Localized plasmon excitation in metal nanoclusters as a tool to study thickness-dependent optical properties of copper phthalocyanine ultrathin films

Thin film sandwich samples have been prepared of copper phthalocyanine ultrathin solid films with incorporated metal (silver, indium) nanoclusters, surrounded by an amorphous silicon environment. The samples were investigated by transmission electron microscopy in both lateral and cross-sectional geometries. In view of the optical properties, we observed a gradual blue wavelength shift of the localized metal cluster plasmon excitation for about 300 nm accompanying an equivalent copper phthalocyanine thickness increase from `zero' to a threshold thickness of about 4 nm. We attribute this behaviour to the formation of bulk-like optical properties of the copper phthalocyanine film, which is completed at the observed equivalent threshold thickness.