Electron microscopy study of mesophase pitch-based graphite fibres

A comprehensive electron microscopic investigation of the structure of the graphitic sheet in mesophase pitch-based fibres is presented.In situ brightfield and (00l) darkfield observation of the sheets in sub micrometre fibres reveals a finely striated structure, associated with three-dimensional order. (hkl) darkfield imaging of the sheets in their edge-on and face-on orientations indicates that the striations correspond to the edge view of a mosaic of graphite grains. The grains have lateral dimensions of 100 to 200 nm on average but are only a few atomic layers thick.In situ lattice imaging of the fibre edges indicates a very high level of lattice perfection of the (00l) domains below the fibre surface, quite in line with the outstanding mechanical and thermal properties of this type of fibres. A variety of surface defects are revealed. Preferential orientation effects of the sheet texture on the fibre electron diffraction pattern are described.