Optical Extinction-Based 3D Nano-Imaging of WS2 on Gold.

Broadband nanoextinction images recorded in tip-enhanced optical spectroscopy geometry track the 3D topography of a single layer of WS₂ on Au substrate. The described nano-optical method is complementary to conventional atomic force microscopy and offers additional information about the buried material-metal interface that is not accessible using conventional topographic imaging. Beyond 3D optical imaging, we observe large variations in the junction plasmon resonance on the nanoscale. The latter is important to understand and account for in tip-enhanced Raman and photoluminescence studies that target low-dimensional materials specifically. Our observations and (coherent) optical scattering-based method are also relevant to emerging efforts aimed at exploring strong coupling and Fano interferences in hybrid plasmonic-low dimensional quantum material systems.