behavior. Superconducting films were obtained on SrTiO3 substrates at temperatures above 800 °C. The best films have onset temperatures of 90 K and loss of resistance as high as 68 K. Epitaxial growth was obtained.
Monte Carlo study of backscattering of β rays from various monoatomic slabs
Authors: Pandey L. N. , Rustgi M. L.
Published: July 2002

A Monte Carlo study of the backscattering coefficients and backscattering intensity of β rays from 204 Tl and 90 Y sources from slabs of Al, Cu, Sn, Tb, and Pb of different thicknesses is carried out. The results for angles of incidence 0°, 30°, 45°, and 60° and absorber thicknesses of 3, 5, 10, 15, 30, and 50 mg/cm2 for 204 Tl β rays and thicknesses of 3, 5, 10, 20, 50, 100, 150, and 190 mg/cm2 for 90 Y β rays are given in tabular form. On using normalization factors good agreement with the measurements of Sharma and Singh is obtained. A phenomenological attempt to investigate a relationship between the backscatter intensity and atomic number Z of the backscatterer indicates that the backscattered intensity is a linear function of ln Z(Z+1). A partial theoretical justification for this relationship is given.
A new theoretical model for transverse acoustoelectric voltage measurements on Si/SiO2 structures
Authors: Palma F.
Published: July 2002

Acoustoelectric interaction measurements, and particularly transverse acoustoelectric voltage (TAV) measurements, have been extensively used for the determination of a number of semiconductor parameters. These measurements are rapidly becoming a powerful tool to study semiconductor processes. In the last years, they have also been proposed as a tool for testing of microstructure geometries. One of the most relevant characteristics of acoustoelectric measurements, which make them particularly attractive, rely on their nondestructive nature. Neither contacts nor technological processes are required on the surface of the semiconductor under test once the separate-medium structure is used. On the other hand, the separate-medium structure is greatly sensitive to the sample position and to the clean condition of the surface. The grade of coupling between the surface acoustic wave and the semiconductor can dramatically affect the amplitude of the detected TAV signal. In order to obtain quantitative measurement, maintaining the nondestructive capability of the technique, it is always necessary to perform a comparison between experimental results and theoretical predictions versus one external, controlled parameter. From these considerations it is clear that measurement precision relies on the availability of a good theoretical model of the acoustoelectric interaction. In this paper a new theoretical model for the acoustoelectric interaction in the Si/SiO2 structure under field effect is presented, and theoretical expression of TAV versus bias voltage is calculated to be used in interface trap density measurements at a Si/SiO2 interface. Experimental verification of the model is also presented together with a procedure for the calculation of the interface trap density.
Investigation of thermally grown copper oxides with inelastic electron tunneling spectroscopy
Authors: Ramsier R. D. , Mallik R. R. , Henriksen P. N.
Published: July 2002

Low energy inelastic electron tunneling spectra are presented for thermally formed oxides on copper films. Thinner oxide tunnel barriers are observed to contain interfacial gradients as evidenced by spectral intensity asymmetries between forward and reverse bias, whereas thicker oxides appear to be more uniform in composition. Spectral results are in good qualitative agreement with reported studies of bulk cuprous oxides, and the semiconducting nature of the oxide layers is reflected in a negative temperature coefficient of resistivity of the tunnel junctions.
Demonstration of completely organic, optically clear radioluminescent light
Authors: Renschler C. L. , Clough R. L. , Shepodd T. J.
Published: July 2002

A new type of radioluminescent light source has been demonstrated. This all-organic system consists of covalently bound tritium within a solid, optically clear polymeric matrix. The matrix contains a set of organic luminophores that capture excitation energy from beta decay and red shift the energy in a stepwise fashion, after which a chosen wavelength is emitted as fluorescence. Both blue and orange lights have been fabricated. Unlike currently available tritium gas tube lights or radioluminescent paints, the brightness of these new systems is, in principle, scalable because self-attenuation and absorption effects are minimized.
A physics-based bipolar transistor model for low-temperature circuit simulation
Authors: Liou J. J. , Yuan J. S.
Published: July 2002

A comprehensive bipolar transistor model based on the Gummel–Poon model [Bell Syst. Tech. J. 49, 827 (1970)] for low-temperature circuit simulation is presented. Relevant low-temperature physics such as doping-dependent dielectric permittivity, temperature-dependent free-carrier mobility and intrinsic carrier density, and de-ionization of impurity dopants are included in the model. Consequently, the model does not require temperature fitting parameters as does the Gummel–Poon model. Comparisons of the present model with the Gummel–Poon model, with experimental data, and with simulation from a two-dimensional device simulator (pisces) are included.
Pressure wave propagation in a partially water-saturated porous medium
Authors: Sniekers R. W. J. M. , Smeulders D. M. J. , van Dongen M. E. H. , van der Kogel H.
Published: July 2002

Reflection and transmission of a stepwise pressure wave incident to a partially water-saturated porous medium is investigated. The strongly dispersive character of the phase velocities and damping due to air bubble resonance causes pressure over- and undershoot in reflection and a fast oscillatory disturbance propagating into the porous medium. Theoretical results are compared with new results from shock tube experiments. A qualitative agreement is found.
Electrochromic properties of rf-sputtered tungstic oxide film prepared from a W metal target
Authors: Akram Hossain , Kitao Michihiko , Yamada Shoji
Published: July 2002

Tungstic oxide film is prepared from a W metal target by the rf sputtering method and its electrochromic characteristics are compared with that from WO3 target. Maximum coloration efficiency found for both kinds of films are equal and about 0.06 cm2 /mC at the wavelength of 600 nm, which is higher than that of typical evaporated films. Films from the W metal target, for the maximum coloration efficiency, can be prepared at a broader oxygen range of sputtering atmosphere than that of a WO3 target. It is found that films from a W metal target can be prepared at higher input power than that of a WO3 target. Therefore, the W metal target is suitable to get films with required thickness and EC characteristics.
Influence of growth temperature on stoichiometry in ZnSe
Authors: Morimoto Keizo
Published: July 2002

The influence of growth conditions such as substrate temperature Ts and [H2Se]/[dimethylzinc] ratio on the electrical and luminescence properties has been investigated for undoped ZnSe films grown on GaAs(100) substrates by metalorganic chemical vapor deposition. The observed electrical and luminescence properties are consistent with each other and depend on the deviation from stoichiometry. The properties of the films and the solubility of NSe using N2 gas confirm that at Ts ≤350 °C the deviation from stoichiometry depends on the VI/II ratio. In contrast, it has been difficult to prepare Zn-rich films at Ts ≥375 °C. The VI/II ratio necessary for preparing stoichiometric films decreases rapidly with increasing Ts . The film with the highest mobility maximum of 7600 cm2/V s at ∼40 K has been grown by controlling the stoichiometry. The concentration of acceptors incorporated during growth is lowest in stoichiometric films. It is suggested that the extended lattice defects which reduce the electron mobility are formed more easily as the composition changes from Zn rich to Se rich. The reduction in the deviation from stoichiometry on the Se-rich side is the most important for obtaining low-resistivity n-type ZnSe. The results are consistent with the reported results for bulk crystals.
Absorption peaks at 2663 and 2692 cm−1 observed in neutron-transmutation-doped silicon
Authors: Zhong Lei , Wang Zhanguo , Wan Shouke , Lin Lanying
Published: July 2002

Two absorption peaks at 2663 and 2692 cm−1 are reported which were observed by Fourier transform infrared at a temperature below 77 K in all fast-neutron-irradiated samples investigated. These peaks are very weak and obscured by the nearby divacancy 3.61-μm band in most cases. However, they are obviously enhanced by the presence of impurity hydrogen. They anneal out at about 200 °C. It is proposed that a single defect center, which may be the di-interstitial, gives rise to the two peaks.
Observations of indentation cracks in brittle coating/substrate systems
Authors: Lu Mei-Chien
Published: July 2002

The indentation-induced cracks in brittle coating/substrate systems are examined. The crack paths induced by indentation with different applied loads are exploited by a post-bending test. Sandwiched bending bars are designed to conduct this post-bending test. The influence of the mechanical properties of each component and the interface and the thickness of coating on the paths of the indentation cracks are addressed.
Preparation of very thin superconducting films of Y-Ba-Cu-O by a layer-by-layer resistive evaporation
Authors: Azoulay Jacob , Goldschmidt Dan , Brener R.
Published: July 2002

We report here on 1/4 -μm-thick superconducting Y-Ba-Cu-O films, produced by a sequential layer-by-layer deposition of Cu, BaF2, and YF3, utilizing solely resistive evaporation from tungsten boats onto SrTiO3 substrates. The films are composed primarily of quasioriented elongated grains and have, on the average, the correct stoichiometry. A transition onset at 75 K and width of ∼25 K have been observed in these films. The shape of the current-voltage curve indicates that Josephson-coupled weak links limit the transport in these films. However, the magnitude of critical current (3000 A/cm2 at ∼10 K) is larger than that found in bulk ceramic superconductors. The origin of weak links in these films is probably in the regions of contact between the elongated grains. The relatively large critical current density, as compared to regular bulk ceramic superconductors, is presumably related to the quasioriented nature of the film.
Photoluminescence studies of Si-implanted InP
Authors: Chang R. , Lile D. L. , Singh S. , Hwang T.
Published: July 2002

Room-temperature integrated photoluminescence of Si-implanted n-type and semi-insulating wafers of single-crystal InP has been investigated as a technique for characterizing the quality of ion-implanted and annealed material. It was found that the intensity of the luminescence is a good indicator of the quality of the annealed samples. Using both rapid thermal annealing and conventional furnace annealing, not only was it possible to monitor the progressive activation of the implanted impurities, but we were also able to characterize the degradation occurring in the InP crystal due to the thermal exposure and to compare the results using different methods of surface protection. Combined with progressive wet etching of the implanted layers, it was also possible to use the photoluminescence response to spatially profile the activation and the degradation of the wafers. The results suggest that annealing, in general, is not able to restore the quality of the original unimplanted semiconductor and that even short transient anneal cycles can lead to detectable thermally induced material degradation, which extends many micrometers into the InP.
Cathodoluminescence mapping, deep-level transient spectroscopy, and electron-beam-induced current measurements on GaAs layers grown on Si substrates by metalorganic chemical vapor deposition
Authors: Papadopoulo A. C. , Bresse J. F. , Legros R. , Azoulay R. , Draidia N. , Gao Y.
Published: July 2002

GaAs layers grown by organometallic chemical vapor deposition (OMCVD) on Si substrates oriented 2° off (100) toward [011] have been studied by 10-K filtered cathodoluminescence, deep-level transient spectroscopy (DLTS), electron-beam-induced current (EBIC), and secondary ion mass spectrometry (SIMS) measurements. The mapping of the near-band-edge emission intensity shows the existence of zones of lower defect density, whose relative volume increases with the layer thickness. Four deep-level energy peaks have been characterized at 1.33, 1.20, 1.15, and 1.02 eV. The 1.33 and 1.20 eV energy peaks are attributed to Si in GaAs. Strong inhomogeneities in the intensity of these two emissions have been observed with depth of the layers, and this behavior has been related to the silicon distribution. From measurements on structures grown with different buffer layers, we show that a GaAs/AlAs supperlattice located at 1 μm from the Si substrate is efficient in decreasing the width of a highly Si-doped interface region. DLTS measurements confirm the decrease in the deep-level concentration with increasing thickness. Furthermore, by EBIC characterization, we measure a minority-carrier diffusion length of 2.7–3 μm on a 5-μm-thick layer. This corresponds to a dislocation density of 8×106 cm−2.
Synthesis of sheet conductive layers on the surface of some insulator ceramics (TiO2, ZrO2, HfO2) by multipulse CO2-laser irradiation in an ammonia atmosphere
Authors: Ursu I. , Mihailescu I. N. , Nistor Leona C. , Teodorescu V. S. , Prokhorov A. M. , Konov V. I. , Nikitin P. I. , Uglov S. A.
Published: July 2002

It is shown that by multipulse TEA-CO2 laser irradiation of some insulator ceramic samples (TiO2, ZrO2, HfO2) in an ammonia atmosphere, surface layers are synthesized exhibiting a complicated morphology and having a complex structure containing, beside metallic nitrides, nonstoichiometric oxygen-depleted oxides, oxinitrides, etc. Such layers have a diminished sheet resistance, and display good conduction characteristics.
Electrochemical studies on CoCr films as a function of substrate temperature and post-deposition heat treatment
Authors: Fartash A. , Oesterreicher H.
Published: July 2002

The corrosion resistance of dc magnetron sputtered Co79Cr21 thin films is studied by electrochemical means as a function of substrate temperature Ts ranging from −196 to 375 °C. The corrosion activity increases with Ts and peaks at ∼300 °C. This behavior correlates with the substrate temperature dependence of saturation magnetization of the films. The source of corrosion is suggested to be primarily associated with the segregated Co-rich material. Heat treatment in vacuum at 500 °C significantly improves the corrosion resistance. Evidence is provided suggesting dilution of Co concentration in segregated Co-rich regions is responsible for this improvement.
Two-channel optical pyrometry of metals irradiated by picosecond laser pulses
Authors: Luther-Davies B. , Radlinski A. P. , Calka A.
Published: July 2002

We have used two-channel optical pyrometry to study the surface color temperature versus time profiles of aluminum and tungsten irradiated with 100 ps, 5 ns, and 60–70 ns duration pulses of Nd-glass laser in the fluence range of 0.5–15 J/cm2. We demonstrate that at fluences of several J/cm2 the temperatures of both materials can rise above 5000 K. The maximum observed cooling rates are 5×1010 K/s, two orders of magnitude less than the theoretical estimation. The importance of these results for the laser annealing experiments on metals and alloys is discussed.
Phase-diagrammatic behavior of Co-Cr sputtered films
Authors: Sagoi Masayuki , Nisikawa Reiji
Published: July 2002

The deviation in saturation magnetization (Ms ) from the Slater-Pauling curve for Co-Cr films was confirmed from several points of view, and was clarified not to be caused by some experimental imperfection, such as the use of a composite target or residual oxygen. There existed a critical value of Cr content, 13 at. %, where the films changed their homogeneity. This critical value was interpreted as corresponding to the Cr solubility limit in the hexagonal close-packed (hcp) solid solution on the phase diagram reported by Hansen [Constitution of Binary Alloys (McGraw-Hill, New York, 1958), p. 466], which has 13 at. % Cr solubility limit and two-phase-mixture area from 13 to 57 at. % Cr contents below 500 °C. The temperature dependence of Ms was also consistent with the tendency of the Hansen phase diagram.