Thermally activated chemical pathways of polyaromatic hydrocarbons on a reactive surface

: the assembly of intermediates towards graphene

Abstract

The interaction of various aromatic hydrocarbon molecules with the Rh(111) substrate was investigated primarily through scanning tunnelling microscope (STM) imaging, with experimental results supported by density functional theory (DFT) calculations. The simplest aromatic molecule, benzene, was studied at different surface coverages, which had an effect on the molecular adsorption site, the intermolecular interactions and the interaction between the molecule and the substrate. The results were compared with those found upon coadsorption of benzene with CO. Other aromatic molecules studied include naphthalene, tetracene and coronene, with particular focus on the kinetically driven chemical pathways to new structures formed through thermal treatment of the sample. A general trend was determined from this study that the larger and more complex the aromatic molecule the higher the temperature required for thermally activated molecular restructuring on the catalytic surface. This is important towards understanding the growth kinetics of graphene on the Rh(111) surface, with potential applications for developing a functionalised molecular feedstock for the controlled growth of high quality doped graphene that can be easily electronically tailored. One idea for such a feedstock was tested; a hexa-peri-hexabenzocoronene with a central borazine core. While the investigation is still in its early stages and ongoing, the initial results show promise with the discovery that the molecule does not appear to break down at temperatures just below graphene synthesis in such a way as to lose the heteroatoms acting as dopants within its structure. This is favourable compared to molecules like pyridine, which is an unsuitable feedstock for doped graphene due to its tendency for thermal breakup, leading to the loss of its nitrogen atom.

Date of Award	21 Jun 2017
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Renald Schaub (Supervisor)