bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation of gas-phase composition with film properties in the plasma-enhanced chemical vapor deposition of hydrogenated amorphous carbon nitride films
Authors: Liu Dongping , Zhou Jie , Fisher Ellen R.
Published: January 2007

Hydrogenated amorphous carbon nitride (a-C:N:H) films were synthesized from CH4∕N2, C2H4∕N2, and C2H2∕N2 gas mixtures using inductively coupled rf plasmas. These deposition systems were characterized by means of optical emission spectroscopy and mass spectrometry (MS). The effects of varying the nitrogen partial pressure on film growth and film properties were investigated, and experimental results indicate that the hydrocarbon species produced in the gas phase contribute directly to film growth. Although the CN radical is formed in the mixed gas systems, it does not appear to be a factor in controlling the rate of film deposition. The nature and energy of the ions in these systems were explored with MS. No clear dependence of ion energy on mass or plasma conditions was observed. Although films formed in the methane and ethylene systems were relatively smooth, a-C:N:H films prepared from acetylene-nitrogen plasmas had comparatively rough surfaces, most likely as a result of the strong gas-phase polymerization process produced by the ion-molecule reactions, CnHy++C2H2→C(n+2)Hy++H2 (n>1, y=1–3). Correlations between the a-C:N:H growth processes and the gas-phase plasma diagnostic data are discussed.
Optical spectroscopy and energy-filtered transmission electron microscopy of surface plasmons in core-shell nanoparticles
Authors: Eggeman Alexander S. , Dobson Peter J. , Petford-Long Amanda K.
Published: January 2007

Silica–silver core-shell nanoparticles were produced using colloidal chemistry methods. Surface plasmon resonances in the silver shells were investigated using optical absorption measurements in ultraviolet-to-visible (UV-vis) spectroscopy and the effect of shell thickness on the wavelength of the resonance was noted. Further studies of the resonances were performed using electron-energy-loss spectroscopy (EELS) and energy-filtered transmission electron microscope (EFTEM) imaging. The plasmon resonance was seen in an EELS spectrum at an energy corresponding to the wavelengths measured in an UV-vis spectrophotometer, and EFTEM images confirmed that the resonance was indeed localized at the surface of the silver shell. Further features were seen in the EELS spectrum and confirmed as bulk-plasmon features of silica and the carbon support film in the TEM specimen.
A method for calculating capacitances and electrostatic forces in atomic force microscopy
Authors: Sacha G. M. , Sahagún E. , Sáenz J. J.
Published: January 2007

A method to calculate electrostatic forces in the context of atomic force microscopy that is useful for the calculation of the electrostatic forces when different length scales are included in the simulation is presented. The versatility of the method allowed for an analysis of the behavior of forces as a function of the tip apex geometry. For example, for flattened, worn out tips, the force at the point of contact with a dielectric sample could be 2.5 times larger than that of a sharp tip. A simple analytical approximation has been also developed for the local characterization of thin films at the nanoscale.
Domain wall cloning in magnetic nanowires
Authors: Allwood D. A. , Xiong Gang , Cowburn R. P.
Published: January 2007

We demonstrate cloning of magnetic domain wall solitons using a nanowire junction. The effect of junction geometry is assessed using several different structure designs to construct operating phase diagrams. A domain wall cloning element is then integrated with a magnetic domain wall NOT gate and feedback loop to unambiguously demonstrate domain wall duplication. Finally, we demonstrate four times digital amplification of a signal by siting cloning elements sequentially. This can be used for signal routing in nanowire circuits or providing readout amplification for interfacing magnetic nanostructures with macroscopic probes such as magneto-optical beams.
Effect of a magnetic field pulse on ultrafast magnetization reversal in a submicron elliptical Permalloy thin film
Authors: Xiao Q. F. , Choi B. C. , Rudge J. , Hong Y. K. , Donohoe G.
Published: January 2007

The characteristics of a magnetic field pulse, its magnitude, direction, and rise and fall time on the mechanism of ultrafast magnetization reversal have been studied by micromagnetic simulations. An elliptically shaped, Permalloy thin film, having dimensions of 400nm long axis, 112nm short axis, and 3.2nm, thickness, was considered. A plot of the magnetic field pulse components describes three types of reversal behaviors, quasicoherent, incoherent, and nonreversal. The optimum magnetic field pulse for the suppression of magnetization ringing is found in the incoherent precession area by finding the lowest remanent total energy at the moment the pulse is cut off. The rise and fall time of the pulse has a significant effect on the reversal behavior only in the incoherent precession region. In this region, whether a reversal can occur depends on the rise time of the pulse. Extending the rise and fall time of the pulse, in the noncoherent rotation region, does not lead to a clear change of the remanent total energy but a rise time longer than 50ps does result in a distinct increase in the remanent exchange energy, which enhances the magnetization ringing.
Computerized ultrasound differentiation of curly birch from silver birch
Authors: Salmi Ari , Hintikka Tuomas , Karppinen Timo , Forsman Pia , Hæggström Edward
Published: January 2007

We report on computerized differentiation of two birch types. Curly birch (CB, Betula pendula var. carelica Sok) commands a higher price than a normal silver birch (SB, Betula pendula Roth). Hence it is crucial to differentiate the two wood types when the trees are young. We studied the possibility to use ultrasound for such differentiation. A propagation velocity of 4MHz longitudinal tone bursts, transmitted through block samples of 20×20mm2 cross section, comprising of both CB and SB woods, was determined. The samples originating from southern Finland were sawed so that the sound propagation direction was longitudinal or radial with respect to the trunk. One sample set comprised of seven different sample thicknesses with a range of 2–12mm. From the time-of-flight measurements of the samples (19±1%weight humidity) the wave propagation velocity under laboratory conditions (50±5%RH, 23±1°C) was determined from a least-squares fit. The results indicate a significant difference (t-test p=0.032 and velocity difference of 24±8%) in longitudinal direction and a highly significant difference (t-test p=0.001 and velocity difference of 22±10%) in the radial direction between the two wood types. A blinded probability of detection test was conducted using 48 samples originating from two different trunks as well as from single trunks’ curly and noncurly sections. The results indicate 93% probability of correct type classification using computerized clusterization.
Melting dynamics of superheated argon: Nucleation and growth
Authors: Luo Sheng-Nian , Zheng Lianqing , Strachan Alejandro , Swift Damian C.
Published: January 2007

We investigate the microscopic melting process of a superheated argon solid using molecular dynamics simulations. We characterize the melting dynamics by following the temperature and time evolutions of liquid atoms and demonstrate the formation of a critical liquid nucleus via fluctuations and subsequent growth. The critical liquid nucleus size (about 120 atoms) obtained from our direct simulations is in accord with the prediction of the classical nucleation theory. The dynamic nucleation and growth of liquid also agree with the Johnson–Mehl–Avrami law, and the growth exponent n∼3 at the early stage followed by a substantial increase in n thereafter.
Using an r-dependent Gaussian width in calculations of the globally uniform semiclassical wave function
Authors: Herman Michael F. , Sergeev Alexey
Published: January 2007

The globally uniform semiclassical wave function expresses the solution to the time independent Schrödinger equation in terms of fixed width Gaussian wave packets traveling along a set of trajectories. There is a globally uniform wave function (GUWF) for each value of the Gaussian width parameter γ. Numerical data show that a small Gaussian width is needed in some regions to obtain accurate results, while a broad Gaussian width provides better results in other regions. Since there is a semiclassically valid GUWF for every positive value of γ, it is reasonable to employ the GUWF corresponding to a Gaussian width that provides good results at each value of r. A criterion for the r dependent choice of γ is proposed and tested on one and two dimensional model problems. The results show that the use of an r dependent γ in the GUWF results in improved accuracy for the model problems considered.
Experimental and theoretical study of the photodissociation reaction of thiophenol at 243nm: Intramolecular orbital alignment of the phenylthiyl radical
Authors: Lim Ivan S. , Lim Jeong Sik , Lee Yoon Sup , Kim Sang Kyu
Published: January 2007

The photoinduced hydrogen (or deuterium) detachment reaction of thiophenol (C6H5SH) or thiophenol-d1 (C6H5SD) pumped at 243nm has been investigated using the H (D) ion velocity map imaging technique. Photodissociation products, corresponding to the two distinct and anisotropic rings observed in the H (or D) ion images, are identified as the two lowest electronic states of phenylthiyl radical (C6H5S∙). Ab initio calculations show that the singly occupied molecular orbital of the phenylthiyl radical is localized on the sulfur atom and it is oriented either perpendicular or parallel to the molecular plane for the ground (B1) and the first excited state (B2) species, respectively. The experimental energy separation between these two states is 2600±200cm−1 in excellent agreement with the authors’ theoretical prediction of 2674cm−1 at the CASPT2 level. The experimental anisotropy parameter (β) of −1.0±0.05 at the large translational energy of D from the C6H5SD dissociation indicates that the transition dipole moment associated with this optical transition at 243nm is perpendicular to the dissociating S–D bond, which in turn suggests an ultrafast D+C6H5S∙(B1) dissociation channel on a repulsive potential energy surface. The reduced anisotropy parameter of −0.76±0.04 observed at the smaller translational energy of D suggests that the D+C6H5S∙(B2) channel may proceed on adiabatic reaction paths resulting from the coupling of the initially excited state to other low-lying electronic states encountered along the reaction coordinate. Detailed high level ab initio calculations adopting multireference wave functions reveal that the C6H5S∙(B1) channel may be directly accessed via a (nπ,σ*)1 photoexcitation at 243nm while the key feature of the photodissociation dynamics of the C6H5S∙(B2) channel is the involvement of the (nπ,π*)3→(nσ,σ*)3 profile as well as the spin-orbit induced avoided crossing between the ground and the (nπ,σ*)3 state. The S–D bond dissociation energy of thiophenol-d1 is accurately estimated to be D0=79.6±0.3kcal∕mol. The S–H bond dissociation energy is also estimated to give D0=76.8±0.3kcal∕mol, which is smaller than previously reported ones by at least 2kcal∕mol. The C–H bond of the benzene moiety is found to give rise to the H fragment. Ring opening reactions induced by the π-π*∕nπ-π* transitions followed by internal conversion may be responsible for the isotropic broad translational energy distribution of fragments.
Shock-induced thermal behavior of aluminum nanoparticles in propylene oxide
Authors: Yan Z. X. , Wu J. H. , Ye S. , Hu D. , Yang X. D.
Published: January 2007

The thermal behavior of aluminum nanoparticles reacting with propylene oxide was investigated in normal incident shock waves. Their reactive temperature, which is about 2705±150K, was experimentally determined by the emission strength of AlO. The reactive products were evaluated by x-ray diffraction, which shows that several different phases of Al2O3 are produced in different temperature regions. The scanning electron microscopy image of the reactive products shows that some holes, which were produced in the process of aluminum nanoparticles violently reacting with suboxides of aluminum, are found on the surface of the products. The data of transmission electron microscopy indicate that the grain diameters of the products were within the range of 20–90nm. The geometry of propylene oxide was calculated and optimized using the Rb31yp function and the 6–311+g(d,p) basis set. The calculated results show that the diameter of the molecule is about 0.435nm. The process of vaporizing and condensing of propylene oxide was investigated by electron microscopy, and the results show that the average drop diameter is 4.03μm at t=70s and then is 2.06μm at t=120s. It suggests that the average drop diameters tend to range from several nanometers to tens of nanometers, which is very close to the diameter of aluminum nanoparticles (average of 70nm). Thus, we may consider them to react with each other in the gas phase in normal incident shock waves in the experiment.
Determination of the entropy changes in the compounds with a first-order magnetic transition
Authors: Liu G. J. , Sun J. R. , Shen J. , Gao B. , Zhang H. W. , Hu F. X. , Shen B. G.
Published: January 2007

Entropy changes in the compounds of La1−xPrxFe11.5Si1.5 (x=0.3 and 0.4) have been experimentally studied. A tower-shaped entropy change of the height of ∼27J∕kgK is obtained based on the analyses of heat capacity, while the Maxwell relation predicts an extra entropy peak of the height of ∼99J∕kgK, slightly varying with Pr content. A careful study indicates that the Maxwell relation cannot be used in the vicinity of the Curie temperature because of the coexistence of paramagnetic and ferromagnetic phases, and the huge entropy peak is a spurious result. Similar conclusions are applicable to MnAs and Mn1−xFexAs, for which huge entropy changes have been reported. Appropriate methods for the determination of entropy change of the compound with phase separation are discussed based on the magnetic data.
Statistical instability of barrier microdischarges operating in townsend regime
Authors: Nagorny V. P.
Published: January 2007

The dynamics of barrier microdischarges operating in a Townsend regime is studied analytically and via kinetic particle-in-cell/Monte Carlo simulations. It is shown that statistical fluctuations of the number of charged particles in the discharge gap strongly influence the dynamics of natural oscillations of the discharge current and may even lead to a disruption of the discharge. Analysis of the statistical effects based on a simple model is suggested. The role of external sources in stabilizing microdischarges is clarified.
Kelvin probe force and surface photovoltage microscopy observation of minority holes leaked from active region of working InGaAs∕AlGaAs∕GaAs laser diode
Authors: Ankudinov A. V. , Evtikhiev V. P. , Ladutenko K. S. , Rastegaeva M. G. , Titkov A. N. , Laiho R.
Published: January 2007

A method for direct observation of carrier leakage from active regions of working semiconductor light-emitting diodes and lasers is suggested. In this method, Kelvin probe force and surface photovoltage microscopies are used to measure local changes in the surface potential of the device mirror on which a high concentration of the leaked carriers is expected. The applicability of the method is demonstrated by studying in detail the leakage current on the mirrors of high-power InGaAs∕AlGaAs∕GaAs laser diodes in action. It is shown that minority holes arrive at the mirror surface from the active zone of the laser and spread over to regions of the n emitter and n substrate. This observation is confirmed by exposing the mirror to external light with photon energy exceeding the band gap of the laser structure and measuring the generated surface photovoltage. Owing to surface channels formed by the surface band bending, the holes can move tens of micrometers from the place of their generation. The leakage currents are evaluated on the basis of the surface potential distributions observed. It is found that as the injection current of the laser increases, the leakage current grows until onset of lasing.
Long-range corrected time-dependent density functional study on fluorescence of 4,4′-dimethylaminobenzonitrile
Authors: Chiba Mahito , Tsuneda Takao , Hirao Kimihiko
Published: January 2007

Dual fluorescence of 4,4′-dimethylaminobenzonitrile (DMABN) was theoretically investigated on the basis of long-range corrected time-dependent density functional theory. Excited-state geometry optimization states and single-point energy calculations with and without solvent effect were carried out. It has been explained that DMABN emits dual fluorescence only in polar solvents through locally excited (LE) and charge transfer (CT) states. It was, however, concluded from this study that although the main spectrum of dual fluorescence in acetonitrile solvent is clearly due to twisted intramolecular CT fluorescence, small secondary fluorescence in acetonitrile may also emanate from CT fluorescence during the DMABN twisting process. This conclusion is supported by an experimental interpretation on polarization spectroscopy. It was also found that the optimized DMABN geometries have certain wagging angles for the CT state and no wagging angle for the LE state. This may support an early experimental hypothesis that the dual fluorescence of DMABN is induced by the wagging mode due to vibronic coupling between LE and CT states. Consequently, the authors propose a fluorescence mechanism of DMABN in gas phase and in acetonitrile solvent: the main absorption proceeds to the CT state in both situations. In gas phase, single fluorescence is chiefly emitted from the LE state through the internal conversion from CT to LE states. Dual fluorescence in acetonitrile solvent may only be emitted from the CT state.
Comprehensive theoretical studies on the CF3H dissociation mechanism and the reactions of CF3H with OH and H free radicals
Authors: Zhang Meiling , Lin Zijing , Song Ce
Published: January 2007

The potential energy surfaces for the CF3H unimolecular dissociation reaction and reactions of CF3H with free radical OH and H were investigated at the B3LYP∕6-311++G** and QCISD(T)∕6-311++G** levels and by the G3B3 theory. All the possible stationary and first-order saddle points along the reaction paths were verified by the vibrational analysis. The calculations account for all the product channels. The reaction enthalpies obtained at the G3B3 level are in good agreement with the available experiments. Canonical transition-state theory with Wigner tunneling correction was used to predict the rate constants for the temperature range of 298–2500K without any artificial adjustment, and tshe computed rate constants for elementary channels can be accurately fitted with three-parameter Arrhenius expressions. The theoretical rate constants of the CF3H+H reaction agree with the available experimental data very well. The theoretical and experimental rate constants for the CF3H+OH reaction are in reasonable agreement. The H abstraction of CF3H by OH is found to be the main reaction channel for the CF3H fire extinguishing reactions while the CF3H unimolecular dissociation reaction plays a negligible role.
Copper hexadecafluorophthalocyanine and copper phthalocyanine as a pure organic connecting unit in blue tandem organic light-emitting devices
Authors: Lai S. L. , Chan M. Y. , Fung M. K. , Lee C. S. , Lee S. T.
Published: January 2007

A nondoped organic system of copper hexadecafluorophthalocyanine (F16CuPc)∕copper phthalocyanine (CuPc) has been investigated as a connecting unit for deep-blue electrofluorescent tandem organic light-emitting devices (OLEDs) based on 2-methyl-9,10-di(2-naphthyl) anthracene emission. Such devices exhibited a doubling in current efficiency from 0.63to1.47cd∕A at J=100mA∕cm2 as compared to the single-unit device. The pure organic connecting unit showed superior optical transparency (∼100%), resulting in minimal microcavity effect in the devices. Interface dipole and band bending on both sides of the F16CuPc∕CuPc interface suggested the formation of an intrinsic p-n junction, which is a prerequisite of an effective connecting unit leading to a dramatic performance improvement in the tandem OLEDs.
Solvent effects on the UV-visible absorption spectrum of benzophenone in water: A combined Monte Carlo quantum mechanics study including solute polarization
Authors: Georg Herbert C. , Coutinho Kaline , Canuto Sylvio
Published: January 2007

The entire ultraviolet-visible absorption spectrum of benzophenone in water is studied and compared with the same spectrum in gas phase. Five transitions are considered, and the corresponding solvatochromic shifts are obtained and compared to experiment. Using a sequential procedure of Monte Carlo simulations and quantum mechanical calculations, liquid configurations were generated and an averaged spectrum of the solution was calculated. The solute polarization was included by an iterative procedure where the atomic charges of the solute were obtained as an average with the solvent distribution. The calculated average dipole moment of benzophenone in water, with MP2∕6-31++G(d,p), converges to the value of 5.84±0.05D, 88% larger than the gas-phase value of 3.11D. Using 100 statistically uncorrelated configurations and solvation shells with 235 explicit water molecules selected by a minimum-distance distribution of solvent shells, instead of the usual radial distribution, the excitation energies were obtained from solute-solvent all-valence-electron INDO/CIS calculations. The shift of the weak n-π* transition is obtained as 2045±40cm−1 and the strong and broad π-π* shift as −1790±30cm−1. These results are in good agreement with the experimental values of 2200 and −1600cm−1, respectively. Standard procedure used by common force fields to generate atomic charges to describe the electrostatic moments of the solute, with HF∕6-31G(d), gives a dipole moment of 3.64D. Using these standard charges in the simulation, the average shifts are calculated as 1395±35 and −1220±25cm−1, both about 600cm−1 smaller in magnitude than those obtained with the average converged fully polarized solute. The influence of the solute polarization in the solute-solvent interaction and, in particular, in solute-solvent hydrogen bonds is analyzed.
The single-valued diffusion coefficient for ionic diffusion through porous media
Authors: Lorente Sylvie , Voinitchi Dorinel , Bégué-Escaffit Pascale , Bourbon Xavier
Published: January 2007

The current literature on ionic diffusion through porous media teaches that the diffusion coefficient is a complicated function depending on concentration, concentration gradient, and electrical potential gradient. This paper documents how natural diffusion tests and migration tests (electrically enhanced transport) lead to the measurement of a unique diffusion coefficient for a given ionic species and a given material. Natural diffusion tests for chloride and a ceramic of TiO2 were implemented at two different concentration levels. The experiments were designed to emphasize the impact of the membrane potential in the pore solution on the chloride flux. By accounting for the membrane potential it is shown that the chloride diffusion coefficient is unique for a given material. An iterative method based on a numerical model solving the continuity equations and the current law is proposed to determine the diffusion coefficient. The approach is applied with success to published results on a cement-based material. Migration tests were also performed with chloride in a cementitious material, where the chloride transport is enhanced by an external electrical field. The experimental results reveal the competition between diffusion and electrical effects in the case of noncontaminated porous materials. By varying the electrical potential difference it is shown that the flux of chloride varies linearly with the electrical field, meaning that the chloride diffusion coefficient does not depend on the electrical field. The main conclusion is that there is only one chloride diffusion coefficient for a given porous material.
Composition dependence of electrical and optical properties in sol-gel MgxZn1−xO thin films
Authors: Ghosh R. , Basak D.
Published: January 2007

Mg x Zn 1 − x O  (x=0.0–0.20) ternary alloy thin films have been deposited by sol-gel technique and the composition related structural, microstructural, electrical, and optical properties are investigated. All the films have the hexagonal wurtzite structure. In the composition range of 0.05<x⩽0.20, a deviation from the Vegard’s law in the value of c-axis lattice constant is observed. The Mg:Zn ratio in the films is found to be much lower than the nominal values for the composition range of 0.05<x⩽0.20. Nonlinearity in the current-voltage (I-V) characteristics is observed for the composition range of 0.10<x⩽0.20. The optical band gap values of the MgxZn1−xO films vary linearly up to x=0.05 and thereafter the values deviate from the linear fit. The photoluminescence results also show that ultraviolet peak position is gradually shifted towards the higher energy side up to x=0.05, above which the change of the peak positions are random. These results suggest that the solubility limit of MgO in sol-gel MgxZn1−xO thin films lies in the composition range of 0.05<x<0.08.
Frequency response in photonic heterostructures consisting of single-negative materials
Authors: Zhang H. Y. , Zhang Y. P. , Wang P. , Yao J. Q.
Published: January 2007

Transmission studies for multiple heterostructures consisting of two kinds of single-negative materials inserted with defects are presented. The results show that multiple-channeled filters can be obtained by adjusting the period number m and thicknesses of defects. These structures provide an excellent way to select useful multiple-channeled optical signals from a stop gap, and it is useful in optical device applications.
Inflation threshold: A nonlinear trapping-induced threshold for the rapid onset of stimulated Raman scattering from a single laser speckle
Authors: Vu H. X. , DuBois D. F. , Bezzerides B.
Published: January 2007

The rapid onset, with increasing laser intensity, of levels of backward stimulated Raman scattering (BSRS) exceeding linear convective predictions, from single laser hot spots was predicted by simulations [Vu et al., Phys. Plasmas 9, 1745 (2002)], and has been observed [Montgomery et al., Phys. Plasmas 9, 2311 (2002)] in nonlinear regimes dominated by electron trapping. A theory for this inflation threshold is given here. The threshold is the result of competition between velocity diffusion and trapping, and is exceeded when the convectively amplified SRS Langmuir wave (LW) achieves an amplitude for which the coherent trapping velocity increment of electrons in the LW (the half-width of the trapping separatrix) exceeds the rms diffusion velocity (resulting from background plasma fluctuations), accumulated in one bounce time, for electrons with mean velocities near the phase velocity of the LW. The results of this theory, when the kinetic theory of the one-dimensional (1D) reduced-description particle-in-cell (RPIC) simulation is used, are in good agreement with a series of 1D RPIC simulations. The theory is naturally generalized to three dimensions, and is compatible with macroscopic laser interaction codes such as pF3d [Berger et al., Phys. Plasmas 5, 4337 (1998)]. Comparison of the LW trapping-induced inflation threshold to the LW threshold for the Langmuir decay instability provides an estimate for the transition between nonlinear saturation regimes. In an independent hot spot model of many hot spots, statistics suggests that the inflation threshold intensity will control the rapid onset of strong BSRS in laser beams smoothed by random phase plates.
Energetics and dipole moment of transition metal monoxides by quantum Monte Carlo
Authors: Wagner Lucas K. , Mitas Lubos
Published: January 2007

The transition metal (TM) oxygen bond appears very prominently throughout chemistry and solid-state physics. Many materials, from biomolecules to ferroelectrics to the components of supernova remnants, contain this bond in some form. Many of these materials’ properties depend strongly on fine details of the TM–O bond, which makes accurate calculations of their properties very challenging. Here the authors report on highly accurate first principles calculations of the properties of TM monoxide molecules within fixed-node diffusion Monte Carlo and reptation Monte Carlo.
Time-resolved observation of the Eigen cation in liquid water
Authors: Amir Wafa , Gallot Guilhem , Hache François , Bratos S. , Leicknam J.-C. , Vuilleumier R.
Published: January 2007

Experimental observation and time relaxation measurement of the hydrated proton Eigen form [H3O+(H2O)3] are presented here. Vibrational time-resolved spectroscopy is used with an original method of investigating the proton excess in water. The anharmonicity of the time-resolved spectra is characteristic of the Eigen-type proton geometry. Proton relaxation occurs in less than 200fs. A calculation of the potential energy confirms the experimental result and the Eigen cation lifetime is in good agreement with previous molecular dynamics simulations.
Monolayer CoPt magnetic nanoparticle array using multiple thin film depositions
Authors: Kim Jung H. , Kim Jeon , Oh Nuri , Kim Young-Ho , Kim Chang Kyung , Yoon Chong Seung , Jin Sungho
Published: January 2007

A monolayer of L10 CoPt nanoparticles was prepared on a polyimide film by depositing Co–Pt and annealing the resulting film stack at 650–800°C. To obtain well-separated magnetic nanoparticles avoiding substantial coarsening often seen on annealing of thicker films, a multiple deposition of thinner Co–Pt alloy films with intentionally increased Co composition was employed. The multiple depositions relying on heterogeneous nucleation on the preexisting CoPt nanoparticles allowed the average particle size to increase from 4to7nm. The monolayer of 7nm sized CoPt nanoparticles exhibited a coercivity of 9.8kOe with a remanence ratio of 0.72.
Predicted stability and structure of (HXeCCH)n(n=2or4) clusters and of crystalline HXeCCH
Authors: Sheng Li , Gerber R. Benny
Published: January 2007

Ab initio calculations predict the existence of the dimer and tetramer of HXeCCH. The interaction energies are −6.66 and −19.40kcalmol−1 for the dimer and tetramer, respectively. For both complexes, larger blue shifts of the Xe–H stretching mode are found, while the Xe–C stretching modes are slightly redshifted. The stability and structure of HXeCCH crystals is predicted by density functional theory calculations with periodic boundary conditions. Strong electrostatic interactions are found between the monomers in the crystal. The results are first evidence for the existence of crystalline materials made of a novel class of noble gas molecules.
Tricritical point induced by smectic ordering of a nematic gel
Authors: Kushibe Yoshinari , Matsuyama Akihiko
Published: January 2007

The authors study volume phase transitions of a nematic gel immersed in a liquid crystal (LC) solvent, which shows a second-order nematic-smectic A phase transition (NST). Combining Flory’s elastic energy [Principles of Polymer Chemistry (Cornell University Press, Ithaca, 1953)] for a swelling of the gel with the McMillan model [Phys. Rev. A 4, 1238 (1971)] for smectic ordering, the authors calculate the equilibrium swelling of the gel and smectic order parameters as a function of temperature. The authors take into account an attractive interaction parameter c between the gel and LC solvents. On increasing the value of the coupling constant c, a second-order NST of the gel is changed to a first-order one and a continuous volume phase transition of the gel is changed to a discontinuous one. The authors find a tricritical point of the gel induced by smectic ordering.
Nanometer-scale order in amorphous Ge2Sb2Te5 analyzed by fluctuation electron microscopy
Authors: Kwon Min-Ho , Lee Bong-Sub , Bogle Stephanie N. , Nittala Lakshmi N. , Bishop Stephen G. , Abelson John R. , Raoux Simone , Cheong Byung-ki , Kim Ki-Bum
Published: January 2007

The phase change material Ge2Sb2Te5 is widely investigated for use in nonvolatile memories. It has been reported that the crystallization speed depends on the thermal history, indicating that structural differences exist between amorphous states. The authors apply fluctuation electron microscopy to quantify differences in the nanometer-scale structural order between several amorphous states of Ge2Sb2Te5. All as-deposited films are found to contain ordered regions. Thermal annealing below the crystallization threshold increases the nanoscale order, and such samples crystallize slightly more rapidly. The authors hypothesize that the nanoscale ordered regions act as the nuclei for crystallization, with the largest regions being the most significant.
Electromigration of single metal atoms observed by scanning tunneling microscopy
Authors: Braun K.-F. , Soe W.-H. , Flipse C. F. J. , Rieder K.-H.
Published: January 2007

The authors show in this letter that single metal atoms on a Ni(111) surface can be pushed by electromigration forces from a scanning tunneling microscope tip. This repulsive interaction is observed over a length scale of 6nm. While for voltages above −300mV the atoms are pulled by the microscope tip, the atoms are pushed away below this threshold. This migration is explained by a resonant scattering of strongly correlated electrons. At small voltages chemical forces are pulling the atom, while for larger voltages the atomic manipulation is assisted by the tunneling current.
Comment on “Dielectric tunability of (110) oriented barium strontium titanate epitaxial films on (100) orthorhombic substrates” [Appl. Phys. Lett. 89, 042903 (2006)]
Authors: Zembilgotov A. G. , Böttger U. , Waser R.
Published: January 2007

A modified thermodynamic potential was derived to describe the phase states and dielectric properties of (110) oriented epitaxial films grown on orthorhombic substrates.
Size-dependent piezoelectricity in zinc oxide nanofilms from first-principles calculations
Authors: Li Chun , Guo Wanlin , Kong Yong , Gao Huajian
Published: January 2007

The size dependence of the piezoelectricity in ZnO nanofilms is investigated using ab initio density-functional theory calculations. The effective piezoelectric constant of ZnO nanofilms increases monotonically with increasing film thickness in the nanoscale simulated in the present work, and surprisingly, exceeds that of the bulk ZnO when the thickness is greater than 2.4nm. The enhancement over the bulk value reaches 11% when the film thickness is 2.9nm.
High pressure photoluminescence and Raman investigations of CdSe∕ZnS core/shell quantum dots
Authors: Fan H. M. , Ni Z. H. , Feng Y. P. , Fan X. F. , Kuo J. L. , Shen Z. X. , Zou B. S.
Published: January 2007

Photoluminescence (PL) and Raman spectroscopies of CdSe∕ZnS core/shell quantum dots (QDs) were studied under hydrostatic pressure (0–160kbars) at room temperature. Two phase transitions, at 69 and 79kbars, respectively, were observed, which correspond to wurtzite-rocksalt and rocksalt-cinnabar structural transformations. The full width at half maximum of PL peaks was found to decrease anomalously approximately 30% with pressure. These experimental data show significant difference between the CdSe∕ZnS core/shell QDs and simple bare CdSe QDs or bulk CdSe, implying the ZnS shell plays a dominant role in structural stability and electronic state of such system.
Extreme ultraviolet holographic lithography: Initial results
Authors: Cheng Yang-Chun , Isoyan Artak , Wallace John , Khan Mumit , Cerrina Franco
Published: January 2007

The authors report the initial results from a holographic lithography technique using extreme ultraviolet (EUV) radiation. This approach removes the need for complex EUV reflective masks and optics, replacing them with a binary, nanopatterned transmission mask. Computer generated holograms were fabricated on 100nm thick silicon nitride membranes with a 100nm thick chromium absorber layer. Reconstructed images have been recorded in an 80nm thick polymethylmetacrylate photoresist using 13nm wavelength EUV radiation from an undulator source. The pattern was characterized by optical and atomic force microscopies, and compared with simulation results from the TOOLSET diffraction simulation program, yielding excellent agreement.
Shaping high-speed Marangoni flow in liquid films by microscale perturbations in surface temperature
Authors: Basu Amar S. , Gianchandani Yogesh B.
Published: January 2007

The authors show that a variety of controlled flow patterns, including toroidal cells and surface doublets, can be generated in 80–400μm thick liquid films by placing scanning microscopy probes with integrated heaters just above the surface (<400μm separation). The probes project sharp temperature gradients on the liquid surface which drive Marangoni flow. Flow velocities approaching 3000μm∕s are experimentally demonstrated on length scales of 20–200μm with <20mW input power. For liquids such as water and oil, in which the surface tension coefficient is ≈0.2mN∕mK, flows >1000μm∕s can be accomplished with surface temperature perturbations <1°C. This technique enables microfluidic manipulation on unpatterned substrates.
Micromagnets for coherent control of spin-charge qubit in lateral quantum dots
Authors: Pioro-Ladrière M. , Tokura Y. , Obata T. , Kubo T. , Tarucha S.
Published: January 2007

A lateral quantum dot design for coherent electrical manipulation of a two-level spin-charge system is presented. Two micron-size permanent magnets integrated to high-frequency electrodes produce a static slanting magnetic field suitable for voltage controlled single qubit gate operations. Stray field deviation from the slanting form is taken into account in the Hamiltonian describing the two-level system, which involves hybridization of a single electron spin to the quantum dot’s orbitals. Operation speed and gate fidelity are related to device parameters. Sub-100-ns π pulse duration can be achieved with lattice fluctuation coherence time of 4ms for GaAs.
Field-induced resistive switching based on space-charge-limited current
Authors: Xia Yidong , He Weiye , Chen Liang , Meng Xiangkang , Liu Zhiguo
Published: January 2007

Polycrystalline (Ba,Sr)(Zr,Ti)O3 thin films sandwiched between two Pt electrodes have been revealed to exhibit hysteretic current-voltage (I-V) characteristics and resistive switching at room temperature. High- and low-resistance states, as well as a less abrupt state transition, occur during the voltage cycle. The maximum ratio between these two resistance states is about 230. Analyses of I-V behaviors have been executed, and it is proposed that space-charge-limited-current conduction in higher voltage region caused by asymmetric electron trapping centers is responsible for such transition of resistance states.
Strains in BaTiO3 thin film deposited onto Pt-coated Si substrate
Authors: Dkhil Brahim , Defaÿ Emmanuel , Guillan Julie
Published: January 2007

The ferroelectric-paraelectric phase transition was investigated in BaTiO3 100nm thick film deposited on platinized Si substrate by measuring the lattice parameters as a function of temperature and the hysteresis loop at room temperature. The transition from paraelectric to ferroelectric phase takes place at ∼420K (instead of 400K for unconstrained single crystals), whereas the film is under high tensile elastic in-plane strain (0.34%) and high inhomogeneous strain (0.69%) along the growth direction. Comparison of the experimental results with recent theoretical calculations suggests a monoclinic ferroelectric phase at room temperature, where interface “dead layer” plays a key role.
Faraday rotation in an InP waveguide
Authors: Zaman T. R. , Guo X. , Ram R. J.
Published: January 2007

Waveguide Faraday rotation was demonstrated in an InP waveguide with magnetic dopants. The modal Verdet coefficient was 10°∕mmT at a wavelength of 1.55μm. It was found that the Verdet coefficient of the Fe:In1−xGaxAsyP1−y (x=0.290, y=0.628) core was 12.5°∕mmT at a wavelength of 1.55μm. The Verdet coefficient dependence on wavelength is in agreement with theory. The loss of the waveguide was 4.34dB∕cm, giving a magneto-optic figure of merit of 23 at a magnetic field of 1T and a wavelength of 1.55μm. This semiconductor waveguide shows promise for monolithically integrated optical isolators.
Sputtered gold as an effective Schottky gate for strained Si∕SiGe nanostructures
Authors: Scott G. D. , Xiao M. , Jiang H. W. , Croke E. T. , Yablonovitch E.
Published: January 2007

Metallization of Schottky surface gates by sputtering Au on strained Si∕SiGe heterojunctions enables the depletion of the two dimensional electron gas at a relatively small voltage while maintaining an extremely low level of leakage current. A fabrication process has been developed to enable the formation of submicron Au electrodes sputtered onto Si∕SiGe without the need of a wetting layer.
Optimized growth of lattice-matched InxAl1−xN∕GaN heterostructures by molecular beam epitaxy
Authors: Schmult S. , Siegrist T. , Sergent A. M. , Manfra M. J. , Molnar R. J.
Published: January 2007

The authors present a systematic study on the growth of the ternary compound InxAl1−xN by molecular beam epitaxy. This work concentrates on In mole fractions x around 0.17, as this composition is in-plane lattice matched to GaN. At a growth temperature of 540°C, high quality material was obtained using a total metal to nitrogen flux ratio of ∼1. Using these growth parameters, high quality GaN∕InAlN superlattices were obtained without growth interruptions.
Epitaxial growth and magnetic properties of the first five members of the layered Srn+1RunO3n+1 oxide series
Authors: Tian W. , Haeni J. H. , Schlom D. G. , Hutchinson E. , Sheu B. L. , Rosario M. M. , Schiffer P. , Liu Y. , Zurbuchen M. A. , Pan X. Q.
Published: January 2007

Epitaxial thin films of the n=1–5 members of the layered Srn+1RunO3n+1 oxide series were produced by reactive molecular-beam epitaxy. X-ray diffraction and high-resolution transmission electron microscopy confirm that these films are epitaxially oriented and nearly phase pure (>98%). The Sr2RuO4 (n=1) and Sr3Ru2O7 (n=2) samples show no ferromagnetic transition in the range from 5to300K, while the Sr4Ru3O10 (n=3), Sr5Ru4O13 (n=4), and Sr6Ru5O16 (n=5) samples show ferromagnetic transitions at 85, 95, and 130K, respectively.
Spectrum of electronic excitations due to the adsorption of atoms on metal surfaces
Authors: Mizielinski M. S. , Bird D. M. , Persson M. , Holloway S.
Published: January 2007

The time-dependent, mean-field Newns-Anderson model for a spin-polarized adsorbate approaching a metallic surface is solved in the wide-band limit. Equations for the time evolution of the electronic structure of the adsorbate-metal system are derived and the spectrum of electronic excitations is found. The behavior of the model is demonstrated for a set of physically reasonable parameters.
Design of plasmon cavities for solid-state cavity quantum electrodynamics applications
Authors: Gong Yiyang , Vučković Jelena
Published: January 2007

Research on photonic cavities with low mode volume and high quality factor garners much attention because of applications ranging from optoelectronics to cavity quantum electrodynamics (QED). The authors propose a cavity based on surface plasmon modes confined by metallic distributed Bragg reflectors. They analyze the structure with finite difference time domain simulations and obtain modes with quality factor of 1000 (including losses from metals at low temperatures), reduced mode volume relative to photonic crystal cavities, Purcell enhancements of hundreds, and even the capability of enabling cavity QED strong coupling.
Gate capacitance coupling of singled-walled carbon nanotube thin-film transistors
Authors: Cao Qing , Xia Minggang , Kocabas Coskun , Shim Moonsub , Rogers John A. , Rotkin Slava V.
Published: January 2007

The electrostatic coupling between singled-walled carbon nanotube (SWCNT) networks/arrays and planar gate electrodes in thin-film transistors (TFTs) is analyzed both in the quantum limit with an analytical model and in the classical limit with finite-element modeling. The computed capacitance depends on both the thickness of the gate dielectric and the average spacing between the tubes, with some dependence on the distribution of these spacings. Experiments on transistors that use submonolayer, random networks of SWCNTs verify certain aspects of these calculations. The results are important for the development of networks or arrays of nanotubes as active layers in TFTs and other electronic devices.
Soft x-ray magnetic circular dichroism study of weakly ferromagnetic Zn1−xVxO thin film
Authors: Ishida Y. , Hwang J. I. , Kobayashi M. , Takeda Y. , Mamiya K. , Okamoto J. , Fujimori S.-I. , Okane T. , Terai K. , Saitoh Y. , Muramatsu Y. , Fujimori A. , Tanaka A. , Saeki H. , Kawai T. , Tabata H.
Published: January 2007

The authors performed a soft x-ray magnetic circular dichroism (XMCD) study of a Zn1−xVxO thin film, which showed a small ferromagnetic moment. Field and temperature dependences of V 2p XMCD signals indicated the coexistence of Curie-Weiss paramagnetic and antiferromagnetic V ions, quantitatively consistent with the magnetization measurements. The authors attributed the paramagnetic signal to V ions substituting for Zn sites, which are somewhat elongated along the c axis. A possible formation of ferromagnetically dead layers in the surface region of the film is also discussed.
Epitaxial growth of BaTiO3 films on TiN∕Si substrates by a hydrothermal-galvanic couple method
Authors: Chieh Yu-Chih , Yu Chin-Chih , Lu Fu-Hsing
Published: January 2007

Highly (111)- and (200)-oriented cubic BaTiO3 films with dense and hemispherelike morphology have been synthesized on different oriented TiN-coated silicon substrates in barium contained concentrated alkaline solutions at temperatures below 100°C. An unconventional hydrothermal technique combining a hydrothermal method with a galvanic couple setup was used to prepare the films. Resultant BaTiO3 films could grow easily and epitaxially on the TiN seeding layer over Si substrates. Compared to the conventional hydrothermal method, such a hydrothermal-galvanic couple technique could significantly enhance the growth rate of BaTiO3.
Asymmetric strain relaxation in patterned SiGe layers: A means to enhance carrier mobilities in Si cap layers
Authors: Buca D. , Holländer B. , Feste S. , Lenk St. , Trinkaus H. , Mantl S. , Loo R. , Caymax M.
Published: January 2007

Strain relaxation in patterned Si0.77Ge0.23 stripes grown on Si(001) by chemical vapour deposition was investigated after He+ ion implantation and annealing. Ion channeling measurements indicate asymmetric strain relaxation with a significantly higher residual strain parallel to the stripes than perpendicular to the stripes. These results are confirmed by plan view transmission electron microscopy showing a much higher density of misfit dislocations running along the stripes than across the stripes. Estimates based on a piezoresistivity model indicate significant enhancements of electron and hole mobilities for asymmetrically strained Si cap layers on such SiGe stripes.
Improvement switching characteristics of toggle magnetic random access memory with dual polarity write pulse scheme
Authors: Lee Yuan-Jen , Hung Chien-Chung , Wang Ding-Yeong , Yen Cheng-Tyng , Chen Wei-Chuan , Yang Shan-Yi , Shen Kuei-Hung , Wang Yung-Hung , Chen Yung-Hsiang , Kao Ming-Jer , Tsai Ming-Jinn
Published: January 2007

The writing probability of toggle magnetic random access memory (MRAM) at built-in bias field is studied by micromagnetic simulation and a dual polarity write pulse scheme has been proposed to enhance the toggle probability at low writing field. The critical writing field can be reduced to 19Oe at strong built-in bias field from CoFe(1.0nm)∕CoFeB(2.0nm)∕Ru∕CoFe(5.0nm) pinned layer structure. From the simulation and experimental results, it is proven that the toggle MRAM can be operated at lower writing field by dual polarity write pulse scheme.