bluuebunny/crossref_metadata_2025 huggingface dataset:
Broadening of rectified potential structures induced by rf currents in a magnetized plasma: Application to ITER scrape-off-layer
Authors: Faudot E. , Colas L. , Heuraux S. , Gunn J. P.
Published: April 2010

Measurements show that the vicinity of powered ion cyclotron range of frequency (ICRF) antennae is biased positively with respect to its environment [J. Gunn et al., Proc. 22nd IAEA Fusion Energy Conference, Geneva 2008, EX/P6-32]. This is attributed to radio-frequency (rf) sheath rectification. The radial penetration of these direct current (dc) potentials from ICRF launchers into the tokamak scrape-off layer (SOL) determines the power deposition on the walls and especially on the antenna structure, which is a key point for long time clean discharges. Within independent flux tube models of rf sheath rectification the radial penetration of dc potentials is determined by the skin depth x0=c/ωpe for the slow wave. When self-consistent exchange of transverse rf current is allowed between neighboring flux tubes, such a structure can be broadened radially up to a characteristic transverse length L. Broadening arises as soon as L>x0. A linear modeling of the process gives a first evaluation of the theoretical length L=(L∥ρci/2)1/2. Within the “flute assumption,” it scales with the length L∥ of open flux tubes and the ion Larmor radius Ωci. This trend has been confirmed by nonlinear fluid simulations using the SEM code taking into account nonlinearities of the sheath dynamics. Parametric regimes are outlined where broadening or nonlinearity arise. Langmuir probe measurements on Tore Supra suggest that the observed broadening is lower than predicted by the code. This suggests that actual rf current exchanges probably do not occur over the whole length of magnetic field lines but only on a fraction of it. This “effective parallel magnetic connection length” L∥eff is estimated from the measurements. The model is finally applied to several potential maps generated by an ITER antenna, with different plasma parameters depending on possible SOL scenarios in ITER, and “reasonable assumptions” about L∥eff. It comes out that L ranges between 1 and 10 cm depending on local L∥eff and on typical ITER plasma parameters.
Threshold voltage in short channel polycrystalline silicon thin film transistors: Influence of drain induced barrier lowering and floating body effects
Authors: Valletta A. , Gaucci P. , Mariucci L. , Pecora A. , Cuscunà M. , Maiolo L. , Fortunato G.
Published: April 2010

The threshold voltage (VT) variations induced by the drain bias (Vds) are investigated in polycrystalline silicon thin film transistors (TFTs), with channel length ranging from 20 to 0.4 μm, by combining experimental measurements and two-dimensional (2D) numerical simulations. A careful analysis of the electrical characteristics in both subthreshold and off regime is performed, by taking in account also the effects of the leakage current field enhanced mechanisms on the overall generation-recombination rate. We show that the main causes of VT variations are the drain induced barrier lowering (DIBL) and floating body effects (FBEs), induced by impact ionization. The relative influence of FBEs and DIBL is analyzed by performing numerical simulations with or without including the impact ionization model. A detailed analysis of the 2D Poisson equation has allowed to identify and evaluate the contributions of DIBL and FBEs to the threshold voltage variation when both are present. It is found that, in short channel TFTs at high drain bias, the VT variations can’t be attributed to DIBL effect alone and there is a noticeable contribution of the FBEs to the threshold voltage reduction. From the numerical simulations, the influence of FBEs and DIBL on the electrostatic barrier at source junction and its reduction for increasing Vds is analyzed for long and short channel TFTs.
Temperature analysis of AlGaN/GaN based devices using photoluminescence spectroscopy: Challenges and comparison to Raman thermography
Authors: Batten T. , Manoi A. , Uren M. J. , Martin T. , Kuball M.
Published: April 2010

Photoluminescence (PL) spectroscopy was used to determine lateral temperature distributions in AlGaN/GaN based devices. Results are compared to Raman thermography data and to thermal modeling to assess challenges in the determination of temperature in devices using PL analysis and corresponding solutions. In conjunction with Raman thermography, the vertical temperature distribution in the devices is determined and the thermal boundary resistance at the GaN/SiC interface extracted.
Enhanced absorption of intense short-pulse laser light by subwavelength nanolayered target
Authors: Cao Lihua , Gu Yuqiu , Zhao Zongqing , Cao Leifeng , Huang Wenzhong , Zhou Weimin , He X. T. , Yu Wei , Yu M. Y.
Published: April 2010

Two-dimensional particle-in-cell simulation shows that a target with subwavelength nanolayered front can reduce the reflection and increase the absorption of the energy of an intense short laser pulse. The electrons within the skin depth on the surfaces of the nanolayers are accelerated by J×B heating to relativistic velocities and ejected into the narrow vacuum spaces between the layers. They then propagate forward with most of the absorbed laser energy along the surfaces of the layers. Conversion of the laser energy into electron energy can be enhanced by optimizing the vacuum spacing between the nanolayers since the phase structure of the laser field in the target is modified. The effects of the layer width, length, and spacing on the energy conversion efficiency are investigated.
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binary condensation in a supersonic Laval nozzle: Presence of small clusters inferred from a macroscopic energy balance
Authors: Tanimura Shinobu , Wyslouzil Barbara E. , Wilemski Gerald
Published: April 2010

We determined the heat released in the condensing flow of a CH3CH2OD/D2O/carrier gas mixture (EtOD/D2O for brevity) through a supersonic Laval nozzle by integrating the equations for supersonic flow with condensation, using the static pressure, temperature, and mole fractions of EtOD and D2O monomers [S. Tanimura, B. E. Wyslouzil, M. S. Zahniser, et al., J. Chem. Phys. 127, 034305 (2007)] as inputs. By considering the depletion of the monomer species, the deviation of the pressure from the isentropic value, and the heat released, we estimated that ∼10% of the EtOD molecules are present as pure clusters (dimer to tetramer) upstream of the onset point of condensation. In contrast, clustering was not detected when only pure EtOD was present under the same conditions (temperature and the partial pressure of EtOD) for which clustering was observed in the EtOD/D2O flow. This suggests that the formation of EtOD clusters is facilitated by D2O in the EtOD/D2O flow. A comparison of the heat released to the flow and the expected heat of dissociation of the EtOD/D2O droplets suggests that small EtOD clusters persist downstream of the onset point. Both upstream and downstream of the onset point of condensation, the concentration of these clusters in the nozzle is higher than that expected at equilibrium. A possible mechanism for the overabundance of pure EtOD clusters is that they form in the mixed EtOD/D2O particles (droplets or clusters) and evaporate from them.
Computational study of the dielectric properties of [La,Sc]2O3 solid solutions
Authors: Momida Hiroyoshi , Cockayne Eric , Umezawa Naoto , Ohno Takahisa
Published: April 2010

First-principles calculations were used to compute the dielectric permittivities of hypothetical [La,Sc]2O3 solid solutions in the cubic (bixbyite) and hexagonal La2O3 phases. Dielectric enhancement is predicted at small Sc concentrations due to the rattling ion effect. Similar calculations for a model amorphous La2O3 structure show little change in permittivity when a small amount of Sc is substituted for La. In this case, the local environment around the Sc changes in a way that compensates for the rattling ion effect.
Double-impurity doping-induced quantum critical behaviors in Sr1−xBaxTi1−yRuyO3
Authors: Guo Y. J. , Wei T. , Zhu C. , Wang K. F. , Gao X. S. , Guan Y. Q. , Liu J.-M.
Published: April 2010

It has been reported both experimentally and theoretically that the Ba2+-doping at the A-site of quantum paraelectric SrTiO3 suppresses the quantum fluctuations by activating the ferroelectric mode, while the Ru4+-doping at the B-site plays the opposite role. For a double-impurity doped SrTiO3, i.e., Sr1−xBaxTi1−yRuyO3, where the two types of opposite effects compete with each other, we propose an improved transverse-field Ising model in order to investigate the effect of the double-impurity doping on the quantum phase transitions and critical behaviors. The calculated quantum behavior is quite well consistent with experimental measurements. A linear relationship between the quantum critical doping concentrations for Ba2+ and Ru4+ is predicted, subsequently validated qualitatively by an anharmonic oscillator model.
Prediction of optical modulation properties of twisted-nematic liquid-crystal display by improved measurement of Jones matrix
Authors: Ma Baiheng , Yao Baoli , Ye Tong , Lei Ming
Published: April 2010

The optical modulation properties of twisted-nematic liquid-crystal display (TN-LCD) can be totally predicted and optimized when its Jones matrix is known. An improved method for determining the Jones matrix of the TN-LCD without knowing its internal parameters is presented in this paper. Only three sets of intensity measurements are needed for the complete determination of the TN-LCD’s Jones matrix for a single wavelength, much less than the procedure offered by Moreno et al. This method is easier and stable in data processing and capable of diminishing the calculation error resulting from the fluctuation of intensity measurement effectively. The validity of this method is verified experimentally, whose results coincide well with the optical modulation properties of the TN-LCD predicted by our determined Jones matrix.
Measuring liquid crystal anchoring energy strength by spectroscopic ellipsometry
Authors: Marino A. , Tkachenko V. , Santamato E. , Bennis N. , Quintana X. , Otón J. M. , Abbate G.
Published: April 2010

We describe an experimental procedure for accurate measurement of anchoring energy strength of liquid crystal cells. This technique is based on the possibility of gathering a large amount of very precise data about the linear optical response of the cell in different experimental conditions, using spectroscopic ellipsometry. Then, a careful data analysis exploiting data inversion method, supplemented by simulations from the elastic theory, is able to provide the searched information. The technique has been applied to vertical aligned nematic cells, chosen for its widespread use in the present display market. The results obtained in this particular case together with a thorough comparison with existing alternative techniques, suggest that our technique can be an optimum candidate for the industrial implementation of such measurement. A particular example is fully worked out, giving a result with a precision of 1.5% and an accuracy of 10%.
Multicalorons revisited
Authors: Nakamula Atsushi , Sakaguchi Jun
Published: April 2010

Analytic Nahm data are re-examined for SU(2) calorons, or periodic instantons, of instanton charge 2. The Nahm equations are solved analytically in terms of Jacobi elliptic functions and the possible matching conditions are classified. The dimensions of framed moduli space for charge 2 caloron are enumerated and the maximal parameter, which is 16 for charge 2, case is identified. The monopole and instanton limits are also considered. It is found that the Nahm data which does not correspond to the standard monopoles play significant role for calorons.
Applicability of different geometry approaches to simulations of turbulence in highly sheared magnetic fields
Authors: Told D. , Jenko F.
Published: April 2010

For more than a decade, Eulerian simulations of plasma turbulence have been using coordinate systems aligned to the background magnetic field in order to exploit the elongated structure of the turbulent eddies. Here, two possible setups of such field-aligned coordinate systems are studied with regard to their behavior under more extreme conditions such as tokamak edge or stellarator geometries where large global and/or local shear are encountered. Turbulence codes employing a Fourier expansion are shown to yield correct solutions also for large shear values, given that the radial resolution chosen is large enough. Codes which compute the radial direction in real space, on the other hand, can benefit from the implementation of the shifted metric approach which may save resolution in the case of large shear.
Steady shear rheometry of dissipative particle dynamics models of polymer fluids in reverse Poiseuille flow
Authors: Fedosov Dmitry A. , Karniadakis George Em , Caswell Bruce
Published: April 2010

Polymer fluids are modeled with dissipative particle dynamics (DPD) as undiluted bead-spring chains and their solutions. The models are assessed by investigating their steady shear-rate properties. Non-Newtonian viscosity and normal stress coefficients, for shear rates from the lower to the upper Newtonian regimes, are calculated from both plane Couette and plane Poiseuille flows. The latter is realized as reverse Poiseuille flow (RPF) generated from two Poiseuille flows driven by uniform body forces in opposite directions along two-halves of a computational domain. Periodic boundary conditions ensure the RPF wall velocity to be zero without density fluctuations. In overlapping shear-rate regimes the RPF properties are confirmed to be in good agreement with those calculated from plane Couette flow with Lees–Edwards periodic boundary conditions (LECs), the standard virtual rheometer for steady shear-rate properties. The concentration and the temperature dependence of the properties of the model fluids are shown to satisfy the principles of concentration and temperature superposition commonly employed in the empirical correlation of real polymer-fluid properties. The thermodynamic validity of the equation of state is found to be a crucial factor for the achievement of time-temperature superposition. With these models, RPF is demonstrated to be an accurate and convenient virtual rheometer for the acquisition of steady shear-rate rheological properties. It complements, confirms, and extends the results obtained with the standard LEC configuration, and it can be used with the output from other particle-based methods, including molecular dynamics, Brownian dynamics, smooth particle hydrodynamics, and the lattice Boltzmann method.
Temperature dependence of photoluminescence characteristics of excitons in stacked quantum dots and quantum dot chains
Authors: Kojima Osamu , Nakatani Hiroaki , Kita Takashi , Wada Osamu , Akahane Kouichi
Published: April 2010

We have investigated the effects of temperature on the photoluminescence (PL) characteristics of excitons in ordinary stacked quantum dots (QDs) and QD chains in which QDs are interconnected along the growth direction. While the temperature dependence of the PL intensity of both samples is similar, that of the PL decay time is different. In addition, the PL decay times of both samples monitored at 150 K clearly depend on the detection energy. This result is attributed to lateral QD coupling. From these results, in ordinary stacked QDs, the exciton transfer owing to the lateral coupling is the only cause of the increase in the PL decay time. On the other hand, in QD chains, the interconnection along the chain direction as well as the lateral coupling is considered to cause the change in the PL characteristics and induce the extremely long exciton lifetime.
Analysis of nanopatterning through near field effects with femtosecond and nanosecond lasers on semiconducting and metallic targets
Authors: Sundaram Vijay M. , Soni Alok , Russo Richard E. , Wen Sy-Bor
Published: April 2010

A systematic study was conducted to understand the size and shape of nanopatterns generated on selected semiconducting (Si and Ge) and metallic (Cr, Cu, and Ag) targets under different laser pulse durations, laser energies, and number of laser pulses. Based on the experimental results, femtosecond laser pulses, compared with nanosecond laser pulses, provide lower damage thresholds to the targets but higher damage thresholds to the near field scanning optical microscope (NSOM) probes at the wavelength (∼400–410 nm) studied. Furthermore, the resulting nanopatterns showed a significant dependence on the optical properties (i.e., absorption coefficient and surface reflectivity) of the target material. By comparing the obtained experimental results, we conclude that the optical energy transport from the NSOM probe to the target dominates the pattern generation when femtosecond laser is applied to the NSOM system. When nanosecond laser is applied, both the thermal and optical energy transported from the NSOM probe to the targets attribute to the obtained morphology of nanopatterns on different targets under the experimental conditions studied.
Positive and negative cluster ions from liquid ethanol by fast ion bombardment
Authors: Kaneda M. , Shimizu M. , Hayakawa T. , Iriki Y. , Tsuchida H. , Itoh A.
Published: April 2010

Secondary ion mass spectra have been measured for the first time for a liquid ethanol target bombarded by 2.0 MeV He+ ions. Positive and negative ion spectra exhibit evidently a series of cluster ions of the forms [(EtOH)nH]+ and [(EtOH)n−H]−, respectively, in addition to light fragment ions from intact parent molecules. It was found that these cluster ions are produced only from liquid phase ethanol. Both positive and negative secondary ion spectra show similar cluster size distributions with almost the same decay slope. We also present for the first time the cluster ion distribution emitted from the liquid at different liquid temperatures.
Modeling of the effect of the buried Si–SiO2 interface on transient enhanced boron diffusion in silicon on insulator
Authors: Bazizi E. M. , Fazzini P. F. , Pakfar A. , Tavernier C. , Vandelle B. , Kheyrandish H. , Paul S. , Lerch W. , Cristiano F.
Published: April 2010

The effect of the buried Si–SiO2 interface on the transient enhanced diffusion (TED) of boron in silicon on insulator (SOI) structures has been investigated. To this purpose, boron marker layers were grown by chemical vapor deposition on Si and SOI substrates and implanted under nonamorphizing conditions with 40 keV Si+ ions. The experimental results clearly confirm that the Si–SiO2 interface is an efficient trap for the Si interstitial atoms diffusing out of the defect region. Based on these experiments, existing models for the simulation of B TED in silicon have been modified to include an additional buried recombination site for silicon interstitials. The simulation results provide an upper limit of ∼5 nm for the recombination length of interstitials at the Si–SiO2 interface.
High pressure phase transition study of B–C–N compound
Authors: Li Ming , Lin Peng , Gao Yang , Gao Chunxiao
Published: April 2010

A phase transition concerning B–C–N compound (g-B0.47C0.23N0.30 to w-B0.47C0.23N0.30) was observed. High pressure synchrotron x-ray diffraction was used to explore its structure in a diamond anvil cell to 30.03 GPa. We found the phase transition is incomplete even till the highest pressure in the experiments. The new phase has a wurtzite structure with space group C6V (P63mc). The lattice parameters of w-B0.47C0.23N0.30 at high-pressure are calculated. Different from the starting materials, the new phase shows much greater isotropy in compressibility with increasing pressure. Bulk modulus was estimated being 275(±26) GPa using a Brich–Murnaghan equation of state, which is one of the highest bulk modulus but smaller than that of w-BN, c-BN, and hexagonal diamond and the value predicted from theory.
Extremely temperature-stable piezoelectric properties of orthorhombic phase in (K,Na)NbO3-based ceramics
Authors: Gao Y. , Zhang J. L. , Zong X. J. , Wang C. L. , Li J. C.
Published: April 2010

Piezoelectric temperature stabilities are often a critical issue for many piezoelectric materials in practical applications. We report an important physical phenomenon recently discovered in a variety of (K,Na)NbO3-based ceramics. Piezoelectric properties are extremely temperature-stable in orthorhombic phase. No or only weak piezoelectric temperature dependence and excellent thermal aging stability are observed over considerably wide temperature intervals, which are broader than 325 °C in (K0.48Na0.52)NbO3 ceramic and 215 °C in (K0.50Na0.50)0.98Li0.02Nb0.82Ta0.18O3 ceramic, respectively. In general, the orthorhombic phase possesses much better piezoelectric temperature stabilities than the tetragonal phase. Thus, we suggest that future compositional designs of (K,Na)NbO3-based lead-free piezoelectric ceramics should take this phenomenon into full consideration.
BaTiO 3 ferroelectric nanoparticles dispersed in 5CB nematic liquid crystal: Synthesis and electro-optical characterization
Authors: Blach J.-F. , Saitzek S. , Legrand C. , Dupont L. , Henninot J.-F. , Warenghem M.
Published: April 2010

We report in this paper studies on a mixture of nematic liquid crystal (5CB) and BaTiO3 ferroelectric nanoparticles (NPs). Apart a drastic change in the electro-optical (EO) properties of this mixture, which is reported as a conclusion, we focused our attention onto the characteristics of those NPs. The initial powder obtained by solid way is first analyzed: this material is crystallized in the ferroelectric phase as shown by x-ray diffraction and Raman spectroscopy. A high speed second milling was performed to obtain NPs: they have been characterized by high resolution transmission electron microscopy (size and structural characterizations) and by dynamic light scattering. Then these NPs were blended with a nematic liquid crystal (5CB). Raman spectroscopy measurements were used to measure and compare the scalar order parameter of both samples. The EO properties were measured in planar liquid crystal cell configuration by using classical EO setup. We amazingly found a significant decrease in the Freedericksz threshold, compared to the pure material. This is to be compared to the Glushchenko’s measurement, who observed no variation, for a similar mixture in concentration, but for smaller NPs. Switching times were measured using the same setup and we noticed a decrease in the “τon” for the 5CB+BTO mixture compared to the pure 5CB one.
Josephson junction in cobalt-doped BaFe2As2 epitaxial thin films on (La,Sr)(Al,Ta)O3 bicrystal substrates
Authors: Katase Takayoshi , Ishimaru Yoshihiro , Tsukamoto Akira , Hiramatsu Hidenori , Kamiya Toshio , Tanabe Keiichi , Hosono Hideo
Published: April 2010

Josephson junctions were fabricated in epitaxial films of cobalt-doped BaFe2As2 on [001]-tilt (La,Sr)(Al,Ta)O3 bicrystal substrates. 10-μm-wide microbridges spanning a 30°-tilted bicrystal grain boundary (BGB bridge) exhibited resistively-shunted-junction (RSJ)-like current–voltage characteristics up to 17 K, and the critical current was suppressed remarkably by a magnetic field. Microbridges without a BGB did not show the RSJ-like behavior, and their critical current densities were 20 times larger than those of BGB bridges, confirming BGB bridges display a Josephson effect originating from weakly-linked BGB.
Nonlinear spacing and frequency effects of an oscillating cylinder in the wake of a stationary cylinder
Authors: Yang Xiaofan , Zheng Zhongquan Charlie
Published: April 2010

Nonlinear responses to a transversely oscillating cylinder in the wake of a stationary upstream cylinder are studied theoretically by using an immersed-boundary method at Re=100. Response states are investigated in the three flow regimes for a tandem-cylinder system: the “vortex suppression” regime, the critical spacing regime, and the “vortex formation” regime. When the downstream cylinder is forced to oscillate at a fixed frequency and amplitude, the response state of flow around the two cylinders varies with different spacing between the two cylinders, while in the same flow regime, the response state can change with the oscillating frequency and amplitude of the downstream cylinder. Based on velocity phase portraits, each of the nonlinear response states can be categorized into one of the three states in the order of increasing chaotic levels: lock-in, transitional, or quasiperiodic. These states can also be correlated with velocity spectral behaviors. The discussions are conducted using near-wake velocity phase portraits, spectral analyses, and related vorticity fields. A general trend in the bifurcation diagrams of frequency spacing shows the smaller the spacing, frequency, or amplitude, the less chaotic the response state of the system and more likely the downstream and upstream wakes are in the same response state. The system is not locked-in in any case when the spacing between the cylinders is larger than the critical spacing. The near-wake velocity spectral behaviors correspond to the nonlinear response states, with narrow-banded peaks shown at the oscillation frequency and its harmonics in the lock-in cases. High frequency harmonic peaks, caused by interactions between the upstream wake and the downstream oscillating cylinder, are reduced in the near-wake velocity spectra of the upstream cylinder when the spacing increases.
Low-threshold 303 nm lasing in AlGaN-based multiple-quantum well structures with an asymmetric waveguide grown by plasma-assisted molecular beam epitaxy on c-sapphire
Authors: Jmerik V. N. , Mizerov A. M. , Sitnikova A. A. , Kop’ev P. S. , Ivanov S. V. , Lutsenko E. V. , Tarasuk N. P. , Rzheutskii N. V. , Yablonskii G. P.
Published: April 2010

We report on AlGaN multiple-quantum-well separate confinement laser heterostructures grown by plasma-assisted molecular-beam epitaxy directly on c-sapphire at low temperatures (<800 °C). Threading dislocation density was reduced down to 109–1010 cm−2 owing to both intentionally introduced strained AlGaN/AlN superlattices and self-organized blocking structures in the AlGaN step-graded buffer layers. The quantum wells were fabricated by a submonolayer digital alloying technique. Calculations of the optical gain and confinement in the optically pumped laser structures yielded its optimum design comprising an asymmetric waveguide. Lasing at 303 nm with the relatively low threshold excitation density of 0.8 MW/cm2 at 295K has been achieved.
Highly efficient orange-red phosphorescent organic light-emitting diode using 2,7-bis(carbazo-9-yl)-9,9-ditolyfluorene as the host
Authors: Jou Jwo-Huei , Shen Shih-Ming , Chen Szu-Hao , Wu Ming-Hsuan , Wang Wei-Ben , Wang Hsi-Ching , Lin Chuen-Ren , Chou Yi-Chieh , Wu Po-Hsien , Shyue Jing-Jong
Published: April 2010

We demonstrate an efficient orange-red organic light-emitting diode using a host, 2,7-bis(carbazo-9-yl)-9,9-ditolyfluorene, doped with tris(2-phenylquinoline) iridium(III). The device exhibits a high current efficiency of 44.8 cd/A at 1000 cd/m2. This may be attributed to the adoption of the host, which favors the injection of holes, as well as the emissive-layer architecture enabling excitons to form on host and hence favoring efficient energy-transfer from host to guest. Moreover, an electron-confining layer is used to modulate excessive holes to be injected into emissive layer and confine the electrons, which would in turn balance the injection of both carriers and improve efficiency.
Terahertz emission characteristics of ErAs:InGaAs-based photoconductive antennas excited at 1.55 μm
Authors: Schwagmann A. , Zhao Z.-Y. , Ospald F. , Lu H. , Driscoll D. C. , Hanson M. P. , Gossard A. C. , Smet J. H.
Published: April 2010

We characterize ErAs:In0.53Ga0.47As superlattices as substrates for photoconductive terahertz emitters excited at 1.55 μm. The bandwidth of the emitted radiation is studied as a function of the superlattice period (or equivalently the electron lifetime) and the applied bias field. The results show that a variation in the electron lifetime from 0.2 to 6.3 ps does not considerably influence the bandwidth of the emitted radiation. However, the bandwidth increases linearly from 2.6 to 3.0 THz as the applied bias field is increased from 7 to 30 kV/cm. At higher bias fields, saturation is observed. The largest measured bandwidth is 3.1 THz.
Light- and ion-gauge-induced space charges in tris-(8-hydroxyquinolate) aluminum-based organic light-emitting diodes
Authors: Noguchi Yutaka , Sato Naoki , Miyazaki Yukimasa , Ishii Hisao
Published: April 2010

We report space charge formation in tris-(8-hydroxyquinolate) aluminum (Alq3)-based organic light-emitting diodes induced by light irradiation and ion-gauge (IG) operation during device fabrication. An analysis of the capacitance-voltage curves of the light-treated devices reveals the presence of uniformly distributed negative space charges in the Alq3 layer. Spatial inhomogeneity of the orientation polarization as well as electrons trapped in the Alq3 film can be the origin of the negative space charge. We also found that positively charged species can be included in the device due to IG operation.
III-V-semiconductor-on-insulator n-channel metal-insulator-semiconductor field-effect transistors with buried Al2O3 layers and sulfur passivation: Reduction in carrier scattering at the bottom interface
Authors: Yokoyama Masafumi , Yasuda Tetsuji , Takagi Hideki , Miyata Noriyuki , Urabe Yuji , Ishii Hiroyuki , Yamada Hisashi , Fukuhara Noboru , Hata Masahiko , Sugiyama Masakazu , Nakano Yoshiaki , Takenaka Mitsuru , Takagi Shinichi
Published: April 2010

We have developed III-V-semiconductor-on-insulator (III-V-OI) structures on Si wafers with excellent bottom interfaces between In0.53Ga0.47As-OI channel layers and atomic-layer-deposited Al2O3 (ALD-Al2O3) buried oxides (BOXs). A surface activated bonding process and the sulfur passivation pretreatment have realized the excellent In0.53Ga0.47As-OI/ALD-Al2O3 BOX bottom interface properties. As a result, the III-V-OI n-channel metal-insulator-semiconductor field-effect transistors under the back-gate configuration showed the peak mobility of 1800 cm2/V s and the higher electron mobility than the Si universal one even in the high effective electric field range because of the reduction in the surface roughness and fixed charges.
Finite-size scaling study of the vapor-liquid critical properties of confined fluids: Crossover from three dimensions to two dimensions
Authors: Liu Yang , Panagiotopoulos Athanassios Z. , Debenedetti Pablo G.
Published: April 2010

We perform histogram-reweighting grand canonical Monte Carlo simulations of the Lennard-Jones fluid confined between two parallel hard walls and determine the vapor-liquid critical and coexistence properties in the range of σ≤H≤6σ and 10σ≤Lx,Ly≤28σ, where H is the wall separation, Lx=Ly is the system size and σ is the characteristic length. By matching the probability distribution of the ordering operator, P(M), to the three-dimensional (3D) and two-dimensional (2D) Ising universality classes according to the mixed-field finite-size scaling approach, we establish a “phase diagram” in the (H,L) plane, showing the boundary between four types of behavior: 3D, quasi-3D, quasi-2D, and 2D. In order to facilitate 2D critical point calculation, we present a four-parameter analytical expression for the 2D Ising universal distribution. We show that the infinite-system-size critical points obtained by extrapolation from the apparent 3D and 2D critical points have only minor differences with each other. In agreement with recent reports in the literature [Jana et al., J. Chem. Phys. 130, 214707 (2009)], we find departure from linearity in the relationship between critical temperature and inverse wall separation, as well as nonmonotonic dependence of the critical density and the liquid density at coexistence upon wall separation. Additional studies of the ST2 model of water show similar behavior, which suggests that these are quite general properties of confined fluids.
Electric field controlled manipulation of the magnetization in Ni/BaTiO3 hybrid structures
Authors: Geprägs S. , Brandlmaier A. , Opel M. , Gross R. , Goennenwein S. T. B.
Published: April 2010

The manipulation of the ferromagnetic magnetization via electric fields is investigated in Ni/BaTiO3 hybrid structures. The application of an electric field to the ferroelectric BaTiO3 induces elastic strain. In the Ni/BaTiO3 hybrids, this strain is transferred into the ferromagnetic Ni layer, affecting its magnetization due to inverse magnetostriction. Two approaches to electrically alter the Ni magnetization are investigated. One approach exploits the strain-induced change of the nickel magnetic coercivity, and allows for both reversible and irreversible magnetization control. The other is based on irreversible ferroelectric domain effects in BaTiO3, and yields two different electro-remanent magnetization states.
Monolayer dual gate transistors with a single charge transport layer
Authors: Spijkman M. , Mathijssen S. G. J. , Smits E. C. P. , Kemerink M. , Blom P. W. M. , de Leeuw D. M.
Published: April 2010

A dual gate transistor was fabricated using a self-assembled monolayer as the semiconductor. We show the possibility of processing a dielectric on top of the self-assembled monolayer without deteriorating the device performance. The two gates of the transistor accumulate charges in the monomolecular transport layer and artifacts caused by the semiconductor thickness are negated. We investigate the electrical transport in a dual gate self-assembled monolayer field-effect transistor and present a detailed analysis of the importance of the contact geometry in monolayer field-effect transistors.
Residual strain in thermally annealed periodic mesoporous silica revealed by x-ray scattering
Authors: Chen G. , Wan C.
Published: April 2010

We have applied x-ray scattering to characterize residual strain in nanostructured glasses. The first sharp diffraction peak (FSDP) and the nanostructures of periodic mesoporous silica were investigated as a function of annealing temperature. It is found that position and width of the FSDP exhibit different temperature dependencies, which correspond to two types of residual strain caused by defects and constrained nanostructures, respectively. The latter appear to be inherent to the periodic mesoporous material as confirmed by the small-angle x-ray scattering analysis. Our study has implications for the structural properties of periodic mesoporous materials.
Perpendicularizing magnetic anisotropy of full-Heusler Co2FeAl films by cosputtering with terbium
Authors: Li X. Q. , Xu X. G. , Zhang D. L. , Miao J. , Zhan Q. , Jalil M. B. A. , Yu G. H. , Jiang Y.
Published: April 2010

In this letter, we fabricated Co2FeAl films with perpendicular-to-plane magnetic anisotropy by cosputtering with terbium (Tb). The as-prepared (Tb+Co2FeAl) films (TCFA) consists of nanocrystalline L21 Co2FeAl and amorphous alloy of Tb(Co, Fe, and Al). The coercivity field (Hc) of the TCFA films is adjustable from 200 to 800 Oe. After annealing, the Hc decreases to 70 Oe. A perpendicularly magnetized spin valve with the TCFA films as free and reference layers shows a current-perpendicular-to-plane magnetoresistance of 1.8% at room temperature. Our result opens a way to fabricate perpendicularly magnetized full-Heusler alloys and makes it possible to realize faster and simple structured magnetic storage bits in the future.
Note: Design and tests of a 13 kA-6.5 kV thyristor switch for a pulsed inductive vacuum ultraviolet source
Authors: Teske C. , Lee B.-J. , Jacoby J. , Schweizer W. , Sun J. Chao
Published: April 2010

In this paper, the design, construction, and test procedure of a closing switch prototype based on thyristors is described. In particular, details are given about the design criteria and about the triggering board architecture, which is a high side biased, self supplied unit using the electrical energy derived from a local snubber network for the gate drive. The structure guarantees a hard firing gate pulse for the required high dI/dt application. Further, the results of the prototype tests are presented and discussed. The stack assembly has a holding voltage of 6.5 kV and is used for switching a series resonant circuit with a ringing frequency of 12 kHz for a pulsed inductive vacuum ultraviolet source. Maximum current amplitudes of 13 kA and pulse energies of more than 600 J were switched during the test procedure.
Prewetting transitions of one site associating fluids
Authors: Khan Sandip , Singh Jayant K.
Published: April 2010

Prewetting transitions are studied for Lennard-Jones (LJ) based dimer forming associating fluids, on a structureless surface represented by LJ 9–3 type potential, for various association strengths using grand-canonical transition matrix Monte Carlo (GC-TMMC) and histogram reweighting techniques. Occurrences of prewetting transition are observed for association strengths: εaf=2.0, 4.0, 6.0, 8.0, and 10.0. Structural properties, monomer fraction, and orientation order profile of thin-thick film of one-site associating fluids are presented. Wetting temperature, Tw, and prewetting critical temperature, Tpwc, increases with increasing association strength, which is in agreement with the results of the density functional theory (DFT). Length of prewetting line, on the other hand, is found to decrease first with increasing association energy until εaf=8.0 and subsequently found to increase substantially for εaf=10. This behavior is contrary to the prediction from the DFT. We observe that the boundary tension of thin-thick film via GC-TMMC and finite size scaling exhibits a maximum with respect to association strength.
Evaluation of a cesium iodide photocathode assisted with MgO-coated multiwall carbon nanotubes
Authors: Lee Jungwoo , Park Taehee , Lee Wonjoo , Park Eunkyung , Lee Donghwan , Han Bongwoo , Han Sung-Hwan , Yi Whikun
Published: April 2010

This paper reports the enhanced photocurrent and relative quantum efficiency of cesium iodide (CsI) films on magnesium oxide (MgO)-coated multiwall carbon nanotubes (MWCNTs) on a silica substrate, i.e., CsI/MgO/MWCNTs/Si, when illuminating with 147 nm photons under an external electric field. The incorporation of MWCNTs resulted in significant enhancement of the photocurrent by several orders of magnitude compared to that of a conventional CsI. An analysis of the photoelectron energy spectrum attributed the phenomena to the creation of a very high electric field through the MgO/CsI film with the subsequent generation of avalanche secondary electrons.
Single-electron transistors based on self-assembled silicon-on-insulator quantum dots
Authors: Wolf Conrad R. , Thonke Klaus , Sauer Rolf
Published: April 2010

We present an approach to fabricate single-electron devices consisting of a silicon quantum dot (QD) between metallic leads. Silicon QDs are obtained by reactive ion etching into a silicon-on-insulator substrate partially protected by a self-assembled etch mask. Electrodes are fabricated and aligned to the QDs by an electromigration process whereby their native oxide serves as tunneling barrier. The devices show Coulomb blockade corresponding to a charging energy of 19.4 meV and can be switched from the nonconducting to a conducting state giving rise to Coulomb diamonds. The behavior is well reproduced by a numerical orthodox theory calculation.
Establishing the mechanism of thermally induced degradation of ZnO:Al electrical properties using synchrotron radiation
Authors: Vinnichenko M. , Gago R. , Cornelius S. , Shevchenko N. , Rogozin A. , Kolitsch A. , Munnik F. , Möller W.
Published: April 2010

X-ray absorption near edge structure and x-ray diffraction studies with synchrotron radiation have been used to relate the electrical properties of ZnO:Al films to their bonding structure and phase composition. It is found that Al-sites in an insulating metastable homologous (ZnO)3Al2O3 phase are favored above a certain substrate temperature (TS) leading to deterioration of both the crystallinity and the electrical properties of the films. The higher film resistivity is associated with lower carrier mobility due to increased free electron scattering. Lower metal to oxygen flux ratios during deposition expand the range of TS at which low-resistivity films are obtained.
Surface Bloch waves mediated heat transfer between two photonic crystals
Authors: Ben-Abdallah Philippe , Joulain Karl , Pryamikov Andrey
Published: April 2010

We theoretically investigate the nonradiative heat transfer between two photonic crystals separated by a small gap in nonequilibrium thermal situation. We predict that the surface Bloch states coupling supported by these media can make heat exchanges larger than those measured at the same separation distance between two massive homogeneous materials made with the elementary components of photonic crystals. These results could find broad applications in near-field technologies.
Current-perpendicular-to-the-plane giant magnetoresistance of an all-metal spin valve structure with Co40Fe40B20 magnetic layer
Authors: You C. Y. , Tian N. , Goripati H. S. , Furubayashi T.
Published: April 2010

A current-perpendicular-to-the-plane giant magnetoresistance is demonstrated at room temperature by using Co40Fe40B20 alloy with an exchange biased stack of IrMn/CoFeB/Cu/CoFeB. The GMR effect is significantly enhanced by inserting a Co75Fe25 layer between CoFeB and Cu spacer to adjust the interfacial resistance and improve the interfacial asymmetric spin scattering at the interfaces with spacer. Microstructure observation shows that boron of the top CoFeB layer prefers to be enriched at the interface with Ru capping layer after annealing.
Quantum cascade lasers emitting near 2.6 μm
Authors: Cathabard O. , Teissier R. , Devenson J. , Moreno J. C. , Baranov A. N.
Published: April 2010

Quantum cascade lasers (QCLs) emitting at wavelengths as short as 2.63–2.65 μm are demonstrated. The InAs/AlSb QCL design was optimized to weaken carrier leakage into the L-valley by reducing coupling between the active InAs quantum wells. The lasers with HR-coated facets operated up to 175 K.
A scalable concept for micropower generation using flow-induced self-excited oscillations
Authors: St. Clair D. , Bibo A. , Sennakesavababu V. R. , Daqaq M. F. , Li G.
Published: April 2010

Inspired by music-playing harmonicas that create tones via oscillations of reeds when subjected to air blow, this paper entails a concept for microwind power generation using flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity. Specifically, when the volumetric flow rate of air past the beam exceeds a certain threshold, the energy pumped into the structure via nonlinear pressure forces offsets the system’s intrinsic damping setting the beam into self-sustained limit-cycle oscillations. The vibratory energy is then converted into electricity through principles of piezoelectricity. Experimental and theoretical results are presented demonstrating the feasibility of the proposed concept.
Synthesis of PbTe/Pb quasi-one-dimensional nanostructure material arrays by electrodeposition
Authors: Zong Zhaocun , Zhang Mingzhe , Lu Hongliang , Xu Dan , Wang Suangming , Tian Huifang , Liu Chang , Guo Haiming , Gao Hongjun , Zou Guangtian
Published: April 2010

The ordered PbTe/Pb quasi-one-dimensional nanowires array was electrodeposited on the SiO2/Si substrate. There are two essential factors for the formation of such kind of change in nanowire morphology and structure. One is the charges distribution at the tips of electrodeposit, the other one is the change in ion concentration in front of growth tip. We research the current versus bias voltage characteristics of single PbTe/Pb nanowire by four-probe scanning tunneling microscopy system.
Fullerene-multiwalled carbon nanotube complexes for bulk heterojunction photovoltaic cells
Authors: Li Cheng , Chen Yuhong , Ntim Susana Addo , Mitra Somenath
Published: April 2010

We demonstrate the implementation of multiwalled carbon nanotubes-fullerene (MWNT-C60) complexes in bulk heterojunction organic photovoltaic (OPV) cells. Such a design takes advantage of the C60 as an electron acceptor, while the MWNTs serve as efficient charge transporters. Two types of chemically functionalized MWNTs were used to synthesize these complexes. The first used carboxylated nanotubes (c-MWNT), while the latter were functionalized with octadecylamine (o-MWNT). All the photovoltaic parameters were found to be superior with c-MWNT, and their combined effect led to eight times higher power conversion efficiency. The enhancement was attributed to the electron withdrawing nature of the short carboxylic group which facilitated fast electron transfer from the C60 to the nanotube backbone, whereas the long alky chain on the o-MWNT served as an electron blocker. Therefore, it is evident that the form of functionalization is expected to have significant effect on the performance of OPVs containing carbon nanotubes.
Numerical simulation of vacuum-ultraviolet irradiation of dielectric layers
Authors: Sinha H. , Ren H. , Sehgal A. , Antonelli G. A. , Nishi Y. , Shohet J. L.
Published: April 2010

Vacuum-ultraviolet irradiation produces trapped charges in dielectrics. The trapped charges often generate self-consistent electric fields. A Monte Carlo simulation coupled with a Poisson equation solver is used to model the relationship between the irradiation photon flux and electrostatic potential. The simulation includes photoconduction, photoemission, photoinjection, and the effects of self-consistent electric fields. Calculations show that photoemission and photoinjection are responsible for changes in the electric potential as photon dose or dielectric thicknesses are varied. Experimental surface-potential measurements were made to compare the results of the simulation.
Quantum conductance modulation in graphene by strain engineering
Authors: Hossain M. Zubaer
Published: April 2010

Ab initio study reveals that strain can influence graphene’s ballistic conductance substantially; however, the effect of biaxial strain is significantly different from that of hydrostatic strain. For hydrostatic strain, tension increases conductance while compression decreases conductance. In contrast, when biaxial compressive strain is applied along the transport direction and the conduction electrons have energies higher than the Fermi energy of the system, conductance remains approximately unchanged. Nevertheless, for biaxial compressive strain with electron energies lower than the Fermi energy and for biaxial tensile strain conductance follows the hydrostatic behavior.
Spatial-Frequency Thresholds for Configural and Featural Discriminations in Upright and Inverted Faces
Authors: Watier Nicholas N , Collin Charles A , Boutet Isabelle
Published: April 2010

Face recognition is thought to rely more on the relative positions of face features (configural information) than on the appearance of the individual face parts (featural information). It also seems to rely on a specific band of spatial frequencies (SFs). In this study, we measured the SFs needed for processing configural and featural information using the method of constant stimuli in combination with a simultaneous-matching paradigm. Stimuli were two-octave-wide bandpass-filtered upright and inverted faces that contained either featural or configural modifications. SF thresholds for featural and configural processing were calculated by interpolating between discrimination accuracy scores. Low-pass and high-pass thresholds for featural and configural processing in upright faces were approximately equal, whereas for inverted faces, the thresholds were closer to the middle of the spectrum for configural processing relative to featural processing. Thus, a broader band of SFs, one that overlapped more with the middle of the frequency spectrum, was needed for configural processing than for featural processing in inverted faces. Our findings emphasise the importance of a narrow mid-range band of frequencies for both configural and featural encoding in upright faces and suggest that configural information is extracted less effectively in inverted faces.