Contrast Reversal on Surface Plasmon Resonance Reflectivity in Nickel and Nickel Alloy Films

We have performed surface plasmon resonance (SPR) experiments in the Kretchmann configuration on prisms coated with metal and alloy films. The experiment is performed at various wavelengths that include 1320 nm and 1550 nm wavelengths that are important for optoelectronic applications. The metal films of 20nm/50nm thickness are grown by magnetron sputtering and are binary alloy films of Nickel and Chromium (Nichrome). The aim of this study is two-fold. Our results would show SPR behavior as a sensitive function of film composition and film thickness. Our results also show two interesting thickness regimes where the reflectance is dominated by different processes that take place at the interface between the metal and the dielectric (fused silica prism in our study). Our measurements reveal a contrast reversal in plasmonic signal as we change the alloy thickness from 50 nm to 20 nm for the shorter wavelength.