Response of Thin Metal Nanodisks to Near- and Far-Field Excitation

Metallic nanostructures support surface plasmons, collective oscillations of their conduction electrons, making them useful for a wide range of applications, from ultrasensitive optical sensing to efficient solar energy harvesting. Surface plasmons also strongly confine and enhance the electromagnetic fields in their vicinity. In recent years, this has motivated significant interest in the plasmons supported by thin metallic nanostructures, for which the degree of confinement and enhancement can be much higher than conventional ones. Here, we investigate how the response of metallic nanodisks to excitation by near- and far-field sources varies with their thickness. In the latter case, which corresponds to a scenario in which the separation between the nanostructure and excitation source is much larger than the wavelength, we find that the response of the nanodisks increases with their thickness. On the other hand, in the opposite limit, the response of the nanodisks decreases with the thickness, a result that we attribute to a near-field source coupling more efficiently with thinner nanodisks. The results of our work provide fundamental insight into the plasmonic properties of thin metallic nanostructures and thus pave the way toward the development of novel applications.