Info

Photon Energy (eV)

Fig. 13.26. Comparison of the room temperature experimental e2(a>) data (left scale) for MjQ, (M = K, Rb, Cs) films on quartz substrates [13.77] with the calculations of Xu et al. [13.105] (thin solid noisy line at the bottom of the figure) (right scale).

was obtained as follows using standard expressions for the optical reflectivity and transmission 2ft and 3~, involving the dielectric function of both the Suprasil substrate and the sample. The M6C60 dielectric function e(w) was expressed in terms of contributions from a sum of Lorentz oscillators, where w0;, wPj, and Tj, respectively, denote the frequency, strength, and damping of the y'th oscillator, and ecore is the core dielectric constant used to approximate interband absorption well beyond the energy range of the experimental data. Values for these Lorentz oscillator parameters were adjusted to obtain the best fit to the and ST spectra simultaneously. From this analysis the experimental curves for e2(o>) shown in Fig. 13.26 were obtained. The parameter values found from these fits are summarized in Table 13.6. The left-hand vertical scale for e2(w) in Fig. 13.26 refers to the three closely spaced experimental curves (heavy solid curve for K^C«,, dotted curve for Rb6C50, and dashed curve for Cs6C60) [13.77],

As can be seen in Fig. 13.26, the optical e2(&>) data for the M6C60 ful-lerides are found to be insensitive to the particular dopant (M = K, Rb, Cs), similar to observations regarding the intramolecular vibrational mode frequencies in M6C60 compounds described in §11.6. Thus, it is concluded that no significant hybridization of the alkali metal and C60 states occurs in n e(w) = ei(fc>) + ie2(w) = ecore + £

Table 13.6

Interband optical parameters of Eq. (13.14) (in eV) for MjC^ (M = K, Rb, Cs) where K, = tlu, V2 = hu, C, = t]g, and C2 = tlu or hg and where ecore = 3.0 [13.77].

Table 13.6

Interband optical parameters of Eq. (13.14) (in eV) for MjC^ (M = K, Rb, Cs) where K, = tlu, V2 = hu, C, = t]g, and C2 = tlu or hg and where ecore = 3.0 [13.77].

Was this article helpful?

0 0

Post a comment