Nanoscale Optoelectronic Characterisation of Hybrid Heterostructures via Scattering-Type Scanning-Near-Field Optical Microscopy

Dimensionally hybrid semiconductor heterostructures and 2D heterostructures have enormous promise for a range of functional technologies. Indeed, heterostructures of planar 2D materials have already found applications in photonics, optoelectronics, straintronics, valleytronics and twistronics; where pushing towards 2D/1D and 2D/0D systems have shown exciting optoelectronic phenomena [1,2]. To understand the effect of this hybridisation, characterisation techniques with high spatial resolution, temporal resolution and depth selectivity are required in order to examine the optoelectronic and chemical properties of individual layers and components of the heterostructure.<br/>In this talk, we present scattering-type scanning near-field optical microscopy (s-SNOM) as a powerful tool for non-destructive optoelectronic characterisation of hybrid heterostructures [3,4]. By coupling radiation to the apex of an atomic force tip, we achieve spatial resolutions way beyond the diffraction limit of light down to 10 nm across wavelengths from the visible to the terahertz range. We perform both imaging and spectroscopy to extract the local material dielectric function on nanometre length scales. By oscillating the tip and changing the tapping amplitude, we can also alter the probing depth to perform nanotomography, enabling us to observe differences in optoelectronic properties in different layers of a material. Here, we present s-SNOM on a range of example heterostructures, including: interlayer charge transfer between 2D TMDC heterostructures [5]; identification of surface layer in InN nanoparticles; nanoscale 3D mapping of dielectric function in topological insulator thin films and nanowires [6].<br/><br/>[1] Pei-Yu Huang <i>et al</i> 2D–1D mixed-dimensional heterostructures: progress, device applications and perspectives, <i>J. Phys.: Condens. Matter</i> 33 493001 (2021)<br/>[2] Basov, D., Averitt, R. & Hsieh, D. Towards properties on demand in quantum materials. <i>Nature Mater</i> 16, 1077–1088 (2017). https://doi.org/10.1038/nmat5017<br/>[3] F. Keilmann and R. Hillenbrand, Near-field microscopy by elastic light scattering from a tip, <i>Philos. Trans. R. Soc. London. Ser. A Math. Phys. Eng. Sci.</i>, vol. 362, no. 1817, pp. 787–805, Apr. 2004, doi: 10.1098/rsta.2003.1347.<br/>[4] Yao, Ziheng, et al. Nanoimaging and nanospectroscopy of polaritons with time resolved s-SNOM. <i>Advanced Optical Materials</i> 8.5 1901042 (2020)<br/>[5] Plankl, M., Faria Junior, P.E., Mooshammer, F. et al. Subcycle contact-free nanoscopy of ultrafast interlayer transport in atomically thin heterostructures. Nat. Photon. 15, 594–600 (2021). https://doi.org/10.1038/s41566-021-00813-y<br/>[6] F. Mooshammer <i>et al.</i>, Nanoscale Near-Field Tomography of Surface States on (Bi 0.5 Sb 0.5 ) 2 Te 3, <i>Nano Lett.</i>, vol. 18, no. 12, pp. 7515–7523, Dec. 2018, doi: 10.1021/acs.nanolett.8b03008.