bluuebunny/crossref_metadata_2025 huggingface dataset:
Electric-pulse-induced capacitance change effect in perovskite oxide thin films
Authors: Liu Shangqing , Wu Naijuan , Ignatiev Alex , Li Jianren
Published: September 2006

A reversible nonvolatile capacitance change effect has been observed in perovskite oxide thin films at room temperature under the application of electrical pulses of low voltage and short duration. The pulse-induced nonvolatile capacitance change is seen to coexist with a pulse-induced nonvolatile resistance change reported earlier. It is shown that the capacitance values of Pr0.7Ca0.3MnO3 samples can be set to either two specific states or to multiple discrete capacitance levels. The observed effect has potential applications including variable capacitors and nonvolatile two-state or multiple-level memories.
The rectifying property and magnetoresistance of La0.67Ca0.33MnO3∕SiO2∕Si heterojunction
Authors: Lang P. L. , Zhao Y. G. , Xiong C. M. , Wang P. , Li J. , Zheng D. N.
Published: September 2006

We have fabricated a heterojunction by depositing La0.67Ca0.33MnO3 film on electron doped silicon wafer with a buffer layer of natural SiO2. The current-voltage measurement shows that it is a diode with a good rectifying property in a wide temperature range. At high positive voltages, the current-voltage curve shows space charge limited (SCL) current behavior, manifesting itself as a SCL diode. At low positive and negative voltages, the resistance of the junction shows a peak at a certain temperature, which decreases with increasing positive voltage and keeps constant at negative voltages. Magnetoresistance of the junction shows a similar temperature dependence as the resistance of the junction. Calculations show that these phenomena can be attributed to the depletion layer of the La0.67Ca0.33MnO3 film. This work also demonstrates that SCL diode can be realized in La0.67Ca0.33MnO3∕SiO2∕Si with the presence of the SiO2 layer.
Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions
Authors: Wang Y. , Zeng Z. M. , Rehana S. , Han X. F. , Sun X. C. , Zhang Z.
Published: September 2006

Barrier shapes and its detailed microstructures in the double barrier magnetic tunnel junctions were intensively investigated by both high resolution transmission electron microscopy and electron holography. Two broad (>2nm) potential wells (i.e., shapes of AlOx layers) with slanted interfaces were observed in the electron hologram of the as-deposited samples. However, in the hologram of the annealed samples, two narrowed (down to 1.18nm) and almost equal (height) potential wells with sharp and steep interfaces were acquired. This indicates that the value of tunnel magnetoresistance can be increased from 12.8% to 29.4% at room temperature by annealing treatment where the sharpness and height of the barriers played a critical role.
Magnetic anisotropy and high frequency permeability of multilayered nanocomposite FeAlO thin films
Authors: Ma Y. G. , Liu Y. , Tan C. Y. , Liu Z. W. , Ong C. K.
Published: September 2006

A cool-down step deposition process (multistep deposition with cool-down interval) was used to grow nanocomposite FeAlO thin films of various thicknesses up to 440nm by magnetron sputtering at a substrate temperature of 15°C. The effect of the number of cool-down steps on the soft magnetic properties and high frequency characteristics of the nanocomposite FeAlO films were investigated. The deposition process was proved very effective in improving the soft magnetic properties and high frequency characteristics of the films. The eight-layered samples, fabricated by eight cool-down step deposition process, of thicknesses of 220 and 440nm had obvious in-plane uniaxial anisotropies while the single-layered films were nearly isotropic. The resulting real permeability value of the eight-layered films was larger than 300 for the 220nm film and between 200 and 300 for the 440nm film.
Time and temperature dependences of the magnetization reversal in a Co∕Pd multilayer film
Authors: Brown C. Scott , Harrell J. W. , Matsunuma S.
Published: September 2006

The time and temperature dependences of the magnetization reversal have been measured in a high-coercivity Co∕Pd multilayer film characterized by nucleation and domain wall motion. The time and field dependences of magnetic relaxation curves at room temperature were interpreted in terms of an energy barrier that depends linearly on reverse field, suggesting a Sharrock-type [M. P. Sharrock and J. T. McKinney, IEEE Trans. Magn. 17, 3020 (1981)] equation for the time and temperature dependences of coercivity with unity exponent. The sweep rate and temperature dependence of the coercivity were analyzed using the Sharrock equation to obtain the temperature dependence of the intrinsic, short-time coercivity H0 and the zero-field energy barrier E0. A single power law behavior was found for H0 versus the saturation magnetization Ms.
A perturbation theory for calculating strain distributions in heterogeneous and anisotropic quantum dot structures
Authors: Wang J. , Chu H. J.
Published: September 2006

By introducing a homogenous comparison material, a perturbation theory based on Green’s function is proposed to calculate the strain distribution inside and outside an arbitrarily shaped and anisotropic quantum dot (QD) embedded in an alien infinite medium. This theory removes the limitations of the previous analytical methods which are based upon the assumption that the QD is isotropic and has the same elastic properties as the surrounding medium. The numerical results for a truncated pyramidal Ge∕Si QD structure demonstrate that the anisotropy of the materials and the difference between the stiffness tensors of the QD and the matrix have a significant influence on the strain field. It is found that the first-order approximate solution obtained by the proposed method can reduce the relative difference of the strain fields induced by the isotropic approximation from 30% to 6%. Moreover, it is shown that the strain fields obtained by the proposed method with the second-order approximate solution are very accurate for the Ge∕Si QD structure.
Experimental and numerical study of transient bubble-elastic membrane interaction
Authors: Turangan C. K. , Ong G. P. , Klaseboer E. , Khoo B. C.
Published: September 2006

A study of the interaction between a membrane and a submerged oscillating bubble is presented. Though the behavior of such a bubble near an elastic (relatively thick) boundary has been studied by several authors, much less attention is focused on the behavior of such a bubble near a (thin) elastic membrane. For membranes, it is the curvature and not the deflection that is responsible for a pressure buildup in the fluid close to the bubble. Due to this difference in physics, it is not a certainty if the dynamics of bubbles near a deformable elastic boundary vis-a-vis a membrane would exhibit any similarity. Our intent is a systematic study on the latter, which can be exploited in future work (e.g., in biomedical applications where elastic membranes are often involved). Experimental observations of transient bubble interaction with a thin elastic membrane are presented and the dynamics of the bubble in the vicinity of the membrane are compared to the boundary element method simulations. The bubble is generated using a very low voltage (only 55V) in contrast to the relatively much higher voltages usually employed in reported works. This is very attractive from a safety viewpoint and accords great simplification of the setup. The comparisons show that the interaction between the transient bubble and the membrane induces a perturbation on the bubble surface that strengthens the bubble contraction and can lead to mushroom shape, bubble elongation, and bubble splitting. The influence of the two main parameters, namely, the distance between the bubble and the membrane and the elasticity of the membrane, are also discussed.
An experimental investigation on the switching reliability of a phase change memory device with an oxidized TiN electrode
Authors: Kang Dae-Hwan , Kim In Ho , Jeong Jeung-hyun , Cheong Byung-ki , Ahn Dong-Ho , Lee Dongbok , Kim Hyun-Mi , Kim Ki-Bum , Kim Soo-Hyun
Published: September 2006

Fluctuations (or drifts) in switching voltages such as programming set/reset voltages and threshold voltage pose serious obstacles to the reliable operation of electrical phase change memory devices. Using a phase change memory device having a GeSb2Te4 phase change material and TiN electrode, these fluctuations are demonstrated to result from device resistances varying with programming cycles. Fluctuating resistances appear to stem primarily from large contact resistances at the interface between the phase change material and the TiN electrode and from inhomogeneous phase distribution across the GeSb2Te4 layer due to unsuccessful heat confinement near the interface with TiN. Oxidation of a TiN electrode surface (via thermal annealing at 350°C under an atmospheric gas mixture of 97.9vol% N2 and 2.1vol% O2) is very effective in the reduction of fluctuations in device resistances and switching voltages hence the resulting increase in the programming cycles by two orders of magnitude. From a high resolution transmission electron microscopy, the oxidized surface was shown to consist of a titanium oxide layer primarily with Ti2O3 crystallites which is presumed to yield enhanced stability of the device by the following two effects. Firstly, Ge, Sb, and Te atoms would have stronger bonds to oxygen atoms than to nitrogen atoms by about 0.5eV, thereby producing more robust interface. Accordingly, the magnitude of contact resistance and its variation are reduced significantly so as to have little influence on the device resistances and their fluctuations. Secondly, thermally and electrically more resistive nature of the oxide layer would tend to yield, by enhanced generation and confinement of Joule heat, more uniform temperature distribution across the phase change material layer, rendering possibly a more homogeneous single phase material hence steadier sheet resistances with programming cycles.
Electronic properties of the Ce∕4H-SiC interface studied by x-ray photoemission spectroscopy
Authors: Kildemo M. , Grossner U. , Raaen S.
Published: September 2006

The deposition and annealing in ultrahigh vacuum of 5–6 ML (monolayers) of cerium on clean reconstructed Si-face 4H-SiC (0001) are studied by x-ray photoemission spectroscopy and low-energy electron diffraction. Band bending as a function of annealing was studied by shifts of the bulk peak contribution in the C 1s and Si 2p spectra relative to the clean reconstructed surface. Silicide formation was studied by low binding energy components in the C 1s and Si 2p spectra. A large relative upward band bending of 0.3–0.4eV takes place upon deposition of Ce on 4H-SiC at room temperature. Upon annealing to 350°C, a disordered CeSixCy interface layer forms, as observed from chemically shifted components in the Si 2p and C 1s spectra. Annealing to 600°C causes the interface to become CeSi2−x, and carbon desorbs from the interface. A maximum relative band bending of 0.6eV is observed from 400to600°C. Further heating of the sample to 850–1000°C results in a relative total upward band bending of approximately 0.4eV and a relatively sharp CeSi2−x peak in the Si 2p spectrum. SiC bulk bonds appear not to be broken and it is found that a Ce overlayer terminates the layer, with a cerium silicide layer at the interface.
Influence of A-site disorder on the half-doped manganites
Authors: Fan Jiyu , Ling Langsheng , Pi Li , Wang Yang , Ying Yue , Zhang Yuheng
Published: September 2006

The electronic transport and magnetism in half-doped Nd0.50Ca0.25Sr0.25MnO3 manganites have been investigated. Contrary to general half-doped system, it only displays a paramagnetic-ferromagnetic phase transition associated with an insulator-metal transition instead of with any features of charge ordering. With the decrease of temperature, an electronic phase separation and spin glass state occur in low temperature. We suggest that the A-site cation disorder induced by the size mismatch between Sr2+ ion and Ca2+ ion is mainly responsible for this phenomenon.
Decay process of a large surface potential of Alq3 films by heating
Authors: Kajimoto Norifumi , Manaka Takaaki , Iwamoto Mitsumasa
Published: September 2006

In order to clarify the decaying process of a large surface potential of as-deposited Alq3 films on a metal electrode by heating and photoexposure, Kelvin probe method and optical second harmonic generation (SHG) measurement were employed. The change of surface potential during heating was not in accordance with the change of SH intensity at a temperature lower than 100°C. For heating at less than 100°C and photoexposure, x-ray diffractions showed no change. We discussed these results from a viewpoint of the disordering of orientational polar structure of Alq3 molecules and the injection of electrons from metal electrodes. Then the following model was suggested. The potential decay process of Alq3 films on aluminum (Al) electrodes by heating was found to be due to electron injection from Al electrode into Alq3 films, which does not accompany the structural change of Alq3 films in the region of temperature lower than 100°C, though the crystallization of Alq3 evaporated film was suggested at a temperature higher than 100°C. On the other hand, the disordering of polar structure of Alq3 film that does not accompany the structural change was elucidated as the potential decay process by photoexposure.
Xe nuclear magnetic resonance line shapes in channels decorated with paramagnetic centers
Authors: Sears Devin N. , Vukovic Lela , Jameson Cynthia J.
Published: September 2006

To make predictions of the Xe NMR line shapes for Xe in channels decorated with paramagnetic centers, we consider a model system using the O2 molecule as the paramagnetic center. The previously calculated quantum mechanical Xe@O2 hyperfine tensor for various configurations of Xe in the presence of O2 provides a model for the hyperfine response of Xe atom to the presence of a paramagnetic center. The averaging is carried out using the same grand canonical Monte Carlo methodology as for calculating NMR line shapes for Xe in diamagnetic channels, modified to include the effects of the hyperfine tensor response. We explore the temperature dependence of the Xe line shapes, the dependence on the concentration, and the symmetry of distribution of embedded paramagnetic centers, on the orientation of the paramagnetic center axis with respect to the channel axis, and on the radial distance of the paramagnetic center from the axis of the channel. We predict Xe line shape signatures of the presence and orientation of paramagnetic centers and deduce which tensor elements provide measures of concentration and radial distance of paramagnetic centers from the channel axis.
Optical cross sections of deep levels in 4H-SiC
Authors: Kato M. , Tanaka S. , Ichimura M. , Arai E. , Nakamura S. , Kimoto T. , Pässler R.
Published: September 2006

We have characterized deep levels in 4H-SiC epilayers grown by cold wall chemical vapor deposition by the deep level transient spectroscopy (DLTS) and the optical-capacitance-transient spectroscopy (O-CTS). Four kinds of DLTS peaks were detected in the epilayers. Three of them are identified as the Z1∕2, EH6∕7, and RD1∕2 centers, while the other one has never been reported previously, and was named the NB center. On the basis of these DLTS data we have estimated the thermal ionization energies. The classical optical ionization energies of these centers, which are given by the sums of thermal ionization energies and Franck-Condon shifts, were estimated via fittings of the measured optical cross sections from O-CTS data by means of a sufficiently general theoretical model. Temperature dependences of nonradiative multiphonon carrier capture cross sections for the Z1∕2 and NB centers were roughly estimated in terms of parametrical dependences on thermal ionization energies and Franck-Condon shifts.
Stability analysis of an electromagnetically levitated sphere
Authors: Priede Jānis , Gerbeth Gunter
Published: September 2006

We present a combined numerical and analytical approach to analyze the static and dynamic stabilities of an electromagnetically levitated spherical body depending on the ac frequency and the configuration of a three-dimensional (3D) coil made of thin winding which is modeled by linear current filaments. First, we calculate numerically the magnetic vector potential in grid points on the surface of the sphere and then use Legendre and fast Fourier transforms to find the expansion of the magnetic field in terms of spherical harmonics. Second, we employ a previously developed gauge transformation to solve analytically the 3D electromagnetic problem in terms of the numerically obtained expansion coefficients. Using this solution, we obtain the electromagnetic reaction force due to both a small displacement of the sphere from its equilibrium position and its velocity of motion which are defined by symmetric stiffness and damping matrices, respectively. Eigenvalues and eigenvectors of the stiffness matrix yield three principal stiffness coefficients, which all have to be positive for the equilibrium state to be statically stable, and three mutually orthogonal directions of principal oscillations. Dynamic instabilities are characterized by critical ac frequencies which, when exceeded, may result either in a spin up or oscillations with increasing amplitude. The effective electromagnetic damping coefficients are found by using a classical eigenvalue perturbation theory. A theoretical approach based on the vector field transformation by a small rotation in combination with a parametric frequency derivative is introduced to find the electromagnetic reaction torque due to a slow rotation of the sphere in a 3D ac magnetic field.
Laser annealing of laser assisted molecular beam deposited ZnO thin films with application to metal-semiconductor-metal photodetectors
Authors: Li Meiya , Anderson Wayne , Chokshi Nehal , DeLeon Robert L. , Tompa Gary
Published: September 2006

We report on the effect of postdeposition laser annealing of undoped zinc oxide (ZnO) thin films grown by laser assisted molecular beam deposition. Hall-effect measurements show that some undoped ZnO films change from n type with mobility values in the range of 200cm2V−1s−1 to p-type material with mobility value of 73cm2V−1s−1, after laser annealing. The photoconductive behavior was clearly seen on the laser-annealed samples, with values of 0.28mΩ−1. The structural and optical properties of the films were improved with laser annealing as shown by scanning electron microscopy, x-ray photoelectron spectroscopy analysis, and photoluminescence measurement. All of the nonlaser and laser annealed samples showed near-band emission at ∼3.3eV. Metal-semiconductor-metal photodetectors were fabricated from the films.
Effect of particle size on the structural and magnetic properties of La0.8Sr0.2MnO3
Authors: Kameli P. , Salamati H. , Aezami A.
Published: September 2006

In this study, we have investigated the effects of grain size on the structural and magnetic properties of La0.8Sr0.2MnO3 powder samples. The Williamson-Hall method was employed on the x-ray peak profile of these powder samples to determine the lattice microstrain. It was found that the microstrain increases by decreasing grain size. The magnetization decreases by decreasing grain size. A decrease in magnetization by decreasing grain size indicates formation of magnetically dead layer at the surface of grains. The thickness of such a magnetically dead layer increases by decreasing particle size. It seems that one of the sources for the formation of this magnetically dead surface layer is the microstrain. By subsequently annealing at a temperature of 800°C, the microstrain was released partially and magnetic properties were improved.
Microscopic current imaging in quantum point contact devices
Authors: Cresti Alessandro
Published: September 2006

The recent development of scanning probe microscope techniques has made possible the imaging of microscopic currents flowing through quantum point contact devices. In this paper we perform numerical simulations for current imaging in a model quantum point contact, by means of the Keldysh Green’s function formalism (Zh. Eksp. Teor. Fiz. 47, 1515 (1964) [Sov. Phys. JETP 20, 1018 (1965)]). The experimental measures are simulated mimicking the effect of the auxiliary microscopic tip by a suitable potential. The results presented here provide a valuable help for the interpretation of the experimental maps and highlight their validity and importance.
Time-resolved photoluminescence spectroscopy of subwetting layer states in InGaAs∕GaAs quantum dot structures
Authors: Mazur Yu. I. , Liang B. L. , Wang Zh. M. , Guzun D. , Salamo G. J. , Tarasov G. G. , Zhuchenko Z. Ya.
Published: September 2006

Time-resolved photoluminescence (PL) measurements are carried out for the InGaAs quantum dots (QDs) grown on (001) and (311) oriented GaAs substrates. The detection energies scan the spectral region from the energy of the QD excitonic transition up to the wetting layer absorption edge. A convex-shaped decay of the PL signal in this region gives evidence of carrier relaxation through the continuum states below the wetting layer similar to a diffusion process. Strong dependence of the decay time on the excitation density observed for the QD ground-state PL is consistent with a presented theoretical model.
Ionic blocking effect in partially crystallized lithium disilicate
Authors: Campos-Júnior Alvimar A. , Rodrigues Ana C. M.
Published: September 2006

A lithium disilicate glass was heat treated at 454°C, the temperature of maximum nucleation rate, up to 25days. At this temperature the growth rate is negligible, and therefore these thermal treatments lead to a glassy matrix in which ellipsoidal crystals of about the same size were randomly dispersed. Crystallized volume fraction (α) of up to 20% was reached. Electrical conductivity of glassy, partially crystallized, and 100% crystallized lithium disilicate was then measured by impedance spectroscopy. The crystallized surface layer was eliminated by polishing in order to solely analyze the effect of bulk crystals. The complex plane plots of impedance data showed one or two semicircles depending on (α). The high frequency semicircle represents the vitreous matrix while the low frequency one was ascribed to the blocking effect imposed to the lithium ions by the existing crystals in the partially crystallized samples. This hypothesis was confirmed by the analysis of the relaxation frequency related to each one of the semicircles and by comparison to the relaxation frequency of lithium disilicate glass and crystal. Results show that the blocking effect produces a second semicircle in the impedance diagram starting from a crystallized volume fraction of 15%.
Sensitivity of a field-effect transistor in detecting DNA hybridization, calculated from the cylindrical Poisson-Boltzmann equation
Authors: McKinnon W. R. , Landheer D.
Published: September 2006

The sensitivity of a DNA biosensor based on a field-effect transistor is calculated from the numerical solution of the Poisson-Boltzmann equation in a cylindrical cell. The sensitivity is typically about half that found from the one-dimensional Poisson-Boltzmann equation for an ion-permeable DNA membrane with the same average charge density. For the combination of low DNA densities and low concentration of ions in solution, however, the discrepancy between the two calculations can be a factor of 10 or higher. The difference in the two calculations is due to accumulation of screening charge around the DNA cylinder, an effect which is ignored in the membrane model.
Characterization of oxide films on 4H-SiC epitaxial (0001¯) faces by high-energy-resolution photoemission spectroscopy: Comparison between wet and dry oxidation
Authors: Hijikata Yasuto , Yaguchi Hiroyuki , Yoshida Sadafumi , Takata Yasutaka , Kobayashi Keisuke , Nohira Hiroshi , Hattori Takeo
Published: September 2006

Wet and dry oxide films-4H-SiC epitaxial (0001¯) C-face interfaces have been characterized by capacitance-voltage (C-V) measurements and soft x-ray excited photoemission spectroscopy (SX-PES) and hard x-ray excited photoemission spectroscopy (HX-PES) using synchrotron radiation. The interface state density for wet oxidation is much smaller than that for dry oxidation at any energy level. In the PES measurements, intermediate oxidation states such as Si1+ and Si3+ were observed. In addition, the areal densities of these states were found to be in a good correspondence with those of the interface states. The reasons for the good electrical characteristics of metal-oxide-semiconductor devices fabricated by wet oxidation are discussed in terms of the depth profiles of oxide films derived from the SX-PES and HX-PES results.
Towards controlled manipulation and assembly of ZnO nanowires for nanoscale imaging applications
Authors: Kouklin N. , Sen S.
Published: September 2006

In this letter the authors develop a technique enabling both facile alignment and placement of ZnO nanorods onto the support electrodes in a highly controlled manner and with high yield. The approach takes advantage of the surface tension effect and the formation of nonvanishing electrical dipoles at the metal-semiconductor and semiconductor/semiconductor interfaces in highly nonpolar solvents. Experimental tests confirmed excellent mechanical resilience of single crystal ZnO nanorods and overall stability of the engineered assemblies. Finally, use of ZnO nanorods as tips for high-resolution atomic force microscope nanoscale imaging is demonstrated.
Mechanism and scalability in resistive switching of metal-Pr0.7Ca0.3MnO3 interface
Authors: Tsui S. , Wang Y. Q. , Xue Y. Y. , Chu C. W.
Published: September 2006

The polarity-dependent resistive switching across metal-Pr0.7Ca0.3MnO3 interfaces is investigated. The data suggest that shallow defects in the interface dominate the switching. Their density and fluctuation, therefore, will ultimately limit the device size. While the defects generated/annihilated by the pulses and the associated carrier depletion seem to play the major role at lower defect density, the defect correlations and their associated hopping ranges appear to dominate at higher defect density. Therefore, the switching characteristics, especially the size scalability, may be altered through interface treatments.
Low-threshold blue-emitting monolithic polymer vertical cavity surface-emitting lasers
Authors: Persano Luana , Camposeo Andrea , Del Carro Pompilio , Mele Elisa , Cingolani Roberto , Pisignano Dario
Published: September 2006

The authors report on a monolithic vertical microcavity blue laser with a carbazole/fluorenyl derivative copolymer active film. The laser is realized by electron-beam deposition of the two dielectric mirrors on the bottom and on the top of the polymeric active layer. The devices exhibit a threshold fluence as low as 1.2μJ∕cm2, with a divergence of the emission beam of 2.8°. The measured lasing threshold and operational lifetimes (>1.5×104 pulses at an excitation density 500 times larger than threshold) are among the best so far reported for blue-emitting polymer lasers, thus making these devices promising candidates for future electrical excitation.
An efficient sampling algorithm for variational Monte Carlo
Authors: Scemama Anthony , Lelièvre Tony , Stoltz Gabriel , Cancès Eric , Caffarel Michel
Published: September 2006

We propose a new algorithm for sampling the N-body density ∣Ψ(R)∣2∕∫R3N∣Ψ∣2 in the variational Monte Carlo framework. This algorithm is based upon a modified Ricci-Ciccotti discretization of the Langevin dynamics in the phase space (R,P) improved by a Metropolis-Hastings accept/reject step. We show through some representative numerical examples (lithium, fluorine, and copper atoms and phenol molecule) that this algorithm is superior to the standard sampling algorithm based on the biased random walk (importance sampling).
Volumes of critical bubbles from the nucleation theorem
Authors: Wilemski Gerald
Published: September 2006

A corollary of the nucleation theorem due to Kashchiev [Nucleation: Basic Theory with Applications (Butterworth-Heinemann, Oxford, 2000)] allows the volume V* of a critical bubble to be determined from nucleation rate measurements. The original derivation was limited to one-component, ideal gas bubbles with a vapor density much smaller than that of the ambient liquid. Here, an exact result is found for multicomponent, nonideal gas bubbles. Provided a weak density inequality holds, this result reduces to Kashchiev’s simple form which thus has a much broader range of applicability than originally expected. Limited applications to droplets are also mentioned, and the utility of the pT,x form of the nucleation theorem as a sum rule is noted.
Hall electron mobility in diamond
Authors: Pernot J. , Tavares C. , Gheeraert E. , Bustarret E. , Katagiri M. , Koizumi S.
Published: September 2006

The low field Hall mobility of electron in diamond was investigated from room temperature to 873K, both experimentally and theoretically. The acoustic deformation potential for electron scattering is determined by fitting of theoretical calculations to experimental data for high quality {111} homoepitaxial phosphorus-doped diamond films. A good agreement is obtained over a large doping range. A discrepancy for the electron mobilities measured under optical excitation is discussed. The maximum Hall mobility achievable at thermodynamical equilibrium in low compensated n-type diamond is shown to be close to 1000cm2∕Vs at room temperature.
Nonvolatile organic bistable devices fabricated utilizing Cu2O nanocrystals embedded in a polyimide layer
Authors: Jung Jae Hun , Kim Jae-Ho , Kim Tae Whan , Song Mun Seop , Kim Young-Ho , Jin Sungho
Published: September 2006

The bistable effects of cuprous oxide (Cu2O) nanoparticles embedded in a polyimide (PI) matrix were investigated. Transmission electron microscopy images and selected area electron diffraction patterns showed that Cu2O nanocrystals were formed inside the PI layer. Current-voltage (I-V) measurements on Al/PI/nanocrystalline Cu2O∕PI∕Al structures at 300K showed a nonvolatile electrical bistability behavior. A bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results. These results indicate that OBDs fabricated utilizing self-assembled inorganic Cu2O nanocrystals embedded in an organic PI layer hold promise for potential applications in nonvolatile flash memory devices.
Emission characteristics of optically pumped GaN-based vertical-cavity surface-emitting lasers
Authors: Chu Jung-Tang , Lu Tien-Chang , You Min , Su Bor-Jye , Kao Chih-Chiang , Kuo Hao-Chung , Wang Shing-Chung
Published: September 2006

The laser emission characteristics of a GaN-based vertical-cavity surface-emitting laser with two dielectric distributed Bragg reflectors were investigated under optically pumped operation at room temperature. The laser emitted wavelength at 415.9nm with an emission linewidth of 0.25nm and threshold pumping energy of 270nJ. The laser has a high characteristic temperature of about 278K and high spontaneous emission coupling factor of 10−2. The laser emission showed single and multiple spot emission patterns with spectral and spatial variations under different pumping conditions.
Approach to magnetic losses and their frequency dependence in Mn–Zn ferrites
Authors: Fiorillo F. , Beatrice C. , Bottauscio O. , Manzin A. , Chiampi M.
Published: September 2006

The frequency dependence of the magnetic energy losses in sintered Mn–Zn ferrites is predicted from the quasistatic regime to the megahertz range. The predicting model is based on the appraisal of the contributions by domain wall (dw) displacements and magnetization rotations and the related relaxation-resonant-type dissipation mechanisms. Eddy currents are demonstrated to play little to negligible role. The frequency dependence of the dw generated losses is calculated from knowledge of the quasistatic losses, whereas the contribution by rotations is obtained via the Landau-Lifshitz-Gilbert equation, assuming distributed anisotropy fields. The model excellently applies to the frequency response of commercial ferrites.
Cooperative absorption of terahertz radiation by plasmon modes in an array of field-effect transistors with two-dimensional electron channel
Authors: Popov V. V. , Tsymbalov G. M. , Fateev D. V. , Shur M. S.
Published: September 2006

The authors computer simulations show that plasmon modes excited in an array of field-effect transistors with two-dimensional electron channel strongly couple to terahertz radiation due to the synchronization of plasma oscillations in different unit cells of the array. It is shown that in such a device the higher-order plasmon modes are excited much more effectively than in a large area two-dimensional electron channel coupled to terahertz radiation by a slit-grating gate. Effective excitation of the higher-order plasmon modes makes it possible to design terahertz plasmonic devices with operating frequencies up to 15THz or even higher.
Graded band gap for dark-current suppression in long-wave infrared W-structured type-II superlattice photodiodes
Authors: Vurgaftman I. , Aifer E. H. , Canedy C. L. , Tischler J. G. , Meyer J. R. , Warner J. H. , Jackson E. M. , Hildebrandt G. , Sullivan G. J.
Published: September 2006

A new W-structured type-II superlattice photodiode design, with graded band gap in the depletion region, is shown to strongly suppress dark currents due to tunneling and generation-recombination processes. The long-wave infrared (LWIR) devices display 19%–29% quantum efficiency and substantially reduced dark currents. The median dynamic impedance-area product of 216Ωcm2 for 33 devices with 10.5μm cutoff at 78K is comparable to that for state-of-the-art HgCdTe-based photodiodes. The sidewall resistivity of ≈70kΩcm for untreated mesas is also considerably higher than previous reports for passivated or unpassivated type-II LWIR photodiodes, apparently indicating self-passivation by the graded band gap.
Scaling laws for pulsed electrohydrodynamic drop formation
Authors: Chen C.-H. , Saville D. A. , Aksay I. A.
Published: September 2006

A pulsed electrohydrodynamic jet can produce on-demand drops much smaller than the delivery nozzle. This letter describes an experimentally validated model for electrically pulsed jets. Viscous drag in a thin nozzle limits the flow rate and leads to intrinsic pulsations of the cone jet. A scale analysis for intrinsic cone-jet pulsations is derived to establish the operating regime for drop deployment. The scaling laws are applicable to similar electrohydrodynamic processes in miniaturized electrospraying systems.
Structure of HfO2 films epitaxially grown on GaAs (001)
Authors: Hsu C.-H. , Chang P. , Lee W. C. , Yang Z. K. , Lee Y. J. , Hong M. , Kwo J. , Huang C. M. , Lee H. Y.
Published: September 2006

High-quality HfO2 films of technologically important thickness ranging from 1.8to17nm have been grown epitaxially on GaAs (001) by molecular beam epitaxy. Thorough structural and morphological investigations were carried out by x-ray scattering and high-resolution transmission electron microscopy. The films exhibit an atomically sharp interface with the substrate and are of a monoclinic phase with predominant (001)-plane epitaxy between the HfO2 films and GaAs, in spite of a large lattice mismatch of >8.5%.
Self-gating in an electron Y-branch switch at room temperature
Authors: Hartmann D. , Worschech L. , Höfling S. , Forchel A. , Reithmaier J. P.
Published: September 2006

The authors have observed a self-gating effect in electron Y-branch switches at room temperature. The devices, with geometrical branch widths smaller than 50nm, were fabricated by electron beam lithography and shallow wet chemical etching from a modulation doped GaAs∕AlGaAs heterostructure with a two-dimensional electron gas approximately 30nm below the surface. The side-gate operation is enhanced by the self-gating effect between the branches. In particular, the differential voltage gain of the Y-branch switch increases approximately quadratically with the bias voltage.
Efficient nondoped white organic light-emitting diodes based on electromers
Authors: Xu Xinjun , Yu Gui , Di Chong’an , Liu Yunqi , Shao Kefeng , Yang Lianming , Lu Ping
Published: September 2006

The authors report excellent white organic light-emitting diodes (WOLEDs) made of 9,9bis[4-(di-p-tolyl)aminophenyl]-2,7-bis(diphenylamino)fluorene (TADPF) or 9,9-bis[4-(di-p-tolyl)aminophenyl]-2,7-bis(9-carbazolyl)fluorene (TAKF). The superposition of a yellow emission coming from the TADPF or TAKF electromer and a blue emission originating from bis(2-(2-hydroxyphenyl)benzothiazolate)zinc gives rise to a pure white-light emission. The multilayer device using TADPF shows a maximum luminance of 5123cd∕m2, a current efficiency of 2.8cd∕A, and Commission Internationale d’Eclairage chromaticity coordinates of (0.33, 0.33). This result is the optimal for WOLEDs based on electromers so far reported.
Recombinant vaccinia/fowlpox NY-ESO-1 vaccines induce both humoral and cellular NY-ESO-1-specific immune responses in cancer patients
Authors: Jäger Elke , Karbach Julia , Gnjatic Sacha , Neumann Antje , Bender Armin , Valmori Danila , Ayyoub Maha , Ritter Erika , Ritter Gerd , Jäger Dirk , Panicali Dennis , Hoffman Eric , Pan Linda , Oettgen Herbert , Old Lloyd J. , Knuth Alexander
Published: September 2006

NY-ESO-1 is a cancer/testis antigen expressed in a range of human malignancies, and a number of vaccine strategies targeting NY-ESO-1 are being developed. In the present study, the safety and immunogenicity of recombinant vaccinia-NY-ESO-1 and recombinant fowlpox-NY-ESO-1 were analyzed in a series of 36 patients with a range of different tumor types. Each construct was first tested individually at two different dose levels and then in a prime-boost setting with recombinant vaccinia-NY-ESO-1 followed by recombinant fowlpox-NY-ESO-1. The vaccines were well tolerated either individually or together. NY-ESO-1-specific antibody responses and/or specific CD8 and CD4 T cell responses directed against a broad range of NY-ESO-1 epitopes were induced by a course of at least four vaccinations at monthly intervals in a high proportion of patients. CD8 T cell clones derived from five vaccinated patients were shown to lyse NY-ESO-1-expressing melanoma target cells. In several patients with melanoma, there was a strong impression that the natural course of the disease was favorably influenced by vaccination.
Multiple determinants influence root colonization and induction of induced systemic resistance by Pseudomonas chlororaphis O6
Authors: HAN SONG HEE , ANDERSON ANNE J. , YANG KWANG YEOL , CHO BAIK HO , KIM KIL YONG , LEE MYUNG CHUL , KIM YONG HWAN , KIM YOUNG CHEOL
Published: September 2006

Colonization of the roots of tobacco by Pseudomonas chlororaphis O6 induces systemic resistance to the soft‐rot pathogen, Erwinia carotovora ssp. carotovara SCC1. A screen of the transposon mutants of P. chlororaphis O6 showed mutants with about a fivefold reduction in ability to induce systemic resistance to the soft‐rot disease. These mutations disrupted genes involved in diverse functions: a methyl‐accepting chemotaxis protein, biosynthesis of purines, phospholipase C, transport of branched‐chain amino acids and an ABC transporter. Additional mutations were detected in the intergenic spacer regions between genes encoding a GGDEF protein and fumarate dehydratase, and in genes of unknown function. The mutants in the ABC transporters did not display reduced root colonization. However, the other mutants had up to 100‐fold reduced colonization levels. Generally the production of metabolites important for interactions in the rhizosphere, phenazines and siderophores, was not altered by the mutations. A reduced induction of systemic resistance by a purine biosynthesis mutant with a disrupted purM gene correlated with poor growth rate, lesser production of phenazines and siderophore and low levels of root colonization. These studies showed that multiple determinants are involved in the induction of systemic resistance, with there being a requirement for strong root colonization.
Transgenic Arabidopsis plants expressing Agrobacterium tumefaciens VirD2 protein are less susceptible to Agrobacterium transformation
Authors: HWANG HAU‐HSUAN , MYSORE KIRANKUMAR S. , GELVIN STANTON B.
Published: September 2006

Agrobacterium tumefaciens causes crown gall disease on many plant species and can result in considerable economic losses. Here we report a new strategy to control crown gall disease by over‐expressing Agrobacterium tumefaciens VirD2 protein in plants. Transgenic Arabidopsis plants over‐expressing virD2 from constitutive or wound‐inducible promoters are less susceptible to Agrobacterium‐mediated transformation. Additionally, the transient introduction of an A. tumefaciens virD2 gene in tobacco BY‐2 cells reduces subsequent Agrobacterium‐mediated transformation.
Review article: management of patients with chronic hepatitis C virus infection and ‘normal’ alanine aminotransferase activity
Authors: ZEUZEM S. , ALBERTI A. , ROSENBERG W. , MARCELLIN P. , DIAGO M. , NEGRO F. , PRATI D. , PUOTI C. , ROBERTS S. K. , SHIFFMAN M. L.
Published: September 2006

Background

Hepatitis C virus infection, a major cause of chronic liver disease, occurs with normal serum alanine aminotransferase activity in approximately 25% of patients. These patients have historically remained untreated but substantial evidence indicates liver damage, progression of disease and impaired quality of life in some individuals.

Aim

To review the current management of patients with chronic hepatitis C and normal alanine aminotransferase activity.

Methods

This review represents the summary of discussions at a Clinical Workshop with a comprehensive literature searching of available databases (PubMed and Embase).

Results

Current limits defining normal serum alanine aminotransferase activity are not representative of a ‘healthy’ status. Most patients with hepatitis C and normal alanine aminotransferase levels have histologically proven liver damage that, although generally mild, may be significant (≥F2) in up to 20% of patients and progresses at approximately 50% of the rate in patients with elevated alanine aminotransferase levels. Some patients have persistently normal alanine aminotransferase activity and may have a more benign outcome, but a significant proportion (≥20%) experience periods of increased serum alanine aminotransferase activity which may be associated with enhanced disease progression.

Conclusions

A treatment approach that considers host and virus‐related variables and optimizes patient and cost benefits may therefore provide more effective management of patients with chronic hepatitis C and normal alanine aminotransferase activity.
Impact on adherence and sustained virological response of psychiatric side effects during peginterferon and ribavirin therapy for chronic hepatitis C
Authors: CASTERA L. , CONSTANT A. , HENRY C. , CHAMPBENOIT P. , BERNARD P.‐H. , DE LEDINGHEN V. , DEMOTES‐MAINARD J. , COUZIGOU P.
Published: September 2006

Background

The psychiatric side effects of interferon, often responsible for dose reduction or treatment discontinuation, represent a major limitation in the treatment of chronic hepatitis C (CHC).

Aim

To prospectively assess the impact on adherence and sustained virological response (SVR) of the occurrence of psychiatric side effects during peginterferon and ribavirin therapy for CHC.

Methods

Ninety‐eight consecutive treatment‐naïve CHC patients receiving a standard course of peginterferon plus ribavirin were systematically screened for psychiatric side effects, using DSM‐IV, at baseline and both during and after treatment.

Results

Psychiatric side effects occurred in 38 patients (39%), mostly within the first 12 weeks (87%), and always consisted of mood disorders. Overall, 68% of patients achieved an SVR (71% of patients with mood disorders and 68% of those without;P = N.S.). Peginterferon and ribavirin dose reductions did not differ between patients with mood disorders and those without (46% vs. 37%, respectively;P = N.S. and 13% vs. 22%, respectively;P = N.S.). Anti‐viral therapy had to be discontinued in four patients (nonresponse: two, hyperthyroidism: one, psychiatric event: one).

Conclusion

Early detection and appropriate management of psychiatric side effects during peginterferon and ribavirin therapy for CHC allow optimizing adherence and virological efficacy.
A prospective 1‐year follow‐up study in patients with functional or organic dyspepsia: changes in gastrointestinal symptoms, mental distress and fear of serious illness
Authors: PAJALA M. , HEIKKINEN M. , HINTIKKA J.
Published: September 2006

Background

Psychosocial factors are common among patients with functional gastrointestinal disorders (FGIDs). Whether they affect the course of the disease remains unresolved.

Aim

To evaluate whether reassuring investigations of primary care patients with functional dyspepsia (FD) and organic dyspepsia (OD) influence gastrointestinal (GI) symptoms and psychological factors, and to assess whether these changes are correlated.

Methods

Four hundred consecutive patients with dyspepsia were referred for thorough examinations. Patients completed questionnaires screening symptoms at baseline and on 1‐year follow‐up.

Results

At baseline, there was no difference in GI symptoms, prevalence of mental distress or fear of serious illness between patients with FD or OD. On follow‐up, the patients with FD had more GI symptoms, but there was no difference in mental distress or fear of serious illness. Relevant GI symptom reduction related to alleviation of mental distress (53.4% vs. 20.5%, P < 0.001) and fear of serious illness (56.5% vs. 23.7%, P = 0.002), but reached statistical significance only in patients with OD.

Conclusions

Gastrointestinal symptoms in FD patients are long lasting compared with those with organic diseases. Reassuring investigations could lower mental distress and fear of serious illness in these patients. Psychological factor change correlates with the change in GI symptom severity and is not specific to FGIDs.
Persistent elevation of serum alanine aminotransferase levels leads to poor survival and hepatocellular carcinoma development in type 1 autoimmune hepatitis
Authors: MIYAKE Y. , IWASAKI Y. , TERADA R. , OKAMAOTO R. , IKEDA H. , MAKINO Y. , KOBASHI H. , TAKAGUCHI K. , SAKAGUCHI K. , SHIRATORI Y.
Published: September 2006

Background

Although the prognosis of type 1 autoimmune hepatitis is generally good with immunosuppressive treatment, the disease progresses in some patients despite the treatment. The prognosis may be determined by the clinical course.

Aim

To evaluate the long‐term prognosis and assess the predictive factors for a serious event, including the development of hepatocellular carcinoma or death.

Methods

Sixty‐nine patients with type 1 autoimmune hepatitis were prospectively followed up regularly, with a median follow‐up period of 96 months (49–201 months).

Results

During the follow‐up period, three patients (4%) developed hepatocellular carcinoma, and two of these three patients died. Another patient died of liver failure. The 10‐year survival rate was 98%, and the 10‐year hepatocellular carcinoma‐free rate was 93%. The four patients experiencing a serious event received higher maintenance doses of corticosteroid during their follow‐up periods than those did not. However, serum alanine aminotransferase levels during the follow‐up period were higher in these four patients than in the others.

Conclusions

Persistent elevation of serum alanine amniotransferase levels during the follow‐up period, rather than factors existing prior to medical treatment is considered to be an important prognostic factor, and it is indicated that poor outcomes may result from the resistance to immunosuppressive treatment.