DYNAMIC FEATURES IN GENERATION AND DISAPPEARANCE OF SI(111)-7X7 DOMAINS

Dynamic features in the growth process of Si(111)-7 x 7 DAS domains ha ve been investigated by in-situ scanning tunneling microscopy (STM) ob servations. Quenching of Si(111) surfaces from higher temperatures abo ve the critical temperature for 7 x 7 --> 1 x 1 phase transition resul ts in the coexistence of small domains of nucleated 7 7 DAS structure and disordered '1 x 1' matrix, After the quenching, although the speci mens are under the supercooling conditions, all the 7 x 7 domains do n ot necessarily grow with monotonous increase in size, instead both gen eration and disappearance of the 7 x 7 domains occur during the growth of the reconstructed 7 x 7 surfaces. The features in domain disappear ance have been observed as follows. (i) 7 x 7 domains smaller than the critical nucleus size disappear. If a 7 x 7 domain size is below the critical nucleus size for domain growth, it tends to shrink and finall y to disappear. (ii) When two 7 x 7 domains with different sizes have a collision, the smaller domain is swallowed by the larger domain. Whe n the two domains have similar sizes, they do not disappear but the bo undary region just fluctuates ceaselessly. This feature is very simila r to the coalescence process found in thin film growth.