A difference in surface morphologies of the CNFs can also be
observed before and after the surface modification. As shown in
Fig. 2a, the pristine CNF typically consists of an inner ordered
graphitic layer and an outer disordered graphitic layer before any
treatment as the CNFs were produced by chemical vapor deposition
followed by heat treatment at 1500 C to convert deposited
amorphous carbon present on the surface of the nanofibers to a
short-range ordered structure. In the surface modification process,
breakage of CNFs occurred to some extent (Fig. 2bi). In addition, a
loss of graphitic structure due to defect formation and introduction
of surface groups can also be observed (Fig. 2bii).