Dynamic buckling of Si tetramers on the Si(111)-7 × 7 surface

The atomic structure of Si tetramers that form on the Si(111)-7 × 7 surface during homoepitaxy is investigated by means of first-principles calculations with the currently available atomistic model as a starting point. It is demonstrated that the rectangular shape of the Si tetramer is unstable against buckling. The comparison of the calculated results with the available scanning tunneling microscopy (STM) data provides a new understanding of the problem, indicating that the recorded STM images are influenced by dynamic buckling.