bluuebunny/crossref_metadata_2025 huggingface dataset:
Multifunctional transducer using poly (vinylidene fluoride) active layerand highly conducting poly (3,4-ethylenedioxythiophene) electrode: Actuator and generator
Authors: Lee C. S. , Joo J. , Han S. , Koh S. K.
Published: September 2004

Monomorph and bimorph multifunctional transducers such as actuators and generators were fabricated using a piezoelectric poly (vinylidene fluoride) (PVDF) films as the active layer and a highly conducting poly (3,4-ethylenedioxythiophene)∕poly (4-styrenesulfonate) [PEDOT∕PSS (DMSO for solvent)] as the electrode. In order to enhance the adhesion of the films, either the PVDF films or PEDOT∕PSS (DMSO) electrodes were modified using an ion-assisted-reaction (IAR) method. The direct (generator) and inverse piezoelectric (motor) effects as well as the pyroelectric effect in the PVDF-PEDOT∕PSS based devices were observed. The tip displacement of the 12mm by 30mm bimorph device made with the PEDOT∕PSS (DMSO) electrodes was 3.5mm at the resonance frequency with an appled potential of 40Vrms. The sinusoidal output voltage of the bimorph type generator consisting of the PVDF active layers and PEDOT∕PSS (DMSO) electrodes increased with increasing tip displacement induced by a vibrator. A maximum output voltage of 4.1V in the pyroelectric PVDF device was generated with a change in temperature.
n
-type conductivity in ultrananocrystalline diamond films
Authors: Williams Oliver A. , Curat Stephane , Gerbi Jennifer E. , Gruen Dieter M. , Jackman Richard B.
Published: September 2004

Hall effect measurements have been carried out to determine the carrier density and mobilities in ultrananocrystalline diamond films grown with added nitrogen. The results show clear n-type conductivity with very low thermal activation energy. Mobility values of 1.5cm2V−1s−1 are found for a sheet carrier concentration of 2×1017cm−2. These measurements indicate that ultrananocrystalline films grown with high nitrogen levels in the growth gas mixture can have bulk carrier concentrations of up to 1021, which is very high for diamond films. The n-type nature of this material was also confirmed by Seebeck effect measurements.
Deep subsurface electronic defect image contrast and resolution amplification in Si wafers using infrared photocarrier radiometry
Authors: Batista Jerias , Mandelis Andreas , Shaughnessy Derrick , Li Bincheng
Published: September 2004

A photocarrier radiometry technique using a secondary subband-gap dc light source is introduced, along with the applications to deep subsurface electronic defect analysis in Si wafers. It is shown that the use of a dc light source, in addition to the modulated laser beam, drastically enhances the potential of the technique in resolving low-level damage otherwise virtually indistinguishable by conventional photothermal techniques. Using this methodology, the overall contrast enhancement was about 386% for amplitude and 5586% in phase over conventional photocarrier radiometry.
Observation of magnetohydrodynamic instability and direct measurement of local perturbed magnetic field using motional Stark effect diagnostic
Authors: Jayakumar R. J. , Makowski M. A. , Allen S. L. , Austin M. E. , Garofalo A. M. , LaHaye R. J. , Reimerdes H. , Rhodes T. L.
Published: September 2004

The local oscillating component of the poloidal magnetic field in plasma associated with magnetohydrodynamic (MHD) instabilities has been measured using the motional Stark effects (MSE) diagnostic on the DIII–D tokamark. The magnetic field perturbations associated with a resistive wall mode rotated by internal coils at 20 Hz was measured using the conventional MSE operation mode. These first observations of perturbations due to a MHD mode were obtained on multiple MSE channels covering a significant portion of the plasma and the radial profile of the amplitude of the perturbed field oscillations was obtained. The measured profile is similar to the profile of the amplitude of the electron temperature oscillation measured by electron cyclotron emission (ECE) measurements. In a new mode of measurement, the amplitude of a tearing mode rotating at a high frequency (∼7 kHz) was observed using the spectral analysis of high frequency MSE data on one channel. The spectrum consists of the harmonics of the light modulation employed in the MSE diagnostics, their mutual beat frequencies and their beat frequencies with the rotation frequency of the tearing mode. The value and time variation of the frequency of the observed perturbations is in good agreement with that measured by Mirnov probes and ECE. The article demonstrates that the MSE diagnostic can be used for observing low and high frequency phenomena such as MHD instabilities and electromagnetic turbulence.
Feasibility of a motional Stark effect system on the TCV tokamak
Authors: Siegrist M. R. , Hawkes N. , Weisen H.
Published: September 2004

This article presents a feasibility study for a motional Stark effect diagnostic on the TCV tokamak. A numerical simulation code has been used to identify the optimal port arrangement and geometrical layout. It predicts the expected measurement accuracy for a range of typical plasma scenarios. With the existing neutral particle injector and a detection system based on current day technology, it should be possible to determine the safety factor with an accuracy of the order of 5%. A vertically injected beam through the plasma center would allow to measure plasmas which are centered above the midplane, a common occurrence in connection with electron cyclotron resonance heating and electron cyclotron current drive experiments. In this case a new and ideally more powerful neutral beam injector would be required.
Mechanical effect of gold nanoparticles labeling used for biochemical sensor applications: A multimode analysis by means of SiNx micromechanical cantilever and bridge mass detectors
Authors: Saya D. , Nicu L. , Guirardel M. , Tauran Y. , Bergaud C.
Published: September 2004

The effect on mechanical properties of monolithic SiNx micromechanical cantilever and bridge by the adsorption of gold colloids is reported by measuring their resonance frequency shifts. It is experimentally demonstrated that higher resonance modes are more sensitive to the added mass than the fundamental resonance mode leading to increased sensitivity. This is even more significant with monolithic SiNx bridge resonators due to the tensile stress within the SiNx layer. Indeed, resonance frequencies are about ten times higher than calculation without taking into account the tensile stress which was estimated at 500 MPa. Another important result is that the adsorbed colloids do not produce significant change in the stiffness of the SiNx micromechanical resonators. Hence, it is pointed out that only the added mass of Au colloid contributes to the change in the mechanical characteristics of the resonators. Sensitivities up to 20 Hz/pg can be obtained with a minimum detectable density of gold colloids about 2.6×10−2 nanoparticles/μm2.
Simple force balance accelerometer/seismometer based on a tuning fork displacement sensor
Authors: Stuart-Watson D. , Tapson J.
Published: September 2004

Seismometers and microelectromechanical system accelerometers use the force-balance principle to obtain measurements. In these instruments the displacement of a mass object by an unknown force is sensed using a very high-resolution displacement sensor. The position of the object is then stabilized by applying an equal and opposite force to it. The magnitude of the stabilizing force is easily measured, and is assumed to be equivalent to the unknown force. These systems are critically dependent on the displacement sensor. In this article we use a resonant quartz tuning fork as the sensor. The tuning fork is operated so that its oscillation is lightly damped by the proximity of the movable mass object. Changes in the position of the mass object cause changes in the phase of the fork’s resonance; this is used as the feedback variable in controlling the mass position. We have developed an acceleration sensor using this principle. The mass object is a piezoelectric bimorph diaphragm which is anchored around its perimeter, allowing direct electronic control of the displacement of its center. The tuning fork is brought very close to the diaphragm center, and is connected into a self-oscillating feedback circuit which has phase and amplitude as outputs. The diaphragm position is adjusted by a feedback loop, using phase as the feedback variable, to keep it in a constant position with respect to the tuning fork. The measured noise for this sensor is approximately 10.0 mg in a bandwidth of 100 Hz, which is substantially better than commercial systems of equivalent cost and size.
Sub-pico-Newton shear-force feedback system in air and liquid for scanning probe microscopy
Authors: Giaccari Philippe , Sqalli Omar , Limberger Hans G.
Published: September 2004

Scanning near-field optical microscopy requires a performant sensor to measure the tip-to-sample distance. In this article, we report on a shear force detection scheme for scanning near-field optical microscopy applications. It is based on an all fiber low-coherence interferometer. This setup makes possible the measurements of the tip oscillation amplitude of less than 50 pm both in air and aqueous environment with a precision of 160 fm/Hz1/2, thus demonstrating the ability to perform topographic measurements both in air and in liquids with a resolution better than 1 nm in tip-sample distance. Stable feedback in air and fluids is obtained with tip-sample interaction forces below 1 pN.
Compact electron beam ion source with high-TC bulk superconductors
Authors: Nakamura Nobuyuki , Nakai Yoichi , Kanai Yasuyuki , Komaki Ken-ichiro , Endo Atsumi , Yamazaki Yasunori
Published: September 2004

We have developed an electron beam ion source (EBIS) assembling three rings made of high-TC superconductor as a solenoid coil, which enables us to construct a “table-top” EBIS operated at the liquid N2 temperature with a strong magnetic field. Optimizing a pulse field magnetization procedure, the assembly yielded a magnetic field as high as 0.8 T under a persistent mode, which stably lasted more than two days. An electron beam of 12 keV-50 mA was compressed to a current density of about 300 A/cm2 and guided by the magnetic field along the axis of the drift tube. After exiting the drift tube, the electron beam was decelerated to 2 keV and collected with an electron collector with an efficiency of more than 99%. We have succeeded in extracting highly charged ions such as Ar17+ and Xe42+.
Evaluation of resolution of flexure parallel mechanisms for ultraprecision manipulation
Authors: Pham Huy-Hoang , Chen I-Ming
Published: September 2004

A method for evaluating the resolution of ultraprecision manipulation systems based on the flexure parallel mechanism (FPM) is presented. The resolution of the open-loop system is theoretically determined by the resolution transmission from the actuated joints to the end–effector and the resolution of actuators. The method studies the definition of the resolution indicators that includes the global resolution transmission scale and the uniformity of resolution over the entire workspace of the flexure mechanism. The computational algorithm for the defined resolution indicators is established based on the sampling method. For illustration, the evaluation method is employed to gauge the resolution performance of a two-degree-of-freedom and a three-degree-of-freedom (3-DOF) planar FPM. To demonstrate its application for optimal design, we use this method for the development of a 3-DOF spatial translational FPM. An experiment is carried out to determine the resolution and the repeatability of the developed FPM and verify the proposed evaluation method. The result shows that the method is suitable for the design of FPM for any desired resolution.
Sputter erosion measurements of titanium and molybdenum by cavity ring-down spectroscopy
Authors: Surla V. , Wilbur P. J. , Johnson M. , Williams J. D. , Yalin A. P.
Published: September 2004

We report cavity ring-down spectroscopy measurements of the gas-phase number density of titanium and molybdenum sputtered by argon ions. A neodymium: yttrium–aluminum–garnet pumped optical parametric oscillator laser system is used to probe optical absorption features of titanium and molybdenum in the 375–400 nm region. For an 18 mA ion beam current, and 750 eV ions, we find that the spatially averaged number density of sputtered atoms is 6.4±0.6×108 and 5.1±0.5×108 cm−3, for titanium and molybdenum, respectively. The measured number densities exhibit the expected linear behavior versus beam current, and are in reasonable agreement with values found from a simple sputtering model. Our current configuration yields number density detection limits of ∼9×106 and ∼7×105 cm−3, for titanium and molybdenum, respectively. The technique may ultimately provide a means to measure sputter erosion rates, which are of particular importance for the electric propulsion field.
Observation of cold atom output from an evanescent-light funnel
Authors: Takamizawa Akifumi , Ito Haruhiko , Yamada Shungo , Ohtsu Motoichi
Published: September 2004

We report the demonstration of an atom funnel composed of evanescent light. The flux intensity of cold Rb atoms output from a 240μm exit hole was 7×107atom∕cm2s at a blue detuning of 1.2GHz. Sisyphus cooling doubled the output efficiency. The estimated flux intensity was 1012atom∕cm2s when the exit-hole diameter was 110μm.
Schottky emission at the metal polymer interface and its effecton the polarization switching of ferroelectric poly(vinylidenefluoride-trifluoroethylene) copolymer thin films
Authors: Xia Feng , Zhang Q. M.
Published: September 2004

In metal/insulator/metal sandwich structure, the interface between the metal and the insulator thin films plays significant roles in the functional performance of the thin films. In ferroelectric poly(vinylidene fluoride-trifluoroethylene) copylmer thin films metallized by different metals, it is found that the polarization switching is asymmetric due to the work function difference of the metal electrodes, and the degree of asymmetry increases with the increasing work function difference. For the samples with high work function metals as both or at least one of the electrodes, the polarization switching is much faster. The current–voltage curves at various temperatures indicated the interface-controlled asymmetric phenomena are mainly determined by the Schottky emission and charge injection at the metal/insulator polymer interface.
Double minimum in the surface stabilized ferroelectric liquid crystal switching response
Authors: Brown C. V. , Hind J. M. , Lymer K. P. , Jones J. C.
Published: September 2004

A double minimum has recently been observed in the time–voltage switching response for a smectic C* liquid crystal layer in the surface stabilized geometry (“Ferroelectric Liquid Crystal Device,” K. P. Lymer and J. C. Jones, U.K. Patent No. GB2338797, 17th June 1999). Liquid crystal continuum theory is used to demonstrate that this unusual switching behavior arises if the equilibrium orientation of the molecular director rotates around the smectic cone as a function of distance through one half of the layer only. The double minimum is shown to evolve for large differences between the ε2 and ε1 components of the smectic C biaxial permittivity tensor.
Synthesis and electrical properties of carbon nanotube polyaniline composites
Authors: Long Yunze , Chen Zhaojia , Zhang Xuetong , Zhang Jin , Liu Zhongfan
Published: September 2004

A multiwalled carbon nanotube∕polyaniline composite with cablelike morphology has been synthesized by an in situ chemical oxidative polymerization directed with cationic surfactant cetyltrimethylammonium bromide. It is interestingly found that with increasing carbon nanotube loading from 0 to 24.8wt%, the conductivity increases by two orders of magnitude and the Mott’s characteristic temperature T0 which depends on the hopping barrier decreases by three orders of magnitude. Furthermore, the low-temperature magnetoresistance has also changed the sign from positive to negative. The results reveal a strong coupling between the carbon nanotube and the tightly coated polymer chains, which enhances the average localization length and the electronic properties of the composites.
Ultrafast absorptive and refractive nonlinearities in multiwalled carbon nanotube films
Authors: Elim H. I. , Ji W. , Ma G. H. , Lim K. Y. , Sow C. H. , Huan C. H. A.
Published: September 2004

By using femtosecond laser pulses at a wavelength range from 720 to 780nm, we have observed absorptive and refractive nonlinearities in a film of multiwalled carbon nanotubes grown mainly along the direction perpendicular to the surface of quartz substrate. The z-scans show that both absorptive and refractive nonlinearities are of negative and cubic nature in the laser irradiance range from a few to 300GW∕cm2. The magnitude of the third-order nonlinear susceptibility, χ(3), is of an order of 10−11esu. The degenerate pump–probe measurement reveals a relaxation time of ∼2ps.
Quantum-well band structure effects on the emission polarization from a spin-polarized electron reservoir
Authors: Agrawal Mukul , Solomon G. S.
Published: September 2004

Many spin-polarized-based devices utilize the optical polarization from semiconductor quantum wells (QWs) as a read out. Under ideal conditions at zero crystal momentum, 100% optical polarization is obtained from these QWs for fully polarized electrons. However, carrier populations typically extend over nonzero crystal momentum states, where band mixing results in nonideal optical polarization. We investigate a single InxGa1−xAs(x=0.2, and 0.08)QW in GaAs in a typical p-i-n spin injector structure, using eight band k.p theory including strain, electric field and quantum-confined Stark effects. By evaluating the carrier distribution and wave functions of the QW states, we find the resulting optical polarization is reduced to ∼60% at 10K, and further for high temperature and high fields. We show that under certain conditions we can flip the sign of the optical polarization, suggesting the possibility of an electric field controlled optical or spin polarization switch.
Synthesis of semiconductor nanowires by annealing
Authors: Zhi C. Y. , Bai X. D. , Wang E. G.
Published: September 2004

Semiconductor nanowires, such as InAs, InP, β-Ga2O3, and GaP are synthesized by annealing semiconductor wafers covered with Au film at an appropriate temperature in the region of 550°–650°C in a N2 atmosphere. The composition of the resulting semiconductor nanowires is determined by both the substrate and the chemical conditions of growth. High-resolution transmission electron microscopy and selected area electron diffraction reveal high degrees of crystallization of the as-grown nanowires. The characteristics of the annealing method for synthesis of semiconductor nanowires are discussed.
Contributions to the effective work function of platinum on hafnium dioxide
Authors: Schaeffer J. K. , Fonseca L. R. C. , Samavedam S. B. , Liang Y. , Tobin P. J. , White B. E.
Published: September 2004

The intrinsic and extrinsic contributions to Fermi level pinning of platinum (Pt) electrodes on hafnium dioxide (HfO2) gate dielectrics are investigated by examining the impact of oxygen and forming gas anneals on the effective work function of Pt-HfO2-silicon capacitors. The effective platinum work function is ∼4.6eV when annealed in forming gas. However, diffusion of oxygen to the Pt∕HfO2 interface increases the platinum work function to a value of ∼4.9eV. Subsequent annealing in forming gas returns the platinum work function to a value comparable to that measured prior to the oxygen anneal. The effective platinum work functions are compared to the prediction of the metal induced gap states (MIGS) model. The presence of interfacial oxygen vacancies or platinum–hafnium bonds is believed to be responsible for a degree of pinning that is stronger than predicted from the MIGS model alone.
Dual-band infrared single-layer metallodielectric photonic crystals
Authors: Drupp Robert P. , Bossard Jeremy A. , Ye Yong-Hong , Werner Douglas H. , Mayer Theresa S.
Published: September 2004

Metallodielectric photonic crystals (MDPCs) consisting of periodic arrays of self-similar two-stage fractal patch metallic elements patterned on thin dielectric substrates are shown to exhibit excellent mid- and far-infrared dual-band response in a single layer structure. This was achieved by optimizing the element size and interelement spacing of cross-dipole and square-patch fractal elements using full-wave periodic method of moments modeling techniques that calculate electromagnetic scattering from the MDPC surface and are able to account for material loss and loading effects. All structures fabricated based on these designs had two measured stopbands with greater than 10dB attenuation positioned at wavelengths determined by element geometry and size as well as interelement spacing. This simple single layer fractal MDPC geometry will facilitate further scaling into the near-IR wavelength regime.
Temperature-dependent studies of Y-junction carbon nanotube electronic transport
Authors: Papadopoulos C. , Yin A. J. , Xu J. M.
Published: September 2004

Electronic transport in Y-junction carbon nanotubes was examined as a function of temperature. Rectifying behavior was observed from 10to300K with the conductance displaying power-law dependencies on temperature and applied bias. The data are consistent with models for tunneling between two tube segments but display asymmetric exponents depending on bias polarity. The conductance asymmetry is found to be essentially independent of temperature and can be understood from the lack of inversion symmetry of the Y-junction geometry, which creates a unique type of mesoscopic rectification for current flow in the nonlinear response regime.
Reinforcement and rupture behavior of carbon nanotubes–polymer nanofibers
Authors: Ye Haihui , Lam Hoa , Titchenal Nick , Gogotsi Yury , Ko Frank
Published: September 2004

High-resolution transmission electron microscopy examination of carbon nanotube–polyacrylonitrile composite fibers synthesized by electrospinning was conducted. Both single-wall carbon nanotubes and multi-wall carbon nanotubes have been used to reinforce the polymer fibers. A two-stage rupture behavior of the composite fibers under tension, including crazing of polymer matrix and pull-out of carbon nanotubes, has been observed. Carbon nanotubes reinforce the polymer fibers by hindering crazing extension, reducing stress concentration, and dissipating energy by pullout. Distribution of nanotubes in the polymer matrix and interfacial adhesion between nanotubes and polymers are two major factors to determine the reinforcement effect of carbon nanotubes in polymer fibers.
Molecular dynamics simulations of bending behavior of tubulargraphite cones
Authors: Liu P. , Zhang Y. W. , Lu C.
Published: September 2004

Molecular dynamics simulations are performed to investigate the bending behavior of tubular graphite cones (TGCs). The second-generation reactive bond-order potential and four different van der Waals potentials are used to describe bonding and nonbonding atomic interactions, respectively. It is shown that the bending behavior is insensitive to the choice of the van der Waals potentials. An increase in the cone apex angle of TGCs moderately improves the bending stiffness due to the low shear resistance between the nanotube walls. A TGC with a high cone apex angle is preferred to a TGC with a low cone apex angle in terms of bending stiffness and stress level. It is also shown that an increase in the diameter of the innermost nanotube effectively increases the bending stiffness of TGCs.
High-frequency surface acoustic wave device based on thin-film piezoelectric interdigital transducers
Authors: Sarin Kumar A. K. , Paruch P. , Triscone J.-M. , Daniau W. , Ballandras S. , Pellegrino L. , Marré D. , Tybell T.
Published: September 2004

Using high-quality epitaxial c-axis Pb(Zr0.2Ti0.8)O3 films grown by off-axis magnetron sputtering onto metallic (001) Nb-doped SrTiO3 substrates, a nonconventional thin-film surface acoustic wave device based on periodic piezoelectric transducers was realized. The piezoelectric transducers consist of a series of ferroelectric domains with alternating polarization states. The artificial modification of the ferroelectric domain structure is performed by using an atomic force microscope tip as a source of electric field, allowing local switching of the polarization. Devices with 1.2 and 0.8μm wavelength, defined by the modulation period of the polarization, and corresponding to central frequencies in the range 1.50–3.50GHz have been realized and tested.
Manipulating the size distributions of quantum dots associated with strain-renormalized surface energy
Authors: Munt T. P. , Jesson D. E. , Shchukin V. A. , Bimberg D.
Published: September 2004

Utilizing computer simulations based on a continuity equation model, we propose a strategy for modifying three-dimensional quantum dot size distributions using a two-stage growth and anneal approach. The method simply requires that individual quantum dots have a minimum in their chemical potential as a function of island size, such as those associated with strain-renormalized surface energy. By depositing material for the required time, the island size distribution can be tuned to a desired size before removing the flux to narrow the distribution.
Replica-molded electro-optic polymer Mach–Zehnder modulator
Authors: Paloczi George T. , Huang Yanyi , Yariv Amnon , Luo Jingdong , Jen Alex K.-Y.
Published: September 2004

A Mach–Zehnder electro-optic polymer amplitude modulator is fabricated by a simple and high-throughput soft-stamp replica-molding technique. The modulator structure incorporates the highly nonlinear and stable chromophore, AJL8, doped in amorphous polycarbonate. Single-arm phase-retardation results in a halfwave voltage (Vπ) of 8.4V at 1600nm. The on/off extinction ratio is better than 19 dB, resulting from precise Y-branch power splitters and good waveguide uniformity. These results indicate that the simple fabrication process allows for good optical performance from high-fidelity replicas of the original master devices.
Silver solid solution piezoelectrics
Authors: Grinberg Ilya , Rappe Andrew M.
Published: September 2004

Using density functional theory calculations, we investigate the feasibility of using silver on the perovskite A-site in high-performance lead-free piezoelectrics. The calculations show that silver atoms are ferroelectrically active and can off-center by 0.5Å. To induce Ag ferroelctric behavior absent in pure AgNbO3 we explore solid solutions of AgNbO3 with well-known simple perovskites PbTiO3, BaZrO3, and BaTiO3. For the AgNbO3–PbTiO3 solid solution, we predict a morphotropic phase boundary near (AgNbO3)3∕8(PbTiO3)5∕8. We find an unusual sequence of compositional phase transitions in AgNbO3–BaZrO3 and AgNbO3–BaTiO3 which are due to the effects of volume expansion in perovskites. For the AgNbO3–BaTiO3 solid solution we find two morphotropic phase boundaries at 12.5% and 37.5% AgNbO3 compositions with favorable piezoeletric properties and indications of high TC.
Photodimerization in dipeptides for high capacity optical digital storage
Authors: Ramanujam P. S. , Berg Rolf H.
Published: September 2004

We have developed peptide materials with chromophores that undergo cycloaddition, suitable for terabit optical digital storage in a 5.25in. disc. The rationale behind this design is that the length and rigidity of the backbone can be adjusted to facilitate the formation of a photodimer without large physical movements of the chromophores on exposure to UV light. Initially strongly absorbing films transmit up to 50% of light on irradiation at dimerizing wavelengths. This property can be utilized to record grey levels. An intensity-dependent transmission behavior has been observed that may enable data to be written and read at the same wavelength.
Si
-capping of Ge nanohuts on Si(001) analyzed by scanning tunneling microscopy and the finite element method
Authors: Goldfarb I. , Banks-Sills L. , Eliasi R.
Published: September 2004

Ge hut nanocrystals were grown on an Si(001) surface and Si-capped by gas-source molecular-beam epitaxy. Growth and capping at 430°C were observed in real time by scanning tunneling microscopy, and analyzed by the finite element method. Observations made here of three-dimensional Si-cap growth (in the shape of pyramids and huts) on Ge, similar to the Ge growth on Si(001), are consistent with energetic arguments based on finite elements in the framework of linear elasticity. These observations are in contrast with the higher-temperature behavior, where Si preferentially sticks to the Ge nanocrystal facets, causing them to develop large flat (001) tops and a reduced height-base ratio.
Microwave photonic crystal with tailor-made negative refractive index
Authors: Vodo P. , Parimi P. V. , Lu W. T. , Sridhar S. , Wing R.
Published: September 2004

Negative refraction and left-handed electromagnetism in a metallic photonic crystal (PC) wedge are demonstrated in free space for both transverse magnetic and electric mode propagation. The experimental results are in excellent agreement with numerical calculations based on the band structure with no fit parameters used in modeling. The results demonstrate precision control on the design and fabrication of the PC to achieve tailor-made refractive indices between −0.6 and +1.
Anisotropy of g-factor and electron spin resonance linewidth in modulation doped SiGe quantum wells
Authors: Malissa H. , Jantsch W. , Mühlberger M. , Schäffler F. , Wilamowski Z. , Draxler M. , Bauer P.
Published: September 2004

We investigate the electron spin resonance of electrons in Si1−xGex quantum wells defined by SiGe barriers (19%–25%Ge). Adding small amounts of Ge changes both g-factor and linewidth and their anisotropy. We explain these effects in terms of the Bychkov–Rashba field that originates from one-sided modulation doping. The main effect arises from the increase in spin–orbit interaction with increasing x. We argue that these effects may be used to tune the g-factor of electrons in quantum dots for a selective spin manipulation.
InGaAs
-on-Si single photon avalanche photodetectors
Authors: Kang Y. , Lo Y.-H. , Bitter M. , Kristjansson S. , Pan Z. , Pauchard A.
Published: September 2004

In this letter, an InGaAs-on-Si single photon avalanche diode (SPAD) for telecommunication wavelengths is presented. This SPAD demonstrates high-single-photon quantum efficiency and low-dark-count probability under gated mode operation. We attributed the good performance of this device to the high absorption coefficient of InGaAs and low noise avalanche multiplication of Si.
A nonvolatile memory element based on an organic field-effect transistor
Authors: Narayanan Unni K. N. , de Bettignies Remi , Dabos-Seignon Sylvie , Nunzi Jean-Michel
Published: September 2004

Organic field-effect transistors were fabricated with pentacene as the active material and a ferroelectric copolymer poly(vinylidene fluoride–trifluoroethylene) as the gate insulator. As-prepared devices showed normal p-type transistor operation. The ON- and OFF-states could be written to the device by applying appropriate voltages to the gate with respect to short-circuited source and drain electrodes. The devices exhibited excellent memory retention properties.
Nonsymmetric current–voltage characteristics in ferromagnet∕superconductor thin film structures
Authors: Touitou N. , Bernstein P. , Hamet J. F. , Simon Ch. , Méchin L. , Contour J. P. , Jacquet E.
Published: September 2004

We found that the current–voltage characteristics measured on La0.66Sr0.33MnO3∕YBa2Cu3O7−δ thin film heterostructures patterned as microbridges are nonsymmetric if the magnetization direction of the La0.66Sr0.33MnO3 film is in plane and perpendicular to the current direction. This effect is attributed to the contribution of the magnetic moment of this film to the vertical component of the field along the edges of the bridge. We suggest that this effect could find an application in the reading process of magnetic memories.
Thin film transistors fabricated by in situ growth of SnO2 nanobeltson Au∕Pt electrodes
Authors: Li Q. H. , Chen Y. J. , Wan Q. , Wang T. H.
Published: September 2004

Thin film transistors are fabricated by in situ growth of SnO2 nanobelts on Au∕Pt electrodes. A linear correlation in the output characteristics is observed at zero gate voltage, indicating Ohmic contacts between the nanobelts and the electrodes. The transistors exhibit n-type behaviors and have a mobility of 1.85cm2∕Vs with a current on∕off ratio above 103. The conductance increases as the pressure in the device chamber is reduced, which indicates that the transistors are promising for oxygen detecting.
GaAs
∕
AlGaAs
nanowires capped with AlGaAs layers on GaAs(311)B substrates
Authors: Tateno K. , Gotoh H. , Watanabe Y.
Published: September 2004

We have investigated GaAs∕AlGaAs nanowires capped with AlGaAs layers for optical device applications. GaAs nanowires are not so stable during AlGaAs capping growth at high temperature. However, AlGaAs nanowires retain their shapes, and GaAs nanowires sandwiched between AlGaAs wires were capped at temperatures as high as 700°C. The capped structures showed sharp photoluminescence peaks at around 730nm at 4K, which originated from excitons in quantum wires. We confirmed that the AlGaAs capping layers were grown smoothly around nanowires so that surface recombination centers in GaAs nanowires were reduced compared with air-exposed GaAs wires.
Mössbauer effect probe of field-induced magnetic phase transitionin LaFe13−xSix intermetallic compounds
Authors: Cheng Zhao-hua , Di Nai-li , Li Qing-an , Kou Zhi-qi , Luo Zhi , Ma Xiao , Wang Guang-jun , Hu Feng-xia , Shen Bao-gen
Published: September 2004

Direct evidence of a field-induced magnetic phase transition in LaFe13−xSix intermetallics with a large magneticaloric effect was provided by Fe57 Mössbauer spectra in externally applied magnetic fields. Moreover, Mössbauer spectra demonstrate that a magnetic structure collinear to the applied field is abruptly achieved in LaFe11.7Si1.3 compound once the ferromagnetic state appears, showing a metamagnetic first-order phase transition. In the case of LaFe11.0Si2.0, the Fe magnetic moments rotate continuously from a random state to the collinear state with increasing applied field, showing that a second-order phase transition is predominant. The different types of phase transformation determine the magnetocaloric effects in response to temperature and field in these two samples.
Mechanisms of nitrogen incorporation in GaAsN alloys
Authors: Reason M. , McKay H. A. , Ye W. , Hanson S. , Goldman R. S. , Rotberg V.
Published: September 2004

We have investigated nitrogen incorporation mechanisms in dilute nitride GaAsN alloys grown by plasma-assisted molecular-beam epitaxy. A comparison of nuclear reaction analysis and Rutherford backscattering spectrometry in channeling and nonchanneling conditions reveals significant composition-dependent incorporation of N into nonsubstitutional sites, presumably as either N–N or N–As split interstitials. Furthermore, we identify the (2×1) reconstruction as the surface structure which leads to the highest substitutional N incorporation, likely due to the high number of group V sites per unit area available for N–As surface exchange.
Magnetic properties of magnetically isolated L1-FePt nanoparticles
Authors: Momose Satoru , Kodama Hiroyoshi , Uzumaki Takuya , Tanaka Atsushi
Published: September 2004

This letter reports the results obtained by measuring the temperature dependence of the coercivity of magnetically isolated L10-FePt nanoparticles in agglomeration-free films deposited by using a dispersion stabilizer and a spin-coat technique. These measurements not only give the basic magnetic parameters of the nanoparticles but also provide information about the nanoparticle ordering process. The temperature at which isolated FePt nanoparticles start to order seems to be about 650°C.
Large magnetostriction in Fe100−xAlx(15⩽x⩽30) melt-spun ribbons
Authors: Liu Z. H. , Liu G. D. , Zhang M. , Wu G. H. , Meng F. B. , Liu H. Y. , Yan L. Q. , Qu J. P. , Li Y. X.
Published: September 2004

Magnetostriction of Fe100−xAlx(15⩽x⩽30) al1oys has been largely improved by using melt-spun method. The large magnetostriction up to −700ppm obtained in Fe81Al19 sample is about 5 times as large as that in conventional bulk samples of Fe–Al composition. It has been ascribed to the high concentration of Al–Al atom pairs created by melting-spinning method and their strongly preferential orientation in [100] textured ribbon plane. The remarkable anisotropic magnetostriction reflects the magnetoelastic competition occurring in those strong textured and thin ribbon samples. The composition dependence of the magnetostriction in ribbon samples has been found to be consistent with bulk materials.
Self-assembling in AlxGa1−xNyAs1−y alloys
Authors: Elyukhin V. A. , Sánchez-R. V. M. , Elyukhina O. V.
Published: September 2004

The self-assembling of the isoelectronic cation impurities in lightly anion-doped AlxGa1−xNyAs1−y alloys with the zinc blende structure is predicted. The tetrahedral surroundings of Ga (Al) impurity atoms should be formed around As (N) impurity atoms in AlN-enriched (GaAs-enriched) alloys. The cation impurity concentrations for the complete Ga (Al) surroundings of all As (N) atoms are estimated at the higher growth and lower annealing temperatures. The advantage of the Al–N and Ga–As bonding over the Al–As and Ga–N bonding is an origin of the self-assembling in lightly isoelectronically-doped AlxGa1−xNyAs1−y alloys.
Noninvasive nature of corona charging on thermal Si∕SiO2 structures
Authors: Dautrich M. S. , Lenahan P. M. , Kang A. Y. , Conley J. F.
Published: September 2004

The corona charging technique is widely utilized in commercial Si∕SiO2 semiconductor device reliability characterization tools and has been used in numerous electron spin resonance (ESR) experiments, by several groups to study defect centers in Si∕SiO2 system. A recent ESR study argued that the corona charging approaches are inherently unreliable and invasive. In this work we show that this is not the case. We find that low-field corona biasing is essentially noninvasive and thus can be utilized in both reliability characterization and fundamental studies of defect structures.
Zero voltage Freedericksz transition in periodically aligned liquid crystals
Authors: Eakin James N. , Xie Yunhe , Pelcovits Robert A. , Radcliffe Marc D. , Crawford Gregory P.
Published: September 2004

Patterned alignment layers have been created through an approach using polarization holography and a photopolymerizable alignment layer. This technique enables continuously periodic boundary conditions on planar surfaces. Polarization gratings have been created using polarization interference from incident right-handed and left-handed circular polarization exposure conditions. A simple phenomenological model is derived to show that the Freedericksz threshold voltage vanishes when the cell gap and grating pitch are comparable.
Transmission electron microscopy study of blisters in high-temperature annealed He and H co-implanted single-crystal silicon
Authors: Frabboni S. , Gazzadi G. C. , Felisari L. , Tonini R. , Corni F. , Ottaviani G.
Published: September 2004

Transmission electron microscopy has allowed us to draw the three-dimensional structure of blisters formed after high-temperature annealing of He-H co-implanted silicon by combining the unique capability of site-selective cross sectioning of the focused ion beam with conventional plan view images. It has been shown that blisters are formed by crystalline lamellae strongly bended, plastically deformed, and suspended over buried empty cavities. The volume of the protruding blister surface is almost equal to the buried empty volumes, thus suggesting a mechanism for blister formation based on H and He precipitation and migration of silicon atoms toward the surface.
Stability of deep centers in 4H-SiC epitaxial layers during thermal annealing
Authors: Negoro Y. , Kimoto T. , Matsunami H.
Published: September 2004

N -type epitaxial 4H-SiC layers grown by hot-wall chemical vapor deposition were investigated with regard to deep centers by capacitance-voltage measurements and deep level transient spectroscopy (DLTS). The DLTS spectra revealed that the concentrations of deep centers were reduced by one order of magnitude by annealing at 1700°C, compared to those in an as-grown material. The Z1∕2 center with an energy level of 0.59±0.03eV and the EH6∕7 center with an energy level of 1.66±0.11eV below the conduction band edge are annealed out at a temperature of 1700°C or higher.
Pentacene field-effect transistors with sub-10-nm channel lengths
Authors: Wang Liang , Fine Daniel , Jung Taeho , Basu Debarshi , von Seggern Heinz , Dodabalapur Ananth
Published: September 2004

The field effect in pentacene thin-film transistors was studied using bottom-contact devices with channel lengths below 10nm. To suppress spreading current in these devices, which have a small channel width-to-length (W-L) ratio, we employed a pair of guarding electrodes as close as 20nm to the two sides of the channel. The responses of these nanometer scale transistors exhibit good gate modulation. Mobilities of 0.046cm2∕Vs and on/off ratios of 97 were achieved in sub-10-nm transistors. We find that the device response is strongly influenced by the nature of the metal-semiconductor contact.
Alternate spintronic analog of the electro-optic modulator
Authors: Bandyopadhyay S. , Cahay M.
Published: September 2004

There is significant current interest in spintronic devices fashioned after a spin analog of the electro-optic modulator proposed by Datta and Das [Appl. Phys. Lett. 56, 665 (1990)]. In their modulator, the “modulation” of the spin-polarized current is carried out by tuning the Rashba spin-orbit interaction with a gate voltage. Here, we propose an analogous modulator where the modulation is carried out by tuning the Dresselhaus spin-orbit interaction instead, using a split gate. Additionally, the magnetization of the source and drain contacts in our device is transverse to the channel, whereas in the Datta-Das device, it is along the channel. Therefore, in the present modulator, there is no magnetic field in the channel unlike in the case of the Datta-Das modulator. This can considerably enhance modulator performance.
High-electron-mobility AlGaN∕AlN∕GaN heterostructures grown on 100-mm-diam epitaxial AlN/sapphire templates by metalorganic vapor phase epitaxy
Authors: Miyoshi M. , Ishikawa H. , Egawa T. , Asai K. , Mouri M. , Shibata T. , Tanaka M. , Oda O.
Published: September 2004

Al 0.26 Ga 0.74 N ∕ Al N ∕ Ga N heterostructures with 1-nm-thick AlN interfacial layers were grown on 100-mm-diam epitaxial AlN/sapphire templates and sapphire substrates by metalorganic vapor phase epitaxy. It was found that AlN/sapphire templates significantly enhanced the electron mobility of the two-dimensional electron gas (2DEG) confined at the GaN channel. This can be explained by the high-crystal-quality GaN channel realized by the use of epitaxial AlN/sapphire templates as substrates. The very high Hall mobilities of approximately 2100cm2∕Vs at room temperature and approximately 17000cm2∕Vs at 77K with a 2DEG density of approximately 1×1013∕cm2 were uniformly obtained for AlGaN∕AlN∕GaN heterostructures on 100-mm-diam epitaxial AlN/sapphire templates. The Hall mobility of AlGaN∕AlN∕GaN heterostructures on epitaxial AlN/sapphire templates reached a very high value of 25500cm2∕Vs at 15K.
Enhanced Curie temperature of InMnP:Zn—TC∼300K
Authors: Shon Yoon , Jeon H. C. , Park Y. S. , Lee W. C. , Lee Seung Joo , Kim D. Y. , Kim H. S. , Kim H. J. , Kang T. W. , Park Y. J. , Yoon Chong S. , Chung K. S.
Published: September 2004

P -type bulk InP was prepared by the liquid encapsulated Czochralski method and subsequently diffused with Mn by heat treatment after the evaporation of Mn on top of InP:Zn using a molecular beam epitaxy system. The characteristics of Mn-diffused InMnP:Zn were investigated by an energy dispersive x-ray spectroscopy, photoluminescence, and a superconducting quantum interference device magnetometer measurements. The samples were characterized by transmission electron microscopy and no evidence of secondary phase formation of InMnP:Zn was found. The results of energy dispersive x-ray peak displayed injected concentration of Mn near 3%. The results of photoluminescence measurement showed that optical broad transitions related to Mn appeared around 1.2eV and it was confirmed that the transitions around 1.2eV were Mn-related band by the diffusion of Mn into InP:Zn. Clear ferromagnetic hysteresis loops were observed at 10 and 300K and the temperature-dependent magnetization showed ferromagnetic behavior around 300K, which is caused by carrier-mediated ferromagnetism in InMnP:Zn. It is found that a ferromagnetic semiconductor at room temperature can be formed in diluted magnetic semiconductor based on GaMnN and InMnP additionally co-doped with Mg and Zn, respectively.
Rapid flash patterning of nanostructures
Authors: Yoon Hyunsik , Lee Kyoung Mi , Khang Dahl-Young , Lee Hong H. , Choi Se-Jin
Published: September 2004

Sub-100nm structures can be fabricated in tens of seconds with an aspect ratio much larger than unity by the general purpose patterning method presented here. A flexible film mold and a rapid flash heating with an infrared lamp are used in this nonphotolithographic patterning technique. Unlike other unconventional methods, the substrate surface can be made exposed and the resulting pattern height is sufficiently high for subsequent etching of the substrate.
Buckling instabilities in multiwalled carbon nanotubes under uniaxial compression
Authors: Waters J. F. , Riester L. , Jouzi M. , Guduru P. R. , Xu J. M.
Published: September 2004

We report experimental observations of shell buckling instabilities in freestanding, vertically aligned multiwalled carbon nanotubes subjected to uniaxial compression. Highly ordered and uniform arrays of carbon nanotubes embedded in an alumina matrix were fabricated and subjected to uniaxial compression using a nanoindenter. The buckling load was found to be on the order of 2μN for nanotubes with 25nm outer radius, 13nm inner radius, and heights of 50 and 100nm. Good agreement was found between the experimental observations and the predictions of linear elastic shell buckling theory.
Level crossing conductance spectroscopy of molecular bridges
Authors: Remacle F. , Levine R. D.
Published: September 2004

A possible mechanism for negative differential resistance is discussed. The level crossing is induced by the source-drain voltage applied across the bridge. The effect is most dramatic when the zero field levels that are resonant with the electrodes are almost degenerate. It is suggested that such degeneracies can arise often when the junctions on either side are weakly coupled by the bridge. Quantitative results for I–V curves are reported on the basis of high-level electronic structure computations for the junction–bridge–junction region and where the electric field is included in the Hamiltonian.
Formation of ohmic contacts to perylene molecular crystals
Authors: Hiramoto Masahiro , Tomioka Akinori , Suemori Kouji , Yokoyama Masaaki
Published: September 2004

Ohmic contacts to perylene molecular crystals were successfully formed at bromine-doped p-type crystal∕platinum junctions and sodium-doped n-type crystal∕aluminum junctions to enable hole and electron injection, respectively. Charge-carrier doping of the organic semiconductor surface that was in direct contact with the metal electrodes was revealed as being a requirement for fabricating organic∕metal junctions that were ohmic in character. The fabrication of ohmic contacts would be applicable to carrier injection in organic electroluminescent devices and carrier extraction from organic solar cells.