bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation of epitaxial yttria-stabilized zirconia on biaxially textured (001) Ni for deposited conductors
Authors: Park C. , Norton D. P. , Verebelyi D. T. , Christen D. K. , Budai J. D. , Lee D. F. , Goyal A.
Published: July 2002

The nucleation of (001)-oriented yttria-stabilized zirconia (YSZ) directly on the (001) Ni surface is realized via nucleation on an oxygen-terminated nickel surface using pulsed-laser deposition. Under conditions where the nickel surface is either oxygen free or substantially covered with NiO, a mixed orientation of YSZ occurs. The epitaxial YSZ layer grown on a biaxially textured Ni(001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding superconducting YBa2Cu3O7 films with high critical current densities, Jc. This architecture eliminates the necessity for a multilayer buffer architecture, since high Jc superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal.
MeV ion-induced suppression of resonance current in InP-based resonant tunneling diodes
Authors: Weaver B. D. , Jackson E. M. , Seabaugh A. C. , van der Wagt P.
Published: July 2002

We present the results of an experiment on 12.5 MeV Si4+ ion-irradiated InP-based resonant tunneling diodes. Radiation damage suppresses the entire resonance in direct proportion to the ion fluence. The suppression is not caused by a change in the tunneling barrier heights or widths, as previously thought; nor is it caused by radiation-induced increases in the leakage current. In fact, none of the internal parameters such as the Fermi energy and the resonant energy of the quantum well are expected to be greatly altered by the irradiation. We propose that radiation-induced disorder decreases the resonance current by scattering carriers out of the reduced-dimensional region of k space in which tunneling is allowed.
Evidence for a self-organized growth in granular Co/Al2O3 multilayers
Authors: Babonneau D. , Petroff F. , Maurice J.-L. , Fettar F. , Vaurès A. , Naudon A.
Published: July 2002

By sequential deposition of thin layers of cobalt and alumina by sputtering, we have fabricated granular multilayers consisting of successive planes of nanosized cobalt clusters separated by alumina along the growth direction. Combining grazing-incidence small-angle x-ray scattering and transmission electron microscopy experiments, we show that, in a given range of thickness, the vertical arrangement of clusters from plane to plane is not random but shows a topology-induced self-organization.
Effective mass enhancement of two-dimensional electrons in a one-dimensional superlattice potential
Authors: Majumdar Amlan , Rokhinson L. P. , Tsui D. C. , Pfeiffer L. N. , West K. W.
Published: July 2002

We report effective mass enhancement of two-dimensional (2D) electrons in an atomically precise one-dimensional AlGaAs/GaAs superlattice potential fabricated by the cleaved-edge overgrowth technique. Magnetotransport measurements reveal that the mobility of the 2D electrons increases with electron density n2D. At low densities (n2D∼1.3×1011 cm−2), the effective mass m* of the 2D electrons is 0.14 me, where me is the free-electron mass. This value of 0.14 me is twice the effective mass of electrons in GaAs (0.067 me). m* increases with n2D and is ∼0.16 me at 2.7×1011 cm−2. We explain these results based on the formation of energy minibands along the superlattice direction. The electron scattering time τ is calculated from the mobility and effective mass data. At 0.3 K, τ increases with n2D from 5 to 11 ps as n2D is varied from 1.1×1011 to 2.7×1011 cm−2.
Phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide
Authors: Fazio Valentina S. U. , Lagerwall Sven T. , Busson Philippe , Hult Anders , Motschmann Hubert
Published: July 2002

True phase-matched second-harmonic generation in a waveguide of crosslinkable ferroelectric liquid crystals is demonstrated. These materials allow the formation of macroscopically polar structures whose order can be frozen by photopolymerization. Homeotropic alignment was chosen which offers decisive advantages compared to other geometries. All parameters contributing to the conversion efficiency are maximized by deliberately controlling the supramolecular arrangement. The system has the potential to achieve practical level of performances as a frequency doubler for low power laser-diodes.
Friction contrast in resonant cantilever vibration mode
Authors: Spychalski-Merle A. , Krischker K. , Göddenhenrich T. , Heiden C.
Published: July 2002

The dynamic scanning friction microscopy technique is based on a well-known lateral sample modulation technique combined with a lock-in amplifier. In this paper, we describe a modified detection scheme in the resonant regime of a cantilever’s bending mode. This resonant mode leads to a couple of advantages in the imaging mode especially applicable under ultrahigh vacuum conditions, as well as an additional spectroscopy mode by measuring the resonance curve. An interpretation of the resonance curves and the images in terms of the friction losses is given, taking into account the cantilever vibration and the observed nonlinear characteristic of the stick–slip interaction.
Electrostatic surface waves in a dusty plasma
Authors: Lee Hee J.
Published: July 2002

Electromagnetic dispersion relation of a surface wave is obtained propagating on an interface between a vacuum and a dusty plasma, which consists of electrons and ions on their respective Boltzmann distributions and cold dust particles providing the inertia of the plasma and carrying a certain portion of the negative charge of the plasma. The electrostatic spectrum is interesting, since the branch of the high frequency electron wave is of an acoustic type whose frequency range is confined to 0.5⩽ω/ωpe<1 (ωpe is the electron plasma frequency). The low frequency ion surface wave resembles the volume dust acoustic wave and may be called a dust acoustic surface wave.
Epitaxial Bi3Fe5O12(001) films grown by pulsed laser deposition and reactive ion beam sputtering techniques
Authors: Adachi N. , Denysenkov V. P. , Khartsev S. I. , Grishin A. M. , Okuda T.
Published: July 2002

We report on processing and comparative characterization of epitaxial Bi3Fe5O12 (BIG) films grown onto Gd3(ScGa)5O12[GSGG,(001)] single crystal using pulsed laser deposition (PLD) and reactive ion beam sputtering (RIBS) techniques. A very high deposition rate of about 0.8 μm/h has been achieved in the PLD process. Comprehensive x-ray diffraction analyses reveal epitaxial quality both of the films: they are single phase, exclusively (001) oriented, the full width at half maximum of the rocking curve of (004) Bragg reflection is 0.06 deg for PLD and 0.05 deg for RIBS film, strongly in-plane textured with cube-on-cube film-to-substrate epitaxial relationship. Saturation magnetization 4πMs and Faraday rotation at 635 nm were found to be 1400 Gs and −7.8 deg/μm in PLD-BIG, and 1200 Gs and −6.9 deg/μm in RIBS-BIG. Ferromagnetic resonance (FMR) measurements performed at 9.25 GHz yielded the gyromagnetic ratio γ=1.797×107 l/s Oe, 1.826×107 l/s Oe; the constants of uniaxial magnetic anisotropy were Ku*=−8.66×104 erg/cm3, −8.60×104 erg/cm3; the cubic magnetic anisotropy K1=−2.7×103 erg/cm3,−3.8×103 erg/cm3; and the FMR linewidth ΔH=25 and 34 Oe for PLD and RIBS films correspondingly. High Faraday rotation, low microwave loss, and low coercive field ⩽40 Oe of BIG/GSGG(001) films promise their use in integrated magneto-optic applications.
Magnetic circular dichroism anisotropy from coherent Raman detected electron paramagnetic resonance spectroscopy: Application to spin-1/2 transition metal ion centers in proteins
Authors: Bingham Stephen J. , Gutschank Jörg , Börger Birgit , Suter Dieter , Thomson Andrew J.
Published: July 2002

Measurement of magnetic circular dichroism (MCD) anisotropy has contributed greatly to the understanding of the electronic structure of transition metal ion centers in both biological and nonbiological materials. Compared to previous methods, optically detected electron paramagnetic resonance experiments can measure MCD anisotropy with dramatically improved orientational resolution. In this paper the relevant theory for systems with an isolated Kramers doublet ground level is derived and its application illustrated using a transition metal ion center in a protein: low spin ferric haem.
Observation of sp3 bonding in tetrahedral amorphous carbon using visible Raman spectroscopy
Authors: Chen Z. Y. , Zhao J. P. , Yano T. , Ooie T. , Yoneda M. , Sakakibara J.
Published: July 2002

Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm−1 was observed. It consisted of two features centered on ∼1270 and ∼1170 cm−1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond.
Control and elimination of biaxial strain in laser-ablated epitaxial BaxSr1−xTiO3 films
Authors: Carlson Chris M. , Parilla Philip A. , Rivkin Tanya V. , Perkins John D. , Ginley David S.
Published: July 2002

We report the in-plane (a) and out-of-plane (c) lattice parameters of epitaxial laser-ablated Ba0.4Sr0.6TiO3 films on MgO for a range of O2 deposition pressures (40–250 mTorr) near the observed transition from ac. From these lattice parameters, we calculate the residual strain and stress in terms of hydrostatic and biaxial components. Both components increase sharply with O2 pressure between 85 and 100 mTorr, consistent with ion peening effects. Postdeposition annealing decreases the hydrostatic strain, but increases the biaxial tension. For both as-deposited and annealed films, we obtain samples with no biaxial strain (i.e., a=c), within experimental uncertainty. Overall, the strain is a combination of hydrostatic and biaxial components, both of which affect the dielectric response. Therefore, consideration and control of both types of strain is important for the optimum performance of devices such as tunable microwave devices and high-density memories.
Selective excitation of diatomic molecules by chirped laser pulses
Authors: Chang Bo Y. , Solá Ignacio R. , Malinovsky Vladimir S. , Santamarı́a Jesús
Published: July 2002

A new method for the selective excitation of diatomic molecules in single vibrational states on excited electronic potentials by two-photon absorption is proposed. The method implies the use of two chirped strong pulse lasers detuned from the optical transition to an intermediate electronic state. We show under what scenarios the method is successful on the time–energy scale in which the pulses operate. They involved a long-time (nanosecond) weak-field regime and a short-time (picosecond) strong-field regime. The adiabatic representation in terms of energy levels or in terms of light-induced potentials is used to interpret the physical mechanism of the excitation. The efficiency and robustness of the scheme are demonstrated by the excitation of the ground vibrational state of the Σg1(4s) electronic potential of the Na2 molecule.
Mapping the three-dimensional strain field around a microindentation on silicon using polishing and Raman spectroscopy
Authors: Puech Pascal , Pinel Stéphane , Jasinevicius Renato G. , Pizani Paolo Sergio
Published: July 2002

The strain field around a Vickers microindentation of crystalline silicon (001) has been mapped using Raman spectroscopy. The nature of the three-dimensional strain field of the microindentation was determined by comparing the parallel and crossed scattering geometries and applying the relations between the optical phonon frequency shift and strain. A surface layer (2 μm) was then removed by abrasive chemical polishing. The strain is preserved by the polishing process and information on microindentation depth is obtained. The produced maps give a good idea of the strain field after unloading. We find a quasicircular zone of plastic deformation where the strain follows a 1/r law.
Transparent p-type conducting CuScO2+x films
Authors: Duan N. , Sleight A. W. , Jayaraj M. K. , Tate J.
Published: July 2002

Transparent films of CuScO2+x have been prepared which show p-type electrical conductivity. The temperature dependence of the conductivity indicates semiconducting behavior with an apparent room temperature activation energy of 0.11 eV. The highest room temperature conductivity observed was 30 S cm−1. Films 110 nm thick show 40% transparency in most of the visible spectrum and become much more transparent in the infrared spectrum. The p-type behavior was confirmed by the Seebeck effect.
A new method for searching for free fractional charge particles in bulk matter
Authors: Loomba Dinesh , Halyo Valerie , Lee Eric R. , Lee Irwin T. , Kim Peter C. , Perl Martin L.
Published: July 2002

We present a new experimental method for searching for free fractional charge in bulk matter; this new method derives from the traditional Millikan liquid drop method but allows the use of much larger drops, 20–100 μm in diameter, compared to the traditional method that uses drops less than 15 μm in diameter. These larger drops provide the substantial advantage that it is then much easier to consistently generate drops containing liquid suspensions of powdered meteorites and other special minerals. These materials are of great importance in bulk searches for fractional charge particles that may have been produced in the early universe.
Thermally induced microbending losses in double-coated optical fibers during temperature cycling
Authors: Shiue Sham-Tsong , Hsu Chen-Sheng
Published: July 2002

The thermally induced microbending losses in double-coated optical fibers during temperature cycling are analyzed. The compressive radial stress at the interface between the glass fiber and primary coating would produce the microbending loss. A simplified closed-form formula to calculate the microbending loss is obtained by the viscoelastic theory. This formula can be extended to calculate microbending losses induced by temperature cycling with any number of stages, if the temperature is linearly raised, linearly dropped, or fixed in each stage of the cycle. Although the temperature change is zero at the end of the temperature cycling, the microbending loss will possibly exist. This microbending loss increases with the number of temperature cycles, and finally approaches a constant. To minimize the interfacial radial stress between the glass fiber and primary coating, the radius, Young’s modulus, thermal expansion coefficient, and Poisson’s ratio of polymeric coatings should be appropriately selected, and the relaxation time of the primary coating should be much shorter than the period of the temperature cycle. The condition for the glass transition temperature range of polymeric coatings within the temperature cycling is discussed. Additionally, microbending losses in single-coated optical fibers during temperature cycling are also considered.
Longitudinal and spanwise vortical structures in a turbulent near wake
Authors: Zhang H. J. , Zhou Y. , Antonia R. A.
Published: July 2002

Approximations to the three vorticity components have been simultaneously obtained using a combination of four X wires in the near wake of a circular cylinder with the view of investigating the most likely interrelationship between quasilongitudinal rib-like structures and spanwise vortical structures. The conditional spanwise vorticity variance, based on detections of spanwise structures, shows a strong peak near the detections. This peak suggests a longitudinal extent of 1.0–1.3 cylinder diameters for the spanwise structures. The conditional streamwise vorticity variance has maxima near the saddle points on both sides of the detections, while the conditional lateral vorticity variance is maximum only downstream of the detections. The observations are interpreted in the context of rib-like structures wrapping around consecutive spanwise structures of opposite sign, a scenario which conforms with previous observations based on flow visualizations and direct numerical simulations. The probability density function of vorticity vectors in the plane of mean shear further suggests that the most likely inclination of the rib-like structures to the streamwise direction is about 50°. About 40% of the variances of streamwise and lateral vorticity components is associated with the spanwise vortical structures, apparently resulting from the three dimensionality of these structures; the “remainder” is largely attributed to the rib-like structures. Spanwise structures account for about 60%–80% of the spanwise vorticity variance.
Diffusion and reaction in rectangular arrays of spheroids
Authors: Lu Shih-Yuan
Published: July 2002

The overall rate constant of surface reaction of diffusing species in rectangular arrays of spheroidal particles is investigated. The surface reaction occurring on the particle surface may be of finite rate. Calculation results for a wide range of array structures are obtained, by varying the particle and array aspect ratios. The normalized overall rate constant, k/k0, is found to be a function of the particle volume fraction (f ), a dimensionless parameter P characterizing the relative rate of diffusive transport vs surface reaction, and the array structure characterized by the particle (ra) and array (re) aspect ratios. When the process is diffusion-limited (P=0), results from the present development agree very well with those from first passage time simulations. When it is surface reaction limited (P→∞), k/k0 is shown to exactly equal 1/(1−f ), independent of the system structure. Generally, k/k0 decreases with increasing P, but increases with increasing f. At a fixed ra,k/k0 decreases with increasing deviation of re from unity, while, for a fixed re,k/k0 increases with increasing deviation of ra from unity. Under some particular circumstances, k/k0 may be less than unity, meaning that particle competition may play a negative role for k/k0. This occurs when the deviation of re from unity is greater than that of ra, i.e., the array is more slender or flat than the particle. An approximate relation for estimation of nondiffusion limited k/k0 based on the corresponding diffusion-limited datum is derived. This approximation works well for systems of small and large P and for array structures not deviating too much from the simple cubic array of spheres.
Semiconducting boron carbonitride nanostructures: Nanotubes and nanofibers
Authors: Yu J. , Ahn J. , Yoon S. F. , Zhang Q. , Rusli  , Gan B. , Chew K. , Yu M. B. , Bai X. D. , Wang E. G.
Published: July 2002

Highly oriented boron carbonitride (BCN) nanostructures consisting of nanotubes and nanofibers have been synthesized by bias-assisted hot-filament chemical vapor deposition from the source gases of B2H6, CH4, N2, and H2. It is found that the B concentration of the BCN nanostructures increases with increasing B2H6 in the gas mixture, and the highest B concentration is 45 at. %. Photoluminescence spectrum shows that the BCN nanostructures, identified as B0.34C0.42N0.24, are semiconductors with a band gap energy of around 1.0 eV.
Viscosity and shear response at the dynamic glass transition of glycerol
Authors: Schröter K. , Donth E.
Published: July 2002

Viscosity measurements in a broad temperature range display a variation over 11 orders of magnitude and show a crossover at about T+=285 K, comparable with dielectric results from a Stickel evaluation. The index R, i.e., the product of dielectric loss peak maximum frequencies times the viscosity, divided by temperature, decreases by a factor of 3.5 while viscosity varies by seven orders of magnitude. Dynamic shear measurements on glycerol are reported for the temperature of T=192.5 K. The shape of the shear dispersion in the α relaxation zone was fitted with Havriliak–Negami and stretched exponential functions. The shape parameters show considerable differences between different relaxation methods. No indications of a separate (β) secondary relaxation were found below the glass temperature Tg.
Reorientational angle distribution and diffusion coefficient for nodal and cylindrical surfaces
Authors: Plewczyński D. , Hołyst R.
Published: July 2002

We present a catalogue of diffusion coefficients and reorientational angle distribution (RAD) for various periodic surfaces, such as I-WP, F-RD, S, and S1 nodal surfaces; cylindrical structures like simple, undulated, and spiral cylinders, and a three-dimensional interconnected-rod structures. The results are obtained on the basis of a simulation algorithm for a diffusion on a surface given by the general equation φ(r)=0 [Hołyst et al., Phys Rev. E 60, 302 (1999)]. I-WP, S, and S1 surfaces have a spherelike RAD, while F-RD has a cubelike RAD. The average of the second Legendre polynomial with RAD function for all nodal surfaces, except the F-RD nodal surface, decays exponentially with time for short times. The decay time is related to the Euler characteristic and the area per unit cell of a surface. This analytical formula, first proposed by B. Halle, S. Ljunggren, and S. Lidin in J. Chem. Phys. 97, 1401 (1992), is checked here on nodal surfaces, and its range of validity is determined. RAD function approaches its stationary limit exponentially with time. We determine the time to reach stationary state for all surfaces. In the case of the value of the effective diffusion coefficient the mean curvature and a connectivity between parts of surfaces have the main influence on it. The surfaces with low mean curvature at every point of the surface are characterized by high-diffusion coefficient. However if a surface has globally low mean curvature with large regions of nonzero mean curvature (negative and positive) the effective diffusion coefficient is low, as for example, in the case of undulated cylinders. Increasing the connectivity, at fixed curvatures, increases the diffusion coefficient.
Transient resonance Raman spectroscopy and density functional theory investigation of iso-polyhalomethanes containing bromine and/or iodine atoms
Authors: Zheng Xuming , Fang Wei-Hai , Phillips David Lee
Published: July 2002

We report additional transient resonance Raman spectra and density functional theory computations for the products formed following ultraviolet photoexcitation of solution phase polyhalomethanes containing bromine and/or iodine atoms. We show that the iso-polyhalomethane photoproduct is responsible for the intense transient absorption band observed in the 350–470 nm region after ultraviolet excitation of polyhalomethanes in the solution phase. We examine the trends and correlation in the density functional theory optimized geometry and intense electronic absorption transition in the 350–470 nm region for the iso-polyhalomethanes containing bromine and/or iodine atoms. We explore the chemical reactivity of the iso-polyhalomethane species using density functional theory computations for the reaction of iso-CH2Br–Br with ethylene as an example. Our results and comparison with experimental data in the literature indicate that the iso-polyhalomethane species is most likely the methylene transfer agent in the cyclopropanation reactions of olefins using ultraviolet photoexcitation of polyhalomethanes in the solution phase. We briefly discuss the possibility that the photochemistry and chemistry of the iso-polyhalomethanes may give significant release of reactive halogens to the atmosphere.
Stacked orthogonal serpentine delay lines with vias for two-dimensional microchannel plate readout
Authors: Lampton M. , Marckwordt M.
Published: July 2002

We demonstrate a multilayer circuit board that has two orthogonal serpentine delay lines on different layers to read out event positions from a microchannel plate (MCP). The top serpentine is directly bombarded by the MCP. The orthogonal buried serpentine receives its charge through thousands of vias that connect to the top surface. Event X and Y positions are decoded with a timing circuit for each axis. The spatial resolution is much finer than the via spacing because every event’s charge footprint spans several vias, and because the timing circuit senses the centroid of the event’s position on each delay line. This construction method eliminates fabrication problems encountered in previous multilayer designs and eliminates the need for crossed conducting fingers with their concomitant degradation of the otherwise excellent phase delay characteristic of serpentine delay lines. Performance data are presented for an anode of this new type. Formulas and graphs are given to assist in creating a variety of anodes of this type.
Atoms in molecules, an axiomatic approach. I. Maximum transferability
Authors: Ayers Paul W.
Published: July 2002

Central to chemistry is the concept of transferability: the idea that atoms and functional groups retain certain characteristic properties in a wide variety of environments. Providing a completely satisfactory mathematical basis for the concept of atoms in molecules, however, has proved difficult. The present article pursues an axiomatic basis for the concept of an atom within a molecule, with particular emphasis devoted to the definition of transferability and the atomic description of Hirshfeld.
Effects of grain cluster size on coercivity and giant magnetoresistance of NiFe/Cu/CoFe/Cu/NiFe pseudo spin valves
Authors: Bae Seongtae , Li Jianguang , Judy Jack H. , Zurn Shayne
Published: July 2002

The effects of grain cluster size on the coercivity (Hc) and giant magnetoresistance in NiFe/Cu/CoFe/Cu/NiFe pseudo spin valves for magnetic random access memory devices has been investigated as a function of the Ar sputtering gas pressure which affects the interfacial roughness and magnetic coercivity differences. It is found that the grain cluster size induced by the differences in the kinetic energy of the sputtered adatoms at different gas pressure plays a crucial role in determining the Hc of NiFe/CoFe bilayers and magnetic interlayer coupling in Si/NiFe/Cu/CoFe/Cu/NiFe pseudo spin valves.
Ferroelectric properties of intergrowth Bi4Ti3O12–SrBi4Ti4O15 ceramics
Authors: Noguchi Yuji , Miyayama Masaru , Kudo Tetsuichi
Published: July 2002

Ferroelectric intergrowth Bi4Ti3O12–SrBi4Ti4O15 has been demonstrated to have a large remanent polarization (2Pr) of 30 μC/cm2 and a high Curie temperature of 610 °C using bulk ceramics. The Rietveld analysis of the powder x-ray diffraction patterns showed that there are two kinds of Bi ions in Bi2O2 layers. One Bi ion in the Bi2O2 layers was displaced to the other Bi ion along the polarization direction by about 2% of parameter a, which would contribute to the large 2Pr.
Calculation of the Ewald summed far-field mobility functions for arbitrarily sized spherical particles in Stokes flow
Authors: Hase Kevin R. , Powell Robert L.
Published: July 2002

The hydrodynamic interactions among an infinite suspension of arbitrarily sized spherical particles are calculated at low Reynolds number. Absolutely convergent expressions for the particle interactions are found that are cast into a form convenient for computational simulation of the motion of suspensions of spherical particles. The convergence of the periodically replicated form of these hydrodynamic expressions is accelerated by means of Ewald summation. The resulting far-field mobility functions that relate forces, torques, and stresslets to the particle velocities, angular velocities, and rate of strain are given for a suspension spherical particles of any size distribution. These mobility functions are used in simulations of particle suspensions that consider the dynamics of each particle. Specifically these mobility functions can be used in Stokesian dynamics simulations of polydisperse suspensions.
Cracking of GaN films
Authors: Etzkorn E. V. , Clarke D. R.
Published: July 2002

Cracking of thick GaN films grown on sapphire is reexamined on the basis of a combination of microstructural observations of cracking and established mechanics of fracture of films. It is argued that cracking is motivated by tensile growth stresses once a critical thickness is reached. Subsequent growth on the cracked films occurs, perpetuating the cracked structure until the crack surfaces approach one another and touch. Continued film growth buries the crack. Once the crack faces touch, there are conditions under which it is energetically favorable for the cracks to close and heal. Crack healing can be kinetically limited. Whether the crack healing is complete within the growth time depends on several factors including, it is suggested, whether impurities have adsorbed to the surface during growth. Conditions under which cracks that have extended into the sapphire substrate during film growth can act as critical flaws for fracture of the substrate on cooling are also presented.
In- and out-of-plane propagation of electromagnetic waves in low index contrast two dimensional photonic crystals
Authors: Foteinopoulou S. , Rosenberg A. , Sigalas M. M. , Soukoulis C. M.
Published: July 2002

Propagation of electromagnetic waves through a two-dimensional triangular lattice has been studied for different values of refractive index contrast between the constituent dielectrics, and for angles of incidence both in and out of the plane of periodicity. Transmission results have been obtained both experimentally and with the transfer matrix technique, and good agreement has been found between the two. Comparison with band structure calculations has also been made.
Semiclassical application of the Mo/ller operators in reactive scattering
Authors: Garashchuk Sophya , Light John C.
Published: July 2002

Mo/ller operators in the formulation of reaction probabilities in terms of wave packet correlation functions allow us to define the wave packets in the interaction region rather than in the asymptotic region of the potential surface. We combine Mo/ller operators with the semiclassical propagator of Herman and Kluk. This does not involve further approximations and can be used with any initial value representation (IVR) semiclassical propagator. Time propagation in asymptotic regions of the potential due to Mo/ller operators reduces the oscillations of the propagator integrand and improves convergence of the results with respect to the number of trajectories. The effectiveness of Mo/ller operators for semiclassical reaction probability calculation is demonstrated for the collinear hydrogen exchange reaction. Full convergence is achieved and the number of classical trajectories is reduced by a factor of 10 compared to the calculation without Mo/ller operators.
Orientation dependence of blistering in H-implanted Si
Authors: Zheng Y. , Lau S. S. , Höchbauer T. , Misra A. , Verda R. , He X.-M. , Nastasi M. , Mayer J. W.
Published: July 2002

The orientation effect on blistering phenomenon in H implanted Si was studied for (100), (111), and (110) Si wafers. It was found that substrate orientation has no observable effects on the underlying blistering mechanisms. Furthermore, the implantation damage, Si–H complex formation in as-implanted samples and surface roughness of the transferred layer appeared to be unaffected by the orientation. However, the blistering kinetics are orientation dependent, with (100) Si having the fastest blistering rate, and (110) Si the slowest. This dependence was attributed to the different density of ruptured Si–Si bonds of different orientations. The magnitude of the observed in-plane compressive stress in the H-implanted Si wafers is rationalized in terms of the formation of platelets in the samples.
Quaternary Znx′Cdy′Mg1−x′−y′Se/ZnxCdyMg1−x−ySe quantum wells grown on InP substrates for blue emission
Authors: Guo S. P. , Zeng L. , Tamargo M. C.
Published: July 2002

Quaternary Znx′Cdy′Mg1−x′−y′Se/ZnxCdyMg1−x−ySe quantum well (QW) structures in which both the well and the barrier layers are composed of quaternary alloys lattice matched to InP and having various well thicknesses have been grown and investigated. A blue emission with narrow linewidth was achieved by using a relatively thick well thickness (40–60 Å). The quaternary QW emission exhibits excitonic recombination behavior and it has higher quantum efficiency than the ternary ZnxCd1−xSe/ZnxCdyMg1−x−ySe QW of comparable thickness. The temperature dependence of the photoluminescence measurements shows a high activation energy of 68 meV, indicating a strong quantum confinement by introduction of Mg in the QW region.
Amplification of ultrasonic wave by plasma
Authors: Nagasawa Takeshi
Published: July 2002

Amplification of an ultrasonic wave by plasma particles is experimentally shown to occur in a weakly ionized (air) plasma under a suitable condition. Since neutral–neutral collisions are dominant, but ion–neutral collisions are not negligible in such a plasma, momentum transfer between plasma ions and neutrals, taking part in the ultrasonic wave, possibly occurs. As a result, interaction with plasma ions causes the amplification of the ultrasonic wave. Observations also indicate that the ultrasonic wave amplitude increases with increasing plasma density.
Calculation of the effects of pumping, divertor configuration and fueling on density limit in a tokamak model problem
Authors: Stacey W. M.
Published: July 2002

Several series of model problem calculations have been performed to investigate the predicted effect of pumping, divertor configuration and fueling on the maximum achievable density in diverted tokamaks. Density limitations due to thermal instabilities (confinement degradation and multifaceted axisymmetric radiation from the edge) and to divertor choking are considered. For gas fueling the maximum achievable density is relatively insensitive to pumping (on or off), to the divertor configuration (open or closed), or to the location of the gas injection, although the gas fueling rate required to achieve this maximum achievable density is quite sensitive to these choices. Thermal instabilities are predicted to limit the density at lower values than divertor choking. Higher-density limits are predicted for pellet injection than for gas fueling.
Observation of instabilities due to three-wave interaction during nonlinear pump wave modulation
Authors: Honzawa Tadao , Hoshina Takao , Takahashi Kunihito
Published: July 2002

Instabilities due to three wave interaction, being just like explosive instabilities, are experimentally shown to occur during the nonlinear modulation of a pump wave (negative energy wave) externally excited in an ion-beam-plasma system. In this experiment, the pump wave is observed to be self-modulated above a threshold because of nonlinear mode coupling among three different waves (ω0,k0), (ω1,k1), and (ω2,k2) and to split into a series of wave packets. Spectral analyses of such evolving waves and identification of all three waves, based on wave pattern observations, make it possible to clarify the feature of the mode coupling characterized by ω0=ω2−ω1 and k0=k2−k1. Furthermore, spectral observations indicate that all the wave powers rapidly increase simultaneously with the increase of the pump power above the threshold described above, although they do not grow infinitely in a finite time. All the above results suggest the realization of instabilities due to three wave interaction, being like explosive instabilities, in the beam-plasma system. Finally, the frequency shifts, the threshold for the instabilities, and the saturation of the instabilities are discussed.
Conceptual design of an active feedback system for the control of the resistive shell mode in tokamaks
Authors: Fitzpatrick Richard
Published: July 2002

A quadratic dispersion relation is derived which governs the feedback-modified stability of the resistive shell mode in a large-aspect ratio, low-β tokamak plasma. The effectiveness of a given feedback scheme is determined by a single parameter, α0, which measures the coupling of different poloidal harmonics due to the nonsinusoidal nature of the feedback currents. Feedback fails when this parameter becomes either too positive or too negative. Feedback schemes can be classified into three groups, depending on the relative values of the poloidal mode number, m0, of the intrinsically unstable resistive shell mode, and the number, M, of feedback coils in the poloidal direction. Group I corresponds to M⩽2m0 and M≠m0; group II corresponds to M=m0; finally, group III corresponds to M>2m0. The optimal group I feedback scheme is characterized by extremely narrow detector loops placed as close as possible to the plasma, i.e., well inside the resistive shell. Of course, such a scheme would be somewhat impractical. The optimal group II feedback scheme is characterized by large, nonoverlapping detector loops, and moderately large, nonoverlapping feedback coils. Such a scheme is 100% effective (i.e., it makes the resistive shell appear superconducting) when the detector loops are located just outside the shell. Unfortunately, the scheme only works efficiently for resistive shell modes possessing one particular poloidal mode number. The optimal group III feedback scheme is characterized by slightly overlapping detector loops, and strongly overlapping feedback coils. Such a scheme is 100% effective when the detector loops are located just outside the shell. In addition, the scheme works efficiently for resistive shell modes with a range of different poloidal mode numbers.
Electron-ion recombination rate constants in dense gaseous argon and krypton: Effects of electric field strength and the addition of N2 or CH4
Authors: Takeda Koki , Kato Ryoichi , Hayashida Masashi , Odaka Takahiro , Shinsaka Kyoji , Kameta Kosei , Odagiri Takeshi , Kouchi Noriyuki , Hatano Yoshihiko
Published: July 2002

The electron mobilities, μe, and electron-ion recombination rate constants, kr, in dense gaseous Ar and Kr with a small amount of N2 or CH4 as a molecular impurity have been measured as a function of electric field strength using a pulse radiolysis dc-conductivity method combined with a new decay-curve analysis method in which a space-charge effect is taken into account to obtain more accurate values of kr. The energy of electrons in recombination is controlled experimentally in two ways; one is heating-up by the electric field and the other is cooling-down by inelastic collisions with additive molecules. A large deviation of kr from the Debye theory obtained in the present experiment has been discussed in terms of the electron mean free paths and electron energies based on recent theories.
Optical detection of charge carriers in multilayer organic light-emitting diodes: Experiment and theory
Authors: Book K. , Nikitenko V. R. , Bässler H. , Elschner A.
Published: July 2002

We have investigated a multilayer organic light-emitting diode with 1,3,5-tris (N,N-bis-(4-methoxyphenyl)aminophenyl)-benzene acting as the hole transporting layer (HTL) and tris (8-hydroxy-quinolinolato) aluminum (Alq3) as the electron transporting layer. Positive charge carriers in the HTL were detected optically as a function of the applied bias. It was found that a hole injecting layer, consisting of 3,4 polyethylene-dioxy-thiophene doped with polystyrenesulfonate, forms an ohmic contact to the HTL by inducing a thin layer of holes in the interfacial region. An analytical model is developed to describe the observed carrier concentrations as well as the current–brightness–voltage characteristics quantitatively.
Pulse saturation recovery, pulse ELDOR, and free induction decay electron paramagnetic resonance detection using time-locked subsampling
Authors: Froncisz W. , Camenisch Theodore G. , Ratke Joseph J. , Hyde James S.
Published: July 2002

Time locked subsampling (TLSS) in electron paramagnetic resonance (EPR) involves the steps of (i) translation of the signal from a microwave carrier to an intermediate frequency (IF) carrier where the (IF) offset between the signal oscillator and local oscillator frequencies is synthesized, (ii) sampling the IF carrier four times in an odd number of cycles, say 4 in 3, where the analog-to-digital (A/D) converter is driven by a frequency synthesizer that has the same clock input as the IF synthesizer, (iii) signal averaging as required for adequate signal to noise, (iv) separating the even and odd digitized words into two separate signal channels, which correspond to signals in phase and in quadrature with respect to the IF carrier, i.e., I and Q, and (v) detecting the envelope of I and also of Q by changing the signs of alternate words in each of the two channels. TLSS detection has been demonstrated in three forms of pulse EPR spectroscopy at X band: saturation recovery, pulse electron–electron double resonance, and free induction decay. The IF was 187.5 MHz, the A/D converter frequency was 250 MHz, the overall bandwidth was 125 MHz, and the bandwidths for the separate I and Q channels were each 62.5 MHz. Experiments were conducted on nitroxide radical spin labels. The work was directed towards development of methodology to monitor bimolecular collisions of oxygen with spin labels in a context of site-directed spin labeling.
Scattering of shear horizontal piezoelectric waves in piezocomposite media
Authors: Alvarez-Mesquida A. A. , Rodriguez-Ramos R. , Comas F. , Monsivais G. , Esquivel-Sirvent R.
Published: July 2002

The theory of shear horizontal wave scattering processes in layered piezoelectric composites is discussed in terms of a recursive system of equations involving the piezoelectric impedance. Piezoelectric materials of hexagonal 6 mm symmetry are considered. The behavior of an incident shear horizontal piezoelectric wave is analyzed as a function of the material properties, layer thicknesses, and frequency (ω). By an appropriate choice of the materials and layer thicknesses, frequencies at which almost all energy is transmitted can be found, optimizing the properties of the system for ultrasound transducers. This behavior is also dependent on the incident angle. Furthermore, most laminated materials are bonded using polymers. We show that adding these polymers hampers the response of the piezoelectric laminated system, localizing the transmission at particular incident angles. Thus, sharp spikes of ultrasonic pulses could be generated with these laminated structures.
Dynamics of spatially nonuniform patterning in the model of blood coagulation
Authors: Zarnitsina V. I. , Ataullakhanov F. I. , Lobanov A. I. , Morozova O. L.
Published: July 2002

We propose a reaction-diffusion model that describes in detail the cascade of molecular events during blood coagulation. In a reduced form, this model contains three equations in three variables, two of which are self-accelerated. One of these variables, an activator, behaves in a threshold manner. An inhibitor is also produced autocatalytically, but there is no inhibitor threshold, because it is generated only in the presence of the activator. All model variables are set to have equal diffusion coefficients. The model has a stable stationary trivial state, which is spatially uniform and an excitation threshold. A pulse of excitation runs from the point where the excitation threshold has been exceeded. The regime of its propagation depends on the model parameters. In a one-dimensional problem, the pulse either stops running at a certain distance from the excitation point, or it reaches the boundaries as an autowave. However, there is a parameter range where the pulse does not disappear after stopping and exists stationarily. The resulting steady-state profiles of the model variables are symmetrical relative to the center of the structure formed.
Electronic states of InAs/GaAs quantum ring
Authors: Li Shu-Shen , Xia Jian-Bai
Published: July 2002

In the framework of effective mass envelope function theory, the electronic states of the InAs/GaAs quantum ring are studied. Our model can be used to calculate the electronic states of quantum wells, quantum wires, and quantum dots. In calculations, the effects due to the different effective masses of electrons in rings and out rings are included. The energy levels of the electron are calculated in the different shapes of rings. The results indicate that the inner radius of rings sensitively changes the electronic states. The energy levels of the electron are not sensitively dependent on the outer radius for large rings. If decreasing the inner and outer radii simultaneously, one may increase the energy spacing between energy levels and keep the ground state energy level unchanged. If changing one of two radii (inner or outer radius), the ground state energy level and the energy spacing will change simultaneously. These results are useful for designing and fabricating the double colors detector by intraband and interband translations. The single electron states are useful for studying the electron correlations and the effects of magnetic fields in quantum rings. Our calculated results are consistent with the recent experimental data of nanoscopic semiconductor rings.
Radial electrostatic flux inferred from core measurements of potential and density fluctuations
Authors: Demers D. R. , Schoch P. M. , Crowley T. P. , Connor K. A. , Ouroua A.
Published: July 2002

Broadband potential fluctuations and electrostatic fluctuation induced particle flux have been measured in the core of a medium size tokamak plasma for the first time. Density fluctuations and wave numbers were simultaneously measured. Measurements indicate that radial electrostatic fluctuation induced particle flux in the core region, at the normalized radii of 0.17<ρ<0.38, due to modes with wave numbers less than 4 cm−1 is small in magnitude, is likely directed inward, and cannot account for particle flux predicted by the continuity equation and particle source codes. Estimates of electrostatic energy flux are also significantly less than values predicted via power balance analysis. Asymmetries in coherent density and potential fluctuation levels on closed flux surfaces are evident. Relative fluctuation levels ñ/n and φ̃ tend to increase with radius, and the fluctuations are Boltzmann-like in the region 0.17⩽ρ⩽0.38. The direction of mode propagation is in the electron diamagnetic drift direction. Corresponding phase velocities, vph∼3.5×105 cm/s, are similar to drift wave velocities.
Quantum dressed classical mechanics
Authors: Billing G. D.
Published: July 2002

We have formulated a new way of making quantum corrections to classical mechanics. The method is based on a time-dependent discrete variable representation (DVR) of the wave function with grid points defined by the Hermite part of a basis set, the Gauss–Hermite basis set. The formulation introduces a set of grid points which follow the classical trajectory in space. With enough trajectories (DVR-points) the method approaches the exact quantum formulation. With just a single grid point in each dimension, we recover classical mechanics.
Ferromagnetic phenomenon revealed in the chalcopyrite semiconductor CdGeP2:Mn
Authors: Sato Katsuaki , Medvedkin Gennadiy A. , Nishi Takao , Hasegawa Youichi , Misawa Ryuji , Hirose Kanta , Ishibashi Takayuki
Published: July 2002

High concentration of Mn atoms has been successfully incorporated into the chalcopyrite type II–IV–V2 semiconductor CdGeP2 by solid-state reaction technique without causing any structural changes. Polycrystalline powder of the chalcopyrite-related material in Cd–Mn–Ge–P quaternary system has been additionally synthesized by sintering technology. Well-defined M–H hysteresis loops were observed at room temperature in CdGeP2:Mn single crystal and polycrystalline powder samples grown independently. The Curie temperature has been determined to be 320 K for single crystal phase CdxMn1−xGeP2 and 310 K for the polycrystalline powder. Magnetic force microscopy (MFM) observation clearly showed a stripe domain pattern on the Mn-diffused surface of CdGeP2 single crystal. The magneto-optical Kerr ellipticity spectrum of CdGeP2:Mn crystal showed a peak around 1.75 eV at T=300 K.