High-resolution transmission electron microscopic study of nanoporous carbon consisting of curved single graphitic sheets

Abstract

A high-resolution transmission electron microscopic study of a nanoporous carbon rich in curved graphitic monolayers is presented. Observations of very thin regions, including the effect of tilting the specimen with respect to the electron beam, are reported. The initiation of single sheet material on an oriented graphite substrate is also observed. When combined with image simulations and independent measurement of the density (1·37 gcm⁻³) and sp³-to-(sp² + sp³) bonding fraction (0·16), these observations suggest that this material is a two-phase mixture containing a relatively low-density aggregation of essentially capped single shells such as squat nanotubes and polyhedra, plus a relatively dense ‘amorphous’ carbon structure which may be described using a random-schwarzite model. Some negatively curved sheets were also identified in the low-density phase. Finally, some discussion is offered regarding the growth mechanisms responsible for this nanoporous carbon and its relationship with the structures of amorphous carbons across a broad range of densities, porosities and sp³-to-(sp² + sp³) bonding fractions.