Kinematic multiplication of elementary steps on a crystal surface

The dynamics of elementary steps on an atomically smooth crystal-liquid interface and, in particular, the process of collisions of steps differing in sign are considered. It is shown that, along with the conventional annihilation of steps in such collisions, both the overthrow of steps to the neighboring row with the formation of a new atomic layer (passage) and the reflection of steps from each other can take place under certain conditions. The overthrow of steps gives a qualitatively new mechanism of the growth of facets in the absence of renewable sources such as grown-in dislocations. Under these conditions, the growth kinetics of a crystal with atomically smooth facets changes substantially. In particular, the processes considered above may form a basis for physical mechanisms of unconventional growth regimes observed for helium crystals at low temperatures.