bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal and luminescence properties of constant-temperature liquid-phase-expitaxial In1−xGaxP (x [inverted lazy s]0.7) grown on (100) GaAs1−xPx (x [inverted lazy s]0.4)
Authors: Macksey H. M. , Lee M. H. , Holonyak N. , Hitchens W. R. , Dupuis R. D. , Campbell J. C.
Published: February 2004

The growth of In1−xGaxP (x [inverted lazy s]0.7) by liquid-phase epitaxy at constant temperature (CT-LPE) on [100]-oriented GaAs1−xPx (x [inverted lazy s]0.4) is described. Spontaneous and stimulated photoluminescence (77°K) of n- and p-type In1−xGaxP crystals is examined. For n-type crystals, laser modes appear only on the lower-energy side of the emission peak, whereas in p-type crystals, laser modes are observed also on the higher-energy side of the emission peak because of the high density of empty acceptor states ([inverted lazy s]5×1018/cm3) above the hole quasi-Fermi level. The decreased absorption near the laser wavelengths of p-type samples yields a value of [inverted lazy s]6.2 for the index expression (n-λdn/dλ) in contrast to a value of [sine wave]7.0 for n-type samples. p-n junctions fabricated by Zn diffusion into the In1−xGaxP epitaxial layers exhibit spectral behavior similar to the photoluminescence spectra of p-type crystals.
Study of excitation transfer in laser dye mixtures by direct measurement of fluorescence lifetime
Authors: Lin Chinlon , Dienes A.
Published: February 2004

By directly measuring the donor fluorescence lifetime as a function of acceptor concentration in the laser dye mixture rhodamine 6G-Cresyl violet, we found that the Stern-Volmer relation is obeyed, from which the rate of excitation transfer is determined. The experimental results indicate that the dominant mechanism responsible for the efficient excitation transfer is that of resonance transfer due to long-range dipole-dipole interaction.
Influence of nucleating surface on sputtered ZnO thin films
Authors: Hillman G. D. , Seguin H. J. J.
Published: February 2004

The strong influence of the nucleating surface on the 〈00.2〉 orientation of ZnO thin films is shown. High-quality longitudinal mode transducers are fabricated by utilizing an ``all'' sputtered technique using excess oxygen in the reactive gas mix. Electroacoustic coupling coefficients, near that of the bulk single crystal, are consistently achieved at practical deposition rates greater than 300 Å/min. Deposition details and operational parameters are specified.
Domain-wall energy in magnetic garnet bubble materials
Authors: Shumate P. W.
Published: February 2004

Analytical and numerical integrations are used to calculate the magnetic domain-wall energy in bubble materials which possess a mixture of cubic and induced uniaxial anisotropies. Limiting cases are considered which take into account the possibility that the magnetization vector may deviate out of the wall plane. It is found that when the magnitudes of the cubic and uniaxial anisotropy constants are equal, the wall energy calculated by ignoring the cubic contribution is too low by more than 5.5% but less than 13%. For epitaxial garnet bubble materials, the magnitude of the uniaxial anisotropy constant is typically several times larger than the cubic. For such materials the value of the wall energy is predicted to vary from that calculated for the purely uniaxial case by at most a few percent.
Mobility of bubbles with small numbers of Bloch lines
Authors: Malozemoff A. P.
Published: February 2004

The translational and radial mobilities of bubbles with small numbers of Bloch lines are investigated in a garnet film with moderately low damping. Depending on the number of Bloch lines, the bubbles propagate at different angles in an applied field gradient, in agreement with previous theory. However, the dependence of translational speed on Bloch line number, though weak, is an order of magnitude larger than predicted unless one attributes an additional coercivity or viscous damping to each Bloch line. Bubbles whose states have been identified by propagation in a gradient field are investigated by the dynamic bubble collapse technique; the ones which deflect at a particular nonzero angle show the largest dynamic collapse velocities. This experiment gives evidence that these bubbles, rather than those showing no deflection, are the ones without any Bloch lines. Such bubbles are investigated over a large range of radial drive fields; they show an initial high-mobility region culminating in a sharp peak, followed by a region of lower but appreciable mobility, followed by a velocity saturation. These features are compared to a theory by Slonczewski. In addition it is shown that the dynamic bubble collapse technique can be extended and its analysis simplified by working at very small threshold fields.
Bubble forces in cylindrical magnetic domain systems
Authors: Goldstein R. M. , Shoji M. , Copeland J. A.
Published: February 2004

The force exerted on a bubble by a current and by other bubbles is calculated. We examine the force on a bubble from straight current-carrying conductors of finite width and length and from conductors that are bent. We find that if the conductor's width is less than or equal to a bubble radius, the force on a bubble from a conductor pattern may be approximated by zero-width connected current-carrying segments. The mutal repulsive force between two bubbles is also determined. An important feature of this calculation is that the mutual decrease in bubble radii that occurs as two bubbles approach one another is taken into account. Bubble-bubble force curves as a function of material thickness are given for bubble spacings corresponding to typical current and field access circuits.
Distribution function of wall-pinning defects in perminvar
Authors: Baldwin John A. , Milstein Frederick , Vinh Nguyen Duc
Published: February 2004

Defects which impede the motion of magnetic domain walls may be described by a distribution function, n, in range z0. The range is the distance the mean position of a wall may move past a defect before it snaps free from the pinning action of the defect. The quantity n(z0) dz0 gives the number of defects per unit volume having a range between z0 and z0+dz0. The distribution function n(z0) for a sample of magnetically annealed perminvar has been completely determined. It is given by n(z0)=(N/z0)q(z0). The density parameter N=3.1×1014 m−3. The function q(z0) is given graphically. This function drops to e−1 of its initial value (unity) at the mean range Z=2.5 μm. The spring constant associated with wall deformation k=9.5×10−3 N/m. The average total number of defects with which a wall interacts at any one time is found to be N0=3×105. Equations are developed to evaluate Z, N, k, and N0 from measurements made on major and minor hysteresis loops. However, to evaluate the spring constant k and range parameter Z, it is necessary to know the total area of domain wall in the sample, or some other equivalent piece of information. The method may be employed to study the production and annealing of defects in magnetic materials which are sufficiently simple. It has the merit that the defects are sorted out by range rather than all being lumped into a single number, such as resistivity change.
Angular dependence of critical currents and transition fields of sputter-deposited superconducting films
Authors: Saito Yukinori , Anayama Takeshi
Published: February 2004

Anisotropies in critical currents and transition fields have been measured for sputter-deposited superconducting films. For thicker films, the peak at θ = 90° in the Ic-θ characteristics is strongly marked. As the film thickness decreases, the peak at θ = 90° tends to reduce, and finally disappears in the film thinner than the critical thickness. Furthermore, the transition fields Ht have been found to be anisotropic with respect to the applied field direction θ. The marked peak at θ = 90° in the Ht-θ characteristics is found for films thicker than the critical thickness.
Critical currents of superconducting conductors measured by a new technique
Authors: Mathur M. P. , Deis D. W. , Ashkin M.
Published: February 2004

A magnetic torque technique for measuring critical current densities is described. Results obtained on Nb–Cu and (Nb–Ti)–Cu composite conductors by this technique are presented and compared with direct transport current measurements.
Parametric excitation of plasma oscillations in Josephson Junctions
Authors: Pedersen N. F. , Samuelsen M. R. , Saermark K.
Published: February 2004

A theory is presented for parametric excitation of plasma oscillations in a Josephson junction biased in the zero voltage mode. A threshold curve for the onset of the parametric excitation is deduced via the stability properties of a Mathieu differential equation obtained by a self-consistent linearization procedure. The important parameters turn out to be the plasma frequency and the circuit losses. The results of the calculation are compared with the experiments performed on a Josephson junction analog and good agreement is obtained. It is suggested that the effect should be observable in tunnel junctions, but perhaps less likely in point contacts.
Epitaxial growth of 6H SiC in the temperature range 1320–1390°C
Authors: Powell J. Anthony , Will Herbert A.
Published: February 2004

High-quality epitaxial layers of 6H SiC have been grown on 6H SiC substrates with the growth direction perpendicular to the crystal c axis. The growth was by chemical vapor deposition from methyltrichlorosilane (CH3SiCl3) in hydrogen. Epitaxial layers up to 80 μm thick were grown at rates of 0.4 μm/min. Attempts at growth on the (0001) plane of 6H SiC substrates under similar conditions resulted in polycrystalline cubic SiC layers. Optical and x-ray diffraction techniques were used to characterize the grown layers.
Effect of temperature on a Bloch domain wall
Authors: Darby M. I. , Collins R.
Published: February 2004

The effects of temperature upon the properties of a one-dimensional Bloch wall are estimated by considering excitations of a wall in which the direction of the spins is allowed to rotate through more than π/2 between the domains. For finite temperatures it is found that the optimum wall width can be several times larger than the zero-temperature value.
Thermodynamic driving forces for shape changes and diffusion in nonhydrostatically stressed solids
Authors: Nolfi F. V.
Published: February 2004

The driving forces for shape changes and diffusion in nonhydrostatically stressed solids have been distinguished. The driving forces for shape changes are related to differences in the chemical potentials of the components of the solid that are defined at the surfaces, e.g., by their vapor pressures, whereas the driving forces for volume diffusion are gradients in the chemical potentials of the components within the solid. For homogeneously but nonhydrostatically stressed solids that are uniform in state throughout, the former potentials are multivalued and directly measurable (e.g., vapor-pressure measurements), whereas the latter potentials are unique functions of the state of the solid. In general, no meaningful connection exists between the two sets of potentials. However, for situations in which, for example, the shape of a solid is changing by volume diffusion, the variations in the two sets of potentials become continuously connected.
Particle emission from low-current break arcs at atmospheric pressure
Authors: McKnight L. G. , Sawina J. M. , Gray E. W.
Published: February 2004

The particle production from low-current (0.48-A short circuit) nominally resistive break arcs between palladium-gold contacts have been examined under ``clean'' and ``activated'' conditions. Particles produced in air and in dry nitrogen were measured using a condensation particle counter which detected particles of approximately 20-Å diameter and larger, with a sensitivity limit of 25 particles cm−3 of air corresponding to about 5000 total particles per break arc under our experimental conditions. The operation of the relay at 15 Hz produced large numbers of particles, the production of which was nonlinear with the repetition rate, and therefore the experiments were carried out at lower cycle rates (<5 Hz). Under these conditions it was observed that after an initial period of about 500 operations, short (<10 μsec) break arcs did not produce any detectable particles. Particles were detected for arcs of greater than 30-μsec duration with the number of particles increasing with the arc duration. Activation of relay contacts with consequent production of particles was found to take place in both filtered air and dry nitrogen showing that the activation process does not require the presence of oxygen or atmospheric particles.
Formation and guiding of high-velocity electrical streamers by laser-induced ionization
Authors: Koopman David W. , Saum K. A.
Published: February 2004

The electrical breakdown characteristics of long spark gaps have been modified by laser-induced ionization. The mean velocity of −500-kV streamers is increased by an order of magnitude, to [inverted lazy s]3×108 cm/sec, and discharge columns are guided over a straight path in air and other atmospheres, by a 1.06 μ optical beam focused to [inverted lazy s]10 11 W/cm2. Time-resolved studies of the experimental phenomena, together with theoretical models for the evolution of laser-induced ionization, indicate that a continuous low-level ionization, rather than the occasional optical breakdown beads along the beam path, is responsible for the observed effects. Analysis of the discharge data and direct measurement of the ionization generated by laser radiation focused to subbreakdown intensities both confirm that positive and negative ion pair densities in the range 1010−1011/cm3 are responsible for directing and increasing the streamer velocities; photodetachment of electrons by the luminous streamer tip enhances the streamer propagation. Our model can also be used to interpret previously reported optical influence on electrical breakdown.
Field-assisted trapping in polyethylene
Authors: Sawa Goro , Kawade Masayuki , Ieda Masayuki
Published: February 2004

Thermally stimulated current (TSC) was obtained under a small bias voltage from low-density polyethylene which had been subjected to a high electric field. Two peaks were found at 50 and 85°C with apparent activation energies of 1.2–1.3 eV and 1.4–1.5 eV, respectively. These peaks were attributable to the drift of thermally released carriers under the external bias field. On comparison of the activation energies obtained from the TSC and the isothermal steady-state conduction currents, the results were explained successfully with a field-assisted trapping model where a trap is surrounded by a Coulomb repulsive barrier for electron capture.
Temperature, stress, and annealing effects on the luminescence from electron-irradiated silicon
Authors: Jones Colin E. , Johnson Eric S. , Compton W. Dale , Noonan J. R. , Streetman B. G.
Published: February 2004

Low-temperature photoluminescence spectra are presented for Si crystals which have been irradiated with high-energy electrons. Studies of isochronal annealing, stress effects, and the temperature dependences of the luminescence are used to discuss the nature of the luminescent transitions and the properties of defects. Two dominant bands present after room-temperature anneal of irradiated material are discussed, and correlations of the properties of these bands are made with known Si defects. A band between 0.8 and 1.0 eV has properties which are related to those of the divacancy, and a band between 0.6 and 0.8 eV has properties related to those of the Si-G 15 (K) center. Additional peaks appear in the luminescence after high-temperature anneal; the influence of impurities and the effects of annealing on these lines are discussed.
Influence of pressure and temperature on switching in vanadium pentoxide
Authors: Vezzoli G. C. , Napier Austin
Published: February 2004

The initial switch in polycrystalline V2O5 specimens (300–400 μ thick) at room temperature is associated with melting caused by power-induced Joule heating and also with a color change from yellow-orange to black. The resulting black material exhibits threshold switching. High-pressure studies show a pressure dependence on threshold power for V2O5, and on threshold field for an amorphous chalcogenide. Low-temperature studies indicate an increase in turnover power with decreasing temperature for V2O5. High-temperature studies show that V2O5 melts with decreasing resistivity at about 690°C.
Performance model for end-pumped miniature Nd:YAlG lasers
Authors: Chesler R. B. , Singh S.
Published: February 2004

A rate equation formulation describing the performance of end-pumped miniature Nd:YAlG lasers is presented. Expressions for the threshold pump power and laser power output above threshold are given. A numerical example is given and a comparison is made to a previously reported measured threshold power.
Test for Ohmic conductivity at turnover in an amorphous chalcogenide sandwich structure
Authors: Thornburg D. D. , Johnson R. I.
Published: February 2004

A simple test is developed to establish the existence of an Ohmic thermally activated conductivity in a chalcogenide glass which is carrying uniform current densities sufficient to cause current-controlled negative differential resistance. The technique involves proper plotting of the turnover voltage data, taken as a function of ambient temperature, according to a theoretical relation obtained for a Joule-heated thin-film sandwich structure. This technique is of particular value in the event that insufficient information is available for a detailed analysis of the current-voltage curve. Experimental data from a thin-film a-As2SeTe2 device are plotted according to this relation and evidence is presented that the chosen conductivity function does not obtain for this glass at high current densities, even though this behavior is observed at low current densities.
Long-pulse breakdown with 10.6-μm laser radiation
Authors: Lowder J. E. , Kleiman H.
Published: February 2004

We have investigated material initiated air breakdown using a long 10.6-μm pulse (tens of microseconds) and attributed the breakdown initiation to a thermal mechanism. In particular, breakdown initiated on glass fibers after irradiation times up to 35 μsec with power densities of 106−107 W/cm2 is reported. Measured parameters included breakdown threshold, time to breakdown, plasma expansion dynamics, and transmission of 10.6-μm radiation through the plasma.
Spatial distribution of ionization in electron-beam-controlled discharge lasers
Authors: Boyer K. , Henderson D. B. , Morse R. L.
Published: February 2004

We explore the uniformity of energy deposition from the primary (ionizing) beam from the electron-beam-controlled discharge laser, especially considering the magnetic deflections and the scattering collisions. We find the addition of a parallel guide magnetic field to be useful.
Electron transport in gas discharge lasers
Authors: Henderson Dale B.
Published: February 2004

We have developed a set of computer codes to treat the transport of the high-energy (primary) electrons in gas discharge lasers of the Los Alamos type. Such electron transport requires no new physical ideas, but must be applied without any of the common restrictions. In contrast to existing theory, we may not specialize to total turning without energy loss; we may not specialize to energy loss without turning or tortuous paths; we are interested in observations other than just those made far from the interaction region; and we must include applied electric and magnetic fields. Our codes meet these requirements and still permit the computation of cases of interesting complexity with the investment of a modest amount of machine time. Several examples are reported as verification of the computation and as its application to laser design.
Scattering of a TM surface wave at a guide deformation
Authors: Tuan Hang-Sheng , Ou Chaur-Hwa
Published: February 2004

Properties of the reflection and mode conversion of the fundamental TM surface wave at a guiding structure deformation are investigated in this paper with the boundary perturbation technique. In order to obtain each order of the scattered fields, it is found that a separate boundary value problem has to be solved. A brief outline of the formulation is given. Numerical results from an example are presented in graphs to show the effect of the geometric shape of the deformation.
Magnetic instability in hard superconductors
Authors: Koyama K.
Published: February 2004

By considering the electric field induced by flux motion, the requirement for stabilization of a hard superconductor against flux jumps has been found to be Jc2 < k 2CsT0[1+(Dt/Dm)]μ0−1, where Cs is the heat capacity per unit volume of the superconductor, T0 is given by - Jc(∂Jc/∂T)−1, Dt and Dm are the thermal and magnetic diffusivities of the superconductor, respectively, and k2 is the smallest number satisfying the following time-independent temperature equation: Δ2 (ΔT′) = −k2ΔT′. Using the above criterion, we derive the stability requirements in both adiabatic and dynamic stability limits. Then we discuss the stability of commercial superconductors covered by normal metal. The stability criteria can be obtained by replacing Dm in the inequality with the average magnetic diffusivity of the normal metal and superconductor.
Effect of flux line lattice history on the critical current in niobium
Authors: Steingart Marvin , Putz Antide G. , Kramer Edward J.
Published: February 2004

The critical current Ic in a plastically deformed Nb single crystal is shown to vary with the method of formation of the flux line lattice (FLL). The largest critical currents are observed when the FLL is formed by cooling the sample from above Tc(H). Passing a current through the sample during the cooling process, in the same direction as it is subsequently swept, increases Ic by up to 60%. By slowly cycling the current at zero voltage, decreases in Ic can be induced with the V-I characteristic asymptotically approaching the characteristic after flux flow. The size of the decrease is found to depend on the number of cycles, and especially for negative current excursions, on the amplitude of these excursions. It is proposed that optimum pinning of the FLL to the underlying pin structure occurs, for thermodynamic reasons, at the moment the FLL is formed. Subsequent changes in the local value of the FLL parameter, either due to changes in magnetic induction or changes in FLL defect structure, lead to decreases in the number of effective pins, and thus to decreases in the critical current.
Perturbation theory for a resistivity shunted Josephson element
Authors: Thompson E. D.
Published: February 2004

We present a systematic perturbation theory, extendable in principle to all orders of magnitude, for the solution of the equations of motion of an ideal Josephson element shunted by a resistance and driven by a dc current source and a small time-dependent source. We present second-order results for the case in which the time dependence is that of a single sinusoid, and these results are compared with other numerical and analytical calculations. Near, but not on, the first constant voltage step where the perturbation theory appears divergent, the current-voltage characteristic is calculated by means of a nonperturbative adiabatic procedure. The impedance and responsivity agree with earlier results.
The effect of an energy-dependent capture cross section on data interpretation using the MOS conductance technique
Authors: Cooper J. A. , Schwartz R. J.
Published: February 2004

In studies of surface states at the SiO2–Si interface, an exponential variation of the electron capture cross section with band-gap energy has recently been observed. In these bias regions, the dispersion parameter σus was also observed to tend toward zero. In this paper, it is shown that the σus values inferred from the data reduction may be spurious results, influenced strongly by the energy dependence of the electron capture cross section.
Submicron thickness calibration of vapor-deposited SiO2 films by infrared spectroscopy
Authors: Wong J.
Published: February 2004

Infrared transmission spectra of a series of SiO2 films vapor deposited on silicon from SiH4 and O2 at 450 °C have been studied as a function of film thickness in the submicron range from 1000 to 9000 Å. Absorbances of band maxima observed in the frequency range 250–1400 cm−1 are shown to obey the Lambert-Bouguer's law in both as-deposited and heat-treated (800–1200 °C) materials. Apparent absorption coefficients calculated for the transmission mimima at 1060, 800, and 450 cm−1 are 2.5 ± 0.1 × 104, 0.24 ± 0.02 × 104, and 0.74 ± 0.02 × 104 cm−1 for as-deposited films and 3.4 ± 0.1 × 104, 0.34 ± 0.02 × 104, and 1.06 ± 0.02 × 104 cm−1 for heat-treated films, respectively. The thickness of SiO2 films as-deposited at 450 °C as well as heat treated to 800 °C and above can be determined nondestructively using the present absorbance data.
Effect of an organic gas additive on a pulse HF chemical laser
Authors: Paulson R. F.
Published: February 2004

The use of a small amount of xylene as a gas additive to a SF6 : H2 mixture in an electrically initiated pulse HF chemical laser has been shown to increase laser peak power output. For the experimental conditions of this work, enhancement of output power was seen only for laser medium pressures greater than 200 Torr. A maximum increase in peak power of 60% was observed for a pressure of 300 Torr.
Photoluminescence determinations of Cd diffusion in ZnSe
Authors: Martin W. E.
Published: February 2004

The diffusion constant D(T) of cadmium into single-crystal zinc selenide was measured using a photoluminescence/etch technique. Diffusions were performed in sealed ampoules using cadmium metal and cadmium selenide powder as dopant sources. For cadmium metal sources D(T) = 6.39 × 10−4 exp(− 1.87 eV/k T) in the range 700–950 °C.
Cavity excitation of coherent hypersound
Authors: Soumpasis D.
Published: February 2004

In this paper, we analyze the generation of hypersonic waves via piezoelectric surface excitation in cavity resonators and derive formulas enabling one to calculate the electromechanical conversion factor and the electric field direction for optimal excitation of any pure acoustic mode, provided the relevant material constants and cavity parameters are known. Quantitative results are given for certain acoustic modes in quartz, CdS, and LiNbO3 crystals.
Dynamic yield, compressional, and elastic parameters for several lightweight intermetallic compounds
Authors: Gust W. H. , Holt A. C. , Royce E. B.
Published: February 2004

Dynamic yield strengths, compression data under uniaxial shock-wave loading, and sonic velocities at 1 bar are reported for polycrystalline TiB2, SiC, Be4B, Be4B+8 wt% BeO, Be2B, AlB12, TiBe12, and ZrBe13. Hugoniot elastic limits were measured as 86, 80, 74, 77, 65, 87, 53, and 71 kbar, respectively. Evidence of phase transitions was seen for the Be4B materials at 500 kbar and for SiC at 240 and 960 kbar.
Elastic and thermoelastic properties of lead, barium, and strontium nitrates
Authors: Michard F. , Plicque F. , Zarembowitch A.
Published: February 2004

Variation in the elastic constants of lead, barium, and strontium nitrates in the range 4–300 K has been investigated with great accuracy using resonance and pulse-echo ultrasonic methods. The thermoelastic behavior of the three nitrates are compared. Strontium nitrate and lead nitrate especially appear to be much more anharmonic than barium nitrate.
Dielectric breakdown of shock-loaded PZT 65/35
Authors: Lysne P. C.
Published: February 2004

The dependence of dielectric breakdown in shock-loaded ferroelectric ceramics on both the shock amplitude and the electric field strength was investigated by employing shock reverberation techniques. In these experiments thick projectile disks were impacted on relatively thin specimens of hot-pressed PZT 65/35 [Pb0.99Nb0.02(Zr0.65Ti0.35)0.98 O3] poled to 10, 20, and 30 μC/cm2. The principal results of this investigation are: (i) dielectric breakdown is not explicitly a function of stress for stress values in the region of this study (<23 kbar), (ii) breakdown is not instantaneous, (iii) for fields greater than the breakdown threshold (≈5 kV/mm) the time between introduction of the shock into the ferroelectric and onset of breakdown decreases rapidly with increasing electric field, (iv) electric fields generated by 10-kbar shocks in specimens poled to 30 μC/cm2 are sufficient to cause breakdown, and (v) axial release waves can travel at a velocity as much as 15% faster than the initial stress wave.
Ion channeling studies of the crystalline perfection of epitaxial layers
Authors: Picraux S. T.
Published: February 2004

Ion channeling and backscattering of 450- to 1340-keV protons were used to study the crystalline perfection of heteroepitaxial Si layers of thicknesses between 1 and 3 μm. An approximate calculation of the dechanneling background was used to obtain the depth profiles of crystalline imperfections in the epitaxial layers. Both the plural scattering theories of Meyer and Keil et al. were used in the calculation and are shown to give similar profiles. Channeling measurements as a function of sample temperature, beam energy, and layer removal were used to check the self-consistency of the analysis. Analysis of these measurements for a given sample gave the same depth profile (±20%) confirming the validity of the technique. The technique provides a convenient evaluation of epitaxial layers containing large numbers of crystalline imperfections.
Correlation of ion channeling and electron microscopy results in the evaluation of heteroepitaxial silicon
Authors: Picraux S. T. , Thomas G. J.
Published: February 2004

The crystalline quality of heteroepitaxial (100) and (111) Si layers on spinel or sapphire substrates has been investigated using ion channeling and electron microscopy. Ion channeling and backscattering give the depth profile of the density of imperfections, and electron microscopy is used to determine the nature of the imperfections as well as give an additional determination of their density. Transmission electron microscopy indicates that stacking faults and microtwins are the dominant types of imperfections in the layers, and these defects are interpreted to be the primary source of scattering centers for the channeled ions. Both channeling and scanning electron microscopy measurements indicate that the density of imperfections decreases with increasing distance from the interface. At equal distances from the interface a lower density of imperfections was observed in the Si layer for (111) Si/spinel and (100) Si/sapphire as compared to (100) Si/spinel. Large differences in the rate of decrease of the density of imperfections were observed for (100) Si/sapphire from different suppliers. The interpretation of the influence of the fault planes on channeling has been achieved by modeling the scattering by these defects. Semiquantitative correlations of scattering center densities from electron microscopy and channeling measurements indicate higher absolute densities for the channeling results, while relative densities determined at various depths by these two techniques are in agreement.
Glide systems and Peierls stresses in fcc and bcc metals from phonon energies
Authors: Boffi S. , Caglioti G. , Rizzi G. , Rossitto F.
Published: February 2004

As an approach to correlate atomistic and mechanical properties of metallic materials, work has recently been performed in order to understand the surface energy for brittle fracture in terms also of frequencies of the normal modes of vibration of the metal itself. In the same frame, the interpretation of the glide systems in fcc and bcc metals has been attempted and is presented here. The one-dimensional model developed by Frenkel and Kontorova for an edge dislocation is reformulated in order to take advantage of the knowledge of interplanar force constants experimentally accessible by neutron inelastic scattering. The numerical solution is given following the procedure proposed by Hobart. Peierls energies and critical shear stresses have been thus evaluated on an atomistic level for some glide systems in fcc (Al, Cu, Ni) and bcc (Fe, W, Ta, Nb) metals.
Piezoelectric waves on layered substrates
Authors: Solie L. P.
Published: February 2004

A set of computer programs has been developed for calculating the velocity of acoustic surface waves on a substrate with or without a film overlay where both the film and the substrate may be arbitrarily anisotropic and piezoelectric. Several examples of practical significance are presented. These include (i) propagation around the curved surface of a wrap-around delay line, (ii) power flow angles for Rayleigh waves on LiNbO3 and Bi12GeO20 substrates, (iii) enhancement in the performance of an interdigital transducer due to the deposition of a film overlay (values of Δν/ν as large as 5.45% have been calculated), (iv) Δν/ν curves for piezoelectric films on nonpiezoelectric substrates.
Propagation of backward surface wave along an annular plasma guide with azimuthal electron density variation
Authors: Nonaka Shigehiko , Akao Yasuo
Published: February 2004

The effect of azimuthal variation of electron density on the surface-wave propagation along the inner surface of an annular plasma column is described experimentally and analytically. Such inhomogeneity of electron density is induced by the earth's magnetic field, which is not parallel to the direction of electron drift along the column axis. In this case the azimuthal distribution of electric field intensity of the surface wave is distorted, and the dipole mode, which is normally degenerate, splits into two modes with different wave numbers. The field distortion becomes more intense as the inhomogeneity increases and the wavelength decreases. The theoretical analysis shows that the distortion results from the coupling between normal modes by the effect of the inhomogeneity. Experiments are carried out by using a mercury-vapor-discharge tube with hot cathode, and the results agree well with the calculations.
Combinations of third-order elastic constants of zinc and cadmium
Authors: Powell B. E. , Skove M. J.
Published: February 2004

Deviations from Hooke's law are caused by the third-order elastic constants. These deviations have been measured for one orientation of cadmium and two orientations of zinc filamentary crystals (whiskers). Expressions for these deviations have been derived and used to calculate values of the linear combinations of third-order moduli. The experimental values of the deviations for zinc are compared with values calculated from published third-order constants.
Three-layer thermal-diffusivity problem applied to measurements on mercury
Authors: Ang C. S. , Tan H. S. , Chan S. L.
Published: February 2004

To adapt and apply the heat-pulse technique for thermal-diffusivity measurements to liquids, the one-dimensional three-layer heat conduction problem has been solved analytically with an adiabatic boundary condition on the front surface and both adiabatic and isothermal boundary conditions on the rear surface. Computed solutions of the three-, two-, and one-layer problems are compared to determine the relative effects of the front layer (window) and the rear layer (cell material) on the temperature pulse shape transmitted through the liquid layer. Measurements at several temperatures from 294 to 267°K on a mercury specimen are analyzed using these results and the deduced diffusivity values are compared with those given by the Thermophysical Properties Research Center.
Pressure dependence of the thermal conductivity of an epoxy resin
Authors: Andersson P. , Bäckström G.
Published: February 2004

The pressure dependence of the thermal conductivity of Araldite has been determined in a cylindrical geometry at 300 K. The pressure coefficient was found to be independent of the percentage of hardener, the conductivity at 25 kbar being higher by the factor 1.75±0.05 than at atmospheric pressure.
Electron mobility in heavily doped gallium arsenide
Authors: Stevens E. H. , Yee S. S.
Published: February 2004

The effects of electron-electron scattering and nonparabolic energy band shape on electron mobility in degenerate materials are investigated. Mobility calculations as a function of electron concentration and temperature are compared to experimental data. Electron-electron scattering is found to only slightly reduce electron mobility. The nonparabolic band shape is found to significantly reduce the magnitude and alter the temperature dependence of electron mobility.
Pressure-induced optical distortion in laser windows
Authors: Sparks M. , Cottis M.
Published: February 2004

Theoretical studies are made of the effects of pressure on candidate materials for use as windows in high-power infrared laser systems. When the window in a laser system is subjected to a uniform static pressure, the resulting deformation can distort the laser beam or fracture the window. Two aspects of this problem are considered: pressure-induced optical distortion and the effect of including pressure in previously calculated figures of merit for thermally-induced optical distortion. An expression for the window thickness required to prevent pressure-induced optical distortion from halving the target intensity is derived, and values are tabulated for various materials. Comparing these values with the minimum thickness required to prevent material fracture indicates that the thickness of large-diameter windows of strong materials is determined by the pressure-induced optical distortion, whereas the thickness of small-diameter windows of strong materials is determined by the pressure-induced fracture. The optical distortion resulting from the static deformation of a window under its own weight is negligible with respect to that from a pressure of 7.3 psi under usual operating conditions. An expression obtained for the strength of a material at which the fracture and pressure-induced optical-distortion effects are equally important should be useful in material-strengthening programs. In previous figures of merit, various materials were compared on the basis of a common fixed value of the window thickness. In many applications, where the window diameter and the pressure have specified values, new figures of merit are required in order to account for the greater thickness required for weaker materials. The new figures of merit, which are simply the values of intensity the window can transmit under specified conditions, change the preference of materials in a number of cases.
Transient photodepopulation measurements of electron trap distributions in thin SiO2 films on silicon
Authors: Thomas J. H.
Published: February 2004

Transient photocurrents associated with optical depopulation of electron trapping centers have been studied as a function of photon energy in thin amorphous silical films grown on silicon wafers. A summary is given of the application of this technique to determine inhomogeneous trap state distributions in silica films. Electron trapping distributions observed at 1.9 eV and 2.5 eV below the conduction band edge of the silica and having densities of 1014/cm3 are reported. Measurements at liquid-nitrogen temperature indicate the presence of shallow trapping states of similar concentration levels in addition to the deep trap distributions.
Minority carrier diffusion length and recombination lifetime in GaAs:Ge prepared by liquid-phase epitaxy
Authors: Ettenberg M. , Kressel H. , Gilbert S. L.
Published: February 2004

The electron diffusion length in p-type GaAs:Ge grown by liquid-phase epitaxy has been measured as a function of hole concentration. The direct measurements were made by two different techniques —a laser beam scan on beveled samples and an α particle scan on cleaved samples. These measurements are in good agreement and show that the diffusion length increases from ∼6 μm at p=1×1019 cm−3 to ∼20 μm at p=7×1016 cm−3. In addition, the diffusion length was estimated from electroluminescent decay times of p-n junctions and the values obtained were in reasonable agreement with those directly measured for the same materials.
Magnetic properties of RT3−x′Nix compounds (R=Dy or Ho and T′=Fe or Co)
Authors: Narasimhan K. S. V. L. , Butera R. A. , Craig R. S.
Published: February 2004

The effect of varying electron concentration on the magnetic ordering in the ternary intermetallic compounds DyCo3−xNix, DyFe3−xNix, HoCo3−xNix, HoFe3−xNix, with 0<x<3, has been investigated by saturation magnetization studies. The results show a filling of the Co and Fe bands and also a polarization of the 3d band of nickel. In the case of the Co compounds an additional contribution from the induced moment on cobalt by the rare-earth exchange field is found to be important.
The Grüneisen parameters of some group-V and group-VI elements
Authors: Sirdeshmukh D. B. , Rao B. Kameswara
Published: February 2004

The Grüneisen parameters of some group-V and group-VI elements have been calculated from recent data on thermal expansion and compressibility and, theoretically, from the Morse function using a modification of Slater's method. These values agree mutually and with those estimated from the pressure variation of compressibility but differ severely from those estimated from logθ-logV plots.
High-field superconducting current-carrying capacities of composite-processed V3Ga tapes
Authors: Tachikawa K. , Tanaka Y. , Iwasa Y.
Published: February 2004

Superconducting V3Ga tapes were produced by fabricating a composite of Cu–Ga alloy and a vanadium core and subsequent heat treatment at 625–-800°C. The critical current of these composite-processed (CP) V3Ga tapes was measured at 4.2 K in magnetic fields up to 210 kOe. In CP-V3Ga tapes, the pronounced ``peak effect'' appears at fields near 170 kOe where a critical-current density Jc of 1×105 A/cm2 is obtained. At the ``peak field'', Jc is nearly independent of the thickness d of the V3Ga layer. On the other hand, at low fields Jc decreases markedly with increasing thickness. When the Cu–Ga alloy matrix is supplemented by a small amount of manganese, the peak effect disappears consequently improving Jc at lower fields.
Scattering of charge carriers in silicon surface layers
Authors: Cheng Y. C. , Sullivan E. A.
Published: February 2004

The mobility of free carriers in a surface layer of a silicon metal-oxide-semiconductor transistor has been computed theoretically. It represents the first realistic approach which attempts to combine Coulomb, phonon, and surface-roughness scattering to account for the mobility behavior over different temperatures and applied fields. An over-all semiquantitative agreement between theory and experiment is obtained for both the channel mobility and magnetoresistance effect.
High electric fields in silicon dioxide produced by corona charging
Authors: Williams R. , Woods M. H.
Published: February 2004

We have applied high electric fields to films of SiO2 thermally grown on silicon. The films were not metallized and high fields were obtained by depositing charge directly onto the surface from a corona discharge in air. After terminating the discharge the surface potential was measured, using a vibrating capacitor plate mounted near the free surface. Both the surface potential and the current through the oxide decrease with time, rapidly at first and then more slowly. When the current level has dropped to 10−9 A/cm2 the surface potential is changing by only a few percent per minute and the field across the oxide has nearly a steady value, Es. We measure Es and compare it with the dielectric breakdown fields that have been reported by others. We distinguish between the operational quantity Es and the breakdown field as usually reported since there appears to be no destruction of the sample in our experiments. We find that Es is independent of the conductivity type and the doping level of the silicon, even when it is degenerate. When the free surface is charged negatively, Es is about twice as large as it is for positive charging.
Influence of high concentrations of solute atoms on the critical flow stress of binary alloys. I. Theoretical foundations
Authors: Boser O.
Published: February 2004

A theory of the flow stress of metal crystals with high concentrations of solute atoms is developed with the help of the theory of stationary random functions. The dislocation model used to calculate the critical flow stress is a Frank-Read source. Under the assumption that at high concentrations of solute atoms the dislocation will interact principally with groups of atoms spread out along the dislocation line rather than with single atoms, no thermal activation can take place. This results in a temperature-independent critical flow stress, which is indeed observed in solid-solution crystals as the so-called plateau stress. The theory requires that the plateau stress increase with solute concentration proportional to [C(1−C)]1/2 and, at fixed concentrations, be proportional to the magnitude of the interaction between solute atoms and dislocation.
dc triode sputtered zinc oxide surface elastic wave transducers
Authors: Hickernell F. S.
Published: February 2004

A piezoelectric film layer in proximity to an interdigital metal electrode provides a simple means for the excitation and detection of surface elastic waves on nonpiezoelectric substrates. These film transducer structures can be effectively used for the study of the surface elastic wave properties of solids and the development of monolithic acoustic and electronic circuit assemblies. Theory predicts that high coupling efficiencies can be obtained using piezoelectric film transducer structures. The properties of dc triode sputtered zinc oxide film transducers on fused quartz and oxidized silicon have been investigated at frequencies near 16 and above 200 MHz. Quantitative data on coupling factor, capacitance, and phase velocity have been obtained on plated and unplated structures for film-thickness-to-acoustic-wavelength ratios from 0.01 to 1.0. The experimental data follow the functional dependencies predicted by theory but differ in certain quantitative aspects. The maximum coupling constants (k2) measured on fused quartz were 0.0043 for low-frequency plated transducers and 0.024 for unplated transducers above 200 MHz. Acoustic propagation losses as low as 1.5 dB/μsec at 215 MHz and 8.0 dB/μsec at 630 MHz were measured. One-microsecond delay lines were fabricated at 213 MHz using zinc oxide on fused quartz which had a total of 12 dB and a 9-MHz 3-dB bandwidth. The measurements show that the surface-wave electroacoustic properties of dc triode sputtered zinc oxide films approach those of single-crystal ZnO layers.