Scanning tunneling microscopy observation of ultrathin epitaxial CoSi$_2$(111) films grown at a high temperature

Scanning tunneling microscopy (STM) is used to study the basic laws of growth of ultrathin epitaxial CoSi$_2$(111) films with Co coverages up to 4 ML formed upon sequential deposition of Co and Si atoms taken in a stoichiometric ratio onto the Co–Si(111) surface at room temperature and subsequent annealing at 600–700$^\circ$C. When the coverage of Co atoms is lower than $\sim$2.7 ML, flat CoSi$_2$ islands up to $\sim$3 nm high with surface structure 2 $\times$ 2 or 1 $\times$ 1 grow. It is shown that continuous epitaxial CoSi$_2$ films containing 3–4 triple Si–Co–Si layers grow provided precise control of deposition. CoSi$_2$ films can contain inclusions of the local regions with (2 $\times$ 1)Si reconstruction. At a temperature above 700$^\circ$C, a multilevel CoSi$_2$ film with pinholes grows because of vertical growth caused by the difference between the free energies of the CoSi$_2$ (111) and Si(111) surfaces. According to theoretical calculations, structures of A or B type with a coordination number of 8 of Co atoms are most favorable for the CoSi$_2$(111)2 $\times$ 2 interface.