bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of quenched disorder on La-modified lead zirconate titanate: Long- and short-range ordered structurally incommensurate phases, and glassy polar clusters
Authors: Viehland Dwight , Dai X. H. , Li J. F. , Xu Z.
Published: July 2002

Structure–property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio by transmission electron microscopy, lattice imaging, and dielectric spectroscopy. Investigations were performed for 65/35⩽Zr/Ti⩽90/10. These investigations have demonstrated a general trend in domain structure and polar order with increasing quenched impurity concentration. For Zr/Ti ratios of 90/10 and 85/15, a structurally incommensurate antiferroelectric (AFEin) state was found to be stabilized with increasing La. Temperature dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (λ) was found to increase significantly with increasing Ti. When λ increased to ∼40 Å, polar clusters began to condense from the AFEin order. For Zr/Ti ratios of 80/20 and 65/35, increasing quenched disorder was found to result in the evolution of polar order through a common sequence of domainlike states including polar clusters, tweedlike structures, and normal micron-sized polydomain structures. These results, in conjunction with dielectric spectroscopy, demonstrate a crossover between a long-period incommensurately modulated state and a relaxor ferroelectric state with increasing quenched disorder. Clearly, both quenched disorder (i.e., random fields) and competing polar orderings (i.e., frustration) underlay the unique behaviors of PLZT.
Surface roughness and in-plane texturing in sputtered thin films
Authors: Whitacre J. F. , Rek Z. U. , Bilello J. C. , Yalisove S. M.
Published: July 2002

Real surfaces are not flat on an atomic scale. Studying the effects of roughness on microstructural evolution is of relevance because films are sputtered onto nonideal surfaces in many applications. To this end, amorphous rough substrates of two different morphologies, either elongated mounds or facets, were fabricated. The microstructural development of films deposited onto these surfaces was examined. In particular, the development of a preferred crystallographic orientation in the plane of growth in 400 nm thick Mo films grown on the rough substrates was studied using scanning electron microscopy, transmission electron diffraction, and high resolution x-ray diffraction (using φ scans in the symmetric grazing incidence x-ray scattering geometry with a synchrotron light source). It was found that the degree of texturing was dependent upon the type of roughness and its orientation during deposition. By limiting the average oblique angle of incident adatom flux, rough surfaces slowed the development of in-plane texture. Comparison between experimental data and theoretical predictions showed that a recent analytical model is able to reasonably predict the degree of texturing in films grown onto these surfaces.
Nitrogen doping of amorphous carbon thin films
Authors: Schwan J. , Batori V. , Ulrich S. , Ehrhardt H. , Silva S. R. P.
Published: July 2002

Nitrogenated and hydrogenated amorphous carbon (a-C:H:N) films have been deposited by a plasma beam source using a gas mixture of C2H2, Ar and N2. The Ar/C2H2 ratio is kept constant at a ratio of 3, with the nitrogen flow allowed to vary. Nonnitrogenated films, with Ar/C2H2 ratios of 3 and 6 were also deposited and analyzed before attempting to identify the modifications to the microstructural properties due to nitrogen doping. The nitrogenated and hydrogenated a-C (a-C:H:N) films deposited in this study reveal interesting properties with regard to their optical gap, electrical conductivity, and mobility of the charge carriers. The optical E04 gap passes through a maximum of 2.7 eV as a function of incorporated nitrogen. The electrical conductivity, too, reaches a peak value of 10−3(Ω cm)−1 with increasing optical gap and remains constant for higher N2 flows. The electrical conductivity process is thermally activated with activation energies in the range 0.1–0.3 eV. This is discussed in terms of the mobility of the charge carriers (determined by Hall measurements) and electronic doping. The defect density (measured by electron spin resonance) is found to decrease with increasing nitrogen incorporation. The films have also been characterized by infrared spectroscopy, photo thermal deflection, and Raman spectroscopy. The microstructure of the deposited a-C:H:N films is discussed in terms of the electronic density of states.
Suitability of drift nonlinearity in Si, GaAs, and InP for high-power frequency converters with a 1 THz radiation output
Authors: Brazis R. , Raguotis R. , Siegrist M. R.
Published: July 2002

We investigate the nonlinear drift response of electrons in Si, GaAs, and InP crystals to high-power electromagnetic waves by means of a Monte Carlo technique, with the aim of developing an efficient frequency converter for 1 THz output radiation. Drift velocity amplitudes and phases determining the conversion efficiency are calculated for the first, third, and fifth harmonics in the pumping wave amplitude range of 10<E1<100 kV/cm, for frequencies between 30 and 500 GHz, and at the lattice temperatures of 80, 300, and 400 K. It is found that the efficiency is a maximum at the pumping wave amplitude of the order of 10 kV/cm depending on the intervalley electron scattering parameters and the lattice temperature. Cooling the nonlinear crystal down to the liquid-nitrogen temperature enhances the efficiency several times in Si and by orders of magnitude in GaAs and InP. This is promising for obtaining a 10% conversion efficiency.
Wavelength selectivity of the complex grating structure formed in a photorefractive phase conjugator
Authors: Lo/bel Martin
Published: July 2002

Experimental results show that the wavelength selectivity and the shape of the detuning curve of the complex grating structure formed in a photorefractive self-pumped BaTiO3 phase conjugator depend strongly on the coherence length of the incident beam. It is observed that the wavelength selectivity becomes larger as the coherence length of the incident beam is decreased. With a coherence length much longer than the dimensions of the conjugator crystal a wavelength selectivity of 0.026 nm is measured. It is shown that this very small wavelength selectivity and the experimental detuning curves are in agreement with a simple model that takes into account the interference between light reflected in 2k gratings and light that has traveled one round trip in the internal loop of the conjugator crystal. The findings explain how the optical feedback generated by the dynamic gratings in the phase conjugator can increase the coherence length of a multimode laser.
Electronic properties of K doped Na-formed Linde type A zeolite
Authors: Sun Qiang , Ye Ling , Xie Xide
Published: July 2002

The electronic properties of potassium adsorbed sodium form zeolite Linde type A (LTA) were studied by using the first-principles tight-binding linear muffin-tin orbitals band method. Two adsorption systems were considered. For the two adsorption systems 6 or 22 potassium atoms were incorporated into the Na-formed zeolite LTA in which 18 sodium atoms are contained per unit cell. For the first adsorption system, which was a lowly doped system, a direct band gap about 2.3 eV was obtained. The calculated band gap is in good agreement with experimental absorption spectra. The charge densities of the system were distributed mainly around the walls of the zeolite framework. An obvious chemical shift (1.8 eV) between Na located at different sites in zeolitic cages was found. For the other adsorption system, which was a highly doped system, the Fermi level was found in the conduction bands and might lead to an insulator-metal transition.
Effect of an inhomogeneous insulating film on the capacitance of metal–insulator–semiconductor structures
Authors: Jauhiainen Anders , Westberg David , Bengtsson Stefan
Published: July 2002

The capacitance of metal–insulator–semiconductor structures with inhomogeneities in the insulating film is significantly influenced by phenomena not present in the capacitance of corresponding ideal structures. These inhomogeneities may be structural ones like a rough surface topography or compositional ones like inclusions of a different material in the film. In the case of a rough surface, three-dimensional simulations of the accumulation capacitance are compared to measurements on aluminum-polycrystalline diamond-silicon devices. The results show that the surface roughness has to be considered when interpreting the measured data. Also, neglecting the effect of the surface roughness results in erroneous values of the permittivity of the insulating film.
Influence of contacts on the conductivity of thin wires
Authors: Ruda H. , Shik A.
Published: July 2002

The conductivity of thin wires was shown to depend noticeably on the properties and, particularly, dimensionality of contacts. Two- and one-dimensional contacts create a strongly nonuniform electric field in a wire which, in turn, causes the redistribution of electron density along a wire and nonlinear current–voltage characteristic. The particular shape of the latter has been calculated for both Ohmic and Schottky contacts of different dimensionality. The case of ac applied voltage is also considered. Spatial distribution of nonequilibrium carriers is found for different signal frequencies ω. The wire conductivity is shown to increase with ω for any type of low-dimensional contacts.
Thermophysical modeling of bump formation during CO2 laser texturing of silicate glasses
Authors: Bennett Ted D. , Krajnovich Douglas J. , Li Lei
Published: July 2002

The thermophysical nature of CO2 laser texturing of glass is explored via numerical simulations. Recent data suggest that laser texture bumps are the product of a local elevation in fictive temperature in the heat affected zone. The numerical model is used to investigate the change in microstructure as manifested in a density change. Using viscosity data, the model employs a dynamic calculation of the glass transition temperature as a function of time scale. The calculation shows that the glass transition temperature increases by 150–300 K over the conventional value in the laser texture process. The maximum thermal penetration depth of the glass transition temperature is numerically determined and the density change calculated. On chemically strengthened glasses, laser texture leads to a density reduction of approximately 2%–3% in the heat affected zone. On unstrengthened glass the density reduction is ∼1.3%
The characteristics of the diffuse phase transition in Mn doped Pb(Fe2/3W1/3)O3 relaxor ceramics
Authors: Zhou Liqin , Vilarinho P. M. , Baptista J. L.
Published: July 2002

The characteristics of the diffuse phase transition of Pb(Fe2/3W1/3)O3 relaxor ceramics doped with different amounts of Mn are investigated. The freezing temperature Tf, obtained by fitting the ω,Tmax to the Vogel–Fulcher relationship, clearly changes with the Mn content. It increases as the Mn content increases, approaching the Tmax(1 MHz) value of the relaxor curve. A concomitant decrease in the frequency dispersion of Tmax is also observed. The freezing temperature also increases as the 1:1 order of Fe3+ and W6+on B sites increases by air annealing but decreases by oxygen annealing. It is suggested that the Mn ions, which are predominantly compensated by oxygen vacancies, form with them defect pairs and that these pairs can couple to the spontaneous polarization vectors, increasing the correlation between the dipole moments and originating the increase of the freezing temperature. It is further suggested that filling up the oxygen vacancies by oxygen annealing will decrease the defect pairs and cause the opposite effect.
Nonisothermal and isothermal discharging currents in polyethylene terephthalate at elevated temperatures
Authors: Neagu Eugen R. , Marat-Mendes Jose N. , Neagu Rodica M. , Das-Gupta Dilip K.
Published: July 2002

The thermally stimulated discharge current and the isothermally final discharging current have been measured, in vacuum and in different ambient gases for “as-received” polyethylene terephthalate specimens, in order to understand the nature of the origin of the released current in the temperature range from glass–rubber transition temperature up to 220 °C. The behavior of the samples thermally treated in oxygen, in nitrogen and in ambient air was analyzed, the gases have been used for detecting the localized states in the material. The current spectrum is determined by the space-charge existing in the as-received sample, and by the adsorbed and/or absorbed gases and water vapors. The movement of the ions, resulting from the interaction of the adsorbed and absorbed gases with the parasitic space charge, in the field produced by the space charge, is responsible for observed change in polarity of the current during nonisothermal and/or isothermal measurements and for the appearance of the ρ or space-charge peak. This movement is considered to be thermally activated with a field-modified activation energy. The calculated activation energy, for the sample thermally treated in oxygen at different temperatures, was in the range (0.9–2.3)±0.1 eV. From the isothermal discharging current measurements, values for the exponent of time in the range from 0.04 to 0.7 were obtained suggesting a dispersive transport of the charge. The total charge density stored in the material is about 4×10−5 C and the corresponding trap density approximately 1023/m3. This charge is substantially larger than that determined by the pulsed electroacoustic method.
Excimer-laser ablation of RuO2 observed by a streak camera
Authors: Fang Xiaodong , Tachiki Minoru , Kobayashi Takeshi
Published: July 2002

In the laser ablation of RuO2, the propagation of oxygen and ruthenium atoms in vacuum and in an oxygen ambient were investigated by observing the fluorescence from excited atoms in the plume using a framing streak camera. An analysis, which took into account the focusing depth of the camera, was introduced. In vacuum the spatial distributions of the oxygen and ruthenium atoms were found to be shifted Maxwellians. The flow velocity and thermal velocity remained almost unchanged for different laser energy densities, suggesting a thermal process during the interaction of laser pulse and target. The kinetic energies of 12 and 19 eV for oxygen and ruthenium atoms, respectively, were found. In the presence of an O2 ambient, atom propagation changed from a free expansion in vacuum to a collision-dominated one. The O2 molecules collide with the species present in the plasma, slowing down their velocities, and the velocities for different atoms equilibrate to almost the same value at a certain distance from the target and at a certain pressure of O2 ambient due to collisions between fast and slow atoms and exchanging of speeds.
Effect of twisting on strain tolerance of Bi-2212 multifilamentary round wires
Authors: Sasaoka T. , Sato J.
Published: July 2002

Silver sheath Bi2Sr2Ca1Cu2Ox superconducting multifilamentary round wires having various twist pitch lengths and an untwisted one were fabricated by the oxide powder-in-Ag-tube method. The twisting process to a pitch length of 4.5 mm at a diameter of 1.45 mm did not influence the superconducting critical current density Jc whose value was about 90 000 A/cm2 at 4.2 K, 0 T. The Jc of the twisted wires is less sensitive to bending strain as twist pitch length becomes shorter. This phenomenon is explained by the calculated results that the filament’s curvature, which is added by the bending, becomes less as pitch length becomes shorter.
Thermoelectric transport properties of n-doped and p-doped Bi0.91Sb0.09 alloy thin films
Authors: Cho Sunglae , DiVenere Antonio , Wong George K. , Ketterson John B. , Meyer Jerry R.
Published: July 2002

In order to understand the doping behavior of extremely narrow band gap materials and to optimize their characteristics for use in a thermoelectric module, we performed n- and p-type doping experiments on semiconducting Bi0.91Sb0.09 alloy thin films using the group VI(IV) element Te(Sn) as donor (acceptor). Thermoelectric power (TEP), electrical resistivity, and Hall effect were studied in the range of temperatures 5–300 K. Increased Sn doping causes the TEP to change sign (from negative to positive) and the maximum in the TEP can be controlled with the dopant concentration. Increased Te doping causes the TEP to decrease. The maximum Te-doped electron concentration was about 5×1020 cm−3 and the highest Sn-doped hole concentration was about 1×1021 cm−3. Highly Sn- and Te-doped samples show degenerate behavior in the electrical resistivity, TEP and Hall measurements.
Observation of magnetic switching in submicron magnetic-tunnel junctions at low frequency
Authors: Lu Yu. , Trouilloud P. L. , Abraham D. W. , Koch R. , Slonczewski J. , Brown S. , Bucchignano J. , O’Sullivan E. , Wanner R. A. , Gallagher W. J. , Parkin S. S. P.
Published: July 2002

Understanding the magnetic switching behavior in micron and submicron scale specimens is important for a number of applications. In this study, magnetic-tunnel junctions of various sizes and shapes were fabricated and their switching behavior was studied in detail. Using exchange bias to offset the magnetic response of one electrode, the response of the other (free) electrode was determined from measurements of junction resistance. Switching threshold curves were measured by sweeping magnetic fields in both easy and hard direction. Single domain like switching was observed in some of our smallest submicron junctions. The observed behavior was compared with predictions from the Stoner–Wohlfarth rotational model and from numerical calculations.
Amorphization of Zr–Al solid solutions under mechanical alloying at different temperatures
Authors: Sheng H. W. , Lu K. , Ma E.
Published: July 2002

The effects of temperature on the amorphization of Zr–Al solid solutions have been investigated by ball milling Zr100−xAlx powder blends at different temperatures. At low milling temperatures, the Zr–Al solid solutions amorphized under the polymorphic constraint imposed by intensive external forcing. At elevated temperatures, the solid solution and the amorphous phases coexisted in an obvious two-phase region, signaling a transition approaching two-phase metastable equilibrium. The Al concentration needed for the complete amorphization of Zr–Al increased with increasing milling temperature. These observations, and in particular, the apparent reentrant liquidus, can be explained in terms of the temperature dependence of the external forcing effects brought in by the nonequilibrium milling process in this dynamic driven system.
Intrinsic electrical properties of Au/SrTiO3 Schottky junctions
Authors: Shimizu Takashi , Okushi Hideyo
Published: July 2002

Intrinsic electrical properties of Au/Nb-doped SrTiO3(001) (STO:Nb) Schottky junctions, fabricated using a proper surface treatment of the STO:Nb and in situ deposition of Au, were investigated in detail. Current–voltage characteristics and photocurrent–wavelength characteristics have shown a temperature-dependent and voltage-dependent Schottky barrier height, while capacitance–voltage characteristics have shown a temperature-independent flat band voltage. Using a temperature-dependent and field-dependent permittivity of the STO in the framework of Devonshire theory, we have performed computer simulation of the Schottky barrier potential to analyze the electrical properties of the junction. It is found that an intrinsic low permittivity layer at the Au/STO:Nb interface explains all the temperature dependence of the electrical properties.
Excess carriers lifetime in InP single crystals: Radiative versus nonradiative recombination
Authors: Liu A. , Rosenwaks Y.
Published: July 2002

We present a comprehensive and systematic study of the minority and majority carrier lifetimes in InP single crystals doped in the range of 1×1015–4×1018 cm−3. Radiative recombination dominates in undoped InP, because the Shockley–Read–Hall lifetime is very long (>10 μs). For S or Sn doped n-type InP with intermediate doping concentration, nonradiative recombination is dominant under low injection conditions, hence the effective lifetime increases with increasing the injection level. On the other hand, the effective lifetime decreases with increasing the injection level under high excitation conditions due to radiative recombination. Thus, the effective lifetime has the largest value (140 ns for S-doped InP with majority carrier concentration n0=2×1017 cm−3, and 110 ns for Sn-doped InP with n0=3×1017 cm−3) for an injection level of around 1×1017 cm−3. Such information is important for the design of devices that operate under high injection levels like lasers and concentrated solar cells. In p-InP, nonradiative recombination and trapping dominate even in low doped samples and the effective lifetimes are much shorter than in n-InP.
Particle features, oxidation behaviors and magnetic properties of ultrafine particles of Ni–Co alloy prepared by hydrogen plasma metal reaction
Authors: Li X. G. , Murai T. , Chiba A. , Takahashi S.
Published: July 2002

Ni–Co ultrafine particles (UFPs) were prepared by hydrogen plasma metal reaction. Particle characteristics, oxidation, and magnetic properties were investigated and compared. fcc structured Ni–Co UFPs with a sphere shape were prepared over the whole composition range. The particles distribute from 5 to 100 nm in size with an average particle size of about 35 nm. They are thermally stable in air below 433 K, but oxidize quickly at the higher temperatures. The saturation magnetization of the UFPs is lower than that of the corresponding bulk alloy, especially in the Co rich side. Formation of oxide layer on the particle’s surface is an important reason for this reduction. Ni–Co UFPs possess large residual magnetization and coercive force above 60% Co. The composition dependence of the saturation magnetization and the coercive force changes remarkably around 60% Co, which implies a large variation in magnetic status around this composition.
Radiation-induced explosive initiation
Authors: Yakovlev M.
Published: July 2002

A model for explosive initiation under the influence of high energy radiation has been developed. The possibility for comparing explosive initiation conditions under the influence of radiation pulse and shock wave loads of microsecond duration has been shown and the initiation conditions as a function of the radiolysis constants have been determined.
Electronic energy states of organic interfaces studied by low-energy ultraviolet photoemission spectroscopy
Authors: Onoda Mitsuyoshi , Tada Kazuya , Nakayama Hiroshi
Published: July 2002

Ionization potentials of conducting polymer/metal interfaces and conducting polymer/poly(p-pyridyl vinylene), PPyV, interfaces were evaluated by a low-energy photoelectron spectroscopic method, and interfacial electronic states were determined. At all the measured interfaces, a shift of the vacuum level was observed, and was attributed to the formation of an interfacial electric dipolar layer. The shifts of the ionization potential at the interface could be expressed as a linear function of the work function of the contact metal. However, for conducting polymers/indium–tin–oxide interfaces, interfacial electronic states could not be determined. This may be related to the novel ionization potential behavior in those systems. The present results clearly demonstrate that characterization of the interfacial electronic states is necessary for a complete understanding of the characteristics of organic electronic devices.
Static and dynamic aspects of the demagnetizing factor in magnetic thin films with random rough surfaces
Authors: Palasantzas George
Published: July 2002

We investigate static and dynamic aspects of the demagnetizing factor N in magnetic thin films with random rough surfaces which are described by the rms amplitude Δ, the correlation length ξ, and the roughness exponent H (0⩽H⩽1). The demagnetizing factor decreases as the surface smoothens (increasing H and/or decreasing ratio Δ/ξ), with the exponent H yielding a comparable contribution to N as the roughness ratio Δ/ξ. Moreover, for growing films with self-affine surfaces, N decreases with film thickness, closely as a power law for large roughness exponents (H∼1). Finally, estimates of the demagnetizing factor based on sinusoidal models are shown to be inadequate since they neglect fine roughness details at short wavelengths (<ξ) as depicted by the roughness exponent H.
Dynamic stability of the time-averaged orbiting potential trap: Exact classical analysis
Authors: Gov S. , Shtrikman S.
Published: July 2002

We calculate exactly the modes of motion of the time-averaged orbiting potential (TOP) trap with its four degrees of freedom, namely the three translations and the spin, taken into account. We find that, when gravity is neglected, there are two parameters in the problem namely, the angular velocity of the rotating field and its strength. We present the stability diagram in these parameters. We find the mode frequencies calculated from the time-averaged potential model used by the inventors of the TOP is an excellent approximation to our exact results. However, for other parameters, this may not be the case.
Ion channeling study of the lattice disorder in neutron irradiated GaP
Authors: Kuriyama K. , Miyamoto Y. , Koyama T. , Ogawa O. , Okada M.
Published: July 2002

The lattice disorder in GaP produced by fast neutrons with a fluence of 2.1×1018 cm−2 has been investigated with 1.5 MeV He+4 channeling. The slight increase in the 〈111〉 aligned yield for irradiated crystals indicates that each primary knock-on (PKO) produces approximately 7×102 displaced atoms. Channeling studies also show a spread distribution of randomly located defects imbedded in the lattice structure. On the other hand, P antisite (PGa) defects produced by neutron irradiation are ∼2 per PKO. Irradiated samples also show a volume expansion of 0.13%. It is suggested that the lattice expansion mainly induced by vacancy–interstitial clusters arises from the displacement atoms rather than PGa defects.
Low-frequency noise gain and photocurrent gain in quantum well infrared photodetectors
Authors: Ershov M. , Liu H. C.
Published: July 2002

We present a theory of the low-frequency noise gain gn and photocurrent gain gp in quantum well infrared photodetectors (QWIPs). Expressions for gn and gp in terms of QW capture probability pc and number of QWs N are obtained. These expressions are valid for any number of QWs N⩾1 and capture probability 0<pc⩽1. The difference of noise gain from photocurrent gain is due to the discrete structure of generation–recombination centers (QWs) in QWIP. The ratio gn/gp ranges from 0.5 (for pc→1) to 1 (for pc→0). QWIP is well described by a conventional photoconductor theory in the case of low capture probability pc→1, which corresponds to practical QWIPs. The assumptions of the model are discussed in detail, and a comparison with previously published results is made.
Effects of precursors and substrate materials on microstructure, dielectric properties, and step coverage of (Ba, Sr)TiO3 films grown by metalorganic chemical vapor deposition
Authors: Gao Y. , He S. , Alluri P. , Engelhard M. , Lea A. S. , Finder J. , Melnick B. , Hance R. L.
Published: July 2002

(Ba, Sr)TiO 3 (BST) thin films have been grown on planar Ir/Si and Pt/Si substrates and on three-dimensional (3D) Ir electrodes by metalorganic chemical vapor deposition using two kinds of β-diketonate-based BST precursors. Film growth was studied as a function of film thickness, composition, and substrate temperature. Growth rate was monitored by in situ spectroscopic ellipsometry. The BST films were characterized ex situ by a variety of techniques including x-ray photoelectron spectroscopy, Auger electron microscopy, atomic force microscopy, transmission and scanning electron microscopy, x-ray diffraction, and impedance analyzer. The results reveal that the two sets of BST precursors, albeit slightly different, show quite different reactivities that strongly affect the step coverage on the 3D structure. However, different reactivities have no apparent effect on the microstructure, surface morphology, and dielectric properties of the stoichiometric BST films. These properties strongly depend on the film composition, substrate material, and growth temperature. In general, the BST films grown on Pt exhibit better crystalline quality, surface smoothness, and dielectric properties compared to those grown on Ir under the optimal growth conditions.
Plasma method for separation of heat-resistant metals
Authors: Smirnov B. M.
Published: July 2002

The regime of burning of a high-pressure arc is considered when its positive column contains an admixture of a heat-resistant metal, which is located in the form of a gaseous compound near walls of the discharge tube and metallic clusters in a hot region of this discharge. Criteria of this discharge regime are given. A cluster instability leads to the growth of metallic clusters in an intermediate region of the discharge. This instability is a basis for separation of a heat-resistant metal in the plasma from its chemical compounds.
Quantitative study on the nonlinear piezoelectric effect in KNbO3 single crystals for a highly efficient surface acoustic wave elastic convolver
Authors: Cho Yasuo , Oota Noriyuki , Odagawa Hiroyuki , Yamanouchi Kazuhiko
Published: July 2002

In this article we describe quantitative studies on the nonlinear piezoelectric effect in KNbO3 single crystals for a highly efficient surface acoustic wave elastic convolver. First, we demonstrate that a simple measurement of the nonlinear piezoelectric constant of e355 is very effective for quantitative estimation of the efficiency of an elastic convolver. Next, the third-order piezoelectric constants, e355, e333, and e344, in rotated Y-cut KNbO3 substrates are measured by varying the velocity under an applied electric field. Using the third-order piezoelectric constants measured, quantitative estimations of the convolution efficiency are discussed.
Experimental and numerical investigations of a hydrogen-assisted laser-induced materials transfer procedure
Authors: Toet D. , Smith P. M. , Sigmon T. W. , Thompson M. O.
Published: July 2002

We present investigations of the mechanisms of a laser-induced transfer technique, which can be used for the spatially selective deposition of materials such as Si. This transfer is effected by irradiating the backside of a hydrogenated amorphous silicon film, deposited on a transparent substrate with an excimer laser pulse. The resulting release and accumulation of hydrogen at the film/substrate interface propels the silicon onto an adjacent receptor wafer. Time-resolved infrared transmission measurements indicate that the amorphous film is melted by the laser pulse and breaks into droplets during ejection. These droplets travel towards the receptor substrate and coalesce upon arrival. The transfer velocity increases as a function of fluence, the rate of increase dropping noticeably around the full melt threshold of the film. At this fluence, the transfer velocity reaches values of around 1000 m/s for typical films. Atomic force microscopy reveals that films transferred below the full melt threshold only partially cover the receptor substrate, while uniform, well-adhering films, which can be smoothed by subsequent laser irradiation, are obtained above it. Transfer of hydrogen-free Si films, on the other hand, does not occur until much higher fluences. The dynamics of the process have been simulated using a semiquantitative numerical model. In this model, hydrogen released from the melt front is instantaneously accumulated at the interface with an initial kinetic energy given by the melting temperature of Si and the enthalpy of solution. The resulting pressure accelerates the Si film, the dynamics of which are modeled using Newtonian mechanics, and the gas cools adiabatically as its kinetic energy is converted to the film’s momentum. The results of the calculations are in good agreement with the experimental data.
A kinetic model for metalorganic chemical vapor deposition from trimethylgallium and arsine
Authors: Tao Meng
Published: July 2002

A kinetic model based on the collision theory of chemical reactions is proposed for gallium arsenide (GaAs) metalorganic chemical vapor deposition from trimethylgallium and arsine. A simplified reaction mechanism is incorporated into the model, which includes four heterogeneous deposition reactions: Ga-containing and As-containing species with Ga and As sites, as well as carbon incorporation reactions. An equation for the overall growth rate of the four deposition reactions is derived, which is simplified under the Ga-rich or As-rich growth condition. A discussion about antisite defects leads to the conclusion that As-rich growth produces stoichiometric GaAs. The relation between temperature and arsine/trimethylgallium ratio for As-rich growth is defined. The concept of competitive adsorption is introduced to understand doping and ternary deposition. Carrier concentration for n-type, p-type, and amphoteric doping as a function of deposition conditions is derived. Conversion from p type to n type with arsine/trimethylgallium ratio due to residual carbon is, for the first time, quantitatively explained within the framework of doping. Film composition as a function of deposition conditions in ternary deposition of aluminum–gallium arsenide (Al1−xGaxAs) and gallium arsenide–phosphide (GaAs1−yPy) is also derived. The distributions of Al and P between gas phase and solid film follow the same physics rule but differ in the nature of impinging species. The quantitative agreement between the model and a wide range of experiments demonstrates the value of this model.
High-resolution spectroscopy and optical hole burning studies of the F7→5D transition of europium-doped calcium fluoride
Authors: Pandher Ranjit S. , Davis Angela , Jackson Andre , Rami Reddy B.
Published: July 2002

High-resolution spectroscopic study of the F07→5D0 transition revealed more than 40 different sites for the rare-earth ion. The multisite behavior was found to be due to clustering of the dopants and dopant induced microscopic defects. Hole-burning efficiencies were measured for some sites.
The grain size effects on the photoluminescence of ZnO/α-Al2O3 grown by radio-frequency magnetron sputtering
Authors: Kim Kyoung-Kook , Song Jae-Hoon , Jung Hyung-Jin , Choi Won-Kook , Park Seong-Ju , Song Jong-Han
Published: July 2002

ZnO thin films were epitaxially grown on α-Al2O3 (0001) substrate by radio-frequency (rf) magnetron sputtering. Among the ZnO films deposited at 550 °C, the film deposited at 80 W has the narrowest full width half maximum (FWHM) of x-ray diffraction (XRD) θ-rocking curve, 0.16°, indicating a highly c-axis oriented columnar structure. The FWHM of XRD θ-rocking curve of the ZnO film deposited at 120 W and 600 °C was 0.13° with a minimum channeling yield, 4%–5%. In photoluminescence (PL) measurement, only the sharp near band edge emission was observed at room temperature (RT). The FWHM of PL peak was decreased from 133 to 89 meV as rf power increased from 80 to 120 W at 550 °C, and that of film deposited at 120 W and 600 °C showed 76 meV which is lower value than any other ever reported. These PL results were somewhat opposite to that of XRD. From transmission electron microscopy analysis, grain size and defects were found to affect the PL properties. In this study, the PL property of undoped ZnO thin films is discussed in terms of the crystalline structure and the size of grain.
Effects of head field pulse shape and rise time on subnanosecond magnetization reversal in longitudinal thin film media
Authors: Schabes Manfred E. , Zhou Hong , Bertram H. Neal
Published: July 2002

Micromagnetic simulations of planar isotropic magnetic thin film recording media are performed to study initial magnetization reversal processes in response to pulses with linear and exponential ramps. Linear ramps lead to smaller zero-crossing times T0 than exponential ramps due to the more rapid field increase during the pulse ramps. It is shown that T0 increases substantially when the pulse amplitude is less than about half the anisotropy field, in which case pulse overshoots are effective to reduce T0. In addition, the effects of exchange coupling and gyromagnetic damping are examined.
Activation volumes in thin film and particulate systems
Authors: Kirby Roger D. , Yu Mingjun , Sellmyer D. J.
Published: July 2002

We consider magnetization reversal and decay in thin film and particulate magnetic systems where thermally activated processes are important. We present measurements on the activation volumes associated with magnetization reversal in CoCrPt thin films. We find that the measured activation volume V* goes through a minimum as the film thickness is decreased from 17.5 to 5.5 nm. We have modeled this behavior qualitatively by assuming that the energy barrier to thermally activated reversal varies as 1/H, as has been predicted for incoherent nucleation processes and thermally activated domain–wall motion. This model also predicts that V* varies as T2 at high temperature in qualitative agreement with measurements on several systems. This behavior is contrasted with that predicted on the basis of coherent rotation of the magnetization in single-domain particles.
Spin-wave theory of double-exchange magnets
Authors: Golosov D. I.
Published: July 2002

An isotropic half-metallic double-exchange magnet with a direct superexchange coupling between the localized spins is studied within the spin-wave (1/S) expansion. The momentum dependence of the spin-wave spectrum (including quantum corrections) in the ferromagnetic phase at T=0 is investigated. Based on the calculated spin-wave spectrum of the canted state, it is shown that as long as the external magnetic field is not too strong, the double exchange–superexchange competition does not result in a stabilization of a two-sublattice canted spin ordering.
Evaluation of the saturation magnetostriction in nearly zero magnetostrictive glass-coated amorphous microwires
Authors: Gonzalez Julian , Zhukov Arcady P. , Blanco Juan Maria , Cobeño Antxon F. , Vazquez Manuel , Kulakowski Krzysztof
Published: July 2002

Measurements of the saturation magnetostriction λs of glass-coated covered (Co1−xMnx)75Si10B15 (x=0.09, 0.10 and 0.105) and Co56.5Fe6.5Ni10B16Si11 amorphous microwires carried out by means of the stress dependence of initial magnetic susceptibility method are reported. The conditions of applicability of this method to the microwires have been analyzed, taking into account the domain structure expected for very low negative magnetostriction of the metallic nucleus. The experimental data of λs obtained in those amorphous microwires are in agreement with those reported in amorphous ribbons with similar compositions.
Dependence of exchange coupling in permalloy/Cr82Al18 bilayers on the constituent layer thickness
Authors: Zhou S. M. , Liu Kai , Chien C. L.
Published: July 2002

Due to a weaker exchange coupling, the coercivity in permalloy/Cr82Al18 bilayers of thicknesses tFM and tAF, respectively, has been found to vary as 1/tFM3/2 at room temperature, a behavior previously only observed at low temperatures. At room temperature, the exchange field decreases when tAF is less than 40 nm and vanishes at 25 nm. Switching in wedged-permalloy/Cr82Al18 bilayers consists of two macroscopic domains with one domain wall moving along the wedge direction.
Hysteresis and relaxation of hard–soft nanocomposite samples
Authors: González J. M. , Montero M. I. , Crespo P. , Marı́n P. , Hernando A.
Published: July 2002

We present experimental results on the hysteresis and relaxation of Fe/Ba hexaferrite composite samples prepared by ball milling starting from precursor Fe and Ba hexaferrite particles. Our results show that, for maximum applied fields of up to 8 kOe, the measured loops show a shift of up to 85 Oe. The compositional dependence of that loop displacement presents two maxima (at approximately x=0.3 and x=0.7) and a minimum at x=0.5. These results are discussed in terms of the dipolar coupling between both phases.
Vector model for the study of hysteresis under stress
Authors: Sasso C. P. , Basso V. , LoBue M. , Bertotti G.
Published: July 2002

A vector model of magnetic hysteresis in biaxial anisotropy structures is presented, in which magnetoelastic effects are explicitly taken into account. The magnetization vector of individual grains is forced to lie along one of the easy axis, and jumps from one easy direction to another one controlled by the sum of the external field and magnetoelastic energy. Hysteresis effects are described by an energy barrier opposing magnetization switching and the total response of the system is obtained by averaging the local magnetization over all grains. Model predictions are compared with experimental results on the hysteresis properties of Si–Fe alloys under compressive stress.
Effect of electron concentration on the magnetic phase diagrams of Cr–Al alloys
Authors: Lodya J. A. , Smit P. , Alberts H. L.
Published: July 2002

An experimental study of the magnetic phase diagrams of Cr–Al alloys doped with V and Mn to respectively decrease and increase the electron concentration per atom (eA), are reported. The eA dependence of the magnetic phase transition temperatures of three Cr–Al alloys is discussed in terms of changes in the nesting parameter of the electron and hole Fermi surface sheets.
Temperature dependence of spin-lattice relaxation in rare-earth iron garnets
Authors: Dionne Gerald F. , Fitch George L.
Published: July 2002

The spin-lattice relaxation rate in iron garnets containing ions of the rare-earth series features a peak in the temperature range from 30 to 100 K that is consistent throughout the group. This effect is important in microwave applications at liquid nitrogen temperatures because magnetic losses increase directly with the intrinsic ferrimagnetic resonance linewidth ΔH, which in turn is proportional to the relaxation rate τ−1. The decrease in X-band linewidth with lowering temperatures is accounted for by the Orbach exponential relation for τ−1 of individual paramagnetic rare-earth ions. To explain the decrease in ΔH above the peak, the Orbach function is multiplied by the magnetic exchange energy between the iron and rare-earth spins. Computations of the linewidth as a function of temperature for Dy3+, Ho3+, Er3+, and Yb3+ are made by utilizing the multiple sublattice molecular-field theory. By fitting theory to data, values are extracted for excited state energy splitting D that enters the exponent (−D/kT) of the Orbach function. Measurement data from high purity yttrium iron garnet also confirm that iron relaxation rates decrease monotonically with reducing temperatures, indicating that microwave magnetic loss at cryogenic temperatures can be reduced below room temperature values if offending rare-earth impurities are removed.
Analytical model for estimation of isolated transition width in perpendicular magnetic recording
Authors: Nakamura Yoshihisa
Published: July 2002

In order to discuss the relationship between the magnetic properties of recording media and the isolated transition widths, an analytical model for the calculation of transition parameters is proposed. In the model, Lorentzian distributions of coercive forces of the magnetic particles in the media are assumed, with half peak widths and mean values corresponding to the coercive forces of media measured in the direction perpendicular to the medium surface. The magnetization distribution after writing an isolated transition can be obtained self-consistently as an arctangent function, in which the writing field gradient of a head, the particle coercive force dispersion of the medium, the demagnetizing field and the interparticle exchange interaction are taken into account.
Optical and magnetic property of LaMnO3
Authors: Ahn K. H. , Millis A. J.
Published: July 2002

A tight binding parameterization of the band structure, along with a mean field treatment of Hund, electron–electron, and electron–lattice couplings, is used to obtain the full optical conductivity tensor of LaMnO3 as a function of temperature. We predict the magnetic phase transition causes striking changes in the functional form and magnitude of the optical absorption. Our results differ from those obtained by the local density-functional approximation techniques. Possible origins of the discrepancy are discussed.
Information dimension analysis of chaotic forward volume spin waves in a yttrium–iron–garnet thin film
Authors: Prabhakar A. , Stancil D. D.
Published: July 2002

Forward volume spin waves were excited in a yttrium–iron–garnet film using a microstrip delay line. Low frequency modulations in output power were captured on a digital oscilloscope for various combinations of microwave input frequency and power. Using the decrease in mutual information as a criterion, an embedding delay time was chosen for each time series. The method of false nearest neighbors was then used to calculate a minimal embedding dimension, D. Despite large changes in input frequency (4.4 GHz<f<4.6 GHz) and power (15.7 dBm<P<22.7 dBm), D⩽3 for each time series, indicating a low dimensional system. Finally, the information dimension, d, was estimated by computing the distance from a collection of reference points to their nearest neighbors. The distribution for d was found to be bimodal. When correlated with the input microwave power and frequency, it was found that values of d<2 occurred close to the auto-oscillation threshold in the vicinity of an even dipole gap. d<3 was observed at higher power levels or at frequencies close to an odd dipole gap.
Competition of exchange and crystal field interactions in cerium monopnictides and monochalcogenides
Authors: Collins Eric M. , Kioussis Nicholas , Lim Say Peng , Cooper Bernard R.
Published: July 2002

We have applied two ab initio based methods to study the dramatic change of magnetic properties across a series of strongly correlated electron systems consisting of cerium monopnictides and monochalcogenides. While, the fully ab initio method gives good results for the magnetic moments in the lighter chalcogenides, it entirely fails to give, even qualitatively, the trend of their unusual magnetic behavior. On the other hand, the second approach, which explicitly takes into account the interplay between the hybridization, the Coulomb exchange, and the crystal-field interactions, gives results in excellent agreement with experiment for all compounds in the series, including the moment collapse from CeSb to CeTe and the trend of moments and ordering temperatures across the series.
A simple treatment of the “scattering-in” term of the Boltzmann equation for multilayers
Authors: Zhang X.-G. , Butler W. H.
Published: July 2002

We present a simple approximation for treating anisotropic scattering within the semiclassical Boltzmann equation for current in plane geometry in magnetic multilayers. This approximation can be used to qualitatively account for the forward scattering that is neglected in the lifetime approximation, and requires only one additional parameter. For the case of a bulk material its effect is a simple renormalization of the scattering rate. The simplicity of this term has allowed quick and simple solution to the Boltzmann equation for magnetic multilayers using realistic band structures. When we use the band structures for Cu|Co multilayers obtained from first-principles calculations, we find an increase in the resistance of the multilayer, compared to the solution without the scattering-in term, due to the higher scattering rates needed to fit the same bulk conductivities. The giant-magnetoresistance ratio is also changed when the vertex corrections are included.