The formation process of stacking-fault (SF) triangles during the Si(111) 1 x 1→7 x 7 reconstruction has been studied using the quantum chemical theoretical calculations. On the basis of the propagation and subsequent merging mechanism of the SF areas proposed by one of authors (I.O.), several reaction paths to complete a single SF triangle have been examined. The most probable formation process of SF triangles has been determined from the their lowest energy reaction path. A comparison of total energy changes along the SF triangle formation both with and without oxygen atoms indicated a preference of oxygen incorporation in the formation of 7 x 7 dimer-stacking-fault (DS) structure, which was compatible with the recent experimental results suggesting the important role of oxygen in the 7 x 7 reconstruction. The effect of the step edge has also been discussed.
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