bluuebunny/crossref_metadata_2025 huggingface dataset:
The relationship between asthma and allergic rhinitis: exploring the basis for a common pathophysiology
Authors: Vignola A. M. , Chanez P. , Bousquet J.
Published: December 2004

Most patients with asthma also have rhinitis, and the same inflammatory cells and mechanisms are present in bronchial and nasal mucosa, thus leading to the concept of ‘one airway, one disease’. This concept is further substantiated by evidence of nasal inflammation in asthma, and bronchial inflammation and hyperresponsiveness in rhinitis. Endobronchial allergen challenge induces nasal and bronchial symptoms as well as reductions in pulmonary function and nasal patency. Likewise, treating rhinitis can improve the symptoms of asthma. There are some notable pathophysiological differences between the nose and the bronchi, for example airway remodelling appears to be less extensive in the nasal mucosa than in the bronchial mucosa. But, in spite of this, it is widely recognized that interrelated mechanisms contribute across the asthma–rhinitis disease spectrum. Of particular note is that the same pro‐inflammatory mediators (e.g. cysteinyl leukotrienes, cytokines, histamine) are involved in nasal and bronchial inflammation, in patients with rhinitis and asthma. It appears there are ‘bidirectional’ relationships between nasal and bronchial inflammation, and that biological events occurring in the nose or lung promote widespread responses, thus mimicking a systemic disease.
Restored Top Carnivores as Detriments to the Performance of Marine Protected Areas Intended for Fishery Sustainability: a Case Study with Red Abalones and Sea Otters
Authors: Fanshawe Samantha , Vanblaricom Glenn R. , Shelly Alice A.
Published: December 2004

Abstract: Marine protected areas are possible solutions to the problems of protecting the integrity of marine ecosystems and of sustaining harvested marine populations. We report demographic data for red abalones (   Haliotis rufescens ) at nine sites along the California coast. Six of our sites are within marine protected areas, and four of those six sites are occupied by sea otters (   Enhydra lutris ). Sea otters are known abalone predators and are believed to have an important role in facilitating biodiversity within coastal kelp forest communities along the North Pacific Rim. We asked whether marine protected areas intended to conserve ecosystems are compatible with use of marine protected areas for abalone fishery sustainability. We found that both sea otters and recreational harvest alter the density, size distribution, and microhabitat distribution of red abalones in qualitatively similar ways. Red abalone populations in marine protected areas outside the current sea otter range have higher density, are composed of larger individuals, and occur in more‐open microhabitats compared with populations in locations lacking sea otters but subject to harvest and with populations in locations with sea otters. The effects of sea otters are stronger than the effects of harvest. Characterization of harvest effects on density may be confounded by other uncontrolled factors. We conclude that coastal marine protected areas off California cannot enhance abalone fisheries if, in the interest of ecosystem integrity, they also contain sea otters. Where restored top carnivores limit the sustainability of commodity harvest, it may be possible to resolve conflicts with two categories of spatially segregated, single‐use marine protected areas, one focusing on ecosystem restoration and the other on fishery development.
Individual, Population, Community, and Ecosystem Consequences of a Fish Invader in New Zealand Streams
Authors: Townsend Colin R.
Published: December 2004

Abstract: Knowledge of the population biology of invading species will often be necessary to develop effective management procedures and policies. But because invaders can have unexpected indirect effects in food webs, invasion ecologists need to integrate processes at the population level and other ecological levels. I describe a series of coordinated studies in New Zealand streams that address the effect of an exotic fish on individual behavior, population, community, and ecosystem patterns. Such case studies are important as an aid to the formulation of policy about invasions that are especially likely to become problematic. At the individual level, grazing invertebrates showed changes in behavior as a result of the introduction of brown trout ( Salmo trutta), a predator that exerts a very different selection pressure than do native fish. At the population level, trout have replaced nonmigratory galaxiid fish in some streams but not others, and have affected the distributions of crayfish and other large invertebrates. At the community level, trout have suppressed grazing pressure from invertebrates and are thus responsible for enhancing algal biomass and changing algal species composition. Finally, at the ecosystem level, essentially all annual production of invertebrates is consumed by trout ( but not by galaxiids), and algal primary productivity is six times higher in a trout stream. This leads, in turn, to an increased flux of nutrients from the water to the benthic community. The trout invasion has led to strong top‐down control of community structure and ecosystem functioning via its effects on individual behavior and population distribution and abundance. Particular physiological, behavioral, and demographic traits of invaders can lead to profound ecosystem consequences that managers need to take into account.
The use of electrical pulses to study the physics of bilayer organic light-emitting diodes
Authors: Pinner D. J. , Friend R. H. , Tessler N.
Published: December 2004

We present detailed experimental and theoretical analysis for both constant-wave and pulsed excitation for a variety of real bilayer organic light-emitting diodes (LEDs). We find from experiment and simulation that the recombination zone may be moved about the polymer-polymer heterojunction as a function of the applied voltage. We suggest a method for spectrally resolving the emission of both polymers of a bilayer LED as a function of time, and show that these results are in good agreement with time-dependent simulation results. The simulation model takes into account both the discontinuities in energy levels and mobilities across the polymer-polymer heterojunction.
On the Si–SiO2 interface trap time constant distribution in metal-oxide-semiconductor transistors
Authors: Manéglia Y. , Rahmoune F. , Bauza D.
Published: December 2004

The reliability of a charge pumping (CP) technique proposed recently, which allows the extraction of the Si–SiO2 interface trap concentration profiles in metal-oxide-semiconductor transistors, from fast to slow traps, is discussed. The shape of the trap concentration profiles measured, the values of the trap cross section extracted, and the integration of the trap profiles, which should give the interface trap density obtained using the conventional CP technique, are discussed with regard to the trap filling function variation and to surface-potential fluctuations. Then, the influence, on these profiles, of both carrier emission, which is neglected in the model used for calculating the profiles, and of the source and drain regions (S/D-R) of the devices, where the threshold and flatband voltages are different from those in the central region of the channel, is investigated. It is shown that carrier emission does not impact on the trap profiles and that the trap time constant distribution measured does not originate from the S/D-R of the devices. A way to detect a significant contribution of these regions to the charge pumping current measured is proposed. Finally, a comparison with noise spectroscopy is carried out. The results obtained using the two techniques agree very well.
Computational analysis of ionic polymer cluster energetics
Authors: Weiland Lisa Mauck , Leo Donald J.
Published: December 2004

In recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model has been developed to predict the equilibrium state of a single cluster of an ionomeric polymer with cluster morphology. No assumptions are made regarding the distribution of charge or the shape of the cluster. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion–ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Expressions are developed to directly account for forces imposed on ions due to ion-cluster surface interaction. Results suggest that ion pairing is rarely complete; this in turn suggests that the classic assumptions will tend to underpredict electromechanical actuation response.
Atomistic simulation of modulus deficit in an aggregate of metal spheres
Authors: Read David T.
Published: December 2004

This paper reports molecular-dynamics modeling of the elastic behavior of a self-assembled aggregate of perfect face-centered-cubic crystal spheres, a morphology suggested by recent experimental observations on thin-film copper electrodeposits. Results of molecular-dynamics calculations on the elastic behavior of nanorods, chains of nanospheres, and self-assembled arrays of nanospheres are presented; an embedded-atom model potential incorporating substantial elastic anisotropy was used. The variety of geometries modeled helped to distinguish between effects of elastic anisotropy and effects of morphology. The results show that a self-assembled aggregate of spheres has a Young’s modulus tens of percent lower than bulk material, while its density is only a few percent below bulk.
Thermal-wave nondestructive evaluation of cylindrical composite structures using frequency-domain photothermal radiometry
Authors: Wang Chinhua , Mandelis Andreas , Liu Yue
Published: December 2004

In this paper, thermal-wave diagnostics by means of laser infrared photothermal radiometry (PTR) have been used for quantitative nondestructive evaluation of cylindrical composite structures. To quantitatively evaluate the thermal-wave field of a cylindrical composite material, the Green function corresponding to the composite structure and the PTR measurement scheme has been developed and subsequently the thermal-wave field has been derived. Furthermore, the characteristics of the thermal-wave field for two cases of practical interest, i.e., a cylindrical material with a surface coating and a cylindrical tube filled with a low thermal-conductivity fluid medium inside, are discussed. Experimental results from a stainless-steel (AISI 302) cylinder are used to validate the theoretical model.
Cd
2
+
∕
N
H
3
-treatment of Cu(In,Ga)(S,Se)2: Impact on the properties of ZnO layers deposited by the ion layer gas reaction method
Authors: Bär M. , Bloeck U. , Muffler H.-J. , Lux-Steiner M. C. , Fischer Ch.-H. , Giersig M. , Niesen T. P. , Karg F.
Published: December 2004

Cu ( In , Ga ) ( S , Se ) 2 - (“CIGSSe”) based solar cells with a ZnO layer deposited by the ion layer gas reaction (ILGAR) method yield superior efficiencies (15.0%) than the references with a chemical bath-deposited CdS buffer (14.1%). However, this high performance is only reached if the absorber is pretreated in a Cd2+- and aqueous ammonia-containing bath prior to the ILGAR-ZnO deposition. The photovoltaic as well as the dark device parameters are strongly influenced by this treatment. Scanning and transmission electron microscopy (TEM) as well as x-ray diffraction measurements reveal a different morphology and structure of ILGAR-ZnO layers on top of Cd2+∕NH3-treated and on as-deposited absorbers, indicating a considerably modified absorber surface. By energy dispersive x-ray analysis in the TEM, Cd could only be identified at the ILGAR-ZnO∕Cd2+∕NH3-treated-CIGSSe interface of the respective cross sections, if the absorber was treated in a bath with an atypically high Cd2+-concentration. In this case a Cd-containing thin layer between ZnO and CIGSSe was observed in TEM images.
Optothermal depth profiling by neural network infrared radiometry signal recognition
Authors: Ravi Jyotsna , Lu Yuekai , Longuemart Stéphane , Paoloni Stefano , Pfeiffer Helge , Thoen Jan , Glorieux Christ
Published: December 2004

The feasibility of a neural network radiometric photothermal depth profiling method is verified using well-defined artificial samples with varying optical properties across the layers. The signal calculation model is shown to be accurate and the neural network approach to solve the inverse problem is shown to be feasible. Both from simulated and experimental radiometric signals, accurate reconstructions are obtained for heat source and optical-absorption coefficient profiles.
Measurement of the spatiotemporal surface charge distribution in an ac plasma display cell using Pockels effect
Authors: Jeong D. C. , Bae H. S. , Whang K. W.
Published: December 2004

We measured the surface charge distribution in a coplanar type alternating current plasma display panel cell by the longitudinal electro-optic amplitude modulation method with BSO (Bi12SiO20) single crystal. The effects of the initialization condition were investigated to take care of the errors coming from the charge relaxation phenomena of the BSO crystal. Using BSO single crystal as the dielectric layer, the two-dimensional spatiotemporal surface charge distribution was successfully measured in a discharge cell with a discharge gas of neon and xenon 4% at the pressure of 100torr driven by square-type sustaining pulses. The temporal behavior of the surface charge is compared with the simulated result and the measurement of the infrared light emission from the discharge. The positive and negative surface charges show somewhat different spatiotemporal characteristics.
Generation of ferroelectric domains in films using atomic force microscope
Authors: Molotskii M.
Published: December 2004

Kinetics of domain formation in ferroelectric films subjected to electric field of atomic force microscope (AFM) is considered for a case of low reversal voltage. Dependence of equilibrium domain sizes on AFM and film parameters is defined. It is shown that formation of domains is possible if the applied voltage exceeds some threshold value. Above this threshold lateral sizes of the domains increase proportionally to the voltage. Dynamic equations of the domain wall motion during the domain formation in films are constructed and solved. For films having high activation fields the domain radius grows logarithmically with time. The time of the domain formation is defined. The calculated results are in agreement with experiments on lead zirconate titanate, lithium tantalate, and lithium niobate films. Kinetics of the domain growth in films with low activation fields is predicted.
Growth of vacuum evaporated ultraporous silicon studied with spectroscopic ellipsometry and scanning electron microscopy
Authors: Kaminska Kate , Amassian Aram , Martinu Ludvik , Robbie Kevin
Published: December 2004

Using a combination of variable-angle spectroscopic ellipsometry and scanning electron microscopy, we investigated the scaling behavior of uniaxially anisotropic, ultraporous silicon manufactured with glancing angle deposition. We found that both the diameter of the nanocolumns and the spacing between them increase with film thickness according to a power-law relationship consistent with self-affine fractal growth. An ellipsometric model is proposed to fit the optical properties of the anisotropic silicon films employing an effective medium approximation mixture of Tauc-Lorentz oscillator and void. This study shows that the optical response of silicon films made at glancing incidence differs significantly from that of amorphous silicon prepared by other methods due to highly oriented nanocolumn formation and power-law scaling.
Simulation of heterojunction organic thin film devices and exciton diffusion analysis in stacked-hetero device
Authors: Kamohara Itaru , Townsend Mark , Cottle Bob
Published: December 2004

A two-dimensional device simulation methodology for organic heterojunction thin film devices has been developed. Multilayer organic light emitting diodes, organic thin film heterojunction field effect transistors, and stacked heterojunction organic complementary devices were simulated. Heterojunction organic layer devices have been analyzed using a two-dimensional simulator with heterointerface models and organic material specific models. The stacked heterojunction organic double carrier device exhibits both horizontal and vertical carrier flow in the organic thin film. This unique dual-directional carrier flow shows efficient electron-hole recombination resulting in exciton generation in the organic heterojunction layers. Furthermore, the enhanced behavior of the generated excitons has been analyzed using a self-consistent exciton diffusion model. The vertical (thickness) diffusion of the excitons and the lateral (along heterointerface) diffusion (accompanied by exciton hopping) were simulated. The exciton diffusion model is applicable to electroluminescent characteristics in organic devices. This feature is one of the essential differences between the present model for high-injected polymer devices and conventional drift-diffusion transport in nonpolymer semiconductor devices.
Influence of pulsed laser deposition growth conditions on the thermoelectric properties of Ca3Co4O9 thin films
Authors: Eng Hank W. , Prellier W. , Hébert S. , Grebille D. , Méchin L. , Mercey B.
Published: December 2004

Thin films of the misfit cobaltite Ca3Co4O9 were grown on (0001)-oriented (c cut) sapphire substrates, using pulsed-laser deposition techniques. The dependence of the thermoelectric/transport properties on the film growth conditions was investigated. The optimal conditions (for low resistivities) were found to be 600°C, 0.1–0.2mbar of oxygen pressure, and 1.7J∕cm2. These films exhibited slightly metallic behavior, consistent with in-plane resistivity curves of single crystals and c-axis magnetically aligned samples. Hall effect measurements showed the density of the holelike carriers was 6.8×1020∕cm3. The in-plane epitaxial relationship between the thin film and the sapphire substrate is investigated.
Local strain, defects, and crystallographic tilt in GaN(0001) layers grown by maskless pendeo-epitaxy from x-ray microdiffraction
Authors: Barabash R. I. , Ice G. E. , Liu W. , Einfeldt S. , Roskowski A. M. , Davis R. F.
Published: December 2004

Polychromatic x-ray microdiffraction, high-resolution monochromatic x-ray diffraction, and finite element simulations have been used to determine the distribution of strain, defects, and crystallographic tilt in uncoalesced GaN layers grown by maskless pendeo-epitaxy. An important materials parameter was the width-to-height ratio of the etched columns of GaN from which occurred the lateral growth of the wings. Tilt boundaries formed at the column/wing interface for samples with a large ratio. Formation of the tilt boundary can be avoided by using smaller ratios. The strain and tilt across the stripe increased with the width-to-height ratio. The wings were tilted upward at room temperature.
Crystallography, morphology, and magnetic properties of Fe nanostructures on faceted α-Al2O3 m plane
Authors: Oster J. , Kallmayer M. , Wiehl L. , Elmers H. J. , Adrian H. , Porrati F. , Huth M.
Published: December 2004

The properties of iron nanostructures prepared by shallow incidence molecular beam epitaxy on faceted α-Al2O3 (101¯0) (m plane) are described. Depending on the angle of deposition with regard to the sapphire surface, the morphology of the structures reaches from pearl-necklet-like strung nanodrops to laced nanowires. Crystallographic measurements reveal at least four epitaxial close to (211)-oriented twins. Magnetization measurements performed at room temperature in a vibrating sample magnetometer and magneto-optical Kerr rotation measurements reveal an easy axis of magnetization close to the facet ridges. Still, the shape of the hysteresis loops depends strongly on the morphology of the samples. The magnetization reversal process can be described by the formation of a magnetic vortex structure.
Thermally induced diffusion in GaInNAs∕GaAs and GaInAs∕GaAs quantum wells grown by solid source molecular beam epitaxy
Authors: Ng T. K. , Djie H. S. , Yoon S. F. , Mei T.
Published: December 2004

The effects of the thermal annealing induced diffusion on the photoluminescence (PL) of a GaAs∕GaInAs∕GaAs∕GaInNAs∕GaAs quantum well (QW) structure grown by solid source molecular beam epitaxy are studied. The PL experimental results in conjunction with the numerical quantum-mechanical modeling that predicts the changes in the QW confining potential with group-III atomic diffusion, have been used to obtain the values for diffusion coefficient. The activation energies of GaInAs∕GaAs QW (ED,GIA) were found to be between 0.49to0.51eV, while that of GaInNAs∕GaAs QW (ED,GINA) showed comparable values of between 0.6 to a 0.67eV, as annealing time increases from 10to30s. The ED,GIA and ED,GINA values are attributed to the same interstitial diffusion mechanism.
A nondestructive technique for determining thermal properties of thermal barrier coatings
Authors: Bennett Ted D. , Yu Fengling
Published: December 2004

A nondestructive technique for determining thermal properties of thermal barrier coatings is developed. Harmonic heating of the film is established using a laser, while the phase of thermal emission is interrogated from the front surface as a function of laser frequency. The thermal emission phase is related to four film properties: the thru-plane thermal diffusivity, the effusivity contrast between the film and substrate, the optical penetration depth of the laser, and the optical thickness of the film relative to the substrate emissivity at the detector wavelength. From these measurements both the thermal conductivity and volumetric specific heat of the film may be determined. Analysis is illustrated with a set of measurements performed on an electron beam physical vapor deposition coating. Uncertainty associated with fitting multiple film parameters using nonlinear regression is studied.
Changes of the electro-optic response of nematic liquid crystal cells due to inserted titania-vanadia films
Authors: Marino S. , Castriota M. , Bruno V. , Cazzanelli E. , Strangi G. , Versace C. , Scaramuzza N.
Published: December 2004

We report a polarity-sensitive electro-optical response observed in nematic liquid crystal cells characterized by asymmetric insertion of thin films of titania-vanadia oxide with a Ti∕V atomic ratio of 1∕1, prepared by sol-gel synthesis on transparent indium tin oxide. The electro-optical effect is opposite to previously reported ones but is obtained using the same materials with a slightly different sol-gel route. The structural properties of titania-vanadia films are extensively studied with particular attention paid to the thermal history of the films. The measurements made of the films and on the nematic liquid crystal cell demonstrate that the crystalline structure of the film is responsible of the observed effect. Thermal annealing of the films results in formation of structures that dramatically change the electric properties of the films. A qualitative model is proposed to explain the surface charge distribution inside the nematic liquid crystal cell that results in the observed electro-optical effect.
Thermal model of nanosecond pulsed laser ablation: Analysis of energy and mass transfer
Authors: Gusarov Andrey V. , Smurov Igor
Published: December 2004

A thermal model of nanosecond laser ablation considering kinetics of surface evaporation is proposed. Equations concerning heat transfer in the target and associated gas dynamics are coupled by mass and energy balances at the surface and Knudsen layer conditions. Rigorous analysis of gas-dynamics related to condensation at the target surface is introduced in this model. Laser energy absorbed by the target is partly spent for evaporation and partly dissipated in the target by thermal conduction. The sum of thermal and kinetic energies of the gas phase is, usually, less than the energy of evaporation. The fraction of energy lost for target heating increases with decrease in laser fluence and attains 100% at the ablation threshold. The dependence of ablated depth on fluence is, thus, determined by energy partition between the solid and gas phases. The gas-dynamic flow accompanying ablation consists of a layer of compressed high-temperature vapor adjacent to the target that expands and pushes the ambient gas from the surface to generate a strong shock wave. Ablation of Al and Au by laser with 193nm wavelength, 12ns full width at half maximum (FWHM) pulses, and 5.3J∕cm2 incident fluence and that of Au by laser with 266nm wavelength, 6ns FWHM, and 3.5J∕cm2 incident fluence is analyzed utilizing the present thermal model. It is concluded that optical breakdown does not occur at the considered conditions. The present model can be applied when the target surface temperature is less than the critical temperature. In case of nanosecond laser ablation of metals this, normally, restricts the value of absorbed fluence by the maximum of several J∕cm2.
Simple analytical model for 2kT current in forward-biased p-n junctions
Authors: Abenante Luigi
Published: December 2004

The junction space-charge region (JSCR) is modeled as a separate region with carrier recombination at the surface and in the bulk. Bulk recombination is modeled according to the idealized model of C. T. Sah, R. N. Noyce, and W. Shockley [Proc. IRE45, 1228 (1957)]. JSCR surface recombination is modeled by combining at high biases the approaches of A. S. Grove [Physics and Technology of Semiconductor Devices (Wiley, New York, 1967), pp. 301–302] and of C. H. Henry, R. A. Logan, and F. R. Merrit [J. Appl. Phys. 49, 3530 (1978)]. In the treatment, it is assumed that the densities of states in the bulk and at the surface are related to each other. The transport equations are solved in JSCR at high biases and an expression for the JSCR recombination current is obtained. The model is adjusted for Si emitters and diodes, in such a way that it agrees with the numerical simulation program PC1D at all voltages.
Low temperature growth of pseudocubic perovskites by off-axis rf magnetron sputtering for the realization of epitaxial ferroelectric-based heterostructures
Authors: Kuffer Olivier , Fischer Øystein
Published: December 2004

We report on the epitaxial growth at low temperature and structural properties of some pseudocubic perovskite thin films using an off-axis rf magnetron sputtering technique. Epitaxial Pb(Zr0.2Ti0.8)O3, Sr(Ru0.37Ti0.63)O3, and La0.67Ca0.33MnO3 thin films have been obtained on (100) SrTiO3 substrates and are characterized using x-ray diffraction, scanning probe microscopy, and transport and polarization hysteresis loop measurements. The obtained films reveal an extremely high degree of structural quality including surfaces with very low corrugation and good transport or ferroelectric properties. Low temperature growth further opens the possibility of producing epitaxial heterostructures where Sr(Ru0.37Ti0.63)O3 or La0.67Ca0.33MnO3 is grown on top of the Pb(Zr0.2Ti0.8)O3 ferroelectric layer. Such ferroelectric field effect devices with inverted structure present good interfaces leading to an important relative change in resistance (ΔR∕R). They are furthermore well adapted to local probe investigations of the field polarized channel.
Observation of photoluminescence related to Lomer–Cottrell-like dislocations in ZnSe epilayers grown on in situ cleaved (110)GaAs surfaces
Authors: Kutrowski M. , Wojtowicz T. , Cywinski G. , Titova L. V. , Martin E. , Liu X. , Furdyna J. K. , Dobrowolska M.
Published: December 2004

We have performed microphotoluminescence (μ-PL) experiments on ZnSe epilayers grown by molecular beam epitaxy on (110)GaAs surfaces cleaved in situ. The experiments revealed a dislocation-related PL emission at 2.72 eV (henceforth referred to as Z0), which is distinctly different from the Y0 exciton line commonly observed in ZnSe, although it shows many characteristics similar to the Y0 emission (such as fine structure, linear polarization, and phonon replicas). Both the Z0 and the Y0 emissions are clearly seen under the microscope in the form of long, narrow blue streaks oriented along the [−110] direction. The Z0 line is strongly linearly polarized in the direction perpendicular to [−110] (i.e., along [001]) and shows an unusually small Huang–Rhys factor, S=0.13. Using the concept of a dislocation exciton, we interpret the Z0 line as the recombination of an exciton bound to a dislocation whose Burgers vector is reminiscent of the Lomer–Cottrell dislocation, and differs from that responsible for the Y0 emission.
Periodic grain-boundary formation in a poly-Si thin film crystallized by linearly polarized Nd:YAG pulse laser with an oblique incident angle
Authors: Kaki Hirokazu , Horita Susumu
Published: December 2004

We investigated the periodic grain-boundary formation in the polycrystalline silicon film crystallized by a linearly polarized Nd:YAG (where YAG is yttrium aluminum garnet) pulse laser with an oblique incident angle θi=25°, compared with the normal incident angle θi=0. The alignment of the grain boundary was uncontrollable and fluctuated in the case of the oblique incident and large irradiation pulse number while that in the case of the normal incident was performed stably. It was found that the main cause for its low controllability was the nonphase matching between the periodic surface corrugation of the crystallized silicon film and the periodic temperature profile induced by the laser irradiation. Also, it was found that, in the case of θi=25°, the dominant periodic width of the grain boundary depended on the pulse number N. That is, it was around λ∕(1+sinθi) for small N≈10 and λ∕(1−sinθi) for large N≈100 at the laser wavelength of λ=532nm. In order to explain this dependence, we proposed a model to take into account the periodic corrugation height proportional to the molten volume of the silicon film, the impediment in interference between the incident beam and diffracted beam on the irradiated surface due to the corrugation height, and the reduction of the liquid surface roughness during melting-crystallization process due to liquid-silicon viscosity.
Antimony orthophosphate glasses with large nonlinear refractive indices, low two-photon absorption coefficients, and ultrafast response
Authors: Falcão-Filho E. L. , de Araújo Cid B. , Bosco C. A. C. , Maciel G. S. , Acioli L. H. , Nalin M. , Messaddeq Y.
Published: December 2004

Antimony glasses based on the composition Sb2O3–SbPO4 were prepared and characterized. The samples present high refractive index, good transmission from 380to2000nm, and high thermal stability. The nonlinear refractive index, n2, of the samples was studied using the optical Kerr shutter technique at 800nm. The third-order correlation signals between pump and probe pulses indicate ultrafast response (<100fs) for all compositions. Enhancement of n2 was observed by adding lead oxide to the Sb2O3–SbPO4 composition. Large values of n2≈10−14cm2∕W and negligible two-photon absorption coefficients (smaller than 0.01cm∕GW) were determined for all samples. The glass compositions studied present appropriate figure-of-merit for all-optical switching applications.
Formation of a hydroxide thin film by laser ablation and conversion to an oxide film with topotaxy
Authors: Kambe Shiro , Sato Kenji , Morita Kazuhide , Sato Fumiaki , Ishii Osamu
Published: December 2004

It is important to control the crystallographic orientation of oxide films for application in electronic devices. In the case of oxide superconductors, the orientation of epitaxial films has been controlled by varying the substrate temperature and the partial pressure of oxygen. To fix the orientation irrespective of the substrate temperature and the pressure of oxygen, the metal layer of the deposited film should be parallel to the substrate, and the formation of the oxide film by heat treatment should preserve this orientation. Hydroxides are one of the promising compounds that satisfy the above condition. By heating the hydroxide to achieve dehydration, oxides will be formed with the atomic arrangement preserved, that is, topotaxially. The purpose of this study is to form a completely oriented [001] Ca(OH)2 thin film, to form a perfectly [111] oriented CaO film after topotaxial dehydration, and to demonstrate formation of Ca(OH)2 and CaO films in vacuum. The [001] oriented Ca(OH)2 film was formed on a MgO substrate by laser ablation, indicating that the Ca layer of the film was parallel to the substrate. Pole figure measurements showed that the planar orientation of the Ca(OH)2 was random. This is due to the mismatch between the film and the substrate. By heating the Ca(OH)2 film at 600–800 °C to achieve dehydration, a [111] oriented CaO film was formed. Pole figure measurements showed that the CaO film is randomly oriented in the plane. This is because the mismatch between the CaO and the MgO is as large as 23%. It is to be noted that a [100] oriented film tends to be formed when the CaO film is deposited directly from a CaO target. The change of the orientation from [001] to [111] is discussed in connection with the topotaxy mechanism. These results show a possibility of “hydrogen bond epitaxy,” that is, formation of an atomically controlled oxide film through a hydroxide.
Influence of Ge concentration and compressive biaxial stress on interdiffusion in Si-rich SiGe alloy heterostructures
Authors: Aubertine D. B. , McIntyre P. C.
Published: December 2004

The Si–Ge interdiffusivity in SiGe alloys grown epitaxially on Si (100) substrates was systematically measured for Ge concentrations between 0.075 and 0.192 over a temperature range of 770–870°C. For several alloy compositions, interdiffusion kinetics were compared between films with nominally identical Ge concentration profiles, but different degrees of misfit strain relaxation. X-ray diffraction measurements of the decay rate of small, periodic, modulations in composition superimposed onto the average background alloy fraction were used to determine interdiffusivity values. The interdiffusion rate was found to increase by about a factor of 2 over the concentration range studied. The measured activation enthalpy for interdiffusion decreased linearly with Ge concentration by 4.05±0.25eV∕unit Ge atomic fraction. The prefactor for interdiffusion was proportional to exp(−35XGe). Extrapolating these trends to a Ge fraction of zero yielded a prefactor and activation enthalpy consistent with accepted values for Si and Ge tracer diffusion in pure Si. Furthermore, it was found that changes in the compressive biaxial misfit strain during postgrowth annealing of these heterostructures yielded no detectable change in measured interdiffusion rates. These results were incorporated into an interdiffusion model that successfully predicted experimental results derived from a large composition-amplitude Si∕Si0.78Ge0.22 superlattice and from intermixing at the interfaces between Si capping layers and both Si0.9Ge0.1 and Si0.78Ge0.22 blanket films.
Nondegenerate four-wave mixing in graded metallic films
Authors: Huang J. P. , Yu K. W.
Published: December 2004

The effective nondegenerate four-wave mixing (NDFM) susceptibility of graded metallic films with weak nonlinearity is exactly derived by invoking the local-field effects. It is found that the presence of gradation in metallic films can yield a broad resonant plasmon band in the optical region, which results in a large enhancement in the NDFM response and thus a large figure of merit.
Exchange biasing of a Néel wall in the nanocontact between NiFe wires
Authors: Miyake K. , Shigeto K. , Yokoyama Y. , Ono T. , Mibu K. , Shinjo T.
Published: December 2004

We fabricated nanocontact structures (typically in a range from 15×13nm2to20×40nm2) between Ni81Fe19 wires using electron-beam lithography and a lift-off process. In the magnetization reversal process for each sample, two kinds of magnetic domain walls with different magnetic configurations were trapped at the nanocontact between the two wires. The directions of the magnetization in the nanocontact were different between the two domain walls. These walls yielded different values of electric resistance and different depinning fields. The magnetization of the nanocontact suppresses or assists the magnetization rotation in the connected magnetic element through exchange interaction (exchange biasing), which causes the differences in the depinning field and dominates the magnetization process of the magnetic element.
Nitrogen oxide γ-band emission from primary and secondary streamers in pulsed positive corona discharge
Authors: Ono Ryo , Oda Tetsuji
Published: December 2004

Nitrogen oxide γ-band emissions (A2Σ+→X2Π) from primary and secondary streamers are observed in O2∕N2 and NO∕N2 pulsed positive corona discharges with the aim of investigating the production of NO molecules and N2(A3Σu+) metastables in these primary and secondary streamers. The spatial distribution of the NO-γ emission shows that the NO-γ emission is mostly observed in the secondary streamer propagation area of the O2∕N2 discharge. That is, NO molecules are mainly produced in the secondary streamer in the O2∕N2 discharge. On the other hand, in the NO∕N2 discharge, the NO-γ emission is observed in the primary streamer propagation area. This result indicates that N2(A3Σu+) metastables are mostly produced in the primary streamer because the NO-γ emission is observed following the process NO(X2Π)+N2(A3Σu+)→NO(A2Σ+)+N2(X2Σg), where NO(X2Π) is distributed uniformly in the background gas in the NO∕N2 discharge.
Exactly realizable bounds on the trapping constant and permeability of porous media
Authors: Pham D. C. , Torquato S.
Published: December 2004

Sandstone, granular media, bone, wood, and cell membranes are just a few examples of porous media that abound in Nature and in synthetic situations. Two important effective properties of fluid-saturated porous media that have been extensively studied are the trapping constant γ and scalar fluid permeability k. Exact expressions for the “void” bounds on γ and k for coated-spheres and coated-cylinders models of porous media are derived. In certain instances, the bounds are shown to be optimal, i.e., the void bounds coincide with the corresponding exact solutions of γ and k for these coated-inclusions models. In the optimal cases, we obtain exact expressions for the relevant length scale that arises in the void bounds, which depends on a two-point correlation function that characterizes the porous medium. By contrast, optimal bounds on the effective conductivity and elastic moduli of composite media have long been known.
Origin of the blue fluorescence in Dominican amber
Authors: Bellani Vittorio , Giulotto Enrico , Linati Laura , Sacchi Donatella
Published: December 2004

We report on optical absorption, fluorescence, and time-resolved fluorescence measurements in Dominican ambers. The “blue” variety reveals an intense fluorescence emission in the visible wavelength region, between 430 and 530nm, with spectral features typical of aromatic hydrocarbons. On the contrary, the “red” and “yellow” varieties have a much weaker and featureless emission. The data for blue amber, including fluorescence lifetime, allow the identification of perylene as the compound responsible for its distinctive showy fluorescence.
Evidence of direct SiO2 etching by fluorocarbon molecules under ion bombardment
Authors: Takada N. , Toyoda H. , Murakami I. , Sugai H.
Published: December 2004

In a beam apparatus, influence of fluorocarbon gas (C5F8, C4F8, and CF4 molecules) flux onto SiO2 etching reaction is investigated in comparison to a case of CF2 radical flux. Fluorocarbon molecules or CF2 radicals are incident onto SiO2 surface with Ar+ beam of energy 100–900eV. Atomic composition of SiO2 surface under the ion and molecule incidence is measured by in situ x-ray photoelectron spectroscopy. Fluorocarbon∕Ar+ co-incidence enhances the SiO2 etching compared with pure Ar+ incidence, suggesting the etching effect of fluorocarbon molecules under Ar+ bombardment. In the case of C5F8∕Ar+ co-incidence, formation of fluorocarbon layer is observed as the case of CF2∕Ar+ co-incidence. Etching yields of SiO2 by C5F8∕Ar+ and CF2∕Ar+ co-incidences are measured for different Ar+ incident energies and fluorocarbon∕Ar+ flux ratios. The etching yield increases monotonically with the Ar+ incident energy, and reaches the value of 2.4 at 900eV in case of C5F8, which is about 1.5 times as high as in the CF2 case. In the case of C5F8 and CF2, a phenomenon like etch stop, with formation of a thick fluorocarbon layer, is observed for larger fluorocarbon flux, with the threshold of the fluorocarbon∕Ar+ flux, ratio between 2.5 and 25. These results suggest a significant contribution of direct SiO2 etching by fluorocarbon molecules in practical etching reactors, especially in case of the C5F8 molecule.
Correlation between morphological defects, electron beam-induced current imaging, and the electrical properties of 4H–SiC Schottky diodes
Authors: Wang Y. , Ali G. N. , Mikhov M. K. , Vaidyanathan V. , Skromme B. J. , Raghothamachar B. , Dudley M.
Published: December 2004

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H–SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current–voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier height within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.
Characterization of interfacial bonding using a scanning Kelvin probe
Authors: Li W. , Li D. Y.
Published: December 2004

Interfaces play a crucial role in determining the ultimate properties and service life of coating and film materials. However, the characterization and measurement of interfacial bonding, in particular of the local strength, is difficult. The high sensitivity of the electron work function (EWF) to surface conditions has attracted increasing interest in applications of the Kelvin probing technique to investigate the mechanical behavior of materials. In this study, the Kelvin method was used to characterize the interfacial bond formed between pure copper and brass after annealing in argon gas. It was demonstrated that low EWF values, small EWF fluctuations, and narrow fluctuation ranges in interfacial regions corresponded to good bonding. Furthermore, there was a strong correlation between the EWF and the interfacial strength determined by the microindentation method using a universal microtribometer. The Kelvin probing technique could be a powerful tool for studying the local property and structure of interfaces.
Photoreactive phase conjugation strength in disperse red 1 doped poly(methylmethacrylate) thin films
Authors: Liu Sean , Wang Wei Lin , Fang Chien Cheng , Huang Tzer-Hsiang , Hsu Chia Chen
Published: December 2004

Near-resonant optical pumping was used to modulate third-order susceptibility χ(3) in disperse red 1 doped poly(methylmethacrylate) thin films. An optically pumped degenerate four-wave mixing (DFWM) experiment was conducted to examine the photoreactive phase conjugation (PC) signals. Experimental results indicated a large anisotropy in PC signals arising from ∣χ3333(3)∣2, and almost isotropic PC signals from ∣χ1331(3)∣2 under s-polarized and p-polarized pump fields. Additionally, a dynamic microscopic model, based on the theory developed by Sekkat et al.[Synth. Met. 54, 373 (1993); J. Phys. Chem. B 106, 12407 (2002); Opt. Commun. 229, 291 (2004)] was presented to describe the observed optical nonlinear responses. Results from the model were generally consistent with those of the optically pumped DFWM experiment.
Annealing and oxidation of silicon oxide films prepared by plasma-enhanced chemical vapor deposition
Authors: Chen X. Y. , Lu Y. F. , Tang L. J. , Wu Y. H. , Cho B. J. , Xu X. J. , Dong J. R. , Song W. D.
Published: December 2004

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiOx, 0<x<2) films by high-vacuum annealing and dry oxidation. The SiOx films were deposited by plasma-enhanced chemical vapor deposition at different nitrous–oxide/silane flow ratios. The physical and optical properties of the SiOx films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000 °C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO2 and elemental Si. This change indicates the phase separation of the SiOx into more stable SiO2 and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. The size of Si NCs increases with increasing Si concentration in the films and increasing annealing temperature. Two photoluminescence (PL) bands were observed in the films after annealing. The ultraviolet (UV)-range PL with a peak fixed at 370–380 nm is independent of Si concentration and annealing temperature, which is a characteristic of defect states. Strong PL in red range shows redshifts from ∼600 to 900 nm with increasing Si concentration and annealing temperature, which supports the quantum confinement model. After oxidation of the high-temperature annealed films, the UV PL was almost quenched while the red PL shows continuous blueshifts with increasing oxidation time. The different oxidation behaviors further relate the UV PL to the defect states and the red PL to the recombination of quantum-confined excitions.