Modeling the crystal growth of cubic silicon carbide by molecular dynamics simulations
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Modeling the crystal growth of cubic silicon carbide by molecular dynamics simulations Nicoletta Resta, Christopher Kohler, and Hans-Rainer Trebin Institut f¨ur Theoretische und Angewandte Physik, Universit¨at Stuttgart, D-70550 Stuttgart, Germany ABSTRACT The crystal growth of a seed of cubic SiC into the amorphous material has been investigated by means of classical molecular dynamics simulations. The crystallization process was studied with ˚ thick layer of crysa set of supercells containing up to 2000 atoms, initially consisting of a 12 A ˚ thick layer of amorphous SiC at high pressure. The dynamic evolution of talline SiC and a 18 A crystallization was then followed for several nanoseconds with the simulated annealing technique performed at constant pressure and temperature. The atomic interactions were described by the Tersoff potential. We studied the dependence of the growth process on the crystallographic orientation of the crystalline/amorphous interface by considering three different crystal planes, namely the {100}, {110}, and {111} planes. Within the pressure-temperature range considered in our simulations, we observed the crystal growth only for the {110} and the {111} orientations, but not for the {100} ones. The atomistic details of the growth mechanism are described and discussed. INTRODUCTION Silicon carbon nitride (Si-C-N) ceramics are novel materials widely used for high temperature applications due to their high thermal, chemical, and mechanical stability in their amorphous state. When annealed at high temperatures, many desirable properties of these amorphous ceramics are eventually lost. In fact, the amorphous Si-C-N undergoes a transition into the thermodynamically stable crystalline phases, namely cubic (β-) SiC, α-Si3 N4 , and graphite. While the complete mechanism of this phase transformation is still not well understood, it is believed to be initiated by a preliminary phase separation into SiC-rich, Si3 N4 -rich, and C-rich amorphous domains [1–3], followed by their crystallization. In order to achieve a better understanding of the global phase transformation in the ceramics, we have separated the study into different parts. In a previous work we have studied the atomic structure of amorphous Si-C-N and its dependence on the composition at room temperature [4]. With the present work, we want describe the crystallization of cubic SiC from the amorphous SiC-rich domains at the atomic scale. To do this, we have simulated the annealing of a crystal seed of cubic SiC in contact with the amorphous material by molecular dynamics (MD) calculations. Besides the crystallization process of the amorphous Si-C-N ceramics, we believe that the crystallization of cubic SiC from the amorphous material is a problem of general scientific interest. In fact, among the different SiC polytypes, crystalline cubic SiC is a widely applied ceramic, having high values of electron mobilities, critical electric field, and thermal conductivity. It can be grown from different phases: gas, liquid (melted silicon)
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