OPTICAL-PROPERTIES AND THE OPTICAL JOINT DENSITY-OF-STATES OF THE MISFIT-LAYER COMPOUNDS (MS)1+XTS2

The complex dielectric constant (epsilon), the absorption coefficient (A), the reflectivity (R), and the optical joint density of states (JDS) of the misfit-layer compounds (MS)1+xTS2 (M = Sn, Pb, Bi, Ce, Sm; T = Ti, Nb) have been derived from reflection electron-energy-loss spectra via Kramers-Kronig analysis. Loss structures arising from interband transitions and a partial plasma resonance have been studied systematically. It is considered that most of the main structures result predominantly from a TS2 layer. A main contribution from an MS layer causes a loosely varied background as a whole, leading to a decrease in depth of a valley at the optical gap of TS2. It also gives a high optical JDS at 3-4 eV for the Sn and Pb compounds and at 6-7 eV for the rare-earth compounds. A reasonable interpretation of most experimental results obtained has been made within the rigid-band model in terms of the electronic structure of each layer, although a small deviation from the model must be considered.