Numerical Studies Of The Dynamics Of Silicon: Relaxation, Nucleation And Energy Landscape
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Numerical Studies Of The Dynamics Of Silicon: Relaxation, Nucleation And Energy Landscape Normand Mousseau∗ and Philippe Beaucage and Francis Valiquette D´epartement de physique and Groupe de recherche en science et technologie des couches minces, Universit´e de Montr´eal, C.P. 6128 succ. Centre-ville, Montr´eal (Qu´ebec), Canada, H3T 1J7
ABSTRACT Using various simulation techniques, such as molecular dynamics and the activationrelaxation technique, we are slowly developing a consistent picture of the dynamical properties of amorphous silicon. For example, results of an extensive search for the activated events surrounding a single minimum, in a well-relaxed model represented by a modified Stillinger-Weber potential, confirm that barrier height at the transition point, for activated mechanisms, is determined essentially by the binding energy of a single bond and not the details of the mechanism. We will discuss these results in some detail as well as recent simulations of nucleation in liquid and amorphous silicon. INTRODUCTION It is commonplace to affirm that the most studied element of all time, silicon, still deserves our attention. Amazingly, though, this affirmation holds true: although we have mapped in great details many of the properties of this material, a number of fundamental questions continue to elude us. This is particularly so of dynamical properties, which are difficult to study both experimentally and theoretically. In this paper, we present the results of simulations attempting to draw a first sketch of two dynamical processes that have received relatively little attention until now: the dynamics of nucleation from the liquid phase and the dynamics of relaxation and diffusion in the amorphous state. Within the last five years, our group and collaborators have spent considerable efforts trying to obtain a reasonably clear picture of the structural and dynamical properties of the amorphous phase of silicon. For example, Barkema and one of us, NM, have developed various methods to generate high-quality a-Si models which can serve as a basis for further structural, dynamical or electronic studies. [1] One of these methods is an optimized version of the Wooten-Winer-Weaire bond-switching algorithm which generates an amorphous network starting from a perfectly 4-fold-coordinated random network. [2, 3] This is achieved using a rather artificial but remarkably satisfactory harmonic Keating potential. Although producing the best models available, this method is essentially static in nature, providing no information as to how real a-Si is produced or how defects relax and diffuse. To look at these aspects of a-Si, we have used another method, the activation-relaxation ∗
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