Spectroscopic characterization of functionalized graphene nanoribbon heterostructures

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Graphene nanoribbons are the latest one-dimensional (1D) sp2-carbon allotrope and combine the best attributes from the nanotube and the graphene worlds, i.e. a variety in possible structures with the possibility of a uniform wafer coating. A key difference between graphene and graphene nanoribbons is that the latter possess a bandgap. Furthermore, the electronic and optical properties of GNRs can be tailored by controlling their width and edge structure. GNRs can be fabricated with atomic precision by a bottom-up approach on a catalytically active metal surface on which precursor molecules react to form the desired structure. The large variety in precursor molecules ensures that GNRs with different physical properties can besynthesized over large areas. Additionally, by using vicinal surfaces the ribbons can be aligned. Within this project we will synthesize, functionalize, and spectroscopically characterize novel graphene nanoribbons and heterostructures made thereof and evaluate their potential applicability in devices. For the synthesis of GNRs we employ on-surface polymerization and will optimize the synthesis parameters. Graphene nanoribbons will be further functionalized by for example evaporation of metals and earth alkali metals on them to achieve high electron doping. Heterostructures of GNRs will be prepared by co-evaporation of different precursors during the synthesis step or by stacking GNRs with different width or doping. The fabricated samples will be characterized using UHV optical spectroscopy, photoelectron spectroscopy, and fluorescence and Raman spectroscopy. Using these methods we will determine fundamental properties of graphene nanoribbons such as effective masses, exciton transition energies, and absorption spectra. We will additionally apply plasmonic enhancement to enhance the light-matter interaction of GNRs. Here a key goal is to reduce the probed area of the sample so that individual nanoribbons may be studied optically. Finally, we will explore the use of GNRs in devices and applications such as gas sensing.