Study of shear force as a distance regulation mechanism for scanning near-field optical microscopy

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Abstract
Results of the investigation into the suitability of the shear-force distance regulation mechanism for scanning near-field optical microscopy (SNOM) are presented. It is shown that there is a range of relative sizes of surface features to tip size that gives rise to malfunctions of the shear-force distance regulation mechanism. If the size of the tip is comparable to the size of any depressions on the sample, the corresponding shear-force image may show contrast reversal. It is also shown that the resolution obtained when imaging a surface with the shear-force scanning microscope may differ for the two perpendicular lateral directions. The resolution along the oscillation axis is usually lower than the one perpendicular to it. This has implications for SNOM images. Therefore, the interpretation of shear force, and hence SNOM images, may become complex when imaging any sample with significant surface roughness.