Graphene as a representative of two-dimensional materials, due to its unique physical properties, such as force, heat, light, electricity, magnetism and so on, has set off a research upsurge in many disciplines. Among them, the two-dimensional transition metal sulfur compounds, including transition metal sulfides (such as MoS2, WS2, res2, etc.), selenides (such as wse2, NbSe2, tise2, inse, fese, etc.) and tellurides (such as wte2, etc.), have simple crystal structure, variable physical properties, and is easy to obtain samples. In recent years, they have become a new research star in the field of two-dimensional materials, as well as flexible semiconductors and optoelectronic devices , superconductivity, spin and so on. However, if these two-dimensional materials are directly exposed to the atmosphere, they are easy to be oxidized by H2O and O2 in the air, which greatly reduces their physical properties. This kind of instability in the atmospheric environment increases the complexity of the device manufacturing process, and also hinders the in-depth physical property research and subsequent industrial application of two-dimensional materials.
In order to solve the problem of environmental stability of two-dimensional transition metal chalcogenides, the research group of Professor Gao Libo, School of physics, Nanjing University, through experimental observation and theoretical prediction, found that the instability of these samples in the atmospheric environment is mainly due to the existence of oxygen bonds and atomic vacancies in two-dimensional materials. On the basis of this understanding, a new two-step vapor deposition method is proposed, i.e. first, the oxygen-free ultra-thin transition metal film is prepared by physical vapor deposition method, then the chemical vapor deposition method is used for selenidation growth, and finally the oxygen free bond and atom free vacancy selenide film is obtained (Fig. 1).