Measurement of the evanescent field using noncontact mode atomic force microscope

Abstract

Using the noncontact mode atomic force microscope (AFM) with frequency modulation detection method, force gradient acting on the AFM tip induced by the evanescent field was measured in a high vacuum. Exponential distance dependence of the force gradient by the evanescent field was successfully measured for the first time. Decay lengths of the force gradient were estimated to be 40±3 nm and 43±3 nm for Ar and He-Ne lasers, respectively, and independent of wavelength within the experimental error. The minimum detectable force was estimated to be about 0.1 pN. There was a tendency for the measured decay length to become shorter at a distance less than z=10 nm in many cases. The force gradient induced by the evanescent field inp-polarization was larger than that ins-polarization.