  Theoretical studies have shown that new physical properties such as tunable
gap openings or quantum spinHall effects could be expected from group-IV
graphene analogs (silicene, germanene, stanene). While therehave been numerous
studies of growth of such Si, Ge, Sn monolayers, the demonstration of their
hexagonalorganization has been often based on postgrowth characterization, and
their analogy to graphene has remainedcontroversial. 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 beforethe formation of a second layer, rejecting the
possible formation of germanene on this substrate within theseexperimental
conditions. The observation by STM of Ge atomic diffusion shows that easy
exchange between Agand Ge atoms is responsible for the Ge-Ag surface alloying
at such temperatures.

Materials Science