Dynamic features in generation and disappearance of Si(111)-7 × 7 domains

Dynamic features in the growth process of Si(111)-7 × 7 DAS domains have been investigated by in-situ scanning tunneling microscopy (STM) observations. Quenching of Si(111) surfaces from higher temperatures above the critical temperature for 7 × 7 → 1 × 1 phase transition results in the coexistence of small domains of nucleated 7 × 7 DAS structure and disordered ‘1 × 1’ matrix. After the quenching, although the specimens are under the supercooling conditions, all the 7 × 7 domains do not necessarily grow with monotonous increase in size, instead both generation and disappearance of the 7 × 7 domains occur during the growth of the reconstructed 7 × 7 surfaces. The features in domain disappearance have been observed as follows. (i) 7 × 7 domains smaller than the criticalnucleus size disappear. If a 7 × 7 domain size is below the critical nucleus size for domain growth, it tends to shrink and finally to disappear. (ii) When two 7 × 7 domains with different sizes have a collision, the smaller domain is swallowed by the larger domain. When the two domains have similar sizes, they do not disappear but the boundary region just fluctuates ceaselessly. This feature is very similar to the coalescence process found in thin film growth.