Combining tip-enhanced Raman, photoluminescence, and nonlinear spectroscopy with active atomic force tip interaction, I will discuss novel approaches for the study of photo-physical and photo-chemical processes in molecules and nano-solids [1,2,3]. In recent examples, we nano-image the exciton behavior and its correlation with defects, grain boundaries, and local strain in different transition metal di-chalcogenides (TMDs). Based on exciton-plasmon coupling we achieve a 105-fold enhancement of the photo-luminescence yield .
Further, we are able to achieve TEPL spectroscopy of the otherwise forbidden radiative emission from excitonic dark states with the optical antenna tip coupling to its out-of-plane transition dipole moment . We achieve room temperature contrast, not possible in conventional approaches, due to the ultrafast radiative dark exciton to the tip-antenna mode with few-nm tip-sample gap localized mode volume induced Purcell factor of > 2x103. With the atomic-force microscope controlled antenna tip we demonstrate correlative nano- opto-mechanical swit- ching and programmable modulation of the dark exciton emission. This hybrid tip- enhanced nano- spectroscopy and -imaging method allows to probe and control neutral-, multi-, localized-, and dark-excitons and their correlation with lattice and electronic structural heterogeneities in 2D materials and molecular systems.
 Park, K. D., Muller, E. A., Kravtsov, V., Sass, P. M., Dreyer, J., Atkin, J. M., and Raschke, M. B. Variable-Temperature Tip-Enhanced Raman Spectroscopy of Single-Molecule Fluctuations and Dynamics. Nano Lett.16, 479-487 (2016),
 Kravtsov, V., Ulbricht, R., Atkin, J. M., and Raschke, M. B. Plasmonic nanofocused four-wave mixing for femtosecond near-field imaging. Nat. Nanotechnol. 11, 459-464 (2016).
 Kravtsov, V., Berweger, S., Atkin, J. M., and Raschke, M. B. Control of Plasmon Emission and Dynamics at the Transition from Classical to Quantum Coupling. Nano Lett. 14, 5270-5275 (2014).
 Park, K.-D. et al., “Hybrid tip-enhanced nanospectroscopy and nanoimaging of monolayer WSe2 with local strain control,” Nano Lett., Vol. 16, No. 4, 2621–2627, 2016.
 Park, K. D., T. Jiang, G. Clark, X. Xu, and Raschke, M. B. “Radiative control of dark excitons at room temperature by nano-optical antenna-tip Purcell effect”, Nature Nanotechnol. (in press), 2017.