Interface-reaction-mediated formation of two-dimensional Si islands on CaF2

The growth of Si on thin (∼3 nm thick) CaF2/Si(111) films in the temperature range of 500–700 °C was investigated using ultrahigh-vacuum noncontact atomic force microscopy. At 500 °C, the morphology is dominated by small cluster-like shaped Si islands due to weak binding between Si and CaF2; with increasing growth temperatures these islands coexist with an increasing amount of triangular-shaped, flat Si islands. The formation of flattened triangular islands is attributed to an increased binding of Si to the CaF2 film at higher temperatures. The binding changes as a result of an interface reaction leading to the removal of fluorine atoms and the formation of Ca–Si bonds.