Revealing the nanoscale infrared properties of graphene-hBN bubbles

Session

Stream 4 (AFM): New Frontiers in Quantum Matter Visualization

Authors

Mr Tom Vincent (1, 2), Dr Matthew Hamer (3), Prof Irina Grigorieva (3), Prof Vladimir Antonov (2, 4), Prof Alexander Tzalenchuk (1, 2), Dr Olga Kazakova (1)

Affiliations

1. National Physical Laboratory
2. Royal Holloway, University of London
3. University of Manchester
4. Skolkovo Institute of Science and Technology

Keywords

SNOM, Raman, graphene, hexagonal boron nitride, strain, mid-infrared, plasmonics

Abstract text

We present a scanning near-field optical microscopy (SNOM) study, which reveals subwavelength infrared (IR) domains within bubbles in a graphene-based heterostructure[1].

Long wavelengths in the mid-IR present a barrier to miniaturisation of optoelectronic devices. But graphene’s plasmonic properties allow extreme subwavelength light concentration, making it ideally suited for a range of electrically tunable, diffraction-beating applications[2]. On top of that, its high stretchability means its optoelectronic properties are particularly susceptible to modification through strain[3]. Interlayer bubbles in 2D heterostructures provide an interesting platform to study strain effects[4]. These could be significant for subwavelength optical devices, which are comparable in size to typical 2D material bubbles.

In this study, we used SNOM to map the nanoscale IR response from a network of bubbles in hexagonal boron nitride (hBN)-encapsulated graphene. We compared these maps with atomic force microscope morphology measurements, and maps of graphene strain and doping, acquired using confocal Raman microscopy and vector decomposition analysis[5].

We found that within individual bubbles there are sharply defined domains, whose nanoscale response to light of ~10 μm wavelength is characterised by a significant phase shift. These domains are bordered by one-dimensional ridges, visible in the topography, which are known to result from uniaxial strain. Lower-resolution strain mapping revealed a complicated distribution, with signatures of both bi- and uniaxial strain.

We conclude that the domains we observed are induced by the strain configuration in our bubbles, which demonstrates that strain can be used as an effective mechanism to control graphene’s nanoscale IR properties. This could lead to new pathways to realise graphene-based mid-IR devices.

References

[1]    T. Vincent, M. Hamer, I. Grigorieva, V. Antonov, A. Tzalenchuk, and O. Kazakova, “Strongly Absorbing Nanoscale Infrared Domains within Strained Bubbles at hBN–Graphene Interfaces,” ACS Appl. Mater. Interfaces, vol. 12, no. 51, pp. 57638–57648, Dec. 2020, doi: 10.1021/acsami.0c19334.

[2]    F. H. L. Koppens, D. E. Chang, and F. J. García de Abajo, “Graphene Plasmonics: A Platform for Strong Light–Matter Interactions,” Nano Lett., vol. 11, no. 8, pp. 3370–3377, Aug. 2011, doi: 10.1021/nl201771h.

[3]    M. A. Bissett, M. Tsuji, and H. Ago, “Strain engineering the properties of graphene and other two-dimensional crystals,” Phys. Chem. Chem. Phys., vol. 16, no. 23, pp. 11124–11138, 2014, doi: 10.1039/c3cp55443k.

[4]    A. V. Tyurnina et al., “Strained Bubbles in van der Waals Heterostructures as Local Emitters of Photoluminescence with Adjustable Wavelength,” ACS Photonics, vol. 6, no. 2, pp. 516–524, Feb. 2019, doi: 10.1021/acsphotonics.8b01497.

[5]    T. Vincent et al., “Probing the nanoscale origin of strain and doping in graphene-hBN heterostructures,” 2D Mater., vol. 6, no. 1, p. 015022, Dec. 2018, doi: 10.1088/2053-1583/aaf1dc.