| Graphyne is a new type of two-dimensional periodic carbon allotrope after graphene,which is composed of carbon atoms in both sp~2-and sp-hybridized states.This hybrid network structure endows graphyne with rich carbon chemical bonding,highπ-conjugation,tunable band gap,uniformly distributed pore structure and good chemical stability.In 2010,the team of Academician Li Yuliang successfully synthesized graphdiyne film in a large area on a copper substrate for the first time,triggering extensive research on graphyne.Depending on the number and position of alkyne bonds,the morphology of graphyne is diverse.In the family of graphynes,γ-graphyne(γ-GY)contains equal amounts of sp~2-hybridized carbon and sp-hybridized carbon,and is the simplest hybrid structure.However,it has higher stability,inherent photoelectric,mechanical and semiconducting properties.This makesγ-GY to be a suitable candidate for several potential applications,including hydrogen storage,toxic gas detection,single-atom catalyst,anode material for lithium-ion batteries and cathode material for fuel cells.A large number of defects and active sites are generated within graphyne after doping with impurity atoms,which can enhance the catalytic activity.Atomic doping at different sites can produce many different doped structures,and the properties of various doped structures can be affected.Experimentally,these different doping types are difficult to be detected in situ,but theoretical simulation methods can effectively identify and characterize the structure of dopedγ-GY.One of the most widely used spectroscopic technology in surface research is X-ray spectroscopy.It can use the energy distribution of the excitation or de-excitation processes of the nuclear orbital electrons of the system to determine the elemental composition of the material and the chemical and electronic states of the contained elements,etc.In this thesis,X-ray photoelectron spectroscopy(XPS)and near-edge X-ray absorption fine-structure(NEXAFS)spectroscopy are mainly used.Among them,X-ray photoelectron spectroscopy is to ionize the electrons in the 1s orbit into the vacuum state,providing information about nuclear orbit and reflecting the different chemical environments of elements.The near-edge X-ray absorption fine-structure spectroscopy excites the electrons in the 1s orbit to the unoccupied orbits,providing information on the unoccupied orbits and thus measuring the electronic and chemical structure of the system.In addition,X-ray photoelectron spectroscopy is sensitive to the doped structure,while near-edge X-ray absorption fine-structure spectroscopy is significantly dependent on the local chemical environment of the doped structure.We can identify different doping configurations based on the different sensitivity and dependence that the spectra exhibit to the local chemical environment of the different doping configurations.In this thesis,the X-ray photoelectron spectroscopy and near-edge X-ray absorption fine-structure spectroscopy of oxygen-and nitrogen-dopedγ-graphyne have been theoretically calculated using various approximation methods based on density functional theory.By analyzing and discussing the profiles of the spectra and the energy positions of the spectral peaks,etc.,we have theoretically characterized the different doping configurations.The study and results of this thesis are as follows:1.X-ray spectra of oxygen-dopedγ-graphyne local structuresSeven oxygen-dopedγ-graphyne configurations are proposed.The C and O 1s X-ray photoelectron spectroscopy and near-edge X-ray absorption fine-structure spectroscopy of these seven doped configurations are simulated theoretically,and compared with the experimental spectral lines,the characteristic peaks of the spectra are assigned.We found that the calculated C 1s ionization energy of pureγ-graphyne with sp~2-hybridized carbon is higher than that of sp-hybridized carbon,which is contrary to previous empirical findings.The near-edge X-ray absorption fine-structure spectroscopy is strongly dependent on the local structure of each doped configuration,and we can identify these several oxygen-dopedγ-graphyne configurations based on the important spectral features.This provides a theoretical approach to identify the different oxygen-doped structures and insight into the structure-spectrum relationship.2.X-ray spectra of the local structure of nitrogen-dopedγ-graphyneNitrogen-dopedγ-graphyne has five typical doping structures.We theoretically simulated the C and N 1s X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy of these five nitrogen-dopedγ-graphyne structures.The calculated X-ray photoelectron spectroscopy fits well with the experimental XPS spectra and can verify the experimental assignment of the spectral peaks.In addition,the X-ray photoelectron spectroscopy roughly exhibits the dependence on the local structure and cannot effectively identify the five nitrogen-doped structures.In contrast to the X-ray photoelectron spectroscopy,the near-edge X-ray absorption fine-structure spectroscopy show strong dependence on different local structures and can effectively identify the five nitrogen-dopedγ-graphyne structures.This thesis has six chapters:Chapter 1 is the introduction which introduces the research progress of oxygen-or nitrogen-dopedγ-graphyne in X-ray;Chapter 2 briefly describes the quantum chemical theory used in this thesis;Chapter 3 is the theoretical part of X-ray spectra;Chapter 4 mainly discusses the theoretical results of the X-ray spectra of oxygen-dopedγ-graphyne local structures;Chapter 5 mainly discusses the theoretical results of the X-ray spectra of nitrogen-dopedγ-graphyne local structures;Chapter 6 is about conclusions and outlooks of this thesis. |
