Measurement of the absolute separation for atomic force microscopy measurements in the presence of adsorbed polymer

We demonstrate that the absolute separation between an atomic force microscope (AFM) tip and a solid substrate can be measured in the presence of an irreversibly adsorbed polymer film. The separation is obtained from the analysis of a scattered evanescent wave that is generated at the surface of the solid. By comparing our scattering measurements to conventional AFM measurements, we also show an example where a conventional AFM measurement gives the incorrect force-distance profile. We validate the measurement of separation from scattering by examining the force-separation profile in the presence of surfactant solution. This validation is possible because the tip can be used to desorb the surfactant film that forms in surfactant solution, so we are able to measure both the scattering and the cantilever deflection when the tip is in contact with the solid substrate. The main limitation of our technique now is the lack of a rigorous method for predicting the intensity of scattering from the tip in contact with a solid that is coated with a film. (c) 2006 American Institute of Physics.