bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral dependencies of terahertz emission from InAs and InSb
Authors: Adomavičius R. , Molis G. , Krotkus A. , Sirutkaitis V.
Published: December 2005

Spectral dependences of the THz radiation from the laser-illuminated surfaces of InAs and InSb have been investigated experimentally at high optical fluences for the laser wavelengths ranging from 0.6 to 2μm. Efficient THz generation was discovered in the excitation range around 1.6μm. The influence of the intervalley scattering was clearly evidenced. The energy position of the subsidiary conduction band valleys was evaluated from this study to be equal 1.08 and 0.53 eV for InAs and InSb, respectively. It has been concluded that THz emission at high excitation fluencies is dominated by the shift current effect.
Periodic Coulomb oscillations in Si single-electron transistor based on multiple islands
Authors: Ohkura Kensaku , Kitade Tetsuya , Nakajima Anri
Published: December 2005

We fabricated highly doped Si single-electron transistors (SETs) with a series of geometrically defined islands. The conduction mechanism was systematically investigated in the temperature range from 4.2Kto100K. Despite their island size variation, some of the SETs showed clear periodic and quasiperiodic Coulomb oscillations. This is in contrast to the conventional idea that only geometrically uniform islands show periodic Coulomb oscillations. We showed theoretically that periodic Coulomb oscillation appears under the small deviation of gate capacitances with the period determined by the average of the capacitances. We also found that the formed charge soliton that was conducted through the islands was spread over the whole array. This may also contribute to the periodicity of the Coulomb oscillation. The SET with multiple islands was applied to an Exclusive-OR circuit and achieved a room temperature operation.
Defect accumulation during channeled erbium implantation into GaN
Authors: Pipeleers Bert , Hogg Susan M. , Vantomme André
Published: December 2005

Gallium nitride films epitaxially grown on sapphire, were irradiated at room temperature with 80keVEr+166 or 170keVEr2+166 ions to fluences ranging from 1×1013cm−2 to 1×1015cm−2. The defects induced by ion implantation (as a result of the nuclear energy transfer) generate a perpendicular elastic strain in the hexagonal GaN lattice. The accumulation of lattice damage and lattice deformation were investigated for Er ions impinging along the GaN⟨0001⟩ axis, i.e., channeled implantation, and compared to random implantation, i.e., the conventional geometry in which the ion beam is tilted 10° off the GaN c axis. For this purpose, Rutherford backscattering and channeling spectrometry and high-resolution x-ray diffraction were used. The defect concentration and the maximum perpendicular strain exhibit the same increasing trend with the ion fluence. Three regimes can be distinguished for both implantation geometries, for low fluences (corresponding to a value below 1 displacement per atom in case of random implantation), the defect concentration remains low due to an effective dynamic annealing process. In the second fluence regime, the defect concentration rises sharply, which is characteristic for nucleation-limited amorphization and finally, a third regime is found where layer-by-layer amorphization of the implanted area starts from the surface. The onset of the steep increase in the case of implantations along the GaN c axis is found at a significantly higher erbium fluence compared to random implantation.
Z-contrast and electron energy loss spectroscopy study of passive layer formation at ferroelectric PbTiO3∕Pt interfaces
Authors: Fu L. F. , Welz S. J. , Browning N. D. , Kurasawa M. , McIntyre P. C.
Published: December 2005

Scanning transmission electron microscopy and electron energy loss spectroscopy have been applied to investigate the possible structural origins of ferroelectric polarization degradation at PbTiO3∕Pt interfaces. The microscopic analysis revealed that an amorphous Ti-rich interfacial layer as well as nanometer size precipitates was formed at PbTiO3∕Pt interfaces. The interfacial layer appears to form through decomposition of the PbTiO3 film due to a ferroelectric-electrode reaction during Pt deposition. The formation of the interfacial layer and precipitates could contribute to the polarization degradation typically observed for Pt-electroded PbTiO3-based ferroelectric capacitors.
Complexes in rare-gas solid solutions
Authors: Karasevskiĭ A. I.
Published: December 2005

It is shown that complexes—equilibrium nanoclusters of impurity atoms—can form in dilute rare-gas solid solutions consisting of two species of atoms with substantially different radii; the thermodynamic stability of these complexes is due to relaxation of the excess elastic energy when the impurity atoms combine into a cluster. Two types of complexes can occur: vacancy complexes (VCs) and cluster complexes (CCs). In the VC case, impurity atoms are bound in the first coordination sphere of a vacancy. The VCs are separate formations, and their equilibrium concentration can be significantly higher than that of isolated vacancies. In the CC case, clusters of n impurity atoms with a volume close to that occupied by n−1 host atoms (in the clustering of n atoms of smaller radius than the host) or n+1 host atoms (in the clustering of n atoms of larger radius) can form. An analysis is made of the particular case of a dilute solution of He4 in He3, where, on account of the mass difference of He3 and He4, the effective radii of the atoms in the crystal are different, giving rise to elastic stresses around a He4 impurity atom in the crystal.
Thermodynamics of quasi-one-dimensional deposits on carbon nanobundles
Authors: Antsygina T. N. , Poltavsky I. I. , Chishko K. A. , Wilson T. A. , Vilches O. E.
Published: December 2005

The low-temperature thermodynamics of helium adsorbed in the outer grooves of carbon nanobundles is investigated theoretically in a lattice-gas model with the use of the Green’s function formalism. The proposed model describes both the formation of a one-dimensional (1D) condensate on the bottoms of the grooves and also the formation of two secondary chains in the groove (a three-chain structure) and thus is adequate for interpreting the behavior of the adsorbate over a rather wide range of coverages in the initial stage of deposition. The temperature dependence of the density of the deposit is obtained for the primary chain and secondary chains. The energy, heat capacity, and heat of adsorption are found as functions of temperature, and the total density of the 1D adsorbate is obtained for several different values of the binding energy with the substrate for atoms deposited in the primary and secondary positions. The adsorption isotherms (the total density of adsorbate as a function of external pressure) are calculated for various temperatures. Experimentally measured adsorption isotherms are presented for He4 deposited on bundles of single-walled carbon nanotubes. The measurements were made in the temperature range 2–15 K. Those experiments and previously published data on the adsorption isotherms of methane are interpreted using a theoretical model developed in this paper.
Kinetic processes at the triple points on the melting curve of He4
Authors: Vekhov E. O. , Mikhin N. P. , Polev A. V. , Rudavskiĭ É. Ya.
Published: December 2005

The kinetics of a bcc–hcp structural phase transition on the melting curve of He4 near the triple points (bcc–hcp–He II and bcc–hcp–He I) in the temperature range 1.25–2.0 K is investigated. The capillary blocking method is used to make the samples, and high-precision pressure measurement is used to investigate the kinetics. It is established that far from the triple points exponential functions describe the pressure change accompanying a temperature change on the melting curve. Anomalous behavior of the pressure and temperature of the sample is observed at a transition through the triple points. This attests to remelting of the crystal at a structural phase transition.
Conductivity of a two-dimensional electronic crystal over He3-He4 liquid solutions
Authors: Sivokon’ V. E. , Nasedkin K. A. , Monarkha Yu. P.
Published: December 2005

Experimental data on and a theoretical analysis of the conductivity of a two-dimensional Wigner crystal (WC) on the surface of weak solutions of quantum liquids He3-He4 (x<0.25% 3He) are presented. The conductivity is determined using resonance excitation of low-frequency coupled longitudinal phonon-ripplon modes of a WC. A strong temperature dependence of the resistance of a WC, differing substantially from that found previously for a nondegenerate electron gas, is found. At the same time the experimental dependence of the resistance on the impurity concentration is found to be quite weak, which shows that the scattering of transverse phonons by ripplons plays the dominant role in the resistance of a two-dimensional WC for x<0.25%.
Generalized permeability of a type II superconductor
Authors: Ignatjev V. K.
Published: December 2005

A generalized electric displacement is constructed for a superconductor in the mixed state by averaging the microscopic fields over a system of Abrikosov vortices moving with a velocity varying in time and space, with the vortex and transport currents of the superconducting component and the conduction current of the normal component taken into account. Expressions are obtained for the linear and nonlinear generalized permeability. It is shown that bulk waves, including longitudinal ones, can exist in a superconductor and that spatial dispersion is manifested even in the rf region of the spectrum and has a substantial influence on higher-harmonic generation.
Investigation of the single-particle Green’s function in a bipartite Hubbard model in the static-fluctuations approximation
Authors: Mironov G. I.
Published: December 2005

The single-particle anticommutator Green’s function of a two-sublattice two-dimensional Hubbard model is calculated in the static-fluctuations approximation taking account of electron transfer to the nearest and second-nearest neighboring sites of the crystal lattice. The behavior of the bipartite Hubbard model for strong and weak coupling is investigated.
Spectral analysis of Hall-effect thruster plasma oscillations based on the empirical mode decomposition
Authors: Kurzyna J. , Mazouffre S. , Lazurenko A. , Albarède L. , Bonhomme G. , Makowski K. , Dudeck M. , Peradzyński Z.
Published: December 2005

Hall-effect thruster plasma oscillations recorded by means of probes located at the channel exit are analyzed using the empirical mode decomposition (EMD) method. This self-adaptive technique permits to decompose a nonstationary signal into a set of intrinsic modes, and acts as a very efficient filter allowing to separate contributions of different underlying physical mechanisms. Applying the Hilbert transform to the whole set of modes allows to identify peculiar events and to assign them a range of instantaneous frequency and power. In addition to 25kHz breathing-type oscillations which are unambiguously identified, the EMD approach confirms the existence of oscillations with instantaneous frequencies in the range of 100–500kHz typical for ion transit-time oscillations. Modeling of high-frequency modes (ν∼10MHz) resulting from EMD of measured wave forms supports the idea that high-frequency plasma oscillations originate from electron-density perturbations propagating azimuthally with the electron drift velocity.
Evaluation of a universal transitional resistance diagram for pipes with honed surfaces
Authors: Allen J. J. , Shockling M. A. , Smits A. J.
Published: December 2005

A method for evaluating a universal transitional resistance diagram for pipes that relates the pressure drop in the pipe to Reynolds number, as a function of relative surface roughness, is presented. The method assumes a universal wake function, a logarithmic overlap region and a power fit in the viscous and buffer layer. Estimates can be made of the friction factor–Reynolds number relationship for arbitrary relative roughness, based on a given surface geometry. The method is illustrated for a pipe with a honed surface finish and uses data of Shockling (“Turbulent flow in a rough pipe,” MSE dissertation, Princeton University, 2005). Honed roughness demonstrates an inflectional behavior in the transitionally rough regime, much like sand grain roughness [Laws of flow in rough pipes, VDI Forschungsh, 361 (1933), 1292 (NACA TM, 1950)], but the method proposed here can be applied to any given roughness behavior. It is suggested that the critical parameter that determines whether the resistance diagram shows inflectional characteristics is the ratio of roughness height to outer layer scale. Based on analysis of data from previous researchers it is suggested that if the relative surface roughness krms∕D<0.0025, where krms is the rms amplitude of the roughness and D is the pipe diameter, inflectional relationships should be observed.
Interaction between dynamos at different scales
Authors: Cattaneo Fausto , Tobias Steven M.
Published: December 2005

We study the interaction between dynamos with different spatial and temporal scales. In particular, we consider cases in which the smaller of the dynamo systems is itself unstable to dynamo action. We find that the degree of interaction depends on the magnetic Reynolds number, and the relative amplitude between the driving velocities at different scales. Even though it is possible to construct cases in which one or other of the two scales has negligible effect on the overall dynamo action, in general the composite system displays a significant interaction between scales.
Family of propagating vortex-wave equilibria for the two-dimensional Euler equations
Authors: McDonald N. Robb
Published: December 2005

A family of translating vortex equilibria for the two-dimensional Euler equations is investigated both analytically and numerically. The equilibria are comprised of a nonlinear wave propagating along an infinitely long vortical interface together with a comoving point vortex and dipole. The vortical interface separates the flow of uniform vorticity from a nontrivial irrotational flow. The analytical construction, though not an exact solution for the equilibria, is a relatively simple model having good quantitative agreement with the numerical solution well into the nonlinear regime. In the limit of small wave amplitude the analytical and numerical solutions approach those obtained using linear theory.
Effects of reversible and irreversible ferroelectric switchings on the piezoelectric large-signal response of lead zirconate titanate thin films
Authors: Gerber P. , Kügeler C. , Böttger U. , Waser R.
Published: December 2005

The effects of reversible and irreversible switching processes on the electromechanical large-signal strain S of tetragonal Pb(Zrx,Ti1−x)O3 thin films are investigated and discussed. Starting from electric small- and large-signal measurements, the percentage of switched unit cells cesw is calculated. The result is then used in combination with the measured electromechanical field-induced small-signal response to calculate the field-induced large-signal strain S. Enhanced models for this calculation are developed improving a known model. Differences between the calculated and measured large-signal strains are discussed in respect to parameter influences and irreversible contributions. In addition, detailed insight on the switching processes in respect to the electromechanical properties is given.
Absence of magnetism in hafnium oxide films
Authors: Abraham David W. , Frank Martin M. , Guha Supratik
Published: December 2005

We establish the limits of magnetism in thin, electronic grade, hafnium oxide, and hafnium silicate films deposited onto silicon wafers by chemical vapor deposition and atomic layer deposition. To the limits of sensitivity of our measurement techniques, no ferromagnetism occurs in these samples. Contamination by handling with stainless-steel tweezers leads to a measurable magnetic signal. The magnetic properties of this contamination are similar to those attributed to ferromagnetic HfO2 in a recent report, including the magnitude of moment, magnetization field dependence, and spatial asymmetry.
Ultrasonic microspectroscopy of congruent LiNbO3 crystals
Authors: Kushibiki Jun-ichi , Ohashi Yuji , Hirohashi Junji
Published: December 2005

Experimental procedures for evaluating the compositional homogeneity of LiNbO3 single crystals were developed using the line-focus-beam ultrasonic material characterization system, and the true congruent composition was determined. First, the relationships among leaky surface acoustic wave (LSAW) velocities (VLSAW), chemical compositions, Curie temperatures, densities, and lattice constants were investigated for crystal evaluation, using X-, Y-, and Z-cut substrates prepared from three LiNbO3 crystals grown along the crystallographic Z axis with different Li2O contents of 48.0, 48.5, and 49.0mol%. We selected VLSAW for Z-cut Y-axis propagating (ZY) LiNbO3 with the highest sensitivity to chemical composition changes [0.0253Li2Omol%∕(m∕s)], and also VLSAW for Y-cut X-axis propagating (YX) LiNbO3 [0.0464Li2Omol%∕(m∕s)] that was advantageous for detailed evaluation of distributions in the chemical composition along the pulling direction as well as the diameter direction.The congruent composition was estimated to be 48.477Li2Omol%. Next, the homogeneities of the three above-mentioned crystals and a commercially available LiNbO3 crystal with a nominally congruent composition were evaluated using data for YX-LiNbO3 specimens. Consequently, compositional changes were observed clearly as VLSAW changes. The commercial crystal specimen had a gradient of −0.0046(m∕s)∕mm from top to bottom. The VLSAW variations for the entire examined region (60×36mm2) exhibited a maximum change of 0.55m∕s, corresponding to the chemical composition change of 0.025Li2Omol%. The relationships between the chemical compositions and the acoustical physical constants (the elastic, piezoelectric, and dielectric constants, and density) were also provided.
Photoluminescence study of Sb-doped p-type ZnO films by molecular-beam epitaxy
Authors: Xiu F. X. , Yang Z. , Mandalapu L. J. , Zhao D. T. , Liu J. L.
Published: December 2005

We investigated photoluminescence (PL) from reliable and reproducible Sb-doped p-type ZnO films grown on n-Si (100) by molecular-beam epitaxy. Well-resolved PL spectra were obtained from completely dopant-activated samples with hole concentrations above 1.0×1018cm−3. From free electron to acceptor transitions, acceptor binding energy of 0.14 eV is determined, which is in good agreement with analytical results of the temperature-dependent PL measurements. Another broad peak at 3.050 eV, which shifts to lower energy at higher temperatures, indicates the formation of deep acceptor level bands related to Zn vacancies, which are created by Sb doping.
Driven dissipative whistler wave turbulence
Authors: Shaikh Dastgeer , Zank Gary P.
Published: December 2005

Driven dissipative whistler wave turbulence in two-dimensional electron magnetohydrodynamics is investigated using very high resolution nonlinear fluid simulations. It is shown that a dual cascade phenomenon of mean magnetic potential and energy invariants is in agreement with predictions based on statistical ensemble and Kolmogorov’s theories. Turbulent length scales larger than the electron skin depth (whistler wave regime) exhibit a spectral break in the vicinity of the forcing wave number that separates the inverse and forward cascade regimes. On the other hand, length scales smaller than the electron skin depth behave like hydrodynamic eddies in which both small and large scale regimes exhibit identical turbulent spectra. In both cases, however, turbulent fluctuations follow an exact Kolmogorov-type spectra. While wave effects are strong in the whistler wave regime, they are absent entirely in the hydrodynamics regime of the driven electron magnetohydrodynamic turbulence.
Testing multiple mapping conditioning mixing for Monte Carlo probability density function simulations
Authors: Wandel Andrew P. , Klimenko A. Y.
Published: December 2005

Mitarai et al. [Phys. Fluids 17, 047101 (2005)] compared turbulent combustion models against homogeneous direct numerical simulations with extinction/recognition phenomena. The recently suggested multiple mapping conditioning (MMC) was not considered and is simulated here for the same case with favorable results. Implementation issues crucial for successful MMC simulations are also discussed.
Competing functionality in multiferroic YMnO3
Authors: Dho Joonghoe , Blamire M. G.
Published: December 2005

We have investigated the dual functionality of multiferroic YMnO3, which simultaneously possesses antiferromagnetic and ferroelectric properties. When the YMnO3 was used as a pinning layer, it gave rise to an exchange bias and enhanced coercivity in a soft ferromagnetic film which depended on the YMnO3 crystal orientation. Significantly, the exchange bias and coercivity were minimal for the (0001) YMnO3 surface, which is optimal for ferroelectric applications. Consequently, although multiferroics, such as YMnO3, can be exploited in magnetic and ferroelectric applications independently, applications which aim to exploit their multifunctionality will be limited by the competing crystal orientations required for each application.
Highly efficient white organic electroluminescent devices based on tandem architecture
Authors: Chang Chan-Ching , Chen Jenn-Fang , Hwang Shiao-Wen , Chen Chin H.
Published: December 2005

Two types of tandem organic light-emitting diodes (OLEDs) with white-light emission have been developed by using Mg:Alq3∕WO3 as the interconnecting layer. While the Commission Internationale d’Eclairage (CIE) coordinates of the tandem device with individual blue- and yellow-emitting OLEDs was sensitive to the viewing angle and the operating time, the tandem device connecting two white-emitting OLEDs was considerably less. At an optimal WO3 thickness of 5nm, the tandem two-unit device produced three higher luminance efficiency than that expected of a single-unit device. A maximum efficiency of 22cd∕A was achieved by the tandem device comprised of two white-fluorescent OLEDs, and the projected half-life under the initial luminance of 100cd∕m2 was over 80000h.
Reflection high energy electron diffraction observation of surface mass transport at the two- to three-dimensional growth transition of InAs on GaAs(001)
Authors: Patella F. , Arciprete F. , Fanfoni M. , Sessi V. , Balzarotti A. , Placidi E.
Published: December 2005

We have followed by reflection high-energy electron diffraction the nucleation of InAs quantum dots on GaAs(001), grown by molecular-beam epitaxy with growth interruptions. Surface mass transport gives rise, at the critical InAs thickness, to a huge nucleation of three-dimensional islands within 0.2 monolayers (ML). Such surface mass diffusion has been evidenced by observing the transition of the reflection high-energy electron diffraction pattern from two- to three-dimensional during the growth interruption after the deposition of 1.59 ML of InAs. It is suggested that the process is driven by the As2 adsorption-desorption process and by the lowering of the In binding energy due to compressive strain. The last condition is met first in the region surrounding dots at step edges where nucleation predominantly occurs.
Scaling of domain size during spinodal decomposition: Dislocation discreteness and mobility effects
Authors: Haataja Mikko , Mahon Jennifer , Provatas Nikolas , Léonard Francois
Published: December 2005

In this letter, we examine the effects of discrete mobile dislocations on spinodal decomposition kinetics in lattice mismatched binary alloys. By employing a novel continuum model, we demonstrate that the effects of dislocation mobility on domain coarsening kinetics can be expressed in a unified manner through a scaling function, describing a crossover from t1∕2 to t1∕3 behavior.
Mechanism of a remarkable enhancement in the light emission from nanocrystalline porous silicon annealed in high-pressure water vapor
Authors: Gelloz Bernard , Koshida Nobuyoshi
Published: December 2005

To clarify the effect of surface passivation on the optical properties of nanocrystalline porous silicon (PS), the photoluminescence (PL) characteristics of PS have been investigated by employing a high-pressure water vapor annealing (HWA). PS samples with various porosities were prepared on (100)-oriented p-type (4Ωcm) single-crystalline silicon wafers by electrochemical anodization. Some samples were then electrochemically oxidized. The HWA treatment was then applied to the prepared PS samples at 0.5–3MPa and 200–300°C for 2–3h. The PL intensities, spectra, and dynamics after HWA were measured in relation to surface analyses by Fourier-transform-infrared (FTIR) spectroscopy. It is shown that the HWA treatment leads to a drastic enhancement in both the PL efficiency and stability. Under the optimum condition, the PS sample exhibits an extremely high external quantum efficiency of 23% at room temperature. According to the FTIR spectra analyses, silicon nanocrystallites in HWA-treated PS are covered with a high-quality SiO2 tissue. The PL decays are found to be longer than those of as-prepared PS, and become closer to a single-exponential behavior near the PL peak wavelength. The observed high efficiency and stability of PL emission from HWA-treated PS is attributed to (i) suppression of nonradiative surface defect density, (ii) uniform passivation by unstrained thin oxides, and (iii) strong localization of excitons in silicon nanocrystals. This low-temperature treatment is very useful for obtaining highly efficient and stable luminescent PS and devices.
On the Debye temperature in the Slack approximation for an estimation of the thermal conductivity of nonmetallic compounds
Authors: Bruls R. , Hintzen H. T. , Metselaar R.
Published: December 2005

The value of the Debye temperature of the acoustic modes, as required in the application of Slack’s approximation [G. A. Slack, Solid State Physics, edited by F. Seitz, D. Turnbull, and H. Ehrenreich, (Academic, New York, 1979), Vol. 34, pp. 1–71] for the thermal conductivity, is not always available. It is shown that for these cases, the value at the minimum of the curve of the Debye temperature versus the temperature obtained from specific-heat data, gives a good approximation.
Interface-sustained magnetic properties displayed by the La2O3−SrO−Co2O3 nanocomposite
Authors: Tay Siok Wei , Hong Liang , Liu Zhaolin
Published: December 2005

The heterogeneous metal oxide composite (1−x)La2O3∕xSrO∕Co3O4 (where x⩾0.8), comprised primarily of the three oxide phases (La2O3, spinel Co3O4, and SrO), exhibits a special temperature-magnetic response profile. The coercivity of the composite decreases with increasing temperature from 70to200K, but increases from 200to298K. This outcome is upheld because of the occurrence of three structures, which are the perovskite La1−αSrαCoO3−β(α⪡x) phase that is formed at the interface region of the above three oxides, the presence of La3+ in the Co3O4 phase, and the interface between SrO and Co3O4 phases (domains). The first two structures are deemed responsible for manifestation of ferromagnetism at low temperature, while the last one for room temperature ferromagnetism. We also noted that the third structure could reveal noticeable magnetic properties only when the three major oxide phases are mixed in nanometer scale as the magnetic behavior is triggered through the deformation of octahedral Co-O cells located at the surface of the spinel domains. To realize such an ultrahigh dispersion of the three oxide phases, pyrolysis of the metal-ion-containing hydrogel made of the three metal ions (La3+, Sr2+, and Co2+) and organic moieties (e.g., citric acid and glycine) is an effective approach. In contrast to the homogeneous perovskite solid solution La1−xSrxCoO3−δ(x⩽0.5), the present type of composite shows stronger coercivity but weaker remanence induction at temperatures below 200K. Other than the temperature effect, the influence of the organic components in the metal-ion-containing hydrogel on the interface-sustained magnetism has also been studied.
Transition from amorphous to crystalline beta phase in co-sputtered FeSi2 films as a function of temperature
Authors: Milosavljević M. , Shao G. , Lourenço M. A. , Gwilliam R. M. , Homewood K. P. , Edwards S. P. , Valizadeh R. , Colligon J. S.
Published: December 2005

A study of the stability of amorphous FeSi2 films and their transition to a crystalline phase as a function of deposition or annealing temperature is presented. Stoichiometric FeSi2 films, 300–400nm thick, were deposited on (100) Si substrates by co-sputtering of Fe and Si. It was found that the films grow in an amorphous form for the substrate temperature ranging from room temperature to 200°C, while from 300–700°C, they grow in form of a crystalline β-FeSi2 phase. In a postdeposition 30min heat treatments, the layers retain the amorphous structure up to 400°C, transforming to the crystalline β phase at 500–700°C. The results are discussed in the frame of the existing models, and compared to those found in the literature. It is shown that in as-deposited films, the growth is controlled by surface diffusion, the crystalline layers growing in a columnar structure strongly correlated to the Si substrate. Postdeposition treatments induce a random crystallization controlled by bulk diffusion, the resulting structure not being influenced by the substrate. The results of this work contribute to a better understanding of the processes involved in a transition of amorphous FeSi2 films to a crystalline phase, and provide a basis to determine the processing parameters in potential applications of this promising semiconducting material.
Analysis of optical interferometric displacement detection in nanoelectromechanical systems
Authors: Karabacak D. , Kouh T. , Ekinci K. L.
Published: December 2005

Optical interferometry has found recent use in the detection of nanometer scale displacements of nanoelectromechanical systems (NEMS). At the reduced length scale of NEMS, these measurements are strongly affected by the diffraction of light. Here, we present a rigorous numerical model of optical interferometric displacement detection in NEMS. Our model combines finite element methods with Fourier optics to determine the electromagnetic field in the near-field region of the NEMS and to propagate this field to a detector in the far field. The noise analysis based upon this model allows us to elucidate the displacement sensitivity limits of optical interferometry as a function of device dimensions as well as important optical parameters. Our results may provide benefits for the design of next generation, improved optical NEMS.
Time-dependent physics of a single-surface multipactor discharge
Authors: Kim H. C. , Verboncoeur J. P.
Published: December 2005

The time-dependent physics of the single-surface multipactor is investigated by using both particle-in-cell (PIC) and Monte Carlo (MC) simulations. An oscillation of the normal surface field and number of electrons at twice the rf was observed in the PIC code. The temporal relationship between the fields normal and parallel to the surface traces a closed curve in the ac saturation state. The shape of the curve depends on the amplitude of the rf electric field normalized to the rf (normalized electric field). In comparison with the PIC simulation result, the oscillation in the MC simulation appears only when the normalized electric field is so large that the time step of the MC simulation is smaller than the rf period.
Runaway electron generation in a cooling plasma
Authors: Smith H. , Helander P. , Eriksson L.-G. , Fülöp T.
Published: December 2005

The usual calculation of Dreicer [Phys. Rev. 115, 238 (1959); 117, 329 (1960)] generation of runaway electrons assumes that the plasma is in a steady state. In a tokamak disruption this is not necessarily true since the plasma cools down quickly and the collision time for electrons at the runaway threshold energy can be comparable to the cooling time. The electron distribution function then acquires a high-energy tail which can easily be converted to a burst of runaways by the rising electric field. This process is investigated and simple criteria for its importance are derived. If no rapid losses of fast electrons occur, this can be a more important source of runaway electrons than ordinary Dreicer generation in tokamak disruptions.
Simulations of binary drop collisions with a multiple-relaxation-time lattice-Boltzmann model
Authors: Premnath Kannan N. , Abraham John
Published: December 2005

In this paper, we report simulations of drop-drop collisions using a multi-relaxation-time multiphase flow lattice Boltzmann model. Employing a multi-relaxation-time (MRT) model in lieu of the Bhatnagar-Gross-Krook (BGK) model used in the standard lattice-Boltzmann equation enables realization of stable computations of drop collisions at relatively lower fluid viscosities without increasing the lattice resolution to prohibitive levels. Head-on and off-center computations of collisions are carried out using axisymmetric and three-dimensional (3D) versions of the MRT model, respectively. Time-resolved results showing the interactions of the interfaces of drops for different characteristic nondimensional parameters are presented. Computations show that at low Weber numbers, We, coalescence with relatively smaller deformation occurs, sometimes entrapping a stable microbubble. At higher We, head-on collisions lead to reflexive separation with or without the formation of satellite droplets. The size of the satellite droplets appears to increase with increase in the We. The Ohnesorge number, Oh, seems to modulate the transient characteristics and the outcome of collisions. It is found that the greater the Oh, the smaller is the size of the satellite droplets formed. For off-center collisions at a given We, at lower values of the impact parameter permanent coalescence is observed, while higher values result in separation by stretching action. These findings are in satisfactory agreement with experimental observations.
Design of a bidirectional actuator for a nanopositioning system with a permanent magnet and an electromagnet
Authors: Kim K. H. , Gweon D. G.
Published: December 2005

A precision bidirectional linear actuator for ultraprecision systems is proposed and designed in this article. The actuator is composed of a symmetric structure with a force generation unit and a guide mechanism. The force generation part consists of a permanent magnet and an electromagnet, which generate a permanent and a reversible flux, respectively. The combination of permanent and reversible fluxes makes various flux densities in its air gaps between the moving part and the fixed yokes. The difference between flux densities in the lower and upper gaps creates forces for bidirectional linear motions of hundreds of micrometers. As a guide mechanism, two circular plates and one shaft are used. Reducing other forces generated by motions, except the z-directional motion, these circular plates in the form of a flexure endow the actuator with smooth motion, freedom from wear, and a high stiffness for a rapid settling time. The function of the shaft is to transfer motion to an object. Finally, the total body has a symmetric structure enabling it to be stable in terms of thermal error. The actuator is designed with the software tools MAXWELL™2D and PRO-MECHANICA™. The designed actuator is evaluated with a linear current amplifier, a laser Doppler vibrometer for nanometer resolution, a dynamic signal analyzer for frequency responses of the proposed actuator, and a simple proportional-integral-derivative controller for its tracking performance.
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-long pulse kinetically enhanced copper vapor laser using wide aperture discharge tube
Authors: Singh B. , Subramaniam V. V. , Daultabad S. R. , Chakraborty A.
Published: December 2005

A wide aperture kinetically enhanced copper vapor laser consisting of a ∼47mm bore and 1450mm length discharge tube is demonstrated with moderate input power of ∼5kW, and overall efficiency of ∼1.45%. The laser pulse durations were observed to be ∼60ns full width at half maximum. An increase in output power from 17to73W at ∼9.4kHz (a factor of ∼4.3) has been achieved due to kinetic enhancement effects in this laser. Output laser pulse shape monitoring was used for optimization of maximum output power from the laser.
Fast and compact multichannel photon coincidence unit for quantum information processing
Authors: Gaertner Sascha , Weinfurter Harald , Kurtsiefer Christian
Published: December 2005

We present a fast and compact multichannel coincidence unit to count all possible single and coincidence detection events in an experiment with eight single-photon detectors at once. Using high-speed electronics and a microcontroller, this device is able to process up to 800000events∕s. The coincidence window can be tuned within a range of 4–12ns. The device can be easily scaled to any number of input channels and is thus ideally suited for efficient multiphoton quantum information processing.
Instrumentation for video-rate near-infrared diffuse optical tomography
Authors: Piao Daqing , Dehghani Hamid , Jiang Shudong , Srinivasan Subhadra , Pogue Brian W.
Published: December 2005

This article describes the design, rationale, and system performance of a rapid imaging near-infrared diffuse optical tomography system that is capable of collecting tomographic measurements at video rate. Data-acquisition speed of 35frames∕s is achieved by spectral encoding of the sources, followed by spectral decoding of all detection channels in parallel in a spectrometer and using charge-coupled-device (CCD)-based detection. The combination of spectral decoding of the source lights horizontally in a spectrometer and spatial separation of the detector positions vertically at the entrance slit provides separate data for the entire set of source-detector pairs which can be acquired at the frame rate of the CCD camera. The described system features eight sources at an overall 785nm center band with an average of 1.25nm spacing in wavelength and eight detectors evenly deployed in a 27mm array designed for imaging with small animal tissues. The system performs with localization error of 2.5mm, and absorption recovering uncertainty of 16.7%. The point spread function of the imaging is estimated to be 4.1mm when near to the edge and 10.4mm at the center of the imaging array. Capture of transient changes of absorption coefficient in a dynamic phantom are also presented.
Gain and carrier losses of (GaIn)(NAs) heterostructures in the 1300–1550 nm range
Authors: Schlichenmaier C. , Thränhardt A. , Meier T. , Koch S. W. , Chow W. W. , Hader J. , Moloney J. V.
Published: December 2005

A microscopic model is used to analyze gain and loss properties of (GaIn)(NAs)∕GaAs quantum wells in the 1.3–1.55μm range, including Auger and radiative recombination. The calculations show that, as long as good material quality can be achieved, growing highly compressively strained samples is preferable due to their specific band structure properties. Optimum laser operation is possible slightly above a peak gain of 1000cm−1.
Growth of ZnO thin films by ultraviolet pulsed-laser ablation: Study of plume dynamics
Authors: Klini A. , Manousaki A. , Anglos D. , Fotakis C.
Published: December 2005

A comparative study is presented on the growth of ZnO thin films by ultraviolet pulsed-laser deposition using nanosecond and femtosecond pulses at 248nm. Different experimental parameters were examined including substrate temperature, oxygen ambient pressure, and laser energy density at the target. At optimum conditions the films grown exhibited high optical transmittance and a preferential orientation along the c axis, both with nanosecond and femtosecond irradiations. However, those produced with the ultrashort laser pulses are composed of smaller dimension crystallites, with higher angular distribution on the substrate and higher roughness, suggesting different film growth mechanism. This was investigated by studying the plume dynamics of the ejected material accompanying laser ablation of the ZnO targets by means of spatially and time-resolved optical emission spectroscopy in order to obtain information on the nature of the ejected species and the distribution of their propagation velocities. Employing irradiation conditions, typically used in the deposition experiments, emission lines assigned to electronically excited neutral zinc atoms (Zn*) were observed both in the case of nanosecond and femtosecond pulses, while the latter additionally gave rise to emission attributable to zinc ions (Zn+*). The mean propagation velocities measured suggest the presence of highly energetic Zn cations in the case of femtosecond ablation, which are likely to be responsible for defect formation on the films, disturbing the smooth growth of crystallites that takes place under nanosecond irradiation, and giving rise to films composed of smaller crystallites with higher mosaicity and roughness.
Molar conductivity calculation of Li-ion battery electrolyte based on mode coupling theory
Authors: Pu Weihua , He Xiangming , Lu Jiufang , Jiang Changyin , Wan Chunrong
Published: December 2005

A method is proposed to calculate molar conductivity based on mode coupling theory in which the ion transference number is introduced into the theory. The molar conductivities of LiPF6, LiClO4, LiBF4, LiAsF6 in PC (propylene carbonate) are calculated based on this method. The results fit well to the literature data. This presents a potential way to calculate the conductivities of Li-ion battery electrolytes.
Magnetic and electrical properties of Fe∕Si core-shell cluster assemblies prepared with double-glow-discharge sources
Authors: Katoh R. , Hihara T. , Peng D. L. , Sumiyama K.
Published: December 2005

Using a double glow-discharge-cluster-source-system, in which one glow discharge is a dc mode and the other an rf discharge mode, Fe and Si clusters have been produced independently and deposited simultaneously on a substrate. When a separation plate is not inserted between two glow-discharge chambers, core-shell clusters are obtained: An Fe core is surrounded by small Si crystallites. The magnetization measurement indicates that the magnetic coercive force of the Fe∕Si core-shell cluster assembly is much smaller than those of Fe cluster assemblies at low temperature and no shift of the field-cooled hysteresis loop related to the zero-field-cooled loop is detected, probably because Si shells prevent Fe cluster surfaces from their oxidation. The temperature dependence of electrical resistance is attributed to electron conduction via Si shell networks above 180K, while it is attributed to variable range electron conduction between Fe clusters.
Nanoscale capacitors based on metal-insulator-carbon nanotube-metal structures
Authors: Jang J. E. , Cha S. N. , Choi Y. , Amaratunga G. A. J. , Kang D. J. , Hasko D. G. , Jung J. E. , Kim J. M.
Published: December 2005

We report the fabrication process and the electrical characteristics of a nanocapacitor structure using metal-insulator-carbon nanotube-metal layers. The structure shows high capacitance and the possibility of ultrahigh integration density due to the unique nanotube structure. Nanoscale and high-aspect-ratio patterns are achieved by electron beam lithography for the fabrication of these vertical nanostructures. This structure can be substituted for capacitors based on the silicon pillar structure in dynamic random access memory or as a nanoscale capacitor for various nanoelectronic devices.
Effect of strain on p-channel metal-oxide-semiconductor field-effect-transistor current enhancement using stress-modulated silicon nitride films
Authors: Lin Cha-Hsin , Pei Zingway , Maikap Siddheswar , Wang Ching-Chiun , Lu Ching-Sen , Lee Lurng-Shehng , Tsai Ming-Jinn , Chan Yi-Jen
Published: December 2005

The stress in chemical-vapor-deposited silicon nitride films (∼100nm thick) is modulated by an ion implantation technique. The tensile-strained silicon nitride film is deposited on the back and front sides of a Si wafer. After implantation of P+, As+, Sb+, or BF2+ ion species, the stress of the silicon nitride film becomes compressive on the front side. It can be explained by strain relaxation of Si–N bond on the front side and highly tensile-strained Si–N bond on the back side of wafer. The compressive stress is increased with a double-implantation process because of more atomic collisions in the silicon nitride film, as well as more strain relaxation of Si–N bond on the front side of wafer. After a thermal annealing process, the compressive stress in the silicon nitride film with P+, As+, or Sb+ implantation is reduced, while compressive stress is increased for BF2+ ion implantation due to formation of the B–N bond in silicon nitride film. To justify the stress-modulated silicon nitride film by the ion implantation technique, the p-channel metal-oxide-semiconductor field-effect transistor (p-MOSFET) is fabricated. The drive current of a p-MOSFET is improved by 7–13% for implanted silicon nitride films, due to the compressive strain-induced effective mass lowering in the channel.
Mega three-photon absorption cross-section enhancement in pseudoisocyanine J-aggregates
Authors: Cohanoschi Ion , Barbot Amel , Belfield Kevin D. , Yao Sheng , Hernandez Florencio E.
Published: December 2005

Herein we report an extraordinary three-photon absorption cross-section (σ3′) enhancement in J-aggregates supramolecular systems. The much higher value of σ3′ in PIC J-aggregate (2.5×10−71cm6s2ph−2) compared to typical values obtained in organic molecules (10−80cm6s2ph−2) is attributed to the strong molecular transition dipole moment coupling in the supramolecular assembly. Three-photon absorption of PIC J-aggregates and monomer aqueous solutions were measured using the well known open aperture Z-scan technique pumping with a 25ps pulse laser-OPG system at 1720nm. This novel result opens new expectations for applications of supramolecular systems in bioimaging and medicine.
Initial reaction of hafnium oxide deposited by remote plasma atomic layer deposition method
Authors: Won Youngdo , Park Sangwook , Koo Jaehyoung , Kim Seokhoon , Kim Jinwoo , Jeon Hyeongtag
Published: December 2005

A remote plasma atomic layer deposition (RPALD) method has been applied to grow a hafnium oxide thin film on the Si substrate. The deposition process was monitored by in situ XPS and the as-deposited structure and chemical bonding were examined by TEM and XPS. The in situ XPS measurement showed the presence of a hafnium silicate phase at the initial stage of the RPALD process up to the 20th cycle and indicated that no hafnium silicide was formed. The initial hafnium silicate was amorphous and grew to a thickness of approximately 2nm. Based on these results and model reactions for silicate formation, we proposed an initial growth mechanism that includes adatom migration at nascent step edges. Density functional theory calculations on model compounds indicate that the hafnium silicate is thermodynamically favored over the hafnium silicide by as much as 250kJ∕mol.
Short-period InAs∕GaSb type-II superlattices for mid-infrared detectors
Authors: Haugan H. J. , Szmulowicz F. , Mahalingam K. , Brown G. J. , Munshi S. R , Ullrich B.
Published: December 2005

Using a newly developed envelope function approximation model that includes interface effects, several InAs∕GaSb Type-II superlattices (SLs) were designed for the 4μm detection threshold. The present model predicts that a given threshold can be reached with a wide range of progressively thinner SL periods and these thinner designs hold a promise of higher mobilities and longer Auger lifetimes, thus higher detector operating temperatures. The proposed SL structures were grown by molecular-beam epitaxy with slow growth rates. As predicted, the band gaps of SLs determined by low-temperature photoluminescence remained constant around 330meV for the samples in the period range from 50.6to21.2Å.