We studied the structure and electronic properties of triple-atomic-layer films formed by Mg or In deposition on the double-layer In/Si(111) (×) surface. The quasi-rectangular lattice of the pristine double-layer film transforms into denser hexagonal arrangements in the triple-layer films of both (In, Mg) and In. These triple-layer films have double circular Fermi surfaces in contrast to the single Fermi circle of the In double-layer film. The Fermi circles originate from the bonding and antibonding states between the top and middle layers without and with a node, respectively, which is a characteristic feature of freestanding double-layer metals. The bottom layer acts as a buffer layer that saturates the dangling bonds of the topmost Si atoms, thereby realizing the nearly freestanding double-layer metals.
Terakawa et al. (Mon,) studied this question.