First-principles Study Of Electronic Structure And Optical Properties Of Hydrogenated Janus MoSSe Monolayer

Two-sided MoSSe(Janus MoSSe)is a new two-dimensional(2D)material,which has attracted a lot of attention due to its special electronic structure and optical properties.In this thesis,the changes of the geometrical structure?stability?charge distribution?electronic structure and optical properties of H atoms adsorbed on different surfaces(Se?S?S/Se)of a monolayer Janus MoSSe have been studied by means of density functional theory.Firstly,the geometrical structure,stability and charge distribution of hydrogenated monolayer Janus MoSSe are studied.The results showed that the geometrical structure of Janus MoSSe is basically unchanged after the adsorption of H atoms,and there is a good structural coupling between H atoms and Janus MoSSe.Secondly,the most stable position of H atoms adsorption on Janus MoSSe monolayer surface is studied.Sets is the most stable location for H adsorption.It is found that hydrogenated Janus MoSSe is stable by calculating the binding energy,formation energy and adsorption energy.The analysis of electron density distribution also showed that Janus MoSSe-Hx formed a stable structure.The electron orbital analysis of hydrogenated Janus MoSSe system showed that there is a strong orbital coupling between H atoms and Janus MoSSe monolayer atoms.By analyzing the bond distribution,it is found that ionic bonds are formed between atoms in the hydrogenated Janus MoSSe system.Then,we also investigated the electronic structure of Janus MoSSe hydrogenated on different surfaces.The results showed that the intrinsic Janus MoSSe is a direct band-gap semiconductor,and the hydrogenated material is an indirect band-gap semiconductor,which will slow down the recombination of photogenerated carriers in the material and is conducive to the application of the material in the fields of optoelectronics and catalysis.With the increase of the number of H atoms adsorbed,the band gap decreases accordingly.The reason for the decrease of band gap is that with the adsorption of H atoms,impurity levels are introduced into the band gap of intrinsic Janus MoSSe,and the number of impurity levels increases with the increase of H atom concentration,which leads to the decrease of the band gap of hydrogenated Janus MoSSe.Meanwhile,with the adsorption of H atoms on the Janus MoSSe surface,the Fermi energy level also shifts.The pure Janus MoSSe is a n-type semiconductor,and the Fermi energy levels of the hydrogenated Janus MoSSe on the Se surface enters the valence band and is a p-type semiconductor.Similarly,the hydrogenated Janus MoSSe on the S?S/Se sides are a n-type semiconductor.Therefore,hydrogenation can effectively regulate the electronic structure of Janus MoSSe.Finally,we also analyzed the optical properties of the hydrogenated Janus MoSSe system.From the discussion of optical properties,it can be seen that the reflectivity of hydrogenated Janus MoSSe is larger in the visible light region and significantly lower in the UV region.The energy loss spectral function(L(?))of the hydrogenated Janus MoSSe system all show a sharp peak value at about 16.8 eV,which can prove the existence of plasma resonance.The absorption region of hydrogenated Janus MoSSe is quite wide,and the main absorption is in the UV region.For the refractive index of the hydrogenated Janus MoSSe system,the refractive index of the hydrogenated material becomes stronger in the visible region.Our results show that hydrogenation of different surfaces of Janus MoSSe results in a better tunability of the electronic structure and optical properties of the material,thus expanding the potential application value of the material in light-energy conversion devices,optoelectronics and photocatalysts.