bluuebunny/crossref_metadata_2025 huggingface dataset:
HCl oxidation conditions for stacking-fault nuclei gettering and for silicon etching
Authors: Hattori Takeshi
Published: February 2003

HCl addition to an oxidiing ambient during thermal oxidation of silicon can prevent the generation of oxidation-induced stacking faults in the crystal during the subsequent standard thermal-oxidation cycles. The gettering action of stacking-fault nuclei from the surface regions of the silicon wafers is induced under appropriate HCl oxidation conditions (temperatures, times, and HCl concentrations). Conditions for an undesirable etching of the silicon surface are also presented. These two phenomena presumably occur when certain concentrations of a chlorine species are incorporated near the silicon–silicon dioxide interface.
A comparison of carrier lifetime measurements by photoconductive decay and surface photovoltage methods
Authors: Chu T. L. , Stokes E. D.
Published: February 2003

Minority-carrier lifetimes in silicon crystals measured by surface photovoltage and photoconductive decay methods have been compared. The results from both measurements are in reasonable agreement provided that the thickness of the sample for surface photovoltage measurements is at least twice the diffusion length.
Effect of annealing on the electrical resistivity of conductive polyvinylchloride-copper composites
Authors: Bhattacharyya Swapan K. , Basu S. , De Sadhan K. , Pal A. K. , Chowdhury S.
Published: February 2003

Polyvinylchloride-copper composites at different volume percent of copper are annealed at 50 °C for 10 days. The effect of temperature on the electrical resistivity of the resulting composites is studied between 0 and 40 °C using a four-electrode device. Three clearly distinguished behaviors of the composites are observed after prolonged annealing. They exhibit (a) a positive temperature coefficient of resistance, (b) higher discrepancy in resistivity values for all metal loadings, and (c) an Ohmic current-voltage relationship. We try to explain the positive temperature coefficient of resistance through the reduction of the contact pressure between the metal particles with increase in temperature.
Electrical properties and charge imbalance for Ca,Ge-substituted garnet films grown by liquid-phase epitaxy from PbO-BO fluxed melts
Authors: Hibiya Taketoshi , Hidaka Yasuharu , Suzuki Kozaburo
Published: February 2003

Ca,Ge-substituted garnet films show p-type conduction when grown from melts of Ca/Ge molar ratio, R5 parameter≡[CaO]/([CaO]+[GeO2]) ≳0.486. n-type conduction is observed for films grown from R5-parameter ?0.275 melts. Through experiments on Ge and/or Ca doping to (Y,Sm)3(Fe,Ga)5O12 garnet films, these dopants are concluded to play important roles in the resistivity, as well as the conduction type. It is inferred that Ca content in films exceeds Ge content for p-type Ca,Ge-substituted garnet films and that Ge content exceeds Ca content for n-type films. These results are obtained from measuring resistivity and the sign of the Seebeck effect for (Y,Eu,Tm,Ca)3(Fe,Ge)5O12 garnet LPE films at room temperature. Both resistivity at melt saturation temperature and the conduction type depend on R5-parameter values. Low-coercivity films are reproducibly obtained from R5∼0.1 melts.
On the thermomigration of liquid wires
Authors: Cline H. E. , Anthony T. R.
Published: February 2003

As a liquid wire migrates through a solid in a thermal gradient, the cross-sectional shape of the liquid is deformed from the symmetric equilibrium shape. A force model of the thermomigration process is derived to calculate both the nonequilibrium shape and the effect of wire size on the migration velocity for thermal gradients of different magnitude and orientation. The forces are related to the thermal gradient, diffusion in the liquid, and interface kinetics. At small wire sizes, the effects of interface kinetics become relatively more important; consequently, it is more difficult for liquid wires to migrate in the direction of the thermal gradient. In the case of a thermal gradient applied to a silicon crystal in the 〈100〉 direction, the shape becomes triangular, and the migration direction is sensitive at small wire sizes to fluctuations in the rate of reaction at the interface, while for a thermal gradient in the 〈111〉 direction, the shape becomes an unsymmetric flattened hexagon in which the migration direction at small wire sizes deviates from the direction of the thermal gradient. At sufficiently large wire sizes, nonuniform thermal gradient forces result in an unstable concave shape. The shape of a migrating wire depends only on the distribution of interface forces over the various facets of the solid-liquid interface and on the cross-sectional area of the liquid wire.
Investigation of minority-carrier diffusion lengths by electron bombardment of Schottky barriers
Authors: Wu C. J. , Wittry D. B.
Published: February 2003

Using a modified Gaussian approximation to the depth distribution of the energy dissipation function for electron bombardment, an analytical expression was derived for electron-beam-induced current (EBIC) at a Schottky barrier parallel to the bombarded surface. Comparison of theory and experiment for the voltage dependence of EBIC for 14 specimens (including p- and n-type GaAs and Si) provided values for the diffusion length of excess carriers, the thickness of the metal layer of the Schottky barrier diode, and the average energy ℰ required to generate a hole-electron pair. Diffusion lengths ranging from 0.41 to 55 μ were determined with an estimated accuracy of ±20%. The values of ℰ were found to be 3.75±0.11 eV for Si and 4.68±0.14 eV for GaAs. The unique advantages of this method for measuring small diffusion lengths are emphasized.
Calculation of two-photon conductivity under nanosecond and picosecond pulse excitation in semiconductors
Authors: Mathur V. K.
Published: February 2003

It has been the usual practice to solve the continuity equation for the case of steady excitation and presume that the same results are valid for pulse excitation of the photoexcited carriers. However, it has been shown in the present analysis that this assumption is valid for the exciting pulse which is of longer duration than the mean lifetime τ of the photoexcited carriers. In the case of excitation of photoconductivity by picosecond pulses, which are now available from the mode-locked laser system, the pulse duration is much smaller than τ and the results of steady-state excitation are no longer applicable. Moreover, the magnitude of the photoconductivity depends on the pulse duration T and is independent of τ. In fact, the photoconductivity is found to exhibit a transient behavior.
Influence of positive ions on the current-voltage characteristics of MOS structures
Authors: Tangena A. G. , Middelhoek J. , de Rooij N. F.
Published: February 2003

A new mathematical approach for the influence of mobile positive ions on the current-voltage characteristics of MOS structures is presented. This new method gives formulations which are more applicable than those described in the literature. Examples of the application of these formulations are presented.
Lead-alloy Josephson-tunneling gates with improved stability upon thermal cycling
Authors: Lahiri S. K. , Basavaiah S.
Published: February 2003

An investigation has been carried out in order to explore means to improve the stability of the in-line Josephson-tunneling gates, which are fabricated using Pb films containing In and/or Au additions as electrodes. The investigation has revealed that incorporation of several modifications in a previously reported gate-fabrication process results in at least a fourfold increase in the stability during thermal cycling from 298 to 4.2 °K. For a total of 38 gates fabricated using the modified process, only about 30% were found to have failed after 500 cycles. In comparison, the same percentage failure was observed after only 120 cycles, even for the most stable set of 19 gates which were fabricated using the previous method. Evaluation of the results indicates that the observed improvement in the stability could be attributed to the use of reduced electrode film thicknesses and an alteration of the base-electrode fabrication process. In this paper the process modifications which resulted in the improved stability and corresponding junction characteristics and cycling data are described.
On the origin of core losses in a manganese zinc ferrite with appreciable silica content
Authors: Jain G. C. , Das B. K. , Kumari Santosh
Published: February 2003

The effect of silica on the magnetic properties and microstructure of a manganese zinc ferrite has been studied. It is found that as silica content increases, the magnetic properties at first improve, then deteriorate around 0.04% silica due to discontinuous grain growth. At still higher silica contents, magnetic properties deteriorate further due to an increase in the total effective magnetic anisotropy.
Theoretical aspects of photoacoustic spectroscopy
Authors: Rosencwaig Allan
Published: February 2003

The exact form of the Rosencwaig-Gersho theory for the photoacoustic effect in solids is used to depict how the magnitude and phase of the photoacoustic signal vary with chopping frequency and normalized length. Applications of the theory to studies of film-substrate systems are discussed.
Excited state formed by B+ impact on metallic Cu and Mo
Authors: Thomas E. W. , Inouye H. , Rausch E. O.
Published: February 2003

Impact of 60–200-keV B+ ions on polycrystalline Cu and Mo targets gives rise to emission from backscattered excited Be and B+. The emission coefficients for these lines are presented as a function of impact energy and analyzed to provide a measure of the survival parameter A/a for the atom or ion recoiling from the target. For B recoiling from both Cu and Mo, this is found to be 1.3×108 cm/sec, while for recoiling B+, it is 2.4×108. In the case of recoiling B+, the radiationless deexcitation must be by the Auger mechanism. Emission coefficients for the 3247, 3274-Å Cu I doublet are also presented and rise slowly throughout the energy range studied.
On the signs of the elasto-optic coefficients
Authors: Smit Jan
Published: February 2003

It is shown that the strain-induced dipole-dipole interaction gives a major contribution to the elasto-optic effect and can explain the opposite signs of the two shear coefficients observed in most alkali halides and alkaline-earth fluorides.
Ultrasonic attenuation in ceramics
Authors: Evans A. G. , Tittmann B. R. , Ahlberg L. , Khuri-Yakub B. T. , Kino G. S.
Published: February 2003

Ultrasonic attenuation has been measured for a range of ceramic polycrystals. An extreme-value approach for attenuation analysis has been developed, based on numerical scattering cross sections and an extreme-value characterization of the microstructure. A good correlation between predicted and measured attenuation has been obtained in each case. The implications of the analysis for ultrasonic failure prediction and microstructural characterization have been explored.
Plasma rate equations for an rf discharge in a magnetic field
Authors: Sanders Steven G.
Published: February 2003

A set of plasma rate equations are obtained which describe the time evolution of the electron density and temperature for an rf discharge in a magnetic field. Numerical solutions to these equations have been obtained for argon at pressures of 0.1–100 mTorr using the classical rf conductivity as the mechanism for transferring energy from the rf field to the electrons, and ambipolar diffusion and disassociative recombination as the dominant loss mechanisms. The typical temperature solution exhibits two well-defined temperature plateaus. The electron-density solution exhibits a monotonic growth to a saturation value which constitutes an appreciable percentage of the initial neutral-particle density. At the higher pressures, such large amounts of power are required to maintain the saturation density that source power may be the principle limitation on the maximum density achievable in the typical rf plasma source.
Parametric interaction between two Alfvén waves
Authors: Seshadri S. R.
Published: February 2003

The first two orders of parametric interaction between two plane Alfvén waves propagating in opposite directions in a spatially uniform inviscid perfectly conducting fluid pumped by a plane progressive sound wave are investigated for the case in which all three waves propagate parallel to the uniform magnetic flux permeating the fluid. The Alfvén waves become evanescent or absolutely unstable depending on the value of the sound wave velocity relative to the Alfvén wave velocity. The important charactristics of the evanescence and the absolute instability have been deduced.. Also, the amplitude-dependent frequency and wave-number shifts of the center of the second-order parametric interaction region have also been determined.
Hydrogen detection in metals by neutron interferometry
Authors: Rauch H. , Seidl E. , Zeilinger A. , Bauspiess W. , Bonse U.
Published: February 2003

The neutron interferometer is used to determine the H and D concentration in V and Nb samples. The hydrogen content changes the average coherent scattering length and, therefore, the phase shift of the coherent beams which can be measured precisely. The results are compared with the weighing and the epithermal neutron scattering method. Characteristic values for the sensitivity obtained with the interferometer method are 0.02–0.06 at.% or 6–12 ppm by weight. As soon as precipitation occurs in the sample, a loss of contrast indicates additional small-angle scattering.
Effect of non-Arrhenius self-diffusional behavior on quasielastic neutron scattering and Mössbauer linewidth
Authors: Wolf Dieter
Published: February 2003

The application of quasielastic-neutron-scattering or Mössbauer experiments to resolve the disputed origin of non-Arrhenius self-diffusional behavior in crystals is proposed. For that purpose, the related line-broadening effects are analyzed in terms of both the prevailing ’’two-defect model’’ and the ’’one-defect model’’ in its formulation, for example, by Gilder and Lazarus. The orientation dependence of the width of diffusion-broadened quasielastic and Mössbauer lines is found to differ for the two models. More importantly, however, it is shown that interpretation of line-broadening data in terms of the two models yields diffusion coefficients which cannot simultaneously agree with tracer data. A numerical analysis is presented for vacancy-induced self-diffusion in bcc crystals, such as sodium metal.
Lateral-current confinement in a GaAs planar stripe-geometry and channeled substrate buried DH laser using reverse-biased p-n junctions
Authors: Tsang W. T. , Logan R. A.
Published: February 2003

Processes have been developed for producing stripe-geometry planar DH lasers and channeled substrate buried DH lasers where lateral-current confinement is obtained with reverse-biased n-p junctions on both sides of the active layer. These current-confinement schemes lead to current flow only through the two superimposed top and bottom stripe windows in otherwise completely reverse-biased n-p junctions. The structures are composed only of as-grown liquid-phase-epitaxy multilayers. These lasers have low threshold current densities, clean stable optical-mode patterns, and excellent linearity in the light-current curves. In addition, the channeled substrate buried DH lasers have optical and carrier confinement in both transverse directions, while also achieving efficient lateral-injection-current confinement. Results from a theoretical analysis, which describes the dependence of the threshold current density Jsth of DH lasers upon stripe width S, are compared to the measured dependence and excellent agreement is obtained.
Excitation processes in a Pb-He discharge
Authors: Cross Lee A. , Gokay M. Cem
Published: February 2003

Measurements of the emission from Pb+ in the afterglow of a pulsed He : Pb discharge in a large-bore tube and of the intensities of Pb+ and Pb emission lines in a small-bore dc discharge tube have been made to clarify the excitation mechanism of the He : Pb laser. In both He :  pure Pb and He : Pb containing a low concentration of Cd to act as a probe, the rate constants for the decay of the Pb+ and Cd+ emission lines obtained using the large-bore tube indicated that the only excitation mechanism was thermal charge exchange between 2S1/2He+ and ground-state Pb atoms. The collision cross section for the He+-Pb reaction was determined to be 4.0×10−16 cm2 from measurements of the variations of the decay rates of the 5608.8-A Pb+, 4386.4-A Pb+, and 5378-A Cd+ emission lines with Pb concentration. The variation of the rate constant of the 4416-A Cd+ line indicated that the collision cross section for the 2s 3S1 He-Pb Penning ionization is 14.8×10−16 cm2. In a small-bore tube, Penning ionization was verified to be the dominant excitation mechanism for the 4245-Å Pb+ emission line but not the 5608-Å Pb+ laser line. The change in the relative importance of the various excitation mechanisms with the discharge-tube diameter, and its ramifications regarding other metal-vapor laser systems, is discussed.
Kinetic model of the sustained discharge excitation of the cadmium mercury excimer
Authors: Fournier G. R. , McGeoch M. W.
Published: February 2003

The results of a theoretical investigation of the discharge excitation of the CdHg* excimer are presented. Estimates are obtained for the efficiency of production of CdHg*, which has potential as an energy-storage medium for the amplification of light pulses at 470 nm. A time-independent analysis using a Boltzmann code was performed on a Cd, Hg mixture with an argon buffer. Seven atomic levels were considered in both Cd and Hg. A very high efficiency is obtained for excitation of the Cd(3P0,1,2) manifold from which the CdHg* excimer forms. The optimum E/N value for the mixture Cd : Hg : Ar=1 : 4 : 20 is 8×10−17 V cm2. The small value of the calculated Townsend coefficient at this E/N value required the consideration of an electron beam as the primary source of ionization. A detailed kinetic model was constructed which included electronic transition rates three-body association rates, dissociative recombination, biexcimer mixing, and biexcimer quenching. The kinetic equations were solved using the time-dependent solution of the Boltzmann equation for the electronic distribution function with a source term to account for the production of slow secondary (∼1-eV) electrons by ionization collisions of the fast (∼100-keV) primary electrons from the sustainer electron beam with the neutral atoms of the gas mixture. The effects of superelastic and inelastic collisions were explicitly included in the evaluation of the distribution function. In the case of a Cd : Hg : Ar mixture of 1 : 4 : 20 and Cd density of 5×1017 atoms/cm3, 40% of the discharge energy was deposited after 1 μsec into the molecular manifold of CdHg*. The sustainer ionization rate was 3.61×1020 electrons/cm3/sec, and the E/N value was 8×10−17 V cm2. The stored-energy density was 7 J/l. A molecular potential diagram for CdHg is given which indicates that 50% of the stored energy could be available for the amplification of subnanosecond optical pulses at 470 nm.
Numerical study of normal-zone evolution and stability of composite superconductors
Authors: Chen W. Y. , Purcell J. R.
Published: February 2003

A numerical procedure has been implemented to dynamically simulate the evolution of a normal zone in a superconducting composite. The model considers the nucleate/film boiling heat transfer of helium, the effect of current sharing, the longitudinal and turn-to-turn conductions, and the temperature variation of the thermal conductivity and specific heat. For a given set of conductor parameters and initial conditions, the evolution of a zone can be followed and its behavior established as either growing or shrinking (recovering). In between these two types of behaviors, a small region exists in which stagnant zones can be observed. Limiting recovery current density JL and heat flux QL tend to converge toward constant values for large LN. Turn-to-turn conduction allows higher JL and QL values as compared to isolated conductor cases. The minimum quench energy is calculated and compared with experimentally measured results, and reasonable agreement is obtained if an optimistic helium heat-transfer characteristic is assumed. The experiment was carried out by Wilson and Iwasa at MIT National Magnet Laboratory.
Amplification of surface magnetic waves in transversely magnetized ferrite slabs
Authors: Bini M. , Filetti P. L. , Millanta L. , Rubino N.
Published: February 2003

The problem of the amplification of surface magnetic waves in transversely magnetized ferrite slabs has been solved in a general planar layered structure. It is found that the amplification indeed exists, but it is confined to a definite (very narrow) frequency range, which depends essentially on the drift velocity of the interacting charge carriers. The amplification depends in a fundamental way on semiconductor conductivity, and also on the magnetic losses of the ferrite. The above results are deemed to constitute all the essential characteristics of the amplification phenomenon. Complex-wave-number magnetostatic (ms) modes in the transversely magnetized slab are also found that complete the already-known real-wave-number ms surface wave. Consideration of these modes is required when performing the exact analysis of the amplification process by numerical computation.
Hole-trapping effects in reverse-biased Si-doped Al Schottky-barrier diodes
Authors: Sullivan M. J. , Reith T. M. , Av-Ron M. , Shatzkes M.
Published: February 2003

The reverse-bias leakage of Si-doped Al rectifying contacts to n-Si, heat treated at 400 °C for 1 h, is observed to increase by more than two orders of magnitude as a result of biasing into avalanche breakdown. The original electrical characteristics are recoverable with moderate heat treatment. Pure Al contacts exhibit the same qualitative behavior, but to a much lesser extent. A mechanism is proposed in which holes, from electron-hole pair generation during avalanche, are trapped within a potential well arising from a crystallized p-doped layer known to exist for the Al-Si system.
Transient response of a cold lossless plasma half-space in the presence of a transverse static magnetic field
Authors: Kalluri Dikshitulu , Prasad R. C.
Published: February 2003

An analytical expression for the transient reflected field is given for the case of normal incidence of a linearly polarized impulsive plane wave on a lossless cold homogeneous plasma half-space in the presence of a transverse static magnetic field of arbitrary strength. This result thus removes the restriction of small anisotropy imposed by previous workers who used the perturbation method. Several curves illustrating the influence of the anisotropy are presented.
Electron backscattering from thin silicon crystals
Authors: Müller H. W. , Schröder B.
Published: February 2003

Very thin silicon crystals (600–7000 Å) were produced by a combined thinning technique starting from silicon wafers. The backscattering of 15–35-keV electrons from these crystals was measured. The reduced backscattering rate is proportional to the thickness of the specimen but is much higher than theoretically expected. Extrapolation to zero backscattering rate, however, leads to a thickness of 140 Å. Both of these facts lead to the conclusion that plural scattering predominates.
Impurity-band conduction in compensated ZnSe crystals
Authors: Sethi B. R. , Mathur P. C. , Woods J.
Published: February 2003

Hall-coefficient and conductivity measurements performed in three single crystals of ZnSe heavily doped with indium have been reported. The In doping is found to result in nearly complete compensation of the free charge carriers, leading to the impurity-band conduction even near room temperature instead of the normal free-electron conduction phenomenon.
Synthesis of stoichiometric InSb thin films by a simple molecular-beam technique
Authors: Baba S. , Horita H. , Kinbara A.
Published: February 2003

In-Sb alloy films, deposited by a two-source molecular-beam technique at substrate temperatures from 500 to 700 K in ultrahigh vacuum, have been examined by Auger electron spectroscopy. The compositional analysis shows that incident atoms of In and Sb react promptly to stabilize as the compound InSb. The stoichiometry of the deposits is disturbed when the surface is saturated with the residual free atoms. The stoichiometric InSb films can be deposited under the beam-intensity condition that JIn<JSb<JIn+n,n (T) =1.6×1029 exp(−2.3×104/T) atoms/cm2 s, where n corresponds to the critical beam intensity for the condensation of antimony.
Electrical properties of n-type epitaxial indium phosphide films
Authors: Tsai Ming-Jong , Bube Richard H.
Published: February 2003

Electrical transport properties have been analyzed by Hall-effect measurements for a series of epitaxial n-type undoped InP films deposited on high-resistivity GaAs : Cr or InP : Fe substrates by metalorganic chemical vapor deposition. For electron densities less than 1016 cm−3, films deposited on GaAs : Cr substrates show a general increase in electron mobility with increase in electron density as small structural potential barriers play a significant role in determining the mobility. All films deposited on InP : Fe substrates had an electron density greater than 1016 cm−3 and exhibited behavior virtually identical to that of bulk single crystals of InP. Electron mobilities at 77 °K as high as 10 500 cm2/V sec on GaAs : Cr substrates and 16 500 cm2/V sec on InP : Fe substrates have been measured.
On the nature of the electric field and the resulting voltage in axially loaded ferroelectric ceramics
Authors: Brown William T. , Chen Peter J.
Published: February 2003

We investigate the electric field produced in a ferroelectric ceramic disk polarized in the axial direction when it is subjected to uniform transient loading over one of its planar surfaces. It is shown that the structure of the electric field depends on the instantaneous piezoelectric response, the degradation of the piezoelectric response due to the time dependent effects of depoling, and the structure of the mechanical disturbance. For the situation when electric field-strain relaxation is much faster than stress-strain relaxation, the voltage obtained by integrating the calculated electric field is in excellent qualitative agreement with the observed behavior of PZT 65/35.
Photoluminescence investigation of the band around 1.41 eV in heated n-GaAs samples
Authors: Rao E. V. K. , Duhamel N.
Published: February 2003

This paper deals with the nature and origin of the ∼1.41-eV emission band observed in the photoluminescence (PL) spectra of n-GaAs samples subjected to diverse treatments. An investigation of the defect center responsible for this emission is carried by performing PL measurements on several samples (n substrates and n/n+ epilayers) subjected to two types of heat treatments (’’preepigrowth’’ and ’’open tube’’) at different temperatures and under varied conditions of surface protection. In light of the different experimental results we propose that the defect under consideration is a complex center formed by the association of arsenic vacancies and Si atoms (SiAs). Also, the existence of this defect in undoped epilayers grown on heavily silicon-doped substrates by the LPE technique, is tentatively explained as due to the contribution of the substrate during the epiprocess.
Secondary-electron-escape probabilities
Authors: Alig R. C. , Bloom S.
Published: February 2003

The probability B that a secondary electron internally excited in an insulator escapes upon reaching the surface is extracted from experiment and discussed theoretically for the first time. It is shown that B=2.5δmε/E0m, where ε is the electron-hole-pair creation energy and δm and E0m are the maximum secondary yield and the primary energy of maximum yield, respectively. It is also shown that ε=2.8Eg, where Eg is the insulator band gap. Values of B are extracted from secondary-electron-emission data for many semiconductors. A simple theory relating B to χ/Eg, the ratio of the electron affinity and the band gap is developed and shown to define an upper bound for the experimental data. The free-particle approximation adequately describes these hot- (energies ≳1 eV) electron phenomena.
Spontaneous explosions in multiatmosphere H2-F2-O2 mixtures
Authors: Truby Frank K.
Published: February 2003

Explosion studies in multiatmosphere H2-F2-O2 mixtures show that the pressures at which such mixtures spontaneously explode are greatly affected by treatment of the explosion cell surfaces prior to filling the cell with H2-F2-O2 mixtures. This strong effect of surface conditioning indicates that the observed explosions in H2-F2-O2 mixtures (covering a wide range in [F2]/[H2] ratios) with total pressures up to 10 atm result from surface-associated initiation processes rather than from purely volume-initiated third-limit processes. These results agree with a kinetic model involving H2O2 production with a chain formation of H2O at the surface.
A possible first step in carbon particle formation: C2+C3
Authors: Mann D. M.
Published: February 2003

A fast-flow system and high-temperature carbon-vapor source have been used to study carbon-vapor condensation. The molecular species C2 and C3 were monitored by resonance fluorescence. The species were determined to interact by the bimolecular gas-phase reaction C2+C3→C5 at a gas kinetic rate. This reaction was interpreted as an initial step in a series of coalescence reactions leading to carbon particulates. Electron micrographs of particulates collected from the system showed uniformly sized spheres of 35-nm diameter. Chaining of spheres into sootlike agglomerates was observed.
The effect of surface recombination on current in AlxGa1−xAs heterojunctions
Authors: Henry C. H. , Logan R. A. , Merritt F. R.
Published: February 2003

We show that the 2kT current in double-heterostructure AlxGa1−xAs p-n junctions is primarily due to surface recombination at the junction perimeter. The rate of surface recombination is evaluated by means of two luminescence experiments. Both experiments provide evidence that the rate of surface recombination increases with bias as exp(eV/2kT) and has the correct magnitude to account for the measured I-V curves. It is shown theoretically that recombination at a depleted surface is proportional to exp(eV/2kT) at high bias. The 2kT behavior is a consequence of the nearly constant ratio of electron and hole densities at the surface. The nearly constant ratio is needed to maintain equality of surface and surface depletion layer charge. p-n junction perimeters of cleaved, etched, and proton-bombarded interfaces are evaluated and found to have similar rates of nonradiative recombination with the rate of surface recombination given by R=s0(np)1/2, where s0 is approximately 4×105 cm/sec.
The effect of harmonics on the capillary instability of liquid jets
Authors: Cline H. E. , Anthony T. R.
Published: February 2003

The instability of a inviscid liquid jet was investigated in both the linear and nonlinear regime. Sound vibrations were used to break up the jet of water into a row of spheres. At small amplitudes, the growth of variations in the jet radius agreed with the calculations of Lord Rayleigh. The distribution of droplets was related to the Fourier coefficients of the periodic vibration. Harmonics and the fundamental component of the vibration grow at different rates which determine the shape of the unstable jet. The analysis of Lord Rayleigh was extended into the nonlinear regime to second order to predict the coupling between the fundamental mode and the second-harmonic mode.
Laser heating and ionization of magnetically confined plasmas in the presence of strong uv and x radiation
Authors: Hoffman A. L. , Crawford E. A.
Published: February 2003

A simple one-dimensional model has been developed to describe the propagation of laser radiation into an underdense magnetically confined moderate-Z plasma. A time-dependent Coronal atomic physics code is used to calculate ionization rates and radiative losses. Radiation losses during the ionization process dominate the energy balance and set an intensity-dependent threshold laser fluence for stripping ions such as neon down to a He-like configuration. Attainment of the He-like configuration is marked by a very large reduction in the soft radiation rate plus a sharp increase in the plasma temperature and laser absorption length. This is manifested by the onset of an exponentially increasing K-shell x-radiation rate which has been observed in a small laser-heated neon theta pinch.
Numerical study of some operating characteristics for argon induction plasmas
Authors: Ebihara Kenji
Published: February 2003

Some operating characteristics of argon induction plasmas at atmospheric pressure were obtained numerically by using magnetohydrodynamic equations. From these characteristics we can estimate the general dependency of plasma temperatures on operating conditions for induction plasmas. Calculated relationships between the sustaining electric field strength at the plasma surface and the electric power input show the existence of a minimum value of the field strength, the reason for which is revealed by detailed investigation of the calculated radial temperature distributions. Further, it was found that the minimum increases almost linearly with increasing frequency. In addition, characteristics of the Poynting vector and heat conduction loss at the plasma surface were obtained. Some characteristics obtained here give practical information on the electromagnetic field which is necessary to maintain the steady plasmas.
Ion-beam investigation of Sb diffusion and solubility in Fe
Authors: Myers S. M. , Rack H. J.
Published: February 2003

The diffusion coefficient and solid solubility of Sb in Fe have been measured over the temperature range 773⩽T⩽873 K by ion-beam methods. This has extended previous diffusion-rate data downward by five orders of magnitude. Diffusion couples formed by ion implanting Sb into Fe were vacuum annealed, with composition versus depth being determined by ion backscattering analysis. Precipitation within the implanted region was characterized by transmission electron microscopy. Theoretical analysis of the data is based on coupled differential equations for the concentration profile and the precipitate radii. The resulting solid solubility of Sb in Fe is given by C0= (22.7 at.%)  exp(−1905K/T) for 773⩽T⩽1273 K, where other data from higher temperatures have been included. The diffusion measurements may be described by D= (80 cm2/s)  exp(−32 460K/T) for 773⩽T⩽873 K. Implications of these results for intergranular embrittlement by grain-boundary segregation of Sb are discussed.
Effects of ion implantation on substrate hardening and film stress reduction and their effect on the yield of bipolar transistors
Authors: Hu S. M. , Schwenker R. O.
Published: February 2003

We report evidence of the occurrence, and some salient features, of two phenomena arising from ion implantation of silicon: one is a hardening effect of the silicon substrate; the other is a stress-reduction effect in silicon nitride films. The method of indentation dislocation rosettes (IDR) was the tool used for this study. The ion species investigated included boron, arsenic, argon, oxygen, and nitrogen, as well as oxygen from recoil implantation by arsenic into a film of thermal SiO2. Arsenic is the least effective among the ions studied, producing an ∼70% increase in the critical stress-of-dislocation movement (τc), whereas boron brought about an order-of-magnitude increase in τc. Other ions are comparable to boron. A plausible explanation is that the 1×1016 ions/cm2 boron implantation at room temperature was below the critical dose for silicon amorphization (∼2×1016 ions/cm2), so that rapid defect annealing via epitaxial regrowth could not occur, leaving much residual damage. The arsenic implantation of the same dose, however, was well above the critical dose for amorphization (∼2×1014 ions/cm2). In silicon nitride films of various thicknesses, reductions of stresses caused by implanting different ion species were studied with respect to the film-edge-induced stress in the silicon substrates. The results were quantitatively indexed regarding the enhanced movements of IDR near the film edges. Finally, the effects of ion implantation on the yield of bipolar devices are also reported, with the results partly explainable in the framework of the above two phenomena.
On the temperature distributions around dislocations in III-V compounds due to Joule heating
Authors: Booyens H. , Vermaak J. S. , Proto G. R.
Published: February 2003

The nonuniform rate of creation of Joule heat due to variations in the electrical conductivity around dislocations in III-V compounds gives rise to variations in the temperature around these dislocations. The general equations and boundary conditions for this temperature distribution are derived for any III-V compound. The specific temperature distributions around 60° and edge dislocations in n-type GaSb are calculated. It is found that the contribution of the dislocations to the temperature becomes significant within 500 Å from the core, while the gradient of temperature reaches significant values at even greater distances.
Specific volume measurements of Cu, Mo, Pd, and Ag and calibration of the ruby R1 fluorescence pressure gauge from 0.06 to 1 Mbar
Authors: Mao H. K. , Bell P. M. , Shaner J. W. , Steinberg D. J.
Published: February 2003

The wavelength shift with pressure of the ruby R1 fluorescence line (Δλ) has been calibrated in the diamond-window pressure cell from 0.06 to 1 Mbar. This was done by simultaneously making specific volume measurements of four metals (Cu, Mo, Ag, and Pd) and referring these results to isothermal equations of state derived from shock-wave experiments. The result is P (Mbar) = (19.04/5) {[(λ0+Δλ)/λ0]5−1}, where λ0 is the wavelength measured at 1 bar.
Current crouding and flux divergence in defected stripe
Authors: Chaug Yi-Shung , Huang Huei Li
Published: February 2003

A mathematical analysis of the variation of resistance and the electric line of force over a greion in a conducting strupe with a geometrical defect is carried out based on the Christoffel-Schwarz transformation. The overall resistance of the sripe with a bump-type defect may turn out to be less than that of homogeneous stripe of the same physical length despite the added resistance due to the current crowding. Possible implications of this effect are pointed out. The electromigration flux divergence at the edige of a void or a cracking is substantially greater than that at the edge of the bump-type defect. This is in line with the notion that stripe cracking or a faceted void in its embryonic stage first nucleated at the grain-boundary triple points.
One-carrier space-charge-limited currents in solids with two sets of traps distributed in energy: Two particular cases
Authors: Rizzo A. , De Blasi C. , Galassini S. , Micocci G. , Tepore A.
Published: February 2003

A study of steady-state one-carrier space-charge limited currents (SCLC) in solids containing two trap distributions is presented for two particular situations in which the presence of two sets of traps is difficult to detect and correctly analyze from the experimental J-V characteristics. Using the regional approximation method and a suitable distribution function for the trapping levels, theoretical current-voltage characteristics are derived for the case where the concentration of the lower trap distribution is equal or larger than that of the upper one and for the case in which the energy separation of the two sets of traps is too small to give rise to a current-voltage characteristic with a nearly vertical TFL (trapped-filled-limit) regime for each trap distribution. The obtained current-voltage theoretical curves are compared with those measured on some GaSe samples. The comparison shows very good agreement between theoretical and experimental results, confirming the correctness of the treatment.
Monte Carlo calculation of microwave and far-infrared hot-carrier mobility in N-Si: Efficiency of millimeter transit-time oscillators
Authors: Zimmermann J. , Leroy Y. , Constant E.
Published: February 2003

A Monte Carlo simulation is proposed and applied to study high-frequency behavior of hot carriers in semiconductors subjected to an arbitrary ac field superimposed on a strong dc field. With this end in view, the classical method was slightly modified into a mesh method: instead of testing the time spent between successive collisions, the scattering probabilities are tested after every time interval of suitable duration. This method checked by applying a static electric field allows us to obtain a few new results. Microwave and far-infrared room-temperature hot-carrier mobility for n-silicon is calculated and discussed. As an example of application, numerical results are used in the calculation of efficiency in millimeter transit-time oscillators which is shown to decrease in the millimeter range.
Stability of magnetic levitation
Authors: Holmes L. M.
Published: February 2003

The levitation forces on metal spheres in magnetic fields of axial symmetry are derived theoretically. Criteria for stability of the center of mass are obtained. It is shown for nonmagnetic samples that the desirable coil configurations are those which provide a constant field gradient along the symmetry axis. The formalism is applied to model coils of axial symmetry as an approximation to real spiral coils. An exact formula is derived for the axial component of the magnetic field on the axis of a spiral coil wound on the surface of a cone, and the transverse fields are evaluated approximately.
The determination of absolute Raman cross sections by indirect measurement of stimulated Raman gain
Authors: Devir Adam D.
Published: February 2003

A new technique for the determination of the Raman cross section by means of the enhancement of CARS signal is presented. This technique was tested on deuterium, and the result obtained is in good agreement with the literature value.
The application of reciprocity theory to scattering of acoustic waves by flaws
Authors: Kino G. S.
Published: February 2003

The reciprocity theorem and the scattering matrix formalism of electromagnetic theory have been adapted to obtain formulas for scattering of acoustic waves from flaws. The technique has been applied, in the Born approximation, to determine scattering of plane waves by small flaws, and with an elastostatic approximation to find the scattering from a flat elliptical crack. A third example is a treatment of the optical approximation to scattering from a curved interface between two media. In all cases results are obtained which are applicable for flaws placed either in the Fresnel region or Fraunöfer region of unfocused transducers, or near the focal point of a focused transducer. A fourth example, given in the Appendix, uses the reciprocity theory to derive the axial field of a piston transducer in contact with the surface of a solid.
Signal enhancement in photoacoustic spectroscopy on powder samples
Authors: Wong K. Y.
Published: February 2003

A simple and efficient way to enhance the photoacoustic signal from solid or powder samples is described. The increase in signal is found to be related mainly to the diffusivity and the ratio of specific heats of the gas which is used to couple the heat variation at the sample surface to the microphone detector. The measured signal enhancement on various powder samples agrees fairly well with the one-dimensional theory by Rosencwaig and Gersho. The effect of physical adsorption of gas by the sample is also examined.
Size considerations in the design of cells for photoacoustic spectroscopy. II. Pulsed excitation response
Authors: Aamodt L. C. , Murphy J. C.
Published: February 2003

The time-dependent response of photoacoustic cells to pulsed excitation is examined both theoretically and experimentally. The theoretical treatment includes both the response of conventional optical absorbers and absorbers containing metastable states. These results should be useful in dye laser applications of photoacoustic spectroscopy on both absorbing and luminescent materials. The experimental results were obtained using a newly developed device in which both electrical heating and optical heating have been shown to produce an equivalent acoustic response. This device should have applications in the design and calibration of cells for photoacoustic spectroscopy.
Dielectric behavior of strontium barium niobate (Sr0.5Ba0.5Nb2O6) crystals
Authors: Cline T. W. , Cross L. E. , Liu S. T.
Published: February 2003

The dielectric behavior along the ferroelectric c axis of melt-grown single crystals of Sr0.5Ba0.5Nb2O6 has been studied under weak fields in the thermally depoled, electrically depoled, and electrically poled single-domain condition. It is shown that the thermally depoled permittivity is high and strongly disperisve, with a marked ’’aging’’ which preferentially removes the slower relaxing components. The single-domain permittivity is much lower, very stable, and nondispersive up to piezoelectric resonance and with low tangent δ. The electrically depoled state is of even lower permittivity, and the difference from the single-domain value is satisfactorily accounted for by clamping of the piezoelectric response. Dielectric data suggest an unusually high density of 180° walls in the thermally depoled condition, and it has not been possible to delineate the domain walls by any of the conventional methods.
Iron-boron metallic glasses
Authors: Hasegawa R. , Ray Ranjan
Published: February 2003

By rapid quenching from the liquid, binary Fe100−xBx glasses are produced over the range 12–28 at.% B. Magnetization measurements in these glasses indicate a compositional dependence of the saturation magnetic moment μs which is consistent with the compositional dependence of the density of the material and reflects electron charge transfer from boron to iron. The extrapolated value of μs for noncrystalline Fe metal is found to be close to that for pure crystalline iron (μs=2.2μB); this is lower than the value of 2.4μB previously estimated for amorphous Fe. Based on x-ray and thermomagnetization data, it is argued that the local atomic arrangements resemble those of bcc iron for the Fe-rich alloys (x<16 at.%) and are similar to those of orthorhombic Fe3B in the vicinity of x=20. For x≳25, the local atomic structure seems like that of tetragonal Fe2B. These structural changes can explain the unexpected decrease of the Curie temperature with decreasing boron content. The decrease of the crystallization temperature with decreasing B content is similar to the compositional trend in the microhardness of the material.
Dielectric properties of shock-wave-compressed PMMA and an alumina-loaded epoxy
Authors: Lysne P. C.
Published: February 2003

One-dimensional shock-compression experiments were performed on specimens of polymethyl methacrylate (PMMA) and an alumina-loaded epoxy. The specimens were placed in an electric field before the introduction of the shock, and displacement currents resulting from shock-induced changes in the size and dielectric properties of the specimen were measured. The observed current histories are in good accord with a model based on a stress-dependent dielectric relaxation function. The relaxation effects in the alumina epoxy are much larger than those in the polymethyl methacrylate.