Furthering nano-optical techniques by integrating tapping-mode AFM and TCSPC

Scanning tip-enhanced optical spectro-microscopy techniques are powerful tools for the investigation of optoelectronic properties of materials surfaces. However, the improved resolution comes at the significant expense of optical signal, requiring the use of higher excitation powers which can be detrimental to samples and nano-optical probes.^1-2 This current experimental paradigm is heavily dependent on of fabrication of extraordinary nano-optical probes that can simultaneously tolerate high excitation densities and greatly enhance the signal of interest for a measurement’s duration. Methods to increase signal/noise in a system without high photon fluences on the sample/tip are thus needed for imaging weak optical interactions, including Raman and nonlinear optical (e.g. SHG) scattering signals. In this study, we present efforts to improve our nano-optical studies by incorporating lock-in detection of tip-enhanced signals using tapping-mode atomic force microscopy scanning. We correlate fast single photon sensitive avalanche photodiodes and time-correlated single photon counting electronics, following the system design first demonstrated by Gerton et al.³ We show successful imaging of the nano-PL from a nanobubble in monolayer WSe₂ on Au, achieving resolutions ~ 10 nm. Our results show the viability of lock-in detection in tip-enhanced experiments and offer a potential path for high-sensitivity nano-optical measurements utilizing photon correlations.

References

[1] Neacsu, C.C., van Aken, B.B., Fiebig, and Raschke, M.B. 2005. Phys. Rev. B 79, 100107.

[2] Yao, K., Zhang, S., Yanev, E., McCreary, K., Chuang, H., Rosenberger, M.R., Darlington, T., Krayev, A., Jonker, B.T., Hone, J.C., Basov, D.N., and Schuck, P.J. 2022. arXiv:2111.06955.

[3] Gerton, J.M., Wade, L.A., Lessard, G.A., Ma, Z., and Quake, S.R. 2004. Phys. Rev. Lett. 93, 180801.

[4] Darlington, T.P. et. al. 2020. Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2 at room temperature, Nature Nanotechnology, 15(10), 854-860.