bluuebunny/crossref_metadata_2025 huggingface dataset:
Symmetry of flow in the Comstock Lode hydrothermal system: Evidence for longitudinal convective rolls in geologic systems
Authors: Singleton Michael J. , Criss Robert E.
Published: March 2004

Hydrothermal fluid flow can be visualized by three‐dimensional (3‐D) kriging and computer contouring of oxygen isotope data on propylitized andesites in the Comstock Lode mining district. This data set consists of δ18O results for 327 samples from surface outcrops, drill cores, and mine workings in a 3.5 km × 1.7 km × 1.0 km block in the hanging wall of the Comstock fault encompassing the region where the most important ore bodies were discovered. The δ18O contours deep in the hanging wall are not simply parallel to the Comstock fault or to the boundary of the Davidson granodiorite stock as would be expected for a hydrothermal convection system dominated by unicellular flow. Instead, the subsurface δ18O values exhibit a high degree of symmetry about a vertical plane directed radially toward the stock, with isotopic contours being predominantly perpendicular to the Comstock fault and the eastern contact of the Davidson granodiorite. A vertical cross section along the Comstock Lode shows a low δ18O core with two symmetrical zones of higher δ18O values to either side where the contours are steeply inclined, which we infer reflects downwelling of fluids shifted by water‐rock exchange or steam loss. This 3‐D visualization of δ18O values provides the first evidence that longitudinal convective rolls can be significant in geologic environments, in this case within a zone of high temperature gradients and permeability near the Comstock fault and the Davidson granodiorite stock.
Evolution of permeability in a natural fracture: Significant role of pressure solution
Authors: Yasuhara Hideaki , Elsworth Derek , Polak Amir
Published: March 2004

A mechanistic model is presented to describe closure of a fracture mediated by pressure solution; closure controls permeability reduction and incorporates the serial processes of dissolution at contacting asperities, interfacial diffusion, and precipitation at the free face of fractures. These processes progress over a representative contacting asperity and define compaction at the macroscopic level, together with evolving changes in solute concentration for arbitrarily open or closed systems for prescribed ranges of driving effective stresses, equilibrium fluid and rock temperatures, and fluid flow rates. Measured fracture surface profiles are applied to define simple relations between fracture wall contact area ratio and fracture aperture that represents the irreversible alteration of the fracture surface geometry as compaction proceeds. Comparisons with experimental measurements of aperture reduction conducted on a natural fracture in novaculite [Polak et al., 2003] show good agreement if the unknown magnitude of microscopic asperity contact area is increased over the nominal fracture contact area. Predictions of silica concentration slightly underestimate the experimental results even for elevated microscopic contact areas and may result from the unaccounted contribution of free face dissolution. For the modest temperatures (20–150°C) and short duration (900 hours) of the test, pressure solution is demonstrated to be the dominant mechanism contributing to both compaction and permeability reduction, despite net dissolution and removal of mineral mass. Pressure solution results in an 80% reduction in fracture aperture from 12 μm, in contrast to a ∼10 nm contribution by precipitation, even for the case of a closed system. For the considered dissolution‐dominated system, fracture closure rates are shown to scale roughly linearly with stress increase and exponentially with temperature increase, taking between days and decades for closure to reach completion.
Velocity field of the western entrance to the Barents Sea
Authors: Ingvaldsen Randi B. , Asplin Lars , Loeng Harald
Published: March 2004

By the use of 4‐year long records from moored current meters between 71°30′N and 73°30′N of the western entrance to the Barents Sea, the velocity field of the Atlantic inflow is examined. The mean velocity field shows the Atlantic inflow as a wide core that occupies most of this section, but the general picture is a velocity field that is dominated by large and frequent fluctuations. The key parameter that to a large degree determines the spatial distribution of the velocity field is sea level changes within the section that are induced by the local wind field. The main process is the Ekman transport through its ability to accumulate water thereby creating strong gradients of barotropic pressure and associated currents. Southwesterly winds along the Norwegian coast and southeasterly winds farther north will, in general, create wide inflows, while northerly winds will result in wide outflows. These flow regimes may be persistent for up to 2–3 weeks and are related to the relative strength and lateral extension of the Icelandic low and the Arctic high, although the alignment of the local isobars must be considered in order to be able to describe the details of the flow.
Late winter water column and sea ice conditions in the northern Bering Sea
Authors: Clement Jaclyn L. , Cooper Lee W. , Grebmeier Jacqueline M.
Published: March 2004

Seasonal sea ice concentration and thickness were evaluated on a weekly basis during two years with contrasting ice coverage, 1998–1999 and 2000–2001, using data provided by the U.S. National Ice Center. Ice in the Bering Sea during 1998–1999 was extensive and thick, but by contrast, in 2000–2001, winter sea ice formed late with thin ice, and ice melt proceeded earlier during spring. The presence and timing of a winter polynya (an area of relatively open water or thin ice surrounded by heavier ice) located south of St. Lawrence Island also varied between these two winters. Shipboard measurements south of St. Lawrence Island during two late winter/early spring cruises in 1999 and 2001 showed that some brine injected water was present, resulting in localized areas of bottom water with salinities approaching, or exceeding, 33 psu. The mean salinity of bottom water was significantly higher in 2001 (32.6 psu) than in 1999 (32.3 psu). These varying degrees of brine injection associated with large differences in ice conditions (heavy in 1998–1999, light in 2000–2001) influenced bottom water salinity and density, but there were indications that variation in water mass structure also can explain differences in salinity observed between the two winters. The mean δ18OH2O values of bottom seawater were significantly higher in 2001 (−0.78 ± 0.16‰ SD) than in 1999 (−0.98 ± 0.20‰ SD) consistent with a more saline, nutrient‐rich water being present in 2001. Consistent with these indications, inorganic nutrients (nitrate, phosphate, and silicate) in bottom water were significantly higher in 2001 than in 1999. Although it is seemingly paradoxical that salinities were higher in 2001 (light ice) than in 1999 (heavy ice) when brine injection might have been more prevalent, the sampling period was approximately 1 month earlier in 2001, when ice formation may have been more active. In addition, δ18OH2O values indicate a higher proportion of Anadyr Water, with higher salinity and nutrients in 2001. Despite these differences in both ice conditions and water mass nutrient chemistry, water column chlorophyll was uniformly low in both years. This indicates that changes in Bering Sea ice regimes during the late winter months, such as may occur under various climate change scenarios, will not necessarily lead to any higher productivity or an earlier onset of seasonal biological production. Despite relatively high inorganic nutrient concentrations in both years, a well‐mixed water column was observed with low water column chlorophyll‐a (chl‐a) concentrations. These observations suggest that there was little primary production during either cruise in spite of the relatively open water and high water column nutrient concentrations during 2001. Strong southerly winds during winter likely impeded ice formation, vertically mixed the water column, and prevented early spring open water primary production.
Effects of biomass burning in Amazonia on climate: A numerical experiment with a statistical‐dynamical model
Authors: Moraes Elisabete C. , Franchito Sergio H. , Brahmananda Rao V.
Published: March 2004

Chou and Suarez's solar and infrared radiation models are incorporated in a statistical‐dynamical model with biosphere and atmosphere interaction in order to study the climatic effects due to biomass burning in Amazonian forest. In the control experiment the mean annual zonally averaged climate is well simulated by the model when compared with observed data. Biomass burning plays an important role on the earth's radiative balance and climate through the release of large amounts of greenhouse gases and aerosols in the atmosphere and the alteration of the land surface characteristics. For investigating the relative importance of these changes five experiments are performed: (1) degradation of the surface, (2) change in the smoke aerosols concentration, (3) change in the CO2 concentration, (4) change in CH4 concentration, and (5) all the changes together. The results show that biomass burning in Amazonian forest causes a reduction in the absorbed solar radiation and net radiation fluxes at the surface in the perturbed region and an increase in the air surface temperature and the net thermal infrared radiation flux at the surface. Also there is a decrease in the latent and sensible heat fluxes, evapotranspiration and precipitation compared to the control case. In general, the greater changes in the radiative balance and climate are due mainly to the changes in the land surface characteristics, followed by those caused by the large amounts of smoke aerosols released in the atmosphere. The changes due to the greenhouse gases CO2 and CH4 are small.
Can stratospheric temperature trends be attributed to ozone depletion?
Authors: Hare Sylvia H. E. , Gray L. J. , Lahoz W. A. , O'Neill A. , Steenman‐Clark L.
Published: March 2004

The effect on stratospheric temperature of changing ozone is investigated by comparing two 5‐member ensembles of 20‐year Unified Model transient runs, one with a linear trend in ozone and one without. A significant stratospheric mean temperature trend of −0.17 K/decade is attributed to ozone depletion. It is found that, although increasing the ensemble size to 20 members would have considerable benefits, increasing the ensemble size further would not dramatically improve confidence in the results. The timeslice approach to climate change modeling is found to produce similar temperature trends to the transient approach for this experiment.
Cloud pressure retrieval using the O2‐O2 absorption band at 477 nm
Authors: Acarreta J. R. , De Haan J. F. , Stammes P.
Published: March 2004

We present an operational method for cloud pressure retrieval from the Earth's reflectance spectrum in the visible, using the O2‐O2 absorption band at 477 nm. The algorithm is simple and robust. Apart from cloud pressure, an effective cloud fraction is also retrieved. Using simulations and Global Ozone Monitoring Instrument (GOME) data the accuracy of the O2‐O2 retrieval method is estimated. The Ozone Monitoring Instrument (OMI), to be space‐borne on board the EOS‐AURA platform in 2004, will use this algorithm to produce an official cloud product. The cloud product will be used to support the cloud correction of several of the OMI trace gas retrievals.
Horizontal variability 1–2 km below the tropical tropopause
Authors: Tuck A. F. , Hovde S. J. , Kelly K. K. , Reid S. J. , Richard E. C. , Atlas E. L. , Donnelly S. G. , Stroud V. R. , Cziczo D. J. , Murphy D. M. , Thomson D. S. , Elkins J. W. , Moore F. L. , Ray E. A. , Mahoney M. J. , Friedl R. R.
Published: March 2004

Two long meridional flights of the WB57F high‐altitude aircraft 1–2 km below the tropical tropopause are examined for ozone and total water variability in the context of a large suite of tracers having lifetimes ranging from 10−2 to 103 years, together with mass spectra of individual aerosol particles. It is concluded that local correlations are predominant; contributing processes to the maintenance of the composition are marine convection, continental convection, in situ chemical production, biomass burning, downward transport from the stratosphere and recirculation.
The BOND project: Biogenic aerosols and air quality in Athens and Marseille greater areas
Authors: Sotiropoulou R. E. P. , Tagaris E. , Pilinis C. , Andronopoulos S. , Sfetsos A. , Bartzis J. G.
Published: March 2004

The role of Secondary Biogenic Organic Aerosol in aerosol budget is examined using the Atmospheric Dispersion of Pollutants over Complex Terrain–Urban Airshed Model–Aerosols (ADREA‐I/UAM‐AERO) modeling system in two representative Mediterranean areas. The areas have been selected, because of their elevated biogenic emission levels and the sufficient degree of meteorological and land use diversity characterizing the locations. Comparison of the model results with and without biogenic emissions reveals the significant role biogenic emissions play in modulating ozone and aerosol concentrations. Biogenic emissions are predicted to affect the concentrations of organic aerosol constituents through the reactions of terpenes with O3, OH and NO3. The ozonolysis of terpenes is predicted to cause an increase in OH radical concentrations that ranges from 10% to 78% for Athens, and from 20% to 95% for Marseilles, depending on the location, compared to the predictions without biogenic emissions. The reactions of this extra hydroxyl radical with SO2 and NOx have as final products increased concentrations of sulfates and nitrates in the particulate phase. As a result, biogenic emissions are predicted to affect the concentrations not only of organic aerosols, but those of inorganic aerosols as well. Thus biogenic emissions should be taken into consideration when models for the prediction and enforcement of abatement strategies of atmospheric pollution are applied.
Temperature‐dependent absorption cross sections of ozone in the Wulf‐Chappuis band at 759–768 nm
Authors: Enami Shinichi , Ueda Junya , Nakano Yukio , Hashimoto Satoshi , Kawasaki Masahiro
Published: March 2004

Absorption cross sections of ozone in the Wulf‐Chappuis band at 759–768 nm have been determined using cavity ring‐down spectroscopy at 215–298 K. Precise measurements at 762.07 and 764.47 nm revealed a slight temperature dependence of the absorption cross sections: (762.07 nm, 298 K) = (2.86 ± 0.04) × 10−22 cm2 molecule−1; (762.07 nm, 215 K) = (2.62 ± 0.04) × 10−22; (764.47 nm, 296 K) = (2.70 ± 0.03) × 10−22; and (764.47 nm, 214 K) = (2.44 ± 0.03) × 10−22. Results at 762.07 nm are indistinguishable within the experimental uncertainties from those reported by Burkholder and Talukdar [1994]. Results from the present work facilitate a more accurate retrieval of atmospheric temperature, cloud height, and cloud coverage data from satellite measurements of absorption by O2 in the A band around 761 nm.
Evaluating the credibility of transport processes in simulations of ozone recovery using the Global Modeling Initiative three‐dimensional model
Authors: Strahan Susan E. , Douglass Anne R.
Published: March 2004

The Global Modeling Initiative (GMI) has integrated two 36‐year simulations of an ozone recovery scenario with an offline chemistry and transport model using two different meteorological inputs. Physically based diagnostics, derived from satellite and aircraft data sets, are described and then used to evaluate the realism of temperature and transport processes in the simulations. Processes evaluated include barrier formation in the subtropics and polar regions, and extratropical wave‐driven transport. Some diagnostics are especially relevant to simulation of lower stratospheric ozone, but most are applicable to any stratospheric simulation. The global temperature evaluation, which is relevant to gas phase chemical reactions, showed that both sets of meteorological fields have near climatological values at all latitudes and seasons at 30 hPa and below. Both simulations showed weakness in upper stratospheric wave driving. The simulation using input from a general circulation model (GMIGCM) showed a very good residual circulation in the tropics and Northern Hemisphere. The simulation with input from a data assimilation system (GMIDAS) performed better in the midlatitudes than it did at high latitudes. Neither simulation forms a realistic barrier at the vortex edge, leading to uncertainty in the fate of ozone‐depleted vortex air. Overall, tracer transport in the offline GMIGCM has greater fidelity throughout the stratosphere than it does in the GMIDAS.
Community Coordinated Modeling Center 2003 Workshop Report
Authors: Robinson Robert
Published: March 2004

The second biennial Community Coordinated Modeling Center (CCMC) Workshop dealt with the progress that the space weather community has made in the two years since the last gathering and the technical challenges yet to be overcome. The 28‐31 October 2003 workshop, held at the Maui High Performance Computing Center in Kihei, Hawaii, built on issues related to the Center's 2000 creation by a consortium of government agencies to enable, support, and perform the research and development needed for the next generation of space weather models.
Enhancement of cathodoluminescence of ZnGa2O4:Mn thin-film phosphor by energetic particle bombardment
Authors: Kim Joo Han , Holloway Paul H.
Published: March 2004

Enhancement of cathodoluminescence of manganese-activated zinc gallate (ZnGa2O4:Mn) thin-film phosphor by energetic particle bombardment is reported. The ZnGa2O4:Mn thin-film phosphor was grown at room temperature on silicon (100) substrates by rf magnetron sputter deposition from a 2 mol % Mn-doped ZnGa2O4 target in an oxygen–argon mixture. After the deposition, the films were annealed at 800 °C for 3 h in air. The influence of energetic particle bombardment on cathodoluminescent (CL) properties of ZnGa2O4:Mn films was investigated by varying a gas pressure during the sputter growth. Our results have shown that CL brightness from ZnGa2O4:Mn films grown at 2 mTorr was more than eight times higher than that of films grown at 20 mTorr. The remarkable improvement in CL brightness from ZnGa2O4:Mn films grown at a low pressure is presumably due to the energetic particle bombardment of the growing film surface yielding a densely packed microstructure and a better crystalline quality with a highly [110]-textured structure.
Timing jitter measurement of single-flux-quantum pulse in Josephson transmission line
Authors: Terai Hirotaka , Wang Zhen , Hishimoto Yoshihito , Yorozu Shinichi , Fujimaki Akira , Yoshikawa Nobuyuki
Published: March 2004

Timing jitter is an important factor in determining the limit of speed and scale of single-flux-quantum circuits. We estimated the timing jitter by a simple method using 2-bit shift registers. It was estimated by observing the transition between 1- and 2-mode operations while changing the bias current to the clock line. A sharp transition was observed in the shift register with a smaller number of Josephson junctions in the clock and data lines, suggesting the existence of a finite timing jitter. The timing jitter per Josephson junction was estimated to be 0.09 ps at a designed bias current. The temperature dependence supported that the timing jitter comes from thermal fluctuation.
Molecular-scale biophotodiode consisting of a green fluorescent protein/cytochrome c self-assembled heterolayer
Authors: Choi Jeong-Woo , Fujihira Masamichi
Published: March 2004

A molecular photodiode that consists of a protein heterolayer is investigated at the molecular scale for construction of a bioelectronic device. Cytochrome c and green fluorescent protein (GFP) were used as an electron acceptor and a sensitizer in the molecular layer by mimicking photosynthesis. A self-assembled monolayer of thiol-modified cytochrome c was formed on Au-coated glass, and then GFP was adsorbed onto the cytochrome c surface by electrostatic attraction. Photoinduced current was generated and the photoswitching property was observed by repeated step illumination. The rectifying property by scanning tunneling spectroscopy based current–voltage characteristics was achieved in the protein heterolayer. Thus, the proposed heterolayer functioned as a biomolecular photodiode with photocurrent generation and the rectifying property.
Angular-dependent vortex pinning mechanisms in YBa2Cu3O7 coated conductors and thin films
Authors: Civale L. , Maiorov B. , Serquis A. , Willis J. O. , Coulter J. Y. , Wang H. , Jia Q. X. , Arendt P. N. , MacManus-Driscoll J. L. , Maley M. P. , Foltyn S. R.
Published: March 2004

We compare the angular-dependent critical current density (Jc) in YBa2Cu3O7 films deposited on MgO templates grown by ion-beam-assisted deposition (IBAD), and on single-crystal substrates. We identify three angular regimes in which pinning is dominated by different types of correlated and uncorrelated defects. Those regimes are present in all cases, but their extension and characteristics are sample dependent, reflecting differences in texture and defect density. The more defective nature of the films on IBAD turns into an advantage as it results in higher Jc, demonstrating that the performance of the films on single crystals is not an upper limit for the IBAD coated conductors.
Nanostructuring the Er–Yb distribution to improve the photoluminescence response of thin films
Authors: Suarez-Garcia A. , Serna R. , Jiménez de Castro M. , Afonso C. N. , Vickridge I.
Published: March 2004

Thin films of amorphous aluminum oxide (a-Al2O3) codoped with Er3+ and Yb3+ ions have been in-depth nanostructured by distributing the rate earth (RE) ions in layers separated in the 0–3 nm range. The Yb to Er concentration ratio is varied from 0 to 3.6. The photoluminescence (PL) response at 1.53 μm exhibits an increase of up to two orders of magnitude with respect to that of films doped only with Er. The PL intensity is improved when Yb3+ and Er3+ ions are in separate layers and the results show that efficient Yb3+ to Er3+ energy transfer can be achieved for separations up to 3 nm. Furthermore, it is shown that designing an adequate RE distribution, for the same total RE content and Yb to Er concentration ratio, can enhance the PL intensity by a further factor of two. It is shown that the Er3+ PL response is improved because of a reduction of the RE clustering and an improvement of the energy transfer from Yb3+ to Er3+ ions.
Solution-processible organic semiconductor for transistor applications: Tetrabenzoporphyrin
Authors: Aramaki Shinji , Sakai Yoshimasa , Ono Noboru
Published: March 2004

We report an organic semiconductor, tetrabenzoporphyrin, that can be used for transistor applications. It can be derived from a soluble precursor compound with bicyclo structure. The precursor film is amorphous and shows good film morphology. Then it is converted into an insoluble crystalline semiconductor film quantitatively at elevated temperature of 150–200 °C. Field-effect transistors were fabricated by this method. Observed mobility of the devices exceeded 10−2 cm2/V s with appropriate process and device structure.
Electrochemical gating of individual single-wall carbon nanotubes observed by electron transport measurements and resonant Raman spectroscopy
Authors: Cronin S. B. , Barnett R. , Tinkham M. , Chou S. G. , Rabin O. , Dresselhaus M. S. , Swan A. K. , Ünlü M. S. , Goldberg B. B.
Published: March 2004

Metal electrodes patterned lithographically on top of individual single-wall carbon nanotubes are used to gate the nanotubes with respect to a reference electrode in an electrolyte drop. The gating is found to have a dramatic effect on both the Raman spectra and electron transport of the nanotubes. Current through metallic nanotubes is found to increase sharply with electrochemical gate voltage, indicating that the Fermi energy reaches valence and conduction band van Hove singularities. Using resonant confocal micro-Raman spectroscopy, we observe a 9 cm−1 upshift of the tangential mode vibrational frequency, as well as a 90% decrease in intensity, by applying 1 V between an individual nanotube and a silver reference electrode in a dilute H2SO4 solution. The mechanisms for the shifts of the Raman mode frequencies are discussed on the basis of changes in the lattice constant of heavily charged nanotubes.
A class of spin injection-precession ultrafast nanodevices
Authors: Osipov V. V. , Bratkovsky A. M.
Published: March 2004

Spin valve ultrafast spin injection devices with small dissipated power are described: an amplifier, a frequency multiplier, and a square-law detector. Their operation is based on injection of spin polarized electrons from one ferromagnet to another through a semiconductor layer and spin precession of the electrons in the semiconductor layer in a magnetic field induced by a (base) current in an adjacent nanowire. The base current can control the emitter current between the magnetic layers with frequencies up to several 100 GHz.
Azafullerene (C59N)2 thin-film field-effect transistors
Authors: Kumashiro Ryotaro , Tanigaki Katsumi , Ohashi Hirotaka , Tagmatarchis Nikos , Kato Haruhito , Shinohara Hisanori , Akasaka Takeshi , Kato Kenichi , Aoyagi Shinobu , Kimura Shigeru , Takata Masaki
Published: March 2004

Thin-film field-effect transistors (FETs) of azafullerene (C59N)2 are fabricated, and their properties are investigated. The (C59N)2 FET exhibits n-channel characteristics with the field-effect electron mobility of 3.8×10−4 cm2 V−1 s−1 and the on–off current ratio of 103 at room temperature. The observed differences are ascribed to the much smaller grain size and the worse crystallinity of (C59N)2 thin films, on a basis of low angle x-ray diffraction structural data. The anticipated dimer to monomer conversion with electron carrier injection is not observed. The FET characteristics are discussed from the temperature evolution of the mobilities between (C59N)2 and C60 FETs.
Density fluctuations in α-decay self-irradiated zircon
Authors: Rı́os Susana , Salje Ekhard K. H.
Published: March 2004

Small-angle x-ray scattering (SAXS) intensities measured in a series of natural zircons, from fully crystalline to fully amorphous, give evidence for nanoscale density fluctuations within the amorphous phase produced by α-decay self-irradiation. At low amorphous fractions (p<0.5), the SAXS intensity is dominated by the signal associated with the sharp crystalline/amorphous interphase. At high amorphous fractions (p>0.8) a peak at Q=3 nm−1 develops, indicating the presence of 1 nm diameter regions that show a high-density contrast with the surrounding matrix. Density fluctuations are interpreted in terms of nanometer size voids.
Sonic boom in soft materials: The elastic Cerenkov effect
Authors: Bercoff Jeremy , Tanter Mickaël , Fink Mathias
Published: March 2004

We report an experimental evidence of an elastic sonic boom in soft materials. Our approach is based on the ultrasonic remote generation, inside soft media, of a supersonic moving source radiating shear waves in a Mach cone. In analogy with the Cerenkov electromagnetic radiation emitted by a beam of charged particles moving at a speed greater than the speed of light, an intense shear wave is radiated in soft materials. Such Mach waves are sensitive to medium elasticity inhomogeneities and are of great interest for ultrasound-based medical imaging applications.
Crystallization kinetics and microstructure-dependent leakage current behavior of ultrathin HfO2 dielectrics: In situ annealing studies
Authors: Kim Hyoungsub , Marshall Ann , McIntyre Paul C. , Saraswat Krishna C.
Published: March 2004

The crystallization kinetics of ∼3 nm HfO2 films grown by atomic layer deposition (ALD) on SiO2-passivated Si (100) wafers were investigated using an in situ transmission electron microscope (TEM) with heating capability. Through gray-scale analysis of dark-field TEM images, it was found that a two-dimensional nucleation and growth mechanism with a decreasing of nucleation rate could account for the observed transformation rate behavior. The effects of crystalline defects (e.g., grain boundaries) on the leakage current were studied using a reduced pressure in situ postdeposition anneal in the ALD system to avoid interfacial SiO2 growth. The leakage current magnitude and temperature dependence were found to be essentially independent of the microstructural changes that accompany crystallization of the HfO2 films.
Polarity determination of ZnO thin films by electron holography
Authors: Xu Q. Y. , Wang Y. , Wang Y. G. , Du X. L. , Xue Q. K. , Zhang Z.
Published: March 2004

The polarity of the ZnO film grown on sapphire using an ultrathin Ga wetting layer has been investigated by electron holography. Spontaneous polarization of the ZnO film leads to localized charges in the surface, which change the potential distribution in the vacuum side of the film. The potential distribution depends on the nature of the bounded charges and change as a function of the distance from the film surface. By studying the dependence of the potential change on the distance from the film surface, the ZnO film with very thin Ga wetting layer is determined to have the [0001] polarity.
Intracavity sum-frequency generation in GaAs quantum cascade lasers
Authors: Bengloan J.-Y. , De Rossi A. , Ortiz V. , Marcadet X. , Calligaro M. , Maurin I. , Sirtori C.
Published: March 2004

Emission of coherent light at 5.75 μm wavelength has been obtained by intracavity frequency doubling of a GaAs-based quantum cascade laser. This nonlinearity originates from the second-order susceptibility of the bulk material hosting the heterostructure and can be exploited by growing the quantum cascade laser on a 〈111〉 substrate.
Efficient polymer-based interpenetrated network photovoltaic cells
Authors: Alem Salima , de Bettignies Remi , Nunzi Jean-Michel , Cariou Michel
Published: March 2004

Organic solar cells based on an interpenetrated network of conjugated polymer as donor and fullerene derivative as acceptor materials have a great potential for improving efficiency. We fabricated a device based on a composite of poly(2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene and [6,6]-phenyl C60 butyric acid methyl ester. Surface treatment, insertion of interfacial layers, and improvement of the morphology of the active layer significantly increase the photovoltaic performances of the structure. We obtain an open circuit voltage of 0.87 V and short circuit current density of 8.4 mA/cm2 under 100 mW/cm2 air-mass 1.5 solar simulator illumination, yielding a 2.9% power conversion efficiency.
2.0 μ
m
wavelength InAs quantum dashes grown on a GaAs substrate using a metamorphic buffer layer
Authors: Balakrishnan Ganesh , Huang Shenghong , Rotter Thomas J. , Stintz Andreas , Dawson L. R. , Malloy Kevin J. , Xu H. , Huffaker D. L.
Published: March 2004

We describe optical and structure characteristics of InAs quantum dashes grown on a GaAs substrate using an AlGaAsSb metamorphic buffer. The metamorphic buffer increases the lattice constant of the growth matrix from 5.653 to 5.869 Å. The increased lattice constant of the growth matrix yields a lattice mismatch with the InAs active region of only 3.2% and accommodates a large In content to access emission wavelengths >2.0 μm. From our comparison with quantum dot structures, we conclude that the elongated quantum dash formation is due to asymmetric surface bonds in the zinc blende crystal structure that control surface migration in low strain conditions.
Competing processes in the surface ordering of InAs islands using a subsurface island superlattice
Authors: Solomon G. S.
Published: March 2004

A subsurface island superlattice is used to create surface spatial ordering in strain-induced InAs islands of quantum-dot scale deposited on (001) GaAs. A rectangular surface unit cell is demonstrated and its structure is attributed to competition between two surface diffusion processes, those related to surface reconstruction and those related to the subsurface island strain. Because the ratio of nearest-neighbor positions does not allow for full translation of the unit cell, only a weakly defined lattice is present which is optimized by controlling the crystal growth process.
Memory effect of oxide/SiC:O/oxide sandwiched structures
Authors: Chang T. C. , Yan S. T. , Yang F. M. , Liu P. T. , Sze S. M.
Published: March 2004

The memory effects of the oxide/oxygen-incorporated silicon carbide (SiC:O)/oxide sandwiched structure were investigated. The memory window is decreased with the increase of the oxygen content in the SiC:O film due to the reduction of dangling bonds. A concise model is proposed to explain the reduction of dangling bonds with increasing oxygen content. Also, a higher breakdown voltage is observed with less oxygen content in the SiC:O film, which is attributed to the high barrier height induced by electron trapping in the SiC:O film.
Significantly enhanced critical current density in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox composite conductors prepared by overpressure processing in final heat treatment
Authors: Yuan Y. , Jiang J. , Cai X. Y. , Larbalestier D. C. , Hellstrom E. E. , Huang Y. , Parrella R.
Published: March 2004

Overpressure (OP) processing otherwise fully treated, commercial Ag-sheathed multifilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) composite conductors increased the critical current density Jc (0.1 T, 77 K) by 37% to 30.8 kA/cm2 and the self-field Jc (SF, 77 K) to 69.6 kA/cm2. These improvements were obtained on full-size high current conductors such that critical current Ic (0.1 T, 77 K) reached 80.6 A and Ic (SF, 77 K) 181.7 A, even though there was a very strong self-field suppression of Ic. Estimated values for the non-self-field-limited Ic and Jc (0 T, 77 K) reached 235 A and 90 kA/cm2. Scanning electron microscopy and superconducting quantum inference device measurement revealed that OP processing effectively suppressed cracks, porosity, and the volume fraction of the Bi2Sr2Ca1Cu2Oy (2212) phase, which are all major current-limiting mechanisms in present 2223 conductors.
Optical properties of superlattice photonic crystal waveguides
Authors: Park Wounjhang , Summers Christopher J.
Published: March 2004

We report theoretical investigations of a superlattice photonic crystal (PC) waveguide in which the holes in the PC are infiltrated with an electro-optic medium and alternate rows biased so as to produce a superlattice structure. The three-dimensional simulations fully incorporate the finite thickness of the PC structure and show that the optical properties become strongly dependent on the direction of light propagation. Depending on the degree of index modulation the light experiences switching, out-coupling, or giant refraction and dispersion.
Effect of gate oxidation method on electrical properties of metal-oxide-semiconductor field-effect transistors fabricated on 4H-SiC C(0001̄) face
Authors: Fukuda Kenji , Kato Makoto , Kojima Kazutoshi , Senzaki Junji
Published: March 2004

The effect of gate oxidation method on the electrical properties of metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated on 4H-SiC C(0001̄) face has been investigated. In the case of SiC MOSFETs fabricated by dry gate oxidation, the peak value of field-effect mobility (μFE) is 16.3 cm2/V s. On the other hand, pyrogenic gate oxidation and pyrogenic gate oxidation followed by H2 postoxidation annealing (POA) considerably decreased the interface trap density (Dit) and the threshold voltage, and markedly improved the μFE. The depth profiles of hydrogen density were measured using secondary ion mass spectroscopy. These verified that pyrogenic gate oxidation increases hydrogen density at the SiO2/SiC interface compared to dry gate oxidation, and that the pyrogenic gate oxidation followed by H2 POA increases considerably it. It is thought that the Dit reduction might be caused by the passivation of interface states by –H or –OH. The peak value of μFE for SiC MOSFETs fabricated by pyrogenic gate oxidation followed by H2 POA is 111 cm2/V s, which is much higher than that of SiC MOSFETs fabricated on a Si(0001) face. Therefore, the 4H-SiC C(0001̄) face is suitable for the fabrication of SiC power MOSFETs.
Evidence on the mechanism of boron deactivation in Ge-preamorphized ultrashallow junctions
Authors: Pawlak B. J. , Surdeanu R. , Colombeau B. , Smith A. J. , Cowern N. E. B. , Lindsay R. , Vandervorst W. , Brijs B. , Richard O. , Cristiano F.
Published: March 2004

We investigate the thermal stability of boron-doped junctions formed by Ge preamorphization and solid phase epitaxial regrowth. Isochronal annealing and characterization by sheet resistance, secondary-ion mass spectrometry, and spreading-resistance measurement are used to extract detailed information on the thermal stability of the boron activation. Using a previously established model of self-interstitial defect evolution from clusters to dislocation loops, we perform simulations of the release of interstitials from the end-of-range region. The simulations indicate that the measured deactivation is driven by interstitials emerging from the end-of-range defect region.
Nondestructive three-dimensional elemental microanalysis by combined helical x-ray microtomographies
Authors: Golosio Bruno , Somogyi Andrea , Simionovici Alexandre , Bleuet Pierre , Susini Jean , Lemelle Laurence
Published: March 2004

A nondestructive x-ray technique combining simultaneous transmission, fluorescence, and Compton microtomography has been developed. Simultaneous three-dimensional structural information and three-dimensional internal elemental composition maps down to trace concentration levels have been obtained by a helical scan of the sample through an x-ray microbeam. With this method quantitative three-dimensional chemical distributions can be obtained at (sub)micrometric resolution in a nondestructive and noninvasive way, opening unique possibilities for the microanalysis of rare and fragile samples from several research fields.
Ammonium sulfide passivation of Type-II InAs/GaSb superlattice photodiodes
Authors: Gin A. , Wei Y. , Hood A. , Bajowala A. , Yazdanpanah V. , Razeghi M. , Tidrow M.
Published: March 2004

We report on the surface passivation of Type-II InAs/GaSb superlattice photodetectors using various ammonium sulfide solutions. Compared to unpassivated detectors, zero-bias resistance of treated 400 μm×400 μm devices with 8 μm cutoff wavelength was improved by over an order of magnitude to ∼20 kΩ at 80 K. Reverse-bias dark current density was reduced by approximately two orders of magnitude to less than 10 mA/cm2 at −2 V. Dark current modeling, which takes into account trap-assisted tunneling, indicates greater than 70 times reduction in bulk trap density for passivated detectors.
Topologic mixing on a microfluidic chip
Authors: Chen Hao , Meiners Jens-Christian
Published: March 2004

Mixing two liquids on a microfluidic chip is notoriously hard because the small dimensions and velocities on the chip effectively prevent turbulence. We present a topological mixing scheme that exploits the laminarity of the flow to repeatedly fold the flow and exponentially increase the concentration gradients to obtain fast and efficient mixing by diffusion. It is based on helical flow channels with opposite chiralities that split, rotate, and recombine the fluid stream in a topology reminiscent of a series of Möbius bands. This geometry is realized in a simple six-stage, two-layer elastomer structure with a footprint of 400 μm×300 μm per stage that mixes two solutions efficiently at Reynolds numbers between 0.1 and 2. This represents more than an order of magnitude reduction in the size of microfluidic mixers that can be manufactured in standard multilayer soft lithography techniques.
Time reversal three-dimensional imaging using single-cycle terahertz pulses
Authors: Buma T. , Norris T. B.
Published: March 2004

We demonstrate three-dimensional imaging using single-cycle terahertz electromagnetic pulses. Reflection-mode imaging is performed with a photoconductive transmitter and receiver and a reconstruction algorithm based on time reversal. A two-dimensional array is synthesized from ten concentric ring annular arrays with numerical apertures ranging from 0.27 to 0.43. The system clearly distinguishes image planes separated by 1.5 mm and achieves a −6 dB lateral resolution of 1.1 mm. In terms of the illuminating terahertz power spectrum, the lateral resolution is 38% and 81% of the peak and mean wavelengths, respectively.
High-resolution strain measurement in shallow trench isolation structures using dynamic electron diffraction
Authors: Kim Miyoung , Zuo J. M. , Park Gyeong-Su
Published: March 2004

We report a versatile electron diffraction strain measurement technique and its application to strain in shallow trench isolation (STI) device structures. Using a nanometer-sized probe formed by convergent-beam electrons in a field-emission transmission electron microscope, electron diffraction patterns were recorded with high spatial resolution. By fitting the diffraction patterns with a pattern matching technique using dynamic theory, it is shown that strain in the device can be measured with high accuracy to quantify the effects of different filling materials in STI structures.
Controlling film growth with selective excitation: Chemical vapor deposition growth of silicon
Authors: Wu Biao , Cohen Philip I. , Feldman L. C. , Zhang Zhenyu
Published: March 2004

We propose a method of controlling the growth mode in an epitaxial system. It takes advantage of differences in the vibrational frequencies of adatom–substrate bonds at terraces and steps. With a properly tuned infrared laser, one can selectively excite only the adatom–substrate bonds at steps and enhance the mobility of these adatoms, consequently promoting step-flow growth and reducing film roughness. The feasibility of this method is shown theoretically with respect to the prototype system of chemical vapor deposition growth of silicon.
Spatial phase separation of GaN selectively grown on a nanoscale faceted Si surface
Authors: Lee S. C. , Sun X. Y. , Hersee S. D. , Brueck S. R. J. , Xu H.
Published: March 2004

This letter reports the growth of spatially separated hexagonal and cubic phases of GaN on a patterned Si(001) substrate by metalorganic vapor-phase epitaxy. The substrate surface was patterned with grooves having a 355 nm period. Each groove consisted of two opposed Si{111} facets that were separated by Si(001) surfaces. Epitaxial growth of GaN on this substrate began selectively on the Si{111} facets and yielded the GaN hexagonal phase. With further growth, the two hexagonal phase regions separately grown on the opposed Si{111} facets coalesced, with strongly misaligned c axes (∼110°). The GaN grown after coalescence was subsequently confirmed, by transmission electron microscopy and photoluminescence, to be of cubic phase.
Stimulated emission in a nanostructured silicon pn junction diode using current injection
Authors: Chen M. J. , Yen J. L. , Li J. Y. , Chang J. F. , Tsai S. C. , Tsai C. S.
Published: March 2004

Stimulated emission at bandgap energy of 1.1 eV was observed in a silicon nanostructured pn junction diode using current injection at room temperature. Nonuniform diffusion using spin-on boron dopant mixed with silicon dioxide nanoparticles was used to fabricate the device. The spatial confinement of carriers through such localization structures contributes to the enhancement of the stimulated emission. The experimental results show a drastic increase in the optical power and multiple spectral peaks at wavelengths longer than the main peak of spontaneous emission through various phonon-assisted radiative recombination processes. When the injection current significantly exceeds a threshold, a single peak dominates, exhibiting stimulated emission.
Strain-compensated InGaAsSb/AlGaAsSb mid-infrared quantum-well lasers
Authors: Li W. , Héroux J. B. , Shao H. , Wang W. I.
Published: March 2004

The use of strain-compensated InGaAsSb/AlGaAsSb quantum wells for the fabrication of type I mid-infrared laser devices grown on GaSb substrates by molecular-beam epitaxy is reported. The creation of a tensile strain in the Al0.25Ga0.75AsySb1−y barriers by the incorporation of an arsenic fraction greater than 2% allows to reduce the average strain in the active region and increase the valence band offset to improve hole confinement in the wells. A 2.82 μm emission wavelength in pulsed mode along with a 660 A/cm2 threshold current density are obtained at room temperature for a type I InGaAsSb/AlGaAsSb double-quantum-well laser diode. By further increasing the indium and arsenic compositions into the wells and barriers, respectively, pulsed lasing at a wavelength of 2.89 μm at room temperature has also been achieved.
Effects of surface passivation on breakdown of AlGaN/GaN high-electron-mobility transistors
Authors: Ohno Yutaka , Nakao Takeshi , Kishimoto Shigeru , Maezawa Koichi , Mizutani Takashi
Published: March 2004

The effect of Si3N4 surface passivation on breakdown of AlGaN/GaN high-electron-mobility transistors was studied in detail by investigating dependences of the off-state breakdown voltage on temperature and gate reverse current, and by measuring electroluminescence distribution. Impact ionization in the channel which was triggered by the gate reverse current was responsible for the off-state breakdown. Surface passivation by Si3N4 film was effective to improve the off-state breakdown voltage. This has been explained by a change in the potential distribution due to suppression of electron trapping at the surface states, based on results of electroluminescence measurements.
High-mobility, sputtered films of indium oxide doped with molybdenum
Authors: Yoshida Yuki , Wood David M. , Gessert Timothy A. , Coutts Timothy J.
Published: March 2004

Thin films of molybdenum-doped indium oxide, an n-type transparent conducting oxide, were deposited on glass substrates by a large-area deposition technique, radio-frequency magnetron sputtering, and their electrical properties were examined. Molybdenum content was varied from 1 to 4 wt%, and the highest mobility achieved was 83 cm2 V−1 s−1 at a carrier concentration of 3.0×1020 cm−3 without any postdeposition treatment for one of the films made from the target with 2 wt% Mo. Temperature-dependent Hall analysis indicated that this high mobility is limited by phonon scattering, whereas the method of four coefficients analysis showed that the conduction band is parabolic.
Synthesis and photoluminescence properties of ZnMnS nanobelts
Authors: Geng B. Y. , Zhang L. D. , Wang G. Z. , Xie T. , Zhang Y. G. , Meng G. W.
Published: March 2004

Mn-doped ZnS nanobelts have been prepared through a thermal evaporation method starting with a mixture of acetylacetonates and H2S at 900 °C. The nanobelts had a uniform single-crystal hexagonal wurtzite structure and grew along [001] direction. Undoped ZnS nanobelts and ZnMnS nanobelts with 1%, 3%, and 5% Mn so obtained have been characterized by x-ray diffraction, energy dispersive x-ray analysis, and photoluminescence (PL) spectra. PL measurements showed that the fluorescence efficiencies increased and the glow peaks shifted to longer wavelengths as the Mn-doped ratios increased, and the doping was found responsible for the changes in the defect-related emission of the ZnS nanobelts.
Surface-topography-induced enhanced transmission and directivity of microwave radiation through a subwavelength circular metal aperture
Authors: Lockyear Matthew J. , Hibbins Alastair P. , Sambles J. Roy , Lawrence Christopher R.
Published: March 2004

Strongly enhanced transmission of microwave radiation (λ0∼5 mm) is observed through a single subwavelength circular aperture of diameter d=2.5 mm in a metallic plate. The phenomenon is caused by resonant excitation of electromagnetic surface waves supported by four concentric grooves surrounding the aperture on the illuminated side of the sample. It is also shown that similar surface patterning on the output face of the sample results in very strong angular confinement (directivity) of the transmitted beam. A finite element code is used to investigate the electromagnetic fields on both the illuminated and the exit side of the structure, the predictions from which show excellent agreement with the experimental results.