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, 2root3- x 2root3 or root3 x root3. A metastable 2root3 x 2root3 phase develops at the deposition of similar to0.1-0.6 ML of Er onto a Si(111) 7 x 7 surface held at similar to300degreesC and disappears upon annealing to similar to500degreesC. The 2root3- x 2root3- phase contains about 0.5 ML of Er and incorporates an incomplete top Si(111) bilayer. A root3 x root3- phase is formed at annealing of similar to0.5-1.0 ML of Er to similar to500-650degreesC. 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 2root3 x 2root3 and root3 x root3 Er/Si(111) submonolayer phases are discussed.