Theoretical issues in noncontact atomic force microscopy

M.Tsukada, ^*N.Sasaki, M.Gauthier, K.Tagami

Dept. of Phys., Univ. of Tokyo,
^*Dept.of Mater. Sci., Univ. of Tokyo

An overview on the present theoretical status is given and important issues are discussed toward establishing sound bases of nc-AFM. First we report the theoretical simulation method of images based on density functional calculations, which is applied to the imaging of the Si(111) sqrt{3}x sqrt{3}-Ag surface. Experimental STM images are reproduced well , if the fluctuation is taken into account between the two phases of this structure. We also discuss the effect of the non-conservative atomic processes causing dissipation of the cantilever oscillation energy. Such processes result in a hysteresis in a tip-surface force curve causing the energy dissipation. How the frequency shift and the Q-value are influenced is shown for a model system. Furthermore, the damping peculiar to the nonlinear cantilever oscillation is discussed as well as its relation to self-driven and external driven systems.