Theoretical Study On Medium-sized Two-Dimensional Carbon Materials

With the rapid development of science and technology,people urgently need more electronic materials with special properties.Especially in 2004,the successful synthesis of monolayer graphene opened a door for two-dimensional materials,and the graphene with unique structure and special properties can be applied to many fields,which further stimulate people to study more novel two-dimensional(2D)carbon materials.A large number of 2D materials had been searched by using the structural search algorithm based on the first-principle calculations,including those that have been discovered and newly undiscovered.Using the density functional principle methods,we systematically investigated a series of medium-sized 2D coronene-based carbon allotropes.Using the first principle symmetric search algorithm,a new graphene-like carbon allotrope with space group was predicted,named azugraphene,and its 38 atoms in the unit cell can be fragmented into three parts,including 5-7 rings named azulene,one hexagon,and two remainder atoms.Azugraphene is a low-energy graphene-like hexagonal carbon allotrope with six Dirac cones in the first Brillouin zone.Due to its stability and the existence of its elementary fragments,azugraphene is potentially synthesizable.In addition,the stable AB stacking bilayer azugraphene is also a Dirac cone material with a band gap of 2.5 me V.Therefore,both the monolayer and bilayer azugraphenes have great potential in physics,chemistry,and nanoelectronics.Based on first-principles calculations,ten 2D based-coronene carbon allotropes(coro-graphene)were predicted,including azugraphene,which are divided into six classes.Furthermore,similar to hexagonal graphene,7-coro-graphene belongs to the P6 m space group.Other 2D based-coronene carbon structures are P6 mmm symmetry.Azugraphene is the only 2D carbon structure with Dirac cones.1C-coro-graphene and 0-coro-graphene are semiconductors with indirect band gaps(2.02 e V and 0.770 e V),respectively.Other structures are metals materials.By doping the nitrogen atoms into the stable two-dimensional coronene-based 2D carbon materials,some new two-dimensional crystals with special properties were found.In particular,only the N-doped two-dimensional structures are planar stable after full relaxation,including N-doped 16-,7-,l A-and 1-coro-graphene structures.N-doped 7-and 1A-coro-graphene are Dirac semi-metal materials,and 16-and 1-coro-graphene structures are metal materials.In addition,by replacing the benzene in the C2N-h2 D with coronene,a new stable two-dimensional structure named coro-C24N6 was predicted.After doped with Li(lithium),Na(sodium),K(potassium),and Rb(rubidium),coro-C24N6X2 become stable two-dimensional structures with Dirac cones.In summary,through the theoretical study on the medium-sized carbon materials,we have found a series of new based-coronene carbon alltropes,including several semi-metals materials with Dirac cones without and with nitrogen doping.In particular,it is possible to synthesize these materials with coronene as the basic fragments.Therefore,this thesis not only expands the research scope of two-dimensional carbon materials to medium size,but also plays an important role in guiding the synthesis of new two-dimensional carbon materials.