bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulations of fingering instabilities in surfactant-driven thin films
Authors: Craster R. V. , Matar O. K.
Published: April 2006

We study the surfactant-induced fingering phenomena in thin liquid films both below and beyond the critical micelle concentration using direct numerical simulations. Two-dimensional numerical solutions of the coupled nonlinear lubrication equations for the film thickness and surfactant interfacial and bulk concentrations are obtained for different values of the deposited surfactant mass M and underlying film thickness b. We show that these parameters have a profound effect on the fingering characteristics. At low to intermediate M, the deposited mound is relatively mobile and acts to “feed” the fingers that grow downstream efficiently; these fingers are essentially at the same elevation as the mound. At relatively high M values, narrower fingers form near the foot of a less mobile mound in a thinned region; this retards the supply rate of fluid from the mound. We also show that increasing b leads to less vigorous fingering. Our results are in agreement with trends observed experimentally.
Excitons in electrostatic traps
Authors: Hammack A. T. , Gippius N. A. , Yang Sen , Andreev G. O. , Butov L. V. , Hanson M. , Gossard A. C.
Published: April 2006

We consider in-plane electrostatic traps for indirect excitons in coupled quantum wells, where the traps are formed by a laterally modulated gate voltage. An intrinsic obstacle for exciton confinement in electrostatic traps is an in-plane electric field that can lead to exciton dissociation. We propose a design to suppress the in-plane electric field and, at the same time, to effectively confine excitons in the electrostatic traps. We present calculations for various classes of electrostatic traps and experimental proof of principle for trapping of indirect excitons in electrostatic traps.
Strain and composition of ultrasmall Ge quantum dots studied by x-ray scattering and in situ surface x-ray absorption spectroscopy
Authors: Dujardin R. , Poydenot V. , Schülli T. U. , Renaud G. , Ulrich O. , Barski A. , Derivaz M. , Colonna S. , Metzger T.
Published: April 2006

Investigations of the structural properties of ultrasmall Ge dots, grown through a thin silicon oxide layer on Si(001), have been performed by combining (i) grazing incidence x-ray diffraction, (ii) grazing incidence small angle x-ray scattering (GISAXS), and (iii) surface extended x-ray absorption fine structure (SEXAFS). Grazing incidence x-ray diffraction observations show that the dots are highly strained to the Si(001) substrate. The dot shape and composition, as determined by GISAXS experiments and in situ SEXAFS, strongly depend on the thickness and the composition of the silicon oxide layer covering the surface of the silicon substrate. Ge dots grown through 1.2nm thick SiO2 are round shaped with a Ge content of about 60% whereas dots grown through 0.3nm thick SiOx are facetted and composed of almost pure Ge.
Thermoelectric properties of Tl–X–Te (X=Ge, Sn, and Pb) compounds with low lattice thermal conductivity
Authors: Kosuga Atsuko , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: April 2006

We prepared polycrystalline-sintered samples of Tl2GeTe3, Tl4SnTe3, and Tl4PbTe3 and evaluated their thermoelectric properties. Although the electrical properties of these compounds were not optimized, the dimensionless figure of merit ZT was relatively high, i.e., 0.74 at 673K for Tl4SnTe3, 0.71 at 673K for Tl4PbTe3, and 0.29 at 473K for Tl2GeTe3, due to the very low lattice thermal conductivity of the compounds. Low lattice thermal conductivity appears to be closely related to the weak bonding of atoms and complex crystal structures of these compounds.
A full band deterministic model for semiclassical carrier transport in semiconductors
Authors: Smirnov S. , Jungemann C.
Published: April 2006

We present a deterministic semiclassical transport model taking into account the full band structure of a solid. The method is based on the spherical harmonics expansion of the distribution function and band structure. As an example the approach is applied to the specific case of stationary hole transport in bulk relaxed silicon and strained silicon exposed to external uniform electric and magnetic fields with arbitrary directions. To keep the structure of the method clear we only consider simple acoustic and optical phonon scatterings. First, the Boltzmann equation is rewritten in terms of energy. The limitations implied by the band structure on this form of the kinetic equation are then discussed. After expansion and projection onto the complete set of spherical harmonics the kinetic equation is reformulated as a system of ordinary differential equations which is solved numerically. Finally, the simulation results obtained for the chosen physical model are shown and discussed. It should be stressed that in contrast to early works not only the group velocity and the density of states are taken from the full band structure but the whole Boltzmann equation is completely treated within the full band picture and, therefore, when it is applicable, the method represents a deterministic equivalent of the full band Monte Carlo method.
Filling and capping multiwall carbon nanotubes with silicon nanocrystals dispersed in SiO2-based spin on glass
Authors: Švrček V. , Pham-Huu C. , Amadou J. , Begin D. , Ledoux M.-J. , Le Normand F. , Ersen O. , Joulié S.
Published: April 2006

Silicon nanocrystals (Si-ncs) are particularly interesting not only for their optical properties but also because recent developments have made possible the production of optoelectronic devices. In the present work, an approach is proposed either to introduce Si-ncs at room temperature inside the multiwall carbon nanotubes (MWCNTs) or to cap Si-nc on one open end of MWCNT. The Si-ncs dispersed in SiO2-based spin on glass solution have been preliminary disaggregated in an ammonia solution and contacted with open MWCNTs with different average inner diameters (IDs) within an ID range of 6–40nm. The ends of MWCNTs have been opened by a thermal annealing at appropriate temperatures that are previously evaluated from thermogravimetric investigations. On the tip of MWCNTs of small inner diameters it has been possible to stick a single Si-nc and cap the open end of the tube (Si-nc∕MWCNT), whereas with increasing IDs of MWCNTs, Si-ncs were introduced inside the tubule (Si-ncs-MWCNT). High resolution transmission electron microscopy and diffraction patterns provide evidence for many Si-ncs incorporated inside the MWCNTs. The capillary forces provided by the opening of the MWCNTs are strong enough to attract and even more to carry the Si-ncs within nanotubes far from their mouth. Photoluminescence properties of Si-nc inside the MWCNTs are investigated at room temperature. Implications on the interest of their composite material, Si-ncs-MWCNT, are discussed in terms of chemical and mechanical stabilizations, wiring, and handling single Si-nc.
Numerical study of jet flow generated by impact on weakly compressible liquid
Authors: Korobkin Alexander A. , Iafrati Alessandro
Published: April 2006

The early stage of two-dimensional jet flow generated by an impulsive start of a wedge, initially floating on a free surface otherwise flat, is investigated taking into account liquid compressibility. During this short initial stage the flow close to the intersection points is self-similar. Velocity of the body is assumed much smaller than the sound speed in the liquid at rest. The acoustic solution of this problem reveals that the flow velocity is singular about the intersection points. In order to obtain a uniformly valid description of the flow, an inner solution is derived by using stretched variables, which are dependent on the Mach number of the problem. It is shown that, for small Mach numbers, the inner flow is approximately potential and is governed by the Laplace equation. The solution of the boundary-value problem is achieved numerically through an iterative procedure. A modified velocity potential, which significantly simplifies the boundary conditions on the free surface, is introduced. Accurate solutions are presented in terms of free surface shapes and jet lengths for different dead-rise angles of the wedge. The analogy between this problem and that of jetting flow caused by shock wave impact on a wedge-shaped cavity is discussed as well.
Reduced models of chemical reaction in chaotic flows
Authors: Vikhansky A. , Cox S. M.
Published: April 2006

We describe and evaluate two reduced models for nonlinear chemical reactions in a chaotic laminar flow. Each model involves two separate steps to compute the chemical composition at a given location and time. The “manifold tracking model” first tracks backwards in time a segment of the stable manifold of the requisite point. This then provides a sample of the initial conditions appropriate for the second step, which requires solving one-dimensional problems for the reaction in Lagrangian coordinates. By contrast, the first step of the “branching trajectories model” simulates both the advection and diffusion of fluid particles that terminate at the appropriate point; the chemical reaction equations are then solved along each of the branched trajectories in a second step. Results from each model are compared with full numerical simulations of the reaction processes in a chaotic laminar flow.
Theoretical studies on tunneling ionizations of helium atom in intense laser fields
Authors: Nagaya K. , Mishima K. , Hayashi M. , Lin S. H.
Published: April 2006

Our generalized Keldysh theory is applied to the simplest many-electron atom, helium atom. For the single ionization (He→He++e) we derive a compact rate formula, which does not contain any series summation or integral and thus is as simple as the Ammosov-Delone-Krainov ionization rates. In addition to its simplicity, our formula can explicitly show the wavelength dependence. Furthermore a simple form of the angular distribution of the photoelectron is available. Our compact formula agrees well with both the exact numerical calculations [A. Scrinzi et al., Phys. Rev. Lett. 83, 706 (1999)] and experimental data [B. Walker et al., Phys. Rev. Lett. 73, 1227 (1994)] in the intensity range of I<5×1015W∕cm2. In higher intensity regions, we suggest to utilize another simple formula which is valid in the tunneling limit.
Multimode wavelet basis calculations via the molecular self-consistent-field plus configuration-interaction method
Authors: Griffin Courtney D. , Acevedo Ramiro , Massey Daniel W. , Kinsey James L. , Johnson Bruce R.
Published: April 2006

Wavelets provide potentially useful quantum bases for coupled anharmonic vibrational modes in polyatomic molecules as well as many other problems. A single compact support wavelet family provides a flexible basis with properties of orthogonality, localization, customizable resolution, and systematic improvability for general types of one-dimensional and separable systems. While direct product wavelet bases can be used in coupled multidimensional problems, exponential scaling of basis size with dimensionality ultimately provides limits on the number of coupled modes that can be treated simultaneously in exact quantum calculations. The molecular self-consistent-field plus configuration-interaction method is used here in multimode wavelet calculations to reduce the basis size without sacrificing flexibility or the ability to systematically control errors. Both two-dimensional Cartesian coordinate and three-dimensional curvilinear coordinate systems are examined with wavelets serving as universal bases in each case. The first example uses standard Daubechies [Ten Lectures on Wavelets (SIAM, Philadelphia (1992)] wavelets for each mode and the second adapts symmlet wavelets to intervals for each of the curvilinear coordinates.
Paramagnetic relaxation of protons in rotationally immobilized proteins
Authors: Korb Jean-Pierre , Diakova Galina , Bryant Robert G.
Published: April 2006

The proton magnetic relaxation dispersion profiles are reported over the proton Larmor frequency range from 0.01to30MHz for cross-linked gels and for the dry lyophilized bovine serum albumin covalently labeled at lysine with diethylenetriaminepentaacetic acid chelates of either Gd(III) or Mn(II) ions. The proton spin-lattice relaxation dispersion for the cross-linked paramagnetic protein gel is accurately represented as a sum of two major relaxation contributions. The diamagnetic term is a power law from the magnetic field dependence of the protein protons. The paramagnetic term is approximately described by the Solomon-Bloembergen-Morgan class of models. However, the paramagnetic relaxation mechanism in the dry lyophilized protein is fundamentally different and we develop a new quantitative description of the dispersion profile. In the dry case, no peak in the proton relaxation dispersion profile is detected from the field dependence of the electron spin relaxation times. The high-field paramagnetic relaxation dispersion is a power law in the Larmor frequency with an exponent of −0.8, which results from modulation of the electron-nuclear coupling by the intramolecular dynamics of the protein which primarily propagates along the primary structure of the protein. The low-field plateau is caused by the interruption of the electron-nuclear spin correlation by electron spin relaxation. This new quantitative description provides a simple approach to the measurement of electron spin-lattice relaxation times in paramagnetic protein systems at room temperature based on the magnetic field dependence of the proton spin-lattice relaxation rate constant.
Conductivity and photoconductivity in undoped ZnSe nanowire array
Authors: Philipose U. , Ruda H. E. , Shik A. , de Souza C. F. , Sun P.
Published: April 2006

Arrays of free-standing ZnSe nanowires with the length of 8–10μm and diameters of 80–150nm were fabricated by Au-catalyzed vapor-liquid-solid growth. Current-voltage characteristics of the arrays over the temperature interval of 90–400K showed a superlinear character. The differential conductance varied between two saturating regimes at low and high biases, respectively. This behavior was explained using a model of nonuniform wires with concentration fluctuations along them. The nanowire photoconductivity had a spectral edge corresponding to the ZnSe band gap and a strong frequency dispersion, presumably due to carrier capture by deep centers.
Voltage effects on the volumetric flow rate in cone-jet mode electrospraying
Authors: Smith K. L. , Alexander M. S. , Stark J. P. W.
Published: April 2006

Electrospray data collected demonstrate the detailed dependence of volumetric flow rate through an electrospray system upon the applied voltage. The sensitivity of nominal flow rate to applied voltage was found to be higher for lower nominal flow rates. For a volumetric flow rate ∼4nL∕s a 25% change in flow rate per kilovolt was recorded over a cone-jet mode stability range spanning ∼1.5kV. This volumetric flow rate voltage sensitivity holds particular significance for potential colloid electrospray propulsion systems, which operate at or near minimum flow rate conditions. Analysis is presented to show that the change in flow rate due to change in voltage cannot be ascribed to evaporation from the meniscus as has been suggested by others.
Theoretical investigations for shot noise in correlated resonant tunneling through a quantum coupled system
Authors: Djuric Ivana , Dong Bing , Cui H. L.
Published: April 2006

We carry out a theoretical analysis of the zero-frequency and finite-frequency shot noise in electron tunneling through a two-level interacting system connected to two leads, when a weak coherent coupling between the two levels is present, by means of recently developed bias-voltage and temperature-dependent quantum rate equations. For this purpose, we generalize the traditional generation-recombination approach for shot noise of two-terminal tunneling devices to properly take into account the coherent superposition of different electronic states (quantum effects). As applications, analytical and numerical investigations have been given in detail for two particular cases: (1) electron tunneling through a quantum dot connected to ferromagnetic leads with intradot spin-flip scattering and (2) spinless fermions tunneling through two coupled quantum dots, focusing on the shot noise as functions of bias-voltage and frequency.
Ion-irradiation-induced phase transformation in rare earth sesquioxides (Dy2O3,Er2O3,Lu2O3)
Authors: Tang M. , Lu P. , Valdez J. A. , Sickafus K. E.
Published: April 2006

Polycrystalline pellets of cubic C-type rare earth structure (Ia3¯) Dy2O3, Er2O3, and Lu2O3 were irradiated at cryogenic temperature (120K) with 300keV Kr++ ions to a maximum fluence of 1×1020Kr∕m2. Irradiated specimens were examined using grazing incidence x-ray diffraction and transmission electron microscopy. Ion irradiation leads to different radiation effects in these three materials. First, Dy2O3 begins to transform to a monoclinic B-type rare earth structure (C2∕m) at a peak dose of ∼5 displacements per atom (dpa), (corresponding to a fluence of 2×1019Kr∕m2). This transformation is nearly complete at a peak dose of 25 dpa (a fluence of 1×1020Kr∕m2). Er2O3 also transforms to the B-type structure, but the transformation starts at a higher irradiation dose of about 15–20 dpa [a fluence of about (6–8)×1019Kr∕m2]. Lu2O3 was found to maintain the C-type structure even at the highest irradiation dose of 25 dpa (a fluence of 1×1020Kr∕m2). No C-to-B transformation was observed in Lu2O3. The irradiation dose dependence of the C-to-B phase transformation observed in Dy2O3, Er2O3, and Lu2O3 is closely related to the temperature dependence of the C-to-B phase transformation found in phase diagrams for these three materials.
Ferroelectric ordering in imidazolium perchlorate
Authors: Pająk Z. , Czarnecki P. , Szafrańska B. , Małuszyńska H. , Fojud Z.
Published: April 2006

Imidazolium perchlorate has been synthesized and studied over a wide range of temperatures by differential scanning calorimetry, x-ray diffraction, proton magnetic resonance, optical observation, and dielectric spectroscopy. Polymorphic solid-solid phase transitions have been disclosed at 487, 373, and 247K. The crystal structure at 298K has been determined as trigonal, space group R3m, Z=1 with a=5.484(1)Å and α=95.18(2)°. The imidazolium cations are strongly disordered, while the perchlorate ions are well ordered. At 385K the crystal structure remains trigonal, space group R3¯m, a=5.554(1)Å and α=95.30(2)°. Both ionic sublattices are orientationally disordered. Temperature evolution of the molecular dynamics of the imidazolium cation has been characterized. In spite of a high cationic disorder, dielectric measurements have revealed the polar properties of the crystal. It appears to be a new ferroelectric compound with the Curie point at 373K. The spontaneous polarization originates predominantly from the behavior of slightly distorted perchlorate anion.
Numerical solution of Dalgarno-Lewis equations by a mapped Fourier grid method
Authors: Cohen S. , Themelis S. I.
Published: April 2006

Inhomogeneous radial differential equations emerging in applications of standard perturbation theory are numerically solved by a novel approach making use of Fourier grid methods in conjunction with a simple mapping scheme. The proposed algorithm is applied along the lines of the Dalgarno-Lewis method [Proc. R. Soc. London, Ser. A 223, 70 (1955)] to the calculation of the static dipole polarizabilities and hyperpolarizabilities of 1s, 2s, and 2p states of hydrogen atom and their frequency dependent dynamic dipole polarizabilities. The high efficiency and accuracy of the algorithm are demonstrated for the above test cases, where exact values are available. Then, the frequency dependent dipole polarizability of the ground state of lithium atom is computed by a variationally stable method combining an effective local potential approach with a second-order energy correction. The obtained results are in perfect agreement with other elaborate theoretical approaches.
Linear stability analysis and dynamic simulations of free convection in a differentially heated cavity in the presence of a horizontal magnetic field and a uniform heat source
Authors: Pelekasis Nikos A.
Published: April 2006

The steady state and stability of two-dimensional free convection flow in a square cavity is examined, in the presence of a uniform internal heat source and a uniform magnetic field that is perpendicular to gravity and parallel to an imposed temperature gradient. The finite element method is used for calculating the steady and dynamic state of the system in the parameter space defined by the dimensionless numbers, Gr, Ha, Pr, and S. The trapezoidal rule is used for time integration. Linear stability analysis is performed by solving a generalized eigenvalue problem. The Arnoldi method is used for the calculation of eigenvalues with significant savings in storage and CPU time requirements. The base solution normally exhibits two recirculation regions when the heat production term is large enough. Stability analysis predicts a Hopf bifurcation to a periodic branch. A neutral stability diagram is constructed for a range of values of Ha, Gr, and S for liquid lithium, Pr=0.0321. Internal heat generation, i.e,. increasing S, enhances instability by decreasing the critical value of Grashof, Grcr, determining the onset of the Hopf branch, whereas intensifying the magnetic field, i.e., increasing Ha, stabilizes the flow by increasing Grcr. Dynamic simulations confirm the above structure, identify the oscillatory solution branch as a supercritical Hopf bifurcation for the entire parameter range that was examined, and recover the time constants predicted by stability analysis. As Gr increases or as Ha decreases symmetric arrangement of the two rolls is eliminated and the steady flow configuration loses stability when Gr>Grcr. Subsequently, time periodicity sets in leading to more or less efficient heat removal in terms of lowering or increasing the average cavity temperature, in comparison with the steady flow configuration for the same Gr, depending on whether Ha lies below or above a critical value, respectively, for fixed S and Pr.
Properties and structure of vapor-deposited polyimide upon electron-beam irradiation
Authors: Tsai F.-Y. , Kuo Y.-H. , Harding D. R.
Published: April 2006

Vapor-deposited polyimide capsules from pyromellitic dianhydride and 4,4′-oxydianiline were irradiated with an electron beam that mimicked the β-radiation emitted by tritium, a fuel that the capsules are to contain during the inertial confinement fusion process. The mechanical properties and gas permeability of the irradiated capsules were measured to examine their radiation resistance. Upon electron-beam irradiation at an energy of 8keV and a dose of 120MGy, the capsules showed 15% and 56% decrease in tensile strength and elongation at break, respectively, without significant change in gas permeability and Young’s modulus. Analyses using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy indicated that the chain cleavage and carbonization occurred but were confined in a thin layer at the top surface of the capsules. The shallow penetration of the low-energy electron beam used, as well as the existence of cross-linking in the vapor-deposited polyimide, may have led to the smaller magnitude of property degradation in the capsules compared to that reported for solution-cast polyimide.
Planar shock cylindrical focusing by a perfect-gas lens
Authors: Dimotakis P. E. , Samtaney R.
Published: April 2006

We document a gas lensing technique that generates a converging shock wave in a two-dimensional wedge geometry. A successful design must satisfy three criteria at the contact point between the gas lens and the wedge leading edge to minimize nonlinear reflected and other wave effects. The result is a single-point solution in a multidimensional parameter space. The gas lens shape is computed using shock-polar analysis for regular refraction of the incident shock at the gas lens interface. For the range of parameters investigated, the required gas-lens interface is closely matched by an ellipse or hyperbola. Nonlinear Euler simulations confirm the analysis and that the transmitted shock is circular. As the converging transmitted shock propagates down the wedge, its shape remains nearly uniform with less than 0.1% peak departures from a perfect circular cylinder segment. Departure from the design criteria leads to converging shocks that depart from the required shape. The sensitivity to incident shock Mach number, as well as the qualitative effects of the presence of boundary layers are also discussed.
A new methodology for Reynolds-averaged modeling based on the amalgamation of heuristic-modeling and turbulence-theory methods
Authors: Yoshizawa Akira , Nisizima Shoiti , Shimomura Yutaka , Kobayashi Hiromichi , Matsuo Yuichi , Abe Hiroyuki , Fujiwara Hitoshi
Published: April 2006

A new methodology for the Reynolds-averaged Navier-Stokes modeling is presented on the basis of the amalgamation of heuristic-modeling and turbulence-theory methods. A characteristic turbulence time scale is synthesized in a heuristic manner through the combination of several characteristic time scales. An algebraic model of turbulent-viscosity type for the Reynolds stress is derived from the Reynolds-stress transport equation with the time scale embedded. It is applied to the state of weak spatial and temporal nonequilibrium, and is compared with its theoretical counterpart derived by the two-scale direct-interaction approximation. The synthesized time scale is justified through the agreement of the two expressions derived by these entirely different methods. The derived model is tested in rotating isotropic, channel, and homogeneous-shear flows. It is extended to a nonlinear algebraic model and a supersonic model. The latter is shown to succeed in reproducing the reduction in the growth rate of a free-shear layer flow, without causing wrong effects on wall-bounded flows such as channel and boundary-layer flows.
Photoreflectance investigation of InAs quantum dashes embedded in In0.53Ga0.47As∕In0.53Ga0.23Al0.24As quantum well grown on InP substrate
Authors: Rudno-Rudziński W. , Kudrawiec R. , Sęk G. , Misiewicz J. , Somers A. , Schwertberger R. , Reithmaier J. P. , Forchel A.
Published: April 2006

Photoreflectance (PR) measurements were performed on molecular-beam-epitaxy-grown self-assembled InAs quantum dashes (QDashes) embedded in an In0.53Ga0.47As∕In0.53Ga0.23Al0.24As quantum well grown on InP substrate. PR resonances related to optical transitions in all relevant parts of the structure, i.e., InAs∕In0.53Ga0.47As QDashes, InAs∕In0.53Ga0.47As∕In0.53Ga0.23Al0.24As quantum well, and in In0.53Ga0.23Al0.24As barriers were observed. By matching the theoretical calculations performed within the effective mass approximation with experimental data, the energy level structure of the whole system was determined. On the basis of the obtained energy level diagram, it was concluded that both electrons and heavy holes are localized within the InAs∕In0.53Ga0.47As QDashes, the structure is of Type I.
Cantilever temperature characterization in low temperature vacuum atomic force microscope
Authors: Kazantsev D. V. , Dal Savio C. , Danzebrink H. U.
Published: April 2006

The frequency response of an atomic force microscope silicon cantilever located in a vacuum cryostat chamber was investigated. The resonance frequency and the peak width were extracted by a Lorentzian fit of the resonance curves for different sample temperatures (15–310K). Frequency shifts significantly less than one could expect from known temperature dependencies of Young’s modulus and the density of silicon were found. The estimations described in this article show that the temperature of a silicon cantilever is mainly defined by the temperature of its holder, mainly due to the thermal conductivity of silicon. Thermal radiation emission plays a minor role in cooling the cantilever. Furthermore, heat transport through tip-sample contact, as well as contact with the environmental gas, could be neglected.
Reduced intermolecular interaction in organic ultrathin films
Authors: Gordan O. D. , Himcinschi C. , Zahn D. R. T. , Cobet C. , Esser N. , Braun W.
Published: April 2006

Submonolayer sensitivity was achieved using in situ ellipsometry to monitor the evolution of the dielectric function of tris(8-hydroxyquinoline)-aluminum(III) (Alq3) layers from submonolayer coverage to thick bulklike layers. The Alq3 layers were deposited under ultrahigh vacuum conditions onto hydrogen passivated silicon. The characteristic vacuum-ultraviolet (VUV) absorption lines of Alq3 were detected using synchrotron radiation as light source. In such ultrathin films the absorption lines corresponding to molecular transitions of the Alq3 are found to be spectrally blueshifted with respect to bulklike layers. We attribute the shift to the effect of reduced intermolecular interaction in the submonolayer regime.
Direct force balance method for atomic force microscopy lateral force calibration
Authors: Asay David B. , Kim Seong H.
Published: April 2006

A new and simple calibration method for atomic force microscopy (AFM) is developed. This nonscanning method is based on direct force balances on surfaces with known slopes. The lateral force calibration is performed during force-distance measurements for normal force calibration. This method requires a substrate with known slopes, the z motion of the piezocalibrated, and the normal spring constant known. This technique determines not only the lateral detector sensitivity (N/V) but also the detector offset (V/m) and off-centering angle (α) for asymmetric cantilever-tip geometries. Because it is nonscanning, the AFM cantilever can be calibrated without dulling the tip.
Identification of unidirectional anisotropy in exchange-biased MnO∕GaMnAs bilayers using ferromagnetic resonance
Authors: Dziatkowski K. , Ge Z. , Liu X. , Furdyna J. K.
Published: April 2006

We report ferromagnetic resonance (FMR) studies of epitaxial MnO∕GaMnAs bilayers. The FMR data have revealed a distinct unidirectional anisotropy about the [11¯0] axis, which we attribute to exchange biasing of ferromagnetic GaMnAs by the adjacent antiferromagnetic MnO layer. The observed unidirectional anisotropy is surprisingly robust with respect to temperature and changing magnetic field.
Formation of the physical vapor deposited CdS∕Cu(In,Ga)Se2 interface in highly efficient thin film solar cells
Authors: Rusu M. , Glatzel Th. , Neisser A. , Kaufmann C. A. , Sadewasser S. , Lux-Steiner M. Ch.
Published: April 2006

We report on the buffer/absorber interface formation in highly efficient (14.5%, air mass 1.5) ZnO∕CdS∕Cu(In,Ga)Se2 solar cells with a physical vapor deposited CdS buffer. For Se-decapped Cu(In,Ga)Se2 (CIGSe) absorbers we observe sulfur passivation of the CIGSe grain boundaries during CdS growth and at the interface a thermally stimulated formation of a region with a higher band gap than that of the absorber bulk, determining the height of the potential barrier at the CdS∕CIGSe interface. For air-exposed CIGSe samples the grain boundary passivation is impeded by a native oxide/adsorbate layer at the CIGSe surface determining the thermal stability of the potential barrier height.
Droplet-based photoresist deposition
Authors: Demirci Utkan
Published: April 2006

Photoresist droplets are ejected onto a wafer surface by an acoustic two-dimensional micromachined ejector array. The spread of single droplets on a silicon wafer surface at varying droplet speeds is studied. Series of photoresist droplets are printed periodically drop on demand on a silicon wafer surface and profiles of a single droplet and two droplets overlapping with varying distances of 25 and 1μm on a silicon wafer are demonstrated. Moreover, 3.4μm thick spinless full coverage of a 4in. wafer with photoresist is demonstrated which indicates a potential for coating wafers in less than a few seconds.
Antisite defect-free Lu3(GaxAl1−x)5O12:Pr scintillator
Authors: Nikl M. , Pejchal J. , Mihokova E. , Mares J. A. , Ogino H. , Yoshikawa A. , Fukuda T. , Vedda A. , D’Ambrosio C.
Published: April 2006

Pr-doped Lu3(GaxAl1−x)5O12:Pr, x=0–1, single crystals were grown by the micro-pulling-down method. We study luminescence and scintillation characteristics of the sample set focusing on their dependence on the gallium content. For x=0.4 we obtain the high figure-of-merit material with elevated density, high efficiency, and very fast scintillation response below 20ns without any slower components. Improvement of scintillation performance is explained as due to the absence of the antisite LuAl defects that was for the first time realized in such bulk garnet single crystals grown from the high temperature melt.
Effect of nanofluid on the heat transport capability in an oscillating heat pipe
Authors: Ma H. B. , Wilson C. , Borgmeyer B. , Park K. , Yu Q. , Choi S. U. S. , Tirumala Murli
Published: April 2006

By combining nanofluids with thermally excited oscillating motion in an oscillating heat pipe (OHP), we developed an ultrahigh-performance cooling device, called the nanofluid oscillating heat pipe. Experimental results show that when the OHP is charged with nanofluid, heat transport capability significantly increases. For example, at the input power of 80.0W, diamond nanofluid can reduce the temperature difference between the evaporator and the condenser from 40.9to24.3°C. This study will accelerate the development of a highly efficient cooling device for ultrahigh-heat-flux electronic systems.
Spatial and temporal sensitivity variations in photorefractive electro-optic field sensors
Authors: Garzarella A. , Qadri S. B. , Wieting Terence J. , Wu Dong Ho
Published: April 2006

Experimental studies of the spatial and temporal fluctuations in photorefractive electro-optic (EO) field sensors have revealed that their maximum intrinsic responsivity is limited by incoherence in the polarization of the probe beam. This incoherence is generated within the irradiated crystal itself. We describe a novel method to measure the incoherence directly while suppressing the temporal fluctuations. Our results indicate that optically induced distributions of birefringence (photorefractivity) generally impair the modulating ability of EO crystals.
Fabrication of silicon-on-SiO2/diamondlike-carbon dual insulator using ion cutting and mitigation of self-heating effects
Authors: Di Zengfeng , Chu Paul K. , Zhu Ming , Fu Ricky K. Y. , Luo Suhua , Shao Lin , Nastasi M. , Chen Peng , Alford T. L. , Mayer J. W. , Zhang Miao , Liu Weili , Song Zhitang , Lin Chenglu
Published: April 2006

A diamondlike-carbon (DLC) layer was used to substitute for the buried SiO2 layer in silicon on insulator (SOI) to mitigate the self-heating effects in our previous study. However, we discovered drawbacks associated with the inferior Si/DLC interface, inadequate thermal stability as well as carbon-silicon interdiffusion at the Si/DLC interface that could hamper future application of this silicon-on-diamond structure to microelectronic devices. In this work, we introduced a silicon dioxide barrier layer between the Si film and DLC buried layer to form a silicon-on-SiO2∕DLC dual-insulator structure to tackle these problems. Cross-sectional high-resolution transmission electron microscopy reveals that the Si/insulator interface is atomically flat and the top Si layer has nearly perfect crystalline quality. The SiO2∕DLC dual-insulator layer retains excellent insulating properties at typical complementary metal oxide silicon processing temperatures. Numerical simulation reveals that the negative differential resistance and channel temperature are significantly reduced compared with those of the same metal oxide semiconductor field effect transistors fabricated in conventional SiO2-based SOI, suggesting that the silicon-on-dual-insulator structure can alleviate the self-heating penalty effectively.
Laser-induced structural modifications in nanocrystalline silicon/amorphous silicon dioxide superlattices
Authors: Kamenev B. V. , Grebel H. , Tsybeskov L.
Published: April 2006

We calculate and experimentally detect the laser melting threshold in nanocrystalline Si/amorphous SiO2 superlattices. Using laser energy density slightly above the melting threshold, we observe two types of laser-induced structural modifications: (i) disappearance of nanocrystalline Si phase in the samples with thin (∼2nm) SiO2 layers and (ii) amorphization of Si nanocrystals in the samples with thicker (⩾5nm) SiO2 layers. The observed Si nanocrystal amorphization increases optical absorption and intensity of visible photoluminescence in nanocrystalline Si/amorphous SiO2 superlattices.
Enhancement of the upper critical field of Nb3Sn utilizing disorder introduced by ball milling the elements
Authors: Cooley L. D. , Hu Y. F. , Moodenbaugh A. R.
Published: April 2006

Nb 3 Sn was prepared by milling Nb and Sn powder mixtures followed by limited reactions to restrict disorder recovery. Although disorder reduced the superconducting critical temperature Tc, the concomitant electron scattering increased the upper critical field μ0Hc2 to as high as 35T at 0K, as determined by the Werthamer-Helfand-Hohenberg equation. Hc2 was higher for longer milling times and lower annealing temperatures. Substitution of 2% Ti for Nb did not appreciably enhance Hc2, suggesting that alloying mitigates the benefits of disorder. Since alloyed Nb3Sn wires have μ0Hc2(0)≈29T, wires based on heavily milled powders could extend the field range for applications if they can be made with high current density.
Transient lateral photovoltaic effect in p-n heterojunctions of La0.7Sr0.3MnO3 and Si
Authors: Zhao Kun , Jin Kui-juan , Lu Huibin , Huang Yanhong , Zhou Qingli , He Meng , Chen Zhenghao , Zhou Yueliang , Yang Guozhen
Published: April 2006

A transient lateral photovoltaic effect (LPVE) has been observed in p-La0.7Sr0.3MnO3∕n-Si heterojunctions. Under the nonuniform irradiation of a pulsed laser, the LPVE shows high sensitivity to the spot position on the La0.7Sr0.3MnO3 surface. A mechanism based on the well established model for the LPVE in conventional semiconductors has been applied to explain the LPVE in the heteroepitaxial junctions of perovskite-type metal oxides. The large LPVE in the heteroepitaxial junctions is expected to make the perovskite-type metal oxide a new and faster candidate for position-sensitive photodetectors.
Fabrication of 100nm metal lines on flexible plastic substrate using ultraviolet curing nanoimprint lithography
Authors: Lee Heon , Hong Sunghoon , Yang Kiyeon , Choi Kyungwoo
Published: April 2006

Since polymer is flexible, lightweight, reliable and transparent and its material properties can easily be modified, it is a suitable substrate material for organic electronic devices, biomedical devices, and especially for flexible displays. To build a nano-device on a polymer substrate, nano to microsized patterning must be done. However, conventional photolithography cannot be used to fabricate patterns on flexible polymer substrate, due to the focusing and substrate handling issue associated with flexibility of polymer substrate and potential interaction between polymer and developer or other organic solvents used in photolithography. Degradation of polymer substrate during resist baking process over 120°C can be another problem. In this study, 100nm sized resist patterns were made on flexible polyethylene-terephthalate (PET) film using newly developed monomer based UV curing imprinting lithography. Compared to conventional imprint lithography, UV curing imprint lithography uses monomer based liquid phase resin and thus patterns can be fabricated without residual layer at room temperature and at much lower pressure (<3–5atm) with UV illumination. No degradation of PET film was observed due to the imprint process and, as a result, 100nm sized Ti–Au metal patterns were successfully formed on PET film using UV curing imprint lithography and lift-off process.
Size-dependent thermal conductivity of zinc oxide nanobelts
Authors: Kulkarni Ambarish J. , Zhou Min
Published: April 2006

The thermal conductivity of [011¯0]-oriented ZnO nanobelts 19–41Å in size is characterized over the temperature range of 500–1500K using the Green-Kubo approach. Values obtained are one order of magnitude lower than that for bulk ZnO single crystal. Surface scattering of phonons and the high surface-to-volume ratios of the nanobelts are primarily responsible for the significantly lower values and the size dependence observed. The conductivity is also found to decrease with temperature and this decrease is attributed to thermal softening of the material, three- and four-phonon processes, and optical phonon interactions.
Internal-friction mapping on solids by resonance ultrasound microscopy
Authors: Ogi H. , Niho H. , Hirao M.
Published: April 2006

An internal-friction microscopy is developed for quantitatively determining material damping on a local surface area by measuring vibrational attenuation of an isolated langasite oscillator point contacting the material. Noncontacting measurement of the resonance frequency and attenuation coefficient of the longitudinal vibration of the oscillator has been achieved with a line antenna, providing high sensitivity to the modulus and damping in the local contacting area. Formulation of the relationship between a material’s local internal friction and attenuation of the resonator system is proposed using the generalized Hertzian-contact model. Results on a dual-phase stainless steel and a Cu∕NbTi composite are shown.
Defining phreatophyte response to reduced water availability: preliminary investigations on the use of xylem cavitation vulnerability in Banksia woodland species
Authors: Froend R. H. , Drake P. L.
Published: April 2006

The consideration of phreatophyte response to changes in water availability is important in identifying ecological water requirements in water-resource planning. Although much is known about water-source partitioning and intra- and interspecific variability in groundwater use by Banksia woodland species, little is known about the response of these species to groundwater draw-down. This paper describes a preliminary study into the use of xylem cavitation vulnerability as a measure of species response to reduced water availability. A response function and critical range in percentage loss of conductance is identified for four Banksia woodland overstorey species. Similarity in the vulnerability curves of B. attenuata R.Br. and B. menziesii R.Br. at low tensions supports the notion that they occupy a similar ecohydrological niche, as defined by their broad distributions relative to depth to groundwater. B. ilicifolia R.Br., however, as an obligate phreatophyte, has a range restricted to environments of higher water availability and shallower depth to groundwater and this is reflected in greater vulnerability to cavitation (relative to other Banksia) at lower tensions. The wetland tree Melaleuca preissiana Schauer generally expressed a greater vulnerability at any given xylem water potential (Ψx). This paper identifies the range in Ψx within which there is an elevated risk of tree mortality, and represents a first step towards quantifying the critical thresholds in the response of Banksia woodland species to reduced water availability.
Prolonged deleterious effects of neonatal handling on reproductive parameters of pubertal male rats
Authors: Mazaro Renata , Lamano-Carvalho Teresa Lúcia
Published: April 2006

The purpose of the present study was to investigate the long-lasting effects of neonatal handling on reproductive parameters of male rats. Neonatal handling (pups separated from their mothers, kept isolated at environmental temperature for 20 min and submitted to 1 min of tactile stimulation) was applied from post partum Days 1 to 14 (a stress-hyporesponsive period, SHRP) and the animals were killed at puberty (61 days of age). The number of mature spermatids and the daily sperm production were estimated in homogenates from the right testes and cauda epididymidis. Histometric parameters (diameter of seminiferous tubule, germinal epithelium thickness and number of Sertoli cells) were evaluated in paraplast sections of the left testes. The association of the slightly aversive stimuli applied during the SHRP proved to have lasting deleterious effects on male reproduction, causing lower testicular weight and reduced values of seminiferous tubule diameter and germinal epithelium thickness at puberty, which resulted in a 25% reduction in the daily sperm production and in the number of mature spermatids. Similarly, the number of Sertoli cells per tubular cross section was 20% smaller and the weight and number of spermatozoa were reduced more than 40% in the cauda epididymidis of animals handled.
Consequences of the selective blockage of chaperone-mediated autophagy
Authors: Massey Ashish C. , Kaushik Susmita , Sovak Guy , Kiffin Roberta , Cuervo Ana Maria
Published: April 2006

Chaperone-mediated autophagy (CMA) is a selective pathway for the degradation of cytosolic proteins in lysosomes. CMA declines with age because of a decrease in the levels of lysosome-associated membrane protein (LAMP) type 2A, a lysosomal receptor for this pathway. We have selectively blocked the expression of LAMP-2A in mouse fibroblasts in culture and analyzed the cellular consequences of reduced CMA activity. CMA-defective cells maintain normal rates of long-lived protein degradation by up-regulating macroautophagy, the major form of autophagy. Constitutive up-regulation of macroautophagy is unable, however, to compensate for all CMA functions. Thus, CMA-defective cells are more sensitive to stressors, suggesting that, although protein turnover is maintained, the selectivity of CMA is necessary as part of the cellular response to stress. Our results also denote the existence of cross-talk among different forms of autophagy.
Self-assembled bifunctional surface mimics an enzymatic and templating protein for the synthesis of a metal oxide semiconductor
Authors: Kisailus David , Truong Quyen , Amemiya Yosuke , Weaver James C. , Morse Daniel E.
Published: April 2006

The recent discovery and characterization of silicatein, a mineral-synthesizing enzyme that assembles to form the filamentous organic core of the glassy skeletal elements (spicules) of a marine sponge, has led to the development of new low-temperature synthetic routes to metastable semiconducting metal oxides. These protein filaments were shown
in vitro
to catalyze the hydrolysis and structurally direct the polycondensation of metal oxides at neutral pH and low temperature. Based on the confirmation of the catalytic mechanism and the essential participation of specific serine and histidine residues (presenting a nucleophilic hydroxyl and a nucleophilicity-enhancing hydrogen-bonding imidazole nitrogen) in silicatein’s catalytic active site, we therefore sought to develop a synthetic mimic that provides both catalysis and the surface determinants necessary to template and structurally direct heterogeneous nucleation through condensation. Using lithographically patterned poly(dimethylsiloxane) stamps, bifunctional self-assembled monolayer surfaces containing the essential catalytic and templating elements were fabricated by using alkane thiols microcontact-printed on gold substrates. The interface between chemically distinct self-assembled monolayer domains provided the necessary juxtaposition of nucleophilic (hydroxyl) and hydrogen-bonding (imidazole) agents to catalyze the hydrolysis of a gallium oxide precursor and template the condensed product to form gallium oxohydroxide (GaOOH) and the defect spinel, gamma-gallium oxide (γ-Ga
2
O
3
). Using this approach, the production of patterned substrates for catalytic synthesis and templating of semiconductors for device applications can be envisioned.