Segregation of metallic germanium atoms at the graphene/metal interface toward germanene growth

Abstract

Germanene, a graphene-like single atomic sheet of germanium (Ge), has attracted much attention due to its exotic properties such as tunable bandgaps and high carrier mobility. However, fabrication of germanene-based electronic devices is difficult due to its chemical instability. To overcome this, we aim to grow germanene at the graphene/metal interface so that the germanene can be protected from oxidation in air. Here, we study Ge segregation in a stacked thin film of graphene/gold (Au)/silver (Ag)/Ge on a silicon substrate to grow germanene. The role of Ag is to suppress Ge segregation at room temperature. In situ X-ray photoelectron spectroscopy revealed that Au/Ag/Ge became an Au–Ag–Ge alloy and metallic Ge atoms were segregated at the graphene/alloy interface by simple heating. The segregation of Ge was unaffected by the existence of the top graphene. An air exposure test clearly proved that the graphene protects Ge from oxidation in air.