bluuebunny/crossref_metadata_2025 huggingface dataset:
Thickness dependence of the dielectric constant and resistance of Al2O3 films
Authors: Birey Hülya
Published: February 2003

Thickness dependence of the dielectric constant and dielectric resistance of aluminum oxide films in the thickness region from ∼30 to 1000 Å is studied at 1 kHz. The dielectric constant is measured at 1 kHz at room temperature, and its bulklike value is found to be nearly 9. The dielectric constant begins to decrease from the bulk value due to the structural discontinuity as the sample thickness is decreased (<200 Å). A peculiar effect is observed for ultrathin films (<60 Å); the higher dielectric constant corresponds to the smaller film thickness. Aging of the samples agrees with capacitance proportional to (time)−n relation. Thickness measurements of the aged films confirm that the change in capacitance is due to a change in film thickness rather than a change in the dielectric constant. The dielectric resistance shows an exponential dependence on thickness for ultrathin film (<50 Å). Such thickness dependence of the resistance measured at low frequency indicates that the tunneling is the dominant current flow mechanism for very thin specimens.
Oxygen partial-pressure dependence of the oxidation-induced surface stacking faults in (100) n silicon
Authors: Murarka S. P.
Published: February 2003

The effect of varying oxidation rates on the growth of the oxidation-induced stacking faults (OISF) in (100) silicon has been investigated. Oxidation rates were varied by changing partial pressures of dry oxygen in the oxidizing ambient of oxygen-nitrogen mixtures. For the first time, it has been shown that in addition to the conventionally observed dependence on time and temperature [i.e., L∝tn exp(−Q/kT)], the length L of the OISF also depends on the partial pressure of oxygen and is given by L∝pmO2. Thus, the length of the OISF is given by L= (const) pmO2tn exp(−Q/kT), where m and n are number exponents. m was found to increase very slightly (from 0.28 at 1050 °C to 0.35 at 1150 °C) with temperature. n decrease very slightly with temperature and was 0.89 at 1050 °C and 0.76 at 1150 °C. At 1119 °C, n was found to increase from 0.78 to 0.84 by changing the oxygen content in the oxidizing ambient from 100 to 10%. The activation energy Q was found to be 2.30±0.05 eV in the temperature range 1050–1150 °C and was independent of variations in the oxygen partial pressures from 10 to 100%. The results have been discussed, and a mechanism incorporating excess of unoxidized silicon at the Si-SiO2 interface and vacancy mechanism of diffusion has been suggested to explain the experimental results.
Superconductive bolometers for submillimeter wavelengths
Authors: Clarke J. , Hoffer G. I. , Richards P. L. , Yeh N. -H.
Published: February 2003

Three types of composite superconductive bolometers are described in which the temperature-sensitive element is a superconducting film at the transition temperature, a superconductor–normal metal–superconductor Josephson junction, or a superconductor–insulator–normal metal quasiparticle tunneling junction. The temperature-sensitive element is evaporated onto a sapphire substrate on the reverse side of which is a bismuth film to absorb the submillimeter radiation. The noise limitations of each type of bolometer are calculated. The fabrication and measured performance of the transition-edge bolometer and the Josephson-junction bolometer are described. The best electrical (noise-equivalent power) NEP obtained with a transition-edge bolometer fabricated on a 4×4×0.005-mm sapphire substrate is (1.7±0.1) ×10−15 W Hz−1/2 at 2 Hz at an operating temperature of 1.27 K. This NEP is within a factor of 2 of the thermal noise limit. The effective absorptivity of the bismuth film is measured to be 0.47±0.05, and the corresponding detectivity D* is calculated to be (1.1±0.1) ×1014 cm W−1 Hz1/2. Suggestions are made for further improvements in sensitivity.
Transient-waveguide effects and lasing time delays in electron-beam-pumped semiconductor lasers
Authors: Garside B. K. , Gouin F. , Shewchun J.
Published: February 2003

The dynamics of electron-beam-pumped semiconductor lasers are strongly affected by transient waveguiding. We have investigated the impact of such effects on the time delay from the start of the pumping pulse to the onset of laser emission in GaAs at liquid-nitrogen temperatures. Time delays were measured as a function of pump current density for three values of the electron-beam energy (20, 30, and 40 keV). Delays up to 200 nsec were observed which are approximately two orders of magnitude larger than the minority-carrier lifetime. A theoretical model is presented for the time-dependent variations of the optical confinement to account for such long delays. The time delay to threshold is determined not by the gain buildup but by the time required to sufficiently decrease the laser-mode diffraction loss in the active layer. Initially, the presence of gain results in a negative change of the refractive index with respect to the passive material. This is opposed by a growing positive index contribution due to the rise in temperature of the pumped layer. The latter eventually dominates, thereby confining the cavity modes. Under appropriate conditions, the ensuing reduction in loss determines the onset of lasing. The importance of the waveguide effect was confirmed by measurements on devices incorporating a permanent index step at the active-passive region interface.
Mechanisms of electromagnetic generation and detection of ultrasonic Lamb waves in iron-nickel alloy polycrystals
Authors: Thompson R. Bruce
Published: February 2003

Measurements of the efficiencies of electromagnetic generation and detection of ultrasonic Lamb waves in Armco iron, 1018 steel, nickel, and Invar are presented as a function of both the static and dynamic magnetic field strengths in a geometry in which both are parallel to the surface. Three distinct coupling mechanisms are suggested by the data, and this is confirmed by a quantitative comparison of the amplitude and phase of the generated waves to theoretical predictions. In the iron, 1018 steel, and nickel, Lorentz forces are the primary mechanisms of transduction for static fields above about 2 kOe, whereas Joule magnetostriction is dominant at lower fields. In Invar, a forced volume magnetostriction mechanism is observed in the 1–10-kOe range that is greater in strength than the Lorentz force mechanism. The data also demonstrate that the amplitudes of waves generated by the Lorentz force mechanism are proportional to the macroscopic magnetic field H rather than the magnetic flux density B.
Modes in SAW grating resonators
Authors: Haus Hermann A.
Published: February 2003

A Rayleigh wave of finite width, propagating along the surface of an isotropic medium, is shown to obey approximately a paraxial wave equation if the width is large compared with a wavelength. Results of laser wave propagation can be applied to the Rayleigh-wave case. Furthermore, an equation is derived for the two-dimensional Rayleigh-wave propagation underneath a grating surface. A grating of finite width is shown to provide transverse confinement (guidance) of the wave. The mode patterns are obtained of the fundamental and higher-order guided modes under uniform gratings of finite width. For a grating resonator formed of two uniform gratings separated by a quarter-wave section, a variational expression is developed for the resonance frequencies. Using a simple mode pattern for the trial solution, the resonance frequencies of the higher-order modes are evaluated. They all lie on the high side of the Bragg frequency, increasing with increasing mode number.
Excitation-dependent emission in Mg-, Be-, Cd-, and Zn-implanted GaAs
Authors: Yu Phil Won
Published: February 2003

The low-temperature properties of the excitation-dependent (moving) emissions in Mg-, Be-, Cd-, and Zn-implanted GaAs layers are investigated with respect to changes in temperature and excitation intensity. The substrates used were epitaxial layers, melt-grown n-type crystals, and Cr-doped semi-insulating crystals. Donor concentrations of the n-type substrates were in the range 5×1013 to 2×1018 electrons cm−3. Models explaining a large energy shift are presented for both Cr-doped and n-type substrates. The moving emissions are classified into three different cases: (a) donor-acceptor-pair emission in relatively pure weakly compensated crystals; (b) donor-acceptor-pair emission in impure strongly compensated crystals; and (c) a radiation transition from the conduction-band tails to the valence band. The donor-acceptor-pair emission in the impure compensated crystals shows the shift to lower energy with an increase of temperature in the temperature range 4–50 °K, while the donor-acceptor-pair emission in pure crystals behaves in the usual manner. This is due to the increase in the random impurity potential. The large shift of emission peaks originates in the impure compensated regions, i.e., the near-surface region due to the out-diffusion of the implanted atoms in Cr-doped substrates, and the highly resistive layer between the p- and n-type region in n-type substrates. Additional compensating donors are found to be defect-type donors, As vacancies. The formation of As vacancies differs depending on the substrate materials. The role of the As vacancy in forming a compensated region is discussed.
Self-absorption effects on the radiative lifetime in GaAs-GaAlAs double heterostructures
Authors: Asbeck P.
Published: February 2003

An analysis is presented of the effects of self-absorption of spontaneously emitted photons on the recombination lifetime of injected carriers in the active region of GaAs-GaAlAs double heterostructures. It is shown that at moderate injection levels (∼100 A/cm2) self-absorption effects may lengthen appreciably the net radiative lifetime of the carriers in heterostructures with thick (?1 μ) active regions. Results of the analysis are in good agreement with data of Ettenberg and Kressel on variation of carrier lifetime with active region thickness. From the analysis it is inferred that the internal quantum efficiency of radiative recombination in the device of Ettenberg and Kressel is greater than 90%.
Electron transfer in SmHfCo alloys
Authors: Orehotsky J. , Washko S. , Gerboc J. , Wahl T.
Published: February 2003

The rare-earth electron-transfer concept in the rare-earth–transition-metal compounds was evaluated for the binary compounds Sm2Co17 and Sm1Co5 from published data. The cobalt moment was found to be consistent with a two-transferred-electron rigid-band model. These results were verified by saturation magnetization measurements on the mixed-valence pseudobinary Sm2(1−x)Hf2xCo17 alloys where the moment per cobalt atom was consistent with a tetravalent-hafnium divalent-samarium electron-transfer mechanism.
Investigation of heterostructures by piezomodulation spectroscopy
Authors: Mathieu H. , Ameziane E. L. , Merle P.
Published: February 2003

Piezomodulation spectroscopy of epitaxial layers is investigated using an original experimental configuration—the piezoreflectance on thin samples with the front and the back faces optically polished. The same spectrum gives structures characteristic of the Eo and Eo+Δo direct transitions in the GaAs1−xPx layer, structures characteristic of the Γ8v→X1c indirect transitions in GaAs1−xPx, and structures characteristic of the Γ8v→X1c indirect transitions in the GaP substrate. It is also shown that, due to the different values of the deformation potentials of X1c, L1c, and Γ1c, the strain-induced modulation of these transitions have a well-defined phase relation. This allows for the identification of the conduction band minimum involved in the indirect process.
Topology of obliquely coated silicon monoxide layers
Authors: Pollack J. M. , Haas W. E. , Adams J. E.
Published: February 2003

Silicon monoxide layers, coated at oblique angles of 45°–87° onto indium oxide coated glass substrates, are examined by TEM for angularly dependent surface topology. ’’Striations’’ observed at angles near 81° are discussed in terms of the aligning influence that these features exert upon nematic liquid crystals. Included are photomicrographs of these striations as well as of a ’’scale’’ feature observed at angles greater than 83°. Existence of the ’’scale’’ feature is correlated to previously observed asymmetric diffuse diffraction effects.
Near-resonant dye laser scattering and two-photon absorption in a sodium neon plasma
Authors: Vriens L.
Published: February 2003

Two possible techniques for determining sodium densities in nonhomogeneous optically thick plasmas are investigated. The first one is single-mode dye-laser scattering in the near wings of the sodium D1 and D2 resonance lines. The second technique is near-resonant two-photon absorption with two counterpropagating single-mode dye-laser beams and detection of the fluorescence. In both cases, the laser frequency(ies) is (are) detuned far enough from (the intermediate) resonance to make the plasma optically thin for the laser beam(s) and for the directly scattered light, hence for the one-step two-quantum transitions. In the scattering experiment, the polarization properties of the scattered light are used for discrimination against the stepwise absorption-reemission (the collision-induced fluorescence). In the two-photon absorption experiment, the residual Doppler broadening is small enough to make a clear distinction between the direct two-quantum and the collision-induced stepwise one-quantum transitions. It is shown that the near-wing scattering directly yields local sodium densities. This is not the case for the two-photon absorption. The technique of near-resonant scattering is also applicable to other metal vapors in discharges and neutral gases.
Measurement of thermoelectric coefficients at the solid-liquid interface of highly doped p-type silicon
Authors: Rötzer Gunther , Lockwood Loren , Gil Z. José L.
Published: February 2003

A new version of the ac/dc method has been developed to measure the Peltier coefficient πms at the solid-liquid interface and the Thomson coefficient τs of the solid phase at the melting point Tf. For silicon with a boron concentration of 1×1020 cm−3 the results are πms=+0.19 V ±25% and τs=−0.38 mV K−1±23%. From the first Kelvin relation, the Seebeck coefficient at the solid-liquid interface αms is found to be +0.11 mV K−1. The absolute Seebeck coefficient αs of the solid phase at Tf can be inferred to be +0.10 mV K−1. The experimental technique also permits the measurement of the interface motion due to thermal convection in the liquid phase.
Dielectric relaxation in cortical bone
Authors: Lakes Roderic S. , Harper Richard A. , Katz J. Lawrence
Published: February 2003

Measurements of the capacitance and conductance of bovine cortical bone have been performed at body temperature as functions of frequency, time, and humidity. A direct-coupled low-frequency bridge containing active circuits was used to study the response below 50 Hz. Results are expressed in terms of permittivity, dielectric loss tangent, and both frequency- and time-dependent electric moduli. The permittivity was found to be extremely sensitive to frequency and humidity; maximum permittivity observed exceeded 105, while the maximum loss tangent was greater than unity. Anisotropy was observed; both the permittivity and the loss tangent were greater if the electric field was parallel to the bone axis.
Plasma density measurements in a gas target
Authors: Bennett M. S. , Haasz A. A. , Orszag M. , Stangeby P. C.
Published: February 2003

Experiments are reported on Stark broadening measurements of electron number density in gas targets under intense electron-beam heating. Plasma recombination is found to be fast on the gasdynamic time scales of the subsonic target configuration studied. The configuration simulates that in the gas-target neuton generator systems under development for fusion technology research.
Plasma rotation by electric and magnetic fields in a discharge cylinder
Authors: Wilhelm H. E. , Hong S. H.
Published: February 2003

A theoretical model for an electric discharge is developed consisting of a spatially diverging plasma sustained electrically between a small ring cathode and a larger ring anode in a cylindrical chamber with an axial magnetic field, to study the rotation of the discharge plasma in the crossed electric and magnetic fields. The associated boundary-value problem for the coupled partial differential equations, which describe the electric potential and the plasma velocity fields, is solved in closed form. The electric field, current density, and velocity distributions are discussed in terms of the Hartmann number H and the Hall coefficient ωτ. As a result of the Lorentz forces, the plasma rotates with speeds as high as 106 cm/sec around its axis of symmetry at typical conditions. As an application, it is noted that rotating discharges of this type could be used to develop a high-density plasma-ultracentrifuge driven by j×B forces, in which the lighter (heavier) ion and atom components would be enriched in (off) the center of the discharge cylinder.
Effect of radial expansion of the laser heating of a magnetically confined plasma
Authors: Lax B. , Yuen S. Y.
Published: February 2003

The laser heating behavior of a plasma column confined by a solenoid magnetic field is analyzed. A quasistatic model is used to account for plasma radial expansion. The ion heating process is studied explicitly. Simple analytic expressions are obtained to describe electron and ion temperatures as well as the behavior of axial heating or ’’bleaching’’-wave propagation.
Copper electromigration in aluminum
Authors: Blech I. A.
Published: February 2003

The apparent effective charge Z**Cu, of copper in aluminum was measured using a quasi-steady-state technique. Z**Cu was measured in the temperature range 325–500 °C at several current densities. The measured values ranged between −4.1 and −14.9. No clear current density or temperature dependence could be seen, except for a possible increase in Z**Cu with decreasing temperature.
Elastic constants and electrical resistivity of Fe3Si
Authors: Rausch J. B. , Kayser F. X.
Published: February 2003

The electrical resistivity and elastic constants of slowly cooled single-crystal specimens of the ordered alloy Fe3Si (cubic, DO3 structure) were measured from 4.2 °K to room temperature. The residual resistivity (ρo) was determined to be 0.6 μΩ cm. We infer from this that had the composition been exactly stoichiometric, which it was not, and the crystal free of internal voids generated during growth from the melt, the ρo would have approached zero—a behavior that has not been reported previously for a (non-superconducting) long-range ordered alloy. The temperature dependences of the directly measured adiabatic elastic constants were found to be as follows (uncorrected for thermal contraction; T in °K): CL(T) ={3.410−0.2696/[exp(367/T)−1]}×1011 N/m2; C (T) ={1.405−0.0563/[exp(227/T)−1]} ×1011 N/m2; C′ (T) ={0.4183−0.1132/[exp(393/T)−1]}×1011 N/m2. Calculated values for the isothermal Young’s modulus (E), the shear modulus (G), and the Poisson ratio (ν) of a polycrystalline aggregate of Fe3Si possessing a random distribution of crystallite orientations are, for T=295 °K, as follows: E=2.15×1011 N/m2, G=0.828×1011 N/m2, and ν=0.299. The Debye temperature of the alloy at 0 °K is 501.1 °K.
Mercury-melting-line determination by latent heat method
Authors: Houck James C.
Published: February 2003

The equilibrium pressure for the melting and freezing of mercury was observed for the temperature range −38.834–0.023 °C by latent heat detection. The corresponding pressure range was 0.14–757.32 MPa (MPa=106 N/m2). The least-squares fit was obtained for this range of pressure with a standard deviation of the residuals of 0.055 MPa for pressure expressed as a third-order polynomial in temperature.
Laser-induced explosion of solid material
Authors: Koo Jackson C.
Published: February 2003

The phenomenon of laser-induced explosion is treated for the case of complex materials such as ceramics and ferrites. An explosion criteria is developed for these materials and applied to two examples for which experimental data exist.
Range profiles of 100–400-keV deuterons in nickel: Experiment and computer simulation
Authors: Möller W.
Published: February 2003

The range profiles of 100–400-keV deuterons have been determined using the D(d,p)T nuclear reaction technique after implantations at normal and oblique incidence. The experimental profiles show a long tail to the surface due to diffusion and a peak which is identified with the original range distribution. From the profiles, the most probable projected range and the longitudinal and lateral range straggling are derived as functions of the implantation energy. Good agreement is obtained with range profiles calculated by computer simulations using the binary-collision model if the depth resolution of the nuclear reaction method is taken into account. The mean projected ranges agree well with predictions from analytical theory.
Instability of cracks under impulse loads
Authors: Kalthoff J. F. , Shockey D. A.
Published: February 2003

A plate impact method was used to produce internal penny-shaped cracks in polycarbonate and to study the response of these cracks to short tensile pulse loads. The observed crack instability behavior could not be explained by classical static fracture mechanics. A short-pulse fracture mechanics was developed from static fracture mechanics concepts. The instability criterion was obtained from considerations of the early time stress intensity histories experienced by cracks struck by short-pulse loads. This criterion, which requires that the dynamic stress intensity exceed the dynamic fracture toughness for a certain minimum time, gave results in accord with the experimental data. Short-pulse fracture mechanics defines the conditions for which simple static expressions can be used to determine dynamic fracture toughness. The dynamic fracture toughness of polycarbonate at a stress intensification rate of 107 MN m−3/2 sec−1 was measured to be 2.2±0.2 MN m−3/2, about 60% of the quasistatic value. This result supports the view that material toughness does not increase sharply at high loading rates, but rather decreases monotonically with increasing stress intensification rate until a constant minimum value is reached.
Position-dependent flux pinning by proton-irradiation damage in thick niobium samples
Authors: Rollins R. W. , Anjaneyulu Y.
Published: February 2003

Pure vacuum-annealed niobium was irradiated at room temperature with 5-MeV protons to a total fluence of 6.8×1016 protons/cm2. The sample thickness was much larger than the range of the protons. The local magnetic induction as a function of distance from the surface was determined in the superconducting mixed state using a previously described ac technique. The measurements show a dramatic increase in pinning to a depth of about 100 μm, which corresponds to the approximate range of the protons. The field profiles were obtained at several applied-field values between Hcl and Hc2 and the magnetic field dependence of the volume pinning force Fv shows a strong ’’peak effect’’ near Hc2. The results are discussed in terms of several disclocation-loop–flux-line-lattice–pinning models using calculations of irradiation damage based on Rutherford scattering and the simple Kinchin-Pease model of atomic displacements. The results are found to be consistent with previous measurements by Agrawal, Kramer, and Loomis on neutron-irradiated niobium and suggest that a quadratic summation rule first proposed by Labusch should be used to obtain the effective volume pinning force Fv.
Magnetic field perturbations due to a hole in a conducting wall near a time changing magnetic field
Authors: Rudmin J. W. , Drake J. R.
Published: February 2003

Plasma confinement devices frequently employ a conducting wall to confine a pulsed magnetic field. Holes in the wall produce perturbations of the uniform field which can affect the plasma equilibrium and field topology. The magnetic field perturbation around such a hole has been calculated using the quasistatic approximation for various cases by analytic and numerical methods, and has been measured for one case experimentally. Simple analytic approximations are presented. The perturbations near a conducting interface are found to be of a much longer range than would be true for fields of the same symmetry in free space.
Origin of superconductivity in copper niobium alloys
Authors: Roberge R. , Fihey J. L.
Published: February 2003

Superconductivity in copper-rich niobium alloys has been investigated. A controlled cooling technique was developed to provide homogeneous distributions of niobium in the copper. Two distinct microstructures were observed depending on the cooling rate. For low cooling rates (<700 °C/sec) and low niobium concentrations a subgrain structure of niobium is evident. These samples are superconducting with low critical current density (<10 A/cm2). For faster cooling rates (≳1000 °C/sec) the subgrain structure is eliminated and a critical concentration for the observation of superconductivity is observed experimentally at 10–12 wt% Nb (7–9 at.% Nb). The experimentally determined critical concentration is explained by a model based on site percolation theory modified for the shape of the precipitate. The model suggests that continuous niobium chains in the copper matrix lead to the observed superconducting properties. The proximity effect, previously suggested as the basis for superconductivity in these alloys, appears to have little contribution to the appearance of superconductivity in these as-cast samples. The only contribution, if any, is to bridge gaps in the otherwise continuous niobium network.
Pb valence in iron garnets
Authors: Scott G. B. , Page J. L.
Published: February 2003

A model for the incorporation of Pb in garnets is presented in which self-compensation occurs via the formation of Pb2+ and Pb4+ and allows an explanation of the following observations: high levels of Pb substitution achievable, the temperature dependence of Pb incorporation, lattice mismatch behavior of epitaxial films of Pb-doped iron garnets, the Pb-induced uniaxial anisotropy behavior in EuIG : Pb, the electrical conductivity type, and the high Pb-induced optical absorption. Spectroscopic evidence for the simultaneous existence of Pb2+ and Pb4+ in Y3Ga5O12 (YGG) is given and analyzed in terms of Pb2+, Pb4+ impurity levels lying respectively 1.1 eV above the valence band and 2.36 eV below the conduction band. Intervalence transition between Pb2+ and Pb4+ occurs at 18 000 cm−1 (2.23 eV) in YGG : Pb. Using the separation of Pb2+ and Pb4+ levels determined in YGG and a simple energy-band model for YIG the Pb-induced absorption processes in YIG : Pb are enumerated and shown to give a qualitative explanation of the absorption spectrum of YIG : Pb.
Microstructure of aged (Co,Cu,Fe)7Sm magnets
Authors: Livingston J. D. , Martin D. L.
Published: February 2003

The microstructure of (Co,Cu,Fe)7Sm magnets has been characterized at various states of aging by transmission electron microscopy. At peak magnet properties, the magnet consists of cells of 17 : 2 phase about 500 Å in diameter, separated by a thin continuous fully coherent 5 : 1 boundary phase. This structure evolved by precipitation of ordered 17 : 2 particles from a disordered 5 : 1 matrix, and coarsens with aging until full coherence is lost and the cellular structure breaks up. The overaged alloy consists of semicoherent 5 : 1 particles in a 17 : 2 matrix, with a single set of interface dislocations accommodating the lattice mismatch. The effect of these various microstructural changes on domain-wall pinning and coercivity is discussed.
Barrier height reduction for graded n-n heterojunctions
Authors: Raymond R. M. , Hayes R. E.
Published: February 2003

We have obtained an expression for the critical grading length which reduces the barrier height from the abrupt junction value to 1kT for a linearly graded, uniformly doped, n-n heterojunction. This critical length, which is temperature dependent, is the product of the extrinsic Debye length and the abrupt junction barrier height normalized to kT.
Saturation of Fe2+ ion concentration in single-crystal YIG(Si)
Authors: Paroli P. , Geller S.
Published: February 2003

The relative Fe2+ ion concentrations in three flux-grown crystals of YIG(Si), containing up to 0.3 Si4+ ion per formula unit, have been determined by optical techniques. The Fe2+ ion concentration appears to reach a maximum or saturation value at Si4+ ion content of 0.1 per formula unit. The Si4+ ions not compensated by Fe2+ or Pb2+ ions, the sum of which is less than the Si4+ ion content, must be compensated by cation vacancies.
Simplified model of ferroelectric energy generation by shock compression
Authors: Mazzie John A.
Published: February 2003

It is shown that in normal mode depoling of PZT 95/5 (lead zirconate/lead titanate) the observed current can be predicted when the PZT is considered simply to be a bulk capacitor of constant capacitance to which a load resistor is connected in parallel. The important design parameter which emerges is the value of the RC time constant relative to the shock transit time.
Derivation of equations which relate the effective surface charge density of a dielectric or electret to measurable parameters
Authors: Mankin R. W. , Callahan P. S.
Published: February 2003

The measurement equations for the capacitive probe, dissectable capacitor, and vibrating capacitor methods of determining the effective or apparent surface charge density on a dielectric are derived as special cases of a single theory. The results agree with those of other authors.
The statistical distribution of carrier number in electron avalanches in gases
Authors: Kondo Yoshitaka , Miyoshi Yasunori
Published: February 2003

Theoretical investigations are given on the statistical distribution functions of the number of electrons in a series of electron avalanches initiated by a high-energy particle at an applied voltage below the sparking voltage. The distribution functions are derived for the electron avalanches started by initial electrons generated at the cathode, using the Poisson and geometric distributions for the initial electrons. Furthermore, the distribution function is obtained for the electron avalanches started by a single initial electron generated at any place in a discharge gap.
A method of cleaning Ga0.5Al0.5Sb surface
Authors: Miyao M. , Sukegawa T. , Hagino M.
Published: February 2003

Bombarding Ga0.5Al0.5Sb with a 500 eV argon-ion beam was found effective for sputtering the oxide layer from its surface. The clean surface thus obtained showed a clear LEED pattern of a 2.5×1 structure after annealing at 320 °C for 2 minutes. Our experience showed that the LEED pattern was obtainable only when the pressure was maintained at 1×10−8 Torr or below.
Current modulation in a pulsed argon ion laser discharge
Authors: Litke John D.
Published: February 2003

Current oscillations have been observed in a pulsed argon ion laser discharge. The current oscillations were fixed in time with respect to the rising edge of the current pulse and were compatible with the presence of ion-acoustic oscillations and high electron temperature. A current modulation characterized by a slowly damped sinusoid was also observed. This modulation was not fixed in time with respect to the current pulse and was compatible with the presence of an unstable linear pinch.
Linear thermal expansion measurements on silicon from 6 to 340 K
Authors: Lyon K. G. , Salinger G. L. , Swenson C. A. , White G. K.
Published: February 2003

Linear thermal expansion measurements have been carried out from 6 to 340 K on a high-purity silicon sample using a linear absolute capacitance dilatometer. The accuracy of the measurements varies from ±0.01×10−8 K−1 at the lowest temperatures to ±0.1×10−8 K−1 or 0.1%, whichever is greater, near room temperature, and is sufficient to establish silicon as a thermal expansion standard for these temperatures. The agreement with previous data is satisfactory at low temperatures and excellent above room temperature where laser-interferometry data of comparable accuracy exist. Thermal expansions calculated from ultrasonic and heat-capacity data are preferred below 13 K where experimental problems occurred.
Enhanced elastic modulus in composition-modulated gold-nickel and copper-palladium foils
Authors: Yang W. M. C. , Tsakalakos T. , Hilliard J. E.
Published: February 2003

The biaxial elastic modulus Y[111] has been measured by bulge testing in Au-Ni and Cu-Pd foils containing short-wavelength one-dimensional composition modulations produced by vapor deposition. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase in modulus—from 0.21 to 0.46 TPa for Au-Ni and from 0.27 to 1.31 TPa for Cu-Pd. For the latter system, the increase was found to be proportional to the square of the amplitude of the modulation. The enhancement of the modulus decreased with increasing wavelength and for wavelengths greater than 3 nm the modulus was the same as that for homogeneous foils. It was also observed that the deformation was non-Hookian; the slope of the stress-strain curves decreased with increasing strain.
Optical transmission of liquid-crystal field-effect cells
Authors: Meyerhofer Dietrich
Published: February 2003

The relationships between the optical transfer characteristics of twisted-nematic liquid-crystal devices and the material and cell parameters were investigated. The dependence of transmission on wavelength, birefringence, cell thickness, and surface alignment was measured as functions of light direction and operating conditions. The experimental results were confirmed by calculations of the transmission using Berreman’s numerical procedure for anisotropic media. The angle over which good contrast is observed increases with increasing wavelength and decreasing cell thickness and birefringence. This is accompanied by a decreasing value of optical threshold. The most uniform response and widest viewing angle is obtained with materials of small birefringence in cells with near-planar alignment.
Photoelastic tensor components of Gd2 (MoO4)3
Authors: Sapriel Jacques , Vacher René
Published: February 2003

The whole set of components of the photoelastic tensor has been determined in Gd2(MoO4)3 at room temperature by a combination of ultrasonic and hypersonic wave measurements. The transverse components are found to be connected by relations derived from the theory of Nelson and Lax on the photoelastic effect in anisotropic media. Gd2(MoO4)3 can be considered as a promising acousto-optical material for intracavity applications like laser mode lockers and cavity dumpers.
10-μm propagation losses in hollow dielectric waveguides
Authors: Hall D. R. , Gorton E. K. , Jenkins R. M.
Published: February 2003

Experiments are described and results presented of measurements of the propagation losses of 10-μm radiation in hollow dielectric tubes of the type commonly used in the fabrication of waveguide CO2 lasers. The dependence of such losses on the waveguide diameter and material were investiated and are compared with values calculated from theory. The attenuation coefficient of the fundamental hybrid EH11 mode is seen to vary inversely as the diameter cubed and to be very sensitive to tube camber and to the presence of impurities adhering to the wall surface.
Relative dominance of bulk or surface absorption in highly transparent materials by transient methods
Authors: Bennett Herbert S. , Forman Richard A.
Published: February 2003

For the case in which a pulsed laser beam passes through the weakly absorbing windows of a gas cell containing a nonabsorbing gas, the time rate of change of the relative pressure rise immediately after the cessation of the laser beam correlates directly with the relative dominance of bulk and surface absorption in highly transparent materials. Whenever bulk absorption dominates, the time derivative of the pressure rise in the gas for times shortly after cessation of the pulse is positive; when surface absorption dominates, it is negative; and when bulk and surface absorption are comparable, it is very close to zero. This, suggests then, a relatively simple experimental procedure by which one may determine nondestructively the relative dominance of bulk or surface absorption in highly transparent materials.
Helicon wave instability in a two-valley semiconductor
Authors: Hsieh H. C.
Published: February 2003

The condition for the instability of the left-hand polarized helicon wave in n-type GaAs subject to parallel applied static electric and magnetic fields (Eo and Bo) is derived from the dispersion relationship. It is shown that a helicon wave may be amplified by either a ’’normal’’ or an ’’anomalous’’ instability, provided that Eo is sufficiently high and the values of Bo, the electron concentration no, and the wave frequency f are proper.
Switching in cadmium boracite single crystals
Authors: Takahashi Tatsuo , Yamada Osamu
Published: February 2003

We have found that a highly insulative Cd boracite crystal becomes conductive when a certain electric voltage is applied at a high temperature (≳300 °C). The threshold voltage for switching is smaller than a few volts for an electrode distance of a few tenths of a millimeter. This corresponds to an electric field of 102–103 V/cm and is much smaller than the dielectric breakdown voltage for an insulator such as boracite. The insulative state is restored after the removal of voltage. The switching has also been investigated by a pulse technique. In this case, two different types of switching are observed. Unstable switching is observed when the pulse voltage is slightly above the threshold and is characterized by a delay time before switching and a residual current after the removal of a voltage pulse; whereas stable switching takes place when the voltage becomes sufficiently high.
Negative magnetoresistance in GaAs containing Mn or Ni acceptors
Authors: Woodbury D. A. , Kennewell J. A. , Blakemore J. S.
Published: February 2003

Transverse magnetoresistance was measured, from 20 to 30 K and for fields up to 1 T, in GaAs crystals doped with enough Mn or Ni acceptors to result in activationless impurity conduction. Anomalies in the weak-field magnetoresistance were seen in the impurity conduction range. Nickel-doped samples showed consistently zero or positive Δρ/ρo, though the near-zero magnetoresistance below 0.5 T for the temperature range 40–100 K suggested cancellation of conventional monotonically increasing positive magnetoresistance by a negative component that saturated for large fields. With manganese-doped crystals, a small negative total magnetoresistance (−Δρ/ρo<4×10−5) was seen for fields up to 0.6 T, but only within the limited temperature range 40–75 K. The field dependence again suggested that total magnetoresistance should be regarded as the algebraic sum of an increasing positive term and a saturating-type negative component. The magnitude and field dependence of the negative magnetoresistance of GaAs : Mn was compared with models such as those based on the magnetic ordering of localized spins, and yielded a localized impurity magnetic moment of 2.2μB when compared with the magnetic ordering model of Pöder.
Beryllium doping and diffusion in molecular-beam epitaxy of GaAs and AlxGa1−xAs
Authors: Ilegems M.
Published: February 2003

p-type doping levels of up to 5×1019 cm−3 in GaAs and 3×1019 cm−3 in Al0.3Ga0.7As have been obtained in molecular-beam epitaxy (MBE) with Be doping. These doping levels are more than one order of magnitude higher than can be achieved with other acceptors excepting ionized Zn, and are obtained while maintaining surface morphologies comparable to those of undoped layers. Mobilities of the Be-doped GaAs MBE layers are comparable to those obtained in liquid-phase epitaxy (LPE) material. Mobilities of Be-doped Al0.3Ga0.7As MBE layers studied in this experiment are lower than those measured in LPE crystals and do not increase with decreasing doping level which indicates a high degree of donor compensation in these samples. Room-temperature photoluminescent efficiencies obtained from the p-MBE GaAs and AlxGa1-xAs layers grown under As-stabilized surface conditions also are significantly lower than those of comparably doped LPE material. This lower efficiency may be related to impurity contamination specific to the dopant source and is not observed during n-type (Sn-doped) GaAs layer growth under otherwise identical conditions. p (Be) -n (Ge) junctions have been evaluated and the results indicate that Be should be a suitable dopant for device fabrication. Doping profile measurements by the differential capacitance technique show that very abrupt (half-width ?350 Å) Be doping pulses can be realized. By observing the out diffusion of Be from these doping pulses during annealing of the diodes a value of D?1×10−15 cm2/sec for the diffusion coefficient of Be at 800° was established. It is concluded that, with the possible exception of ionized Zn, Be should emerge as the preferred acceptor in MBE growth of III–V compounds.
Temperature dependence of J
c in superconducting Nb3Ge
Authors: Daniel Michael R. , Braginski A. I. , Roland G. W. , Gavaler J. R. , Bartlett R. J. , Newkirk L. R.
Published: February 2003

Measurements are presented of the temperature variation of the critical current density Jc for superconducting Nb3Ge in the field range 0–65 kG. Samples prepared either by sputtering or chemical vapor deposition (CVD) show a behavior similar to that exhibited by Nb3Sn. The data can be approximated by the relationship Jc∼[Hc2(t)]n. The n values range from 1 for self-field Jc to 5 at a field intensity of 50 kG.
Heating effects in high-frequency metallic Josephson devices: Voltage limit, bolometric mixing, and noise
Authors: Tinkham M. , Octavio M. , Skocpol W. J.
Published: February 2003

In this paper, we analyze nonequilibrium effects within a simple heating approximation for the case of metallic Josephson weak links which have a favorable three-dimensional cooling geometry. Our principal conclusions are the following: (1) The temperature in the center of the junction with voltage V applied is Tm=[Tb2+3 (eV/2πk)2]1/2, where Tb is the bath temperature, e is the electronic charge, and k is Boltzmann’s constant. This Tm can be as high as 70 K in Nb point contacts on a high Josephson step; thus the device noise temperature TN? (1/2)(Tb+Tm) can greatly exceed Tb. (2) The critical current falls approximately as exp(−P/Po), where P is the power dissipated in the junction and Po is typically 10 μW for Al, Sn, Pb, and Nb, but much smaller for Nb3Sn. This leads to a decrease in the amplitude of Josephson steps at high voltages which is in good agreement with data on the best Sn variable-thickness microbridges and Nb point contacts. In a junction of optimized resistance level, the overall maximum voltage at which microwave-induced steps can still exceed the noise is predicted to be proportional to Tc[Ωξ (0)/ρo]2/7× (ν1/Tc)1/7, where Ω is the solid angle of the three-dimensional cooling, ξ (0) is the extrapolated coherence length at T=0, ρo is the residual resistivity of the metal, and ν1 is the microwave frequency. (3) The thermal response should be fast enough (∼τGL) to allow detection (heterodyne or square law) with bandwidth as large as the energy gap frequency; it is estimated that this bolometric detection effect will dominate true Josephson detection for carrier frequencies above ∼3 THz (i.e., λ≲100 μm) in junctions with resistance 10 Ω or less.
Propagation of an unneutralized intense relativistic electron beam in a magnetic field
Authors: Miller R. B. , Straw David C.
Published: February 2003

In this paper the results of a series of electron-beam vacuum propagation experiments are presented and compared with theoretical predictions. Important conclusions pertaining to time-dependent diode behavior, virtual cathode formation, and various equilibrium and stability criteria are reported.
Magnetic cutoff in high-current diodes
Authors: Creedon John M.
Published: February 2003

The process of magnetic cutoff in diodes is investigated for several geometrical configurations. Generalized coordinates are used to show that the cutoff mechanism has certain basic properties which are common to all of the configurations considered. Theoretical solutions for two different one-dimensional flow patterns are compared and shown to have similar mathematical properties. Measurements are compared to theory for several types of magnetic cutoff.
Kinetic theory of a spherical probe in a stationary collision-dominated isothermal plasma
Authors: Brailsford A. D.
Published: February 2003

Constitutive equations for the charge carrier fluxes in a stationary collision-dominated isothermal plasma surrounding a spherical electrode are derived, from the Boltzmann equation, by a moment method using a two-stream Maxwellian distribution of the type introduced by Lees. In contrast to previous treatments, the constraint of uniform temperature is imposed and its importance emphasized. This condition, together with particle conservation, is shown to necessitate the use of a four-parameter Lees distribution and leads to generalized hydrodynamic equations. These are shown to reduce to conventional flux equations in terms of diffusion and mobility components only when the fields are spatially slowly varying. In addition, boundary conditions are derived by the same formalism. They are formulated for typical physical processes which may be operative at a real probe surface. As an example, the effect of the nonlinearity on the pure diffusion problem is analyzed in detail in the Appendix. A semiquantitative discussion of the current-voltage characteristics for negative probe potentials is also presented. It is shown that the charge carrier distribution around the probe conforms to the ’’free-fall’’ model only at low probe voltages. Otherwise, the model proposed by Su and Lam holds. The domain covered by the present analysis is determined by the following conditions on the probe radius rp, mean free path l, and Debye length λ: (i) l3≪λ2rp, (ii) (e ‖φp ‖l/kTrp) <1 for l<λ, and (iii) (e ‖φp ‖l/kTrp) ≪λ2/l2 for l≳λ, where φp is the probe voltage. Analytic approximations to the current-voltage characteristics in both these regimes are presented.
On the crystallization of amorphous selenium films: Thermal effects and photoeffects
Authors: Gross G. , Stephens R. B. , Turnbull D.
Published: February 2003

We have characterized the morphology and crystallography of interface cylindrites and filamentary crystals, formed in the crystallization of amorphous Se films, more definitively. In ’’ideal’’ cylindrites, each of the radiating arms is in a particular crystallographic orientation such that the c axis makes a characteristic angle ϑ, often but not always 90°, with the radial direction. In ’’nonideal’’ cylindrites the orientation may be fixed within an arm, but varies from arm to arm. The effects of varying cylindrite structure on the optical extinction behavior were noted and interpreted. The arms are thinner, and the greater their frequency of branching, the lower the temperature of crystallization; further, in low-temperature growth the arms may develop pronounced curvature. Filamentary crystals form preferentially at interarm boundaries and especially at arm branching points. Thin filaments grown at room temperature were single crystals with c axes perpendicular to and [110] directions parallel with the filament axes. Frequently cylindrites were generated by the impingement of filaments on the interface or the free surface. The rates of elongation, ?F, of one type of filament were about 101 times greater than the thickening rates ?IC, but about 103 times less than the radial growth rates ?IC of the interface cylindrites. However, the temperature dependence of ?F and ?IC are described by activation energies which are about the same, 32.7±1.5 kcal/mole. Photoillumination with white light sharply increases both ?IC and l̇F while not appreciably affecting ?IC in the highest-purity films. Such illumination also markedly increases the rate of heterogeneous nucleation and the rate of impingement of filament tips on the free surface, but it produces no measurable homogeneous nucleation.