Abstract:

The atomic structure of graphene influences its chemical, electronic,mechanical and magnetic properties. Aberration-corrected transmission electron microscopy is a leading approach for direct imaging of graphene with single atom sensitivity and sub-Angstrom spatial resolution.By using monochromation of the electron source, we reduce chromatic aberration effects and combined with spherical aberration correction,we can achieve 80 pm resolution at an accelerating voltage of 80 kV.This enables single atoms to be fully resolved in graphene and subsequently the position of carbon atoms to be accurately located and the length of C-C bonds locally measured. We have realized a method for nanoscale spatial control of defect addition using a focussed electron beam at 80 keV energy.

This permits the tudy of monovacancies, divacancies, dislocation pairs,grain boundaries and dopants. In order to understand the HRTEM images,we perform multi-slice image simulations based on accurate atomic models from DFT calculations. This enables us to provide correlations between charge density distributions and C-C bond lengths within defect structures.Our HRTEM studies provide the most accurate description to date of defect structures in graphene and help form the basis of suitable models for theoretical predictions of graphene properties.