Engineering electronic structures and optical properties of a MoSi(2)N(4) monolayer via modulating surface hydrogen chemisorption

Recently, a MoSi(2)N(4) 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 MoSi(2)N(4) was energetically most favored. Upon H chemisorption, the band gap values gradually decreased from 1.89 eV (for intrinsic MoSi(2)N(4)) to 0 eV (for MoSi(2)N(4)-16H) and 0.25 eV (for MoSi(2)N(4)-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 MoSi(2)N(4) (MoSi(2)N(4)-32H) manifested a higher absorption coefficient than that of semi-hydrogenated MoSi(2)N(4) (MoSi(2)N(4)-16H) in the visible light range. This work can provide theoretical guidance for rational engineering of optical and optoelectronic properties of MoSi(2)N(4) monolayer materials via surface hydrogenation towards emerging applications in electronics, optoelectronics, photocatalysis, etc.