Effect of High gate-voltage application on the molecular adsorption on Graphene*

The electronic properties of graphene are well tuned by guest chemical species due to its 2D nature. We have clarified that the charge transfer between molecules and graphene proceeds by a electrochemical process based on the fact that the kinetics of the charge transfer decreases with down and up shift of the Fermi energy of graphene for electrons and holes, respectively. In this study, the electrochemical potential is widely varied by graphene FET in order to induce various electro chemical reactions for the charge transfer phenomena. In the case of the hole doping by oxygen adsorption on graphene, the lower gate-voltage, the slower hole doping reactions as we reported [1] and finally no charge doping occurs at enough higher gate-voltage around -80 V. Interestingly, further lowering of the gate-voltage results in the electron doping by the oxygen adsorption on graphene. Even in this condition, the doping kinetics are accelerated by the presence of water molecule. This suggests that different electrochemical reactions are responsible for the charge transfer by oxygen adsorption on graphene between the higher gate-voltage region and lower voltage region.
[1] Y. Sato, et al Nano Lett., 11 (2011) 3468