Infrared fingerprints of natural 2D talc and plasmon-phonon coupling in graphene-talc heterostructures

Ingrid David Barcelos, Alisson Ronieri Cadore, Ananias Borges Alencar, Francisco Carlos Barbosa Maia, Edrian Mania, Rafael Furlan de Oliveira, Carlos César Bof Bufon, Angelo Malachias, Raul O. Freitas, Roberto L. Moreira, Helio Chacham

Index: 10.1021/acsphotonics.7b01017

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Abstract

Two-dimensional (2D) materials occupy noteworthy place in nanophotonics providing for subwavelength light confinement and optical phenomena dissimilar to those of their bulk counterparts. In the mid-infrared, graphene-based heterostructures and van der Waals crystals of hexagonal boron nitride (hBN) overwhelmingly concentrate the attention by exhibiting real-space nano-optics from plasmons, phonon-polaritons and hybrid plasmon phonon-polaritons quasiparticles. Here we present the mid-infrared nanophotonics of talc, a natural atomically flat layered material, and graphene-talc (G-talc) heterostructures using broadband synchrotron infrared nano-spectroscopy. We achieve wavelength tuning of the talc resonances, assigned to in- and out-of-plane vibrations by changing the thickness of the crystals, which serves as its infrared fingerprints. Moreover, we encounter coupling of the graphene plasmons polaritons with surface optical phonons of talc. As in the case of the G-hBN heterostructure, this coupling configures hybrid surface plasmon phonon-polariton modes causing 30 % increase in intensity for the out-of-plane mode and blue-shift to the in-plane mode. Our results promote talc and G-talc heterostructures as appealing materials for nanophotonics, like hBN and G-hBN, with potential applications for controllably manipulating infrared electromagnetic radiation at the subdiffraction scale.