Theoretical Studies Of New 2-dimensional Carbon Allotropes

In view of the experimental progresses in fabricating carbon nanostructures,we have carried out detailed investigations of new two-dimensional(2D)carbon allotropes by using the density functional theory calculations and the evolutionary algorithm.One of the studied 2D carbon allotropes is the planar structure composed of the 5,6,8carbon rings.We started our research by performing global minimum structure search by employing evolutionaryalgorithm.Three new carbon allotropes were proposed,which were named as phographenes(pentagon-hexagon-octagon-graphene).Including the previously reported ones,we assigned them as ?,?,?,?,?phases.The?and?phases account for the previously reported HOP-graphene and pentahexocite.All of these phographenes are metallic,which would turn to large gap semiconductors under hydrogenation.Among those phographenes,?-phographene show remarkablestructural stabilities.Its mechanical properties are comparable to those of graphene.The ?-phographene is energetically more stable than most of the previously reported carbon 2D allotropes,which in fact is almost degenerate in energy with the ?-phographene and phagraphene(composed of 5-6-7 carbon rings).According to our calculations,the methodology of electron injection could be used to suppressthe formation of phagraphene.Further analyses on the structural motifs of ?-and ?-phographenes favorites the formation of the ?-phographene.Thus,the ?-phographene may gain priority in experimental studies to fabricate large-scale high-quality 2D crystal structure.Attributed to the topological arrangement of the 5 and 8 carbon rings,the phographenes is found to be more reactive than graphene.The adsorption of Au and Pt clusters would be enhanced,showing the promise in supporting precious metal particles to form high performance complex catalyst nanostructures.Also,we studied a number of biphenylene-based carbon sheets,which were named as PB(polymerized-biphenylene).According to the previous experiment studies,the biphenylene has 2 different polymerization patterns,resulting in 2 kinds of nanoribbons with chirality and width dependent electronic structures.Several biphenylene based carbon sheets were predicted previously.Here,we proposed 2 new polymerizationplanar sheets that are energetically more favorable.Careful analyses showthat ?-PB hasbetter stability,suggesting the possibilities for experimental realization.Our calculations of lithium adsorption on PB show the promising applications for Li battery electrode and gas sensor detector.Finally,a new stable 2D carbon isomer with Dirac cone was predicted.This new carbon 2D allotrope is composed of 5 and 6 membered carbon rings.For the fact that it has similar structural features with fullerene,we named it as fl-graphene(fullerene-like graphene).Due to its structural feature,fl-graphene is energetically more favorable than penta-graphene(entirely composed of 5 carbon rings)and has comparable in-plane stiffness with h-BN.Compared to the purelysp2 hybridized Dirac cone in graphene,some sp3 characteristices were mixed into the Dirac cone in fl-graphene due to its buckling structure,resulting in a enhanced spin-orbit bandgap,which is obviously larger than that in graphene.Besides,the bandstructure engineering methods commonly used in graphene can also be applied to fl-graphene to modify its electronic properties.