Thesis defense of Ismail Baltaci

Here we present the first experimental comparative study of theobromine monolayers on Au(111), few-layer graphene on 6H-SiC(0001) and on Cu(100). Wherein up to 3 graphene layers are called few-layer graphene. The self-assembly of theobromine is characterized utilizing scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Additionally, LEED pattern simulations are performed and compared with the experimental data as well as with 2D-fast Fourier transforms (2D-FFT) of STM measurements. On Au(111) and few-layer graphene on 6H-SiC(0001) we found that the adsorbate unit cell is rectangular and consists of 4 theobromine molecules. Whereas the orientations of the molecules within the unit cell differ. On Au(111), the molecules are prochiral, which is explained by glide reflections. The self-assembly on the Cu(100) substrate shows no periodic structure for our experimental set up which could be due to a strong adsorbate-substrate interaction. Different heating temperatures at the substrate do not lead to a periodic adsorbate structure. The molecules desorbe at a temperature of 180 °C. LEED simulations predict 6 theobromine domains on Au(111) with a rotation of 30° and 3 domains on the graphene substrate with a rotation of 60° relative to each other. Further a possible structure model for theobromine molecules on Au(111) is presented based on the results concerning glide reflection symmetry. On few-layer graphene/6H-SiC(0001) intramolecular STM images are utilized to find the orientation of the molecules. Additionally, a Moiré-pattern on graphene is explained by the supposed theobromine adsorbate structure. The Moiré-pattern is explained by the misfit of the rectangular theobromine lattice to the hexagonal 6 × 6-reconstruction of graphene on 6H-SiC(0001).

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