Characteristic dihydride chain formation was observed on a Si(1 0 0)-2 x 1-H surface. The dihydride chains are formed only at S-B step edges and are accompanied with a structure transformation from a rebonded to non-rebonded structure at the edges. The mechanism of the dihydride chain migration is suggested based on experimental observations and theoretical calculations. (C) 2004 Elsevier B.V. All rights reserved.