Exploring Mesoscale Contact Mechanics by Atomic Force Microscopy

Mesoscale contact junctions, formed by mechanical interaction of elastic, viscoelastic, and elastoplastic solids, play a crucial role in a wide range of physical phenomena, going from rubber friction and adhesion to biological adhesion in filamentary attachment pads and cell adhesion and interaction with physical scaffolds. Moreover, they affect the response of several microelectromechanical systems and impact the performance of novel lithographies that manipulate objects, pattern surfaces, and transfer molecules with nanoscale accuracy. It is well known that the behavior of contact spots is highly complex since it depends on different factors, namely, contact geometry, bulk and surface (visco)elasticity, plasticity, physical and chemical adhesion. The introduction of novel experimental strategies, aimed to tightly correlate the junction response with their relevant interfacial properties, is certainly mandatory and highly promising. In this chapter, we present atomic force microscopy as an ideal tool for contact mechanics investigations on individual and multiple contact junctions. In particular, we focus on the fabrication of custom probes, with characteristic size from a few hundred nanometers to several microns, and on their use in nanoindentation studies. We also discuss paradigmatic experiments addressing the role of interfacial roughness, viscoelasticity, plasticity, and adhesion on the mechanical response of mesoscale contacts.