bluuebunny/crossref_metadata_2025 huggingface dataset:
Comment on “The α-relaxation process in simple glass forming liquid m-toluidine. II. The temperature dependence of the mechanical response” [J. Chem. Phys. 114, 7124 (2001)]
Authors: Dreyfus C. , Gupta R. , Bonello B. , Bousquet C. , Taschin A. , Ricci M. , Pratesi G.
Published: July 2002

In a recent paper, Cutroni and Mandacini [J. Chem. Phys. 114, 7124 (2001)] measured sound velocities and absorption coefficients in m-toluidine by an ultrasonic technique. They reported velocities that differ from previous published data and attributed some of these discrepancies to a possible difference between the local temperature which actually prevails at the place where the velocity is determined in these previous measurements, and the real temperature of the liquid. We compare their results with other data and discuss their assumption.
Phase-only modulation by nanosized polymer-dispersed liquid crystals
Authors: Lucchetta D. E. , Karapinar R. , Manni A. , Simoni F.
Published: July 2002

We report the preparation methods and electro-optical characterization of polymer-dispersed liquid crystals with nanosized liquid crystal domains obtained by using a multifunctional monomer in a prepolymer mixture that is suitable for a fast photopolymerization process. The electric-field-induced optical phase shift has been measured using a Mach–Zender interferometer, getting values up to π/2 with an applied voltage of about 20 V/μm with no dependence on the light polarization. The high transmittance of the samples make them suitable for photonic devices and telecom applications.
High-frequency dispersion of ultrasonic velocity and attenuation of single-crystal 0.72 Pb(Mg1/3Nb2/3)O3–0.28 PbTiO3 with engineered domain structures
Authors: Jiang Wenhua , Cao Wenwu , Han Pengdi
Published: July 2002

Using ultrasonic spectroscopy, the frequency dispersions of ultrasonic velocity and attenuation were measured for single crystal 0.72 Pb(Mg1/3Nb2/3)−0.28 PbTiO3 (PMN−28%PT) with engineered domain structures in the frequency range of 50–110 MHz. We found that the velocity dispersion and attenuation are very small for the longitudinal wave propagating along [001] of the pseudotetragonal state. Our results imply that the developed domain-engineered PMN-PT single crystals, which have extremely large d33 and k33, have great potential for high-frequency applications.
Measurement of barrier heights in high permittivity gate dielectric films
Authors: Zafar S. , Cartier E. , Gusev E. P.
Published: July 2002

Based on theoretical studies of tunneling current phenomenon, a method for measuring barrier heights in metal–oxide–semiconductor structures is illustrated. Using this method, barrier heights associated with the Al2O3 gate dielectric films are investigated. Also, the main conduction mechanism in Al2O3 gate dielectric films is identified to be tunneling.
Density-functional theory studies of acetone and propanal hydrogenation on Pt(111)
Authors: Alcalá R. , Greeley J. , Mavrikakis M. , Dumesic J. A.
Published: July 2002

Self-consistent periodic slab calculations based on gradient-corrected density-functional theory (DFT-GGA) were conducted to probe the potential-energy diagram for the hydrogenation of propanal and acetone on Pt(111). Calculations for molecularly adsorbed species indicate that acetone and propanal are both weakly bound to the surface through oxygen (i.e., energy changes of adsorption near −20 kJ/mol). The activation energy barriers are calculated to be ∼60 and 40 kJ/mol for the addition of an adsorbed hydrogen atom to adsorbed acetone and propanal, leading to adsorbed isopropoxy and n-propoxy species, respectively. The subsequent hydrogenation steps to form adsorbed alcohol species have activation barriers near 15 kJ/mol. These results would suggest that the rate of propanal hydrogenation over Pt should be faster compared to acetone hydrogenation, in contrast to the behavior observed experimentally [G.M.R. van Druten and V. Ponec, Applied Catalysis A: General 191, 153 (2000)]. The origin for the experimentally observed slower rate of propanal hydrogenation over Pt appears to be related to the formation of strongly adsorbed spectator species formed by removal of the α–H atom from adsorbed propanal. The calculated energy change for cleavage of this C–H bond, leading to adsorbed propionyl and adsorbed hydrogen atom, is exothermic by 76 kJ/mol.
Giant electrostriction and stretched exponential electromechanical relaxation in 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 crystals
Authors: Bokov A. A. , Ye Z.-G.
Published: July 2002

Unipolar electric field-induced strain was studied in the [001]cub-oriented 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 crystals with the composition close to the morphotropic phase boundary, which are known to show enhanced piezoelectric properties. Polarized-light microscopy was used to study the domain structure. In the samples containing the mixture of rhombohedral and tetragonal ferroelectric phases, a giant electrostrictive effect was found to exist after poling, in addition to the piezoelectric effect. The a domains of the tetragonal phase with polarization perpendicular to the poling field were observed. Their existence in the poled crystals is due to the elastic interactions with the rhombohedral domains. The electromechanical response of the tetragonal a domains, which should be purely electrostrictive due to the crystal symmetry, is suggested to provide the intrinsic contribution to the observed electrostriction. The extrinsic contribution to electrostriction is explained by the 90° reorientation of the a domains into the c domain state. Upon application of the driving field, the onset of extrinsic electromechanical response was found to follow the stretched exponential relaxation pattern.
Optical properties of SrSe thin films grown by molecular beam epitaxy
Authors: Jiang L. F. , Shen W. Z. , Wu H. Z.
Published: July 2002

Absorption, reflection and Raman scattering measurements have been carried out for the optical properties of a SrSe thin film grown by molecular beam epitaxy on a BaF2 (111) substrate. The film quality and lattice constant have been assessed by x-ray diffraction, where the good quality of the SrSe thin film is evident in a full width at half maximum value of 310 arcsec. Temperature-dependent indirect band gaps are obtained with the aid of temperature-dependent absorption measurements from 16 to 300 K on the SrSe thin film. By fitting the far-infrared reflection spectra, transverse optical phonon reflection bands in the binary SrSe thin film have been assigned, which are further verified by temperature-dependent Raman scattering measurements.
Rapid biaxial texture development during nucleation of MgO thin films during ion beam-assisted deposition
Authors: Brewer Rhett T. , Atwater Harry A.
Published: July 2002

We propose a mechanism for the nucleation of highly aligned biaxially textured MgO on amorphous Si3N4 during ion beam-assisted deposition. Using transmission electron microscopy, reflection high-energy electron diffraction, energy dispersive x-ray analysis, and ellipsometery, we have observed that highly aligned biaxially textured grains emerge from a “diffraction-amorphous” film when the film thickens from 3.5 to 4.5 nm. Transmission electron microscopy dark-field images also show the onset of rapid grain growth during this same film thickness interval. These results suggest biaxial texturing through aligned solid phase crystallization.
Electronic structure and spectroscopic properties of electronic states of ScC3 and ScC3−
Authors: Roszak S. , Majumdar D. , Balasubramanian K.
Published: July 2002

Theoretical studies on the electronic and thermodynamic properties of several electronic states are presented for the ScC3 molecule and the ScC3− anion employing state-of-the-art techniques that included up to 13 million configurations. The ground and the low-lying electronic states of these two species have been predicted to have C2v ring structures. On the basis of our computed results on the low-lying excited electronic states, we have suggested assignment of the observed anion photodetachment spectra of ScC3−. Thermodynamic properties of reactions involving ScC3 are corrected using the computed gas-phase properties of the molecule and the partition functions. Thermodynamic functions of ScC3− are also determined by fitting the available experimental data with thermodynamic energy cycles. The nature of bonding in the neutral and the anionic carbides has been considered.
Scaling laws for hydrodynamically similar implosions with heat conduction
Authors: Murakami Masakatsu , Iida Shigeki
Published: July 2002

Scaling laws for hydrodynamically similar implosions are derived by applying Lie group analysis to the set of partial differential equations for the hydrodynamic system. Physically this implies that any fluid system belonging to a common similarity group evolves quite in the same manner including hydrodynamic instabilities. The scalings strongly depend on the description of the energy transport, i.e., whether the fluid system is heat conductive or adiabatic. Under a fully specified group transformation the hydrodynamic similarity can still be preserved even when the system is cooperated with such other energy sources as classical laser absorption, hot electrons, local alpha heating, and bremsstrahlung loss. The results are expected to give the basis of target design and diagnostics for scaled high gain experiments in the future.
The mobility and diffusivity of a knotted polymer: Topological deformation effect
Authors: Sheng Yu-Jane , Tsao Heng-Kwong
Published: July 2002

The effect of topological deformation on the mobility and diffusivity of a polymer chain in a good solvent is investigated by off-lattice dynamic Monte Carlo simulations. The topological deformation of the polymer is expressed through the knotted structure. The Nernst–Einstein relation is obeyed and thus the diffusivity is proportional to the mobility. As the crossing number of the knotted polymer, which characterizes the extent of the deformation, is increased, the mobility declines. A scaling analysis confirmed by simulations indicates that the deformation yields an extra contribution to the resistance ζN associated with a linear chain, αN−3/5p8/5, where N is the chain length and p is the length-to-diameter ratio associated with a maximum inflated knot. The mobility of the polymer chain is further reduced due to the confinement in a cylindrical tube. Nevertheless, the confinement only slightly increases the friction coefficients ζ and the internal friction constant α. Our numerical results for the Rouse model are qualitatively different from those anticipated on the basis of scaling arguments for the Zimm model.
Few-cycle mid-infrared pulse generation, characterization, and coherent propagation in optically dense media
Authors: Gruetzmacher Julie A. , Scherer Norbert F.
Published: July 2002

The generation of four- to five-cycle mid-infrared pulses using a single-stage potassium niobate optical parametric amplifier (OPA) is demonstrated. The OPA is pumped by a gain-switched Ti:Sapphire regenerative amplifier and is seeded with the near-infrared portion of a white light continuum. The OPA is continuously tunable from 2700 to 4700 nm, and maintains sub-65 fs pulses that are fully characterized using cross-correlation frequency-resolved optical gating (XFROG). These are the shortest near-transform-limited pulses reported over this large infrared spectral range. This apparatus is used to measure ultrafast vibrational responses, specifically, pulse profiles modified by the free-induction decay (FID) of O–H oscillators. Both the intensity and instantaneous phase of these pulses are determined after traversing samples of isotopically diluted water (HDO in D2O) using XFROG, representing a new application of the XFROG technique to the study of (dipolar) molecular responses. Pronounced beating of the trailing edges of FID-modified pulses is observed even below optical densities of one, and the details of these features are found to depend on the chirp of the field used to generate the FID. These results indicate that discretion should be used in the selection of sample conditions for nonlinear infrared spectroscopic measurements.
Ultrathin zirconia/SiO2 dielectric stacks grown by ultraviolet–ozone oxidation
Authors: Ramanathan Shriram , McIntyre Paul C.
Published: July 2002

High-dielectric-constant materials such as zirconia are currently being investigated to replace SiO2 as the gate dielectric in future complementary metal–oxide–semiconductor devices. In this letter, we present the electrical properties of ultrathin zirconia/SiO2 dielectric stacks in which both layers are grown in situ at room temperature by the ultraviolet–ozone oxidation technique. A capacitance-based equivalent oxide thickness of 15 Å (without accounting for quantum-mechanical corrections), leakage current of 1.8×10−4 A/cm2 at 1 V from flatband, and negligible hysteresis has been obtained from these films. It is shown that in order to grow dielectric stacks of high electrical quality, it is important to understand the oxidation kinetics of these films.
A beam-maser instability: Direct amplification of radiation
Authors: Chen Y. P. , Zhou G. C. , Yoon Peter H. , Wu C. S.
Published: July 2002

The cyclotron maser instability has been applied in the past to laboratory microwave generation devices, and radiation from planetary magnetospheres, such as Earth’s kilometric radiation and Jovian decametric radiation. Recently, the same concept was put forth to explain solar coronal radio bursts. In particular, it was suggested that the ordinary (O) mode propagating in antiparallel direction with respect to the electron beam may be important. For this reason, this article revisits the maser instability theory with a particular emphasis on understanding the key difference between forward- and backward-propagating O-mode masers. It is found that the O-mode maser instability is excited over a significant range of wave phase angle which corresponds to the backward propagation. Of the various physical parameters the average beam speed and the ratio of plasma-to-gyro-frequencies, ωp/Ω, play important roles. Past discussions have emphasized the role of ωp/Ω. The present analysis also includes the effects of average beam speed on the instability. It is shown that there is a critical beam speed for the instability onset, beyond which the growth rate is quasi-independent of the beam speed. Such a finding has not been reported in the literature before.
Electron field emission from excimer laser crystallized amorphous silicon
Authors: Tang Y. F. , Silva S. R. P. , Boskovic B. O. , Shannon J. M. , Rose M. J.
Published: July 2002

We show field emission from excimer laser crystallized (ELC) hydrogenated amorphous silicon (a-Si:H) at current densities and threshold fields suitable for display applications. The laser crystallized a-Si:H gives rise to a densely packed and relative sharp surface morphology that gives emission currents of the order of 10−5 A (current densities≈0.04 A/cm2) at threshold fields less than 15 V/μm in a diode configuration, without the need for a forming process. With the progress in utilizing ELC in flat panel driver electronics, a fully integrated field emission display on a single glass substrate can now be envisaged.
Experimental measurement of chaotic attractors in solid mechanicsa)
Authors: Moon Francis C.
Published: July 2002

In this paper a review is given of experimental techniques in chaotic dynamics of solid mechanical systems based on modern ideas of nonlinear dynamics. These methods include Poincaré maps, double Poincaré sections, symbol dynamics, and fractal dimension. The physical problems discussed include nonlinear elastic beams, forced motion of a string, flow-induced vibration of a rod, forced motions of a magnetic pendulum, and rigid body dynamics of a magnet and high-temperature superconductor.
Dynamics of a pair of spherical gravitating shells
Authors: Miller Bruce N. , Youngkins V. Paige
Published: July 2002

The dynamical N body problem for a system of mass points interacting solely through gravitational forces is not integrable. The difficulties which arise in constructing accurate numerical codes for simulating the motion over long time scales are legend. Thus, in order to test their theories, astronomers and astrophysicists resort to simpler, one-dimensional models which avoid the problems of binary formation, escape, and the singularity of the inverse square force law. To date, the most frequently employed “test’’ model consists of a system of parallel mass sheets moving perpendicular to their surface. While this system avoids all of the above problems, the time scale for reaching equilibrium is extremely long and probably arises from the system’s weak ergodic properties, which become manifest even in the three sheet system. Here we consider a different one-dimensional gravitating system consisting of nonrotating concentric mass shells. For the case of two shells we investigate the structure of the phase space by studying the stability of periodic trajectories. By employing an event driven algorithm, we are able to directly investigate the influence of the singularity without having to resort to regularization of the force. Although stable structures are present at every energy, we find that the ergodic properties of this system are more robust than its planar counterpart.
Spatiotemporal dynamics in the coherence collapsed regime of semiconductor lasers with optical feedback
Authors: Masoller Cristina
Published: July 2002

This paper presents a spatiotemporal characterization of the dynamics of a single-mode semiconductor laser with optical feedback. I use the two-dimensional representation of a time-delayed system (where the delay time plays the role of a space variable) to represent the time evolution of the output intensity and the phase delay in the external cavity. For low feedback levels the laser output is generally periodic or quasiperiodic and with the 2D representation I obtain quasiperiodic patterns. For higher feedback levels the coherence collapsed regime arises, and in the 2D patterns the quasiperiodic structures break and “defects” appear. In this regime the patterns present features that resemble those of an extended spatiotemporally chaotic system. The 2D representation allows the recognition of two distinct types of transition to coherence collapse. As the feedback intensity grows the number of defects increases and the patterns become increasingly chaotic. As the delay time increases the number of defects in the patterns do not increase and there is a signature of the previous quasiperiodic structure that remains. The nature of the two transitions is understood by examining the behavior of various chaotic indicators (the field autocorrelation function, the Lyapunov spectrum, the fractal dimension, and the metric entropy) when the feedback intensity and the delay time vary.
Data compression and information retrieval via symbolization
Authors: Tang X. Z. , Tracy E. R.
Published: July 2002

Converting a continuous signal into a multisymbol stream is a simple method of data compression which preserves much of the dynamical information present in the original signal. The retrieval of selected types of information from symbolic data involves binary operations and is therefore optimal for digital computers. For example, correlation time scales can be easily recovered, even at high noise levels, by varying the time delay for symbolization. Also, the presence of periodicity in the signal can be reliably detected even if it is weak and masked by a dominant chaotic/stochastic background.
A method for visualization of invariant sets of dynamical systems based on the ergodic partition
Authors: Mezić Igor , Wiggins Stephen
Published: July 2002

We provide an algorithm for visualization of invariant sets of dynamical systems with a smooth invariant measure. The algorithm is based on a constructive proof of the ergodic partition theorem for automorphisms of compact metric spaces. The ergodic partition of a compact metric space A, under the dynamics of a continuous automorphism T, is shown to be the product of measurable partitions of the space induced by the time averages of a set of functions on A. The numerical algorithm consists of computing the time averages of a chosen set of functions and partitioning the phase space into their level sets. The method is applied to the three-dimensional ABC map for which the dynamics was visualized by other methods in Feingold et al. [J. Stat. Phys. 50, 529 (1988)].
Transient chaotic mixing during a baroclinic life cycle
Authors: von Hardenberg J. , Fraedrich K. , Lunkeit F. , Provenzale A.
Published: July 2002

We discuss how atmospheric eddies affect transport and mixing of tracers at midlatitudes. To this purpose, we study baroclinic life cycles in a simple dynamical model of the atmosphere. We consider the trapping properties of the developing eddies and the characteristics of meridional transport, and we identify regions of increased mixing. Although the flow is in principle three-dimensional, we illustrate how some of the concepts developed in the study of two-dimensional chaotic advection provide useful information on tracer dynamics in more complicated flows.
Effect of xenon on the electron temperatures of rf discharge CO2 laser gas mixtures
Authors: Vidaud P. , Hall D. R.
Published: July 2002

Electrostatic double-probe measurements of the electron temperature Te, in rf excited laser discharge mixtures of CO2/N2/He to which Xe is added, reveal that the addition of Xe causes Te to be lowered. A possible mechanism for the beneficial effect of xenon on the operation of CO2 lasers is briefly discussed.
Output performance of a liquid-N2-cooled, para-H2 Raman laser
Authors: Midorikawa K. , Tashiro H. , Aoki Y. , Ohashi K. , Nagasaka K. , Toyoda K. , Namba S.
Published: July 2002

Stimulated rotational Raman scattering (SRRS) of a transversely excited atmosphere-CO2 laser in para-H2 was studied with a liquid-N2-cooled multiple-pass cell. Line-tunable output from 13.7 to 17.2 μm was obtained by changing CO2 pump lines. Threshold pump energies required for SRRS were measured to be 0.9 and 1.5 J for the 9P(20) and 10P(20) CO2 lines, respectively. Above the threshold, the Stokes output energies for the 10-μm band pumping increased in proportion to the increase of the pump energies, while the increase of the Stokes output for the 9-μm band pumping was limited. Para-H2 pressure dependence of the Stokes output energy showed that the Stokes gain became constant for pressures above 250 Torr at 100 K.
Polarized neutron study of the compounds Y2Fe14B and Nd2Fe14B
Authors: Givord D. , Li H. S. , Tasset F.
Published: July 2002

Outstanding permanent magnet properties were recently observed in a Nd-Fe-B compound which was shown to crystallize in a new phase, R2Fe14B. Polarized neutron measurements are reported on Y2Fe14B and Nd2Fe14B single crystals. The 3d Fe moment on different sites in Y2Fe14B at 4.2 K is closely related to local environment. Its value is maximum for atoms in σ-like layers at the center of an Fe antiprism. On the contrary, it is reduced to 1.95 μB by 4d-3d electron transfer and hybridization for Fe atoms which have the largest coordinance number of Y atoms, 4. The measurements at 250 K reveal a larger thermal decrease of the 3d moment for Fe atoms which exhibit shortest Fe-Fe interatomic distances. This property reveals a reduction of 3d magnetic interactions for short distances as was previously observed in R2Fe17 compounds. In Nd2Fe14B, the low values obtained at 4.2 K for Nd magnetic moments suggest that the magnetic structure, determined by a competition between 3d-4f exchange interactions and crystal-field interactions, is not collinear. Thus only the projection of the Nd moment along the direction of the spontaneous magnetization is measured. Additional contributions to the 3d moments induced by 4f interactions are evidenced, especially for those Fe atoms surrounded by 4 Nd neighboring atoms.
Magnetic and structural effects of anelastic deformation of an amorphous alloy
Authors: Haimovich J. , Jagielinski T. , Egami T.
Published: July 2002

We present the first direct evidence of structural anisotropy due to anelastic polarization produced by mechanical creep, in the form of the anisotropic diffraction intensities observed by energy dispersive x-ray diffraction method. We suggest that this structural anisotropy is the origin of the creep-induced magnetic anisotropy.
Heisenberg spin chains: Quantum-classical crossover and the Haldane conjecture
Authors: Parkinson J. B. , Bonner J. C. , Müller G. , Nightingale M. P. , Blöte H. W. J.
Published: July 2002

A comprehensive investigation has been made of the spectral excitations and static properties of Heisenberg antiferromagnetic chains of spin 1/2, 1, 3/2, and 2, using Lanczös, Bethe Ansatz, and Monte Carlo techniques. An unusual and unanticipated crossover mechanism for spin chains with 1/2≤S≤∞ has been discovered. The validity of the Haldane conjecture concerning the presence of a spectral excitation gap for integer-spin chains has been investigated by exact finite chains calculations of (a) the primary singlet-triplet excitation gap, (b) higher excitation gaps, and (c) the Fourier transform of the ground state correlation functions. A new Monte Carlo method has extended the spin-1 gap calculations to N=32.
Point explosion simulation by fast spark discharges
Authors: Loeb A. , Loebenstein M. , Ludmirsky A. , Eliezer S. , Maman S. , Gazit Y.
Published: July 2002

It is shown here that the late hydrodynamic effects of fast spark discharges (dI/dt‖t=0≥1010 A/sec), i.e., after the discharge period, can be described by a point explosion simulation. The solution is not self-similar since counterpressure has to be taken into consideration. This non-self-similar model is confirmed experimentally by shock wave position and velocity measurements.
Thermal forces on ferromagnetic domain walls, associated with the wall entropy
Authors: Berger L.
Published: July 2002

At any finite temperature, an entropy S* is stored in the thermal spin disorder of a ferromagnetic domain wall. Thus, a domain wall moving across a temperature gradient dT/dx constitutes a thermal engine carrying entropy and heat from a hot to a cold reservoir, and transforming it partly into work. This work is performed through a force Fx applied to the wall. Using the first and second laws, we find Fx=−S*dT/dx. Rough estimates of S* are obtained from the temperature dependence of the wall surface energy. They suggest that this ‘‘wall-entropy force’’ may be comparable in magnitude to the force caused by the Nernst effect, described earlier.
Formation of negative hydrogen ions on a cesiated W(110) surface; the influence of hydrogen implantation
Authors: van Amersfoort P. W. , Geerlings J. J. C. , Kwakman L. F. Tz. , Hershcovitch A. , Granneman E. H. A. , Los J.
Published: July 2002

The negative hydrogen ion formation process on a cesiated W(110) surface is studied by scattering a proton beam from such a surface. The primary energy ranges from 50 to 3000 eV. The angle of incidence with respect to the surface normal is 45° or 70°. A maximum negative-ion formation probability of 0.67 is measured. This quantity does not depend on the angle of incidence. However, it is strongly influenced by the time the surface has been exposed to the beam. This effect is attributed to hydrogen implantation.
Electromagnetic surface waves: New formulas and their application to determine the electrical properties of the sea bottom
Authors: King Ronold W. P.
Published: July 2002

Electromagnetic surface waves can propagate along boundaries between electrically different media like air and earth or sea water and rock. They have unusual properties that make them valuable tools in geophysical prospecting and diagnostics. They are not suited to deep sounding. Much of the current theory for their geophysical application has been limited to ranges of the parameters and variables that permit the use of Norton’s graphs which were developed for radio communication over the earth. A recently derived set of accurate, very general, and simple formulas for the surface-wave fields of antennas near a boundary surface has provided an expanded horizon for understanding and using surface waves as distinct from plane waves that travel down into the earth. The new formulas are given and used to assist in the interpretation of available measurements and then applied to the determination of the average conductivity and permittivity of the part of the lithosphere very close to the sea bottom where the lateral waves travel.
Cryogenic-pressure response of optical transitions in quantum well and bulk GaAs: A direct comparative study
Authors: Weinstein B. A. , Hark S. K. , Burnham R. D.
Published: July 2002

Cryobaric (11–100 K and 300 K, 0–65 kbar) measurements of photoluminescence in GaAs/AlxGa1−xAs multiquantum well structures are described. Results on a narrow-well (38 Å wide) structure exhibiting both quantum well and bulk GaAs emission (from a thick buffer region) allow direct comparison of the two for the first time. We find that transitions between Γ-derived n=1 confined levels have the same pressure coefficient, within ±0.2 meV/kbar, as the bulk E0 gap, 11.4 meV/kbar. An interaction between n=1 electron states and a state 35–40 meV below the X-conduction minima is observed within the pressure-induced Γ-X crossover region for our narrow-well sample. The proposed origin of the latter state is residual interface impurities.
An atomistic study of the GaAs–Pd interface
Authors: Kobayashi Akiko , Sakurai T. , Hashizume T. , Sakata T.
Published: July 2002

The interface of GaAs–Pd was investigated on an atomic scale by a time-of-flight (TOF) atom-probe field ion microscope (FIM). It was found that Pd reacts strongly with Ga even at room temperature to form a stable PdGa compound. Depending upon heat treatment conditions, several types of Pd–(Ga, As) ternary compounds were also formed. A thin layer (less than a few monolayers) of As was quite often detected at the outermost surface layer when the interface was heated up to 400 °C. Above 400 °C only the most stable PdGa phase was observed at the interface. At a temperature range between 200 and 400 °C, the segregated Ga phase was also found beneath the As layer. The interfacial reactions can be understood by the following two processes: (1) Pd atoms diffuse into the GaAs substrate to form a stable Pd–Ga bond and (2) As, whose bonding with Ga is broken, becomes loose and migrates to the surface and desorbs.
Photopyroelectric versus photoacoustic characterization of photovoltaic cells
Authors: Faria I. F. , Ghizoni C. C. , Miranda L. C. M. , Vargas H.
Published: July 2002

The photothermal pyroelectric technique is applied to the characterization of photovoltaic cells and a comparison with the photoacoustic detection is presented. The difference between the photoacoustic and the pyroelectric data is interpreted in terms of a simple model for a junction-type solar cell.
Electrical conductivity of electron-irradiated hydrogenated amorphous silicon
Authors: Yacobi B. G. , von Roedern B.
Published: July 2002

Results on electrical conductivity in keV-electron-irradiated hydrogenated amorphous silicon are presented. Increases in both the conductivity activation energy and the resistivity are observed in irradiated samples. Some possible uses of this effect are discussed.
Interface excitations in layered structures with metallized surfaces
Authors: Kushwaha Manvir S.
Published: July 2002

A theoretical investigation has been made of the interface excitations associated with the double inversion layers of semiconductor-insulator-semiconductor structure with metallized surfaces. The general dispersion relation has been derived using the local electromagnetic theory. The numerical computation is performed in the nonretardation limit (c→∞) for the structure assumed to be made up of n-type silicon-silicon-dioxide-p-type silicon. Theoretical results for finite oxide thickness with respect to separation of the metallic surfaces are shown. These excitations can be regarded as the uncoupled (for infinite oxide thickness) and coupled modes (for finite oxide thickness) whose components are the two-dimensional-electron-gas plasmon and the two-dimensional-hole-gas plasmon. The finiteness of the structure presents some interesting variations in the frequencies of the plasma modes.
On-line p,T calibration based on well-known phase transitions
Authors: Secco R. A. , Schloessin H. H.
Published: July 2002

The fluid encapsulation technique allows for simultaneous in situ pressure and temperature calibration, at present up to 6 GPa and 800 °C, using on-line data processing. Each experimental run is done quasi-isobarically with continuous variation of temperature. Temperature is determined by the thermal emf’s of S- or K-type thermocouples placed in contact with accepted standard calibration materials which undergo pressure and temperature dependent phase transitions. In the course of this study, the phase diagrams of Bi, Hg, Sn, Tl, Pb, and Fe have been reinvestigated and self-consistency between transitions of all of these materials was used to determine the p,T(emf) coordinations. Thermal emf’s, for the S-type thermocouple, are converted to temperature using a 20-degree polynomial that fits the IPTS-68 data to within 0.4 K and is continuously differentiable in the temperature range from 0 to 1705 °C.
Infrared study of KTiOPO4 single crystals hydrothermally grown in H2O and D2O solutions
Authors: Ahmed Fakhruddin , Belt Roger F. , Gashurov Gleb
Published: July 2002

A detailed infrared study has identified the spectral features of potassium titanate orthophosphate, KTiOPO4 (KTP), between 4000 and 2200 cm−1. KTP single crystals grown by hydrothermal and flux methods were examined. By using ordinary and heavy water in separate runs to grow KTP crystals hydrothermally, features that depend on the presence of H2O or D2O in the growth process have been distinguished from features that do not. The effect of multiple OH sites in KTP has been linked with crystal quality and specific trace impurities, e.g., Fe+3.
Resistive filamentation of self-pinched electron beams
Authors: Hughes Thomas P. , Uhm Han S.
Published: July 2002

A model for resistive filamentation of a self-pinched slab electron beam is presented. The lowest-order modes are found to consist of a body mode which leads to bunching of the beam, and a surface mode which leads to rigid rippling of the beam. The dispersion relations for these modes are compared to results from a linearized particle simulation code. The analytic model and simulation code are applied to the interpretation of a recent experiment in which filamentation was observed in a self-pinched annular electron beam propagating in low-pressure air.
Upconversion-pumped infrared erbium laser
Authors: Pollack S. A. , Chang D. B. , Moise N. L.
Published: July 2002

A study of upconversion processes in Er3+ ions in CaF2 has led to an unambiguous demonstration of IR lasing produced by upconversion pumping alone. The study has shown: (1) strong upconversion lines originating from the 4I11/2 state; (2) the existence of both two-photon and three-photon upconversion processes; (3) an optimum concentration of 5–10 mol % for Er3+; and (4) upconversion efficiencies for the visible bands as high as 10% at 77 K and 1% at 300 K. Measurements of lasing between the 4I11/2 and 4I13/2 levels show that even though the lifetime of the upper (4I11/2) state is only half that of the lower state, self-quenching does not occur. Upconversion is implicated for this transition both by the nonpersistence of a ‘‘red shift’’ during a lasing pulse, and by the opposite dependence on concentration of laser threshold energy and upconversion-produced fluorescent intensity. A simple theoretical model shows that a 2.8-μm laser operating between the 4I11/2 and 4I13/2 levels can be pumped solely by upconversion of ions in the excited 4I13/2 state produced by absorption of a 1.54-μm pulse. In addition, (1) a minimum of 1.54-μm pump energy is required; (2) lasing occurs with a delay inversely proportional to the pump energy; and (3) lasing can persist for as long as the lifetime of the lower (4I13/2) state. These predictions have been experimentally verified. The lasing experiments give a lower limit for the upconversion coefficient of α=10−16 cm3 s−1.
The occurrence of cross hatch during GaAs homoepitaxy
Authors: Cunningham J. E. , Chiu T. H. , Ourmazd A. , Shah J. , Tsang W. T.
Published: July 2002

We report on the observation of a morphological defect structure, ‘‘cross-hatch’’ and the experimental circumstances that lead to its occurence during GaAs homoepitaxy. Photoluminescence, x-ray diffraction and transmission electron miscroscopy (TEM) results obtained on cross-hatched samples are presented and discussed in regards to the nature and origin of the defect structure.
Lifetime and carrier-concentration profile of B+-implanted p-type HgCdTe
Authors: Fraenkel A. , Schacham S. E. , Bahir G. , Finkman E.
Published: July 2002

The lifetime and carrier-concentration profile of Hg1−xCdxTe photodiodes (x=0.2–0.3) formed by implantation of B+ ions (100 keV, 1013–1014 cm−2) into a p-type substrate was investigated. Using graded C-V measurements, concentration of carriers around the n+p junction was obtained. It was found that the junction is located at a depth of 0.7–1.5 μm, depending on the bulk hole concentration. The technique enables profiling of the same sample after annealing. The annealing process was shown to make the electron concentration shallower and thus to bring the junction closer to the surface. Various techniques were used to measure excess carrier lifetimes. All indicate that the extent of degradation of the excess electron lifetime in the p region is very limited. For all tested samples, an etch of 2 μm was enough to recover the bulk lifetime. These results contradict the general assumption of deep damages in the p-type substrate. Thus, the contribution of the n+ side to the saturation current and to the R0A product cannot be neglected.
Comparisons of the different configurations of the second-order reflection grating
Authors: Park Wee Sang , Seshadri S. R.
Published: July 2002

Three canonical equations governing the characteristics of the second-order reflection grating for the transverse magnetic mode are derived. Based on the solution of the canonical equations, the input coupling efficiency for the Gaussian beam is deduced. The characteristics of the four different operating schemes of the reflection grating are compared with reference to such applications as the frequency selective filter, the output coupler, and the input coupler.
Characterization of ion-implantation doping of strained-layer superlattices. I. Structural properties
Authors: Myers D. R. , Picraux S. T. , Doyle B. L. , Arnold G. W. , Biefeld R. M.
Published: July 2002

We have characterized the effects of Be+ implantation and controlled-atmosphere annealing on the structure of Ga(AsP)/GaP strained-layer superlattices (SLSs). Damage and strain distributions within the implanted layers were examined by cantilever-beam bending measurements, double-crystal x-ray rocking curves, and a variety of ion-channeling techniques. Implantation-induced displacement damage produces additional stress in the SLS, in this case reaching 4.5×109 dyn/cm2, a value comparable to that of the built-in stresses in these SLSs. The depth distribution of ion damage as measured by ion channeling agrees well with the predictions of the trim code, although substantial recovery occurs during the room-temperature implant. Rocking curve analysis indicates that the interlayer strain in the SLS is retained despite the ion damage, and that the ion damage can be modelled as an independent additional source of strain in the as-implanted structure. The linear expansion of the layers due to point defect generation for the 1×1015 Be/cm2 implant is determined to be approximately 0.3% by all three techniques. After controlled-atmosphere annealing at the nominal SLS growth temperature, both the x-ray and ion-channeling measurements indicate removal of the implant damage with the as-grown strain retained and no resolvable intermixing of the layers in the SLS. These results demonstrate that ion-implantation technologies developed for bulk semiconductors can successfully be applied to strained-layer superlattice systems.
Magnetic anisotropies and spin reorientations of R2Fe14B-type compounds
Authors: Abache C. , Oesterreicher J.
Published: July 2002

Magnetic anisotropy of R2T14B (R=rare earth and T=transition metals such as Fe and Co) and partly substituted derivatives thereof are studied over a range of temperatures. The salient features are axial anisotropy for Y2Fe14B versus planar anisotropy for Y2Co14B. Only R with negative second-order Stevens’ factor (such as Nd) will show axial anisotropy contributions near room temperature. However, even in this case nonaxial contributions compete at cryogenic temperature, leading to a spin reorientation for R=Nd and Ho with TRs=140 and 62 K, respectively, for the Fe-based compounds. The symbol R is used to amplify the point that the spin reorientation is primarily triggered by an internal competition of R in question. The origin of this anisotropy competition is further illuminated by studies on partly R substituted materials, such as (Nd1−xRx)2Fe14B. Several contributions to the complex situation are considered including: (a) different site contributions (4f, 4g), (b) different order crystal-field terms, such as V02, V22, and V04 on 4f and 4g, (c) relative magnitude of exchange and crystal field, and (d) the trend for smaller R to preferentially occupy the 4f site. Another type of spin reorientation is observed when R and T sublattice anisotropies compete. An example is Er2Fe14B with TR-Ts=326 K. More complex mixed cases are either observed or predicted.
Effects of emitter-base junction gradation on the minority-carrier transport in the base region of bipolar junction transistors
Authors: Sukulal K. , Bhat K. N.
Published: July 2002

The effects of emitter-base junction gradation, mobility gradients, and electric field gradients on the injected minority-carrier density distributions in the base region of narrow-base transistors are analyzed. It is shown that the collector current of transistors having a graded emitter-base junction deviates from the ideal characteristics. The factors which contribute to this departure are analyzed in this paper. It is also shown that the emitter-base forward bias voltage affects the transit time significantly in narrow-base transistors, even when high injection level conditions are absent.
Refractive index determination in diamond anvil cells: Results for argon
Authors: Grimsditch M. , Letoullec R. , Polian A. , Gauthier M.
Published: July 2002

The pressure dependence of the refractive index of argon has been measured in a diamond anvil cell up to 15 GPa. We describe in detail the novel technique used, which offers considerably higher accuracy than the others previously utilized. Our results on Ar agree with previous results at lower pressures and are compared with theoretical calculations at high pressure.
Single crystals of Nb-Ta superlattice grown by molecular-beam epitaxy
Authors: Nishihata Yasuo , Nakayama Masaaki , Kato Hiromu , Sano Naokatsu , Terauchi Hikaru
Published: July 2002

Single crystals of Nb-Ta superlattice have been grown by molecular-beam epitaxy. The epitaxial relations between the samples and several kinds of sapphire substrates have been determined using x-ray diffraction. The interface region between Nb and Ta layers is estimated to be about 6 Å. A terraced structure of the superlattice is discussed. Reflection high-energy electron diffraction patterns of Nb and Ta surfaces observed in situ show half-order streaks and an elongation of lattice constant in the growth direction.
Disilicide solid solutions, phase diagram, and resistivities. I. TiSi2–WSi2
Authors: Gas P. , Tardy F. J. , d’Heurle F. M.
Published: July 2002

The pseudobinary system TiSi2–WSi2 has been investigated from about 85% TiSi2 to 100% WSi2 up to a temperature of 1100 °C. The equilibrium phase diagram which has been established contains a continuous (from 15% to 100% WSi2) solid solution with a hexagonal structure (TaSi2 type) at low temperatures, below ∼550 °C. At about 550 °C WSi2-rich alloys split into two phases, the normal tetragonal phase of WSi2, which has a very limited solubility for TiSi2, and the hexagonal (TaSi2) phase with the amount of WSi2 in solution decreasing with increasing temperature at about 50% at 1100 °C. The resistivity of the different alloys has been studied as a function of annealing temperature. There is considerable excess resistivity due to alloy scattering and no evidence of a marked difference in resistivity between the two phases.
Growth of InAsSb alloy and InAsSb/GaSb superlattice lattice matched to (100) GaSb by molecular-beam epitaxy
Authors: Chiu T. H. , Tsang W. T. , Ditzenberger J. A. , Chu S. N. G. , van der Ziel J. P.
Published: July 2002

The growth conditions to achieve high-quality InAsSb alloy and abrupt InAsSb/GaSb heterostructure by molecular-beam epitaxy are described. The present results indicate that optical pyrometry is a reliable method to determine the growth temperature, and a stable substrate temperature is of critical importance in achieving homogeneous InAsSb composition throughout the growth period. The quality of these epilayers is evaluated by double x-ray diffraction measurement, reflection high-energy electron diffraction study, Nomarsky microscopy, and low-temperature photoluminescence. The optical quality is further demonstrated by the optically pumped coherent emission at ∼3.9 μm observed from an InAsSb active layer.
Hydrogen out-diffusion suppression effect of overlayers in H+2 -implanted magnetic bubble garnet
Authors: Imura R. , Sugita Y.
Published: July 2002

Hydrogen out-diffusion suppression effect of overlayer deposited on H+2 -implanted magnetic bubble garnet has been investigated using gas mass spectroscopy and secondary ion mass spectroscopy. It has been found that oxide films such as SiO2, SiO, TiO2, and Al2O3 or nitride film such as Si3N4 effectively suppress out-diffusion of hydrogen during annealing, keeping a large anisotropy field change induced by hydrogen implantation after the annealing. Hydrogen depth profiles have also been found to have a sharp peak at the boundary between overlayer and garnet which can suppress out-diffusion of hydrogen. Metal films such as Au, Mo, and Ni–Fe alloy have been found not to act as suppressors of hydrogen out-diffusion. Annealing hydrogen-implanted garnet with an oxide overlayer on the surface is useful for ion-implanted bubble device fabrication because of thermal stability of large anisotropy change induced by implantation.
Analytical theory of electron-beam-induced damage in organic materials
Authors: Garcia-Molina Rafael , Gras-Marti Alberto
Published: July 2002

We calculate analytically the damage produced in a slab of organic material irradiated by an electron beam as a function of electron energy. The treatment is based on a Boltzmann-type transport equation. We assume that the damage is directly related to the number of carbon K-shell ionizations produced by the electron bombardment. An acceptable agreement between our calculations and experimental data is found.
Nonequilibrium ionization of nitrogen: The role of stepwise ionization from metastable states in the presence of superelastic electronic collisions
Authors: Paniccia F. , Gorse C. , Cacciatore M. , Capitelli M.
Published: July 2002

Electron impact ionization rate coefficients involving N2 metastable electronic states have been calculated in discharge and postdischarge conditions by using the electron energy distribution functions which take into account both the presence of superelastic electronic (SEC) and vibrational (SVC) collisions [J. Appl. Phys. 59, 4004 (1986)]. The results show that stepwise ionization from metastable states can overcome the corresponding rates from the ground state especially in the absence of SVC. Finally, a comparison of the present results with those coming from associative ionization involving metastable electronic and vibrational states is presented and discussed.