s-SNOM (scattering-type Scanning Near-field Optical Microscopy) delivers material-characteristic maps of chemical and optical properties of sample surface at the spatial resolution of an atomic force microscope (AFM). Tuning the illumination wavelength, i.e. „color“ of the light source used for measurements provides spectroscopic information at the nanoscale.
Basic probing principle:
- focus laser light onto a sharp AFM tip;
- illuminated tip creates a strong near-field nano-focus at its apex;
- nano-focus probes optical properties of the sample below the tip, modifying the tip-scattered light;
- all-optical interferometric detection recovers both amplitude and phase of the tip-scattered light, delivering complete information about the sample’s complex optical properties (e.g. absorption and reflectivity).
Challenge: Small size of the nano-focus demands for a state-of-the-art detection to extract weak near-field signal from the dominant background.
neaspec developed and patented all detection technologies that provide guaranteed 100% background suppression for reliable and reproducible near-field imaging and spectroscopy across THz, mid-IR, near-IR and Visible spectral ranges.
s-SNOM is based in on an asymmetric interferometer where the AFM tip and the sample are located in one of the interferometer arms. The light from the tip-sample arm is recombined with the reference beam at the detector. Patented interferometric detection based on varying the reference mirror position, thus reference phase, allows for simultaneous recording of phase and amplitude of the tip-scattered light, which relate to the local reflectivity and absorption. Modulating the reference phase also enables complete suppression of scattering background. This way, s-SNOM returns pure optical/chemical near-field maps free of mechanical artifacts – all simultaneously with AFM topography and phase.
List of s-SNOM detection technologies invented and patented by neaspec – all providing 100% background suppression:
- PsHet (Pseudo-Heterodyne): golden standard for nanoscale imaging.
- P-Spec: PsHet-quality s-SNOM point spectroscopy by laser sweeping.
- HSH (High-Speed Holography): fastest imaging method for screening of large sample areas with the best S/N quality of all known s-SNOM imaging methods.
- nano-FTIR: the only method for nanoscale spectroscopy and hyperspectral imaging with broadband illumination sources.