bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase diagram of a square-shoulder, square-well fluid revisited
Authors: Rżysko W. , Pizio O. , Patrykiejew A. , Sokolowski S.
Published: September 2008

We report here the phase diagrams for a model square-shoulder, square-well fluid obtained by histogram reweighting Monte Carlo simulations. The critical points corresponding to the gas-liquid condensation and to the liquid-liquid transition have been located. Also, we have estimated the temperatures and densities at the triple points. We believe that our results are more precise and complete than those published so far.
Study of effective properties of modified 1-3 piezocomposites
Authors: Li-kun Wang , Li Li , Lei Qin , Weiwei Wu , Tianxiao Dong
Published: September 2008

Based on the piezoelectric theory and a homogeneous mass assumption, the piezoelectric equations for a modified 1-3 (1-3-2) composite, having as structure a piezoelectric ceramic plate and a 1-3 piezoelectric composite, are deduced. The formulas used to calculate the effective parameters of modified 1-3 piezoelectric composites are derived. The influence of piezoelectric phase volume fraction on the properties of the modified 1-3 composites has been analyzed. In addition, some composite samples were fabricated by dice-fill technology and their properties were measured. The results calculated by using the derived formulas agreed with measured data for the piezoceramic volume fraction in the range of 0.4<v1<0.8.
Continuous near-field electrospinning for large area deposition of orderly nanofiber patterns
Authors: Chang Chieh , Limkrailassiri Kevin , Lin Liwei
Published: September 2008

A continuous near-field electrospinning (NFES) process has been developed to deposit solid nanofibers with orderly patterns over large areas. Before the onset of electrospinning, a bias voltage is applied to a semispherical shaped polymer droplet outside of a syringe needle, and a probe tip mechanically draws a single fiber from the droplet to initiate continuous NFES. Contrary to the conventional electrospinning process, we show that decreasing electrical field in continuous NFES results in smaller linewidth deposition, and nanofibers can be assembled into controlled complex patterns such as circular shapes and grid arrays on large and flat areas.
Room temperature constant-stress creep of a brittle solid studied by spherical nanoindentation
Authors: Basu Sandip , Radovic Miladin , Barsoum Michel W.
Published: September 2008

Understanding room-temperature dislocation-based plastic deformation, in general, and time dependent deformation, in particular, in brittle solids is nontrivial. Herein, we describe a new constant-stress, spherical nanoindentation technique to study the creep of A-plane (112¯0) ZnO single crystal. The time dependent deformation follows a power-law behavior, with a threshold stress, and a stress exponent of ≈3.1±0.3, attributed to the movement of dislocation pileups on basal planes. The results are used to estimate the time dependencies of the threshold stresses, number of pileup dislocations, and the distance between them. The method described herein can also be used to quantify other time dependent mechanical properties, such as fatigue and subcritical crack growth, at the submicron, and even nanoscale. The results can then—as done here—be compared to long established macroscale relationships thus elucidating the nature of the former.
Analysis of planar defect structures in three-dimensional layer-by-layer photonic crystals
Authors: Chen Ji-Feng , Hong Rong-Tai , Yang Jaw-Yen
Published: September 2008

The properties of planar defect structures, which are created by changing the dielectric distribution at the central layer of a three-dimensional (3D) layer-by-layer photonic crystal, are theoretically investigated by utilizing a parallel 3D finite-difference time-domain method and the plane-wave expansion method. Two different kinds of resonant modes, the defect mode and the band-edge resonant mode, have been clarified by spectrum analysis and calculated mode profiles. It is shown that the resonant modes can be controlled by changing the periodicity, the thickness, or the dielectric constant of materials at the defect layer. Besides, photonic band edges can be shifted by applying dislocation to a layer of dielectric rods.
Boron nanowires for flexible electronics
Authors: Tian Jifa , Cai Jinming , Hui Chao , Zhang Chendong , Bao Lihong , Gao Min , Shen Chengmin , Gao Hongjun
Published: September 2008

Flexible boron nanowires have been synthesized via thermoreduction in boron-oxygen compounds with magnesium. These as-prepared nanowires, which are structurally uniform and single crystalline, represent good semiconductor at high temperature. Tensile stress measurements demonstrate excellent mechanical property of boron nanowires as well as resistance to mechanical fracture even under a strain of 3%. Importantly, simultaneous electrical measurement reveals that the corresponding electrical conductance is very robust and remains constant under mechanical strain. Our results can be briefly explained by Mott’s variable range hopping model.
Transport in the presence of inverse bremsstrahlung heating and magnetic fields
Authors: Ridgers C. P. , Thomas A. G. R. , Kingham R. J. , Robinson A. P. L.
Published: September 2008

Electron transport in the presence of long (nanosecond) laser pulses can be significantly different from that of magnetohydrodynamics calculations using Braginskii’s transport theory, due to the distortion of the underlying electron distribution function from a Maxwellian. To correctly model the transport under conditions relevant to direct and indirect-drive inertial fusion plasmas, the Vlasov–Fokker–Planck equation for the electrons should be solved; however, this is computationally intensive. Modified transport coefficients have been calculated for a distribution function appropriate to a plasma heated by inverse-bremsstrahlung, i.e., a super-Gaussian. The resulting transport was then compared to a Vlasov–Fokker–Planck code. Furthermore, it was shown that existing magnetohydrodynamics codes can be modified using the new transport coefficients and made more accurate by up to ten times with a modest computational cost.
Characterization of the streamer regime in dielectric barrier discharges
Authors: Siliprandi R. A. , Roman H. E. , Barni R. , Riccardi C.
Published: September 2008

The streamer regime of a dielectric barrier discharge device is studied by performing a detailed statistical analysis of current-voltage measurements in air. A wide bandwidth Rogowski coil, designed to work down to the nanoseconds time scale, is used to record the discharge current. The temporal structure of the latter is identified and characterized by its probability density distribution as a function of the applied voltage. The results suggest the existence of two discharge regimes, separated by a well defined voltage threshold, reflecting the different behaviors of the microdischarges. The autocorrelations of the discharge signal are evaluated as a function of the applied voltage, indicating the presence of strong correlations at short-time scales (up to the order of 102 ns) and residual correlations at longer times. The latter are shown to be due to the nonstationarity of the discharge process.
Size- and temperature-dependent second-order optical effects in copper-doped cadmium iodide nanocrystals
Authors: Miah M. Idrish
Published: September 2008

Size and temperature dependences of second-order optical effects in Cu-doped cadmium iodide nanocrystals are studied. A large enhancement of photoinduced second harmonic generation (PSHG) with decreasing thickness of the nanocrystals or temperature is observed. The PSHG is also found to be enhanced with increasing Cu doping. However, due to the formation of the metallic agglomerates, the PSHG for the crystals with high Cu contents decreases. The results are presented by discussing photoinduced kinetics of the electron-phonon anharmonic interaction and nanosized quantum confined effect, the crucial roles played in the observed effects.
Coexistence and competition between superconductivity and magnetism in La2−xSrxCu0.94M0.06O4 (M=Mn and Ru)
Authors: Xu Jingtao , Tan Shun , Pi Li , Zhang Yuheng
Published: September 2008

The infrared (IR) transmission, Raman Scattering, magnetic measurement, and electronic resistance measurement have been carried out in La2−xSrxCu0.94Mn0.06O4 and La2−xSrxCu0.94Ru0.06O4 systems. The superconductivity that is suppressed by impurity reappears as Sr content increases and forms a new relationship of the Meissner volume and Tconset versus Sr doping content. The Mn4+ doping system exhibits twice superconductive phase transitions while Ru4+ doping system exhibits only one superconductive phase transition. Coexistence and competition between superconductivity and magnetism are observed. We suggest that these surprising phenomena should be attributed to the compensation effect that is the electrons on high valence impurities are compensated by holes introduced through Sr doping. This compensation effect is confirmed by our IR spectra results. We also find that the compensation effect is strong for the localized 3d electrons of Mn4+ while very weak for the itinerant 4d electrons of Ru4+.
Coherent flow states in a square duct
Authors: Wedin Håkan , Biau Damien , Bottaro Alessandro , Nagata Masato
Published: September 2008

The flow in a square duct is considered. Finite amplitude approximate traveling wave solutions, obtained using the self-sustaining-process approach introduced by Waleffe [Phys. Fluids 9, 883 (1997)], are obtained at low to moderate Reynolds numbers and used as initial conditions in direct numerical simulations. The ensuing dynamics is analyzed in a suitably defined phase space. Only one among the traveling wave solutions found is capable of surviving for a long time, with the flow trajectory forming quasiregular loops in phase space. Eventually, also this trajectory escapes along the manifold of a chaotic saddle and relaminarization ensues.
The initial atomic layer deposition of HfO2∕Si(001) as followed in situ by synchrotron radiation photoelectron spectroscopy
Authors: Tallarida Massimo , Karavaev Konstantin , Schmeisser Dieter
Published: September 2008

We have grown HfO2 on Si(001) by atomic layer deposition (ALD) using HfCl4 and H2O as precursors. The early stages of the ALD were investigated with high-resolution photoelectron spectroscopy and x-ray absorption spectroscopy. We observed the changes occurring in the Si2p, O1s, Hf4f, Hf4d, and Cl2p core level lines after each ALD cycle up to the complete formation of two layers of HfO2. From the analysis of those variations, we deduced the growth properties of HfO2. The first layer consists of a sparse and Cl-contaminated oxide because of the incomplete oxidation, and the second layer is denser than the first one and with an almost stoichiometric O∕Hf ratio. At the completion of the second layer, the x-ray absorption spectra revealed the change of the Hf-oxide chemical state due to the transition from the thin Hf-oxide to the bulklike HfO2.
Design criteria for scanning tunneling microscopes to reduce the response to external mechanical disturbances
Authors: Ast Christian R. , Assig Maximilian , Ast Alexandra , Kern Klaus
Published: September 2008

We present a simple one-dimensional model to find design criteria for a scanning tunneling microscope (STM) minimizing the response of the tip-sample distance to external mechanical disturbances. The underlying concept—achieving a response that is in phase and same amplitude—goes beyond the conventional approach to construct the STM as stiff as possible. It introduces optimization conditions relating the resonance frequencies of the different components to the STM assembly, which can be implemented accordingly during the STM design process. In this way an improvement in the response to external disturbances of several orders of magnitude can be achieved. Calculations for three typical STM designs are presented along with the corresponding optimization criteria. For one of the designs an improvement in performance has been experimentally verified. The results can also be extended to other scanning probe techniques.
Ionoluminescent response of several phosphor screens to keV ions of different masses
Authors: Jiménez-Rey D. , Zurro B. , García G. , Baciero A. , Rodríguez-Barquero L. , García-Munoz M.
Published: September 2008

We have characterized the ionoluminescent response of several phosphor powder materials when irradiated with ions of different masses (H+,He+,Ar+) accelerated to keV energies. In particular, we have determined the absolute luminosity in terms of the number of photons per incident ion emitted by luminescent screens of Y2O2S:Tb (P45), Y3Al5O12:Ce (P46), Y2SiO5:Ce (P47), Y2O3:Eu (P56), and SrGa2S4:Eu (TG-green). Their ionoluminescence has been studied as a function of ion beam energy and current and ion fluency. The energy trend and mass dependence of selected experimental results are compared relative to stopping and range of ions in matter (SRIM) code predictions.
Isothermal variation of the entropy (ΔST) for the compound Gd5Ge4 under hydrostatic pressure
Authors: Carvalho A. Magnus G. , Coelho A. A. , Gama S. , von Ranke P. J. , Alves C. S.
Published: September 2008

In the present work, the isothermal variation of the entropy (ΔST) for the compound Gd5Ge4 was studied at different applied hydrostatic pressures (from 0 up to 0.58 GPa). In all pressure ranges, we observe the giant magnetocaloric effect. The ΔST data for the compound Gd5Ge4 at zero applied pressure present two peaks: the lowest temperature peak is due to irreversible processes and the highest temperature peak is due to magnetostructural transitions. Increasing the pressure, the lowest temperature peak displaces to lower temperatures and disappears. The magnitude of the other peak has a nonlinear behavior with pressure. Different protocols were used to obtain ΔST at zero applied pressure and the results indicate that ΔST strongly depends on the initial and final states of Gd5Ge4 compound. We also present a T-P magnetic phase diagram built from the available magnetic data.
Compositional evolution during the synthesis of FePt nanoparticles
Authors: Srivastava Chandan , Nikles David E. , Thompson Gregory B.
Published: September 2008

A series of FePt nanoparticles was synthesized by the thermal decomposition of iron pentacarbonyl and reduction in platinum acetylacetonate in phenyl ether solvent. A range of precursor molar ratios of 2, 1.5, and 1 between iron pentacarbonyl and platinum acetylacetonate was studied. After 30 min of reflux, the synthesis method produced a wide distribution in composition and size for the nanoparticles. Given 200 min of reflux, it was observed that the particle-to-particle composition and size narrowed, and the atomic ratio of Fe to Pt, for the majority of nanoparticles, approached the initial precursor molar ratios except for the molar ratio of 1. It is speculated that the compositional variability may be a result of the slow kinetics of iron pentacarbonyl’s decomposition in the reaction.
Synchronization of two different chaotic systems using novel adaptive fuzzy sliding mode control
Authors: Roopaei M. , Zolghadri Jahromi M.
Published: September 2008

In this paper, an adaptive fuzzy sliding mode control (AFSMC) scheme is proposed for the synchronization of two chaotic nonlinear systems in the presence of uncertainties and external disturbance. To design the reaching phase of the sliding mode control (SMC), a fuzzy controller is used. This will reduce the chattering and improve the robustness. An AFSMC is used (as an equivalent control part of the SMC) to approximate the unknown parts of the uncertain chaotic systems. Although the above schemes have been proposed in the past as separate stand-alone control schemes, in this paper, we integrate these methods to propose an effective control scheme having the benefits of each. The stability analysis for the proposed control scheme is provided and simulation examples are presented to verify the effectiveness of the method.
The permanent electric dipole moments and magnetic ge factors of neodymium monoxide
Authors: Linton Colan , Ma Tongmei , Wang Hailing , Steimle Timothy C.
Published: September 2008

Stark and Zeeman spectra of the [16.7]3-X4 transition of neodymium monoxide (NdO) have been obtained at a resolution of less than 40MHz. Analysis of the Stark spectra yielded permanent electric dipole moments μel of 3.742(16) and 3.369(13)D for the [16.7]3 and X4 states, respectively. The ground state value μel is compared to that of isovalent uranium monoxide (UO) and those of other lanthanide monoxides using a molecular orbital description. Analysis of the Zeeman spectra yielded magnetic ge factors of 2.084(6) and 2.178(8) for the J=3 and 4 rotational levels, respectively, of the [16.7]3 state and a ge factor of 2.116(6) for the X4 state. A comparison with the ge factor expected from the ab initio [Allouche et al., J. Chem. Phys. 124, 184317 (2006)] and the ligand field theory [P. Carette and A. Hocquet, J. Mol. Spectrosc. 131, 301 (1988)] predictions for the X4 ground state is given.
Electronic energy transfer on CaO surfaces
Authors: Joly Alan G. , Beck Kenneth M. , Hess Wayne P.
Published: September 2008

We excite low-coordinated surface sites of nanostructured CaO samples using tunable UV laser pulses and observe hyperthermal O-atom emission indicative of an electronic excited-state desorption mechanism. The O-atom yield increases dramatically with photon energy, between 3.75 and 5.4eV, below the bulk absorption threshold. The peak of the kinetic energy distribution does not increase with photon energy in the range from 3.9to5.15eV. These results are analyzed in the context of a laser desorption model developed previously for nanostructured MgO samples. The data are consistent with desorption induced by exciton localization at corner-hole trapped surface sites following electronic energy transfer from higher coordinated surface sites.
Effect of grafting density of the side chains on spontaneous curvature and persistence length of two-dimensional comblike macromolecules
Authors: Potemkin Igor I. , Popov Konstantin I.
Published: September 2008

We develop a theory that predicts the response of a two-dimensional (2D) comblike macromolecule (brush) to the bending which is accompanied by redistribution of the side chains with respect to the backbone. The brush is considered under poor solvent conditions, i.e., monomer units of the side chains and of the backbone attract each other. The line tension is explicitly taken into account. It is shown that densely grafted brushes (or brushes with long side chains) demonstrate spontaneous curvature. This curvature is induced by elasticity of the side chains: asymmetrically distributed side chains forming curved segments of the brush possess smaller elastic free energy than symmetrically distributed ones forming rectilinear segments of the brush. Sparsely grafted brushes (or brushes with short enough side chains) exhibit elastic response to the bending. In this case, a role of the elasticity of the side chains diminishes and main contributions to the elastic response of the brush come from the mixing entropy of the side chains and from the line tension. It is shown that persistence length of the sparsely grafted brushes λ as a function of the number of segments in the side chain M can be approximated by a power function, λ=const⋅Mα, with the exponent α⩽2. This persistence length is much smaller than that of the 2D brush with fixed distribution of the side chains. Our theoretical predictions are consistent with computer simulations.
Structural, electronic, and magnetic properties of YnO (n=2–14) clusters: Density functional study
Authors: Yang Zhi , Xiong Shi-Jie
Published: September 2008

The geometries stability, electronic properties, and magnetism of YnO clusters up to n=14 are systematically studied with density functional theory. In the lowest-energy structures of YnO clusters, the equilibrium site of the oxygen atom gradually moves from an outer site of the cluster, via a surface site, and finally, to an interior site as the number of the Y atoms increases from 2 to 14. Starting from n=12, the O atom falls into the center of the cluster with the Y atoms forming the outer frame. The results show that clusters with n=2, 4, 8, and 12 are more stable than their respective neighbors, and that the total magnetic moments of YnO clusters are all quite small except Y12O cluster. The lowest-energy structure of Y12O cluster is a perfect icosahedron with a large magnetic moment 6μB. In addition, we find that the total magnetic moments are quenched for n=2, 6, and 8 due to the closed-shell electronic configuration. The calculated ionization potentials and electron affinities are in good agreement with the experimental results, which imply that the present theoretical treatments are satisfactory.
Symmetry-based imaging condition in time reversed acoustics
Authors: Ulrich T. J. , Griffa M. , Anderson B. E.
Published: September 2008

Introduced in this paper is a new method of determining and investigating focal positions of time reversed elastic wave fields. This method exploits the temporally symmetric nature of time reversed acoustics focused signals as they are akin to the autocorrelation function of the forward propagation received signals. Contrasting this symmetry with the degree of asymmetry at regions away from the focal location provides details about the original source that cannot be retrieved when using other standard imaging conditions.
Thermal instability of the half-metallic CrO2 film epitaxially grown on TiO2
Authors: Dho Joonghoe , Kim Do-Hyung , Kwon Daeyoung , Kim Bog G.
Published: September 2008

We have investigated the thermal instability of the half-metallic CrO2 films epitaxially grown on the (002) and (200) TiO2 (rutile) substrates by chemical vapor deposition. The temperature-dependent x-ray diffraction measurement directly revealed that the epitaxial CrO2 film on TiO2 was decomposed above 250 °C and recrystallized to the heteroepitaxial Cr2O3 film above 300–350 °C. These results will be a guide for a thermal instability parameter in a development of spintronic devices using the half-metallic CrO2 film.
An asymptotic model for the Kelvin–Helmholtz and Miles mechanisms of water wave generation by wind
Authors: Shtemler Yuri M. , Mond Michael , Cherniavskii Vladimir , Golbraikh Ephim , Nissim Yaakov
Published: September 2008

The generalized Kelvin–Helmholtz (KH) and Miles mechanisms of the water wave generation by wind are investigated for two-layer piecewise linear model of the wind profile. It is shown by asymptotic expansions in small air-to-water density ratio that two mechanisms of the instability operate in quite different scales. Miles’ short waves are generated by weak winds, in particular, Miles’ regime is responsible for initiation of the instability at the minimum wind speed, while the generalized KH regime dominates at strong winds and raises moderately short waves.
Collision-induced hyper-Rayleigh spectrum of H2–Ar gas mixture
Authors: Bancewicz Tadeusz , Głaz Waldemar , Godet Jean-Luc , Maroulis George
Published: September 2008

The collision-induced hyper-Rayleigh (CIHR) spectra of the gaseous H2–Ar mixture are discussed in the binary regime on the basis of our ab initio computed H2–Ar collision-induced (CI) first dipole hyperpolarizability tensor Δβ(R). A method for the computation of the spherical, rotationally adapted components ΔβλL(s,K)(R) of Δβ(R) needed for spectroscopic line shape analysis is proposed. Both the vector and the septor parts of the H2–Ar CIHR spectrum are evaluated at room (T=295 K) temperature. The spectra are calculated assuming the full quantum computations based on the Schrödinger equation of the relative translational motion of H2–Ar as well as semiclassical methods (classical trajectory approach and Birnbaum–Cohen model translational profiles). The H2–Ar pair CIHR septor spectrum has been found stronger than the vector one.
Energy dependence of differential and integral cross sections for O(D1)+H2(υi=,ji=)→OH(υf,jf)+H reaction
Authors: Lin Shi Ying , Guo Hua
Published: September 2008

State-to-state differential and integral cross sections for the title reaction have been calculated using a dynamically exact quantum mechanical wave packet method on the ab initio ground H2O(XA′1) electronic state potential energy surface of Dobbyn and Knowles. We focus on the energy dependence of the cross sections up to 0.15eV. The total integral cross section and rate constant, obtained by summing the state-to-state integral cross sections over all open product rovibrational channels, are in excellent agreement with experimental measurements. Also in agreement with experimental data, the OH product is found to have highly inverted rotational state distributions and monotonically decaying vibrational state distributions. The calculated total differential cross section is roughly forward-backward symmetric, consistent with experimental data. The vibrational state-resolved differential cross sections are found to depend on the collision energy. The calculated results confirm the dominance of the insertion mechanism and provide a stringent test of the potential energy surface.
Femtosecond laser-induced periodic surface structure formation on tungsten
Authors: Vorobyev A. Y. , Guo Chunlei
Published: September 2008

In this paper, we demonstrate the generation of periodic surface structures on a technologically important material, tungsten, at both 400 and 800 nm, despite that the table values of dielectric constants for tungsten at these two wavelengths suggest the absence of surface plasmons, a wave necessary for forming periodic structures on metals. Furthermore, we find that the structure periods formed on tungsten are significantly less than the laser wavelengths. We believe that the dielectric constants of tungsten change significantly due to intense laser pulse heating and surface structuring and roughening at nanometer scales, permitting surface plasmon excitation and periodic structure formation.
A method to determine the onset voltage of single and arrays of electrospray emitters
Authors: Krpoun Renato , Shea Herbert R.
Published: September 2008

This paper reports on an accurate and rapid method to compute the onset voltage of a single or an array of electrospray emitters with complex geometries and on the correlation of the simulation with experimental data. This method permits the exact determination of the onset voltage based only on the surface tension of the sprayed liquid and on the emitter geometry. The approach starts by determining the voltage at which electrostatic forces and surface tension forces are equal for a sharpening conic surface at the tip of a capillary as a function of the apex radius of the liquid. By tracing the curve of this computed equilibrium voltage as a function of the apex radius, the onset voltage for a liquid surface with the Taylor half-angle of 49.3° or larger can be determined. For smaller cone half-angles the method is only applicable to ionic sprays as an approximate knowledge of the critical field for ion emission is necessary. The combination of analytical models and finite element tools used to compute the necessary parameters is described. The method is validated on a complex microelectromechanical system emitter geometry as well as on a linear array of electrospray emitters. Finally an empirical model of the behavior of the electric field near the apex of a conic surface with asymptotes at a fixed half-angle is proposed, which allows establishing a simple method for onset voltage determination.
Field emission effects of nitrogenated carbon nanotubes on chlorination and oxidation
Authors: Ray S. C. , Palnitkar U. , Pao C. W. , Tsai H. M. , Pong W. F. , Lin I-Nan , Papakonstantinou P. , Ganguly Abhijit , Chen L. C. , Chen K. H.
Published: September 2008

With reference to our recent reports [Appl. Phys. Lett. 90, 192107 (2007); Appl. Phys. Lett. 91, 202102 (2007)] about the electronic structure of chlorine treated and oxygen-plasma treated nitrogenated carbon nanotubes (N-CNTs), here we studied the electron field emission effects on chlorination (N-CNT:Cl) and oxidation (N-CNT:O) of N-CNT. A high current density (J) of 15.0 mA/cm2 has been achieved on chlorination, whereas low J of 0.0052 mA/cm2 is observed on oxidation compared to J=1.3 mA/cm2 for untreated N-CNT at an applied electric field EA of ∼1.9 V/μm. The turn-on electric field (ETO) was ∼0.875. The 1.25 V/μm was achieved for N-CNT:Cl and N-CNT:O, respectively, with respect to ETO=1.0 V/μm for untreated one. These findings are due to the formation of different bonds with carbon and nitrogen in the N-CNT during the process of chlorine (oxygen)-plasma treatment by the charge transfer, or else that changes the density of free charge carriers and hence enhances (reduces) the field emission properties of N-CNTs:Cl (N-CNTs:O).
Structural and transport properties of ferromagnetically coupled Fe/Si/Fe trilayers
Authors: Naik S. R. , Rai S. , Chattopadhyay M. K. , Sharma V. K. , Majumdar S. , Lodha G. S.
Published: September 2008

We report structural, transport, and magnetic studies on ion beam deposited Fe(30,50 Å)/Si(15,20,25,30,40 Å)/Fe(30,50 Å) trilayers. Grazing incidence x-ray reflectivity, grazing incidence x-ray diffraction, and x-ray photoelectron spectroscopy techniques are used to characterize the trilayers. From these studies we infer the formation of silicide interlayers at both Fe/Si and Si/Fe interfaces. Above 25 Å nominal thickness of the Si layer, a uniform density layer of pure Si is formed. But below 25 Å nominal thickness of Si layer, a nonuniform density layer of Si and silicide is found. The electrical resistance of trilayers depends on both Fe and Si layer thicknesses. Resistance decreases with the increase in temperature between 30 and 300 K. Attempts are made to analyze the temperature dependence of resistance with the help of semiconducting and electron hopping mechanisms. Magneto-optical Kerr effect results suggest that ferromagnetic correlations are established between the Fe layers of the trilayers.
Ab initio investigations of the phonon anomaly and superconductivity in fcc La
Authors: Tütüncü H. M. , Srivastava G. P.
Published: September 2008

We have employed the ab initio plane wave pseudopotential method within a generalized gradient approximation of the density functional theory and a linear response approach to investigate the phonon anomaly and superconductivity in fcc La. Our results confirm the presence of the experimentally observed softening behavior of the transverse acoustic branch along the [111] direction for both zero pressure. This behavior is found to be present even at a pressure of 50 kbar. With a reasonable choice of 0.1 for the Coulomb pseudopotential μ∗, our estimate of the superconducting critical temperature of 6.44 K at zero pressure is in good agreement with the experimental value of 6.0 K. Our work further suggests that at 50 kbar the critical temperature will increase to 9.26 K.
Optical and electrical characterization of sputter-deposited FeSi2 and its evolution with annealing temperature
Authors: Tan K. H. , Chi D. Z. , Pey K. L.
Published: September 2008

Optical and electrical properties of sputter-deposited FeSi2 thin films on p-Si(100) and SiO2/p-Si(100) substrates as well as their evolution with rapid thermal annealing (RTA) temperature have been investigated. Optical absorption measurements were carried out to determine the absorption spectra of FeSi2 based on the proposed optical absorption model for the double-layer and triple-layer structures. A direct band gap behavior was concluded for both amorphous and polycrystalline semiconducting FeSi2. An absorption coefficient in the order of 105 cm−1 at 1 eV and a band gap value of ∼0.86 eV were obtained for the β-FeSi2. Hall effect measurements at room temperature indicate heavily doped and n-type conductivity for the FeSi2 films on p-Si, whose residual carrier concentration was found to be closely correlated with the observed subgap optical absorption via band tailing. The carrier mobility was shown to increase with decreasing residual carrier concentration when the RTA temperature was increased.
Ultraintense proton beams from laser-induced skin-layer ponderomotive acceleration
Authors: Badziak J. , Jabłoński S. , Parys P. , Rosiński M. , Wołowski J. , Szydłowski A. , Antici P. , Fuchs J. , Mancic A.
Published: September 2008

The results of studies of high-intensity proton beam generation from thin (1–3 μm) solid targets irradiated by 0.35 ps laser pulse of energy up to 15 J and intensity up to 2×1019 W/cm2 are reported. It is shown that the proton beams of terawatt power and intensity around 1018 W/cm2 at the source can be produced when the laser-target interaction conditions approach the skin-layer ponderomotive acceleration requirements. The proton beam parameters remarkably depend on the target structure and can be significantly increased with the use of a double-layer Au/PS target (plastic covered by 0.1–0.2 μm Au front layer).
Leibniz algebra deformations of a Lie algebra
Authors: Fialowski Alice , Mandal Ashis
Published: September 2008

In this note we compute Leibniz algebra deformations of the three-dimensional Heisenberg Lie algebra n3 and compare it to its Lie deformations. It turns out that there are three extra Leibniz deformations. We also describe a versal Leibniz deformation of n3 with the versal base.
An improved correlation method for determining the period of a torsion pendulum
Authors: Luo Jie , Wang Dian-Hong
Published: September 2008

Considering variation of environment temperature and unhomogeneity of background gravitational field, an improved correlation method was proposed to determine the variational period of a torsion pendulum with high precision. The result of processing experimental data shows that the uncertainty of determining the period with this method has been improved about twofolds than traditional correlation method, which is significant for the determination of gravitational constant with time-of-swing method.
A Monte Carlo study of charge transfer in DNA
Authors: Jakobsson Mattias , Stafström Sven
Published: September 2008

A model describing charge (hole) transport in DNA has been developed. The individual charge transfer steps in the transport process are described by Marcus theory modified to account for electron delocalization over adjacent identical nucleobases. Such a modification, as well as introducing a distance dependence in the reorganization energy, is necessary in order to reach an agreement with the observed transfer rates in well defined model systems to DNA. Using previously published results as a reference for the reorganization energy and with the delocalization described within the Hückel model we obtain an excellent agreement with experimental data.
Surface tension of liquid ternary Fe–Cu–Mo alloys measured by electromagnetic levitation oscillating drop method
Authors: Wang H. P. , Luo B. C. , Qin T. , Chang J. , Wei B.
Published: September 2008

For the liquid Fe–Cu–Mo ternary system, the surface tensions of three selected alloys, i.e., three typical monotectic alloys, were measured by the electromagnetic levitation oscillating drop method over a broad temperature range, including both superheated and undercooled states. The maximum undercooling attained is up to 173 K. The experimental results show a good linear correlation between the surface tension and the temperature. By applying on the Butler equation, the surface tensions were also calculated and they are in good agreement with the measured ones, except that in the undercooled state, the calculated value is slightly larger than the measured results. Interestingly, both the measured and calculated results indicate that the enriched element on the droplet surface is much more conspicuous than other elements in influencing the surface tension. Besides, the viscosity and the density of the liquid Fe–Cu–Mo ternary alloys are also derived on the grounds of the experimentally measured surface tensions.
Effects of annealing on the valence band offsets between hafnium aluminate and silicon
Authors: Chiam S. Y. , Chim W. K. , Ren Y. , Pi C. , Pan J. S. , Huan A. C. H. , Wang S. J. , Zhang J.
Published: September 2008

In this work, we examine the valence band offset of hafnium aluminate (HfAlO), a material of interest for use as a high dielectric constant (high-k) gate oxide, following postdeposition annealing. It is observed that annealing leads to a change in the band offset between the high-k oxide and the semiconductor. Our results conclusively show that the change is due to the existence of an electrostatic dipole field at the interface between HfAlO and the silicon substrate. This provides evidence to partly account for the observed flatband voltage shifts in high-k dielectric stack structures in the literature. The origin of the dipole field is also discussed in terms of the interfacial permittivity.
Room temperature photoluminescence of CdTe nanocrystals embedded in a SiO2 matrix deposited on silicon by reactive rf sputtering
Authors: Mota-Pineda E. , Meléndez-Lira M.
Published: September 2008

CdTe nanocrystals embedded in a SiO2 matrix were fabricated by radio frequency sputtering employing the texture of a SiO2 layer as template. The SiO2 film texture was controlled through the O2 partial pressure (OPP) in the working atmosphere. The CdTe crystallinity was better for the samples synthesized on rougher SiO2 films. For these samples, the room temperature photoluminescence spectra showed a signal at 1.74 eV, related to the CdTe nanoparticles. Additional photoluminescence signals at 1.65 and 1.68 eV have been associated to recombination processes at the nanoparticle/matrix interfaces. The results indicate that the employed methodology produces, in a single step, CdTe nanoparticles with light emission at room temperature. After thermal annealing all the samples presented emission due to quantum confinement effects. The photoluminescence emission may be varied from 1.69 to 2.15 eV by appropriate control of the OPP.
Systematic study of the ferroelectric properties of Pb(Zr0.5Ti0.5)O3 nanowires
Authors: Hong Jiawang , Fang Daining
Published: September 2008

The ferroelectric properties of Pb(Zr0.5Ti0.5)O3 (PZT) nanowires are investigated using Landau–Ginzburg–Devonshire theory, taking account into the nanowire size, polarization gradient, temperature, and axis stress. It is shown that the Curie temperature, coercive electric field, remnant polarization, dielectric permittivity, and piezoelectric coefficient are all size dependent. It is revealed that the ferroelectric properties disappear below a critical diameter, which depends on the temperature, but they can be recovered under an appropriate axis tension. Our results further show that an unusual thermal fluctuation exists in PZT nanowires with small diameter.
Enhancement in low field nuclear magnetic resonance with a high-Tc superconducting quantum interference device and hyperpolarized H3e
Authors: Liao Shu-Hsien , Yang Hong-Chang , Horng Herng-Er , Chen Hsin-Hsien , Yang Shieh-Yueh , Chen Ming-Jye , Yang Chang-Hau
Published: September 2008

In this work, we present a design that improves signals produced by nuclear magnetic resonance (NMR) and magnetic resonance imaging by using optical pumping and a high-Tc superconducting quantum interference device (SQUID) magnetometer. In our design for a NMR detection system, a pickup coil is coupled to the spin procession of a H3e nucleus; the input coil is coupled to a high-Tc SQUID magnetometer; and the capacitor is connected in series to form a tank circuit resonating at the Larmor frequency of the H3e nucleus in the measuring field. A signal-to-noise ratio gain of 2.67 over a conventional Faraday detection coil was obtained with the high-Tc SQUID detection system in a measuring magnetic field equaling 0.1128 mT, at which the central frequency was 3.66 kHz for H3e nucleus. The improvement in the NMR signal for large-size, hyperpolarized H3e coupled to a high-Tc SQUID-based spectrometer in low magnetic fields at room temperature is significant compared to that without flux coupling. This result may be of interest given its potential for use in a low field imager.
Local structures of fluid with discrete spherical potential: Theory and grand canonical ensemble Monte Carlo simulation
Authors: Zhou Shiqi , Lajovic A. , Jamnik A.
Published: September 2008

Grand canonical Monte Carlo simulation and theoretical calculations based on Ornstein–Zernike (OZ) integral equation and thirdorder+secondorder perturbation density functional theory (DFT) are performed to study a system of spherical particles interacting through a core-softened (CS) potential combining a repulsive square soft core and an attractive square well. Both theoretical predictions and simulation results reveal peculiar homogeneous and inhomogeneous local structures originating from the discontinuous nature of the CS potential. The bulk radial distribution function displays discontinuities at the distances coinciding with the ranges of the successive repulsive and attractive parts in the CS potential function. The density profiles of confined CS fluid show the shapes arising from the complex interplay among the steric effects and the competition between the repulsive and attractive parts of the CS potential. Satisfactory agreement between the theoretical results and simulation data leads to the following conclusions: (i) a modified hypernetted chain approximation combined with a hard sphere bridge function, which has been recently proposed by one of the authors of this study, is sufficiently reliable for the structural studies of CS fluid, and (ii) the thirdorder+secondorder perturbation DFT, which has proven successful for the study of inhomogeneous structure of model fluids with continuous intermolecular potential function, posses a high adaptability to be applied for various types of interaction potentials and performs well also in the case of discontinuous CS model.
Functional decoupling of nanostructured areas in superconducting strips for electromagnetic detectors
Authors: Gerbaldo R. , Ghigo G. , Gozzelino L. , Laviano F. , Lopardo G. , Minetti B. , Mezzetti E. , Cherubini R. , Rovelli A.
Published: September 2008

We studied high temperature superconducting devices created by means of local nanostructuring with high-energy heavy-ion lithography. Linear arrays of alternate nanostructured and as-grown YBa2Cu3O7−x film regions are patterned on the microscale. The density of the induced nanostructures is tuned in such a way to locally depress the superconducting properties until a functional electromagnetic decoupling between nanostructured and as-grown microzones is achieved in suitable regions of the (B,T) phase diagram. Pilot prototypes engineered for operating as magnetic field detectors in harsh cryogenic environment are characterized by electric transport and surface morphology analysis at microscale and nanoscale. Sensitivity, linearity range, and bandwidth limits of the pilot prototype are established from electrical transport characterization. The morphological analysis reveals the salient aspects of the surface modifications occurring with high-fluence heavy-ion lithography. Radiation annealing experiments with 3.5 MeV proton energy were performed to check out the reliability of the prototype operating in harsh environments. These measurements demonstrate the robustness of this approach aimed at creating dissipative microscale units that are sensitive to magnetic fields in a continuous dissipationless superconducting material.
Selection of the divergence waves on a model viscoelastic coating under a potential flow
Authors: Reutov V. P. , Rybushkina G. V.
Published: September 2008

The paper is concerned with the established regimes of generation of the divergence (quasistatic) waves on a model viscoelastic coating under a potential flow of an incompressible liquid. Parameters of the effective coating that consists of a strongly damped flexible plate supported by an extended spring foundation are evaluated using the condition of modeling the deformation of the viscoelastic layer of a rubberlike material in the available experiments. The local nonlinearity due to the dependence of a stiffness coefficient of the spring foundation on surface displacement is taken into account together with the generalized Karman nonlinearity. The system of equations and boundary conditions of the problem are simplified and reduced to the dimensionless form in the limit of large losses in the plate. The perturbed potential flow is found to be quasistationary. A system of coupled equations describing the resonant and nonresonant (energetic) interactions of multiple harmonics of the surface displacement is derived for weak bending of the surface and small perturbation of flow velocity potential. Conditions for the selection of the period of the established waves are elucidated in this approximation. For the description of large amplitude divergence waves observed experimentally, the numerical procedure is elaborated based on the usage of an orthogonal curvilinear coordinate system following the surface bending. The onset of the essentially nonsinusoidal large amplitude divergence waves and the selection of their period are simulated numerically.
Generation and reduction in SiO2/Si interface state density during plasma etching processes
Authors: Ishikawa Yasushi , Ichihashi Yoshinari , Yamasaki Satoshi , Samukawa Seiji
Published: September 2008

During plasma processes, the SiO2/Si interface state is generated by UV photon irradiation. We measured Pb centers (Si dangling bond at SiO2/Si interface) in SiO2/Si film by electron spin resonance spectroscopy. The density of Pb centers increased with increasing UV photon energy. This result indicates that high-energy photons effectively generate Pb centers because of the absorption at the SiO2/Si interface. At the same time, we found that UV photon flux is also an important factor in increasing the density of Pb centers. On the other hand, ion irradiations were not a significant factor in the generation of Pb centers. Ions can penetrate only the surface (less than 5 nm) but they cannot induce a Pb center at the SiO2/Si interface. Furthermore, pulse-time-modulated plasmas were used to reduce the UV photon irradiation during the plasma processes. The reduction in UV photon irradiation could completely eliminate the Pb centers compared with the use of a conventional continuous wave plasma.
Experimental off-axis electron holography of focused ion beam-prepared Si p-n junctions with different dopant concentrations
Authors: Cooper David , Ailliot Cyril , Truche Robert , Barnes Jean-Paul , Hartmann Jean-Michel , Bertin Francois
Published: September 2008

Silicon p-n junction specimens with a range of dopant concentrations have been prepared using focused ion beam milling for examination by off-axis electron holography. Here we show that phenomenon such as the electrically “inactive” thickness is strongly dependent on the dopant concentration of the specimens. We also show a dependence on both the specimen geometry and intensity of the electron beam on the phases measured across the junctions and a good reproducibility of results if care is taken during examination.
Brownian dynamics simulations of two-dimensional model for hopping times
Authors: Mon K. K.
Published: September 2008

Brownian dynamics simulations are used to study the mean first passage time for a hard disk diffusing in a channel. The disk has to hop pass another disk with the same diameter σ but fixed in contact with the wall. This mean first passage time is expected to diverge with an exponent η as the channel width (2Rp) approaches that of the nonpassing limit (2σ) for one disk to hop pass another. Our one disk model is similar to a disk diffusing in a two-dimensional container, shaped as a simplified configuration space of two passing disks in a flat channel of Kalinay. The Kalinay model was proposed recently to elucidate the disagreements between two different theoretical predictions for the exponent η of the two disk hopping time divergences. For the one disk model, simple transition state theory and a Fick–Jacobs type of dimensional reduction approach predict exponents of 1 and 1∕2, respectively. Our Brownian dynamics simulation, results are consistent with a value of 1.