Dielectric function of solid C70 films

Using variable-angle ellipsometry and normal incidence reflection/transmission optical techniques we have measured the dielectric function ε(ω) at room temperature for solid C70 films over the photon energy range 0.5≤E≤5.3 eV. The onset of absorption across the highest-occupied-molecular-orbit (HOMO)–lowest-unoccupied-molecular-orbit (LUMO) gap is measured to be 1.25 eV. Furthermore, structure in the interband absorption at 2.41, 3.10, 3.50, and 4.45 eV is observed. The refractive index at zero frequency is estimated to be n(0)=1.94 as compared to the value n(0)=1.90, which we obtained for solid C60 from our previous study.