Chiral plasmonic nanohelices

Abstract

Chirality of three-dimensional structures, i.e. structures that cannot be superimposed on their mirror image, is a very common geometric property in nature. Chirality has generated a lot of excitement in recent years, as man-made chiral metamaterials have, for example, greatly improved biosensors [1]. Fabrication of such complex three-dimensional nanostructures is a challenging process, particularly for visible light applications, where the corresponding structure sizes are on the nanoscale. Here, we show how electron beam induced deposition can be used to fabricate periodic arrays of core-shell (fused silica - gold) nanohelices. We detail the fabrication process used to create these nanoscopic, chiral plas- monic structures, focusing on the procedure that allows us to create arrays of identical helices. Transmission measurements on the chiral plasmonic nanohelices are used to differentiate between the way in which right- and left-circularly polarized light interact with these structures, an effect called optical activity. We measure the optical activity of arrays of plasmonic nanohelices and determine how the optical activity is influenced by different helix heights. Experimental results are compared with calculations for better understanding.