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Nanoscale optical spectroscopy of monolayer WS₂ using photo-induced force Ji, Yu


Photo-induced force microscopy is a scanning nearfield optical microscopy technique that was developed within the last decade and has been used to study polymer structures with near 10 nm spatial resolution. We seek to push the boundaries of this technique by extending the working wavelength range into the visible region and use it to study hard materials known as transition metal dichalcogenides (TMDs). TMDs have strong and controllable excitonic effects that has been the subject of many research studies in the past 10 years. However, there has not been much comparable nearfield measurements done. In this work, we were able to measure local absorption spectra of monolayer, bilayer, and encapsulated WS₂ all in agreement with that from traditional far field spectroscopic techniques. We also demonstrated 40 nm spatial resolution on WS₂ monolayers. Our results show that of photo-induced force microscopy spectroscopy is a promising technique that can be applied to study nanoscale effects in TMDs.

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