Solid-state Synthesis of Cobalt Germanides in Epitaxial Ge/$\alpha$-Co(001) and Ge/$\beta$-Co(110) Nanofilms

The experimental results of a study of solid-state synthesis of cobalt germanides in epitaxial Ge/$\alpha$-Co(001) and Ge/$\beta$-Co(110) nanofilms are presented. For both polymorphic modifications of cobalt, it is demonstrated that the Co$_5$Ge$_7$ phase occurs at $\sim275^\circ$ C. When the annealing temperature increases to $\sim300^\circ$ C, the CoGe$_2$ phase forms, which sharply reduces the electric resistance and magnetic characteristics of the samples. The order of the formation of phases and the temperatures at which the phases are formed are not changed based on the polymorphic modification of cobalt.