ATOMIC-STRUCTURE OF LONGITUDINAL SECTIONS OF A PITCH-BASED CARBON-FIBER STUDIED BY STM

Longitudinal sections of pitch-based carbon fibers have been studied w ith scanning tunneling microscopy. A hexagonal superstructure due to a rotation of 9.5-degrees of the top graphitic plane with respect to th e underlying bulk was observed. Remarkably this superstructure was mod ulated near defects by a (square-root 3 X square-root 3)R30-degrees mo dulation. The same modulation was found on the images with atomic reso lution. It was concluded that the atomic structure of the fiber resemb les the hexagonal structure of graphite. But locally this structure is disturbed. From the modulation of the superstructure it is deduced th at this disturbance extends at least two layers into the bulk.