Tuning the electronic properties of doped bilayer graphene with small structural changes

Bilayer graphene simultaneously doped with two different second-row atoms (aluminum and phosphorus) was investigated employing first-principle density functional calculations (LDA, VDW-DF and M06-L). In agreement with the results obtained for bilayer graphene doped with one type of heteroatom, we found that at 1.56% atomic doping of Al and 1.56% atomic doping of P. the structure with sheets not linked is more stable than that with an Al-P bond. While all methods agreed in predicting the most stable structure, the relative energies of the structural isomers were different at the three levels of theory considered. The electronic properties of doped bilayer graphene showed an unusual variation upon small conformational changes. In effect, metallic, semiconducting and semimetallic properties were observed upon variation of the protruding orientation of the heteroatoms. The electronic properties of bilayer graphene seem to be determined by the layer whose heteroatom protrudes into the interlayer region. When Al protrudes in and P out metallic properties are observed. However, when P protrudes in and Al in a small band gap semiconductor is obtained. This work shows that the electronic properties of bilayer graphene can be more easily tuned than those of monolayer graphene because a small conformational change can induce a metallic to semiconductor transition or vice versa. (C) 2011 Elsevier B.V. All rights reserved.