bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of adsorbed species on the surface potential of AgBr
Authors: Tan Y. T. , Lam W. , Reed K.
Published: February 2003

The effect of adsorbed species on the surface potential of AgBr sheet crystals has been determined by use of the Kelvin method. Molecules which act as chemical sensitizers for the photographic process decrease the magnitude of the surface potential and hence the ionic surface space-charge layer. Variations in adsorbed bromide or silver ions can also affect the size of the space-charge layer.
Even and odd subharmonic frequencies and chaos in Josephson junctions: Impact on parametric amplifiers?
Authors: Levinsen M. T.
Published: February 2003

The Stewart-McCumber model of a Josephson junction has been shown to exhibit period-doubling bifurcation cascades, as described by the Feigenbaum bifurcation theory. Chaotic states, sometimes associated with the bifurcations, are also prevalent. The present paper deals with the questions of subharmonic generation and chaotic states in the aforementioned model, and in addition with the problem of the ubiquitous noise rise found in Josephson junction parametric amplifiers. The bifurcation is first discussed by drawing on analytical results on the Duffing equation which is an approximation to the complete ac-driven Stewart-McCumber model. The complete model is then solved on an analog computer. Thereafter it is shown that besides the even subharmonics predicted by the bifurcation theory, the natural subharmonic to expect at small dc currents is the odd. This may then have associated its own bifurcation tree. The role of spontaneous symmetry breaking will be discussed. This reconciles the earlier treatment of the 3-photon amplifier with the Feigenbaum scheme. Finally, analog calculations on a model of an externally pumped Josephson junction parametric amplifier will be discussed. The conclusion seems to be that chaotic noise cannot account for the noise rise.
Characterization of surfaces by deconvolution of ultrasonic echoes using extended bandwidth
Authors: Cohen Tenoudji F. , Quentin G.
Published: February 2003

From deconvolution of the echo scattered by a surface, it is theoretically possible to obtain the impulse response of this scatterer. In some cases, this response can be closely related to the geometry of the scatterer and can be used for its characterization. In practice, even in the field of ultrasonic spectroscopy, the transducers always exhibit a finite bandwidth. We suggest a method for extending the Fourier spectrum which leads to better results after deconvolution. The experiments are performed with targets consisting either of small plane surfaces with various shapes, or of large randomly rough surfaces. The results are in good agreement with those expected using the Kirchhoff-Helmholtz approximation.
A hydrophone with a liquid delay line oscillator
Authors: Toda K. , Urabe H.
Published: February 2003

A hydrophone using a liquid delay line oscillator has been developed. The delay line consists of two pairs of interdigital transducers on the same substrate surface and a diaphragm used as a reflecting plate of the sound beam. The interdigital transducer operates as a sound beam radiator or a detector at a liquid-solid interface. The oscillation frequency is dependent upon the sound pressure level applied to the diaphragm. Performances of the hydrophone are described, including sensitivity and its frequency dependence.
Aluminum, calcium, and titanium imploding plasma experiments on the BLACKJACK 5 pulse generator
Authors: Clark W. , Gersten M. , Katzenstein J. , Rauch J. , Richardson R. , Wilkinson M.
Published: February 2003

The 10 TW BLACKJACK 5 pulse generator has been used to create both plasmas with electron densities on the order of 5×1020 cm−3 and electron temperatures between 0.5 and 2 keV by imploding cylindrical arrays of fine aluminum, calcium, and titanium wires and ribbons. Visible streak photographs indicate that the wires are ionized by the prepulse and expand to ∼1-mm diameter before imploding toward the central array axis to form a dense pinch. The individual plasmas assemble on axis at approximately peak current, at which time a 20–25-ns FWHM pulse of K-shell x-ray radiation is emitted. Emission from H-, He-, and Li-like ionization states has been observed with curved crystal spectrographs, and electron temperatures and densities have been inferred from these measurements. Pinhole photographs show intense emitting regions and kink structures in the plasma column.
Electrostatic plugging of leaks in a multidipole device
Authors: Hershkowitz Noah , Hendricks Kyle , Carpenter R. T.
Published: February 2003

Electrostatic plugging is used to improve plasma confinement in a multidipole ion source. A conventional multidipole device is modified by placing positively biased electrodes on both sides of each magnetic line cusp. As the electrode bias voltage is increased from zero, plasma density increases by approximately a factor of 2 and the plasma potential follows the electrode potential. The density enhancement is reduced as neutral pressure is increased or if the electrode-gap width is decreased. Similar behavior is observed when a negatively biased grid is present. A model which assumes that the main electron-loss mechanism at high electrode bias is diffusion across the cusp magnetic field lines is shown to be in qualitative agreement with measurements.
Two-stream, free-electron lasers
Authors: Bekefi G. , Jacobs K. D.
Published: February 2003

Two parallel, relativistic electron streams with different velocities support unstable, exponentially growing space-charge waves, and efficient electron bunching may be achieved in the submillimeter wavelength range. Injection of the prebunched streams into a static, periodic (wiggler) magnetic field enhances the intensity of the parametrically excited, backscattered electromagnetic wave. Calculations are presented of the amplitude enhancement and of the linear growth rate of the wave in the Raman regime, for the case of two cold, perfectly intermingled electron streams.
Estimation of wavenumber and frequency spectra using fixed probe pairs
Authors: Beall J. M. , Kim Y. C. , Powers E. J.
Published: February 2003

We introduce the concept of the local wavenumber and frequency spectral density, which can be estimated using spatially fixed, point data sources (’’fixed probe pairs’’), and discuss the relationship of this spectral density to the conventional wavenumber and frequency spectral density and the cross-power spectral density. The local wavenumber and frequency spectral density is shown to be equivalent to the conventional wavenumber and frequency spectral density when the fluctuation is stationary and homogeneous and consists of a superposition of wave packets; such a fluctuation is the basic model used in many turbulence theories. A digital method for estimating the local wavenumber spectrum is described and applied to the study of drift-wave turbulence in an rf-excited discharge. The statistical dispersion relation and wavenumber spectral width, computed from the local wavenumber and frequency spectrum of the drift-wave turbulence, are compared with the conventional spectral moments computed using the correlation method of Iwama and Tsukishima; good agreement is found over a wide range of frequency. A frequency-integrated wavenumber spectrum is computed; both frequency and wavenumber spectral indices are found independently. The local wavenumber and frequency spectrum is a completely new approach to the use of fixed-probe data, and we believe it can greatly extend the quantity of information available from fixed probes, which are the principle tools in many, if not most, fluctuation experiments.
Electrically resonant transducer for a gravitational wave antenna
Authors: Narici Livio
Published: February 2003

One of the leading problems in gravitational wave detection is the construction of an optimized transducer capable of reaching the predicted sensitivity limit set by the amplifier noise. Existing transducers, when used with ultra-low noise amplifiers, are far from this limit. In this paper, electrical tuning is proposed to improve the match between the mechanical oscillator and the amplifier in the case of an inductively coupled electromechanical transducer. A detailed calculation of the sensitivity of this device is carried out. This calculation shows substantial improvement over the untuned system. The requirement on the tuning is shown to be noncritical. The most severe requirement is the one imposed by the electrical losses in the resonating capacitor.
Knock-on particle preheat in ion beam fusion targets
Authors: Slutz Stephen A.
Published: February 2003

The elastic scattering of beam ions is shown to cause a potentially damaging flux of penetrating secondary knock-on particles. These secondary particles will be more penetrating than the primary ions if the atomic mass of the primary is larger than the secondary. A calculation, using the specific example of helium ions incident on an absorbing material containing hydrogen, reveals that the knock-on protons have a range greater than five times the range of the primary helium ions, and can cause a preheat problem. Thus, this effect is shown to be an important design consideration.
Magnetic induction of ferromagnetic prolate spheroidal bodies and infinitesimally thin current bands
Authors: Baker F. Edward , Brown Samuel H.
Published: February 2003

This paper discusses the solution of the vector Laplace’s equation using the method of separation of variables to determine the magnetic field of three systems consisting of infinitesimally thin prolate spheroidal current bands and a ferromagnetic prolate spheroidal shell. Two configurations consist of a ferromagnetic spheroidal shell with an internal or external current band. The third configuration consists of a spheroidal shell with both internal and external current bands. The solutions are limited to dc currents and linear shell materials. They provide a method for calculating the interaction between the ferromagnetic material and the current band for symmetric and nonsymmetric current bands and a prolate spheroidal shell.
Electric properties and distribution of sulfur implants in GaAs
Authors: Kwor R. , Yeo Y. K. , Park Y. S.
Published: February 2003

The electrical properties of sulfur-implanted GaAs have been studied in detail using the Hall effect/sheet resistivity measurement technique for various ion doses, ion energies, and annealing temperatures. The electrical activation efficiency is found to increase with annealing temperature at a given dose and to decrease with increasing ion dose at a given ion energy for the ranges investigated. At a dose of 4×1013 cm−2, the electrical activation increases with ion energy up to 300 keV and then decreases with further increase in ion energy. A maximum activation efficiency study of secondary ion mass spectroscopy (SIMS) atomic profiles and electrical carrier profiles has also been made. The electrical profiles are in good agreement with the SIMS profiles in the deep side of the active layers, where there is no significant implantation damage.
Lattice attenuations in CdS measured by acoustic domains in a conventional square pulse application
Authors: Tokunaga Yoshiaki , Hata Tomonobu
Published: February 2003

This paper describes a measurement of CdS lattice attenuation αl with an acoustic domain caused by a conventional square pulse. Observing the current oscillations and the intensities of 0.4 and 2.0 GHz acoustic fluxes in the initial and successive generations of the domains, we could find the shock-excited fluxes in addition to the fluxes amplified from thermal phonons. It has been found that the αl∝ f2.0 (f:frequency) is, as Akhiezer expected, obtained in the frequency range 0.4–2.0 GHz when the domains of the successive generations are used to measure the CdS lattice attenuation. The frequency spectra of the domains’ acoustic fluxes are compared experimentally between those with or without the shock. The fluxes caused by the shock are composed of frequencies 2 GHz or lower, although the fluxes evaluated from a small signal theory are close to 3 GHz. The frequency spectrum of the acoustic fluxes is also discussed regarding the domain reflected from a central electrode between a generation region and a measured region.
Simulation of high-voltage breakdown in the post-arc column
Authors: Novak J. P. , Shoucri M. M.
Published: February 2003

A simple model of the nonequilibrium discharge in molecular gas has been developed based on the assumption that partition of heavy species is governed by the common kinetic temperature of heavy particles. The model has been used to simulate high-voltage breakdown in the post-arc column in nitrogen at a pressure of 20 atm. Axial homogeneity has been assumed and electrode effects were neglected. The initial conditions were given by the arbitrary radial distributions of the electron and heavy-particle temperatures. The electric-field impulse was applied to the column after a period of forced cooling, which lasted approximately 30 μs. The gas sustained fields of up to 18 kV cm−1 and breakdown occurred at 24 kV cm−1.
Spectroscopy and atomic physics of highly ionized krypton for tokamak plasmas
Authors: Bhatia A. K. , Feldman U.
Published: February 2003

We present calculations of electron-impact collision strengths and spontaneous radiative decay rates for krypton ions of the Li I through F I isoelectronic sequences for transitions between levels of the 2s22pk, 2s2pk+1, and 2pk+2 configurations. From these atomic data, excitation rate coefficients are calculated, as well as populations of levels within the three configurations mentioned above. The calculations of level populations are carried out at three electron temperatures—2×107, 3×107, and 5×107 K (1.7, 2.6, and 4.4 keV)—which are expected to be typical for future tokamak plasmas.
Continuous-wave laser fluorescence spectroscopy of impurities in tokamaks
Authors: Young C. E. , Pellin M. J. , Gruen D. M. , Norem J. H.
Published: February 2003

Laser-induced fluorescence spectroscopy has been applied as an in-situ diagnostic for impurity atoms in the edge region of the plasma in the Argonne Plasma Engineering Experiment (APEX) tokamak. Zirconium atoms introduced from a moveable probe were excited by a cw single-mode ring dye laser and monitored on lines of the a3F-z3F0 manifold. The fluorescence signal from a 0.03 cm3 volume was recorded at 1-ms intervals with a computer-controlled 4-channel 100-MHz scaler system. Acousto-optic modulation of the laser beam at 100 kHz allowed subtraction of plasma background light. Absolute calibration by Rayleigh scattering gave a detectability limit ∼1010 Zr atoms/cm3 in this apparatus. The detectability limit was determined by a detailed consideration of power and transit time broadening. The effects of several experimental parameters were examined and suggestions for increasing detection sensitivity are presented. Doppler-shift experiments indicated a thermal-velocity distribution for the detected Zr atoms. Intrinsic-velocity resolution of the experiments, calculated from effective excitation linewidths, was ∼25 m/s.
Experimental observations of cathode-spot surface phenomena in the transition from a vacuum metal-vapor arc to a nitrogen arc
Authors: Porto Deborah R. , Kimblin C. W. , Tuma D. T.
Published: February 2003

This paper provides experimental data on the crater dimensions associated with low-current (50 A) arcs burning for periods of 100 ms on copper cathodes. The cathodes were arced in metal-vapor and nitrogen ambients, and the resulting cathode surface contamination was measured for each arcing condition. As the ambient pressure increased from 10−6 to 100 Torr, the crater diameters in the heavily arced areas decreased from 48–58 to 7–17 μm, the current carried per cathode spot decreased, and the surface contamination increased. We consider that the smaller crater dimensions are associated with the reduction in the maximum current per spot and that the maximum cathode-spot current is influenced by the thin layer of surface contamination. We compare the trend of pressure-related crater-size reduction with previous observations of crater sizes as a function of current for vacuum arcs. We conclude that an individual cathode spot operating at a given current level in a gaseous ambient has many of the same basic characteristics as an individual cathode spot operating at the same current level in vacuum. An unexpected feature though, confirmed by our measurements, is that the erosion rate at higher pressures can be significantly lower than the minimum vacuum erosion rate associated with the characteristic 8– 10% ion current. Redeposition may be a plausible explanation.
Behavior of cholesteric-nematic mixtures under compressional deformations
Authors: Bertolotti M. , Sbrolli L. , Scudieri F.
Published: February 2003

The response properties of cholesteric-nematic mixtures to compressional deformations are studied. The behavior of transmitted and scattered light as a function of frequency and under pulsed operation is considered, looking both at the finger structure and the time response. It is shown that the system is able to oscillate at very low frequencies (to 0.1 Hz).
Crystallization characteristics of Cu-Zr metallic glasses from Cu70Zr30 to Cu25Zr75
Authors: Altounian Z. , Guo-hua Tu , Strom-Olsen J. O.
Published: February 2003

The crystallization characteristics of glassy Cu-Zr has been studied by differential scanning calorimetry, x-ray diffraction, and measurement of electrical resistance and magnetic susceptibility. Our results allow us to remove many discrepancies between previously published data; they also suggest that the equiatomic Cu-Zr does not exist as a single phase in the crystalline state. We observe parallel changes on crystallization between the magnetic susceptibility and the electrical resistance, which we interpret through changes in the d density of states.
Computational methods for solving the Dirichlet problem via Fredholm integral equations
Authors: Caldwell James
Published: February 2003

The numerical solution of potential problems of the Dirichlet type based on Fredholm integral equations is considered. The method is illustrated for the case of a unit sphere. In solving the integral equations there are advantages in extrapolating in the order of Gaussian quadrature, and this is done by introducing an empirical formula for curve fitting purposes. An iterative solution which overcomes the peaked nature of the kernel in the integral equations is also considered, together with a discussion of convergence and error accumulation.
The emission characteristics of an aluminum liquid metal ion source
Authors: Bell A. E. , Schwind G. A. , Swanson L. W.
Published: February 2003

A study of the composition and energy distribution of a beam of ions obtained from an Al liquid metal ion source supports the field evaporation mechanism for ion formation at low currents. The beam composition varies as Al+≫Al++≳A+ 2≳ Al+ 3≳ Al+ 4≳ Al+ 5 and the energy spread ΔE varies as Al++<Al+≪Al+ 5< Al+ 4< Al+ 3 <Al+ 2. Both ΔE and the ratio of Al+n/ Al+ increase with total current. Because of the strong mass dependence of ΔE, Al+ exhibits an angular intensity twice as large as Ga+ for ΔE values between 5 and 10 eV.
Theoretical study of 16-μm laser action from CO2 at low temperatures under conditions of pulsed discharge and externally applied 9.6-μm transfer laser
Authors: Chatterjee U. K. , Nath A. K.
Published: February 2003

An earlier model developed by others to study the 10.6-μm laser transition in CO2 has been extended for studying the 16-μμ (0200)→(0110) laser transition in cold CO2. The rate equations take into account the rotational relaxation and collisional transfer of population among (0200), (1000), and (0220) levels of CO2. The model has been used to study the effect of various parameters on the 16-μm output. It has been found that at higher pressures the collisional relaxation of the (0200) level can be overcome by application of a more powerful 9.6-μm pulse to achieve an inversion between the (0200) and (0110) levels of CO2. It is predicted that if transverse excitation is used in these cold mixtures, pulsed powers in excess of 100 kW could be obtained on 16 μm.
Atomic structure at the (111) Si-SiO2 interface
Authors: Haight R. , Feldman L. C.
Published: February 2003

The structure and stoichiometry at the (111) Si-SiO2 interface has been studied by ion backscattering channeling methods. In qualitative agreement with other oxide covered Si surfaces studied by this technique, we find the oxide to be stoichiometric to approximately one monolayer of the interface and a thin region (1–2 monolayers) of distorted Si crystal. Further measurements were carried out to evaluate the magnitude and direction of the Si atomic displacements at the interface.
NiSi formation at the silicide/Si interface on the NiPt/Si system
Authors: Ottaviani G. , Tu K. N. , Chu W. K. , Hung L. S. , Mayer J. W.
Published: February 2003

Alloy films of NiPt were e-beam codeposited on n-type Si and annealed up to 700 °C in a purified- He ambient furnace. Silicide formation was monitored using MeV4 He Rutherford backscattering and glancing-angle x-ray diffraction. At low temperatures (300–350 °C), Ni segregates at the Si/ silicide interface and the first phases detected are NiSi and PtSi. At intermediate temperatures (400– 500 °C), there is further accumulation of Ni at the Si/silicide interface, and at later stages an incursion of Pt to the interface. The barrier height increase reflects the presence of Pt. At 700 °C, the Ni and Pt redistribute to form a uniform ternary.
Growth and dissolution kinetics of ternary III-V heterostructures formed by liquid phase epitaxy. III. Effects of temperature programming
Authors: Ghez R. , Small M. B.
Published: February 2003

The kinetics of growth and dissolution and compositional grading in the solid are computed when a liquid-phase epitaxial system is subjected to temperature programming. We solve the transport equations (including the effect of interface motion) by means of series expansions in powers of t1/2. This requires a careful analysis of the phase relations that hold at the crystal-fluid interface, because these are now explicitly time dependent. The theory is applied to a specific active layer of a (GaAl)As heterostructure laser, but the calculations can be extended to any III-V ternary system, and indeed to any multicomponent system.
Reducing the grain size of polycrystalline lead films by the use of nucleants
Authors: Ronay Maria , Aliotta C. F. , Serrano C. M.
Published: February 2003

Thin layers of La, Y, Au, Pd, Pt, Ag, and Sn were evaporated at room temperature as nucleants prior to the evaporation of 2000 Å Pb. The correlations of grain size, surface morphology, and the phase diagrams of lead nucleant showed that the grain size of lead was reduced only if the nucleant formed a compound with lead and a eutectic between the compound and lead. In such a case the surface morphology was hemispherical, indicating that crystallization from the vapor took place through the liquid phase. The various sources of undercooling explaining the presence of the liquid phase are discussed. It is shown that the necessary condition for heterogeneous nucleation is the same as the condition for lamellar or rodlike eutectic growth; therefore, the occurrence of such eutectic in the phase diagram indeed indicates the possibility of heterogeneous nucleation. A vapor-liquid-heterogeneous nucleation mechanism of crystallization is suggested. Factors affecting the surface morphology of nucleated films are discussed.
Molecular beam epitaxial growth of InGaAlP on (100) GaAs
Authors: Asahi H. , Kawamura Y. , Nagai H.
Published: February 2003

InGaAlP epitaxial layers that are lattice matched to (100) GaAs substrates have been successfully grown for the first time by molecular beam epitaxy. The surface of the grown crystal is mirror smooth, and the full width at half-maximum of the double crystal x-ray diffraction pattern is less than 100 sec. The energy gap at the Γ point increases from 1.9 eV (InGaP) to 2.5 eV (InAlP) with increasing AlP mole fraction. The optical waveguide effect was also observed in InGaP/InGaAlP double heterostructure wafers.
Indium antimonide-bismuth compositions grown by molecular beam epitaxy
Authors: Noreika A. J. , Takei W. J. , Francombe M. H. , Wood C. E. C.
Published: February 2003

Thin films of InSb-InBi solid solutions have been prepared by molecular beam epitaxy. Using in situ reflection electron diffraction, conditions for epitaxial growth of stoichiometric layers were established on (001) and (110) surfaces of both InSb and GaAs wafers. Bi is shown to modify the diffraction patterns of (001) InSb from C(8×2) and (√2×√2) 45° to (1×3). Surface residence times of Bi were found indefinitely long (≳10 min) at temperatures ?420 °C. Bi incorporation into InSb during growth by molecular beam epitaxy is strongly dependent on Bi surface concentration, and influenced by substrate temperature and surface nonstoichiometry. Secondary ion mass spectrometry depth profiling and 2.5 MeV ion dechanneling spectra showed that ∼3% Bi can be incorporated substitutionally in Sb sites, under In rich growth conditions (largest available concentration of VSb sites). Increased Bi surface accumulation and interstitial incorporation are observed under Sb-rich surface conditions and as the relative flux of Bi is increased. Excess surface Bi forms liquid alloys with excess In during growth above 280 °C which alters the incorporation. These alloys solidify on the surface of grown films on cooling. Absorption cut-off wavelengths are unaffected by interstitial Bi concentrations; however, cutoffs out to ≳9.5 μm at 77 K are observed for Bi-doped films grown under In-rich conditions.
Manganese incorporation behavior in molecular beam epitaxial gallium arsenide
Authors: DeSimone D. , Wood C. E. C. , Evans C. A.
Published: February 2003

A secondary ion mass spectrometric study of the substrate temperature and As4/Ga flux-ratio dependence of the chemical incorporation behavior of manganese in molecular beam epitaxial GaAs is presented. At molecular beam epitaxial growth temperatures, manganese competitively surface segregates, desorbs, and complexes with As at the surface. No significant diffusion was observed. The incorporation model of Wood et al. qualitatively explains the observed behavior.
Theoretical modeling of a 16-μm CO2 gasdynamic laser in the intracavity cascading mode
Authors: Saito Shigeki , Obara Minoru , Fujioka Tomoo
Published: February 2003

A theoretical analysis based on a conventional CO2 gasdynamic laser (GDL) revealed the possibility of 16-μm cascade lasing, in which a 9.4-μm stimulating beam is internally generated, and subequently a 16-μm emission is produced in a cascade manner. In this simulation, cascade- type 16-μm lasing of 3–10 μJ/cm3 energy and 1–1.5 W/cm3 power is achievable on the P(15) line of the (0200)—(0110) transition at a position 15 cm downstream from the nozzle throat. Because of its high average power capabilities, without requiring a separate CO2 laser as a stimulating beam source, the 16-μm cascade operation of a CO2 GDL will be practically usable.
Magnetic flux density distribution in superconducting cylinders of arbitrary cross section subjected to an axial magnetic field
Authors: Fournet G.
Published: February 2003

We show here how the application of the critical state model allows one to determine the magnetic flux density B⃗ in each point of a superconducting cylinder with an arbitrary cross section subjected to axial magnetic fields Hz; the B = 0 boundaries of the regions occupied by the vortices are so defined. We successively consider the cases where the critical current density Jc is either isotropic (constant or an arbitrary function of B) or tensorial, which means, for our problem, the use of two components Jcx and Jcy (either constant or depending on B but Jcx/Jcy remaining constant).
Transport of magnetic bubbles by domain interaction
Authors: Weng R. , Muller M. W.
Published: February 2003

We examine the deformation of stripe domains used to transport magnetic bubbles in self- structured multilayer bubble devices as a function of loading by the bubbles. We find that the effect of the loading, depending on the arrangement of the bubbles, is similar to the deformation of the stripe by the coercive or the damping self-forces acting on its own walls.
The effects of neon implantation on the magnetic properties of garnet layers
Authors: Algra H. A. , de Roode W. H.
Published: February 2003

The results of a study on the effects on neon implantation on the magnetic properties of La, Ga:YIG (yttrium-iron-garnet) and Tm, Ca, Ge:YIG films are presented. The implantation dosage ranged from 5×1013 to 1016 ions/cm2, while the energy was kept constant at 300 keV. The films were studied by the ferromagnetic resonance technique and by double-crystal x-ray diffraction. The observed resonance spectra, also recorded after successive etch steps, were compared with the relevant theory by solving the equation of motion numerically. This comparison yielded profiles for the field for uniform resonance, and for the ratio of the exchange stiffness constant and the saturation magnetization through the ion-implanted part of the layer. For the latter, a reduction to 55% of its initial value is found at the depth at which also the maximum in the strain distribution occurs. It is found that the field for uniform resonance in the ion-implanted part of the film is considerably higher than for the bulk of the film, and varies only slowly as a function of depth. When the interface between the ion-implanted region and the bulk is reached, a steep change takes place to the bulk value. Good agreement was found between the maximum of the strain profile, as deduced from the double x-ray measurements, and the extremes in the profiles mentioned above.
Photoluminescence of undoped In0.53Ga0.47As/InP grown by the vapor phase epitaxy technique
Authors: Towe E.
Published: February 2003

Optical properties of undoped, n-type In0.53Ga0.47As/InP grown by the vapor phase epitaxy technique are presented, including the temperature dependence of the band gap which can be described by the empirical relation Eg = 0.821−2.30×10−4 T−2.39×10−7 T2 eV. The photoluminescence emission intensity is found to decrease with increasing temperature. This temperature dependence of the intensity can be characterized by a nonradiative recombination process with an activation energy of Ea≃27 meV.
Spectral response of ZnSe-Zn1−xCdxTe heterojunction
Authors: Chikamura T. , Fujiwara S. , Fukai M.
Published: February 2003

The spectral response of ZnSe-Zn1−xCdxTe (0⩽x⩽1) heterojunction is described. The heterojunction is formed by vacuum evaporation of ZnSe and Zn1−xCdxTe doped with In2Te3. The spectral response of this heterojunction is discussed for two cases, illuminated from the ZnSe side and from the Zn1−xCdxTe side. The theoretical results, based upon the assumption that the carriers excited by incident light are mainly transported by drift field, are in good agreement with the experimental results. Moreover, we could obtain a high internal quantum efficiency of 0.9 over the visible light range in this heterojunction.
Annealing of indium-implanted CdTe
Authors: Kalish R. , Deicher M. , Schatz G.
Published: February 2003

The local environment of 111In implanted in CdTe has been studied by means of the perturbed angular correlation technique as a function of annealing conditions and temperatures. It is found that the damage correlated with the implantation process anneals at 200 °C. At 250–500 °C a new defect exists which is shown to be correlated with loss of Cd and can be inhibited when the escape of Cd can be suppressed. Outdiffusion of In starts at about 500 °C, and at 650 °C almost no In remains in the sample. These results agree with, and add to, published results on the annealing of In-implanted CdTe obtained by other techniques.
Study of phosphorus implantation in silicon by channeling and nuclear resonance techniques
Authors: Kido Y. , Kakeno M. , Yamada K. , Hioki T. , Kawamoto J.
Published: February 2003

Depth profiles of 31P implanted in Si were measured nondestructively by the 31P( p,γ)32S nuclear resonant reactions. It was observed that a large amount of the implanted 31P migrated to the front surface by annealing at 600 °C for 10 min and escaped from the surface by annealing at 800 °C for 10 min in a high vacuum. Channeling analysis revealed this phenomenon to be intimately related to thermal recovery of the damaged layer introduced by high-dose implantation. The implantation dose and energy dependence of the distributions of lattice disorder was also measured by channeling methods.
Assessment of the extent of atomic mixing from sputtering experiments
Authors: Wittmaack K.
Published: February 2003

Ion-bombardment-induced atomic mixing effects are investigated, taking into account the depth dependence of the quantities of relevance. It is shown that in the dilute limit the fluence dependence of tracer (overlayer) atom removal is characterized by an exponential tail. The slope σi of this tail is determined by the differential escape rate of the dopant atoms, as well as the shape of the ’’mixing profile.’’ The extent of mixing (and selective sputtering) in a given system can be characterized by the ratio Ym/σi, where Ym is the matrix sputtering yield. Intermixing of Au with Si is found to be much stronger than expected on the basis of mere collisional relocation of atoms. Some comments are made concerning the use of Rutherford backscattering spectrometry and Auger electron spectroscopy for the determination of escape rates and selective sputtering effects.
The surface topography of Ag/Cu alloys sputtered by bombardment with 35–100-keV argon ions
Authors: Bibic N. , Wilson I. H. , Nenadovic T.
Published: February 2003

The surface topography of two phase Ag/Cu alloys was studied after argon ion bombardment. The parameters investigated include ion beam energy (35–100 keV), dose (1017–1019 ions cm−2) and alloy composition (20, 40, and 50 at. % Ag). At the lower doses the topography revealed the microstructure of the alloy due to higher sputtering rate of the silver crystallites in the eutectic mix of copper and silver crystallites. At intermediate doses the topography reflected the tendency of surfaces to rotate the angle for maximum sputtering yield, and sharp ridges were formed. At the highest dose a dense forest of cones was formed in the eutectic mix regions. The variation of cone angle and height with ion energy was found to be in agreement with previous measurements and theoretical predictions. All the topographic features that have been observed on pure copper were observed on the copper grains which were standing proud of eutectic mix. Rounding of the cone tip and deformation of the cones were observed. It is proposed that this resulted from minimumization of surface energy by diffusion and plastic deformation.
Scanning electron-beam annealing of arsenic- and bismuth-implanted silicon
Authors: Bontemps A. , Smith H. J. , Danielou R.
Published: February 2003

〈100〉 samples of Si implanted with As (120 keV, 3×1015–1017 cm−2) and Bi ions (120 keV, 2×1014–3×1015 cm−2) have been annealed by a multiscan electron-beam technique. Lattice reordering and impurity behavior have been studied by 4He backscattering and channeling. The lattice recrystallizes in the solid phase from the original crystalline-amorphous interface towards the surface with an annealing time depending on the initial amorphous layer thickness. Simultaneously, the corresponding As atoms go into substitutional sites. For the two highest As doses (3×1016 and 1017 cm−2) a marked outdiffusion is observed. For Bi implantations, lattice recrystallization takes place and two stages are observed for the highest dose (3×1015 cm−2). The Bi atoms tend to take substitutional sites for short annealing times and then progressively leave their sites as the irradiation time increases.
Properties and structure of a-SiC:H for high-efficiency a-Si solar cell
Authors: Tawada Y. , Tsuge K. , Kondo M. , Okamoto H. , Hamakawa Y.
Published: February 2003

A series of experimental investigations on optical and optoelectronic properties of methane- and ethylene-based a-SiC:H films has been made. The chemical bonding structure of two kinds of a- SiC:H films has also been explored from infrared (IR) absorption structural analysis. An experimental verification for the wide gap window material in the amorphous silicon solar cell is shown on methane- and ethylene-based a-SiC:H. The methane-based a-SiC:H film shows one or two orders of magnitude larger photoconductivity recovery effect of doping than the ethylene- based one. IR absorption analysis shows that the methane-based a-SiC:H film is recognized as a rather ideal amorphous SiC alloy as compared with the ethylene-based one. It has been found through these investigations that the methane-based a-SiC:H film is superior to the ethylene- based one as a window material. Utilizing the methane-based a-SiC:H, an 8% efficiency barrier has been broken through with an a-SiC:H/a-Si:H heterojunction structure.
Calculation of velocity autocovariance and hot carrier noise from small-signal microwave conductivity in semiconductors
Authors: Chatterjee A. , Das P.
Published: February 2003

Velocity autocovariance functions and noise power spectral densities for hot electrons are related to small-signal microwave conductivities of semiconductors. Closed form expressions for the autocovariance tensor (single-valley case) are derived. The effects of nonzero collision duration, which can be a significant fraction of momentum and energy relaxation times in very small devices, are demonstrated. For silicon, it is found that inclusion of nonzero collision duration contributes to a negative swing and possibly oscillations in the velocity autocovariance functions. An experimental procedure for determining collision duration and relaxation times is suggested.
Traps at the Al2O3/CdSe interface
Authors: Freeman E. C. , Luo F.-C.
Published: February 2003

The effect of traps at the Al2O3/CdSe interface on thin-film transistors (TFT’s) is experimentally measured and mathematically modelled. These traps are shown to lead to a decay of the ON current with time which has a t−αkT behavior for the first msec, decreases to log t for about 20 sec, and then saturates. The OFF current increases with log2 t for as much as 200 h before saturating. Capacitance and conductance measurements are reported which characterize the fast and slow states. The temperature dependence of the drift in the TFT characteristics is presented. A model for the origin of the fast and slow states at and near the Al2O3/CdSe interface is developed. It is then shown how the presence of the fast traps improves TFT characteristics for application in a liquid crystal flat panel display.
Modeling the space-charge-layer boundary of a forward-biased junction
Authors: Warner R. M. , Lee Kwyro
Published: February 2003

In a p-n junction under forward bias, however large or small, the space-charge-layer boundaries are well defined in the sense that surfaces exist on both sides of the junction at which electric field reverses. Each zero-field surface lies within a layer of space charge attributable exclusively to imbalance of the excess-carrier densities. With the assumption of negligible recombination, an analytical solution for the boundary regions can be written. The solution defines surfaces lying on either side of each zero-field surface, separated from it by distances that are bias independent. The analytical solution for the boundary region has been joined to a numerical solution for the balance of the sample. The analytical solution defines clearly the position at which quasineutrality gives way to gross space charge.
Field effect studies in a p-type SnTe metal-insulator-semiconductor structure
Authors: Dawar A. L. , Mohammed A. O. , Taneja O. P. , Mathur P. C.
Published: February 2003

Field effect studies have been made on the electrical properties of a silver mica p-type Sn Te thin film metal-insulator-semiconductor structure in the temperature range 100-300 K. It has been observed that the Hall coefficient decreases with an increase in the negative gate field, while the effect of a positive gate field is the opposite. The mobility, however, increases with an increase in the positive gate field in the low temperature region, and decreases sharply as the temperature increases. The negative field, on the other hand, reduces the mobility in the whole temperature range. The results have been explained on the basis of a two valence band model of Sn Te.
Performance of a transverse electric atmospheric CO2 laser with high levels of O2 contamination
Authors: Howells S. , Cridland J. V.
Published: February 2003

An investigation of the effect of O2 on the power output operating parameters and laser efficiency is described. Homogenous discharges were possible with O2 contents of approximately 35% in a 1CO2:1N2:1He gas mixture.
Observation of anomalous behavior in the thermal and electrical conductivity of a standard reference material SRM-735
Authors: Goldratt E. , Greenfield A. J.
Published: February 2003

Measurements have been carried out over the temperature range 360–480 K of both the thermal conductivity κ(T) and the electrical resistivity ρ(T) for the austenitic stainless steel material chosen by the U.S. National Bureau of Standards as the Standard Reference Material for these two properties in the temperature range 4–1200 K. These measurements show a ripple in κ(T) vs. T centered at 410 K. The amplitude of the observed ripple is within the ±5% experimental scatter of previous data. Measurements of κ(T) for ordinary 304 stainless steel over the same temperature range show no sign of such a ripple. Measurements of the electrical resistivity of the Standard Reference Material also show an unusual structure centered at 410 K.
Single-carrier space-charge controlled conduction
Authors: Schmidt Pierre E. , Octavio Miguel , Callarotti Roberto C. , Henisch Heinz K.
Published: February 2003

Single-carrier space-charge controlled conduction in metal-insulator-metal structures has been studied. The dc J-V characteristics have been calculated over an extended range of current for insulator films of different thicknesses with and without traps. It is found: (i) The current is proportional to voltage at low currents, the proportionality factor depending on the injecting contact carrier concentration, insulator thickness, and trap density. (ii) At moderate currents, the J-V characteristics can be approximated only over a limited range of currents by a power law with the exponent n depending on the injecting contact carrier concentration, insulator thickness, and trap content. (iii) At high currents the conduction is ohmic and the characteristics are identical for insulators with or without traps. The special case of identical carrier concentrations at both contacts is also discussed. It is found that in this particular case the square law in voltage and the cubic dependence in thickness become only good approximations when the normalized trap density M⩾103. The proportionality factor is slightly larger than the value 1.125 obtained from the Mott–Gurney simplified theory and varies slowly with insulator thickness.
Small-signal ac conductivity and velocity overshoot in semiconductor materials
Authors: Teitel S. , Wilkins J. W.
Published: February 2003

We consider the response of a semiconductor to small perturbations in the applied electric field away from a steady uniform dc field. Both ac conductivity and time-dependent velocity response are calculated for a relaxation model described by moment equations for the average electron velocity and energy. Our model involves only three parameters determined by the energy and momentum relaxation rates and their derivatives. Two of them, the momentum relaxation rate Γm which sets the frequency and time scales and the ratio (dJ/dE)/(J/E), are easily obtained from dc conductivity measurements. The third can be obtained from a measurement of the value of the peak ac conductivity in the case where the peak occurs at a nonzero frequency. The form of the conductivity is explored as a function of these parameters, and consistency tests are suggested to determine the applicability of the model. The cutoff frequency where the ac conductivity drops to half its zero-frequency value is shown to be determined largely by the dc parameters Γm and (dJ/ dE)/(J/E). Precise restrictions on the parameters are given for the existence of velocity overshoot in the presence of the dc bias field. It is shown that observation of a peak ac conductivity at a nonzero frequency always implies the presence of velocity overshoot. The cutoff frequency for a spatially uniform system is shown to be insensitive to the presence of velocity overshoot.
A coordinate-free approach to wave propagation in anisotropic media
Authors: Chen Hollis C.
Published: February 2003

This paper considers of a coordinate-free approach to wave propagation in anisotropic media. Based on the direct manipulation of vectors, dyadics, and their invariants, the approach eliminates the use of coordinate systems. It facilitates solutions and provides results in a greater generality. The paper contains the following results in coordinate-free forms: The formulation of eigenvalue problems, the dispersion equation, the polarization of waves in magnetic crystals, and the determination of the directions of field vectors.
Interfacial layer-thermionic-diffusion theory for the Schottky barrier diode
Authors: Wu Ching-Yuan
Published: February 2003

A synthesis theory for majority-carrier transports across the Schottky barrier diode has been developed by including the transport mechanisms across the interfacial layer and the effects of both thermionic emission and diffusion in the space-charge region of the semiconductor. This theory incorporates the thermionic emission theory, diffusion theory, thermionic-diffusion theory, and interfacial layer theory into a single theory: the interfacial layer-thermionic-diffusion theory. The major improvement of the proposed theory over the thermionic-diffusion theory is that the applied voltage drop and transmission coefficient across the interfacial layer are included, thus enabling us to interpret the characteristics observed from the Schottky barrier diodes fabricated with different metals and substrate materials by means of different fabrication conditions. Moreover, based on the developed interfacial layer-thermionic-diffusion theory, the characteristic parameters of the Schottky barrier diode, such as the barrier height, ideality factor, and the reverse current, have also been derived and discussed.
Normally-on and normally-off camel diode gate GaAs field effect transistors for large scale integration
Authors: Thorne R. E. , Su S. L. , Kopp W. , Fischer R. , Drummond T. J. , Morkoç H.
Published: February 2003

Normally-off and normally-on camel gate GaAs field effect transistors have been fabricated from structures grown by molecular beam epitaxy. These new devices use a camel diode gate formed from n+ and p+ layers instead of a Schottky barrier gate as used in metal-semiconductor field effect transistors. The camel diode gate provides these devices with several advantages over metal-semiconductor field effect transistors, including elimination of the metallurgical difficulties of the metal-semiconductor contact, relatively easy adjustment of the built-in voltage, and the potential for improved reliability in adverse environments and under conditions of high power dissipation. Fabrication of these devices does not require precision etching, making them compatible with large scale integrated circuit technology. Fabricated devices have yielded transconductances of 80 ms/mm in long channel (3 μm gate length) normally-on and normally-off field effect transistors and of 120 ms/mm in short channel (1 μm gate length) normally-on field effect transistors. Significantly improved gate-drain breakdown voltages and, in devices with AlxGa1−xAs buffer layers, excellent saturation characteristics have been observed. A simple theory providing analytical expressions describing the performance of normally-on and normally-off camel gate field effect transistors has been developed and good agreement with experiment has been obtained.