Intramolecular force mapping at room temperature using Non-Contact Atomic Force Microscopy

Scanning Probe Microscopy (SPM) methods allow for investigations on the molecular and atomistic scale in real space. While Scanning Tunneling Microscopy (STM) images the electronic structure of a molecular sample, its chemical structure can be resolved, and precise conformation can be determined, by Non-Contact Atomic Force Microscopy (NC-AFM). Acquisition of dense, three-dimensional (3D) force fields with intramolecular resolution via NC-AFM has yielded enormous progress in characterizing molecular and two-dimensional materials at the atomic scale. To date, intramolecular force mapping has been performed exclusively at cryogenic temperatures, due to the stability afforded by low temperature operation, and as the carbon monoxide functionalization of the metallic scanning probe tip, normally required for submolecular resolution, is only stable at low temperature. An additional technical difficulty of operating a STM with atomic precision at room temperature, is the relative positional drift between the tip and sample. In this thesis, the experimental apparatus and development of the thermal drift correction methodology needed to gather high-resolution 3D force maps at room temperature are described. The physical limitations of room temperature operation are overcome using semiconducting materials to
inhibit molecular diffusion and to create robust tip apexes, while the challenge due to thermal drift is
overcome with atom tracking based feedforward correction. The results chapters present 3D force maps comparable in spatial and force resolution to those acquired at low temperature, permitting a quantitative analysis of the adsorption induced changes in the geometry of the molecule at the picometer level. The capability of intramolecular force mapping is widened to larger area maps, of multiple molecules for avariety of systems, demonstrating the versatility and flexibility of the drift correction procedure.