On the structure and stability of Si(111)-(7 × 7) fragments created during growth of AgSi(111)-(3 × 3)

During reactive growth of Ag on Si(111) we observe remnants of the Si(111)-(7 × 7) surface which do not react to form the (3 × 3) structure. In one case the fragment that remains is smaller than a half unit cell of (7 × 7) and appears to have undergone a (7 × 7) to (5 × 5) phase transformation. The height variation of the adatoms in this fragment correlates with observations at the (7 × 7)(3 × 3) interface and provides insight into the local structure and electronic properties of this interface. A mechanism for the formation of such silicon fragments is proposed.