We investigate, experimentally and theoretically, the initial stage of the formation of Ca/Si and Si/F structures that occurs during the adsorption of CaF${}_2$ molecules onto a bare Si(100) surface heated to 1000 K in a low-coverage regime (0.3 monolayer). A low-temperature (5 K) scanning tunneling microscope (STM) is used to observe the topographies and the electronic properties of the exposed silicon surfaces. Our atomic-scale study reveals that several chemical reactions arise during CaF${}_2$ deposition, such as dissociation of the CaF${}_2$ molecules and etching of the surface silicon dimers. The experimental and calculated STM topographies are compared using the density functional theory, and this comparison enables us to identify two types of reacted structures on the Si(100) surface. The first type of observed complex surface structure consists of large islands formed with a semiperiodic sequence of 3 × 2 unit cells. The second one is made of isolated Ca adatoms adsorbed at specific sites on the Si(100)-2 × 1 surface.

• Received 15 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.155433