bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic domains in (Gd0.5Y2.5)(Ga1Fe4)O12 garnet films
Authors: Reisinger A. R. , Tseng S. C. , Powell C. G.
Published: February 2003

We present a model which explains the behavior of the magnetization and the resultant stripe domain patterns in thin films of (Gd0.5Y2.5) (Ga1Fe4)O12 grown by liquid-phase epitaxy on [111]-oriented GGG substrates under the influence of dc or pulsed in-plane magnetic fields.
Magnetostriction vs Co content in amorphous alloys of Fe-Co-P-B-Al
Authors: Brooks H. A.
Published: February 2003

Magnetostriction measurements have been made on metallic glasses. Samples were of composition (Fe1−xCox)0.75P0.16B0.06Al0.03 and were produced in the amorphous state by the roller-quenching technique. The magnetostriction was found to range from λ=20 μs for x=0 to λ=−4 μs for x=0.97 with zero magnetostriction occurring when x=0.96.
Photocount time interval distribution for superposed coherent and chaotic radiation
Authors: Lachs Gerard , Voltmer David R.
Published: February 2003

There has been considerable interest in recent years in the statistical properties of optical frequency electromagnetic fields. Of particular interest is the study of photon bunching and the probability density for waiting time between adjacent photocounts. In this paper we derive an expression for the probability density of the time interval distribution as well as some other quantities of interest in photon bunching for the case where the incident radiation is comprised of superposed coherent and chaotic radiation of arbitrary spectral shapes. Calculations show that the key parameters are the average number of chaotic counts per coherence time and the ratio of the strengths of coherent and chaotic parts (signal-to-noise ratio).
Barrier modulation in Ag-diffused Au-CdS diodes
Authors: Lubberts G.
Published: February 2003

In a previous publication it was demonstrated that light-induced barrier modulation occurs in Cu-diffused Au-CdS diodes. In this paper the effect is examined in Ag-diffused Au-CdS Schottky barriers with a junction width of 4000 Å. Photoemission experiments at zero bias and logJ-V measurements indicate that a barrier reduction of 0.15–0.2 V occurs under band-gap illumination. This barrier decrease gives rise to a forward-bias current increase of 103–104. Detailed photoemission experiments have also demonstrated modulation of the barrier height by applied voltage, which is consistent with the occurrence of a conduction-band maximum within the CdS. These characteristics provide further evidence for a model that assumes a ’’humped’’ -barrier profile in diffused or ion-implanted Schottky barriers.
Grain-size effects on dielectric properties in barium titanate ceramics
Authors: Kinoshita Kyoichi , Yamaji Akihiko
Published: February 2003

Measurements of the dielectric constant κ in high-purity BaTiO3 ceramics as a function of temperature show that κ is quite dependent on grain size in the ferroelectric state while it is almost independent of grain size in the paraelectric state. In the ferroelectric orthorhombic and rhombohedral phases, κ decreases rapidly with lowering temperature when grain size is reduced smaller than 3 μm. It is also observed that the Curie temperature Tc is decreased very slightly, but the lower two transition points are shifted to higher temperatures as grain size decreases.
Spin-wave spectrum measurements in YIG by means of the spin-Raman effect
Authors: Thomas G. , Lin Pink-Kuo
Published: February 2003

The strong momentum-matching restrictions on spin-Raman scattering allow the measurement of the spin-wave spectrum when the laser and the dc magnetic fields are suitably oriented. When the laser beam is parallel to the magnetic field, spin-Raman interaction takes place at only two values of magnetic field. However, experimental observations show continuous interaction over a wide range of magnetic fields. This indicates that either the spin waves excited by the microwave field are essentially incoherent, or the spin-wave vector is constant and of an orientation and magnitude which does not change over a wide range of magnetic fields. The latter interpretation of the results is consistent with the results obtained for standing spin waves in YIG spheres.
Injection laser coupling to optical waveguides with integral lenses
Authors: Kohanzadeh Y.
Published: February 2003

Cylindrical and spherical lenses have formed on single-mode and multimode optical waveguides. The coupling efficiencies from injection lasers to these waveguides are compared experimentally. A theoretical analysis is made for multimode fibers. Coupling efficiencies as high as 72% for multimode and 37% for single-mode fibers are reported. The effect of refractive-index profile of the waveguide on coupling was studied. Step waveguides show about a factor of 2 better coupling than parabolic index waveguides.
High-power isolator for the 10-μm region employing interband Faraday rotation in germanium
Authors: Phipps C. R. , Thomas S. J.
Published: February 2003

Interband Faraday rotation in intrinsic germanium has been employed to construct a room-temperature optical isolator for use in the intermediate infrared region. The device was tested at 9.55- and 10.59-μm wavelengths, and exhibited an isolation level of 41 dB at 106 W cm−2. The rotation is shown to be relatively insensitive to temperature at the two wavelengths and linear in magnetic field intensity up to 83 kG. The isolator figure of merit is about 60 deg per dB attenuation.
Optical storage using refractive index changes induced by two-step excitation
Authors: von der Linde D. , Glass A. M. , Rodgers K. F.
Published: February 2003

Multiphoton excitation allows reversible photorefractive recording without the disadvantage of erasure during readout. The light intensity required for two-photon storage can be drastically reduced if two-step excitation via long†lived real intermediate states is used. Experimental results for LiNbO3:Cr3+ and LiTaO3:Cr3+ demonstrate the advantages of the two-step process. The energy and intensity requirements for optical two-step recording are within reach of presently available repetitively pulsed lasers.
Continuous-wave operation of Nd : YVO4 at 1.06 and 1.34 μ
Authors: Tucker A. W. , Birnbaum M. , Fincher C. L. , DeShazer L. G.
Published: February 2003

Continuous-wave plane-polarized outputs of 1 W at 1.06 μ and 0.35 W at 1.34 μ were obtained by end pumping small samples of Nd : YVO4 with an argon-ion laser. Slope efficiencies and material losses were determined. At 1.06 and 1.34 μ, Nd : YVO4 lasers can substantially outperform Nd : YAG lasers. Self-Q-switched operation of Nd : YVO4 at both wavelengths was obtained by resonator misalignment.
Energy reflected from solid targets bombarded with keV protons and helium ions
Authors: Andersen H. H. , Lenskjaer T. , Sidenius G. , So/rensen H.
Published: February 2003

The energy-reflection coefficient γ has been measured for keV protons impinging on Cu, Au, and Pb and helium impinging on Si, Ag, Ta, and Pb. The results are obtained by entirely independent techniques in three different laboratories. They agree within the stated accuracies of 10%. For a given projectile, γ is found to depend on the target material through the Thomas-Fermi reduced energy ε only. Hence, extrapolation to other target materials may easily be performed. The results are in good agreement with those obtained from recent computer simulations.
Switching in polystyrene films: Transition from on to off state
Authors: Segui Y. , Ai Bui , Carchano H.
Published: February 2003

Experiments on polystyrene films formed by a glow-discharge technique shows a reproducible bistable switching. Various interpretations are briefly reviewed. It is shown that the resistance of the on state is strictly related to the energy needed by the on-off transition. From the value of this energy it is concluded that the most probable explanation is that the on current takes place along a filamentary path constituted by carbon atoms. A quantitative analysis is made on the basis of the heat balance equation. Formation of carbonated chains is confirmed by a chromatography analysis in vapor phase which shows an hydrogen release.
Optimization of the statistical accuracy of the SANDYL transport code and comparison with an experiment by Motz
Authors: Albright N. W.
Published: February 2003

SANDYL, a Monte Carlo computer code of electron and photon transport, contains parameters whose values must be chosen properly in order to produce accurate calculations. These parameters have a wide range of possible values, and this paper gives simple rules for choosing these values. A series of computer calculations using SANDYL are compared with the experimental results of Motz.
Optical absorption in semiconducting vanadium zinc borate glasses prepared by sputtering
Authors: Koffyberg F. P. , Koziol N. J.
Published: February 2003

Semiconducting vanadium zinc borate glasses with widely varying V4+/V5+ ratios have been prepared by rf sputtering in argon/oxygen atmospheres. The optical band gap ranges from 2.4 eV (70% V2O5) to 2.8 eV (30% V2O5), and the absorption edge shows an intense temperature-dependent Urbach tail. Glasses containing V4+ show very broad crystal field absorption bands at 1.2 and 2.3 eV.
Analytic modeling of gain-switched lasers. I. Laser oscillators
Authors: Casperson Lee W.
Published: February 2003

Detailed mathematical models are derived for the evolution of light pulses in gain-switched laser oscillators. Unlike previous instantaneous-switching models, arbitrary pump and spontaneous relaxation rates are considered. Explicit expressions are obtained for the gain and pulse characteristics in several practical situations, and both homogeneous and inhomogeneous limits are considered. By proper adjustment of the laser pump any output-pulse shape can be obtained. The results are especially relevant for recent short-pulse ultraviolet lasers and also for more conventional devices such as TEA CO2 lasers.
Channeled substrate buried heterostructure GaAs- (GaAl)As injection lasers
Authors: Kirkby P. A. , Thompson G. H. B.
Published: February 2003

A technique for fabricating stripe geometry GaAs/(GaAl)As injection lasers with optical and carrier confinement not only in the plane perpendicular but also parallel to the p-n junction is reported. This independently developed channeled substrate technique is a simple extension of conventional liquid phase epitaxy requiring no regrowth and relies on the strong tendency of epitaxial layers to smooth out as they grow. The active regions of the preliminary 10- and 20-μm-wide stripe lasers that have been fabricated to date are parabolic in cross section, tapering gradually to zero at the edges and completely embedded in GaAlAs. Unlike the ’’etched buried heterostructure lasers’’ recently reported by Burnham and Scifres, the n- (GaAl)As layer is continuous, thus preventing the direct injection of carriers into the substrate. Room-temperature pulsed threshold currents are in the range 150–350 mA with efficiencies up to 30%. This paper describes the LPE growth techniques that we used to produce the two preliminary wafers. A first-order theory is presented which describes the transverse mode structure of the unusually shaped waveguide which forms the active region of the lasers. The observed mode structure agrees closely with that calculated. A mode selection effect has been observed which favors low-order transverse mode operation close to threshold in the multimode waveguides which we produced. Finally, we report the cw operation of these lasers and discuss the more significant aspects of their operation.
Comparison of experimental and theoretical carrier concentrations in heavily doped n-type silicon
Authors: Finetti M. , Mazzone A. M. , Passari L. , Pietra S. , Susi E.
Published: February 2003

The Hall coefficient and conductivity of p-doped Si samples have been measured in a range of temperatures varying from 200 to 30 °K; from the elaboration of these measurements and neutron activation analysis, both donor and free-carrier concentrations were obtained. Comparison between the theoretical and experimental values of the electron density brought out that in these samples a modified conduction band coexists with an impurity band, thus confirming the results obtained in the same range of impurity concentration for As-doped Si. Some limitations of the theoretical approaches to the density of states versus energy relationships are discussed.
Electrical properties of electron-irradiated n-type silicon
Authors: Sigfridsson B. , Lindström J. L.
Published: February 2003

Investigations of electron-irradiated n-type silicon show that the conductivity decreases with increasing dose, achieves intrinsic value, then converts into p type and increases again, reaching a saturation value. It is shown analytically that this behavior [for float-zone silicon irradiated in the (111) direction] can be described by assuming that three main damage levels (two acceptor levels and one donor level) occur simultanously due to the irradiation. The deepest acceptor level determines the dose at which the minimum value of the conductivity occurs. The two acceptor levels (at Ec−0.44 eV and Ec−0.58 eV) are responsible for the decrease in conductivity at low doses. When the density of damage centers at Ec−0.58 eV exceeds the initial doping concentration, emission of holes from this level gives a significant contribution to the conductivity causing the conductivity to increase with dose. The donor level at Ev+0.27 eV causes the saturation at large doses. A zero-current approximation is given for the conductivity versus dose dependence for an unlimited number of levels involved. These levels may be either independent levels or levels associated with different charge states of the same defect. By introducing the three levels above in this model a very good agreement with experiments on dose versus conductivity was obtained in the resistivity range 100 Ω cm to 50 kΩ cm. The results indicate that the two acceptor levels at Ec−0.44 eV and Ec−0.58 eV may be associated with the single- and double-charge state, respectively, of the divacancy. The donor level does not seem to be correlated with the acceptor levels. The positive charge state of the divacancy may therefore have a larger energy or be masked by some other defect. Besides the zero-current approximation, numerical calculations are performed, giving field distributions, charge distributions, and I-V characteristics for one simple contract structure. These calculations show (assuming sufficient electron injection but negligible hole injection) that heavily irradiated n samples are p conducting at low currents but convert back to n conducting at large currents.
Thermally induced changes of CuxS films and effect on CdS-CuxS solar-cell response
Authors: Burton L. C. , Windawi H. M.
Published: February 2003

Changes in the electrical sheet resistance and optical density of copper-sulfide (CuxS) films have been measured as functions of thermal aging in air. It was found that sheet resistance (or bulk resistivity) and optical density (or absorption coefficient) both initially increase with aging, and subsequently decrease. Maximum bulk resistivity and absorption coefficient values, corresponding to the chalcocite phase of CuxS, were found to be about 0.1Ω cm and 5×104 cm−1 (at 1.8 eV photon energy), respectively. CdS/CuxS solar-cell short-circuit current and efficiency were monitored as functions of thermal aging time, degradation being directly related to CuxS sheet resistance. The dependence of sheet resistance on CuxS stoichiometry is discussed. Several possible mechanisms are proposed to account for the observed behavior.
Peltier cooling at a In-InP interface
Authors: Abul-Fadl A. , Stefanakos E. K.
Published: February 2003

The cooling due to the Peltier effect was measured by passing electrical current across the liquid-solid interface in a vertical liquid-phase epitaxy system. Application of a steady-state heat-transfer analysis yielded values for the Peltier coefficient of InP (ND −NA?3×1016 cm−3) between 0.21 and 0.50 V in the 300–600 °C temperature range. The cooling temperatures observed could be effectively used for the growth of InP epitaxial layers.
Passive secondary magnetic damping for superconducting Maglev vehicles
Authors: Atherton David L. , Eastham A. R. , Sturgess K.
Published: February 2003

We analyze a passive magnetic damping scheme for the secondary suspension of a superconducting Maglev vehicle. The unsprung levitation or linear synchronous motor magnets are coupled electromagnetically to short-circuited aluminum damper coils mounted on the underside of the sprung mass. Relative motion between the magnets and the passenger compartment causes a time-dependent flux linkage which induces dissipative currents in the coils. Analysis for the typical Canadian Maglev vehicle design shows that a damping factor of 1 sec−1 can be obtained with a total coil mass of approximately 100 kg, for a secondary/primary suspension stiffness ratio of 0.2. This scheme appears to offer a design alternative to conventional frictional or hydraulic dampers.
Frequency analysis of the voltage oscillation of an ac- and dc-current-biased resistively shunted Josephson-junction analogue
Authors: Hendricks E. , Lindelof P. E.
Published: February 2003

We have frequency analyzed the voltage osicllation of a current-biased resistively lshunted Josephson-junction (RSJ) model. In particular we have been interested in the situation where there is an ac (microwave) -induced step in the I-V characteristic. Conversion of the Josephson oscillation into other frequency modes is studied under various bias conditions.
Simple analysis of torque measurement of magnetic thin films
Authors: Miyajima Hideki , Sato Katsuo , Mizoguchi Tadashi
Published: February 2003

In order to analyze experimental data of torque measurements for magnetic thin films, a (L/H)2-vs-L plot is proposed, where L represents the torque of a film in a field of H whose direction is 45° to the film plane. The saturation magnetization M and perpendicular anisotropy energy K⊥ are obtained without any approximation from the slope A and intercept B of this plot as follows: M= (2B)1/2/V, K⊥= (B/V) (1/A−4π/V), where V is the volume of the film.
Effect of high ν/γ electron beams for collective ion acceleration
Authors: Straw David C. , Miller Robert B.
Published: February 2003

Experimental observations of collective-effect acceleration with electron beams of various ν/γ (ν is the Budker parameter and γ is the usual relativistic factor) values injected into neutral low-pressure gases show, for beams with ν/γ near unity, that the peak accelerated ion energy exceeds the energy usually obtained from the deep stationary potential-well stage. It is suggested that high ν/γ electron beams, with a large transverse kinetic-energy content, undergo a longer transition period from the stationary to the moving phase and translate with a lower velocity than that expected solely on the basis of space-charge neutralization processes. Ion trapping during and following the transition stage results in final ion energies much greater than 3Ee, where Ee is the electron beam kinetic energy.
Interpretation of an optically thick resonance line emitted from laser-heated spherical plasmas
Authors: Apruzese J. P. , Davis J. , Whitney K. G.
Published: February 2003

An interpretation is provided for the radiation emitted by optically thick resonance lines produced from laser-heated plasmas. The profiles and total intensities are shown to be sensitive to the spatial profiles of the laser energy deposition. Results are presented for the helium-like resonance line of Al XII. It is also shown that Holstein’s photon escape approximation badly underestimates the emitted line radiation.
Vapor-cone angles of neutrals and ions emanating from the cathode of a dc mercury vacuum arc
Authors: Eckhardt Gisela
Published: February 2003

A stream of ions and neutrals emerges from the cathode of a vacuum arc discharge. Measurements made on a spot-anchored dc mercury vacuum arc show that, beyond the region of heavy-particle collisions, ions and neutrals are confined to the same circular vapor cone, and that the angle of this cone depends on the electron-to-atom emission ratio. This result is interpreted as indicative of the generation of the ions at the cathode spots in the form of highly directional vapor jets.
Interferometric study of laser-produced plasmas
Authors: Reintjes J. F. , Lee T. N. , Eckardt R. C. , Andrews R. A.
Published: February 2003

High-quality interferograms of laser-produced plasmas with spatial resolution of 15 μm are obtained using a relatively simple Jamin-type interferometer and a precisely timed 30-psec probing laser pulse from a mode-locked Nd : YAG laser, frequency doubled to 532 nm. The spatial resolution attainable with the present arrangement is limited by the velocity of the expanding plasma and the finite duratiaon of the probing pulse. The plasmas are produced by focusing a Nd : glass Q-switched laser pulse (0.5 GW, 1011–1013 W cm−2) onto slab targets of Al, Mg, and (CH2)n. The electron density distribution, plasma dimension, and expansion velocity for both point and line foci are studied as a function of time delay between the mode-locked and Q-switched laser pulses. The results obtained with different durations of the heating (Q-switched) pulse and with the various target material are compared.
Mechanism of charge transfer to a polymer surface by a conducting liquid contact
Authors: Chudleigh P. W.
Published: February 2003

Measurements are presented of charge transfer to FEP polymer surfaces by conducting liquid contacts consisting of ethyl alcohol, water, and 0.01M aqueous solutions of HCl and NaOH. Contact angles between the liquid-vapor interfaces and the polymer surfaces were also measured. The results are interpreted in terms of a model in which charge transfer is controlled by the interaction of electrostatic and molecular forces on ions in the charge double layer at the polymer-liquid interface. Basic parameters of the double layer, including adsorbed charged density at the interface and Stern potential, have been derived from the charge-transfer measurements using this model.
Thermal expansion of mixed-alkali silicate glasses
Authors: Shelby J. E.
Published: February 2003

Thermal-expansion measurements were made for five varieties of mixed-alkali silicate glasses (Na-K, Na-Rb, Na-Cs, K-Rb, and K-Cs), with special emphasis on the Na-K silicates. Negative deviations from additivity were observed in the glass transformation temperature in every case, with the deviations increasing with total alkali-oxide concentration. Positive deviations from additivity were noted in the thermal-expansion coefficients in all but one case (Na-Cs), where a small negative deviation was observed. The deviations in both properties were maximized when the radius ratio of the two alkali ions was approximately 1.4, i.e., for the Na-K glasses. These results are quite similar to those reported for mixed-alkali germanate glasses which suggests that they are due to ion-ion interactions rather than to gross alterations of the glass network.
Tensile strength and fatigue of optical fibers
Authors: Olshansky Robert , Maurer Robert D.
Published: February 2003

A method is presented for analyzing laboratory measurements of tensile strength and fatigue failure rates of glass fibers. This method provides the physical basis for extrapolating laboratory data to the multikilometer lengths and long lifetimes which will be characteristic of field use of optical fibers in telecommunication systems.
A diffusion model for GaP red LED degradation
Authors: Jordan A. S. , Ralston J. M.
Published: February 2003

The long-term degradation of GaP red LED’s has been analyzed in terms of a diffusion model. In this paper, the reduction in electroluminescent efficiency (ηt) during aging time (t) at elevated junction temperatures (Tj) and under forward current stress (Is) is attributed to the formation of nonradiative recombination centers near the junction. It is shown that the concentration of these centers is proportional to the degradation-induced increase in the decay rate of the minority-carrier electrons which, in turn, can be expressed as a simple function of normalized efficiency (r=ηt/η0). In order to quantitatively treat the time evolution of the nonradiative center concentration, we postulate the diffusion and accumulation of an undesirable charged defect as the rate-limiting step. It is further assumed that atomic motion at Tj can only proceed when the repelling p-n junction potential is reduced by the forward voltage. From these considerations, we derive an explicit expression between r and t which provides a good description of degradation data obtained on all our samples at various Tj′s and Is′s. In addition, it is shown that the temperature dependence of the diffusivity (D) follows the Arrhenius law with an activation energy of 0.7 eV. At a constant Tj, D is a linear function of Is which is consistent with an energy-barrier model for diffusion coupled with simple diode theory. Furthermore, LED’s processed from different lots are characterized by nearly the same D, indicating a similarity in their degradation mechanism. Finally, the nature of the diffusant and killer center are discussed and attention is paid to the alternative ’’phonon-kick’’ mechanism of degradation which may be important in the recently observed decrease in Zn-O pair concentration during short aging times.
Analysis of circular craze
Authors: Wilczynski A. , Liu C. H. , Hsiao C. C.
Published: February 2003

The analysis of the displacement and stress fields in the neighborhood of a circular craze has been made possible by considering a simple membrane model on an elastic foundation. In a simple tension field, with proper boundary conditions, solution to the governing differential equation is obtained and results are presented for an exponential modulus function of the radius of the craze.
Photoinduced discharge in sulfur single crystals using strongly and weakly absorbed light
Authors: Falcony C. , Mendoza J. , Sinencio F. Sanchez , Many A. , Helman J. S.
Published: February 2003

We report on the photoinduced discharge of sulfur single crystals using light in the range 400–580 nm, i.e., from strongly to weakly absorbed light. The results are interpreted in terms of a phenomenological model consistent in an equivalent RC circuit.
Theory of shape stability in crystal growth from the melt
Authors: Surek T.
Published: February 2003

A criterion is presented for the stability of the external shape of the crystal in crystal growth from the melt. The criterion takes cognizance of the finding that the constant cross-sectional growth of crystals by a meniscus-controlled process, such as Czochralski, floating-zone, and edge-defined film-fed growth (EFG), requires that the angle φ between the meniscus and the growth axis equal φ0 (a constant; for silicon, φ0=11°). Shape stability requires further that a change in crystal shape (whenever φ≠φ0) should be such that φ approaches φ0 again as a result of the shape change. The criterion is applied to the various melt-growth techniques; Czochralski growth is shown to be inherently unstable, whereas the usual floating zone techniques are shown to provide stability of the crystal shape. An application of the criterion is made to the EFG growth of various crystal shapes, with particular emphasis on EFG silicon ribbon growth, and the conditions under which shape stabilization is obtained in EFG are identified.
Nonlinear susceptibility of zinc telluride
Authors: Sharma T. P. , Singh S. , Singh V. P.
Published: February 2003

A one-dimensional model proposed by Garrett has been used to explain the electro-optic susceptibility reported by Pursey et al. It has been demonstrated that the electronic contribution to the anharmonicity is in itself sufficient to explain satisfactorily the data of Pursey et al.
Hardening of GaAs by solute-vacancy pairs
Authors: Swaminathan V. , Copley S. M.
Published: February 2003

The effect of various thermal and thermomechanical treatments on the yield stress and the dislocation substructure of heavily Si-doped GaAs is presented. It is shown that the yield stress at 400 °C of samples annealed at 1100 °C, quenched and subsequently aged at an intermediate temperature, increases with increasing aging time, and for constant aging time, decreases with increasing temperature. A defect model based on the principles of chemical thermodynamics of imperfections is proposed to calculate the concentrations of the various possible defect species in Si-doped GaAs as a function of temperature. The correlation between the concentrations of the various defects and the mechanical behavior observed in this investigation along with the optical and electrical measurements and the microstructural observations of previous investigators demonstrates the important role of solute-vacancy pairs in determining a variety of properties. The solute-vacancy pair model may be applied to explain the mechanical behavior of undoped GaAs and GaAs doped with Te, Ge, Sn, S, Cr, and Zn as well as the mechanical behavior of other compound semiconductors.
Thermally stimulated discharge in polymer electrets: Compatibility and impurity effects
Authors: Alexandrovich P. , Karasz F. E. , MacKnight W. J.
Published: February 2003

Polymer electrets have been prepared and studied by measuring thermally stimulated discharge currents. Two current maxima have been observed for samples of polystyrene, poly(p-chlorostyrene), and a random copolymer of styrene and p-chlorostyrene. These maxima are attributed to dipole reorientation accompanying the glass transition and to real charge drifts. Poly(2,6 dimethyl-1,4-phenylene oxide) and blends of this polymer with the three aforementioned polymers were also studied. In these systems unresolved and nonreproducible peaks were obtained, and these difficulties have been attributed to impurities present.
Longitudinal acoustic mode in polymers
Authors: Hsu S. L. , Krimm S.
Published: February 2003

The theory of the longitudinal vibrations of a composite ’’crystalline-amorphous’’ elastic rod with perturbing forces at the ends has been developed. The longitudinal-acoustic-mode fundamental frequencies are tabulated as a function of the relative elastic moduli, relative densities, and relative composition of the components, as well as of the magnitude of the perturbing forces. It is shown that this model can explain the behavior of the observed Raman-active low-frequency bands associated with this mode in polyethylene and in isotactic polypropylene.
Determination of the depth of impurity atoms in bulk material by proton-induced x rays
Authors: Benka O. , Geretschläger M. , Paul H.
Published: February 2003

We attempt to determine the target composition of one homogeneous layer of foreign atoms in bulk material by comparing the yields for proton-induced x rays at two different energies. The problem is formulated mathematically and an approximate method of solution is given. The method uses a calibration curve which is given by the ratio of the yields at the two energies for a pure foil of the foreign material of known surface density. Both thickness and location in depth of the foreign layer can be determined. The method is applied to sandwich targets (Ag-Cu-Ag and Ge-Cu-Ge) of known layer thickness (determined by Rutherford backscattering). By measuring the same target under various conditions, and by comparison to backscattering, it is shown that a mean depth of Cu atoms of about 1 mg/cm2 can be measured to an accuracy of about 4%.
Effect of saturation current on noise in IMPATT diodes under large-signal conditions
Authors: Perichon Robert , Constant Eugène
Published: February 2003

A large-signal noise theory for IMPATT diodes, not neglecting the effect of the parasitic injected current (saturation and/or tunnel current) is presented. Under large-signal conditions, it is found that the noise increase is much less for high effective saturation current than for a low one. The theoretical conclusions are experimentally evidenced. The true physical mechanism behind the effective saturation is briefly explained.
Bubble formation in gelatin: A model for decompression sickness
Authors: Yount David E. , Strauss Richard H.
Published: February 2003

Decompression sickness follows a reduction in ambient pressure and is a result of bubble formation in blood or tissue. A striking feature of the syndrome is that almost any body part, organ, or fluid can be affected, including bone. This generality suggests a common basis in the physical and chemical properties of water, particularly those relating to cavitation. We report here a systematic study of some of these properties, carried out with transparent gelatin—an aqueous medium that is especially convenient for this purpose since it yields bubbles that are stationary and can be counted and measured.
Conductivity of powdered ZnO with chemisorbed oxygen during photodesorption
Authors: Morgen P. , Onsgaard J. H. , Tougaard S.
Published: February 2003

We have investigated the connection between changes in surface conductivity of ZnO with chemisorbed oxygen, and the number of gas molecules photodesorbed with band-gap illumination. Experiments under UHV conditions with powdered samples show that the initial stages of photodesorption are not described by a simple electron transfer mechanism, while later stages can be reasonably well explained in that way.
Single and multiple excitation of bulk and surface plasmons on clean ZnO surfaces
Authors: Dorn R. , Lüth H.
Published: February 2003

Electron energy loss measurements in reflection with primary energies between 80 and 900 eV have been performed on clean cleaved ZnO polar {0001} and nonpolar {11̄00} surfaces in ultrahigh vacuum (p<10−10 Torr). The identification of surface and bulk plasmon loss peaks is possible from the observation of multiple losses and from the dependence of the spectra on primary energy. Surface and bulk plasmon excitation energies are obtained to be at 16 and 18.5 eV, respectively.
Influence of crystallography and purity on brightness of LaB6 cathodes
Authors: Verhoeven J. D. , Gibson E. D. , Noack M. A.
Published: February 2003

The brightness of single-crystal cathodes of LaB6 oriented in the 〈100〉, 〈110〉, and 〈111〉 directions and six other random directions has been measured. The 〈111〉 cathodes produced currents and brightnesses significantly lower than all other orientations. The other orientations studied produced maximum brightnesses in the range 0.7–1.0 MA/cm2 sr, although the 〈100〉 orientation consistently produced currents higher than other orientations and brightnesses as high or higher than most orientations. A change in impurity level from 1540 ppm to less than 1 ppm had no statistical effect on brightness for crystals of the same orientation.
Use of titanium-doped quartz to eliminate carbon deposits in an atomic iodine photodissociation laser
Authors: Padrick T. D. , Palmer R. E.
Published: February 2003

The use of titanium-doped quartz as the laser tube in an iodine photodissociation laser eliminates the deposition of carbon on the tube wall. Shock waves arising from absorption of flashlamp light by these carbon deposits are also eliminated.
Observation of electrical breakdown and negative resistance in an epitaxial GaAs film of a field effect structure
Authors: Mimura T. , Fukuta M. , Yokoyama N. , Ishikawa H.
Published: February 2003

We have observed electrical breakdown and current-controlled negative differential resistance (NDR) in an epitaxial n-GaAs film at room temperature by using a field effect structure. The breakdown is attributed to the impact excitation of electrons trapped in 0.9-eV centers of concentration ∼1016 cm−3. The origin of NDR is explained by the theory which was originally developed for the breakdown phenomenon in Ge at low temperatures.
High-temperature thermal expansion of iridium (revised results)
Authors: Wimber R. T.
Published: February 2003

Results of an earlier thermal-expansion study have been revised using values for the specimen temperature obtained by an improved method.
Measurement of demagnetizing factors using magnetoelastic Rayleigh-wave convolution
Authors: Robbins William P.
Published: February 2003

A simple method of experimentally determining the demagnetization factors of nonellipsoidal samples using the convolution of contradirected magnetoelastic Rayleigh waves is described. The experimental results are in reasonable agreement with first-order theoretical expressions for the demagnetizing factors.
Vapor properties of gold at extreme temperatures by pulsed-electron-beam measurement
Authors: Benson D. A.
Published: February 2003

Currently, only limited vapor-pressure information exists for materials at temperatures above 3000 K. To provide additional information in this range, a new transient method has been developed for measuring the pressure–internal-energy states of the liquid-vapor phase boundary at high-vapor-pressure levels (above 1 MPa). To study these vapor states, samples are rapidly heated and the vapor is inertially confined by a dynamic graphite crucible for 2 to 20 μs. A thermomechanical model of the mixed-phase material is described which relates the observed crucible expansion to total vapor pressure. The internal energy state of the vapor sample, which is heated by a pulsed electron beam, is determined from electron absorption diagnostics. Application of the method to gold has given new total vapor-pressure information between 3 and 600 MPa (30 and 6000 bar) which is consistent with extrapolation of static vapor data. Temperatures associated with these pressures range in excess of 10 000 K. Preliminary evidence for independent flow of the mixed phases is also obtained from analysis of these high-temperature expansion measurements.
Digital normalization of iodine filter structure in quasielastic light scattering
Authors: Lyons K. B. , Fleury P. A.
Published: February 2003

A molecular iodine filter may be used to reduce the elastic component in a light scattering experiment by several orders of magnitude. However, this introduces extraneous structure into the spectrum due to subsidiary iodine absorptions. A technique is reported here to compensate quantitatively for this structure by a digital normalization scheme based upon a tandem pressure-scanned Fabry-Perot interferometer interfaced to a minicomputer. This technique has allowed the extraction of quantitative line-shape information in studies of low-energy (0–3.0 cm−1) excitations in both crystalline and amorphous solids.
Extrinsic absorption in KCl and KBr at CO2 laser frequencies
Authors: Rowe J. M. , Harrington J. A.
Published: February 2003

Extrinsic absorption has been studied in KCl and KBr using the technique of tunable CO2 laser calorimetry. The transparency of these hosts is limited by an extrinsic absorption mechanism common to both KCl and KBr. In particular, an extrinsic absorption band near 9.6 μm in both materials has been studied in detail. The features of this band are compared to a recent theory on impurity induced absorption at CO2 wavelengths. A bulk absorption in KBr of 1×10−5 cm−1 at 10.6 μm was measured for the best sample—the lowest value observed to date for any material at this frequency.
Magnetic torque on a shielded superconducting gyroscope
Authors: Holdeman L. B. , Holdeman J. T.
Published: February 2003

The torque on a superconducting sphere rotating in an arbitrary magnetic field is calculated. The result is expressed in terms of the coefficients of the expansion of the magnetic field in spherical harmonic functions, but in general a boundary-value problem must be solved to obtain these coefficients. The boundary-value problem is solved and the torque calculated for configurations pertinent to the gyroscope relativity experiment, a proposed satellite experiment which is to test various theories of gravitation. Typical numerical results for these torques are given and compared with the predicted relativistic effects.
Avalanche buildup time of silicon reach-through photodiodes
Authors: Kaneda Takao , Takanashi Hirobumi , Matsumoto Hideo , Yamaoka Toyoshi
Published: February 2003

The avalanche buildup time t, which is related to the multiplication factor (M) by t=τ1 M, where τ1 is the intrinsic response time, is studied for silicon reach-through avalanche photodiodes (RAPD’s) by a shot-noise measurement in the GHz region. The dependences of t on both the length of the avalanche region la and the wavelength exciting the avalanche process (λ) are investigated. The τ1 values obtained increase with la in the region la≳1.0 μm and also take larger values for λ∼6300 Å than for λ∼8300 Å. These values are in good agreement with a calculation using the modified Emmons equation τ1=Nkeffla/vs except for the very narrow avalanche region (la≲0.4 μm), where N is a constant dependent on la, keff is the effective ratio of hole to electron ionization rates, and vs is the carrier saturation velocity. These results are very useful to investigate the frequency response of RAPD’s. The diodes discussed are used extensively in fiber transmission systems.
Collection velocity of excess minority carriers at metal-semiconductor contacts in solar cells
Authors: Card H. C.
Published: February 2003

An expression for the collection velocity S of excess minority carriers at metal-semiconductor contacts is derived analytically for both the Schottky barrier and the Ohmic contact. Short-circuit conditions are assumed, appropriate to the collection of optically generated minority carriers by Schottky barriers or Ohmic contacts in solar cells or photodetectors. This analysis is then applied to the calculation of S for the materials of primary interest in solar cells (Si, GaAs, and CdS). It is found that S increases with the minority-carrier mobility and with the doping concentration according to S∼μp N1/2d (for the contact: metal–n-type semiconductor), but is independent of the barrier height φb or diffusion potential Vdo, provided qVdo≳ few KT. This means that, for Ohmic contacts, S depends on whether the contact is achieved by using high Nd (for which S?109 cm/s for Si cells) or by low φb but moderate Nd (S?107 cm/s for Si cells). More generally, S varies between ?106 cm/s (for CdS cells, low Nd) and ?1010 cm/s (p-type GaAs cells, high Nd). Also defined are the conditions under which the finite collection velocity at the contact limits the collected minority-carrier current.
Growth and electrical properties of epitaxial PbSexTe1−x layers
Authors: Hohnke D. K. , Hurley M. D.
Published: February 2003

Epitaxial layers of PbSexTe1−x (0⩽x⩽1) have been grown on the (111) faces of cleaved BaF2 and SrF2 single crystals by vacuum deposition of the evaporated binary compounds. Structural studies indicate that the layers are single crystals with widely spaced low-angle grain broundaries that propagate from the substrates. Due to the smaller thermal expansion of the substrate the layers are strained, except at x=0 and x=1. The functional dependence of the elastic strain on layer composition, ε∝x (1−x), and its magnitude suggest that the thermal expansion and/or elastic constants of PbSexTe1−x are nonlinear functions of x. The Hall mobilities decrease from about 1×103 cm2/V s (300 K) and 3×104 cm2/V s (77 K) at x (1−x) =0 to about 3×102 cm2/V s (300 K) and 5×103 cm2/V s (77 K) at x=0.5, apparently as a result of alloy scattering.
Defect structure of Cd-doped PbTe
Authors: Vydyanath H. R.
Published: February 2003

Hall-effect and solubility measurements are carried out on Cd-doped PbTe crystals equilibrated with (Pb,Cd) alloys of various compositions at T=700 and 800 °C and quenched to room temperature. In Pb-saturated conditions, while most of the Cd is found to be incorporated as neutral Cd on Pb sites CdxPb, a fraction of the total amount of Cd is present as positively charged interstitial species Cdi compensated by electrons. A complete defect model which can predict the behavior of Cd-doped PbTe in Cd-rich atmospheres as well as in Te-rich atmospheres is proposed.
Defect structure of Cd-doped Pb0.8Sn0.2Te
Authors: Vydyanath H. R.
Published: February 2003

Pb0.8Sn0.2Te single crystals are equilibrated with (Pb0.8Sn0.2)x Cd1−x alloys of various compositions at 700 and 800 °C and quenched to room temperature. Cd solubility and Hall-effect measurements as a function of the activity of Cd have led to the development of a defect model for Cd-doped Pb0.8Sn0.2Te according to which most of the Cd is present as neutral CdxPb, a small fraction being present as positively charged Cdi compensated by negatively charged vacancies of Pb, V′Pb. The model can also be used to predict the behavior of Cd-doped Pb0.8Sn0.2Te in Cd-rich atmospheres and Te-rich atmospheres.
Defect structure of Zn-doped PbTe
Authors: Vydyanath H. R.
Published: February 2003

PbTe single crystals are equilibrated with (Pb,Zn) alloys of various compositions at 700 and 800 °C and quenched to room temperature. Hall-effect and solubility measurements of these crystals indicate that zinc acts as a donor in PbTe, being incorporated in interstitial sites as Zni compensated by electrons. A complete defect model for Zn-doped PbTe is arrived at, which predicts the behavior of PbTe crystals in metal-rich as well as Te-rich atmospheres.
Polarization and dielectric constant of potassium tantalate
Authors: Siegwarth J. D. , Holste J. C. , Morrow A. J.
Published: February 2003

The polarization of a KTaO3 single crystal and some KTaO3 ceramic specimens has been measured using a dc technique. A remanent polarization was found as well as hysteresis in the polarization as a function of field. Peaks in the ac dielectric constant were also observed. These dielectric properties are attributed to dielectric relaxation effects and the existence of an electret state.
Study of titanium diffusion in lithium-niobate low-loss optical waveguides by x-ray photoelectron spectroscopy
Authors: Pearsall T. P. , Chiang S. , Schmidt R. V.
Published: February 2003

We have used x-ray photoelectron spectroscopy to determine the valence of diffused titanium in LiNbO3. Our measurements show Ti ions only in the +4 valence state within the sensitivity of the measurement technique. Further analysis of our data indicates that the Ti ions occupy a unique site in the LiNbO3 unit cell.
Surface acoustic wave energy transfer in an air-gap-coupled Bi12GeO20-CdS system
Authors: Cambon G. , Saïssy A. , Rouzeyre M.
Published: February 2003

We report on high-energy transfer between two surface acoustic waves propagating on CdS and Bi12 GeO20 crystals separated by an air gap. We use first a simple one-dimensional model and second a perturbation approach to show that under special conditions a strong coupling can occur. We have performed experiments using Rayleigh modes, and found minimum transfer losses of 7 dB at 25 MHz and 13 dB at 65 MHz with an air gap of a few thousand angstroms.
Studies of defects introduced by electron irradiation at 4.2 °K in p-silicon by thermally stimulated capacitance technique
Authors: Brabant J. C. , Pugnet M. , Barbolla J. , Brousseau M.
Published: February 2003

Point defects, introduced at 4.2 °K in p-type silicon by 1.5-MeV electron irradiation, are studied by means of the thermally stimulated capacitance technique. Electronic states associated with the vacancy and the divacancy are observed, which enables us to study their correlated annealing. The respective donor energy levels, hole thermal emission rates, and annihilation activation energies are measured.