Sinno, Talid

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2003 - 2009132010 - 20126
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  • Publication
    Monte Carlo Analysis of Stress-Directed Phase Segregation in Binary Thin Film Alloys Under Nonisothermal Annealing
    (2008-01-01) Nieves, Alex M; Vitek, Vaclav; Sinno, Talid
    The use of patterned stress fields to direct phase separation in thin film alloys is investigated computationally with Monte Carlo simulations in which atomic interactions are represented by a Lennard-Jones potential. We show that careful design of annealing schedules based on consideration of the system phase diagram can lead to vastly enhanced patterning kinetics. In particular, by avoiding the low temperature formation of highly stable nuclei within the entire system, the kinetics of patterning are accelerated by rapid monomerdiffusion, rather than classical Ostwald ripening in which small precipitates must dissolve to feed larger ones.
  • Publication
    Entropic Origins of Stability in Silicon Interstitial Clusters
    (2008-12-05) Kapur, Sumeet; Sinno, Talid
    The role of entropy in the thermodynamic properties of small interstitial clusters in crystalline silicon is investigated using an empirical potential. It is shown that both vibrational and configurational entropies are potentially important in setting the properties of small silicon interstitial clusters and, in particular, contribute to the formation of “magic” sizes that exhibit special stability, which have been inferred by experimental measurements of dopant diffusion. The results suggest that a competition between formation energy and entropy of small clusters could be linked to the selection process between various self-interstitial precipitate morphologies observed in ion-implanted crystalline silicon.
  • Publication
    Coarse-grained lattice kinetic Monte Carlo simulation of systems of strongly interacting particles
    (2008-05-15) Seider, Warren D.; Dai, Jianguo; Sinno, Talid
    A general approach is presented for spatially coarse-graining lattice kinetic Monte Carlo (LKMC) simulations of systems containing strongly interacting particles. While previous work has relied on approximations that are valid in the limit of weak interactions, here we show that it is possible to compute coarse-grained transition rates for strongly interacting systems without a large computational burden. A two-dimensional square lattice is employed on which a collection of (supersaturated) strongly interacting particles is allowed to reversibly evolve into clusters. A detailed analysis is presented of the various approximations applied in LKMC coarse graining, and a number of numerical closure rules are contrasted and compared. In each case, the overall cluster size distribution and individual cluster structures are used to assess the accuracy of the coarse-graining approach. The resulting closure approach is shown to provide an excellent coarse-grained representation of the systems considered in this study.
  • Publication
    Internally Consistent Approach for Modeling Solid-State Aggregation: I. Atomistic Calculations of Vacancy Clustering in Silicon
    (2003-07-15) Prasad, Manish; Sinno, Talid R
    A computational framework is presented for describing the nucleation and growth of vacancy clusters in crystalline silicon. The overall approach is based on a parametrically consistent comparison between two representations of the process in order to provide a systematic method for probing the details of atomic mechanisms responsible for aggregation. In this paper, the atomistic component of the overall framework is presented. First, a detailed set of targeted atomistic simulations are described that characterize fully the thermodynamic and transport properties of vacancy clusters over a wide range of sizes. It is shown that cluster diffusion is surprisingly favorable because of the availability of multiple, almost degenerate, configurations. A single large-scale parallel molecular dynamics simulation is then used to compute directly the evolution of the vacancy cluster size distribution in a supersaturated system initially containing 1000 uniformly distributed vacancies in a host lattice of 216,000 Si atoms at 1600 K. The results of this simulation are interpreted in the context of mean-field scaling theory based on the observed power-law evolution of the size distribution moments. It is shown that the molecular dynamics results for aggregation of vacancy clusters, particularly the evolution of the average cluster size, can be very well represented by a highly simplified mean-field model. A direct comparison to a detailed continuum model is made in a subsequent article.
  • Publication
    Atomistic Analysis of Phase Segregation Patterning in Binary Thin Films Using Applied Mechanical Fields
    (2010-03-02) Nieves, Alex M; Vitek, Vaclay; Sinno, Talid
    The patterned compositional evolution in thin films of a binary alloy controlled by modulated stress fields is studied by employing Monte Carlo simulations. General features of stress-patterned phase segregation are probed using a binary Lennard-Jones potential in which the lattice misfit between the two components of the alloy is varied systematically. In general, patterning of the microstructure is found to be more robust in the low-mismatch binary systems because large lattice mismatch promotes plastic, and therefore, irreversible relaxation, during annealing. It is shown that some control over the relaxation process can be achieved by careful design of the applied thermal annealing history. Additional calculations have been performed using two other potentials for binary metallic systems, an embedded-atom method (EAM) potential for Cu–Ag and a modified embedded-atom method (MEAM) potential for Cu–Ni that represent examples of high and low-mismatched systems, respectively. The results obtained with generic Lennard-Jones potentials are in excellent agreement with those from the EAM and MEAM potentials suggesting that it is possible to derive general guidelines for accomplishing stress-patterned segregation in a variety of thin films of binary alloys.
  • Publication
    Computational Analysis of Binary Segregation During Colloidal Crytallization with DNA-mediated Interactions
    (2010-06-17) Scarlett, Raynaldo T; Crocker, John C; Sinno, Talid
    A detailed computational study of compositional segregation during growth of colloidal binary solid-solution crystals is presented. Using a comprehensive set of Metropolis Monte Carlo simulations, we probe the influence of colloid size, interaction strength, and interaction range on the segregation process. The results are interpreted in terms of a simple, but descriptive mechanistic model that allows us to connect to studies of binary segregation in atomic systems. The validity of Metropolis Monte Carlo simulations for the nonequilibrium phenomena investigated in this work is established theoretically and by connections to Brownian dynamics and molecular dynamics simulations. It is demonstrated that standard Metropolis Monte Carlo, properly applied, can provide an efficient framework for studying many aspects of crystallization in colloidal systems.
  • Publication
    Monte Carlo Analysis of Stress-Directed Phase Segregation in Binary Thin Film Alloys Under Nonisothermal Annealing
    (2008-11-14) Nieves, Alex M; Vitek, Vaclav; Sinno, Talid
    The use of patterned stress fields to direct phase separation in thin film alloys is investigated computationally with Monte Carlo simulations in which atomic interactions are represented by a Lennard-Jones potential.We show that careful design of annealing schedules based on consideration of the system phase diagram can lead to vastly enhanced patterning kinetics. In particular, by avoiding the low temperature formation of highly stable nuclei within the entire system, the kinetics of patterning are accelerated by rapid monomer diffusion, rather than classical Ostwald ripening in which small precipitates must dissolve to feed larger ones.
  • Publication
    Vacancy Self-trapping During Rapid Thermal Annealing of Silicon Wafers
    (2006-11-06) Frewen, Thomas A; Sinno, Talid
    The density and spatial distribution of oxide precipitates within a crystalline silicon wafer is of paramount importance for microelectronic device yield. In this letter, the authors show how the formation of previously unconsidered, very small vacancy aggregates can explain macroscopic spatial variations in the oxide precipitate density, which are observed following certain rapid thermal annealing conditions. The formation of these nanometer-sized voids is predicted on the basis of their recent model for vacancy aggregation that accounts for high temperature entropic effects.
  • Publication
    Feature Activated Molecular Dynamics: An Efficient Approach for Atomistic Simulation of Solid-State Aggregation Phenomena
    (2004-11-08) Prasad, Manish; Sinno, Talid R
    A new approach is presented for performing efficient molecular dynamics simulations of solute aggregation in crystalline solids. The method dynamically divides the total simulation space into “active” regions centered about each minority species, in which regular molecular dynamics is performed. The number, size and shape of these regions is updated periodically based on the distribution of solute atoms within the overall simulation cell. The remainder of the system is essentially static except for periodic rescaling of the entire simulation cell in order to balance the pressure between the isolated molecular dynamics regions. The method is shown to be accurate and robust for the Environment-Dependant Interatomic Potential (EDIP) for silicon and an Embedded Atom Method (EAM) potential for copper. Several tests are performed beginning with the diffusion of a single vacancy all the way to large-scale simulations of vacancy clustering. In both material systems, the predicted evolutions agree closely with the results of standard molecular dynamics simulations. Computationally, the method is demonstrated to scale almost linearly with the concentration of solute atoms, but is essentially independent of the total system size. This scaling behavior allows for the full dynamical simulation of aggregation under conditions that are more experimentally realizable than would be possible with standard molecular dynamics.
  • Publication
    Lattice kinetic Monte Carlo simulations of convective-diffusive systems
    (2009-03-05) Flamm, Matthew H; Diamond, Scott L; Sinno, Talid
    Diverse phenomena in physical, chemical, and biological systems exhibit significant stochasticity and therefore require appropriate simulations that incorporate noise explicitly into the dynamics. We present a lattice kinetic Monte Carlo approach to simulate the trajectories of tracer particles within a system in which both diffusive and convective transports are operational. While diffusive transport is readily accounted for in a kinetic Monte Carlo simulation, we demonstrate that the inclusion of bulk convection by simply biasing the rate of diffusion with the rate of convection creates unphysical, shocklike behavior in concentrated systems due to particle pile up. We report that elimination of shocklike behavior requires the proper passing of blocked convective rates along nearest-neighbor chains to the first available particle in the direction of flow. The resulting algorithm was validated for the Taylor–Aris dispersion in parallel plate flow and multidimensional flows. This is the first generally applicable lattice kinetic Monte Carlo simulation for convection-diffusion and will allow simulations of field-driven phenomena in which drift is present in addition to diffusion.