Selective Reflectivity and High Absorption in Plasmonic Films

A. Siahmakoun, M. Syed, C. Bolinger
Rose-Hulman Institute of Technology, US

Keywords: plasmonics, reflectivity, absorption, alloy nanofilms, metamaterials

Summary:

In this paper we will show, both theoretically and experimentally, that a strong plasmonic absorption and reflection can occur as film thickness is reduced beyond a critical value for metal and alloy layers. Although this appears to be at odds for the conditions under which high reflectivity and absorption losses occur in plasmonic films but experimental results show irrefutably that this effect takes place for certain thickness of the metal/alloy films and for a given wavelength of a probing laser. At this critical thickness (less than 30 nm for most films), however, it seems that the plasmonic film behaves more like a metamaterial structure with selective reflection and strong absorption of the optical energy whose characteristic dimensions can be found with effective medium approximation. The spectroscopic ellipsometric measurements of dielectric function reveals that such a plasmonic film possesses a small positive real part and an order of magnitude greater imaginary part. We have performed reflectivity experiments in the Kretchmann configuration on prisms coated with Ni and Ni-alloy films. The experiment is performed at various wavelengths that include 1320 nm/1550 nm wavelengths that are important for optoelectronic applications.