bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient deformation and drag of decelerating drops in axisymmetric flows
Authors: Wadhwa Amrita R. , Magi Vinicio , Abraham John
Published: November 2007

Transient deformation and drag coefficients of decelerating drops in axisymmetric flows are numerically computed. The drag coefficients are compared with those of solid spheres. In the case of drops, the behavior of the drag coefficient is dependent on the deformation and internal circulation of the drops in addition to the factors which are important for solid spheres. These, in turn, are dependent on the gas-based Weber number (Weg) and the Ohnesorge number (Ohl). At the relatively low Weg of 1, when the deformation is small, the drag coefficients are about the same for the solid sphere and drop. When Weg is increased, the deformation increases and the difference increases. At the highest Weg of 100, the drop reaches a point of secondary breakup. In general, oblate shapes result in greater drag and prolate shapes in lower drag relative to the solid sphere. Increasing Ohl, which implies increasing viscous forces in the liquid relative to surface tension forces, leads to less deformation and hence lesser differences between solid and drop drag coefficients for a given Weg.
Precipitates and hydrogen passivation at crystal defects in n- and p-type multicrystalline silicon
Authors: Geerligs L. J. , Komatsu Y. , Röver I. , Wambach K. , Yamaga I. , Saitoh T.
Published: November 2007

The effects of phosphorous gettering and hydrogenation on the minority carrier recombination at crystal defects in directionally solidified multicrystalline silicon are described. Representative industrial wafers, both p- and n-type, and current technologies for the gettering and hydrogenation are used. The main result of this work is a strong link between activation of extended crystal defects (ECDs) by gettering and their passivation by hydrogenation. It is shown that gettering or annealing increases the recombination at active as well as inactive ECDs. Surprisingly, hydrogenation can neutralize this change in activity due to the gettering. However, it neutralizes only part, at most, of the ECD activity already present before the gettering. Therefore, under current industrial processing techniques, these two high-temperature process steps individually give large change but together much less net change of the crystal defect activity. Related phenomena are observed in wafers with strongly varying impurity concentration. Finally, there is little difference in these observations between n- and p-type wafers.
Onset of convection in two liquid layers with phase change
Authors: McFadden G. B. , Coriell S. R. , Gurski K. F. , Cotrell D. L.
Published: November 2007

We perform linear stability calculations for horizontal fluid bilayers that can undergo a phase transformation, taking into account both buoyancy effects and thermocapillary effects in the presence of a vertical temperature gradient. We find that the entropy difference between the phases plays a crucial role in determining the stability of the system. For small values of the entropy difference between the phases, the system can be linearly unstable to heating from either above or below. The instability is due to the Marangoni effect in combination with the effects of buoyancy (for heating from below). For larger values of the entropy difference, the system is unstable only to heating from below, and the driving force for the instability is thermodynamic in nature, dominating the Marangoni effect. This long-wavelength instability can be understood qualitatively in terms of a variation of the classical morphological stability analysis of a phase boundary. The interface is unstable if either of the adjacent bulk phases is thermodynamically unstable. To help elucidate the mechanisms driving the instability on heating from below, we have performed both long-wavelength and short-wavelength analyses of the two-phase system, and have performed numerical calculations using materials parameters for a water-steam system. The two-phase system also allows a conventional Rayleigh-Taylor instability if the heavier fluid overlies the lighter fluid; applying a temperature gradient allows a stabilization of the interface.
An electrostatic glass actuator for ultrahigh vacuum: A rotating light trap for continuous beams of laser-cooled atoms
Authors: Füzesi F. , Jornod A. , Thomann P. , Plimmer M. D. , Dudle G. , Moser R. , Sache L. , Bleuler H.
Published: November 2007

This article describes the design, characterization, and performance of an electrostatic glass actuator adapted to an ultrahigh vacuum environment (10−8mbar). The three-phase rotary motor is used to drive a turbine that acts as a velocity-selective light trap for a slow continuous beam of laser-cooled atoms. This simple, compact, and nonmagnetic device should find applications in the realm of time and frequency metrology, as well as in other areas of atomic, molecular physics and elsewhere.
A new gyrokinetic quasilinear transport model applied to particle transport in tokamak plasmas
Authors: Bourdelle C. , Garbet X. , Imbeaux F. , Casati A. , Dubuit N. , Guirlet R. , Parisot T.
Published: November 2007

The scope of this paper is to present and benchmark the first version of a quasilinear calculation, QuaLiKiz, based on a fast linear gyrokinetic code, Kinezero [C. Bourdelle, X. Garbet, G. T. Hoang, J. Ongena, and R. V. Budny, Nucl. Fusion 42, 892 (2002)] accounting for all unstable modes and summing over a wave-number spectrum. The fluctuating electrostatic potential frequency and wave-number spectra are chosen based on turbulence measurements and nonlinear simulations results. A peculiar focus on particle transport is developed. The directions of compressibility and thermodiffusion convections of ions and electrons are analytically derived for passing and trapped particles in both ion and electron turbulence. Also, the charge and mass dependence of trace heavy impurity convection is analytically estimated. These results are compared with quasilinear simulations done by QuaLiKiz. Finally, the impact of accounting for all unstable modes and of summing over the wave-number spectrum is shown to reverse in some cases the direction of particle fluxes.
Wave power absorption: Experiments in open sea and simulation
Authors: Eriksson M. , Waters R. , Svensson O. , Isberg J. , Leijon M.
Published: November 2007

A full scale prototype of a wave power plant based on a direct drive linear generator driven by a point absorber has been installed at the west coast of Sweden. In this paper, experimentally collected data of energy absorption for different electrical loads are used to verify a model of the wave power plant including the interactions of wave, buoy, generator, and external load circuit. The wave-buoy interaction is modeled with linear potential wave theory. The generator is modeled as a nonlinear mechanical damping function that is dependent on piston velocity and electric load. The results show good agreement between experiments and simulations. Potential wave theory is well suited for the modeling of a point absorber in normal operation and for the design of future converters. Moreover, the simulations are fast, which opens up for simulations of wave farms.
A maximum-likelihood algorithm for reduction of Langmuir probe data
Authors: Martin Adam K. , Koelfgen Syri J.
Published: November 2007

The reduction of Langmuir triple and quadruple probe data, i.e., the determination of the electron temperature Te from the measured voltages and currents, requires the solution of an implicit transcendental equation in Te, at every point in time. Random errors and noise in the measurements occasionally precludes solution of the equation, resulting in an indeterminate temperature at those times. We present a method for overcoming this problem that uses the method of maximum likelihood. The experimental uncertainties, assumed to be normally distributed, are used in solving the implicit equation in Te. At every point in time, a likelihood function is calculated, and the temperature which maximizes this function is taken to be the solution Te. The uncertainty in the resulting measurement is taken to be the width of the likelihood function. Examples of this technique are shown.
Electron source concept for single-shot sub-100 fs electron diffraction in the 100 keV range
Authors: van Oudheusden T. , de Jong E. F. , van der Geer S. B. , ’t Root W. P. E. M. Op , Luiten O. J. , Siwick B. J.
Published: November 2007

We present a method for producing sub-100 fs electron bunches that are suitable for single-shot ultrafast electron diffraction experiments in the 100 keV energy range. A combination of analytical estimates and state-of-the-art particle tracking simulations show that it is possible to create 100 keV, 0.1 pC, 30 fs electron bunches with a spot size smaller than 500 μm and a transverse coherence length of 3 nm, using established technologies in a table-top setup. The system operates in the space-charge dominated regime to produce energy-correlated bunches that are recompressed by radio-frequency techniques. With this approach we overcome the Coulomb expansion of the bunch, providing a single-shot, ultrafast electron diffraction source concept.
Integration of minisolenoids in microfluidic device for magnetic bead–based immunoassays
Authors: Liu Yan-Jun , Guo Shi-Shang , Zhang Zhi-Ling , Huang Wei-Hua , Baigl Damien , Chen Yong , Pang Dai-Wen
Published: November 2007

Microfluidic devices with integrated minisolenoids, microvalves, and channels have been fabricated for fast and low-volume immunoassay using superparamagnetic beads and well-known surface bioengineering protocols. A magnetic reaction area can be formed in the microchannel, featuring a high surface-to-volume ratio and low diffusion distances for the reagents to the bead surface. Such a method has the obvious advantage of easy implementation at low cost. Moreover, the minisolenoids can be switched on or off and the magnetic field intensity can be tuned on demand. Fluids can be manipulated by controlling the integrated air-pressure-actuated microvalves. Accordingly, magnetic bead–based immunoassay, as a typical example of biochemical detection and analysis, has been successfully performed on the integrated microfluidic device automatically in longitudinal mode. With a sample consumption of 0.5μl and a total assay time of less than 15min, goat immunoglobulin G was detected and the method exhibited a detection limit of 4.7ng∕ml.
Mediation of room temperature ferromagnetism in Co-doped SnO2 nanocrystalline films by structural defects
Authors: Liu X. F. , Yu R. H.
Published: November 2007

Co-doped SnO2 nanocrystalline films have been fabricated by magnetron sputtering to investigate the effects of structural defects on mediating ferromagnetism in this system. X-ray photoelectron spectroscopy analysis reveals that Co element is incorporated into SnO2 lattice and is in 2+ oxidation state in all samples. High-resolution transmission electron microscopy observation indicates that along the film growth direction, Sn1−xCoxO2 films change from amorphous structure to columnar grain except for the film deposited at room temperature. With the decrease of film thickness, deposition rate, and deposition temperature, a relative proportion of structural defects in films increases, resulting in an enhancement of the saturated magnetic moment of Sn1−xCoxO2 film. Bound magnetic polaron mechanism is adopted to explain the mediation effect of structural defects on ferromagnetism in this system.
Spectroscopic study of laser-induced Al plasmas with cylindrical confinement
Authors: Shen X. K. , Sun J. , Ling H. , Lu Y. F.
Published: November 2007

The cylindrical confinement of laser-induced plasmas in round pipes has been investigated by optical emission spectra and fast imaging. An obvious enhancement in the emission intensity of Al atomic lines was observed when a round pipe was placed to confine the laser-induced Al plasmas. The enhancement factor for the emission intensities of the Al atomic lines was measured to be around 9 at a time delay of 12μs when the pipe diameter is 10.8mm. Assuming local thermodynamic equilibrium conditions, the plasma temperatures are estimated to be in the range from 4000to5800K. It shows that the plasma temperature increased by around 1000K when the cylindrical confinement was applied. Images of the laser-induced Al plasmas show that the plasmas were compressed into a smaller volume with a pipe presented. The spatial-confinement effects are attributed to the reflection and compression of the shock wave.
Three-dimensional aspects of fluid flows in channels. I. Meniscus and thin film regimes
Authors: Ledesma-Aguilar R. , Hernández-Machado A. , Pagonabarraga I.
Published: November 2007

We study the forced displacement of a fluid-fluid interface in a three-dimensional channel formed by two parallel solid plates. Using a lattice-Boltzmann method, we study situations in which a slip velocity arises from diffusion effects near the contact line. The difference between the slip and channel velocities determines whether the interface advances as a meniscus or a thin film of fluid is left adhered to the plates. We find that this effect is controlled by the capillary and Péclet numbers. We estimate the crossover from a meniscus to a thin film and find good agreement with numerical results. The penetration regime is examined in the steady state. We find that the occupation fraction of the advancing finger relative to the channel thickness is controlled by the capillary number and the viscosity contrast between the fluids. For high viscosity contrast, lattice-Boltzmann results agree with previous results. For zero viscosity contrast, we observe remarkably narrow fingers. The shape of the finger is found to be universal.
Extended Hamiltonian systems in multisymplectic field theories
Authors: Echeverría-Enríquez Arturo , de León Manuel , Muñoz-Lecanda Miguel C. , Román-Roy Narciso
Published: November 2007

We consider Hamiltonian systems in first-order multisymplectic field theories. We review the properties of Hamiltonian systems in the so-called restricted multimomentum bundle, including the variational principle which leads to the Hamiltonian field equations. In an analogous way to how these systems are defined in the so-called extended (symplectic) formulation of nonautonomous mechanics, we introduce Hamiltonian systems in the extended multimomentum bundle. The geometric properties of these systems are studied, the Hamiltonian equations are analyzed using integrable multivector fields, the corresponding variational principle is also stated, and the relation between the extended and the restricted Hamiltonian systems is established. All these properties are also adapted to certain kinds of submanifolds of the multimomentum bundles in order to cover the case of almost-regular field theories.
Symbol calculus and zeta-function regularized determinants
Authors: Kaynak Burak Tevfik , Turgut O. Teoman
Published: November 2007

In this work, we use semigroup integral to evaluate zeta-function regularized determinants. This is especially powerful for nonpositive operators such as the Dirac operator. In order to understand fully the quantum effective action, one should know not only the potential term but also the leading kinetic term. In this purpose, we use the Weyl type of symbol calculus to evaluate the determinant as a derivative expansion. The technique is applied both to a spin-0 bosonic operator and to the Dirac operator coupled to a scalar field.
Higher-order, asymmetric orbit multipactors
Authors: Riyopoulos Spilios
Published: November 2007

Multipactors involving asymmetric back-and-forth orbits with different flight times and launch phases are studied. Resonant orbits with the rf involve periodic sequences of two or more different impact phases. Such orbits appear when the rf field and emission velocity reach values that make the usual symmetric orbits unstable, through a stability bifurcation process. The number of resonant impact phases contained in each orbit doubles at each bifurcation, leading to higher-order multipactor. Existence of second- and third-order multipactors is demonstrated, extending the theoretical upper-field boundary for multipactor discharge. The study focuses on orbital properties, without addressing secondary yield in detail.
Optimal expansion of a heated working fluid for maximum work output with generalized radiative heat transfer law
Authors: Song Hanjiang , Chen Lingen , Sun Fengrui
Published: November 2007

The optimal configuration of the expansion process of a heated working fluid inside a cylinder for maximum work output with a movable piston and generalized radiative heat transfer law q̇∝Δ(Tn) is determined. The optimal process that maximizes the work output of the working fluid with fixed initial energy, initial volume, and final volume is obtained using optimal control theory. The optimal process consists of at most three stages, including an initial adiabatic branch, one intermediate Euler-Lagrange arc, and a final adiabatic branch. The analytical solutions of the intermediate Euler-Lagrange arc are obtained for different heat transfer laws, including n=−1, n=1, n=2, n=3, and n=4. Numerical examples for the optimal configurations are provided. Finally, the obtained results are compared with each other.
Field-induced meniscus dynamics and its impact on the nanoscale tip-surface interface
Authors: Xie Xian Ning , Chung Hong Jing , Tong Dian Min , Sow Chorng Haur , Wee Andrew Thye Shen
Published: November 2007

We describe the spatiotemporal evolution of the nanoscale tip-surface junction during field-induced water meniscus formation in the junction. The motion of the meniscus and tip was analyzed on the basis of typical parameters concerning the nanoscale meniscus and tip-surface configuration. Being attracted by the electric field, the meniscus generates a repulsive hydrodynamic impact force counteracting the electrostatic force on the tip. The imbalance of the forces leads to an increase of the tip-surface separation distance, and the increase is related to the initial experimental parameters including tip bias voltage and tip spring constant. An explicit equation was derived for the estimation of the tip-surface junction enlargement effect. The theoretical results were confirmed by atomic force microscope (AFM) in situ observations of tip repulsion under electric fields. The induced tip-surface junction enlargement has significant implications in AFM nanolithography, e.g., it could facilitate the formation of nanostructures with high vertical dimensions/aspect ratios.
Fabrication and characterization of metal-oxide-nitride-oxynitride-polysilicon nonvolatile semiconductor memory device with silicon oxynitride (SiOxNy) as tunneling layer on glass
Authors: Jung Sungwook , Kim Jaehong , Son Hyukjoo , Hwang Sunghyun , Jang Kyungsoo , Lee Jungin , Lee Kwangsoo , Park Hyungjun , Kim Kyunghae , Yi Junsin , Chung Hokyoon , Choi Byoungdeog , Lee Kiyong
Published: November 2007

A nonvolatile semiconductor memory (NVSM) device with a metal-oxide-nitride-oxynitride-polysilicon (MONOS) structure on a rough polysilicon (poly-Si) surface was fabricated using a low-temperature process and poly-Si thin film transistor (TFT) technology on glass. For the fabrication of the NVSM device on glass, plasma-assisted oxynitridation was carried out using nitrous oxide (N2O) as a reactive gas, due to the very rough surface of the poly-Si on glass annealed using an excimer laser. The ultrathin SiOxNy films obtained using the N2O plasma have a very uniform distribution on poly-Si and similar contents of oxygen and nitrogen in the peaks and valleys of the grains. The NVSM devices having a MONOS structure with a tunneling layer of ultrathin SiOxNy on glass have suitable switching and charge retention characteristics for data storage. The results demonstrate that the NVSM device made using low-temperature poly-Si TFT technology on glass reported in this paper can be used in various types of display devices.
Covalent attachment of protein to the tip of a multiwalled carbon nanotube without sidewall decoration
Authors: Maruyama Hiroyuki , Yoshimura Shige H. , Akita Seiji , Nagataki Atsuko , Nakayama Yoshikazu
Published: November 2007

We have demonstrated covalent bonding of protein molecules to an oxidized multiwall carbon nanotube (MWCNT) in an aqueous buffer solution. A chemical reaction using carbodi-imide forms chemical bonds between open-ended tips of MWCNTs and protein molecules. The statistical examination indicated that proteins were attached at the open-ended tip of MWCNT at a probability as high as 50% although proteins attached to the sidewall of the MWCNT were washed out after rinsing with running water.
Storage and light scattering of microparticles in a ring-type electrodynamic trap
Authors: Kolomenskii Al. A. , Jerebtsov S. N. , Stoker J. A. , Scully M. O. , Schuessler H. A.
Published: November 2007

We employ a Paul-Straubel ring-type electrodynamic trap for studies of single microparticles. Such a trap provides ready access for laser beams to a stored species and is especially suited for scattering and spectroscopic studies of fine particles. We derive the pseudopotential for such a trap and determine the stability regions for confinement of charged particles considering also the viscous force of a buffer medium and the force of gravity. The dynamics of microparticles in such a trap is numerically simulated. The diffraction pattern of light scattered on a polystyrene particle of about 10μm diameter was registered. For measuring Raman spectra from a single dipicolinic acid microparticle, we used excitation at 488nm and detection with a fiber optics spectrometer. To improve the collection of light, the trap with the stored particle was placed inside an elliptical mirror.
Relationship between structural features of MoS2 nanotubes and crystalline structure of precursor
Authors: Rivera-Muñoz Eric M.
Published: November 2007

Mo S 2 nanotubes have been synthesized by thermal decomposition of ammonium thiomolybdate (ATM) precursor and by using the aluminum oxide template method. Hollow tubes of very specific diameter and wall thickness were obtained presenting the so-called “bamboo” texture. These nanotubes are closed in sections; each one 29nm wide and a length of 63nm in average. Evidence of a strong relationship between these structural features of MoS2 nanotubes and crystalline structure of precursor is exposed, suggesting that both size and shape of tube sections are determined by crystalline structure of ATM precursor as well as by the diameter of template pores.
Langmuir probe data analysis for a magnetized inductive radio-frequency discharge
Authors: Popescu S. , Ohtsu Y. , Fujita H.
Published: November 2007

The properties of an inductively coupled argon plasma in a uniform magnetic field, at pressures of the order of 0.1 Pa, in the presence of a weak current-free electric double layer, are measured with a plane Langmuir probe. The static current-voltage probe characteristics, recorded on the symmetry axis of the experimental device, both in the plasma source and in the main chamber of the setup, showed the existence of two electron populations with different temperatures. The axial profiles of plasma parameters, such as the plasma potential and the cold and hot electron temperatures, offered a new insight into such a complex system. However, both the external magnetic field and the two electron populations contribute to the difficulty of calculation of the local plasma density. A method for solving this problem, involving the definition of an effective electron temperature, is also presented.
Correlated photon emission in a thick barrier coupled quantum dot
Authors: Yamauchi Shohgo , Shikanai Amane , Morohashi Isao , Furue Shigenori , Komori Kazuhiro , Sugaya Takeyoshi , Takagahara Toshihide
Published: November 2007

Correlated photon emission from a thick barrier coupled quantum dot (QD) has been observed by using selective two-color excitation spectroscopy and second-order photon correlation spectroscopy. Surprisingly, the carrier creation in both QDs induced an anomalous increase in the luminescence intensity, and furthermore the cross photon correlation spectrum between two QDs exhibited photon antibunching with a long recovery time. These significant findings can be interpreted in terms of the electromagnetic interaction between QDs with a thick barrier layer.
Kinetics, stoichiometry, morphology, and current drive capabilities of Ir-based silicides
Authors: Larrieu G. , Dubois E. , Wallart X. , Katcki J.
Published: November 2007

A detailed study of the formation of iridium silicide obtained by ultrahigh vacuum annealing and atmospheric rapid thermal processing is proposed using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electrical characterizations. Using XPS analysis, the stoichiometry of each silicide phase (IrSi, IrSi1.6) is identified. A model based on the variation of the measured intensity of the Ir 4f spectra is used to obtain the kinetic coefficients of reaction of Ir silicidation (EA=2.48eV, D0=9cm2∕s). TEM cross sections indicate that the roughness of the silicide∕silicon interface increases with temperature. Lastly, electrical characteristics are used to identify the optimum annealing temperature to obtain an iridium silicide contact with the lowest Schottky barrier height to holes.
Modeling of electron mobility in gated silicon nanowires at room temperature: Surface roughness scattering, dielectric screening, and band nonparabolicity
Authors: Jin Seonghoon , Fischetti Massimo V. , Tang Ting-wei
Published: November 2007

We present a theoretical study of electron mobility in cylindrical gated silicon nanowires at 300 K based on the Kubo-Greenwood formula and the self-consistent solution of the Schrödinger and Poisson equations. A rigorous surface roughness scattering model is derived, which takes into account the roughness-induced fluctuation of the subband wave function, of the electron charge, and of the interface polarization charge. Dielectric screening of the scattering potential is modeled within the random phase approximation, wherein a generalized dielectric function for a multi-subband quasi-one-dimensional electron gas system is derived accounting for the presence of the gate electrode and the mismatch of the dielectric constant between the semiconductor and gate insulator. A nonparabolic correction method is also presented, which is applied to the calculation of the density of states, the matrix element of the scattering potential, and the generalized Lindhard function. The Coulomb scattering due to the fixed interface charge and the intra- and intervalley phonon scattering are included in the mobility calculation in addition to the surface roughness scattering. Using these models, we study the low-field electron mobility and its dependence on the silicon body diameter, effective field, dielectric constant, and gate insulator thickness.
Modified resistive switching behavior of ZrO2 memory films based on the interface layer formed by using Ti top electrode
Authors: Lin Chih-Yang , Wu Chung-Yi , Wu Chen-Yu , Tseng Tseung-Yuen , Hu Chenming
Published: November 2007

The influence of Ti top electrode material on the resistive switching properties of ZrO2-based memory film using Pt as bottom electrode was investigated in the present study. When Ti is used as top electrode, the resistive switching behavior becomes dependent on bias polarity and no current compliance is needed during switching into high conducting state. This phenomenon is attributed to the fact that a series resistance between Ti and ZrO2 film, composed of a TiOx layer, a ZrOy layer, and even the contact resistance, imposed a current compliance on the memory device. Besides, our experimental results imply that switching the device into high conducting state is a field driven process while switching back into low conducting state is a current driven process.
Crystallization kinetics and recording mechanism of a-Si∕Ni bilayer for write-once blue-ray recording
Authors: Her Yung-Chiun , Jean Sen-Tsun , Wu Jyun-Lin
Published: November 2007

For the a-Si∕Ni bilayer with a thickness ratio of 4:1, the formation of NiSi and NiSi2 phases took place in the temperature range between 200 and 350°C and only ∼9% of unreacted a-Si would crystallize to c-Si, which will not cause appreciable reflectivity change. As the thickness ratio of a-Si to Ni was increased to 20:1, the formation of NiSi2 phase and subsequent crystallization of a-Si mediated by NiSi2 precipitates were clearly observed. The crystallization temperature of a-Si in the a-Si∕Ni bilayer with a thickness ratio of 20:1 was significantly reduced to around 350°C, which was 130°C lower than that in the a-Si∕Cu bilayer. The activation energies for NiSi2 phase formation and crystallizations of a-Si for the a-Si∕Ni bilayer with a thickness ratio of 20:1 were determined to be 1.12±0.09 and 2.19±0.08eV, respectively. The crystallization behavior of the a-Si(20nm)∕Ni(1nm) bilayer recording film under pulsed laser irradiation is similar to that under thermal annealing. During the recording process, the NiSi2 phase will precipitate first and serve as the nucleation sites for the following crystallization of the remaining amorphous Si. The maximum value of carrier to noise ratio for 3T could reach 43dB for the write-once blue-ray disk with layer structure of a-Si(20nm)∕Ni(1nm), demonstrating a high potentiality for practical use.
Temperature-dependent structural stability and optical properties of ultrathin Hf–Al–O films grown by facing-target reactive sputtering
Authors: He G. , Zhang L. D. , Meng G. W. , Li G. H. , Fang Q. , Zhang J. P.
Published: November 2007

The structural stability and optical properties of ultrathin HfAlOx films grown by facing-target reactive sputtering, depending on the postannealing temperature, have been determined via x-ray photoelectron spectroscopy and spectroscopic ellipsometry (SE). By virtue of the chemical shifts of Hf4f, Al2p, and Si2p core-level spectra, it has been found that the structural stability of HfAlOx∕Si system sustains up to 800°C. However, the breaking of the Hf–Al–O bond and the phase separation take place drastically at the annealing temperature of 900°C. In particular, the information of an interfacial Si–O–Si bond as the dominant reaction during the postannealing treatment has been observed, confirmed by Fourier transform infrared spectroscopy. Analysis by SE, based on the Tauc-Lorentz model, has indicated that increase in the refractive index and reduction in thickness has been observed as a function of annealing temperature, originating from the annealing-induced higher packing density. The change of the complex dielectric functions and bandgap Eg correlated with the annealing temperature are discussed in detail.
Elastometric sensing using higher flexural eigenmodes of microcantilevers
Authors: Spletzer Matthew , Raman Arvind , Reifenberger Ron
Published: November 2007

We present a method to detect with high sensitivity the viscoelastic property changes of sensor coatings on microcantilever arrays due to radiation, analyte binding, or adsorption. The method uses higher order flexural eigenmodes to identify the location and magnitude of the nonuniform elasticity changes in the microcantilever coating. We demonstrate the method by monitoring the time evolution of resonance frequencies and Q factors of different flexural eigenmodes of microcantilevers functionalized with a small drop of a photosensitive polymer as it is exposed to ultraviolet radiation. The method is particularly well suited for measuring quantitatively the time varying viscoelastic properties of thin films or biological materials attached to microcantilevers.
A soft effective segment representation of semidilute polymer solutions
Authors: Pierleoni Carlo , Capone Barbara , Hansen Jean-Pierre
Published: November 2007

A coarse-grained effective segment description of polymer solutions is presented, based on soft, transferable effective interactions between bonded and nonbonded effective segments. The number of segments is chosen such that the segment density does not exceed their overlap threshold, allowing polymer concentrations to be explored deep into the semidilute regime. This quantitative effective segment description is shown to preserve known scaling laws of polymer solutions and provides accurate estimates of amplitudes, while leading to a orders-of-magnitude increase in the simulation efficiency and allowing analytic calculations of structural and thermodynamic properties.
Size-dependent excitation spectra and energy transfer in Tb3+-doped Y2O3 nanocrystalline
Authors: Meng Qingyu , Chen Baojiu , Xu Wu , Yang Yanmin , Zhao Xiaoxia , Di Weihua , Lu Shaozhe , Wang Xiaojun , Sun Jiashi , Cheng Lihong , Yu Tao , Peng Yong
Published: November 2007

Nanocrystal Y2O3 powders with different grain sizes and various doping concentrations of Tb3+ were prepared by an autocombustion reaction. The size and surface effects on the 4f-5d transitions and energy transfers between Tb3+ ions were studied by using x-ray diffraction, transmission electron microscopy, fluorescent spectra, and luminescent decay. It was found that the excitation spectra are composed of two parts: one is the contribution from the Tb3+ at/near the nanoparticle surfaces; another is from the Tb3+ inside the nanoparticles. The study on the concentration quenching and luminescent decay indicated that the energy transfers depopulating the D53 and D54 level were assigned to the mechanisms of electric dipole-dipole and exchange interaction, respectively. The size confinement greatly affects the energy transfer quenching the emission from the D53 level, but slightly affects the energy transfer quenching the emission from the D54 level.
Resonance magnetoelectric effects in magnetostrictive-piezoelectric three-layer structures
Authors: Filippov D. A. , Laletsin U. , Srinivasan G.
Published: November 2007

A theory is discussed for magnetoelectric (ME) interactions at electromechanical resonance in a heterogeneous ferromagnetic-piezoelectric three-layer structure. An expression has been obtained for the transverse ME coefficients αE,T as a function of interface coupling β between the layers. For 0<β<1, the theory predicts resonance enhancement of αE,T at two interrelated radial modes. As β is increased from 0, the low-frequency resonance occurs at progressively increasing frequency until it merges with the high-frequency mode when β=1. These predictions are in general agreement with representative data for a permendur-PZT-permendur trilayer composite.
The effect of the substrate temperature on extended defects created by hydrogen implantation in germanium
Authors: David M. L. , Pailloux F. , Babonneau D. , Drouet M. , Barbot J. F. , Simoen E. , Claeys C.
Published: November 2007

H implantation in Ge was carried out at two substrate temperatures, room temperature (RT) and 150 °C. The microstructure of the as-implanted Ge samples was studied by transmission electron microscopy and grazing incidence small-angle x-ray scattering. Small (001) and {111} platelets and {113} defects are nucleated at RT. For higher substrate temperature, microcracks, cavities, and platelike cavity clusters are created as well. The formation of these types of defects is ascribed to the interplay between dynamic and kinetic effects occurring during the implantation.
Current-induced magnetization reversal mechanisms of pseudospin valves with perpendicular anisotropy
Authors: Guo J. , Jalil M. B. A. , Bae Seongtae , Tan S. G.
Published: November 2007

We present a numerical simulation of current-induced magnetization switching (CIMS) in pseudospin-valve (PSV) structures exhibiting perpendicular anisotropy. The PSV structures consist of a reference layer of Co/Pt and Co/Ni multilayers and a free layer composed of Co/Ni multilayers. The spin torque induced by the passage of a spin-polarized current is modeled by means of a modified Landau–Lifshitz–Gilbert equation, which incorporates two additional spin-torque terms. Numerical micromagnetic simulations of the magnetization switching process predict a critical current density of the order of 107 A∕cm2, a value consistent with available experimental results. In addition, we investigate the influence of the current sweep rate and the ratio of the in-plane and out-of-plane torque coefficients on the stability of the magnetization switching process. Our analysis provides a useful guide for optimal utilization of the CIMS effect in perpendicularly magnetized multilayers, for use in prospective spintronic applications.
Nonparabolicity and dielectric effects on addition energy spectra of spherical nanocrystals
Authors: Planelles J. , Royo M. , Pi M.
Published: November 2007

An extension of the spin density functional theory simultaneously accounting for dielectric mismatch between neighboring materials and nonparabolicity corrections originating from interactions between conduction and valence bands is presented. This method is employed to calculate ground state and addition energy spectra of homogeneous and multishell spherical quantum dots. Our calculations reveal that corrections become especially relevant when they come into play simultaneously in strong regimes of spatial confinement.
Thermal stability of surface and interface structure of atomic layer deposited Al2O3 on H-terminated silicon
Authors: Gao K. Y. , Speck F. , Emtsev K. , Seyller Th. , Ley L.
Published: November 2007

Using the atomic layer deposition technique, 1.2nm Al2O3 films were deposited as high-k gate dielectric layer on hydrogen-terminated silicon and annealed in vacuum and pure hydrogen in order to elucidate the effects of growth and annealing on the structure of film, interface, and surface. As analytical tools, high resolution core level spectroscopy using synchrotron radiation as variable photon source and Fourier Transform Infrared absorption spectroscopy in the attenuated total refraction mode were employed. For Al2O3 on H-terminated Si(111) and (100) surfaces the Si–H bonds are preserved at the interface, while Si–O–Al bonds provide the atomically abrupt interface between Al2O3 and Si. The chemical and structural integrity of the interface is maintained upon annealing except for a gradual loss of Si–H bonds. Growth of a SiO2 layer is observed after annealing, that is unambiguously located at the Al2O3 surface and not at the interface. Stress-induced emission of Si atoms from the interface is identified as the source of SiO2 based on a substantial broadening of the Si 2p core lines. A thermally induced reaction between Si and Al2O3 to form volatile SiO and Al2O is suggested to be responsible for the significant thickness reduction of Al2O3 that accompanies annealing at temperatures of 750°C. Conclusions for the likely effects of forming gas anneals on Al2O3∕Si are drawn from this work.
Particle formation in acetylene very low-pressure high density magnetized plasmas
Authors: Calafat Maria , Escaich David , Clergereaux Richard , Raynaud Patrice , Segui Yvan
Published: November 2007

Particle formation in cold plasmas is a matter of a large number of studies in capacitive, high-pressure, and low-density discharges. Conversely, under very-low working pressure and high plasma density conditions, as in microwave multipolar plasma excited at distributed electron cyclotron resonance (MMP-DECR), particle formation is generally not favored: the gas phase interaction probability is low due to the very-low working pressure. However, in this work, we report observations and analyses of particles formed in acetylene MMP-DECR discharges. It is proposed that the presence of the magnetic field compensates for the very-low working pressure inducing an increase in the gas phase interaction probability: negative ions are repelled by the sheath and confined within the magnetic field. Thus, particles can be formed similarly to in rf plasma.
Constructing a class of solutions for the Hamilton-Jacobi equation in field theory
Authors: Bruno Danilo
Published: November 2007

A new approach leading to the formulation of the Hamilton-Jacobi equation for field theories is investigated within the framework of jet bundles and multisymplectic manifolds. An algorithm associating classes of solutions to given sets of boundary conditions of the field equations is provided. The paper also puts into evidence the intrinsic limits of the Hamilton-Jacobi method as an algorithm to determine families of solutions of the field equations, showing how the choice of the boundary data is often limited by compatibility conditions.
Reactive nanojets: Nanostructure-enhanced chemical reactions in a defected energetic crystal
Authors: Nomura Ken-ichi , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: November 2007

Nanofluidics of chemically reactive species has enormous technological potential and computational challenge arising from coupling quantum-mechanical accuracy with largescale fluid phenomena. Here, we report a million-atom reactive force field molecular dynamics simulation of shock initiation of an energetic crystal with a nanometer-scale void. The simulation reveals the formation of a nanojet which focuses into a narrow beam at the void. This, combined with the excitation of vibrational modes through enhanced intermolecular collisions by the free volume of the void, catalyzes chemical reactions that do not occur otherwise. We also observe a pinning-depinning transition of the shock wave front at the void at increased particle velocity and the resulting localization-delocalization transition of the vibrational energy.
Microlens array for focusing airborne ultrasound using heated wire grid
Authors: Cai Liang-Wu , Sánchez-Dehesa José
Published: November 2007

This letter reports on the focusing of airborne ultrasound by a simple grid of heated wires. The focusing is analogous to that of an array of optical microlenses. The focusing pattern is determined by the spacing between wires, and the focusing areas are tightly confined with a great “depth of field.” Such acoustical microlens arrays have great potentials for shaping beams produced by ultrasonic transducers, in applications such as ultrasonic cleaning and nondestructive testing.
Strong optical confinement and multimode emission of organic photonic dots
Authors: Langner M. , Gehlhaar R. , Schriever C. , Fröb H. , Lyssenko V. G. , Leo K.
Published: November 2007

We report on the optical mode structure of laterally confined organic microcavities. For preparation, an organic semiconductor is evaporated through a mask with square sized holes, resulting in photonic dots with approximately 5μm diameter. Using a microscope setup, we observe a complex mode structure in transmission and photoluminescence. From the mode mapping, we conclude a strong three-dimensional optical confinement. The near and far field spectra are modeled by transfer matrix calculations and a Fourier transform of the internal electric field distribution, respectively.
A method to identify shallow dopants in semiconductor nanowires
Authors: Huo H. B. , Liu C. , Dai L. , You L. P. , Yang W. Q. , Ma R. M. , Zhang Y. F. , Qin G. G.
Published: November 2007

In this paper, an electrical measurement method to identify shallow dopants in lowly doped semiconductor nanowires was suggested. Room temperature electrical measurement indicates that electron concentrations of the n-GaN nanowires are about 5.4×1017cm−3. Temperature-dependent measurement of conductivities of single nanowires in low temperature region gives activation energy of 13.3meV, which is consistent with the reported activation energy of 14meV for Si donor in n-GaN films with donor concentration of 7.4×1017cm−3. Our results confirm that the shallow donors in the as-synthesized GaN nanowires are silicon. We consider such a method may be applicable to other semiconductor nanowires.
Study of nonpolar m-plane InGaN∕GaN multiquantum well light emitting diodes grown by homoepitaxial metal-organic chemical vapor deposition
Authors: Kim Kwang-Choong , Schmidt Mathew C. , Sato Hitoshi , Wu Feng , Fellows Natalie , Jia Zhongyuan , Saito Makoto , Nakamura Shuji , DenBaars Steven P. , Speck James S. , Fujito Kenji
Published: November 2007

Nonpolar m-plane (11¯00) InGaN-based light emitting diodes (LEDs) grown on low-extended defect density bulk m-plane GaN substrates offer great potential for high performance devices due to the absence of polarization-related internal electric fields. To optimize the quantum well (QW) structure, systematic sets of near blue-ultraviolet LEDs using different well widths, barrier widths, and QW periods were packaged and tested. With increasing current, high power LEDs were realized with fairly flat external quantum efficiency and blueshift-free peak wavelength for QWs with thicknesses from 8to20nm, barrier widths from 10to22nm, and QW numbers from 4 to 10.
Reducing exciton-longitudinal-optical phonon interaction with shrinking ZnO quantum dots
Authors: Hsu Wei-Tse , Lin Kuo-Feng , Hsieh Wen-Feng
Published: November 2007

The exciton-longitudinal-optical-phonon (LO-phonon) interaction was observed to decrease with reducing ZnO particle size to its exciton Bohr radius (aB). The unapparent LO-phonon replicas of free exciton (FX) emission and the smaller FX energy difference between 13 and 300K reveal decreasing weighting of exciton-LO phonon coupling strength. The diminished Fröhlich interaction mainly results from the reducing aB with size due to the quantum confinement effect that makes the exciton less polar.
On spectral and thermal behaviors of AlGaInP light-emitting diodes under pulse-width modulation
Authors: Manninen Pasi , Orreveteläinen Pasi
Published: November 2007

Behavior of the emission spectrum, junction temperature, and charge carrier temperature of low-power AlGaInP light-emitting diodes (LEDs) with different colors under pulse-width-modulation (PWM) dimming is investigated. The blueshift of the peak wavelength and the bandwidth narrowing in the emission spectra of the studied LEDs with shortening pulse are found. A linear relation of the junction temperature and carrier temperature of the studied LEDs to their duty cycle is detected. Perceivable changes in color of AlGaInP LEDs under the PWM scheme are observed.
Diffuse double layer charging in nonpolar liquids
Authors: Beunis F. , Strubbe F. , Marescaux M. , Neyts K. , Verschueren A. R. M.
Published: November 2007

The presence of charges in nonpolar liquids is usually neglected. However, in some applications, they have important effects. In this work, an analytical description is given for the dynamics of diffuse double layers when a voltage step of the order of kT∕e is applied. Part of the result is an expression for the current, which is consistent with current measurements on nonpolar liquids and with other works. In measurements for higher voltages, we observe and briefly discuss nonlinear effects. From measurements both at high and at low voltages, we can obtain the same properties of the liquid.
Experiment demonstrates quantum entanglement between atoms a meter apart
Authors: Schwarzschild Bertram
Published: November 2007

Quantum entanglement can't be mimicked by classical objects. That's what makes it at once so problematic for philosophers and so promising for computer scientists.
New sheet structures may be the basis for boron nanotubes
Authors: Miller Johanna
Published: November 2007

The triangular boron lattice has too many electrons, and the hexagonal lattice has too few. But a hybrid of the two is just right.
CERN's fix-it man
Authors: Guinnessy Paul
Published: November 2007

As director general of CERN, Robert Aymar has perhaps the most visible job in particle physics today.
Sandia heads up new nanoengineering institute
Authors: Feder Toni
Published: November 2007

Preparing students to work in teams that cut across disciplines and research sectors is a key aim of Sandia's latest educational program.
Surface-enhanced Raman scattering
Authors: Kneipp Katrin
Published: November 2007

The remarkable 14-order-of-magnitude signal enhancement that can occur during Raman scattering from molecules on metallic nanostructures turns the normally weak inelastic-scattering effect into a single-molecule spectroscopic probe.