bluuebunny/crossref_metadata_2025 huggingface dataset:
Emissions of major gaseous and particulate species during experimental burns of southern African biomass
Authors: Keene William C. , Lobert Jürgen M. , Crutzen Paul J. , Maben John R. , Scharffe Dieter H. , Landmann Tobias , Hély Christelle , Brain Conrad
Published: February 2006

Characteristic vegetation and biofuels in major ecosystems of southern Africa were sampled during summer and autumn 2000 and burned under semicontrolled conditions. Elemental compositions of fuels and ash and emissions of CO2, CO, CH3COOH, HCOOH, NOX, NH3, HONO, HNO3, HCl, total volatile inorganic Cl and Br, SO2and particulate C, N, and major ions were measured. Modified combustion efficiencies (MCEs, median = 0.94) were similar to those of ambient fires. Elemental emissions factors (EFel) for CH3COOH were inversely correlated with MCEs; EFels for heading and mixed grass fires were higher than those for backing fires of comparable MCEs. NOX, NH3, HONO, and particulate N accounted for a median of 22% of emitted N; HNO3emissions were insignificant. Grass fires with the highest EFels for NH3corresponded to MCEs in the range of 0.93; grass fires with higher and low MCEs exhibited lower EFels. NH3emissions for most fuels were poorly correlated with fuel N. Most Cl and Br in fuel was emitted during combustion (median for each = 73%). Inorganic gases and particulate ions accounted for medians of 53% and 30% of emitted Cl and Br, respectively. About half of volatile inorganic Cl was HCl indicating significant emissions of other gaseous inorganic Cl species. Most fuel S (median = 76%) was emitted during combustion; SO2and particulate SO42−accounted for about half the flux. Mobilization of P by fire (median emission = 82%) implies large nutrient losses from burned regions and potentially important exogenous sources of fertilization for downwind ecosystems.
Aqueous processes at Gusev crater inferred from physical properties of rocks and soils along the Spirit traverse
Authors: Cabrol N. A. , Farmer J. D. , Grin E. A. , Richter L. , Soderblom L. , Li R. , Herkenhoff K. , Landis G. A. , Arvidson R. E.
Published: February 2006

Gusev crater was selected as the landing site for Spirit on the basis of morphological evidence of long‐lasting water activity, including possibly fluvial and lacustrine episodes. From the Columbia Memorial Station to the Columbia Hills, Spirit's traverse provides a journey back in time, from relatively recent volcanic plains showing little evidence for aqueous processes up to the older hills, where rock and soil composition are drastically different. For the first 156 sols, the only evidence of water action was weathering rinds, vein fillings, and soil crust cementation by salts. The trenches of Sols 112–145 marked the first significant findings of increased concentrations of sulfur and magnesium varying in parallel, suggesting that they be paired as magnesium‐sulfate. Spirit's arrival at West Spur coincided with a shift in rock and soil composition with observations hinting at substantial amounts of water in Gusev's past. We used the Microscopic Imager data up to Sol 431 to analyze rock and soil properties and infer plausible types and magnitude of aqueous processes through time. We show the role played early by topography and structure. The morphology, texture, and deep alteration shown by the rocks in West Spur and the Columbia Hills Formation (CHF) suggest conditions that are not met in present‐day Mars and required a wetter environment, which could have included transport of sulfur, chlorine, and bromine in water, vapor in volcanic gases, hydrothermal circulation, or saturation in a briny fluid containing the same elements. Changing conditions that might have affected flow circulation are suggested by different textural and morphological characteristics between the rocks in the CHF and those of the plains, with higher porosity proxy, higher void ratio, and higher water storage potential in the CHF. Soils were used to assess aqueous processes and water pathways in the top layers of modern soils. We conclude that infiltration might have become more difficult with time.
Mössbauer mineralogy of rock, soil, and dust at Gusev crater, Mars: Spirit's journey through weakly altered olivine basalt on the plains and pervasively altered basalt in the Columbia Hills
Authors: Morris R. V. , Klingelhöfer G. , Schröder C. , Rodionov D. S. , Yen A. , Ming D. W. , de Souza P. A. , Fleischer I. , Wdowiak T. , Gellert R. , Bernhardt B. , Evlanov E. N. , Zubkov B. , Foh J. , Bonnes U. , Kankeleit E. , Gütlich P. , Renz F. , Squyres S. W. , Arvidson R. E.
Published: February 2006

The Mössbauer spectrometer on Spirit measured the oxidation state of Fe, identified Fe‐bearing phases, and measured relative abundances of Fe among those phases for surface materials on the plains and in the Columbia Hills of Gusev crater. Eight Fe‐bearing phases were identified: olivine, pyroxene, ilmenite, magnetite, nanophase ferric oxide (npOx), hematite, goethite, and a Fe3+‐sulfate. Adirondack basaltic rocks on the plains are nearly unaltered (Fe3+/FeT < 0.2) with Fe from olivine, pyroxene (Ol > Px), and minor npOx and magnetite. Columbia Hills basaltic rocks are nearly unaltered (Peace and Backstay), moderately altered (WoolyPatch, Wishstone, and Keystone), and pervasively altered (e.g., Clovis, Uchben, Watchtower, Keel, and Paros with Fe3+/FeT ∼ 0.6–0.9). Fe from pyroxene is greater than Fe from olivine (Ol sometimes absent), and Fe2+ from Ol + Px is 40–49% and 9–24% for moderately and pervasively altered materials, respectively. Ilmenite (Fe from Ilm ∼3–6%) is present in Backstay, Wishstone, Keystone, and related rocks along with magnetite (Fe from Mt ∼10–15%). Remaining Fe is present as npOx, hematite, and goethite in variable proportions. Clovis has the highest goethite content (Fe from Gt = 40%). Goethite (α‐FeOOH) is mineralogical evidence for aqueous processes because it has structural hydroxide and is formed under aqueous conditions. Relatively unaltered basaltic soils (Fe3+/FeT ∼ 0.3) occur throughout Gusev crater (∼60–80% Fe from Ol + Px, ∼10–30% from npOx, and ∼10% from Mt). PasoRobles soil in the Columbia Hills has a unique occurrence of high concentrations of Fe3+‐sulfate (∼65% of Fe). Magnetite is identified as a strongly magnetic phase in Martian soil and dust.
Dating ice flow change near the flow divide at Roosevelt Island, Antarctica, by using a thermomechanical model to predict radar stratigraphy
Authors: Martín Carlos , Hindmarsh Richard C. A. , Navarro Francisco J.
Published: February 2006

Radar‐detected internal layering contained in some ice divides shows upwarped arches termed Raymond bumps. The distribution of their amplitude with height can date the onset of divide flow, reflecting changes in the basin structure of the ice sheet. The distribution depends on rheology, surface geometry, accumulation rate, and temperature. Conway et al. (1999) used an isothermal parameterized ice flow model to estimate a date of 3200 years B.P., with no error estimate, for the onset of divide flow in Roosevelt Island, Ross Ice Shelf, which they associated with grounding line retreat of the West Antarctic Ice Sheet. No other retreat dating exists for an area of the Ross Ice Shelf distant from geological exposures. Employing a full thermomechanically coupled transient model, we use a direct search to determine which ice rheology best fits the observed bump distribution and surface profile, estimating the sensitivity of the dating to model parameters and exploring possible reasons for the observed asymmetry of the surface profile. Our main results are as follows: (1) A best estimate of the date of grounding line retreat near Roosevelt Island is 3000 years B.P., bounded by 2300 and 4200 years B.P. (2) Standard rheology (power n = 3) can only match the observed bump distribution for unrealistic isothermal models. (3) For thermomechanically coupled models a high power (n = 4) in Glen's law is required. (4) Low‐power rheologies and wind scouring cannot produce correct bump amplitude distributions. (5) Asymmetric accumulation cannot explain the observed asymmetry of the surface profile. (6) Modeling isochrones in flanking regions also indicates changes in flow around 3000 years B.P.
Partitioning evapotranspiration in sparsely vegetated rangeland using a portable chamber
Authors: Stannard David I. , Weltz Mark A.
Published: February 2006

A portable chamber was used to separate evapotranspiration (ET) from a sparse, mixed‐species shrub canopy in southeastern Arizona, United States, into vegetation and soil components. Chamber measurements were made of ET from the five dominant species, and from bare soil, on 3 days during the monsoon season when the soil surface was dry. The chamber measurements were assembled into landscape ET using a simple geometric model of the vegetated land surface. Chamber estimates of landscape ET were well correlated with, but about 26% greater than, simultaneous eddy‐correlation measurements. Excessive air speed inside the chamber appears to be the primary cause of the overestimate. Overall, transpiration accounted for 84% of landscape ET, and bare soil evaporation for 16%. Desert zinnia, a small (∼0.1 m high) but abundant species, was the greatest water user, both per unit area of shrub and of landscape. Partitioning of ET into components varied as a function of air temperature and shallow soil moisture. Transpiration from shorter species was more highly correlated with air temperature whereas transpiration from taller species was more highly correlated with shallow soil moisture. Application of these results to a full drying cycle between rainfalls at a similar site suggests that during the monsoon, ET at such sites may be about equally partitioned between transpiration and bare soil evaporation.
Bipolar carrier transport in a conjugated polymer by complex admittance spectroscopy
Authors: Poplavskyy Dmitry , So Franky
Published: February 2006

We report the bipolar transport properties of the LUMATION™ (Sumitomo Chemical) 1300 Series green-emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single-carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes, in combination with the analysis of current-voltage characteristics, provide evidence that the dual injection diodes operate in space-charge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual-carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual-carrier devices.
Extraction of strained-Si metal-oxide-semiconductor field-effect transistor parameters using small signal channel conductance method
Authors: Dalapati G. K. , Chattopadhyay S. , Driscoll L. S. , O’Neill A. G. , Kwa K. S. K. , Olsen S. H.
Published: February 2006

Channel conductance has been employed to extract several important parameters such as threshold voltage, gain, effective channel length, series resistance, and mobility for strained-Si metal-oxide-semiconductor field-effect-transistors fabricated on relaxed silicon-germanium virtual substrates with Ge composition up to 25%. Analytical models have been developed by taking into account the effect of strain (i.e., Ge composition) on these parameters. The low field mobility of the devices has been found to increase linearly up to a Ge composition of 25% in the virtual substrate. A modified channel conductance technique has been used to extract critical fields accurately. This has also been used to predict the dependence of mobility on electric field in a strained-Si device. The critical field for silicon devices has been found to be 65kVcm−1, while for strained-Si devices, it has been found to decrease from 62.5 to 30kVcm−1 with increasing Ge composition (15% to 25%) in the virtual substrate. The reported results are useful for the design and simulation of strained-Si devices.
Néel wall pinning on amorphous CoxSi1−x and CoyZr1−y films with arrays of antidots in the diluted regime
Authors: Pérez-Junquera A. , Rodríguez-Rodríguez G. , Vélez M. , Martín J. I. , Rubio H. , Alameda J. M.
Published: February 2006

The magnetization reversal process has been studied in amorphous magnetic films patterned with ordered arrays of antidots in the diluted limit (i.e., with small enough antidot density so that the original film anisotropy is maintained and the flux closure structures around each dot are independent from each other). The role of the material parameters in the final behavior has been analyzed comparing the results on films made of two different Co-based amorphous alloys, CoxSi1−x and CoyZr1−y, that present a similar intrinsic uniaxial anisotropy but have a different saturation magnetization. The patterned holes are found to act as weak pinning centers for the motion of the Néel walls involved in the reversal process which results in an enhancement of coercivity in certain angular ranges. However, they are only effective in the material with the lower saturation magnetization (CoxSi1−x) which can be related with the different relative sizes of the patterned holes and the Néel walls in each case.
Microstructure and nonbasal-plane growth of epitaxial Ti2AlN thin films
Authors: Beckers M. , Schell N. , Martins R. M. S. , Mücklich A. , Möller W. , Hultman L.
Published: February 2006

Thin films of the Mn+1AXn (MAX) phase (M: early transition metal; A:A-group element; X: C and/or N; n=1–3) Ti2AlN were epitaxially grown onto single-crystal MgO(111) and MgO(100) substrates by dc reactive magnetron cosputtering from Ti and Al targets in an Ar∕N2 gas mixture at a temperature of 690 °C. To promote the nucleation of the MAX phase, a fcc (Ti0.63Al0.37)N seed layer was deposited before changing to Ti2AlN growth parameters. The nucleation processes have been studied by real-time in situ specular x-ray reflectivity. Independent of substrate orientation, the seed layer shows no roughening until its final thickness of approximately 100 Å, indicating pseudomorphic layer-by-layer growth. The MAX phase shows heteroepitaxial layer-by-layer growth on MgO(111), with increased surface roughening up to approximately 200 Å, whereas on MgO(100) the growth mode changes to Volmer-Weber-type already after three monolayers. X-ray scattering in Bragg-Brentano geometry of the final, approximately 1000 Å thick, Ti2AlN film reveals lattice parameters of c=13.463Å and a=2.976Å on the MgO(111) substrate and c=13.740Å and a=2.224Å on the MgO(100) substrate. From pole figure measurements the orientational relationship between film and substrate lattice was determined to be MgO{111}⟨110⟩∕∕Ti2AlN{101¯2}⟨1¯21¯0⟩, regardless of the substrate orientation. This tilted, nonbasal-plane growth leads to a threefold grain orientation of Ti2AlN along the MgO⟨110⟩ directions and a polycrystalline morphology confirmed by cross-sectional transmission electron microscopy. The growth can be assumed to take place in a lateral step-flow mode, i.e., emerging low surface free-energy (0001) planes, on which arriving atoms can diffuse until finding a step where they are bound to A facets. This growth process is irrespective of orientational relationship between substrate and film. However, in the present low-temperature case the partitioning of arriving Al and Ti atoms during nucleation is suppressed, which as a result of interfacial adaptation between substrate and film induces standing a-type planes during growth.
Rotational spectroscopy and dipole moment of cis-cis HOONO and DOONO
Authors: Fry Juliane L. , Drouin Brian J. , Miller Charles E.
Published: February 2006

The rotational spectrum of cis-cis HOONO has been studied over a broad range of frequencies, 13–840 GHz, using pulsed beam Fourier-transform microwave spectroscopy and room-temperature flow cell submillimeter spectroscopy. The rotational spectrum of the deuterated isotopomer, cis-cis DOONO, has been studied over a subset of this range, 84–640 GHz. Improved spectroscopic constants have been determined for HOONO, and the DOONO spectrum is analyzed for the first time. Weak-field Stark effect measurements in the region of 84–110 GHz have been employed to determine the molecular dipole moments of cis-cis HOONO [μa=0.542(8)D,μb=0.918(15)D,μ=1.07(2)D] and DOONO [μa=0.517(9)D,μb=0.930(15)D,μ=1.06(2)D]. The quadrupole coupling tensor in the principal inertial axis system for the N14 nucleus has been determined to be χaa=1.4907(25)MHz,χbb=−4.5990(59)MHz,χab=3.17(147)MHz, and χcc=3.1082(59)MHz. Coordinates of the H atom in the center-of-mass frame have been determined with use of the Kraitchman equations, ∣aH∣=0.516Å and ∣bH∣=1.171Å. The inertial defects of HOONO and DOONO are consistent with a planar equilibrium structure with significant out-of-plane H atom torsional motion. Comparisons of the present results are made to ab initio calculations.
Characteristic of rapid thermal annealing on GaIn(N)(Sb)As∕GaAs quantum well grown by molecular-beam epitaxy
Authors: Zhao H. , Xu Y. Q. , Ni H. Q. , Zhang S. Y. , Wu D. H. , Han Q. , Wu R. H. , Niu Z. C.
Published: February 2006

Effect of rapid thermal annealing on photoluminescence (PL) properties of InGaAs, InGaNAs, InGaAsSb, and InGaNAsSb quantum wells (QWs) grown by molecular-beam epitaxy was systematically investigated. Variations of PL intensity and full width at half maximum were recorded from the samples annealed at different conditions. The PL peak intensities of InGaAs and InGaNAs QWs initially increase and then decrease when the annealing temperature increased from 600to900°C, but the drawing lines of InGaAsSb and InGaNAsSb take on an “M” shape. The enhancement of the PL intensity and the decrease of the full width at half maximum in our samples are likely due to the removal of defects and dislocations as well as the composition’s homogenization. In the 800–900°C high-temperature region, interdiffusion is likely the main factor influencing the PL intensity. In–N is easily formed during annealing which will prevent In out diffusion, so the largest blueshift was observed in InGaAsSb in the high-temperature region.
Simulation of the writing on the patterned optical phase-change recording media
Authors: Small Evan , Yang Yizhang , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: February 2006

Irregularities in the edge of the bit marks is one of the most critical sources of the noise that lead to timing jitter in optical phase change recording. The maximum linear bit density achievable at a given wavelength and lens numerical aperture is often limited by jitter. Jitter is largely determined by the combined optical, thermal, and crystallization properties of the medium and by the optical quality and recording strategy of the laser beam. Media with a patterned phase-change layer are proposed for controlling the mark edge jitter by making distinct mark edges. The preliminary simulation results from writing on the transverse and longitudinal patterns look promising in producing rectangular bit marks with distinct boundaries. The bit marks written on patterned media also have a smaller size compared to those written on continuous media. An interesting and unexpected result is the disappearance of the crescent-shaped trailing edge in all the bit marks on the patterned media, the shape and existence of which can have a great effect on the trailing edge jitter. Writing on grooved media has also been simulated for further comparison. In the present investigation a simulation code is developed using commercial finite element analysis software for the heat transfer simulation, with a custom-integrated crystallization model.
Influence of an inert background gas on bimetallic cross-beam pulsed laser deposition
Authors: Irissou Eric , Vidal François , Johnston Tudor , Chaker Mohamed , Guay Daniel , Ryabinin Anatoly N.
Published: February 2006

A cross-beam pulsed laser deposition (CBPLD) system operated at variable pressure in an inert (He) background atmosphere was used to deposit films from two dissimilar targets (Pt–Ru and Pt–Au). Using this setup, we showed that films with mixed Pt–Au and Pt–Ru composition can be prepared over the whole compositional range, from [Pt] = 0 to 100at.%. Films deposited at He pressure higher than 1.6Torr are fairly homogeneous and the standard deviation of the Pt concentration over the whole area of the deposit is less than 1at.%. Using a diaphragm located at the interaction zone between the two plasmas, a drastic reduction of the normalized droplet density was observed, from about 700×102cm−2nm−1 in conventional PLD to 6×102cm−2nm−1 in CBPLD. The deposition rate increases as the pressure is increased from vacuum to an optimal He pressure. The deposition rate decreases again for higher He pressure. The optimal operating conditions are P(He)=2Torr for Pt–Ru and P(He)=4Torr for Pt–Au. In these conditions, the deposition rates are, respectively, ∼32% and ∼22% of what they would be in conventional PLD. The behavior of the deposition rate with the He pressure is consistent with what can be concluded from a visual observation of the interaction of the plasma plumes at various pressures. A simple model considering the quadratic dependence of the velocity on the flow resistance of heavy particles in the rarefied light ambient particles is developed to understand the role of the background gas in the deposition rate. This model succeeds in predicting a maximum in the deposition rate versus He pressure curve, allowing us to get a better physical understanding of what is going on during the interaction between the two plasma plumes.
Photocurrent pattern formation in polymer/methanofullerene blends imaged by near-field scanning photocurrent microscopy
Authors: McNeill C. R. , Dastoor P. C.
Published: February 2006

The dimensional dependence of micron-sized current inhomogeneities in poly[2-methoxy-5-(2′-ehtylhexyloxy)-1,4-phenylene vinylene]/1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61 (MEH-PPV/PCBM) solar cells on processing conditions has been investigated. These current inhomogeneities typically consist of a central PCBM aggregate surrounded by a larger region of poor photocurrent production. For films spin coated from chlorobenzene, both the diameter of the current inhomogeneities and the size of the corresponding PCBM aggregates systematically increase with the time allowed for the film to dry. These observations indicate that the current inhomogeneities are a consequence of the nucleation and growth of the central PCBM cluster at the expense of PCBM from the surrounding area. In contrast to the results observed with chlorobenzene as the solvent, no micron-sized current inhomogeneities are observed using toluene as the solvent, despite the increased density of PCBM clusters in the film. The solubility of PCBM and the solvent volatility are identified as key parameters determining the formation of micron-sized current patterns. Also discussed is the influence of these current features on overall device performance, along with the influence of the film nanomorphology as processing conditions are changed.
Temperature-dependent photoluminescence from patterned InAs quantum dots formed using metalorganic chemical vapor epitaxy
Authors: Huffaker D. L. , Hains C. P. , Nuntawong N. , Xin Y. C. , Wong P. S. , Xue L. , Brueck S. R. J. , Lester L.
Published: February 2006

We analyze temperature-dependent photoluminescence (PL) behavior of patterned InAs∕GaAs quantum dots (PQDs) formed by selective area epitaxy using metalorganic chemical vapor deposition. The processing scheme, described here, yields an ensemble of electronically isolated PQDs with PL characteristics that significantly differ from self-assembled (SA) QDs since neither a wetting layer nor neighboring QDs are available for coupling. The isolated nature of the PQDs supports a non-Fermi (nonequilibrium) carrier distribution which yields very different PL characteristics compared to the Fermi (equilibrium) distribution of the SAQDs especially at temperatures >100K. Thus, the PQDs demonstrate a constant PL linewidth within the temperature range of 80–300K along with improved temperature stability of PL intensity in comparison to SAQDs. The increased temperature stability allowed by electronic isolation may prove very important for high speed, temperature-insensitive QD laser development.
Self-assembling of Mg and O isoelectronic impurities in ZnS
Authors: Elyukhin V. A. , Elyukhina O. V.
Published: February 2006

Self-assembling of Mg and oxygen isoelectronic impurities in ZnS is presented. The occurrence of the 1O4Mg tetrahedral cells is predicted in ZnS-rich MgxZn1−xOyS1−y (x⩾4y) in the ultradilute oxygen impurity limit. Under certain conditions that are estimated for the lower growth and higher annealing temperatures of 300 and 500°C, respectively, the alloys with the separated oxygen impurities surrounded by Mg atoms are more thermodynamically preferable than the random alloys. The origin of this phenomenon is a thermodynamic advantage of MgO and ZnS bonding over MgS and ZnO bonding and the smaller strain energy of the self-assembled alloys.
Superconductivity in polycrystalline boron-doped diamond synthesized at 20GPa and 2700K
Authors: Dubrovinskaia Natalia , Eska Georg , Sheshin Grigorii A. , Braun Hans
Published: February 2006

Bulk sample (∼7.5mm3) of boron-doped diamond containing 2.6(0.6)at.%B was synthesized by means of direct reaction between boron carbide and graphite in multianvil apparatus at 20GPa and 2700K. Electrical resistance of the sample of B-doped polycrystalline diamond was measured in the temperature interval from 10mK to 300K and revealed a transition to superconducting state at 2.4–1.4K. Our results imply that increase of synthesis pressure from 8–9GPa [Ekimov et al., Nature 428, 542 (2004)] to 20GPa does not significantly affect boron content in diamond but decreases the temperature of the transition to superconducting state. We observed sharpening of the temperature interval of the transition to superconducting state in magnetic field that may suggest that superconductivity in our samples could arise from filaments of zero-resistant material.
Linear ethanol sensing of SnO2 nanorods with extremely high sensitivity
Authors: Chen Y. J. , Nie L. , Xue X. Y. , Wang Y. G. , Wang T. H.
Published: February 2006

The SnO2 nanorods with a diameter down to 3nm are synthesized through a hydrothermal route and their sensing properties are investigated. The small size is confirmed by the results of x-ray diffraction, transmission electron microscope and Raman scattering spectrum. The sensitivity is up to 83.8 as the nanorod sensor is exposed to 300ppm ethanol vapor in air. Moreover, the linear dependence of the sensitivity on the ethanol concentration is observed for each of the 20 sensors. Compared with the measured results of 80–180nm tin oxide particles, such linear dependence is related to the small size effect.
Theoretical model for a tetrad of hydrogen bonds and its application to interpretation of infrared spectra of salicylic acid
Authors: Boczar Marek , Boda Łukasz , Wójcik Marek J.
Published: February 2006

Theoretical model of vibrational interactions in hydrogen-bonded salicylic acid dimer is presented which takes into account the adiabatic couplings between high- and low-frequency O–H and O⋯O stretching vibrations, resonance interactions between both intermolecular hydrogen bonds and between inter- and intramolecular hydrogen bonds, and Fermi resonance between the O–H stretching fundamental and the first overtone of the O–H in-plane bending vibrations. The model is used for theoretical simulation of the νs stretching bands of salicylic acid and its OD derivative at 300 K. The effect of deuteration is successfully reproduced by our model. Infrared, far infarared, Raman, and low-frequency Raman spectra of the polycrystalline salicylic acid and its deuterated derivative have been measured. The geometry and experimental frequencies are compared with the results of density-functional theory calculations performed at the B3LYP∕6-31++G**, B3LYP/cc-pVTZ, B3PW91∕6-31++G**, and B3PW91/cc-pVTZ levels. O–H, O–D, and O⋯O stretching frequencies are used in theoretical simulation of the νs stretching bands.
Operation of a segmented Hall thruster with low-sputtering carbon-velvet electrodes
Authors: Raitses Y. , Staack D. , Dunaevsky A. , Fisch N. J.
Published: February 2006

Carbon fiber velvet material provides exceptional sputtering resistance properties exceeding those for graphite and carbon composite materials. A 2kW Hall thruster with segmented electrodes made of this material was operated in the discharge voltage range of 200–700V. The arcing between the floating velvet electrodes and the plasma was visually observed, especially, during the initial conditioning time, which lasted for about 1h. The comparison of voltage versus current and plume characteristics of the Hall thruster with and without segmented electrodes indicates that the magnetic insulation of the segmented thruster improves with the discharge voltage at a fixed magnetic field. The observations reported here also extend the regimes wherein the segmented Hall thruster can have a narrower plume than that of the conventional nonsegmented thruster.
Study on nitrogenated amorphous carbon films prepared by unbalanced magnetron sputtering
Authors: Shi J. R.
Published: February 2006

Nitrogenated amorphous carbon (a-CNx) films were prepared by unbalanced magnetron sputtering (UBMS) at different N2∕Ar gas flow rate ratios and different bias voltages. The films were characterized using x-ray photoelectron spectroscopy, Raman scattering, nanoindenter, atomic force microscopy nanoscratch, and contact angle measurement. It was found that a negative bias of 150V is the optimal condition for the formation of sp3 bonded carbon atoms. As the N2∕Ar flow rate ratio changes from 0 to 0.47, the nitrogen to carbon ratio in deposited films increases from 0 to 0.22, and the sp3 fraction of carbon atoms decreases from 0.51 to 0.28. The pure carbon film has the highest sp3 faction of carbon atoms and therefore the highest hardness and the lowest scratching depth. Comparing to the films prepared by conventional magnetron sputtering, all the a-CNx films prepared by UBMS show a lower scratching depth. The a-CNx films have a hydrophilic characteristic with a surface free energy from 56.6to65.6mN∕m and a predominant polar component.
Optical properties of SrTiO3 thin films deposited by radio-frequency magnetron sputtering at various substrate temperatures
Authors: Ma J. H. , Huang Z. M. , Meng X. J. , Liu S. J. , Zhang X. D. , Sun J. L. , Xue J. Q. , Chu J. H. , Li J.
Published: February 2006

SrTiO 3 thin films were deposited on vitreous silica substrates at various substrate temperatures (300–700°C) by rf magnetron sputtering technique. The transition from amorphous phase to polycrystalline phase for the films occurred at the substrate temperatures of 300–400°C. Their optical properties were investigated by transmittance measurements. The fitting method was used to calculate the refractive index and the film thickness from the transparent region of the transmittance spectra. The refractive index increased and the film thickness decreased with the substrate temperatures increasing. The dispersion of the refractive index was studied by considering a single electronic oscillator model. The band gaps of the films were estimated from Tauc’s law and showed a decreasing tendency to that of the bulk SrTiO3 with the substrate temperatures increasing. These results provide some useful references for the potential application of SrTiO3 films in integrated optics devices.
Contributions to giant magnetoimpedance from different domain regions of Co68.15Fe4.35Si12.5B15 amorphous wire
Authors: Mandal K. , Sinha S. , Anil Kumar P.
Published: February 2006

The frequency dependence of magnetoimpedance (MI) of amorphous wire Co68.15Fe4.35Si12.5B15 has been studied in the presence of various tensile stresses up to 285MPa to understand the contributions to giant magnetoimpedance from different domain regions. The external stress affects MI of these materials to a large extent as magnetocrystalline anisotropy is absent and magnetoelastic anisotropy is the main source of anisotropy in these materials. At a particular frequency, a stress-induced anisotropy changes the domain structure, magnetization dynamics, and hence MI. Single peak MI characteristics obtained at lower frequencies (approximately a few kilohertz) are changed to a double-peak behavior with the application of a tensile stress or increase in frequency. Asymmetry between the two peaks has also been developed only by sending a dc of 5mA. Hysteresis loop measurement of amorphous wire at various frequencies and tensile stresses helps us understand the MI results.
Absorption cross sections and Auger recombination lifetimes in inverted core-shell nanocrystals: Implications for lasing performance
Authors: Nanda J. , Ivanov S. A. , Htoon H. , Bezel I. , Piryatinski A. , Tretiak S. , Klimov V. I.
Published: February 2006

We study inverted core-shell nanocrystals (NCs), in which a core of a wide-gap semiconductor (ZnSe) is overcoated with a shell of a narrower gap material (CdSe). Depending on the core radius and the shell thickness, these NCs can exhibit either type-I or type-II behavior. We show that these heterostructures can be used to significantly increase the absorption cross sections and simultaneously decrease the efficiency of Auger recombination compared to monocomponent CdSe NCs emitting at the same wavelength. These properties enhance the lasing performance of inverted core-shell structures and allow, in particular, efficient amplified spontaneous emission in the range of blue colors.
Lifetime-limited current in Cu-gate metal-oxide-semiconductor capacitors subjected to bias thermal stress
Authors: Lipp E. , Kohn A. , Eizenberg M.
Published: February 2006

Increased oxide conductance is widely observed in Cu-gate metal-oxide-semiconductor capacitors subjected to bias thermal stress. Prior to oxide breakdown, the increased conductivity enables the leakage of minority carriers from the Si inversion layer, resulting in permanent deep-depletion capacitance-voltage characteristics. Furthermore, under such conditions the minority-carrier generation statistics in the Si cannot be calculated from capacitance-time measurements. To quantify this phenomenon, a model is proposed, which relates oxide leakage current with the rate at which minority-charge carriers are generated in the depleted Si. Using this model, the minority-carrier generation statistics can be calculated from current and capacitance measurements. We show that the proposed model fits well with the experimental data and that the calculated generation parameters are within the expected range for Cu-affected Si.
Quantitative evaluation of bonding energy for the interfaces in Cu metallization systems
Authors: Kamiya Shoji , Suzuki Shigeori , Yamanobe Kiichiro , Saka Masumi
Published: February 2006

The toughness of two different interfaces in Cu metallization systems (Cu∕barrier metals and Cu∕cap layer) was evaluated by developed techniques. To establish the measurement technique at first, the effect of Cu film thickness on the evaluated toughness of the interface between Cu and barrier metal was examined. A small-scale yielding condition was realized even with ductile thin-film systems, and the toughness obtained was almost independent of the film thickness. The difference in the interface toughness among different Cu deposition techniques (sputtered and vacuum evaporated) was also quantitatively discussed. The method was then expanded to the Cu films as thin as those in the commercial integrated circuit. Finally, the toughness of interfaces between nanometer-scale cap layer materials and Cu was also evaluated by using a modified configuration of the specimens.
Particle growth in silane-hydrogen discharges
Authors: Kujundzic Damir , Gallagher Alan
Published: February 2006

The growth of silicon particles has been measured in silane-hydrogen radio-frequency (rf) discharges using a typical hydrogen/silane dilution ratio (20) and the pressure range (1.2–2.2Torr) used for the production of amorphous and microcrystalline silicon films and devices. By operating brief discharges without gas flow, the particle size is obtained from the afterglow diffusion and the particle density from the scattered-light intensity. These small-reactor data thus provide the expected particle size and density versus location-in a commercial large-area–isothermal-flowing-gas reactor. Particle growth rate is a strong function of pressure, whereas film growth rate is almost independent of pressure. Both growth rates are sensitive to rf voltage, although particle growth is more sensitive.
Statistical analysis of field electron emission from nanostructured carbon films
Authors: Park Kyung Ho , Lee Soonil , Koh Ken Ha
Published: February 2006

The field-emission properties of nanostructured carbon films (NSCFs), such as carbon nanotubes and carbon nanoparticles, were measured using a microtip and a large-area phosphor-screen anode. Except at small bias-voltage range, the current-versus-voltage curves measured with a large-area anode were fitted well to a simplified Fowler-Nordheim (FN) equation with a series-resistance effect. From the mapping of the turn-on field using a microtip anode, it was deduced that the field-enhancement factor β of NSCFs had an asymmetric distribution with a large-β tail. The asymmetric β distribution led to explanations of the slight curvature in FN plots at the low-voltage regime and of the exponential increase of emission-site densities dependent on the applied field.
Kinetics of low-temperature activation of acceptors in magnesium-doped gallium nitride epilayers grown by metal-organic vapor-phase epitaxy
Authors: Litwin-Staszewska E. , Piotrzkowski R. , Dmowski L. , Prystawko P. , Czernecki R. , Konczewicz L.
Published: February 2006

The annealing process of magnesium-doped gallium nitride (GaN:Mg) epilayers grown by metal-organic vapor-phase epitaxy was investigated by in situ measurements of electrical transport properties. The resistivity ρ and the Hall effect were studied as functions of time and temperature in the range of 20–600°C. A time-dependent p-type conductivity was observed at temperatures as low as 350°C. Activation energy of about Eact=1.5eV was found for the magnesium acceptor (Mg) from the isothermal measurements of ρ(t) kinetics in the range of 350–550°C. This value corresponds well to the theoretical prediction for the thermal dissociation of magnesium-hydrogen complexes (Mg–H). The annealing at temperatures higher than 600°C leads obviously to the activation of Mg acceptors, but the final resistivity of the sample is higher than the result obtained after annealing at 520°C. The ionization energy of electrically active Mg acceptor level of about EA=170meV was found from the temperature dependences of the resistivity ρ(T).
Electrical properties of multiple-layer structures formed by implantation of nitrogen or oxygen and annealed under high pressure
Authors: Antonova Irina V. , Misiuk Andrzej , Londos Charalampos A.
Published: February 2006

Silicon-on-insulator-like structures formed in either oxygen- or nitrogen-implanted silicon during anneals under atmospheric and enhanced hydrostatic pressure are characterized by means of electrical techniques (current-voltage and capacitance-voltage measurements). It was found that the application of high pressure (∼1GPa) stimulates the formation of a perfect top silicon layer and results in the degradation of the properties of the buried insulator. The latter effect is caused by defect accumulation in the buried insulator and leads to a decrease in the effective thickness of the insulator layer as extracted from capacitance-voltage measurements. Pressure-stimulated formation of electrically active centers (donors and acceptors) in the top silicon layer and substrate was found. The fixed charge in the oxide was found to be independent on the pressure applied during anneals, whereas the negative charge in the nitride increased with pressure.
The origin of x-ray luminescence from CdTe nanoparticles in CdTe∕BaFBr:Eu2+ nanocomposite phosphors
Authors: Chen Wei , Zhang Jun , Westcott Sarah L. , Joly Alan G. , Malm Jan-Olle , Bovin Jan-Olov
Published: February 2006

X-ray luminescence from CdTe nanoparticles is observed when CdTe nanoparticles are encapsulated into BaFBr:Eu2+ phosphors. In contrast, negligible x-ray luminescence is observed from the unencapsulated nanoparticles, either in solution or in solid form. The origin of the x-ray luminescence is attributed to the effective energy transfer from Eu2+ ions to CdTe nanoparticles in the nanocomposite materials. The x-ray luminescence of these nanocomposites is dose dependent and the emission wavelength is size adjustable which may allow use as a type of dosimeter for both in vitro and in vivo applications.
Electromagnetic forces in the air gap of a permanent magnet linear generator at no load
Authors: Nilsson K. , Danielsson O. , Leijon M.
Published: February 2006

The basis for the work is the slow speed energy conversion of ocean wave energy into electricity using a direct-drive three-phase permanent magnetized linear generator. One of several important issues is the normal forces in the air gap, which is critical when designing the support structure of the generator. The electromagnetic forces in the air gap have been analyzed using Maxwell stress tensor method implemented in a two- dimensional finite element code. Simplified analytic calculations are made in order to validate the results from the extensive computer calculations. The normal electromagnetic forces in the air gap, Fδ, are analyzed for a two-sided linear generator at no load. An unstable condition of the global force on the piston occurs due to the fast increasing normal force as the air gap width decreases. A horizontal displacement of the piston from a neutral position with 3mm air gap on both sides produces a resulting horizontal force on the piston, increasing with the displacement. A displacement of 1mm gives a resulting horizontal force on the piston of 5.5kN per pole and meter of core length, which is increased to 9kN per pole and meter of core length for a displacement of 1.5mm. Furthermore, the normal force varies due to cogging as the piston moves vertically. At a constant air gap width of 3mm the normal forces per pole are varying between 9.9 and 11.3kN∕m of core length as the piston is moving from one pole to the next.
Spectral analysis of a three-dimensional photonic quantum ring laser with a square microcavity
Authors: An Sung-Jae , Yoon Junho , Lee Jawoong , Kwon O'Dae , Minogin Vladimir G.
Published: February 2006

Three-dimensional photonic quantum ring lasers with a square microcavity were fabricated and their spectra were explained by combining two conditions: the off-normal Fabry-Pérot resonance and quadruple-bounced whispering-gallery mode. The angular distribution of the emission modes and their discrete wavelengths were in excellent agreement with a three-dimensional Rayleigh-Fabry-Pérot model. The three-dimensional model also showed that the slope of the spectral mode spacing and the value of the angular mode spacing as a function of the length of a square side L are inversely proportional to L2 and L, respectively.
Radiative recombination of Ar2+ and enhanced dissociation of O2 in a glow discharge
Authors: Al-Jalal Abdulaziz , Khan Mohammad Aslam
Published: February 2006

We have recently reported a significant enhancement in the atomization of O2 in an Ar–O2 glow discharge. During our investigations of energy transfer between Ar and O2, we have observed a strong continuum emission from Ar2+ in the 350–600 nm spectral region in a pure Ar discharge. We believe that capture of a free electron by the Ar2+ ion leading to the formation of excited dimer Ar2* is responsible for this continuum. The dimer subsequently dissociates into Ar atoms. We further observe that in the presence of small amount of O2, resonant charge-exchanging collisions yield O2+ that subsequently capture free electrons and dissociate yielding up to a 30-fold increase in atomic O compared with the O-atom yield in pure O2 discharge. In addition, the Ar line at 763.5 nm appears to be fed by the dissociating Ar2*.
Geometry-enhanced magnetoresistance of narrow Au∕InAs hybrid structures incorporating a two-dimensional electron system
Authors: Hoener Matthias , Kronenwerth Oliver , Heyn Christian , Grundler Dirk , Holz Matthias
Published: February 2006

We have investigated the magnetoresistance of metal-semiconductor hybrid structures at 4.2 K. The devices consisted of polycrystalline Au and an InAs-based heterostructure that hosted a high-mobility two-dimensional electron system. We have varied the electrical parameters and, in particular, the width-to-length ratio W∕L of the linear hybrid structures. The recently discovered extraordinary magnetoresistance effect is most pronounced for narrow devices with W∕L⩽0.05, consistent with our theoretical prediction. Relative resistance changes with a factor of 1000 are observed at 1 T. To achieve this an interface resistance of only 10−8Ωcm2 is a prerequisite. This can be prepared routinely by in situ cleaved edge overgrowth.
The nonmonotonic dose dependence of optically stimulated luminescence in Al2O3:C: Analytical and numerical simulation results
Authors: Chen R. , Pagonis V. , Lawless J. L.
Published: February 2006

Nonmonotonic dose dependence of optically stimulated luminescence (OSL) has been reported in a number of materials including Al2O3:C which is one of the main dosimetric materials. In a recent work, the nonmonotonic effect has been shown to result, under certain circumstances, from the competition either during excitation or during readout between trapping states or recombination centers. In the present work, we report on a study of the effect in a more concrete framework of two trapping states and two kinds of recombination centers involved in the luminescence processes in Al2O3:C. Using sets of trapping parameters, based on available experimental data, previously utilized to explain the nonmonotonic dose dependence of thermoluminescence including nonzero initial occupancies of recombination centers (F+ centers), the OSL along with the occupancies of the relevant traps and centers are simulated numerically. The connection between these different resulting quantities is discussed, giving a better insight as to the ranges of the increase and decrease of the integral OSL as a function of dose, as well as the constant equilibrium value occurring at high doses.
Study of superparamagnetic clusters in Co2+-exchanged NaY zeolite
Authors: Mukadam M. D. , Yusuf S. M. , Sasikala R. , Kulshreshtha S. K.
Published: February 2006

Magnetic properties of Co2+-exchanged NaY zeolite have been investigated using a dc magnetization technique. In the presence of low applied magnetic fields, a difference between zero-field-cooled and field-cooled magnetizations is observed below ∼3.4K. At T>5K, the M vs H∕T curves superimpose and these curves could be fitted well using the Langevin function, which yields a saturation moment of 3.2μB per Co2+ ion and a cluster moment of 6.66μB. This indicates that there are superparamagnetic clusters which are formed due to a positive exchange coupling among the Co2+ ions. For T<5K, the M vs H∕T curves do not superimpose on the curves for T>5K. The analysis of the low-temperature M vs H data suggests the building up of weak antiferromagnetic-type correlation between the superparamagnetic clusters at T<5K.
Silicide phase formation in Ni∕Si system: Depth-resolved positron annihilation and Rutherford backscattering study
Authors: Abhaya S. , Amarendra G. , Panigrahi B. K. , Nair K. G. M.
Published: February 2006

Silicidation in Ni∕Si thin-film junction has been investigated using depth-resolved positron annihilation spectroscopy (PAS) and Rutherford backscattering spectrometry (RBS). Identification of various silicide phases from an analysis of the positron annihilation parameters is consistent with the RBS results. Absence of vacancy defects in the silicide region is clearly brought out by PAS.