bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropy of domain switching in prepoled lead titanate zirconate ceramics under multiaxial electrical loading
Authors: Liu Yuan-Ming , Li Fa-Xin , Fang Dai-Ning
Published: January 2007

The authors report an observation of anisotropic domain switching process in prepoled lead titanate zirconate (PZT) ceramics under multiaxial electrical loading. Prepoled PZT blocks were obliquely cut to apply an electric field at discrete angles θ (0°–180°) to the initial poling direction. Both the coercive field and switchable polarization are found to decrease significantly when sinθ increases from zero to unity. The measured strain curves show that most domains that accomplished 180° domain switching actually experienced two successive 90° switching. The oriented domain texture after poling plus the induced nonuniform stress are used to explain the observed domain switching anisotropy.
Grid-based energy density analysis: Implementation and assessment
Authors: Imamura Yutaka , Takahashi Asuka , Nakai Hiromi
Published: January 2007

Grid-based energy density analysis (grid-EDA) that decomposes the total energy into atomic energies by a space-partitioning function is proposed. The kinetic energy, nuclear attraction, and exchange-correlation functional are evaluated on grid points and are split into atomic contributions. To reduce numerical errors in the conventional scheme of numerical integration, the electronic Coulomb and HF exchange interactions are evaluated by the pseudospectral method, which was first applied to an ab initio method by Friesner [Chem. Phys. Lett. 116, 39 (1985)], and are decomposed into atomic contributions. Grid-EDA using the pseudospectral method succeeds in ensuring less than 1kcal∕mol error in total energies for small molecules and providing reliable atomic energy contributions for the problematic lithium cluster, which exhibits a strong basis-set dependence for Mulliken-type EDA. Also, site-dependent atomization energies are estimated by grid-EDA for cluster models such as Li48, C41H60, and Mg32O32. Grid-EDA reveals that these models imitate crystal environments reasonably because atomization energies estimated from the inner atoms of the models are close to the experimental cohesive energies.
Probing supercritical water with the n-π* transition of acetone: A Monte Carlo/quantum mechanics study
Authors: Fonseca Tertius L. , Coutinho Kaline , Canuto Sylvio
Published: January 2007

The n-π* electronic transition of acetone is a convenient and important probe to study supercritical water. The solvatochromic shift of this transition in supercritical water (adopting the experimental condition of P=340.2atm and T=673K) has been studied theoretically using Metropolis NPT Monte Carlo (MC) simulation and quantum mechanics (QM) calculations based on INDO/CIS and TDDFT-B3LYP∕6-31+G(d) methods. MC simulations are used to analyze hydration shells, solute-solvent interaction, and for generating statistically relevant configurations for subsequent QM calculations of the n-π* transition of acetone. The results show that the average number of hydrogen bonds between acetone and water is essentially 1∕3 of that in normal water condition of temperature and pressure. But these hydrogen bonds have an important contribution in the solute stabilization and in the solute-solvent interaction. In addition, they respond for nearly half of the solvatochromic shift. The INDO/CIS calculations explicitly considering all valence electrons of the water molecules, using different solvation shells, up to the third shell (170 water molecules), give a solvatochromic shift of 670±36cm−1 in very good agreement with the experimentally inferred result of 500–700cm−1. It is found that the solvatochromic effect on n-π* transition of acetone in the supercritical condition is essentially given by the first solvation shell. The time-dependent density-functional theory (TDDFT) calculations are also performed including all solvent molecules up to the third shell, now represented by point charges. This TDDFT-B3LYP∕6-31+G(d) also gives a good but slightly overestimated result of 825±65cm−1. For comparison the same study is also made for acetone in water at normal condition. Finally, all average results reported here are statistically converged.
Effects of nonproductive binding on the kinetics of enzymatic reactions with patterned substrates
Authors: Nag Ambarish , Zhao Tong , Dinner Aaron R.
Published: January 2007

Existing models of ligand-receptor binding kinetics suggest that clustering surface-associated molecules tends to decrease the rates with which solution phase molecules associate and dissociate. Here, the authors use kinetic Monte Carlo simulations to study the case of an enzyme catalyzing the turnover of substrate molecules immobilized on a surface. The simulations reveal a crossover in the overall reaction rates for randomly distributed and clustered substrate molecules as the enzyme unbinding rate is varied. Approximate expressions for the effective kinetic parameters are introduced, and they show that the observed behavior derives from sequestration of the enzyme in the strong-sticking limit.
Energy contribution of the solvent to the charge migration in DNA
Authors: Berashevich Julia A. , Chakraborty Tapash
Published: January 2007

The authors have investigated the interactions of the reaction centers, participating in the charge transfer reaction within the DNA molecule with the phosphate backbones and the solvent molecules, and have estimated the contribution of these interactions into the charge migration in DNA. They have determined the unequal shift of the energy surfaces of the initial and final transition states of the transfer reaction along the energy axis and the dependence of the magnitude of the energy shift on the nature of the reaction centers and the surrounding environment. The nonuniform distribution of the negative charge in the DNA phosphate backbones results in an increase of the positive shift of the energy surface of the DNA base pairs in the center of the structure, where the maximum density of the negative charge is concentrated. Localization of the positive charge on the guanine and the adenine in the DNA base pairs in the oxidized state results in a dependence of the free energy of reaction in the solvent on the pair sequences and their arrangement in the DNA chain. As an example, for the G-C/A-T configuration the positive charges are localized on the same strand that results in a decrease of the free energy of reaction in the solvent for charge migration from G-C to A-T pair by 0.125eV.
Field emission of silicon nanowires grown on carbon cloth
Authors: Zeng Baoqing , Xiong Guangyong , Chen Shuo , Wang Wenzhong , Wang D. Z. , Ren Z. F.
Published: January 2007

A low operating electric field has been achieved on silicon nanowires grown on carbon cloth. The silicon nanowires were grown on carbon cloth via the vapor-liquid-solid reaction using silane gas as the silicon source and gold as catalyst from the decomposition of hydrogen gold tetrachloride. An emission current density of 1mA∕cm2 was obtained at an operating electric field of 0.7V∕μm. Such low field is resulted from a high field enhancement factor of 6.1×104 due to the combined effects of the high intrinsic aspect ratio of silicon nanowires and the woven geometry of carbon cloth. Such results may lead silicon nanowire field emitters to practical applications in vacuum microelectronic devices including microwave devices.
Optimal and robust control of small disturbances in a channel flow with a normal magnetic field
Authors: Debbagh K. , Cathalifaud P. , Airiau C.
Published: January 2007

Active closed-loop control of subcritical and supercritical instabilities amplified in a channel flow submitted to a constant normal magnetic field is investigated. Control is carried out at both the upper and lower walls by blowing and suction (velocity control) or by a perturbation of the normal magnetic field (magnetic control). Even if a velocity control is more efficient than a magnetic one, we found that magnetic control succeeds in stabilizing supercritical instabilities. Development of new actuators using magnetic field for flow control may thus be promising. Closed-loop control modifies the optimal perturbation but does not destruct the lift-up effect.
Multichannel scattering calculations using absorbing potentials and mapped grids
Authors: Grozdanov T. P. , McCarroll R.
Published: January 2007

The authors investigate the use of absorbing potentials and discrete variable representation grid methods in multichannel time-independent scattering calculations. An exactly solvable, coupled-two-channel problem involving square-well potentials is used to assess the quality of numerical results. Special emphasis is given to the description of scattering resonances and near-threshold regions. Numerical treatment of close vicinities of thresholds requires the introduction of nonequidistant grids through a mapping procedure of the scattering coordinate.
Theory of charged dust clouds: Equilibrium
Authors: Avinash K.
Published: January 2007

Gravitational equilibria of low density dust clouds imbedded in plasma background are studied. These are a new class of astrophysical objects, in which the electric field in quasineutral plasma balances the self-gravity of the dust. Heuristic arguments based on the total potential energy of a uniform dust ball are given for the existence of stable equilibrium and the mass limit for the maximum dust mass MAS, which can be supported against its self-gravity. The gravitational collapse is initiated by the destabilization of the fundamental radial mode as the mass of the dust cloud MD→MAS. The physics of the mass limit is similar to the Chandrasekhar’s mass limit for compact objects. One parameter family of spherically symmetric, static solutions of radius R(≈0.1AU) and the total mass of the dust cloud MD(≈1019g), for given central dust density, are constructed. A finite flux of photoelectrons is shown to decrease R and MD. Two-dimensional rotating dust disk equilibrium, characterized by a sharp and diffuse boundary, is also constructed. These dust equilibria (spherical clouds, rotating disks), which are predicted to be within the interstellar clouds, could be relevant for planet formation, as they provide locations where a significant quantity of dust can be stably trapped. The accretion and coagulation interaction between these trapped dust grains may lead to planet formation.
The spin-orbit transition of atomic chlorine in solid H2, HD, and D2
Authors: Raston Paul L. , Anderson David T.
Published: January 2007

Essential to understanding the reaction dynamics of spin-orbit (SO) excited atomic chlorine (P1∕22) with molecular hydrogen is experimental measurements of the SO splitting of Cl in the van der Waals region of the entrance channel to reaction. Here we report high-resolution direct absorption studies of the SO transition (P1∕22←P3∕22) of atomic chlorine isolated in solid molecular hydrogen (H2, HD, and D2).
Origin of negative differential resistance in molecular junctions of Rose Bengal
Authors: Bandyopadhyay Anirban , Wakayama Y.
Published: January 2007

Negative differential resistance (NDR) is tuned at the junctions of electronically different dimers and trimers of Rose Bengal. Isolated molecule did not show any NDR. But it was induced to show double and triple NDRs with large peak to valley ratio (1.8–3.1) at 300K by varying number of neighbors and charging them by an electrical pulse. One could destroy or regenerate NDR by separating them or bringing together by a scanning tunneling microscope tip. NDR was also independent of polaronic nature. Bits 1 and 0 for cationic NDR (in dimer) and 0, 1, 2, and 3 for dianionic NDR (trimer) were written in an atomic scale junction. Importance of junction electronics and effective exposure is revealed.
Dynamics of the laser-induced ferroelectric excitation in BaTiO3 studied by x-ray diffraction
Authors: Istomin Konstantin , Kotaidis Vassilios , Plech Anton , Kong Qinqyu
Published: January 2007

Ultrafast time resolved x-ray powder scattering is used to reveal the structural dynamics in BaTiO3 powder excited by femtosecond laser pulses. The lattice excitation close to the Curie point of BaTiO3 is analyzed by refining the powder pattern (Rietveld method) to obtain the lattice state and the atomic positions. It is found that the tetragonal distortion of the ferroelectric phase is diminished within the 100ps time resolution of the experiment. The unit cell polarization, however, is not affected by this excitation, evidenced by the preserved Ti and oxygen displacement. The change in splitting relaxes on the nanosecond time scale.
Electron-electron interactions in Al0.15Ga0.85N∕GaN high electron mobility transistor structures grown on Si substrates
Authors: Liang C.-T. , Lin Li-Hung , Huang J. Z. , Zhang Zhi-Yao , Sun Zhe-Hau , Chen Kuang Yao , Chen N. C. , Chang P. H. , Chang Chin-An
Published: January 2007

We report on magnetotransport studies of Al0.15Ga0.85N∕GaN high electron mobility transistor (HEMT) structures grown on p-type Si (111) substrates. A small but significant decrease of the Hall slope with increasing temperature is observed. Moreover, the converted conductivities reveal that the mobility of the HEMT shows a linear dependence on temperature. All these experimental results can be ascribed to electron-electron interaction (EEI) effects in AlxGa1−xN∕GaN HEMT structures grown on Si. The existence of EEI effects can be utilized to design and optimize GaN-based quantum devices on Si such as single-electron transistors and quantum point contacts since EEI effects can strongly modify the transport in semiconductor devices.
0.15
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3.72
THz
absorption of aqueous salts and saline solutions
Authors: Xu Jing , Plaxco Kevin W. , Allen S. James , Bjarnason Jon E. , Brown Elliott R.
Published: January 2007

It has recently been suggested that near-field terahertz ionic contrast microscopy can be employed to image subtle changes in ionic concentrations arising from neuronal activity. To do so, however, requires that solvated ions exhibit significant absorbance at terahertz frequencies. The authors have investigated this issue and find that, at room temperature, the molar extinctions of both sodium chloride and guanidine hydrochloride are approximately two orders of magnitude below some previous measurements and are, therefore, too low to support the proposed imaging application.
Nested optical band gaps for a cholesteric elastomer slab under stress
Authors: Rivera Margarita , Reyes Juan Adrian
Published: January 2007

Using the equilibrium configuration adopted by a cholesteric elastomer elongated by the influence of a uniaxial transverse stress, the authors calculate the solution of the boundary-value problem for the reflection and transmission of obliquely incident plane waves due to a elastomer slab. The authors find a left-circularly polarized thin reflection band immersed in a wider right-circularly polarized band reflection when the elastomer is under a stress near to the critical value. Also, a deformation of the reflection band and the reduction of its bandwidth were obtained. These band gap features suggest to design a finely tuning polarization-universal optical filter.
Infrared characterization of hafnium oxide grown by atomic layer deposition using ozone as the oxygen precursor
Authors: Wang Y. , Dai M. , Ho M.-T. , Wielunski L. S. , Chabal Y. J.
Published: January 2007

Hf O 2 growth on H-terminated Si surfaces by atomic layer deposition (ALD) is studied with in situ Fourier transform infrared spectroscopy and ex situ Rutherford backscattering, using tetrakis-(ethyl-methyl-amino) hafnium and ozone as the hafnium and oxygen precursors, and compared to water-vapor-based ALD growth. The reaction pathways are different for the two oxygen precursors, leading to a lower growth rate for ozone (∼0.05nm∕cycle) than for water-based growth and to incorporation of different impurities in the HfO2 film. Furthermore, interfacial SiO2 is readily formed with ozone at the growth temperature (∼100°C), in contrast to water-based HfO2 growth.
Gallium nitride based microcavity light emitting diodes with 2λ effective cavity thickness
Authors: Pattison P. Morgan , David Aurelien , Sharma Rajat , Weisbuch Claude , DenBaars Steven , Nakamura Shuji
Published: January 2007

Gallium nitride based microcavity light emitting diodes less than 400nm thick emitting at a peak wavelength of 455nm have been fabricated. The epitaxial structure was grown by metal organic chemical vapor deposition, and the device was fabricated using a laser lift-off process. Cavity thinning was carried out using inductively coupled plasma etching until a cavity length of roughly 2λ (∼375nm, corresponding to a cavity order of 4 for λ=455nm in GaN) was achieved. Devices are presented that show perfectly detuned angular emission and perfectly resonant emission between the cavity length and emission wavelength.
Epitaxial growth of ZnO nanowall networks on GaN/sapphire substrates
Authors: Kim Sang-Woo , Park Hyun-Kyu , Yi Min-Su , Park Nae-Man , Park Jong-Hyurk , Kim Sang-Hyeob , Maeng Sung-Lyul , Choi Chel-Jong , Moon Seung-Eon
Published: January 2007

Heteroepitaxy of vertically well-aligned ZnO nanowall networks with a honeycomblike pattern on GaN∕c-Al2O3 substrates by the help of a Au catalyst was realized. The ZnO nanowall networks with wall thicknesses of 80–140nm and an average height of about 2μm were grown on a self-formed ZnO thin film during the growth on the GaN∕c-Al2O3 substrates. It was found that both single-crystalline ZnO nanowalls and catalytic Au have an epitaxial relation to the GaN thin film in synchrotron x-ray scattering experiments. Hydrogen-sensing properties of the ZnO nanowall networks have also been investigated.
Growth, structural, and magnetic characterizations of nanocrystalline γ′-FeNiN(220) thin films
Authors: Prieto P. , Pirota K. R. , Sanz J. M. , Jiménez E. , Camarero J. , Maccherozzi F. , Panaccione F. G.
Published: January 2007

The authors have developed a fabrication process of nanocrystalline γ′-FeNiN[220] thin ferromagnetic films by using a dual ion beam sputtering system. The films show well defined in-plane magnetic uniaxial anisotropy, with high anisotropy field and high macroscopic saturation magnetization, requisites of crucial importance for high-frequency applications. The estimated ferromagnetic resonance frequency goes within the gigahertz regime, and the magnetic response can be tailored by the deposition conditions. Element-selective measurements reveal a reduction of the total Fe and Ni magnetic moments in γ′-FeNiN with respect to pure Fe and Ni due to hybridization between Fe and Ni 3d and N 2p states.
Band gap tuning of lead-substituted BaSnO3 for visible light photocatalysis
Authors: Borse Pramod H. , Joshi Upendra A. , Ji Sang Min , Jang Jum Suk , Lee Jae Sung , Jeong Euh Duck , Kim Hyun Gyu
Published: January 2007

The Pb substitution effect was investigated experimentally and theoretically on the crystal structure of BaSnO3 and on the photo-oxidation activity of H2O. The chemically doped Pb in BaSnO3 induced a concentration-dependent redshift of the experimental band gap (BG). The BaPb0.8Sn0.2O3 system produced 32μmol∕h of O2 under λ⩾420nm photons, but no O2 for BaSnO3. The DFT calculations of BaPbxSn1−xO3 (x=0,0.5,1) by using generalized approximation, implying the BG alteration and the photocatalytic activity of BaPbxSn1−xO3, are due to the induced Pb 6s orbital in the BG of BaSnO3. Thus Pb modified the insulating nature of BaSnO3 to semiconducting and semimetallic.
Towards better DNA chip hybridization using chaotic advection
Authors: Raynal Florence , Beuf Aurélien , Plaza Frédéric , Scott Julian , Carrière Philippe , Cabrera Michel , Cloarec Jean-Pierre , Souteyrand Éliane
Published: January 2007

Numerical studies for two protocols of micromixing based on chaotic advection to improve DNA chip hybridization are presented. The first protocol uses syringes; the other one, pumps. For both protocols, numerical Poincaré sections and Lyapunov exponents of the three-dimensional, time-periodic flow are investigated as functions of the period. Model experiments also confirm numerical results. Homogeneity of the dispersion of particles inside the chamber is of primary importance to achieve best chip reliability: although global chaos was obtained for both protocols, we find that the one employing the pumps is more likely to achieve better and more rapid hybridization.
Electric switching and memory devices made from RbAg4I5 films
Authors: Liang X. F. , Chen Y. , Chen L. , Yin J. , Liu Z. G.
Published: January 2007

Electric switching and memory effects were observed on devices composed of a RbAg4I5 film sandwiched between Ag and Pt electrodes. The RbAg4I5 films were prepared by pulsed laser deposition and the lateral size of devices was scaled down to 300nm by focused ion beam lithography. The device can be switched between high- and low-resistance states with a ratio of ∼103 by applying voltage with opposite polarities. The read-write cycles could be repeated at 1kHz and for 104 times. The switching characters are attributed to the formation or breakdown of Ag filaments in RbAg4I5 films induced by electrochemical reactions.
Manipulation of spin reorientation transition of ultrathin Co films by using an artificially roughened Pd(111) substrate
Authors: Jeong Jong-Ryul , Bland J. A. C. , Lee Jeong-Won , Park Yong-Sung , Shin Sung-Chul
Published: January 2007

The authors present a simple method to control the spin reorientation transition (SRT) in ultrathin Co films using an artificially roughened substrate prepared by ion bombardment with varying the incident angle φ from 0° to 80°. The combined study of surface magneto-optical Kerr effects and scanning tunneling microscopy revealed a drastic increase of the onset thickness of the SRT (tc) by up to 41% for the substrate sputtered at φ=80°, whereas there is an 18% reduction for the φ=20° sample relative to the SRT in the smooth surface. The second- and fourth-order surface anisotropies (K2s and K4s) responsible for the drastic change in the SRT are determined from a theoretical fit to the magnetization orientation in the spin reorientation region.
Amorphous/nanocrystalline silicon biosensor for the specific identification of unamplified nucleic acid sequences using gold nanoparticle probes
Authors: Martins Rodrigo , Baptista Pedro , Raniero Leandro , Doria Gonçalo , Silva Leonardo , Franco Ricardo , Fortunato Elvira
Published: January 2007

Amorphous/nanocrystalline silicon pi′ii′n devices fabricated on micromachined glass substrates are integrated with oligonucleotide-derivatized gold nanoparticles for a colorimetric detection method. The method enables the specific detection and quantification of unamplified nucleic acid sequences (DNA and RNA) without the need to functionalize the glass surface, allowing for resolution of single nucleotide differences between DNA and RNA sequences—single nucleotide polymorphism and mutation detection. The detector’s substrate is glass and the sample is directly applied on the back side of the biosensor, ensuring a direct optical coupling of the assays with a concomitant maximum photon capture and the possibility to reuse the sensor.
High order mode formation of externally coupled hybrid photonic-band-gap cavity
Authors: Jeon Seok-Gy , Shin Young-Min , Jang Kyu-Ha , Han Seong-Tae , So Jin-Kyu , Joo Young-Do , Park Gun-Sik
Published: January 2007

The electromagnetic field distribution obtained from a finite-difference-time-domain simulation shows that a hybrid photonic-band-gap (PBG) cavity enveloped by a dielectric lattice and three metallic walls provides a better field uniformity of a high order mode, TMmn0, than a conventional one does under an external coupling with the maintenance of a high quality factor of the metallic cavity. Experimentally measured reflection and transmission scattering matrices of a TM550 mode show that the hybrid PBG structure improves the field uniformity to within 10% compared with a larger variation reaching a few tens of a percent with the conventional cavity under critical coupling.
Control of guided resonance in a photonic crystal slab using microelectromechanical actuators
Authors: Kanamori Yoshiaki , Kitani Takashi , Hane Kazuhiro
Published: January 2007

A wavelength-selective variable-reflection filter is proposed, in which a guided resonance in a photonic crystal (PC) slab is controlled by microelectronic mechanical actuators. A narrow wavelength response is generated by the guided resonance of PC slab, and the variable optical response at the wavelength is caused by evanescent-wave coupling to a substrate. The coupling is controlled by microelectromechanical actuators. The proposed filter has been fabricated by silicon micromachining and the mechanism has been confirmed.
Temperature dependence of the first-order metal-insulator transition in VO2 and programmable critical temperature sensor
Authors: Kim Bong-Jun , Lee Yong Wook , Chae Byung-Gyu , Yun Sun Jin , Oh Soo-Young , Kim Hyun-Tak , Lim Yong-Sik
Published: January 2007

For VO2-based two-terminal devices, the first-order metal-insulator transition (MIT, jump) is controlled by an applied voltage and temperature, and an intermediate monoclinic metal phase between the MIT and the structural phase transition (SPT) is observed. The conductivity of this phase linearly increases with increasing temperature up to TSPT≈68°C and becomes maximum at TSPT. Optical microscopic observation reveals the absence of a local current path in the metal phase. The current uniformly flows throughout the surface of the VO2 film when the MIT occurs. This device can be used as a programmable critical temperature sensor where the applied voltage is controlled by a program.
Assessment of the local supercurrent densities in long superconducting coated conductors
Authors: Zehetmayer M. , Fuger R. , Eisterer M. , Hengstberger F. , Weber H. W.
Published: January 2007

The authors report on measurements of the local supercurrent density in long Y1Ba2Cu3O7−δ based coated conductors by the magnetoscan technique. Significant inhomogeneities were found, which are well resolved by the resulting magnetic field map. A single central line scan along the length of the conductor reflects the inhomogeneities over the entire width of the sample, thus offering the possibility of very fast characterization. Modifying the applied field leads to different results highlighting either the overall critical current or details of the defect structure. In addition, numerical simulations of the current dynamics were carried out for a qualitative and quantitative interpretation of the results.
Nanoimprint of gratings on a bulk metallic glass
Authors: Chu J. P. , Wijaya H. , Wu C. W. , Tsai T. R. , Wei C. S. , Nieh T. G. , Wadsworth Jeffrey
Published: January 2007

The authors demonstrate that optical gratings with 600 and 1500nm periods on a Pd40Ni40P20 bulk metallic glass (BMG) can be faithfully imprinted in air from Si dies. Results of scanning electron microscopy, atomic force microscopy, and optical diffraction analysis show the fine line feature of ∼150nm. The gratings have smooth and uniform surface profiles with comparable optical properties as the original Si dies. The BMG gratings can be further used to imprint the second-generation replicas on polymethylmethacrylate. Thereby, BMG is a suitable material not only for imprinting nanostructured parts such as gratings, but also as a good die material for nanoimprints.
Trap elimination and injection switching at organic field effect transistor by inserting an alkane (C44H90) layer
Authors: Ogawa Satoshi , Kimura Yasuo , Niwano Michio , Ishii Hisao
Published: January 2007

Recently, it was proposed in the literature that the electron trap on a hydroxyl-containing dielectric interface of an organic field effect transistor (OFET) hinders its n type operation. The authors fabricated pentacene and fullerene OFETs with a hydroxyl-free insulating material, a long-chain alkane, i.e., tetratetracontate (TTC), C44H90 layer coated on the SiO2 dielectric layer. The displacement current measurements clearly demonstrated that the electron trap of the SiO2 surface is suppressed by the TTC layer. For a pentacene FET with an Al electrode and SiO2 dielectric layer, a p type operation was observed, while the operation mode was switched to the n type by the insertion of TTC on the SiO2 interface. By simple patterning of the TTC layer to produce a bipolar injection, the authors fabricated an ambipolar pentacene FET with a single kind of metal electrode. Thus TTC is a good material for the surface modification of a dielectric layer in OFETs.
Simple protocol for secure decoy-state quantum key distribution with a loosely controlled source
Authors: Wang Xiang-Bin , Peng Cheng-Zhi , Pan Jian-Wei
Published: January 2007

The method of decoy-state quantum key distribution requests different intensities of light pulses. Existing theory has assumed exact control of intensities. Here the authors propose a simple protocol which is secure and efficient even there are errors in intensity control. In their protocol, decoy pulses and signal pulses are generated from the same father pulses with a two-value attenuation. Given the upper bound of fluctuation of the father pulses, their protocol is secure provided that the two-value attenuation is done exactly. They propose to use unbalanced beam splitters for a stable attenuation.
Wavelength control across the near IR spectrum with GaInNAs
Authors: Williams R. S. , McGee W. M. , Ashwin M. J. , Jones T. S. , Clarke E. , Stavrinou P. , Zhang J. , Tomić S. , Mulcahy C. P. A.
Published: January 2007

Accurate control of the photoluminescence (PL) emission wavelength over the range of 1.00–1.55μm has been achieved using GaIn(N)As multiple quantum well (MQW) structures, grown by plasma-assisted molecular beam epitaxy. By limiting the In content to 30%, hence limiting the overall strain, wavelength-specific MQWs can be grown through simple control over the N content (0%–5%). High crystalline quality and compositional control are demonstrated using high-resolution x-ray diffraction, secondary-ion mass spectroscopy, PL, and subsequent comparison to theoretical calculations using a ten-band k∙p band-anticrossing model. The results reveal adherence to Vegard’s law over a larger compositional range for GaInNAs than GaNAs.
High-resolution mapping of the three-dimensional point spread function in the near-focus region of a confocal microscope
Authors: Nasse Michael J. , Woehl Jörg C. , Huant Serge
Published: January 2007

Fluorescent nanobeads with a diameter of 20nm were used to map the three-dimensional point spread function in the near-focus region of a confocal microscope at high spatial resolution. Fluorescence images were taken in 109 equidistant planes (50nm apart) parallel to the focal plane; postacquisition stacking of these images allows the reconstruction of the point spread function in the axial plane. The experimental distribution is compared to theoretical calculations based on an integral representation for the light intensity in the focus region that takes into account stratified media, polarization, the Gaussian illumination profile, and the finite exit pinhole size.
Large-scale optical traps on a chip for optical sorting
Authors: Sun Y. Y. , Yuan X.-C. , Ong L. S. , Bu J. , Zhu S. W. , Liu R.
Published: January 2007

The authors present a power-efficient large-scale lensless optical traps on a chip (OTOCs) as an optofluidic element for optical sorting of microparticles. Based on the well-known Talbot self-imaging effect in the Fresnel region, the OTOC makes use of a two-dimensional microfabricated chessboardlike structure to create an optical lattice near its emergent plane. Simultaneous trapping of hundreds of microparticles in a regular array (>200×200μm2) is proved experimentally without adopting an external optical projection lens configuration. Furthermore, the authors demonstrate experimental results for large-scale sorting of microparticles by sizes using the OTOC.
Multiplexed hydraulic valve actuation using ionic liquid filled soft channels and Braille displays
Authors: Gu Wei , Chen Hao , Tung Yi-Chung , Meiners Jens-Christian , Takayama Shuichi
Published: January 2007

Pneumatic actuation with multilayer soft lithography enables operation of up to thousands of valves in parallel using far fewer control lines. However, it is dependent on macroscopic switches and external pressure sources that require interconnects and limit portability. The authors present a more portable and multiplexed valve actuation strategy that uses a grid of mechanically actuated Braille pins to hydraulically, rather than pneumatically, deform elastic actuation channels that act as valves. Experimental and theoretical analyses show that the key to reliable operation of the hydraulic system is the use of nonvolatile ionic liquids as the hydraulic fluid.
Spectral broadening in electroluminescence of white organic light-emitting diodes based on complementary colors
Authors: Kim Young Min , Park Young Wook , Choi Jin Hwan , Ju Byeong Kwon , Jung Jae Hoon , Kim Jai Kyeong
Published: January 2007

The authors report the optical and electroluminescent (EL) properties of white organic light-emitting diodes (OLEDs) which have two emitters with similar structures: 1, 1, 4, 4-tetraphenyl-1, 3-butadiene and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline have an emission peak of 400nm around the near ultraviolet, and tris-(8-hydroxyquinoline) aluminum doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran has an emission peak of 580nm producing a yellow color. The EL spectra of the white OLED have shown a broadening through visual range from 400to780nm. This spectral broadening is related to an exciplex emission at the organic solid interface.
Self-assembly of vesicle nanoarrays on Si: A potential route to high-density functional protein arrays
Authors: Ramanujan C. S. , Sumitomo K. , de Planque M. R. R. , Hibino H. , Torimitsu K. , Ryan J. F.
Published: January 2007

The authors show that 100nm unilamellar thiol-tagged vesicles bind discretely and specifically to Au nanodots formed on a Si surface. An array of such dots, consisting of 20nm Au–Si three-dimensional islands, is formed by self-assembly on terraces of small-angle-miscut Si(111) after Au deposition. Consequently, both the formation of the nanopattern and the subsequent attachment of the vesicles are self-organized and occur without the need for any “top-down” lithographic processes. This approach has the potential to provide the basis of a low-cost, high-density nanoarray for use in proteomics and drug discovery.
Charge offset stability in tunable-barrier Si single-electron tunneling devices
Authors: Zimmerman Neil M. , Simonds Brian J. , Fujiwara Akira , Ono Yukinori , Takahashi Yasuo , Inokawa Hiroshi
Published: January 2007

The problem of charge offset drift in single-electron tunneling (SET) devices can preclude their useful application in metrology and integrated devices. We demonstrate that in tunable-barrier Si-based SET transistors there is excellent stability, with a drift that is in general less than 0.01e; these devices exhibit some unwanted sensitivity to external perturbations including temperature excursions. Finally, we show that these devices can be “trained” to minimize their sensitivity to abrupt voltage changes.
Influence of Ge substrate crystallinity on Co germanide formation in solid-state reactions
Authors: Opsomer K. , Deduytsche D. , Detavernier C. , Van Meirhaeghe R. L. , Lauwers A. , Maex K. , Lavoie C.
Published: January 2007

A strong influence of substrate crystallinity is observed for thin-film Co∕Ge reactions. For the detected phases (CoGe, Co5Ge7, and CoGe2), the formation temperatures on amorphous Ge (a-Ge) are found to be the lowest, while the highest are on single-crystalline Ge(100). Moreover, while the phase sequence on Ge(100) and polycrystalline Ge (poly-Ge) was unaltered, the formation of intermediate Co5Ge7 was not observed on a-Ge. It is likely that this is due to a promoted CoGe2 formation on a-Ge, resulting in a ∼200°C decrease in formation temperature (depending on the ramp rate). These observations suggest a strong competition among the formation of these Ge-rich phases.
Plasmalike negative capacitance in nanocolloids
Authors: Shulman J. , Tsui S. , Chen F. , Xue Y. Y. , Chu C. W.
Published: January 2007

A negative capacitance has been observed in a nanocolloid between 0.1 and 10−5Hz. The response is linear over a broad range of conditions. The low-ω dispersions of both the resistance and capacitance are consistent with the free-carrier plasma model, while the transient behavior demonstrates a possible energy storage mechanism. A collective excitation, therefore, is suggested.
Buckling characterization of vertical ZnO nanowires using nanoindentation
Authors: Ji Liang-Wen , Young Sheng-Joue , Fang Te-Hua , Liu Chien-Hung
Published: January 2007

Nanomechanical characterization of vertical well-aligned single-crystal ZnO nanowires on ZnO:Ga/glass templates was performed by nanoindentation technique. The buckling loads were found to be 1465 and 215μN for the ZnO nanowires of 100 and 30nm diameters, respectively. Furthermore, the buckling energies for the ZnO nanowires of 100 and 30nm diameters were 3.62×10−10 and 3.69×10−11J, respectively. Based on the Euler buckling model, Young’s modulus of the individual ZnO nanowire has been derived from two possible modes in this work.
Novel liquid flow sensor based on differential pressure method
Authors: Liu Zhizhuang , Hong Tiansheng , Zhang Wenzhao , Li Zhen , Chen Haibo
Published: January 2007

In this article, a novel liquid flow sensor which is composed of a special structure conduit main body and a differential pressure sensor was designed, fabricated, and calibrated. The conduit main body includes an inlet channel section with a branch conduit connecting one end of the pressure sensor, a throat channel section, and an outlet channel section with a branch conduit connecting another end of the pressure sensor. The basic principle is to employ a differential pressure sensor to measure the pressure difference between the inlet channel and outlet channel of the conduit main body when fluid passes through it. The pressure difference between the two ends of the differential pressure sensor (i.e., the two branch conduits located in the inlet and outlet channel sections) is of either forward or backward flow and directly interrelates with the volume flow rate (mass flow rate or flow velocity) via the conduit main body, so the volume flow rate or mass flow rate or flow velocity can be calculated and the flow direction can be determined from the detected pressure difference. This liquid flow sensor is characterized by using only one differential pressure sensor of a simple structure, the error of which is less than 1%.
Bimodal vortex shedding in a perturbed cylinder wake
Authors: Konstantinidis Efstathios , Balabani Stavroula , Yianneskis Michael
Published: January 2007

Cylinder wakes display distinct modes of vortex shedding when perturbed by appropriate means. By investigating experimentally the wake of a circular cylinder perturbed by a periodic fluctuation imposed on the inflow velocity, it is shown that bimodal behavior is possible. During a given experiment, the wake switches back and forth between two different vortex shedding modes, more specifically, a 2S↔2P transition is observed. No discernible change in the timing of vortex formation is found to accompany the transition. Modal decomposition of the velocity field is employed to exemplify the interaction of the imposed symmetrical perturbation and the intrinsic antisymmetrical instability of the near wake.
Breakdown of Chapman-Enskog expansion and the anisotropic effect for lattice-Boltzmann models of porous flow
Authors: Nie Xiaobo , Martys Nicos S.
Published: January 2007

Lattice-Boltzmann based models are frequently used to study fluid flow in porous media. The macroscopic governing equations as well as the viscosity and the permeability for such models are usually determined using a Chapman-Enskog expansion approach. However, this approach has been validated numerically only for a narrow range of the viscosity and the permeability. We have analytically derived the exact macroscopic governing equations of the lattice-Boltzmann model for the case of simple shear flows in porous media. We find that the effective viscosity in the governing equations is different from the one obtained from the Chapman-Enskog expansion. These findings have been validated numerically. We also find that the effective viscosity is anisotropic. Implications for modeling flow in porous media are discussed.
Lagrangian velocity structure functions in Bolgiano turbulence
Authors: Bistagnino A. , Boffetta G. , Mazzino A.
Published: January 2007

Single-particle Lagrangian velocity statistics in the Bolgiano–Obukhov regime of two-dimensional turbulent convection is investigated. At variance with flows displaying the classical K41 phenomenology, here the leading contribution to the Lagrangian velocity fluctuations is given by the largest eddies. This implies a linear behavior in time for a typical velocity fluctuation in the time interval t. The contribution to the Lagrangian velocity fluctuations of local eddies (i.e., with a characteristic time of order t), whose space/time scalings are ruled by the Bolgiano–Obukhov theory, is thus not detectable by standard Lagrangian statistical observables. To disentangle contributions arising from the large eddies from those of local eddies, a strategy based on exit-time statistics has successfully been exploited. Lagrangian velocity increments in Bolgiano convection thus provide a physically relevant example of a signal with more than smooth fluctuations.
Superheated liquid fragility and thermodynamic refinement for evaluation of metallic glass-forming ability
Authors: Meng Q. G. , Zhang S. G. , Xia M. X. , Li J. G. , Zhou J. K.
Published: January 2007

Based on the super-Arrhenius equation and Angell’s fragility concept [J. Non-Cryst. Solids 131, 13 (1991)], the expression of the fragility parameter for superheated liquid is deduced as M=E∞∕kBTl, where E∞ is the activation energy, kB the Boltzmann constant, and Tl the liquidus temperature. It exhibits a negative correlation with the glass-forming ability (GFA) of the referenced metallic glasses in the same system rather than in the different systems, while the parameter ε based on order-disorder competition is just the opposite. The refined fragility parameter M* (=M∕ε) gives a much better reflection of the GFA for the metallic glasses.
Experimental results from sea trials of an offshore wave energy system
Authors: Waters R. , Stålberg M. , Danielsson O. , Svensson O. , Gustafsson S. , Strömstedt E. , Eriksson M. , Sundberg J. , Leijon M.
Published: January 2007

A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and significant insights discovered. Energy absorption dependency on load as well as output voltage and power is demonstrated. It is shown that great overload capability of the directly driven linear generator is critical, and indicated that, for resistive loads, optimal load does not vary with wave climate. Future grid supplying energy production would necessitate parks of wave power plants in order to reduce power fluctuations.
Initial formation mechanisms of the supersaturation region and the columnar structure in ZnO thin films grown on n-Si (001) substrates
Authors: Yuk J. M. , Lee J. Y. , Jung J. H. , Kim T. W. , Son D. I. , Choi W. K.
Published: January 2007

ZnO thin films were grown on n-Si (001) substrates by using plasma-assisted molecular beam epitaxy. A cross-sectional bright-field transmission electron microscopy (TEM) image showed that small ZnO columnar grains were embedded into large columnar grains, and a selected-area electron diffraction pattern, and an x-ray diffraction pattern showed that the ZnO thin film were nearly c-axis oriented. The evolution of the ZnO columnar structure was analyzed by using the evolution of the strain due to the interaction of the columnar grains, as observed by using high-resolution TEM. The initial formation mechanisms of the supersaturation region and the columnar grains are described.
Infrared scanning near-field optical microscopy observation of low-frequency electromagnetic field effects on functional groups in eukaryotic cells
Authors: Cricenti A. , Generosi R. , Luce M. , Ronci F. , Perfetti P. , Vobornik D. , Margaritondo G. , Sanghera J. S. , Aggarwal I. D. , Tolk N. H. , Piston D. W. , Grimaldi S. , Lisi A. , Rieti S.
Published: January 2007

The authors observed changes in the biochemical properties of eukaryotic cells exposed to an ac magnetic field by infrared scanning near-field optical microscopy. They specifically investigated the changes in the distribution of the inner chemical functional groups and in the cell morphology induced by a 24h exposure to a 1mT (rms), 50Hz sinusoidal magnetic field in a temperature-regulated solenoid. These results accentuate the crucial questions—raised by several recent studies—about the impact of low-frequency electromagnetic field on human cells.
Inelastic buckling of carbon nanotubes
Authors: Wang Q. , Duan W. H. , Liew K. M. , He X. Q.
Published: January 2007

A hybrid continuum mechanics and molecular mechanics model is developed in this letter to predict the critical strain of the inelastic buckling of armchair and zigzag carbon nanotubes (CNTS) with beamlike buckle shapes. The explicit analytical buckling results of the hybrid model are verified by molecular dynamics simulations via the MATERIALS STUDIO software package and by available research findings. The simplicity and effectiveness of the model make it possible to further predict and produce benchmark solutions for the size-dependent buckling results of CNTs. The hybrid model enables thorough understanding of the stability behavior of CNTs and is useful for their applications.
Improved hydrogen storage properties of LiBH4 destabilized by carbon
Authors: Yu X. B. , Wu Z. , Chen Q. R. , Li Z. L. , Weng B. C. , Huang T. S.
Published: January 2007

The hydrogen storage properties of LiBH4 ball milled with various ratios of carbon nanotubes (Cnano) were investigated. The LiBH4∕Cnano mixtures showed superior dehydrogenation, hydrogen desorption starting at 250°C, and the majority of hydrogen being released below 600°C. The rehydrogenation results revealed that the Li2C2, formed during the dehydrogenation, could be reversed to LiH, in which the hydrogen capacity corresponds to 1∕4 of the original hydrogen content of LiBH4, and C at 10MPa hydrogen pressure and 400°C.
Influence of a large oblique incident angle on energetic protons accelerated from solid-density plasmas by ultraintense laser pulses
Authors: Zhou C. T. , He X. T.
Published: January 2007

The acceleration of energetic electron, proton, and heavy ion beams produced by ultrahigh-intensity laser pulses through thin plastic targets is studied using two-dimensional hybrid particle-in-cell simulation. When the laser is incident at a large angle, the proton beams accelerated from the front and rear surfaces of the target deviate from the normal direction because of the formation of non-Gaussian asymmetric sheath field at the target surfaces. In particular, the simulations clearly show that the proton beam in the backward direction can have higher Bragg peak energy than that of the forward direction if the incident angle is sufficiently large.
Control of the defect in the liquid crystal director field on the slit of the patterned vertical alignment cell
Authors: Lee Gi-Dong , Son Jung-Hee , Choi Yong-Hyun , Lju Jae-Jin , Kim Kyeong Hyeon , Lee Seung Hee
Published: January 2007

In this letter the authors studied the method to control the position of the generated defect on the slit of the patterned vertical alignment liquid crystal (LC) cell with dynamic stability. The authors modeled the LC director field with a defect on the slit and proposed an advanced wing pattern with a defect trap to stick the defect outside the active area. This shape can prevent the generation of the defect on the slit in the active area even if the authors increase the operation voltage, so that the LC dynamics on the slit is very stable and optical transmittance becomes higher.