Plasmonic characteristics of Ag and ITO/Ag ultrathin films as-grown by sputtering at room temperature and after heating

Abstract

Ag and ITO/Ag ultrathin films have been prepared by magnetron sputtering on unheated glass substrates. The Ag mass thickness was varied from 6 to 30 nm by increasing the deposition time, whereas the ITO film thickness was fixed at 30 nm. The optical, structural and morphological properties of the samples were analysed as-grown at room temperature and after heating at 300 °C in flowing nitrogen. The optical characteristics of the Ag samples have been modelled according to a system which has different contributions from bulk-like features to surface-plasmon characteristics arising from spheroidal particles with reduced carrier mobilities. The as-grown Ag morphological data are consistent with particle clusters that are loosely connected at the lowest deposition times and become wetted in a smooth film only when the deposition time increases. For the uncoated Ag samples, the heating at 300 °C produced surface migrations and reorganizations that resulted in films with a higher crystallite size in preferential Ag (1 1 1) orientation, together with significant changes in the surface roughness and the optical absorption. The ITO coating deposition process induced also some morphological changes, but the optical characteristics of the ITO/Ag stacks remained practically unchanged with respect to the analogous uncoated silver samples. Besides, the ITO coating has avoided that the underlying silver could migrate and agglomerate during the thermal treatment, although it has allowed the Ag (1 1 1) recrystallization.