AFM and SNOM characterization of carboxylic acid terminated silicon and silicon nitride surfaces

Silicon and silicon nitride surfaces have been successfully terminated with carboxylic acid monolayers and investigated by atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). On clean Si surface, AFM showed topographical variations of 0.3–0.4 nm while for the clean Si3N4 surface the corrugation was around 3–4 nm. After material deposition, the corrugation increased in both samples with a value in topography of 1–2 nm for Si and 5–6 nm for Si3N4. The space distribution of specific chemical species was obtained by taking SNOM reflectivity at several infrared wavelengths corresponding to stretch absorption bands of the material. The SNOM images showed a constant contribution in the local reflectance, suggesting that the two surfaces were uniformly covered.