[~rm ] t~i i i | I I M | I M 11 I I 11 ; 1 I I I 11 I I I | 1 m ' | ' M 1 1 1 ' | 1 1 M T 0 1 2 3 4 5 6

Fig. 13.13. Optical density of solid C^ on a Suprasil substrate derived from ellipsometry measurements (+) together with the frequency dependent optical density measured directly for Qo on Suprasil by normal incidence transmission spectroscopy (•). For comparison, the solution spectrum for Cm dissolved in decalin (dotted curve) is shown below the spectra for the films [13.73]. The inset is a plot of — lm(l/e) vs. E comparing the peaks in the optical data with the peaks in the high-resolution electron energy loss spectrum (HREELS).

ble to identify the origin of the interband transitions in C60 [13.96-99]. In these experiments the stoichiometry was monitored by simultaneous electrical conductivity measurements [13.100] and the interband transitions were identified by noting the transitions that were induced by doping and those that were quenched by doping [13.96-99]. The resulting identifications are given in Table 13.4.

Two theoretical approaches have been applied to calculate the contribution to the optical dielectric function for solid C60. The first approach is based on the electronic band structure of Cm calculated self-consistently using an orthogonalized linear combination of atomic orbitals in the local density approximation (LDA) [13.104], The second approach considers the solid to be composed of weakly coupled molecules with an intermolecular

Energies (eV) of the electronic transitions in thin films of pristine C60 [13.99],

Identification Transition energy (eV)

Identification Transition energy (eV)

Energies (eV) of the electronic transitions in thin films of pristine C60 [13.99],

hu hg

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