Optical absorption of continuous-network-structure Ag and Ir films: Presence of particlelike and conduction-electron-localized regions

Abstract

Optical absorption of continuous-network-structure (CNS) Ag and Ir films has been measured in the photon-energy range of 0.5--6.5 eV. As absorption due to conduction electrons, optical plasma-resonance absorption (OPRA), reported for Ag island films consisting of Ag particles, and weak Drude-type absorption (DTA) were found for the CNS Ag films, and only the weak DTA appeared in the CNS Ir films. The finding of the OPRA indicates that particlelike regions, where plasma oscillations of conduction electrons occur as in Ag particles, are present in the CNS Ag films. When the particlelike regions are formed, the region, where DTA occurs, is reduced. This reduction results in the weakening of the DTA. Thus the weak DTA supports the presence of the particlelike regions. If particlelike regions are present in the CNS Ir films also, conduction-electron localization as in Ir particles should occur in the particlelike regions. In this case, only the DTA, weak as in the CNS Ag films, must appear. This agrees with the above appearance. Thus conduction-electron-localized regions are present in the CNS Ir films.