Scanning Probe Microscopy Characterization of Organic Self-Assembled Monolayers

作者：Evangelia‐Nefeli Athanasopoulou · 发表于：Infoscience (Ecole Polytechnique Fédérale de Lausanne) · 年份：2018 · DOI：10.5075/epfl-thesis-8274 · 研究领域：Force Microscopy Techniques and Applications、Molecular Junctions and Nanostructures、Surface and Thin Film Phenomena

As technology advances, surface coatings become more and more important to assure materials performances. In recent years, molecular coatings have found larger acceptance and uses. Among them, self-assembled monolayers (SAMs) are attractive because they are versatile and their manufacturing approach is easy to scale up. Their mechanical properties, such as elasticity, are generally considered an important quality indicator. The molecular structure and ordering of SAMs is believed to be one of the key causes for their mechanical properties. A direct set of structure-property relationships has not been obtained yet. This is mainly due to the difficulty in achieving mechanical and structural information about SAMs at the same time. Most information currently available on intermolecular interactions in SAMs pertains to highly ordered systems on ideal flat surfaces, i.e. the easiest systems to study. This thesis presents a novel approach to address the question of determining structure and mechanical properties of self-assembled monolayers at the same time. The effective Youngâ s modulus, E*, of SAMs was measured using the Atomic Force Microscope operated in the bimodal excitation and detection scheme (bimodal AFM) while at the same time imaging at high resolution. Bimodal AFM was first used on alkanethiol molecules self-assembled on Au (111), a model system for SAMs. Surface elasticity has been reliably determined and found to be ligand-length dependent. An interpretation of this...