Kinetic smoothening and habit change during crystal growth

Abstract

Crystal faces with no strong bonds along them are atomistically rough under equilibrium conditions. The growth of such faces has been considered to be governed by an adhesive growth mechanism. In the present study, the growth of such a face of a two-dimensional crystal is investigated based on a concept of crystal growth where, under certain conditions, the incorporation of growth units onto kink sites by a series process via step sites can be faster than the direct incorporation. This concept reveals a new growth mechanism similar to the two-dimensional nucleation-growth. The new mechanism predicts that surface structure can change from rough under equilibrium conditions to smooth in growth and dissolution processes, resulting in kinetic smoothening. The new mechanism also offers a general explanation of growth habit change from one polyhedral shape to another, something which could not be explained by the published theories of growth in pure systems.