bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption from alkane+perfluoroalkane mixtures at fluorophobic and fluorophilic surfaces. II. Crossover from critical adsorption to complete wetting
Authors: Bowers James , Zarbakhsh Ali , Querol Aranzazu , Christenson Hugo K. , McLure Ian A. , Cubitt Robert
Published: November 2004

Using neutron reflectometry, adsorption from an equimolar mixture of hexane+perfluorohexane to a fluorophobic, octadecyl-coated, silicon substrate has been investigated as a function of temperature in the one-phase region upon approach to liquid-liquid coexistence. The composition of the investigated mixture, xF=0.50, is well removed from the critical composition of xF=0.36, where xF is the perfluorohexane mole fraction. To aid the modeling, mixtures with three different neutron refractive index contrasts have been used: namely, mixtures of C6H14+C6F14 (H–F), C6D14+C6F14 (D–F), and a mixture of C6H14+C6D14+C6F14 which has been adjusted to have the same refractive index as silicon (CMSi). For all three contrasts, the principal features of the composition profile normal to the interface follow similar trends as the temperature T is reduced towards T0, the coexistence temperature. These features consist of: (i) a hexane-rich primary adsorption layer appended to the octadecyl coupled layer. This primary layer is 22±5 Å thick and becomes increasingly enriched in hexane as T0 is approached. (ii) A tail that decays exponentially towards the bulk composition with a characteristic decay length ζ. As T0 is approached, ζ increases. The scattering length density profiles have been converted to volume fraction profiles and the surface excess of hexane Γ has been determined as a function of temperature for all three contrasts. As T0 is approached Γ increases, and its behavior can be represented using the scaling law Γ∼|T−T0|−m. The resulting values of m are 0.71±0.09, 0.68±0.04, and 0.68±0.06 for the D–F, H–F, and CMSi contrasts, respectively. The behavior of Γ with temperature does not adhere to the Γ∼|T−T0|−1/3 law expected for complete wetting in systems with van der Waals interactions nor does it correspond to Γ∼|T−Tc|−0.305 expected for critical adsorption. The magnitude of the exponent m indicates that the adsorption resides in the crossover region between critical adsorption and complete wetting.
Orientational structures in confined smectic-C domains in Langmuir monolayers
Authors: Reigada R. , Abad E. , Crusats J. , Claret J. , Ignés-Mullol J. , Sagués F.
Published: November 2004

Droplet smectic-C domains in films of surfactant molecules exhibit different orientational textures. For these systems we formulate a kinetic model based on a free energy functional containing bulk (elastic) and surface interactions. Numerical simulations for the corresponding relaxational equation show the existence of two different equilibrium configurations with a centered defect. In particular, when the elastic terms dominate, bend-shaped textures appear, whereas for strong boundary effects mixed bend/splay conformations are displayed. A variational analysis for the free energy functional confirms the validity of the above numerical results. The stability of textures with centered defects with respect to the formation of periferic defects (boojums) is also discussed qualitatively. The above theoretical predictions are compared with experimental results from Brewster angle microscopy imaging of azobenzene Langmuir monolayers.
Structure formation in films of weakly charged block polyelectrolyte solutions
Authors: Kyrylyuk A. V. , Fraaije J. G. E. M.
Published: November 2004

A mean-field dynamic density functional theory is used to describe a phase diagram of concentrated solutions of weakly charged flexible block polyelectrolytes in a film. Electrostatics is taken into account by applying the local electroneutrality constraint (the Donnan membrane equilibrium approach). In the Donnan limit it is assumed that a salt added to the solution perfectly screens long-range electrostatic interactions. The phase diagram of a solution of a triblock polyelectrolyte in a film as a function of the solvent concentration and the charge of the polyelectrolyte (solvophilic) block is calculated for a given film thickness. The phase behavior of the block polyelectrolyte film arises from the interplay between surface-induced alignment and the electrostatically-driven structure formation. The observed mesoscopic structures (lamellar, perforated lamellar, cylindrical, micellar, and mixed phases) are oriented parallel to the surfaces for the considered case of morphologies unfrustrated by the film thickness. Structures with connections between parallel layers (bicontinuous, etc.) are not formed. As a result of surface-induced ordering, the region of ordered phases in a film is wider than in bulk and the phase boundary between ordered and disordered phases is more diffuse. As in the case of unconfined block polyelectrolyte solution, the solution in a film does not follow the lyotropic sequence of phases of such a block copolymer upon increase in the charge of the polyelectrolyte block. Upon changing the charge of the solvophilic copolymer block, transformations of copolymer morphology take place via change in curvature of polymeric domains. Due to confinement of a polyelectrolyte film, no swelling of solvophilic domains is observed.
Line-imaging velocimeter for shock diagnostics at the OMEGA laser facility
Authors: Celliers P. M. , Bradley D. K. , Collins G. W. , Hicks D. G. , Boehly T. R. , Armstrong W. J.
Published: November 2004

A line-imaging velocity interferometer has been implemented at the OMEGA laser facility of the Laboratory for Laser Energetics, University of Rochester. This instrument is the primary diagnostic for a variety of experiments involving laser-driven shock-wave propagation, including high-pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh–Taylor experiments, and shock timing experiments for inertial confinement fusion research. Using a laser probe beam to illuminate a target, the instrument measures shock breakout times at temporal resolutions as low as 20 ps, and spatial resolution ∼4 μm. For velocity measurements the detection limit is <0.1 km/s, and velocities of interfaces, free surfaces, and shock fronts traveling through transparent media can be measured with accuracies ∼1% over the range from 4 km/s to greater than 50 km/s. Quantitative measurements of the optical reflectance of ionizing shock fronts can also be obtained simultaneously with the velocity measurements.
Precise formation of nanoscopic dots on polystyrene film using z-lift electrostatic lithography
Authors: Juhl Shane , Phillips David , Vaia Richard A. , Lyuksyutov Sergei F. , Paramonov Pavel B.
Published: November 2004

Z -lift electrostatic lithography on thin (10–50nm) polystyrene (PS) films is discussed. The height of nanostructures can be controlled via mechanically drawing or depressing the cantilever height (z-lift) during the application of a voltage. Since polymer is not removed or crosslinked during structure formation, the features are erasable. Various aspects such as voltage doses, film thickness, z-lift height, and rate are explored. Structure height formation relies mainly on, and is proportional, to the z-lift magnitude; however, only a narrow range of voltages yields structures for any given film thickness. Structures ranging from 0–10nm are produced on a 40nm thick PS film using −36V by varying the z-lift on a 0.1–0.9N∕m cantilever from −20nm to +400nm.
Theoretical optimization of the self-organized growth of nanoscale arrays through a figure of merit
Authors: Vasco E.
Published: November 2004

A figure of merit is proposed in order to optimize the self-organized growth of nanoscale elements into one-/two-dimensional arrays via a fine selection of the deposition/annealing conditions. This figure of merit has been designed to account for the most significant defects inherent in such arrays. Its versatility has been studied by kinetic Monte Carlo simulations of self-organized growth of metal clusters on the 7×7 reconstructed Si(111) surface. The optimization relationships between deposition/annealing conditions and characteristics of the metal-on-Si(111)7×7 systems are obtained and analyzed within the framework of competition between thermodynamical tendencies and kinetic limitations.
Femtosecond broadband stimulated Raman spectroscopy: Apparatus and methods
Authors: McCamant David W. , Kukura Philipp , Yoon Sangwoon , Mathies Richard A.
Published: November 2004

The laser, detection system, and methods that enable femtosecond broadband stimulated Raman spectroscopy (FSRS) are presented in detail. FSRS is a unique tool for obtaining high time resolution (<100 fs) vibrational spectra with an instrument response limited frequency resolution of <10 cm−1. A titanium:Sapphire-based laser system produces the three different pulses needed for FSRS: (1) A femtosecond visible actinic pump that initiates the photochemistry, (2) a narrow bandwidth picosecond Raman pump that provides the energy reservoir for amplification of the probe, and (3) a femtosecond continuum probe that is amplified at Raman resonances shifted from the Raman pump. The dependence of the stimulated Raman signal on experimental parameters is explored, demonstrating the expected exponential increase in Raman intensity with concentration, pathlength, and Raman pump power. Raman spectra collected under different electronic resonance conditions using highly fluorescent samples highlight the fluorescence rejection capabilities of FSRS. Data are also presented illustrating our ability: (i) To obtain spectra when there is a large transient absorption change by using a shifted excitation difference technique and (ii) to obtain high time resolution vibrational spectra of transient electronic states.
Strong charge carrier confinement in purely strain induced GaAs∕InAlAs single quantum wires
Authors: Schuster R. , Hajak H. , Reinwald M. , Wegscheider W. , Schuh D. , Bichler M. , Abstreiter G.
Published: November 2004

We report on micro-photoluminescence studies of single quantum wires which were grown by molecular beam epitaxy. Employing the cleaved edge overgrowth technique, quantum wires located in an overgrown (011) oriented GaAs quantum well originate purely from the tensile strain field of InAlAs layers grown along the [100] direction. These stressor layers are separated by 1-μm-wide AlGaAs barriers so that the photoluminescence signals of different quantum wires can be resolved individually. Their confinement energy varies systematically with the widths of the stressor and overgrown layers, reaching values as high as 51.5meV. The quantum wire signals are characterized by a smooth line shape even for the lowest excitation powers, indicating the absence of pronounced exciton localization.
Anisotropic photoconductivity of InGaAs quantum dot chains measured by terahertz pulse spectroscopy
Authors: Cooke D. G. , Hegmann F. A. , Mazur Yu. I. , Ma W. Q. , Wang X. , Wang Z. M. , Salamo G. J. , Xiao M. , Mishima T. D. , Johnson M. B.
Published: November 2004

We report results of time-resolved terahertz (THz) pulse spectroscopy experiments on laterally ordered chains of self-assembled InGaAs quantum dots photoexcited with 400nm, 100fs laser pulses. A large anisotropy in the transient photoconductive response is observed depending on the polarization of the THz probe pulse with respect to the orientation of the dot chains. Fast (3.5–5ps) and efficient carrier capture into the dots and one-dimensional wetting layers underneath the dot chains is observed below 90K. At higher temperatures, thermionic emission into the two-dimensional wetting layers and barriers becomes significant and the anisotropy in the photoconductive signal is reduced.
Precipitate-free films of La1−xSrxMnO3 grown on the substrates with artificial step edges
Authors: Ishii Y. , Sato H. , Sawa A. , Yamada T. , Akoh H. , Endo K. , Kawasaki M. , Tokura Y.
Published: November 2004

We have fabricated precipitate-free La0.7Sr0.3MnO3 (LSMO) films by locating precipitate nucleation at artificial step edges patterned on SrTiO3 substrates and absorbing excess species of off-stoichiometry by getter effect. The precipitate-free and atomically flat area of about 10μm width can be obtained along the step edges by pulsed-laser deposition at a substrate temperature Ts of ∼900°C. Thermally activated processes are shown to be involved in such chemical reactions between the precipitates and surface migrating species. LSMO∕SrTiO3∕LSMO tunnel junctions fabricated by this method showed an excellent uniformity of the junction resistances.
Vertically emitting annular Bragg lasers using polymer epitaxial transfer
Authors: Green William M. J. , Scheuer Jacob , DeRose Guy , Yariv Amnon
Published: November 2004

Fabrication of a planar semiconductor microcavity, composed of cylindrical Bragg reflectors surrounding a radial defect, is demonstrated. A versatile polymer bonding process is used to transfer active InGaAsP resonators to a low-index transfer substrate. Vertical emission of in-plane modes lasing at telecom wavelengths is observed under pulsed optical excitation with a submilliwatt threshold.
Quantitative comparison of rare-gas cold cathode discharge metastable atomic beam sources
Authors: Palmer A. J. , Baker M. , Sang R. T.
Published: November 2004

Two commonly used cold cathode discharge sources to create rare gas metastable atomic beams are experimentally compared with respect to the output flux and the most probable velocity of the resulting beams. The systems are characterized with the same detection system thereby enabling an unambiguous performance comparison. The results of the experiments show that there is a clear distinction between the output beam characteristics of the beam sources.
Moissanite (SiC) as windows and anvils for high-pressure infrared spectroscopy
Authors: Liu Zhenxian , Xu Jian , Scott Henry P. , Williams Quentin , Mao Ho-kwang , Hemley Russell J.
Published: November 2004

The optical properties of the moissanite (single-crystal 6H-SiC) and its performance as anvil material for high-pressure infrared spectroscopic measurements have been examined. Tests were carried out to 53 GPa using moissanite anvil cells combined with synchrotron radiation and globar as infrared sources. In the region of characteristic phonon absorption of diamond (1900–2300 cm−1), the transmitted signal measured through 4 mm of moissanite single crystals is 5–10 times higher than that obtained with type-II diamond anvils. No significant change of the transmission spectra through the moissanite anvils was observed over the pressure range studied; however, we also present mid infrared absorption spectra of powdered SiC to 43 GPa.
Fractal character of the spectrum in the vicinity of a local mode in linear chains with isotopic impurities
Authors: Ivanov M. A. , Molodid V. S. , Skripnik Yu. V.
Published: November 2004

The vibrational spectrum of a one-dimensional disordered chain of atoms with light isotopic substitutional impurities is calculated numerically for frequencies near a local mode of an isolated impurity atom. It is shown that in the entire frequency region accessible to the calculation, the spectrum does indeed have the characteristic features of a fractal. Series of lines clustered around the lines of an isolated impurity atom or of two and three impurity atoms are examined. It is shown that in these cases a self-similar structure is preserved at arbitrary reductions of the scale both outside and inside the concentration broadening region.
Low-temperature ESR spectrum in a powder sample of Cu(C10H8N2)(H2O)2SO4
Authors: Kravchyna O. , Kaplienko A. , Kajnakova M.
Published: November 2004

The ESR spectrum of a powder sample of the metal-organic complex Cu(C10H8N2)(H2O)2SO4 is investigated in the temperature interval 2–30 K. It is found that the orbital ground level of the Cu2+ ion in this compound is the Kramers doublet |x2−y2〉. The temperature dependences of the effective g-factor components and of the resonance linewidth ΔH of individual powder particles are obtained. Low-temperature broadening of the resonance line connected with short-range magnetic order in the system is observed. An estimate of the value of the exchange coupling in the magnetic system is made.
Femtosecond time-resolved dispersion relation of complex nonlinear refractive index in a semiconductor quantum well
Authors: Inuzuka Fumikazu , Misawa Kazuhiko , Nishi Kenichi , Lang Roy
Published: November 2004

We present simultaneous measurement of femtosecond time-resolved nonlinear phase and amplitude changes around the excitonic resonance of the AlGaAs∕GaAs quantum well using polarization-division Sagnac interferometer. The nonlinear complex refractive index of the semiconductor material for all-optical devices is successfully determined from directly measured nonlinear phase and amplitude changes.
Fabrication and performance of efficient blue light emitting III-nitride photonic crystals
Authors: Chen Lu , Nurmikko Arto V.
Published: November 2004

We have fabricated and characterized a light emitting photonic crystal slab in the blue near 460nm, based on InGaN quantum well active material. A multilayer nanopattern transfer technique was developed to fabricate these optical structures. The dependence of the photoluminescence enhancement on specific pattern dimension, coupled with distinct polarization characteristics of emission, was found to be in good agreement with theoretical simulations, thereby supporting the existence of photonic crystal band gap. The results suggest that practical fabrication of photonic crystal slabtype light emitting diodes for enhanced external quantum efficiency in the blue and ultraviolet is feasible.
Observation of negative thermo-optical coefficient in cubic MgZnO thin films
Authors: Zhou H. P. , Shen W. Z. , Chen N. B. , Wu H. Z.
Published: November 2004

We report on the investigation of thermo-optical coefficient (dn∕dT) in cubic MgZnO thin films through temperature-dependent (10–295K) optical transmission measurements. As a result of potential fluctuation, we observe an anomalous thermal behavior of the band gap in the ternary MgZnO alloy, which limits the observation of negative dn∕dT up to 200K. The negative dn∕dT is evidenced by the phase shift from the prominent Fabry-Pérot interference fringes and modeled by taking into account the thermal and electronic background contribution, as well as the Wannier exciton effect. It is found that the large thermal expansion in cubic MgZnO plays a key role in the observed negative dn∕dT.
Current transport mechanism in InGaP∕GaAsSb∕GaAs double-heterojunction bipolar transistors
Authors: Yan B. P. , Hsu C. C. , Wang X. Q. , Yang E. S.
Published: November 2004

We have developed InGaP∕GaAsSb∕GaAs double-heterojunction bipolar transistors (DHBTs) with low turn-on voltage and high current gain by using a narrow energy bandgap GaAsSb layer as the base and an InGaP layer as the emitter. The current transport mechanism is examined by measuring both of the terminal currents in forward and reverse mode. The results show that the dominant current transport mechanism in the InGaP∕GaAsSb∕GaAs DHBTs is the transport of carriers across the base layer. This finding suggests that the bandgap offset produced by incorporating Sb composition into GaAs mainly appears on the valence band and the conduction-band offset in InGaP∕GaAsSb heterojunction is very small.
Z
eff
profile measurements from bremsstrahlung imaging in the MAST spherical tokamak
Authors: Patel A. , Carolan P. G. , Conway N. J. , Akers R. J.
Published: November 2004

A bremsstrahlung diagnostic has been deployed on the Mega Ampere Spherical Tokamak (MAST), with matrix viewing of the full plasma cross section in a narrow region of the continuum free of spectral lines. An uncooled CCD detector is used to provide 100 Hz 128×128 matrix viewing of the plasma emissivity which is spectrally selected using an interference filter of only ∼0.5 nm bandwidth. The apparently conflicting demands of a large field of view for the plasma and the small solid angle for narrow spectral bandwidth is accommodated in a compact lens, filter, and detector arrangement. Using measured electron temperature and density profiles the Zeff profile evolution is determined.
Design and construction of a four-point bending based set-up for measurement of piezoresistance in semiconductors
Authors: Lund Eivind , Finstad Terje G.
Published: November 2004

We describe an experimental set-up for measurement of piezoresistivity coefficients of crystalline semiconductors, especially p-type silicon. We have aimed at good control of doping and temperature as well as the magnitude and the direction of applied stress and electric field. This is realized by applying the stress by the well known four point bending technique to a Si beam cut from a wafer. The set-up allows for high precision mechanical loading and alignment. The mechanical loading is done by a piezoelectric actuator. This allows us to cycle the load within a closed environment. A fiber optical interferometer has been developed to measure the center deflection of the Si beams. We derive analytical expressions relating center deflection to mechanical stress. From the analytical expressions we estimate the measurement uncertainty due to imperfections in alignment and machining. We also evaluate other factors. We have good accuracy and excellent repeatability and we find that thermal effects sets the limit of uncertainty of our measurements. We measure the coefficients of piezoresistivity with an accuracy of 2%–3% when we compensate for thermal drift during the measurement.
Transport properties of highly conductive n-type Al-rich AlxGa1−xN(x⩾0.7)
Authors: Nakarmi M. L. , Kim K. H. , Zhu K. , Lin J. Y. , Jiang H. X.
Published: November 2004

We report here the growth and transport studies of conductive n-type AlxGa1−xN alloys with high Al contents (x⩾0.7). Si-doped AlxGa1−xN alloys were grown by metalorganic chemical vapor deposition on AlN-epilayer∕sapphire substrates with very smooth surface. Low n-type resistivities have been obtained for Al-rich AlxGa1−xN alloys. The resistivity was observed to increase rapidly with increasing x due to the deepening of the Si donor energy level. Transport measurements have indicated that we have achieved n-type conduction in pure AlN. From the temperature dependence of the resistivity, the donor activation energy was estimated to vary from 23to180meV as x was increased from 0.7 to 1.0.
Improving the sensitivity of frequency modulation spectroscopy using nanomechanical cantilevers
Authors: Chernobrod B. M. , Berman G. P. , Milonni P. W.
Published: November 2004

It is suggested that nanomechanical cantilevers can be employed as high-Q filters to circumvent laser noise limitations on the sensitivity of frequency modulation spectroscopy. In this approach, a cantilever is actuated by the radiation pressure of the amplitude modulated light that emerges from an absorber. Numerical estimates indicate that laser intensity noise will not prevent a cantilever from operating in the thermal noise limit, where the high Q’s of cantilevers are most advantageous.
Subpicosecond Faraday effect in Cd1−xMnxTe and its application in magneto-optical sampling
Authors: Rey-de-Castro R. , Wang D. , Zheng X. , Verevkin A. , Sobolewski Roman , Mikulics M. , Adam R. , Kordoš P. , Mycielski A.
Published: November 2004

We present our studies on a subpicosecond Faraday effect in diluted magnetic semiconducting Cd1−xMnxTe single crystals and its application in a magneto-optical (MO) sampling system for time-resolved detection of ultrafast current pulses. The measurements were performed at 10 K. We used the Cd0.38Mn0.62Te crystal as the active MO medium and a low-temperature-grown free-standing GaAs photoconductive switch integrated into a coplanar transmission line as the picosecond electrical pulse generator. We observed subpicosecond MO transients that correspond to the intrinsic MO low-temperature response in the Cd1−xMnxTe system with the high Mn concentration. The current sensitivity of our MO system was found to be ∼0.1mA. We have demonstrated that the MO sampling technique using the Cd0.38Mn0.62Te transducer is as fast as the standard LiTaO3, electro-optical sampling technique and allows for a complementary (magnetic-field component) characterization of electrical picosecond transients in ultrafast switching devices. Observation of the subpicosecond Faraday effect in Cd1−xMnxTe crystals makes them very attractive for ultrafast optical modulators.
Low-cost apparatus for measuring undispersed particles in extruded plastic ribbon
Authors: Barshick C. M. , Jameson M. N. , Cockerham K. C.
Published: November 2004

An apparatus was designed and constructed that quantitatively measures the number and size of poorly dispersed particles ( >3 μm diameter) that protrude above the surface of an extruded plastic ribbon (0.10–0.15 mm thick). Major components of the apparatus include a set of in-house fabricated dispensing and take-up wheels for guiding the ribbon’s path, a commercially available variable differential transducer, and custom-designed software based on National Instruments’ LABVIEW platform. The reproducibility and repeatability of the technique are presented, along with data comparing this approach to more conventional, albeit labor-intensive manual approaches.
Kelvin probe force microscopy as a tool for characterizing chemical sensors
Authors: Grover R. , Carthy B. Mc , Zhao Y. , Jabbour G. E. , Sarid D. , Laws G. M. , Takulapalli B. R. , Thornton T. J. , Gust D.
Published: November 2004

We report on the use of Kelvin probe force microscopy in measuring the shift of the contact potential difference of micron-scale areas. The experimental results provide important information required for understanding and modeling the electrical characteristics of chemically sensitive field-effect transistors (ChemFETs). The temporal evolution in the shift of the contact potential difference of chemically sensitive monolayers of free-base porphyrin and zinc-porphyrin on exposure to pyridine gas was studied and their different behavior observed. The Kelvin probe force microscopy data on nanometer-scale areas were in agreement with those obtained with a conventional Kelvin probe on centimeter-scale areas. The accuracy of the measured shift in contact potential difference upon exposure to trace amounts of gas indicates the utility of Kelvin probe force microscopy as a means to characterize the operation of exposed-gate ChemFETs.
Visualization of graphite atomic arrangement by stereo atomscope
Authors: Matsui Fumihiko , Daimon Hiroshi , Guo Fang Zhun , Matsushita Tomohiro
Published: November 2004

The direct visualization of an atomic arrangement is essential for understanding the nature of materials. The rotation of forward focusing peaks in photoelectron angular distribution (PEAD) patterns excited by circularly polarized light with the opposite helicities are found to be the same as the parallax in stereo view. Taking advantage of this phenomenon of PEAD circular dichroism, the three-dimensional atomic arrangement image of graphite crystal was realized. Taking a stereo picture around carbon atom, which has been thought difficult due to a small angular momentum of photoelectron, proved that this method is applicable to all materials including biomolecules.
Bistable bend-splay liquid crystal display
Authors: Yu X. J. , Kwok H. S.
Published: November 2004

A bistable liquid crystal display based on the bend and splay configurations has been demonstrated. This display can be switched between the bend and splay deformation in a three-electrode configuration and has infinite bistable lifetime. It also has wide viewing angles, excellent contrast ratios, and very fast selection. Selection electric pulse duration of 50μs can be used to switch this display, implying the possibility of a high information content applications.
The photocapacitor: An efficient self-charging capacitor for direct storage of solar energy
Authors: Miyasaka Tsutomu , Murakami Takurou N.
Published: November 2004

A light-driven self-charging capacitor was fabricated as an efficient solar energy storage device. The device, which we name the photocapacitor, achieves in situ storage of visible light energy as an electrical power at high quantum conversion efficiency. The photocapacitor was constructed on a multilayered photoelectrode comprising dye-sensitized semiconductor nanoparticles/hole-trapping layer/activated carbon particles in contact with an organic electrolyte solution, in which photogenerated charges are stored at the electric double layer. Repeated charge-discharge cycles with a charging voltage of >0.45V yielded a capacitance of 0.69Fcm−2.
Determination of the nitrogen distribution in InGaNAs∕GaAs quantum wells by transmission electron microscopy
Authors: Litvinov D. , Gerthsen D. , Rosenauer A. , Hetterich M. , Grau A. , Gilet Ph. , Grenouillet L.
Published: November 2004

We report on measurements of the nitrogen-concentration profile in an InGaNAs heterostructure by high-resolution transmission electron microscopy. Two samples grown by gas-source molecular-beam epitaxy on GaAs(001) substrates were investigated which contain InGaAs and InGaNAs wells with the same thickness and In concentration. The indium concentration was determined by high-resolution x-ray diffractometry. Indium-concentration profiles were obtained with the composition evaluation by lattice fringe analysis (CELFA) technique from the sample with the InGaAs wells exploiting the chemical sensitivity of the diffracted (002) beam. Nitrogen-concentration profiles were measured in the InGaNAs wells by comparison of the CELFA results observed in the samples with and without nitrogen.
Surface acoustic wave ultraviolet photodetectors using epitaxial ZnO multilayers grown on r-plane sapphire
Authors: Emanetoglu Nuri W. , Zhu Jun , Chen Ying , Zhong Jian , Chen Yimin , Lu Yicheng
Published: November 2004

A surface acoustic wave (SAW) ultraviolet (UV) photodetector is made of a zinc oxide (ZnO) based epitaxial multilayer structure on an r-plane sapphire (r-Al2O3) substrate. Piezoelectric and semiconducting ZnO layers are used for SAW excitation and photodetection, respectively. A thin Mg0.2Zn0.8O layer grown between the two ZnO layers isolates the semiconducting layer from the piezoelectric one. In contrast to previously reported SAW UV detectors on GaN and LiNbO3, the Sezawa SAW mode in the ZnO∕r-Al2O3 system is used for its high acoustic velocity and large maximum effective piezoelectric coupling constant. The interaction of the SAW with the photogenerated carriers in the semiconducting ZnO layer results in a phase shift and an insertion loss change, as functions of light wavelength and power. The ZnO SAW UV detector can be used as a passive zero-power remote wireless UV sensor.
High-order corrected fields of ultrashort, tightly focused laser pulses
Authors: Hua J. F. , Ho Y. K. , Lin Y. Z. , Chen Z. , Xie Y. J. , Zhang S. Y. , Yan Z. , Xu J. J.
Published: November 2004

High-order correction to the fields of ultrashort, tightly focused laser pulses expressed in power series of ε=1∕(ω0t0) and s=1∕(k0w00) (ω0=ck0 the central oscillatory frequency, t0 the pulse duration for half period, w00 the beam waist radius at the central frequency ω0), are derived. These expressions can be used to describe accurately the fields of laser pulses, and are suitable for practical calculations. The first-order correction terms to the fields based on paraxial approximation are explicitly given. They are applied to a simulation study of electron dynamics in laser pulse field with special attention given to the vacuum laser acceleration scheme. We found that as long as ω0t0>20, the zeroth-order approximation (long pulse approximation) is adequate for describing the interaction. For ω0t0<20, higher-order corrections have to be taken into account.
Influence of image force potential on the shot noise properties of field emitters
Authors: Rangaswamy K. , Cahay M. , Jensen K. L.
Published: November 2004

The shot noise power spectrum of the emission current from planar metallic cathodes is calculated taking into account the effects of the image force potential in front of the cathode. For metals with low work function, the Fano factor which characterizes the reduction of the shot noise power SIem below the Schottky result 2qIem (where q is the magnitude of the charge of the electron and Iem is the time average of the emitted current) is calculated as a function of the applied external electric field and is found to be reduced substantially below the value calculated when the effects of the image charge potential are neglected. A study of the temperature dependence of the Fano factor can be used to estimate the temperature dependence of the work function of the cathode material.
Composition profiling of InAs∕GaAs quantum dots
Authors: Lemaître A. , Patriarche G. , Glas F.
Published: November 2004

We propose a simple and straightforward technique to measure the composition distribution of In(Ga)As∕GaAs quantum dots (QDs). This method is based on the quantitative analysis of 002 dark field image contrast in cross-sectional transmission electron microscopy. InAs∕GaAs QDs show strong InGaAs alloying resulting in the formation, prior to capping, of an inverted indium composition gradient, with higher In concentration at the top. Such a mechanism implies a large Ga mass transport from the substrate. The capping process is also investigated. It strongly affects the QD shape by dissolving the apex via surface migration of indium atoms away from the dot.
Current modulation of a hygroscopic insulator organic field-effect transistor
Authors: Bäcklund T. G. , Sandberg H. G. O. , Österbacka R. , Stubb H.
Published: November 2004

We have fabricated solution processable polymer transistors with high conductivity, requiring only a few volts for obtaining good current modulation. The devices can be fabricated and operated in air and the operation is greatly enhanced in humid atmosphere. Devices reach an On∕Off ratio of about 600 and a subthreshold swing of 500mV per decade operating on voltages less than 2V. In this letter the mechanism behind the current modulation is investigated, and we show that the current is modulated through ion-assisted oxidation and reduction of the semiconductor by ions moving vertically in the insulator material to the transistor channel.
Periodic precipitation of crystalline Ge nanoparticles in Ge–B–SiO2 thin glass films
Authors: Nishiyama Hiroaki , Miyamoto Isamu , Matsumoto Shin-ichi , Saito Mitsunori , Fukumi Kohei , Kintaka Kenji , Nishii Junji
Published: November 2004

Crystalline 20- to 40-nm-diam Ge nanoparticles were precipitated periodically in Ge–B–SiO2 thin glass films fabricated by the plasma-enhanced chemical vapor deposition method. Such a periodic structure was created by exposure to an interference pattern with a KrF excimer laser (248nm wavelength) and successive annealing at 600°C. Nanoparticles were precipitated predominantly in the unirradiated region after photoinduced refractive index change was erased completely after annealing up to 500°C.
Preparation of ruthenium dioxide nanorods and their field emission characteristics
Authors: Hsieh Chih-Sung , Tsai Dah-Shyang , Chen Reui-San , Huang Ying-Sheng
Published: November 2004

RuO 2 nanometer-sized rods with pyramidal tips have been grown on Cu-coated Si(100) substrates using metalorganic chemical vapor deposition. The geometry of these nanorods resembles an obelisk with an off-center tip. The aspect ratios of nanorod tips are between 0.55 and 0.73. The field emission properties of the RuO2 nanorods are studied and the stability of its emission current is assessed. The field emission results demonstrate that RuO2 nanorods material is an emitter of potential.
Scanning probe microscopy with inherent disturbance suppression
Authors: Sparks A. W. , Manalis S. R.
Published: November 2004

We introduce a general approach for inherently suppressing out-of-plane disturbances in scanning probe microscopy that enables higher-resolution imaging, particularly in noisy environments. In this approach, two distinct sensors simultaneously measure the probe–sample separation. One sensor measures a spatial average over a large sample area while the other responds locally to topography underneath the nanometer-scale probe. When the localized sensor is used to control the probe–sample separation in feedback, the spatially distributed sensor signal reveals only topography. We implemented this approach on a scanning tunneling microscope using a microcantilever with an integrated tunneling tip and interferometer. For disturbances applied normal to the sample, we measure −50dB of disturbance suppression at 1Hz, compared to 0dB with conventional imaging.
High-efficiency and low-voltage p-i-n electrophosphorescent organic light-emitting diodes with double-emission layers
Authors: He Gufeng , Pfeiffer Martin , Leo Karl , Hofmann Michael , Birnstock Jan , Pudzich Robert , Salbeck Josef
Published: November 2004

We demonstrate high-efficiency organic light-emitting diodes by incorporating a double-emission layer (D-EML) into p-i-n-type cell architecture. The D-EML is comprised of two layers with ambipolar transport characteristics, both doped with the green phosphorescent dye tris(phenylpyridine)iridium. The D-EML system of two bipolar layers leads to an expansion of the exciton generation region. Due to its self-balancing character, accumulation of charge carriers at the outer interfaces is avoided. Thus, a power efficiency of approximately 77 lm∕W and an external quantum efficiency of 19.3% are achieved at 100cd∕m2 with an operating voltage of only 2.65 V. More importantly, the efficiency decays only weakly with increasing brightness, and a power efficiency of 50 lm∕W is still obtained even at 4000cd∕m2.
Single-molecule spontaneous emission close to absorbing nanostructures
Authors: Thomas M. , Greffet J.-J. , Carminati R. , Arias-Gonzalez J. R.
Published: November 2004

The spontaneous emission of a single molecule is substantially modified close to a metallic nanostructure. We study the spectral behavior of the radiative and nonradiative decay rates and of the local-field factor in the vicinity of a plasmon resonance. We show that the highest fluorescence enhancement is obtained for an emission wavelength redshifted from the plasmon resonance, and that quenching always dominates at plasmon resonance. These results may have experimental implications in spectroscopy and monitoring of elementary light sources.
Tunable laser using micromachined grating with continuous wavelength tuning
Authors: Liu A. Q. , Zhang X. M. , Tang D. Y. , Lu C.
Published: November 2004

This letter develops a method that is able to optimize the grating pivot position to obtain maximum continuous tuning range for a Littrow laser, and also verifies the method by implementation of a single-chip integrated laser using the microelectromechanical systems (MEMS) technology. The laser consists of a semiconductor gain chip, a microlens, and a MEMS blazed grating arranged in the Littrow configuration. The laser is integrated onto a single silicon chip while maintaining the ability of continuous tuning in a large range. It has a compact size of 2.0mm×1.5mm×0.6mm, and has obtained a tuning range of 30.3nm with a resolution of 0.03nm∕V2, a maximum power of 0.4dBm and a side mode suppression ratio of 26dB. Other merits include fast tuning speed, improved mechanical/wavelength stability, batch fabrication, and low cost.
Giant exchange anisotropy observed in Mn–Ir∕Co–Fe bilayers containing ordered Mn3Ir phase
Authors: Imakita Ken-ichi , Tsunoda Masakiyo , Takahashi Migaku
Published: November 2004

Exchange anisotropy of Mn73Ir27∕Co70Fe30 bilayers fabricated on a 50-nm-thick Cu under layer by changing the substrate temperature (Tsub) during the deposition of Mn–Ir layer was investigated, correlating with the crystallographic structure of Mn–Ir layer. The unidirectional anisotropy constant (JK) of the bilayers remarkably varied as a function of Tsub. After the thermal annealing of bilayers at 320 °C in a magnetic field of 1 kOe, JK steeply increased from 0.3 to 1.3erg∕cm2, as Tsub was raised from room temperature to 170 °C. The blocking temperature was enhanced from 270 to 360 °C, simultaneously. The JK of 1.3erg∕cm2 is nearly ten times larger than the values reported in Mn–Ir∕Co–Fe bilayers early in the research of them. The x-ray diffraction profiles showed that the ordered Mn3Ir phase was formed in the antiferromagnetic layer with increasing Tsub. From the coincidence of enhancing JK and increasing peak intensity of superlattice diffraction lines, the Mn3Ir phase was suggested to be an origin of the giant JK and the high blocking temperature.
Hydrophobic hydration of alkanes: Its implication for the property of amorphous solid water
Authors: Souda Ryutaro
Published: November 2004

We measured the incorporation of adsorbed alkanes in and their desorption from the amorphous solid water (ASW) by means of secondary ion mass spectroscopy and temperature programmed desorption. The heavier alkanes such as butane and hexane are incorporated completely in the bulk of the nonporous ASW layer below 100 K probably due to the preferential formation of ice structures around the solute molecules. The self-diffusion of water molecules occurs above the glass transition temperature (136 K). The liquid water emerges above 165 K, as evidenced by simultaneous occurrence of the dehydration of alkanes and the morphological change of the water layer induced by the surface tension.
Modelling of nutrient partitioning in growing pigs to predict their anatomical body composition. 2. Model evaluation
Authors: Halas V. , Dijkstra J. , Babinszky L. , Verstegen M. W. A. , Gerrits W. J. J.
Published: November 2004

The objective of the present paper was to evaluate a dynamic mechanistic model for growing and fattening pigs presented in a companion paper. The model predicted the rate of protein and fat deposition (chemical composition), rate of tissue deposition (anatomical composition) and performance of pigs depending on nutrient intake. In the model evaluation, the predicted response of the pig to changes in model parameters and to changes in nutrient intakes is presented. As a result of the sensitivity analysis, changes in the maintenance energy requirements and the fractional degradation rate of muscle protein had the greatest impact on tissue deposition rates. The model was also highly sensitive to changes in the maximum velocity and steepness parameter of the lysine utilisation for muscle protein synthesis. The model was further tested by independent published results. The model successfully predicted the response of pigs to a wide range of variation in nutrient composition. Consequently, the model can be applied to develop feeding strategies to optimise pig production. It also enables prediction of the slaughter performance and the meat quality.
Strain-Specific Effects of Alachlor on Murine Olfactory Mucosal Responses
Authors: Genter Mary Beth , Goss Kathleen H. , Groden Joanna
Published: November 2004

Chloracetanilide herbicides are multisite carcinogens in rodents. Progression of alachlor-induced olfactory tumors in rats is accompanied by cytoplasmic accumulation and nuclear localization of β-catenin, suggesting activation of Wnt signaling. Female CD-1 mice were resistant to alachlor-induced olfactory carcinogenesis. The current studies were performed to determine whether ApcMin /+ mice, which have activated Wnt signaling due to mutation of the second allele of Apc, would be susceptible to alachlor olfactory carcinogenesis. Female and male ApcMin /+ mice, as well as Apc+ /+ littermates received alachlor in the diet (260 mg/kg/d) for up to 3 months. Female A/J and C57BL/6J wild-type mice were also treated (for 10 and 14 months, respectively), as these strains vary in sensitivity to many respiratory tract insults. No olfactory mucosal tumors were observed in any of the mice, although alachlor-treated ApcMin /+ mice developed histological changes similar to those in alachlor-treated rats. Alachlor-treated A/J mice developed pronounced intracellular accumulation of amorphous eosinophilic material in the olfactory mucosa, foci of respiratory-like metaplasia, and hyperplasia of nasal mucus glands. A similar but less intense response was seen in C57BL/6J mice. Mice and rats had equivalent levels of the putative bioactivating enzyme (CYP2A) in olfactory mucosa, and mice had induced hepatic CYP3A and CYP2B enzymes with alachlor treatment, which may increase alachlor elimination. These studies extend previous observations by describing alachlor-induced olfactory mucosal changes in mice and suggest that hepatic metabolic enzyme induction may be responsible for resistance of mice to alachlor-induced olfactory carcinogenesis.
Eye Movements of Highly Skilled and Average Readers: Differential Effects of Frequency and Predictability
Authors: Ashby Jane , Rayner Keith , Clifton Charles
Published: November 2004

This study offers a glimpse of the moment-by-moment processes used by highly skilled and average readers during silent reading. The eye movements of adult readers were monitored while they silently read sentences. Fixation durations and the spatial–temporal patterns of eye movements were examined to see whether the two groups of readers exhibited differential effects of frequency and/or predictability. In Experiment 1, high- and low-frequency target words were embedded in nonconstraining sentence contexts. In Experiment 2, the same participants read high- and low-frequency target words that were either predictable or unpredictable, embedded in highly constraining sentence contexts. Results indicated that when target words appeared in highly constraining sentence contexts, the average readers showed different effects of frequency and predictability from those shown in the highly skilled readers. It appears that reading skill can interact with predictability to affect the word recognition processes used during silent reading.
The Molecular Adapter Carma1 Controls Entry of IκB Kinase into the Central Immune Synapse
Authors: Hara Hiromitsu , Bakal Christopher , Wada Teiji , Bouchard Denis , Rottapel Robert , Saito Takashi , Penninger Josef M.
Published: November 2004

Carma1 (also known as caspase recruitment domain [CARD]11, Bimp3) is a CARD-containing membrane-associated guanylate kinase family protein that plays an essential role in antigen receptor–induced nuclear factor κB activation. We investigated the role of Carma1 in the assembly of signaling molecules at the immune synapse using a peptide-specific system. We report that Carma1 is essential for peptide-induced interleukin 2 and interferon γ production, but dispensable for proliferation in T cells. Recruitment and distribution of T cell receptor, lymphocyte function associated 1, lipid rafts, and protein kinase C (PKC)θ to central and peripheral immune synapse regions occur normally in Carma1−/− T cells. Carma1 controls entry of IκB kinase (IKK) into lipid raft aggregates and the central region of the immune synapse, as well as activation of IKK downstream of PKC. Our data provide the first genetic evidence on a new class of molecular scaffold that controls entry of defined signaling components, IKK, into the central supramolecular activation cluster at T cell–antigen-presenting cell interfaces without having any apparent effect on the overall organization and formation of immune synapses.