Temperature threshold for localized surface plasmon resonance in glancing angle deposited ultra-thin silver films

Low thickness Silver (Ag) coatings (thickness ~25 nm) were fabricated by electron beam evaporation technique equipped with glancing angle deposition (GLAD, 86o) arrangement at varrying substrate heating temperatures (viz. 30oC, 75oC, 125oC and 150oC). Although all the GLAD-Ag films prepared up to 125oC temperature were found to be plasmonic in nature, the localized surface plasmon resonance (LSPR) band was more prominent at 125oC and disappeared at 150oC temperature. The dielectric contribution in the overall dispersion of sample structure was maximum for 125oC with dominating metallic contribution observed for 150oC. Detailed investigation of 125oC deposited GLAD-Ag sample revealed sharpening of the LSPR band with reduction in film thickness. The ultra-thin coating (~5 nm) was found to be purely dielectric in nature with the most prominent LSPR band among the others. Overall, the substrate heating temperature of 125oC was found to be the threshold for fabricating plasmonic GLAD-Ag films with the best result observed for the ultra-thin (~5 nm) specimen.