Characterization of reflection scanning near-field optical microscopy and scanning tunnelling optical microscopy photon scanning tunnelling microscopy working in preliminary approach constant height scanning mode

The resolution in near-field images is currently determined by the visual inspection of recorded images. One of the major questions in near-field optical microscopy is 'what resolution can be reached, the tip-to-sample distance being known?' This knowledge is critical when choosing the scanning step and the distance between the tip and the sample, in a preliminary scan. This preliminary scan is often the only way to detect the interesting parts of the sample, with limited risk of tip crash and topographical artefacts. The method proposed here needs two scans of the same area, of the same sample, in constant height mode, recorded at two tip-to-sample distances. The pseudo-transfer function is the ratio of the Fourier transform of these two data maps. This function enables the evaluation of the limit of resolution. Theoretical considerations are introduced to assess the method.