bluuebunny/crossref_metadata_2025 huggingface dataset:
Photomixing and photoconductor measurements on ErAs/InGaAs at 1.55 μm
Authors: Sukhotin M. , Brown E. R. , Gossard A. C. , Driscoll D. , Hanson M. , Maker P. , Muller R.
Published: May 2003

We report here the fabrication and demonstration of the photomixers made from In0.53Ga0.47As epitaxial material lattice-matched to InP. The material consists of layers of ErAs nanoparticles separated by InGaAs and compensated with Be to reduce the photocarrier lifetime to picosecond levels and to increase the resistivity to ∼100 Ω cm. Interdigitated-electrode and planar-antenna structures were fabricated by e-beam lithography and tested for dc electrical characteristics, 1.55-μm optical responsivity, and difference-frequency photomixing. The measured responsivity of 8 mA/W and photomixer output of >0.1 μW beyond 100 GHz are already comparable to GaAs photomixers and suggest that coherent THz generation is now feasible using the abundant 1.55-μm-semiconductor-laser and optical-fiber technologies.
A coil combination for magnetic resonance perfusion imaging of mice in vivo at 7 T
Authors: Streif Jörg U. G. , Lanz Titus , Griswold Mark , Rommel Eberhard , Haase Axel
Published: May 2003

A radio frequency (rf) coil combination of a birdcage resonator and a receive-only surface coil was developed for in vivo magnetic resonance imaging of mice at 7.0 T. Since this coil was designed for spin labeling perfusion measurements, the length of the birdcage resonator needed to be 110 mm at a diameter of 35 mm. This was challenging since this length extended 1/10 of the wavelength at the spectrometer Larmor frequency of 300.3 MHz. Symmetric drive with homogeneous B1 field was achieved by introduction of a new rf coupling scheme using an additional conductor path ring at zero potential. This design allowed a balanced drive of the coil without the use of an additional balun. The receive-only surface coil was realized as a single loop with a diameter of 24 mm. To avoid coupling between the coils, active decoupling using p-i-n diode switches was integrated. These switches showed good characteristics and the coil combination was not sensitive to effects such as contrast alterations, rf shielding of the transmit pulse by the receive coil, and possible receive coil destruction during transmission. The improved performance of the coil combination with respect to a stand-alone surface coil or a stand-alone birdcage resonator was demonstrated in phantoms and mice. In comparison with a stand-alone suface coil, the coil combination provided more uniform contrast behavior and an extended depth of view. In addition, the combination showed an improved signal-to-noise ratio with respect to a stand-alone birdcage resonator.
On the significance of the period fitting method
Authors: Shao C. G. , Luan E. J. , Luo J.
Published: May 2003

We analyze the influence of the higher order harmonic oscillations, the drift, and the nonharmonic 1/f noise of the torsion pendulum on the period fitting method, and find that the period of the torsion pendulum determined by this method is not only independent of the higher order harmonic oscillations, but also insensitive to the drift and the low frequency part of nonharmonic 1/f noise.
Accurate frequency measurement of a submillimeter wave gyrotron output using a far-infrared laser as a reference
Authors: Idehara T. , Mitsudo S. , Saito S. , Ogawa I. , Okajima S.
Published: May 2003

Accurate measurement of gyrotron frequency has been carried out by using a far-infrared (FIR) molecular laser as a reference. Highly stable operation of a FIR laser enables us to make the resolution of frequency measurement so precisely that both the frequency width Δf and the frequency fluctuation level δf can be studied within the accuracy of 1 kHz or less. When our submillimeter wave gyrotron operates in cw mode, the observed frequency width Δf is around 2 kHz and the fluctuation level δf 10 kHz. Such an accurate measurement is a useful tool for development of high quality gyrotrons with stable frequency.
Multichannel detector–collimator for powder diffraction measurements at energy scanning x-ray absorption spectroscopy synchrotron radiation beamlines for high-pressure and high-temperature applications
Authors: Filipponi Adriano , Giordano Valentina M. , De Panfilis Simone , Di Cicco Andrea , Principi Emiliano , Trapananti Angela , Borowski Michael , Itiè Jean-Paul
Published: May 2003

We describe a modular detector system suitable to intercept the diffracted x-ray radiation (Debye–Scherrer rings) in a transmission geometry setup at monochromatic tunable synchrotron radiation beamlines. The detector consists of several independent channels composed of a motorized front slit and a rear detector slit system which can be mounted in either a vertical or a horizontal configuration. The detectors are placed at fixed scattering angles 2θ and the diffraction scan is performed by tuning the monochromator energy. The availability of a multidetector system allows one to cover a wide range of scattering vectors with limited range energy scans. The photon sensitive elements are based on CdZnTe solid state detectors which are used at ambient temperature for high efficiency photon counting in the 10–60 keV range. In alternative, conventional NaI(Tl) scintillation detectors can be integrated in the setup. The system can be mounted in a high-resolution configuration and typical widths in the range ΔE/E≃10−3 have been obtained for Bragg peaks. In these conditions the sensitivity to changes in the lattice spacing is better than 10−4. This detector system fully complements the experimental devices usually available at x-ray absorption spectroscopy beamlines and the short range structural information obtained using the x-ray absorption fine structure technique. Typical applications include high-pressure and high-temperature investigations of condensed matter.
The high-flux backscattering spectrometer at the NIST Center for Neutron Research
Authors: Meyer A. , Dimeo R. M. , Gehring P. M. , Neumann D. A.
Published: May 2003

We describe the design and current performance of the high-flux backscattering spectrometer located at the NIST Center for Neutron Research. The design incorporates several state-of-the-art neutron optical devices to achieve the highest flux on sample possible while maintaining an energy resolution of less than 1 μeV. Foremost among these is a novel phase-space transformation chopper that significantly reduces the mismatch between the beam divergences of the primary and secondary parts of the instrument. This resolves a long-standing problem of backscattering spectrometers, and produces a relative gain in neutron flux of 4.2. A high-speed Doppler-driven monochromator system has been built that is capable of achieving energy transfers of up to ±50 μeV, thereby extending the dynamic range of this type of spectrometer by more than a factor of 2 over that of other reactor-based backscattering instruments.
Improved planar radio frequency inductively coupled plasma configuration in plasma immersion ion implantation
Authors: Tang D. L. , Fu R. K. Y. , Tian X. B. , Chu P. K.
Published: May 2003

Plasmas with higher density and better uniformity are produced using an improved planar radio frequency (rf) inductively coupled plasma configuration in plasma immersion ion implantation (PIII). An axial magnetic field is produced by external electromagnetic coils outside the discharge chamber. The rf power can be effectively absorbed by the plasma in the vicinity of the electron gyrofrequency due to the enhanced resonant absorption of electromagnetic waves in the whistler wave range, which can propagate nearly along the magnetic field lines thus greatly increases the plasma density. The plasma is confined by a longitudinal multipolar cusp magnetic field made of permanent magnets outside the process chamber. It can improve the plasma uniformity without significantly affecting the ion density. The plasma density can be increased from 3×109 to 1×1010 cm−3 employing an axial magnetic field of several Gauss at 1000 W rf power and 5×10−4 Torr gas pressure. The nonuniformity of the plasma density is less than 10% and can be achieved in a process chamber with a diameter of 600 mm. Since the plasma generation and process chambers are separate, plasma extinction due to the plasma sheath touching the chamber wall in high-energy PIII can be avoided. Hence, low-pressure, high-energy, and high-uniformity ion implantation can be accomplished using this setup.
Revised characterization of the controlled clearance piston gauge
Authors: Newhall D. H. , Newhall W. C. , Malloy B. T.
Published: May 2003

A revised equation is presented for the effective piston area of controlled clearance deadweight testers from the theory of elasticity which accounts for the semi-infinite loading of the measured pressure cylinder. The concept of pressure transmissibility expressed in terms of transmission delay threshold pressure and the importance in the choice of operating fluids is discussed. Test results illustrating pressure transmissibility for 25 different fluids at pressure between 138 MPa (20 000 psi) and 1380 MPa (200 000 psi) are presented, together with proposed ranking of the fluids based on their relative pressure transmissibility. The linear nature of the stall curve with fluids of high transmissibility and the resulting linear nature of the adjustments to the effective area are shown. The linearity allows the use of considerable extrapolation for making reasonable estimates of effective area, where direct knowledge of the slope of the stall curve is not known. The robustness of the new equation is demonstrated by applying the equation to data from two mercury point experiments at Harwood (9 years apart), several National Institute of Standards and Technology (NIST) characterizations of controlled clearance gauges, some other experiments at Harwood, and the data from NIST’s experiment using a controlled clearance piston gauge to isolate the transition pressure of bismuth from Bi I to Bi II. The conclusions reached indicate that with suitable operating fluids, there is a negligibly small difference between pressure values calculated from the method discussed here and that used by NIST based on experimental determination of the jacket pressure coefficient.
Development of a five-band multi-spectral infrared radiometer for low temperature measurements
Authors: Minato Hideyuki , Ishido Yoshinari
Published: May 2003

A five-band infrared radiometer has been developed for the measurement of spectral radiance and radiance temperature at low temperatures. The optical system of this radiometer consists of a scanning plane reflecting mirror, five narrow-band interference filters in the 6–12 μm band, a mirror-type rotating chopper, a cold source, a hot source, and a HgCdTe semiconductor detector. Measurement of radiance temperature and spectral radiance using this radiometer is carried out automatically using a personal computer. The calibration of the output signal for each spectral channel of the radiometer is carried out exactly using a blackbody source with an accurate temperature controller. The short-time stability of the radiometer is estimated to be within 0.2% mean deviation for the main spectral channel. The temperature detection sensitivity of a radiometer is evaluated as the noise equivalent temperature difference (NETD) for the optical and measuring system; the NETD for the main spectral channel is estimated to be about <0.2 °C. The minimum detectable radiance for the main spectral channel is also estimated to be about <0.002 mW/cm2 sr μm. For confirmation of the long-time stability of the radiometer, the measurement of the radiometer output ratio between the blackbody source at a temperature of 15 °C and the hot source at a constant temperature of 40 °C is carried out over 3 h; the long-time stability of measurement for the main spectral channel is estimated to be within ±0.3 °C mean deviation. The variation over time of the spectral radiance and the radiance temperature of the cloud in the sky was actually measured using the radiometer, and its usefulness was clarified.
Two-color photoionization spectroscopy using vacuum ultraviolet synchrotron radiation and infrared optical parametric oscillator laser
Authors: Qian Ximei , Zhang Tao , Ng C. Y. , Kung A. H. , Ahmed Musa
Published: May 2003

A two-color, vacuum ultraviolet (VUV)-infrared (IR), photoionization study using monochromatized undulator VUV synchrotron radiation and high-repetition rate IR optical parametric oscillator (OPO) laser source has been demonstrated at the Chemical Dynamics Beamline of the Advanced Light Source. The OPO setup, optical alignment, and ion detection arrangement are described. The VUV-IR ionization spectrum of Ar has been recorded in the energy region between the ionization thresholds for Ar+(2P3/2) and Ar+(2P1/2) to illustrate the feasibility and efficacy of this scheme as a general approach for high-resolution two-color photoionization studies. The autoionization resonances of the Ar(np′ and nf′) Rydberg series are resolved up to the principal quantum number of n=57, showing that the optical resolution of 0.3 cm−1 (full width at half maximum) achieved in this two-color photoionization study is mostly limited by the bandwidth of the IR OPO laser and the Doppler width due to the random motion of the Ar sample.
Dependence of morphology on miscut angle for Si(111) etched in NH4F
Authors: Fu Joseph , Zhou Hui , Kramar John , Silver Richard , Gonda Satoshi
Published: May 2003

Hydrogen-terminated silicon surfaces are important and commonly used in several nanotechnology applications. A significant obstacle to their widespread use has been the repeatable preparation of large, flat surfaces. Using scanning probe microscopy, we have examined the surfaces of several vicinal Si(111) samples, with miscut angles ranging from 1.1° to 0.01°, produced by etching in a NH4F aqueous solution. Although the miscut angle sets the nominal terrace width, we have found that with wet chemical etch processing, as the vicinal angle decreases, the terrace width increases only to a maximum of ∼200 nm, limited by the etching anisotropy. The result is that for miscut angles below a critical angle, the surface roughness actually increases.
Polarized Raman scattering of impurity modes in beryllium-doped cubic boron nitride single crystals
Authors: Watanabe Kenji , Taniguchi Takashi , Kanda Hisao , Shishonok Elena M.
Published: May 2003

Impurity-induced modes at 212 and 535 cm−1 have been studied by using Raman scattering spectroscopy in Be-doped cubic boron nitride single crystals, which have been grown by the temperature-gradient method under high pressure. Those bands show prominent polarization properties of T2 and A1 modes for the 212 and 535 cm−1 bands, respectively. Based on the polarization properties and a simple calculation of a molecular model, the origin of the bands is explained by postulating resonance modes of substitutional Be with a weak force constant between the host atoms and the Be. Anomalies of a forbidden transverse optical mode and the T2 mode due to phonon–plasma coupling caused by photoexcited free carriers have been also observed in high excitation density.
Full-relativistic calculations of the SrTiO3 carrier effective masses and complex dielectric function
Authors: Marques M. , Teles L. K. , Anjos V. , Scolfaro L. M. R. , Leite J. R. , Freire V. N. , Farias G. A. , da Silva E. F.
Published: May 2003

We perform fully relativistic band-structure calculations for cubic SrTiO3, which are used to obtain carrier effective masses and the frequency behavior of its complex dielectric function ε(ω). The obtained values and anisotropy of the carrier effective masses are shown to be highly influenced by the relativistic contributions. In order to evaluate the static dielectric constant, the low-frequency behavior of ε(ω) is obtained by taking into account also the optical phonon contributions to the imaginary part of ε(ω), adopting a simplified classical oscillator dispersion model. It is found that the phonon contribution leads to about 240 times (at T=85 K) the value of the bare electronic contribution to the dielectric constant. The calculated temperature dependence of the dielectric constant is shown to be consistent with that observed in bulk SrTiO3 static permittivity measurements.
Rubbing-induced polar ordering in nylon-11
Authors: Hong Seok-Cheol , Zhang Chun , Shen Y. R.
Published: May 2003

Sum-frequency vibrational spectroscopy was used to show that mechanical rubbing could induce domains of ferroelectric ordering in films of odd-numbered nylon. In each domain, the dipole groups of NH and CO were aligned perpendicular to the rubbing direction and parallel to the surface.
Stacking and translation of microscopic particles by means of 2×2 beams emitted from a vertical-cavity surface-emitting laser array
Authors: Sumiyama Fumika , Ogura Yusuke , Tanida Jun
Published: May 2003

We report on an optical manipulation method to achieve stacking of multiple particles by simultaneous emission of vertical-cavity surface-emitting laser sources. In the experiment, up to seven polystyrene particles of 10-μm diameter were stacked vertically by illuminating 2×2 beams. Furthermore, we could translate the particles keeping the stacked state without mechanical movement. The maximum number of stackable particles was obtained when the focal spots of the beams were located 20 μm above the sample stage. We also found that the relation between the spot pitch and the particle diameter is an important factor to achieve stacking. This manipulation method is expected to be useful for microfabrication of a three-dimensional structure and collective translation of materials capsuled in microparticles.
Spatial inhomogeneity of imprint and switching behavior in ferroelectric capacitors
Authors: Gruverman A. , Rodriguez B. J. , Kingon A. I. , Nemanich R. J. , Cross J. S. , Tsukada M.
Published: May 2003

Piezoresponse force microscopy has been used to perform nanoscale characterization of the spatial variations in the imprint and switching behavior of (111)-oriented Pb(Zr,Ti)O3-based capacitors on Pt electrodes. Mapping of polarization distribution in the poled capacitors as well as local d33–V loop measurements revealed a significant difference in imprint and switching behavior between the peripheral and inner parts of the capacitors. It has been found that the inner regions of the capacitors are negatively imprinted (with the preferential direction of the normal component of polarization upward) and tend to switch back after application of the positive poling voltage. On the other hand, switchable regions at the edge of the integrated capacitors generally exhibit more symmetric hysteresis behavior. Application of an ac switching voltage, contrary to what was expected, resulted in an increase of the negatively imprinted regions. The observed effect has been explained by incomplete or asymmetric switching due to the mechanical stress conditions existing in the central parts of the capacitors.
Quantum dot amplifiers with high output power and low noise
Authors: Berg Tommy W. , Mørk Jesper
Published: May 2003

Quantum dot semiconductor optical amplifiers have been theoretically investigated and are predicted to achieve high saturated output power, large gain, and low noise figure. We discuss the device dynamics and, in particular, show that the presence of highly inverted barrier states does not limit the performance of these devices.
Nanostructure and magnetic properties of BN-encapsulated Fe(B) and Fe2N nanoparticles prepared by dual ion-beam sputtering
Authors: Babonneau D. , Jaouen M. , Denanot M.-F. , Guérin P. , Petroff F.
Published: May 2003

BN–Fe nanocomposite films have been produced by dual ion-beam sputtering codeposition. The effect of using a reactive nitrogen assistance beam during the elaboration process has been studied by transmission electron microscopy, selected area electron diffraction, grazing incidence small-angle x-ray scattering, and magnetic measurements. Experimental results show that without assistance, we produce nearly spherical Fe(B) nanoparticles (2–3 nm in diameter) exhibiting a superparamagnetic behavior. When growing under assistance, we obtain vertically elongated nanoparticles of paramagnetic ζ-Fe2N encapsulated in disordered hexagonal BN. This study demonstrates the possibility of producing encapsulated nanoparticles with high shape anisotropy by activating the surface diffusion of the incoming deposited species.
Narrow-band polarized light emission from organic microcavity fabricated by sol-gel technique
Authors: Song Qinghai , Liu Liying , Ling Tao , Xu Lei , Wang Wencheng
Published: May 2003

We report the fabrication and optical properties of an organic light-emitting microcavity. The cavity is a laser dye-doped polycarbonate film sandwiched between two Bragg reflectors, fabricated by alternately depositing TiO2 and SiO2 sol-gel thin films. Reflectivity up to 98% was achieved using the Bragg reflectors. The cavity has a photonic band gap between 597 and 789 nm with a defect state inside the gap. Narrow-band optical pumped light emission from the cavity and its polarization dependence were observed. A cavity quality factor as high as 354 was achieved. Angular and polarization dependence of light emission were analyzed using the transfer matrix method. All experimental results agree well with theoretical calculations.
A stabilizer for superconducting quantum interference device gradiometers for operation in lightly shielded environments
Authors: Yokosawa Koichi , Kandori Akihiko , Miyashita Tsuyoshi , Suzuki Daisuke , Tsukada Keiji , Tsukamoto Akira
Published: May 2003

A stabilizer for superconducting quantum interference device (SQUID) magnetometers operating in lightly shielded environments is proposed. When the stabilizer is applied in an electrical gradiometer, which operates by obtaining differences between the outputs of the two SQUID magnetometers, the intrinsic noise of the stabilizer can be neglected. The operation of an electrical gradiometer where the SQUID magnetometers are of the high-critical-temperature (high-Tc) type is shown to be substantially more stable in a lightly magnetically shielding cylinder with the addition of the stabilizer function. Very clear magnetocardiograms were obtained by a gradiometer of this type.
Surface-scattering effects in polycrystalline silicon thin-film transistors
Authors: Valletta A. , Mariucci L. , Fortunato G. , Brotherton S. D.
Published: May 2003

Mobility reduction, induced at high gate fields by scattering with surface acoustic phonons and surface roughness, has been investigated in self-aligned polycrystalline silicon (polysilicon) thin-film transistors (TFTs). The analysis of this effect can be influenced by the presence of parasitic resistance effects, and a precise evaluation of this effect has been obtained by measuring the transfer characteristics in devices with different channel lengths. In this way, we could reliably determine the mobility reduction effect, which was then analyzed by using two-dimensional numerical simulations. The mobility reduction in polysilicon TFTs can be accurately described by Lombardi’s model, originally proposed for c-Si metal-oxide-semiconductor field-effect transistors.
Demonstration of a nanophotonic switching operation by optical near-field energy transfer
Authors: Kawazoe Tadashi , Kobayashi Kiyoshi , Sangu Suguru , Ohtsu Motoichi
Published: May 2003

We have demonstrated the operation of a nanophotonic switch that uses three CuCl quantum cubes with a size ratio of 1:√:2. The switching mechanism is based on resonant optical near-field energy transfer between the resonant quantized excitonic energy levels of the quantum cubes. Using near-field optical spectroscopy, we observed a switching rise time of less than 100 ps and a repetition rate of 80 MHz. These results suggest the possibility of making a nanophotonic switching device smaller than 20 nm with a figure of merit 10–100 times higher than that of a conventional photonic switch.
Optimized surface-enhanced Raman scattering on gold nanoparticle arrays
Authors: Félidj N. , Aubard J. , Lévi G. , Krenn J. R. , Hohenau A. , Schider G. , Leitner A. , Aussenegg F. R.
Published: May 2003

In this letter, we show that tuning the maximum of the surface plasmon resonance of elongated gold nanoparticles to a wavelength, the position of which is precisely midway between the exciting laser line and the Raman line, results in an optimization of the surface-enhanced Raman-scattering effect.
Room-temperature electro-optic up-conversion via internal photoemission
Authors: Russell K. J. , Appelbaum Ian , Temkin H. , Perry C. H. , Narayanamurti V. , Hanson M. P. , Gossard A. C.
Published: May 2003

We describe the fabrication and operation of a device which performs linear optical up-conversion at room temperature. The mechanism for up-conversion is based on internal photoemission from a Schottky contact. We then describe the voltage dependence of this device and interpret it in terms of total energy conservation. Although an AlGaAs/GaAs system is employed here, the functionality is not material-specific and therefore should be widely applicable to different materials systems, such as GaN/InGaN.
Influence of interfacial nitrogen on edge charge trapping at the interface of gate oxide/drain extension in metal–oxide–semiconductor transistors
Authors: Chen T. P. , Huang J. Y. , Tse M. S. , Tan S. S. , Ang C. H. , Fung S.
Published: May 2003

In this work, the edge charge trapping at the interface of gate oxide/drain extension caused by Fowler–Nordheim injection is determined quantitatively by using a simple approach to analyze the change of the drain band-to-band tunneling current. For both pure and nitrided oxides with an oxide thickness of 6.5 nm, positive edge charge trapping is observed while the net charge trapping in the oxide above the channel is negative. It is found that the nitrogen at the interface can enhance the edge charge trapping. The results could be explained in terms of the creation of positive fixed oxide charges at the interface as a result of the electrochemical reactions involving holes and hydrogen ions.
Time evolution of depletion region in poled silica
Authors: Triques A. L. C. , Carvalho I. C. S. , Moreira M. F. , Carvalho H. R. , Fischer R. , Lesche B. , Margulis W.
Published: May 2003

The electric field recorded in silica samples thermally poled during various intervals was measured by etching. The field is nearly uniform and increases to a maximum (∼3.6×108 V/m) in few minutes of poling and subsequently decreases slowly toward a steady level (∼1.4×108 V/m). The depletion layer becomes neutral even before the field reaches steady state. An upper limit of (0.7±0.2) μm was found for the thickness of the negatively charged edge of the depletion region. The value of χ(3) is the same for all poling times.
Growth and physical properties of Ga2O3 thin films on GaAs(001) substrate by molecular-beam epitaxy
Authors: Yu Z. , Overgaard C. D. , Droopad R. , Passlack M. , Abrokwah J. K.
Published: May 2003

We report effusive evaporation of Ga2O3 thin films on GaAs(001) substrates in a production-type molecular-beam epitaxy system. A polycrystalline Ga2O3 charge heated in a high-temperature effusion cell is used as the evaporation source. The Ga2O3–GaAs structures are characterized by atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), ellipsometry, and transmission electron microscopy (TEM). The Ga2O3 films are amorphous and stoichiometric by transmission electron diffraction and RBS, respectively. Under optimal growth conditions, the Ga2O3 film surface has a typical roughness of 2–3 Å as revealed by AFM, while the Ga2O3–GaAs interface is atomically abrupt as confirmed by the cross-sectional TEM. Such amorphous and stoichiometric Ga2O3 oxide paves the way for GaAs gate dielectrics applications.
Measuring electrical current during scanning probe oxidation
Authors: Pérez-Murano F. , Martı́n C. , Barniol N. , Kuramochi H. , Yokoyama H. , Dagata J. A.
Published: May 2003

Electrical current is measured during scanning probe oxidation by performing force versus distance curves under the application of a positive sample voltage. It is shown how the time dependence of the current provides information about the kinetics of oxide growth under conditions in which the tip–surface distance is known unequivocally during current acquisition. Current measurements at finite tip–sample distance, in particular, unveil how the geometry of the meniscus influences its electrical conduction properties as well as the role of space charge at very small tip–sample distances.
CuAu-I-type ordered structures in InxAl1−xAs epilayers grown on (001) InP substrates
Authors: Lee Ho Seong , Lee Jeong Yong
Published: May 2003

Transmission electron microscopy (TEM) measurements were carried out to investigate the spontaneously ordered structure in InxAl1−xAs epitaxial layers grown on (001) InP substrates. The selected area diffraction pattern showed two sets of superstructure reflections with symmetrical intensity at (100) and (010) positions, indicating that CuAu-I-type ordered structures with two different variants were formed in the InxAl1−xAs epitaxial layers. The dark-field TEM image showed that the size of the CuAu-I-type ordered domains with a needle-like shape was approximately 3∼4 nm thick, with lengths ranging from 10 to 20 nm. Based on the TEM results, explanations are given to describe the formation of only two variants of CuAu-I-type ordering.
Boundary migration in Zn bicrystal induced by a high magnetic field
Authors: Sheikh-Ali A. D. , Molodov D. A. , Garmestani H.
Published: May 2003

A bicrystal of Zn with an originally flat 89° 〈101̄0〉 symmetric tilt boundary was annealed in a magnetic field of 25 T. The boundary migrated under the action of a magnetic driving force in the direction of the grain with higher diamagnetic susceptibility. In addition, the boundary changed its crystallographic orientation, decreasing length and becoming almost perpendicular to the free surfaces. The results were interpreted in terms of magnetically forced grain boundary motion due to the anisotropy of the magnetic susceptibility in Zn. The absolute boundary mobility was measured to be about 5.1×10−9 m4/J s.
Atoms on demand: Fast, deterministic production of single Cr atoms
Authors: Hill S. B. , McClelland J. J.
Published: May 2003

We have realized a method for producing single Cr atoms on demand by suppressing the stochastic nature of the loading and loss processes of a magneto-optic trap. We observe single-atom trap occupation probabilities as high as (98.7±0.1)% and demonstrate ejection with greater than 90% efficiency at rates up to 10 Hz. Monte Carlo simulations agree well with extraction measurements and are used to predict ultimate performance. Such a deterministic atom source has potential applications in nanotechnology, quantum information processing, and fundamental quantum investigations.
Temperature dependence of resonant Raman scattering in double-wall carbon nanotubes
Authors: Ci Lijie , Zhou Zhenping , Song Li , Yan Xiaoqin , Liu Dongfang , Yuan Huajun , Gao Yan , Wang Jianxiong , Liu Lifeng , Zhou Weiya , Wang Gang , Xie Sishen
Published: May 2003

The temperature-dependent frequency shift of resonant Raman spectra of double-wall carbon nanotubes is investigated in the range of 78–650 K. We show here that different radial breathing mode (RBM) peaks, which are relative to different tube diameters, have a different temperature coefficient of frequency shift, and the larger diameter carbon nanotubes have more RBM frequency downshift with increasing temperature. We attribute the RBM frequency variation to the temperature dependence of the stretching force constant of C–C bond.
Transport properties of LaTiO3+x films and heterostructures
Authors: Schmehl A. , Lichtenberg F. , Bielefeldt H. , Mannhart J. , Schlom D. G.
Published: May 2003

We report on the transport properties of LaTiO3+ε and LaTiO3.5 films. The LaTiO3+ε samples show metallic transport and several samples exhibit a hysteretic drop of resistance during cooldown at ∼240 K. The ferroelectric LaTiO3.5 samples, grown in capacitor structures, have nonlinear, diode-like and hysteretic V(I) characteristics. Two charge-controlled transport regimes are found, which can be utilized for switching the devices between two voltage states.
Selective oxidation behavior of W/WN/polycrystalline-Si1−xGex gate structure in H2O+H2 ambient
Authors: Ahn Tae-Hang , Yeo In-Seok , Kim Joong-Jung , Roh Jae-Sung , Lee Jung-Ho
Published: May 2003

Selective oxidation behavior, i.e., oxidation of polycrystalline-Si1−xGex (poly-SiGe) without metal oxidation, of the W/WN/poly-SiGe structure was investigated for gate electrode applications. While the dry oxidized samples showed a dramatic increase of the oxidation rate with increasing Ge content, the oxidation rate in the selectively oxidized (in a H2O+H2 ambient) samples was found to be very low irrespective of the Ge content. The oxides grown in a H2O+H2 ambient are identified to be only SiO2 even up to 60% Ge, other than the dry oxidized samples that consist of nearly pure SiO2 underneath a mixed oxide alloy of (Si,Ge)Ox. Different oxidation mechanisms based on the competition between the oxidation rate and the Ge diffusion rate in Si are suggested to explain a remarkable difference in the oxide thickess and composition. For dependable applications of poly-SiGe in metal-shunted gate structures, this oxidation feature enables a very clean sidewall profile with an improved reliability of gate oxides after selective oxidation process.
Dry-etching method for fabricating photonic-crystal waveguides in nonlinear-optical polymers
Authors: Inoue Shin-ichiro , Kajikawa Kotaro , Aoyagi Yoshinobu
Published: May 2003

Nonlinear optical (NLO) polymer is proposed as one of the best candidates for nonlinear photonic crystal (PC) waveguides. A dry etching technique for this material is established at the suboptical wavelength scale needed to fabricate NLO polymer PC waveguides, with the good processability achieved in this material demonstrated by the successful fabrication of a PC waveguide in NLO polymer. Sharp resonances originating from coupling to photonic band modes are observed in the optical reflectance spectra of this waveguide, with resonant frequencies found to depend on the angle and in-plane propagation lattice direction of incident light.
Nanometer-scale switches using copper sulfide
Authors: Sakamoto T. , Sunamura H. , Kawaura H. , Hasegawa T. , Nakayama T. , Aono M.
Published: May 2003

We describe a nanometer-scale switch that uses a copper sulfide film and demonstrate its performance. The switch consists of a copper sulfide film, which is a chalcogenide semiconductor, sandwiched between copper and metal electrodes. Applying a positive or negative voltage to the metal electrode can repeatedly switch its conductance in under 100 μs. Each state can persist without a power supply for months, demonstrating the feasibility of nonvolatile memory with its nanometer scale. While biasing voltages, copper ions can migrate in copper sulfide film and can play an important role in switching.
Single spatial mode selection in a layered square microcavity laser
Authors: Moon Hee-Jong , An Kyungwon , Lee Jai-Hyung
Published: May 2003

We propose a scheme for mode selection in a square-shaped two-dimensional layered microcavity laser. By using a fused-silica square-shaped capillary containing a dye-doped liquid as a layered microcavity, whose refractive index was smaller than that of the fused silica, we could realize our idea for single spatial-mode lasing. By analyzing the amount of peak shift induced by varying the refractive index of inner liquid, we could confirm that the lasing modes originate by the free-running trajectories that are constrained on the outer layer by the presence of the inner boundary in such a way that only the ray having a refraction angle of 45° in the inner gain layer could be selected.
Anisotropy, damping, and coherence of magnetization dynamics in a 10 μm square Ni81Fe19 element
Authors: Barman A. , Kruglyak V. V. , Hicken R. J. , Kundrotaite A. , Rahman M.
Published: May 2003

We have studied magnetization precession in a square Ni81Fe19 element, of 10 μm width, by time-resolved scanning Kerr effect microscopy. From the frequency of precession, we deduce a fourfold in-plane anisotropy of about 30 Oe at the center of the square. Larger damping of the precession was observed at the center of the element when the static field was applied parallel to a diagonal rather than to an edge of the square. Dynamic images show that the apparent increase in damping is associated with nonuniformity of the dynamic magnetization that is associated with the sample shape.
Only one catalase, katG, is detectable in Rhizobium etli, and is encoded along with the regulator OxyR on a plasmid replicon
Authors: del Carmen Vargas María , Encarnación Sergio , Dávalos Araceli , Reyes-Pérez Agustín , Mora Yolanda , García-de los Santos Alejandro , Brom Susana , Mora Jaime
Published: May 2003

The plasmid-borneRhizobium etlikatGgene encodes a dual-function catalase-peroxidase (KatG) (EC 1.11.1.7) that is inducible and heat-labile. In contrast to other rhizobia,katGwas shown to be solely responsible for catalase and peroxidase activity inR. etli. AnR. etlimutant that did not express catalase activity exhibited increased sensitivity to hydrogen peroxide (H2O2). Pre-exposure to a sublethal concentration of H2O2allowedR. etlito adapt and survive subsequent exposure to higher concentrations of H2O2. Based on a multiple sequence alignment with other catalase-peroxidases, it was found that the catalytic domains of theR. etliKatG protein had three large insertions, two of which were typical of KatG proteins. Like thekatGgene ofEscherichia coli, theR. etlikatGgene was induced by H2O2and was important in sustaining the exponential growth rate. InR. etli, KatG catalase-peroxidase activity is induced eightfold in minimal medium during stationary phase. It was shown that KatG catalase-peroxidase is not essential for nodulation and nitrogen fixation in symbiosis withPhaseolus vulgaris, although bacteroid proteome analysis indicated an alternative compensatory mechanism for the oxidative protection ofR. etliin symbiosis. Next to, and divergently transcribed from the catalase promoter, an ORF encoding the regulator OxyR was found; this is the first plasmid-encodedoxyRgene described so far. Additionally, thekatGpromoter region contained sequence motifs characteristic of OxyR binding sites, suggesting a possible regulatory mechanism forkatGexpression.
n-Hexane sensitivity of Escherichia coli due to low expression of imp/ostA encoding an 87 kDa minor protein associated with the outer membrane
Authors: Abe Shigeo , Okutsu Tomohisa , Nakajima Harushi , Kakuda Nobuto , Ohtsu Iwao , Aono Rikizo
Published: May 2003

MostEscherichia colistrains are resistant to n-hexane.E. coliOST4251 is a n-hexane-sensitive strain that was constructed by transferring the n-hexane-sensitive phenotype from a n-hexane-sensitive strain by P1 transduction. OST4251 is resistant to diphenyl ether, which is less harmful than n-hexane to micro-organisms. The genetic determinant responsible for this subtle difference in the solvent resistance is mapped at 1·2 min on theE. colichromosome. Nucleotide sequence analysis showed that IS2and IS5had integrated upstream of theimp/ostAstructural gene in OST4251. The integration of IS2decreased the activity of theimp/ostApromoter. A product of the gene was identified immunologically as an 87 kDa minor protein associated with the outer membrane. Upon transformation with plasmids containing theimp/ostAgene, OST4251 produced a high level of the gene product in the membrane and acquired n-hexane resistance. Thus, the low level of promoter activity resulted in low Imp production and the n-hexane-sensitivity phenotype. It is likely that the gene product contributes to n-hexane resistance by reducing the influx of n-hexane.
An inducible tellurite-resistance operon in Proteus mirabilis
Authors: Toptchieva Anna , Sisson Gary , Bryden Louis J. , Taylor Diane E. , Hoffman Paul S.
Published: May 2003

Tellurite resistance (Ter) is widespread in nature and it is shown here that the natural resistance of Proteus mirabilis to tellurite is due to a chromosomally located orthologue of plasmid-borne ter genes found in enteric bacteria. The P. mirabilis ter locus (terZABCDE) was identified in a screen of Tn5lacZ-generated mutants of which one contained an insertion in terC. The P. mirabilis terC mutant displayed increased susceptibility to tellurite (Tes) and complementation with terC carried on a multicopy plasmid restored high-level Ter. Primer extension analysis revealed a single transcriptional start site upstream of terZ, but only with RNA harvested from bacteria grown in the presence of tellurite. Northern blotting and reverse transcriptase-PCR (RT-PCR) analyses confirmed that the ter operon was inducible by tellurite and to a lesser extent by oxidative stress inducers such as hydrogen peroxide and methyl viologen (paraquat). Direct and inverted repeat sequences were identified in the ter promoter region as well as motifs upstream of the −35 hexamer that resembled OxyR-binding sequences. Finally, the 390 bp intergenic promoter region located between orf3 and terZ showed no DNA sequence identity with any other published ter sequences, whereas terZABCDE genes exhibited 73–85 % DNA sequence identity. The ter operon was present in all clinical isolates of P. mirabilis and Proteus vulgaris tested and is inferred for Morganella and Providencia spp. based on screening for high level Ter and preliminary PCR analysis. Thus, a chromosomally located inducible tellurite resistance operon appears to be a common feature of the genus Proteus.
An iron-regulated gene required for utilization of aerobactin as an exogenous siderophore in Vibrio parahaemolyticus
Authors: Funahashi Tatsuya , Tanabe Tomotaka , Aso Hiroaki , Nakao Hiroshi , Fujii Yoshio , Okamoto Keinosuke , Narimatsu Shizuo , Yamamoto Shigeo
Published: May 2003

A previous investigation using the Fur titration assay system showed that Vibrio parahaemolyticus possesses a gene encoding a protein homologous to IutA, the outer-membrane receptor for ferric aerobactin in Escherichia coli. In this study, a 5·6 kb DNA region from the V. parahaemolyticus WP1 genome was cloned and two entire genes, iutA and alcD homologues, were identified which are absent from Vibrio cholerae genomic sequences. The V. parahaemolyticus IutA and AlcD proteins share 43 % identity with the Escherichia coli IutA protein and 24 % identity with the Bordetella bronchiseptica AlcD protein of unknown function, respectively. Primer extension analysis revealed that the iutA gene is transcribed in response to low-iron availability from a putative promoter overlapped with a sequence resembling a consensus E. coli Fur-binding sequence. In agreement with the above finding, V. parahaemolyticus effectively utilized exogenously supplied aerobactin for growth under iron-limiting conditions. Moreover, insertional inactivation of iutA impaired growth in the presence of aerobactin and incapacitated the outer-membrane fraction from iron-deficient cells for binding 55Fe-labelled aerobactin. These results indicate that the V. parahaemolyticus
iutA homologue encodes an outer-membrane protein which functions as the receptor for ferric aerobactin. Southern blot analysis revealed that the iutA homologues are widely distributed in clinical and environmental isolates of V. parahaemolyticus. However, additional genes required for ferric aerobactin transport across the inner membrane remain to be clarified.
Fluorescence in situ hybridization (FISH) for direct visualization of bacteria in periapical lesions of asymptomatic root-filled teeth
Authors: Sunde Pia T. , Olsen Ingar , Göbel Ulf B. , Theegarten Dirk , Winter Sascha , Debelian Gilberto J. , Tronstad Leif , Moter Annette
Published: May 2003

Whether micro-organisms can live in periapical endodontic lesions of asymptomatic teeth is under debate. The aim of the present study was to visualize and identify micro-organisms within periapical lesions directly, using fluorescence in situ hybridization (FISH) in combination with epifluorescence and confocal laser scanning microscopy (CLSM). Thirty-nine periapical lesions were surgically removed, fixed, embedded in cold polymerizing resin and sectioned. The probe EUB 338, specific for the domain Bacteria, was used together with a number of species-specific16S rRNA-directed oligonucleotide probes to identify bacteria. To control non-specific binding of EUB 338, probe NON 338 was used. Alternatively, DAPI (4′,6′-diamidino-2-phenylindole) staining was applied to record prokaryotic and eukaryotic DNA in the specimens. Hybridization with NON 338 gave no signals despite background fluorescence of the tissue. The eubacterial probe showed bacteria of different morphotypes in 50 % of the lesions. Rods, spirochaetes and cocci were spread out in areas of the tissue while other parts seemed bacteria-free. Bacteria were also seen to co-aggregate inside the tissue, forming microcolonies. Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythensis and treponemes of phylogenetic Group I were detected with specific probes. In addition, colonies with Streptococcus spp. were seen in some lesions. A number of morphotypes occurred that could not be identified with the specific probes used, indicating the presence of additional bacterial species. CLSM confirmed that bacteria were located in different layers of the tissue. Accordingly, the FISH technique demonstrated mixed consortia of bacteria consisting of rods, spirochaetes and cocci in asymptomatic periapical lesions of root-filled teeth.
Alginate gene expression by Pseudomonas syringae pv. tomato DC3000 in host and non-host plants
Authors: Keith Ronald C. , Keith Lisa M. W. , Hernández-Guzmán Gustavo , Uppalapati Srinivasa R. , Bender Carol L.
Published: May 2003

Pseudomonas syringaeproduces the exopolysaccharide alginate, a copolymer of mannuronic and guluronic acid. Although alginate has been isolated from plants infected byP. syringae, the signals and timing of alginate gene expressionin plantahave not been described. In this study, analgD : : uidAtranscriptional fusion, designated pDCalgDP, was constructed and used to monitor alginate gene expression in host and non-host plants inoculated withP. syringaepv. tomato DC3000. When leaves of susceptible collard plants were spray-inoculated with DC3000(pDCalgDP),algDwas activated within 72 h post-inoculation (p.i.) and was associated with the development of water-soaked lesions. In leaves of the susceptible tomato cv. Rio Grande-PtoS,algDactivity was lower than in collard and was not associated with water-soaking. The expression ofalgDwas also monitored in leaves of tomato cv. Rio Grande-PtoR, which is resistant toP. syringaepv. tomato DC3000. Within 12 h p.i., a microscopic hypersensitive response (micro-HR) was observed in Rio Grande-PtoRleaves spray-inoculated withP. syringaepv. tomato DC3000(pDCalgDP). As the HR progressed, histochemical staining indicated that individual bacterial cells on the surface of resistant tomato leaves were expressingalgD. These results indicate thatalgDis expressed in both susceptible (e.g. collard, tomato) and resistant (Rio Grande-PtoR) host plants. The expression ofalgDin an incompatible host–pathogen interaction was further explored by monitoring transcriptional activity in leaves of tobacco, which is not a host forP. syringaepv. tomato. In tobacco inoculated with DC3000(pDCalgDP), an HR was evident within 12 h p.i., andalgDexpression was evident within 8-12 h p.i. However, when tobacco was inoculated with anhrcCmutant of DC3000, the HR did not occur andalgDexpression was substantially lower. These results suggest that signals that precede the HR may stimulate alginate gene expression inP. syringae. Histochemical staining with nitro blue tetrazolium indicated that the superoxide anion () is a signal foralgDactivationin planta. This study indicates thatalgDis expressed whenP. syringaeattempts to colonize both susceptible and resistant plant hosts.