Localized surface plasmon resonance of Ag nanoparticle thin films deposited by direct-current magnetron sputtering

This study investigates the localized surface plasmon resonance (LSPR) of Ag nanoparticle (NP) thin films deposited by magnetron sputtering on an alkaline-free aluminosilicate-glass substrate at a substrate temperature of 600 degrees C. The equivalent film thickness was controlled to be 5, 10, 20, and 50 nm by adjusting the deposition time. The deposited Ag thin films formed NPs with uniform diameter and spacing for all Ag thicknesses. The NP diameters ranged approximately from 16 to 88 nm, corresponding to the equivalent film thickness. Due to the formation of isolated NPs, all Ag thin films exhibited a singlet LSPR peak in their extinction spectra. The LSPR peak position in the extinction spectra shifted with the refractive index of the environmental solvent media when the Ag NP thin films were immersed in these media. In addition, the insertion of a MgO, Nb2O3, or TiO2 underlayer shifted the LSPR peak position in the extinction spectra according to the refractive index of each underlayer material. A peak shift corresponding to the refractive index of the environmental solvent media was also observed for Ag NP thin films deposited on underlayers. The relatively low sensitivity of the LSPR peak shift to the refractive index of the environmental solvent media suggests that the solvent media only covered the top surface of the Ag NPs distributed on the substrate but did not infiltrate the spaces between them. The results of this study demonstrate the applicability of sputter-deposited Ag NP thin films to solid LSPR devices.