Organometallic hexahapto-functionalized graphene: Band gap engineering with minute distortion to the planar structure

Motivated from experimentally realized Cr-chemisorbed graphene, we have systematically explored the electronic properties of organometallic complexes of graphene with covalent monohexahapto-TM (TM = Cr, Fe, Ni) bonds using density-functional theory (DFT) calculations. We show that besides Cr, Fe and Ni can also bind strongly with the graphene. At the experimentally suggested coverage ratio (TM:C = 1:18, TM = Cr, Fe, Ni), our calculations suggest that the computed band gap of perfectly arranged networks of (η⁶- graphene)-Cr(CO)₃, (η⁶-graphene)-Fe(CO)₂, and (η⁶-graphene)-NiCO can be enlarged to 1.08, 0.61, and 0.29 eV, respectively. The inconsistency between the computed gap (1.08 eV) and the experimental gap (∼10 meV) for the (η⁶-graphene)-Cr(CO) ₃ is explained, which is possibly due to the existence of regions with relatively lower coverage ratio, in view of the much smaller band gap for (η⁶-graphene)-Cr(CO)₃ with Cr:C = 1:32 (54 meV) and with Cr:C = 1:50 (20 meV), respectively. Both band gap values are much closer to the measured band gap (∼10 meV). Yet, the functionalized graphene shows little structural distortion from its original planar structure. The notable features of the direct band gaps along with the planar structure render the TM-functionalized graphenes quite appealing for applications not only in nanoelectronics but also in optoelectronics such as the infrared detector and solar cell photoanode. © 2013 American Chemical Society.