Abstract
Raman-scattering and transmission-electron-microscopy (TEM) experiments are reported which provide information on the microstructure of fluorine-intercalated graphite fibers (F) for stoichiometries in the range 7.8≥x≥2.9. Lorentzian fits to our Raman spectra indicate the presence of a doublet near 1600 and a broad line near 1360 . An anomalous frequency downshift of the doublet was observed in F fibers upon increase in the intercalate concentration, unlike the behavior observed in other acceptor graphite intercalation compounds. This downshift in frequency of the doublet can be understood in terms of a decrease in the hole concentration in the graphene layers with increasing fluorine concentration, resulting in an increase in the in-plane lattice constant and a decrease in the in-plane mode frequency. These Raman results are consistent with high-resolution TEM experiments on the same fibers. Lattice fringe images of F fibers show wavy fringes, and the waviness is identified with semi-ionic (covalent) bonding. Evidence for unintercalated graphite regions is also presented. As the fluorine concentration of the F fibers increases to high values, the amount of waviness increases.
- Received 15 July 1991
DOI:https://doi.org/10.1103/PhysRevB.45.6883
©1992 American Physical Society