bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural, Magnetic, and Magneto-Optic Properties of Ti-Substituted MnBi Films
Authors: Unger W.K. , Wolfgang E. , Harms H. , Haudek H.
Published: February 2004

Structural, magnetic, and magneto-optic properties of Mn1−xTixBi films (0≤x≤0.2) prepared by a vacuum-evaporation technique are reported. The crystallographic structure and the order of phase transformations of unsubstituted MnBi films were not altered by Ti. Both low-temperature (LT) phase and quenched high-temperature (HT) phase films were oriented with the hexagonal c axis and the magnetization normal to the film plane. The Curie temperature of HT films was decreased by Ti. There is a strong effect of Ti on the kinetics of the crystallographic phase transformations in the films. Particularly, the speed of the HT-phase-to-LT-phase transformation is reduced by up to three orders of magnitude, depending on the Ti concentration and the temperature. At room temperature the specific Faraday rotation of LT (HT) phase films decreased with increasing Ti concentration from 9.8 × 105 deg/cm (4.3 × 105 deg/cm) for x = 0 to 3.8 × 105 deg/cm (1.6 × 105 deg/cm) for x = 0.18, measured with light of 632.8-nm wavelength. The optical absorption coefficient, typically 5.3 × 105 cm−1 at 25°C and 632.8 nm, was not changed appreciably by Ti.
Continuous-Wave Overtone Bands in a CS2–O2 Chemical Laser
Authors: Sadie F. G. , Büger P. A. , Malan O. G.
Published: February 2004

The carbon monoxide overtone band has been observed in a continuous-wave (cw) CS2–O2 chemical laser. A total of fifteen vibrational transitions have been resolved in the region between 2.3 and 2.9 μ. The influence of the total pressure has also been studied.
Solid-Solid Reactions in Pt–Si Systems
Authors: Muta Hiroki , Shinoda Daizaburo
Published: February 2004

Identifications of microscopic compositions in alloyed layers of heat-treated Pt–Si contacts and analysis of chemical kinetics of solid-solid reactions between Pt and Si have been carried out. The layer structure of the Pt–Si contact sequentially changes, through Pt–Pt2Si–Si, Pt–Pt2Si–PtSi–Si, and Pt2Si–PtSi–Si, into PtSi–Si during heat treatment at temperatures ranging from 200 to 500 °C. The rate-determining step of the solid-solid reaction in the Pt–Si system is the interdiffusion process of Pt and Si. The rate constants are well represented by the following Arrhenius relationships: kPt2Si=1.5×10−3 exp(−24 100/RT) cm2/sec and kPtSi=2.5×10−1 exp(−33 900/RT) cm2/sec.
Burgers Vector of Dislocations Generated by Small Stresses in Copper Crystals
Authors: Young F. W. , Sherrill F. A.
Published: February 2004

In an x-ray topography study of the deformation of copper, the dislocations which were generated during the beginning stage of deformation were determined by the external geometry of the crystal in addition to the usual requirements of the maximum resolved shear stress.
Epitaxy at Low Temperatures by Vapor Deposition of Pd, Pt, Rh, and Ir Observed by Field Ion Microscopy
Authors: Graham W. R. , Reed D. A. , Hutchinson F.
Published: February 2004

The minimum substrate temperature required to form epitaxial layers by vapor deposition of Pd, Pt, Rh, and Ir on either Ir or Rh is determined to be 50, 100, 180 and 300°K, respectively, using a field ion microscope. This shows that the minimum temperature increases with the binding energy of the deposited metal. It is suggested that a very few jumps before an incident atom settles in a site, plus the possible displacement of an adsorbed atom by an incident one, will give epitaxy in these fcc metals. Any involvement of foreign adsorbed atoms in the formation of epitaxy is ruled out by the good (<10−9 Torr) vacuum used in these experiments.
Photon Appearance Potential Spectroscopy of Thorium
Authors: Redhead P. A. , Richardson G. W.
Published: February 2004

Evaporated films of thorium on a tungsten substrate have been examined by photon appearance potential spectroscopy (PAPS) with incident electron energies in the range 80–1000 eV (O5 to N3 levels). For low coverage, the peaks corresponding to the O5, O4 and N7, N6 levels were immediately observed. As coverage was increased, these peaks increased slightly and the other O and N peaks appeared suddenly; the N3 was the last to appear. Peak shape and position were independent of coverage. After exposure to oxygen, the major peaks were not significantly shifted but new satellites of the O4, N7, and N6 peaks were observed.
Population Inversion in Laser Plasmas
Authors: Peyraud J. , Peyraud N.
Published: February 2004

We define the conditions for which a population inversion with respect to the ground state, due to recombination at high electron densities, can appear in cold laser plasmas. We point out the interest of giant and short laser pulses for producing such plasmas.
Helium Migration in Glass-Forming Oxides
Authors: Shelby J.E.
Published: February 2004

Permeation, diffusion, and solubility of helium in vitreous B2O3, SiO2, and GeO2 have been measured. The permeability and diffusivity decrease in the order B2O3>SiO2>GeO2, whereas the solubility decreases in the order SiO2>B2O3>GeO2. Differences in the activation energy for diffusion between vitreous SiO2 and GeO2 are due to the greater strain energy necessary to distort the GeO2 structure sufficiently to allow passage of a helium atom from one interstice to another. Changes in the frequency factor for diffusion appear to be primarily related to the activation entropy. The solubility appears to be a function of the distribution of interstice sizes, but cannot be predicted by present techniques.
AlxGa1−xAs Grown-Diffused Electroluminescent Planar Monolithic Diodes
Authors: Shih K. K. , Blum J. M.
Published: February 2004

AlxGa1−xAs p-n junctions have been grown on p-type GaAs substrates by the push-pull liquid-phase-epitaxy method. Zn was subsequently diffused to form planar monolithic grown-diffused p-n junctions which produce high-efficiency light with excellent luminance characteristics. A description will be given of the preparation and processing of the structures. The properties of the epitaxial layers and the grown-diffused p-n junctions will be discussed.
Amorphous Semiconducting 3As2Se3·2Sb2Se3 Films. II. Electrical Properties
Authors: Chaudhari P. K. , Chenette E. R. , Van Der Ziel A.
Published: February 2004

This paper reports measurements on amorphous 3As2Se3·2Sb2Se3 films of electrical conductivity as a function of temperature, applied field, and illumination. The low-field dc conductivity between 230 and 370°K varies exponentially with reciprocal temperature. The steep slope of the data suggests excitation across a mobility gap which has the 0°K value (assuming a symmetrical band model) of 1.64±0.02 eV. Above about 7×104 V/cm, the current increases with the field according to the Poole-Frenkel law I∼exp(βFV1/2), where βF=(1/KBT) ×(q3/πεε0d)1/2. By extrapolating the lnI-vs-V1/2 straight lines at various temperatures to the high-field region, a breakdown field strength of about 2×106 V/cm is found. The trap level, using this field strength, is located at 0.446 eV below the conduction band. The spectral response measured from 0.5 to 0.9 μ suggests an intrinsic-type transport with Eph=1.70 ± 0.02 eV as determined from the wavelength, λ1/2, at which the spectral response reaches half of its maximum value. The results of these measurements, together with those reported in Paper I, are interpreted in terms of a plausible energy-band diagram.
Thermoluminescence Mechanism in Dosimetry LiF
Authors: Christy R. W. , Mayhugh M. R.
Published: February 2004

The high-temperature dosimetry glow peaks in LiF: Mg are thought to result from thermal release of electrons from traps associated with the Mg impurity. There is also evidence, however, that the visible-light emission in the same glow peaks is due to recombination of mobile holes. These observations were reconciled by a mechanism proposed by Mayhugh in which the thermally ionized electron frees a V3-center hole, which then emits a photon at another recombination center. We find that this model is supported by new measurements of Podgoršak, Moran, and Cameron on glow peaks which occur below room temperature.
Transient Thermal Response of Electrical Conductivity Due to Joule Self-Heating
Authors: Barnes Russell H. , Freud Paul J.
Published: February 2004

Calculations of the time-dependent conductance of a sample exhibiting an activated conductivity and undergoing Joule self-heating have been performed for a transient approximation. Measurements of the time-dependent conductance of the compound NixMn3−xO4 using fast-rise-time pulsing are in agreement with the calculated response. A thin-disk cylindrical geometry was utilized.
Steady-state characteristics of a thermally switching cylindrical insulator
Authors: Altcheh L. , Klein N. , Katz I.N.
Published: February 2004

Normalized steady-state temperature and current density distributions and V-I characteristics were determined for thermally switching cylindrical insulators. The results were obtained by solving the equation of conduction of heat by numerical methods, assuming that the electrical conductivity σ obeys the relation σ3=Ae−B/T. Comparison with the analytical solution of the heat conduction equation for the case that σ2=SeaT shows that the two cases differ considerably. In the latter case, on switching, highly concentrated current filaments are formed at relatively small temperature rises. By contrast, in the first case, filaments either do not form, or are much less concentrated, though the temperature rises are relatively large.
Secondary electron emission from scandium, erbium, scandium deuteride, and erbium deuteride under deuteron bombardment
Authors: Wurtz J.L. , Tapp C.M.
Published: February 2004

Secondary electron emission under deuteron bombardment at normal incidence over the energy range 50–170 keV was measured for scandium and erbium metals and their deuterides. Electron yields reported for the metals were taken from surfaces shown by in situ Auger spectroscopy to have a minimum amount of contamination. The secondary ratio at 100 keV was measured to be 1.30±0.05 for scandium and 1.43±0.05 for erbium. Emission coefficients for the deuterides were measured after a moderate vacuum bakeout and are significantly higher than for the metals.
Techniques for the measurement of electron scattering using the de Haas-van Alphen effect: application to dislocations in copper
Authors: Terwilliger D.W. , Higgins R.J.
Published: February 2004

Measurement of the local electronic lifetimes via the de Haas-van Alphen (dHvA) effect depends on the development of reliable techniques for amplitude measurements in well-characterized crystals. Some methods for avoiding both systematic and random errors were developed in a study of the effect of lattice dislocations on the dHvA scattering temperature in copper, using the field-modulation technique. The techniques described here include characterization of crystal purity and microstructure; precise orientation of the crystal in situ; precise field homogenization; control of modulation amplitude; and avoiding errors due to incomplete penetration of the modulation field, magnetic interaction, and magneto-resistance oscillations. In addition, representative amplitude measurements are presented for copper crystals containing a well-defined array of lattice dislocations. The results demonstrate that consistently high values of the scattering temperature typically observed in earlier measurements have an explanation as a dislocation effect. This effect is several orders of magnitude stronger in dHvA measurements than in electrical resistivity, and will therefore be important in any application of the dHvA effect to study scattering problems.
Channeling measurements in As-doped Si
Authors: Haskell J. , Rimini E. , Mayer J.W.
Published: February 2004

Channeling-effect measurements with 1.8-MeV helium ions on silicon samples doped with arsenic to concentrations up to 1.5×1021 atoms/cm3 indicate that greater than 90% of the arsenic atoms occupy substitutional lattice sites. A narrowing of the angular-yield profile is observed for arsenic concentrations in excess of 1020 atoms/cm3. A movement of arsenic atoms off substitutional lattice sites is observed after bombardment with MeV helium ions. The initial rate of movement (1017 As atoms/cm/μC) is independent of the arsenic concentration. In arsenic-diffused samples subjected to prolonged heat treatment at temperatures between 650–900°C an increase is seen in both silicon and arsenic aligned yields. The relative increase in the arsenic aligned yield is less than the relative increase in sheet resistance.
L-S coupling interpretation of high-resolution LMM Auger spectra of Cu and Zn
Authors: Yin L. , Tsang T. , Adler I. , Yellin E.
Published: February 2004

High-resolution LMM Auger spectra of Cu and Zn obtained by x-ray excitation are shown to contain fine structures which have not been reported previously. An attempt has been made to classify these fine structures in terms of pure L-S coupling of the final vacancies of the atom. The agreement between the calculated and the observed energy separations of the fine-structure lines is good within the accuracy of the Hartree-Fock approximation.
Electron paramagnetic resonance of the lattice damage in oxygen-implanted silicon
Authors: Brower K.L. , Beezhold Wendland
Published: February 2004

The nature of the lattice damage produced at room temperature in ion-implanted intrinsic and n-type silicon has been studied as a function of 160-keV O+ ion fluence using electron paramagnetic resonance (EPR). The known EPR spectra observed were the negative divacancy (Si-G7), the neutral vacancy-oxygen (Si-S1), the neutral 4-vacancy (Si-P3), and the isotropic resonance at g = 2.0055 which is indicative of amorphous silicon. In addition, a new spectrum, labeled Si-S2, was observed which may be the negative 4-vacancy. Concentrations (number/cm2) for the various paramagnetic defects were determined as a function of ion fluence for fluences ranging from 1010 to 1017 O+/cm2. From these measurements we conclude that the lattice damage produced in crystalline silicon by individual ions whose maximum calculated energy density into atomic processes is ≲ 15 eV/Å ion consists of simple defects such as observed in electron- and neutron-irradiated silicon. Furthermore, overlap effects in the lattice damage produced by ion implantation are small providing the maximum energy density into atomic processes is ≲ 1.5 × 1019 keV/cm3. For energy densities into atomic processes between ∼ 1.5 × 1019 and ∼ 1021 keV/cm3, there appears to be an accumulation of defect complexes which are characterized by a high concentration of defects whose electrons tend to be delocalized among the defects within the complex. Finally, our measurements indicate that ∼ 1021 keV/cm3 of energy into atomic processes must be accumulated in the form of lattice damage in order to convert crystalline silicon to the amorphous state.
Photostability of polymethine saturably absorbing dye solutions
Authors: Pastor R.C. , Soffer B.H. , Kimura H.
Published: February 2004

We have studied the photostability of polymethine dye solutions with low-power irradiation in the wavelength range 0.38–1.06 μm. The resulting bleaching is essentially reversible. The kinetics of recovery for one of the dyes was studied in detail.
Electro-optic and hydrodynamic properties of nematic liquid films with free surfaces
Authors: Meyerhofer D. , Sussman A. , Williams R.
Published: February 2004

The electro-optic and hydrodynamic properties of unconstrained films of MBBA have been studied using both freely suspended films with two free surfaces and suspended layers having a single free surface. Orientation in the bulk can be different from that at the surface and is influenced by magnetic fields and by flow. Changes in orientation near the surface can account for the observed optical rotation, domain boundaries, and electro-optic effects. At frequencies below the dielectric relaxation frequency, electric fields also give rise to hydrodynamic flow and flow alignment which is demonstrated visually.
Hot-probe measurements of space potential oscillations in a plasma
Authors: Motley R. W.
Published: February 2004

The amplitude and phase of space potential oscillations are readily measured with a hot electron-emitting probe. Measurements performed in a collisional cesium plasma, unstable to drift waves, are presented and compared with linear drift-wave theory.
Mode-coupling effects in thin platelet semiconductor lasers
Authors: Dupuis R. D. , Holonyak N. , Macksey H. M. , Zack G. W.
Published: February 2004

Mode-coupling effects in an active InAsP semiconductor platelet coupled to a passive CdS auxiliary cavity are discussed. A large spectral linewidth is photoexcited (77 °K) in degenerate n-type InAsxP1−x(x [inverted lazy s] 0.13) platelets, and the longitudinal edge-to-edge cavity modes of the InAsP are modulated by the broad spatially orthogonal thin-dimension modes of a CdS platelet coupled to the active sample. In a separate case of a thinner CdS platelet coupled to thin InAsxP1−x, longitudinal edge-to-edge CdS cavity modes split the longitudinal edge-to-edge modes of the active sample and give a reduced mode spacing [Δλ(CdS)<Δλ(InAsP)] determined by the width of the passive auxiliary cavity.
Site occupancy of copper and gadolinium in PbMoO4 single crystals
Authors: Azarbayejani G. H.
Published: February 2004

Optical and electron-spin resonance measurements, at 78 and 300 °K, of copper-doped lead molybdate (PbMoO4) single crystals, with and without gadolinium trace impurity, have shown that: (i) Gd3+ occupies the Pb2+ substitutional site, (ii) copper enters the lattice as both Cu2+ and Cu+ in Gd-free crystals but mostly as Cu+ in Gd-doped crystals, and (iii) Cu2+ occupies several distinct sites, none of which has the S4 symmetry of the sites of either Pb2+ or Mo6+.
Longitudinal electro-optic effects in barium strontium niobate (Bax Sr1−x Nb2 O6)
Authors: Fox A. J.
Published: February 2004

The longitudinal electro-optic effect in ferroelectric tetragonal barium strontium niobate has been investigated in thin 45° plates of composition x = 0.3. The half-wave voltage for the linear electro-optic effect at room temperature is approximately 1 kV. The half-wave voltage decreases as the temperature approaches the transition and reaches a minimum value of about 100 V at 55 °C. The linear effect is observed to become quadratic near the transition and to remain quadratic up to the limit of observation (90 °C). Around the transition temperature the quadratic effect has a low half-wave voltage, and is a slowly varying function of temperature. The high half-wave voltage for the room-temperature linear electro-optic effect is attributed to the occurrence of a strongly nonlinear polarization characteristic. The quadratic effect is thought to occur when the material is in a depoled ferroelectric state or in a degenerate 4̄2m phase.
An analysis of pyromagnetic phenomena: uniaxial ferromagnet in the molecular field approximation
Authors: Bené R. W. , Walser R. M.
Published: February 2004

We present a thermodynamic analysis of the pyromagnetic effect for the case of a ferromagnet with uniaxial anisotropy using the molecular field approximation (MFA). We have divided the response function into a product of terms which we believe gives the best insight into the requirements of a material for a good pyromagnetic detector. In particular, we find that one should use a material with the largest magnetic heat capacity possible. Also, for small fields, we may realize the best detector with H along the hard axis and the pickup along the easy axis. Our analysis suggests that certain of the critical point exponents, as well as the anisotropy power law behavior, may be more easily measured using the pyromagnetic technique.
Dielectric breakdown induced by sodium in MOS structures
Authors: DiStefano T. H.
Published: February 2004

Scanning internal photoemission measurements of several MOS structures, which contained mobile sodium ions, displayed nonuniform contact barriers at the Si–SiO2 interface. A direct correspondence was found between the areas at which the contact barrier was a minimum and the point at which subsequent dielectric breakdown occurred. The direct relationship between barrier reduction and breakdown may result from enhanced electronic injection at the areas with a lower contact barrier.
Finite-difference simulation of an electrical discharge in water
Authors: Robinson James W.
Published: February 2004

The growth of an electrical discharge channel in water has been simulated by a finite-difference solution of the partial differential equations of motion along with the descriptive equations of the medium. The computation is based upon a set of parameters which describe experimentally controllable conditions. Close agreement is obtained between simulations and experiments by adjusting arbitrary parameters included in the description of the medium. However, the simulation is relatively insensitive to these parameters.
Effect of a finite substrate length upon polymer crystal lamellar growth rate
Authors: Lauritzen John I.
Published: February 2004

The polymer crystal lamellar growth rate G is an often-measured property of semicrystalline polymers. In this paper, we investigate the dependence of G upon the length of the substrate, L, the surface nucleation rate of new growth layers per unit length per unit time, i, the velocity with which the growth layer covers the substrate, g, and the thickness of the growth layer, b. For the purposes of this paper, L is the average length where the polymer segments in the substrate are in crystallographic register. We show that G = biL/n̄, where n̄ is the average number of nuclei that contribute to each growth layer. We show that n̄ depends only on the dimensionless parameter z = iL2/4g. We have not obtained n̄ explicitly, but we can place upper and lower limits on n̄ that closely define G in regime I, where G ≃ biL and into a transition region between regime I and regime II where G ∞ b(ig)1/2. The experimental results for several polymers are analyzed and some are found to be in or near regime I, and others in or near regime II.
Transition from primary streamer to arc in negative point-to-plane corona
Authors: Suzuki Toshio
Published: February 2004

This paper reports on measurements with multiple techniques delineating the complete sequence of events from the primary streamer to the arc phase in the common spark transition for relatively small negative point-to-plane gaps applied by pulsed potential. The observations cover a range of gaps, in room air, from 3 to 7 cm long, covering the whole range of potentials from streamer onset to in excess of 30% above the standard sparking threshold. It is shown that starting with the primary streamer, which usually fades in midgap and occasionally crosses the gap, the secondary and tertiary streamers are produced by a succession of ionizing waves of potential and due to an increase of the potential applied across the gap. If overvoltage exceeds 30%, the tertiary streamer comes close to the anode and induces return ionizing waves, which lead to the thermalization of the arc. At lower overvoltages there is a dark phase lasting for about 10 μsec. During the dark period, the resultant positive ions and electrons move separately to the cathode and to the anode. The arrival of these new electrons at the plane causes very fast luminous ionizing waves which lead to the thermalization of the arc. After the last pulse, the thermalization follows through gas heating for a time from 100 to 150 nsec.
Magnetic properties of ErAg
Authors: Nereson Norris
Published: February 2004

Neutron diffraction data from a powder sample of ErAg show two antiferromagnetic transitions at temperatures of 18 ± 1 K and 9.5 ± 0.5 K. The magnetic superlattice reflections for the two structures can be indexed on a tetragonal magnetic cell which has basal plane edges twice that of the chemical cell (am = 2a0) and the same dimension in the unique c-axis direction (cm = c0). Between 18 and 9.5 K the magnetic ordering is similar to HoAg and conforms to a sinusoidally modulated magnetization wave propagating in the 〈100〉 direction with the moments tilted from the c axis at angles ranging from 40° (at 18 K) to 80° (at 10 K). The modulation wavelength of 53 ± 2 Å (7.4am) is incommensurate with the unit chemical cell and is temperature independent. In this incommensurate ordering region the ordered moment increases with decreasing temperature to a maximum value of 6.8μB at T = 10 K. Below 9.5 K, the antiferromagnetic ordering is a commensurate (+ − + −) layer-type structure similar to that of DyAg and TbAg, in which adjacent (110) ferromagnetic planes have oppositely directed moments. The tilt of the moments from the c axis is 85° at T = 9 K and decreases to 75° at T = 4 K. The ordered moment on the Er atom sites is 7.2 ± 0.2μB at T = 4 K.
Barkhausen noise power versus size of a minor hysteresis loop
Authors: Baldwin John A. , Milstein Frederick
Published: February 2004

It has been observed that Barkhausen noise is quite low in the Rayleigh region and that it appears rather abruptly when the hysteresis loop departs from the Rayleigh region. These facts are explained in terms of the interaction between domain walls and crystalline defects. Only defects which have saturated (pressure independent of wall position) contribute to Barkhausen noise. The noise power is proportional to the cube of the defect strength. On a small minor hysteresis loop only weak defects saturate. Thus the noise is low. On large minor loops substantially all defects saturate, and the noise is high. The transition between the two cases is relatively abrupt. The noise is always small near the initial end of a branch of a loop of any size and reaches a maximum at the final end.
Electrical properties of cadmium sulfide thin films in the thickness direction
Authors: Leighton William H.
Published: February 2004

High-resistivity photoconductive thin films of CdS have been obtained by dc sputtering and by dual source evaporation, without the use of post-deposition heat treatments. Light-to-dark conductivity ratios up to 105 have been observed in the films. Spectral response and sensitivity are similar for photoconductivity in the thickness direction and in the plane of the films, but appreciable space-charge effects and current saturation were observed for current flow in the thickness direction. In darkness, the films exhibit space-charge-limited transient current in the presence of a high trap density, while under photoexcitation current flow is linear up to a definite saturation field, and constant at higher fields. The current saturation, attributed to piezoelectric effects in the CdS, occurs at (2–4) × 104 V/cm. Transient currents in excess of the saturation level are observed for short periods of time. Although the dc current-voltage characteristic is linear below saturation, small-signal ac conductivity is proportional to dc current. A model is presented that explains the ac and dc characteristics in terms of a distribution of localized centers in the vicinity of the dark Fermi level of the material. The density of these states is sufficient to suppress space-charge effects in the steady-state photocurrent and dark current by trapping nearly all injected charge in a distance short compared to the film thickness.
Carrier and gain spatial profiles in GaAs stripe geometry lasers
Authors: Hakki B. W.
Published: February 2004

The spontaneous emission generated in the active region of stripe geometry GaAs double-heterostructure (DH) laser diodes is observed through the n-GaAs substrate. The spatial variation of the spontaneous intensity along the junction plane is measured in a direction normal to the stripe axis at current levels below and above lasing threshold. It is observed that the carrier concentration profile is consistent with a model in which carriers out diffuse along the junction plane away from the active region. No evidence has been found of a local depletion of carrier concentration due to regenerative optical oscillations. Analytical expressions for the concentration profiles are obtained from a diffusion model. A comparison of the analytical expressions with experiment yields the carrier diffusion lengths inside and outside of the active region. The computed profiles are in excellent agreement with measurement. From the computed carrier concentration profiles and measurements of mode gain dependence on current it is possible to obtain the spatial variation of local gain in the active region. Coupling of the fundamental optical mode to this nonuniform gain distribution reduces the electronic gain. The lasing threshold of the fundamental mode in the stripe geometry laser is shown analytically to increase as the stripe width is decreased relative to a carrier diffusion length. Finally, the gain dependence on current density has been evaluated and shown to be in agreement with analytical results based on band-to-band recombination in lightly doped active regions.
Q switching a CO2 laser by a plasma
Authors: Box S. J. , John P. K.
Published: February 2004

A transversely excited pulsed CO2 laser is Q switched by means of a plasma. The plasma was produced in an electromagnetic shock tube and was used to cut off the trailing edge of the laser pulse at a predetermined time and Q switch the rest. Up to an order-of-magnitude relative increase in power is obtained for the Q switched portion of the output.
Crystallization of amorphous selenium films. I. Morphology and kinetics
Authors: Kim K. S. , Turnbull D.
Published: February 2004

We report a study of the morphology and kinetics of crystallization of films of a-Se vapor deposited on mica substrates. Morphological examination was facilitated by the complete dissolution of the amorphous component of the films by CS2, while the crystalline component was left essentially intact. Crystallization begins (in the temperature range 30–100°C) with the formation and radial growth of crystalline aggregates, with a cylindrite (two-dimensional analog of spherulite) morphology, at the mica-film interface. Filamentary crystals stem from the less regular regions of these cylindrites and grow upwards through the film. Upon reaching the vicinity of the free surface, some of the filamentary tips develop into cylindrites which grow in and parallel with the free-surface plane. The interface cylindrites were about 500 Å thick and their presence apparently is responsible for the phenomenon of ``visual'' darkening often seen in a-Se films. They are composed of small crystal domains each oriented so that the Se chain axes are parallel with the interface and perpendicular to the disk radius. In the regular morphology, favored by higher-temperature crystallization, the domains are stacked into lamellae which extend radially from the inner regions to the outer edge of the cylindrites. These lamellae are interconnected by less regularly oriented domains and are much thicker and less regular in cross section than the crystals formed by linear polymers. The radial growth rates of the regular interface cylindrites in films of the highest purity were constant in time and quite reproducible at a given temperature. They are among the highest rates reported for a-Se and about two orders of magnitude higher than the corresponding rates for free-surface cylindrites. Their temperature dependence is described by u = 6 × 1015 exp[(− 32.7 kcal/mole)/ RT] cm/sec.
Direct observation of ferroelectric domains in modified PZT ceramics by transmission electron microscopy
Authors: Hardiman B. , Zeyfang R. , Reeves C.
Published: February 2004

Ferroelectric domain configurations and other crystal imperfections in tin-modified PZT ceramics were directly observed by high-resolution transmission electron microscopy. Specimens in both the unpoled and poled conditions were examined. 90° domain walls appear to predominate, and typical examples are given for both cases. The implications of this direct method for development of ferroelectric devices are outlined.
Positive ion and neutral particle sampling in dc discharges of He–SO2–CO and He–SO2–CO2 mixtures
Authors: Kuehn D. G. , Chanin L. M.
Published: February 2004

Mass spectrographic studies have been conducted on the positive ions and neutral species in glow discharges containing 1.0% each of SO2 and CO in helium and also 1.1% each of SO2 and CO2 in helium. Ion species observed in these mixtures included S+, SO+, SO2+, O+, O2+ C+, CO+, and CO2+ with lesser amounts of SO3+, [CO]2+, SCO+, and [SO·CO]+ (or CS2+). The functional dependencies of the various ion and neutral species on pressure and discharge current for He–SO2–CO mixtures were consistent with the interpretation that CO reacted with the SO formed in the discharges to produce CO2 and sulfur. Measurements in He–SO2–CO2 mixtures also indicated the removal of SO2 through the formation of CO2 and S.
Thermal diffusion measurements using spatially periodic temperature distributions induced by laser light
Authors: Eichler H. , Salje G. , Stahl H.
Published: February 2004

Two light waves with different directions of propagation derived from a pulsed Nd:YAG laser are superimposed in an absorbing sample and generate an interference field. Due to absorption, a spatially periodic temperature distribution occurs, producing a spatial modulation of the refractive index which can be considered a thermal phase grating. The light of an argon laser simultaneously incident on the sample is diffracted by the thermal grating. When excitation is over, the decay time of the diffracted light is measured. From this decay time the thermal diffusivity of the sample is determined. Measurements on colored methanol and glycerin as well as on ruby compare favorably with the results of other authors. The possibility of exciting and detecting temperature waves (second sound) in solids by the method of light-induced gratings is discussed.
Binary SiO2–B2O3 glass system: Refractive index behavior and energy gap considerations
Authors: Wemple S. H. , Pinnow D. A. , Rich T. C. , Jaeger R. E. , Van Uitert L. G.
Published: February 2004

A recent investigation of the binary borosilicate glass system has led to the realization of a useful cladding material for pure fused silica core fiber optical waveguides. The feature which makes the borosilicate glass useful is that its index of refraction is sufficiently less than that of pure fused silica to allow light guidance in silica core-borosilicate clad fibers. The previous work offered no explanation for the observed but unexpected behavior of the borosilicate refractive index. Continued studies of this glass system have now led to a quantative explanation of the refractive index behavior. Two theoretical approaches are discussed. One is based on the Sellmeier dispersion model and the other on a molar refractivity analysis. The main quantities of interest turn out to be density, composition, structure, and ionicity. An important prediction based on this work is that properly quenched borosilicate glass can have a refractive index even lower than previously observed. This prediction was subsequently confirmed and has the the practical consequence of allowing the waveguide designer greater latitude in his choice of variables. A further observation is that borosilicate glasses exhibit larger ``energy gaps'' than composite glasses such as soda-lime-silicates, and may therefore be more desirable from the point of view of absorption loss.
Optical-coupling efficiency of GaP : N green-light-emitting diodes
Authors: Bachrach R. Z. , Joyce W. B. , Dixon R. W.
Published: February 2004

Optical-coupling efficiencies of slurry-diced GaP : N green-light-emitting electroluminescent diodes have been measured. Light losses due to absorption in such structures are complicated by the irregular diode geometry, the large refractive index, and the significant energy-dependent optical absorption present in the green spectral region. We show that the optical-coupling efficiency can be represented as a product of the red-emission random-path optical-coupling efficiency and a ratio of the integrated external spectrum to the integrated internal spectrum. Optical-coupling efficiencies of encapsulated green diodes in the range 25 ± 5% have been obtained from the measurements, i.e., three times more light is internally absorbed than is usefully transmitted to the ambient. Unencapsulated diodes have about one-half of this optical-coupling efficiency.
Superconducting properties, electrical resistivities, and structure of NbN thin films
Authors: Shy Y. M. , Toth L. E. , Somasundaram R.
Published: February 2004

Superconducting properties and electrical resistivities of NbN thin films have been studied as a function of sputtering parameters, film structure, and composition. A good correlation exists between superconducting Tc's and film structure and composition regardless of the sputtering conditions used to achieve this structure. The most important parameters affecting Tc are lattice parameter, crystal structure, island structure, and impurity content. Substrate temperature, Ar/N2 ratio, and impurity content are the principal sputtering parameters affecting film structure, and thus Tc.
Determining accurate superconducting tunneling energy gaps: Anisotropy in single-crystal Nb
Authors: Bostock J. , Agyeman Kofi , Frommer M. H. , MacVicar M. L. A.
Published: February 2004

Superconducting tunneling experiments on niobium single crystals with indium and lead-bismuth counterelectrodes show an isotropic energy-gap value of 3.12±0.05 meV, or 3.93kTc, for 26 junction orientations. Self-consistent analysis criteria have been developed for the determination of gap values. These criteria are not met in the existing literature on transition-metal tunneling.
Eddy-current compensating deflection yokes
Authors: Wardly G. A.
Published: February 2004

Three electron beam deflection yoke models have been built to experimentally test the concept of compensated coil pairs. The yokes were placed in three different conductive tubes. Eddy-current compensation was achieved, thus verifying earlier computations of the author. In particular, the uncorrected error of the cross-axial field follows the reciprocal square root of the time following a change in deflection yoke current, and can be neutralized.
Pyroelectric response and D* of thin pyroelectric films on a substrate
Authors: van der Ziel A.
Published: February 2004

The pyroelectric response and the D* of thin pyroelectric films on, a substrate are calculated as a function of the substrate and film thickness. It is found that for low-frequency applications the pyroelectric layer should not be made too thin, preferably several micrometers thick, that the substrate should be as thin as possible, and that the product of its specific heat, density, and heat conductivity should be as small as possible. For thick substrates there is an intermediate frequency region where the value of D* is practically independent of frequency. This intermediate frequency region extends to higher frequencies if the pyroelectric layer is made thinner, but D* decreases with decreasing film thickness in that region.
The detection of fatigue damage by exoelectron emission
Authors: Baxter William J.
Published: February 2004

Plastic deformation of metal enhances the photoelectron emission producing so-called exoelectrons In our experiments the metal surface is scanned by a small spot of ultraviolet light and the electron emission is recorded as a function of position of the light spot. Results for aluminum and steel demonstrate that fatigue deformation produces exoelectron emission after less than 1% of the fatigue life. The regions of emission are very localized; some are beyond the resolution of the apparatus (15 μm). The localized emission increases throughout the fatigue life, and failure finally occurs in the region of most intense emission. The regions of intense emission are attributed to the development and propagation of fatigue cracks.
Melting and freezing behavior of polyethylene oxide
Authors: Warfield R. W. , Hartmann Bruce
Published: February 2004

A compressibility pressure-temperature cycle has been developed for polyethylene oxide (PEO) by which both the melting and freezing points of this polymer are easily determined. It was found that PEO supercools about 10°C and that the pressure dependencies of the melting and freezing points are approximately the same. Using the pressure dependence of the bulk modulus for PEO the Gruneisen constant, γ, was calculated to be about 5 and was found to have an anomalous temperature dependence. It is shown that the Gruneisen constant and the Rao constant are approximately equal and that Wada's rule holds for transitions in which the volume does not change.
Plasmon theory of electron-hole pair production: efficiency of cathode ray phosphors
Authors: Rothwarf A.
Published: February 2004

Fast electrons in solids lose energy primarily to plasmons which subsequently decay into an electron-hole pair. The electron and hole may create additional electron-hole pairs if they have sufficient energy. The average energy to create an electron-hole pair, Ex, is thus given essentially by ℏ ωp/n, where ℏ ωp is the plasmon energy and n is the number of pairs which are created by the plasmon and its decay products. The values of n and hence Ex depend on the ratio ℏωp/Eg, where Eg is the usual band gap in semiconductors and insulators. We have found that for a simple model of direct and indirect materials, sharp thresholds exist for various values of n. For direct-gap materials, n=1 for 1< ℏωp/Eg<4, n=3 for 4< ℏωp/Eg<12, etc. Similar relations for indirect-gap materials have also been obtained. Consideration of phonon losses, effective masses, and problems with k conservation indicate that the changes in n vs ℏωp/Eg should be smoothed for real materials. but not eliminated. Our theoretical values for Ex/Eg allow values lower than previous treatments and give good agreement with known experimental values. Some problems associated with determining the theoretical value of ωp for materials with d electrons are discussed. Some experiments for testing the theory are suggested. The importance of Ex in determining the efficiency of phosphors is also discussed.
Magnetic fields produced by a hollow superconducting cylinder and a coaxial solenoid
Authors: Smith Todd I.
Published: February 2004

Numerical solutions have been obtained for the magnetic field produced by eddy currents induced in a hollow superconducting cylinder by a centered coaxial solenoid. As the dimensions of the cylinder and the solenoid are arbitrary, the solutions are useful in the design of many types of cryogenic apparatus. The results of studies of the performance of superconducting shields as a function of the length-to-diameter ratio, of the effectiveness of a shield in containing the field of an interior solenoid, and of the use of a superconducting cylinder to homogenize the field produced by a solenoid are discussed. The conclusions apply to all thin-walled conducting cylinders as long as the wall thickness is greater than the skin depth at the frequency of interest.
Water adsorption and ice nucleation on silver iodide surfaces
Authors: Fukuta N. , Paik Y.
Published: February 2004

The potentials and the isosteric heats of water adsorption on the basal planes of β-AgI were computed, using 1–4-6–12-type potentials. The heat ranges from 12.5 to 13 kcal mole−1 at low coverage. Using a simple model, it is shown that the lateral interaction among water molecules adsorbed at identical positions (semilayer) lowers the adsorption potential and makes the molecular orientation more random. The interaction between two different semilayers at their minima allows a further and larger reduction in the potential, by as much as 15%, indicating the formation of isolated islands of adsorbed molecules as the coverage increases. Considering the special feature of the potential on the Ag+ exposed surface which is likely to appear at the beginning of photodecomposition of AgI, an explanation is presented for the mechanism of the activated ice nucleation experimentally observed. The results are applied to explain the tendency for random orientation and easier rotation among adsorbed molecules as the adsorption proceeds. It is shown that this easier rotation acquired by the molecules at larger coverage allows the system to practically avoid the entropy effect in ice nucleation.
Study of electron energy relaxation times in GaAs and InP
Authors: Glover G. H.
Published: February 2004

The phenomenological energy relaxation times for electrons in GaAs and InP have been determined as functions of electric field. The results were obtained by interpreting measurements of the differential microwave (34 GHz) conductivity of bulk-grown samples on the basis of a single-relaxation-time model. The low-field values for GaAs and InP were found to be 2.5 and 1.7 psec, respectively. The relaxation times showed monotone-increasing field dependence up to the bulk-effect threshold values, with the most rapid change occurring near those values. The measured results are in accord with theoretical estimates based on energy loss rates for polar optical and intervalley modes. The faster energy relaxation process observed in InP tends to favor slightly a two-level transport model over the three-level model recently proposed.
Infrared laser emission from discharges through gaseous sulfur compounds
Authors: Ultee C. J.
Published: February 2004

Laser oscillation at 1.402 μ has been observed in pulsed discharges through sulfur compounds. The line is assigned to the 4p 3P2 − 3s 3p5 3P2 transition of SI.
Field ion microscope study on the interaction of gallium with metals. II. Alloy formation with molybdenum and anisotropic binding force in Mo3Ga
Authors: Nishikawa O. , Utsumi T.
Published: February 2004

Gallium was deposited on a molybdenum tip by making contact between the tip and liquid gallium in vacuum. Pseudomorphic gallium could not be observed clearly. The product of the Mo–Ga reaction above 600 °C was found to be the ordered alloy, Mo3Ga, with the β-W structure and no other structure was observed. The difference between the crystal structure and the observed image of the (001), (130), (120), and (110) planes of the alloy are explained by the unobservability of the gallium atom and by the variation of the stability of the molybdenum surface atoms. The observed differences in the stability of the surface atoms on these planes are interpreted in terms of anisotropic binding forces in the β-W structure of the alloy.
X-ray diffraction topographs of silicon crystals with superposed oxide film. II. Pendellösung fringes: comparison of experiment with theory
Authors: Patel J. R. , Kato Norio
Published: February 2004

The computational and theoretical procedures developed in the preceding paper are applied to the problem of x-ray dynamical diffraction effects observed at the edges of a thin oxide film thermally grown on highly perfect silicon. The experimental observations have mainly been of the section type which reveal the fine details of the diffraction phenomena as extra hook-shaped ``Pendellösung'' fringes in the silicon crystal. The observed position of the fringes and their phases agree reasonably well with theoretical calculations. Measurements have been made for a number of thicknesses of oxide film grown under different conditions. From the analysis it is possible to evaluate the stress in the film. The results indicate that for oxides grown at different temperatures and under different conditions, the stress in the film is constant. Possible implications of this result with regard to the thermal history of the oxide are discussed.
Theory of the constant property arc
Authors: Whitman Alan M. , Cohen Ira M.
Published: February 2004

The canal model for arc discharges is examined and shown to yield a unique consistent solution when the canal boundary temperature T* is specified as a gas property. Electrical and thermal conductivities are taken as constants appropriate to T*. Solutions are obtained for both cylindrical and planar arc columns. Both are qualitatively similar and show a distinct minimum in the current-electric field characteristic. This is attributed to the competition between the growing arc diameter with current and the increasing conduction to the wall of the dissipated energy. Favorable comparison is shown between this simple model and more exact calculations for arc discharges.