bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a general approach for predicting the pressure fields of unsteady gas flows through granular media
Authors: Britan A. , Ben-Dor G. , Igra O. , Shapiro H.
Published: May 2006

Two approaches for treating the shock-induced gas filtration, namely, a solution of the complete system of the conservation equations, and a solution of a simplified version of the conservation equations, which was originally proposed by Morrison [Ind. Eng. Chem. Fundam. 11, 191 (1972); Trans. ASME J. Fluids Eng. 8, 567 (1976); Trans. ASME J. Fluids Eng. 12, 779 (1977)] are examined and analyzed. The capability of these approaches in accurately simulating the dynamic parameters of the gas filtration process through granular columns is investigated. A simple and practical reconstruction method of the gas pressure history inside long granular columns is proposed and verified experimentally by shock tube data with rather long (2.5m) granular columns, which was obtained in the course of the present study. Several important features based on Morrison’s simplified approaches are demonstrated. Applying a dimensional analysis to the complete system of the governing equations resulted in a dimensionless presentation of the pressure histories. Similarly, the pressure signals at the shock-tube end wall, for granular samples of different geometrical characteristics, are demonstrated. As a result, experiments with a large variety of the geometrical and physical parameters of the granular material, which have been conducted at various laboratories, are now numerically predicted by one general numerical code.
Structure refinement, far infrared spectroscopy, and dielectric characterization of (1−x)La(Mg1∕2Ti1∕2)O3−xLa2∕3TiO3 solid solutions
Authors: Salak Andrei N. , Khalyavin Dmitry D. , Ferreira Victor M. , Ribeiro José L. , Vieira Luís G.
Published: May 2006

Dielectric properties of (1−x)La(Mg1∕2Ti1∕2)O3−xLa2∕3TiO3 [(1−x)LMT-xLT] ceramics (0⩽x⩽0.52) have been studied at radio, microwave, and far infrared (FIR) frequency ranges. The crystal structure sequence in (1−x)LMT-xLT reported by different authors has been analyzed and revised. FIR spectroscopy was used to characterize the lattice contribution to the dielectric response at microwave frequencies. The complex dielectric function was evaluated from the reflectivity data and extrapolated down to a gigahertz range. Compositional variations of the fundamental microwave dielectric parameters estimated by different methods are compared and discussed. The dependence of the quality factor on the composition in LMT-LT is interpreted in terms of the reduction of spatial phonon correlations originated from the increasing amount of La vacancies. This approach could account for the compositional behavior of the dielectric loss commonly observed in a number of microwave mixed systems.
Structure, magnetostriction, and magnetic properties of melt-spun Fe–Ga alloys
Authors: Liu G. D. , Dai X. F. , Liu Z. H. , Chen J. L. , Wu G. H.
Published: May 2006

Six samples of Fe100−xGax (15⩽x⩽30) were prepared by melt spinning for a systemic investigation of the structure, magnetostriction, and magnetic properties of Fe–Ga alloys. A large magnetostriction (>750ppm) that increases with increasing Ga concentration has been observed in Fe100−xGax (15⩽x<25) ribbons melt spun at a wheel speed of 10m∕s. When x was equal to or greater than 25, the samples demonstrated magnetostriction of less than 200ppm. The abrupt decrease in magnetostriction at x=25 was attributed to the change in structure from disordered bcc to an ordered phase (DO3). The melt-spun Fe100−xGax (15⩽x⩽30) samples exhibited large saturation magnetization and high Curie temperature, which allowed the alloys to achieve the saturation magnetostriction under easily attainable fields. The angle dependence of the magnetostriction and the effect of the wheel speed are also discussed.
All particle simulations of cathodic arc plasmas
Authors: Cooper I. J. , McKenzie D. R.
Published: May 2006

The early stages of the expansion of fully ionized cathode spot cathodic arc plasmas from a localized initial volume are simulated by an all particle molecular dynamics model. The particles are given an initial temperature and interact by Coulomb forces. Although there are limits on the number of particles and the starting density, the model is relevant in describing processes occurring in cells that are the smallest structures of a cathodic arc. Our model predicts that a cell undergoes an explosive expansion leading to a halo of electrons surrounding an ion-rich core. The ion kinetic energies are lower than experimental observation but may be consistent with them after extrapolation to higher initial densities. For mixed charge state plasmas, the ion kinetic energy increases with ion charge state.
Film and contact resistance in pentacene thin-film transistors: Dependence on film thickness, electrode geometry, and correlation with hole mobility
Authors: Pesavento Paul V. , Puntambekar Kanan P. , Frisbie C. Daniel , McKeen John C. , Ruden P. Paul
Published: May 2006

We describe variable temperature contact resistance measurements on pentacene organic thin-film transistors via a gated four-probe technique. The transistors consist of Au source and drain electrodes contacting a pentacene film deposited on a dielectric/gate electrode assembly. Additional voltage sensing leads penetrating into the source-drain channel were used to monitor potentials in the pentacene film while passing current between the source and drain electrodes during gate voltage sweeps. Using this device structure, we investigated contact resistance as a function of film thickness (60–3000Å), deposition temperature (25 or 80°C), gate voltage, electrode geometry (top or bottom contact), and temperature. Contact resistance values were approximately 2×103–7×106Ωcm, depending on film thickness. In the temperature range of 77–295K, the contact resistance displayed activated behavior with activation energies of 15–160meV. Importantly, it was observed that the activation energies for the source and drain resistances were nearly identical for all device configurations. Contact resistance was found to be dependent on the film mobility in a power law fashion with exponents in the range of −0.58 to −1.94. The activation energy and the dependence of resistance on mobility suggest that contact resistance is not determined by a barrier at the metal-pentacene interface, but rather, drift/diffusion of carriers near the metal-pentacene interface. Two-dimensional device modeling of gated four-probe structures was performed to examine the validity of the source and drain resistance determination.
Magnetic properties of Fe films and Fe∕Si∕Fe trilayers grown on GaAs(001) and MgO(001) by ion-beam sputter epitaxy
Authors: Damm Thorsten , Buchmeier Matthias , Schindler Alexandra , Bürgler Daniel E. , Grünberg Peter , Schneider Claus M.
Published: May 2006

We grow monocrystalline Fe(001) films and Fe∕Si∕Fe(001) trilayers by ion-beam sputter epitaxy on GaAs(001) and MgO(001) substrates. Ion-beam sputtering parameters such as substrate presputtering time, substrate temperature, beam voltage, and target angle are optimized for 10-nm-thick Fe(001) films with respect to epitaxial growth and magnetic properties. In situ low-energy electron diffraction patterns confirm the epitaxial and monocrystalline nature of the sputtered films, surprisingly even on untreated and thus oxidized substrates. The magneto-optical Kerr effect and ferromagnetic resonance are employed to investigate the magnetic properties, and the structural properties are characterized by atomic force microscopy and x-ray reflectivity measurements. Using the optimized set of parameters that yields the best magnetic properties for single Fe films on GaAs, we deposit epitaxial Fe∕Si∕Fe(001) structures and observe antiferromagnetic interlayer exchange coupling for epitaxially sputtered Fe∕Si∕Fe(001) trilayers on GaAs(001). The total coupling strength reaches values of up to 2mJ∕m2 at a Si thickness of 15Å.
Correction masks for large-area ion beam etching and figuring of optics
Authors: Savvides N.
Published: May 2006

Broad beam ion sources, which produce a Gaussian distribution of the ion current density, are considered in designing correction masks to achieve uniform etching and to impart a deterministic shape or figure to large-area rotating optically polished substrates. Phase-shifting optical interferometry is used to obtain digitized maps of the test surfaces before and after etching. The maps are then used to determine the experimental etch rate and the surface figure of the optical substrate, and to test for convergence of the etched surface to some end figure.
Photoelectrochemical etching measurement of defect density in GaN grown by nanoheteroepitaxy
Authors: Ferdous M. S. , Sun X. Y. , Wang X. , Fairchild M. N. , Hersee S. D.
Published: May 2006

The density of dislocations in n-type GaN was measured by photoelectrochemical etching. A 10× reduction in dislocation density was observed compared to planar GaN grown at the same time. Cross-sectional transmission electron microscopy studies indicate that defect reduction is due to the mutual cancellation of dislocations with equal and opposite Burger’s vectors. The nanoheteroepitaxy sample exhibited significantly higher photoluminescence intensity and higher electron mobility than the planar reference sample.
Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods
Authors: Kalarickal Sangita S. , Krivosik Pavol , Wu Mingzhong , Patton Carl E. , Schneider Michael L. , Kabos Pavel , Silva T. J. , Nibarger John P.
Published: May 2006

Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.
Finite dimensional representations of the Euclidean algebra e(2) having two generators
Authors: Douglas Andrew
Published: May 2006

The Euclidean algebra e(2) is the Lie algebra of the group E(2) of Euclidean transformations of the plane. This paper examines finite dimensional representations of e(2) having two generators. To each representation with two generators we associate a graph. In term of graphs, we give a criterion for the indecomposability of such representations and describe an invariant for indecomposable representations. We also classify the indecomposable representations of dimensions 5 and 6, regardless of the number of generators (dimensions less than 5 have been classified). In each case there are finitely many such representations. Next, we show that for each dimension ⩾8 there are infinitely many nonequivalent indecomposable representations.
Extensive ab initio study of the valence and low-lying Rydberg states of BBr including spin-orbit coupling
Authors: Yang Xinzheng , Boggs James E.
Published: May 2006

The electronic states of the BBr molecule, including 12 valence states and 12 low-lying Rydberg states, have been studied at the theoretical level of MR-CISD+Q with all-electron aug-cc-pVQZ basis sets and Douglas-Kroll [Ann. Phys. (N.Y.) 82, 89 (1974)] scalar relativistic correction. The spin-orbit coupling effect in the valence states was calculated by the state interaction approach with the full Breit-Pauli Hamiltonian. This is the first multireference ab initio study of the excited electronic states of BBr. Potential energy curves of all states were plotted with the help of the avoided crossing rule between electronic states of the same symmetry. The structural properties of these states were analyzed. Computational results reproduced most experimental data well. The transition properties of the aΠ0+3, aΠ13, and AΠ11 states to the ground state XΣ0++1 transitions were obtained, including the transition dipole moments, the Franck-Condon factors, and the radiative lifetimes. The evaluated radiative lifetime of the aΠ0+3, and aΠ13 states are near 1ms, much longer than that of the AΠ11 state.
Dynamics of potential surface modes in a nonuniform plasma waveguide with finite electron temperature
Authors: Fedutenko E. A. , Olefir V. P. , Sporov A.
Published: May 2006

In this paper we study the mechanisms of wave-energy transformation in nonuniform waveguide plasmas maintained by surface modes in the presence of local upper-hybrid resonance. The dispersion equation is derived for such waves in the potential case with the following effects taken into account: the finite magnetic field, the finite electron temperature, and electron-neutral collisions. Numerical and analytical solutions for the dispersion and for eigenfield distributions of the waves are presented. The thermal conversion of the surface wave into the upper-hybrid volume modes at a finite electron temperature is shown to completely change the structure of the wave field distribution and to make the surface wave wavelength and the spatial damping rate very sensitive to slight shifts of the surface wave frequency.
Enhancement of near-band-edge photoluminescence of ZnO thin films in sandwich configuration at room temperature
Authors: Hong Ruijin , Shao Jianda , He Hongbo , Fan Zhengxiu
Published: May 2006

ZnO/ITO/ZnO sandwich structure films were fabricated. The effects of buffer layer on the structure and optical properties of ZnO films were investigated by x-ray diffraction (XRD), photoluminescence, optical transmittance, and absorption measurements. XRD spectra indicate that a buffer layer has the effects of lowering the grain orientation of ZnO films and increasing the residual stresses in the films. The near-band-edge emissions of ZnO films deposited on both single indium tin oxide (ITO) buffer and ITO/ZnO double buffers are significantly enhanced compared with that deposited on a bare substrate due to the quantum confinement effect.
Rigorous approach to the nonlinear saturation of the tearing mode in cylindrical and slab geometry
Authors: Arcis N. , Escande D. F. , Ottaviani M.
Published: May 2006

The saturation of the tearing mode instability is described within the standard framework of reduced magnetohydrodynamics in the case of an r-dependent or uniform resistivity profile. Using the technique of matched asymptotic expansions, where the perturbation parameter is the island width w, the problem can be solved in two ways: with the so-called flux coordinate method, which is based on the fact that the current profile is a flux function, and with a new perturbative method that does not use this property. The latter is applicable to more general situations where an external forcing or a sheared velocity profile are involved. The calculation provides a new relationship between the saturated island width and the Δ′ stability parameter that involves a lnw∕w0 term, where w0 is a nonlinear scaling length that was missing in previous work. It also yields the modification of the equilibrium magnetic-flux function.
Optical absorption of semiconducting and metallic nanospheres with the confined electron-phonon coupling
Authors: Lee J. D.
Published: May 2006

We study the optical absorption, especially the (far-) infrared absorption by phonons, of semiconducting and metallic nanospheres. In the nanoscopic sphere, phonons as well as states of electronic excitations are quantized by confinement. It is also known that in the nanoscopic geometry, the confined electron-phonon interaction has a different form from the usual one in the bulk. First, we analyze the phonon and electron contributions to the dielectric response of nanospheres like ε(q,ω)=εph(q,ω)+εel(q,ω) or 1∕ε(q,ω)=1∕εsc−ph(q,ω)+1∕εel(q,ω) from the confined electron-phonon interaction for three cases: the intrinsic semiconductor, the doped semiconductor, and the metal. From the dielectric response, the optical absorption spectra are calculated within the semiclassical framework concentrating on the (far-) infrared region and compared to the spectra without imposing confinement. Nontrivial differences of the spectra with confined phonons stem from two features: the electron-phonon coupling matrix has a different form and the phase space q of the confined phonon is reduced because of its quantization to qn. Finally, size distribution effects in an ensemble of isolated nanospheres are briefly discussed. Those effects are found to be important in metallic spheres with rapid sweepings of resonances by a small change of the sphere size.
Investigation into chiral active waveplates
Authors: Davidson A. J. , Elston S. J. , Raynes E. P.
Published: May 2006

An examination into a chiral liquid crystal active waveplate device using a one-dimensional model, giving numerical results, is presented. The model calculates the director and flow configuration by minimizing the free energy of the chiral nematic modeled with fixed boundary conditions. The static case of varying the flexoclectric coefficients, electric field magnitude, and dielectric anisotropy is examined and it is shown that both flexoelectricity and dielectric effects alter the birefringence of the device in the presence of an electric field. The dynamic reaction to a rotating electric field is then examined.
Magnetic domain structure and magnetization reversal in (311)B Ga0.91Mn0.09As films
Authors: Pross A. , Bending S. J. , Wang K. Y. , Edmonds K. W. , Campion R. P. , Foxon C. T. , Gallagher B. L. , Sawicki M.
Published: May 2006

We have used scanning Hall probe microscopy to image domain structures and magnetization reversal in optimally annealed Ga0.91Mn0.09As films grown on (311)B GaAs substrates. Unmagnetized films exhibit a disordered mazelike domain structure consistent with a composite state of regions with magnetization along [0,1,0] and [0,0,1] out-of-plane easy axes. The characteristic stripe width of ∼3μm exhibits almost no temperature dependence in the range of 5–90K, consistent with recent theoretical predictions, while the peak domain fields drop almost linearly with increasing temperature. With an applied field perpendicular to the zero-field-cooled film magnetization proceeds by the motion of rather ordered stripe-shaped domains which form preferentially along one of the [0,1,0]∕[0,0,1] easy axes. Surprisingly, stripelike domains are not clearly observed during reversal from the magnetized state, which appears to involve the propagation of magnetic “bubbles.” Weak image contrast in the magnetized state points to the existence of residual magnetic disorder in the films on an ∼2–3μm length scale. Abrupt breaks within single images indicate the occurrence of large Barkhausen events when domain walls suddenly jump over ∼1μm distances. This implies the existence of strong pinning sites on this length scale and this, as well as the residual magnetic disorder, may be related to microscopic Mn-rich regions formed during sample growth.
Mechanisms of several photoluminescence bands in hafnium and zirconium silicates induced by ultraviolet photons
Authors: Ito Toshihide , Kato Hiromitsu , Ohki Yoshimichi
Published: May 2006

Two photoluminescence (PL) components with peaks around 2.8–3.0 and 3.8eV were induced in hafnium silicates by the irradiation of synchrotron radiation photons at 8.0eV, while two similar ones were induced in zirconium silicates around 2.7–3.0 and 3.8eV. By examining PL excitation spectra, PL decay characteristics, and vacuum-ultraviolet absorption spectra, it is assumed that the origin of the PL component around 2.7(2.8)–3.0eV is the same as that of the PL component around 2.7–2.9eV observed in hafnia and zirconia. In the band gaps of hafnium silicates, zirconium silicates, hafnia, and zirconia, luminescent centers responsible for the PL components around 2.7(2.8)–2.9(3.0)eV have their respective upper and lower states with a certain constant energy difference that does not change by the hafnium or zirconium content. Electrons (or holes) excited by ultraviolet photons to tail states at the band edges first relax to the upper state of the luminescent centers, and then they are deexcited to the lower state, which induces the PL components.
Temperature dependence of reverse-bias leakage current in GaN Schottky diodes as a consequence of phonon-assisted tunneling
Authors: Pipinys P. , Lapeika V.
Published: May 2006

Temperature-dependent reverse-bias current-voltage data obtained by Miller et al. [Appl. Phys. Lett. 84, 535 (2004)] for Schottky diodes fabricated on n-GaN are reinterpreted in terms of a phonon-assisted tunneling model. It is shown that the temperature dependence of the reverse-bias leakage current may be caused by the temperature dependence of the electron tunneling rate from traps in the metal-semiconductor interface to the conduction band of the semiconductor. A good fit of the experimental data with this theoretical model is obtained in the entire temperature range from 80to400K, when an effective mass of 0.222me and a phonon energy of 70meV are used for the calculation. The reverse current-voltage data for GaN diodes are also explained on the basis of this model.
Control of microcantilevers in dynamic force microscopy using time delayed feedback
Authors: Yamasue Kohei , Hikihara Takashi
Published: May 2006

It has been recently shown that microcantilever sensors in dynamic force microscopes possibly exhibit chaotic oscillations due to the nonlinear tip-sample interaction force. In this article, we propose elimination of the chaotic oscillations using the time delayed feedback control method, which has an ability to stabilize unstable periodic orbits embedded in chaotic attractors. An extended operating range of the microscopes is numerically estimated by stability analysis of the target periodic oscillation. We also discuss an improved transient response of oscillation, which allows us to accelerate the scanning rate of the microscopes without reducing their force sensitivity.
Growth and characteristics of Cr3+:YAG crystal fiber for fluorescence decay temperature sensor
Authors: Ye Linhua , Zhang Jinfeng , Shi Ying
Published: May 2006

YAG crystal fibers with end Cr3+ doped have been grown by the laser heated pedestal growth method as the temperature sensor probe using fluorescence decay. The crystal fibers show good optical properties and mechanical strength and offer advantages of compact construction, high performance, and ability to withstand high temperature. The fluorescence characteristics of the Cr3+:YAG crystal fiber probe with temperature were investigated from −20to500°C. The experimental results indicate that Cr3+:YAG crystal fiber shows a monotonic relationship between the fluorescence lifetime and temperature over a wide temperature range. This fiber was found to be an excellent material to be used as fluorescence decay optical fiber temperature sensor.
Unstable longitudinal plasma oscillations in a magnetic field: Nonrelativistic and relativistic considerations
Authors: Tautz R. C. , Lerche I. , Schlickeiser R.
Published: May 2006

The nonrelativistic and relativistic stability properties are investigated of longitudinal waves propagating in a plasma embedded in an ambient magnetic field, when the wave propagation direction is not necessarily either parallel or perpendicular to the ambient magnetic field. The analysis is based on the concept introduced by Harris [Phys. Rev. Lett. 2, 34 (1959)] of neutral points in wavenumber space to determine plasma instability to one side or the other of such neutral points. The critical need is to determine whether a particular plasma distribution function permits the existence of a neutral point. Relativistic considerations, although necessary to include for many astrophysical plasmas, complicate significantly the determination of instability conditions. In this paper it is shown how one can provide a general argument for such neutral point determination and for determining instability rates in the neighborhood of such neutral points. Only waves independent of resonant wave-particle effects are considered.
Spectral diagnostics of laser wakefield in capillary tubes
Authors: Andreev N. E. , Chegotov M. V. , Cros B. , Mora P. , Vieux G.
Published: May 2006

The modification of the spectrum of a probe pulse traveling in a linear plasma wave created in the wake of a pump pulse guided inside a capillary tube is analyzed for the cases of narrow or broad chirped probe spectra. It is shown that in both cases the measurement of the spectrum can be used as a diagnostic for the amplitude of the plasma wave. The results of full-scale numerical modeling confirm the developed analytical theory of wake-field diagnostics.
Interaction of a weakly relativistic soliton in the magnetized plasma
Authors: Wang Yunliang , Zhou Zhongxiang , Jiang Xiangqian , Hou Chunfeng , Jiang Yongyuan , Sun Xiudong , Qin Ruhu , Zhang Haifeng
Published: May 2006

The results of analytical investigations on the properties of two-dimensional (2D) magnetosonic solitons with a relativistic amplitude are presented in the presence of an applied static and uniform magnetic field B⃑0. In the weakly relativistic limit, a Kadomtsev-Petviashvili (KP) equation is derived for the 2D relativistic magnetosonic soliton by a reductive perturbation method. The N line-soliton solution of the KP equation is presented. The interaction law of the line solitons is studied by figure analysis, which shows that the elastic and inelastic interactions of the line solitons are all possible and determined by the Wronskian determinant.
Mechanisms of reversible stretchability of thin metal films on elastomeric substrates
Authors: Lacour Stéphanie P. , Chan Donald , Wagner Sigurd , Li Teng , Suo Zhigang
Published: May 2006

Gold films on an elastomeric substrate can be stretched and relaxed reversibly by tens of percent. The films initially form in two different structures, one continuous and the other containing tribranched microcracks. We have identified the mechanism of elastic stretchability in the films with microcracks. The metal, which is much stiffer than the elastomer, forms a percolating network. To accommodate the large elongation of the elastomeric substrate, the metal network twists and deflects out of the plane but remains bonded to the soft substrate. Consequently, the metal film experiences only small strains and deforms elastically without suffering fatigue.
Current reversal equilibrium configurations in the alternating-current operation of tokamaks
Authors: Yu Jun , Wang Shaojie , Li Jiangang
Published: May 2006

The equilibrium configurations with central current density reversal and those with two oppositely flowing current components on the high-field side and low-field side have been numerically modeled by using the exact solution of the Grad-Shafranov-Helmholtz equation, with the parameters chosen according to the tokamak alternating-current operation experiments. The modeling results (the magnetic flux surface configurations, the current density profiles, the plasma pressure, and the loop voltage) agree well with the experimental observations.
Short light pulse amplification and compression by stimulated Brillouin scattering in plasmas in the strong coupling regime
Authors: Andreev A. A. , Riconda C. , Tikhonchuk V. T. , Weber S.
Published: May 2006

Short light pulse amplification using the stimulated Brillouin backscattering mechanism is considered. The novel feature is that the interaction process takes place in the strongly coupled regime and therefore the pulse compression is not limited by the ion-acoustic wave period. The mechanism is very efficient due to the large ratio of light frequency to the characteristic ion-acoustic wave frequency. Although large-amplitude ion-acoustic waves are generated and subsequent wave breaking takes place, the fluid and kinetic nonlinearities do not intervene with the amplification itself.
A kinetic approach to the theory of heterogeneous nucleation on soluble particles during the deliquescence stage
Authors: Djikaev Y. S. , Ruckenstein Eli
Published: May 2006

Deliquescence is the dissolution of a solid nucleus in a liquid film formed on the nucleus due to vapor condensation. Previously, the kinetics of deliquescence was examined in the framework of the capillarity approximation which involves the thermodynamic interfacial tensions for a thin film and the approximation of uniform density therein. In the present paper we propose a kinetic approach to the theory of deliquescence which avoids the use of the above macroscopic quantities for thin films. The rates of emission of molecules from the liquid film into the vapor and from the solid core into the liquid film are determined through a first passage time analysis whereas the respective rates of absorption are calculated through the gas kinetic theory. The first passage time is obtained by solving the single-molecule master equation for the probability distribution of a “surface” molecule moving in a potential field created by the cluster. Furthermore, the time evolution of the liquid film around the solid core is described by means of two mass balance equations which involve the rates of absorption and emission of molecules by the film at its two interfaces. When the deliquescence of an ensemble of solid particles occurs by means of large fluctuations, the time evolution of the distribution of composite droplets (liquid film+solid core) with respect to the independent variables of state is governed by a Fokker-Planck kinetic equation. When both the vapor and the solid soluble particles are single component, this equation has the form of the kinetic equation of binary nucleation. A steady-state solution for this equation is obtained by the method of separation of variables. The theory is illustrated with numerical calculation regarding the deliquescence of spherical particles in a water vapor with intermolecular interactions of the Lennard-Jones kind. The new approach allows one to qualitatively explain an important feature of experimental data on deliquescence, namely the occurrence of nonsharp deliquescence, a feature that the previous deliquescence theory based on classical thermodynamics could not account for.
Nitridation for HfO2 high-k films on Si by an NH3 annealing treatment
Authors: Cho M.-H. , Chung K. B. , Whang C. N. , Ko D.-H. , Lee J. H. , Lee N. I.
Published: May 2006

The characteristics of nitrided HfO2 films suggest that the diffusion of Si from the Si substrate to the film surface is induced by annealing in an NH3 ambient and that the incorporation of N is closely related to the diffusion of Si. Changes in the core-level energy state of the N 1s peaks of nitrided HfO2 films indicate that the quantity of N incorporated into the film drastically increases with increasing annealing temperature, especially at temperatures over 900°C. The incorporated N is mostly bonded to Si that diffused from the Si substrate into the film, while some N is incorporated to HfO2 at high annealing temperature. Some molecular N2 is generated in the film, which is easily diffused out after additional annealing. Moreover, the chemisorbed N in the film is not completely stable, compared to that at the interfacial region: i.e., the N in the film predominantly out diffuses from the film after additional annealing in a N2 ambient.
Piezoelectric nonlinearity due to motion of 180° domain walls in ferroelectric materials at subcoercive fields: A dynamic poling model
Authors: Trolier-McKinstry Susan , Bassiri Gharb Nazanin , Damjanovic Dragan
Published: May 2006

A mechanism is described whereby 180° domain wall motion can contribute to the electrically induced strain in a ferroelectric material at subcoercive ac electric fields. The field-dependent, largely reversible motion of ferroelectric, 180° domain walls due to an applied ac electric field is considered. The Rayleigh law is modified to describe the piezoelectric response of the system. This results in both a linear dependence of the piezoelectric coefficient on the amplitude of the applied electric field and the creation of a second order harmonic of strain which adds to the electrostrictive response. The model was experimentally confirmed in Pb(Zr1−xTix)O3 thin films.
180° domain structure and its evolution in Ca0.28Ba0.72Nb2O6 ferroelectric single crystals of tungsten bronzes structure
Authors: Lu C. J. , Nie C. J. , Duan X. F. , Li J. Q. , Zhang H. J. , Wang J. Y.
Published: May 2006

Ferroelectric domain structure and its evolution in uniaxial relaxor Ca0.28Ba0.72Nb2O6 single crystals were investigated using transmission electron microscopy. It was found that there exists a high density of 180° domain walls in the crystals. The domains appear predominantly spike shaped along the polar axis and have a typical diameter of 50–500nm. Domain wall motion was occasionally induced by electron beam irradiation. Macrodomains-to-microdomains switching has been observed corresponding to the normal-to-relaxor ferroelectrics transition during an in situ heating experiments. At temperature just below ferroelectric phase transition temperature TC, zero-field-cooled needlelike nanodomains were also observed.
Quasiphase matching of second-harmonic generation in quantum cascade lasers by Stark shift of electronic resonances
Authors: Belkin Mikhail A. , Troccoli Mariano , Diehl Laurent , Capasso Federico , Belyanin Alexey A. , Sivco Deborah L. , Cho Alfred Y.
Published: May 2006

We demonstrate a quasiphase matching scheme for second-harmonic generation in quantum cascade lasers with integrated resonant nonlinearity. Modulation of the nonlinear susceptibility is achieved by the periodic modulation of the bias voltage along the ridge waveguide leading to a periodic shift of electronic resonances and a change in the electron population in different energy levels. An up to tenfold enhancement of the conversion efficiency is observed. This technique is applicable to any resonant nonlinear optical process in quantum wells.
Synthesis and ethanol sensing properties of indium-doped tin oxide nanowires
Authors: Xue X. Y. , Chen Y. J. , Liu Y. G. , Shi S. L. , Wang Y. G. , Wang T. H.
Published: May 2006

Indium-doped tin oxide (ITO) nanowires are synthesized in mass production via thermal evaporation of In2O3, SnO, and graphite mixture powders. The transverse sizes of these nanowires range from 70 to 150 nm, and the lengths are up to several tens of micrometers. The three elements In, Sn, and O uniformly distribute over the whole nanowire, respectively. The atomic concentration of In is about 5%. The gas sensors realized from these ITO nanowires are very sensitive to ethanol gas, and the sensitivity is about 40 against 200ppm ethanol at the work temperature of 400°C. Both the response and recovery time are shorter than 2s. These results suggest that ITO nanowires are good candidates for fabricating gas sensors.
Self-assembly from the branch pattern to parallel wire array in electrodeposition
Authors: Zhang Mingzhe , Zuo Guihong , Zong Zhaocun , Chen Haiyong , He Zhi , Yang Chunming , Li Dongmei , Zou Guangtian
Published: May 2006

We report a self-organized copper electrodeposition without imposed templates and induced additives. The deposit morphology on the silicon substrate varies from a branch to a parallel pattern by changing the applied voltage. We suggest that there are two essential factors for the formation of such kind of copper wire arrays. One is a proper electric potential distribution near the tip of the copper wire which dictates the direction of the solute transport. The other one is that the cathode overpotential and the equilibrium potential of reaction should remain unchanged at the growing interface.
Distributed-feedback GaInAs∕AlAsSb quantum-cascade lasers operating at 300K
Authors: Yang Q. , Bronner W. , Manz C. , Raynor B. , Menner H. , Mann Ch. , Köhler K. , Wagner J.
Published: May 2006

Short-wavelength (λ∼4μm) single-mode distributed-feedback GaInAs∕AlAsSb quantum-cascade lasers operating in pulsed mode up to room temperature (300K) have been demonstrated by etching an index-coupled first-order distributed-feedback grating into the upper GaInAs separate confinement layer. The temperature-dependent wavelength shift of the distributed-feedback lasers is −0.14cm−1∕K (0.238nm∕K). For devices with a size of 18μm×2.9mm mounted epilayer-up with as-cleaved facets, a maximum peak power per facet of 840mW has been achieved at 77K and 4mW at 300K. The characteristic temperature T0 of the threshold current density is 105K.
Quantum-well saturable absorber at 1.55μm on GaAs substrate with a fast recombination rate
Authors: Le Dû M. , Harmand J.-C. , Mauguin O. , Largeau L. , Travers L. , Oudar J.-L.
Published: May 2006

We propose and realize a structure designed for fast saturable absorber devices grown on GaAs substrate. The active region consists of a 1.55μm absorbing GaInNAsSb quantum well (QW) surrounded by two narrow QWs of GaAsN with a N concentration up to 13%. Photoexcited carriers in the GaInNAsSb QW are expected to recombine by tunneling into the wide distribution of subband gap states created in the GaAsN QW. An absorption study shows that edge energy and excitonic peak intensity of the GaInNAsSb QW are not affected by the proximity of the GaAsN QWs. Pump-probe measurements provide information on the carrier relaxation dynamics which is dependent on spacer thickness, as expected for a tunneling process. We show that this process can be enhanced by increasing the N content in the GaAsN layers. Using this design, we have realized a monolithic GaAs-based saturable absorber microcavity with a 1∕e recovery time of 12ps.
Cooperative atomic motions and core rearrangement in dislocation cross slip
Authors: Pendurti Srinivas , Jun Sukky , Lee In-Ho , Prasad Vish
Published: May 2006

Atomistic study of cross slip of a screw dislocation in copper is presented using the action-optimization numerical technique which seeks the most probable dynamic pathway on the potential-energy surface of the atomic system during the cross-slip process. The observed mechanism reveals features of both competing mechanisms postulated in literature, i.e., the Fleischer mechanism and the Friedel-Escaig mechanism. Due to cooperative atomic motions and complex core rearrangement during the process, the activation energies of the current cross-slip mechanism are around 0.5eV less than the lowest ever reported in corresponding studies using atomistic numerical techniques.
Band alignment at the La2Hf2O7∕(001)Si interface
Authors: Seguini G. , Spiga S. , Bonera E. , Fanciulli M. , Reyes Huamantinco A. , Först C. J. , Ashman C. R. , Blöchl P. E. , Dimoulas A. , Mavrou G.
Published: May 2006

In the perspective of exploring alternative gate dielectrics for the future generation of microelectronic devices, we investigated experimentally and theoretically the interface energy barriers induced on (001) silicon by La2Hf2O7, whose growth has been recently attained by molecular-beam epitaxy. Experimental results show that the 5.6±0.1eV band gap of La2Hf2O7 is aligned to the band gap of silicon with a valence band offset of 2.4±0.1eV and a conduction band offset of 2.1±0.1eV. Density functional theory calculations yield valence band offset values ranging between 1.8 and 2.4eV.
Black nonreflecting silicon surfaces for solar cells
Authors: Koynov Svetoslav , Brandt Martin S. , Stutzmann Martin
Published: May 2006

We present a wet chemical process for nanoscale texturing of Si surfaces, which results in an almost complete suppression of the reflectivity in a broad spectral range, leading to black Si surfaces. The process affects only the topmost 200–300nm of the material and is independent of the surface orientation and doping. Thus, it can be applied to various structural forms of bulk silicon (single, poly-, or multicrystalline) as well as to thin Si films (amorphous or microcrystalline). The optical properties of various black Si samples are presented and discussed in correlation with the surface morphology.
Memory emission of printed carbon nanotube cathodes
Authors: Feng Tao , Dai Lijuan , Jiang Jun , Wang Xi , Liu Xianghuai , Zou Shichang , Li Qiong , Xu Jingfang
Published: May 2006

The memory emission (ME) effect of printed carbon nanotube cathodes (PCNTCs) was reported. If the surface of PCNTCs is marked in a pattern by some methods, the emission image of this cathode will be the figure of the same pattern, just like the PCNTCsremember what happened in the past. We named this phenomenon as “memory emission.” According to the finding of field emission scanning electron microcopy, we suggested that the connecting CNT bundles protruding to the substrate and the electron conductive probability increasing from the substrate to the topside CNT emitter, which result in the emission enhancement of the marked place, were the reasons of the ME effect of PCNTCs. With the help of the ME effect of PCNTCs, the well-patterned emission image could easily be obtained.
Copper phthalocyanine based hybrid p-type permeable-base transistor in vertical architecture
Authors: Feng Chengang , Yi Mingdong , Yu Shunyang , Ma Dongge , Feng Chengang , Zhang Tong , Meruvia Michelle S. , Hümmelgen Ivo A.
Published: May 2006

We demonstrate the production of copper phthalocyanine (CuPc) based p-type hybrid permeable-base transistors, which operate at low voltages having high common-base current gains. These transistors are prepared by evaporating a thin metal layer (Ag or Al) that acts as base on top of a Si substrate that acts as collector. In the sequence CuPc and Au are thermally sublimated to produce the emitter, constituting a quite simple device production procedure with the additional advantage of allowing higher integration due to its vertical architecture.
Electroluminescence from ZnO nanowires in n-ZnO film/ZnO nanowire array/p-GaN film heterojunction light-emitting diodes
Authors: Jeong Min-Chang , Oh Byeong-Yun , Ham Moon-Ho , Myoung Jae-Min
Published: May 2006

ZnO nanowire-array-embedded n-ZnO∕p-GaN heterojunction light-emitting diodes were fabricated by growing Mg-doped p-GaN films, ZnO nanowire arrays, and polycrystalline n-ZnO films consecutively. Electroluminescence emission having the wavelength of 386nm was observed under forward bias in the heterojunction diodes and the UV-violet light was emerged from the ZnO nanowires. The heterojunction diode was thermal treated in hydrogen ambient to increase the electron injection rate from the n-ZnO films into the ZnO nanowires. High concentration of electrons supplied from the n-ZnO films activated the radiative recombination in the ZnO nanowires, i.e., increased the light-emitting efficiency of the heterojunction diode.
n
-type AlN layer by Si ion implantation
Authors: Kanechika Masakazu , Kachi Tetsu
Published: May 2006

n -type AlN layer was obtained by Si ion implantation and the subsequent activation annealing. Si ions were implanted to an unintentionally doped AlN layer grown on a sapphire substrate at an acceleration energy of 90keV with a dose of 5×1015cm−2. The activation annealing was performed at 1400°C for 10min in a nitrogen ambient. We characterized it by Hall-effect measurements in a temperature range from 373to873K. These revealed that the carrier type exhibited n type, the carrier concentration at 373K was approximately 8.8×1015cm−3, and that the Hall mobility at 373K was as high as 20cm2V−1s−1. The donor ionization energy was 294meV. The Hall mobility varied as T−1.1 (T is the absolute temperature) above 523K.
Influence of alkyl chain substitution on sexithienyl-metal interface morphology and energetics
Authors: Duhm S. , Glowatzki H. , Rabe J. P. , Koch N. , Johnson R. L.
Published: May 2006

The interface between Ag(111) and vacuum sublimated α,ω-dihexylsexithienyl (DH6T) was investigated using ultraviolet photoelectron spectroscopy and atomic force microscopy. While the monolayer of DH6T is lying flat on the metal surface, we found that already in the second molecular layer the molecules are almost standing upright. This abrupt change in molecular orientation lowered the hole injection barrier (Δh) of DH6T/Ag by 0.5eV between monolayer and multilayer. Δh for DH6T multilayers was even lowered by 0.8eV compared to unsubstituted sexithienyl multilayers. The reduction of Δh is attributed to the electronic decoupling of molecules in the first from those in the second layer via the hexyl chains.
Systematic approach for analyzing reflectance-difference spectra: Application to silicon-dielectric interfaces
Authors: Brinkley M. K. , Powell G. D. , Aspnes D. E.
Published: May 2006

We describe a combinatorial approach for analyzing reflectance-difference/reflectance-anisotropy (RD/RA) spectra that avoids the need to establish null orientations experimentally, suppresses experimental artifacts, signal averages, and allows RD/RA spectra to be assessed systematically for secondary contributions at principal angles different from that of the dominant contribution. Application to rapid-thermal-annealed oxidized and nitrided vicinal (111) Si-dielectric interfaces demonstrates the effectiveness of the procedure.
Degradation mechanisms in InGaN laser diodes grown on bulk GaN crystals
Authors: Marona L. , Wisniewski P. , Prystawko P. , Grzegory I. , Suski T. , Porowski S. , Perlin P. , Czernecki R. , Leszczyński M.
Published: May 2006

We have investigated the aging processes in InGaN laser diodes fabricated by metal organic vapor phase epitaxy on low-dislocation-density, high-pressure-grown bulk gallium nitride crystals. The measured threshold current turned out to be a square root function of aging time, indicating the importance of diffusion for device degradation. The differential efficiency, in contrast, was roughly constant during these experiments. From these two observations we can conclude that the main reason for degradation is the diffusion-enhanced increase of nonradiative recombination within the active layer of the laser diode. Additionally, microscopic studies of the degraded structures did not reveal any new dislocations within the active area of the aged diodes, thus identifying point defects as a source of nonradiative processes.
Laser-induced microexplosion confined in a bulk of silica: Formation of nanovoids
Authors: Juodkazis Saulius , Misawa Hiroaki , Hashimoto Tomohiro , Gamaly Eugene G. , Luther-Davies Barry
Published: May 2006

We report on the nanovoid formation inside synthetic silica, viosil, by single femtosecond pulses of 30–100nJ energy, 800nm wavelength, and 180fs duration. It is demonstrated that the void is formed as a result of shock and rarefaction waves at pulse power much lower than the threshold of self-focusing. The shock-compressed region around the nanovoid is demonstrated to have higher chemical reactivity. This was used to reveal the extent of the shock-compressed region by wet etching. Application potential of nanostructuring of dielectrics is discussed.
Microwave plasma burner and temperature measurements in its flames
Authors: Hong Yong Cheol , Cho Soon Cheon , Bang Chan Uk , Shin Dong Hun , Kim Jong Hun , Uhm Han Sup , Yi Won Ju
Published: May 2006

An apparatus for generating flames and more particularly the microwave plasma burner for generating high-temperature large-volume plasma flame was presented. The plasma burner is operated by injecting liquid hydrocarbon fuels into a microwave plasma torch in air discharge and by mixing the resultant gaseous hydrogen and carbon compounds with air or oxygen gas. The microwave plasma torch can instantaneously vaporize and decompose the hydrogen and carbon containing fuels. It was observed that the flame volume of the burner was more than 50 times that of the torch plasma. While the temperature of the torch plasma flame was only 550K at a measurement point, that of the plasma-burner flame with the addition of 0.025lpm (liters per minute) kerosene and 20lpm oxygen drastically increased to about 1850K. A preliminary experiment was carried out, measuring the temperature profiles of flames along the radial and axial directions.