Growth of step bunches formed by the drift of adatoms

Abstract

We study power-law growth of step bunches produced by the drift of adatoms. When evaporation of the adatoms is neglected (conserved system), the terrace width between the bunches increases as L∝ t β with β≈1/2 through a hierarchical bunching. The time dependence of L is not affected by the form of step repulsion. When the adatoms evaporate to the atmosphere (non-conserved system), the motion of the steps changes drastically: isolated steps are always present in large terraces, and collision of the steps with the bunches is repeated. When the drift of adatoms is fast, the terrace width grows by ‘effective coalescence’ of the bunches as L∝ t 1/2, similarly to the bunching in the conserved system. When the drift of adatoms is slow, the bunches grow by ‘bunch size exchange’ with β smaller than 1/2 and the terrace width saturates in a late stage. The exponent β increases with increasing drift velocity and approaches β≈1/2.