bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformable large-area position-sensitive photodetectors based on luminescence-collecting silicone waveguides
Authors: Bartu Petr , Koeppe Robert , Arnold Nikita , Neulinger Anton , Fallon Lisa , Bauer Siegfried
Published: June 2010

Position sensitive detection schemes based on the lateral photoeffect rely on inorganic semiconductors. Such position sensitive devices (PSDs) are reliable and robust, but preparation with large active areas is expensive and use on curved substrates is impossible. Here we present a novel route for the fabrication of conformable PSDs which allows easy preparation on large areas, and use on curved surfaces. Our device is based on stretchable silicone waveguides with embedded fluorescent dyes, used in conjunction with small silicon photodiodes. Impinging laser light (e.g., from a laser pointer) is absorbed by the dye in the PSD and re-emitted as fluorescence light at a larger wavelength. Due to the isotropic emission from the fluorescent dye molecules, most of the re-emitted light is coupled into the planar silicone waveguide and directed to the edges of the device. Here the light signals are detected via embedded small silicon photodiodes arranged in a regular pattern. Using a mathematical algorithm derived by extensive using of models from global positioning system (GPS) systems and human activity monitoring, the position of light spots is easily calculated. Additionally, the device shows high durability against mechanical stress, when clamped in an uniaxial stretcher and mechanically loaded up to 15% strain. The ease of fabrication, conformability, and durability of the device suggests its use as interface devices and as sensor skin for future robots.
Influence of the thiourea/CdCl2 concentration ratio used for the chemical bath deposition of CdS thin films, upon the CdS/CdTe interface recombination velocity in CdTe/CdS/glass structures.
Authors: Marín E. , Santoyo J. , Calderón A. , Vigil-Galán O. , Contreras-Puente G.
Published: June 2010

In this work we study the influence of the thiourea/CdCl2 concentration ratio used for the chemical bath deposition of CdS thin films on glass substrates, upon the CdS/CdTe interface recombination velocity in CdTe/CdS/glass structures, where the CdTe layer was grown on the CdS thin film by close space vapor deposition (CSVT)-hot wall technique. The interface recombination velocity was measured by means of the photoacoustic (PA) technique in a heat transmission configuration, in which minority carriers are photoexcited at the CdTe layer after illumination through the substrate and the CdS thin film. For data processing, a theoretical model was developed for the generation of the PA signal. We show a reduction in the value of the recombination velocity respecting those obtained for samples where CdS was grown by CSVT, and we observe that a minimal value appears for a thiourea/CdCl2 ratio in the CdS deposition solution equal to 5. These results show a good correlation with those of electrical measurements performed in solar cell devices.
Refractive phenomena in the shock wave dispersion with variable gradients
Authors: Markhotok A. , Popovic S.
Published: June 2010

In this article the refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are described. In the case of a finite-gradient boundary, the effect of the SW dispersion is remarkably stronger than in the case of a step change in parameters. In the former case the vertical component of velocity for the transmitted SW (the refraction effect) must be taken into account. Results of comparative calculations based on the two-dimensional model corrected for the refraction effect show significant differences in the shapes of the dispersed SW fronts.
Molecular model for carbon dioxide optimized to vapor-liquid equilibria
Authors: Merker Thorsten , Engin Cemal , Vrabec Jadran , Hasse Hans
Published: June 2010

A molecular model for carbon dioxide is presented, and the parameters of the Lennard-Jones sites, the bond length, and the quadrupole moment are optimized to experimental vapor-liquid equilibrium data. The resulting molecular model shows mean unsigned deviations to the experiment over the whole temperature range from triple point to critical point of 0.4% in saturated liquid density, 1.8% in vapor pressure, and 8.1% in enthalpy of vaporization. The molecular model is assessed by comparing predicted thermophysical properties with experimental data and a reference equation of state for a large part of the fluid region. The average deviations for density and residual enthalpy are 4.5% and 1.7%, respectively. The model is also capable to predict the radial distribution function, the second virial coefficient, and transport properties, the average deviations of the latter are 12%.
Time-dependent transport through molecular junctions
Authors: Ke San-Huang , Liu Rui , Yang Weitao , Baranger Harold U.
Published: June 2010

We investigate transport properties of molecular junctions under two types of bias—a short time pulse or an ac bias—by combining a solution for Green’s functions in the time domain with electronic structure information coming from ab initio density functional calculations. We find that the short time response depends on lead structure, bias voltage, and barrier heights both at the molecule-lead contacts and within molecules. Under a low frequency ac bias, the electron flow either tracks or leads the bias signal (resistive or capacitive response) depending on whether the junction is perfectly conducting or not. For high frequency, the current lags the bias signal due to the kinetic inductance. The transition frequency is an intrinsic property of the junctions.
Infrared signatures of high carrier densities induced in semiconducting poly(3-hexylthiophene) by fluorinated organosilane molecules
Authors: Khatib O. , Lee B. , Yuen J. , Li Z. Q. , Di Ventra M. , Heeger A. J. , Podzorov V. , Basov D. N.
Published: June 2010

We report on infrared (IR) absorption and dc electrical measurements of thin films of poly(3-hexylthiophene) (P3HT) that have been modified by a fluoroalkyl trichlorosilane (FTS). Spectra for FTS-treated films were compared to data for electrostatically-doped P3HT in an organic field-effect transistor (OFET). The appearance of a prominent polaron band in mid-IR absorption data for FTS-treated P3HT supports the assertion of hole doping via a charge-transfer process between FTS molecules and P3HT. In highly-doped films with a significantly enhanced polaron band, we find a monotonic Drude-type absorption in the far-IR, signifying delocalized states. Utilizing a simple capacitor model of an OFET, we extracted a carrier density for FTS-treated P3HT from the spectroscopic data. With carrier densities reaching 1014 holes/cm2, our results demonstrate that FTS doping provides a unique way to study the metal-insulator transition in polythiophenes.
Design of arbitrarily directional cloaks by solving the Laplace’s equation
Authors: Mei Zhong Lei , Bai Jing , Niu Tiao Ming , Cui Tie Jun
Published: June 2010

We propose a robust method to design arbitrarily directional cloaks by solving the Laplace’s equation. The method is based on the orthogonality between light rays and eikonal curves. By employing the analogy between light rays and electric force lines, and the equivalence between eikonal curves and isopotential lines, the original problem in the geometrical optics is converted into a boundary value problem in electrostatics. Examples are given and the simulation results validate the design. The method can also be used to design other optical-transformation devices and be extended to solve three-dimensional problems. The medium parameters designed by the method are easily realized using metamaterials or normal materials, and hence, the method can find applications in the optical and microwave engineering.
Determination of polar anchoring energy of dye-doped liquid crystals by measuring capacitance
Authors: Huang Chia-Yi , Cheng Zuo-Zhong , Lo Kuang-Yao , Lee Chia-Rong
Published: June 2010

Polar anchoring energy of a dye-doped liquid crystal (DDLC) cell is determined based on capacity measurements. Experimental results indicate that under the illumination of a pump beam, the polar anchoring energy (7.90×10−6 J/m2) includes the adsorption-induced anchoring energy (5.74×10−6 J/m2) and the preexisting-dye-induced anchoring energy (2.16×10−6 J/m2). The latter is attributed to the torque, which is induced by the dye molecules on the boundary surface even before illumination. After the illumination, the adsorption-induced anchoring energy remains and the preexisting-dye-induced anchoring energy disappears, with the former revealing that weak anchoring affects the decay time and threshold voltage of the DDLC cell. Moreover, plotting the polar angle distributions in the DDLC cell reveals its correlation with variations in the capacitance of the DDLC cell.
Surface-induced p-type conductivity in ZnO nanopillars investigated by scanning probe microscopy
Authors: Latu-Romain E. , Gilet P. , Chevalier N. , Mariolle D. , Bertin F. , Feuillet G. , Perillat-Merceroz G. , Ferret P. , Levy F. , Muret P. , Chelnokov A.
Published: June 2010

Scanning probe microscopy (SPM) characterizations were performed on nonintentionally doped n-type ZnO nanopillars (NPs) embedded in a polymer matrix. Transport properties investigations using scanning capacitance microscopy revealed local p-type space charge regions spreading over the outer shell of the polymer-coated ZnO NP. Correlatively, different electrical behaviors were found for the core and shell parts of the NPs using scanning spreading resistance microscopy. From SPM imaging at various voltage biases and local I-V curves, an electrical transport analysis was carried out based on surface states arising from the surrounding environment. Surface barrier potential inducing p-type conductivity in polymer-coated ZnO NPs was discussed and estimated to amount to several hundreds of milli-electron-volt. As a further consequence a critical diameter under which full p-type conductivity occurs in the NPs was demonstrated both theoretically and experimentally.
High resolution mass analysis of N- and C-terminal negative ions resulting from resonance electron capture by aliphatic amino acids
Authors: Shchukin Pavel V. , Muftakhov Mars V. , Morré Jeff , Deinzer Max L. , Vasil’ev Yury V.
Published: June 2010

High mass resolving power was applied to study resonance electron capture by glycine, alanine, and valine, and accurate mass measurements helped to distinguish between some negative ions having the same nominal masses. It was established that the C- and N-terminal negative ions of the same nominal masses were formed at different electron energies from different resonance states. The typical fragmentation pathways in deprotonated amino acids via loss of water initiated by collisional activation were not observed upon resonant electron capture by aliphatic amino acids. Instead, [M-18]− negative ions in the vicinity of 5 eV were found to be associated with simultaneous loss of either ammonia and a hydrogen atom or an amino group and a hydrogen molecule.
High frequency instability of a magnetized spherical electron sheath
Authors: Stenzel R. L.
Published: June 2010

A positively biased spherical electrode in a magnetized plasma exhibits a ring of energetic electrons in the equatorial plane where the sheath electric field is normal to the magnetic field. High frequency waves are excited which propagate with the average E×B drift and form toroidal eigenmodes. Up to 20 harmonic eigenmodes are observed in the spectrum. Injected test waves are amplified. The drift wave can excite whistler modes. Electron inertia produces the instability.
An algebraic proof of generalized Wick theorem
Authors: Kong Liguo , Nooijen Marcel , Mukherjee Debashis
Published: June 2010

The multireference normal order theory, introduced by Kutzelnigg and Mukherjee [J. Chem. Phys. 107, 432 (1997)], is defined explicitly, and an algebraic proof is given for the corresponding contraction rules for a product of any two normal ordered operators. The proof does not require that the contractions be cumulants, so it is less restricted. In addition, it follows from the proof that the normal order theory and corresponding contraction rules hold equally well if the contractions are only defined up to a certain level. These relaxations enable us to extend the original normal order theory. As a particular example, a quasi-normal-order theory is developed, in which only one-body contractions are present. These contractions are based on the one-particle reduced density matrix.
Hall magnetohydrodynamic effects for current sheet flapping oscillations related to the magnetic double gradient mechanism
Authors: Erkaev N. V. , Semenov V. S. , Biernat H. K.
Published: June 2010

Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the “kink” and “sausage” flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating along the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.
Intermolecular potential energy surface of the water-carbon dioxide complex
Authors: Makarewicz Jan
Published: June 2010

A complete intermolecular potential energy surface (PES) of the H2O–CO2 complex has been constructed using a large scale ab initio calculations. This PES was sampled at 23 000 points of a five dimensional configuration space of the intermolecular coordinates. The interaction energy was calculated using the second order Møller–Plesset perturbation method in conjunction with the standard aug-cc-pVTZ basis set supplemented by bond functions. Single-point energy values were used to construct the analytical many-body representations of the PES that was further improved using a set of the interaction energy values calculated along the one-dimensional cuts of PES by employing the coupled cluster singles and doubles including connected triples method. The accurate data on the structure and energetics of the complex considered have been reported. The analysis of the PES determined revealed its complex structure. A few bifurcations were found on the minimum energy paths along the coordinates describing the radial and angular motions. For the torsional motion, four symmetrically equivalent potential barriers were found as a consequence of the bifurcations, so earlier models of this motion assuming two equivalent potential barriers were justified only for the lowest torsional states.
Communications: Is quantum chemical treatment of biopolymers accurate? Intramolecular basis set superposition error (BSSE)
Authors: Balabin Roman M.
Published: June 2010

The accuracy of quantum chemical treatment of biopolymers by means of density functional theory is brought into question in terms of intramolecular basis set superposition error (BSSE). Secondary structure forms—β-strands (C5; fully extended conformation), repeated γ-turns (C7), 310-helices (C10), and α-helices (C13)—of homopolypeptides (polyglycine and polyalanine) are used as representative examples. The studied molecules include Ace(Gly)5NH2, Ace(Gly)10NH2, Ace(Ala)5NH2, and Ace(Ala)10NH2. The counterpoise correction procedure was found to produce reliable estimations for the BSSE values (other methods of BSSE correction are discussed). The calculations reported here used the B3LYP, PBE0 (PBE1PBE), and BMK density functionals with different basis sets [from 6-31G(d) to 6-311+G(3df,3pd)] to estimate the influence of basis set size on intramolecular BSSE. Calculation of BSSE was used to determine the deviation of the current results from the complete basis set limit. Intramolecular BSSE was found to be nonadditive with respect to biopolymer size, in contrast to claims in recent literature. The error, which is produced by a basis set superposition, was found to exceed 4 kcal mol−1 when a medium-sized basis set was used. This indicates that this error has the same order of magnitude as the relative energy differences of secondary structure elements of biopolymers. This result makes all recent reports on the gas-phase stability of homopolypeptides and their analogs questionable.
Self-focused acoustic ejectors for viscous liquids
Authors: Hon S. F. , Kwok K. W. , Li H. L. , Ng H. Y.
Published: June 2010

Self-focused acoustic ejectors using the Fresnel zone plate (FZP) have been developed for ejecting viscous liquids, without nozzle, in the drop-on-demand mode. The FZP is composed of a lead zirconate titanate piezoelectric plate patterned with a series of annular electrodes, with the unelectroded region of the plate removed. Our results show that the acoustic waves are effectively self-focused by constructive interference in glycerin (with a viscosity of 1400 mPa s), giving small focal points with a high pressure. Due to the high attenuation, the wave pressure decreases significantly with the distance from the FZP. Nevertheless, the pressure at the focal points 2.5 and 6.5 mm from the FZP is high enough to eject glycerin droplets in the drop-on-demand mode. Driven by a simple wave train comprising a series of sinusoidal voltages with an amplitude of 35 V, a frequency of 4.28 MHz, and a duration of 2 ms, the ejector can eject fine glycerin droplets with a diameter of 0.4 mm at a repetition frequency of 120 Hz in a downward direction. Droplets of other viscous liquids, such as the prepolymer of an epoxy with a viscosity of 2000 mPa s, can also be ejected in the drop-on-demand mode under similar conditions.
Structures of gas-phase Ag–Pd nanoclusters: A computational study
Authors: Negreiros Fabio R. , Kuntová Zdenka , Barcaro Giovanni , Rossi Giulia , Ferrando Riccardo , Fortunelli Alessandro
Published: June 2010

Gas-phase Ag–Pd clusters in the size range of 38–100 atoms are studied via a combined density-functional/empirical-potential (DF-EP) approach. Many-body EPs describing Pd–Pd, Ag–Ag, and Ag–Pd interactions are reparametrized and used in thorough global optimization searches at sizes N=38, 60, and 100 and compositions 25%, 50%, and 75%. The results are analyzed in terms of structural families, whose lowest-energy isomers are reoptimized at the DF level to investigate the crossover among structural motifs. It is found that the reparametrized EPs show a better qualitative and quantitative agreement with DF results when compared to the original potentials taken from literature: Both methods agree on which is the lowest-energy isomer at each size and composition, and the energy differences in the various isomers are in good qualitative agreement, especially for 60- and 100-atom clusters. The reparametrized potentials should thus be applicable to large clusters, where DF calculations are not feasible any more.
Methods for finding transition states on reduced potential energy surfaces
Authors: Burger Steven K. , Ayers Paul W.
Published: June 2010

Three new algorithms are presented for determining transition state (TS) structures on the reduced potential energy surface, that is, for problems in which a few important degrees of freedom can be isolated. All three methods use constrained optimization to rapidly find the TS without an initial Hessian evaluation. The algorithms highlight how efficiently the TS can be located on a reduced surface, where the rest of the degrees of freedom are minimized. The first method uses a nonpositive definite quasi-Newton update for the reduced degrees of freedom. The second uses Shepard interpolation to fit the Hessian and starts from a set of points that bound the TS. The third directly uses a finite difference scheme to calculate the reduced degrees of freedom of the Hessian of the entire system, and searches for the TS on the full potential energy surface. All three methods are tested on an epoxide hydrolase cluster, and the ring formations of cyclohexane and cyclobutenone. The results indicate that all the methods are able to converge quite rapidly to the correct TS, but that the finite difference approach is the most efficient.
Waves in expanding electronegative plasmas containing double layers
Authors: Kawamura E. , Lichtenberg A. J. , Lieberman M. A.
Published: June 2010

Expanding electronegative (EN) plasmas have been previously observed, experimentally, to generate wave activity. Using a particle-in-cell (PIC) code we have investigated these waves in expanding EN plasmas containing a double layer (DL) between an upstream source region and an expanded downstream region. Oxygen reaction rates were used but modified to correspond more closely to experimental conditions. Under a subset of pressures, for which a DL existed, waves were observed traveling upstream in the expanded region, and growing in amplitude in the direction of travel. Both slow and fast waves were observed. The fast wave existed only over part of the slow wave pressure range. The PIC results were compared to both fluid and kinetic theory, both of which assumed axial uniformity. The results of a somewhat simplified fluid theory, ignoring fast wave coupling and collisions with the background gas, gave a remarkable result: if the theory predicted a slow wave instability for any axial parameters in the downstream region, the instability was observed in the simulation. Conversely, if no instability was predicted at any axial position, no instability was observed. More accurate kinetic calculations, including electron and ion Landau damping, and also collisional damping against the background gas, gave wavelengths and growth rates that were consistent with the PIC simulations, and with the fluid results. The kinetic theory also indicated that the fast waves were always stable but became weakly damped for conditions of unstable slow waves. We postulate that nonlinear and nonuniformity effects excite the fast waves.
Strain states in semipolar III-nitride semiconductor quantum wells
Authors: Funato M. , Inoue D. , Ueda M. , Kawakami Y. , Narukawa Y. , Mukai T.
Published: June 2010

Strain states in wurtzite III-nitride semiconductor quantum wells (QWs) are investigated. X-ray diffraction (XRD) reciprocal space mapping using semipolar (112¯2) and (11¯01) InGaN/GaN QWs as test samples demonstrates that the projections of reciprocal lattice vectors of unstrained GaN and pseudomorphically strained InGaN on the interface agrees, indicating continuity of layers across the interface. High resolution transmission electron microscopy supports the XRD analysis. Based on the experimental results, strain tensor elements are extracted for arbitrary crystalline orientation. Furthermore, expansion of the model to arbitrary crystal structures is suggested.
Electrical properties of monodispersed detonation nanodiamonds
Authors: Chaudhary Aysha , Welch Joseph O. , Jackman Richard B.
Published: June 2010

The electrical properties of monodispersed detonation nanodiamonds (DNDs) have been studied; a resistivity of the order of 1012 Ω/sq has been determined, with only one significant conduction pathway being observed. The dielectric character of the DND particles is also good, with dielectric loss tangent values in the range 0.05–0.5 being recorded. These combined observations suggest DNDs behave in electrical terms similar to thin film diamond, and that electrical applications for DNDs are worthy of pursuit. Since a simple room temperature sonication process has been used for their deposition, coating a wide-range of three-dimensional substrate materials will be possible. A limitation on the electrical use the monodispersed DNDs, at least in the untreated, as-deposited from solution form used here, is the catastrophic loss of diamond-like character at temperatures above 400 °C.
Dielectrophoretic separation of mouse melanoma clones
Authors: Sabuncu Ahmet C. , Liu Jie A. , Beebe Stephen J. , Beskok Ali
Published: June 2010

Dielectrophoresis (DEP) is employed to differentiate clones of mouse melanoma B16F10 cells. Five clones were tested on microelectrodes. At a specific excitation frequency, clone 1 showed a different DEP response than the other four. Growth rate, melanin content, recovery from cryopreservation, and in vitro invasive studies were performed. Clone 1 is shown to have significantly different melanin content and recovery rate from cryopreservation. This paper reports the ability of DEP to differentiate between two malignant cells of the same origin. Different DEP responses of the two clones could be linked to their melanin content.
A study on laser drilling of thin steel sheet in air and underwater
Authors: Nath A. K. , Hansdah D. , Roy S. , Choudhury A. Roy
Published: June 2010

In laser drilling of a thin stainless steel sheet in air with Nd:YAG laser pulses of 0.5–1 ms durations it was observed that the 0.5 ms duration laser pulse was more effective in drilling a through-hole than the relatively longer laser pulses with proportionately more energy. Further, laser drilling could be readily done when the sheet was placed at the focal point of the lens and below it but not above the focal point. On the other hand, the underwater laser drilling could be done when the sheet was placed above the focal point. An attempt has been made to explain these experimental observations considering various processes involved in laser drilling in air and underwater. While the recoil pressure of the vapor and plasma played an important role in laser drilling in air; the radial gradient of recoil pressure of evaporation, the Marangoni force induced by the surface tension gradient in melt pool and the cavitation effect of bubble collapse were believed to be responsible for the material removal in underwater drilling process.
Magnetic fluctuation and frustration in new iron-based layered SrFe1−xCoxAsF superconductors
Authors: Wang W. , Li B. , Liu S. , Liu M. , Xing Z. W.
Published: June 2010

By using the first-principle calculations, we study structural, electronic, and magnetic properties of the SrFeAsF compound and its Co-doped counterpart SrFe1−xCoxAsF (x=0.125). It is shown that for SrFeAsF, the competition between exchange couplings J1 and J2 of the nearest and next-nearest neighboring Fe ions gives rise to a striped antiferromagnetic (AFM) order, accompanied by structural distortions. At the Co doping of x=0.125, we obtain J1/2J2∼1, suggesting that the AFM order encounter frustration and the system be in a critical state between the spin density wave state and disordered spin glass state with strong magnetic fluctuations. By comparing the doped compound with the undoped one, it is found that the itinerancy of Fe 3d electrons increases and the density of states at the Fermi level increases significantly, favorable for superconductivity due to magnetic fluctuations.
A time-dependent semiempirical approach to determining excited states
Authors: Bartell Lizette A. , Wall Michael R. , Neuhauser Daniel
Published: June 2010

We study a time-dependent semiempirical method to determine excitation energies, TD-PM3. This semiempirical method allows large molecules to be treated. A Linear-response Chebyshev approach yields the TD-PM3 spectrum very efficiently. Spectra and excitation energies were tested by comparing it with the results obtained using TD-DFT (Time Dependent-Density Functional Theory), using both small and large basis sets. They were also compared to PM3-CI, Time Dependent-Hartree Fock using the STO-3G basis set, and to experiment. TD-PM3 results generally match better the large-basis set calculations than the small-basis TD-DFT do; excitation energies are almost always accurate to within about 20% or less, except for a few small molecules. Accuracy improves as the molecules get larger.
Computational analysis of binary segregation during colloidal crystallization with DNA-mediated interactions
Authors: Scarlett Raynaldo T. , Crocker John C. , Sinno Talid
Published: June 2010

A detailed computational study of compositional segregation during growth of colloidal binary solid-solution crystals is presented. Using a comprehensive set of Metropolis Monte Carlo simulations, we probe the influence of colloid size, interaction strength, and interaction range on the segregation process. The results are interpreted in terms of a simple, but descriptive mechanistic model that allows us to connect to studies of binary segregation in atomic systems. The validity of Metropolis Monte Carlo simulations for the nonequilibrium phenomena investigated in this work is established theoretically and by connections to Brownian dynamics and molecular dynamics simulations. It is demonstrated that standard Metropolis Monte Carlo, properly applied, can provide an efficient framework for studying many aspects of crystallization in colloidal systems.
Gradient index metamaterial based on slot elements
Authors: Paul Oliver , Reinhard Benjamin , Krolla Bernd , Beigang René , Rahm Marco
Published: June 2010

We present a gradient-index (GRIN) metamaterial based on an array of annular slots. The structure allows a large variation in the effective refractive index under normal-to-plane incidence and thus enables the construction of GRIN devices consisting of only a small number of functional layers. Using full-wave simulations, we demonstrate the annular slot concept by means of a three-unit-cell thin GRIN lens for the terahertz (THz) range. In the presented realizations, we achieved an index contrast of Δn=1.5 resulting in a highly refractive flat lens which is suitable for focusing THz radiation to a spot size smaller than the wavelength.
Efficient hybrid organic-inorganic light emitting diodes with self-assembled dipole molecule deposited metal oxides
Authors: Park Ji Sun , Lee Bo Ram , Lee Ju Min , Kim Ji-Seon , Kim Sang Ouk , Song Myoung Hoon
Published: June 2010

We investigate the effect of self-assembled dipole molecules (SADMs) on ZnO surface in hybrid organic-inorganic polymeric light-emitting diodes (HyPLEDs). Despite the SADM being extremely thin, the magnitude and orientation of SADM dipole moment effectively influenced the work function of the ZnO. As a consequence, the charge injection barrier between the conduction band of the ZnO and the lowest unoccupied molecular orbital of poly(9,9′-dioctylfluorene)-co-benzothiadiazole could be efficiently controlled resulting that electron injection efficiency is remarkably enhanced. The HyPLEDs modified with a negative dipolar SADM exhibited enhanced device performances, which correspond to approximately a fourfold compared to those of unmodified HyPLEDs.
Ambipolar ballistic electron emission microscopy studies of gate-field modified Schottky barriers
Authors: Che Y. L. , Pelz J. P.
Published: June 2010

Four-terminal ambipolar ballistic electron emission microscopy studies are conducted on Au/Si and Cu/Si Schottky contacts fabricated on back-gated silicon-on-insulator wafers, allowing the electric field to be varied so that both electron (n)- and hole (p)-Schottky barrier heights can be measured at the same sample location. While the individual n- and p-Schottky barrier heights varied by more than 200 meV between the Au/Si and Cu/Si contacts, for a given sample they sum to within 15 meV of the same value, indicating that the individual variations are due to variations in a local surface dipole as compared with tip effects or variations in local composition.
Charge-transfer absorption band in Zn1−xMxO (M: Co, Mn) investigated by means of photoconductivity, Ga doping, and optical measurements under pressure
Authors: Gilliland S. G. , Sans J. A. , Sánchez-Royo J. F. , Almonacid G. , Segura A.
Published: June 2010

The nature of the charge-transfer absorption band in undoped and Ga-doped Zn1−xMxO (M: Co, Mn) thin films is investigated by means of photoconductivity and optical absorption measurements under pressure. Internal transitions in the crystal field split Co 3d shell do not contribute to the photoconductivity spectrum and have very low pressure coefficient. Broad absorption bands at photon energies just below the band gap in both ZnMnO and ZnCoO clearly contribute to the photoconductivity spectra, indicating that they create free carriers and are consequently charge-transfer transitions. Under pressure, charge transfer bands have a pressure coefficient close to or larger than the band gap, in contrast to the expected low or negative pressure coefficient in a valence-band-to-localized level transition. Finally, the expected Burstein–Moss shift in the fundamental edge of heavily Ga-doped samples of ZnMO is associated to a larger shift and intensity decrease in the pre-edge band, confirming that charge-transfer transitions in ZnMO should be ascribed to transitions from the Co or Mn 3d shell to the conduction band.
The permanent electric dipole moment of vanadium monosulfide
Authors: Zhuang Xiujuan , Steimle Timothy C.
Published: June 2010

A number of low-J lines of the C Σ4−←X Σ4− (0,0) band of a supersonic molecular beam sample of vanadium monosulfide (VS) have been recorded at a resolution of approximately 50 MHz by laser excitation spectroscopy. The electric field induced shift and splitting have been analyzed to give the permanent electric dipole moments μ of the C Σ4−(υ=0) and X Σ4−(υ=0) states as 2.38(13) and 5.16(5) D, respectively. An electrostatic model is used to predict μ for VS and VO. A molecular orbital correlation diagram is used to rationalize the trends in experimentally observed μ values of the 3d-monosulfides and 3d-monoxides. A comparison with theoretical predictions is made.
A surface diffusion model for Dip Pen Nanolithography line writing
Authors: Saha Sourabh K. , Culpepper Martin L.
Published: June 2010

Dip Pen Nanolithography is a direct write process that creates nanoscale dots and lines. Models typically predict dot and line size via assumption of constant ink flow rate from tip to substrate. This is appropriate for dot writing. It is however well-known, though models rarely reflect, that the ink flow rate depends upon writing speed during line writing. Herein, we explain the physical phenomenon that governs line writing and use this to model tip-substrate diffusion in line writing. We accurately predict (i) the increase in flow rate with writing speed and (ii) line width within 12.5%.
Reconfigurable electromagnetic band gap device using plasma as a localized tunable defect
Authors: Lo J. , Sokoloff J. , Callegari Th. , Boeuf J. P.
Published: June 2010

Electromagnetic band gap (EBG) structures have interesting properties in terms of electromagnetic wave propagation. Using a plasma discharge in an EBG structure may increase its reconfigurability. The use of microplasma arrays in the design of EBG structures is however complex and may cause energy losses. In this paper, we show through experiments and simulations that EBG effects can be obtained in structures where a single discharge plasma is used to create a defect in a periodic structure of metallic rods.
Energy level evolution of air and oxygen exposed molybdenum trioxide films
Authors: Irfan  , Ding Huanjun , Gao Yongli , Small Cephas , Kim Do Young , Subbiah Jegadesan , So Franky
Published: June 2010

The evolution of electronic energy levels of controlled air and oxygen exposed molybdenum trioxide (MoO3) films has been investigated with ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and x-ray photoemission spectroscopy. We found that while most of the electronic levels of as deposited MoO3 films remained largely intact, the reduction in the work function (WF) was substantial. The gradual surface WF change from 6.8 to 5.3 eV was observed for air exposed film, while oxygen exposed film the surface WF saturated at ∼5.7 eV. Two distinct stages of exposure are observed, the first dominated by oxygen adsorption for <1013 Langmuir (L) exposure and at the final step moisture absorption >1013 L.
Optoelectronic conversion by polarization current, triggered by space charges at organic-based interfaces
Authors: Hu Laigui , Noda Yukiko , Ito Hiroshi , Kishida Hideo , Nakamura Arao , Awaga Kunio
Published: June 2010

We report that a highly efficient optoelectronic conversion can be achieved by photogenerated space charges, which usually damp photocurrent. Theoretical analysis of metal-organic insulator-organic semiconductor-metal photocells indicates the generation of a large transient current that is triggered by photogenerated space charges and governed by the dielectric properties of the insulator layer. We experimentally demonstrated this mechanism with model photocells, revealing that the quantum efficiency can be dramatically increased by increasing the dielectric constant of the insulator.
Transient characteristics of inverted polymer solar cells using titaniumoxide interlayers
Authors: Schmidt H. , Zilberberg K. , Schmale S. , Flügge H. , Riedl T. , Kowalsky W.
Published: June 2010

Organic bulk heterojunction solar cells using titania interlayers as electron selective layers prepared by atomic layer deposition or wet processing are reported. Pristine devices show low filling factors (FFs) and consequently low efficiencies. Upon illumination with ultraviolet (UV) light, a significant increase in the FF is found. We study the impact of various ambient conditions (air, vacuum, and oxygen) on the dynamics of the decay of the FF after UV illumination. The interaction of oxygen and titania is evidenced as the dominant mechanism for the transient behavior of the polymer solar cells.
Extrinsic doping in silicon revisited
Authors: Schwingenschlögl U. , Chroneos A. , Schuster C. , Grimes R. W.
Published: June 2010

Both n-type and p-type doping of silicon is at odds with the charge transfer predicted by Pauling electronegativities and can only be reconciled if we no longer regarding dopant species as isolated atoms but rather consider them as clusters consisting of the dopant and its four nearest neighbor silicon atoms. The process that gives rise to n-type and p-type effects is the charge redistribution that occurs between the dopant and its neighbors, as we illustrate here using electronic structure calculations. This view point is able to explain why conventional substitutional n-type doping of carbon has been so difficult.
Generalized mean spherical approximation for the multicomponent restricted primitive model
Authors: Sánchez-Díaz L. E. , Vizcarra-Rendón A. , Medina-Noyola M.
Published: June 2010

The generalized mean spherical approximation of Stell and Sun [J. Chem. Phys. 63, 5333 (1975)] for the binary charge-symmetric restricted primitive model (electroneutral mixture of equally sized hard spheres) is extended to charge-asymmetric binary electrolytes and to the generally multicomponent, but still restricted (i.e., equally sized) primitive model.
Cu/p-Si Schottky barrier-based near infrared photodetector integrated with a silicon-on-insulator waveguide
Authors: Casalino M. , Sirleto L. , Iodice M. , Saffioti N. , Gioffrè M. , Rendina I. , Coppola G.
Published: June 2010

In this letter, a near infrared all-silicon (all-Si) photodetector integrated into a silicon-on-insulator waveguide is demonstrated. The device is based on the internal photoemission effect through a metal/Si Schottky junction placed transversally to the optical field confined into the waveguide. The technological steps utilized to fabricate the device allow an efficiently monolithic integration with complementary metal-oxide semiconductor compatible structures. Preliminary results show a responsivity of 0.08 mA/W at 1550 nm with a reverse bias of 1 V and an efficient behavior both in C and L band. Finally, an estimation of bandwidth for GHz range is deduced.
Optical transmission properties of C-shaped subwavelength waveguides on silicon
Authors: Lopatiuk-Tirpak O. , Ma J. , Fathpour S.
Published: June 2010

Optical properties of C-shaped subwavelength waveguides in metallic (silver) films on silicon substrates are studied in the range of 0.6–6 μm. Power throughput and resonant wavelengths of several transmission modes are studied by varying the waveguide length (or metal thickness). Among three types of transmission modes, the fundamental order of the Fabry–Perot-type mode was shown to attain remarkably high power throughputs (as high as 12). With optimized design of the aperture, the resonant wavelength of this mode occurs in the 1–2 μm wavelength range, suggesting that such apertures can be utilized to achieve plasmonic-enhanced silicon photonic devices at telecommunication wavelengths.
Migrant Workers in the Urban Labour Market of Shenzhen, China
Authors: Wang Mark Y , Wu Jiaping
Published: June 2010

In view of recent changes in both migration patterns and urban labour market conditions, the permanent settlement migration paradigm has become insufficient to guide our understanding of rural-to-urban migrant workers in China's market transition. Using Shenzhen City as a case study we consider migrant workers as enabling agents who interact with the urban labour market. We therefore examine the ways that migrant workers' social capital accumulation, migration experience, and job mobility influence urban labour market dynamics. In painting a picture of migrant workers we complement existing institutional and labour market analyses. As we demonstrate, by frequently changing jobs and destination cities, migrant workers accumulate social and human capital so as to improve their opportunities in the urban labour market. This is evidenced by migrants' improved occupational positions and increased wage earnings.
Magnonics
Authors: Kruglyak V V , Demokritov S O , Grundler D
Published: June 2010

Magnonics is a young field of research and technology emerging at the interfaces between the study of spin dynamics, on the one hand, and a number of other fields of nanoscale science and technology, on the other. We review the foundations and recent achievements in magnonics in view of guiding further progress from studying fundamental magnonic phenomena towards applications. We discuss the major challenges that have to be addressed in future research in order to make magnonics a pervasive technology.
Brillouin light scattering studies of planar metallic magnonic crystals
Authors: Gubbiotti G , Tacchi S , Madami M , Carlotti G , Adeyeye A O , Kostylev M
Published: June 2010

The application of Brillouin light scattering to the study of the spin-wave spectrum of one- and two-dimensional planar magnonic crystals consisting of arrays of interacting stripes, dots and antidots is reviewed. It is shown that the discrete set of allowed frequencies of an isolated nanoelement becomes a finite-width frequency band for an array of identical interacting elements. It is possible to tune the permitted and forbidden frequency bands, modifying the geometrical or the material magnetic parameters, as well as the external magnetic field. From a technological point of view, the accurate fabrication of planar magnonic crystals and a proper understanding of their magnetic excitation spectrum in the gigahertz range is oriented to the design of filters and waveguides for microwave communication systems.
Abundance trends of two neon flying squid (Ommastrephes bartramii) stocks in the North Pacific
Authors: Chen Chih-Shin
Published: June 2010

Chen, C-S. 2010. Abundance trends of two neon flying squid (Ommastrephes bartramii) stocks in the North Pacific. – ICES Journal of Marine Science, 67: 1336–1345. Two stocks of neon flying squid (Ommastrephes bartramii) have been identified in the North Pacific, with differing life-history traits and geographic distributions, one in the Northeast Pacific and the other in the Northwest Pacific, each with seasonal cohorts. Both stocks are targeted by commercial fishing fleets from China, Japan, and Taiwan. The variability in abundance for each stock has been studied independently, but a comparable analysis between the two stocks is lacking. The abundance trends for the two stocks were examined using catch data from the Taiwanese squid fishery between 1986 and 2006. A time-series of monthly catch per unit effort and three explanatory variables, sea surface temperature in the presumed hatching grounds, the Southern Oscillation Index, and the number of vessels, were analysed using dynamic factor analysis to quantify squid abundance. The optimal model contained one common trend and all three explanatory variables. The Northwest Pacific and Northeast Pacific stocks exhibited opposing trends in abundance, and the results suggest that large-scale environmental factors, rather than regional factors, are more critical in influencing the abundance of oceanic squid species.
Charge storage mechanism in nanoporous carbons and its consequence for electrical double layer capacitors
Authors: Simon Patrice , Gogotsi Yury
Published: June 2010

Electrochemical capacitors, also known as supercapacitors, are energy storage devices that fill the gap between batteries and dielectric capacitors. Thanks to their unique features, they have a key role to play in energy storage and harvesting, acting as a complement to or even a replacement of batteries which has already been achieved in various applications. One of the challenges in the supercapacitor area is to increase their energy density. Some recent discoveries regarding ion adsorption in microporous carbon exhibiting pores in the nanometre range can help in designing the next generation of high-energy-density supercapacitors.
A thermochemical study of ceria: exploiting an old material for new modes of energy conversion and CO
2
mitigation
Authors: Chueh William C. , Haile Sossina M.
Published: June 2010

We present a comprehensive thermodynamic and kinetic analysis of the suitability of cerium oxide (ceria) for thermochemical fuel production. Both portions of the two-step cycle, (i) oxygen release from the oxide at 1773 and 1873 K under inert atmosphere, and (ii) hydrogen release upon hydrolysis at 1073 K, are examined theoretically as well as experimentally. We observe gravimetric fuel productivity that is in quantitative agreement with equilibrium, thermogravimetric studies of ceria. Despite the non-stoichiometric nature of the redox cycle, in which only a portion of the cerium atoms change their oxidation state, the fuel productivity of 8.5–11.8 ml of H
2
per gram of ceria is competitive with that of other solid-state thermochemical cycles currently under investigation. The fuel production rate, which is also highly attractive, at a rate of 4.6–6.2 ml of H
2
per minute per gram of ceria, is found to be limited by a surface-reaction step rather than by ambipolar bulk diffusion of oxygen through the solid ceria. An evaluation of the thermodynamic efficiency of the ceria-based thermochemical cycle suggests that, even in the absence of heat recovery, solar-to-fuel conversion efficiencies of 16 to 19 per cent can be achieved, assuming a suitable method for obtaining an inert atmosphere for the oxygen release step.