bluuebunny/crossref_metadata_2025 huggingface dataset:
Grain Boundary Engineered Lead Alloys
Authors: Lehockey E. M. , Palumbo G. , Brennenstuhl A. , Lin P.
Published: April 2011

The present work reports oii the effect of grain boundary structure on intergranular corrosion and creep by grain boundary diffusion in polycrystalline lead (Pb). “Special” boundaries characterized by low-Σ misorientations in the Coincident Site Lattice (CSL) model have been shown to exhibit resistance to grain boundary sliding and corrosion. PbCa and PbCaSn alloys having “special” grain boundary frequencies greater than 50% showed a 30 fold reduction in steady-state creep compared with corresponding as-received alloys containing 10% to 28% of low-Σ CSL boundaries in the microstructure of comparable grain size. At the same time, increasing the frequency of “special” boundaries enhanced alloy ductility with no compromize in tensile strength. Results from electrochemical corrosion tests on polarizied Pb alloys immersed in H2SO4 (S.G.=1.28) at 70°C indicate a clear correlation between the frequency of “special” boundaries and the prolifíeration of intergranular corrosion resulting in bulk weight loss from grain-dropping. Collectively, these results advocate adopting a “gram boundary design” approach in developing advanced lead-acid battery electrodes.
Theoretical Calculations of Elastic Properties of Metallic Superlattices
Authors: Yamaguchi Akira , Nakajima Hideo
Published: April 2011

Elastic constants of metallic multilayered film have been calculated using MEAM (Modified Embedded Atom Method) potential. Structural relaxation has been performed to obtain relaxed model structure of (111) stacked multilayers which consist of two fee metal elements. The composition modulation wavelength dependence of elastic constants was found to be large, and we could not observe any large enhancement of elastic modulus in the calculated systems.
Bicrystals with Strain Gradient Effects
Authors: Shu John Y. , Fleck Norman A. , King Wayne E.
Published: April 2011

The boundary between two perfectly bonded single crystals plays a very important role in determining the deformation of the bicrystal. This work addresses the role of the grain boundary by considering the elevated hardening of a slip system due to a slip gradient. The slip gradients are associated with geometrically necessary dislocations and their effects become pronounced when a representative length scale of the deformation field is comparable to the dominant microstructural length scale of a material. A new rate-dependent crystal plasticity theory is presented and has been implemented within the finite element method framework. A planar bicrystal under uniform in-plane loading is studied using the new crystal theory. The strain is found to be continuous but non-uniform within a boundary layer around the interface. The lattice rotation is also non-uniform within the boundary layer. The width of the layer is determined by the misorientation of the grains, the hardening behavior of slip systems, and most importantly by the characteristic material length scales. The overall yield strength of the bicrystal is also obtained. A significant grain-size dependence of the yield strength, the Hall-Petch effect, is predicted.
Interfacial Engineering: An Overview
Authors: Evans D. Fennell
Published: April 2011

In order to develop programs in education, technology transfer and research to achieve these goals, a partnership between the University of Minnesota, industries and government was established. The Center for Interfacial Engineering was born and the strategic plan is shown in Figure 1. Some statistics for this year are as follows. The budget is $6.5 M of which 41% is contributed by the NSF, 25% by the University of Minnesota and 34% by 54 industrial members. Sixty four faculty members from 6 departments are involved in the Center with 18 core CIE faculty. There are 244 graduate students and postdoctoral fellows, 41 undergraduates and 69 industrial researchers directly involved in center projects.
Interfaces Studied by Electromechanical Pull-Out Testing
Authors: Fu Xuli , Chung D. D. L.
Published: April 2011

The experimental technique of electromechanical pull-out testing is introduced to study the interface between fiber and matrix. The technique involves measuring both the contact electrical resistivity and the shear bond strength of a fiber-matrix interface. Samples that are identically prepared differ in contact resistivity and bond strength, which correlate. The correlation allows determination of even small differences in bond strength due to differences in sample preparation conditions. It also gives information on the structure of the interface and allows the bond strength to be nondestructively determined by measuring the contact resistivity. The technique is demonstrated for the interface between steel fiber and cement.
Nonlinear Current-Voltage Characteristics of Homojunctions Made by Zinc Oxide Single Crystals
Authors: Harada Takeshi , Nakamura Yoshinobu , Kishimoto Akira , Motohira Naobumi , Yanagida Hiroaki
Published: April 2011

Zinc oxide (ZnO) single crystals are grown by the traditional chemical vapor reaction method and ZnO crystal pairs with a single boundary are successfully obtained. The obtained specimens with one ZnO–ZnO boundary (ZnO homojunction) show nonlinear current-voltage (I–V) characteristics without the addition of Bi2O3, CoO, MnO2, and/or rare earth metal oxides. A specimen with higher breakdown voltage shows superior nonlinearity with negative resistivity in its I–V characteristics. Electrical characterization of the ZnO homojunction is conducted and extremely slow response with the current (or voltage) stress is confirmed. The phenomenon had never been observed in commercial ZnO varistors. The surface temperature of the ZnO homojunction is enhanced by larger applied current. The effect of the Joule heat on the nonlinearity in the I–V curves of the ZnO homojunction is discussed.
Power-Law Phenomena in Adhesive De-Bonding
Authors: Kendall G. , Cote P. J. , Crayon D. , Bonetto F. J.
Published: April 2011

Acoustic emission (AE) events were recorded during the peeling of pressure-sensitive adhesive (PSA) tape from a silicate glass surface. The distributions of AE event durations and energies are found to have the form of power laws. Power-law dependencies (hyperbolic distributions) are recognized as a consequence of self-organized criticality (SOC), resulting from the absence of any characteristic length or time scales. In these studies, standard optical microscopy was used to characterize the fractal nature of the PSA-glass interface. The present results suggest that it is the inherent static structural features found at the fractal PSA-glass interface which produce the observed hyperbolic distributions in AE events, rather than a true SOC process.
Evidence of a Passive Layer Formation from a Conductive Polymer Coating on Aluminum Alloys
Authors: Racicot R. J. , Yang S. C. , Brown R.
Published: April 2011

Evidence for the formation of a passive layer between a conductive polymer coating and aluminum alloy surfaces is reported Experimental results from electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) on aluminum alloys coated with a novel double strand conductive polymer coating based on polyaniline reveal the evidence for the formation of passive layer. The key results are: (1) Modeling of EIS data is best fit with a three RC circuit, indicating a third interface between the polymer coating and the alloy's surface; (2) EIS testing in acidic salt solutions shows the conductive polymer coating performs differently and better than a typical anodized or chromáte conversion coating indicating a possibly different interface layer than a typical aluminum oxide and (3) SEM studies of the aluminum surface, after the polymer film is removed, indicates that this interfacial layer has a dense and smooth “oxide type” surface morphology. The experimental results are consistent with a mechanism in which the conducting polymer serves as a surface conversion agent that oxidizes the aluminum metal surface to form a passive layer.
The Grain Boundary Diffusion Kinetics in Nanocrystalline Zirconia
Authors: Zhilyaev A. P. , Gertsman V. Y. , Szpunar J. A.
Published: April 2011

It is expected that the grain boundary diffusion is the principal contributor to the transport properties of nanocrystalline zirconia, and that it controls the oxidation kinetics and hydrogen permeation. This process depends on the grain boundary character distribution (i.e. the fractions of different grain boundary types) and on the topological characteristics of the grain boundary network. Modeling of the random walk problem on a planar honeycomb network for different types of the grain boundary misorientation distributions (GBMD) in nanocrystalline zirconia film is presented in the current paper. The GBMD was calculated using the model texture. Changes of the oxidation rate for different types of the grain boundary character distribution and different ratios of the bulk and grain boundary diffusion coefficients are analyzed. In this study it was found that an increase of the frequency of low energy boundaries lowers the oxidation rate.
Investigations of the Bonding Changes Associated with Grain Boundary Embrittlement
Authors: Keast V. J. , Bruley J. , Williams D. B.
Published: April 2011

The embrittlement of materials through the segregation of impurities to the grain boundaries is a common and industrially important problem. Despite considerable investigation, the mechanism by which the impurity elements cause embrittlement is not well understood. A change in the electron energy loss near edge structure (ELNES) has been observed at Cu grain boundaries containing Bi. This result provides experimental evidence that a change in the electronic structure at the grain boundary is responsible for embritdement.
Domain Wall Contributions to the Piezoelectric Properties of Ferroelectric Ceramics and Thin Films, and Their Significance in Sensor and Actuator Applications
Authors: Damjanovic D. , Taylor D. V. , Kholkin A. L. , Demartin M. , Brooks K. G. , Setter N.
Published: April 2011

The piezoelectric and dielectric properties of ferroelectric thin films and ceramics were investigated in detail as a function of the frequency and amplitude of the driving field. A description, which is based on the theories of domain wall pinning by randomly distributed imperfections in magnetic materials, is used to interpret the electromechanical behaviour of several ferroelectric bulk ceramic and thin film compositions. With this approach, it is possible to make quantitative estimates of the domain wall contributions to the electromechanical properties of ferroelectric sensors and actuators.
Finite Element Modelling of Adaptive Composite
Authors: Wen Y. , Denis S. , Gautier E. , Roytburd A.
Published: April 2011

The deformation of adaptive composite with active polydomain components has been calculated by finite element modelling (FEM). The average deformation, the distribution of stresses and the elastic energy of the composite as a function of different extent of twinning of the composite active component are calculated. Comparing the results of the FEM with the results of the analytical theory demonstrates the effect of the microstresses on the mechanics of the adaptive composite.
Application of Porous Silicon to Bulk Silicon Micromachining
Authors: Kaltsas G. , Nassiopoulos A. G.
Published: April 2011

A fully C-MOS compatible process for bulk silicon micromachining using porous silicon technology and front-side lithography is developed. The process is based on the use of porous silicon as a sacrificial layer for the fabrication of deep cavities into monocrystalline silicon, so as to avoid back side lithography. Cavities as deep as several hundreds of micrometers are produced with very smooth surface and sidewalls. The process is used to produce : a) suspended monocrystalline silicon membranes, b) free standing polysilicon membranes in the form of bridges or cantilevers with lateral dimensions from a few μms to several hundreds of μms. Important applications to silicon integrated devices as sensors, actuators, detectors etc., are foreseen.
Flexible Graphite as A Strain/stress Sensor
Authors: Luo Xiangcheng , Chung D.D.L.
Published: April 2011

Flexible graphite sandwiched by copper, after stabilization by two cycles of compressive stress, is an effective piezoresistive compressive strain/stress sensor for stresses up to 4 MPa and strains up to 25%. The stress sensitivity (fractional change in resistance per unit stress) is up to 5.4 MPa−1 and strain sensitivity (fractional change in resistance per unit strain) is up to 6.2 in the direction perpendicular to the sheet. The electrical resistance decreases reversibly upon compression, due mainly to reversible decrease in the contact resistivity between graphite and copper. Stabilization removes most of the irreversible effects. The strain/stress sensitivities decrease with increasing strain/stress.
A Study of the Rubber-Like Behavior of Mono-Domain Au-Cd Martensite
Authors: Ren Xiaobing , Otsuka Kazuhiro
Published: April 2011

The origin of the rubber-like behavior in mono-domain Au-Cd martensite was explained in terms of a new model that focused attention on the change of long-range elastic interaction energy among vacancies during a domain reversion. Vacancies in martensite, the lower-symmetry phase, produce stress fields with lower symmetry. During martensite aging, vacancies tend to rearrange themselves to lower elastic interaction energy. The low-symmetry elastic field results in a low-symmetry vacancy configuration. When a stabilized martensite domain reverts to a new domain (twin) under external stress, the original vacancy configuration is inherited to the new domain, but such a configuration becomes a high energy configuration because of the lower symmetry of elastic field, and thus it tends to restore the original configuration by reverse twinning. The above vacancy reconfiguration model is consistent with the fact that the rubber-like behavior is closely related to vacancies.
Improvement of the Corrosion Resistance of NiTi Stents by Surface Treatments
Authors: Trépanier C. , Tabrizian M. , Yahia LH. , Bilodeau L. , Piron D. L.
Published: April 2011

Because of its optimal radiopacity, superelasticity and shape memory properties Nickel-Titanium (NiTi) is an ideal material for the fabrication of stents. Indeed, these properties can facilitate the implantation and precise positioning of those devices. However, in vitro studies on NiTi report the dependency of the alloy biocompatibility and corrosion behavior to surface treatments. Oxidation of the surface seems to be very promising to improve both the corrosion resistance and the biocompatibility of NiTi. The present study investigate the effect of electropolishing, heat treatment (in air and in a salt bath) and nitric acid passivation to modify the oxide layer on NiTi stents. Techniques such as potentiodynamic polarization tests, Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) have been used to develop relationships between corrosion behavior, surface characteristics and surface treatment. Results show that all surface treatments improve the corrosion behavior of the alloy. SEM results indicate that treated stents which exhibit a smooth and uniform surface show a higher corrosion resistance than non treated stents which possess a very porous oxide layer. AES results, indicate that the best corrosion behavior was observed for the stents which exhibit the thinnest oxide layer (electropolished and passivated samples).
In-Situ Control of the Direction of Spontaneous Polarization in Ferroelectric thin Films by RF-Magnetron Sputtering
Authors: Iijima K. , Niihara K.
Published: April 2011

La-modified PbTiO3thin films were grown on (100)MgO by rf-magnetron sputtering. Thin films were prepared by “two step method” in which the different Pb/Ti ratios during the growth were used for the first step (0–4nm of thickness) and the subsequent second step (>4nm). The Pb/Ti ratios of the first step were selected from 1.2 to 1.5. The Pb/Ti ratio of the second step, on the other hand, was fixed at 1.4. Strong dependency of the direction of the spontaneous polarization (Ps) to the Pb/Ti ratio of the first step was observed. It is concluded that the direction of the Ps in the films is determined by the atomic species of the first layer of the films.
Structural Defects in the 18R Martensite of CuZnAi Shape Memory Alloys
Authors: Condo A. M. , Lovey F. C.
Published: April 2011

The lattice relaxation at the type I faults in the 18R martensite was studied by high resolution TEM. Local atomic plane rotations and small changes of the interplanar distances were observed over a distance of 1.5 nm. It is shown that this distorted region can be rationalized as an intermediate structure between the martensite and the second variant of the parent phase.
Corrosion Kinetics of Laser Treated NiTi Shape Memory Alloy Biomaterials
Authors: Villermaux F. , Nakatsugawa I. , Tabrizian M. , Piron D. L. , Meunier M. , Yahia U'H.
Published: April 2011

NiTi shape memory alloy presents interesting mechanical properties as surgical implants. However, due to its high amount of Ni which may dissolve and release toxic ions in human fluids, the medical use of this material is a great concern. We have developed a laser treatment which modifies the oxide layer and enhances uniform and localised corrosion resistance of NiTi alloy.

In this paper we further analysed the effect of this treatment with potentiostatic and AC impedance measurements in physiological Hank's solution. We conclude that the laser treatment creates a stable passive film which results in improved corrosion resistance of this alloy.
A Quantitative Micro-Deformation Field Study of Shape Memory Alloys by High Sensitivity Moiré
Authors: Sun Q. P. , Xu Terry T. , Zhang X. Y. , Tong P.
Published: April 2011

Quantitative micro-macro combined experimental research on the deformation field of single crystal CuAINi shape memory alloy (SMA) is performed by using high sensitivity Moiré technique. The study is focused on the micro-macro correspondence of the deformation behavior of single crystal uniaxial tensile specimen during stress induced forward and reverse transformations. The aim of the experiment is to quantitatively relate the macroscopic applied stress with the deformation field in the mesoscale. The large deformation due to the lattice distortion during transformation was first successfully recorded by Moiré interferometry. Some important microstructure-related deformation features of single crystal SMA under uniaxial tension are first reported.
Dielectric Properties of Piezoelectric Polyimides
Authors: Ounaies Z. , Young J. A. , Simpson J. O. , Farmer B. L.
Published: April 2011

Molecular modeling and dielectric measurements are being used to identify mechanisms governing piezoelectric behavior in polyimides such as dipole orientation during poling, as well as degree of piezoelectricity achievable. Molecular modeling on polyimides containing pendant, polar nitrile (CN) groups has been completed to determine their remanent polarization. Experimental investigation of their dielectric properties evaluated as a function of temperature and frequency has substantiated numerical predictions. With this information in hand, we are then able to suggest changes in the molecular structures, which will then improve upon the piezoelectric response.
Maintaining Chaos
Authors: Spano Mark L. , In Visarath , Ditto William L.
Published: April 2011

The recognition of chaos as a new type of behavior for complex systems initially spurred efforts to avoid it and, later, to control it. Yet in many cases chaos may be beneficial. We present a method for maintaining chaos in physical systems and implement the method on a simple magnetomechanical system. Application to other systems is discussed briefly.
Giant Magnetostrictive, Spring Magnet Type Multilayers and Torsion Based Microactuators
Authors: Betz J. , Mackay K. , Peuzin J.-C. , Givord D. , Halstrup B.
Published: April 2011

There is a need for powerful active materials in microsystem actuators. Research on thin film magnetostrictive materials has concentrated on optimising the magnetostrictive response notably by reducing the required driving magnetic field. Here we present a novel type of multilayer, where 2 alloys having different properties are coupled together. The resulting composite system represents a new material with novel characteristics, which can not be fulfilled by simple alloys. In particular here we have investigated magnetostrictive multilayers, with remarkable low field performances (i.e. very large ∂λ / ∂H).

Most magnetostrictive microactuators are based on a bimorph structure. However, these simple structures are prone to thermal drift. We present here also some results on a torsion based magnetostrictive microactuator prototype being insensitive to thermal drift.
Innovative Process Development of Sx2(Nb0.5Ta0.5)O7/PVDF Hybrid Materials for Sensors and Actuators
Authors: Kowfael W. , Chellappa V. , Wither J. C. , Crocker M. J. , Wada B.
Published: April 2011

Over the past several years interest in adaptive ‘smart'materials development has gained momentum. Smart structures utilize both polymeric sensors and lead-based piezo-ceramic actuators. This paper addresses the development of an alternative smart material which consists of a novel lead-free piezo-ceramic/PVDF hybrid composite, to be used as a single component system capable of performing multiple tasks. A lead-free controlled porosity perovskite ceramic of the type A2B2O7 (Sr2 (Nb.5Ta.5)2O7 was developed utilizing hot forging. Long, oriented grains along the x-y plane, perpendicular to the forging direction were obtained in the ceramics. PVDF was subsequently infiltrated into the porous piezo-ceramic resulting in a three dimensional architecture in which the piezo-ceramic is oriented perpendicular to the PVDF. It is anticipated that manufacturability combined with the ease of functional tailorability of such a class of lead-free hybrid materials can be useful in a variety of smart structures applications.
Variation of the Rate of Extension of Actin Networks
Authors: Olbris Donald J. , Herzfeld Judith
Published: April 2011

Self-assembling protein filaments are important components of a cell's superstructure. Among these, actin filaments form the backbone of protrusions and extensions such as pseudopodia. The rates at which these structures extend cover a startlingly wide range: the acrosomal process of the sea cucumber may extend 90 μm in 10 seconds, which is more than 20 times the speed at which an epithelial goldfish keratocyte crawls. We seek to explain this range by examining the delivery of actin monomers to the growing filament ends. We show that the diffusive flux of actin monomers is adequate for fueling the slower movement of crawling cells, but is insufficient to propel the quicker acrosomal process of the sea cucumber. By introducing bulk fluid flow in response to the diffusive movement of water through the cell membrane, actin delivery can be enhanced. We compare the calculated speeds to experimental observations and discuss future refinements to the model.
Dynamically-Stabilized Pores in Bilayer Membranes
Authors: Moroz J. D. , Nelson P.
Published: April 2011

Zhelev and Needham have recently created large, quasi-stable pores in artificial lipid bilayer vesicles. Initially created by electroporation, the pores remain open for up to several seconds before quickly snapping shut. This result is surprising in light of the large line tension for holes in bilayer membranes and the rapid time scale for closure of large pores. We show how pores can be dynamically stabilized via a new feedback mechanism. We also explain quantitatively the observed sudden pore closure as a tangent bifurcation. Finally we show how Zhelev and Need-ham's experiment can be used to measure accurately the pore line tension, an important material parameter. For their SOPC/CHOL mixture we obtain a line tension of 3.0 × 10−6dyn.
Collision of a Field-Driven Polymer with a Post: Implications for Electrophoresis in Microlithographic Arrays
Authors: Sevick E. M. , Williams D.R.M.
Published: April 2011

We study the simplest model of a polyelectrolyte impinging upon a point, frictionless obstacle in the presence of a field. Using numerical simulation, we show that the wide range of impacts, ranging from direct impact forming a long-lived hairpin conformation, to glancing impacts where the chain slides off of the obstacle in short time, can be described universally. In strong field, the average collision time, 〈tc〉, and average distance traveled during collision, 〈zc〉, depend upon the impact and follow universal curves over a large range of molecular weights and field strengths. This result provides analytic formulas for the chain's mobility in an array of posts and yields insight into the effect of post spacing.
Hydration of Biological Macromolecules: From Small Solutes to Proteins and Nucleic Acids
Authors: Garde Shekhar , Hummer Gerhard , Paulaitis Michael E. , Garcia Angel E.
Published: April 2011

We present a method that uses two- and three-particle correlation functions between solute atoms and water molecules to approximate the density profile of water surrounding biomolecules. The method is based on a potential of mean force expansion and uses X-ray crystallography, NMR, or modeling structural input information on the biomolecule. For small hydrophobic solutes, we have calculated entropies of hydration using the predicted water densities that are in good agreement with experimental results. We have also predicted the hydration of thecatabolite activator protein-DNAcomplex. The method is extremely efficient and makes possible the study of hydration of large biomolecules within CPU minutes.
Colloidal Aggregation with a Drift: A computer simulation
Authors: González Agustín E. , Leyvraz François
Published: April 2011

Preliminary results of an aggregation model that takes into account both the Brownian motion as well as the gravitational drift experienced by the colloidal particles and clusters is presented. It is shown that for high strengths of the drift the system crosses over to a regime different from diffusion-limited colloid aggregation, for which there is an increase of the fractal dimension, a speeding up of the aggregation rate and a widening of the cluster size distribution, becoming algebraically decaying with an exponent τ.
Phase Transitions, Patterns and Statistical Mechanics of Front Propagation in a Dynamic Random Impurity Model for Strip, Unusual Trees and Other Geometries
Authors: Vandewalle N. , Ausloos M.
Published: April 2011

A dynamic random impurity model is studied lor describing the evolution of an advancing interface through a multiphase random medium containing mobile impurities. A short range repulsion between the Iront and the impurities leads to an aggregation process along the front, and to the trapping of aggregates behind the front. The patterns of trapped impurities are found to be self-organized. Some theoretical treatment is performed through a transfer matrix technique in various geometries: trees with loops instead of branches, chains of squares and triangles joined by vertices. Arguments are given for applications of such concepts, techniques and models in various cases: chemistry, biology, trafic, sociology, economy,…
Fluctuations, Lindemann Criterion and Liquid-Solid Transition in Thin Films
Authors: Tkachenko Alexei V. , Rabin Yitzhak
Published: April 2011

A simple model of confinement-induced freezing in thin liquid layers is presented. Under boundary conditions of vanishing displacement field at the walls, confinement suppresses the amplitude of fluctuations in a solid film below a critical value determined by the Lindemann criterion of melting. The resulting increase of the melting temperature compared to that of a bulk solid, is estimated and the connection with experiments is discussed.
Foam Drainage: Extended Large-Q Potts Model Simulation
Authors: Jiang Yi , Glazier James A.
Published: April 2011

We study foam drainage using the large-Q Potts model extended to include gravity on a three dimensional lattice. Without adding liquid, homogeneously distributed liquid drains to the bottom of the foam until equilibrium between capillary effects and gravity is reached, while in an ordered dry foam, if a fixed amount of liquid is added from the top, a sharp fiat interface between the wet and dry foam develops. The wetting front profile forms a downward moving pulse, with a constant velocity. The pulse decays over time while its leading edge for a brief time behaves like a solitary wave. With continuous liquid addition from the top, the pulse does not decay and we observe a soliton front moving with a constant velocity. Continuously adding liquid to an initially wet foam keeps the liquid profile constant. Our simulations agree with both experimental data and simplified mean field analytical results for ordered foams but predict an unstable interface for disordered foams.
Dynamics of Grains in Driven Granular Media
Authors: Menon Narayanan , Durian Douglas J.
Published: April 2011

We 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

Recent 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

One 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

In 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

We 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

A 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

A 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

We 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

A 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

We 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

Metastable 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

We 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

Tritium, 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

Hydrogen 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

We 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

We 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

The 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

Measurements 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

Nanostructured 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

Uniform 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

Dopant 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.