Consideration of atom movement during Si surface reconstruction

Si(111) surface reconstructions are classified into two families, the 2 x 2 family (2 x 2, c2 x 4, c2 x 8 and √3 x √3) and n x n DAS family. By in-situ atomic scale observation of Si(111) surface reconstruction and by a statistical argument on the nucleation of a daughter phase in Si(111) matrix, we have found that the 2 x 2 family is a result of random motion of adatoms on a Si(111)-1 x 1 substrate, while the n x n DAS family can never be formed only by the movement of adatoms but some cooperative movement of substrate Si atoms is necessary.