bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and magnetic properties of Ni50Mn37Sn13 Heusler alloy ribbons
Authors: Santos J. D. , Sanchez T. , Alvarez P. , Sanchez M. L. , Sánchez Llamazares J. L. , Hernando B. , Escoda Ll. , Suñol J. J. , Varga R.
Published: February 2008

The Heusler alloy Ni50Mn37Sn13 was successfully produced as ribbon flakes of thickness around 7–10μm melt spinning. Fracture cross section micrographs in the ribbon show the formation of a microcrystalline columnarlike microstructure, with their longer axes perpendicular to the ribbon plane. Phase transition temperatures of the martensite-austenite transformation were found to be MS=218K, Mf=207K, AS=224K, and Af=232K; the thermal hysteresis of the transformation is 15K. Ferromagnetic L21 bcc austenite phase shows a Curie point of 313K, with cell parameter a=0.5971(5)nm at 298K, transforming into a modulated 7M orthorhombic martensite with a=0.6121(7)nm, b=0.6058(8)nm, and c=0.5660(2)nm, at 150K.
Transient dimer formation in supercritical carbon dioxide as seen from Raman scattering
Authors: Cabaço M. Isabel , Longelin S. , Danten Y. , Besnard M.
Published: February 2008

The polarized and depolarized Raman profiles of supercritical CO2 have been measured in the region of the ν2 bending mode (forbidden transition at about 668cm−1) and for the Fermi dyad (1285 and 1388cm−1) along the isotherms 307, 309, 313, and 323K in a reduced density domain 0.04<ρ*=ρ∕ρC<2.04 (ρC∼467.6kgm−3, ρC is the critical density). The spectral features associated with the ν2 mode (degeneracy removal of the mode and Raman intensity activation) are found to be due to the formation of transient complexes. This is supported by the spectral signatures predicted for parallel slipped dimer and trimers (cyclic and noncyclic) from ab initio calculations taking into account the frequency anharmonicity. The band-shape analysis of the Fermi doublet (observed in the spectral range of 1260–1400cm−1) shows that on the subpicosecond time scale of the Raman spectroscopy, a tagged CO2 molecule probed two kinds of environment in its first shell of neighbors independent of local density enhancement phenomenon. The first one involves interactions of CO2 with surrounding molecules in the first shell whereas the latter is associated with a transient dimer formation. Finally, a broad band observed between the Fermi dyad (at about 1335cm−1) is assessed from symmetry considerations and from its depolarization ratio as a further evidence of transient complex formation in supercritical CO2.
Highly charged ion beam applied to lithography technique (invited)
Authors: Momota Sadao , Nojiri Yoichi , Taniguchi Jun , Miyamoto Iwao , Morita Noboru , Kawasegi Noritaka
Published: February 2008

In various fields of nanotechnology, the importance of nanoscale three-dimensional (3D) structures is increasing. In order to develop an efficient process to fabricate nanoscale 3D structures, we have applied highly charged ion (HCI) beams to the ion-beam lithography (IBL) technique. Ar-ion beams with various charge states (1+ to 9+) were applied to fabricate spin on glass (SOG) and Si by means of the IBL technique. The Ar ions were prepared by a facility built at Kochi University of Technology, which includes an electron cyclotron resonance ion source (NANOGAN, 10GHz). IBL fabrication was performed as a function of not only the charge state but also the energy and the dose of Ar ions. The present results show that the application of an Ar9+ beam reduces the etching time for SOG and enhances the etching depth compared with those observed with Ar ions in lower charged states. Considering the high-energy deposition of HCI at a surface, the former phenomena can be understood consistently. Also, the latter phenomena can be understood based on anomalously deep structural changes, which are remarkable for glasses. Furthermore, it has also been shown that the etching depth can be easily controlled with the kinetic energy of the Ar ions. These results show the possibilities of the IBL technique with HCI beams in the field of nanoscale 3D fabrication.
Colossal magnetoresistance properties of Nd-doped Bi0.5Sr0.5MnO3
Authors: Savitha Pillai S. , Santhosh P. N. , Markandeyulu G. , John Thomas P. , Tuna F.
Published: February 2008

We have studied structure, transport, and magnetic properties of NdxBi0.5−xSr0.5MnO3 (NBSMO) (x=0.2 and 0.4) through x-ray diffraction, magnetoresistance, and magnetization measurements. The Rietveld analysis of the x-ray diffraction data shows that the NBSMO crystallizes in an orthorhombic perovskite structure with Pbnm space group for x=0.2 and Imma space group for x=0.4. The lattice variations indicate that the highly polarizable 6s2 lone pair of Bi ion is screened and the structural changes occur in accordance with change in the average radius of A-site cations. Magnetotransport studies reveal that both samples are variable range hopping semiconductors and the hopping depends on the orientation of localized spin moment of the electrons. Magnetic studies confirm that substituting Bi with Nd collapses the charge ordered antiferromagnetic (AFM) state of Bi0.5Sr0.5MnO3 to ferromagnetic state, with TC’s∼276 and ∼278K, for x=0.2 and 0.4, respectively. The observed enhancement in colossal magnetoresistance effect in NBSMO compared to Bi0.5Sr0.5MnO3 is attributed to the presence of competing ferromagnetic and charge ordered AFM state.
The use of particle-in-cell codes for designing electron cyclotron resonance ion sources (invited) (abstract)
Authors: Smithe David N.
Published: February 2008

We illustrate how particle-in-cell simulation techniques have been useful in past design and modeling of electron cyclotron resonance (ECR) ion sources, and discuss advances that will benefit how they can continue to be useful in the future. Electromagnetic particle-in-cell codes excel in situations of interesting geometry and magnetic field nonuniformity. We review early particle-in-cell design work leading up to the validation of volume heating effects in carefully tailored flat-field-type ECR sources. Modern computing power now favors fully three-dimensional simulation, with more realistic rf injection and accessibility modeling, and confinement field representation, for more optimal design capability, and more thorough investigation of electromagnetic transport in novel, more efficient ECR heating concepts. We also demonstrate algorithm advances, including particle-fluid hybrid methods that promise relief from computational restrictions of earlier simulations, specifically the scaling requirements associated with the small Debye length of the ECR plasma relative to its total size. Particle-in-cell codes also offer the potential for accurate modeling of particle creation, destruction, and transport dynamics. We will illustrate these capabilities from recent work incorporating neutral transport, ionization, and recombination physics, aimed at optimization of ion current in heavy ion sources. This work involves accurate modeling of geometrically localized sources, and points toward future integrated models covering the full range of physics from ion production to extraction.
Ni implanted ZnO single crystals: Correlation between nanoparticle formation and defect structure
Authors: Zhou Shengqiang , Potzger K. , Kuepper K. , Grenzer J. , Helm M. , Fassbender J. , Arenholz E. , Denlinger J. D.
Published: February 2008

We show that metallic secondary phase formation inside ZnO(0001) single crystals implant-doped with Ni at an atomic concentration of 5% can be suppressed. All the Ni ions are in the 2+ valence state after mild postannealing. The suppression is achieved by means of annealing of the crystals in high vacuum prior to implantation and is correlated with the introduction of structural disorder. The observed ferromagnetic properties of the preannealed crystals are evidently induced by defects and not primarily by the Ni doping. They degrade at ambient temperature within several days.
Microfabricated water immersion zone plate optical tweezer
Authors: Schonbrun Ethan , Rinzler Charles , Crozier Kenneth B.
Published: February 2008

We demonstrate the trapping of beads in water with a microfabricated Fresnel zone plate. Beads are loaded onto the microfabricated optical traps using conventional optical tweezers and fluorescence microscopy is used to track bead position. Analysis of the bead position as a function of time is used to determine trapping stiffness. We present experiments showing the three-dimensional trapping of 2μm diameter beads with trapping stiffnesses that are comparable to conventional optical tweezers when the zone plate efficiency is taken into account.
On the pressure-induced loss of crystallinity in orthophosphates of zinc and calcium
Authors: Shakhvorostov Dmitry , Müser Martin H. , Mosey Nicholas J. , Munoz–Paniagua David J. , Pereira Gavin , Song Yang , Kasrai Masoud , Norton Peter R.
Published: February 2008

A recently suggested mechanism for the stress memory of various metal phosphates is investigated experimentally. Based on first-principles simulations [N. J. Mosey et al., Science 307, 1612 (2005)], it had been argued that atoms with flexible coordination, such as zinc or heavy-metal cations, act as network-forming agents, undergoing irreversible pressure-induced changes in bonding that lead to increased connectivity between phosphate anions. In the present study, orthophosphates of zinc and calcium were exposed to high pressures on surfaces and in diamond anvil cells. An additional set of first-principles simulations was accomplished on α-orthophosphate of zinc, which suggested that this material was already cross-linked before compression but that it nevertheless underwent a reversible coordination change under pressure in agreement with the experimental results presented here. Raman spectra indicate an irreversible, pressure-induced loss of long-range crystallinity. The pressures required to induce these changes are around 7GPa for the zinc phosphates, while they are close to 21GPa for the calcium phosphates. Hydrogenation of the metal phosphate lowers the threshold pressure by approximately 2–3GPa in both cases. Moreover, α-orthophosphate of zinc could be partially amorphisized under nonisotropic pressure on copper foils.
Understanding self-assembly of rod-coil copolymer in nanoslits
Authors: Cheng Lisheng , Cao Dapeng
Published: February 2008

Rod-coil diblock copolymers are a special kind of molecule containing a rigid rod and a flexible part. We present a systematic study on self-assembly of the rod-coil copolymers in nanoslits using a hybrid density functional theory. The self-assembly of the rod-coil molecule is driven by the bulk concentration, and there exists a critical bulk concentration beyond which the rod-coil molecule self-assembled into ordered lamellar structures in the slit, otherwise it is in a disordered state. By monitoring the effect of the interaction (εTT*) of molecular tail on the self-assembly, we found that in the nanoslit of H=13σ, it is at εTT*=8 rather than εTT*=10 or εTT*=12 that the minimal critical bulk concentration occurs. It may be because the strong tail-tail interaction leads to aggregation of the copolymer molecules in bulk phase, and the resulting supramolecular structures are fairly difficult to enter the slit due to the depletion effect. At a fixed slit, the structural evolution of the self-assembled film with the bulk concentration is observed, including trilayer and five-layer lamellar structures, smectic-A, smectic-C, and a mixture of smectic-A and smectic-C liquid crystal phases and so on. We found that the critical bulk concentration, corresponding to the disordered-ordered phase transition, greatly depends on the separation between two walls, and it changes periodically with the increase of the slit width. In addition, it is also found that the molecular flexibility is one of key factors determining the self-assembled structure in the slit, and the critical bulk density increases with the molecular flexibility.
Critical gradients and plasma flows in the edge plasma of Alcator C-Mod
Authors: LaBombard B. , Hughes J. W. , Smick N. , Graf A. , Marr K. , McDermott R. , Reinke M. , Greenwald M. , Lipschultz B. , Terry J. L. , Whyte D. G. , Zweben S. J. ,   Alcator C-Mod Team
Published: February 2008

Recent experiments have led to a fundamental shift in our view of edge transport physics; transport near the last-closed flux surface may be more appropriately described in terms of a critical gradient phenomenon rather than a diffusive and/or convective paradigm. Edge pressure gradients, normalized by the square of the poloidal magnetic field strength, appear invariant in plasmas with the same normalized collisionality, despite vastly different currents and magnetic fields—a behavior that connects with first-principles electromagnetic plasma turbulence simulations. Near-sonic scrape-off layer (SOL) flows impose a cocurrent rotation boundary condition on the confined plasma when B×∇B points toward the active x-point, suggesting a link to the concomitant reduction in input power needed to attain high-confinement modes. Indeed, low-confinement mode plasmas are found to attain higher edge pressure gradients in this configuration, independent of the direction of B, evidence that SOL flows may affect transport and “critical gradient” values in the edge plasma.
Electronic transport properties of amorphous indium-gallium-zinc oxide semiconductor upon exposure to water
Authors: Park Jin-Seong , Jeong Jae Kyeong , Chung Hyun-Joong , Mo Yeon-Gon , Kim Hye Dong
Published: February 2008

The effect of water exposure on amorphous indium-gallium-zinc oxide (a-IGZO) semiconductors was reported. It was found that water can diffuse in and out of the a-IGZO film, reversibly affecting the transistor properties. Two competing mechanisms depending on the thickness of the active channel were clarified. The electron donation effect caused by water adsorption dominated for the thicker a-IGZO films (⩾100nm), which was manifested in the large negative shift (>14V) of the threshold voltage. However, in the case of the thinner a-IGZO films (⩽70nm), the dominance of the water-induced acceptorlike trap behavior was observed. The direct evidence for this behavior was that the subthreshold swing was greatly deteriorated from 0.18V/decade (before water exposure) to 4.4V/decade (after water exposure) for the thinnest a-IGZO films (30nm). These results can be well explained by the screening effect of the intrinsic bulk traps of the a-IGZO semiconductor.
360° domain wall generation in the soft layer of magnetic tunnel junctions
Authors: Hehn M. , Lacour D. , Montaigne F. , Briones J. , Belkhou R. , Moussaoui S. El , Maccherozzi F. , Rougemaille N.
Published: February 2008

High spatial resolution x-ray photoemission electron microscopy technique has been used to study the influence of the dipolar coupling taking place between the NiFe and the Co ferromagnetic electrodes of micron sized, elliptical shaped magnetic tunnel junctions. The chemical selectivity of this technique allows us to observe independently the magnetic domain structure in each ferromagnetic electrode. The combination of this powerful imaging technique with micromagnetic simulations allows us to evidence that a 360° domain wall can be stabilized in the NiFe soft layer. In this letter, we discuss the origin and the formation conditions of those 360° domain walls evidenced experimentally and numerically.
Criticality of bistability phenomenon in deformed helix ferroelectric liquid crystal
Authors: Prakash J. , Mehta D. S. , Choudhary A. , Kaur S. , Rathore V. , Biradar A. M.
Published: February 2008

The dynamics of bistability in deformed helix ferroelectric liquid crystal have been investigated by electro-optical method. The threshold value of the voltage required to switch the molecules of deformed helix ferroelectric liquid crystals (DHFLC) material has been studied by applying triangular wave pulse and texture observation under polarizing microscope. Two peaks have been observed in low and high frequency regimes on the application of triangular wave pulse to the sample. It has been proposed that the first peak is due to helix unwinding-winding process and the second is due to molecular reorientation process. The occurrence of double peak has been predicted to have close correlation with the observance of memory effect in DHFLC material, which is critically dependent on frequency and applied voltage, on the application of time delayed square wave pulse to the sample cell. The conditions for dynamic and static memory effects in DHFLC material have also been discussed in detail.
Self-consistent field theory for lipid-based liquid crystals: Hydrogen bonding effect
Authors: Lee Won Bo , Mezzenga Raffaele , Fredrickson Glenn H.
Published: February 2008

A model to describe the self-assembly properties of aqueous blends of nonionic lipids is developed in the framework of self-consistent field theory (SCFT). Thermally reversible hydrogen bonding between lipid heads and water turns out to be a key factor in describing the lyotropic and thermotropic phase behavior of such systems. Our model includes reversible hydrogen bonding imposed in the context of the grand canonical ensemble and exact conditions of binding equilibrium. The lipid molecules are modeled as a rigid head and a flexible Gaussian tail, and the water molecules are treated explicitly. Here, we focus on systems where the lipid molecule has a relatively small hydrophilic head compared to the hydrophobic tail, such as monoolein in water. Experimentally, this system has both normal phase sequences (inverted hexagonal to inverted double gyroid cubic phase) and reverse phase sequences (lamellar to inverted double gyroid cubic phase) as the water volume fraction increases. From SCFT simulations of the model, two phase diagrams corresponding to temperature independent or dependent interaction parameters χ are constructed, which qualitatively capture the phase behavior of the monoolein-water mixture. The lattice parameters of the simulated mesophases are compared with the experimental values and are found to be in semiquantitative agreement. The role of various structural and solution parameters on the phase diagrams is also discussed.
Dynamics of an electron driven by relativistically intense laser radiation
Authors: Galkin A. L. , Korobkin V. V. , Romanovsky M. Yu. , Shiryaev O. B.
Published: February 2008

The dynamics of an electron driven by a relativistically intense laser pulse is analyzed on the basis of the equation of motion with the Lorentz force in the cases of linear and circular polarizations. Laser fields with nonplane phase fronts accelerate electrons in the longitudinal direction. An electron initially at rest is found not to move along figure-eight trajectories for the linear polarization, and not to move along circular trajectories for the circular polarization.
Electron capture induced dissociation of nucleotide anions in water nanodroplets
Authors: Liu B. , Haag N. , Johansson H. , Schmidt H. T. , Cederquist H. , Brøndsted Nielsen S. , Zettergren H. , Hvelplund P. , Manil B. , Huber B. A.
Published: February 2008

We have studied the outcome of collisions between the hydrated nucleotide anion adenosine 5′-monophosphate (AMP) and sodium. Electron capture leads to hydrogen loss as well as water evaporation regardless of the initial number m of water molecules attached to the parent ion (m⩽16). The yield of dianions with microsecond lifetimes increases strongly with m, which is explained from dielectric screening of the two charges by the water nanodroplet. For comparison, collision induced dissociation results in water losses with no or very little damage of the AMP molecule itself.
Leakage mechanisms in bismuth ferrite-lead titanate thin films on Pt∕Si substrates
Authors: Khan Mikael A. , Comyn Tim P. , Bell Andrew J.
Published: February 2008

( 1 − x ) Bi Fe O 3 – x Pb Ti O 3  (0.5<x<0.3) thin films have been reported to exhibit high remanent polarizations but device integration is hindered by the presence of leakage currents. An insight into the nature of leakage mechanisms in the films is presented. Films with x=0.4 and 0.5 exhibit lower leakage currents as compared to x=0.3 films. At applied fields above 190kVcm−1, in the region of the coercive field of these films, x=0.4 and 0.5 exhibit a Poole–Frenkel mechanism while films with x=0.3 exhibit a combination of space charge limited current and the Schottky effect.
Comment on “A new derivation of the plasma susceptibility tensor for a hot magnetized plasma without infinite sums of products of Bessel functions” [Phys. Plasmas 14, 092103 (2007)]
Authors: Lerche I. , Schlickeiser R. , Tautz R. C.
Published: February 2008

This Comment discusses the representations of infinite sums of Bessel functions that occur in plasma problems involving collisionless plasmas treated from a plasma kinetic viewpoint. In addition, the influence of such summation techniques on dispersion relations for plasma waves involving a background magnetic field is discussed.
Structural and magnetic properties of magnetite-containing epitaxial iron oxide films grown on MgO(001) substrates
Authors: Kado T.
Published: February 2008

The structural and magnetic properties of three kinds of Fe oxide films—Fe3O4, a berthollide type of Fe oxide, and a composite of Fe3O4 and FeO—grown on MgO(001) substrates epitaxially at 423K by pulsed laser deposition were investigated by magnetoresistance measurement and grazing incidence x-ray diffraction. The Fe3O4 film had the largest negative magnetoresistance and the roughest film-substrate interface. The very close lattice matching of single-phase Fe3O4 and MgO facilitates the formation of antiphase boundaries due to natural growth defects and of a rough interface probably due to cation interdiffusion.
Magnetoelectric characteristics of a dual-mode magnetostrictive/piezoelectric bilayered composite
Authors: Li Lei , Chen Xiang Ming
Published: February 2008

The magnetoelectric characteristics of a Terfenol-D∕Pb(Zr,Ti)O3 bilayered composite were investigated, and an additional bending vibration mode due to the asymmetrical structure was observed besides the length vibration mode which also acted in the symmetrical trilayered composites. The module of magnetoelectric coefficient for the bilayered composite at 1kHz was significantly lower than those for the trilayered composites, and one more resonant peak was observed at a lower frequency of 15.57kHz. The combination of bending and length vibration modes was responsible for the unique magnetoelectric characteristics of the dual-mode bilayered composite. Moreover, theoretical discussion indicated that the shape of the lower-frequency resonant peak was variable and determined by the module and phase differences for the two vibration modes.
The influence of Schottky contact metals on the strain of AlGaN barrier layers
Authors: Lin Zhaojun , Zhao Jianzhi , Corrigan Timothy D. , Wang Zhen , You Zhidong , Wang Zhanguo , Lu Wu
Published: February 2008

Ir and Ni Schottky contacts on strained Al0.25Ga0.75N∕GaN heterostructures, and the Ni Schottky contact with different areas on strained Al0.3Ga0.7N∕GaN heterostructures have been prepared. Using the measured capacitance-voltage curves and the current-voltage curves obtained from the prepared Schottky contacts, the polarization charge densities of the AlGaN barrier layer for the Schottky contacts were analyzed and calculated by self-consistently solving Schrodinger’s and Poisson’s equations. It is found that the polarization charge density of the AlGaN barrier layer for the Ir Schottky contact on strained Al0.25Ga0.75N∕GaN heterostructures is different from that of the Ni Schottky contact, and the polarization charge densities of the AlGaN barrier layer for Ni Schottky contacts with different areas on strained Al0.3Ga0.7N∕GaN heterostructures are different corresponding to different Ni Schottky contact areas. As a result, the conclusion can be made that Schottky contact metals on strained AlGaN∕GaN heterostructures have an influence on the strain of the AlGaN barrier layer.
Systematic investigation on structure and excitonic-related transitions: An evidence for Zn1−xCoxO alloy film as a wide gap semiconductor
Authors: Xiao Zhiyan , Matsui Hiroaki , Hasuike Noriyuki , Harima Hiroshi , Tabata Hitoshi
Published: February 2008

Systematic investigations were performed concerning the crystal structure and excitonic-related transitions of Zn1−xCoxO layers. The substitution of Co atoms for Zn sites was initially identified from the intra-emissions originating from the 3d levels of the Co2+ ions. Microresonant Raman scattering (μ-RRS) revealed that the local crystal structure of the host was disordered even at Co concentrations of a few percent, as determined by monitoring the A1(LO) mode and also supported by the ω-rocking curves obtained from x-ray diffraction. A critical point (Γ-edge) derived from magnetic circular dichroism systematically shifted to higher energy with increasing x, representing clear evidence for a widening of the band gap, and that the photoluminescent peaks correlated closely with absorption peaks related to excitonic transitions. The obvious excitonic structures gradually became diffuse with the appearance of photoexcited charge-transfer levels of Co2+ ions when x exceeded 2%. This allowed for observations of excitonic luminescence of samples with a Co content not exceeding 0.8%. The excitonic luminescence for all Co-doped ZnO layers was superimposed distinctly with Stokes and anti-Stokes LO phonons. This was attributed to outgoing multiphonon resonance Raman scattering due to a Fröhlich interaction based on strong coupling between photoexcited carriers and LO phonons, and further supported by the results of μ-RRS.
Photoelectric effects in x-ray preionization for excimer laser gases
Authors: Azarov A. V. , Peters P. J. M. , Boller K.-J.
Published: February 2008

We present detailed measurements on the x-ray preionization electron density in a discharge chamber filled with different gases relevant to discharge pumped high-pressure excimer lasers. By comparing experimental results with the theoretical electron densities, we conclude that the observed preionization is inconsistent with the standard picture of direct ionization through x-ray absorption in the gas. We conclude that depending on the gas pressure, type of gas, and the gap length between the discharge electrodes used, x-ray preionization in excimer gases is, to a significant extent or even dominantly, based on a different mechanism. We identify that this mechanism is based on fast photoelectrons emitted by the cathode into the discharge chamber.
Design, implementation, and control of a six-axis compliant stage
Authors: Hu Kaixuan , Kim Jung H. , Schmiedeler James , Menq Chia-Hsiang
Published: February 2008

This paper presents the development of a new compact six-axis compliant stage employing piezoelectric actuators to achieve six-axis actuation with nanometer resolution. The integration of direct metrology in the object space, based on real-time visual feedback, enables high-precision motion control. In order to achieve greater motion range, the simple and compact decoupled mechanical structure utilizes two-tap displacement amplifiers for in-plane motion and semibridge amplifiers for out-of-plane motion. The kinematic analysis of the stage is presented. Laterally sampled white light interferometry was implemented to measure the out-of-plane motion of the stage, and a measurement model associated with the designed target patterns is developed to estimate the in-plane motion in real time. Together, they form a visual tracking system and are integrated with the six-axis compliant stage to realize precision six-axis real-time visual servo-control. Experimental results demonstrate that the six-axis compliant stage has the motion range of 77.42μm, 67.45μm, 24.56μm, 0.93mrad, 0.95mrad, and 3.10mrad, and the resolution of ±5nm, ±8nm, ±10nm, ±10μrad, ±10μrad, and ±20μrad for x-axis, y-axis, and z-axis translation and rotation, respectively.
Laser action in LaAlO3:Nd3+ single crystal
Authors: Dereń P. J. , Bednarkiewicz A. , Goldner Ph. , Guillot-Noël O.
Published: February 2008

The spectral and laser properties of Nd3+ doped (1wt%) LaAlO3 single crystal are presented. The energy levels of the Nd3+ ion in the LaAlO3 matrix were assigned. The Judd–Ofelt parameters Ω2=1.346, Ω4=4.490, and Ω6=5.168 (all ×10−20cm−2) were evaluated. The absorption σabs and emission σemi cross sections at the respective pumping and emission wavelengths were calculated to be σabs(789.7nm)=2.42×10−20cm2, σemi(909nm)=5.02×10−20cm2, and σemi(1080nm)=7.03×10−20cm2. Continuous-wave laser action at 1080nm in LaAlO3:Nd3+ was obtained.
Turning electrospun poly(methyl methacrylate) nanofibers into graphitic nanostructures by in situ electron beam irradiation
Authors: Duan H. G. , Xie E. Q. , Han L.
Published: February 2008

Using ultrathin electrospun poly(methyl methacrylate) (PMMA) nanofibers as precursor, graphitic nanofibers, nanobridges, nanocones, and fullerenelike onions could be prepared by electron beam irradiation in a controlled manner. With the help of the high resolution transmission electron microscopy, the real time processing of the carbonization and graphitization of the PMMA nanofibers could be investigated. This way to obtain graphitic nanostructures has promising applications in graphitic carbon nanostructure electronics and devices. Because PMMA is a widely used standard high resolution electron resist, this graphitization could be combined with electron beam lithography to obtain high resolution patterned graphitic circuits.
Surface roughness influence on the quality factor of high frequency nanoresonators
Authors: Palasantzas G.
Published: February 2008

Surface roughness influences significantly the quality factor of high frequency nanoresonators for large frequency–relaxation times (ωτ>1) within the non-Newtonian regime, where a purely elastic dynamics develops. It is shown that the influence of short wavelength roughness, which is expressed by the roughness exponent H for the case of self-affine roughness, plays a significant role in comparison with the effect of the long wavelength roughness parameters such as the rms roughness amplitude and the lateral roughness correlation length. Therefore, the surface morphology can play an important role in designing high frequency resonators operating within the non-Newtonian regime.
Generation of ultrashort optical pulses using multiple coherent anti-Stokes Raman scattering in a crystal at room temperature
Authors: Matsubara Eiichi , Sekikawa Taro , Yamashita Mikio
Published: February 2008

We demonstrate Fourier synthesis of multiple coherent anti-Stokes Raman scattering signals in a LiNbO3 crystal at room temperature. The signals up to the 20th order (470–800nm) were generated by two crossing femtosecond Ti:sapphire laser pulses. Angle dispersion of the signals was compensated into one white-continuum beam by modifying a conventional 4f configuration. Spectral phase of the signal was measured by spectral phase interferometry for direct electric-field reconstruction. Isolated pulses with 25fs duration at 1kHz were generated only by appropriately aligning the angle-dispersion compensator. This result opens the possibility of the generation of subfemtosecond pulses in the visible region.
Red single-photon emission from an InP∕GaInP quantum dot embedded in a planar monolithic microcavity
Authors: Roßbach Robert , Reischle Matthias , Beirne Gareth J. , Jetter Michael , Michler Peter
Published: February 2008

Using micro-photoluminescence, we demonstrate single-photon emission in the visible (red) spectral range using self-assembled InP quantum dots embedded in a planar microcavity realized by monolithically grown high reflectivity AlGaAs distributed Bragg reflectors. A full width at half maximum of 130μeV at 5K was observed from a single quantum dot coupled to the fundamental cavity resonance. Photon correlation measurements performed under continuous wave excitation show a clear antibunching behavior [g(2)(0)=0.13] as expected for a single-photon emitter. Saturation count rates up to 1.5MHz (8.1MHz into the first lens, with an extraction efficiency of 4.1%) were observed.
Precision nanoscale domain engineering of lithium niobate via UV laser induced inhibition of poling
Authors: Sones C. L. , Muir A. C. , Ying Y. J. , Mailis S. , Eason R. W. , Jungk T. , Hoffmann Á. , Soergel E.
Published: February 2008

Continuous wave ultraviolet laser irradiation at λ=244nm on the +z face of undoped and MgO doped congruent lithium niobate single crystals has been observed to inhibit ferroelectric domain inversion. The inhibition occurs directly beneath the illuminated regions, in a depth greater than 100nm during subsequent electric field poling of the crystal. Domain inhibition was confirmed by both differential domain etching and piezoresponse force microscopy. This effect allows the formation of arbitrarily shaped domains in lithium niobate and forms the basis of a high spatial resolution microstructuring approach when followed by chemical etching.
Performance improvement of TiO2∕P3HT solar cells using CuPc as a sensitizer
Authors: Shen Liang , Zhu Guohui , Guo Wenbin , Tao Chen , Zhang Xindong , Liu Caixia , Chen Weiyou , Ruan Shengping , Zhong Zhicheng
Published: February 2008

In this work, a new type of TiO2/polymer solar cells was fabricated. The device structure was indium tin oxide titanium dioxide (TiO2)/ copper phthalocyanine (CuPc)/poly(3-hexylthiophene) (P3HT)/Au. In this architecture, TiO2 was designed to act as electron acceptor, and P3HT was electron donor. CuPc was used as a sensitizer to enhance photon absorption. The results show that by inserting CuPc between P3HT and TiO2 layers, the light absorption, excitons separation, and photocurrent under illumination are dramatically improved. The device has a short current density (JSC) of 1.15mA∕cm2 and power conversion efficiency (η) of 0.28% without CuPc layer. However, JSC and η turn to be 2.22mA∕cm2 and 0.66%, respectively, with a 20nm thickness CuPc layer under air mass 1.5 global (AM1.5G) illumination with the intensity of 100mW∕cm2. The performance improvement can be attributed to the higher carrier mobility and the stronger photon absorption using CuPc as a sensitizing layer.
Temperature dependent photoluminescence study on phosphorus doped ZnO nanowires
Authors: Shan C. X. , Liu Z. , Hark S. K.
Published: February 2008

We report temperature dependent photoluminescence studies on phosphorus doped ZnO nanowires. The shape of the spectra is very similar to those of phosphorus doped ZnO films. The photoluminescence spectrum at 10K is dominated by neutral acceptor bound exciton (AX0) emissions. The acceptor binding energy determined also agrees with the corresponding value in phosphorus doped films. Studies on the AX0 intensity show two quenching channels, associated with the thermal dissociations of AX0 to a free exciton and of shallow residual donors. The residual donors revealed provide a clue for the difficulty in p doping of ZnO.
Photovoltaic effects and its oxygen content dependence in BaTiO3−δ∕Si heterojunctions
Authors: Xing Jie , Jin Kui-Juan , Lu Huibin , He Meng , Liu Guozhen , Qiu Jie , Yang Guozhen
Published: February 2008

Three oxide heterojunctions made of BaTiO3−δ∕Si have been fabricated under various oxygen pressures by laser molecular beam epitaxy. They all exhibited nonlinear and rectifying I-V characteristics but with a large difference in the rectification behaviors. Their photoelectric properties and dependences on oxygen contents in BaTiO3−δ films have been experimentally studied. We found that the photovoltaic effects depended strongly on the oxygen contents of the BaTiO3−δ films. The possible mechanism was proposed based on the band structure of the p-n heterojunctions.
Control of spontaneous emission coupling factor β in fiber-coupled microsphere resonators
Authors: Takashima Hideaki , Fujiwara Hideki , Takeuchi Shigeki , Sasaki Keiji , Takahashi Masahide
Published: February 2008

The spontaneous emission coupling factor β is studied for fiber-coupled microspheres with a thin gain layer of phosphorus codoped sol-gel erbium silica-aluminum glass. From the input-output characteristics of the lasing, β=0.039 is estimated for a sample with a gain layer on the sphere surface. β is estimated to increase to 0.19 when an additional silica glass thin layer is overcoated to improve the overlap between the gain layer and the optical mode of the lasing inside the sphere.
Effect of postdeposition annealing on the interfacial and electrical properties of high-k NdOxNy gate dielectrics
Authors: Pan Tung-Ming , Hou Sung-Ju
Published: February 2008

The authors proposed a high-k NdOxNy gate dielectric grown on silicon substrate by reactive rf sputtering. It is found that the NdOxNy gate dielectric after annealing at 700°C exhibits excellent electrical properties such as high capacitance value, small interface state, low leakage current, and almost no hysteresis in the capacitance-voltage curves. This indicates that annealing at 700°C treatment can suppress the interfacial layer and silicate formation, reduce interface traps, and anneal out defects.
Influence of 100MeV oxygen ion irradiation on Ni∕n-Si (100) Schottky barrier characteristics
Authors: Kumar Sandeep , Katharria Y. S. , Kanjilal D.
Published: February 2008

The influences of high energy ion irradiation on the Ni∕n-Si Schottky barrier are discussed as a function of irradiation fluence. The variations in Schottky diode parameters are studied by using in situ current-voltage characterization in a fluence range between 1×109 and 1×1013ions∕cm2. The ion irradiation results in an increase of Schottky barrier height from a value of 0.59eV for unirradiated diode to 0.68eV after irradiation at a fluence of 1×1013ions∕cm2. A decrease of the leakage current by about two orders of magnitude was observed after ion irradiation. These results are interpreted in terms of the ion irradiation induced defects inside the materials.
Doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide
Authors: Achatz P. , Pernot J. , Marcenat C. , Kacmarcik J. , Ferro G. , Bustarret E.
Published: February 2008

We report an experimental determination of the doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide. Low temperature transport measurements down to 360mK and temperature dependent Raman experiments down to 5K, together with secondary ion mass spectroscopy profiling, suggest a critical aluminum concentration lying between 6.4 and 8.7×1020cm−3 for the metal-insulator transition in these epilayers grown by the vapor-liquid-solid technique. Preliminary indications of a superconducting transition in the metallic sample are presented.
Cross-talk in multiple dielectric barrier discharge actuators
Authors: Do H. , Kim W. , Cappelli M. A. , Mungal M. G.
Published: February 2008

Phase locked particle image velocimetry (PIV) is used to study flow alteration by dielectric barrier discharge actuators mounted on a bluff body. Images from these PIV experiments confirm the importance of negative ions in the actuation process and demonstrate cross-talk interactions between adjacent actuators.
Magnetoresistance in triphenyl-diamine derivative blue organic light emitting devices
Authors: Shakya P. , Desai P. , Kreouzis T. , Gillin W. P.
Published: February 2008

Magnetoresistance measurements have been performed on thin layers of the triphenyl-diamine derivative, N,N′-diphenyl-N,N′ bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′ diamine (TPD). At low drive voltages, where the current transport is solely hole mediated, no magnetoresistance is observed. At higher drive voltages, where electron injection into the TPD is occurring, magnetoresistance is seen and the sign of the magnetoresistance depends on the current density in the device.
Analysis of squareness in demagnetization curve of Nd–Fe–B magnet produced by the hydrogenation-disproportionation-desorption-recombination process
Authors: Maki Tomohito , Hirosawa Satoshi
Published: February 2008

An analysis of squareness in demagnetization curve of Nd–Fe–B fine-grained alloys prepared by the hydrogenation-disproportionation-desorption-recombination (HDDR) process was carried out in reference to the melt-spun and sintered magnets by measurements of their recoil curves. The recoil curves of the HDDR magnet and the melt-spun magnet suggested that the magnetization process associated with the recoil behavior of the HDDR magnet is dominated by rotation of magnetization, while that of the sintered magnet suggested that domain wall movement is involved. The recoil susceptibilities for recoil curves that returns to nearly demagnetized state were 0.095 and 0.048T−1 in the isotropic and anisotropic HDDR magnets, respectively, when normalized by saturation magnetization. The normalized susceptibilities could be reproduced quantitatively, assuming that the magnetization recoil process within a grain in the HDDR magnet is described by the coherent rotation of magnetization and a simple model of orientation distribution of the easy axes. It appears that the anisotropic HDDR magnet has a wide distribution of orientation of the easy axes, which should be one of the reasons for poor squareness of the demagnetization curve of the HDDR magnet.
Wireless powering of single-chip systems with integrated coil and external wire-loop resonator
Authors: Segura-Quijano Fredy , García-Cantón Jesús , Sacristán Jordi , Osés Teresa , Baldi Antonio
Published: February 2008

A procedure for inductive wireless powering of single-chip systems is presented. An integrated spiral coil is used as the power receiving component. An external resonator formed by a wire-loop inductor connected to a capacitor is placed in close proximity to the chip. The sinusoidal magnetic field generated at a distant transmitting loop is amplified by the resonator. The present approach enables delivering power in the order of tens of microwatts to a few milliwatts at distances longer than 10cm using a frequency of 13.5MHz. The integrated coil used here can be fabricated with any integrated circuit fabrication technology.
Diurnal variation of non-methane hydrocarbons in the subantarctic atmosphere
Authors: Bonsang Bernard , Al Aarbaoui Amine , Sciare Jean
Published: February 2008

Environmental context. The ocean surface is known to be supersaturated in some non-methane hydrocarbons and particularly alkenes. This oceanic source, though small on a global scale, can be a dominant component of the background atmosphere in remote areas. Attempts have been made to quantify this source, in order to estimate its magnitude in the budgets of these gases in the water column and the atmosphere. A main difficulty is to determine the production processes involved under the effects of plankton activity and solar and UV radiation penetration in the water column.
Abstract. Non-methane hydrocarbons (NMHCs) play a key role in the photochemistry of the remote atmosphere. They are oxidised by OH radicals and subsequently lead to a net formation of peroxy radicals, which have a crucial role in the budget of tropospheric ozone. Whereas in polluted areas, the effect of light hydrocarbons results in a net formation of ozone, in non- or low-polluted areas, the self-reaction of peroxy radicals dominates and leads eventually to ozone destruction, which in turn acts significantly on the OH budget. In remote environments, the origin of the NMHC background level is clearly attributed to a marine production, but a great uncertainty still exists about its geographical, seasonal and diurnal variability. Here, we present in situ measurements of NMHCs and particularly of alkenes in subantarctic areas, which show very systematic diurnal trends in agreement with an origin clearly dependent on photochemical processes on the surface seawater. The diurnal variability of alkene atmospheric mixing ratios appears strongly related to solar irradiance at the ocean surface. The magnitude of this marine source is deduced from a simple 1-D model of the alkene budget in the marine boundary layer. It appears that the required source must be approximately one order of magnitude greater than the source deduced from concentration measured at 1-m depth, and consistent with probable high concentration gradients close to the ocean surface.
Methyl and ethyl nitrate saturation anomalies in the Southern Ocean (36 - 65°S, 30 - 70°W)
Authors: Hughes Claire , Chuck Adele L. , Turner Suzanne M. , Liss Peter S.
Published: February 2008

Environmental Context. The alkyl nitrates are a group of organic compounds that are known to be produced naturally in seawater. The sea-to-air flux of alkyl nitrates is believed to contribute significantly to the ‘odd nitrogen’ reservoir of the atmosphere and to play an important role in regulating tropospheric ozone levels in remote marine regions. Here we expand our knowledge of alkyl nitrate concentration distributions and saturation anomalies to Southern Ocean waters.
Abstract. We report the first coupled atmosphere and seawater alkyl nitrate measurements for the Southern Ocean in the area bounded by 36–65°S, 30–70°W (November/December, 2004). Methyl and ethyl nitrate concentrations in seawater were 3.1–194.9 and 0.3–71.8 pmol L–1, respectively. Atmospheric mixing ratios ranged from 1.0 to 71.5 ppt for methyl nitrate and 0.6 to 16.6 ppt for ethyl nitrate. No correlations between alkyl nitrate distributions, and sea surface temperature, windspeed or chlorophyll a were observed. However, methyl and ethyl nitrate were well correlated in both the air and seawater, which suggests a common source. Calculations based on these observations estimate median saturation anomalies of –40% (–95 to 220%) for methyl nitrate and –11% (–98 to 174%) for ethyl nitrate. Positive saturation anomalies were spatially patchy, which suggests that some methyl and ethyl nitrate production was taking place in isolated areas of the study region. Overall our negative median saturation anomaly values suggest that during late austral spring (2004) the region of the Southern Ocean in which our measurements were made was not a net source of methyl or ethyl nitrate to the atmosphere. These results reinforce previous findings which suggest that whilst the equatorial ocean is a major source of methyl and ethyl nitrates to the atmosphere, higher latitude waters are generally at equilibrium or under-saturated. More measurements are required to assess how representative our results are of other areas of the Southern Ocean.
Clinical significance of questionnaire-elicited or clinically reported anorectal symptoms for rectal Neisseria gonorrhoeae and Chlamydia trachomatis amongst men who have sex with men
Authors: Lister Nichole A. , Chaves Nadia J. , Pang Chee W. , Smith Anthony , Fairley Christopher K.
Published: February 2008

Background: Although Neisseria gonorrhoeae (Ng) and Chlamydia trachomatis (Ct) are common infections in men who have sex with men, it is unclear from previous studies whether anorectal symptoms are reliable clinical indicators of infection. Aim: The objective of the study was to investigate the clinical significance of questionnaire-elicited or clinically reported anal symptoms for rectal Ng and Ct. Methods: During 2002 to 2003, men who have sex with men (MSM) screened or tested for Ng or Ct according to the national guidelines were invited to participate in a questionnaire. Results: During the study period, 366 MSM were enrolled into the study (88% recruitment rate), of whom 20 (5%) and 25 (7%) were diagnosed with rectal Ng or Ct, respectively. Overall, ‘any’ anorectal symptoms on a questionnaire were reported equally by those with and without rectal Ng (75 v. 74%, P = 0.69), but heavy anal discharge (P < 0.01) and anal pain (P = 0.04) were more common in those with rectal Ng. Symptoms on the questionnaire were not different among those with and without Ct. Any anal symptoms were reported substantially more often via questionnaire than in a clinical consultation (75 v. 16%, P < 0.01) and symptoms reported in a clinical consultation were not associated with Ng or Ct detection. Conclusion: The weak or absent association between symptoms and the presence of Ct or Ng highlights the importance of annual sexually transmitted infection screening in MSM regardless of symptoms.