Masayuki ABE¹ , Takayuki UCHIHASHI¹ , Masahiro OHTA² , Hitoshi UEYAMA² , Yasuhiro SUGAWARA² and Seizo MORITA²

¹Department of Physics, Faculty of Science, Hiroshima University, Kagamiyama1-3-1, 739 Higashihiroshima, Japan,
²Department of Electronic Engineering, Faculty of Engineering, Osaka University, Yamadaoka 2-1, 565 Suita, Japan

(Received August 17, 1996; Accepted November 1, 1996)

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 in p-polarization was larger than that ins-polarization.

Key words : evanescent field - force gradient - noncontact mode atomic force microscope - frequency modulation detection method

*This paper was originally presented at the first Asia-Pacific Workshop on Near Field Optics, which was held on August 17 and 18, 1996 at Seoul Education and Culture Center, Seoul, Korea, organized by Condensed Matter Research Institute, Seoul National University.