Study On The Regulation Of Intrinsic Defects On The Electronic Structure And Photoelectric Properties Of Two-dimensional PtSe₂

Since graphene was successfully prepared in 2004,two-dimensional materials have received extensive attention from researchers due to their unique geometric structure and their electronic structure and optoelectronic properties that are quite different from bulk materials.The two-dimensional material has a nearly infinite volume-to-surface ratio and can provide enough positions for reactions to occur,making it have characteristics that three-dimensional materials do not have in the fields of photoelectrocatalysis and photoelectromagnetic sensing.The transition metal dichalcogenides(TMDs)family of two-dimensional materials has the characteristics of wide band gap width distribution.Among them,PtSe2 is very sensitive to the number of layers due to its photoelectric properties and can effectively adjust the band gap by means of strain and defects.The characteristics of it make it show excellent properties in the field of solar-hydrogen energy conversion,target gas optical sensors and magnetic sensors.Inevitable intrinsic defects in materials can effectively change the electronic structure,optical and catalytic properties of semiconductor materials,so it is a commonly used method to control performance.However,in PtSe2 materials,the research on the ability of intrinsic defects to control the electronic structure and photoelectric properties needs further exploration.Therefore,in view of the ability of intrinsic defects to control electronic structure and optoelectronic properties,the main work of this thesis is to study the influence of intrinsic defects on the optoelectronic properties of PtSe2 materials in the TMDs family,the optical sensing properties of the target gas,and the adjustment of magnetic properties.The main research contents and results of this paper are as follows:(1)The effect of vacancy defects,anti-site defects and interstitial defects on the photocatalytic water splitting activity of monolayer PtSe2 was studied for the first time.First-principles calculations have confirmed that the PtSe2 monolayer containing Pt@Se anti-site defects,Se@Pt anti-site defects and Se-inter defects not only retains the water-splitting ability of pure PtSe2 monolayer,but also increases the spatial distance between photogenerated electrons and holes,reduces the recombination rate,and can respond to a wider range of light and increase the absorption coefficient.It is verified that the introduction of these three kinds of defect enhanced the weaker interaction between water molecules and the surface of the material to varying degrees.In particular,the Pt@Se anti-site defect transforms the weak van der Waals effect into a stronger chemical effect,which acts as an active reaction site.It shows that the introducion of intrinsic defects,especially Pt@Se anti-site defects,is an effective means to improve the photocatalytic water splitting activity of PtSe2 monolayers.(2)As an optical gas sensor material,the high-efficiency sensing properties of PtSe2 monolayer containing intrinsic defects for CO,N2 and O2 gases are studied for the first time.Through first-principles calculations,the adsorption capacity of these three gases on the surface of pure PtSe2 monolayer materials with different intrinsic defects was analyzed,and it was confirmed that in the structure with specific intrinsic defects,the adsorption of target gas molecules would change the optical absorption spectrum of material,it indicates that the PtSe2 monolayer containing specific intrinsic defects can be an excellent photoelectric sensor for detecting CO,N2 and O2 gases.The calculation results show that the PtSe2 monolayer structure containing Pt@Se anti-site defects significantly improves the adsorption capacity of CO and N2.When studying the adsorption performance of O2,similar changes have also appeared in the PtSe2 monolayer containing Pt vacancy defects,Se vacancy defects and Pt@Se anti-site defects.In addition,the PtSe2 monolayer containing Pt@Se anti-site defects will cause changes in the optical absorption spectrum after the adsorption of CO and N2,and the PtSe2 monolayer containing Pt vacancy defects,Se vacancy defects and Pt@Se anti-site defects also changes to varying degrees after O2 adsorption(3)The effects of the layer number,different forms of vacancy defects and external stress on the magnetic properties of two-dimensional PtSe2 materials containing Pt vacancy defects are studied for the first time.Through first-principles calculations and transition state search theory,it is determined that only adjacent molecular layer can significantly affect the magnetic properties of PtSe2 with Pt vacancy defects;It is found that under normal temperature conditions,the effect of the thermal motion of atoms makes the Pt vacancy defect easily converted into two new vacancy defects,which makes the magnetism disappear;It is proved that for the PtSe2 monolayer containing Pt vacancy defects,the magnetic moment can be disappeared by a slight compressive stress,and for the PtSe2 bilayer containing Pt vacancy defects,a compressive stress greater than 4%is required to make the magnetic moment disappear.The theoretical basis of PtSe2 as a magnetic sensor is provided,and temperature and external stress are the main reasons that affect the performance of the PtSe2 magnetic sensor are pointed out.