Morphological control in any chemically vapor deposited film would require an understanding of gas-phase chemistry, transport of gas phase species to the surface and gas-surface chemistry. Attempts are typically made to correlate process variables such as temperature, pressure and gas phase precursors to the resulting crystal morphology. However, these efforts are not capable of relating macroscopic phenomena to molecular level processes on growing surfaces. The inadequate knowledge of gas-surface phenomena makes it necessary to use theoretical methods for predicting kinetics of growth.

In this project, Kinetic Monte Carlo Simulations are used to understand the kinetic pathways of evolution of diamond crystals. The basic methodology of KMC simulations is simple; it begins with a cluster of a few atoms, called the “seed”. Rules of growth in the form of adsorption and desorption reactions are applied to the growing cluster by picking up reaction events based on a random number generator. The simulation is stopped when the final morphology is achieved.

Apart from diamond crystal growth, KMC simulations can be used to understand Gelation process, Polymer synthesis, Silicon surface etching, control of morphology of FCC metals crystals such as germanium, gold, copper, and oxide films of YBCO.

The following illustrates an example where KMC can be used to understand faceting of twinned diamond crystals. KMC simulations were used to differentiate the kinetic rules that give rise to a star-decahedral crystal with a dimple and a decahedral crystal without a dimple. Both these crystals grow under lean growth conditions (higher desorption vs. adsorption). However, star-decahedral crystals grow under slow kink nucleation and fast kink propagation, and decahedral crystals grow under fast kink nucleation and slow kink propagation events. Click on the movies below to see the crystal evolutions. (Pictures to attached soon)