Intercalated nanographite: Structure and electronic properties

Structural and electronic properties of K, ${\mathrm{Br}}_2,$ and ${\mathrm{I}}_2$ intercalated nanographite compounds, prepared using standard intercalation techniques, were investigated. The staging phenomenon observed in bulk-graphite-intercalation compounds is absent in the case of intercalation compounds of nanographite, as expected for a finite-size host-guest system. K-intercalated samples contain a small fraction of potassium clusters apart from forming homogeneous mixtures of several stages. Many Raman features of K-intercalated nanographite were found to be similar to K-doped single-wall carbon nanotubes. The first evidence of charge transfer from nanographite to iodine, which is absent in bulk graphite, is revealed based on Raman scattering results. The charge transfer per carbon atom $f_{\mathrm{C}}$ follows the order $\mathrm{potassium}>\mathrm{bromine}>\mathrm{iodine},$ which is similar to the trends observed in bulk-graphite-intercalation compounds. Intercalation of strong donors such as potassium makes the contribution of edge inherited nonbonding π states, which uniquely characterize pristine nanographite, less important. This is explained considering the large charge transfer and the accompanying shift of the Fermi level away from the edge states. In case of weak acceptors such as ${\mathrm{I}}_2,$ however, there is an enhancement in density of states that indicates a smaller shift in the Fermi level, keeping it in the vicinity of edge states.