bluuebunny/crossref_metadata_2025 huggingface dataset:
Using limited time period trends as a means to determine attribution of discrepancies in microwave sounding unit–derived tropospheric temperature time series
Authors: Randall Robb M. , Herman Benjamin M.
Published: March 2008

Limited time period running trends are created from various microwave sounding unit (MSU) difference time series between the University of Alabama in Huntsville and Remote Sensing System (RSS) group's lower troposphere (LT) and mid troposphere to lower stratosphere channels. This is accomplished in an effort to determine the causes of the greatest discrepancies between the two data sets. Results indicate the greatest discrepancies were over time periods where NOAA 11 through NOAA 15 adjustments were applied to the raw LT data over land. Discrepancies in the LT channel are shown to be dominated by differences in diurnal correction methods due to orbital drift; however, discrepancies from target parameter differences are also present. Comparison of MSU data with the reduced Radiosonde Atmospheric Temperature Products for Assessing Climate radiosonde data set indicates that RSS's method (use of climate model) of determining diurnal effects is likely overestimating the correction in the LT channel. Diurnal correction signatures still exist in the RSS LT time series and are likely affecting the long‐term trend with a warm bias. Our findings enhance the importance of understanding temporal changes in the atmospheric temperature trend profile and their implications on current climate studies.
An asymmetric mode of tropical Indian Ocean rainfall variability in boreal spring
Authors: Wu Renguang , Kirtman Ben P. , Krishnamurthy V.
Published: March 2008

An analysis of observational estimates has revealed an asymmetric mode of boreal spring rainfall and wind variability over the tropical Indian Ocean. The asymmetric mode is characterized by opposite rainfall and surface wind anomalies north and south of the equator. This mode is associated with a cross‐equatorial gradient in sea surface temperature anomalies. The evolution of this mode is related to air‐sea interactions in the tropical Indian Ocean. In particular, surface heat fluxes play an important role in the initiation, development, and decay of this mode. The occurrence of this mode in observations is closely linked to both El Niño‐Southern Oscillation (ENSO) and the Indian Ocean Dipole mode. Coupled general circulation model experiments indicate that this mode can occur in the absence of ENSO. The variability associated with this mode enhances ENSO's teleconnection to the Indian Ocean and affects the seasonal transition in the tropical Indian Ocean.
Extent of the low‐velocity region in the lowermost mantle beneath the western Pacific detected by the Vietnamese Broadband Seismograph Array
Authors: Takeuchi N. , Morita Y. , Xuyen N. D. , Zung N. Q.
Published: March 2008

We present evidence showing the extent of the low‐velocity region in the lowermost mantle beneath the western Pacific. We analyzed S, sS, ScS‐S, and sScS‐sS travel times observed by the Vietnamese broadband seismograph array deployed as part of the Ocean Hemisphere Project. The abrupt changes in ScS‐S and sScS‐sS travel times suggest that the western geographical boundary of the low‐velocity region is located around 140°E and is sharp (more than 4% velocity contrast within 200 km). The dependency of S and sS travel time anomalies of epicentral distances suggests that the strong low‐velocity region is confined to within 400 km from the CMB (core‐mantle boundary). The existence of lateral heterogeneities with a 100 km scale inside the low‐velocity region is also suggested by the abrupt changes in S and ScS waveforms.
Structural context of the great Sumatra‐Andaman Islands earthquake
Authors: Shapiro Nikolai M. , Ritzwoller Michael H. , Engdahl E. Robert
Published: March 2008

A new three‐dimensional seismic model and relocated regional seismicity are used to illuminate the great Sumatra‐Andaman Islands earthquake of December 26, 2004. The earthquake initiated where the incoming Indian Plate lithosphere is warmest and the dip of the Wadati‐Benioff zone is least steep along the subduction zone extending from the Andaman Trench to the Java Trench. Anomalously high temperatures are observed in the supra‐slab mantle wedge in the Andaman back‐arc. The subducting slab is observed along the entire plate boundary to a depth of at least 200 km. These factors contribute to the location of the initiation of rupture, the strength of seismic coupling, the differential rupture properties between the northern and southern segments of the earthquake, and the cause of convergence in the Andaman segment.
Measurement Analysis of Glass Transition Temperature for Sucrose and Trehalose Aqueous Solutions
Authors: Frank G. A.
Published: March 2008

Glass transition temperatures (Tg) for sucrose, trehalose, and water have been determined by numerous studies in the past. Literature values appear to be fairly scattered and compromise the applicability of the Gordon–Taylor equation for aqueous solutions. This work deals with the effect of the sample history and heating process on the Tg values. Consistent estimates for the glass transition temperature of both disaccharides in aqueous solution can be made from these observations.
Thermodynamics of Enzyme-Catalyzed Reactions: Part 7—2007 Update
Authors: Goldberg Robert N. , Tewari Yadu B. , Bhat Talapady N.
Published: March 2008

This review serves to update previously published evaluations of equilibrium constants and enthalpy changes for enzyme-catalyzed reactions. For each reaction, the following information is given: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used], the data and their evaluation, and, sometimes, commentary on the data and on any corrections which have been applied to the data or any calculations for which the data have been used. The review contains data from 119 references which have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is also a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.
Wavelengths, Transition Probabilities, and Energy Levels for the Spectra of Potassium (KI through KXIX)
Authors: Sansonetti J. E.
Published: March 2008

Energy levels, with classifications and uncertainties, have been compiled for the spectra of the neutral atom and all positive ions of potassium (Z=19). Wavelengths with classifications, intensities, and transition probabilities are also tabulated. In addition, ground states and ionization energies are listed. For many ionization stages experimental data are available; however for those for which only theoretical calculations or fitted values exist, these are reported.
Erratum: “Improved Critical Compilations of Selected Atomic Transition Probabilities for Neutral and Singly Ionized Carbon and Nitrogen” [J. Phys. Chem. Ref. Data 36, 1287–1345 (2007)]
Authors: Wiese W. L. , Fuhr J. R.
Published: March 2008

Corrected reference numbers for Table 8 (C II: Allowed Transitions).
The electronic structure of the four nucleotide bases in DNA, of their stacks, and of their homopolynucleotides in the absence and presence of water
Authors: Ladik János , Bende Attila , Bogár Ferenc
Published: March 2008

Using the ab initio Hartree-Fock crystal orbital method in its linear combination of atomic orbital form, the energy band structure of the four homo-DNA-base stacks and those of poly(adenilic acid), polythymidine, and polycytidine were calculated both in the absence and presence of their surrounding water molecules. For these computations Clementi’s double ζ basis set was applied. To facilitate the interpretation of the results, the calculations were supplemented by the calculations of the six narrow bands above the conduction band of poly(guanilic acid) with water. Further, the sugar-phosphate chain as well as the water structures around poly(adenilic acid) and polythymidine, respectively, were computed. Three important features have emerged from these calculations. (1) The nonbase-type or water-type bands in the fundamental gap are all close to the corresponding conduction bands. (2) The very broad conduction band (1.70eV) of the guanine stack is split off to seven narrow bands in the case of poly(guanilic acid) (both without and with water) showing that in the energy range of the originally guanine-stack-type conduction band, states belonging to the sugar, to PO4−, to Na+, and to water mix with the guanine-type states. (3) It is apparent that at the homopolynucleotides with water in three cases the valence bands are very similar (polycytidine, because it has a very narrow valence band, does not fall into this category). We have supplemented these calculations by the computation of correlation effects on the band structures of the base stacks by solving the inverse Dyson equation in its diagonal approximation taken for the self-energy the MP2 many body perturbation theory expression. In all cases the too large fundamental gap decreased by 2–3eV. In most cases the widths of the valence and conduction bands, respectively, decreased (but not in all cases). This unusual behavior is most probably due to the rather large complexity of the systems. From all this emerges the following picture for the charge transport in DNA: There is a possibility in short segments of the DNA helix of a Bloch-type conduction of holes through the nucleotide base stacks of DNA combined with hopping (and in a lesser degree with tunneling). The motivation of this large scale computation was that recently in Zürich (ETH) they have performed high resolution x-ray diffraction experiments on the structure of the nucleosomes. The 8 nucleohistones in them are wrapped around by a DNA superhelix of 147 base pairs in the DNA B form. The most recent investigations have shown that between the DNA superhelix (mostly from its PO4− groups) there is a charge transfer to the positively charged side chains (first of all arginines and lysines) of the histones at 120 sites of the superhelix. This would cause a hole conduction in DNA and an electronic one in the proteins.
Effect of hydrogen codoping on magnetic ordering and conductivity in Cr:ZnO thin films
Authors: Roberts Bradley K. , Pakhomov Alexandre B. , Krishnan Kannan M.
Published: March 2008

We explore the effects of codoping with hydrogen on magnetism, conductivity, and spin polarization of carriers in Cr-doped ZnO. Zn0.99Cr0.01O:H films sputter deposited on sapphire show a correlation between magnetization and conductivity when H is introduced. In the first method, dielectric and weakly magnetic films grown in pure Ar are subsequently annealed at 400°C in a 5% H2 95% Ar 1atm flowing tube furnace. These films show increases in conductivity and saturation and remnant magnetization postanneal. In the second method, conducting ferromagnetic films are grown in the H∕Ar mixture. They are magnetic as grown but show a small decrease in saturation and remnant magnetization and conductivity post-H∕Ar anneal. Ferromagnetic CrO2 with TC=390K or antiferromagnetic phases are not detected in hydrogenated films. We studied spin polarization of carriers using anomalous Hall effect; however, initial experiments show no such signs, hence spin polarization is not yet confirmed. Hydrogen doped in dielectric Cr:ZnO may contribute to the conductivity and ferromagnetism in a noncausal relationship.
First order reversal curves identification procedures for vector models of hysteresis
Authors: Stoleriu Laurentiu , Andrei Petru , Stancu Alexandru
Published: March 2008

The first order reversal curves (FORCs) technique has been extensively used in the last years for the identification of parameters of Preisach-type models of hysteresis. The technique proved both accurate and robust for the identification of the Preisach distribution function but due to the relatively high computational complexity, it has only been applied to scalar models of hysteresis. The theoretical foundations of the procedure for the identification of parameters of vector Preisach models by using FORCs were established by Mayergoyz. However, to our knowledge, the numerical implementation of the technique has received very little attention in the literature and there is no experimental testing of this technique either. In this paper, we present for the first time results obtained for the identification of the vector Preisach distribution by using FORC diagrams for a magnetic tape with uniaxial anisotropy. We also tested the model with simulated data produced by a vectorial Preisach model in which the pseudoparticles’ equilibrium state was calculated with a Landau–Lifshitz–Gilbert algorithm.
On the plasmon mechanism of high-Tc superconductivity in layered crystals and two-dimensional systems
Authors: Pashitskii E. A. , Pentegov V. I.
Published: March 2008

The results of numerical calculations, in different approximations, of the screened Coulomb and retarded electron-plasmon interactions in quasi-two-dimensional layered crystals and two-dimensional (2D) systems with a quasi-acoustic or square-root plasmon spectrum are subjected to a detailed comparative analysis. It is shown that even in the simplest, random-phase approximation the effective attraction due to the exchange of virtual plasmons can bring about a transition to a superconducting state with a relatively high critical temperature Tc. The extended saddle-point singularities typical of the 2D band spectrum of layered crystals of cuprate metaloxide compounds and also the many-particle Coulomb correlations described by Coulomb vertices (three-poles) make for a substantial increase in the maximum values of Tc, which agree with the experimental data for high-Tc superconductors. It is shown that the plasmon mechanism leads to Cooper pairing in both the d-wave and s-wave Cooper channels, but the superconductivity in the s-wave channel is suppressed by exchange-correlation effects. Calculations also indicate the possibility of obtaining rather high-Tc superconductivity in 2D systems (of the graphene type).
New method of making point contacts
Authors: Fisun V. V. , Khotkevich A. V. , Konopatskyi B. L. , Kamarchuk G. V. , Morlok S. V. , Alexandrov Yu. L.
Published: March 2008

A new method of making point contacts of small size by twisting (twining) metal wire electrodes is proposed and investigated. Clean, stable contacts with reproducible electrical characteristics are obtained at low temperatures. High-intensity point-contact spectra of the electron–phonon (e–ph) interaction in copper and also the spectra of the e–ph interaction in copper/gold hetero-contacts are observed. For molybdenum, point-contact spectra with more detail than in the previously known spectra are obtained, revealing their fine structure, and the integral parameters of the e–ph interaction are determined. The characteristics of superconducting point contacts of solid mercury are investigated. Titanium contacts are used at room temperature as gas sensors for analysis of human exhalate.
Application of fractional factorial design for improving performance of 60W transverse flux linear motor
Authors: Hong Do-Kwan , Woo Byung-Chul , Kang Do-Hyun
Published: March 2008

This paper presents an optimum design procedure of permanent-magnet-type 60W transverse flux linear motor to reduce the weight of the machines with the constraints of thrust and detent forces using fractional factorial design and response surface methodology (RSM). RSM is well adapted to make the analytical model of minimum weight with constraints of thrust and detent forces, and it enables objective functions to be easily created, and a great deal of computation time can be saved. Therefore, the usefulness of this method is verified through the comparison of the performances of the optimal model and those of the initial model.
Segmental versus chain dynamics of linear polymers
Authors: Brodin Alexander
Published: March 2008

Segmental dynamics of relatively short linear polymers are discussed in terms of two distinct contributions, one related to the local segmental motion (α relaxation) and the other to polymer-specific effects that reflect Brownian dynamics of the polymer under chain connectivity constraints (Rouse relaxation modes). These two aspects of polymer dynamics are reflected, though differently, in relaxation spectra of different experimental techniques. Two contrasting cases of the (collective) dipolar response (dielectric techniques) versus the individual segmental response (e.g., NMR spin-lattice relaxation spectroscopy) are considered. The second-rank orientational correlation function of an elementary (Kuhn) segment, directly related to NMR observables, is derived in terms of Rouse normal modes. The effect of α dynamics is estimated under the assumption of a separation of time scales which, as it is argued, is a necessary precondition of the Rouse approach. The relative magnitude of the polymer-related dynamics is expressed through the number of elementary Rouse units in the chain and the number of Kuhn segments in a Rouse unit. The results are discussed in the context of recent literature.
Lateral- and layer-resolved magnetization reversals in a spin-valve array
Authors: Lee D. R. , Choi Y. , Freeland J. W. , Keavney D. J. , Srajer G. , Metlushko V. , Ilic B.
Published: March 2008

Using element-sensitive x-ray resonant magnetic scattering, layer-resolved magnetic hysteresis loops were measured on a periodic square frame nanostrucutre. Taking advantage of the lateral periodicity, we measured hysteresis loops at several x-ray diffraction orders to extract hysteresis loops from different regions of the square frame structures. The layer- and spatially resolved magnetic measurements revealed distinct magnetic reversal mechanisms in different regions due to interplay between the shape anisotropy and interlayer dipolar coupling. The assumed vortex state during the reversal in our analysis was confirmed by photoemission electron microscopy imaging.
Quadrupolelike electrostatic guiding for cold polar molecules
Authors: Xia Yong , Yin Yaling , Chen Haibo , Deng Lianzhong , Yin Jianping
Published: March 2008

We demonstrate electrostatic guiding of cold heavy water (D2O) molecules over a distance of 44.5cm by using a quadrupolelike electrostatic field, which is generated by the combination of two parallel charged poles and two grounded metal plates. We measure the transverse spatial distribution of the guided D2O molecular beam and study the dependence of the relative guiding efficiency and the transverse temperature of the guided molecular beam on the guiding voltage. Our study shows that the maximum guiding efficiency of ∼50% can be obtained, and our experimental results are in good agreement with ones of theoretical calculation and Monte Carlo simulations, and this guiding scheme has some potential applications in molecule optics, such as molecular-beam splitter, integrated molecular optics, etc.
Modeling of dielectric barrier discharge plasma actuator in air
Authors: Likhanskii Alexandre V. , Shneider Mikhail N. , Macheret Sergey O. , Miles Richard B.
Published: March 2008

A detailed physical model for asymmetric dielectric barrier discharge (DBD) in air at low voltages (1.5–2 kV) is developed. Modeling of DBD with an applied sinusoidal voltage is carried out in two dimensions. The leading role of charging the dielectric surface by electrons in the cathode phase is shown to be critical, acting as a harpoon that pulls positive ions forward and accelerates the gas in the anode phase. The positive ion motion back toward the exposed electrode is shown to be a major source of inefficiency in the sinusoidal or near-sinusoidal voltage cases. Based on understanding of the DBD physics, an optimal voltage waveform is proposed, consisting of high repetition rate, short (a few nanoseconds in duration), negative pulses combined with a positive dc bias applied to the exposed electrode.
Theoretical study of the three-phase contact line and its tension in adsorbed colloid-polymer mixtures
Authors: Vandecan Yves , Indekeu Joseph O.
Published: March 2008

We perform a theoretical study of the three-phase contact line and the line tension in an adsorbed colloid-polymer mixture near a first-order wetting transition, employing an interface displacement model. We use a simple free-energy functional to describe a colloid-polymer mixture near a hard wall. The bulk phase behavior and the substrate-adsorbate interaction are modeled by the free-volume theory for ideal polymers. The large size of the colloidal particles and the suppression of the van der Waals interaction by optical matching of colloid and solvent justify the planar hard wall model for the substrate. Following the Fisher–Jin scheme, we derive from the free-energy functional an interface potential V(ℓ) for these mixtures. For a particle diameter of 10–100nm, the calculations indicate a line tension τ≈10−12–10−13N at room temperature. In view of the ultralow interfacial tension in colloid-polymer mixtures, γ≈10−7N∕m, this leads to a rather large characteristic length scale τ∕γ in the micrometer range for the three-phase contact zone width. In contrast with molecular fluids, this zone could be studied directly with optical techniques such as confocal scanning laser microscopy.
Magnetic energy-barrier distributions for ferrihydrite nanoparticles formed by reconstituting ferritin
Authors: Gorham N. T. , St. Pierre T. G. , Chua-Anusorn W. , Parkinson G. M.
Published: March 2008

The spherical cage-like protein ferritin was reconstituted with varying numbers of iron atoms per protein shell (ranging from approximately 20 to 1100) at temperatures of both 25 and 50 °C to produce iron(III) oxyhydroxide (ferrihydrite) particles with different average particle sizes and degrees of crystallinity. After characterization of the structural properties of the resulting iron-oxyhydroxide nanoparticles with transmission electron microscopy and Mössbauer spectroscopy, magnetic viscosity measurements were made in zero applied magnetic field and the resulting data were used to calculate the apparent magnetic-moment-weighted energy barrier distributions for the samples. The distributions measured were typically comprised of both a lognormal distribution and an exponential decay of barrier frequency with increasing barrier height. Evidence that the lognormal component of this distribution arises from the distribution of particle volumes and moments within the ensemble is strongly supported by the increase in the mode of the energy barrier distribution with increasing particle size. The exponentially decaying distribution has a relatively higher contribution to the overall distribution for the more crystalline reconstituted ferritin samples suggesting that it may be associated predominantly with uncompensated spins at particle surfaces.
Thermal and fast neutron detection in chemical vapor deposition single-crystal diamond detectors
Authors: Almaviva S. , Marinelli M. , Milani E. , Prestopino G. , Tucciarone A. , Verona C. , Verona-Rinati G. , Angelone M. , Lattanzi D. , Pillon M. , Montereali R. M. , Vincenti M. A.
Published: March 2008

Recently, a compact solid-state neutron detector capable of simultaneously detecting thermal and fast neutrons was proposed [M. Marinelli et al., Appl. Phys. Lett. 89, 143509 (2006)]. Its design is based on a p-type/intrinsic/metal layered structure obtained by Microwave Plasma Chemical Vapor Deposition (CVD) of homoepitaxial diamond followed by thermal evaporation of an Al contact and a L6iF converting layer. Fast neutrons are directly detected in the CVD diamond bulk, since they have enough energy to produce the C12(n,α)B9e reaction in diamond. Thermal neutrons are instead converted into charged particles in the L6iF layer through the L6i(n,α)T nuclear reaction. These charged particles are then detected in the diamond layer. The thickness of the L6iF converting layer and the CVD diamond sensing layer affect the counting efficiency and energy resolution of the detector both for low- (thermal) and high-energy neutrons. An analysis is carried out on the dynamics of the L6i(n,α)T and the C12(n,α)B9e reactions products, and the distribution of the energy released inside the sensitive layer is calculated. The detector counting efficiency and energy resolution were accordingly derived as a function of the thickness of the L6iF and CVD diamond layers, both for thermal and fast neutrons, thus allowing us to choose the optimum detector design for any particular application. Comparison with experimental results is also reported.
Sil'nikov chaos of the Liu system
Authors: Zhou Liangqiang , Chen Fangqi
Published: March 2008

A new chaotic attractor is discovered for the Liu system. The homoclinic and heteroclinic orbits in the Liu system have been found by using the undetermined coefficient method. It analytically demonstrates that there exists one heteroclinic orbit of the Sil'nikov type that connects two nontrivial equilibrium points, and therefore Smale horseshoes and the horseshoe chaos occur for this system via the Sil'nikov criterion. In addition, there also exists one homoclinic orbit joined to the origin. The convergence of the series expansions of these two types of orbits is proved.
Geometry and transport in a model of two coupled quadratic nonlinear waveguides
Authors: Stirling James R. , Bang Ole , Christiansen Peter L. , Zakynthinaki Maria S. , Johansen Steffen Kjær
Published: March 2008

This paper applies geometric methods developed to understand chaos and transport in Hamiltonian systems to the study of power distribution in nonlinear waveguide arrays. The specific case of two linearly coupled χ(2) waveguides is modeled and analyzed in terms of transport and geometry in the phase space. This gives us a transport problem in the phase space resulting from the coupling of the two Hamiltonian systems for each waveguide. In particular, the effect of the presence of partial and complete barriers in the phase space on the transfer of intensity between the waveguides is studied, given a specific input and range of material properties. We show how these barriers break down as the coupling between the waveguides is increased and what the role of resonances in the phase space has in this. We also show how an increase in the coupling can lead to chaos and global transport and what effect this has on the intensity.
Nanoscale perpendicular magnetic island arrays fabricated by extreme ultraviolet interference lithography
Authors: Luo F. , Heyderman L. J. , Solak H. H. , Thomson T. , Best M. E.
Published: March 2008

Magnetic island arrays with a period of 50nm and uniform over 20×20μm2 have been fabricated by depositing Co∕Pd multilayer films on prepatterned SiOx pillars produced by extreme ultraviolet interference lithography. Scanning electron microscopy and magnetic force microscopy measurements made on the same islands give a direct, island-by-island comparison of the size and remanent switching field. The results demonstrate that the switching field distribution (SFD) is not primarily due to magnetostatic interactions, and a strong dependence of SFD on size is also not observed, indicating that a distribution of material properties is likely to be responsible for the SFD.
Dependence of magnetization processes on vortex helicities in Permalloy nanorings
Authors: Lai Mei-Feng , Liao Chun-Neng , San Zheng-Hong , Lee Chung-Peng , Hsieh Yi-Ping , Ho Tung-Feng
Published: March 2008

Two different magnetization reversal processes, which are caused by the helicities of the two small vortex domain walls in the two sides of the onion state, are found numerically to exist in thin film rings. When the two vortex domain walls are in the same helicity, the onion state will transform to flux closure state (vortex state) with increasing of the field, and then transform from the flux closure state (vortex state) to the reverse onion state with further increasing of the field. When the two vortex domain walls are in opposite helicities, however, with increasing of the field, the onion state will transform directly to the reverse onion state skipping the flux closure state (vortex state).
Drift solitons and shocks in inhomogeneous quantum magnetoplasmas
Authors: Haque Q. , Mahmood S.
Published: March 2008

Linear and nonlinear drift waves are studied in inhomogeneous electron-ion quantum magnetoplasma with neutrals in the background. The Korteweg–de Vries–Burgers equation is derived by using the quantum hydrodynamic model for nonlinear drift waves with quantum corrections. Both soliton and shock solutions are obtained in different limits. It is noticed that the width of the solitary hump is decreased with the increase in the quantum parameter. However this effect is reversed for the solitary dip case. It is also found that oscillatory shock wave is dependent on the quantum parameter. However, the monotonic shock formation is independent of the quantum parameter.
Temperature dependence of effective g factor in diluted magnetic semiconductor (Ga,Mn)As
Authors: Zhou R. , Sun B. Q. , Ruan X. Z. , Luo H. H. , Ji Y. , Wang W. Z. , Zhang F. , Zhao J. H.
Published: March 2008

Time resolved magneto-optic Kerr rotation measurements of optically induced spin quantum beats are performed on heavily doped bulk (Ga,Mn)As diluted magnetic semiconductors (DMS). An effective g-factor of about 0.2–0.3 over a wide range of temperature for both as-grown and annealed (Ga,Mn)As samples is obtained. A larger effective g-factor at lower temperature and an increase of the spin relaxation with increasing in-plane magnetic field are observed and attributed to the stronger p-d exchange interaction between holes and the localized magnetic ion spins, leading to a larger Zeeman splitting and heavy-hole–light-hole mixing. An abnormal dip structure of the g-factor in the vicinity of the Curie temperature suggests that the mean-field model is insufficient to describe the interactions and dynamics of spins in DMS because it neglects the short-range spin correlation effect.
Flatband voltage instability characteristics of HfO2-based GaAs metal-oxide-semiconductor capacitors with a thin Ge layer
Authors: Kim Hyoung-Sub , Ok I. , Zhang M. , Zhu F. , Park S. , Yum J. , Zhao H. , Lee Jack C. , Oh Jungwoo , Majhi Prashant
Published: March 2008

This work investigates the flatband voltage instability of HfO2-based GaAs metal-oxide-semiconductor (MOS) capacitor with a thin germanium (Ge) interfacial passivation layer (IPL). Both positive and negative dc gate biases are used as stress condition. By studying various samples such as the devices with extremely thin equivalent oxide thickness of 8.7Å, with optimum, thick Ge IPLs, and without Ge IPL at a given HfO2 thickness, as well as the devices with varying thicknesses of HfO2 on the optimum Ge IPLs, it is found that both the interface trap and the bulk trap of HfO2 are crucial in affecting the flatband voltage instability characteristics of HfO2 GaAs MOS capacitors. The results indicate that the minimum flatband voltage instability requires a higher quality interface and a thinner HfO2 layer, which can be achieved by employing Ge IPL technique in GaAs system.
Scanning capacitance microscopy detection of charge trapping in free-standing germanium nanodots and the passivation of hole trap sites
Authors: Wong K. M. , Chim W. K. , Huang J. Q. , Zhu L.
Published: March 2008

An array of freestanding germanium (Ge) nanodots was fabricated on a highly doped silicon substrate using an anodic alumina membrane as an evaporation mask. Approximately half of the Ge nanodots exhibit contrast reversal and hole trapping characteristics during scanning capacitance microscopy (SCM) measurements, as shown by a negative peak in the SCM differential capacitance (dC∕dV) versus probe tip-to-substrate bias profile. The disappearance of the negative dC∕dV characteristic peak after forming gas anneal at 450°C show the complete passivation of the hole trap sites by hydrogen. This is a demonstration on the spectroscopic detection of hole trapping in Ge nanodots and hydrogen passivation of hole trap sites using SCM. Partial passivation of electron trap sites after the relatively low temperature forming gas anneal was also observed as compared with complete passivation of hole trap sites. This suggests that hole traps sites are possibly located at or closer to the surface of the Ge nanodots as compared to electron traps which may be located deeper within the Ge nanodots.
Multiple critical layer thicknesses in retro-graded heterostructures
Authors: Ayers J. E.
Published: March 2008

We determined the critical layer thicknesses for the glide of strain-relaxing dislocations in retrograded semiconductor layers using force balance. For a retro-graded layer, the lattice mismatch varies with distance from the interface y as f=f0+Cfy with sgn(Cf)=−sgn(f0). For a particular combination of f0 and Cf, there may be three different critical thicknesses for which the line tension and glide force of the dislocation are equal. Lattice relaxation by positive glide of grown-in dislocations is favorable for thicknesses in the range hc1<hhc3. If the grading is sufficiently steep, lattice relaxation will only proceed if h>hc3.
Demonstration of transverse-magnetic dominant gain in quantum dot semiconductor optical amplifiers
Authors: Yasuoka Nami , Kawaguchi Kenichi , Ebe Hiroji , Akiyama Tomoyuki , Ekawa Mitsuru , Tanaka Shinsuke , Morito Ken , Uetake Ayahito , Sugawara Mitsuru , Arakawa Yasuhiko
Published: March 2008

We demonstrated transverse-magnetic (TM)-mode dominated gain at the 1.5μm wavelength in semiconductor optical amplifiers (SOAs) with columnar quantum dots (QDs). We show that we can control the polarization dependence of optical gain in QD-SOAs by changing the height and tensile-strained barrier of columnar QDs. The TM mode gain is 17.3dB and a gain of over 10dB was attained over a wide wavelength range of 200nm. The saturation output power is 19.5dBm at 1.55μm.
Impulsive chromospheric heating of two-ribbon flares by the fast reconnection mechanism
Authors: Ugai M.
Published: March 2008

Chromospheric heating of two-ribbon flares is quantitatively studied for different values of R0, the ratio of the chromospheric plasma density to the coronal one, on the basis of the spontaneous fast reconnection model. In general, occurrence of impulsive chromospheric joule heating is delayed for the larger R0 because of more Alfvén traveling time in the chromosphere. Once the chromospheric heating occurs, the temperature becomes more than 30 times its initial value for the case of R0=400 in a pair of layers of deep chromosphere, and the region of high temperature shifts upward and becomes broader with time, since the chromospheric thin layer of joule heating shifts upward according to a pileup of reconnected field lines in the flare loop; then, chromospheric evaporation grows and extends outward, and its velocity becomes comparable with the coronal downflow velocity inside the loop boundary. The impulsive chromospheric heating is caused by drastic evolution of the flare current wedge, through which some part of the coronal sheet current suddenly turns its direction to be concentrated into the chromospheric thin layer; simultaneously, a magnetohydrodynamic (MHD) generator arises ahead of the flare loop top to provide a new current circuit inside the large-scale flare current wedge. Hence, it is concluded that the powerful MHD generator, sustained by the fast reconnection jet, drives the flare current wedge to evolve, leading to the impulsive chromospheric heating.
Ozone production by nanoporous dielectric barrier glow discharge in atmospheric pressure air
Authors: Cho J. H. , Koo I. G. , Choi M. Y. , Lee W. M.
Published: March 2008

This study is aimed at demonstrating plasma-chemical ozone production based on low temperature atmospheric pressure glow discharge through nanoporous dielectric barriers. The 20kHz ac driven discharge is formed in air or oxygen gas flowing in the axial direction of the cylindrical plasma reactor containing four parallel aluminum rods covered with nanoporous alumina films. The discharge utilizing nanoporous dielectric barrier is more uniform and more energy efficient in ozone generation than the discharge through smooth-surface dielectric barriers.
Magnetic domain patterns in an asymmetric zigzag permalloy nanowire
Authors: Verma L. K. , Ng V.
Published: March 2008

Zigzag nanowires are potential candidates to study the shape dependence of nanoscale magnetic properties. Zigzag nanowires of modulated widths were studied at remanence by magnetic force microscopy, showing unique arrangements of magnetic domains. The alignment of magnetic moments changes with the orientation of the external field when applied along different sections of the nanowire and gives rise to different domain arrangements. The modulated widths of the nanowire sections define the directions for the magnetic moments to rearrange after the field is removed.
Bandgap engineering in amorphous BexZnyO thin films
Authors: Khoshman J. M. , Ingram D. C. , Kordesch M. E.
Published: March 2008

Reactive sputtering was used to grow thin films of BexZnyO on Si (100) substrates. X-ray diffraction patterns of the films revealed no structure, suggesting that the films have an amorphous nature. The optical “bandgap” energy of the amorphous BexZnyO (a-BexZnyO) films was derived from vacuum ultraviolet variable angle spectroscopic ellipsometry measurements. The value of the energy bandgap of the films can be efficiently engineered to vary from the amorphous ZnO bandgap of 3.35to7.91eV by changing the Be doping level in the a-BeZnO. The a-BeZnO films could be used for fabricating excellent a-ZnO based electronic devices.
Ultrahigh-frequency ferromagnetic properties of FeCoHf films deposited by gradient sputtering
Authors: Li Shandong , Huang Zhigao , Duh Jenq-Gong , Yamaguchi Masahiro
Published: March 2008

Nanocrystalline FeCoHf films with Hf composition gradient were prepared by gradient sputtering method at room temperature. A uniaxial magnetic anisotropy with high anisotropy field Hk up to 547Oe was achieved after magnetic annealing with external field along the gradient direction. Ultrahigh ferromagnetic resonance frequency over 7GHz was obtained in magnetic annealed gradient sputtered films. The origin of ultrahigh ferromagnetic properties in gradient sputtered films is discussed.
Temperature influence on the dynamics of vertically aligned liquid crystal displays
Authors: Vanbrabant Pieter J. M. , Dessaud Nathalie , Strömer Jan F.
Published: March 2008

The strong influence of the complex reverse flow phenomenon on the dynamic temperature behavior of vertically aligned liquid crystal displays (VA-LCDs) has been demonstrated. Good agreement was obtained between theoretical and experimental switching profiles over a wide temperature range (25–75°C). This was achieved using the Leslie–Ericksen theory in a one-dimensional model with material viscosity coefficients obtained from an improved estimation procedure. Such accurate numerical simulations can have a large impact on further improvements of VA-LCDs (e.g., the development of temperature-compensating driving schemes).
Doping characterization of InAs∕GaAs quantum dot heterostructure by cross-sectional scanning capacitance microscopy
Authors: Zhao Z. Y. , Zhang W. M. , Yi C. , Stiff-Roberts A. D. , Rodriguez B. J. , Baddorf A. P.
Published: March 2008

In order to better understand dopant incorporation in quantum dot infrared photodetectors, the application of cross-sectional scanning capacitance microscopy (SCM) has been used to investigate carrier occupation/distribution in a multilayer InAs∕GaAs quantum dot (QD) heterostructure for different doping techniques. The doping schemes in the QD structure include direct doping (in InAs QD layers) and remote doping (in GaAs barrier layers), each with different doping concentrations. The SCM image suggests that large band bending occurs due to highly doped, remote-doping layers, thereby causing electron redistribution in direct-doping layers. The experimental result is supported by a band structure calculation using the Schrödinger–Poisson method by NEXTNANO3.
Top-gated graphene field-effect-transistors formed by decomposition of SiC
Authors: Wu Y. Q. , Ye P. D. , Capano M. A. , Xuan Y. , Sui Y. , Qi M. , Cooper J. A. , Shen T. , Pandey D. , Prakash G. , Reifenberger R.
Published: March 2008

Top-gated, few-layer graphene field-effect transistors (FETs) fabricated on thermally decomposed semi-insulating 4H-SiC substrates are demonstrated. Physical vapor deposited SiO2 is used as the gate dielectric. A two-dimensional hexagonal arrangement of carbon atoms with the correct lattice vectors, observed by high-resolution scanning tunneling microscopy, confirms the formation of multiple graphene layers on top of the SiC substrates. The observation of n-type and p-type transition further verifies Dirac Fermions’ unique transport properties in graphene layers. The measured electron and hole mobilities on these fabricated graphene FETs are as high as 5400 and 4400cm2∕Vs, respectively, which are much larger than the corresponding values from conventional SiC or silicon.
A scaling method to enhance detection of a nonlinear elastic response
Authors: Scalerandi M. , Gliozzi A. S. , Bruno C. L. E. , Masera D. , Bocca P.
Published: March 2008

The signature of nonlinearity in the elastic response of a specimen to an impingent ultrasonic wave is usually determined through Fourier analysis, which provides low amplitude signals, often below noise level. We suggest here an alternative, based on the amplitude dependence of the response of the system. Our procedure is conceptually simple and easy to implement. In addition, it keeps simultaneously into account the nonlinear signature effects on phases, amplitudes, and frequencies of the response. The sensitivity of the approach to the presence of nonlinearity is proven experimentally.
A single-layer permeation barrier for organic light-emitting displays
Authors: Mandlik Prashant , Gartside Jonathan , Han Lin , Cheng I-Chun , Wagner Sigurd , Silvernail Jeff A. , Ma Rui-Qing , Hack Michael , Brown Julie J.
Published: March 2008

Films of a hybrid material with part-SiO2 part-silicone character are deposited as environmental barriers on bottom-emitting and on transparent organic light-emitting diodes. Devices coated with this barrier have lifetimes of up to ∼7500h when stored at 65°C and 85% relative humidity, by far exceeding the industrial requirement of 1000h. The intensity of the Si–O–Si absorption at the wavenumber of 1075cm−1, the wetting angle by water, and the indentation hardness support the interpretation of a homogeneous material with the properties of a SiO2-silicone hybrid. The films remain intact over 58600cycles of bending to ∼0.2% tensile strain.
Single crystalline highly epitaxial Pt thin films on (001) SrTiO3
Authors: Xu X. M. , Liu J. , Yuan Z. , Weaver J. , Chen C. L. , Li Y. R. , Gao Hongjun , Shi N.
Published: March 2008

(001) oriented Pt thin films with excellent single crystal quality were epitaxially grown on (001) SrTiO3. The interface relationship was determined and shown to be (001)Pt∥(001)STO and [100]Pt∥[100]STO. Two unexpected “transitions” were found at 138 and 34K in the evolution of resistivity with temperature as the samples were heated up, which can probably be attributed to phase transitions of the single crystalline SrTiO3. The fact that epitaxial (001) Pt film growth is observed under oxygen plasma is believed to be a result of oxygen ashing of S-containing impurities in the Pt target.
Grain boundary disordering in binary alloys
Authors: Luo Jian , Shi Xiaomeng
Published: March 2008

This letter reports a grain boundary (GB) premelting/prewetting model based on the Miedema model and computational thermodynamics, predicting that GB disordering can start at as low as 60%–85% of the bulk solidus temperatures in selected systems. This model quantitatively explains the long-standing mystery of subsolidus activated sintering in W–Pd, W–Ni, W–Co, W–Fe and W–Cu, and it has broad applications for understanding GB-controlled transport kinetics and physical properties. Furthermore, this study demonstrates the necessity of developing GB “phase” diagrams as a tool for material design.
A facility for characterizing the steady-state and dynamic thermal performance of microelectromechanical system thermal switches
Authors: Cho J. H. , Richards C. D. , Richards R. F.
Published: March 2008

A facility to characterize microelectromechanical system (MEMS) thermal switches by measuring two pertinent figures of merit is described. The two figures of merit measured are the ratio of thermal resistance of the switch in the off and on states, Roff∕Ron, and the time required to switch from the off to the on state, τswitch. The facility consists of two pieces of equipment. A guard-heated calorimeter is used to measure heat transfer across the thermal switch under steady-state conditions. Measuring heat transfer across a thermal switch in both the off and on states then gives the thermal resistance ratio Roff∕Ron. A thin-film radial heat-flux sensor is used to measure heat transfer across the thermal switch under dynamic conditions. Measuring heat transfer across a thermal switch as the switch changes from the off to the on state gives the thermal switching time τswitch. The test facilities enable the control of the applied force on the thermal switch when the thermal switch is on, the thickness of the gas gap when the thermal switch is off, and the gas species and pressure in the thermal switch gas gap. The thermal performance of two MEMS thermal switches employing two different thermal contact materials, a polished silicon surface and an array of liquid-metal microdroplets, is characterized and compared.
Electrohydrodynamic size stratification and flow separation of giant vesicles
Authors: Lecuyer S. , Ristenpart W. D. , Vincent O. , Stone H. A.
Published: March 2008

We demonstrate an electrohydrodynamic (EHD) technique for separating giant unilamellar vesicles by size in polydisperse suspensions. An oscillatory electric field (∼30Hz) generates EHD flow around each vesicle close to an electrode. Nearby vesicles are entrained in the flow and the vesicles move toward one another. Upon aggregation, smaller vesicles are pulled underneath the larger vesicles, which ultimately lifts them off of the electrode. A brief spike in the electric field then serves to irreversibly adhere the bottom layer of smaller vesicles to the electrode, and the large vesicles are subsequently removed by flow. We demonstrate that a single application of this technique can remove more than 90% of the smallest vesicles (diameter <20μm) from a suspension of electroformed giant lipid vesicles.
Role of Mn and H in formation of cubic and hexagonal GaMnN
Authors: Lazarov V. K. , Cheung S. H. , Cui Y. , Li L. , Gajdardziska-Josifovska M.
Published: March 2008

Electron microscopy studies are carried out to determine the structure of GaMnN films grown on 6H-SiC(0001) and MgO(111) substrates by plasma-assisted molecular beam epitaxy. For the Mn∕GaN multilayer growth, cubic zinc blende GaMnN is observed in the nominal Mn∕GaN multilayer region and surface microprotrusions, indicative of high Mn mobility. In contrast, for the H-assisted growth of Mn-doped GaN, single phase hexagonal wurtzite GaMnN is obtained, but with columnar structure, indicative of reduced Mn mobility during growth.
Power law carrier dynamics in semiconductor nanocrystals at nanosecond timescales
Authors: Sher P. H. , Smith J. M. , Dalgarno P. A. , Warburton R. J. , Chen X. , Dobson P. J. , Daniels S. M. , Pickett N. L. , O’Brien P.
Published: March 2008

We report the observation of power law dynamics on nanosecond to microsecond timescales in the fluorescence decay from semiconductor nanocrystals and draw a comparison between this behavior and power law fluorescence blinking from single nanocrystals. The link is supported by comparison of blinking and lifetime data measured simultaneously from the same nanocrystal. Our results reveal that the power law coefficient changes little over the nine decades in time from 10nsto10s, in contrast with the predictions of some diffusion based models of power law behavior.