bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of Ni Silicides Synthesis with Excimer Laser Pulses Studied by TRR
Authors: Černý R. , PŘkryl P. , El-Kader K.M.A. , Engst P. , KubÁt P. , ChÁb V.
Published: September 2012

Time resolved reflectivity curves (TRR) in combination with non-equilibrium thermal model are used to estimate the temperature interval of chemical reactions in the systems Ni-Si (100) and Ni-SiO2-Si (100) for a ∼ 500 nm thick Ni layer depending on the pulse energy density ranging from 0.5 J/cm 2 to 1.0 J/cm2. Numerical simulations are performed to calculate the temperature field within the system and to analyze the reactivity of the system.
Application of Novel Epitaxy Techniques to the Growth of CrSi2
Authors: Fathauer R.W. , George T. , Jones E.W. , Pike W.T. , Short K.T. , Vasquez R.P. , White Alice E. , Wilkens B.J.
Published: September 2012

CrSi2 is of technological interest because it is a silicon-based semiconductor with a small band gap. Due to the lack of success with conventional molecular beam epitaxy of CrSi2 on Si, growth on mesotaxy-produced template layers and allotaxy have been attempted. After removal of the Si capping layer, epitaxy of additional CrSi2 on template layers formed by mesotaxy was found to be possible. However, single-crystal continuous films were not obtained, due at least in part to the presence of a network of cracks in the starting template. Allotaxy of CrSi2 was found to allow the formation of large grains of CrSi2 embedded in a single-crystal Si matrix, but coalescence of these grains into a continuous layer was not achieved.
Optical Properties of Semiconducting Silicides
Authors: Lange H. , Henrion W. , Jahne E. , Giehler M. , GÜnther O. , Schumann J.
Published: September 2012

The optical properties of polycrystalline layers of CrSi2, MnSi1.73, β-FeSi2, and Ir3Si5 prepared by single layer and codeposition methods on different substrates are measured over the spectral range from the infrared to 24 eV. The spectral features in the interband region are attributed to transitions between Si p-metal d bonding and antibonding states mediated by energy dependent matrix elements. The IR spectra of CrSi2 and β-FeSi2, exhibiting six phonon modes, are simulated by an oscillator model.
Point-Contact-Spectroscopy of VSi2, Nbsi2 and Tasi2
Authors: Gottlieb U. , Balkashin O.P. , Jansen A.G.M. , Laborde O. , Madar R.
Published: September 2012

We present point-contact-spectroscopy measurements on VSi2, NbSi2 and TaSi2 high quality single crystals. These three compounds crystallise in the same hexagonal structure (structure C40, space group P6222) and they are isoelectronic. Phonon spectra deduced by this technique are in good agreement with phonon parameters previously obtained from resistivity and low temperature specific heat measured on the same samples.
A Titanium Salicide Process Suitable for Submicron CMOS Applications
Authors: Blair C. , Demirlioglu E. , Yoon E. , Pierce J.
Published: September 2012

This paper reports a titanium salicide process capable of fabricating low resistance salicide (<5 ohms/sq.) on narrow polysilicon leads (line widths less than 0.35 μm) which are heavily doped with arsenic and boron. The process utilizes conventional processing but avoids excessive vertical scaling of the titanium silicide film. The process has been demonstrated on a 0.35 μm CMOS technology and results show that a process window exists which is suitable for technologies of 0.35 μm and below. The most serious scaling issue for titanium salicide appears to be the silicide film thickness.
Electrical Characterisation of Epitaxial (100) CoSi2/Si Contacts Obtained Using a Ti/Co Bilayer
Authors: Lauwers A. , Vercaemst A. , Van Hove M. , Larsen K. Kyllesbech , Verbeeck R. , Van Meirhaeghe R. , Maex K. , Van Rossum M.
Published: September 2012

In this paper the electrical properties of epitaxial CoSi2 on Si obtained by solid-state reaction of a Ti/Co bimetallic layer are investigated. Low temperature resistivity, magnetoresistance and Hall data are presented. The CoSi2ISi Schottky diodes are characterised by current - voltage and capacitance - voltage measurements at temperatures varying between - 100°C and 60°C.
Epitaxial Semiconducting and Metallic Iron Silicides
Authors: Von KÄNel H. , Kafader U. , Sutter P. , Onda N. , Sirringhaus H. , MÜller E. , Kroll U. , Schwarz C. , Goncalves—conto S.
Published: September 2012

We discuss the properties of semiconducting iron silicides, grown epitaxially on Si(001) and Si(111) by molecular beam epitaxy. The growth on Si (111) involves phase transitions from epitaxially stabilized metallic phases, leading to larger epitaxial β-FeSi2 grains than most other deposition procedures. The structural and electric properties of β-FeSi2/Si(001) are improved considerably for growth temperatures above 650 °C. Hall mobilities of p—conducting films reach values up to 600 cm2/Vsec at 100 K, at carrier densities below 1017 cm−3. Despite of the high majority carrier mobility and low carrier density, the photoelectric response of p-β-FeSi2/n-Si(001) diodes does not yield any significant contribution from the silicide, however, in accordance with the expected band structure diagram.
Nature of Environmentally Assisted Fractures in Polycrystals
Authors: GoluboviĆ Leonardo , Peredera Anatoli
Published: September 2012

Environmentally assisted fracture is in practice one of the most important fracture modes. It is especially dramatic in polycrystalline super-alloys, which are believed to be embrittled by oxygen diffusing along their grain boundaries. We used a large scale atomistic Monte-Carlo simulation to study phenomena of the environmentally assisted fracture nucleation in solids with grain boundaries exposed to an oxygen atmosphere. We find nucleation of inter-granular microcavities in a region which is well in front of the oxidized zone of the sample, apparently due to inhomogeneous stresses induced by the presence of oxide particles. This effect increases with decreasing oxidation rate since then the oxidation front becomes fuzzier and inhomogeneous stresses stronger. These findings compare well with the experimental data on super-alloys which indicate that the environmental embrittlement effects are strong for slower oxidation rates, whereas at higher oxidation rates the embrittlement may be suppressed.
Computer Simulation of Bending Plastic Deformation and Creation of Dislocations in Copper Thin Films
Authors: Tsukahara H. , Niwa Y. , Takayama T. , Doyama Masao
Published: September 2012

A small single crystal of copper with a notch has been bent by use of the molecular dynamics method. The bend axis was [110]. Dislocations were created near the tip of the notch and moved on (111) slip plane. Pulling a copper single crystal, half dislocations were created in such a way that the bending was compensated.
Dendritic Growth in Terrestrial and Microgravity Conditions
Authors: Glicksman M.E. , Koss M.B. , Bushnell L.T. , Lacombe J.C. , Winsa E.A.
Published: September 2012

Dendritic growth is the most ubiquitous form of crystal growth encountered when metals and alloys solidify under low thermal gradients. The growth of thermal dendrites in pure melts is generally acknowledged to be controlled by the diffusive transport of latent heat from the moving crystal-melt interface into its supercooled melt. However, this formulation is incomplete, and the physics of an additional selection rule, coupled to the transport solution, is necessary to predict uniquely the dendrite tip velocity and radius of curvature as a function of the supercooling. Unfortunately, experimental confirmation or evidence is ambiguous, because dendritic growth can be severely complicated by buoyancy induced convection. Recent experiments performed in the microgravity environment of the space shuttle Columbia (STS-62) quantitatively show that convection alters tip velocities and radii of curvature of succinonitrile (SCN) dendrites. In addition, these data can be used to evaluate how well the Ivantsov diffusion solution, coupled to a scaling constant, matches the dendritic growth data under microgravity conditions.
Rupture of Random Fuse Networks: Ductile to Brittle Crossover
Authors: Angulo Rafael F. , Medina Ernesto
Published: September 2012

We study the rupture process of Random Fuse Networks (RFN's) with quenched disorder in the microscopic threshold voltages. If lattices are driven to breakdown in one blow by an externally applied voltage the RFN's are shown to be equivalent to the toughest percolation backbone. Critical path analysis holds exactly in this case for all disorder distributions. For gradual rupture, it is shown that the existence of a lower cutoff in the disorder distributions entails a crossover from ductile to brittle behavior. The crossover length is a function of microscopic disorder and diverges in the limit of infinite disorder.
Fracture Characteristics of Iron-Copper Sintered Compacts
Authors: Tabeshfar Kamran
Published: September 2012

A study of fatigue cracking in iron-copper compacts was carried out to compare and analyse the performance of four different types of commercially used iron powders. The compacts were all sintered at above the iron copper peritectic temperature to facilitate liquid phase sintering. Results showed that the powder with a high specific surface had inferior fatigue properties, especially at high stress levels. The other powders, however, had very similar fatigue properties, except that at low stresses the grade with the large average particle diameter resulted in significantly longer fatigue lives. The differences in performance were discussed in terms of the microstructure of the compacts and the powder characteristics.
Dynamic Scaling in Electrochemical Deposition
Authors: Iwasaki Hiroshi , Iwamoto Atsushi , Sudoh Koichi , Yoshinobu Tatsuo
Published: September 2012

Static and dynamic scaling behavior in copper electrochemical deposition in the stable growth condition (non-bulk fractal growth) was studied by atomic force microscopy and numerical simulation. We found two distinct scaling regimes with roughness exponent α of 0.6 and 0.87α0.05 corresponding to the concentrations of the “brightener” organic additive higher and lower than 1 mℓ/ℓ, respectively. The rms surface width of the whole measured area of the surfaces in the former regime was smaller than that in the latter regime. For the latter rougher surface, we observed dynamic scaling behavior for longer length scales as well as the stationary scaling behavior for shorter length scales: surface width did not further increase with linear size of the area for longer length scales than a characteristic correlation length and increased as a power of deposition time with the dynamic exponent β of 0.45. The sum of α + (α/β) was larger than the value expected for KPZ local growth, 2. This was understood that in electrochemical deposition there is enhancement of growth at protrusions owing to non-local Laplacian field effect. The smoother (α =0.6) and the rougher (0.87) surfaces were reproduced by numerical solutions of KPZ + (the growth term proportional to height) for the shorter and the longer growth times, respectively. Bifurcation of the surface morphology is understood as a result of decrease of weight of the additional term owing to increase of the additive.
Pulsed Electrodeposition of Tree-Like Copper Aggregates
Authors: HuttEl Y. , Chassaing E. , Rosso M. , Sapoval B.
Published: September 2012

Using pulsating current technique, we have been able to grow self-sustained, tree-like copper aggregates with a length of a few mm. The size of these aggregates allowed us to perform impedance and scanning electron microscope analysis. The morphology of the aggregates is found to be more compact than for deposits obtained in fixed-current dc conditions. However, their structure is still very irregular, and depends on the parameters characterizing the pulse sequence.
Recent Progress in Electrochemical Deposition without Supporting Electrolyte
Authors: Fleury V. , Rosso M. , Chazalviel J.-N.
Published: September 2012

Electrochemical deposition (ECD) of metals is a very old subject[l], which has considerable applications in the context of electroshaping or electroplating. Electrochemists and chemical engineers have long known the different growth conditions of these metal aggregates and the different parameters which drive morphological changes, at least empirically [2-4]. However, in the recent years, after the introduction of the concept of fractal aggregation[5,6], in the field of non-linear pattern formation[7,8], a lot of work has been devoted to the specific problem of growth of electrodeposits from binary electrolytes [9-51] (i.e. without supporting electrolyte). These studies aimed at understanding the morphology, on the large scale (∼1cm) of the deposits and, more specifically, the transitions between morphologies. It is the aim of this paper to review the progress which has been achieved in the past five years on this question.
Fractal Structure of A Porous Cross-Linked Polymer Resin and Dynamical Behavior of Adsorbed Solvents
Authors: Korb J.-P. , Chachaty C.
Published: September 2012

The fractal distribution of pore sizes in a poly-4-vinylpyridine resin cross-linked by diamagnetic (Cd2+) or paramagnetic (VO2+, Cu2+) divalent metallic ions has been characterized by small-angle-X-ray scattering, nuclear paramagnetic relaxation and proton-pulsed-field gradient. These complementary techniques show a continuity in the fractal distribution of pore sizes through the same surface fractal dimension, Df = 2.6, over four orders of magnitude between 3 nm to 50 μm. Electron spin resonance yields a direct estimate of the overall fraction of solvent into the adsorption shell of the cross-linked polymer network as well as the dynamics and local viscosity of the solvent in this disordered material.
Diffusion-Limited Aggregation as Branched Growth
Authors: Halsey Thomas C.
Published: September 2012

I present a first-principles theory of diffusion-limited aggregation in two dimensions. A renormalized mean-field approximation gives the form of the unstable manifold for branch competition, following the method of Halsey and Leibig [Phys. Rev. A 46, 7793 (1992)]. This leads to a result for the cluster dimensionality, D ≍ 1.66, which is close to numerically obtained values. Quenched and annealed multifractal dimensions can also be computed in this theory; the multifractal dimension τ(3) = D, in agreement with a proposed “electro- static” scaling law.
New Scaling for AC Properties of Percolating Composite Materials
Authors: Brouers F. , Sarychev A.K.
Published: September 2012

In real conductor-insulator composites one observes a sharp change of the dc resistivity and a large increase of the low frequency dielectric constant at the percolation threshold Pc. However in many cases the a.c. data do not follow the scaling behaviour predicted by the percolation theory. To account for these discrepancies, we have proposed an alternative model which incorporates quantum tunnelling into the percolation theory. This models leads to a new “tunnelling” scaling law for the complex conductivity which gives rise for concentration below Pc to an exponential variation of the d.c. conductivity with concentration and a dispersion of the ac complex conductivity with non universal exponents. This new scaling law depends on two new exponents and reduces to the usual one for metal concentration well above Pc:. We apply this more general scaling to discuss the relation between the film morphology and the low frequency dispersion in granular metallic composites.
Scalar Transport by Diffusion and Random Advection
Authors: Araujo Mariela
Published: September 2012

The transport of a scalar by jump-type random advection and diffusion is described by a mean field formulation in terms of a Langevin equation for the fluctuations of the scalar. It is shown how the distribution of the scalar fluctuations is sensistive to the relative strength of advection versus diffusion, and the details of the advection process.
Damping and Spatial Distribution of Percolation Fractons
Authors: Russ S. , Sapoval B.
Published: September 2012

The damping of the vibrations of very irregular discretized systems embedded in a viscous fluid is studied in the particular case of the vibrations of percolation clusters. We develop a formal description for the “regularity” of a vibrational mode. This permits us to measure numerically how the local fluctuations in the vibration amplitude contribute to the viscous damping. The fact that the regularity is found to be larger than that of a single localized state on a linear chain is indicative of the very structure of the percolation cluster made of blobs and red bonds.
Fem Based Simulation of Percolation Features of Disordered Heterogeneous Media Elastic Properties
Authors: Timan S.A. , Oshmian V.G.
Published: September 2012

The mechanical properties of the 2D elastic rigid-nonrigid disordered system in dependence on the concentrations of the rigid phase are studied. The system is constructed on the basis of the square lattice and finite element method (FEM) approximation. The elasticity threshold of the FE system and the critical exponents are detemined by the phenomenological renormalization (PR) of the Monte Carlo data.
Scaling of Transport Properties of Reservoir Material at Low Saturations of a Wetting Phase
Authors: Araujo Y. Carolina , Toledo Pedro G. , Gonzalez Hada Y.
Published: September 2012

Transport properties of natural porous media have been observed to obey scaling laws in the wetting phase saturation. Previous work relates power-law behavior at low wetting phase saturations, i.e., at high capillary pressures, to the thin-film physics of the wetting phase and the fractal character of the pore space of porous media. Here, we present recent combined porousplate capillary pressure and electrical conductivity data of Berea sandstone at low saturations that lend support to the scaling laws. Power law is interpreted in terms of the exponent m in the relation of surface forces and film thickness and the fractal dimension D of the interface between pore space and solid matrix. Simple determination of D from capillary pressure and m from electrical conductivity data can be used to rapidly determine wetting phase relative permeability and capillary dispersion coefficient at low wetting phase saturations.
Film Growth: Control of Surface Morphology from Monodisperse Nanoparticles Through Fractals to Flat Epitaxial Heterostructures
Authors: Williams R. Stanley , Tong William M. , Ngo Tue T.
Published: September 2012

The study of the morphology of surfaces produced by vapor deposition began over 125 years ago with Lord Kelvin. Since then, many researchers have addressed this topic from very different theoretical viewpoints, including thermodynamics, kinetics, fractal geometry, and numerical simulations. Only recently, however, have scanning probe microscopes become available to measure the three dimensional topography of a deposited film, which provided the quantitative experimental data necessary to test the different models of film growth. The concept of scaling provides a good first description of the morphology of vapor deposited films of all types, but for heteroepitaxial films, scaling is only approximately valid. The competition between the surface roughening caused by island nucleation and growth versus the smoothening actions of surface diffusion and desorption can lead to the formation of correlated structures on a surface with a dominant spatial frequency. By rational control of the film growth conditions, one can produce a surface covered by a low density of nearly monodisperse nanoparticles, an essentially fractal surface, or a planar film surface.
Roughening by Ion Bombardment: A Stochastic Continuum Equation
Authors: Cuerno R. , Barabasi A.-L.
Published: September 2012

In the context of linear cascade theory, we derive a stochastic nonlinear equation to describe the evolution and scaling properties of surfaces eroded by ion bombardment. The coefficients appearing in the equation are calculated explicitly in terms of the physical parameters characterizing the sputtering process. We find that transitions may take place between various scaling behaviors when experimental parameters such as the angle of incidence of the incoming ions or their average penetration depth, are varied.
Structural Characterisation of Iron-Copper Multilayers Using Transmission Electron Microscopy
Authors: Lloyd S. J. , Somekh R. E. , Dunin-Borkowski R.E. , Stobbs W. M.
Published: September 2012

Coherent iron-copper multilayers of a wavelength of 2.5nm that were measured to be nonmagnetic were structurally characterised using high resolution and Fresnel techniques. A measurement of the tetragonal distortion from layer to layer and as a whole would allow an assessment of the degree to which the material exhibits any anomaly in its elastic behaviour. The modelling of the distortions requires however the measurement of the abruptness of the interfaces and this requires the quantification of the Fresnel contrast. The degree to which the measurements can be obtained to the required accuracies is considered.
Aging and Glassy Dynamics in Complex Systems: Some Theoretical Ideas
Authors: Bouchaud Jean-Philippe
Published: September 2012

We discuss some recent experimental results on the non-stationary dynamics of spin-glasses, which serves as an excellent laboratory for other complex systems. Inspired from Parisi's mean-field solution, we propose that the dynamics of these systems can be though of as a random walk in phase space, between traps characterized by trapping time distribution decaying as a power law. The average exploration time diverges in the spin-glass phase, naturally leading to time-dependent dynamics with a charateristic time scale fixed by the observation time tw itself (aging). By the same token, we find that the correlation function (or the magnetization) decays as a stretched exponential at small times t ≪ tw crossing over to power-law decay at large times t ≫ tw. Finally, we discuss recent speculations on the relevance of these concepts to real glasses, where quenched disorder is a priori absent. Keywords: Aging, slow dynamics, spin-glasses, glasses.
Characterizing Fractal and Hierarchical Morphologies Beyond the Fractal Dimension
Authors: Blumenfeld Raphael , Ball Robin C.
Published: September 2012

We present a novel correlation scheme to characterize the morphology of fractal and hierarchical patterns beyond traditional scaling. The method consists of analysing correlations between more than two-points in logarithmic coordinates. This technique has several advantages: i) It can be used to quantify the currently vague concept of morphology; ii) It allows to distinguish between different signatures of structures with similar fractal dimension but different morphologies already for relatively small systems; iii) The method is sensitive to oscillations in logarithmic coordinates, which are both admissible solutions for renormalization equations and which appear in many branching patterns (e.g., noise-reduced diffusion-limited-aggregation and bronchial structures); iv) The methods yields information on corrections to scaling from the asymptotic behavior, which is very useful in finite size analysis. Markovian processes are calculated exactly and several structures are analyzed by this method to demonstrate its advantages.
Laser Scanning of Natural and Artificial Snow Packs
Authors: Itagaki Kazuhiko , Lemieux G.E. , Ji Nina
Published: September 2012

In an effort to numerically describe a snow pack as a disordered aggregate of irregularlyshaped particles, a new optical analysis system was conceived. The system measures light transmission through snow samples impregnated with an opaque fluid. The analysis of the results is presented.
Fracture and Fractals in Glasses
Authors: Chechetkina Elena A.
Published: September 2012

Original model of bond waves is atpplied to the problem of fracture in glasses when considering it from the fractal point of view. Bond waves are assumed to be traveling above Tg, the glass transition temperature, and frozen in solid material(T<Tg), and just alone the stopped wavefronts (WF) populatedwith weakened bonds the fracture occurs. Crack, initiating at a given WF, then develops along WF's belonging to this system (a given bond wave) and/or another set (coexisting bond wave), and may oscillate between them. The arising surface represents a natural fractal whose fractal dimension depends on the mode of bond waves interaction and their arrangement relatively to the crack direction.
Cooperative Strategies and Genome Cybernetics in Formation of Complex Bacterial Patterns
Authors: Ben-Jacob Eshel , Shochet Ofer , Cohen Inon , Tenenbaum Adam , CzirÓk Andras , Vicsek Tamas
Published: September 2012

We present a study of interfacial pattern formation during growth of bacterial colonies. Growth of bacterial colonies bears similarities but presents an inherent additional level of complexity in comparison with non-living systems. In the former case, the building blocks themselves are living systems, each with its own autonomous self-interest and internal degrees of freedom. The bacteria have developed sophisticated communication channels, which they utilize when growth conditions are tough. Here we present a non-local communicating walkers model to study the effect of local bacterium-bacterium interaction and communication via chemotaxis signaling. We demonstrate how communication enables the colony to develop complex patterns in response to adverse growth conditions. This self-organization of the colony, which can be achieved only via cooperative behavior of the bacteria, may be viewed as the outcome of an interplay between the micro-level (the individual bacterium) and the macro-level (the colony). Some qualitative features of the complex morphologies can be accounted for by invoking ideas from pattern formation in non-living systems together with a simplified model of chemotactic “feedback”.
Optical Properties of Fractal Nanocomposites
Authors: Markel V. A. , Stechel E. B. , Kim W. , Armstrong R. , Shalaev Vladimir
Published: September 2012

Optical prossesses in nanostructured fractal composites are shown to be strongly enhanced. The enhancement occurs because of a localization of dipolar eigenmodes in subwavelength areas.
Wavelet Based Structural Analysis of Electroless Deposits in the Diffusion Limited Regime
Authors: Arneodo A. , Argoul F. , Kuhn A. , Muzy J.F.
Published: September 2012

We discuss the actual relevance of thin gap geometry electrodeposition to generate fractal patterns that mimic the morphology of Witten and Sander's diffusion-limited aggregates (DLA). Eliminating migration and convection, as well as electrochemical side reactions, we show that electroless deposition is a good candidate to meet the requirements for diffusion to be the rate limiting step of the growth process. We use the wavelet transform microscope to achieve a comparative structural characterization of both experimental electroless deposits and numerical DLA clusters. The fact that five-fold symmetry and Fibonacci hierarchical ordering are found as common predominant statistical features is, to our knowledge, the first demonstration, relying on an appropriate structural fractal analysis, of the existence of DLA morphologies in an experimental context.
Kinetic and Equilibrium Cluster-Size Distributions of Antibody-Antigen-Induced Colloidal Aggregation
Authors: Sherman Derin A. , Cohen Richard J.
Published: September 2012

Our colloidal system is composed of antigens covalently coupled to polystyrene microspheres. When monoclonal antibodies are added to solution, they reversibly bind to the antigens causing aggregation. Unlike many other similar systems, our system is thermodynamicallyreversible: the aggregates will dissociate in the presence of free antigen, and the aggregation process reaches a state of thermodynamic equilibrium. This system is of interest as it can be used to model many different chemical, physical and biological processes. In particular, this system can be used to quantify the interactions between the biomoleculesattached to the microspheres1 and also to explore the statistical mechanics of reversible particle aggregation.
Structure Factor Scaling in Fractal Aggregation of Colloidal Clusters
Authors: Ramírez-Santiago Guillermo , González Agustín E.
Published: September 2012

We report the observation of spatial ordering of clusters that leads to a spinodal-type scaling of the structure factor S(q), in the 3D simulations of diffusion-limited colloid aggregation. We are able to clearly identify the peak in S(q) as arising from the correlation between particles belonging to nearest neighbor clusters. The S(q) has a terminal shape that corresponds to a close-packing of the clusters after gelation, in a concentration range larger than the one found in recent experiments.

PACS numbers: 02.70.-e, 05.40.+j, 64.60.Qb, 81.10.Dn
The Scientist in the Sandbox: Complexity and Dynamics in Granular Flow
Authors: Behringer R. P.
Published: September 2012

Granular materials exhibit a rich variety of dynamical behavior, much of which is poorly understood. Fractal-like stress chains, convection, a variety of wave dynamics, including waves which resemble capillary waves, and fractional Brownian motion provide examples. Although granular materials consist of collections of interacting particles, there are important differences between the dynamics of a collections of grains and the dynamics of a collections of molecules; in particular, the ergodic hypothesis is generally invalid for granular materials, so that ordinary statistical physics does not apply. Nonlinear Dynamics, Mathematics, Molecular Dynamics, and Condensed Matter Physics as well as traditional Engineering fields have all contributed to recent insights for these phenomena.
Dynamics of Granular Materials: Flows, Relaxation and Convection
Authors: Hong Daniel C. , Yue Su , Kurtze Douglas A.
Published: September 2012

Using the diffusing void model of granular flows, we study the dynamic response of granular materials, in particular, the relaxation of granular pile, pipe flow of granular materials, and the convection of granular media in a two dimensional box subjected to vibrations. We first study the relaxation of a one dimensional granular pile of height L in a confined geometry under repeated tapping within the context of the diffusing void model. The reduction of height as a function of the number of taps is proportional to the accumulated void density at the top layer. The relaxation process is characterized by the two dynamic exponents z and z' which describe the time dependence of the height reduction, Δh(t) ≈ tz and the total relaxation time, T(L) ≈ Lz'. While the governing equation is nonlinear, we find numerically that z=z'=l, which is robust against perturbations and independent of the initial void distributions. We then show that the existence of a steady state traveling wave solution is responsible for such a linear behavior. Next, we examine the case where each void is able to maintain its overall topology as a round object that can subject itself to compression. In this regime, the governing equations for voids reduce to traffic equations and numerical solutions reveal that a cluster of voids arrives at the top periodically, which is manifested by the appearance of periodic solutions in the density at the top. In this case, the relaxation proceeds via a stick-slip process and the reduction of the height is sudden and discontinuous. We then carry out the long wave analysis to demonstrate the existence of the KdV solitons in the traffic equations. Finally, we show our preliminary studies on granular convection in a box. We observe the appearance of two rolls when the control parameter exceeds the critical value, which then undergoes bifurcations to four rolls.
Direct Observation of Size Segregation: Convection and Arching Effect
Authors: Duran J. , Mazozi T. , Clement E. , Rajchenbach J.
Published: September 2012

We report an experimental study of the ascent of a large disc imbedded in a 2D packing ofsmall beads vertically vibrated. Two distinct mechanisms leading to size segregation are observedin situ. At high acceleration, the convection process associated with surface trapping is predominates. At low acceleration, we examine the effect of the size ratio on the dynamics of the segregation which is either intermittent or continuous. This isdue to the successive formation and destruction of arches.
Id Excited Granular Media: Clustering and Equation of State
Authors: Williams D.R.M. , Mackintosh F.C.
Published: September 2012

We study a one-dimensional granular system, excited by white noise, with inelastic interactions between the particles. When the coefficient of restitution,η, is one, the particles are totally uncorrelated. As η decreases the particles cluster. A computer simulation of the system shows equilibrium clustering with a power law particle-particle correlation function. This correlation function is independent of the average kinetic energy of the particles but depends strongly on η We give simple analytical arguments to describe this clustering. We also present an “equation of state” for the particles, which relates the noise amplitude to the particle density and the average particle speed.
Reversible Axial Segregation in Rotating Granular Media
Authors: Hill K. M. , Yarusso L. , Kakalios J.
Published: September 2012

Binary mixtures of granular media having differing diameters are combined in a horizontal cylinder and rotated like a drum mixer about its long axis. Within a few minutes of rotation at 15 rpm axial segregation occurs and the mixture separates into relatively pure alternating bands of the individual components along the axis of rotation. We describe an experimental system whereby the mixed state can be restored by changing the speed of rotation. The sensitivity of the reversible axial segregation effect to systematic variations of the glass bead diameter is reported. Measurements of the dynamic angle of repose of the mixed and segregated phases support an explanation for the reversible axial segregation effect involving the competition between axial drift and diffusion currents, leading to a diffusion equation with a negative effective diffusion coefficient.
Mixing of a Granular Material in a Bidimensional Rotating Drum
Authors: Clement Eric , Rajchenbach Jean , Duran Jacques
Published: September 2012

We report experimental measurements on mixing properties in bidimensional rotating drum. Using an image processing device, we follow the trajectories of tracer particles in a monodisperse assembly of beads. Tracer particles with different size ratios exhibit a violent segregation effect: a smaller particle has a tendency to stay in the centre and a larger one will rather dwell on the edges. Furthermore, for a tracer of identical size, we evidence a specific dispersion property where the centre and the edges are competing attractors of the mixing dynamics.
Supersonic Rupture Pulses in an Earthquake Model
Authors: Leibig Michael
Published: September 2012

In this work, I study the supersonicrupturepulse in a two dimensionalelastic sheet. There is a friction force acting at the edge of the sheet which is composed of a term that dependson the local displacement at the edge and a viscous dissipation term. I consider the case where the sheet is driven forward by a force acting in the bulk, but is held back by the interfacial friction. I present the equations which describe such a system and then look for solutions which describe a slip pulse propagatingthough a region which is uniformly stressed. Such a pulse will allow the entire interface to move forward and partially relieve the stress. I present the integral equation that such a pulse solution must satisfy, and then discuss the behavior observed in numericalsolutions of this equation.
The Geometry of Dla: Different Aspects of the Departure from Self-Similarity
Authors: Mandelbrot B.B. , Vespignani A. , Kaufman H.
Published: September 2012

In order to understand better the morphology and the asymptotic behavior in Diffusion Limited Aggregation (DLA), we studied a large numbers of very large off-lattice circular clusters. We inspected both dynamical and geometric asymptotic properties, namely the moments of the particle's sticking distances and the scaling behavior of the transverse growth crosscuts, i.e., the one dimensional cuts by circles. The emerging picture for radial DLA departs from simple self-similarity for any finite size. It corresponds qualitatively to the scenario of infinite drift starting from the familiar five armed shape for small sizes and proceeding to an increasingly tight multi-armed shape. We show quantitatively how the lacunarity of circular clusters becomes increasingly “compact” with size. Finally, we find agreement among transverse cuts dimensions for clusters grown in different geometries, suggesting that the question of universality is best addressed on the crosscut.
Fractal Properties of Fracture Surfaces: Roughness Indices and Relevant Lengthscales
Authors: Bouchaud Elisabeth
Published: September 2012

Experiments aiming at the measurement of the roughness index ζ of “rapid” fracture surfaces are briefly reviewed. For rapid crack propagation, measured values of ζ are close to 0.8, which seems to be a universal exponent. However, it is argued, by re-writing the Griffith criterion for a self-affine crack, that the self-affine correlation length ξ might depend upon the microstructure, and hence on the fracture toughness. More recent experiments are also described, which reveal at smaller lengthscales the existence of a quasi-static fracture regime separated from the previously studied rapid fracture regime by a crossover length which decreases with increasing crack velocity.
Boron Transient Enhanced Diffusion in Heavily Phosphorus Doped Silicon
Authors: Huang M. B. , Myler U. , Simpson T. W. , Simpson P. J. , Mitchell I. V.
Published: September 2012

A study has been made of B transient enhanced diffusion (TED) in heavily P-doped Si using secondary ion mass spectroscopy (SIMS) and positron annihilation spectroscopy (PAS). The Pdoped silicon was implanted with boron ions of 40 keV energy to a dose of 3 × 1014 cm-2, and then annealed at temperatures ranging from 700–1000°C in a N2 ambient for varying durations. As P doping concentration increased from 3 × 1019 to 1 × 1020 cm-3, boron diffusivity and the immobile boron fraction decreased. Our experimental results are inconsistent with the predictions of the Fermi-level model and suggest that the clustering between B atoms and Si interstitials should be invoked in order to explain the immobile portion of the B peak during TED.
An Electronic Stopping Power Model in Single-Crystal Silicon from a Few KeV to Several MeV
Authors: Morris S. J. , Obradovic B. , Yang S.-H. , Tasch A. F. , Rubin L.
Published: September 2012

An electronic stopping power model for boron, arsenic, and phosphorus ion implantation into single-crystal Si is reported over the energy range from a few keV to several MeV, for both offand on-axis implant angles relative to the <100> crystallographic direction. Combined with previously developed models for damage accumulation, this model allows physically-based simulation of 3-D profiles over an extremely wide range of implant conditions. In particular, this allows modeling of MeV implants which are being used more and more frequently.
Annealing Properties of Defects in BF2+ Implanted Silicon
Authors: Kitano T. , Watanabe M. , Yaoita A. , Oguro S. , Uedono A. , Moriya T. , Tanigawa S. , Kawano T. , Suzuki R. , Ohdaira T. , Mikado T.
Published: September 2012

The annealing properties of defects in BF2+ implanted silicon were investigated using positron annihilation, TEM and SIMS techniques. For the as-implanted specimens, the major species of defects was identified to be divacancies. After thermal annealing, vacancy-fluorine complexes were formed. The size of open volume in the vacancy-fluorine complexes became larger with increasing annealing temperature. Even after 1100 °C , the vacancy-fluorine complexes were still stable with the size of open volume close to V5. The depth profile of vacancy-fluorine complexes was not largely changed after re-crystallization. In this way, the fluorine atoms played an important role in forming the defects with a large size of open volume. After 1100°C annealing, the fluorine atoms piled up at two regions; the projected range of fluorine and the original amorphous/crystalline interface, where bubbles were observed by TEM. The vacancy-fluorine complexes detected by positron annihilation might be precursors of the bubbles observed by TEM.
Mask-Edge Distributions Produced by 80 keV As+ Ion Implantation into Si
Authors: Danailov D. , Karpuzov D. , Almazouzi A. , Almeida P. De , Victoria M.
Published: September 2012

The 2D-dopant and defect distributions resulting from 80 keV ion implantation of As+ ions into Si through a high-edge mask are presented. The distributions are obtained by means of an efficient computer procedure using the results of Monte Carlo simulation. Two versions of the computer code TRIM are used. The 2D-target atom redistribution is obtained as a result of cascade collisions. The simulation reveals the effect of near-mask-edge target atom depletion. This effect is related to the recoil phenomena and can be explained on the basis of simple model.
Secondary Defect Formation and Gettering in MeV Self-Implanted Silicon
Authors: Brown R. A. , Kononchuk O. , Radzimski Z. , Rozgonyi G. A. , Gonzalez F.
Published: September 2012

Secondary defect and impurity distributions in MeV self-implanted Czochralski (Cz) and float-zone (FZ) silicon have been investigated by transmission electron microscopy, optical microscopy with preferential chemical etching, and secondary ion mass spectroscopy. We found that the ion fluence and the oxygen content of the implanted wafers affect the number and depth distribution of extended defects remaining after annealing. Intrinsic oxygen also redistributes during annealing of Cz wafers, producing two regions of relatively high oxygen concentration: one at extended defects near the ion projected range, and another, shallower region, which correlates with the distribution of vacancy-type defects. Both of these regions are also able to getter metallic impurities, depending on the implantation and annealing conditions. These defect issues may adversely affect the quality of the near surface device region, and must be controlled for successful gettering by ion implantation.
X-Ray Photoelectron Spectroscopy Investigation of the Interaction of NF3 with Silicon
Authors: Little T. W. , Ohuchi F. S.
Published: September 2012

The interaction of nitrogen trifluoride (NF3) with silicon (Si) surfaces has been investigated by x-ray photoelectron spectroscopy (XPS). Si (100) surfaces were subjected to NF3 ion bombardment as a means of approximating plasma processing under controlled conditions. Samples were also exposed to actual NF3 DC plasmas and the results compared to ion beam and plasma processing using nitrogen (N2). The results indicate that nitridation of silicon is possible using NF3 although it seems to be limited by simultaneous etching. Additionally, results suggest bonding between both Si-F and Si-N species and perhaps F-N-Si moieties. NF3 plasma processing has lead to curious results for F ls spectra which are not fully understood at present.
Elevated Temperature Implantation of GaAs with Si Ions.
Authors: Brown R. A. , Williams J. S.
Published: September 2012

The formation of amorphous layers in GaAs during ion bombardment at elevated temperatures, where dynamic annealing of radiation-induced defects is substantial, is shown to be extremely sensitive to the ion flux, fluence, and implantation temperature. For example, with increasing fluence, damage can first build up extremely slowly, then suddenly collapse to the amorphous phase. Alternatively, for a constant ion fluence, a change in flux by one order of magnitude can change the critical temperature for amorphisation by 27°C, and at constant flux and fluence, a change of only 6°C can alter the residual damage from small clusters barely visible by conventional transmission electron microscopy and Rutherford backscattering to a thick amorphous layer. The temperature at which this occurs is strongly dependent upon the ion flux and fluence.
Electron Beam Enhanced Precipitation in Highly Carbon Doped GaAs Layers
Authors: Werner P. , Gösele U. , Kohda H.
Published: September 2012

Highly carbon doped GaAs layers grown by metal organic vapor phase epitaxy (MOVPE) have been investigated by transmission electron microscopy (TEM). Electron irradiation has been applied to generate point defects interacting with native defects, e.g., substitutional carbon. This irradiation induces periodically arranged striations perpendicular to the growth direction, which were observed in situ by TEM. Furthermore, precipitates (Ø= 10–15nm) were formed containing non-crystalline material, which most likely is gallium. To explain these phenomena a precipitation mechanism is proposed. It involves small fluctuations of the incorporated C as well as the interaction of irradiation induced point defects, mainly As and C interstitials and As vacancies.
Effect of Energy and Dose on Transient-Enhanced Diffusion and Defect Microstructure in Low Energy High Dose As+ Implanted Si
Authors: Krishnamoorthy V. , Venables D. , Moeller K. , Jones K. S. , Freer B.
Published: September 2012

(001) CZ silicon wafers were implanted with arsenic (As+) at energies of 10–50keV to doses of 2×1014 to 5×1015/cm2. All implants were amorphizing in nature. The samples were annealed at 700°C for 16hrs. The resultant defect microstructures were analyzed by XTEM and PTEM and the As profiles were analyzed by SIMS. The As profiles showed significantly enhanced diffusion in all of the annealed specimens. The diffusion enhancement was both energy and dose dependent. The lowest dose implant/annealed samples did not show As clustering which translated to a lack of defects at the projected range. At higher doses, however, projected range defects were clearly observed, presumably due to interstitials generated during As clustering. The extent of enhancement in diffusion and its relation to the defect microstructure is explained by a combination of factors including surface recombination of point defects, As precipitation, As clustering and end of range damage.
The Fabrication of High-Speed Electronic Devices by Ion-Beam Synthesis of GexSi1-x Strained Layers
Authors: Elliman R. G. , Jiang H. , Wong W. C. , Kringhøj P.
Published: September 2012

GexSi1-x, strained layers can be fabricated by Ge implantation and solid-phase epitaxy and can be used in electronic devices to improve their performance. Several important materials science issues are addressed, including the effect of the strain on solid-phase-epitaxy, the effect of oxidation on the implanted Ge distribution, and the effect of Ge on the oxidation rate of Si. The potential of this process is demonstrated by comparing the performance of metal-oxidesemiconductor field-effect-transistors (MOSFETs) employing ion-beam synthesised GeSi strained layer channel regions with that of Si-only devices.