Study of carbon fiber surfaces by scanning tunnelling microscopy, part i. carbon fibers from different precursors and after various heat treatment temperatures

Abstract

Scanning Tunnelling Microscopy (STM) has been applied to the study of the surfaces of carbon fibers. The results have clearly shown the difference in surface features and the structural discrepancies between carbon fibers from different precursors and after various heat treatments. At large scales, some common surface features are always present on a series of petroleum mesophase pitch-based carbon fibers. They are characterized by the ribbons, the smaller stripe-form crystallite stackings and the discontinuous boundaries. For coal mesophase pitch-based carbon fiber, the ribbons are more like twisted strands, whereas for PAN-based carbon fiber (M40), the ribbons are not discerned, but the surface displays rougher rock-like stacks. At atomic resolution scales, at least three kinds of graphitic organisations have been observed on the ex-pitch carbon fibers: the nodular texture, the step-like texture and the graphene, whereas only the graphene and the step-like textures have been visualized on M40 fiber. The results have also revealed that even at carbonization temperatures, the carbon fibers exhibit a high degree of organisation, which is enhanced by the graphitization treatment. The experimental results are presented and discussed.