bluuebunny/crossref_metadata_2025 huggingface dataset:
Miniature pulsed magnet system for synchrotron x-ray measurements
Authors: van der Linden Peter J. E. M. , Mathon Olivier , Strohm Cornelius , Sikora Marcin
Published: July 2008

We have developed a versatile experimental apparatus for synchrotron x-ray measurements in pulsed high magnetic fields. The apparatus consists of a double cryostat incorporating a liquid nitrogen bath to cool the miniature pulsed coil and an independent helium flow cryostat allowing sample temperatures from 4 up to 250K. The high duty cycle miniature pulsed coils can generate up to 38T. During experiments at 30T a repetition rate of 6pulses∕min was routinely reached. Using a 4kJ power supply, the pulse duration was between 500μs and 1ms. The setup was used for nuclear forward scattering measurements on Fe57 up to 25T on the ESRF beamline ID18. In another experiment, x-ray magnetic circular dichroism was measured up to 30T on the ESRF energy dispersive beamline ID24.
A hierarchical transition state search algorithm
Authors: del Campo Jorge M. , Köster Andreas M.
Published: July 2008

A hierarchical transition state search algorithm is developed and its implementation in the density functional theory program deMon2k is described. This search algorithm combines the double ended saddle interpolation method with local uphill trust region optimization. A new formalism for the incorporation of the distance constrain in the saddle interpolation method is derived. The similarities between the constrained optimizations in the local trust region method and the saddle interpolation are highlighted. The saddle interpolation and local uphill trust region optimizations are validated on a test set of 28 representative reactions. The hierarchical transition state search algorithm is applied to an intramolecular Diels–Alder reaction with several internal rotors, which makes automatic transition state search rather challenging. The obtained reaction mechanism is discussed in the context of the experimentally observed product distribution.
Top grating index-coupled distributed feedback quantum cascade lasers
Authors: Carras M. , Garcia M. , Marcadet X. , Parillaud O. , De Rossi A. , Bansropun S.
Published: July 2008

We report on the modeling and design of top grating distributed feedback (DFB) quantum cascade lasers (QCLs). A low loss, index-coupled, DFB design that is very robust against technological spreads is proposed. Strong DFB coupling conditions are obtained while maintaining a high laser output power. Following this design, DFB QCL lasers with InP cladding layers and InGaAs∕AlInAs active regions have been fabricated. Room temperature monomode QCLs with 30dB side mode suppression ratios are demonstrated over a 4–8μm wavelength range.
Hydrogen peroxide formation following the vacuum ultraviolet photodissociation of water ice films at 90K
Authors: Yabushita Akihiro , Hama Tetsuya , Iida Daisuke , Kawasaki Masahiro
Published: July 2008

The production of gaseous OH radicals from the 300–350nm photodissociation of H2O2 that was photolytically produced on a water ice surface following the 157nm photolysis of water ice at 90K was directly monitored using resonance-enhanced multiphoton ionization. The translational energy distribution estimated by the time-of-flight spectrum of the OH products is represented by a Maxwell–Boltzmann energy distribution with a translational temperature of 3750±250K. The rotational temperature was estimated by a spectral simulation to be 225±25K. Surface defects produced by HCl deposition on the water ice contributed to the higher production rate of H2O2 in the 157nm photoirradiation of water ice while surface coverage caused by CD3OH deposition decreased the H2O2 production rate.
Piris natural orbital functional study of the dissociation of the radical helium dimer
Authors: Piris M. , Matxain J. M. , Ugalde J. M.
Published: July 2008

We have investigated the dissociation behavior of the radical helium dimer He2+ using the Piris natural orbital functional (PNOF). This system is particularly challenging to be described by standard density functionals. The restricted open formulation of the PNOF-2, as well as the PNOF-2 energy plus the extended Koopmans’ vertical ionization potential calculations of the neutral helium dimer, have been tested for calculating the ground-state energies of He2+ as a function of the internuclear distance. For comparison, we present the dissociation curve obtained with the diffusion Monte Carlo method. The dissociation energies, equilibrium bond lengths, and rovibrational levels are reported. The obtained potential energy curves indicate that PNOF-2 yields a correct and accurate dissociation behavior for the helium radical dimer.
Nonthermal power dissipation and nonlinear wave dynamics in a plasma penetrated by a momentum-scattered relativistic electron stream
Authors: Guillory J. , Rose D. V. , Beall J. H.
Published: July 2008

A previous analysis of the nonlinear dissipative equilibrium of a beam-penetrated plasma with nonthermal electron “tails” [D. V. Rose, J. Guillory, and J. H. Beall, Phys. Plasmas 9, 1000 (2002)] is extended to the case of a relativistic, momentum-angle-scattered electron beam (with or without accompanying ions) penetrating a fully ionized low-density nearly collisionless plasma, and to include the energy balance of the nonthermal plasma tail electron population on electron collisional timescales long compared with the primary instability growth time. Quasistationary nonlinear “dissipative equilibrium” states are quantified for various ranges of relativistic beam parameters and various tail-enhanced Landau damping rates for shorter-wavelength space-charge waves. Conditions for quasisteady wave populations are found, and for energy balance between beam energy input to and dynamic friction cooling of the nonthermal “tail electrons.” Finally, some potentially incorrect inferences based on a thermal interpretation of bremsstrahlung from such a plasma are quantified. All of these microphysical processes evolve on timescales inaccessible to conventional magnetohydrodynamic modeling of astrophysical jets, and may lead to energetics corrections to such fluid models.
Analysis on magnetic field dependence of magneto-optical Faraday effect
Authors: Wang Wei , Liu Gongqiang
Published: July 2008

In this paper, the complicated relations between Faraday rotation and external magnetic field in various circumstances are theoretically deduced using magneto-optical four-level model. A linear field dependence of the Faraday rotation in extremely strong magnetic field or at high temperatures is revealed. Our theory also shows that the Faraday rotation presents an obvious nonlinear field-dependence property in a general magnetic field and at low temperatures. Furthermore, this nonlinear relationship can be simply described as θF=θFs+aHe+bHe2. In addition, a fit to the experimental results in Dy3−xBixFe5O12 (Bi-DyIG) under different magnetic fields is obtained. Meanwhile, it is pointed out that the parameters V1 and V2 have the anisotropy and temperature-dependence characteristic, which will also result in the anisotropic and temperature properties of magneto-optical Faraday effect in Bi-DyIG.
Reversing exchange bias in thermally assisted magnetic random access memory cell by electric current heating pulses
Authors: Papusoi C. , Sousa R. C. , Dieny B. , Prejbeanu I. L. , Conraux Y. , Mackay K. , Nozières J. P.
Published: July 2008

The temperature required to set the exchange bias of a ferro∕antiferromagnetic (F∕AF) storage bilayer as a function of the heating pulse width was studied on magnetic tunnel junctions (MTJs) of thermally assisted magnetic random access memories. Heating is produced by a pulse of electric current flowing through the junction. For sufficiently long heating pulse (>20ns), a quasiequilibrium temperature profile is reached in the MTJ. In this stationary regime, a relationship between the temperature of the storage layer and the power of the pulse was established by using an Arrhenius–Néel model of thermal relaxation. The introduction of thermal barriers between the junction tunnel barrier and the electrodes allows a significant reduction of the power required to achieve a given temperature rise of the storage layer. When the heating pulse duration is reduced from 1sto2ns, the heating power required for setting the F∕AF storage bilayer increases by about 80%. This experimental observation is quantitatively interpreted by combining the Arrhenius–Néel model with thermodynamic simulations of heat diffusion with source term given by the experimentally known heating power dissipated in the tunnel barrier by Joule effect.
Microscopic solvation of a lithium atom in water-ammonia mixed clusters: Solvent coordination and electron localization in presence of a counterion
Authors: Pratihar Subha , Chandra Amalendu
Published: July 2008

The microsolvation structures and energetics of water-ammonia mixed clusters containing a lithium atom, i.e., Li(H2O)n(NH3), n=1–5, are investigated by means of ab initio theoretical calculations. Several structural aspects such as the solvent coordination to the metal ion and binding motifs of the free valence electron of the metal are investigated. We also study the energetics aspects such as the dependence of vertical ionization energies on the cluster size, and all these structural and energetics aspects are compared to the corresponding results of previously studied anionic water-ammonia clusters without a metal ion. It is found that the Li–O and Li–N interactions play a very important role in stabilizing the lithium-water-ammonia clusters, and the presence of these metal ion-solvent interactions also affect the characteristics of electron solvation in these clusters. This is seen from the spatial distribution of the singly occupied molecular orbital (SOMO) which holds the ejected valence electron of the Li atom. For very small clusters, SOMO electron density is found to exist mainly at the vicinity of the Li atom, whereas for larger clusters, it is distributed outside the first solvation shell. The free dangling hydrogens of water and ammonia molecules are involved in capturing the SOMO electron density. In some of the conformers, OH{e}HO and OH{e}HN types of interactions are found to be present. The presence of the metal ion at the center of the cluster ensures that the ejected electron is solvated at a surface state only, whereas both surface and interiorlike states were found for the free electron in the corresponding anionic clusters without a metal ion. The vertical ionization energies of the present clusters are found to be higher than the vertical detachment energies of the corresponding anionic clusters which signify a relatively stronger binding of the free electron in the presence of the positive metal counterion. The shifts in different vibrational frequencies are also calculated for the larger clusters, and the results are discussed for some of the selective modes of water and ammonia molecules that are directly influenced by the location and hydrogen bonding state of these molecules in the clusters.
Influence of gallium supersaturation on the properties of GaN grown by metalorganic chemical vapor deposition
Authors: Mita S. , Collazo R. , Rice A. , Dalmau R. F. , Sitar Z.
Published: July 2008

A thermodynamic supersaturation model for gallium (Ga) was developed to describe GaN growth characteristics in low-pressure metalorganic chemical vapor deposition. The model takes into account the simplified GaN chemical reaction that occurs at the growth interface, Ga+NH3=GaN+3/2H2. The supersaturation was varied in two ways: (1) by the V/III ratio and (2) by the choice of the diluent gas. Two diluent gases were considered: H2, a commonly used diluent gas, and N2, a reaction inert gas. The choice of the diluent played a role in the degree of Ga supersaturation; since H2 is the product in the GaN formation, the addition of hydrogen significantly lowered the supersaturation. Atomic force microscopy revealed that surface morphology was associated with the different Ga supersaturation and the Burton–Cabrera–Frank model was used to relate it to the observed spiral size and terrace width. In addition to growth morphology, the degree of Ga supersaturation also influenced the carrier compensation level in n-type GaN. Secondary ion mass spectrometry studies identified that the trend of carbon incorporation followed that of the compensation level and inversely that of the Ga supersaturation. For samples intentionally doped with Si, it was found that GaN became semi-insulating when the carbon concentration exceeded that of silicon. In general, it has been shown that two growth processes at seemingly different conditions will be equivalent if the corresponding Ga supersaturation is the same. This finding showed that the supersaturation is a much more universal parameter than any other growth parameter alone.
Strain distribution in Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass investigated by in situ tensile tests under synchrotron radiation
Authors: Stoica M. , Das J. , Bednarcik J. , Franz H. , Mattern N. , Wang W. H. , Eckert J.
Published: July 2008

We report on the evolution of the atomic-scale strain tensor of ductile Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass under tensile loading by using x-ray synchrotron radiation. The same kind of samples was previously investigated under compressive loading and revealed yielding at 1690 MPa together with large deformability of up to 160% strain. In tension the samples fracture at a lower stress, 1500 MPa, with no sign of yielding or plastic deformation. With no macroplasticity observed under tension, large differences in the elastic constants obtained from the strain tensor and from ultrasonic sound velocity measurements are revealed. This paper presents in detail the measuring procedure as well as the calculation of the tensile tensor and pair distribution functions of Zr64.13Cu15.75Ni10.12Al10 at different stages of deformation. The results are discussed in comparison with other reported data obtained from x-ray diffraction measurements using synchrotron radiation.
Electric current-induced relaxations of conductivity in phase-separated La0.5Ca0.5Mn0.95Fe0.05O3
Authors: Yan Z. B. , Dong S. , Wang K. F. , Lu C. L. , Guo H. X. , Liu J.-M.
Published: July 2008

The conduction relaxations of polycrystalline La0.5Ca0.5Mn0.95Fe0.05O3 upon imposing rectangle electric current pulses (with minute time scale) are studied in details. We observe clear “overshooting” features of the conduction relaxation at both the front and rear edges of the current pulse so long as the pulse is sufficiently high. The Joule heating effect and the intrinsic stabilization of the ferromagnetic metal phase by the current pulse are linked in understanding our observations, and these effects may be applicable for resistance switching function.
The photophysics of all-trans polyenes from ttbP5, a nonphotolabile pentaene
Authors: Catalán Javier , Pérez Pilar , Hopf Henning , Klein Dagmar
Published: July 2008

The all-trans pentaene, 3,12-di(tert-butyl)-2,2,13,13-tetramethyl-3,5,7,9,11-tetradecapentaene (ttbP5) fluoresces in two different regions of the visible spectrum. It produces an extremely weak emission in the gas phase that can also be detected in the condensed phase; such an emission exhibits a negligible Stokes shift with respect to the 1Ag→1Bu absorption transition and can in principle be assigned to the 1Bu→1Ag emission of the compound. ttbP5 also exhibits a second fluorescence emission at approximately 520nm in both the gas phase and the condensed phase. The emission in the condensed phase increases in strength and structure, with no change in spectral position, as the solvent viscosity increases by effect of the solution temperature being lowered. The spectral behavior of this pentaene (ttbP5) is different enough from that reported [J. Catalán et al., J. Chem. Phys. 128, 104504 (2008)] for its tetraene counterpart (ttbP4) to warrant a separate analysis in order to facilitate a better understanding of the way the photophysics of these polyenes changes as their chain is lengthened.
Ferroelectric bimorph cantilever with self-assembled silane layer
Authors: Nadtochiy Andriy , Hollis T. Keith , Ostrovskii Igor
Published: July 2008

Bimorph ferroelectric microcantilevers are fabricated at the locations of the interdomain walls of inversely poled lithium niobate. The cantilevers are excited via the piezoelectric effect using a rf voltage and the natural vibrations are observed via optical detection. The self-assembling layers of two different silanes are chemically deposited on the microcantilevers. The presence of the silane layers is detected by two independent methods: optical detection of a low frequency shift of cantilever natural vibrations and the analysis of Raman spectral lines from the Silane layers. Possible applications include smart biosensors in real time domains.
Electroluminescence from monolayer ZnO nanoparticles using dry coating technique
Authors: Lee Chun-Yu , Hui Yuen-Yung , Su Wei-Fang , Lin Ching-Fuh
Published: July 2008

We report ultraviolet electroluminescence from ZnO nanoparticle-based devices prepared by the dry-coating technique. With dry-coating process, the structure of the ZnO nanoparticle monolayer (90nm) in the device can be easily achieved. The method reduces the density of pinhole defects in the ZnO nanoparticles. The confirmation for dry coating is investigated using field-emission scanning electron microscopy. The devices show the ZnO band-gap emission peak at 380nm and the background emission from the interface between the host matrix and Aluminum tris-8-hydroxyquinoline. The origins of the ZnO band-gap emission and background emission are also discussed.
Resonant x-ray diffraction as a tool to calculate mixed valence ratios: Application to Prussian Blue materials
Authors: Ferreira Fabio Furlan , Bueno Paulo R. , Setti Grazielle O. , Giménez-Romero David , García-Jareño José Juan , Vicente Francisco
Published: July 2008

An approach is proposed here to calculate mixed valence ratios in molecular compounds. Synchrotron x-ray powder diffraction experiments were conducted to determine the Fe+3∕Fe+2 ratio in Prussian Blue compounds, which were elected as an example of the use of this approach. As a result, a resonant x-ray diffraction measurement provided direct evidence that the vacant [Fe(CN)6] group was randomly absent from ∼31% of the structure, which was indicated by structural differences caused by variations in the anomalous dispersion term. These findings are very important for a deeper understanding of the changes occurring in properties during in situ compositional variations.
Study of interfacial diffusion in Al2O3/ZnO and MgO/ZnO heterostructures
Authors: Wang R. S. , Ong H. C.
Published: July 2008

We have studied the thermal stability of Al2O3 and MgO on ZnO films by using photoluminescence. It is found that the near interfacial regions of both Al2O3/ZnO and MgO/ZnO degrade significantly upon thermal annealing, which are evident by the decrease in band-edge emission and the increase in deep-level emissions. By using secondary ion mass spectroscopy and diffusion model, the dependence of luminescence on annealing temperature and duration can be simulated and the degradation of oxide/ZnO can be attributed to the outdiffusion of Zn into the oxide layer from ZnO. The activation energies and diffusion constants for the diffusion process occurring in these two systems have been determined accordingly.
Morphological evolution of tilted grain-boundary thermal grooving by surface diffusion in bicrystal thin solid films having strong anisotropic surface Gibbs free energies
Authors: Ogurtani Tarik Omer , Akyildiz Oncu , Oren Ersin Emre
Published: July 2008

The variational extremum method is further extended to give the full coverage for the inclined (tilted) grain-boundary (GB) configuration with respect to the sidewalls of a bicrystal thin solid film having strong anisotropic specific surface Gibbs free energy associated with the singular directions (faceting). A set of critical computer simulation experiments is performed on the asymmetrically disposed (inclination) bicrystal thin metallic films having four- and sixfold anisotropic specific surface Gibbs free energies to demonstrate the various GB-groove root topologies. Special computer runs are also designed using the realistic structural and physicochemical properties to simulate the thermal grooving profile of polycrystalline alumina (Lucalox™), and tungsten, which undergone heat treatments for 90 and 120 min at 1650 and 1350 °C in air and vacuum (10−4 Pa), respectively. The simulation profiles almost perfectly agree with the published experimental atomic force microscopy photographs after linewidth matching procedures, and the simulations produced very accurate mean surface (mass) diffusivities of alumina and tungsten given by DAl2O3≅6.45×10−12 m2/s and DW≅5.2×10−13 m2/s, respectively. These findings are in good agreement with the diffusivities reported in the literature.
Effects of Sr2+ doping on the persistent luminescence properties of CaAl2O4:Eu2+, Nd3+
Authors: Wang Lei , Wang Yuhua , Xu Xuhui
Published: July 2008

To reveal the components of defects responsible for persistent luminescence properties of CaAl2O4:Eu2+, Nd3+, a slight amount of Sr2+ ions were doped in host lattice. Their thermoluminescence (TL) and decay curves were investigated. The results showed that the concentration of traps in CaAl2O4:Eu2+, Nd3+ decreased linearly with the increase in Sr2+. Furthermore, both of their initial luminance and decay time also decreased. As Sr2+ ions preferred to occupy Ca2+ vacancies, the suppression of TL and persistent luminescence reflected that some isolated Ca2+ vacancies might be acting as bridges to transport carriers between trapping centers and emission centers. On the basis of these results, the manner of carriers’ transport in CaAl2O4:Eu2+, Nd3+ is discussed in detail, and a possible structural defects unit is designed as well.
Growth of InAs∕Sb:GaAs quantum dots on silicon substrate with high density and efficient light emission in the 1.3μm band
Authors: Li Lin , Guimard Denis , Rajesh Mohan , Arakawa Yasuhiko
Published: July 2008

We report on the growth of self-assembled InAs∕Sb:GaAs quantum dots (QDs) on silicon substrate by antimony-mediated metal organic chemical vapor deposition. We obtained arrays of InAs∕Sb:GaAs∕Si QD chains along [0−11], with density as high as 7×1010cm−2 and low coalescence. These QDs yield emission in the 1.3μm band. The temperature dependence of the photoluminescence intensity indicates the good optical quality of the grown QDs. Together, these results are promising for the fabrication of InAs∕GaAs QD laser on silicon substrate.
Quantum dynamic of sticking of a H atom on a graphite surface
Authors: Morisset S. , Allouche A.
Published: July 2008

A quantum study of the sticking of a hydrogen atom chemisorbed onto graphite (0001) surface was carried out also including the phonon modes of the system in the collinear scattering approximation. A new model was developed to extract the substrate vibrational modes from density functional theory (DFT) calculation and include them in the total system dynamics. The resulting coupled-channel equations are numerically developed along time using the wave packet methods. The sticking coefficients are calculated for hydrogen atoms incident energies ranging from 0.17 and 1.3eV for a surface temperature of 10K and between 0.17 and 0.2eV for a surface temperature of 150K. The results are found to be in good agreement with the experimental work.
Surface electronic properties of ZnO nanoparticles
Authors: Ton-That Cuong , Phillips Matthew R. , Foley Matthew , Moody Steve J. , Stampfl Anton P. J.
Published: July 2008

The surface electronic structure of ZnO nanoparticles has been studied with photoemission and x-ray absorption spectroscopies. Contrary to expectation, ZnO:Zn phosphor nanoparticles were found to contain a lower oxygen vacancy density on the surface than undoped ZnO counterparts, but oxygen vacancies are in different chemical environments. Cathodoluminescence shows intense green luminescence from the ZnO:Zn surface, while the undoped nanoparticles exhibit only the near-band-edge emission. The results indicate the roles of surface oxygen vacancies and their environment in the previously unexplained green luminescence from the ZnO:Zn material.
On eigenfunctions of continuous and discrete (anti)symmetric multivariate Fourier transforms
Authors: Atakishiyev N. M. , Klimyk A. U.
Published: July 2008

We derive various full sets of eigenfunctions of Fourier transforms (continuous and discrete sine and cosine Fourier transforms in one variable, discrete symmetric and antisymmetric multivariate exponentials, sine and cosine Fourier transforms, and continuous symmetric and antisymmetric multivariate sine and cosine Fourier transforms), associated with Hermite polynomials in one variable. Symmetric and antisymmetric multivariate exponential Fourier transforms F satisfy the relation F4=1, whereas symmetric and antisymmetric multivariate sine and cosine Fourier transforms F satisfy the relation F2=1.
High electron mobility of phosphorous-doped homoepitaxial ZnO thin films grown by pulsed-laser deposition
Authors: Brandt Matthias , von Wenckstern Holger , Schmidt Heidemarie , Rahm Andreas , Biehne Gisela , Benndorf Gabriele , Hochmuth Holger , Lorenz Michael , Meinecke Christoph , Butz Tilman , Grundmann Marius
Published: July 2008

The transport properties of phosphorous-doped ZnO thin films, grown by pulsed-laser deposition on thermally pretreated hydrothermally grown ZnO single-crystal substrates, are reported. The ZnO:P thin films show very good morphological and structural properties as confirmed by atomic force microscopy (AFM), high resolution x-ray diffraction, and Rutherford backscattering (RBS) channeling. Steps of height c/2 are visible in AFM investigations for all samples. For an oxygen partial pressure of 0.1 mbar, two-dimensional growth was found. RBS channeling of a ZnO:P film shows a minimum yield of 0.034 which is comparable to that of an annealed substrate (0.033). Hall effect measurements revealed that all films are n-type for the present growth conditions. Peak mobilities of 800 cm2/Vs have been observed around 70 K, in line with the high structural quality of the samples. Room-temperature mobility in ZnO:P is up to 170 cm2/Vs.
Electrical analysis of individual ZnO nanowires
Authors: Subannajui K. , Kim D. S. , Zacharias M.
Published: July 2008

We report the electrical properties of individual as-grown ZnO nanowires (NWs) on SiO2∕Si and GaN/sapphire substrates. Carrier transport in metal-semiconductor-metal junction is interpreted in terms of thermionic emission and tunneling current which was assumed to dominate independently on reverse and forward contacts. Current flow in ZnO NWs grown on SiO2∕Si was dominated by thermionic emission. In contrast, both thermionic emission and tunneling current contributed to the transport in ZnO NWs epitaxially grown on GaN/sapphire. Carrier concentrations of ZnO NWs were estimated to be around 8.88×1017cm−3 if grown on SiO2∕Si and 1.18×1018cm−3 if grown on GaN/sapphire, respectively.
Modulation of TiSiN effective work function using high-pressure postmetallization annealing in dilute oxygen ambient
Authors: Lee Joonmyoung , Park Hokyung , Choi Hyejung , Hasan Musarrat , Jo Minseok , Chang Man , Lee Byoung Hun , Park Chang Seo , Kang Chang Yong , Hwang Hyunsang
Published: July 2008

To increase the effective work function of a W∕TiSiN metal gate stack without an equivalent oxide thickness (EOT) increase, we developed a process for high-pressure postmetallization annealing in diluted oxygen ambient. Compared with annealing in an atmospheric pressure, oxygen postmetallization annealing (PMA) in a high-pressure ambient (1–20atm) showed further modulation of the effective work function (4.6–4.8eV) without an EOT increase. These differences can be attributed to total amounts of oxygen supplied to gate stack system. Additionally, the origin of EOT increase after the oxygen PMA was attributed to oxidation of the capping metal.
Production and heating of overdense plasmas by mode-converted electron Bernstein waves at very low toroidal field in the Compact Helical System
Authors: Ikeda R. , Toi K. , Takeuchi M. , Suzuki C. , Shoji T. , Akiyama T. , Isobe M. , Nishimura S. , Okamura S. , Matsuoka K. ,   CHS Experimental Group
Published: July 2008

In the Compact Helical System [S. Okamura et al., Nucl. Fusion 39, 1337 (1999)], overdense plasmas whose electron density exceeds the cutoff density were produced and heated for the first time by perpendicularly and/or obliquely launching of 2.45GHz electron cyclotron waves (ECWs) at very low toroidal field in a very wide range of magnetic field of 20%–120% for the resonant field Bres(=0.0875T). In these overdense plasmas, absorbed ECW power density measured by the power modulation technique concentrated inside the high density region beyond the cutoff layer for various magnetic configurations where electron cyclotron and upper hybrid resonance layers are scanned in space widely. This fact clearly demonstrates that the electron Bernstein wave (EBW) excited mainly through “fast extraordinary wave-to-EBW” and/or “ordinary wave-to-slow extraordinary wave-to-EBW” mode conversion processes plays a key role in producing and heating overdense plasmas.
Dynamics of pattern formation in bacterial swarms
Authors: Steager Edward B. , Kim Chang-Beom , Kim Min Jun
Published: July 2008

To gain a more thorough understanding of the dynamics of swarming bacteria, a nonlabeled cell tracking algorithm was used to study the velocity field of flagellated bacteria, Serratia marcescens, swarming on a soft agar plate. The average velocities for local regions regularly arranged over the entire flow field were investigated. The velocity field of the bacteria typically featured the combination of curvilinear translation and vortex modes. They repeated these patterns for short periods of time, forming several groups and dissipating. To further investigate the flow patterns generated by the collective motion of the swarming bacteria, the velocity field on the swarm was spatially correlated. The highest velocities and correlation lengths have been found to occur in the region from 0.5to1mm from the swarm edge, followed by a steady decline as distance from the edge increases, and a sudden decrease in motion typically occurs between 2 and 4mm from the swarm edge.
Cylindrical-to-plane-wave conversion via embedded optical transformation
Authors: Jiang Wei Xiang , Cui Tie Jun , Ma Hui Feng , Zhou Xiao Yang , Cheng Qiang
Published: July 2008

We investigate the conversion from cylindrical waves to plane waves in a short range through a metamaterial layer which has a circular shape in the inner outline and a square shape in the outer outline. Based on an embedded optical transformation, analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer which converts the cylindrical waves to plane waves. The designed conversion materials are validated by full-wave simulations using the finite-element method. The proposed structure can be used either as a four-beam antenna or a compact range for near-field measurement of plane waves.
[0001] composition modulations in Al0.4Ga0.6N layers grown by molecular beam epitaxy
Authors: Wise A. , Nandivada R. , Strawbridge B. , Carpenter R. , Newman N. , Mahajan S.
Published: July 2008

Al 0.4 Ga 0.6 N layers grown by molecular beam epitaxy on (0001) AlN/sapphire composite substrates were examined using transmission electron microscopy. The layers show modulated structures consisting of Al-rich and Ga-rich regions. 1:1 atomic ordering on the (0001) planes was not observed. To rationalize the formation of modulations, we invoke the presence of phase separation induced Al-rich and Ga-rich regions at the AlGaN/composite interface, the development of surface undulations due to the presence of two-dimensional stresses between these regions and asymmetry in the wetting characteristics of the Al-rich and Ga-rich regions. Arguments are also developed to explain the absence of 1:1 ordering in these layers.
Predictive first-principles simulations of strain-induced phenomena at water-silica nanotube interfaces
Authors: He Yao , Cao Chao , Trickey S. B. , Cheng Hai-Ping
Published: July 2008

Via ab initio simulation, we study the behavior of interfaces of water with silica nanotubes. We find profound differences between zero and finite tensile strains and between unconfined (exterior) versus confined (interior) water. For these distinct cases, we characterize the fracture dynamics of the silica nanotube and the underlying physical mechanisms.
On the importance of radiative and Auger losses in GaN-based quantum wells
Authors: Hader J. , Moloney J. V. , Pasenow B. , Koch S. W. , Sabathil M. , Linder N. , Lutgen S.
Published: July 2008

Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN∕GaN quantum wells. Auger losses are found to be negligible in contrast to recent speculations on their importance for the experimentally observed efficiency droop. Good agreement with experimentally measured threshold losses is demonstrated. The results show no significant dependence on details of the well alloy profile.
Anisotropic medium with parabolic dispersion
Authors: Shen Linfang , Wu Jin-Jei , Yang Tzong-Jer
Published: July 2008

A layered metamaterial which is predicted by the effective medium theory to be an anisotropic medium with partial zero permittivities is analyzed carefully. It is shown that such a material has a dispersion relation in parabolic form, which is quite different from the known ones. This material may be viewed as a homogeneous medium but is spatially dispersive strongly. The structured medium may support either forward wave or backward wave, depending on the magnitude of the wave vector. Moreover, it is demonstrated that this medium with parabolic dispersion is especially suitable for the transmission of Gaussian beam with subwavelength width.
Sol-gel derived nanostructured cerium oxide film for glucose sensor
Authors: Ansari Anees A. , Solanki Pratima R. , Malhotra B. D.
Published: July 2008

Sol-gel derived nanostructured cerium oxide (CeO2) film deposited on gold (Au) electrode has been utilized for physisorption of glucose oxidase (GOx). X-ray diffraction, atomic force microscopy, UV-visible spectroscopy, and electrochemical techniques have been used to characterize sol-gel derived CeO2∕Au electrode and GOx∕CeO2∕Au bioelectrode. The response characteristics of the glucose bioelectrode (GOx∕CeO2∕Au) indicate linearity, detection limit and shelf-life as 50–400mg∕dL, 12.0μM, and 12weeks, respectively. The value of apparent Michaelis–Menten constant (Km) of GOx∕CeO2∕Au bioelectrode has been found to be 13.55μM.
Electromigration induced high fraction of compound formation in SnAgCu flip chip solder joints with copper column
Authors: Xu Luhua , Han Jung-Kyu , Liang Jarrett Jun , Tu K. N. , Lai Yi-Shao
Published: July 2008

To overcome the effect of current crowding on electromigration-induced pancake-type void formation in flip chip solder joints, two types of Cu column in 90μm flip chip SnAgCu solder joints have been studied. They were (1) the solder contacts the Cu column at bottom and side walls and (2) the solder wets only the bottom surface of the copper column. With a current density of 1.6×104A∕cm2 at 135°C, no failure was detected after 1290h. However, the resistance increased by about 10% due to the formation of a large fraction of intermetallic compounds. We found that electromigration has accelerated the consumption rate of copper column and converted almost the entire solder joint into intermetallic compound. Mechanically, drop impact test indicates a brittle fracture failure in the intermetallic. The electromigration critical product for the intermetallic is discussed.
Strong localization of positive charge in DNA induced by its interaction with environment
Authors: Burin A. L. , Uskov D. B.
Published: July 2008

We investigate a quantum state of positive charge in DNA. A quantum state of electron hole is determined by the competition of the pi-stacking interaction b sharing a charge between different base pairs and the interaction λ with the local environment which attempts to trap charge. To determine which interaction dominates, we investigate charge quantum states in various (GC)n sequences choosing DNA parameters that satisfy experimental data for the balance of charge transfer rates G+↔Gn+, n=2,3. We show that experimental data can be consistent with theory only assuming b⪡λ, meaning that charge is typically localized within the single G site. Consequently, as follows from our modeling consideration, any DNA duplex including the one consisting of identical base pairs cannot be considered as a molecular conductor. Our theory can be verified experimentally, measuring balance of charge transfer reactions G+↔Gn+, n⩾4 and comparing the experimental results with our predictions.
On the local representation of the electronic momentum operator in atomic systems
Authors: Bohórquez Hugo J. , Boyd Russell J.
Published: July 2008

The local quantum theory is applied to the study of the momentum operator in atomic systems. Consequently, a quantum-based local momentum expression in terms of the single-electron density is determined. The limiting values of this function correctly obey two fundamental theorems: Kato’s cusp condition and the Hoffmann-Ostenhof and Hoffmann-Ostenhof exponential decay. The local momentum also depicts the electron shell structure in atoms as given by its local maxima and inflection points. The integration of the electron density in a shell gives electron populations that are in agreement with the ones expected from the Periodic Table of the elements. The shell structure obtained is in agreement with the higher level of theory computations, which include the Kohn–Sham kinetic energy density. The average of the local kinetic energy associated with the local momentum is the Weizsäcker kinetic energy. In conclusion, the local representation of the momentum operator provides relevant information about the electronic properties of the atom at any distance from the nucleus.
Tiny bubble removal by gas flow through porous superhydrophobic surfaces: Ostwald ripening
Authors: Chang Feng-Ming , Sheng Yu-Jane , Cheng Shao-Liang , Tsao Heng-Kwong
Published: July 2008

The fact that tiny bubbles are easily formed on the rough, hydrophobic surface results in difficulties in bubble detachment and removal. We show that bubbles captured by porous superhydrophobic surfaces merge into larger ones, which can detach by buoyancy. The responsible mechanism is convective Ostwald ripening because networklike pores in the superhydrophobic film remain nonwetted and provide passage for gas flow between adhered bubbles. A large bubble grows spontaneously by absorbing all small adhered bubbles due to capillary pressure differences. Our results demonstrate that porous hydrophobic film can be an efficient, passive way of bubble removal in microfluidic systems.
A three-dimensional isotropic transmission-line metamaterial topology for free-space excitation
Authors: Iyer Ashwin K. , Eleftheriades George V.
Published: July 2008

This work proposes a three-dimensional isotropic transmission-line metamaterial topology for free-space excitation whose negative-refractive-index properties are validated by full-wave simulation. The topology is based on a physical realization of the symmetrical condensed node of transmission-line matrix modeling, but reverses the positions of the inductive and capacitive lumped elements in order to yield an isotropic negative refractive index and good matching to free space.
Size dependence of twin formation energy in cubic SiC at the nanoscale
Authors: Zhang Yongfeng , Shim Hyun Woo , Huang Hanchen
Published: July 2008

This letter reports the size dependence of twin formation energy in cubic SiC at the nanoscale, while the bulk value is nearly zero. Atomic edges surround the twin boundary of SiC nanowires, and they are responsible for the finite twin formation energy and its size dependence. Based on classical molecular statics calculations, the average formation energy of convex and concave edges is 73meV∕nm. Effectively, the twin formation energy is inversely proportional to the length of edges surrounding the twin boundary. Results of this letter make it possible to understand large separations of twin boundaries in SiC nanowires.
Size dependence of intrinsic spin transfer switching current density in elliptical spin valves
Authors: Heindl R. , Russek S. E. , Silva T. J. , Rippard W. H. , Katine J. A. , Carey M. J.
Published: July 2008

We studied current-induced magnetization reversal in elliptical spin valves with CoFeB free layers. The data obtained from high-speed pulsed switching experiments showed that the intrinsic switching current densities were size dependent and 50%–100% higher than predicted by a single-domain model. Micromagnetic simulations reveal a complex behavior of magnetization switching in which end-mode oscillations are important, and indicate that the switching current density depends on the device dimensions. Experimental values for the intrinsic switching current density agree with those predicted by micromagnetic simulations.
Enhanced photoluminescence from embedded PbSe colloidal quantum dots in silicon-based random photonic crystal microcavities
Authors: Yang Jun , Heo Junseok , Zhu Ting , Xu Jian , Topolancik Juraj , Vollmer Frank , Ilic Rob , Bhattacharya Pallab
Published: July 2008

The experimental observation of enhanced photoluminescence from high-Q silicon-based random photonic crystal microcavities embedded with PbSe colloidal quantum dots is being reported. The emission is optically excited at room temperature by a continuous-wave Ti-sapphire laser and exhibits randomly distributed localized modes with a minimum spectral linewidth of 4nm at 1.5μm wavelength.
Three-dimensional magnetic microstructures fabricated by microstereolithography
Authors: Kobayashi Kengo , Ikuta Koji
Published: July 2008

Our group has developed a magnetically modified photocurable polymer for use in microstereolithography to fabricate magnetic microstructures and microactuators having three-dimensionally complex structures. This polymer is prepared by mixing a photocurable polymer with magnetic particles together with a viscosity-increasing agent for preserving the dispersion of the particles. In this study, we conducted experiments to evaluate the curing and magnetic characteristics of this magnetically modified photocurable polymer. We then rapidly fabricated truly three-dimensional magnetic microstructures by microstereolithography using this polymer. We expect that this achievement will lead to the development of magnetic microactuators.
Improved electrical properties of Ge metal-oxide-semiconductor capacitor with HfTa-based gate dielectric by using TaOxNy interlayer
Authors: Zhang X. F. , Xu J. P. , Li C. X. , Lai P. T. , Chan C. L. , Guan J. G.
Published: July 2008

HfTa-based oxide and oxynitride with or without TaOxNy interlayer are fabricated on Ge substrate to form metal-oxide-semiconductor (MOS) capacitors. Their electrical properties and reliabilities are measured and compared. The results show that the MOS capacitor with a gate stack of HfTa-based oxynitride and thin TaOxNy interlayer exhibits low interface-state/oxide-charge densities, low gate leakage, small hysteresis, small capacitance equivalent thickness (∼0.94nm), and high dielectric constant (∼24). All these should be attributed to the blocking role of the TaOxNy interlayer against penetration of O into the Ge substrate and interdiffusions of Hf, Ge, and Ta, thus effectively suppressing the formation of unstable low-k GeOx and giving a superior TaOxNy∕Ge interface. Moreover, incorporation of N into both the interlayer and high-k dielectric greatly improves device reliability through the formation of strong N-related bonds.
Photonic nanojet-induced modes in chains of size-disordered microspheres with an attenuation of only 0.08dB per sphere
Authors: Yang Seungmoo , Astratov Vasily N.
Published: July 2008

By using spatially resolved spectroscopy the authors demonstrate that the periodical focusing of light in straight chains of touching 5μm polystyrene microspheres is characterized with the periodicity of photonic nanojets corresponding to the size of two spheres. In transmission spectra of long (>20 spheres) chains they observe Fabry–Pérot fringes with propagation losses of only 0.08dB per sphere in the maxima of transmission peaks. Due to mechanical robustness, tight focusing of the beam, high optical throughput, and broad spectral transmission properties such chains can be used in a variety of biomedical applications as optical microprobes with subwavelength spatial resolution.
Stability and interface quality of GeO2 films grown on Ge by atomic oxygen assisted deposition
Authors: Molle Alessandro , Spiga Sabina , Fanciulli Marco
Published: July 2008

The composition of GeO2 films grown on Ge has been studied for different molecular deposition processes and after exposure to ambient air. The stoichiometry, the interaction with moisture, and the interfacial details of the films are shown to be dramatically process dependent.
Accurate solid-state band gaps via screened hybrid electronic structure calculations
Authors: Brothers Edward N. , Izmaylov Artur F. , Normand Jacques O. , Barone Verónica , Scuseria Gustavo E.
Published: July 2008

The band energy differences of solids calculated with screened hybrid density functionals, such as the functional of Heyd–Scuseria–Ernzerhof (HSE), reproduce experimental band gaps with a high degree of accuracy. This unexpected result is here rationalized by observing that band energy differences obtained from generalized Kohn–Sham calculations with screened (short-range) Hartree–Fock–type exchange approach the excitation energies obtained via time-dependent density functional calculations with the corresponding unscreened functional. The latter are expected to be the accurate predictions of the experimental optical absorption spectra. While the optimum screening parameter (ω) is system dependent, the HSE standard value of ω=0.11 bohr−1 represents a reasonable compromise across diverse systems.
Extraordinary electroconductance in metal-semiconductor hybrid structures
Authors: Wang Yun , Newaz A. K. M. , Wu Jian , Solin S. A. , Kavasseri V. R. , Jin N. , Ahmed I. S. , Adesida I.
Published: July 2008

We report the phenomenon of extraordinary electroconductance in microscopic metal-semiconductor hybrid structures fabricated from GaAs epitaxial layer and a Ti thin film shunt. Four-lead Van der Pauw structures show a gain of 5.2% in electroconductance under +2.5kV∕cm with zero shunt bias. The increase in the sample conductance results from the thermionic field emission of electrons and the geometrical amplification. A model provides good agreement with the experimental data and clearly demonstrates the geometry dependence of the field effect in extraordinary electroconductance (EEC). The differences between EEC devices and field effect transistors, such as junction field effect transistor (FET) and Schottky barrier gate FET, are discussed.
Controlled fabrication of single electron transistors from single-walled carbon nanotubes
Authors: Stokes Paul , Khondaker Saiful I.
Published: July 2008

Single electron transistors (SETs) are fabricated by placing single-walled carbon nanotubes (SWNTs) on a 100nm wide local Al∕Al2O3 bottom gate and then contacting with Pd electrodes. Coulomb oscillations up to 125K were observed and charging energies of 12–15meV with level spacing of ∼5meV were measured from the Coulomb diamond, in agreement with a dot size of ∼100nm, implying that the local gate defines the dot size by bending SWNT at the edges and controls its operation. This “mechanical template” approach may facilitate large scale fabrication of SET devices using SWNT.