Modeling vacancies and hydrogen impurities in graphene: A molecular point of view

Abstract

We have followed a 'molecular' approach to study impurity effects in graphene. This is thought as the limiting case of an infinitely large cluster of benzene rings. Therefore, we study several carbon clusters, with increasing size, from phenalene, including three benzene rings, up to coronene 61, with 61 benzene rings. The impurities considered were a chemisorbed H atom, a vacancy, and a substitutional proton. We performed HF and UHF calculations using the STO-3G basis set. With increasing cluster size in the absence of impurities, we find a decreasing energy gap, here defined as the HOMO-LUMO difference. In the case of H chemisorption or a vacancy, the gap does not decrease appreciably, whereas it is substantially reduced in the case of a substitutional proton. The presence of an impurity invariably induces an increase of the density of states near the HOMO level. We find a zero mode only in the case of a substitutional proton. In agreement with experiments, we find that both the chemisorbed H, the substitutional proton, and the C atom near a vacancy acquire a magnetic moment. The relevance of graphene clusters for the design of novel electronic devices is also discussed.

Electric Field Activated Hydrogen Dissociative Adsorption to Nitrogen-Doped Graphene

“…As reported previously, the H 2 molecule is weakly adsorbed on pristine graphene, which is the reason why many people paid a lot of attention to modify graphene through doping or by other methods to enhance the interaction between hydrogen and graphene. 9,32 The energetic favorable position of an H 2 molecule adsorbed on graphene is at the hallow site of the carbon hexagon as reported by DFT calculations, 9,33 which is shown in Figure 1 In addition, in order to investigate the effect of the simulation cell size on the results, which was found to have a significant effect on the cluster model, 35 we also performed our calculations using a 4 × 4 supercell and found d H2-graphene is 2.650 Å with adsorption energy E b-H2 ) -0.158 eV, which is 0.3% lower than the result obtained with the 2 × 2 supercell.…”

Role of H Distribution on Coherent Quantum Transport of Electrons in Hydrogenated Graphene

“…The Curie temperature of an hydrogenated graphene layer or multilayer has been estimated [17], and the tendency towards the formation of H or D clusters has been predicted theoretically [23] and observed experimentally via STM [24]. Again, quantum chemical model calculations on large carbon clusters, such as coronene, have been instrumental to detect the onset of magnetism in these hydrogenated carbon systems [19,25] (see also [4,26]). …”

“…The H adatoms can form bonds with the carbon atoms, changing their hybridization state from sp 2 to sp 3 , with a strong, but easy to formulate impact on the electronic structure of the material: one site of the G lattice is not accessible to the electron transport (i.e., an effective "vacancy" forms). Evidence of the modified electronic properties of graphene due to hydrogen adatoms or vacancies is already available from quantum-chemistry calculations for such impurities in large benzene-like molecules [4], as well as in their effect on the local density of states and conductivity of graphene [5].…”

Electronic and magnetic properties of graphene, silicene and germanene with varying vacancy concentration

“…6 The calculated magnetic moment in graphene with vacancies varies broadly (1.04 1.84 µ B ), depending on the vacancy concentration. 32,[37][38][39] In case of silicene and germanene, several theoretical studies have focused on the structures, energetics and transport of vacancies. Berdiyorov and Peeters reported a significant role of vacancies in tuning the electronic structure of silicene and reducing the thermal stability of silicene.…”