bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic magnetization properties of a superferromagnetic metal-insulator multilayer observed by magneto-optic Kerr microscopy
Authors: Bedanta S. , Rhensius J. , Kleemann W. , Parashar P. , Cardoso S. , Freitas P. P.
Published: March 2009

Longitudinal magneto-optical Kerr effect (MOKE) magnetometry and microscopy have been performed on a superferromagnetic (SFM) metal-insulator multilayer of [Co80Fe20(tn=1.3 nm)/Al2O3(3 nm)]10 to understand the dynamic behavior of the SFM domains. Frequency dependent hysteresis loops measured by MOKE show that the coercive field Hc increases as the rate (frequency) of magnetization reversal is increased similar to dynamic hysteresis loops observed on conventional ferromagnetic ultrathin films. This dynamic hysteresis behavior arises due to SFM friction-controlled domain wall motion which is observed by MOKE microscopy. We see that the nucleation field for SFM domains increases for hysteresis loops with higher frequency as expected for a ferroic system.
Uniaxial anisotropy and novel magnetic behaviors of CoFe2O4 nanoparticles prepared in a magnetic field
Authors: Gao Qian , Hong Guangyan , Ni Jiazuan , Wang Wendong , Tang Jinke , He Jibao
Published: March 2009

CoFe 2 O 4 nanoparticles prepared by chemical coprecipitation method in a magnetic field exhibit novel magnetic properties. The average particle diameter was about 2 nm and larger depending on the post annealing temperature. Magnetization measurements indicate that smaller nanoparticles are superparamagnetic above their respective blocking temperatures. In the blocked state, these nanoparticles exhibit interesting behaviors in the magnetic hysteresis measurements. Constricted, or wasp waisted with extremely narrow waist, hysteresis curves have been observed in the magnetization versus field sweeps. For larger nanoparticles, the room temperature hysteresis is typical of a ferromagnet with an open loop, but the loop closes at lower temperature. The novel magnetic behavior is attributed to the directional order of Co ions and vacancies in CoFe2O4 established during the coprecipitation of the nanoparticles under an applied field.
An explicit expression of supremum of bounded quantum observables
Authors: Xu Xiao-Ming , Du Hong-Ke , Fang Xiaochun
Published: March 2009

Bounded observables corresponding to a quantum system are usually represented by S(H), the set of all bounded linear self-adjoint operators on a Hilbert space H. In 2006, Gudder introduced a logic order, ≼, on S(H). For A,B∊S(H), A≼B if and only if there exists C∊S(H) such that AC=0 and A+C=B. Given A,B∊S(H), let A∨B be the least upper bound (supremum) for A and B with respect to the Gudder order. In 2007, Pulmannová and Vincenková proved that A∨B exists if and only if A and B have an upper bound for the Gudder order. In this paper, we present some new necessary and sufficient conditions for which A∨B exists and give an explicit representation of A∨B (if A∨B exists).
Field induced structural phase transition at temperatures above the Curie point in Gd5(SixGe1−x)4
Authors: Hadimani R. L. , Melikhov Y. , Snyder J. E. , Jiles D. C.
Published: March 2009

Gd 5 ( Si x Ge 1 − x ) 4 exhibits a field induced first order phase transition from a monoclinic paramagnetic to an orthorhombic ferromagnetic at temperatures above its Curie temperature for 0.41≤x≤0.51. The field required to induce the transition increases with temperature. This field induced first order phase transition was observed even above the projected second order phase transition temperature of the orthorhombic phase. This may be due to the fact that the applied magnetic field is so high that it causes the broadening to a wider range of higher temperatures of the second order phase transition of the orthorhombic phase, and at such high magnetic fields the magnetic moment is still quite large, therefore, causing the transition. This hypothesis seems to be confirmed by the various magnetic moment versus magnetic field, magnetic moment versus temperature, and strain versus magnetic field measurements carried out on single crystal Gd5Si1.95Ge2.05 and Gd5Si2Ge2 samples at magnetic fields of 0–9 T and at temperatures of 265–305 K.
Effects of eddy currents due to a vacuum chamber wall in the airgap of a moving-magnet linear actuator
Authors: Jansen J. W. , Lomonova E. A. , Rovers J. M. M.
Published: March 2009

This paper discusses the effects of eddy currents induced in an electrically conducting plate which is placed in the airgap of a linear synchronous actuator with moving permanent magnets. The eddy currents induced in this plate, which is part of a controlled atmosphere chamber, cause not only damping but also deteriorate the actuator performance by disturbing the position measurement with Hall sensors. Furthermore, feed-forward controllers are less effective due to the suppression of high frequent armature fields. These effects are analyzed with an analytical model and verified with finite element simulations and measurements.
Heterojunction topology versus fill factor correlations in novel hybrid small-molecular/polymeric solar cells
Authors: Schubert Marcel , Yin Chunhong , Castellani Mauro , Bange Sebastian , Tam Teck Lip , Sellinger Alan , Hörhold Hans-Heinrich , Kietzke Thomas , Neher Dieter
Published: March 2009

The authors present organic photovoltaic (OPV) devices comprising a small molecule electron acceptor based on 2-vinyl-4,5-dicyanoimidazole (Vinazene™) and a soluble poly(p-phenylenevinylene) derivative as the electron donor. A strong dependence of the fill factor (FF) and the external quantum efficiency [incident photons converted to electrons (IPCE)] on the heterojunction topology is observed. As-prepared blends provided relatively low FF and IPCE values of 26% and 4.5%, respectively, which are attributed to significant recombination of geminate pairs and free carriers in a highly intermixed blend morphology. Going to an all-solution processed bilayer device, the FF and IPCE dramatically increased to 43% and 27%, respectively. The FF increases further to 57% in devices comprising thermally deposited Vinazene layers where there is virtually no interpenetration at the donor/acceptor interface. This very high FF is comparable to values reported for OPV using fullerenes as the electron acceptor. Furthermore, the rather low electron affinity of Vinazene compound near 3.5 eV enabled a technologically important open circuit voltage (Voc) of 1.0 V.
Magnetic coupling in bis-nitronylnitroxide radicals: The role of aromatic bridges
Authors: Barone Vincenzo , Cacelli Ivo , Ferretti Alessandro
Published: March 2009

Configuration interaction calculations have been applied to the study of the magnetic coupling in bis-nitronyl nitroxide radicals with benzene bridges. Molecular orbitals obtained with different localization schemes have been considered in the generation of the CI space, with the aim of investigating the role played by the various fragments in the magnetic interaction. The aromatic bridge is found significant, while fragments outside the magnetic-bridge-magnetic moiety can be neglected. Using simplified model molecular species, an accurate analysis of the ferromagnetic/antiferromagnetic coupling in the meta and para diradicals is reported.
Composition dependence of glass transition temperature and fragility. I. A topological model incorporating temperature-dependent constraints
Authors: Gupta Prabhat K. , Mauro John C.
Published: March 2009

We present a topological model for the composition dependence of glass transition temperature and fragility. Whereas previous topological models are derived for zero temperature conditions, our approach incorporates the concept of temperature-dependent constraints that freeze in as the system is cooled from high temperature. Combining this notion of temperature-dependent constraints with the Adam–Gibbs model of viscosity, we derive an analytical expression for the scaling of glass transition temperature and fragility in the binary GexSe1−x system. In the range of 0≤x≤1/3, we reproduce the modified Gibbs–DiMarzio equation of Sreeram et al. [J. Non-Cryst. Solids 127, 287 (1991)] but without any empirical fitting parameters. The modified Gibbs–DiMarzio equation breaks down for 1/3<x≤2/5, where the glass transition temperature decreases with increasing germanium content.
Global well posedness and limit behavior of the solutions to the viscous Degasperis–Procesi equation
Authors: Tian Lixin , Liang Shujuan
Published: March 2009

This paper is concerned with the global well posedness and limit behavior of the solutions to the viscous Degasperis–Procesi equation. We prove the global existence and uniqueness of solution to the viscous Degasperis–Procesi equation for u0∊L2(R). The local well posedness for u0∊L2(R) has been proven based on the energy estimate. The strong and weak limit behaviors of solution to the viscous Degasperis–Procesi equation are obtained.
Study of the dynamics of poly(ethylene oxide) by combining molecular dynamic simulations and neutron scattering experiments
Authors: Brodeck M. , Alvarez F. , Arbe A. , Juranyi F. , Unruh T. , Holderer O. , Colmenero J. , Richter D.
Published: March 2009

We performed quasielastic neutron scattering experiments and atomistic molecular dynamics simulations on a poly(ethylene oxide) (PEO) homopolymer system above the melting point. The excellent agreement found between both sets of data, together with a successful comparison with literature diffraction results, validates the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field used to produce our dynamic runs and gives support to their further analysis. This provided direct information on magnitudes which are not accessible from experiments such as the radial probability distribution functions of specific atoms at different times and their moments. The results of our simulations on the H-motions and different experiments indicate that in the high-temperature range investigated the dynamics is Rouse-like for Q-values below ≈0.6 Å−1. We then addressed the single chain dynamic structure factor with the simulations. A mode analysis, not possible directly experimentally, reveals the limits of applicability of the Rouse model to PEO. We discuss the possible origins for the observed deviations.
Excited state calculations using phaseless auxiliary-field quantum Monte Carlo: Potential energy curves of low-lying C2 singlet states
Authors: Purwanto Wirawan , Zhang Shiwei , Krakauer Henry
Published: March 2009

We show that the recently developed phaseless auxiliary-field quantum Monte Carlo (AFQMC) method can be used to study excited states, providing an alternative to standard quantum chemistry methods. The phaseless AFQMC approach, whose computational cost scales as M3-M4 with system size M, has been shown to be among the most accurate many-body methods in ground state calculations. For excited states, prevention of collapse into the ground state and control of the Fermion sign/phase problem are accomplished by the approximate phaseless constraint with a trial wave function. Using the challenging C2 molecule as a test case, we calculate the potential energy curves of the ground and two low-lying singlet excited states. The trial wave function is obtained by truncating complete active space wave functions, with no further optimization. The phaseless AFQMC results using a small basis set are in good agreement with exact full configuration-interaction calculations, while those using large basis sets are in good agreement with experimental spectroscopic constants.
Perspectives on high-energy-density physics
Authors: Drake R. P.
Published: March 2009

Much of 21st century plasma physics will involve work to produce, understand, control, and exploit very nontraditional plasmas. High-energy-density (HED) plasmas are often examples, variously involving strong Coulomb interactions and ⪡1 particles per Debye sphere, dominant radiation effects, and strongly relativistic or strongly quantum-mechanical behavior. Indeed, these and other modern plasma systems often fall outside the early standard theoretical definitions of “plasma.” Here the specific ways in which HED plasmas differ from traditional plasmas are discussed. This is first done by comparison of important physical quantities across the parameter regime accessible by existing or contemplated experimental facilities. A specific discussion of some illustrative cases follows, including strongly radiative shocks and the production of relativistic, quasimonoenergetic beams of accelerated electrons.
Lattice kinetic Monte Carlo simulations of convective-diffusive systems
Authors: Flamm Matthew H. , Diamond Scott L. , Sinno Talid
Published: March 2009

Diverse phenomena in physical, chemical, and biological systems exhibit significant stochasticity and therefore require appropriate simulations that incorporate noise explicitly into the dynamics. We present a lattice kinetic Monte Carlo approach to simulate the trajectories of tracer particles within a system in which both diffusive and convective transports are operational. While diffusive transport is readily accounted for in a kinetic Monte Carlo simulation, we demonstrate that the inclusion of bulk convection by simply biasing the rate of diffusion with the rate of convection creates unphysical, shocklike behavior in concentrated systems due to particle pile up. We report that elimination of shocklike behavior requires the proper passing of blocked convective rates along nearest-neighbor chains to the first available particle in the direction of flow. The resulting algorithm was validated for the Taylor–Aris dispersion in parallel plate flow and multidimensional flows. This is the first generally applicable lattice kinetic Monte Carlo simulation for convection-diffusion and will allow simulations of field-driven phenomena in which drift is present in addition to diffusion.
Potential energy curves and interpretation of electronic spectrum of the rhodium monoxide
Authors: Suo Bingbing , Han Huixian , Lei Yibo , Zhai Gaohong , Wang Yubin , Wen Zhenyi
Published: March 2009

Potential energy curves of 17 electronic states of rhodium monoxide (RhO) are calculated by multireference configuration interaction with single and double excitations (MRCISD). The ground state of RhO is determined to be a Σ4− state with equilibrium bond length of 1.710 Å and harmonic vibrational frequency of 825 cm−1 at the MRCISD level of theory. It dissociates into Rh(F4)+O(P3) with a dissociation energy of 3.77/4.26 eV (MRCISD/MRCISD+Q), which is in agreement with the experimental value of 4.19±0.43 eV. Two low-lying excited states a Σ2− and bΠ2 are located at 4152 and 7154 cm−1 above the ground state. The bΠ2 with the adjacent Δ2, Δ4, and Π2(II) states can be strongly coupled via spin-orbit interaction leading to a large splitting between b Π23/2-b Π21/2 states with the value of 2422 cm−1, which is comparable with the experimental value of 2400 cm−1. Two higher doublets, cΠ2 and dΠ2, have the same dominant configuration, 10σ211σ212σ15π46π32δ3, and their transitions to the ground state, i.e., cΠ2→Σ4− and dΠ2→Σ4−, correspond to the two visible bands of RhO.
Simple driven chaotic oscillators with complex variables
Authors: Marshall Delmar , Sprott J. C.
Published: March 2009

Despite a search, no chaotic driven complex-variable oscillators of the form ż+f(z)=eiΩt or ż+f(z¯)=eiΩt are found, where f is a polynomial with real coefficients. It is shown that, for analytic functions f(z), driven complex-variable oscillators of the form ż+f(z)=eiΩt cannot have chaotic solutions. Seven simple driven chaotic oscillators of the form ż+f(z,z¯)=eiΩt with polynomial f(z,z¯) are given. Their chaotic attractors are displayed, and Lyapunov spectra are calculated. Attractors for two of the cases have symmetry across the x=−y line. The systems’ behavior with Ω as a control parameter in the range of Ω=0.1–2.0 is examined, revealing cases of period doubling, intermittency, chaotic transients, and period adding as routes to chaos. Numerous cases of coexisting attractors are also observed.
Modeling solute clustering in the diffusion layer around a growing crystal
Authors: Shiau Lie-Ding , Lu Yung-Fang
Published: March 2009

The mechanism of crystal growth from solution is often thought to consist of a mass transfer diffusion step followed by a surface reaction step. Solute molecules might form clusters in the diffusion step before incorporating into the crystal lattice. A model is proposed in this work to simulate the evolution of the cluster size distribution due to the simultaneous aggregation and breakage of solute molecules in the diffusion layer around a growing crystal in the stirred solution. The crystallization of KAl(SO4)212H2O from aqueous solution is studied to illustrate the effect of supersaturation and diffusion layer thickness on the number-average degree of clustering and the size distribution of solute clusters in the diffusion layer.
Depth-resolved positron annihilation studies of argon nanobubbles in aluminum
Authors: Dhaka R. S. , Gururaj K. , Abhaya S. , Amarendra G. , Amirthapandian S. , Panigrahi B. K. , Nair K. G. M. , Lalla N. P. , Barman S. R.
Published: March 2009

The formation of Ar bubbles in Al has been investigated by using depth-resolved positron annihilation spectroscopy and transmission electron microscopy. Due to Ar bubble formation, the Doppler-broadening S parameter decreases, while the W parameter increases compared to the reference unimplanted Al sample. The effect of Ar ion fluence and annealing temperature on these parameters has been investigated. The presence of Ar at near-surface region has been confirmed by Rutherford backscattering spectroscopy. Transmission electron microscopy also shows that the Ar bubbles are in solid state with fcc structure after annealing at 870 K. The average diameter and lattice parameter of these solid Ar bubbles are estimated to be about 4±1 nm and 0.495±0.005 nm, respectively.
Temperature-stable giant dielectric response in orthorhombic samarium strontium nickelate ceramics
Authors: Liu Xiao Qiang , Wu Yong Jun , Chen Xiang Ming , Zhu Hai Yan
Published: March 2009

The crystalline structure and dielectric properties of Sm1.5Sr0.5NiO4 ceramics are presented. The present ceramics is refined as orthorhombic Bmab phase and the orthorhombic strain may change the statue of charge ordering. The temperature-stable giant dielectric constant (∼100 000) with low dielectric loss of ∼0.1 is observed at frequency up to 5 MHz over a broad range of temperature (150–500 K) and frequency (100 kHz–5 MHz). The grain interior should be the dominative factor which contributes the giant dielectric response in the present ceramics after the equivalent circuit fitting, and the thermal activated small polaronic hopping related to the charge ordering is that factor. Compared to other giant dielectric materials, the present materials have a great potential in the practical application, especially for the high frequency application.
Epitaxial growth of 20 nm InAs and GaAs quantum dots on GaAs through block copolymer templated SiO2 masks
Authors: Alizadeh Azar , Hays David , Taylor Seth T. , Keimel Chris , Conway Ken R. , Denault Lauraine , Krishnan Kasiraman , Watkins Vicki H. , Neander Rosalyn , Brown Jay S. , Stintz Andreas , Krishna Sanjay , Blumin Marina , Saveliev Igor , Ruda Harry E. , Braunstein Edit , Jones Colin
Published: March 2009

We report on selective area growth of InAs and GaAs quantum dots (QDs) on GaAs through ∼20 nm SiO2 windows prepared by block copolymer lithography. We discuss the mechanisms of growth through these masks, highlighting the variation of the resulting morphology (dot size, spacing, uniformity, and areal density) as a function of growth parameters. We have obtained highly uniform arrays of InAs and GaAs QDs with mean diameters and areal densities of 20.6 nm and 1×1011 cm−2, respectively. We have also investigated the optical characteristics of these QDs as a function of temperature and drawn correlations between the optical response and their crystalline quality.
Direct evidence for mode-specific vibrational energy relaxation from quantum time-dependent perturbation theory. II. The ν4 and ν7 modes of iron-protoporphyrin IX and iron porphine
Authors: Zhang Yong , Straub John E.
Published: March 2009

The mode-specific vibrational energy relaxation (VER) of the iron-protoporphyrin IX (the heme) was studied using a non-Markovian time-dependent perturbation theory at the UB3LYP/6-31G(d) level. The derived VER time constants of the excited ν4 and ν7 modes, 1.2±0.1 and 2.1±0.1 ps, respectively, agree well with previous experimental results for MbCO (1.1±0.6 ps for the ν4 mode and 1.9±0.6 ps for the ν7 mode). The energy transfer pathways from the excited ν4 and ν7 modes were identified. The different symmetries of the ν4 and ν7 modes are reflected in distinct relaxation pathways. No direct energy transfer between the ν4 and ν7 modes was observed. The overtone of the ∼350 cm−1 iron out-of-plane γ7 mode was observed to be strongly coupled to the ν7 mode and essential to its relaxation. The two isopropionate side chains of the heme were found to play an essential role in the VER mechanism for both ν4 and ν7 modes, providing the mode-specific level explanation to previous observations. Comparison of the results for VER in iron porphine (FeP) to results for the imidazole-ligated porphine model (FeP-Im) demonstrates that the axial Im ligand has little effect on the ν4 or ν7 mode relaxation processes. By considering the VER process as a multistep reaction and the third order Fermi resonance parameters the reaction rate constants, the VER kinetics of FeP was examined by solving the master equation.
Gigahertz bandwidth electrical control over a dark exciton-based memory bit in a single quantum dot
Authors: McFarlane J. , Dalgarno P. A. , Gerardot B. D. , Hadfield R. H. , Warburton R. J. , Karrai K. , Badolato A. , Petroff P. M.
Published: March 2009

An optical write-store-read process is demonstrated in a single InGaAs quantum dot within a charge-tunable device. A single dark exciton is created by nongeminate optical excitation allowing a dark exciton-based memory bit to be stored for over ∼1 μs. Read-out is performed with a gigahertz bandwidth electrical pulse, forcing an electron spin-flip followed by recombination as a bright neutral exciton, or by charging with an additional electron followed by a recombination as a negative trion. These processes have been used to determine accurately the dark exciton spin-flip lifetime as it varies with static electric field.
Ion-energy distributions at a substrate in reactive magnetron sputtering discharges in Ar/H2S from copper, indium, and tungsten targets
Authors: Seeger S. , Harbauer K. , Ellmer K.
Published: March 2009

Ion-energy distributions from copper, indium, and tungsten targets were measured during reactive sputtering in argon-hydrogen sulfide (H2S) mixtures, since reactive magnetron sputtering of sulfides from metallic targets is of increasing interest, especially for photovoltaic applications (buffer and absorber layers, i.e., CuInS2, In2S3, or WS2). The mass spectra of the ions show a wide range of molecules HxSn derived from H2S by plasma-assisted attachment both for positive (n≤9) and for negative (n≤6) ions. From the copper and the indium targets metallic ions (Cu+, In+) could be detected. While tungsten and indium sulfur compounds were found, copper does not form compounds with sulfur, caused by its lower chemical reactivity. Positive (Ar+, S+, W+, Cu+, In+, etc.) as well as negative ions (S−, InS−, WS3−) were measured for dc and rf (27 MHz) plasma excitations. The positive ions originate mainly from the plasma in front of the substrate and exhibit energies of about 12 eV for the dc and 18 eV for the rf discharge for the substrate at floating potential. The energy difference is caused by the higher electron temperature in the rf compared to the dc discharge. The ion-energy distributions of negative ions exhibit two distinct peaks. The high-energetic peak can be attributed to ions accelerated in the cathode dark space to a high energy (up to more than 400 eV) corresponding to the cathode (target) voltage. The second peak has its maximum at zero energy decreasing steeply up to energies of about 100 eV. These ions are generated by charge-exchange collisions of energetic species from the target (reflected neutral argon, negative sulfur ions, etc.) on their passage from the target to the substrate caused by the high charge-exchange cross section. rf magnetron sputtering leads to significantly lower energies of negative ions from the target, caused by the lower discharge voltages, which could be advantageous for the deposition of active semiconducting sulfide films.
Structure and photoemission spectroscopy of strain-controlled metal-insulator transition in NdNiO3 thin films
Authors: Eguchi R. , Okamoto Y. , Hiroi Z. , Shin S. , Chainani A. , Tanaka Y. , Matsunami M. , Takata Y. , Nishino Y. , Tamasaku K. , Yabashi M. , Ishikawa T.
Published: March 2009

We study epitaxial NdNiO3 thin films on NdGaO3(001) single-crystal substrates grown using a pulsed-laser deposition method. The films show a clear first-order metal-insulator transition (MIT) at TMI∼240 K, which is significantly higher than TMI∼190 K in bulk NdNiO3. The x-ray reciprocal space map shows in-plane tensile and out-of-plane compressive strain, stabilizing the more distorted NdNiO3 thin films with the higher transition temperature. Hard x-ray photoemission shows changes across the MIT and the bandwidth-controlled charge-transfer gap opens due to the reduced p-d hybridization in the low-temperature insulating phase.
Variation of structural and magnetic properties with Co-doping in Zn1−xCoxO nanocrystals
Authors: Li Jian-jun , Hao Wei-chang , Xu Huai-zhe , Wang Tian-min
Published: March 2009

The Zn1−xCoxO (x=0–0.20) nanocrystals synthesized via sol-gel method have been systematically investigated by using x-ray diffraction, transmission electronic microscopy (TEM), Raman spectrometer (Raman), UV-vis spectrometer (UV-vis), and vibrating sample magnetometer. It is found that the crystal lattice constant (a) and the cell volume of Zn1−xCoxO are irrespective of the Co composition x when x<0.05, while it expands gradually as x increasing from 0.05 to 0.2. This result is different from the existent reports, which indicated the lattice constant (a) and the cell volume both increase consecutively with Co-doping. Detailed Raman, UV-vis, and TEM study suggest the expansion of lattice constant when x>0.05 is attributed to the formation of the Co3O4 phase in Zn1−xCoxO due to the self-purification mechanism in nanocrystals growth process. The formation of the antiferromagnetic Co3O4 well explains the decrease in Zn1−xCoxO ferromagnetism with the increase in Co-doping when x>0.05.
Evaluation of microstructures and carrier transport behaviors during the transition process from amorphous to nanocrystalline silicon thin films
Authors: Song C. , Chen G. R. , Xu J. , Wang T. , Sun H. C. , Liu Y. , Li W. , Ma Z. Y. , Xu L. , Huang X. F. , Chen K. J.
Published: March 2009

Hydrogenated amorphous Si thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited samples were thermally annealed at various temperatures to obtain nanocrystalline Si. The microstructures and carrier transport behaviors were evaluated during the transition process from amorphous to nanocrystalline structures. Raman scattering spectroscopy and Fourier-transform infrared spectroscopy were used to characterize the changes in microstructures and bonding configurations. It is found that hydrogen is completely effused from the film at the annealing temperature of 600 °C, while crystallization occurs at around 700 °C. The carrier transport characteristics in nanocrystallized films are different from those in the amorphous Si films. The carrier transport in the amorphous silicon films is strongly influenced by the defect states resulting from the effusion of hydrogen. The dual activation energies are found in temperature-dependent conductivity results which can be attributed to the two different conduction paths in the samples. In the case of the nanocrystallized Si films obtained by high temperature annealing, the transport process is accounted for in the framework of a three-phase model comprised of amorphous and nanocrystalline phases and the grain boundary in the films.
Physical and optical properties of binary amorphous selenium-antimony thin films
Authors: Sharma Pankaj , Sharma Ishu , Katyal S. C.
Published: March 2009

Amorphous thin films with compositions Se1−xSbx (x=0, 0.025, 0.05, 0.075, and 0.10 at. %) have been deposited by thermal evaporation (at ∼10−4 Pa) from bulk samples. The compositional dependence of their optical properties, refractive index, extinction coefficient, absorption coefficient, and optical band gap with increasing Sb content is investigated using transmission spectra in the range of 400–1200 nm. The refractive-index dispersion has been analyzed on the basis of the Wemple–DiDomenico single-oscillator approach. It has been found that the refractive index increases with increasing Sb content. The behavior of the optical band gap, when the composition of the material is varied, shows, as expected, just the opposite trends. The optical band gap decreases from 2.025 to 1.753 eV with ±0.001 eV uncertainty. Band gap calculated theoretically also shows a decrease with the increase in Sb content. The optical behavior is supported by physical properties, i.e., decrease in optical band gap is supported by the decrease in cohesive energy of the system. Some other physical properties, viz., coordination number, lone-pair electrons, and glass transition temperature, are also investigated theoretically. The optical results may lead to yield more sensitive detectors based on amorphous selenium, and physical properties may be useful in achieving more stable alloys which are favorable in x-ray imaging applications.
Three-dimensional Monte Carlo study of three-terminal junctions based on InGaAs/InAlAs heterostructures
Authors: Sadi Toufik , Dessenne François , Thobel Jean-Luc
Published: March 2009

We apply a three-dimensional (3D) semiclassical ensemble Monte Carlo simulation method to study T-branch junctions based on InGaAs/InAlAs heterostructures and obtain an accurate insight into the physics behind the operation of such structures. Electron transport in these devices is investigated and their rectifying behavior is demonstrated at 77 and 300 K and for different branch sizes. Detailed device analysis is performed to establish the relationship between the extent of ballistic transport and the rectifying behavior of the junctions and show the influence of surface charge effects, which are carefully included in the model. Results from the simulation of a T-branch junction with a Schottky gate terminal are presented, demonstrating the necessity of using 3D simulation models to study the physics of semiconductor junctions.
Etching gold tips suitable for tip-enhanced near-field optical microscopy
Authors: Eligal Lior , Culfaz Ferhat , McCaughan Vincent , Cade Nicholas I. , Richards David
Published: March 2009

We describe a simple method of fabricating gold tips for tip-enhanced near-field optical microscopy using a single step direct current electrochemical etch. Smooth gold tips with a radius of curvature ∼40 nm and with an aspect ratio suitable for shear force measurement have been produced in a few minutes. A detailed analysis of the etching process has enabled production of reproducible high quality tips. Near field images of single quantum dots using tips etched with this technique are shown.
Experimental design for the determination of the injection barrier height at metal/organic interfaces using temperature dependent current-voltage measurements
Authors: Helander M. G. , Wang Z. B. , Greiner M. T. , Qiu J. , Lu Z. H.
Published: March 2009

Determination of the injection barrier height for holes or electrons at metal/organic interfaces is essential to understanding the device physics of organic electronics. Due to the disordered molecular packing of organic semiconductors, careful consideration is required in the design of both the device structure and the experimental measurement technique used to extract the barrier height. We report a methodology for extracting the injection barrier height at metal/organic interfaces from temperature dependent current-voltage measurements. This methodology includes the design of single carrier devices with specific consideration of the intrinsic properties of organic semiconductors, as well as the design of a variable temperature cryostat suited to the measurement of organic electronic device architectures. Experimental results for single carrier hole-only devices using two commonly studied hole transport materials, namely N,N′-diphenyl-N,N′-bis-(1-naphthyl)-1-1′-biphenyl-4,4′-diamine (α-NPD) and 4,4′,4″-tris(N-3- methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA) are also presented as examples.
The estimation of charge footprint size of ultraviolet photon counting imaging detector with induction readout
Authors: Zhang Xinghua , Zhao Baosheng , Zhao Feifei , Liu Yong’an , Miao Zhenhua , Zhu Xiangping , Yan Qiurong
Published: March 2009

The structure and work principle of an ultraviolet photon counting imaging detector based on wedge and strip anode with induction readout mode are introduced. Two methods of estimating the charge footprint size are presented. One way is theoretical calculation and simulation. The physical course of electrons is simulated from the microchannel plate output side to the readout anode. The calculated results show that the final charge footprint size is sensitive to the thickness of ceramic and not sensitive to the charge footprint size on the Ge layer. The other way is experimental image estimation. The final charge footprint size can be estimated according to the position where the light line of resolution board image begins to bend. Both methods show that the charge footprint size is sensitive to the ceramic substrate. The two methods are simple and effective for estimation of charge footprint size of photon counting imaging detector with induction readout.
All-inorganic light emitting device based on ZnO nanoparticles
Authors: Neshataeva E. , Kümmell T. , Bacher G. , Ebbers A.
Published: March 2009

We report on room-temperature electroluminescence from an all-inorganic light emitting device based on spin-coated ZnO nanoparticles. A tight submicron thick layer was fabricated on a fluorine doped tin oxide glass as a substrate using commercially available ZnO nanoparticles from the gas phase. After the evaporation of the top Al electrode, a diodelike I-V characteristic was obtained. An emission peak at around 390 nm and a broad defect-related electroluminescence in the visible range were observed at voltages below 10 V and ambient air conditions.
Super high voltage Schottky diode with low leakage current for x- and γ-ray detector application
Authors: Kosyachenko L. A. , Gnatyuk V. A. , Aoki T. , Sklyarchuk V. M. , Sklyarchuk O. F. , Maslyanchuk O. L.
Published: March 2009

A significant improvement in x-/γ-ray detector performance has been achieved by forming both rectifying and near-Ohmic contacts by the deposition of Ni on opposite surfaces of semi-insulating CdTe crystals pretreated by special chemical etching and Ar-ion bombardment with different parameters. The reduced injection of the minority carriers from the near-Ohmic contact in the neutral part of the diode provides low leakage current even at high bias (<50 nA/cm2 at 2000 V and 293 K). The electrical properties of the detectors are well described quantitatively by the generation-recombination Sah–Noyce–Shockley theory excepting the high reverse voltage range where some injection of minority carriers takes place.
High-Q terahertz Bragg resonances within a metal parallel plate waveguide
Authors: Harsha S. Sree , Laman N. , Grischkowsky D.
Published: March 2009

One-dimensional (1D) Bragg waveguides are demonstrated at terahertz (THz) frequencies. Lithographically made 1D symmetric and asymmetric dielectric gratings on metallized high conductivity Si chips are incorporated within metal parallel plate waveguides to form Bragg waveguides. These waveguides have high throughput and have Bragg resonances with linewidths approaching 6 GHz and Q as high as 430. These high-Q resonant Bragg waveguides are excellent structures for applications in THz sensing.
Pattern formation during vapor deposition of organic films on inorganic substrates-continuum modeling vs experiments
Authors: Vree C. , Mayr S. G.
Published: March 2009

The early stages during low temperature vapor deposition of organic materials onto inorganic substrates are frequently characterized by surface pattern formation on a characteristic length scale, accompanied by dramatic roughening, while these structures level at higher film thicknesses. Unexplainable by traditional liquid-state dewetting scenarios, we employ a combined experimental/modeling study to track down the underlying physics using poly(bisphenol A carbonate) (PC) on GaAs (100) as a model system. We present a minimum continuum model, which incorporates only material deposition and chemical potential driven surface diffusion as material processes, whose numerical solution is capable of reproducing key experimental features.
A simple method for filling nanogap electrodes with polymer
Authors: Govor L. V. , Bauer G. H. , Parisi J.
Published: March 2009

We have developed a relatively simple and cost-effective procedure capable to fill nanogap electrodes with a polymer. The polymer deposit into nanogap electrodes was achieved via pinning the solution droplet edge over the nanogap. During solvent evaporation from the droplet, a ringlike deposit forms along its edge. Pinning of the solution droplet was performed by a needle connected to a micromanipulator. After drying, the surplus of the nitrocellulose deposit was removed by the motion of another solvent droplet driven across the nanogap electrodes.
Doppler frequency up conversion of electromagnetic waves in a slotline on an optically excited silicon substrate
Authors: Bae Jongsuck , Xian Yuan Jun , Yamada Sho , Ishikawa Ryo
Published: March 2009

The Doppler frequency up conversion of microwaves in a slotline on an optically excited silicon substrate was experimentally observed. An array of 24 optical fibers with different lengths was used to effectively tilt the wave front of a 532 nm neodymium-doped yttrium aluminum garnet laser beam with a pulse duration of 33 ps. The tilted laser beam produced electron-hole surface plasma whose boundary moved at a relativistic velocity of about c/3.4 (c is the speed of light) along the slotline. The experiments showed that microwaves reflected at the moving boundary of the plasma in the slotline are converted to millimeter waves with a frequency up conversion ratio of 3.82.
A simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air
Authors: Dong Lifang , Zhang Yanzhao , Liu Weiyuan , Yang Li , Chen Junying
Published: March 2009

We report a simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air. It consists of two parallel water electrodes with a distance adjusting micrometer. With increasing the applied voltage, the discharge becomes homogeneous. The electron temperature, vibrational temperature (TV) of N2, and rotational temperature (TR) of N2+ are estimated by optical emission spectroscopy. Both TV and TR remain unchanged along the slot in the homogeneous discharge regime. The trend of the TV with respect to the applied voltage is opposite from that of TR, while the electron temperature keeps constant with the increasing applied voltage.
A microtubule depolymerizing kinesin functions during both flagellar disassembly and flagellar assembly in
Chlamydomonas
Authors: Piao Tian , Luo Minna , Wang Liang , Guo Yan , Li De , Li Peng , Snell William J. , Pan Junmin
Published: March 2009

Cilia and flagella are dynamic organelles that are assembled and disassembled during cell differentiation, during stress, and during the cell cycle. Although intraflagellar transport (IFT) is well documented to be responsible for transport of ciliary/flagellar precursors from the cell body to the flagella, little is known about the molecular mechanisms for mobilizing the cell body-localized precursors to make them available for transport during organelle assembly or for disassembling the microtubule-based axoneme during shortening. Here, we show that
Chlamydomonas
kinesin-13 (CrKinesin-13), a member of the kinesin-13 family of microtubule depolymerizing kinesins best known for their roles in the cell cycle, functions in flagellar disassembly and flagellar assembly. Activation of a cell to generate new flagella induces rapid phosphorylation of CrKinesin-13, and activation of flagellar shortening induces the immediate transport of CrKinesin-13 via intraflagellar transport from the cell body into the flagella. Cells depleted of CrKinesin-13 by RNAi assemble flagella after cell division but are incapable of the rapid assembly of flagella that normally occurs after flagellar detachment. Furthermore, they are inhibited in flagellar shortening. Thus, CrKinesin-13 is dynamically regulated during flagellar assembly and disassembly in
Chlamydomonas
and functions in each.
Multiple ERK substrates execute single biological processes in
Caenorhabditis elegans
germ-line development
Authors: Arur Swathi , Ohmachi Mitsue , Nayak Sudhir , Hayes Matthew , Miranda Alejandro , Hay Amanda , Golden Andy , Schedl Tim
Published: March 2009

RAS-extracellular signal regulated kinase (ERK) signaling governs multiple aspects of cell fate specification, cellular transitions, and growth by regulating downstream substrates through phosphorylation. Understanding how perturbations to the ERK signaling pathway lead to developmental disorders and cancer hinges critically on identification of the substrates. Yet, only a limited number of substrates have been identified that function in vivo to execute ERK-regulated processes. The
Caenorhabditis elegans
germ line utilizes the well-conserved RAS–ERK signaling pathway in multiple different contexts. Here, we present an integrated functional genomic approach that identified 30 ERK substrates, each of which functions to regulate one or more of seven distinct biological processes during
C. elegans
germ-line development. Our results provide evidence for three themes that underlie the robustness and specificity of biological outcomes controlled by ERK signaling in
C. elegans
that are likely relevant to ERK signaling in other organisms: (
i
) multiple diverse ERK substrates function to control each individual biological process; (
ii
) different combinations of substrates function to control distinct biological processes; and (
iii
) regulatory feedback loops between ERK and its substrates help reinforce or attenuate ERK activation. Substrates identified here have conserved orthologs in humans, suggesting that insights from these studies will contribute to our understanding of human diseases involving deregulated ERK activity.
Label-free biosensing with functionalized nanopipette probes
Authors: Umehara Senkei , Karhanek Miloslav , Davis Ronald W. , Pourmand Nader
Published: March 2009

Nanopipette technology can uniquely identify biomolecules such as proteins based on differences in size, shape, and electrical charge. These differences are determined by the detection of changes in ionic current as the proteins interact with the nanopipette tip coated with probe molecules. Here we show that electrostatic, biotin-streptavidin, and antibody-antigen interactions on the nanopipette tip surface affect ionic current flowing through a 50-nm pore. Highly charged polymers interacting with the glass surface modulated the rectification property of the nanopipette electrode. Affinity-based binding between the probes tethered to the surface and their target proteins caused a change in the ionic current due to a partial blockade or an altered surface charge. These findings suggest that nanopipettes functionalized with appropriate molecular recognition elements can be used as nanosensors in biomedical and biological research.
Progesterone receptor polymorphism is associated with pelvic organ prolapse risk
Authors: CHEN HUEY‐YI , CHUNG YA‐WEN , LIN WEI‐YONG , CHEN WEN‐CHI , TSAI FUU‐JEN , TSAI CHANG‐HAI
Published: March 2009

Progesterone and progesterone receptors (PGR) are known to play important roles in the pathophysiology of pelvic organ prolapse (POP). We investigated whether the PGR gene polymorphisms were associated with POP by conducting a case–control association study in 87 women with POP and 150 women without POP. Genotypes of the PGR gene polymorphisms (rs500760 and rs484389) were determined by polymerase chain reaction, followed by restriction fragment length polymorphism analysis. There was significant difference between women with and those without POP in the distribution of the PGR rs484389 genotypes evaluated. Using multivariable logistic regression, older age, increased body mass index, menopausal status, and PGR rs484389 genotype CT were significantly associated with POP. The present study shows that PGR genotype may be associated with POP.
First-principles study of the (001) surface of cubic PbHfO3and BaHfO3
Authors: Ni Guang-Xin  , Wang Yuan-Xu
Published: March 2009

Using first-principles techniques, we investigate the (001) surfaces of cubic PbHfO3(PHO) and BaHfO3(BHO) terminated with both AO (A = Pb and Ba) and HfO2. Surface structure, partial density of states, band structure, and surface energy are obtained. The BaO surface is found to be similar to its counterpart in BHO. For the HfO2-terminated surface of cubic PHO, the largest relaxation appears on the second-layer atoms but not on the first-layer ones. The analysis of the structure relaxation parameters reveals that the rumpling of the (001) surface for PHO is stronger than that for BHO. The surface thermodynamic stability is explored, and it is found that both the PbO- and the BaO-terminated surfaces are more stable than the HfO2-terminated surfaces for PHO and BHO, respectively. The surface energy calculations show that the (001) surface of PHO is more easily constructed than that of BHO.
Use of Tannic Acid as Dough Oxidizing and Vitamin C Protective Agent
Authors: Mendes da Silva Claudio Ernani , da Fonseca Sabóia Amorim Mariza Vieira , Leal de Medeiros Márcia Maria , de Morais Selene Maia
Published: March 2009

Trials with tannic acid in three concentrations (0.1, 0.2, and 0.3%) in a wheat flour dough were run to test its property to preserve the ascorbic acid degradation during baking and its performance in the dough viscoelasticity measured by its extensigraphic properties. The addition of tannic acid to the dough in the cited concentrations increased its resistance to extension (RE) and consequently reduced its extensibility (E) in the same way that ascorbic acid performed but using concentrations 10× smaller. In a dough containing ascorbic acid 0.02% and tannic acid 0.3%, the ascorbic acid retention after 10 days of storage was 34.8%, which represents 154% of the recommended daily intake of vitamin C by FAO/WHO (2002) for an adult (19–65 years old). The addition of tannic acid to the dough also increased the bread specific volume.