bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal variation of carbon monoxide in northern Japan: Fourier transform IR measurements and source‐labeled model calculations
Authors: Koike M. , Jones N. B. , Palmer P. I. , Matsui H. , Zhao Y. , Kondo Y. , Matsumi Y. , Tanimoto H.
Published: August 2006

Tropospheric carbon monoxide (CO) was measured throughout 2001 using ground‐based Fourier transform IR (FTIR) spectrometers at Moshiri (44.4°N) and Rikubetsu (43.5°N) observatories in northern Japan, which are separated by 150 km. Seasonal and day‐to‐day variations of CO are studied using these data, and contributions from various CO sources are evaluated using three‐dimensional global chemistry transport model (GEOS‐CHEM) calculations. Seasonal maximum and minimum FTIR‐derived tropospheric CO amounts occurred in April and September, respectively. The ratio of partial column amounts between the 0–4 and 0–12 km altitude ranges is found to be slightly greater in early spring. The GEOS‐CHEM model calculations generally reproduce these observed features. Source‐labeled CO model calculations suggest that the observed seasonal variation is caused by seasonal contributions from various sources, in addition to a seasonal change in chemical CO loss by OH. Changes in meteorological fields largely control the relative importance of various source contributions. The contributions from fossil fuel (FF) combustion in Asia and photochemical CO production have the greatest yearly averaged contribution at 1 km among the CO sources (31% each). The Asian FF contribution increases from winter to summer, because weak southwesterly wind in summer brings more Asian pollutants to the observation sites. The seasonal variation from photochemical CO production is small (±17% at 1 km), likely because of concurrent increases (decreases) of photochemical production and loss rates in summer (winter), with the largest contribution between August and December. The contribution from intercontinental transport of European FF combustion CO is found to be comparable to that of Asian FF sources in winter. Northwesterly wind around the Siberian high in this season brings pollutants from Europe directly to Japan, in addition to southward transport of accumulated pollution from higher latitudes. The influences are generally greater at lower altitudes, resulting in a vertical gradient in the CO profile during winter. The model underestimates total CO by 12–14% between March and June. Satellite‐derived fire‐count data and the relationship between FTIR‐derived HCN and CO amounts are generally consistent with biomass burning influences, which could have been underestimated by the model calculations.
Field experiments and numerical modeling of mass entrainment in snow avalanches
Authors: Sovilla Betty , Burlando Paolo , Bartelt P.
Published: August 2006

Snow entrainment alters the speed and hence the run‐out distance of avalanches, yet little is known about this significant process. We studied entrainment in snow avalanches using observations from (1) the Swiss Vallée de la Sionne test site, (2) the Italian Pizzac site, (3) catastrophic avalanches that occurred during the winter 1998–1999 in Switzerland, and (4) a medium‐sized spontaneous avalanche that occurred in 2000 in Davos, Switzerland. We determined mass and energy balances for 18 avalanche events. On average, the mass increased by a factor of 4. The primary mode of entrainment appeared to be frontal ploughing, although entrainment behind the avalanche front was also observed. Step entrainment, where a snow cover layer fractures and is entirely consumed by the avalanche, also occurred. Basal erosion was negligible. Mass availability and snow cover structure were the limiting factors governing entrainment. Other factors such as track topography and avalanche dimension played a secondary role. Using the experimental results, we introduced an entrainment model into a Saint‐Venant type flow model where the internal shear deformation of the avalanche is governed by a Bagnold law and the shear stress at the basal layer is treated as a Voellmy fluid. The model with entrainment not only improves the prediction of the velocities and flow heights in comparison to measurements, but also reproduces the variations in run‐out distances, which characterize avalanches with similar terminal velocities but different masses.
Continental response to active ridge subduction
Authors: Haschke M. , Sobel E. R. , Blisniuk P. , Strecker M. R. , Warkus F.
Published: August 2006

Apatite fission track ages from a ∼2000 m elevation transect from the Patagonian fold and thrust belt (47.5°S) allow us to quantify the denudational and orographic response of the upper plate to active ridge subduction. Accelerated cooling started at 17 Ma, predating the onset of ridge collision (14–10 Ma), and was followed by reheating between 10 and 6 Ma. Thermal modeling favors reheating on the order of 60°C at ∼28°C/Ma due to east‐migration of a slab window after the ridge‐trench collision. Final rapid cooling since 4 Ma of ∼18°C/Ma (geothermal gradient of 14°C/km) correlates with the presence of an orographic barrier and >1 km rock uplift in this region between 17.1 and 6.3 Ma. Increased precipitation and erosion since 4 Ma caused asymmetric exhumation, with 3–4 km on the leeside. Repeated crustal unroofing in response to active ridge subduction can explain the positive gravity anomaly south of the Chile Triple Junction.
Thermal annealing study of swift heavy-ion irradiated zirconia
Authors: Costantini Jean-Marc , Kahn-Harari Andrée , Beuneu François , Couvreur François
Published: August 2006

Sintered samples of monoclinic zirconia (α-ZrO2) have been irradiated at room temperature with 6.0GeV Pb ions in the electronic slowing down regime. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed unambiguously that a transition to the “metastable” tetragonal phase (β-ZrO2) occurred at a fluence of 6.5×1012cm−2 for a large electronic stopping power value (≈32.5MeVμm−1). At a lower fluence of 1.0×1012cm−2, no such phase transformation was detected. The back-transformation from β- to α-ZrO2 induced by isothermal or isochronal thermal annealing was followed by XRD analysis. The back-transformation started at an onset temperature around 500K and was completed by 973K. Plots of the residual tetragonal phase fraction deduced from XRD measurements versus annealing temperature or time are analyzed with first- or second-order kinetic models. An activation energy close to 1eV for the back-transformation process is derived either from isothermal annealing curves, using the so-called crosscut method, or from the isochronal annealing curve, using a second-order kinetic law. Correlation with the thermal recovery of ion-induced paramagnetic centers monitored by electron paramagnetic resonance spectroscopy is discussed. Effects of crystallite size evolution and oxygen migration upon annealing are also addressed.
Physical properties of lanthanum monosulfide thin films grown on (100) silicon substrates
Authors: Cahay M. , Garre K. , Wu X. , Poitras D. , Lockwood D. J. , Fairchild S.
Published: August 2006

Thin films of lanthanum monosulfide (LaS) have been deposited on Si (100) substrates by pulsed laser deposition. The films are golden yellow in appearance with a mirrorlike surface morphology and a sheet resistance around 0.1Ω∕◻, as measured using a four-probe measurement technique. The thin films are characterized by atomic force microscopy (AFM), x-ray diffraction (XRD) analysis, high resolution transmission electron microscopy (HRTEM), ellipsometry, and Raman spectroscopy. The root-mean-square variation of (1μm thick) film surface roughness measured over a 1μm2 area by AFM was found to be 1.74nm. XRD analysis of fairly thick films (micrometer size) reveals the growth of the cubic rocksalt structure with a lattice constant of 5.863(7)Å, which is close to the bulk LaS value. HRTEM images reveal that the films are comprised of nanocrystals separated by regions of amorphous material. Two beam bright field TEM images show that there is a strain contrast in the Si substrate right under the interface with the LaS film and penetrating into the Si substrate. This suggests that there is an initial epitaxial-like growth of the LaS film on the Si substrate that introduces a strain as a result of the 8% lattice mismatch between the film and substrate. Ellipsometry measurements of the LaS films are well characterized by a Drude-Lorentz model from which an electron concentration of about 2.52×1022cm−3 and a mobility around 8.5cm2∕Vs are derived. Typical crystalline LaS features were evident in Raman spectra of the films, but the spectra also revealed their disordered (polycrystalline) nature.
Gold nanorod extinction spectra
Authors: Prescott Stuart W. , Mulvaney Paul
Published: August 2006

Geometrical factors suitable for use in Mie–Gans theory are derived from discrete dipole aproximation generated spectra for a number of pseudonanorods permitting the rapid calculation of extinction spectra. It is shown that the rod width, rod end-cap geometry (flat, oblate spheroid, and sphere) and the rod size distribution all have a significant effect on the position of the peak absorbance. Moreover, it is shown that spectrometric characterization of nanorods is possible given an independent measure of rod width and suitable assumptions regarding the end-cap geometry and the form of the rod-length distribution; under such conditions the full width half maximum and the extinction peak uniquely determine the average rod length and the breadth of the distribution.
A photoemission model for low work function coated metal surfaces and its experimental validation
Authors: Jensen Kevin L. , Feldman Donald W. , Moody Nathan A. , O’Shea Patrick G.
Published: August 2006

Photocathodes are a critical component many linear accelerator based light sources. The development of a custom-engineered photocathode based on low work function coatings requires an experimentally validated photoemission model that accounts the complexity of the emission process. We have developed a time-dependent model accounting for the effects of laser heating and thermal propagation on photoemission. It accounts for surface conditions (coating, field enhancement, and reflectivity), laser parameters (duration, intensity, and wavelength), and material characteristics (reflectivity, laser penetration depth, and scattering rates) to predict current distribution and quantum efficiency (QE) as a function of wavelength. The model is validated by (i) experimental measurements of the QE of cesiated surfaces, (ii) the QE and performance of commercial dispenser cathodes (B, M, and scandate), and (iii) comparison to QE values reported in the literature for bare metals and B-type dispenser cathodes, all for various wavelengths. Of particular note is that the highest QE for a commercial (M-type) dispenser cathode found here was measured to be 0.22% at 266nm, and is projected to be 3.5 times larger for a 5ps pulse delivering 0.6mJ∕cm2 under a 50MV∕m field.
A note on electron confinement to a two-dimensional quantum disk
Authors: Tomita Isao , Suzuki Akira
Published: August 2006

The confinement properties of an electron to a two-dimensional quantum disk surrounded with a finite-height potential barrier are investigated. It is shown that since the confining barrier is distorted by a centrifugal potential arising from nonzero electron angular momentum, the electron can tunnel out through a thin part of the distorted barrier, which takes place when the radius of the disk is smaller than a critical radius. It is found that since the barrier for zero electron angular momentum is deformed by a centripetal potential characteristic of two dimensions, although no electron leaks out at any radii, bound-energy levels ascend as the disk radius decreases and become tied up at the top of the confining potential well, resulting in high density of states. Some experimental methods are outlined to observe those leaky and confining phenomena.
Optical spectroscopic analysis of selected area epitaxially regrown n+ gallium nitride
Authors: Wang D. , Park M. , Saripalli Y. N. , Johnson M. A. L. , Zeng C. , Barlage D. W. , Long J. P.
Published: August 2006

Gallium nitride (GaN) metal-insulator-semiconductor field-effect transistor with regrown by selected area metal organic vapor-phase-epitaxy n+ layer has been analyzed by micro-Raman and microphotoluminescence (micro-PL) spectroscopy. The material properties of the regrown n+ layer and the intrinsic layer in the gate region were extracted by using both spectroscopies. The free-carrier concentration of the regrown GaN layer and the intrinsic layer were determined by line shape analysis of the coupled plasmon-phonon mode to be 4.7×1017 and <3×1016cm−3, respectively. The inefficient substitutions of Ga vacancy (VGa) by Si result in relatively low carrier concentration in the regrown GaN layer. From the shift of E2(2) Raman peak and the near-band-edge (NBE) PL peak, the biaxial compressive stress in the intrinsic layer was found to be 0.4GPa. The residual stress was found to be fully relaxed in the regrown layer. The Si doping concentration in the regrown layer was determined to be 2×1019cm−3 based on the potential fluctuations introduced redshift of its NBE PL peak.
Theoretical investigation of a photoconductively switched high-voltage spark gap
Authors: Broks B. H. P. , Hendriks J. , Brok W. J. M. , Brussaard G. J. H. , van der Mullen J. J. A. M.
Published: August 2006

In this contribution, a photoconductively switched high-voltage spark gap with an emphasis on the switching behavior is modeled. It is known experimentally that not all of the voltage that is present at the input of the spark gap is switched, but rather a fraction of it drops across the spark gap. This voltage drop depends on the voltage that is present at the input of the spark gap with higher voltages resulting in a smaller drop. We have investigated two possible causes of this: the cathode fall and the resistance of the plasma arc. Using an analytical model of the cathode fall, we have established that the cathode fall can be excluded as the cause of the observed voltage drop. A one-dimensional, time-dependent non-local thermal equilibrium fluid model of the arc plasma has been made. Using this model, the plasma properties have been analyzed for various values of the switched current with emphasis on the conductivity. A good qualitative match between the observed and the simulated dissipation in the gap was found. This indicates that the finite arc resistance is the cause of the observed voltage drop.
Dielectric and ferroelectric properties of c-axis oriented strontium bismuth tantalate thin films applied transverse electric fields
Authors: Kotani K. , Kawayama I. , Tonouchi M. , Hotta Y. , Tabata H.
Published: August 2006

The in-plane dielectric and ferroelectric properties of c-axis oriented epitaxial strontium bismuth tantalate (SBT) thin films were investigated by interdigital surface electrode measurement. The four types of SBT thin films, which have various Sr∕Bi atomic ratios, were prepared on MgO substrates by pulsed laser deposition. The dielectric properties at kilohertz and megahertz frequencies were studied from 20to870K. Above room temperature, all the films show the phase transition. Sr0.99Bi1.61Ta2O9, Sr0.97Bi2.10Ta2O9, and Sr0.88Bi1.79Ta2O9 thin films show frequency dispersions near phase transition temperature. At low temperatures, dielectric and ferroelectric properties of Sr0.97Bi2.10Ta2O9 and Sr0.83Bi2.08Ta2O9 thin films were investigated. Both dielectric constant and remanent polarization show a tendency to decrease as temperature decreases, and the rapid change, which may indicate a phase transition, was observed in Sr0.97Bi2.10Ta2O9 near 80K.
Morphology dependence of cathodoluminescence from cubic boron nitride films deposited by chemical vapor deposition
Authors: Yu J. , Ong H. C. , Wong K. Y. , Lau W. M. , Matsumoto S.
Published: August 2006

Morphology dependence of cathodoluminescence from cubic boron nitride (cBN) films was investigated in detail. Bright emission images were observed at surface pits and edge area of the film. Raman measurements show that hexagonal boron nitride (hBN) grows in the pits and edge area. The emission intensity of cathodoluminescence from the hBN was found to be 40–1000 times greater than that from cBN. The characteristic emission peak at 2.08eV for cBN and that of hBN at 3.23eV were determined. The peak position fluctuates between the above two peaks depending on the hBN concentration in cBN films.
Fractal growth of sp3-bonded 5H-BN microcones by plasma-assisted laser chemical vapor deposition
Authors: Komatsu Shojiro , Kazami Daisuke , Tanaka Hironori , Moriyoshi Yusuke , Shiratani Masaharu , Okada Katsuyuki
Published: August 2006

It was reported previously that sp3-bonded 5H-BN films grown by plasma-assisted laser chemical vapor deposition (PAL-CVD) exhibited cone-shaped units with dimensions on the order of ∼10μm prevailing over the surface, and which contributed to excellent electron field emission properties. Here we show that these cone-shaped electron emitters form fractal distribution patterns on Si(100) substrates. The fractal samples exhibited nested cellular patterns with irregular polyhedral shapes scaling from 10mmto100μm, where the fractal dimensions estimated by box-counting method ranged from 1.064 to 1.623. Contrary to the Arrhenius law, the growth rates of the films in PAL-CVD decreased with increased substrate temperature, and which was consistently explained by a simple photochemically activated growth model. The growth rates of the films in PAL-CVD were 60 times faster than that by mere plasma-assisted chemical vapor deposition at the Ts of 300°C, which also supports the photochemical growth mechanism. A clear transition from uniform to fractal growth was found at a critical substrate temperature around 700°C, suggesting a strong nonlinearity inherent in this “forced-oscillatory photochemical vapor growth phenomenon.”
Surface electronic structure of Ca-deposited tris(8-hydroxyquinolato) aluminum studied by synchrotron radiation photoemission
Authors: Pi Tun-Wen , Liu Che-Hung , Hwang J.
Published: August 2006

Synchrotron radiation photoemission was used to investigate the interfacial electronic structure of calcium and tris(8-hydroxyquinolato) aluminum (Alq3). Two phases of interaction are identified, marked out by a critical thickness θc of approximately 7Å. Below θc, both N 1s and O 1s core-level spectra exhibit simultaneous charge-transfer components at binding energies lower than that of the original components. The induced O 1s component, which appears at 1.6eV above the original component, remains fixed in intensity below θc. However, the induced N 1s component develops at the expense of the original component, and becomes a sole peak at θc. No signs of an ionized state are seen below θc, with respect to the Ca 2p core-level spectra, suggesting that the interfaced Ca appears not as ionized atoms at the vicinity of the pyridyl ring, but rather a form of cluster. We propose that all N 1s, O 1s, and Ca 2p core-level results can be attributed to charge hopping between the pyridyl rings. Above θc, Ca begins to decompose the Alq3 molecules, and the core-level spectra of all constituent atoms exhibit decomposed components with binding energies even lower than those shown below θc. The decomposed components, accompanied by the appearance of a doubly ionized Ca 2p core level, are associated with direct bonds with Ca.
Evenly curved two-dimensional electron systems in rolled-up Hall bars
Authors: Mendach S. , Schumacher O. , Welsch H. , Heyn Ch. , Hansen W. , Holz M.
Published: August 2006

We present evenly curved two-dimensional electron systems in Hall-bar geometry. Expanding the method of self-rolling strained layers to fragile thickness modulated layer systems enables us to roll-up complete Hall-bar geometries into microscrolls. These structures represent model systems for the investigation of transport phenomena in sinusoidally modulated magnetic fields. The sinusoidal shape of the modulation and the tunability of the modulation phase are illustrated by comparing finite element calculations with transport data in the classical regime. Furthermore, we demonstrate the tunability of the carrier density in our structures using rolled-in metal gates.
In situ characterization of GaN quantum dot growth with reflection high-energy electron diffraction and line-of-sight mass spectrometry
Authors: Brown Jay S. , Koblmüller Gregor , Averbeck Robert , Riechert Henning , Speck James S.
Published: August 2006

We have investigated the Ga-adlayer mediated growth of GaN quantum dots at 707°C on AlN (0001) by simultaneous use of in situ reflection high-energy electron diffraction and line-of-sight quadrupole mass spectrometry during rf-plasma assisted molecular beam epitaxy (PA-MBE). We have found that the Ga-adsorbate coverage of 1.0 ML (monolayer) is critical in the mediation of a fundamental change in the GaN Stranski-Krastanov (SK) growth mode on AlN. When the Ga-adsorbate coverage was less than 1.0 ML, the SK transition occurred during GaN growth. For larger Ga-adsorbate coverages, the SK transition occurred after the desorption of the Ga coverage in excess of 1.0 ML. We performed variable GaN coverage growth experiments followed by desorption of the Ga adsorbate and subsequent GaN thermal decomposition to determine that the critical GaN coverage for the SK transition was less than 2.0 ML under Ga-droplet PA-MBE growth conditions.
Optical limiting in defective quadratic nonlinear photonic crystals
Authors: Zeng Yong , Chen Xiaoshuang , Lu Wei
Published: August 2006

By using a nonlinear transfer matrix method and an iteration method, we investigated an optical limiting in a defective quadratic nonlinear photonic crystal under strong pump-depletion conditions. Due to a giant enhancement of the second harmonic (SH) generation induced by the strong localization of light near the defective band, the progress of the energy exchange from the forward fundamental frequency (FF) channel to the SH channels (both forward and backward) and the backward FF channel is speeded up. The structure can therefore be used as a high-efficient compact optical power limiter. We have also studied the effects of two important parameters of the defective nonlinear periodic structure, the number of the periods and the nonlinear efficiency of the composite material, on the optical limiting.
Influence of argon and oxygen on charge-state-resolved ion energy distributions of filtered aluminum arcs
Authors: Rosén Johanna , Anders André , Mráz Stanislav , Atiser Adil , Schneider Jochen M.
Published: August 2006

The charge-state-resolved ion energy distributions (IEDs) in filtered aluminum vacuum arc plasmas were measured and analyzed at different oxygen and argon pressures in the range of 0.5–8.0mTorr. A significant reduction of the ion energy was detected as the pressure was increased, most pronounced in an argon environment and for the higher charge states. The corresponding average charge state decreased from 1.87 to 1.0 with increasing pressure. The IEDs of all metal ions in oxygen were fitted with shifted Maxwellian distributions. The results show that it is possible to obtain a plasma composition with a narrow charge-state distribution as well as a narrow IED. These data may enable tailoring thin film properties through selecting growth conditions that are characterized by predefined charge state and energy distributions.
Hydrogenic impurities in parabolic quantum-well wires in a magnetic field
Authors: An Xing-Tao , Liu Jian-Jun
Published: August 2006

The properties of a hydrogenic impurity in a parabolic GaAs quantum-well wire in the presence of the magnetic field are investigated using the finite-difference method within the quasi-one-dimensional effective potential model. The magnetic effects on the energies and binding energies of the ground and lowest excited states of a hydrogenic impurity in a parabolic GaAs quantum-well wire are studied for various parabolic potentials. The calculated results indicate that the interplay of the spatial confinement and the magnetic confinement of electrons in the quantum-well wires leads to complicated binding energies of the hydrogenic impurity, and high magnetic fields significantly increase the binding energies of the hydrogenic impurity in the case of weak spatial confinement.
Postbuckling of carbon nanotubes by atomic-scale finite element
Authors: Leung A. Y. T. , Guo X. , He X. Q. , Jiang H. , Huang Y.
Published: August 2006

This paper employs an atomic-scale finite element method (AFEM) to study the postbuckling behavior of carbon nanotubes (CNTs). The computed energy curves and critical strain for the (8, 0) single-walled CNT (SWNT) agree well with atomistic simulations. The AFEM is very fast and versatile owing to the efficiency of the finite element method. For the SWNT, the strain energy curves have obvious jumps at morphology changes, and during the smooth continuation stages of postbuckling, the strain energy varies approximately linearly with the strain. For the double-walled CNT, there are only small strain energy releases, and the strain energy also changes approximately piecewise linearly with the strain. The morphologies are obtained in detail. AFEM is computationally fast and is an alternative efficient way to study the postbuckling of CNTs.
Impedance spectroscopy study of strontium modified lead zirconate titanate ceramics
Authors: Sen Shrabanee , Choudhary R. N. P. , Tarafdar Abhijit , Pramanik P.
Published: August 2006

( Pb 0.97 Sr 0.03 ) ( Zr 0.05 Ti 0.95 ) O 3 nanocrystalline powder was prepared by a solution based chemical method. Preliminary x-ray diffractogram analysis of some aspects of crystal structure showed that a single-phase compound was formed exhibiting a tetragonal system. Impedance spectroscopy study showed the presence of both bulk and grain boundary effects in the material, which is also evident from the scanning electron microscope micrographs. The bulk conductivity indicates an Arrhenius-type thermally activated process. The ac conductivity spectrum obeyed the Jonscher power law. Modulus analysis indicated the possibility of hopping mechanism for electrical processes in the system with a nonexponential type of conductivity relaxation.
Optical absorption coefficients in two-dimensional semiconductors under strong magnetic field
Authors: Yu L. Y. , Cao J. C. , Zhang C.
Published: August 2006

We calculate the photon absorption coefficient of hot two-dimensional electrons in the presence of a strong magnetic field. The electrons interact strongly with the optical phonons and the acoustic phonons in quantum wells. The dependence of the optical absorption on the magnetic field is obtained by using the quantum mechanical kinetic theory. It is found that the photon absorption spectrum displays a local magnetophonon resonance. The magnetophonon absorption resulting from inelastic scattering between Landau levels is more pronounced at higher temperature. The effect of subband nonparabolicity on the absorption coefficient is also discussed.
A three-dimensional simulation of quantum transport in silicon nanowire transistor in the presence of electron-phonon interactions
Authors: Jin Seonghoon , Park Young June , Min Hong Shick
Published: August 2006

Based on the nonequilibrium Green’s function formalism, we have developed a three-dimensional (3D) simulation framework capable of handling electronic transport in nanoscale silicon devices within the effective mass and Hartree approximations. Using the deformation potential theory and the self-consistent Born approximation, we obtain the spatially local self-energy functions for the intravalley and intervalley phonon scattering mechanisms. To make the 3D simulation practicable, we reduce the computational complexity by using the mode space approach suitable for the device whose cross section is relatively uniform along the transport direction. We also obtain the expression for the phonon-limited low field mobility in the long channel limit from the linear response theory. As an application, we study the quantum transport of the silicon nanowire transistor whose channel length is 15nm in the ballistic limit and in the presence of the electron-phonon interactions. We can observe various effects of the electron-phonon interactions such as the reduction of the drain current, broadening of the local density of states, and the energy relaxation of the electrons injected from the source.
Improved ferromagnetism of (Zn0.93Mn0.07)O through rapid thermal annealing
Authors: Lee Sejoon , Shon Yoon , Lee Seung-Woong , Hwang Sun Jae , Lee Hye Sung , Kang Tae Won , Kim Deuk Young
Published: August 2006

After annealing at 900°C, the ferromagnetic properties of (Zn0.93Mn0.07)O thin films were dramatically improved. The resultant remanent magnetization (Mr) and Curie temperature (TC) were 1.17μB∕Mn and 83K. The improvement of ferromagnetism was confirmed to as resulting from the enhancement of magnetic anisotropy. This result is attributed to the improvement of crystallinity and the stabilization of unstably bonded Mn2+ ions by thermal treatments. These results suggest that ferromagnetism of (Zn1−xMnx)O thin films can be improved by modifying the crystal magnetic anisotropy through postgrowth thermal treatments.
Decomposition and metastable phase formation in the bulk metallic glass matrix composite Zr56Ti14Nb5Cu7Ni6Be12
Authors: Bracchi A. , Huang Y.-L. , Seibt M. , Schneider S. , Thiyagarajan P.
Published: August 2006

Decomposition in the undercooled liquid phase and crystallization during isothermal annealing in the glassy matrix of the bulk Zr56Ti14Nb5Cu7Ni6Be12 composite were investigated by x-ray diffraction, small angle neutron scattering (SANS), scanning electron microscopy, and transmission electron microscopy (TEM). Upon isothermal annealing near the glass transition temperature TEM images show the presence of quasicrystals, while SANS data exhibit an interference peak indicating a quasiperiodic arrangement of these metastable crystals. Samples annealed in the solid state show a transformation into the more stable Zr2 TM-type (TM=Nb,Cu,Ni,Ti) phases. These results have been discussed on the basis of a phase separation process that determines the formation of the metastable quasicrystalline phase that is in good agreement with the behavior of other known bulk metallic glass-forming systems.
Field-effect modulation of the transport properties of nondoped SrTiO3
Authors: Shibuya Keisuke , Ohnishi Tsuyoshi , Uozumi Takayuki , Sato Taisuke , Lippmaa Mikk , Kawasaki Masashi , Nakajima Kiyomi , Chikyow Toyohiro , Koinuma Hideomi
Published: August 2006

We have fabricated SrTiO3 (100) single crystal field-effect transistors with amorphous and epitaxial CaHfO3 gate insulator layers. The devices with amorphous insulator layers showed nearly temperature independent behavior. The transistors with epitaxial interfaces exhibited a large improvement over the amorphous devices. The field-effect mobility was found to increase at low temperature, reaching 35cm2∕Vs at 50K. This result shows that the carriers accumulated by the field effect on the SrTiO3 side of the gate interface behaved as would be expected for electron-doped SrTiO3. An insulator-metal transition, induced by field-effect doping, was observed in epitaxial SrTiO3-based transistors.
Study of the annealing kinetic effect and implantation energy on phosphorus-implanted silicon wafers using spectroscopic ellipsometry
Authors: Lioudakis Emmanouil , Christofides Constantinos , Othonos Andreas
Published: August 2006

In this work, we have studied the changes in the optical properties on crystalline silicon implanted wafers (1×1013–1×1016P+∕cm2) using an extensive ellipsometric analysis. The effects of implantation energy (20–180KeV) and subsequent isochronical annealing temperature (300–1100°C) on the electronic band structure of material are investigated. The evolution of pseudodielectric functions is studied using a temperature dependent multilayer model for each implantation dose and energy. The temperature evolution of integrated damage depth profile for each wafer is presented depicting the amorphous/crystalline transition temperatures. Finally, the critical implantation dose and energy of crystalline to amorphous silicon phase are given.
High-light-output scintillator for photodiode readout: LuI3:Ce3+
Authors: Birowosuto M. D. , Dorenbos P. , van Eijk C. W. E. , Krämer K. W. , Güdel H. U.
Published: August 2006

In this paper, we investigated the scintillation properties of LuI3:Ce3+. Radioluminescence, light output, energy resolution, and γ-scintillation decay are reported. We find an extremely high light output of 98000±10000photons∕MeV. LuI3:Ce3+ also gives a very high electron-hole (e-h) pair response when it is coupled with an avalanche photodiode (APD) (92000±9000e-hpairs∕MeV). With an APD, a best energy resolution (full width at half maximum over the peak position) of 3.3%±0.3% for 662keV γ quanta is observed. A combination of an extremely high light output and a good energy resolution makes LuI3:Ce3+ an ideal scintillator for radiation sensor applications. Some drawbacks due to the hygroscopicity and the difficult growth of LuI3:Ce3+ crystals are also discussed.
Distribution of local Seebeck coefficient in M∕T∕M and M∕T∕M∕T∕M (M=Cu or Ni and T=Bi or Bi0.88Sb0.12) composite materials
Authors: Yamashita Osamu , Odahara Hirotaka
Published: August 2006

The local Seebeck coefficient αl was measured at a step of 0.5mm along the cylindrical M∕T∕M and M∕T∕M∕T∕M (M=Cu or Ni and T=Bi or Bi0.88Sb0.12) composites welded with T, using two thermocouples set at an interval of 2mm, in order to investigate the reason why the resultant Seebeck coefficient α of these composites is enhanced significantly. When one probe is placed on T and another on metal M, αl of M∕T∕M has a local maximum much higher in absolute value than that of the intrinsic thermoelectric material T, while when both are put on T, αl was almost the same as those of thermoelectric materials T. As a result, the enhancement in the resultant α of composites was thus found to be attributed to an enhancement in αl in the region near the boundary of T, where the barrier thermo-emf is produced by a sharp temperature gradient generated at the interface. A similar phenomenon was also observed for touching M∕T composites. However, the resultant α of M∕T∕M∕T∕M was lower than that of M∕T∕M, so that the multilayering of the thermoelectric material has no effect on the enhancement in α. Of course, this increase in the resultant α of composites results in the improvement of the energy conversion coefficient when they are employed for thermoelectric generators.
Diffuse phase transition in BaTi1−xSnxO3 ceramics: An intermediate state between ferroelectric and relaxor behavior
Authors: Shvartsman V. V. , Kleemann W. , Dec J. , Xu Z. K. , Lu S. G.
Published: August 2006

Dielectric relaxation and polar structures of BaTi1−xSnxO3 ceramics, x=0.10–0.20, are investigated by means of dielectric spectroscopy and piezoresponse force microscopy. A transition regime between “normal” ferroelectric and relaxor behaviors is encountered. In the compositions with x=0.10, a complex domain pattern confirming the ferroelectric state is observed. Strong dielectric relaxation around Tm is attributed to domain wall motion. On the other hand, the dielectric spectra in the sample with x=0.20 are very similar to those observed in relaxor ferroelectrics. Analysis of the relaxation spectra at the intermediate concentration, x=0.15, reveals both domain wall response and an additional contribution related to mesoscale polar structures. The appearance of relaxor behavior in BaTi1−xSnxO3 is discussed within the framework of the random field model.
Measurement of the ion feature of collective Thomson scattering in collisionless plasmas
Authors: Olivares I. E. , Kunze H.-J.
Published: August 2006

It is demonstrated that the collisionless theory of Salpeter [Phys. Rev. 120, 1528 (1960)] can be fitted rather well to the ion feature of collective Thomson scattering on dense plasmas in equilibrium for elements up to argon.
Microwave plasma in hydrocarbon liquids
Authors: Nomura Shinfuku , Toyota Hiromichi , Mukasa Shinobu , Yamashita Hiroshi , Maehara Tsunehiro , Kuramoto Makoto
Published: August 2006

The generation of microwave plasma in liquid with vapor bubbles has been achieved and will soon be applied to high-speed chemical vapor deposition. Vapor bubbles are induced from an electrode by heating. The deposition rate of diamondlike carbon films depends on the pressure and the power of the microwave supply. Polycrystalline silicon carbide is synthesized on a silicon substrate in a mixture of n-dodecane and silicone oil. The dispersion of water droplets in liquid creates many pores on the silicon carbide films. The synthesis of carbon nanotubes can be achieved in liquid benzene.
Raman spectroscopy of (Mn, Co)-codoped ZnO films
Authors: Du C. L. , Gu Z. B. , Lu M. H. , Wang J. , Zhang S. T. , Zhao J. , Cheng G. X. , Heng H. , Chen Y. F.
Published: August 2006

Raman spectra of (Mn, Co)-codoped ZnO films were investigated as functions of laser line and temperature. It is shown that the Raman shifts for different phonon modes exhibit redshift with temperature increasing, which can be attributed to the anharmonic effect in the material. Strong resonant Raman spectra of multi-LO phonons were observed as well for the films with the exciting photon energy higher than the direct band gap. Compared with the Raman spectra for ZnO films, the Mn, Co codoping effect on the spectra is revealed by the presence of additional phonon modes at 275 and 642cm−1 and another intensive phonon mode at around 524cm−1. With postannealing, Raman intensity of these phonon modes decrease, owing to the incorporation of oxygen into the films. Origins of the different phonon modes in the spectra are discussed as well.
Melting and solidification study of as-deposited and recrystallized Bi thin films
Authors: Zayed M. K. , Elsayed-Ali H. E.
Published: August 2006

Melting and solidification of as-deposited and recrystallized Bi crystallites, deposited on highly oriented 002-graphite at 423K, were studied using reflection high-energy electron diffraction (RHEED). Films with mean thickness between 1.5 and 33 ML (monolayers) were studied. Ex situ atomic force microscopy was used to study the morphology and the size distribution of the formed nanocrystals. The as-deposited films grew in the form of three-dimensional crystallites with different shapes and sizes, while those recrystallized from the melt were formed in nearly similar shapes but different sizes. The change in the RHEED pattern with temperature was used to probe the melting and solidification of the crystallites. Melting started at temperatures below the bulk melting point of Bi, T0=544.5K, and extended over a temperature range that depended on the size distribution of the crystallites. The as-deposited 1.5 ML film started to melt at T0−50K and melted completely at T0−20K. For films with higher coverage, the size distribution was observed to spread over a wider range with a larger mean value, resulting in a shift in the melting temperature range towards higher temperatures. Due to the shift in size distribution to higher values upon recrystallization, the recrystallized Bi crystallites showed a melting temperature range higher than that of the as-deposited crystallites. For the investigated conditions, all films were completely melted below or at T0 of Bi. The characteristic film melting point, defined as the temperature at which the film melting rate with temperature is the fastest, showed a linear dependence on the reciprocal of the average crystallite radius, consistent with theoretical models. Of these models, the surface-phonon instability model best fits the obtained results. During solidification, the Bi films showed high amount of supercooling relative to T0 of Bi. The amount of liquid supercooling was found to decrease linearly with the reciprocal of the average crystallite size.
On the structure of simple molecular liquids SbCl5 and WCl6
Authors: Pusztai László , McGreevy Robert L.
Published: August 2006

Neutron diffraction measurements on liquid antimony pentachloride and tungsten hexachloride have been carried out using the Studsvik liquids and amorphous diffractometer (SLAD) at the Studsvik Neutron Research Laboratory. The corrected structure factors have been interpreted by means of reverse Monte Carlo modeling which provides large structural models, containing thousands of atoms, that are consistent with the experimental data within their uncertainties. From these models, partial structure factors and pair correlation functions can be calculated. It is demonstrated that the intramolecular structure can be determined on the basis of data extending up to 10Å−1. SbCl5 is found to have a trigonal bipyramidal shape in the liquid, while liquid WCl6 consists of octahedral molecules. The intermolecular structure of liquid SbCl5 and WCl6 seems to be determined largely by steric effects (excluded volume and molecular shape).
In situ stress measurements in zirconium and zirconium oxide films prepared by direct current sputtering
Authors: Drese Robert J. , Wuttig Matthias
Published: August 2006

The evolution of stress during growth of thin zirconium and zirconium oxide films deposited from a metallic target using direct current magnetron sputtering has been analyzed in situ. The oxygen flow during the deposition was varied to obtain films with different stoichiometries ranging from metallic zirconium to fully stoichiometric zirconium oxide. The stresses in the metallic films depend strongly on the pressure during deposition. Films created at low pressure possess tensile stresses in the beginning of growth, which turn highly compressive with increasing film thickness. Films created at high pressures show only tensile stresses similar to evaporated metals of low mobility. The transition between metallic and oxidic zirconium films has been analyzed. The compressive stresses in the metallic film turn tensile once low amounts of oxygen are let into the chamber. This behavior is related to a structural change of the zirconium film, which was confirmed by x-ray analysis. Upon further increasing oxygen flow, the tensile stresses turn compressive again.
Operation of metallic base transistors with fullerene emitter
Authors: Rossi Lucieli , Meruvia Michelle S. , Hümmelgen Ivo A. , Schwarzacher Walther , Pasa André A.
Published: August 2006

Hybrid organic-inorganic metal-base transistors with C60 fullerene emitter, metallic polymer base layer, and n-Si collector are straightforward to fabricate and show common-base current gains up to 1.0. Ag contacts to the C60 layer and a reduction in the latter’s thickness lead to a significant performance improvement compared to previously reported devices. Two-terminal electrical measurements suggest that the devices function by charge transfer across a rectifying C60∕Si junction formed in naturally occurring holes in the base layer and confirm the presence of barriers at the C60/metal and metal/Si junctions.
Improved liquid crystals for vertical alignment applications
Authors: Chen Cheng , Bos Philip J. , Kim Julie , Li Quan , Anderson James E.
Published: August 2006

Liquid crystals with a large negative dielectric anisotropy are difficult to align vertically on silicon oxide surfaces and sometimes even on polyimides. An interesting method has been found to generate high quality vertical alignment by doping the host liquid crystal with materials that have a cyanogroup along their long molecular axis. The effect is explained by considering both long range and short range interactions between liquid crystal and the alignment layer. Using this method we propose a way to design new liquid crystal mixtures with large negative dielectric anisotropy that have improved aligning ability for applications requiring vertical alignment. The method also allows for increased birefringence.
Itinerant-electron metamagnetic transition and giant magnetocaloric effect in La0.8Ce0.2Fe11.4Si1.6 compound
Authors: Xu Chao , Li Guo-dong , Wang Li-gang
Published: August 2006

The itinerant-electron metamagnetic (IEM) transition and magnetocaloric effects (MCE’s) in the La0.8Ce0.2Fe13−xSix (x=1.6,1.4,1.2,1.0) compounds have been investigated by x-ray powder diffraction and magnetic measurements. The La0.8Ce0.2Fe11.4Si1.6 compound exhibits giant values of the isothermal magnetic entropy change ΔSM around the Curie temperature TC∼186K in low magnetic fields. The maximum value ∣ΔSM∣max∼78.29J∕kgK is under a field of 3T. Such large MCE’s are attributed to the sharp change of the magnetization, the field-induced IEM transition and a strong temperature dependence of the critical field BC. The substitution of Ce for part of La in La0.8Ce0.2Fe11.4Si1.6 increases the value of a(T)c(T)∕b(T)2 and enhances the property of IEM.
Maximizing uniaxial tensile strain in large-area silicon-on-insulator islands on compliant substrates
Authors: Peterson R. L. , Hobart K. D. , Yin H. , Kub F. J. , Sturm J. C.
Published: August 2006

Recently we have demonstrated a process for generating uniaxial tensile strain in silicon. In this work, we generate uniaxially strained silicon and anisotropically strained silicon germanium on insulator with strain in both ⟨100⟩ and ⟨110⟩ in-plane directions. The strain is uniform over fairly large areas, and relaxed silicon-germanium alloy buffers are not used. The magnitude of uniaxial strain generated by the process is very dependent on the in-plane crystal direction, and can be modeled accurately using the known mechanical properties of silicon and germanium. A maximum uniaxial silicon strain of 1.0% in the ⟨100⟩ direction is achieved. Numerical simulations of the dynamic strain generation process are used to identify process windows for achieving maximum uniaxial silicon strain for different structural geometries.
A comparative molecular simulation study of the glass former ortho-terphenyl in bulk and freestanding films
Authors: Ghosh Jayeeta , Faller R.
Published: August 2006

We performed molecular dynamics simulations of the low-molecular weight organic glass former ortho-terphenyl in bulk and freestanding films. The main motivation is to provide molecular insight into the confinement effect without explicit interfaces. Based on earlier models of ortho-terphenyl we developed an atomistic model for bulk simulations. The model reproduces literature data both from simulations and experiments starting from specific volume and diffusivity to mean square displacement and radial distribution functions. After characterizing the bulk model we form freestanding films by the elongation and expansion method. These films give us the opportunity to study the dynamical heterogeneity near the glass transition through in-plane mobility and reorientation dynamics. We finally compare the model in bulk and under confinement. We found qualitatively a lower glass transition temperature for the freestanding film compared to the bulk.
Broadband quasi-phase-matched second-harmonic generation in a nonlinear photonic crystal
Authors: Tomita Isao , Asobe Masaki , Suzuki Hiroyuki , Yumoto Junji , Yoshikuni Yuzo
Published: August 2006

We analyze the properties of quasi-phase-matched second-harmonic generation (SHG) from a defect waveguide in photonic-crystal (PhC) slabs embedded in a periodically χ(2) inverted material with a collinear beam configuration. We show that by controlling the material dispersion with the structural dispersion of a defect waveguide in PhC slabs of infinite height, it is possible to realize a much wider frequency range for quasi-phase-matched SHG than without the PhC structure. Also, taking the fabrication of actual devices into consideration, we examine the case for PhC slabs of finite height and show that, although guided modes are index confined in the vertical direction (while they are confined by the PhC structure in the horizontal direction), the effect that the PhC structure has on the broadening of the frequency range remains and that the broadened range can be comparable to that for the PhC slabs of infinite height if appropriate structural parameters are taken.