TAPPING-MODE TUNING FORK FORCE SENSING FOR NEAR-FIELD SCANNING OPTICAL MICROSCOPY

A tapping-mode tuning fork force-sensing method for near-field scannin g optical microscope is reported. Use of the tapping-mode tuning fork with mechanically asymmetric excitation generates better stability and sensitivity than in the shear force mode. Comparison of force curves for the two methods demonstrate that the tapping-mode tuning fork meth od provides a simpler and more sensitive method for near-field measure ments. The method is demonstrated by imaging a sample consisting of 50 0 nm standard polystyrene spheres on silica in both air and water. (C) 1998 American Institute of Physics. [S0003-6951)(98)02145-7].