bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron beam diagnostics for a superconducting radio frequency photoelectron injector
Authors: Kamps Thorsten , Arnold Andre , Boehlick Daniel , Dirsat Marc , Klemz Guido , Lipka Dirk , Quast Torsten , Rudolph Jeniffa , Schenk Mario , Staufenbiel Friedrich , Teichert Jochen , Will Ingo
Published: September 2008

A superconducting radio frequency (SRF) photoelectron injector is currently under construction by a collaboration of BESSY, DESY, FZD, and MBI. The project aims at the design and setup of a continuous-wave SRF injector including a diagnostics beamline for the ELBE free electron laser (FEL) and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development, serving a multitude of operation settings. In this paper the layout and the rationale of the diagnostics beamline are described. Furthermore detailed information on specific components is given, together with results from laboratory tests and data taking.
Noncontact modulated laser calorimetry of liquid silicon in a static magnetic field
Authors: Kobatake Hidekazu , Fukuyama Hiroyuki , Minato Izuru , Tsukada Takao , Awaji Satoshi
Published: September 2008

Accurate thermal transport properties of high-temperature liquid silicon, such as those of heat capacity, emissivity, and thermal conductivity, are required for improving numerical modeling to produce high-quality silicon crystals using the Czochralski method. However, contamination from contact material and convection complicates measurements of these properties. The authors developed a noncontact modulated laser calorimetry using electromagnetic levitation in a static magnetic field. The isobaric molar heat capacity, thermal conductivity, and hemispherical total emissivity of liquid silicon were measured simultaneously at temperatures of 1750–2050 K. Convection in the levitated liquid silicon was suppressed above a static magnetic field of 2 T.
Strain effect and channel length dependence of bias temperature instability on complementary metal-oxide-semiconductor field effect transistors with high-k/SiO2 gate stacks
Authors: Liao J. C. , Fang Y. K. , Hou Y. T. , Hung C. L. , Hsu P. F. , Lin K. C. , Huang K. T. , Lee T. L. , Liang M. S.
Published: September 2008

The strain effect and channel length dependence of bias temperature instability on dual metal gate complementary metal-oxide-semiconductor field enhanced transistors with HfSiON dielectric were studied in detail. For channel length larger than 0.1 μm, both positive and negative bias temperature instabilities (PBTI and NBTI) were not affected by the tensile strain obviously. As the channel scaling down to less than 0.1 μm, the degradation after PBTI stress was still not influenced by the strain, however, the NBTI degradation was enhanced significantly. In addition, the dependence of BTI on channel length was extensively investigated under constant voltage and field stress.
The magnetic field structure of a snowflake divertor
Authors: Ryutov D. D. , Cohen R. H. , Rognlien T. D. , Umansky M. V.
Published: September 2008

The snowflake divertor exploits a tokamak geometry in which the poloidal magnetic field null approaches second order; the name stems from the characteristic hexagonal, snowflakelike shape of the separatrix for an exact second-order null. The proximity of the poloidal field structure to that of a second-order null substantially modifies edge magnetic properties compared to the standard X-point geometry (with a first-order null); this, in turn, affects the edge plasma behavior. Modifications include: (1) The flux expansion near the null-point becomes 2–3 times larger. (2) The connection length between the equatorial plane and divertor plate increases. (3) Magnetic shear just inside the separatrix becomes much larger. (4) In the open-field-line region, the squeezing of the flux-tubes near the null-point increases, thereby causing stronger decoupling of the plasma turbulence in the divertor legs and in the main scrape-off layer. These effects can be used to reduce the power load on the divertor plates and/or to suppress the “bursty” component of the heat flux. It is emphasized that the snowflake divertor can be created by a relatively simple set of poloidal field coils situated outside the toroidal field coils. Analysis of the robustness of the proposed divertor configuration with respect to changes of the plasma current distribution is presented and it is concluded that, even if the null is close to the second order, the configuration is robust.
Enhanced growth instability of strained film on wavy substrate
Authors: Wang Hangyao , Zhang Yu , Liu Feng
Published: September 2008

We demonstrate that the growth of a strained film is inherently less stable on a wavy substrate than on a flat substrate. For small surface undulation, the lowest strain energy state is for the film surface to adopt the same wavelength as the substrate surface in an antiphase configuration at the early stage of growth. The critical wavelength (λc) of growth instability on a wavy substrate is half of that on a flat substrate (λ0). It increases linearly with increasing film thickness (t) as λc=λ0/2+πt. Implications for strain directed self-assembly on patterned substrate are discussed.
A simple method to characterize the afterpulsing effect in single photon avalanche photodiode
Authors: Yen H. T. , Lin S. D. , Tsai C. M.
Published: September 2008

A simple method is introduced for studying the afterpulsing effect in InGaAs single photon avalanche photodiode. The afterpulsing probability is obtained through measuring the detection efficiencies of various biasing pulses, while the incident photons are kept constant. The effect of excess bias and temperature on the afterpulsing probability is investigated. When the device temperature is higher than 170 K, the afterpulsing probability is lower than 5% for all excess bias voltages because the trapped carrier lifetime is much shorter than the repetition period.
Mercury Bromide (HgBr2): A promising nonlinear optical material in IR region with a high laser damage threshold
Authors: Liu T. , Qin J. , Zhang G. , Zhu T. , Niu F. , Wu Y. , Chen C.
Published: September 2008

Nonlinear optical (NLO) crystals have played a key role in laser technology, and the existing materials for the IR range showed relatively low laser damage threshold in common. A NLO material HgBr2 is presented here. It shows a powder second harmonic generation about ten times as large as that of KH2PO4, a wide transparency in whole mid-IR region (from 2.5 to 25 μm), and a good stability to the environment. Most importantly it exhibits a high laser damage threshold of about 0.3 GW/cm2. Therefore, it is believed that HgBr2 is a promising candidate for NLO materials in the IR region.
Two-component relativistic hybrid density functional computations of nuclear spin-spin coupling tensors using Slater-type basis sets and density-fitting techniques
Authors: Autschbach Jochen
Published: September 2008

Computations of indirect nuclear spin-spin coupling constants using two-component relativistic density functional theory with a hybrid functional are reported. The program implementation makes use of a Slater-type orbital expansion of the molecular orbitals and the zeroth-order regular approximation for the treatment of relativistic effects. Exact exchange terms in the Kohn–Sham response kernel were computed using a fitting procedure. Computations with the PBE0 hybrid functional were carried out for heavy-atom-ligand-one-bond couplings in PbH4, Pb(CH3)2H2, Pb(CH3)3H, three platinum complexes, the interhalogen diatomics such as ClF, ClBr, ClI, BrF, BrI, IF, and the series Tl-X with X=F, Cl, Br, I. The hybrid functional computations performed very well. In particular, for the isotropic coupling and the coupling anisotropy of Tl-X, the PBE0 hybrid functional yielded considerably improved agreement with experiment.
The geometric, optical, and magnetic properties of the endohedral stannaspherenes M@Sn12 (M=Ti, V, Cr, Mn, Fe, Co, Ni)
Authors: Chen Xuan , Deng Kaiming , Liu Yuzhen , Tang Chunmei , Yuan Yongbo , Tan Weishi , Wang Xin
Published: September 2008

The geometric, optical, and magnetic properties of the M@Sn12 clusters (M=Ti, V, Cr, Mn, Fe, Co, Ni) are studied using the relativistic density-functional method. The geometric optimization shows that the ground states of these clusters are probably very close to the Ih structure. Our calculations demonstrate that the optical gaps of the M@Sn12 can be tuned from infrared to green, and the magnetic moments of them vary from 2 μB to 5 μB by doping d transition metal atoms into Sn12 cage, suggesting that M@Sn12 could be a new class of potential nanomaterials with tunable magnetic and optical properties.
Magnetic phase transition in Zn1−xMnxO doped by nitrogen
Authors: Yuldashev Sh. U. , Igamberdiev Kh. T. , Kang T. W. , Pelenovich V. O. , Shashkov A. G.
Published: September 2008

The specific heat measurement was used to study the magnetic phase transition in Zn0.95Mn0.05O. The magnetization dependencies on the magnetic field, M(H) curve, and on the temperature, M(T) curve measured by superconducting quantum interference device, indicate the ferromagnetic-paramagnetic phase transition in Zn0.95Mn0.05O doped by nitrogen has a Curie temperature of about 80 K. The temperature dependence of the specific heat reveals a pronounced λ shaped peak at 75 K for the nitrogen-doped sample. Such dependencies indicate a well defined second-order phase transition in this sample.
Experimental investigation of turbulent diffusion of slightly buoyant droplets in locally isotropic turbulence
Authors: Gopalan Balaji , Malkiel Edwin , Katz Joseph
Published: September 2008

High-speed inline digital holographic cinematography is used for studying turbulent diffusion of slightly buoyant 0.5–1.2 mm diameter diesel droplets and 50 μm diameter neutral density particles. Experiments are performed in a 50×50×70 mm3 sample volume in a controlled, nearly isotropic turbulence facility, which is characterized by two dimensional particle image velocimetry. An automated tracking program has been used for measuring velocity time history of more than 17 000 droplets and 15 000 particles. For most of the present conditions, rms values of horizontal droplet velocity exceed those of the fluid. The rms values of droplet vertical velocity are higher than those of the fluid only for the highest turbulence level. The turbulent diffusion coefficient is calculated by integration of the ensemble-averaged Lagrangian velocity autocovariance. Trends of the asymptotic droplet diffusion coefficient are examined by noting that it can be viewed as a product of a mean square velocity and a diffusion time scale. To compare the effects of turbulence and buoyancy, the turbulence intensity (ui′) is scaled by the droplet quiescent rise velocity (Uq). The droplet diffusion coefficients in horizontal and vertical directions are lower than those of the fluid at low normalized turbulence intensity, but exceed it with increasing normalized turbulence intensity. For most of the present conditions the droplet horizontal diffusion coefficient is higher than the vertical diffusion coefficient, consistent with trends of the droplet velocity fluctuations and in contrast to the trends of the diffusion timescales. The droplet diffusion coefficients scaled by the product of turbulence intensity and an integral length scale are a monotonically increasing function of ui′/Uq.
Ultrafast probing of light-matter interaction in a midinfrared quantum cascade laser
Authors: Parz Wolfgang , Müller Thomas , Darmo Juraj , Unterrainer Karl , Austerer Max , Strasser Gottfried , Wilson Luke R. , Cockburn John W. , Krysa Andrey B. , Roberts John S.
Published: September 2008

In this work, we study the interaction of ultrashort midinfrared pulses with the active medium of an InGaAs∕InAlAs∕InP quantum cascade laser emitting at an 11.7μm wavelength. Applying an electro-optic sampling technique allowed us to measure the complete phase resolved transmission spectra at operating conditions below and above lasing threshold in a spectral range much broader than the gain band width. Far below threshold, we locate broadband resonant absorption, which spectrally overlaps with the electrically induced gain, forming areas of net absorption and net gain. Above threshold, gain clamping is seen, and it is found that echoes delayed by the round trip time experience spectral pulse shaping converging toward the emission spectrum.
Stochastic chemical kinetics and the total quasi-steady-state assumption: Application to the stochastic simulation algorithm and chemical master equation
Authors: MacNamara Shev , Bersani Alberto M. , Burrage Kevin , Sidje Roger B.
Published: September 2008

Recently the application of the quasi-steady-state approximation (QSSA) to the stochastic simulation algorithm (SSA) was suggested for the purpose of speeding up stochastic simulations of chemical systems that involve both relatively fast and slow chemical reactions [Rao and Arkin, J. Chem. Phys. 118, 4999 (2003)] and further work has led to the nested and slow-scale SSA. Improved numerical efficiency is obtained by respecting the vastly different time scales characterizing the system and then by advancing only the slow reactions exactly, based on a suitable approximation to the fast reactions. We considerably extend these works by applying the QSSA to numerical methods for the direct solution of the chemical master equation (CME) and, in particular, to the finite state projection algorithm [Munsky and Khammash, J. Chem. Phys. 124, 044104 (2006)], in conjunction with Krylov methods. In addition, we point out some important connections to the literature on the (deterministic) total QSSA (tQSSA) and place the stochastic analogue of the QSSA within the more general framework of aggregation of Markov processes. We demonstrate the new methods on four examples: Michaelis–Menten enzyme kinetics, double phosphorylation, the Goldbeter–Koshland switch, and the mitogen activated protein kinase cascade. Overall, we report dramatic improvements by applying the tQSSA to the CME solver.
A first-principles study of linear and nonlinear optical properties of 4-nitro-4′-methylbenzylidene aniline
Authors: Luo S. J. , Du W. F. , Wang H. Z.
Published: September 2008

First-principles calculations of two second-order optical response functions as well as the dielectric function for 4-nitro-4′-methylbenzylidene aniline are performed. Specifically, we evaluate the dielectric function and the second-harmonic generation (SHG) response coefficient over a wide frequency range. Electronic structure obtained from the full-potential projected augmented wave method is adopted in the calculation of optical properties. The calculated results of the refractive indices and the SHG are in good agreement with the experimental values. The linear and nonlinear optical spectra are analyzed and the origins of the peaks in the spectra are discussed in terms of the calculated electronic structure. It is found that the origin of the large nonlinear optical susceptibility is the charge transfer due to the strong “push-pull” effect. The study of the contributions of different transitions to the SHG coefficients shows that the virtual electron process is main. The contribution to the largest component χ11(2) of the virtual hole process is about 30% of the total static limit of the SHG coefficient. The prominent features in the spectrum of χ11(2) are successfully correlated with the features of the linear dielectric function ε(ω) in terms of single-photon and two-photon resonances.
Polarization-dependent fluorescence of proteins bound to nanopore-confined lipid bilayers
Authors: Li R.-Q. , Marek A. , Smirnov Alex I. , Grebel H.
Published: September 2008

Lipid bilayers are essential structural component of biological membranes of all the living species: from viruses and bacteria to plants and humans. Biophysical and biochemical properties of such membranes are important for understanding physical mechanisms responsible for drug targeting. Binding events between proteins and the membrane may be ascertained by introducing fluorescence markers (chromophores) to the proteins. Here we describe a novel biosensing platform designed to enhance signals of these fluorescence markers. Nanoporous aluminum oxide membranes with and without gold (Au) surface coating have been employed for optical detection of bound conjugated streptavidin to biotinylated lipid bilayers—a model system that mimics protein docking to the membrane surface. Unexpectedly, it was found that fluorescence signals from such structures vary when pumped with E-polarized and H-polarized incident optical beams. The origin of the observed polarization-dependent effects and the implications for enhanced fluorescence detection in a biochip format are being discussed.
Force autocorrelation function in linear response theory and the origin of friction
Authors: Petravic Janka
Published: September 2008

Vanishing of the equilibrium fluctuation expression for the friction coefficient of a massive particle in a finite-volume liquid has been well documented and discussed in literature. This paper investigates the decay of the friction force in the corresponding nonequilibrium situation, when the massive particle moves through a finite volume at a constant velocity. The friction force ultimately vanishes (with the decay form as predicted by the equilibrium integral) because of the finite mass of the rest of the system, which allows it to be dragged by the moving particle. However, it is sufficient to have two infinite masses moving relative to each other in a finite liquid volume for the friction force to be finite at all times.
Relaxation and fluctuations of the number of particles in a membrane channel at arbitrary particle-channel interaction
Authors: Zitserman Vladimir Yu. , Berezhkovskii Alexander M. , Pustovoit Mark A. , Bezrukov Sergey M.
Published: September 2008

We analyze the relaxation of the particle number fluctuations in a membrane channel at arbitrary particle-channel interaction and derive general expressions for the relaxation time and low-frequency limit of the power spectral density. These expressions simplify significantly when the channel is symmetric. For a square-well potential of mean force that occupies the entire channel, we verify the accuracy of the analytical predictions by Brownian dynamics simulations. For such a channel we show that as the depth of the well increases, the familiar scaling of the relaxation time with the channel length squared is transformed into a linear dependence on the length.
Nano-Ag on vanadium dioxide. I. Localized spectrum tailoring
Authors: Xu Gang , Huang Chun-Ming , Jin Ping , Tazawa Masato , Chen De-Ming
Published: September 2008

We report on the utilization of localized surface plasmon resonance (LSPR) of Ag nanoparticles to tailor the optical properties of VO2 thin film. Interaction of nano-Ag with incident light yields a salient absorption band in the visible-near IR region and modifies the spectrum of VO2 locally. The wavelength of modification occurs in a limited spectral region rather than affects the full spectrum. The wavelength of modification shows a strong dependence on the metal nanoparticle size and shifts toward the red as the particle size or the mass thickness of nano-Ag increases. Also, we found that the wavelength can be shifted into the IR further by introducing a thin layer of TiO2 onto the nano-Ag. Interestingly, with the help of LSPR effects the VO2 film exhibits an anomalous thermochromic behavior in the modification wavelength region, which may be useful in optical switching applications.
Spectral characteristics of continuous wave broadband from a fiber laser with a low dispersion fiber in the cavity
Authors: Venkitesh Deepa , Vijaya R.
Published: September 2008

The spectral width of the continuous wave broadband generated in an erbium doped fiber ring laser containing a dispersion shifted fiber (DSF) in a filterless cavity is found to be governed by the nature of the gain spectrum of the doped fiber, in addition to the nonlinear effects. This dependence is studied experimentally with different lengths of the doped fiber and the DSF. Spectral broadening is demonstrated in the conventional (C) and long wavelength (L) bands using pump powers less than 200 mW, with an appropriate choice of cavity parameters. The generated broadband is demultiplexed in the C-band to prove its utility in optical communication systems.
Electronic stress tensor description of chemical bonds using nonclassical bond order concept
Authors: Szarek Paweł , Sueda Yutaka , Tachibana Akitomo
Published: September 2008

The stress tensors are used widely for description of internal forces of matter. For some time it is also applied in quantum theory in studies of molecular properties in chemical systems. Electronic stress tensors measure effects caused by internal forces acting on electrons in molecules and particularly those between bonded atoms. Utilized here stress tensor originated bond orders express bond strengths in terms of these internal forces. The unique concept of energy density and electronic chemical potential based bond orders gives natural evaluation of interaction strength compared with classical definition, considering delocalized nature of electrons. In addition to other causes, the relation to electronic energy may be used to predict relative stabilities of geometrical isomers or even conformers.
Exploring remnants of invariants buried in a deep potential well in chemical reactions
Authors: Teramoto Hiroshi , Komatsuzaki Tamiki
Published: September 2008

We revisit the concept of “remnant of invariant manifolds” originally discussed by Shirts and Reinhardt in a two degrees of freedom Hénon–Heiles system [J. Chem. Phys. 77, 5204 (1982)]. This is regarded as the remnants of a destroyed invariant manifold that can dominate the transport in phase space even at high energy regions where most of all tori vanish. We present a novel technique to extract such remnants of invariants from a sea of chaos in highly nonlinear coupled molecular systems in terms of the canonical perturbation theory based on Lie transforms. As an illustrative example we demonstrate in HCN isomerization reaction that the conventional procedure based on a finite order truncation of the coordinate transformation prevent us from detecting remnants of invariants. However, our technique correctly captures the underlying remnants of invariants that shed light on the energetics of chemical reaction, that is, how the reactive mode acquires (releases) energy from (to) the other vibrational mode in order to overcome the potential barrier (to be trapped in the potential well). We also found the qualitative difference between the two potential wells, HCN and CNH, which coincides with the nearest neighbor level spacing distribution of the vibrational quantum states within the wells.
Growth and spectroscopic properties of Pr3+:NaLa(MoO4)2 crystal
Authors: Guo Weijie , Lin Yanfu , Gong Xinghong , Chen Yujin , Luo Zundu , Huang Yidong
Published: September 2008

A Pr3+:NaLa(MoO4)2 (NLM) single crystal has been grown by the Czochralski method. Thermal expansion coefficients of the crystal were measured. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were recorded at room temperature. Detailed polarized spectroscopic analysis on the crystal has been carried out. The relationship between the Judd–Ofelt intensity parameters and the visible emissions from the P30-multiplet of Pr3+ ions has been discussed. The results of spectroscopic analysis imply that Pr3+:NLM crystal is a potential gain medium for visible laser and self-stimulated Raman scattering laser application.
Shock wave propagation in neutral and ionized gases
Authors: Podder N. K. , Wilson IV R. B. , Bletzinger P.
Published: September 2008

Preliminary measurements on a recently built shock tube are presented. Planar shock waves are excited by the spark discharge of a capacitor, and launched into the neutral argon or nitrogen gas as well as its ionized glow discharge in the pressure region 1–17 Torr. For the shock wave propagation in the neutral argon at fixed capacitor charging voltage, the shock wave velocity is found to increase nonlinearly at the lower pressures, reach a maximum at an intermediate pressure, and then decrease almost linearly at the higher pressures, whereas the shock wave strength continues to increase at a nonlinear rate over the entire range of pressure. However, at fixed gas pressure the shock wave velocity increases almost monotonically as the capacitor charging voltage is increased. For the shock wave propagation in the ionized argon glow, the shock wave is found to be most influenced by the glow discharge plasma current. As the plasma current is increased, both the shock wave propagation velocity and the dispersion width are observed to increase nonlinearly.
Hollow cathode conditioning and discharge initiation
Authors: Rubin Binyamin , Williams John D.
Published: September 2008

In the framework of developing a fast-starting hollow cathode, one must understand how a cathode is conditioned for operation. The desorption of known contaminates as a function of heater power was measured to quantify cathode conditioning characteristics. In addition to conditioning, a study of hollow cathode emission characteristics under vacuum conditions was performed. Results of these two studies are described herein along with measurements of the temperature of the cathode as a function of time and heater power. The data are used to validate a transient surface diffusion model that describes the migration and surface coverage fraction of low-work-function material from the interior of the hollow cathode to the orifice barrel and to the exterior surface of the orifice plate of the cathode. A sufficiency condition is presented for our cathode geometry of vacuum emission current level and the ability to start a hollow cathode discharge once gas flow is initiated.
Taylor dispersion in polymerase chain reaction in a microchannel
Authors: Lee Jinkee , Kulla Elejdis , Chauhan Anuj , Tripathi Anubhav
Published: September 2008

Polymerase chain reaction (PCR) is commonly used for a wide range of DNA applications such as disease detection, genetic fingerprinting, and paternity testing. The importance of PCR has led to an increased interest in performing PCR in a microfluidic platform with a high throughput while using very small DNA quantities. In this paper we solve convection-diffusion equations for the DNA and deoxynucleoside triphosphate (dNTP) under conditions suitable for PCR operation in a microchip. These include pressure driven flow accompanied by temporal temperature changes that lead to an amplification reaction, which is modeled as a first order reaction. The convection-diffusion-reaction equations are solved by using the method of multiple time scales to yield average equations that can be solved to obtain the long time evolution of the concentration profiles. The results obtained by solving the averaged equations agree well with full numerical solutions. The averaged equations are also solved to simulate the PCR to illustrate some interesting aspects of this operation in a microfluidic device. It is shown that insufficient nucleotide concentrations can lead to complete depletion of NTP at certain axial locations, which leads to termination of DNA amplification at these locations, resulting in formation of a plateau in DNA concentration.
A better nondimensionalization scheme for slender laminar flows: The Laplacian operator scaling method
Authors: Weislogel M. M. , Chen Y. , Bolleddula D.
Published: September 2008

A scaling of the two-dimensional Laplacian operator is demonstrated for certain solutions (at least) to Poisson’s equation. It succeeds by treating the operator as a single geometric scale entity. The belated and rather subtle method provides an efficient assessment of the geometrical dependence of the problem and is preferred when practicable to the hydraulic diameter or term-by-term scaling for slender fully developed laminar flows. The improved accuracy further reduces the reliance of problems on widely varying numerical data or cumbersome theoretical forms and improves the prospects of exact or approximate theoretical analysis. Simple example problems are briefly described that demonstrate the application and potential of the method.
Polarization of defect related optical transitions in chalcopyrites
Authors: Hönes Katja , Eickenberg Michael , Siebentritt Susanne , Persson Clas
Published: September 2008

We investigate the symmetry of shallow acceptors in Cu chalcopyrites by polarization dependent photoluminescence measurements and density functional calculations. We determine the influence of the band symmetry versus the site symmetry. The polarization of the emitted or absorbed light is parallel to the c-axis in the case of CuGaSe2 and perpendicular to the c-axis in the case of CuInSe2. The symmetry of the defects depends in each case on the symmetry of the topmost band. Neither does the site symmetry affect the defect symmetry nor do the defects change the symmetry of the band.
Marked improvement in electroluminescence characteristics of organic light-emitting diodes using an ultrathin hole-injection layer of molybdenum oxide
Authors: Matsushima Toshinori , Jin Guang-He , Murata Hideyuki
Published: September 2008

We show that the performance of organic light-emitting diodes (OLEDs) is markedly improved by optimizing the thickness of a hole-injection layer (HIL) of molybdenum oxide (MoO3) inserted between indium tin oxide and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD). From results of the electroluminescence (EL) characteristics of OLEDs with various thicknesses of a MoO3 HIL, we found that the OLED with a 0.75-nm-thick MoO3 HIL had the lowest driving voltage and the highest power conversion efficiency among the OLEDs. Moreover, the operational lifetime of the OLED was improved by about a factor of 6 by using the 0.75-nm-thick MoO3 HIL. These enhanced EL characteristics are attributable to the formation of an Ohmic contact at the interfaces composed of ITO/MoO3/α-NPD.
Realization of write-once-read-many-times memory devices based on poly(N-vinylcarbazole) by thermally annealing
Authors: Lin Jian , Ma Dongge
Published: September 2008

A nonvolatile write-once-read-many-time (WORM-time) memory device based on poly(N-vinylcarbazole) (PVK) films was realized by thermally annealing. The device can be fabricated using a simple spin coat method. It was found that the control of PVK film surface morphology by thermally annealing plays an important role in achieving the WORM memory properties. The memory device showed an ON/OFF current ratio as high as 104 and the retention time was over 2000 s without degradation. The formation and damage of the interface dipole at different electric fields have been attributed to the switching transition processes, leading to the transition from an Ohmic current of ON state to a tunneling injection limited current of OFF state. The achievement of easily fabricating WORM memory device based on soluble PVK film opens up an application field for polymer materials in organic electronics.
Exciton transfer in quantum dot arrays: Comparison of eigenbasis and site basis representations
Authors: Kubota Yoji , Nobusada Katsuyuki
Published: September 2008

We discuss differences between eigenbasis and site basis representations for models of exciton transfers in an array of quantum dots. The exciton relaxation processes are well described by the master equation in the eigenbasis representation. The site basis evolution equation up to the second order of the interdot interaction is straightforwardly derived from the eigenbasis equation by using perturbation theory when the interaction is sufficiently small compared to the energy difference between the exciton states in each quantum dot. Although the higher order site basis equations can be derived similarly, the resultant equations are too complicated to use in the actual calculations. The master equation in the eigenbasis representation has several advantages over the site basis one: (i) the system described in terms of the eigenbasis representation can evolve into thermal equilibrium because the equation satisfies the detailed balance, (ii) the site basis equation does not reasonably describe the exciton state trapped in a local energy minimum at very low temperature, and (iii) it is computationally less demanding to carry out the eigenbasis evolution equation.
Simulation of nanosecond pulsed laser ablation of copper samples: A focus on laser induced plasma radiation
Authors: Aghaei M. , Mehrabian S. , Tavassoli S. H.
Published: September 2008

A thermal model for nanosecond pulsed laser ablation of Cu in one dimension and in ambient gas, He at 1 atm, is proposed in which equations concerning heat conduction in the target and gas dynamics in the plume are solved. These equations are coupled to each other through the energy and mass balances at interface between the target and the vapor and also Knudsen layer conditions. By assumption of local thermal equilibrium, Saha–Eggert equations are used to investigate plasma formation. The shielding effect of the plasma, due to photoionization and inverse bremsstrahlung processes, is considered. Bremsstrahlung and blackbody radiation and spectral emissions of the plasma are also investigated. Spatial and temporal distribution of the target temperature, number densities of Cu and He, pressure and temperature of the plume, bremsstrahlung and blackbody radiation, and also spectral emissions of Cu at three wavelengths (510, 516, and 521 nm) are obtained. Results show that the spectral power of Cu lines has the same pattern as CuI relative intensities from National Institute of Standard and Technology. Investigation of spatially integrated bremsstrahlung and blackbody radiation, and also Cu spectral emissions indicates that although in early times the bremsstrahlung radiation dominates the two other radiations, the Copper spectral emission is the dominant radiation in later times. It should be mentioned that the blackbody radiation has the least values in both time intervals. The results can be used for prediction of the optimum time and position of the spectral line emission, which is applicable in some time resolved spectroscopic techniques such as laser induced breakdown spectroscopy. Furthermore, the results suggest that for distinguishing between the spectral emission and the bremsstrahlung radiation, a spatially resolved spectroscopy can be used instead of the time resolved one.
The α−γ−ε triple point of iron investigated by high pressure–high temperature neutron scattering
Authors: Klotz S. , Le Godec Y. , Strässle Th. , Stuhr U.
Published: September 2008

We present high pressure–high temperature diffraction data in the 0–10 GPa and 300–1000 K range of all three main iron phases. The refinements of the diffraction patterns give molar volumes to high precision and show that the α−γ−ε triple point is located at 8.2±0.1 GPa and 678 K. These values are significantly lower than currently admitted (10.4 GPa/740 K), but are consistent with reported in situ x-ray diffraction data obtained in multianvil presses. These measurements have been made possible by the use of a high P/T cell which uses metallic toroidal gaskets and which suffers from less absorption, gives clean diffraction patterns, and shows better pressure performance than other setups.
Modulation instability of ion thermal waves in a pair-ion plasma containing charged dust impurities
Authors: Sabry R.
Published: September 2008

Modulation instability of ion thermal waves (ITWs) is investigated in a plasma composed of positive and negative ions as well as a fraction of stationary charged (positive or negative) dust impurities. For this purpose, a linear dispersion relation and a nonlinear Schrödinger equation are derived. The latter admits localized envelope solitary wave solutions of bright (pulses) and dark (holes, voids) type. The envelope soliton depends on the intrinsic plasma parameters. It is found that modulation instability of ITWs is significantly affected by the presence of positively/negatively charged dust grains. The findings of this investigation should be useful in understanding the stable electrostatic wave packet acceleration mechanisms in pair-ion plasma, and also enhances our knowledge on the occurrence of instability associated to the existence of charged dust impurities in pair-ion plasmas. Our results should be of relevance for laboratory plasmas.
Formation of single pinched plasma point in the cathode plasma jet of a multipicosecond laser-triggered vacuum discharge
Authors: Moorti A. , Naik P. A. , Gupta P. D. , Bhat R. K.
Published: September 2008

Characteristics of cathode plasma jet pinching and x-ray emission from a multipicosecond laser-triggered vacuum discharge are presented. Discharge was created in between a planar Al cathode and a conical point-tip Ti anode (separation: 2–15 mm, circuit inductance of ∼0.53 μH, peak discharge current of ∼3 kA, and rise time of ∼400 ns). For anode-cathode separation of ∼13.5 mm, only a single pinched plasma point was formed in the cathode plasma jet at a distance of ∼9.5 mm from the cathode. Quantitative analysis of the x-ray signals recorded using a pin diode with different filters and viewing different regions of the discharge, shows soft (∼keV photon energy) x-ray emission from the plasma point with a flux of ∼(3–5)×1010 photons/sr, and multi-keV x-ray emission from the Ti anode with Kα (∼4.51 keV) photon flux of ∼1010 photons/sr.
Atomic force microscope local oxidation nanolithography of graphene
Authors: Weng Lishan , Zhang Liyuan , Chen Yong P. , Rokhinson L. P.
Published: September 2008

We demonstrate the local oxidation nanopatterning of graphene films by an atomic force microscope. The technique provides a method to form insulating trenches in graphene flakes and to fabricate nanodevices with sub-nanometer precision. We demonstrate fabrication of a 25-nm-wide nanoribbon and submicron size nanoring from a graphene flake. We also found that we can write either trenches or bumps on the graphene surface depending on the lithography conditions. We attribute the bumps to partial oxidation of the surface and incorporation of oxygen into the graphene lattice.
Room temperature midinfrared electroluminescence from InSb/InAs quantum dot light emitting diodes
Authors: Carrington P. J. , Solov'ev V. A. , Zhuang Q. , Krier A. , Ivanov S. V.
Published: September 2008

Self-assembled InSb submonolayer quantum dots (QDs) in an InAs matrix have been grown by molecular beam epitaxy using Sb2 and As2 fluxes. The structures exhibit bright midinfrared photoluminescence up to room temperature. Intense room temperature electroluminescence with a peak at wavelength near 3.8 μm was observed from p-i-n light emitting diode structures containing ten InSb submonolayer QD sheets inserted within the InAs active region.
Ultrathin epitaxially grown bismuth (111) membranes
Authors: Payer T. , Rajković I. , Ligges M. , von der Linde D. , Horn-von Hoegen M. , Meyer zu Heringdorf F.-J.
Published: September 2008

An ex situ cleaning and etching technique was applied to NaCl single crystals to prepare atomically flat and clean NaCl surfaces. These were used as substrates for molecular beam epitaxial growth of ultrathin continuous Bi(111) films. The high film quality—as studied with low energy electron diffraction, atomic force microscopy, and transmission electron diffraction—is attributed to the commensurate 10:7 ratio of the lattice constants. Dissolving the NaCl substrates in water allows the fabrication of freestanding 20 nm thin Bi(111) membranes of centimeter size.
Biomimetic hierarchical structure for self-cleaning
Authors: Bhushan Bharat , Koch Kerstin , Jung Yong Chae
Published: September 2008

Hierarchical roughness is beneficial for superhydrophobicity. Surfaces with microstructure, nanostructure, and hierarchical structure were fabricated by replication of micropattern and self- assembly of hydrophobic alkanes. The fabrication technique used is a low cost two step process, which provides flexibility in the fabrication of a variety of hierarchical structures. Fabricated structures and surface chemistry mimic the hierarchical surfaces of superhydrophobic and self-cleaning plant surfaces. The influence of structure on superhydrophobicity at different length scales is demonstrated by the investigation of static contact angle, hysteresis and tilt angles, and propensity of air pocket formation as well as adhesive forces.
Compact high power broadband Er3+−Yb3+-codoped superfluorescent fiber source
Authors: Song Feng , Cheng Zhenzhou , Zou Changguang , Han Lin , Yu Xiaochen , Zhang Jiaxiang , Jiang Xueping , Han Peize , Tian Jianguo
Published: September 2008

Compact high power broadband superfluorescent fiber source has been demonstrated using an ultrashort Er3+−Yb3+-codoped phosphate glass fiber. The fiber is 10.4-cm-long and at 1.68 W pump power, an output power of 16.85 mW, a mean wavelength of 1540.9 nm, a bandwidth of 18.4 nm, and a slope efficiency of 18.6% have been obtained. The dependence of output power, mean wavelength, and bandwidth stability on pump power and fiber length are also studied, and there is an excellent agreement between the theoretical results and experimental data.
Multimode analysis of bubble growth in saturated film boiling
Authors: Tomar G. , Biswas G. , Sharma A. , Welch S. W. J.
Published: September 2008

The bubble formation sites in film boiling are the nodes of the instability occurring at the liquid-vapor interface. We perform a linear stability analysis with a time dependent base state, accounting for the growth of the film due to evaporation, in order to identify the most dominant wavelength. Choosing a domain size of five times the wavelength predicted by Berenson [ASME J. Heat Transfer 83, 351 (1961)] and an initial liquid-vapor interface profile having a spectrum of wave numbers, we perform numerical simulations to address the effects of decay and growth of the wave numbers on bubble spacing. Numerical simulations have been performed using a coupled level set and volume of fluid algorithm.
Exciton dissociation in tris(2-phenylpyridine) iridium (III) probed by electric field-assisted time-resolved photoluminescence
Authors: Mezyk J. , Meinardi F. , Tubino R. , Cocchi M.
Published: September 2008

We have investigated the mechanism of exciton dissociation in organometallic phosphorescent emitters by measuring the electric field-dependent time-resolved photoluminescence for thin vacuum-evaporated films of a model compound—tris(2-phenylpyridine) iridium (III) [Ir(ppy)3]. We have shown that the dissociation occurs from higher lying spin-mixed states before their relaxation to the lowest emissive levels, the lifetime of the latter not being significantly affected by external electric field. Knowledge about the mechanism of exciton dissociation in this class of materials is relevant for theoretical simulations of exciton kinetics in phosphorescent diodes as well as for optimization of the performances of these devices.
Low frequency electrostatic and electromagnetic modes of ultracold magnetized nonuniform dense plasmas
Authors: Saleem H. , Ahmad Ali , Khan S. A.
Published: September 2008

A coupled linear dispersion relation for the basic electrostatic and electromagnetic waves in the ultracold nonuniform magnetized dense plasmas has been obtained which interestingly is analogous to the classical case. The scales of macroscopic phenomena and the interparticle quantum interactions are discussed. It is important to point out that hydrodynamic models cannot take into account strong quantum effects and they are not applicable to very dense plasmas. The analysis is presented with applications to dense plasmas which are relevant to both laboratory and astrophysical environments.
Atomic scale analysis of the effect of the SiO2 passivation treatment on InAs/GaSb superlattice mesa sidewall
Authors: Herrera M. , Chi M. , Bonds M. , Browning N. D. , Woolman Joseph N. , Kvaas Robert E. , Harris Sean F. , Rhiger David R. , Hill Cory J.
Published: September 2008

We have analyzed by electron microscopy techniques the effect of the deposition of a SiO2 passivation layer on an InAs/GaSb type-II superlattice (SL) mesa with applications as a photodetector. Our images reveal good conformal coverage by the SiO2 upon an undulating edge of the SL mesa. However, we have observed scarce As clusters at the interface between the SL mesa and the passivation layer and some degree of oxidation of the mesa sidewall. The strong reduction in surface leakage currents demonstrates that the observed imperfections do not have a substantial detrimental effect on the passivation capabilities of the SiO2 layer.
Formation of extremely high current density LaB6 field emission arrays via e-beam deposition
Authors: Qi K. C. , Lin Z. L. , Chen W. B. , Cao G. C. , Cheng J. B. , Sun X. W.
Published: September 2008

In this paper, we report a Spindt-type field emission array (FEA) with LaB6 as the emitting material. The LaB6 emitters were deposited by e-beam evaporation with low oxide content. As LaB6 in its vapor form is active and absorbs large quantity of residual gases, which oxidizes the LaB6 films, a special e-beam configuration was designed to ensure high evaporation rate which is essential for depositing pure phase LaB6. FEAs with LaB6 emitter tips exhibited an average emission current as high as about 0.23 μA/tip suggesting that LaB6 emitters are promising candidates for high current density vacuum electronic devices.
Bias-stress-induced stretched-exponential time dependence of threshold voltage shift in InGaZnO thin film transistors
Authors: Lee Jeong-Min , Cho In-Tak , Lee Jong-Ho , Kwon Hyuck-In
Published: September 2008

The experimental and modeling study of bias-stress-induced threshold voltage instabilities in amorphous indium-gallium-zinc oxide thin film transistors is reported. Positive stress results in a positive shift in the threshold voltage, while the transfer curve hardly moves when negative stress is induced. The time evolution of threshold voltage is described by the stretched-exponential equation, and the shift is attributed to the electron injection from the channel into interface/dielectric traps. The stress amplitudes and stress temperatures are considered as important factors in threshold voltage instabilities, and the stretched-exponential equation is well fitted in various bias temperature stress conditions.
Electric control of spatial beam position based on the Goos–Hänchen effect
Authors: Wang Yi , Cao Zhuangqi , Li Honggen , Hao Jun , Yu Tianyi , Shen Qishun
Published: September 2008

A structure of symmetrical metal-cladding waveguide, which contains optically nonlinear material in the guiding layer, is proposed to control the lateral shift of the reflected beam via an external electric field. Owing to the high sensitivity of ultrahigh-order modes, any minute index change of the waveguide will lead to a dramatic variation of the resonance condition, which gives rise to a change of the lateral beam displacement. Experimental result shows that the electric control of the lateral beam shift is realized in a range of 720μm.
Inhomogeneous origin of the interface roughness broadening of intersubband transitions
Authors: Khurgin Jacob B.
Published: September 2008

The impact of the interface roughness on intersubband transitions (ISTs) in quantum wells is analyzed as an inhomogeneous broadening due to localization rather than a traditional scattering process. The results offer simple explanation for the temperature dependent spectra of gain and absorption in quantum cascade lasers and also for the strong IST polariton phenomena.