bluuebunny/crossref_metadata_2025 huggingface dataset:
Plastic relaxation via twist disclination motion in polymers
Authors: Gilman J. J.
Published: February 2004

Measurements of the internal friction in polymers exhibit a spectrum of peaks at low temperatures that are related to the plastic behavior at higher temperatures. This manuscript deals with a particular supramolecular defect that behaves mechanically in a manner consistent with the observations. The defect is a twist disclination consisting of two molecules that cross over one another. The energies of formation and motion for the twist disclination are calculated in terms of the width of the twisted region, the displacement that is produced by the twist, the molecular radius, and the elastic stiffnesses of the molecules. For motion to occur dilatations caused by contour modulations of the molecules must be overcome. This effect yields expressions for the motion activation energy and stress for nonactivated motion. It is shown that molecular bending occurs more readily by elastic deformation than by conformation-change deformation unless the radius of curvature is less than a critical value (of the order of atomic dimensions).
Static hysteresis of glass fibers
Authors: Hyodo Shin-ichi , Togami Yuji
Published: February 2004

Since the high strength of undamaged glass can be further increased by lowering temperature, load-extension measurements at large strains (up to 13%) were carried out for as-drawn sodium-silicate glass fibers at temperatures from −78 to −196 °C. Elastic hysteresis loops were observed when the strain amplitude exceeded 4%. A detailed study of this hysteresis showed that it is indeed the static hysteresis of glass because the magnitude of internal friction, while rather insensitive to strain rate, is obviously amplitude dependent. To interpret the results, a model somewhat analogous to that of pinned dislocation loops used by Granato and Lücke is presented. It is assumed in the model that the number of breaks in the glass network will show an exponential increase with increasing tensile strain and that no breaks will ``heal'' during unloading until the network is again free from applied stress. Torsion pendulumn measurements were also made for the specimens under static tension. The two types of measurements have shown that static tensile strain raises the background in the internal friction vs temperature curve and, at temperatures higher than −150 to ∼ −120 °C, activates the relaxation processes that are superimposed on the background and generally attributed to the migration of alkali ions.
Continuously tunable ultraviolet radiation at 2535 Å
Authors: Sato Takuzo
Published: February 2004

A continuously tunable ultraviolet source around 2535 Å has been obtained by mixing a narrow-band ruby-laser beam with a broad-band dye-laser beam in a 90° phase-matched ADP crystal. The 90° phase matching was achieved at convenient temperatures around 23°C. The rates of wavelength change of the mixed light with the 90° phase-matching temperature and with the phase-matching angle for fixed temperature were evaluated and found to be dλM/dTM=1.7 Å/°K and dλM/dθM = 24 sin 2θM Å deg−1. The spectral bandwidth of the mixed light at half-intensity was also evaluated and compared with the experimental result of 0.7 Å.
A theory of oscillator noise and its application to IMPATT diodes
Authors: Fikart Josef L. , Goud Paul A.
Published: February 2004

A large-signal theory of oscillator noise is presented, which is applicable to oscillators employing active elements that can be described by a time-dependent differential equation with a Langevin noise source. The method uses a modified quasistationary perturbation theory with an rf amplitude-dependent perturbing noise voltage (current) source, which has been mathematically expressed in terms of the ``initial'' (preoscillation) amplitude and phase noise modulation rates. The usual requirement that this noise voltage (current) be a member of a normal random process, which results in equality of the two initial power spectra, is not invoked here. The rf amplitude dependence of the open-circuit perturbing noise voltage (short-circuit noise current) has been obtained from the differential equation of the active element, under the condition of sinusoidal current (voltage) excitation at the frequency at which it would normally oscillate. Upon linearizing in stochastic quantities, expanding the deterministic terms by means of Fourier series and Fourier transforming the result, a system of linear equations in the frequency domain is obtained for the noise voltages (currents) at frequencies about multiples of the excitation frequency and at the baseband frequency. In this way, most of the conversion processes in the active element can be taken into account. The Fourier transforms and power spectra of the initial modulation rates have been determined in terms of the upper- and lower-sideband noise voltages (currents); they are used in the modified formulas of a quasistationary perturbation theory to obtain the AM and FM noise spectra of the oscillator output. The theory has been applied to IMPATT diode oscillators and the computed spectra have been compared with various experimental data. A good agreement between the theoretical predictions and experimental data has been found. Additional insight into IMPATT diode noise has been provided, since the above method has made it possible to separately evaluate the dependence of the AM and FM noise spectra on the rf output power of the oscillator as well as on other diode and circuit parameters. As a result, guidelines have been obtained for determining the optimum parameters of an IMPATT diode oscillator, for minimum noise.
Magnetic and thermal studies on ErCo2–ErAl2
Authors: Oesterreicher Hans
Published: February 2004

Details of the magnetization behavior of the pseudobinary system ErCo2–ErAl2 at temperatures from 1.6 to about 70 K are presented and compared with previous neutron diffraction experiments. ErCo2 shows a first-order phase transition at 33 K from ferrimagnetic order to paramagnetism. Replacement of Co by Al destroys this unusual feature and initially results in enhanced magnetic exchange with increasing ordering temperatures, although the Co moment is rapidly decreasing due to electron transfer. The moment on Co sites is completely quenched beyond 30 mole% ErAl2. Disordered magnetic components on Er sites which develop in the pseudobinary region and have been identified with neutrons can be partly forced into the field direction, but the saturation values are limited by the anisotropy. The origin of disorder is discussed as being either a consequence of the disorder on crystallographic sites or of the changing valence electron concentration. Differential thermal analysis shows only the onset of magnetic ordering and no signs of subsequent magnetic transitions at lower temperatures (down to 4.2 K) for materials with only partial magnetic order.
Fluctuation effects in superconducting films
Authors: Smith J. M. , Strandberg M. W. P.
Published: February 2004

The electrical noise properties of superconducting films in a perpendicular magnetic field have been investigated. Tin films were used and the dominant source of noise was found to be a flux-flow mechanism. Coherent voltage pulses were also detected in some of these films, but the exact origin of these pulses is unknown.
Comment on ``Habit and morphology of copper precipitates in silicon''
Authors: Fiermans L. , Vennik J.
Published: February 2004

The morphology of copper precipitate colonies in silicon is determined completely by a dislocation climb and glide mechanism. Interstitial dislocation loops, originating from three-dimensional nucleation centers are involved. Preferential climb in 〈110〉 directions of the 〈100〉 oriented edges of interstitial loops parallel to {110} planes and with b=〈110〉 determines the orientation of the colonies. The memory effect is ascribed to lattice defects which remain after complete out-diffusion of the copper.
Effect of charge inhomogeneities on silicon surface mobility
Authors: Cheng Y. C.
Published: February 2004

A calculation is presented to estimate the effect on silicon surface mobility of the potential fluctuation due to a random distribution of localized charges near the interface. With a choice of reasonable values for two parameters, the mean—square charge deviation and the correlation length, the theoretical mobility agrees rather well with experiments at low gate voltage and very low temperatures.
Optical absorption and electrical conduction in polyethylene
Authors: Tanaka Toshikatsu
Published: February 2004

The dependence of the optical absorption of polyethylene on photon energy is analyzed and correlated with electrical conduction. The optical gap is obtained as 7.35 eV, with a band tail of about 1 eV. Electrons transport by hopping according to μ0 exp(−Eμ/kT), where μ0 = 5 cm2/V sec and Eμ = 0.24 eV at 20–80°C. Electrons are supplied from deep donors which lie at 2 eV and more below the conduction band. The deep donors are considered to be responsible for the increase in the conductivity at high field, which might be explained by the Poole-Frenkel effect.
Temperature dependence of the pyroelectric voltage response to step infrared signals in triglycine sulphate
Authors: Simhony M. , Shaulov A. , Maman A.
Published: February 2004

An expression is derived for the pyroelectric (PE) voltage response to step radiation signals which can be applied up to temperatures close to the Curie point Tc under a ``small-signal'' condition. Based on the Curie-Weiss law and the thermodynamic theory of a second-order ferroelectric transition, a discussion is given of the temperature dependence of the parameters of the PE voltage response: initial slope, peak value, rise time, and fall time as functions of sample parameters and load resistance. It is found that the PE voltage may reach a maximum close to Tc, and expressions are derived for this value as well as for the temperature at which it occurs. These results were checked in detail on 12 samples of single-crystalline triglycine sulphate for temperatures from 20 °C to the Curie point, and good agreement between theory and experiment was observed. The application of the results to PE detection of ir is considered.
Relationship between sputter cleaning parameters and surface contaminants
Authors: Houston J. E. , Bland R. D.
Published: February 2004

In an abnormal dc glow discharge sputtering system the current at a constant voltage and pressure is often found to decrease from an initially high value to a steady-state level as the cathode surface is sputtered. We have investigated the relationship between this decrease in current and the level of cathode surface contamination by periodically analyzing the surface during sputter cleaning using the soft x-ray appearance potential technique. We find that the excess initial current results from contaminating gas liberated from the chamber wall and cathode surface by the action of the discharge. The rate at which cathode surface contaminants are removed and the residual level that is indicated by the steady-state discharge current are both strongly dependent on the over-all cleanliness of the discharge system. With proper attention to cleanliness, however, it is found that the steady-state discharge current can be used as a process control variable, indicating the attainment of a relatively clean cathode surface.
Microstructure, growth, resistivity, and stresses in thin tungsten films deposited by rf sputtering
Authors: Petroff P. , Sheng T. T. , Sinha A. K. , Rozgonyi G. A. , Alexander F. B.
Published: February 2004

The growth process and the microstructure of very thin W films (80–500 Å) deposited by rf sputtering on SiO2 and Si substrates have been observed by transmission electron microscopy (TEM). The resistivity and stress in these films have been related to the film microstructure, composition, and to the deposition conditions (substrate bias and rf deposition power). Thin W films deposited on silicon dioxide substrates under zero or positive bias have been found to grow in two distinct growth stages. Stage I corresponds to the formation of a thin continuous film (80–100 Å thick) of β-W. The β-W phase has the A-15 crystal structure and has been identified as a faulted W3W compound. A small grain size (50–100 Å) is characteristic of the β-W film. Stage II corresponds to the transformation of the β-W film into a pure α-W film with the bcc crystal structure. This thermally activated phase transformation takes place in the temperature range 100–200 °C. It is characterized by the growth of α-W nuclei until complete coalescence of the α-W islands; the resulting α-W film consists of large grains (1500–2500 Å) which are free of dislocations. The end of stage II occurs for a critical film thickness tc beyond which the film is a continuous α-W film. The value of tc is controlled by the rf deposition power and the substrate temperature. On the other hand, films deposited on negatively biased substrates do not contain the β-W phase. These films consist of large α-W grains (1500–2000 Å) with a high dislocation density. The resistivity of thin W films deposited under zero or positive bias is controlled by the amount of β-W present in the film. The pure β-W films have a high resistivity (100–300 μΩ cm); after the complete transformation β-W→α-W the large resistivity (30–40 μΩ cm) of these films is attributed to scattering by impurities. In particular, the lower resistivity of W films deposited under negative bias is related to their lower oxygen content. The sign and magnitude of the stress in these films are also controlled by the film microstructure, It is found that the stress in the films containing the β-W phase is always tensile with a σ of (6–12) × 109 dyn/cm2. The films consisting of α-W are always compressively stressed in the range (2–12) × 109 dyn/cm2.
Recombination in light-pulse excited silicon at medium-high carrier concentration levels
Authors: Tove P. A. , Andersson L. G.
Published: February 2004

Recombination in silicon has been studied by exciting gold on n_type silicon surface-barrier diodes. The excitation was short light pulses from a superradiant laser and the diodes were reverse biased at more than the depletion voltage. The energy in the light pulse was monitored and a comparison was made with the measured charge in the resulting current pulse in the diode. In this way recombination losses could be determined. At high light intensities (1010−6×1011 photons/cm2 in a 1-nsec excitation pulse) superlinear recombination of carriers is observed, causing the collected charge to decrease by up to 50% of the value expected from the observed quantum detection efficiency of approximately unity observed at lower levels. This is attributed to recombination near the surface at the high carrier densities reached, both during the light pulse and during the charge reservoir time tA (the time for extraction of space-charge-limited current from the cathode). This causes the recombined charge to increase with both light intensity and tA. The observed recombination may be of practical importance when operating semiconductor detectors at high light levels or with heavily ionizing nuclear particles.
Determination of the sputtering rate by the fluorescence of sputtered atoms
Authors: Ratinen H.
Published: February 2004

An rf sputtering apparatus was equipped with an optical spectrometer with which the characteristic lines of sputtered species were observed. A specially designed CaO disk or a thin CaO layer on a quartz plate were used as the targets. It was observed that the intensity of the calcium peak increased more rapidly than the thicknesses of the films obtained as a function of the argon gas pressure. This was assumed to be due to the resputtering of calcium oxide from the substrate. The effect of the substrate temperature on the film thickness was also studied. The temperature was changed from 100 to 350 °C. No change in the film thickness was observed.
Invar anomalies
Authors: Window B.
Published: February 2004

Mössbauer results for iron nickel alloys and for iron in copper-based alloys suggest the physical concepts used in formulating a model for the magnetic properties of iron nickel alloys. A change in the magnetic state of an iron atom when it has more than five iron near neighbors leads to giant moment behavior for alloys at the Invar composition. The falloff in the saturation magnetization occurs because the cluster centers get further apart as the iron concentration is increased, and at the Invar composition the clusters on average just touch. Estimates yield more than 17μB for these clusters, and they include about 25 atoms around the magnetic nucleus. The formation and magnetization of these spin clusters result in the iron atoms which are not magnetic centers being magnetized with an increase in volume due to exchange interactions. By using the dependence on the concentration and temperature of the expansion anomaly, it is deduced that interatomic exchange between iron atoms which have lost their ferromagnetic tendencies produces the positive volume magnetostriction and the expansivities, lattice parameters, and forced volume magnetostrictions calculated on this model. The Mössbauer results show that in some regions of the sample the giant moments are weakly coupled to the mean magnetization, and it is the polarizing of the other iron atoms by these giant moments which produces the unusual temperature dependence of the low-temperature forced volume magnetostriction observed by Schlosser et al. A calculation using couplings derived from the Mössbauer results gives excellent agreement with experiment. It is obvious from this work that Invar is best considered as an inhomogeneous ferromagnet, analogous to PdFe or critical CuNi alloys
Localized vibrational modes for implanted oxygen in germanium
Authors: Stein H. J.
Published: February 2004

The first observation of localized vibrational modes for an implanted ion in Ge is reported. The localized mode for interstitial oxygen at 856 cm−1 and additional weak oxygen-associated absorption bands between 700 and 850 cm−1 have been observed by infrared absorption following oxygen implantation at 200 °C. Infrared detection of the vibrational modes for oxygen implanted into Ge at room temperature is precluded by ion-induced disorder and by absorption presumably associated with free carriers in the implanted layer.
Hole drift velocity in high-purity Ge between 8 and 220 °K
Authors: Ottaviani G. , Canali C. , Nava F. , Mayer J. W.
Published: February 2004

The hole drift velocity in high-purity Ge as a function of electric field (2−104 V/cm and temperature (8–220 °K) has been measured with the time-of-flight technique. The electric field was applied parallel to the 〈100〉 axis. The drift mobility in the Ohmic regime is in agreement with measurements of Hall mobility in high-purity Ge and with theoretical predictions. At temperatures below 100 °K the drift velocity reaches limiting values, and at 8 °K it is 1.3×107 cm/sec.
Thermomagnetic switching of single-crystal MnBi films
Authors: Kusuda Tetsuzo , Honda Shigeo , Hosokawa Yoshiteru , Nomura Takanobu
Published: February 2004

Thermomagnetic writing of single-crystal MnBi films has been investigated. The magnetic state of the spot heated with a laser beam is reversed by the stray field resulting from the surrounding saturated film. The reversed spot serves as a magnetic nucleus from which magnetic domains emanate by wall motion due to the demagnetizing field. Thus the magnetic state of the film switches from the remanent saturated state to the demagnetized state of lower energy. The reverse domain does not penetrate into the adjacent crystals beyond the potential barriers of the crystal boundary.
Minimal diffraction cuts for acoustic surface wave propagation on Bi12GeO20
Authors: Slobodnik A. J. , Szabo T. L.
Published: February 2004

Techniques are described for the theoretical prediction of acoustic surface wave orientations on anisotropic crystalline substrates having minimal diffraction spreading. These techniques are illustrated by the theoretical and experimental discovery of a minimal diffraction cut on Bi12GeO20 having diffraction retarded by at least two orders of magnitude over isotropic materials. Euler angles for this orientation are 45°, 40.04°, and 90°, while the surface wave velocity and the Δv/v parameter are 1827 m/sec and 0.0031, respectively.
Kerr response of nematic liquids
Authors: Johnston Alan R.
Published: February 2004

The Kerr response of seven nematic substances has been measured just above their nematic-isotropic transition temperature, in their isotropic state. If the reciprocal of the Kerr constant B is plotted against temperature, a linear relationship analogous to the Curie-Weiss dielectric relationship in ferroelectrics is found in all cases. The transient Kerr response—that is, the variation of induced birefringence with time in response to a field step—was also measured in three of the compounds. In p-(p-ethoxybenzylidene) amino benzonitrile (EBAB), a maximum Kerr constant of 175×10−10 cm2 V−1 was observed, together with a response time of 13 nsec. The extremely short response time indicates that molecular association does not take place. On the other hand, n-(p-methoxybenzylidene)-p-butylaniline (MBBA) under similar conditions showed a response time of 3 μsec, indicating that a high degree of association does take place in the isotropic phase.
Experimental technique for the precise determination of H and D concentration in rutile (TiO2)
Authors: Johnson O. W. , DeFord John , Shaner J. W.
Published: February 2004

Results of a precise determination of the ir absorption strength of H and D in rutile are presented, which permit determination of H or D concentration to an accuracy of 3%. The integrated absorption per ion was (2.51±0.09)×10−17 and (1.33±0.05)×10−17 cm for H and D, respectively. The procedure for calculating the H or D concentration in a particular sample from the ir absorption peaks is illustrated. Used in conjunction with the results of the theoretical analysis of the preceding paper, this technique makes possible the accurate determination of the energy and density of all electron trapping levels in TiO2 crystals. We also describe results showing that heat treatment in a dry H2 atmosphere at ∼800 °C results in the introduction of Ti intersititials but negligible H in the crystal, as predicted by the preceding paper. A technique for measuring diffusion parameters of H and D under conditions of strict chemical equilibrium, thus avoiding the large departures from Fick's law which usually plague such measurements in materials such as TiO2, is also described.
Ionization-enhanced diffusion: Ion implantation in semiconductors
Authors: Bourgoin J. , Peak D. , Corbett J. W.
Published: February 2004

A model for the diffusion of implanted interstitials during implantation is introduced and shown to be able to account for the tails observed in ion profiles. It is argued that mechanisms of ionization-enhanced diffusion can explain some of the anomalous diffusion mechanisms observed in semiconductors. Indications for the existence of such mechanisms in the field of ion implantation in semiconductors are discussed.
X-ray study of stacking faults in a double hexagonal close-packed Au–Cd–In alloy
Authors: Rao Y. Babu , Lele Shrikant , Rao P. Rama
Published: February 2004

A study of the x-ray powder pattern resulting from a cold-worked hexagonal close-packed Au–Cd–In alloy containing 17.5 at.% Cd and 5.0 at.% In has been made. Quantitative analysis of observed anomalous peak broadening, peak shifts, and peak asymmetry in the powder pattern shows evidence for only three of the nine faults, which have earlier been postulated for this structure, namely intrinsic-ch, intrinsic-h, and intrinsic-2h with respective fault probabilities of αch=0.045, αh=0.036, and α2h=0.002.
Theory of infrared absorption and material failure in crystals containing inclusions
Authors: Sparks M. , Duthler C. J.
Published: February 2004

Two effects of inclusions in or on the surface of infrared-transmitting materials are to increase the average value of the optical absorption coefficient β and to cause localized heating that could lead to material failure at high-power levels. Volume fractions as low as 10−7−10−8 of such inclusions can give rise to a value of the optical absorption coefficient β of 10−4cm−1, a typical value of current interest. For various types of inclusions the frequency dependence of β ranges from increasing as ω2, to independent of ω, to exponentially decreasing with ω. The temperature dependence ranges from independent of T to increasing as Tp in the high-temperature limit, where p≃2–4 typically. Simple expressions for the absorption cross section are derived for various cases of practical interest. The cross sections are used to derive expressions for β for the four cases of large inclusions of strong and weak absorbers and of small inclusions of dielectric and metallic particles. The material failure resulting from local heating of inclusions is a far greater problem in high-intensity short-pulse systems than in low-intensity long-pulse or cw systems having the same average intensity. Microsecond pulses with energy densities as low as a few joules per square centimeter can cause material failure.
Nuclear magnetic resonance relaxation of 23Na in porous media containing NaCl solution
Authors: Headley L. C.
Published: February 2004

Nuclear magnetic resonance (NMR) longitudinal and transverse relaxation rates and repetitive pulse steady-state magnetizations were measured in porous media containing solutions of NaCl in water. Longitudinal rates show a linear relationship with sample specific surface area, but transverse rates show more complicated behavior. These results are discussed in terms of diffusion and adsorption in the media. Experimental results for steady-state magnetizations achieved by repetitive pulsing are compared with theoretical calculations presented here. Theoretical expressions are also presented for use in optimizing fast repetitive pulse experiments.
Transient thermal profile in optically pumped laser rods
Authors: Koechner W.
Published: February 2004

Expressions are derived for the transient temperature distribution in optically pumped cylindrical laser rods for single-shot and repetitively pulsed operations. The analysis is performed for both solid and hollow cylindrical laser rods. The solutions are evaluated numerically and temperature histories applicable to a wide range of system parameters are presented graphically. The computations show the dependence of the transient thermal profile on the cooling condition of the rod. The results reveal that in practical situations (cooling factor: A = 2 to 10) the thermal relaxation processes are considerably slower than in the case where a zero thermal impedance (A = ∞) between the rod surface and the cooling fluid is assumed. This explains the discrepancy which existed between the theory and measured decay times of thermal effects in laser rods.
Optical switching and modulation in parallel dielectric waveguides
Authors: Taylor H. F.
Published: February 2004

Coupling of electromagnetic energy between parallel single-mode dielectric waveguides is investigated theoretically. Expressions giving the decrease in coupling length due to an antisymmetric change in refractive index are derived. The minimum parallel-guide path length, l, required for switching or modulation is determined from coupling length calculations. It is shown that, for large waveguide separations, Δnl=3λ/4, where λ is the free-space wavelength and Δn is the magnitude of the antisymmetric index change. Calculations for slab and square-cross-section waveguide geometries indicate that antisymmetric index changes are much more effective than symmetric changes for switching or modulation.
Liquid-phase sintering of magnetically isotropic and anisotropic compacts of BaFe12O19 and SrFe12O19
Authors: Arendt R. H.
Published: February 2004

This report shows that magnetically isotropic and anisotropic compacts of BaFe12O19 or SrFe12O19 sinter to high density with controlled microstructure in the presence of a liquid phase. The liquid-phase compositions are in the systems MO–SiO2 and MO–Al2O3–SiO2, M=Ba, Sr. Further, it is shown that systems containing MB2O4 as an additional component will give similar results at significantly lower temperatures. The resultant magnetic properties meet or exceed the appropriate magnet industry criteria for hard ferrite magnets.
Josephson junction mixing
Authors: Thompson E. D.
Published: February 2004

It is shown that a Josephson junction, biased at a voltage V0 and driven simultaneously by two monochromatic sources at the frequencies ω1 and ω2, produces an output power at the frequency ω3 = ω1 — nω2 and that this frequency is independent of the Josephson frequency ω0 = 2eV0/ℏ. The power output depends upon the dc bias, showing fine structure with a voltage periodicity of ℏω2/2e.
Reply to ``Comment on `Determination of dislocation velocities and densities'''
Authors: Bodner S. R. , Baruch J.
Published: February 2004

The basic assumptions of the writers' earlier paper (Ref. 2) on the properties of dislocation motion during the passage of a deformation wave are further discussed in view of the discussion of van der Beukel et al. (Ref 1). It is shown that those assumptions are physically realistic while alternative ones are inconsistent.
Comment on ``Laser evaporation and elemental analysis''
Authors: Baldwin Jon M.
Published: February 2004

Recently reported work by Kliwer does not represent the first instance in which pulsed lasers were used to deposit thin films of metals for elemental analysis. Moreover, the results of a large number of elemental analyses of thin alloy films deposited by laser-induced evaporation do not agree with the assertion that stoichiometry of the alloy is preserved through the evaporation process. The disparity between Kliwer's results and those of the present work requires that the analytical chemical significance of samples prepared by laser-induced vaporization be assessed with caution.
Verification of sensitivity enhancement factors for cw ultrasonic resonators
Authors: Heyman Joseph S. , Miller J. G.
Published: February 2004

Sensitivity enhancement factors predicted by an analysis of cw ultrasonic resonator systems using the propagating wave model are verified. Absorption and dispersion sensitivity factors were obtained by producing small changes in the acoustic properties of a CdS resonator with a light beam.
Volume charge distribution in carnauba wax electrets
Authors: Walker David K. , Jefimenko Oleg
Published: February 2004

Internal charge distribution in carnauba wax thermoelectrets was measured. It was found that substantial volume charges exist within the electrets. These charges form a characteristic permanent volume charge distribution which is essentially the same for all investigated (over 100) electrets regardless of the magnitude of the electric field used for polarizing the electrets, duration of polarization, electret age, surface charge, or storage conditions. The existence of this characteristic volume charge distribution indicates that the primary mechanism responsible for the electret effect in the carnauba wax thermoelectrets is a trapping of electric charges within the electret material rather than a permanent microscopic polarization of the material.
Electron-ion recombination measurements in CO at high pressures
Authors: Center R. E.
Published: February 2004

The electron-ion recombination rate has been measured in a high-pressure CO discharge at room temperature and at pressures from 100 to 700 Torr. The effective two-body rate coefficient was found to be in the range 10−7−10−6 cm3/sec, with an electron temperature dependence of Te−1.6 associated with the average electron energy from 0.2 to 0.7 eV. The results indicate a small pressure dependence, of less than a factor of 2, over the experimental pressure range. The principal ion at these pressures was probably the dimer, C2O2+, or a high-order polymer ion based on ion-molecule reactions in CO reported in the literature.
Thermodynamics of the first phase of exploded conductors
Authors: Vlastós Antonios E.
Published: February 2004

For cylindrical conductors made of thin copper and tungsten and heated by the electrical pulse from a high-voltage condenser bank which had inductance and resistance much lower than those of the conductors, the following items were studied as functions of the diameter and the applied voltage: (i) the variations in time of the temperature and resistance of the conductors up to the time they reach their melting points; (ii) the dips on the recordings of the current derivative and the voltage across the conductors which appear near their melting points; (iii) the first current-pulse crest and the time to the current-pulse crest, as well as the influence of the ambient pressure on the current crest and on the time to the current crest; and (iv) the events occurring at the tail of the first current pulse and the beginning of the dwell time, which may have a decisive effect on the type of restrike mechanism which will follow the conductor explosion.
Instabilities of intense laser beams in air
Authors: Reichert John D. , Wagner W. G. , Chen W. Y.
Published: February 2004

Various aspects of the propagation of an intense laser beam through the atmosphere are considered. The basic laser-fluid equations are presented and a linearized analysis of these equations is given which predicts a very low power threshold for Brueckner-Jorna-type convective instabilities. Another class of instabilities is predicted to be of more practical importance than the convective instabilities and an effective Reynolds number is derived which may help to characterize these turbulent instabilities. In the following paper by the same authors a computer solution of the full set of nonlinear equations is described and the initial development of the laser-fluid interaction is investigated.
Propagation of an intense Gaussian laser pulse in air
Authors: Reichert John D. , Wagner W. G. , Chen W. Y.
Published: February 2004

A numerical solution of the nonlinear macroscopic laser-fluid equations for propagation of a Gaussian laser pulse in air is described. The concept of ``utility analysis'' of numerical differencing schemes is introduced. With the computation scheme used, the laser pulse could be followed for only 10−5 sec; so enormous energy was put into the pulse to enhance the interaction with the fluid. Thus the initial pulse distortion could be observed. Analytical evaluation of the computer results produces a detailed quantitative check and suggests that a combination of analytic and numerical methods would allow a pulse to be conveniently followed for much longer periods of time. The preceding paper by the same authors describes various types of instabilities to be anticipated for propagation over long periods of time or with large powers.
Crystal growth of ZnxCd1−xTe solid solutions and their optical properties at the photon energies of the lowest band-gap region
Authors: Ebina Atsuko , Saito Kazuyuki , Takahashi Tadashi
Published: February 2004

Single crystals of ZnxCd1−xTe solid solutions have been grown from a melt under an Ar pressure of about 50 atm. The crystals of uniform composition were grown over the whole range of molar composition, when the crystal growth was performed in excess Zn and/or Cd. A grown boule of 30 × 15 mm φ contained several single-crystal domains of size 7 × 5 × 5 mm. On the basis of Vegard's law, the molar composition x was determined from x-ray measurements of lattice constants. The variation of x throughout a single-crystal domain was found to be less than ± 1%. Optical experiments including transmittance and reflectance measurements have been made on the cleaved (110) planes at room temperature. The variation of the lowest band gap with x was determined from the peak positions in the reflectivity spectra. The bowing parameter, which is a measure of the deviation from the linear change, of this gap was found to be 0.33 eV.
Point-contact tunneling device
Authors: Moore S. E. , Meincke P. P. M.
Published: February 2004

A simple point-contact tunneling device for examination of the properties of almost any metal, alloy, or compound of almost any shape is described. The device has a small mass to permit dipping into liquid helium directly from room temperature. The stability and accuracy of the drive mechanism permit it to be used for single-particle superconductive tunneling as well as for Josephson devices, weak links, and metal-metal bridges. Experimental results showing a recording of the drive characteristics of the differential screw, the transition from Josephson weak-link behavior to single particle tunneling for a Nb–I-Vycor (Pb) sample, a well-resolved energy gap for niobium, and the phonon structure of lead are presented.
Low-frequency parallel pumping
Authors: Jackson D. R. , Huang C. Y.
Published: February 2004

Parallel pumping in the region below 500 MHz provides a convenient tool for measuring the elastic and magnetic relaxation parameters of low-loss ferrities and garnets. This frequency region is of particular interest in microwave acoustic and cylindrical domain applications and is not readily accessible by conventional resonance and pulse-propagation techniques. We find that the usual treatments of parallel pumping, in which the normal modes are considered to be plane waves, fail at low frequencies because of multiple surface reflections. A theory is developed which does not contain the plane-wave assumption and is found to agree with our experimental results for YIG. Our experiments were performed at room temperature with a pump frequency of 42 MHz. The magnetic relaxation parameter determined from these experiments is two orders of magnitude larger than the value that would be deduced from microwave uniform-precession resonance measurements and is in accord with the domain wall mobility measurements of Hagedorn and Gyorgy, Wanas, and Vella-Coleiro et al.
X-ray diffraction topography of magnetic domains in orthoferrites
Authors: Patel J. R. , Van Uitert L. G. , Mathiot A.
Published: February 2004

Under usual conditions the domain configuration in rare-earth orthoferrites shows no contrast by x-ray diffraction topography. In the reorientation range of temperatures, where the net magnetization rotates away from the c axis, the domain configuration is favorable for x-ray observations. Domains have been revealed in a cobalt-substituted orthoferrite where the reorientation range is at room temperature. The observed contrast does not obey the simple rules that apply to similar observations in Fe–Si and YIG. Possible reasons for the observed contrast are discussed in terms of the domain distortion.
Application of a nondestructive single-spectrum proton activation technique to study oxygen diffusion in zinc oxide
Authors: Robin R. , Cooper A. R. , Heuer A. H.
Published: February 2004

18O diffusion coefficients were measured directly and without serial sectioning, using proton activation analysis of 18O via the nuclear reaction 18O (p, α)15N. In this technique, the α-particle spectrum recorded during proton irradiation is used to determine the 18O concentration profile; submicron resolution can be achieved. The suitability of this approach was demonstrated by studying oxygen self-diffusion along the c axis of ZnO single crystals. In the temperature range 940–1140°C and at Po2 of 700 mm, D=1.2(−0.6+1.1)10−10exp[−(29.6±1.6) kcal/RT] (cm2/sec). The results are interpreted as indicating extrinsic behavior; the activation energy is then that for oxygen mobility only. The surface exchange coefficient, characteristic of the reaction between gaseous and lattice oxygen, was also determined, in the temperature range 940–1040°C, as K=5.7(−4.6+23.8)105 exp[−(91.2±4.0 kcal)/RT] (cm/sec). A detailed analysis of the technique is presented. Using a convolution procedure, the oxygen self-diffusion coefficient, at a given temperature, is determined in a single irradiation run with a precision better than 10%, which is limited only by counting statistics. However, uncertainty in the values of the stopping powers for protons and alphas may cause an additional systematic uncertainty in D of up to [inverted lazy s]50%; since this error is identical for all temperatures, it causes an uncertainty in the preexponential but not in the activation energy. The technique is optimum for determining D in the range [inverted lazy s]5 × 10−12−[inverted lazy s]5 × 10−17 cm2/sec and is useful for testing models of the exchange kinetics.
Diffusion of carbon in nickel
Authors: Berry B. S.
Published: February 2004

Results of Diamond and Wert on the kinetics of the reorientation of carbon pairs in nickel are used to demonstrate that the low activation energy reported by Massaro and Petersen for diffusion of carbon in nickel at 350–-700°C cannot be explained by a change in the mechanism for the lattice migration of carbon. Boundary diffusion also appears incapable of explaining the results, and it is concluded that there may be unsuspected difficulties with the particular method of measurement employed for the diffusion measurements.
Ion-acoustic waves in a bounded plasma
Authors: Tang B. S. , Roberts J. A.
Published: February 2004

A systematic study was made of some of the oscillatory phenomena which are found to occur in bounded dc discharge plasmas. The nature of the oscillator patterns was explored over a pressure interval (0.01≤P≤1.5 Torr), a current interval (0.5≤I≤10 mA), and a discharge-voltage interval (0.8≤V≤3.5 kV) in order to establish the conditions for onset of oscillatory modes within the plasma. An rf pickup coil, to detect the oscillations, was placed such that it contained the plasma filament coaxially. Signals having a frequency range of 20–200 kHz were observed to be coming from the plasma. These frequencies were found to be sensitive to pressure, current, and discharge voltages for a given geometry tube. The gases considered in this investigation were N2, O2, CO2, air (atmospheric), H2, D2, He, and argon. Electron densities calculated from the ``resonant'' conditions for the ions are presented.
Excitation mechanism of the Cr3+ luminescence center in SrTiO3
Authors: Ghosh Amal K. , Addiss R. R. , Lauer R. B.
Published: February 2004

From thermoluminescence (TL), thermally stimulated currect (TSC), and photoluminescence and photoconductivity kinetic response measurements, the excitation mechanism of the Cr3+ luminescence center in SrTiO3 is explored. Based primarily on the strong correlation between TSC and TL, it is concluded that the dominant excitation mechanism is a charge-transfer process, although a contribution from a resonance-transfer process cannot be completely ruled out. The superficial differences which exist between photoluminescence and photoconductivity kinetics can be accounted for completely within the framework of a charge-transfer model by recognizing that the photocurrent is controlled primarily by the electron traffic through the conduction band, while the photoluminescence is controlled primarily by the hole traffic through the luminescence center.
LEED study of the (111) surface of β-rhombohedral boron
Authors: Rovida G. , Maglietta M.
Published: February 2004

The LEED pattern characteristic of a regular structure of the (111) surface of β-rhombohedral boron was obtained after heating at temperatures higher than 1400 °C. As indicated by Auger spectroscopy, this treatment is sufficient to eliminate oxygen and carbon, the main impurities present on the initial surface. A small amount of nitrogen remains on the surface. The LEED pattern observed in these conditions is in agreement with the unit mesh of the bulk (111) planes.
Luminescence of rf-sputtered oxide films during sputtering
Authors: Ratinen H.
Published: February 2004

A Sputtering apparatus was equipped with an optical spectrometer by which both the fluorescence from the glow discharge and the luminescence from the growing film could be detected and measured separately. Calcium, magnesium, and lanthanum oxide layers doped with samarium or terbium were used as targets. It was observed that the luminescence appeared when calcium or magnesium oxides were used as host materials, but was absent in the case of lanthanum oxide. The thickness of the layer in which the excitation took place was found to be a few hundred angstroms. The possible reason for the weaker luminescence efficiency of lanthanum oxide in comparison with calcium and magnesium oxides has been discussed.
Ferroelectric, piezoelectric, and optical properties of SrTeO3 single crystals and phase-transition points in the solid-solution systems
Authors: Yamada Tomoaki , Iwasaki Hiroshi
Published: February 2004

Temperature dependences of dielectric, ferroelectric, elastic, piezoelectric, and optical properties of a new ferroelectric crystal, SrTeO3, have been measured. Ferroelectricity in this crystal is confined to the temperature range between 312 and 485°C. All the measured constants exhibit abrupt changes at 312°C, which shows the phase transition at this temperature to be of the first order. The electromechanical coupling factors k21 and k22 at 312°C are 0.34 and 0.37, respectively, which are large in spite of the small value of the spontaneous polarization; 0.037 C/m2. The temperature dependence of the piezoelectric constant d22 is well explained by the dielectric constant and the spontaneous polarization, while that of d21 seems to be peculiar; i.e., it monotonically decreases to nearly zero at the upper transition point. The elastic compliances S11D and S22D show no anomaly in the ferroelectric temperature range. The obtained value of 17.3 eV for the dispersion energy of the refractive index nb indicates that this crystal may be built up by the tetrahedral framework. Phase-transition temperatures in the solid-solution systems Sr1−xBaxTeO3 and Sr1−xCaxTeO3 are studied on ceramic samples. The two transition points decrease with increasing x in both systems.
Reactions of silicon with surfaces of close-packed metals. III. Silicon on beryllium
Authors: Jona F.
Published: February 2004

Deposition of silicon onto a clean Be (0001) surface results in an ordered superstructure which is characterized by the presence of (1/3)-order spots in the low-energy electron diffraction pattern of the clean surface. This is the √3×√3−30° structure that was predicted in an earlier report. Epitaxial growth of crystalline Si films is hindered, however, at low temperatures by the low mobility of the adsorbed atoms (the Si films are amorphous) and at high temperatures by the rapid diffusion of Si into the interior of the substrate.
Structure of dislocations in germanium
Authors: Phillips Victor A. , Wagner R.
Published: February 2004

Two-beam tilt {111} lattice images were made of dislocations in germanium crystals deformed by compression or torsion. {110} slices were cut out normal to the main glide planes and chemically thinned. The displacement field was measured around a 60° dislocation running normally through a foil cut from a twisted crystal, which gave a lattice image with perfect symmetry about the terminating fringe. After suitable correction, the measured width on the Peierls-Nabarro model was 5.2 Å, about a factor of 2.5 greater than expected from a theory by Labusch. The measurement involved the assumption that a direct correspondence exists between fringe and lattice plane positions in the special case studied.