Molecular Dissociation on the SiC(0001) 3×3 Surface.

In the framework of density functional theory, the adsorption of the halogenated polycyclic aromatic hydrocarbon 2,11-diiodohexabenzocoronene (HBC-I2 ) on the SiC(0001) 3×3 surface has been investigated. Nondissociative and dissociative molecular adsorption is considered, and simulated scanning tunneling microscopy (STM) images are compared with the corresponding experimental observations. Calculations show that dissociative adsorption is favorable and reveal the crucial importance of the extended flat carbon core on molecule-surface interactions in dissociative adsorption; the iodine atom-surface interaction is of minor importance. Indeed, removing iodine atoms does not significantly affect the STM images of the central part of the molecule. This study shows that the dissociation of large halogenated polycyclic aromatic hydrocarbon molecules can occur on the SiC surface. This opens up interesting perspectives in the chemical reactivity and functionalization of wide band gap semiconductors.