Open Access

Materials exhibit dramatically different mechanical properties when probed and confined on nanometer length scales. These size effects can arise from both the nature of individual contacts and the reduced dimensions of the interacting bodies. In this thesis, multimode atomic force microscopy techniques have been applied to study mechanical size effects of friction and plasticity in bulk and ultrathin film crystalline materials. Incipient plasticity of crystal surfaces has been studied by a novel atomic force microscopy based indentation method. High resolution imaging after indentation of Cu(100) and KBr(100) surfaces revealed the resulting dislocation structure. The distribution of discontinuities observed in indentation force curves correlated to the creation of individual dislocation loops. The shear stress acting at the point of first yield was consistent with density functional theory predictions for the ideal shear strength of the crystal. Friction and dissipation in epitaxial ultrathin films was then studied by the combined techniques of non-contact force microscopy, Kelvin probe force microscopy, and friction force microscopy. Films as thin as one and two atomic layers exhibit atomic stick-slip friction loops similar to their bulk forms. Edge sites of KBr films grown on Cu(100) are prone to wear while substrate steps overgrown by the film are stable. This phenomenon can be understood in terms of enhanced interaction at low-coordinated sites as reveled by atomic-resolution imaging. The tribological benefits of a closed KBr ultrathin layer are found to be consistent with macroscopic experiments. Single layer graphene films grown on SiC(0001) exhibit a reduced local work function compared to bilayers, allowing an unambiguous identification of layer thickness. Friction on SiC is greatly reduced by a single layer of graphene, and reduced by another factor of two on bilayer graphene. The friction contrast between single and bilayer graphene arises from a diff