Self-organized trench-island structures in epitaxial cobalt silicide growth on Si(111)

Sub-monolayer Co deposition on clean Si(111)-(7 × 7) surfaces has been found to form nanoscale CoSi2 islands with a surrounding trench of one Si bilayer depth and mainly hexagonal shape. The trench surface structure is largely like that of the disordered '1 × 1' phase of the Si(111)-7 × 7 ↔ '1 × 1' phase transition and comprises mostly disordered Si adatoms with small ordered patches of (11 × 11), (9 × 9), c(5 × √5), c(4 × 4) and (2 × 2) structures along with some Co-ring clusters. This disordered '1 × 1' structure within the trench has formed at 600 °C, the growth temperature of CoSi2 in reactive deposition epitaxy, much below the order-disorder phase transition temperature on Si(111)-(7 × 7). The structure around the trench remains (7 × 7). Electronically the trench is semiconducting. The surrounding 7 × 7 structure being metallic, the island-trench structure forms a lateral metal-semiconductor-metal structure.