Functionalization of single-layer nitrogene by vacancy, adatoms, and molecules

Despite its strong N2 molecule, recent studies have shown that nitrogen, the lightest group V element, remains stable in the free-standing, single-layer buckled honeycomb structure with two-dimensional (2D) hexagonal lattice. This structure is called nitrogene and is predicted to be a nonmagnetic, wide band gap semiconductor or insulator. In this paper, we investigated the formation of a single vacancy, as well as the adsorption of selected single adatoms and molecules on 2D nitrogene, using the supercell method within the density functional theory. Through the consideration of large supercells, the couplings between adjacent vacancies and adspecies are minimized; hence, the results are taken to represent single, isolated defect and adspecies. We found that a single vacancy contributes a local magnetic moment and filled and empty localized gap states at low temperature but is prone to instability due to thermal excitations. Adatoms are bound to the surface of nitrogene and form localized gap states contributing a diversity of electronic and magnetic properties. Adsorption of adatoms, such as B, C, Si, and N, however, give rise to local and strong reconstruction in nitrogene in their close proximity. Notably, a N adatom forms a strong N2 molecule by removing one N atom from nitrogene and leaves a vacancy behind. Conversely, the interactions between selected molecules, such as H2, O2, H2O, and N2, and the surface of nitrogene are rather weak and do not induce any change in the physical properties. However, H2 and O2 can be dissociated at the edges of a nitrogene flake and concomitantly can remove host N atoms to form NH2 and NO2 molecules. Calculated properties of adatoms adsorbed to nitrogene differ dramatically from the properties of those adsorbed to single-layer structures of other group V elements.