title: Nitrogen Doping Enables Covalent-Like π-π Bonding between Graphenes.
abstract: The neighboring layers in bilayer (and few-layer) graphenes of both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) π-π bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the π-π overlap across the vdW gap while the individual layers maintain their in-plane π-conjugation and are accordingly planar. The existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.
authors.affiliation: †College of Life Sciences, Research Center of Analytical Instrumentation, Sichuan University, Chengdu, Sichuan 610064, P. R. China.
authors.forename: Yong-Hui
authors.initials: YH
authors.lastname: Tian
authors.affiliation: ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
authors.forename: Jingsong
authors.initials: J
authors.lastname: Huang
authors.affiliation: †College of Life Sciences, Research Center of Analytical Instrumentation, Sichuan University, Chengdu, Sichuan 610064, P. R. China.
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Sheng
authors.affiliation: ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
authors.forename: Bobby G
authors.initials: BG
authors.lastname: Sumpter
authors.affiliation: ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
authors.forename: Mina
authors.initials: M
authors.lastname: Yoon
authors.affiliation: §Department of Chemistry, Georgetown University, 37th and O Streets, NW, Washington, D.C. 20057, United States.
authors.forename: Miklos
authors.initials: M
authors.lastname: Kertesz
keywords: graphene; interlayer separation; nitrogen doping; pancake bonding; van der Waals; π−π bonding