bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflex discharge in cusp and uniform magnetic fields
Authors: Friedman S. , Jerde L. , Carr W. , Seidl M.
Published: February 2003

Hot-cathode reflex discharges are operated in both uniform and cusp magnetic fields and compared with regard to efficiency of ion production, current-voltage characteristics, electron-energy distribution functions, and stability. While the uniform field gives better electron confinement and hence higher efficiency, the cusp-field discharge is stable over a wider range of neutral densities and magnetic field strengths. The experimental results can be explained on the basis of classical electron transport. This is shown using simple physical arguments, along with Monte Carlo computer calculations of electron trajectories, taking into account ionization, excitation, and elastic collisions with neutrals.
Calculation of x-ray production rate and ionization-state density in hot aluminum plasma
Authors: Salzmann D. , Krumbein A.
Published: February 2003

Ionization-state density and x-ray production rates are calculated for hot dense homogeneous Al plasmas for electron temperatures of 15–10 000 eV and ion densities of 1018–1024 cm−3. The calculation is based on the assumption that the plasma is in a quasi-steady-state and includes the following processes: (a) electron-impact ionization, (b) radiative recombination, (c) dielectronic recombination, and (d) three-body recombination. The ionization potential reduction and electron degeneracy at high densities, as well as the influence of population distribution among the excited states, are taken into account.
Growth behavior of oxidation stacking faults and microdefects in silicon during high-temperature annealing
Authors: Kishino Seigô , Isomae Seiichi , Tamura Masao , Maki Michiyoshi
Published: February 2003

Growth behavior of oxidation stacking faults (OSF’s) and microdefects (MD’s) induced in bulk Si by high-temperature annealing is studied. X-ray section topography has been mainly utilized; however, both etching and electron microscopic observation have also supported the study. Both OSF’s and MD’s have grown at high temperature in wet O2 atmospheres and their activation energies are 2.7 and 2.6 eV, respectively. However, only MD’s have grown at high temperature in N2 atmospheres atmospheres where the activation energy is 5.1 eV. The growth rate of these defects is also investigated. Based on these investigations, the roles of O2 diffusion and Si self-diffusion in the defect generation are discussed.
Antiplane line force in a three-phase anisotropic medium
Authors: Barad Karen M. , Chou Y. T.
Published: February 2003

By proper coordinate transformations, the method of images is applied to analyzing the displacement and stress fields of an antiplane line force in a three-phase anisotropic medium. The general solutions include several special cases of technological interest, such as thin plates, materials with surface film, and composite materials with lamellar structure. Application of the results to determine the elastic fields of screw dislocations is illustrated.
Electrical properties of Al2O3 under isentropic compression up to 500 GPa (5 Mbar)
Authors: Hawke R. S. , Duerre D. E. , Huebel J. G. , Keeler R. N. , Wallace W. C.
Published: February 2003

The magnetic compression technique was used to measure the electrical properties of Al2O3 during isentropic compression. Details of the experiment are described. This compound remained an electrical insulator up to at least 500 GPa (5 Mbar). Comparisons are made between these results and other dynamic and static compression data.
On impact damage in the elastic response regime
Authors: Evans A. G.
Published: February 2003

The damage created by the impact of soft projectiles onto a brittle target has been examined. The character of the damage near the threshold has been evaluated, and damage parameters that indicate the important target properties affecting the incidence of damage have been derived. The fracture toughness and elastic-wave velocity have been identified as target variables of primary importance, and their significance has been verified experimentally.
Cuts of lead potassium niobate, Pb2KNb5O15, for surface acoustic wave (SAW) applications
Authors: O’Connell R. M.
Published: February 2003

Calculations of the surface acoustic wave (SAW) properties of lead potassium niobate, Pb2KNb5O15, have produced several cuts which are attractive for SAW applications. Each of these cuts possesses a small first-order temperature coefficient of time delay, a small electromechanical power flow angle, and a large piezoelectric coupling constant. Three cuts have the added attraction of less than isotropic diffraction spreading. The piezoelectric coupling of this material is as much as 17 times as large as it is for ST-cut quartz, making it attractive for use in temperature-stable broadband low-insertion-loss SAW devices.
Single-crystal-aluminum Schottky-barrier diodes prepared by molecular-beam epitaxy (MBE) on GaAs
Authors: Cho A. Y. , Dernier P. D.
Published: February 2003

Metal-semiconductor surface barriers were formed by epitaxially grown Al(001) on GaAs(001) with MBE at room temperature. The diodes exhibit nearly ideal electrical characteristics. It is also demonstrated that different barrier heights may be achieved by growing Al layers on MBE GaAs surfaces with different surface stoichiometries.
Nonsynchronous scattering loss in surface-acoustic-wave reflective-array-compression filters
Authors: Otto O. W. , Gerard H. M.
Published: February 2003

Nonsynchronous scattering of the incident surface wave by topographic reflecting grooves into bulk and surface waves is identified as a significant loss mechanism in surface-acoustic-wave reflective array devices. Since scattering loss is groove-depth and therefore position dependent, the resulting loss characteristic differs from that which applies to propagation loss. A phenomenological model is presented for predicting the effect of this scatttering loss on the passband of large time-bandwidth (TB) product reflective-array-compression (RAC) filters. The importance of correctly modeling the scattering loss is demonstrated using a 16 200 : 1 RAC filter as an example.
Microwave propagation in InSb powder: Magnetoplasma and helicon-wave excitations
Authors: Chen K. K. , Furdyna J. K.
Published: February 2003

Microwave propagation in narrow-gap semiconductor powders shows a strong gyrotropic behavior in the presence of an externally applied dc magnetic field B. This behavior is interesting as a possible tool for the study of electrical transport in small grains; it shows some promise for application in microwave nonreciprocal devices; and, finally, the interaction of electromagnetic waves with a particulate magnetoplasma is interesting as an electrodynamic phenomenon in its own right. Microwave propagation was investigated experimentally in powdered pure n-type InSb at 35 GHz, in magnetic fields up to 22 kG, and in the temperature range 90–300 K. The experiments were carried out as a function of particle size and conductivity, using irregular powders, as well as aggregates of spherical particles. Measurements of transmitted amplitude and phase were performed with incident circular polarization in the Faraday geometry (k∥B, where k is the wave vector). Faraday rotation arising from the gyrotropy was also investigated. The above experiments reveal that the observed gyrotropy is associated with two distinct resonant interactions: Magnetoplasma resonance (MPR) and dimensional resonance (DR). These powder resonances occur at the condition for resonant scattering of individual particles, shifted through multiparticle effects. At microwave frequencies, powder grains satisfy the dipole limit (D≪λ0, where λ0 is the free-space wavelength and D is the largest dimension of the particle). Using the recently developed theory of electromagnetic resonances in a gyrotropic sphere, we identify MPR as an electric dipole interaction occurring when D≪λ, where λ is the wavelength in the particle interior (Rayleigh scattering). DR, on the other hand, is a magnetic dipole interaction, occurring when λ is comparable to the particle dimensions. Thus, although the particles are nonmagnetic, the powder as a whole must be described by an effective permeability, particularly in the vicinity of DR. In our parameter range, the DR interaction involves resonant absorption of heliconlike waves. Finally, in the case of Rayleigh scattering, particle-particle interaction can be expressed through a ’’powder depolarizing factor’’, which provides a measure of the local Lorentz field in a dense particle distribution.
Use of a Hall accelerator in the production of negative hydrogen ions in cesium vapor
Authors: Kamperschroer J. H. , Post R. S.
Published: February 2003

Atomic hydrogen particles from a Hall accelerator were utilized in low-energy (<2 keV) negative-hydrogen-ion-production experiments in cesium vapor. Cell thicknesses in the range 8×1011 to 6×1015 Cs atoms/cm2 were studied for H− current densities on the order of 1 mA/cm2. Anomalously, large H− fractions of up to 30–60% were observed at intermediate cell thicknesses when protons were not removed from the dominantly H0 incident beam. These observations indicate either the presence of excitation of the H0 beam or the existence of two space-charge phenomena: a focusing effect inside of the cesium cell, due to a buildup of positive space charge in the beam line, and a divergence effect as the H− beam emerges from the cesium cell due to a lack of space-charge neutralization.
The measurement of fluorescence polarization at high pressure
Authors: Chryssomallis G. S. , Drickamer H. G. , Weber G.
Published: February 2003

High pressure was used to change the viscosity isothermally for the measurement of polarization of fluorescence of small fluorescent molecules in solution. A new technique, necessary for the measurements, as well as a new instrument to perform them, are described and discussed. Although the apparatus is not well suited for determining absolute polarization values, it is quite accurate in detecting changes in polarization due to change in pressure. Independent readings of polarization at 1 atm were therefore obtained using a different instrument. For the sample system, quinine sulfate in isobutanol, there is good agreement between the data obtained by pressure variation and those obtained by temperature variation. The extension of the method to study polymers and proteins in solution and its advantages over previous methods are also discussed.
Collisional quenching of Xe+(2P) and He 23S metastables by calcium and strontium metal vapors
Authors: Butterfield K. B. , Gerstenberger D. C. , Shay T. , Little W. L. , Collins G. J.
Published: February 2003

Excitation-transfer cross sections have been measured for Penning and charge-transfer reactions in He-Ca, He-Sr, Xe-Ca, and Xe-Sr discharges. In low-current low-pressure discharges of helium, excitation transfer to ionic levels of calcium and strontium was found to be dominated by collisions with 23S helium metastables with measured cross section σ (He 23S–Ca) =4.1×10−15 cm2 and σ (He 23S–Sr) =1.6×10−15 cm2. In xenon discharges, charge-transfer cross sections between xenon ions and calcium and strontium atoms, σ (Xe+-Ca) and σ (Xe+-Sr), were measured to be 2.2×10−16 and 2.3×10−16 cm2, respectively.
Physical mechanisms of carrier leakage in DH injection lasers
Authors: Wu Chii-Ming , Yang Edward S.
Published: February 2003

The physical mechanisms of the breakdown of carrier confinement are considered using both the thermionic-emission and diffusion models. It is shown that, for most practical AlGaAs/GaAs DH lasers, the diffusion current is responsible for carrier leakage. The thermionic emission of minority carriers is important when the confinement barrier or the mobility is very large. The theory presented here is also applicable to structures other than the AlGaAs/GaAs laser.
Room-temperature continuous operation of a ruby fiber laser
Authors: Burrus C. A. , Stone J.
Published: February 2003

As-grown single-crystal ruby fibers have been operated continuously as end-pumped lasers, in air at room temperature, without active cooling. The fiber laser elements were about 40 μm in diameter and 0.25 cm long, with a Cr3+ concentration of 0.02%. The pump source was a Kr laser. Continuous operation was in a single transverse mode at one to five longitudinal resonant frequencies, the observed relaxation oscillations were regular and periodic, and the output was plane polarized. Fiber growth is described, and both transient and steady-state heating effects in the laser due to pump absorption are discussed.
The temperature dependence of degradation mechanisms in long-lived (GaAl)As DH lasers
Authors: Ritchie S. , Godfrey R. F. , Wakefield B. , Newman D. H.
Published: February 2003

An investigation into the effects of temperature on degradation mechanisms in GaAs/GaAlAs DH lasers has been carried out. A mechanism (or mechanisms) independent of stimulated light levels is found to be relatively insensitive to temperature. This suggests that a residual failure mechanism may be associated with defect motion being enhanced by nonradiative recombination. A statistical analysis of the lifetest results and photoluminescence studies of lifetested devices suggest that there may be different mechanisms in operation at different temperatures. Thus, great care must be exercised before using conventional extrapolation techniques to predict laser lives at room temperature.
The optically pumped mercury vapor laser
Authors: Holmes N. C. , Siegman A. E.
Published: February 2003

We present the results of an investigation into the optically pumped cw mercury vapor laser at 546.1 nm. A steady-state rate-equation analysis is used to describe the variation of laser gain and output power as a function of nitrogen pressure and other parameters and to describe the effects of isotopic mixing in Hg lasers containing multiple Hg isotopes. A qualitative treatment of the effects of tube diameter, pumping rates, and Hg density is also presented. A number of experiments showing the variation of laser gain and output power as a function of nitrogen pressure are also described and compared with the theory. Using indirect techniques, the quenching rate across the 546.1-nm transition in nitrogen is measured to be 7×105 sec−1 Torr−1±50%, and the pressure broadening on this line is inferred to be ∼26 MHz/Torr±30%. The effects of tube diameter, pumping rates, and Hg density are also presented.
Theoretical and experimental performance of a high-power cw electron-beam-sustained electric laser
Authors: Yoder M. J. , Legner H. H. , Jacob J. H. , Ahouse D. R.
Published: February 2003

Computer-code predictions of small signal gain, optical quality (medium refraction), and output power are presented for cw CO2 electric lasers. The fluid mechanics, plasma dynamics, and kinetic rate equations have been solved simultaneously for two cavity configurations: flow parallel and flow transverse to the electric field. We consider both recombination- and attachment-dominated discharges. Experiments were carried out to test some of the theoretical predictions using an electron-beam-sustained electric-discharge flowing carbon dioxide subsonic cw laser in which the gas flow is parallel to the electric field. Input power, electron density, electric field, and other experimental parameters were measured. Small signal gains and interferometric gas density measurements show a significant fraction of the input energy to be ’’hung up’’ in the vibrational excited states in agreement with theory. As a result, meaningful medium homogeneity (optical quality) measurements must be obtained under lasing conditions and cannot be extrapolated from zero-flux results.
Effects of a varying velocity on MHD boundary-layer control
Authors: Chuang Hsing
Published: February 2003

A steady two-dimensional MHD boundary-layer flow on a flat plate with a uniform transpiration through the plate, a constant hydrostatic pressure, and a varying free-stream velocity along the flow direction is considered. The momentum boundary-layer thickness is found to increase substantially with the magnetic interaction number and injection. The shearing stress at the wall decreases with the increasing magnetic interaction number and injection. Both increases will certainly enhance the chance of a flow separation from the plate.
A critique of the throughput limit in mass spectrographs
Authors: Forrester A. T. , Perel J. , Mahoney J.
Published: February 2003

It has been asserted previously that isotope separation in mass-spectrograph-type separators will cease when the ion density becomes so large that the time for Coulomb collisions between the two isotopic species becomes comparable to the transit time through the machine. It is shown here that the first effect of such collisions will be to increase, not destroy, the separation, but that the current densities required for the effect are so far from the state of the art as to be regarded as inaccessible.
The characterization of a laser-produced negative-hydrogen-ion plasma
Authors: Gekelman W. , Vanek V. , Wong A. Y.
Published: February 2003

The parameters of a plasma produced by irradiation of alkali hydride targets with a ruby-laser pulse are experimentally measured. Positive- and negative-ion abundances are determined with a quadrupole mass analyzer. Electron temperature was measured with rapidly swept Langmuir probes. Negative (H−) ion temperature was obtained using the mass analyzer and focusing grids. The electron density near the target was determined by optical holography. The quantity of negative ions produced per laser pulse make the source attractive for the future development of high-energy neutral-beam systems.
Magnetostriction of hcp and dhcp Co-Fe single crystals
Authors: Wakiyama T. , Brooks H. A. , Gyorgy E. M. , Bachmann K. J. , Brasen D.
Published: February 2003

Magnetostriction was measured at room temperaure in various crystallographic directions in hcp Co–0.63 at.% Fe and dhcp Co–2.28 at.% Fe single crystals using a strain-gauge technique in magnetic fields up to 16 kOe. Anomalous strain variations were observed for the ac plane of a dhcp crystal when the field was parallel to the c axis. Marked differences in the magnetostriction constants were found to exist between the hcp and dhcp crystals. For example, the fractional change in volume associated with domain rotation from the c axis to the basal plane was found to be contraction, −30×10−6, for the hcp crystal, while there was an expansion, +6×10−6, for the dhcp crystal.
Modified lattice-statics approach to dislocation calculations. II. Application
Authors: Esterling Donald M. , Moriarty John A.
Published: February 2003

The atomic structure of a 〈110〉 screw dislocation core in aluminum is calculated by the modified lattice-statics method developed in the preceding paper. The method includes anharmonic as well as harmonic forces and permits relaxation of the atoms in all three dimensions. All forces used in the present calculations were derived from a first-principles interatomic pair potential obtained via pseudopotential theory. Several significant differences from the ordinary lattice statics results are noted, including the displacement field, Peierl’s energy barrier, and the equilibrium core-center location.
Electrical response of relaxing dielectrics compressed by shock waves: The axial-mode problem
Authors: Lysne P. C.
Published: February 2003

Axial-mode conditions occur in studies of the dielectric properties of materials compressed by shock waves whenever the electrical vectors are perpendicular to a planar shock front. These conditions are readily obtained in shock experiments, and the analysis of the experiments is one dimensional. This work considers the electrical response of shock-wave-compressed dielectrics and piezoelectrics where changes in the polarization due to imposed electric fields do not occur instantaneously with field changes. Experiments are proposed in which the effective impedance shunting the specimen is either negligible or a series inductive-resistive network. These latter experiments are useful in discriminating between dielectric relaxation and other relaxation phenomena. Several example problems are solved, and they suggest profitable areas of future work.
Electrical conduction and persistent internal polarization in sisal wax
Authors: Singh Ranjit , Datt S. C.
Published: February 2003

A detailed study of the current as a function of voltage, temperature, and thickness coupled with that of persistent internal polarization under different field and temperature conditions has been undertaken in sisal wax. The study of electrical conduction indicates that all the results are consistent with the assumption of an exponential distribution of trapping states in the band gap which is found to be about 7.38 eV wide. The dependence of the initial and final charge densities on the polarizing field and the temperature, and the decay of initial charge density with time have shown that bulk polarization is due to trapping of both holes and electrons. The slow isothermal charge decay and persistence of charge have been considered to be due to the thermal release of charge carriers from the trapping levels and fast retrapping in the shallow levels.
The thermoluminescence mechanism in LiF (TLD-100): Extension of the Mayhugh-Christy model
Authors: Cooke D. Wayne
Published: February 2003

Thermoluminescence (TL) and emission spectra from LiF (TLD-100) have been studied over the temperature range from 90 to 500 K. It is shown that over a small temperature interval (130–160 K), shallow trapped electrons may recombine directly with Vk centers and produce emission in the uv (∼270 nm). At approximately this same temperature, the Vk centers may be thermally annealed and produce emission near 400 nm by direct recombination at an activator–F-center complex. It is also shown that it is possible to produce both uv and visible emission over this limited temperature range solely by the release of electrons. Mayhugh and Christy have previously suggested a model for the TL mechanism in LiF (TLD-100) which explains the production of TL from 25 to 200 °C. Low-temperature TL measurements of Podgorsak, Moran, and Cameron indicated that the model was incorrect or that it must be modified to explain the uv emission observed at low temperatures. Our results suggest that the existing model is correct; moreover, when the model is extended to low temperatures, it adequately explains the resultant emission obtained in the present work and also reconciles the data of Podgorsak, Moran, and Cameron with the Mayhugh-Christy model.
Infrared-induced changes in the emission spectra of ZnS powder phosphors
Authors: Kramer Bernard , Izaguirre Francisco , Kalikstein Kalman
Published: February 2003

The effect of infrared (0.8 and 1.25 μ) on the luminescent spectra of copper, silver, and self-activated ZnS powder phosphors was investigated at room and liquid-nitrogen temperatures under ultraviolet excitation. The equilibrium change in luminescence (quenching or enhancement) was found to depend on the portion of the emission spectrum observed, as well as on the temperature and the infrared wavelength used. These effects can be explained by noting that the freed holes may be retrapped at nonionized activator levels or recombine nonradiatively with trapped electrons.
Theory of lateral-collection photodiodes
Authors: Holloway H.
Published: February 2003

An analysis is given for the quantum efficiency, capacitance, junction resistance, and detectivity of lateral-collection photodiodes. These devices are shown to be capable of yielding substantial reductions in junction capacitance and, in some cases, significant increases in detectivity from the values obtained with conventional photodiodes.
A suggested technique for determining in-material longitudinal and shear particle velocity histories in a single-inclined-plate impact experiment
Authors: Swegle J. W.
Published: February 2003

A technique has recently been developed for the internal measurement of longitudinal and shear particle velocity histories in an inclined-plate impact experiment. Measurements must be made in two experiments having identical impact conditions in order to uniquely determine both quantities. A modification to the technique is suggested which will allow both to be uniquely determined in a single experiment, thus avoiding the complication of having to exactly reproduce the impact configuration.
Si epitaxial regrowth and grain structure of Al metallization on 〈100〉 Si
Authors: Magee T. J. , Peng J.
Published: February 2003

Regrowth structures and dissolution pitting on 〈100〉 Si substrates resulting from heating of Al metallization layers have been investigated by transmission electron microscopy/diffraction, scanning electron microscopy, and Auger electron spectroscopy profiling. Si regrowth from solution in solid Al has been shown to nucleate rapidly at grain boundaries in both doped and undoped Al films. Dissolution pitting was shown not to occur randomly on the substrate, but, instead, was shown reproducibly to be correlated with the sites of Al grains containing large concentrations of microstructural defects.
Melt-back approach to liquid-phase epitaxial growth
Authors: Sumner B. E.
Published: February 2003

A liquid-phase epitaxial technique, utilizing a melt-back approach, has been developed for growing layers of gallium-doped silicon on silicon. Best results were obtained by supercooling gallium melts from 600 °C and heating the substrate for dissolution by the melt at 12 °C/min. This technique is readily applicable to monolithic silicon technology with its clear advantages for arrays of uniform quality and reduced costs.
EPR studies on amorphous Ge-Al and Ge-Cu films
Authors: Randhawa H. S. , Malhotra L. K. , Chopra K. L.
Published: February 2003

Electron paramagnetic resonance in amorphous germanium (a-Ge) alloy films containing varying concentrations of Al and Cu has been studied. The concentration of free spins (dangling bonds) is found to decrease rapidly on alloying to less than 5×1017/cm3 for about 8 at.% Al and 10 at.% Cu concentrations. The g factor and line shape remain unaffected on alloying. The linewidth, however, shows minor changes.
A quantitative study of anomalous annealing phenomena in quenched aluminum
Authors: Ronander E. , Kritzinger S.
Published: February 2003

It is demonstrated how a quantitative study of some anomalous thin-foil annealing phenomena, if interpreted correctly, leads to the determination of important physical constants. The necessary theory is developed and applied to measure the activation energy for dislocation pipe diffusion in thin aluminum foils from the annealing rate of quenched-in and subsequently truncated faulted dislocation loops. The results are compatible with those obtained from void annealing by another group. Triangular faulted defects present in bulk-aged and thinned samples of aluminum are shown to consist of a mixture of extrinsic and intrinsic loops. They can readily be distinguished by their annealing rates. From the relative values of these rates, the relation between the intrinsic and extrinsic stacking-fault energies has been determined.
Crystallography of PtSi films on (001) silicon
Authors: Ben Ghozlene Hédi , Beaufrère Pierre , Authier André
Published: February 2003

Platinum silicide is widely used to make Ohmic contacts and Schottky-barrier diodes. These contacts are formed by evaporation of platinum on a (001) silicon substrate. During evaporation, two phases are formed: Pt2Si and/or or PtSi, depending on the process used. After sintering, the final phase is PtSi. This study shows that PtSi grains in epitaxy on (001) silicon are oriented along two separate sets of orientation: the already known (11̄0) and a newly determined (12̄1) orientation. The ratio of the number of grains oriented along the latter and former orientations depends on the wafer temperature during evaporation. The two orientations may be caused by two different formation mechanisms: evaporation on silicon substrates at 320 °C under which Pt2Si is formed at first and then transformed into the PtSi phase with the (11̄0) orientation during sintering and evaporation on silicon substrates at 400 °C under which PtSi is formed directly along the (12̄1) plane and undergoes no change during further heat treatments. For intermediate temperatures, both mechanisms are present.
Comparative calculations for thin-film and bulk single-crystal Schottky-barrier solar cells
Authors: Soukup R. J. , Akers L. A.
Published: February 2003

A mathematical analysis of the expected short-circuit current density in Schottky-barrier solar cells is presented. For a solar cell with the Schottky barrier on the bottom, back illuminated, the active semiconductor material, GaAs for this example, must be a thin film for maximum efficiency. A comparison between this cell and a single-crystal solar cell with the Schottky barrier on the top, front illuminated is made. This comparison shows that solar cells made from polycrystalline films could deliver the same short-circuit current as a single-crystal solar cell provided that the minority-carrier diffusion length in the polycrystalline films can be kept to within one order of magnitude lower than that for the single-crystal material. The reason for this is that solar-reflection losses for the back-illuminated thin-film cell can be minimized, while for the front-illuminated single-crystal cell the losses must always be high.
Work functions and structures of alkaline-earth thin films
Authors: Gaudart Louis , Renucci Pierrette , Rivoira René
Published: February 2003

The work functions of thin and ultrathin films of barium were studied by means of photoemission. The films were obtained by thermal evaporation and condensation on a quartz substrate in ultrahigh vacuum. The mass-thickness dependence of the quantum yield is dominated by a single peak. The work function Φ shows a minimum and reaches a constant value for the thick films. The structures of calcium, strontium, and barium were studied using the replication and the zinc-coverage technique. The mass thicknesses ranged from 0.5 to 100 nm. Three main structures were observed: granular, lacunar, and quasicontinuous structures. The work-function minimum is always observed with passage of the granular film to the lacunar film.
Performance limits of a Josephson-junction mixer
Authors: Claassen J. H. , Richards P. L.
Published: February 2003

We present the results of extensive analog-computer simulations of a Josephson junction used as a mixer with an external local oscillator. The resistively shunted junction model was used throughout, and the effects of intrinsic junction noise were included. When the source impedance is much greater than the junction resistance R, our simulations permit predictions of conversion efficiency, noise temperature, and saturation level to be made for a wide range of experimental parameters. The possibility of harmonic mixing has also been considered. With a source resistance comparable to R (i.e., conventional ’’matching’’) the behavior of the system is too complicated to permit such general predictions of performance. From the results of simulations for a particular set of parameters, it appears that the best noise temperature will usually be achieved for a source impedance somewhat greater than R. An upper limit for the mixer-noise temperature is ∼40T over a broad range of junction parameters, where T is the effective temperature of the junction. The conversion efficiency under these circumstances should be comparable to what is potentially available from Schottky-diode mixers. Our simulations show that with stronger microwave coupling it is possible to obtain conversion gain—i.e., a conversion efficiency exceeding unity. This, however, will probably be at the expense of a higher mixer-noise temperature. Saturation can be important even for source temperatures ∼300 K. To avoid saturation it is necessary either to restrict the coupling bandwith or use an array of junctions.
Influence of strain on Nb3Sn multifilament conductors
Authors: Ziegler Günther
Published: February 2003

In Nb3Sn multifilament conductors, the superconducting component is subjected to compressive stress. This affects both the superconducting critical temperature and the critical current. After removal of the matrix by a chemical treatment, the degradation of the critical temperature is partly reversed and the critical current increases. With the aid of a model, which takes into account the plastic behavior of the components, the strains resulting from thermal shrinkage are calculated. The resulting degradation of Tc and the measured Tc values are in fairly good agreement. The strain-dependent change of critical current is solely caused by a change of the upper critical field; the pinning force function remained almost unaltered.
Critical-current changes in neutron-irradiated Nb3Sn as a function of irradiation temperature and initial metallurgy
Authors: Brown B. S. , Blewitt T. H. , Scott T. L. , Wozniak D. G.
Published: February 2003

Fast-neutron irradiations have been performed on Nb3Sn wires to determine the roles of irradiation temperature and the unirradiated value of the critical-current density (Jc0) on the changes in Jc. Four experiments were performed: low- (6 K) and high- (350 K) temperature irradiation of high- (2×1010 A/cm2 at 5 T and 4.2 K) and moderate- (0.8×1010 A/cm2) Jc0 material. The large increases in Jc for the moderate-Jc0 material were independent of irradiation temperature; the increases were smaller for the high-Jc0 material, and a significant difference was found for the two irradiation temperatures. The difference is attributed to the greater pinning capability of defect cascades over defect clusters in the high-Jc0 material. The smaller amount of Jc recovery after a 300 K anneal, when compared with NbTi, can also be understood in terms of the defects responsible for the flux pinning.
Experimental investigation of resonances in low-Q Josephson interferometer devices
Authors: Zappe H. H. , Landman B. S.
Published: February 2003

Resonance dc structures are experimentally investigated in two-junction interferometers in which the device Q is adjusted to low values with an external resistor connected across the main device inductance. The measurements agree well with the results of a recent analytic theory of interferometer resonances and show that practical interferometer devices with low and adjustable resonance amplitudes can be built.
Growth of a positive leader in long nonuniform air gaps
Authors: Menemenlis C. , Shirmohammadi D.
Published: February 2003

The leader stage of the discharge in a long rod-plane air gap was investigated. Based on the assumption that optimum conditions for the advancement of the leader are obtained when the field prevailing around the leader tip maintains a constant optimum value, mathematical expressions are developed relating the gradient along the leader with quantities directly measurable during breakdown tests.
Ionization processes in the positive column of the low-pressure Hg-Ar discharge
Authors: Vriens L. , Keijser R. A. J. , Ligthart F. A. S.
Published: February 2003

Recent experiments and calculations have indicated that mutual collisions between excited 6 3P0, 6 3P1, and 6 3P2 atoms may be important for the ion formation in low-pressure Hg–noble-gas discharges. We calculate various rates for electron-impact and for excited-atom-collisional ionization for a range of conditions relevant to the Hg-Ar fluorescent lamp (pAR=3 Torr, R=1.8 cm, Twall=20–80 °C, and I=0.2–0.8 A). In the analysis use is made of experimentally determined values for particle densities and electron temperatures. Deviations from a Maxwellian electron-energy distribution, which substantially reduce the electron-impact ionization rates, are taken into account. We find that 6 3P–6 3P collisions become even more important for the ion formation than electron impact at the higher Hg vapor pressures. Both Hg+ and Hg+2 will be formed. The 6 3P–6 3P collisions are indicated to be mainly responsible for the well-known decrease in uv efficiency of the Hg–noble-gas discharge at temperatures above 40 °C.
Erosion products from the cathode spot region of a copper vacuum arc
Authors: Tuma D. T. , Chen C. L. , Davies D. K.
Published: February 2003

Combined electrical, optical, and spectroscopic measurements have been used to determine the total flux, ion flux, particle flux, and neutral atom flux emitted from the cathode spot region of a copper vacuum arc of 80 A total current and 2-sec duration. It is found that the cathode erosion products consist predominantly of ions and particles, the emission of neutral atomic flux from the cathode being less than 1% of the total flux. The total and particle flux distributions are peaked in the direction of the cathode plane, whereas the ion-flux distribution is forward peaked. However, both ions and particles are detected in the cathode shadow, a result which is contrary to the hypothesis of purely collisionless transport of cathode erosion products. The neutral atom density measurements are consistent with a model assuming the source of the vapor to be evaporation in flight from the hot particles emitted from the cathode spot region. The size distribution of the particles has a maximum for particles of diameter in the range 0–1 μ.
Transport studies of cusp and multichannel REB fusion concepts
Authors: Wright Thomas P.
Published: February 2003

Single-particle trajectory calculations have been used to study the effectiveness of beam concentration near a target pellet in two relativistic electron-beam-driven inertial fusion concepts: magnetic cusps and multiple current-carrying channels in a wagon-wheel configuration. Angular momentum constraints favor the multichannel transport scheme. The role of angular momentum nonconserving reflections from plugged-cusp loss cones is discussed. Minimum radii are calculated for various injection conditions in a 40-channel configuration. The resulting superposition of beams may provide an order-of-magnitude improvement in beam concentration over single-beam results.
Energy-transport experiments in 10-μm laser-produced plasmas
Authors: Mitchell K. B. , Godwin R. P.
Published: February 2003

X-ray experiments were conducted giving data on radiation and electron transport from plasmas produced by the interaction of 10.6-μm laser light focused on layered targets. The targets employed were evaporated aluminum on SiO2 and copper substrates. The penetration depth of the plasma was measured from the thickness of aluminum required to produce a 1/e attenuation of the highly ionized silicon lines (1s 2p-1s2) and (1s 3p-1s2). The penetration of the plasma into the target surface was 95 Å for incident 10.6-μm laser irradiances of 3×1013 W/cm2. Estimates of electron energies produced in the plasma directed toward the target were made from measurements of the attenuation of the K line of the substrate as a function of aluminum thickness. End-point electron energies were calculated from the best fit of experimental data with targets of SiO2 and copper substrates for laser irradiances from 3×1013 to 4×1014 W/cm2. When the laser irradiance (IL) is increased, there is an increased dependence of electron energies absorbed by the target. For irradiances greater than 1014 W/cm2 the effective end-point energy is proportional to I1/2L.
Rate coefficients and inelastic momentum transfer cross sections for electronic excitation of N2 by electrons
Authors: Cartwright David C.
Published: February 2003

Rate coefficients, as a function of the electron temperature, have been determined from the integral cross sections for excitation of the 19 singlet and triplet electronic states of N2 within 14.2 eV of the ground state. For electron temperatures less than 10 eV, the rates for excitation of the A 3Σ+u, B 3Πg, W 3Δu, and a 1Πg are all greater than that for excitation of the C 3Πu state. The differential cross sections for excitation of these same electronic states were also used to calculate the inelastic momentum transfer associated with the excitation of these states. The total momentum transfer cross section for electrons in N2, as a function of the electron energy, was obtained by adding the inelastic momentum transfer to that associated with elastic scattering. Inelastic momentum transfer accounts for about 25% of the total momentum transfer above 15 eV. Over the energy range 20–60 eV, inelastic scattering contributes 20–25% to the total N2 electron scattering cross section. The total scattering cross section obtained here is in good agreement with a recent direct measurement of this cross section.
Structural defects in annealed silicon containing oxygen
Authors: Staudinger Annemarie
Published: February 2003

The purpose of this paper is to report the results of a transmission-electron-microscopy (TEM) characterization of structural defects observed in a Czochralski-grown silicon crystal after a two-step anneal, i.e., 3 h at 700 °C and 1 h at 1000 °C. Six types of defects were identified, i.e., extrinsic stacking faults, microprecipitates on or near the plane of the stacking fault, particles, generator-dislocation loops, small strain centers, and a ’’new’’ precipitate structure, whose characterization is emphasized in this study. It was concluded that the new defect structure places the surrounding matrix in a compressive condition, i.e., it is of interstitial type. The possibility of carbon or oxygen being responsible for this precipitate structure was discussed. It was suggested that future electron energy-loss spectroscopy work should, in principle, distinguish between an oxide and a carbide.
Concentration variations within small crystallites studied by x-ray diffraction line profile analysis
Authors: Mittemeijer E. J. , Delhez R.
Published: February 2003

An analysis is given of the x-ray diffraction line broadening caused by concentration variations occurring within coherently diffracting crystallites. The sine Fourier coefficients of the line profile are employed. The method is applied to sintered and unsintered AuPt alloy catalysts. In the interior of the crystallites of the sintered specimen, the concentration maintained a constant value which agreed very well with the average composition. The surface region was enriched by gold, in agreement with experimental results from other methods and with theoretical predictions. Concentration variations in the unsintered specimen were much larger. The crystallites consisted of a platinum-rich nucleus surrounded by a gold-rich shell as may be expected from the preparation method (chemical reduction of platinum and gold ions in solution). In addition, a method for correction of the ’’hook’’ effect in line profile analysis is suggested.
Zero-bias resistance of grain boundaries in neutron-transmutation-doped polycrystalline silicon
Authors: Seager C. H. , Castner T. G.
Published: February 2003

We have characterized the electrical transport properties of neutron-transmutation-doped polycrystalline silicon. Zero-bias measurements of resistance have been made as a function of temperature on both bulk specimens and individual grain boundaries in this material. Below a doping level of ∼2×1015 phosphorus/cm3, the bulk resistance has a nearly Arrhenius behavior with an activation energy of ∼0.55 eV; above this donor concentration the resistivity is markedly curved on an Arrhenius plot with values of slope which decrease with decreasing temperature. Potential probe measurements show that a large spread in grain-boundary impedances exist in these higher-doped specimens. We compare our data to theoretical expressions for current flow across grain-boundary potential barriers and good agreement is observed; these comparisons indicate that the largest grain-boundary state densities observed in our samples consist of ∼6×1011 available single-electron-states/cm2 located within ∼0.2 eV from the center of the forbidden gap. The chemical potential of these grain-boundary regions is found to lie at midgap, in agreement with previous data on thin-film polycrystalline silicon. We note that the considerably higher orientation-independent state densities found in thin-film polycrystalline silicon contrasts strongly with the present data and suggest the presence of serious contamination effects in previously studied material.
Ultrasound-produced rolls in nematic liquid crystals as studied through the spatial coherence of scattered light
Authors: Bertolotti M. , Scudieri F. , Sturla E.
Published: February 2003

The study of the spatial coherence properties of light scattered by ultrasound-produced rolls in MBBA allows one to obtain information on the hydrodynamics of the process. In particular, the correlation length ln of refractive-index fluctuations is first found to increase and then to decrease with the voltage V applied to the piezoelectric transducer. The onset of ’’turbulent’’ motion is clearly visible at the voltage at which dln/dV changes sign.
Shock propagation in the one-dimensional lattice at a nonzero initial temperature
Authors: Batteh Jad H. , Powell John D.
Published: February 2003

Recent studies of shock propagation in a one-dimensional discrete crystal lattice are extended to include the case for which the lattice is at a nonzero intitial temperature. The lattice is assumed to be monatomic, and its atoms are assumed to interact via a Morse-type interatomic potential. Behind the shock front, a spectrum of well-defined stable pulses (solitons) is observed to propagate amid the thermal background of the lattice. The solitons have varying amplitude and propagation velocities, and the different velocities introduce a spreading effect which prevents the shock profile from approaching a steady state. The velocity distribution function of atoms well behind the front is calculated and indicates an approach to thermal equilibrium at an elevated temperature in this region of the crystal. The implications of the nonsteady behavior and the slow approach to thermal equilibrium for currently used theories of detonation are noted and discussed.
Pseudopotential of gold fitted to elastic data
Authors: Barua B. P. , Sinha S. K.
Published: February 2003

The pseudopotential of gold using Harrison’s modified point-ion form has been calculated by fitting with the experimental elastic data and is compared with the pseudopotential curve obtained from the Fermi surface data. This pseudopotential has been used to calculate the third-order elastic constants of gold.
Optical properties in titanium-diffused LiNbO3 strip waveguides
Authors: Fukuma Masaharu , Noda Juichi , Iwasaki Hiroshi
Published: February 2003

Optical insertion losses in embedded strip waveguides fabricated in LiNbO3 by Ti diffusion have been examined at a 0.633-μm wavelength, taking into account resultant near-field patterns. It is confirmed that the main factors influencing optical insertion losses are radiation loss by the deficient refractive-index change of a waveguide, scattering loss by insufficient diffused residual titanium oxide film on a waveguide, and coupling loss between a waveguide and a fiber. A diffusion condition for making a low-loss waveguide is presented, although suppression of lateral diffusion is necessary to achieve further insertion-loss reduction.
Laser-induced dichroism and birefringence in two- and three-level systems of neon
Authors: Delsart C. , Keller J.-C.
Published: February 2003

We have observed the Doppler-free dichroism and birefringence induced by a linearly polarized laser beam (pump beam) by monitoring the polarization and amplitude changes of a weak probe beam through an analyzer. The effects have been observed in two-level systems and also in three-level systems of Ne I. At rather low pump power, a typical refractive-index anisotropy of 10−8 has been measured. We have shown that, when the normal resonance curve exhibits a broad background due to collisions, our method allows the elimination of this background. In addition, using a rotating analyzer, we have obtained simultaneously the dichroism and birefringence curves, i.e., the imaginary and real part of the anisotropic-induced susceptibility.