Submonolayer Er phases on Si(111)

Using scanning tunneling microscopy, formation and structure of the submonolayer Er/Si(111) phases have been studied. Depending on the growth conditions, one of two submonolayer phases is formed, 2√3 × 2√3 or √3 × √3. A metastable 2√3 × 2√3 phase develops at the deposition of ∼0.1-0.6 ML of Er onto a Si(111) 7 × 7 surface held at ∼300°C and disappears upon annealing to ∼500°C. The 2√3 × 2√3 phase contains about 0.5 ML of Er and incorporates an incomplete top Si(111) bilayer. A √3 × √3 phase is formed at annealing of ∼0.5-1.0 ML of Er to ∼500-650°C. It exhibits a honeycomb-like structure and accumulates 2/3 ML of Er and a complete top Si(111) bilayer. The possible structures of the 2√3 × 2√3 and √3 × √3 Er/Si(111) submonolayer phases are discussed.