bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross sections and ion kinetic energy analysis for the electron impact ionization of acetylene
Authors: Feil S. , Głuch K. , Bacher A. , Matt-Leubner S. , Böhme D. K. , Scheier P. , Märk T. D.
Published: June 2006

Using a Nier-type electron impact ion source in combination with a double focusing two sector field mass spectrometer, partial cross sections for electron impact ionization of acetylene are measured for electron energies up to 1000eV. Discrimination factors for ions are determined using the deflection field method in combination with a three-dimensional ion trajectory simulation of ions produced in the ion source. Analysis of the ion yield curves obtained by scanning the deflectors allows the assignment of ions with the same mass-to-charge ratio to specific production channels on the basis of their different kinetic energy distributions. This analysis also allows to determine, besides kinetic energy distributions of fragment ions, partial cross sections differential in kinetic energy. Moreover a charge separation reaction, the Coulomb explosion of the doubly charged parent ions C2H2++ into the fragment ions C2H+ and H+, is investigated and its mean kinetic energy release (⟨KER⟩=3.88eV) is deduced.
Determination of pair correlation functions of dense colloidal systems by means of indirect Fourier transformation
Authors: Fritz Gerhard
Published: June 2006

The interparticle pair correlation g(r) function is determined by the small angle scattering data of interacting, monodisperse, globular colloidal particles. The new approach to this problem requires that the form factor and the particle number density must be known. Instrumental broadening effects and experimental imperfections are included in a way that makes it unnecessary to deconvolute the scattering function from beam profiles. The applicability of the approach is demonstrated by the simulated data of a charged colloidal dispersion and by way of the neutron scattering data of nonionic micellar solutions. In both cases, g(r) functions are obtained that are in good agreement with the known behavior of the systems.
Molecular conduction: Do time-dependent simulations tell you more than the Landauer approach?
Authors: Sánchez Cristián G. , Stamenova Maria , Sanvito Stefano , Bowler D. R. , Horsfield Andrew P. , Todorov Tchavdar N.
Published: June 2006

A dynamical method for simulating steady-state conduction in atomic and molecular wires is presented which is both computationally and conceptually simple. The method is tested by calculating the current-voltage spectrum of a simple diatomic molecular junction, for which the static Landauer approach produces multiple steady-state solutions. The dynamical method quantitatively reproduces the static results and provides information on the stability of the different solutions.
An analysis of molecular packing and chemical association in liquid water using quasichemical theory
Authors: Paliwal A. , Asthagiri D. , Pratt L. R. , Ashbaugh H. S. , Paulaitis M. E.
Published: June 2006

We calculate the hydration free energy of liquid TIP3P water at 298K and 1bar using a quasichemical theory framework in which interactions between a distinguished water molecule and the surrounding water molecules are partitioned into chemical associations with proximal (inner-shell) waters and classical electrostatic∕dispersion interactions with the remaining (outer-shell) waters. The calculated free energy is found to be independent of this partitioning, as expected, and in excellent agreement with values derived from the literature. An analysis of the spatial distribution of inner-shell water molecules as a function of the inner-shell volume reveals that water molecules are preferentially excluded from the interior of large volumes as the occupancy number decreases. The driving force for water exclusion is formulated in terms of a free energy for rearranging inner-shell water molecules under the influence of the field exerted by outer-shell waters in order to accommodate one water molecule at the center. The results indicate a balance between chemical association and molecular packing in liquid water that becomes increasingly important as the inner-shell volume grows in size.
Electronic states and luminescence in higher fullerene/porous Si nanocrystal composites
Authors: Wu X. L. , Deng Z. H. , Xue F. S. , Siu G. G. , Chu Paul K.
Published: June 2006

Photoluminescence (PL) measurements have been performed on the nanocomposites of higher fullerene-coupled porous silicon (PS) nanocrystals. For the C70∕PS and C76(78)∕PS nanocomposites, the PL spectra show a pinning wavelength at ∼565nm and for the C84∕PS and C94∕PS nanosystems the pinning wavelength is at ∼590nm. The PL pinning property is closely related to the sorts of the coupled fullerenes. A band mixing model of direct and indirect gaps in a nanometer environment consisting of nc-Si core, SiO2 surface layer, and coupled fullerene has been proposed for calculation of electronic states. Good agreement is achieved between the experiments and theory.
Test of classical nucleation theory on deeply supercooled high-pressure simulated silica
Authors: Saika-Voivod Ivan , Poole Peter H. , Bowles Richard K.
Published: June 2006

We test classical nucleation theory (CNT) in the case of simulations of deeply supercooled, high density liquid silica, as modeled by the van Beest–Kramer–van Santen potential [Phys. Rev. Lett. 64, 1995 (1990)]. We find that at density ρ=4.38g∕cm3, spontaneous nucleation of crystalline stishovite occurs in conventional molecular dynamics simulations at temperature T=3000K, and we evaluate the nucleation rate J directly at this T via “brute force” sampling of nucleation events in numerous independent runs. We then use parallel, constrained Monte Carlo simulations to evaluate ΔG(n), the free energy to form a crystalline embryo containing n silicon atoms, at T=3000, 3100, 3200, and 3300K. By comparing the form of ΔG(n) to CNT, we test the ability of CNT to reproduce the observed behavior as we approach the regime where spontaneous nucleation occurs on simulation time scales. We find that the prediction of CNT for the n dependence of ΔG(n) fits reasonably well to the data at all T studied. Δμ, the chemical potential difference between bulk liquid and stishovite, is evaluated as a fit parameter in our analysis of the form of ΔG(n). Compared to directly determined values of Δμ extracted from previous work, the fitted values agree only at T=3300K; at lower T the fitted values increasingly overestimate Δμ as T decreases. We find that n*, the size of the critical nucleus, is approximately ten silicon atoms at T=3300K. At 3000K, n* decreases to approximately 3, and at such small sizes methodological challenges arise in the evaluation of ΔG(n) when using standard techniques; indeed even the thermodynamic stability of the supercooled liquid comes into question under these conditions. We therefore present a modified approach that permits an estimation of ΔG(n) at 3000K. Finally, we directly evaluate at T=3000K the kinetic prefactors in the CNT expression for J, and find physically reasonable values; e.g., the diffusion length that Si atoms must travel in order to move from the liquid to the crystal embryo is approximately 0.2nm. We are thereby able to compare the results for J at 3000K obtained both directly and based on CNT, and find that they agree within an order of magnitude. In sum, our work quantifies how certain predictions of CNT (e.g., for Δμ) break down in this deeply supercooled limit, while others [the n dependence of ΔG(n)] are not as adversely affected.
Surface freezing in normal alkanes: A statistical physics approach
Authors: Zhang Yong , Ou-Yang Zhong-can , Iwamoto Mitsumasa
Published: June 2006

The present paper aims to understand the surface freezing occurring on the interface between liquid normal alkane and air. After proposing a simple microscopic model, it reveals that the model can describe the surface freezing of normal alkanes. Subsequently, surface freezing is immediately proved to be a first order phase transition, which has been illustrated by numerous experiments. Moreover, our calculation predicts a new first order phase transition on the interface. These two transitions correspond to the liquid to monolayer and monolayer to perfect solid transitions, respectively. A phase diagram is obtained directly from the calculations as well. The model indicates that both van der Waals interaction and the entropy influenced by the surface are essential for explaining the surface phase transition.
Multielement spectrometer for efficient measurement of the momentum transfer dependence of inelastic x-ray scattering
Authors: Fister T. T. , Seidler G. T. , Wharton L. , Battle A. R. , Ellis T. B. , Cross J. O. , Macrander A. T. , Elam W. T. , Tyson T. A. , Qian Q.
Published: June 2006

Nonresonant x-ray Raman scattering (XRS) is the inelastic scattering of hard x rays from the K shell of low-Z elements or the less tightly bound shells of heavier elements. In the limit of low momentum transfer q, XRS is determined by the same transition matrix element as is measured by x-ray absorption spectroscopies. However, XRS at higher q can often access higher order multipole transitions which help separate the symmetry of various contributions to the local density of states. The main drawback of XRS is its low cross section—a problem that is compounded for a q-dependent study. To address this issue, we have constructed a multielement spectrometer to simultaneously measure XRS at ten different values of q. By means of example, we report new measurements of the XRS from the L- and K-edges of Mg. This instrument is now available to general users at the Advanced Photon Source as the lower energy resolution inelastic x-ray scattering (LERIX) spectrometer.
On the evaluation of quadratic response functions at the four-component Hartree-Fock level: Nonlinear polarization and two-photon absorption in bromo- and iodobenzene
Authors: Henriksson Johan , Ekström Ulf , Norman Patrick
Published: June 2006

The nonlinear polarization and two-photon absorption parameters have been determined for dibromo- and di-iodobenzene in their meta- and ortho-conformations and with relativistic effects accounted for to a varying degree. By exclusion of small component integrals in the calculations of the first-order hyperpolarizability, results within 1% of fully relativistic four-component Hartree-Fock values are obtained at a cost of 8.7 times the corresponding nonrelativistic calculations. It is shown that the nonlinear absorption in bromobenzene (and even more so in iodobenzene) is broad banded due to spin-orbit interactions among the excited states, and nonrelativistic and scalar relativistic calculations are not to be used in this case.
Matrix elements of N-particle explicitly correlated Gaussian basis functions with complex exponential parameters
Authors: Bubin Sergiy , Adamowicz Ludwik
Published: June 2006

In this work we present analytical expressions for Hamiltonian matrix elements with spherically symmetric, explicitly correlated Gaussian basis functions with complex exponential parameters for an arbitrary number of particles. The expressions are derived using the formalism of matrix differential calculus. In addition, we present expressions for the energy gradient that includes derivatives of the Hamiltonian integrals with respect to the exponential parameters. The gradient is used in the variational optimization of the parameters. All the expressions are presented in the matrix form suitable for both numerical implementation and theoretical analysis. The energy and gradient formulas have been programed and used to calculate ground and excited states of the He atom using an approach that does not involve the Born-Oppenheimer approximation.
Relativistic calculation of nuclear magnetic shielding using normalized elimination of the small component
Authors: Kudo K. , Maeda H. , Kawakubo T. , Ootani Y. , Funaki M. , Fukui H.
Published: June 2006

The normalized elimination of the small component (NESC) theory, recently proposed by Filatov and Cremer [J. Chem. Phys. 122, 064104 (2005)], is extended to include magnetic interactions and applied to the calculation of the nuclear magnetic shielding in HX (X=F,Cl,Br,I) systems. The NESC calculations are performed at the levels of the zeroth-order regular approximation (ZORA) and the second-order regular approximation (SORA). The calculations show that the NESC-ZORA results are very close to the NESC-SORA results, except for the shielding of the I nucleus. Both the NESC-ZORA and NESC-SORA calculations yield very similar results to the previously reported values obtained using the relativistic infinite-order two-component coupled Hartree-Fock method. The difference between NESC-ZORA and NESC-SORA results is significant for the shieldings of iodine.
Precision of gray level response time measurements of medical liquid crystal display
Authors: Liang Hongye , Badano Aldo
Published: June 2006

We characterized the instrumentation needed for accurate measurements of temporal response of liquid crystal displays for medical imaging applications. We investigated the effect of display and detector noise on the minimum measurable gray level (or luminance) difference. For a typical display, a gray level difference of 5 at high gray levels and 20 at low gray levels is needed to obtain an accurate measurement. A less noisy light emitting diode light source is employed to study the smallest measurable luminance difference at different luminance levels. We found that luminance differences of the order of 0.5cd∕m2 can be measured with an uncertainty of 10%.
Patterning ∼20nm half-pitch lines on silicon using a self-assembled organosilicate etch mask
Authors: Sundström Linnea , Krupp Leslie , Delenia Eugene , Rettner Charles , Sanchez Martha , Hart Mark W. , Kim Ho-Cheol , Zhang Ying
Published: June 2006

Lines of ∼20nm half-pitch were generated on silicon surface using a self-assembled organosilicate nanostructure. A mixture of a poly(styrene-b-ethylene oxide) (PS-b-PEO) with an organosilicate precursor that is selectively miscible with PEO was used to create lamellar phase whose orientation was controlled perpendicular to the surface by tuning the surface energy of substrates. Thermal cross-linking of the organosilicate precursor followed by thermal decomposition of the PS-b-PEO leaves a robust organosilicate line pattern of sublithographic length scales on the surface. Line patterns on silicon substrate were created by transferring this self-assembled pattern into the underlying silicon substrate using anisotropic plasma etching.
Electron transfer processes on Ag and Au clusters supported on TiO2(110) and cluster size effects
Authors: Canário Ana Rita , Esaulov Vladimir A.
Published: June 2006

The results of a detailed study of Li+ neutralization in scattering on Ag and Au clusters and thin films supported on TiO2 are presented. A very efficient neutralization is observed on small clusters with a decrease for the smallest clusters. These results closely follow the size-effects observed in the reactivity of these systems. The energy dependence of the neutralization was studied for the larger clusters (>4nm) and observed to be similar in trend to the one observed on films and bulk (111) crystals. A general discussion of possible reasons of the enhancement in neutralization is presented and these changes are then tentatively discussed in terms of progressive modifications in the electronic structure of clusters as a function of reduction in size and as it evolves from metallic-like to discretised states. The highest neutralization efficiency would appear to correspond to clusters sizes for which a metal to nonmetal transition occurs. The relative position of the Li level and the highest occupied molecular orbital in the molecular cluster can be expected to strongly affect the electron transfer processes, which in this case should be described in a molecular framework.
Ab initio studies on the reaction of O2 with Ban (n=2,5) clusters
Authors: Li S. F. , Xue Xinlian , Chen G. , Yuan D. W. , Jia Yu , Gong X. G.
Published: June 2006

Ab initio theoretical calculations have been performed to study the reaction of O2 with Ban (n=2,5) clusters. Our results show that O2 can easily chemisorb and dissociate on small Ban clusters and there is no obvious energy barrier in the process of the dissociation. The local magnetic moment contributed by oxygen must vanish during the intermediate states before the O2 dissociation. Correspondingly, local magnetic moment only decreases from 2μB to about 1μB if O2 molecularly adsorbs onto Ba5 cluster. The electronic structure analysis indicates that the charge transfer from Ban cluster to O2 as well as the orbital hybridization between the cluster and the oxygen molecule may play a key role in O2 dissociation.
Electrostatic attraction between cationic-anionic assemblies with surface compositional heterogeneities
Authors: Velichko Y. S. , Olvera de la Cruz M.
Published: June 2006

Electrostatics play a key role in biomolecular assembly. Oppositely charged biomolecules, for instance, can be coassembled into functional units, such as DNA and histone proteins into nucleosomes and actin-binding protein complexes into cytoskeleton components, at appropriate ionic conditions. These cationic-anionic coassemblies often have surface charge heterogeneities that result from the delicate balance between electrostatics and packing constraints. Despite their importance, the precise role of surface charge heterogeneities in the organization of cationic-anionic coassemblies is not well understood. We show here that coassemblies with charge heterogeneities strongly interact through polarization of the domains. We find that this leads to symmetry breaking, which is important for functional capabilities, and structural changes, which is crucial in the organization of coassemblies. We determine the range and strength of the attraction as a function of the competition between the steric and hydrophobic constraints and electrostatic interactions.
An elongation method for first principle simulations of electronic structures and electron transport properties of finite nanostructures
Authors: Jiang Jun , Liu Kai , Lu Wei , Luo Yi
Published: June 2006

An effective elongation method has been developed to study electronic structures and electron transport properties of nanoelectronic and bioelectronic devices at a hybrid density functional theory level. It enables to treat finite nanostructures consisting of as many as 28000 electrons and has been successfully applied to sub-120-nm-long conjugated polymers, sub-60-nm-long single-walled carbon nanotubes, and 30 base-pair DNA molecules. The calculated current-voltage characteristics of different systems are found to be in good agreement with the experiments. Some unexpected behaviors of these nanosized devices have been discovered.
In situ and real time determination of metallic and semiconducting single-walled carbon nanotubes in suspension via dielectrophoresis
Authors: Mureau Natacha , Mendoza Ernest , Silva S. R. P. , Hoettges Kai F. , Hughes Michael P.
Published: June 2006

We report an alternative method combining dielectrophoresis and impedance spectroscopy to provide rapid, accurate measurement of dielectrophoretic collection of single-walled carbon nanotubes (SWNTs) in real time. We analyzed a Triton X-100 suspension of mixed SWNTs to measure their precise dielectrophoretic collection behavior. Results indicate that our sample contains 21.5% of metallic and 78.5% of semiconducting carbon nanotubes before separation, and that the range of 1–15MHz is ideal to collect only the metallic ones. Optical absorption was used to confirm these proportions. We discuss the possible errors associated with using purely a Raman technique to validate the type of SWNTs collected in suspension.
A spectroscopic characterization of the electronic ground state of rhodium monoboride
Authors: Chowdhury Pradyot K. , Balfour Walter J.
Published: June 2006

A laser-induced fluorescence electronic spectrum of RhB is reported. It is the first such known example for a metal monoboride. RhB10 and RhB11 species are observed in natural abundance. The molecular ground state has Σ+1 symmetry, an r0 bond length of 0.169nm, and a vibrational frequency of ∼920cm−1.
Infrared spectroscopy of hydrogen-bonded CHCl3–SO2 in the gas phase
Authors: Chung Susan , Hippler Michael
Published: June 2006

A molecular association between chloroform and sulfur dioxide in the gas phase at room temperature was studied by Fourier transform infrared spectroscopy. Since the intensity of the CH-stretching fundamental vibration of monomer chloroform is very weak but much stronger upon complexation, a simple subtraction procedure isolated the CH-stretching vibration spectrum of the complex. The presence of a 1:1 complex was confirmed by two dilution series, where the monomer concentrations were varied. The molecular association manifested itself as a shift of the peak absorbance of the CH-stretching vibration of CHCl3–SO2 by +7cm−1 and of the CD-stretching vibration of CDCl3−SO2 by +5cm−1 to higher wave numbers compared to monomer chloroform, accompanied by a considerable broadening of the band contour. In agreement with previous ab initio calculations, this indicates a “blueshifting” or more appropriately, a “C–H contracting” hydrogen bond between chloroform and sulfur dioxide. An estimate of the complex concentration was made based on ab initio calculations for the integrated band strength and the measured spectrum. With this estimate, the equilibrium constant Kp (295K)=0.014 (po=105Pa) for the dimerization was calculated, providing one of the very few cases where the formation of a hydrogen-bonded gas phase complex at room temperature could be quantitatively studied by infrared spectroscopy.
Cross-plane lattice and electronic thermal conductivities of ErAs:InGaAs∕InGaAlAs superlattices
Authors: Kim Woochul , Singer Suzanne L. , Majumdar Arun , Vashaee Daryoosh , Bian Zhixi , Shakouri Ali , Zeng Gehong , Bowers John E. , Zide Joshua M. O. , Gossard Arthur C.
Published: June 2006

We studied the cross-plane lattice and electronic thermal conductivities of superlattices made of InGaAlAs and InGaAs films, with the latter containing embedded ErAs nanoparticles (denoted as ErAs:InGaAs). Measurements of total thermal conductivity at four doping levels and a theoretical analysis were used to estimate the cross-plane electronic thermal conductivity of the superlattices. The results show that the lattice and electronic thermal conductivities have marginal dependence on doping levels. This suggests that there is lateral conservation of electronic momentum during thermionic emission in the superlattices, which limits the fraction of available electrons for thermionic emission, thereby affecting the performance of thermoelectric devices.
Single-crystalline cubic structured InP nanosprings
Authors: Shen G. Z. , Bando Y. , Zhi C. Y. , Yuan X. L. , Sekiguchi T. , Golberg D.
Published: June 2006

Cubic structured nanosprings, InP nanosprings, have been synthesized via a simple thermochemical process using InP and ZnS as the source materials. Each InP nanospring is formed by rolling up a single InP nanobelt with the growth direction along the ⟨111⟩ orientation. The formation of these novel nanostructures is mainly attributed to the minimization of the electrostatic energy due to the polar charges on the ±(002) side surfaces of cubic InP. Cathodoluminescence properties were also studied, which reveal that the InP nanosprings have three emission bands centered at ∼736, ∼920, and ∼980nm.
Engineering the cap structure of individual carbon nanotubes and corresponding electron field emission characteristics
Authors: Wang M. S. , Wang J. Y. , Peng L.-M.
Published: June 2006

Electron field emission measurements on individual carbon nanotubes (CNTs) were performed inside a transmission electron microscope. Controlled removal of carbon atoms at the tip of the CNT was realized and various tip structures were fabricated. In particular, a capped CNT was opened and an opened CNT was converted into a capped CNT, and corresponding field emission characteristics were measured. Our results show that the electron field emission properties of CNTs are highly sensitive to the emission tip structures. The ability to modify the tip structure thus provides a way to control the field emission property of the CNT and vice versa.
An off-lattice Wang-Landau study of the coil-globule and melting transitions of a flexible homopolymer
Authors: Parsons Drew F. , Williams David R. M.
Published: June 2006

The Wang-Landau Monte Carlo approach is applied to the coil-globule and melting transitions of off-lattice flexible homopolymers. The solid-liquid melting point and coil-globule transition temperatures are identified by their respective peaks in the heat capacity as a function of temperature. The melting and theta points are well separated, indicating that the coil-globule transition occurs separately from melting even in the thermodynamic limit. We also observe a feature in the heat capacity between the coil-globule and melting transitions which we attribute to a transformation from a low-density liquid globule to a high-density liquid globule.
High electrical power density from PbTe-based quantum-dot superlattice unicouple thermoelectric devices
Authors: Harman T. C. , Reeder R. E. , Walsh M. P. , LaForge B. E. , Hoyt C. D. , Turner G. W.
Published: June 2006

We describe the first demonstration of PbTe-based, cross-plane quantum-dot superlattice (QDSL) unicouple thermoelectric generator devices fabricated from nanostructured, thick-film materials (∼100μm). Both n- and p-type QDSL materials were investigated. With ∼220K temperature difference across small thermoelements (∼95μm length, 4mm2 cross-sectional area), electrical power outputs up to 89mW and power densities up to 2.2W∕cm2 have been demonstrated for both n- and p-type materials. The devices consist of a substrate-free, bulklike slab of molecular beam epitaxy grown PbSeTe∕PbTe QDSL material as the n- or p-type leg and a copper wire as the other p-type leg.
Liquid-phase-epitaxy-grown InAsxSb1−x∕GaAs for room-temperature 8–12μm infrared detectors
Authors: Peng Changtao , Chen NuoFu , Gao Fubao , Zhang Xingwang , Chen Chenlong , Wu Jinliang , Yu Yude
Published: June 2006

High-quality InAsxSb1−x (0<x⩽0.3) films are grown on GaAs substrates by liquid phase epitaxy and electrical and optical properties of the films are investigated, revealing that the films exhibit Hall mobilities higher than 2×104cm2V−1s−1 and cutoff wavelengths longer than 10μm at room temperature (RT). Photoconductors are fabricated from the films, and notable photoresponses beyond 8μm are observed at RT. In particular, for an InAs0.3Sb0.7 film, a photoresponse of up to 13μm with a maximum responsivity of 0.26V∕W is obtained at RT. Hence, the InAsxSb1−x films demonstrate attractive properties suitable for room-temperature, long-wavelength infrared detectors.
Energy-dispersive coherent scatter computed tomography
Authors: Delfs J. , Schlomka J.-P.
Published: June 2006

We present a reconstructive x-ray imaging technique that yields the spatially resolved coherent scatter form factor of macroscopic objects. High spectral resolution is obtained by the energy and angle analyses of coherently scattered photons. In comparison with transmission x-ray computed tomography structural information about the materials under investigation is obtained. The combination of the attenuation contrast and the scatter contrast obtained with this technique can be applied, e.g., in medical imaging or baggage inspection.
Engineering of quantum dot emission wavelength using conductive layer coating
Authors: Zhao Kai , Choi Jaehyuck , Lo Yu-Hwa
Published: June 2006

Semiconductor quantum dot with a conducting half-shell was studied experimentally and theoretically. We sputtered a thin layer of gold on the semispherical surface of CdSe∕ZnS quantum dots. At room temperature, the emission wavelength for the half-metal-coated quantum dots was found to be redshifted by 10nm (38meV) from the wavelength of uncoated quantum dots, indicating the change of excitonic binding energy due to the gold cap layer. A theoretical model is presented to explain this effect. The results suggest that coating the quantum dots with a conducting shell can change the emission color of the quantum dots. The technique can significantly increase the number of quantum dot fluorescent labels for simultaneous observation of the activities of multiple biomolecules.
Substrate patterning for liquid crystal alignment by optical interference
Authors: Lu Xuemin , Lee Fuk Kay , Sheng Ping , Kwok H. S. , Chigrinov V. , Tsui Ophelia K. C.
Published: June 2006

Inhomogeneous liquid crystal (LC) alignment surfaces comprising a succession of microdomains favoring different LC alignment directions have been demonstrated for a number of optoelectronic applications. However, the prevalent method used to fabricate these surfaces is time consuming and produce functional areas that are too small for practical use. Here, we demonstrate a simple method based on photopatterning of an azodye layer with an interference pattern produced by intercepting two coherent UV beams. This method can produce alignment patterns within seconds with a practical size of ∼(0.5cm)2.
Growth mode and structural characterization of GaSb on Si (001) substrate: A transmission electron microscopy study
Authors: Kim Y. H. , Lee J. Y. , Noh Y. G. , Kim M. D. , Cho S. M. , Kwon Y. J. , Oh J. E.
Published: June 2006

Growth mode and structural properties of GaSb layers grown on silicon substrate by molecular beam epitaxy method are investigated by transmission electron microscopy. It is found that the GaSb grows to three-dimensional islands and grains are tilted to reduce a lattice mismatch through twin boundaries when they are directly grown on Si substrate. A low-temperature (LT) AlSb buffer plays a key role in transferring the growth mode from a three-dimensional island to a layer-by-layer structure. When the LT AlSb layer is used as a buffer, 90° misfit dislocations, with the Burgers vector b of 1∕2a⟨110⟩, are observed on the interface.
Wide-band transmission of nondistorted slow waves in one-dimensional optical superlattices
Authors: Ghulinyan M. , Galli M. , Toninelli C. , Bertolotti J. , Gottardo S. , Marabelli F. , Wiersma D. S. , Pavesi L. , Andreani L. C.
Published: June 2006

Few micron-thick one-dimensional optical superlattices were designed and grown, in which an optimized choice of external dielectric layers allows the formation of a wide and high transmission miniband of coupled cavity states. In such structures a reduction in light group velocity and minimal line shape distortion of propagating optical signal was observed. Group velocity reduction by a factor of 5, obtained both from phase (white-light interferometry) and from time-resolved measurements, is in reasonably good agreement with those calculated through a transfer matrix approach. Time-resolved experiments confirm the minimal line shape distortion for optical pulses of 1.8THz bandwidth at λ=1.5μm wavelength.
High-sensitivity surface plasmon resonance spectroscopy based on a metal nanoslit array
Authors: Jung Yun Suk , Sun Zhijun , Wuenschell Jeff , Kim Hong Koo , Kaur Palwinder , Wang Lei , Waldeck David
Published: June 2006

We have chemically modified metal nanoslit array surfaces with alkanethiol self-assembled monolayers and have characterized the resulting spectral shift of optical transmission. Adsorption of a self-assembled monolayer (1.5nm thick) on a silver nanoslit array (slit width of 30–50nm and grating period of 360nm) is found to cause an 11nm redshift of the main transmission peak. Strong confinement of optical fields in the narrow slit region allows sensitive transduction of surface modification into a shift of surface plasmon resonance wavelength.
Oxygen transport and reaction mechanisms in rhenium gate contacts on hafnium oxide films on Si
Authors: Pezzi R. P. , Copel M. , Gordon M. , Cartier E. , Baumvol I. J. R.
Published: June 2006

Oxygen transport and incorporation were investigated following postdeposition annealing of metal-oxide-semiconductor structures having ultrathin rhenium films as metal electrode and HfO2 films as dielectric on Si(001). Isotopic tracing, nuclear reaction analysis, narrow resonant nuclear reaction profiling, and x-ray photoelectron spectroscopy were used to pursue this investigation. For annealing temperatures below 400°C, oxygen from the gas phase incorporates mainly in near-surface regions of the overlying Re cap. Significant oxygen incorporation into the HfO2 films is observed only after annealing at 500°C. The present results are discussed considering that supplying oxygen to the metal/dielectric interface can cause device threshold voltage shifts.
Magnetic property mapping system for analyzing three-dimensional magnetic components
Authors: Tsukada Keiji , Kiwa Toshihiko
Published: June 2006

A magnetic measurement system utilizing a vector magnetic sensor for analyzing and mapping low frequency magnetic properties of metals has been developed for nondestructive evaluation. The measurement system consists mainly of an induction coil which can expose a large sample area, a vector magnetic sensor for detecting magnetic fields emanating from a sample, a lock-in amplifier, and a two-dimensional scanning stage. The system was determined to have a high magnetic sensitivity corresponding to less than 1nT in the locked-in state. The magnetic field strength change was detected in a sample that contained a slit of width greater than 1mm. Time sequential vector component (normal and tangential) maps were developed. An iron plate as an example of a ferromagnetic metal and an aluminum plate as an example of a good conducting and nonferromagnetic material were compared using this system. Analyzing the vector component maps could differentiate differences in the magnetic properties, such as permeability, eddy current distribution, and residual magnetism.
Photoacoustic signal normalization method and its application to the measurement of the thermal diffusivity for optically opaque materials
Authors: Balderas-López J. A.
Published: June 2006

A normalized photoacoustic method, especially suitable for thermal diffusivity measurements of highly optically opaque materials, is described. The photoacoustic signal for normalization in this case, unlike other normalized photoacoustic methodologies, corresponds to a semi-infinite reference material in the front photoacoustic configuration. The amplitude and phase of the sample’s photoacoustic signal, in transmission, are normalized with the corresponding ones of the reference. The normalization methodology yields, in this way, two independent thermal diffusivity values. This thermal property was measured for two polymers (black paint and black plastic tape); good agreement between the two thermal diffusivities measured for each material was obtained.
Lateral force calibration of an atomic force microscope with a diamagnetic levitation spring system
Authors: Li Q. , Kim K.-S. , Rydberg A.
Published: June 2006

A novel diamagnetic lateral force calibrator (D-LFC) has been developed to directly calibrate atomic force microscope (AFM) cantilever-tip or -bead assemblies. This enables an AFM to accurately measure the lateral forces encountered in friction or biomechanical-testing experiments at a small length scale. In the process of development, deformation characteristics of the AFM cantilever assemblies under frictional loading have been analyzed and four essential response variables, i.e., force constants, of the assembly have been identified. Calibration of the lateral force constant and the “crosstalk” lateral force constant, among the four, provides the capability of measuring absolute AFM lateral forces. The D-LFC is composed of four NdFeB magnets and a diamagnetic pyrolytic graphite sheet, which can calibrate the two constants with an accuracy on the order of 0.1%. Preparation of the D-LFC and the data processing required to get the force constants is significantly simpler than any other calibration methods. The most up-to-date calibration technique, known as the “wedge method,” calibrates mainly one of the two constants and, if the crosstalk effect is properly analyzed, is primarily applicable to a sharp tip. In contrast, the D-LFC can calibrate both constants simultaneously for AFM tips or beads with any radius of curvature. These capabilities can extend the applicability of AFM lateral force measurement to studies of anisotropic multiscale friction processes and biomechanical behavior of cells and molecules under combined loading. Details of the D-LFC method as well as a comparison with the wedge method are provided in this article.
KEMP: A program script for automated biological x-ray absorption spectroscopy data reduction
Authors: Korbas Malgorzata , Fulla Marsa Daniel , Meyer-Klaucke Wolfram
Published: June 2006

Automation of x-ray absorption spectroscopic (XAS) data reduction is essential to cope with high-throughput data collection becoming available at an increasing number of synchrotron radiation centers. A flexible script called KEMP has been developed and implemented at the XAS beamline at EMBL Hamburg. It automatically processes fluorescence XAS data. The pipeline includes dead time correction, energy calibration, selection of fluorescence detector channels, as well as the extraction of x-ray absorption near-edge structure and extended x-ray-absorption fine structure. The output is quickly available and thus can be included in the design of further experiments, which results in a more efficient use of the beam time.
Superhydrophobicity of a material made from multiwalled carbon nanotubes
Authors: Hong Yong Cheol , Uhm Han Sup
Published: June 2006

Superhydrophobic carbon nanotubes (CNTs) were prepared by low-pressure CF4 glow plasma to provide roughness and fluorination in CNTs. The water droplet falling freely on the superhydrophobic CNT powders bounced dynamically. The superhydrophobicity resulted from the combined effects of the chemical modification and surface roughness. Using the contact angles obtained from the capillary rise method based on the Washburn equation, the total surface free energy of CNT powder treated by CF4 plasma for 20min was calculated to be drastically decreased from 27.04to4.06×10−7mJ∕m2.
Next generation of oxide photonic devices: ZnO-based ultraviolet light emitting diodes
Authors: Ryu Yungryel , Lee Tae-Seok , Lubguban Jorge A. , White Henry W. , Kim Bong-Jin , Park Yoon-Soo , Youn Chang-Joo
Published: June 2006

Results are presented for ZnO-based ultraviolet light emitting diodes (LEDs) that employ a BeZnO∕ZnO active layer comprised of seven quantum wells. Arsenic and gallium are used for p-type and n-type layers. The ZnO-based LEDs show two dominant electroluminescence peaks located in the ultraviolet spectral region between 360 and 390nm, as well as a broad peak at 550nm.
Wavelength conversion in nonlinear optical polymer waveguides
Authors: Ju Jung Jin , Park Seung Koo , Park Suntak , Kim Jongbae , Kim Min-su , Lee Myung-Hyun , Do Jung Yun
Published: June 2006

We developed a polyimide side-chain polymer under the key guidelines of low losses at interacting wavelengths and high nonlinearity as well as thermal stability and fabricated quasi-phase-matched waveguide devices for second harmonic generation (SHG) and difference frequency generation (DFG). In addition, waveguide structures and periodic poling electrode widths were optimized for large mode overlap and efficient phase matching between the interacting optical fields (0.775 and 1.55μm), respectively. The polymeric waveguide (1cm length) records a normalized SHG efficiency of 5.4%W−1cm−2 and demonstrates DFG with −50dB conversion efficiency for an input pump power of 10mW (cw) at room temperature.
Redshift phenomenon of the excitation light of long life emission phosphor
Authors: Liu Liyan , Li Chengyu , Wang Shubin , Su Qiang
Published: June 2006

We observed that the SrMg2(PO4)2:Eu phosphor could emit long life phosphorescence with the excitation light whose wavelength was shorter than 420nm, however, when La, Ce, or Gd was codoped, the wavelength of the excitation light to cause the phosphorescence had a redshift of 40nm. A possible mechanism and related discussion for this redshift phenomenon of the excitation light was given. It was suggested that the threshold between the trap and valence band was decreased with the addition of the codopants.
Cobalt(II) Perfluorooctane Sulfonate Catalyzed Highly Efficient Aerobic Oxidation of Alcohols in Fluorous Biphasic Systems
Authors: Yi Wen-Bin , Cai Chun
Published: June 2006

Cobalt(ii) perfluorooctane sulfonate (Co(OPf)2) acts as a novel homogeneous pre-catalyst for the oxidation of various types of alcohols to carbonyl compounds under atmospheric pressure of molecular oxygen in fluorous biphasic systems. By simple separation of the fluorous phase, which contains only pre-catalyst, the reaction can be repeated several times.
Studies Towards the Synthesis of Salvinorin A
Authors: Lingham Anthony R. , Hügel Helmut M. , Rook Trevor J.
Published: June 2006

Salvinorin A 1, a psychoactive neoclerodane diterpenoid from the Mexican sage S. divinorum, has gained interest as a selective κ-opioid receptor agonist. Non-racemic 3-furylamines 9a and 9b have been prepared from (+)-pseudoephedrine and (–)-ephedrine for application in the stereoselective synthesis of the ketone ring of 1. Diels–Alder reaction of 9b with methyl acrylate in aqueous media, followed by selective ether bridge cleavage, has allowed access to the cyclohexenone 17 with preservation of stereochemistry at C2. A model route to the lactone ring has also been achieved through a one-pot deconjugation/esterification procedure of 2-bromocrotonyl chloride 20 to the furyl alcohol 19 followed by Reformatski-mediated ring closure.
Phosphonium-Based Ionic Liquids as Efficient Borane Carriers
Authors: Ramnial Taramatee , Hauser Michelle K. , Clyburne Jason A. C.
Published: June 2006

Phosphonium-based ionic liquids form new ionic liquids when treated with borane (BH3), and these ionic liquids are useful for reduction reactions involving carbonyl compounds. Alane (AlH3) reacts with the phosphonium cation, nevertheless the resulting solutions are capable of reducing esters to aldehydes. Phosphonium-based ionic liquids may serve as useful materials for reactive gas transport, and hence may serve as a fluid alternative to porous materials and may provide a convenient method of safely transporting boron hydrides for a variety of applications.
Dinuclear Eu(III), Gd(III), and Tb(III) Complexes of meso-1,2-Bis(ethylsulfinyl)ethane with 2,2′:62,2′′-Terpyridine as Co-ligand
Authors: Li Jian-Rong , Zhang Ruo-Hua , Bu Xian-He
Published: June 2006

Three dinuclear lanthanide complexes of flexible disulfoxide ligand meso-1,2-bis(ethylsulfinyl)ethane (L), [Ln2(L)2(μ-L)(tpy)4](ClO4)6(CHCl3)4 (Ln = Eu 1, Gd 2) and [Tb2(L)4(μ-L)(tpy)2](ClO4)6(CHCl3) 3 with 2,2′:6′,2′′-terpyridine (tpy) as co-ligand were synthesized and structurally characterized. In 1 and 2, the metal centre is nine-coordinated to two tpy and one-and-a-half L ligands, whereas in 3 it coordinates with one tpy and two-and-a-half L, which may be attributed to the influence of the lanthanide contraction. In such complexes the disulfoxide ligands perform two kinds of coordination modes, bridging and chelating, indicating their flexibility in the formation of such complexes.
Crystal Structure and Infrared Spectroscopy of Bis(2-hydrazinopyridine)palladium(II) Chloride and its Isotopomers
Authors: Drożdżewski Piotr , Musiała Marta , Kubiak Maria
Published: June 2006

Two forms of [Pd(hypy)2]Cl2 complex have been prepared. The reaction of PdCl2 with 2-hydrazinopyridine (hypy) ligand carried out in DMF solution produces the title complex 1, whereas its recrystallization from methanol gives [Pd(hypy)2]Cl2·2MeOH 2. The latter compound was the subject of full, single-crystal X-ray analysis, which revealed the planar structure of the metal vicinity and trans-orientation of the ligands, chelating the metal through amine and pyridine nitrogen atoms. The vibrations of the complex cation [Pd(hypy)2]2+ were investigated using IR spectroscopy and DFT modelling employing the B3LYP functional and LanL2DZ basis set. The vibrations of the hydrazine moiety and palladium(ii) environment, detected by N-deuteration and 104Pd/110Pd stable isotope labelling, were also reproduced in the calculations.
Discrete Metal Complexes of Two Multiply Armed Ligands
Authors: Al-Mandhary Muna R. A. , Fitchett Christopher M. , Steel Peter J.
Published: June 2006

The syntheses and metal complexes of 1,2,4,5-tetrakis(8-quinolyloxymethyl)benzene 1 and hexakis(8-quinolyloxymethyl)benzene 2 are described. X-Ray crystal structures are reported of the free ligand 1, a binuclear silver(i) and a tetranuclear copper(i) complex of 1, as well as a binuclear cobalt(ii) and trinuclear palladium(ii) and silver(i) complexes of 2. Within these discrete metal complexes the ligands are found to adopt a range of coordination modes, with considerable variation in the relative orientations of the ligand arms as a result of the flexibility imparted by the CH2O linker units.
Advancing age has differential effects on DNA damage, chromatin integrity, gene mutations, and aneuploidies in sperm
Authors: Wyrobek A. J. , Eskenazi B. , Young S. , Arnheim N. , Tiemann-Boege I. , Jabs E. W. , Glaser R. L. , Pearson F. S. , Evenson D.
Published: June 2006

This study compares the relative effects of advancing male age on multiple genomic defects in human sperm [DNA fragmentation index (DFI), chromatin integrity, gene mutations, and numerical chromosomal abnormalities], characterizes the relationships among these defects and with semen quality, and estimates the incidence of susceptible individuals for a well characterized nonclinical nonsmoking group of 97 men (22–80 years). Adjusting for confounders, we found major associations between age and the frequencies of sperm with DFI and fibroblast growth factor receptor 3 gene (FGFR3) mutations associated with achondroplasia (P< 0.01) with no evidence for age thresholds. However, we found no associations between age and the frequencies of sperm with immature chromatin, aneuploidies/diploidies,FGFR2mutations (Apert syndrome), or sex ratio in this cohort. There were also no consistent correlations among genomic and semen-quality endpoints, except between DFI and sperm motility (r= −0.65,P< 0.001). These findings suggest there are multiple spermatogenic targets for genomically defective sperm with substantially variable susceptibilities to age. Our findings predict that as healthy males age, they have decreased pregnancy success with trends beginning in their early reproductive years, increased risk for producing offspring with achondroplasia mutations, and risk of fathering offspring with Apert syndrome that may vary across cohorts, but with no increased risk for fathering aneuploid offspring (Down, Klinefelter, Turner, triple X, and XYY syndromes) or triploid embryos. Our findings also suggest that the burden of genomic damage in sperm cannot be inferred from semen quality, and that a small fraction of men are at increased risk for transmitting multiple genetic and chromosomal defects.
Network motif identification in stochastic networks
Authors: Jiang Rui , Tu Zhidong , Chen Ting , Sun Fengzhu
Published: June 2006

Network motifs have been identified in a wide range of networks across many scientific disciplines and are suggested to be the basic building blocks of most complex networks. Nonetheless, many networks come with intrinsic and/or experimental uncertainties and should be treated as stochastic networks. The building blocks in these networks thus may also have stochastic properties. In this article, we study stochastic network motifs derived from families of mutually similar but not necessarily identical patterns of interconnections. We establish a finite mixture model for stochastic networks and develop an expectation-maximization algorithm for identifying stochastic network motifs. We apply this approach to the transcriptional regulatory networks of
Escherichia coli
and
Saccharomyces cerevisiae
, as well as the protein–protein interaction networks of seven species, and identify several stochastic network motifs that are consistent with current biological knowledge.