Evolution Of Plasmonic Nanostructures Under Ultra-Low-Energy Ion Bombardment

Metal nanostructures supported on a dielectric substrate possess unique plasmonic properties that are highly dependent on their morphologies. We show that such nanostructures can be modified upon exposure to an ultra-low-energy ion-beam bombardment (< 100 eV) near the sputtering threshold of the metal. This plasma treatment can be easily implemented in a vacuum deposition chamber and allows the achievement of morphologies, and therefore optical properties, that are difficult to achieve otherwise by physical vapor deposition. We present the effects obtained (i) on self-organized Ag nanoparticles with unidirectional orientation and bimodal distribution, and (ii) on Ag layers in the form of percolated, quasi-continuous or island thin films. Our results show that the plasmonic dichmism of self-organized assemblies can be tuned thanks to the preferential sputtering of the smaller particles associated with gradual erosion of the larger ones. Ion-induced modifications of percolated or quasi-continuous films lead to the formation of isolated tiny particles with areal densities smaller than 500 mu m(-2). In both cases, the duration of the ion bombardment makes it possible to finely control the desired structural and plasmonic modifications.