Self Assembly And Polymerization Of QX Molecules On Metel Surfaces

Graphene nanoribbons,as a new type of carbon-based semiconductor material,have received much attention since their inception.The research results on the preparation of graphene nanoribbons by a bottom-up surface synthesis method have been widely reported.Therefore,it is crucial to investigate the self-assembled structures obtained during the surface synthesis of graphene nanoribbons and the factors influencing the polymerization reaction to reveal the specific mechanism of the reaction process.Considering the excellent ability of the introduction of complex physical or chemical structures to improve the properties of organic semiconductor materials and the great advantage of the surface synthesis method for the preparation of two-dimensional organic materials,the preparation of a porous graphene nanoribbon with heteroatom doping by the above method would be a meaningful work.In this thesis,the structural investigation of adsorption self-assembly was carried out by studying the assembly properties of 5,8-dibromo-2,3-diphenylquinoxaline(QX)on Au(111)and Ag(111)surfaces successively using QX as a precursor.The graphene nanoribbons were synthesized by the secondary reaction of surface Ullmann coupling reaction and cyclization dehydrogenation.Finally,the energy change and charge transport properties of the surface synthesis during its selfassembly were investigated by theoretical calculations focusing on the synthesis of the surface;the structure of the synthesized products and the properties such as the energy band structure were further verified;and the self-assembly and reaction principles of QX molecules on metal surfaces were revealed.The details of the study are as follows:First,scanning tunneling microscopy(STM)was used as the main tool to investigate the process of surface self-assembly of QX molecules on Au(111)and Ag(111)surfaces.The periodic structure and lattice parameters of the self-assembled structures were clarified,the evaporation temperature of the molecules and the process and specific reaction conditions of the surface Ullmann synthesis reaction were investigated,and the graphene nanoribbon structures were successfully prepared on the Au(111)surface by the secondary reaction.Next,theoretical calculations of the three self-assembled structures as well as the synthesized graphene nanoribbons were carried out using density functional theory.The specific model of self-assembly is verified,and the self-assembly dynamics of QX molecules on the surface and the magnitude of adsorption energy on the metal surface are also clarified.The strength of the adsorption ability of the two metal substrates for organic molecules and the charge density of the self-assembled structures with STM simulation images are further verified.The prepared graphene nanoribbons were finally determined to be an organic semiconductor with an indirect band gap of 1.3875 e V.In this paper,graphene nanoribbons were prepared by the bottom-up surface synthesis method,and a new two-dimensional organic semiconductor structure was successfully constructed and the self-assembly principle and electronic properties of the assembled structure were investigated during the reaction process.This work provides a new idea for the research progress of two-dimensional carbon-based materials.