bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of ΔH(M,ΔM)-technique for identification of switching field distributions in the presence of thermal relaxation
Authors: Hovorka O. , Evans R. F. L. , Chantrell R. W. , Liu Y. , Dahmen K. A. , Berger A.
Published: December 2010

The potential of hysteresis loop-based methods for the characterization of granular magnetic materials is investigated in the presence of thermal relaxation effects. Specifically, we study the reliability of the ΔH(M,ΔM)-method to recover the intrinsic switching field distribution in the presence of thermal relaxation. As input data, we use the computational results obtained from kinetic Monte Carlo simulations of interacting Stoner–Wohlfarth particle arrays including the anisotropy field and grain size distributions, and then analyze them using the hysteron-based ΔH(M,ΔM)-method to identify the accuracy limits of this methodology. It is found that the accuracy of the ΔH(M,ΔM)-method is not substantially changed by the presence of thermal relaxation.
Radial electric fields in the vicinity of locked magnetic islands
Authors: Nishimura S. , Itoh K. , Yagi M. , Ida K. , Itoh S.-I.
Published: December 2010

The radial electric field in the vicinity of magnetic islands locked by resonant magnetic perturbations (static error fields) is numerically studied using a set of reduced two-fluid equations. The asymmetric radial electric fields across locked magnetic islands are observed, which are due to the symmetry breaking effects such as the cylindrical geometry and inhomogeneous electron diamagnetic drift. It is found that the magnitude of the difference (between maximum and minimum radial electric fields around O-point) is proportional to the averaged electron diamagnetic drift frequency inside magnetic islands and the square of the island width, but inversely proportional to the square root of the ion viscosity.
Ultrafast photodynamics of furan
Authors: Fuji Takao , Suzuki Yoshi-Ichi , Horio Takuya , Suzuki Toshinori , Mitrić Roland , Werner Ute , Bonačić-Koutecký Vlasta
Published: December 2010

Ultrafast photodynamics of furan has been studied by time-resolved photoelectron imaging (TRPEI) spectroscopy with an unprecedented time resolution of 22 fs. The simulation of the time-dependent photoelectron kinetic energy distribution (PKED) has been performed with ab initio nonadiabatic dynamics “on the fly” in the frame of time-dependent density functional theory. Based on the agreement between experimental and theoretical time-dependent photoelectron signal intensity as well as on PKED, precise time scales of ultrafast internal conversion from ${\rm S}_{\rm 2}$S2 over ${\rm S}_{\rm 1}$S1 to the ground state ${\rm S}_{\rm 0}$S0 of furan have been revealed for the first time. Upon initial excitation of the ${\rm S}_{\rm 2}$S2 state which has ${\rm \pi \hbox{-} \pi }^{\rm *}$π-π* character, a nonadiabatic transition to the ${\rm S}_{\rm 1}$S1 state occurs within 10 fs. Subsequent dynamics invokes the excitation of the C–O stretching and C–O–C out of plane vibrations which lead to the internal conversion to the ground state after 60 fs. Thus, we demonstrate that the TRPEI combined with high level nonadiabatic dynamics calculations provide fundamental insight into ultrafast photodynamics of chemically and biologically relevant chromophores.
Deuterium-induced passivation of boron acceptors in polycrystalline diamond
Authors: Habka N. , Chikoidze E. , Jomard F. , Dumont Y. , Chevallier J. , Barjon J. , Mer C. , Bergonzo P.
Published: December 2010

In monocrystalline boron-doped diamond (BDD), the diffusion of deuterium induces an electrical passivation of acceptors by the formation of (B,D) complexes. However, device applications based on this process are presently limited by the small size of available monocrystalline substrates. In this work, we show that the grain size of polycrystalline diamond is a key parameter in order to achieve efficient deuterium diffusion by trapping on boron atoms. As a result, we present the first clear evidences of the electrical passivation of boron acceptors in the case of polycrystalline diamond layers with an average grain size of 50 μm. We show that, for a boron concentration of 2×1019 cm−3, the room temperature hole mobility increases from 70 to 120 cm2 V−1 s−1 after deuteration. More surprisingly, the compensation ratio keeps the same order of magnitude which suggests a passivation effect on both acceptors and donors.
Organic field-effect transistor-based biosensors functionalized with protein receptors
Authors: Maddalena Francesco , Kuiper Marjon J. , Poolman Bert , Brouwer Frank , Hummelen Jan C. , de Leeuw Dago M. , De Boer Bert , Blom Paul W. M.
Published: December 2010

An organic field-effect transistor with integrated proteins (Bio-FET) for sensing of sulfate ions is presented. A sulfate receptor was engineered to contain a thiol group for surface-anchoring without affecting its binding activity. The modified receptor was covalently coupled to a maleimide-functionalized polystyrene layer, and integrated as gate dielectric in a dual-gate transducer. The binding of sulfate ions in dry conditions was detected by a shift in the threshold voltage. Combined with surface density measurements by atomic force microscopy , an effective charge of −1.7q per protein was found, as expected from the Bio-FET operation model.
Discrete perturbation theory applied to Lennard-Jones and Yukawa potentials
Authors: Chapela Gustavo A. , del Río Fernando , Benavides Ana Laura , Alejandre José
Published: December 2010

Discrete perturbation theory (DPT) is a powerful tool to study systems interacting with potentials that are continuous but can be approximated by a piecewise continuous function composed of horizontal segments. The main goal of this work is to analyze the effect of several variables to improve the representation of continuous potentials in order to take advantage of DPT. The main DPT parameters chosen for the purpose are the starting location and size of the horizontal segments used to divide the full range of the potential and its maximum reach. We also studied the effect of having each segment aligned to the left, to the right, or centered on the continuous function. The properties selected to asses the success of this strategy are the orthobaric densities and their corresponding critical points. Critical parameters and orthobaric densities were evaluated by DPT for each of an ample set of variables and compared with their values calculated via discontinuous molecular dynamics. The best sets of DPT parameters are chosen so as to give equations of state that represent accurately the Lennard-Jones and Yukawa fluids.
General implementation of the relativistic coupled-cluster method
Authors: Nataraj Huliyar S. , Kállay Mihály , Visscher Lucas
Published: December 2010

We report the development of a general order relativistic coupled-cluster (CC) code. Our implementation is based on Kramers-paired molecular spinors, utilizes double group symmetry, and is applicable with the full Dirac–Coulomb and several approximate relativistic Hamiltonians. The available methods include iterative and perturbative single-reference CC approaches with arbitrary excitations as well as a state-selective multi-reference CC ansatz. To illustrate the performance of the new code, benchmark calculations have been performed for the total energies, bond lengths, and vibrational frequencies of the monoxides of Group IVa elements. The trends due to the simultaneous inclusion of relativity as well as higher-order electron correlation effects are analyzed. The newly developed code significantly widens the scope of the ab initio relativistic calculations, for both molecules and atoms alike, surpassing the accuracy and reliability of the currently available implementations in the literature.
A twisted periscope arrangement for transporting elliptically polarized light without change in its polarization state
Authors: Arora Ashish , Ghosh Sandip
Published: December 2010

The authors describe a dual-mirror 90 \documentclass[12pt]{minimal}\begin{document}$^\circ$\end{document}∘ twisted periscope arrangement for transporting polarized light in air, wherein a general elliptic polarization state of the light is preserved at all wavelengths. It is experimentally demonstrated that in the wavelength range 400–1000 nm, this arrangement preserves the polarization state fairly well when using either metallic or dielectric mirrors.
Long distance fiber-optic displacement sensor based on fiber collimator
Authors: Shen Wei , Wu Xiaowei , Meng Hongyun , Zhang Guanbin , Huang Xuguang
Published: December 2010

A simple fiber-optic displacement sensor based on reflective intensity modulated technology is demonstrated using a fiber collimator. The sensing range is over 30 cm, which is over 100 times that of the conventional fiber-optic displacement sensor based on the normal single-mode fiber. The measured data are fitted into linear equation very well and the values of R-square are more than 0.995. The sensitivity of the device achieves 0.426 dB/cm over the range of 5–30 cm. By applying the relative technique, the errors resulted from the fluctuation of light source and influences of environment are effectively eliminated, and the stability for wide range measurement can be improved. The simplicity of the design, high dynamic range, stability and the ease of the fabrication make it suitable for applications in industries.
Effect of tip shape on line edge roughness measurement based on atomic force microscopy
Authors: Li Ning , Wang Fei , Zhao Xuezeng
Published: December 2010

Atomic force microscopy (AFM) is an important tool in line edge roughness (LER) measurements, where accuracy for line edge identification is influenced by the shape of the tip. In this article, the effect of tip shape on LER measurement based on AFM is studied theoretically. The formulas for calculating the distance between the measured and actual line edge of the sample are presented. The effects of the three kinds of tips with different shapes are experimentally compared for validation. Suggestions on how to reduce measuring error caused by tip shape are also given.
Functionalization, self-assembly, and photoswitching quenching for azobenzene derivatives adsorbed on Au(111)
Authors: Cho Jongweon , Berbil-Bautista L. , Levy Niv , Poulsen Daniel , Fréchet Jean M. J. , Crommie Michael F.
Published: December 2010

We have used scanning tunneling microscopy to investigate the structure and photoswitching behavior of azobenzene molecules functionalized with bulky spacer groups and adsorbed onto Au(111). We find that positioning tert-butyl “legs” in a canted arrangement on the azobenzene phenyl rings quenches photoisomerizability of the molecule on Au(111). Addition of cyano groups at the para positions changes the molecular self-assembly significantly, but does not alter the quenched photoisomerizability. This behavior likely arises from a combination of molecule–surface interactions, molecule–molecule interactions, and alteration of azobenzene electronic structure resulting from the position-specific addition of tert-butyl groups.
Laplace–Runge–Lenz symmetry in general rotationally symmetric systems
Authors: Ben-Ya'acov Uri
Published: December 2010

The universality of the Laplace–Runge–Lenz symmetry in all rotationally symmetric systems is discussed. The independence of the symmetry on the type of interaction is proven using only the most generic properties of the Poisson brackets. Generalized Laplace–Runge–Lenz vectors are definable to be constant (not only piecewise conserved) for all cases, including systems with open orbits. Applications are included for relativistic Coulomb systems and electromagnetic/gravitational systems in the post-Newtonian approximation. The evidence for the relativistic origin of the symmetry are extended to all centrally symmetric systems.
Spectral finite element method modeling of ultrasonic guided waves propagation in layered viscoelastic film/substrate materials
Authors: Luo Ying , Li Hong , Xu BaiQiang , Xu Gui Dong
Published: December 2010

The propagation of ultrasonic guided waves in layered viscoelastic film/substrate materials has been investigated. Based on the plane strain theory, a numerical model of the guided waves propagating in thin film on the substrate is developed in the frequency domain by employing the spectral finite element method. The surface normal displacement and the propagating characteristic are obtained and analyzed, which depends not only on the material parameters of the film, but also on those of the substrate. If the substrate velocity is faster than that of the film, the dispersion takes on the normal, otherwise, the anomalous dispersion will appear, and thin film properties for different film/substrate systems can be identified. The guided wave is attenuated gradually due to energy dissipation caused by material viscosity and rapidly at the location near the source. With the receiver distance increasing, it becomes slower. Clearly models for ultrasonic generation and propagation in layered viscoelastic film/substrate materials must include the effect of viscoelasticity on the dispersive wave.
Carrier dynamics in β-Ga2O3 nanowires
Authors: Othonos Andreas , Zervos Matthew , Christofides Constantinos
Published: December 2010

Carrier dynamics have been investigated in β-Ga2O3 nanowires (NWs) grown by the vapor-liquid-solid mechanism, using ultrashort transient absorption spectroscopy in conjunction with time-correlating single photon counting photoluminescence. UV femtosecond pulse excitation has been utilized to generate nonequilibrium carrier distributions near the band edge of the NWs and nondegenerate pump-probe techniques have been employed to follow carrier relaxation through the defect related states located within the band gap of the NW semiconductor. Relaxation of the photogenerated carriers through these states appears to be biexponential with a fast component on the order of 3–5 ps and the slower component around 40–90 ps depending on the states being probed. Transient absorption intensity measurements reveal that recombination mechanisms such as Auger and bimolecular become contributing factors to the relaxation dynamics for absorbed fluences larger than 90 μJ/cm2. In the low fluence regime, time-correlated single photon counting photoluminescence measurements revealed a nonradiative relaxation mechanism with time constants ranging from 0.6–1 ns and a radiative relaxation with a time constant of approximately 4 ns.
Intraband photon absorption in edge-defined nanowire superlattices for optoelectronic applications
Authors: Gómez-Campos F. M. , Rodríguez-Bolívar S. , Luque-Rodríguez A. , López-Villanueva J. A. , Carceller J. E.
Published: December 2010

We calculate the conduction miniband energy dispersion relation in an edge-defined silicon quantum wire periodic nanostructure embedded in SiO2. Our main aim is to predict the behavior of these nanostructures when used as components in optoelectronic devices such as, for example, photodetectors or intermediate-band solar cells. We take into consideration the effects of nonparabolicity and anisotropy and the different electron states arising from each valley when solving the Schrödinger equation. From these results, we investigate the intraband photon absorption coefficient for those transitions between minibands arising from the conduction band. We analyze the influence of light polarization and level of doping of the system in order to ascertain the best conditions for operation.
Reliability of Al2O3-doped ZrO2 high-k dielectrics in three-dimensional stacked metal-insulator-metal capacitors
Authors: Zhou Dayu , Schroeder U. , Xu Jin , Heitmann J. , Jegert G. , Weinreich W. , Kerber M. , Knebel S. , Erben E. , Mikolajick T.
Published: December 2010

In this paper, we report reliability evaluation results for nanomixed amorphous ZrAlxOy and symmetrically or asymmetrically stacked ZrO2/Al2O3/ZrO2 dielectric thin films grown by atomic layer deposition method in cylindrical metal-insulator-metal capacitor structure. Clear distinctions between their I-V asymmetry and breakdown behavior were correlated with the differences in compositional modification of bottom interface, defect density, and conduction mechanism of the film stacks. The thermochemical molecular bond breakage model was found to explain the dielectric constant dependent breakdown field strength and electric field acceleration parameter of lifetime very well.
Continuous-wave laser annealing of Si-rich oxide: A microscopic picture of macroscopic SiSiO2 phase separation
Authors: Khriachtchev Leonid , Nikitin Timur , Räsänen Markku , Domanskaya Alexandra , Boninelli Simona , Iacona Fabio , Engdahl Anders , Juhanoja Jyrki , Novikov Sergei
Published: December 2010

We report on the first observation of the macroscopic (long-range) SiSiO2 phase separation in Si-rich oxide SiOx (x<2) obtained by continuous-wave laser annealing of free-standing SiOx films. The effect is analyzed by a unique combination of microscopic methods (Raman, transmission, photoluminescence, and infrared spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy). Three regions can be distinguished on a SiOx free-standing film after 488 nm laser annealing at intensities above ∼104 W cm−2: central spot, ring around the central spot, and pristine film outside the irradiated area. In the pristine SiOx material, small Si nanocrystals (Si-nc) (diameters of a few nanometer) are surrounded by SiO2 with an addition of residual suboxides, the Si-nc being produced by annealing at 1100 °C in a furnace. The central spot of the laser-annealed area (up to ∼30 μm wide in these experiments) is practically free of Si excess and mainly consists of amorphous SiO2. The ring around the central spot contains large spherical Si-nc (diameters up to ∼100 nm) embedded in amorphous SiO2 without the presence of suboxides. Laser-induced temperatures in the structurally modified regions presumably exceed the Si melting temperature. The macroscopic SiSiO2 phase separation is connected with extensive diffusion in temperature gradient leading to the Si concentration gradient. The present work demonstrates the advantages of high spatial resolution for analysis in materials research.
Optical absorption at its onset in sputter deposited hafnia–titania nanolaminates
Authors: Cisneros-Morales Massiel Cristina , Aita Carolyn Rubin
Published: December 2010

The onset of the fundamental optical absorption edge in sputter deposited HfO2–TiO2 nanolaminate films grown on unheated substrates was investigated. Three bilayer architectures were examined, representing overall film chemistry from 0.51 to 0.72 atom fraction Hf. The goal was to determine the absorption coefficient, α(E), versus incident photon energy, E, and to model this dependence in terms of the absorption behavior of specific functional units within the nanolaminate. Persistence and amalgamation models were applied, representing the extremes of segregated cation and mixed cation structures, respectively, and both were found to be unsatisfactory. Consideration of physiochemical data for the nanolaminates led to the development of a modified persistence model for absorption. α(E) was decomposed into contributions from (I) broad (9 nm-thick) interfacial regions that were chiefly o-HfTiO4, and (II) regions remote from interfaces that contained material based on a highly defective m-HfO2 lattice. The absorption edge at its onset in all nanolaminates was determined by short-range atomic order characteristic of o-HfTiO4. An indirect band gap of EG=3.25±0.02 eV was determined for this compound.
Trap states and space charge limited current in dispersion processed zinc oxide thin films
Authors: Bubel S. , Mechau N. , Hahn H. , Schmechel R.
Published: December 2010

The electric transport properties of nanoparticulate zinc oxide (ZnO) thin films are investigated in nitrogen and ambient atmosphere with respect to the effects of polymer adsorbates, in order to study the origin of hysteresis behavior of ZnO thin film transistors. A strong dependence on the polymer adsorbate of the conductivity in nitrogen atmosphere is observed. Utilizing the space charge limited current theory, the trap depth and concentration in the films have been estimated. According to this analysis, the low conductivity of polymer free thin films in ambient atmosphere is caused by an increase in deep traps, compensating free charge carriers and not by a reduction in donorlike defect states. Furthermore, polymeric additives seem to induce similar trap states, which make the transport properties less sensitive against atmospheric influences. However, the strongly compensated semiconductor created in this way, causes a slow trap and release behavior resulting in a strong hysteresis in the transistor characteristics and long-term instabilities. It is shown, that ignoring these time-dependent characteristics, straight forward derived transistor parameters like the field effect mobility can be easily overestimated.
Intrinsic Josephson junction characteristics in the stripe-ordered La1.6−xNd0.4SrxCuO4 bulk single crystals
Authors: Ding J. F. , Xie L. , Sun X. F. , Li X. G.
Published: December 2010

The current-voltage (I-V) properties along the c axis of stripe-ordered La1.6−xNd0.4SrxCuO4 (LNSCO, x=0.10, 0.12, 0.15, and 0.18) bulk single crystals are studied. For all the samples, the I-V curves exhibit Josephson junctionlike characteristics, the voltage jumps at some critical currents and clear hysteresis without multiple branches appears below the superconducting transition temperatures. With increasing Sr doping level, the characteristics of intrinsic Josephson junctions in LNSCO change from a superconductor-insulator-superconductor type to a superconductor-normal metal-superconductor one. The field dependence of critical current Ic exhibits a periodical perturbation with a large scale of magnetic field. A fourfold symmetry of the angular dependent Ic for the rotation of the CuO2 plane in magnetic fields confirms the vortex pinning effect of the static stripes. The abrupt jump of voltage at a rather large Ic in LNSCO may be used as a high-power current restrictor or switch.
Exploiting classical nucleation theory for reverse self-assembly
Authors: Miller William L. , Cacciuto Angelo
Published: December 2010

In this paper we introduce a new method to design interparticle interactions to target arbitrary crystal structures via the process of self-assembly. We show that it is possible to exploit the slope of the crystal nucleation free-energy barrier to sample and select optimal interparticle interactions for self-assembly into a desired structure. We apply this method to find interactions to target two simple crystal structures: a crystal with simple cubic symmetry and a two-dimensional plane with square symmetry embedded in a three-dimensional space. Finally, we discuss the potential and limits of our method and propose a general model by which a functionally infinite number of different interaction geometries may be constructed and to which our reverse self-assembly method could in principle be applied.
Observation of the integer quantum Hall effect in high quality, uniform wafer-scale epitaxial graphene films
Authors: Pan Wei , Howell Stephen W. , Ross Anthony Joseph , Ohta Taisuke , Friedmann Thomas A.
Published: December 2010

We report the observation of the integer quantum Hall states at Landau level fillings of ν=2, 6, and 10 in a Hall bar device made of a single-layer epitaxial graphene film on the silicon-face of silicon-carbide prepared via argon-assisted graphitization. The two-dimensional electron gas exhibits a low-temperature (at 4 K) carrier mobility of ∼14 000 cm2/V s at the electron density of 6.1×1011 cm−2. Furthermore, the sheet resistance obtained from four-probe measurements across the whole area (12×6 mm2) of another specimen grown under similar condition displays roughly uniform values (∼1600 Ω/square), suggesting that the macroscopic steps and accompanying multilayer graphene domains play a minor role in the low-temperature electronic transport.
Extraction of contact resistance in carbon nanofiber via interconnects with varying lengths
Authors: Li Ke , Wu Raymond , Wilhite Patrick , Khera Vinit , Krishnan Shoba , Sun Xuhui , Yang Cary Y.
Published: December 2010

A method to extract the contact resistance and bulk resistivity of vertically grown carbon nanofibers (CNFs) or similar one-dimensional nanostructures is described. Using a silicon-compatible process to fabricate a terrace test structure needed for the CNF length variation, the contact resistance is extracted by measuring in situ the resistances of individual CNFs with different lengths and within a small range of diameters using a nanoprober inside a scanning electron microscope. Accurate determination of contact resistances for various combinations of catalysts and underlayer metals can lead to eventual optimization of materials’ growth and device fabrication processes for CNF via interconnects.
Super-rolloff electron tunneling transduction of nanomechanical motion using frequency downmixing
Authors: Kan M. R. , Fortin D. C. , Finley E. , Cheng K.-M. , Freeman M. R. , Hiebert W. K.
Published: December 2010

A downmixed transduction technique is demonstrated which eliminates the high-frequency cutoff problem in traditional electron tunneling instrumentation. We measure the ∼1 MHz vibrational modes of a micromechanical beam two orders of magnitude above the electronic bandwidth of our readout circuitry with no fundamental limitations anticipated up to microwave frequencies. The displacement sensitivity of 40 fm/Hz1/2 demonstrates the viability of this technique as a sensitive displacement transducer for high-frequency nanoelectromechanical systems. Backaction from the tunneling tip on the device induces resonance frequency shifts of order 1%.
Determination of diminished thermal conductivity in silicon thin films using scanning thermoreflectance thermometry
Authors: Aubain Max S. , Bandaru Prabhakar R.
Published: December 2010

The variation of optical reflectance from silicon thin films in response to a change in temperature, i.e., the thermoreflectance, was used to monitor heat conduction processes within the films and confirm reduction of their in-plane thermal conductivity with decreasing film thickness. The measurements were also fit to numerical solutions of the heat conduction equation through which it was found that observed conductivity values were consistent with predictions based on phonon dispersion and phonon-boundary scattering considerations. The methods used may have practical implications for monitoring heat dissipation in silicon-on-insulator based microdevices.
Relationship of deep defects to oxygen and hydrogen content in nanocrystalline silicon photovoltaic materials
Authors: Hugger Peter G. , Cohen J. David , Yan Baojie , Yue Guozhen , Yang Jeffrey , Guha Subhendu
Published: December 2010

We report measurements of the structural and compositional properties of a range of hydrogenated nanocrystalline films. We employed Raman spectroscopy for crystallinity and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) for impurity characterizations. The crystalline volume fractions and impurity levels are correlated with the deep state densities determined by drive level capacitance profiling. Those defects were found to have a thermal emission energy of 0.65±.05 eV. We found that the overall crystallinity correlated reasonably well with the density of such defect states and also found a strong correlation between the defect density and the levels of oxygen impurities. Possible origins of these defects are discussed.
Enhanced force sensitivity and noise squeezing in an electromechanical resonator coupled to a nanotransistor
Authors: Mahboob I. , Flurin E. , Nishiguchi K. , Fujiwara A. , Yamaguchi H.
Published: December 2010

A nanofield-effect transistor (nano-FET) is coupled to a massive piezoelectricity based electromechanical resonator integrated with a parametric amplifier. The mechanical parametric amplifier can enhance the resonator’s displacement and the resulting electrical signal is further amplified by the nano-FET. This hybrid amplification scheme yields an increase in the mechanical displacement signal by 70 dB resulting in a force sensitivity of 200 aN Hz−1/2 at 3 K. The mechanical parametric amplifier can also squeeze the displacement noise in one oscillation phase by 5 dB enabling a factor of 4 reduction in the thermomechanical noise force level.
Thermo-optic detection of terahertz radiation from a quantum cascade laser
Authors: van Kolck A. , Amanti M. , Fischer M. , Beck M. , Faist J. , Lloyd-Hughes J.
Published: December 2010

We investigate the asynchronous detection of terahertz radiation from a quantum cascade laser using an electro-optic sampling apparatus. The signal does not vary substantially upon rotating the detection crystal, while a characteristic angle dependence is exhibited for synchronized time-domain pulses from a photoconductive emitter. Upon increasing the electrical modulation frequency of the cascade laser the unsynchronized signal decreases in good agreement with a thermal detector. Rather than being electro-optic in origin, we therefore ascribe the unsynchronized signal to a thermo-optic modulation of the refractive index. A simple model is in good agreement with the effect’s frequency dependence.
Dynamics of charged particles in spatially chaotic magnetic fields
Authors: Ram Abhay K. , Dasgupta Brahmananda
Published: December 2010

The spatial topology of magnetic field lines can be chaotic for fields generated by simple current configurations. This is illustrated for a system consisting of a circular current loop and a straight current wire. An asymmetric configuration of the current system leads to three-dimensional spatially chaotic magnetic fields. The motion of charged particles in these fields is not necessarily chaotic and exhibits intriguing dynamical properties. Particles having initial velocities closely aligned with the direction of the local magnetic field are likely to follow chaotic orbits in phase space. Other particles follow coherent and periodic orbits; these orbits being the same as in the symmetric current configuration for which the field lines are not chaotic. An important feature of particles with chaotic motion is that they undergo spatial transport across magnetic field lines. The cross-field diffusion is of interest in a variety of magnetized plasmas including laboratory and astrophysical plasmas.
Asymmetric Pt/Au coated catalytic micromotors fabricated by dynamic shadowing growth
Authors: Gibbs John G. , Fragnito Nicholas A. , Zhao Yiping
Published: December 2010

Asymmetric Pt/Au coated catalytic micromotors are fabricated by a dynamic shadowing growth method, and the exposed Au surface area A is changed systematically. The average moving speed u is found to follow the scaling relationship u∝A3/2, which agrees with the self-electrophoresis mechanism. Motion behaviors of micromotors with similar sizes and morphologies operating under a non-self-electrophoresis mechanism are compared with the Pt/Au micromotors, and in general, the self-electrophoresis mechanism gives higher activity for motors with similar sizes and morphologies.
Photoelectric conversion behavior based on direct interfacial charge-transfer from porphyrin derivative to silicon nanowires
Authors: Wen Liping , Liu Xiaofeng , Yang Nailiang , Zhai Jin , Huang Changshui , Li Yuliang , Jiang Lei
Published: December 2010

A porphyrin derivative was prepared, and the photoelectric conversion behaviors of porphyrin derivative sensitized silicon nanowires had been studied that showed the maximum photocurrent generation that occurred at the near infrared region, which can be attributed to the direct interfacial charge-transfer from the highest occupied molecular orbital of porphyrin derivative to the conduction band of silicon nanowires. These properties open up the possibility of constructing photovoltaic devices and light-harvesting systems using various dyes and semiconductors.
Reproducible and controllable organic resistive memory based on Al/poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate)/Al structure
Authors: Wang Z. S. , Zeng F. , Yang J. , Chen C. , Yang Y. C. , Pan F.
Published: December 2010

We report reproducible and controllable bipolar resistive memory devices based on Al/poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate)/Al, which show an on/off current ratio as large as 104, reproducibility of more than 103 dc sweeping cycles, and retention time of 104 s. The switching mechanism is confirmed to be the filamentary switching. We show that the compliant current can effectively control the formation of filaments and the performance of the device, including the on-state resistance, the reset current, and the switching-off threshold voltage. In addition, the lowest reset power and the critical compliant current for resistive switching are determined.
Quantitative evaluation of defect-models in superconducting phase qubits
Authors: Cole J. H. , Müller C. , Bushev P. , Grabovskij G. J. , Lisenfeld J. , Lukashenko A. , Ustinov A. V. , Shnirman A.
Published: December 2010

We use high-precision spectroscopy and detailed theoretical modeling to determine the form of the coupling between a superconducting phase qubit and a two-level defect. Fitting the experimental data with our theoretical model allows us to determine all relevant system parameters. We observe a strong qubit-defect coupling with a nearly vanishing longitudinal component. We quantitatively compare several existing theoretical models for the microscopic origin of two-level defects.
Color display using micromechanically coupled mirrors
Authors: Han Won , Cho Young-Ho
Published: December 2010

We present interferometric modulators, reproducing green, blue, and red colors using selective actuation of mechanically coupled mirror arrays having an identical air gap for simple fabrication process. The present interferometric modulators reproduce green, blue, and red colors at switching modes of (000), (010), and (101), where the spectrum peaks for the colors are measured at wavelengths of 511±5, 478±3, and 644±9 nm with maximum intensities of 77±5%, 73±2%, and 81±5%, respectively. Therefore, we experimentally demonstrated the color reproduction capability of the present interferometric modulators for display applications.
Pulsed laser deposition of SrTiO3/LaGaO3 and SrTiO3/LaAlO3: Plasma plume effects
Authors: Aruta C. , Amoruso S. , Bruzzese R. , Wang X. , Maccariello D. , Miletto Granozio F. , Scotti di Uccio U.
Published: December 2010

The pulsed laser deposition of SrTiO3/LaGaO3 and SrTiO3/LaAlO3 interfaces is analyzed with a focus on the kinetic energy of the ablated species. LaGaO3 and LaAlO3 plasma plumes were studied by fast photography and space-resolved optical emission spectroscopy. Reflection high energy electron diffraction was performed proving a layer-by-layer growth up to 10−1 mbar oxygen pressure. The role of the energetic plasma plume on the two-dimensional growth and on the presence of interfacial defects at different oxygen growth pressures is discussed in connection with the conducting properties of the polar/nonpolar interfaces.
Electronic structure and thermoelectric properties of In32−xGexO48 (x=, 1, 2, and 3) at low temperature
Authors: Yan Yu Li , Wang Yuan Xu
Published: December 2010

The electronic properties of In32−xGexO48 (x=0, 1, 2, 3, 4, 5, 6, and 7) are studied by using the density functional theory. The transport coefficients of In32−xGexO48 (x=0, 1, 2, and 3) are then calculated within the semiclassical Boltzmann theory. The largest Seebeck coefficient is nearly seven times larger than that of Bi2Te3. Most strikingly, the thermoelectric power factor with respect to relaxation time is nearly 70 times larger than that of conventional thermoelectric materials. Our theoretical calculations give a valuable insight on how to enhance the thermoelectric performance of In32−xGexO48.
Cu penetration into low-k dielectric during deposition and bias-temperature stress
Authors: He Ming , Novak Steven , Vanamurthy Lakshmanan , Bakhru Hassaram , Plawsky Joel , Lu Toh-Ming
Published: December 2010

Cu penetration into low-k dielectrics can cause serious reliability issues in on-chip interconnect systems. Using secondary ion mass spectrometry with both front-side and back-side depth profiling strategies, Cu was found to diffuse into SiCOH low-k dielectric in a Cu/SiCOH/Si capacitor during Cu deposition. After bias-temperature stressing the capacitor at 270 °C and 2.5 MV/cm, Cu penetrates further into SiCOH, but its distribution profile is the same as that after the same temperature annealing without electrical bias, suggesting no Cu ion drift. The implication of these findings on the Cu/low-k dielectric time-dependent dielectric breakdown modeling is discussed.
Trends of polyfluoroalkyl compounds in marine biota and in humans
Authors: Sturm Renate , Ahrens Lutz
Published: December 2010

Environmental context Polyfluoroalkyl compounds are used in a variety of industrial and consumer applications, including polymer production and for surface treatment of textiles and paper. Research over the last 10 years has shown that these compounds are ubiquitous environmental contaminants â they are extremely persistent, show toxic effects and accumulate in the food chain. We evaluate global, temporal and spatial trends of these important emerging contaminants. Abstract This review gives an overview of existing knowledge of polyfluoroalkyl compounds (PFCs) in humans and in marine biota. Temporal trends and spatial distribution of PFCs were globally compared in humans, marine mammals, seabirds and fish. In general, PFC concentrations in the environment have increased significantly from the beginning of the production up to the 1990s. After the phase-out of perfluorooctane sulfonyl fluoride (POSF) production starting in 2000, PFC concentrations in humans generally decreased. In marine biota no clear temporal trends were observed. The temporal trends depended on the species, their trophic levels and the geographical locations. PFC patterns in humans and in marine wildlife species were compared regarding perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), their shorter and longer chain homologues (C4–C15) and precursor compounds. Finally knowledge gaps were identified and recommendations for future work were presented.
Gaseous mercury in coastal urban areas
Authors: Soerensen Anne L. , Skov Henrik , Johnson Matthew S. , Glasius Marianne
Published: December 2010

Environmental context Mercury is a neurotoxin that bioaccumulates in the aquatic food web. Atmospheric emissions from urban areas close to the coast could cause increased local mercury deposition to the ocean. Our study adds important new data to the current limited knowledge on atmospheric mercury emissions and dynamics in coastal urban areas. Abstract Approximately 50% of primary atmospheric mercury emissions are anthropogenic, resulting from e.g. emission hotspots in urban areas. Emissions from urban areas close to the coast are of interest because they could increase deposition loads to nearby coastal waters as well as contribute to long range transport of mercury. We present results from measurements of gaseous elemental mercury (GEM) and reactive gaseous mercury (RGM) in 15 coastal cities and their surrounding marine boundary layer (MBL). An increase of 15–90% in GEM concentration in coastal urban areas was observed compared with the remote MBL. Strong RGM enhancements were only found in two cities. In urban areas with statistically significant GEM/CO enhancement ratios, slopes between 0.0020 and 0.0087 ng m–3 ppb–1 were observed, which is consistent with other observations of anthropogenic enhancement. The emission ratios were used to estimate GEM emissions from the areas. A closer examination of data from Sydney (Australia), the coast of Chile, and Valparaiso region (Chile) in the southern hemisphere, is presented.
Induced pluripotent stem cell–derived human platelets: one step closer to the clinic
Authors: Gekas Christos , Graf Thomas
Published: December 2010

The era of induced pluripotent stem (iPS) cells carries with it the promise of virtually unlimited sources of autologous cells for regenerative medicine. However, efficiently differentiating iPS cells into fully functional mature cell types remains challenging. A new study reporting the formation of fully functional platelets from human iPS (hiPS) cells improves upon recent efforts to generate this enucleated cell type, which remains in high demand for therapeutic transfusions. Notably, their lack of nucleus renders platelets unable to retain the pluripotent or tumorigenic properties of iPS cells.
Gene Encoding a c-Type Cyclin in Mycosphaerella graminicola Is Involved in Aerial Mycelium Formation, Filamentous Growth, Hyphal Swelling, Melanin Biosynthesis, Stress Response, and Pathogenicity
Authors: Choi Yoon-E , Goodwin Stephen B.
Published: December 2010

Mycosphaerella graminicola is an important wheat pathogen causing Septoria tritici blotch. To date, an efficient strategy to control M. graminicola has not been developed. More significantly, we have a limited understanding of the molecular mechanisms of M. graminicola pathogenicity. In this study, we attempted to characterize an MCC1-encoding c-type cyclin, a gene homologous to FCC1 in Fusarium verticillioides. Four independent MCC1 knock-out mutants were generated via Agrobacterium tumefaciens–mediated transformation. All of the MCC1 mutants showed consistent multiple phenotypes. Significant reductions in radial growth on potato dextrose agar (PDA) were observed in all of the MCC1 mutants. In addition, MCC1 gene-deletion mutants produced less aerial mycelium on PDA, showed delayed filamentous growth, had unusual hyphal swellings, produced more melanin, showed an increase in their stress tolerance response, and were reduced significantly in pathogenicity. These results indicate that the MCC1 gene is involved in multiple signaling pathways, including those involved in pathogenicity in M. graminicola.
Effects of Jasmonic Acid, Ethylene, and Salicylic Acid Signaling on the Rhizosphere Bacterial Community of Arabidopsis thaliana
Authors: Doornbos Rogier F. , Geraats Bart P. J. , Kuramae Eiko E. , Van Loon L. C. , Bakker Peter A. H. M.
Published: December 2010

Systemically induced resistance is a promising strategy to control plant diseases, as it affects numerous pathogens. However, since induced resistance reduces one or both growth and activity of plant pathogens, the indigenous microflora may also be affected by an enhanced defensive state of the plant. The aim of this study was to elucidate how much the bacterial rhizosphere microflora of Arabidopsis is affected by induced systemic resistance (ISR) or systemic acquired resistance (SAR). Therefore, the bacterial microflora of wild-type plants and plants affected in their defense signaling was compared. Additionally, ISR was induced by application of methyl jasmonate and SAR by treatment with salicylic acid or benzothiadiazole. As a comparative model, we also used wild type and ethylene-insensitive tobacco. Some of the Arabidopsis genotypes affected in defense signaling showed altered numbers of culturable bacteria in their rhizospheres; however, effects were dependent on soil type. Effects of plant genotype on rhizosphere bacterial community structure could not be related to plant defense because chemical activation of ISR or SAR had no significant effects on density and structure of the rhizosphere bacterial community. These findings support the notion that control of plant diseases by elicitation of systemic resistance will not significantly affect the resident soil bacterial microflora.
Linked, if Not the Same,Mi-1Homologues Confer Resistance to Tomato Powdery Mildew and Root-Knot Nematodes
Authors: Seifi Alireza , Kaloshian Isgouhi , Vossen Jack , Che Daidi , Bhattarai Kishor K. , Fan Junmei , Naher Zabun , Goverse Aska , Tjallingii W. Freddy , Lindhout Pim , Visser Richard G. F. , Bai Yuling
Published: December 2010

On the short arm of tomato chromosome 6, a cluster of disease resistance (R) genes have evolved harboring the Mi-1 and Cf genes. The Mi-1 gene confers resistance to root-knot nematodes, aphids, and whiteflies. Previously, we mapped two genes, Ol-4 and Ol-6, for resistance to tomato powdery mildew in this cluster. The aim of this study was to investigate whether Ol-4 and Ol-6 are homologues of the R genes located in this cluster. We show that near-isogenic lines (NIL) harboring Ol-4 (NIL-Ol-4) and Ol-6 (NIL-Ol-6) are also resistant to nematodes and aphids. Genetically, the resistance to nematodes cosegregates with Ol-4 and Ol-6, which are further fine-mapped to the Mi-1 cluster. We provide evidence that the composition of Mi-1 homologues in NIL-Ol-4 and NIL-Ol-6 is different from other nematode-resistant tomato lines, Motelle and VFNT, harboring the Mi-1 gene. Furthermore, we demonstrate that the resistance to both nematodes and tomato powdery mildew in these two NIL is governed by linked (if not the same) Mi-1 homologues in the Mi-1 gene cluster. Finally, we discuss how Solanum crops exploit Mi-1 homologues to defend themselves against distinct pathogens.
Pectin Methylesterase Is Induced in Arabidopsis upon Infection and Is Necessary for a Successful Colonization by Necrotrophic Pathogens
Authors: Raiola Alessandro , Lionetti Vincenzo , Elmaghraby Ibrahim , Immerzeel Peter , Mellerowicz Ewa J. , Salvi Giovanni , Cervone Felice , Bellincampi Daniela
Published: December 2010

The ability of bacterial or fungal necrotrophs to produce enzymes capable of degrading pectin is often related to a successful initiation of the infective process. Pectin is synthesized in a highly methylesterified form and is subsequently de-esterified in muro by pectin methylesterase. De-esterification makes pectin more susceptible to the degradation by pectic enzymes such as endopolygalacturonases (endoPG) and pectate lyases secreted by necrotrophic pathogens during the first stages of infection. We show that, upon infection, Pectobacterium carotovorum and Botrytis cinerea induce in Arabidopsis a rapid expression of AtPME3 that acts as a susceptibility factor and is required for the initial colonization of the host tissue.
Identification and Characterization of 2′-Deoxyuridine from the Supernatant of Conidial Suspensions of Rice Blast Fungus as an Infection-Promoting Factor in Rice Plants
Authors: Ando Sugihiro , Sato Yuko , Shigemori Hideyuki , Shimizu Takafumi , Okada Kazunori , Yamane Hisakazu , Jikumaru Yusuke , Kamiya Yuji , Yamada Kosumi , Akimoto-Tomiyama Chiharu , Tanabe Shigeru , Nishizawa Yoko , Minami Eiichi
Published: December 2010

We previously detected infection-promoting activity in the supernatant of the conidial suspension (SCS) of the rice blast fungus. In the present study, a molecule carrying the activity was purified and identified as 2′-deoxyuridine (dU). The infection-promoting activity of dU was strictly dependent on its chemical structure and displayed characteristics consistent with those of the SCS. Notably, the activity of dU was exclusively detected during interactions between rice and virulent isolates of the fungus, the number of susceptible lesions in leaf blades was increased by dU, and nonhost resistance in rice plants was not affected by treatment with dU. In addition, the expression of pathogensis-related genes, accumulation of H2O2, and production of phytoalexins in rice in response to inoculation with virulent fungal isolates was not suppressed by dU. The infection-promoting activity of dU was not accompanied by elevated levels of endogenous abscissic acid, which is known to modify plant-pathogen interactions, and was not detected in interactions between oat plants and a virulent oat blast fungus isolate. Taken together, these results demonstrate that dU is a novel infection-promoting factor that acts specifically during compatible interactions between rice plants and rice blast fungus in a mode distinct from that of toxins and suppressors.