bluuebunny/crossref_metadata_2025 huggingface dataset:
Unified approach to the formation of phase holograms in ferroelectric crystals
Authors: Su S. F. , Gaylord T. K.
Published: February 2003

The description of the formation of thick-phase holograms over the entire range of exposures has been accomplished using numerical methods. The internal electric field distributions (and thus the refractive-index profiles for linear electro-optic crystals) generated through diffusion and through drift of charge carriers are calculated. The treatment allows for the presence of an effective electric field due to the photovoltaic effect and an externally applied electric field. The results of this approach reduce to the existing analytic expressions for the limiting cases of the initial and the steady-state stages of hologram formation. This approach establishes the limits of validity for the analytic expressions in terms of exposure and material parameters.
Effects of Zn cross diffusion on the properties of n (AlxGa1−xAs) -p (GaAs) heterojunctions
Authors: Cheung D. T. , Shen C. C. , Pearson G. L.
Published: February 2003

Properties of n (AlxGa1−xAs) -p (GaAs) heterojunctions grown by liquid-phase epitaxial (LPE) techniques were investigated. It was found that an energy barrier in the form of a ’’spike’’ can be formed at the interface as a result of Zn out diffusion from the GaAs layer. When Ge was substituted for Zn as the p-type dopant, no such energy barrier was observed. The results are interpreted in terms of the graded-gap heterojunction model.
Platinum as a lifetime-control deep impurity in silicon
Authors: Lisiak K. P. , Milnes A. G.
Published: February 2003

From transient capacitance measurements of emission rates determinations have been made of the electron capture cross section of the PtI acceptor in n-type Si, and of the hole capture cross sections of the PtI donor and the PtII acceptor in p-type Si. Diffusion length measurements, on a scanning electron microscope, show Pt to be a good lifetime controller in Si (at high carrier injection τn=τp=4.5×10−9 sec for a 1000 °C Pt diffusion). The PtII acceptor is determined to be the lifetime controller and its electron capture cross section is inferred to be 3×10−14 cm2. The generation component of leakage current for Pt-doped diodes is 2 orders of magnitude less than for gold-doped diodes of equal lifetime at 300 °K.
Transient conduction in insulators at high fields
Authors: Arnett P. C.
Published: February 2003

Transient and steady-state conduction in insulators at high fields are studied through a one-carrier single trap level insulator model. It is found that at high fields the conduction-band (electron) density generally produces a negligible field distortion. Therefore, attention is focused on calculating the spatial and temporal behavior of the trapped electron distribution. This behavior, during the initial transient, is dominated under high-injection conditions by trapping and under low-injection conditions by detrapping. By relating the trapped electron distribution to externally measured currents and voltages the trap density and capture cross section can be determined under trapping conditions and the trap depth and insulator dynamic dielectric constant determined under detrapping conditions. Extending the measurements to steady-state conditions facilitates determining the injecting contact-current–field relations and the attempt-to-escape frequency. Thus, all of the parameters of this model are uniquely determinable by experiment. This model has been successfully applied to the study of silicon nitride.
The electrical properties of polycrystalline silicon films
Authors: Seto John Y. W.
Published: February 2003

Boron doses of 1×1012–5×1015/cm2 were implanted at 60 keV into 1-μm-thick polysilicon films. After annealing at 1100 °C for 30 min, Hall and resistivity measurements were made over a temperature range −50–250 °C. It was found that as a function of doping concentration, the Hall mobility showed a minimum at about 2×1018/cm3 doping. The electrical activation energy was found to be about half the energy gap value of single-crystalline silicon for lightly doped samples and decreased to less than 0.025 eV at a doping of 1×1019/cm3. The carrier concentration was very small at doping levels below 5×1017/cm3 and increased rapidly as the doping concentration was increased. At 1×1019/cm3 doping, the carrier concentration was about 90% of the doping concentration. A grain-boundary model including the trapping states was proposed. Carrier concentration and mobility as a function of doping concentration and the mobility and resistivity as a function of temperature were calculated from the model. The theoretical and experimental results were compared. It was found that the trapping state density at the grain bound was 3.34×1012/cm2 located at 0.37 eV above the valence band edge.
Domains in sintered Co-Cu-Fe-Sm magnets
Authors: Livingston J. D.
Published: February 2003

Magnetic domain behavior in a sintered Co-Cu-Fe-Sm magnet was studied using the Kerr effect. Magnetic reversal initiated in thin bands along most grain boundaries and extended from these bands into the interior of the grains. Domain walls were immobile at low fields. Transmission electron microscopy and microprobe analysis were used to supplement the domain studies.
Temperature and compositional dependence of magnetic bubble properties of amorphous Gd-Co-Mo films
Authors: Hasegawa Ryusuke
Published: February 2003

It is shown that the temperature and compositional dependence of the magnetic bubble properties of amorphous Gd-Co-Mo sputtered films can be described satisfactorily by simple models based on mean field analysis of the experimental data. Using the fitting parameters obtained, bubble properties such as 4πMs, l, Q, and Hs (collapse field) are predicted as a function of temeprature for 1-, 0.5-, and 0.25-μm-diam bubbles. Optimum compositions for small temperature derivatives are suggested by this analysis. Some consideration of the dynamic properties for the present ternary films is also given.
Mössbauer studies in the glass system Na2O⋅B2O3⋅Fe2O3
Authors: Raman T. , Nagesh V. K. , Chakravorty D. , Rao G. N.
Published: February 2003

Mössbauer measurements have been carried out in the glass system x Na2O ⋅ 6 Fe2O3 ⋅ (94−x) B2O3 (mole percent) with x varying between 10 and 35 to study the boron anomaly. A sharp decrease of isomer shift has been observed in the composition range between 20 and 25 mole% Na2O. A possible explanation is given on the basis of the existence of nonbridging oxygen atoms in glasses containing alkali ions beyond the above concentration.
Mixed−field measurements on the magnetic semiconductors CdCr2Se4 and HgCr2Se4
Authors: Manasse Fred K. , Kyllonen Eric W.
Published: February 2003

A simplified FMR system based on a solid−state self−oscillating resonant cavity permits simple dc and microwave measurements to be made on the ferromagnetic semiconductors CdCr2Se4 and HgCr2Se4. The interactions between charge carriers and the magnetic spin system in these materials were investigated through dc magnetoresistance measurements and combined electrical and FMR measurements. A technique for making rough Curie temperature approximations based on FMR effects has also been demonstrated using this apparatus.
Photocathodes for use in an electron image projector
Authors: Scott J. P.
Published: February 2003

In this paper factors influencing the choice of photocathode for an image projector are discussed. First of all, a description is given of the principles of operation of an image projector. It is shown that ionic insulators are likely to be the best materials, and the most likely ones are considered. Of these, cesium iodide is the best. In the last section a table is given comparing the observed properties of cesium iodide to those of palladium which has been used up to this time.
Uniform trapping in heat−treated magnesium phthalocyanine sandwich cells
Authors: Morel D. L. , Berger H.
Published: February 2003

Current−voltage dependencies characteristic of uniform trapping are observed in magnesium phthalocyanine sandwich cells with silver electrodes. Annealing the samples promotes them from an α to β phase involving an increase in resistivity of four orders of magnitude which may be attributable to the mobility. The resulting parameters of the system are a Fermi level of 0.373 eV above the valence band, a trap concentration of 2.09×1017/cm3 eV, and a mobility−density−of−states product of 4.22×1011 (cm V sec)−1.
Parametric excitation of plasma oscillations in a Josephson tunnel junction
Authors: Bak C. K. , Kofoed B. , Pedersen N. F. , Saermark K.
Published: February 2003

Experimental evidence for subharmonic parametric excitation of plasma oscillations in Josephson tunnel junctions is presented. The experiments described are performed by measuring the microwave power necessary to switch a Josephson−tunnel junction biased in the zero−voltage state to a finite−voltage state.
Current saturation in AgInSe2
Authors: Tell B. , Kasper H. M.
Published: February 2003

Current saturation has been observed in AgInSe2 for pulsed electric fields greater than ∼700 V/cm. The saturation has been attributed to acoustoelectric interactions and represents the first observation of such effects in a chalcopyrite semiconductor. The saturation occurs for electron drift velocities exceeding (2−3) ×105 cm/sec.
Thickness determination of wet protein microcrystals: Use of Laue zones in cross−grating electron diffraction patterns
Authors: Dorset Douglas L. , Parsons Donald F.
Published: February 2003

The kinematical shape transform is applied successfully to derive crystal thicknesses, using the electron diffraction patterns from tilted crystals of both wet and negatively stained beef−liver catalase.
Coupling coefficients and propagation constants in guided wave distributed−feedback lasers
Authors: Streifer William , Burnham Robert D. , Scifres Donald R.
Published: February 2003

Coupling coefficients and propagation constants in guided−wave distributed−feedback lasers are calculated. It is shown that higher−order transverse modes often have substantially larger coupling coefficients than do low−order transverse modes. Thus, higher−order modes require lower net gains at threshold. Grating spacings which resonate these higher−order modes are calculated and shown to differ significantly from the values appropriate to low−order modes. Higher−order modes also resonate at greater frequency separations, thus facilitating single−mode operation.
Speculation on diffusion−induced work hardening in ionic crystals
Authors: Okongwu D. A.
Published: February 2003

It is postulated that the diffusion potential can induce work hardening in ionic crystals in much the same way as external electric fields. Order−of−magnitude estimates of this diffusion potential yield sufficiently large fields capable of generating and moving dislocations.
On the critical conductive filler loading in antistatic composites
Authors: Janzen Jay
Published: February 2003

Conductive particulate inclusions in a continuous insulating matrix typically impart a precipitous drop in electric resistivity commencing at a threshold volume fraction φcrit which depends on filler particle form and spatial distribution. An illuminating formulation relating threshold composition to the morphology of particles having density ρ is φcrit=1/(1+4ρν), where ν is the readily measurable specific void space in a random dense−packed bed of the (powder) filler. Use of this simple expression permits the first satisfactory semiquantitative rationalization not only of most data obtained recently for model systems comprised of polymer−embedded metal spheres, but also of known behavior of rubbers containing carbon blacks having varied complicated sintered−aggregate (aspherical) morphologies.
Shock−wave compression of single−crystal beryllium
Authors: Pope L. E. , Johnson J. N.
Published: February 2003

Beryllium single crystals were shock loaded by planar impact along the a and c axes as well as along off−axis directions. The orientation of primary (basal), secondary (first−order prism), and tertiary (second−order pyramidal) slip systems, in addition to the relative magnitudes of their yield stresses, permits the study of dynamic yield behavior on each system separately. Slip on the primary system is activated by shock loading in directions which make angles of ϑ=23°−61° with respect to the c axis. The dynamic shear yield strength on the basal plane varies from 0.6 to 1.9 kbar depending on the shock−propagation direction: this effect is thought to be due to differences in compressive strain perpendicular to the basal plane. In all single crystals the rise times of the elastic waves are on the order of a few nanoseconds in contrast to the relatively long rise times reported for shock compression of polycrystalline beryllium. Dynamic yielding on secondary and tertiary planes results in significant stress relaxation behind the elastic wave front. This suggests that dislocations on these planes are undergoing rapid multiplication on a submicosecond time scale. The method of characteristics for rate−dependent material response is used to study dislocation multiplication and plastic wave propagation in crystals shock loaded along the a axis. The phenomenon of multiple plastic wave propagation is also observed and compared with finite−difference solutions for plane shock−wave propagation in anisotropic media. The shock−wave behavior of single−crystal beryllium is more complicated than one would expect on the assumed basis of elastic−perfectly plastic response of the three known slip systems.
Information from measured current in exploding wires
Authors: Phung P. V. , Miles D. O.
Published: February 2003

Measured current waveforms in an RLC circuit are used as a basis for obtaining information on the behavior of wire material at various stages of the explosion. In the premelt region, there is, as expected, complete agreement between measured current and current calculated on the assumption that temperature and resistivity are linear with energy input. After absorption of an energy which under static condition leads to solid−liquid transition, the fit is unsatisfactory but can be improved by treating the wire as a superheated solid for a period of about 20 nsec. During the vaporization stage, resistance and energy are derived from the measured current. If all the energy input is assigned as latent heat of vaporization, the calculated current deviates drastically from the measured current, indicating that for all capacitor voltages used in this study, the process is far from static condition. Furthermore, the higher the energy input rate, the greater the containment forces and the more energy is required to expand a given portion of the wire. A sharp boundary is assumed to separate the unvaporized conducting core from the nonconducting sheath of vapor. The inward displacement of the boundary is determined from calculated data for resistance and energy.
Measurement of thermal conductivity of (neutrally and nonneutrally buoyant) stationary suspensions by the unsteady−state method
Authors: Ahuja Avtar Singh
Published: February 2003

The thermal conductivity of neutrally buoyant suspensions containing polystyrene spheres is shown to decrease with increasing particle concentration and to satisfy Maxwell’s formula up to the investigated concentration of 40% (within the limits of experimental error). However, the thermal conductivity of nonneutrally buoyant suspensions (density difference between suspension components about 1.5%) is shown to be higher (at high concentrations) than predicted by Maxwell’s formula. This is attributed a priori to the wake created by gravity settling of aprticle assemblages. By similarity arguments, the augmentation in the thermal conductivity of unbounded suspensions is seen to be a function of particle concentration, Reynolds number, and Peclet number (both the numbers based on the particle size and its settling velocity). The transient technique (adapted for electrically conducting fluids) was employed in a relative method of determining the thermal conductivity of the unknown liquid relative to
GaAs planar technology by molecular beam epitaxy (MBE)
Authors: Cho A. Y. , Ballamy W. C.
Published: February 2003

GaAs integrated circuits require planar growth of isolated devices on an insulating substrate. A new approach to achieve planar growth has been demonstrated by molecular beam epitaxy (MBE). In the MBE process polycrystalline and monocrystalline GaAs are selectively grown producing a pattern which consists of areas of device−quality single−crystal material isolated by semi−insulating polycrystalline material. The active device positions were defined by windows in SiO2 layers which covered the Cr−doped semi−insulating GaAs substrate.
Characteristics of an argon−laser−pumped ruby laser
Authors: Szabo A.
Published: February 2003

The characteristics of a quasi−cw single−mode ruby laser which is pumped by an argon laser are described. Particular emphasis is given to aspects which govern the linewidth. By heterodyning two independent lasers, linewidths as narrow as 0.5 MHz have been observed, averaged over a few seconds.
60−J 1−nsec iodine laser
Authors: Hohla K. , Brederlow G. , Fuss W. , Kompa K. L. , Raeder J. , Volk R. , Witkowski S. , Witte K.−J.
Published: February 2003

A systems description is given for a two−stage oscillator−amplifier iodine laser setup. Detailed technical data are reported and information is given on the pressure dependence of the oscillator pulse, the gas composition for the oscillator and amplifiers, the small−signal amplification, and the energy storage and energy extraction in the amplifier stages. These performance data demonstrate the suitability of this new laser system for high−energy short−pulse operation.
Thermal activation energy of the gold−acceptor level in silicon
Authors: Engström O. , Grimmeiss H. G.
Published: February 2003

The thermal emission rates of electrons and holes at gold−acceptor levels in silicon have been measured in P+N junctions as a function of temperature using the dark−current transient method. From these measurements the linearly extrapolated absolute zero thermal activation energies of electrons (553 meV) and holes (641 meV) have been determined taking the temperature dependence of the hole capture rate into account. The latter has been determined by measuring the diffusion length at different temperatures. Using earlier optical results which showed that the energy distance of the gold−acceptor center from the conduction band is independent of temperature, the thermal activation energies of electrons and holes are calculated as a function of temperature. These results are to within a few meV in agreement with previously published optical data. Using the principle of detailed balance in thermal equilibrium, values of ctp=1×10−7 cm3/s, ctn=2×10−3 cm3/s, and gA?3.2 are estimated for the capture rates and the degeneracy factor, respectively, at room temperature.
A thin−film ring distributed−feedback laser
Authors: Tsang Won−Tien , Wang Shyh
Published: February 2003

We report the construction and operation of a ring distributed−feedback laser formed by incorporating a periodic structure as part of the plain ring laser. The characteristics of the observed spectrum are in general agreement with theoretical analysis. Mode selection and bandwidth narrowing have been observed.
Optical properties of semiconductor superlattice
Authors: Tsu R. , Koma A. , Esaki L.
Published: February 2003

Reflectivity measurements for a GaAs−AlAs superlattice and a Ga0.5Al0.5As alloy were performed. Analyses of these results permit the determination of both refractive indices and absorption coefficients. The absorption edges for the alloy and superlattice are approximately 2 and 1.63 eV, respectively. A shift of 0.11 eV from the absorption edge of GaAs compares favorably with transport measurements showing that the lowest energy state in such a superlattice is about 0.1 eV above the bottom of the conduction band of GaAs.
Dependence of the characteristics of a photoconductor−dielectric optical converter on photogeneration and charge transfer parameters of the photoconductor
Authors: Rossier D. , Dumont F.
Published: February 2003

The problem of computing the transfer characteristics of an optical converter consisting of an amorphous photoconductor coupled to an electro−optic dielectric has been solved by an iteration method. The total exposure of the photoconductor is considered as the sum of a series of elementary exposures each of which creates a narrow sheet of charge carriers which drift in the photoconductor under the influence of an externally applied field and that of the field due to the trapped carriers situated in the photoconductor and at the photoconductor−dielectric interface. The performance of the converter is shown to be limited by the charge trapping of the carriers and by the field−dependent photogeneration efficiency. Comparison of the results of the calculation with the measured characteristics of the Phototitus converter permits to make an estimate of the range of electrons and holes in amorphous selenium, at the
Amalgamation in the Ag3Sn−Hg system. II. Strength analysis and stage 3
Authors: Reynolds C. L. , Wawner F. E. , Wilsdorf H. G. F.
Published: February 2003

The tensile strength of Ag3Sn amalgams has been measured as a function of time. There is an initially low strength due to the presence of liquid in the specimens. The strength curve is then shown to consistently rise up to 3 h, after which there is a significant increase in strength up to 6 h. This is postulated to result from the merging of the new phases with the undissolved Ag3Sn. Scanning electron micrographs are presented which confirm this. It has also been shown that the mode of fracture changes from interparticle initially to intraparticle in the later stages.
Amalgamation in the Ag3Sn−Hg system. III. Resistivity measurements
Authors: Reynolds C. L. , Wilsdorf H. G. F.
Published: February 2003

The relative resistivity change of Ag3Sn amalgams has been measured as a function of time. These measurements have been shown to be useful in obtaining information on the amalgamation process and are consistent with strength measurements presented earlier. As the bonding between the matrix phases and spherical Ag3Sn particles increases, the resistivity decreases and reaches a minimum approximately 7−8 h after the initiation of trituration. There is then a gradual increase in resistivity due to the formation of porosity in the matrix phases. A complete mechanism for the amalgamation of Ag3Sn has been given.
Further studies of electron emission areas on electropolished copper surfaces in vacuum
Authors: Farrall G. A. , Owens M. , Hudda F. G.
Published: February 2003

A lead transfer technique described in an earlier publication has been applied to the problem of locating electron emission areas on broad−area electrodes in vacuum. The objective of this work is to identify and analyze microscopic emission areas on electropolished copper and to determine their Fowler−Nordheim characteristics. The results suggest that insulating inclusions play an important part in the emission from such surfaces and indeed have emission characteristics which are similar to those expected for metallic emitters.
ac (50 Hz) and dc electrical breakdown of vacuum gaps and with variation of air pressure in the range 10−9−10−2 Torr using OFHC copper, nickel, aluminum, and niobium parallel planar electrodes
Authors: Hackam Reuben , Altcheh Leo
Published: February 2003

Breakdown potentials of vacuum gaps are measured over a wide range of air pressure using both direct and alternating (50 Hz) applied voltage and employing four different electrode materials. The air pressure is varied in the range 2×10−9−2.5×10−2 Torr for dc and 6×10−7−2.5×10−2 Torr for ac applied voltage. OFHC copper, nickel, aluminum, and niobium are used to fabricate the electrodes. It is found that the peak ac breakdown voltage is usually higher than the dc voltage for a fixed electrode separation and a fixed gas pressure. Under certain conditions considerable improvement in the insulating property of the gap can be obtained in semivacuum. The improvement in the breakdown voltage of the gap is considerable and can reach up to 62% in some cases. The higher breakdwon voltage is attributed to the increased work function of the metal−gas adsorbate system.
Nonstationary self−focusing of a Gaussian pulse in a plasma
Authors: Sodha M. S. , Prasad S. , Tripathi V. K.
Published: February 2003

In this paper the self−focusing of a cylindrically symmetric Gaussian (in space and time) electromagnetic pulse in collisionless and collisional plasmas has been studied by considering the ponderomotive force and the nonuniform heating (and consequent redistribution of electrons) as the sources of nonlinearity. The duration of the pulse is considered larger than the characteristic time of nonlinearity; the WKB and paraxial ray approximations have been used to solve the wave equation. It is found that the beam is focused in a moving filament. Because of relaxation effects the peak of the pulse is shifted to higher values of t−z/vg (in the case of collisional plasmas) and the pulse is severely distorted because of self−focusing; the shift of peak in the case of collisionless plasmas is not significant.
A study of the electrical resistivity of zone−refined tungsten at high temperatures
Authors: Williams R. K.
Published: February 2003

The electrical resistivity ρ of a zone−refined tungsten sample (residual resistivity ratio 7×104) was determined between 1100 and 2500 K. The error analysis indicates that the data are accurate to about 1%, and comparison of the results with other ρ data indicates that the error analysis may be somewhat pessimistic. The effects of thermionic charge transport on the ρ data and the performance of uninsulated W97Re3:W75Re25 thermocouples were also investigated. Comparison of the data with standard transport theory indicates that most of the nonlinear ρ behavior observed at high temperatures is due to thermal expansion effects.
Recrystallization of thermally evaporated CdS films via an H2S heat−treatment process
Authors: Fraas L. M. , Bleha W. P. , Braatz P.
Published: February 2003

It is observed that CdS films, evaporated so that a preferred c−axis columnar crystalline structure exists, undergo a recrystallization of texture in a postevaporation H2S heat−treatment process. This recrystallization process does not involve heavy−metal group−IB impurity doping and takes place at low enough temperatures so that soda−lime glass substrates may be used. These recrystallized films contain crystals of tens of microns in size and possess properties nearer those of CdS crystals than is usually found in CdS films.
Study of phonon−phonon interaction and electron−lattice interaction in alkali metals
Authors: Kor S. K. , Mishra P. K.
Published: February 2003

Second− and third−order elastic constants have been used to evaluate the ultrasonic attenuation suffered by longitudinal waves propagating along 〈100〉 and 〈110〉 directions and by shear waves polarized along 〈100〉 and 〈11̄0〉 directions for lithium, sodium, potassium, rubidium, and cesium, through the Grüneisen constant 〈γ〉, the average square Grüneisen constant 〈γ2〉, and the nonlinearity constant D, due to phonon viscosity (Akhieser loss) and thermoelastic phenomena at 300 °K. The Akhieser loss is found to be the dominating one. In metals, both electrons and phonons carry thermal energy, but in equilibrating the phonon temperature only the thermal energy carried by phonons comes into play. Hence all the evaluations except the thermoelastic loss have been made by separating the lattice conductivity from the electronic conductivity. Phonon viscosity and both types of dislocation drag coefficients (screw and edge) are also discussed. Moreover, the low−temperature ultrasonic attenuation due to electron−lattice interaction in lithium, sodium, and rubidium has been evaluated theoretically.
Electrical properties of saline ice at 1 kHz down to −150 °C
Authors: Addison J. R.
Published: February 2003

The temperature dependence of the dielectric properties of artificial sea ice are reported at 1 kHz, over a temperature range from −25 to −150 °C. Evidence is seen of predicted eutectic processes near −37, −42, and −54 °C, plus an additional one at −47 °C. The solidus point appears to lie between −70 and −75 °C. Brief reviews are given of relevant recent work involving pure and impure ices. The variation with temperature of the relaxation time and strength of the protonic relaxation process, the only one active below −80 °C, is analyzed and the results compared with this work. Their behavior is reasonably well understood in terms of the fluoride content of the original brine. There seems to be no direct evidence of doping which may be attributed to substitutionally included chloride.
Effects of pressure and magnetic field upon physical processes in laser−induced gas breakdown
Authors: Cohn D. R. , Hacker M. P. , Lax B. , Halverson W.
Published: February 2003

Experimental measurements of the pressure and magnetic field dependence of the threshold energy of CO2−laser−induced gas breakdown have been made in hydrogen, helium, nitrogen, and argon gases. These measurements clearly exhibit the effects of diffusion, laser pulse length, and elastic and inelastic energy losses. A simplified phenomenological theory of laser−induced gas breakdown which takes these effects into account is outlined. The predictions of this theory are compared with experimental results. The theory correctly predicts all of the qualitative trends in the data, and in the case of helium a quantitative fit is obtained.
Arc duration reduction in an organic atmosphere by electrode implantation of low ionization potential materials
Authors: Gray Eoin W. , McCaughan Daniel V. , Pharney Julian R. , White C. W.
Published: February 2003

The effects of low ionization potential impurities in electrical contacts have been examined in terms of arc duration reduction in typical 0.5−A 50−V nominally resistive systems. A sodium doping of ∼1.6×1017 cm−2 in pure Pd, Au, and Ag−Pd showed, in a highly activating atmosphere of naphthalene (C8H10), a substantial reduction (more than an order of magnitude) in the average arc duration over that obtained from the pure metal. These results suggest that charge exchange and subsequent field−assisted drift of the organics to the contact surface, as proposed by Gray, McKnight, and Sawina, may be an important part of the contact activation (arc duration enhancement) mechanism in these low−energy applications where electrodes are exposed to atmospheres containing trace organic contaminants.
Dependence of resistivity on the doping level of polycrystalline silicon
Authors: Fripp A. L.
Published: February 2003

The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as−deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 1016 atoms/cm3 was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.
Field−effect mobilities of gold−doped MOS structures
Authors: Sproul M. E. , Nassibian A. G.
Published: February 2003

Field−effect mobilities in the inversion layer of gold−doped MOSFETs have been investigated as a function of temperature in conjunction with control MOSFETs. In devices of low−density fast interface traps, gold can act as a weak ionized impurity scattering center in the inversion layer. In devices with high interface−trap density, gold increases the mobilitiy by quenching the traps, and the reduction of these interface traps is more important in increasing the field−effect mobility than is the reduction of charged oxide centers, such as Qss, and QAAu, the charge due to gold−acceptor interface states close to the valence band. Results show that Qss and QAAu become effective as scattering centers at very high densities, ≳1012 cm−2. In both gold−doped and control MOSFETs of low−density fast−interface traps, field−effect mobilities follow approximately a T+3/2 dependence at low temperatures and a T−3/2 dependence at high temperatures, and can approach the bulk mobility values. In control devices of high interface−trap density however, a dependence between T+1 and T+1/2 has been observed, together with very low mobility values. This temperature dependence has also been observed in control MOSFETs of very high Qss and gold−doped MOSFETs of very high QAAu.
The rate−equation approach in gas−laser theory: Analytical solution for one−mode operation
Authors: Bambini A. , Troup G. J.
Published: February 2003

A detailed treatment of gas−laser operation is given in the rate−equation approach. One running mode and one standing mode operations are fully developed and analytical formulas are deduced for the gain and the dispersion curves. While well known, this method suggests itself for its simplicity and for its good agreement with experimental results. The aim of the present paper is to give the final form of analytical formulas, i.e., the nonlinear Voigt profile. Furthermore, these formulas turn out to be a good starting point in a deeper investigation of the nonlinear dispersion relations, because the only approximation used here is in the interaction model, while the analytical treatment is not perturbative. The modified Kramers−Kronig (MKK) relations are, in fact, satisfied for running−mode formulas.
The role of the interfacial layer in metal−semiconductor solar cells
Authors: Fonash Stephen J.
Published: February 2003

Recent work has been reported on metal−semiconductor (Schottky barrier) solar cells in which efficiencies comparable to silicon p−n devices have been achieved. In these devices, the interfacial layer is believed to play an important role. In this discussion the nature of that role is examined. It is shown that the interfacial layer can enhance performance, and an outline for optimizing that enhancement is presented. The results are presented assuming n−type semiconductor material; however, the conclusions are equally valid for structures using p−type material.
Calculated reflectance of aluminum in the vacuum ultraviolet
Authors: Chow H. C. , Sparks M.
Published: February 2003

A calculation of the absorptance A of aluminum in the vacuum ultraviolet (vuv) indicates that the lowest values measured to date, A=0.08−0.10 for h/ω=3−12 eV, are very near the intrinsic limit. Operating at low temperature, purifying the metal, or improving the surface are not expected to decrease A by more than ∼0.02, and metallic reflectors better than aluminum are not likely to be found. Thus, values of A<0.06 for metals without reflection−enhancing coatings are not likely to be attained in the vuv, and lasers with such reflectors will continue to be limited by the performance of the reflectors.
Electro−optic modulation of a laser beam by a traveling high−field domain in a GaAs Gunn diode
Authors: Ohta Kimihiro , Kawashima Mitsuo , Kataoka Shoei
Published: February 2003

The light beam from a GaAs injection laser (9050 Å) was modulated at 0.1 GHz by the Pockels effect of a traveling high−field domain in a GaAs Gunn diode at room temperature. The Gunn diode is 80 μm thick, 600 μm wide, and 1 mm long, and has carrier concentration of 6.3×1013 cm−3. The laser beam was focused on the center of the wider surface of the Gunn diode through a lens and a polarizer and the transmitted light was detected with a Si photodiode through an analyzer in a cross arrangement. It was found that the detected output was modulated with a S/N ratio better than 10. The Franz−Keldysh effect of the high−field domain was also measured, and a quantitative correction was made to the observed Pockels effect. It is shown that the retardation is linearly proportional to the square root of the domain voltage and also that the electric field of the domain calculated by the corrected value of the Pockels effect agrees well with the one measured by a capacitance probe.
Thickness and magnetization variation in magnetic bubble materials
Authors: Druyvesteyn W. F.
Published: February 2003

Local variations in thickness or in magnetization of magnetic bubble films give rise to changes in the bubble radius and to translational forces. The translational forces are calculated for several cases of thickness and magnetization variations. Situations where the variations in thickness or magnetization extend over a small region (of the order of the bubble radius) are considered, as well as situations where these variations extend over a much larger region. The influence of magnetization variations on the bubble radius is more than a factor of 2 stronger than the influence of thickness
Measurements of high−current relativistic electron diode plasma properties with holographic interferometry
Authors: Kelly J. G. , Mix L. P.
Published: February 2003

Double−exposure interference holography has been used to measure the temporal and spatial dependence of plasma densities and velocities in relativistic electron beam diodes. In this paper some of the physics revealed by a detailed analysis of holograms from one such dioe is presented. Abel inversion of holograms taken on the Reba accelerator (100 kA, 1.5 MV) incorporating a 0.6−cm−diam glass rod cathode show the axial and radial structure of the diode plasmas. Finge−shift analysis has yielded densities of 5×1017−5×1019 electrons/cm3, and magnetohydrodynamic pressure balance implies a plasma temperature of about 0.3 keV. In addition, exposure variation of the fringe pattern and motion of plasmas between pictures taken at different times during the pulse have indicated plasma velocities vs spatial position that vary from 106 to 107 cm/sec.
Brewster angle for a plasma medium moving at relativistic speed
Authors: Kalluri Dikshitulu , Shrivastava R. K.
Published: February 2003

The Brewster angle for parallel−polarized electromagnetic waves incident on a relativistically moving isotropic plasma half−space is investigated. There exist two Brewster angles for certain ranges of the medium velocity irrespective of whether the medium moves parallel or normal to the interface. In the case of parallel motion, it is found that there are no Brewster angles for wave frequencies less than the plasma frequency.
Addendum: Excitation mechanisms in He−Cd and He−Zn ion lasers
Authors: Collins G. J.
Published: February 2003

The addendum resolves fundamental ambiguities in the original paper, relating to the authorship of the figures and tables employed and support of some of the work quoted.
Modulation transfer function of an image passing through thin glass foil
Authors: Nomicos C. D.
Published: February 2003

The modulation transfer funciton (MTF) of an image passing through thin glass foil is estimated for various glass thicknesses. The calculation is based on measurements of the angular distribution of light emitted by a phosphor on a glass foil, which to a good approximation was found Lambertian.
Surface recombination velocity in p−type InSb upon etching and alpha−particle bombardment
Authors: Euthymiou P. C. , Skountzos P. A. , Polychronakis K. S.
Published: February 2003

The influence of 3.5−MeV α−particle bombardment on p−type InSb surfaces that have been etched for various lengths of time was investigated. To this effect the surface recombination velocity (S) was studied by photomagnetoelectric (PME) measurements at 64 °K. The value of S determined for a mechanically polished but unetched specimen diminishes as the etching time increases. The surface recombination velocity after an etching time of T (ST) increases upon bombardment with α−particles to the value Stot and the ratio (Stot−ST)/ST decreases with increasing T. We have explained this change using a model based on different damage distributions of α−particles in ’’disordered’’ and crystalline regions due to channeling.
Saturation effects in the forced orientation relaxation of anisotropic particles in high electric fields
Authors: Tolles W. M.
Published: February 2003

The Brownian rotational relaxation time of nonspherical particles in a fluid suspension is observed to be a function of an applied electric field. The theory is developed for transient rotational diffusion in the presence of an electric field. An effective relaxation time is observed which decreases significantly at high values of the field, in agreement with theory.
Mechanism of electrical breakdown in SiO2 films
Authors: Ridley B. K.
Published: February 2003

The breakdown field associated with impact ionization and avalanche is estimated, using simple energy−momentum balance equations, for low−gap semiconductors and for high−gap insulators. Reasonable agreement is obtained in the former case, but estimated fields in the latter case turn out to be nearly an order of magnitude higher than those observed. This suggests that mechanisms other than avalanche are responsible for breakdown in insulators. A mechanism for SiO2 films, based on Fowler−Nordheim injection from a cathodic protuberance, filamentary Joule heating, and activation of mobile positive ions, which enhance the injecting field, is explored. The protuberance is taken to be spheroidal, with a dimension related to the thickness of the film and of order 100 Å. A mechanism for lateral spreading of the initial discharge and subsequent quenching by the substrate resistance gives the extent of the damaged area to be of the observed order in self−healing breakdowns. The breakdown field and its dependence on film thickness are in reasonable agreement with experiment.
Auger spectroscopy studies of the oxidation of amorphous and crystalline germanium
Authors: Henrich Victor E. , Fan John C. C.
Published: February 2003

We have used Auger−electron spectroscopy and ion−beam etching to study the room−temperature oxidation of sputtered and electron−beam−evaporated Ge films. Both amorphous and polycrystalline films were examined, as well as single−crystal Ge. Electron−escape−depth effects were removed by a deconvolution procedure in order to obtain the O distribution function. Large differences of O distribution were found between sputtered and e−beam amorphous films. Sputtered amorphous films oxidize in the same manner as single−crystal Ge, with the O confined to the first 5−10 Å of the surface. In e−beam amorphous films, the depth of O penetration is more than 200 Å, although the heavily oxidized region is still only 10−12 Å thick. Polycrystalline films have heavily oxidized layers 6−9 Å thick, with some O present to a depth of 100−200 Å.
Magnetic properties and pressure dependence of the Curie temperature of LaCo5xCu5−5x
Authors: Brouha M. , Buschow K. H. J.
Published: February 2003

The magnetic properties of the series LaCo5xCu5−5x were studied. All compounds were found to crystallize in the hexagonal CaCu5 structure type. As a function of composition x the following properties were determined: the lattice constants, the Curie temperatures and their pressure dependence up to 40 kbar, the anisotropy fields, the saturation moments at 4.2 K, and the initial compressibilities. Attempts have been made to explain the variation of the magnetic properties in terms of the collective electron model with a 3d band shape that depends on Cu concentration, taking account, however, of a certain extent of localization of the 3d electrons.
Thermal boundary resistance (Kapitza resistance) at interfaces between copper and type−II superconductors
Authors: Schmidt C.
Published: February 2003

A thermal boundary resistance (Kapitza resistance) occurs at interfaces between two metals if one of these metals is superconducting. Experiments performed on interfaces of Nb−Cu and NbTi−Cu indicated values of the Kapitza resistance which exceeded the prediction based on the acoustic mismatch theory. In light of these studies it is shown that the thermal boundary resistance must not be neglected in the stability considerations of technical multifilament superconductors.
Anomalous low−temperature ferromagnetic resonance behavior of thin Permalloy films
Authors: Bajorek C. H. , Wilts C. H.
Published: February 2003

Ferromagnetic resonance measurements between 4 and 300 °K, of 81% Ni−19% Fe evaporated uncoated and Al−overcoated 50−1000−Å−thick films, at frequencies from 1 to 8 GHz, with the static magnetic field parallel and perpendicular to the film have been performed. The unprotected films exhibit the following anomalous low−temperature resonance characteristics: the onset of a resonance field shift below 80 °K, unsymmetric resonance field hysteresis below 20 °K, and a linewidth maximum near 80 °K. The amplitude of all these effects varies with temperature and is inversely proportional to the film thickness. The resonance field shift of a 100−Å−thick film is as large as 200 Oe at 4 °K. The Al−protected films, overcoated immediately after the evaporation of Permalloy, do not exhibit these anomalies, suggesting that these are caused by an oxide layer on the unprotected films. These results are in part explained by partial pinning of the bulk magnetization at the film−oxide interface. The characteristic temperatures are ascribed to critical transitions within the oxide. The extent of pinning at 4 °K is consistent with an additional effective surface anisotropy energy of 0.07 erg/cm2. The resonance behavior is in part consistent with previous low−temperature hysteresis loop investigations. The complex nature of the oxide is described in the following paper.
Surface composition and chemistry of evaporated Permalloy films observed by x−ray photoemission spectroscopy and by Auger electron spectroscopy
Authors: Pollak R. A. , Bajorek C. H.
Published: February 2003

Auger electron spectroscopy (AES) and x−ray photoemission spectroscopy (XPS) are addressed to the problem of characterizing the air−formed oxide layer on 50−2000−Å−thick Permalloy films. Ar+ ion sputter etching is employed to obtain an elemental profile with AES and a chemical profile with XPS. The films were prepared in a vacuum of 5×10−7 Torr and exposed to the laboratory environment for three weeks. The surface of these unprotected Permalloy films is found to have a composition and chemistry quite different from that of pure Permalloy. For thin films (50 Å) this abnormal region constitutes a sizeable portion of the film. A complex chemisorption layer is observed on top of a 12−Å oxide layer. The Fe−to−Ni ratio in the oxide layer is twice that of the film bulk and the concentration of oxidized Ni falls off faster with depth than that of oxidized Fe. A localized depletion layer of iron, approximately 12 Å thick, is observed between the oxide layer and bulk Permalloy which appears at a depth of 25 Å into the film. These results suggest a consistent although far more complex surface than that implied from previous investigations. The influence of this oxide on the low−temperature ferromagnetic resonance of these films is discussed in the preceding paper.