Scanning tunneling microscopy (STM) was used to characterize the surface
topography of polyacrylonitrile (PAN)-based carbon fibers before and after
electrochemical treatment, stretch resistance test, and high-temperature treatment.
A new kind of spiral structures was found, which was not only on the surface but
also in the inner layer. The spiral structure of the fibers was caused by the spinning
process. The fiber structure contained the shape of the precursor. There were some
large cracks in the carbon fibers after the stretching resistance test. The large cracks
can result in carbon fiber breaking under certain stress conditions. The difference in
the structures of the carbon fibers before and after the high-temperature treatment
was determined.