bluuebunny/crossref_metadata_2025 huggingface dataset:
Scales of variability of surface vegetation: Calculation and implications for climate models
Authors: Salmun Haydee , Molod Andrea , Albrecht Jochen , Santos Fernanda
Published: April 2009

The presence in the vegetation landscape of many varied scales of organization implies a complex set of land/atmosphere interactions. Larger scales of variability at the surface induce boundary layer heterogeneity and may induce secondary boundary layer circulation patterns. The quantification of the scales of heterogeneity in the surface vegetation, therefore, is essential to the understanding and modeling of the land/atmosphere interactions. The present study analyzes the scales of heterogeneity in the surface vegetation by using a satellite‐derived land class category map and a discrete analysis tool. Results show substantial variability in scales near 1000 km for most land class categories other than Deciduous Broadleaf Forest. Implications for GCM modeling approaches to the land/atmosphere interactions were drawn based on the results of the study. Results are consistent with the use of a ‘mosaic’ rather than a ‘mixture’ approach and with extending the ‘mosaic’ approach up through the boundary layer.
Structure and kinematics of the Indo‐Burmese Wedge: Recent and fast growth of the outer wedge
Authors: Maurin Thomas , Rangin Claude
Published: April 2009

The northern Sunda subduction zone, offshore Burma, and the associated Indo‐Burmese Wedge mark the active eastern boundary of the Burma Platelet jammed between the India Plate and the Sunda Plate. The aim of this paper is to provide a structural and kinematics analysis of the Indo‐Burmese Wedge based on seismic reflection, geodetic, and geological field data. We found out that the Indo‐Burmese Wedge is the place of diffuse strain partitioning: right‐lateral shearing in the innermost part and E‐W shortening in the outermost part. In the outer wedge, thick‐skinned deformation overprints thin‐skinned deformation. It can be explained by the required preservation of the critical taper after the fast westward propagation of the outer wedge above a very efficient clayey décollement layer. The thick‐skinned deformation is here characterized by major right‐lateral strike‐slip faults (the Kaladan Fault and the Chittagong Coastal Fault) and yet a typical internal deformation of the Indo‐Burmese Wedge. We suggest that the westward migration of internal right‐lateral shear deformation allows preservation of the strain‐partitioning ratios between internal N‐S trending right‐lateral shearing and external E‐W shortening. Some seismic lines show that the outer wedge deformation is not older than 2 Ma. Its propagation could have been enhanced by the large amount of sediments filling up the Sylhet flexural basin formed after the Pliocene tectonic uplift of the Shillong Plateau.
Slab segmentation revealed by anisotropic P‐wave tomography
Authors: Ishise Motoko , Koketsu Kazuki , Miyake Hiroe
Published: April 2009

Seismic anisotropy is a useful indicator for identifying the physical and chemical condition of the Earth's interior, such as stress and flow fields, and in situ constituent minerals. Using traveltime tomography, we examined three‐dimensional anisotropic P‐wave velocity structure of the Kii Peninsula, southwest Japan, where source regions of megathrust earthquakes along the Nankai Trough are presumed to exist. The tomography revealed that the Philippine Sea slab beneath the peninsula is segmented, i.e., a high‐velocity slab with E–W anisotropy obtained during seafloor spreading is broken by an anomalous low‐velocity region with N–S anisotropy. The anomaly lies along the segmentation boundary of two previous rupture zones, the 1944 Tonankai and 1946 Nankai earthquakes, and can be explained by the occurrence of a fracture zone with N–S oriented fractures and fault planes revealed by wide‐angle seismic data. It is likely that this anomalous region will form a clear segmentation boundary during future earthquakes.
Manual annotation of the mouse genome: HAVANA and EUCOMM
Authors: Thomas Mark
Published: April 2009

The European Conditional Mouse Mutagenesis (EUCOMM) project aims to establish a mutant resource containing up to 13,000 conditional mouse mutations in C57BL/6N embryonic stem cells. As part of this resource, up to 8,000 targeted conditional mutations will be generated for genes that can not be readily trapped by random gene trapping methods. Non-symmetrical critical exons are identified as part of the targeting approach, which when deleted produce a knockout (KO) transcript that is susceptible to nonsensemediated decay (NMD). The success of this approach is dependent on detailed and accurate genome annotation, which is provided by the Human and Vertebrate Analysis and Annotation (HAVANA) group at the Wellcome Trust Sanger Institute. Based on a combination of EST, cDNA and protein evidence, HAVANA produces high quality manual annotation of gene structures, that includes alternative splice variants, polyadenylation features, pseudogenes and gene family clusters. Using this annotation we are able to identify suitable exons for targeting, whilst minimising potential disruption to adjacent genomic features. Annotation of both gene and KO transcripts can be viewed through the Vertebrate Genome Annotation (VEGA) browser ("http://vega.sanger.ac.uk":http://vega.sanger.ac.uk).More information on the EUCOMM resource and the targeted genes is available at "http://www.eucomm.org":http://www.eucomm.org. Targeting vector design information can also be viewed through the Ensembl genome browser ("http://www.ensembl.org":http://www.ensembl.org) as DAS resources ("http://das.sanger.ac.uk/das/KO_designs":http://das.sanger.ac.uk/das/KO_designs ; "http://das.sanger.ac.uk/das/KO_vectors":http://das.sanger.ac.uk/das/KO_vectors). In addition to the EUCOMM project, HAVANA also contributes towards the mouse Consensus Coding DNA Sequence (CCDS) project and is involved in collaborations with RefSeq and MGI.
Stressed multidirectional solid-phase epitaxial growth of Si
Authors: Rudawski N. G. , Jones K. S. , Morarka S. , Law M. E. , Elliman R. G.
Published: April 2009

The study of the solid-phase epitaxial growth (SPEG) process of Si (variously referred to as solid-phase epitaxy, solid-phase epitaxial regrowth, solid-phase epitaxial crystallization, and solid-phase epitaxial recrystallization) amorphized via ion implantation has been a topic of fundamental and technological importance for several decades. Overwhelmingly, SPEG has been studied (and viewed) as a single-directional process where an advancing growth front between amorphous and crystalline Si phases only has one specific crystallographic orientation. However, as it pertains to device processing, SPEG must actually be considered as multidirectional (or patterned) rather than bulk in nature with the evolving growth interface having multiple crystallographic orientations. Moreover, due to the increasingly ubiquitous nature of stresses presented during typical Si-based device fabrication, there is great interest in specifically studying the stressed-SPEG process. This work reviews the progress made in understanding the multidirectional SPEG and, more importantly, stressed multidirectional SPEG process. For the work reviewed herein, (001) Si wafers with ⟨110⟩-aligned, intrinsically stressed Si3N4/SiO2 patterning consisting of square and line structures were used with unmasked regions of the Si substrate amorphized via ion implantation. It is revealed that the stresses generated in the Si substrate from the patterning, both in line and square structures, alter the kinetics and geometry of the multidirectional SPEG process and can influence the formation of mask-edge defects which form during growth to different degrees as per differences in the substrate stresses generated by each type of patterning. Likewise, it is shown that application of external stress from wafer bending during SPEG in specimens with and without patterning can also influence the geometry of the evolving growth interface. Finally, the effect of the addition of SPEG-enhancing impurities during multidirectional stressed growth is observed to alter the evolution of the growth interface, thus suggesting that stress influences on growth are much less than those from dopants. Within the context of prior work, attempts are made to correlate the prior observations in single-directional stressed SPEG with the observations from patterned stressed SPEG reviewed herein. However, as is argued in this review, it ultimately appears that much of the research performed on understanding the single-directional stressed-SPEG process cannot be reasonably extended to the multidirectional stressed-SPEG process.
Monte Carlo simulation of hot electron energy growth in a layered optimization scheme of ZnS thin film
Authors: Xu Zheng , Zhao Suling , He Qingfang , Ji Guorui , Zhang Fujun , Xu Xurong
Published: April 2009

We carried out Monte Carlo simulation and clarified the variation in electron energy in layered optimized electroluminescent ZnS with high electric field. We found that the following: (1) 8 eV is necessary for the energy of primary electrons entering the luminescent layer with an electric field of 4 MV/cm in order to enhance the excitation of luminescence. (2) The distributions of both the density of states and the hot electron energy concentrate and shift to the high energy end when the electric field increases; thus most of the hot electrons are effective in the excitation of luminescence. (3) The average energy of hot electrons is found to reach a second plateau in a stepwise manner along the increase in electric field corresponding to the second jump in electroluminescence in a layered optimization scheme.
Analytical solution of the skin effect problem with the displacement current in Maxwell plasma by the source method
Authors: Alabina Y. F. , Latyshev A. V. , Yushkanov A. A.
Published: April 2009

We found the analytical solution to the problem of the skin effect for Maxwell plasma with the use of the kinetic equation, where the frequency of electron collisions is constant. We use the specular reflection of electrons from the surface as a boundary condition. The behavior of impedance near to a plasma resonance is considered. We consider limiting cases of skin effect.
Study of thickness variation, morphology, and magnetic properties of Permalloy on organic monolayers
Authors: Ahmad S. N. , Shaheen S. A.
Published: April 2009

We have sputtered different thicknesses of Permalloy (Ni79Fe21) on self-assembled monolayers (SAMs) with polar (–COOH) and nonpolar (–CH3) organic functional groups and have observed interesting changes in morphology and magnetic properties. At very low thicknesses (∼1.5–3 nm) the morphology and magnetic properties of the deposited Permalloy are similar to those observed for isolated superparamagnetic clusters on both types of SAM surface. Further increase in the deposition (∼4 nm and above) of Permalloy results in a ferromagnetic film formation on the polar SAM, and superparamagnetic cluster formation remains apparent on the nonpolar SAM up to a thickness of 8 nm. The polarity of the organic underlayer plays a critical role in this regime. At higher thicknesses (∼12 nm and above) Permalloy exhibits usual ferromagnetic behavior on both types of SAM surfaces.
Drift ion acoustic shock waves in an inhomogeneous two-dimensional quantum magnetoplasma
Authors: Masood W. , Karim S. , Shah H. A. , Siddiq M.
Published: April 2009

Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous quantum plasma with neutrals in the background employing the quantum hydrodynamics (QHD) model. In this regard, a quantum Kadomtsev–Petviashvili–Burgers (KPB) equation is derived for the first time. It is shown that the ion acoustic wave couples with the drift wave if the parallel motion of ions is taken into account. Discrepancies in the earlier works on drift solitons and shocks in inhomogeneous plasmas are also pointed out and a correct theoretical framework is presented to study the one-dimensional as well as the two-dimensional propagation of shock waves in an inhomogeneous quantum plasma. Furthermore, the solution of KPB equation is presented using the tangent hyperbolic (tanh) method. The variation of the shock profile with the quantum Bohm potential, collision frequency, and ratio of drift to shock velocity in the comoving frame, v∗/u, are also investigated. It is found that increasing the number density and collision frequency enhances the strength of the shock. It is also shown that the fast drift shock (i.e., v∗/u>0) increases, whereas the slow drift shock (i.e., v∗/u<0) decreases the strength of the shock. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.
Strongly subluminal regime of optical-to-terahertz conversion in GaP
Authors: Bakunov M. I. , Tsarev M. V. , Bodrov S. B. , Tani M.
Published: April 2009

We introduce and investigate a special regime of terahertz generation in electro-optic crystals with ultrashort laser pulses, in which neither phase-matching nor Cherenkov radiation mechanism are efficient. This regime occurs under the conditions that the optical group refractive index is larger than the low-frequency phase refractive index of the crystal, and the spectral bandwidth of the laser pulse is smaller than the frequency of the phase-matched terahertz wave. In this regime, that can be realized for a Ti:sapphire laser in GaP, terahertz generation is provided by transient processes at the crystal boundaries. We study the peculiarities of the terahertz emission from a slab of GaP excited with a Ti:sapphire laser. In particular, we demonstrate a possibility to implement a pointlike source of terahertz radiation that can increase the resolution of terahertz apertureless near-field microscopy.
Correlated structural reordering and dopant redistribution in annealed polycrystalline CdTe
Authors: Consonni V. , Feuillet G.
Published: April 2009

Postdeposition heat treatments are found to strongly influence the structural and optical properties of chlorine doped polycrystalline CdTe films. From scanning electron microscopy images and diffraction measurements, annealing is shown to induce a major structural reordering. The strong texturation along the ⟨100⟩ orientation indicates that the overall crystalline quality has been considerably improved. Upon annealing, a bimodal distribution of grain sizes is also observed, which points out an abnormal grain growth mechanism. Additionally, deformation twins, which are detrimental for the transport properties, are replaced by thicker annealing twins. Through time-of-flight secondary ion mass spectroscopy and 4 K cathodoluminescence measurements, an overall decrease in the chlorine concentration and a spatial redistribution of chlorine atoms are evidenced and clearly correlated with the observed structural reordering: β acceptor complexes, which are commonly predominant in as-grown chlorine doped polycrystalline CdTe, are found to dissociate into chlorine donors and A centers upon annealing. This is attributed to the thermally activated diffusion of chlorine, which leads to its re-evaporation from the films. Furthermore, the low chlorine concentration in the annealed films allows one to infer a value of 135±3 meV for the ionization energy of the chlorine A centers, as deduced from the donor-acceptor pair position in the cathodoluminescence spectra.
Nonadiabatic corrections to rovibrational levels of H2
Authors: Pachucki Krzysztof , Komasa Jacek
Published: April 2009

The leading nonadiabatic corrections to rovibrational levels of a diatomic molecule are expressed in terms of three functions of internuclear distance: corrections to the adiabatic potential, the effective nuclear mass, and the effective moment of inertia. The resulting radial Schrödinger equation for nuclear motion is solved numerically yielding accurate nonadiabatic energies for all rovibrational levels of the H2 molecule. Results for states with J≤10 are in excellent agreement with previous calculations by Wolniewicz, and for states with J>10 are new.
Addition effect of SnO in optical property of Bi2O3-containing aluminoborate glass
Authors: Masai Hirokazu , Takahashi Yoshihiro , Fujiwara Takumi
Published: April 2009

We have found that an addition of SnO in a bismuth-containing aluminoborate glass, (CaO–B2O3–Bi2O3–Al2O3–TiO2) (CaBBAT), decreases both the optical absorption coefficient in the visible region and the relative intensity of x-ray photoelectron spectroscopy (XPS) signal at 157 eV. Since signal intensity of electron spin resonance (ESR) at g=1.95 also decreased with increasing amount of SnO, it is suggested that bismuth radical-like species exist in the glass and that SnO reacts with the bismuth species. Concentration dependence of SnO in the XPS and in the ESR spectra shows that we can assign the observed signal to bismuth radical species in the glass. We, therefore, conclude that there is qualitative correlation between the optical absorption in the visible region and bismuth radical species in the CaBBAT glass.
High temperature thermoelectric properties of double-filled InxYbyCo4Sb12 skutterudites
Authors: Peng Jiangying , He Jian , Su Zhe , Alboni Paola N. , Zhu Song , Tritt Terry M.
Published: April 2009

Void filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proved effective in enhancing their thermoelectric performance. In this paper we report the effects of (In,Yb) double filling on the high temperature thermoelectric properties of CoSb3. The InxYbyCo4Sb12 (0≤(x,y)≤0.2) samples have been prepared via a melting-annealing-sintering procedure and characterized by means of x-ray powder diffraction, scanning electron microscopy, Hall coefficient, electrical and thermal conductivities, and Seebeck coefficient measurements. As compared to the In and Yb single-filling approach, the (In,Yb) double-filling approach can effectively reduce the lattice thermal conductivity without degrading the power factor. As a result, several compositions achieve ZT values around unity, while a maximum ZT value of 1.1 is obtained in In0.2Yb0.1Co4Sb12 at 700 K. The difference in the effects of In and Yb filling on the thermoelectric properties is discussed.
Void shape evolution and formation of silicon-on-nothing structures during hydrogen annealing of hole arrays on Si(001)
Authors: Sudoh K. , Iwasaki H. , Hiruta R. , Kuribayashi H. , Shimizu R.
Published: April 2009

We have studied the structural evolution of voids in the Si substrate and the formation of silicon-on-nothing (SON) structures upon spontaneous reshaping of square arrays of cylindrical holes on Si(001) substrates by hydrogen annealing. Vertically elongated voids covered with {111}, {100}, {110}, and {113} facets are initially formed by the closure of the hole inlets. This step is followed by volume preserving shape changes of the faceted voids in the bulk Si. In situations where the hole-hole separation is sufficiently small, void coalescence occurs due to the shape changes of individual voids, leading to the formation of a SON structure. Until void coalescence, the shapes of individual voids change without being affected by the adjacent voids. Numerical simulations of the shape change of a completely faceted void via solely surface diffusion have been performed and have reproduced the observed shape change.
Exciton and biexciton emission from a single InAs/InP quantum dash
Authors: Sęk G. , Podemski P. , Musiał A. , Misiewicz J. , Hein S. , Höfling S. , Forchel A.
Published: April 2009

Molecular beam epitaxy grown InAs/InGaAlAs/InP quantum dashes designed for the 1.5 μm range were investigated by microphotoluminescence spectroscopy. The exciton and biexciton emission from a single quantum dash was detected revealing a biexciton binding energy of about 0.4 meV. The dependence of the photoluminescence intensity versus the excitation power density was determined and analyzed using the three level rate equation model, which allowed to confirm that the observed lines originate from the same single quantum dash.
Performance optimization of resonant cavity enhanced n-GaAs homojunction far-infrared detectors: A theoretical study
Authors: Zheng M. M. , Zhang Y. H. , Shen W. Z.
Published: April 2009

The n-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared (FIR) detector is investigated to improve the quantum efficiency by simulation. The main structure, the bottom mirror, and the top mirror for the resonant cavity enhanced detector are optimized step by step. Two designs of the bottom mirror are suggested and compared. One consists of a bottom contact layer and one period of undoped/doped GaAs layers; the other is composed of a bottom contact layer, an undoped GaAs layer, and a gold layer. The results show that both mirrors enhance the quantum efficiency significantly and the gold mirror seems to be a better choice if not considering the technical difficulty. Preliminary study of the top mirror is also conducted. The top mirror shows a satisfactory effect under the condition that the reflectivity of the bottom mirror is high enough. The resulting quantum efficiency can be as high as 29.0% theoretically, which is much higher than p-GaAs and Si HIWIP FIR that was ever reported.
Osmotic compression of droplets of hard rods: A computer simulation study
Authors: Trukhina Yu. , Jungblut S. , van der Schoot P. , Schilling T.
Published: April 2009

By means of computer simulations, we study how droplets of hard, rodlike particles optimize their shape and internal structure under the influence of the osmotic compression caused by the presence of spherical particles that act as depletion agents. At sufficiently high osmotic pressures, the rods that make up the drops spontaneously align to turn them into uniaxial nematic liquid-crystalline droplets. The nematic droplets or “tactoids” that are formed this way are not spherical but elongated, resulting from the competition between the anisotropic surface tension and the elastic deformation of the director field. In agreement with recent theoretical predictions, we find that sufficiently small tactoids have a uniform director field, while large ones are characterized by a bipolar director field. From the shape and director-field transformation of the droplets, we are able to estimate the surface anchoring strength and an average of the elastic constants of the hard-rod nematic.
Effect of ion suprathermality on arbitrary amplitude dust acoustic waves in a charge varying dusty plasma
Authors: Tribeche Mouloud , Mayout Saliha , Amour Rabia
Published: April 2009

Arbitrary amplitude dust acoustic waves in a high energy-tail ion distribution are investigated. The effects of charge variation and ion suprathermality on the large amplitude dust acoustic (DA) soliton are then considered. The correct suprathermal ion charging current is rederived based on the orbit motion limited approach. In the adiabatic case, the variable dust charge is expressed in terms of the Lambert function and we take advantage of this transcendental function to show the existence of rarefactive variable charge DA solitons involving cusped density humps. The dust charge variation leads to an additional enlargement of the DA soliton, which is less pronounced as the ions evolve far away from Maxwell–Boltzmann distribution. In the nonadiabatic case, the dust charge fluctuation may provide an alternate physical mechanism causing anomalous dissipation the strength of which becomes important and may prevail over that of dispersion as the ion spectral index κ increases. Our results may provide an explanation for the strong spiky waveforms observed in auroral electric field measurements by Ergun et al. [Geophys. Res. Lett. 25, 2025 (1998)].
Obliquely propagating low frequency electromagnetic shock waves in two dimensional quantum magnetoplasmas
Authors: Masood W.
Published: April 2009

Linear and nonlinear propagation characteristics of low frequency magnetoacoustic waves in quantum magnetoplasmas are studied employing the quantum magnetohydrodynamic model. In this regard, a quantum Kadomtsev–Petviashvili–Burgers (KPB) equation is derived using the small amplitude expansion method. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. Furthermore, the solution of KPB equation is presented using the tangent hyperbolic (tanh) method. The variation in the fast and slow magnetoacoustic shock profiles with the quantum Bohm potential via increasing number density, obliqueness angle θ, magnetic field, and the resistivity are also investigated. It is observed that the aforementioned plasma parameters significantly modify the propagation characteristics of nonlinear magnetoacoustic shock waves in quantum magnetoplasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.
Spatial evolution of a film flowing down a fiber
Authors: Duprat C. , Ruyer-Quil C. , Giorgiutti-Dauphiné F.
Published: April 2009

We report the response to a forcing at the inlet of a film flowing down a vertical fiber. Parameters are chosen in order to examine the effects of both inertia and surface tension. The spatial response of the film to inlet forcing depends on the ratio of the forcing frequency ffor to the frequency fM corresponding to the maximum linear growth rate. At ffor≈fM, the primary instability leads directly to the formation of a saturated wavetrain at the forcing frequency, whereas at low forcing frequencies ffor<fM, this formation is preceded by a sequence of periodic coalescence events. The amplitude, speed, profiles, and inner flow pattern of traveling waves have been characterized and compared to the solutions to the two-equation model obtained by Ruyer-Quil et al. [J. Fluid Mech. 603, 431 (2008)], showing a remarkable agreement. A steepening of the waves is observed when inertia becomes dominant. An excellent correlation between data is observed when the amplitude and speed of the waves are made dimensionless with reference to the substrate thickness and free-surface velocity.
Frequency noise in frequency modulation atomic force microscopy
Authors: Kobayashi Kei , Yamada Hirofumi , Matsushige Kazumi
Published: April 2009

Atomic force microscopy (AFM) using the frequency modulation (FM) detection method has been widely used for atomic/molecular-scale investigations of various materials. Recently, it has been shown that high-resolution imaging in liquids by the FM-AFM is also possible by reducing the noise-equivalent displacement in the cantilever displacement sensor and by oscillating the cantilever at a small amplitude even with the extremely reduced Q-factor due to the hydrodynamic interaction between the cantilever and the liquid. However, it has not been clarified how the noise reduction of the displacement sensor contributes to the reduction in the frequency noise in the FM-AFM in low-Q environments. In this article, the contribution of the displacement sensor noise to the frequency noise in the FM-AFM is described in detail to show how it is important to reduce the noise-equivalent displacement in the displacement sensor especially in low-Q environments.
Integrated simulations of implosion, electron transport, and heating for direct-drive fast-ignition targets
Authors: Solodov A. A. , Anderson K. S. , Betti R. , Gotcheva V. , Myatt J. , Delettrez J. A. , Skupsky S. , Theobald W. , Stoeckl C.
Published: April 2009

A thorough understanding of future integrated fast-ignition experiments combining compression and heating of high-density thermonuclear fuel requires hybrid (fluid+particle) simulations of the implosion and ignition process. Different spatial and temporal scales need to be resolved to model the entire fast-ignition experiment. The two-dimensional (2D) axisymmetric hydrocode DRACO [P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)] and the 2D/three-dimensional hybrid particle-in-cell code LSP [D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. A 464, 134 (2001)] have been integrated to simulate the implosion and heating of direct-drive, fast-ignition fusion targets. DRACO includes the physics required to simulate compression, ignition, and burn of fast-ignition targets. LSP simulates the transport of hot electrons from the place where they are generated to the dense fuel core where their energy is absorbed. The results from integrated simulations of cone-in-shell CD targets designed for fast-ignition experiments on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997); C. Stoeckl et al., Fusion Sci. Technol. 49, 367 (2006)] are presented. Target heating and neutron yields are computed. The results from LSP simulations of electron transport in solid-density plastic targets are also presented. They confirm an increase in the electron divergence angle with the laser intensity in the current experiments. The self-generated resistive magnetic field is found to collimate the hot-electron beam and increase the coupling efficiency of hot electrons with the target. Resistive filamentation of the hot-electron beam is also observed.
Critical cavity in the stretched fluid studied using square-gradient density-functional model with triple-parabolic free energy
Authors: Iwamatsu Masao
Published: April 2009

The generic square-gradient density-functional model with triple-parabolic free energy is used to study the stability of a cavity introduced into the stretched liquid. The various properties of the critical cavity, which is the largest stable cavity within the liquid, are compared with those of the critical bubble of the homogeneous bubble nucleation. It is found that the size of the critical cavity is always smaller than that of the critical bubble, while the work of formation of the former is always higher than the latter in accordance with the conjectures made by Punnathanam and Corti [J. Chem. Phys. 119, 10224 (2003)] deduced from the Lennard–Jones fluids. Therefore their conjectures about the critical cavity size and the work of formation would be more general and valid even for other types of liquid such as metallic liquid or amorphous. However, the scaling relations they found for the critical cavity in the Lennard–Jones fluid are marginally satisfied only near the spinodal.
The electronic spectrum of the fluoroborane free radical. I. Theoretical calculation of the vibronic energy levels of the ground and first excited electronic states
Authors: Sunahori Fumie X. , Clouthier Dennis J. , Carter Stuart , Tarroni Riccardo
Published: April 2009

The fluoroborane (HBF) free radical has a large vibronic interaction which splits the orbitally degenerate Π2 state in the linear configuration into two separate electronic states, one strongly bent and one linear. The observed vibrational structure of the electronic transition between the Renner–Teller pair of states is very complex. As an aid to understanding the spectrum, the vibronic energy levels of the ground and first excited states have been calculated from high-level ab initio potential energy surfaces using a variational method. The vibrational frequencies and anharmonicities have been derived from these energy levels and the boron and hydrogen isotope shifts have been predicted. Although the ground state energy levels are for the most part well behaved, the excited state levels show substantial Renner–Teller mixing with nearby ground vibrational states. The calculations in the present work have been successfully used in the companion paper to make vibrational assignments of the laser-induced fluorescence spectra of HBF and DBF.
The electronic spectrum of the fluoroborane free radical. II. Analysis of laser-induced fluorescence and single vibronic level emission spectra
Authors: Sunahori Fumie X. , Clouthier Dennis J.
Published: April 2009

Subsequent to our spectroscopic detection of the HBX (X=F, Cl, Br) free radicals (S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)), the electronic spectrum of the Ã A2″Π-X̃ A2′ system of the fluoroborane (HBF) radical in the 600–745 nm region has been studied in detail using the pulsed discharge jet technique. The band system involves a linear-bent transition between the two Renner–Teller components of what would be a Π2 state at linearity. Using the results of our theoretical study of the ground and excited state vibrational energy levels and B11–B10 isotope shifts (see the companion paper), the vibrational quantum numbers of the bands in the laser-induced fluorescence (LIF) spectra have been assigned. Rotational and vibrational analyses of the LIF and wavelength resolved emission spectra have been carried out, from which the linear excited state and the bent ground state equilibrium configurations have been confirmed. The ground state molecular geometry of HBF has been determined as r0(BH)=1.214(2) Å, r0(BF)=1.303 4(5) Å, and θ=120.7(1)°. Based on high-level ab initio calculations and symmetry considerations, predissociation of the excited state into H(S2)+BF(Σ1+) on the ground state potential energy surface is identified as the cause of the breaking off of fluorescence in the LIF spectra.
Dynamics of normal to diffuse and relaxor phase transition in lead metaniobate-based ferroelectric ceramics
Authors: Venet Michel , M’Peko Jean-Claude , Zabotto Fabio Luis , Guerrero Fidel , Garcia Ducinei , Eiras José Antonio
Published: April 2009

Tetragonal tungsten bronze-structured materials based on lead metaniobate (PbNb2O6) were studied in terms of thermal dynamics of dielectric properties, showing ferroelectric-to-paraelectric phase transition of diffuse and relaxor type in some specific cases. These features are normally ascribed to defects-induced structural disorder and compositional fluctuations associated with an arbitrary lattice site occupation between dopant and host ions. Nevertheless, for these lead metaniobate-based materials, the drastic change in the phase transition from normal to diffuse and relaxor is shown to take place when dopants are able to significantly shift the transition toward low temperatures, where these compounds are known to exhibit incommensurate superstructures that naturally present diffuse and relaxor dielectric characteristics.
Excited states of Nb3N2 and Nb3C2: Density functional theory, CASSCF, and MRCI studies
Authors: Addicoat Matthew A. , Metha Gregory F.
Published: April 2009

Complete active space self-consistent field (CASSCF) and multireference configuration interaction (MRCI) methods are used to investigate the Nb3N2 and Nb3C2 clusters in order to determine the agreement between multireference methods, density functional theory (DFT), and experiment. These two clusters are ideal candidates to study as the known spectroscopy can serve to validate the computational results, yet there is still room for the calculations to inform further spectroscopic experiments. We find that the MRCI leading configuration for each of the ground states is in agreement with that predicted by DFT but only accounts for up to 70% of the total configuration. CASSCF and DFT geometries are also in general agreement. Transition energies between the neutral and cationic manifolds are found to be poorly predicted by MRCI relative to the computationally cheap DFT method. For Nb3C2 we find that a higher energy isomer may have an electronic transition in the spectral vicinity as the lowest energy isomer.
Mediation of chain reactions by propagating radicals during halogenation of H-masked Si(100): Implications for atomic-scale lithography and processing
Authors: Ferng Shyh-Shin , Wu Shiao-Ting , Lin Deng-Sung , Chiang Tai C.
Published: April 2009

Scanning tunneling microscopy reveals a free radical-induced surface chain reaction in the chlorination of nanoscale patterns on an otherwise H-passivated (masked) Si(100). While scanning probe methods can be used to pattern active surface regions with single-bond precision, follow-up selective chemical vapor deposition with polyatomic molecules can produce various filling characteristics. On active surface regions, molecular Cl2 undergoes an atom abstraction reaction in which a Si dangling bond abstracts one atom of the incident Cl2 molecule while the complementary Cl atom is scattered away from the initial abstraction site either back into the vacuum or to be captured by a second dangling bond and adsorbed there, or to react with a nearby adsorbed H atom to form volatile HCl. In contrast, I2 undergoes only dissociative adsorption on two immediately neighboring dangling bonds, whereby two I–Si bonds are formed simultaneously upon cleavage of the I2 bond. The different chemisorption processes of the two model diatomic molecular gases place intrinsic limitations on atomic-scale lithography and processing: Adsorption of Cl2 results in spillage over the prepatterned regions of active bonds. In contrast, adsorption of I2 is a pair process and results in under-filling.
Nanoposition sensors with superior linear response to position and unlimited travel ranges
Authors: Lee Sheng-Chiang , Peters Randall D.
Published: April 2009

With the advancement in nanotechnology, the ability of positioning/measuring at subnanometer scale has been one of the most critical issues for the nanofabrication industry and researchers using scanning probe microscopy. Commercial nanopositioners have achieved direct measurements at the scale of 0.01 nm with capacitive sensing metrology. However, the commercial sensors have small dynamic ranges (up to only a few hundred micrometers) and are relatively large in size (centimeters in the transverse directions to the motion), which is necessary for healthy signal detections but making it difficult to use on smaller devices. This limits applications in which large materials (on the scale of centimeters or greater) are handled with needs of subnanometer resolutions. What has been done in the past is to combine the fine and coarse translation stages with different dynamic ranges to simultaneously achieve long travel range and high spatial resolution. In this paper, we present a novel capacitive position sensing metrology with ultrawide dynamic range from subnanometer to literally any practically desired length for a translation stage. This sensor will greatly simplify the task and enhance the performance of direct metrology in a hybrid translational stage covering translation tasks from subnanometer to centimeters.
Corner liquid imbibition during capillary penetration in lithographically made microchannels
Authors: Girardo S. , Cingolani R. , Chibbaro S. , Diotallevi F. , Succi S. , Pisignano D.
Published: April 2009

The authors investigate the formation of liquid layers at corners of lithographically made microchannels during capillary filling. The microflow and shape of the liquid-air interface is studied through an optically transparent microfluidic device. The experimental findings at early stages of layer formation are supported by three-dimensional lattice Boltzmann simulations, allowing to predict the shape and dynamics of the corner films and highlighting their dependence on the fluid contact angle.
Improvement of subthreshold swing of n-channel transistor by uniaxial tensile stress due to a quantum mechanical mechanism instead of physical thinning
Authors: Lau W. S. , Yang Peizhen , Lai Seow Wei , Lo V. L. , Siah S. Y. , Chan L.
Published: April 2009

Physical thinning of the gate dielectric due to uniaxial tensile stress is expected to improve the subthreshold swing (Sts) of both n-channel and p-channel metal-oxide-semiconductor (MOS) transistors. However, experimentally, we observed a small improvement in Sts of n-channel MOS transistors but a small degradation in Sts of p-channel MOS transistors due to the application of uniaxial tensile stress. Uniaxial tensile stress modifies the out-of-plane effective mass of electrons or holes, resulting in a change in Sts, which can be predicted by quantum mechanics.
Study of a nitrogen-doped ZnO film with synchrotron radiation
Authors: Zou C. W. , Yan X. D. , Han J. , Chen R. Q. , Gao W. , Metson J.
Published: April 2009

X-ray absorption near-edge spectroscopy (XANES) and photoelectron spectroscopy (PES) with synchrotron radiation have been applied to investigate the structure and chemical states of nitrogen atoms in ZnO:N films with different annealing temperatures. The high-resolution XANES and PES spectra of N 1s reveal the chemical states of N dopants and give a direct observation of nitrogen location in the ZnO films. The results indicate that only the nitrogen atoms incorporated substitutionally at O sites act as acceptors, and contribute to the p-type characteristic of the ZnO:N film.
Absolute vacuum ultraviolet flux in inductively coupled plasmas and chemical modifications of 193 nm photoresist
Authors: Titus M. J. , Nest D. , Graves D. B.
Published: April 2009

Vacuum ultraviolet (VUV) photons in plasma processing systems are known to alter surface chemistry and may damage gate dielectrics and photoresist. We characterize absolute VUV fluxes to surfaces exposed in an inductively coupled argon plasma, 1–50 mTorr, 25–400 W, using a calibrated VUV spectrometer. We also demonstrate an alternative method to estimate VUV fluence in an inductively coupled plasma (ICP) reactor using a chemical dosimeter-type monitor. We illustrate the technique with argon ICP and xenon lamp exposure experiments, comparing direct VUV measurements with measured chemical changes in 193 nm photoresist-covered Si wafers following VUV exposure.
Mn–Mn couplings in Mn-doped CdS nanocrystals studied by magnetic circular dichroism spectroscopy
Authors: Taguchi Seiji , Ishizumi Atsushi , Tayagaki Takeshi , Kanemitsu Yoshihiko
Published: April 2009

We report on the optical and magnetic properties of Mn-doped CdS nanocrystals coated with a ZnS shell layer (CdS:Mn/ZnS core-shell nanocrystals) by magnetic circular dichroism (MCD) spectroscopy. The magnetic field and temperature dependences of the MCD spectrum show paramagnetic behavior of the CdS:Mn/ZnS core-shell nanocrystals. The MCD intensity increases with the Mn concentration up to a few mol %, and then starts to decrease rapidly. This Mn-concentration dependence of the MCD intensity can be explained by the formation of Mn–Mn pairs in heavily doped nanocrystals.
Time-reversal focusing of therapeutic ultrasound on targeted microbubbles
Authors: Couture Olivier , Aubry Jean-François , Tanter Mickael , Fink Mathias
Published: April 2009

Targeted microbubbles bind specifically to molecular markers of diseases and their unique acoustic signature is used to image cellular processes in vivo. The ability of time-reversal processing to focus waves through heterogeneities on such targeted microbubbles is demonstrated. For this purpose, microbubbles were deposited on a gelatin phantom and their specific signal was recorded by a high intensity ultrasonic array. The amplified time-reversed signal was re-emitted and shown to focus back in the region where the bound microbubbles were present. This proof of concept emphasizes that molecular-time-reversal focusing could guide energy deposition on early, diffuse, or metastatic disease.
Manipulation of spin polarization by charge polarization in GaMnN ferromagnetic resonant tunneling diode
Authors: Wang Jiqing , Liu Yan , Mao Huibing , Zhao Qiang , Yu Jianguo , Zhang Yong , Zhu Ziqiang , Chu Junhao
Published: April 2009

We have investigated the dependence of spin polarization on charge polarization at room temperature in GaMnN-based ferromagnetic resonant tunneling structures with different Mn doping positions. Our results show that compared to the nonpolarization case, the degree of spin polarization can be enhanced by two to four times and resonant current intensity increases about fourfold at a moderate polarized-charge concentration of 1012/cm2. In addition, the dipole right case in magnetic resonant diodes has stronger impact on spin tunneling than the opposite one. These results demonstrate that tailoring charge polarization is a feasible way to tune electron spin polarization in piezoelectric-type ferromagnetic heterostructures.
Effect of vacancy defects in graphene on metal anchoring and hydrogen adsorption
Authors: Kim Gyubong , Jhi Seung-Hoon , Lim Seokho , Park Noejung
Published: April 2009

The dispersion of transition and alkaline-earth metals on defective graphenes is studied using first-principles calculations. The effect of vacancy defects on binding properties of metal atoms to the graphene and with hydrogen molecules is particularly investigated. It is shown that vacancy defects enhance efficiently the metal binding energy and thus its dispersion, particularly for alkaline-earth metals. Mg on vacancy defects shows a substantial increase in its binding energy and hydrogen uptake capacity. Among metals considered, Ca-vacancy complexes are found to exhibit the most favorable hydrogen adsorption characteristics in terms of the binding energy and the capacity.
Theory of competitive adsorption-nucleation in polypeptide-mediated biomineralization
Authors: Muthukumar M.
Published: April 2009

The process of biomineralization occurs in various natural organisms with astonishing ease by the interplay between polymers and mineralization but eludes a fundamental understanding. In addressing how specific polymers direct selection of mineral morphologies and their growth kinetics, we present a new model based on a competition between adsorption of polymers onto selective interfaces and nucleation growth of minerals. The model is couched in the context of zinc oxide, crystallized from solutions containing polypeptides, where systematic experimental data are available. Adsorption of the polymer onto certain crystallographic planes leads to poisoning of the surfaces, and as a result these surfaces are arrested from further growth. By this mechanism, originally disfavored growth sectors are promoted to grow by suppressing the initial faster growing sectors. Our theory predicts the relative growth rates of different sectors altered by selective adsorption of polymers. Theoretical prediction of the dependence of the aspect ratio on polypeptide concentration is in agreement with experimental results, providing credence to the applicability of adsorption-nucleation models to polymer-mediated biomineralization.
Scaling of light emitting transistor for multigigahertz optical bandwidth
Authors: Wu C. H. , Walter G. , Then H. W. , Feng M. , Holonyak N.
Published: April 2009

We report for an n-InGaP/p-AlGaAs/i-InGaAs-QW/n-GaAs heterojunction bipolar light emitting transistor (HBLET) the record spontaneous optical-signal bandwidth, at −3 dB, of 1.8–4.3 GHz (corresponding to an effective carrier recombination lifetime of 37 ps). Besides the improved circuit matching of three-terminal device operation, the extension in performance is achieved by the lateral reduction in the emitter aperture size DA from 13 to 5 μm to provide higher injection current densities and better confinement of the radiative recombination in the base region. By reducing the carrier loss to lateral extrinsic recombination, we obtain with HBLETs higher current gains β(=ΔIC/ΔIB>30) and simultaneously >4 GHz optical bandwidths.
Foreword to Special Issue: Papers from the 50th Annual Meeting of the APS Division of Plasma Physics, Dallas, Texas, 2008
Authors: Bhattacharjee Amitava , Davidson Ronald C.
Published: April 2009

The year 2008 marked the 50th Anniversary of the Division of Plasma Physics (DPP) of the American Physical Society. This Special Issue presents many of the Review, Tutorial, and Invited papers that were presented at the 2008 Annual Meeting of the DPP, which was held 17–21 November, in Dallas, Texas. We are very pleased that many of the speakers have submitted an archival-quality version of their presentation for peer review and publication in Physics of Plasmas.