Engineering electronic structures and optical properties of a MoSi2N4 monolayer via modulating surface hydrogen chemisorption.

Recently, a MoSi2N4 monolayer has been successfully synthesized by a delicately designed chemical vapor deposition (CVD) method. It exhibits promising (opto)electronic properties due to a relatively narrow bandgap (∼1.94 eV), high electron/hole mobility, and excellent thermal/chemical stability. Currently, much effort is being devoted to further improving its properties through engineering defects or constructing nanocomposites (e.g., van der Waals heterostructures). Herein, we report a theoretical investigation on hydrogenation as an alternative surface functionalization approach to effectively manipulate its electronic structures and optical properties. The calculation results suggested that chemisorption of H atoms on the top of N atoms on MoSi2N4 was energetically most favored. Upon H chemisorption, the band gap values gradually decreased from 1.89 eV (for intrinsic MoSi2N4) to 0 eV (for MoSi2N4-16H) and 0.25 eV (for MoSi2N4-32H), respectively. The results of optical properties studies revealed that a noticeable enhancement in light absorption intensity could be realized in the visible light range after the surface hydrogenation process. Specifically, full-hydrogenated MoSi2N4 (MoSi2N4-32H) manifested a higher absorption coefficient than that of semi-hydrogenated MoSi2N4 (MoSi2N4-16H) in the visible light range. This work can provide theoretical guidance for rational engineering of optical and optoelectronic properties of MoSi2N4 monolayer materials via surface hydrogenation towards emerging applications in electronics, optoelectronics, photocatalysis, etc.