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 syste m at the proximity of a surface is discussed. The attractive tip-surface in teraction is simply described with a Van der Waals dispersive term and a sp here-plane geometry. We show that the non linear behaviour of the oscillato r is able to explain the observed shifts of the resonance frequency as a fu nction of the tip-surface distance without the need of introducing a partic ular short range force. (C) 1999 Elsevier Science B.V. All rights reserved.