bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved polycrystalline ceramic lasers
Authors: Greskovich C. , Chernoch J. P.
Published: February 2004

Improved polycrystalline ceramic laser rods, composed of cubic solid solutions of 89–96.5 mole% Y2O3, 10–2.5% ThO2, and 1% Nd2O3, were synthesized by a conventional sintering process. This material, called Nd-doped Yttralox (NDY) ceramic, was produced with laser threshold energies lower than that of the best commercially available Nd:glass laser rod and with a lasing efficiency ∼94% that of laser glass at 40 J of input energy under pulsed mode conditions. In a similar operating mode a NDY rod, containing 5 mole% ThO2 and having dimensions 7.6×0.46 cm, delivered 0.41 J of optical energy when using an input energy of 162 J, a pump pulse of 150 μsec, and output mirror reflectivity of 70%. The lasing efficiencies depended strongly on the method of powder preparation and processing, composition, and the cooling rate from the sintering temperature. The dependence of the fluorescent linewidth on the NDY composition provides a means of appreciably varying the material gain coefficient. Active attenuation coefficients for AR - coated NDY laser rods were about 2% per cm as compared to 0.76% per cm for an OI ED-2 laser glass rod measured in the same optical cavity. The absorption component of the optical attenuation was measured to be 0.38% per cm at λ = 1.06 μ, indicating that the scattering component is the major contribution to the attenuation coefficient. Considerable evidence is presented which shows that submicroscopic scattering centers exist in the solid - solution matrix and are related to composition fluctuations arising from (i) chemical segregation in the starting powder which is not entirely eliminated during the high - temperature sintering process and (ii) the formation of extended defects or ordered zones in the solid - solution phase during specimen cooling from the sintering temperature.
Radiation emission during the on state in a noncrystalline chalcogenide threshold switch
Authors: Vezzoli G. C. , Walsh P. J. , Kisatsky P. J. , Doremus L. W.
Published: February 2004

Two types of radiation emission have been detected during the on state of threshold switching events in noncrystalline chalcogenide thin films having a transparent SnO2 (NESA) bottom electrode and a heat conducting top electrode. The common form of the radiation is an emission at about 1.2–1.4 μm which (i) is propagated through a wide solid angle, (ii) is relatively independent of time during the on-state pulse (iii) has an integrated intensity which is approximately a linear function of on-state power and a superlinear function of on-state current, and (iv) requires a minimum on-state current for initiation. The second type of emission is between 0.75 and 3 μm and is detected rather rarely. This latter emission has a characteristic intensity which is a steeply peaked function of on-state time and appears to be possibly highly collimated. The peaked emission has been detected in pulsed modes using single set pulses and has also been detected continuously using low-frequency repetitive threshold set pulses. Both radiation effects appear to be nonthermal in origin.
Experimental verification of a model for the magnetization reversal in RCo5 particles
Authors: Searle Clark W.
Published: February 2004

A model relating the nucleation field for RCo5 particles (R stands for any rare-earth element) to the domain-wall energy has been refined and it now predicts some interesting experimentally observable effects. The experimental verification of the predicted effects puts the model on a strong experimental foundation. The model explains the origin of the superior magnetic properties for SmCo5 particles observed at the Air Force Materials Laboratory.
Preparation of new β-W phases by film-deposition techniques
Authors: Kammerdiner L. , Luo H. L.
Published: February 2004

By sputtering and evaporation simultaneously, β-W phases Nb3In, Nb3Pb, and Nb3Tl have been prepared. Lattice constants were measured for all samples and found to increase with decreasing substrate temperatures. These values were respectively: 5.303±0.002 A, 5.333±0.005 A, and 5.297±0.005 A. The extended range in producing unstable phases by film-deposition techniques as opposed to conventional methods is considered.
Limitations on stress compensation in AlxGa1 −xAs1−yPy–GaAs LPE layers
Authors: Afromowitz Martin A. , Rode D. L.
Published: February 2004

It has been shown previously that the room-temperature lattice mismatch between GaAs and AlxGa1−xAs may be reduced by the incorporation of small amounts of phosphorus in the alloy. By measuring the curvature of thin (2 μ) freely suspended foils of AlxGa1−xAs1−yPy grown by LPE, we have determined the gradient in the lattice parameter in foils which have been substantially stress-compensated. This gradient is caused by depletion of aluminum and phosphorus from the melt during growth. Such depletion limits the extent to which this stress-compensating technique may be applied to the growth of GaAs heterostructure lasers. Present results imply that stress reductions of about a factor of 10 may be obtained for 2-μ quaternary layers, although greater factors are achievable for thinner layers.
The field emitter: Electric field calculation
Authors: Roth T. A.
Published: February 2004

A model for the field-emitting electron gun is proposed in this paper. The cathode is a sphere on cone and the anode and tip holder are represented by a potential on a larger sphere. The potential everywhere is shown to be expandable in terms of Legendre functions of noninteger order. Some properties of these functions are discussed in an Appendix. The model gives equipotentials in the region of the tip with realistic shape and can also explain the variations in the total emission current as a function of tip-anode distance in good agreement with experimental data. Other models have realistic equipotentials near the tip but cannot take tip holders into account and cannot explain the emission data.
Electrical breakdown of a point-plane gap in high vacuum and with variation of pressure in the range 10−7−10−2 Torr of air, nitrogen, helium, sulphur hexafluoride, and argon
Authors: Hackam Reuben , Raju G. R. Govinda
Published: February 2004

The dc breakdown potential of a point-plane electrode configuration is measured in high vacuum (∼10−7 Torr) using the positive and the negative voltage polarity of the point electrode as a function of gap separation. Air, nitrogen, helium, sulphur hexafluoride, and argon are used in turn to alter the electrode coverage by adsorption of various gases in high vacuum. It has been found that helium gives the highest breakdown voltage at a given gap length, in high vacuum. It has also been found that very high sparking potential values are obtained using positive-point-negative-plane electrodes (90 kV at 0.3 mm gap length, helium at 3×10−7 Torr). The effect of ac (50 Hz) glow discharge conditioning on the dielectric strength of the gap is investigated and found to give considerable improvement in the voltage that the gap can withstand before a vacuum breakdown occurs. The effect of introducing various gases in the pressure range 10−7−10−2 Torr on the breakdown potential of point-plane gaps is investigated. Maxima are observed in the breakdown voltage and pressure curves in the range 10−4−10−3 Torr. Helium and nitrogen give the highest breakdown voltage of about 90 kV for a gap length of 0.2 mm at about 10−4 Torr. The observed improvements in the breakdown potential that the gap can withstand with certain gases are attributed to the increase in the work function of the combined metal-gas system.
Microwave radiometric investigation of the electron velocity distribution in nitrogen plasmas
Authors: Sahni Omesh , Jennings W. C. , Noon J. H.
Published: February 2004

A microwave radiometric technique has been used to investigate the electron velocity distribution function f(v) during the afterglow of a pulsed N2 discharge. The technique involves comparing radiation temperature measurements taken around electron cyclotron resonance with theoretical computations based on a chosen form for f(v). Non-Maxwellian forms of f(v) displaying either an excess or depletion of high-energy electrons have been observed in the afterglow for different experimental conditions. The technique does not have the necessary sensitivity to determine f(v) during the active discharge.
Interferometric measurement of electron and vapor densities in a high-current vacuum arc
Authors: Boxman Raymond L.
Published: February 2004

Electron and vapor densities in a 0.4–4.0-kA copper vapor (vacuum) arc were investigated by means of optical interferometry. Nonsimultaneous measurements were made with a visible wavelength (0.63 μm) and an infrared wavelength (10.6 μm) to separate the electron and vapor contributions. The electron contribution to the index of refraction was found to dominate at both wavelengths. An upper limit to the ratio of copper vapor density to electron density of 2.8 could be set as a result of the 0.63-μm measurement. The integral of the electron density over the optical pathlength was measured at various lateral positions of the arc by means of the 10.6-μm interferometer; the Abel transformation was applied to these results to obtain the radial profile of the electron density. A diffuse electron density profile is observed, with the axial densities ranging from 1 × 1014/cm3 at 0.4 kA to 2 × 1015/cm3 at 4 kA. At the transition from the diffuse or quiescent mode to the high-voltage or constricted mode, which occurred at about 3 kA with the electrode geometry used in this study, a sudden decrease in electron density from 1.7 × 1015/cm3 to 0.7 × 1015/cm3 was observed in the center of the discharge. The measured densities were compared with existing theoretical predictions.
Fabrication of channel optical waveguides in glass by cw laser heating
Authors: Pavlopoulos T. G. , Crabtree K.
Published: February 2004

By focusing the 488-nm line of an argon-ion cw laser beam with the aid of a microscopic objective on the surface of a moving piece of highly absorbing glass, low-loss channel optical waveguides at longer wavelengths are produced. At the laser beam focal point, glass is evaporated, producing grooves 2–8 μm wide. Strong confinement of light was observed beneath the grooves. An explanation for the occurrence of waveguiding is given together with experimental data on waveguide width as a function of applied laser power and sample speed. This method allows us to fabricate channel waveguides possessing periodic structure for frequency-selective guiding.
Generalized Maxwell Garnett equations for rough surfaces
Authors: Chan E. C. , Marton J. P.
Published: February 2004

An optical model of a rough surface is made up of a layer of metal particles of sizes much smaller than a wavelength, dispersed in a dielectric medium. The metal particles are approximated by a layer of dipoles of identical dipole moment arranged in square or hexagonal planar array. The two-dimensional dipole-dipole interaction results in surface anisotropy represented by a pair of Maxwell Garnett-type equations. This surface anisotropy due to surface geometry may be a good indication of the degree of roughness of a given surface.
Preparation and properties of a multifilamentary V3Ga composite
Authors: Critchlow P. R. , Gregory E. , Marancik W.
Published: February 2004

The manufacture of a multifilamentary vanadium/gallium-copper composite and its subsequent heat treatment to form V3Ga is described. The growth of the V3Ga is discussed in terms of reaction time, temperature, and gallium concentration of the gallium-copper matrix. Superconducting transition temperatures and critical current densities are presented. Values of Jc, at 4.2 K and 80 kG, in excess of 5×105 A/cm2 were observed.
X-ray continuum from thick elemental targets for 10–50-keV electrons
Authors: Rao-Sahib T. S. , Wittry D. B.
Published: February 2004

The x-ray continuum from thick elemental targets was investigated from 1–10 Å using a crystal spectrometer and electron energies of 10–50 keV in an electron probe microanalyzer. Experimental results corrected for absorption, atomic number, and stray radiation agreed well with theoretical calculations based on Sommerfeld's cross section and Bethe's retardation law. The calculations used an improved version of the empirical formula of Kirkpatrick and Wiedmann for the cross section. Theory and experiment agreed best for J = 11.5Z in Bethe's law, but taking account of known inaccuracies in the Sommerfeld cross section, the Berger-Seltzer values are recommended. Results did not verify the linear atomic number dependence of the Kulenkampff-Kramers equation; for fixed electron energy E0 and photon energy Ev the intensity varied as Zn, where n ranged from 1.18 to 1.38 depending on Z, E0, and Ev. For fixed Z and Ev the intensity varied approximately as (E0 − Ev). Agreement of theory and experiment indicated that the correction procedures commonly used for characteristic lines can be applied to the continuum but the atomic number correction using Duncumb and Reed's procedure differed for the continuum compared to that for characteristic lines. Absorption correction using f(χ) of Andersen and Wittry gave good results for f(χ)≥0.4 but lower values could not be conclusively tested because of errors due to stray radiation which is shown to be caused by electrons backscattered from the specimen. Nevertheless, it was possible to use the Z dependence of the continuum to estimate certain mass absorption coefficients.
Improved detection of lattice defects in x-ray topography
Authors: Mardix S.
Published: February 2004

Detection of lattice defects is limited by the statistical nature of the x-ray photon flux. Improvement over techniques employing normal x-ray exposure and examination of films with transmitted light can be obtained by very high exposure followed by reflected-light examination. A substantial increase in the number of detected individual lattice defects was achieved by this method and closely spaced lines that appear as a single image with regular exposure could be resolved. Interference fringe techniques are introduced to achieve quantitative reflected-light microdensitometry.
Motion of two screw dislocations in a lattice
Authors: Flytzanis N. , Celli V. , Nobile A.
Published: February 2004

In a simple model of a cubic lattice with piecewise linear and nearest-neighbor interactions a solution is obtained for the motion of two parallel screw dislocations of the same sign, under the action of a constant applied stress. The only damping mechanism considered is the emission of sound waves. The important parameters are the external strain s and the dislocation separation α. They are determined by energy balance and the boundary conditions imposed by the force law. The main result is the existence of multiple branches in the strain versus velocity curve, the lowest of which corresponds to an external strain less than that of a single dislocation. However, in the snapping bond model, two dislocations, as well as a single dislocation, cannot move at supersonic velocities without causing a breakdown of the crystal.
Time evolution of developed contours in poly-(methyl methacrylate) electron resist
Authors: Greeneich James S.
Published: February 2004

The time evolution of exposure contours in poly-(methyl methacrylate) (PMMA) electron resist is calculated for several time-dependent developers comprised of various proportions of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA). Contours are calculated for a line of charge incident on 4000 Å of resist coated on a low-atomic-number substrate. Parameters such as beam energy, incident charge per unit length, original molecular weight, and developer temperature are considered. The use of a time-dependent developer greatly influences the shape of the developed contours and the development time. The more active the developer (expressed in terms of the PMMA solubility rate), the greater the influence of developer time on the contours. Use of higher beam energies results in developed contours confined closer to the beam axis and less sensitive to development time. The incident charge per unit length is very important. For the MIBK developer and at low doses the characteristic undercut phenomenon is not obtained except for long development times, resulting in an increase in linewidth and a reduction in original resist thickness. The principal result of using lower original molecular weight and/or higher developer temperature is to reduce the development time for a given contour.
Electrical properties of CuGaS2 single crystals
Authors: Yu Phil Won , Downing D. L. , Park Y. S.
Published: February 2004

The resistivity and Hall coefficient for undoped p-type CuGaS2 were measured at temperatures between 77 and 400°K. The crystals were grown from both the stoichiometric melt and the vapor phase. The crystals were heat treated under an excess sulfur atmosphere in the temperature range 400–660°C. An analysis of the hole concentration data showed that the heat treatment changed the acceptor concentration from 6×1014 to 2×1018 cm−3. The acceptor ionization energy increased from 0.073 to 0.39 eV with the decrease of the acceptor concentration. The effective mass of the hole in CuGaS2 from the Hall analysis was ∼0.69me. The formation energy of the Cu vacancy, which is presumably an intrinsic acceptor, was ∼0.68 eV in CuGaS2. The acceptor energy of the Cu vacancy in the lower concentration limit was ∼0.12 eV. The mobility shows the dominance of lattice scattering through a deformation potential at higher temperatures than 110°K, while the observed mobility data at lower temperatures can be reasonably explained by taking into account the effect of space-charge scattering.
High field critical current densities for a thick Nb12Al3Ge superconductor made by high-rate sputtering
Authors: Dahlgren S. D. , Suenaga M. , Luhman T. S.
Published: February 2004

High current densities were measured for a 66-μm-thick sputter-deposited Nb12Al3Ge superconductor in magnetic fields from 100 to 210 kOe. Critical currents at 4.2°K were 2.5×105 A/cm2 at 100 kOe, 1.3×105 A/cm2 at 150 kOe, 2.6×104 A/cm2 at 200 kOe, and 1.5×104 A/cm2 at 210 kOe. The current densities were comparable to current densities reported for Nb3Sn and V3Ga. The deposit was made at a rate of 1 μm/min and heat treated 20 days at 750°C prior to the current density measurements.
Indexing of diffracting planes using the Kikuchi pattern
Authors: Wu W. , Chen L.-J. , Washburn J. , Thomas G.
Published: February 2004

Two types of ambiguity concerning indexing of electron diffraction patterns have been cleared up by making use of the Kikuchi lines. A convenient unambiguous method of uniquely indexing patterns is suggested assuming the beam is always along the viewing direction no matter how the picture is printed. It is shown that there are two completely equivalent ways of indexing the Kikuchi pattern, e.g., [111] or [1̄1̄1̄]. The method is also useful in interpreting dark-field pictures when top-bottom contrast is concerned.
Intergranular forces of dynamic coalescence in very thin metallic films
Authors: Desrousseaux G. , Carlan A.
Published: February 2004

Because of the polarization by the electromagnetic field, the grains of very thin metallic films spread over an amorphous substratum are under bipolar interaction forces. One of them, F0, is created by the field due to the electromagnetic oscillations at zero temperature. Another one, FT, is due to the field maintaining the radiation of the thermodynamic equilibrium. A third one, FE, is superimposed onto the first ones, F0 and FT, at the time of illumination of the films by the evaporating cell or by an auxiliary source. F0, FT, and FE are expressed with the same function φ(ω) depending upon not only the permittivity εg of the grains and the permittivity εs of the substratum but also on the shape of the grains, their distances, and their dimensions. The last two modify εg, which is very different from ε∞ in the bulk metal. φ(ω) shows a first maximum which is dependent upon geometrical data, located in the infrared or the visible. Its amplitude is limited only by the imaginary part of F0. However, the main part of F0 is concentrated in the far ultraviolet. Nevertheless, an intense illumination in the first-maximum spectral interval can superimpose a nonnegligible force FE onto F0 and FT. The relative magnitude of these forces can be discussed in the case of granular films of silver on carbon. The fact is that structural modification can be obtained by illumination of these films when they are maintained under ultravacuum until 21 h after their formation.
uv-stimulated photocurrent spectroscopy and trapping kinetics of a 2.1-eV trap in anodic Ta2O5 films
Authors: Thomas J. H.
Published: February 2004

A new experimental technique, uv-stimulated photocurrent spectroscopy, has been used to study a trapping effect observed in the anodic oxide of sputtered β-Ta films. Experimental results indicate the presence of a discrete trap level peaked at 2.1 eV below the oxide conduction band, in addition to the 1.5-eV trap band as previously reported by Hickmott and later by Thomas. A kinetic model involving a single trap level in the oxide was used to analyze transient data. The results of this analysis indicate that the 2.1-eV trap is a positive Coulombic center having an electron capture cross section of 3.2×10−14 cm2, a photon capture cross section (at 2.1 eV) of 10−17 cm2, a density of states of 3×1018/cm3, and a ratio of filled to unfilled states of 0.06 during uv stimulation.
Nonlinear effects in heavy-ion sputtering
Authors: Andersen H. H. , Bay H. L.
Published: February 2004

To test the suggestion that an enhancement of sputtering occurs in very dense collision cascades, the sputtering yield per atom was compared for atomic and molecular ions. In all cases tested, the yield per atom was higher for the molecular ions. This effect is the more pronounced the heavier the projectile and the target. In the molecular cases the overlapping cascades have higher energy densities than those initiated by the atomic ions; our results, therefore, support the suggestion of a sputtering enhancement in dense cascades.
Radar cross section of thin wires at all angles of incidence
Authors: Tavis M. T.
Published: February 2004

The approximate theory of radar reflection from thin wires by Van Vleck, Bloch, and Hamermesh gives very good average radar cross-section (RCS) results and good angular RCS results (except end-on) when compared with the results of others. The nature of this end-on discrepancy is discussed, and it is found that more accurate RCS results are predicted for all angles of incidence (except in the RCS nulls away from end-on incidence) and for all wire-length-to-wavelength ratios between 0.45 and 50. This is true only if approximations made to simplify the calculation of the average RCS over all angles of incidence are not made. RCS results are verified by comparing them with data generated by a source distribution technique (SDT) computer program.
Polymorphic phase transformation rates in shock-loaded potassium chloride
Authors: Hayes D. B.
Published: February 2004

Single crystals of potassium chloride (KCl) were impacted on quartz stress gauges at velocities ranging from 0.0363 to 0.0755 cm/μsec, producing plane shocks with stress amplitudes between 17 and 31 kbar. Stresses greater than 21 kbar are sufficient to induce a polymorphic phase transformation in KCl. For impact stresses above the phase transition point, the theory of continuum mechanics is used to relate measured stress history at the impact interface to transformation rate between the phases. Experimental results show that, when shocked above the measured dynamic transition pressure of 20.8±0.5 kbar, KCl rapidly transforms to a metastable nonequilibrium mixture of phases. Phase transformation to these initial metastable states proceeds at a rate greater than 500 μsec−1 for shock propagation along the 〈100〉 and 〈111〉 directions, based on the magnitude of initial transformation and the minimum response time of the measuring system. The degree of partial transformation is observed to depend only on impact velocity and is independent of crystallographic orientation of the KCl. The observed metastable states are consistent with the postulate that the heat of formation of the nonequilibrium high-pressure phase is characterized by a specific entropy 3.9 × 10−6 cm2 μsec−2°K−1 higher than the equilibrium high-pressure phase. Subsequent phase transformation proceeds at a rate that depends on crystallographic orientation of the KCl. When the shock propagates along a 〈111〉 direction, it is observed that transformation proceeds from the metastable state to completion at a rate of 25±5 μsec−1, with final states in agreement with thermodynamic equilibrium calculations. When the shock propagates along a 〈100〉 direction, transformation proceeds at a rate of less than 5 μsec−1. For the 〈100〉 orientation, data are inadequate to allow determination of whether transformation was completed during the experiment, because of uncertainty in late-time quartz gauge response.
Contact-free conductivity in an inhomogeneous medium: Vitreous semiconductors
Authors: Strom U. , Taylor P. C.
Published: February 2004

Contactless low-frequency (2- to 20-Hz) electrical conductivity measurements employing a torsion pendulum immersed in a rotating magnetic field can distinguish between homogeneous and inhomogeneous samples. A quadratic dependence of the conductivity on a cylindrical sample radius is derived for a medium with noninteracting inhomogeneities. Measurements in glassy Tl2SeAs2Te3 indicate the inhomogeneous nature of this vitreous semiconductor. Similar measurements on single-crystal dislocation-free silicon cylinders confirm the homogeneous nature of these samples and provide a calibration of the apparatus.
Heat treatment effects in Cu2S–CdS heterojunction photovoltaic cells
Authors: Fahrenbruch Alan L. , Bube Richard H.
Published: February 2004

The photovoltaic properties of single-crystal Cu2S–CdS heterojunctions have been investigated as a function of heat treatment by detailed measurements of the dependence of short-circuit current on photon energy, temperature, and the state of optical degradation or enhancement. A coherent picture is formulated for the relationship between enhancement and optical degradation and for their effect on the transport of short-circuit photoexcited current and dark forward-bias current in the cell. Optical degradation in the Cu2S–CdS cell is shown to be closely identical to optical degradation of lifetime in a homogeneous CdS: Cd: Cu crystal, which indicates that the CdS: Cu layer near the junction interface controls carrier transport in the cell. It is proposed that both the photoexcited short-circuit current and the dark forward-bias current are controlled by a tunneling-recombination process through interface states. Changes in the junction profile resulting from enhancement and/or optical degradation modify the electric field at the barrier to modulate both currents.
Superatmospheric double-discharge CO2 laser
Authors: Blanchard M. , Gilbert J. , Rheault F. , Lachambre J. L. , Fortin R. , Tremblay R.
Published: February 2004

Experimental results on the operation of a Laflamme double-discharge laser structure up to pressures of several atmospheres are presented. With an electrical energy input of 30 J/liter atm, a multimode pulse output of 1 J is obtained at 6 atm from a 1/3-liter active volume, containing 7.5% CO2, 7.5% N2, and 85% He. It is found that a high level of energy deposition into the CO2 gas can be achieved, provided that the plasma E/p is optimized in both the main discharge and the preionizing discharge. On the basis of the understanding gained during this investigation, a ruggedized Laflamme structure capable of withstanding prolonged arcing conditions has been developed.
CO2 gas laser excitation and gain
Authors: Mills C. B.
Published: February 2004

Calculations of laser-beam amplification have been made by integration of energy-conservation equations using excitation rates and interlevel vibrational-energy-exchange rates. The vibrational-energy-level populations were used in laser gain equations. Excitation rates were determined by integration of the Boltzmann equation to obtain the electron energy distribution. The excitation cross sections were taken from Phelp's work, and the potential gradient per molecule (E / N) was determined by solution of the current continuity equation using transport constants derived by methods described by Phelps. The laser gain equations were then used to predict the optimum laser energy storage, which was about 10% of the electrical energy supplied. This is not a strong function of any single parameter except time and E / N.
Superconducting composite of copper and niobium—a metallurgical approach
Authors: Tsuei C. C.
Published: February 2004

Superconducting composites of niobium filaments in copper have been prepared by casting and subsequent cold working. In the cast copper-rich Nb alloys, there is a somewhat uniform distribution of Nb particles (∼ 10μm average diameter) resulting from liquid-state precipitation. After cold rolling or drawing, these Nb primary dendrites are elongated and aligned, and they eventually form quasicontinuous superconducting paths. Alloys containing more that 5 at.% Nb and with a cross-sectional area reduction ratio of ∼400 to :1 show a sharp resistive superconducting transition around 9°K. As an example, an alloy of composition Cu90Nb10 gives a critical current density Jc at 4.2°K and zero magnetic field of the order of 2×104 A/cm2 and a critical field of ∼10 kG. It is found that the addition of a small amount (a few at%) of Al to the basic Cu–Nb alloys greatly improves the continuity of the Nb filaments. This in turn results in more uniform superconducting properties in various sections of a long wire. No degradation of the superconducting properties were observed after a 0.25-mm wire sample was bent and straightened more than 50 times around a 1-in. mandrel. In fact, the critical current density increases with the amount of bending. For example, Jc at 4.2°K and zero magnetic field of a 0.25-mm wire of Cu90Nb10 increases from 1.5×104 to 105 A/cm2 after 20 bends.
Hydrostatics and steady dynamics of spatially varying electromechanical flow structures
Authors: Jones Thomas B.
Published: February 2004

The hydrostatic and steady laminar hydrodynamic equilibria of spatially varying electromechanical flow structures are investigated. Under certain conditions the relationship between the dielectric height of rise and the applied voltage is found to be double valued. It is found that one of the two equilibrium values is always unstable. This gives rise to the experimentally observed spontaneous rise of the fluid to the top of the structure, once a certain critical voltage is reached. Starting above this critical voltage with the structure completely filled and decreasing the applied voltage toward the critical value results in pinch-in failure at an intermediate point along the structure and trapping of dielectric fluid at the top. The simple mathematical model developed predicts all these phenomena, without recourse to tedious point-by-point surface force equilibrium determination. Experiments are reported which verify the results for the hydrostatic case.
High-power 2- to 6-μm window material figures of merit with edge cooling and surface absorption included
Authors: Sparks M. , Chow H. C.
Published: February 2004

Values of the total power P that a window can transmit under specified conditions are calculated for use as figures of merit for window materials. New features of the figures of merit are consideration of edge as well as face cooling, treatment of surface as well as bulk absorption, use of P rather than intensity as the figure of merit, effects of improving materials, and calculation for 3.8 and 5.25 μm. New results include the following: For continuous operation, large-diameter windows should be face cooled, but small-diameter window may be edge cooled, and P often decreases as the diameter D increases. For pulsed operation, P increases as D increases, as was intuitively expected. Values of the diameter DEF, above which face cooling should be used, are surprisingly large, ranging between 7 and 100 cm, typically. For pulsed operation and for D > DEF in cw operation, P is independent of thermal conductivity K while for D < DEF in cw operation, P∝K. The alkaline-earth fluorides have the greatest figures of merit for large-diameter windows with P=76 MW, ΔT = 50 K, and l=0.5 cm for a 1-sec pulse on a 10-cm-diam window of BaF2 at 3.8 μm with a bulk absorption coefficient of 10−4 cm−1. For small-diameter windows (1-cm diameter), Si, BaF2, and GaAs have the greatest values of P=1.8, 0.94, and 0.76 MW, respectively, for cw or 1-sec pulse duration.
Diffusion coefficient and electromigration velocity of copper in thin silver films
Authors: DiGiacomo G. , Peressini P. , Rutledge R.
Published: February 2004

The objective of this work was to determine the Cu diffusion coefficient in silver thin films as a function of temperature, and Cu electromigration velocity as a function of electric current density and to test whether linearity between electromigration and current density was preserved at high current stress. An Ag stripe was doped with Cu in a limited region, and the movement of Cu out of this region under temperature and current stressing was measured by electron probe. The experiment was conducted at 200, 250, and 300°C and at current densities of 106, 2×106, and 3×106 A/cm2. From the copper concentration profile, the diffusion coefficient D and the electromigration velocity V were calculated. Results show that the diffusion of Cu in Ag films obtained by extrapolation to use conditions (D=10−15 cm2/sec at 55°C) is about 2 orders of magnitude greater than bulk, and that electromigration under ∼106−A/cm2 stress is negligible when compared to thermal diffusion of Cu, even at ambient temperature. At high current density (3×106 A/cm2), the electromigration velocity becomes much greater than the value predicted on the basis of linearity between V and J. This indicates a departure from the Nernst-Einstein relationship of ion shift in a field.
Multiplex imaging with multiple-pinhole cameras
Authors: Brown Chris
Published: February 2004

When making photographs in x rays or γ rays with a multiple-pinhole camera, the individual images of an extended object such as the sun may be allowed to overlap; then the situation is in many ways analogous to that in a multiplexing device such as a Fourier spectroscope. Some advantages and problems arising with such use of the camera are discussed, and expressions are derived to describe the relative efficacy of three exposure/postprocessing schemes using multiple-pinhole cameras.
Laser-generated plasmas as a source of x rays for medical applications
Authors: Mallozzi P. J. , Epstein H. M. , Jung R. G. , Applebaum D. C. , Fairand B. P. , Gallagher W. J. , Uecker R. L. , Muckerheide M. C.
Published: February 2004

High-resolution medical radiographs have been produced with a laser-generated plasma x-ray source. The nanosecond pulse width is capable of arresting biological motion. In addition, the soft x rays from this source have been transmitted through a new type of x-ray beam handling device, the x-ray pipe, which is an x-ray analogue of the conventional light pipe. This may allow new medical applications such as channeling soft x rays to internal locations of the body without damaging intervening tissue.
Statistical studies of 1/f noise from carbon resistors
Authors: Moore W. J.
Published: February 2004

The statistical behavior of the amplitude probability density for 1/f noise from carbon resistors has been investigated both experimentally and theoretically. It is found that some carbon resistors exhibit a 1/f noise which is in agreement with the behavior expected for a stationary normally distributed process, while other carbon resistors exhibit a type of pulse noise in addition to 1/f noise which serves to modify the measured statistical properties of the noise. It is concluded that 1/f noise itself is not significantly different from other noises in its statistical properties.
Observations on magnetically induced anodic-arc-region behavior
Authors: Murphree David L. , Carter Richard P.
Published: February 2004

The experimentally observed magnetically induced dynamics of the anodic arc region of an argon arc discharge are presented for Lorentz and retrograde motion. The same externally applied conditions were employed for both modes of motion. The anodic arc region proceeds in the Lorentz direction through the formation of anode arc spots on the Lorentz side of the arc discharge. During retrograde motion, a new anodic arc region is created on the retrograde side of the original anodic arc region by a discharge initiating between the anodic and cathodic arc regions. The separation of the positive column and the original anodic arc region during retrograde motion results in an anodic arc spot where the original anodic arc region existed.
Thermal conductivity of ultrathin metal films in multilayer structures
Authors: Chopra K. L. , Nath Prem
Published: February 2004

Thermal and electrical conductivities of 28 layers of 100-Å-thick and 6 layers of 500-Å-thick polycrystalline copper films, each individually sandwiched between 25-Å-thick amorphous Ge or SiO films, have been measured. The results show that, provided no interfacial alloying occurs (as is the case with SiO films), the effective values of the conductivities of the multilayer structure are very close to those of the individual (100 or 500 Å) copper films. This equivalence of the transport behavior enables the measurements of the thermal conductivity of ultrathin metal films. Further, it indicates no significant enhancement of diffuse scattering of electrons and phonons at the surfaces of the copper films due to the presence of multiple interfaces.
Light scattering from boron trioxide through the glass transition
Authors: Bucaro J. A. , Dardy H. D.
Published: February 2004

Light scattering from boron trioxide has been studied as a function of temperature in the melt near the glass transformation temperature and in the solid. Both polarized and depolarized spectra were obtained. At all temperatures (20–516°C) the scattering consists of a polarized contribution associated with density fluctuations and a depolarized component presumably connected with the anisotropic nature of the B2O3 glass network. Quantitative results are presented confirming that the polarized scattering from density fluctuations in the solid is determined by the equilibrium compressibility of the melt at the fictive temperature. It is shown that the anisotropic scattering also appears to be ``frozen-in'' at the fictive temperature.
Late-time gain of the CF3 I iodine photodissociation laser
Authors: Palmer R. E. , Gusinow M. A.
Published: February 2004

The gain of the CF3I iodine photodissociation laser is observed to decrease exponentially with time. The decay rate increases dramatically with a small increase in flashlamp energy. Assuming that the rise in the gas temperature increases as the flashlamp energy is increased, this indicates that the process causing the decrease in the gain has an activation energy. It appears that CF3I pyrolysis is the source of the loss in gain, and from the observed decay rate the gas temperature is calculated to be about 1200°K. Measurement of the late-time iodine-iodine recombination rate also yields this temperature. The stimulated-emission cross section measured under the same conditions is (2.6±0.5)×10−18 cm2.
Phase modulation nonlinearity of double-heterostructure p-n junction diode light modulators
Authors: Wilson L. O. , Reinhart F. K.
Published: February 2004

The phase modulation due to the linear electro-optic effect of GaAs–AlxGa1−xAs double-heterostructure (DH) p-n junction diode light modulators can be a strong function of the applied bias voltage. The observed nonlinear voltage dependence of the phase difference Δφ between the phases of the TE and TM modes is in good agreement with the predictions of a mathematical dielectric slab waveguide model with five stepwise constant dielectric layers, if a suitably defined average junction electric field is used. The magnitude of Δφ and its nonlinear voltage dependence measurably depend on the properties of the optical dielectric waveguide and on the p-n junction doping profile. Within the accuracy of our measurements, we have not been able to identify contributions due to higher-order electro-optic effects. Our results emphasize that large modulation effects and good modulation linearity of Δφ modulation can be achieved by appropriately controlled p-n junction doping profiles. Conversely, Δφ measurements as a function of bias provide a novel tool for studying p-n junction doping profiles and for determining the Al concentration of the AlxGa1−xAs layers of DH diodes.
Growth-induced anisotropy in garnets with mixed diamagnetic rare-earth ions: Y3−xLuxFe5O12
Authors: Callen Herbert
Published: February 2004

It is shown that the observations of Gyorgy, Sturge, and Van Uitert, on the anisotropy of Y3−xLuxFe5O12, are in excellent agreement with the mechanism suggested by Akselrad and Callen. The data are consistent with a tetrahedral iron mechanism, although they do not exclude an octahedral iron mechanism. The relative contributions of the two sublattices and the relevant physical considerations are discussed. The mechanism of preferential site ordering is also discussed further, with particular reference to relative site sizes.
Application of the Lifshitz-Slyozov theory to precipitation of phosphorus in silicon-germanium thermoelectric alloys
Authors: Burgess E. L. , Nasby R. D.
Published: February 2004

The applicability of the Lifshitz-Slyozov model for predicting phosphorus precipitation rates in the phosphorus-SiGe system is investigated. Model parameters are determined from short-term anneals of less than 2000 h for SiGe alloys varying in silicon content from 67 to 81 at.% and prepared by zone leveling or hot pressing. Using these parameters in the model, resistivity changes are predicted for phosphorus-doped SiGe thermoelectric elements which had been life tested from 4000 to 40 000 h. It is concluded that the Lifshitz-Slyozov model is applicable to the phosphorus-SiGe system. The results of this study can be used to calculate long-term degradation of thermoelectric performance in SiGe alloys due to phosphorus precipitation.
Dielectric measurements using alternating currents and ionic thermocurrents
Authors: Perlman M. M. , Unger S.
Published: February 2004

The microscopic relaxation parameters, activation energy and lifetime, are measured for the single-and double-dipolar systems KCl : Eu++ and KCl : Eu++, Yb++ using both ac bridge and ionic thermocurrent (ITC) techniques. The two methods are compared and contrasted. A theory is developed to calculate dielectric constant and loss tangent for the single and double systems from the measured ITC, and comparisons are made with bridge measurements. The theory of peak cleaning, used in the ITC technique, is also presented.
Transient electric field and space-charge behavior for unipolar ion conduction
Authors: Zahn Markus , Tsang Cheung Fung , Pao Shing-Chong
Published: February 2004

New analysis is presented using a unipolar ion-mobility conduction model in planar geometry which solves for the transient behavior of the bulk electric field and space-charge distributions as a function of time and space, as well as the resulting time dependence of the terminal quantities of voltage and current. The charge-conservation quasilinear partial differential equation is solved using Lagrange's method with the method of characteristics. The analysis is generalized to handle any physically allowed initial and boundary conditions for any type of applied excitation. Special cases are examined of the turn-on transient with the application of a step voltage or current, contrasting the behavior between space-charge-limited conditions where the emitter electric field is zero to those where the emitter field is nonzero. Much of the analysis yields closed-form expressions.
An asymptotic approximation for reaction rates in ion drift tubes
Authors: Barnhill Maurice V.
Published: February 2004

The dependence on the ratio of the electric field to the neutral particle number density of reaction rate constants measured in drift tubes can be approximated asymptotically near zero field by the logarithm of the relative speed distribution of an ion and a neutral molecule, evaluated at the threshold velocity. This approximation adequately represents the field dependence of the rate constant into the region where experimental measurements of the rate constant can be obtained, allows a quick determination of the threshold velocity from rate constant measurements, and gives a consistency check on proposed ion-molecule relative speed distributions.
Energy dissipation in a thin polymer film by electron beam scattering
Authors: Hawryluk R. J. , Hawryluk Andrew M. , Smith Henry I.
Published: February 2004

Monte Carlo calculations have been performed to determine the spatial distribution of energy dissipated in a 4000-Å-thick film of polymethyl methacrylate (PMMA), due to an incident electron beam. The calculations were performed for 5-, 10-, and 20-keV electrons on a silicon substrate and also for 20-keV electrons on copper and gold substrates. The effect of varying the beam diameter from 250 to 3000 Å was evaluated. A detailed comparison is made between the Monte Carlo results and analytic models used to predict the energy dissipated. The plural scattering model is found to be in good agreement with the Monte Carlo calculations, whereas discrepancies are found with the multiple scattering model. The large-angle backscattering model is found to have several important limitations. Energy dissipation is calculated for the exposure of dots, isolated lines, and arrays of closely spaced lines—geometries that are of significance in electron beam lithography.
A comparison of calculated images generated by six modes of transmission electron microscopy
Authors: Engel A. , Wiggins J. W. , Woodruff D. C.
Published: February 2004

Six modes of transmission electron microscopy (TEM) are compared by a numerical simulation of the image formation. The comparison includes five modes of the conventional electron microscope (CEM) (axial bright field, Unwin's phase plate, central stop dark field, tilted beam dark field, conical illumination dark field) and the annular detector mode of the scanning transmission electron microscope (STEM). It is assumed that the illumination is perfectly coherent and that the interaction between electron beam and specimen may be described as an entirely elastic event. Furthermore, the influence of radiation damage and noise is neglected. The restrictions due to these approximations are discussed and shown to be unessential to the conclusions. Recent results from single-atom scattering theory are used to describe the specimen, a one-dimensional model of a thin carbon film carrying six osmium atoms. The calculated through-focus series demonstrates the nonlinearity of most modes of the CEM, which generates interference artifacts and introduces focusing difficulties and the risk of misinterpretation of the micrographs. STEM images, however, are shown not to be subject to these artifacts, which thereby explains the excellent quality of micrographs generated by this new instrument.
Undoped high-resistivity cadmium telluride for nuclear radiation detectors
Authors: Triboulet R. , Marfaing Y. , Cornet A. , Siffert P.
Published: February 2004

Starting with highly purified feed material, single crystals of semiinsulating CdTe were grown by the use of the traveling heater method, without external chemical compensation. Evaluation of the crystals by the use of electrical and optical measurements showed decisive improvements in quality. Nuclear radiation detectors prepared by the use of this material resulted in an energy resolution (FWHM), at room temperature, of 4.6 and 8.5 keV for γ rays at energies of 122 and 662 keV, respectively. The energy resolution at 122 keV decreased to 3.8 keV at a temperature of −30°C. No polarization effect was observed.