bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical calculations of electron mobility in ternary III-V compounds
Authors: Harrison J. W. , Hauser J. R.
Published: February 2003

Theoretical calculations have been made of the electron mobility in several ternary III-V semiconductor systems. The scattering mechanisms included in the analysis are polar-optical-phonon scattering, piezoelectric scattering, alloy scattering, and ionized-impurity scattering. Models are also presented and discussed for the variations of material parameters with alloy composition which are needed in the mobility calculations.
1/f resistor noise
Authors: DeFelice Louis J.
Published: February 2003

Specific carbon composition resistors are shown to have excess noise that is 1/f and is proportional to the square of the current they carry, in a frequency band defined by 10-Hz high- and 100-Hz low-pass 3-dB points. Similar resistors are constructed with volumes in the ratio 1:4:9:16, but which have equal Ohmic values. The effect of volume scaling on excess noise is thereby separated from Johnson noise. Autocorrelation functions are used to analyze the noise data. The results are consistent with the hypothesis that 1/f noise is inversely proportional to volume. The concept that the main factor in 1/f-noise generation is the mean energy dissipated per charge carrier is also discussed. A unitless index of excess noise is suggested as a manufacturer specification.
Electron-beam-controlled N2 infrared laser
Authors: Newman L. A. , DeTemple T. A.
Published: February 2003

Laser action in N2 on the first positive system (B3Πg→A3E+u) has been obtained in an electron-beam-controlled discharge. Pressures of up 200 Torr (limited by the sustainer voltage available) were used resulting in a maximum output of 30-kW 2-mJ pulses at an efficiency of 0.01%. The addition of a small amount (∼1 Torr) of SF6 resulted in a doubling of the output power and energy.
Bend contours maps in titanium and mica thin films
Authors: Silva E. , van Dun A. , Riquelme J.
Published: February 2003

Bend or extinction contours maps in titanium and mica are interpreted and indexed. They were constructed from a series of electron micrographs taken using beam energy of 100 keV of epitaxial titanium film about 700 Å in thickness, and thin mica (muscovite) film about 1000 Å in thickness prepared by cleavage in air.
Thermal diffusivity of dispersed composites
Authors: Lee H. J. , Taylor R. E.
Published: February 2003

The thermal diffusivity of a series of copper whiskers-copper spheres dispersed in solder was measured by the flash method at room temperature. These diffusivity values are compared with the calculated thermal diffusivity values using effective thermal conductivity values computed with Maxwell’s dispersion equation. The results show that the concept of an effective thermal diffusivity is valid at least for particle-to-matrix diffusivity ratios between 1 and 3.5 and volume specific heat ratios between 0.02 to 0.52 in randomly dispersed composites containing up to 30 volume% of dispersed particles. These results were not influenced by changing the particle size or shape over fairly wide ranges (at room temperature). The conditions of heterogeneity used were far outside the limits implied by a previous mathematical derivation.
Detonation reaction time in diluted nitromethane
Authors: Mallory H. Dean
Published: February 2003

It is established that the dark zone in impedance-mirror streak-camera records defines the reaction-zone region in detonating liquid explosives. A strongly boostered solution of 75/25 nitromethane/acetone shows a shortened reaction zone out to about 25 cm of free run. The steady-state reaction time is 0.4 μsec.
Formation of ultrashort pulses in dye lasers with saturable absorbers
Authors: Yasa Z. A. , Teschke O. , Braverman L. W.
Published: February 2003

Passive mode locking of dye lasers is studied with the inclusion of the relaxation times. An equation derived for the integrated gain coefficient is used to explain the shortening mechanism in the long pulse stage in which gain saturation is shown to have an emphasized role in the compression of the trailing edge.
Thermal properties of Nb from acoustic and electrical resistivity measurements in the temperature range 60–340 K
Authors: Cannelli Gaetano , Cannelli Giovanni Bosco
Published: February 2003

The thermal diffusivity and the relative difference in molar heat capacities, (Cp−Cv)/Cv, of polycrystalline niobium have been derived from acoustic measurements in the temperature range 60–340 K. The electrical resistivity has also been measured from 8 to 340 K; 0.833 μΩ cm, 18.7, and 9.25 K being the values of residual resistivity ρ0, resistance ratio ρ (300 K)/ρ0, and superconducting transition temperature, respectively. The thermal conductivity, Lorenz ratio, and molar heat capacity at constant volume have been calculated for the temperature range 60–340 K, using present values of thermal diffusivity, electrical resistivity, and literature values of specific heat Cp. A shallow maximum in the derived thermal conductivity curve is observed around 180 K where the Lorenz ratio assumes the maximum value 3.15×10−8 W Ω K−2. It is suggested that the thermal conductivity maximum may originate in the phonon contribution.
Radiative recombination efficiencies in Ga(As,P)  : N and (In,Ga)P : N
Authors: Kleiman George G.
Published: February 2003

The recombination kinetic equations for a III-V mixed crystal alloy containing isolated nitrogen impurities [e.g., Ga(As,P)  : N and (In,Ga)P : N] and acceptor impurities are solved in steady state, and the internal quantum efficiency is calculated for compositions greater than that at the direct-indirect crossover. The model which is considered treats three states of the nitrogen: neutral nitrogen, electrons bound to the nitrogen by a short-range potential (i.e., the Koster-Slater model), and hydrogenic excitons bound to the nitrogen. In addition, intervalley scattering is included. Because of the large densities of states of the indirect X minimum and the valence band, a simple appoximation is derived which is roughly valid for nitrogen and acceptor concentrations less than the corresponding densities of states associated with the X minimum and the valence band. From the short thermalization times for bound electrons and bound excitons, the roles of the X minimum in efficiently pumping electrons into the nitrogen level and of the valence band in supplying holes to the bound excitonic states are elucidated. In addition, the bound-exciton radiative lifetime is found to be dominant in determining the composition dependence of the efficiency. The internal quantum efficiency for a large excitonic hole capture cross section is proportional to the product of the nitrogen and free-hole concentrations and is in good agreement with light-emitting-diode experiments. These results emphasize the importance of nitrogen for light emission in these systems.
Stimulated emission in gallium phosphide excited by two-photon optical pumping
Authors: Adduci F. , Catalano I. M. , Cingolani A. , Minafra A.
Published: February 2003

The luminescence properties of GaP (Te) have been investigated under strong optical pumping by a ruby laser (two-photon excitation) at 80 °K. Stimulated emission is observed at 5413 Å with a pumping threshold of 13 MW/cm2. Gain measurements at various intensities are also reported.
dc electrical conduction in thin Ta2O5 films. II. Highly imperfect films
Authors: Young Peter L.
Published: February 2003

Experimental results on the dc conduction characteristics of highly imperfect Ta2O5 films are presented. Two regions with distinct conduction mechanisms have been identified. In the high-field region the conduction mechanism is bulk limited. In the low-voltage region the conduction mechanism is electrode limited and obeys a modified field-emission equation. Quantitative comparison between theory and experiment is possible. As a result, the nature of the Ta2O5-metal interface is identified. Based on reasonable estimates of the donor density and the effective mass of conduction electrons, the energy diagram of Ta2O5 can be deduced. There is also some experimental evidence which appears to be contradictory to the present interpretation. Plausible explanations for these discrepancies are discussed.
Energy deposition of superpinched relativistic electron beams in aluminum targets
Authors: Perry F. C. , Widner M. M.
Published: February 2003

Dynamic response data, which traditionally have been used to obtain equation-of-state (EOS) information of materials, were instead used here to study energy deposition of an intense (∼1011 W/cm2) tightly focused relativistic electron beam (REB). Measurements of the REB-induced shock-wave transit time and average rear-surface velocity were compared with two-dimensional hydrodynamic calculations which contain well-known EOS information for 6061-T6 aluminum. The experimental results were consistent with classical electron deposition, i.e., a one-dimensional Monte Carlo transport calculation. In addition, peak pressures in the range 1–2 Mbar (0.1–0.2 TPa) were implied. Two anomalous effects were observed: (i) a low-amplitude (free-surface velocity ∼104 cm/sec) precursor signal, preceding the REB-induced shock wave and (ii) a velocity distribution of material behind the rear surface of the target following the arrival of the REB-induced shock wave.
1/f noise of deformed crystals
Authors: Stroeken J. T. M. , Kleinpenning T. G. M.
Published: February 2003

It is investigated whether dislocations produced by plastic deformation have an effect on resistivity, mobility, free-carrier density, and 1/f noise in p-type silicon and n-type germanium. In all cases the resistivity increases and the mobility decreases with increasing deformation. The relative 1/f noise spectral density can be represented by SV(f)/V2=α/Nf, where V is the voltage, f is the frequency, N is the total number of free carriers, and α is a constant. The constant α is found to be independent of the degree of plastic deformation. It is found that the 1/f noise in liquid mercury can also be characterized by the above expression with the same constant α.
Dependence of surface recombination velocity of InSb on temperature and α bombardment dose
Authors: Skountzos P. A. , Euthymiou P. C.
Published: February 2003

The influence of temperature on surface recombination velocity S is studied by photomagnetoelectric measurements, for four specimens of n InSb before and after α particle bombardment at room temperature. A maximum is observed in all curves. The influence of dose on S is confirmed to be linear. We try to explain the observed maxima proposing a model for the position of energy levels Et of the recombination centers into the energy gap at higher and lower values of temperature than its value To at which the observed maximum occurs.
Coaxial digital pulse compression for high-power Nd : glass lasers
Authors: Dubé George
Published: February 2003

A new method is suggested for using a single exploding mirror to efficiently combine any number of temporally separated coaxial laser pulses so that all pulses simultaneously irradiate a small target. Besides increasing the output and efficiency of the large Nd : glass laser systems being used in fusion research, this method would also isolate the laser from target reflections and protect the target from premature irradiation by amplified spontaneous emission.
Collisional dynamics of charge exchange in xerographic developers
Authors: Ahuja S. K.
Published: February 2003

A model of the dynamics of charge exchange between metal and polymer spheres is applied to charging of xerographic carriers and toners. The model shows that the magnitude of charge exchange during mixing of carrier and toner particles depends upon a material rate constant (barrier height of carrier-toner contact), temperature at contact, geometry of carrier and toner surfaces (sizes), velocity of approach between carrier and toner, and the ratio of volume of voids to that occupied by the solid matter in the cavity. Using thermionic emission as the mechanism of charge transfer across the carrier-toner interfacial layer, an expression showing the dependence of current density on the barrier height of the carrier-toner contact and the temperature at the contact is investigated in depth. If we assume surface state charges to be much greater than the space charges on the toner surface, the barrier height will depend upon the work-function difference between carrier and toner, the density of surface states of toner, and the level to which states are filled up on the neutral surface. From the expression of current density, we derive an equation for charge on the carrier sphere resulting from collisions with a single or a group of toner spheres.
Voltage-frequency thresholds for MBBA viewed in transverse electric fields
Authors: Jennings B. R. , Watanabe H.
Published: February 2003

Observations have been made of the behavior of MBBA nematic liquid crystal by viewing perpendicular to the direction of applied electric fields. Voltage threshold characteristics and dynamic-scattering patterns were different from those commonly seen when viewed parallel to the applied field direction.
Far-vacuum-ultraviolet transmission spectrum of uracil thin films
Authors: Hou Pon-Wei , Rampling R. P.
Published: February 2003

The method of directly subliming a thin film of specimen onto a scintillator has been used to extend its vacuum ultraviolet (VUV) transmission spectrum. With He light the far-VUV transmission spectrum of a thin film of uracil from 4 to 21 eV (300–60 nm) has been obtained and is presented here. The results are in good agreement with VUV spectra previously obtained up to 10 eV and with electron energy loss measurements up to 21 eV.
Determination of interface and bulk-trap states of IGFET’s using deep-level transient spectroscopy
Authors: Wang K. L. , Evwaraye A. O.
Published: February 2003

A transient capacitance technique for measuring the interface states and bulk traps in IGFET’s is described. When the source and drain are biased properly, IGFET’s may be pulsed from deep depletion to accumulation. The change of surface potential and the space-charge region as a result of the pulsing affects the occupation of the interface states and bulk traps in the band gap. The capacitance transient when the pulse is restored represents the emission of majority carriers, and from this transient the interface-state and bulk-trap energies may be determined. Similarly, the emission transient of minority carriers may also be measured in terms of the gate capacitance transient by pulsing the source and drain to invert the surface.

Au-implanted IGFET’s were used as an example to demonstrate the technique. In addition to the gold levels in silicon, other defect levels were observed. These may be complexes of gold with other impurities and defects.
Traps in Al2O3 detected by tunneling
Authors: Skarlatos Y. , Barker R. C. , Yelon A.
Published: February 2003

New structure, quite different from inelastic tunneling peaks, has been observed in electron tunneling spectra of MOM junctions. A capacitance peak is associated with this structure, which is attributed to traps in the oxide at energies smaller than those previously reported. The C-V characteristics calculated using a single-energy trap model agree with experimental results; however, no satisfactory explanation has yet been found to account for the strong temperature dependence of the trap energy levels.
Photoconductive processes in Al2O3 films
Authors: Powell R. J.
Published: February 2003

Photocurrents have been measured in pyrolytic Al2O3 films on silion using strongly absorbed vacuum uv radiation. These currents show a behavior similar to that observed in SiO2 films; namely, there is a primary photocurrent component and a secondary component which results after the trapping of holes in the oxide enhances tunnel injection of electrons from the silicon electrode. The electron injection is observed with smaller applied fields in Al2O3 because of the trap-assisted tunneling mechanism known to be active in this material. Interpretation of the results is complicated by the presence of both electron and hole traps. Nevertheless, two limiting models are proposed to provide a qualitative explanation.
Interface state density and oxide charge measurements on the metal–anodic-oxide-InSb system
Authors: Etchells A. , Fischer C. W.
Published: February 2003

The electrical properties of the interface between anodically grown In2O3 and n-type InSb have been studied by constructing MOS-type devices and measuring the capacitance-voltage characteristic of these at 77 K. Oxides having thicknesses between 400 and 9000 Å were prepared by anodization at constant current in 0.1N KOH. The voltage shift between the experimental and ideal theoretical curves is used to find the magnitude and sign of the surface state charge and the metal-semiconductor work-function difference. We find that the oxides consistently exhibit a positive surface state charge and on those having an Al gate electrode the work-function difference is practically zero. Bias-temperature-stress measurements on thick (tox≳2000 Å) oxides are used to evaluate the sign of the ions which are mobile at 300 K. These ions, believed to be Sb, carry a positive charge. Bias-temperature-stress measurements on thin (tox<2000 Å) oxides show effects attributed to electron injection from the InSb into traps in the oxide. At 77 K a trapped negative charge layer can change the apparent sign of the surface state charge.
Composition versus a0 and T
c relations in superconducting ’’Nb3Ge’’ thin films
Authors: Rogowski Donald A. , Roy Rustum
Published: February 2003

A large series of well-crystallized ’’Nb3Ge’’ thin films have been prepared by carefully controlled rf sputtering. The compositions expressed as Nb/Ge ratios for these essentially single-phase ’’Nb3Ge’’ thin films were determined by electron microprobe (EMP) analysis, ion scattering spectrometry, and wet chemistry (WC). Based on lattice-parameter considerations, this series of films spanned the entire homogeneity range of ’’Nb3Ge’’ phases, from the metastable Ge-rich end (a0<5.167 Å) to the metastable Nb-rich end (a0≳5.176 Å). The data from the different analytical methods and annealing experiments suggest that typical films are Ge enriched at the substrate interface and germanium and/or oxygen enriched for almost 600 Å from the exposed surface. Intercorrelations of increased reliability have now been established between Tc, the Nb/Ge ratio, and a0. An extrapolation of the EMP Nb/Ge ratio versus a0 and Tc data predict an a0 of 5.127 Å and a Tc of 23.4 °K for a phase of Nb3Ge stoichiometry. The correlation between the EMP Nb/Ge ratio and a0 obtained from a single-phase bulk ’’Nb3Ge’’ sample was found to be in excellent agreement with the data obtained from the present study’s rf-sputtered ’’Nb3Ge’’ thin films.
Low-field magnetic properties of Fe80B20 glass
Authors: O’Handley R. C. , Mendelsohn L. I. , Hasegawa R. , Ray R. , Kavesh S.
Published: February 2003

The low-field magnetic properties of Fe80B20 glass are examined. Measurements are reported for straight strips, stressed and unstressed, for as-cast/as-wound toroids and for field-annealed toroids. Due to the positive magnetostriction (λs=31×10−6) of the alloy, the low-field magnetic properties of strips are improved by applied tensile stress. Similarly, toroids annealed to remove compressive stresses induced by winding (cooled in a magnetic field) are superior to unannealed toroids. Field-annealed Fe80B20 toroids show a coercivity of ∼0.04 Oe, a permeability of 4000 at 20 G, and a remanence ratio of 0.77Bs(Bs=16 kG). The approach of the magnetization to saturation for field-annealed toroids indicates a magnetic anisotropy energy density of about 5×103 erg/cm3. This low magnetic anisotropy, as well as the low coercivity and high resistivity (145 μΩ cm±10%) exhibited by Fe80B20 lead to low core loss under ac excitation, i.e., 0.10 W/kg (measured at 1 kHz and a maximum induction of 1 kG on a field-annealed toroid).
Dy-doped MnCuBi0.86 films for magneto-optic storage application
Authors: Katsui A.
Published: February 2003

Magnetic and magneto-optic properties of MnCu1−XDyXBi0.86 (0⩽X⩽0.30) films prepared by vacuum deposition are reported. The rectangularity of the magnetic hysteresis loops and their relative remanence of MnCuBi0.86 films are improved remarkably by dysprosium doping. The coercive field increases considerably with increasing dysprosium concentration X. At the wavelength 6328 Å, the Faraday rotation at room temperature decreases with increasing dysprosium concentration from 2.7×105 deg/cm for X=0 to 1.5×105 deg/cm for X=0.30. The Faraday rotation increases gradually with decreasing wavelength. The maximum Faraday rotation appears at about 5100 Å wavelength. The magneto-optic figure of merit for transmission-type memory use decreases from about 1.3 deg for X=0 to 0.85 deg for X=0.30 at a wavelength of 6328 Å. These figures of merit are one-third to one-half of those of MnBi, but they are still greater than those of the other magneto-optic materials. The MnCu1−XDyXBi0.86(0⩽X⩽0.30) films, with excellent magnetic hysteresis characteristics, have been shown to be suitable for magneto-optic storage media.
Magnetization and magnetic anisotropy in evaporated GdCo amorphous films
Authors: Taylor R. C. , Gangulee A.
Published: February 2003

Saturation magnetizations and magnetic anisotropy constants were determined for a series of amorphous GdCo films prepared by thermal evaporation. The films covered the composition range from Gd0.05Co0.95 to Gd0.40Co0.60 and were studied by means of ferromagnetic resonance and a force balance magnetometer. The films, in contrast to those prepared by sputtering, had a hard perpendicular direction of magnetization when Co was less than 91 at.%, and easy and moderate directions within the plane of the film. The anisotropy constant can be expressed in terms of sublattice magnetizations by Ku=0.660MCo2 +2.218MCoMGd+0.097MGd2. The results are explained based on a pair-ordering mechanism. The composition and temperature dependence of saturation magnetization is essentially the same in evaporated and sputtered films.
Simple stability criterion for feedback control of unstable waves
Authors: Crowley Joseph M.
Published: February 2003

Feedback control of instabilities in a continuum is a useful technique, but the analysis of such controlled systems is complicated by the coupling of the normal modes in the feedback loop. A simpler analysis is developed here which shows that mode coupling can be neglected if the feedback is not too large. This simpler method is applied to several examples, and comparisons with earlier more exact results show good agreement over the range of validity of the approximation.
Model for switching surge breakdown of a point-to-plane air gap
Authors: Salama M. M. A. , Parekh H. , Srivastava K. D.
Published: February 2003

A theoretical model for streamer propagation and subsequent breakdown in a long air gap is proposed. A rod-to-plane geometry is considered and a switching voltage of positive polarity is applied to the rod electrode. Results are obtained for different rod radii and gap lengths. The computed results are compared with the experimental results.
Fast-rising magnetic field with long pulse duration—a new technical concept for large plasma experiments
Authors: Wilhelm R.
Published: February 2003

A new technical concept makes possible the production of fast-rising magnetic fields (rise time ≲1 μs) with very long pulse durations (decay up to 100 ms), as required in future pulsed plasma experiments. The concept is based on a transient transformer system using iron cores inside a closed coil. Problems concerning the properties of the iron at extreme pulse conditions (effective μ, energy losses) are discussed. According to a large-scale model experiment (coil current 1 MA, rise time ∼1 μs, decay ∼6 ms) a fast megavolt compression with a pulse duration up to 100 ms should be achievable in a large torus (belt pinch).
Ion bunching in electronic space-charge regions
Authors: Johnson W. L. , Johnson G. B. , Verdyen J. T.
Published: February 2003

This experimental work demonstrates that energy can be transferred from an electron beam to ions in a volumetric plasma source. Furthermore, it is shown that the resulting space-charge neutralized ion pulse can be compressed or ’’bunched’’ in time. These experiments also demonstrate some unique transient interactions between the electron beam and the background plasma.
Particle distribution parameters in an electron storage ring
Authors: Chao Alexander W. , Lee Martin J.
Published: February 2003

The distribution function of particles in a plasma can often be found by solving the Fokker-Planck equation. This technique can also be used to find the average particle distribution in an electron storage ring in the presence of coupling between the particle coordinates and momenta. Using a smooth approximation, the beam distribution parameters, such as the transverse beam size, can be described in terms of the eigenvalues and eigenvectors of the coupling matrix. For some case, analytic expressions for these quantities can be obtained directly. This method offers us a straightforward means to find the functional dependence of the beam-shape parameters upon various machine parameters which are essential for storage-ring design.
Measurement of temperature fluctuations and wave-induced losses associated with the drift-Alfvén instability in a finite-β collisional plasma
Authors: Holt J. L. , Luhmann N. C. , Tang J. T.
Published: February 2003

Detailed measurements of temperature fluctuations associated with drift-Alfvén instability in a finite-β collisional plasma column are reported. The experimentally determined magnitude and phases of density, temperature, floating potential, and plasma potential fluctuations are in agreement with values calculated assuming an adiabatic equation of state. In addition, the radial wave-induced diffusion is found to be comparable to Bohm diffusion and much larger than classical diffusion for the drift-wave branch of the instability and comparable to both Bohm and classical diffusion for the Alfvén branch.
Measurement and analysis of temperature-dependent rf impedance of discontinuous metal films on glass substrates
Authors: Harkay J. R. , Crowell A. D.
Published: February 2003

The electrical impedance of evaporated films of Mo, Pt, Al, and Cu was measured as a function of frequency from 0.5 to 30 MHz at temperatures in the range 100–450 K. The films were evaporated onto glass substrates held at various temperatures and had final thicknesses such that they were discontinuous. The impedance of such films is frequency dependent but may be represented by an equivalent circuit of frequency-independent resistance and capacitance parameters, Rb, Rg, and Cg. Rb is associated with conduction within the grains of the film and was observed in most cases to be metallic, i.e., to possess a positive temperature coefficient of resistance (TCR). Rg and Cg are associated with intergranular conductivity, and Rg was observed to have a negative TCR and is assumed to be the result of an activated process, i.e., Rg(T) =Rg(∞)  exp(Ea/kT). The behavior of the various films is discussed in terms of the relationship among values of Rb, Rg, Rg(∞), and Ea. A scheme to classify film-substrate systems according to relative activation energies and relative interangular barriers is proposed.
Atmospheric-pressure H2-F2 laser initiated by electron-beam-irradiated discharge
Authors: Hofland R. , Ching A. , Lundquist M. L. , Whittier J. S.
Published: February 2003

Initial performance of an electric-discharge-initiated chemical laser pumped by the H2-F2 chain reaction is presented. Uniform microsecond-scale discharges in atmospheric-pressure laser mixtures have been obtained after a short-duration ionizing pulse of high-energy electrons. Care in discharge pulse shaping is required to avoid late-time arcs. Informaiton is presented on the effects of several parameters on laser performance. With a 3 H2 : 6 F2 : 54 He : 37 Ar mixture as much as 28 J/liter of discharge energy could be deposited in the mixture, and laser energies up to 42 J/liter were obtained. This corresponds to a chemical efficiency of 6.3%, based on the H2 content, and an electrical ’’efficiency’’ of 148%, based on the available lasing volume and total energy input to the medium.
Liquid-phase epitaxial growth of 6H-SiC by the dipping technique for preparation of blue-light-emitting diodes
Authors: Suzuki A. , Ikeda M. , Nagao N. , Matsunami H. , Tanaka T.
Published: February 2003

Epitaxial growth of 6H-SiC has been carried out at 1500–1650 °C on 6H-SiC substrates dipped into a Si melt in a graphite crucible. Epitaxial layers up to 100 μm thick have been deposited on the {0001} faces after 5 h growth. Layers grown on the Si faces at 1600 and 1650 °C have fairly flat and smooth surfaces. Undoped layers show n-type conduction with a typical carrier concentration of 6.3×1017 cm−3 and mobility of 130 cm2/V sec at 300 °K. n- and p-layers of higher carrier concentrations are obtained by the doping of nitrogen and aluminum, respectively. A p-n junction is prepared in one growth run by an overcompensation procedure. Blue electroluminescence observed under the forward bias has enough brightness under room light at room temperature. The peak wavelength is 485 nm. The external quantum efficiency is 1.0×10−5 photons/electron at 300 °K.
Point defects in fully conjugated polymers
Authors: Baughman R. H. , Chance R. R.
Published: February 2003

Formation thermodynamics is examined for two different types of point defects which interrupt conjugation in polydiacetylene crystals: bond-alternation and orbital-flip defects. While bond-alternation defects in these polymers are analogous to previously investigated radical pair defects in the polyenes, much lower equilibrium concentrations are expected in the polydiacetylenes than in the polyenes. For polydiacetylenes with small substituent groups or high-energy side-group packing, orbital-flip defects provide a more plausible rationale for explaining observed thermochromism and carrier trapping effects in photoconductivity. During the formation of this type of defect, a π orbital at each of the two neighboring sp2 carbon atoms is rotated by 90°, so that the rotated π orbitals become conjugated with the out-of-plane orbitals neighboring sp carbon atoms. Thereby the system of overlapping π orbitals is interrupted without substantially decreasing the electronic stabilization energy. With an intramolecular strain energy increase of only about 2.6 kcal/mole, the polymer chain can return to lattice register within one monomer unit of the defect center. Since the electronic stabilization energy change is even smaller (about 0.2 kcal/mole), the major contribution to defect formation energy arises from the side-group rotations.
Epitaxial crystallization of polyoxymethylene
Authors: Rickert S. E. , Baer E.
Published: February 2003

Epitaxial growth of synthetic polymers on alkali-halide surfaces usually proceeds along the preferred 〈110〉 directions parallel to the {100} plane of the substrate. Polyoxymethylene was epitaxially crystallized as thin films on alkali halides and analyzed using the electron microscope. The metastable orthorhombic crystal form was obtained on substrates which exhibited a lattice match with the [100] distance of the orthorhombic form. Matching was not necessary for the growth of the normal hexagonal crystal form, although it did affect both the nucleation process and the growth rate of the epitaxial crystallization. The technique seems to be quite generally applicale in affecting the general morphology of the crystallization and the formation of metastable polymeric forms.
Iterative approaches describing atomic diffusion in finite single- and two-phase systems
Authors: Houska C. R. , Unnam J.
Published: February 2003

Iterative solutions are given for planar one-dimensional atomic diffusion in finite single- and two-phase systems. They are usable for any continuous variation of the interdiffusion coefficient D (C) within each phase, and need not be fitted to special functions such as a power series or an exponential function. Modified integral functions similar to one first proposed by Boltzmann are used along with a conservation criterion to locate the interface position ξ. Computer time for the iterative solutions is about two to three magnitudes shorter than finite-difference (F-D) calculations because of the rapid convergence of the integral equations. The accuracy of these approximate forms is considered. Excellent agreement was obtained between F-D calculations and the iterative approach for semi-infinite single-phase systems. Good agreement is also found for two-phase systems; however, the accuracy varies with the solubility gap size Cβα−Cαβ. The best results are obtained for gaps larger than 0.7 which includes most eutectic systems. Calculations of composition profiles which are based upon the maximum solid solubilities for the Cu-Ag system are within 1% of the F-D calculations.
Acoustic characteristics of twinning in indium
Authors: Van Doren Stephen L. , Pond Robert B. , Green Robert E.
Published: February 2003

With the increased use of acoustic emission as a nondestructive testing tool, it has become extremely important to document and to understand the emissions characteristic of various modes of deformation and fracture. In the present work, results are reported of acoustic emission measurements made during mechanical deformation of indium single crystals. Although the metal indium is of little structural importance, it develops well-delineated twins with associated acoustic emissions, and therefore affords an excellent medium with which to develop techniques and to generate interpretations which can be applied to structurally important materials. By recording the acoustic emission signals on a video-tape recorder it was possible to play them back as often as desired and to observe them in slow and stop motion. The experimental results show that a correspondence exists between the duration of the acoustic signal and the volume of twinned material as determined by cinematographic observation of the generation and growth of twin bands. Repetition of some waveform features was demonstrated not to be the result of multiple reflections of the emitted elastic waves from bounding surfaces, but to be related to actual physical events associated with the twinning process. It was also demonstrated that the direction of the stress, tensile, or compressive, induced in the body of the crystal due to twinning, can be determined from the polarity of the elastic wave emitted by the twin as detected by the transducer.
Detection and origins of crystal defects in GaAs/GaAlAs LPE layers
Authors: Woolhouse G. R. , Blakeslee A. E. , Shih K. K.
Published: February 2003

We report the discovery that shallow growth pits develop on the surfaces of GaAs/GaAlAs double-heterostructure wafers prepared by liquid phase epitaxy where the surfaces are intersected by crystal defects. The growth pits enable nondestructive defect characterization of such wafers to be made by optical microscopy. It is found that pits due to stacking faults are more readily detected than pits due to undissociated dislocations. The results of a search for the origins of the defects in the material are also presented. Characteristic ’’star’’ patterns develop when the material is etched. TEM observations show that these are due to clusters of crystal defects which originate at inclusions buried in the grown material.
Nucleation and growth of an epitaxial monolayer of Cd on Ge(111): A simultaneous RHEED–molecular-beam study
Authors: Matysik K. J.
Published: February 2003

The nucleation and growth of an epitaxial monolayer of Cd on Ge(111) was studied by simultaneously employing RHEED and the mass spectrometric molecular beam (MSMB) technique. The MSMB spectra are discussed in terms of the atomistic rate theory of nucleation and the correlation between structures and spectra is presented. The results suggest that a convention of nucleation rate theory, that growing clusters act as monomer capture centers which increase in capture efficiency with time, does not hold at submonolayer coverages for this system. A model where capture efficiency decreases with cluster size is considered and from this model an estimate of the heat of adsorption and the activation energy for diffusion of monomers is obtained. Independent of the model we find that the nucleation process precedes the epitaxial alignment of clusters.
Current runaway in insulators affected by impact ionization and recombination
Authors: Klein N. , Solomon P.
Published: February 2003

When impact ionization occurs, current runaway can arise in insulators, due to a regenerative effect between the rate of ionization and the rate of current injection at the cathode. Solving a set of conduction equations analytically, the critial field for current runaway ?r was determined as a function of insulator properties, when the effect of impact ionizations is opposed by recombinations. Current transients were obtained by computer solutions for fields both smaller and larger than the critical field ?r. The current transients can be used to determine the ionization coefficient and the recombination cross section. For fields larger than ?r times to current runaway tr were found to decrease quasiexponentially with increasing field.
Grain-boundary diffusion in thin films. II. Multiple grain boundaries and surface diffusion
Authors: Gilmer G. H. , Farrell H. H.
Published: February 2003

Diffusion in polycrystalline thin films is investigated using both analytical and numerical methods. Bulk, grain-boundary, and interfacial diffusion are all included in the analysis, and the conditions under which each process influences the concentration profile are evaluated. The thin film is treated as a slab of finite thickness containing uniformly spaced grain boundaries that are perpendicular to the plane of the film. One surface of the slab is assumed to be in contact with an infinite reservoir of the diffusing species. Three limiting cases are considered in which the second surface is (i) a barrier to diffusion, (ii) a plane with an infinite surface diffusion coefficient, and (iii) a zero-concentration surface.
Lattice dislocation near a surface
Authors: Jagannadham K.
Published: February 2003

The lattice model for a screw dislocation and for an edge dislocation near a surface and parallel to it are obtained. It has been shown that η/d, which is taken as the width of the dislocation for a Peierls-Nabarro dislocation, increases as the edge or the screw dislocation approaches the surface. The properties of the lattice dislocations are derived. The attractive image stress acting on the dislocation is obtained.
Preliminary investigation of elongational flow of dilute polymer solutions
Authors: Peng S. T. J. , Landel R. F.
Published: February 2003

A tubeless siphon apparatus has been set up to measure extensional flow. In this apparatus the liquid is continuously drawn into a capillary and, after steady flow has been established, the tube is raised above the liquid surface. With viscoelastic liquids the flow continues and a column can be lifted from the reservoir. At the capillary entrance an oscillating bead of excess liquid collects, which interferes both with the flow and the measurements. This can be minimized by careful control of the liquid column height. For homogeneous solutions the column is symmetrical and tapers steadily from the liquid surface to the capillary entrance, with no bulging. Preliminary results show tensile viscosities 103 times that of the Trouton coefficient 3ηS0, where ηS0 is the zeroshear-Rate shear viscosity, and having a very strong dependence on deformation rate. A concentration-stretch-rate-reduced variable scheme is proposed.
Time dependence of small-angle x-ray measurements on segmented polyurethanes following thermal treatment
Authors: Wilkes Garth L. , Emerson John A.
Published: February 2003

Using the method of small-angle x-ray scattering (SAXS), the time-dependent structural changes in some linear-segmented urethanes have been investigated. The results directly support the time- and temprature-dependent morphological model proposed earlier by one of the authors. Specifically, upon heating of many linear urethanes, the degree of domain structure is decreased. Upon quenching to ambient temperature, there is a significant period of time required to reestablish the domain structure which, in turn, strongly influences the time-dependent mechanical behavior.
Rayleigh-Brillouin light-scattering studies on atactic polystrene
Authors: Coakley R. W. , Mitchell R. S. , Stevens J. R. , Hunt J. L.
Published: February 2003

Rayleigh-Brillouin light-scattering studies have been carried out on atactic polystyrene thermally polmerized under vacuum from scrupulously clean styrene monomer. The ratio of the central Rayleigh intensity IR to the total Brillouin intensity 2IB appears to be a function of T−1. Depolarization intensities have also been measured and, in particular, we find that ρH=1 for this polymeric glass. Theoretical predictions for IR/2IB are discussed in light of these results. We conclude that local isotropy due to strain fields frozen into glass is negligible or in low concentration. Annealing studies confirm this result which is in disagreement with our previous results for poly(butyl) methacrylate. In addition, we find that the change in slope of the Brillouin frequency shift ω versus absolute temperature T defines a Tg 10–12 K below that measured by DSC and that ω (glass) increases with decreasing molecular weight, in agreement with previous results. A study of the relaxation of a few degrees below Tg for periods of a month and more does not shift Tg (from ω vs T) to lower temperatures for these high-molecular-weight polystyrene samples.
Application of the Dugdale model to crazing and fracture in rubber-modified polystyrene
Authors: Hoffman R. D. , Richmond O.
Published: February 2003

The fracture toughness of impact (rubber-modified) polystyrene can be more adequately described by a strain criterion than by a stress criterion, such as KIC. Recent work from other laboratories has resulted in several theories which relate plastic-zone length (craze length), applied stress, and crack-opening displacement for edge-notched finite-width strips pulled in tension. Experimental data on impact polystyrene show that a solution of the problem due to Ashbaugh gives the best representation of crack-opening displacement as a function of craze length, but with a significant deviation from experiment even so. Within experimental error, fracture initiation occurs at a constant crack-opening displacement. The applied stress required to generate a given craze length is higher than predicted by the Asbaugh theory for rotatable grips.
Reduction of the ac losses of multifilament superconductors by the use of low twist rates
Authors: Kwasnitza K. , Horvath I.
Published: February 2003

The ac losses of differently twisted samples of a multifilament superconductor in a magnetic field B=Bs +B0 sinωt have been measured. The over-all loss per cycle has a maximum at a frequency fm, which shifts to smaller frequency values with decreasing twist rate. At certain frequencies a multifilament superconductor has lower over-all losses when its twist rate is decreased. The reason is that the coupling current losses in the matrix decrease with increasing twist for f<fm but increase with increasing twist rate for f≳fm.
The possibility of high-energy-storage lasers using the auroral and transauroral transitions of column-VI elements
Authors: Murray J. R. , Rhodes C. K.
Published: February 2003

An analysis of laser systems involving the auroral and transauroral transitions of photolytically excited column-VIA elements is given. Excitation mechanisms, kinetic processes, and collisionally stimulated radiation are examined. Photolytic production of the VIA 1S metastable using rare-gas excimer radiation is emphasized. Oxygen at 5577 Å, sulfur at 7727 and 4589 Å, and possibly selenium at 4888 Å appear as attractive candidates suitable for high-energy-storage short-pulse applications.
X-ray topographic observations of magnetic domains in Czochralski-grown nickel single crystals in anomalous transmission geometry
Authors: Kuriyama Masao , Boettinger William J. , Burdette Harold E.
Published: February 2003

The anomalous transmission effect has been observed in nickel single crystals grown by the Czochralski technique. Sample crystals prepared for x-ray topography are 1.5–2.5 cm in diameter and thicker than 0.4 mm; the product of the ordinary linear absorption coefficient and thickness ranges from 17 to 45 for Cu Kα radiation. Topographs taken with an asymmetric-crystal-topographic (ACT) camera have revealed extremely straight line images and rectangular arrangements of short line-segment images, along with the images of crystal imperfections. The line images change their arrangement upon application of magnetic fields. These images are attributed to magnetic domains in the interior of crystals. The formation of domain walls near the crystal surface is also observed and distinguished clearly from magnetic domains in the bulk with the use of the ACT camera.
New magneto-optic thin films for storage application
Authors: Katsui A. , Shibukawa A. , Terui H. , Egashira K.
Published: February 2003

A new magneto-optic thin film having a composition defined by Mnx(Cu1−y′Niy′)yBiz, where x+y+z=1, 0.15?x?0.70, 0.10?y?0.55, 0.11?z⩽0.55, and 0<y′<1, was prepared by vacuum deposition. In this composition range the film has a Curie point between 100 and 200 °C and satisfactorily large magneto-optic figures of merit. It is stable against moisture. The maximum value of the magneto-optic figure of merit 2F/α is 1.1 deg for a wavelength of 6328 Å, where F is the specific Faraday rotation and α is the absorption coefficient. The hysteretic characteristics of the film can be improved by adding Ti, V, or Cr. The film is suitable for a magneto-optic storage medium.
Near-uv photon efficiency in a TiO2 electrode: Application to hydrogen production from solar energy
Authors: Desplat J.-L.
Published: February 2003

An n-type (001) TiO2 electrode irradiated at 365 nm was tested under anodic polarization: a saturation current independent of pH and proportional to light intensity has been observed. Accurate measurements of the incident power lead to a 60% photon efficiency. A photoelectrochemical cell built with such an electrode, operated under solar irradiation without concentration, produced an electrolysis current of 0.7 mA cm−2 without applied voltage.
Influence of the secondary electron emission coefficient of argon on Paschen breakdown curves in ac plasma panels for neon+0.1% argon mixture
Authors: Sahni O. , Lanza C.
Published: February 2003

A generalized expression has been derived for the effective secondary electron emission coefficient γ, in Penning mixtures which incorporates the effect of both the majority and minority ions. Specific calculations for ac panels having an Ne+0.1%Ar mixture show that even a relatively small value of γAr not only significantly lowers the breakdown voltages, but also moves the voltage minimum to higher p0d values and makes the right-hand side of the Paschen curve less steep. This sensitivity of the effective coefficient γ on γAr is sufficient to explain the critical dependence of the shape of the measured breakdown voltage curves in ac panels on minor changes in the surface properties of the deposited insulator surfaces.
A measurement of interface states in MIS structures by thermally stimulated charge decay
Authors: Yamashita K. , Hino T.
Published: February 2003

Thermally stimulated charge decay is applied to determine the energy distribution of interface states at the insulator-semiconductor interface. TSCD is measured in open circuit and the surface potential of the semiconductor can be easily obtained. A method to estimate the energy distribution from TSCD is explained using experimental results in Al-SiO2-Si MIS structure.