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This technique provides information about the complex optical properties of the nanoscale region of the sample under a metallized tip. Specifically, both the optical amplitude and phase of the scattered light can be measured.
With appropriate models, these measurements can estimate the complex optical constants (n, k) of the material. Additionally, the optical phase versus wavelength provides a good approximation to a conventional IR absorption spectrum usually grazing Incidence.
The s-SNOM technique works on a variety of materials, but the best signal to noise tends to be on harder materials with high reflectivity, high dielectric constants, and/or strong optical resonances
Ultrafast-broadband scattering SNOM spectroscopy probing molecular vibrational information. Laser interferogram of Polytetrafluoroethylene (PTFE) shows coherent molecular vibration in the form of free-induction decay in time domain (top). The highlighted feature in sample interferogram is due to the beating of symmetric and antisymmetric mode of C-F modes in the resulting the frequency domain (bottom left). Monolayer sensitivity of nano-FTIR is demonstrated on a monolayer pNTP (bottom right). Data courtesy of Prof. Markus Raschke, University of Colorado, Boulder, US