bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of residual stresses in Pb(Zr0.53Ti0.47)O3 thin films with Raman spectroscopy
Authors: Xu Wei-Hua , Lu Dexin , Zhang Tong-Yi
Published: July 2002

The present work uses Raman spectra to measure residual stresses in Pb(Zr0.53Ti0.47)O3 thin films. Based on thermodynamic analysis, a linear relationship is found between the stress and the square of the Raman frequency in the A1 [transverse optical3 (TO3)] and E [longitudinal optical3 (LO3)] modes. We calibrate the linear relationship by measuring the Raman spectra of stressed bulk Pb(Zr0.53Ti0.47)O3 samples. Then, we assess residual stresses in the lead zirconate titanate thin films at different thicknesses and different annealing temperatures. The residual stresses extracted from the A1(TO3) mode are consistent with those from the E(LO3) mode, which are more or less the same as those measured by the x-ray diffraction sin2 ψ method.
Critical lateral size for stress domain formation in InAs/GaAs square nanomesas: A multimillion-atom molecular dynamics study
Authors: Su Xiaotao , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya , Madhukar Anupam
Published: July 2002

Lateral size effects on the stress distribution and morphology of InAs/GaAs square nanomesas are investigated using molecular dynamics (MD) method. Two mesas with the same vertical size but different lateral sizes are simulated. For the smaller mesa, a single stress domain is observed in the InAs overlayer, whereas two stress domains are found in the larger mesa. This indicates the existence of a critical lateral size for stress domain formation in accordance with recent experimental findings. The InAs overlayer in the larger mesa is laterally constrained to the GaAs bulk lattice constant but vertically relaxed to the InAs bulk lattice constant.
Optical properties of undoped and Gd-doped CeO2 nanocrystalline thin films
Authors: Suzuki Toshio , Kosacki Igor , Petrovsky Vladimir , Anderson Harlan U.
Published: July 2002

The results of studies of the preparation, structure, and optical properties of undoped and Gd-doped CeO2 thin films are presented. Dense films with 4–150 nm grain size have been obtained on monocrystalline sapphire substrates using a polymeric precursor spin coating method. The results of the optical measurements are presented and correlated with the microstructure of the films. The transmission spectra have been used to determine the energy dependence of the refractive index, n and the extinction coefficient, k. Both n and k of the thin films decreased as grain size decreased and these results showed that this change could be related to the transition from crystalline to amorphous CeO2. The effect of dopant has little influence on n, <5%, but doping resulted in about a 30%–40% reduction of k compared to undoped specimens, which could be related to the decrease of absorption centers due to the replacement of Ce by Gd.
Quantum superintegrability and exact solvability in n dimensions
Authors: Rodrı́guez Miguel A. , Winternitz Pavel
Published: July 2002

A family of maximally superintegrable systems containing the Coulomb atom as a special case is constructed in n-dimensional Euclidean space. Two different sets of n commuting second-order operators are found, overlapping in the Hamiltonian alone. The system is separable in several coordinate systems and is shown to be exactly solvable. It is solved in terms of classical orthogonal polynomials. The Hamiltonian and n further operators are shown to lie in the enveloping algebra of a hidden affine Lie algebra.
Stability of field emission current from porous n-GaAs(110)
Authors: Tondare V. N. , Naddaf M. , Bhise A. B. , Bhoraskar S. V. , Joag D. S. , Mandale A. B. , Sainkar S. R.
Published: July 2002

Field electron emission from porous GaAs has been investigated. The emitter was prepared by anodic etching of n-GaAs (110) in 0.1 M HCl solution. The as-etched porous GaAs shows nonlinear Fowler–Nordheim (FN) characteristics, with a low onset voltage. The emitter, after operating for 6 h at the residual gas pressure of 1×10−8 mbar, shows a linear FN characteristics with a relatively high onset voltage and poor field emission current stability as compared to the as-etched emitter. The change in the behavior was attributed to the residual gas ion bombardment during field electron emission. X-ray photoelectron spectroscopic investigations were carried out on as-etched sample and the one which was studied for field emission. The studies indicate that the as-etched surface contains As2O3 and the surface after field electron emission for about 6 h becomes gallium rich. The presence of As2O3 seems to be a desirable feature for the stable field emission current.
New evaluation beamline for soft x-ray optical elements
Authors: Koike Masato , Sano Kazuo , Yoda Osamu , Harada Yoshihisa , Ishino Masahiko , Moriya Naoji , Sasai Hiroyuki , Takenaka Hisataka , Gullikson Eric , Mrowka Stanley , Jinno Masafumi , Ueno Yoshihiro , Underwood James H. , Namioka Takeshi
Published: July 2002

An evaluation system capable of measuring the wavelength and angular characteristics of the absolute reflectivity (or diffraction efficiency) of soft x-ray optical elements has been designed and constructed. The system was installed on a beamline (BL-11) of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. To cover a wavelength range of 0.5 nm<λ<25 nm, this system incorporates two types of Monk–Gillieson monochromators. One is a conventional type equipped with three varied-line-spacing gratings, allowing a choice of two included angles. The other is a new type that employs a scanning mechanism based on surface normal rotation. The outline of the system and some preliminary experimental data obtained in the course of test runs are described.
Calculations of nonlinear spectra of liquid Xe. II. Fifth-order Raman response
Authors: Cao Jianshu , Yang Shilong , Wu Jianlan
Published: July 2002

The polarization dependence and temporal profile of the fifth-order Raman response function and corresponding correlation function in liquid Xe are studied both analytically and numerically. Based on the symmetry of an isotropic sample, the fifth-order Raman response function has twelve distinct tensor elements, ten of which are independent, and the corresponding correlation function has twelve distinct tensor elements, seven of which are independent. The coefficients for decomposition into independent components are calculated explicitly based on the tensor property of an isotropic sample and are used to identify different coupling mechanisms in liquid Xe. The two-dimensional profile of the fifth-order Raman response function is evaluated by a simple hydrodynamic expression derived using the Gaussian factorization scheme. An alternative approach reduces the fifth-order Raman response function to time correlation functions that are easy to compute.
Scanning force microscopy of domain structures in Pb(Zn1/3Nb2/3)O3-8% PbTiO3 and Pb(Mg1/3Nb2/3)O3-29% PbTiO3
Authors: Abplanalp M. , Barošová D. , Bridenbaugh P. , Erhart J. , Fousek J. , Günter P. , Nosek J. , Šulc M.
Published: July 2002

Domain structures of unpoled as well as poled (along [001]- and [110]-direction) Pb(Zn1/3Nb2/3)O3 (PZN)-8% PbTiO3 (PT) and Pb(Mg1/3Nb2/3)O3 (PMN)-29% PT single crystals have been investigated by scanning force microscopy (SFM) in the piezoresponse mode, at room temperature. Antiparallel domain structures have been detected mostly in unpoled crystals of both materials, with a fingerprint pattern in (001)-oriented PZN-8% PT crystal. The ferroelastic domain wall has been identified in poled (110)-oriented PZN-8% PT crystal. “Writing” of ferroelectric domains has been performed by applying a dc voltage to the SFM tip. Local re-poling has been observed for all unpoled as well as for poled (001)-oriented crystals at the voltage ±60 V. Local electrical switching was successful in poled (110)-oriented PMN-29% PT at higher voltage (±120 V) but was not successful in poled (110)-oriented PZN-8% PT crystal. Domain-engineered crystals poled in [110]-direction seem to exhibit more stable (in the sense of local re-poling properties) domain arrangement. Hysteretic d(E) dependencies were observed by local application of an ac voltage.
Kelvin–Helmholtz instability in a Hele-Shaw cell
Authors: Plouraboué F. , Hinch E. J.
Published: July 2002

A linear stability analysis is presented for the Kelvin–Helmholtz instability in a Hele-Shaw cell, an analysis based on the Navier–Stokes equation to improve on the previous Euler–Darcy study that Gondret and Rabaud [Phys. Fluids 9, 3267 (1997)] made of their own experiments.
Perpendicular giant magnetoresistance of CoFeB/Cu single and dual spin-valve films
Authors: Oshima Hirotaka , Nagasaka Keiichi , Seyama Yoshihiko , Shimizu Yutaka , Eguchi Shin , Tanaka Atsushi
Published: July 2002

We present giant magnetoresistance measurements in the current-perpendicular-to-plane mode on single and dual spin valves whose areas are from 0.1 to 1.0 μm2. Dependence on the magnetic layer thickness and the structure was investigated. It was revealed that magnetoresistance change increases 20% by insertion of a nonmagnetic spacer layer in the free layer. The results were analyzed within the framework of the two-current series-resistor model, and proved to be consistent with the theory.
Tensor form of magnetization damping
Authors: Safonov Vladimir L.
Published: July 2002

A tensor form of phenomenological damping is derived for small magnetization motions. This form reflects basic physical relaxation processes for a general uniformly magnetized particle or film. Scalar Landau–Lifshitz damping is found to occur only for two special cases of system symmetry.
Film structure dependence of the magnetoresistive properties in current perpendicular to plane spin valves and its relation with current in plane magnetoresistive properties
Authors: Hosomi Masanori , Makino E. , Konishiike I. , Sugawara N. , Ohkawara S.
Published: July 2002

The magnetoresistive properties of current perpendicular to plane (CPP) spin valves (SV) were investigated for various film structures. CPP-SV elements were fabricated by photolithography and ion-beam etching. As an unexpected result, resistivity change-area product (dRA) improved up to 60% with increasing the PtMn layer thickness from 20 to 40 nm in the bottom synthetic spin valve structure, even though the PtMn layer cannot contribute to the spin dependent scattering. For the free layers, dRA improved with increasing the free layer thickness, although a saturation magnetization (Ms) and free layer thickness were restricted for the head application. Aiming at the enhancement of the spin dependent scattering on the interface, CoFe/NiFe multilayer is adopted as the free layer. Although NiFe improves dR, dRA was not improved with increasing the number of interfaces between CoFe and NiFe when total thickness is kept constant. It also becomes clear that NiFe is the appropriate material in terms of the bulk scattering point of view, although the combination with CoFe at the interface with the Cu spacer is required to avoid intermixing. Dual synthetic spin valve showed better properties, and a dRA of 3.0 mΩ μm2 was obtained. Since the fabrication of CPP elements requires a time-consuming process, it is desirable to predict the CPP properties in the CIP mode. Although the simple comparison between dR in the CPP mode and conductance change (dG) in the CIP mode through experimental results was attempted, it was recognized that further considerable arrangements were necessary.
Growth of epitaxial NdNiO3 and integration with Si(100)
Authors: Tiwari Ashutosh , Narayan J. , Jin C. , Kvit A.
Published: July 2002

We have grown epitaxial NdNiO3 films on Si(100) substrate under ambient oxygen pressure using a pulsed-laser deposition method. The integration of NdNiO3 with Si(100) was accomplished by lattice-matching epitaxy of MgO and SrTiO3 and domain matching epitaxy of TiN on Si(100). During domain matching epitaxy, four lattice constants of TiN match with three of silicon across the TiN/Si(100) interface. High-quality epitaxial NdNiO3 film on SrTiO3/MgO/TiN/Si(100) showed a very sharp metal–insulator (MI) phase transition at 200 K. Observed MI transition in epitaxial NdNiO3 is much sharper than that usually observed in bulk and polycrystalline films with more than four orders of magnitude change in resistivity. This MI transition is understood to arise because of the opening of charge transfer gap between Ni3+(3d) and O2−(2p) band.
Fast reversal dynamics of disk media (perpendicular and longitudinal)
Authors: Miles Jim , Middleton Barry , Olson Terry , Wood Roger
Published: July 2002

A dynamic micromagnetic model of granular thin film magnetic recording media has been employed to study the reversal modes of longitudinal and perpendicular thin films. Different reversal modes can be produced by using vector applied fields which either rotate or are applied off axis. When axial fields are applied the reversal of grains is incoherent, with an interaction energy barrier, high coercivity, long dynamic reversal times, and behavior characteristic of heavy damping. In contrast, for rotational fields in longitudinal media and for off-axis fields in perpendicular media the reversal is coherent, with a reduced energy barrier, lower coercivity, fast dynamic reversal, and behavior characteristic of light damping.
Ultrasmall grain size control in longitudinal recording media for ultrahigh areal densities
Authors: Piramanayagam S. N. , Xu Y. F. , Dai D. Y. , Huang L. , Pang S. I. , Wang J. P.
Published: July 2002

In this study, we propose a new “atomic wall” approach to underlayer design. In this design, a CrX underlayer is used where X and Cr are not miscible in the bulk phase, resulting in a reduced grain size. We have studied the addition of Zr to Cr layers and found that CrZr gives magnetic properties comparable to those of CrMo underlayers. In addition, a CrZr underlayer gives rise to a smaller grain size of 5.5 nm, in comparison to a grain size of 6.2 nm in the case of CrMo underlayers. To our knowledge, this is the smallest grain size reported for Co-alloy recording media. The recording measurements also show a higher signal to noise ratio for CrZr underlayers than for CrMo underlayers, suggesting that CrZr underlayers have potential for use in ultrahigh areal densities.
Magnetic domains in epitaxial nanomagnets with uniaxial or fourfold crystal anisotropy
Authors: Pulwey R. , Zölfl M. , Bayreuther G. , Weiss D.
Published: July 2002

In order to prepare submicron sized particles with strong magnetocrystalline anisotropies high quality epitaxial bcc-Fe films were grown on GaAs(110) and GaAs(001) by molecular beam epitaxy. Whereas Fe(110) on GaAs(110) is a model system with uniaxial in-plane anisotropy, Fe(001) on GaAs(001) has a strong fourfold anisotropy for films thicker than ∼5 nm. Various shapes like circular, square, or rectangular elements with sizes from 200 nm up to 6 μm were fabricated by electron beam lithography and ion beam etching. The remanent states after saturation along different directions or ac demagnetization along the easy axis were examined by using magnetic force microscopy. The experimental results clearly reflect the interplay of the different magnetocrystalline and shape anisotropies depending on the different magnetic histories.
Nanoencapsulation of ZnS:Ag particulates with indium tin oxide for field emission displays
Authors: Ollinger M. , Craciun V. , Singh R. K.
Published: July 2002

Cathodoluminescence degradation measurements showed that by applying a nanometer-scale indium tin oxide (ITO) coating on micron-sized ZnS:Ag particles, the degradation lifetime was dramatically improved. X-ray photoelectron spectroscopy (XPS) analysis showed that the Zn 2p3/2 and S 2p peaks of the electron beam irradiated ZnS:Ag were shifted to higher binding energies, which correspond to oxidized elements with respect to those found for the commercial ZnS:Ag particulates. The XPS analysis for the ITO coated ZnS:Ag showed a broadening of the Zn 2p3/2 and S 2p peaks, which were a convolution of several peaks. In this case, the Zn 2p3/2 and S 2p peaks corresponding to ZnS were still present together with another shoulder corresponding to the oxidized elements. This difference in the XPS results shows that the ITO coating reduced the degradation rate by slowing the surface chemical changes on the ZnS:Ag powder.
Transmission spectroscopy of photonic crystal based waveguides with resonant cavities
Authors: Moosburger Jürgen , Kamp Martin , Forchel Alfred , Oesterle Ursula , Houdré Romuald
Published: July 2002

Photonic crystal waveguides including resonant cavities have been fabricated and investigated by transmission spectroscopy. The waveguides consist of two missing rows in a triangular lattice of air holes in a GaAs/AlGaAs slab–waveguide structure. The mirrors of the cavities are formed by adding two rows of holes perpendicular to the guiding direction inside the waveguide. The spectrally broad photoluminescence of an InAs quantum dot layer in the heterostructure is used to probe the transmission. Depending on the resonator size, characteristic resonant peaks are observed in the transmission spectra. Finite difference time domain calculations of the transmission of the investigated structures show good agreement with experimental data.
Interlayer coupling in (In,Mn)As/InAs/(In,Mn)As magnetic semiconductor trilayer structures
Authors: Yanagi S. , Munekata H. , Kitamoto Y. , Oiwa A. , Slupinski T.
Published: July 2002

p- (In,Mn)As /n- InAs /p- (In,Mn)As trilayer structures have been prepared by molecular beam epitaxy on GaSb/GaAs/GaAs(001) substrates. Ferromagnetic coupling has been found between the two magnetic p-(In,Mn)As layers with a rather thick n-InAs layer (d∼30 nm). The magnitude of the ferromagnetic coupling is estimated to be J=7.6×10−3 mJ/m2, being one order of magnitude larger than that extracted for the (Ga,Mn)As-based trilayer structures [D. Chiba et al., Appl. Phys. Lett. 77, 1873 (2000)].
Heating and cooling effect of giant magnetoresistive heads during writing operations
Authors: Jang Eunkyu , Wang Geng , Cho Keung Youn , Lee Hyung
Published: July 2002

The temperature change of giant magnetoresistive (GMR) heads is studied at various write frequencies and write currents by measuring the dc resistance of GMR heads during writing operations. To investigate the effect of a disk on the temperature rise, the test was performed at two different conditions: first, head loaded on a disk, and second, head unloaded. There are five kinds of heating sources of spin valve (SV) heads during writings; (1) dc interconnect heating, (2) dc write coil heating, (3) ac interconnect heating, (4) write-to-read cross-talk of interconnect, and (5) ac write coil heating. The primary cause for the temperature rise of the SV head during writing is write-to-read cross-talk of interconnect, when the head is loaded on a disk. When the head is unloaded, dc or ac heating of the write coil is the main cause of temperature rise of the SV head. It was found that a disk plays an important role in the temperature change of GMR heads during writing as a cooling source. The disk hardly reduces the heat generated by read bias current and cross-talk induced current, but it significantly reduces the heat from the dc or ac write coil heating.
Analysis of magnetic forces in magnetically saturated permanent magnet motors by considering mechanical and magnetic coupling effects
Authors: Hwang Geun-Bae , Hwang Sang-Moon , Jung Weui-Bong , Kang Beom-Soo , Hwang I.-Cheol , Kim Chul-U.
Published: July 2002

Vibrations of magnetically induced origins are becoming more serious with the trend of high speed use in industrial applications. Vibration of motors with the rotor eccentricity, which may result from working allowances or errors in manufacturing processes, is a coupled phenomenon between mechanical and magnetic performance and dynamic characteristics of permanent magnet motors. This article investigates magnetic forces for interior permanent magnet (IPM) motors when the rotor eccentricity exists. An IPM motor, widely used in high speed applications, is significantly effected by the rotor eccentricity due to the magnetic saturation. Due to the magnetic saturation, amplitudes and frequency contents of magnetic forces for IPM motors are worse in vibration viewpoint than those for without the rotor eccentricity.
Magnetization processes of storage and back layers in double-layered perpendicular magnetic recording media observed using anomalous and planar Hall effects
Authors: Nakagawa Shigeki , Sasaki Ichiro , Naoe Masahiko
Published: July 2002

An anomalous Hall effect (AHE) and a planar Hall effect (PHE) represent a perpendicular component and an in-plane component of the magnetization in the double-layered media. Since AHE and PHE have different symmetries regarding to the applied magnetic field H, it is easy to distinguish the AHE component, which is proportional to M, and PHE component, which is proportional to M2, from the measured Hall voltage VH. The Hall voltage of the double-layered film composed of Co–Cr–Ta and Ni–Fe layers was observed when the magnetic field is applied at an angle (α) of 30° from the normal to the film plane. The perpendicular and the in-plane components, which are regarded as the magnetization process of Co–Cr–Ta and that of the Ni–Fe layer, respectively, can be easily determined from these characteristics. The Hall measurement is useful to study the magnetization characteristics in the double-layered media.
Systematic study of anisotropic properties of CeNiGe2
Authors: Jung M. H. , Lacerda A. H. , Pagliuso P. G. , Sarrao J. L. , Thompson J. D.
Published: July 2002

We have studied the anisotropic properties of CeNiGe2 by measuring the electrical resistivity, magnetic susceptibility, and magnetization. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at TNI=4 K and TNII=3 K as reported earlier on polycrystalline samples. CeNiGe2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H∥b)/M(H⊥b) at 2 K is estimated to be about 15 at 5 T. The resistivity ratio ρ∥b/ρ⊥b increases from 5 to 65 on heating from 2 to 200 K. The in-plane resistivity ρ∥b(T) shows double maxima typical of that expected when an interplay of crystal-field and Kondo effects plays a role.
A method to characterize the dielectric and interfacial properties of metal–insulator-semiconductor structures by microwave measurement
Authors: Lue Hang-Ting , Tseng Tseung-Yuen , Huang Guo-Wei
Published: July 2002

We have developed a method to investigate the dielectric and interfacial properties of gate dielectric thin films by microwave measurement. Ba0.5Sr0.5TiO3 (BST) thin films were deposited on 10 Ω cm (normal) and 10 k Ω cm [high-resistivity, (HR)] silicon substrates at the same time by rf magnetron sputtering. For the BST/HR-silicon, coplanar waveguides (CPW) were fabricated and measured at microwave frequencies with thru-reflect-line calibration while capacitance (C–V) measurements were carried out for BST/normal silicon. From the phase change of CPW transmission line and the maximum capacitance in C–V measurement, the dielectric constants of both the BST thin film and interface layer can be determined. Furthermore, the behaviors of insertion loss versus bias voltage were investigated. The results indicate that our method can provide useful information to study the dielectric and interfacial properties of metal–insulator–semiconductor structures.
Enhanced efficiency of PbWO4:Mo,Nb scintillator
Authors: Nikl M. , Bohacek P. , Mihokova E. , Solovieva N. , Vedda A. , Martini M. , Pazzi G. P. , Fabeni P. , Kobayashi M. , Ishii M.
Published: July 2002

The effect of Nb codoping on the optical properties of the PbWO4:Mo scintillator is investigated by radio- and thermoluminescence, scintillation decay, and light yield measurements. Steady-state radioluminescence efficiency of PbWO4:Mo,Nb with optimized doping concentrations (2750 and 350 molar ppm, respectively) becomes up to 20 times higher with respect to that of undoped PbWO4 and is comparable to that of Bi3Ge4O12. However, slow components down to several tens of microseconds appear in the time decay. Their existence may be related to the presence of traps monitored by thermoluminescence.
High resolution electronic spectroscopy of three n-alkylbenzenes: ethyl-, propyl-, and butylbenzene
Authors: Borst David R. , Joireman Paul W. , Pratt David W. , Robertson Evan G. , Simons John P.
Published: July 2002

Rotationally resolved S1−S0 fluorescence excitation spectra of ethylbenzene, two conformers of n-propylbenzene, and two conformers of n-butylbenzene have been observed and assigned. The data obtained provide information about the equilibrium properties of each molecule, including their geometries in the S1−S0 states, their electronic distributions, and their dynamical behavior following the absorption of light. Trans structures are found to have S1 states that are Lb1 in character with relatively long fluorescence lifetimes. Gauche structures are found to have S1 states that are mixed (1Lb/1La) in character with relatively short fluorescence lifetimes. Possible reasons for these differences in properties are discussed.
Calculation of the group-based pressure in molecular simulations. I. A general formulation including Ewald and particle-particle–particle-mesh electrostatics
Authors: Hünenberger Philippe H.
Published: July 2002

A general formulation is given for the calculation of the isotropic or anisotropic group-based instantaneous pressure in molecular simulations under periodic boundary conditions. The equations, derived from the statistical mechanical definition of the pressure, apply to groups defined as single atoms (atomic pressure) or whole molecules (molecular pressure), but also to any other arbitrary atom grouping. Different definitions lead to different pressure fluctuations, but to the same average pressure. Two sets of equations are derived for the calculation of the group-based virial. The “traditional” set, which is the one commonly used to compute molecular pressures in simulations, has two main drawbacks: (i) it requires bookkeeping of group definitions in the inner loop of the nonbonded interaction calculation, (ii) it cannot be applied when electrostatic interactions are computed through lattice-sum methods. The “alternative” set is based on the remarkable result that any group-based virial can be computed from the atomic virial by adding a computationally inexpensive correction term to account for atom grouping. This new formalism presents the following advantages: (i) it requires no bookkeeping of group definitions in the inner loop of the nonbonded interaction calculation, (ii) the isotropic virial corresponding to each homogeneous pairwise interaction term can be computed directly from the corresponding interaction energy contribution without knowledge of the pairwise forces, (iii) application to lattice-sum electrostatics is straightforward. Traditional and alternative virial expressions are derived for all terms typical of interaction functions used in molecular simulations, namely covalent, Lennard-Jones (and long-range correction), truncated electrostatic (and reaction-field correction), and lattice-sum electrostatic (Ewald and particle-particle–particle-mesh including self-energy) terms.
Radiation sources and diagnostics with ultrashort electron bunches
Authors: Catravas P. , Esarey E. , Leemans W. P.
Published: July 2002

The basic principles and design of radiation sources (transition radiation, Cerenkov radiation, radiation from periodic structures, etc.) and radiation-based diagnostics will be discussed, with an emphasis on radiation from ultrashort electron bunches. Ultrashort electron bunches have the potential to produce high peak flux radiation sources that cover wavelength regimes where sources are currently not widely available (coherent THz/IR) as well as ultrashort x-ray pulses (3–100 fs). While radiation from the electron bunch contains the full signature of the electron beam and/or medium it has traveled through, the deconvolution of a single property of interest can be difficult due to a large number of contributing properties. The experimental implementation of novel solutions to this problem will be described for beams from 30 MeV to 30 GeV, including fluctuational interferometry, source imaging, phase matched cone angles and laser-based techniques, which utilize optical transition radiation, wiggler and Cerenkov radiation, and Thomson scattering. These novel diagnostic methods have the potential to resolve fs bunch durations, slice emittance on fs scales, etc. The advantages and novel features of these techniques will be discussed.
Nonresonant Kerr effect in microporous silicon: Nonbulk dispersive behavior of below band gap χ(3)(ω)
Authors: Lettieri S. , Maddalena P.
Published: July 2002

Although in recent years resonant optical nonlinearities in quantum confined silicon generated significant interest, no experimental work has been dedicated to the nonresonant regime, which is the range of interest for optical switching applications. In this article we report a systematic investigation on the different types of optical nonlinearities which can be activated in quantum-sized silicon. In particular, original measurements of nonresonant nonlinear refraction (Kerr effect) are reported at different wavelengths, spanning the infrared middle-gap range. The dispersive scaling rule and values of the nonlinear refractive index are clearly incompatible with those of three-dimensional semiconductors. Hence the quantum confined density of states plays a key role in determining the frequency dispersion of the nonresonant third-order susceptivity χ(3)(ω). Also, this suggests the need of further investigation of the influence of quantum-size effects (and related density of states modifications) on below-gap χ(3).
Dielectric relaxation of WO3 thick films from 10 Hz to 1.8 GHz
Authors: Schmitt R. , McCann D. , Marquis B. , Kotecki D. E.
Published: July 2002

The dielectric relaxation of thick (∼50 μm) films of WO3 was investigated from 10 Hz to 1.8 GHz at a temperature of 200 °C. Three separate measurement techniques were employed: time-domain discharge voltage measurement, frequency-domain impedance measurement, and frequency-domain reflection coefficient measurement, with overlapping frequency ranges. Four distinct regions of dispersion were observed: below 100 Hz, the permittivity and loss tangent rise, implying a relaxation process; between 25 kHz and 1 MHz a second region of dispersion is observed with a loss peak at 80 kHz; from 1 to 300 MHz the dielectric response obeys the w−m power law of the Jonscher universal response with m=0.11; and above 500 MHz, another region of Debye-like loss is observed.
Carbon: A bane for giant magnetoresistance magnetic multilayers
Authors: Yang David X. , Chopra Harsh Deep , Shashishekar B. , Chen P. J. , Egelhoff W. F.
Published: July 2002

This study reports the highly deleterious role of a small amount of carbon on the structure and magnetic properties of “giant” magnetoresistance (GMR) NiO–Co–Cu-based spin valves. Controlled incorporation of 1–3 at. % carbon in the Co/Cu layers has been shown to completely eliminate the GMR effect. The presence of carbon gives rise to highly discontinuous Co/Cu layers, resulting in the formation of pinholes, and associated degradation of structure-sensitive magnetic properties. In addition, carbon promotes the formation of a high density of stacking faults in the Co/Cu layers, with carbon nanoprecipitates forming in the vicinity of the stacking faults. Results have implications for other multilayers and magnetoelectronics devices.
The Doppler-free two-photon absorption spectroscopy of naphthalene with Zeeman effects
Authors: Okubo Mitsushi , Misono Masatoshi , Wang Jinguo , Baba Masaaki , Kato Hajime
Published: July 2002

The Doppler-free spectrum and the Zeeman effect of the A 1B1u(v4=1:b1u)←X 1Ag(v=0) transition of naphthalene in the 33 576.4–33 578.0 cm−1 range has been measured by means of two-photon absorption spectroscopy with counter propagating light beams of identical wavelength within an external cavity. Rotational lines were fully resolved, and 1098 Q(K)Q(J) lines of J=0–42, K=0–24 were assigned. The molecular constants of the A 1B1u(v4=1:b1u) state were determined. Deviations from the line positions calculated using the molecular constants were observed for several lines. Perturbations were not observed for K=0 but were observed to increase with increasing K. The perturbations were therefore identified as originating from a parallel Coriolis interaction. The Zeeman splittings for lines of a given J were observed to be maximum at K=0 and to decrease with increasing K. Analysis of these results indicate that the magnetic moment lies along the c axis (perpendicular to the molecular plane). Any lines broader than our instrumental resolution (5 MHz) were not observed at H=0 T. The J and K dependence of the Zeeman splittings of the A 1B1u(v4=1:b1u)←X 1Ag(v=0) transitions were observed to be regular. This observation and the small number of perturbed lines, leads to the conclusion that the resonance interaction of the A 1B1u state with the T1 3B3u and T2 3B1u states are small and negligible in the observed region.
Temperature dependence of nonradiative transitions: A nonperturbative theory
Authors: Hizhnyakov V. , Kaasik Helle
Published: July 2002

The temperature dependence of multiphonon nonradiative transitions, caused by linear diagonal and quadratic nondiagonal vibronic interactions, is investigated on the basis of nonperturbative quantum theory. Both transitions up and down in energy are considered. It was found that the usual increase in transition rate with temperature may not hold near some (critical) value(s) of a nondiagonal interaction and temperature, when the rate becomes very high (comparable to mean phonon frequency), and its temperature dependence exhibits a maximum. The results may be important for understanding the mechanisms of catalysis in chemical reactions.
Free surface boundary conditions at a bubbly/weakly splashing air–water interface
Authors: Brocchini M.
Published: July 2002

Following the analysis of Brocchini and Peregrine for the interaction of strong turbulence with an air–water surface approximate boundary conditions are derived under the assumption of a thin, bubbly/weakly splashing surface layer. With this assumption, results obtained by the level-set method of Hong and Walker are recovered. These boundary conditions are particularly suited for k−ε models of breaking water waves.
Numerical simulation of mark formation in dual-stack phase-change recording
Authors: Meinders E. R. , Borg H. J. , Lankhorst M. H. R. , Hellmig J. , Mijiritskii A. V.
Published: July 2002

Dual-stack phase-change recording is an option to further increase the data capacity of rewritable optical disks. Such disks consist of two recording stacks that are both recorded and read from the same side of the disk. Consequently, the first recording stack needs therefore to be semitransparent to allow recording in the second recording stack. Thick nontransparent metal layers can therefore not be used in the first recording stack, which makes the first recording stack the most challenging stack from a thermal point of view. A numerical model based on crystal growth was developed to study formation and erasure of amorphous marks in phase-change stacks that are based on fast-growth doped SbTe phase-change materials. The validity of the model was demonstrated from transmission electron microscopy analyses of recorded marks that showed a good correspondence with the calculated mark shapes in a conventional single-stack recording stack. The model was subsequently applied to analyze formation and erasure of marks in slow-cooling phase-change stacks for digital versatile disk, (DVD) and digital video recording (DVR) recording conditions. The effect of the recording velocity, the erase power, and the crystal growth velocity on the erasability of amorphous marks was simulated. The calculated phenomena are in good agreement with the phenomena observed from DVD and DVR erasability measurements. Mark formation in slow-cooling recording stacks is characterized by severe recrystallization during writing. Two possible solutions are indicated in this article, aiming at reducing the heat accumulation and the resulting recrystallization during writing of amorphous marks. Additional semitransparent heat sinks improve the mark formation considerably but also require higher write powers. Another solution is the application of modified write strategies. Modeling and recorder results are discussed for both approaches.
Interdiffusion, stress, and microstructure evolution during annealing in Co/Cu/Co trilayers
Authors: Brückner W. , Baunack S. , Thomas J. , Hecker M. , Schneider C. M.
Published: July 2002

In order to find interdiffusion and microstructural changes on sputtered 90 nm Co/180 nm Cu/90 nm Co trilayers during annealing, the evolution of the stress and electrical resistance was studied in situ during temperature ramps and isothermal annealing as well as concentration-depth profiles, the grain morphology, and the phase and texture formation were investigated after heat treatment at various temperatures. Up to 450 °C, no distinct lattice interdiffusion was observed. Grain-boundary diffusion of Cu through the Co top layer to the surface as well as a distinct growth of Cu grains into the Co top layer start to occur at about 450 °C. The conclusions corroborate findings on Cu/Co nanoscale multilayers, which show a deterioration of the giant magnetoresistance effect at high temperatures due to similar microscopic mechanisms.
Coherent suppression of magnetic ringing in microscopic spin valve elements
Authors: Schumacher H. W. , Chappert C. , Crozat P. , Sousa R. C. , Freitas P. P. , Bauer M.
Published: July 2002

We demonstrate the coherent suppression of magnetic precession in microscopic spin valve elements after the decay of ultrashort magnetic field pulses. The magnetization dynamics in 1 μm×4 μm wide giant magnetoresistance devices are studied by measuring the magnetotransport response to ultrashort magnetic field pulses (pulse length 0.2–4 ns). Under the influence of a static field perpendicular to the pulsed field, pronounced magnetic precession is observed after the onset of the pulse as well as upon pulse termination. The precession after the pulse decay (“ringing”) can be effectively suppressed by adapting the effective pulse length to the precession period.
Reentrant waves and their elimination in a model of mammalian ventricular tissue
Authors: Biktashev V. N. , Holden A. V.
Published: July 2002

The vulnerability to reentrant wave propagation, its characteristics (period, meander, and stability), the effects of rotational transmural anisotropy, and the control of reentrant waves by small amplitude perturbations and large amplitude defibrillating shocks are investigated theoretically and numerically for models based on high order, stiff biophysically derived excitation equations.
Systematic derivation of amplitude equations and normal forms for dynamical systems
Authors: Ipsen M. , Hynne F. , So/rensen P. G.
Published: July 2002

We present a systematic approach to deriving normal forms and related amplitude equations for flows and discrete dynamics on the center manifold of a dynamical system at local bifurcations and unfoldings of these. We derive a general, explicit recurrence relation that completely determines the amplitude equation and the associated transformation from amplitudes to physical space. At any order, the relation provides explicit expressions for all the nonvanishing coefficients of the amplitude equation together with straightforward linear equations for the coefficients of the transformation. The recurrence relation therefore provides all the machinery needed to solve a given physical problem in physical terms through an amplitude equation. The new result applies to any local bifurcation of a flow or map for which all the critical eigenvalues are semisimple (i.e., have Riesz index unity). The method is an efficient and rigorous alternative to more intuitive approaches in terms of multiple time scales. We illustrate the use of the method by deriving amplitude equations and associated transformations for the most common simple bifurcations in flows and iterated maps. The results are expressed in tables in a form that can be immediately applied to specific problems.
Thermally stimulated currents from corona-charged polypropylene films: A thermal effect of vacuum deposition of metallic electrodes
Authors: Baba Atushi , Ikezaki Kazuo
Published: July 2002

It is demonstrated that the thermally stimulated currents (TSC) from positively or negatively corona-charged polypropylene strongly depend on the order of the following two processes: a process of vacuum deposition of Al electrodes on the sample polymer and a process of heat-treatment of the polymer. Observed results are explained by a thermal effect which is introduced during the vacuum deposition of metallic electrodes. This thermal effect of the vacuum deposition of metallic electrodes is the largest for Al and the smallest for Bi among Al, Au, Ag, and Bi. Observed TSC spectra have three peaks at about 68, 142, and above 147 °C for positively charged samples and four peaks at about 48, 90, 142, and above 147 °C for negatively charged samples, respectively. Origins of these TSC peaks are discussed in some detail.
Critical phenomena: Some recent theoretical developments (invited)
Authors: Fisher Michael E.
Published: July 2002

The aim of this contribution is to draw attention to some recent developments in the theory of critical phenomena and phase transitions that may be of interest to the magnetism community in that magnetic systems have provided a fertile testing ground for modern theoretical ideas concerning ordering and phase transitions while, on the other hand, many aspects of observed magnetic phase behavior have required sophisticated theory for their proper elucidation. The new works in question have been published or will appear shortly: accordingly, only an outline is presented here together with references to the main literature sources which, in turn, include fuller references to earlier work not explicitly mentioned. Four linked topics are addressed: (i) finite-size effects at first-order transitions; (ii) asymptotic degeneracy in transfer matrices, which is intimately related to long-range order; (iii) some consequences of the conformal covariance of fluctuations at a critical point in bulk and in finite systems, especially in two spatial dimensions; (iv) the discovery of ‘‘exactly soluble’’ two-dimensional models exhibiting two infinite classes of distinct critical and multicritical points.
Superconducting and structure properties of niobium nitride prepared by rf magnetron sputtering
Authors: Cukauskas E. J. , Carter W. L. , Qadri S. B.
Published: July 2002

The properties of rf-magnetron-sputtered NbN have been investigated for substrate temperatures from 200°C to 750°C as a function of the partial pressure of methane introduced into the Ar–N2 sputtering gas mixture. The best films were prepared at elevated substrate temperatures with approximately 2% methane added to the sputter gas. These films also had resistivities approximately 70 μΩ cm. At lower substrate temperature, T∼200°C, the best attained Tc was approximately 13.3 K with a resistivity of 140 μΩ cm. The crystal structure of these materials was investigated using x-ray diffraction and Read x-ray photographs. Those films prepared with no added methane were found to be two-phase δ and ε NbN. The addition of a small amount of methane produced single δ phase NbN with a predominant (200) preferrential orientation. The δ phase lattice parameter was determined to vary approximately from 4.39 Å to 4.45 Å as the amount of methane was increased. The effect of hydrogen doping on NbN was to produce multiphase NbN with the ε, δ phases and some evidence of the β phase. These material properties are of importance for the design and fabrication of NbN electrode Josephson tunnel junctions.
Shortening of electron conduction pulses by electron attacher C3F8 in Ar, N2, and CH4
Authors: Wang W. C. , Lee L. C.
Published: July 2002

The attachment rate constants of C3F8 in the buffer gases of Ar, N2, and CH4 are measured using a parallel-plate drift-tube apparatus. The dependences of the electron drift velocities on the contents of C3F8 in various buffer gases are investigated. Electrons are produced by irradiating the cathode with ArF laser photons. The transient voltage pulses induced by the electron motion are observed. We find that the C3F8-CH4 mixture has the desirable characteristics of both electron drift velocity and attachment rate constant for the application of diffuse-discharge opening switches.
The determination of the void structure of microporous coals by small-angle neutron scattering: Void geometry and structure in Illinois No. 6 bituminous coal
Authors: Gethner Jon S.
Published: July 2002

The access of solvents and reactants to the microvoid volume in porous materials such as coal plays an important role in determining the overall chemistry which takes place during a variety of chemical transformations including oxidation, combustion, and pyrolysis. The structure and surface composition of these voids were studied using small-angle neutron scattering techniques to examine selectively the subset of the overall void volume distribution which comprises the microvoid volume. Powdered Illinois No. 6 coal containing approximately 20% void volume was slurried in several different aqueous and cyclohexane solutions. The solutions used had various hydrogen-to-deuterium ratios in order to contrast match most of the open pore volume thereby making the microvoid volume visible. The microvoid volume observed is characterized as elongated voids having a fairly well-defined diameter and surface composition. The scattering intensity from the microvoid volume shows a well-defined Porod region, indicating that the smallest void dimension is resolved by the instrumental configuration employed. A Guinier region exhibiting Q−1 behavior, which is characteristic of elongated structures, is also observed. The average radius of a circular cross section of these voids is found to be 25.4 Å. The microvoids are found to be completely filled by aqueous solutions so that the residual neutron scattering, which is not eliminated by the contrast-matching aqueous solution, is due to the organic matrix structure. Nonaqueous mixtures of cyclohexane cannot fill the entire microvoid volume as effectively as the aqueous mixtures. The scattering differences observed between the aqueous and nonaqueous filled coal indicates that the surface of the microvoids is predominantly aliphatic in character with the principal compositional variation being the presence or absence of acidic functionality on the surface.
Efficiency of chemical oxygen-iodine lasers: Theoretical simulation and experiment
Authors: Watanabe K. , Kashiwabara S. , Fujimoto R.
Published: July 2002

A theoretical study on the efficiency of chemical oxygen-iodine laser (COIL) oscillators is described together with experimental data obtained using an efficient COIL system. In order to evaluate chemical oxygen-iodine laser performance, three types of efficiencies (power conversion efficiency, extractable efficiency, and chemical efficiency) were introduced in this investigation. The dependencies of these efficiencies on initial gas components are investigated by theoretical simulation in which the theoretically attainable values of the efficiencies are also given. The validity of this simulation is confirmed by comparing the results with our experimental data. The experiments yielded a high-extractable power efficiency of 75%, which is comparable to the theoretically determined attainable value of 88%.