bluuebunny/crossref_metadata_2025 huggingface dataset:
Further accuracy and convergence results on the modeling of flows down inclined planes by weighted-residual approximations
Authors: Ruyer-Quil Christian , Manneville Paul
Published: July 2002

We study the reliability of two-dimensional models of film flows down inclined planes obtained by us [Ruyer-Quil and Manneville, Eur. Phys. J. B 15, 357 (2000)] using weighted-residual methods combined with a standard long-wavelength expansion. Such models typically involve the local thickness h of the film, the local flow rate q, and possibly other local quantities averaged over the thickness, thus eliminating the cross-stream degrees of freedom. At the linear stage, the predicted properties of the wave packets are in excellent agreement with exact results obtained by Brevdo et al. [J. Fluid Mech. 396, 37 (1999)]. The nonlinear development of waves is also satisfactorily recovered as evidenced by comparisons with laboratory experiments by Liu et al. [Phys. Fluids 7, 55 (1995)] and with numerical simulations by Ramaswamy et al. [J. Fluid Mech. 325, 163 (1996)]. Within the modeling strategy based on a polynomial expansion of the velocity field, optimal models have been shown to exist at a given order in the long-wavelength expansion. Convergence towards the optimum is studied as the order of the weighted-residual approximation is increased. Our models accurately and economically predict linear and nonlinear properties of film flows up to relatively high Reynolds numbers, thus offering valuable theoretical and applied study perspectives.
Effects of aperture displacement in broad-beam ion extraction systems
Authors: Tartz M. , Hartmann E. , Deltschew R. , Neumann H.
Published: July 2002

Low-energy broad-beam ion sources cover a wide range of applications. Geometrical perturbations of the axial-symmetric extraction channels by off-axis shifts of the accelerator grid holes give rise to an ion beamlet tilt which under certain conditions is dependent on the beamlet current. In this study, the characteristics of the beamlet deflection are presented which were obtained by a three-dimensional trajectory simulation.
Remarks on several 2+1 dimensional lattices
Authors: Tam Hon-Wah , Hu Xing-Biao , Qian Xian-Min
Published: July 2002

In this paper, five 2+1 dimensional lattices considered by several authors are revisited again. First of all we will show that two lattices proposed by Blaszak and Szum [J. Math. Phys. 42, 225 (2001)] become the so-called differential-difference KP equation due to Date, Jimbo, and Miwa [J. Phys. Soc. Jpn. 51, 4116 (1982); 51, 4125 (1982); 52, 388 (1983); 52, 761 (1983); 52, 766 (1983)] by simple variable transformations, while another lattice found by Blaszak and Szum can be viewed as a higher-dimensional generalization of a lattice given by Wu and Hu [J. Phys. A 32, 1515 (1999)]. Some integrable properties on these three lattices are derived. Second, it is shown that a 2+1 dimensional Toda-like lattice studied by Cao, Geng, and Wu [J. Phys. A 32, 8059 (1999)] can be transformed into the bilinear equation given by Hu, Clarkson, and Bullough [J. Phys. A 30, L669 (1997)]. For this bilinear version we also present some rational solutions and Lie symmetries. Finally, a lattice due to Levi, Ragnisco, and Shabat [Can. J. Phys. 72, 439 (1994)] is transformed into coupled bilinear equations. It is shown that these coupled bilinear equations do not have two-soliton solutions. This further confirms that the lattice under consideration is not completely integrable.
Effect of Co or Ge doping on the intergranular magnetic coupling in nanocrystalline Fe89Zr7B3Cu1
Authors: Suzuki K. , Cochrane J. W. , Cadogan J. M. , Xiong X. Y. , Hono K.
Published: July 2002

The Curie temperature of the residual amorphous phase in nanocrystalline Fe89Zr7B3Cu1 is enhanced by Ge addition and the magnetic hardening at elevated temperatures is suppressed. On the other hand, the addition of Co brings about severe deterioration of the magnetic softness for the same alloy presumably because of the induced anisotropy effect. The Mössbauer and atom probe field ion microscopy analyses indicate that Ge-induced magnetic softening is due to the preferential enrichment of Ge into the residual amorphous phase which results in an enhancement of the exchange stiffness in the intergranular region.
Excimer-laser-irradiation-induced effects in C60 films for photovoltaic applications
Authors: Narayanan K. L. , Yamaguchi M. , Azuma H.
Published: July 2002

Thin films of fullerene C60 deposited by the molecular-beam epitaxy method have been subjected to a 248 nm excimer laser for various timings. Reduction in the electrical resistance of the films and the spectral evolution of the D and G bands in the Raman spectra, due to the sharp tendency towards graphitization accompanied by an increasing level of structural disorder, are observed during laser irradiation. Based on the above results, an attempt has been carried out on these irradiated C60 films to make a device sandwiched with n-type Si, and the photovoltaic parameters are reported as a function of the laser exposure times.
Growth of ferromagnetic semiconducting cobalt-doped anatase titanium thin films
Authors: Shim In-Bo , An Sung-Yong , Kim Chul Sung , Choi Se-Young , Park Yong Wook
Published: July 2002

Heteroepitaxial and polycrystalline anatase Ti1−xCoxO2 (0.0⩽x⩽1.0) thin films were prepared by soft chemical processing on LaAlO3 (001) and thermally oxidized silicon substrates and the crystallinity and magnetic properties were investigated. X-ray diffraction (XRD) spectrum of the Ti1−xCoxO2 films on LaAlO3 (001) substrate shows (004) and (008) peaks of heteroepitaxy anatase without any impurity phase. The full-width at half maximum of the (004) peak rocking curve is 0.4°. The XRD patterns of thin films deposited on the SiO2/Si(001) substrate are anatase type polyscrystalline structure. Microstructural characterization on Ti1−xCoxO2 thin film employing atomic force microscope showed island type grains in 20 nm in size and the surface roughness of typical thin films was 1.5 nm. Sharp hysteresis loops, indicating a well-ordered ferromagnetic structure, appeared in the magnetization versus magnetic field curves when the magnetic field was applied in the plane of the film. This result clearly indicates that the anatase Ti1−xCoxO2 thin films fabricated on LaAlO3 (001) by soft chemical process have crystal quality equivalent to high-vacuum technique.
Reactive scattering of F+HD→HF(v,J)+D: HF(v,J) nascent product state distributions and evidence for quantum transition state resonances
Authors: Harper Warren W. , Nizkorodov Sergey A. , Nesbitt David J.
Published: July 2002

Single collision reactive scattering dynamics of F+HD→HF(v,J)+D have been investigated exploiting high-resolution (Δν≈0.0001 cm−1) infrared laser absorption for quantum state resolved detection of nascent HF(v,J) product states. State resolved Doppler profiles are recorded for a series of HF rovibrational transitions and converted into state resolved fluxes via density-to-flux analysis, yielding cross-section data for relative formation of HF(v,J) at Ecom≈0.6(2), 1.0(3), 1.5(3), and 1.9(4) kcal/mol. State resolved HF(v,J) products at all but the lowest collision energy exhibit Boltzmann-type populations, characteristic of direct reactive scattering dynamics. At the lowest collision energy [Ecom≈0.6(2) kcal/mol], however, the HF(v=2,J) populations behave quite anomalously, exhibiting a nearly “flat” distribution out to J≈11 before dropping rapidly to zero at the energetic limit. These results provide strong experimental support for quantum transition state resonance dynamics near Ecom≈0.6 kcal/mol corresponding classically to H atom chattering between the F and D atoms, and prove to be in remarkably quantitative agreement with theoretical wave packet predictions by Skodje et al. [J. Chem. Phys. 112, 4536 (2000)]. These fully quantum state resolved studies therefore nicely complement the recent crossed beam studies of Dong et al. [J. Chem. Phys. 113, 3633 (2000)], which confirm the presence of this resonance via angle resolved differential cross-section measurements. The observed quantum state distributions near threshold also indicate several rotational states in the HF(v=3) vibrational manifold energetically inaccessible to F(2P3/2) reagent, but which are consistent with a minor (≲5%) nonadiabatic contribution from spin–orbit excited F*(2P1/2).
Temperature discontinuity at the surface of an evaporating droplet
Authors: McGaughey A. J. H. , Ward C. A.
Published: July 2002

In a series of experiments, a temperature discontinuity has been found to exist at the surface of an evaporating water droplet. Statistical rate theory has been used to predict the pressure in the vapor to within the experimental uncertainty during each of the experiments. While the qualitative trend of the D2 law is observed to be consistent with the measurements, it underpredicts the measured rate of evaporation by 21%–37%. When the temperature discontinuity is taken into account in the D2 law, the difference between the predicted and measured values is at most 7%. The results suggest that the rate limiting process in the experiments is not diffusion in the gas phase, as is assumed in the D2 law, but is the interface kinetics.
G-quartet biomolecular nanowires
Authors: Calzolari A. , Di Felice R. , Molinari E. , Garbesi A.
Published: July 2002

We present a first-principle investigation of quadruple helix nanowires, consisting of stacked planar hydrogen-bonded guanine tetramers. Our results show that long wires form and are stable in potassium-rich conditions. We present their electronic band structure and discuss the interpretation in terms of effective wide-band-gap semiconductors. The microscopic structural and electronic properties of the guanine quadruple helices make them suitable candidates for molecular nanoelectronics.
Novel generalized Born methods
Authors: Lee Michael S. , Salsbury Freddie R. , Brooks Charles L.
Published: July 2002

The generalized Born (GB) model is a simple continuum dielectric model for the calculation of molecular electrostatic solvation energies. It is a pairwise approximation to the solution of the Poisson equation for continuum electrostatic solvation. Key to the GB method is the calculation of Born radii for every atom in the system. We introduce two new methods for determining Born radii. The first is a two-parameter grid-based method that uses nearly the same molecular volume that is used in conventional Poisson calculations. The second is a five-parameter analytical method that utilizes a molecular volume built from a superposition of atomic functions. The analytical method, distinct from the grid-based algorithm, is amenable to force-based calculations, e.g., energy minimization and molecular dynamics. Unlike other Born radii methods, both algorithms employ a new empirically determined correction term that includes energetic effects beyond the Coulomb field approximation. With this correction term, the grid-based algorithm generally yields Born radii with greater than 0.99 correlation versus converged numerically derived Poisson Born radii. The analytical method reproduces Born radii with approximately 0.95 correlation versus Poisson-derived Born radii. With respect to absolute solvation energies, the grid-based method achieves an overall 1.3% error versus converged Poisson solutions for a set of 3029 single-chain proteins obtained from the Brookhaven Protein Data Bank. On the other hand, the analytic method delivers modest 2–4 % errors versus the Poisson solutions for the same data set. Results concerning absolute solvation energies of RNA and relative solvation energies in two sets of protein conformations are also presented.
Towards atomic force microscopy up to 100 MHz
Authors: Kawakatsu H. , Kawai S. , Saya D. , Nagashio M. , Kobayashi D. , Toshiyoshi H. , Fujita H.
Published: July 2002

An atomic force microscope for nanocantilevers measuring from a few 100 nm to a few μm in length was implemented. The natural frequencies of the nanocantilevers lie in the range of 1 MHz to 1 GHz, and optical detection schemes adapted to their size and frequency range was selected. A helium neon laser with a beat frequency of 890 MHz was used as the laser source. The beat was shifted to 1090 MHz by an acousto-optical-modulator, and used as the carrier for heterodyne laser Doppler measurement. This enabled velocity measurement up to around 100 MHz. The probe beam of the Doppler interferometer was guided to the nanocantilever by a single mode polarization-maintaining optical fiber terminated by a collimating lens, a quarter wave plate, and a focusing lens. Reflected light was collected by the same optics and mixed with the reference beam. Self-excitation of the nanocantilever at its lowest natural frequency was implemented for an amplitude of 1 nmp-p at 36 MHz. The Q factor of the cantilever was 8000. Noise effective amplitude of the Doppler interferometer was smaller than 10 pmp-p above 10 MHz. Frequency detection was possible for a nanowire measuring 100 nm in width.
Hall magnetometry on a single iron nanoparticle
Authors: Li Yongqing , Xiong Peng , von Molnár Stephan , Wirth Steffen , Ohno Yuzo , Ohno Hideo
Published: July 2002

High-sensitivity magnetometry over a wide temperature range has been achieved using submicron GaAs/GaAlAs Hall gradiometry. The sensitivity and versatility of the technique was demonstrated by the successful measurement of the magnetization switching of a single Fe nanoparticle with m∼5×105 μB (∼5×10−15 emu) at temperatures as high as 75 K.
Nonlinear optical properties of semiconductor superlattices
Authors: Chang Yia-Chung
Published: July 2002

Theoretical calculations of the third-order susceptibility χ(3) in GaAs-AlxGa1−xAs and Hg1−xCdxTe-HgyCd1−yTe superlattices are reported. The conduction–band nonparabolicity effect and the photoexcited plasma effect are both considered.
Physical and electrochemichromic properties of rf sputtered tungsten oxide films
Authors: Kaneko H. , Nishimoto S. , Miyake K. , Suedomi N.
Published: July 2002

The physical and electrochemical coloration characteristics of tungsten oxide films rf sputtered from a compressed powder WO3 target have been investigated. Oxide films with 3600–9800 Å thickness were deposited on substrates maintained at 200 °C at a total pressure of 0.5–8×10−2 Torr in Ar gas or an Ar-0.5-50% O2 gas mixture. Physical properties of the oxide films depend on the oxygen concentration and total pressure of the sputtering atmosphere. The films prepared at 4×10−2 Torr in a mixture of Ar-0.5-20% O2 gas are transparent and amorphous, and their electrical resistivity ranges from 6.5×108 to 2.4×1011 Ω cm. The films prepared at pressures between 4 and 6×10−2 Torr in an Ar-50% O2 gas mixture are transparent, and have crystallites with a composition of WO3. The films prepared at 1×10−2 Torr in a mixture of Ar-0.5 and 5.0% O2 gas are blue colored and transparent, respectively, and these films are crystallites with a composition of WO2.83. Electrochemichromic properties of the rf sputtered tungsten oxide films depend on the film structure, or on the sputtering conditions under which the films are prepared. The amorphous and crystalline WO3 films formed at a high total pressure of 3–8×10−2 Torr have good electrochemichromic properties and are colored deep blue. However, the crystalline WO2.83 films formed at a low total pressure of 0.5–1.5×10−2 Torr have poor electrochemichromic properties and are hardly colored. The amorphous oxide films with resistivity of 108–109 Ω cm and low density of ∼6.0 g/cm3, formed at a deposition rate higher than ∼100 Å/min, have very good coloration characteristics. The optical properties and density of the oxide films are also described.
Application of a gas tunnel to high-energy-density plasma beams
Authors: Arata Yoshiaki , Kobayashi Akira
Published: July 2002

The characteristics of high-temperature and high-energy-density plasma beams in a ‘‘gas tunnel’’ were experimentally clarified. A strong vortex flow at a high flow rate forms a radial pressure distribution with a sharp gradient. This produces a ‘‘gas tunnel’’ in the center, where the pressure is very low. In this study, this type of gas tunnel was applied to the production of plasma, and high-temperature and high-energy-density plasma beams were easily obtained. The plasma arc produced in this gas tunnel has a higher temperature and electron density than a conventional plasma arc because of a strong thermal pinch effect. Measurement of the properties of this plasma arc was primarily carried out by means of spectroscopy, and it was found that almost fully ionized plasma was obtained in the gas tunnel even at a small current of 200 A. In addition, a temperature of more than 3×104 K was achieved by increasing the arc current. A plasma jet generated in the gas tunnel has a very high electrical potential gradient of more than 40 V/cm and high thermal efficiency, and it is relatively easy to obtain an extremely high power of more than 200 kW.
Resistivity, carrier concentration, and carrier mobility of electrochemically deposited CdTe films
Authors: Takahashi Makoto , Uosaki Kohei , Kita Hideaki , Yamaguchi Shoji
Published: July 2002

The electrical type, resistivity, and donor or acceptor concentration of CdTe films deposited electrochemically at various potentials were measured. The carrier mobilities of the films were determined from these results. The deposition potential dependence of the mobility was small and the deposition potential dependence of the resistivity was mainly controlled by the deposition potential dependence of the donor or acceptor concentration. The carrier mobilities were very small compared with those in single crystals due to the scattering of the carriers at grain boundaries.
Equilibria of a rigidly rotating, fully ionized plasma column
Authors: Kim C. , Jensen R. V. , Krishnan M.
Published: July 2002

Due to the quadratic dependence of the centrifugal force on the rotation frequency, a single-fluid model of a rigidly rotating, semi-infinite plasma column has two equilibrium solutions. When the potential and pressure gradients across the column nearly balance each other, the rotation equilibria correspond to a low frequency which is small compared to the ion cyclotron frequency, and a high frequency which is roughly equal to the negative of the cyclotron frequency. This communication describes the different plasma properties which characterize these two equilibria.
Quantitative analysis of acoustic emission signals
Authors: Yu Zhen-zhong , Clapp Philip C.
Published: July 2002

Acoustic emission (AE) signals emanating from various deformation processes in materials are of a broadband nature. It is also well established that the ultrasonic attenuation caused by grain boundary scattering in polycrystalline materials is strongly frequency dependent. It is worth noting that distortions of AE signals due to grain boundary scattering (Rayleigh or stochastic type) have been inadequately treated in some previous quantitative AE studies. We propose a quantitative approach to estimating AE source parameters with proper care taken of the frequency-dependent media attenuation. Without getting involved in the complete measurement of media attenuation, the present approach is designed to find some characteristic quantities in both the frequency and time domains that are least sensitive to attenuation. The node frequency in the amplitude spectra and the peak time in real-time signals are found to be the most suitable for the purpose. They can be used to infer the source parameters such as the final size and the average velocity of source expansion.
The effects of various alloying elements on modifying the elevated temperature magnetic properties of sintered Nd-Fe-B magnets
Authors: Xiao Y. , Liu S. , Mildrum H. F. , Strnat K. J. , Ray A. E.
Published: July 2002

The effects of the alloying elements Co, Dy, Er, Al, and Nb on modifying the elevated temperature properties of sintered Nd-Fe-B–based permanent magnets have been studied in our laboratory. The results are summarized and analyzed. Small Nb additions increase coercivity and improve elevated temperature properties. Higher Nb additions lead to decomposition of the 2:14:1 phase into a 2:17 phase and a new magnetic phase with a Curie point around 350 °C. The effectiveness of Nb additions appears to be associated with the rare-earth content of the magnets.
Determination of activation energy for thermal regeneration of EL2 from its metastable state by thermally stimulated photocurrent measurements
Authors: Mohapatra Y. N. , Kumar Vikram
Published: July 2002

It is shown that thermally stimulated photocurrent measurements provide a simple and effective method of determining the activation energy of thermal regeneration rate of EL2 from the metastable state to the normal state in undoped semi-insulating GaAs. The thermal regeneration rate r is found to be 2.5×108 exp(−0.26 eV/kT) s−1.
Collision broadening of optical gain in semiconductor lasers
Authors: Ahn Doyeol
Published: July 2002

The energy-dependent intraband relaxation with polar-optical-phonon scattering is incorporated in the calculation of the linear gain and the refractive index change of the GaAs injection laser with an undoped active region. Comparison with the conventional model, which assumes a constant intraband relaxation, shows that it is difficult to fit the overall gain spectra exactly by single, energy-independent intraband-relaxation time. Moreover, the calculated gain spectra wth phonon broadening show strong temperature dependence due to the change of the relaxation time and the Fermi functions.
Optical-emission studies on the interaction between halogenated carbon species and noble gas during fluoropolymer sputtering
Authors: Sugimoto Iwao , Miyake Shojiro
Published: July 2002

Using optical-emission spectroscopy, the interaction between metastable-excited noble gas and fluorocarbon species is investigated for poly-chloro-tri-fluoro-ethylene (PCTFE) sputtering under a mixture of noble gas and CF3Cl gas flow conditions. Among a variety of noble gases, He and Ne in an excited state were quenched through energy transfer which induced the ionization and self-decomposition of the halogenated carbon species. Such an inactivation was not observed in the Ar, Kr, and Xe cases, in accordance with the ionization energy in CF3Cl derived from photoelectron spectroscopy. Instability in a radio-frequency (rf) plasma was observed in the pure Xe case. However, the plasma was stabilized in the case of a mixture with CF3Cl. The CF2 band which is characteristic of PCTFE sputtering was not detected in the Xe case. In addition, it was confirmed that the oxygen introduced into the rf plasma was more likely to react with CF2(3B1) than with CF2(1B1) or CF3(1B1).
Impurity effects on the generation, velocity, and immobilization of dislocations in GaAs
Authors: Yonenaga Ichiro , Sumino Koji
Published: July 2002

The effects of various kinds of impurities, Al, In, Si, Te, and Zn, on the dynamic behavior of dislocations in GaAs crystals are investigated. The dislocation generation from a surface scratch is suppressed by the doping of the impurities. Generally, the suppression effect of any given kind of impurities depends on the type of dislocations to be generated. However, no systematic dependence on the size misfit or the electrical activity of the impurity atom is found in the suppression efficiency. The immobilization of originally fresh dislocations due to aging at elevated temperature is investigated. The results are interpreted to be due to the gettering of impurities by the dislocations. The feature of the suppression effect in dislocation generation is well correlated to that of the dislocation immobilization due to impurity gettering. It is concluded that the suppression of dislocation generation by impurity doping originates from dislocation immobilization due to impurity gettering. Isovalent impurities are found not to affect the velocities of dislocations of any type in motion. On the other hand, the effect of electrically active impurities on dislocation velocity depends on both the electrical property of the impurities and the type of dislocations in motion.
Rate equation analysis of microcavity lasers
Authors: Yokoyama H. , Brorson S. D.
Published: July 2002

We describe the light output properties of single mode lasers having cavity dimensions on the order of the emitted wavelength. A simple rate equation formula is derived for a four-level laser assuming enhanced spontaneous emission into the cavity. These rate equation analyses show that increasing the coupling of spontaneous emission into the cavity mode causes the lasing properties to become quite different from those of usual lasers having cavity dimensions much larger than a wavelength. We find that the lasing threshold disappears, the light emission efficiency increases, relaxation oscillations do not occur, and the dynamic response speed is improved. It is shown that the spontaneous emission rate alteration caused by the cavity plays an essentially important role for these characteristics.
Magnetomechanical coupling in Bridgman-grown Tb0.3Dy0.7Fe1.9 at high drive levels
Authors: Clark A. E. , Teter J. P. , Wun-Fogle M. , Moffett M. , Lindberg J.
Published: July 2002

It is now possible to achieve substantial magnetomechanical transduction in modified Bridgman-grown samples of Tb0.3Dy0.7Fe1.9 (Terfenol-D) which are grain-oriented to achieve nearly complete [112] alignment. Large magnetic-field excursions can be converted into large fractional dimension changes (ΔL/L>10−3). In this paper measurements are reported of the average magnetomechanical coupling factor determined by (i) large field drives (>1000 Oe) and (ii) large pressure changes (> 20 MPa). By extending the small-signal magnetomechanical expressions to difference relationships Δε=sH Δσ+d ΔH and ΔB=d*Δσ+μσ ΔH, it is possible to determine large-signal coupling factors by k2=1−με/μσ, and (2) k2=1−sB/sH. Here με and μσ are the average magnetic permeabilities (ΔB/ΔH) at constant strain ε, and at constant stress σ, and sB and sH are the large signal elastic compliances (Δε/Δσ) at constant induction B, and constant field H. The square of the coupling factor is defined by k2=1−dd*/sHμσ. Using an apparatus which was designed to minimize demagnetizing effects, με, μσ, sB, sH, d, and d* were measured in large Bridgman-grown samples (10 cm×3.75 cm diam) for compressive stresses up to 49.1 MPa with field excursions from ±250 to ±750 Oe and pressure excursions from ±3.7 to ±19.0 MPa.
Spreading of liquid droplets on cylindrical surfaces: Accurate determination of contact angle
Authors: Wagner H. D.
Published: July 2002

The characterization of the physicochemical nature of interfaces is a key problem in the field of advanced fibrous composites. The macroscopic regime contact angle, which reflects the energetics of wetting at the solid-liquid interface, is difficult to measure by usual methods in the case of very thin cylindrical fibers, but it may be calculated from the shape of a liquid droplet spread onto a cylindrical monofilament using a method developed by Yamaki and Katayama [J. Appl. Polym. Sci. 19, 2897 (1975)], and B. J. Carroll [J. Coll. Interf. Sci. 57, 488 (1976)]. Unfortunately, measurements of the contact angle based on this method are, so far, unable to provide an accuracy of better than about 5°. In the present article two simple extensions of the method of Yamaki and Katayama and Carroll, are presented, from which highly accurate values of the contact angle may be obtained. This is demonstrated experimentally from the spreading of glycerol droplets on carbon fibers and epoxy droplets on aramid fibers.
Spin-wave envelope solitons in thin ferromagnetic films (invited)
Authors: Kalinikos B. A. , Kovshikov N. G. , Slavin A. N.
Published: July 2002

The process of spin-wave (SW) envelope soliton formation and propagation has been studied experimentally in thin yttrium-iron-garnet (YIG) films at microwave frequencies. The formation of solitons has been observed in perpendicularly and tangentially magnetized YIG films in the spectral regions of high dispersion near the ‘‘dipole gaps’’ in the dipole-exchange SW spectrum. With the increase of the input pulse duration or/and amplitude, the multisoliton regime of SW propagation and the regime of SW modulational instability have been observed. With a further increase of input power the spectrum of SW modulational instability became more complicated and a SW strange attractor was formed through the destruction of two-frequency quasiperiodic motion. The theoretical interpretation of the observed nonlinear SW phenomena is given in the framework of nonlinear Schrodinger equation (NSE) model taking into account peculiarities of the thin-film dipole-exchange SW spectrum. The results of numerical calculations of SW envelope profiles performed using NSE model are compared to the results of the experiments.
Physical description of a viscoelastically loaded AT-cut quartz resonator
Authors: Reed C. E. , Kanazawa K. Keiji , Kaufman J. H.
Published: July 2002

In this work, the electrical admittance of this plane-parallel resonator loaded on one face with a viscoelastic medium is described directly in terms of the physical properties of the system. This description is based on the detailed matrix equations for the piezoelectric quartz and includes the piezoelectric effect of the quartz transducer and the shear modulus and viscosity of the overlayer. This physically based analysis has proven invaluable in relating the admittance behavior directly to the materials’ properties. Initial comparisons of the theory with experimental data are given, including the appearance of even harmonics as described by Benes [E. Benes, J. Appl. Phys. 56, 608 (1984)] for the asymmetrically loaded resonator. Additionally, measurements on a series of perfluoropolyether fluids of differing molecular weights indicate that they cannot be described as simple viscous liquids in the MHz range. The assignment of a frequency-dependent viscosity with a relaxation time proportional to the molecular weight resolves some of the discrepancies. Because this study relates the complete admittance spectrum of the loaded resonator to the overlayer material properties, it opens the possibility of studying more than just the changes in resonant frequency. A detailed analysis of the resonance spectrum using an impedance analyzer would provide data which can be fit to the material’s properties and would be particularly helpful with viscoelastic media.
Intersubband transitions in an asymmetric quantum well with a thin barrier or a delta-function potential
Authors: Pandey L. N. , George Thomas F. , Rustgi M. L.
Published: July 2002

The changes in the bound-state energies and oscillator strength for intersubband transitions brought about by a thin barrier in the middle of an asymmetric quantum well are calculated, with a particularly close look at such changes as the middle barrier height approaches the bound-state energies. It is found that the oscillator strength goes through a slight change as the barrier height approaches the ground-state energy but an abrupt change when it approaches the excited bound-state energy. A suitable explanation for this change is provided. A similar tailoring of the intersubband transitions is also achieved by placing a delta-function potential in the vicinity of the middle of the well but without any abrupt change in the oscillator strength.
A microstructure based magnetization reversal model in sintered Fe-Nd-B magnets. II. Effect of post sintering treatments
Authors: Ramesh R.
Published: July 2002

The effect of post sintering heat treatments on the intrinsic coercivity of Fe-Nd-B magnets is studied. It is shown that the large anisotropy in thermal expansion coefficients in the a and c directions of the tetragonal unit cell as well as the anisotropy in thermal expansion properties between the matrix and the grain boundary phase, will lead to stresses upon quenching from the sintering temperature. The effect of stresses due to water quenching have been incorporated into the model developed in the companion paper (Part I). This quenching stress manifests itself as a stress anisotropy constant, which opposes the magnetocrystalline anisotropy constant. Thus, the effective anisotropy field, near the interfaces, is reduced from its value in an optimally cooled sample, leading to a lower iHc. It is also shown through step quenching experiments that the effect of quenching stresses can be nullified by cooling slowly to below a specific temperature following which quenching does not influence the intrinsic coercivity.
Optical properties of reduced lithium niobate single crystals
Authors: Dhar Ajay , Mansingh Abhai
Published: July 2002

The optical transmission of LiNbO3 single crystals has been measured in the wavelength range 200–900 nm, for different degrees of reduction, to study the effect of reduction on the optical characteristics of LiNbO3 near the fundamental absorption edge. The optical transitions in LiNbO3 were found to be indirect and the band gap decreased with increasing degree of reduction. The band observed at 2.48 eV in the absorption spectrum in heavily reduced samples has been attributed to the formation of polarons, and the theoretical model of Reik and Heese [J. Chem. Solids 28, 581 (1967)] for small polarons is used to correlate the optical and electrical properties.
Oxidation and reduction of copper oxide thin films
Authors: Li Jian , Vizkelethy G. , Revesz P. , Mayer J. W. , Tu K. N.
Published: July 2002

We have employed 16O(α,α)16O oxygen resonance measurement and transmission electron microscopy to study the oxidation and reduction of copper oxide thin films. The in- and out-diffusion of oxygen-induced oxygen concentration variations and microstructural changes in the films were monitored. The study of reduction was carried out by annealing CuO and Cu4O3 thin films in vacuum. Dark-field microscopic images show that isolated and large Cu2O grains emerge from the small CuO and Cu4O3 grain matrices. The growth of Cu2O grains in both CuO and Cu4O3 matrices has been measured to be linear with time, and have activation energies 1.1 and 0.7 eV, respectively. The main controlling mechanism to the discontinuous morphology of the Cu2O grain growth is the migration of the phase boundaries between the oxides induced by oxygen out-diffusion along the moving boundary. An oxygen in-diffusion study was performed by annealing Cu2O and Cu4O3 in an oxygen ambient. The CuO phase nucleates randomly and rapidly in both Cu2O and Cu4O3 matrices. The small grain growth rate of CuO suggests that nucleation rather than grain growth is the predominant event during oxidation. The kinetics study of the reduction and oxidation of copper oxides shows that the two processes are asymmetrical and the latter is faster.
Laser texturing for low-flying-height media
Authors: Ranjan R. , Lambeth D. N. , Tromel M. , Goglia P. , Li Y.
Published: July 2002

A novel selective-area texturing process using a pulsed laser to produce a new form of texture in only the landing zone is discussed. By rotating the media under the focused pulsed-laser beam, a row of crater shaped dimples are created in the landing zone only. The rest of the disk remains smooth and untextured. Contact start-stop (CSS) test results from a lubricated C/CoCrTa/Cr media on the laser-textured substrate exhibited a constant static friction coefficient of 0.17 even after 12-K CSS cycles, with no apparent friction buildup. This unique behavior is attributed to the rounded and smooth surface topography of the laser-textured media.
Development of the ground state within the UTSi system
Authors: de Boer F.R. , Brück E. , Klaasse J. C. P. , Nakotte H. , Buschow K. H. J. , Havela L. , Sechovsky V. , Nozar P. , Sugiura E. , Ono M. , Date M. , Yamagishi A.
Published: July 2002

Magnetic properties and specific heat are reported on compounds of the type UTSi, where T is a transition metal. A tendency towards magnetism is found for the compounds with the late transition metals: UCoSi, URuSi, and UIrSi are nonmagnetic, whereas UNiSi, URhSi, UPdSi, and UPtSi are magnetically ordered. This observation agrees well with the expected behavior on the basis of 5f-d hybridization.
On the flow of a thin liquid film over a rotating disk
Authors: Kim S. , Kim J. S. , Ma F.
Published: July 2002

The depletion of thin liquid films due to the combined effect of centrifugation, surface roughness, and air shear has recently been studied. While surface roughness of a rotating solid disk can be represented by deterministic curves, it has been argued that spatial random processes provide a more realistic description. Chiefly because of surface roughness, there is an asymptotic limit of retention of a thin film flowing on the rotating disk. The aim of this article is twofold. First, the effect of disjoining pressure on the retention of a thin film is investigated. It is found that incorporating disjoining pressure term has small but still appreciable effect on the asymptotic limits of lubricant retention. For a partially wetting lubricant, the two components of the disjoining pressure function tend to have opposite influence on the lubricant retention; one enhances the retention, while the other diminishes it. Second, the robustness of stochastic description of surface roughness is examined. For a given mean and variance, it is noted that different probability distributions of the surface fluctuations lead, in the absence of air shear, to significantly different asymptotic limits of thin-film retention. If air shear is incorporated, this sensitivity is substantially attenuated.
Calculated structures for [001] symmetrical tilt grain boundaries in silicon
Authors: Levi A. A. , Smith D. A. , Wetzel J. T.
Published: July 2002

The structures of [001] tilt boundaries in silicon have been systematically investigated by computer modeling, using the harmonic Keating potential to describe the interatomic forces. The full angular range of symmetrical tilt boundaries can be described in terms of linear combinations of characteristic groupings of atoms. More than one stable relaxed structure has been found for most grain boundaries. In all cases the relaxed bicrystal consists of localized groups of pure edge or 45° dislocation cores embedded in a tetrahedrally coordinated, stable structure.
Oxidation of titanium nitride in room air and in dry O2
Authors: Tompkins Harland G.
Published: July 2002

The oxidation of TiN in room air and in dry O2 at various partial pressures at temperatures of 350, 400, and 450 °C has been studied using ellipsometry, Auger electron spectroscopy, Rutherford backscattering spectrometry, and x-ray photoelectron spectroscopy. The film that forms is TiO2 and the oxidation kinetics are quadratic for both room air and dry O2. An initiation time prior to the quadratic growth is observed that is a function of the oxidation temperature, with longer times required for lower temperature. The partial pressure affects the growth as the cube root of the concentration of O2.
Terahertz time-domain measurement of the conductivity and superconducting band gap in niobium
Authors: Nuss Martin C. , Goossen K. W. , Gordon J. P. , Mankiewich P. M. , O’Malley M. L. , Bhushan M.
Published: July 2002

We measure the complex conductivity of thin superconducting niobium films using coherent time-domain terahertz spectroscopy. Both real and imaginary part of the conductivity are measured simultaneously without referring to the Kramers–Kronig relations. We also measure the superconducting band gap directly from the onset of absorption and compare our results with theory.
A one-dimensional model of dc glow discharges
Authors: Schmitt Wolfgang , Köhler Walter E. , Ruder Hanns
Published: July 2002

A one-dimensional continuum model for a dc-glow-discharge plasma between parallel-plate electrodes is presented, which is based on the local balance equations for particle densities and fluxes of electrons and ions, as well as on the local electron energy balance and the Poisson equation. In addition to similar treatments, the inertia term in the ion momentum balance equation leading to a singularity at the ion sound velocity, as well as the electron energy losses by excitation of atomic levels, have been taken into account. The system of nonlinear first-order differential equations supplemented by suitably chosen boundary conditions has been solved by the numerical procedure Henyey method ordinary differential equation solver, which allows also for the occurrence of removable singular points. Calculations for an argon plasma have been performed and the influence of parameter choices on the solution has been investigated. In general, the features typical for dc discharges are reproduced and agreement with the spatial profiles obtained by other authors with different methods is found.
Calorimetric measurements of the thermal relaxation in nanocrystalline platinum
Authors: Tschöpe A. , Birringer R. , Gleiter H.
Published: July 2002

The enthalpy release during the heating of nanocrystalline platinum samples has been measured and at least two different contributions to the excess Gibbs free energy have been identified by controlling the grain size. About one half of the excess enthalpy is released during a first relaxation process without any measurable variation of grain size followed by a second relaxation which can be attributed to grain growth. The isothermal heat release of the grain growth is analyzed to calculate the excess grain boundary enthalpy.
Piezoelectrically-induced switching of 90° domains in tetragonal BaTiO3 and PbTiO3 investigated by micro-Raman spectroscopy
Authors: Li Z. , Foster C. M. , Dai X.-H. , Xu X.-Z. , Chan S.-K. , Lam D. J.
Published: July 2002

Domain switching of 90° ferroelectric domains in tetragonal BaTiO3 and PbTiO3 is induced by the application of stress along specific crystallographic axes. For BaTiO3, single-domain crystals are obtained from twinned specimens by the application of ∼1.1 MPa of stress parallel to the a axis and twin boundaries are induced by application of ∼0.22 MPa of stress parallel to the c axis. Similar piezoelectrically-induced domain switching was observed in PbTiO3 at elevated temperature. We observed the rotation of the crystallographic axes associated with domain switching via micro-Raman spectroscopy. These results were consistent with optical microscope images of the domain switching which demonstrates the usefulness of micro-Raman spectroscopy for the study of ferroelectric domain structures. A phenomenological treatment of domain switching in a piezoelectrically-coupled system is described.
Preparation and characterization of off-congruent lithium niobate crystals
Authors: Bordui P. F. , Norwood R. G. , Jundt D. H. , Fejer M. M.
Published: July 2002

Vapor transport equilibration was used to prepare lithium niobate crystals of a variety of controlled off-congruent compositions. Crystals were characterized through measurement of the ferroelectric Curie temperature Tc and measurement of the temperature for noncritical phase matching TPM of second-harmonic generation from both 1.064- and 1.32-μm laser sources. Across the majority of the single-phase region, both Tc and TPM were observed to vary nearly linearly with Li/Nb ratio. The variation in TPM with Li/Nb ratio was observed to change direction within the single-phase region at some small but finite compositional interval away from the Li-rich phase boundary. Crystals equilibrated to the Li-rich phase boundary had excellent optical homogeneity. Preparation of Li-poor crystals was hampered by extremely slow lithium diffusivity and problems with second-phase precipitation.
Application of disjoining and capillary pressure to liquid lubricant films in magnetic recording
Authors: Mate C. Mathew
Published: July 2002

The behavior of liquid lubricant films on the disk surfaces in magnetic recording is analyzed using the concepts of disjoining and capillary pressure. Particular examples analyzed include lubricant distributions on rough and porous disk surfaces, lubricant flow, and the meniscus force acting on the recording slider sitting on the disk surface.
Precipitate drifting and coarsening caused by electromigration
Authors: Ma Q. , Suo Z.
Published: July 2002

A mechanism is proposed to explain electromigration-enhanced precipitate coarsening in Al-Cu alloy interconnects. The interface between the α-phase matrix and a θ-phase Al2Cu precipitate is incoherent, along which both Al and Cu atoms diffuse under an applied electric field. Depending on the relative mobility of Al and Cu, the diffusion causes the precipitate to migrate toward either the positive or the negative electrode. The velocity of a spherical precipitate is proportional to the electric field and the mobilities and inversely proportional to its radius. A critical electric field or precipitate radius exists, above which the precipitate can penetrate a grain boundary. Consequently, the precipitates agglomerate by the synergism between the Ostwald ripening and the current-induced migration. The resulting particles are distantly separated, depleting Cu atoms from the rest of the interconnect. The mechanism appears to limit the lifetime of interconnects having bamboo-like grains, tested below 300 °C, less than half of the melting temperature of Al. Experiments taking advantage of migration of various inhomogeneities are suggested which may illuminate several basic issues in the field of electromigration.
Reactive-flow simulation of the hot-filament chemical-vapor deposition of diamond
Authors: Kondoh Eiichi , Tanaka Kenji , Ohta Tomohiro
Published: July 2002

Two-dimensional reactive-flow simulations of a hot-filament chemical-vapor-deposition system were carried out. The set of coupled partial differential equations maintaining steady-state conservation of mass, momentum, energy, and chemical species was numerically solved with set boundary conditions to obtain spatial distributions of the gas temperature, fluid velocity, and partial pressures of the chemical species. From the obtained temperature distribution, it is shown that most of the source gas is not heated to the level of the filament temperature. This is due to the friction between the fluid and the filament, so that the gas velocity around the filament is greatly decreased. The species diffusion makes a uniform species distribution between the filament and the substrate; in particular, atomic hydrogen diffuses broadly, suppressing the formation of gaseous C2− species. However, the product distribution among H, H2, CH3, and CH4 is not influenced by the effect of diffusion, since the reaction H+CH4⇄H2+CH3 is in partial equilibrium with the superequilibrium of H atoms; in other words, the plug-flow assumption reported in the literature is valid for the product distribution among those species. The numerical results are compared with a previous deposition study for a wide variety of deposition parameters. It was found that the CH3 concentration agreed well with the deposition rate in terms of the variation in the deposition parameters. This finding supports CH3 being a growth species in the CH4-H2 hot-filament system.
Monte Carlo study of hole transport in silicon
Authors: Dewey Jim , Osman M. A.
Published: July 2002

The steady state and transient drift velocity of holes in silicon have been investigated using Monte Carlo techniques. The valence band is modeled by warped nonparabolic heavy and light hole bands, and a spherical spin-orbit band. The nonparabolicity of the heavy and light hole bands is included using piecewise continuous functions. The calculated velocities are in better agreement with experimental steady state drift velocity values compared to previous Monte Carlo calculations using only a heavy hole band. Transient calculations show the magnitude of the velocity overshoot for holes is smaller than electrons in silicon but is significantly higher than the steady state drift velocity when high fields are applied.