Modelo teórico da interação entre a ponta do Microscópio de Força Atômica (AFM) e uma superfície plana

Abstract

Several models have been proposed in the literature to relate the force and the distance of interaction between the atoms that compose the AFM tip and the atoms that compose the surface of the analyzed sample (modeled as flat, homogeneous and isotropic), but there is not until now a mathematical equation which satisfies a more complete description of the physical quantities involved in this interaction. In this work are considered regions with low relative humidity, because in these conditions the Van der Waals force is predominant in the interaction, fact which was observed experimentally. The force-distance relationship is modeled for a tip in the form of a sharp cone and the attractive term of Van der Waals represents the adhesion force in this interaction. Some approximations are made, according to experimental results reviewed in the literature. Thus, relationships were found for the Van der Waals force modeled for tips with different geometries (cone, sphere, cylinder and pyramid). These relationships have provided a numerical simulation done in scientific analysis software (ORIGIN), who helped us foresee the adhesion force and mechanical stability point (where the attractive force is maximum) of the AFM tip and a mica surface, considering different geometries for the tip. Then, comparing the result obtained in the numerical simulation with the experiment made in the PUC-RJ, where was used a sample of mica and a tip of silicon nitride (Si3N4), it was observed what the theoretical result of adhesion force for pyramidal geometry kept right off of experimental result, confirming the geometry of tip informed by the maker.