Oxidized Silicon Sulfide:Stability And Electronic Properties Of A Novel Two-dimensional Material

Along with the rapid development of science and technology,the demand for high-performance miniaturized optoelectronic devices has become more and more urgent.As Moore's Law of silicon-based semiconductors is going to end,the successful exfoliated of graphene brought a new direction for researchers in the 2004,which led to the development of two-dimensional?2D?materials in the 21st century.In the past ten years,many 2D materials have been prepared in the laboratory,such as graphene,silicene,transition metal dichalcogenides?TMDs?and phosphorene.The potential applications of 2D materials in low-dimensional piezoelectrics,ferroelectrics,thermoelectrics,electrochemics and optoelectronics have been well explored in both theory and experiment.After years of development,researchers recognize that many 2D materials have their own insuperable limitations,which lowered the application potential of them.For example,graphene has large specific surface area and dramatic charge carrier mobility,but it is a semimetal with zero band gap at Dirac point.As a representative material of TMDs,MoS₂ has a direct band gap of 1.8 eV,and other properties such as high transparency,flexibility and good thermal stability.However,its low charge carrier mobility with 10² cm²/?V s?obstructs the application in electronics.The 2D phosphorene exfoliated in 2014 has a direct band gap of 1.51eV and high charge carrier mobility to 10⁴ cm²/?V s?,but its stability is poor in air.As the isoelectric counterpart of phosphorene,monolayer silicon monosulfide?SiS?has been predicted shortly afterwards and the group-IV monochalcogenide family?GeSe,SnSe,SnTe,...?have become an important group of the 2D materials with their interesting novel properties.SnSe,SnS,GeSe and GeS have shown good electrical properties and superior stability than phosphorene.However,the study of another group-IV monochalcogenide SiS is insufficient.This paper focuses on four allotropes 2D SiS,?-SiS,?-SiS,Pma2-SiS and Silicene Sulfide.This study includes the following two parts:Isolated oxygen impurities and fully oxidized structures of four stable 2D SiS structures are investigated by ab initio density functional calculations.Binding energies of oxygen impurities for all the four 2D SiS structures are found larger than those for phosphorene,due to the lower electronegativity of Si atoms.The most stable configurations of isolated oxygen impurities for different 2D SiS structures are decided and the corresponding fully oxidized structures are predicted.The phonon spectrum calculation shows that only?-SiSO among the four fully oxidized structures has good dynamic stability.Electronic structure calculations indicate that?-SiSO monolayer is semiconducting with a direct band gap at?point of 2.28 eV,which can be transformed to an indirect gap under in-layer compression in both directions.The in-layer strain can also regulate the value of band gap.The study of unsaturated oxidation structure?-SiSO_x?x<1?shows that the value of band gap and thermodynamic stability are sensitively depending on the saturation level of oxygen.Our molecular dynamics?MD?simulations show that?₂-SiSO_0.5 and?-SiSO_0.25 structures with unsaturated oxidation surfaces are unstable under room temperature,?₁-SiSO_0.5 and?-SiSO structures with saturated oxidation on one or both surfaces keep the stable structures under high temperature,which indicates that these two structures could be used as the protecting layer for the pristine 2D structure.