Evolution Of Self-Assembled C₆₀ Structures On AnCA Templates

Ordering and stability of supramolecular structures from molecular self-assembly are very important to the function and performance of molecular devices. In this thesis, we investigated the structural ordering of 9-anthracene carboxylic acid(AnCA) on Ag(111)surface and C60 on selected AnCA templates. We also investigated the thermal stability of AnCA-templated C60 structures, and identified two interesting C60 ordered structures with enhanced thermal stability from annealing.Depending on the molecular surface density, four spontaneously formed and one annealed AnCA ordered phases were observed, namely a straight belt phase, a zigzag double-belt phase, two simpler dimer phases, and a kagome phase. This structural diversity stems from a complicated competition of different interactions of AnCA molecules on metal surface, including intermolecular and molecular-substrate interactions,as well as the steric demand from high molecular surface density.The self-assembly process of C60 molecules on two simpler dimer phases of AnCA as templates was then studied. We found the structural stability of the AnCA templates influence the growth modes of C60 molecules. Either laterally separated AnCA–C60elongated domain arrays or an “epitaxial” C60 dimer structure over AnCA can be formed depending on the selected AnCA template. Our experimental observations suggest a pathway of molecular nanostructure control through the choice of suitable template.The structure evolution of AnCA-templated C60 structures with annealing was investigated. After annealing at 100°C, the AnCA-templated C60 structures on Ag(111)transition into two novel structures, a “self-hosted” C60 dimer structure and a linear C60 chain structure, with increased thermal stability. Most interestingly, C60 molecules in the chain structure possess alternative configurations on the surface across the chains, either rotational free or frozen into specific azimuth with 6:6 bond as the topmost feature. The thermal instability of the originally templated structure provides a probability to form new structures with interesting features which cannot be accessed otherwise.