Shear force distance control in near-field optical microscopy: experimental evidence of the frictional probe- sample interaction

摘要

The properties of the probe-surface contact for anear-field optical microscope driven in the shear force modehave been studied applying lateral amplitudes of the probingfiber tip larger than 15 nm. Electric current measurementsbetween a conductive tip and a conductive sample reveal apulsed current behavior at the very beginning of the approachcurve. In the upper part of the approach curve it turns to thequasiconstant current. From this observation a conclusion isdrawn about the presence of permanent mechanical contactbetween the probe and the surface in the shear force mode. Ashift of the approach curve along the z-axis as a function ofdither amplitude was discovered. These results are incontradiction to the established conception of possible physicalmechanisms of shear force interaction. To settle this issue thefriction model is proposed according to which the damping ofthe probe vibrations is caused by the friction between the tip and the surface.