Atomic scale STM study of pitch-based carbon fibers: Influence of mesophase content and heat treatment temperature

The surface micro-structure of several carbon fibers with different mesophase contents (Mc, < 10, 80 and 100%) and heat treatment temperatures (carbonization and graphitization) were studied by scanning tunneling microscopy (STM) at atomic resolution. At the carbonization temperature (1000 degrees C), the low Mc fiber (< 10%) surface remain largely amorphous while the crystalline structure is well developed for the mesophase (Mc=80%) fiber. The graphitization by heat treatment (2300-2500 degrees C) increases the crystallinity in all the fibers. The low Mc fiber (< 10%) shows several peculiar structures, for instance, the occurrence of a ''ring type'' image pattern. Even for the high Mc and graphitized samples, the surface is always very heterogeneous in surface crystallinity, with some regions much less ordered. These surface features of carbon fibers are very different from commercial products we studied before, indicating perhaps different manufacture and heat-treatment conditions. Copyright (C) 1996 Elsevier Science Ltd.