ABSTRACT

The key to the successful operation of an AFM (Binnig et al., 1986) in the materials sensitive regime (Burnham and Colton, 1989; Miyamoto et al., 1990; Mizes et al., 1991) is the measurement of the interaction forces between the tip and the sample surface. The tip would ideally consist of only one atom, which is brought in the vicinity of the sample surface. A crude estimation shows that the interaction forces between the AFM tip and the sample surface should be smaller than about 10

N for bulk materials and preferably well below 10

N for organic macromolecules. On the other hand, there are indications that the measured values, especially of the pull-off force, are considerably off from the theoretically expected values. The reasons are manifold: the shape and size of the tip is not well known (Godowski et al., 1995; Lekka et al., 1997; Ramirez-Aguilar and Rowlen, 1998). The composition of the surfaces of the tip and the sample might differ strongly from their bulk values. Another possibility is that the continuum mechanical models (Johnson, 1992; 1996; Johnson et al., 1971; Maugis, 2001) usually employed to analyze the data might fail.