bluuebunny/crossref_metadata_2025 huggingface dataset:
Coalescence of two magnetic flux ropes via collisional magnetic reconnection
Authors: Furno Ivo , Intrator Thomas P. , Hemsing Erik W. , Hsu Scott C. , Abbate S. , Ricci Paolo , Lapenta Giovanni
Published: May 2005

Quasi-two-dimensional coalescence of two parallel cylindrical flux ropes and the development of three-dimensional merged structures are observed and studied in the reconnection scaling experiment [Furno et al., Rev. Sci. Instrum. 74, 2324 (2003)]. These experiments were conducted in a collisional regime with very strong guide magnetic field (Bguide⪢Breconnection), which can be adjusted independently of plasma density, current density, and temperature. During initial coalescence, a reconnection current sheet forms between the two flux ropes, and the direction of the current is opposite to the flux rope currents. The measured current sheet thickness is larger than the electron skin depth but smaller than the ion skin depth. Furthermore, the thickness does not vary for three different values of the strong external guide field. It is shown that the geometry of the observed current sheet is consistent with the Sweet–Parker model using a parallel Spitzer resistivity. The flux ropes eventually become kink unstable due to increasing current and fast-gated camera images show the development of three-dimensional merged structures.
Experimental study of plasma compression into the sheet in three-dimensional magnetic fields with singular X lines
Authors: Frank Anna G. , Bogdanov Sergey Yu. , Markov Vladimir S. , Ostrovskaya Galya V. , Dreiden Galina V.
Published: May 2005

The formation and evolution of the plasma sheets resulting from the plasma compression in diversified three-dimensional (3D) magnetic configurations with singular X lines are reported on. The research was focused on the correlation between the structure of a plasma sheet and the topology of the initial 3D magnetic configuration, especially on the impact of the guide field aligned with the X line. It has been demonstrated experimentally that plasma compression and formation of extended plasma sheets can take place in configurations with the X lines in the presence of a strong guide field. The electron density distributions in the plasma sheets were found to be rather sensitive to the magnetic field topology. The experiments revealed the effect of progressive decrease of the plasma compression ratio in response to increasing guide field. This effect has two basic manifestations: a decrease of the maximum plasma density and an enlargement of the sheet thickness. Based on the experimental data we advanced a concept that the deterioration of plasma compression into the sheet is due to enhancement of the guide field inside the sheet over its initial value, and due to excitation of additional currents in the plane perpendicular to the singular X line and to the original current in the sheet.
Experimental study of the stabilization of Tollmien–Schlichting waves by finite amplitude streaks
Authors: Fransson Jens H. M. , Brandt Luca , Talamelli Alessandro , Cossu Carlo
Published: May 2005

It has recently been found by using temporal and spatial numerical simulations that steady optimal streaks of moderate amplitude, i.e., sufficiently large but not exceeding the critical amplitude for the inflectional instability, are able to reduce the growth of Tollmien–Schlichting (TS) waves up to their complete suppression. This investigation aims at experimentally verifying this stabilizing effect by generating stable and symmetric, close to sinusoidal, streaks of moderate amplitudes (∼12% of the free-stream velocity) by means of a spanwise array of cylindrical roughness elements. The three-dimensional (3D) streaky base flow is then subjected to a secondary instability generated through a spanwise slot in the plate by means of regulated blowing and suction. In this study the stabilizing role of the streaks on TS waves is unambiguously confirmed and by increasing the height of the roughness elements, thus inducing larger amplitude streaks, we are also able to show that the stabilizing action on the TS waves increases with the streak amplitude. These results are the first to confirm the numerical predictions reported in earlier works. The full cross-stream plane has been measured at different downstream positions allowing a complete evaluation and comparison of the different amplitude measures used in previous experimental works. Furthermore, theoretical impulse response analysis and stability calculations are applied to the present experimental streaky base flow enabling a qualitative comparison of the 3D modulated TS wave distribution.
The influence of magnetic and electronic inhomogeneities on magnetotransmission and magnetoresistance of La0.67Sr0.33MnO3 films
Authors: Sukhorukov Yu. P. , Nosov A. P. , Loshkareva N. N. , Mostovshchikova E. V. , Telegin A. V. , Favre-Nicolin E. , Ranno L.
Published: May 2005

The optical (absorption of light and magnetotransmission of IR radiation), magnetic, and transport properties of the epitaxial La0.67Sr0.33MnO3 films of different thickness grown by laser ablation on the (100) SrTiO3 and LaAlO3 substrates were investigated. The effect of magnetotransmission reaches 6% at the temperature of 350K while magnetoresistance reaches 7.6% at 354K in a magnetic field of 8kOe. The factors, which influence the values of magnetotransmission and magnetoresistance of manganite films, are discussed.
The structure of indium phosphide (001) treated with trimethylantimony in a metalorganic vapor-phase epitaxy reactor
Authors: Sun Y. , Cheng S. F. , Chen G. , Woo R. L. , Hicks R. F.
Published: May 2005

Indium phosphide (001) surfaces were exposed to 0.61-mTorr trimethylantimony in a metalorganic vapor-phase epitaxy reactor. The antimony surface composition increased rapidly with dosage and saturated at 22.0at.% for temperatures between 450 and 600°C. The results indicate that a thin layer of InSb formed on the surface, ∼6.8Å thick. Strain from the lattice mismatch caused faceting in the [110] direction, whereas the formation of Sb dimer bonds relieved the strain in the [−110] direction. As a result, narrow ridges formed that ranged from 4to10nm wide and from 3.0to18.0Å high, depending on the antimony coverage.
Nanostructure formation during ion-assisted growth of GaN by molecular beam epitaxy
Authors: Cui Bentao , Cohen P. I. , Dabiran A. M.
Published: May 2005

Ion-beam-assisted molecular beam epitaxy was used to grow GaN on sapphire by reacting Ga from an effusion cell with ammonia. With the ion beam at low glancing angle and energy between 60–500eV, periodic, nanoscale ripple and dots were observed both with and without growth. By changing the growth parameters, the dimensions could be tuned from 40to800nm. The ripple wavelength was analyzed in terms of continuum models. However, the time constant for pattern formation was several orders of magnitude less than that predicted by linear or nonlinear theories. The mobile adatom concentration was calculated and found to be quantitatively reasonable, increasing with increasing net growth rate. The ripple wavelength was observed to be well developed for nitrogen ion beams, but not with Ar ions within our energy and flux range. Adding growth reduced the measured wavelength rather than increasing it.
Dust-ion-acoustic solitons with transverse perturbation
Authors: Moslem Waleed M. , El-Taibany W. F. , El-Shewy E. K. , El-Shamy E. F.
Published: May 2005

The ionization source model is considered, for the first time, to study the combined effects of trapped electrons, transverse perturbation, ion streaming velocity, and dust charge fluctuations on the propagation of dust-ion-acoustic solitons in dusty plasmas. The solitary waves are investigated through the derivation of the damped modified Kadomtsev–Petviashivili equation using the reductive perturbation method. Conditions for the formation of solitons as well as their properties are clearly explained. The relevance of our investigation to supernovae shells is also discussed.
Formation and disruption of Alfvénic filaments in Hall magnetohydrodynamics
Authors: Dreher J. , Laveder D. , Grauer R. , Passot T. , Sulem P. L.
Published: May 2005

In magnetohydrodynamics with Hall effect (Hall-MHD), weakly nonlinear quasimonochromatic dispersive Alfvén waves propagating along an ambient magnetic field can develop to transverse instabilities leading to the formation of intense magnetic filaments. This phenomenon, described as a transverse collapse within the asymptotic approach provided by the nonlinear Schrödinger equation for the pump envelope, was also reproduced by spectral direct numerical simulations of the Hall-MHD system. We address here the dynamics at longer times, using a finite difference scheme with adaptive mesh refinement to reproduce a strong filamentation regime, supplemented by a shock capturing scheme in the final phase of the simulations. We observe a strong distortion of the early time cylindrical filaments, associated with flattening and twisting of the structures and the transition from nonlinear waves to a hydrodynamic regime, characterized by intense current sheets and a strong acceleration of the plasma. A configuration where the intensity of the magnetic filaments saturates while the velocity field is still growing is also identified in the spectral simulation of a regime with moderate scale separation.
Electronic, elastic, and optical properties of Y2O2S
Authors: Li Sa , Ahuja Rajeev
Published: May 2005

We have calculated the electronic structure, elastic constants, and dielectric function of Y2O2S by means of an accurate first-principles method using the full-potential linear muffin-tin orbital method. The conductivity anisotropy is analyzed using the electronic band structure. A bulk modulus of 125 GPa has been calculated from the elastic constants and the elastic anisotropy is investigated. Our calculated dielectric functions are in good agreement with the data of Itoh and Inabe [Phys. Rev. B 68, 035107 (2003)]. The calculated band gap of 3.0 eV is consistent with the calculation by Mikami and Oshiyama. We believe that the band-gap energy 6.77 eV reported by Itoh and Inabe is overestimated and that the true band gap should be around 4.6 eV. The calculated dielectric constant of 5.3 is comparable to the experimental data of 4.67.
Strong-electric-field eigenvalue asymptotics for the Iwatsuka model
Authors: Shirai Shin-ichi
Published: May 2005

We consider the two-dimensional Schrödinger operator, Hg(b)=−∂2∕∂x2+[(1∕−1)(∂∕∂y)−b(x)]2−gV(x,y), where V is a non-negative scalar potential decaying at infinity like (1+∣x∣+∣y∣)−m, and (0,b(x)) is a magnetic vector potential. Here, b is of the form b(x)=∫0xB(t)dt and the magnetic field B is assumed to be positive, bounded, and monotonically increasing on R (the Iwatsuka model). Following the argument as in Refs. 15, 16, and 17 [Raikov, G. D., Lett. Math. Phys., 21, 41–49 (1991); Raikov, G. D, Commun. Math. Phys., 155, 415–428 (1993); Raikov, G. D. Asymptotic Anal., 16, 87–89 (1998)], we obtain the asymptotics of the number of discrete spectra of Hg(b) crossing a real number λ in the gap of the essential spectrum as the coupling constant g tends to ±∞, respectively.
Spin-cluster effect and lattice-deformation-induced Kondo effect, spin-glass freezing, and strong phonon scattering in La0.7Ca0.3Mn1−xCrxO3
Authors: Wu Bai-Mei , Li Bo , Zhen Wei-Hua , Ausloos M. , Du Ying-Lei , Fagnard J. F. , Vanderbemden Ph.
Published: May 2005

Besides the Kondo effect observed in dilute magnetic alloys, the Cr-doped perovskite manganate compounds La0.7Ca0.3Mn1−xCrxO3 also exhibit Kondo effect and spin-glass freezing in a certain composition range. An extensive investigation for the La0.7Ca0.3Mn1−xCrxO3 (x=0.01, 0.05, 0.10, 0.3, 0.6, and 1.0) system on the magnetization and ac susceptibility, the resistivity and magnetoresistance, as well as the thermal conductivity is done at low temperature. The spin-glass behavior has been confirmed for these compounds with x=0.05, 0.1, and 0.3. For temperatures above Tf (the spin-glass freezing temperature) a Curie–Weiss law is obeyed. The paramagnetic Curie temperature θ is dependent on Cr doping. Below Tf there exists a Kondo minimum in the resistivity. Colossal magnetoresistance has been observed in this system with Cr concentration up to x=0.6. We suppose that the substitution of Mn with Cr dilutes Mn ions and changes the long-range ferromagnetic order of La0.7Ca0.3MnO3. These behaviors demonstrate that short-range ferromagnetic correlation and fluctuation exist among Mn spins far above Tf. Furthermore, these interactions are a precursor of the cooperative freezing at Tf. The “double bumps” feature in the resistivity-temperature curve is observed in compounds with x=0.05 and 0.1. The phonon scattering is enhanced at low temperatures, where the second peak of double bumps comes out. The results indicate that the spin-cluster effect and lattice deformation induce Kondo effect, spin-glass freezing, and strong phonon scattering in mixed perovskite La0.7Ca0.3Mn1−xCrxO3.
Metal-insulator transition temperature enhancement in La0.7Ca0.3MnO3 thin films
Authors: Salvato M. , Vecchione A. , De Santis A. , Bobba F. , Cucolo A. M.
Published: May 2005

The effect of oxygen annealing on the structural and transport properties of La0.7Ca0.3MnO3 thin films deposited on SrTiO3 substrates has been investigated by x-ray diffraction analysis and resistive measurements. The as-grown films are fully tensile strained on the substrates and show a depressed metal-insulator transition temperature Tp=131K. As the oxygen content is increased due to longer annealing times, significantly higher Tp are measured, up to 247 K. Correspondingly, an increase of the out-of-plane lattice parameter is observed while the in-plane lattice constants do not change with respect to the as-grown films, which prevents any interpretation of a Tp dependence on the strain. The large increase in Tp is then interpreted in terms of a combined effect of the Mn4+∕Mn3+ ratio variation, the change in the carrier density in the a-b planes, and the increase in the hydrostatic strain with the oxygen annealing.
Study of interdiffusion in GaInNAs∕GaAs quantum well structure emitting at 1.3μm by eight-band k∙p method
Authors: Dang Y. X. , Fan W. J. , Ng S. T. , Yoon S. F. , Zhang D. H.
Published: May 2005

The interdiffusion effect of GaInNAs∕GaAs single quantum well (QW) has been investigated with the eight-band k∙p method. The as-grown 64-Å Ga0.64In0.36N0.017As0.983∕250-Å GaAs QW is experimentally determined to emit at 1.27μm in the literature. The compositional profile of the QW after interdiffusion is modeled by an error function distribution. Varying the diffusion length, the effects of interdiffusion on the unstrained band gap, in-plain strain, and confinement profiles are studied. The curve of the ground-state transition (C1-HH1) energy dependence on the interdiffusion length is obtained. Our work shows that the interdiffusion effect on the strain can greatly change the confinement profile of the lighthole (LH), which is confined in the GaAs layer, not in the GaInNAs layer. From the transition energy curve, a blueshift of 51 meV is derived. This interdiffusion mechanism can be utilized in the tuning of the laser operation wavelength.
Surface nanostructuring by nano-/femtosecond laser-assisted scanning force microscopy
Authors: Chimmalgi A. , Grigoropoulos C. P. , Komvopoulos K.
Published: May 2005

Surface nanostructuring with lateral resolutions beyond the capabilities of conventional optical lithography techniques was demonstrated in this study. Various nanoscopic surface features, such as grids, craters, and curves, were produced on thin metal and semiconductor films and bulk silicon by using the enhanced electric field underneath a proximity scanning probe tip irradiated with a laser beam. Nanoscale melting and crystallization of amorphous silicon films illustrates the capacity of the present scheme to provide an effective nanolaser source. Numerical simulations yield insight into the spatial distribution of the enhanced field intensity underneath the tip and associated physical phenomena. Calculations of the temperature distribution in the microprobe tip and possible tip expansion show that the main reason for the highly localized nanostructuring achieved with this technique is the enhancement of the electric field in the tip–sample gap. Possible applications of the developed nanostructuring process are anticipated in various nanotechnology fields.
Tunable conductivity and conduction mechanism in an ultraviolet light activated electronic conductor
Authors: Bertoni Mariana I. , Mason Thomas O. , Medvedeva Julia E. , Freeman Arthur J. , Poeppelmeier Kenneth R. , Delley Bernard
Published: May 2005

A tunable conductivity has been achieved by controllable substitution of an ultraviolet light activated electronic conductor. The transparent conducting oxide system H-doped Ca12−xMgxAl14O33 (x=0,0.1,0.3,0.5,0.8,1.0) presents a conductivity that is strongly dependent on the substitution level and temperature. Four-point dc-conductivity decreases with x from 0.26S∕cm (x=0) to 0.106S∕cm (x=1) at room temperature. At each composition the conductivity increases (reversibly with temperature) until a decomposition temperature is reached; above this value, the conductivity drops dramatically due to hydrogen recombination and loss. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Mg-substituted system with x=0, 1, and 2. The Seebeck coefficient is essentially composition and temperature independent, the later suggesting the existence of an activated mobility associated with small polaron conduction. The optical gap measured remains constant near 2.6eV while transparency increases with the substitution level, concomitant with a decrease in carrier content.
Stability of stationary and moving hydraulic jumps in inclined conduits of arbitrary cross section
Authors: Dyment A.
Published: May 2005

A criterion of stability of stationary and moving hydraulic jumps occurring in conduits of arbitrary shape is proposed, and application is made to some examples of flow, such as roll waves and periodic slugs.
Linear stability of cylindrical Couette flow in the convection regime
Authors: Ali Mohamed E. , McFadden G. B.
Published: May 2005

The instability of steady circular Couette flow with radial heating across a vertically oriented annulus with a rotating inner cylinder and a stationary outer cylinder is investigated using a linear stability analysis. The convection regime base flow is developed for an infinite aspect ratio geometry and constant fluid properties with buoyancy included through the Boussinesq approximation. The base flow is characterized by a dimensionless stratification parameter γ that is proportional to the vertical temperature gradient. Critical stability boundaries are calculated for this assumed base flow with respect to both toroidal and helical disturbances. The numerical investigation is primarily restricted to a radius ratio of 0.6 at a Prandtl number of 100. Critical stability boundaries in Taylor–Grashof number space are presented for two values of the stratification parameter γ (4 and 13). The results follow the development of critical stability from Taylor cells at small Grashof numbers up to a maximum Grashof number used in this calculation of 20 000 and 80 000 for γ=4 and 13, respectively. Results show that increasing the stratification parameter stabilizes the isothermal Taylor vortices, followed by a destabilization at higher azimuthal mode numbers (n>0). The results also show that for γ=4 (close to the conduction regime), two modes are obtained: one is axisymmetric and the other is nonaxisymmetric. However, for the convection regime (large γ) six asymmetric modes are obtained. Finally, the disturbance wavelength, phase speed, and spiral inclination angle are presented as a function of the critical Grashof number for the stratification parameters considered in this work.
DNA translocation through α-hemolysin nanopores with potential application to macromolecular data storage
Authors: Khulbe Pramod K. , Mansuripur Masud , Gruener Raphael
Published: May 2005

Digital information can be encoded in the building-block sequence of macromolecules, such as RNA and single-stranded DNA. Methods of “writing” and “reading” macromolecular strands are currently available, but they are slow and expensive. In an ideal molecular data storage system, routine operations such as write, read, erase, store, and transfer must be done reliably and at high speed within an integrated chip. As a first step toward demonstrating the feasibility of this concept, we report preliminary results of DNA readout experiments conducted in miniaturized chambers that are scalable to even smaller dimensions. We show that translocation of a single-stranded DNA molecule (consisting of 50 adenosine bases followed by 100 cytosine bases) through an ion channel yields a characteristic signal that is attributable to the two-segment structure of the molecule. We also examine the dependence of the translocation rate and speed on the adjustable parameters of the experiment.
Electrical and thermal transport properties of icosahedral Al70Pd22.5(Re1−xMnx)7.5 quasicrystals
Authors: Kuo Y. K. , Sivakumar K. M. , Lin C. R. , Lue C. S. , Lin S. T.
Published: May 2005

This work presents measurements of the electrical resistivity (ρ), Seebeck coefficient, and thermal conductivity (κ) of icosahedral Al70Pd22.5(Re1−xMnx)7.5 quasicrystals from 10to300K. A series of quasicrystals was prepared with x=0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, and 1.0 to systematically study the effect of substitution. The electrical resistivity increases as the temperature decreases, suggesting a semiconductinglike behavior in these alloys. The room-temperature values of the Seebeck coefficient vary from −5μV∕K to +65μV∕K, showing a significant dependence on the value of x. However, κ exhibits a rather weak composition dependence in the temperature range investigated. The room-temperature dimensionless thermoelectric figure of merit (ZT) of this system is optimized at x=0.1. With further appropriate heat treatments, high ZT is presumably available at elevated temperatures in the Al70Pd22.5(Re0.9Mn0.1)7.5 sample.
Experimental characterization of the reflectance of 60° waveguide bends in photonic crystal waveguides
Authors: Shih M. H. , Kim Woo Jun , Kuang Wan , Cao J. R. , Choi Sang-Jun , O’Brien John D. , Dapkus P. Daniel
Published: May 2005

Photonic crystal waveguides with two 60° bends were fabricated in an InGaAsP∕InP suspended membrane geometry. The transmission spectrum was measured and the reflectance of the 60° bend was evaluated from Fabry–Perot oscillations using Fourier analysis. It is shown that the reflectance agrees well with the results of a finite element method simulation.
Study of orientation effect on nanoscale polarization in BaTiO3 thin films using piezoresponse force microscopy
Authors: Kim Il-Doo , Avrahami Ytshak , Tuller Harry L. , Park Young-Bae , Dicken Matthew J. , Atwater Harry A.
Published: May 2005

We have investigated the effect of texture on in-plane (IPP) and out-of plane (OPP) polarizations of pulsed-laser-deposited BaTiO3 thin films grown on Pt and La0.5Sr0.5CoO3 (LSCO) buffered Pt electrodes. The OPP and IPP polarizations were observed by piezoresponse force microscopy (PFM) for three-dimensional polarization analyses in conjunction with conventional diffraction methods using x-ray diffraction and reflection high energy electron diffraction measurements. BaTiO3 films grown on Pt electrodes exhibited highly (101) preferred orientation with higher IPP component whereas BaTiO3 film grown on LSCO/Pt electrodes showed (001) and (101) orientations with higher OPP component. Measured effective d33 values of BaTiO3 films deposited on Pt and LSCO/Pt electrodes were 14.3 and 54.0pm∕V, respectively. Local piezoelectric strain loops obtained by OPP and IPP-PFM showed that piezoelectric properties were strongly related to film orientation.
Ti Kα radiography of Cu-doped plastic microshell implosions via spherically bent crystal imaging
Authors: King J. A. , Akli K. , Zhang B. , Freeman R. R. , Key M. H. , Chen C. D. , Hatchett S. P. , Koch J. A. , MacKinnon A. J. , Patel P. K. , Snavely R. , Town R. P. J. , Borghesi M. , Romagnani L. , Zepf M. , Cowan T. , Habara H. , Kodama R. , Toyama Y. , Karsch S. , Lancaster K. , Murphy C. , Norreys P. , Stephens R. , Stoeckl C.
Published: May 2005

We show that short pulse laser generated Ti Kα radiation can be used effectively as a backlighter for radiographic imaging. This method of x-ray radiography features high temporal and spatial resolution, high signal to noise ratio, and monochromatic imaging. We present here the Ti Kα backlit images of six-beam driven spherical implosions of thin-walled 500-μm Cu-doped deuterated plastic (CD) shells and of similar implosions with an included hollow gold cone. These radiographic results were used to define conditions for the diagnosis of fast ignition relevant electron transport within imploded Cu-doped coned CD shells.
CdSe nanocrystal quantum-dot memory
Authors: Fischbein M. D. , Drndic M.
Published: May 2005

Memory effects in the electronic transport in CdSe nanocrystal (NC) quantum-dot arrays have been observed and characterized. Conduction through a NC array can be reduced with a negative voltage and then restored with a positive voltage. Light can also be used to restore or even increase the NC array conduction. We have studied the switching of the conduction in CdSe NC arrays and found the behavior to be highly sensitive to the value and duration of the laser and voltage pulses.
Improved hole mobilities and thermal stability in a strained-Si∕strained-Si1−yGey∕strained-Si heterostructure grown on a relaxed Si1−xGex buffer
Authors: Gupta Saurabh , Lee Minjoo L. , Fitzgerald Eugene A.
Published: May 2005

A dual channel heterostructure consisting of strained-Si∕strained-Si1−yGey on a relaxed Si1−xGex buffer (y>x), provides a platform for fabricating metal–oxide–semiconductor field-effect transistors with high hole mobilities. Ge outdiffusion during high temperature processing steps from the strained-Si1−yGey layer into the relaxed Si1−xGex buffer reduces the hole mobilities in these heterostructures. We present a strained-Si∕strained-Si1−yGey∕strained-Si heterostructure on relaxed Si1−xGex, in which the strained-Si layer between the strained-Si1−yGey and relaxed Si1−xGex reduces Ge outdiffusion. Improved hole mobilities in this heterostructure are also observed over similar dual channel heterostructures which could be a result of better hole confinement in the strained-Si1−yGey layer of the proposed heterostructure.
Optical properties of poly(di-n-hexylsilane)–zirconia hybrid thin films: suppression of thermochromism and large thermo-optic coefficients
Authors: Marusaki Masahiro , Naito Hiroyoshi , Matsuura Yukihito , Matsukawa Kimihiro
Published: May 2005

Optical properties of hybrid thin films, poly(di-n-hexylsilane) (PDHS) dispersed in a zirconia matrix prepared by a sol–gel method, have been studied by means of optical absorption, photoluminescence and ellipsometry measurements. It is found that thermochromism of PDHS is suppressed in the PDHS–zirconia hybrid thin films, and that the refractive index of the hybrid, n, is continuously decreased with increasing temperature, T. The thermo-optic (TO) coefficient of the hybrids, dn∕dT, is found to be −4×10−4°C−1 and thus such a high value of dn∕dT enables us to apply the hybrids to optical devices such as TO switches and optical deflectors.
Ru-doped La0.6Sr0.4MnO3 thin films as a coercivity tunable electrode for magnetic tunnel junctions
Authors: Yamada Hiroyuki , Kawasaki M. , Tokura Y.
Published: May 2005

We have fabricated the epitaxial thin films of La1−xSrxMn1−yRuyO3 (x=0.4, y=0, 0.05, and 0.1) with an atomically flat surface by a pulsed-laser deposition method. The Ru doping enhances the coercive field from 40Oe (y=0) to 300Oe (y=0.05) and 600Oe (y=0.1) at 5K. The moderate Ru doping (y=0.05) even increases the ferromagnetic transition temperature from 340to355K, while hardly affecting the highly metallic conductivity. In these remarkable features, important roles may be played by the charge-transfer reaction of Mn4++Ru4+→Mn3++Ru5+, where Mn ferromagnetic spins are coupled antiferromagnetically with Ru spins showing a large single-ion anisotropy.
An ultrasmall amplitude operation of dynamic force microscopy with second flexural mode
Authors: Kawai Shigeki , Kitamura Shin-ichi , Kobayashi Dai , Meguro Sakae , Kawakatsu Hideki
Published: May 2005

Selective detection of short-range interaction forces was carried out with the second flexural mode of a commercially available dynamic mode cantilever. A higher mode has a higher spring constant and a lower mechanical quality factor, which are suitable for the small amplitude operation in dynamic force microscopy. With 0.70Å amplitude of the second flexural mode, atomically resolved constant frequency shift images of the Si(111)−7×7 reconstructed surface were obtained. The ultrasmall amplitude operation enabled imaging with high stability, due to the detection of the interaction force gradients at relatively long distances from the sample surface, and is an effective way to observe reactive surfaces while avoiding modifications and damaging of the tip and the sample.
Effects of low-temperature postannealing on a n+-p shallow junction fabricated by plasma doping
Authors: Baek Sungkweon , Hwang Hyunsang , Im Kiju , Ahn Chang-Geun , Yang Jong-Heon , Baek In-Bok , Lee Seongjae , Cho Won-ju
Published: May 2005

A low-temperature activation annealing process following plasma doping (PLAD) was investigated. A dramatic reduction of sheet resistance Rs occurred in the postactivation annealing temperature range of 400°C–480°C after PLAD. The Rs of 30Ω∕sq. and the junction depth Xj of 30nm was obtained without the additional diffusion of a dopant from the postactivation annealing in the fabricated junction. The electrical characteristics of a n+-p junction diode fabricated by PLAD were also improved after low-temperature postannealing.
Characteristics of a tunneling quantum-dot infrared photodetector operating at room temperature
Authors: Bhattacharya P. , Su X. H. , Chakrabarti S. , Ariyawansa G. , Perera A. G. U.
Published: May 2005

We report high-temperature (240–300K) operation of a tunneling quantum-dot infrared photodetector. The device displays two-color characteristics with photoresponse peaks at ∼6μm and 17μm. The extremely low dark current density of 1.55A∕cm2 at 300K for 1V bias is made possible by the tunnel filter. For the 17μm absorption, the measured peak responsivity is 0.16A∕W (300K) for a bias of 2V and the specific detectivity D* is 1.5×107cmHz1∕2∕W (280K) for a bias of 1V. Excellent performance characteristics are also measured for the 6μm photoresponse.
Low-resistance ohmic contacts to p-ZnMgO grown by pulsed-laser deposition
Authors: Yang Hyuck Soo , Li Y. , Norton D. P. , Ip K. , Pearton S. J. , Jang Soohwan , Ren F.
Published: May 2005

Electron-beam deposited Ni∕Au is found to produce ohmic contacts to p-type ZnMgO (p∼1016cm−3) after annealing in the range 300–450°C. A minimum specific contact resistance of ∼10−2Ωcm2 at room temperature and of 4×10−5Ωcm2 at 473K from circular transmission line measurements was obtained after annealing at 350°C for 1min in air. Higher anneal temperatures produced higher contact resistances and reaction of the contact metallurgy with diffusion of Ni to the surface of the Au layer where it became oxidized. The effective barrier height obtained from the measurement temperature dependence of the specific contact resistance, assuming thermionic emission, showed a value of 0.39±0.01eV, much lower than the theoretical value of ∼2.4eV. The difference in theoretical and experimental values is a clear indication of the strong role played by surface states, as reported earlier for Au Schottky contacts on ZnO.
Temperature-dependent transition to progressive breakdown in thin silicon dioxide based gate dielectrics
Authors: Suñé Jordi , Wu Ernest Y.
Published: May 2005

The transition between well-defined soft and hard breakdown modes to progressive breakdown in ultrathin silicon dioxide based dielectrics is studied by means of the statistics of residual time (the time from first breakdown to device failure). By stressing metal-oxide-semiconductor test capacitors with an oxide thickness of 2.2nm under different gate bias and temperatures, it is demonstrated that low voltages and temperatures favor stable hard and soft breakdown modes, while high temperatures and voltages lead to a progressive breakdown controlled regime. Our results support the idea that no significant change of the involved physics occurs in the transition from one breakdown regime to the other. The continuous transition from one regime to the other permits one to clearly identify progressive breakdown as hard breakdown, which always requires a certain time to reach the device failure conditions.
Intergrowth Bi2WO6–Bi3TiNbO9 ferroelectrics with high ionic conductivity
Authors: Yi Z. G. , Li Y. X. , Wen Z. Y. , Wang S. R. , Zeng J. T. , Yin Q. R.
Published: May 2005

Two dielectric relaxation loss peaks associated with oxygen-ion diffusion in the intergrowth Bi2WO6–Bi3TiNbO9(Bi5TiNbWO15) bismuth layered ferroelectrics were observed. The activation energy and the relaxation time at infinite temperature, for these two peaks, were determined to be (0.89 eV, 1.3×10−13s) and (0.84 eV, 3.6×10−10s). The ac impedance spectroscopy indicated that the Bi5TiNbWO15 ceramic is an ionic conductor with an electrical conductivity of approximately 2.6×10−2S∕cm at a temperature of 1073 K.
Midinfrared sensors meet nanotechnology: Trace gas sensing with quantum cascade lasers inside photonic band-gap hollow waveguides
Authors: Charlton Christy , Temelkuran Burak , Dellemann Gregor , Mizaikoff Boris
Published: May 2005

An integrated midinfrared sensing system for trace level (ppb) gas analysis combining a quantum cascade laser with an emission frequency of 10.3μm with a frequency matched photonic band-gap hollow core waveguide has been developed, demonstrating the sensing application of photonic band-gap fibers. The photonic band-gap fiber simultaneously acts as a wavelength selective waveguide and miniaturized gas cell. The laser emission wavelength corresponds to the vibrational C–H stretch band of ethyl chloride gas. This sensing system enabled the detection of ethyl chloride at concentration levels of 30ppb (v∕v) with a response time of 8s probing a sample volume of only 1.5mL in a transmission absorption measurement within the photonic band-gap hollow core waveguide, which corresponds to a sensitivity improvement by three orders of magnitude compared to previously reported results obtained with conventional hollow waveguides.
Electromechanical strain in conjugated polymer diodes under forward and reverse bias
Authors: Dennler Gilles , Sariciftci Niyazi Serdar , Schwödiauer Reinhard , Bauer Siegfried , Reiss Howard
Published: May 2005

Organic polymeric semiconductor diodes based on poly(paraphenylene vinylene) exhibit electromechanical strain under reverse and forward bias operation. Under reverse bias, the strain in the organic diode is created by Maxwell forces (“electrostrictive” actuation). Under forward bias, the large electrical current results in Joule heating and thus in a thermally induced electromechanical strain. These electromechanical effects might be used for transducer applications of organic electronic materials.
Selective epitaxial growth of submicron complex oxide structures by amorphous SrTiO3
Authors: Morales P. , DiCiano M. , Wei J. Y. T.
Published: May 2005

A chemical-free technique for fabricating submicron complex oxide structures has been developed based on selective epitaxial growth. The crystallinity and hence the conductivity of the complex oxide is inhibited by amorphous SrTiO3 (STO). Using a combination of pulsed laser deposition and electron-beam lithography, amorphous STO barriers are first deposited on a single-crystal substrate. A thin film is then deposited on the patterned substrate with the amorphous STO barriers acting to electrically and physically isolate different regions of the film. Since no chemical or physical etchants come in contact with the deposited film, its integrity and stability are preserved. This technique has produced submicron YBa2Cu3O7−δ and La2∕3Ca1∕3MnO3 structures.
Three-dimensional optical memory using photoluminescence change in Sm-doped sodium borate glass
Authors: Lim Jinhyong , Lee Myeongkyu , Kim Eunkyoung
Published: May 2005

The feasibility of three-dimensional (3D) optical memory has been demonstrated by utilizing the photoluminescence (PL) spectrum change in a Sm-doped fluoride glass [K. Miura, J. Qiu, S. Fujiwara, S. Sakasuchi, and K. Hirao, Appl. Phys. Lett. 80 2263 (2002)]. We here report on a femtosecond laser-induced PL change in a Sm-doped sodium borate glass that is easier to synthesize and its potential application to 3D memory. Irradiation with a femtosecond pulsed laser (800 nm, 1 kHz, 100 fs) induced a PL peak near 682 nm, resulting from the photoreduction of the Sm ions. A multilayer pattern (bit size=1μm,layer separation=8μm) formed by femtosecond laser irradiation was read out by a reflection-type fluorescent confocal microscope, which detected the emission at 682 nm as a signal. High-contrast pattern images were obtained without crosstalk.
Large negative persistent photoconductivity in InAs∕AlSb quantum wells
Authors: Sadofyev Yu. G. , Ramamoorthy A. , Bird J. P. , Johnson S. R. , Zhang Y.-H.
Published: May 2005

Negative persistent photoconductivity in backgated InAs∕AlSb quantum wells under red and blue light emitting diode illumination is observed to depend on both illumination energy and intensity. During these experiments the electron sheet density is varied by one order of magnitude from 5.6×1011 to 5.8×1010cm−2. This behavior is attributed to the role of optically excited holes in the AlSb barrier layers near the InAs quantum well. Furthermore, a long relaxation time in the electron sheet density is observed and attributed to the slow movement of electrons from the InAs quantum well to ionized deep levels in the AlSb barriers.
Rotational motion of microsphere packs on acoustically excited surfaces
Authors: Peri M. D. Murthy , Cetinkaya Cetin
Published: May 2005

The generation of uniform rotational motion of polystyrene latex microsphere packs on silicon oxide dry surfaces in base-excited acoustic fields is demonstrated. The physics of microparticle dynamics on surfaces is substantially different from its counterparts in meso/macroscale due to the domination of intermolecular forces in microscale objects. The stability of packs presented in the current experimental study suggests that rolling resistance due to elasticity and adhesion plays an essential role in pack formation. The control of the rotational speed of microspheres with the pulse repetitive frequency of the pulser circuit is illustrated. The present work could lead to a motion excitation mechanism for microscale systems.
Reduction of dislocations in GaN epilayers using templated three-dimensional coherent nanoislands
Authors: Jeganathan K. , Shimizu M. , Okumura H.
Published: May 2005

Low-dislocation-density GaN layers have been grown on 6H–SiC(0001) substrates by molecular-beam epitaxy using high-density (∼4×1011cm−2) self-assembled Stranski–Krastanov GaN nanoislands buffer. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that the insertion of coherent nanoislands as a buffer reduces the defect migration from the interface to the GaN epitaxial layers. The dislocation density is dramatically dropped to ∼107cm−2 in GaN layers grown on coherent nanoislands as compared to ∼109cm−2 in the typical GaN layers grown on the AIN buffer.
Dynamic polarization filtering in anisotropically strained M-plane GaN films
Authors: Omae K. , Flissikowski T. , Misra P. , Brandt O. , Grahn H. T. , Kojima K. , Kawakami Y.
Published: May 2005

The dynamic optical polarization filtering for anisotropically strained M-plane GaN films on LiAlO2 is investigated by pump and probe spectroscopy. Due to a very large polarization anisotropy in the absorption coefficient, these films exhibit an intrinsic polarization filtering, which appears as a rotation of the polarization vector after transmission of linearly polarized light through the film. For dynamic filtering, the polarization rotation is controlled by the pump, since the photoexcited carriers remove the intrinsic linear dichroism by selective bleaching of the anisotropic absorption. The dynamic behavior of the polarization rotation is mainly determined by the redistribution of holes between the two uppermost valence bands and by the recombination time. The latter is comparable to the measured decay time of the dynamic rotation of about 15ps. For M-plane GaN films, the maximum dynamic rotation reaches 35°, while the maximum static polarization rotation is about 40°.
Epitaxial growth of NaxCoO2 thin films by pulsed-laser deposition
Authors: Krockenberger Y. , Fritsch I. , Cristiani G. , Matveev A. , Alff L. , Habermeier H.-U. , Keimer B.
Published: May 2005

Single-phase thin films of NaxCoO2 have been grown epitaxially by pulsed-laser deposition technique. The growth conditions were studied based on the logpO2−1∕T phase diagram of Co–O2 using different types of substrate materials. For Na0.58CoO2, metallic behavior is found down to 4.2K.

At the request of the authors, this article is being retracted effective 4 January 2006.
Formation of epitaxial β-Sn islands at the interface of SiO2∕Si layers implanted with Sn ions
Authors: Lopes J. M. J. , Zawislak F. C. , Fichtner P. F. P. , Papaléo R. M. , Lovey F. C. , Condó A. M. , Tolley A. J.
Published: May 2005

180 nm SiO2 layers on Si (100) were implanted with Sn ions producing a profile with a peak concentration of 3 at. % at the middle of the oxide. After high temperature (900–1100 °C) annealing, an array of β-Sn islands epitaxially attached to the Si was observed at the SiO2∕Si(100) interface due to the migration of the implanted Sn atoms. The breakdown of the planar SiO2∕Si interface and the appearance of the island system is discussed in terms of the Sn–Si equilibrium properties. Our results reveal a new method to create a high density of nanosized islands with good uniformity in size and shape.
HIV-1-specific IFN-γ/IL-2-secreting CD8 T cells support CD4-independent proliferation of HIV-1-specific CD8 T cells
Authors: Zimmerli Simone C. , Harari Alexandre , Cellerai Cristina , Vallelian Florence , Bart Pierre-Alexandre , Pantaleo Giuseppe
Published: May 2005

Functional and phenotypic characterization of virus-specific CD8 T cells against cytomegalovirus, Epstein-Barr virus, influenza (flu), and HIV-1 were performed on the basis of the ability of CD8 T cells to secrete IFN-γ and IL-2, to proliferate, and to express CD45RA and CCR7. Two functional distinct populations of CD8 T cells were identified: (i) dual IFN-γ/IL-2-secreting cells and (ii) single IFN-γ-secreting cells. Virus-specific IFN-γ/IL-2-secreting CD8 T cells were CD45RA-CCR7-, whereas single IFN-γ CD8 T cells were either CD45RA-CCR7-or CD45RA+CCR7-. The proportion of virus-specific IFN-γ/IL-2-secreting CD8 T cells correlated with that of proliferating CD8 T cells, and the loss of HIV-1-specific IL-2-secreting CD8 T cells was associated with that of HIV-1-specific CD8 T cell proliferation. Substantial proliferation of virus-specific CD8 T cells (including HIV-1-specific CD8 T cells) was also observed in CD4 T cell-depleted populations or after stimulation with MHC class I tetramer-peptide complexes. IL-2 was the factor responsible for the CD4-independent CD8 T cell proliferation. These results indicate that IFN-γ/IL-2-secreting CD8 T cells may promote antigen-specific proliferation of CD8 T cells even in the absence of helper CD4 T cells.
Endothelial dysfunction: role in obesity-related disorders and the early origins of CVD
Authors: Singhal Atul
Published: May 2005

Atherosclerotic CVD is the most common cause of death in the West. Yet, its pathogenesis and early development are only partially understood. Central to the early atherosclerotic process is impairment of vascular endothelial function. Endothelial dysfunction can be measured non-invasively and is evident in children before clinical manifestations of atherosclerosis in adulthood. Factors in early life, such as conventional cardiovascular risk factors, or programming by perinatal growth and nutrition strongly affect endothelial function and hence the development of atherosclerosis and CVD. For instance, low birth weight and faster growth early in infancy have a detrimental effect on vascular structure and function. Childhood obesity, a key independent risk factor for CVD, also adversely affects early vascular health. Obesity is associated with endothelial dysfunction and greater arterial stiffness from as early as the first decade of life, while weight loss is beneficial. This effect on vascular function is probably mediated in part by low-grade inflammation and insulin resistance associated with obesity or by the production by adipose tissue of cytokine-like molecules, collectively termed adipokines. A high leptin concentration, in particular, is found in obese individuals and is strongly associated with vascular changes related to early atherosclerosis. The present review focuses on the early origins of endothelial dysfunction, emphasising the role of obesity. It also considers the mechanisms by which obesity impairs endothelial function, understanding of which will be important to further scientific knowledge and to improve public health.
Fatty acids and the metabolic syndrome
Authors: Roche Helen M.
Published: May 2005

The metabolic syndrome is a very common condition, characterised by insulin resistance, dyslipidaemia, abdominal obesity and hypertension, that is associated with a high risk of type 2 diabetes mellitus (T2DM) and CVD. Obesity is a key aetiological factor in the development of the metabolic syndrome. In light of the increasing prevalence of obesity, there is a high requirement to reduce the impact of the adverse health effects associated with the metabolic syndrome. The aetiological role of nutrient-derived metabolic stressors, in particular fatty acids, in the development of obesity and the metabolic syndrome is explored. Also, the evidence that pro-inflammatory stressors may predispose to obesity-induced insulin resistance is reviewed. The present paper explores the concept that reducing the impact of metabolic and inflammatory stressors may reduce the adverse health effects of obesity and slow the progression towards the metabolic syndrome and T2DM. Evidence from human dietary intervention studies that have investigated the potential therapeutic effects of dietary fatty acid modification is explored. The present review highlights the requirement to take account of genetic background, within the context of nutrient regulation of gene expression and individual responsiveness to dietary therapy. This approach will further the understanding of the interaction between fatty acids in the pathogenesis and progression of the metabolic syndrome.
Understanding the aetiology of childhood obesity: implications for treatment
Authors: Wardle Jane
Published: May 2005

Childhood obesity poses one of the greatest challenges to paediatric health in the 21st century. Developing effective strategies for treatment and prevention is therefore a priority for clinical medicine and public health. This process is taking place at a time of unprecedented change in the understanding of the role of genetic factors in human health and disease, and genetic research into obesity has challenged assumptions about causal processes. In the spirit of the conference theme, the present paper will discuss the implications of the understanding of genetic and environmental influences on obesity for the development of effective behavioural treatments.