Diffusion controlled on-surface reactions: formation of N-doped nanoarchitectures

The bottom-up approach aims at forming tailored nanoarchitectures by manipulating organic molecules at atomic level and it is one of the most effective strategies used in nanotechnology. Catalytic surfaces are often used to prompt a particular reaction as they are very successful in modifying a particular molecule in selected ways. For example, transition metal surfaces are very efficient catalysers of dehydrogenation reactions in Polycyclic Aromatic Hydrocarbon (PAH), usually upon thermal activation. They can act in different ways, depending on the strength of the interaction between the surface and the adsorbate. When a PAH is deposited on a reactive surface, such as Pt(111), the molecule does not diffuse, so the as-deposited molecule sticks where it lands. When this system is annealed, the molecule dehydrogenates which results in an intramolecular transformation, as no intermolecular interaction is allowed as the molecules do not ‘see’ each other. However, when deposited on a weakly reactive surface the precursors diffuse. In this case, the thermal activation allows dehydrogenation and an intramolecular structural transformation; however, as the molecules diffuse they interact with each other, causing also intermolecular covalent bonding. So by simply changing the nature of the surface, we can obtain two completely different outcomes.

The picture shows how the two selected molecular precursor can either transform into N-doped fullerenes or nanographene on a highly reactive surface, where diffusion is prevented (left hand side), or they can react with each other to form covalent chains on a weakly reactive surface (right hand side).


This work has been performed by combining different experimental techniques, such as STM, XPS, NEXAFS (synchrotron radiation based) and DFT theoretical methods.

The results have been published in: ACS Nano 7 (2013) 3676.

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