  Graphene plasmonic resonators have been broadly studied in the terahertz and
mid-infrared ranges because of their electrical tunability and large
confinement factors which can enable dramatic enhancement of light-matter
coupling. In this work, we demonstrate that the characteristic scaling laws of
graphene plasmons change for smaller (< 40 nm) plasmonic wavelengths, expanding
the operational frequencies of graphene plasmonic resonators into the
near-infrared (NIR) and modifying their optical confinement properties. We
utilize a novel bottom-up block copolymer lithography method that substantially
improves upon top-down methods to create resonators as narrow as 12 nm over
centimeter-scale areas. Measurements of these structures reveal that their
plasmonic resonances are strongly influenced by non-local and quantum effects,
which push their resonant frequency into the NIR (2.2 um), almost double the
frequency of previous experimental works. The confinement factors of these
resonators, meanwhile, reach 137 +/- 25, amongst the largest reported in
literature for an optical cavity. While our findings indicate that the
enhancement of some 'forbidden' transitions are an order of magnitude weaker
than predicted, the combined NIR response and large confinement of these
structures make them an attractive platform to explore ultra-strongly enhanced
spontaneous emission.
