A NOVEL FORCE MICROSCOPE AND POINT-CONTACT PROBE

The mechanical properties of very small volumes of material can vary g reatly from bulk properties. These modified properties are of interest in many areas including the operation of atomic force microscopy (AFM ), the study of adhesion and fracture, and the evaluation of electrica l contact response. Despite the importance of these properties, AFM ha s not yet been successfully utilized for their investigation. Most exi sting AFMs still rely on the control and monitoring of displacements, with forces being inferred from spring constants. This would be fine i f other interactions, such as those between the tip and the surface, w ere minor perturbations. However, this is frequently not the case, par ticularly for contact mode AFM. Hence very little is known about the f orces applied in the contact and their affect on both the tip and the sample. In this article we describe an AFM probe where forces rather t han displacements are applied to the tip. This allows absolute determi nation of contact compliance and hence provides a measure of the tip-s urface interaction. As an example of its use we show quantitatively th e effect of the adsorbed water and meniscus forces present in ambient probe microscopy.