Experimental study of probe–surface interaction in near-field optical microscopy

The physical mechanism of shear-force interaction between a fiber tip and a sample in near-field optical microscopy has been studied using tunneling current measurements between the tip and a sample. Optical and non-optical (tuning fork) shear-force distance controls have been used. In both cases a tunneling current between the tip and the sample has been detected at the very beginning of shear-force approach curve when the amplitude of tip vibration was just slightly smaller than its initial value. These results indicate that fiber-tips generally mechanically touch samples under shear-force distance feed-back control.