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.