We show that the different bond orders of individual carbon-carbon bonds in polycyclic aromatic hydrocarbons (PAHs) and fullerenes can be distinguished using noncontact atomic force microscopy (NC-AFM) with a CO-functionalized tip. Two different contrast mechanisms were found, which were corroborated by density functional theory calculations: The greater electron density in bonds of higher bond order led to a stronger Pauli repulsion, which enhanced the brightness of these bonds in high-resolution AFM images. The apparent bond length in the AFM images decreased with increasing bond order because of tilting of the CO molecule at the tip apex.
By: Leo Gross, Fabian Mohn, Nikolaj Moll, Bruno Schuler, Alejandro Criado, Enrique Guitian, Diego Pena, André Gourdon, Gerhard Meyer
Published in: RZ3871 in 2012
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