bluuebunny/crossref_metadata_2025 huggingface dataset:
Filamentation in silicon-on-sapphire homogeneous thin films
Authors: Pontius D. H. , Smith W. B. , Budenstein P. P.
Published: February 2004

Dynamic temperature configuration and current filamentation in single-crystal silicon films on sapphire substrates were studied with high-amplitude constant-current pulse excitation using Sunshine's stroboscopic technique. Temperature configurations vary greatly depending upon the pulse duration and amplitude, electrode geometry magnitude of heat flow into the substrate, and magnitude of transverse heat flow. Filamentation occurs in two steps, each accompanied by a voltage drop. An initial broad filament forms as local regions rise in temperature beyond the peak of the resistivity-temperature curve of the silicon. The second filamentation is a narrow melt channel that forms interior to the initial filament. A time-dependent computer simulation is presented that includes both the heat flow into the substrate and transverse heat conduction. The model shows that a stable-current filament can exist without a melt transition, but only for a very restricted range of current levels.
Large-aperture Nd-glass laser amplifier for high-peak-power application
Authors: Lubin M. J. , Soures J. M. , Goldman L. M.
Published: February 2004

A 110-mm-square aperture face pumped Nd-glass amplifier has been designed and tested under input beam energy density conditions of up to 5 J/cm2. The measured gain of 120-psec pulses compares favorably with the calculated values based on a three-level model of the amplifying medium. Maximum storage efficiency of 2.3%, high repetition rate of ½ pulse/min, and minimum beam distortion combine to make this design attractive for high-peak-power applications.
Hole mobility and Poole-Frenkel effect in CdTe
Authors: Ottaviani G. , Canali C. , Jacoboni C. , Quaranta A. Alberigi , Zanio K.
Published: February 2004

We have performed, with the time-of-flight technique, an extensive investigation of the transport properties of holes in high-resistivity CdTe as a function of temperature between 130 and 430 °K and for electric fields between 5 kV/cm and 50 kV/cm. In all investigated samples, at temperatures below 300 °K, the experimental hole mobility decreases on lowering either the temperature or the electric field. These features have been interpreted on the basis of the electric field effect on trapping and detrapping phenomena (Poole-Frenkel effect) which cause a reduction of the mobility. A critical review of the existing theories of the Poole-Frenkel effect is presented. The Poole-Frenkel constant obtained by comparing the experimental data with the most reliable theories of the Poole-Frenkel effect is in excellent agreement with its theoretical value. By analysis of the experimental data it was also possible to estimate the activation energy (Et=0.14 eV) and the concentration (NT=5×1016 cm−3) of the traps which caused the reduction of the mobility. These traps may be due to cadmium vacancies and the value of their concentration found here is in good agreement with previous estimates made in the same material.
Preflashover mass spectrometry
Authors: Panitz J. A.
Published: February 2004

A bakeable time-of-flight mass spectrometer has been combined with a novel probe assembly in order to directly investigate the ion species formed prior to and during the flashover of an ultrahigh-vacuum diode. Species are identified by their known kinetic energy and the time correlation between their arrival at a detector and a high-voltage pulse applied to the cathode of the diode. By varying the ratio of the pulse amplitude to a positive bias applied to the anode, the extent of ion production in the gap can be probed. Observations at 300 °K and 10−9 Torr indicate the presence of both highly charged metal anode ions and adsorbed residual gas prior to flashover. No detected species were formed in the gap, in contrast to what was expected from the results of Davies and Biondi. It is suggested that the absence of such ions may be related to the magnitude of the macroscopic field in the gap, since preliminary observations at flashover show a noticeable change in the nature and abundance of ion species. Electron-induced desorption appears to be the primary preflashover production mechanism, although field-enhanced desorption may also be significant.
Limitations upon photoinjection studies of charge distributions close to interfaces in MOS capacitors
Authors: Brews J. R.
Published: February 2004

Carriers can be injected into the oxide of a metal-oxide-semiconductor (MOS) capacitor by illuminating either electrode with ultraviolet light. Once injected, a voltage across the capacitor will cause the injected carriers to flow, constituting a photocurrent. The voltage dependence of this photocurrent is affected by any charge distribution which may exist in the oxide near the injecting electrode. Such oxide charge affects the photocurrent in two ways. First, the oxide charge affects the barrier position, or the distance that an electron must travel before it becomes a candidate for injection. Since the probability of a scattering event en route increases with this distance, the effect of the charge on the barrier position will modify the photocurrent. Second, the oxide charge contributes to the electrostatic potential within the oxide and hence to the barrier height. Any such effect of the oxide charge on the barrier height will affect the number of electrons injected, and hence also the photocurrent. In this paper the two limiting cases when either one effect or the other dominates are examined. The minimum distance from the interface at which charge can be detected is determined for both limiting cases. It is found that this minimum distance is of the order of the scattering length of the injected carriers for the ``barrier-position'' limit of measurement, and is limited only by the minimum absolute photocurrent detectable experimentally for the ``barrier-height'' limit. Applying these results to the measurements of Powell and Berglund on gold-oxide-silicon structures we find that 90% of the so-called ``fixed charge'' always found at the Si–SiO2 interface cannot extend more than one scattering length (≈34 Å) into the SiO2. This result is obtained without assuming any special form for the charge distribution normal to the interface but assuming lateral uniformity parallel to the interface. Consequently, loss of sensitivity due to charge discreteness effects has not been considered. However, it is argued that such effects can be minimized by using the ``barrier-height'' mode of measurement at low voltages. It is also suggested that lateral nonuniformities may be measurable via the dependence of the photocurrent on barrier position in the ``barrier-height'' mode of measurement.
Photoluminescence from He, Ar, Fe, and Cr ion-implanted MgO
Authors: Crawford J. R. , Dragsdorf R. Dean
Published: February 2004

Powdered and single-crystal MgO, implanted with 60 keV He, Ar, Fe, and Cr ions, have been examined by laser-stimulated photoluminescence. The photoluminescence from damage-related defects, centered at 14 350 cm−1, and from MgO : Cr3+ zero-phonon line at 14 325 cm−1 are discussed. The annealing behavior of the introduced defects and impurities is characterized by the room-temperature and liquid-nitrogen-temperature photoluminescence observed before and after 1 h anneals of 325, 600, and 900 °C. A comparison is made between the ion-implanted and the impurity-grown systems. Speculation is made on the nature of the damage-related defects as the source of the broad emission centered at 14 350 cm−1. Correspondence to the previously observed absorption band at 17 420 cm−1 is made.
Microwave properties of n-type InSb in a magnetic field between 4 and 300 °K
Authors: Eldumiati I. I. , Haddad G. I.
Published: February 2004

A two-band conduction model is used to determine the properties of shallow-type impurity semiconductors in the presence of microwave and dc magnetic fields as a function of temperature. Measurements using cavity perturbation techniques are employed to determine the properties of n-type InSb and theoretical and experimental results between 4 and 300 °K are compared. The hot-electron effect was found to be insignificant between 77 and 300 °K, and the scattering mechanisms are dominated by acoustic and polar modes over the same temperature range.
``Elastic'' constants and wave phenomena in bubble lattices
Authors: Höfelt M. H. H.
Published: February 2004

The ``elastic'' properties of lattices of reversely magnetized perfectly cylindrical domains (bubbles) are studied. Expressions are presented for the ``elastic'' constants determining the forces resulting from displacements in a general bubble lattice. Numerical results are given for the hexagonal (triangular) lattice and for various bubble spacings. ``Elastic'' wave phenomena in these lattices are investigated and the velocities of propagation are determined under the assumptions that the domain-wall damping and the coercive field can be neglected. Finally, an estimate is made of the attenuation properties and of the quality factor of a resonating bubble lattice of finite dimensions.
Physical properties of Fe–Ni–Sn Invar alloys-Mössbauer effect study
Authors: Eliezer Z. , Weiss B. Z. , Ron M. , Nadiv S.
Published: February 2004

The influence of an addition of Sn on the physical properties of a Fe–Ni Invar alloy was studied, the addition being designed to improve the mechanical properties of the Invar by precipitation hardening. Mössbauer effect with Fe57 and Sn119, magnetic and dilatometric measurements, as well as hardness tests were applied. It was found that the solubility of Sn at 1130°C is at least 4.73 at.%, and 1.8 at.% at 700°C. Precipitation hardening was achieved by the formation of an intermetallic compound identified as Ni3Sn2. The hardness of the alloy increases, as does the coefficient of thermal expansion with Sn content. To counterbalance the Ni depletion of the matrix due to the formation of the intermetallic compound, a corresponding quantity of Ni has to be added. When this is done, the alloy exhibits an approximately 50% increase in hardness and an optimal coefficient of thermal expansion of 2.6 × 10−6 °C−1.
Growth-induced magnetic anisotropy in seven different mixed rare-earth iron garnets
Authors: Hagedorn F. B. , Tabor W. J. , Van Uitert L. G.
Published: February 2004

We have measured the noncubic magnetic anisotropy in seven different compositions of rare-earth iron garnets, using bulk single-crystal samples grown from a flux. Several of these compositions supported magnetic bubble domains. The noncubic anisotropy is growth induced, and for each composition we investigated samples from both types of growth facets which occur in bulk garnet growth. Anisotropy energies as large as 7×104 erg/cm3 were found, and three distinct anisotropy orientations were resolved. The results have been analyzed within the framework of a two-parameter model for growth-induced anisotropy, and we find general agreement although there are some discrepancies. For one composition, Y2Gd1Al0.8Fe4.2O12, we have measured the dependence of the noncubic anisotropy on temperature over the range 4.2–300°K. Only part of the observed temperature dependence is in good agreement with a microscopic calculation done by Sturge. Finally, we report on the annealing characteristics of the noncubic anisotropy. Typically tens of hours near 1200°C are required to anneal it away.
Field distributions in the vicinity of a superconducting flux exclusion tube
Authors: Martin F. , Lorant S. J. St.
Published: February 2004

The distributions of the magnetic field inside and around a superconducting flux exclusion tube due to currents induced in the material by an external magnetic field are examined. A simple macroscopic model for the superconductor is assumed, based on the concept of a field-dependent critical current density, and London's equations are used to calculate the magnetic potentials in the three regions of interest. The magnetic field inside the tube was mapped using an electron beam, and the results compared with the calculations. It is concluded that the major contribution to the magnetic field present in the tube can be ascribed to the induced dipole and sextupole current distributions in the superconductor. By contrast, the effect of direct field penetration through the narrow slits in the structure is very small.
In situ transmission electron microscope investigation of the annealing of copper precipitate colonies in silicon
Authors: Nes E. , Solberg J. K.
Published: February 2004

The annealing of copper precipitate colonies in silicon single crystals has been followed in situ in the electron microscope hot stage. The colony dissolution was found to be a two-stage process; the first stage involved the enveloping dislocations and the precipitates attached to these only. The onset of the second stage was associated with a phase transformation and the generation of dislocations from all of the colony precipitates.
The dragging of precipitate particles by climbing dislocations in silicon
Authors: Nes E. , Solberg J. K.
Published: February 2004

In situ transmission electron microscope investigation of the annealing of copper precipitate colonies in silicon has demonstrated that the precipitates may be dragged by the climbing dislocations. Both chemical forces, due to the vacancy supersaturation, and elastic line tension forces may cause the particle dragging.
Velocity measurements of microwave ultrasonic waves in quartz
Authors: Hill Edward J. , Burgess James H.
Published: February 2004

The velocities of microwave ultrasonic waves at 9.2 GHz have been measured using pulse-echo techniques in X-cut and Z-cut quartz rods. In the X-cut quartz, the longitudinal mode velocity was (5.71±0.05)×105 cm/sec and the transverse mode velocities were (5.20±0.05)×105 cm/sec. The longitudinal velocity for the Z-cut quartz was (6.33±0.03)×105 cm/sec. In contrast with the measurements of Ogawa and Sakamoto these results agree with the low—frequency velocities reported by McSkimin [J. Acoust. Soc. Am. 34, 1271 (1962)].
Comment on ``Luminescence from LiNbO3''
Authors: Glass A. M.
Published: February 2004

It is suggested that the luminescence from LiNbO3 is misinterpreted by Hordvik and Schlossberg.
Comments on ``Multiphonon, Raman, and two-photon excitation of rare-earth ions in crystals: photon and phonon noise in 10-μm quantum counters''
Authors: Byer N. E. , Ensign T. C.
Published: February 2004

An analysis made in a recent publication indicates that two-photon, Raman, and thermal excitation noise contributions in a 10-μm infrared quantum counter (IRQC) are insignificant compared to that due to the background (300 K) radiation. This conclusion is found to be unwarranted because of several errors in the analysis, foremost of which is an overestimation by 9 orders of magnitude of the transition rate Wα′αbir induced by background radiation. The revised calculation presented here demonstrates that the background radiation, far from being the dominant noise source, is at most comparable in magnitude with the other noise mechanisms.
Simple internal photoemission method for determining shape of yield curves of negative electron affinity semiconductors
Authors: Escher J. S. , Williams B. F.
Published: February 2004

Internal photoemission quantum yield curves using a water electrolyte Schottky contact have been shown to be identical to vacuum photoemission activation yield curve shapes near threshold for negative electron affinity semiconductors GaAs, Ga0.81In0.19As, and GaAs/Ga0.52In0.48P/GaP. Reflection and semitransparent cathode Schottky yield curves can be generated on the bench in a matter of minutes.
Elastic energies of disclinations in hexagonal crystals
Authors: Chou Tsu-Wei , Pan Yen-Cheng
Published: February 2004

The aim of this paper is to investigate the elastic fields of a twist disclination loop and a wedge disclination line in hexagonal crystals. The plane of the twist disclination loop and the wedge disclination line are assumed to be parallel and normal to the basal planes, respectively. Closed-form solutions have been obtained for disclination stress fields and elastic energies. It is noted that the elastic field of twist loops in thin hexagonal crystals and nonhomogeneous systems can be found by the method of images. Energy values for several common hexagonal crystals are calculated.
Investigation of the gun aspects of a rotating plasma source
Authors: Harder C. R. , Forsen H. K.
Published: February 2004

A crossed field or rotating plasma gun is investigated to determine detailed processes taking place during the ionization and acceleration phases. Measurements suggest that the gun breaks down via a spoke which subsequently rotates at the limiting velocity. Internal shorting occurs subsequent to break down and limits the usefulness of the source. Methods of reducing the effects of this shorting are presented as are some measurements of the properties of the plasma after it leaves the gun region. These suggest that about 1019 particles can be accelerated to energies of several hundred eV.
Grüneisen constants of polymers
Authors: Mopsik F. I. , Broadhurst M. G.
Published: February 2004

One result of recent interest in Grüneisen constants, γ = − d lnν/d lnV, of polymers is a considerable spread of reported γ's for solids like polyethylene. From elasticity data (bulk modulus or sound velocities for example) one finds γ ≈ 6 for linear polymer solids. Values of γ from thermal data are much lower than 6 because the relationship usually employed, γ = αB V/CV, is not valid for polyatomic solids. Measurements of the shifts in lattice frequencies with volume strains are the most direct way of measuring γ. However, the results for pressure-induced strains differ from those for temperature-induced strains, and both differ from the results from elasticity data. In this paper we consider vibrations in a simple anharmonic well and show how the apparent shifts in vibrational frequency with pressure and temperature can be derived from changes in force constants.
Small-angle x-ray scattering from amorphous polycarbonate
Authors: Lin Wen , Kramer Edward J.
Published: February 2004

Small-angle x-ray scattering (SAXS) from amorphous polycarbonate (PC) exhibits a sharp rise in intensity at ultrasmall angles (2θ <0.08° for Cu Kα radiation). At much higher angles, SAXS is superimposed on a diffuse halo centered at an angle corresponding to a spacing of [inverted lazy s]10 Å. Since doping the PC with small amounts of I2 results in a reversible decrease in SAXS intensity, SAXS is not due to voids but is probably attributable to the ``nodule'' structure observed in PC with electron microscopic techniques. The invariant, ∫0∞θ2I(θ)dθ and lim[θ4 I(θ)] as θ → ∞, are used to compute a specific surface of 150 m2/cm3 based on the assumption of 0.5 volume fraction of spherical nodules. The ``range of inhomogeneity'' of the nodules is then found to be 130 Å. From absolute intensity measurements the minimum relative density fluctuation between the nodules and their surroundings is 1.6%; an upper limit of 1.8% is found for fcc close packing of nodules. This result demonstrates that the model of Yeh, which assumes crystalline density for the nodules and predicts a relative density fluctuation of 21% is much too extreme.
Evidence for structure in polyisobutylene from positron lifetimes
Authors: Stevens J. R. , Rowe R. M.
Published: February 2004

The lifetimes and intensities of positrons annihilating in polyisobutylene were determined over a temperature range from − 100 °C through its glass transition to + 20 °C. The glass transition was determined to occur at − 70 °C compared with a value of − 63 °C determined by differential scanning calorimetry. The intermediate and long lifetimes are concluded to be associated with positrons annihilating in the ordered and amorphous regions, respectively, of the polyisobutylene sample usually considered to be completely amorphous under normal conditions. Depending upon the thermal history, it was determined that between 40 and 50% of the polyisobutylene molecules are aligned in some manner at room temperature. This is to be compared with about 30% in cis 1–2 polybutadiene at the same temperature. The existence of this significant amount of structure in polyisobutylene is offered as an explanation for the sluggish response of butyl rubber to stress even at temperatures 80–90 °C above Tg.
Theory and observations of polymer crystal thickening
Authors: Sanchez I. C. , Colson J. P. , Eby R. K.
Published: February 2004

The thickening of polymer crystals during isothermal annealing is usually observed to be an irreversible process. Phenomenological laws that govern such processes take the form of simple proportionalities—flux being proportional to force. For polymer crystals, a thermodynamic force capable of driving the thickening phenomenon arises from the unequal free energies of the fold and lateral surfaces. By analogy with other irreversible phenomena, the rate of crystal thickening is taken to be proportional to the derivative of the surface free energy with respect to crystal thickness. After certain assumptions, integration yields an equation in which three parameters characterize the system: an initial thickness l0, an equilibrium thickness l*, and a relaxation time τ which is a function of the ``undercooling''. The theory provides a basis for considering the effects of parameters such as time, temperature, thermal history, pressure, and liquids on the thickening rate. In particular, the theory adequately describes the time and temperature dependence of crystal thickening in random copolymers of tetrafluoroethylene and hexafluoropropylene which exhibit thickening behavior completely analogous to that of homopolymers. During thickening, the unit cell dimensions of these quenched-crystallized copolymers decrease in a manner that is consistent with the concept of complete comonomer inclusion upon crystallization.
Extension of theory of growth of chain-folded polymer crystals to large undercoolings
Authors: Lauritzen John I. , Hoffman John D.
Published: February 2004

The kinetic theory of the rate of growth G and the initial lamellar thickness lg* of chain-folded crystals is extended so that it is applicable at high undercoolings. Attention is centered on the details of how the first step element and the first fold are put down on the substrate. A parameter φ that varies between zero and unity, which apportions the free energy of attachment of the step element between the forward and backward reactions, is used to denote variations in this process. Expressions for G are derived from flux equations for two limiting cases: regime I, single surface nucleation act with rapid substrate completion and regime II, numerous surface nucleation acts with very slow substrate completion. Data from the literature on G for isotactic polystyrene (regime II) and polyethylene single crystals (regime I) are analyzed to obtain surface free energies, and these are used with the revised theory for lg* to predict the lamellar thickness of these polymers. Good agreement between lg* and published data is found for 1 > φ > 0. Values of φ below unity imply that the molecules are physically adsorbed onto the substrate prior to actual crystallographic attachment. A discussion is given of the segmental transport effects that dominate the behavior of G at high undercoolings in bulk polymers.
Structure of lanthanum-hexaboride-coated rhenium filaments
Authors: Ford R. R. , Lichtman David
Published: February 2004

Rhenium filaments electrophoretically coated with lanthanum hexaboride have been studied using a scanning electron microscope. Activation of these filaments appears to produce a coalesced layer of lanthanum hexaboride, nearest to the rhenium surface. This coalescence does not, however, extend to the surface of the filament, owing presumably to the relatively low thermal conductivity of the material. A definite cavity exists between the coalesced inner layer and the primary crystals in the surface layer which may partially explain the thermal ion desorption data from these surfaces. The results confirm that the preferential diffusion of lanthanum to the surface of the boride is not the activation mechanism for the low work function of these materials, and that the rhenium is acting as a truly inert support.
Ion-implanted nitrogen in gallium arsenide
Authors: Kachare A. H. , Spitzer W. G. , Kahan A. , Euler F. K. , Whatley T. A.
Published: February 2004

Several gallium arsenide samples were implanted at room temperature with 14N+ ions. Infrared absorption measurements at ≃ 80 °K showed a broad band near 480 cm−1 which is attributed to the localized vibrational mode of NAs,N substitutional on an As site. Measurements were made of the dependence of the integrated absorption I on the fluence φ for 1.0 × 1016 ≤ φ ≤ 2.0 × 1017 ions/cm2, on flux from 2.4 × 1012 to 1.2 × 1013 ions/cm2 sec, and on ion energies between 1.0 and 3.0 MeV. I increases linearly with φ until φ [inverted lazy s] 1017 ions/cm2 and decreases substantially at larger fluences probably due to the presence of short-range lattice disorder. The implanted samples were annealed isochronally from 473 to 1073 °K, and isothermally at 973 °K. The isochronal anneal for φ≲1017 ions cm−2 showed no appreciable change in I up to 873 °K. The short-range disorder in the φ≳1×1017 ions cm−2 samples annealed at much lower temperature. For all φ values the I decreased substantially after 973 °K anneal and after 1073 °K the I was virtually zero. The high-temperature decrease in I is irreversible. The isothermal anneal indicates that the annealing mechanism is not simple and cannot be explained by a simple integral-order kinetic process. Ion microprobe analysis of the same sample before and after 1073 °K annealing shows nearly identical approximately Gaussian peaks in the 14N+ concentration indicating negligible out-diffusion of nitrogen. The depth and the peak are in reasonable agreement with LSS predictions. The formation of GaN after high-temperature anneal is unlikely since infrared measurements do not show the GaN characteristic lattice modes. The disappearance of the 480-cm−1 band after high-temperature annealing is tentatively attributed to the formation of N2 molecules which are infrared inactive.
X-ray diffraction topographs of silicon crystals with superposed oxide film. III. Intensity distribution
Authors: Ando Y. , Patel J. R. , Kato N.
Published: February 2004

Following previous studies by Kato and Patel under the same title, the intensity distribution of section and traverse topographs of a silicon single crystal partly covered with a superposed oxide film is studied theoretically. The results of the basic theory are summarized and a practical computation procedure is outlined. The details of the characteristic black and white contrast observed in section topographs can be fairly accurately computed. The elasticity solution used by Blech and Meieran for the strain distribution is essentially correct in slightly distorted regions, where the fringes are observed. A strain relaxation must be introduced in the highly distorted region, close to the oxide boundary, in order to succesfully compute the observed intensity contrast.
Precipitation of copper in silicon
Authors: Das Gobinda
Published: February 2004

The structure and morphology of precipitates of copper, decorating dislocations in high-purity nearly perfect silicon single crystals were determined by high-voltage (1 MV) transmission electron microscopy and are discussed in light of the covalent bond formation by copper in silicon. The precipitates are observed to form during cooling, in clusters or colonies, on and around dislocations. They are spherical, 50–500 Å in size, and exhibit parallel moiré fringes. Those which are heterogeneously nucleated on dislocations are always found to be in the larger size range. Dislocations are thought to be present prior to precipitation and they climb down, emitting vacancies for precipitating substitutional copper atoms, and thus become heavily jogged. No ``rel-rod'' streaks are found in diffraction patterns. Only a few extra spots are found and then only when the precipitate density is very high (5×1014/cm3). The crystal structure of the precipitates was determined by combined analyses of moiré spacings and the few extra spots. It is found to be diamond cubic (B3 type, a0=5.72 Å), isomorphous with the structure (A4). The B3 structure is derived from the diamond cubic (A4) silicon lattice by replacing corner (000) and face-center (1/2 1/2 0, 1/2 0 1/2, 0 1/2 1/2) sites by copper atoms. The precipitate has a chemical composition of Cu–Si and is not stable at room temperature but is thought to be stabilized by strain energy of the precipitate/matrix system. The new interpretation of covalency of copper in the diamond cubic silicon is given on the basis of stereochemical considerations. The proposed tetrahedral coordination of copper atoms implies d10sp3 orbitals which are rationalized in terms of state of ionization (triple acceptor) of copper in silicon. The choice of conductivity type, reduction in conductivity after precipitation, and quick recovery time in depletion-capacitance measurements are qualitatively explained in terms of the proposed covalency of copper.
Dielectric coaxial waveguide
Authors: DeVore R. , Toth J. F. , Caldecott R.
Published: February 2004

Modal cutoff, dispersion, and attenuation characteristics for the dielectric coaxial waveguide (three interfaces) are presented for representative parameters. These properties change considerably as the guide geometry and dielectric properties are varied. Discussion of dielectric guide operation and comparison of a particular design with a metal waveguide is given.
A 337-μ HCN laser interferometer for plasma diagnostics
Authors: Heckenberg N. R. , Tait G. D. , Whitbourn L. B.
Published: February 2004

A self-modulating laser interferometer incorporating a 337-μ HCN laser is described and a simple theory of its operation is developed. This theory shows that the long lifetimes of levels involved in molecular laser transitions may cause a peaked frequency response in such an instrument. Experimental observations indicate a flat frequency response up to the maximum attained fringing rate of 10 kHz. The interferometer was used to make electron density measurements in the range 2 × 1012 cm−3−1014 cm−3 for an effective path length of 150 cm in a decaying helium plasma. The interferograms obtained show a marked time variation in fringe amplitude which is attributed to the refractive effects of electron density gradients in the plasma.
Electron-neutral transport cross section of mercury
Authors: Morris J. C. , Walker J. H.
Published: February 2004

The electron-neutral transport cross section and the electrical conductivity of Hg have been determined using a constricted dc Hg arc. This arc has a novel configuration which permits the precise measurement of the pressure, the voltage gradient, the temperature profile, and the total current. For the temperature range 5000–6500 °K, the electron-neutral transport cross section was found to be 1 × 10−14 cm2 with a precision of ± 6% and an absolute accuracy of ± 20%. A description of the apparatus and technique is presented as well as a comparison with other existing data.
Far-field analysis of nonlinear shock waves in a lattice
Authors: Tasi James
Published: February 2004

An analysis is made of the far-field behavior of a longitudinal shock wave propagating in a one-dimensional semi-infinite elastic lattice with a velocity step applied to the first mass. The nonlinear part of the elastic interaction force is assumed to be of parabolic form. Using the method of matched asymptotic expansions and stretched coordinates, for small nonlinearity, the original lattice equations of motion are replaced by a partial differential equation that governs the slow evolution of the wave with distance. A numerical solution of the partial differential equation shows the transition as the wave propagates from an oscillatory shock profile in the near field to a sequence of solitary waves in the far field of the lattice. The individual solitary waves at the head of the pulse eventually achieve essentially the same steady maximum amplitude and the same steady form, while continuing to spread apart from each other. The maximum particle velocity for the far-field solitary waves is found to be approximately 1.76 times as great as the velocity applied to the first mass. For the first-order nonlinear theory that is derived, the existence of a maximum amplitude of particle velocity that is found to be steady with distance as the wave propagates also implies that amplitude is independent of the magnitude of the nonlinearity, so long as the nonlinearity is small, but nonzero.
Dynamic response of partially compacted porous aluminum during unloading
Authors: Butcher B. M.
Published: February 2004

Compressed gas gun impact experiments were designed to measure relief wave velocities in 2.16-g/cm3 porous 2024 aluminum compacted to near solid density. The experimental measurements showed that as the porosity decreased to zero, the velocity of the first part of the unloading wave approached the dilatational wave velocity of solid aluminum. Similar results were also obtained from ultrasonic velocity measurements on samples under various degrees of static prestress. These statically loaded samples were laterally confined to simulate the dynamic condition of uniaxial strain. The experimentally measured relief wave and sonic velocities are compared with predictions obtained from the theoretical elastic moduli relations derived by Budiansky, and by Hashin and Shtrikman. Deviations from theoretical predictions were observed for compacted densities less than 90% of solid density; the deviations are attributed to the initial nonspherical void shapes.
Effects of stress on metal-oxide-semiconductor structures
Authors: Fonash Stephen J.
Published: February 2004

Metal-oxide-semiconductor (MOS) structures contain built-in stress fields. Such fields could be related to surface-state density, interface charge, and may influence migration, collection, and precipitation of impurities as well as modify the properties of the oxide layer and cause shifts in the band structures of the metal and semiconductor. Consequently these fields may be an important factor in the reliability problems of MOS devices; unfortunately, previous studies have produced results and conclusions which are quite varied. To be able to appraise these various possible effects, shifts in the C-V characteristics of a device due to band structure modifications resulting from stress, which have been suggested to be large, and oxide layer modifications resulting from stress are explored analytically. It is concluded that these contributions to any shift of the C-V characteristics, even for stresses of the order of 1010 dyn/cm2, must be small. These results then permit the effects of stress on generation recombination, surface states, interface structure, and ion drift to be explored experimentally and appraised. The experimental work produced no evidence for stress-induced changes for stresses up to 109 dyn/cm2 even though, for the loading configurations used, these externally imposed stresses substantially changed the built-in field across the interfaces.
Laser-induced deformation modes in thin metal targets
Authors: O'Keefe J. D. , Skeen C. H. , York C. M.
Published: February 2004

Thin metal targets were irradiated with a Q-switched neodymium laser. The absorption of the laser energy produced a high-temperature and -pressure plasma which drove stress waves into the targets. In some cases the plasma was confined using the technique developed by Anderholm and it was found that the magnitude of the stress increased with confinement. The histories of the deformations were measured using quartz and single-slit diffraction gauges and two distinct deformation modes were discovered. The first occurred on a time consistent with the acoustic transit time through the target and the second occurred in terms of transit times, up to an order of magnitude later. This latter late-time deformation mode resulted in the permanent deformation of the targets.
Trap-assisted charge injection in MNOS structures
Authors: Svensson Christer , Lundström Ingemar
Published: February 2004

Injection of charge carriers into the nitride in an MNOS structure by direct tunneling to traps in the nitride is studied in this paper. It is shown that this injection mechanism is very important for MNOS structures with thin oxides at low nitride fields (1–4 MV/cm). The dependence on field, temperature, and oxide thickness of this injection current are examined both theoretically and experimentally. It is furthermore proposed that this mechanism may be of considerable importance for charge transport in most insulators.
Performance of a large-bore high-power argon ion laser
Authors: Wang C.P. , Lin Shao-Chi
Published: February 2004

Further experimental results on the performance of a large-bore high-power argon ion laser are presented. The output power is found to increase more than linearly with the discharge tube length. The intensity distribution of the output beam is found to be sensitive to the mode of operation but not too sensitive to the power output up to a 150-W level.
Magnetic properties of RCo2 Ge2 compounds (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y)
Authors: McCall W. M. , Narasimhan K. S. V. L. , Butera R. A.
Published: February 2004

The magnetic properties of the RCo2 Ge2 compounds with R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y have been investigated. It was found that the compounds for which R=La, Ce, Sm, Er, Tm, Yb, and Y exhibit paramagnetic behavior down to 4.2 °K with ErCo2Ge2 and TmCo2Ge2 probably ordering at lower temperatures. The compounds for which R=Gd, Tb, Dy, and Ho order antiferromagnetically. PrCo2Ge2 and NdCo2Ge2 show an unusual magnetic behavior. PrCo2Ge2 exhibits a susceptibility which decreases from 4.2 °K, then rises to a peak at 27.5 °K. NdCo2Ge2 has two peaks in the susceptibility-vs-temperature curve at 13.5 and 27.5 °K. The Néel points for the heavy rare-earth compounds follow the de Gennes function, and the equation χM = χ0,M + CM/T−θ is used to interpret the susceptabilities in the paramagnetic region. χM is the molar susceptibility; χ0,M is a temperature independent contribution to the susceptibility; CM is the Curie constant; T is the temperature and θ is the Weiss constant.
Quantitative trace element analyses in thick samples with heavy-ion-induced x-ray fluorescence
Authors: Shabason L. , Cohen B. L. , Wedberg G. H. , Chan K. C.
Published: February 2004

A procedure is described for obtaining quantitative analysis of trace elements in a thick sample by heavy-ion-induced x-ray fluorescence. The method avoids difficulties involved in preparing thin uniform samples and yields absolute abundances of impurity elements without utilizing internal standards.
Differential etching of ion-implanted garnet
Authors: Johnson W. A. , North J. C. , Wolfe R.
Published: February 2004

A new technique for generating precise surface structures in single-crystal garnet materials is described. The crystals are ion implanted in localized areas using photoresist as an implantation mask. The photoresist is removed and the crystals are etched in phosphoric acid. The damaged volumes produced by the ion implantation etch at a substantially greater rate than the undamaged material, thereby producing surface structures. Groove depth can be precisely defined and reproduced by controlling the implantation parameters: ion species, energy, and dose. Undercutting is minimal and etching conditions are not stringent. The method is superior to both standard chemical etching and ion milling. The process has been characterized for H, He, and Ne implantations. It is shown that the temperature dependence of the etching rates for damaged and undamaged material is the same. The increase in etching rate is proportional to the damage concentration. The etching rate profiles are therefore synonymous with the damage profiles produced by the implantation. Etching rates more than three orders of magnitude greater than that of undamaged material have been observed. The etching rates for the three elements used correlate fairly well with the theoretical nuclear stopping power, and the groove depths obtained correlate with the theoretical ion ranges. This method has been used to produce serrated edge grooves which serve as rails for magnetic bubble propagation in conductor-groove bubble propagation circuits.
Nuclear microanalysis of oxygen concentration in liquid-phase epitaxial gallium phosphide
Authors: Lightowlers E. C. , North J. C. , Jordan A. S. , Derick L. , Merz J. L.
Published: February 2004

The total bulk oxygen concentration has been determined in GaP layers grown by liquid-phase epitaxy. Layers were grown doped with 18O enriched oxygen, and the 18O concentrations were measured by detecting α particles emitted during proton irradiation using the nuclear reaction 18O(p, a)15N. The relative concentrations of 18O and 16O were determined from exciton luminescence of the LiI–LiGa–OP complex at 4.2°K after Li diffusion, thus enabling the total bulk oxygen concentrations to be determined. The total solid solubility of oxygen in GaP containing the optimum zinc concentration for efficient luminescence from Zn-O nearest-neighbor pairs, 5 × 1017 cm−3, ranged from [sine wave] 5 × 1016 cm−3 at [sine wave] 1040°C to [sine wave] 9 × 1016 cm−3 at ≳1100°C. Measurements on a layer doped with tellurium and oxygen failed to detect any 18O, indicating that the total oxygen concentration was probably < 4 × 1016 cm−3. The experimental results confirmed the presence of Ga2O3 coprecipitates when the oxygen added to the liquid phase was greater than the solubility. Channeling experiments to determine the oxygen site location were done, but the results were inconclusive. The methods of crystal preparation and 18O doping are described, and the techniques employed to prevent oxygen isotope exchange are discussed. Other experimental techniques which are described include a large solid angle α-particle detector arrangement which also allowed sample orientation, a graded thickness foil which stopped backscattered protons and preserved the α-particle resolution, and the methods for minimizing and correcting for boron background which occurs through the reaction 11B(p, α)8Be*.
Kinks, jogs, and a regeneration mechanism for Volterra disclinations
Authors: Das E. S. P. , deWit R. , Armstrong R. W. , Marcinkowski M. J.
Published: February 2004

A regenerative mechanism is proposed which can lead to unlimited multiplication of disclinations. This mechanism consists of a glissile segment of a disclination pinned by two sessile ``jogs'', and therefore is similar to a Frank-Read source for dislocations. It is also possible to have a U-mill, Z-mill, and L-mill for disclination multiplication. It is further shown that a single source can give rise to disclinations of opposite signs (and this allows rotation in both directions of that part of the crystal above the source, relative to the part below), depending upon the direction in which the source operates.
Elastic and piezoelectric surface waves guided by thin films
Authors: Sinha B. K. , Tiersten H. F.
Published: February 2004

A system of approximate two-dimensional surface-wave equations and edge conditions in one scalar variable is derived from Hamilton's principle for linear piezoelectric media by assuming suitable depth behavior and integrating with respect to depth. The assumed behavior with depth is determined from the known straight-crested surface-wave solutions of the three-dimensional equations for the plated and unplated substrate in connection with the known variable-crested solutions for the isotropic substrate. The influence of the inertia, stiffness, and electrical shorting of the film is included in the analysis. The application of the derived equations to the problems for isotropic substrates treated earlier by an ad hoc technique indicates that the derived equations are extremely accurate. Among other things, the analysis reveals that a slot in an aluminum-oxide film on a T-40 glass substrate exhibits guiding characteristics twice as good as the combination of aluminum on T-40 glass in the essentially nondispersive range. The derived equations are used in the determination of the dispersion curves for piezoelectric surface waves guided by gold strips on y-cut lithium niobate for propagation in the x and z directions, respectively. Although the dispersion curves for z propagation turn out as expected, the dispersion curves for x propagation have an interesting and unusual shape indicating two ranges of essentially nondispersive propagation. The unusual shape is a consequence of the fact that two straight-crested surface waves couple strongly in the propagation range of interest.
Asymmetric deformation in fatigue of body-centered-cubic single crystals
Authors: Nine Harmon D.
Published: February 2004

Asymmetric deformation, the movement of material on single-crystal surfaces in only one crystallographic direction under net zero strain cycle deformation, has been observed in single crystals of iron, niobium, and molybdenum. The effect leads to rapid local deformation and rapid fatigue failure. A dislocation mechanism involving asymmetric slip on {112} and {123} planes and repeated cross slip is proposed to explain the effect.
Nucleation of voids and their growth during electromigration
Authors: Suhl H. , Turner P. A.
Published: February 2004

The growth and distribution of voids formed by vacancy agglomeration during electromigration is examined. It is demonstrated for the first time that a critical current density must be exceeded for void production.
Interaction of a relativistic electron beam with a turbulent plasma
Authors: Korn P. , Sandel F. , Wharton C. B.
Published: February 2004

The interaction of a relativistic electron beam (ν/γ[inverted lazy s]2) with the turbulent phase of a Z discharge is examined. An enchancement in heating is observed when the electron current due to the Z discharge is in the opposite direction to the beam current and the plasma is highly turbulent. The ion energy distribution is examined for turbulent heating, beam heating, and combined beam and turbulent heating.
Pressure response of a solid pulse heated through a polymorphic phase transition: α-β inversion in quartz
Authors: Gauster W. B. , Perry F. C. , Buckalew W. H.
Published: February 2004

Using 70-ns bursts of 3-MeV average energy electrons as the heating source, inertial thermomechanical stresses were produced in X-cut quartz disks. The range of peak absorbed energy density was from 30 to 360 cal/g. The stress pulses propagated through the samples (direction perpendicular to the c axis), and the ensuing rear surface motion was recorded with a laser interferometer. At the highest dose, the peak temperature produced in the absorber was calculated to exceed 1600 K, well in excess of the α-β transition temperature. Comparison of the experimental results with a model calculation, taking into account the shift of transition temperature with pressure, suggests that the phase transition occurred and that the response was not associated with a metastable state.
Theory of metal-insulator-metal tunneling for a simple two-band model
Authors: Gundlach K. H.
Published: February 2004

The one-band effective mass approximation for the dispersion relationship in the barrier of a metal-insulator-metal (MIM) tunnel junction fails if the barrier height is a considerable portion of the band gap of the insulator. This paper reports on results when the more realistic dispersion relation of Franz and Kane is used and displays the sensitivity of the tunnel effect to the band model. We illustrate some examples of the energy distribution of the current. Characteristic features of tunneling through trapezoidal-like barriers will be discussed, including maxima in the logarithmic derivative curves, in the thermal I-V characteristics, and the zero-bias offset of the conductance minimum. Calculations are performed by integrating the tunnel equation numerically, and analytical approximations for this equation are also presented from which the effect of various parameters on the tunneling characteristic can be estimated.