Formation and evolution of epitaxial Co 5 Ge 7 film on Ge (001) surface by solid-state reaction in an in situ ultrahigh-vacuum transmission electron microscope

Abstract

A thin metallic cobalt (Co) layer was deposited on a single-crystal Ge (001) surface at room temperature by the electron-beam evaporation of a pure Co metal source in an ultrahigh-vacuum transmission electron microscope. The formation and epitaxial growth of a cobalt germanide Co5 Ge7 phase on the Ge (001) surface was studied in situ by gradually heating the sample from room temperature to ∼350 °C. The occurrence of an epitaxial hexagonal-close-packed Co and the reaction between Co and Ge were observed at ∼225 °C. After annealing at ∼300 °C for 26.5 h, a continuous epitaxial Co5 Ge7 film formed on the Ge (001) substrate. With further annealing at a higher temperature, the continuous Co5 Ge7 layer broke up and formed three-dimensional islands in order to relieve the strain energy in the epitaxial Co5 Ge7 layer. Two epitaxial relationships between Co5 Ge7 and Ge, i.e., Co5 Ge7 〈110〉 (001) Ge 〈100〉 (001) and Co5 Ge7 〈001〉 (110) Ge 〈100〉 (001) were found by electron diffraction. © 2005 American Institute of Physics.