  Plasmonic structures are often fabricated by lithographic patterning of a
thin metallic film. Properties of the thin film are intimately related to the
quality of the resulting structures. Here we compare two kinds of thin gold
films on silicon nitride membrane: a conventional polycrystalline thin film
deposited by magnetron sputtering, and monocrystalline gold microplates which
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. Structural and optical properties of the nanorods
were characterized by analytical transmission electron microscopy. The
dimensions of the nanorods in both substrates reproduced well the designed size
of $240 \times 80\ \mathrm{nm^2}$ 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,
monocrystal nanorods featured inclined boundaries while the boundaries of the
polycrystal nanorods were upright. Q factors and peak loss probabilities of the
modes in both structures are within the experimental uncertainty identical. We
conclude that the optical response of the plasmonic antennas is not
deteriorated when the polycrystalline metal is used instead of the
monocrystalline metal.
