First Principle Study On The Geometry And Properties Of Adsorption Of Doped Graphene

Graphene is a two-dimensional Carbon materials,which has been research focus of nano materials science in the field of sensors since its discovery due to the physical and chemical properties.Compared with CNT,graphene has a larger surface area and better adsorption perf ormance,which might be used as superior quality sensors.In order to obtain a greater understan ding of graphene adsorption performance,the adsorption of 5 different gas molecules on intrins ic graphene,B-doped graphene,N-doped graphene,B and N-doped graphene are studied by u sing the first-principles method based on density functional theory.The adsorption performanc e,charge density difference,band structure and the electronic density of states of each system are calculated,and we get a meaningful result from the computation.The thesis is organized as follows:In Chapter 1,the typical structure,discovery,synthesis,physical and chemical properties,applications and the background of graphene are introduced.In Chapter 2,the first-principles method,density functional theory,some common exchange-correlation functional and our DFT-based packages used in the thesis are introduced.In Chapter 3,we have studied the adsorption of 5 different gas molecules(Cl2,F2,NO,NO2,NH3)at three different high symmetry sites(B,H and T)of intrinsic graphene by using the first-principles method.We have calculated the stable adsorption structure,adsorption energy,charge density difference,band structure and the electronic density of states.The change of adsorption position won't affect the adsorption properties of 5 different gas molecules on graphene.Thereinto,the orbital hybridization is observed in the F2 and graphene system,which illustrates that F2 molecule is chemical adsorption.Charge transfer are obvious between NO2,NH3,NO gas molecules and graphene.The interaction between graphene and NO2,NH3,NO gas molecules are weaker than F2 molecule.The electronic structure of Cl2 gas molecules adsorbed on graphene is invariant after adsorption,which illustrates that Cl2 is physical adsorption,and the interaction is weakest.The electronic property of intrinsic graphene is only sensitive to the presence of F2,NO and NO2 molecules.In Chapter 4,we have studied the adsorption of 5 different gas molecules at three different high symmetry sites of B-doped graphene.The change of adsorption position won't affect the adsorption properties of Cl2,NO and NO2 gas molecules on B-doped graphene.We find that charge transfer are obvious between NO2,NO molecule and B-doped graphene,and the adsorption energies are high.The interactions between B-doped graphene and NO2,NO are strong,so they are chemical adsorption.There is no charge transfer between Cl2 Molecules and B-doped graphene,which illustrates that Cl2 is physical adsorption.F2 and NH3 are more stable at B and T sites than H site by adsorbing on B-doped graphene.Charge transfer is obvious between F2 molecule and B-doped graphene at the three sites which illustrates F2 is chemical adsorption.We find that charge transfer are obvious between NH3 molecule and B-doped graphene at B and T sites except H site.The adsorption height is large and adsorption energy is low,so NH3 is physical adsorption at H site.The electronic property of B-doped graphene is only highly sensitive to the presence of F2 molecule at B and T sites.And B-doped graphene is also sensitive to the presence of NO molecule.B-doped graphene is less sensitive to the presence of NO2 molecule than NO molecule.B-doped graphene is only sensitive to the presence of NH3 molecule at B and T sites.Doping graphene with B dopants significantly increases the adsorption energy of these systems,which is expected to induce significant changes in the electrical conductivity of the systems.So B-doped graphene is more suitable for gas molecules detection compared with intrinsic graphene.In Chapter 5,we have studied the adsorption of 5 different gas molecules at three different high symmetry sites of N-doped graphene.The interaction between Cl2,NO,NO2,NH3 and N-doped graphene are weak,respectively.There are no charge transfer between Cl2,NH3 and N-doped graphene.So Cl2 and NH3 are physical adsorption.Charge transfer are obvious between NO2,NO molecule and N-doped graphene,and the adsorption energies are high.So NO2 and NO are more inclined to chemical adsorption.The interaction between F2 and graphene is strong,especially when F2 adsorbed at B site.Because F2 molecule has strong oxidizing,and N-doped graphene is of typical n-type.So F2 is chemical adsorption.The electronic properties of N-doped graphene is only very sensitive to the presence of F2 molecule at B site.N-doped graphene is sensitive to the presence of NO molecule,and N-doped graphene is less sensitive to the presence of Cl2,NO2 molecules.But N-doped graphene is not sensitive to the presence of NH3 molecule.In Chapter 6,we have studied the adsorption of 5 different gas molecules at three different high symmetry sites of BN-doped graphene.The change of adsorption position won't affect the adsorption properties of Cl2,NO and NH3 gas molecules on BN-doped graphene.There is no charge transfer between Cl2,NH3 gas molecules and BN-doped graphene.The adsorption height is large and adsorption energy is low,so Cl2 and NH3 gas molecules are physical adsorption at the three sites.We find that F2 move towards the graphene only at B site.The charge transfer will take place between F2 molecule and BN-doped graphene.The orbital hybridization is strongly observed In DOS,and energy level splitting is observed in valence band.Therefore,the interaction between F2 and BN-doped graphene will become more strongly,which is chemical adsorption at B site.Charge transfer are obvious between NO2,NO molecule and BN-doped graphene,and the adsorption energies are high.So NO2 and NO are chemical adsorption.The electronic properties of BN-doped graphene is only sensitive to the presence of F2 molecule at B site.And BN-doped graphene is very sensitive to the presence of NO and NO2 molecules,but BN-doped graphene is not sensitive to the presence of Cl2 and NH3 molecules.In Chapter 7,the summary of the thesis and prospect of future work are introduced.