bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic viscosity far and close to equilibrium in the superparamagnetic alloy
Authors: Maraner A. , Zhang X. , Cavalleri A. , Tejada J. , Vitale S.
Published: July 2002

We report on the simultaneous measurements of the magnetic viscosity and of the ac linear magnetic susceptibility for a sample of Cu90Co10. The magnetic viscosity S=(1/M0) [dM/d ln(t)], with M the sample magnetization and M0 the magnetization value at the beginning of the logarithmic relaxation, is measured by a standard method that involves the application to the sample of a large field step after saturation. The ac susceptibility is measured both directly at very low (≊microersteds) ac field amplitudes and from the thermal magnetization noise in the sample, the two values always being found in quantitative agreement. The imaginary susceptibility is found to be a frequency independent value χ0″(T) at low frequencies, a behavior that translates, when expressed in the time domain, to logarithmic relaxation (dM/d ln t)=(2/π)χ0″(T)H0, of the magnetization after a step excitation H0. Both S and χ0″(T) are found to be proportional to the temperature for temperatures ≤4.2 K. In addition, S and χ0″(T) are found to be of the same order of magnitude. We discuss how these results are in agreement with the idea that in both kinds of experiments one is probing an energy barrier height distribution and that, in addition, the size of the distribution involved in the ‘‘critical state,’’ prepared by relaxation experiments, is of the same order of magnitude as that involved in the quasiequilibrium state probed by the ac susceptibility measurements.
Optical response of Cu3Ge thin films
Authors: Guizzetti G. , Marabelli F. , Pellegrino P. , Sassella A. , Aboelfotoh M. O.
Published: July 2002

We report an investigation on the optical properties of Cu3Ge thin films displaying very high conductivity, with thickness ranging from 200 to 2000 Å, deposited on Ge substrates. Reflectance, transmittance, and ellipsometric spectroscopy measurements were performed at room temperature in the 0.01–6.0, 0.01–0.6, and 1.4–5.0 eV energy range, respectively. The complex dielectric function, the optical conductivity, the energy-loss function, and the effective charge density were obtained over the whole spectral range. The low-energy free-carrier response was well fitted by using the classical Drude–Lorentz dielectric function. A simple two-band model allowed the resulting optical parameters to be interpreted coherently with those previously obtained from transport measurements, hence yielding the densities and the effective masses of electrons and holes.
Step width enhancement in a pulse-driven Josephson junction
Authors: Maggi S.
Published: July 2002

The response of an overdamped current biased Josephson junction to a pulsed rf drive has been investigated by both numerical and analog simulations. The rf signal was a periodic rectangular pulse of varying amplitude and duration. A considerable increase of the width of the rf-induced steps with respect to those of an equivalent junction driven by a sinusoidal signal has been obtained. In the limiting case of a pulse repetition frequency much lower than the junction RC cutoff frequency, all steps have a maximum width which is independent of the step order n and increases with decreasing pulse duration.
Synthesis and characterization of iron carbonitride ultrafine particles
Authors: Zhao X. Q. , Liang Y. , Hu Z. Q. , Liu B. X.
Published: July 2002

Iron carbonitride (ICN) ultrafine particles (20–80 nm in size) have been synthesized by laser-induced pyrolysis of Fe(CO)5–NH3–C2H4 mixture. The surface morphology, structural characteristics, oxidation behavior, and the magnetic properties of the ICN particles were reported. The role the thin carbon layer formed on the particle surface played in the oxidation behavior and in the enhancement of the magnetic properties has been studied. A carbon layer (1–2 nm) seems to protect the particles effectively from reaction of the iron carbonitride with oxygen, and the ICN particles thereby exhibit a high saturation magnetization of 142 emu/g. Additionally, the unilateral lattice expansion of the ICN compound was interpreted in terms of the structural and chemical bonding features of the ICN compound.
Magnetic interaction and remanence properties in CoNiPt(SiO2) granular films for high-density longitudinal recording
Authors: Murayama Akihiro , Ohshima Kiyoshi , Miyamura Masao , Maekawa Mikako , Kondoh Shinji
Published: July 2002

Magnetic interaction and remanence properties in (Co81Ni7Pt12)100−x(SiO2)x films (x=0–8) have been studied for high-density longitudinal recording. Films with SiO2 contents of 6 and 8 mol %, in which sufficiently isolated CoNiPt grains with a diameter of about 10 nm and a random orientation of the c axis of hcp structure are observed, show a significant low-noise property as well as high coercivity. Both frequency dependence of the media noise and magnetic domain structure in the remanent-magnetized state show that the exchange interaction between grains is eliminated by the grain boundary of the SiO2 phase with the width of 2 nm. In such films, high coercive squareness of 0.9 on the remanence curve is obtained, while the squareness on the hysteresis curve decreases as the SiO2 content increases. Henkel plot indicates that ‘‘ferromagnetic’’ interaction among the grains sustains such high squareness on the remanence curve. The strength of the interaction depends on the film thickness and is proportional to the squareness on the remanence curve. The origin of the ‘‘ferromagnetic’’ interaction among grains is discussed, mainly based on the magnetostatic interaction.
Highly strained InGaAsP films with high critical thicknesses
Authors: Bolkhovityanov Yu. B. , Jaroshevich A. S. , Nomerotsky N. V. , Revenko M. A. , Trukhanov E. M.
Published: July 2002

Elastically strained InGaAsP films with band gaps from 1.4 to 1.8 eV were grown on GaAs(111)B substrates by liquid phase epitaxy. For elastic strains up to 1% the critical thicknesses of the films substantially exceeded the predictions of the energy equilibrium theory by Matthews and Blakeslee. Among the various stress-relieving mechanisms proposed in the literature a stress-induced surface roughening has been found to be most relevant in our case.
Incorporation of arsenic and phosphorus in GaxIn1−xAsyP1−y alloys grown by molecular-beam epitaxy using solid phosphorus and arsenic valved cracking cells
Authors: Baillargeon J. N. , Cho A. Y. , Cheng K. Y.
Published: July 2002

Growth of GaxIn1−xAsyP1−y was performed on (001) InP by molecular-beam epitaxy employing solid phosphorus and arsenic valved sources. Relative anion incorporation rates were found strongly dependent upon the Ga mole fraction, growth temperature, and incident As and P beam fluxes. The relative incorporation of As and P can be predicted from the ratio of the square of the incident column-V fluxes. Although the As anion always incorporated preferentially into the lattice, significant enhancement in P incorporation was observed as growth temperature and Ga mole fraction increased. Strong spinoidal decomposition and a temperature-dependent surface morphology was found for lattice-matched compositions having peak photoluminescence emission wavelengths between 1.25 and 1.36 μm. Heterojunction laser diodes utilizing different GaxIn1−xAsyP1−y active regions were fabricated with emission ranging from 1.21 to 1.53 μm. The best broad area threshold current density obtained for a 500 μm cavity length was 1.7 kA/cm2 with a maximum two facet slope efficiency of 0.24 W/A, which is comparable to the state-of-art performance.
Giant transversal magnetoimpedance and Hall-effect measurements in Co70.4Fe4.6Si15B10
Authors: Mendes K. C. , Machado F. L. A. , Pereira L. G. , Rezende S. M. , Montenegro F. C. , Altoé M. V. P. , Missell F. P.
Published: July 2002

We report room-temperature transversal magnetoimpedance (TMI) and Hall-effect measurements performed in ribbons of the zero-magnetostriction soft-ferromagnet Co70.4Fe4.6Si15B10 alloy annealed at 587 K for 15 min at a dc magnetic field of 2 kOe. The annealing showed little effect on the magnetostriction of the samples. The frequency f and the amplitude Iac of the current used in the measurements, and the measuring magnetic field H were varied in the intervals 10≤f≤105 Hz, 2.5≤Iac≤25 mA, and −15≤H≤15 kOe, respectively. The magnetic field dependence of the TMI shows a peak which is strongly dependent on f and on Iac. It reaches the giant value of 28% at H=350 Oe for f=100 kHz and Iac=25 mA. This TMI giant value is of the same order of the giant longitudinal magnetoimpedance (GLMI) but its peak is positioned in a magnetic field two orders of magnitude larger than the value obtained for the GLMI. The Hall effect yielded a value of RS=0.43 μΩ cm kOe−1. Peaks which are also frequency dependent were observed at the Hall voltage.
Important factors included in nondestructive readout of GMR MRAM (abstract)
Authors: Nakamura Y. , Wang Z.
Published: July 2002

We proposed a new type of magnetoresistive random access memory (MRAM) using a weakly coupled GMR effect. It operates on the general principle of storing a binary digit in hard component and sensing its remanent state by switching the soft component in such a way that the magnetic state of the hard component is unaltered. It is believed that this structure could have nondestructive readout (NDRO) characteristics. However, in experiments we found that NDRO was not always achieved; i.e., NDRO was dependent on the polarity of the excitation field. We take an example for mode ‘‘0’’ (corresponding to a + remanent state). Although tests involving 3×108 plus excitation pulses indicated that the element was still stable, stability against minus disturb pulses could not be expected. The remanent state of 0 was degrading gradually and was finally destroyed after nenormous numbers of readout switching. An analytical model, in which the hard component follows the Rayleigh law, can explain the above phenomenon. It is because the irreversible magnetization processes cause disturbed states (0′ or 1′). Obviously the worst case for mode 0 is being excited by continous minus pulses whereas the worst case for mode 1 is being excited by continous plus pulses. We think that two methods will be effective to eliminate the unstability. One is to obtain a rectangular hysteresis loop for the hard component. The other is to imporve the excitation method, for example, to employ bipolar pulses for excitation signals.
Locally resolved photothermally modulated ferromagnetic resonance investigation of magnetic anisotropies in a (001) Fe wedge film
Authors: Meckenstock R. , Harms K. , von Geisau O. , Pelzl J.
Published: July 2002

Photothermally modulated ferromagnetic resonance (PM-FMR) was used to investigate the lateral dependence of the magnetic parameters in an epitaxially grown (001) Fe wedge. The wedge thickness varied from 2.2 to 12.8 nm on a length of 10 mm. The PM-FMR measurements, which were carried out with a lateral resolution of 50 μm, permitted to determine the surface anisotropy with a high accuracy. In addition, a small uniaxial in-plane anisotropy was detected which shows an increase with the Fe-film thickness.
Magnetization of nanocrystalline dysprosium: Annealing effects
Authors: Mulyukov Kh. Ya. , Korznikova G. F. , Nikitin S. A.
Published: July 2002

The magnetization of dysprosium (Dy) in its different structures (from a nanocrystalline one to a coarse grained structure) is investigated. In the nanocrystalline state Dy is ferromagnetic up to a temperature 160 K and no antiferromagnetism is detected at any temperature when Dy is in an intermediate structural state, coexistence of the ferro- and antiferromagnetic orders is observed in the temperature range from 110 to 160 K. Finally, magnetic properties of coarse-grained Dy coincide with those reported in literature for the bulk.
Low-temperature mobility of two-dimensional electrons in (Ga,In)As–(Al,In)As heterojunctions
Authors: Greally M. G. , Hayne M. , Usher A. , Hill G. , Hopkinson M.
Published: July 2002

We report an investigation of the scattering mechanisms affecting the two-dimensional electron system in modulation-doped Ga0.47In0.53As–Al0.48In0.52As single heterojunctions. Low-temperature magnetotransport measurements were used to determine the dependence of the electron mobility μ on the density Ns of the two-dimensional carriers. For Ns≤4×1011 cm−2, we find that μ increases with Ns, leveling off as Ns is further increased. This behavior is a clear indication that, contrary to some theoretical predictions, μ is chiefly limited by ionized-impurity scattering in this regime. We develop a theoretical model of the scattering mechanisms present in our systems whose results agree with our experiments. We find that alloy and interface-roughness scattering become important only when Ns≥5×1011 cm−2.
Correlation of photon emission with electric-field-initiated nanometer-scale surface modification
Authors: Strozewski K. J. , McBride S. E. , Wetsel G. C.
Published: July 2002

Photon emission during electric-field-initiated material transfer has been measured using a scanning tunneling microscope configured for surface modification. The instrument has been integrated with a photon-counting system that measures the emission originating from the tip–sample junction under both quiescent and transient conditions. The transient photon emission recorded during nanometer-scale surface modification of gold samples is correlated with the type of feature formed on the sample surface.
Effect of an interlayer on the emission characteristics of a white-light-emitting electroluminescent device with a Pr and Ce doubly doped ZnS phosphor layer
Authors: Lee Y. H. , Ju B. K. , Song M. H. , Hahn T. S. , Oh M. H. , Kim D. H.
Published: July 2002

We have investigated light-emission characteristics of a white-light-emitting electroluminescent device with a doubly doped ZnS:Pr,Ce,F phosphor layer. We found that optimum codoping of Ce enhances the emission characteristics compared to the electroluminescent device with a singly doped ZnS:Pr,F layer. We also found that introducing an additional thin-insulating SixNy interlayer between the lower insulating layer and the phosphor layer significantly stabilizes the aging characteristics and improves the luminous efficiency.
Effects of high temperature rapid thermal annealing using a flat gas flame on the electrical properties of phosphorus-doped polycrystalline silicon films
Authors: Qu W. F. , Masaki Y. , Kitagawa A. , Suzuki M.
Published: July 2002

The effects of high temperature rapid thermal annealing (HT-RTA) using a flat gas flame on the electrical properties of phosphorus-doped polycrystalline silicon (poly-Si) films in association with their microscopic structure were studied. Samples with a phosphorus concentration of 3.1×1017–6.0×1020 cm−3 were prepared and annealed by HT-RTA ranging from 1150 to 1350 °C. During HT-RTA, the sample surface was laterally swept by gas flames. The resistivity of the samples decreased with increasing annealing temperature, and the lowest resistivity was 4.8×10−4 Ω cm for the sample doped with P of 6.0×1020 cm−3 when annealed at 1350 °C. Hall mobility, on the other hand, increased first and then decreased with increasing P concentration. The highest Hall mobility was 71.3 cm2/V s for the sample annealed at 1350 °C of which the P concentration was 3.5×1019 cm−3. The results suggest that the grain boundary potential barriers for carriers decreased with increasing doping concentration and annealing temperature, and that the total area of grain boundaries in the films decreased with increasing annealing temperature because of secondary grain growth and the shrinkage of boundary width.
‘‘Concerted’’ regeneration of electroformed metal-insulator-metal devices
Authors: Sharpe R. G. , Palmer R. E.
Published: July 2002

Filament regeneration has been investigated in electroformed Cu-SiOx-Cu sandwich devices at cryogenic temperatures (≊125 K). The initial regeneration characteristics can be modeled by proposing a new scheme, which we term ‘‘concerted regeneration.’’ This is the preferential regeneration of filaments located close to intact filaments (which generate a local increase in temperature via power dissipation). This coordination in the regeneration of filaments can also cause ‘‘explosive regeneration,’’ the rapid regeneration of a batch of filaments, and thus a sudden jump in the device current, and also ‘‘concerted rupture,’’ a sudden drop in conductivity due to a batch of filaments rupturing simultaneously.
Small mesas and holes in split-gate quantum wires acting as ‘‘artificial impurities’’ fabricated with scanning tunneling microscope
Authors: Yamada Syoji , Yamamoto Masafumi
Published: July 2002

This article discusses fabrication of ‘‘artificial impurities’’ such as small mesas and holes with a scanning tunneling microscope (STM) in split-gate quantum wires and their transport properties. In order to make and properly place these small structures on the wire surface, we employed a combined STM/scanning electron microscope system operated in vacuum. The fabrication method involves simple electrical evaporation with a Tungsten tip. In a wire having a small mesa (70 nm diameter and 15 nm height) at the center, clear Coulomb blockades and staircases corresponding to the size of the mesa were observed at 0.3 K. In a wire with a hole (200–300 nm upper diameter and 100–150 nm depth) near the gate electrode, both quantized plateaus and damage-induced telegraphic switching were observed in the two-terminal conductance also at 0.3 K. This means that a deep hole at the wire edge can behave, depending on the evaporation condition, either as a simple constriction or as a constriction with electron traps.
Significance of blackbody radiation in deep-level transient spectroscopy
Authors: Bonde Nielsen K. , Andersen E.
Published: July 2002

Deep-level transient spectroscopy has been combined with ion implantation in low-temperature investigations of deep centers in silicon. We demonstrate that thermal radiation, originating from vacuum chamber walls, can influence in situ recording of emission rates significantly. As an example, the emissivity (en) of the hydrogen E3′ center was found to be dominated by an optical contribution at temperatures below ≊65 K. A typical value, en(op)≊5.5 s−1, has been recorded in measurements with unshielded Au Schottky diodes. This effect of thermal radiation vanishes when a diode is fully encapsulated and thereby in thermal equilibrium with the radiation field. The optically induced emissivity is particularly large for the hydrogen center used here to illustrate the effect but has been observed for other deep centers as well.
Transport properties of Tl2Ba2CaCu2O8 weak links on LaAlO3 bicrystal substrates
Authors: Chen Y. F. , Ivanov Z. G. , Stepantsov E. A. , Tzalenchuk A. Ya. , Zarembinski S. , Claeson T. , Johansson L.-G.
Published: July 2002

Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been fabricated in ex situ epitaxial Tl2Ba2CaCu2O8 films on bicrystal LaAlO3 substrates with symmetric 32° [001] tilt grain boundaries. The critical temperature Tc, of the junctions was in the range 105–107 K and the critical current densities at 77 K varied between 3×102 and 3×104 A/cm2, two or three orders of magnitude less than those of the film. The I–V curves are described by a resistively shunted junction model. Close to Tc, the temperature dependence of the critical current was described by (1−T/Tc)2. The flux noise spectra SΦ(f) of dc SQUIDs were measured in the locked-loop regime with constant current bias at temperatures up to 94 K. The white noise level was 50μΦ0/√Hz at 77 K. The crossover frequency to 1/f noise was low, about 5 Hz, and the flux noise level at 1 Hz was 440μΦ0/√Hz.
Reduction of laser-induced dark traces in LiNbO3:Mg and LiNbO3:Zn by heat treatment
Authors: Deng Jiachun , Kong Yongfa , Li Jiang , Wen Jinke , Li Bing
Published: July 2002

The dark traces induced by high-power laser radiation in LiNbO3:Mg and LiNbO3:Zn are found to be reduced by annealing the crystals in an O2 atmosphere. Most of the decrease of the second-harmonic generation efficiency η for 1064–532 nm conversion due to dark traces can be recovered in heat-treated crystals. The transmission loss spectra ΔT(λ) of dark traces show a complex absorption band ranging from 365 nm to near infrared, which can be decomposed into three main peaks at 3.1, 2.5, and 1.6 eV. Maximum transmission loss due to dark traces after 1200 shots with an input power density of 18 MW/cm2 is 17% and 25% for as-grown LiNbO3:Zn and LiNbO3:Mg crystals respectively, and it is reduced to 4.6% and 3.8% respectively for heat-treated crystals.
Sheath electric field oscillation and ion kinetics in radio-frequency discharges
Authors: Fadlallah Majida , Booth Jean-Paul , Derouard Jacques , Sadeghi Nader , Belenguer Philippe
Published: July 2002

Time resolved maps of the electric field magnitude in the sheath of discharges in pure H2 have been determined as a function of pressure (0.6 and 1 Torr) and excitation frequency (30 kHz, 1, and 2.78 MHz). The electric field was determined from the Stark splitting of the n=6 level of atomic hydrogen using 2+1 photon laser-induced fluorescence of ground state hydrogen atoms. The sheath electric field oscillations throughout the rf cycle were observed for different values of the rf driving frequency, corresponding to different regimes. We observe a ‘‘low’’ frequency regime at 30 kHz, a ‘‘high’’ frequency regime at 2.78 MHz, and an intermediate regime at 1 MHz, depending on whether the ion density profile is modulated during the rf cycle. This is the first observation of an intermediate regime where the ion transit time across the sheath is comparable to the rf period. Fluid model simulations were carried out and are in good agreement with our experimental observations.
Open tube zinc diffusion into GaAs0.8P0.2 using AlN and SiNx cap films
Authors: Ogihara M. , Taninaka M. , Nakamura Y.
Published: July 2002

The open-tube diffusion of zinc in GaAs0.8P0.2 from a zinc-doped silica film was investigated in detail. Aluminum nitride (AlN) and silicon nitride (SiNx) films were used as the anneal caps. The dependence of diffusion depth on the thickness of an AlN-cap was found to differ from its dependence on SiNx-cap thickness. The selective masked diffusion of zinc using an AlN diffusion-mask was also systematically studied. The diffusion depth in selective masked diffusion was found to depend on both AlN-cap thickness and AlN-diffusion-mask thickness. The experimental results suggest that diffusion depth is not necessarily governed by either cap thickness or diffusion-mask thickness. From this standpoint, the role of film stress on diffusion depth was then quantitatively investigated. It was found that diffusion depth can be scaled well with total film stress in the measured film-thickness range. In this sense, it can be concluded that total film stress is the primary factor that determines the diffusion depth under the measured diffusion conditions.
Comparison of quantum well and single heterojunction structures for acoustic charge transfer devices
Authors: Hayden R. K. , Woods R. C. , Kumagai S. , Yamanouchi K. , Grey R.
Published: July 2002

A number of acoustic charge transfer devices have been fabricated, using both a single heterojunction structure and a quantum well structure. The single heterojunction structure was found to give a signal-to-noise ratio comparable to that given by the quantum well structure. In both cases the ratio was less than unity. The experimental results show that the performance of acoustic charge transfer devices using heterostructures is less dependent on the quality of the epitaxial growth than has previously been believed. The single heterojunction structure has been modelled to show that a device with high signal-to-noise ratio is difficult to obtain. However, the experimental results show that this is not essential for observation of acoustic charge transfer. This combination of results and the present limitations of epitaxial growth show that quantum well structures have little or no practical advantage over single heterojunction structures for use as acoustic charge transfer devices.
Magnetic and magneto-optical properties of MnxPt1−x−yZny
Authors: Wierman Kurt W. , Kirby Roger D.
Published: July 2002

In this work we have prepared thin films of the ternary alloy MnxPt1−x−yZny by magnetron sputtering onto quartz substrates. We have found a wide range of compositions which are strongly ferromagnetic at room temperature. A transition from a cubic to tetragonal phase with decreasing Pt content is confirmed by x-ray diffraction. X-ray diffraction measurements also show a strong (001) reflection consistent with long range order along the c axis for the tetragonal phase. These films show large complex Kerr rotations (up to 0.7°) in the visible spectrum. This combined with their anisotropic structure suggests that they may be suitable for magneto-optic data storage applications.
Phase relations in the system of (Na1/2Bi1/2)TiO3–PbTiO3. I. Structure
Authors: Park Seung-Eek , Hong Kug Sun
Published: July 2002

The region of the (Na1/2Bi1/2)1−xPbxTiO3 phase diagram from 0≤x≤0.2 was established through analysis of structure and thermal anomalies associated with changes in temperature and composition. The rhombohedral-tetragonal morphotropic phase boundary (MPB) was investigated considering the dependence of the rhombohedral lattice distortion of (Na1/2Bi1/2)TiO3 (NBT) on chemical stoichiometry and fabrication processes. It was found that the MPB would lie in the composition range 0.13<x<0.15 when the lattice constant and lattice distortion of (Na1/2Bi1/2)TiO3 are 3.886 Å and 89.6°, respectively. The phase transition sequence of (Na1/2Bi1/2)1−xPbxTiO3 was rhombohedral↔tetragonal↔cubic as that of pure NBT when x was less than MPB composition. However, the intermediate tetragonal phase has either low tetragonal distortion for compositions with x<xrc (composition where rhombohedral↔cubic transition exists) or high tetragonal distortion for compositions with x≳xrc. The changes in structure and phase transition behavior of this solid solution system with temperature and composition are discussed.
Ferroelectric behavior in fluoro-nylons
Authors: Jayasuriya Ambalangodage Champa , Tasaka Shigeru , Ohtani Michitaka , Inagaki Norihiro
Published: July 2002

Ferroelectric behavior was investigated in two fluoro-polyamides (fluoro-nylon) [-NH(CH2)mNHCO(CF2)nCO-]x=m,n+2F. The fluoro-nylons (7,5F, 9,5F) were synthesized by interfacial polycondensation between alkyldiamines and perfluoroglutrichloride. Quenched samples of these polyamides exhibited D−E hysteresis loops with remanent polarization in the range of 29–33 mC/m2 close to the room temperature. After crystallization by annealing near the melting temperature, no ferroelectric behavior was observed. The dipole rotation is considered to be influenced by the substitution of fluorine atoms behalf on hydrogen atoms in the polymers.
Thermal analysis of float-zone traveling solvent crystal growth of LaB6
Authors: Louchev Oleg A. , Otani Shigeki , Ishizawa Yoshio
Published: July 2002

We analyze the thermal regime of float-zone traveling solvent crystal growth of LaB6. We construct a one-dimensional analytical approximation of the process taking into account relevant phase diagram, phase transition kinetics, and the effects of natural and Marangoni convection. We show that convection plays a crucial role in the formation of the thermal and mass transfer regimes of the process. First, convection strongly inhibits the temperature inside the melt. Second, convection inhibits even more strongly the mass transfer resistance of the molten zone and the temperature difference between the dissolution and solidification interface. Natural convection depends strongly on the molten zone height so that increase of the molten zone leads to a strong decrease in the temperature difference between solid/liquid interfaces. The action of Marangoni convection on the heat and mass transfer is shown to be considerably stronger; however, its influence does not depend strongly on the molten zone dimensions. It is shown that only the action of Marangoni convection can enhance mass transport between the dissolution and solidification interfaces to a rate sufficient to implement the growth of LaB6 at a pulling rate of 1 cm/h.
Time decay of excited chromium- and neodymium-doped yttrium aluminum perovskite
Authors: Rotman S. R. , Luria E. , Mares J. A. , Boulon G. , Brenier A. , Lou L.
Published: July 2002

It often occurs that, when dopant ions are introduced into solid matrices, the majority of ions go into a particular site (the main sties) while a small fraction go into sites with other symmetries (subsites). A new model for the decay of excited ions present in both main sites and subsites in crystal matrices is presented. Data from chromium–neodymium doped yttrium aluminum perovskite is analyzed to illustrate this model.
A two-dimensional model of laser ablation of frozen Cl2: A possible neutral beam source for etching applications
Authors: Ventzek Peter L. G. , Suzuki Motoyuki , Date H. , Sakai Y. , Tagashira H. , Kitamori K.
Published: July 2002

Charge damage considerations are prompting the development of neutral beam sources for etching applications. Anisotropic etching with hyperthermal Cl2 and SF6 beams has been demonstrated. We describe a two-dimensional plasma chemistry fluid model of laser ablation of frozen Cl2 in vacuum as a neutral beam source. In this scheme an externally applied electric field would be used to enhance the dissociation rate of Cl2 potentially providing an enhanced Cl content in the beam for a greater etch rate. Laser ablation generated neutral beams also may contain a desirable and controllable ion content which may be used to further enhance the etch rate. Limitations of the concept are discussed.
Optimization of charge sensitivity of a single electron tunneling transistor with a superconducting grain
Authors: Hanke Ulrik , Chao K. A. , Galperin Yu. M.
Published: July 2002

Assuming the absence of 1/f noise, we have calculated the charge sensitivity (CS) of a capacitive-coupled double-junction single electron tunneling transistor (SETT) with a superconducting grain, operating at low temperature and low bias voltage such that the tunneling current is dominated by the Andreev process. In this case the effect of co-tunneling is suppressed without using the complicated fabrication method. We have used a realistic sample to demonstrate the procedure of optimizing the CS of a SETT with respect to relevant physical parameters and structure parameters. With the presently available fabrication technology, our theoretical analysis can serve as a guide for increasing the CS of a SETT beyond 10−6 e/√Hz.
Statistical physics approach to heat transfer in gases
Authors: Dharmadurai G.
Published: July 2002

In view of the difficulty encountered in extending the electrical analogy approach to study axial heat transfer in a cylindrical column of rarefied gas, a statistical physics approach is proposed for evaluating the thermal conductivity of a gas in terms of the probability for collision free travel of a gas molecule in the gaseous column. The resulting expression for thermal conductance of a gas is found to be more realistic than some existing interpolation formulas, as it uniquely defines the criterion for rarefaction. Moreover, acoustic mode of heat transport can be readily incorporated to understand anomalous heat transfer during heat pulse propagation in gaseous columns.
Monte Carlo study of electron transport in III–V heterostructures with doped quantum wells
Authors: Thobel J. L. , Sleiman A. , Bourel P. , Dessenne F. , Baudry L.
Published: July 2002

The transport properties of AlGaAs/GaAs/AlGaAs heterostructures with doped GaAs quantum well have been investigated by means of an ensemble Monte Carlo method. The model accounts for nonparabolicity, size quantization in all valleys, and degeneracy. The influence of doping profile, density of donors and electrons, well width, and temperature are discussed. Both steady state and transient transport have been studied, and the possibility of strong velocity overshoot has been demonstrated. The electron velocity may be strongly influenced by the spatial distribution of impurities. The choice of a doping plane located at one edge of the well allows for obtaining the highest values of mobility, static peak velocity, and maximum transient velocity. At high fields, some parasitic conduction takes place in the barriers and the transport properties are strongly affected by the characteristics of the AlGaAs layers.
Critical current density and flux pinning in Ho-doped melt-processed YBa2Cu3Oy
Authors: Feng Yong , Zhou Lian , Du Shejun , Wu Xiaozu , Tholence J. L. , Vallier J. C. , Monceau P. , Yin B. , Li Jinwei , Zhao Zhongxian , Zhang Yuheng
Published: July 2002

We fabricated highly textured Y1−xHoxBa2Cu3Oy (x=0, 0.2, 0.4, and 0.6) bulk samples by a ‘‘powder melting process’’ method under identical conditions and investigated their critical current densities and flux pinning behavior with a superconducting quantum interference device magnetometer. The dependence of Jc on the magnetic field, estimated by the Bean model, is studied. The results indicate that Jc drops with the magnetic field according to a power law Jc∝H−n (n<0.5), which implies that the Jc value of these samples is controlled by the flux pinning rather weak links. It is found that Jc and flux pinning can be significantly improved by Ho substitution for Y in Y-based superconductors. The reduction of the size of Y2BaCuO5 particles, stress-field pinning, and magnetic pinning created by the Ho addition are considered to be responsible for the increase in Jc and flux pinning.
Fast and slow current tuning of lead-chalcogenide diode lasers
Authors: Kastner J. F. , Richter G. , Herrmann C. , Tacke M.
Published: July 2002

Mid-infrared lead-chalcogenide diode lasers can be operated at convenient operation temperatures using short current pulses and thus allow a wide range of potential applications. Our goal was to optimize the spectral characteristics of pulsed lasers by well-defined current pulse shaping. The high-frequency current tuning coefficient has been evaluated experimentally for this reason. Different tuning mechanisms are discussed by use of a model calculation. The qualitative features can be explained by assuming a separate temperature for the carriers that form a thermodynamic system of their own and are heated by the current. The tuning characteristics can be explained due to carrier concentration variations induced by free-carrier absorption.
Microcavity effect in the optical intersubband absorption of a multiple-quantum-well structure
Authors: Liu Ansheng
Published: July 2002

In a nonlocal semiclassical local-field approach, the linear optical intersubband absorption coefficient of a multiple-quantum-well (MQW) structure inside a microcavity is derived. It is shown that intersubband absorption spectra of the MQW structure are strongly dependent of the effective cavity length. When the cavity length is comparable to the wavelength of light, it is demonstrated that a notable splitting of the intersubband absorption line may occur for the MQW structure having a sufficient number of quantum wells.
Electrical properties of buried oxide–silicon interface
Authors: Dimitrakis P. , Papaioannou G. J. , Cristoloveanu S.
Published: July 2002

A systematic approach of the origin of the generation-recombination mechanism (GR) at the back interface of buried oxide in separation by implanted oxygen (SIMOX) substrates is presented. Metal oxide semiconductor capacitors fabricated on the oxide are synthesized by SIMOX technique and evaluated by C–V, I–V and deep level transient spectroscopy (DLTS) techniques. A shift of flat-band voltage to negative values was observed, denoting the presence of a high density of positive charges into the oxide. They are mainly due to the large concentration of E′ centers. The concentration of interface states was high enough (1012 cm−2 eV−1) compared to that of thermal oxides and to govern the generation-recombination mechanisms at the interface. The activation energy of GR mechanism is very close to the half of Si energy gap. This mechanism affects the temperature formation of the inversion layer. The hold-off time of buried oxide capacitors was obtained by DLTS generation spectra analysis. Oxide charge instability was detected after stress under a relatively low electric field at 450 K. The generation-recombination mechanism was changed after stress, affecting also the hold-off time.
Effective charge parametrization for 7Li, 11B, 12C, 14N, 16O, 27Al, 28Si, 31P, 32S, and 35Cl projectiles traversing Mylar targets
Authors: Porter L. E.
Published: July 2002

Some recent measurements of the stopping powers of Mylar foils for 0.2–2.1 MeV/u 7Li, 11B, 12C, 14N, 16O, 27Al, 28Si, 31P, 32S, and 35Cl projectiles have been subjected to analysis in terms of the modified Bethe–Bloch theory in order to obtain values of projectile effective charge parameters. Although both one- and two-parameter fits were attempted, only the former yielded meaningful results. The one-parameter fits manifested considerable internal consistency, and reasonable consistency with results obtained in recent similar analyses of Kapton, Havar, and nickel stopping powers for 7Li, 11B, 12C, 14N, and 16O projectiles.
Interfaces in Si/Ge atomic layer superlattices on (001)Si: Effect of growth temperature and wafer misorientation
Authors: Baribeau J.-M. , Lockwood D. J. , Syme R. W. G.
Published: July 2002

We have used x-ray diffraction, specular reflectivity, and diffuse scattering, complemented by Raman spectroscopy, to study the interfaces in a series of (0.5 nm Ge/2 nm Si)50 atomic layer superlattices on (001)Si grown by molecular beam epitaxy in the temperature range 150–650 °C. X-ray specular reflectivity revealed that the structures have a well-defined periodicity with interface widths of about 0.2–0.3 nm in the 300–590 °C temperature range. Offset reflectivity scans showed that the diffuse scattering peaks at values of perpendicular wave vector transfer corresponding to the superlattice satellite peaks, indicating that the interfaces are vertically correlated. Transverse rocking scans of satellite peaks showed a diffuse component corresponding to an interface corrugation of typical length scale of ∼0.5 μm. The wavelength of the undulations is a minimum along the miscut direction and is typically 30–40 times larger than the surface average terrace width assuming monolayer steps, independently of the magnitude of the wafer misorientation. The amplitude of the undulation evolves with growth temperature and is minimum for growth at ∼460 °C and peaks at ∼520 °C. Raman scattering showed the chemical abruptness of the interfaces at low growth temperatures and indicated a change in the growth mode near 450 °C.
Photoluminescence and Raman scattering studies of 2 MeV Yb+-implanted InP as a function of etching depth
Authors: Katsumata Hiroshi , Uekusa Shin-ichiro , Sai Hironobu , Kumagai Masao
Published: July 2002

In ion-implanted semiconductors, details of the defects involved and annealing mechanisms which determine the final disorder structure are complicated and difficult to characterize. To investigate the residual defect distribution of the implanted layers, optical experiments, photoluminescence, photoluminescence excitation, and Raman scattering have been performed on 2 MeV Yb+-implanted InP and subsequently annealed at 750 °C for 15 min as a function of chemical etching depth (d) down to d=4.51×Rp (Rp: projected range =410 nm). Their results were compared with those obtained from Rutherford backscattering spectrometry (RBS) channeling analysis. The above optical experiments showed that two residual defective regions are present at depths of d=0.34–0.80×Rp and about d=2.56×Rp, whereas RBS channeling analysis indicated the existence of the only former region. We assign the type of the two defective regions to ‘‘clamshell’’ defects in the former region and to ‘‘end-of-range’’ defects in the latter region.
Ion beam mixing at the Fe2O3/Al2O3 interface
Authors: Marest G. , Ogale S. B. , Hannoyer B. , Joshi S. , Benyagoub A. , Moncoffre N.
Published: July 2002

Thin Fe2O3 layers (44 and 55 nm) were deposited by pulsed excimer laser ablation on single-crystal alumina (α-Al2O3) substrates heated at 675 °C. The ion beam mixing of these α-Fe2O3/α-Al2O3 couples was carried out using 300 keV Kr3+ ions at a fluence of 2×1016 ions/cm2. The mixing effect was followed by Rutherford backscattering spectrometry (RBS), conversion electron Mössbauer spectroscopy, and grazing incidence x-ray diffraction method. RBS spectra do not show any evidence of mixing at the interface, whereas the data obtained with the two other techniques display phases like oxygen deficient Fe3O4, Fe3−yAlyO4, and Fe1+xAl2−xO4. For this last phase, x is determined as being equal to about 0.5. It is shown that ion beam mixing is more efficient for the thinner Fe2O3 layer, in accordance with the projected range of the Kr3+ ions.
Statistical modeling of dynamic random access memory data retention characteristics
Authors: Hiraiwa A. , Ogasawara M. , Natsuaki N. , Itoh Y. , Iwai H.
Published: July 2002

A statistical model to investigate the distribution of dynamic random access memory data retention times is proposed. The model assumes that the retention time is determined by a junction leakage current generated at carrier traps by a Shockley–Read–Hall process, and that the trap levels are randomly distributed not only among the memory cells but also within a cell. Monte Carlo results based on the model were in excellent agreement with experimental results, which confirmed the validity of the model. An analytical expression of the retention time distribution was also derived, and proved a good approximation near the 50% cumulative probability. Based on the model, variation in the retention time distributions among samples was found to be related to different trap-level distributions at the SiO2/Si interface.
Thermoelectric amplification of phonons in bulk semiconductors under a strong magnetic field
Authors: Rodrigues C. , Fonseca A. L. A. , Nunes O. A. C.
Published: July 2002

We consider the problem of phonon instability in an electron-phonon system of a semiconductor in a temperature field upon variation of a strong (quantizing) static magnetic field. It is found that the phonons may become unstable when certain values for the temperature gradient-drift velocity and the magnetic field are exceeded. However, even after the thresholds are exceeded, it is predicted that there exist alternate bands of the magnetic field, in which the phonons are unstable in one band, stable in the next band, unstable again in the following band, etc. These alternate bands have their origin in the discreteness of the Landau levels of the electrons. An application is made for a GaAs sample.
A simple transport model for submicron semiconductor device analysis
Authors: Bark J. O. , Gildenblat G.
Published: July 2002

A modified hydrodynamic model for the analysis of submicron semiconductor devices is derived from the first four moments of a Boltzmann transport equation without invoking any phenomenological relations. Instead, the balance equations are truncated using a suitable ansatz for the electron distribution function in the fourth moment equation. Both conventional and modified hydrodynamic models are applied to an n+n−n+ ballistic diode, and the results are compared. The new approach successfully suppresses spurious velocity overshoot without increasing the complexity of the model. Finally, the simulation of a two-dimensional submicron metal-oxide-semiconductor field-effect transistor by the modified hydrodynamic model is presented.
Exponential critical state model applied to ac susceptibility data for the superconductor YBa2Cu3O7−δ
Authors: Araújo-Moreira F. M. , Ortiz W. A. , de Lima O. F.
Published: July 2002

We derive new expressions for the average magnetization loops, M(H), based on the exponential critical state model. The components χ′ and χ″ of the complex susceptibility are calculated and an algorithm to fit ac susceptibility data is discussed. This algorithm is employed to study the intergranular response χ′(Hm) and χ″(Hm) measured for two samples of YBa2Cu3O7−δ as a function of the ac field amplitude Hm. One sample is a porous sintered cylinder and the other is a very dense melt-textured bar. In both cases good fits of the calculated components χ′ and χ″ are obtained using an algorithm that involves two free parameters, the full penetration field, Hp, and the sample quality factor, p. An interesting result for the melt-textured sample is the observation of a step in χ′(Hm) curves at very low Hm, possibly associated with grain clustering.
Frequency–temperature relations of thickness-shear and flexural vibrations of contoured quartz resonators
Authors: Lee P. C. Y. , Wang J.
Published: July 2002

The two-dimensional first-order equations of incremental vibrations superposed on the steady and homogeneous thermal deformations of crystal plates by Lee and Yong are reduced to a set of four coupled equations for frequencies up to and including those of the fundamental x1x2 (or slow) thickness-shear mode. These equations are employed to study the frequency–temperature relations of the thickness-shear and flexural vibrations of beveled plates of AT cut of quartz. Closed form solutions for the uniform portion and analytical solutions in terms of infinite power series for the contoured portions are obtained. By requiring these solutions to satisfy the continuity conditions and traction-free edge conditions, the frequency equation is obtained. Effects of the contouring and the orientation angle of the plate are examined systematically by computing the frequency changes as a function of temperature increment for various values of geometric parameters and the orientation angle of the plate. Similar results for the uniform and finite plates are also computed and presented for comparison.
Epitaxial thin-film ruby as an ion-irradiation damage sensor
Authors: Wen Q. , Yu Ning , Clarke D. R.
Published: July 2002

The fluorescence from a thin ruby film, formed by epitaxial growth on a sapphire substrate, is shown to be a sensitive monitor of both the irradiation dose and the strain produced by irradiation of argon ions having an end of range exceeding the thickness of the ruby film. Decreases in fluorescence intensity are detectable for doses in excess of 1012 cm2, whereas no damage is detectable by Rutherford backscattering spectrometry/channeling until doses almost two orders of magnitude larger. Using the systematic shift in fluorescence frequency observed with irradiation, it is concluded that lattice strain accumulates rapidly for doses in excess of 1014 cm2.
Raman spectroscopic analysis of stress on GaAs-SiO2 interface and the effect of stress on tin diffusion in GaAs
Authors: Rashid A. B. M. Harun-ur , Kishi Masato , Katoda Takashi
Published: July 2002

Stress generated on GaAs-SiO2 interface during annealing and the effect of this stress on tin diffusion in GaAs have been investigated using laser Raman spectroscopy. It was found that compressive stress exists on the surface of GaAs after annealing, which increases with increase of the SiO2 cap layer thickness. The compressive stress on GaAs is generated during annealing and is due to the difference of the thermal expansion coefficients between GaAs and SiO2. The increase of compressive stress on the surface of GaAs decreases the diffusion coefficient of tin in GaAs. This occurs due to the reduction of Ga vacancy in a compressively stressed sample from the equilibrium Ga vacancy of an unstressed sample.