bluuebunny/crossref_metadata_2025 huggingface dataset:
Channeling and random equivalent depth distributions of 150 keV Li, Be, and B implanted in Si
Authors: Comas James , Wilson Robert G.
Published: February 2003

Atomic depth distributions for the low atomic number ions 73Li, 94Be, and 115B implanted into channeled and random equivalent orientations in crystalline silicon have been studied. The atomic depth distributions were obtained by secondary ion mass spectrometry measurements on samples implanted to fluences low enough to preserve the integrity of the channeling components. All implants were performed at 150 keV into the 〈100〉 and 〈110〉 directions and into the (111) random equivalent orientation of float-zoned (low-oxygen) silicon crystals. The results show that in the three orientations studied the ion ranges decrease with increasing atomic number Z1. This is indicative of the strong increase in electronic stopping Se for the Z1=3, 4, 5 sequence. The increase in ion penetration in the channeling orientation is greater with decreasing Z1 in the lower electronic stopping 〈110〉 channel than in the higher electronic stopping 〈100〉. Values of Se determined for channeled Li and Be at an ion velocity of 1.5×108 cm/s are in agreement with published calculations and the Se for B is consistent with experimental measurements.
Fundamental impact-welding parameters—an experimental investigation using a 76-mm powder cannon
Authors: Botros K. K. , Groves T. K.
Published: February 2003

A specially designed 76-mm cannon was used to drive small metal plates (copper, 3.175 mm thick) against metal target plates (steel, 6.250 mm thick) in order to study the fundamental parameters involved in the high-velocity impact-welding process. This method of study allowed experimental examination of the influence of each variable separately, in the classical mode. The results of these experiments were analyzed to define the required impact conditions for welding. A line of optimum weldability was identified and shown to be characterized by invariance in the metallic jet velocity. The analysis was also used to identity conditions applying to the transition zone between laminar and wavy interfaced welds.
Effect of clusters on long-wavelength optical phonons in Ga1−xInxAs
Authors: Yamazaki Susumu , Ushirokawa Akio , Katoda Takashi
Published: February 2003

The phonon spectra of Ga1−xInxAs have been studied by measuring the infrared reflectivity at near-normal incidence in the 180 ∼400-cm−1 frequency range. Only one reststrahlen band corresponding to the GaAs-like mode was observed for x≲0.2, and two bands were observed for the remaining composition. The data were analyzed by using the Kramers-Kronig relationship and the dependence of the mode frequencies on alloy composition was interpreted on the basis of the modified cluster model including the effect of clusters. The fact that the calculated oscillator strength for the InAs-like mode is substantially zero in the composition range x≲0.2 explains the reason why phonons of the InAs-like mode are not detected experimentally for x≲0.2. The clustering parameter representing the effect of clusters is determined by fitting the measured mode frequencies to the calculated compositional dependence and takes the maximum value near the midrange of alloy composition.
Electrode shape effects on oxide conduction in films thermally grown from polycrystalline silicon
Authors: Lee Han-Sheng , Marin Samuel P.
Published: February 2003

The electrical properties of the oxide films thermally grown from polycrystalline silicon have been examined. Without the electrode shape effects the films can sustain high electric fields (6.5 MV/cm) and do not trap a significant number of electrons at those fields. The high oxide leakage current found in the bumpy injection electrodes is correlated to the shape of the bump. The electric field distribution between two parallel bell-shaped electrodes was computed numerically. Solutions suggest that the field enhancement cause by the geometrical shape of the injection electrode is the major cause for the observed high oxide current in the polycrystalline silicon-(poly-oxide)-polycrystalline silicon structure.
Magnetoacoustic effects of nonparabolic band structure in nondegenerate piezoelectric semiconductors
Authors: Wu Chhi-Chong , Tsai Jensan
Published: February 2003

Effects of ultrasonic waves propagating at an angle ϑ relative to the direction of a dc magnetic field in nondegenerate piezoelectric semiconductors such as n-type InSb have been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The interaction of conduction electrons with waves is via deformation-potential and piezoelectric couplings. Results show that variation of the direction of the magnetic field with respect to the direction of propagation of ultrasonic waves will affect the ultrasonic absorption coefficient and change in sound velocity. Therefore the absorption coefficient and change in sound velocity depend strongly on the dc magnetic field, the sound frequency, the temperature, and the direction of the propagation of ultrasonic waves relative to that of the field.
Lithium ion conduction in rapidly quenched Li2O-Al2O3, Li2O-Ga2O3, and Li2O-Bi2O3 glasses
Authors: Glass A. M. , Nassau K.
Published: February 2003

Glasses containing Al2O3, Ga2O3, and Bi2O3 with Li2O have been prepared by twin roller quenching. These glasses are found to exhibit reasonably high ionic conductivities and low electronic conductivities for Li2O concentrations exceeding 50 mole %. The conductivity increases rapidly with increasing Li2O content but does not differ greatly from system to system despite the large difference in the ionic radii of the trivalent cations, Al3+, Ga3+, and Bi3+ . A simple model for the behavior is discussed.
The work function of carburized rhenium
Authors: Pallmer P. G. , Gordon R. L. , Dresser M. J.
Published: February 2003

Variations of the electronic work function of carburized rhenium foils containing approximately 5 at.% carbon have been observed using the contact potential difference technique. Surface work function was observed to vary between 5.25 and 4.1 eV, with the work function of pure rhenium taken as 5.0 eV. Decrease in work function has been ascribed to the formation of graphitic layers on the surface at temperatures below the temperature of saturated solubility. The high work function surface was observed with all carbon in solution and has been ascribed to the presence of amorphous carbon near the surface.
Microstructure-property relationships of rare-earth–zinc-oxide varistors
Authors: Williams P. , Krivanek O. L. , Thomas G. , Yodogawa M.
Published: February 2003

The microstructure and properties of ZnO varistors containing Ba, Co, and rare-earth–metal oxides, which give values of α [α=d(log I)/d(log V)] as high as 29, are examined. Mean ZnO grain size is 11 μm, and the grains are uniformly doped with Co. The barium and rare earth metals concentrate into 1.5-μm-wide particles embedded in a matrix of ZnO grains. Within the grains and at grain boundaries, the barium and rare-earth–metal concentration is below the detection limit of the energy-dispersive spectrometer technique (about 0.5%). No intergranular films, amorphous or crystalline, are detected, to within 10 Å resolution. These results are shown to be consistent with the grain boundary charge depletion model for the voltage barrier formation and breakdown.
Shock precursor observations
Authors: Duff Russell E. , Peterson Frank I.
Published: February 2003

An experimental investigation has demonstrated that the previously observed wall-supported shock precursor, in high-explosive-driven argon-containing shock tubes, rapidly grows to a maximum length at a tube length-to-diameter ratio of 2. It then gradually decreases in length and grows in width as a steady-state configuration is apparently asymptotically approached. All experiments were done in 10.2-cm tubes varying in length from 10 to 80 cm. The explosive was Comp C-4, and the exterior surface of the tube was surrounded by a 4-mm-thick layer of Deta-sheet to minimize wave attenuation. The experimental assembly was tamped in sand. The precursor was observed with a smear camera as the wave system interacted with a thin aluminum foil covering the end of the tube.
Solid phase regrowth of Si on sapphire in the Si/Al/Al2O3 system
Authors: Magee T. J. , Peng J. , Chiang S. W.
Published: February 2003

Solid phase regrowth of Si on sapphire has been investigated in the Si (amorphous)/Al (poly)/Al2O3 (crystal) system. Using transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, and Hall-effect measurements, it has been shown that Si is transported through an Al film at 550 °C to produce p-type Si films on the sapphire substrate. The growth process has been shown to be initiated at Si nucleation sites on the substrate. These sites expand by mass accretion, forming island structures that coalesce to yield continuous large grained polycrystalline Si films on the sapphire surface.
ND : YAG regenerative amplifier
Authors: Murray J. E. , Lowdermilk W. H.
Published: February 2003

The Nd : YAG regenerative amplifier produces short-duration, optical pulses with the stability and pulse width range characteristic of actively mode-locked lasers and the pulse energy characteristic of passively mode-locked lasers. Other important properties, including large amplification and optical pulse storage, have also been achieved.
Electromagnetic scattering from buried inhomogeneities—a general three-dimensional formalism
Authors: Kristensson Gerhard
Published: February 2003

We will in the present paper derive a general three-dimensional formalism for electromagnetic scattering from buried inhomogeneities. We will exploit the transition matrix formalism, originally given by Waterman, to electromagnetic scattering in the presence of an infinite surface and a buried bounded inhomogeneity. The analysis explicitly assumes that the sources are located above the ground, but this restriction can easily be relaxed and a parallel derivation can be made for sources located in the ground or inside the buried obstacle. No explicit symmetry assumptions are made for the bounded inhomogeneity or the interface between the halfspaces, except that the interface be bounded by two parallel planes. The scattered field above the ground is calculated in terms of an expansion where the expansion coefficients are solutions of a matrix equation. The expression for the scattered field is separated into a directly scattered term, as if no scatterers were present, and the so called anomalous field, reflecting the presence of the inhomogeneity. We give some numerical examples for a flat interface and an inhomogeneity consisting of one or two buried spheres or a perfectly conducting spheroid.
Prism coupling into clad uniform optical waveguides
Authors: Revelli J. F. , Sarid D.
Published: February 2003

The theory of prism coupling into multilayered dielectric slab waveguides is presented. In addition to including the possibility of high index cladding, the present theory also extends the region of validity of previously reported work to cover the regime of ’’strong coupling’’. The limiting conditions for validity of the present theory are that both αm/k and αm±p/k be much smaller than either unity or ‖βm−βm±p‖, where m is the mode under consideration, αm is the leakage of that mode, and ‖βm−βm±p‖ is the separation of the effective indices of adjacent modes. A numerical example is presented in which the coupling efficiency into a uniform or slab waveguide with Δn=0.002 is calculated for various cladding thicknesses with a cladding index of 2.5. The introduction of cladding is found to reduce coupling efficiency in this example due to increased phase mismatch between the incident and ’’ideal’’ beams.
Optoacoustic images
Authors: Busse G. , Ograbeck A.
Published: February 2003

By laser beam scanning the optoacoustic signal as a function of the sample coordinates is obtained. Examples for surface and subsurface imaging and for image contrasting are presented.
An elastic interface wave guided by a thin film between two solids
Authors: Rokhlin S. , Hefets M. , Rosen M.
Published: February 2003

The waveguide properties of a thin film separating two elastic half-spaces possessing a shear modulus higher than the shear modulus of the film are investigated. It is shown analytically and experimentally that such a film is capable of localizing the energy of elastic waves near the interface. The velocity of the interface wave is determined by shear modulus, density, thickness of the film, and by the elastic properties of the substrates. The velocity of the interface wave lies between that of the Rayleigh and that of the shear waves in the solid half-spaces. It is shown that the interface wave can be used to estimate the elastic and dissipation properties of thin interface layers.
Capillary oscillations on liquid jets
Authors: Wetsel Grover C.
Published: February 2003

Capillary oscillations on modulated liquid jets have been investigated using laser illumination and electronic detection of the magnified jet shadow. The amplitudes of several wave harmonics of a growing spatial instability were measured as a function of distance from the orifice for a range of jet velocities and initial-disturbance amplitudes. The experimentally determined growth rates at the fundamental frequency are compared with theories of capillary-wave propagation. An empirically derived explanation of the suppression of satellite formation is given. Experimental evidence for infinite-wavelength capillary oscillations is reported; a description of these oscillations in terms of the Rayleigh theory is presented.
Population inversions by the interaction of an expanding plasma with a background gas
Authors: Wägli P. , Bohn W. L.
Published: February 2003

Results of a hydrodynamic computer code are presented, which describes the expansion of a laser generated plasma into an ambient gas. The theoretical model includes diffusion, thermal conduction, elastic collision interaction and the detailed kinetics of excited atomic and ionic levels. The retarded plasma motion results in a slow electron density decay. Effective electron cooling is achieved in the diffusion region where the plasma mixes with the background gas. Quasisteady-state population inversions occur in the resulting cold and dense plasma.
Transient equations of a two-temperature discharge
Authors: Novak Jaroslav P. , Shoucri Magdi M.
Published: February 2003

Transport equations for mass, momentum, energy, and heat flux based on the thirteen-momentum approximation of the Boltzmann equation are analyzed in the isobaric approximation. The left-hand-side terms are estimated and compared with terms representing the collisional transfer for the transient case of nonequilibrium two-temperature discharges in monoatomic gases. A simplified form of the equations is derived and the corresponding conditions are expressed as functions of the physical properties of the plasma. The system of equations is solved for a 0.5-A argon discharge at atmospheric pressure. The arbitrary initial distributions are allowed to relax to the equilibrium state, which is compared to previous results for a 0.4-A free-burning discharge in argon.
The implication of flow-rate dependencies in plasma etching
Authors: Chapman B. N. , Hansen T. A. , Minkiewicz V. J.
Published: February 2003

One of the problems in the understanding and implementation of the plasma etching process is the general lack of quantitative information about the effect of the many process parameters involved. We have been studying the effect of gas flow rates in the etching of silicon materials in fluorocarbon gases, and have been led to define a utilization factor to describe the extent to which the reaction gas is converted to volatile products of the plasma etching process. The experimental evidence for the importance of a utilization factor in plasma etching is shown, and some of the surprisingly many ways in which flow rates influence the whole etching process are illustrated.
Ion beams from laser-generated plasmas
Authors: Hughes R. H. , Anderson R. J. , Manka C. K. , Carruth M. R. , Gray L. G. , Rosenfeld J. P.
Published: February 2003

Space-charge-limited heavy ion beams have been produced by utilizing the plasma blowoffs generated by 20-MW bursts of 1.06-μ radiation from an active Q-switched Nd:Yag laser. Laser power densities near a moment 1011 W/cm2 on solid targets generate thermalized plasma plumes which drift to a 15-kV gridded extraction gap where the ions are extracted, accelerated, and subsequently electrostatically focused. The spatially defined ion beams are then magnetically analyzed to determine the charge-state content in the beams. Results are presented for the more significant amounts of charge states Z?5 contained in the beams formed from carbon, aluminum, copper, and lead targets. The extraction and acceleration technique preserves time-of-flight (TOF) information in the plasma drift region, which allows plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.
Production of a cylindrical plasma shell
Authors: Bengtson Roger D. , Honea D. L. , Pease D. , Degnan James H. , Golobic Robert A.
Published: February 2003

We describe an apparatus which forms a hollow cylindrical plasma shell of 3×2 cm2 cross section 40 cm in diameter by injecting a neutral gas shell of argon via supersonic injection nozzles and ionizing this shell with a high-voltage electrical discharge.
Large optical cavity AlGaAs injection lasers with multiple active regions
Authors: Katz J. , Bar-Chaim N. , Margalit S. , Yariv A.
Published: February 2003

A new type of AlGaAs injection laser is described. The structure consists of alternating p- and n-type layers of GaAs and Alx Ga1−xAs . The electrical mode of operation of the device is that of a Shockley diode (SCR). Optically the device operates as a large optical cavity. Single transverse mode operation was observed with optical cavities larger than 4 μm.
Ion-implanted Se in GaAs
Authors: Lidow A. , Gibbons J. F. , Deline V. R. , Evans C. A.
Published: February 2003

Electrical measurements are combined with the technique of secondary-ion mass spectrometry (SIMS) in order to experimentally analyze and correlate the diffusion and activation of ion-implanted selenium in GaAs. A theory is presented based on the assumption of four chemically different species of selenium: (1) substitutional selenium, (2) interstitial selenium, (3) selenium complexed with a gallium vacancy, and (4) precipitated selenium. It is proposed that the interaction between these four species dictates the resulting redistribution and electrical activation of ion-implanted layers. The factors governing these interactions are investigated, and it is speculated that only substitutional selenium is a shallow donor. In addition, it is speculated that the species responsible for redistribution of impurity profiles is the selenium-gallium vacancy complex. Precipitates and interstitial selenium appear to neither diffuse nor act like donors in GaAs. A model is developed which formalizes these observations in a set of five coupled differential equations. By employing a minimum number of simplifying assumptions, we are able to extract quantitative predictions from this model which accurately describe not only our experimental results but those of other workers.
Electron-electron interaction and screening effects in hot electron transport in GaAs
Authors: Inoue Masataka , Frey Jeffrey
Published: February 2003

The influence of electron-electron scattering processes on high-field transport properties of electrons in GaAs, and the usefulness of a drifted Maxwellian approximation to the distribution function in analysis of devices in which these effects are important, have been studied. Monte Carlo simulations of transport both with and without electron-electron scattering included are compared with drifted Maxwellian distribution functions over a range of doping and electric field values typical of submicron-scale devices. Electron-electron scattering is found to have a significant effect on the shape of the distribution function derived by MC simulation, but little effect on the average electron velocity. The degree of approximation involved in device analyses when the drifted Maxwellian is used instead of the correct distribution function is discussed.
Hole photogeneration in aggregate photoreceptors
Authors: Borsenberger P. M. , Hoesterey D. C.
Published: February 2003

The photogeneration of holes in aggregate photoreceptors has been investigated as a function of electric field, temperature, and excitation wavelength. The experimental results are describable by the Onsager theory. The fraction of absorbed photons that produce thermalized electron-hole pairs is 0.58 and is independent of wavelength and temperature. At room temperature, the pair separation distance is 44 Å. This distance is independent of wavelength and increases linearly with temperature. It is concluded that the photogeneration of free carriers can be explained by the surface dissociation of a thermalized exciton.
I-V relationship for the Cu2S/CdS solar cell
Authors: Lazarev G. L.
Published: February 2003

The ’’diode’’ equation, which describes the behavior of the Cu2S/CdS solar cell, was derived from the first principles. The key results are the independence of the Voc from the field in CdS and an explanation of the intersection of the dark and illuminated portions of the I-V curves. The limiting factors and correlation with experimental results are discussed.
Photovoltaic properties of ZnO/CdTe heterojunctions prepared by spray pyrolysis
Authors: Aranovich Julio A. , Golmayo Dolores , Fahrenbruch Alan L. , Bube Richard H.
Published: February 2003

An extended investigation has been made of the electrical and photovoltaic properties of heterojunctions prepared by spray-pyrolysis deposition of thin ZnO films on single-crystal p-type CdTe. The principal experimental variables were the substrate temperature and the postdeposition temperature for annealing in H2. Under actual sunlight the optimum cell showed an open-circuit voltage of 0.54 V, a short-circuit current of 19.5 mA/cm2, and a solar efficiency (referred to the active area) of 8.8%, the highest value obtained to date for an authentic heterojunction on CdTe. The nature of the forward transport mechanism has been investigated, and a tunneling model in which bulk and interface deep traps control the forward characteristics is shown to provide good correlation with the experimental data.
Dipole layers at the metal-SiO2 interface
Authors: Hickmott T. W.
Published: February 2003

The existence of dipole layers at the metal-insulator interface or dipole layers in the bulk of the insulator can play an important role in determining electrical conduction and dielectric loss in insulators, and the nature of the barrier to electron injection into the insulator. The conventional analysis of metal-SiO2-semiconductor (MOS) structures is extended to include the effect of dipoles on capacitance-voltage (C-V) characteristics. The occurrence of both dipole layers and trapped charge can be established by measuring the flat-band voltage of MOS capacitors as a function of oxide thickness. Such measurements are suitable for measuring changes in the work function at the metal-insulator interface due to metal-insulator reaction. C-V measurements of Au-SiO2-Si capacitors are combined with thermally stimulated ionic conductivity (TSIC) measurements of Na+ in SiO2 to show that annealing of the Au-SiO2 interface between 150° and 250 °C produces a positive dipole at the Au-SiO2 contact while annealing between 250° and 400 °C results in a negative dipole at the Au-SiO2 interface as well as introducing negative charge into the insulator. C-V measurements give the magnitude of work function changes while TSIC measurements show that the changes occur at the Au-SiO2 interface. Annealing the Al-SiO2 interface at 400 °C in nitrogen or forming gas produces a dipole layer that increases the Al-SiO2 barrier height by about 0.2 eV. The work function at the metal-insulator interface is not a well-defined constant but depends on metal-insulator interactions that depend, in turn, on processing of the interface.
Deep level defects in polycrystalline cadmium sulfide
Authors: Besomi Paul , Wessels Bruce
Published: February 2003

Properties of deep level defects in polycrystalline CdS junctions were investigated using transient capacitance spectroscopy. A total of seven electron traps and one hole trap was observed with activation energies of 0.16, 0.31, 0.38, 0.42, 0.53, 0.69, 0.96, and 0.32 eV, respectively. The emission rate, capture cross section and concentration of the traps are presented. The temperature dependence of the capture cross section for the electron traps at 0.53 and 0.69 eV are also given.
Quantum noise in Josephson junctions
Authors: van der Ziel A.
Published: February 2003

The work of Rogovin and Scalapino on noise in Josephson junctions is applied to the cases of zero-bias junctions, forward-biased junctions at relatively low frequencies, and to the case of arbitrary bias and frequency. In the latter case there is an infinity in the noise at the bias voltage V0=hf/2e; these quantum effects are caused by Cooper pairs. The effect appears to be measurable at 100 GHz and 2 °K, in which case the infinity in the noise occurs at 0.207-mV bias.
Operation of near ideal spectroscopic heat pipes
Authors: Melton L. A. , Wine P. H.
Published: February 2003

An analytical model has been developed to describe the operation of simple and concentric gas-loaded heat pipes and to assess the extent of deviations from ideal behavior due to diffusion, viscosity, and sonic flow. The model predicts, with reasonable accuracy, the start-up power, the maximum heat transport, and the thermal regulation (=Δ density/Δ input power). Experimental results will be presented for Li/He heat pipes. This approximate analytical model should enable spectroscopic and kinetic heat pipe users to design and operate heat pipes optimally without extensive and costly computer solutions of the full Navier-Stokes equations. The model is based on approximate solutions of diffusion/convection equations, in which the convective velocity distribution of a nearly ideal hat pipe is assumed to be identical to that of an ideal heat pipe. The vapor is treated as a one-dimensional compressible fluid. Among the more important results are (1) The start-up power QSU, defined as the power required to bring the metal vapor density to 95% of n0, the stagnation density, at the exit of the heated zone (or adiabatic zone if present) is virtually independent of n0. (2) For a heat pipe whose thermal losses are dominated by radiation, the start-up power varies as T9/40, where T0, the stagnation temperature, is defined by n(T0)=n0. (3) The sonic flow limit QCF may be approximated as QCF= 1/2 hfg An0c(T0), where hfg is the heat of vaporization per atom, A is the cross-sectional area, and c(T0) is the speed of sound at T0. (4) The thermal regulation properties of a concentric heat pipe may be approximated from the thermal regulation properties of simple heat pipes.
Annealing of nitrogen-implanted GaAs1−xPx by a swept line electron beam
Authors: Yu T. , Soda K. J. , Streetman B. G.
Published: February 2003

Photoluminescence studies and emission profiling are used to evaluate the effectiveness of swept (as opposed to rastered) electron beams in activating ion implanted nitrogen in GaAs1−xPx . Both direct- and indirect-gap compositions are studied as a function of nitrogen concentration and electron beam intensity. We find this annealing method produces comparable or superior nitrogen activation as compared with furnace annealed material, with reduced implantation-induced damage diffusion. This is the first use of a swept line electron beam for annealing, a method which offers advantages over raster-scanned focused lasers or electron beams.
Diffusion enhancement due to low-energy ion bombardment during sputter etching and deposition
Authors: Eltoukhy A. H. , Greene J. E.
Published: February 2003

The effects of low-energy ion bombardment on enhancing elemental diffusion rates at both heterojunction interfaces during film deposition and over the compositionally altered layer created during sputter etching alloy targets have been considered. Depth dependent enhanced interdiffusion coefficients, expressed as D*(x)=D*(0) exp(−x/Ld), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb/GaSb multilayer structures deposited by multitarget bias sputering. D*(0) was determined from the amplitude u of the compositional modulation in the multilayered films (layer thicknesses between 20 and 45 Å) as measured by superlattice x-ray diffraction techniques. The value of D*(0) was found to increase from 3×10−17 to 1×10−16 cm2/sec as the applied substrate bias was increased from 0 to −75 V. However even at Va=0, the diffusion coefficient was enhanced owing to an induced substrate potential with respect to the positive space-charge region in the Ar discharge. The diffusion length of Ld of the ion bombardment created defects was ∼1000 Å. Enhanced diffusion also has a significiant effect on the altered layer thickness xe and the total sputtering time te (or ion dose) required to reach steady state during ion etching of multielement targets. The effects of using an exponentially depth dependent versus a constant value of the enhanced diffusion coefficient on calculated values of xe and te in single-phase binary alloys were considered. The results show that both xe and te are considerably larger using a depth dependent D*(x), when Ld<D*(0)/v, where v is the steady-state surface recession velocity during sputter etching. However, when Ld≳D*(0)/v, the usual case for most sputtering applications, the two solutions approach each other.
Hydrogen absorption and its effect on low-temperature electric properties of niobium
Authors: Isagawa S.
Published: February 2003

The excess resistivity of niobium foil samples due to doped hydrogen increases with concentration up to 8–12 at.% H, which is almost independent of temperature. The Nb-H structure at room temperature or above is quenched to 77 K or 9.5 K by relatively rapid cooling. The abrupt decrease of resistivity is observed, which corresponds to the precipitation of the ordered orthorhombic hydride phase. The superconducting transition temperature Tc is rather insensitive to hydrogen concentration in α solid solution. Hydride phase, however, shows no sign of superconductivity down to 1.3 K. Hydrogen is found to be reabsorbed in niobium after UHV outgassing by storage in air or by immersion in etchants. This is confirmed by weighing the samples and cross-checked by the proton NMR measurements.
Laser purification of silane: impurity reduction to the sub-part-per-million level
Authors: Hartford Allen , Huber Elmer J. , Lyman John L. , Clark John H.
Published: February 2003

Selective ultraviolet photolysis of AsH3 and PH3 impurities in SiH4 has been employed to photochemically purify the SiH4. At ambient temperature, initial impurity levels of 50 ppm each of AsH3 and PH3 in SiH4 were reduced to less than 0.5 ppm upon irradiation with a 193-nm ArF excimer laser. Lowering the temperature at which the photolysis is carried out to below ambient results in a substantial reduction in the laser energy required for impurity removal.
Electromigration in fine-line sputter-gun Al
Authors: Vaidya S. , Fraser D. B. , Lindenberger W. S.
Published: February 2003

The electromigration behavior of Al films, deposited by the sputter gun (varian s-gun) and ranging in alloy content from 0.5% Cu to 2% Si has been evaluated for 2.5 cm long, 1–4 μm wide conducting stripes. An inverse square dependence of lifetime on current density has been verified. Furthermore, it has been shown that film composition affects the electromigration lifetime through its contribution to the grain structure, in that, an increase in lifetime accompanies an increase in grain size and a decrease in spread of the grain size distribution. Increasing the Si content is detrimental, since it results in a reduction in grain size. Failures occur by the random growth of subsurface voids along the conductor length. The s-gun films have a completely random orientation in contrast to electron beam evaporated Al-0.5% Cu, which exhibits a prominent 〈111〉 fiber texture. This preferred grain orientation in the case of the latter is held responsible for its superior lifetime in comparison to the sputtered films.
Electromagnetic scattering from an eccentrically coated infinite metallic cylinder
Authors: Roumeliotis John A. , Fikioris John G. , Gounaris George P.
Published: February 2003

In this work the scattering from an eccentrically coated infinite metallic cylinder is considered. The problem is solved using classical separation of variables techniques combined with translational addition theorems. For small eccentricities κd, where d is the distance between the two axes and κ the wave number of the dielectric coating, exact closed-form expressions of the form S(d)=S(0)[1+g′(κd)+g″(κd)2+O(κd)3] are obtained for the scattered field and the various scattering cross sections of the problem. Both polarizations are considered for normal incidence. Numerical and graphical results for various values of the parameters are also discussed.
Variation of secondary ion emission yield with atomic concentrations of Fe, Ni, and Cr ternary alloys and oxides: Application to the analysis of thin oxide films
Authors: Pivin J. C. , Roques-Carmes C. , Slodzian G.
Published: February 2003

For binary and ternary alloys of Fe, Ni, and Cr covered with oxygen and for solid oxides of these elements, the emission yield of monoatomic ions, Fe+, Ni+, and Cr+, are linear functions of the atomic concentrations CFe, CNi, and CCr . This empirical law suggest that the emission of M+ ions obeys a binary process, involving dynamic electronic exchanges between the M sputtered atoms and their neighbors during inelastic collisions. The determined formula for the interrelationship between the M+ intensities and the atomic concentrations is applied to the quantitative analysis of oxide films developed at high temperature on a refractory alloy.
The effects of irradiation and electrodiffusion on the sodium acoustic loss peak in synthetic quartz
Authors: Doherty S. P. , Martin J. J. , Armington A. F. , Brown R. N.
Published: February 2003

The acoustic loss peak near 50 K in 5-MHz 5th overtone AT-cut synthetic quartz resonators has been used to determine the behavior of the Al-Na+ center under irradiation. The center was found to be stable for irradiations carried out at temperatures below 200 K. Above 200 K the Na+ was found to be mobile in the radiation field and was replaced by a hydrogen to form the Al-OH− center. The decrease in the height of the sodium acoustic loss peak following irradiation at temperatures between 200 and 250 K correlates strongly with the growth of the Al-OH− and (Ale+)0 centers over the same temperature range. Electrodiffusion has been carried out directly on plano-convex AT-cut resonator blanks. Using the technique Na has been swept into, as well as removed from AT-cut resonators. Direct sweeping of AT-cut resonator blanks should reduce the number of steps needed in the fabrication of radiation-hardened crystals.
A new dc method of measuring the magnetoconductivity tensor of anisotropic crystals
Authors: Spal R.
Published: February 2003

A dc method is described for measuring the magnetoconductivity tensor of an anisotropic crystal when the magnetic field is along a crystallographic symmetry axis. The method is particularly suited for compounds with large anisotropies, for which conventional techniques are not practical. The sample to be measured is a rectangular parallelepiped, each of whose faces is either free or on a highly conducting substrate. The electrodes are arbitrarily located point contacts. Special attention is given to self-consistency checks for verifying that the conditions required to apply the method are satisfied. A convenient alternative to the usual procedure of separating resistive and Hall voltages by magnetic field reversal is presented.This new procedure is based on a reciprocity theorem in a magnetic field, proved here apparently for the first time.
Ion-implantation-induced damage and resonant levels inPb1−xSnxTe
Authors: Gresslehner K. H. , Palmetshofer L.
Published: February 2003

The dependence of the carrier concentration on the implantation dose and on the temperature was investigated in ion-implanted thin films of Pb1−xSnxTe (0⩽x<0.1). By assuming a twofold defect level in the conduction band we are able to fit the experimental results. With increasing tin content the energy of the defect level shifts towards the conduction-band edge. By extending the results to SnTe a general model for the understanding of the electrical properties of ion-implanted Pb1−xSnxTe (0⩽x⩽1) is suggested.
Bright dc electroluminescence in ZnSe-ZnS:Mn thin films
Authors: Doi T. , Ohnishi H. , Ieyasu K. , Hamakawa Y.
Published: February 2003

A dc-operated thin-film electroluminescent cell with the threshold voltage of ∼53 V has been developed in the system of ITO-(ZnSe→ZnS:Mn)-Al. The emissive layer of the cell is made of compound which varies from ZnSe to ZnS:Mn in composition. The brightnesses of up to 241 and 48.3 fL have been measured in the injection level of 50 mA/cm2 and 4.45 mA/cm2, respectively, at power efficiencies in the range 1.12×10−4–2.58×10−4 W/W.
ZnO single crystals with an intermediate layer of metal oxides—A macroscopic varistor model
Authors: Schwing Ulrich , Hoffmann Bernd
Published: February 2003

Crystalline ZnO plates with an intermediate layer consisting of a mixture of Bi2O3, MnO2, and Co3O4 were prepared and sintered for 1 h at 1223 K in air. The sandwiches were used as a macroscopic model system substituting the grain boundary contacts in ceramic varistor materials. Measurements of the current-voltage characteristics confirm a breakthrough voltage of 3.5 V. Microscopic investigation supports the concept of a heterojunction with depletion layers being responsible for the nonlinear varistor properties.
ZnTe extrinsic photodetector for visible integrated optics
Authors: Hamdi H. , Valette S.
Published: February 2003

Oxygen implantation in ZnTe may be used to obtain optical absorption at wavelengths higher than 0.55 μm, which is the normal absorption edge in this compound semiconductor. Optical waveguides obtained by boron implantation in this material are associated with detectors using that extrinsic absorption effect in the presence of a Schottky barrier depletion layer. The responsivity of the photodetector is about 5×10−2 A/W at 0.61 μm and the rise time is less than 3 ns.
Thermoelastic stress analysis of pulsed electron beam recrystallization of ion-implanted silicon
Authors: Schoen N. C.
Published: February 2003

The time and spatial dependence of the temperature rise produced in ion-implanted silicon subjected to pulsed electron beam bombardment has been numerically calculated. The temperature profiles generated were then used to calculate the thermoelastic stresses produced by the deposited energy. Experimental measurements of the incident energy density thresholds for fracture of the silicon have beem compared with damage threshold levels suggested by this analysis. The temperature calculations have been qualitatively verified by diffusion profile measurements as compared with calculated profiles based on dopant diffusion in liquid silicon. The shear forces produced by the large temperature gradients have been proposed as the primary cause of fracture which occurs at high beam fluences.
Fluctuation studies in interaction of lasers with two-photon media
Authors: Bohidar H. , Chopra S.
Published: February 2003

The propagation of a laser beam through a two-photon absorber (TPA) is discussed for the incident laser working at, above, and below its threshold of oscillation. It is shown that the fluctuation behavior characterized by the normalized moments 〈I〉/〈I0〉, 〈I2〉/〈I0〉2, and 〈I2〉/〈I〉2 and the variances 〈(ΔI)2〉 and 〈(Δn)2〉 change significantly throughout the absorption process. We also calculate the time-dependent factorial moments of the laser field near threshold as it propagates inside the media and discuss this aspect of fluctuation behavior.
Dynamic pressure-shear loading of materials using anisotropic crystals
Authors: Chhabildas L. C. , Swegle J. W.
Published: February 2003

An experimental technique is described which uses anisotropic crystals to generate dynamic pressure-shear loading in materials. The coupled longitudinal and shear motion generated upon planar impact of the anisotropic crystal can be transmitted into a specimen bonded to the rear surface of the crystal, and monitored using velocity interferometer techniques. Test results using y-cut quartz generators and x-cut quartz and y-cut quartz samples indicate that shear stresses up to 0.35 GPa can be transmitted across epoxy-bonded interfaces. The technique has been successfully used to detect a 0.2 GPa shear wave in 6061-T6 aluminum at 0.7 GPa longitudinal stress. The shear wave velocity profiles have an accuracy of ±12%. The use of longer delay legs in the interferometer is suggested to improve the accuracy. Results obtained in this investigation are compared with numerical solutions obtained using the finite-difference wave propagation code TOODY.
An x-ray optical study of layered phase growth in Au-Al thin film couples
Authors: Wagendristel A. , Schurz H. , Ehrmann-Falkenau E. , Bangert H.
Published: February 2003

Specular x-ray reflections originating at grazing incidence at the boundary planes of thin laminated structures interfere to give the known Kiessig fringes. The change of this interference pattern during diffusion in thin multilayers is used for the study of phase formation in Au-Al thin film couples. Layered growth of Au2Al obeying a parabolic growth relation was observed in the temperature range from 50 to 80 °C. The activation energy of the process was found to be 1.05 eV.
An analytical theory for the scattering of surface acoustic waves by a single electrode in a periodic array on a piezoelectric substrate
Authors: Datta Supriyo , Hunsinger Bill J.
Published: February 2003

An analytical theory is presented that leads to the scatter matrix of a sngle electrode for an acoustic surface wave propagating through a periodic array of electrodes on an anisotropic piezoelectric substrate. The scatter matrix elements are obtained analytically as functions of frequency and metallization ratio, considering only the electrical loading by the electrodes; mechanical loading effects are neglected. The results may be used directly in the broad band analysis of surface acoustic wave reflectors and multistrip couplers. Previous works have provided these parameters numerically for electrically shorted and open arrays at stop band frequencies (frequencies where the array period is an integer number of half wavelengths). This work extends the analysis in three ways: (a) the analysis is valid for all frequencies, (b) the external electrical load connected to the electrodes is included as a parameter, and (c) the scatter matrix elements are determined analytically instead of numerically.
Charge trapping studies in SiO2 using high current injection from Si-rich SiO2 films
Authors: DiMaria D. J. , Ghez R. , Dong D. W.
Published: February 2003

The high electron injection phenomenon of Si-rich SiO2 films deposited on top of SiO2 can be used for novel charge trapping studies of sites normally present or purposely introduced in the SiO2. From the position and extent of current ledges observed in dark current as a function of ramped gate voltage, the capture cross section and total number of traps can be determined. Using these measurements with capacitance as a function of gate voltage, the trap distribution centroid and number of trapped charges can also be found. Several experimental examples are given including trapping in thermal SiO2, in chemically vapor deposited (CVD) SiO2, and on W, less than a monolayer thick, sandwiched between thermal and CVD SiO2. These stepped insulator metal-insulator-silicon (SI-MIS) ramp I-V results for the trapping parameters are shown to be in good agreement with those determined using the conventional photo I-V and avalanche injection with flat-band voltage tracking techniques. A numerical simulation of the ramp I-V measurements, assuming electric field-enhanced Fowler-Nordheim tunneling at the Si-rich-SiO2–SiO2 interface, is described and is shown to give good agreement with the experimental data. These techniques for SI-MIS structures are faster and easier, although less accurate than the conventional techniques.
One-carrier thermally stimulated currents and space-charge-limited currents in naphthalene crystals: Doped and irradiated samples.
Authors: Campos M. , Mergulhão S.
Published: February 2003

Measurements of space-charge-limited currents (SCLC) and thermally stimulated currents (TSC) were done in naphthalene single crystals grown from the melt and also from solution. Crystals grown from the melt were irradiated with x rays to a dose that ranged between 8×104 and 6×106 R. These crystals were also doped with beta naphthol with concentrations that varied from 10−4 to 10−2 in mole fraction. Melted crystals showed a trap level at 0.71 eV using SCLC and 0.79 eV using TSC, whereas solution crystals showed 0.43 eV using SCLC and 0.78 eV using TSC. Irradiated samples showed a trap level at 0.50 eV. In the case of doped samples the impurities originate a trap level at a depth of 0.53 eV that was possible to predict theoretically. Results showed that care must be exercised to obtain a valid comparison between the SCLC and TSC measurements and also that trapping of charge carriers is greatly influenced by the conditions under which the crystals were grown.
Transport properties of Sn-doped AlxGa1−xAs grown by molecular beam epitaxy
Authors: Morkoç Hadis , Cho A. Y. , Radice C.
Published: February 2003

Transport properties of Alx Ga1−x As layers having AlAs mole fractions between 0.17 and 0.375 and grown by molecular beam epitaxy were investigated. The Al cell temperature was kept at 1075 °C while the Ga cell temperature was changed between 910 and 950 °C to obtain the aforementioned AlAs mole fractions. The donor levels of Sn in Alx Ga1−x As obtained from the temperature dependence of the net donor concentration are below 3, 30, and 40 meV for x=0.17, x=0.29, and x=0.375, respectively. Al0.22 Ga0.78 As layers having a net electron concentration of about 1.7×1018 cm−3 and grown at 630 °C exhibited a mobility of 868 and 1095 cm2/V sec at 300 and 78 °K, respectively. The mobility was found to be strongly dependent on the substrate temperature during the growth. The lower substrate temperatures resulted in lower electron mobility.
A study of the deep carrier traps in a Te-Se-Cd rectifying structure
Authors: Housin M. , Bastide G. , Sagnes G. , Rouzeyre M. , Champness C. H. , El-Azab M. I.
Published: February 2003

Deep level transient spectroscopy, by means of capacitance transients, is applied to characterize deep carrier traps located in the depleted zone of a rectifying Te-Se-Cd structure. Preliminary observations, such as electron beam induced current and secondary electron and x-ray emission, show that the depleted region is situated in the p-type epitaxially grown Se film. Measurements of the thermal emission rate of trapped carriers are made in the 80–340 °K temperature range. From these, the existence of three deep hole traps in Se is demonstrated with the following values of the thermal activation energy ET, capture cross section σe, and volume density NT: 290 meV, 1.2×10−16 cm2, 7.0×1013 cm−3; 400 meV, 2.5×10−15 cm2, 3.0×1013 cm−3; 700 meV, 1.5×10−14 cm2, 3.0×1014 cm−3. The frequency dependence of the differential capacitance is measured between 100 Hz and 1 MHz and is attributed to a shallow hole trap (ET∼100 meV), with a high volume density in the 1019–1020 cm−3 range. This last result agrees with the conclusions deduced from thermally stimulated currents (TSC) experiments on the same type of material.