bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetism and magneto-optics of nanocrystalline Ni∕Pt multilayers grown by e-beam evaporation at room temperature
Authors: Papaioannou E. Th. , Angelakeris M. , Flevaris N. K. , Fumagalli P. , Mueller Ch. , Troupis A. , Spanou A. , Karoutsos V. , Poulopoulos P. , Kapaklis V. , Politis C.
Published: January 2007

We report on magnetic and magneto-optic property aspects of nanocrystalline Ni∕Pt multilayers grown by e-beam evaporation at room temperature. X-ray diffraction and atomic force microscopy measurements show high degree of multilayer sequencing and formation of nanocrystals with a relatively narrow size distribution. Magneto-optic polar Kerr effect experiments reveal a spin-polarized Pt contribution at around 3.3eV and enhanced room temperature Kerr rotation for samples with very thin Pt layers surrounded by thicker Ni layers. The uniaxial anisotropy constants are obtained by simulating the magnetization curves and a tendency for perpendicular magnetic anisotropy is observed.
Electronic collective transport in disordered array of C49-phase TiSi2 nanocrystals in Si
Authors: Ruffino F. , Piro A. M. , Piccitto G. , Grimaldi M. G.
Published: January 2007

We have studied the longitudinal electronic collective transport properties in a disordered array of TiSi2 nanocrystals (with surface density of 1012cm−2) embedded in Si polycrystalline matrix as a function of temperature. The system is characterized by a high degree of disorder compared to the standard disordered nanocrystal array usually studied in the literature. Despite of this fundamental difference, we demonstrate that the theoretical models used to describe the collective electronic transport in standard systems are adequate to describe the electrical behavior of such a “nonstandard” system. In particular, we show that two different conduction regimes, separated by a crossover temperature T*, exist: at T<T* the collective electronic transport is characterized by a Coulomb blockade phenomenon (with a positive threshold voltage) and a scaling behavior characteristic of a two-dimensional transport. Above T*, at low field, a thermally activated conduction mechanism is evident, and at high field the collective electron transport is again characterized by a two-dimesional scaling behavior with an effective negative threshold voltage.
Capacitor-loaded split ring resonators as tunable metamaterial components
Authors: Aydin K. , Ozbay E.
Published: January 2007

Transmission through split ring resonator (SRR) structures loaded with capacitors is investigated both experimentally and numerically. Magnetic resonance frequency (ωm) is observed to shift to lower frequencies when capacitors are mounted to the various capacitive regions of the SRR structure. The amount of change in ωm depends strongly on the place where the capacitors are loaded. The magnetic resonance is obtained at 0.99GHz with subwavelength SRR size of λ∕42 when the capacitor (C=2.2pF) is integrated at the split region of the outer ring.
Role of spatial distortions on the quadratic nonlinear optical properties of octupolar organic and metallo-organic molecules
Authors: Bidault Sébastien , Brasselet Sophie , Zyss Joseph , Maury Olivier , Le Bozec Hubert
Published: January 2007

Following on the recent experimental demonstration of a discrepancy between the nonlinear optical (NLO) behavior of several π-conjugated chromophores and their assumed octupolar symmetry, the authors investigate how geometrical distortions influence the NLO response of multipolar push-pull molecules. Their analytical model is set on a basis of valence-bond and charge-transfer states to estimate the hyperpolarizability of organic and metallo-organic chromophores using the lowest possible number of variables. Since symmetry breakdown changes the definition of the molecular Cartesian framework, tensorial spherical coordinates are implemented. The evolution of the nonlinear molecular anisotropy with possible rotational deviations is then evaluated for two recently studied chromophores. Zero-frequency calculations show that, outside optical resonance, weak geometrical distortions lead to strong anisotropy variations in agreement with experimental data. Their goal is to underscore which molecular engineering strategies should be applied when designing a photoisomerizable nonlinear octupole.
Density functional theory and multireference configuration interaction studies on low-lying excited states of TiO2
Authors: Grein Friedrich
Published: January 2007

Using density functional theory at the BPW91∕6-311+G(3df) level, optimized geometries and energies of the lowest singlet, triplet, and quintet A1, A2, B1, B2(C2v) states of the TiO2 molecule were obtained. TiO2 has a A11 ground state in C2v symmetry. Adiabatic excitation energies of the low-lying singlet and triplet states range from 2.1to3.0eV. The A21,3 states optimize at bond angles of about 140°, lying only 0.06eV below linear Δu1,3, whereas B11,3 and B21,3, with bond angles of 120° and 96°, respectively, lie 0.3–0.4eV below the respective Πu1,3 or Δu1,3 states. Minima with short O–O distances of ∼1.46Å, at energies of 4.2 and 4.7eV, were found for A11 and A13. The C2v minima of the lowest B11 and B13 states are saddle points, suggesting lower-energy structures in Cs symmetry. The C2v quintet states start at energies of 5.7eV. Multireference configuration interaction (MRCI) methods, employing a polarized valence triple-zeta basis set, lead to similar geometries and energies. MRCI vertical excitation energies up to 4.6eV and oscillator strengths are given. The calculated excitation energy of 2.2eV for B21 agrees well with 2.3eV from a fluorescence spectrum. The vertical electron detachment energy of TiO2− is 1.5eV, in good agreement with 1.6eV from anion photoelectron spectroscopy. An observed second photoelectron band corresponds to B21 and/or B23, but the assignment of a third band could not be verified. Vibrational frequencies, ionization energies, electron affinities, and dissociation energies are given.
Fabrication of three-dimensional calixarene polymer waveguides using two-photon assisted polymerization
Authors: Ishihara Jiro , Komatsu Kyoji , Sugihara Okihiro , Kaino Toshikuni
Published: January 2007

Low-loss three-dimensional (3D) polymer optical waveguide was fabricated using a two-photon assisted polymerization method. Calixarene derivatives were selected as core material with good thermal stability and transparency. To fabricate 3D waveguide, photopolymerizable polymers composed of two types of monomers were used. Core shape was controlled by adjusting an astigmatism of objective lens. Refractive index difference between a core and a cladding was formed by exclusion effect of one monomer. Propagation loss at 1.3μm wavelength was low, 0.72dB∕cm, without using deuterium or fluorine but using hydrogen. Using this technique, 3D 1×3 splitter polymer waveguide was fabricated.
Measurement and analysis of thermopower and electrical conductivity of an indium antimonide nanowire from a vapor-liquid-solid method
Authors: Seol Jae Hun , Moore Arden L. , Saha Sanjoy K. , Zhou Feng , Shi Li , Ye Qi Laura , Scheffler Raymond , Mingo Natalio , Yamada Toshishige
Published: January 2007

It has been suggested by theoretical calculation that indium antimonide (InSb) nanowires can possess improved thermoelectric properties compared to the corresponding bulk crystal. Here we fabricated a device using electron beam lithography to measure the thermopower and electrical conductivity of an individual InSb nanowire grown using a vapor-liquid-solid method. The comparison between the measurement results and transport simulations reveals that the nanowire was unintentionally degenerately doped with donors. Better control of the impurity doping concentration can improve the thermoelectric properties.
Improved performances of organic light-emitting diodes with metal oxide as anode buffer
Authors: You Han , Dai Yanfeng , Zhang Zhiqiang , Ma Dongge
Published: January 2007

We demonstrate extremely stable and highly efficient organic light-emitting diodes (OLEDs) based on molybdenum oxide (MoO3) as a buffer layer on indium tin oxide (ITO). The significant features of MoO3 as a buffer layer are that the OLEDs show low operational voltage, high electroluminescence (EL) efficiency and good stability in a wide range of MoO3 thickness. A green OLED with structure of ITO∕MoO3∕N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidene (NPB)∕NPB: tris(8-hydroxyquinoline) aluminum (Alq3):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)∕Alq3∕LiF∕Al shows a long lifetime of over 50000h at 100cd∕m2 initial luminance, and the power efficiency reaches 15lm∕W. The turn-on voltage is 2.4V, and the operational voltage at 1000cd∕m2 luminance is only 6.9V. The significant enhancement of the EL performance is attributed to the improvement of hole injection and interface stability at anode.
Defect-free twisted-nematic cells with low pretilt using chiral polyimide surfaces
Authors: Choi Suk-Won , Takanishi Yoichi , Ishikawa Ken , Takezoe Hideo
Published: January 2007

The authors have demonstrated a technique for rodlike liquid crystal alignment using polyimide films with chiral carbons in the side chains. The authors succeeded in lifting degeneracy of two twisted configurations in the 90° twisted-nematic cells, even though the pretilt angle in the cell with rubbed polyimide (PI) surfaces is low (Θ⩽1°). This phenomenon is due to chirality of molecular level on the PI surfaces, which is transferred to the bulk and acts as a kind of symmetry breaking powers.
Control of hole distribution through isovalent R-cation substitution in Cu2Ba2RCu2O8 superconductors
Authors: Karppinen M. , Abe Y. , Grigoraviciute I. , Chen J. M. , Liu R. S. , Yamauchi H.
Published: January 2007

Superconductive Cu2Ba2RCu2O8 samples with R ranging from Gd to Tm have been synthesized through a sol-gel route. Both iodometric titration and Cu L-edge x-ray absorption near-edge structure (XANES) spectroscopy data indicate that the average Cu valence remains constant, whereas Tc increases with decreasing size of the R constituent. An explanation for this trend is revealed from O K-edge XANES spectra, which show that the smaller-for-larger R-cation substitution results in a shift of holes from the Cu2O2 charge reservoir to the superconductive CuO2 planes. Since Cu2Ba2RCu2O8 samples are underdoped, such a shift of holes raises the value of Tc.
Efficient current injection scheme for nitride vertical cavity surface emitting lasers
Authors: Castiglia A. , Simeonov D. , Buehlmann H. J. , Carlin J.-F. , Feltin E. , Dorsaz J. , Butté R. , Grandjean N.
Published: January 2007

The authors report the realization of InGaN∕GaN light emitting diodes (LEDs) with an electrical injection design suitable for vertical cavity surface emitting lasers. Controlled oxidation of an AlInN interlayer lattice matched to GaN allows confining the injected current in a 3μm diameter aperture. Submicron-scale characterization of the current flow and optical properties is achieved by means of microelectroluminescence measurements. LEDs can be safely driven, in continuous mode operation, up to current densities higher than 20kA∕cm2.
Optical fiber taper coupling and high-resolution wavelength tuning of microdisk resonators at cryogenic temperatures
Authors: Srinivasan Kartik , Painter Oskar
Published: January 2007

A system for studying microcavity resonators at cryogenic temperatures (∼10K) through evanescent coupling via optical fiber taper waveguides is reported, and efficient fiber coupling to AlGaAs microdisk cavities with embedded quantum dots is demonstrated. As an immediate application of this tool, the authors study high-resolution tuning of microdisk cavities through nitrogen gas adsorption, as first discussed by Mosor et al. [Appl. Phys. Lett. 87, 141105 (2005)]. By proper regulation of the nitrogen gas flow and delivery of the gas to the sample surface, continuous tuning can be achieved with modest gas flows, and overall wavelength shifts as large as 4nm are achieved.
Fast all-optical switching using ion-implanted silicon photonic crystal nanocavities
Authors: Tanabe Takasumi , Nishiguchi Katsuhiko , Shinya Akihiko , Kuramochi Eiichi , Inokawa Hiroshi , Notomi Masaya , Yamada Koji , Tsuchizawa Tai , Watanabe Toshifumi , Fukuda Hiroshi , Shinojima Hiroyuki , Itabashi Seiichi
Published: January 2007

On-chip all-optical switching based on the carrier plasma dispersion in an argon ion (Ar+) implanted photonic crystal (PhC) nanocavity that is connected to input/output waveguides is described. A high dose of Ar+ is introduced, and annealing is used to recrystallize the silicon and thus create dislocation loops at the center of the PhC slab. Dislocation loops enable the fast recombination of the carriers, which allows a fast switching recovery time for PhC switches. The switching window (∼70ps) is three times smaller than that without ion implantation, while the required operating energy remains almost the same (<100fJ).
Hybrid inorganic/organic microstructured light-emitting diodes produced using photocurable polymer blends
Authors: Gu E. , Zhang H. X. , Sun H. D. , Dawson M. D. , Mackintosh A. R. , Kuehne A. J. C. , Pethrick R. A. , Belton C. , Bradley D. D. C.
Published: January 2007

Light-emitting diodes (LEDs) in the form of a one-dimensional array of microstripes emitting at 370nm were fabricated from AlInGaN inorganic semiconductor. These microlight sources were then used to “directly write” microstructures in photocurable blends of organic light-emitting polymers (LEPs) spin coated onto the LED surface. In this way, thin microstripes of LEP as narrow as 50μm have been fabricated and integrated with the micro-LEDs. These “self-aligned” polymer microstripes serve as wavelength downconverters under further excitation by the UV micro-LEDs, producing hybrid inorganic/organic microstructured LEDs.
Irreversibility of magnetization rotation in exchange biased Fe/epitaxial-FeF2 thin films
Authors: Olamit Justin , Liu Kai , Li Zhi-Pan , Schuller Ivan K.
Published: January 2007

Magnetization reversal via rotation is typical in ferromagnet/antiferromagnet exchange biased systems. The reversibility of the rotation is a manifestation of the microscopic reversal process. The authors have investigated the magnetization reversal in Fe/epitaxial-FeF2 thin films using vector magnetometry and first-order reversal curves. The reversal is predominantly by rotation as the applied field makes an angle with the antiferromagnet spin axis, mostly irreversible at small angles and reversible at larger angles. A modified Stoner-Wohlfarth model reproduces the overall trend of the irreversibility evolution. The remaining discrepancies between the modeled and measured irreversibilities may be attributed to local incomplete domain walls.
Role of external cavity reflectivity for achieving polarization control and stabilization of vertical cavity surface emitting laser
Authors: Arizaleta Arteaga Mikel , López-Amo Manuel , Thienpont Hugo , Panajotov Krassimir
Published: January 2007

The authors present the experimental results showing how the external mirror reflectivity affects the polarization properties of a vertical cavity surface emitting laser subject to optical feedback from an extremely short external cavity. The amplitude of modulation of the polarization switching current with the external cavity length is found to be proportional to the external mirror reflectivity, confirming its key role in achieving polarization control and stabilization of such lasers using optical feedback. Numerical simulations presented here show good agreement with experiments.
Mitigating plasma constriction using dielectric barriers in radio-frequency atmospheric pressure glow discharges
Authors: Shi J. J. , Liu D. W. , Kong M. G.
Published: January 2007

It is known that radio-frequency (rf) atmospheric glow discharges with bare electrodes are susceptible to plasma constriction at large discharge currents. This is undesirable for large-scale applications, even though large currents usually lead to abundant plasma reactive species and high application efficiency. In this letter, an experimental investigation is presented to demonstrate that plasma constriction can be mitigated by introducing dielectric barriers to the electrodes. The resulting atmospheric rf dielectric-barrier discharge is shown to operate in the γ mode of large discharge current while maintaining its discharge volume. This improves significantly plasma stability and the application potential.
Conductivity of carbon nanotube polymer composites
Authors: Wescott James T. , Kung Paul , Maiti Amitesh
Published: January 2007

Dissipative particle dynamics simulations were used to investigate methods of controlling the assembly of percolating networks of carbon nanotubes (CNTs) in thin films of block copolymer melts. For suitably chosen polymers the CNTs were found to spontaneously self-assemble into topologically interesting patterns. The mesoscale morphology was projected onto a finite-element grid and the electrical conductivity of the films computed. The conductivity displayed nonmonotonic behavior as a function of relative polymer fractions in the melt. Results are compared and contrasted with CNT dispersion in small-molecule fluids and mixtures.
Uniformity enhancement of carbon nanofiber emitters via electrical discharge machining
Authors: Ok Jong Girl , Kim Bo Hyun , Sung Woo Yong , Chu Chong Nam , Kim Yong Hyup
Published: January 2007

A very simple, clean, and effective method based on a reliable machining process called electrical discharge machining (EDM) was introduced in order to enhance the field emission uniformity of carbon nanofibers (CNFs). After an EDM post-treatment, the uniformity of the CNF emitters was clearly improved without contaminations, damages, or crystalline deteriorations of the CNFs. As a result, field emission uniformity was apparently enhanced at a low electric field range, promising that the method can be practical for applications requiring both large size and fine uniformity such as in a backlight unit.
SiGeO layer formation mechanism at the SiGe/oxide interfaces during Ge condensation
Authors: Balakumar S. , Peng Suo , Hoe K. M. , Agarwal A. , Lo G. Q. , Kumar R. , Balasubramanian N. , Kwong D. L. , Tripathy S.
Published: January 2007

The letter presents the fabrication processes to realize high Ge content SiGe on insulator using Ge condensation technique with and without intermittent oxide etching. During condensation process with intermittent silicon oxide etching, the formation of an undesirable amorphous SiGeO is observed. This is due to uncontrolled oxidation of silicon when the oxide layer is etched away. In the case of Ge condensation process without oxide etching, the authors could achieve a SiGe layer with 91% Ge concentration. A crystalline SiGeO layer at the interfaces of the top silicon oxide and buried oxide with SiGe was also observed. Possible formation mechanisms of amorphous and crystalline SiGeO are presented. Ge condensation process without SiO2 etching utilizes four steps of oxidation and intermittent annealing cycles at each temperature resulted in Si0.09Ge0.91OI substrate.
Dissipative force modulation Kelvin probe force microscopy applying doubled frequency ac bias voltage
Authors: Nomura Hikaru , Kawasaki Kenichiro , Chikamoto Takuma , Li Yan Jun , Naitoh Yoshitaka , Kageshima Masami , Sugawara Yasuhiro
Published: January 2007

The authors propose a surface potential measurement technique using dissipative force modulation (DM) method with an ac bias voltage of doubled harmonic frequency (2ω) of the oscillating cantilever (2ωDM method). The effect of the stray capacitance between a cantilever and a sample on electrostatic force spectroscopy/Kelvin probe force microscopy measurement is almost completely removed in 2ωDM method, since the distance dependence of the modulated electrostatic force increases from 1∕z to 1∕z2. 2ωDM method has an advantage of high force sensitivity due to the high Q factor of the cantilever in vacuum. The authors demonstrate quantitative surface potential measurement by using dissipative tip-sample interactions.
Studies on the cluster sizes in the mixed-phase thin films
Authors: Zhou Qing-li , Jin Kui-juan , Lu Hui-bin , Hu Chun-lian , Zhao Kun , Guan Dong-yi , Yang Guo-zhen
Published: January 2007

Based on the phase separation scenario, by simulating the resistivity of La0.33Pr0.34Ca0.33MnO3 film with the known coexisting-phase sizes, the authors have obtained the theoretical ferromagnetic (FM) cluster sizes of La2∕3Ca1∕3MnO3 film, showing around 0.6μm near Tc. Subsequently the insulator-metal transition occurs when the cluster grows up to 0.7μm, and the abrupt drop in resistivity occurs when the size is around 0.9μm. Furthermore, the FM cluster sizes grow with the magnetic field. The obtained results indicate that the model and method can be used to predict the critical size of the clusters at the phase transition for the mixed-phase materials.
Sol-gel prepared β-Ga2O3 thin films for ultraviolet photodetectors
Authors: Kokubun Yoshihiro , Miura Kasumi , Endo Fumie , Nakagomi Shinji
Published: January 2007

β - Ga 2 O 3 thin films have been prepared on (0001) sapphire substrates by the sol-gel method. X-ray diffraction showed that β-Ga2O3 polycrystalline films were formed at heat-treatment temperatures above 600°C. With increasing heat-treatment temperature above 900°C, the lattice constants of the β-Ga2O3 films decreased, while the band gap increased. Planar geometry photoconductive detectors based on the sol-gel prepared β-Ga2O3 thin films have been fabricated. They showed the photoresponse only for the wavelengths shorter than 270nm, which correspond to the solar-blind region. The peak wavelength in the spectral response depended on the heat-treatment temperature in the sol-gel process.
Large scale ab initio molecular dynamics simulations of hydrogen-induced degradation of Ta diffusion barriers in ultralow-k dielectric systems
Authors: Dai Ling , Tan V. B. C. , Yang Shuo-Wang , Wu Ping , Chen Xian-Tong
Published: January 2007

In ultralow-k dielectric systems, the porous dielectrics are normally sealed by a SiC film before the deposition of a Ta diffusion barrier layer. However, the Ta barrier effects are negated when the SiC films are fabricated by plasma-enhanced chemical vapor deposition (PECVD). Through large scale ab initio molecular dynamics simulations, the authors found that the barrier degradation is due to H atoms introduced during PECVD. The H impurities diffuse into and transform an otherwise dense Ta layer into a loose amorphous phase which is ineffective as a diffusion barrier.
Hexagon and square patterned air discharges
Authors: Dong Lifang , He Yafeng , Liu Weili , Gao Ruiling , Wang Hongfang , Zhao Haitao
Published: January 2007

Hexagon and square patterned air discharges are realized by using a dielectric barrier discharge device with two water electrodes. With increasing voltage, the filaments (plasma columns) tend to be dense and regularly arranged, and the current in each half cycle changes from several peaks to one leading peak followed by a broad hump of current peaks. It shows that the spatiotemporal correlation between filaments is enhanced with increasing voltage. A phase diagram of hexagon patterned air discharge with different gas gap widths as a function of air pressure and applied voltage is presented.
Organic photovoltaic devices with Ga-doped ZnO electrode
Authors: Owen J. , Son M. S. , Yoo K.-H. , Ahn B. D. , Lee S. Y.
Published: January 2007

The authors report two organic photovoltaic devices using a Ga-doped ZnO (GZO) film as a transparent conducting electrode. In the first structure, the conventional In2O3:Sn hole-collecting anode was replaced by GZO and an efficiency of 0.35% was obtained. The second has the inverse structure where GZO was used as the electron-collecting cathode and gave a nonoptimized device efficiency of about 1.4%. Furthermore, this inverse structure of GZO devices provides a passivation layer to protect the active layer from the atmosphere.
Ferrite-ferroelectric hybrid wave phase shifters
Authors: Ustinov A. B. , Srinivasan G. , Kalinikos B. A.
Published: January 2007

A dual, electric and magnetic field tunable microwave phase shifter based on the propagation of hybrid spin-electromagnetic waves in a ferrite-ferroelectric bilayer is discussed. The bilayer consists of a single-crystal yttrium iron garnet film and a ceramic barium strontium titanate slab. The electrical tunability of the differential phase shift Δφ is achieved through the application of a voltage across barium strontium titanate. An insertion loss of 20dB and a continuously variable Δφ as high as 650° in the frequency range of 4.5–8GHz are measured.
Correlation between diamond grain size and hydrogen retention in diamond films studied by scanning electron microscopy and secondary ion mass spectroscopy
Authors: Michaelson Sh. , Ternyak O. , Hoffman A. , Lifshitz Y.
Published: January 2007

The present work studies the incorporation of hydrogen in chemical vapor deposited polycrystalline diamond films with different grain sizes. Scanning electron microscopy and secondary ion mass spectroscopy were applied to investigate the film microstructure and hydrogen retention in the films, respectively. The present study provides the direct evidence of hydrogen concentration dependence on diamond grain size. The hydrogen retention in the diamond films increases with decreasing grain size, indicating that hydrogen is bonded and trapped in the grain boundary region. The two different sources—methane and hydrogen molecules—contribute to the hydrogen retention according to their abundance in the gas mixture.
Control of strain status in SiGe thin film by epitaxial growth on Si with buried porous layer
Authors: Usami Noritaka , Kutsukake Kentaro , Nakajima Kazuo , Amtablian Sevak , Fave Alain , Lemiti Mustapha
Published: January 2007

Single crystalline Si with buried porous layers was utilized as a substrate for the epitaxy of 100-nm-thick Si0.73Ge0.27. Raman spectroscopy revealed that the strain status in SiGe systematically changes according to the variation in the porosity of the substrate and that the strain relaxation in SiGe was found to proceed with increasing porosity. Furthermore, Si was found to be tensilely strained to reduce the compressive strain in SiGe. These results suggest that the appropriate design of the porosity and the thickness of the thin Si layer on the buried porous layer offers an alternative way to control strain status in SiGe.
Magnetic anisotropy in the ferromagnetic Cu-doped ZnO nanoneedles
Authors: Herng T. S. , Lau S. P. , Yu S. F. , Yang H. Y. , Wang L. , Tanemura M. , Chen J. S.
Published: January 2007

Copper-doped ZnO (ZnO:Cu) nanoneedles exhibiting room-temperature ferromagnetism were fabricated by an ion beam technique using Cu plate and ZnO film. A saturated magnetization moment of 0.698emu∕cm3 was found in the nanoneedles when a field of 10kOe was applied perpendicular to the substrate, which was 15% larger than the field applied parallel to the substrate. The magnetic ordering of the nanoneedles was enhanced significantly to 0.968emu∕cm3 after annealing of 400°C for 20min. However, the magnetic anisotropy at high field is vanished but an “easy plane” ferromagnetism becomes apparent at low field region. The possible mechanisms of the magnetic ordering and anisotropy in the ZnO:Cu nanoneedles are discussed.
Enhanced tunable properties of Ba0.6Sr0.4TiO3 thin films grown on Pt∕Ti∕SiO2∕Si substrates using MgO buffer layers
Authors: Zhu Weicheng , Cheng Jinrong , Yu Shengwen , Gong Jia , Meng Zhongyan
Published: January 2007

Ba 0.6 Sr 0.4 Ti O 3 (BST) thin films were prepared on MgO buffered Pt(111)∕Ti∕SiO2∕Si substrates by pulsed laser deposition. The crystallographic structure, interface characteristics, and dielectric properties of BST thin films are strongly dependent on MgO thickness. BST thin films exhibit (111) preferred orientation when MgO layer is thicker than 5nm. The MgO layer can mitigate the interdiffusion between BST and Pt, causing the dielectric loss and leakage current of BST thin films to decrease significantly. The dielectric loss, tunability, and the largest figure of merit of BST thin films on 10nm MgO achieve 0.009, 30%, and 33.4, respectively.
Fabrication and characterization of red-emitting electroluminescent devices based on thiol-stabilized semiconductor nanocrystals
Authors: Bertoni Cristina , Gallardo Diego , Dunn Steve , Gaponik Nikolai , Eychmüller Alexander
Published: January 2007

Thiol-capped CdTe nanocrystals were used to fabricate light-emitting diodes, consisting of an emissive nanocrystal multilayer deposited layer by layer, sandwiched between indium tin oxide and aluminum electrodes. The emissive and electrical properties of devices with different numbers of nanocrystal layers were studied. The improved structural homogeneity of the nanocrystal multilayer allowed for stable and repeatable current- and electroluminescence-voltage characteristics. These indicate that both current and electroluminescence are electric-field dependent. Devices were operated under ambient conditions and a clear red light was detected. The best performing device shows a peak external efficiency of 0.51% and was measured at 0.35mA∕cm2 and 3.3V.
Highly efficient transparent organic light-emitting diodes by ion beam assisted deposition-prepared indium tin oxide cathode
Authors: Ryu Seung Yoon , Choi Sang Hun , Kim Jong Tae , Kim Chang Su , Baik Hong Koo , Jeong Hee Seong
Published: January 2007

The authors have investigated the effects of indium tin oxide (ITO) deposited by ion beam assisted e-beam evaporation on the performance of polymer light-emitting diodes. ITO was evaporated as a cathode onto a thin Mg:Ag layer by an e-beam process, and its performance as a transparent cathode was subsequently compared to that of Mg:Ag and sputtering-prepared ITO. Polymer devices’ luminance and efficiency were improved by more than ten times by ion beam assisted deposition (IBAD)-prepared ITO deposition, with little observable damage to the organic layer. Implementation of the IBAD process resulted in the reduction of the interfacial energy barrier which induced band bending. Furthermore, outcoupling with ITO resulted in enhanced luminance.
Towards a generalized representation of surface effects on pressure-driven liquid flow in microchannels
Authors: Chakraborty Suman
Published: January 2007

This letter postulates a generalized fundamental formulation to model the influence of surface characteristics on pressure-driven liquid transport through microchannels. Probabilistic effects pertaining to the influence of roughness elements and uncertainties in wall conditions due to the presence of a random distribution of nanobubbles are represented spectrally by employing a stochastic version of the Navier-Stokes equations. A generalized mathematical expression is eventually arrived at, by normalizing these characteristics, which can act as a fundamental scientific guideline towards the design of microfluidic channels.
Corticothalamic feedback enhances stimulus response precision in the visual system
Authors: Andolina Ian M. , Jones Helen E. , Wang Wei , Sillito Adam M.
Published: January 2007

There is a tightly coupled bidirectional interaction between visual cortex and visual thalamus [lateral geniculate nucleus (LGN)]. Using drifting sinusoidal grating stimuli, we compared the response of cells in the LGN with and without feedback from the visual cortex. Raster plots revealed a striking difference in the response pattern of cells with and without feedback. This difference was reflected in the results from computing vector sum plots and the ratio of zero harmonic to the fundamental harmonic of the fast Fourier transform (FFT) for these responses. The variability of responses assessed by using the Fano factor was also different for the two groups, with the cells without feedback showing higher variability. We examined the covariance of these measures between pairs of simultaneously recorded cells with and without feedback, and they were much more strongly positively correlated with feedback. We constructed orientation tuning curves from the central 5 ms in the raw cross-correlograms of the outputs of pairs of LGN cells, and these curves revealed much sharper tuning with feedback. We discuss the significance of these data for cortical function and suggest that the precision in stimulus-linked firing in the LGN appears as an emergent factor from the corticothalamic interaction.
Linkage proof for
PTPN22
, a rheumatoid arthritis susceptibility gene and a human autoimmunity gene
Authors: Michou Laëtitia , Lasbleiz Sandra , Rat Anne-Christine , Migliorini Paola , Balsa Alejandro , Westhovens René , Barrera Pilar , Alves Helena , Pierlot Céline , Glikmans Elodie , Garnier Sophie , Dausset Jean , Vaz Carlos , Fernandes Manuela , Petit-Teixeira Elisabeth , Lemaire Isabelle , Pascual-Salcedo Dora , Bombardieri Stefano , Dequeker Jan , Radstake Timothy R. , Van Riel Piet , van de Putte Leo , Lopes-Vaz Antonio , Prum Bernard , Bardin Thomas , Dieudé Philippe , Cornélis François ,   European Consortium on Rheumatoid Arthritis Families
Published: January 2007

The tyrosine phosphatase
PTPN22
allele
1858T
has been associated with rheumatoid arthritis (RA) and other autoimmune diseases. RA is the most frequent of those multifactorial diseases. The RA association was usually restricted to serum rheumatoid factor positive disease (RF
+
). No interaction was shown with
HLA-DRB1
, the first RA gene. Many case-control studies replicated the RA association, showing an allele frequency increase of ≈5% on average and large variations of population allele frequencies (2.1–15.5%). In multifactorial diseases, the final proof for a new susceptibility allele is provided by departure from Mendel's law (50% transmission from heterozygous parents). For
PTPN22–1858T
allele, convincing linkage proof was available only for type 1 diabetes. We aimed at providing this proof for RA. We analyzed 1,395 West European Caucasian individuals from 465 “trio” families. We replicated evidence for linkage, demonstrating departure from Mendel's law in this subset of early RA onset patients. We estimated the overtransmission of the
1858T
allele in RF
+
families:
T
= 63%,
P
< 0.0007. The
1858T
allele frequency increased from 11.0% in controls to 17.4% in RF
+
RA for the French Caucasian population and the susceptibility genotype (
1858T
/
T
or
T
/
C
) from 20.2% to 31.6% [odds ratio (OR) = 1.8 (1.2–2.8)]. In conclusion, we provided the linkage proof for the
PTPN22–1858T
allele and RF
+
RA. With diabetes and RA,
PTPN22
is therefore a “linkage-proven” autoimmunity gene.
PTPN22
accounting for ≈1% of the RA familial aggregation, many new genes could be expected that are as many leads to definitive therapy for autoimmune diseases.
Regulatory network construction in
Arabidopsis
by using genome-wide gene expression quantitative trait loci
Authors: Keurentjes Joost J. B. , Fu Jingyuan , Terpstra Inez R. , Garcia Juan M. , van den Ackerveken Guido , Snoek L. Basten , Peeters Anton J. M. , Vreugdenhil Dick , Koornneef Maarten , Jansen Ritsert C.
Published: January 2007

Accessions of a plant species can show considerable genetic differences that are analyzed effectively by using recombinant inbred line (RIL) populations. Here we describe the results of genome-wide expression variation analysis in an RIL population of
Arabidopsis thaliana
. For many genes, variation in expression could be explained by expression quantitative trait loci (eQTLs). The nature and consequences of this variation are discussed based on additional genetic parameters, such as heritability and transgression and by examining the genomic position of eQTLs versus gene position, polymorphism frequency, and gene ontology. Furthermore, we developed an approach for genetic regulatory network construction by combining eQTL mapping and regulator candidate gene selection. The power of our method was shown in a case study of genes associated with flowering time, a well studied regulatory network in
Arabidopsis
. Results that revealed clusters of coregulated genes and their most likely regulators were in agreement with published data, and unknown relationships could be predicted.
Octopamine modulates honey bee dance behavior
Authors: Barron Andrew B. , Maleszka Ryszard , Vander Meer Robert K. , Robinson Gene E.
Published: January 2007

Honey bees communicate the location and desirability of valuable forage sites to their nestmates through an elaborate, symbolic “dance language.” The dance language is a uniquely complex communication system in invertebrates, and the neural mechanisms that generate dances are largely unknown. Here we show that treatments with controlled doses of the biogenic amine neuromodulator octopamine selectively increased the reporting of resource value in dances by forager bees. Oral and topical octopamine treatments modulated aspects of dances related to resource profitability in a dose-dependent manner. Dances for pollen and sucrose responded similarly to octopamine treatment, and these effects were eliminated by treatment with the octopamine antagonist mianserin. We propose that octopamine modulates the representation of floral rewards in dances by changing the processing of reward in the honey bee brain. Octopamine is known to modulate appetitive behavior in a range of solitary insects; the role of octopamine in dance provides an example of how neural substrates can be adapted for new behavioral innovations in the process of social evolution.
A Transformer Bridge for Accurate Measurement of Relative Permittivities of Gases and Vapors at Low Pressures
Authors: Kai Bergström  , Lennart Stigmark  , Stig Sunner
Published: January 2007

A transformer bridge suitable for measurements of the temperature dependence of the relative permittivities of compounds in the gas phase has been developed. The transformer has a 1:1 winding ratio, capacitor arrangement is symmetrical and measurements are made with a substitution technique. The operating frequency is 10 kHz. Capacitance resolution is 2 aF, which is equal to a relative sensitivity of 2 parts in 108. As a test of the performance of the instrument, the relative permittivity of pure nitrogen was measured at 25, 35, and 45°C. The results, reduced to 20°C and 101 325 Pa were identical within any single standard deviation. An estimation of possible systematic errors leads to a final absolute value of εrfor nitrogen at 20°C and 101 325 Pa of εr= 1 + (547.3 ± 0.3) × 10-6.
Performance of a Photoionized CO2TEA Laser Seeded with Organic Vapors
Authors: E Daniels  , B Hartmann  , R Lidholt  , G Spångstedt  , O Steinvall
Published: January 2007

The properties of a TEA laser with flash lamp photoionized seed gas have been studied. Many organic compounds were found useful as seed gas. Optimum output was obtained with xylene. Laser action was observed for all lines fromP(8) toP(30) in the 10 micron band, with one resonator mirror replaced by a grating. Numerical calculations served to estimate the influence of excitation parameters on the electron density obtainable in the laser volume. Maximum output energy of 440 mJ in a 0.15 μs pulse was obtained at 10.59 μm, i.e., theP(20) line in a 1:1:1 mixture of He/CO2/N2at atmospheric pressure.
Excited States in Odd Sn Nuclei, A = 109-125
Authors: G Ch Madueme  , L O Edvardson  , L Westerberg
Published: January 2007

Gamma-ray and internal conversion studies of the odd Sn isotopes investigated through (α,n) and (d,p) reactions are reported. A level scheme is proposed for each nucleus. An odd parity state at moderate excitation energy above the 1h
11/2 single quasiparticle state is identified or proposed in each nucleus, some of which are observed for the first time. Individual level structure and the level systematics in the odd tin isotopes are discussed.
Ultraviolet Absorption Spectrum of the CaH Molecule III. A comparison between CaH and CaD spectra in the region 2800-3200 Å
Authors: B Kaving  , B Lindgren
Published: January 2007

The absorption spectrum of CaD has been studied between 2 800 and 3 200 Å. A rotational analysis of ten observed bands and a comparison with the corresponding CaH bands confirm the earlier CaH analysis. A transition with its 0-0 band around 3 061 Å corresponds to the proposed transition from the 5pcomplex of CaH. The 5pσ and 5pπ levels are separated 48.1 cm-1and are close to Hund's coupling case (d). The proposed 4dcomplex in CaD, with transitions around 2 855 and 2 881 Å, is perturbed but does not contradict thed-complex hypothesis.
Parametric Excitation of Standing Electromagnetic Waves
Authors: Egil Leer
Published: January 2007

The threshold for parametric excitation of standing electromagnetic waves by a standing electromagnetic pump wave with the same frequency is derived. We consider a homogeneous plasma and a method based on energy balance is being used. The threshold is found to depend (1) on the amplitude of the electron motion in the pump wave, and (2) on the angle between the direction of this motion and the electric component of the excited wave. Waves in the same mode as the pump wave can more easily be excited than waves in the opposite mode. This instability may be important in ionospheric modification experiments.
The Relative Permittivity of Argon, Carbon Dioxide, and Hydrogen, Determined at 10 kHz Using a Transformer Bridge Method
Authors: Kai Bergström  , Stig Sunner
Published: January 2007

The relative permittivities of argon, carbon dioxide, and hydrogen, were measured at 25°C and atmospheric pressure using a 10 kHz transformer bridge [1]. The results, reduced to 20.0°C and 101 325 Pa and expressed in units of (εr- 1) × 106, were for argon 516.7 ± 0.3; carbon dioxide 922.2 ± 0.4; and hydrogen 253.8 ± 0.2. Errors given are upper limits estimates including (known causes of) systematic errors inherent in the method.
Molecular Dynamics of Methane at Low and Moderate Densities Studied by Cold Neutron Scattering
Authors: L G Olsson
Published: January 2007

In order to study the molecular dynamics of methane at low and moderate densities cold neutron scattering experiments were undertaken with the following target samples:

gas: Temperature 295 K and pressures 15, 70 and 130 atm.

Temperature 198 K and pressure 60 atm.

liquid: Temperature 184 K and pressure 45 atm.

To interpret the experimental data it is necessary to assume that the rotational and translational motions of the molecule scatter neutrons independently. The following result is then obtained:

1. The rotational motion is fairly well reproduced by models close to the free rotation behaviour for all the investigated states.

2. The translational motion at 295 K is described by the ideal gas model only for very dilute systems. Already at the pressure 15 atm the collision narrowing effect is visible. For pressures 15 to 130 atm and the temperature 295 K the rigid sphere model gives the best agreement with the experimental data, while for states around the critical point no available model can satisfactorily reproduce the measured spectra. The observed discrepancies are manifested in a somewhat larger width of the experimental, quasielastic peak than predicted by the theoretical models based on the picture of freely streaming particles making binary collisions.
Polymorphism of Metals. III. Theory of the Temperature-Pressure Phase Diagram of Iron
Authors: Göran Grimvall
Published: January 2007

The temperature-pressure phase diagram of iron is analysed in terms of the microscopic contributions to the free energy, i.e. vibrational, electronic and magnetic excitations. It is shown that the thermodynamic data, when combined with other experimental and theoretical information, require persistent disordered localized magnetic moments in the paramagnetic bcc, fcc and liquid phases but not so for the hcp phase. The bcc-fcc transitions are mainly caused by differences in the electronic and magnetic free energies while the vibrational part plays a minor role.
Experimental and Theoretical Absorptance Profiles of Tracks of Fast Heavy Ions in Nuclear Emulsion
Authors: M Jensen  , L Larsson  , O Mathiesen  , R Rosander
Published: January 2007

Transverse absorptance profiles of 27 tracks of cosmic ray nuclei recorded in Ilford G5 nuclear emulsion have been measured by a nuclear track photometer. Included in the study were nuclei with atomic numbers 14, 16, 20, 24 and 26 with velocities relative to that of light within the interval 0.3 ⩽ 0.8. The experimental absorptance profiles have been compared with theoretical profiles calculated from the δ-ray theory of track formation developed by Katz and coworkers. Taking into account the rescattering of light into the cone of acceptance of the photometer, good agreement has been found between experimental and theoretical profiles within the entire charge and velocity interval. The semi-empirical formula for high aperture photometry is discussed in some detail, as well as the theory of δ-ray production and the transport of electrons and their energy dissipation in nuclear emulsion.
Measured and Calculated Absorptance of Tracks of Fast Heavy Ions in Ilford G5 Nuclear Emulsion
Authors: M Jensen  , O Mathiesen
Published: January 2007

A modified form of the δ-ray theory of track formation developed by Katz and coworkers has been used to calculate the absorptance of tracks of fast heavy ions in Ilford G5 nuclear emulsion. The theoretical data have been compared with results of different photometrical investigations reported in the literature. In most cases the theoretical predictions are found to be in good agreement with experiments. This suggests that the theory can be used in the planning and execution of future experiments, i.e. to optimize the geometry of the photometer and to obtain an absolute charge calibration of the detector. It is shown that the basic photometrical properties of an emulsion stack can be described by a single quantity which can be determined from measurements. Knowing this quantity it is possible to predict the response of the detector system, for different types of photometers. The practical limits of the use of the modified theory at high and low levels of energy dose are discussed.
The Importance of the Time Scale in Radiation Detection Exemplified by Comparing Conventional and Avalanche Semiconductor Detectors
Authors: P A Tove  , Z H Cho  , G C Huth
Published: January 2007

The profound importance of the time scale of a radiation detection process is discussed in an analysis of limitations in energy resolution and timing, with emphasis on semiconductor detectors used for x-ray detection. The "basic event detection time" involves stopping of the particle and creating a distribution of free electrons and holes containing all desired information (energy, time position) about the particle or quantum, in a time ≃ 10-12 s. The process of extracting this information usually involves a much longer time because the signal is generated in the relatively slow process of charge collection, and further prolongation may be caused by signal processing required to depress noise for improving energy resolution. This is a common situation for conventional semiconductor detectors with external amplifiers where time constants of 10-5 - 10-4 s may be optimum, primarily because of amplifier noise. A different situation applies to the avalanche detector where internal amplification helps in suppressing noise without expanding the time scale of detection, resulting in an optimum time of 10-9 - 10-8 s. These two cases are illustrated by plotting energy resolution vs. time constant, for different magnitudes of the parallel and series type noise sources. The effects of the inherent energy spread (due to statistics) and spatial inhomogeneities are also discussed to illustrate the potential of these two approaches for energy and time determination. Two constructional approaches for avalanche detectors are briefly compared, viz. the deep Ga diffused and the Read-diode type design and their respective merits are pointed out. The similar use of internal gain in other types of detectors (gas ionization, scintillation counters) is compared. Although the noise analysis is done for nuclear radiation events, it applies also to the detection of bursts of optical photons such as are encountered in pulsed laser, radar, or high-speed digital optical communications.