On-surface reactions of alkyne molecules on calcite (10.4)
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Abstract
For fabrication of future electronic nanoscale devices, directly on a support surface, suitable building block units have to be identified. A promising approach is the so-called molecular electronics, which suggests single molecules or molecular groups as substitute for electronic components. For the creation of electronic circuits, conductive wire-like molecular arrangements are necessary to connect these functional units.
To create well-defined aggregates in a fast and serial manner at the molecular level, self-assembly has proven to be a promising approach. Nevertheless, since self-assembly relies on reversible interactions, the obtained structures are somewhat fragile. To stabilize molecular structures, on-surface synthesis has been proven to be a highly versatile tool. The stabilization is obtained by the formation of covalent bonds directly on an appropriate substrate surface.
In the view of molecular electronics, the on-surface created molecular structures need to be conductive. Therefore, conjugated molecular structures have been suggested as promising candidates. Additional, it is mandatory to decouple the formed molecular devices from the support surface.
Therefore, the aim of this thesis is to create wire-like conjugated molecular structures on a bulk insulator surface. To reach this goal, molecular precursors equipped with terminal alkyne and diyne functionalities were chosen. The experiments were performed in ultra-high vacuum using frequency-modulated atomic force microscopy. For all investigated molecules, first the structure formation of the as deposited monomer precursors was characterized at the nanoscopic scale. Secondly, the initiation of the reaction was performed upon thermal, photochemical and sometimes even combined stimulation experiments. For two molecular precursors, density functional theory (DFT) calculation were done. The optimizations provide insights into the molecular arrangement after deposition and the structure formation of the precursors after reaction initiation. Additional, detailed parameter variations of e.g., time, wavelengths and temperature were performed to investigate the influence of these parameters on the structure formation. Finally, this thesis provides, for the first time, evidence for a successful diacetylene polymerization, an acetylene polymerization and a homocoupling reaction on a bulk insulator surface. For the two first named reactions, molecular wire-like structures were obtained, which are interesting as molecular wires for future molecular electronics.