Effects of interaction of electron donor and accepter molecules on the electronic structure of graphene

Effects of interaction of graphene with electron donor and acceptor molecules have been investigated by employing Raman spectroscopy. The G band softens progressively with the increasing concentration of tetrathiafulvalene (TTF) which is an electron donor while the band stiffens with increasing concentration of tetracyanoethylene (TCNE) which is an electron-acceptor molecule. Both TTF and TCNE broaden the G-band. The 2D band position is also affected by interaction with TTF and TCNE. The intensity of the 2D-band decreases markedly with the concentration of either. The ratio of intensities of the 2D and G bands decreases with increase in TTF and TCNE concentrations. The electrical resistivity of graphene varies in opposite directions on interaction with TTF and TCNE. All these effects occur due to molecular charge-transfer, as evidenced by the observation of charge-transfer bands in the electronic absorption spectra.