bluuebunny/crossref_metadata_2025 huggingface dataset:
The correlation dimension of rat hearts in an experimentally controlled environment
Authors: Dori Guy , Fishman Shmuel , Ben-Haim S. A.
Published: July 2002

The electric response of several isolated rat hearts in a controlled environment was studied experimentally. The correlation dimension D2 was estimated and was found to be between 4 and 6.5 when the response was nearly periodic. The variation of D2 with the concentration of calcium was studied and a general trend of its increase with increasing concentration was found. Two types of ventricular fibrillation (VF) were observed, one that corresponds to a stochastic signal where D2 is unbounded and the other to a low dimensional dynamical system with 3.5⩽D2⩽4. It was found also that for the heart the correlation dimension is only an approximate concept. A new method for the estimation of D2, that is suitable for the case when it is only approximate was introduced. A surrogate data method suitable for the analysis of nearly periodic series was implemented.
Anomalous diffusion in two-dimensional potentials with hexagonal symmetry
Authors: Panoiu N.-C.
Published: July 2002

The diffusion process in a Hamiltonian dynamical system describing the motion of a particle in a two-dimensional (2D) potential with hexagonal symmetry is studied. It is shown that, depending on the energy of the particle, various transport processes can exist: normal (Brownian) diffusion, anomalous diffusion, and ballistic transport. The relationship between these transport processes and the underlying structure of the phase space of the Hamiltonian dynamical system is investigated. The anomalous transport is studied in detail in two particular cases: in the first case, inside the chaotic sea there exist self-similar structures with fractal properties while in the second case the transport takes place in the presence of multilayered structures. It is demonstrated that structures of the second type can lead to a physical situation in which the transport becomes ballistic. Also, it is shown that for all cases in which the diffusive transport is anomalous the trajectories of the diffusing particles contain long segments of regular motion, the length of these segments being described by Lévy probability density functions. Finally, the numerical values of the parameters which describe the diffusion processes are compared with those predicted by existing theoretical models.
Modulational instability of ionization waves
Authors: Ohe Kazuyuki , Hashimoto Masashi
Published: July 2002

The modulation instability evolving from a continuously amplitude-modulated perturbation is observed in the ionization waves excited in the He positive column of a glow discharge. The degree of modulation increases with wave propagation, and an isolated pulse-like wave evolves. The so-called envelope soliton propagates toward the anode, retaining its own waveform. The measured growth rate of the modulational instability agrees well with that of the calculated one. The growth rate becomes maximum at a certain modulation frequency, as is predicted by a coupled mode theory.
Contactless tunneling to semiconductors
Authors: Sonnenfeld Richard , Moreland John , Hansma P. K. , Adams Arnold , Kvaas R.
Published: July 2002

We present current versus voltage characteristics for two metal-insulator-semiconductor systems: lead-insulator-mercury cadmium telluride and silver-insulator-silicon. A previously developed new technique allows us to suspend the metal <20 Å above the semiconductor so that the insulator is simply the space between them. The Si studies at room temperature show features suggestive of electron tunneling between the metal and semiconductor, while the HgCdTe studies in liquid helium conclusively show the Pb superconducting energy gap, demonstrating that contactless tunneling studies of semiconductor surfaces are possible.
Plane-wave diffraction by a dielectric-coated corrugated surface
Authors: Dahleh Mohammed , Nevels Robert , Tsang Leung
Published: July 2002

Electromagnetic wave scattering from a dielectric-coated sinusoidal diffraction grating is considered. The incident field is assumed to be TE (P) polarized. The analysis technique is based on the extended boundary condition method. Numerical tests show that both energy conservation and reciprocity principles are obeyed. Mode coupling efficiencies as a function of angle of incidence are presented for dielectric coated gratings consisting of: (i) a perfect conductor, (ii) silver, and (iii) aluminum. These three cases exhibit anomalous behavior at a predicted angle of incidence.
Determination of absolute light-scattering cross sections of molten salts
Authors: Raptis C.
Published: July 2002

Systematic measurements have been made of absolute light-scattering cross sections of molten alkali halides by comparing in situ the scattering intensities of the melts to that of the 992-cm−1 line of benzene which has been used as intensity standard. All measurements have been made at about 30° above the melting point and from a low-frequency shift (ν̄) limit of 4 cm−1 to the highest possible, depending on the salt. The experimental method and comparison procedures (including data corrections) are described along with calculations of the solid angle of collection of the optical system. The resulting differential cross sections for polarized scattering vary between 2.3 × 10−29 (LiCl) and 1.2 × 10−28 cm2/ion pair sr (CsI), showing, in general, the anticipated trends with ion size and polarizability, that is, the larger the ion (the higher the polarizability), the more efficient the scatterer.
dc magnetron- and diode-sputtered polycrystalline Fe and amorphous Tb(FeCo) films: Morphology and magnetic properties
Authors: Hong M. , Gyorgy E. M. , van Dover R. B. , Nakahara S. , Bacon D. D. , Gallagher P. K.
Published: July 2002

We have prepared polycrystalline Fe and amorphous Tb(FeCo) films using both dc diode- and magnetron-sputtering techniques. Magnetic properties and aging characteristics of these films were measured by a vibrating sample magnetometer and an automatic torque magnetometer. Film morphologies were studied by transmission electron microscopy. The magnetic and aging characteristics are closely correlated to the film morphology. It was also found that different sputtering methods can be tailored to produce a similar film morphology. Among the sputtering parameters, the Ar pressure during deposition at room or lower temperature strongly influences the film morphology.
Free-electron electrochromic modulation in crystalline LixWO3
Authors: Cogan S. F. , Plante T. D. , Parker M. A. , Rauh R. D.
Published: July 2002

The reflective and absorptive contributions to the optical modulation in sputter-deposited thin films of crystalline LixWO3 have been determined as a function of lithium concentration (0<x<0.5). The magnitude of the reflective response increases with increasing substrate temperature (Ts) during deposition for Ts≤466 °C. For Ts>466 °C, the reflective component decreases. The lithium concentration dependence of the absorption coefficients supports the hypothesis that absorption in crystalline LixWO3 arises from free-electron scattering.
Magnetization buckling in a prolate spheroid
Authors: Aharoni Amikam
Published: July 2002

Using a rigorous lower bound to the magnetostatic self-energy, it is proved that no buckling can take place in a ferromagnetic prolate spheroid, whose aspect ratio is less than 4.6:1. The only possible reversal modes for this aspect ratio are the coherent rotation for small radii, and the curling for larger ones. Even for more elongated spheroids, a plausible argument suggests that the buckling mode is rather unlikely, except for the limit of an infinite circular cylinder.
Raman characterization of twinning in heteroepitaxial semiconductor layers: GaAs/(Ca,Sr)F2
Authors: Landa G. , Carles R. , Renucci J. B. , Fontaine C. , Bedel E. , Muñoz-Yague A.
Published: July 2002

Detailed analysis of Raman spectra recorded from (100)-oriented GaAs layers grown by molecular-beam epitaxy on the lattice-matched insulator (Ca,Sr)F2 gives evidence of internal misorientation effects (twins). This analysis accounts for the various phenomena (doping, disorder, electron-phonon coupling) likely to modify the scattering efficiency. Calculations are performed in order to obtain quantitative evaluations of the misoriented volume amount.
Reaction chemistry at the Si (100) surface—control through active-site manipulation
Authors: Bozack M. J. , Choyke W. J. , Muehlhoff L. , Yates J. T.
Published: July 2002

Thermal desorption methods have been used to investigate the interaction of propylene (C3H6) with Si(100)-(2×1). The adsorption characteristics depend strongly on the availability of active sites at the Si(100) surface. Reactivity is enhanced by production of active sites during ion prebombardment. Adsorption of C3H6 to a disordered, ion-bombarded Si(100) surface results in nearly complete dissociation of C3H6 for ion fluences as small as 1015 Ar+ ions/cm2. In contrast, for a thermally annealed and ordered Si(100) surface, only 65% of the C3H6 dissociates. The remainder of the propylene chemically bonds to the surface as an undissociated molecule which desorbs intact at 550 K. The increase in reactivity is due to an increase in dissociative chemisorption which occurs at defect sites produced by ion bombardment. Reactivity is suppressed by capping of active sites using atomic hydrogen preadsorption. Hydrogen passivates the Si(100) surface by occupation of silicon dangling bonds, which prevents adsorption of C3H6. By controlling the number and kind of active surface sites in this way, it is possible to manipulate the reactive ability of the Si(100) surface.
Schottky-barrier behavior of a Ti-W alloy on Si(100)
Authors: Aboelfotoh M. O.
Published: July 2002

The Schottky-barrier height of a Ti-W alloy of 23 at. % Ti concentration, on both n-type and p-type Si(100), has been measured in the temperature range 170–295 K using current-voltage technique. Auger electron spectroscopy/depth-composition profiling, Rutherford backscattering spectroscopy, and glancing-angle x-ray diffraction were used to monitor the reaction between the alloy and Si. The results showed that the interdiffusion of Ti and Si dominates the interfacial reaction in this alloy-Si (100) system. Further, Ti rather than W dominated the barrier height. The n- and p-type barrier heights for both the metal and the silicide phase were found to decrease with increasing temperature with the sum equal, within the experimental error, to the Si indirect energy gap at any measured temperature. These results indicate that the change in barrier heights with temperature are mainly due to the temperature dependence of the indirect energy gap in Si. Further, the temperature coefficients of the n- and p-type barrier heights were found to be the same within the experimental error, and they were approximately equal to one-half the temperature coefficient of the Si indirect gap, consistent with the predictions of a recent model of barrier formation based on Fermi-level pinning in the center of the indirect gap.
Scanning tunneling microscopy
Authors: Hansma Paul K. , Tersoff Jerry
Published: July 2002

A scanning tunneling microscope (STM) can provide atomic-resolution images of samples in ultra-high vacuum, moderate vacuum, gases including air at atmospheric pressure, and liquids including oil, water, liquid nitrogen, and even conductive solutions. This review contains images of single-crystal metals, metal films, both elemental and compound semiconductors, superconductors, layered materials, adsorbed atoms, and even DNA. A discussion of results on lithography leads into speculations on a bright future in which STMs may not only observe, but also manipulate surfaces, right down to the atomic level.
Detection of singularities in the reversible transverse susceptibility of an uniaxial ferromagnet
Authors: Pareti L. , Turilli G.
Published: July 2002

The reversible transverse susceptibility χt of a ferromagnet having a positive uniaxial anisotropy has been measured as a function of the applied magnetic field. The presence of peaks in the χt (H) curve of a polycrystal was predicted by theoretical calculations based on the Stoner and Wohlfarth model [A. Aharoni, E. M. Frei, S. Shtrikman, and D. Treves, Bull. Res. Counc. Isr. A 6, 215 (1957)]. Unlike previous measurements, our data verify the predictions of such a theory. An explanation for the failure of previous attempts to detect the peaks in the χt (H) curve is given. It is also experimentally shown that the χt (H) measurement allows a precise determination of both coercive and anisotropy fields in a uniaxial ferromagnet provided it is made by single domain particles.
Secondary electron emission-capacitive probes for plasma potential measurements in plasmas with hot electrons
Authors: Wang En Yao , Hershkowitz N. , Diebold D. , Intrator T. , Majeski R. , Persing H. , Severn G. , Nelson B. , Wen Y. J.
Published: July 2002

It is shown that a secondary electron emission-capacitive probe can determine the plasma potential when Te ≥50 eV. The probe is wideband (1 Hz to greater than 20 MHz) and relatively simple to operate. The Phaedrus-B tandem mirror plasma where Te ∼40–60 eV and n≂5×1012 cm−3 is used to verify this technique.
Bloch lines, cross ties, and taffy in permalloy (invited)
Authors: Herman D. A. , Argyle B. E. , Petek B.
Published: July 2002

Cross ties and their attendant Bloch lines have been imaged optically for the first time in permalloy films. Kerr effect images, recorded with our laser magneto-optic microscope (LAMOM), on 50-μm square films (300, 800, and 5800 Å thick), are consistent with wall types seen in large sheet films by other methods. In the 300- and 800-Å samples 180° domain walls are cross-tie type; ties do not occur in the 5800-Å sample. We observe several effects of film-edge proximity on the 180° walls not previously reported. In the thinner films, the density of ties (and Bloch lines) increases as a wall is driven closer to an edge. Magnetization sectoring occurs about the edge side of a wall when it is forced sufficiently close. For all three thicknesses, the 180° walls bow toward the nearest edge, the bow increasing with proximity.   The 180° walls arise from the lowest-energy demagnetized state (Kittel configuration for a square) by applying a bias field which displaces the cluster knot formed by two intersecting 90° walls on the square’s diagonals. At a threshold on the order of 10 Oe, the cluster splits, forming two triplet knots connected by the 180° wall. Following bifurcation, all walls bisect the angles between adjacent domain magnetizations. This indicates that the energies of formation for the 180° wall and the extra knot stem from magnetic charge accumulated near the walls and film edges prior to the transformation. Knot displacement and bifurcation can be reversed provided no wall makes contact with an edge. Edge contact (followed by bias reduction) nucleates complex domain structures which are not simply returned to the Kittel state. When the drive is cycled, the process is reminiscent of pulling taffy.
Synthetic magnetic rare-earth Dy-Y superlattices
Authors: Hong M. , Fleming R. M. , Kwo J. , Schneemeyer L. F. , Waszczak J. V. , Mannaerts J. P. , Majkrzak C. F. , Gibbs Doon , Bohr J.
Published: July 2002

The long-range helimagnetic order in synthetic rare-earth Dy-Y superlattices has been studied. The magnetic spiral of Dy maintains its coherence in a (Dy38 Å-Y38.6 Å)80 superlattice, but not in a (Dy38Å-Y120.4 Å)80 superlattice where the intervening Y layers are 42 atomic planes thick. Furthermore, the spiral periodicity shows a markedly different temperature dependence from that of bulk Dy, including a smaller range of variation and a ‘‘lock-in’’ at low temperature.
NMR study of the change in the direction of magnetization of HoCo2
Authors: Guimarães A. P. , Alves K. M. B. , Alves N. , Gratz E.
Published: July 2002

The intermetallic compound HoCo2 is magnetically ordered and changes its directon of magnetization around 15 K, as the temperature is increased, from [110] to [100]. We report a 59Co pulsed NMR study of HoCo2 in the temperature range 4–65 K. The NMR spectra show two peaks at low temperature and one peak at high temperatures, as expected from a model whereby the magnetic equivalence of the cobalt sites is determined by the direction of magnetization. This change in the spectra can be simulated from lattice sums of the magnetic dipolar fields acting on the cobalt sites. The present results are consistent with a change of direction of magnetization from [110] to [100] through intermediate directions contained in the plane z=0.
High-energy-density pulsed ion-beam irradiation of Co/Si, Pt/Si, and Au/Si
Authors: Fastow R. , Mayer J. W.
Published: July 2002

Pulsed ion beams have been used to irradiate Pt/Si, Co/Si, and Au/Si samples. The thicknesses and compositions of the reacted layers were determined using Rutherford backscattering spectrometry. The phases in the reacted layers were identified using x-ray diffraction and transmission electron microscopy. Low-energy-density irradiation produced interfacial layers having near-eutectic compositions. High-energy-density irradiation produced interfacial layers having graded compositions (ranging between two solidus phases). The experimentally determined compositions, compositional gradients, and phases are consistent with interfacial melting at temperatures at or above the eutectic.
Spectroscopic studies of an argon plasma produced in a relativistic electron beam gas puff Z pinch
Authors: Stewart R. E. , Dietrich D. D. , Egan P. O. , Fortner R. J. , Dukart R. J.
Published: July 2002

The spectra of argon ions emitted from a plasma created by discharging a 3-TW relativistic electron beam generator through an argon gas column are reported. New lines have been classified for 2s 2pn–2pn+1 transition arrays in Ar XI–XV and energy levels have been derived for lithiumlike argon XVI. The effects of mass motion Doppler shifts on the spectra have been measured and systematic shifts of transition energies with charge state are observed in the data.
Low-loss epitaxial ZnO optical waveguides on sapphire by rf magnetron sputtering
Authors: Wu Mu-Shiang , Azuma Atsushi , Shiosaki Tadashi , Kawabata Akira
Published: July 2002

Optical waveguide loss of about 0.55 dB cm−1 has been measured on epitaxial ZnO films on sapphire by magnetron sputtering. Measurements were also made of the refractive index of those films. The experimental results are compared with theory when TE and TM guided waves propagate in the plane at an arbitrary angle with respect to the c axis where the c axis is lying in the plane of the film. Surface acoustic wave (SAW) properties were also measured for SAW propagating along the c axis of ZnO film on the (011̄2)-oriented Al2O3 substrate.
Heavy-ion excitation of rare-gas excimers
Authors: Ulrich A. , Körner H. J. , Krötz W. , Ribitzki G. , Murnick D. E. , Matthias E. , Kienle P. , Hoffmann D. H. H.
Published: July 2002

Beams of high-energy heavy ions (Ar and U) from the UNILAC accelerator have been used to excite rare gases at pressures near 1 bar. The dominant spectroscopic feature observed in Ar, Kr, and Xe gases was molecular excimer emission at the second excimer continuum at 130, 150, and 170 nm, respectively. The excimer radiation was studied as a function of time (with respect to the excitation pulse), ion-beam current, pressure, and excitation density. The efficiency of excimer production from heavy-ion-beam energy was found to be several percent. Details of spectral shape, especially the ratio of first-to-second continuum emission, were found to depend on pressure and exciting beam type.
Oblique grain boundaries: Analysis of light and electron beam induced current profiles in silicon
Authors: Mittiga A. , Capizzi M. , Coluzza C. , Frova A. , Parisi V. , Cavalcoli D. , Moro L. , Prudenziati M.
Published: July 2002

Asymmetrical light and electron beam induced current profiles have been previously attributed to a difference of the diffusion length on the two sides of the grain boundary. We show that this feature is instead due to the grain boundary not being perpendicular to the surface. In this geometry, the equations describing the minority-carrier diffusion are not solvable by analytical procedures. A method for their numerical solution is hereby introduced, fast enough to allow the use of minimization procedures. A good agreement has been found between fitted values of the grain boundary inclination and those directly measured.
High-energy electron distribution in electron beam excited Ar/Kr and Ne/Xe mixtures
Authors: Kannari F. , Kimura W. D.
Published: July 2002

The electron energy distribution in electron beam (e beam) excited Ar/Kr and Ne/Xe gas mixtures is examined in detail. The binary rare-gas mixtures are similar to those used in excimer lasers. Cooling processes for the secondary electrons generated in the gas mixture plasma by the e beam are calculated using a reduced Boltzmann equation in which elastic and electron-electron collisions for electron energy distributions above the first excitation threshold of the rare gas are ignored. During the calculations for the Ar/Kr and Ne/Xe mixtures, all electron-related reactions and the interaction between the two different rare gases in the mixture are simultaneously considered. The high-energy secondary electrons produce a steady-state distribution within a very short time; however, it is found that the distribution is not Maxwellian. W values [eV/electron-ion pair] and yields of rare-gas excited states calculated from the steady-state high-energy electron distribution show a dependence on the mixture composition, especially for mixtures with low concentrations of the minor rare gas. This implies that the practice in excimer kinetics models of using the W values determined from pure rare gases is not entirely accurate.
On the magnetic structure of noncollinear γ-Fe70Mn30
Authors: Takahashi T. , Ukai T. , Mori N.
Published: July 2002

The approximate d bands for a noncollinear γ-FeMn alloy are formulated by using Deegan’s method and the formulas of Slater and Koster, and by taking into account the exchange interaction terms to produce the multi-spin-density-wave state. The electronic energies for the noncollinear γ-Fe70Mn30 alloy with the spin directions parallel to [100], [110], and [111] are calculated and the anisotropy energy is determined. It is seen that the state with the spin direction [111] becomes the lowest and the multi-spin-density-wave state is realized in it. For other noncollinear γ-FeMn alloys some discussions are given on the magnetic structure for them. Additionally, the anisotropy energies for noncollinear and collinear γ-FeMn alloys are discussed in detail.
Analytical and numerical modeling of amorphous silicon p-i-n solar cells
Authors: Misiakos K. , Lindholm F. A.
Published: July 2002

Analytical and equivalent-circuit models based on numerical solutions for a-Si:H solar cells are presented. The dependencies among such variables as recombination rate and electrical field on terminal and optical excitation are discussed. Based on our physical interpretation of the numerical solutions, we propose an equivalent-circuit model which separates the currents into photocollected and back injected components. This model clarifies the concept of the limiting carrier and points out that the limiting carrier is the carrier with the least photocollected current. Analytical expressions for uniformly and strongly absorbed light are derived.
Mass loss of exploding foils
Authors: Pereira N. R. , Terry R. E.
Published: July 2002

A thin asymmetrically driven exploding foil loses mass when the acceleration of the bulk of the foils exceeds the acceleration of the foil’s back. A simplified but exactly solvable model clarifies the mass erosion process.
Zn diffusion in doped InP: Interstitial charge state and apparent activation energy
Authors: Kazmierski C.
Published: July 2002

Use of models without doping effects on the interstitial-substitutional interchange can lead to the identification of an apparently larger charge state of the interstitial and will increase the apparent activation energy of diffusion. This increase is approximately equivalent to the zinc-solubility activation energy for substrate doping near the substitutional-zinc concentration at the surface.
Optical investigation of organometallic vapor phase epitaxially grown AlxGa1−xP
Authors: Bour D. P. , Shealy J. R. , Ksendzov A. , Pollak Fred
Published: July 2002

We have grown films of AlxGa1−xP by organometallic vapor phase epitaxy with composition x≤0.8. The electronic and vibrational properties of the alloys were investigated using electrolyte electroreflectance and Raman spectroscopy, respectively. The compositional dependence of the phonon frequencies and electronic transition energies E0 and E1 were evaluated from the measured spectra. There are significant discrepancies between the vibrational frequencies obtained in this experiment and some previous results. The dependence of E0 and E1 on composition is in good agreement with a previous experiment (x≤0.58). However, because of our greater composition range, we have been able to evaluate the nonlinear composition dependence (bowing parameter) for these two transitions.
Deuterium magnetic resonance and permeability in porous media
Authors: Thompson A. H. , Sinton S. W. , Huff S. L. , Katz A. J. , Raschke R. A. , Gist G. A.
Published: July 2002

Deuterium nuclear magnetic resonance relaxation studies were performed on sandstones, carbonates, and synthetic porous samples. The magnetization decay in the rotating frame T1ρ is a stretched exponential in rock samples.The relaxation time in porous media is related to the absolute permeability by the relation k=C(T1ρ)2φ2. We show that T1ρ is proportional to the width of the pore size distribution and the permeability, and is proportional to the water saturation in partially saturated rock. These results provide new methods for estimating absolute permeability and saturation.
Free-surface velocity measurement of shock-compressed alumina powder compact using a Fabry–Perot interferometer
Authors: Taniguchi T. , Yasuo H. , Kondo K. , Sawaoka A. B.
Published: July 2002

A Fabry–Perot interferometer system was used to measure the free-surface velocity of α-alumina powder compact. In situ pressure profile measurements using a pair of manganin gauges were also carried out to clarify the compaction process during compression and stress release. The Fabry–Perot system indicates that the reflectivity of the free surface of the powder material does not significantly change during the stress release process. An observed feature of the powder’s stress release curve as determined by the manganin gauge suggests the existence of the residual voids in the shock compressed powder matrix even in the high shock pressure regime.
Bounds on the thermoelastic properties of suspensions of spheres
Authors: Torquato S.
Published: July 2002

Three-point upper and lower bounds on the effective thermal expansion coefficient and specific heats of statistically isotropic suspensions of mutually impenetrable spheres are computed for the first time. The three-point bounds depend upon the microstructure via a three-point spatial correlation function of the medium. Both equisized and multisized spheres are considered, and hence the effect of polydispersivity in sphere size on the thermoelastic properties is determined. For reasons of mathematical analogy, the results of this study for the thermal expansion coefficient translate immediately into equivalent results for the hygroscopic expansion coefficient.
Electronic structure and magnetic properties of Fe-rich ternary compounds: YFe10V2 and YFe10Cr2
Authors: Jaswal S. S. , Ren Y. G. , Sellmyer D. J.
Published: July 2002

These compounds are prototypes of the Fe-rich ternary systems of ThMn12 structure which are of considerable current interest as permanent magnet materials. The electronic structure of YFe10V2 and YFe10Cr2 have been studied with photoemission and spin-polarized calculations. The Fe d states dominate the calculated density of states (DOS) near the Fermi energy and there is a good correspondence between the DOS and the experimental spectra. The calculated magnetization is in very good agreement with the experimental data. The calculations give a magnetic moment of ∼1 μB at the V or Cr site antiferromagnetically coupled to the Fe moments. This leads to a significant reduction in the average moment per Fe atom in these systems. The charge transfers are, in general, small and are mostly from V or Cr to Y atoms. These charges are used to show that the point-charge model alone cannot explain the crystal-field data.
Investigation of the expanding plasma of an anodic vacuum arc
Authors: Katsch H.-M. , Mausbach M. , Müller K. G.
Published: July 2002

An aluminum plasma is produced by an anodic vacuum arc (25 A, 17 V) with a consumable anode. The plasma expands from the anode to the walls and is investigated by Langmuir probes, a quadrupole mass spectrometer, a retarding field ion energy analyzer, and a quartz-crystal oscillator for mass flow detection. The electron density ranges within 2×1015–3×1017 m−3 and the electron temperature within 0.4–0.9 eV. At a target, ion fluxes of 1.5×1019–8×1020 m−2 s−1 and total particle fluxes of 3×1020–4×1021 m−2 s−1 are measured. The ions are accelerated in the expanding plasma towards the target and gain a few eV. By a simple collisionless transport model of the expanding plasma, the plasma potential and floating potential are calculated and compared with experimental data.
Zn diffusion-enhanced disordering and ordering of InGaAsP/InP quantum well structures
Authors: van Gurp G. J. , van de Wijgert W. M. , Fontijn G. M. , Thijs P. J. A.
Published: July 2002

The effect of zinc diffusion on InGaAsP/InP single and multiple quantum well structures was studied by secondary ion mass spectrometry (sims), Auger electron spectroscopy (AES), capacitance-voltage measurements, photoluminescence, and x-ray diffraction. Significant interdiffusion of In and Ga is found. The structures are stale against annealing without the presence of zinc. Interdiffusion of As and P is negligible. In a multiple quantum well Zn diffusion at 500 °C causes In and Ga intermixing: The AES profiles have become flat. At higher diffusion temperatures an ordering is found such that now the Ga concentration is at a maximum in the original InP layers. This can be explained by minimization of the free energy, which is balanced by an increasse in mismatch strain energy. Photoluminescence shows the interdiffusion starts at temperatures above 420 °C. By the Zn diffusion the lattice parameter values of the InGaAsP and InP layers are changed and the average value is decreased, as was shown by x-ray diffraction on a multiple quantum well structure. This is substantiated by results of x-ray rocking curves.
Picosecond spectral dynamics of gain-switched quantum-well lasers and its dependence on quantum-well structures
Authors: Sogawa T. , Arakawa Y.
Published: July 2002

Time-resolved spectra of gain-switched GaAs/AlGaAs quantum-well (QW) lasers are measured by a streak camera with a monochromator to investigate effects of QW structures on picosecond lasing dynamics. The result shows that both pulse forms and spectral dynamics strongly depend on the number of the QWs: The pulse duration and spectral width are both broadened when the number of QWs is smaller. This dependence mainly results from the difference in the gain profile at the initial stage of the pulse formation due to the difference in the carrier concentration per well (cm−2). In addition, the overflow effect of carriers outside of QWs also plays a significant role when the number of QWs is smaller. Theoretical discussions considering dynamic behavior of the gain and the capturing effect of carriers into QWs explain the experimental results well.
Amorphization by solid-state reaction of crystalline aluminum and platinum multilayers prepared by cold rolling
Authors: Bordeaux F. , Yavari A. R.
Published: July 2002

Amorphous Al2Pt has been synthesized by solid-state reaction (SSR) of composite metal multilayers produced by mechanical deformation of elemental metal ribbons. The amorphization reaction takes place during the mechanical deformation near ambient temperature and is also observed for samples picked up during deformation and annealed at appropriate temperatures. The resulting material was investigated by means of differential scanning calorimetry, x-ray diffraction, and scanning electron microscopy. The activation energy that controls amorphization by SSR is evaluated for isochronal and isothermal annealing and structural characteristics of the Al2Pt amorphous phase are given.
High-quality p-type HgCdTe grown by molecular beam epitaxy
Authors: Wijewarnasuriya P. S. , Boukerche M. , Faurie J. P.
Published: July 2002

The galvanomagnetic transport in (111)B HgCdTe p-type layers, grown by molecular beam epitaxy, was studied as a function of temperature and magnetic field strength. Experimental data on the Hall coefficient and conductivity tensor versus magnetic field have been analyzed with the assumption of three charge carriers involved in the conduction mechanism: one carrier coming from the conduction band and the other two from the complex nature of the valence band. Indeed, two kinds of positive charge carriers with completely different mobilities in the extrinsic region are seen. The extracted parameters are in very good agreement with the intrinsic concentration over a wide temperature range.
Microwave effective linewidth in thin metal films
Authors: Moosmüller H. , McKinstry K. D. , Patton C. E.
Published: July 2002

An effective linewidth technique for characterizing microwave losses in thin ferromagnetic metal films, similar to the technique for ferrites, has been developed. The extension to metal films is nontrivial. A numerical solution of the electromagnetic boundary value problem for the fields inside the film must be used to evaluate the on- and off-resonance losses, and these calculated losses must be directly related to changes in the microwave cavity Q on an absolute scale. Specific measurements and analyses were done for polycrystalline permalloy on glass. Measurements at 10 GHz yield a change in 1/Q with field which is in accord with theory and can be modeled off resonance to obtain intrinsic losses. The analysis yielded an intrinsic Landau–Lifshitz damping parameter of 5.5×107 rad/s for permalloy. This corresponds to a half-power effective linewidth of 27 Oe, which is comparable to the best published 10 GHz linewidth for single-crystal iron films.
High-concentration boron diffusion in silicon: Simulation of the precipitation phenomena
Authors: Solmi S. , Landi E. , Baruffaldi F.
Published: July 2002

An extensive investigation on the diffusion of boron implanted at high concentration in preamorphized silicon has been carried out for rapid thermal annealing and conventional furnace annealing. The rapid process of epitaxial regrowth of the amorphous layer brings B atoms into substitutional positions, and thus electrically active, up to a concentration threshold of about 3.5×1020 cm−3. This value is nearly independent of the annealing temperature and of the implanted dose. Since the concentration of dopant in solution is higher than the solubility value, precipitation phenomena occur in concomitance to diffusion during the annealing. The kinetics of precipitation has been investigated at 800, 900, and 1000 °C with isothermal treatments ranging between 10 s and 171 h. A simulation program taking into account precipitation phenomena has been developed modifying the suprem iii code. The density of nuclei of the new phase has been evaluated on the base of the models of classic nucleation theory, while the rate of precipitation growth has been determined following Ham’s theory. Excellent agreement with experimental data has been obtained in a wide range of experimental conditions. The model represents a significative improvement of the simulation of high-concentration B diffusion in Si; the more commonly used process simulations are inadequate to correctly foresee the dopant redistribution in supersaturated conditions.
Diffusion of hydrogen in post-plasma-hydrogenated amorphous silicon film
Authors: Nakamura Minoru , Misawa Yutaka
Published: July 2002

In order to elucidate the diffusion mechanism of hydrogen in post-plasma-hydrogenation of amorphous silicon (a-Si) film prepared by chemical vapor deposition (CVD), the change in the hydrogen depth profiles with plasma exposure time and with successive hydrogenation of hydrogen isotopes were measured by secondary ion mass spectrometry and infrared absorption. The post-hydrogenation process of the CVD a-Si film is explained by a model composed of fast diffusion (small activation energy) of atomic hydrogen through weakly bound sites such as interstitials, its capture by reactive sites such as weak SiSi bonds and dangling bonds, and an exchange between weakly bound and bonded hydrogens.
Effect of substrate temperature on recrystallization of plasma chemical vapor deposition amorphous silicon films
Authors: Nakazawa Kenji , Tanaka Keiji
Published: July 2002

The effect of substrate temperature on the recrystallization of plasma chemical vapor deposition amorphous silicon films is investigated. The grain size of polycrystalline silicon films recrystallized at 600 °C increases as the substrate temperature decreases. The enlargement in the grain size is attributed to the decrease in the nucleation rate. The nucleation rate is suppressed by an increase in structural disorder of the Si network. Electrical properties of recrystallized films are improved by the increase in the grain size.
Observation of recombination center-assisted tunneling current in Al(Cu)-penetrated PtSi Schottky barrier diodes
Authors: Bindal A. , Wachnik R. , Ma W.
Published: July 2002

The electrical transport characteristics of Al(Cu)-penetrated PtSi Schottky barrier diodes were investigated. It has been observed for the first time that diodes with Al(Cu) penetration show a multistep recombination center-assisted tunneling current in the forward direction instead of a thermionic emission current over the Al(Cu) alloy barrier. According to this electron transport mechanism an electron tunnels through a series of closely packed local recombination centers in the depletion region to traverse from the semiconductor to the metal side. When the penetrated diodes are reverse biased, Zener tunneling becomes the dominant conduction mechanism in the reverse direction. Al(Cu) penetration in PtSi Schottky barrier diodes produces high leakage currents and unpredictable turn-on voltage characteristics which result in various design problems in logic circuits.
Magnetron reactive ion etching of GaAs: Residual damage study
Authors: McLane G. F. , Meyyappan M. , Cole M. W. , Wrenn C.
Published: July 2002

Residual damage of GaAs samples etched in a magnetron reactive ion etcher has been studied. Aligned yields from ion channeling measurements show that the amount of dechanneling in the etched samples is virtually identical to that of an unetched control sample, which indicates low concentration of disorder. Transmission electron microscopy reveals that the surface morphology of etched samples is extremely good with defects in the form of small dislocation loops of 20–40 Å diam. It is shown that magnetron reactive ion etching is capable of yielding high etch rates with little surface damage.
Separation of perpendicular anisotropy components in dc-magnetron sputtered TbFe amorphous films
Authors: Cheng Shih-Cheng N. , Kryder Mark H.
Published: July 2002

Different anisotropy components originating from various mechanisms in dc-magnetron sputtered Tb39Fe70 films have been identified. The inverse magnetostrictive anisotropy component was determined by comparing the anisotropy of Tb30Fe70 films when they were removed from their substrates and when they were still attached to their substrates. The single-ion anisotropy component was then derived by subtracting the pair-ordering anisotropy, which was determined as the anisotropy of Gd21Fe79 films which had been removed from their substrates, from the anisotropy of Tb30Fe70 films which had been removed from their substrates. By this method, single-ion and inverse magnetostrictive anisotropies were found to contribute 30–60% and 30–65%, depending on argon sputtering pressure, of the total anisotropy, respectively. Pair-ordering was responsible for less than 10% of the total anisotropy in dc-magnetron sputtered Tb30Fe70 films. Thermal stability of each anisotropy component was studied by annealing films when still attached to their substrates. The anisotropies of films, which had been annealed and removed from their substrates were then compared with those of films, which had also been removed from their substrates but without annealing. Effects of Ar sputtering pressure on the thermal stability of anisotropy were also investigated. Better thermal stability was found in single-ion and pair-ordering anisotropy than in magnetostrictive anisotropy. Films deposited at lower argon pressures show better thermal stability of single-ion and pair-ordering anisotropy than those deposited at higher argon sputtering pressures.
Constant rate of change of magnetization hysteresis loop tracer
Authors: Cammarano R. , Street R. , McCormick P. G. , Evans M. E.
Published: July 2002

An experimental procedure has been developed by which magnetization curves may be traversed at a constant rate of change of magnetic polarization, J̇. The new technique involves, in an iterative procedure, the use of a combination of closed- and open-loop digital strategies to control the magnetic field so that J̇ remains constant over the majority of the hysteresis loop. As an application of the effectiveness of the technique, results obtained using Alnico permanent magnet materials are presented. The limitations of this method are reviewed in relation to material properties and the type of measurement system utilized. The consequences of using a digital control system and digital measurement techniques in the characterization of magnetic materials are discussed.
Micromagnetic studies of coherent rotation with quartic crystalline anisotropy
Authors: Chang Ching-Ray
Published: July 2002

The nucleation fields under coherent rotation for uniaxial ferromagnets are rigorously determined including the second anisotropy constant K2. Theoretical studies cover the whole range of the relationships between K1 and K2. We show that the reversal processes can be classified into eight types depending on the parameters characterizing the magnetic materials. The results show that the value of K2 affects both the hysteresis loop and nucleation field significantly. The nucleation field along the c-axis is not always equal to 2K1/Ms. For certain values of second anisotropy, the easy axes may be oblique to the c-axis. When the ratio of K2 and K1 is large, the easy cone or hard cone will form at a certain oblique angle. The effects of K2 on the saturation field of hard axis loops have also been investigated. It is suggested that the values of K1 and K2 can be determined independently from the slope and saturation field of hard axis loops.
Effects of energy gap and band structure on free-carrier nonlinear susceptibilities in semiconductors
Authors: Meyer J. R. , Bartoli F. J. , Youngdale E. R. , Hoffman C. A.
Published: July 2002

Using dispersion relations from the Kane band model, we obtain limiting forms for the third-order nonlinear susceptibilities due to nonparabolicity, thermal-carrier generation, and nonequilibrium optical-carrier generation. We show that whereas χ(3)’s for all three processes increase with decreasing energy gap, there is no further benefit once Eg becomes smaller than either the Fermi or thermal energies. In fact, simultaneous optimization of both the magnitude of χ(3) and the saturation properties favors materials with a large direct gap and large effective mass, coupled with a smaller thermal gap which may be indirect in either real or momentum space.
Thermal conversion of n-type GaAs:Si to p type in excess arsenic vapor
Authors: Ky Nguyen Hong , Pavesi L. , Araújo D. , Ganière J. D. , Reinhart F. K.
Published: July 2002

Annealing in excess arsenic vapor at 650 °C introduces thermal conversion of n-type Si-doped GaAs samples (n = 1.3 × 1018 cm−3) into p type. The observations are made by current-voltage and electron-beam induced current measurements. The donor concentration on the n side near the junction decreases after annealing. We present a comparison between the photoluminescence spectra of samples annealed under different conditions and an analysis of depth profile of the photoluminescence spectra. Our results underline the important role of gallium vacancies and gallium vacancy-silicon donor complex in the thermal conversion.
Unpinned GaAs Schottky barriers with an epitaxial silicon layer
Authors: Costa J. C. , Miller T. J. , Williamson F. , Nathan M. I.
Published: July 2002

We present experimental results of Al/n- and Al/p-type GaAs Schottky barrier structures grown in situ by molecular-beam epitaxy with thin Si epitaxial interfacial layers. The barrier heights are measured by the I-V, thermal activation, C-V, and photoresponse methods. Barrier heights in the range of 0.3<φbN<1.04 eV for n-type GaAs and 0.28 < φbP<1.01 eV for p-type GaAs were obtained for Si layer thicknesses between 6 and 100 Å. Annealing studies conducted on the samples indicate that the structures are thermally stable to temperatures up to 450 °C. These results imply that the GaAs surface Fermi level at the Si/GaAs interface is unpinned from its customary near-midgap value. A model which involves the energy-band discontinuities ΔEC and ΔEV between GaAs and Si, the thickness, and the doping of the Si layer is suggested to account for the different barrier-height values obtained.
Optical properties of InSb films deposited on sapphire substrates by rf sputtering
Authors: Miyazaki Takayuki , Adachi Sadao
Published: July 2002

We have deposited InSb films by rf sputtering on sapphire substrates of various surface orientations [(0001), (112̄0), (011̄2), and (011̄0)]. The epitaxial InSb(111) films are grown only on (0001) sapphire substrates at substrate temperatures 280–320 °C, while the films deposited on (112̄0), (011̄2), and (011̄0) sapphires show that they have polycrystalline structures even when they were deposited at high substrate temperatures. Optical properties of these films are investigated by using spectroscopic ellipsometry. A linear regression analysis and a Bruggeman effective-medium approximation reveal that the epitaxial film has a few void networks in the film. Polycrystalline InSb films, on the other hand, contain a large number of void networks deep in the film medium. Both epitaxial and polycrystalline films have rough-surface overlayers of a few tens of Å.
A model for the degradation of Ga(Al)As single-quantum-well lasers
Authors: Martins R. B. , Henoc P. , Akamatsu B. , Palmier J. F.
Published: July 2002

The degradation during cw operation or under electron beam bombardment of the graded index separate-confining heterostructure laser devices grown on Si and on GaAs substrates was investigated. The induced current and the cathodoluminescence modes of a scanning electron microscope were used to observe the cleaved face of these devices as a function of the stage of degradation. Our findings strongly suggest that the degradation starts owing to a mechanism of donor annihilation and complex formation within the space-charge region of the device. Two different methods allowing the evaluation of the donor concentration within the depletion zone were developed. One method is based on the measurement of the direct bias necessary to recover the initial microscopic characteristics of a damaged device. The other one relies on a numerical calculation of the partition of nonequilibrium carriers which takes into account the detailed structure of the device. This calculation is based on a three-dimensional analytical function describing the energy losses of the primary electrons.