bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-acoustic solitons in a plasma with a relativistic electron beam
Authors: Esfandyari A. R. , Khorram S. , Rostami A.
Published: July 2002

Ion-acoustic solitons in a collisionless plasma consisting of warm ions, hot isothermal electrons, and a relativistic electron beam are studied by using the reductive perturbation method. The basic set of fluid equations is reduced to Korteweg–de Vries (KdV) and modified Korteweg–de Vries (mKdV) equations. The effects of ion temperature and relativistic electron beam on ion-acoustic solitons are investigated. It has been shown that the four ion-acoustic modes can be propagated in this plasma system. The compressive and rarefactive ion-acoustic solitons satisfies the KdV equation for a given soliton velocity, beam density much smaller than the background electron density and the bulk ion temperature smaller than the background electron temperature for two modes. Also it has been illustrated that there exist mKdV solitons for some critical value of electron beam density in these cases. These critical values decrease as ion temperature increases for one of two modes and increase for the other one. Finally, it has been remarked that for another two modes only rarefactive KdV ion-acoustic solitons can be obtained. One of these modes exists for the electron beam density much smaller than the bulk electron density, and the other exists for almost all values of the beam density, even if it is greater than the background electron density.
Characterization of nanostructured metal films by picosecond acoustics and interferometry
Authors: O’Hara K. E. , Hu Xiaoyuan , Cahill David G.
Published: July 2002

Picosecond interferometry is used to study the acoustics waves created by heating Pt films with a subpicosecond laser pulse. Both the period of the initial oscillations in the metal film and the amplitude of the sound wave in the substrate are measured quantitatively. The platinum films are roughened by irradiation with energetic ions. The amplitude of the sound wave is doubled at those irradiation levels where the platinum coverage has been reduced by about one-half. A theory for the amplitude of the launched acoustic wave predicts that the acoustic amplitude is proportional to the mean square film thickness. Thus changes in the morphology of a partially perforated metal film can be observed using a simple, nondestructive optical technique.
Molecular dynamics simulation of proton transport with quantum mechanically derived proton hopping rates (Q-HOP MD)
Authors: Lill Markus A. , Helms Volkhard
Published: July 2002

A very efficient scheme is presented to simulate proton transport by classical molecular dynamics simulation coupled with quantum mechanically derived proton hopping. Simulated proton transfer rates and proton diffusion constants for an excess proton in a box of water molecules are in good agreement with experimental data and with previous simulations that employed empirical valence bond (EVB) theory. For the first time, the proton occupancy of an aspartic acid residue in water was computed directly by MD simulations. Locally enhanced sampling or multi copy techniques were used to facilitate proton release in simulations of an imidazole ring in a solvent box. Summarizing, a quasiclassical description of proton transfer dynamics has been able to capture important kinetic and thermodynamic features of these systems at less than 50% computational overhead compared to standard molecular dynamics simulations. The method can be easily generalized to simulate the protonation equilibria of a large number of titratable sites. This should make it an attractive method to study proton transport in large biological systems.
High-frequency modulation without the relaxation oscillation resonance in quantum cascade lasers
Authors: Paiella Roberto , Martini Rainer , Capasso Federico , Gmachl Claire , Hwang Harold Y. , Sivco Deborah L. , Baillargeon James N. , Cho Alfred Y. , Whittaker Edward A. , Liu H. C.
Published: July 2002

Quantum cascade (QC) lasers, based on intersubband transitions in semiconductor quantum wells, are characterized by ultrafast (picosecond) carrier lifetimes. An important consequence of this unique property is the expected absence of relaxation oscillations in the transient response of these devices. Here, we discuss and experimentally verify this prediction by measuring the modulation response of several 8-μm-QC lasers, properly processed and packaged for high-speed operation, up to 10 GHz.
Molecular dynamics in tilted bilayer smectic phases: A proton nuclear magnetic resonance relaxometry study
Authors: Carvalho A. , Sebastião P. J. , Ribeiro A. C. , Nguyen H. T. , Vilfan M.
Published: July 2002

A proton nuclear magnetic resonance (NMR) relaxation study of molecular dynamics in the liquid crystal 4-octylphenyl 2-chloro-4-(4-cyanobenzoyloxy)benzoate (DB8Cl) is presented. DB8Cl molecules possess a strong polar terminal group and form, in addition to the nematic phase, three different smectic phases: bilayer smectic A, bilayer smectic C, and anticliniclike smectic C phase. The proton spin-lattice relaxation times were measured in all mesophases over a broad frequency range of six decades by applying conventional and fast field-cycling NMR techniques. The parameters obtained in the analysis of the experimental data give quantitative information on molecular motions, particularly for the tilted smectic phases of DB8Cl. In contrast to former conjectures, we found that the low-frequency relaxation in the bilayer smectic C phases results from director fluctuations about the layer normal, which occur without distortion of the layers, and from layer undulations, similar to those in the smectic A phase. In the low-temperature bilayer smectic C phase, a considerable slowing-down of molecular translational diffusion is observed. It confirms indirectly the anticlinic character of this mesophase. Measurements of angular dependence of the relaxation times at 60 MHz support the conclusions obtained from the frequency dispersion data.
Fatigue-free samarium-modified bismuth titanate (Bi4−xSmxTi3O12) film capacitors having large spontaneous polarizations
Authors: Chon Uong , Kim Ki-Bum , Jang Hyun M. , Yi Gyu-Chul
Published: July 2002

Fatigue-free and highly c-axis oriented Bi3.15Sm0.85Ti3O12 (BSmT) thin films were grown on Pt/TiO2/SiO2/Si(100) substrates using the method of metalorganic sol decomposition. The BSmT film capacitor with a top Pt electrode showed significantly improved values of the remanent polarization (2Pr) and the nonvolatile charge as compared to those of the Bi4−xLaxTi3O12 (x=0.75) film capacitor, recently known as the most promising candidate for nonvolatile memories. The 2Pr value of the BSmT capacitor was 49 μC/cm2 at an applied voltage of 10 V while the net nonvolatile switching charge was as high as 20 μC/cm2 and remained essentially constant up to 4.5×1010 read/write switching cycles at a frequency of 1 MHz. In addition to these, the capacitor demonstrated excellent charge–retention characteristics with its sensing margin of 17 μC/cm2 and a strong resistance against the imprinting failure.
Probing interaction forces in colloidal monolayers: Inversion of structural data
Authors: Quesada-Pérez M. , Moncho-Jordá A. , Martı́nez-López F. , Hidalgo-Álvarez R.
Published: July 2002

The knowledge of the potential between interacting colloidal particles is essential to describe and control the aggregation processes in which they are involved. However, interaction forces also bring out spatial ordering phenomena, which has been used to obtain helpful information on them in three-dimensional dispersions. In this paper we look into this possibility for colloidal monolayers spread at the water–air interface. The radial distribution function has been determined for an assembly of negatively charged polystyrene particles at low concentration and without an additional electrolyte. A simple inversion scheme based on the HNC closure has been proved to give reliable information on u(r), providing that particles are not strongly correlated. Apart from the expected repulsive forces, the application of the inversion procedure suggests the possibility of a long-ranged attractive interaction.
Direct observation of the triplet lifetime quenching of single dye molecules by molecular oxygen
Authors: Hübner Christian G. , Renn Alois , Renge Indrek , Wild Urs P.
Published: July 2002

The influence of oxygen on the photophysical properties of individual DiI18 molecules has been investigated by means of both wide field and confocal scanning optical fluorescence microscopy. Excited close to saturation intensity, single-molecule fluorescence detected in wide field by a charge-coupled device camera showed a dramatic increase at exposure to air compared to the fluorescence when the sample was protected from oxygen by nitrogen flush. The change of the triplet lifetime of individual dye molecules due to oxygen quenching was measured in real time by means of time resolved single photon counting. In the presence of oxygen, the triplet state lifetime decreases from several tens of milliseconds down to fractions of a millisecond, whereas no changes of the intersystem crossing quantum yield and the fluorescence lifetime are observed. The triplet lifetimes in the presence and absence of oxygen, respectively, are anti-correlated indicative of heterogeneity of the polymer surrounding the dye molecules.
Integrated THz technology for label-free genetic diagnostics
Authors: Nagel M. , Haring Bolivar P. , Brucherseifer M. , Kurz H. , Bosserhoff A. , Büttner R.
Published: July 2002

We report on a promising approach for the label-free analysis of DNA molecules using direct probing of the binding state of DNA with electromagnetic waves at THz frequencies. Passive THz resonator devices based on planar waveguides are used as sample carriers and transducers for THz transmission analysis. In comparison to a formerly used free-space detection scheme, this method provides a drastically enhanced sensitivity enabling analysis down to femtomol levels. We examine the potential of our approach on biologically relevant DNA samples and demonstrate the detection of single base mutations on DNA molecules.
Measurements of secondary electron emission and plasma density enhancement for plasma exposed surfaces using an optically isolated Faraday cup
Authors: Qin Shu , Bradley Michael P. , Kellerman Peter L. , Saadatmand Kourosh
Published: July 2002

We present secondary electron yield and plasma enhancement factor data for silicon surfaces exposed to Ar, He, N2, O2, H2, and BF3 plasmas, for incident ion energies from 0.5–10 keV. A fiber-optic isolated Faraday cup was used to directly measure the ion current Jion, allowing a direct measurement of the secondary electron yield. This method automatically accounted for the effect of pulse-induced plasma density enhancement due to the ionization of neutral gas by accelerated secondary electrons, which we observed and measured quantitatively. The values of the secondary electron yields measured by this method were higher than published values measured by the conventional (ultraclean surface and ultrahigh vacuum) methods but lower than published values measured by previous plasma immersion ion implantation methods.
Polarization-dependent spectroscopic study of M-plane GaN on γ-LiAlO2
Authors: Ghosh Sandip , Waltereit P. , Brandt O. , Grahn H. T. , Ploog K. H.
Published: July 2002

We investigate the polarization dependence of the absorption, reflectance, and photoreflectance spectra of a compressively strained, M-plane, wurtzite GaN(11̄00) film grown by molecular-beam epitaxy on a γ-LiAlO2(100) substrate. The measurements are done with the electric-field vector (E) of the probe light being parallel (∥) and perpendicular (⊥) to the c axis of GaN, which lies in the growth plane. We observe a significant increase in the effective optical band gap of the M-plane GaN film for E∥c compared to its value for E⊥c. This result is explained by including the effect of the M-plane biaxial compressive strain on the electronic band structure of GaN. We also determine the extraordinary refractive index of GaN at energies below its band gap from the reflectance measurements.
Theoretical study of the reactions of Ar++HX(v=0) and Ar+HX+(v) (X=H and D) at E=0.1 eV using the trajectory surface hopping method
Authors: Sizun Muriel , Song Ju-Beom , Gislason Eric A.
Published: July 2002

Trajectory surface hopping calculations have been carried out for collisions of Ar++H2 (v=0), Ar++HD (v=0), H2+(v)+Ar, and HD+(v)+Ar, where v=0, 1, and 2 on the Kuntz–Roach diatomics-in-molecules potential surfaces at a relative energy of 0.1 eV. The importance of the mutual “capture” of the two particles on the attractive ground potential energy surface is shown clearly. The fact that capture does not occur on every collision is attributed to an effect of the vibrational phase of the H2 or HD molecule. This vibrational phase effect can explain the drop in the experimental rate constant seen at very low temperatures in the Ar++H2 system. For H2+(v=2)+Ar and HD+(v=2)+Ar we also find that many trajectories hop to the first excited potential surface as the particles approach. Since these trajectories cannot reach small separations, this further reduces the reactive cross section for v=2 and higher levels. The ground potential energy surface has a fairly deep well, particularly when the Ar–H–H angle is near 90°. Hence, once capture occurs in the (Ar–H–D)+ system, the Ar–H and Ar–D distances rapidly interchange. The product ArD+ is always favored over ArH+ because the H atom can more easily escape the complex. Finally, the reactivity of Ar++H2 (v=0) is seen to be intermediate between that of H2+ (v=1) and H2+ (v=2) with Ar.
Improved light out-coupling in organic light emitting diodes employing ordered microlens arrays
Authors: Möller S. , Forrest S. R.
Published: July 2002

We demonstrate that ordered microlens arrays with 10 μm diam poly-dimethyl-siloxane lenses attached to glass substrates increase the light output of organic light emitting devices (OLED) by a factor of 1.5 over unlensed substrates. The lenses, which are considerably smaller than, and not aligned to the OLEDs, outcouple light that is emitted outside of the escape cone of the substrate. We show that an electrophosphorescent device based on a fac tris(2-phenylpyridine)Iridium (Ir(ppy)3) doped emitting layer has its external quantum efficiency increased from 9.5% using a flat glass substrate, to 14.5% at low current densities using a substrate with microlenses. No change in the emission spectrum is observed for different viewing angles using the lens arrays.
Formation of the cyclic ice hexamer via excitation of vibrational molecular modes by the scanning tunneling microscope
Authors: Morgenstern Karina , Rieder Karl-Heinz
Published: July 2002

Starting from water monomers adsorbed on Cu(111), we have induced the formation of small ice clusters via the tip of a low temperature scanning tunnelling microscope. We show that diffusion, formation, and structural changes of clusters are induced by electrons coupling to vibrational modes of the molecule. The manipulation transfers enough energy into the system to induce stable clusters both two-dimensional and three-dimensional ones, including the important cyclic hexamer. Only the three-dimensional clusters develop a localized gap around the Fermi energy of ≈76 meV, which varies for different positions on a cluster.
Enhancement of laser-induced optical breakdown using metal/dendrimer nanocomposites
Authors: Ye Jing Yong , Balogh Lajos , Norris Theodore B.
Published: July 2002

We demonstrate that dendrimer nanocomposites (DNC) can be used to remarkably change the laser-induced optical breakdown (LIOB) threshold of a material, owing to a large enhancement of the local electric field. We have implemented LIOB using femtosecond laser pulses in a gold/dendrimer hybrid nanocomposite as a model system. Third-harmonic generation measurements have been employed as a sensitive way for monitoring the LIOB in situ and in real time. The observed statistical behavior of the breakdown process is attributed to a laser-driven aggregation of individual DNC particles. The breakdown threshold value of the DNC has been found to be up to two orders of magnitude lower than that of pure dendrimers or normal tissues.
Role of the Barker–Henderson diameter in thermodynamics
Authors: Tang Yiping
Published: July 2002

Sensitivity of thermodynamics to the Barker–Henderson (BH) diameter for the Lennard-Jones (LJ) potential is discussed, which covers both its approximation in calculation and improvement in rationality. With regarding to the approximation, pressure and internal energy for the LJ fluid, LJ chains and LJ chain mixtures are investigated. It is found that internal energy is much more sensitive to an approximation to the diameter than pressure for pure fluids, and both pressure and internal energy are very sensitive to the diameter for mixtures. It is also found that the approximating expression given by Cotterman et al. (1986) covers the widest range of temperatures. The rationality of the BH diameter itself at very high temperatures and densities is also analyzed. Through a functional expansion of Helmholtz free energy, we conclude that a density-dependent BH diameter is fundamentally more appropriate. The proposed diameter yields almost the same results as the original BH diameter at normal conditions and remedies its deficiencies at extreme ones. The density-dependent diameter provides a convenient way to study the LJ systems undergoing gas-solid phase transition or freezing.
Vapor etching of ion tracks in fused silica
Authors: Musket R. G. , Yoshiyama J. M. , Contolini R. J. , Porter J. D.
Published: July 2002

We have used vapor etching of ion tracks to create high aspect ratio (i.e., length much greater than diameter), isolated cylindrical holes through ∼600-nm-thick films of thermally fused silica on silicon. Samples were exposed to the vapor from water-based liquids with various HF and HF+HCl concentrations. Independent control of the temperatures of the vapor and the samples provided the means to vary separately the etching rates for the tracks and the track-free material. The very rapid etching of the small latent track zone can be explained by preferential capillary condensation. Holes with diameters of ∼24 to ∼80 nm have been documented with length/diameter ratios of up to 22. Although we have restricted this study to thin-film silica, we have evidence that such holes are also formed in bulk fused silica.
Latent track formation in GaAs irradiated with 20, 30, and 40 MeV fullerenes
Authors: Colder A. , Canut B. , Levalois M. , Marie P. , Portier X. , Ramos S. M. M.
Published: July 2002

Microstructural observations of gallium arsenide single crystals irradiated with a few tens of MeV C60 incident clusters (fullerenes) were performed. Normal and grazing incidences were investigated. Similar to in the case of silicon and germanium, cylindrical amorphous tracks whose diameters vary as a function of the projectile energy were found. However, for a given energy of the clusters, the track diameters are slightly different from one material to another. Also depending on the fullerene, energy is the length of the amorphous cylinder that formed along the projectile’s path. The recrystallization process under an electron beam during transmission electron microscopy observation was analyzed and a higher growth rate for gallium arsenide compared to that of germanium was seen.
β-cubic phase transition of scandia-doped zirconia solid solution: Calorimetry, x-ray diffraction, and Raman scattering
Authors: Fujimori Hirotaka , Yashima Masatomo , Kakihana Masato , Yoshimura Masahiro
Published: July 2002

Differential scanning calorimetry and Raman spectroscopy measurements have been performed to investigate the β-cubic (c) phase transition of the compositionally homogeneous ZrO2-22 mol % ScO1.5 solid solution. The enthalpy of transition (1.11 kJ/mol of cation) and thermal hysteresis between β- and c-phases were smaller than those between monoclinic (m) and tetragonal (t) phases of ZrO2, reflecting the structural information that the cell volume ratio of β- to c-phases is smaller than that of m- to t-phases. Raman spectroscopy allowed us to observe the β-c phase transition, and we could obtain Raman spectra of the c-phase in the ZrO2–ScO1.5 system. This result was strongly supported by the observation of x-ray diffraction patterns at high temperatures.
Raman study on the Ni/SiC interface reaction
Authors: Kurimoto E. , Harima H. , Toda T. , Sawada M. , Iwami M. , Nakashima S.
Published: July 2002

Ni/SiC interface reaction was investigated by Raman scattering. The specimen consisted of a 200 nm Ni layer deposited on a both-side polished 6H–SiC wafer with postannealing at 500–1100 °C. Raman spectra were observed from both faces of the specimen, i.e., from the Ni layer side and from the opposite (SiC wafer) side. The spectra showed that nickel silicides were formed by annealing at above 500 °C, and diffusion of Si atoms into the Ni layer played a key role in forming an ohmic contact at above ∼900 °C. It was also found that carbon atoms that did not react with Ni formed nanometer-size clusters. This work clearly demonstrates that Raman scattering is useful for studying interface reactions between metallic electrodes and SiC.
Boundary conditions in an electric current contact
Authors: Titov O. Yu. , Giraldo J. , Gurevich Yu. G.
Published: July 2002

In most electronic devices, the electric current of both types (electrons and holes) flows through a junction. Usually the boundary conditions have been formulated exclusively for open circuit. The boundary conditions proposed here bypass this limitation. Besides, these boundary conditions correctly describe the current flow in a circuit, i.e., closed circuit conditions, which are the usual operation conditions for electronic devices and for the measurement of many transport properties. We also have generalized the case (as much as it is possible in a classical treatment), so self-consistent boundary conditions that describe the current flow through a contact between two arbitrary conducting media are developed in the present work. These boundary conditions take into account a recently developed theory: influence of temperature space inhomogeneity due to the interfaces and quasiparticles temperature mismatch on thermogeneration and recombination. They also take into account surface resistance, surface recombination rates, and possible temperature discontinuities at the interface due to finite surface thermoconductivity. The temperature difference between current carriers and phonon subsystems is also included in this approach.
Ab initio potentials for the S(3Pj)–rare gas dimers: Implementation for elastic and inelastic collisions and comparison with scattering potentials
Authors: Kłos J. , Chałasiński G. , Krems Roman V. , Buchachenko A. A. , Aquilanti Vincenzo , Pirani Fernando , Cappelletti David
Published: July 2002

The interaction potentials between the ground state S(3P) atom and rare gas atoms Rg (He, Ne, Ar, Kr, and Xe) in Π3 and Σ−3 states are calculated ab initio using an unrestricted CCSD(T) level of theory and extended correlation consistent basis sets augmented by bond functions. For NeS, the effects of extending the basis set, of a more accurate treatment of triple excitations within the coupled cluster method, and of the frozen core approximation are analyzed. The spin–orbit interaction is taken into account by the commonly used atomic model, whose validity is verified by the direct ab initio calculations of spin–orbit coupling matrix elements. The ab initio potentials are tested in the calculations of the absolute total scattering cross sections measured in molecular beams and compared with the potentials derived from the same data. This comparison, along with an analysis in terms of correlation formulas, proves the high accuracy of ab initio potentials and characterizes the sensitivity of scattering cross sections to the properties of interaction potentials. Both ab initio and scattering derived potentials are implemented in the study of inelastic fine structure transitions in S+Rg collisions. The relaxation rate constants are calculated and compared with those for O+Rg collisions.
In situ ordering of FePt thin films with face-centered-tetragonal (001) texture on Cr100−xRux underlayer at low substrate temperature
Authors: Xu Yingfan , Chen J. S. , Wang J. P.
Published: July 2002

In situ ordered FePt thin films with face-centered-tetragonal (fct)-(001) texture have been prepared by magnetron sputtering the FePt layer onto the Cr100−xRux underlayer at relatively low temperature. The dependence of FePt texture on the Ru content in the Cr underlayer and the substrate temperature is investigated. Addition of Ru in Cr underlayer results in the formation of the FePt ordered phase in a lower substrate temperature (350 °C) with c-axis orientation perpendicular to the film plane. Good perpendicular magnetic properties are obtained in films with Cr91Ru9 underlayer. A thin Pt intermediate layer is introduced between the FePt layer and the CrRu underlayer, which is found to effectively resist the Cr diffusion from the CrRu underlayer into the FePt layer and results in better FePt fct-(001) texture and improved magnetic properties.
Ferromagnetic properties of Zn1−xMnxO epitaxial thin films
Authors: Jung S. W. , An S.-J. , Yi Gyu-Chul , Jung C. U. , Lee Sung-Ik , Cho Sunglae
Published: July 2002

We report on ferromagnetic characteristics of Zn1−xMnxO (x=0.1 and 0.3) thin films grown on Al2O3(00⋅1) substrates using laser molecular-beam epitaxy. By increasing the Mn content, the films exhibited increases in both the c-axis lattice constant and fundamental band gap energy. The Curie temperature obtained from temperature-dependent magnetization curves was 45 K for the film with x=0.3, depending on the Mn composition in the films. The remanent magnetization and coercive field of Zn0.9Mn0.1O at 5 K were 0.9 emu/g and 300 Oe, respectively. For Zn0.7Mn0.3O, the remanent magnetization at 5 K increased to 3.4 emu/g.
Constructive role of noise: Fast fluctuation asymptotics of transport in stochastic ratchets
Authors: Doering Charles R. , Dontcheva Lubomira A. , Klosek Malgorzata M.
Published: July 2002

The constructive role of random fluctuations is studied in the context of transport in stochastic ratchets. We discuss the interplay of independent white (thermal) and discrete (external) noises and their generation of transport in anisotropic potentials. The constructive cooperation of such fluctuations is most apparent in the asymptotic limit of fast discrete-valued noise, a limit which presents some interesting mathematical features. We describe the asymptotic analysis of the current in the limit of fast external noise, pointing out the strong qualitative dependence of the current on the interplay of the independent noise sources and its surprising sensitivity to the regularity of the underlying anisotropic ratchet potential.
Electron heating in silicon dioxide and off-stoichiometric silicon dioxide films
Authors: DiMaria D. J. , Theis T. N. , Kirtley J. R. , Pesavento F. L. , Dong D. W. , Brorson S. D.
Published: July 2002

Electron heating in silicon dioxide (SiO2) at electric fields ≲5 MV/cm is demonstrated using three different experimental techniques: carrier separation, electroluminescence, and vacuum emission. Gradual heating of the electronic carrier distribution is demonstrated for fields from 5 to 12 MV/cm with the average excess energy of the distribution reaching ≳4 eV with respect to the bottom of the SiO2 conduction band edge. Off-stoichiometric SiO2 (OS-SiO2) layers are shown to behave similarly to very thin SiO2(≲70 Å in thickness) with a transition occurring from ‘‘cool’’ to ‘‘hot’’ electrons as the conduction mechanism changes from direct tunneling between silicon (Si) islands in the SiO2 matrix of the OS-SiO2 material to Fowler-Nordheim emission into the conduction band of the SiO2 regions. The relationship of electron heating to electron trapping, positive charge generation, interface state creation, and dielectric breakdown is treated. The importance of various scattering mechanisms for stabilizing the electronic field-induced heating in the SiO2 and preventing current runaway and impact ionization is discussed. Scattering may be due to disorder, trapped charges, and acoustical phonons, as well as longitudinal optical phonons.
Near-field optical-scanning microscopy
Authors: Dürig U. , Pohl D. W. , Rohner F.
Published: July 2002

Near-field optical-scanning (NFOS) microscopy or ‘‘optical stethoscopy’’ provides images with resolution in the 20-nm range, i.e., a very small fraction of an optical wavelength. Scan images of metal films with fine structures presented in this paper convincingly demonstrate this resolution capability. Design of an NFOS microscope with tunnel distance regulation, its theoretical background, application potential, and limitations are discussed.
Profiling of defects using deep level transient spectroscopy
Authors: Stievenard D. , Vuillaume D.
Published: July 2002

Deep level transient spectroscopy of p–n junctions, Schottky barriers, or metal-oxide-semiconductor (MOS) capacitors is widely used to obtain the concentrations of defects and their profiles in semiconductors. The use of this technique for profiling presents several difficulties, some of which have not been taken into account in the works previously published. The aim of this paper is to describe the exact analysis which should be performed to obtain correct profiles. The analysis is tested on a constant defect profile, induced by electron irradiation in n-GaAs, in order to illustrate the effect of each correction. It is then applied to defect profiling of a silicon MOS capacitor and on the EL2 defect in annealed GaAs.
Magnetic and other properties and sputtering behavior of Co-base amorphous alloy films
Authors: Hayashi K. , Hayakawa M. , Ochiai Y. , Matsuda H. , Ishikawa W. , Iwasaki Y. , Aso K.
Published: July 2002

Magnetic and other properties of Co-base amorphous alloy films prepared by sputtering are investigated. A detailed magnetic phase diagram with saturation magnetic flux density, crystallization temperature, and zero-magnetostrictive line on Co-Ta-Zr amorphous alloys were obtained, and the technical knowhow to make a film with well-reproducible characteristics by widely changing the sputtering conditions was related with these physical properties. Especially on alloy sputtering, a phenomenological model for elucidating a composition difference between film and target is presented. After these studies, the film characteristics of Bs=12 kG, Tx=450 °C, ‖λs‖<10−8, Hc<10 mOe, and permeabilities of μ(1 MHz)=7000, μ(100 MHz)=2000 for the single film of 2 μm in thickness and of μ(1 MHz)=4000, μ(100 MHz)=800 for the insulator-sandwiched multilayered film of 10 μm are obtained, and these well-balanced values enable us to apply the materials for high-frequency recording head.
Standing wave enhanced scattering in multilayer structures
Authors: Kortright J. B. , Fischer-Colbrie A.
Published: July 2002

X-ray standing waves inside a tungsten-carbon periodic multilayer structure are shown to act as localized probes in the coherent scattering from amorphous interatomic correlations making up the layers of the structure. The distorted wave approximation describes the standing wave formation, and kinematical theory describes the scattering of this standing wave by the amorphous atomic correlations. Possible use of this technique for the study of atomic arrangements and interfaces in multilayer structures is discussed.
Ion formation in alloy liquid-metal-ion sources
Authors: Ishitani T. , Umemura K. , Kawanami Y.
Published: July 2002

Mass and energy analyses are carried out for ions emitted from liquid-metal-ion sources (LMISs) using Cu-P base, Pt-P, and Ni-B-Si alloys. A strong matrix effect of about 10−1 and 1 is observed on the intensity ratio of P++/P+ for Cu-P and Pt-P alloys, respectively. The electric field at the ion emitting surface is estimated to be 27–30 V/nm from the post-ionization model. A difference of only 10% in the field strength between these alloys is responsible for this matrix effect. The Ni-B-Si alloy LMIS, on the other hand, does not present an identical field strength for each component. The relationships of [ΔE(M++)/2≤ΔE(M+) <ΔE(M++)] for the energy width and [Ep(M+)≥Ep(M++)/2] for their most probable energy are observed in the energy analysis of mass-analyzed ions. Most M++ ions are formed in the post-ionization process on field-evaporated M+ ions.
On making cuts for magnetic scalar potentials in multiply connected regions
Authors: Kotiuga P. R.
Published: July 2002

The problem of making cuts is of importance to scalar potential formulations of three-dimensional eddy current problems. Its heuristic solution has been known for a century [J. C. Maxwell, A Treatise on Electricity and Magnetism, 3rd ed. (Clarendon, Oxford, 1981), Chap. 1, Article 20] and in the last decade, with the use of finite element methods, a restricted combinatorial variant has been proposed and solved [M. L. Brown, Int. J. Numer. Methods Eng. 20, 665 (1984)]. This problem, in its full generality, has never received a rigorous mathematical formulation. This paper presents such a formulation and outlines a rigorous proof of existence. The technique used in the proof expose the incredible intricacy of the general problem and the restrictive assumptions of Brown [Int. J. Numer. Methods Eng. 20, 665 (1984)]. Finally, the results make rigorous Kotiuga’s (Ph. D. Thesis, McGill University, Montreal, 1984) heuristic interpretation of cuts and duality theorems via intersection matrices.
Spin-glass dynamics from magnetic noise, relaxation, and susceptibility measurements (invited)
Authors: Alba M. , Hammann J. , Ocio M. , Refregier Ph. , Bouchiat H.
Published: July 2002

We present a quantitative comparison between dynamic measurements on spin glasses. The case of CdIn0.3Cr1.7S4 is discussed in detail and references are made to CsNiFeF6 and Ag:Mn (2.6%). The measured quantities are the relaxation of the thermoremanent magnetization MTRM(t) in the range of observation times 1–105 s, the out-of-phase susceptibility χ″(ω) in the range 10−3–5×104 Hz, and the magnetic noise power spectrum M2(ω) between 10−2 and 103 Hz. The aging of the thermoremanent magnetization relaxation is analyzed on the basis of a phenomenological theory of time scaling which allows to derive the form of the equilibrium relaxation. It is shown that the measured values of χ″ and ∼(M2(ω)) are related according to the fluctuation dissipation theorem (FDT). The consequences of the applicability of the FDT in the frequency domain are discussed, with reference to the expected violation of the theorem in the spin-glass phase at ω=0. An important modification of the frequency dependence of χ″(ω) is observed at Tg, supporting a previous dynamic scaling approach. There is good agreement between the low-temperature stationary behaviors of MTRM(t) and χ″(ω), but they show an unexplained discrepancy close to Tg.
New varistor material
Authors: Modine F. A. , Hyatt H. M.
Published: July 2002

A composite varistor material containing silicon carbide, a conductor, and an insulator has been developed. The material has rubberlike flexibility and is easily formed. A higher leakage resistivity (∼1012 Ω cm) and greater nonlinearity (∼10) than for silicon carbide varistors permit the material to be used as a gapless surge suppressor. The breakdown voltage (1–10 kV/cm) and other properties of the material vary with composition. High current capability (>200 A/cm2) and good energy absorption (>40 J/cm3) are obtained. Also, the material exhibits a low-temperature coefficient (∼4×10−3/K) and a low dielectric constant (∼10) with no observed loss peak.
Solution procedure for the Laplace equation in bispherical coordinates for two spheres in a uniform external field: Parallel orientation
Authors: Stoy Richard D.
Published: July 2002

A solution procedure is developed for the Laplace equation in bispherical coordinates for two spheres which are embedded in an infinite medium and which are aligned parallel to an external field which is uniform at infinity. The boundary conditions, continuity of the potential and continuity of the normal component of the flux density at the surfaces of the two spheres, are often encountered in several branches of the macroscopic field theory of linear media: electrostatics, magnetostatics, and steady-state diffusion, electric current, and flow of heat.
Anharmonicity and the equation of state for gold
Authors: Anderson Orson L. , Isaak Donald G. , Yamamoto Shigeru
Published: July 2002

The temperature dependence of the thermodynamic and the elastic properties of elemental gold are found from published data. It is shown that measurements for (∂KT/∂P)T near 5.5 are more thermodynamically consistent than are higher values of this parameter which have been reported earlier. Using 5.5 for (∂KT/∂P)T, we find that (∂KT/∂T)V is not zero but −11.5×10−3 GPa K−1 for high temperatures (T>θD, where θD is the Debye temperature). One consequence of this is that above θD the thermal pressure, PTH, along the room-pressure isobar can be expressed as PTH(T)−PTH(300)=[7.14×10−3 +(∂K T/∂T)v ln(Va/V)] ×(T−300) GPa for T at absolute temperature and Va being the volume at ambient conditions. These results give thermal pressure values near those previously reported at small compressions, but give lower thermal pressures at large compressions. This study suggests that in order to ensure thermodynamic consistency, the value of d ln γ/d ln V is near 2.5–3.0 which is higher than values of 1.0 and 1.7 reported previously (γ is the Grüneisen ratio). Calculations giving the compressional and shear wave velocities, vp and vs, are also presented. One result is that the quantity ∂ ln vs/∂ ln vp at constant pressure is about 1.85 and is independent of temperature.
Raman scattering investigation of a single-crystal-like YBa2Cu3O7−y film
Authors: Farrow L. A. , Venkatesan T. , Bonner W. A. , Wu X. D. , Inam A. , Hegde M. S.
Published: July 2002

Room-temperature Raman spectra from a single-crystal-like film of YBa2Cu3O7−y fabricated by pulsed laser deposition are compared with similar spectra of a single crystal of YBa2Cu3O7−y. The comparison shows that not only is the axis perpendicular to the plane of the film, but that in addition the a-b axes are well oriented in the film plane. The data also show that the film is spatially uniform with respect to this orientation.
An exact solution for the effective thermal conductivity of cracked bodies with oriented elliptical cracks
Authors: Benveniste Y. , Miloh T.
Published: July 2002

A microgeometry is constructed for a cracked body with oriented elliptical cracks and an exact analytic solution is derived for its effective thermal conductivity. It is proved that the prediction of the ‘‘generalized self-consistent scheme’’ for the case of a cracked body with oriented elliptical cracks coincides with the obtained exact solution for the constructed microgeometry. Results are given for elliptical cracks of different aspect ratios.
Theory for a quantum modulated transistor
Authors: Sols Fernando , Macucci M. , Ravaioli U. , Hess Karl
Published: July 2002

We present a theoretical study of semiconductor T-structures which may exhibit transistor action based on quantum interference. The electron transmission through a semiconductor quantum wire can be controlled by an external gate voltage that modifies the penetration of the electron wavefunction in a lateral stub, affecting in this way its interference pattern. The structures are modeled as ideal two-dimensional electron waveguides and a tight-binding Green’s function technique is used to compute the electron transmission and reflection coefficients. The calculations show that relatively small changes in the stub length can induce strong variations in the electron transmission across the structure. Operation in the fundamental transverse mode appears to be important for applications. We also show that a bound state of purely geometrical origin nucleates at the intersection between waveguide and stub. The performance of the device can be improved by inserting additional stubs of slightly different lengths. Taking into account the applicable scaling rules, we give estimates of the experimental parameters that optimize the transmission characteristics and speed of operation of the proposed transistor.
The equation of state of platinum to 660 GPa (6.6 Mbar)
Authors: Holmes N. C. , Moriarty J. A. , Gathers G. R. , Nellis W. J.
Published: July 2002

Platinum metal was shock compressed to 660 GPa using a two-stage light-gas gun to qualify this material as an ultrahigh-pressure standard for both dynamic and static experiments. The shock velocity data are consistent with most of the previously measured low-pressure data, and an overall linear us−up relationship is found over the range 32–660 GPa. As a part of this work, we have also extended the Hugoniot of the tantalum standard we use to 560 GPa; we have included these data into a new linear fit of the tantalum Hugoniot between 55–560 GPa. We also present the results of a first-principles theoretical treatment of compressed platinum. The fcc phase is predicted to remain stable to beyond 550 GPa. In addition, we have calculated the 300-K pressure-volume isotherm and the Hugoniot. The latter is in excellent agreement with experimental results and qualifies the former to at least 10% accuracy.
Improved boundary conditions for the time-dependent Schrödinger equation
Authors: Mains R. K. , Haddad G. I.
Published: July 2002

An improved boundary condition treatment for the time-dependent Schrödinger equation applied to resonant-tunneling diode simulation has been developed. This treatment is half-implicit, or centered in time, and allows larger time steps than the previous explicit treatment. The method does not complicate the time-dependent calculation since the resulting matrix is still tridiagonal.
Solving electromagnetic scattering problems at resonance frequencies
Authors: Murphy W. D. , Rokhlin V. , Vassiliou M. S.
Published: July 2002

The ‘‘resonance problem’’ is that at certain values of the wave number k (the resonant k’s), the second-kind integral equation for solving scattering problems can become extremely ill-conditioned. This adversely affects both the accuracy and speed of numerical solutions. We consider transverse-magnetic scattering from a conductor (Dirichlet problem). The integral equation (derived using double-layer potentials) is discretized using approximately fourth-order convergent quadrature formulas. At resonant k’s for circular and elliptical scatterers, we find very large condition numbers for the discrete matrices [up to O(107) ], generally leading to poor solutions. We apply two approaches to alleviate the resonance problem. The first is to use a different integral equation, based on both single- and double-layer potentials. This leads to low condition numbers and good solutions at resonant k. The second method is to use the original second-kind integral equation, introduce a small imaginary part in k, and extrapolate back to the real axis. Solutions obtained by the two methods are in excellent agreement. The extrapolation technique will be particularly useful in the case of the exterior Neumann problem, when the application of the first technique will be numerically more difficult. By solving the resonance problem, we ensure that fast and accurate solutions are obtainable at any arbitrary wave number.
Probe measurements of the space potential in a radio frequency discharge
Authors: Godyak V. A. , Piejak R. B.
Published: July 2002

The dc and radio frequency (rf) components (and harmonics) of the probe potential have been measured in the midplane of a 13.56-MHz parallel-plane rf discharge in argon over a wide range of discharge voltages and at gas pressures between 10 mTorr and 1.0 Torr. rf potential measurements were made with different input capacitances to determine the true magnitude of the rf plasma potential and the probe capacitance. For a symmetrically driven rf discharge, the rf plasma potential Vrf is mainly composed of the second harmonic of the driving voltage Vdr over a wide range of gas pressures. For high values of Vdr, Vrf ≊0.1 Vdr while the dc probe potential Vdc is about 0.4 Vdr. These results are in good agreement with corresponding theoretical predictions found in the literature. For an asymmetrically driven rf discharge with equal electrode area, the rf plasma potential has an additional fundamental harmonic component equal to half the rf driving voltage. Values of rf plasma potential and probe capacitance given here allow us to specify the requirements on probe circuitry for different kinds of probe measurements in rf discharges.
Correlation between x-ray diffraction studies and conductivity dependence of Ag loading in thick-film thermistors
Authors: Vittal Nitya , Srinivasan G. , Aiyer C. R. , Karekar R. N.
Published: July 2002

Manganite (Mn1.5Co1Ni0.5O4 ) based thermistors in bulk form are well known. We have earlier reported that the electronic properties [sheet resistivity Rs and temperature coefficient of resistance (TCR)] of Ag-loaded, manganite-based thick-film thermistor pastes show a sudden reduction in sheet resistivity (from MΩ/sq to Ω/sq) and a reversal of TCR [from negative temperature coefficient (NTC) to positive temperature coefficient (PTC)], above a critical percentage of Ag loading (50% by weight) and that this behavior follows a modified percolation theory. Here the above pastes are characterized by x-ray diffraction analysis. Our x-ray diffraction results do indicate the formation of a Ag complex upon Ag loading (30%–60% by weight) as postulated in the earlier paper. However, the system seems to be still more complex, as the channel formation required for percolation theory may not be of a single material but of two materials, i.e., Ag and an Ag complex.
The synthesis of high-quality diamond in combustion flames
Authors: Hirose Yoichi , Amanuma Shuji , Komaki Kunio
Published: July 2002

High-quality diamond with good crystallinity has been successfully synthesized on a substrate using an oxy-acetylene combustion flame in the atmosphere. The crystal grains under some conditions have good optical transparency. The deposition rate of transparent diamond depended strongly on substrate temperatures and the O2/C2H2 ratio and averaged ∼30 μm/h. The substrate temperature for the growth of optically transparent crystals was 500–750 °C, which is relatively low compared with other chemical vapor deposition methods. The optical transparency is attributed to the low defect densities in the crystals, as determined by transmission electron microscope, which results from the low substrate temperatures and moderate growth rates. Raman spectroscopy and x-ray diffraction data on the synthesized crystals were comparable with that of natural diamond. The synthesis conditions and corresponding diamond quality as well as emission spectrum analysis of the combustion flame during diamond synthesis are described.
Electron-beam probe measurements of electric fields in rf discharges
Authors: Sato A. H. , Lieberman M. A.
Published: July 2002

An electron-beam probe has been used to make time- and space-resolved measurements of the electric field in a parallel plate rf discharge. Measurements were taken at a time resolution of 5 ns and a field resolution ±1 V/cm at increments of 0.32 cm from the powered electrode. The detection method provides the weighted average of the electric field along the beam trajectory. Measurements of fields less than 20 V/cm were made throughout the entire discharge. Data were obtained for 13.6-MHz argon discharges at 2.3 and 20 mTorr, and at rf voltage amplitudes of 100 and 600 V at each pressure. The data for the 2.3-mTorr, 600-V case show (1) that a propagating double layer forms during the collapse of the sheath, (2) that the field near the electrode points in toward the plasma at the extreme collapse of the sheath, (3) that the collapse and expansion of the sheath proceeds asymmetrically for measurable field values, and (4) that the trajectory averaged electric field in the plasma has an anomalous phase shift and magnitude. Similar phenomena are observed for the remaining three discharge cases.