MEASUREMENT OF THE EVANESCENT FIELD USING NONCONTACT MODE ATOMIC-FORCE MICROSCOPE

Using the noncontact mode atomic force microscope (AFM) with frequency modulation detection method, force gradient acting on the AFM tip ind uced ty the evanescent field was measured in a high vacuum. Exponentia l distance dependence of the force gradient by the evanescent field wa s successfully measured fur the first time. Decay lengths of the force gradient were estimated to be 40+/-3 nm and 43+/-3 nm for Ar and He-N e lasers, respectively, and independent of wavelength within the exper imental error. The minimum detectable force was estimated to be about 0.1 pN. There was a tendency for the measured decay length to become s horter at a distance less than z = 10 nm in many cases. The force grad ient induced by the evanescent field in p. polarization was larger tha n that in s-polarization.