Imaging edges of nanostructured graphene

Graphene, as the forefather of 2D-materials, attracts much attention due to its extraordinary properties like transparency, flexibility and outstanding high conductivity, together with a thickness of only one atom. However, graphene also possesses no band gap, which makes it unsuitable for many electronic applications like transistors. It has been shown theoretically that by nanostructuring pristine graphene, e.g. with regular holes, the electronic properties can be tuned and a band gap introduced. The size, distance and edge termination of these “defects” influence the adaptability. Such nanostructuring can be done experimentally, but especially characterization at atomic level is a huge challenge.
High-resolution TEM (HRTEM) is used to characterize the atomic structure of graphene. We optimized the imaging conditions used for the FEI Titan ETEM. To reduce the knock-on damage of the carbon atoms in the graphene structure, the microscope was operated at 80kV. As this strongly increases the influence of the chromatic aberration of the lenses, the energy spread of the electron gun was reduced to <0.2eV by using a monochromator. Together with the objective-lens Cs-corrector a resolution better then 1.2Å can be achieved, which allows us to resolve the second order reflection of graphene and to visualize the atomic structure in HRTEM. With this tool we tackle the challenge of imaging the introduced “defects” and their atomic structure.