bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parameter Optimization of a Microfabricated Surface Acoustic Wave Sensor for Inert Gas Detection
Authors: Ahuja S. , DiVenere A. , Ross C. , Chien H. T. , Raptis A. C. 
Published: April 2011

ABSTRACTThis work is related to designing, fabricating, and testing a surface acoustic wave sensor to be used for detecting metastable inert gases, particularly helium. The assembly consists of two microsensor configurations: (a) a reference device with no deposition at the delay line and (b) a sensing device with an Au-activated TiO2 e-beam-deposited thin film on the delay line. The interdigitated transducers and delay lines are fabricated by photolithography techniques on a single Y-cut LiNbo3 substrate oriented for Z-propagation of the acoustic waves. Variation in electrical conductivity of the Au-activated TiO2 film due to exposure to metastable He is translated as a frequency change in the assembly. Various characteristics of the surface acoustic microsensor have been studied to better understand and optimize the variation of acoustic wave velocity and the operating frequency of the microdevice. Methods for the TiO2 thin-film deposition are discussed.
Synthesis and Spectroscopie Analysis of Smart Photochromic Materials
Authors: Mo Yeon-Gon , Dillon R. O. , Snyder P. G. 
Published: April 2011

ABSTRACTSol-gel processing was used to dope photochromic materials into metal alkoxide-polymer and pure polymer materials. The films on silicon and quartz substrates were examined, with and without UV irradiation, by UV/VIS spectroscopy, ellipsometry and FTIR.The UV/VIS spectroscopy showed that the doped matrices were photochromic in the visible and near infrared.The ellipsometric data were obtained with a variable angle of incidence spectroscopie ellipsometer (VASE). The Cauchy and a combined Cauchy-Lorentz model were used to fit the unirradiated and irradiated films, respectively. The optical constants of the films showed significant changes upon irradiation. This means that the absorption coefficient and hence the emissivity of the films is being modulated with UV irradiation. The VASE-fitted thicknesses of the films were in the range of 1 to 6 microns.In the FTIR spectra, the spiropyran doped samples have shown IR transmission changes in the two spectral regions (6–7 μm and 7.5–8.5 μm) where changes are expected due to band opening. The transmission ratio for UV irradiated to unirradiated samples decreased by as much as about 24% at aparticular IR wavelength.
Local Viscoelasticity of Biopolymer Solutions
Authors: Schnurr B. , Gittes F. , Olmsted P. D. , Schmidt C. F. , Mackintosh F. C. 
Published: April 2011

AbstractWe describe a new, high-resolution technique for determining the local viscoelastic response of polymer gels on a micrometer scale. This is done by monitoring thermal fluctuations of embedded probe particles. We derive the relationship between the amplitude of fluctuations and the low-frequency storage modulusG′, as well as the relationship between the fluctuation power spectrum, measured between 0.1 Hz and 25kHz, and the complex shear modulusG((ω). For both, semiflexible F-actin solutions and flexible polyacrylamide (PAAm) gels we observe high-frequency power-law dependence in the spectra, which reflects the behavior of the shear modulus. However, we observe distinctly different scaling exponents forG((ω)in F-actin and PAAm gels—presumably due to the semiflexible nature of the actin filaments.
Front propagation in laser-tweezed lipid bilayer tubules
Authors: Olmsted Peter D. , Mackintosh Fred C. 
Published: April 2011

AbstractWe study the mechanism of the ‘pearling’ instability seen recently in experiments on lipid tubules under a local applied laser intensity. We argue that the correct boundary conditions are fixed chemical potentials, or surface tensions Σ, at the laser spot and the reservoir in contact with the tubule. While most qualitative conclusions of previous studies remain the same, the ‘ramped’ control parameter (surface tension) implies several new features. We also explore some consequences of front propagation into a noisy unstable medium.
Conformal Map on Rough Boundaries Application to Fracture
Authors: Roux Stéphane , Vandembroucq Damien 
Published: April 2011

ABSTRACTA conformai mapping technique is presented which allows to solve efficiently harmonic and bi-harmonic problems in semi-infinite domains limited by a rough boundary. This technique is applied to obtain the statistical distribution of flux and elastic stress in the vicinity of a self-affine boundary. This computation justifies the occurence of Weibull statistics for the strength of glass fibers, with Weibull modulus depending on the roughness amplitude. Another application concerns the determination of the local mode III stress intensity factor ahead of a rough crack. Extension of the method to surface stress-corrosion, and interfacial crack propagation are discussed.
A Model of Crack Propagation in a 2D Heterogeneous Material
Authors: Daguier P. , Bouchaud E. , Lapasset G. 
Published: April 2011

ABSTRACTA continuous numerical model of pure mode I crack propagation in a bidimensional heterogeneous material is presented. This model describes the propagation of a macrocrack into a two-phases brittle material containing a finite density of second phase precipitates. The morphology of cracks produced for various mechanical and microstructural conditions is analysed. It is shown that the simulated cracks are self-affine with a roughness index ≃ 0.6 independent of the microstructure. Relevant length scales, on the contrary, strongly depend on the microstructural parameters, and indicate an optimum density leading to a maximum fracture toughness.
Anomalous Relaxation in Disordered Media
Authors: Araujo Mariela , Gonzalez Orlando 
Published: April 2011

ABSTRACTSeveral random walk-algorithms are used to model relaxation processes on disordered structures. Substrates are regular lattices in d = 1,2 with disorder variables attached to each lattice site. For the simulations, we consider diffusing particles obeying different rules according to the transport process being studied. Relaxation description is done in the time domain by calculating the characteristic function F(k,t), and in the frequency domain through the study of the complex susceptibility χ(k,ω). Two types of relaxation mechanisms are seen both in simulations and in Nuclear Magnetic Resonance (NMR) experiments done on sandstones. These are expressed as stretched exponential forms of the relaxation function, and the Cole-Cole form of the imaginary part of the complex susceptibility. Longitudinal and transversal NMR measurements were done on fully saturated samples at 90 MHz. NMR relaxation data can be qualitatively understood using the random walk models proposed here.
Kinetics of Periodic Pattern Formation in Diffusion-Reaction in a Gel
Authors: Kuo C-S. , Bansil R. , Cabarcos E. L. 
Published: April 2011

ABSTRACTA video photographic study of the kinetics of the precipitation reaction Na2HPO4 + CaCl2 → CaHPO4 in agarose gels is presented. Periodic precipitation, known as Liesegang bands, are observed when one of the reactants is incorporated in the gel and the other allowed to diffuse in. The time evolution of the first Liesegang band's profile provides a direct confirmation of the supersaturation model, with a decrease in intensity as the monomer concentration is depleted and the formation of a broad plateau behind the sharp band from large particles left after the incorporation of the smaller mobile particles into the rapidly growing aggregate front. The time dependence of leading edge of the precipitate front agrees with the predictions of the reaction-diffusion-supersaturation model of Liesegang band formation.
Diffusion Limited Wetting
Authors: Steiner U. , Klein J. 
Published: April 2011

ABSTRACTWe have measured the growth with time t of a wetting layer (of thickness l(t)) at the surface of a thin film of a binary liquid (polymer) mixture. Over a wide range of experimental parameters, our data is well described by a model of diffusion limited wetting which takes into account the finite film thickness. In this model, l(t) is a function of time which sensitively depends on the nature of the interfacial potential: a detailed comparison shows that long range van-der-Waals forces provide the main driving force for the build-up of the wetting layer.
Adsorption Monolayer Formation in Confined Geometry: Apparent Fractal Dimension
Authors: Qkunev A.G. , Aristov Yu.I. 
Published: April 2011

ABSTRACTHere we present experimental results on adsorption of fatty acids, aliphatic alcohols, and acetone on the mesoporous silica gels with various porosity. Conclusion has been drawn that fractal resolution analysis of the silica surface may lead to apparent values of the surface dimension. These data are suggested to be analyzed by a simple model taking into account adsorbed layer thickness and steric difficulties of monolayer formation in narrow pores.
Phase Transitions of Organic Fluids Confined in Porous Silicon
Authors: Faivre C. , Dolino G. , Bellet D. 
Published: April 2011

ABSTRACTThis paper reports experimental data on both the solid-liquid and liquid-vapour phase transitions of an organic fluid confined in the pore network of porous silicon, by using respectively differential scanning calorimetry and X-ray diffraction. Due to the nanometric pore sizes of this material, the surface effects have a strong influence, shifting the transition parameters (lower melting temperature and lower condensation vapour pressure respectively). In particular, the effect of chemical dissolution on the pore size distribution of porous silicon layers has been investigated.
Electron Escape from a Quantum Well
Authors: Lavine James P. , Picker Harvey S. 
Published: April 2011

ABSTRACTThe quantum mechanical escape rate is calculated for an electron in a one-dimensional potential well. First-order time-dependent perturbation theory is used for the bound-to-bound and the bound-to-free transitions. The bound-to-free transition probability decays exponentially with bound energy. The fraction of one-electron systems in a bound state decays exponentially with time. The characteristic time constant grows exponentially with an increasein the depth of the potential well.
Photophysics of High Concentration Systems at a Solution / Solid Interface: An Evanescentwave Study
Authors: Elliott J.A. , Rumbles G. , De Mello A.J. , Anderson H.L. 
Published: April 2011

ABSTRACTFor many species the study of photophysical behaviour by fluorescence spectroscopy has been confined to low concentration as a result of the influence of the inner filter effect. In this paper we report how the total internal reflection technique of evanescent wavefluorescence spectroscopy (EWIFS) allows both the collection of distortion free steady-state fluorescence emission spectra and quantitative analysis of such species, in ‘bulk’ solution environment, to significantly higher concentration than can be achieved with a conventional ( right-angle ) geometry. A study of two species, the laser dye rhodamine 101 and anovel meso-substituted zinc prophyrin is presented.
Glass-Forming Liquids in Mesopores Probed by Solvation Dynamic and Dielectric Techniques
Authors: Yan X. , Streck C. , Richert R. 
Published: April 2011

ABSTRACTThe orientational dynamics of organic supercooled liquids of low molecular weight confined to the geometry of porous glasses are studied by two highly related techniques, the optical method of probing the dynamics of solvation regarding a chromophoric host molecule and dielectric relaxation spectroscopy. The dielectric results display marked effects of the confinement to mesopores in terms of altered structural dynamics which appear to separate into a raster and slower responses relative to the bulk liquid. We also demonstrate that there is no trivial relation between the ε*(ω) data and the liquid dynamics in these heterogeneous samples. These effects are partially paralleled by the solvation dynamics results, but with the spatial range inherent in the optical technique being inconsistent with associating the fast and slow dynamical components to spatially distinct regimes. We conclude on the slow component being a signature of non-ergodicity which arises from the competition between the length scale of cooperativity and the pore size.
Scanning Probe Microscope Study of Mixed Chain-Length Phase-Segregated Langmuir-Blodgett Monolayers
Authors: Koleske D.D. , Barger W.R. , Lee G.U. , Colton R.J. 
Published: April 2011

ABSTRACTUsing a scanning probe microscope, the influence of adhesion on measured film height of mixed-chain-length fatty acid Langmuir-Blodgett monolayers was investigated. A 1:1 mixture of CH3[CH2]22COOH and CH3[CH2]14COOH, was deposited in which the long chain-length acid, C24, was segregated from the short chain-length acid, C16. Two experiments were performed, contact scanning and force curve mapping. From both experiments, the film height difference measured between the C16 and C24 regions was larger than expected. Adhesion of the tip was 20% larger over the C16 acid regions. Using a compressional modulus derived from film pressure vs. area isotherms of the pure components, the adhesion difference and apparent filmheight difference over the two regions can be understood.
Polymer Brushes in Strong Shear Flow
Authors: Grest Gary S. 
Published: April 2011

ABSTRACTPolymers end-grafted to a surface in the presence of a shear flow are studied by molecular dynamics simulations. The solvent velocity field is observed to penetrate only a short distance into the brush consistent with predictions based on self-consistent field theory. The deformation of the brush is small except when the shear rate γ is very large. In this limit, while some of the polymer chains are stretched in the direction of flow, the brush height actually decreases slightly, in contrast to several theoretical predictions. When two surfaces bearing end-grafted chains are brought into contact, the normal force increases rapidly with decreasing plate separation, while the shear force is significantly smaller. For low relative velocityvwof the two walls, the surfaces slide pass each other with almost no change in the chain's radius of gyration or the amount of interpenetration, while for very largevw, there is significant stretching and some disentanglement of the chains. The results are in qualitatively good agreement with recent experiments using the surface force apparatus.
Reactivity and Migration of Hydrogen in A-SI:H
Authors: Biswas R. , Li Qiming , Pan B. C. , Yoon Y. 
Published: April 2011

ABSTRACTTight-binding molecular dynamics calculations reveal a new mechanism for hydrogen diffusion in hydrogenated amorphous silicon. Hydrogen diffuses through the network by successively bonding with nearby silicon and breaking their Si-Si bonds. The diffusing hydrogen carries with it a newly created dangling bond. These intermediate transporting states are densely populated in the network and have lower energies than H at the center of stretched Si-Si bonds.
Role of Material Structure on Molecular Diffusion of Hydrogen in a-Si:C:H Films
Authors: Ullersma E. H. C. , Inia D. K. , Habraken F.H.P.M. , Van Sark W.G.J.H.M. , Van Der Weg W. F. , Westerduin K. T. , Van Veen A. 
Published: April 2011

ABSTRACTWe used Fourier Transform Infra-Red (FTIR) analysis of bi-layers of plasma-grown hy-drogenated amorphous silicon-carbide films to investigate the role of the material structure in the hydrogen diffusion process. In the bi-layers one layer was deposited using CH4/SiH4 and in the other layer CD4/SiD4 was applied. The carbon concentration was 20 at.%. In previous work we showed, using Elastic Recoil Detection (ERD) and Thermal Desorption Spectrometry (TDS), that the hydrogen moves molecular through these films in the temperature range 325 < T < 450 °C [1]. Using FTIR we obtained information about the number of Si-H and Si-D bonds and their change upon annealing. The FTIR data indicate a structural change during annealing. A comparison with the TDS spectra led us to the conclusion that at higher temperatures the out-diffusion of hydrogen stops because of the hindrance of the molecular transport.
Growth Mechanism of Hydrogen Clusters
Authors: Nickel N. H. , Anderson G. B. , Johnson N. M. , Walker J. 
Published: April 2011

ABSTRACTIt is demonstrated that the exposure of polycrystalline silicon (poly-Si) to monatomic hydrogen results in the formation of H clusters. These H stabilized platelets appear in the near-surface region ( 100 nm) and are predominantly oriented along {111} crystallographic planes. Platelet concentrations of ≈5×1015, 1.5×1016-cm−3, and 2.4×1017 cm−3 were observed in nominally undoped poly-Si, phosphorous doped poly-Si (P=1017 cm−3), and phosphorous doped single crystal silicon (P>3×1018 cm−3), respectively. Results obtained on doped c-Si demonstrate that platelet generation occurs only at Fermi-level positions of Ec -EF < 0.4 eV.
An NMR Investigation of H Cluster Configurations in A-SI:H
Authors: Todd Stephen J. , Rutland Jonathan M. , Han Daxing , Wu Yue 
Published: April 2011

ABSTRACTIn this work the characteristics of hydrogen clusters in hot filament assisted CVD and conventional glow discharge a-Si:H films are discussed. Computer simulations of the observed free-induction decays of the 1H NMR signals indicate that the distribution of the nearest-neighbor distances between H atoms in the H clusters is quite narrow in hot filament assisted CVD a-Si:H whereas the distribution is larger in glow discharge a-Si:H. This is clear evidence of improved structural order in hot filament assisted CVD a-Si:H. The relaxed hydrogenated divacancy and multi-vacancy models reproduce the main features of the observed free-induction decay in hotwire a-Si:H very well. Computer simulations of the multiple-quantum NMR spectra indicate that a relaxed hydrogenated divacancy configuration leads to good agreement with experimental observations in device quality glow discharge a-Si:H. Results of simulations based on other H cluster configurations are also discussed. These results provide restrictions on the possible models for H clusters in a-Si:H.
Influence of Defects on Excess Charge Carrier Kinetics Studied by Transient PC and Transient PA
Authors: Feist H. , Kunst M. , Swiatkowski C. 
Published: April 2011

ABSTRACTBy comparison of transient photoconductivity (TPC) and transient photoinduced absorption (PA) the influence of the density of states in the bandgap on excess charge carrier kinetics is studied for a-Si:H films deposited at different temperatures and for state of the art a-Si:H films in two different states of light soaking. In both series the rising deep defect density leads to an enhancement of electron trapping rather than recombination via deep defects. The samples deposited at temperatures lower than 250°C additionally show a lower effective electron mobility, i.e. a broader conduction band tail.
Space Charge Memory Effect in a-Si:H at low Temperatures
Authors: Heck S. , Stradins P. , Fritzsche H. 
Published: April 2011

ABSTRACTSpace charges build up near one or both electrodes of a photoconductor unless the thermoionic current balances the photocurrent. Space charges built up also when a voltage U is applied at low T to a semiconductor containing a non-equilibrium distribution of carriers. The presence of a space charge is observed as a relaxation-current transient when the sample is illuminated at zero bias. If one type of carrier is immobile the steady state photocurrent becomes zero.
Electronic Properties and Device Applications of Hot-Wire CVD Polycrystalline Silicon Films
Authors: Middya A. R. , Guillet J. , Brenot R. , Perrin J. , Bouree J. E. , Longeaud C. , Kleider J. P. 
Published: April 2011

ABSTRACTPolycrystalline silicon films (5 to 30 μm thick) have been deposited on glass substrates at low temperatures (400–550 °C) with a rate of 15 Å/s by hot-wire chemical vapour deposition (HWCVD). The homogeneity of the deposited layer is ±5% on a 8 cm diameter substrate. The films have columnar microstructure and a textured surface. The undoped films (carrier concentration, 1011 cm−3) have a resistivity of 105-106 Ω-cm, activation energy of 0.50 ± 0.05 eV and Hall mobility of 14 ± 4 cm2 /V.s. By in situ gas phase doping, resistivity can be varied by six to seven orders of magnitude. Incorporation of dopant atoms such as boron into the film, strongly influences its morphological and crystallographic structure. The mobility lifetime product of undoped films is low (10−8 cm2/V), possibly due to the presence of a high density of dangling bonds defects and broad band-tails. This product can be improved by a factor of 5 to 10 by using in-situ hydrogen passivation in the same reactor at lower temperature (350–400 °C) within one hour. The results of many complementary experiments suggest that hydrogen treatment mainly improves carrier mobility by a factor of 3 to 4 by passivating extended defects. Preliminary results on application of these types of materials in unoptimized P-I-N solar cells on c-Si and glass substrates are presented.
Electronic Properties of Microcrystalline Silicon
Authors: Carius R. , Finger F. , Backhausen U. , Luysberg M. , Hapke P. , Houben L. , Otte M. , Overhof H. 
Published: April 2011

ABSTRACTThe electronic and optical properties of microcrys tall ine silicon films prepared by plasma enhanced chemical vapour deposition are investigated with Hall-effect, electrical conductivity, photothermal deflection spectroscopy and photoluminescence measurements. In particular, the influence of the grain size and the crystalline volume fraction on the conductivity, the carrier density and the Hall mobility is investigated in highly doped films. A percolation model is proposed to describe the observed transport data. Photoluminescence properties were studied in un-doped films. It is proposed that the photoluminescence is due to recombination at structural defects similar to those observed in crystalline silicon.
Electroabsorption Spectra of Hydrogenated Amorphous and Microcrystalline Silicon
Authors: Jiang Lin , Schiff E. A. , Finger F. , Hapke P. , Koynov S. , Schwarz R. , Wyrsch N. , Shah A. , Yang J. , Guha S. 
Published: April 2011

ABSTRACTWe report on electroabsorption spectra for plasma deposited thin films of hydrogenated silicon ranging from amorphous (a-Si:H) to microcrystalline (μc-Si-H) structures. The EA spectrum of a-Si:H deposited from silane with low hydrogen dilution were consistent with previous works; material prepared with high hydrogen dilution showed a 0.07 eV blue shift of the spectrum and somewhat stronger electroabsorption. μc-Si-H specimens have a sharp peak at 1.19eV; the spectrum is blue shifted by 0.03 eV and is significantly stronger than electroabsorption reported in single crystal silicon. Spectral features which have no correspondence to single crystal silicon were also observed in μc-Si-H. Specimens deposited using “cyclic” deposition and chemical annealing had electroabsorption spectra with both the 1.19 eV, crystalline feature and a band peaking at 2.02 eV which we attribute to strongly hydrogenated a-Si:H. We discuss applications of electroabsorption to determining the crystal fraction of microcrystalline material and to determining grain size distributions.