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Bias Voltage (bias + voltage)
Selected AbstractsEffect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion PlasmaCONTRIBUTIONS TO PLASMA PHYSICS, Issue 10 2007M. Kr. Abstract This article reports about the ion sheath thickness variation occurring in front of a negatively biased plate immersed in the target plasma region of a double plasma device. The target plasma is produced due to the local ionization of neutral gas by the high energetic electrons coming from the source region (main discharge region). It is observed that for an increase in cathode voltage (filament bias voltage) in the source region, the ion flux into the plate increases. As a result, the sheath at the plate contracts. Again, for an increase in source anode voltage (magnetic cage bias), the ion flux to the plate decreases. As a result, the sheath expands at the plate. The ion sheath formed at the separation grid of the device is found to expand for an increase in cathode voltage and it contracts for an increase in the anode voltage of the main discharge region. One important observation is that the applied anode bias can control the Bohm speed of the ions towards the separation grid. Furthermore, it is observed that the ion current collected by the separation grid is independent of changes in plasma density in the diffusion region but is highly dependent on the source plasma parameters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quantized Double-Layer Charging of Iron Oxide Nanoparticles on a-Si:H Controlled by Charged Defects in a-Si:HELECTROANALYSIS, Issue 12 2007Martin Weis Abstract Sequential single-electron charging of iron oxide nanoparticles encapsulated in oleic acid/oleyl amine envelope and deposited by the Langmuir-Blodgett technique onto Pt electrode covered with undoped hydrogenated amorphous silicon film (a-Si:H) is reported. Quantized double-layer charging of nanoparticles is detected by cyclic voltammetry as current peaks and the charging effect can be switched on/off by the excess of negative/positive charged defect states in the a-Si:H layer. The particular charge states in a-Si:H are created by the simultaneous application of a suitable bias voltage and illumination before the measurement. [source] Robustness of Spin Polarization in Graphene-Based Spin ValvesADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Masashi Shiraishi Abstract The decrease of spin polarization in spintronics devices under the application of a bias voltage is one of a number of currently important problems that should be solved. Here, an unprecedented robustness of the spin polarization in multilayer-graphene spin valves at room temperature is revealed. Surprisingly, the spin polarization of injected spins is constant up to a bias voltage of +2.7,V and ,0.6,V in positive- and negative-bias voltage applications at room temperature, respectively, which is superior to all spintronics devices. This finding is induced by suppression of spin scattering due to an ideal-interface formation. Furthermore, an important accordance between theory and experiment in molecular spintronics is found by observing the fact that the signal intensity in a local scheme is double that in a nonlocal scheme, as theory predicts, which provides construction of a steadfast physical basis in this field. [source] Force Spectroscopic Investigations During the Local Oxidation of n -Octadecyltrichlorosilane Monolayers,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2006S. Hoeppener Abstract Scanning force spectroscopy (SFS) is a powerful tool for investigating surface properties with high precision. Unlike most common spectroscopic techniques, information about local properties can also be obtained from surface areas with nanometer dimensions. This makes SFS a useful investigative tool for small lithographic structures. We apply the continuous recording of force curves to extract valuable information about the local oxidation of a monolayer of n -octadecyltrichlorosilane molecules self-assembled on silicon. The oxidation is carried out while simultaneously recording the force curves during the application of a bias voltage to the tip. The dynamics of the induced surface modifications and changes in the surface properties are followed by analyzing specific spots in the force curves. [source] Encapsulated-Dye All-Organic Charged Colored Ink Nanoparticles for Electrophoretic Image DisplayADVANCED MATERIALS, Issue 48 2009Sun Wha Oh Electrophoretic ink nanoparticles with high mobility are successfully fabricated by dispersion polymerization. The color of test cells can be changed by applying a bias voltage, as shown in the figure: the lower row shows the same cells as the upper row but with an applied voltage. These all-organic, encapsulated-dye, electrophoretic ink particles are expected to reduce the fabrication cost of e-ink in electrophoretic image display cells. [source] Optical properties of a novel fluorene-based thermally stable conjugated polymer containing pyridine and unsymmetric carbazole groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2009Der-Jang Liaw Abstract A new diiodo monomer containing heterocyclic pyridine and carbazole groups was synthesized via Chichibabin reaction and used in the preparation of a conjugated polymer via Suzuki coupling approach. The conjugated polymer was highly soluble in common organic solvents such as NMP, THF, dichloromethane, chloroform, toluene, xylene, and benzene at room temperature. The polymer had high glass transition temperature at 191 °C and Td10 at 434 °C in nitrogen atmosphere. The pristine polymer exhibited the UV,vis maximum absorption at 355 nm and shifted to 420 nm after protonation. The emission of the polymer in THF solution changed from the blue region with maximum peak at 400 nm to the yellow region with maximum peak at 540 nm after protonated by HCl, and the intensity of emission depended on the concentration of acid. The polymer also showed electrochromic behavior under applied voltage. The emission color of the polymer film changed from blue (435 nm) to yellow (570 nm) when 2.5 V bias voltage was applied. The polymer also exhibited write-once and read-many-times (WORM) polymer memory effect with tristable states. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 991,1002, 2009 [source] ZnO-based photodetector with internal photocurrent gainPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2010L. A. Kosyachenko Abstract The photoresponsive structures prepared by magnetron sputtering of ZnO on p-Si substrates followed by vacuum evaporation of semitransparent Ni film on ZnO surface are investigated. The obtained Ni/n-ZnO/p-Si structures show high sensitivity that sharply increases with increase in applied voltage. Under a bias voltage of 5,V, the responsivities at ,,=,390,nm and ,,=,850,nm were equal to 210 and 110,A/W, which correspond to quantum efficiencies of 655 and 165, respectively. It is assumed that the observed strong response is attributed to internal gain in the Ni/n-ZnO/p-Si phototransistor structure containing Ni/n-ZnO Schottky contact as the emitter junction and n-ZnO/p-Si heterostructure as the collector junction. The response time of the device is ,10,7,s. Alternative mechanisms of photocurrent multiplication in such structures are also discussed. [source] Influence of insulating barrier thickness on the magnetoresistance properties of a magnetic tunnel junction with Zr-alloyed Al oxide barrierPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004Chul-Min Choi Abstract We have investigated the magnetoresistive properties and thermal and electrical stability of a magnetic tunnel junction (MTJ) with a high-quality, ultra-thin Zr-alloyed Al oxide (ZrAl oxide) barrier of below 1.0 nm. We obtained the highest bias voltage and breakdown voltage of 711 mV and 1.75 V for a 1.6-nm-thick barrier. The resistance drops from 1850 , to 72 , as the ZrAl thickness decreases from 1.6 to 0.6 nm, respectively. A significant TMR (Tunneling Magneto-resistance) value of 17% and a junction resistance of 98 , were obtained for a MTJ with a ZrAl oxide barrier thickness of 0.8 nm. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Efficient and reliable method for the simulation of scanning tunneling images and spectra with local basis setsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2006Óscar Paz Abstract Based on Bardeen's perturbative approach to tunneling, we have found an expression for the current between tip and sample, which can be efficiently coded in order to perform fast ab initio simulations of STM images. Under the observation that the potential between the electrodes should be nearly flat at typical tunnel gaps, we have addressed the difficulty in the computation of the tunneling matrix elements by considering a vacuum region of constant potential delimited by two surfaces (each of them close to tip and sample respectively), then propagating tip and sample wave functions by means of the vacuum Green's function, to finally obtain a closed form in terms of convolutions. The current is then computed for every tip-sample relative position and for every bias voltage in one shot. The electronic structure of tip and sample is calculated at the same footing, within density functional theory, and independently. This allows us to carry out multiple simulations for a given surface with a database of different tips. We have applied this method to the Si(111)-(7 × 7) and Ge(111)- c (2 × 8) surfaces. Topographies and spectroscopic data, showing a very good agreement with experiments, are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic transport through large quantum dots in the Kondo regimePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003P. Stefa Abstract Conductance through a large two-level quantum dot is investigated theoretically in the strong coupling regime. In large quantum dots the separation between discrete levels becomes smaller than the level width due to strong hybridization with electrodes. In such circumstances, apart from strong electronic correlations in the quantum dot, the indirect interaction between both the spatial levels comes into play. It takes place in lateral quantum dots, where the spatial level index is not conserved during the hybridization process with electrodes. This interaction shifts the Kondo resonance peak in the density of states out of the Fermi surface and alters its intensity. This feature can be observed in the differential conductance dependence vs. bias voltage. The virtual inter-level mixing is suppressed for temperatures above the Kondo temperature of the system. The results of theoretical predictions are compared with the results of experimental conductance measurements performed on large quantum dots and some non-typical conductance features are clarified. [source] Polarization field crossover in semi-polar InGaN/GaN single quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010H. Shen Abstract We present an electroreflectance study of the polarization field in semi-polar (10) and (112) oriented InGaN quantum wells (QW). For the () sample, the flat-QW condition (the electric field in the QW is zero) is at a reverse bias voltage. For the (112) sample, the flat-QW condition is at a forward bias voltage larger than the turn on voltage of the diode. However, the flat-barrier condition (the electric field in the barrier region is zero) is at a forward bias voltage less than the turn on voltage of the diode. The flat-QW condition and the flat-barrier condition are determined by examining the zero-crossing and the Franz-Keldysh oscillations in the electroreflectance signal for (10) and (112) InGaN QWs, respectively. From the corresponding bias voltages, we deduce the polarization field in the QWs and conclude that in the semi-polar InGaN/GaN QW there is a crossover angle between the polar and non-polar orientations where the polarization field vanishes. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Observation of the second-nearest-neighbor Bloch oscillation in a GaAs/AlAs superlatticePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008T. Hasegawa Abstract We have systematically investigated the quantum beat of the miniband excitons and the Bloch oscillation in the Wannier-Stark (WS) localization as a function of applied bias voltage in a GaAs (6.8 nm)/AlAs (0.9 nm) superlattice embedded in a p - i - n diode structure. The coherent dynamics behaviors were detected with a reflection-type pump-probe technique. We clearly observed the transformation process from the miniband-exciton quantum beat to the Bloch oscillation with an increase in applied bias voltage producing an internal electric field. The noteworthy finding is the fact that the Bloch oscillation with the frequency of vBO = 2eFD /h appears in a weak localization regime in addition to the usual Bloch oscillation with vBO = eFD /h in a strong localization regime, where F is the electric field, and D is the superlattice period. The frequency of 2eFD /h indicates that the newly observed Bloch oscillation is due to the wave-packet motion in the second-nearest-neighbor space range. The results described above are explained by the electric-field-strength dependence of the envelope-function localization, which is estimated from the envelope-function profile calculated by a transfer-matrix method and the excitonic transitions observed by electroreflectance spectroscopy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristic variation of superconducting thin films modified by an atomic force microscopePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2005Hyeong-Gon Kang Abstract Superconducting thin film surfaces were modified in order to test a possibility as a channel of superconducting flux flow transistor (SFFT) by AFM lithography. A conventional lithography method has been employed for superconducting strips which were patterned on LaAlO3 substrates. A region of the strips was selectively oxidized by an AFM probe in the presence of the electric field between the probe and the strip. Then the modified surface was analyzed by AFM, EPMA, and I-V curves. The thickness of the strips increases with the bias voltage as well as the scanning number due to the oxidation. The nonsuperconducting material produced by an AFM lithography process affects the characteristics of SFFT in the flux creep mode of I,V curves. This study represents a dynamic idea to fabricate the superconducting flux flow transistors with nano-channel by the AFM lithography. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Shot noise in tunneling through a quantum dot arrayPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003G. Kiesslich Abstract The shot noise suppression in a sample containing a layer of self-assembled InAs quantum dots has been investigated experimentally and theoretically. The observation of a non-monotonic dependence of the Fano factor on the bias voltage in a regime where only few quantum dot ground states contribute to the tunneling current is analyzed by a master equation model. Under the assumption of tunneling through states without Coulomb interaction this behaviour can be qualitatively reproduced by an analytical expression. [source] Helianthos: Roll-to-Roll Deposition of Flexible Solar Cell ModulesPLASMA PROCESSES AND POLYMERS, Issue 3 2007Edward A. G. Hamers Abstract In the development of the roll-to-roll deposition of amorphous silicon by means of plasma enhanced chemical vapor deposition, a number of different plasma aspects have been of importance. First, the understanding of process windows in terms of a dust free plasma has led to the formulation of an empirical scaling law for the dust free to dust forming transition in terms of the crucial process parameters such as, e.g., power and gas flows. Second, the homogeneity of deposition on an effective width of 30 cm has been demonstrated to be better than 5%. Increasing the deposition rate might be achieved by increasing the power density, but it scales only as (power density)0.77. A last important issue in roll-to-roll processing of long runs is process stability and on-line quality control. The accurate measurement of self bias voltage and optical thickness of the deposited stacks have proven to be very useful in this context. [source] Identification of degradation mechanisms in field-tested CdTe modulesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2006Thomas Carlsson Abstract Field tests and accelerated ageing tests were conducted on CdTe photovoltaic modules with Sb-based back contacts. Significant performance degradation was observed during one and a half years of outdoor exposure. Small-area samples were prepared from field tested modules and characterized with current,voltage, capacitance,voltage and resistance measurements. Results show that module performance degradation in the field can be partly attributed to a decrease in doping concentration close to the CdS/CdTe junction and an increased resistance in the transparent front contact. A comparison with results in the literature indicates that bias voltage may play a role in the degradation process. Copyright © 2005 John Wiley & Sons, Ltd. [source] Structure and mechanical properties of nanocrystalline boron nitride thin films ,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2001Paolo M. Ossi Abstract Boron nitride thin films have been deposited on (100) Si wafers, kept at low temperature, by radio frequency (r.f.) magnetron sputtering. The r.f. target power was fixed at 150,W and the substrate bias voltage ranged between ,50 and ,130,V. Film composition was checked by Auger electron spectroscopy; the structure was investigated by Fourier transform IR spectroscopy, glancing-angle X-ray diffraction and micro-Raman spectroscopy. Film hardness and Young's modulus were measured by nanoindentation. Film composition is nearly equiatomic, with a low degree of gaseous contamination. All samples are very fine grained, and nanocrystalline. Film coordination is mixed sp2,sp3, and the fraction of tetrahedral coordination depends critically on the bias voltage value. In hexagonal sp2 -bonded films the hardnesses and Young's moduli are low and increase considerably with the content of sp3 -coordinated cubic phase. Copyright © 2001 John Wiley & Sons, Ltd. [source] Orientation Ordering of Nanoparticle Ag/Co Cores Controlled by Electric and Magnetic FieldsCHEMPHYSCHEM, Issue 7 2008Katarína Gmucová Dr. Abstract The effect of electric and magnetic fields on the sandwich structure Pt/hydrogenated amorphous silicon (a-Si:H)/stearic acid monolayer/Langmuir,Blodgett film of Ag/Co nanoparticles encapsulated in an organic envelope is studied. This structure is used as a working electrode in an electrochemical cell filled with NaCl solution (1 mM) and equipped with an Ag/AgCl reference electrode. Reversible changes in voltammograms are observed due to treatments (negative or positive bias voltage and simultaneous laser irradiation) applied to the designed structure before measurements. As an explanation of the observed phenomena we suggest that both the Co-up and Ag-up (on the a-Si:H surface) orientation orderings of nanoparticle Ag/Co cores are repeatedly reached. The role of the photovoltaic material (a-Si:H) in the observed behavior is explained. Voltammetric measurements with an applied magnetic field support our idea about the orientation ordering of nanoparticle cores. [source] Contact Angle Analysis During the Electro-oxidation of Self-Assembled Monolayers Formed by n -OctadecyltrichlorosilaneADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Nicole Herzer Abstract The electrochemical oxidation process of self-assembled monolayers formed by n -octadecyltrichlorosilane (OTS) molecules on silicon wafers has been studied in a droplet of water by means of in situ water contact angle measurements. The application of different bias voltages between the substrate and a counter electrode placed into the droplet resulted in changes of the chemical nature of the monolayer, which yielded a significant alteration of the surfaces properties. Due to the changes of the wetting properties of the monolayer during the electro-oxidation process a change in the contact angles of the water droplet is concomitantly observed. This allows the in situ monitoring of the electro-oxidation process for large modified areas of several millimeters in diameter. The chosen approach represents an easy way to screen the major parameters that influence the oxidation process. Afterwards, the oxidized regions are characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) measurements, and atomic force microscopy (AFM) investigations to obtain more information about the electro-oxidation process. The observations are correlated to experimental results obtained for oxidations performed on a smaller dimension range in the water meniscus of a conductive, biased AFM tip. A good correlation of the results in the different dimension ranges could be found. [source] Resistive switching polymer materials based on poly(aryl ether)s containing triphenylamine and 1,2,4-triazole moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2008Kun-Li Wang Abstract A series of poly(aryl ether)s were successfully prepared via aromatic nucleophilic substitution reaction from various bisphenols and a novel bipolar aryl difluoride monomer containing electron-donor triphenylamine and electron-acceptor 1,2,4-triazole moieties. The poly(aryl ether)s exhibited excellent solubility in organic solvents such as dimethylformamide, chloroform, and tetrahydrofuran at room temperature. The poly(aryl ether)s showed high thermal stability with Td10 higher than 500 °C and glass transition temperatures (Tg) higher than 187 °C. The thin films of the poly(aryl ether)s indicated bistable resistive switching behavior with ON/OFF current ratios as high as 103. The switching on and switching off bias voltages of the poly(aryl ether)s were affected by the bisphenol moiety. The good resistive switching behavior of the poly(aryl ether)s made them promising candidates for future nonvolatile memory applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6861,6871, 2008 [source] High-field actively detuneable transverse electromagnetic (TEM) coil with low-bias voltage for high-power RF transmissionMAGNETIC RESONANCE IN MEDICINE, Issue 6 2007Nikolai I. Avdievich Abstract The design and construction of a 4T (170 MHz) transverse electromagnetic (TEM) actively detuneable quadrature head coil is described. Conventional schemes for active detuning require high negative bias voltages (>300 V) to prevent leakage of RF pulses with amplitudes of 1,2 kW. To extend the power handling capacity and avoid the use of high DC bias voltages, we developed an alternate method of detuning the volume coil. In this method the PIN diodes in the detuning circuits are shorted when the RF volume coil is tuned, and negatively biased with ,12 V when the coil is detuned. To preserve the high QU/QL ratio of the TEM coil, we modified the method of Nabetani and Watkins (Proceedings of the 13th Annual Meeting of ISMRM, Kyoto, Japan, 2004, abstract 1574) by utilizing a high-impedance (,200 ,), lumped-element, quarter-wavelength transformer. A QU of 500 was achieved for the detuneable TEM, such that incorporation of the detuning network had minimal effect (<1 dB) on the performance of the coil in vivo. Magn Reson Med 57:1190,1195, 2007. © 2007 Wiley-Liss, Inc. [source] About charge-transport mechanisms in mesoporous silicon under adsorption of plant virusesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2009Yuriy Vashpanov Abstract Changes in the electric parameters and the charge-transport mechanism in a mesoporous silicon under adsorption of TORSV (tomato ringspot virus) and GFLV (grapevine fan leaf virus) NEPO-viruses are analyzed. The mechanism influencing the electric characteristics of the mesoporous silicon under adsorption of the plant viruses is related with the changes in parameters of a potential-barrier system due to redistribution of voltages at the silicon structure. The mechanism of charge transport in the mesoporous silicon is more likely connected to the changes in parameters of isotopic heterojunction barriers under small bias voltages, and it can be interpreted as Poole,Frenkel and tunnel conductivity for large bias. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Aharonov,Bohm effect of a quantum ring in the Kondo regimePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003U. F. Keyser Abstract We investigate a small tuneable quantum ring fabricated by direct local oxidation using an atomic force microscope. The device contains very few electrons and is tuned into the Kondo regime. We study this Kondo effect by temperature dependent measurements. At finite bias voltages we observe additional peaks. These vanish with increasing temperature indicating Kondo correlations for these excited states. Additionally, the geometry of our device allows to study Aharonov,Bohm oscillations in the Kondo regime for a device containing less than ten electrons. We observe a modulation of the Kondo effect with a reduced Aharonov,Bohm period explained by electron,electron interaction in our small quantum ring. [source] Polarization field crossover in semi-polar InGaN/GaN single quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2010H. Shen Abstract We present an electroreflectance study of the polarization field in semi-polar (10) and (112) oriented InGaN quantum wells (QW). For the () sample, the flat-QW condition (the electric field in the QW is zero) is at a reverse bias voltage. For the (112) sample, the flat-QW condition is at a forward bias voltage larger than the turn on voltage of the diode. However, the flat-barrier condition (the electric field in the barrier region is zero) is at a forward bias voltage less than the turn on voltage of the diode. The flat-QW condition and the flat-barrier condition are determined by examining the zero-crossing and the Franz-Keldysh oscillations in the electroreflectance signal for (10) and (112) InGaN QWs, respectively. From the corresponding bias voltages, we deduce the polarization field in the QWs and conclude that in the semi-polar InGaN/GaN QW there is a crossover angle between the polar and non-polar orientations where the polarization field vanishes. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin densities in parabolic quantum wires with Rashba spin-orbit interactionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006Sigurdur I. Erlingsson Abstract Using canonical transformations we diagonalize approximately the Hamiltonian of a gaussian wire with Rashba spin-orbit interaction. This proceedure allows us to obtain the energy dispersion relations and the wavefunctions with good accuracy, even in systems with relatively strong Rashba coupling. With these eigenstates one can calculate the non-equilibrium spin densities induced by applying bias voltages across the sample. We focus on the z -component of the spin density, which is related to the spin Hall effect. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN/GaN dual-gate high electron mobility transistors on SiC substrates for high-power mixersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005K. Shiojima Abstract We have demonstrated dual-gate AlGaN/GaN high-electron-mobility transistors on SiC substrates for high-power mixers and examined DC and up-conversion RF measurements with drain-source bias voltages (VDS) to analyze the possible output level. The 0.7 × 300 µm-gate device exhibited the maximum transconductance of 47 mS, maximum RF power of 19.6 dBm and up-conversion gain of 11 dB at 2 GHz when VDS = 15 V. For VDS of over 15 V, the devices occasionally broke down, because, although the device can handle more drain current, but the voltage swing reached the breakdown voltage of about 30 V. These results indicate that a Watt-class output mixer can be easily achieved with this simple dual-gate structure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of Ion Bombardment on the Characteristics of Ti Based Biocompatible CoatingsPLASMA PROCESSES AND POLYMERS, Issue S1 2007Alina Vladescu Abstract TiN and TiAlN coatings were deposited on CoCr alloy, 316L stainless steel, and Si substrates by cathodic arc method. Various ion bombardment conditions were obtained by different DC and pulsed bias voltages applied on the substrates. A comparative analysis of the coating characteristics for different substrate biasing conditions was performed. [source] Electron Tunneling through Molecular Media: A Density Functional Study of Au/Dithiol/Au SystemsCHEMPHYSCHEM, Issue 9 2005Qiang Sun Dr. Abstract We report a density functional theory study of the electronic properties of n -alkanedithiols (CnS2, with n=4, 8 and 12) sandwiched between two Au(111) infinite slab electrodes. We investigate the influence of the distance between the two electrodes and of the molecular chain length, tilt angle, and coverage on the local density of states (LDOS) at the Fermi energy (Ef). We find that the (small) value of the LDOS at Efnear the center of the molecular wires,a quantity that is related to the tunneling current,is mainly determined by the length n of the alkane chains: it originates from the tails of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) which are broadened by the interaction with the electrodes, and decays exponentially with the length of the molecular wire. This opens a nonresonance tunneling channel for charge transport at small bias voltages. While the length of the hydrocarbon chain appears to be the determining factor, the tilt angle of the molecular wires with respect to the electrode surfaces, and therefore the distance between these, has a small influence on the LDOS at the center of the molecule, while the effect of coverage can be ignored. The picture which emerges from these calculations is totally consistent with a through-bond tunneling mechanism. [source] | |||||||||||||||||||