bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics of Grains in Driven Granular Media
Authors: Menon Narayanan , Durian Douglas J. 
Published: April 2011

ABSTRACTWe use diffusing-wave spectroscopy (DWS) to study microscopic dynamics in the interior of 3-dimensional granular systems. We study two granular systems where particle motions are excited by different driving mechanisms – gravity-driven channel flow and a gas-fluidized bed. In both instances we obtain detailed information about short-time collisional dynamics such as rms velocity fluctuations, mean free paths, and collision frequencies. We also observe a slow crossover from short-time ballistic motions to long-time, grain-scale diffusive motions.
Flexible membranes with anchored polymers
Authors: Lipowsky Reinhard , Döbereiner Hans-Günther , Hiergeist Christin , Indrani Vasudevamurthy 
Published: April 2011

AbstractRecent work on flexible membranes such as lipid bilayers with anchored polymers is briefly reviewed. These polymers exert bending moments onto the membranes and, thus, lead to a polymer–induced curvature. From the theoretical point of view, this curvature depends (i) on the membrane–polymer interactions; (ii) on the size of the polymers; and (iii) on the polymer coverage. Experimentally, these curvature effects can be deduced from systematic studies of polymer–decorated vesicles in which one monitors the vesicle shape with varying solvent conditions.
Normal-Strain Induced Change in Lattice-Type for Confined Cyclohexane Films
Authors: Curry J.E. , Cushman J.H. 
Published: April 2011

ABSTRACTOne to three layer cyclohexane films confined between mica-like surfaces are studied to elucidate changes in the films' lattice-type. The laterally confined film is in equilibrium with the bulk fluid that is well into the liquid regime of its phase diagram. Monte Carlo simulations are conducted at constant chemical potential, temperature, and V=Ah, where A is the lateral area and h is the separation between the walls. One and two layers of fluid freeze as h increases. The one layer fluid has a triangular lattice, while the two layer fluid exhibits first a square lattice and then a triangular lattice with increasing surface separation. In contrast to previous studies, solidlike order is induced primarily by the strong fluid-solid interaction and is largely a function of pore width. A shift in the relative alignment of the surfaces perturbs the solidlike fluid structure but does not cause the sudden shear melting transition associated with epitaxial alignment of the fluid atoms with the surface. There is a correlation between the shear stress calculated in the computer experiments and that measured in Surface Forces Apparatus experiments.
Revisiting Experimental tests of the Laplace-Kelvin Equation
Authors: Van Swol Frank , Douglas Frink Laura J. 
Published: April 2011

ABSTRACTIn this paper we focus on two experimental techniques for testing predictions made by Laplace-Kelvin theory (LKT). The first technique employs the surface forces apparatus (SFA) to measure pull-off forces, the second uses a beam bending (BB) technique to determine the bending forces in a microporous film produced with a sol-gel technique. We use density functional theory (DFT) to analyze the two experiments. We find that the pull-off force in a crossed cylinder geometery contains a minimal solid-liquid contribution, which can explain why the LKT result is found at saturation. We demonstrate that a pore size distribution essential to produce a bending stress that is always compressive and has a dependence on the vapor pressure that coincides with LKT.
Critical Current Fluctuations in Disordered Superconducting Wire Networks Carlos Bonetto
Authors: Israeloff N. E. 
Published: April 2011

AbstractWe report results of an investigation of magnetic-field dependent critical currents in artificially disordered superconducting Al wire networks well below Tc. Aperiodic but reproducible variations with field are found, in sharp contrast with the periodic oscillations observed close to Tc. Critical currents also exhibited strong variations on cycling the current at low fields reflecting variations in frozen-in metastable vortex patterns. Both the variations in field and on cycling vanished above a critical field set by the disorder strength.
Reaction Dynamics and Chemical Pattern Formation in Capillary Tubes Resulting from the Competition Between Two Elementary Complex Formation Reactions
Authors: Lin Anna L. , Yen Andrew , Lee Koo Yong-Eun , Vilensky Baruch , Taitelbaum Haim , Kopelman Raoul 
Published: April 2011

AbstractA system of competing elementary reactions is investigated experimentally usingthe reaction of xylenol orange with Cr3+ in aqueous solution. The two reagents areinitially separated in a long, thin capillary tube and meet in the center, forming a reactionfront (s). The geometry of the reactor and the initial separation of the reagents makes the system effectively one-dimensional. Aqueous Cr3+ solution has a very rich chemistryand provides two different chemical Cr3+ reactants which compete to react with xylenolorange. Rich spatio-temporal patterns are observed experimentally and are explained by a reaction-diffusion model. Results from exact enumeration simulations predict that when the concentrations of the competing species are very different and the microscopic rate constants of the competing species are such that the majority species reaction rate is much faster than the reaction rate of the minority species, the reaction front splits into two distinct regions. The spatio-temporal patterns generated by theory and experiment agree quantitatively. Also in agreement with the theory are the experimental early time and asymptotic time global rate behaviors, which exhibit multiple crossovers.
The Anomalous Diffusion-limited Reaction Kinetics of a Phototrapping Reaction
Authors: Monson Eric , Lin Anna L. , Kopelman Raoul 
Published: April 2011

AbstractA focused laser beam acts as both a “phototrap”, bleaching fluorophore molecules which diffuse into the beam path, and as a confocal probe, detecting the excited, unbleached fluorophore molecules still present in the trap. With this focused laser beam, we observe anomalous asymptotic rate laws similar to those predicted for a diffusion-controlled elementary trapping reaction, A + T → T, in one and two dimensions. One dimensional diffusion-limited trapping kinetics are approached in capillaries with 10 μm diameters while two dimensional diffusion limited trapping kinetics are observed with unstirred samples having a quasi 2-D geometry. In the presence of stirring, the 2-D samplesexhibit the classical, constant trapping rate over time.
Computer Studies on free and Confined Amorphous Polymer Films
Authors: Pätzold G. , Heermann D.W. , Linke A. , Hapke T. 
Published: April 2011

ABSTRACTWe study surface effects in amorphous polymer systems by means of computer simulation. In the framework of molecular dynamics, we present two different methods to prepare such surfaces. Free surfaces are stabilized solely by van-der-Waals interactions, whereas confined surfaces emerge in the presence of repelling plates. The buildup of density and pressure profiles from zero to their bulk values depends on the surface preparation method. In the case of confined surfaces, we find density and pressure oscillations next to the repelling plates. For free surfaces, we attest chain-end enrichment and present a comparison between density profile and particle coordination number.
Chaos and Force Fluctuations in Frictional Dynamics
Authors: Rozman M. G. , Klafter J. , Urbakh M. 
Published: April 2011

ABSTRACTA model is presented of a particle that interacts with two periodic potentials, representing two confining plates, one of which is externally driven. The model leads to various behaviors in the motion of the top driven plate: stick-slip, intermittent regime, characterized by force fluctuations, and two types of sliding above a critical driving velocity vc. Similar behaviors are typical of a broad range of systems including thin sheared liquids. A detailed analysis of the different regimes displays a transition between the stick-slip and the kinetic regimes, ω−2 power spectra of the force over a wide range of velocities below vc, and a decrease of the force fluctuations that follows (vc – v)½ for v < vc. The velocity dependent Liapunov exponents demonstrate that the stick-slip motion is characterized by a chaotic behavior of the top plate and the embedded particle. An extension of the model to an embedded chain is introduced and preliminary results are presented and confronted with the single particle case. The role of the internal excitations of the chain in frictional dynamics is discussed.
Wall Slip of a Polymer Melt on a Polymer Brush
Authors: Durliat E. , Hervet H. , Léger L. 
Published: April 2011

AbstractWe have investigated simple shear flows of poly-dimethyl-siloxane (PDMS) melts on PDMS brushes with well controlled grafting density Σ, using optical techniques based on near field laser anemometry to measure the local velocity of a polymer melt at a solid interface. We have observed a slip transition from a weak slip regime to a strong one as the shear rate crosses a critical value γ*. The influence of the molecular weight of the melt Mm, of the molecular weight of the brush chains Mb and of Σ on γ*, has been investigated to elucidate the molecular mechanisms. The results are compared with an existing molecular model.
Light-Soaking Effects on Photoconductivity in a-Si:H Thin Films
Authors: Morgado E. , Rebelo da Silva M. , Henriques R. T. 
Published: April 2011

ABSTRACTMetastable defects have been created by light exposure in thin films of a-Si:H. The samples have been characterized by Photothermal Deflection Spectroscopy, Electron Spin Resonance, dark- and photo-conductivity. The experimental results are consistent with numerical calculations with a recombination model involving band tails and one class of correlated dangling-bond states. The effects of light-soaking on the ligh intensity and defect density dependences of photoconductivity are reproduced by the calculations. The model allows to explain the experimental trends by changes in the electronic occupation of the gap states produced by light-induced defects.
Deuterium in Crystalline and Amorphous Silicon
Authors: Borzi R. , Ma H. , Fedders P. A. , Leopold D. J. , Norberg R. E. , Boyce J. B. , Johnson N. M. , Ready S. E. , Walker J. 
Published: April 2011

ABSTRACTWe report deuteron magnetic resonance (DMR) measurements on aged deuterium-implanted single crystal n-type silicon and comparisons with amorphous silicon spectra. The sample film was prepared six years ago by deuteration from a-D2 plasma and evaluated by a variety of experimental methods. Deuterium has been evolving with time and the present DMR signal shows a smaller deuteron population. A doublet from Si-D configurations along 〈111〉 has decreased more than have central molecular DMR components, which include 47 and 12 kHz FWHM gaussiane. Transient DMR magnetization recoveries indicate spin lattice relaxation to para-D2 relaxation centers.
An Infrared and Luminescence Study of Tritiated Amorphous Silicon
Authors: Sidhu L. S. , Kosteski T. , Kherani N. P. , Gaspari F. , Zukotynski S. , Shmayda W. 
Published: April 2011

ABSTRACTTritium, has been incorporated into amorphous silicon. Infrared spectroscopy shows new infrared vibration modes due to silicon-tritium (Si-T) bonds in the amorphous silicon network. Si-T vibration frequencies are related to Si-H vibration frequencies by simple mass relationships. Inelastic collisions of β particles, produced as a result of tritium decay, with the amorphous silicon network results in the generation of electron-hob pairs. Radiative recombination of these carriers is observed. Dangling bonds associated with the tritium decay reduce luminescence efficiency.
Determination of Hydrogen Density of States in Amorphous Silicon Using Fractional Evolution Experiments
Authors: Franz A. J. , Jackson W. B. , Gland J. L. 
Published: April 2011

ABSTRACTHydrogen plays an important role in the electronic behavior, structure and stability of amorphous silicon films. Therefore, determination of the hydrogen density of states (DOS) and correlation of the hydrogen DOS with the electronic film properties are important research goals. We have developed a novel method for determination of hydrogen DOS in silicon films, based on fractional evolution experiments. Fractional evolution experiments are performed by subjecting a silicon film to a series of linear, alternating heating and cooling ramps, while monitoring the hydrogen evolution rate. The fractional evolution data can be analyzed using two complementary memods, the fixed frequency factor approach and Arrhenius analysis. Using a rigorous, mean-field evolution model, we demonstrate the applicability of the two approaches to obtaining the hydrogen DOS in silicon films. We further validate both methods by analyzing experimental fractional evolution data foran amorphous silicon carbide film. Both types of analysis yield a similar double peaked density of states for the a-Si:C:H:D film.
New Results on the Microstructure of Amorphous Silicon as Observed by Internal Friction
Authors: Crandall R. S. , Mahan A. H. , Iwaniczko E. , Jones K. M. , Liu X. , White B. E. , Pohl R. O. 
Published: April 2011

ABSTRACTWe have measured the low temperature internal friction (Q−1) of amorphous silicon (a-Si) films. Electron-beam evaporation leads to the well-known temperature-independent plateau common to all amorphous solids. For hydrogenated amorphous silicon (a-Si:H) with about 1 at.% H produced by hot wire chemical vapor deposition, however, the value of is over two hundred times smaller than for e-beam a-Si. This is the first observation of an amorphous solid without any significant low energy excitations. This finding offers the opportunity to study amorphous solids containing controlled densities of tunneling defects, and thus to explore their nature.
The Influence of the Substrate Temperature on the Recombination Processes in a-Si:H
Authors: Lubianiker Y. , Balberg I. , Fonseca L. , Weisz S. Z. 
Published: April 2011

ABSTRACTWe have studied the four phototransport properties as a function of temperature in undoped a-Si:H films deposited with different substrate temperatures in the range 150 – 225°C. The analysis of the results indicates how Ts determines the densities of the various defects. The general trend of decrease of both the density of dangling bonds and the Urbach energy is in agreement with the weak bond breaking model. However, we conclude that a slight modification of this model is required.
Influence of Deposition Conditions on the 1/f Noise in Hydrogenated Amorphous Silicon
Authors: West P. W. , Quicker D. , Dyalsingh H. M. , Kakalios J. 
Published: April 2011

ABSTRACTThe electronic properties of a series of n-type doped hydrogenated amorphous silicon (a-Si:H) films grown with deposition rates ranging from 2 Å/s to 33 Å/s have been studied. Infrared absorption spectroscopy shows an increase in S1-H2 content with deposition rate, concurrent with a decreasing conductivity, increasing thermal equilibration relaxation time, and increasing disorder at the mobility edge as measured by the difference in thermopower and dark conductivity activation energies. The current 1/f noise properties become highly nonstationary, with increased variability and inapplicability of statistical analysis as the deposition rate increases.
Cooling of Hot Electrons in Amorphous Silicon
Authors: Vanderhaghen R. , Hulin D. , Cuzeau S. , White J. O. 
Published: April 2011

ABSTRACTMeasurements of the cooling rate of hot carriers in amorphous silicon are made with a two-pump, one-probe technique. The experiment is simulated with a rate-equation model describing the energy transfer between a population of hot carriers and the lattice. An energy transfer rate proportional to the temperature difference is found to be consistent with the experimental data while an energy transfer independent of the temperature difference is not. This contrasts with the situation in crystalline silicon. The measured cooling rates are sufficient to explain the difficulty in observing avalanche effects in amorphous silicon.
Nanostructured Silicon thin films Deposited by PECVD in the Presence of Silicon Nanoparticles
Authors: Viera G. , Roca i Cabarrocas P. , Hamma S. , Sharma S. N. , Costa J. , Bertran E. 
Published: April 2011

ABSTRACTNanostructured silicon thin films have been deposited by plasma enhanced chemical vapor deposition at low substrate temperature (100 °C) in the presence of silicon nanoparticles. The nanostructure of the films was revealed by transmission electron microscopy, Raman spectroscopy and X-ray diffraction, which showed ordered silicon domains (1–2 nm) embedded in an amorphous silicon matrix. These ordered domains are due to the particles created in the discharge that contribute to the film growth. One consequence of the incorporation of nanoparticles is the accelerated crystallization of the nanostructured silicon thin films when compared to standard a-Si:H, as shown by the electrical characterization during the annealing.
Optical and Structural Characterization of Silicon Microstructures Fabricated by Laser Interference Crystallization
Authors: Toet D. , Aichmayr G. , Mulato M. , Santos P. V. , Spangenberg A. , Bergmann R. B. 
Published: April 2011

ABSTRACTUniform gratings of sharply defined polycrystalline silicon lines with micrometer-sized periods were created by laser interference crystallization of amorphous silicon. Atomic force microscopy (AFM) reveals that lines fabricated with high pulse energies (380 mJ/cm2) contain large grains (dimensions up to 1.5 μm), growing in a direction perpendicular to the lines. We assign this strong lateral growth to the melting of the material in the center of the lines combined with the presence of small grains, which act as nuclei, at the interfaces with the amorphous regions. Spatially resolved Raman spectroscopy shows that size effects dominate the Raman line shape at the edge of the line, confirming the AFM results, while stress increases towards the center of the line. The spectra measured in the middle of lines created with high energies show doping effects caused by the diffusion of boron atoms from the substrate upon exposure.
Dopant Activation During Solid Phase Crystallization of Poly-Si and Influence of Fluorine and Hydrogen
Authors: Kaan Kalkan A. , Kingi Reece M. , Fonash Stephen J. 
Published: April 2011

ABSTRACTDopant activation for ion implanted solid phase crystallized (SPC) a-Si:H films, deposited by low temperature PECVD, was investigated. The impact of film thickness, the effect of subsequent hydrogenation, and a possible role for fluorine in this process have been studied.
Crystallization of Germanium-Carbon Alloys - Structure and Electronic Transport
Authors: John T.-M. , Bläsing J. , Veit P. , Drüsedau T. 
Published: April 2011

ABSTRACTAmorphous Ge1-xCx alloys were deposited by rf-magnetron sputtering from a germanium target in methane-argon atmosphere. Structural investigations were performed by means of wide and small angle X-ray scattering, X-ray reflectometry and cross-sectional transmission electron microscopy. The electronic transport properties were characterized using Hall-measurements and temperature depended conductivity. The results of X-ray techniques together with the electron microscopy clearly proof the existence of a segregation of the components and cluster formation already during deposition. The temperature dependence of the electronic conductivity in the as-prepared films follows the Mott' T−1/4 law, indicating transport by a hopping process. After annealing at 870 K, samples with x≤0.4 show crystallization of the Ge-clusters with a crystallite size being a function of x. After Ge-crystallization, the conductivity increases by 4 to 5 orders of magnitude. Above room temperature, electronic transport is determined by a thermally activated process. For lower temperatures, the σ(T) curves show a behaviour which is determined by the crystallite size and the free carrier concentration, both depending on the carbon content.
Improved Stability Against Light-Exposure in Deuterated Amorphous Silicon Alloy Solar Cells
Authors: Sugiyama S. , Yang J. , Guha S. 
Published: April 2011

ABSTRACTWe have studied light-induced degradation in hydrogenated and deuterated amorphous silicon alloy solar cells in which intrinsic layers were deposited by using SiH4+H2 and SiD4+D2 gas mixtures respectively. Replacing hydrogen with deuterium in the intrinsic layer of the cell improves stability against light exposure. On the other hand, cells in which intrinsic layers were deposited from SiD4+H2 and SiH4+D2 do not show any improvement in stability. This result shows that improved stability in deuterated cell does not originate from simple replacement of hydrogen with deuterium. From deuterium/hydrogen effusion measurements, we found similar effusion at low temperature (400 °C) in both deuterated film and hydrogenated film prepared with heavy dilution. The latter film was shown to have oriented microstructure which was correlated with higher stability. This correlation strongly indicates that microstructure of the material plays a key role in improving the stability.
Intentional Reconstruction of Silicon Network on the Surface and within Sub-Surface by H and Ar
Authors: Futako W. , Fukutani K. , Shimizu I. 
Published: April 2011

ABSTRACTSilicon thin films were prepared by “Chemical Annealing” where the deposition of thin layer (<3 nm thick) by RF glow discharge of SiH4 and the treatment with hydrogen atoms (H) or triplet state of argon (3Ar) were repeated alternatating. Consequently, wide gap a-Si:H with the gap of 2.1 eV was made by H-treatmentat rather low substrate temperature (Ts<150 °C), while a-Si:H with the gap narrower than 1.6 eV was obtained by the treatment with 3Ar at high Ts (>300 °C), resulting from the release of excessive hydrogen. Both the wider or the narrower gap films exhibited low defect density lower than 1016 cm−3 and obvious improvements in the stability for light soaking.
Real-Time Kinetic Analysis of Hydrogen Abstraction and Etching Reactions Using Pulsed-Gas PECVD of Amorphous and Microcrystalline Silicon
Authors: Srinivasan Easwar , Parsons Gregory N. 
Published: April 2011

ABSTRACTHydrogen elimination reactions, abstraction and etching, are monitored in real-time using a differentially pumped mass spectrometer, while intermittently exposing a hydrogenated silicon surface to atomic deuterium. The mass spectrometer signals are used to predict the kinetics of the abstraction reaction, and to qualitatively treat the etch reaction.
Polarized Electroabsorption in Pulse and Continuous Light-Soaked a-Si:H - Structural Change other than Defect Creation
Authors: Hata H. , Kamei T. , Okamoto H. , Matsuda A. 
Published: April 2011

ABSTRACTExperimental results on structural change other than defect creation upon light-soaking of hydrogenated amorphous silicon (a-Si:H) are reported. A-Si:H films were light-soaked with laser pulses or with continuous (cw) light to steady-states, and then annealed at 170 °C in vacuum. The changes in electro-absorption (EA) signal, and defect density (Nd) from subgap absorption were measured as functions of light-soaking/annealing time. The results are: (1) EA ratio, which is defined as the ratio of anisotropie to isotropie components in EA signal, increases upon light-soaking with a time constant shorter by almost two orders of magnitude than that for Nd increase, and (2) shows saturation when extensively light-soaked. (3) The saturated values of EA ratio are comparable for both pulsed and cw light-soaking. (4) Both the EA ratio and Nd show recovery to the values in the annealed states. It is suggested that light-soaking causes a structural change in a short time, as manifested by EA ratio, and this changed structure works as the pathway leading to the defect creation. Thermal annealing is also discussed.