Field emission mechanisms of graphitic nanostructures
  Field emission (FE) and the electronic-states origin of graphitic nanostructures were investigated by first-principles calculations based on time-dependent density-functional theory. We find that the FE current from graphitic ribbons changes remarkably depending on the hydrogen termination and the direction of the applied electric field. Also, the FE current from graphene sheets shows a dramatic increase around vacancy defects. We verified, through the analysis of local electronic structures and energy distributions of emitted electrons, that the dangling-bond (or $\sigma$) character is responsible for these results and governs the nature of the FE of graphitic nanostructures. 
Masaaki Araidai, Yasuhiro Nakamura, and Kazuyuki Watanabe