Surface functionalization of molybdenum dinitride nanosheets by halogen and alkali atoms: a first-principles study

Abstract

Utilizing first-principles calculations, we have investigated the structures and properties of fully functionalized MoN₂ sheets, i.e. MoN₂X₂ ones with X = F, Cl, Br, Li, Na, K. It is found that the surface functionalization could stabilize the trigonal prismatic H-type structures in MoN₂X₂ sheets, which possess robust energetic, dynamic and thermal stabilities for X = F, Cl, Li, Na, and K cases. Compared to the pristine MoN₂ sheet, the functionalized systems exhibit diverse electronic properties depending on the decorated atoms. The MoN₂F₂ and MoN₂Cl₂ sheets are semiconductors with indirect band gaps, while the alkali functionalized ones can be semiconducting/semimetallic/metallic in the Li-/Na-/K-decorated systems. More interestingly, the positively charged alkali metal surfaces attract nearly free electron (NFE) states near the Fermi level, which are even partially occupied in these alkali-decorated systems. The delocalized electrons in MoN₂Na₂ and MoN₂K₂ sheets form an intrinsic two-dimensional electron gas in the free space (2DEG-FS) state, which can be used for the electron transport without nuclear scattering. Our study demonstrates that the surface functionalization on MoN₂ sheets brings robust structural stabilities and diverse electronic properties, which enable potential applications in nano-devices and nano-electronics.