Theoretical Study On High-precision Two-dimensional NO₂ Sensing Materials With Optical Discernibility

Industrial processes such as metallurgy will produce a large amount of NO₂ which is extremely harmful to humans and the environment.People who are exposed to NO₂ for a long time will suffer from respiratory distress and even faint.In addition,NO₂ emissions will also bring environmental problems such as acid rain.Due to the excellent electrical properties of two-dimensional(2D)materials,they have been widely studied in NO₂detection.The selectivity for materials is not absolute,other gases that have a weak interaction with the substrate will also generate electrical signals,which will affect the accuracy of the test results.It is an effective method to improve the sensing accuracy by using the changes in optical properties of the substrate before and after the gas is adsorbed to distinguish the types of gases.WSe₂(tungsten diselenide)and Tl₂O(thallium oxide)have high sensitivity to light and are widely used in the field of photoelectric detection.Therefore,it is very important to use the discernibility of its optical performance to study its influence on the detection accuracy of NO₂ gas.The main research contents and results of this thesis are summarized as follows:Firstly,the first principles is used to compare the selectivity and sensitivity parameters(adsorption energy_aE,charge transfer?Q,adsorption distance d,CDD and ELF)to the pure WSe₂and doped X-WSe₂(X=Si,P,S,Te,As)monolayer to nine common gases(NO,NO₂,CO,CO₂,N₂,O₂,SO₂,H₂S,and NH₃),and it is found that As-WSe₂ has strong sensitivity to both NO₂ and SO₂.The results of co-adsorption indicate that NO₂ will dominate the process.The calculation results of the changes in optical properties before and after the gas adsorbed on the substrate show that the optical properties of different adsorption systems are theoretically discernible.Then,the sensitivity,the selectivity and the optical properties of the corresponding system of the pure Tl₂O and the doped X-Tl₂O monolayer(X=In,Cd,Y,Pb,Ga,Si)to the above nine gases are calculated.The results show that In-Tl₂O has the most advantage in the adsorption of NO₂.The results of the optical properties of the adsorption system show that the adsorption system that interferes with the detection of NO₂ can be clearly distinguished by the reflectance and light absorption of the system in the visible light region,which provides a strong guarantee for the accurate detection of NO₂.In addition,the current-voltage calculation results of the NO₂/In-Tl₂O and In-Tl₂O systems show that after the adsorption of NO₂,the output current value of the system is about 8 times that of the value of doped substrate.Therefore,In-Tl₂O has its unique advantages in sensing NO₂.By comparing the NO₂ sensing performance of In-Tl₂O and As-WSe₂ substrates,it is found that In-Tl₂O has more advantages in improving the accuracy of NO₂ sensing.This laid a theoretical foundation for high-precision NO₂ sensing.At the same time,the research provides solutions for trace NO₂ detection,and provides a theoretical basis for NO₂ detection in complex environments.