Experimental determination of the momentum-dependent dielectric response of stage-1 FeCl3-intercalated graphite

The momentum-dependent dielectric function $\epsilon \mathrm{}(q,E)\mathrm{}$ has been determined for stage-1 Fe${\mathrm{Cl}}_3$-intercalated graphite by a Kramers-Kronig analysis of electron-energy-loss spectra measured from 0.2 to 100 eV. Similar measurements and analysis performed on pristine graphite indicate that critical points in $\epsilon \mathrm{}(q,E)\mathrm{}$ are retained in the intercalated material and that the graphite band structure is not significantly altered. In the intercalated compound the $\pi \to {\pi }^{*}$ interband gap is measured. The experimental results are compared both with a calculation of excitations in a tight-binding model of the $\pi$ bands and with optical-reflectivity measurements on graphite and the intercalated compound.