Theoretical Study On The Adsorption Of Nitrogen-oxide Gases On The Defect-engineered And Noble-metal-doped Tellurene

While meeting the energy demand of today’s society,fossil fuels also discharge a large number of pollutants into the environment.Nitrogen Oxide（NO_X）,as an important source of pollution,can cause acid rain,haze,greenhouse effect and ozone layer depletion and other environmental pollution.Therefore,it is vital to invent a kind of highly sensitive gas sensor for monitoring and cleaning of NO_X.Tellurene,a new 2D material of group-VI,is expected to be a kind of 2D gas sensor with great development prospect because of its unique structure and electronic properties.In this paper,based on first-principles calculation,the theoratical exploration of gas sensitive adsorption properties of tellurene with different surface modifications on nitrogen-oxide gases was carried out at atomic scale.The concrete research content is as follows:1)First,we designed three point defects on simple tellurene,namely Stone-Wale（SW）defects and single vacancy defects.We named these three defects as SW defect,SV-1 defect and SV-2 defect.We calculated the adsorption properties and electronic properties of gas molecules（N₂O,NO and NO₂）on P-tellurene,SW,SV-1 and SV-2 defects.The calculation results show that compared with P-tellurene,the introduction of defects causes obvious changes of electronic properties with the band gap narrowed in different degress.Particularly,the introduction of SV-2defects causes the transformation of tellurene from a medium band gap semiconductor to a conductor.Besides the introduction of defects can also enhance the adsorption strength of NOx molecules.The band structure and electronic（DOS）show that the changes around the Fermi level are mainly contributed by the p orbitals of N,O and Te atoms.The results of work function and I-V curve showed that the SV-1 defect can improve the NO₂ adsorption performance and enhance the sensitivity and selectivity of NO₂ adsorption.In conclusion,the introduction of point defects can adjust the adsorption strength and electronic properties of tellurene,thus improving the sensitivity and selectivity of tellurene as a gas sensor.2)In view of the promoting effect of the noble metals on gas sensitivity in the previous studies,we select 7 noble metals（M=Rh,Pd,Ag,Os,Ir,Pt,Au）to replace the Te atoms in the upper and middle layers of the P-tellurene.14 doping systems are therefore established through structure optimization,and we named the system Te-M-1（noble metal substitution doping upper atom）and Te-M-2（noble metal substitution doping middle atom）.It is found that the 14 doping systems are stable after the doping of noble metals.In terms of the change in its electronic properties,except Te-Pd-1,Te-Pd-2,Te-Pt-1 and Te-Pt-2,the band gaps of the other doping systems are all reduced to 0 e V,which changes the properties of the materials from medium gap semiconductor to conductor.In the electronic DOS,the interaction between the doped atom and the Te atom near the Fermi level results in the hybridization of the orbital to form the impurity levels,which is mainly attributed to the p orbital of the Te atom and the d orbital of the noble metal atom.The work function results show that when Au and Rh metal replace the Te atom in the upper layer of the doped tellurene,the work function changes greatly,reflecting the change of the electron current density3)Based on the above systems of noble metal doped tellurene,we studied the adsorption of NO_X gas and compared it with the adsorption performance of P-tellurene.After the introduction of doping atoms,the interaction between gas molecules and tellurene system is more intense,and the adsorption energy is significantly increased,therefore,the doping of noble metals is beneficial to the adsorption of tellurene on gas molecules（N₂O,NO and NO₂）.Based on the theory that excessive adsorption energy is not conducive to the gas sensor,we chose Te-Rh-1,Te-Pd-1,Te-Ag-1and Te-Pt-1 systems,and their adsorption energies of N₂O,NO and NO₂ gases are all between-0.8～-2.0 e V.Compared with the P-tellurene,the electronic properties of the four systems also change obviously after the adsorption of gas molecules.The electronic DOS shows that the changes around the Fermi energy level are mainly attributed to the d orbital of the noble metal and the p orbitals of N,O atom.In particular,by adjusting the adsorption strength and electronic properties,noble metal modification can produce novel synergic effects that improve the sensitivity and selectivity of tellurene-based gas sensors.This theoretical study can not only deepen our understanding on gas sensing mechanism of the two-dimensional materials modified by defects and metal atoms,but also provide theoretical reference for the experimental design of novel gas sensors with high selectivity and sensitivity.