Computational Studies of Defects in Nanoscale Carbon Materials
Atomic Pathways Towards the Synthesis of Fullerenes and Triazafullerenes from Polycyclic Aromatic Hydrocarbons
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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 with efficiency of ~100%, as we recently report . The PAHs (C60H30 and C57N3H33) chosen as precursors for fullerenes and triazafullerenes (C60 and C57N3), 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 work, we focus our attention on both experimental and theoretical results.
Large scale first principles DFT calculations have been carried out, using both an efficient local orbital basis[2-3] and standard plane-wave approaches[4-5] . 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.
In this work, we have reached an efficient fullerene and heterofullerene size controlled production method via surface catalyzed cyclo dehydrogenation; furthermore our method opens to other possibilities, such as encapsulation (endohedral fullerene) and formation of other carbon nanostructures.
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