NORMAL AND LATERAL FORCES IN SCANNING FORCE MICROSCOPY

With an atomic force/friction force microscope operating in the constant force mode and with an optical lever technique as a deflection sensor, we have investigated the total force acting on the cantilever tip during the raster scanning of the sample surface. A model including the normal and lateral components of the force has been worked out. The normal force is related to the cantilever loading. The lateral force has two components, dissipative and nondissipative, having opposite symmetry with respect to the scanning direction. Within our model, the nondissipative component, which is related to the topography, can be distinguished from the friction component in two different ways, both leading to ''pure friction'' images. The first method is based on the comparison of two images acquired in the forward and backward scanning direction, respectively. The second method is based on the comparison of the topographic and lateral force images acquired in the same scanning direction. This latter way does not need correction for the nonlinear behavior of the piezoelectric transducer. Results from various samples are reported.