Modulation of surface plasmons coupling for enhancement of optical transmittance of silver-coated alkaline-earth metal films

Abstract

We enhanced the optical transmittance of silver-coated alkaline-earth metal films by modulation of surface plasmons (SPs) coupling. The result indicates that the optical transmittance of a metal film is controlled by the SPs coupling at the interface of the metal with a dielectric substrate. Because the SPs originate from the coupling between the free charge at the surface of the metal and the incident light, there exists the SPs coupling in an Ag layer with the dielectric substrate. These SPs lead to longitudinal surface charge density fluctuations that propagate along the substrate/Ag interface, resulting in the decreased transmittance property (47.9% in the visible region) of the 10 nm thick Ag layer on the dielectric substrate. Because both alkaline-earth metal and Ag have negative dielectric constants, the incident light cannot induce the SPs in the alkaline-earth metal/Ag double layer. Thus, inserting a thin alkaline-earth metal layer between Ag and the dielectric substrate could modulate the SPs coupling at the Ag/substrate interface and, hence, the optical transmittance of alkaline-earth metal/Ag films. Both alkaline-earth metal and Ag could be formed by thermal evaporation and in situ synchrotron radiation photoelectron spectroscopy results showed that the thermally evaporated alkaline-earth metal (Ca) film is composed of metallic (Ca) and metal-oxide (CaO) components. It is found that the SPs modulation optimized alkaline-earth metal/Ag (10 nm/10 nm) film has obtained a higher optical transmittance (69.8%) in the visible region than that of an Ag layer. This led to the enhanced maximum luminance of organic light emitting diodes with the alkaline-earth metal/Ag electrode from 24 300 cd m−2 to 32 700 cd m−2.