Alkali cluster films on insulating substrates: comparison between scanning force microscopy and extinction data

Extinction spectra of alkali cluster films on mica substrates are recorded as a function of alkali metal deposition time. They are reproduced quantitatively by theoretical spectra of oblate spheroids, using cluster number density n, average cluster semi-axis 〈a〉 parallel to the mica surface, and mean ellipticity 〈R⊥〉 perpendicular to the surface obtained from scanning force microscopy images. It is found that reliable values of average cluster semi-axes can be obtained from optical spectra only by taking the distribution of perpendicular-plane ellipticities into account.