Dokument

Summary:
Low-dimensional carbon-based nanostructures are considered for the fabrication of modern electronic devices. For the realization of such devices, it is of utmost importance to achieve a high control over the structural quality. As a result, the field of on-surface synthesis, which aims at producing well-defined structures from tailor-made molecular precursors, has grown rapidly over the past decade. The reaction most frequently used to conduct on-surface synthesis is the Ullmann coupling reaction. Although a lot of work has already been invested, the fundamental principles determining the outcome of this reaction have not fully been understood to date. One prototypical case for such a situation is the product formation on the basis of precursor molecules that can either form long oligomer chains or macrocycles. This cumulative dissertation thesis contains a number of articles investigating the reaction products of different precursor molecules bearing these characteristics. They are investigated on metal single-crystal surfaces by scanning tunneling microscopy and complementary surface science techniques such as X-ray photoelectron spectroscopy or angle-resolved photoemission spectroscopy, accompanied by Monte Carlo simulations. The ring/chain ratio formed by the model system 1,3-dibromoazulene on Cu(111) was studied. By this means new insights on how the ring/chain ratio can be tunedby variation of coverage and temperature were gained based on fundamental physicochemical considerations. An alternative approach to steer the reaction outcome was used by applying a surface template, i.e., a vicinal Ag surface, to exclusively form long, perfectly aligned oligomer chains from the 4,4''-dibromo-1,1':3',1''-terphenyl precursor. Furthermore, the 2,6-dibromoazulene precursor, which can exclusively form chains, was used to generate nanoribbons of the non-alternant graphene allotropes phagraphene and tetra-penta-hepta-graphene on Au(111). The structures of these species have been unambiguously elucidated by non-contact atomic force microscopy experiments carried out in a collaboration project. As a last project, the structural polymorphism of the pure self-assembly of 1,1':3',1'':4'',1'''-quaterphenyl-4,4'''-dicarbonitrile on the Ag(111) surface was investigated. This molecule shows an adsorbate structure containing flat-lying and upright-standing molecules. Such a structure had not been reported so far. Along with the structures formed, the performance of organic-electronic devices is also crucially dependent on the interactions between the substrate and the organic layer itself. To contribute to this field of research, studies on different model systems, i.e., porphyrins, corroles, and the non-alternant aromatic molecule azulene, have been performed in collaboration projects mostly involving synchrotron radiation beamtimes. In addition to the results already published in scientific journals, some unpublished results are part of this thesis. These are the investigation of the 1,3-dibromoazulene precursor on the Ag(111) surface with co-deposited Cu atoms and the successful initial operation of a commercially available atomic layer injection device. The experimental results are supplemented by the development and construction of technical instrumentation, which expands the capabilities of the measurement setup in the laboratory of the Gottfried group in Marburg.

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