Investigation On The Electronic Structures Of Novel Two-dimensional Penta-graphene

Since the mechanical exfoliation of graphene by Geim and Novoselov in 2004,a series of novel two-dimensional(2D)materials have drawn enormous research attentions in the fields of materials science and condensed matter physics,such as hexagonal boron nitride monolayer,molybdenum disulfide monolayer,germanene,phosphorene,and borophene.In 2015,another new 2D carbon allotrope,named penta-graphene,composed entirely of carbon pentagons,has been proposed,which is a quasi-direct band-gap semiconductor.Penta-graphene shows good thermal stability and mechanical stability together with negative poisson's ratio and ultrahigh mechanical strength.Along with the rapid development of computer technology,computational materials science has become more and more important in materials science.In order to further investigate the potential applications of penta-graphene in microelectronic devices,it is of great necessity to theoretically investigate the modulation of the electronic structures of penta-graphene.This dissertation is to study the effects of the adsorption of alkali metal atoms and applied biaxial strain on the geometrical structures and electronic structures using first-principles density functional theory.This will be helpful in the design of penta-graphene based devices.The main results are summarized as below.(1)A systematic study has been carried out to investigate the geometrical structures and electronic structures of penta-graphene.The results reveal that penta-graphene shows buckled structure,containing sp3-and sp2-hybridized carbon atoms.The results of electronic structure calculations show that penta-graphene can be considered as a quasi-direct band gap semiconductor with a band gap of 3.22 eV.(2)A systematic study has been carried out to investigate the effects of the adsorption of alkali metal atoms(Li,Na and K)on the geometrical structures and electronic structures of penta-graphene.The calculation results indicate that the bridge site over the carbon atoms of the third layer(B33)is the most stable adsorption site,and there is charge transfer from the adsorbed alkali metal atom to penta-graphene.After the adsorption of alkali metal atom,the conduction band of penta-graphene as well as the valence band moves down,and the Fermi level moves upward.As the atomic number of adsorbed alkali metal atoms increases,the work function of penta-graphene decreases monotonically.It can be seen that for the adsorption of K atom on penta-graphene the adsorption energy and the charge transfer are the largest,and the decrease of work function is the biggest.(3)A systematic study has been carried out to investigate the effects of applied tensile and compressive strains on the geometrical structures and electronic structures of penta-graphene.The results show that the strain has great influence to sp3-hybridized carbon atoms,and the deformation of penta-graphene within-10 % to 25 % is elastic deformation.Under the applied strain,penta-graphene turns from quasi-direct band-gap semiconductor completely to indirect band-gap semiconductor.The band gap of penta-graphene gradually decreases as the increase of the compressive strain,while the band gap increases and then decreases as the increase of the tensile strain.