Growth of germanium-silver surface alloys followed by in situ scanning tunneling microscopy: Absence of germanene formation

Theoretical studies have shown that new physical properties such as tunable gap openings or quantum spin Hall effects could be expected from group-IV graphene analogs (silicene, germanene, stanene). While there have been numerous studies of growth of such Si, Ge, Sn monolayers, the demonstration of their hexagonal organization has been often based on postgrowth characterization, and their analogy to graphene has remained controversial. Our real-time scanning tunneling microscopy (STM) observation during Ge deposition on Ag(111) in the 380--430 K temperature range reveals that Ag atoms are involved in all the structures observed before the formation of a second layer, rejecting the possible formation of germanene on this substrate within these experimental conditions. The observation by STM of Ge atomic diffusion shows that easy exchange between Ag and Ge atoms is responsible for the Ge-Ag surface alloying at such temperatures.