Band-gap manipulations of monolayer graphene by phenyl radical adsorptions: A density functional theory study

Phenyl radical (Ph^.) adsorption on monolayer graphene sheets is used to investigate the band-gap manipulation of graphene through density functional theory. Adsorption of a single Ph^. on graphene breaks the aromatic π-bond and generates an unpaired electron, which is delocalized to the ortho or para position. Adsorption of a second radical at the ortho or para position saturates the radical by electron pairing and results in semiconducting graphene. Adsorption of a second radical at the ortho position (ortho-ortho pairing) is found to be more favorable than adsorption at the para position (ortho-para pairing), and the ortho-ortho pairing has stronger effects on band-gap opening compared with ortho-para pairing. Adsorption of even numbers of Ph^. on graphene by ortho-ortho and ortho-para pairings, in general, increases the band gap. Our study shows promise of band-gap manipulation in monolayer graphene by Ph^. adsorption, leading to potential wider applications of graphene. A radical manipulation: Density functional theory (DFT) reveals that the ortho-ortho or ortho-para adsorption pairings of phenyl radicals on graphene can manipulate graphene′s band gap.