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 me sophase contents (Mc, < 10, 80 and 100%) and heat treatment temperatur es (carbonization and graphitization) were studied by scanning tunneli ng microscopy (STM) at atomic resolution. At the carbonization tempera ture (1000 degrees C), the low Mc fiber (< 10%) surface remain largely amorphous while the crystalline structure is well developed for the m esophase (Mc=80%) fiber. The graphitization by heat treatment (2300-25 00 degrees C) increases the crystallinity in all the fibers. The low M c fiber (< 10%) shows several peculiar structures, for instance, the o ccurrence of a ''ring type'' image pattern. Even for the high Mc and g raphitized samples, the surface is always very heterogeneous in surfac e crystallinity, with some regions much less ordered. These surface fe atures of carbon fibers are very different from commercial products we studied before, indicating perhaps different manufacture and heat-tre atment conditions. Copyright (C) 1996 Elsevier Science Ltd.