Detection of Ring and Adatom Defects in Activated Disordered Carbon via Fluctuation Nanobeam Electron Diffraction.

How the structure of disordered porous carbons evolves during their activation is particularly poorly understood. This problem endures primarily because of a lack of high-resolution 3D techniques for the characterization of amorphous and highly disordered structure. To address this, the measurement of the 3D pair-angle distribution function using nanodiffraction patterns from high-energy electrons is demonstrated. These rich multiatom correlations are measured for a disordered carbon and they clearly show the structural evolution during activation. They provide previously inaccessible bond-angle information and direct evidence for the presence of ring and adatom defects. An increase in the short-range order and the number of fivefold ring defects with activation are observed, indicating stress relaxation by increasing curvature. These observations support models of disordered porous carbons based on curved graphene networks and explain how large amounts of free volume can be created with surprisingly small changes in the average ratios of tetrahedral to graphitic bonding.