Relationship between the non linear dynamic behaviour of an oscillating tip–microlever system and the contrast at the atomic scale

In this paper, the dynamic behaviour of an oscillating tip–microlever system at the proximity of a surface is discussed. The attractive tip–surface interaction is simply described with a Van der Waals dispersive term and a sphere–plane geometry. We show that the non linear behaviour of the oscillator is able to explain the observed shifts of the resonance frequency as a function of the tip–surface distance without the need of introducing a particular short range force. q1999 Elsevier Science B.V. All rights reserved.