bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure-related optical properties of (Pb,La)(Zr,Ti)O3 thin films on indium tin oxide∕quartz substrates
Authors: Leng W. J. , Yang C. R. , Ji H. , Zhang J. H. , Chen H. W. , Tang J. L.
Published: November 2006

To be suitable for integrated optical devices, (Pb,La)(Zr,Ti)O3 (PLZT) ferroelectric thin films require high crystalline quality, low surface roughness, high optical index, and high transparency. In this paper, PLZT thin films have been grown in situ on indium tin oxide (ITO) coated quartz substrates by rf magnetron sputtering. X-ray diffraction, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to investigate the structural properties of these PLZT films. The results show that the ferroelectric films exhibit satisfying crystallization with the highly (110)-oriented growth from 550°C, and the surface roughness value (∼3.1nm) in studied films is within the optimum range so that a low optical loss can be obtained. High quality PLZT ferroelectric thin films were further investigated by electrical measurements, showing that the remnant polarization Pr and coercive field Ec are approximately 11.3μC∕cm2 and 56.2kV∕cm, respectively. Spectroscopic ellipsometry (SE) was employed to characterize the depth profiles, the microstructural inhomogeneities (void and surface roughness), refractive index n, and extinction coefficient k of the PLZT film. In the analysis of the measured SE spectra, a three-layer Lorentz model with four oscillators was adopted to represent the optical properties of the PLZT film. In this model, the film was assumed to consist of two layers (a bottom bulk PLZT and a surface layer composed of bulk PLZT as well as void). Good agreement was obtained between the measured spectra and the model calculations. The film thickness measured from SEM is consistent with that obtained by SE, while the root mean square roughness determined by AFM is also close to our fitted effective surface layer thickness obtained by SE. The PLZT thin film on ITO-coated quartz substrate is highly transparent in the visible near infrared wavelength region, and the band gap energy Eg is estimated to be 3.54eV. The experimental results above tend to demonstrate the suitability of the PLZT films in situ grown on ITO∕quartz substrates for optical applications.
Real-time x-ray studies of gallium adsorption and desorption
Authors: Özcan Ahmet S. , Wang Yiyi , Ozaydin Gozde , Ludwig Karl F. , Bhattacharyya Anirban , Moustakas Theodore D. , Siddons D. Peter
Published: November 2006

Real-time grazing-incidence small-angle x-ray scattering has been employed to study the adsorption and desorption of Ga on c-plane sapphire and Ga-polar GaN surfaces. Formation of self-organized liquid Ga nanodroplets has been observed on sapphire during Ga exposure from an effusion cell at high flux. Subsequent to the Ga deposition, the nanodroplets were nitridated in situ by a nitrogen plasma source, which converted the droplets into GaN nanodots. In addition to the droplet studies, at lower Ga flux, the adsorption and desorption of Ga have been studied in the predroplet regime. For identical processing conditions, significantly different Ga adsorption∕desorption rates were observed on sapphire and GaN surfaces.
⟨100⟩-textured self-assembled square-shaped polycrystalline silicon grains by multiple shot excimer laser crystallization
Authors: He Ming , Ishihara Ryoichi , Metselaar Wim , Beenakker Kees
Published: November 2006

Strong preference for ⟨100⟩ surface and in-plane orientations has been observed in polycrystalline silicon film on SiO2 after crystallization with multiple excimer laser pulses. Laser induced periodic surface structure (LIPSS) is developed in the film, constructing self-assembled square-shaped grains. The clear texture can be observed in a relatively wide energy density window, from 250to275mJ∕cm2, for a 30nm thick α-Si layer. It is speculated that the lateral growth velocity of ⟨100⟩-oriented grains is the fastest, and the orthogonal in-plane ⟨100⟩ directions are developed due to the alternate directions of melting and solidification during the LIPSS formation.
Scanning photoelectron microscopic study of top-emission organic light-emitting device degradation under high-bias voltage
Authors: Shin H. J. , Song H. J. , Lee J. , Yoon H. J. , Chung J. , Lee J. C.
Published: November 2006

The degradation process of a top-emission organic light-emitting device (TOLED) under high-bias voltage was investigated using a scanning photoelectron microscope (SPEM). The TOLED was in situ biased to reveal the degraded area inside the SPEM chamber. The SPEM data showed a volcano-type structure inside the degraded area. The overall results of the spectroscopic analysis suggest that strong degradation was accompanied by an eruption underneath the cathode layer. It is posited that the hot gases from the erupted area separated the cathode layer from the organic layer, forming a large bubble, and that, as the bubble exploded, the pressure of the gas blew away the cathode layer.
Femtosecond coherent anti-Stokes Raman-scattering polarization beat spectroscopy of I2–Xe complex in solid krypton
Authors: Kiviniemi Tiina , Kiljunen Toni , Pettersson Mika
Published: November 2006

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the “free” and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2–Xe complex. The harmonic frequency of the I2–Xe complex is found to be redshifted by 0.90cm−1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat higher than that of the free iodine molecule in solid Kr, showing that the complexation affects dephasing, although not dramatically. Molecular dynamics simulations are carried out to find the conformation of the complex, and wave packet simulations are used to reproduce the CARS signal to confirm the assignments of the observed beatings as quantum and polarization beats. The results show that the polarization beats are a useful tool for investigating weak interactions in condensed phase.
A simple equation predicting the amplitude of motion of quartz crystal resonators
Authors: Johannsmann Diethelm , Heim Lars-Oliver
Published: November 2006

The amplitude of motion of quartz crystal resonators, u0, has been calculated on the basis of the transmission line model by Mason [Piezoelectric Crystals and Their Applications to Ultrasonics (Van Nostrand, Princeton, 1948)]. It is predicted to be u0=4∕(πn)2 Qd26Uel,0, where n is the overtone order, Q is the quality factor, d26 is the piezoelectric strain coefficient, and Uel,0 is the amplitude of the driving voltage. This simple result is in good agreement with previous numerical calculations, with an experimental value from the literature, and with our own experimental checks. As a side result, an equation is provided which allows to estimate the active area of the crystal from the product of the motional resistance R1 and the Q factor.
Time-of-flight photoelectron spectromicroscopy of single MoS2 nanotubes
Authors: Gloskovskii A. , Nepijko S. A. , Cinchetti M. , Schönhense G. , Fecher G. H. , Kandpal H. C. , Felser C. , Therese H. A. , Zink N. , Tremel W. , Oelsner A.
Published: November 2006

There is a recent interest in nanoscale materials, in particular, nanotubes based not only on carbon. In this study, photoemission spectra of single MoS2 nanotubes deposited on a Si surface were recorded in order to explain their electronic structure. The photoelectrons were excited by a femtosecond laser oscillator resulting in two-photon photoemission. A spectromicroscopic technique based on imaging time-of-flight detection was used to record the spatially resolved photoelectron spectra. Self-consistent electronic structure calculations for MoS2 slabs using the full potential linear augmented plane wave method are used to explain the peculiarities of the observed spectra. It turns out that the MoS2 nanotubes are semiconducting with a band gap of about 1eV. The two-photon transitions proceed through intermediate states in a region with high density of states; this gives rise to a high photoemission intensity.
Band gap optimization of finite photonic structures using apodization method
Authors: Wu Jiu Hui , Liu A. Q. , Ang L. K.
Published: November 2006

In this paper, the photonic band diagram and the density of states in finite photonic structures are analyzed and optimized for broad bandwidths using the apodization method. Based on the effective propagation constant, the group refractive index can be computed for the finite structures, which is adopted to reveal the physical explanation on the optimal band gaps. The surface states of the finite photonic crystal and the mode matching at the interfaces are also considered. It is found that the high group index of the photonic structures can obtain broad bandwidths and also enhance the mode matching at the interfaces. By slowly varying the radii of the cylinders monotonously in two dimensions, the first band gap can be increased from 10.6% to 20.04%. This work provides a useful tool for the optimal design of finite photonic crystals.
Isomorphisms between C*-ternary algebras
Authors: Park Choonkil
Published: November 2006

In this paper, we prove the Hyers-Ulam-Rassias stability of homomorphisms in C*-ternary algebras and of derivations on C*-ternary algebras for the following generalized Cauchy–Jensen additive mapping:2f(∑j=1pxj2+∑j=1dyj)=∑j=1pf(xj)+2∑j=1df(yj).This is applied to investigate isomorphisms between C*-ternary algebras. The concept of Hyers-Ulam-Rassias stability originated from the Rassias stability theorem that appeared in his paper: On the stability of the linear mapping in Banach spaces, see Proc. Amr. Math. Soc. 72, 297–300 (1978).
Quaternionic diffusion by a potential step
Authors: De Leo Stefano , Ducati Gisele C.
Published: November 2006

In looking for qualitative differences between quaternionic and complex formulations of quantum physical theories, we provide a detailed discussion of the behavior of a wave packet in the presence of a quaternionic time-independent potential step. In this paper, we restrict our attention to diffusion phenomena. For the group velocity of the wave packet moving in the potential region and for the reflection and transmission times, the study shows a striking difference between the complex and quaternionic formulations which could be matter of further theoretical discussions and could represent the starting point for a possible experimental investigation.
The Selberg trace formula for Dirac operators
Authors: Bolte Jens , Stiepan Hans-Michael
Published: November 2006

We examine spectra of Dirac operators on compact hyperbolic surfaces. Particular attention is devoted to symmetry considerations, leading to nontrivial multiplicities of eigenvalues. The relation to spectra of Maaß-Laplace operators is also exploited. Our main result is a Selberg trace formula for Dirac operators on hyperbolic surfaces.
Comment on “Theoretical analysis of numerical aperture increasing lens microscopy” [J. Appl. Phys. 97, 053105 (2005)]
Authors: Sheppard Colin J. R. , Huat Goh Szu
Published: November 2006

In a recent paper, Ippolito et al. [J. Appl. Phys. 97, 053105 (2005)] analyzed focusing at high numerical aperture into a dielectric medium. They considered three geometries, those of focusing through a level planar interface and through spherical interfaces arranged in concentric or aplanatic positions. The treatment for focusing through a planar interface is based on a different model from that presented elsewhere. It is shown that this model describes the aberration effect only approximately, in contrast to the previous, rigorous treatment.
Effect of the Rashba spin-orbit interaction on transport in a multichannel ferromagnet/semiconductor nanowire
Authors: Li Yu-Xian , Di Bing
Published: November 2006

Using the mode-matching method, spin-dependent electron transport properties in multichannel ferromagnet/semiconductor/ferromagnet nanowires are studied. The significant quantum confinement and Rashba spin-orbit interaction are considered simultaneously. As the width of the wire varies, corresponding channels for electrons are opened, and the conductance oscillates as a function of the length of the semiconductor. As the strength of the spin-orbit interaction increases, the phase of the conductance changes and the resonant peaks shift to the right. When two electron channels are open, the conductance oscillates anomalously and the polarization becomes smaller than that for only one open channel.
Effects of turbulence and flame instability on flame front evolution
Authors: Yuan Jiao , Ju Yiguang , Law Chung K.
Published: November 2006

The effects of turbulence and flame instabilities on the flame front evolution at Lewis number (Le) 1.0 and 0.7 were computationally investigated using a sixth-order central difference scheme and nonreflective boundary conditions. The turbulence intensity varies from 1% to 50% and the resulting turbulent flames are in the thin wrinkled flame region. It is shown that when the turbulence intensity is weak (u′=1%–5%), hydrodynamic instability dominates the growth of the flame cells. However, when the turbulent intensity is large (u′=50%), the turbulent motion wrinkles the flame front and dominates the evolution process. It is also demonstrated that curvature stretch dominates the total stretch rate for flames with either weak or large turbulent intensities, and therefore plays a significant role in turbulent flame modeling.
Sheath and potential characteristics in rf magnetron sputtering plasma
Authors: Kakati H. , Pal A. R. , Bailung H. , Chutia Joyanti
Published: November 2006

Using an emissive probe with an additional compensating electrode, the axial and radial variations of potential are determined in a rf planar magnetron discharge at constant argon flow. The axial potential structure shows the sheath formation near the powered electrode (cathode). In the cathode sheath, the high potential drop in the racetrack region indicates the existence of a strong electric field required for effective sputtering. Results reveal that the potential structure along a line parallel to the surface of the powered electrode exhibits radial variations. Dependence of potential structure in the cathode sheath due to the negative dc self-bias at different applied rf powers has also been observed. The ion density and the electron temperature are measured at different axial and radial positions with the help of a compensating Langmuir probe to correlate with the results found from emissive probe measurements.
Effect of dislocations on open circuit voltage in crystalline silicon solar cells
Authors: Kieliba Thomas , Riepe Stephan , Warta Wilhelm
Published: November 2006

The dislocation dependence of open circuit voltage is studied based on Donolato’s model for the effect of dislocations on minority carrier effective diffusion length [J. Appl. Phys. 84, 2656 (1998)]. Experimental data measured on thin-film solar cells show a strong decrease of open circuit voltage Voc with an increase in defect density. The analysis of the recombination currents indicates that Voc is largely reduced by space charge region recombination. For a quantitative study on the relationship between dislocation density, effective diffusion length, and Voc the data are fitted with an extended version of Donolato’s model. Taking into account the base recombination current as well as the space charge region recombination current, the modeled curves fit very well to the experimental data. However, satisfactory fitting results require that the region of high recombination is set wider than the “effective depletion region width,” which is calculated from the electrical field strength in a planar p-n junction. This effect can be explained with the assumption of a geometrical enlargement of the p-n junction due to defects like dislocations.
Surface properties of fluids of charged platelike colloids
Authors: Bier Markus , Harnau Ludger , Dietrich S.
Published: November 2006

Surface properties of mixtures of charged platelike colloids and salt in contact with a charged planar wall are studied within density functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model [J. Chem. Phys. 39, 1714 (1963)] and the charges of the particles are concentrated at their centers. The density functional applied is an extension of a recently introduced functional for charged platelike colloids. It provides a qualitative approach because it does not determine the relation between the actual and the effective charges entering into the model. Technically motivated approximations, such as using the Zwanzig model, are expected not to influence the results qualitatively. Analytically and numerically calculated bulk and surface phase diagrams exhibit first-order wetting for sufficiently small macroion charges and isotropic bulk order as well as first-order drying for sufficiently large macroion charges and nematic bulk order. The asymptotic wetting and drying behaviors are investigated by means of effective interface potentials which turn out to be asymptotically the same as for a suitable neutral system governed by isotropic nonretarded dispersion forces. Wetting and drying points as well as predrying lines and the corresponding critical points have been located numerically. A crossover from monotonic to nonmonotonic electrostatic potential profiles upon varying the surface charge density has been observed. Nonmonotonic electrostatic potential profiles are equivalent to the occurrence of charge inversion. Due to the presence of both the Coulomb interactions and the hard-core repulsions, the surface potential and the surface charge do not vanish simultaneously, i.e., the point of zero charge and the isoelectric point of the surface do not coincide.
The environmental effect on the radial breathing mode of carbon nanotubes. II. Shell model approximation for internally and externally adsorbed fluids
Authors: Longhurst M. J. , Quirke N.
Published: November 2006

We have previously shown that the upshift in the radial breathing mode (RBM) of closed (or infinite) carbon nanotubes in solution is almost entirely due to coupling of the RBM with an adsorbed layer of fluid on the nanotube surface. The upshift can be modeled analytically by considering the adsorbed fluid as an infinitesimally thin shell, which interacts with the nanotube via a continuum Lennard-Jones potential. Here we extend the model to include internally as well as externally adsorbed waterlike molecules, and find that filling the nanotubes leads to an additional upshift of two to six wave numbers. We show that using molecular dynamics, the RBM can be accurately reproduced by replacing the fluid molecules with a mean field harmonic shell potential, greatly reducing simulation times.
Quantitative measurements of indentation moduli by atomic force acoustic microscopy using a dual reference method
Authors: Stan Gheorghe , Price William
Published: November 2006

Atomic force acoustic microscopy (AFAM) was used to quantitatively determine material indentation moduli by measuring local mechanical responses. A dual reference method has been shown to be capable of extracting the modulus of a material within 3% of the calculated expected value without any assumptions of the probe’s mechanical properties. The use of this developed method also allows for the calculation of the maximum precision in the quantitative determination of the indentation modulus of materials using AFAM. A parallel analysis of the single and dual reference AFAM techniques isolates the inaccuracy induced by the assumption that the indentation modulus of the atomic force microscopy probe used is the same as bulk silicon.
Absolute calibration for a broad range single shot electron spectrometer
Authors: Glinec Y. , Faure J. , Guemnie-Tafo A. , Malka V. , Monard H. , Larbre J. P. , De Waele V. , Marignier J. L. , Mostafavi M.
Published: November 2006

This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.
Thermoelectrical properties of A-site substituted Ca1−xRexMnO3 system
Authors: Flahaut D. , Mihara T. , Funahashi R. , Nabeshima N. , Lee K. , Ohta H. , Koumoto K.
Published: November 2006

Ca Mn O 3 is an electron-doped compound which belongs to the perovskite family. Despite its high Seebeck coefficient S value, the figure of merit at high temperature remains low due to its large resistivity ρ(ρ300K=2Ωcm). To optimize the performance of this material in terms of thermoelectric properties, several substitutions have been attempted on the Ca site to decrease the ρ. Structure and thermoelectric properties of polycrystalline samples Ca1−xAxMnO3 (A=Yb, Tb, Nd, and Ho) have been investigated. Although ρ strongly depends on the ionic radius ⟨rA⟩ and carrier concentration, we have shown that the thermal conductivity κ is mainly driven by the atomic weight of the A site and decreases with it. Therefore, it seems that the S, ρ, and κ could be controlled separately. For instance, the highest dimensionless ZT (=0.16) has been obtained at 1000K in the air for Ca0.9Yb0.1MnO3.
Ferromagnetic resonance investigation of maghemite-silica nanocomposites
Authors: Pereira A. R. , Miranda K. L. C. , Sartoratto P. P. C. , Morais P. C. , Bakuzis A. F.
Published: November 2006

Maghemite-silica nanocomposites were prepared from water-based magnetic fluids through the sol-gel method. X-ray diffraction revealed that the maghemite nanoparticles had a size of 5nm. Electron magnetic resonance of the composites was studied as a function of temperature and nanoparticle concentration. The resonance field was found to decrease upon increasing the maghemite concentration, while the linewidth increased. The effect was interpreted in terms of interparticle as well as intraparticle magnetic interactions. The data analysis suggests the presence of small agglomerates in the maghemite-silica nanocomposite for higher particle concentrations.
Measurements of forward scattered laser radiation from intense sub-ps laser interactions with underdense plasmas
Authors: Walton B. R. , Mangles S. P. D. , Najmudin Z. , Tatarakis M. , Wei M. S. , Gopal A. , Marle C. , Dangor A. E. , Krushelnick K. , Fritzler S. , Malka V. , Clarke R. J. , Hernandez-Gomez C.
Published: November 2006

Two experiments studying the interaction of high intensity laser pulses (1×1019–5×1020W∕cm2) with underdense plasma are compared. The experiments used lasers that differed in power and focused intensity but had similar pulse duration (∼1ps). Spectroscopic measurements of the forward scattered light (sidebands) near the fundamental laser frequency produced by the self-modulation instability were performed and the energies of electrons accelerated in the interaction are measured and compared. It is found that at high intensities the sideband intensities and the electron energies were not directly correlated, implying that relativistic plasma wave generation is not the most important mechanism for electron acceleration in the ultrahigh intensity regime. Simulation results for the forward scattered spectrum agree well with experimental results.
Site-directed electronic tunneling through a vibrating molecular network
Authors: Caspary Maytal , Peskin Uri
Published: November 2006

The effect of electronic-nuclear coupling on electronic transport through a complex molecular network is studied. Electronic tunneling dynamics in a network of N donor/acceptor sites, connected by molecular bridges, is shown to be controlled by electronic-nuclear coupling at the bridges. Particularly, electronic coupling to an accepting nuclear mode at the contact site between the donor and the rest of the network is shown to affect the tunneling path selection to specific acceptors. In the “deep” tunneling regime, the network is mapped onto an N-level system using a recursive perturbation expansion, enabling analytical treatment of the electronic dynamics. The analytic formulation is applied for two model systems, demonstrating site-directed tunneling by electronic-nuclear coupling. Numerical simulations suggest that this phenomenon is not limited to the deep tunneling regime.
Properties of plasma flames sustained by microwaves and burning hydrocarbon fuels
Authors: Hong Yong Cheol , Uhm Han Sup
Published: November 2006

Plasma flames made of atmospheric microwave plasma and a fuel-burning flame were presented and their properties were investigated experimentally. The plasma flame generator consists of a fuel injector and a plasma flame exit connected in series to a microwave plasma torch. The plasma flames are sustained by injecting hydrocarbon fuels into a microwave plasma torch in air discharge. The microwave plasma torch in the plasma flame system can burn a hydrocarbon fuel by high-temperature plasma and high atomic oxygen density, decomposing the hydrogen and carbon containing fuel. We present the visual observations of the sustained plasma flames and measure the gas temperature using a thermocouple device in terms of the gas-fuel mixture and flow rate. The plasma flame volume of the hydrocarbon fuel burners was more than approximately 30–50 times that of the torch plasma. While the temperature of the torch plasma flame was only 868K at a measurement point, that of the diesel microwave plasma flame with the addition of 0.019lpm diesel and 30lpm oxygen increased drastically to about 2280K. Preliminary experiments for methane plasma flame were also carried out, measuring the temperature profiles of flames along the radial and axial directions. Finally, we investigated the influence of the microwave plasma on combustion flame by observing and comparing OH molecular spectra for the methane plasma flame and methane flame only.
Refinement trajectory and determination of eigenstates by a wavelet based adaptive method
Authors: Pipek János , Nagy Szilvia
Published: November 2006

The detail structure of the wave function is analyzed at various refinement levels using the methods of wavelet analysis. The eigenvalue problem of a model system is solved in granular Hilbert spaces, and the trajectory of the eigenstates is traced in terms of the resolution. An adaptive method is developed for identifying the fine structure localization regions, where further refinement of the wave function is necessary.
Harmonic Fourier beads method for studying rare events on rugged energy surfaces
Authors: Khavrutskii Ilja V. , Arora Karunesh , Brooks Charles L.
Published: November 2006

We present a robust, distributable method for computing minimum free energy paths of large molecular systems with rugged energy landscapes. The method, which we call harmonic Fourier beads (HFB), exploits the Fourier representation of a path in an appropriate coordinate space and proceeds iteratively by evolving a discrete set of harmonically restrained path points—beads—to generate positions for the next path. The HFB method does not require explicit knowledge of the free energy to locate the path. To compute the free energy profile along the final path we employ an umbrella sampling method in two generalized dimensions. The proposed HFB method is anticipated to aid the study of rare events in biomolecular systems. Its utility is demonstrated with an application to conformational isomerization of the alanine dipeptide in gas phase.
Morphology and electronic properties of the pentacene on cobalt interface
Authors: Tiba M. V. , de Jonge W. J. M. , Koopmans B. , Jonkman H. T.
Published: November 2006

In this paper, we report the structural and electronic properties of pentacene thin films grown on a polycrystalline Co film using atomic force microscopy and ultraviolet photoemission spectroscopy (UPS), respectively. Investigation of this type of interface is of importance for the engineering of hybrid organometallic spintronic devices for which the use of spin polarized electrodes is a prerequisite. Uniform single crystalline areas of pentacene as large as several micrometers, with molecules arranging almost perpendicular to the substrate, were obtained. For the electronic properties at this interface, we have found an energy barrier for the hole injection of about 1eV, in spite of the fact that the ionization potential of pentacene reported previously equals the work function of Co. A shift of the vacuum level of the same magnitude has also been observed. A comparison of the UPS spectra of the pentacene films with the gas phase spectrum directly indicates that hybridization effects are present at this interface.
Order parameters of α,ω-diphenylpolyenes in a nematic liquid crystal from an integrated computational and C13 NMR spectroscopic approach
Authors: Benzi Caterina , Barone Vincenzo , Tarroni Riccardo , Zannoni Claudio
Published: November 2006

The orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining C13 NMR measurements and quantum mechanical computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present experiments. The rank-two order parameter ⟨P2⟩ in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range. The molecular biaxiality order parameter ⟨D022⟩ is found to be small and essentially constant with temperature, giving further support to the common assumption of effective uniaxiality for these probes.
Coupling effects on energy transduction in coupled polymer chains with perturbation of noise
Authors: Li Ya Ping , Cao Wei Liang
Published: November 2006

Noise-assistant transduction was investigated in coupled polymer chains where one subsystem was exposed to environment noise. It was found that coupling could transfer oscillation from one subsystem disturbed by noise to the other not disturbed by noise and play a role of a noise filtering for the other. Then, a sort of coupling-induced synchronization was investigated as a function of noise intensity and coupling strength. In particular, we calculated the minimum coupling strength to reach synchronization and pointed out that noise dominated at small coupling strength, otherwise, coupling dominated.
Coupled-cluster with active space selected higher amplitudes: Performance of seminatural orbitals for ground and excited state calculations
Authors: Köhn Andreas , Olsen Jeppe
Published: November 2006

The active space approach for coupled-cluster models is generalized using the general active space concept and implemented in a string-based general coupled-cluster code. Particular attention is devoted to the choice of orbitals on which the subspace division is based. Seminatural orbitals are proposed for that purpose. These orbitals are obtained by diagonalizing only the hole-hole and particle-particle block of the one-electron density of a lower-order method. The seminatural orbitals are shown to be a good replacement for complete active space self-consistent field orbitals and avoid the ambiguities with respect to the reference determinant introduced by the latter orbitals. The seminatural orbitals also perform well in excited state calculations, including excited states with strong double excitation contributions, which usually are difficult to describe with standard coupled-cluster methods. A set of vertical excitation energies is obtained and benchmarked against full configuration interaction calculations, and alternative hierarchies of active space coupled-cluster models are proposed. As a simple application the spectroscopic constants of the C2 BΔg1 and B′Σg+1 states are calculated using active space coupled-cluster methods and basis sets up to quadruple-zeta quality in connection with extrapolation and additivity schemes.
The Morse oscillator under time-dependent external fields
Authors: de Lima Emanuel F. , Hornos José E. M.
Published: November 2006

A method to solve the equations for the Morse oscillator under intense time-dependent external fields is presented. Exact analytical formulas for the dipole matrix elements are calculated by the use of the hypergeometric algebra. The continuum is described by an expansion using Laguerre functions. The full algorithm for the calculation of wave functions can be controlled by the convergence of series and by the errors of a first order integration method. We apply our technique to the selective preparation of high overtones by femtosecond laser pulses. The population of the target state is optimized as a function of the intensity and frequency. Introducing a second simultaneous laser, we study the effects of relative frequency and phase over the target state population and dissociation channels. The calculations exhibit a rich interference pattern showing the enhancement and the suppression of the target population by varying the laser parameters.
Effective Hamiltonians by optimal control: Solid-state NMR double-quantum planar and isotropic dipolar recoupling
Authors: Tošner Zdeněk , Glaser Steffen J. , Khaneja Navin , Nielsen Niels Chr.
Published: November 2006

We report the use of optimal control algorithms for tailoring the effective Hamiltonians in nuclear magnetic resonance (NMR) spectroscopy through sophisticated radio-frequency (rf) pulse irradiation. Specifically, we address dipolar recoupling in solid-state NMR of powder samples for which case pulse sequences offering evolution under planar double-quantum and isotropic mixing dipolar coupling Hamiltonians are designed. The pulse sequences are constructed numerically to cope with a range of experimental conditions such as inhomogeneous rf fields, spread of chemical shifts, the intrinsic orientation dependencies of powder samples, and sample spinning. While the vast majority of previous dipolar recoupling sequences are operating through planar double-or zero-quantum effective Hamiltonians, we present here not only improved variants of such experiments but also for the first time homonuclear isotropic mixing sequences which transfers all Ix, Iy, and Iz polarizations from one spin to the same operators on another spin simultaneously and with equal efficiency. This property may be exploited to increase the signal-to-noise ratio of two-dimensional experiments by a factor of 2 compared to conventional solid-state methods otherwise showing the same efficiency. The sequences are tested numerically and experimentally for a powder of Cα13,Cβ13-L-alanine and demonstrate substantial sensitivity gains over previous dipolar recoupling experiments.
Characterization of natural nanostructured hydroxyapatite obtained from the bones of Brazilian river fish
Authors: Coelho T. M. , Nogueira E. S. , Steimacher A. , Medina A. N. , Weinand W. R. , Lima W. M. , Baesso M. L. , Bento A. C.
Published: November 2006

In this study, the characterization of the optical properties of natural hydroxyapatite (HAp) [Ca10(PO4)6(OH)2] is discussed. In the first stage of the experiment, natural HAp was processed from the bones of Brazilian river fish such as pintado (Pseudoplatystoma corruscans), jaú (Paulicea lutkeni), and cachara (Pseudoplatystoma fasciatum). The bones were calcined at 900°C for different amounts of time (4–12h) and reduced to powder using two different milling times (2 and 4h) in a high-energy ball mill, in order to determine the best procedure for obtaining natural nanostructured HAp powder for the study. In the second stage, material calcined for 8h was milled for 2, 4, 8, and 16h. The techniques of photoacoustic spectroscopy, scanning electron microscopy, and flame atomic absorption spectrometry were applied to characterize these samples. The O–H stretching shown by photoacoustic spectroscopy was correlated to the HAp nanostructure. Structural analysis indicated a Ca∕P ratio close to 1.67 (∼1.64±0.04) and the presence of morphology and particle phase structure in the nanostructured HAp powder.
Analytical current-voltage model for nanocrystalline silicon thin-film transistors
Authors: Hatzopoulos A. T. , Pappas I. , Tassis D. H. , Arpatzanis N. , Dimitriadis C. A. , Templier F. , Oudwan M.
Published: November 2006

An analytical model for the drain current above threshold voltage, based on an exponential energy distribution of band tail states, has been applied to bottom-gated nanocrystalline silicon (nc-Si) thin-film transistors (TFTs). Analysis of the model shows that the slope of the exponential band tails determines the behavior of the device current-voltage characteristics. Comparison with experimental data shows that few fundamental model parameters, related to the material quality and different physical effects, can be used to describe consistently both output and transfer characteristics of nc-Si TFTs over a wide range of channel lengths.
Approximate scaling properties of the density functional theory Tc for atoms
Authors: Liu Shubin , Morrison Robert C. , Parr Robert G.
Published: November 2006

Revealed are scaling properties for Tc[ρ], the kinetic-energy component of the correlation energy density functional for atoms, in terms of the total number of electrons N, the nuclear charge Z, and the total electron density at the nucleus ρ(0). Tc scales well as Nρ(0)∕Z8∕3 for both neutral atoms up to Z=18 and the four-electron Be-like cationic species. A model is given that describes these findings, involving a density encoding the cusp information and an effective potential going like r−4∕3.
On-chip detection of ferromagnetic resonance of a single submicron Permalloy strip
Authors: Costache M. V. , Sladkov M. , van der Wal C. H. , van Wees B. J.
Published: November 2006

The authors measured ferromagnetic resonance of a single submicron ferromagnetic strip, embedded in an on-chip microwave transmission line device. The method used is based on detection of the oscillating magnetic flux due to the magnetization dynamics, with an inductive pickup loop. The dependence of the resonance frequency on applied static magnetic field agrees very well with the Kittel formula, demonstrating that the uniform magnetization precession mode is being driven.
Polarization-resolved optical absorption in single V-groove quantum wires
Authors: Palmgren S. , Weman H. , Schoenberg A. , Karlsson K. F. , Dupertuis M.-A. , Leifer K. , Rudra A. , Kapon E.
Published: November 2006

Optical transitions associated with all three linear polarization directions were investigated in single GaAs V-groove quantum wires of different wire thicknesses. This was accomplished by combining absorption measurements in V-groove waveguide geometry with surface-excited photoluminescence excitation spectroscopy. The observed transitions were identified with the aid of model calculations. It is shown that excitonic intersubband coupling should be accounted for in order to explain the optical transitions associated with confined light-hole-like states. The results are relevant for the design of efficient quantum wire waveguide modulators and lasers.
Photonic crystal quantum cascade lasers with improved threshold characteristics operating at room temperature
Authors: Höfling S. , Heinrich J. , Hofmann H. , Kamp M. , Reithmaier J. P. , Forchel A. , Seufert J.
Published: November 2006

The authors have fabricated GaAs∕Al0.45Ga0.55As quantum cascade lasers (QCLs) with two-dimensional photonic crystal (PhC) mirrors. The monolithically integrated PhC mirrors consist of a triangular lattice of ∼14μm deeply etched semiconductor pillars. The PhC is designed to exhibit a photonic band gap for both the ΓM and the ΓK crystal orientation and provides reflectivities of >80%. Compared to a reference laser with the same cavity length of 600μm but as-cleaved facets, the QCLs with ΓM and ΓK oriented PhCs show reductions of the threshold current by 34% and 30%, respectively.
Inserting one single Mn ion into a quantum dot
Authors: Maingault Laurent , Besombes L. , Léger Y. , Bougerol C. , Mariette H.
Published: November 2006

A method of growth to get one single Mn in self-assembled semiconductor quantum dot is presented. With a simple quantitative model, the appropriate low Mn density needed prior to the quantum dot nucleation is estimated. Such a low Mn concentration was reached by inserting a thin ZnTe spacer between a Zn1−xMnxTe buffer and the CdTe quantum dot layer. The control of Mn density is made by changing the thickness of the ZnTe spacer, with good reproducibility. Qualitative and quantitative comparisons of optical spectra for different samples assess the relevance of this growth method.
Radiation loss of coupled-resonator waveguides in photonic-crystal slabs
Authors: Povinelli M. L. , Fan Shanhui
Published: November 2006

The authors characterize the intrinsic radiation loss of coupled-resonator optical waveguides by defining a waveguide-quality factor Q. They find that tuning an isolated resonator in a photonic-crystal slab to maximize its Q can also increase the waveguide Q. Due to interference between different resonators, the waveguide can have far lower loss than the isolated cavity; in other cases it can have far greater loss. They show that the dependence of waveguide Q on wave vector can largely be predicted by the shifting of the light cone within a tight-binding model.
Silicon layer transfer by hydrogen implantation combined with wafer bonding in ultrahigh vacuum
Authors: Fecioru Alin Mihai , Senz Stephan , Scholz Roland , Gösele Ulrich
Published: November 2006

A layer transfer method was developed by combining in situ photothermal activation of hydrogen passivated surfaces, ultrahigh vacuum bonding, and hydrogen-implantation induced splitting. Structural and electrical investigations showed that ultrathin, single crystalline silicon layers can be transferred to appropriate substrates without the involvement of an intermediate layer such as an oxide or solder. Significant current flow across such produced silicon-silicon bonded interfaces was observed, making this approach very attractive for material integration.
Ti
Al
N
∕
Ti
Al
O
N
∕
Si
3
N
4
tandem absorber for high temperature solar selective applications
Authors: Barshilia Harish C. , Selvakumar N. , Rajam K. S. , Sridhara Rao D. V. , Muraleedharan K. , Biswas A.
Published: November 2006

A tandem absorber of TiAlN∕TiAlON∕Si3N4 is prepared using a magnetron sputtering process. The graded composition of the individual component layers of the tandem absorber produces a film with a refractive index increasing from the surface to the substrate, which exhibits a high absorptance (0.95) and a low emittance (0.07). The tandem absorber is stable in air up to 600°C for 2h, indicating its importance for high temperature solar selective applications. The thermal stability of the tandem absorber is attributed to high oxidation resistance and microstructural stability of the component materials at higher temperatures.
Rapid synthesis of carbon nanotubes via inductive heating
Authors: Sosnowchik Brian D. , Lin Liwei
Published: November 2006

A rapid yet simple methodology to synthesize carbon nanotubes (CNTs) in a room temperature environment has been demonstrated using an inductive heating system. Substrates of either heavily doped silicon or nickel-coated, lightly doped silicon have been used to synthesize CNTs using Fe as the catalyst. Aligned carbon nanotubes with growth rates as high as 200μm∕min have been achieved in less than 1min. Transmission electron micrographs illustrated average diameters of 8 and 6.8nm for CNTs grown under average temperatures of 760 and 910°C, respectively. This system allows the synthesis of CNTs that is easy to set up, fast, clean, and inexpensive.
Structural transition in rare earth oxide clusters
Authors: Nicolas D. , Masenelli B. , Mélinon P. , Bernstein E. , Dujardin C. , Ledoux G. , Esnouf C.
Published: November 2006

Size effects, such as structure transition, have been reported in small clusters of alkali halide compounds. We extend the study to rare earth sesquioxide (Gd2O3) clusters which are as ionic as the alkali halide compounds, but have a more complicated structure. In a clean and controlled environment (ultra high vacuum), such particles are well crystallized, facetted and tend to adopt a rhombic dodecahedron shape. This indicates the major role of highly ionic bonds in preserving the crystal lattice even at small sizes (a few lattice parameter). Based on both cathodo-luminescence and transmission electron microscopy, we report the existence of a structural transition from bcc to monoclinic at small sizes.
Successive inverse polynomial interpolation to optimize Smagorinsky’s model for large-eddy simulation of homogeneous turbulence
Authors: Geurts Bernard J. , Meyers Johan
Published: November 2006

We propose the successive inverse polynomial interpolation method to optimize model parameters in subgrid parameterization for large-eddy simulation. This approach is illustrated for the Smagorinsky eddy-viscosity model used in homogeneous decaying turbulence. The optimal Smagorinsky parameter is resolution dependent and provides minimal total error in the resolved kinetic energy. It is approximated by starting with a “bracketing interval” that is obtained from separate “no-model” and “dynamic eddy-viscosity” large-eddy simulations. The total error level is reduced 3–6 times compared to the maximal initial errors. The computational overhead of the full optimization at resolution N3 is comparable to a single simulation at (3N∕2)3 grid cells. The increased accuracy is higher than obtained with dynamic modeling at a resolution of (4N)3.
A theoretical approach to substituent effects. Stabilities and rotational barriers of β-substituted ethyl anions
Authors: Pross A , Radom L
Published: November 2006

Ab initio molecular orbital
theory is used to study substituent effects in a series of substituted ethyl
anions, XCH2CH2- (X = Li, BeH,
BH2, CH3, NH2, OH and F). All substituents
stabilize the anion relative to the corresponding neutral ethane. For electronegative
substituents (NH2, OH and F) as well as CH3, this
stabilization is achieved through enhanced hyperconjugative
donation from the occupied 2p(C-) orbital to a vacant π*(CH2X)
or π*(CH2) orbital; electropositive groups (Li, BeH and BH2) stabilize the anion primarily by
1,3-overlap between the occupied 2p(C-) orbital and the vacant
2p(X) orbital where such an interaction is possible. The importance of
1,3-interactions contrasts with the situation for cations
XCH2CH2+ in which hyperconjugative
interactions appear to be dominant.