First Principle Study On Stability,Optical And Electrical Properties And Gas Sensitive Properties Of Modified Graphene

Graphene,a two-dimensional honeycomb-like crystal with monolayer carbon atom thickness formed by sp2 orbital hybridization,was first successfully prepared in experiments in 2004.Because of its unique structure and properties,it is widely used in electronic devices,photonic devices,energy acquisition and storage,sensors and other fields.The stability,thermodynamic properties and electronic and optical properties of N,Au and N-Au co-doped graphene at different doping concentrations are systematically studied based on density functional theory and density functional perturbation theory and ab initio molecular dynamics methods.The adsorption behavior of Pd doped graphene on gas molecules and the influence of adsorbed gas molecules on the electronic structure,work function and optical properties of Pd doped graphene are systematically studied.The main conclusions are as follows:(1)The structural stability,thermal stability and thermodynamic properties of pure graphene(PG)and N,Au and N-Au co-doped graphene at different doping concentrations were systematically investigated.The formation energy,phonon dispersion curves,heat capacity,free energy and entropy of all systems are calculated.The results show that N doped graphene has better structural stability and thermal stability than Au and N-Au co-doped graphene,which is easier to synthesize experimentally.The thermal capacity and entropy of PG and doped systems increase with increasing temperature,while the free energy decreases.When the temperature is fixed,the effect of Au doping on graphene thermal capacity,free energy and entropy is more significant than that of N doping.(2)The electronic and optical properties of N,Au and N-Au co-doped graphene at different doping concentrations were systematically investigated.The results show that N doped graphene and Au doped graphene have metallic properties,while N-Au co-doped graphene has semiconductor properties.Au doped graphene can absorb light at a specific wavelength in the ultraviolet region,its absorption intensity depends on the doping concentration of Au;at 7.0?9.0 eV the AuxG and NxAuxG have a certain reflectivity and a large absorption coefficient in the frequency range of 0 eV,where the reflectivity increases with the increase of doping concentration,so their transmittance decreases accordingly in that frequency range.(3)The effects of O2?CO?NO?N2O?NO2 and SO2 adsorption on the electronic and optical properties of Pd doped graphene(PdG)were systematically studied.The calculated results show that six gas molecules belong to chemisorption due to their large adsorption energy and small adsorption length;gas adsorption can cause PdG charge redistribution and changes in electronic properties.PdG changed from semiconductor properties to metallicity after adsorption O2?NO2 and SO2;compared with PdG,CO@PdG(PdG adsorption CO system)and N2O@PdG still maintain semiconductor properties,but the band gap width decreases;the band gap shows semimetallicity.Gas adsorption also causes changes in the PdG function work,whose value depends on the direction and number of charge transfer.Moreover,gas adsorption can cause changes in PdG absorption spectra:unlike PdG,under E(?)polarization,new absorption peaks appear in the visible region of O2@PdG?N2O@PdG and NO@PdG.Consequently,adsorption of different gas molecules can effectively regulate the optical properties of PdG.