| Graphene,a two-dimensional honeycomb structure of single carbon atomic layer,was successfully separated from graphite material in 2004.Due to its light weight,large specific surface area,high carrier mobility and high conductivity,graphene has been widely applied in nano-electronic devices,energy storage devices,spintronic devices,solar cell technology,sensors and supercapacitors and so on.In this paper,by using first-principles calculation method based on density functional theory(DFT),the adsorption of hydrogen cyanide(HCN)on pristine graphene,defect graphene and hetero-atom-doped graphene were investigated systematically.The effect of gas molecule adsorption on the electronic and magnetic properties of Mn-doped graphene(MnG)and the effect of the external electric field on the adsorption performance of the composite systems were also investigated.The results are as follows:(1)The adsorption and gas sensitivity of hydrogen cyanide(HCN)molecules on pristine graphene(PG)and modified graphene,including single vacancy defect graphene(SVG)and Li,B,N,Mg,Al,S,Ca,Ti,Cr,Mn,Fe,Co5 Ni,Pt,Au,Ag and Cu substitutional doped graphene(XG)S were investigated.It is found that HCN undergoes weakly physisorption on PG,BG,NG and SG,and HCN adsorption failed to cause the change of the density of states near the Fermi level.Therefore,the substrates(PG,BG,NG and SG)are not sensitive to HCN molecule.Although the introduction of single vacancy defect increases interaction between the substrate and HCN molecule,the electronic properly of the system hardly change before and after HOSN adsorption.HCN molecule is chemisorbed on LiG,MgG,A1G,CaG,TiG,CrG,MnG,FeG,CoG,NiG,PtG,AuG9 AgG and CuG.Among them,the electronic properties of LiG,MnG,CuG,AgG and AuG have changed significantly:LiG transforms from metallic to semiconducting,MnG transforms from half-metallic to semiconducting,AuG transforms from half-metallie to metallic,AgG transforms from metallie to semiconducting and CuG transforms from half-metallic to semiconducting,these transformations suggest that the electrical conductivity changes obviously.However,other substrates still retain original characters.Therefore,LiG,MnG,CuG,AgG and AuG are more suitable for HCN detection among all of mentioned substrates.(2)The effect of gas molecule(H2CO,NO,NO2,O2 and SO2)adsorption on the electronic and magnetic features of Mn-doped graphene(MnG)was investigated.Our study reveals that after H2CO,NO,NO2 and SO2 adsorption,MnG transforms from half-metallic to semiconducting,and this transformation indicates that MnG's conductivity is changed significantly.Meanwhile,O2 adsorption has no influence on MnG's original electronie property.Therefore,the substrate of MnG is highly sensitive to H2CO,NO,NO2 and SO2.The reconfiguration of electron distribution caused by gas adsorption dramatically alters the spin polarization distribution of the combined system,that is,H2CO and NO2 adsorption leads to local spin polarization and the spin density is almost completely localized on MnG,whereas O2,NO and SO2 adsorption can result in complete spin polarization.The difference is that for the adsorption of NO and SO2,the polarization direction of the gas molecule and the substrate is opposite,and the spin polarization direction of NO and SO2 is different After the adsorption of O2,the polarization direction of the gas molecule and the substrate has the same direction.Therefore,the above five gases can be effectively distinguished and identified according to the different spin polarization distribution characteristics of the composite system.In addition,the external electric field(E-field)is varied from-0.50 V/A to+0.50 V/A then applied to the adsorption system.A strong interaction is observed between gas and MnG with a positive E-field as reflected in the enhancement of adsorption energy.The interaction is obviously weakened by introducing the E-field in the negative direction.Hence,the adsorption strength and sensitivity of gas on MnG can be effectively tuned by the E-field. |
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