bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous subsidiary absorption in single-crystal YIG and evaluation of spin-wave linewidth
Authors: Patton Carl E. , Jantz Wolfgang
Published: February 2003

Measurements of the subsidiary absorption spin-wave instability threshold hcrit in high-quality single crystals of yttrium iron garnet reveal anomalous structure over a field interval extending several hundred Oe below the butterfly curve minimum at Hc. Such measurements have now been extended to cover the entire butterfly curve for sphere and plate samples. At the low-field end of the structure region, hcrit increases rapidly as the static field H is decreased to a ’’kink’’ field H′c. As H is reduced further, the increase in hcrit is much more gradual. The nature of the onset changes drastically at H′c, from a gradual increase to an abrupt jump in reflected power at threshold. Theoretical analysis of the data shows: (1) The instability at Hc is for spin waves with a polar angle ϑk of 22° rather than the 35° value often cited. (2) The field interval for the instability of zero wave number (k=0) modes is not confined to H≳Hc, but extends over a wide range down to H′c. (3) The kink at H′c corresponds to an abrupt transition to k≠0 spin waves at lower fields. These features are all due to the effect of the k dependence of ΔHk, the spin-wave linewidth, on hcrit. However, a steplike increase of ΔHk for k≠0 modes, rather than the linear dependence inferred from parallel pumping, is needed for a quantitative fit. This observation, while in partial agreement with the existing three-magnon confluence theory, shows the need for a refined calculation. The structure between Hc and H′c varies with sample shape and appears to be related to low-k magnetostatic mode excitations in the spin-wave spectrum.
Generation of dc and ac voltages by moving domain walls in ferromagnetic metals
Authors: Berger L.
Published: February 2003

The predicted dragging of domain walls by a dc current (domain-drag effect) has been observed recently in amorphous Gd-Co-Mo and Gd-Co-Au films and in bulk Co. Inversely, moving walls are predicted to generate a dc electric voltage or current in a metal. We show how the well-known elastic rigidity of domains can be used to achieve wall motions of the kind needed to perform that ’’inverse drag’’ experiment. Also, a dc transformer can be built by combining domain drag and inverse drag. Finally, when walls move, the voltage seen by two Hall probes very close to each other fluctuates every time a wall passes by. The voltage across two Ohmic probes exhibits similar ac components. We calculate the magnitude of these fluctuations in the case of stripe domains.
The structure, magnetic characterization, and oxidation of colloidal iron dispersions
Authors: Griffiths C. H. , O’Horo M. P. , Smith T. W.
Published: February 2003

Colloidal iron dispersions have been prepared by the thermolysis of Fe(CO)5 in solutions of functional polymers. The structure of the particles was very disordered at sizes ≲100 Å but changed to become single crystal with a disordered core as the size increased to 100–200 Å. Particles ≲100 Å were superparamagnetic, and particles in the 100–200-Å range had a time-dependent hysteresis. On exposure to the atmosphere an ∼30-Å-thick γ-Fe2O3 oxide film was produced on the surface of the particles. This is the ’’passive oxide film’’ detected previously by a number of techniques but never before imaged directly in situ. As water was absorbed from the atmosphere the chlorinated solvent-based dispersions reacted further to give β-FeOOH. This reaction was promoted by chloride-ion impurity. The magnetic moment decayed with oxidation roughly in proportion to the quantities of Fe, γ-Fe2O3, and β-FeOOH present. Disorder in the structure of ≲100-Å particles formed in nonchlorinated solvent-based dispersions produced an initial oxide film with magnetic characteristics distinct from those of γ-Fe2O3.
Magnetization reversal in Fe80B15Si5 metallic glass with large uniaxial magnetostrictive anisotropy
Authors: den Broeder F. J. A. , van der Borst J.
Published: February 2003

Several experiments are described in which the mode of magnetization reversal of Fe80B15Si5 metallic glass ribbons with a large uniaxial magnetostrictive anisotropy is investigated. Although theoretically possible, magnetization is never found to occur by uniform spin rotation, but always by a domain wall process. The failure to observe coercivities approaching the theoretical limit, i.e., the anisotropy field, is ascribed to the presence of defects. These defects are of macroscopic size, as follows from the observed linearity between the coercive force and the square root of the applied stress at high stress levels. Magnetization reversal mostly starts by the detachment of probably one domain wall pinned at a defect, after which the wall propagates in a ’’Sixtus and Tonks way’’ through the ribbon. In the ’’saturated’’ state many of these residual walls are present, but the coercive force is determined by the weakest pinned wall. It is argued that metallic glass ribbons with a large uniaxial magnetostrictive anisotropy behave magnetically as single crystals.
Pyroelectric effects and discharge currents in polyethylene terephthalate (PET)
Authors: Wintle H. J. , Turl/o Jozefina
Published: February 2003

We have studied the depolarization of polyethylene terephthalate (PET) films under short-circuit conditions, using white light as a probe. Working at room temperature with times in the range 1–104 sec (i.e., in the minimum between the α and β dielectric loss peaks) we have established that the discharge is almost entirely of dipolar origin, that the enhanced current under illumination is due to warming and not to detrapping, and that the transient pyroelectric response is accounted for quantitatively by thermal expansion of the polarized material in the thickness direction. The observed magnitude of the pyroelectric current falls with thickness and the time constant rises, but these are largely artifacts due to lateral thermal gradients in the material. A representative value for the pyroelectric coefficient is 4 nC m−2 K−1. The frozen-in polarization is thickness dependent, and this suggests a nonuniform distribution of dipoles across the film. Excess charge injected by using uv light during polarization plays no significant part in the discharge, indicating that any stored charge remains deeply trapped.
Phase measurements in the frequency domain photoacoustic spectroscopy of solids
Authors: Mandelis A. , Teng Y. C. , Royce B. S. H.
Published: February 2003

Photoacoustic spectroscopy provides information about both the amplitude and phase of the response of a system to an optical excitation process. This paper presents a theoretical model of photoacoustic processes in the frequency domain which includes the relaxation time of the radiationless deexcitations and a two-layer absorbing system. Emphasis is placed on the effect of these conditions on the phase of the photoacoustic signal and the utility of this measurement in evaluating material parameters. Circumstances under which the phase may be used to measure the optical absorption coefficient of the solid and the nonradiative relaxation times are defined. The value of the phase measurement in the study of surface films is discussed.
Refractive index profiles and range distributions of silicon implanted with high-energy nitrogen
Authors: Hubler G. K. , Malmberg P. R. , Smith T. P.
Published: February 2003

Single-crystal silicon has been implanted with nitrogen ions at MeV energies, to fluences between 0.25×1018 and 1.65×1018 ions/cm2 at a substrate temperature of 700 °C. Infrared transmission and reflection spectra in the range of 1.25–40 μm were measured and interference fringes were observed which are produced by the interference of light which has been multiply reflected between the front surface and the buried layers. By detailed theoretical analyses of the interference fringes we obtain refractive-index profiles, which, under suitable interpretation, provide accurate measurements of the range and straggling of the implanted ions. Rutherford backscattering measurements on the same samples confirm this interpretation. Between the energies of 0.67 and 3.17 MeV, the measured values of the projected range agree with theory after adjusting the electronic stopping power, but the straggling measurements are lower by ∼30%. It is demonstrated that the asymmetry of the range distribution can be measured with this technique as well.
Secondary emission and ion feedback in a straight semiconducting channel
Authors: Bouchard C. , Carette J. D.
Published: February 2003

A simple calculation is presented in which the equation giving the current-voltage characteristic of a self-triggered channel ion source is derived. The source is made from a straight channel electron multiplier operated in the self-sustained cascade mode. An analysis is given on each of the following topics: secondary emission and amplification in the channel, current saturation, and ion feedback. Comparison with experimental measurements is also presented.
Extension of the theorem of orthogonality for piecewise continuous eigenfunctions
Authors: Wirth Patricia E. , Rodin Ervin Y.
Published: February 2003

A nonstandard inner product is utilized to guarantee the orthogonality of the eigenfunctions in an n-layered Sturm-Liouville problem. The parameters of the interface conditions are required to satisfy an inequality constraint providing an extension of the previous theorem in which an equality condition was demanded.
Recrystallization of vacuum-deposited ultrathin CdS films by the H2S heat-treatment process
Authors: Srivastava R. S. , Prakash K. , Badwe M. V.
Published: February 2003

Recrystallization of vacuum-deposited ultrathin CdS films activated with Ag on a glass substrate is studied by the H2S flow heat-treatment process at 300 °C. Observation of the recrystallized films under a polarizing microscope reveals void formation and distinct hexagonal uniaxial crystals at the edge of the voids: The x-ray diffraction pattern shows a sharp peak at the (002) axis. It is found that the combined action of the Ag activator and the H2S flow heat-treatment process has a tendency of lowering the recrystallization temperature in these films.
Aluminum-silicide reactions. I. Diffusion, compound formation, and microstructure
Authors: van Gurp G. J. , Daams J. L. C. , van Oostrom A. , Augustus L. J. M. , Tamminga Y.
Published: February 2003

Material reactions as a result of thermal treatment were studied on thin-film Al/silicide/Si systems with CoSi2, PtxNi1−xSi, and MoSi2 for the silicide. Auger electron spectroscopy and Rutherford backscattering analysis showed the transport of Si and the metal released from the silicide into the Al and transport of Al into the silicide. X-ray diffraction showed the formation of Co2Al9 at 400 °C, PtAl2, NiAl3, and PtNiAl2 at 275 °C, of which the latter disappeared above 450 °C, and MoAl12 at 535 °C, as well as free Si. The Co2Al9 formation followed a linear time dependence with an activation energy of 2.3 eV. The MoAl12 formation followed a parabolic time dependence with an activation energy of 3.6 eV. A thin tungsten layer between Al and the silicide proved to be effective as a diffusion barrier below 500 °C, at which temperature WAl12 was formed. The microstructure was studied by scanning and transmission electron microscopy, electron microprobe analysis, and scanning Auger electron spectroscopy. The reaction resulted in the formation of Si islands with a size up to about 10 μm, containing Al-rich inclusions, and the intermetallic compound with Si inclusions in between the islands.
Aluminum-silicide reactions. II. Schottky-barrier height
Authors: van Gurp G. J. , Reukers W. M.
Published: February 2003

The Schottky-barrier height of Al/silicide layers to n-type Si was measured as a function of annealing temperature with CoSi2, MoSi2, and PtxNi1−xSi for the silicide. The barrier heights before annealing were 0.64, 0.69, and 0.74 eV, respectively, in the systems mentioned. On annealing, these values changed first due to Al diffusion through the silicide and compound formation and subsequently by Si precipitation. This change took place at a higher temperature when Al/Si was used. No change was found up to 500 °C when a thin W or Ti/W layer was used between the silicide and Al.
Inhomogeneities of surface potential in the thermally grown Si-SiO2 interface
Authors: Werner C. , Bernt H. , Eder A.
Published: February 2003

The standard deviation σs of the surface potential fluctuation on the Si-SiO2 interface was measured by means of the conductance technique of Nicollian and Goetzberger on a number of wafers with oxide charge densities Qox in the range (1–15) ×1010 cm−2. We could not find a proportionality between σ2s and Qox as was derived in theoretical considerations by Brews but rather we have found a correlation between σ2s and the surface state density Nss. We show that the reason for this is that only charges in the immediate vicinity of the interface contribute to σs. In a second experiment, mobile ions were drifted through the oxide by performing a temperature-bias stress. The resulting change in σ2s is directly proportional to the accompanying change in Qox, but the ratio of Δσ2s to ΔQox is three times higher than would be expected from Brews’s model. A reason for this behavior might be that the interface charge is concentrated in some small patches rather than distributed homogeneously. The assumption of negative surface charge in our samples, however, is not necessary.
Microstructure and Schottky barrier height of iridium silicides formed on silicon
Authors: Ohdomari I. , Kuan T. S. , Tu K. N.
Published: February 2003

Direct correlations between iridium silicides and their Schottky barrier heights on Si have been studied by combining TEM observations and I-V and C-V measurements. It has previously been shown that three iridium silicides IrSi, Ir2Si3, and IrSi3 can be formed by annealing Ir films on Si at temperatures around 400, 600, and 960 °C, respectively. The Schottky barrier height of these silicides on 〈100〉 Si have been determined to be 0.93 eV (IrSi), 0.85 eV (Ir2Si3), and 0.94 eV (IrSi3). Along with the I-V measurement, a computer fitting of current transport across Schottky diodes has been used to analyze the I-V data so that the barrier height from nonideal diodes can be determined. The question of a parallel diode formed by a mixture of two phases at the contact area has also been addressed. It is shown that I-V measurements, which are very sensitive to the presence of a lower barrier phase, tend to give a lower barrier height than a corresponding C-V measurement since the latter depends on the major phase in the contact area.
Transmission electron microscopy of Au-based Ohmic contacts to n-AlxGa1−xAs
Authors: Chang C. C. , Sheng T. T. , McCoy R. J. , Nakahara S. , Keramidas V. G. , Ermanis F.
Published: February 2003

Contacts to n-type AlxGa1−xAs have been previously fabricated by sequential deposition of Al, Sn, and Au, and then heating near 400 °C. Such contacts exhibit excellent electrical properties, but contact adhesion strength was erratic. Transmission electron microscope experiments revealed an almost continuous void separating the metal from the semiconductor. The void is about 100 Å wide, and frequently widens into large pores; it is essentially completely formed after Au deposition, before heat treatment. The voids probably grow by a Kirkendall-type mechanism during Au deposition, due to rapid diffusion of Sn into the Au. One simple method of eliminating the voids, that of moving the Sn layer away from the metal-semiconductor interface by depositing a thin layer of Au before putting down the Sn, is shown to produce contacts with no detectable interface void. With this new metallization, adhesion is greatly improved, without any loss of the excellent electrical properties previously achieved.
Control of dihydride bond density in reactive sputtered amorphous silicon
Authors: Jeffrey F. R. , Shanks H. R. , Danielson G. C.
Published: February 2003

Data are presented which demonstrate how the dihydride bonding density in hydrogenated amorphous silicon produced by reactive rf sputtering may be controlled through variation of the rf sputtering power. It is suggested that as the power is increased, the temperature of the ions and neutral atoms above the substrate surface increases until particles incident on the surface have enough energy to prevent or destroy the dihydride bonding configuration. Conductivity data are also presented which show a decrease in dark conductivity and photoconductivity as dihydride bond density is increased. It is concluded that the dihydride bonding reduces carrier mobility.
ac loss of a multifilamentary superconducting composite in a transverse ac magnetic field with large amplitude
Authors: Sumiyoshi F. , Irie F. , Yoshida K. , Funakoshi H.
Published: February 2003

A general study is made of ac losses of a multifilamentary superconducting composite carrying no transport current in a transverse ac magnetic field with large amplitude. In the case of applying a magnetic field below the current-saturation condition in an outermost layer, an eddy current loss as well as a hysteresis loss is calculated by taking account of the hysteresis effect of a superconducting filament on these losses with an apparent complex permeability of the filament. It is shown that the frequency characteristics of the eddy current loss are considerably different from those calculated from previous theories. In the case above the saturation condition, a loss calculation is made taking account of the phase difference between the applied magnetic field and the internal one. It is shown in this case that the hysteresis loss increases rapidly with frequency around the critical frequency. These calculated results are confirmed by experiments with Nb-Ti multifilamentary composites. General features of ac losses are also given for the composite design.
Fabrication of Nb-NbOx-Pb Josephson tunnel junctions using rf glow-discharge oxidation
Authors: Karulkar Pramod C. , Nordman James E.
Published: February 2003

An rf glow-discharge oxidation technique has been applied to the fabrication of Nb-NbOx-Pb Josephson tunnel junctions which exhibit quasiparticle current densities up to 104 A/cm2 at the sum of the gaps (i.e., junction resistances as low as 10−7 Ω cm2). The dependence of the impedance level and the shape of the junction V-I curve on the oxidation parameters (e.g., oxidation time, rf bias voltage, the composition, and the pressure of the argon-oxygen mixture) have been investigated. Good junctions were obtained by using very low rf peak-to-peak voltage (?60 V) and an oxidation period of 10 min or less. The junction resistance can be controlled by varying the partial pressure of oxygen (less than 3×10−4 Torr) while using a partial pressure of argon high enough (?10−2 Torr) to sustain a steady rf glow discharge. The results also indicate that sputter removal of niobium oxide is virtually absent in this rf glow-discharge oxidation process. The dependence of the junction resistance on the glow-discharge parameters is qualitatively explained by considering the effects of the parameters on the concentration of the oxidizing species in the vicinity of the substrate.
Breathers and other exact solutions from Josephson’s equation in 2+1 dimensions
Authors: Leibbrandt George
Published: February 2003

We derive for Josephson’s equation [∂2/∂x2 +∂2/∂y2−∂2/∂ (ct)2]ψ=j0 sinψ +VGint cosψ, some simple exact solutions, including a breatherlike solution of topological charge zero. We label these solutions fluxon solutions since they carry through the two-dimensional Josephson junction an integral number of magnetic-flux quanta.
Variational principles and bounds for the conductance of a heterogeneous locally anisotropic body
Authors: Mullins W. W.
Published: February 2003

Variational expressions are obtained for the conductance 𝒞 and for the resistance ℛ=𝒞−1 of a body of arbitrary geometry composed of an anisotropic medium whose conductivity σ is a function of position. Using these expressions, and their associated inequalities, conclusions are drawn concerning the changes in 𝒞 due to changes in σ. In particular, the upper and lower bounds on 𝒞 originally introduced and rationalized, but not strictly proved, by Rayleigh, and then further developed by Maxwell, are established and slightly generalized (anisotropy). Also, the well-known parallel and series bounds for the equivalent conductivity σe of a composite body are rederived and extended to the anisotropic case. The variational expressions comprise a basis for the use of the method of trial functions (e.g., finite-element analysis) to calculate the approximate conductance of a body.
Backscattering of a laser beam from electrostatic waves in a magnetized plasma
Authors: Bilikmen Sinan , Willett Joseph E.
Published: February 2003

Stimulated backscattering which arises from the parametric decay of an intense electromagnetic wave into an electrostatic wave and a backscattered electromagnetic wave is investigated. The analysis is facilitated by derivation of a pair of coupled differential equations for the amplitudes of the backscattered and scatterer waves. The absolute backscatter instability in homogeneous and inhomogeneous, bounded and unbounded plasmas is studied without invoking approximations which would permit independent treatment of the high-frequency electron modes and the low-frequency ion modes. A numerical study of a CO2 laser beam propagating through a magnetized hydrogen plasma is presented which illustrates the breakdown of the independent treatment of the electron and ion modes.
Grain-boundary segregation in a commercial ZnO-based varistor
Authors: Clarke D. R.
Published: February 2003

By using thin-film x-ray spectroscopy, it is found that the grain boundaries of a commercially available ZnO-based varistor which are devoid of a discrete intergranular phase are nevertheless enriched in bismuth. No direct measurement of the bismuth concentration could be made but an estimate is obtained by comparing the observed intensity of the bismuth peaks from the grain boundary to that from a bismuth containing thin intergranular film of measurable thickness. In this manner, it is estimated that bismuth is concentrated to within about 20 Å of either side of the grain boundary, a value commensurate with that obtained previously by Auger electron spectroscopy.
Statistics and grain size in zinc oxide varistors
Authors: Emtage P. R.
Published: February 2003

A ZnO varistor is a ceramic with grains of various sizes. Therefore, some of the electrical breakdown characteristics of the ceramic reflect variations in the voltage impressed upon a grain, rather than the breakdown characteristics of an average grain boundary. It is found that the mean breakdown voltage per grain in the ceramic is less than that of an isolated grain boundary because there are chains of long grains through the ceramic; the density of such chains is finite even in a thick sample. The maximum value of the coefficient of nonlinearity αmax, which measures the rapidity of breakdown, is found to be characteristic of the grain boundaries when αmax is moderate, that is, if αmax <50. The high values of αmax observed at low temperatures appear to be limited by statistical effects rather than being representative of the boundaries.
Lattice defects in silicon doped by neutron transmutation
Authors: Corish J. , Beniere F. , Agrawal V. K. , Haridoss S. , Defeux C.
Published: February 2003

The method of silicon doping by thermal neutron transmutation (producing phosphorus atoms) is compared to the conventional method. Both the electronic and atomic lattice defects are considered. From accurate radioactive and electrical measurements, the numbers of carriers and phosphorus atoms are measured separately in order to derive the concentration of electronic defects. Diffusion profiles of gallium are determined by activation analysis as well as ion microprobe before and after neutron doping, which gives the influence of the doping on the concentration of the atomic defects responsible for diffusion. No difference between the methods of doping can be detected within the range of experimental errors.
Optical studies of Be-implanted GaAs
Authors: Kwun Sook-Il , Spitzer W. G. , Anderson C. L. , Dunlap H. L. , Vaidyanathan K. V.
Published: February 2003

Infrared reflection and transmission measurements of Be-implanted GaAs have been made as functions of Be-ion fluence and annealing temperatures from 500 to 800 °C. Semi-insulating material was implanted with 280-keV ions with fluences of 1×1015, 3×1015, 6×1015, and 10×1015 ions/cm2. Hole carrier concentrations calculated from the optical measurements as functions of fluence and annealing temperature compare favorably with those determined from sheet Hall-effect data. The absorption cross section used was obtained from measurements of acceptor-doped GaAs with concentrations similar to those of the implanted and annealed samples. After annealing at 500 °C a free-hole plasma layer contribution to the electric susceptibility was observed by measurements of reflection interference effects. Except for the highest-fluence case the disorder effect on the dielectric constant was largely removed by this anneal. For the highest-fluence case the annealing results were more complicated. There are regions which still have significantly different optical properties due to residual disorder. The present results are consistent with redistribution effects produced by thermal aging at the higher temperatures.
Shock-wave compression of lithium niobate from 2.4 to 44 GPa
Authors: Stanton P. L. , Graham R. A.
Published: February 2003

Shock compression of lithium niobate above the Hugoniot elastic limit (about 2.5 GPa) reveals a succession of unusual features. Just above the Hugoniot elastic limit, the shock velocity is observed to be well below the bulk sound speed, indicative of a drastic reduction of shear strength. The shock velocity is observed to increase with particle velocity at an unusually large rate due to the reduction of strength in a very stiff material and an anomalously large pressure derivative of the bulk modulus. This later behavior may be due to the effects of localized shock heating resulting from heterogeneous shear deformation in ferroelectrics like lithium niobate and lithium tantalate in which increases in temperature are shown to have a strong effect on bulk modulus. A shock-induced polymorphic phase transition occurs at 13.9 GPa. Above the transition point the slope of the Hugoniot curve relating shock velocity and particle velocity is unusually low, indicative of a broad mixed phase region of undetermined extent. Limited work is reported on the isomorphous crystal, lithium tantalate, which exhibits features similar to lithium niobate with a Hugoniot elastic limit of 4 GPa and a phase transition in the vicinity of 19 GPa.
Isothermal LPE growth of thin graded band-gap AlxGa1−xAs layers
Authors: Kordos P. , Pearson G. L. , Panish M. B.
Published: February 2003

Liquid-phase-epitaxial growth experiments, using saturated Ga-Al-As solutions and GaAs substrates, were carried out under isothermal conditions. It was found that graded band-gap AlxGa1−xAs growth occurs under these conditions. The layer thicknesses were between 400 and 700 Å and the Al composition in the layer increased monotonically toward the surface. When a saturated Ga-As solution was brought into the contact with an AlxGa1−xAs solid and held at constant temperature, partial dissolution of the AlxGa1−xAs was observed. The resulting processes of compositional graded growth or partial dissolution follow from thermodynamic nonequilibrium between solid and liquid. It can be expected that similar processes will occur in other AIII-BIII-CV systems.
HCl pulsed chemical laser: An experimental study and modeling
Authors: Ameur Y. , Delaporte T. , Menard J. , Menard-Bourcin F.
Published: February 2003

Two pulsed chemical HCl lasers using the reaction between H2 and Cl2 with two types of electrode structure are described. Peak power output up to 215 kW is obtained with a plane electrode configuration, and 175 kW with a helical electrode configuration. Laser action is observed on 22 vibrational-rotational lines from H35Cl and 8 lines from H37Cl. The pulse shape and relative intensity of lasing lines obtained by using a selective cavity for the laser with helical electrode configuration are compared with computations from a model which includes kinetic processes and stimulated emission on one single line or a pair of close lines. Computed and observed results are in fair agreement for lines of (2→1) and (3→2) bands. However, for the (1→0) band the comparison suggests that an additional process occurs to populate the v=1 level.
A helical TE N2 laser with circular beam cross section
Authors: Krahn K.-H.
Published: February 2003

In this paper the operation of a helical TE N2 laser is reported which, according to its radial gain profile caused by the helical electrode geometry, produces a circular symmetric laser beam that is easily focused by ordinary spherical optics. Exhibiting a circular beam cross section together with a 20-mm near-field beam diameter the helical TE N2 laser generates output pulse peak powers of typically 480 kW within a pulse width (FWHM) of 5 ns. We believe the device is the first helical TE N2 laser producing output data that favorably compare with those of conventional designs.
Self-sustained oscillations in (AlGa)As oxide-defined stripe lasers
Authors: Channin D. J. , Ettenberg M. , Kressel H.
Published: February 2003

Experimental results are presented for the incidence statistics and physical characteristics of self-sustained oscillations in the output of (AlGa)As oxide-defined stripe lasers. Oscillations near threshold are found to be associated with aging but not necessarily to output degradation. The morphology, frequency relationship with current and time resolved near-field characteristics are presented. These observations are consistent with a rate equation model incorporating saturable absorption. Implications of this model to laser stability are discussed.
Laser performance of a glass-clad LiNdP4O12 rectangular waveguide
Authors: Kubodera Ken’ichi , Otsuka Kenju
Published: February 2003

A LiNdP4O12 rectangular waveguide clad by sputtered SK5 glass was fabricated. Quasi-cw laser operations at 1.048 and 1.317 μm were obtained both in an Ey00 single-transverse mode, by argon-laser coaxial pumping (0.5145 μm). The round-trip cavity losses were evaluated to be 14.3% (1.05 μm) and 6.5% (1.32 μm). Waveguide-mode calculation, observed laser-characteristics analysis, and transverse-pumping estimation are also described.
Acoustic harmonic generation due to fatigue damage in high-strength aluminum
Authors: Morris W. L. , Buck O. , Inman R. V.
Published: February 2003

It is shown that acoustic second harmonic generation is a useful tool for studying surface microcrack development during fatigue of a high-strength aluminum alloy. A fundamental (5 MHz) surface acoustic wave (SAW) was transmitted across the gauge section of flexural fatigue specimens of Al 7075-T6. The second harmonic amplitude was determined after several increments of fatigue, as a function of external load and the amplitude of the fundamental. It was found that the second harmonic signal is at a maximum close to zero external load and increases with progressing fatigue. Harmonic generation, attributable to microcracking at the surface, has been observed as early as 10–20% of the expended fatigue life. A simple analysis to obtain a coefficient of harmonic-generation efficiency versus applied surface stress is described. This analysis considers the effect of changes in attenuation of the fundamental and harmonic waves associated with degree of surface microcrack opening as a function of surface stress. It is shown that acoustic harmonic generation may be a useful tool for reliable monitoring of the state of fatigue of a structural material.
Inverse methods for elastic waves in stratified media
Authors: Berryman James G.
Published: February 2003

Two methods of solving the inverse problem for elastic waves at normal incidence on horizontally stratified media are discussed: Goupillaud’s equal-travel-time-layer approach, and Ware and Aki’s inverse-scattering method. The scattering method is simplified by showing that the impedance is proportional to the square of the Jost solution at zero frequency. The scattering method is discretized and a recursion relation is found for the impedance. In the continuum limit, the two methods are equivalent where the impedance is continuous but nonequivalent at points of discontinuity. The scattering method assigns the arithmetic average across the jump to the jump point.
A method for measuring shear-band temperatures
Authors: Dao K. C. , Shockey D. A.
Published: February 2003

We have designed an experiment for measuring temperatures accompanying the formation of bands of intense plastic strain. Shear bands intersecting the specimen surface were produced in machining chips of 4340 steel and 2014-T6 aluminum by orthogonal cutting using a lathe. An infrared microscope was then focused on the chip near the cutting tool to record temperature variations as shear bands swept through the focal area. We report preliminary estimates of temperatures, strains, and strain rates.
Orthotropic elastic stiffnesses of a boron-aluminum composite
Authors: Ledbetter H. M.
Published: February 2003

Measuring 18 separate ultrasonic velocities in a uniaxial boron-fiber-reinforced aluminum-matrix composite by a 10-MHz pulse-echo technique reveals orthotropic symmetry and provides nine independent elastic-stiffness constants, which compare favorably with those measured previously by a resonance method at lower frequency.
The influence of temperature on the oxidation of cesiated GaAs
Authors: Ebbinghaus G. , Simon A.
Published: February 2003

We report on investigations of the oxidation process of cesiated (100) GaAs surfaces by means of photoelectron spectroscopy (UPS; hν=21.2 eV). Discrete steps of the reaction are found as a function of temperature and interpreted in terms of molecular adsorption layers at 90 K, cesium suboxides at 170 K, and As–O bonds at 280 K. Cesium suboxides are discussed as essential surface compounds in negative electron affinity (NEA) photocathodes because of their low work function. According to our results the existence of these compounds would be limited to a very narrow range of oxidation.
Comparison of two kinds of oxygen donors in silicon by resistivity measurements
Authors: Kanamori Akihiro , Kanamori Masaru
Published: February 2003

Donor formation during heat treatment of silicon in the 550–800 °C temperature range has been investigated by resistivity measurements. The maximum donor concentration obtained here is about 1×1016/cm3 in p-type Czochralski-grown silicon. The donor is confirmed to be correlated with oxygen impurity as is the ’’thermal donor’’ formed in 300–500 °C annealing. The new donor, however, differs greatly in annealing behavior from the thermal donor. Preannealing at 470–550 °C and/or high carbon concentration promote the new donor generation at 650 °C annealing. A two-step reaction is proposed to interpret the donor-formation mechanism.
Bimolecular recombination in aggregate organic photoconductors
Authors: Mey W. , Walker E. I. P. , Hoesterey D. C.
Published: February 2003

Bimolecular recombination in xerographic photoconductors can contribute to effects which are essentially reciprocity failures. Such failures have been observed in aggregate photoconductors by comparing the surface potential—exposure behavior for low-intensity emission-limited discharge—with the behavior resulting from high-intensity flash exposures. The results show a high-intensity reciprocity failure which can be understood with a model based upon Langevin-type bimolecular recombination.
Intrinsic carrier concentration of Hg1−xCdxTe
Authors: Nemirovsky Y. , Finkman E.
Published: February 2003

The intrinsic carrier concentration ni is measured for Hg1−xCdxTe with 0.205⩽x⩽0.22 and x=0.29 and 150<T<320 K. The measurements are based on Hall data of uncompensated well-characterized samples. In addition to the galvanomagnetic measurements, photoconductive response and infrared transmittance have been used to determine and to verify the uniformity and composition of the samples. The experimental data are compared with calculations of the intrinsic carrier concentration which are based on an expression for the band gap recently measured. The following expression for the intrinsic carrier concentration is obtained: ni=[1.265×1016T3/2(6+x)−3/2 E3/2G]{1+[1+22.72(6+x)3/2E−3/2G  exp(EG/KT)]1/2}−1 (cm−3), where the band gap EG is given by EG(eV) =6.006×10−4T (1−1.89x)+1.948x−0.337.
Annealing effects in tunnel junctions (thermal annealing)
Authors: Konkin M. K. , Adler J. G.
Published: February 2003

This paper describes the results of subjecting Al-oxide-Pb tunnel junctions to thermal annealing. By looking at the junction resistance, barrier parameters (thickness, average barrier height, and the separation between the barrier heights at the Al and Pb electrodes), and inelastic electron tunneling (IET) peak intensities, one can study time-dependent effects occurring in the junction. These observations indicate changes in the tunneling barrier and IET spectra, and suggest that surface hydroxyl (-OH) groups experience reorientation.
Fundamental criteria for the design of high-performance Josephson nondestructive readout random access memory cells and experimental confirmation
Authors: Henkels W. H.
Published: February 2003

Fundamental design criteria for Josephson nondestructive readout random access memory (NDRO RAM) cells are presented, within the context of an LSI array environment. Emphasis is placed upon principles which are relevant to high performance. The criteria are elucidated via a specific design which is simulated and then experimentally evaluated in a technology with a smallest critical dimension of 5 μm. The specific cell differs from previously tested Josephson NDRO cells in several respects; namely, the cell stores only ∼8Φ0, employs interferometer gates and an external damping resistor, allows switching into device resonances, and eliminates the need for a special initialization cycle. The cell-selection scheme, employing triple coincidence, results in larger operating margins and smaller operating currents than have previously been achieved. The large operating margins and all basic cell design criteria were experimentally verified. The experimental interferometer gate characteristics were analyzed in detail and found to be describable by simple models. In addition, it was discovered that single flux quantum transitions in the interferometer gates could be exploited beneficially in order to enhance the insensitivity of operating margins to fabrication tolerances.
Thermally stimulated discharge current study of surface charge release in polyethylene by corona-generated excited molecules, and the crossover phenomenon
Authors: Kao K. J. , Bamji S. S. , Perlman M. M.
Published: February 2003

Thermally stimulated discharge (TSD) current studies on negatively-corona-charged low-density polyethylene reveal a deep surface trap distribution centered at 95 °C and a shallow surface and bulk distribution centered at 55 °C. TSD also shows that corona-generated neutral excited gas molecules in the surrounding air free the shallow surface trapped charge which moves into the bulk under its own field, and can be retrapped or transit through the sample. Crossover in surface potential decay curves is caused by these molecules, and can be eliminated by removing them from the corona discharge.
Wavelength dependence of the emission of a double-heterojunction GaAs-AlGaAs injection laser in a strong magnetic field
Authors: Bluyssen H. J. A. , van Ruyven L. J.
Published: February 2003

The emission energy of continuously operated double-heterostructure GaAs-AlGaAs lasers has been measured in magnetic fields up to 15 T and temperatures of 4.2 and 50 K. For lasers with a p-active region the observed shift in the emission energy can be described by a change in the position of the quasi-Fermi level of the conduction band as a function of the magnetic field. The measurements provide a determination of the carrier density at threshold and verify the assumption that the matrix element for the optical transition is in first order independent of the applied magnetic field.
Measurements of absorption in the CdHg excimer system
Authors: West John B. , Komine Hiroshi , Stappaerts Eddy A.
Published: February 2003

The CdHg excimer has received attention as a possible efficient visible laser medium. In the experiments described here, a pulsed tunable laser was used to excite the Cd(5 3P1) atomic state, which forms CdHg excimers in three-body collisions with Hg and Ar. Gain and absorption measurements were performed by using an argon-ion laser to probe several wavelengths within the 470-nm excimer emission band. Net absorption was observed at all wavelengths investigated. Acoustic and thermal disturbances which might mimic absorption have been carefully considered and it is determined that these are not important. We conclude that the CdHg excimer exhibits net absorption within its 470-nm emission band. These results cast considerable doubt on the possibility of efficient laser action in CdHg.
CO chemical laser utilizing combustor-generated reactants
Authors: Richardson R. J. , Ageno H. Y. , Lilenfeld H. V. , Menne T. J. , Smith J. A. , Wiswall C. E.
Published: February 2003

A CO chemical laser utilizing combustor-generated CS and S is described. The combustor is fueled with NF3-CH4-H2-CS2 and produces CS and S and the side products HF and N2. A common supersonic expansion mixing nozzle is used to extract the CS and S from the combustor and mix O2 and diluent (N2 or He) into the flow stream. A chain reaction between CS and O2 in the mixed flow stream, initiated by S atoms, produces vibrationally excited CO. The maximum power obtained from the laser was 700 W operating with He in a free expansion. Pressure and temperature measurements of the supersonic flow stream are compared with the results of a one-dimensional fluid-dynamics model, and the results of mass-spectrometric sampling are presented. It is concluded that the power extraction efficiency could be greatly improved by operation of the laser with either a combustor fuel–oxidizer combination that does not produce HF or an improved supersonic mixing nozzle. Nevertheless, it has been demonstrated that the output power of this device scales with mass flowrate.
Ultrasonic nonspecular reflectivity near longitudinal critical angle
Authors: Ngoc Tran D. K. , Mayer Walter G.
Published: February 2003

A numerical integration method is developed to determine the intensity profile of an ultrasonic beam reflected from a liquid-solid interface near the longitudinal critical angle. The profiles are calculated for different combinations of frequencies and beam widths with the angle of incidence being varied about the longitudinal critical angle for a water-Plexiglas interface. These calculations demonstrate the existence of nonspecular reflectivity near this particular critical angle and provide a quantitative description of its basic features. Theoretical results and experimental measurements are compared.
Ge photocapacitive MIS infrared detectors
Authors: Binari S. C. , Miller W. E. , Sher A. , Tsuo Y. H.
Published: February 2003

An undoped Ge photocapacitive detector is reported which has peak normalized detectivities D*λ at wavelengh 1.4 μm and chopping frequencies 13–103 Hz of 9×1012, 1×1012, 4×109 cm Hz1/2/W, operating respectively at temperatures 77, 195, and 295 °K. The observed temperature, spectral, and frequency response of the signal and noise are explained in terms of the measured space charge and interface state properties of the device.
Nondestructive analysis of laser fusion microsphere targets using rotational Raman spectroscopy
Authors: Drake Michael C. , Rosasco Gregory J. , Schneggenburger Roger , Nolen Robert L.
Published: February 2003

The use of rotational Raman scattering for nondestructive analysis of laser fusion microsphere targets is reported. Typical hollow-glass-microsphere sample characteristics are 100 μm in diameter, 1.0 μm in glass wall thickness, and 0.5 nl in volume, containing a mixture of hydrogen, deuterium, and tritium gases at pressures of 10–70 atm (total gas sample weights of 5 ng). Relative species mole fraction measurements for all hydrogen isotope species are determined from spectral peak height analysis of rotational Raman spectra. Accuracies of ±0.01 (mole fraction) are obtained from spectra requiring 20 min scan time. Individual species detectability limits are less than 100 picogram. Absolute partial pressure measurements (accurate to ±20%) are obtained using calibration spheres of known diameter and pressure.
The formation of waveguides and modulators in LiNbO3 by ion implantation
Authors: Destefanis G. L. , Gailliard J. P. , Ligeon E. L. , Valette S. , Farmery B. W. , Townsend P. D. , Perez A.
Published: February 2003

Ion implantation is an attractive method for writing optical circuits for use in integrated optics. In LiNbO3 it is shown that there are large changes produced in both refractive indices n0 and ne by the energy deposited in nuclear collisions between the implanted ions and the lattice. The process is insensitive to ion species and at 300 K a universal curve exists for the decrease of n0 as a function of deposited energy by nuclear collisions. Saturation changes of −6% occur at 300 °K, and larger values are noted for 77 K implants. The saturation condition is reached after the deposition of ∼1022 keV cm−3 from the ion beams. Because the indices are reduced, ion beams have been used to write low index boundaries to define waveguiding regions. By using energetic light ions (e.g., 2-MeV He+) negligible change is produced in the surface layer where the energy loss is primarily electronic and thus the low index region is formed deep within the solid. The computed and measured mode characteristics are in good agreement. The guides show complex annealing characteristics but absorption losses are negligible after annealing at 200 °C. Guiding action exists after heat treatments up to some 400 °C. The surface layers retain crystallinity and electro-optic properties; as a demonstration of this we report results from three-dimensional modulators formed by helium-ion implantation.
Characterization of grain boundaries using deep level transient spectroscopy
Authors: Spencer Michael , Stall Richard , Eastman Lester F. , Wood Colin E.C.
Published: February 2003

Using the rectifying characteristics of grain boundaries, modified deep-level transient spectroscopy (DLTS) and optical deep-level transient spectroscopy (ODLTS) sensitive techniques have been developed for identification and for quantitative estimation of electron and hole traps in the region of grain boundaries. This method has been used in conjunction with conventional surface oriented Schottky barrier DLTS and ODLTS techniques to show accumulation of native defects, enhanced segregation, and diffusion of copper from the substrate along grain boundaries during epitaxy of GaAs.