Contact nucleation of steps: theory and Monte Carlo simulation

Abstract

Freely floating crystals are not common during growth. In most cases, the crystals are in contact with a foreign body, such as other crystals, the wall or bottom of the growth system or a mount to keep the specimen fixed. Then, growth steps are often preferentially nucleated at the intersection line between the crystal surface and the foreign body. In this study the phenomenon of contact nucleation is investigated by kinetic Monte Carlo simulation and analytical description. Depending on supersaturation, the length of the contact line and the different edge free energies involved, six modes of crystal growth are encountered: “free growth”, thermally and kinetically rough growth, mono and poly contact nucleation and birth-and-spread growth. Phase diagrams displaying the existence domains of the different growth modes are constructed from Monte Carlo simulation results as well as from analytical expressions. Growth rates and the slope of the crystal surface adjacent to the foreign body are measured by simulation and calculated using a microscopic description of contact nucleation. The “free growth” and both rough growth modes are analysed in terms of the kinematic wave theory for crystal shape evolution, in which the junction between crystal and foreign body acts as a velocity source that locally accelerates growth.