Gas Sensing Propensity Of Two-dimensional Stanene And SnS₂ Materials Towards Common Molecules:a First Principle Study

In 2004,Since the successful fabrication of graphene from mechanical exfoliation,graphene-like two-dimensional?2D?materials and transition metal dichalcogenides?TMDs?have attracted widespread attentions due to their excellent performance in nanoelectronic devices.Then it is applied to the physical and chemical photoelectric fields,such as solar cells and light-emitting diodes.This thesis mainly based on DFT of the Vienna Ab-initio Simulation Package?VASP?by first principles calculation method to study the gas sensing properties of small gas molecules?CO,H₂O,NH₃,NO and NO₂?adsorbed on 2D nano-materials?Stanene,SnS₂?,Also,by using the external factors,such as electric field and biaxial strain,to adjust the electronic properties and gas sensor properties of adsorption systems.The main results and innovation points are given as follows.?1?We focus on the electronic structures of small gas molecule?such as CO,H₂O,NH₃,NO,and NO₂?-adsorbed stanene monolayers by first-principles method.The results show that H₂O,NH₃,and CO molecules are physisorbed on stanene monolayer,while NO and NO₂ molecules are found to be chemisorbed on stanene with quite large charge transfer,sizable adsorption energy,and strong covalent?Sn-O?bonds.Moreover,our spin-orbit coupling calculations show that the band gaps of the molecule-adsorbed stanene monolayers can be tuned effectively.In particular,our results also show that when the biaxial strains and electric field are applied,the adsorption energies and charge transfer between gas molecules and stanene monolayers change dramatically,which indicates that external factors on stanene monolayers are highly preferred.These results indicate that stanene is promising for wide-ranging applications as superior gas sensors and electrical devices.?2?Using first-principle atomistic simulations,we focused on the electronic structures of small gas molecules?CO,H₂O,NH₃,NO,and NO₂?adsorbed on the S-vacancy SnS₂ monolayer.The results show that H₂O and CO molecules were physisorbed on the S-vacancy SnS₂ monolayer,whereas NH₃,NO,and NO₂ molecules were chemisorbed on the S-vacancy SnS₂ monolayer via strong covalent bonds.Moreover,our calculations show that H₂O and NH₃ act as charge donors,whereas CO,NO,and NO₂ gas molecules act as acceptors.Different adsorption behaviors of common gas molecules on the S-vacancy SnS₂ monolayer provide a feasible way to exploit chemical gas sensors and electrical devices.In particular,our results also show that under applied biaxial strains,the adsorption energy and charge transfer of gas molecules on the S-vacancy SnS₂monolayer dramatically changed,which indicates that external factors on the S-vacancy SnS₂monolayer are highly preferred.?3?2D nanostructures materials have attracted an exceptional interest in the structural,electronic and optical characteristics due to their ultrathin and flexible nature.Using first-principle simulations,we studied the electronic structures of NO₂ adsorbed monolayer and bilayer SnS₂nanosheets.The results demonstrate that NO₂ is physisorbed on monolayer and bilayer SnS₂nanosheets acting as acceptors with obvious charge transfer from the basal to the adsorbate.Moreover,our results show that electric field and biaxial strains can drastically change the adsorption energy,electronic properties and charge transfer of NO₂ adsorbed SnS₂ systems.Namely,these external conditions are highly preferred and provide a practicable method for adjustable SnS₂ based electrical devices and gas sensors.Especially,the giant Stark effect can easily render the NO₂-adsorbed SnS₂ system from semiconducting to metallic.With the bias voltage further increasing,the current dramatically raises.The calculation results for the preparation of gas-sensitive detection device and related experimental study provides a theoretical reference.