Structural and optical properties of monocrystalline and polycrystalline gold plasmonic nanorods

The quality of lithographically prepared structures is intimately related to the properties of the metal film from which they are fabricated. Here we compare two kinds of thin gold films on a silicon nitride membrane: a conventional polycrystalline thin film deposited by magnetron sputtering and monocrystalline gold microplates that were chemically synthesised directly on the membrane's surface for the first time. Both pristine metals were used to fabricate plasmonic nanorods using focused ion beam lithography. The structural and optical properties of the nanorods were characterized by analytical transmission electron microscopy including electron energy loss spectroscopy. The dimensions of the nanorods in both substrates reproduced well the designed size of 240×80 nm² with the deviations up to 20 nm in both length and width. The shape reproducibility was considerably improved among monocrystalline nanorods fabricated from the same microplate. Interestingly, monocrystalline nanorods featured inclined boundaries while the boundaries of the polycrystalline nanorods were upright. Q factors and peak loss probabilities of the modes in both structures are within the experimental uncertainty identical. We demonstrate that the optical response of the plasmonic nanorods is not deteriorated when the polycrystalline metal is used instead of the monocrystalline metal.