15:00-16:00
Atomic Pathways Towards the Synthesis of Fullerenes and Triazafullerenes from Polycyclic Aromatic Hydrocarbons
Dr. Giulio Biddau (Department of Theoretical Physics of Condensed Matter,Universidad Autonoma de Madrid, Madrid (Spain))
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True fullerene-based molecular electronics are limited by the current production methods. Standard techniques, such as graphite vaporization, do not permit a real control on size, and, particularly, on doping (e.g. heterofullerenes and endohedral fullerene). This has promoted an intense research activity directed towards more rational and efficient synthesis methods. We have recently achieved the formation of closed fullerenes (C60) and triazafullerenes (C57N3) by thermal annealing using polycyclic aromatic hydrocarbons (PAHs) adsorbed on Pt(111) surfaces[1]. The PAHs (C60H30 and C57N3H33) chosen as precursors for fullerenes and triazafullerenes (C60 and C57 N3), are characterized by easy synthesis and doping processes, paving the way to the formation of doped fullerene with specific characteristics. We have combined STM, XPS, NEXAFS and thermal desorption measurements with first principles calculations, to study the adsorption of C60H30 and C57N3H33 on Au(111) and Pt(111) surfaces, and the possibility of closed fullerene formation by thermal annealing using these molecules as precursors.
In this talk, we focus on the theoretical aspects of the above work and present large scale first principles DFT calculations using both an efficient local orbital basis and standard plane-wave approaches. These simulations give support for the interpretation of experiments that confirm the feasibility of the formation process and provide insight into the atomic pathways leading from the planar PAHs to the closed fullerenes and triazafullerenes. In particular, we characterize the adsorption and STM images of both the planar precursors and the final closed molecules, considering different coverages and the influence of surface defects (like surface vacancies). Furthermore, we explore the closure process for partially and fully dehydrogenated precursors with the NEB method, identifying the relevant steps and showing that the energy barriers are low enough so they can be overcome with the available thermal energy during the annealing process.
Reference
[1] Otero G, Biddau G et al, Nature 454, 865-869 (2008)
