An ability to induce and control an electrical and/or optical bandgap is an important consideration for graphene material science and devices. Here we report the emergence of an electrical bandgap of up to 150 meV in bilayer graphene through the interaction with physisorbed molecules, such as F2-HCNQ, DMC, DDQ and TTF, on one surface of bilayer graphene.  The electrical bandgap is found to scale linearly with induced carrier density though a slight asymmetry is found between n-type dopants, where the bandgap varies as 47 meV/10 cm, and p-type dopants where the bandgap varies as 38 meV/10 cm. Optical gaps corresponding to the important 3-5 μm region are also found. The emergency of bandgap is explained in terms of the asymmetric charge distributions on the upper graphene layer, which is in contact with the molecules. The high binding energy found upon adsorption of some of these molecules results in an attractive way to a permanent bandgap. Comparison is made with electrical bandgaps induced using dual gate geometries and prospects for graphene based devices are explored.
 Alexander J. Samuels and J. David Carey, ACS Nano , 2790 (2013).