  The O2 dissociation and O atoms adsorption on free-standing germanene are
studied by using first-principles calculations in this letter. Compared with
the spontaneous dissociation of oxygen molecule on free-standing silicene in
air, germanene is more stable than silicene from kinetic point of view, with
overcoming energy barrier of about 0.55 eV. Especially, in contrast with the
unique chemical adsorption of O2-dissociation-induced O atoms on silicene,
oxygen molecule can behave a correspondingly stable adsorption on germanene
surface. Moreover, single O atom adsorption on germanene is also different to
that on silicene, resulting in two opposite migration pathways on germanene
surface. Furthermore, once the oxygen molecule dissociates into O atoms on
germanene surface, the migration and desorption of O atoms are relatively
difficult under room temperature due to the strong Ge-O bonds in the O-adsorbed
germanene, in favor of forming germanium oxides. The results provide compelling
evidence to show that free-standing gemanene is relatively stable in
oxygen,which is different to silicene essentially.
