Optical reflectivity of ultrathin Pb layers and the quantum size effect

We have studied in situ the reflectance difference (RD) during deposition of ultrathin Pb epitaxial film onto Si(111)-(6x6) substrates Au held at 100 K in UHV conditions. S- and p-polarized radiation with energy within range from 0,5 eV to 3.0 eV was used to excite electron transitions in the Pb samples showing the quantum size effects (QSE). The optical reflection data were analysed using classical QSE theories. Observed thickness-dependent reflectivity variations were corrected with previously measured electrical resistivity oscillations. Scattering time τ of electrons involved in the optical transitions was determined and compared with the corresponding results obtained from the electrical resistivity measurements. Evidences of optical diamagnetic and paramagnetic response of electrons in the metallic quantum well are presented and discussed. (author)