Band gap opening in bilayer graphene by the simultaneous adsorption of electron donating and electron acceptor molecules

•The adsorption of F4-TCNQ and radical DMBI induce a charge imbalance in bilayer graphene.•As a consequence, Mexican hat-like energy bands are observed.•Carrier mobilities were not significantly altered.

We have employed dispersion corrected density functional theory to study the adsorption of strong electron acceptor and electron donating molecules onto bilayer graphene. Radical 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) was selected as n-type dopant while 2,3,5,6-tetrafluoro-7,7,8,8-tetra-cyanoquinodimethane (F4-TCNQ) played the role of p-type dopant. When one of these molecules is adsorbed onto bilayer graphene the adsorption energies are 0.14 eV larger than those computed for monolayer graphene. However, when they are concomitantly adsorbed on opposite sides of bilayer graphene the adsorption energy is larger than the sum of the individual interaction energies due to a synergic effect obtained from the combination of electron donor and acceptor molecules. Although radical N-DMBI and F4-TCNQ shift the position of the Fermi level and induce p-type and n-type character on bilayer graphene, respectively, when they are co-adsorbed a different behavior is seen since a charge imbalance is induced. As a consequence, a gap of 0.21 eV is opened and Mexican hat-like energy bands were observed. This finding may pave the way towards the development of new graphene based field effect transistors.

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