First-principles Study Of Armchair Graphene Nanoribbons

Graphene has been paid more attention due to the unique geometric structures and novel properties. The edges of graphene nanoribbons determine the optical, magnetic, electrical, electronic properties, etc. Particularly, termination, chemical functionalization, and reconstruction of graphene nanoribbons edges lead to crucial changes in the properties of graphene nanaribbons. So the control the edges of graphene nanoribbons is critical to the development of its applications in electronics, spintronics, and optoelectronics. In this dissertation, DFT calculations have been performed on the edges termination by diverse hydrogen atoms and B-doped graphene nanoribbons.In chapter one, we briefly introduce the discovery, the electronic properties, the experimental techniques of graphene, and we mianly introduce the characteristics of the nanoribbons with different edge-shapes. At the same time, we give the research objects in this dissertation.In chapter two, we briefly present the theoretical basis (density functional theory DFT), exchange-correlation energy functional, and the computational programs used in the dissertation (DMol3, VASP).In chapter three, we investigate the effect of the diverse edges termination by hydrogen atoms on armchair graphene nanoribbons (Na-GNRs, Na=3-30). The results are as follows:1) The geometry structure of the Na-AGNRs-H-2H (Na=3-30) keeps as a2D plane like graphene and they are all non-magnetic.2) The electronic structure of Na-AGNRs-H-2H (Na=3-30) exhibit three distinct family behaviors (Na=3p,3p+1,3p+2, with p an integer), with△3p+2>△3p+1>△3p(△3p≠0). The band gaps decrease with the increase of the width of nanoribbons and they are all direct bandgap.3) It is found that the pz orbital of the edge C atom has contribution to the HOMO, LUMO orbital.In chapter four, we investigate the effect of B-doping on the configurations and electronic structure of Na-AGNRs-B-H (Na=3-20). We list the mian results as follows:1) Upon doping, the Na-AGNRs-B-H (Na=3,4,5,6,7,8,11,14,17, and20) change into conductors, The dirac point emerge in the bandstructure of the Na-AGNRs-B-H (Na=9) and the system (Na=10,12,13,15,16,18, and19) keep still semi-conductor with the value of the band gap being smaller than undoped AGNRs.2) The electronic state near fermi level mianly derive from the p electrons of boron atoms.3) The boron atoms have a main contribution for the dirac point of the special structure (B1(C-C)7B1). It is found that the system presents as a conductor without the spin-obrit coupling, however, it will present as a semi-conductor with zero bandgap on the other hand.