bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tribological Behavior of Very Thin Confined Films
Authors: Müser M. H. 
Published: April 2011

AbstractThe tribological properties of two smooth surfaces in the presence of a thin confined film are investigated with a generic model for the interaction between two surfaces and with computer sim- ulations. It is shown that at large normal contact pressures, an ultra thin film automatically leads to static friction between two flat surfaces - even if the surfaces are incommensurate. Commen- surability is nevertheless the key quantity to understand the tribological behavior of the contact. Qualitative differences between commensurate and incommensurate contacts remain even in the presence of a thin film. The differences mainly concern the thermal diffusion of the contact and the transition between smooth sliding and stick-slip.
Observation of Laser Speckle Effects in an Elementary Chemical Reaction
Authors: Monson Eric , Kopelman Raoul 
Published: April 2011

AbstractAn experimental demonstration is shown for non-classical reaction kinetics in a homogeneous system with an elementary reaction, A+B→C. Sensitivity to the initial distribution of reactants is observed, along with a new reaction-kinetics regime which is a direct consequence of speckles in the laser beam. The long-time regime gives the first experimental demonstration of the asymptotic self-segregation (“Zeldovich”) effect, in spite of the non-random, speckled initial distribution of reactant B. Monte-Carlo simulation results are consistent with the experiments, and spatial analysis of these results correlates the excess of long-wavelength components in the initial reactant distribution with an anomalous slowing of the reaction progress.
Mechanical Measurements at a Submicrometric Scale: Viscoelastic Materials
Authors: Basire Charlotte , Fretigny Christian 
Published: April 2011

AbstractAdhesive and tribological properties of the tip of an AFM on viscoelastic samples are studied. The kinetics of the indentation process is shown to be governed by bulk rather than by contact edge dissipations. It is shown that the transition from static to dynamic friction regimes takes place at a critical strain. During the static friction regime, the contact size remains nearly constant. Owing to this property, viscoelastic moduli is measured in this regime. Obtained results, characteristic of a micrometric domain are in a very good agreement with the same properties measured on centimetric samples using dynamical mechanical analysis. Finally, a stick-slip friction regime is observed in a range of velocities.
Adsorption in Ordered Porous Silicon: a Reconsideration of the Origin of the Hysteresis Phenomenon in the Light of new Experimental Observations
Authors: Coasne B. , Grosman A. , Dupont-Pavlovsky N. , Ortega C. , Simon M. 
Published: April 2011

AbstractPorous silicon formed in p+ single crystal silicon is an interesting material for the study of the behavior of a fluid confined in mesoporous media, because it is a simple system of non interconnected straight pores, all perpendicular to the substrate and it can be well characterized by different methods. Moreover, the pores may be closed at one end when the porous layer is supported by the substrate or opened at both ends when the layer is removed from the substrate. Surprising results have been obtained. A hysteresis loop of type H2 (IUPAC classification), which is generally obtained for highly interconnected porous material, is also observed. Furthermore, a hysteresis of same type is also observed in pores closed at one end which is in contradiction with the Cohan model. The steep desorption process does not account for the large pore size distribution extracted from transmission electronic microscopy study. It is believed that, during the desorption process, the presence of an adsorbed layer on the external surface of the pores and/or the coupling between the pores via the silicon walls must be taken into account.
A Grand Canonical Monte-Carlo Study of Argon Adsorption/Condensation in Mesoporous Silica Glasses: Application to the Characterization of Porous Materials
Authors: Pellenq R.J.-M. , Rodts S. , Levitz P. E. 
Published: April 2011

AbstractWe have studied adsorption of argon in a mesoporous silica Controlled Porous Glass (CPG) means of Grand Canonical Monte-Carlo (GCMC) simulation. A numerical sample of the CPG adsorbent has been obtained by using an off-lattice reconstruction method recently introduced to reproduce topological and morphological properties of correlated disordered porous materials. The off-lattice functional of (100 m2/g)-Vycor is applied to a simulation box containing silicon and oxygen atoms of cubic cristoballite with an homothetic reduction of factor 2.5 so to obtain 30Å-CPG sample. A realistic surface chemistry is then obtained by saturating all oxygen dangling bonds with hydrogen. The Ar, Kr and Xe adsorption/desorption isotherms are calculated at different temperatures. At sufficiently low temperature, they exhibit a capillary condensation transition with a finite slope by contrast to that theoretically predicted for simple pore geometriessuch as slits and cylinders. In the low pressure and temperature domain, we have identified different adsorption scenarios, which can be interpreted on the basis of a Zisman-type of criterium for wetting. We demonstrate that the BET surface area is strongly related to this criterion. At higher pressure, we demonstrate that the pore size distribution obtained by using the standard BJH analysis applied to both adsorption and desorption data qualitatively reproduces the main features of the chord length distribution.
The Influence of Boundary Conditions and Surface Layer Thickness on Dielectric Relaxation of Liquid Crystals Confined in Cylindrical Pores
Authors: Nazario Z. , Sinha G. P. , Aliev F.M. 
Published: April 2011

AbstractDielectric spectroscopy was applied to investigate the dynamic properties of liquid crystal octylcyanobiphenyl (8CB) confined in 2000 Å cylindrical pores of Anopore membranes with homeotropic and axial (planar) boundary conditions on the pore walls. Homeotropic boundary conditions allow the investigation of the librational mode in 8CB by dielectric spectroscopy. We found that the dynamics of the librational mode is totally different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependence of relaxation times and of the dielectric strength of the librational mode needs the involvement of the temperature dependence of orientational order parameter. For samples with axial boundary conditions, layers of LCs with different thickness were obtained on the pore walls as a result of controlled impregnation of porous matrices with 8CB from solutions of different liquid crystal concentration. The process due to rotation of molecules around their short axis with single relaxation time observed for bulk 8CB is replaced by a process with a distribution of relaxation times in thin layers. This relaxation process broadens with decreasing layer thickness.
Studies of Temperature-Dependent Excimer-Monomer Conversion in Dendrimeric Antenna Supermolecules by Fluorescence Spectroscopy
Authors: Caoa Youfu , Moore Jeffrey S. , Kopelman Raoul 
Published: April 2011

AbstractPhenylacetylene (PA) dendrimer labeled with perylene (See Fig 1) is discovered to exhibit temperature-dependent emission spectra in certain organic solvents over the temperature range of 20-65°C. The monomer signal is increasing rapidly when temperature increases, while the excimer signal decreases slowly. Models of excimer formation and weakly associated pairs (M+M) dissociation dynamics are included, and the equilibrium constants at different temperatures are calculated. This behavior suggests potential applications in fluorescence-based thermometry.
Isotopes in Neutron Diffraction – Detailed Structural Analysis at the Metal-Insulator Transition in SmNiO3
Authors: Weller Mark T. , Henry Paul F. , Wilson C.C. 
Published: April 2011

ABSTRACTThe use of isotopically enriched materials on high intensity neutron powder diffractometers allows the derivation of much higher quality structural information than has hitherto been possible. The technique can be applied to materials such as ferroelectrics, superconductors and oxides exhibiting colossal magneto-resistance, where small structural changes associated with phase transitions need to be characterised. Three isotopically pure samples of samarium nickelate have been studied around the metal-insulator transition at 403 K. Simultaneous multi-histogram refinements permit extraction of very high quality structural information that shows smooth variations in bond lengths and angles with all nickel oxygen distances decreasing as the electrons localise.
Deposition and Characterization of Y3Al5O12 (YAG) Films and Powders by Plasma Spray Synthesis
Authors: Parukuttyammaa Sujatha D. , Margolis Joshua , Liu Haiming , Parise John B. , Grey Clare P. , Sampath Sanjay , Gouma Perina , Herman Herbert 
Published: April 2011

ABSTRACTYAG powders and coatings were developed for the first time by a novel precursor plasma spraying technique using the radio frequency (RF) induction plasma technique. The XRD of the as -sprayed coating confirms the presence of YAG, H-YAP or O-YAP or a mixture of the above depending on the spray conditions. 27Al MAS NMR of the YAG coating corroborates the x-ray results. TEM studies on the coatings confirm that the coating consists of nano-structured particles. The successful spraying of these complex oxide coatings proves that chemistry of phase formation can be controlled in the plasma, thus opening up new avenues in material synthesis.
Photocarrier capture properties of light-induced defects in a-Si:H
Authors: Stradins Paul , Shimizu Satoshi , Kondo Michio , Matsuda Akihisa 
Published: April 2011

ABSTRACTLight-induced degradation of photoconductive properties is investigated as a function of lightinduced Si dangling bond defect concentration and subgap absorption. This relation is studied for a variety of sample preparation techniques including a-Si:D, wide range of temperatures during light exposure and annealing, and sample degradation pre-history. Under a given exposure condition, light-induced defects have a fixed effective electron capture coefficient, while its value varies greatly with exposure conditions (temperature during exposure or stepwise anneal) and with sample microstructure. This explains commonly observed non-linear dependences and hysteresis between defect concentration and mobility-lifetime product. Creation efficiency of less-stable defects with large capture coefficients is not influenced by the presence of a large number of stable defects. Structural change accompanying the defect creation, if any, is strongly related to the defect creation and is likely to occur locally around the defects, modifying their capture coefficients. Capture can vary both because of the changes in intrinsic capture probabilities and due to changes in the net defect charge balance. The former may be increased by the presence of H or photocarrier trap (e.g. weak bond tail state) in a close vicinity of Si dangling bond. The latter may be caused by a wide distribution of defect states in the gap or by simultaneous creation of negatively charged floating bond states near VB edge.
Hydrogen Equilibration and Metastability in Amorphous Silicon
Authors: Branz Howard M. , Zhang S.B. 
Published: April 2011

ABSTRACTWe review evidence for the vital role of H in metastability and defect equilibration in hydrogenated amorphous silicon. H pairs act both as an H reservoir that equilibrates with DB's and dopants and as the metastable H state of light-induced metastability. With ab initio pseudopotential theory, we calculate energies and configurations for two novel H pairing sites associated with small hydrogenated vacancies. We describe microscopic models of equilibration and metastability based on our calculations.
Model of Hydrogen-Mediated Metastable Changes in a Two-Domain Amorphous Silicon Network
Authors: Baugh Jonathan , Han Daxing 
Published: April 2011

ABSTRACTA phenomenological model for the light-induced metastability of a-Si:H is proposed in which a two-domain model of the amorphous network plays a central role. Boundaries between high and low density domains are associated with a significant fraction of the clustered Si-H in aSi:H. Weakly bonded hydrogen at these boundaries catalyzes metastable local configuration changes in the Si network due to non-radiative carrier recombination, leading qualitatively to both the gross structural changes and the increase in electronic defect density that are observed experimentally.
Hydrogen Distributions and Model Lineshapes of ESR Signals of Dangling Bonds in a-Si:H
Authors: Fedders P. A. 
Published: April 2011

ABSTRACTFor many years it has been assumed widely that hydrogen is involved in some way in the formation of light induced defects. However recently some doubt has been cast on this because of experimental evidence that there is little H near light induced dangling bonds. In this paper we present a number of model calculations comparing ESR spectra of dangling bonds with and without correlations with H positions. The above models include different distributions of H and correlations or anti correlations of nearby H. In all cases the spectra are compared to those with no correlations or clustering. Our results coupled with published experimental data strongly suggest that dangling bonds are not correlated positively with the presence of nearby H and, in fact, it appears that light induced dangling bonds are negatively correlated with nearby H.
Electronic transport study of high deposition rate HWCVD a-Si:H by the microwavephotomixing technique
Authors: Sheng S.R. , Braunstein R. , Nelson B.P. , Xu Y. 
Published: April 2011

ABSTRACTThe electronic transport properties of high deposition rate a-Si:H films prepared by HWCVD have been investigated in detail by employing the microwave photomixing technique. The high deposition rates (up to 1 µm/min.) were achieved by adding a second filament, increasing deposition pressure, silane flow rate, and decreasing filament-to-substrate distance. The effect of the deposition rate on the resultant film properties with respect to the substrate temperature, deposition pressure and silane flow rate was studied. It was found that the film transport properties do not change monotonically with increasing deposition rate. The photoconductivity peaks at ∼70-90 Å/s, where both the drift mobility and lifetime peak, consistent with the deposition rate dependence of the range and depth of the potential fluctuations. High quality, such as a photoconductivity-to-dark-conductivity ratio of ∼105 and nearly constant low charged defect density, can be maintained at deposition rates up to ∼150 Å/s, beyond which the film properties deteriorate rapidly as a result of an enhanced effect of the long-range potential fluctuations due to a considerable increase in the concentration of the charged defects. Our present results indicate that medium silane flow rate, low pressure, and higher substrate temperature are generally required to maintain high quality films at high deposition rates.
Study of Electrical Properties of Microcrystalline Silicon Films Using AC Measurements
Authors: Dirani Ely A. T. , Nardes Alexandre M. , Andrade Adnei M. , Fonseca Fernando J. , Muccillo Reginaldo 
Published: April 2011

ABSTRACTHydrogenated amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon films are indispensable materials for large area electronic devices like solar cells, image sensors and thin film transistors (TFTs). The interest of the µc-Si:H films arise from the fact that they combine the high optical absorption of a-Si:H and the electrical transport properties close to those of crystalline silicon. In this work we show the correlation between substrate deposition temperature, crystallinity and electrical properties of a-Si:H and µc-Si:H films. The films were prepared by a conventional PECVD (13.56 MHz) RF system from PH3/SiH4/H2 gas mixtures in the temperature range of 100 to 250°C. While phosphorus doped (n) a-Si:H are deposited yielding conductivity values no better than 10−2 S/cm, (n) µc-Si:H layers deposited at substrate temperature of 250°C show conductivity values higher than 101 S/cm, crystalline fraction up to 80% and Hall mobility of about 0.9 cm2. V−1.s−1. It was observed that a change in the dark conductivity behavior occurs around 140°C, with a large increase in the conductivity values. A corresponding increase is not seen in the average grain size and in the crystalline volume fraction, which shows an almost linear increase with the deposition temperature. This stronger influence of the temperature in the electrical characteristics of the µc-Si:H films may be related to the phosphorus activation, which occurs in higher degree at higher deposition temperatures. The correlation among Raman spectroscopy, Hall effect and AC conductivity measurements (frequency range 6 Hz to 13 MHz) shows that the crystalline phase dominates the electrical transport mechanism in µc-Si:H films. Preliminary results of AC measurements indicate that the electrical resistivity of each phase of this material can be determined.
Effects of low-temperature annealing on the initial and stabilized performance of amorphous silicon solar cells
Authors: Carlson D. , Ganguly G. , Lin G. 
Published: April 2011

ABSTRACTWe have recently observed that the initial performance of amorphous silicon (a-Si) solar cells can be improved by up to several % by annealing the cells at successively lower temperatures for successively longer times. For some devices, we also observed an improvement in performance after light soaking that was statistically significant. We have also observed an improvement in the stabilized performance of cells that were subjected to reverse bias annealing after light soaking. This effect was clearly evident in single-junction p-i-n cells with amorphous silicon-carbon (a-SiC) i-layers where the density of metastable centers is very high (> 1018cm-3). When we light-soaked a-SiC cells and then subjected them to low-temperature reverse bias annealing, they exhibited clear evidence of improved short-wavelength response after a second light soaking. These annealing effects are explained in terms of hydrogen motion within the a-Si network and within microvoids.
A Novel Poly-Si Solar Cell using Grain Boundary Etching Treatment and Transparent Conducting Oxide
Authors: Lim Dong Gun , Lee Wook Jae , Yi Junsin 
Published: April 2011

ABSTRACTThis paper deals with a novel structure of polycrystalline silicon (poly-Si) solar cell for terrestrial applications. Grain boundary (GB) in poly-Si degrades a conversion efficiency of poly-Si solar cell. To reduce the GB side-effect, we investigated various parameters such as the preferential GB etch, etchtime, ITO electrode, heat treatment, and emitter layer effect. Among various preferential etchants such as Sirtl, Yang, Secco, and Schimmel, a Schimmel etchant illustrated an excellent preferential etching property. We observed a 10μm deep trench along grain boundaries and randomly textured grain surface with pyramid structure. We used rf magnetron sputter grown tin doped indium oxide (ITO) film as a top contact metal. ITO films showed a resistivity of 1.14 ×10-4 Ω-cm and transmittance of 90.5% for the wavelength of 594 nm. ITO films served as a top electrode as well as an effective AR coating layer. ITO film properties were strongly influenced by the preparation temperatures. Substrate temperature of 400oC gave the highest conversion efficiency of poly-Si solar cell. With well-fabricated poly-Si solar cells, we were able to achieve conversion efficiency as high as 16% at the input power of 20 mW/cm2.
Density of States in a-Si:H from SCLC and Its Application in Modeling a Vertical TFT
Authors: Sedghi Naser , Eccleston Bill 
Published: April 2011

ABSTRACTSteady-state space-charge limited current (SCLC) measurements are used to investigate the density of states (DOS) in the mobility gap of hydrogenated amorphous silicon (a-Si:H). The density of states is calculated by different methods based on both continuous DOS and discrete traps assumptions. The density of states found by the SCLC measurements is used to set the trap densities and trap energy levels to model a vertical a-Si:H thin-film transistor (TFT) using the Medici device simulation package. The effect of different sets of traps in the bulk of a-Si:H and variation of the physical dimensions of the device on the characteristics of the vertical TFT is studied. The simulation on the space-charge limited current is performed to verify the validity and accuracy of the SCLC method.
Metastable changes of the electrical conductivity in microcrystalline silicon
Authors: Nickel N. H. , Rakel M. 
Published: April 2011

ABSTRACTThe temperature dependence of the dark conductivity, σD, of as-grown and H depleted µproportional σc-Si was measured. While σD of the H depleted samples did not exhibit any influence of thermal treatment prior to the measurements, in as-grown σproportional µc-Si the dark conductivity increased by 2 orders of magnitude below 300 K upon rapid thermal quenching. The frozen-in state is reversible and an anneal at 440 K followed by a slow cool completely restores the initial state. The time and temperature dependence of the relaxation of the quenched-in state reveals two competing processes. At short times σD increases due to the activation of a donor complex and at long times σD decreases due to the dissociation of bond-center H complexes.
Radical Species Distributions in Hot-Wire Chemical Vapor Deposition Probed Via Threshold Ionization Mass Spectrometry and Direct Simulation Monte Carlo Techniques
Authors: Holt Jason K. , Swiatek Maribeth , Goodwin David G. , Atwater Harry A. , Muller R.P. , Goddard W.A. 
Published: April 2011

ABSTRACTMonte Carlo simulations of hot-wire chemical vapor deposition (HWCVD) gas ambients indicate different flux ratios (SiH3/Si and H/SiHx) under conditions for amorphous or polycrystalline silicon growth. Gas-phase reactions of Si with ambient SiH4studied usingabinitiomethods reveals that collisional stabilization of the adduct (H3SiSiH) is unlikely under typical HWCVD growth pressures, but an energetically favorable, low-pressure pathway has been identified that leads to the formation of Si2H2and H2. Threshold ionization mass spectrometry has revealed significant quantities of the radical SiH2at HWCVD growth pressures, indicative of heterogeneous pyrolysis. Mass spectrometry at low pressures suggests that incident silane dissociatively adsorbs at the wire and undergoes sequential H elimination to produce subhydrides. Disilicon species were not detected in significant quantities at HWCVD growth pressures. Finally, hot wire operation in a pure H2ambient yields SiH4as the dominant etching product from the silicon-coated walls of the growth chamber.
Material properties and growth process of microcrystalline silicon with growth rates in excess of 1 nm/s
Authors: Hamers E.A.G. , Smets A.H.M. , Smit C. , Hoefnagels J.P.M. , Kessels W.M.M. , Sanden M.C.M. van de 
Published: April 2011

ABSTRACTThe expanding thermal plasma (ETP) has been used to deposit microcrystalline silicon (µc-Si:H) with rates up to 2.7 nm/s. Typical material properties of well crystallised material are crystallite sizes of 20 nm, photo- and dark conductivity of 2×10−5 and 2x10−7 S/cm respectively, and an activation energy of 600 meV. The radical densities of SiH3, SiH, and Si present in the gas phase have been quantified. In conditions where [.proportional µc-Si:H is deposited the atomic hydrogen flux towards the surface is of the same magnitude or higher as the flux of deposited radicals. Furthermore, the abundance of radicals such as SiH and Si is large and may contribute several tens of percent to the deposition rate.