Natural electron oscillations in granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals

Granular aluminum films deposited on rough surfaces of NaCl and KCl single crystals form a two-layer coating. In the lower layer, a low-frequency band of plasma resonance is excited due to the joint action of a light-wave field and a field induced by granules-dipoles. In a small amount of granules of the upper layer isolated from each other, a high-frequency band with a frequency ω0 of natural electron oscillations in the granules is excited. Using the measured frequencies ω0 and the known dielectric constants of NaCl and KCl, a plasma frequency of aluminum is calculated that agrees well with the known plasma frequency of solid samples.