bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual beam spectrometer using laser-induced breakdown spectroscopy
Authors: Yaroshchyk Pavel , Morrison Richard J. S. , Body Doug , Chadwick Bruce L.
Published: November 2004

A laser-induced breakdown spectroscopy (LIBS) analog of a dual beam spectrometer is described and applied to the determination of trace components present in aqueous samples. It is shown that the complexity of such an instrument can be greatly reduced by using a single imaging spectrograph and two-dimensional detector to record the LIBS spectrum from the analyte and reference channels simultaneously. Implementation of the dual beam technique results in substantial spectral simplification and corresponding lower detection limits in LIBS analysis of liquids.
Model for small-sample bias of free-energy calculations applied to Gaussian-distributed nonequilibrium work measurements
Authors: Wu Di , Kofke David A.
Published: November 2004

We present a model for the bias of free-energy differences when determined using the nonequilibrium work (NEW) formalism due to Jarzynski. Input to the model is the distribution of work values underlying the NEW calculation, and the bias is estimated by assuming that all of the inaccuracy is incurred by failure to sample work values beyond a specific point in the tail of the distribution. The model is formulated considering both small- and large-sample NEW calculations. It is then applied to the study of bias for cases in which the work distribution is Gaussian. The model is shown to give an excellent description of the bias in situations where the bias is a more significant source of error than the sample variance. A scaling law is presented and it is shown that the bias as a function of sampling can be reduced to a single universal curve, approximately valid for all Gaussian work distributions. This result is used to formulate a simple criterion that can be applied to test if a NEW calculation is effectively free of bias. The criterion is shown to be effective even though it uses the measured (and perhaps biased) free energy as an input.
Chopped sample heating for quantitative profile analysis of low energy electron diffraction spots at high temperatures
Authors: Kury P. , Zahl P. , Horn-von Hoegen M. , Voges C. , Frischat H. , Günter H.-L. , Pfnür H. , Henzler M.
Published: November 2004

Spot profile analysis low energy electron diffraction (SPA-LEED) is one of the most versatile and powerful methods for the determination of the structure and morphology of surfaces even at elevated temperatures. In setups where the sample is heated directly by an electric current, the resolution of the diffraction images at higher temperatures can be heavily degraded due to the inhomogeneous electric and magnetic fields around the sample. Here we present an easily applicable modification of the common data acquisition hardware of the SPA-LEED, which enables the system to work in a pulsed heating mode: Instead of heating the sample with a constant current, a square wave is used and electron counting is only performed when the current through the sample vanishes. Thus, undistorted diffration images can be acquired at high temperatures.
Two-dimensional charged particle image inversion using a polar basis function expansion
Authors: Garcia Gustavo A. , Nahon Laurent , Powis Ivan
Published: November 2004

We present an inversion method called pBasex aimed at reconstructing the original Newton sphere of expanding charged particles from its two-dimensional projection by fitting a set of basis functions with a known inverse Abel integral. The basis functions have been adapted to the polar symmetry of the photoionization process to optimize the energy and angular resolution while minimizing the CPU time and the response to the cartesian noise that could be given by the detection system. The method presented here only applies to systems with a unique axis of symmetry although it can be adapted to overcome this restriction. It has been tested on both simulated and experimental noisy images and compared to the Fourier-Hankel algorithm and the original Cartesian basis set used by [Dribinski et al.Rev. Sci. Instrum. 73, 2634 (2002)], and appears to give a better performance where odd Legendre polynomials are involved, while in the images where only even terms are present the method has been shown to be faster and simpler without compromising its accuracy.
Parametric excitation of circular micromachined polycrystalline silicon disks
Authors: Kaajakari Ville , Lal Amit
Published: November 2004

Center anchored polycrystalline silicon plates are parametrically excited using ultrasonic substrate motion generated by a lead zirconate titanate oxide (PZT) plate bonded to the silicon die. Parametric excitation is used to achieve large amplitude, greater than 100 nm, transverse plate vibrations in atmospheric pressure with sub-3 VPP drive on the PZT plate with corresponding surface velocities over 1.5 m/s. The preferred parametrically excited modes are observed to be “whispering gallery” plate modes with no radial nodal points. The possible nonlinear mechanisms are analyzed and the parametric excitation is explained with in-plane plate stresses due to the lateral plate anchor motion. The effect of in-plane stresses is modeled with von Kármán plate equations. Parametric instability is demonstrated with the use of nonlinear Floquet transition matrix.
Single-crystal Nb-doped Pb(Zr,Ti)O3 thin films on Nb-doped SrTiO3 wafers with different orientations
Authors: Gong Wen , Li Jing-Feng , Chu Xiangcheng , Gui Zhilun , Li Longtu
Published: November 2004

Single-crystal Nb-doped Pb(Zr,Ti)O3 (PNZT) films were grown on electric conducting single-crystal Nb-doped SrTiO3 (Nb:STO) wafers by a sol-gel method. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PNZT film was formed on the {100} surface of the Nb:STO substrate, whereas [111]-oriented rhombohedral PNZT film on the {111} surface. The PNZT films on SrTiO3 substrates showed considerably high remnant polarization and low coercive field, as compared with conventional PZT films on Si wafers. In particular, high d33 value was obtained in the [001]-oriented PNZT films.
Optical lever detection in higher eigenmode dynamic atomic force microscopy
Authors: Stark Robert W.
Published: November 2004

The optical lever detection scheme is widely used in atomic force microscopy for the detection of the cantilever deflection. Laser spot size as well as adjustment of the laser along the cantilever determine the zeros of the transfer function of the signal path from the tip-sample forces to the optical readout. This can cause (almost) pole-zero cancellations which lead to a significantly reduced sensitivity in the detection of higher mode vibrations of the cantilever. Physically, the light lever detection integrates over the slope of the cantilever. However, the sign of the slope of higher flexural modes varies along the cantilever. Thus, integration can lead to a significantly decreased sensitivity to higher eigenmode vibrations. Illuminating only the area between the free end and the next zero crossing of the slope of the modal shape provides a good compromise between high and low frequency sensitivity.
Sensitive measurement of reversible parallel and transverse susceptibility by alternating gradient magnetometry
Authors: Barbic Mladen
Published: November 2004

Reversible susceptibility tensor measurements reveal important information about the switching fields and anisotropies of magnetic materials. We show that a simple reconfiguration of an alternating gradient magnetometer can be used to measure both reversible parallel and transverse susceptibilities with high sensitivity. It is demonstrated that positioning the sample off axis with respect to the magnetometer gradient field coils results in a signal at twice the frequency of the gradient field that is directly proportional to the reversible susceptibility. Offsetting the sample along the x axis results in a sensor signal proportional to the reversible parallel susceptibility, while rotating the sample holder by 90° and offsetting it along the y axis results in a sensor signal proportional to the reversible transverse susceptibility. Examples of reversible parallel and transverse susceptibility measurements of aligned nanoparticle systems are demonstrated.
High pressure cells for magnetic measurements—Destruction and functional tests
Authors: Kamarád J. , Machátová Z. , Arnold Z.
Published: November 2004

The design of nonmagnetic CuBe and multilayer (CuBe+MP35N) hydrostatic pressure cells for magnetization and magnetostriction measurements in a pressure range up to 2 GPa at temperatures down to 5 K and in fields up to 14 T is presented. The safety operation of the cells is based on destruction tests described in this work. An influence of the pressure cells on measured magnetic magnitudes and the temperature induced pressure changes in the clamped cells have been carefully studied in a temperature range from 350 K down to 5 K using different pressure transmitting media.
Impurity condensation in liquid and solid helium
Authors: Gordon E. B.
Published: November 2004

It is shown from an analysis of x-ray structural and IR spectroscopic studies that when impurity particles are introduced into liquid or solid helium, the clusters formed in the cold part of a gas jet have a pronounced spatial separation of impurities with different volatility. In particular, in the condensation of partially dissociated diatomic molecules the atoms are highly concentrated near and on the surface of the clusters. Segregation of this kind is preserved in the condensate in liquid helium, which consists of clusters stuck together into a porous structure; in solid helium clusters are isolated. The presence of high concentrations of atoms in the surface layer at the boundary with condensed helium explains the specifics of condensate behavior observed by methods of optical spectroscopy, ESR, and thermometry. An experimental strategy is developed for detecting the formation of an impurity–helium solid.
Relaxation and dissipative processes in the phonon–impuriton system of concentrated superfluid mixtures of He3 in He4
Authors: Zadorozhko A. A. , Kal’ko T. V. , Rudavskiı̆ É. Ya. , Chagovets V. K. , Sheshin G. A. , Nemchenko K. E.
Published: November 2004

The effective thermal conductivity of superfluid mixtures of He3 in He4 with an initial concentration of 9.8% He3 is investigated in the temperature interval 70–500 mK. The results, together with previously available experimental data on the thermal conductivity, viscosity, and mass and spin diffusion, are analyzed in the framework of the kinetic theory of the phonon–impuriton system of superfluid mixtures. It is shown that the experimental results for all the kinetic coefficients can be described from a unified viewpoint if the corresponding impuriton–impuriton scattering times are used as adjustable parameters. The role of each relaxation process in the complex hierarchy of relaxation times is determined as a function of temperature and concentration. It is found that even in concentrated mixtures a substantial contribution to the establishment of equilibrium is made by three-phonon processes. The phonon–impuriton relaxation times are calculated by integrating over the phonon energy in the entire region where such processes are allowed.
Drag of superfluid current in bilayer Bose systems
Authors: Fil D. V. , Shevchenko S. I.
Published: November 2004

An effect of nondissipative drag of a superfluid flow in a system of two Bose gases confined in two parallel quasi-two-dimensional traps is studied. Using an approach based on the introduction of density and phase operators, we compute the drag current at zero and finite temperatures for arbitrary ratio of particle densities in the adjacent layers. We demonstrate that in a system of two ring-shaped traps the “drag force” influences the drag trap in the same way as an external magnetic flux influences a superconducting ring. This allows one to use the drag effect to control persistent current states in superfluids and opens up the possibility of implementing a Bose analog of the superconducting Josephson flux qubit.
Transport of charge carriers in a superconductor–semiconductor contact
Authors: Kuznetsov G. V.
Published: November 2004

The changes in the passage of charge carriers through a superconducting metal–semiconductor contact with a tunnel-thin intermediate insulating layer upon the transition of the metal to the superconducting state are analyzed. The transition of the metal to the superconducting state leads to a decrease of the forward current and an increase of the reverse current of thermionic emission in such a contact. For a tunneling mechanism of carrier transport a decrease in thickness of the intermediate insulating layer and in the degree of doping of the semiconductor leads to an increase in the nonlinearity parameter of the current–voltage characteristic.
Spectrum of dynamic magnetic susceptibility of a randomized f–d magnet with spin–lattice coupling. II. “Opening” of the spin excitation bands
Authors: Beznosov A. B. , Orel E. S.
Published: November 2004

The transformation of the magnetic absorption spectra of a narrow-band ferromagnetic conductor containing local f and quasilocal d magnetic moments under conditions of weak spin–lattice coupling and spatial randomization of the g factors of the quasilocal and local spin subsystems is investigated. It is shown that randomization of the g factors (e.g., as a result of the introduction of an impurity) leads mainly to the “opening” (i.e., to the appearance in the magnetic absorption spectrum) of acoustic and optical magnon bands formed in the system while not affecting the position and shape of the narrow magnetic resonance lines comprising the spectrum of the impurity-free crystal. The effects of spin–lattice coupling, besides the “opening” of the phonon and magnon bands, lead to a shift and a temperature smearing of the narrow resonance lines. The relative corrections to the effective magnon masses generated by the spin–lattice coupling in a 4f–5d metal amount to ∼2×10−4 for an acoustic mode and to ∼4×10−4 for an optical mode.
On the theory of the formation of equilibrium domain structure in antiferromagnets
Authors: Gomonay E. V. , Loktev V. M.
Published: November 2004

A model is proposed which describes the formation and reversible rearrangement of the equilibrium domain structure in bulk antiferromagnets with a rather strong magnetoelastic coupling. The model is based on the assumed existence of a microscopic ordering of a tensor nature—the microstress tensor that arises due to magnetoelastic coupling during the formation of the magnetic moment. It is necessary to take such a parameter into account for adequate description not only of the macroscopic internal stresses and the spontaneous strains corresponding to them but also of the microstructure of the crystal (e.g., the domain structure). The microstresses arising locally in each unit cell are equivalent, from a formal standpoint, to elastic dipoles, and they create long-range fields whose contribution to the free energy of the crystal is analogous to that of the magnetostatic energy in ferromagnets and favors a decrease in the macroscopic strain of the sample through the formation of an equilibrium domain structure. The corresponding contribution is given the name “destressing energy” by the authors. It is shown that taking this energy into account in antiferromagnetic crystals allows one not only to explain the cause of the formation of the domain structure but also to trace its dependence on the shape of the crystal and the external fields.
Dielectric behavior of PbZr0.52Ti0.48O3 thin films: Intrinsic and extrinsic dielectric responses
Authors: Ang Chen , Yu Zhi
Published: November 2004

The dc electric-field (E) dependence of the dielectric constant (ε) in PbZr0.52Ti0.48O3 (PZT) thin films has been studied at cryogenic temperatures in the dc electric-field range of 0–820kV∕cm. Significant suppression of ε is observed by an application of E up to 400kV∕cm. The relation of ε versus E can be well described by the “multi-polarization mechanism” model, i.e., ε(E)=ε(0)∕[1+αε(0)3E2]1∕3+(Pjxj∕ε0)[cosh(Exj)]−2. By this equation, the field dependence of the extrinsic dielectric response can be subtracted from the whole dielectric response. The results indicate that the analysis of the relation of ε versus E could be a way to separate the intrinsic and extrinsic contributions in PZT.
Nanoscale velocity–drag force relationship in thin liquid layers measured by atomic force microscopy
Authors: Mechler Ádám , Piorek Brian , Lal Ratnesh , Banerjee Sanjoy
Published: November 2004

The relationship between velocity and drag force acting on a nanoprobe has been measured with an atomic force microscope (AFM). A special nanoprobe “whisker” was partially submerged in thin layers of glycerol–water mixtures and moved by using the AFM in scanning mode. The viscous drag force-caused torsion of the cantilever probe was recorded as a function of scanning speed and submersion depth. A linear drag force–velocity function was determined for cylindrical bodies with diameters of the order of 50nm. The experimental results were supported by calculations for the torsional force exerted on an AFM probe dragged through a viscous medium. The viscosity was calculated for each experiment assuming no slip conditions and was in agreement with the macroscopically determined values. With some refinements, this offers a possible means of determining viscosity in thin liquid layers.
Edge pedestal structure
Authors: Stacey W. M.
Published: November 2004

The hypothesis is advanced and it is investigated that, in between or in the absence of edge-localized modes, the structure of the edge pedestal is determined by the transport requirements of plasma particle, momentum and energy balance, and by recycling neutral atoms. A set of “pedestal equations” following from this hypothesis are presented and applied to calculate the edge density, temperature, rotation velocity, and radial electric field profiles in a DIII-D H (high)-mode plasma. It is found that a pedestal structure in the density profile and sharp negative peaks in the radial electric field and poloidal velocity just inside the separatrix are predicted as natural consequences of the conservation of particle and momentum, in qualitative and quantitative agreement with measured values. Detailed examination of the calculation reveals a sequence of mechanisms by which the ionization of recycling neutrals affect the structure of the density profile in the edge pedestal.
Abnormal reduction of Eu ions and luminescence in CaB2O4:Eu thin films
Authors: Hao J. H. , Gao J.
Published: November 2004

Thin films of CaB2O4:Eu were deposited on glass substrates by spray pyrolysis. The abnormal reduction of Eu3+ to Eu2+ in as-grown thin films was found at the growth temperatures from 300to500°C. Blue cathodoluminescence was observed by annealing films in air, correlating with further abnormal reduction of Eu ions and crystallization of compounds. These phenomena were explained by an electron transfer mechanism. The chromaticity coordinates were x=0.193 and y=0.089 with a dominant wavelength of 455nm. Our results indicate calcium borate doped with Eu is a blue phosphor at temperatures suitable for the use of glass substrates in flat panel applications.
Terahertz emission from electrically pumped gallium doped silicon devices
Authors: Lv P.-C. , Troeger R. T. , Kim S. , Ray S. K. , Goossen K. W. , Kolodzey J. , Yassievich I. N. , Odnoblyudov M. A. , Kagan M. S.
Published: November 2004

Current pumped terahertz (THz) emitting devices have been fabricated from gallium doped silicon. The time resolved peak power was 12μW per facet at a peak pumping current of 400mA, and the emission was observed up to temperatures near 30K. The spectra occurred in two distinct series at 7.9–8.5THz, and at 13.2–13.8THz. The emission was attributed to the radiative transitions of holes from the split sublevels of the 1Γ8 excited state to the sublevels of the 1Γ8+ ground state and the 1Γ7+ ground state, yielding an energy separation of 22±0.07meV between the two ground states. These results indicated that emitters based on Ga impurity transitions open up a range of THz frequencies, and the properties of their spectra can improve the understanding of impurity level physics.
Nanovoids in InGaAs∕GaAs quantum dots observed by cross-sectional scanning tunneling microscopy
Authors: Lenz A. , Eisele H. , Timm R. , Becker S. K. , Sellin R. L. , Pohl U. W. , Bimberg D. , Dähne M.
Published: November 2004

We present cross-sectional scanning tunneling microscopy data of a type of InGaAs∕GaAs quantum-dot structure characterized by a hollow center. This void structure develops during a long growth interruption applied after deposition of a quantum dot layer and a thin cap layer, resulting in an eruption of indium-rich material. Subsequent fast overgrowth does not fill the void completely. This growth behavior demonstrates limitations of current strategies to grow large quantum dots.
Ultraviolet photonic crystal laser
Authors: Wu X. , Yamilov A. , Liu X. , Li S. , Dravid V. P. , Chang R. P. H. , Cao H.
Published: November 2004

We fabricated two-dimensional photonic crystal structures in zinc oxide films with focused-ion-beam etching. Lasing is realized in the near-ultraviolet frequency at room temperature under optical pumping. From the measurement of lasing frequency and spatial profile of the lasing modes, as well as the photonic band structure calculation, we conclude that lasing occurs in the strongly localized defect modes near the edges of photonic band gap. These defect modes originate from the structure disorder unintentionally introduced during the fabrication process.
Experiments with rf ovens in ECR ion sources
Authors: Cavenago M. , Kulevoy T. , Petrenko S.
Published: November 2004

A 34 mm diameter radio frequency (rf) oven system previously developed on bench was inserted and tested into the Electron Cyclotron Resonance (ECR) Ion Source Alice, producing beams from natural copper and silver samples; charge range was typically i=10–13 for copper and i=10–19 for silver, which well compares to previous source yield for xenon (charges 11–20). Some issues of oven design, including wire section effects, and circuit matching, are discussed; taps on the coupling transformer improved the flexibility of rf matching to different crucible materials (tantalum or steel). Details of operating experience (cleaning the oven and replacing sample) are reported; sample duration was more than 100 h and temperature Ts in excess of 1750 K were demonstrated. The ion source operation depends on both the oven distance Loe from ECR plasma and the bias voltage Vb of the sample. Best conditions were found for close (Loe≅70 mm) or preferably intermediate positions (Loe≅106 mm) and for sample negative respect to ECR chamber Vb<−400 V. Final results of current for silver [for example I(107Ag17+) about 1000 nA] are well comparable to xenon case [for example I(129Xe18+) about 500 nA] after correcting for isotopic abundance. Memory effect of metal ion generation was also important and is discussed as well as other time dependent effects and an empirical fit for the aggregate results of silver mass flow. New oven prototypes reached Ts≅2250 K in development tests.
Accelerated UV weathering device based on integrating sphere technology
Authors: Chin Joannie , Byrd Eric , Embree Ned , Garver Jason , Dickens Brian , Finn Tom , Martin Jonathan
Published: November 2004

An ultraviolet (UV) weathering device based on integrating sphere technology has been designed, fabricated, and implemented for studying the accelerated weathering of polymers. This device has the capability of irradiating multiple test specimens with uniform, high intensity UV radiation while simultaneously subjecting them to a wide range of precisely and independently controlled temperature and relative humidity environments. This article describes the integrating sphere-based weathering system, its ability to precisely control temperature and relative humidity, and its ability to produce a highly uniform UV irradiance.
Thermal fatigue testing of thin metal films
Authors: Mönig R. , Keller R. R. , Volkert C. A.
Published: November 2004

An experimental method is described for performing thermal fatigue testing of thin films and lines on substrates. The method uses Joule heating from alternating currents to generate temperature, strain, and stress cycles in the metal structures. The apparatus has been installed in a scanning electron microscope and allows in situ observations of the fatigue damage evolution. First observations on Cu films reveal that fatigue damage forms in submicrometer thick films and is strongly affected by the film thickness and grain size. In addition, results from a special test structure confirm that the damage is caused by fatigue and not by electromigration.
Effect of coiling on the electronic properties along single-wall carbon nanotubes
Authors: Castrucci P. , Scarselli M. , De Crescenzi M. , El Khakani M. A. , Rosei F. , Braidy N. , Yi J.-H.
Published: November 2004

Straight and coiled single-wall carbon nanotubes (SWCNTs) synthesized by laser vaporization were dispersed on highly oriented pyrolitic graphite. Their morphology and electrical properties were investigated by scanning tunneling microscopy (STM). STM images revealed that the SWCNTs (either straight or coiled) often self-organize into bundles of two or more tubes and are rarely found alone. The conductance measured along a periodically coiled CNT was found to increase at locations where the CNT is squeezed, while it decreases significantly in unsqueezed regions characterized by an unperturbed hexagonal network. This provides experimental evidence of significant conductance modulation along a one-dimensional system on the nanometer scale.
Characterization of light-induced modification of the nonlinear refractive index using a one-laser-shot nonlinear imaging technique
Authors: Boudebs G. , de Araújo Cid B.
Published: November 2004

We report the exploitation of a one-laser-shot measurement technique to study photo-induced effects in semiconductor-doped glasses. The technique, based on the use of a phase object in a 4f coherent imaging system, allows one to characterize the kinetics of the nonlinear refractive index of samples versus the light exposure time.
Giant optical nonlinearity of a Bi2Nd2Ti3O12 ferroelectric thin film
Authors: Gu Bing , Wang Yue-Hua , Peng Xian-Chu , Ding Jian-Ping , He Jing-Liang , Wang Hui-Tian
Published: November 2004

We investigate the optical nonlinearity of a Bi2Nd2Ti3O4 ferroelectric thin film using the top-hat Z scan technique at a wavelength of 532nm with 35ps duration pulses. The film exhibits the fast and giant optical nonlinearities having the two-photon absorption coefficient of 3.1×104cm∕GW and the nonlinear refraction coefficient of 0.7cm2∕GW, respectively. The mechanism of the optical nonlinearity is discussed in detail. In particular, we also give two important formulas for the top-hat Z scan, which are very valuable and helpful for estimating the nonlinear optical coefficients when the material possesses the simultaneous nonlinear absorption and nonlinear refraction.
Deposition of HfO2 on germanium and the impact of surface pretreatments
Authors: Van Elshocht S. , Brijs B. , Caymax M. , Conard T. , Chiarella T. , De Gendt S. , De Jaeger B. , Kubicek S. , Meuris M. , Onsia B. , Richard O. , Teerlinck I. , Van Steenbergen J. , Zhao C. , Heyns M.
Published: November 2004

The deposition behavior of HfO2 by metalorganic chemical vapor deposition on germanium has been investigated. HfO2 films can be deposited on Ge with equally good quality as compared to high-k growth on silicon. Surface preparation is very important: compared to an HF-last, NH3 pretreatments result in smoother films with strongly reduced diffusion of germanium in the HfO2 film, resulting in a much better electrical performance. We clearly show that much thinner interfacial layers can be obtained, approximately half the thickness of what is typically found for depositions on silicon, suggesting the possibility of more aggressive equivalent oxide thickness∕leakage scaling.
Zinc oxide nanodisk
Authors: Xu C. X. , Sun X. W. , Dong Z. L. , Yu M. B.
Published: November 2004

Using the mixture of zinc oxide and graphite powders as source materials, zinc oxide nanodisks with bulk quantity were fabricated by vapor-phase transport method. The nanodisks have perfect hexagonal shape with about 3μm in diagonal and 300nm in thickness. The growth is favored along six symmetric directions of ±[101¯0], ±[11¯00], and ±[011¯0] with the typical growth along [0001] direction suppressed, which directly leads to the formation of zinc oxide nanodisk. The microstructure and growth mechanism are discussed.
Surface structures of cerium oxide nanocrystalline particles from the size dependence of the lattice parameters
Authors: Tsunekawa S. , Ito S. , Kawazoe Y.
Published: November 2004

Cerium oxide nanocrystalline particles are synthesized and monodispersed in the size range from 2 to 8nm in diameter. The dependence of the lattice parameters on particle size is obtained by x-ray and electron diffraction analyses. The size dependence well coincides with the estimation based on the assumption that the surface is composed of one layer of Ce2O3 and the inside consists of CeO2. The effect of particle size on lattice parameters is discussed from the differences in the fabrication method and the surface structure.
Suppression of spin accumulation in nonmagnet due to ferromagnetic ohmic contact
Authors: Kimura T. , Hamrle J. , Otani Y. , Tsukagoshi K. , Aoyagi Y.
Published: November 2004

We experimentally demonstrate that the ohmic contact of a Ni–Fe wire additionally connected to a Cu strip between an injector and detector in a nonlocal spin-valve structure signicantly suppresses the spin polarization induced in the Cu strip. This behavior is attributable to spin current absorption into the connected additional Ni–Fe wire.
Proximity effect of electron beam lithography for single-electron transistor fabrication
Authors: Hu Shu-Fen , Sung Chin-Lung , Huang Kuo-Dong , Wan Yue-Min
Published: November 2004

In this letter, we shall describe a method, utilizing the proximity effect in electron beam lithography, suitable for fabricating silicon dots and devices, and demonstrate the electronic characteristics of the Si single-electron transistor. The drain current (Id) of the device oscillates against gate voltage. The electrical characteristics of the single-electron transistor were observed to be consistent with the expected behavior of electron transport through gated quantum dots, at up to 150K. The dependence of the electrical characteristics on the dot size reveals that the Id oscillation follows from the Coulomb blockade by poly-Si grains in the poly-Si dot. The method of fabrication of this device is completely compatible with complementary metal–oxide–semiconductor technology, raising the possibility of manufacturing large-scale integrated nanoelectronic systems.
Room temperature operation of InGaAs∕InGaAsP∕InP quantum dot lasers
Authors: Jang J. W. , Pyun S. H. , Lee S. H. , Lee I. C. , Jeong Weon G. , Stevenson R. , Dapkus P. Daniel , Kim N. J. , Hwang M. S. , Lee D.
Published: November 2004

The growth conditions for InGaAs∕InGaAsP∕InP quantum dots (QDs) have been optimized and QDs of high luminescence efficiency and the room temperature operation of QD lasers emitting at ∼1.5μm have been demonstrated. Lattice-matched InGaAsP (λg=1.0–1.1μm) was used as a barrier layer for the InGaAs QDs and the emission wavelength was controlled by the QD composition. High-density InGaAs QDs with an areal density as high as 1.13×1011cm−2 have been grown. The integrated and peak intensity of the photoluminescence (PL) spectra at room temperature are as high as 25% and 10% of those at 10K, respectively. The room temperature PL peak intensity is about 50% that of a high-quality InGaAs∕InP quantum well. Room temperature, pulsed operation at ∼1.5μm has been achieved from broad area lasers with a 1mm cavity length. Threshold current density per QD stack of ∼430A∕cm2 is measured for the five-, seven-, and ten-stack QD lasers.
Fabrication of a three-dimensional terahertz photonic crystal using monosized spherical particles
Authors: Takagi Kenta , Seno Kazunori , Kawasaki Akira
Published: November 2004

Three-dimensional artificial crystals with periodicity corresponding to terahertz wave lengths were fabricated by self-assembling monosized metal spherical particles. The metal crystals were weakly sintered to utilize them as templates. The metal templates were inverted to air spheres crystal embedded in dielectric resin though infiltration and etching. The resulting resin inverted crystals clearly presented the photonic stop gaps within terahertz wave region and the frequencies of the gaps were confirmed to agree well with calculation by plane wave expansion method.
Efficiency and harmonic enhancement trends in GaN-based Gunn diodes: Ensemble Monte Carlo analysis
Authors: Sevik C. , Bulutay C.
Published: November 2004

Gallium nitride can offer a high-power alternative for millimeter-wave Gunn oscillators. Hence, an ensemble Monte Carlo-based comprehensive theoretical assessment of efficiency and harmonic enhancement in n-type GaN Gunn diodes is undertaken. First, the effects of doping notch/mesa and its position within the active channel are investigated which favors a doping notch positioned next to cathode. It is then observed that the width of the notch can be optimized to enhance the higher-harmonic operation without degrading its performance at the fundamental mode. Next, the effects of dc bias and channel doping density are investigated. Both of these have more significant effects on the higher-harmonic efficiency than the fundamental one. The lattice temperature is observed to have almost no influence up to room temperature but severely degrades the performance above room temperature. As a general behavior, the variations of temperature, channel doping, and the notch width primarily affect the phase angle between the current and voltage wave forms rather than the amplitude of oscillations. Finally, the physical origin of these Gunn oscillations is sought which clearly indicates that the intervalley scattering mechanism is responsible rather than the Γ valley nonparabolicity or the effective mass discrepancy between the Γ and the lowest satellite valleys.
The generation of highly monodisperse droplets through the breakup of hydrodynamically focused microthread in a microfluidic device
Authors: Xu Qingyi , Nakajima Mitsutoshi
Published: November 2004

We used a controllable three-stream laminar flow system to hydrodynamically focus a viscous stream, flowing between two inviscid streams, to cause instability and eventual breakup. The characteristics of the focusing and breakup of the viscous stream are presented here. Breakup occurred as the viscous stream was focused to a characteristic width of several micrometers. Highly monodisperse droplets with diameters smaller than the width of the junction of the three inlet channels were formed through the rapid periodic breakup of the focused microthread. Size, production rate, and patterning can be precisely controlled with this approach.
Modification of drain current on metal–oxide–semiconductor field-effect transistor by magnetic field induced by remanent magnetization
Authors: Wakiya Naoki , Shimizu Kan , Mizukami Satoshi , Shinozaki Kazuo , Mizutani Nobuyasu
Published: November 2004

We propose a concept of drain current (Ids) modification in a metal–oxide–semiconductor field-effect transistor (MOSFET) using the Lorentz force from an external magnetic field and a magnetic field induced by remanent magnetization. We fabricated a Pt∕MZF∕YSZ∕MOSFET structure (MZF:Mn0.60Zn0.30Fe2.10O4,YSZ:Y0.15Zr0.85O1.93), based on this concept and examined the effect of the magnetic field on electrical properties. The magnetic field increased the Ids when the carriers were pushed away from the interface. A magnetic field of the opposite direction increased Ids slightly. This phenomenon is related to the potential change and carrier mobility. It may be useful for use in memory devices.
Wetting-layer transformation for Pb nanocrystals grown on Si(111)
Authors: Feng R. , Conrad E. H. , Tringides M. C. , Kim C. , Miceli P. F.
Published: November 2004

We present the results of in situ x-ray scattering experiments that investigate the growth of Pb nanocrystalline islands on Si(111). It is conclusively shown that the Pb nanocrystals do not reside on top of a Pb wetting layer. The nucleating Pb nanocrystals transform the highly disordered Pb wetting layer beneath the islands into well-ordered fcc Pb. The surface then consists of fcc Pb islands directly on top of the Si surface with the disordered wetting layer occupying the region between the islands. As the Pb nanocrystals coalesce at higher coverage we observe increasing disorder that is consistent with misfit strain relaxation. These results have important implications for predicting stable Pb island heights.
Template-free synthesis on single-crystalline InP nanotubes
Authors: Yin L. W. , Bando Y. , Golberg D. , Li M. S.
Published: November 2004

A simple template-free thermal chemical route has been developed to prepare InP nanotubes with zinc blende structure by controlling the reaction temperature and flowing gas. The synthesized InP nanotubes are single-crystalline, free from defects and dislocations, and partially filled with In. The presence of metallic indium at tips of and within the synthesized InP nanotubes indicated a vapor–liquid–solid mechanism for the formation of InP nanotubes. The synthesized InP single-crystalline nanotubes grew along [1¯10] direction. The synthesized InP nanotubes have a uniform outer diameter of 50–60 nm and a wall thickness of 7–10 nm. The photoluminescence spectrum at room temperature exhibits a great shift from the bulk band gap of 1.35 eV to high energy of 1.49 eV.
Enhanced infrared absorption spectra of self-assembled alkanethiol monolayers using the extraordinary infrared transmission of metallic arrays of subwavelength apertures
Authors: Rodriguez Kenneth R. , Shah Summit , Williams Shaun M. , Teeters-Kennedy Shannon , Coe James V.
Published: November 2004

The surface-plasmon-mediated, extraordinary transmission of metallic arrays of subwavelength apertures has been used as the light source for absorption studies of self-assembled monolayers on metal. Enhanced infrared absorption spectra of a sequence of alkanethiol self-assembled monolayers on copper were recorded for carbon chain lengths varying from 8 to 18 atoms. Transition positions and intensities are presented over a large range of the infrared region. The connection between the vibrational modes of the CH2 wagging progression and the infinite methylene chain is explored using a traditional coupled oscillator approach and a new cluster perspective.
Olfactory Epithelial Lesions Induced by Various Cancer Chemotherapeutic Agents in Mice
Authors: Kai Kiyonori , Satoh Hiroshi , Kajimura Tetsuyo , Kato Michiyuki , Uchida Kazuyuki , Yamaguchi Ryoji , Tateyama Susumu , Furuhama Kazuhisa
Published: November 2004

In order to examine and compare the potential toxicity in the olfactory epithelium, the antitumor drug vincristine sulfate (VCR), vinblastine sulfate (VBL), vindesine sulfate (VDS), paclitaxel (PTX), mitomycin C (MMC), 5-fluorouracil, (5-FU) or cisplatin (CDDP) was intravenously injected once (designated as day 1) at an estimated 10% lethal dose (LD10) to male BALB/c mice. The animals were necropsied on days 2, 5 and 15, and nasal tissues were examined by light-microscopy, counting of epithelial cells positive for terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick-end labeling (TUNEL), immunohistochemical staining with keratin antibody, and electron microscopy. Further, to delineate the drug disposition in the target organ, whole-body radioluminography was performed 1 hour and 24 hours after treatment with the LD10 of PTX or 5-FU. Of the antitumor drugs employed, only the antimicrotubule agents, VCR, VBL, VDS, and PTX, induced single cell death in the olfactory epithelium, especially sensory cells on day 2, atrophy of the olfactory epithelium on day 5, and myelin fragmentation in the trigeminal nerve on day 15. PTX induced the strongest changes among the 4 antimicrotubule agents. The cell death was confirmed to be apoptosis by TUNEL assay and electron microscopy, whereas the change in horizontal basal cells of the olfactory epithelium was shown not to be apoptosis by keratin staining. In quantitative radioluminography, radioactivity of PTX in the nasal tissues both 1 hour and 24 hours after administration was about 4- or 5-fold higher than those of 5-FU. These results suggest that tubulin-targeting antitumour drugs could induce apoptosis in the olfactory epithelial cells of mice and that high drug distribution may effect the onset of the olfactory lesions.
Unintentional Processing of Motivational Valence
Authors: Moors Agnes , De Houwer Jan , Hermans Dirk , Eelen Paul
Published: November 2004

Recent motivational affective priming studies (Moors & De Houwer, 2001; Moors, De Houwer, & Eelen, 2004) showed that primes that indicate success on a goal-inducing task facilitate positive target responses whereas primes that indicate failure on that task facilitate negative target responses. In the current studies, we examined whether these priming effects depend on consciously intentional processing of the motivational valence of the primes. In Experiment 1, the outcome of success or failure was presented not only immediately before the target (i.e., the prime) but also a second time after the target response. This should encourage participants to ignore the prime. In Experiment 2, participants were asked to respond to the targets within 600 ms after target onset. As a result, participants had little opportunity to process the motivational prime valence in a consciously intentional way. Nevertheless, strong affective priming effects were found in both studies. These results provide additional support for the claim that motivational valence can be processed without the conscious intention to do so.
Loss of Bim Allows Precursor B Cell Survival But Not Precursor B Cell Differentiation in the Absence of Interleukin 7
Authors: Oliver Paula M. , Wang Michael , Zhu Yanan , White Janice , Kappler John , Marrack Philippa
Published: November 2004

Interleukin (IL)-7 is a stromal cell–derived cytokine required for the survival, proliferation, and differentiation of B cell precursors. Members of the Bcl-2 family of proteins are known to have profound effects on lymphocyte survival, but not lymphocyte differentiation. To distinguish the relative dependence on IL-7 of B cell precursor survival versus B cell differentiation, the combined effects of lack of IL-7 and lack of the proapoptotic Bcl-2 relative, Bim, were studied. Bim is expressed to varying degrees in all B cell precursors and B cells. Lack of Bim compensated for lack of IL-7 in the survival of pro–, pre–, and immature B cells; however, lack of Bim did not substitute for the requirement for IL-7 in B cell precursor differentiation or B cell precursor proliferation. Precursor B cell survival is more dependent on sufficient levels of IL-7 than precursor B cell differentiation because the number of B cells and their precursors were reduced by half in mice heterozygous for IL-7 expression, but were restored to normal numbers in mice also lacking Bim. Hence, Bim and IL-7 work together to control the survival of B cell precursors and the number of B cells that exist in animals.
Evidence for the Involvement of VAR2CSA in Pregnancy-associated Malaria
Authors: Salanti Ali , Dahlbäck Madeleine , Turner Louise , Nielsen Morten A. , Barfod Lea , Magistrado Pamela , Jensen Anja T.R. , Lavstsen Thomas , Ofori Michael F. , Marsh Kevin , Hviid Lars , Theander Thor G.
Published: November 2004

In Plasmodium falciparum–endemic areas, pregnancy-associated malaria (PAM) is an important health problem. The condition is precipitated by accumulation of parasite-infected erythrocytes (IEs) in the placenta, and this process is mediated by parasite-encoded variant surface antigens (VSA) binding to chondroitin sulfate A (CSA). Parasites causing PAM express unique VSA types, VSAPAM, which can be serologically classified as sex specific and parity dependent. It is sex specific because men from malaria-endemic areas do not develop VSAPAM antibodies; it is parity dependent because women acquire anti-VSAPAM immunoglobulin (Ig) G as a function of parity. Previously, it was shown that transcription of var2csa is up-regulated in placental parasites and parasites selected for CSA binding. Here, we show the following: (a) that VAR2CSA is expressed on the surface of CSA-selected IEs; (b) that VAR2CSA is recognized by endemic plasma in a sex-specific and parity-dependent manner; (c) that high anti-VAR2CSA IgG levels can be found in pregnant women from both West and East Africa; and (d) that women with high plasma levels of anti-VAR2CSA IgG give birth to markedly heavier babies and have a much lower risk of delivering low birth weight children than women with low levels.
Single‐chain antibodies for the conformation‐specific blockade of activated platelet integrin αIIbβ3 designed by subtractive selection from naïve human phage libraries
Authors: Schwarz Meike , Röttgen Peter , Takada Yoshiazuku , Gall Fabrice Le , Knackmuss Stefan , Bassler Nicole , Büttner Claudia , Little Melvyn , Bode Christoph , Peter Karlheinz
Published: November 2004

Binding of fibrinogen to platelet integrin αIIbβ3 mediates platelet aggregation, and thus inhibition of αIIbβ3 represents a powerful therapeutic strategy in cardiovascular medicine. However, the currently used inhibitors of αIIbβ3 demonstrate several adverse effects like thrombocytopenia and bleeding, which are associated with their property to bind to non‐activated αIIbβ3. To circumvent these problems, we designed blocking single‐chain antibody‐fragments (scFv) that bind to αIIbβ3 exclusively in its activated conformation. Two naïve phage libraries were created: a natural phage library, based on human lymphocyte cDNA, and a synthetic library, with randomized VHCDR3. We performed serial rounds of subtractive panning with depletion on non‐activated and selection on activated αIIbβ3, which were provided on resting and ADP‐stimulated platelets and CHO cells, expressing wild‐type or mutated and thereby activated αIIbβ3. In contrast to isolated, immobilized targets, as generally used for phage display, this unique cell‐based approach for panning allowed the preservation of functional integrin conformation. Thereby, we obtained several scFv‐clones that demonstrated exclusive binding to activated platelets and complete inhibition of fibrinogen binding and platelet aggregation. Interestingly, all activation‐specific clones contained an RXD pattern in the HCDR3. Binding studies on transiently expressed point mutants and mouse‐human domain‐switch mutants of αIIbβ3 indicate a binding site similar to fibrinogen. In conclusion, we generated human activation‐specific scFvs against αIIbβ3, which bind selectively to activated αIIbβ3 and thereby potently inhibit fibrinogen binding to αIIbβ3 and platelet aggregation.