bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation temperature and radiation power of thermal phonon radiators using diamond as transmission medium
Authors: Kappus W. , Weis O.
Published: February 2004

Thermal phonon radiators allow short pulses of incoherent thermal phonon beams to generate in a simple manner and the center frequency of the broad frequency distribution of the emitted phonons to vary up to the acoustic cutoff frequencies. This paper reports experimental investigations of the connection between radiation temperature and radiation power using films of several metals (copper, nickel, gold, and lead) as phonon radiators on diamond. The measured dependencies of the radiation temperature on the radiation power show that the radiation process is by far better described by assuming acoustic mismatch between radiator and transmission medium than using the model of perfect match. Some metals on diamond give a phonon radiation power of several kilowatts per square millimeter radiator area. With a diamond substrate held at liquid-helium temperature, a radiation temperature of a few hundred degrees Kelvin was achieved. If the phonon radiator deposited on diamond is immersed in liquid helium, the transport of heat to the liquid helium becomes important at radiation temperature below 30 °K and is dominant below 20 °K. This effect can be explained by assuming a thin vapor layer between the hot radiator and the liquid helium, and a gas kinetic energy transfer.
Effect of concentration-dependent diffusion coefficients in diffusion couples with fixed surface composition
Authors: Brown L. C.
Published: February 2004

The problem of diffusion coefficients with fixed surface composition and variable diffusion coefficients is considered in the present paper. The rate of solute uptake or loss is given using the same equations as for constant diffusion coefficients taking the diffusion coefficient equal to D lim = approximately the first moment of the diffusion coefficient about the surface composition. When a new phase forms on the surface of the diffusion couple and it has a small composition range the rate of movement of the phase boundary is given by the same equations as for constant diffusion coefficients, but using D̄, the weighted mean diffusion coefficient. As the composition range of the phase increases, the diffusion coefficient to be used deviates towards the value of the diffusion coefficient at the surface. The results are illustrated with calculated single-and two-phase composition profiles for carburization of a steel specimen.
Acoustic surface-wave scattering on a homogeneous three-quarter space
Authors: Munasinghe M. , Farnell G. W.
Published: February 2004

The full-wave solution to the problem of acoustic surface-wave scattering on a homogeneous isotropic three-quarter space of Poisson's ratio σ=0.245 has been obtained by a finite-difference iterative method. The amplitude coefficients for Rayleigh wave transmission and reflection at the 270° corner were found to be 0.28±0.02 and 0.09±0.01, respectively, while the corresponding phase shifts were 140±10° and −125±10°. All of these results, which are independent of wavelength, agree well with previously published experimental and theoretical work. About 90% of the incident energy is lost to body waves and the scattered energy-density pattern indicates that over half of this energy sweeps past the corner and propagates into the body of the medium in the form of bulk modes. Some of the incident energy tends to follow the free surface by swinging around the corner while the reflected wave appears to be launched mainly by the action of a virtual source located at the corner which is excited by the incoming wave and radiates into the three-quarter space. The accuracy of the finite-difference technique has also been verified by comparing the iterated results for Rayleigh wave propagation on a homogeneous isotropic semi-infinite half-space with the analytically exact results. This basic method may be extended to solve problems involving layered geometries.
New carrier-heated electron-hole instability in semiconductor plasmas
Authors: Soltis J. J. , Rowe J. E.
Published: February 2004

A study of the quasistatic hybrid mode in high-electron-mobility semiconductor plasmas subject to perpendicular static electric and magnetic fields shows that when carrier-heating effects are fully taken into account an entirely new mode arises as a result of the carrier heating. This mode has properties suitable for readily generating the two-stream instability and the interaction of this mode with hole-cyclotron harmonics is much stronger than that of any unheated mode.
General properties of electromagnetic scattering by inhomogeneous anisotropic composite obstacles of arbitrary shape
Authors: Okamoto Naomichi , Yamada Ryozo
Published: February 2004

General properties of plane-wave scattering by inhomogeneous anisotropic obstacles of arbitrary shape and of arbitrary number are presented on the basis of the reciprocity relations and the forward-scatter theorem. For the composite obstacles with symmetrical tensor characteristics, it is shown that interchange of the direction of incidence and that of observation keeps the bistatic scattering cross section unchanged on a condition, and that reversion of the incident direction gives the same extinction cross sections (or the same scattering cross sections in case of lossless obstacles) on the other conditions. For the composite obstacles with unsymmetrical tensor characteristics the following results are shown: Interchange of the direction of incidence and that of observation accompanied with transposition of all the tensor characteristics keeps the bistatic scattering cross section unchanged on a condition. Moreover, reversing the incident direction and transposing all the tensor characteristics, we have the same extinction cross sections on the other conditions. In case some of the obstacles are perfectly conducting, we have the same results as before. For the two-dimensional problems which can be decomposed into E wave and H wave, the above-mentioned results hold without condition.
Perturbation solution for shock waves in a dissipative lattice
Authors: Tasi James
Published: February 2004

A perturbation solution is obtained for the propagation of longitudinal shock waves in a one-dimensional dissipative lattice with a velocity step applied to the first mass. The nonlinear part of the elastic interaction force between neighboring particles is assumed to be of parabolic form. Linear dissipation interaction forces are assumed. Within the range of validity of the solution, the dispersive oscillations at the head of the shock wave are found to grow, remain essentially steady, or diminish with distance, depending on the conflicting effects of nonlinearity of the elastic forces and the dissipative forces.
Leaky waves in a heteroepitaxial film
Authors: Hall D. B. , Yeh C.
Published: February 2004

Theoretical as well as experimental investigations were carried out for the propagation of leaky waves along an important class of optical thin-film waveguides. For this type of guiding structure which may consist of heteroepitaxial deposition of ZnS or ZnSe on GaAs, the dielectric constant of the thin film is less than that of the substrate. Consequently, only the leaky type of guided waves may exist. Theoretical results show that the attenuation constants of leaky modes, which may be TE or TM, are inversely proportional to (thickness of layer)3 and directly proportional to (wavelength)2, and that TM modes are more lossy than TE modes. The existence of these leaky modes has also been demonstrated for three different thicknesses.
Profiling of periodic structures (GaAs–GaAlAs) by nuclear backscattering
Authors: Mayer J. W. , Ziegler J. F. , Chang L. L. , Tsu R. , Esaki L.
Published: February 2004

In aiming at an electronic superlattice, epitaxial structures consisting of alternating layers of GaAs and GaAlAs have been grown by molecular-beam evaporation. The technique of He-ion backscattering provides a unique method for the direct and non-destructive profiling of these structures for superlattice layers of a few hundred angstroms if detailed account is made of the backscattering process. The results of Raman spectroscopy and scanning electron microscopy are shown also to furnish complementary information on compositions and thicknesses, respectively. The three techniques give similar results.
Light-wave coupling to optical waveguides by a tapered cladding medium
Authors: Sohler W.
Published: February 2004

A transition from a symmetric to an asymmetric waveguide can serve as a mode- and polarization-dependent light-wave coupler. Coupling experiments with an efficiency up to 70% are reported. Furthermore, total reflection occurs at the transition if the angle of incidence of the guided wave exceeds a critical value. Coupling and total reflection are explained, using the concept of the effective refractive index.
Comment on ``Calibration procedure to correct for the effect of dielectric containers in microwave plasma density measurements''
Authors: Schulz-DuBois E. O.
Published: February 2004

In a recent issue of this journal Wellenstein, Frommhold, and Robertson identified two reasons for systematic error in microwave electron density measurements and described a calibration procedure to eliminate the error. In this paper, use of a polar gas for calibration purposes is recommended and the choice of suitable cavity modes for this measurement technique is discussed.
Temperature dependence of electron drift velocity in silicon
Authors: Haas G. A. , Pankey T. , Harris F. H.
Published: February 2004

Time-of-flight electron drift velocity measurements have been made for Si between 300 and 415 °K in the range of electric fields near the velocity saturation knee. The results show a more pronounced decrease from saturation values at the higher temperatures.
Influence of oxygen on electrical properties of styrene thin film polymerized in a glow discharge
Authors: Morita Shinzo , Sawa Goro , Ieda Masayuki
Published: February 2004

The conductivity and the capacitance of thin polystyrene films polymerized in the atmosphere of a glow discharge were measured in vacuum, argon, oxygen, and air. The conduction current did not change apparently with an introduction of argon, but decreased abruptly with an introduction of oxygen. Such a trend was also found on the capacitance. The concurrent changes in conductivity and capacitance may be due to a reaction of free radical with oxygen. These experimental results can be interpreted as a disappearance of space charge on exposure to oxygen.
Negative electron affinity surfaces on silicon using a rubidium/oxygen dipole layer
Authors: Martinelli Ramon U.
Published: February 2004

Rubidium/oxygen dipole layers have been used to generate negative electron affinity (NEA) surfaces on Si (100). Rb/O layers behave exactly as Cs/O layers with respect to the activation schedule and to the electron emission characteristics. Rb/O layers show the same crystallographic anisotropy as Cs/O layers in that only the Si (100) surface activates to NEA. The spectral photoresponse curves for each layer are identical. The characteristics of the Si/Cs/O and Si/Rb/O surfaces are compared to III-V NEA emitters and to conventional emitters for which an Rb/O surface layer produces a less efficient emitting surface. These results are explained by the fact that the dipole layer on NEA Si (100) is very well ordered with specific sites for the anions and the cations. The geometrical arrangement of the dipole layers most strongly determines their characteristics, as opposed to the chemical nature of the Cs/O or Rb/O compounds. Among other possible substitutes for Cs and O, neither Cs/I, Cs/F, and Cs/S layers nor Na/O and K/O layers produced NEA on Si (100).
Perfectly stirred reactor - new concept for a cw chemical laser
Authors: Osgerby I. T.
Published: February 2004

The concept of a stirred reactor as a cw chemical laser device is described. The system of equations which define the coupled interaction between finite rate chemistry and stimulated emission/absorption processes for a hydrogen/fluorine/helium flame is discussed, and results of preliminary computer calculations are presented. Power output is calculated as a function of mass flow rate per unit reactor volume for several prescribed radiation flux densities in the cavity. Lasing transitions are assumed to occur between the first excited vibrational level and the ground state to simplify the computations. Computed results indicate that significant power output is possible; however, several assumptions were made to make the simplified analysis possible, and experimental verification is essential for further development of the concept.
The system Ga–As–Sn: Incorporation of Sn into GaAs
Authors: Panish M. B.
Published: February 2004

Liquidus isotherms have been determined experimentally and computed with a ``simple solution'' model for the Ga–As–Sn system. Electrical properties of the Sn-doped GaAs crystals grown from the equilibrium liquidus were determined and several incorporation mechanisms inferred. Tin is taken to incorporate primarily as the donor SnGa, and also to a lesser extent as a deep acceptor SnAs·mVGa, with m probably 2. At the temperatures and growth rates used in this work the incorporation of Sn from the liquid phase into the solid is controlled by equilibrium between the liquid and the crystal surface. The incorporation is therefore influenced by the position of the Fermi level at the growing solid surface rather than in the bulk of the crystal. Subsequently, the donors and acceptors associate extensively to form neutral species so that the total Sn in the crystals is much greater than ND +NA.
Rectification, space-charge-limited current, photovoltaic and photoconductive properties of Al/tetracene/Au sandwich cell
Authors: Ghosh Amal K. , Feng Tom
Published: February 2004

Tetracene thin films sandwiched between two evaporated metal electrodes show rectification and photovoltaic effects. The rectification does not follow the J-V equation for Schottky barriers or p-n junctions. A theory is presented to explain the rectification and photovoltaic response. The forward current of the diode (Au positive) is space-charge-limited current (SCLC) and is attributed to hole injection from the gold electrode. The forward current varies as Vl+1/d2l+1, where V is the voltage, d the thickness and 1=(Tc/T)∼3. The SCLC is related to an exponential distribution of traps ∼7×1019/cm3. Other results related with trapping are also presented. No variation of capacitance with voltage is found, indicating that the tetracene film is completely depleted. In the photovoltaic mode, the Au electrode is positive and the Al negative. The photovoltaic current and voltage are related by the relation V=V0(1−e−aJ). The short-circuit photocurrent varies as Fn where n varies between 0.6 and 1 and F is the incident light intensity. This again indicates a possible exponential trap distribution. The open-circuit photovoltage is attributed to the difference in work function of the two electrode materials. Electron microscopy pictures indicate that the tetracene films are possibly polycrystalline. The spectral responses of the short-circuit photocurrent or photocurrent with an applied voltage are different for light incident on the two electrodes indicating the importance of metal/tetracene interface on the carrier generation process.
Self-excited luminescence in GaAs
Authors: Kameda Satoshi , Carr William N.
Published: February 2004

A certain fraction of the photon flux absorbed within the passive bulk of a GaAs photosource results in the creation of further photons. It is the subject of this report to measure the fraction of internal absorption events that do result in the further generation of spontaneous photons at band-edge energy in GaAs. The luminescence described here is a special case of photoluminescence where the source excitation is the same energy range as the resulting generation. We have chosen to call this special case self-excited luminescence (SEL). Measurements using cross- and parallel-axis polarizer pairs are used to measure SEL quantum efficiency. Most GaAs samples tested indicate an SEL efficiency of less than 1% at 300°K. As a check on experimental precision, the photopeak energy of the source excitation was increased by approximately 0.04 eV and the quantum efficiency for the resulting internal luminescence increased to 3.3% at 300°K for one sample.
Electron excitation efficiency of CO2 lasers
Authors: Suhre D. R. , Coleman P. D. , DeTemple T. A.
Published: February 2004

Using a double-excitation-pulse technique, the measured relative excitation efficiency of a CO2 laser as a function of E/p was found to be in qualitative agreement with the theoretical calculation of Nighan for the ν3 mode.
Acoustic radiation from a high coupling cut of lithium niobate
Authors: Daniel Michael R.
Published: February 2004

Conductance and signal measurements are presented for interdigital transducers on rotated Z-cut X-propagating lithium niobate. The +41.5° rotated cut is shown to be a superior one for Rayleigh wave generation compared to the conventional Y-cut Z-propagating material. It has a higher electromechanical coupling constant and noticeably greater freedom from bulk wave generation at least up to the third harmonic Rayleigh wave frequency.
Defect and impurity thermodynamics in rutilelike systems
Authors: DeFord John W. , Johnson O. W.
Published: February 2004

An analysis is presented of the thermodynamics of lattice defects and H or D in rutile. It is shown that the solubility of these imperfections depends strongly on electron Fermi level, which in turn depends on the concentration of the imperfections. A method is presented for using hydrogen solubility to determine conduction band parameters and the energies and densities of electron traps in the crystal. The conditions for obtaining large or small concentrations of H,D or lattice defects are discussed. The use of the method presented depends on an accurate calibration of the oscillator strengths of the H-D ir absorption in rutile. Such a calibration is presented in the following paper.
Twin and antiphase boundary formations in TiNi through inhomogeneous shear mechanism
Authors: Wang Frederick E.
Published: February 2004

The atomic mechanism, based on the previously proposed ``inhomogeneous'' shear, leading to the formation of twinning and antiphase boundaries in TiNi with the CsCl-type structure is described. The twinning mechanism described herein explains the electrical resistivity anomaly due to ``incomplete'' thermal cyclings observed previously in TiNi. This explanation is in keeping, in a qualitative manner, with the ``memory'' effects observed in relation to the electrical resistivity anomaly.
Acoustoelectric effect in piezodielectric semiconductor layered structure
Authors: Kmita A. M. , Medved' A. V.
Published: February 2004

In this paper we report on the observation of acoustoelectric effect (transversal and longitudinal) in the layered structure LiNbO3–Si by means of capacity probes, situated on one side of LiNbO3 thin plate with surface acoustic waves propagating along the opposite side adjacent to the Si plate. These effects arise due to the penetration into the silicon plate of the electric fields of the surface acoustic wave propagating along the LiNbO3 plate. The transversal effect was revealed to be even (i.e., did not change its sign with a reversal of the direction of surface acoustic wave propagation). The longitudinal effect was revealed to be odd. In high-conductivity Si samples (σ≥10−4 Ω−1 cm−1) the transversal effect predominated, in low-conductivity samples the longitudinal effect predominated. Experimental results on the investigation of the transversal acoustoelectric effect as a function of acoustic intensity, conductivity of the silicon specimen, and dc-drift electric field are given. The comparison of these results with the theory of acoustoelectric effect in layered structures is carried out.
Perturbation of a plasma by a focused CO2 laser beam
Authors: Kerr R. D. , Smy P. R. , Offenberger A. A.
Published: February 2004

The perturbation introduced in a plasma by absorption of pulsed CO2 laser radiation has been measured as a function of laser energy and plasma density using a piezoelectric probe. Results have relevance to CO2 laser-plasma diagnostics and gas breakdown.
Corona produced by splashing of water drops on a water surface in a strong electric field
Authors: Phelps Christopher T. , Griffiths Richard F. , Vonnegut Bernard
Published: February 2004

Investigations of corona discharges associated with water drops splashing on a water surface in the presence of a strong vertical electric field are reported. When the ambient electric field strength equals or exceeds a critical value, a hydrodynamic instability occurs at the tip of the jet thrown up during the splash. This instability causes the tip suddenly to assume a conical shape from which corona, characteristic of impulse excitation, is produced. The observed critical field strength is inversely related to the falling drop momentum and is independent of the electric field polarity. The minimum critical field for freely falling drops is approximately 1.8×105 V m−1 for 3-mm-radius drops falling at terminal velocity. A quantity of charge in the range 10−7−10−6 C is liberated by each splash depending on the drop momentum and the field strength. This process should be important in determining the response of the ocean to large rapid electric field changes where it is raining.
On the optimization of energy transfers between a magnetic field of finite extension and a thin conducting plate
Authors: Kant Michel , Mouillet Alain
Published: February 2004

We study the theoretical case of a thin conducting plate, carried at constant velocity (solid plate) or linearly variable (liquid plate), in an external magnetic field of finite extension. We assume the solid plate to be of finite dimensions (length and width); while the liquid plate is supposed to have an infinite width. We introduce the notion of ``complex'' efficiency, using Poynting's theorem, to determine the energy transfer between the plate and the magnetic field. This complex efficiency is composed of two distinct parts: an ``energetic'' efficiency and a ``magnetic'' efficiency. Maximization of these efficiencies defines the magnetic field, ensuring an optimal energy transfer in the given system. The resulting magnetic field appears in the form of two waves travelling at different velocities. For the solid plate, one wave is synchronous to the plate, the other asynchronous and modulated by an even function of the width. When considering the liquid plate, we note that the two waves are asynchronous and that their amplitudes undergo logarithmic variation along the length of the plate. The maximization of active energy, transferred from the plate to the external field, indicates a slight difference between the velocities of the field and the plate; an opposite effect takes place in the case of stored magnetic energy. The greatest power factor of electromagnetic conversion corresponds to an external bipolar magnetic field. This study may prove most useful when applied to the design and construction of coils for diverse electrical systems with open magnetic circuit and/or armature composed of one massive conductor.
Crack propagation in woven fabric
Authors: Freeston W. Denney , Claus William D.
Published: February 2004

The occurrence of crack propagation in flexible fiber assemblies, specifically woven fabric, is studied. The speed of propagation of a strain wave down a constrained filament is analyzed. Expressions for the strain energy released as the crack propagates and the kinetic energy and shear energy of the retracting material are developed, and the physical significance and relationships between the various forms of energy are studied. The effects of fiber and yarn properties, fabric construction, and coating properties on fabric resistance to crack propagation are analyzed. The analysis developed shows that high-modulus fibers woven into fabrics with shear stiffness, e.g., long float weaves, can support the greatest applied load without propagating a crack. In the case of coated fabric, a coating with a low modulus at high shear rates applied in a manner whereby it does not penetrate the fabric structure gives the best performance. However, the most promising method for preventing the propagation of crack in coated as well as uncoated fabric is to use fabric with bundles of large yarns woven periodically in both the warp and filling directions.
Desorption of solid hydrogen by energetic protons, deuterons, and electrons
Authors: Erents S. K. , McCracken G. M.
Published: February 2004

The yield of condensed gas released from liquid-helium-cooled surfaces under particle bombardment has been measured as a function of surface coverage. The yield has been found to increase at low coverage, then become roughly independent of coverage, and finally to decrease at very high coverage. The observed value of the yield has been found to exceed 104 atoms/ion and this value has been explained in terms of a thermal spike model. Where the condensed layer thickness is greater than the range of the incident ions the yield is typically 102−103 atoms/ion. This cannot be explained either by thermal spike or conventional sputtering, and it is suggested that ionization of the condensed gas leads to gas release.
Microwave Faraday rotation and self-focusing of helicon waves in n-InSb
Authors: Tewari D. P. , Pandey H. D. , Agarwal A. K. , Tripathi V.K.
Published: February 2004

Simultaneous propagation of two otherwise independent modes of a magnetoactive medium has been studied, when the power of the modes is high enough to invoke appreciable nonlinearities. A high-mobility sample of n-InSb is chosen and the transverse intensity profiles for both modes are taken to be Gaussian. Even though the presence of either mode affects the propagation of the other considerably, the nonlinearity-induced convergence is very different for the two modes. As a result, the ellipticity of the beam is changed drastically. In the helicon limit the focusing of the propagating mode has been predicted in a length ∼ 1 cm at the axial field intensity of 0.3 esu. This focusing is effective only when |ω−ωc|> ν and ωc/ω<10.
Pulse response of dc electroluminescent ZnS : Mn powdered phosphor
Authors: Yamamoto Ryoichi , Yamazoe Hiroshi
Published: February 2004

Copper-coated ZnS : Mn powdered phosphors which can be excited with dc field were prepared and time responses of electroluminescence to unidirectional rectangular voltage pulses were studied at room temperature. Over the manganese concentration range studied (5×10−4−8×10−3 g/g Mn) emission decay time was found to be nearly proportional to the average nearest distance of Mn2+ to Mn2+ luminescent centers. An electroluminescent panel using the phosphor with 1×10−3 g/g Mn was most efficient under the pulsed voltage which has pulse width of 120 μs and repitition rate of 60 Hz.
Dye laser tuning with pellicles
Authors: Mumola P. B.
Published: February 2004

Thin nitrocellulose membranes (pellicles) are shown to exhibit properties which make them suitable for intracavity tuning elements in high-energy pulsed dye lasers. Uncoated pellicles of 2-μm and 8-μm thickness with surface figures of λ/1 are shown to closely approximate the properties of low-finesse etalons with wide free spectral ranges. Pellicles of 8-μm thickness and coated on both surfaces with 50% reflectivity multilayer dielectrics are shown to be effective as spectral narrowing elements with peak transmission greater than 80% and resultant laser linewidths of 0.57 nm full width at half-maximum (FWHM).
Dependence of threshold and electron lifetime on acceptor concentration in GaAs–Ga1−xAlxAs lasers
Authors: Hwang C. J. , Dyment J. C.
Published: February 2004

Results are presented to show that at threshold the normalized current density increases and the spontaneous electron lifetime decreases, with increasing acceptor concentration in the active region of double heterostructure stripe geometry lasers. It is shown that, regardless of the acceptor concentration in the range from 2×1017 to 3×1019 cm−3, an injected electron density of about 2×1018 cm−3 is needed in order to achieve lasing in a 12-μm-wide stripe laser. Our threshold data confirm earlier experimental results of higher optical loss and a theoretical prediction of lower gain at a given current for heavily doped material. Variations in threshold current density and spontaneous lifetime as a function of acceptor concentration indicate that the laser transition proceeds by a band-to-band recombination mechanism rather than by a band-to-acceptor mechanism.
Luminescence from In0.5Ga0.5P prepared by vapor-phase epitaxy
Authors: Kressel H. , Nuese C. J. , Ladany I.
Published: February 2004

The photoluminescence from n- and p-type In1−xGaxP with x≃0.5, prepared by vapor-phase epitaxy on GaAs substrates, has been studied between 4.2 and 300 K. This material is of particular practical interest because of its close lattice-parameter match with GaAs and direct energy band gap of 1.9 eV. At very low temperatures, four major emission bands have been identified, involving intrinsic recombination, donor—to—valence-band transitions, conduction-band—to—acceptor transitions, and donor-acceptor transitions. The intrinsic recombination dominates in all the samples above about 150 K. The spectra are consistent with a shallow donor ionization energy of 7±1 meV, the same value as in InP. The spectral data of Cd-doped samples (with p varying from 1.8×1016 to 9.3×1017 cm−3) suggest a consistent shift of the Cd acceptor ionization energy to lower values with increasing doping. The extrapolated value for very low doping is 59±2 meV at 50 K. The residual donor density is low in all the p-type samples studied (≲ 1016 cm−3). In the case of highly p-type Zn-doped material, a major new emission band is seen 0.19 eV below the band-gap energy at 77 K and may contribute to the low radiative efficiency of this material. The band is believed to be due to a complex center involving Zn. The photoluminescence data presented for Zn-doped material indicate that the radiative efficiency falls off steeply with increasing doping at 300 K in In0.5Ga0.5P with p > 1018 cm−3, in contrast to the case of GaAs. The relevance of the present data to homojunction laser diode fabrication is discussed.
Electric contacts. I. Application of interference fringe microscopy to electric contact problems
Authors: Cuthrell R. E. , Tipping D. W.
Published: February 2004

The utility of laser interference fringe microscopy is demonstrated in a variety of electric contact problems. The technique is used for quantitative surface topography, measurement of load-bearing areas, lubricant film characterization, wetting angle measurements, and particulate contaminant size determinations.
Maximum frequency of propagation of magnetic bubbles by Permalloy overlay circuits
Authors: Chen Y. S. , Nelson T. J.
Published: February 2004

Experimental evidence is presented in support of a simple model, containing one adjustable parameter, which accounts for the dependence of the limiting frequency of single bubble propagation on bias field, rotating field intensity, and circuit period. The parameter, which characterizes the design of the overlay, is defined as the magnetic pole strength per unit of in-plane field. Having the dimensions of area, it is referred to as the cross section σ. Data taken on the same circuit designs at different periods (λ) confirm the expectation that σ is proportional to λ2. We found σ/λ2=0.016 for T-X circuits, 0.014 for T-Bar circuits, and 0.012 for a 3-bar chevron design.
Eddy currents in flat metal-filled superconducting braids
Authors: Morgan G. H.
Published: February 2004

Flat braids partially soldered together with a soft nonsuperconducting alloy have superior electrical stability and mechanical properties as compared to braids made from fully insulated superconducting wires. Eddy currents induced by a changing field, however, may cause undesirable field shape changes and power loss in magnets. An analysis of these eddy currents for the case of constant rate of change of field is presented, and comparisons made with observed field distortions or power loss in two magnets.
Extension of the analysis for an optical magnetometer to include cubic anisotropy in detail
Authors: Shumate P. W.
Published: February 2004

It has been shown that effective uniaxial anisotropy fields Hk″ of epitaxial magnetic-garnet bubble materials can be found from an optical measurement of the sample's easy-axis susceptibility. The susceptibility is influenced by the cubic anisotropy which the materials possess in addition to their induced uniaxial anisotropy. This paper examines in detail how the optical measurements are affected by various ratios of cubic and uniaxial anisotropies. In particular, it is found that Hk″ can be found accurately using this technique for a wide range of material parameters which includes bubble materials. A procedure which corrects for sample misalignment is presented along with a method by which the cubic and uniaxial anisotropy constants for a material can be calculated from measurements of its Hk″ and magnetization.
Iodination of silver films in the α-Agl phase region
Authors: Shiojiri M. , Hasegawa Y. , Konishi K. , Tsujikura Y.
Published: February 2004

The reaction of iodine with silver at temperatures from 150 to 300 °C has been studied with a quartz crystal microbalance. Below 200 °C, the reaction approximately obeys the parabolic law and the reaction rate decreases with increasing temperature. Above 200 °C, the reaction obeys the linear law and its kinetic energy is roughly estimated to be 5 kcal/mole.
Defect dragging contribution to dislocation damping in electron-irradiated high-purity polycrystalline aluminum
Authors: Seiffert S. L. , Simpson H. M. , Sosin A.
Published: February 2004

A study by internal friction and Young's modulus measurements has been made on high-purity polycrystalline aluminum of the effects on dislocation damping by 1-MeV electron irradiation in the temperature range 78–360 °K. These measurements confirm the presence of an internal friction ``peaking'' effect in aluminum in agreement with the defect dragging model proposed by Simpson and Sosin. In particular it is observed that during electron irradiation and for specific mechanical and thermal histories of the sample, the logarithmic decrement δ increases and later decreases. The increase is found to be generally strain amplitude independent and to be highly structure dependent, disappearing after a suitable high-temperature anneal. Simultaneous modulus measurements show little or no effect due to electron irradiation between 78 and 240 °K, but the modulus increases monotonically for irradiations above 240 °K. The corresponding point-defect kinetics exhibit a complex annealing behavior.
X-ray K absorption edges of alloys. IV. Mn solid solutions with Cu, Ni, Co, and Fe
Authors: Pease Douglas M. , Azároff Leonid V.
Published: February 2004

The x-ray K absorption spectra of the constituent atoms in fcc solid solutions of Mn in Cu, Ni, Co, and Fe show systematic changes taking place with increasing manganese concentration which it is not possible to explain in terms of the rigid-band model for alloys. A decline in the initial rise in absorption with increasing Mn content is observed for all absorption edges except for Mn in Mn–Fe solid solutions, in which case an increase takes place. A tentative explanation, based on hybridization of the outer states upon alloying, is proposed for Mn–Cu and Mn–Ni alloys.
Theory of corrugated distributed-feedback laser
Authors: De Wames R. E. , Hall W. F.
Published: February 2004

A mathematical formalism is presented for calculating the mode spectrum and threshold condition for a corrugated distributed-feedback laser. The procedure is applied to the case where the active medium is bounded by metallic walls. An expression for the coupling constant κ which measures the amount of feedback per unit length is obtained. The complex transcendental equations relating the key parameters are shown to be of the same form as those deduced by Kogelnik and Shank for a periodic index variation.
Correction of calculated vacancy diffusion length at 1000°C in silicon
Authors: Fair Richard B.
Published: February 2004

In attempting to calculate the anomalous transistor profiles published by Ziegler, Cole, and Baglin, it was necessary to assume the shape of the initial B profile. A complementary error function distribution was used, based upon their published junction depth and sheet resistance measurements. However, subsequent measurements of the initial B profile (unpublished results provided by Ziegler) showed that it did not have a complementary error function shape. In this paper, the calculations are repeated using the corrected initial B profile.
Optical detection of magnetic domains in birefringent crystals
Authors: Sage Jay P.
Published: February 2004

An optical detection configuration is described in which a magnetically saturated piece of the same crystal that is under observation is used as a compensating crystal. The mathematical description is simple and general and allows a demonstration of the absolute maximum intensity that can be achieved for the bright domains when the dark domains are totally extinguished. An important practical advantage is achieved because the detector is automatically optimized at all wavelengths regardless of dispersion.
Phonon dispersion relations and thermal expansion of erbium
Authors: Rao R. Ramji , Menon C. S.
Published: February 2004

The lattice dynamics, second- and third-o rder elastic constants, and the temperature variation of the lattice thermal expansion of erbium are worked out on the basis of Keating's method. The ten third-order elastic constants are calculated using four third-order anharmonic parameters. The model used here reproduces the measured pressure derivatives of the second-order elastic constants of erbium well. The low- and high-temperature limits γ̄L and γ̄H of the lattice thermal expansion are evaluated and the calculated γ̄H is compared with that obtained from the thermal expansion and specific heat data. The dispersion relations in erbium are found to be similar to those in holmium.
Heating and melting of a film on a substrate
Authors: Stern Frank
Published: February 2004

Approximate results are given for the time required to melt a film on a thick substrate if the time dependence of the film temperature is known up to the melting point. Results for temperature versus time are given for a uniformly heated film and for a film heated by very strongly absorbed light incident either from the free surface or through the substrate. The calculations assume one-dimensional heat flow, but a simple model with radial heat flow is treated in the Appendix.
Determination of the electric field enhancement factor and crater dimensions in aluminum from scanning electron micrographs
Authors: Hackam Reuben
Published: February 2004

An electron stereoscan microscope is used to examine the surfaces of an aluminum cathode and an aluminium anode which have been subjected to repeated sparkings, under an ultrahigh vacuum (10−9 Torr), at voltages of up to 45 kV. The cathode surface is observed to contain large numbers of protrusions which give rise to an enhanced local electric field at the tip of the protrusions. The field enhancement factor, β, at the microprojections is determined from the scanning electron micrographs. The values of β are in resonable agreement with those obtained from the Fowler-Nordheim theory when applied to the current-voltage measurements in the region prior to breakdown. The anode surface is completely devoid of protrusions and contains large numbers of craters. The diameters and the depths of typical craters are also determined.
Cryogenic thin-film electron emitters
Authors: Onn David G. , Smejtek P. , Silver M.
Published: February 2004

Thin-film electron emitters are described, which operate below 200°K and below a limiting critical applied voltage (νc) in a stable temperature-independent regime. Current-voltage characteristics and normal electron energy distributions are presented. Fabrication and operation criteria are outlined. Comparison with temperature-dependent emitters is made, and possible conduction mechanisms discussed briefly.
Structure and dc electrical properties of a Au–Rh-glass thick-film system
Authors: Biesterbos J. W. M.
Published: February 2004

A study has been made of the structure and the dc electrical properties of a metal-glass thick-film system. The metal part is formed by thermal decomposition of an organometallic solution and consists of Au and Rh. The glass component is a lead boroaluminosilicate. The influence of the firing treatment, of the composition of the metal part, and of the metal-to-glass ratio on the structure and the electrical properties of the film has been investigated. Some glasses, derived from the original glass component, have been used. In this system it is possible to have very small temperature coefficients of resistance in a wide temperature range. Sheet resistances can vary by several orders of magnitude. Under certain conditions the conduction behaves anomalously below 186 K. The different types of conduction in this thick-film system are correlated with the different structures.
Mode structure and beam divergence of a large-bore high-power argon ion laser
Authors: Wang C. P. , Lin Shao-Chi
Published: February 2004

Experimental observations on the mode structure and beam divergence of a large-bore high-power argon ion laser are discussed. The gain medium, 185 cm in length and 12 mm in diameter, is capable of generating a steady-state multiline multimode laser output of more than 125 W in the blue-green. Various stable resonance cavity configurations have been investigated. Littrow prism and small aperture have also been used to obtain single-line and low-order transverse mode operations, respectively. The beam intensity profiles at two widely separated distances from the output coupling mirror are measured by scanning the beam across a small aperture affixed to a photodetector, using a rotating mirror. The two measured beam diameters are found to increase with the transverse mode volume (or output power) at a nearly constant ratio. The far-field beam divergence angle deduced from these measurements is found to vary linearly with the initial beam diameter and to be of the order of 1 mrad at the highest output power.
Transverse phonon-helicon interaction in a semiconductor
Authors: Hsieh H. C.
Published: February 2004

It is shown that under a proper condition the coupling between the left-hand circularly polarized drifting helicon wave and the transverse sound wave, propagating along the applied static parallel electric and magnetic fields in a heavily doped n-type indium antimonide, may lead to the amplification of the helicon wave. The necessary condition for amplification and the condition for the maximum interaction are also derived.
Methyl branches in hydrocarbon crystals: Calculation of relaxation effects
Authors: Farmer B. L. , Eby R. K.
Published: February 2004

A two-site model for a relaxation process has been used in conjunction with the results of illustrative potential-energy calculations on a model system to examine the effects of isolated methyl branches on the chain packing and mechanical relaxations of a linear hydrocarbon host crystal. The results indicate that a branched molecule can be accommodated in an array of linear chains in two different modes of packing and that each mode has two orientations. For one of the modes, the two orientations have nearly equal energies. Upon mechanical deformation of the array, this mode gives rise to a relaxation. The relative strengths are evaluated for different deformations, some of which yield values of the order of those observed experimentally. This relaxation is much weaker for unbranched chains in the planar zigzag conformation.
Vapor-grown tungsten whiskers induced by vacuum discharges
Authors: Okuyama Fumio
Published: February 2004

Characteristic vapor-grown tungsten whiskers on tungsten substrates were studied by means of a field emission and a transmission electron microscope. The whisker growth was found to be induced by high-field vacuum discharges caused by tungsten oxide vapors. By transmission electron microscopy of a typical specimen, evidence was obtained that the whisker growth can be accounted for by the screw-dislocation mechanism of crystal growth.
Materials aspects of thermally addressed smectic and cholesteric liquid crystal storage displays
Authors: Taylor Gary N. , Kahn Frederic J.
Published: February 2004

New improved materials for smectic liquid crystal storage displays are described which have the advantages of image generation at lower laser power, independence of image generation over a wider range of laser scanning speeds, improved contrast, and near ambient temperature (24°C) storage. The electric erase characteristics, laser writing speeds, and contrast are demonstrated to be dramatically dependent on both the smectic liquid crystal and added dopants. Local electric erase is observed only for smectic liquid crystals having a nematic phase or incipient nematic range. Better contrast and a wider range of laser writing speeds are obtained when dopants are added which are soluble in the isotropic phase and insoluble in the smectic phase. Enhanced contrast (higher scattering center density) obtained by adding certain dopants is considered to result from enhanced nucleation in the bulk and stabilization of singularities resulting therefrom by reduction of the associated core and strain energies.
Phase-matched electromagnetic generation and detection of surface elastic waves on nonconducting solids
Authors: Talaat H. , Burstein E.
Published: February 2004

We have generated and detected surface elastic waves at a fundamental frequency of 15.5 MHz on high-resistivity silicon. The generation process involved the Lorentz forces exerted by a static magnetic field on the current-carrying elements of an evaporated aluminum meander line whose spatial periodicity matched that of the surface waves. The detection process involved the motional emf induced by the magnetic field in the vibrating elements of the receiver meander line. The generation-detection signal amplitude shows a B2 dependence and is a maximum when the magnetic field is parallel to the direction of propagation.
Attachment instability in an externally ionized discharge
Authors: Douglas-Hamilton D. H. , Mani S. A.
Published: February 2004

A new type of plasma instability is described in an electron-beam ionized discharge. This instability occurs in the form of current oscillations in gas mixtures in which the dissociative attachment rate increases strongly with electric field. It has been observed experimentally in He : H2O 74 : 2 and in He : CO2 1 : 1 and 9 : 1 mixtures. A theoretical analysis which describes the onset of instability is presented, and a physical explanation is given. The region of instability in parameter space of ionization source function S and electric field E is presented for certain gas mixtures. The transient phenomena in this type of discharge appear to be controlled by electron attachment, and a theoretical explanation of the observed current overshoot has been provided.