bluuebunny/crossref_metadata_2025 huggingface dataset:
Single magnetic particle detection: Experimental verification of simulated behavior
Authors: Wirix-Speetjens Roel , Fyen Wim , De Boeck Jo , Borghs Gustaaf
Published: June 2006

In the past, magnetoresistive sensor based biosensors, using superparamagnetic particles, have shown to be promising candidates for highly sensitive biosensors. These sensors can detect a single micron-sized magnetic particle. For single particle detection, research groups have developed models to predict the signal per particle. In these models, the separation distance plays an important role for the quantitative determination of the signal. However, mostly only the passivation layer thickness is included as the separation distance. In this paper, we describe a detection system based on a magnetic spin-valve sensor that is capable of giving position-time information of the magnetic behavior of one single bead. The results obtained with this system for the detection of a single particle signature are then compared with simulations. For this comparison, we developed a model where an additional particle-substrate separation distance is included. This distance is determined by a force balance of the perpendicular forces acting on the magnetic particle, including the magnetic and electrostatic force. These simulations agree well with the single particle detection experiment.
Thermoelectric and thermophysical properties of ErPdX (X=Sb and Bi) half-Heusler compounds
Authors: Sekimoto Takeyuki , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: June 2006

Half-Heusler compounds ErPdX (X=Sb and Bi) were prepared by a spark plasma sintering technique. Their thermoelectric properties at high temperature and thermophysical properties at room temperature were measured. The electrical resistivity ρ and thermoelectric power S of ErPdSb are larger than those of ErPdBi, and both compounds indicate semiconductorlike characteristics at high temperature. ErPdSb has the large power factor (=S2∕ρ)>10μW∕K2cm above room temperature. From the lnρ-1∕T plot, the band gap energies Eg were estimated to be 0.28 and 0.05eV for ErPdSb and ErPdBi, respectively. The S-T and S-lnρ plots indicate that the conduction mechanism of the carriers is an intrinsic conduction at high temperature. The differences of ρ and S between both compounds are caused by the difference of the carrier concentration, whose magnitude originated in the difference of Eg and the deviation from the stoichiometric composition. The total thermal conductivity κ of ErPdBi exceeds that of ErPdSb because of the large carrier thermal conductivity κC. The maximum values of the dimensionless figure of merit ZT (=S2T∕ρκ) of ErPdSb and ErPdBi are 0.16 around 699K and 0.075 at 495K, respectively.
Cd
Cl
2
treatment, S diffusion, and recombination in polycrystalline CdTe
Authors: Metzger W. K. , Albin D. , Romero M. J. , Dippo P. , Young M.
Published: June 2006

Time-resolved photoluminescence measurements on glass∕SnO2∕CdTe and glass∕SnO2∕CdTe∕CdS structures indicate that the CdCl2 process, without any S present, significantly reduces recombination. However, S diffusion is required for lifetimes comparable to those observed in high-efficiency solar cells. Low-temperature photoluminescence, cathodoluminescence, and scanning electron images indicate how defect chemistry, grain-boundary passivation, and morphology are affected by S diffusion and the CdCl2 treatment.
Enhancement of the photoprotection and nanomechanical properties of polycarbonate by deposition of thin ceramic coatings
Authors: Mailhot B. , Rivaton A. , Gardette J.-L. , Moustaghfir A. , Tomasella E. , Jacquet M. , Ma X.-G. , Komvopoulos K.
Published: June 2006

The chemical reactions resulting from ultraviolet radiation produce discoloration and significant changes in the surface properties of polycarbonate (PC). To prevent photon absorption from irradiation and oxygen diffusion and to enhance the surface nanomechanical properties of PC, thin ceramic coatings of ZnO and Al2O3 (both single- and multi-layer) were deposited on bulk PC by radio-frequency magnetron sputtering. The samples were irradiated at wavelengths greater than 300nm, representative of outdoor conditions. Despite the effectiveness of ZnO to protect PC from irradiation damage, photocatalytic oxidation at the PC/ZnO interface was the limiting factor. To overcome this deficiency, a thin Al2O3 coating was used both as intermediate and top layer because of its higher hardness and wear resistance than ZnO. Therefore, PC∕Al2O3∕ZnO, PC∕ZnO∕Al2O3, and PC∕Al2O3∕ZnO∕Al2O3 layered media were fabricated and their photodegradation properties were examined by infrared and ultraviolet-visible spectroscopy. It was found that the photocatalytic activity at the PC/ZnO interface was reduced in the presence of the intermediate Al2O3 layer that limited the oxygen permeability. Nanomechanical experiments performed with a surface force apparatus revealed that the previous coating systems enhanced both the surface nanohardness and the elastic modulus and reduced the coefficient of friction in the order of ZnO, Al2O3, and Al2O3∕ZnO∕Al2O3. Although irradiation increased the nanohardness and the elastic modulus of PC, the irradiation effect on the surface mechanical properties of ceramic-coated PC was secondary.
Electroluminescence properties of the Gd3+ ultraviolet luminescent centers in SiO2 gate oxide layers
Authors: Sun J. M. , Prucnal S. , Skorupa W. , Dekorsy T. , Müchlich A. , Helm M. , Rebohle L. , Gebel T.
Published: June 2006

Electroluminescence (EL) properties in the ultraviolet (UV) range were studied on Gd-implanted indium tin oxide/SiO2:Gd∕Si metal-oxide-semiconductor light emitting devices. The efficient UV line at 316nm from Gd3+ centers shows a maximum power density of 2mW∕cm2 and a quantum efficiency above 5%. The Gd3+ luminescent center has an excitation cross section above 7.4×10−15cm2 with an EL decay time around 1.6ms at a Gd concentration of 3%. A decrease of the EL efficiency is observed by a cross relaxation at a high Gd concentration and by clustering of Gd atoms at an annealing temperature of 1000°C. A strong quenching of the UV EL due to electron trapping around optically active Gd3+ centers is observed during the injection of hot electrons.
The application of an InGaAs∕GaAsN strain-compensated superlattice to InAs quantum dots
Authors: Zhang Wei , Uesugi Katsuhiro , Suemune Ikuo
Published: June 2006

Application of InGaAs∕GaAsN strain-compensated superlattice (SCSL) to InAs quantum dots (QDs) has been studied with atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), and temperature-dependent photoluminescence (PL) measurements. The insertion of a tensile-strained GaAsN layer between InGaAs layers with high In concentrations can compensate the compressive strain in the InGaAs layers and reduce the flattening of QDs during the growth of the successive InGaAs layers. Compared with QDs capped with a single InGaAs layer of a high In concentration, QDs capped with such SCSLs can achieve almost the same redshift of emission wavelength, while the optical property is highly improved. The mechanism responsible for this is discussed based on the AFM, RHEED, and PL measurements.
Dynamics of ferroelectric domain growth in the field of atomic force microscope
Authors: Agronin A. , Molotskii M. , Rosenwaks Y. , Rosenman G. , Rodriguez B. J. , Kingon A. I. , Gruverman A.
Published: June 2006

Application of very high voltage to atomic force microscope tip leads to the growth of narrow, stringlike domains in some ferroelectrics, a phenomenon that was named “ferroelectric domain breakdown.” In this work the dynamics of domain breakdown have been studied experimentally and theoretically in stoichiometric lithium niobate (LN). The theory has been found to be in a good agreement with the measured domain radius temporal dependence. Dynamics of domain growth has also been studied in ultrathin LN crystals, where the domain breakdown phenomenon does not take place. It is also shown that domain formation processes occurring in bulk and ultrathin crystals are very different, and this is ascribed to the observed difference in depolarization energy dependence on the domain length.
Life cycle of a tungsten cold field emitter
Authors: Yeong K. S. , Thong J. T. L.
Published: June 2006

This paper studies a tungsten cold field emitter throughout its life cycle. The field emission properties and corresponding tungsten emitter evolution throughout its life cycle fall into three distinct regions which are discussed. It was found that adsorbate dynamics affect field emission current stability significantly, while adsorbate induced current instability showed different behaviors in different regions of the life cycle. It was found that emitter failure at the end of the lifetime was due to adsorbate related nanoprotrusion buildup on the emitter surface, a failure mechanism that is different from models previously reported in the literature. The buildup process of this nanoprotrusion and how it initiates arcing and destroys the tungsten tip are reported and discussed.
Atomically resolved observation of the quenched Si(111) surface with small amplitude dynamic force microscopy
Authors: Kawai Shigeki , Rose Franck , Ishii Takanori , Kawakatsu Hideki
Published: June 2006

Metastable reconstructed phases and highly disordered regions of the quenched Si(111) “1×1” phase with many silicon clusters were atomically resolved with a constant frequency mode of small amplitude dynamic force microscopy with the second flexural mode of a commercially available dynamic mode cantilever. Improved sensitivity due to the small amplitude dynamic force microscopy could operate at a relatively far distance from the sample surface with a given resolution and enable highly stable imaging with small interaction forces even on the Si(111) 1×1 metastable phases with silicon clusters. All of the individual atoms in the silicon cluster were atomically observed while avoiding deformations of the sample surface and the tip apex. In the case that the interaction forces of the imaging parameters were intently set to be ten times larger than those for stable imaging, arrangements of adatoms could easily be modified by mechanical interaction forces between the tip and the sample surface. The Si(111)-c(2×8) and √3×√3 phases of the 1×1 domain were found to have different contact potentials, which make a topographic height gap in a constant frequency shift image. An ultrasmall amplitude operation for the selective detection of electrostatic forces revealed that deviations of the observed height in the 1×1 domain were larger than that in the 7×7 domain due to the contact potential difference of the c(2×8) and √3×√3 phases in the atomic level.
Optimization of compact stellarator configuration as fusion devices
Authors: Najmabadi Farrokh , Rene Raffray A. , Ku Long-Poe , Lyon James F. , team ARIES
Published: June 2006

Optimization of the stellarator configuration requires tradeoffs among a large number of physics parameters and engineering constraints. An integrated study of compact stellarator power plants, ARIES-CS, aims at examining these tradeoffs and defining key R&D areas. Configurations with a plasma aspect ratio of A⩽6 and excellent quasiaxisymmetry (QA) in both two and three field period versions were developed while reducing α-particle losses to <10%. Stability to linear ideal MHD modes was attained, but at the expense of reduced QA (and increased α-particle losses) and increased complexity of the plasma shape. Recent experimental results indicate, however, that linear MHD stability limits may not be applicable to stellarators. By utilizing a highly efficient shield-only region in strategic areas, the minimum standoff was reduced by ∼30%. This allows a comparable reduction in the machine size. The device configuration, assembly, and maintenance procedures appear to impose severe constraints: three distinct approaches were developed, each applicable to a certain blanket concept and/or stellarator configuration. Modular coils are designed to examine the geometric complexity and to understand the constraints imposed by the maximum allowable field, desirable coil-plasma separation, coil-coil spacing, and other coil parameters. A cost-optimization system code has also been developed and will be utilized to assess the tradeoff among physics and engineering constraints in a self-consistent manner in the final phase of the ARIES-CS study.
Physics of organic bulk heterojunction devices for photovoltaic applications
Authors: Waldauf Christoph , Scharber Marcus C. , Schilinsky Pavel , Hauch Jens A. , Brabec Christoph J.
Published: June 2006

We present investigations of organic photovoltaic devices consisting of bulk heterojunction layers made from several material combinations. All of the investigated systems reveal close similarities to the behavior of classical pn-junction devices. The consequences of the pn-junction-like behavior on the device parameters and performance are presented. Furthermore, device characteristics and parameters of the pristine materials are correlated, resulting in a model that permits an identification of high potential materials, a performance prediction, and a device optimization. The resulting model is able to predict an open circuit voltage and a fill factor and their evolution with the light intensity or thickness of the active layer. It simplifies the identification of the internal morphology and therefore the choice of appropriate solvents. Necessary parameters concerning the choice of electrode materials are also provided.
Structural and electrical characterization of amorphous lanthanum hafnium oxide thin films
Authors: Loo Yim Fun , Taylor Stephen , Murray Robert T. , Jones Anthony C. , Chalker Paul R.
Published: June 2006

This paper describes the structural and electronic characterization of lanthanum hafnium oxide thin films deposited by metal organic chemical vapor deposition using a novel precursor mixture. Structural characterization is obtained using x-ray diffraction and cross-sectional transmission electron microscopy and indicates that the as-deposited films and films annealed up to 900°C remain effectively amorphous. Capacitance voltage and current voltage measurements on metal-oxide-semiconductor capacitors made using the films as a gate dielectric show the films exhibit good electrical integrity following post deposition annealing at temperatures up to 950°C. A dielectric constant, k for the films of 20±1.5 is determined and a density of interface states (at midgap) Dit of 3.9×1011cm−2eV−1 was measured.
Entropically driven self-assembling of softened multi-walled carbon nanotubes into a reversibly water dispersible coherent solid
Authors: Xie Huaqing , Pikhitsa Peter V. , Kim Young Jeong , Youn Wonjin , Altman Igor S. , Nam Jung Gun , Lee Seung Jong , Choi Mansoo
Published: June 2006

A bulk multi-walled carbon nanotube pellet has been produced by self-arrangement after drying the aqueous suspension of the carbon nanotubes (CNTs) oxidized by boiling CNTs in concentrated acid. The solid can be re-dispersed in water and self-assembled again. The centimeter order bulk CNT pellet unexpectedly showed compact domains of highly aligned parts of long CNTs which size is much larger than the domain size. Viscosity measurements confirmed that the system in question is completely different from a rigid-rod nematic. We reveal the mechanism of the entropy-driven self-alignment of treated worm-like CNTs in analogy to semiflexible liquid crystalline polymer. The polymer-like behavior of treated CNTs brings the CNTs into a genus of robust polymers.
The effect of atomic vacancies and grain boundaries on the mechanical properties of single-crystal GaN nanotubes
Authors: Xu B. , Pan B. C.
Published: June 2006

We present calculations of the Young modulus of some single-crystal GaN nanotubes with defects by using the empirical Stillinger-Weber potential. Our results indicate that dilute single vacancies and inversion domain grain boundaries (with wrong bonds and without wrong bonds) in single-crystal GaN nanotubes do not significantly affect the Young modulus of the tubes. However, the grain boundary at which the interface is normal to the axis of a nanotube may greatly lower the Young modulus of the single-crystal GaN nanotube.
Application of the diffraction theory for photothermal deflection to the measurement of the temperature coefficient of the refractive index of a binary gas mixture
Authors: Rohling Jurandir H. , Shen Jun , Zhou Jianqin , Gu Caikang Elton , Medina Antonio N. , Baesso Mauro L.
Published: June 2006

The application of recently developed diffraction theory for continuous wave photothermal deflection (PD) spectroscopy in the measurement of the temperature coefficient of the refractive index, dn∕dT, of a gas as a deflecting medium was presented. Both amplitude and phase signals were elucidated for a better interpretation and a simultaneous measurement of the thermal diffusivity αg and dn∕dT. The probe-beam size effect (PBSE) on the PD phase signal was also quantitatively analyzed to clearly show its physical meaning. A distance-scan method to measure the distance x between the probe beam and sample, which was difficult to determine in the PD, but a necessary parameter for measuring dn∕dT, was proposed. The consistent values of x measured respectively from the amplitude and the phase could not be obtained without considering the PBSE. αg and dn∕dT of pure gases (O2, N2, and CO2) and binary gas mixtures (O2-CO2 and N2-CO2) were precisely measured with the measured x. The measured αg and dn∕dT of pure gases were in very good agreement with the literature values, and furthermore the measured dn∕dT values of the pure gases had one more significant figure than the literature ones, demonstrating the high precision of this method. It was found the behavior of αg and dn∕dT of a binary gas mixture versus concentration could be described by a thermodynamic theory and the Lorentz-Lorenz formula, respectively.
Optical properties of stacked InGaAs sidewall quantum wires in InGaAsP∕InP
Authors: Zhou D. , Nötzel R. , van Otten F. W. M. , Eijkemans T. J. , Wolter J. H.
Published: June 2006

We report on the optical properties of threefold stacked InGaAs sidewall quantum wires (QWires) with quaternary InGaAsP barriers grown on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent quantum wells (QWells) into the QWires at low temperature, thermally activated repopulation of the QWells at higher temperature, and negligible localization of carriers along the QWires. Strong broadening of power dependent PL indicates enhanced state filling in the QWires compared to that in the QWells. Clear linear polarization of the PL from the QWires confirms the lateral quantum confinement of carriers. These results demonstrate excellent optical quality of the sidewall QWire structures with room temperature PL peak wavelength at 1.55μm for applications in fiber-based optical telecommunication systems.
Liquid crystal infiltration of InP-based planar photonic crystals
Authors: Martz J. , Ferrini R. , Nüesch F. , Zuppiroli L. , Wild B. , Dunbar L. A. , Houdré R. , Mulot M. , Anand S.
Published: June 2006

A procedure for the infiltration of planar photonic crystals (PhCs) with liquid crystals (LCs) is presented. InP-based PhCs are infiltrated with the nematic LC-K15 in a specially designed high-vacuum chamber. The infiltration technique is validated and systematically characterized by measuring the transmission through the infiltrated PhCs at different temperatures and for different polarizations. The reproducibility and reliability of our procedure are demonstrated and a high filling efficiency is obtained.
Correlation of Mn local structure and photoluminescence from CdS:Mn nanoparticles
Authors: Zhou Huijuan , Hofmann Detlev M. , Alves Helder R. , Meyer Bruno K.
Published: June 2006

The structure and luminescence properties of Mn2+ in CdS nanoparticles are studied. Electron paramagnetic resonance measurements show the existence of three distinct Mn2+ centers with different local structures in CdS nanocrystals: Mn ions substitutionally incorporated on Cd sites [Signal SI: g=2.0025 and a hyperfine interaction constant A of 64.6×10−4cm−1 (6.9mT)], Mn located near the surface [Signal SII: g=2.0013 and A=89×10−4cm−1 (9.5mT)], and a broad background signal (SIII) correlated to interacting Mn ions or Mn clusters. Luminescence studies indicate that only substitutional ions located in the core of the nanocrystals contribute to the typical T14 to A16 (2.12eV) emission. The colloidal preparation process of the nanoparticles allows selective incorporation of the Mn ions, i.e., core/shell doping of the nanoparticles. It shows that Mn located in the shell quenches the total luminescence via nonradiative processes.
Screening effects on dynamic electron captures in nonideal plasmas
Authors: Chang Won-Seok , Chang Dong-Man , Jung Young-Dae
Published: June 2006

The dynamic plasma screening effects on the electron capture process are investigated in nonideal plasmas. The semiclassical version of the Bohr-Lindhard model with the impact parameter method is applied to obtain the electron capture probability in nonideal plasmas as a function of the impact parameter, debye length, thermal energy, and collision energy. The result shows that the electron capture radius and capture probability decrease with the increasing thermal energy. The dynamic screening effects on the capture probability are found to be more significant near the position of the maximum capture probability. It is also found that the electron capture radius and capture probability including the dynamic screening effects are found to be greater than those including the static screening effects.
Aluminum incorporation into AlGaN grown by low-pressure metal organic vapor phase epitaxy
Authors: Huang G. S. , Yao H. H. , Lu T. C. , Kuo H. C. , Wang S. C.
Published: June 2006

Aluminum (Al) incorporation in AlxGa1−xN films grown by low-pressure metal organic vapor phase epitaxy using trimethylaluminum (TMAl) and trimethylgallium as group III precursors has been systematically studied. The solid phase Al composition of the AlxGa1−xN films varied nonlinearly with the Al gas phase composition. The incorporation kinetics of AlxGa1−xN alloy has been analyzed by using an adsorption-trapping model. Two parameters were used to characterize the properties of Al incorporation, i.e., the capture radius and the adsorption time of Al atoms. An exponential function of the Al composition of the AlxGa1−xN films versus the TMAl gas flow rate was obtained. It was demonstrated that the adsorption time of the Al atom was larger than the growth time of one atomic layer. The effects of ammonia flow rate, crystal growth rate, and growth temperature on the adsorption parameters were also discussed.
Interpretation of an anomalous peak in low-temperature photoluminescence measurements of bulk GaAs1−xNx on GaAs
Authors: Cheah W. K. , Fan W. J. , Yoon S. F. , Loke W. K. , Liu R. , Wee A. T. S.
Published: June 2006

Low-temperature (10K) photoluminescence measurements of GaAs1−xNx epitaxial layers grown on GaAs reveal an anomalous second peak in solid-source molecular beam epitaxy. Rapid thermal annealing (RTA) of a specific GaAsN sample reveals a lower energy peak (γ) which redshifts and a higher energy peak (α) which blueshifts under increasing annealing temperature. The band-anticrossing model is used to identify the origins of the two peaks and we propose a model to explain the RTA observations by the concept of increased confinement in areas of higher N concentrations by trapped N localized states. The γ peak is due to the accumulation of N content near the GaAs∕GaAsN interface. Hence, this abnormal annealing behavior occurs in layers with nonuniform N concentration at the GaAsN∕GaAs interface.
1
Å
-resolution chemical imaging by phase contrast technique
Authors: Iwamoto C. , Statonaka S. , Yamamoto T. , Ikuhara Y. , Matsuhata H.
Published: June 2006

Atomic-resolution high-voltage electron microscopy (ARHVEM) was applied to map chemical compositions of GaN∕AlN∕AlGaN layers. Image simulation showed that image variation of the GaN was faster than that of the AlN with an increase in the sample thickness. However, at less than approximately 3nm thickness, images of the GaN and AlN closely resembled their atomic structures simultaneously at an adequate defocus condition. Under this experimental condition, the GaN and AlN layers, both having the same wurtzite structure, were discriminated by contrasts of the cations. Contrasts of the N enabled us to determine thickness variation between the GaN and AlN. ARHVEM observation showed that, although the morphology of the interface between the GaN and AlN seems to be rough, the interface is locally sharp on an atomic scale.
Persistent currents in carbon nanotori: Effects of structure deformations and chirality
Authors: Zhang Zhenhua , Yuan Jianhui , Qiu Ming , Peng Jingcui , Xiao Fuliang
Published: June 2006

The persistent currents as a function of the dimension, chirality, and deformation for various chiral carbon nanotori are investigated theoretically. It has been found that, for the undeformed torus, its persistent current is inversely proportional to the torus radius R, but independent of the torus width r, and becomes very strong as its chiral angle θ approaches ±15°; whereas for the deformed torus, its energy gap Eg and persistent current are very sensitive to the deformation and chirality. In general, the persistent current can be fitted to the form I=±Asin(2πΦ∕Φ0) as long as the deformation occurs except in the case of tanα=0 and εL=εJ, where Φ is the magnetic flux enclosed in the torus, Φ0(=h∕e) is the flux quantum, α represents the shear strain, and εL and εJ denote the strains due to tension or compression along the directions of tube and torus circumferences, respectively. When the strain reaches 1%, the persistent current declines by four orders of magnitude.
High current density tris(8-hydroxyquinoline) aluminum-based hybrid transistor in vertical architecture
Authors: Yi Mingdong , Yu Shunyang , Ma Dongge , Feng Chengang , Zhang Tong , Meruvia M. S. , Hümmelgen Ivo A.
Published: June 2006

We report the construction of hybrid permeable-base transistors, in vertical architecture, using tris(8-hydroxyquinoline) aluminum as emitter, a thin gold layer as base, and n-type silicon as collector. These transistors present high common-base current gain, can be operated at low driving voltages, and allow high current density.
Effects of hydrogen on the electronic properties of synthetic melanin
Authors: Gonçalves P. J. , Filho O. Baffa , Graeff C. F. O.
Published: June 2006

In this work the influence of thermal treatments on the structural and electronic properties of synthetic melanins was investigated. To that end, thermal gravimetry, infrared spectroscopy, electron spin resonance, and dc conductivity were employed. Our results indicate that the water corresponds to 10%–20% of the mass of synthetic melanin and also show that the latter is rich in mobile interlayer hydrogens or protons. Extended heating above 60°C decreases the conductivity by three orders of magnitude and increases the spin density by a factor of 3. This enhanced spin concentration and decreased conductivity are stable at room temperature, but can be reestablished by rehydration. Evidence is given that these properties are related to the presence of mobile interlayer protons. Prolonged heating is responsible for proton trapping by carboxylic groups forming COOH moieties, leading to the changes observed in electronic properties.
Optimization of harmonic generation from boron plasma
Authors: Ganeev R. A. , Baba M. , Suzuki M. , Kuroda H.
Published: June 2006

The plateau pattern of the harmonic distribution up to the 65th order (λ=12.24nm) and the 5×10−7 conversion efficiency were achieved after the propagation of femtosecond pulses through the laser-produced boron plasma. The optimization of high-order harmonics generation was carried out at the focusing conditions when the confocal parameter of fundamental radiation was close to the plasma sizes. A study of cutoff energy showed its dependence on the second ionization potential of nonlinear medium. The spatial distribution of the radiation propagating through the boron plume showed the appearance of ringlike pattern at the intensities exceeding a saturated intensity of singly charged ions.
Enhanced hole transport in poly(p-phenylene vinylene) planar metal-polymer-metal devices
Authors: Tanase Cristina , Blom Paul W. M. , Mulder Minte , de Leeuw Dago M.
Published: June 2006

In planar metal-poly(p-phenylene vinylene) (PPV)-metal devices the experimental current is five to six orders of magnitude larger as compared to the expected space-charge limited current. Comparing these measurements with field-effect transistors demonstrates that the enhanced current originates from a high surface charge carrier density at the polymer/substrate interface. This surface charge is found to be only weakly dependent on the substrate, device geometry, and chemical treatment of the substrate. The presence of such a conducting channel due to charging of the surface obscures the intrinsic in-plane conducting properties of PPV.
Fermi interaction between the ν1 and the ν2+4νs bands of Ar⋯DN2+
Authors: Verbraak H. , Snels M. , Botschwina P. , Linnartz H.
Published: June 2006

Two rotationally fully resolved vibrational bands have been assigned unambiguously to the linear deuteron bound Ar⋯DN2+ complex by using ground state combination differences. The ionic complex is formed in a supersonic planar plasma expansion optimized and controlled by a mass spectrometer and is detected in direct absorption using tunable diode lasers and applying production modulation spectroscopy. The band origins are located at 2436.272 cm−1 and at 2435.932cm−1 and correspond to the ν1 band (NN stretch) and to the ν2+4νs combination band (DN and intermolecular stretch), respectively. The two bands overlap strongly and the large intensity of the combination band is explained in terms of a Fermi interaction. This interaction perturbs the observed transitions, particularly for low J values. Least-squares fitting yields values for the Fermi interaction parameters of F0=0.332cm−1 and FJ=−0.00146cm−1 and results in accurate rotational constants. These are discussed both from an experimental and a theoretical point of view.
Comparative assessment of density functional methods for 3d transition-metal chemistry
Authors: Zhao Yan , Truhlar Donald G.
Published: June 2006

In the present study, we comparatively assessed the newly developed M05 functional against a data set of reaction energies for transition-metal chemistry. The functionals to which we compare are BLYP, B3LYP, B97-2, MPWLYP1M, TPSS, and TPSSh. We draw the following conclusions: (1) TPSS gives the best performance for calculating the binding energies of three transition-metal dimers (Sc2, Ni2, and V2) that have severe multireference character, (2) B97-2 gives the best performance for calculating the binding energies of the nine metal-ligand diatomics (three monohydrides, three monoxide, and three monofluorides), and (3) M05 gives the overall best performance for all 18 data in the assessment, and it has a mean unsigned error 55% lower than the popular B3LYP functional. Since the M05 functional also gives good performance for main-group thermochemistry, for noncovalent chemistry, and for calculating barrier heights, M05 can be applied to a wide range of problems where nonhybrid functionals or functionals designed for kinetics fail.
Perturbed-chain equation of state for the solid phase
Authors: Cochran T. W. , Chiew Y. C.
Published: June 2006

A perturbed chain equation of state for the solid phase has been derived. Although the equation is general with respect to intermolecular potential, we incorporate the Lennard-Jones potential in this work in order to compare results from the model with available Monte Carlo simulation data. Two forms of the radial distribution function for the hard-sphere solid chain reference state are used in the model. First, a theoretically rigorous approach is taken by using a correlation of actual solid-phase Monte Carlo hard-sphere chain data for the radial distribution function. This results in good agreement with the Monte Carlo data only at high density. Second, a simple extended-density approximation was used for the radial distribution function. This second approach was found to work well across the entire density range including the vicinity of the solid-fluid equilibrium.
Quantum Monte Carlo study of the Ne atom and the Ne+ ion
Authors: Drummond N. D. , López Ríos P. , Ma A. , Trail J. R. , Spink G. G. , Towler M. D. , Needs R. J.
Published: June 2006

We report all-electron and pseudopotential calculations of the ground-state energies of the neutral Ne atom and the Ne+ ion using the variational and diffusion quantum Monte Carlo (DMC) methods. We investigate different levels of Slater-Jastrow trial wave function: (i) using Hartree-Fock orbitals, (ii) using orbitals optimized within a Monte Carlo procedure in the presence of a Jastrow factor, and (iii) including backflow correlations in the wave function. Small reductions in the total energy are obtained by optimizing the orbitals, while more significant reductions are obtained by incorporating backflow correlations. We study the finite-time-step and fixed-node biases in the DMC energy and show that there is a strong tendency for these errors to cancel when the first ionization potential (IP) is calculated. DMC gives highly accurate values for the IP of Ne at all the levels of trial wave function that we have considered.
Fluorescence excitation and single vibronic level emission spectroscopy of the ÃA″1←X̃A′1 system of CHCl
Authors: Tao Chong , Mukarakate Calvin , Reid Scott A.
Published: June 2006

We report new fluorescence excitation and single vibronic level emission spectra of the ÃA″1↔X̃A′1 system of CHCl. A total of 21 cold bands involving the pure bending levels 20n with n=1–7 and combination bands 20n301(n=4–7), 20n302(n=4–6), 10120n(n=5–7), 10120n301(n=4–6), and 10120n302(n=4) were observed in the 450–750nm region; around half of these are reported and/or rotationally analyzed here for the first time. Spectra were measured under jet-cooled conditions using a pulsed discharge source, and rotational analysis typically yielded band origins and rotational constants for both isotopomers (CH35Cl,CH37Cl). The derived ÃA″1 vibrational intervals are combined with results of Chang and Sears [J. Chem. Phys. 102, 6347 (1995)] to determine the excited state barrier to linearity [Vb=1920(50)cm−1]. The ÃA″1 state C–H stretching frequency is determined here for the first time, in excellent agreement with ab initio predictions. Following our observation of new bands in this system, we obtained the single vibronic level (SVL) emission spectra which probe the vibrational structure of the X̃A′1 state up to ∼9000cm−1 above the vibrationless level. The total number of X̃A′1 levels observed is around three times than that previously reported, and we observe five new ãA″3 state levels, including all three fundamentals. The results of a Dunham expansion fit of the ground state vibrational term energies, and comparisons with the previous experimental and recent high level ab initio studies, are reported. Our data confirm the previous assignment of the ãA″3 origin, and our value for T00(ã−X̃)=2172(2)cm−1 is in excellent agreement with theory. By exploiting SVL spectra from excited state levels with Ka′=1, we determine the effective rotational constant (A–B¯) of the triplet origin, also in good agreement with theory. Our results shed new light on the vibrational structure of the X̃A′1, ÃA″1, and ãA″3 states of CHCl, and, more generally, spin-orbit coupling in the monohalocarbenes.
Some experimental and theoretical results on the anodic patterns in plasma discharge
Authors: Gurlui S. , Agop M. , Strat M. , Strat Georgeta , Bacaita Simona , Cerepaniuc Adina
Published: June 2006

The dynamics of an interface plasma-plasma self-structured as a double anodic layer using the fractal space-time theory is established. So, for the fractal dimension D=2, the Schrödinger “fluid” is obtained as an irrotational movement of a Navier-Stokes fluid with an imaginary viscosity coefficient. In the deterministic case, the anodic double layer is described by a set of diffusion-reaction equations, a situation in which the equal diffusion curves are of the Koch-type and the self-structuring is given by means of the coherence of the electron-ion pairs. In the nondeterministic case, the anodic double layer is described by a set of time-dependent Schrödinger-type equations and the self-structuring is given by means of the negative differential resistance and the pulsation-potential linear dependence. Through the spontaneous symmetry breaking the Langmuir’s relations, the distributions of the potential field and charge densities have been obtained. The model was verified by means of our experimental data too.
Gyrokinetic linear theory of the entropy mode in a Z pinch
Authors: Ricci Paolo , Rogers B. N. , Dorland W. , Barnes M.
Published: June 2006

The linear gyrokinetic theory of the entropy mode is presented in a Z-pinch configuration in the regime of plasma β⪡1, focusing primarily on the parameter regime in which the ideal interchange mode is stable. The entropy mode is a small-scale, nonmagnetohydrodynamic mode that typically has peak growth rates at kρs∼1[ρs2=(T0e+T0i)∕(miΩci2)], with magnitudes comparable to those of ideal modes. The properties of this mode are studied as a function of the density and temperature gradients, plasma collisionality, and electron to ion temperature ratio.
Efficient diode-pumped Yb:Gd2SiO5 laser
Authors: Li Wenxue , Pan Haifeng , Ding Liang’en , Zeng Heping , Lu Wei , Zhao Guangjun , Yan Chengfeng , Su Liangbi , Xu Jun
Published: June 2006

An efficient diode-pumped laser was demonstrated by using an ytterbium-doped laser crystal, Yb:Gd2SiO5 (Yb:GSO), wherein Yb3+ ions exhibit the largest ground-state splitting among all the ytterbium-doped crystals. The Yb:GSO laser can be operated at a low pumping threshold, and the most efficient laser occurs around 1088nm since the corresponding emission band has the largest emission cross section and the lowest thermal population. A slope efficiency of 75% was demonstrated for a continuous-wave Yb:GSO laser at 1094nm, and self-pulsed lasers were achieved within the tunable range of 1091–1105nm, which are the longest laser wavelengths achieved for Yb3+ lasers.
Study of obliquely propagating dust acoustic solitary waves in magnetized tropical mesospheric plasmas with effect of dust charge variations and rotation of the plasma
Authors: Mushtaq A. , Shah H. A. , Rubab N. , Murtaza G.
Published: June 2006

The characteristics of obliquely propagating Dust Acoustic Waves (DAWs) in rotating and magnetized dusty plasma in the dayside tropical mesosphere are examined by incorporating adiabatic dust charge fluctuations. A Korteweg-de Vries equation is derived, which may support a nonlinear dust acoustic wave on a very slow time scale. The meteoritic dust in mesospheric plasmas on the dayside is charged positively due to photo- and thermionic emissions. The dynamics of the DAW with electronic, ionic, thermionic, and photoelectric currents along with obliqueness and effective gyrofrequency are studied. It is observed that the amplitude of the soliton depends directly on the obliqueness θ and dust charge variation, respectively, while the width is modified inversely with these parameters. It is also observed that the effective gyrofrequency modifies the width inversely.
Radial electric field formation by the gyrocenter shifts of the charge exchange reactions at the boundary of fusion device
Authors: Lee K. C.
Published: June 2006

As an important future energy source nuclear fusion researchers have been trying to solve the problem of radial electric field formation: the key factor of H-mode (high confinement mode) phenomena. Although a profound analysis has been developed on the turbulence suppression by E×B flow (E is the electric field and B is the magnetic field) as a basic mechanism of H-mode transition, the origin of the electric field and its relation with the neutrals are not fully explained. In this paper a novel model of radial electric field formation achieved by gyrocenter shifts during the charge exchange reactions and ion elastic scatterings with the neutrals is analyzed. From this analysis the formula of radial current density by the poloidal momentum sink at the reactions of charge exchange with boundary neutrals is developed with an example calculation for a given plasma condition similar to the experiment. The profile and absolute value of the saturated radial electric field are in agreement with the experimental results. An H-mode transition scenario is discussed by the gyrocenter shift model.
Polymer-based device for efficient mixing of viscoelastic fluids
Authors: Gan Hiong Yap , Lam Yee Cheong , Nguyen Nam-Trung
Published: June 2006

We demonstrated rapid mixing of viscoelastic fluids in microchannels constructed based on polymethyl methacrylate. Viscoelastic mixing without diffusion was achieved with an effective mixing length of less than 5mm and a relatively fast flow rate. With an abrupt contraction microgeometry (8:1 contraction ratio), we mixed two different viscoelastic fluids experimentally at very low Reynolds numbers, but enormous Peclet and elasticity numbers. This special geometrical configuration triggers flow instability, leading to turbulent and efficient mixing. This flow regime has negligible inertia effects but significant elastic effects.
Laser-induced-fluorescence observation of ion velocity distribution functions in a plasma sheath
Authors: Claire N. , Bachet G. , Stroth U. , Doveil F.
Published: June 2006

Experimental results obtained by laser-induced-fluorescence on metastable ion velocity distribution functions (MIVDF) in electrostatic presheaths and sheaths in argon plasmas produced by the thermoionic effect in a multipolar dc discharge are presented. The shape of the measured MIVDF are in qualitative agreement, for the presheath, with Emmert’s model and exhibit: (1) a Maxwellian profile at the center of the device where the potential is zero; (2) a distribution function’s shape made of three distinct parts at the entrance of the presheath. Inside the sheath the recorded MIVDF recovers a Maxwellian profile with a width unexpectedly related to the background neutral pressure. The velocity and potential profiles that can be deduced from the measured MIVDF show a strong influence of the primary electrons emitted by the filaments.
Effects of various axial flow profiles on the magneto-Rayleigh-Taylor instability in Z-pinch implosions
Authors: Zhang Y. , Ding N.
Published: June 2006

The stabilizing effect of different axial flow profiles on the magneto-Rayleigh-Taylor (MTR) instability in Z-pinch implosions is investigated with a compressible skin-current model. The numerical results show that the mitigation effect of the axial flow on the MRT instability is caused by the radial velocity shear, and it is highly susceptible to the shear value nearby the plasma outer surface. By adjusting the flow profile, the mitigation effect can be improved markedly.
Optical geometry analysis of the electromagnetic self-force
Authors: Sonego Sebastiano , Abramowicz Marek A.
Published: June 2006

We present an analysis of the behavior of the electromagnetic self-force for charged particles in a conformally static spacetime, interpreting the results with the help of optical geometry. Some conditions for the vanishing of the local terms in the self-force are derived and discussed.
Self-consistent nonlinear transverse waves in relativistic plasmas
Authors: Schaefer-Rolffs U. , Lerche I.
Published: June 2006

Previous investigations of the relativistic Weibel instability provide motivation to consider the nonlinear domain because, for asymmetric particle distributions, there is only an isolated unstable Weibel mode—reminiscent of nonlinear wave-types of behavior. From the collisionless Boltzmann equation together with Maxwell’s equations, a nonlinear, self-consistent wave equation is derived that is solvable for a broad range of distribution functions. For monochromatic electrons the nonlinear equation can be solved exactly, but results in an unphysical behavior of the magnetic field due to the compact support required of the distribution function. The general equation can be solved by asymptotic representation producing physically correct nonlinear wave solutions over bounded domains with varying internal structure of the electric and magnetic fields that range from nearly Gaussian to “sawtooth” in shape. A lower limit on the nonlinear wave amplitude is required in order that the nonlinear wave be of limited extent and so not represent a sinusoidal disturbance with no bounding domain. Limits for the nonlinear wave maximum magnetic field, and particle number density within the nonlinear wave, are given by considering the constraints on the nonlinear wave due to radiation processes, electron collision effects, and electron degeneracy pressure. The basic physical scale results are depicted mostly conducive for astrophysical applications involving relativistic flows and γ-ray emission, for which detailed investigations will be given elsewhere.
Multidimensional short-pulse space-charge-limited flow
Authors: Koh W. S. , Ang L. K. , Kwan T. J. T.
Published: June 2006

The two-dimensional models of the space-charge-limited (SCL) current density at the short pulse limit for which the electron pulse length is comparable or smaller than the electron transit time across the gap (i.e., XCL⩽1) have been developed. In particular, the scaling laws for short-pulse SCL electron emission in a planar diode with a circular emitting strip and a cylindrical diode with a finite length have been obtained and verified with particle-in-cell simulation. It is found that the enhancement (in terms of the long-pulse SCL current density) is proportional to XCL−1 for small XCL for both planar and cylindrical cases. The enhancement of the cylindrical short-pulse SCL current density is also found to be larger for the convergent flow (cathode outside) than divergent flow (cathode inside). Multidimensional effects are important only for small emitting strips with size comparable to the effective penetration distance (into the gap) of the short-pulse electron beam. Smooth transition between the short-pulse regime and the long pulse (steady-state) regime is demonstrated.
Simulations of Kelvin-Helmholtz modes in partially ionized dusty plasmas comparing different charge numbers, charge polarities, and masses of the dust
Authors: Wiechen Heinz M.
Published: June 2006

Results of multifluid simulations of Kelvin-Helmholtz modes in partially ionized, dusty plasmas are presented assuming different masses and charges of the dust. The results show a stabilizing effect for more massive dust grains and indicate a destabilizing effect for higher charge numbers. No significant dependence on the charge polarity of the dust was found.
Planar MgB2 superconductor-normal metal-superconductor Josephson junctions fabricated using epitaxial MgB2∕TiB2 bilayers
Authors: Chen Ke , Cui Y. , Li Qi , Xi X. X. , Cybart Shane A. , Dynes R. C. , Weng X. , Dickey E. C. , Redwing J. M.
Published: June 2006

We have fabricated planar superconductor-normal metal-superconductor MgB2 Josephson junctions using TiB2 as the barrier material. On a bilayer film of MgB2∕TiB2 on SiC substrate, MgB2 was locally removed to create a gap of ⩽50nm, separating the MgB2 film into two electrodes. A Josephson coupling is established through the TiB2 film across the gap by proximity effect. The junctions exhibit resistively shunted junction like current-voltage characteristics up to 31K. An ac Josephson effect was observed and the behavior of the Shapiro steps are in good agreement with theoretical predictions. The magnetic field modulation of the critical current also agrees with the thin film planar junction behavior.