Molecular vibrational imaging at nanoscale.

The demand to visualize the spatial distribution of chemical species based on vibrational spectra is rapidly increasing. Driven by such a need, various Raman and infrared spectro-microscopies with a nanometric spatial resolution have been developed over the last two decades. Despite rapid progress, a large gap still exists between the general needs and what these techniques can achieve. This Perspective highlights the key challenges and recent breakthroughs of the two vibrational nano-imaging techniques, scattering-type scanning near-field optical microscopy and tip-enhanced Raman scattering.