Correlated SPM–TERS Imaging: Revealing Unexpected Nanoscale Heterogeneities in 2D Semiconductors.

Here I report on the application of scanning probe microscopy (SPM) cross-correlated with tip enhanced Raman scattering (TERS) and photoluminescence (TEPL) imaging for detection of unexpected heterogeneities in TMDs.
I’ll demonstrate that few-layer flakes of WSe₂ exfoliated to gold or silver may possess doping heterogeneity with domains within 30-300nm range. These domains identified by Kelvin probe imaging showed different TERS response and generated photocurrent of opposite polarity.
I’ll further discuss how scanning capacitance microscopy can identify the grain boundaries (GB) in CVD-grown MoSe2 crystals, while TERS characterization of such crystals transferred to gold reveals possible etching of MoSe₂ along GB during the transfer, an effect beneficial for photocatalytic activity.
3-rd example of the use of cross-correlated SPM and TERS/TEPL imaging of 2D semiconductors is a discovery of the nature of strong PL of WS₂ and WSe₂ transferred to gold via heat-assisted exfoliation. Through TERS/TEPL it was identified that PL is coming from nanoscale bubbles formed in TMD layers. Exciton funneling towards the bubbles was also discovered, which resulted in strong enhancement of Raman/PL response from the bubbles, and in significant suppression of TERS/TEPL signal in adjacent area.