Strain Modulation Theory Study On Gas-sensing Properties Of Two-dimensional Tin Sulfide

Tin sulfide is a typical group Ⅳ-Ⅵ mono-chalcogenides with a black phosphoruslike structure,and due to its promising chemical stability,tin sulfide has drawn extensive attention from researchers in the field of gas-sensing in recent years.As for semiconductor materials with wrinkled structures,the mechanical strain has a significant effect on their electronic properties and gas-sensing characteristics.In this paper,based on the first-principles calculation method of density functional theory,using Materials Studio software,the modulation effect of strain on the gas-sensing properties of tin sulfide is investigated.Various adsorption configuration of three oxidizing gases(nitrogen dioxide,ozone and sulfur trioxide)and three reducing gases(ammonia,hydrogen sulfide and carbon monoxide)on pristine tin sulfide have been constructed.Based on the adsorption energy as well as the equilibrium distance,the optimal adsorption configuration for six gases were obtained.Combined with the corresponding density of states curves,it was observed that: three oxidizing gas molecules are chemisorbed on the surface of tin sulfide,a new impurity peak is introduced at the edge of the energy band,which reduces the band gap and further enhances the conductivity of the material.While the interaction between three reducing gas molecules and tin sulfide monolayer is weak,gas molecules are physisorbed on the surface of the material.Based on the structural parameters of tin sulfide under biaxial strain,it has been observed that compressive strain could efficiently reduce the bond length and bond angle of the material,thus improving its stability and gas-sensing properties.By studying the band structure and density of states curves of tin sulfide under biaxial strain,it has been found that biaxial compressive strain could modulate the band gap which will adjust the conductivity of the material.Biaxial tensile strain could regulate the position of the conduction band minimum,which causes the transition from indirect band gap to direct band gap.The carrier effective masses of tin sulfide monolayers under various biaxial strains were obtained by quadratic fitting calculation method.Biaxial strain could modulate the carrier effective mass effectively,and the variation of the electron effective mass was consistently larger than that of the hole effective mass.The adsorption of gas molecules on tin sulfide under biaxial strain was investigated based on the optimal adsorption configuration of six gas molecules on pristine tin sulfide monolayer.Through the adsorption energy,equilibrium distance and charge transfer,it is concluded that the biaxial compression strain could enhance the sensitivity properties of tin sulfide monolayer to six gas molecules,especially for the reducing gases.The work function and recovery time of the adsorption configuration suggest that biaxial compression strain could improve the selectivity and sensitivity of the material to gas molecules.The charge transfer of the adsorbed system was further studied by charge density difference and electron localization function.CDD reveals that the biaxial compressive strain makes the electron stacking more intense and the interaction between the material and the gas molecules is enhanced.Meanwhile,the ELF value shows the bonding state of the gas molecules to the tin sulfide monolayer.For reducing gases,the application of biaxial compressive strain could effectively increase the ELF value,indicating that the adsorption of gas molecules on the material surface is further enhanced,which contributes to the promotion of tin sulfide as a recyclable gas sensor.