bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning Electron Microscope Characterization of GaP Red-Emitting Diodes
Authors: Hackett W. H. , Saul R. H. , Dixon R. W. , Kammlott G. W.
Published: February 2004

Accurate measurements of the near-junction properties of three different red-emitting GaP p-n junction structures have been made using the scanning electron microscope (SEM). The structures consisted of similar Zn, O-doped p-type liquid-phase-epitaxial (LPE) layers grown on different Te-doped n-type substrates, which include solution-grown (SG) crystals, liquid-encapsulated Czochralski (LEC) crystals, and LPE layers grown on LEC crystals. These junctions have yielded diodes with electroluminescent efficiencies as high as 6.0, 2.0, and 4.5%, respectively. These measurements, which include minority-carrier diffusion lengths, the spatial distributions of luminescent efficiency, and the detailed properties of the space-charge region, have provided a self-consistent picture of the factors which determine electroluminescent efficiency. In this study, all of the junctions were determined to be n+-p structures which exhibit uniform red luminescent efficiencies in the p region near the junction. The differences between the structures were found to lie in the relative contributions of nonradiative recombination centers, which tend to reduce both luminescent efficiency in the p region and injection efficiency into the p region. These centers were found to be most prominent for the LEC single LPE junctions, to a lesser degree for the LEC double LPE junctions due to a buffering effect of the additional n layer, and least of all in the SG single LPE junctions. For these 6.0% SG single LPE diodes, the injection efficiencies and luminescent efficiencies were determined to be 50% and 20%, respectively, allowing for 60% external coupling efficiencies. These values are consistent with those obtained from diode electrical and electroluminescent measurements, and agree with photoluminescent measurements in the p region.
High-Vacuum Codeposition of Niobium Nitride
Authors: Sterling S. A.
Published: February 2004

A technique has been developed for the reactive high-vacuum codeposition of niobium nitride at rates in excess of several hundred Å/sec. With gaseous ammonia as the nitrogen source, films with transition temperatures in excess of 13°K have been fabricated. The depression of the transition temperature from values reported for sputtered films is attributed to ammonia decomposition chemistry. In addition, 4.2°K critical currents in excess of 106 A/cm2 have been measured for 1-μ-thick films.
Beam Efficiency, Inelastic Scatter, and Radiation Damage in the High-Voltage Microscope
Authors: Parsons D. F.
Published: February 2004

The composite plasmon-free atom scattering theory of Crick and Misell has been used to calculate the angular intensity distribution of inelastic scatter from a model biological object (50 Å of amorphous carbon) at 100- and 1000-kV acceleration voltage. It is shown that in most situations of electron microscope imaging of supramolecular structures the damage associated with viewing and recording of the image is related to the ratio of inelastic scatter/elastic scatter (I/E) or to I/(I+E), and that these ratios are approximately the same at 100 and 1000 kV. It is concluded that there is no intrinsic improvement in beam radiation damage in using higher acceleration voltage (1000 kV). In current use, the radiation damage in the high-voltage microscope (HVEM) is frequently much higher than in a conventional (100 kV) microscope, because of the decreased sensitivity of photographic emulsions at 1000 kV. Special emulsions are required for high-voltage biological electron microscopy.
Concept of Generalized Chladni Forces: Application to an Electron-Optical Light Pipe
Authors: Little W.A.
Published: February 2004

It is shown that a particle moving in a time-dependent spatially inhomogeneous field is acted upon by a time-averaged force which acts along the negative of the gradient of the oscillatory kinetic energy. This force is a generalization of the concept of the forces which act to move particles of sand towards the nodal lines in classic Chladni sand figures. Its use in electromagnetic phenomena suggests some novel applications. In this paper the phenomenon is demonstrated and is used in a device which is an electron-optical analogue to the optical light pipe.
Precipitation of Dopants in Silicon-Germanium Thermoelectric Alloys
Authors: Nasby R. D. , Burgess E. L.
Published: February 2004

Precipitation of phosphorus and boron dopants has been observed in a silicon-germanium alloy thermoelectric couple. The couple was life tested in a thermal gradient of 1050 to 370 °C for 39 210 h. Electrical resistivity, Seebeck coefficient, and the derived carrier concentration are reported as a function of temperature.
Diode-Pump-Modulated Nd:YAG Laser
Authors: Danielmeyer H. G. , Ostermayer F. W.
Published: February 2004

We have investigated the response of a luminescent diode-pumped cw Nd:YAG laser to a sinusoidal modulation of the pump intensity. For small modulation depths we found exact agreement with the relaxation oscillation resonance predicted by the linearized treatment of the coupled rate equations. For large modulation depths we obtained regular spikes at repitition rates between approximately 4 and 6 kHz with peak powers up to 100 times the cw power. Both the relaxation oscillation resonance (∼ 10–20 kHz depending on pump power) and the spiking could be self-excited by means of a feedback loop.
Surface-Charge Decay in Insulators with Nonconstant Mobility and with Deep Trapping
Authors: Wintle H. J.
Published: February 2004

The motion of space charge initially located at the free surface of an insulator is studied as a function of time. Analytic results are given for the following cases: (a) mobility proportional to a power of the field; (b) mobility proportional to a power of the free-carrier concentration; and (c) fast deep trapping which goes to completion. After one transit time, the surface voltage becomes a unique function of time, independent of its initial value. The available experimental data for polyethylene do not fit these simple models, and the discrepancies are discussed. It is also shown that the observation of thermally stimulated currents in thin-film electrets implies that they are electrically inhomogeneous.
Ion Machining of Diamond
Authors: Spencer E. G. , Schmidt P. H.
Published: February 2004

It is demonstrated that argon-ion beams are effective in drilling holes in diamonds. Truncated conical holes were made with basal diameters as small as ∼0.375 mm and tapering to ∼0.05-mm diameter at the top. Larger holes with diameters at the two surfaces of 1.45 and 2.26 mm were milled through a 1.58-mm-thick diamond. Milling rates of up to 2 μ/min were obtained. The inside surfaces of the holes are essentially polished, with adjacent regions appearing to be damage free. The technique also has the capability of milling holes of arbitrary shape and of finely polishing the inside surfaces.
Plasma Instabilities in High-Current Field-Emission Diodes
Authors: Toepfer Alan J. , Bradley Laird P.
Published: February 2004

Striations in electron-energy-deposition profiles from high-current field-emission diodes utilizing razor-blade cathodes have been observed. The variation of wavelength in the striations with cathode geometry indicates that the current-carrying plasma at the surface of the cathode undergoes a tearing instability during the initial stages of breakdown.
Electronic Properties of Furan-Quinone Pigments. II. Photoinjection and Photoemission Studies
Authors: Pfister Gustav , Nielsen P.
Published: February 2004

The positions of the valence, conduction, and vacuum levels of the vacuum-deposited yellow furan-quinone pigments 8, 13-dioxodinaphtho (2, 1−b:2′, 3′−d)-furan-6-(2-pyridyl)-carboxamide (DFC) and 8, 13-dioxodinaphtho (2, 1−b:2′, 3′−d)-furan (DF) with respect to the Fermi level of the substrate Au, Al, or Cu were determined from measurements of the internal and external photoeffect. The structure of the conduction and vacuum levels for the two pigments is the same within experimental error. A weak photoresponse due to bulk states was observed below 2 eV photon energy. These states position the Fermi level about 2.7 eV above the valence band edge. An experimental value of 3.55 ± 0.13 eV for the separation of the valence and conduction bands was obtained. An interfacial dipole layer was found for all substrates investigated. The resulting drop of the vacuum level of the pigment with respect to the vacuum level of the substrate increases with increasing substrate work function. From the voltage dependence of the injection current, a mean free path for the scattering of the photoinjected carriers, in the image-force potential well between the emitter and the potential maximum in the pigment, was calculated. Qualitative agreement was obtained with the screening length derived from the bending of the band-type energy states close to the pigment/substrate interface. Depending upon bias polarity, strong polarization effects were observed for DFC deposited on Au and DF deposited on Al substrates. The experimental results are compared with the theoretical predictions made from molecular energy level calculations.
Effects of Stoichiometry and Impurities on the Metal-to-Semimetal Transition in NiS
Authors: Koehler R. F. , Feigelson R. S. , Swarts H. W. , White R. L.
Published: February 2004

A study of the effects of stoichiometry and impurity content on the temperature of the metal-to-semimetal transition in hexagonal NiS has been made. It was found that the cation-anion ratio was the only factor significantly affecting Tt. Substitution of impurity ions for nickel or sulfur produced minor effects unless those impurities could affect the cation-anion ratio by forming a second phase. An annealing process was used to remove sulfur from single crystals of NixS in order to obtain samples with desired values of x between 0.96 and 1.
A Study of Compressed Spatially Non-Gaussian Optical Pulses from Mode-Locked Lasers
Authors: Kim Dae M. , Rabson T. A. , Ruiz H. J. , Tittel F. K.
Published: February 2004

The effect on the grating-induced phase and spatial modulations by multiple transverse modes simultaneously present in mode-locked laser pulses is investigated. Our analysis shows that the dispersions of the grating pair become strongly dependent on wavelength because of the energy exchanges occuring among transverse modes. As a result, the maximum-intensity trace at the output of the grating is shown to be curved and the grating-induced pulse-compression rate is shown to vary significantly across the beam cross section. Also, a discussion is presented relating our analysis to existing experimental data on the wavelength-dependent chirping rates of mode-locked laser beams.
Magnetic Characteristics of Some Binary and Ternary 2–17 Compounds
Authors: Schaller H. J. , Craig R. S. , Wallace W. E.
Published: February 2004

The magnetic anisotropy of R2Co17 and R2Co17−xTx compounds with R=Y, Ce, Pr, Nd, Th and T=Mn, Fe has been investigated. The directions of easy magnetization were determined by x-ray studies on oriented powders. The several R2Co17 compounds, except for Ce2Co17, have an easy basal plane; the behavior of Ce2Co17 could not be clarified. Replacement of Co by Mn or Fe changes the easy magnetization direction from the basal plane to the c axis. Anisotropy fields were measured on magnetically aligned powders. The values for the anisotropy fields range between 12 and 24 kOe. Curie temperatures and saturation magnetization data for R2Co17−xTx compounds with T=Mn, Ru and R=Ho, Y are reported. The decrease of the magnetization with increasing x observed in the system Y2Co17−xTx is accounted for by assuming either a reduced Co moment or an antiparallel coupling of the T transition-metal spin. Similar considerations hold for Ho2Co17−xTx ternaries.
High-Frequency Response of Josephson Point Contacts
Authors: Kanter H. , Vernon F. L.
Published: February 2004

For a current-driven Josephson junction shunted by an Ohmic resistance, the dc voltage response and impedance to external high-frequency currents is calculated with a second-order perturbation method based on the unperturbed solution for the time evolution of the voltage as given by Aslamazov and Larkin. The response is proportional to signal power and has three characteristic-frequency regions depending on whether the internal self-generated Josephson frequency, ω0, is larger than, equal to, or smaller than the signal frequency, ω. For ω0< or >ω the response could be expressed by easily observable parameters of the dc voltage-current characteristics. This permits comparison of the predictions with experimental results obtained on point-contact junctions whose dc characteristics were only approximately represented by the simple model chosen for analysis. For ω0≪ω the response is found to be proportional to (i) the slope of the dc characteristic, (ii) the inverse square of the applied frequency, (iii) the inverse battery current in terms of the critical current, and (iv) the voltage amplitude of the inherent Josephson oscillations. For ω0≫ω ``classical'' detection proportional to curvature is obtained. For ω0∼ω resonance detection occurs, which depends to a considerable degree on fluctuations of the average contact voltage. These predictions are in reasonable agreement with experiments in which point-contact junctions were illuminated with klystron radiation at 10 and 90 GHz. Evidence is presented that the voltage fluctuations limiting the resonance response are the result of noise generated in the junction. Comparison of the noise-equivalent power expected from the simple model with measured results suggests that parasitic elements, such as shunt capacity, are not negligible at 90 GHz.
Electron Depth-Dose Distribution Measurements in Finite Polystyrene Slabs
Authors: Rosenstein Marvin , Eisen Harvey , Silverman Joseph
Published: February 2004

Experimental depth-dose curves for 2.00-MeV electrons incident on layers of polystyrene were obtained for broad-beam geometry as a function of slab thickness and incident beam angle. Calibrated radiochromic dye films were used as dosimeters. Continuous spatial absorbance changes in the irradiated film were recorded with the aid of a scanning densitometer. Data were obtained for the following conditions: (a) polystyrene thicknesses 0.42, 0.63, and 1.5 times the electron range, and (b) electron-beam incidence angles of 0°, 15°, 30°, 45°, 60°, and 75° to the normal. Comparisons were made with theoretical depth-dose histograms generated by the Monte Carlo computer code ETRAN. Close agreement was found for the two thicker slabs, but energy absorption in the thin slab was observed to be lower than that predicted by the calculations by 5–15%.
The Role of Internal Conversion Electrons in Gadolinium-Exposure Neutron Imaging
Authors: Harms A.A. , Norman G.R.
Published: February 2004

A radiation conversion and radiation transport model applicable to gadolinium-exposure neutron imaging is formulated. The resultant linear optical density representation is found to be in good agreement with experiment. The distinct conversion-electron contributions thus identified confirm the supposition about the dominant mode of image formation in gadolinium-exposure neutron imaging.
Tunable-Laser Spectroscopy of the ν1 Band of SO2
Authors: Hinkley E.D. , Calawa A.R. , Kelley P.L. , Clough S.A.
Published: February 2004

Individual transitions of the ν1 vibration-rotation band of SO2 in the 8.7-μm-wavelength region have been observed, using tunable semiconductor diode lasers, and compared with theoretical calculations based on pure-rotation data from microwave absorption measurements. A new value of 1151.71 ± 0.01 cm−1 has been found for the ν1-band center. Pressure-broadening coefficients and intensities of individual lines were determined from the high-resolution data, and a value was obtained for total band intensity.
Characteristics of Temperature-Stable Eu-Based Garnet Films for Magnetic Bubble Applications
Authors: Bonner W.A. , Geusic J.E. , Smith D.H. , Rossol F.C. , Van Uitert L.G. , Vella-Coleiro G.P.
Published: February 2004

Epitaxial garnet films Y3−xEuxAlyFe5−y O12, with x=1.5–2.0 and y=0.7–1.2 and small additions of Yb, are reported: with 1–7-μ bubbles; with bubble diameters that are relatively constant versus temperature; and in which bubble velocities greater than 1500 cm/sec have been observed. These materials show promise for bubble device applications.
Computer simulation studies of the a/2 〈111〉 edge dislocation in α-iron
Authors: Schiffgens J.O. , Garrison K.E.
Published: February 2004

Core characteristics of the stable a/2 〈111〉 edge dislocation in α-iron are presented for three two-body interatomic potentials, and the importance of properly defining boundary conditions is demonstrated. The boundary requirements adopted for this analysis are as follows: (i) The coordinate of the dislocation line along the axis parallel to the burgers vector is such that, above and below the slip plane, the lattice to the right and left of the extra half-planes of atoms forming the dislocation is symmetric. (ii) The coordinate of the dislocation line in the direction perpendicular to the slip plane is such that the slope of the strain energy curve in the linear region of the lattice agrees with the slope in the continuum. (iii) The positions of atoms at the lattice-continuum interface are made to agree with the predictions of linear elasticity theory. Four interatomic potentials are examined, one of which is shown to be unsatisfactory. Results with the other three potentials are quite reasonable. Core radii of 4.6, 4.8, and 5.4 Å and corresponding core energies of 0.479, 0.539, and 0.701 eV per (112) plane are calculated. The stable core configuration in each case is consistent with the particular character of the interatomic potential. The results suggest that the core characteristics are not sensitive to the value of the cohesive energy associated with each potential.
Elastic constants of terbium between 78 and 300 K
Authors: Salama K. , Brotzen F.R. , Donoho P.L.
Published: February 2004

The adiabatic elastic constants of terbium were determined in the temperature range 78–300 K, using high-purity single crystals. The constants were obtained from the ultrasonic wave velocities (20 MHz) measured by the pulse-superposition method. The values of the constants c33, c44, c11, c12, and c13 at room temperature in units of 1011 dyn/cm2 are 7.225, 2.140, 6.788, 2.432, and 2.299, respectively. Using these values, the Debye temperature was computed to be 176.6 K. The velocities tend to vary with temperature in an anomalous fashion near the magnetic phase transitions, i.e., the Néel and Curie temperatures, 229 and 221 K, respectively. The relative change of the longitudinal velocity in the [0001] direction, near the Néel temperature, TN, could be described by a logarithmic function of the reduced temperature (T-TN)/TN. The rate of the relaxation process of this relationship was estimated to be 6×109 sec−1.
Calculation of electric field breakdown in quartz as determined by dielectric dispersion analysis
Authors: Lynch W.T.
Published: February 2004

A classical theory of electron energy loss is used to calculate the breakdown field of quartz as 1.0×107 V/cm. The method makes use of the dielectric dispersion curves to determine the electron energy loss via interaction with the longitudinal optical (LO) phonon modes. The 0.153-eV LO mode is the dominant mode in determining the breakdown. The results for quartz should also be applicable to amorphous SiO2 since the optical phonon modes are strongly localized and the nearest-neighbor configuration is maintained for both silica and quartz. The 1.0×107 V/cm breakdown calculation is in excellent agreement with the highest breakdown fields measured for amorphous SiO2 films.
Motion of a screw dislocation in a crystal at finite temperature
Authors: Flytzanis N. , Celli V.
Published: February 2004

In a simple model of a cubic lattice with piecewise linear nearest-neighbor interactions, a solution is obtained for the motion of a straight screw dislocation at finite temperature T, under the action of a constant applied stress. This external stress is balanced by the frictional stress due to the scattering and emission of phonons by the core of the dislocation. The results are compared with those obtained by the authors and others for the case of zero temperature. It is found that the thermal agitation greatly affects the dislocation motion for T comparable to the Debye temperature. At low T, the shape of the stress-velocity curve is the same as at T=0, except that an additional phonon-scattering term, proportional to the number of phonons, is present.
Effect of plasma resistance on electron temperature measurement by means of an electrostatic probe
Authors: Matsumura S. , Chen Sin-Li
Published: February 2004

The effect of the equivalent plasma resistance between the probe and the reference electrode on the gradient of the semilog plot of the electron-current curve vs voltage of a probe has been studied theoretically for the probes of plane, cylindrical, and spherical types. The probe current-voltage characteristic actually measured deviates from its regular curve because of drawing current through the bulk plasma not having an infinite conductivity. The electron temperature Te determined from the measured electron-current curve by using the usual graphical method will be higher than its true value. The theoretical maximum errors in Te determination for the three kinds of probe studied are all within a factor of 2. Some experiments are also presented and discussed.
Shock response of porous copper, iron, tungsten, and polyurethane
Authors: Linde Ronald K. , Seaman Lynn , Schmidt David N.
Published: February 2004

For guidance in constructing a mathematical model for porous materials, impact tests were conducted with a light-gas gun on samples of porous copper, iron, tungsten, and polyurethane foam using manganin and quartz transducer techniques. Both Hugoniot (thick flyer) and attenuation (thin flyer) experiments were conducted on the porous metal specimens, which were initially at 70% of solid density. The Hugoniot elastic limits were 1, 2.5, and 10 kbar and maximum stresses attained were 60, 50, and 140 kbar in copper, iron, and tungsten, respectively. In impacts above 20 kbar, porous iron and copper compacted to solid but tungsten was not consolidated at 140 kbar. The mathematical model was incorporated into a one-dimensional wave propagation computer program, and stress histories were computed to compare with the transducer records. Computed peak stresses and arrival times agreed with the recorded values within 20%.
Gallium phosphide high-temperature electroluminescent p-n-p-n switches and controlled rectifiers
Authors: Keune D.L. , Craford M.G. , Herzog A.H. , Fitzpatrick B.J.
Published: February 2004

Electroluminescent gallium phosphide p-n-p-n switches (dynistors) and controlled rectifiers (thyristors) which are operable in the temperature range 0 ≤ T ≤ 500°C have been fabricated by diffusion of Zn into GaP n-p-n structures grown by liquid-phase epitaxy. Gallium phosphide thyristor forward and reverse blocking voltages as large as 280 and 80 V, respectively, have been observed. These thyristors can be switched to the low-impedance state by the application of < 5 A/cm2 gate current and exhibit holding current densities of ≈ 15 A/cm2 at a forward voltage of 2.2 V. Forward blocking voltages as large as 380 V at room temperature and 310 V at 415°C have been observed for GaP dynistors. When forward biased into the low-impedance state, these devices operate as high-brightness light emitters with room-temperature emission in the green portion of the spectrum.
Observations of negative resistance in Ti–TiO2–Au diodes
Authors: Soukup R.J.
Published: February 2004

Studies made on thin-film diodes revealed a number of interesting effects seen in the current-voltage characteristics. These Ti–TiO2–Au diodes were rectifiers with the positive direction of current flow being Au biased positively. Most of the diodes exhibited a slow-switching negative-resistance region. The I-V characteristics were different for dc and pulse measurements with the pulse measurements having a higher activation energy. Hysteresis in the curves was noted while measuring the I-V characteristics on a dc basis, with a resultant memory. A possible explanation for the observed results is that a temperature-dependent current-flow mechanism is coupled with the emptying of filled traps in the oxide or the capture of holes at the cathode. In addition, field-induced ion migration is possible.
The importance of lattice mismatch in the growth of GaxIn1−xP epitaxial crystals
Authors: Stringfellow G.B.
Published: February 2004

The importance of lattice-parameter mismatch between the GaAs substrate and the GaxIn1−xP epitaxial layer on crystal growth and properties has been investigated. Three major effects were observed: (i) The crystal morphology and substrate/epitaxial-layer interface were found to be nearly perfect for a0 ≈ a0 GaAs and very poor including melt inclusions at the interface for other epitaxial-layer compositions. (ii) The dislocation density was found to depend on a0 - a0 GaAs varying from 105 to > 108 cm−2. (iii) The excess energy due to lattice-parameter mismatch was found to perturb the solid composition from the chemical-equilibrium composition toward the composition which minimizes mismatch; i.e., epitaxial layers with x=0.51±0.01 are grown from Ga–In–P liquids with chemical-equilibrium solidus compositions ranging from 0.46 to 0.62. The result is that under the growth conditions used, highly perfect epitaxial layers could be grown only near x=0.51 with band gaps near 1.9 eV. Other compositions with EG>1.9 eV were highly imperfect with poor morphology, melt inclusions, and large numbers of dislocations.
Thermionic injection and space-charge-limited current in reach-through p+np+ structures
Authors: Chu J.L. , Persky G. , Sze S.M.
Published: February 2004

The current transport mechanisms of reach-through p+np+ and its related structures have been studied. It has been established that when the applied voltage is slightly greater than the reach-through voltage, at which the n layer is completely depleted, the current increases exponentially with voltage by thermionic injection or diffusion over the potential barrier. The current-voltage relationship is given by J ≅ A*T2 exp[−q(VFB − V)2/4kTVFB], where A* is the effective Richardson constant, T the temperature, V the applied voltage, and VFB the flat-band voltage defined as qNDL2/2εs, where ND and L are the ionized impurity density and the length of the n layer, respectively. When the injected carrier density rises to a value comparable to the impurity density, the space-charge-limited (SCL) effect causes the current to vary less rapidly with the applied voltage. The SCL effect is derived based on an accurate expression of the velocity-field relation, i.e., vs/(1 + Es/E), where vs is the scattering-limited velocity and Es is the critical field given by the ratio of vs to the low-field mobility. In the high-current limit, we obtain the linear current-voltage expression J ≃ qNDvs(V/VFB). Experimental structures are made from epitaxial n on p+ silicon substrate with an epitaxial layer thickness of 8.5 μm and doping concentration of 5 × 1014 cm−3. The second p+ layer of about 1 μm is formed by diffusion. Good agreement has been obtained between the experimental results and theoretical predictions.
Role of defects in determining the electrical properties of CdS thin films. I. Grain boundaries and surfaces
Authors: Kazmerski L.L. , Berry W.B. , Allen C.W.
Published: February 2004

The relationship between the electronic properties of mobility and resistivity, and electron scattering from film defects in slowly deposited cadmium sulphide polycrystalline thin films is investigated. The correlation of these properties is accomplished in a direction parallel to the substrate (``in-plane'') where the defects of interest are grain boundaries and surfaces. The Petritz (grain boundary) theory is incorporated with surface-scattering theory to formulate a simple model which predicts the effect of these defects on the electron mobility. Typical values for the grain-boundary potential and surface-scattering length are 0.07 eV and 1100 Å at a substrate temperature of 180°C for these glass-deposited films. The mobility is found to depend strongly on grain size, which was a function of substrate temperature. Hall data are presented as a function of evaporation rate, substrate temperature, film thickness, and film temperature. Finally, the grain-boundary potential is found to depend on the fabrication parameters, especially the deposition rate.
Dynamics of bubble domains
Authors: Cape J.A.
Published: February 2004

A simple unifying phenomenological model is developed which makes it possible to relate various motions of either bubble or stripe domains to the basic ``wall mobility'' and ``wall coercivity'' and permits the interpretation of several possible experiments in terms of these same basic quantities. A recent micromagnetics formulation of bubble-domain dynamics, when modified, yields similar predictions and provides a definition of the bubble-domain mobility in terms of microscopic quantities (A, K, Ms) and the Gilbert damping parameter. It also includes domain-wall inertial effects which are absent in the simple model. The combined theory suggests several experiments for the determination of the wall-mobility mass and coercivity, and possible independent measurements of the Gilbert parameter. Some experimental results are presented for domains in oscillatory and pulsed field gradients. The results indicate that the new experiments, as interpreted by the present theory, are promising procedures for studying bubble-domain materials.
Thermoelastic wave propagation from cylindrical and spherical cavities in the two-temperature theory
Authors: Warren William E.
Published: February 2004

A linear two-temperature theory of thermoeleasticity is used to investigate cylindrical and spherical wave propagation emanating from a cavity. Transform methods of solution to specific boundary-value problems are employed and interest is directed to wave speeds and traveling discontinuities. A comparison with classical one-temperature coupled thermoelastic effects is presented.
Determination of the defect nature of MoO3 films using dielectric-relaxation currents
Authors: Nadkarni G. S. , Simmons J. G.
Published: February 2004

A new technique, based on stimulated dielectric-relaxation currents (DRC), has been successfully used to analyse the defect properties of Al–MoO3–Al systems. The particular aspect of the DRC technique used here consists of cooling the system to low temperatures with a voltage applied to the electrodes and then raising the sample temperature at a uniform rate with the electrodes short-circuited. Pronounced structure is observed in the current-temperature characteristics, which may be related directly to the donor (or trap) density and the donor (or trap) distribution. The measurements obtained from the Al–MoO3–Al samples have confirmed the existence of Schottky barriers at the interfaces and revealed the existence of a donor band in the MoO3, which is centered about an energy 0.27 eV below the bottom of the conduction band. The half-width of the donor band is about 0.07 eV, and its density is approximately 1.5×1018 cm−3. These results are in excellent agreement with those obtained from previous ac and dc measurements. It has also been confirmed that an electrode-limited to bulk-limited transition occurs at about 0.6 V. The DRC technique is compared to the thermally stimulated current (TSC) technique, and it is concluded that the DRC method is the superior of the two, at least as far as thin films are concerned. Finally, the effect of Schottky barriers on conduction processes in thin films in general is discussed and it is shown that if they are present but overlooked, the interpretation of the data is invalid.
Electromechanical coupling near the ferroelectric phase transition of TGS
Authors: Zucker J.
Published: February 2004

Interdigital transducers deposited on glass were used to couple acoustic waves in the 10–50-MHz frequency range into a b-cut (010) TGS plate from room temperature to slightly above the ferroelectric phase transition temperature, Tc = 49.1°C. The coupling peaked near Tc. Two major modes were observed. Evidence is given identifying the higher frequency mode with a longitudinal bulk wave and the lower frequency mode with a bulk shear wave. The velocities of the upper and lower frequency modes for temperatures near Tc were found from their resonant frequencies to be (4.18±0.06)×105 and (2.56±0.06)×105 cm/sec, respectively. Data on the temperature variation of the velocity of the low frequency mode are given. Estimates of the effective piezoelectric coupling constants for the two modes are deduced from the data.
Internal friction in germanium at low temperatures
Authors: Haworth W. L. , Mattas R. , Birnbaum H. K.
Published: February 2004

The internal friction of germanium crystals having various dislocation densities in the range 103−107 cm−2 was measured in the low kHz frequency range from 80 to 473 °K and in the MHz frequency range at 300 °K. No evidence for a dislocation contribution to the internal friction was obtained. The internal friction in the kHz range did not depend significantly on the dislocation density and did not exhibit any internal-friction peaks which could be associated with dislocation motion. The internal friction was amplitude independent and could be accounted for by thermoelastic damping. A small increase in attenuation in the MHz frequency range was observed on increasing the dislocation density. This increase could not be accounted for using the theories of dislocation damping but was less consistent with phonon scattering from the static dislocation dipole strain fields. These results were independent of the doping levels of the germanium crystals and of their orientations. They suggest that the activation energy for kink motion along dislocations in germanium is greater than about 17 kcal/mole. A small internal-friction peak was observed at about 210 °K, which was shown to be caused by surface abrasion.
Small-angle x-ray scattering study of complex particle growth in an MgO–Al2 O3–ZrO2–SiO2 glass
Authors: Neilson G. F.
Published: February 2004

The characteristics and kinetics of a phase-separation process involving ZrO2 upon isothermal heat treatment of a glass at 850 °C was studied by means of small-angle x-ray scattering (SAXS), employing electron microscopy (EM) and x-ray powder diffraction as supplementary tools. The various results indicate the initial formation of spherical particles, which at a later time transform to clumps of ZrO2 crystallites. The crystallite clumps then grow by a diffusion-limited mechanism. For analysis of the scattering data, a Walker-Guinier-type particle-diffusion zone model was found adequate. For following the kinetics of growth, emphasis is placed on the variation with time of values of particle size and I(0) parameters derived from the scattering data. Reasonable agreement in the values of the SAXS and EM determined particle-size parameters is obtained.
Self-focusing of microwaves in InSb
Authors: Sodha M. S. , Tewari D. P. , Kamal Jyoti , Tripathi V. K.
Published: February 2004

The nonlinear propagation of a cylindrically symmetric microwave beam (having the radial distribution of intensity Gaussian in nature) in n-InSb has been analyzed. The analysis is phenomenological and is based on the first-order perturbation approximation. The focusing effects are mainly due to the nonparabolicity of energy bands and are seen to be important at commonly employed fields. The absorption suppresses the self-focusing effect.
Theory of parametric upconversion of thermal images
Authors: Falk Joel , Tiffany W. B.
Published: February 2004

This paper extends the theory of parametric upconversion to describe the detection of a thermal image via sum-frequency generation. The theory developed describes the power output, resolution, contrast and spectral bandwidth to be expected from a thermal upconverter. It is shown that current technology is adequate for upconversion of a 100-resolution-element high-contrast thermal scene. Difficulties preventing detection of a near-room-temperature low-resolution scene are discussed.
Simulation of transient space-charge flow in a semiconductor under ionizing irradiation
Authors: Norris C. B.
Published: February 2004

This paper describes some promising initial results in the development of a numerical procedure for the direct simulation of transient space-charge flow in a semiconductor. A computer code is described that employs a simulation technique to predict the internal dynamics and terminal response of a reverse-biased p- n junction subjected to high-level transient ionizing irradiation in a circuit environment. By comparing the predictions of the simulation code and a mathematically based code in regard to a specific problem, it is shown that the simulation technique can yield accurate solutions for analytically intractable problems in a realistic amount of computing time. The adaptability of the simulation technique to certain studies not feasible with the mathematically based codes is pointed out.
Effects of pulsed laser radiation on thin aluminum films
Authors: AboelFotoh M. O. , von Gutfeld R. J.
Published: February 2004

Data are presented on experiments in which micron-sized holes are produced in thin aluminum films on Mylar with an argon laser. Three-dimensional heat-flow calculations indicate that the temperature of the film need only reach the melting temperature with sufficient energy to also supply the latent heat of fusion in order for material displacement to occur. Vaporization does not seem to play a role anywhere in the formation of the laser-produced hole, contrary to other recently reported work. Additional evidence of melting is presented from scanning electron micrographs of regions after laser irradiation.
Anisotropy of the critical current density in the NbTi filaments of round composite superconductors
Authors: Mathur M. P. , Walker M. S. , Deis D. W. , Jones C. K.
Published: February 2004

Magnetization measurements have been performed on several multifilament NbTi wires in transverse and longitudinal magnetic fields. The ratio of circumferential and axial critical current densities for the individual filaments is deduced from the measurements and appears to be an increasing function of the magnitude of the magnetic field and the amount of cold work in the filaments. The results suggest that filaments may be less stable in longitudinal magnetic fields than calculations utilizing standard critical current data would indicate. Transverse swept field magnetization data confirm the theory of coupling in the composite.
Edge-spread function in neutron radiography
Authors: Harms A. A. , Garside B. K. , Chan P. S. W.
Published: February 2004

A model of the imaging process in neutron radiography has been employed to determine the edge-spread function for a given radiographic system. As an aid to the numerical evaluation of this function, approximate analytical representations of the resolution function have been examined. This has facilitated the formulation of an analytical technique for determining the effects of neutron beam divergence. Comparisons are presented between computational results and a series of experiments designed to test the validity of the theoretical model. The agreement obtained is very satisfactory.
On the conditions for recombinative space-charge injection
Authors: Queisser Hans J.
Published: February 2004

High-resistivity GaAs double-injection devices have recently been investigated by Ferro and Gandhi. They found a sublinear ``current saturation'' in oxygen-doped n-type material but not in chromium-doped p-type GaAs, causing them to refute an interpretation by the relaxation-case theory in favor of field-enhanced trapping. We demonstrate that simple relaxation-case arguments in fact correctly predict the different behavior. Sublinear current-voltage characteristics as resulting from recombinative space-charge injection are more probable in n-type than in p-type materials by a factor b2, where b is the mobility ratio.
Admittance probe measurements in the double inverse pinch device
Authors: Baum P. J. , Pollack J.
Published: February 2004

A floating voltage swept double probe is described and the components of the plasma sheath admittance (Y = 1/R + jωC) are measured as a function of time in argon and hydrogen. The measurements are carried out in the double inverse pinch device (DIPD Mark I), a pulsed device, which generates a quadrupole magnetic field. The probe is swept at 500 kHz with a sinusoidal voltage. Sheath capacitance and resistance are measured at one point in space and at a variety of times following preionization. The plasma sheath parameters are discussed in terms of equivalent circuits which are found to simulate the plasma sheath response. The sheath capacitance is larger than predicted by present theories. Estimates of plasma temperature and density are made from the sheath measurements and are found to be low owing to the theoretical uncertainty in capacitance. With improvement in sheath theory, the technique should give accurate temperature and density measurements in transient plasmas.
Photoelectric emission from copper phthalocyanine films
Authors: Pong W. , Smith Jerel A.
Published: February 2004

Photoemission measurements on copper phthalocyanine films were made for photon energies of 7–23 eV. The spectral quantum yield was determined. The energy distribution of the photoemitted electrons for photon energies above 16 eV shows structure characteristic of the density of states. In addition, the attenuation length of electrons photoinjected into copper phthalocyanine was measured. For electrons of approximately 1.5 eV above the vacuum level, the electron-electron mean free path is estimated to be 11 Å.
Acoustical determination of stress relaxation functions for polymers
Authors: Nunziato Jace W. , Sutherland Herbert J.
Published: February 2004

An analysis of acoustic waves in viscoelastic materials reveals that the stress relaxation function for such materials can be evaluated from acoustic dispersion data. In this paper we illustrate this method by evaluating the longitudinal stress relaxation function for the solid polymer, polymethyl methacrylate (PMMA) using previously reported acoustic data. From this result, we deduce the relaxation function appropriate for describing the shock wave response of PMMA by specifying the time-scale characteristic of plate impact experiments. This relaxation function compares well with the function determined from the experimental observations of steady shock waves in PMMA.
Specific energy loss of 4He ions in silicon (amorphous, polycrystalline, and single crystal)
Authors: Ziegler J. F. , Brodsky M. H.
Published: February 2004

The specific energy loss of 4He ions in silicon has been determined in the energy range 420–2750 keV. Several different methods of determining the specific energy loss were used to check the results. Studies were made of the variation of specific energy loss with silicon density and showed that lower-density amorphous silicon has relatively higher specific energy losses. Studies were also made of the specific energy loss of 4He ions in radiation-damaged silicon, polycrystalline silicon, and single-crystal silicon. The values were then used in a thick-target calculation to generate spectra of 4He backscattering from silicon targets. These calculations were compared to experimental spectra over a range of energies and backscattering angles. All calculations were within 2% of the experimental spectra. The ``random'' spectrum from a spinning crystal target was compared to thick-target calculations and shown to be useful as a normalizing spectrum with an accuracy of ±5%.
Optical and electrical properties of proton-bombarded p-type GaAs
Authors: Dyment J. C. , North J. C. , D'Asaro L. A.
Published: February 2004

The effect of 300-keV proton bombardment and subsequent annealing on the optical absorption and electrical resistivity of bulk p-type (p=2×1018 and 1.4×1019 cm−3) GaAs has been studied. Proton doses were in the range 1013−1017 cm−2. It is found that bombardment-induced optical absorption increases monotonically, but sublinearly, with proton dose. The shape of the optical transmission spectrum indicates that bombardment creates a distribution of energy levels extending into the forbidden gap. Activation energies for annealing of the optical absorption have been determined from isothermal annealing data and range from ∼1.5 to ∼3.4 eV, which indicates that at least two kinds of defects are involved. Current-voltage measurements show that the average electrical resistivity of the bombarded layers goes through a maximum at ∼2.5×105 Ω cm at a proton dose of ∼3×1015 cm−2. It is shown that annealing can eliminate the bombardment-induced optical absorption while still retaining a high electrical resistivity. The optimum annealing time and temperature is a function of the proton dose. From these results a set of useful conditions for the proton-bombardment fabrication of stripe-geometry GaAs lasers is determined. Many qualitative similarities exist between the results presented here and those obtained in GaP, which are presented in the following paper.
Theoretical and experimental study of GaAs IMPATT oscillator efficiency
Authors: Salmer G. , Pribetich J. , Farrayre A. , Kramer B.
Published: February 2004

This theoretical and experimental study was motivated by a specific need for a solid-state microwave generator with an output efficiency exceeding 20% and focused on the properties of GaAs avalanche transit-time devices. First, the dependence of the ionization rates and drift carrier velocities as a function of electric field and temperature is established. Then several methods of calculation, exact enough to take into account all the important efficiency-limiting effects in the device, are discussed and used to derive theoretical figures for the efficiency of a GaAs IMPATT oscillator, special attention being given to the influence of the doping profile. Finally, the experimental study is described, including device realization and experimentally measured efficiencies, and a comparison between these and the calculated values is done. It is shown that the best calculated performances can reach 30% efficiency and that it is possible to obtain experimentally cw oscillation efficiencies exceeding 20% with GaAs IMPATT devices having special types of doping profile.
Quantitative analysis of damping and modulus effects in copper crystals using the ``vibrating-string'' dislocation model
Authors: Paré V. K. , Guberman H. D.
Published: February 2004

Internal friction and modulus measurements were made between 13 and 38 kHz as a function of temperature on several copper crystals into which a low density (∼ 105–106 cm−2) of dislocations had been introduced by deformation in compression. The dislocation contributions to damping and modulus defect were determined by comparison with duplicate measurements made after the dislocations had been immobilized by irradiation. Dislocation densities were evaluated by etch-pit counting, and as a result enough information was obtained to determine absolute values for the loop length and drag coefficient in the vibrating-string (Koehler/Granato-Lücke) model of dislocation damping. The loop length was found to have appreciable temperature dependence and the drag coefficient was found to be higher by a factor of ∼ 15–∼65 than values obtained for copper by MHz damping and dislocation velocity measurements. Similar results were obtained in several samples and it is noted that the measured damping and modulus values are not greatly different from those obtained by other experiments. It thus appears that for the kHz frequency range in pure copper crystals basic elements of the string model require revision.