2 research outputs found
Reaching the Theoretical Resonance Quality Factor Limit in Coaxial Plasmonic Nanoresonators Fabricated by Helium Ion Lithography
Optical antenna structures have revolutionized
the field of nano-optics
by confining light to deep subwavelength dimensions for spectroscopy
and sensing. In this work, we fabricated coaxial optical antennae
with sub-10-nanometer critical dimensions using helium ion lithography
(HIL). Wavelength dependent transmission measurements were used to
determine the wavelength-dependent optical response. The quality factor
of 11 achieved with our HIL fabricated structures matched the theoretically
predicted quality factor for the idealized flawless gold resonators
calculated by finite-difference time-domain (FDTD). For comparison,
coaxial antennae with 30 nm critical dimensions were fabricated using
both HIL and the more common Ga focus ion beam lithography (Ga-FIB).
The quality factor of the Ga-FIB resonators was 60% of the ideal HIL
results for the same design geometry due to limitations in the Ga-FIB
fabrication process
Tunneling Plasmonics in Bilayer Graphene
We report experimental signatures
of plasmonic effects due to electron tunneling between adjacent graphene
layers. At subnanometer separation, such layers can form either a
strongly coupled bilayer graphene with a Bernal stacking or a weakly
coupled double-layer graphene with a random stacking order. Effects
due to interlayer tunneling dominate in the former case but are negligible
in the latter. We found through infrared nanoimaging that bilayer
graphene supports plasmons with a higher degree of confinement compared
to single- and double-layer graphene, a direct consequence of interlayer
tunneling. Moreover, we were able to shut off plasmons in bilayer
graphene through gating within a wide voltage range. Theoretical modeling
indicates that such a plasmon-off region is directly linked to a gapped
insulating state of bilayer graphene, yet another implication of interlayer
tunneling. Our work uncovers essential plasmonic properties in bilayer
graphene and suggests a possibility to achieve novel plasmonic functionalities
in graphene few-layers