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 i nspection of recorded images. One of the major questions in near-field opti cal microscopy is 'what resolution can be reached, the tip-to-sample distan ce being known?' This knowledge is critical when choosing the scanning step and the distance between the tip and the sample, in a preliminary scan. Th is preliminary scan is often the only way to detect the interesting parts o f the sample, with limited risk of tip crash and topographical artefacts. T he method proposed here needs two scans of the same area, of the same sampl e, in constant height mode, recorded at two tip-to-sample distances. The ps eudo-transfer function is the ratio of the Fourier transform of these two d ata maps. This function enables the evaluation of the limit of resolution. Theoretical considerations are introduced to assess the method.