Evolution of the optical functions of aluminum films during nucleation and growth determined by real-time spectroscopic ellipsometry

We report the first measurements of the optical functions of polycrystalline metal films throughout nucleation and growth. The dielectric function of aluminum, evaporated onto ${\mathrm{SiO}}_2$, was determined versus thickness d by real-time multichannel ellipsometry (1.3≤hν≤4.1 eV). We find that the electron relaxation time for the (200) parallel-band transition is independent of particle size during nucleation (d<50 Å) and increases abruptly only after coalescence. This behavior is not consistent with a classical size effect and suggests that the atomic structure of the particles dominates their optical properties.