bluuebunny/crossref_metadata_2025 huggingface dataset:
Cumulative reaction probabilities and transition state properties: A study of the F+H2 reaction and its deuterated isotopic variants
Authors: Aoiz F. J. , Herrero V. J. , Rábanos V. Sáez
Published: July 2008

A comparative quantum mechanical (QM) and quasiclassical trajectory (QCT) study of the cumulative reaction probabilities (CRPs) is presented in this work for the F+H2 reaction and its isotopic variants for low values of the total angular momentum J. The agreement between the two sets of calculations is very good with the exception of some features whose origin is genuinely QM. The agreement also extends to the CRP resolved in the helicity quantum number k. The most remarkable feature is the steplike structure, which becomes clearly distinct when the CRPs are resolved in odd and even rotational states j. The analysis of these steps shows that each successive increment is due to the opening of the consecutive rovibrational states of the H2 or D2 molecule, which, in this case, nearly coincide with those of the transition state. Moreover, the height of each step reflects the number of helicity states compatible with a given J and j values, thus indicating that the various helicity states for a specific j have basically the same contribution to the CRPs at a given total energy. As a consequence, the dependence with k of the reactivity is practically negligible, suggesting very small steric restrictions for any possible orientation of the reactants. This behavior is in marked contrast to that found in the D+H2 reaction, wherein a strong k dependence was found in the threshold and magnitude of the CRP. The advantages of a combined QCT and QM approaches to the study of CRPs are emphasized in this work.
Thermal stability of electrical and structural properties of GaAs-based metal-oxide-semiconductor capacitors with an amorphous LaAlO3 gate oxide
Authors: Koveshnikov S. , Adamo C. , Tokranov V. , Yakimov M. , Kambhampati R. , Warusawithana M. , Schlom D. G. , Tsai W. , Oktyabrsky S.
Published: July 2008

We report on thermal stability of the electrical and structural properties of metal-oxide-semiconductor capacitors with amorphous LaAlO3 high dielectric constant (high k) oxide on GaAs epitaxial layers with and without an interface amorphous silicon (a-Si) passivation layer to prevent Fermi level pinning at the III-V/high-k interface. The electrical properties of a-Si passivated GaAs improved with annealing temperature, demonstrating reduced equivalent oxide thickness, small (∼50mV) hysteresis of capacitance-voltage characteristics, and low interface state density (⩽2×1011eV−1cm−2). Transmission electron microscopy with x-ray microanalysis revealed densification of the amorphous LaAlO3 and its reaction with an oxidized a-Si layer.
Morphologies and nonlinear scaling of laser damage on glass surfaces by tightly focused femtosecond pulses
Authors: Herbstman Jeffrey F. , Hunt Alan J. , Yalisove Steven M.
Published: July 2008

We examine the relationship between pulse energy and the morphology of damage by a femtosecond pulsed laser, tightly focused onto the back surface of glass. For fluences up to three times that of threshold, an unexpected discontinuity in the scaling of damage size is caused by ejection of rings of material surrounding central damage that appear above a sharp threshold fluence. A mechanism for the production of these structures via thermal expansion and shockwave generation is proposed.
Rapid thermal annealing of FePt nanoparticles
Authors: Yano Kazuaki , Nandwana Vikas , Poudyal Narayan , Rong Chuan-Bing , Liu J. Ping
Published: July 2008

We report a systematic study on rapid thermal annealing (RTA) of FePt nanoparticles. FePt particles with an average size of 8nm were synthesized by a chemical solution method, and then annealed using RTA and conventional furnace annealing (FA). It was observed that FePt nanoparticles can be transformed from disordered A1 phase to ordered L10 phase at 650°C for 10s using RTA, which is much shorter than the time needed for FA. The transmission electron microscopy and x-ray diffraction studies have revealed that the particle agglomeration and grain growth in the RTA treated samples are much less than in the FA treated samples. A linear correlation between the coercivity and the square root of the treatment time t was observed in the RTA treated samples, which implies that the phase transition is related to atomic diffusion of Fe atoms from Fe-rich shells into the Pt-rich cores.
Role of the buffer layer thickness on the formation of basal plane stacking faults in a-plane GaN epitaxy on r-sapphire
Authors: Wu Z. H. , Fischer A. M. , Ponce F. A. , Yokogawa T. , Yoshida S. , Kato R.
Published: July 2008

The thickness of low temperature AlGaN buffer layers grown on r-sapphire substrates has been found to directly affect the crystalline structure of the buffer layer as well as the structural and optical properties of subsequently grown a-plane GaN films. A buffer layer with a thickness of 30nm results in randomly distributed fine domains without extended defects. Increasing the thickness to 90nm leads to a uniform and largely coalesced crystalline structure, with well-defined stacking faults. GaN films grown on the thinner buffer layer contain a lower density of larger stacking faults, and exhibit brighter stacking-fault luminescence as compared to films grown on thicker buffer layers. Our studies indicate that the optimum buffer layer thickness for growth of a-plane GaN is about 30nm.
High-pressure in situ density measurement of low-Z noncrystalline materials with a diamond-anvil cell by an x-ray absorption method
Authors: Sato Tomoko , Funamori Nobumasa
Published: July 2008

We have developed techniques for high-pressure in situ density measurement of low-Z noncrystalline materials with a diamond-anvil cell (DAC) by an x-ray absorption method. In DAC experiments, accurate determination of the sample thickness is difficult. Moreover, since the sample in a DAC is thin and the interaction between low-Z materials and x rays is small, not the sample but the anvils absorb most of x rays. This makes the measurement quite difficult. We have overcome such difficulties and have successfully measured the density of SiO2 glass, a low-Z noncrystalline material, as a function of pressure up to 35GPa.
A high-energy inelastic neutron scattering investigation of the Gd–Co exchange interactions in GdCo4B: Comparison with density-functional calculations
Authors: Isnard Olivier , Kuz’min Michael D. , Richter Manuel , Loewenhaupt Michael , Bewley Robert
Published: July 2008

Inelastic neutron scattering is used to quantify the Gd–Co exchange interaction in GdCo4B. A significant reduction is observed in comparison with the GdCo5 compound. A mean value of 130T is obtained for the exchange field on the two Gd sites in GdCo4B. The experimental results are compared with density-functional calculations. The local atomic magnetic moments calculated using the LSDA+U approximation are reported for each atomic site of the GdCo4B crystal structure. These calculations demonstrate that the two nonequivalent Gd crystal sites experience a significantly different exchange interaction, a difference that is discussed in the light of the local atomic environment. The observed reduction of the exchange field occurring upon substituting B for Co in GdCo5 is mainly caused by the decrease of the Co magnetic moment, whereas the Gd–Co coupling constant is found to be almost the same in both GdCo5 and GdCo4B.
Continuous wave operation of diode lasers at 3.36μm at 12°C
Authors: Shterengas L. , Belenky G. , Hosoda T. , Kipshidze G. , Suchalkin S.
Published: July 2008

GaSb-based type-I quantum-well diode lasers emitting at 3.36μm at 12°C with 15mW of continuous wave output power are reported. Devices with two or four InGaAsSb compressively strained quantum wells and AlInGaAsSb quinternary barriers were fabricated and characterized. It was shown that increase in the quantum-well number led to improved laser differential gain and reduced threshold current.
An efficient ring polymer contraction scheme for imaginary time path integral simulations
Authors: Markland Thomas E. , Manolopoulos David E.
Published: July 2008

A quantum simulation of an imaginary time path integral typically requires around n times more computational effort than the corresponding classical simulation, where n is the number of ring polymer beads (or imaginary time slices) used in the calculation. However, this estimate neglects the fact that the potential energies of many systems can be decomposed into a sum of rapidly varying short-range and slowly varying long-range contributions. For such systems, the computational effort of the path integral simulation can be reduced considerably by evaluating the long-range forces on a contracted ring polymer with fewer beads than are needed to evaluate the short-range forces. This idea is developed and then illustrated with an application to a flexible model of liquid water in which the intramolecular forces are evaluated with 32 beads, the oxygen-oxygen Lennard-Jones forces with seven, and the intermolecular electrostatic forces with just five. The resulting static and dynamic properties are within a few percent of those of a full 32-bead calculation, and yet they are obtained with a computational effort less than six times (rather than 32 times) that of a classical simulation. We hope that this development will encourage future studies of quantum mechanical fluctuations in liquid water and aqueous solutions and in many other systems with similar interaction potentials.
Optimizing the sampling and staging for simulations of rare events via forward flux sampling schemes
Authors: Borrero Ernesto E. , Escobedo Fernando A.
Published: July 2008

In this work, we present an adaptive algorithm to optimize the phase space sampling for simulations of rare events in complex systems via forward flux sampling (FFS) schemes. In FFS, interfaces are used to partition the phase space along an order parameter λ connecting the initial and final regions of interest. Since the kinetic “bottleneck” regions along the order parameter are not usually known beforehand, an adaptive procedure is used that first finds these regions by estimating the rate constants associated with reaching subsequent interfaces; thereafter, the FFS simulation is reset to concentrate the sampling on those bottlenecks. The approach can optimize for either the number and position of the interfaces (i.e., optimized λ phase staging) or the number M of fired trial runs per interface (i.e., the {Mi} set) to minimize the statistical error in the rate constant estimation per simulation period. For example, the optimization of the λ staging leads to a net constant flux of partial trajectories between interfaces and hence a constant flux of connected paths throughout the region between the two end states. The method is demonstrated for several test systems, including the folding of a lattice protein. It is shown that the proposed approach leads to an optimized λ staging and {Mi} set which increase the computational efficiency of the sampling algorithm.
Measurement of nonequilibrium entropy from space-time thermodynamic integration
Authors: Athènes Manuel , Adjanor Gilles
Published: July 2008

The entropy of a system transiently driven out of equilibrium by a time-inhomogeneous stochastic dynamics is first expressed as a transient response function generalizing the nonlinear Kawasaki–Crooks response. This function is then reformulated into three statistical averages defined over ensembles of nonequilibrium trajectories. The first average corresponds to a space-time thermodynamic perturbation relation, while the two following ones correspond to space-time thermodynamic integration relations. Provided that trajectories are initiated starting from a distribution of states that is analytically known, the ensemble averages are computationally amenable to Markov chain Monte Carlo methods. The relevance of importance sampling in path ensembles is confirmed in practice by computing the nonequilibrium entropy of a driven toy system. We finally study a situation where the dynamics produces entropy. In this case, we observe that space-time thermodynamic integration still yields converged estimates, while space-time thermodynamic perturbation turns out to converge very slowly.
Local structure of liquid Ti: Ab initio molecular dynamics study
Authors: Lee Byeongchan , Lee Geun Woo
Published: July 2008

Local order of liquid Ti is studied by ab initio molecular dynamics to address the unique liquid structure factor in experiments reported recently. The present study reveals that the local order of liquid Ti is in the form of fragments of the distorted icosahedral short range order, where the distortion is induced by strong bond order effects. We show that the fragments in the short-bond rich region separated from the background liquid account for the pronounced feature in structure factor of liquid Ti.
Harnessing piecewise-linear systems to construct dynamic logic architecture
Authors: Peng Haipeng , Yang Yixian , Li Lixiang , Luo Hong
Published: July 2008

This paper explores piecewise-linear systems to construct dynamic logic architecture. We present three schemes to obtain various basic logic gates, adders, and memory by using piecewise-linear systems. These schemes can switch easily among different operational roles by changing parameters. The proposed schemes are computationally efficient and easy to use. It is convenient for us to study and analyze them with the theory of linear systems.
Characterization of carbon nitride deposition from CH4∕N2 glow discharge plasma beams using optical emission spectroscopy
Authors: Hu Wei , Tang Jun-Yi , Wu Jia-da , Sun Jian , Shen Yi-qun , Xu Xiao-feng , Xu Ning
Published: July 2008

The properties of plasmas in a CH4∕N2 dc abnormal glow discharge with the percentage of methane from 1% to 20% have been studied in order to understand the effect of precursor incorporation into the carbon nitride (CNx) films. The appearance of CN radicals as well as C2, CH, and NH has been revealed by optical emission spectroscopy (OES). The evolution of CN, N2, N2+, and C2 emission lines from mixed CH4∕N2 and pure N2 plasma on changing mixture ratio and polarity of discharge-field has been studied. The possible mechanisms behind their variations have been discussed. Besides, a CH4∕N2 ratio of 1∕50 and a top-needle anode is considered to be the best conditions for synthesis of β-C3N4, which has been confirmed in the as-deposited carbon nitride films with quite good crystalline features by XRD analyses.
Observer-based adaptive fuzzy synchronization for hyperchaotic systems
Authors: Xingyuan Wang , Juan Meng
Published: July 2008

In this paper, the synchronization problem of hyperchaotic systems is investigated. An adaptive fuzzy observer is proposed based on the Takagi–Sugeno fuzzy model. Theoretical analysis based on Lyapunov stability theory is provided to verify the feasibility of the proposed synchronization scheme. Numerical simulation of the hyperchaotic Lü system is given to demonstrate the application of the proposed scheme. The form of the proposed scheme is simple, and it is general and robust.
An ultrahigh stability, low-noise laser current driver with digital control
Authors: Erickson Christopher J. , Van Zijll Marshall , Doermann Greg , Durfee Dallin S.
Published: July 2008

We present a low-noise, high modulation-bandwidth design for a laser current driver with excellent long-term stability. The driver improves upon the commonly used Hall–Libbrecht design. The current driver can be operated remotely by way of a microprocessing unit, which controls the current set point digitally. This allows precise repeatability and improved accuracy and stability. It also allows the driver to be placed near the laser for reduced noise and for lower phase lag when using the modulation input. We present the theory of operation for our driver in detail, and give a thorough characterization of its stability, noise, set-point accuracy and repeatability, temperature dependence, transient response, and modulation bandwidth.
Essential self-adjointness of the graph-Laplacian
Authors: Jorgensen Palle E. T.
Published: July 2008

We study the operator theory associated with such infinite graphs G as occur in electrical networks, in fractals, in statistical mechanics, and even in internet search engines. Our emphasis is on the determination of spectral data for a natural Laplace operator associated with the graph in question. This operator Δ will depend not only on G but also on a prescribed positive real valued function c defined on the edges in G. In electrical network models, this function c will determine a conductance number for each edge. We show that the corresponding Laplace operator Δ is automatically essential self-adjoint. By this we mean that Δ is defined on the dense subspace D (of all the real valued functions on the set of vertices G0 with finite support) in the Hilbert space l2(G0). The conclusion is that the closure of the operator Δ is self-adjoint in l2(G0), and so, in particular, that it has a unique spectral resolution, determined by a projection valued measure on the Borel subsets of the infinite half-line. We prove that generically our graph Laplace operator Δ=Δc will have continuous spectrum. For a given infinite graph G with conductance function c, we set up a system of finite graphs with periodic boundary conditions such the finite spectra, for an ascending family of finite graphs, will have the Laplace operator for G as its limit.
The competition of double-, four-, and three-ring tubular B3n (n=8–32) nanoclusters
Authors: Tian Fu-Yang , Wang Yuan-Xu
Published: July 2008

The geometry and electronic properties of three-ring tubular B3n clusters (n=8–32) are studied systematically with the density functional theory. It is composed of three staggered rings with the diameter of the middle ring larger than those of the two outer rings. With the increase in boron atom numbers, the three-ring tubular clusters are energetically more stable than the double-ring and four-ring tubular clusters and the buckled sheet clusters with hexagon holes. The average binding energy tends to the finite value. The stability is further analyzed through the natural bond orbital population analysis. The highest occupied and lowest unoccupied energy gaps become small, which demonstrates a favorable metallic property.
Accurate ab initio density fitting for multiconfigurational self-consistent field methods
Authors: Aquilante Francesco , Pedersen Thomas Bondo , Lindh Roland , Roos Björn Olof , Sánchez de Merás Alfredo , Koch Henrik
Published: July 2008

Using Cholesky decomposition and density fitting to approximate the electron repulsion integrals, an implementation of the complete active space self-consistent field (CASSCF) method suitable for large-scale applications is presented. Sample calculations on benzene, diaquo-tetra-μ-acetato-dicopper(II), and diuraniumendofullerene demonstrate that the Cholesky and density fitting approximations allow larger basis sets and larger systems to be treated at the CASSCF level of theory with controllable accuracy. While strict error control is an inherent property of the Cholesky approximation, errors arising from the density fitting approach are managed by using a recently proposed class of auxiliary basis sets constructed from Cholesky decomposition of the atomic electron repulsion integrals.
The work function of submonolayer cesium-covered gold: A photoelectron spectroscopy study
Authors: LaRue J. L. , White J. D. , Nahler N. H. , Liu Z. , Sun Y. , Pianetta P. A. , Auerbach D. J. , Wodtke A. M.
Published: July 2008

Using visible and x-ray photoelectron spectroscopy, we measured the work function of a Au(111) surface at a well-defined submonolayer coverage of Cs. For a Cs coverage producing a photoemission maximum with a He–Ne laser, the work function is 1.61±0.08 eV, consistent with previous assumptions used to analyze vibrationally promoted electron emission. A discussion of possible Cs layer structures is also presented.
Response to “Comment on ‘Resonant dissociative electron transfer of the presolvated electron to CCl4 in liquid: Direct observation and lifetime of the CCl4∗− transition state’ [J. Chem. Phys. 129, 027101 (2008)]”
Authors: Wang C.-R. , Drew K. , Luo T. , Lu M.-J. , Lu Q.-B.
Published: July 2008

In our recent paper [J. Chem. Phys.128, 041102 (2008)], we reported a femtosecond time-resolved laser spectroscopic study of the electron transfer reaction of CCl4 in liquid ethanol. Our results provide direct evidence of the resonant dissociative electron transfer (RDET) of the presolvated electron to CCl4, and indicate that RDET can be an efficient process in an aqueous environment. In a recent Comment, the author argues that the relevance of diethanolamine (DEA) induced destruction of chlorofluorocarbons (CFCs) in the polar stratosphere as a possible pathway for chemical ozone destruction should not be a motivation for further studies of DEA on CFC molecules, as no correlation is observed between polar chemical ozone loss and cosmic ray activity. Here, we show that this claim is misleading: it is made by using inconclusive and ambiguous data while ignoring pronounced and well-documented data.
Thermodynamics of strongly coupled repulsive Yukawa particles in ambient neutralizing plasma: Thermodynamic instability and the possibility of observation in fine particle plasmas
Authors: Totsuji Hiroo
Published: July 2008

The thermodynamics is analyzed for a system composed of particles with hard cores, interacting via the repulsive Yukawa potential (Yukawa particulates), and neutralizing ambient (background) plasma. An approximate equation of state is given with proper account of the contribution of ambient plasma and it is shown that there exists a possibility for the total isothermal compressibility of Yukawa particulates and ambient plasma to diverge when the coupling between Yukawa particulates is sufficiently strong. In this case, the system undergoes a transition into separated phases with different densities and we have a critical point for this phase separation. Examples of approximate phase diagrams related to this transition are given. It is emphasized that the critical point can be in the solid phase and we have the possibility to observe a solid-solid phase separation. The applicability of these results to fine particle plasmas is investigated. It is shown that, though the values of the characteristic parameters are semiquantitative due to the effects not described by this model, these phenomena are expected to be observed in fine particle plasmas, when approximately isotropic bulk systems are realized with a very strong coupling between fine particles.
Driving force for Sn whisker growth in the system Cu–Sn
Authors: Sobiech M. , Welzel U. , Mittemeijer E. J. , Hügel W. , Seekamp A.
Published: July 2008

The evolution of residual stress gradients in Sn thin films on Cu substrates upon aging at ambient temperature has been investigated, for specimens which do exhibit and which do not exhibit Sn whisker growth, by performing x-ray diffraction stress measurements at constant penetration depths. Comparison of the measured near-surface stress-depth profiles for both types of specimens, as function of aging time at ambient temperature, showed that a significant negative stress gradient from the surface toward the Sn∕Cu interface is decisive for Sn whisker growth in the system Cu–Sn.
Low-voltage organic transistors based on solution processed semiconductors and self-assembled monolayer gate dielectrics
Authors: Wöbkenberg Paul H. , Ball James , Kooistra Floris B. , Hummelen Jan C. , de Leeuw Dago M. , Bradley Donal D. C. , Anthopoulos Thomas D.
Published: July 2008

Reduction in the operating voltage of organic transistors is of high importance for successful implementation in low-power electronic applications. Here we report on low-voltage n-channel transistors fabricated employing a combination of soluble organic semiconductors and a self-assembled gate dielectric. The high geometric capacitance of the nanodielectric allows transistor operation below 2V. Solution processing is enabled by analysis of the surface energy compatibility of the dielectric and semiconductor solutions. Electron mobilities in the range of 0.01–0.04cm2∕Vs and threshold voltages ⩽0.35V are demonstrated. The present work paves the way toward solution processable low-voltage/power, organic complementary circuits.
Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature
Authors: Kitano Haruhisa , Ohashi Takeyoshi , Maeda Atsutaka
Published: July 2008

We present a high-resolution microwave spectrometer to measure the frequency- dependent complex conductivity of a superconducting thin film near the critical temperature. The instrument is based on a broadband measurement of the complex reflection coefficient, S11, of a coaxial transmission line, which is terminated to a thin film sample with the electrodes in a Corbino disk shape. In the vicinity of the critical temperature, the standard calibration technique using three known standards fails to extract the strong frequency dependence of the complex conductivity induced by the superconducting fluctuations. This is because a small unexpected difference between the phase parts of S11 for a short and load standards gives rise to a large error in the detailed frequency dependence of the complex conductivity near the superconducting transition. We demonstrate that a new calibration procedure using the normal-state conductivity of a sample as a load standard resolves this difficulty. The high quality performance of this spectrometer, which covers the frequency range between 0.1 and 10GHz, the temperature range down to 10K, and the magnetic field range up to 1T, is illustrated by the experimental results on several thin films of both conventional and high temperature superconductors.
Two-color InGaAs∕GaAs quantum dot infrared photodetectors by selective area interdiffusion
Authors: Fu L. , Li Q. , Kuffner P. , Jolley G. , Gareso P. , Tan H. H. , Jagadish C.
Published: July 2008

We report the postgrowth fabrication of two-color InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs). By capping half of the as-grown QDIP structure with titanium dioxide (TiO2) and performing rapid thermal annealing under the optimized condition, a blueshifted photoluminescence from the uncapped region was obtained compared with the TiO2 covered region. The corresponding device spectral photoresponse from the two adjacent regions exhibited a shift of 0.8μm around the wavelength of 6μm. This is a result of the simultaneous promotion and suppression of thermal interdiffusion during rapid thermal annealing.
Asymmetric reflectivity from surfaces with distributed dipoles and IR experiments on poled polyvinylidene difluoride films
Authors: Chen Jun-Lang , Shieh Min-Yen , Yu Hsin Her , Liao Chungpin , Chang Hsien-Ming , Yang Bin-Huang , Zhao Zi-Peng
Published: July 2008

It is widely accepted that as a monochromatic unpolarized light beam impinges on a flat surface at an angle, the reflection occurs symmetrically with a calculable amount of power in accordance with the Fresnel equations. Furthermore, reversing the light path offers no difference owing to the inherent symmetry. However, this picture changes when the interface is a distributed double layer responsive to the incident light. Theoretical elaboration and then IR experiments on poled polyvinylidene difluoride films were conducted to verify the emergence of asymmetric reflections at varying incident angles, as well as the inverse dependence of reflectivity on the impinging light intensity.
Manipulating spins by cantilever synchronized frequency modulation: A variable resolution magnetic resonance force microscope
Authors: Fong K. C. , Banerjee P. , Obukhov Yu. , Pelekhov D. V. , Hammel P. C.
Published: July 2008

We report a new spin manipulation protocol for periodically reversing the sample magnetization for magnetic resonance force microscopy (MRFM). The protocol modulates the microwave excitation frequency synchronously with the position of the oscillating detection cantilever, thus allowing manipulation of the spin magnetization independent of both magnetic field gradient strength and cantilever response time. This allows continuous variation of the detected sample volume and is effective regardless of spin relaxation rate. This enhanced flexibility improves the utility of MRFM as a generally applicable imaging and characterization tool.
Stretchable and compressible thin films of stiff materials on compliant wavy substrates
Authors: Xiao J. , Carlson A. , Liu Z. J. , Huang Y. , Jiang H. , Rogers J. A.
Published: July 2008

This letter presents experimental, numerical, and analytical studies of Au thin films on elastomeric substrates of poly(dimethylsiloxane) that are designed with sinusoidal, “wavy” features of surface relief. Such systems can be useful as stretchable conductors in electronic or sensory devices. The maximum film strain is obtained in terms of film and substrate elastic moduli, film thickness, amplitude and wavelength of the wavy profile, and the applied strain. These analytical solutions agree well with both finite element analysis and experimentally measured changes in the sinusoidal profile under small, uniaxial strains. A simple expression for the system stretchability and compressibility is established.
Effects of reoxidation on band alignment in N-incorporated SiON films as a function of sequential thermal annealing in NO and NH3
Authors: Lee W. J. , Cho M.-H. , Chung K. B. , Lee Y. S. , Kim D. C. , Choi S. Y. , Chung U. I. , Moon J. T.
Published: July 2008

The effects of reoxidation on the band structure of N-incorporated SiON films were investigated as a function of thermal treatment in NO and NH3. Reoxidation-associated changes in band gap and valence band offset of the N-incorporated SiON films prepared by sequential thermal annealing in both NO and NH3 were less than those observed for the nitrided film prepared by thermal annealing in only NH3. The differences in band-alignment characteristics of the nitrided films that resulted from use of different nitridation methods were strongly related to the depth distribution of N and the chemical states of N bonded to Si.
A compact asymmetric chaotic optical cavity with long optical path lengths
Authors: Qu Dongxia , Liu Zhijun , Gmachl Claire
Published: July 2008

We demonstrate an asymmetric multipass cavity with meter-scale optical path lengths in a volume of 68cm3 and diameter of 5.24cm. The cavity is machined from copper and coated with gold. For the characterization of the optical path length in the cavity, we perform a pulse-delay experiment by measuring the time delay between a laser pulse coupled into and out of the cavity. A midinfrared quantum cascade laser is employed as the source. By rotating the cavity, a variety of reentrant patterns and path lengths ranging from 2.0to6.0m can be obtained with straightforward optical alignment.
Twenty times lower ignition threshold for laser driven fusion using collective effects and the inhibition factor
Authors: Hora H. , Malekynia B. , Ghoranneviss M. , Miley G. H. , He X.
Published: July 2008

Hydrodynamic analysis for ignition of inertial fusion by Chu [Phys. Fluids 15, 413 (1972)] arrived at extremely high thresholds of a minimum energy flux density E* at 4×108J∕cm2 which could be provided, e.g., by spark ignition. In view of alternative schemes of fast ignition, a re-evaluation of the early analysis including later discovered collective stopping power and the inhibition factor results in a 20 times lowering of the threshold for E*.
Influence of hydrogen dispersive diffusion in nitrided gate oxide on negative bias temperature instability
Authors: Yang J. B. , Chen T. P. , Tan S. S. , Ng C. M. , Chan L.
Published: July 2008

Influence of hydrogen dispersive diffusion in nitrided gate oxide on negative bias temperature instability (NBTI) is examined by using the analytical reaction-dispersive-diffusion (RDD) model, which was developed within a framework of the classical reaction-diffusion model by incorporating the dispersive transport nature of the diffusion. The NBTI experiments verify that by taking the dispersive transport into account, the RDD model well describes the NBTI degradation including its dependence on the stress time, stress temperature and interfacial nitrogen concentration and its power-law behaviors as well. This in turn gives an insight into the roles of the hydrogen dispersive diffusion in the NBTI process.
Diffusion based degradation mechanisms in giant magnetoresistive spin valves
Authors: Hawraneck Matthias , Zimmer Jürgen , Raberg Wolfgang , Prügl Klemens , Schmitt Stephan , Bever Thomas , Flege Stefan , Alff Lambert
Published: July 2008

Spin valve systems based on the giant magnetoresistive effect as used, for example, in hard disks and automotive applications consist of several functional metallic thin film layers. We have identified by secondary ion mass spectrometry two main degradation mechanisms: one is related to oxygen diffusion through a protective cap layer and the other one is interdiffusion directly at the functional layers of the giant magnetoresistive stack. By choosing a suitable material as cap layer (TaN), the oxidation effect can be suppressed.
Characterization of intrinsic donor defects in ZnO ceramics by dielectric spectroscopy
Authors: Cheng Pengfei , Li Shengtao , Zhang Le , Li Jianying
Published: July 2008

With the existence of depletion layer, the intrinsic donor defect structure of ZnO ceramics has been investigated by broadband dielectric spectroscopy in a wide temperature range. Two loss peaks originating from electronic relaxation of oxygen vacancy and zinc interstitial, respectively, are observed in ZnO ceramics simultaneously, implying the coexistence of these two intrinsic defects. The corresponding activation energy for electronic relaxation of zinc interstitial and oxygen vacancy are 0.26 and 0.36eV, respectively, which is consistent with other reports
Lead zirconate titanate thick film with enhanced electrical properties for high frequency transducer applications
Authors: Zhu B. P. , Wu D. W. , Zhou Q. F. , Shi J. , Shung K. K.
Published: July 2008

Piezoelectric Pb(Zr0.52Ti0.48)O3 thick film with the thickness around 10μm has been deposited on the (111) Pt∕Ti∕SiO2∕Si substrate using a ceramic powder/sol-gel solution modified composite method. X-ray diffraction analysis and scanning electron microscopy revealed that the film was in the well-crystallized perovskite phase and crack-free. At 1kHz, the dielectric constant and the loss were 1925 and 0.015, respectively. The remnant polarization was 42.0μC∕cm2 at room temperature. A high frequency single element acoustic transducer fabricated with this film showed a bandwidth at −6dB of 50% at 156MHz.
Ultrasmall radio frequency driven microhollow cathode discharge
Authors: Mahony C. M. O. , Gans T. , Graham W. G. , Maguire P. D. , Petrović Z. Lj.
Published: July 2008

We have operated 25-100μm diameter radio frequency microhollow cathode discharges stably, for many hours, in neon and in argon. Electrical and spectroscopic measurements were used to explore three possible electron heating modes and obtain detail regarding the electron energy distribution. Analysis points to the possibility of pendular electron heating at low voltages.
Study of MgB2∕I∕Pb tunnel junctions on MgO (211) substrates
Authors: Chen Ke , Cui Y. , Li Qi , Zhuang C. G. , Liu Zi-Kui , Xi X. X.
Published: July 2008

Mg B 2 ∕ insulator ∕ Pb tunnel junctions have been made using MgB2 films on MgO (211) substrates. The c axis of the bottom electrode MgB2 film, parallel to the MgO [111] direction, was tilted with respect to the film normal, exposing the ab planes for electron tunneling. Tunneling contributions from both the σ and π bands were present in the tunneling spectra. The temperature and the magnetic field dependences of both gaps were studied, shedding light on the two-gap properties of MgB2.
Enhancement of light reflectance and thermal stability in Ag–Cu alloy contacts on p-type GaN
Authors: Son Jun Ho , Jung Gwan Ho , Lee Jong-Lam
Published: July 2008

The mechanism for thermally stable Ag–Cu alloy Ohmic contact on p-type GaN was investigated. Ag–Cu contact showed lower contact resistivity as low as 8.6×10−6Ωcm2, higher reflectance of 84% at 460nm, and better thermal stability than Ag contact after annealing in air ambient. The formation of Ag–Ga solid solution lowered the contact resistivity. Additionally the formation of Cu oxide suppresses the Ag oxidation and increases the work function of the Ag–Cu contact via decreasing the Schottky barrier height for hole injection. Precipitation of Cu oxide at grain boundaries suppresses the Ag agglomeration, leading to enhanced light reflectance as well as thermal stability.
Polymer Schottky contact on O-polar ZnO with silane coupling agent as surface protective layer
Authors: Gunji R. Y. , Nakano M. , Tsukazaki A. , Ohtomo A. , Fukumura T. , Kawasaki M.
Published: July 2008

We report on a Schottky junction fabricated on O-polar ZnO surfaces with a silane-coupling agent as a protective layer, and a conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a deep work function metal electrode, simply by using wet processes. The silane-coupling agent prevented the O-polar ZnO surface from an etching reaction in contact with the acidic PEDOT:PSS solution, resulting in a good rectification with a current rectification ratio of 107 at ±1V. The junction characteristics were systematically controlled in accord with the electron density in ZnO ranging from 8×1014to4×1016cm−3.
Spontaneous generation and propagation of transverse coaxial traveling waves in multiwalled carbon nanotubes
Authors: Liu P. , Gao H. J. , Zhang Y. W.
Published: July 2008

Spontaneous generation and propagation of a class of transverse and coaxial traveling waves in multiwalled carbon nanotubes annealed at high temperatures were observed by molecular dynamics simulation. It was found that these traveling waves are generated by end resonance. The observed wave velocity is consistent with that predicted by a continuum multiwalled shell model. The observed phenomenon may be used to measure the mechanical properties of carbon nanotubes or as a vibration generator in nanomechanical devices.
Voltage tunable two-color InAs∕GaAs quantum dot infrared photodetector
Authors: Ma W. Q. , Yang X. J. , Chong M. , Yang T. , Chen L. H. , Shao J. , Lü X. , Lu W. , Song C. Y. , Liu H. C.
Published: July 2008

We report a bias voltage tunable two-color InAs∕GaAs quantum dot infrared photodetector working under the normal incidence infared irradiation. The two-color detection of our device is realized by combining a photovoltaic and a photoconductive response by bias voltage tuning. The photovoltaic response is attributed to the transition of electron from the ground state to a high continuum state. The photoconductive response arises from the transition of electron from the ground state to the wetting layer state through the barrier via Fowler–Nordheim tunneling evidenced by a broad feature of the photocurrent peak on the high energy side.
Dynamic tuning of an infrared hybrid-metamaterial resonance using vanadium dioxide
Authors: Driscoll T. , Palit S. , Qazilbash M. M. , Brehm M. , Keilmann F. , Chae Byung-Gyu , Yun Sun-Jin , Kim Hyun-Tak , Cho S. Y. , Jokerst N. Marie , Smith D. R. , Basov D. N.
Published: July 2008

We demonstrate a metamaterial device whose far-infrared resonance frequency can be dynamically tuned. Dynamic tuning should alleviate many bandwidth-related roadblocks to metamaterial application by granting a wide matrix of selectable electromagnetic properties. This tuning effect is achieved via a hybrid-metamaterial architecture; intertwining split ring resonator metamaterial elements with vanadium dioxide (VO2)-a material whose optical properties can be strongly and quickly changed via external stimulus. This hybrid structure concept opens a fresh dimension in both exploring and exploiting the intriguing electromagnetic behavior of metamaterials.
Giant magnetoelectric effect in Pb(Zr,Ti)O3-bimorph/NdFeB laminate device
Authors: Xing Zengping , Li Jiefang , Viehland D.
Published: July 2008

A Pb(Zr,Ti)O3-bimorph/NdFeB laminate device has a giant magnetoelectric (ME) effect. Our results reveal a giant ME coefficient of 16V∕cmOe or 62nC∕cmOe at a low (subresonant) frequency of 10Hz, and one of 250V∕cmOe or 960nC∕cmOe at a first order resonant bending mode frequency of ∼60Hz. The findings show a simple means by which to achieve magnetoelectric effects, without the use of magnetostrictive material.
Ag-induced spin-reorientation transition of ultrathin Fe films on Pt(111)
Authors: Chen Y. J. , Kuo M. H. , Shern C. S.
Published: July 2008

The spin-reorientation transition (SRT) was observed when Ag overlayers deposited on Fe∕Pt(111) by magneto-optical Kerr effect measurements. The easy axis of the magnetization changes completely from the in-plane to out-of-plane direction after the coverage of Ag is 1 ML. The polar Kerr intensity and its coercivity as a function of Ag coverage are investigated during SRT. The easy axis of magnetization can be reversed back to the in-plane direction after the Ag overlayers are removed by sputtering. The chemical compositions of the interfaces are measured by Auger electron spectroscopy. The mechanism of SRT induced by Ag is discussed.
Exchange bias of spin valve structure with a top-pinned Co40Fe40B20∕IrMn
Authors: You C. Y. , Goripati H. S. , Furubayashi T. , Takahashi Y. K. , Hono K.
Published: July 2008

We have investigated the exchange bias of a directly top-pinned Co40Fe40B20∕IrMn structure. An exchange bias was realized on the as-deposited samples, in which Co40Fe40B20 exhibits a fully amorphous structure. A current-in-plane giant magnetoresistance effect was demonstrated on simple Ru∕CoFeB∕Cu∕CoFeB∕IrMn∕Ru stacks prior to and after annealing. The amorphous CoFeB layer partially crystallized from the interface with a Cu spacer layer after annealed at 280°C.
Effect of MgO barriers on ferromagnetic metallic layers studied by polarized neutron reflectivity
Authors: Laloë J.-B. , Ionescu A. , Easton S. , Steinke N.-J. , Hayward T. J. , Kurebayashi H. , Bland J. A. C. , Charlton T. R. , Dalgliesh R. M. , Langridge S.
Published: July 2008

The effect of MgO tunnel barriers on the magnetic moment of ultrathin magnetic Fe and Co layers is studied by polarized neutron reflectivity. The MgO barriers were grown by molecular beam epitaxy using either direct evaporation from a source crystal or evaporation of Mg in an oxygen background atmosphere. A decrease of the magnetic moment is observed for both Fe and Co, and atomic intermixing of 1.5–3.5 ML at interfaces between the Fe, Co, and MgO is determined. Evaporation from a MgO source crystal yields a tunnel layer which displays better stoichiometry and epitaxy than is obtained using the other growth method.
Ag nanocrystal-incorporated germano-silicate optical fiber with high resonant nonlinearity
Authors: Lin Aoxiang , Liu Xueming , Watekar Pramod R. , Chung Youngjoo , Han Won-Taek
Published: July 2008

Silver nanocrystal-incorporated germano-silicate optical fiber was fabricated by modified chemical vapor deposition and solution doping techniques. By measuring the wavelength shift of the fringes obtained from the long-period fiber grating pair, upon pumping with an argon-ion laser at 499 nm, the resonant nonlinear refractive index around 1550 nm was estimated to be 5.4×10−16 m2/W. The observed high resonant optical nonlinearity of the silver nanocrystal-incorporated fiber is attributed to the contribution from the surface plasmon resonance of silver nanocrystals embedded in the fiber core.
Integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides
Authors: Bernini Romeo , Testa Genni , Zeni Luigi , Sarro Pasqualina M.
Published: July 2008

We report the fabrication and the characterization of an integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides. The light is confined inside a low refractive index liquid core by antiresonant reflecting optical waveguide. Several asymmetric Mach–Zehnder interferometers have been realized with standard silicon technology. An optical characterization of the devices has been carried out by measuring the spectrum of optical transmitted intensity from two different Mach–Zehnder configurations. The results show that interferometers with a good visibility can be achieved in good agreement with the theoretical results.
Enhanced Zeeman splitting in Ga0.25In0.75As quantum point contacts
Authors: Martin T. P. , Szorkovszky A. , Micolich A. P. , Hamilton A. R. , Marlow C. A. , Linke H. , Taylor R. P. , Samuelson L.
Published: July 2008

The strength of the Zeeman splitting induced by an applied magnetic field is an important factor for the realization of spin-resolved transport in mesoscopic devices. We measure the Zeeman splitting for a quantum point contact etched into a Ga0.25In0.75As quantum well, with the field oriented parallel to the transport direction. We observe an enhancement of the Landé g-factor from |g∗|=3.8±0.2 for the third subband to |g∗|=5.8±0.6 for the first subband, six times larger than in GaAs. We report subband spacings in excess of 10 meV, which facilitates quantum transport at higher temperatures.
Electromagnetic wave absorption properties of porous carbon/Co nanocomposites
Authors: Liu Qinglei , Zhang Di , Fan Tongxiang
Published: July 2008

Porous carbon/Co nanocomposites were fabricated by a sol-gel method. The electromagnetic parameters were measured in the 2–18GHz range. Compared with porous carbon composite, porous carbon/Co nanocomposite has larger dielectric loss due to the enhanced interfacial polarization relaxation loss and Ohmic loss. The maximum reflection loss of the porous C(Co) nanocomposite can reach 40dB at 4.2GHz with 5mm in thickness and the primary microwave absorptive mechanism is ascribed to the dielectric loss. The effect of porous structure on microwave absorption property of the carbon/Co nanocomposite was also discussed.
Ensemble of electrophoretically captured gold nanoparticles as a fingerprint of Boltzmann velocity distribution
Authors: Hong S. H. , Kang M. G. , Lim J. H. , Hwang S. W.
Published: July 2008

An ensemble of electrophoretically captured gold nanoparticles is exploited to fingerprint their velocity distribution in solution. The electrophoretic capture is performed using a dc biased nanogap electrode, and panoramic scanning electron microscopic images are inspected to obtain the regional density of the captured gold nanoparticles. The regional density profile along the surface of the electrode is in a quantitative agreement with the calculated density of the captured nanoparticles. The calculated density is obtained by counting, in the Boltzmann distribution, the number of nanoparticles whose thermal velocity is smaller than the electrophoretic velocity.
Cross-plane thermal conductivity reduction of vertically uncorrelated Ge∕Si quantum dot superlattices
Authors: Alvarez-Quintana J. , Alvarez X. , Rodriguez-Viejo J. , Jou D. , Lacharmoise P. D. , Bernardi A. , Goñi A. R. , Alonso M. I.
Published: July 2008

A drastic reduction in temperature dependent cross-plane thermal conductivity κ⊥ occurs in Ge quantum dot superlattices (QDSLs), depending on the vertical correlation between dots. Measurements show at least a twofold decrease of κ⊥ in uncorrelated dot structures as compared to structures with the same Si spacer of 20nm but good vertical dot alignment. The observed impact of disorder on the conductivity provides an alternative route to reduce the thermal conductivity of QDSLs. The results of this work have implications for the development of highly efficient thermoelectric materials and on-chip nanocooling devices.