bluuebunny/crossref_metadata_2025 huggingface dataset:
Central configurations with a quasihomogeneous potential function
Authors: Jones Robert T.
Published: May 2008

For the classical N-body problem, if the masses are paced at rest in the configuration that is central, then the masses will tend to the origin and result in a simultaneous collision [A. Winter, The Analytical Foundations of Celestial Mechanics, 1st ed. (Princeton University Press, Princeton, 1941)]. However, if the potential is quasihomogeneous in nature, that is, the potential is of the form U=V+W, where W=∑i≠jamimjrij−α and V=∑i≠jbmimjrij−β, then we will dramatically get different results. This paper determines the orbits that will result when the potential function is quasihomogeneous. It also shows when there existences a relative equilibrium solution for the regular N-gon configuration. This is one-half of Perko’s theorem for a homogeneous potential. Finally, we show the existence of a central configuration which is not central for either W or V. This configuration is the placement of two mutual equal pairs of masses placed at the vertices of a square. This shows that the reverse implication of Perko’s theorem for the regular N-gon does not hold for quasihomogeneous potentials.
Atomistic and orthoatomistic effect algebras
Authors: Tkadlec Josef
Published: May 2008

We characterize atomistic effect algebras, prove that a weakly orthocomplete Archimedean atomic effect algebra is orthoatomistic and present an example of an orthoatomistic orthomodular poset that is not weakly orthocomplete.
Structural features of bicomponent dust Coulomb balls formed by the superposition of fields of different origin in plasma
Authors: Psakhie S. G. , Zolnikov K. P. , Skorentsev L. F. , Kryzhevich D. S. , Abdrashitov A. V.
Published: May 2008

A binary mixture of dust particles in plasma which are in an external electrostatic harmonic confining field as well as in the field consisting of gravitational, thermophoretic, and electrostatic force is simulated. The interparticle interaction is described by the Yukawa isotropic pair potential. The structural properties of the binary mixture of particles depending on composition are investigated. The segregation features of a system of particles of two species under the conditions of recent experiments on Coulomb ball formation are studied. It is shown that particles form a shell structure in which every shell contains only its own species of particles; in so doing, smaller-sized particles make up outer shells with respect to larger-sized particles. When the size difference between the particles becomes more and more pronounced, they are spatially separated up to the formation of two independent Coulomb balls.
Ductile to brittle transition in dynamic fracture of brittle bulk metallic glass
Authors: Wang G. , Han Y. N. , Xu X. H. , Ke F. J. , Han B. S. , Wang W. H.
Published: May 2008

We report an unusual transition from a locally ductile to a pure brittle fracture in the dynamic fracture of brittle Mg65Cu20Gd10 bulk metallic glass. The fractographic evolution from a dimple structure to a periodic corrugation pattern and then to the mirror zone along the crack propagation direction during the dynamic fracture process is discussed within the framework of the meniscus instability of the fracture process zone. This work might provide an important clue in understanding of the energy dissipation mechanism for dynamic crack propagation in brittle glassy materials.
Integration of ultrasonic transducers in fast prototyping microfluidic devices
Authors: Guo S. S. , Lau S. T. , Lam K. H. , Deng Y. L. , Zhao X. Z. , Chen Y. , Chan H. L. W.
Published: May 2008

Bulk acoustic wave induced mixing in microfluidic systems has been studied by using a pair of small size ultrasonic transducers integrated into a prototype polydimethylsiloxane device. The acoustic properties of the integrated ultrasonic transducers were evaluated, demonstrating the generation of bulk acoustic wave in the mixing chamber when a low ac voltage is applied. Then, the mixing efficiency of the device was studied by using two stream laminar flows and taking into account the particular geometry of the mixing chamber. Because of the limited power consumption, the system should be compatible with the requirements of a number of applications in both analytical chemistry and biology.
CoCr/Pt multilayers with adjustable perpendicular anisotropy
Authors: Papaioannou E. Th. , Lenz K. , Charilaou M. , Fumagalli P. , Poulopoulos P. , Angelakeris M. , Flevaris N. K. , Wilhelm F. , Rogalev A.
Published: May 2008

CoCr/Pt multilayers are studied with respect to their structure, magnetic, and magneto-optical properties in an effort to produce novel films suitable for perpendicular magnetic recording. The multilayered structure and the face centered cubic stacking of the films are evidenced by x-ray diffraction. Hysteresis loops are recorded via the magneto-optic polar Kerr effect and superconducting quantum interference device magnetometry in order to study the effect of Pt thickness and Cr concentration on the magnetic behavior. Ferromagnetic resonance measurements were carried out to determine the easy axis of magnetization from an analysis of the angular dependence of the resonance field. It is shown that the perpendicular magnetic anisotropy term of the multilayers is strongly dependent on the thickness of Pt layers. The presence of spin-polarized Pt, which was evidenced via x-ray magnetic circular dichroism, also drives the strong magneto-optic enhancement in the ultraviolet region between 4.5 and 5 eV.
Thermodynamic measurements of submilligram bulk samples using a membrane-based “calorimeter on a chip”
Authors: Cooke David W. , Michel K. J. , Hellman F.
Published: May 2008

Calorimetry offers a direct measurement of thermodynamic properties of materials, including information on the energetics of phase transitions. Many materials can only be prepared in thin film or small crystal (submilligram) form, negating the use of traditional bulk techniques. The use of micromachined, membrane-based calorimeters for submilligram bulk samples is detailed here. Numerical simulations of the heat flow for this use have been performed. These simulations describe the limits to which this calorimetric technique can be applied to the realm of small crystals (1–1000μg). Experimental results confirm the feasibility of this application over a temperature range from 2to300K. Limits on sample thermal conductivity as it relates to the application of the lumped and distributed τ2 models are explored. For a typical sample size, the simulations yield 2.5% absolute accuracy for the heat capacity of a sample with thermal conductivity as low as 2×10−5W∕cmK at 20K, assuming a strong thermal link to the device. Silver paint is used to attach (both thermally and physically) the small samples; its heat capacity and reproducibility are discussed. Measurements taken of a submilligram single crystal of cobalt oxide (CoO) compare favorably to the results of a bulk calorimetric technique on a larger sample.
X-ray photoelectron studies of clean and oxidized α-GeTe(111) surfaces
Authors: Yashina L. V. , Püttner R. , Neudachina V. S. , Zyubina T. S. , Shtanov V. I. , Poygin M. V.
Published: May 2008

Clean and oxidized (104–1015 L of O2) surfaces of α-GeTe have been investigated with x-ray photoelectron spectroscopy by using the synchrotron radiation facility BESSY II as well as an Al Kα source. To understand the first steps of oxidation, complementary quantum chemical calculations were performed. The cleaved surfaces of α-GeTe were found to be rumpled with (111) domains that can be related to the domain (twin) structure of the bulk. Both the Ge 3d and the Te 4d spectra of freshly cleaved surfaces exhibit at least three components, which are explained by a Ge or Te termination of the surface domains with possible contributions of a surface reconstruction. The surface oxidation starts at exposures of 104 L and proceeds via several steps. At low exposures, only changes in the Ge spectra are observed. Consequently, the first step of the reaction is associated with the formation of intermediate peroxidelike structures, wherein both oxygen atoms are bonded to germanium atoms. In the range of exposures between 1010 and 1015 L, a layer of a relatively stable oxidation product with the approximate stoichiometry Ge1+δ+4Te1−δ0O2(1+δ)2− is formed, which shows growth kinetics that obey a time-logarithmic law. At this stage, the peroxidelike structures are still present at the oxide/crystal interface. Once the oxidized layer exceeds a thickness of ≈2.5 nm at ∼1013 L, a transformation of the Te0 state into the Te+4 state is observed at the surface of the oxide layer. The final oxidation product can be described as mGeO2×nTeO2.
Spectroscopic properties and laser performance of Tm3+-doped NaLa(MoO4)2 crystal
Authors: Guo Weijie , Chen Yujin , Lin Yanfu , Luo Zundu , Gong Xinghong , Huang Yidong
Published: May 2008

Detailed polarized spectral properties of Tm3+:NaLa(MoO4)2 crystal have been investigated. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves were measured at room temperature. The fluorescence decay mechanisms of the G14 and H34 multiplets were discussed. Spectroscopic parameters related to the laser operation at around 1.9 μm via the F34→H36 transition have been evaluated. Room-temperature quasi-cw 1.9 μm laser emission from a Ti:sapphire laser pumped Tm3+:NaLa(MoO4)2 crystal has been demonstrated. The maximum output power of 0.5 W has been achieved with a slope efficiency of 50%.
Deuterium influence on the field emission from inorganic nanowires
Authors: Nemanic Vincenc , Zumer Marko , Zajec Bojan , Mihailovic Dragan , Vengust Damjan , Podobnik Bostjan
Published: May 2008

We report the initial conditioning procedure and achieved properties of nanowires composed of molybdenum sulfur iodine and directly grown on the top of a macroscopic molybdenum wire. Such a wire with nanowires, which were mostly perpendicularly grown to the surface, was applied as a radial field emitter with a 20 mm2 geometric area positioned inside a cylindrical metal anode. A stable current density of ∼2 mA/cm2 was achieved at a relatively low macroscopic electric field. Simultaneous recording of gases released from the anode exhibits linear relationship with the dissipated power. The most unexpected result was a reversible field emission current dependence induced by varying the deuterium pressure within the range from 10−8 to 10−4 mbar. The maximum increase for a factor of 7 was registered. Possible mechanisms responsible for the observed phenomena are discussed.
The nonlinear dynamics of tapping mode atomic force microscopy with capillary force interactions
Authors: Hashemi N. , Dankowicz H. , Paul M. R.
Published: May 2008

We study the nonlinear dynamics of a tapping mode atomic force microscope with tip-surface interactions that include attractive, repulsive, and capillary force contributions using numerical techniques tailored for hybrid or discontinuous dynamical systems that include forward-time simulation with event handling and numerical pseudo-arclength continuation. We find four branches of periodic solutions that are separated by windows of complex and irregular dynamics. The branches of periodic solutions end where the cantilever comes into grazing contact with event surfaces in state space, corresponding to the onset of capillary interactions and the onset of repulsive forces associated with contact. These windows of irregular dynamics are found to coexist with the periodic branches of solutions as well as exist beyond the termination of the periodic solution. Finally, we show that these details can be overlooked unless one is careful to sample the dynamics appropriately.
Thermal equations of state and melting of lithium deuteride under high pressure
Authors: Zhang Jianzhong , Zhao Yusheng , Wang Yuejian , Daemen Luke
Published: May 2008

Based on in situ high-pressure and high-temperature neutron diffraction experiments at pressures of up to 4.1 GPa and temperatures of up to 1280 K, thermoelastic parameters were derived by using a Birch–Murnaghan equation of state. With the pressure derivative of the bulk modulus, K0′, fixed at 4.0, we obtained the ambient bulk modulus K0=31.5±0.7 GPa, the temperature derivative of bulk modulus at constant pressure (∂K/∂T)P=−2.7×10−2 GPa/K, the volumetric thermal expansivities αT(K−1)=9.8±0.71×10−5+12.62±1.09×10−8T at atmospheric pressure and αT(K−1)=5.45±1.17×10−5+6.53±1.45×10−8T at 3.0 GPa, and the pressure derivative of thermal expansion (∂α/∂P)T=−2.72×10−5 GPa−1 K−1. Within the experimental uncertainties, the ambient bulk modulus and volumetric thermal expansion determined from this work are in good agreement with previous experimental results, whereas the derived (∂KT/∂T)P and (∂α/∂P)T values provide the thermoelastic equation-of-state parameters for LiD. We also determined the melting temperature of LiD under high pressure. Our results reveal a substantially increased thermal stability for crystalline LiD when compared to a previous theoretical prediction that used a combined technique of two-phase simulation and first-principles molecular dynamics.
Intense electron beam generation in a high power cylindrical diode with a bipolar pulse
Authors: Roy Amitava , Menon R. , Mitra S. , Kumar D. D. P. , Kumar Senthil , Sharma Archana , Mittal K. C. , Nagesh K. V. , Chakravarthy D. P.
Published: May 2008

Our previously reported results demonstrated that an intense gigawatt relativistic electron beam can be generated in a cylindrical diode in the presence of prepulse. This article reports intense electron beam generation in a cylindrical electron beam diode when subjected to a high voltage bipolar pulse. The experimental results are compared to the Langmuir–Blodgett law. The diode perveance in the positive voltage pulse linearly increases with time due to the increase in the emission area. It was found that the electron beam can be generated from the diode during the negative voltage pulse due to a very little gap closure during the positive voltage pulse.
Random existence of charge ordered stripes and its influence on the magnetotransport properties of La0.6Sr0.4MnO3 perovskite substituted with diamagnetic ions at Mn sublattice
Authors: Vijayanandhini K. , Kutty T. R. N.
Published: May 2008

Phase-singular solid solutions of La0.6Sr0.4Mn1−yMeyO3 (0⩽y⩽0.3) [Me=Li1+, Mg2+, Al3+, Ti4+, Nb5+, Mo6+ or W6+] [LSMey] perovskite of rhombohedral symmetry (space group: R3¯c) have been prepared wherein the valence of the diamagnetic substituent at Mn site ranged from 1 to 6. With increasing y-content in LSMey, the metal-insulator (TM-I) transition in resistivity-temperature ρ(T) curves shifted to low temperatures. The magnetization studies M(H) as well as the M(T) indicated two groups for LSMey. (1) Group A with Me=Mg, Al, Ti, or Nb which are paramagnetic insulators (PIs) at room temperature with low values of M (<0.5μB∕Mn); the magnetic transition [ferromagnetic insulator (FMI)-PI] temperature (TC) shifts to low temperatures and nearly coincides with that of TM-I and the maximum magnetoresistance (MR) of ∼50% prevails near TC (≈TM-I). (2) Group-B samples with Me=Li, Mo, or W which are FMIs with Ms=3.3–3.58μB∕Mn and marginal reduction in TC∼350K as compared to the undoped LSMO (TC∼378K). The latter samples show large temperature differences ΔT=Tc-TM-I, reaching up to ∼288K. The maximum MR (∼60%) prevails at low temperatures corresponding to the M-I transition TM-I rather than around TC. High resolution lattice images as well as microscopy analysis revealed the prevalence of inhomogeneous phase mixtures of randomly distributed charge ordered-insulating (COI) bistripes (∼3–5nm width) within FMI charge-disordered regions, yet maintaining crystallographically single phase with no secondary precipitate formation. The averaged ionic radius ⟨rB⟩, valency, or charge/radius ratio ⟨CRR⟩ cannot be correlated with that of large ΔT; hence cannot be used to parametrize the discrepancy between TC and TM-I. The M-I transition is controlled by the charge conduction within the electronically heterogeneous mixtures (COI bistripes+FMI charge disordered); large MR at TM-I suggests that the spin-ordered FM-insulating regions assist the charge transport, whereas the TC is associated with the bulk spin ordered regions corresponding to the FMI phase of higher volume fraction of which anchors the TC to higher temperatures. The present analysis showed that the double-exchange model alone cannot account for the wide bifurcation of the magnetic and electric transitions, contributions from the charge as well as lattice degrees of freedom to be separated from spin/orbital ordering. The heterogeneous phase mixtures (COI+FMI) cannot be treated as of granular composite behavior
Organization of liquid crystals on submicron scale topographic patterns with fourfold symmetry prepared by thiolene photopolymerization-based nanoimprint lithography
Authors: Yi Y. W. , Khire V. , Bowman C. N. , Maclennan J. E. , Clark N. A.
Published: May 2008

The organization of nematic liquid crystals in thin cells with one surface topographically patterned by thiolene step and flash nanoimprint lithography was studied using depolarizing transmission light microscopy. Planar bistable organization was observed for 2 and 4μm wide square grid patterns in agreement with model calculations, and with 600nm scale square and checkerboard patterns. We also demonstrate that thin films of an isotropic liquid (ethylene glycol) can be used to achieve random planar surface anchoring.
Staebler–Wronski-like formation of defects at the amorphous-silicon–crystalline silicon interface during illumination
Authors: Plagwitz Heiko , Terheiden Barbara , Brendel Rolf
Published: May 2008

The effective surface recombination velocity of amorphous-silicon-coated crystalline silicon wafers is measured after illumination for various durations to investigate the stability of the surface passivation. We develop a defect model to determine the densities of dangling bond states at the a-Si:H/c-Si interface from fitting the experimental lifetime data. The surface recombination velocity of both p-type and n-type substrates is Seff=3±1 cm/s at τn=1015 cm−3 in the as-deposited state. Illumination induces an increase to Seff=16±5 cm/s due to an increase in the dangling bond density by one order of magnitude. This increase is reversible by annealing at 300 °C for 5 min.
Electro-thermal tuning in a negative dielectric cholesteric liquid crystal material
Authors: Natarajan Lalgudi V. , Wofford Jeremy M. , Tondiglia Vincent P. , Sutherland Richard L. , Koerner Hilmar , Vaia Richard A. , Bunning Timothy J.
Published: May 2008

The thermal and electrical tunability of a cholesteric liquid crystal containing a negative dielectric anisotropy liquid crystal in a planar alignment was studied. The physical, optical, and electro-optical characteristics of mixtures containing different ratios of chiral dopant S811 and the negative dielectric anisotropy liquid crystal ZLI-2806 were examined. A smectic A phase was seen at room temperature for S811 loadings >20wt%. Below 20%, a room temperature cholesteric phase was observed. Upon heating mixtures with composition S811 >20%, the selective reflection notch of the cholesteric phase appeared and blueshifted with temperature. Thermal tuning from 2300to500nm was observed over the temperature range of 23–55°C. Polarized optical microscopy, differential scanning calorimetry, and x-ray studies were utilized to confirm the temperature-dependent phase behavior. Tuning of ∼50nm by the application of a direct current electric field was also observed with no onset of electrohydrodynamic instabilities for voltages up to ∼300V. Bandwidth broadening but not tuning was obtained with the application of alternating current fields. Electrical tuning is likely due to pitch contraction brought about through the annealing of defects.
Microthermogravimetry using a microcantilever hot plate with integrated temperature-compensated piezoresistive strain sensors
Authors: Lee Jungchul , King William P.
Published: May 2008

This paper reports thermogravimetric analysis of nanogram samples of paraffin using a microcantilever hot plate. The microcantilever hot plate has an integrated temperature-controlled heater and integrated temperature-compensated strain-sensing piezoresistors. The microcantilever vibration amplitude was measured using either a laser and a position sensitive photodiode, or using the piezoresistors. The cantilever resonance was measured as the cantilever was heated, such that the analyte mass could be measured as a function of temperature. Both optical and piezoresistive methods were employed to generate thermogravimetric curves for analytes in the range of 1–3ng, and the results of the two methods compared well.
Changes in surface state density due to chlorine treatment in GaN Schottky ultraviolet photodetectors
Authors: Lee Ching-Ting , Lin Chih-Chien , Lee Hsin-Ying , Chen Po-Sung
Published: May 2008

A chlorination surface treatment was used to reduce the surface density of states of a n-type GaN surface, which improves the Schottky performances of the resultant metal-semiconductor contact. Using capacitance-frequency measurement, the surface state density of the chlorine-treated GaN surface was about one order less than that without chlorination treatment. The dark current of the chlorine-treated GaN ultraviolet photodetectors (UV-PDs) is 1.5 orders of magnitude lower than that of those without chlorination treatment. The products of quantum efficiency and internal gain of the GaN Schottky UV-PDs without and with chlorination treatment under conditions of −10 V reverse bias voltage at a wavelength of 330 nm were 650% and 100%, respectively. The internal gain in chlorine-treated GaN UV-PDs can therefore be reduced due to a decrease in the surface state density.
Dynamic phase transitions for ferromagnetic systems
Authors: Ma Tian , Wang Shouhong
Published: May 2008

This article presents a phenomenological dynamic phase transition theory for ferromagnetism, leading to a precise description of the dynamic transitions and to a physical prediction on the spontaneous magnetization. The analysis also suggests asymmetry of fluctuations in both the ferromagnetism and the PVT systems.
Equilibrium of an elastically confined liquid drop
Authors: Kwon Hyuk-Min , Kim Ho-Young , Puëll Jérôme , Mahadevan L.
Published: May 2008

When a liquid drop is confined between an elastic plate and a rigid substrate, it spreads spontaneously due to the effects of interfacial forces, eventually reaching an equilibrium shape determined by the balance between elastic and capillary effects. We provide an analytical theory for the static shape of the sheet and the extent of liquid spreading and show that our experiments are quantitatively consistent with the theory. The theory is relevant for the first step of painting when a brush is brought down on to canvas. More mundanely, it allows us to understand the stiction of microcantilevers to wafer substrates occurring in microelectromechanical fabrication processes.
Optimal covariant measurement of momentum on a half line in quantum mechanics
Authors: Shikano Yutaka , Hosoya Akio
Published: May 2008

We cannot perform the projective measurement of a momentum on a half line since it is not an observable. Nevertheless, we would like to obtain some physical information of the momentum on a half line. We define an optimality for measurement as minimizing the variance between an inferred outcome of the measured system before a measuring process and a measurement outcome of the probe system after the measuring process, restricting our attention to the covariant measurement studied by Holevo [Rep. Math. Phys. 13, 379 (1978)]. Extending the domain of the momentum operator on a half line by introducing a two dimensional Hilbert space to be tensored, we make it self-adjoint and explicitly construct a model Hamiltonian for the measured and probe systems. By taking the partial trace over the newly introduced Hilbert space, the optimal covariant positive operator valued measure of a momentum on a half line is reproduced. We physically describe the measuring process to optimally evaluate the momentum of a particle on a half line.
Magnetism of the fcc Rh and Pd nanoparticles
Authors: Jeon Yoon Tae , Lee Gang Ho
Published: May 2008

We produced the fcc Rh and Pd nanoparticles with average particle diameters of 3 and 4 nm, respectively, in solution. We observed hysteretic behaviors in M-H curves and estimated lower bound magnetic moments of 4.8×10−3 and (3.8×10−3)μB/atom from unsaturated M-H curves at an applied field of 5 T and at 5 K for Rh and Pd nanoparticles, respectively. This implies that both Rh and Pd nanoparticles are ferromagnetic. We attributed this ferromagnetism to the lattice expansions, especially along the (200) planes (i.e., the expansion of d200), as observed in the x-ray diffraction patterns.
Current-voltage characteristics of a graphene-nanoribbon field-effect transistor
Authors: Ryzhii V. , Ryzhii M. , Satou A. , Otsuji T.
Published: May 2008

We present an analytical device model for a field-effect transistor based on a heterostructure, which consists of an array of nanoribbons clad between the highly conducting substrate (the back-gate) and the top gate controlling the source-drain current. The equations of the model of a grapheme-nanoribbon field-effect transistor (GNR-FET) include the Poisson equation in the weak nonlocality approximation. By using this model, we find explicit analytical formulas for the spatial distributions of the electric potential along the channel and for the GNR-FET current-voltage characteristics (the dependences of the source-drain current on the drain voltages as well as on the back-gate and top-gate voltages) for different geometric parameters of the device. It is shown that the shortening of the top gate can result in a substantial modification of the GNR-FET current-voltage characteristics.
Improved gate oxide integrity of strained Si n-channel metal oxide silicon field effect transistors using thin virtual substrates
Authors: Yan L. , Olsen S. H. , Escobedo-Cousin E. , O’Neill A. G.
Published: May 2008

This work presents a detailed study of ultrathin gate oxide integrity in strained Si metal oxide silicon field effect transistors (MOSFETs) fabricated on thin virtual substrates aimed at reducing device self-heating. The gate oxide quality and reliability of the devices are compared to those of simultaneously processed Si control devices and conventional thick virtual substrate devices that have the same Ge content (20%), strained Si channel thickness, and channel strain. The thin virtual substrates offer the same mobility enhancement as the thick virtual substrates (∼100% compared to universal mobility data) and are effective at reducing device self-heating. Up to 90% improvement in gate leakage current is demonstrated for the strained Si n-channel MOSFETs compared to that for the bulk Si controls. The lower leakage arises from the increased electron affinity in tensile strained Si and is significant due to the sizeable strain generated by using wafer-level stressors. The strain-induced leakage reductions also lead to major improvements in stress-induced leakage current (SILC) and oxide reliability. The lower leakage current of the thin and thick virtual substrate devices compares well to theoretical estimates based on the Wentzel–Kramers–Brillouin approximation. Breakdown characteristics also differ considerably between the devices, with the strained Si devices exhibiting a one order of magnitude increase in time to hard breakdown (THBD) compared to the Si control devices following high-field stressing at 17 MV cm−1. The strained Si devices are exempted from soft breakdown. Experimental based analytical leakage modeling has been carried out across the field range for the first time in thin oxides and demonstrates that Poole–Frenkel (PF) emissions followed by Fowler–Nordheim tunneling dominate gate leakage current at low fields in all of the devices. This contrasts to the frequently reported assumption that direct tunneling dominates gate leakage in ultrathin oxides. We also show that PF emissions are reduced in strained Si devices compared to bulk Si devices. The gate leakage, interface trap density, bulk oxide traps, breakdown characteristics, and SILC are further improved in the thin virtual substrate devices compared to the thick virtual substrate devices. The difference is attributed to surface roughness. The thick virtual substrates exhibit characteristic cross-hatching morphology, whereas the thin virtual substrates do not since they relax primarily through point defects rather than misfit dislocations. Virtual substrate growth techniques that minimize surface roughness will, therefore, benefit all state-of-the-art devices featuring strained Si, strained Si-on-insulator, and strained Ge that are generated by using relaxed SiGe platforms.
Flux-line cutting in rotating type-II superconductors in parallel geometry
Authors: Romero-Salazar C. , Hernández-Flores O. A.
Published: May 2008

Experimental results of a type-II superconductor, undergoing slow oscillations in a static magnetic field, have been theoretically investigated. The theoretical description considers the occurrence of flux-line cutting since the critical currents have a parallel component to the magnetic induction B. For this purpose, the elliptic flux-line-cutting critical-state model has been employed to calculate the magnitude B and orientation α(x) of the magnetic induction. Hysteresis loops, at different initial magnetic states and, at relatively small and large amplitudes of oscillation, are calculated numerically and compared with experimental data of a Nb disk. The complex behavior of the hysteresis loops is associated with the magnetic induction consumption. Our results are compared with those obtained employing the generalized double critical-state model. Our elliptic model is not restricted by the isotropic condition, that establishes that the electric field E is parallel to the current density J, but considers an induced anisotropy by flux line cutting. The limits of applicability of the elliptic model are discussed.
Synthesis and characterization of composite MgFe2O4–BaTiO3 multiferroic system
Authors: Tan S. Y. , Shannigrahi S. R. , Tan S. H. , Tay F. E. H.
Published: May 2008

Multiferroic ceramics with the general formula (x)MgFe2O4–(1−x)BaTiO3 (x=0.4, 0.5, and 0.6) were synthesized by solid-state sintering process. From the x-ray diffraction analysis, it was observed that almost no chemical reaction occurs between the ferrite and the ferroelectric materials used to form the diphase composite systems. No impure phase was observed in all the sintered composite systems. Leakage current density, ferroelectric properties and dielectric properties were found to improve with the addition of the ferroelectric phase. For the composite with the least amount of ferrite, the values of remnant polarization (2Pr) before and after dc magnetic poling at 7kOe for 1h were found to be 1.35 and 2.12μC∕cm2, respectively. This showed marked improvement as high as 57% and confirmed the coupling of the electrical dipoles with the magnetic field applied. All the studied composite systems proved to be multiferroic in nature. The highest magnetoelectric coupling coefficient of 50.2mV∕cmOe was measured at dc magnetic field of 10kOe along with ac frequency of 50Hz at room temperature for the 0.6MgFe2O4–0.4BaTiO3 composite system. Magnetoelectric effect at resonance frequency increases by a factor of 80 compared to the other frequencies for such composite systems.
Effect of Ir–Mn composition on exchange bias and thermal stability of spin valves with nano-oxide layers
Authors: Liu Y. F. , Cai J. W. , Lai W. Y. , Yu G. H.
Published: May 2008

The Ir–Mn bottom-pinned spin valves with nano-oxide layers (NOLs), Ta∕Ni81Fe19∕Ir–Mn∕Co90Fe10∕NOL∕Co90Fe10∕Cu∕Co90Fe10∕NOL∕Ta, were fabricated by dc magnetron sputtering. The magnetoresistance (MR), magnetization, and exchange bias have been studied as a function of Ir–Mn composition and annealing temperature. It was observed that the spin valves with the Ir–Mn layer containing relatively low Mn content (58.9–72.4at.% Mn) show the best thermal endurance. For these samples, the Mn diffusion is effectively hampered by the NOL with a large MR value of about 12.5% even after annealing at 300°C. On the other hand, the exchange bias field of the pinned CoFe layer shows a maximum at Mn content of about 72.4at.%, which is different from the widely adopted composition, Ir-80at.% Mn, optimized from the top-pinned NiFe∕Ir–Mn system. Moreover, the blocking temperature of the Ir–Mn∕CoFe system with 72.4at.% Mn is higher than that with 80.6at.% Mn. The present results suggest that the Ir–Mn∕CoFe pinning system with Mn content at about 72% renders the most favorable exchange bias and the best thermal stability for the bottom-pinned specular spin valves.
Determination of the magnetic moment and geometrical dimensions of the magnetotactic bacteria using an optical scattering method
Authors: Logofătu Petre Cătălin , Ardelean Ioan , Apostol Dan , Iordache Iuliana , Bojan Mihaela , Moisescu Cristina , Ioniţă Bogdan
Published: May 2008

We adapted an experimental technique for characterizing the magnetotactic bacteria and simplified it by transferring the burden to literal and numerical computation, which is an advantageous tradeoff. In a magnetic field the bacteria tend to orient their magnetic axes along the direction of the magnetic field, resulting in an anisotropic distribution of the orientation and, consequently, a significant change of the directional distribution of the scattering efficiency of light. We made a simple experimental arrangement for measuring the scattering efficiency of light by the bacteria in certain directions for various values of an external magnetic field applied to the bacteria. We inferred from the fitting of the experimental to the theoretical data the most probable values for the magnetic moment and the dimensions of the magnetotactic bacteria. In the experiments a wild-type Magnetospirillum gryphiswaldense strain was used.
Large anisotropy of spin polarization in Heusler alloy Ni2MnGa induced by martensitic transformation
Authors: Zhu Z. Y. , Zhang H. W. , Xu S. F. , Chen J. L. , Cao Z. X. , Wu G. H.
Published: May 2008

Spin polarization both in the cubic austenitic and tetragonal martensitic phases of the Ni2MnGa alloy has been investigated using first-principles calculations combined with classical Bloch–Boltzmann transport theory. It is shown that the degree of spin polarization, while decreasing from 42% in the ⟨001⟩ directions of the austenitic phase to 30% in the [100] direction of the martensitic phase, rises to 75% in the [001] direction of the martensitic phase, resulting from a preferential reconstruction of the spin-down Fermi surfaces upon martensitic transformation. With this finding, various recent intriguing electrical measurements upon Ni2MnGa across the martensitic transformation can find an explanation. This also opens a way of searching for giant magnetoresistance materials.
Single-crystalline transparent and conductive oxide films with the perovskite structure: Sb-doped SrSnO3
Authors: Liu Q. Z. , Wang H. F. , Chen F. , Wu Wenbin
Published: May 2008

Perovskite-type transparent and conductive oxide films, Sb-doped SrSnO3 (SSSO), were grown on SrTiO3(001) substrates by the pulsed laser deposition method. It is revealed that the films can be grown at relatively lower temperatures and show high single crystallinity with a cubic perovskite structure with lattice constant of 4.036Å. These films show good optical transmittance in the visible range, with the direct allowed band gap of 4.53eV, and behave as an n-type semiconductor with resistivity of 23mΩcm at room temperature. The effect of growth temperature on structural, electrical, and optical properties of the SSSO films was probed, and a diode based on n-SSSO∕p-La0.67Ca0.33MnO3 structure was also demonstrated.
Bioinspired construction of Mg–Li alloys surfaces with stable superhydrophobicity and improved corrosion resistance
Authors: Liu Kesong , Zhang Milin , Zhai Jin , Wang Jun , Jiang Lei
Published: May 2008

A facile method was utilized for the construction of the bioinspired superhydrophobic Mg–Li alloy surfaces with peonylike micronanoscale hierarchical structures. The resultant materials were characterized by scanning electron microscope, x-ray photoelectron spectroscopy, and water contact angle measurements. The obtained Mg–Li alloy surfaces presented the dramatically improved corrosion resistance and long-term stable superhydrophobic properties with a static water contact angle of about 160° and a small sliding angle of less than 5°, which may extend the practical application of Mg–Li alloys in industrial and high-technology fields.
Multifunctional liquid crystal elastomers: Large electromechanical and electro-optical effects
Authors: Hashimoto Shigehiro , Yusuf Yusril , Krause Simon , Finkelmann Heino , Cladis P. E. , Brand Helmut R. , Kai Shoichi
Published: May 2008

A multifunctional main chain liquid crystal elastomer (MCLCE) with large mechanical and optical effects in applied electric fields is investigated, when MCLCE is swollen in a low molecular weight liquid crystal, 4-n-pentyl-4-cyanobiphenyl, a nematic solvent. The size change by the field effects is linearly proportional to the transmittancy change. This suggests the possibility of broad application as a field-induced-optical actuator device.
The origin of the energy-dose window in separation-by-implanted-oxygen materials processing
Authors: Kögler R. , Ou Xin , Skorupa W. , Möller W.
Published: May 2008

The energy-dose (ED) window (so called Izumi window) for the formation of a perfect planar and homogeneous buried oxide layer in silicon using ion implantation is controlled by the interaction of excess radiation defects and the local oxygen concentration. The ED window is defined by an appropriate correlation between the distribution of implantation-induced excess defects and the position of the finally formed oxide layer. A quantitative relation is established on the basis of collisional computer simulations. The findings are discussed in terms of oxide precipitation under the influence of defects.
The Lorentz extension as consequence of the family symmetry
Authors: Wang Hai-Jun
Published: May 2008

In this paper, we postulate an algebraic model to explain how the symmetry of three lepton species plays its role in the Lorentz extension. Inspired by the two-to-one mapping between the SL(2,C) group and the Lorentz group, we design a mapping between the SL(3,C) group, which displays the family symmetry, and a generalized Lorentz group. Following the conventional method, we apply the mapping results to the Dirac equation to discuss its transformation invariance, and it turns out that only when the vertex matrix γμ is extended to the combination c1γμ+c2γ5γμ can the Dirac-equation form be reserved. At the same time, we find that the Lorentz group has to be extended with an additional generator γ5. The generalized vertex matrix is helpful in understanding the axial-like form of weak interaction and the neutrino oscillations.
A subnanosecond pulsed ion source for micrometer focused ion beams
Authors: Höhr C. , Fischer D. , Moshammer R. , Dorn A. , Ullrich J.
Published: May 2008

A new, compact design of an ion source delivers nanosecond pulsed ion beams with low emittance, which can be focused to micrometer size. By using a high-power, 25fs laser pulse focused into a gas region of 10−6mbar, ions at very low temperatures are produced in the small laser focal volume of 5μm diameter by 20μm length through multiphoton ionization. These ions are created in a cold environment, not in a hot plasma, and, since the ionization process itself does not significantly heat them, have as a result essentially room temperature. The generated ion pulse, up to several thousand ions per pulse, is extracted from the source volume with ion optical elements that have been carefully designed by simulation calculations. Externally triggered, its subnanosecond duration and even smaller time jitter allow it to be superimposed with other pulsed particle or laser beams. It therefore can be combined with any type of collision experiment where the size and the time structure of the projectile beam crucially affect the achievable experimental resolution.
A new eight vertex model and higher dimensional, multiparameter generalizations
Authors: Abdesselam B. , Chakrabarti A.
Published: May 2008

We study statistical models, specifically transfer matrices corresponding to a multiparameter hierarchy of braid matrices of (2n)2×(2n)2 dimensions with 2n2 free parameters (n=1,2,3,…). The simplest, 4×4 case, is treated in detail. Powerful recursion relations are constructed by explicitly giving the dependence on the spectral parameter θ of the eigenvalues of the transfer matrix at each level of coproduct sequence. A brief study of higher dimensional cases (n⩾2) is presented, pointing out features of particular interest. Spin chain Hamiltonians are also briefly presented for the hierarchy. In a long final section, basic results are recapitulated with systematic analysis of their contents. Our eight vertex 4×4 case is compared to standard six vertex and eight vertex models.
Performance of poly(3-hexylthiophene) organic field-effect transistors on cross-linked poly(4-vinyl phenol) dielectric layer and solvent effects
Authors: Sethuraman Kunjithapatham , Ochiai Shizuyasu , Kojima Kenzo , Mizutani Teruyoshi
Published: May 2008

Bottom-contact organic field-effect transistors (OFETs) were fabricated using a polymer gate insulator cross-linked poly(4-vinyl phenol) with regioregular poly(3-hexylthiophene) (RR-P3HT) as an active layer from different organic solvents. With this polymer dielectric, a field-effect mobility of 0.084±0.006cm2V−1s−1 was obtained. Solvents and interfacial properties have pronounced effects in determining the crystallinity and device performance of RR-P3HT on the polymer gate layer. Morphology correlation with the charge carrier mobility of RR-P3HT OFETs is investigated. Large nanoscale crystalline island densities of this polymer play an important role in the high charge carrier mobility of devices.
Stable microwave coaxial cavity plasma system at atmospheric pressure
Authors: Song H. , Hong J. M. , Lee K. H. , Choi J. J.
Published: May 2008

We present a systematic study of the development of a novel atmospheric microwave plasma system for material processing in the pressure range up to 760torr and the microwave input power up to 6kW. Atmospheric microwave plasma was reliably produced and sustained by using a cylindrical resonator with the TM011 cavity mode. The applicator and the microwave cavity, which is a cylindrical resonator, are carefully designed and optimized with the time dependent finite element Maxwell equation solver. The azimuthal apertures are placed at the maximum magnetic field positions between the cavity and the applicator to maximize the coupling efficiency into the microwave plasma at a resonant frequency of 2.45GHz. The system consists of a magnetron power supply, a circulator, a directional coupler, a three-stub tuner, a dummy load, a coaxial cavity, and a central cavity. Design and construction of the resonant structures and diagnostics of atmospheric plasma using optical experiments are discussed in various ranges of pressure and microwave input power for different types of gases.
Controlling the temperature coefficient of resistance and resistivity in RuO2–TiO2 thin films by the intermixing ratios between RuO2 and TiO2
Authors: Kwon Se-Hun , Kang Sang-Won , Kim Kwang-Ho
Published: May 2008

The temperature coefficient of resistance (TCR) properties and resistivities, depending on the RuO2 intermixing ratios for RuO2–TiO2 thin films and their thermal stability in the temperature range of 200–700°C, were investigated. The TCR values for the RuO2–TiO2 thin films ranged from −557.17to−54.923ppm∕K for the RuO2 intermixing ratios ranging from 0.52 to 0.81, with resistivities remaining in the range of 2600–370μΩcm. Moreover, the high structural stability and its stable oxide form of the RuO2–TiO2 thin films resulted in minimal change in both TCR values and resistivities even after O2 annealing process at 700°C.
Demonstration of a tunable two-frequency projected fringe pattern with acousto-optic deflectors
Authors: Dupont S. , Kastelik J. C.
Published: May 2008

We report on a fringe projector for three-dimensional shape measurement. The developed instrument is able to project a two-frequency fringe pattern, each frequency is independently controlled by electronics. Moreover, each phase of the two fringe patterns is also independently adjusted. The projection system is based on the use of a pair of custom large bandwidth (40MHz) and high efficiency (60%) TeO2 deflectors. The developed instrument offers the combined advantages of a static two-frequency fringe projector and of a tunable single frequency fringe projector.
Elasticity mapping of precipitates in polycrystalline materials using atomic force acoustic microscopy
Authors: Kumar Anish , Rabe Ute , Hirsekorn Sigrun , Arnold Walter
Published: May 2008

We determined the isotropic indentation modulus of precipitates in cubic materials by using the indentation modulus of the matrix as a reference. This eliminates major practical difficulty of repeatedly switching between a sample and a reference for measurement of indentation modulus using atomic force acoustic microscopy. The methodology has been demonstrated for mapping the elastic stiffness of ∼500nm sized M23C6 precipitates in alloy 625 and ferritic steel with a spatial resolution of ∼50nm.
Current-induced magnetization excitation in a pseudo-spin-valve with in-plane anisotropy
Authors: Guo Jie , Jalil Mansoor Bin Abdul , Tan Seng Ghee
Published: May 2008

We study the magnetization dynamics of a pseudo-spin-valve structure with in-plane anisotropy, which is induced by the passage of a perpendicular-to-plane spin-polarized current. The magnetization dynamics is described by a modified Landau–Lifshitz–Gilbert (LLG) equation, which incorporates two spin torque terms. The simulation results reveal two magnetization excitation modes: (a) complete magnetization reversal and (b) persistent spin precession. The existence of these dual modes may be explained in terms of the competition between the four terms of the modified LLG equation. Our results give indications to the optimal operating conditions for current-induced magnetization dynamics for possible device applications.
Electrical characteristics of single-component ambipolar organic field-effect transistors and effects of air exposure on them
Authors: Sakanoue Tomo , Yahiro Masayuki , Adachi Chihaya , Takimiya Kazuo , Toshimitsu Akio
Published: May 2008

We investigated the electrical characteristics of single-component ambipolar organic field-effect transistors (OFETs) by controlling the device structure and preparation and the measurement conditions. Six organic semiconductor materials (copper-phthalocyanine, tris-(8-hydroxyquinoline)aluminum (Alq3), alpha-sexithiophene, 4-4′-bis-styrylphenyl, 2,7-diphenyl[1]benzothieno[3,2-b]benzothiophene, or a photopolymerized polydiacethylene derivative (PDA) were used as the active layer, and all were found to transport both holes and electrons. The PDA-based FETs had the highest hole and electron mobilities (0.12 and 0.025 cm2/V s, respectively). We also investigated the effect of air exposure on the OFETs. The hole mobility was barely affected by the exposure while the electron mobility was significantly affected. The threshold voltage for p-channel operation was shifted by the exposure while that for n-channel operation was not, indicating that the hole density in the active layer is increased by air exposure whereas the electron density is independent of air exposure. Furthermore, we prepared an Alq3-based p-channel OFET and investigated the effect of air exposure on it. While its operation was stable in vacuum, air exposure degraded its characteristics. These behaviors indicate that irreversible chemical reactions occur between cationic Alq3 species and oxygen or water molecules.