bluuebunny/crossref_metadata_2025 huggingface dataset:
Destination Marketing: Future Issues — Strategic Challenges
Authors: Fyall Alan , Leask Anna
Published: March 2007

Although pivotal to the travel and tourism system, the destination is widely acknowledged to be one of the most difficult products to manage and market. Over the coming decade, the challenges facing destination marketers are likely to be even greater with a whole host of issues likely to impact on the future marketing of destinations. This paper seeks to utilise an exploratory framework that brings together those issues deemed to be of significance to the future marketing of the destination product and examine the extent to which the framework can be applied to the marketing of two major destinations in the UK: London and Edinburgh. Both London and Edinburgh represent significant destinations for both domestic and international tourists and have been impacted by forces external and internal to the UK in recent years. For example, externally, 911 in the United States and SARS in South East Asia have both impacted on international travel patterns while the outbreak of Foot and Mouth Disease in 2001 and the devolution and ‘regionalisation’ of tourism within the UK has impacted on the management and marketing of destinations within the UK at the local, sub-regional, regional and national levels. In addition to conducting a thorough review of the relevant literature and organising focus group sessions within their working environments, the authors also conducted a series of face-to-face interviews with appropriate stakeholders in the two destinations to identify and explore those future issues and strategic challenges facing those marketing destinations in the future generally, and specifically to the two destinations representing the focus of enquiry in this study. The one consistent finding — and the one that perhaps best encapsulates those 15 challenges identified in the proposed framework — is the issue of collaboration and the need for those within the destinations to work together in solving problems deemed too demanding to solve in isolation. For collaboration to succeed in the context of destinations, the destination management organisation needs to act as a strong unifying force that is able to bring all component parts of the destination together and develop the wider destination in its entirety. To conclude, both London and Edinburgh have ambitious growth targets for the future. Collaboration is key to the achievement of such targets as is the need to continue to diversify markets. The need to be cognisant of all those issues and forces impacting on their future direction is, however, vital if both destinations are to keep abreast of competing destinations; both at home and overseas.
Laser sintering of thick-film conductors for microelectronic applications
Authors: Kinzel Edward C. , Sigmarsson Hjalti H. , Xu Xianfan , Chappell William J.
Published: March 2007

This paper investigates fabrication of functional thick metal films using simultaneous laser sintering and patterning along with the fundamental physical phenomena that govern the laser sintering process. The effects of the processing parameters on the quality of the fabricated components are investigated through a heat transfer analysis. We show that our process has potentials for metallization of microelectronics directly onto substrates whose melting temperatures are much lower than the temperature needed for sintering, which is only possible by properly controlling the temperature field during laser sintering. Optimum properties of the fabricated components are obtained when certain thermal conditions are produced during laser heating.
Pressure and temperature dependence of hydrophobic hydration: Volumetric, compressibility, and thermodynamic signatures
Authors: Moghaddam Maria Sabaye , Chan Hue Sun
Published: March 2007

The combined effect of pressure and temperature on hydrophobic hydration of a nonpolar methanelike solute is investigated by extensive simulations in the TIP4P model of water. Using test-particle insertion techniques, free energies of hydration under a range of pressures from 1to3000atm are computed at eight temperatures ranging from 278.15to368.15K. Corresponding enthalpy, entropy, and heat capacity accompanying the hydration process are estimated from the temperature dependence of the free energies. Partial molar and excess volumes calculated using pressure derivatives of the simulated free energies are consistent with those determined by direct volume simulations; but direct volume determination offers more reliable estimates for compressibility. At 298.15K, partial molar and excess isothermal compressibilities of methane are negative at 1atm. Partial molar and excess adiabatic (isentropic) compressibilities are estimated to be also negative under the same conditions. But partial molar and excess isothermal compressibilities are positive at high pressures, with a crossover from negative to positive compressibility at ∼100–1000atm. This trend is consistent with experiments on aliphatic amino acids and pressure-unfolded states of proteins. For the range of pressures simulated, hydration heat capacity exhibits little pressure dependence, also in apparent agreement with experiment. When pressure is raised at constant room temperature, hydration free energy increases while its entropic component remains essentially constant. Thus, the increasing unfavorability of hydration under raised pressure is seen as largely an enthalpic effect. Ramifications of the findings of the authors for biopolymer conformational transitions are discussed.
Longitudinal excitations in Mg–Al–O refractory oxide melts studied by inelastic x-ray scattering
Authors: Pozdnyakova I. , Hennet L. , Brun J.-F. , Zanghi D. , Brassamin S. , Cristiglio V. , Price D. L. , Albergamo F. , Bytchkov A. , Jahn S. , Saboungi M.-L.
Published: March 2007

The dynamic structure factor S(Q,ω) of the refractory oxide melts MgAl2O4 and MgAl4O7 is studied by inelastic x-ray scattering with aerodynamic levitation and laser heating. This technique allows the authors to measure simultaneously the elastic response and transport properties of melts under extreme temperatures. Over the wave vector Q range of 1–8nm−1 the data can be fitted with a generalized hydrodynamic model that incorporates a slow component described by a single relaxation time and an effectively instantaneous fast component. Their study provides estimates of high-frequency sound velocities and viscosities of the Mg–Al–O melts. In contrast to liquid metals, the dispersion of the high-frequency sound mode is found to be linear, and the generalized viscosity to be Q independent. Both experiment and simulation show a weak viscosity maximum around the MgAl4O7 composition.
Hybrid metallic nanoparticles for excitation of surface plasmon resonance
Authors: Zhu Shaoli , Luo Xiangang , Du Chunlei , Li Fei , Yin Shaoyun , Deng Qiling , Fu Yongqi
Published: March 2007

A Ag nanostructure was put forward in this paper. There are two types of Ag nanoparticles, spherical and pyramidal particles. Both of them have the same period, but different height and shapes. The hybrid nanoparticles can produce the localized surface plasmon resonance (LSPR), which couples each other and leads to an extra peak transmission. Our UV-visible-IR spectrophotometer measurement results show that some extra small and sharp peaks appear besides the normal LSPR wave peaks in the transmittance spectrum. The hybrid Ag nanoparticles being used as nanosensors will be more sensitive and selective than the conventional LSPR-based nanosensors.
Low- T c Josephson junctions with tailored barrier
Authors: Weides M. , Schindler C. , Kohlstedt H.
Published: March 2007

Nb ∕ Al 2 O 3 ∕ Ni 0.6 Cu 0.4 ∕ Nb based superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions with a thickness step in the metallic ferromagnetic Ni0.6Cu0.4 interlayer were fabricated. The step was defined by optical lithography and controlled etching. The step height is on the scale of a few angstroms. Experimentally determined junction parameters by current-voltage characteristics and Fraunhofer pattern indicate uniform ferromagnetic layer thicknesses and the same interface transparencies for etched and nonetched F layers. This technique could be used to tailor low-Tc Josephson junctions having controlled critical current densities at defined parts of the junction area, as needed for tunable resonators, magnetic-field driven electronics, or phase modulated devices.
Avalanche of flux jumps in polycrystalline MgB2 superconductor
Authors: Felner I. , Awana V. P. S. , Mudgel Monika , Kishan H.
Published: March 2007

Dc magnetization studies were carried out on a polycrystalline MgB2 superconductor, which was synthesized at 750°C in Fe tube encapsulation under a vacuum of 10−5Torr. Zero resistances at H=0 and 8T are obtained at 38 and 22K, respectively. The material possesses a sharp diamagnetic transition in the zero-field-cooled branch, whereas the field-cooled branch exhibits the paramagnetic-Meissner-effect-like phenomenon below Tc, indicating strong pinning in this compound. The critical current density at 20K and 2T, estimated by the Bean model is higher than 105A∕cm2. Due to the strong pinning, we observed the presence of flux avalanches below H=2T at temperatures below 20K. The magnetization M(H) grows (as usual) slowly with H and falls sharply to near zero moment value, and further grows again in a common way. The flux avalanches were seen quite symmetric in both increasing∕decreasing the field in all four quadrants of the M(H) loops. The dynamics behavior of sinusoidal-like symmetric reproducible flux avalanches is discussed.
Surface electronic structure and magnetism of NiAs structured MnAs(0001) and MnSb(0001)
Authors: Lee J. I. , Hong S. C.
Published: March 2007

We investigated the surface electronic structure and magnetism of the NiAs structured MnAs(0001) and MnSb(0001) using first-principles full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation. We considered the Mn- and anion(As or Sb)-terminated surfaces for both the MnAs(0001) and MnSb(0001) systems. The calculated magnetic moments of the surface Mn atoms for Mn-terminated MnAs(0001) and MnSb(0001) systems are much enhanced to have 3.79μB and 4.04μB, respectively, compared to the corresponding center layer values, 3.10μB and 3.32μB. The anion atoms in the Mn- and anion-terminated systems have negative magnetic moments with the values between −0.09μB and −0.18μB. The effects of surface termination and the band hybridization on the magnetism and the electronic structure are discussed with the calculated density of states.
Fabrication of RE–Fe–B films with highly c-axis texture and excellent hard magnetic properties
Authors: Tang S. L. , Gibbs M. R. J. , Davies H. A. , Liu Z. W. , Lane S. C. , Mateen N. E. , Du Y. W.
Published: March 2007

RE–Fe–B films were prepared on a Ta buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The structure, magnetic structure, and magnetic properties of RE–Fe–B films were studied. The results show the preparation procedure of deposition at 470°C to obtain a strong c-axis RE2Fe14B texture coexisting with an amorphous phase and following annealing at 590°C can effectively fabricate RE–Fe–B thin films with highly texture. The result shows that the film, which was deposited at 470°C and following annealing at 590°C, has a high perpendicular coercivity μ0Hci=1.8T and large magnetic energy product (BH)max=238kJ∕m3.
Reactive sputtering synthesis of Co–CoO∕Ag nanogranular and multilayer films containing core-shell particles
Authors: Muñoz T. , De Toro J. A. , Normile P. S. , Andrés J. P. , González J. A. , Muñiz P. , Barbero A. J. , Riveiro J. M.
Published: March 2007

We present magnetic characterization of two series of samples grown by reactive sputtering of Co and Ag: (i) thin films obtained by cosputtering of these metals at different oxygen pressures, and (ii) Co∕Ag multilayer films deposited with fixed Co layer thickness (1.1nm) and oxygen pressure (2×10−5mbar), and varying Ag layer thickness tAg. For certain preparation conditions the samples obtained with both synthesis methods consist of a dispersion of core-shell Co–CoO nanoparticles embedded in a Ag matrix. Regarding series (i), it is remarkable that the interesting core-shell/matrix structure, suggested by exchange-bias and giant magnetoresistance properties, could be achieved using the simple one-step technique of reactive cosputtering. In series (ii), the exchange-bias and coercivity fields strongly depend on the spacer layer thickness for tAg<4nm, and then become roughly thickness independent. A discontinuous-continuous transition in the silver layers with increasing tAg, similar to that observed in a previous study, is hypothesized as the origin of the behavior in both fields.
Artifacts identification in apertureless near-field optical microscopy
Authors: Gucciardi P. G. , Bachelier G. , Allegrini M. , Ahn J. , Hong M. , Chang S. , Jhe W. , Hong S.-C. , Baek S. H.
Published: March 2007

The aim of this paper is to provide criteria for optical artifacts recognition in reflection-mode apertureless scanning near-field optical microscopy, implementing demodulation techniques at higher harmonics. We show that optical images acquired at different harmonics, although totally uncorrelated from the topography, can be entirely due to far-field artifacts. Such observations are interpreted by developing the dipole-dipole model for the detection scheme at higher harmonics. The model, confirmed by the experiment, predicts a lack of correlation between the topography and optical images even for structures a few tens of nanometers high, due to the rectification effect introduced by the lock-in amplifier used for signal demodulation. Analytical formulas deduced for the far-field background permit to simulate and identify all the different fictitious patterns to be expected from metallic nanowires or nanoparticles of a given shape. In particular, the background dependence on the tip-oscillation amplitude is put forward as the cause of the error-signal artifacts, suggesting, at the same time, specific fine-tuning configurations for background-free imaging. Finally a careful analysis of the phase signal is carried out. In particular, our model correctly interprets the steplike dependence observed experimentally of the background phase signal versus the tip-sample distance, and suggests to look for smooth variations of the phase signal for unambiguous near-field imaging assessment.
Long wavelength bulk GaInNAs p−i−n photodiodes lattice matched to GaAs
Authors: Ng J. S. , Soong W. M. , Steer M. J. , Hopkinson M. , David J. P. R. , Chamings J. , Sweeney S. J. , Adams A. R.
Published: March 2007

We report bulk GaInNAs p−i−n photodiodes lattice-matched to GaAs substrates, grown by solid source molecular beam epitaxy with photoresponses out to ∼1.3 μm. The as-grown samples were characterized optically, structurally, and electrically. A low background doping concentration in the range of 1014–1015 cm−3 was obtained in the samples. One of the samples with a 0.5 μm thick GaInNAs absorbing layer gave a responsivity of 0.11 A/W for a band edge of 1.28 μm at reverse bias of 2 V.
The rotational spectra, potential function, Born-Oppenheimer breakdown, and magnetic shielding of SnSe and SnTe
Authors: Bizzocchi Luca , Giuliano Barbara M. , Hess Mareike , Grabow Jens-Uwe
Published: March 2007

The pure rotational spectra of 27 isotopic species of SnSe and SnTe have been measured in the frequency range of 5–24GHz using a Fabry-Pérot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by laser ablation of suitable target rods and were stabilized in supersonic jets of Ar. Global multi-isotopolog analyses of all available high-resolution data produced spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as Born-Oppenheimer breakdown (BOB) coefficients δ01 for Sn, Se, and Te. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the XΣ+1 electronic state of both SnSe and SnTe. Additionally, the magnetic hyperfine interaction produced by the dipolar nuclei Sn119, Sn117, Se77, and Te125 was observed, yielding first determinations of the corresponding spin-rotation coupling constants.
Rotational spectroscopy and molecular structure of 1,1,2-trifluoroethylene and the 1,1,2-trifluoroethylene-hydrogen fluoride complex
Authors: Leung Helen O. , Marshall Mark D.
Published: March 2007

Fourier transform microwave rotational spectra in the 6–22GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen fluoride, including the normal isotopomer, the two singly substituted C13 species, and the complex obtained with DF. A unique planar structure for the complex is determined from a combined analysis of the rotational constants derived from the spectra and atomic positions obtained using Kraitchman [Am. J. Phys. 21, 17 (1953)] substitution coordinates. Consistent with this structure, no hyperfine splitting of rotational lines due to the nuclear quadrupole coupling interaction is observed for the D-containing species. Although the primary interaction in the complex is a hydrogen-fluorine hydrogen bond, as is the case for all previously studied Lewis acid-fluoroethylene complexes, the CF2CHF–HF complex adopts a distinctly different geometry in which both the primary and secondary interactions occur between the HF molecule and a F atom and a H atom, respectively, bonded to the same carbon of CF2CHF. The 2.020(41)Å hydrogen bond has hydrogen fluoride as the donor and 1,1,2-trifluoroethylene as the acceptor and forms a 109.0(13)° C–F⋯H angle. The secondary interaction between the hydrogen fluoride F atom and the H atom geminal to the acceptor F atom causes the hydrogen bond to deviate 41.6(51)° from linearity. Structural comparisons with analogous complexes formed with mono- and difluorinated ethylenes suggest that the primary hydrogen bond strength and the fluoroethylene fluorine atom basicity both decrease with increasing fluorine substitution. In the course of this work, it was necessary to obtain additional rotational spectra for the 1,1,2-trifluroethylene monomer and to improve the precision of the values of the structural parameters for this molecule.
Electrostatically actuated conducting polymer microbridges
Authors: Zhang G. , Chu V. , Conde J. P.
Published: March 2007

All-polymer microbridge electrostatic actuators based on a blended conductive polymer are fabricated using surface micromachining on glass substrates. A fabrication process is developed that allows the preservation of the electrical conductivity of the polymer structural layer and the suspension of the polymer microbridges. The electromechanical properties of the microbridges are studied using electrostatic actuation and optical and electrical detections. The pull-in phenomena and a dependence of the bridge deflection with the square of the applied voltage are observed. Compared to the silicon-based microbridges, the polymer structures present higher deflection amplitude for the same applied electrical force. The resonance frequency of the polymer bridges occurs in the megahertz range with quality factors of the order of 100 when measured in vacuum. The mechanical properties of the polymer device are affected by residual stress.
Modeling nonisothermal interaction kinetics in the condensed state: A diagram of phase formation mechanisms for the Ni–Al system
Authors: Khina Boris B.
Published: March 2007

Nonisothermal interaction in condensed Ni–Al system takes place during combustion synthesis (CS) or the so-called self-propagating high-temperature synthesis, which is characterized by a high heating rate, high final temperature, fast accomplishment of interaction, and unconventional, nonequilibrium phase formation mechanisms. In this work, a kinetic model for phase formation during CS of nickel monoaluminide in a layered Ni–Al system is developed basing on the diffusion-controlled growth of a solid product layer in strongly nonisothermal conditions. The model includes competition between the growth of NiAl and its dissolution in the parent phases (Al-base melt and solid or liquid Ni-base solution). For numerical calculations, real values of diffusion parameters in NiAl and the Ni–Al phase diagram are used. Simulation has revealed the existence of critical heating rates that correspond to a transition from the common diffusion-controlled growth mechanism to quasiequilibrium dissolution-precipitation pattern and then to nonequilibrium crystallization route. Thereby the existence of uncommon interaction pathways during CS of intermetallics, which were observed experimentally and debated in literature, is proved theoretically ex contrario. A map of phase formation mechanisms for reaction Ni+Al→NiAl in nonisothermal conditions is constructed, which defines the applicability domains of previously known theoretical approaches and permits predicting the interaction route.
A conceptual model of light coupling by pillar diffraction gratings
Authors: Catchpole K. R. , Green M. A.
Published: March 2007

Diffractive structures such as pillar gratings are a promising way of coupling light into or out of thin semiconductor devices, for applications in thin film solar cells and light-emitting diodes. In this paper we show that the diffuse transmittance behavior of pillar gratings can be understood using the concept of grating mode interference and that the optimum heights of the grating and an estimate of the optimum period can be predicted with the effective index method. Furthermore, the method also gives good results for structures outside the range for which it was derived, including circular pillars and quasiperiodic structures. We also show that pillar gratings offer substantially improved performance over groove gratings for thin film silicon solar cells.
Third harmonic generation in undoped and X doped ZnO films (X: Ce, F, Er, Al, Sn) deposited by spray pyrolysis
Authors: Sofiani Zouhair , Sahraoui Bouchta , Addou Mohammed , Adhiri Rahma , Lamrani Mehdi Alaoui , Dghoughi Leila , Fellahi Nabil , Derkowska Beata , Bala Waclaw
Published: March 2007

There is a current interest in research of wide band gap semiconductor materials for the purposes of third order nonlinear optical properties in view of optoelectronics applications. Materials for nonlinear optics should present important changes of nonlinear intensity, dependence on changes of nonlinear refractive index, short response time, and weak absorption losses. We report the results of the third order nonlinear optical susceptibilities of undoped and doped (cerium, fluorine, erbium, aluminum, and tin) zinc oxide films using the third harmonic generation technique at 1064 nm wavelength region in picoseconds regime. Thin films were grown on glass substrate by the spray pyrolysis technique at different temperatures of substrates and characterized by using the x-ray diffraction, scanning electron microscope, transmission, and photoluminescence. A strong third harmonic signal was obtained from the studied films with a good crystallinity and roughness. We have found that at high conductivity, there is a big conversion of the third harmonic signal at different dopants and at an appropriate concentration. We might say that the morphology and the crystalline quality of the films are the main factors for this high conversion.
Submicron patterning of a catalyst film by scanning probe nanolithography for a selective chemical vapor deposition of carbon nanotubes
Authors: Parisse P. , Verna A. , Rinaldi M. , Bussolotti F. , Grossi V. , Passacantando M. , Nardone M. , Santucci S. , Ottaviano L.
Published: March 2007

Submicrometric catalyst patterns have been fabricated by atomic force nanolithography and the subsequent selective growth of carbon nanotubes has been successfully verified. Rectangular stripes (∼350 nm wide) were engraved onto a polymethylmethacrylate film, deposited onto SiO2/Si, by polymer removal with atomic force microscopy nanoindentation. Metallic catalyst patterns were subsequently obtained after 3 nm Ni deposition and lift-off of the residual polymer. Multiwalled carbon nanotubes were then grown by thermal chemical vapor deposition onto the Ni stripes. The various steps of nanopatterning and of carbon nanotubes growth are also studied by scanning electron microscopy and Raman measurements.
Carrier trapping effects on photoluminescence decay time in InGaN∕GaN quantum wells with nanocluster structures
Authors: Lu Yen-Cheng , Chen Cheng-Yen , Wang Hsiang-Chen , Yang C. C. , Cheng Yung-Chen
Published: March 2007

Carrier dynamics in InGaN∕GaN quantum wells (QWs) with compositional fluctuations is studied with time-resolved photoluminescence (PL) experiments and Monte Carlo simulations of exciton hopping and recombination. In particular, the effects of indium-rich nanoclusters in such a QW structure on the photon-energy-dependent PL decay time are investigated. In our experiments, two InGaN∕GaN QW samples of different silicon doping conditions are used for demonstrating the two cases of different nanocluster densities. An increasing trend of PL decay time on the high-energy side of the PL spectrum is observed in the sample with high nanocluster density. Such a trend is not observed in another sample with few clusters. This difference is consistent with the simulation results which can help us in identifying the origin of the increasing trend as exciton trapping by the local potential minima in the spectral range of the free-carrier states.
Effective mass density of liquid composites: Experiment and theory
Authors: Yang W. Z. , Huang J. P.
Published: March 2007

We present an effective medium theory based on the Maxwell-Garnett [J. C. Maxwell Garnett, Philos. Trans. R. Soc. London, Ser. A 203, 385 (1904); J. C. Maxwell Garnett, Philos. Trans. R. Soc. London, Ser. A 205, 237 (1906)] and Bruggeman [D. A. G. Bruggeman, Ann. Phys. (Leipzig) 24, 636 (1935)] approximations, to investigate the effective mass density of binary and ternary liquid composites. Excellent agreement between our experiment and theory is shown. The results are well interpreted in terms of intermolecular interactions, which affect the miscibility between liquid components. Thus, it becomes possible to theoretically predict the effective mass density of liquid composites.
Bubble formation in lattice Boltzmann immiscible shear flow
Authors: Qin R. S.
Published: March 2007

Bubble formation and the effect of shear on bubble formation in a van der Waals fluid is investigated by means of lattice Boltzmann mesoscale simulations. In the absence of shear, the maximum number of formed bubbles increases with undercooling but the incubation time before bubble formation decreases dramatically. The results are in agreement with classical phase transition theory. In shear flow, the maximum number of bubbles is not affected by shear but the bubble growth rate is accelerated. The effect of shear on bubble growth rate weakens at large undercoolings. The reasons are twofold. On the one hand the highly undercooled system takes less time to complete phase transition due to the large driving force so that there is less time to accumulate the flow effect. On the other hand the mechanism for bubble growth changes from coarsening to coalescence at large undercoolings.
Structural stability and characteristics of the metastable Ag–W phases studied byab initioand molecular dynamics calculations
Authors: Dai X. D. , Li J. H. , Guo H. B. , Liu B. X.
Published: March 2007

For the immiscible Ag–W system, ab initio calculations identify the relatively stable structures of the metastable Ag75W25, AgW, and Ag25W75 phases to be L60, B2, and L12, respectively. Based on a newly derived Ag–W potential under an extended Finnis-Sinclair formalism, molecular static and dynamics calculations predict that for the Ag100−xWx alloy, a bcc structure is more stable than a fcc one when 80<x⩽100, and that bcc and fcc structures have almost similar formation energies when 0⩽x<80. Moreover, molecular dynamics simulations show that an amorphous state has lower formation energy than its fcc or bcc counterpart in a composition range of 20⩽x⩽80, which is therefore the glass-forming ability/range of the Ag–W system. Interestingly, moderate phase segregation is observed in the Ag–W amorphous alloy upon simulations, and the segregation tendency is found to strongly depend on the alloy composition as well as on the temperature.
High harmonic generation and molecular orbital tomography in multielectron systems
Authors: Patchkovskii Serguei , Zhao Zengxiu , Brabec Thomas , Villeneuve D. M.
Published: March 2007

High harmonic radiation is produced when atoms or molecules are ionized by an intense femtosecond laser pulse. The radiated spectrum has been shown experimentally to contain information on the electronic structure of the molecule, which can be interpreted as an image of a single molecular orbital. Previous theory for high harmonic generation has been limited to the single-active-electron approximation. Utilizing semisudden approximation, the authors develop a theory of the recombination step in high harmonic generation and tomographic reconstruction in multielectron systems, taking into account electron spin statistics and electron-electron correlations within the parent molecule and the ion. They show that the resulting corrections significantly modify the theoretical predictions, and bring them in a better agreement with experiment. They further show that exchange contributions to harmonic radiation can be used to extract additional information on the electronic wave function.
Electric field effect analysis of thin PbTe films on high-ε SrTiO3 substrate
Authors: Butenko A. V. , Kahatabi R. , Sandomirsky V. , Schlesinger Y. , Sipatov A. Yu. , Volobuev V. V.
Published: March 2007

Thin PbTe films (thickness 500–600Å), deposited on SrTiO3, have been investigated by electric field effect (EFE). The high resistivity of such thin films warrants a high sensitivity of the EFE method. The SrTiO3 substrate serves as the dielectric layer in the gate-dielectric-PbTe structure. Due to the large dielectric constant of SrTiO3, particularly at low temperatures, the electric displacement D in the film reaches the high value of ∼108V∕cm, and the EFE introduced charge into the PbTe film amounts to ∼8μC∕cm2. The high D permits to measure the EFE resistance and Hall constant over a wide region of D, revealing the characteristic features of their D dependence. An appropriate theoretical model has been formulated, showing that, for such films, one can measure the dependence of the Fermi level on D. In fact, we demonstrate that by shifting the Fermi level across the gap by varying D, the density of states of the in-gap states can be mapped out. Our results show that the PbTe layers studied possess a mobility gap exceeding the gap of bulk PbTe.
Thermodynamic consistency between the energy and virial routes in the mean spherical approximation for soft potentials
Authors: Santos Andrés
Published: March 2007

It is proven that, for any soft potential φ(r) characterized by a finite Fourier transform φ̃(k), the virial and energy thermodynamic routes are equivalent if the Fourier transform of the total correlation function divided by the density ρ, h̃(k)/ρ, is an arbitrary function of ρβφ̃(k), where β is the inverse temperature. This class of approximations includes the mean spherical approximation as a particular case.
Interplay between steps and nonequilibrium effects in surface diffusion for a lattice-gas model of O∕W(110)
Authors: Mašín M. , Vattulainen I. , Ala-Nissila T. , Chvoj Z.
Published: March 2007

The authors consider the influence of steps and nonequilibrium conditions on surface diffusion in a strongly interacting surface adsorbate system. This problem is addressed through Monte Carlo simulations of a lattice-gas model of O∕W(110), where steps are described by an additional binding energy EB at the lower step edge positions. Both equilibrium fluctuation and Boltzmann-Matano spreading studies indicate that the role of steps for diffusion across the steps is prominent in the ordered phases at intermediate coverages. The strongest effects are found in the p(2×1) phase, whose periodicity Lp is 2. The collective diffusion then depends on two competing factors: domain growth within the ordered phase, which on a flat surface has two degenerate orientations [p(2×1) and p(1×2)], and the step-induced ordering due to the enhanced binding at the lower step edge position. The latter case favors the p(2×1) phase, in which all adsorption sites right below the step edge are occupied. When these two factors compete, two possible scenarios emerge. First, when the terrace width L does not match the periodicity of the ordered adatom layer (L∕Lp is noninteger), the mismatch gives rise to frustration, which eliminates the effect of steps provided that EB is not exceptionally large. Under these circumstances, the collective diffusion coefficient behaves largely as on a flat surface. Second, however, if the terrace width does match the periodicity of the ordered adatom layer (L∕Lp is an integer), collective diffusion is strongly affected by steps. In this case, the influence of steps is manifested as the disappearance of the major peak associated with the ordered p(2×1) and p(1×2) structures on a flat surface. This effect is particularly strong for narrow terraces, yet it persists up to about L≈25Lp for small EB and up to about L≈500Lp for EB, which is of the same magnitude as the bare potential of the surface. On real surfaces, similar competition is expected, although the effects are likely to be smaller due to fluctuations in terrace widths. Finally, Boltzmann-Matano spreading simulations indicate that even slight deviations from equilibrium conditions may give rise to transient peaks in the collective diffusion coefficient. These transient structures are due to the interplay between steps and nonequilibrium conditions and emerge at coverages, which do not correspond to the ideal ordered phases.
Method to improve the quality of acousto-optic imaging using an ultrashort and focused ultrasound pulse
Authors: Weng Cuncheng
Published: March 2007

The letter shows that the optical scattering and the length of ultrasound-wave train are key factors affecting the quality of acousto-optic imaging. A method using an ultrashort and focused ultrasound pulse is provided. The method has the potential to improve the quality of acousto-optic imaging.
Rotational fluctuation of molecules in quantum clusters. I. Path integral hybrid Monte Carlo algorithm
Authors: Miura Shinichi
Published: March 2007

In this paper, we present a path integral hybrid Monte Carlo (PIHMC) method for rotating molecules in quantum fluids. This is an extension of our PIHMC for correlated Bose fluids [S. Miura and J. Tanaka, J. Chem. Phys. 120, 2160 (2004)] to handle the molecular rotation quantum mechanically. A novel technique referred to be an effective potential of quantum rotation is introduced to incorporate the rotational degree of freedom in the path integral molecular dynamics or hybrid Monte Carlo algorithm. For a permutation move to satisfy Bose statistics, we devise a multilevel Metropolis method combined with a configurational-bias technique for efficiently sampling the permutation and the associated atomic coordinates. Then, we have applied the PIHMC to a helium-4 cluster doped with a carbonyl sulfide molecule. The effects of the quantum rotation on the solvation structure and energetics were examined. Translational and rotational fluctuations of the dopant in the superfluid cluster were also analyzed.
Rotational fluctuation of molecules in quantum clusters. II. Molecular rotation and superfluidity in OCS-doped helium-4 clusters
Authors: Miura Shinichi
Published: March 2007

In this paper, quantum fluctuations of a carbonyl sulfide molecule in helium-4 clusters are studied as a function of cluster size N in a small-to-large size regime (2⩽N⩽64). The molecular rotation of the dopant shows nonmonotonic size dependence in the range of 10⩽N⩽20, reflecting the density distribution of the helium atoms around the molecule. The size dependence on the rotational constant shows a plateau for N⩾20, which is larger than the experimental nanodroplet value. Superfluid response of the doped cluster is found to show remarkable anisotropy especially for N⩽20. The superfluid fraction regarding the axis perpendicular to the molecular axis shows a steep increase at N=10, giving the significant enhancement of the rotational fluctuation of the molecule. On the other hand, the superfluid fraction regarding the axis parallel to the molecular axis reaches 0.9 at N=5, arising from the bosonic exchange cycles of the helium atoms around the molecular axis. The anisotropy in the superfluid response is found to be the direct consequence of the configurations of the bosonic exchange cycles.
Efficiency of composite boron nitride neutron detectors in comparison with helium-3 detectors
Authors: Uher J. , Pospisil S. , Linhart V. , Schieber M.
Published: March 2007

It has been clearly demonstrated that the composite boron nitride (BN) semiconductor polycrystalline bulk detectors with BN grains embedded in a polymer matrix operate as an effective detector of thermal neutrons even if they contain natural boron only. A reasonable signal to noise ratio has been achieved with detector thickness of about 1mm. A Monte Carlo simulation of neutron reactions in the BN detector was done to estimate the thermal neutron detection efficiency. The result was compared with widely used He3 based detectors to prove advantages of BN detectors, which are especially promising for neutron imaging and for large area sensors.
Nanoscale x-ray magnetic circular dichroism probing of electric-field-induced magnetic switching in multiferroic nanostructures
Authors: Zhao T. , Scholl A. , Zavaliche F. , Zheng H. , Barry M. , Doran A. , Lee K. , Cruz M. P. , Ramesh R.
Published: March 2007

The magnetic structure as well as its response to an external electric field were studied in ferrimagnetic CoFe2O4 nanopillars embedded in an epitaxial ferroelectric BiFeO3 film using photoemission electron microscopy and x-ray magnetic circular dichroism. Magnetic switching was observed in both Co and Fe magnetic sublattices after application of an electric field. About 50% of the CoFe2O4 nanopillars were measured to switch their magnetization with the electric field, implying an elastic-mediated electric-field-induced magnetic anisotropy change.
Chip cooling with integrated carbon nanotube microfin architectures
Authors: Kordás K. , Tóth G. , Moilanen P. , Kumpumäki M. , Vähäkangas J. , Uusimäki A. , Vajtai R. , Ajayan P. M.
Published: March 2007

Efficient cooling of silicon chips using microfin structures made of aligned multiwalled carbon nanotube arrays is achieved. The tiny cooling elements mounted on the back side of the chips enable power dissipation from the heated chips on the level of modern electronics demands. The nanotube fins are mechanically superior compared to other materials being ten times lighter, flexible, and stiff at the same time. These properties accompanied with the relative simplicity of the fabrication makes the nanotube structures strong candidates for future on-chip thermal management applications.
Highly stable three-band white light from an InGaN-based blue light-emitting diode chip precoated with (oxy)nitride green/red phosphors
Authors: Yang Chih-Chieh , Lin Chih-Min , Chen Yi-Jung , Wu Yi-Tsuo , Chuang Shih-Ren , Liu Ru-Shi , Hu Shu-Fen
Published: March 2007

A three-band white light-emitting diode (LED) was fabricated using an InGaN-based blue LED chip that emits 455nm blue light, and green phosphor SrSi2O2N2:Eu and red phosphor CaSiN2:Ce that emit 538nm green and 642nm red emissions, respectively, when excited by the 455nm blue light. The luminous efficacy of this white LED is about 30lm∕W at a dc of 20mA. With increasing dc from 5.0to60mA, both the coordinates x and y of the white LED tend to be the same, and consequently the Tc is the same and the Ra increases to 92.2.
Quantum instanton evaluation of the thermal rate constants and kinetic isotope effects for SiH4+H→SiH3+H2 reaction in full Cartesian space
Authors: Wang Wenji , Feng Shulu , Zhao Yi
Published: March 2007

The quantum instanton calculations of thermal rate constants for the gas-phase reaction SiH4+H→SiH3+H2 and its deuterated analogs are presented, using an analytical potential energy surface. The quantum instanton approximation is manipulated by full dimensionality in Cartesian coordinate path integral Monte Carlo approach, thereby taking explicitly into account the effects of the whole rotation, the vibrotational coupling, and anharmonicity of the reaction system. The rates and kinetic isotope effects obtained for the temperature range of 200–1000K show good agreements with available experimental data, which give support to the accuracy of the underlying potential surface used. In order to investigate the sole quantum effect to the rates, the authors also derive the classical limit of the quantum instanton and find that it can be exactly expressed as the classical variation transition state theory. Comparing the quantum quantities with their classical analogs in the quantum instanton formula, the authors demonstrate that the quantum correction of the prefactor is more important than that of the activation energy at the transition state.
c
-axis correlated pinning behavior near the irreversibility fields
Authors: Awaji Satoshi , Namba Masafumi , Watanabe Kazuo , Miura Masashi , Yoshida Yutaka , Ichino Yusuke , Takai Yoshiaki , Matsumoto Kaname
Published: March 2007

The authors found that the peak at the parallel external field (B‖c) to the c axis in the angular dependence of Jc shrinks and almost disappears with increasing a magnetic field but it grows again with further increasing of a magnetic field at various temperatures for high-Jc Sm1+xBa2−xCu3Oy films. These behaviors can be explained by the flux pinning properties of the interstitial vortices, which locate in between the vortices pinned by the c-axis correlated disorders. From the obtained experimental results, the collective correlated pinned glass state is proposed in a high field region in the vortex glass states.
Resistance switching of copper doped MoOx films for nonvolatile memory applications
Authors: Lee Dongsoo , Seong Dong-jun , Jo Inhwa , Xiang F. , Dong R. , Oh Seokjoon , Hwang Hyunsang
Published: March 2007

Nonvolatile and reversible resistance switching of copper doped MoOx film was studied. Hysteretic-type resistive switching was observed under dc. Reproducible resistance switching over 106cycles was observed under alternative voltage pulses. Two resistance states can be maintained for 25h at 85°C. The authors proved that resistance switching might be strongly related with the rupture and generation of multifilaments confirmed by spreading resistance images of a conducting atomic force microscope as well as filamentary conduction by double logarithmic plots. Based on the x-ray photoelectron spectroscopy analysis, local conducting filaments could be formed by thermally diffused copper into MoOx film from the bottom electrode.
Nucleation switching in phase change memory
Authors: Karpov V. G. , Kryukov Y. A. , Savransky S. D. , Karpov I. V.
Published: March 2007

The authors propose a simple physical model of threshold switching in phase change memory cells based on the field induced nucleation of conductive cylindrical crystallites. The model is solved analytically and leads to a number of predictions including correlations between the threshold voltage Vth and material parameters, such as the nucleation barrier and radius, amorphous layer thickness, as well as Vth versus temperature and switching delay time. The authors have carried out verifying experiments, and good agreement is achieved.
Effect of processing temperature on high field critical current density and upper critical field of nanocarbon doped MgB2
Authors: Yeoh W. K. , Horvat J. , Kim J. H. , Xu X. , Dou S. X.
Published: March 2007

Correlation of upper critical field (Hc2) and critical current density (Jc) with processing temperature of nano-C doped MgB2 has been studied in comparison to SiC and pure MgB2. SiC and C doped MgB2 exhibit opposite trends in the dependence of Jc and Hc2 on sintering temperature. This is explained by different reactivities of carbon available upon creation of MgB2 for the two types of doping. Nanocarbon doped MgB2 requires sintering temperatures in excess of 900°C to obtain high boron substitution for carbon, enhancing the vortex pinning and impurity scattering of charge carriers. However, carbon substitution in nano-SiC doped MgB2 occurs at less than 650°C, allowing lower sintering temperature and high degree of carbon substitution. Both pure and SiC doped MgB2 benefit from low sintering temperature, which results in more grain boundary defects. Substantial carbon substitution can compensate for the disadvantage of sintering at high temperature of nano-C doped MgB2, giving the best Jc of 4.8×103A∕cm2 at 4.5K and 12T. This is comparable to the low-temperature sintered nano-SiC doped MgB2 wires.
Air-stable ambipolar organic transistors
Authors: Anthopoulos Thomas D. , Anyfantis G. C. , Papavassiliou G. C. , de Leeuw Dago M.
Published: March 2007

The authors report on ambipolar organic transistors based on the soluble dithiolene derivative (diphenylethylenedithiolato)(1,3-dithiol-2-thione-4,5-dithiolato)nickel [Ni(dpedt)(dmit)]. Due to its small band gap, efficient injection of holes and electrons from gold source/drain electrodes is possible. Both carrier mobilities are estimated to be approximately equal with maximum value on the order of 10−4cm2∕Vs. The transistors exhibit excellent ambient stability with a shelve lifetime exceeding 3months. The pronounced stability of Ni(dpedt)(dmit) as well as of several other molecules studied here is correlated to their redox potential. The present findings can be used as a general guide towards design and synthesis of air-stable ambipolar/n-channel molecules.
Anomalous behavior of AlGaN∕GaN heterostructure field-effect transistors at cryogenic temperatures: From current collapse to current enhancement with cooling
Authors: Sun H. F. , Bolognesi C. R.
Published: March 2007

While current collapse affects AlGaN∕GaN heterojunction field-effect transistors (HFETs) around room temperature, it gradually gives place to a current enhancement with cooling—below 200K, electrically stressed devices do show higher currents than in their prestressed state. This behavior can be explained by increased levels of channel impact ionization at lower temperatures. The positive hole charge generated by impact ionization compensates (and eventually dominates) the parasitic negative charge that is responsible for current collapse at higher temperatures (i.e., the “virtual gate charge”). Cooling of AlGaN∕GaN HFETs may potentially alleviate some of the nonidealities that have so far plagued this technology.
Effects of plasma immersion ion nitridation on dielectric properties of HfO2
Authors: Wang L. , Xue K. , Xu J. B. , Huang A. P. , Chu Paul K.
Published: March 2007

Plasma immersion ion nitridation is used to produce thin HfO2 films with improved thermal and electrical properties. The film composition is investigated by examining the chemical shifts of the Hf 4f, Si 2p, and N 1s core-level spectra using x-ray photoelectron spectroscopy. The improved thermal stability and interfacial microstructure are further confirmed by high-resolution cross-sectional transmission electron microscopy. Electrical studies show an equivalent oxide thickness of about 1.25nm, a negligible hysteresis of about 5mV, and a low fixed charge density.
Properties of Ga1−xMnxAs with high Mn composition (x>0.1)
Authors: Chiba D. , Nishitani Y. , Matsukura F. , Ohno H.
Published: March 2007

A series of Ga1−xMnxAs layers with high Mn compositions x (=0.075–0.200) has been grown and investigated. Magnetization, magnetotransport, and magneto-optical properties reveal that the layers have single ferromagnetic phase as in the case of typical (Ga,Mn)As. The authors also describe the variation of magnetic anisotropy with x and the effect of low temperature annealing on Curie temperature.