bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical Slowing of Fluctuations in a Nematic Liquid Crystal
Authors: Litster J. D. , Stinson Thomas W.
Published: February 2004

We have used a high-resolution spherical Fabry-Perot interferometer and a single-frequency laser to measure the time dependence of local fluctuations of order in the isotropic phase of a nematic liquid crystal. We find a critical slowing of the fluctuations analogous to the critical slowing of spin fluctuations in a ferromagnet. The fluctuations relax exponentially with a single relaxation time τ. Over two decades of τ we find that τ∼ (T−Tc)−γ with γ≃43 and Tc slightly below the temperature at which the first-order transition to the nematic phase occurs.
Acoustoelectric Amplification in a Many-Carrier System
Authors: Fischler C.
Published: February 2004

Acoustoelectric amplification, in the linear approximation, is considered for a system containing several types of carriers in the two limiting cases of fast and slow carrier equilibration. The pertinent expressions are first derived for a piezoelectric semiconductor and then expanded to the more practical case of a layered system containing one or more semiconducting layers coupled to a piezoelectric element. An experimental example is given in the form of a guided elastic plate wave in lead zirconate titanate coupled to a plate of near-intrinsic Ge.
Raman Scattering in ZnTe
Authors: Irwin J. C. , LaCombe J.
Published: February 2004

The Raman spectrum of ZnTe has been investigated. The fundamental frequencies have been found to be v̄LO=208.3±0.5 cm−1 and v̄TO= 177.5±0.5 cm−1. The temperature variation of v̄LO has been examined between room temperature and 4°K. The zone boundary frequencies at the critical points X, L, and W have been estimated from the second-order Raman spectrum. In determining these frequencies a theoretical model was used to assist in the assignment of the frequencies and as a check on the consistency of the results. The values obtained were further checked using regularities previously observed in the phonon spectra of zinc-blende semiconductors.
X-Ray Investigation of Solid Helium
Authors: Fain S. C. , Lazarus D.
Published: February 2004

Specimens of hcp 4He used for thermal conductivity measurements have been examined by an x-ray method. This method is described and several Laue photographs are shown. These photographs are an excellent test of specimen quality. The number of reflections observed for high-quality crystals is sufficient for orientation determinations.
Etching of Submicron Pores in Irradiated Mica
Authors: Bean C. P. , Doyle M. V. , Entine G.
Published: February 2004

As discovered by Price and Walker, small uniform pores may be created in muscovite by etching in HF thin samples that have been subjected to fission particle irradiation. The process of pore growth is followed by monitoring the conductance across a thin sample as the etching proceeds. For irradiation with 252Cf the tracks quickly etch to a radius of 33 Å-the region of primary damage. Further radial etching in the undamaged material is slow but increases to a fixed rate as the radius increases. This radius dependence of etching is interpreted by a kinetic analog of the Kelvin equation for vapor pressure over curved surfaces. With suitable assumptions on the mechanism of attack, the surface energy of the muscovite-solution interface is calculated to be about 300 ergs/cm2.
Excess Velocity Potential of the Needle Crystal
Authors: Holzmann Ernest G.
Published: February 2004

Starting with the traditional time-invariant paraboloidal model to represent the diffusion-controlled growth of a needle-shaped crystal in a pure supercooled melt, the effect of thermal imbalance at the solid-liquid interface is calculated. In particular, the diffusion field equations are solved for the initial excess velocity distribution at the interface, on the assumption that the shape constraint is suddenly replaced by the constraint of heat conservation. The computed results show that the hypothetical paraboloid tends to bulge everywhere behind the tip, with a pronounced circumferential peak bulge at one radius from the tip of the needle. The analytical result correlates well with the observed shape of dendritic needle crystals whose side branches protrude from (rather than oscillate about) the paraboloidal root shape. The paper concludes with the suggestion that the formation of side branches may be usefully regarded as the self-induced oscillation of a nonlinear system. To minimize deviations from the law of heat conservation, the analytic model should include traveling interface waves.
Thermodynamics of Crystalline Elastic-Visco-Plastic Materials
Authors: Kratochvil J. , Dillon O. W.
Published: February 2004

The basic objective is the presentation of a description of rate-sensitive plastic materials which agrees with events on the microscopic level and with macroscopic experiments and which is internally consistent. We utilize the framework of the thermodynamics with internal state variables formulated recently by Coleman and Gurtin. The internal state variables in the present theory are considered to be average quantities related to properties of the crystal defects in the material. Rate-dependent phenomena, (e.g., a time-dependent stress-strain relation, creep, etc.) are studied in detail. The theory is illustrated with a simple example.
Diffusion of Cobalt in Beta-Uranium
Authors: Dariel M. P. , Blumenfeld M. , Kimmel G.
Published: February 2004

The solute diffusion of cobalt in beta-uranium was measured using the thin-layer sectioning technique. The results can be expressed by D= 1.54×10−2 exp(−27 450/RT) cm2/sec. The diffusivities of cobalt are higher by about three orders of magnitude than the self-diffusion coefficients in beta-uranium. The possibility of cobalt diffusing by means of the combined substitutional-interstitial mechanism has been examined.
Mass Spectrometer Ion Source with High Yield
Authors: Swingler D. L.
Published: February 2004

An electron impact ion source suitable for use with a quadrupole mass filter is described. Ion formation occurs throughout a relatively large volume since no magnetic field collimation of the ionization electron stream is used. A sensitivity of 8 Torr−1 was obtained for an ion energy of 50 eV rising to a constant sensitivity of 12 Torr−1 for ion energies in excess of 250 eV. Trajectory tracing has been used to give some insight into the efficient operation of the ion source.
Experimental Investigation of the Relative Light Distribution in a High-Pressure Rapidly Alternating dc Glow Discharge
Authors: Hotz R. F.
Published: February 2004

Measurements have been made of the relative light intensity distribution in an rf glow discharge (exhibiting the characteristics of a rapidly alternating dc glow discharge) maintained between copper electrodes in air at atmospheric pressure. Both the spatial distribution and the dependence on time of the light intensity were examined. The face diameter of each electrode was 3 mm and the electrode separation was 0.5 mm± 0.025 mm. All data were taken with a discharge frequency of 0.2 MHz and a discharge current of 0.6 A. Image converter data are presented as well as photomultiplier tube data. The experimental data presented verify that the cathode glow does definitely shift position from one electrode to the other in alternating half-cycles and that essentially a total light turn-off occurs prior to reignition in the next half-cycle.
Reignition Voltage in a High-Pressure rf Discharge
Authors: Schwab H. A. , Hotz R. F.
Published: February 2004

rf glow discharges at high pressure are quenched after every half-cycle and must be reignited in the following half-cycle. The reignition voltage Vi was investigated experimentally in the frequency range 0.15–1 MHz. It was found that Vi grows with electrode distance d up to a certain value dmax. At dmax, Vi decreases distinctly and stays low for a further increase of d. The explanation given for this effect is that at relatively small electrode distances all charge carriers can be removed from the discharge gap before reignition and breakdown must take place without support from space charges. For large d, however, the charge carriers cannot travel through the whole gap in the given time. Some remain in the gap and facilitate breakdown. Therefore a smaller value of Vi can reignite a long gap. The measured frequency response of Vi supports this explanation. A theoretical estimate of values of dmax is within a factor of 1.6 of experimental values.
Charge Separation in a Quasineutral Plasma by Application of an External Voltage
Authors: Schwab H. A.
Published: February 2004

The application of an electric voltage to two electrodes between which a quasineutral plasma is contained results in charge transport and charge separation in the plasma. In this paper, the charge distribution, field distribution, and current density in the plasma resulting from the application of a monotonously increasing voltage are computed. The solution is derived under the assumption that the current in the plasma is essentially ion and electron current, and that displacement current can be neglected.
Analysis of Thermal Induction Plasmas Dominated by Radial Conduction Losses
Authors: Eckert H. U.
Published: February 2004

The energy balance equation is applied to induction plasmas in thermal equilibrium. Approximate, iteration-type, solutions are obtained for cases where heat losses by radiation, axial conduction, and convection can be disregarded. It is assumed that the electric conductivity rises in proportion to the heat conduction potential and that the radial distribution of the induced electric field can be represented by a power law. Under these conditions, the equation can be transformed into Bessel's equation and solved for the heat conduction potential. With a uniform field, the solution reduces to that for a dc arc. The condition of vanishing temperature at the enclosing wall establishes an eigenvalue for the induced electric field at the circumference. Absolute temperature distributions can be calculated as a function of gas properties and applied conditions. It is shown that the latter are given by the time rate of change of primary magnetic flux through the discharge section. The method is applied to argon plasmas at atmospheric pressure. For these plasmas, optimum conversion of magnetic energy into heat should occur at a primary flux rate of 48 V. This value is lowered by the secondary current in the plasma to an actual burning voltage of 32 V. Both values are independent of driving frequency and plasma radius. Skin depth ratio and conversion efficiency at the optimum point agree closely with the values known from induction heating of metals. Experimental data indicate that the discharge has a tendency to operate near this point. Comparison of temperature distributions obtained by this method with exact computer solutions show that the axis temperature is over-estimated by about 15%, but the general shape of the profile is well approximated.
Mechanism of Undamped Output Pulsations in Maser Oscillators
Authors: Dmitrevsky S.
Published: February 2004

A mechanism has been proposed to explain the undamped spiking of the output power occurring in some multilevel maser oscillators. The phenomenon is explained in terms of the coupling between the signal frequency energy storage and the circuit properties at the pump frequency induced by the dependence of the pump level populations on the former. Approximate numerical calculations have shown that the coupling may be strong enough to render the operation of the oscillator unstable. Theoretical results obtained are in qualitative agreement with some of the observed properties of the spiking phenomenon.
Fast Modulator for Extraction of Internal Laser Power
Authors: Maydan D.
Published: February 2004

General design considerations for internal laser acousto-optic modulators are given. Calculations are carried out for the time dependence of the power within the cavity and of the external pulsed power. Based on these calculations, acousto-optic quartz modulators were designed to be inserted inside He–Ne and argon folded cavities. Light pulses, with duration continuously variable from 15 nsec to cw and with repetition rate variable from single pulses to a few MHz have been extracted from the cavities. After dumping out most of the cavity energy, the time required for the internal power to rise from 10% to 90% of its steady-state value is of the order of 3 μsec. With a pulse repetition rate of 1 MHz, the average light power was essentially the same as of the cw power capability of the lasers. The peak power intensity of the scattered light could reach the value of more than 50 times the cw power which was about 5 W for a 100mW He–Ne laser and 100 W for a 2-W argon laser. The ability to pulse modulate the laser power at high repetition rates with negligible sacrifice in average power is important in many applications, including optical memories and laser machining.
New Magnetic Phenomenon in Type-II Superconductors
Authors: LeBlanc M. A. R. , Mattes H. G.
Published: February 2004

The variation of a transverse magnetic field induces a magnetic moment along the axis of a cylinder of a hysteretic type-II superconductor provided that a static axial field is present. We argue that an axial moment appears perpendicular to the inducing field in order to relax the magnetic pressure or Lorentz forces. Our observations show that the induced electric currents do not flow exactly along the direction of the impressed (induced) electric fields.
Design and Operation of Stable rf-Biased Superconducting Point-Contact Quantum Devices, and a Note on the Properties of Perfectly Clean Metal Contacts
Authors: Zimmerman J. E. , Thiene Paul , Harding J. T.
Published: February 2004

Point-contact devices are described which have exhibited long-term stability and reliability. A particular mode of operation of the devices as rf-biased low-frequency detectors is described in detail, including a description of how the device drives a resonant circuit to which it is coupled. In this mode of operation the sensitivity of the devices to low-frequency fields is of the order of 10−9 G per root cycle bandwidth. Perfectly clean contacts were made by breaking a notched niobium member at 4.2°K and then remaking contact at the break. Quantum behavior of such contacts is identical to that of ordinary contacts, but effects of microscopic multiple connections at the contact were not observed.
Quantum Phase Fluctuations in Resistive Circuits Containing Weakly Superconducting Junctions
Authors: Harding J. T. , Zimmerman J. E.
Published: February 2004

Experimental evidence is presented which shows that quantization of the phase integral is not a necessary condition for the occurrence of quantum interference effects in superconducting weak-link circuits. Interference patterns observed with weak-link geometries containing resistive sections differ from their superconducting couterparts only in the effect of Johnson noise which causes a random walk in quantum phase.
Heterodyne Detection with Superconducting Point Contacts and Enhanced Heterodyne Signals from Tightly Coupled Contacts
Authors: Zimmerman J. E.
Published: February 2004

Several modes of operation of point contacts as heterodyne detectors in the frequency range 0 to 1010 Hz were investigated experimentally. A point contact in a superconducting loop, under the application of two externally generated ac fields, behaved as expected on the basis of a model given previously. Likewise, a point contact in a partly resistive loop, in which an externally generated signal is heterodyned with the Josephson oscillation of the contact, gave the expected results. In both cases the heterodyne signal amplitude exhibits a decaying oscillatory (Bessel-function-like) dependence on applied signal level; the heterodyne power at the first peak being approximately 0.1φ02f0/L, where f0 is the heterodyne frequency, L the loop inductance, and φ0 the flux quantum. On the other hand, an anomalously large heterodyne signal was obtained from a pair of closely coupled Josephson-oscillating contacts. No explanation of this result is offered, but it appears that a sort of amplification of the heterodyne signal is effected when the Josephson frequencies are larger than the heterodyne frequency.
Hysteresis Effects in the Superconducting Pb–In Alloy System
Authors: Dubeck L. W. , Aston D. R. , Rothwarf F.
Published: February 2004

A method is presented for transforming hysteretic magnetization curves into their corresponding reversible magnetization curves. This procedure permits the determination of the thermodynamic critical field Hc; the lower critical field Hc1; the upper critical field Hc2; and the Ginzburg-Landau parameters κ1 and κ2, which are found to be equal for each corrected magnetization curve for samples containing up to 28 at.% In. Large, composition-dependent, hysteresis effects are noted in the magnetization curves of these Pb–In samples.
Electroluminescence in Amphoteric Silicon-Doped GaAs Diodes. I. Steady-State Response
Authors: Byer N. E.
Published: February 2004

Steady-state measurements were made of the optical emission and electrical properties of amphoteric Si-doped GaAs diodes. The width of the emitting region of these diodes is explained in terms of a theory involving the drift of electrons across a semi-insulating p-region. At low currents radiative recombination occurs in the p-region within a diffusion length of the junction. However, at high currents a considerable number of injected electrons drift across the p-region and light emanates from the entire p-region. The theory is consistent with the observed I-V characteristics and also with the spreading of the emission into the p-region.
Electroluminescence in Amphoteric Silicon-Doped GaAs Diodes. II. Transient Response
Authors: Byer N. E.
Published: February 2004

An electrical and optical study has been made of the transient response of amphoteric Si-doped GaAs diodes. The luminescent turn-on and turn-off times were found to increase both with decreasing photon energy and with decreasing current drive. These results are consistent with a theory based on the wavy band model in which the recombination is from deep localized donor states and deep localized acceptor states.
Saturation Magnetization and Perpendicular Anisotropy of Nickel Films
Authors: Baron Rinehart , Hoffman R. W.
Published: February 2004

Polycrystalline nickel films between 26 and 296 Å in thickness were obtained by evaporation at normal incidence from tungsten filaments onto microscope-slide glass substrates maintained at 75°C, at pressures between 6×10−10 and 12×10−10 Torr. In the same vacuum the substrates with their films were arranged to be parts of an automated torsion magnetometer in which the sample rotated about an axis in its own plane perpendicular to the magnetic field. Measurements were made of the torque as a function of the magnetic field required to maintain the plane of the sample at various fixed angles θ0 ranging from 3° to 84° with respect to the magnetic field, at sample temperatures of about 300°, 77°, and 4.2°K. The torque data were analyzed by a new method which permits detailed investigation of models for the magnetization. It is shown that for a single-domain model with an out-of-plane uniaxial anisotropy, the saturation magnetization MS and the total anisotropy field S can be calculated from the magnitude and slope of the torque/field curve at any field strength H′ and any angle θ0. The single-domain model was verified for four samples with thicknesses of 87, 109, 182, and 296 Å. For these samples, both MS and S were independent of H′ and θ0. This shows that for films thicker than 87 Å, MS is independent of thickness within the experimental error of ±2%, and has the temperature dependence of bulk material, decreasing by 6.2±1.0% between 4.2° and 300°K. The anisotropy field was completely accounted for by the shape demagnetizing field, and by magnetostriction and strain in nickel film. The torque data from the thinnest film, which was 26- Å thick and electrically discontinuous, did not fit the single-domain model. The characteristic torque behavior of such very thin films probably indicates that they contain islands small enough to be superparamagnetic, This conclusion was supported by a theoretical analysis which showed that a film model consisting of identical, noninteracting, superparamagnetic particles does indeed give rise to torque curves like those of the 26- Å film. If such a superparamagnetic film is erroneously assumed to be a single domain, its MS values appear to be less than the bulk values. Therefore, a detailed analysis of torque curve shapes is required to obtain reliable values for MS.
Acoustic and Magnetic Effects Involving the 19F Nuclei in Antiferromagnetic KMnF3
Authors: Mahler R. J. , James L. W.
Published: February 2004

A simple model which allows spin-½ nuclei in antiferromagnetic crystals to interact with phonons is presented and an order of magnitude calculation predicts the one- and two-phonon effects observed in KMnF3.
Photoplastic Effect in ZnO
Authors: Carlsson Lennart , Svensson Christer
Published: February 2004

A physical model is proposed for the photoplastic effect in ZnO, i.e., the reversible increase in flow strength upon illumination. The model is based on the assumption of Coulomb interaction between dislocations, which are negatively charged, and photoionized traps, which contain excess positive charge. Negative charge on dislocations has been observed in silicon, germanium, cadmium sulfide, and other semiconductors. The excess positive charge appears when interstitial Zn+ atoms are doubly ionized to Zn2+ under the influence of light. Several measurements were made of the photoplastic effect which confirmed the proposed model. First it was found that the photoplastic effect depended on the deformation rate so that at a high strain rate, 5×10−2 sec−1, the effect disappeared, presumably because of the high propagation velocity of the dislocations, which did not allow sufficient time for the photoionization to grow. At lower strain rates, 5×10−4 sec−1, a repeated yielding occurred, also explained by the model. In a second experiment photoconductivity at high dislocation densities was studied. An analysis of the photoconductivity data made it possible to predict the saturation illumination intensity and the time constant of the photoplastic effect. Agreement with the observed values was found. In a third experiment it was found that the flow stress, with and without illumination, depended on the square root of the density of interstitial zinc atoms.
Strength Characteristics of Glass Fibers Under Dynamic Loading
Authors: Armenàkas A. E. , Garg S. K. , Sciammarella C. A.
Published: February 2004

The main purpose of the present investigation was to characterize the behavior of S-glass fibers at quasistatic strain rates. The experimental results presented herein, representing over 1600 individual tests, are a first step in the statistical characterization of fiber properties. It has been established that fiber strength decreases with increasing strain rate. Moreover, the experimental results demonstrate that Weibull distribution can adequately represent fiber strength distribution for quasistatic strain rates. For the type of glass tested, strength was observed to be maximum at or near room temperature (+75°F). The strength dependence on strain rate is greatest at room temperature. At higher or lower temperatures the dependence on strain-rate is not so marked. Tests were also performed to determine the elastic modulus at various temperatures and strain rates. The elastic modulus increases with both an increase in strain rate and a decrease in temperature.
Hardnesses of Carbides and Other Refractory Hard Metals
Authors: Gilman J. J.
Published: February 2004

In a carbide or biboride the excess binding energy associated with metal—metalloid interactions must be overcome for a dislocation to move through the crystal structure. This makes possible a simple calculation of the indentation hardness number in terms of the heat of formation and the molecular volume. Good agreement with measurements is found for twelve representative compounds.
Maker Fringes: A Detailed Comparison of Theory and Experiment for Isotropic and Uniaxial Crystals
Authors: Jerphagnon J. , Kurtz S. K.
Published: February 2004

A complete theory of Maker fringes in nonabsorbing isotropic and uniaxial crystals has been derived which includes all the corrections necessary for making precise determinations of nonlinear optical co-efficients. These corrections include finite beamwidth effects and multiple reflection corrections. Comparison of this theory with extensive experimental data on the Maker fringes in quartz, ADP, and KDP shows agreement to within the experimental accuracy of about 5% on the Maker fringe envelopes and to better than 1% on the coherence lengths. We conclude from this study that a careful analysis of Maker fringes can yield precise values of the nonlinear optical coefficients and coherence lengths in isotropic and uniaxial crystals. This is of great importance in establishing accurate and reliable standards in the field of nonlinear optics.
Interaction of High-Power Ruby-Laser Light Pulses with Metal Colloids in Transparent Crystals
Authors: Kuzmany H. , Ritter G. J.
Published: February 2004

The effects of intense Q-switched ruby laser radiation on the colloidal systems NaCl[Au] and CaF2[Ca] were investigated by microscope and absorption spectroscopy techniques. A dependence of the width and depth of the surface crater on the incident laser pulse energy was established. In the case of NaCl[Au] a shift of the absorption maximum towards shorter wavelengths was observed. This was interpreted in terms of Mie's theory. Calculations on the temperatures generated in the colloids and its surroundings were done using Goldenberg's theoretical results.
Light Microprobe Investigation of Cu2S–CdS Heterojunctions
Authors: Gill W. D. , Bube R. H.
Published: February 2004

The minority carrier diffusion lengths on both sides of Cu2S–CdS heterojunctions have been measured directly by light microprobe techniques. In approximately 1 Ω cm CdS the hole diffusion length was found to be between 3×10−4 and 7×10−4 cm. The high-conductivity Cu2S formed on the CdS by a chemical dip was found to have electron diffusion lengths ranging from ≤1×10−5 to 4×10−5 cm. Light-induced breakdown was observed at small reverse bias for photon energies greater than the CdS bandgap. The reverse breakdown was correlated with visible defects on the junctions where photocurrent gains as large as 2000 were observed. A model for the breakdown is proposed in which Zener breakdown at high-field points along the junction is modulated by photoinjected holes.
Retuning Effects and Dynamic Instability of a Radio-Frequency Capacitive Discharge
Authors: Hatch Albert J. , Heuckroth L. E.
Published: February 2004

A discharge plasma is established in air at pressures of 0.2–20 Torr in the rf electric field between parallel-plate electrodes in a resonant circuit at 14 MHz. By adjusting a calibrated tuning capacitor in parallel with the electrodes, one can observe a wide range of plasma conditions extending from normal extinction at low rf potential and power to an apparent dynamic instability at high potential and power. The loading effect of the plasma is found to be that of a lossy capacitance. Net input rf power to the plasma-loaded circuit at the tuning condition just below the threshold for dynamic instability is found to be ∼10 times that for a plasma maintained at the tuning condition for the resonant circuit without plasma. The retuning effects are discussed on the basis of the nonlinearity of the plasma medium, and a possible mechanism for the dynamic instability is proposed.
Absorption of He–Ne Laser Radiation in an Exploded Lithium-Wire Plasma
Authors: Oktay Erol , Bach David R.
Published: February 2004

Calculations of the absorption coefficients for inverse bremsstrahlung in the field of ions and neutral atoms in ground and excited states and for photoionization are presented for the absorption of He–Ne laser radiation in dense Li plasmas. These are compared with those measured in an exploded Li-wire plasma and the two values differ at most by a factor of five. The electron density and temperature in the plasma are estimated from the time-resolved spectroscopic measurements using the Stark broadening of the Li 6103 line and the intensity ratios of various neutral and ionized Li lines. The plasma diameter and the total neutral atom densities are estimated from the framing and streak pictures of the plasma.
Effect of O+ and Ne+ Implantation on the Surface Characteristics of Thermally Oxidized Si
Authors: Chou N. J. , Crowder B. L.
Published: February 2004

The effects of ion implantation in an MOS structure were investigated. It was found that depending on the choice of implantation parameters, the effects may include: (1) displacement damage in the oxide, (2) creation of fast states and positive fixed charge near the Si/SiO2 interface, and (3) doping in the substrate. MOS capacitance measurements, used in conjunction with isothermal annealing, indicate that the fast states are located in the center of the forbidden gap and are most likely physically associated with point defects created by implantation. In O+ implanted specimens, a residual positive charge was formed after an annealing treatment which removed the fast states. The residual charge is probably attributable to a reoxidation effect during annealing.
Quasistatic Approximation for Semiconductor Avalanches
Authors: Kuvås R. , Lee C. A.
Published: February 2004

A time-dependent differential equation for the average conduction current density in a semiconductor avalanche has been derived in the quasistatic approximation. For generality, unequal ionization rates and drift velocities have been assumed. The functional form of the resulting differential equation is simplified by introducing macroscopic quantities like the multiplication and the intrinsic response time. It is shown that in obtaining the correct quasistatic limit the carrier-induced displacement current must be included, since this current modifies the intrinsic response time and also gives rise to a reactive term. Simplified analytical expressions are obtained for correction factors due to these effects in special cases, e.g., like assuming the ratio between the ionization rates to be independent of the electric field. The modification of the intrinsic response time is shown to be of special importance in the design of avalanche photodiodes. Analytical design criteria for such diodes are given. The small-signal admittance is derived and compared with experimental susceptance measurements. It is shown that a special plot of the data can give a fairly accurate determination of the intrinsic response time, since this plot allows systematic experimental errors to be removed.
Nonlinear Analysis of Multifrequency Operation of Read Diodes
Authors: Kuvås R. , Lee C. A.
Published: February 2004

An analytical development is given for multifrequency operation of avalanche diodes with a narrow ionization layer. The current response from the avalanche is evaluated in the quasistatic limit. The continuity equations are solved separately in the drift regions. The efficiency at the lowest harmonic is derived. It is found to be necessary to limit the generation of carriers due to the positive space-charge resistance of the drift regions. The theoretical results are used to analyze two-frequency operation of two Read diode structures. The analytical approach is quite simple at small and intermediate perturbations. An analog computer program was developed to calculate large signal perturbations. For an effective avalanche width of 0.69-μ optimum efficiencies of 23% and 34% are predicted for single and two-frequency operation, respectively.
Preparation of Zinc Diphosphides and the Low-Temperature Luminescence and Absorption of the Tetragonal Polymorph
Authors: Rubenstein M. , DEAN P. J.
Published: February 2004

The preparation of single crystals of black monoclinic and red tetragonal ZnP2 from the elements is described. The crystals contain 50 to 100 ppm Si as an impurity. The melting point of monoclinic ZnP2 is 992±1°C and of tetragonal ZnP2 is 985±1°C. Interplanar spacings are presented for both the red and black polymorphs of ZnP2. Two bands have been observed in the near-bandgap luminescence of tetragonal ZnP2 at low temperatures. Both bands exhibit sharp lines, respectively, near 2.144 and 2.020 eV, due to no-phonon decay of bound excitons, and contain much fine structure due to associated phonon-assisted transitions. These spectra are identical with luminescence bands reported by Akopyan et al., but are attributed to recombinations in the ternary compound semiconductor ZnSiP2. Preliminary measurements of the indirect-type absorption-edge spectrum at low temperatures indicate that the energy gap of tetragonal ZnP2 is close to 2.220 eV at 4.2°K and ∼2.14 eV at 300°K.
Thermodynamical Limits on the Bandwidth and Conversion Efficiency of Incoherent Recombination Radiation from a Semiconductor Diode
Authors: Feist Wolfgang , Wade Glen
Published: February 2004

The second law of thermodynamics imposes a limit on the maximum efficiency achievable with any rectifier in converting radiation into dc power. By using the second law and Bose photon statistics, a general expression is derived showing that this efficiency depends upon the bandwidth and effective temperature of the incoming radiation. Only for completely coherent radiation can the conversion efficiency be unity. The theoretical implications are illustrated by examining specific thermodynamic cycles involving idealized recombination diodes and thermodynamically ideal rectifiers. The relationship between minimum bandwidth of radiation and bias voltage in a recombination diode is derived. The connection between conversion efficiency and Carnot efficiency is made clear.
Intrinsic Concentration and Heavy-Hole Mass in InSb
Authors: Cunningham R. W. , Gruber J. B.
Published: February 2004

The intrinsic carrier concentration of holes in InSb has been redetermined from the temperature variation of the Hall coefficient without the assumption of acoustic mode scattering. Seven samples were used, three p type and four n type. The best statistical fit to the data yielded ni=5.76×1014T3/2exp(−0.129/kBT)over the temperature range 150°≤T≤300°K. Error analysis indicates ni is accurate to within one percent. The heavy-hole band structure proposed by Kane was used to derive a theoretical expression for the heavy-hole density of states mass which was then estimated from the value of ni determined experimentally. At low temperatures the mass was found to be 0.430 m0 and to increase with increasing temperature. When the mass value reported here was compared to cyclotron resonance data, agreement was obtained.
Study of the Morphology of Epitaxial CdS Films
Authors: Strehlow W. H.
Published: February 2004

Epitaxial films of CdS were grown on CdS, ZnS, GaAs, Ge, mica, and SrF2 substrates using a chemical transport reaction. Electron diffraction, ion blocking and scattering, microscopy, and etch studies of the CdS films were carried out. The surface morphology of the films was studied. A correlation between some structures on the surface of the films and the experimentally and theoretically derived equilibrium forms of CdS crystals was noted. It is concluded that the principal growth mechanism of the epitaxial CdS films is through surface nucleation.
Activation Energy of Holes in Zn-Doped GaAs
Authors: Hill Dale E.
Published: February 2004

The Hall effect and resistivity have been measured as a function of temperature for lightly Zn-doped GaAs of better quality than previously available. Analysis of the Hall coefficient data yields activation energies which change with doping level. These results, along with earlier results on more heavily doped samples, can be represented by EA=0.0308−2.34×10−8(NIA)1/3 eV. The Hall mobility as a function of temperature leads to μL=400(300/T)2.41 for the lattice mobility of p-type GaAs.
Electron Transport in a Space-Charge Field
Authors: Thomas G. , Lin Ping-Kuo
Published: February 2004

The transport of electrons across the space-charge region of a p-n junction is examined by means of the exact solution of the time-dependent Boltzmann equation in which the scattering integral is written in terms of the relaxation time approximation. The relaxation time approximation is only valid for elemental semiconductors over the range of temperatures where the device is normally used, and could also be valid for polar semiconductors but only at high temperatures. It is shown that for transition regions which are thick compared to the mean-free path the effective mobility of the electrons is the high field mobility (exactly the same results are obtained as those derived by Gunn), however when the space-charge region width is less than the mean-free path the distribution function is more nearly that obtained for low fields.
Hot Electron Effects and Saturation Velocities in Silicon Inversion Layers
Authors: Fang F. F. , Fowler A. B.
Published: February 2004

Carrier mobility variations were measured for electrons in silicon inversion layers. Near liquid-helium temperatures and with electron densities less than about 2×1012 cm−2, the mobility increased with field and temperature. Correlation of the electron temperature with field indicates that ΔT varies with the field approximately as F3/2. Temperature dependence of the amplitude of the oscillatory magnetoconductance gave similar consistent results. At very high fields, the mobility decreased at all temperatures and electron densities. The electron drift velocity was measured for different surface orientations, substrate dopings, and ambient temperatures from 4.2° to 300°K. The drift velocity was found to saturate for fields greater than a few times 104 V/cm, depending upon the low field mobility, and was found to be lower than the reported bulk values. For (100), (111), and (110) surfaces, the limiting velocities at 300°K are (6.5±0.5) × 106, (5.5±0.5) × 106, and (4.0±0.5) × 106 cm/sec, respectively.
Investigation of Energy Gain, Resolution, and Harmonics of an Aperiodic Radio-Frequency Mass Spectrometer with 5- and 7-Grid Energy Modulators
Authors: Lall H. B. , Gill P. S.
Published: February 2004

In this work the possibilities of three- and four-stage Bennett-type aperiodic rf mass spectrometers with energy modulators of 5 and 7 grids have been explored. The expressions for the energy gain, resolving power, harmonics, and their relative peak heights have been obtained. The oscillatory behavior of the energy-modulating functions has been analyzed using an IBM 1620 Computer, and graphical representations are given which permit the determination of the energy interval over which the analyzer can be operated. Resolution for the most favored combinations of stage separations has been calculated at Vr1 and 90% values of the retarding voltage level, A grid with improved microoptics and relatively higher ionic transmission coefficient has been developed for use in rf mass analyzers.
Computer Simulation of Vapor Deposition on Two-Dimensional Lattices
Authors: Abraham Farid F. , White George M.
Published: February 2004

Vapor deposition simulation programs have been developed using Monte Carlo methods to determine the molecular dynamics of condensation, evaporation, and migration on the lattice. The simulation methods employed in the programs are developed in detail. The principle application will be to systems that permit a comparison with Honig's work, although the simulation methods are easily applied to a variety of other problems. The results of the simulations demonstrate that Honig's treatment is quite accurate and is a substantial improvement over previous treatments. This agreement also serves to build confidence in the use of Monte Carlo methods in simulating molecular dynamics for vapor deposition studies.
Transport Properties, Microstructure, and Conduction Model of Cosputtered Au–SiO2 Cermet Films
Authors: Miller N. C. , Hardiman B. , Shirn G. A.
Published: February 2004

High-resistivity Au–SiO2 cermet films have been cosputtered. Their transport and structural properties have been examined and a model for electrical conduction is proposed. The electrical resistivity was found to be thermally activated, and the activation energy increased linearly as the metal content decreased. Activation energies varied from 0.01 to 0.07 eV. At a fixed temperature, the resistivity increased exponentially as the weight percent gold decreased. The cermets obeyed Ohm's law. No Hall effect was observed. Transmission electron micrographs showed very small (30–100 Å) discontinuous gold particles separated by very small SiO2 regions. Films were deposited at 20°, 500°, 520°, and 600°C. Gold particle size increased with increasing gold content or with increasing substrate temperature. Only polycrystalline gold was observed by electron diffraction. The typical infrared spectrum of SiO2 was recorded. 20°C cermets annealed at 600°C showed large particle growth and twinning. Electrical conduction in Au–SiO2 cermets is described by a model for conduction in island metal films. Good agreement is obtained between activation energies calculated from measured gold particle diameters and separations, and measured activation energies. From gold particle separations and estimated barrier height, calculations show that charge carriers tunnel through the SiO2. Many other models were considered, but none fit all the experimental relationships.
Long-Term Time-Dependent Conductivity in Alkali Halide Single Crystals
Authors: Harris L. B.
Published: February 2004

A very slow change in the dc conductivity below 200°C of certain alkali halide single crystals, not previously investigated, cannot be understood in terms of current theory of homogeneous crystals, but follows first-order kinetics and correlates with dislocation substructure. Electrical decoration of the dislocation substructure suggests that conduction flow is inhomogeneous, a conclusion confirmed by experiments on bicrystals and on specimens containing subboundaries.
Dislocation Dissociations in hcp Metals
Authors: Mendelson S.
Published: February 2004

Equations are derived for nonplanar dissociations of dislocations in hcp metals. Various components of AB, Aμ, φθ, [AB+φθ], and s′ [AB+φθ] dislocations on the basal, prism, and pyramidal planes meet the criteria for dissociation into twinning partials on{2̄11l} and{1̄01l} planes, and the Burgers vectors of the twinning partials are consistent with minimum shear strain and small atomic shuffling criteria for twinning. The repulsive force γm on each twinning partial is computed using anisotropic elasticity and compared with estimates of the twin lamella distortion energies γ. For [AB+φθ] and φθ dislocations γm is quite large and γm/γ > 1 in many cases. In several cases γm/γ > 1 for dissociation of AB on the basal and prism planes, leading to an increase in dislocation resistance, locking, or twinning at lower temperatures. The results are consistent with the difference in flow behavior of metals like Zr and Ti on one hand and Cd and Zn on the other. Successive dissociations for twin growth and double twinning processes are studied, with the latter shown to be consistent with reported behavior in magnesium.
Maxwell-Wagner Effect in Silver Bromide Emulsions
Authors: Van Biesen J.
Published: February 2004

Dielectric measurements effected on silver bromide emulsions in the frequency range 102−107 Hz show a maximum in the absorption curve. This dielectric absorption is interpreted as a consequence of the conductivity of the interstitials in the AgBr crystals. According to this interpretation, the influence of the morphology and size of the AgBr grains, and of the addition of stabilizing agent on the conductivity of the AgBr grains can be detected in a simple manner. A continuous transition from surface conductivity towards bulk conductivity of the AgBr grain is observed.
New X-Ray Topographic Technique for Detection of Small Defects in Highly Perfect Crystals
Authors: Chikawa Jun-ichi , Asaeda Yuhko , Fujimoto Isao
Published: February 2004

A new topographic method is described to obtain kinematical images of small defects in highly perfect crystals. In this method, x rays diffracted by strain fields around defects are recorded separate from those by perfect regions of crystals. The capability of the method is demonstrated by observing some small defects in a dislocation-free Si crystal which cannot be revealed by Lang and Borrmann topographic techniques. The observed images are due to defects which are revealed as shallow pits by the Sirtl etching. By assuming that the defects are dislocation loops, their sizes are roughly estimated: the majority of the defects is less than 5000 Å in size. It is concluded that the present technique is capable of detecting short-range strains in crystals which are very small compared with extinction distances.
Photometric Study of the Oxygen Diffusivity in an Aluminosilicate Glass
Authors: Lawless W. N. , Wedding Brent
Published: February 2004

The diffusivity of oxygen in an aluminosilicate glass from 630° to 830°C is derived from optical transmission measurements, wherein the rate of bleaching of Ti3+ color centers by the diffusing oxygen at temperature was measured. The finite-thickness solution to the heat equation is used to interpret the data; the oxygen diffusivity on this temperature range can be represented by D=28.4 exp (−39.6±3.4 kcal/RT)cm1/sec. It is concluded that the oxygen diffuses interstitially as molecular oxygen, because the activation energy is smaller than the energy to split an Si–O bond: 50 kcal/mole. As a check on the technique and results, penetration measurements were made on a moving color boundary, with identical results.
Chemical Diffusion in Cadmium Telluride
Authors: Zanio Kenneth
Published: February 2004

The chemical diffusion coefficients of single crystals of cadmium telluride DCdTe were determined as a function of temperature and composition using high-temperature electrical conductivity measurements. In the temperature range 550° to 800°C, DCdTe can be approximated by 4 exp[− (1.15±0.1) eV/kT] and is nearly independent of cadmium partial pressure pCd, for pCd extending over two decades from the cadmium-rich liquidus. The measured and calculated values of DCdTe are in good agreement, and the results favor an interstitial mechanism for cadmium self-diffusion.
Noncontinuum Unipolar Charging of Aerosols: The Role of External Electric Fields
Authors: Brock J. R.
Published: February 2004

An approximate theory is developed for the charging by heavy ions of submicron aerosol particles in external electric fields. The theory proceeds from a nonintuitive basis established by kinetic theory and reproduces the general features found in the relevant experimental data.
Energy Distribution of Electrons Emitted from Silicon Surface-Barrier Diodes
Authors: Itoh Tohru
Published: February 2004

The energy distribution of electrons emitted from surface-barrier diodes made of p-type silicon with aluminum contacts has been investigated in an attempt to clarify the behavior of electrons in a high electric field in silicon. Free electrons have been produced in the p-type silicon by irradiated light and accelerated in the depletion layer of a reverse-biased diode to escape into vacuum from the cesium-treated surface of the thin aluminum contact. Energy distributions of the emitted electrons have been measured under various conditions using the retarding field method. The energy distributions of the electrons in the silicon have been obtained from those of the emitted electrons. They cover the energy region from 1.5 to 4 eV above the conduction-band bottom of silicon. Different energy distributions have been found for [111] and [100] directions of the accelerating electric field. By using Keldysh's theory with known parameters, the mean-free paths of hot electrons between phonon scattering have been determined to be 45 and 52 Å by fitting the experimental energy distributions to the calculated ones for acceleration of electrons in the [111] direction and for acceleration of electrons in valleys of easy acceleration in the [100] direction respectively.