bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of freshets on the flux of groundwater nitrate through streambed sediments
Authors: Gu Chuanhui , Hornberger George M. , Herman Janet S. , Mills Aaron L.
Published: May 2008

The passage of a flood wave over sandy stream sediments can cause changes in the discharge of groundwater to the stream that range from a transient reduction in the discharge rate to a reversal of flow and temporary storage of stream water in the stream sediments. These phenomena were examined in laboratory studies with an intact core and by numerical modeling to assess the effect of both physical and biological processes on the nitrate flux from nitrate‐contaminated groundwater to a stream. The balance between the rates of groundwater flow through organic‐rich sediments and of denitrification ultimately determines the efflux of nitrate to the stream. The transient impact on nitrate loading suggested by results from the numerical model indicates that high flood stage and low‐sediment hydraulic diffusivity can result in excess nitrate loading to surface water following storm events, whereas large‐sediment hydraulic diffusivity, regardless of the size of stream stage changes, facilitates greater removal of NO3− by denitrification by allowing for a longer residence time of water in the subsurface.
Interannual temperature predictions using the CMIP3 multi‐model ensemble mean
Authors: Laepple Thomas , Jewson Stephen , Coughlin Katie
Published: May 2008

We present a simple method to make multi‐year surface temperature forecasts using the climate change simulations of the CMIP3 database prepared for the IPCC AR4 report. By calibrating the multi‐model ensemble mean with current observations, we are able to make skillful interannual forecasts of mean temperatures. The method is validated using extensive hindcast experiments and is shown to perform favorably compared to a recent forecast method based on a global circulation model with assimilated initial conditions. Five year forecasts for the global mean temperature, the Northern Hemispheric mean temperature and the summer sea surface temperatures (SSTs) in the main development region for hurricanes (MDR) are presented.
Vulnerability of east Siberia's frozen carbon stores to future warming
Authors: Khvorostyanov D. V. , Ciais P. , Krinner G. , Zimov S. A.
Published: May 2008

East Siberia’s permafrost contains about 500 GtC of frozen highly labile carbon deposits, a so‐called Yedoma. Using a permafrost carbon cycle model we analyzed mobilization of this huge carbon stock in a future warming. Conditions necessary to trigger the irreversible Yedoma thawing maintained by deep respiration and methanogenesis are studied. Once started, this process could release 2.0–2.8 GtC yr−1 during years 2300–2400 transforming 75% of initial carbon stock into CO2 and methane. The time when the fast deep‐soil decomposition starts is inversely proportional to the warming rate, while the corresponding (critical) temperature anomaly slightly increases at larger warming rates. This second‐order effect is due to the deep‐soil heat storage caused by external warming, which leads to more homogeneous soil heating when the warming is slower, and so a smaller external warming is needed to thaw the permafrost. The effect of specific microbial heat that accompanies oxic decomposition is of comparable importance to that of the warming rate on the critical temperature anomaly, while it is of minor importance on the time when deep decomposition starts.
Observational evidence on the effects of clouds and aerosols on net ecosystem exchange and evapotranspiration
Authors: Wang Kaicun , Dickinson Robert E. , Liang Shunlin
Published: May 2008

Clouds and aerosols control variations in the ratio of diffuse to total incident solar radiation (Rd/Rs) and so determine to a large extent variations in both Light‐Use Efficiency (LUE) and in the Evaporative Fraction (EF). Five years (2002–2007) of continuous ground measurements collected at twenty‐three sites in the U.S. were analyzed to quantify this effect. Our results show that LUE is 19.4% and 203% larger for patchy clouds, and thick clouds than those for clear skies while LUE is about −6% for aerosols or thin clouds than those for clear skies. EF is 15.4%, 17.9% and 23.2% larger for aerosols or thin clouds, patchy clouds, and thick clouds than those for the clear sky when Eddy Covariance (ECOR) data are used, respectively. The values are 9.0%, 11.3% and 23.3% when Energy Balance Bowen Ratio (EBBR) data are used. This is the first systematic observational study on effects of Rd/Rs on EF and further study is needed.
High-pressure synthesis of orthorhombic SrIrO3 perovskite and its positive magnetoresistance
Authors: Zhao J. G. , Yang L. X. , Yu Y. , Li F. Y. , Yu R. C. , Fang Z. , Chen L. C. , Jin C. Q.
Published: May 2008

The orthorhombic SrIrO3 perovskite was synthesized under 5GPa and 1000°C. It is paramagnetic below about 170K and transfers to an unknown magnetism under higher temperature. A band type metal to insulator transition caused by a pseudogap was observed at about 44K. Interestingly a positive magnetoresistance, i.e., resistance increased with applying magnetic field, was observed in the orthorhombic SrIrO3 perovskite below about 170K.
Equilibrium calculations of viscosity and thermal conductivity across a solid-liquid interface using boundary fluctuations
Authors: Petravic Janka , Harrowell Peter
Published: May 2008

We calculate viscosity and thermal conductivity in systems of Lennard–Jones particles consisting of coexisting solid and liquid with different interface wetting properties using the recently developed equilibrium boundary fluctuation theory. We compare the slip length and equivalent liquid length obtained from these calculations with those obtained from nonequilibrium molecular dynamics. The equilibrium and nonequilibrium calculations of the slip length and the sum of the thermal equivalent lengths are in good agreement. We conclude that for both interfacial properties, the nonequilibrium simulations were probing the linear response. The significant dependence of the intrinsic equivalence length on the interfacial temperature difference used to generate the thermal gradient is explained as a consequence of the different thermodynamic states of the two interfaces.
Interplay between bonding and magnetism in the binding of NO to Rh clusters
Authors: Ghosh Prasenjit , Pushpa Raghani , de Gironcoli Stefano , Narasimhan Shobhana
Published: May 2008

We have studied the binding of NO to small Rh clusters, containing one to five atoms, using density functional theory in both spin-polarized and non-spin-polarized forms. We find that NO bonds more strongly to Rh clusters than it does to Rh(100) or Rh(111), suggesting that Rh clusters may be good catalysts for NO reduction. However, binding to NO also quenches the magnetism of the clusters. This (local) effect results in reducing the magnitude of the NO binding energy, and also washes out the clear size-dependent trend observed in the nonmagnetic case. Our results illustrate the competition present between the tendencies to bond and to magnetize, in small clusters.
On the performance of quantum chemical methods to predict solvatochromic effects: The case of acrolein in aqueous solution
Authors: Aidas Kestutis , Møgelhøj Andreas , Nilsson Elna J. K. , Johnson Matthew S. , Mikkelsen Kurt V. , Christiansen Ove , Söderhjelm Pär , Kongsted Jacob
Published: May 2008

The performance of the Hartree–Fock method and the three density functionals B3LYP, PBE0, and CAM-B3LYP is compared to results based on the coupled cluster singles and doubles model in predictions of the solvatochromic effects on the vertical n→π* and π→π* electronic excitation energies of acrolein. All electronic structure methods employed the same solvent model, which is based on the combined quantum mechanics/molecular mechanics approach together with a dynamical averaging scheme. In addition to the predicted solvatochromic effects, we have also performed spectroscopic UV measurements of acrolein in vapor phase and aqueous solution. The gas-to-aqueous solution shift of the n→π* excitation energy is well reproduced by using all density functional methods considered. However, the B3LYP and PBE0 functionals completely fail to describe the π→π* electronic transition in solution, whereas the recent CAM-B3LYP functional performs well also in this case. The π→π* excitation energy of acrolein in water solution is found to be very dependent on intermolecular induction and nonelectrostatic interactions. The computed excitation energies of acrolein in vacuum and solution compare well to experimental data.
Linear oscillations of a compressible hemispherical bubble on a solid substrate
Authors: Shklyaev Sergey , Straube Arthur V.
Published: May 2008

The linear natural and forced oscillations of a compressible hemispherical bubble on a solid substrate are under theoretical consideration. The contact line dynamics is taken into account by application of the Hocking condition, which eventually leads to nontrivial interaction of the shape and volume oscillations. Resonant phenomena, mostly pronounced for the bubble with the fixed contact line or with the fixed contact angle, are found out. A double resonance, where independent of the Hocking parameter, an unbounded growth of the amplitude occurs, is detected. The limiting case of weakly compressible bubble is studied. The general criterion identifying whether the compressibility of a bubble can be neglected is obtained.
Nitrogen-induced intermixing of InAsN quantum dots with the GaAs matrix
Authors: Ivanova L. , Eisele H. , Lenz A. , Timm R. , Dähne M. , Schumann O. , Geelhaar L. , Riechert H.
Published: May 2008

We investigated the influence of nitrogen incorporation on the growth of InAsN∕GaAs quantum dots (QDs) using cross-sectional scanning tunneling microscopy. Nitrogen exposure during InAs growth leads to a rather strong dissolution and the formation of extended almost spherical InGaAs QDs with a very low nitrogen content. Nitrogen atoms are instead observed in the surrounding GaAs matrix, and indium atoms are even found underneath the nominal base plane of the QDs. These effects are related to a rather low solubility of nitrogen within InAs, leading to high strain between indium-rich QDs and the surrounding nitrogen-rich matrix.
Potassium induced phase transition of FePc thin films
Authors: Roth F. , König A. , Kraus R. , Knupfer M.
Published: May 2008

We have studied the structure and stoichiometry of potassium doped iron phthalocyanine (FePc) films using a combination of electron diffraction and core level excitation studies. We show that iron phthalocyanine undergoes structural phase transitions upon potassium addition, which can be described by the formation of two potassium doped phases with K2FePc and K4FePc composition.
Electron programing and hole erasing in silicon nanocrystal Flash memories with fin field-effect transistor architecture
Authors: Corso D. , Muré G. , Lombardo S. , Ciná G. , Tripiciano E. , Gerardi C. , Rimini E.
Published: May 2008

We investigated the feasibility of electron programing and hole erasing in silicon nanocrystal Flash memory cells with fin field-effect transistor architecture having ultrashort channels (90nm). Experiments show that, by choosing a proper program/erase condition, very large threshold voltage windows can be achieved, compatible with the needs of multilevel cells. These performances are coupled to excellent retention at high temperature. The obtained results evidence that hole trapping is less affected by electric field and temperature stress compared to electron trapping. Qualitative explanations for this behavior are given.
Comparison of algorithms for the calculation of molecular vibrational level densities
Authors: Hansen K.
Published: May 2008

Level densities of vibrational degrees of freedom are calculated numerically with formulas based on the inversion of the canonical vibrational partition function. The calculated level densities are compared with other approximate equations from literature and with the exact Beyer–Swinehart values, for which a simplified but equivalent version is given. All approximate equations agree at high excitation energies, but our results are vastly superior at low energies for large molecules. The results presented here are therefore of particular relevance for thermal processes of very large molecules, e.g., of biological nature, for which the exact state counting can be prohibitively slow. Furthermore, it is valid for situations where anharmonic motion significantly influences the thermal properties.
Resistivity of V2O3 thin films deposited on a-plane (110) and c-plane (001) sapphire by pulsed laser deposition
Authors: Allimi B. S. , Alpay S. P. , Xie C. K. , Wells B. O. , Budnick J. I. , Pease D. M.
Published: May 2008

Thin films of V2O3 with thickness of 215nm were grown on a- and c-plane sapphire by pulsed laser deposition with (001)V2O3∥(001)Al2O3 and (110)V2O3∥(110)Al2O3 epitaxy. The effects of the growth direction on the electrical resistivity of the films were examined. Films on c-plane sapphire displayed a metal-to-insulator transition at T=180K compared to T=160K in single-crystal V2O3. The films on a-plane sapphire, however, showed an insulator-to-insulator transition at T=186K. The variation in the phase transformation characteristics and the resistivity can be attributed to different levels of strain and commensurate changes in the film morphology.
Form-invariant Poisson brackets of hydrodynamic type with several spatial variables
Authors: Bogoyavlenskij O. , Reynolds P.
Published: May 2008

Form-invariant Poisson brackets of hydrodynamic type with several spatial variables x1,…,xp are introduced for any commuting vector fields U1,…,Um on a manifold Mn. The incompressibility equation for certain parameters of the Poisson brackets is derived. Poisson brackets connected with an arbitrary dynamical system on Mn are constructed. A gauge transform for the Poisson brackets with one spatial variable x is defined and its action onto the tensor invariants is studied. A general identity between the coefficients bkij(u) and gij(u) is found.
Line defects of M-plane GaN grown on γ-LiAlO2 by plasma-assisted molecular beam epitaxy
Authors: Lo Ikai , Hsieh Chia-Ho , Chen Yen-Liang , Pang Wen-Yuan , Hsu Yu-Chi , Chiang Jih-Chen , Chou Ming-Chi , Tsai Jenn-Kai , Schaadt D. M.
Published: May 2008

The edge and threading dislocations of M-plane GaN epilayers grown on γ-LiAlO2 have been studied by high-resolution transmission electron microscope. We found that edge dislocations were grown in [11¯00] direction while threading dislocations were generated along a1 or −a2 axes. We also observed a single stacking fault in the M-plane GaN epilayer.
Morphology and grain structure evolution during epitaxial growth of Ag films on native-oxide-covered Si surface
Authors: Hur Tae-Bong , Kim Hong Koo , Perello David , Yun Minhee , Kulovits Andreas , Wiezorek Jörg
Published: May 2008

Epitaxial nanocrystalline Ag films were grown on initially native-oxide-covered Si(001) substrates using radio-frequency magnetron sputtering. Mechanisms of grain growth and morphology evolution were investigated. An epitaxially oriented Ag layer (∼5 nm thick) formed on the oxide-desorbed Si surface during the initial growth phase. After a period of growth instability, characterized as kinetic roughening, grain growth stagnation, and increase of step-edge density, a layer of nanocrystalline Ag grains with a uniform size distribution appeared on the quasi-two-dimensional layer. This hierarchical process of film formation is attributed to the dynamic interplay between incoming energetic Ag particles and native oxide. The cyclic interaction (desorption and migration) of the oxide with the growing Ag film is found to play a crucial role in the characteristic evolution of grain growth and morphology change involving an interval of grain growth stagnation.
Terahertz wave localization at a three-dimensional ceramic fractal cavity in photonic crystals
Authors: Miyamoto Yoshinari , Kanaoka Hideaki , Kirihara Soshu
Published: May 2008

A three-dimensional microphotonic crystal with diamond structure, in which a cube cavity of the stage 2 Menger sponge fractal is embedded, was designed in order to localize effectively terahertz waves. The crystal was fabricated from alumina ceramics by a computer aided design∕computar aided manufacturing microstereolithography and sintering process. The localization frequency was in good agreement with both the simulated frequency determined by the transmission line modeling method and the calculated frequency by using the empirical equation. The simulated amplitude distribution of electric field oscillations showed that three different resonance modes exist in substructures of the sponge with each half wavelength oscillation. The wave leakage from the single sponge fractal was effectively blocked by the outer diamond structure.
A Landau mode in current-carrying carbon nanotube and effects on electrical breakdown
Authors: Matsunaga Yasushi , Kato Tomokazu , Hatori Tadatsugu
Published: May 2008

On the basis of the Landau quantization, the bound state is discussed, which includes the finite length effect, induced magnetic field, and electric field in a current-carrying nanotube. Using a slab model and evaluating the matching of the wave function in the radial direction, the authors obtained the conditions of a Landau mode in which the momentum in the axial direction is reversed in the outer side and inner side of the nanotube shell. The mode arises over a threshold electric current, influences more long tubes than short tubes, and does not contribute to the net electric current. The authors compared the theoretical results to the experimental data, estimating the minimum voltage condition, the relations between the tube length and the current for the obtained Landau mode, and the tube length and current data in the experiments. It is plausible that the Landau mode plays an important role in the eventual electrical breakdown and the thinning phenomena. The wave function broadly spreading in the outer side in the radial direction activates the air and triggers the destruction of atomic bonds. Another factor influencing the electrical breakdown phenomena was found.
Effects of thermal treatment under different atmospheres on the spectroscopic properties of nanocrystalline TiO2
Authors: Zhang Huarong , Xie Chaofei , Zhang Yanfang , Liu Guangsheng , Li Zonghui , Liu Caiyun , Ma Xingping , Zhang W. F.
Published: May 2008

The anatase nanocrystalline TiO2 samples were synthesized by a sol-gel method with a thermal treatment under air and oxygen atmospheres at 500 °C and investigated by x-ray powder diffraction, ultraviolet-visible diffuse reflectance spectra (UV-vis DRSs), Raman spectra, and photoluminescence (PL) spectra, respectively. Compared to the sample calcined in air, there were slight differences in the lattice parameter and Raman line shape for the sample calcined in oxygen. UV-vis DRSs exhibited a visible redshift of the absorption edge, which could be understood by Burstein–Moss effect. Different calcination atmospheres led the obvious variations of intensity, position, and linewidth in the PL spectra, which could be attributed to the surface oxygen defect changes.
Structure, magnetic properties, and electrical transport in layered cobaltites Sr2−xPrxCoO4
Authors: Ang R. , Sun Y. P. , Luo X. , Hao C. Y. , Zhu X. B. , Song W. H.
Published: May 2008

We present the results of systematic study of structure, magnetic properties, and electrical transport in layered cobaltites Sr2−xPrxCoO4 (0.5≤x≤1.5). The variations of Jahn–Teller distortion of CoO6 octahedron reflected by two different Co–O bond lengths indicate that all the samples are mostly accommodated in the t2g orbital states. For x<1 samples, with increasing Pr-doping level, the tolerance factor decreases and the distortion of CoO6 octahedron enhances, which result in the increased bending of Co–O–Co bond, the narrowing of the bandwidth, and the decrease of the mobility of eg electrons caused by the substitution of smaller Pr3+ ions for a larger Sr2+ ion. For x>1 samples, the contribution of carrier density should be considered besides the tolerance factor.
Effect of microwave irradiation on the emission and capture dynamics in silicon metal oxide semiconductor field effect transistors
Authors: Prati Enrico , Fanciulli Marco , Calderoni Alessandro , Ferrari Giorgio , Sampietro Marco
Published: May 2008

Microwave irradiation causes voltage fluctuations in solid state nanodevices. Such an effect is relevant in atomic electronics and nanostructures for quantum information processing, where charge or spin states are controlled by microwave fields and electrically detected. Here, the variation of the characteristic times of the capture and emission of a single electron by an interface defect in submicron metal oxide semiconductor field effect transistor is calculated and measured as a function of the microwave power. In the model, the frequency of the voltage modulation is assumed to be large if compared to the inverse of the characteristic times. The variation of the characteristic times under microwave irradiation is quantitatively predicted from the microwave frequency dependent stationary current generated by the voltage fluctuation itself. The expected values agree with the experimental measurements. The reported effect has to be carefully considered in electrically detected single electron spin resonance experiments. In such experiments, a spurious change of the power of the microwave coupled to the device could be confused with the single spin resonance.
Quantitative broadband chemical sensing in air-suspended solid-core fibers
Authors: Euser T. G. , Chen J. S. Y. , Scharrer M. , Russell P. St. J. , Farrer N. J. , Sadler P. J.
Published: May 2008

We demonstrate a quantitative broadband fiber sensor based on evanescent-field sensing in the cladding holes of an air-suspended solid-core photonic crystal fiber. We discuss the fabrication process, together with the structural and optical characterization of a range of different fibers. Measured mode profiles are in good agreement with finite element method calculations made without free parameters. The fraction of the light in the hollow cladding can be tuned via the core diameter of the fiber. Dispersion measurements are in excellent agreement with theory and demonstrate tuning of the zero dispersion wavelength via the core diameter. Optimum design parameters for absorption sensors are discussed using a general parameter diagram. From our analysis, we estimate that a sensitivity increase of three orders of magnitude is feasible compared to standard cuvette measurements. Our study applies to both liquid and gas fiber sensors. We demonstrate the applicability of our results to liquid chemical sensing by measuring the broad absorption peak of an aqueous NiCl2 solution. We find excellent agreement with the reference spectrum measured in a standard cuvette, even though the sample volume has decreased by three orders of magnitude. Our results demonstrate that air-suspended solid-core photonic crystal fibers can be used in quantitative broadband chemical-sensing measurements.
Defect reduction of GaAs/Si epitaxy by aspect ratio trapping
Authors: Li J. Z. , Bai J. , Major C. , Carroll M. , Lochtefeld A. , Shellenbarger Z.
Published: May 2008

We report on the metallorganic chemical vapor deposition growth of GaAs on patterned Si (001) substrates, which utilizes the aspect ratio trapping method. It was found that when growing GaAs above the SiO2 trenched region, coalescence-induced threading dislocations and stacking faults originated on top of the GaAs/SiO2 interfaces. These defects were found to be indirectly related to the initial defect-trapping process during trenched GaAs growth. Causes of coalescence defect formation and its reduction were experimentally investigated by employing a two-step growth optimization scheme. Improvement of material quality has been characterized by cross-sectional and plan-view transmission electron microscopy and x-ray diffraction.
The effect of Fe atoms on the adsorption of a W atom on W(100) surface
Authors: Houze J. , Kim Sungho , Kim Seong-Gon , Park Seong-Jin , German Randall M. , Horstemeyer M. F.
Published: May 2008

We report a first-principles calculation that models the effect of iron (Fe) atoms on the adsorption of a tungsten (W) atom on W(100) surfaces. The adsorption of a W atom on a clean W(100) surface is compared to that of a W atom on a W(100) surface covered with a monolayer of Fe atoms. The total energy of the system is computed as the function of the height of the W adatom. Our result shows that the W atom first adsorbs on top of the Fe monolayer. Then, the W atom can replace one of the Fe atoms through a path with an energy barrier of 0.99 eV and reduce its energy further. This intermediate site makes the adsorption (and desorption) of W atoms a two-step process in the presence of Fe atoms and lowers the overall adsorption energy by nearly 2.4 eV. This effect results in a more efficient adsorption and desorption of W atoms in the presence of Fe atoms. Our result provides a fundamental mechanism that can explain the activated sintering of tungsten by Fe atoms.
Absorption recovery time reduction in InGaN/GaN quantum well saturable absorbers
Authors: Lin F. , Xiang N. , Chua S. J. , Irshad A. , Roither S. , Pugzlys A. , Baltuska A. , Chen P. , Chow S. Y.
Published: May 2008

In this work, a simple method to reduce the absorption recovery time of the InGaN/GaN quantum well saturable absorber was demonstrated. The recovery time of the saturable absorber grown by metal organic chemical vapor deposition was effectively controlled by controlling the crystal quality. Transmission electron microscopy results showed that, for saturable absorbers with reduced GaN buffer thicknesses, increased dislocations were introduced into the quantum well regions. The degraded crystal quality would therefore cause an increased density of nonradiative recombination centers, which were responsible for the fast recovery of the absorption. In addition, with the as-grown thin GaN buffers, the severe interference-induced reflectivity fluctuations were successfully suppressed.
Device physics and design of germanium tunneling field-effect transistor with source and drain engineering for low power and high performance applications
Authors: Toh Eng-Huat , Wang Grace Huiqi , Samudra Ganesh , Yeo Yee-Chia
Published: May 2008

The device physics and electrical characteristics of the germanium (Ge) tunneling field-effect transistor (TFET) are investigated for high performance and low power logic applications using two dimensional device simulation. Due to the high band-to-band tunneling rate of Ge as compared to Si, the Ge TFET suffers from excessive off-state leakage current Ioff despite its higher on-state current Ion. It is shown for the first time that the high off-state leakage due to the drain-side tunneling in the Ge TFET can be effectively suppressed by controlling the drain doping concentration. A lower drain doping concentration reduces the electric field and increases the tunneling barrier width in the drain side, giving a significantly reduced off-state leakage. To increase Ion with a steeper subthreshold swing S, source doping concentration is increased to reduce the bandgap and narrow the tunneling width. Device design and physics detailing the impact of drain and source engineering on the performance of Ge TFET are discussed.
Spacerless metal-manganite pseudo-spin-valve structure
Authors: Cheng W. F. , Ruotolo A. , Chan Y. K. , Wong K. H. , Leung C. W.
Published: May 2008

We fabricated pseudo-spin-valves by using La0.7Sr0.3MnO3 and Co33Fe67 as ferromagnetic electrodes. A natural interface layer present between metal and manganite layers eliminated the need of depositing any nonmagnetic spacers. The magnetic layers were decoupled from each other, and the structure exhibited a positive magnetoresistive behavior. Direct comparison between magnetic and transport measurements concluded the occurrence of giant magnetoresistive effect in such a spacerless metal-oxide pseudo-spin-valve structure. The results have implications for a simple route to fabricate oxide-based spintronic devices.
Current-driven output magnetization switching in a magnetic nanowire with a three-terminal Y junction
Authors: Nam Chunghee , Jang Youngman , Lee Ki-Su , Cho B. K.
Published: May 2008

Electrically induced magnetization switching was investigated in a three-terminal magnetic Y junction. Two input wires acted as domain wall (DW) injection sources, one of which was used for electrical gating. This configuration made it possible to detrap a DW that was pinned at the Y junction. The magnetization of the output wire was controlled by current-driven DW motion that was induced by the isolated-gating input wire. The active gating performance of the current-driven DW motion is more effective than that induced by a magnetic field.
Effects of hydrogen implantation temperature on InP surface blistering
Authors: Chen Peng , Di Zengfeng , Nastasi M. , Bruno Elena , Grimaldi Maria Grazia , Theodore N. David , Lau S. S.
Published: May 2008

We have investigated the effects of hydrogen implantation temperature on the ion-cut process of InP by examining the correlation between surface blistering and the ion induced damage, hydrogen distribution, and strain. Using Rutherford backscattering spectrometry, elastic recoil detection, and x-ray diffraction, it was found that both the point defects induced by the hydrogen implantation and the in-plane compressive stress were necessary for hydrogen trapping and H-platelet nucleation and growth. The control of implantation temperature is crucial for creating sufficient defects and strain to induce surface blistering or layer exfoliation.
Comment on “On the tensile strength distribution of multiwalled carbon nanotubes” [Appl. Phys. Lett. 87, 203106 (2005)]
Authors: Lu Chunsheng
Published: May 2008

In a recent letter, Barber, Andrews, Schadler, and Wagner, Appl. Phys. Lett. 87, 203106 (2005). indicated that Weibull–Poisson statistics could accurately model the nanotube tensile strength data, and then concluded that the apparent strengthening mechanism in a multiwalled carbon nanotube (MWCNT) grown by chemical vapor deposition (CVD) is most likely caused by an enhanced interaction between the walls of the nanotube. In this comment, we show that their conclusion seems to be inconsistent with the assumption introduced in the data analysis by using a two-parameter Weibull distribution. Further statistical analysis provides a new explanation on the scattered strengths of MWCNTs. The effectiveness of Weibull–Poisson statistics at nanoscales is also discussed.
High-temperature quenching of electrical resistance in graphene interconnects
Authors: Shao Q. , Liu G. , Teweldebrhan D. , Balandin A. A.
Published: May 2008

The authors reported on the experimental investigation of the high-temperature electrical resistance of graphene. The test structures were fabricated by using the focused ion beam from the single and bilayer graphene produced by mechanical exfoliation. It was found that as temperature increases from 300to500K, the resistance of the single, and bilayer graphene interconnects drops down by 30% and 70%, respectively. The quenching and temperature dependence of the resistance were explained by the thermal generation of the electron-hole pairs and carrier scattering by acoustic phonons. The obtained results are important for the proposed graphene interconnect applications in integrated circuits.
Cotunneling assisted sequential tunneling in multilevel quantum dots
Authors: Aghassi Jasmin , Hettler Matthias H. , Schön Gerd
Published: May 2008

We investigate the conductance and zero-frequency shot noise of interacting, multilevel quantum dots coupled to leads. We observe that cotunneling assisted sequential tunneling (CAST) processes play a dominant role in the transition region from Coulomb blockade to sequential tunneling. We analyze for intermediate coupling strength the dependence of the conductance due to CAST processes on temperature, coupling constant, and gate voltage. Remarkably, the width of the CAST transport feature scales only with temperature, but not with the coupling constant. While the onset of inelastic cotunneling is associated with a super-Poissonian noise, the noise is even stronger above the threshold for CAST processes.
Tuning the field in a microwave resonator faster than the photon lifetime
Authors: Sandberg M. , Wilson C. M. , Persson F. , Bauch T. , Johansson G. , Shumeiko V. , Duty T. , Delsing P.
Published: May 2008

We have fabricated and characterized tunable superconducting transmission line resonators. To change the resonance frequency, we modify the boundary condition at one end of the resonator through the tunable Josephson inductance of a superconducting quantum interference device. We demonstrate a large tuning range (several hundred megahertz), high quality factors (104), and that we can change the frequency of a few-photon field on a time scale orders of magnitude faster than the photon lifetime of the resonator. This demonstration has implications in a variety of applications.
Built-in electric field and large Stokes shift in near-lattice-matched GaN∕AlInN quantum wells
Authors: Franssen G. , Suski T. , Kryśko M. , Khachapuridze A. , Kudrawiec R. , Misiewicz J. , Kamińska A. , Feltin E. , Grandjean N.
Published: May 2008

Near-lattice-matched GaN∕AlInN quantum wells are investigated by means of contactless electroreflectance (CER) and temperature-dependent photoluminescence (PL). Large Stokes shifts, up to 400meV, between PL peak energies and CER resonances are identified. This Stokes shift is attributed to large potential profile fluctuations (PPFs) in the AlInN barriers. Further evidence for such PPFs and for the additional influence of QW width fluctuations is provided by temperature-dependent PL measurements, demonstrating large PL halfwidths and clear “S-shape” behavior. The influence of a large Stokes shift on the correct determination of the value of the built-in electric field is discussed, and it is shown that PL measurements may lead to a significant overestimation of the built-in electric field in GaN∕AlInN QWs.
Molecular-beam epitaxial growth of III–V semiconductors on Ge∕Si for metal-oxide-semiconductor device fabrication
Authors: Choi Donghun , Kim Eunji , McIntyre Paul C. , Harris James S.
Published: May 2008

We describe the fabrication of III–V metal-oxide-semiconductor (MOS) devices on Ge∕Si virtual substrates using molecular-beam epitaxy. Migration-enhanced epitaxy and low temperature normal GaAs growth produced a sufficiently smooth surface to deposit gate oxides. A 300nm thick GaAs buffer layer was grown, followed by a 10nm growth of In0.2Ga0.8As high mobility channel layer. An 8.5nm thick Al2O3 layer was deposited ex situ by atomic-layer deposition. Capacitance-voltage (C-V) characteristics show the unpinning of Fermi level. This work suggests this materials combination as a promising candidate for the design of advanced, nonclassical complementary MOS and optoelectronic devices on Si substrates.
Optical fiber sensor for small angle and infinite angle detection
Authors: Lü Tao , Lang Xianli , Han Yanling
Published: May 2008

An optical fiber angle sensor that consists of a cam, linear displacement attenuators, and a sensitive Fabry–Pérot cavity (FPC), is demonstrated to simultaneously measure small angle and infinite angle with high resolution. When the cam is driven to rotate by a fixed rotary shaft, a linear displacement transformed from an angle will be further attenuated by linear displacement attenuators and will subsequently modulate the FPC, which causes the reflected interference intensity of FPC to vary. By using the method of interferometric fringe counting, we can measure an infinite angle accurately and continuously. Moreover, a small angle measurement can be performed in a locally linear region. Experimental results show that two resolutions of 0.5 and 1.5s in the angle range of 0.1944° and 3.5496° are achieved, respectively.
Impact of thermal annealing on deep-level defects in strained-Si∕SiGe heterostructure
Authors: Zhang Renhua , Rozgonyi George A. , Yakimov Eugene , Yarykin Nikolai , Seacrist Mike
Published: May 2008

Si ∕ Si 1 − x Ge x ∕ Si heterostructures consisting of relaxed SiGe layers of graded and constant (x=0.2) composition with a strained-Si layer on top have been studied by the capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS), and electron-beam induced current (EBIC) techniques. Analysis of the C-V and EBIC data shows that electrically active defects are introduced during growth into both the graded and constant-composition SiGe layers in a high concentration (∼1016cm−3). The defects are attributed to dislocation trails, i.e., the quasi-two-dimensional extended defects formed behind gliding threading dislocations. Electrical activity of the dislocation trails is reduced following the annealing at 800°C. The DLTS measurements reveal a much lower density of deep-level defects which are mainly located in the graded SiGe layer. The 800°C annealing also gives rise to an additional DLTS peak. The deep-level centers corresponding to this peak are located close to the strained-Si∕SiGe interface and can be attributed to partial relaxation of the strained-Si layer.
Stimulated Brillouin scattering pulse compression to 175ps in a fused quartz at 1064nm
Authors: Marcus Gilad , Pearl Shaul , Pasmanik Guerman
Published: May 2008

Stimulated Brillouin scattering pulse compression of a 2.5ns laser into a 175ps pulse using a fused quartz is demonstrated without optical damage. The synchronization and the time jitter between the initial and the compressed pulses were measured (σ<80ps) and analyzed numerically.
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drive voltage GaAs∕AlGaAs substrate removed Mach–Zehnder intensity modulators
Authors: Shin JaeHyuk , Chang Yu-Chia , Dagli Nadir
Published: May 2008

Push-pull driven Mach–Zehnder intensity modulators with a record low drive voltage of 0.3V were realized in substrate removed very compact GaAs∕AlGaAs optical waveguides at 1.55μm. The modulator electrode is 7mm long, corresponding to a drive voltage length product of 0.21Vcm. The modulation is due to linear electro-optic and carrier depletion effects and has a high speed potential. The propagation loss was 8dB∕cm, making moderately long devices possible.
Cubic metallic phase of aluminum hydride showing improved hydrogen desorption
Authors: Scheicher R. H. , Kim D. Y. , Lebègue S. , Arnaud B. , Alouani M. , Ahuja R.
Published: May 2008

We report on our results calculated from density functional theory and GW of the dehydrogenation properties in a cubic phase of AlH3. The metallic nature of the electronic structure entails a more favorable hydrogen removal energy which is lowered by 75% compared to the insulating hexagonal phase. This remarkable reduction in the Al–H bond strength bears important consequences for feasible applications of AlH3 as an on-board hydrogen storage material for mobile applications. We suggest that the cubic phase could be prepared and stabilized experimentally at ambient pressure by off-board quenching.
Systematic investigation of InAs∕InP quantum-dash based lasers under external optical feedback
Authors: Azouigui S. , Dagens B. , Lelarge F. , Accard A. , Make D. , Le Gouezigou O. , Merghem K. , Martinez A. , Zou Q. , Ramdane A.
Published: May 2008

The tolerance to optical feedback of InAs∕InP quantum dash-based lasers is reported for several structures exhibiting differing values of the linewidth enhancement factor and damping factor. An analysis of the onsets of coherence collapse is carried out based on the experimental dynamic parameters extracted for each structure. It is shown that the relevant significant parameter to explain the optical feedback tolerance for this low dimensional material system is the differential gain.
Perpendicular critical-state susceptibility of square superconducting films
Authors: Chen D.-X. , Navau C. , Del-Valle N. , Sanchez A.
Published: May 2008

In order to better study the electromagnetic properties of superconducting films, the perpendicular critical-state ac susceptibility χ=χ′−jχ″ of a square superconducting film is numerically calculated using a magnetic energy minimization procedure as a function of the field amplitude Hm. The emphasis is put on the calculation accuracy of the low-Hm limit χ0 and the Hm at χ″=χm″. It is shown that after having accurate χ0, χ(Hm) of the square film can be accurately scaled from the analytical χ(Hm) of a thin disk.
Cooper pair wavefunction approach to the Josephson effect
Authors: Kim Yong-Jihn
Published: May 2008

We introduce an approach to the Josephson effect in the superconductor-insulator-superconductor (SIS) tunnel junctions. The Josephson coupling energy is calculated from the overlap of real space Cooper pair wavefunctions in two superconductors through an insulating barrier. It is shown that the Josephson tunneling is limited by the size of the Cooper pair and its shrinking during the tunneling. Therefore, the Josephson coupling energy and the critical current become extremely small in high Tc superconductors, including MgB2. This shrinking also causes the observed direct current (dc) supercurrent in low Tc superconductors, such as Nb, Pb, and Sn, to fall off much faster than 1∕Rn for tunneling resistance Rn above a few ohms. Consequently, there is a material-dependent threshold resistance, above which the supercurrent decreases much faster with increasing resistance. Spectacular confirmation is provided by the MgB2 break and tunnel junctions, where only small gap shows the supercurrents, while the big gap does not. The impurity-induced shrinking is also shown to limit the critical current. Furthermore, the (weak) temperature dependence of the Cooper pair size is found to contribute to the temperature dependence of the dc supercurrent. This understanding may lead to the discovery of better materials for SIS junctions other than Nb and the optimum miniaturization of the SIS junctions for the petaflops superconducting supercomputers.
Uniform resistive switching with a thin reactive metal interface layer in metal-La0.7Ca0.3MnO3-metal heterostructures
Authors: Hasan Musarrat , Dong Rui , Choi H. J. , Lee D. S. , Seong D.-J. , Pyun M. B. , Hwang Hyunsang
Published: May 2008

A thin samarium (Sm) metal layer was introduced to improve the resistive hysteresis and switching uniformity. Sm reacts with the La0.7Ca0.3MnO3 and forms a thin interface oxide layer, which is responsible for the switching. The switching occurs without any forming process. Compared with conventional resistive memory device based on localized filament formation, Sm∕La0.7Ca0.3MnO3 devices show area-dependent resistance which indicates uniform resistive switching. Under a positive bias, electromigration of oxygen ions (O2−) forms thicker oxide (SmOx), which dissociates under a negative bias, causes high and low resistance states, respectively. Estimated data retention of more than 10yr was observed at 85°C.
Concentration dependence of self-interstitial and boron diffusion in silicon
Authors: Windl Wolfgang
Published: May 2008

We show that recent experimental data and ab initio calculations agree on the charge state as a function of the Fermi energy of the dominant species for diffusion of self-interstitials (+, +, and 0) and boron atoms (+) in silicon. By mapping the experimental data onto the activation energy versus Fermi-level representation commonly used to display ab initio results, we can show that the experimental results are consistent with each other. While theoretical values for the boron activation energy as a function of the Fermi level agree well with experiment, values for self-interstitials are low, despite using total-energy corrections.
Famous Faces as Icons. The Illusion of Being an Expert in the Recognition of Famous Faces
Authors: Carbon Claus-Christian
Published: May 2008

It is a common belief that we are experts in the processing of famous faces. Although our ability to quickly and accurately recognise pictures of famous faces is quite impressive, we might not really process famous faces as faces per se, but as ‘icons’ or famous still pictures of famous faces. This assumption was tested in two parallel experiments employing a recognition task on famous, but personally unfamiliar, and on personally familiar faces. Both tests included (a) original, ‘iconic’ pictures, (b) slightly modified versions of familiar pictures, and (c) rather unfamiliar pictures of familiar persons. Participants ( n = 70 + 70) indeed recognised original pictures of famous and personally familiar people very accurately, while performing poorly in recognising slightly modified, as well as unfamiliar versions of famous, but not personally familiar persons. These results indicate that the successful processing of famous faces may depend on icons imbued in society but not on the face as such.
University Botany in Colonial Victoria: Frederick McCoy's Botanical Classes and Collections at the University of Melbourne
Authors: Gillbank Linden
Published: May 2008

Botany was part of the broad intellectual territory of one of the University of Melbourne's four foundation chairs. From his appointment in 1854 until his death in 1899, Frederick McCoy was the Professor of Natural Science and, for most of that time, also honorary Director of the Colony of Victoria's National Museum. McCoy gained ideas about botany and botanic gardens and museums while studying and working at the University of Cambridge, where he attended Professor John Stevens Henslow's botany lectures in 1847. With help from Henslow and Victoria's Government Botanist, Ferdinand Mueller, McCoy acquired botanical collections and developed a class (system) garden at the University of Melbourne, where he taught botany to arts and medical students from 1863 until the establishment of the science degree and arrival of the Professor of Biology in 1887 left him only a rarely-taken botanical subject.
Testing island biosecurity systems for invasive rats
Authors: Russell James C. , Beaven Brent M. , MacKay Jamie W. B. , Towns David R. , Clout Mick N.
Published: May 2008

Rats continue to invade rat-free islands around the world, and it remains difficult to successfully intercept them before they establish populations. Successful biosecurity methods should intercept rats rapidly, before they can establish a population. Current island biosecurity practice employs techniques used for high-density rat eradication, assuming that they will be equally effective on low-density invaders. However, such approaches are often untested. Adult male Norway rats (Rattus norvegicus) were individually released onto forested rat-free islands in New Zealand to test methods of detecting and eliminating a single invader. Only half the rats released were caught within a two-week timeframe, although the mean time to interception was just under 14 days. Permanent island biosecurity surveillance systems performed better than contingency responses. Success rates were higher on islands where complete coverage could be obtained, although surveillance systems using multiple devices eventually detected most invading rats. For some rats a change of methods was necessary. Single invading rats left a rat-free island despite the presence of excessive natural food resources. With surveillance systems comprising an array of tested island biosecurity devices, and where necessary a contingency response using alternative methods, it should be possible to maintain islands as rat-free even when they have a high reinvasion rate.