Abstract
We determine, by means of density functional theory, the stability and the structure of graphene nanoribbon (GNR) edges in presence of molecules such as oxygen, water, ammonia, and carbon dioxide. As in the case of hydrogen-terminated nanoribbons, we find that the most stable armchair and zigzag configurations are characterized by a non-metallic/non-magnetic nature, and are compatible with Clar's sextet rules, well known in organic chemistry. In particular, we predict that, at thermodynamic equilibrium, neutral GNRs in oxygen-rich atmosphere should preferentially be along the armchair direction, while water-saturated GNRs should present zigzag edges. Our results promise to be particularly useful to GNRs synthesis, since the most recent and advanced experimental routes are most effective in water and/or ammonia-containing solutions.
Highlights
Narrow graphene nanoribbons[1] are carbon allotropes that promise to combine the high carrier mobility of graphene[2] with a semiconducting nature due to quantum confinement in the lateral direction
density functional theory (DFT) calculations were performed with the PWSCF code of the Quantum ESPRESSO suite[36] in a planewave/ultrasoft-pseudopotential approach, adopting the Generalised Gradient Approximation (GGA) from Ref.[37] for the exchange-correlation functional
In these cases we restricted our study to O/H/N contents as fixed by the respective molecular stoichiometries, which corresponds to the description of experiments carried out in pure water or ammonia atmospheres
Summary
Narrow graphene nanoribbons[1] are carbon allotropes that promise to combine the high carrier mobility of graphene[2] with a semiconducting nature due to quantum confinement in the lateral direction. Among the variety of reported experimental approaches, three routes, intensely explored in the last couple of years, seem at the frontier of current research: i) lithographic patterning[3,4,5,6]; ii) sonochemical methods[7,8]; iii) metallic nanoparticle chemical etching (unzipping) of graphite/graphene (nanotubes)[9,10,11,12,13,14]. The observation of graphene edges[15,16] and/or GNR7,14 profiles at atomicscale resolution indicates that the mentioned experimental methods are capable of producing smooth, likely nonchiral (i.e. no mixing of zigzag and armchair direction), edges. Little is known on how to achieve either zigzag or armchair edges, and about the actual chemical termination of the unsaturated carbon bonds
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