Ultra-confined plasmonic hotspots inside graphene nanobubbles

Z. Fei, J. J. Foley, W. Gannett, M. K. Liu, S. Dai, G. X. Ni, A. Zettl, M. M. Fogler, G. P. Wiederrecht, S. K. Gray, D. N. Basov

Nano Letters (2016)
We report on a nano-infrared (IR) imaging study of ultra-confined plasmonic hotspots inside graphene nanobubbles formed in graphene/hexagonal boron nitride (hBN) heterostructures. The volume of these plasmonic hotspots is more than one million times smaller than what could be achieved by free-space IR photons and their real-space distributions are controlled by the sizes and shapes of the nanobubbles. Theoretical analysis indicates that the observed plasmonic hotspots are formed due to a significant increase of the local plasmon wavelength in the nanobubble regions. Such an increase is attributed to the high sensitivity of graphene plasmons to its dielectric environment. Our work presents a novel scheme for plasmonic hotspots formation and sheds light on future applications of graphene nanobubbles for plasmon-enhanced IR spectroscopy.