bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric and oceanic excitation of decadal‐scale Earth orientation variations
Authors: Gross Richard S. , Fukumori Ichiro , Menemenlis Dimitris
Published: September 2005

The contribution of atmospheric wind and surface pressure and oceanic current and bottom pressure variations during 1949–2002 to exciting changes in the Earth's orientation on decadal timescales is investigated using an atmospheric angular momentum series computed from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis project and an oceanic angular momentum series computed from a near‐global ocean model that was forced by surface fluxes from the NCEP/NCAR reanalysis project. Not surprisingly, since decadal‐scale variations in the length of day are caused mainly by interactions between the mantle and core, the effect of the atmosphere and oceans is found to be only about 14% of that observed. More surprisingly, it is found that the effect of atmospheric and oceanic processes on decadal‐scale changes in polar motion is also only about 20% (xcomponent) and 38% (ycomponent) of that observed. Therefore redistribution of mass within the atmosphere and oceans does not appear to be the main cause of the Markowitz wobble. It is also found that on timescales between 10 days and 4 years the atmospheric and oceanic angular momentum series used here have very little skill in explaining Earth orientation variations before the mid to late 1970s. This is attributed to errors in both the Earth orientation observations prior to 1976 when measurements from the accurate space‐geodetic techniques became available and to errors in the modeled atmospheric fields prior to 1979 when the satellite era of global weather observing systems began.
Wetland seasonal dynamics and interannual variability over northern high latitudes, derived from microwave satellite data
Authors: Mialon A. , Royer A. , Fily M.
Published: September 2005

A new accurate determination of the spatial and temporal variations of northern wetland area extent, during the snow‐free period, is retrieved from the 19‐ and 37‐GHz passive microwave Special Sensor Microwave/Imager (SSM/I) brightness temperature database. The total fraction of water surface (FWS) area, corresponding to small lakes or reservoirs (area < 25 × 25 km2), inundated surfaces and natural wetland areas, computed on a weekly basis and averaged over the 1988–2001 period, gives a maximum summer extent of 10.10 ± 0.21 × 105 km2 for Canada and Alaska and 12.7 ± 0.35 × 105 km2 for Eurasia, above 50°N. The mean seasonal dynamics of wetland and inundated surfaces shows a maximum area extent during the months of July‐August‐September over North America (48°N–68°N) and between June and September over northern Eurasia. The interannual variations of the yearly total FWS area since 1988 show a slight increase (8% ± 3%) in Canada‐Alaska, mainly due to a decrease in the snow cover extent. The FWS interannual variability in the Ob River basin, which is well explained by the water discharge variations, shows an increase of 8.5% ± 1.5% between 1988 and 2001. The microwave‐derived FWS estimate and its dynamics present an interesting potential for studying the climate‐driven variability of wetlands and inundated areas.
Coupled thermal oscillations in explosive activity at different craters of Stromboli volcano
Authors: Ripepe Maurizio , Harris Andrew J. L. , Marchetti Emanuele
Published: September 2005

Thermal infrared thermometers deployed ∼250 m from Stromboli's active craters can detect thermal emissions during strombolian explosions. Explosions appear as spikes in thermal time series, with variations in the mass erupted during each event revealed by pulses in the time series. During May 2001, Stromboli's NE and SW craters showed consistently different thermal signatures. SW crater events were characterized by long lasting (>10 s), higher amplitude thermal signals with significant fluctuations, whereas the NE crater was characterized by short (<5 s), impulsive, lower amplitude signatures. The two craters showed well‐correlated variations in thermal amplitude evolving over periods of several hours and providing strong evidence for linkage of the craters to a common feeding system affected by cyclic processes that drive steady variations in the style of emission.
Aerosol anthropogenic component estimated from satellite data
Authors: Kaufman Y. J. , Boucher O. , Tanré D. , Chin M. , Remer L. A. , Takemura T.
Published: September 2005

Satellite instruments do not measure the aerosol chemical composition needed to discriminate anthropogenic from natural aerosol components. However the ability of new satellite instruments to distinguish fine (submicron) from coarse (supermicron) aerosols over the oceans, serves as a signature of the anthropogenic component and can be used to estimate the fraction of anthropogenic aerosols with an uncertainty of ±30%. Application to two years of global MODIS data shows that 21 ± 7% of the aerosol optical thickness over the oceans has an anthropogenic origin. We found that three chemical transport models, used for global estimates of the aerosol forcing of climate, calculate a global average anthropogenic optical thickness over the ocean between 0.030 and 0.036, in line with the present MODIS assessment of 0.033. This increases our confidence in model assessments of the aerosol direct forcing of climate. The MODIS estimated aerosol forcing over cloud free oceans is therefore −1.4 ± 0.4 W/m2.
Storm‐time plasma signatures observed by IMAGE/MENA and comparison with a global physics‐based model
Authors: Denton M. H. , Jordanova V. K. , Henderson M. G. , Skoug R. M. , Thomsen M. F. , Pollock C. J. , Zaharia S. , Funsten H. O.
Published: September 2005

We present energetic neutral atom (ENA) fluxes measured by the medium energy neutral atom (MENA) imager onboard the IMAGE satellite for the geomagnetic storm of 21 October 2001 at energies of 6 and 12 keV. The fluxes indicate strong low altitude emissions close to the Earth and a nightside peak close to local midnight. The fluxes are compared with theoretical ENA fluxes calculated using the ring current‐atmosphere interaction model (RAM). We find good quantitative agreement between MENA data and RAM results, both of which indicate a peak in ENA emissions on the nightside, close to local midnight which varies in radial location between ∼2 and ∼5 Re during the period of study. We demonstrate the validity of comparing RAM results with MENA data and pave the way for further study of plasma sheet entry to the inner magnetosphere during storm‐times.
Modeling seismically induced deformation and fluid flow in the Nankai subduction zone
Authors: Ge S. , Screaton E.
Published: September 2005

Fluid pressure changes induced by seismic strains in the Nankai subduction zone were investigated through numerical modeling. Seismic strains resulting from dislocations along fault surfaces were coupled to pore pressure generation, and subsequent transient fluid flow was simulated. This study is distinct from previous efforts that modeled homogeneous systems. Effects of variable mechanical and hydrologic properties were investigated by assigning different mechanical and hydrological properties to marine sediments, the decollement zone, and the upper oceanic crust. Model sensitivity studies suggest that for a reasonable range of parameter scenarios, transient pressure head signals caused by discrete dislocations of a few meters in the updip region of the seismogenic zone can be observed over large areas of the margin from within shallow depths of the sediment wedge to the oceanic crust below the decollement.
Differential eddy diffusion of biogeochemical tracers
Authors: Pasquero C.
Published: September 2005

The marine ecosystem dynamics in the subtropical regions is controlled by the availability of nutrients. Their supply depends on lateral transport from higher latitudes, which is affected by the characteristics of the oceanic mesoscale turbulence. In many cases turbulent transport is parameterized in terms of eddy diffusion. We here test the validity of this approach in a mesoscale turbulence model coupled to a simple ecosystem model. We show that the parameterization can be profitably used, provided that an effective eddy diffusion coefficient that depends on the reaction time scale of the transported tracers is used. If the diffusion coefficient valid for conservative tracers is used to express diffusion of nutrients and plankton, turbulent transport and biological productivity can be significantly overestimated.
Geotail observations of signatures in the near‐Earth magnetotail for the extremely intense substorms of the 30 October 2003 storm
Authors: Miyashita Y. , Miyoshi Y. , Matsumoto Y. , Ieda A. , Kamide Y. , Nosé M. , Machida S. , Hayakawa H. , McEntire R. W. , Christon S. P. , Evans D. S. , Troshichev O. A.
Published: September 2005

Two coronal mass ejections associated with the X17 and X10 solar flares reached the Earth's environment at very high speeds on 29 and 30 October 2003, respectively, causing very intense geomagnetic storms (Dst ∼ −400 nT). The present study focused on the main phase of the 30 October storm during which the Geotail spacecraft was within the near‐Earth magnetotail at X ∼ −8 RE. A number of extremely intense substorms occurred during this period. In one of them, the intensity of the westward auroral electrojet exceeded 3000 nT, which was one of the largest magnitudes ever observed. The energetic particle observations from the low‐altitude, polar‐orbiting NOAA satellites indicate that the auroral oval shifted equatorward to magnetic latitudes much lower than usual, as low as 50°. Throughout the interval, the magnetic field in the near‐Earth magnetotail, and possibly the plasma density, was much larger than usual, indicating a considerable degree of energy accumulation in the lobe region and compression of the plasma sheet and very intense cross‐tail currents. The dense plasma may be responsible for the intense auroral electrojet and the intense ring current. Very large, rapid dipolarizations occurred in relation to the intense substorms. High‐energy particle fluxes were an order of magnitude higher than usual, and their increases took place immediately after the dipolarizations. Fast tailward flows with large southward magnetic fields as well as fluxes of energetic heavy ions (oxygen) were also observed, suggesting that the magnetic reconnection took place in the near‐Earth magnetotail, associated with the very intense substorms. This location is much closer to the Earth than usual, probably as close to the Earth as ever reported. These magnetotail and auroral observations as well as other results reported previously suggest that the entire magnetosphere was considerably distorted during the storm.
Calicivirus translation initiation requires an interaction between VPg and eIF4E
Authors: Goodfellow Ian , Chaudhry Yasmin , Gioldasi Ioanna , Gerondopoulos Andreas , Natoni Alessandro , Labrie Louisette , Laliberté Jean‐François , Roberts Lisa
Published: September 2005

Unlike other positive‐stranded RNA viruses that use either a 5′‐cap structure or an internal ribosome entry site to direct translation of their messenger RNA, calicivirus translation is dependent on the presence of a protein covalently linked to the 5′ end of the viral genome (VPg). We have shown a direct interaction of the calicivirus VPg with the cap‐binding protein eIF4E. This interaction is required for calicivirus mRNA translation, as sequestration of eIF4E by 4E‐BP1 inhibits translation. Functional analysis has shown that VPg does not interfere with the interaction between eIF4E and the cap structure or 4E‐BP1, suggesting that VPg binds to eIF4E at a different site from both cap and 4E‐BP1. This work lends support to the idea that calicivirus VPg acts as a novel ‘cap substitute’ during initiation of translation on virus mRNA.
Mechanism of carrier transport across the junction of narrow band-gap planar n+p HgCdTe photodiodes grown by liquid-phase epitaxy
Authors: Zemel A. , Lukomsky I. , Weiss E.
Published: September 2005

The dark current of n+p Hg1−xCdxTe (x∼0.22) photodiodes fabricated on layers grown by liquid-phase epitaxy was studied systematically as a function of applied voltage (reverse and forward), temperature, and junction dimensions. The carrier transport mechanisms in different ranges of bias voltage and temperature have been identified and interpreted using the conventional models for carrier transport mechanisms in p-n junction devices. It is found that the forward current is dominated by a combination of bulk- and surface-related tunneling currents. In large-area diodes bulk tunneling current dominates the diode current and in small-area diodes surface tunneling dominates the diode forward current. Most probably, the tunneling mechanism across the n+p junction is via energy levels located within the diode depletion region. Modification of the existing theoretical model for forward-bias tunneling in p-n junction devices is needed in order to account for the experimental findings. Above 90K, the reverse current is found to be dominated by diffusion carrier transport mechanism. Below 90K, band-to-band reverse tunneling currents become dominant. No clear evidence for generation-recombination currents was found over the entire bias voltage and temperature range measured. The results of the present work demonstrate that the measurement of the temperature dependence of the zero-bias dynamic resistance is insufficient for determining the mechanism of carrier transport across the Hg1−xCdxTe junction and a detailed measurement of the current-voltage characteristics at various temperatures should be carried out.
High resolution electronic spectra of 7-azaindole and its Ar atom van der Waals complex
Authors: Kang Cheolhwa , Yi John T. , Pratt David W.
Published: September 2005

Rotationally resolved fluorescence excitation spectra of the S1←S0 origin band of 7-azaindole [1H-pyrrolo(2,3-b)pyridine] and its argon atom van der Waals complex have been recorded and assigned. The derived rotational constants give information about the geometries of the two molecules in both electronic states. The equilibrium position of the argon atom in the azaindole complex is considerably different from its position in the corresponding indole complex. Furthermore, the argon atom moves when the UV photon is absorbed. There are significant differences in the intermolecular potential energy surfaces in the two electronic states. A large, vibration-state-dependent rotation of the S1←S0 electronic transition moment vector of 7-azaindole relative to that of indole suggests that these differences have their origin in S1∕S2 electronic state mixing in the isolated molecule, a mixing that is enhanced by nitrogen substitution in the six-membered ring.
Diffusion in interstitial compounds with thermal and stoichiometric defects
Authors: Hillert Mats , Höglund Lars , Ågren John
Published: September 2005

The ordinary flux equation for diffusion, which considers the composition gradient as the driving force, is seldom of much use in studying closely stoichiometric phases. Depending on the defect structure it would instead be profitable to use an appropriate function of the activity. Such functions will now be derived and it will be shown how the operating defect mechanism of diffusion can be identified from information on the variation of the activity inside a phase during diffusion. However, it is usually very difficult to measure the activity profile inside a phase. It will be shown how it can be obtained by combining results from several experiments. The method will be used to analyze experimental information on the formation of surface layers of Fe4N and Fe3C.
Numerical study on microdischarges in plasma display panels with arbitrary cell geometry
Authors: Kawano Satoyuki , Misaka Takashi
Published: September 2005

In this study, a plasma display panel (PDP) cell is modeled in a two-dimensional cross-sectional region and plasma discharge characteristics are analyzed by numerical simulations based on the finite difference method developed here. An orthogonal curvilinear coordinate system is introduced to apply to the arbitrary PDP cell geometry for systematic computations. Wall voltage transfer curves derived through experiments and computation are compared in detail. They show good agreement. The effect of PDP cell geometry on the voltage margin and on ultraviolet (UV) photon production efficiency are also studied. Results show that the thickness of front dielectric layer has a marked effect on the voltage margin and UV photon production efficiency. Furthermore, the dielectric ribs prevent the crosstalk of discharge in two ways: they decrease a number of excited species leaking to adjacent PDP cells and decrease charge distribution on the dielectric surface near the cell boundaries.
Impact of deep levels on the electrical conductivity and luminescence of gallium nitride codoped with carbon and silicon
Authors: Armstrong A. , Arehart A. R. , Green D. , Mishra U. K. , Speck J. S. , Ringel S. A.
Published: September 2005

The impact of C incorporation on the deep level spectrum of n-type and semi-insulating GaN:C:Si films grown by rf plasma-assisted molecular-beam epitaxy (MBE) was investigated by the combination of deep level transient spectroscopy, steady-state photocapacitance, and transient deep level optical spectroscopy. The deep level spectra of the GaN:C:Si samples exhibited several band-gap states. A monotonic relation between systematic doping with C and quantitative trap concentration revealed C-related deep levels. A deep acceptor at Ec−2.05eV and a deep donor at Ec−0.11eV are newly reported states, and the latter is the first directly observed deep level attributed to the CGa defect. A configuration-coordinate model involving localized lattice distortion revealed strong evidence that C-related deep levels at Ec−3.0eV and Eν+0.9eV are likely identical and associated with the yellow luminescence in C-doped GaN films. Of the deep levels whose trap concentration increase with C doping, the band-gap states at Ec−3.0 and 3.28eV had the largest concentration, implying that free-carrier compensation by these deep levels is responsible for the semi-insulating behavior of GaN:C:Si films grown by MBE. The differing manner by which C incorporation in GaN may impact electrical conductivity in films grown by MBE and metal-organic chemical-vapor deposition is discussed.
Microcanonical unimolecular rate theory at surfaces. III. Thermal dissociative chemisorption of methane on Pt(111) and detailed balance
Authors: Bukoski A. , Abbott H. L. , Harrison I.
Published: September 2005

A local hot spot model of gas-surface reactivity is used to investigate the state-resolved dynamics of methane dissociative chemisorption on Pt(111) under thermal equilibrium conditions. Three Pt surface oscillators, and the molecular vibrations, rotations, and the translational energy directed along the surface normal are treated as active degrees of freedom in the 16-dimensional microcanonical kinetics. Several energy transfer models for coupling a local hot spot to the surrounding substrate are developed and evaluated within the context of a master equation kinetics approach. Bounds on the thermal dissociative sticking coefficient based on limiting energy transfer models are derived. The three-parameter physisorbed complex microcanonical unimolecular rate theory (PC-MURT) is shown to closely approximate the thermal sticking under any realistic energy transfer model. Assuming an apparent threshold energy for CH4 dissociative chemisorption of E0=0.61eV on clean Pt(111), the PC-MURT is used to predict angle-resolved yield, translational, vibrational, and rotational distributions for the reactive methane flux at thermal equilibrium at 500K. By detailed balance, these same distributions should be observed for the methane product from methyl radical hydrogenation at 500K in the zero coverage limit if the methyl radicals are not subject to side reactions. Given that methyl radical hydrogenation can only be experimentally observed when the CH3 radicals are kinetically stabilized against decomposition by coadsorbed H, the PC-MURT was used to evaluate E0 in the high coverage limit. A high coverage value of E0=2.3eV adequately reproduced the experimentally observed methane angular and translational energy distributions from thermal hydrogenation of methyl radicals. Although rigorous application of detailed balance arguments to this reactive system cannot be made because thermal decomposition of the methyl radicals competes with hydrogenation, approximate applicability of detailed balance would argue for a strong coverage dependence of E0 with H coverage—a dependence not seen for methyl radical hydrogenation on Ru(0001), but not yet experimentally explored on Pt(111).
Large transport eddy-current loss in quasisaturated CoFeSiB amorphous wire
Authors: Chen D.-X. , Li Y.-F.
Published: September 2005

The transport eddy-current loss of a nearly nonmagnetostrictive CoFeSiB amorphous wire under a large longitudinal bias field can be several times greater than the value commonly expected by the classical model. Related to the overlarge circular susceptibility under the same condition, this is attributed to the formation of disklike soft-magnetic microstructures around hard magnetic inclusions randomly embedded in a soft magnetic matrix.
Temperature-induced dynamical conformational disorder in 4-vinyl benzoic acid molecular crystals: A molecular simulation study
Authors: Murugan N. Arul
Published: September 2005

Extensive molecular simulations are carried out as a function of temperature to understand and quantify the conformational disorder in molecular crystals of 4-vinyl benzoic acid. The conformational disorder is found to be dynamic and associated with a flip-flop motion of vinyl groups. The population of minor conformer is less than 3% up to 300K and is 13.2% at 350K and these results are consistent with the experimental observations. At still higher temperatures, the population of minor conformer increases up to 25%. The evolution of structure at both molecular and unit-cell level of the molecular crystal as a function of temperature has been characterized by various quantities such as radial distribution functions, average cell parameters, volume, and interaction energies. The van’t Hoff plot shows a nonlinear behavior at lower temperatures as it has been reported recently by Ogawa and co-workers in the case of stilbene, azobenzene [J. Am. Chem. Soc. 126, 3539 (2004)], and N-(4-methylbenzylidene)-4-methylaniline [Acta Crystallogr, Sect. B. Struct. Sci. B60, 589 (2004)] molecular crystals. A set of rigid body simulations were also carried out to quantify the effect of conformational disorder on structural quantities such as unit-cell volume and interaction energy. The anomalous shrinkage of vinyl CC bond length as a function of temperature has been explained by combining the results of simulations and a set of constrained optimizations using ab initio electronic structure calculations for various molecular structures differing in torsional angle.
Density functional theory based molecular-dynamics study of aqueous iodide solvation
Authors: Heuft J. M. , Meijer E. J.
Published: September 2005

We study the solvation of iodide in water using density functional theory based molecular-dynamics simulations. Detailed analysis of the structural and dynamical properties of the first solvation shell is presented, showing a disruptive influence of the ion on the local water structure. Iodide-water hydrogen bonding is weak, compared to water-water hydrogen bonds. This effective repulsive ion-water interaction leads to the formation of a quite unstructured solvation shell. The dynamics of water molecules surrounding the iodide is relatively fast. The intramolecular structural and electronical properties of water molecules around the ion are not affected.
Optical properties of transparent copper nanorod and nanowire arrays embedded in anodic alumina oxide
Authors: Zong Rui-Long , Zhou Ji , Li Bo , Fu Ming , Shi Shi-Kao , Li Long-Tu
Published: September 2005

Transparent copper nanorod/nanowire arrays and anodic alumina oxide composite films have been prepared by alternating current electrodeposition, and their linear optical properties have been systematically characterized by absorption spectra. In the experimental spectra, there exist transverse and longitudinal resonance peaks, which are caused by the surface-plasmon resonance along the diameter and the length of the copper nanorods, respectively. The transverse resonance peak is affected by the diameter and aspect ratio of the nanorod. The longitudinal resonance peak appears at longer wavelength when a polarized light illuminates the film with an angle of incidence of about 70°, where the angle is defined with respect to the surface normal. Moreover, the longitudinal resonance mode is sensitive to the polarization direction when compared with the transverse resonance mode.
Impact of titanium addition on film characteristics of HfO2 gate dielectrics deposited by atomic layer deposition
Authors: Triyoso D. H. , Hegde R. I. , Zollner S. , Ramon M. E. , Kalpat S. , Gregory R. , Wang X.-D. , Jiang J. , Raymond M. , Rai R. , Werho D. , Roan D. , White B. E. , Tobin P. J.
Published: September 2005

The impact of 8-to45-at.% Ti on physical and electrical characteristics of atomic-layer-deposited and annealed hafnium dioxide was studied using vacuum-ultraviolet spectroscopic ellipsometry, secondary ion mass spectroscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, and x-ray reflectometry. The role of Ti addition on the electrical performance is investigated using molybdenum (Mo)-gated capacitors. The film density decreases with increasing Ti addition. Ti addition stabilizes the amorphous phase of HfO2, resulting in amorphous films as deposited. After a high-temperature annealing, the films transition from an amorphous to a polycrystalline phase. Orthorhombic Hf–Ti–O peaks are detected in polycrystalline films containing 33-at.% or higher Ti content. As Ti content is decreased, monoclinic HfO2 becomes the predominant microstructure. No TiSi is formed at the dielectric/Si interface, indicating films with good thermal stability. The band gap of Hf–Ti–O was found to be lower than that of HfO2. Well-behaved capacitance-voltage and leakage current density-voltage characteristics were obtained for Hf–Ti–O. However, an increased leakage current density was observed with Ti addition. The data from capacitance-voltage stressing indicate a smaller flatband voltage (Vfb) shift in the HfO2 films with low Ti content when compared with the HfO2 films. This indicates less charge trapping with a small amount of Ti addition.
Conical intersection between the lowest spin-aligned Li3(A′4) potential-energy surfaces
Authors: Brue Daniel A. , Li Xuan , Parker Gregory A.
Published: September 2005

We have calculated new potential-energy surfaces for the lowest two spin-aligned A′4 states of the Li3 trimer. This calculation shows a seam of conical intersections between these states resulting from the extra symmetry of the system when the atoms are in a collinear arrangement. This seam is especially important because of its proximity to the three-body dissociation limit of the system; ultracold scattering calculations and the bound-state energies of the system will be affected by the presence of this conical intersection. In this paper we discuss the calculation of the potential-energy surface and the location of the conical intersection seam.
A close-coupling study of vibrational-rotational quenching of CO by collision with hydrogen atoms
Authors: Yang Benhui , Stancil P. C. , Balakrishnan N.
Published: September 2005

Quantum-mechanical scattering calculations were performed for the rovibrational relaxation of CO in collisions with H atoms using the close-coupling approach for collision energies between 10−6 and 1500cm−1. We adopted the H–CO interaction potential of Werner, Keller, and Schinke and computed the state-to-state and total cross sections for the quenching of the υ=1, j=0–2 levels of CO. Numerous resonances, as a consequence of the van der Waals potential, are observed and the cross sections are found to approach the Wigner limit at low energies. Also, by averaging the cross sections over a Boltzmann distribution of velocities of the incoming atom, quenching rate coefficients are obtained and found to be consistent with previous infinite-order sudden approximation calculations for temperatures between 100 and 300K.
Ion channeling effects on quantum well intermixing in phosphorus-implanted InGaAsP∕InGaAs∕InP
Authors: Barba D. , Salem B. , Morris D. , Aimez V. , Beauvais J. , Chicoine M. , Schiettekatte F.
Published: September 2005

Photoluminescence, time-resolved photoluminescence, and Raman characterization techniques have been used to study In0.73Ga0.27As0.57P0.43∕In0.53Ga0.47As∕InP single quantum well heterostructure after 20-keV phosphorus ion implantation followed by rapid thermal annealing. The annealing process induces intermixing in the heterostructures and results in the blueshift of the quantum well peak emission. In order to investigate ion channeling effects on this band-gap tuning process, room-temperature implantations have been performed at tilt angles of 0° and 7° with respect to the sample (001)-growth axis. We show that the ion channeling increases the blueshift from 24 to 42 nm, while it reduces both the density of the nonradiative defects within the active layer and the structure disordering. These features are attributed to the nature of the damage generated by channeled ions. The band-gap increase observed in the sample implanted at 0° is consistent with the formation of a compressive strain at the barrier/quantum well interface, whose intensity is measured by Raman spectroscopy.
An aerosol-mediated magnetic colloid: Study of nickel nanoparticles
Authors: Sahoo Y. , He Y. , Swihart M. T. , Wang S. , Luo H. , Furlani E. P. , Prasad P. N.
Published: September 2005

A method is presented for the synthesis of high-quality nickel nanoparticles. Laser-driven decomposition of nickel carbonyl vapors is used to produce particles in the form of an aerosol, followed by exposure to a solvent containing an appropriate surfactant to yield a stable dispersion of particles. This method is scalable and yields a substantially monodisperse distribution of particles at a relatively high rate of production. The particles produced by this method are subjected to a detailed characterization using transmission electron microscopy, atomic force microscopy, energy dispersive spectroscopy, and dc magnetization. They have an average diameter of 5 nm, and the observed magnetization curves show no hysteresis above 200 K. The normalized magnetization curves follow a scaling law proportional to the quotient of the applied field over temperature. This data indicates the presence of randomly oriented superparamagnetic particles. The measured magnetization is significantly smaller than that of the bulk, probably due to an effective surface anisotropy and spin canting. The coercivity is the same in either direction of the applied field which indicates that there is negligible exchange coupling between the nickel particles and any possible antiferromagnetic oxide layer on their surfaces.
Variation of domain-wall structures and magnetization ripple spectra in permalloy films with controlled uniaxial anisotropy
Authors: Gentils A. , Chapman J. N. , Xiong G. , Cowburn R. P.
Published: September 2005

We have studied domain-wall structures and magnetization ripple in permalloy films with widely varying values of anisotropy field and thickness. Both the Fresnel and differential phase contrast imaging modes of Lorentz microscopy have been used, the latter proving particularly valuable for providing reliable quantitative data. Cross-tie walls were frequently observed but the density of the cross ties increased markedly with anisotropy field while the cross-tie length decreased. In accord with expectation, the mean ripple wavelength and magnitude of the ripple decreased with increasing anisotropy field, albeit the variation was more rapid than could be accounted for using simple theories. Generally the root-mean-square dispersion angle was found to be greater than that in earlier experimental work, a factor that was ascribed to the use of an incomplete analysis procedure in the past.
Thermally driven non-contact atomic force microscopy
Authors: Gannepalli Anil , Sebastian Abu , Cleveland Jason , Salapaka Murti
Published: September 2005

In this letter a thermally driven frequency modulated atomic force microscopy (FM-AFM) technique is developed. Thermal fluctuations of the cantilever are employed to estimate the cantilever’s equivalent resonant frequency. The corresponding cantilever oscillations are the smallest possible at a given temperature. Related experiments that establish the feasibility of thermally driven FM-AFM in ambient room conditions have achieved tip-sample separations less than 2nm with long term separation stability (>30min). Employing this method a narrowband 250Hz modulation of the tip-sample separation was detected with a vertical resolution of 0.25Å in a 0.4Hz bandwidth. The corresponding estimated force sensitivity is 7 fN. In all experiments the cantilever tip was maintained in the attractive regime of the tip-sample interactions. This demonstrates a thermally driven non-contact mode operation of AFM. It also provides a limits of performance study of small amplitude FM-AFM methods.
Alternating current dielectrophoresis of carbon nanotubes
Authors: Zhang Zhi-Bin , Liu Xian-Jie , Campbell Eleanor E. B. , Zhang Shi-Li
Published: September 2005

We report on the deposition of individual semiconducting single-walled carbon nanotubes (s-SWNTs), suspended in an aqueous solution of sodium dodecylsulfate (SDS), onto predefined electrodes using alternating current dielectrophoresis up to 100 MHz. The successful deposition is attributed to the formation of an ionic double layer encapsulating the nanotubes by surface adsorption of the SDS molecules. The nanotube-micella complex formed has a greater polarization than that of the s-SWNTs, which is theoretically shown to be frequency dependent up to 10 GHz. Carbon nanotube field-effect transistors showing large on∕off-state current ratios of 108 were demonstrated.
Room-temperature defect tolerance of band-engineered InAs quantum dot heterostructures
Authors: Oktyabrsky S. , Lamberti M. , Tokranov V. , Agnello G. , Yakimov M.
Published: September 2005

Using photoluminescence (PL) at 77–420K and high-energy proton implantation (1.5MeV, dose up to 3×1014cm−2) we have studied the thermal quenching of PL and defect tolerance of self-assembled shape-engineered InAs quantum dots (QDs) embedded into GaAs quantum wells (QWs). At room temperature, QDs appeared to withstand two orders of magnitude higher proton doses than QWs without PL degradation. A simple dynamic model was used to account for both dose and temperature dependence of PL efficiency. At low temperatures, the defect-related quenching is mainly controlled by a reduction in the density of defect-free QDs. At and above room temperature, both thermal and defect-related quenching of PL are due to the escape of carriers from dots to wells that act as barriers with low damage constants. A relatively large barrier for escape (450meV) as well as low nonradiative recombination rate in QDs is shown to account for unsurpassed room-temperature defect tolerance and high PL efficiency at room and elevated temperatures.
Aerosol mass spectrometer for the in situ analysis of chemical vapor synthesis processes in hot wall reactors
Authors: Lee In-Kyum , Winterer Markus
Published: September 2005

We present a modified aerosol mass spectrometer (AMS) for the in situ analysis of chemical vapor synthesis processes in hot wall reactors and describe the transfer function of the velocity and kinetic-energy measurement. The AMS is a combination of a quadrupole mass spectrometer (QMS) and a particle mass spectrometer (PMS) and enables the in situ analysis of aerosols with high number concentrations up to 1018m−3. Size distributions of ultrafine particles in the range of 104–107u (amu) can be measured in the PMS. Simultaneously, molecular species up to 300u can be detected in the QMS. In the setup described here a furnace was developed to enable measurement directly at the reactor exit. The formation of silicon carbide (SiC) nanoparticles by thermal decomposition of tetramethylsilane (TMS) was investigated. TMS started to decompose at about 900K and carbosilanes with two [–Si–C–] units were identified as growth species in the synthesis of SiC from TMS. With increasing temperatures particles were formed and grew by coagulation. At higher temperatures sintering of the particles became an important process. Although the particle mass reduced slightly due to a smaller residence time at higher temperatures in the reactor, the particle velocity in the molecular beam of the AMS decreased significantly. A simple model is used to compare the particle velocity in a molecular beam as a function of particle mass. The significant difference in the particle velocity can be explained by a change in the particle shape factor (κp) due to sintering.
Speckle-visibility spectroscopy: A tool to study time-varying dynamics
Authors: Bandyopadhyay R. , Gittings A. S. , Suh S. S. , Dixon P. K. , Durian D. J.
Published: September 2005

We describe a multispeckle dynamic light scattering technique capable of resolving the motion of scattering sites in cases that this motion changes systematically with time. The method is based on the visibility of the speckle pattern formed by the scattered light as detected by a single exposure of a digital camera. Whereas previous multispeckle methods rely on correlations between images, here the connection with scattering site dynamics is made more simply in terms of the variance of intensity among the pixels of the camera for the specified exposure duration. The essence is that the speckle pattern is more visible, i.e., the variance of detected intensity levels is greater, when the dynamics of the scattering site motion is slow compared to the exposure time of the camera. The theory for analyzing the moments of the spatial intensity distribution in terms of the electric-field autocorrelation is presented. It is tested for two well-understood samples, a colloidal suspension of Brownian particles and a coarsening foam, where the dynamics can be treated as stationary and hence can be benchmarked by traditional methods. However, our speckle-visibility method is particularly appropriate for samples in which the dynamics vary with time, either slowly or rapidly, limited only by the exposure time fidelity of the camera. Potential applications range from soft-glassy materials, to granular avalanches, to flowmetry of living tissue.
A frequency stabilization method for diode lasers utilizing low-field Faraday polarimetry
Authors: Kerckhoff J. A. , Bruzewicz C. D. , Uhl R. , Majumder P. K.
Published: September 2005

We present a method of diode laser frequency stabilization based on the Faraday rotation of linearly polarized light passing through an atomic sample in the presence of a very modest (1mT) magnetic field. Near the zero crossing of this spectroscopic feature, an optical system capable of very precise polarimetry detects and corrects for very small frequency fluctuations via a feedback system, which keeps the rotation signal at zero. In our application, we have demonstrated robust frequency stabilization over time scales from 10ms to 1h at the 1MHz level or below. We utilize this technique to lock our laser to a “forbidden” M1∕E2 transition in thallium at 1283nm, for which saturated absorption techniques are not straightforward. This technique has broad applicability to spectroscopy of various atomic systems as we also demonstrate using a Rb cell and a 780nm diode laser.
Electrical delay technique in the picosecond thermoreflectance method for thermophysical property measurements of thin films
Authors: Taketoshi Naoyuki , Baba Tetsuya , Ono Akira
Published: September 2005

A new picosecond thermoreflectance measurement system using an electrical delay control has been developed in order to extend observation time of temperature response of thin films after pulse heating. The new system uses two picosecond titanium sapphire lasers, one for heating a specimen and the other for probing temperature change on the film surface. Temperature history of the film surface is observed by changing the delay time of the probe pulse from the pump pulse electrically instead of changing the difference of path length between the pump beam and the probe beam. It is not difficult to observe temperature history over longer time than the repetition period of the picosecond laser pulses using the electrical delay technique. The electrical delay technique can get rid of the fluctuation of focused position of the beam on the specimen surface which is hard to eliminate after traveling through the optical delay line of variable path length. Temperature history curves of sputtered tungsten thin films of 140, 200, and 300 nm thick on glass substrates have been observed much longer than the repetition period of picosecond laser pulses for the first time. An analytical model is proposed to explain temperature response after repetitive picosecond laser pulses considering heat diffusion across the thin film, heat diffusion parallel to the film face, and heat effusion into substrate. Based on this model, thermal diffusivity values of the tungsten thin films calculated from the observed temperature history curves are about 40% of that of bulk tungsten. This electrical delay technique can realize thermophysical property measurements of a wide variety of thin films such as thicker metal films, nonmetal thin films, low thermal diffusivity materials, and multilayered thin films, the heat diffusion time of which could not be covered by the optical delay technique.
Tailoring of high-temperature photoluminescence in InAs∕GaAs bilayer quantum dot structures
Authors: Mazur Yu. I. , Wang Zh. M. , Tarasov G. G. , Kunets Vas. P. , Salamo G. J. , Zhuchenko Z. Ya. , Kissel H.
Published: September 2005

Temperature-dependent photoluminescence is investigated in bilayer InAs∕GaAs quantum dot structures with constant InAs deposition θ1 in the seed layer, but variable deposition θ2 in both the second layer and the GaAs spacer layer. It is shown that interlayer coupling, leading to the formation of asymmetric quantum dot pairs, strengthens the high-temperature photoluminescence and strongly influences carrier relaxation channels. We report that radiative recombination and carrier capture efficiency by the quantum dots in the second layer can be tailored using the deposition θ2 and the GaAs spacer thickness.
Thermal stability of the interfaces between Co-, Ni-, and Fe-based ferromagnets in contact with selected nitrides MN (M=Al, B, Nb, Ta, Ti, and V)
Authors: Yang Ying , Chang Y. Austin , Yang Jianhua , Ji Chengxiang , Ladwig Peter F. , Liu Feng , Pant Bharat B. , Schultz Allan E.
Published: September 2005

Nitride tunnel barriers have potential applications in magnetic tunnel junctions (MTJs). Thermal stability of the interfaces between Co-, Ni-, and Fe-based ferromagnets and these nitride tunnel barriers is critical to device performance. With guidance from low-temperature ternary isothermal phase diagrams of the Co–M–N, Ni–M–N, and Fe–M–N systems (M=Al, B, Nb, Ta, Ti, and V), the interfaces in Co∕MN, Ni∕MN, and Fe∕MN structures were evaluated in terms of two criterions: the phases in contact must (1) be in equilibrium with each other (i.e., connected by a stable tie line) and (2) have negligible mutual solubility in the phase diagram at the temperatures of interest. Of the investigated interfaces, Co∕AlN, Co∕BN, Co∕NbN, Co∕TaN, Co∕TiN, Ni∕BN, Ni∕TaN, Fe∕BN, Fe∕NbN, Fe∕TaN, and Fe∕TiN were found to be thermodynamically stable. However, in light of some simplifications made in this analysis, the current evaluation of interfacial stability serves as a useful step in preselecting candidate nitride-based MTJ tunnel barrier materials for detailed study.
Nanopositioning system for macroscopic components based on shear-force detection
Authors: Grosjean T. , Fahys A. , Courjon D.
Published: September 2005

We present and describe an alternative device for positioning two massive optical elements at distances smaller than 1μm to each other. The developed technique is derived from the conventional nonoptical shear-force distance control usually used in scanning near-field optical microscopy (SNOM). It is suitable whatever the nature of the involved elements (metal, semiconductor, or dielectric) and is well adapted to solid immersion microscopy and virtual tip near-field microscopy.
Low-temperature growth of β-Ga2O3 nanobelts through a simple thermochemical route and their phonon spectra properties
Authors: Geng B. Y. , Liu X. W. , Wei X. W. , Wang S. W. , Zhang L. D.
Published: September 2005

Monoclinic structured β-Ga2O3 nanobelts have been synthesized through a simple thermochemical route at low temperature in range of 400–500°C. Each nanobelt has a uniform width of about several hundred nanometers and a thickness of about 10nm along its entire length. Micro-Raman spectrum of the β-Ga2O3 nanobelts shows that the four weak Raman bands at 112, 146, 170, and 266cm−1 which seem to correspond to infrared (IR)-active transverse optical (TO) Au mode and∕or longitudinal optical (LO) Bu mode, respectively. The IR-active bands in the Raman spectrum and the surface mode in the IR spectrum may relate to the nanoscale morphology of the nanobelts.
Properties of W–Ge–N as a diffusion barrier material for Cu
Authors: Rawal S. , Norton D. P. , Anderson T. J. , McElwee-White L.
Published: September 2005

The properties of W–Ge–N thin films are reported, focusing on issues relevant to their use as diffusion barriers for Cu metallization on silicon. The amorphous W–Ge–N thin films were deposited on thermally grown SiO2∕Si using reactive sputter deposition. This was followed by in situ deposition of Cu films. Annealing studies for W–Ge–N were then carried out in a vacuum to investigate Cu diffusion and barrier film crystallization. X-ray diffraction was used to assess the crystallinity of the films upon annealing. The results show that W–Ge–N has a recrystallization temperature that is higher that that for WNx. Auger electron spectroscopy was used to measure the depth profile of Cu diffusion through the barrier layer. Little or no Cu diffusion was detected for a relatively high annealing temperature. The W–Ge–N films were conductive, although the resistivity is somewhat higher than that for WNx. The results suggest that W–Ge–N may be an attractive diffusion barrier material for Si or SiGe devices.
Enhancement of bipolar carrier transport in oligofluorene films through alignment in the liquid-crystalline phase
Authors: Chen Li-Yin , Hung Wen-Yi , Lin Yu-Ting , Wu Chung-Chih , Chao Teng-Chih , Hung Tsung-His , Wong Ken-Tsung
Published: September 2005

We investigate the formation of aligned liquid-crystal glasses of an oligofluorene and perform comparative studies of carrier-transport properties of the oligofluorene in both amorphous films and glassy liquid-crystal films. With mesophase-mediated molecular alignment, the bipolar carrier-transport capability of oligofluorene solid films is enhanced by more than an order of magnitude. High bipolar carrier mobilities, up to 2.0×10−2cm2∕Vs for holes and up to 2.3×10−2cm2∕Vs for electrons, are observed in the aligned glassy liquid-crystal films.