Atomic structure of Ge clusters on Si(111)-(7 x 7) by non-contact AFM

We present non-contact (NC) AFM results of Ge clusters on a Si(111)-(7 x 7) reconstructed surface. The low temperature NC-AFM allows us to directly observe the atomic structure of the Ge clusters on the Si(111). The Ge clusters reside in the middle of a half unit cell in the (7 x 7) reconstruction surface and they are ∼1.4 A higher than the Si adatoms. By direct NC-AFM observation, the features of the Ge clusters on the Si(111) became clear. First, the Ge atoms reside in spaces between Si adatoms and on the Si/Ge atoms on the Si(111). Second, the Si adatoms shift from their original position through Ge adsorption, and interact with the Ge atoms accompanied by surface relaxation and a change in their spatial heights. In addition, the interatomic distance between the Ge atoms inside the clusters is approximately 4.0 A, which is larger than that between the Ge atoms in the bulk (2.4 A). Our NC-AFM results of Ge clusters provide valuable information for the basic study of clusters on semiconductor surfaces and may be useful for the manipulation and assembly of clusters for the realization of diverse nanostructures at the atomic level