Hydrogenation of monolayer molybdenum diselenide via hydrogen plasma treatment

Abstract

Functionalization of transition metal dichalcogenides has been studied with the aim of tuning their electrical and optical properties, but structural information during functionalization and its reversibility have not been elucidated. We report a simple and effective method for hydrogenation of monolayer MoSe₂ using hydrogen plasma treatment. The covalent bonding of hydrogen to MoSe₂ was confirmed by X-ray photoelectron spectroscopy, and the degree of hydrogenation was modulated from 32% to 80% by increasing the plasma treatment time from 5 to 40 s. Transmission electron microscopy confirmed a 1.5% reduction in the lattice constant of hydrogenated MoSe₂ without structural damages or defects; crystal structures of hydrogenated MoSe₂ and as-prepared MoSe₂ were identical. Photoluminescence (PL) investigation of hydrogenated MoSe₂ showed charge transfer from hydrogen to MoSe₂. Furthermore, reversible desorption of hydrogen from hydrogenated MoSe₂ was achieved by heat treatment. The optical and electrical properties of as-prepared and hydrogenated MoSe₂ samples were compared. The PL peak of hydrogenated MoSe₂ returned to the as-prepared one after heat treatment at 500 °C. Furthermore, the electron mobility of MoSe₂ decreased from 29 to 9 cm² V⁻¹ s⁻¹ after hydrogenation and was restored to 27 cm² V⁻¹ s⁻¹ upon heat treatment at 500 °C. This reversible hydrogen adsorption and desorption lends control over the optical and electrical properties of monolayer MoSe₂ and contributes to the hydrogen functionalization of monolayer transition metal dichalcogenides and other two-dimensional materials.