bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature as a mechanism for the buildup of successive streamers in low-voltage breakdown
Authors: Geary John M. , Penney Gaylord W.
Published: February 2004

A form of spark discharge preceded by a train of streamers of increasingly large current which occurs in air at atmospheric pressure at voltages as low as 5 kV per cm of gap length is investigated. A mechanism involving the development of a heated channel of air in the gap is proposed to explain the increase of streamer size in the discharge. This mechanism is verified by means of a scanning interferometer which measures the phase shift caused by the altered index of refraction of the heated air. The dimensions and temperature of the heated channel are such that the peak phase shift produced is about one-tenth of one wavelength. Analysis of the phase shift data permits the growth of the heated channel to be observed as a function of time and space. Further experimentation involving time-resolved photography of the streamers is used to demonstrate a correlation of the streamers paths with the development of the heated channel. An appendix is included describing a numerical method for solving the Abel integral equation which was used to analyze the inteferometer data.
Temperature deposition caused by shock interactions with material interfaces
Authors: Urtiew P. A. , Grover R.
Published: February 2004

In shock-wave compression experiments in which the interface temperature between two different materials is important, it is necessary to take account of more than the usual ideal shock impedance matching conditions. Several examples are discussed by means of hydrodynamic analysis of the interaction of strong shock waves with nonideal interfaces. It is demonstrated that significant residual thermal inhomogeneities exist near the interface which may be of use in understanding and measuring thermal properties of shock-compressed materials.
Thermal relaxation at interfaces following shock compression
Authors: Grover R. , Urtiew P. A.
Published: February 2004

Thermal conduction processes at material interfaces representative of those produced by shock compression are studied in order to understand the temperature history at the interface. The transient effects due to small gaps and thin layers are calculated, as well as the modifications due to a melting transition in one of the materials.
Electron-irradiation effect in the Auger analysis of SiO2
Authors: Thomas Simon
Published: February 2004

The principal features in the Auger electron spectrum from a SiO2 surface are presented. The primary electron beam bombarding the SiO2 surface has a profound influence on its composition, in that it dissociates the surface leaving it enriched in elemental silicon. The main parameters affecting the dissociation are found to be the electron-beam current density, the beam energy, the presence of impurities on the surface, and the residual gas pressure of oxygen. The effects of these parameters on the dissociation have been studied and some suggestions to minimize the dissociation are made. The results of the present study do not agree with the mechanism proposed by Lineweaver for oxygen release from electron-irradiated glass.
High-energy CO2 laser pulse transmission through fog
Authors: Lowder J. E. , Kleiman H. , O'Neil R. W.
Published: February 2004

Observations of high-energy CO2 laser pulse transmission through artificial fogs with water contents ranging from 1 to 20 g/m3 are presented. The transmitted energy is found to be in fair agreement with theoretical predictions and fog was found to behave as a saturable absorber for intense CO2 laser pulses.
Current transport in MSM devices
Authors: Baccarani G. , Calzolari P. U. , Graffi S.
Published: February 2004

A theoretical treatment of the current transport in MSM devices is presented. It is based upon the application of the thermionic diffusion theory to both junctions and makes it possible to relate the current density to the total voltage applied to the device by a single expression valid for any voltage above reach through. So doing, the contributions of the different transport mechanisms, i.e., thermionic injection over the energy barriers at the junctions and drift diffusion within the semiconductor, may be evaluated both for majority and minority carriers. It turns out that before the flat-band condition the current is limited by transport phenomena in the semiconductor, while above flat band neither mechanism definitely prevails. However, in spite of the different physical models, numerical results are of the same order of magnitude as those obtained by Sze et al.
Degradation of a laser medium due to ionization by a laser pulse
Authors: Elliott C. James
Published: February 2004

An important consideration in building large-volume gas amplifiers, given the pulse duration, is the maximum output intensity which the amplifying medium can support. We consider this problem in detail for CO2 lasers to be used in laser fusion experiments. We describe a new means of computing properties of the electron distribution function using a Monte Carlo model, and compare computations by this method with a more common Laplace transform technique. The physics of the models is carefully considered, and the previously ignored effect of Penning ionization is shown to be of potential importance. The computations strongly suggest that for a 1.3-nsec pulse at 10.6 μ, using conventional pumping techniques, an intensity of 2.3 × 109 W/cm2 results in less than a 10% energy propagation loss, and that an intensity of 3 × 109 W/cm2 results in more than a 10% loss.
Using the semiconductor junction in quantum interference devices
Authors: Simmonds M. B.
Published: February 2004

We have fabricated small-area tunnel junctions of a lead-tellurium-lead structure. These have been used in conjunction with bulk superconductors to make hybrid quantum interference devices. We have successfully operated these devices at bias frequencies of 30 MHz, 300 MHz, and 10 GHz.
Stopping power of cadmium sulfide for helium ions
Authors: Engel P. F. , Borders J. A. , Chernow F.
Published: February 2004

A new experimental technique has been used to measure the stopping power of CdS for He ions. This technique consists of measuring the energy spectrum of either He ions backscattered from implanted Bi or of α particles emitted by an implanted radioactive isotope, such as Po210. A thin layer is then etched off the surface of the sample and the energy spectrum is measured again. The stopping power is calculated from these two spectra and the known thickness of the removed layer. These measurements and calculations have been made for energies ranging from 0.963 to 5.3 MeV with accuracies between 12% and 16%.
Propagation of magnetic domain walls by a self-induced current distribution
Authors: Carr W. J.
Published: February 2004

Calculations are made for the motion of a domain wall surrounded by a perturbed region of current density resulting from the action of the magnetic field of the domain on a uniform impressed current density. The perturbed region follows the motion of the domain wall and produces a magnetic field which causes the domain to propagate. In particular, a ferromagnetic layer containing a cylindrical domain, with a Hall-effect overlayer, is considered.
Preparation and high-field superconducting properties of vapor-deposited Nb3Sn alloys
Authors: Enstrom Ronald E. , Appert John R.
Published: February 2004

Nb3Sn alloyed with Si, Ti, V, Ta, Bi, or Mo has been grown from the vapor phase on stainless-steel (Hastelloy) ribbon substrates. Compared to a value of 185 kOe observed for unalloyed Nb3Sn, 1.3% Si increased Hc2 to 225 kOe, while 0.002% Bi or 0.05% V raised Hc2 to about 215 kOe. Whereas 0.0006% Ti or 3.7% Ta did not affect Hc2 appreciably, 0.4% Mo decreased Hc2 to 140 kOe. Diffusion of Ni from the stainless-steel substrate into the Nb3Sn layer appears to be responsible for the observed Hc2 value of 196 kOe for the unalloyed (but carbon doped) ribbon since the same Nb3Sn layer on a Nb substrate has an Hc2 value of 225 kOe. The effect of the Ni outdiffusion on Hc2 can be reduced by reducing the Nb3Sn growth temperature or by increasing the Nb3Sn layer thickness. Hc2 does not appear to correlate directly with Tc since Tc is about 15.5°K for both the Si- and Mo-alloyed Nb3Sn, as well as for the unalloyed Nb3Sn deposited on a Nb substrate, while Hc2 ranges from 140 to 225 kOe. The intermediate phase region between the Nb3Sn layer and the stainless-steel substrate consists of a rich variety of phases including NbNi, NbNi3, Ni3Sn, Ni3Sn2, and MoNi. Alloying Nb3Sn with Bi, Ti, V, and Mo reduces Jc by a factor of 2 to 4 compared to the unalloyed sample. Ta does not significantly affect Jc and Si significantly increases Jc above 120 kOe. CO2 or C2H6 additions can increase Jc for the alloy ribbons by up to a factor of 8, but not to values greater than observed for unalloyed Nb3Sn doped with carbon. Si alloys doped with carbon are an exception and have higher Jc values above 120 kOe than the carbon-doped unalloyed ribbon.
Diffraction patterns and vortex structure of asymmetrical and cross Josephson junctions
Authors: Stuehm D. L. , Wilmsen C. W.
Published: February 2004

The critical current of an asymmetrical Josephson junction as a function of magnetic field has been computed for junction lengths of 2λJ and 6λJ. The boundary conditions for the asymmetrical and cross junction (with an assumed current distribution) are derived. Similarity between the computed asymmetrical junction diffraction patterns and experimental patterns for the cross junction plus identical boundary conditions indicate that the current flow in the cross junction is the same as in the asymmetrical junction. Profiles of the current density in the linear and asymmetrical Josephson junctions are compared.
Electron affinities of the alkaline earth chalcogenides
Authors: Tsou K. Y. , Hensley E. B.
Published: February 2004

The electron affinities of SrSe, SrTe, CaSe, and CaTe have been determined using measurements of the temperature dependences of the electrical conductivity and the thermionic emission. The values obtained were 1.77, 2.40, 2.32, and 3.53 eV, respectively. Using these values together with previously obtained values for BaO, BaS, BaSe, BaTe, and CaO and a correlation with the lattice spacings, estimates of the electron affinities of SrO, SrS, CaS, MgO, MgS, and MgSe were obtained by extrapolation.
Band-bending effects in Na2KSb and K2CsSb photocathodes
Authors: Fisher D. G. , McDonie A. F. , Sommer A. H.
Published: February 2004

The Na2KSb photocathode has a longer threshold wavelength than the K2CsSb photocathode. This contradicts the general experience that cathode materials containing Cs tend to have longer threshold wavelengths. An attempt is made to explain this contradiction in terms of the energy-band models for the two materials.
Thermal diffusivity of uranium monophosphide from 570 to 1660 K
Authors: Nasu Shoichi , Takahashi Tadashi , Kikuchi Takeo
Published: February 2004

The thermal diffusivity of uranium monophosphide was determined between 570 and 1660 K by a laser pulse method. An anomaly around 970 K found by Menshikova et al. in the heat-capacity-vs-temperature curve was not clearly observed in the thermal-diffusivity-vs-temperature curve.
Pressure and temperature dependences of acoustic-wave velocities in polycrystalline bismuth
Authors: Fritz I. J.
Published: February 2004

Ultrasonic velocity measurements have been made on polycrystalline bismuth as a function of temperature and pressure over the temperature and pressure ranges 23–160°C (at atmospheric pressure) and 0–28.4 kbar (at 23°C), respectively. Special care was taken with the room-temperature and pressure measurements in an attempt to resolve discrepancies in previously reported sound velocity measurements. The data have been used to determine the pressure-temperature dependences of various elastic parameters, including the (discontinuous) changes across the I–II and II–III phase boundaries. The pressure data are the first that have been taken under truly hydrostatic conditions, and they are compared to results obtained with solid pressure transmitting media.
Mössbauer electric field gradient study in FeS2 (pyrite)
Authors: Garg V. K. , Liu Y. S. , Puri S. P.
Published: February 2004

Mössbauer absorption of Fe57 in single crystals of FeS2 (pyrite) has been studied as a function of the orientation of the crystal axes with respect to the unpolarized γ-ray beam. Using a point charge model, the quadrupole splitting has been calculated to be 0.58 mm/sec, taking only first immediate neighbors into consideration.
Scaling laws for high-density plasmas
Authors: Muehe C. E.
Published: February 2004

The classical ``similarity laws'' for electrical discharges in gases are rederived and shown to apply only to cases where the charge density is low enough so that the only important collisions are with gas molecules and there is no appreciable gas heating. If the charge density is high enough to be well above the transition from free to ambipolar diffusion, then the distribution functions of all the particles, and particularly the charge density, can be scaled by dividing by the neutral gas density N0 at some point in the discharge. The usual similarity laws scale the charge density by dividing by the square of the neutral gas density. These new high-density plasma scaling laws are shown to apply to the experimental results of the current limit at which striations will appear in argon discharges as reported by two investigators. Here the pressure-current product was plotted as a function of the pressure-radius product and found to form one curve over a 4:1 range of tube radii. We believe that these high-density scaling laws apply to a large group of plasma phenomena. Limitations of the new scaling laws are pointed out in connection with the spontaneous emission of excited states, three-body collision, magnetic fields produced by the currents in a discharge, the rf shielding effect in a discharge of sufficiently high conductivity, and gravitational effects.
Annealing characteristics of ion-implanted p-channel MOS transistors
Authors: Nakamura Kunio , Kamoshida Mototaka
Published: February 2004

The annealing characteristics of 50-keV (2–3) × 1011/cm2 11B+-implanted p-channel MOS transistors were investigated from 300 to 900°C. Below 500°C, the number of activated atoms NII decreased rapidly with decreasing anneal temperature and the C-V characteristics showed gradual distortions. This was presumably due to surface states induced by the ion implantation. Above 500°C, NII increased only slightly with increasing anneal temperature and the slope of the C-V characteristics in the transition region was larger than that of the unimplanted sample. Corresponding to the above features, the gain term increased near 500°C to a value about 30% larger than that of the unimplanted sample, while the breakdown voltage decreased below 500°C. Equivalent noise voltage decreased abruptly from 500 to 600°C. However, at lower drain current levels, the generation-recombination noise spectrum did not disappear, even after a 900°C anneal. In addition, reverse-annealing-like phenomena were observed in the equivalent noise voltage between 350 and 450°C. The results of surface recombination velocity measurements were consistent qualitatively with the results of equivalent noise-voltage measurements. Furthermore, device stability was confirmed by positive and negative bias-temperature treatments (250°C, 1 h, Eox = ± 6.7 × 105 V/cm) for devices annealed above 450°C.
Stress relaxation in ionic solids
Authors: Tangri K. , Lloyd D. J.
Published: February 2004

The stress relaxation behavior of single-crystal MgO, single-crystal CaF2, and polycrystalline AgCl has been examined to assess if the assumption of constancy of structure during relaxation is valid. It is shown that structural change occurs in all three materials, being severe at small plastic strains in the case of MgO and CaF2. In polycrystalline AgCl, the structural change is due to recovery and increases with increasing plastic strain.
Piezoelectric waves on a layered cylinder
Authors: Sun C. T. , Cheng N. C.
Published: February 2004

Acoustic surface waves propagating around a piezoelectric cylinder with metallic overlays are investigated. The piezoelectric core is assumed to possess the hexagonal symmetry, and the layer is electrically shorted. The dispersion equation is derived. Numerical results for the phase velocities, the displacement, and potential profiles are presented for different layer materials with various thicknesses. It is found that the thickness of the gold and chromium has a substantial effect on the dispersion, while in the case of aluminum layers little influence is observed. An asymptotic expansion for the dispersion equation is also derived and is found to yield results in good agreement with the exact solution.
Formation of hexagonal pyramids and hexagonal flat tops on the surface of heteroepitaxial (0001) CdS films
Authors: Christmann M. H. , Jones K. A. , Olsen K. H.
Published: February 2004

The various growth morphologies of CdS films grown epitaxially on SrF2 substrates were investigated by studying films grown at different supersaturations on smooth and intentionally pitted substrate surfaces. By correlating the growth conditions with photomicrographic and x-ray topographic studies, cathodoluminescence, and low-temperature uv excited edge emission we show that the hexagonal flat top is the equilibrium growth form produced by two-dimensional nucleation. Using the same studies we show that the hexagonal pyramids are associated with an excess amount of cadmium, and that they could be formed by growth around a cadmium droplet. The cadmium droplets form when conditions exist which do not allow the cadmium adatoms sufficient time to diffuse to their equilibrium position.
Dynamics and stability of a gas cavity in generalized viscoelastic liquids
Authors: Yang Wen-Jei , Lawson M. L.
Published: February 2004

A general theory is developed to determine the dynamic characteristics and stability of a gas cavity situated in viscoelastic liquids whose rheological state is described by the generalized model of the Kelvin or Maxwell type. The characteristic function of the bubble-liquid system is obtained by the first-order perturbation method, including the effects of surface tension, vapor pressure, and thermodynamic behavior of the gas confined in the cavity. The zeros of the characteristic function determine the types of bubble growth, bound on unbound. The Hurwitz (or Routh) stability is employed to determine the conditions for the onset of incipient cavitation. The applications of the theory are demonstrated in some liquids having simpler shear-stress-shear-strain relationship.
1/f noise of point contacts affected by uniform films
Authors: Vandamme L. K. J.
Published: February 2004

An experimental investigation has been carried out to confirm that contact noise of two crossed semiconductor bars with native oxide films in between can be understood as a volume 1/f noise. Noise and contact resistance have been measured as functions of the force F on the crossed bars. F varies between 6 N and 6×10−5 N. From a simple model, an equation is derived which relates the 1/f noise intensity C to the contact resistance R. The calculations are in agreement with the experimental C-R plots. Two extreme situations are possible: constriction dominated and film dominated. Which situation actually occurs can be seen in the C-R plot as well as in the R-F plot.
Elastic constants of some MAl2 single crystals
Authors: Schiltz R. J. , Smith J. F.
Published: February 2004

Elastic constants of single crystals of the cubic Laves phases CaAl2, YAl2, LaAl2, and GdAl2 have been measured over the temperature range 4.2–300 K. The ferromagnetic transition in GdAl2 near 170 K is evident by changes in slope in plots of the three independently measured elastic constants of GdAl2 as functions of temperature. Debye temperatures at 0 K were evaluated as 474 K for CaAl2, 484 K for YAl2, 374 K for LaAl2, 399 K for magnetically disordered GdAl2, and 406 K for magnetically ordered GdAl2. It was inferred from the data that the valence electron distributions in nonsuperconducting YAl2 and GdAl2 are much alike, but the valence electron distribution in superconducting LaAl2 is significantly different. Thus the results support a theoretical calculation indicating an admixture of 4f character into the valence bands of LaAl2.
Photostimulated exoelectron emission and slip-step geometry during tensile and compressive deformation
Authors: Baxter William J.
Published: February 2004

Photostimulated exoelectron emission produced by tensile deformation is much more intense than that produced by compressive deformation. This result is demonstrated for a number of metals and apparently is quite general. The strain required for the onset of emission is not appreciably different for either mode of deformation. However the intensity of emission increases rapidly with increasing tensile strain, whereas additional compressive strain has little further effect. In both cases the natural surface oxide cracks to reveal a fresh metal surface of lower work function, thereby increasing the photoelectric yield. The differing effects of tensile and compressive deformation can be correlated with the geometry of the slip steps as observed by scanning electron microscopy.
Diffusion of an interstitial solute in a dilute ternary fcc alloy
Authors: Stark J. P.
Published: February 2004

A kinetic theory is developed for diffusion of an interstitial solute in a dilute ternary fcc alloy. The development includes kinetic interpretations for off-diagonal terms in the matrix of diffusion coefficients and a concentration-dependent heat of transport for thermal diffusion and effective charge for electromigration. The associated chemical potential is shown to reflect the tendency towards interstitial and interstitial-substitutional pair formation.
New absorptive mode reflective liquid-crystal display device
Authors: White Donald L. , Taylor Gary N.
Published: February 2004

A new liquid-crystal alphanumeric display device is described. The device is of the guest-host type and involves the orientational change of a pleochroic dye (guest) in a cholesteric liquid-crystal mixure (host) by the application of an external electric field. The cholesteric nature of the host permits the operation of the device in the reflective mode with excellent brightness since no external polarizers are required. Good contrast ratios have been obtained for new pleochroic dyes (guests) which have higher optical order parameters than those previously employed. The theory of light absorption in a cholesteric liquid crystal having both homogeneous and homeotropic boundary conditions is developed and aspects of contrast ratio and its relation to human perception are described.
Solid-state traveling-wave amplification in the collisionless regime
Authors: Gover Avraham , Burrell Keith H. , Yariv Amnon
Published: February 2004

Traveling-wave interaction between flowing plasma and electromagnetic wave supported by external slow wave structure is analyzed in the collisionless regime. The plasma is described with the collisionless Boltzmann equation and the interaction is analyzed using the coupled-mode approach. The analysis is applied to a plasma consisting of drifiting charge carriers in a solid. Illustrative examples demonstrate interaction leading to wave growth for frequencies in the far-infrared regime. It is suggested that experimental measurement of wave growth or damping due to this effect can provide information about the velocity distribution of drifting carriers in the solid.
Investigation of infrared loss mechanisms in high-resistivity GaAs
Authors: Christensen C. P. , Joiner R. , Nieh S. T. K. , Steier W. H.
Published: February 2004

The absorption coefficient of GaAs has been measured by calorimetry as a function of wavelength in the 9–11-μ band and as a function of temperature. The samples measured were the best available material grown by several laboratories and by several techniques. The results suggest that infrared loss near 10 μ in these samples is dominated by an intrinsic absorption mechanism.
New directional coupler for integrated optics
Authors: Auracher F. , Witte H.-H.
Published: February 2004

We report a new structure for directional couplers for integrated optics. The proposed structure consists of two waveguides coupled via a third waveguide which is separated from the other two by a thin dielectric film of slightly lower refractive index than any of the waveguide cores. This new structure should be easy to fabricate as it does not require as tight a tolerance as the conventional structure consisting of only two coupled waveguides.
Steady-state and transient heating of narrow conductor lines on garnet substrates
Authors: Hempstead Robert D.
Published: February 2004

Calculations are given of the steady-state thermal conductance for narrow conductors on garnet substrates, as found for control lines of bubble circuits. The transient heating of these lines is also analyzed and they are found to have rise times in the microsecond range.
Nonlinear reversible processes in YIG: An explanation for the Rayleigh loop anomalies
Authors: Feu Alfonso , Trueba Antonio
Published: February 2004

A magnetic field modulation technique with synchronous detection is applied to measure the reversible permeability μr and the derivative of the magnetization M with respect to the field H in YIG samples. The measurements develop a nonlinear and reversible dependence of M upon H (nearly M = aH + bH3) before the appearance of any Rayleigh behavior. If H is increased, the Rayleigh dependence in H2 is superimposed to the former, giving rise to anomalous Rayleigh loops. A model based on the elasticity of the Bloch wall is proposed and resolved. The theoretical solution fits the experimental curves.
Effects of a nonuniform current distribution on the kinetic inductance of a thin superconducting film
Authors: Baker J. W. , Lejeune J. D. , Naugle D. G.
Published: February 2004

Kinetic inductance measurements were used to probe the current uniformity in thin amorphous Bi0.97 Tl0.03 films. Measurements were made on films having widths of 0.5 and 0.2 mm with thick thicknesses ranging from 300 to 2000 Å condensed on both quartz plates and Nb shield planes. The results for films without shield planes are compared to predictions based on approximate expressions for the current density in a thin film. The Nb shield plane appears to produce considerable smoothing of the current distribution. Measurements of the kinetic inductance of films on such a shield plane appear to provide a good method for the determination of the penetration depth in a-Bi.
Role of nitrogen atoms in ``ion-nitriding''
Authors: Tibbetts Gary G.
Published: February 2004

It is shown that pure Fe and 1020 steel are nitrided in an N2–H2 plasma principally by neutral nitrogen atoms.
Optical-gain measurements in a cw transverse-discharge transverse-gas-flow CO2 : N2 : He planar-waveguide laser
Authors: McMullen J. Don , Anderson Dean B. , Davis Richard L.
Published: February 2004

Optical-gain measurements are reported for a dc-excited planar-hollow-waveguide CO2 : N2 : He laser for which the gas flow and discharge current are collinear, and both are transverse to the optical axis of the waveguide. A spatially uniform thin-sheet glow discharge was demonstrated for gas pressures between 80 and 400 Torr, using transverse dc excitation. The dependence of optical gain upon gas composition, gas pressure, discharge current, and wall temperature was characterized for a 1-mm-high planar hollow waveguide. Optimum gain was 4 dB/m at a pressure of 100 Torr and a wall temperature of 233 °K.
New cw laser oscillation in He–Zn hollow cathode laser
Authors: Iijima Tetsuo , Sugawara Yoshihiko
Published: February 2004

A new cw laser line in ZnII has been observed using an improved hollow cathode laser tube. The wavelength and the transition assignment are 7732.5 Å and 5p 2P1/20−5s 2S1/2, respectively. The new laser line and the strong laser line at 7588 Å have a common lower laser level 5s2S1/2, and the anode temperature (metal vapor pressure) dependence of the threshold current of these two laser lines showed a similar tendency.
Fluorescence in lithium neodymium ultraphosphate single crystals
Authors: Yamada Tomoaki , Otsuka Kenju , Nakano Jun'ichi
Published: February 2004

Single crystals of lithium neodymium ultraphosphate (probably LiNdP4O12) were grown by the Kyropoulos method from a melt. The crystal belongs to the orthorhombic system with space group Imma (D2h28), and the Nd content is 4.37×1021 cm−3. Fluorescence and optical absorption were examined. The lifetime of 4F3/2 levels was measured to be 120±10 μs. The effective emission cross section at the line peak (1.047 μ) was found to be (9.0±0.4)×10−19 cm2, which is very close to that of Nd:YAG.
Dynamic dislocation behavior in iron-doped magnesium oxide crystals containing dislocation dipoles
Authors: Singh R. N. , Coble R. L.
Published: February 2004

Edge- and screw-dislocation velocities in iron-doped magnesium oxide single crystals containing dislocation dipoles and 90 ppm iron have been measured as a function of the stress (at stresses below the macroscopic yield stress), temperature, and valence state of the iron impurities to identify the rate-controlling drag mechanisms for dislocation mobility. Edge dislocations have been observed to move faster than screw dislocations in the Fe2+ and Fe3+ valence states over the stress and temperature regimes investigated. The edge and screw dislocations move faster in reduced samples than in oxidized samples. From the analysis of the edge- and screw-dislocation velocity data in terms of the activation parameters (volume, enthalpy, total enthalpy, and the stress exponent of dislocation velocity), it is proposed that the screw-dislocation mobility in MgO single crystals containing dislocation dipoles and 90 ppm iron in the oxidized state is controlled by the interaction of dislocations with noncentrosymmetric defects (FeMg  ·−V″Mg). However, the edge-dislocation mobility in the oxidized crystals is governed by the interaction of the edge dislocations with the dislocation dipoles. Moreover, the edge- and screw-dislocation mobilities in the reduced state are also controlled by the interaction of the edge dislocations with the dislocation dipoles.
Ultrasonic attenuation in spheroidized steel
Authors: Latiff R. H. , Fiore N. F.
Published: February 2004

Theories of grain scattering in single-phase microstructures are briefly reviewed. A discussion of multiphase scattering is given with emphasis on an extension of theory which allows computation of attenuation α in two-phase systems. The expanded theory predicts that α should increase with frequency f and decrease with radius a of the scattering particle at constant scatterer volume fraction. Attenuation measurements made at 7–50-MHz on spheroidized Fe-0.8C steel are described. Attenuation increases as f2 in comparison to the f4 dependence of single-phase grain scattering theory. It also passes through a minimum as a function of tempering time, because of combined grain scattering and particle scattering losses. The magnetic component of attenuation passes through a maximum at 50 MHz as predicted by microeddy current magnetic damping theory.
Small-signal transit-time analysis of a planar mobility-dominated ion sheath
Authors: Oliver B. M. , Smy P. R. , Clements R. M.
Published: February 2004

The effective impedance of a planar collision-dominated ion sheath for frequencies below the electron plasma frequency has been obtained from a solution of the small-signal equations of motion expressed in Eulerian coordinates. The analysis assumes a well-defined sheath boundary and is similar to a previous study by Llewellyn on collisionless diodes. The results of the present analysis show a sheath capacitance component which is highly dependent on the probing frequency relative to the ion transit time in the sheath. Good agreement is obtained between theoretical predictions and experimental measurements of the sheath capacitance as a function of frequency, probe potential, and probe current. The plasma source was the positive column of a high-pressure (10 Torr) helium dc discharge with a plasma electron density between 5 × 1015 and 4 × 1017 m−3 and a temperature ≈ 23 000°K.
Titanium impurity center induced in irradiated silicate glasses
Authors: Arafa S. , Assabghy F.
Published: February 2004

The induced ESR spectra in silicate glasses is examined with particular emphasis on the reported ESR line centered at g∼1.96. This resonance is shown to arise from an induced center associated with titanium which is present in the glass as a trace impurity. The optical absorption band corresponding to this center was observed, at 2.4 eV, in the Gaussian resolution of the induced optical absorption spectrum. It is argued that the interpretation of induced ESR and optical absorption spectra in silicate glasses should take into account this induced titanium center in all glasses whose purity has not been the object of considerable attention.
Properties and structure of B2O3–GeO2 glasses
Authors: Shelby J. E.
Published: February 2004

The viscosity, thermal expansion, and density of B2O3–GeO2 glasses exhibit negative deviations from additivity for all intermediate glasses, whereas the refractive index exhibits positive deviations from compositions. This behavior is due to the changes in the environment of the network-forming units as the over-all composition is varied between GeO2 and B2O3. There is no evidence of macroscopic phase separation in these glasses. It is concluded that all binary glassformer systems should exhibit such deviations from additivity in their properties; however, the nature of these deviations will depend upon the specific glassformers involved.
Optically induced injection of hot electrons into SiO2
Authors: Ning T. H. , Yu H. N.
Published: February 2004

An experiment using the effect of optically induced hot-electron injection in MOS transistor structures to study electron traps in SiO2 films is described. By simultaneously monitoring the gate current and the surface channel conductance shift, information on the trapping efficiency, the capture cross sections, and the trap concentrations could be obtained. Trap centers with capture cross sections differing by more than two orders of magnitude could probably be separated and their cross sections determined depending on their concentrations. Experimental results are presented for electron traps using n -channel silicon-gate structures, with SiO2 layers thermally grown in dry oxygen. Two electron-capture cross sections of 3.3 × 10−13 and 2.4 × 10−19 cm2 were measured. Although there was evidence indicating the presence of other electron traps their capture cross sections could not be unambiguously determined. The injection current can be described by Schottky-emission processes at an effective electron temperature Te. By measuring Te for two substrate resistivities it was concluded that the hot electrons were not at equilibrium with the local electric field as they drifted from the bulk towards the Si–SiO2 interface. The field gradient played an important role in determining the hot-electron energy distribution. This technique could also be used to study hole traps in SiO2 by using p -channel structures.
Flow resistance and electric oscillations in the flux-flow state of Nb-25 at.% Zr wires
Authors: Matsunaga Sakuro
Published: February 2004

The current-voltage (Is-Vs) characteristics of Nb-25 at.% Zr wires with three kinds of strong pinning forces were measured in the region of magnetic field 15–62.4 kOe and temperature 1.95–5.5°K, using a measuring method which controlled the catastrophic transition from the superconducting to the normal state by connecting a shunt resistor of a few micro-ohms with the sample. The Is-Vs characteristics of the sample with strong pinning force showed negative resistance. The negative resistance appears even in the region where Joule heat decreases with the increase of Vs, and it is strongly dependent on the strength of the pinning force rather than the temperature rise by Joule heat. This negative resistance is interpreted as being a negative flux-flow resistance, which appears when the pinning force is strong, as shown from the local model—a modification of the London model by pinning force. The abrupt change of Vs in the Is-Vs characteristics occurs when the absolute value of negative flux-flow resistance is smaller than the shunt resistance. The oscillations of Is and Vs appear in the whole region of negative flux-flow resistance, and the fundamental frequency of Is varies only by strength of the pinning force. The behavior of oscillations depends strongly on the pinning force, which, however, cannot be explained with usual theories.
High-precision measurements of lattice parameter changes in neutron-irradiated copper
Authors: Larson Bennett C.
Published: February 2004

The dose dependence of the lattice parameter change for neutron-irradiated copper has been measured in the range (1.0–10.8)×1018 neutrons/cm2. The lattice parameter changes were measured directly by using a multiply reflecting monochromator, and an analysis of the effects of misalignment in the geometry has been given. The lattice parameter changes, showing a pronounced saturation with dose, were analyzed using second-order elasticity theory applied to the case of dislocation loops.
Electrode erosion by particle ejection in low-current arcs
Authors: Gray Eoin W. , Pharney Julian R.
Published: February 2004

Examination of the electrode damage due to various types of low-current (< 5 A) atmospheric pressure arcs has led to the conclusion that a similar contact erosion mechanism exists for each. These arcs have included high-voltage-gas-breakdown arcs, resistive-make arcs, and both resistive-and inductive-break arcs. Material transfer is considered to result from the ejection of molten metal out of the electrode craters by the recoil force, which follows the abrupt cessation of ion bombardment. In the so-called ``cathode arcs'', i.e., arcs burning predominantly in cathode material, metal droplets have been observed on the anode. In ``anode'' arcs, i.e., arcs burning predominantly in anode material, droplets have been observed on the cathode, an observation that is consistent with the above model using electron instead of ion bombardment.
High-frequency breakdown in ionic crystals
Authors: Holway Lowell H.
Published: February 2004

A Fokker-Planck (F-P) formulation is used to describe electron avalanche breakdown in a high-frequency field. It is shown that the dispersion term dominates the ``average electron'' term. The effect of the statistical fluctuations is to reduce the breakdown field and increase the rate of buildup of the electron population compared to the average electron theory. The F-P coefficients, which are derived for an energy-dependent collision frequency with an arbitrary ratio of laser frequency to collision frequency, are also useful for obtaining energy distributions in the theory of gaseous discharges. Numerical results are obtained for the e-folding time in sapphire based on coefficients which were previously given by Zverev et al. in the context of average electron theory.
Optical absorption and photoluminescence studies of thin GaAs layers in GaAs–AlxGa1−xAs double heterostructures
Authors: Sell D. D. , Casey H. C.
Published: February 2004

A three-layered AlxGa1−xAs–GaAs–Alx Ga1−xAs structure has been used to measure the optical absorption and photoluminescence in thin GaAs layers prepared by liquid-phase epitaxy. The results presented here are for lightly doped n-type GaAs with free-carrier concentrations near 1016 cm−3; however, the technique can be used for arbitrarily doped material. The absorption coefficient α was measured between 1.4 and 2.2 eV at 2 and 298 K. The absorption strength at the band gap was found to be (1.15×104)±1000 cm−1 at 2 K and (0.99×104)±1000 cm−1 at 298 K. At 1.96 eV, the energy of the He–Ne laser commonly used for photoexcitation of GaAs, α at 298 K was measured to be 4.4×104 cm−1. A value of 3.8 meV for the room-temperature exciton binding energy was inferred from the temperature dependence of the interband absorption strength. This value together with previous reflectivity data for high-purity GaAs gives the energy gap of pure unstrained GaAs at 298 K as 1.424±0.001 eV. The effects of strain due to lattice mismatch in the three-layered structures were observed in the absorption edge at 2 K. The calculated photoluminescence spectrum obtained through the principle of detailed balance from the absorption data agrees well with the measured photoluminescence at 298 K. A comparison of the photoluminescence from the excited surface and back surface permits assignment of an upper limit of 5×104 cm/sec for the room-temperature GaAs–AlxGa1−xAs interface recombination velocity for x ≈ 0.5. This comparison of the front and back photoluminescence also shows that the minority-carrier diffusion length at 298 K for a sample with an electron concentration of 2×1016 cm−3 is at least 2.5 μ. The data presented here can be used to calculate the intrinsic carrier concentration ni, the thermal radiative generation rate G, and the radiative constant B (=Rr/np). The values at 298 K (corrected where necessary to a band-gap energy Eg =1.424 eV) are as follows: ni =1.8×106 cm−3, G =4500 cm−3/sec, and B=1.4×10−9 cm3/sec.
Carrier mobilities at weakly inverted silicon surfaces
Authors: Chen J. T. C. , Muller R. S.
Published: February 2004

A theory for carrier mobilities at weakly inverted Si surfaces is described. The theory treats transport of carriers across barriers in regions of statistically variable surface potentials. The potential variations are related to an earlier model proposed by Nicollian and Goetzberger to explain trapping phenomena. Measurements of surface conductance at inverted Si surfaces are presented which extend to lower free-carrier populations than previously reported work. For both p and n surface channels, the measurements show a region of near constancy in mobility at very low surface densities followed by a rapidly increasing mobility at voltages near the conventional inversion threshold. The general features of these measurements and of their temperature variations correlate well with the theoretical model proposed.
Determination of carrier mobilities in semi-insulating GaAs
Authors: Philadelpheus A. Th. , Euthymiou P. C.
Published: February 2004

In a semiconductor in which the effect of mixed conduction is dominant, the determination of carrier mobilities only by Hall measurements is impossible. Magnetoresistance measurements provide the lacking equation which, in conjunction with the expressions for RH and μn in the mixed conduction region, may be used to determine μn and b. As the analytical solution is difficult, we solved the system by an approximative method under the main assumption that b≫1. This method was applied to measurements of semi-insulating Cr-doped GaAs (which is a typical example of a semiconductor in which mixed conduction is dominant), with good results. Further application to intrinsic InSb at room temperature, using known data, confirmed the validity of the method.
Photoplastic effect in alkali halides
Authors: Cabrera J. M. , Agulló-López F.
Published: February 2004

The photoplastic effect first reported by Nadeau has been extensively investigated in colored crystals of NaCl, KCl, KBr, and KI. Detailed data on its dependence on strain level, F-center concentration, strain rate, light intensity, and light wavelength have been obtained. The excitation spectrum of the photoplastic effect follows closely the shape of the F absorption band at room temperature as well as liquid-nitrogen temperature. On the other hand, the magnitude Δτ of the effect fits the law Δτ = C1(1 + C2v/I)−1, v being the average dislocation speed, I the light intensity, and C1 and C2 constants. A theoretical model which takes into account the light-induced formation of an electron cloud around charged moving dislocations is proposed. Quantitative expressions for the dependence of the effect on light intensity and wavelength have been obtained which are in accordance with experimental data. Other implications of this work on light-induced dislocation pinning and dislocation-induced photoconductivity are briefly analyzed.
Multiple scattering from finite inhomogeneous media
Authors: Tang C.C.H.
Published: February 2004

By utilizing the characteristic information on the apparent phase constant difference between the electric and magnetic fields propagating in an inhomogeneous medium, a theoretical analysis on the multiple scattering of electromagnetic waves in finite inhomogeneous media is presented. The solution is obtained by first approximating the coefficients of a pair of exact coupled first-order differential equations and then solving the equations by first-order iteration. The present first-order approximate solution with multiple scattering considerations is shown to be more accurate than the WKB solution. Methods to improve the accuracy of the first-order solution further are discussed. Application of the solution to slowly varying finite media with periodic properties demonstrates the validity of the solution. The same approach can be extended to frequencies in the optical region by retaining additional terms in the coefficients of the coupled differential equations. Further investigations are required to treat the case of oblique incidence in proper perspectives.
Plasma production from solid targets by nanosecond prepulses
Authors: Goldman E. B. , Leising W. , Brauer A. , Lubin M. J.
Published: February 2004

A model of the laser-plasma-solid system is developed to study the dynamics of the laser prepulse interaction with initially solid slabs. Experiments are conducted using aluminum wires and fast-rise ruby lasers and the results are used to verify the theoretical model. The results of numerical experiments are used to investigate the dependence of plasma formation on the prepulse parameters and to find those parameters which lead to efficient coupling of a subsequent giant heating pulse with the target material.
ac properties of biased MIM structures
Authors: Fonash Stephen J. , Roger Jean-Alain , Pivot Jacques , Cachard Alain
Published: February 2004

Metal-insulator-metal (MIM) systems are considered for the general case where there may or may not be interfacial barriers at the metal-insulator junctions. In the analysis developed, the effects of bias are included. The ac properties of such a general system are derived in the analysis. The resulting expressions for the parallel equivalent resistance and the parallel equivalent capacitance exhibit a wide variety of behavior depending on the interplay of the parameters characterizing the system and the bias. As outlined, the expressions presented may be used to extract information concerning the interface regions, the electric field in the interior of the insulator, and the appropriate energy-band model.
Transition temperatures and crystal structures of single-crystal and polycrystalline NbNx films
Authors: Oya Gin-ichiro , Onodera Yutaka
Published: February 2004

Single-crystal cubic NbNx films with thicknesses of a few thousand angstroms were epitaxially grown on cleaved (100) planes of single-crystal MgO plates by the vapor phase growth technique. By heat treatment of some of these films in NH3+H2 or in H2 alone, films having the superlattice structures of Nb4N3, NbN, or Nb4N5 were prepared. The maximum Tc was observed in cubic NbNx. Both Nb4N3 and Nb4N5, the tetragonal phases with long-range-ordered arrangement of vacancies, exhibited superconductivity. NbN1.0 and Nb5N6, both with hexagonal structure, did not exhibit superconductivity down to 1.77 K. As the composition of cubic NbNx became close to stoichiometric, its Tc increased. However, the maximum Tc of cubic NbNx with nearly stoichiometric composition was limited by the lattice instability of cubic NbNx and by the resulting cubic NbNx to hexagonal NbN transformation. It might be expected that a higher Tc for compounds of the NbN family could be obtained if a NaCl-type crystal with less vacancies could exist as a stable or metastable phase at ordinary temperatures.