bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal conductivity of cast iron: Models and analysis of experiments
Authors: Helsing Johan , Grimvall Göran
Published: July 2002

Cast iron can be viewed as a composite material. We use effective medium and other theories for the overall conductivity of a composite, expressed in the conductivities, the volume fractions, and the morphology of the constituent phases, to model the thermal conductivity of grey and white cast iron and some iron alloys. The electronic and the vibrational contributions to the conductivities of the microconstituents (alloyed ferrite, cementite, pearlite, graphite) are discussed, with consideration of the various scattering mechanisms. Our model gives a good account of measured thermal conductivities at 300 K. It is easily extended to describe the thermal conductivity of other materials characterized by having several constituent phases of varying chemical composition.
Microwave dielectric measurements of zirconia-alumina ceramic composites: A test of the Clausius–Mossotti mixture equations
Authors: Robertson W. M. , Arjavalingam G. , Shinde S. L.
Published: July 2002

The complex dielectric properties of a series of zirconia-alumina ceramic composites are characterized in the 15–140 GHz frequency range. The measured dielectric constants are compared to various forms of mixture equations derived from local field considerations, and to theoretical relations that define bounds on the range of possible values. The closest agreement is obtained with the effective medium theory.
Origin of superparamagnetism in nickel oxide
Authors: Richardson J. T. , Yiagas D. I. , Turk B. , Forster K. , Twigg M. V.
Published: July 2002

It has been known for some time that particles of nickel oxide of less than about 100 nm in size show superparamagnetism that increases as the particle size decreases. The origin of the particle magnetic moment responsible for this behavior has never been fully explained. This research indicated that the size of the particle rather than the presence of nonstoichiometry or impurities of reduced nickel determines the moment. The critical experiment was the measurement of magnetization versus magnetic field for a sample of nickel oxide prepared under conditions that preclude metallic nickel. Almost identical results were found for the original sample, which was black in color and thus nonstoichiometric, and after mild reduction in hydrogen at 400 K, which produced stoichiometry and changed the color to green. The magnetic susceptibility was inversely proportional to the particle size for a given method of preparation. This is consistent with a simple model of incomplete edges on the bounding planes of the crystallite and provides a possible basis for a practical method for measuring particle size in nickel oxide-containing samples.
Comparison between conventional and plasma source ion-implanted femoral knee components
Authors: Chen A. , Scheuer J. T. , Ritter C. , Alexander R. B. , Conrad J. R.
Published: July 2002

Nitrogen ion implantation of Ti-6Al-4V knee joint femoral components was carried out by both plasma source ion implantation (PSII), a non-line of sight technique, and conventional beamline implantation. Implantation using the PSII process was performed on a flat sample as well as a 2×2 square array of components to demonstrate batch processing capability. The retained dose of the flat sample and at different locations on the implanted components was measured by a scanning auger microprobe (SAM). The variation in dose of the PSII treated component was found to be within the SAM error, while the dose at one location on the beamline implanted component was found to be significantly low. For the beamline case, the SAM results show good agreement with the PC profile computer simulation, which includes the angular dependence of sputtering.
Granular cobalt in a metallic matrix
Authors: Childress J. R. , Chien C. L.
Published: July 2002

Ultrafine face-centered-cubic Co particles in a conducting Cu matrix have been produced by annealing of sputtered metastable CoxCu1−x alloy films (0.10≤x≤0.80). The average size of the particles, and therefore the magnetic properties of these materials, can be easily controlled by the processing parameters. Single-domain behavior results in coercivities in excess of 600 Oe, while the magnetization is determined by the choice of alloy composition. The evolution of the structural and magnetic properties have been studied as a function of annealing conditions, and are compared to those previously observed with Fe-based materials.
Efficient photo-enhancement of GaP and AlGaP growth in chemical beam epitaxy
Authors: Yoshimoto M. , Ozasa K. , Matsunami H.
Published: July 2002

The growth rate of GaP and AlGaP epitaxial layers was efficiently enhanced by N2-laser irradiation at low substrate temperatures in chemical beam epitaxy. The photo-enhancement efficiency, defined as the ratio of the number of deposited Ga atoms to the number of irradiating photons per unit area per unit time, is estimated to be 7×10−4. The decomposition of triethylaluminum was also enhanced by the irradiation, but less efficiently.
Reflection of electroacoustic waves in piezoelectric solids: Mode conversion into four bulk waves
Authors: Every A. G. , Neiman V. I.
Published: July 2002

In the analysis of the reflection of plane electroacoustic waves at the boundary of a piezoelectric half-space, four partial waves are required in the reflection field in order that the mechanical and the electrical boundary conditions can be satisfied. It is usually assumed that at least one of these waves is evanescent. The purpose of this paper is to point out that in strongly piezoelectric solids all four reflected waves may, for certain reflection geometries, be homogeneous bulk waves. This will be the case when the longitudinal sheet of the acoustic slowness surface possesses negatively curved regions, thus permitting a re-entrant longitudinal mode. Calculations are reported on Rochelle salt and Ba2NaNb5O15, which show that for an incident longitudinal wave the reflection coefficient for the fourth bulk wave may be as large as unity, depending on the angle of incidence.
Arrhenius parameters for the rate process leading to catastrophic damage of AlGaAs-GaAs laser facets
Authors: Moser A. , Latta E. E.
Published: July 2002

The time dependence of catastrophic optical mirror damage (COMD) is investigated for cw operation of AlGaAs-GaAs quantum well lasers. The apparent Arrhenius parameters (i.e., the activation energy and pre-exponential factor) for the rate process leading to COMD are determined. In particular, we compare the rate process for various cleaved facets with and without a subsequent plasma oxidation step. Analysis of the experimental Arrhenius parameters indicates that surface reactions on the corroded facets are responsible for facet degradation accompanied by heating. A tentative model of the facet heating that ultimately leads to COMD is presented.
Optical and electrical characterization of magnesium-doped bismuth substituted lutetium iron garnet thin films
Authors: Butler J. C. , Kramer J. J. , Lee J. N. , Ings J. B. , Belt R. F.
Published: July 2002

Near-infrared optical absorption and Faraday rotation have been studied, in addition to the room-temperature sheet resistance, in a series of magnesium-doped bismuth substituted lutetium iron garnet (Bi:LuIG) thin films grown by liquid phase epitaxy. Faraday rotation was measured at 1150 and 1300 nm as a function of the MgO concentration in the melt. Optical absorption data indicate valence exchange as a possible mechanism for increased optical absorption at compositions different from charge compensation. Faraday rotation data display a magnesium doping dependent behavior, as do the I-V characteristics. Additionally, the I-V data of unetched and etched films near compensation suggest a two-layer structure to the films.
The effect of molecular ions on the plasma parameters in a medium pressure rare gas radio frequency discharge positive column
Authors: Chang Jen-Shih , Ichikawa Y. , Hobson R. M. , Matsumura S. , Teii S.
Published: July 2002

A rare gas positive column plasma theory that takes into account the effect of various chemical processes on the production, loss, and interconversion of metastable and ion species is developed and compared with experimental results. The experimental measurements have been made in a 4 cm i.d. radio frequency (rf) discharge tube for He, Ne, and Ar. An electrostatic triple probe was used to monitor the electron temperature and plasma density, and a mass spectrometer was used to analyze the ion species. The results show that the molecular ion becomes important when gas pressure is above 1 Torr in the Ar and Ne plasmas. For a He plasma, the molecular ion always plays an important role in the plasma process. Good agreement has been observed between present model and experiments.
Two-dimensional modeling of electron cyclotron resonance plasma production
Authors: Yasaka Yasuyoshi , Fukuyama Atsushi , Hatta Akimitsu , Itatani Ryohei
Published: July 2002

For the numerical simulation of electron cyclotron resonance plasma production, a two-dimensional model that describes wave propagation and plasma transport is developed. The modeling code calculates profiles of electromagnetic wave fields, power absorption of electrons, and temporal evolution of plasma densities in a bounded, inhomogeneous, cylindrical system. The calculation of the plasma production in a mirror magnetic field shows that the plasma production property is very sensitive to the antenna location.
Effects of defect scattering on guided electron waves in two coupled quantum wires
Authors: Wang Jian-Qing , Gu Ben-Yuan , Yang Guo-Zhen
Published: July 2002

We have investigated how the presence of a defect in two coupled quasi-one-dimensional quantum wires influences the propagation properties of guided electron waves in the system. The defect potential in the two dimensional electron gas is modeled by a two dimensional δ function. In elastic scattering, the transfer of the electron among various eigenstates of the uncoupled quantum wires and from one wire to the other is largely affected by the defect potential. For the single mode shallow potential well system, the defect causes incomplete energy transfer between the channels. As the position of the defect varies along the channel, the characteristics of the mode amplitude functions change dramatically as the defect passes through nodes of the amplitude function of the incident waves in the channel. When the defect position is away from these nodes the amplitude functions of the transmitted waves reduce greatly due to the large reflection by the defect. And their variation never reaches zero as in the case without defect. When the defect position is near these nodes the tunneling characteristics between the two channels are as if the defect is absent since the reflection is minimal. For the strong scatterer we find a pinning effect in that the mode amplitude function of the channel where the defect is located always has one of its transmission minima pinned down to the defect. We introduce a possible way of injecting the propagating electron into a particular channel and at a given longitudinal position, by controlling the position of the defect in the structure. In the multimode deep potential well structure, the transfer from an eigenstate of the uncoupled quantum wires to the other states is greatly enhanced and the characteristics of the amplitude functions are dramatically changed by intersubband scatterings.
Model for spin coating in microelectronic applications
Authors: Yonkoski R. K. , Soane D. S.
Published: July 2002

A thorough investigation of the mass and momentum equations pertaining to the spin-coating process has been performed. A scaling analysis forms the foundation to determine the relevant characteristic quantities of the process and allows the assumptions and simplifications made by previous authors to be critically examined. Based on this analysis, the complete equations are reduced to a two-dimensional set of equations while retaining the essential physics of the problem. By further assuming a uniform film thickness over the disk, a one-dimensional model has been developed to assess the importance of the coupling between fluid flow and mass transfer during spin coating. The model predictions for the final film thickness can be presented in such a manner that the results superimpose onto one curve. In this way the film thickness and its relationships with process and material properties, initial solvent content, and spinning conditions can be succinctly expressed in terms of two characteristic parameters. The literature confusion over the exponent of the power-law dependence of the final film thickness on the rotational speed is also clarified. The model predicts an exponent of −1/2 which agrees with most experimental investigations. However, when the total spin time is too short, the exponent may deviate from −1/2. Finally, a split mechanism model that assumes that the spin-coating process could be divided into two stages, one where fluid flow is occurring exclusively and the other where only mass transfer occurs, has been shown to be quantitatively inaccurate.
Comment on ‘‘A Comment on dielectric theory: Differential equations and permittivity’’
Authors: Alison J. M.
Published: July 2002

A number of models for the non-Debye dielectric response have been developed during the last few years. One such example reported by Kliem [J. Appl. Phys. 70, 1861 (1991)] from the work by Guo and Guo [J. Phys. C 16, 1955 (1983)] is not compatible with linear response theory, except under the condition of a step-function electric field; this has lead to a confusion of this model with those commensurate with linear response theory. The present communication resolves this ambiguity.
Transport and near-infrared optical properties of ErSi2 thin films
Authors: Sagnes I. , Vincent G. , Badoz P. A.
Published: July 2002

We present the study of the resistivity and Hall coefficient of ErSi2 thin films epitaxially grown on a Si substrate as a function of temperature and film thickness. Then, we report the first study of the complex index at energies below the silicon band gap (0.5–1 eV). From these data we calculate the absorption length in ErSi2, which is a critical parameter for the design of an efficient silicide silicon photodetector.
Step-function current in a metallic foil as a step-function heat-flux source
Authors: Miller Martin S.
Published: July 2002

An exact solution is derived to the one-dimensional, time-dependent, heat-conduction equation for a two-layer, semi-infinite, composite solid with uniform heat generation in the surface layer, no heat transfer through the surface plane, and uniform initial temperature. The interface between the two layers is assumed to have no thermal contact resistance. This solution enables a discussion of the ideality with which a step-function electric current in a metallic foil can generate a step-function heat flux into a contacting semi-infinite solid. Previous measurements of thermal diffusivity (based on the above conditions) have relied on the idealized constant-flux solution for data reduction. It is shown here that the temperature errors in the substrate arising from nonideality of the constant-flux boundary condition increase with depth into the substrate, foil thickness, and decreasing thermal conductivity/diffusivity of the substrate.
Photoluminescence characteristics of CuAlxIn1−xSe2 solid solutions grown by iodine transport technique
Authors: Miyake Hideto , Sugiyama Koichi
Published: July 2002

Photoluminescence (PL) characteristics at 77 K have been investigated for CuAlxIn1−xSe2 chalcopyrite quaternary crystals (x=0∼1) grown by an iodine chemical vapor transport technique. The effect of annealing of the crystals in various atmospheres on the PL spectra is also studied. The emission bands in the PL spectra are found to be classified into five types. The origins of those bands are discussed.
The variation of anisotropy and magnetization orientation with temperature in Tb/Fe multilayers
Authors: Wang Y. J. , Luo C. P. , Kleemann W. , Scholz B. , Brand R. A. , Keune W.
Published: July 2002

On the basis of the co-effect of the crystal field with a random distribution and the molecular field and using anisotropic static magnetic couplings, we calculated the polar angle Θ of the magnetic moment in 15×(26 Å Tb/40 Å Fe)+40 Å Fe multilayers as function of temperature from 4.2 to 300 K, which agrees well with experiment. As a result of the calculation, the width of interface mixing layer and the coefficient of the crystal field are determined.
The effect of deposition process on the magnetic properties of coupled permalloy thin films
Authors: Hill E. W. , Li J. P. , Birtwistle B. K.
Published: July 2002

Double layer thin films of permalloy (layer thickness 200–1300 Å) with tantalum (50 Å) as a nonmagnetic spacer have been prepared by e-beam evaporation. The effect of deposition parameters, especially the substrate temperature on the magnetic properties of these films has been examined. The coercivity(Hc) of the double layer films was found to be very sensitive to the substrate temperature in the permalloy layer thickness range of 200–600 Å. The coercivity of the films deposited at 40 °C is lower than at 300 °C and is almost independent of the Permalloy layer thickness. The XRD patterns and STM images of these two films exhibit large differences in permalloy grain size and grain orientation. However, the Hc of the single layer films deposited under the same conditions as the double layer films shows no significant change in this thickness region. The results indicate that the change of interface condition is primarily responsible for the Hc variation in the coupled films deposited at different substrate temperatures and strongly suggest that interface roughness plays a dominant role in the coupling between the permalloy layers.
Synthesis of nano-sized barium ferrite particles using an inorganic dispersing phase
Authors: Lee Chung-Kook , Speyer Robert F. , Spratt Geoffrey W. D.
Published: July 2002

Nano-sized barium ferrite powders were successfully synthesized at temperatures below 600 °C without melting in a 0.313 BaO-0.258 B2O3-0.100, Na2O-0.330 Fe2O3 system, from an aqueous solution of corresponding salts. The change in crystallization behavior with varying decomposition conditions, and resultant magnetic properties were analyzed using x-ray diffraction, TEM, and vibrating-sample magnetometry, respectively. The defects which acted as nucleation sites for heterogeneous crystallization originated from decomposable constituents remaining up to the crystallization temperature. These defects were eliminated by spray drying and proper oxidation of the starting mixture before crystallization. Barium ferrite powders, having average particle size of 50–70 nm, showed a saturation magnetization (MS) of 38.37 emu/g, coercivity (HC) 2.9 kOe, and a squareness of 0.528.
Defect band behavior in p-Cd0.96Zn0.04Te by hydrogen passivation
Authors: Kim M. D. , Kang T. W. , Kim J. M. , Kim H. K. , Jeoung Y. T. , Kim T. W.
Published: July 2002

Photoluminescence measurements were carried out in order to investigate the dependence of the optical properties of p-Cd0.96Zn0.04Te single crystals on hydrogen passivation conditions. After the p-Cd0.96Zn0.04Te was annealed at 500 °C in a Cd atmosphere for 5 h, the luminescence due to the recombination of the electrons in the conduction band with acceptors (eA°) and to the donor–acceptor pair (DAP) transitions disappeared. After the p-Cd0.96Zn0.04Te was hydrogenated, the intensity of the exciton luminescence increased so that the (eA°) and DAP peaks related to the Cd vacancies disappeared, and the defect band in the low energy range between 1.4 and 1.5 eV also vanished. These results indicate that hydrogen atoms passivated not only shallow donors but also deep acceptor impurities and that the hydrogen atoms were separated from the hydrogenated samples at 400 °C due to their thermal energy.
Optically induced recovery by near band gap photons (1.4 eV<hν<1.5 eV) of EL2 level from its metastable state in semi-insulating GaAs
Authors: Jiménez Juan , Alvárez Alejandro , Chafai Mohammed , Sanz Luis F. , Bonnafé Jacques
Published: July 2002

The study of the recovery of the EL2 related photocurrent by photons of the near-band gap spectral range (1.4–1.51 eV), after photoquenching reveals that the amount of EL2 levels that can be quenched depends on the excitation conditions. In particular light of the 1.44 eV, photocurrent band, produces an increase in the amount of EL2 quenchable levels. This is discussed in terms of an actuator level, whose charge state controls the transition to the metastable state and on the other hand ensures the electrical compensation when EL2 is in the metastable configuration, for which it is in its neutral charge state, and hence unable to compensate the ionized shallow acceptors.
Investigation of room-temperature ion beam hydrogenation for the removal of traps in silicon ion beam damaged metal-oxide-silicon structures
Authors: Kar S. , Ashok S.
Published: July 2002

Electrically active defects were generated in metal-oxide-silicon (MOS) structures by implantation of 16 keV Si ions into the oxide (350 Å thick) of oxidized silicon wafers. Subsequently, hydrogenation was carried out at room temperature by 400 eV H ions from a Kaufman source. To examine the nature of interaction between the H ions and the electronic traps and the efficacy of ion beam hydrogenation, current-voltage, and comprehensive admittance-voltage-frequency measurements were made. The measured data were analyzed to yield information on the trap and other important parameters of the MOS structure. The experimental data indicated impressive passivation of the ion beam induced damage by room-temperature hydrogenation. Many and most of the insiduous effects of radiation damage were removed, some completely. However, the results also indicated generation of some H-defect complexes during hydrogenation, leading to residual traps in the hydrogenated samples.
Ultrashort-pulse propagation in dye laser amplifiers
Authors: Jiang Shuanghua , Casperson Lee W.
Published: July 2002

A semiclassical model is presented for ultrashort-pulse dye laser amplifiers. The model permits a discussion of important aspects of short-pulse amplification such as pulse shape, pulse energy, and gain saturation. Coherence effects are found to be important in characterizing the evolution of amplified pulses in the subpicosecond and femtosecond regimes. The results are compared with those obtained using the corresponding rate equation model.
Dielectric polarizabilities of ions in oxides and fluorides
Authors: Shannon R. D.
Published: July 2002

A set of 61 ion polarizabilities has been derived from the dielectric constants of 129 oxides and 25 fluorides using a least squares refinement technique in conjunction with the Clausius–Mosotti equation. These polarizabilities can be used to estimate mean dielectric constants of ‘‘well-behaved’’ compounds. They should be particularly useful in calculation of mean dielectric constants of compounds whose dielectric constants have not been determined. They can also be used as a framework for distinguishing unusual dielectric behavior from normal dielectric behavior where deviations can frequently be attributed to piezo- or ferroelectricity, conductivity (ionic or electronic), ‘‘rattling’’ or ‘‘compressed’’ cations with correspondingly high or low polarizabilities, or the presence of dipolar impurities. Deviations observed from calculated dielectric constants can be used to search for unusual physical behavior.
Determination of diffusion profiles of neodymium in lithium niobate by means of spatially resolved fluorescence measurements
Authors: Hempstead Martin
Published: July 2002

The application of spatially resolved measurements of fluorescence intensity to the determination of diffusion profiles, in this case of neodymium ions into lithium niobate, and to the concentration dependence of the fluorescence lifetime is discussed. The technique permits a precise determination of diffusion depth, but extraction of detailed point-by-point concentration measurements is not possible. A detailed analysis of the effect on the accuracy of the method of systematic uncertainties, including quantum electrodynamical corrections and concentration-dependent lifetimes, is given. The overall systematic error in measurement of diffusion coefficient is shown to be approximately 10%. The diffusion coefficients measured are consistent with previous values, but the fluorescence lifetimes obtained are probably shorter than for bulk-doped Nd:LiNbO3.
Electronic structure of silicon nitride studied by both soft x-ray spectroscopy and photoelectron spectroscopy
Authors: Sénémaud C. , Driss-Khodja M. , Gheorghiu A. , Harel S. , Dufour G. , Roulet H.
Published: July 2002

The valence and conduction band states of crystalline silicon nitride α-Si3N4 have been studied by using two complementary experimental methods. The total valence band distribution has been analyzed by x-ray induced photoelectron spectroscopy. The Si 3p valence states and the Si p conduction states have been probed selectively by x-ray emission and absorption spectroscopies, respectively. The experimental curves have been compared in the same energy scale referred to the Fermi level. Our results show clearly that the N 2pπ states of Si3N4 are located at the top of the valence band while Si 3p states, mixed to N 2p states and, respectively, to N 2s states are located at about EF−8.4 eV and EF−19.6 eV. Our experimental results are in very good agreement with theoretical simulations of the spectra made from recent density of states calculations by Robertson [Philos. Mag. B 63, 47 (1991)] in a tight binding approach.
Simulations and experiments of SiC heteroepitaxial growth on Si(001) surface
Authors: Kitabatake Makoto , Deguchi Masahiro , Hirao Takashi
Published: July 2002

Mechanism of SiC heteroepitaxial growth by the carbonization of the Si(001) surface was studied at the atomic scale using molecular dynamics (MD) simulations and molecular beam epitaxy (MBE) experiments. Heteroepitaxial growth of single crystal 3c-SiC on the Si(001) surface (3c-SiC[001]∥Si[001] and 3c-SiC[110]∥Si[110]) was observed in both the MD simulations and MBE experiments. Breaking of the Si—Si bonds and shrinkage of the [110] Si rows with C atoms are possible mechanisms for the heteroepitaxial growth of SiC on Si(001). Microscopic structures and mechanisms of the twin formations and pit formations are discussed. Ultraviolet light irradiation is proposed and confirmed to enhance the epitaxial growth of SiC in the MBE experiments.
Bias dependence of Schottky barrier height in GaAs from internal photoemission and current-voltage characteristics
Authors: Ishida Toshiki , Ikoma Hideaki
Published: July 2002

Bias dependence of Schottky barrier height φB was directly measured using an internal photoemission effect in Au-n-GaAs Schottky barrier diodes under both the forward and reverse applied voltages. φB increased by about 0.015–0.016 eV as the forward bias increased from 0 to 0.3 V. This is probably due to an applied-voltage-induced change in electron population in the interface states. The results were compared with the bias dependence derived from dark forward current-voltage (I-V) characteristics. Both bias dependences were in good agreement, indicating that nonideal forward I-V characteristics (a deviation from the ideal thermionic emission theory) could be fully explained by the bias dependence of φB for diodes of a relatively good quality (an ideality factor, n=1.02–1.07). The effective Richardson constant A** was calculated to be about 1.3–1.4×105 A K−2 m−2 for the diodes of the lower n values using the value of the measured Schottky barrier height at zero bias. These values of A** were higher than the calculated value of about 8×104 A K−2 m−2 and that of 0.41±0.15×104 A K−2 m−2 reported by Missous and Rhoderick [J. Appl. Phys. 69, 7142 (1991)]. This is probably due to an enhancement of an electron tunneling through the high density interface states in our case. φB decreased by about 0.05–0.06 eV when the reverse voltage increased from 0 to 3.0 V. An image force lowering effect could not account for this large reverse bias dependence of the barrier height. The nonideal reverse I-V characteristics could not be interpreted solely by the bias dependence of φB. This discrepancy was attributed to other leakage current mechanisms.
γ-ray diagnostics of α slowing in inertial confinement fusion targets
Authors: Dendooven Peter G. , Drake R. Paul , Cable Michael D.
Published: July 2002

For large inertial confinement fusion deuterium-tritium targets, a way to diagnose α slowing might be via capture reaction γ rays. Calculations are presented for two such methods: one uses the α+T direct capture γ rays, the other is based on a series of resonant α-capture reactions. For small targets (ρR≤0.02 g/cm2), the total α+T γ-ray yield relative to the DT neutron yield is temperature independent and proportional to the ρR value. For large targets (ρR≥0.2 g/cm2), this quantity becomes temperature dependent and ρR independent. Some experimental aspects are discussed.
Millimeter wavelength attenuation efficiencies of fibrous aerosols
Authors: Bruce C. W. , Jelinek A. V. , Halonen R. M. , Stehling M. J. , Pedersen J. C. , Waterman P. C.
Published: July 2002

Extinction cross sections normalized to particle volume for two fibrous graphitic aerosols were measured at 0.319 cm (94 GHz) and 0.857 cm (35 GHz). Characterization of the aerosol was performed using several techniques, that is, dosimetrically, through time correlation of millimeter wavelength extinction signals with scattered radiation at much shorter wavelengths, through time correlation with a nearly colinear measurement of extinction at visible wavelengths and using a purpose-built time resolved particle collector system. Results compare well with existing detailed theory.
Determination of thermal parameters and the optical gap of poly(3-butylthiophene) films by photopyroelectric spectroscopy
Authors: Melo W. L. B. , Pawlicka A. , Sanches R. , Mascarenhas S. , Faria R. M.
Published: July 2002

Thermal parameters and the optical gap of undoped poly(3-butylthiophene) films were determined by photopyroelectric spectroscopy, using a PVDF film as the pyroelectric detector. The band gap energy was determined using both the amplitude and the phase curves for different chopping frequencies. When the theoretical model developed by Mandelis and Zver [J. Appl. Phys. 57, 4421 (1985)], was applied to the experimental results comprising amplitude and phase difference spectra, the thermal diffusivity and the thermal conductivity were obtained as fitting parameters.
Effects of ferroelectric switching on the dielectric and ferroelectric properties in lead zirconate titanate ceramics and their modeling
Authors: Pan Wuyi , Sun Shan , Fuierer Paul
Published: July 2002

Effects of ferroelectric switching on dielectric and ferroelectric properties in lead zirconate titanate ceramics are investigated. Ferroelectric switching induces rejuvenation of weak field dielectric constant, K, and ferroelectric polarization, P, initially through the ac field deaging effect, and then induces accelerated decrease in K and P through the ferroelectric fatigue effect. ‘‘On shelf’’ aging of K, ferroelectric switching induced decrease of K, ac field deaging induced augmentation in K and P, and ferroelectric polarization fatigue are illustrated and intercompared. The experimental results are modeled and explained by the phenomenological principles and atomistic mechanisms for the participation of domain walls and bulk polarization in on shelf aging, ac field deaging, and ferroelectric fatigue effects.
Particle size and cooperative behavior effects on KNO3 phase transitions
Authors: Westphal M. J.
Published: July 2002

Particle size effects on the phase transition temperatures of KNO3 at atmospheric pressure were characterized using heat-flow calorimetry. The phase II–I transition temperature was relatively unaffected by particle size, whereas the phase I–III transition temperature was reduced up to 4 °C for particle sizes <38 μm. The phase III–II transition temperature decreased sharply for particle sizes <240 μm, and for 38 μm particles was 44 °C lower than that reported for bulk material. Utilizing 22 μm SiC powder to separate the same range of KNO3 particle sizes, it was shown that cooperative behavior played a significant, but lesser role than the KNO3 particle size in determining the phase transition temperatures. The phase II–I transition temperature increased with decreasing particle size for particle sizes <240 μm when physically separated by SiC particles. The phase I–III transition temperature was relatively unaffected by cooperative behavior. For particle sizes <61 μm, cooperative behavior was unimportant and particle size assumed the dominant role in controlling the phase III–II transition temperature. The general trend of transition temperature as a function of particle size was similar to reported results for KNO3 thin films, but exhibited significant differences when compared to reported results for KNO3 powder. The dependence of transition enthalpy on particle size for the three phase transitions is discussed and the specific heat of KNO3 powder in phase III at atmospheric pressure is reported.
X-ray reflectometry study of interdiffusion in Si/Ge heterostructures
Authors: Baribeau J.-M.
Published: July 2002

Interdiffusion in molecular-beam-epitaxy-grown Si-Ge heterostructures has been investigated by grazing incidence x-ray reflectometry. Measurements on Si1−xGex/Si superlattices reveal that the thickness of the Si1−xGex layers increases when intermixing is induced by high-temperature annealing. This results from a strong composition dependence of the Ge diffusion coefficient in Si1−xGex. Experiments on coherently strained superlattices show that the diffusion rate is faster in the early stage of annealing, before the strain is relieved. This suggests that strain enhances interdiffusion at the interfaces. Similar experiments performed on (SimGen)p atomic layer superlattices show that considerable intermixing occurs in these heterostructures even after moderate annealing treatments (i.e., 20 s at 700 °C). Due to the very low diffusion rate of Ge in Si-rich Si1−xGex alloys, interdiffusion is more pronounced in structures of smaller periodicity or in which the interfaces are initially intermixed.
A rate-dependent constitutive model for molybdenum
Authors: Steinberg D. J.
Published: July 2002

The Steinberg–Guinan–Lund rate-dependent constitutive model has been successfully applied to molybdenum [D. J. Steinberg and C. M. Lund, J. Appl. Phys. 65, 1528 (1989)]. The model reproduces yield strength versus strain rate and temperature data and also successfully simulates rate-dependent phenomena, such as shock-smearing, precursor decay, and precursor on reshock, as observed in one-dimensional gas gun experiments. The spall strength of molybdenum was determined to be 1.5 GPa.
Dynamic response of domain walls on the air-bearing surface of thin-film heads
Authors: Shi X. , Liu F. H. , Li Yuet , Kryder M. H.
Published: July 2002

The domain configurations on the air-bearing surface (ABS) of inductive thin-film recording heads were studied. It was found that, instead of being a single domain structure, the ABS of a thin-film head usually has multidomains. The direction of the domain walls is neither parallel nor perpendicular to the gap plane. The magnetization was found to be in the plane of the ABS along the track width, with the magnetizations on the two sides of the domain walls either ‘‘head-to-head’’ or ‘‘tail-to-tail.’’ The domain walls are slanted in order to spread the magnetic charges along the wall over a larger region, thereby reducing magnetostatic energy in this configuration. The responses of the domain walls are not all in phase, and they are generally out of phase with the rotational process along the gap edge. The magnetization configuration on the ABS and in the throat and the sloped region were investigated in one head and correlated with the domain walls on the ABS.
Study of the Raman peak shift and the linewidth of light-emitting porous silicon
Authors: Yang Min , Huang Daming , Hao Pinghai , Zhang Fulong , Hou Xiaoyuan , Wang Xun
Published: July 2002

The correlation between the Raman peak shift and the linewidth of porous silicon is studied. The experimental result does not fit with the relationship predicted by the phonon confinement model. By taking into account both the phonon confinement and the effect of strain, the calculated Raman line shape coincides fairly well with the measured spectrum. The built-in strain of porous silicon varies with the porosity of the sample and is on the order of 10−3.
Semiclassical study of the wave vector dependence of the interband impact ionization rate in bulk silicon
Authors: Wang Yang , Brennan Kevin F.
Published: July 2002

We present calculations of the interband impact ionization rate calculated using a wave vector dependent (k-dependent) semiclassical formulation of the transition rate. The transition rate is determined using Fermi’s golden rule from a two-body screened Coulomb interaction assuming energy and momentum conservation. The transition rate is calculated for the first two conduction bands of silicon by numerically integrating over the full Brillouin zone. The overlap integrals in the expression for the transition rate are determined numerically using a 15 band k⋅p calculation. It is found that the transition rate depends strongly on the initiating electron wave vector (k vector) and that the transition rate is greatest for electrons originating within the second conduction band than the first conduction band. An ensemble Monte Carlo simulation, which includes the numerically determined ionization transition rate as well as the full details of the first two conduction bands, is used to calculate the total impact ionization rate in bulk silicon. Good agreement with the experimentally determined electron ionization rate data is obtained.
Stress distributions and defect nucleation in buried heterostructure laser diodes
Authors: Bangert U. , Harvey A. J. , Howells S. , Faux D. A. , Dieker C.
Published: July 2002

Shear stress distributions, arising at the corners of the active region of buried heterostructure laser diodes, are calculated for a given mismatch and various dimensions of the buried stripe and also for a single and a multiple quantum well structure. The locations of high stresses are compared to the nucleation sites of shear stress induced defects, as observed by transmission electron microscopy in real lasers. The implications of the defects are illustrated and discussed for the case of an overstress tested diode as well as possibilities to prevent the defect formation.
Dependence of the glasslike characteristics of relaxor ferroelectrics on chemical ordering
Authors: Viehland Dwight , Li Jie-Fang
Published: July 2002

The complex susceptibility of lead scandium tantalate relaxor ferroelectrics has been investigated for samples with varying degrees of long-range chemical ordering. The development of correlations between polar moments occurred relatively sharply near freezing in the highly ordered state, whereas the development of correlations in the partially ordered state occurred over a broadened temperature interval. The relaxation time distributions were also calculated. A sharp peak in the distribution was found on freezing in the highly ordered state, characteristic of a distinct condensation. The distribution in the partially ordered state was diffuse near freezing. It is proposed that in the highly ordered state the polar moments ‘‘freeze’’ into configurations with correlation lengths approaching the macroscopic scale typical of a normal ferroelectric, whereas in the partially ordered state the moments freeze into a polar state with glasslike characteristics.
The Young’s modulus of silica beads/epoxy composites: Experiments and simulations
Authors: Monette L. , Anderson M. P. , Wagner H. D. , Mueller R. R.
Published: July 2002

The effect of particulate volume fraction vp and diameter dp on the composite Young’s modulus Ec is studied both experimentally, using a silica bead/epoxy system, as well as with the help of computer simulations. The experimental and simulation results show that for a given particulate size, the overall Ec vs vp curve displays a concave upward shape and not a linear shape. This superlinear trend of the data implies that the average strain normalized to the applied strain λ=ε̄p/εc transferred to the particulates increases with volume fraction. The above finding is explained in terms of a mean-field picture, where a single particle interacts with an effective medium consisting of the remaining particles embedded in the matrix. As the modulus of the effective medium surrounding a reference particle increases with vp, the modulus mismatch between the reference particulate and the medium is consequently reduced. This leads to an overall increase in the normalized average strain λ transferred to each particulate as vp is increased. The experimental results using silica particulates with various sizes dp, as well as the simulation results, show that smaller particulates provide an increased composite modulus as compared to larger particulates, at constant vp. General equations are developed, which relate the composite modulus to the average particle stress or strain, given only information about the volume fraction and the Young’s modulus of each of the phases present.

Through the application of these relations, it is found that smaller particulates display a greater amount of normalized average strain λ transferred than larger particulates. The effect of particulate Young’s modulus Ep in combination with particulate size on the resulting Ec is also studied using simulations only. It is found that for a low particulate to matrix modulus ratio Ep/Em, the particulate size has very little influence on Ec. Moreover, the shape of the Ec vs vp curve can be well approximated by a straight line up to large values of vp. On the other hand, as the ratio Ep/Em is increased, the superlinear trend of the composite modulus Ec vs vp data is more apparent. This results in a smaller range of the Ec vs vp curve, which can be approximated by a linear function. It is also found that the extent of this linear region also decreases with particle size.
Low-temperature ohmic Au/Sb contacts to n-type Si
Authors: Werner Jürgen H. , Spadaccini Uwe , Banhart Florian
Published: July 2002

Au/Sb films annealed at temperatures as low as 370 °C yield ohmic contacts to n-type Si. The contact formation is based on a liquid-phase epitaxy process of Sb-doped Si from Au solution. Measured contact resistivities range around 3×10−2 Ω cm2 and are at least one order of magnitude higher than what is expected from the solid solubility of Sb in Si. The discrepancy stems from local inhomogeneous etching and epitaxial regrowth of the (100)-oriented Si surface by and from the Au solution. Only a small fraction of the macroscopic contact area is doped by Sb and contributes to current transport across the Au/Si(100) interface.
High magnetic performance in isotropic α-Fe+Sm2Fe17Nx
Authors: Ding J. , Liu Y. , Street R. , McCormick P. G.
Published: July 2002

The structure and magnetic properties of nanocrystalline, two-phase Sm2Fe17Nx+α-Fe alloys prepared by mechanical alloying and heat treatment have been studied. Remanence enhancement and single-phase magnetic behavior were observed in isotropic powders crystallized at low temperatures (about 600 °C), while crystallization at high temperatures resulted in two-phase demagnetization curves due to increase of the grain size of the soft phase. With increasing Sm concentration the coercivity increased and the remanent magnetization decreased.
Quantum-size effects on the band edge of CdTe clusters in glass
Authors: Potter B. G. , Simmons J. H. , Kumar P. , Stanton C. J.
Published: July 2002

The measurement of quantum-size behavior in semiconductor crystals has been examined through an analysis of the size dependence of the semiconductor’s absorption edge. In past studies, there appeared to be little agreement between theory and experiment for very small crystals. In this paper, the effects of crystal-size distribution and tunneling of the carrier wave functions into the quantum well barrier are considered. An analysis of the microstructure size and absorption edge of CdTe clusters in a glass matrix is conducted with samples ranging from 0.16 to 0.8 times the exciton Bohr diameter at the Γ point and from 1 to 5 times the exciton Bohr diameter at the L point. Results show fully coupled exciton behavior at the L point and a more complex process at the Γ point. In the latter, the band-gap energy increase with decreasing cluster size is significantly smaller than that calculated using a model in which the photoexcited carriers are assumed to be confined to a monosize set of clusters bounded by an infinite potential well. Analysis presented here shows that this discrepancy can be explained in part by inhomogeneous broadening of the absorptive transition and by carrier penetration into the insulator. The quantum-size behavior of CdTe crystals at the Γ point is subsequently found to follow fully decoupled carrier behavior modeled by Efros and Efros [Sov. Phys. Semicond. 16, 772 (1982)] when the inhomogeneous broadening and tunneling effects are taken into account.
On spin-canting in maghemite particles
Authors: Linderoth S. , Hendriksen P. V. , Bo/dker F. , Wells S. , Davies K. , Charles S. W. , Mo/rup S.
Published: July 2002

The degree of alignment of the magnetic moments of Fe3+ ions in ultrafine maghemite particles has been studied in samples with induced magnetic texture. The textured samples were prepared by freezing ferrofluids, containing 7.5 nm maghemite particles, in a magnetic field. Mössbauer spectroscopy studies of the textured samples in large magnetic fields demonstrate that the lack of full alignment is not an effect of large magnetic anisotropy, as suggested recently, but that the effect is rather due to canting of individual spins.
Shock-wave compression and release of aluminum/ceramic composites
Authors: Johnson J. N. , Hixson R. S. , Gray G. T.
Published: July 2002

Several composite materials consisting of ceramic particles embedded in a 6061-T6 aluminum matrix have been studied under conditions of shock-wave compression and release, including spallation. The 6061-T6 matrix represents a material for which high-rate shock-wave response has been extremely well characterized for thermoelastic-plastic deformation. The ceramic particles (alumina and mullite) are also well characterized, particularly in the elastic regime. Experimental tests consist of quasistatic, uniaxial-stress compression of both virgin and shock-recovered samples as well as time-resolved velocity interferometer measurements under conditions of flat-plate impact. The latter tests were performed with lithium fluoride windows for transmitted wave studies and free surfaces for spallation measurement. Theoretical analysis of the data is carried out with a pseudodissipation model originated by Barker [J. Composite Mat. 5, 140 (1971)] for application to elastic deformation of layered composites and generalized here to include thermoelastic-plastic properties of the constituents. For a pseudodissipative model to apply to composite material response, significant geometrical randomization must be present in the composite structure; this is something that all commercially produced composites naturally possess. Randomization produces mechanical energy traps, which convert some fraction of regular, directed motion into random elastic vibrations behind the shock front. Within a few microseconds (depending on the pinned dislocation segment density) this macroscale, continuum vibrational energy is converted to heat by means of the anelastic properties of the metal matrix. The use of pseudodissipation as a means of representing dispersive composite material behavior is thus placed on a more secure physical foundation.