AVS 45th International Symposium
    Nanometer-scale Science and Technology Division Thursday Sessions
       Session NS-ThP

Paper NS-ThP11
Force Measurement of Optical Evanescent Field using Kelvin-Null Method

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Nanometer-Scale Science and Technology Division Poster Session
Presenter: K. Sawada, Osaka University, Japan
Authors: K. Sawada, Osaka University, Japan
M. Abe, Osaka University, Japan
Y. Sugawara, Osaka University, Japan
Y. Andoh, Osaka University, Japan
S. Morita, Osaka University, Japan
Correspondent: Click to Email
We have measured an optical evanescent field using a noncontact mode atomic force microscope (AFM) combined with a frequency modulation detection method.@footnote 1@ Using a semiconductor AFM tip, the surface photo voltage (@delta@@phi@) is induced by the optical evanescent field. It causes the electrostatic force acting on the tip. This force (F) can be expressed by F=(V-@phi@)(@delta@C/@delta@z)@delta@@phi@. Here, V, @phi@, C, and z are the bias voltage, the contact potential difference, the capacitance and the distance between the tip and the sample, respectively. In this method, the electrostatic force is affected not only by the potential change @delta@@phi@ due to the evanescent field but also by the contact potential difference @phi@ between tip and sample which is not uniform on the surface. In this paper, we propose a novel method to detect only the variation of the surface photo voltage due to the optical evanescent field without the influence of the contact potential difference. Applying Kelvin-Null method,@footnote 2@ bias voltage V is controlled so that V-@phi@ is kept constant. Simultaneously, the incident beam is modulated at a frequency w, and the w component of the force gradient is measured which is proportional to the optical evanescent field. @FootnoteText@ @footnote 1@M. Abe, Y. Sugawara, Y. Hara, K. Sawada and S. Morita, Jpn. J. Appl.Phys. Vol. 37 (1998) pp. L167-L169 @footnote 2@M. Nonnenmacher, M. P. O'Boyle and H. K. Wickramasinghe, Appl. Phys. Lett. Vol. 58, No. 25, (1991) pp. 2921-2923