Sample preparation for NSOM/SNOM requires flat, clean, and firmly mounted samples on suitable substrates to enable close probe access within a few nanometers. No special chemical treatment is generally needed; physical stability and surface cleanliness are most critical for high-resolution imaging.
Vobornik, D., & Vobornik, S. (2008). Scanning near-field optical microscopy. Bosnian journal of basic medical sciences, 8(1), 63.