Atomically Precise Graphene Nanoribbons: Aggregation, Thin Film Fabrication and Gas Sensing Properties

Theoretical and experimental studies show that graphene nanoribbons (GNRs) can possess intriguing physical properties, such as a tunable electronic bandgap and a peculiar magnetic ordering for certain types of nanoribbon edges. However, in order to realize these properties, GNRs should be synthesized with atomic precision. In Chapter 1, I provide a comprehensive review on the bottom-up synthesis of atomically precise GNRs, their physical and chemical properties, and discuss synthetic challenges and opportunities. While there has been a considerable progress in the bottom-up synthesis of GNRs, a very limited number of publications have described their applications. One of the most serious challenges is the low solubility of GNRs in conventional solvents, which results in their poor processability for characterization and device studies. Thus, the main objective of this project was to study aggregation behavior of GNRs, develop a procedure to form uniform thin films of GNRs suitable for device fabrication and investigate their electrical properties. First, we studied aggregation of solution-synthesized chevron GNRs in liquids and on surfaces (Chapter 2). In liquids, GNRs tend to aggregate via π-π stacking, while on surfaces we observed the formation of µm-long one-dimensional structures. Interplay of these two assembly modes can result in the formation of interesting GNR structures with promising device characteristics. Chapter 3 describes a new fabrication approach for large-scale uniform thin films of non-functionalized solution-synthesized chevron GNRs. These films can be transferred to various substrates including Si/SiO2 and used for the streamlined fabrication of arrays of GNR-based devices. In Chapter 4, we demonstrate an alternative approach to fabricate transparent thin films of GNRs from perylenetetracarboxylic dianhydride (PTCDA) using a chemical vapor deposition (CVD) technique, which allows growing GNRs on semiconducting and insulating substrates. We demonstrate that these GNRs are terminated with dianhydride groups and have enhanced sensor responses to gases of nucleophilic nature. Finally, in Chapter 5 I summarize the results of this work and discuss directions for future research in the framework of this project