Doping efficiencies and physisorption of small molecules on graphene
Since its first successful isolation in 2004, graphene has attracted a huge interest in the scientific community due to its unique electronic, optical and mechanical properties. Graphene is already considered of such importance to the fields of electronics and solid state physics that the 2010 Nobel Prize for physics was awarded to Geim and Novoselov for “groundbreaking experiments regarding the two-dimensional material graphene“.
Stimulated by recent reports of single molecule detection using graphene based sensors; Ab initio calculations have been employed to study the doping efficiencies of environmental toxic gases NO2, NO and NH3 on graphene.
We have used both the local density approximation (LDA) and the generalised gradient approximation (GGA) to obtain the molecular binding energies and have employed the Hirshfeld charge partitioning method to calculate the electron charge transfer. Spin polarised calculations were used for the open shell molecules (NO and NO2) and we explored the effects of different adsorption sites and orientations.
Doping efficiencies and physisorption of small molecules on graphene: Understanding charge transfer, Alexander J. Samuels and David Carey, American Physical Society March Meeting, Dallas, March 2011.
Doping efficiencies and physisorption of small molecules on graphene, Alexander J Samuels and J David Carey, Oral presentation at the 1st UK-Japan Graphene workshop, Lancaster University, February 2011.
Molecular doping and charge transfer of graphene, Alexander J Samuels and J David Carey, European Materials Research Society, Spring Meeting, Strasburg, June 2010.
Charge Transfer and Environmental Doping of Graphene, Alexander J. Samuels and David Carey, Materials Research Society, Spring meeting, San Francisco, April 2010.
It was found that for all orientations of the molecule and using both LDA and GGA functionals that the adsorption of NO2 results in p-type doping of graphene with 0.06e transferred to the molecule. For NO, LDA calculations show a p-type behaviour with 0.03e transferred per molecule but both n and p-type doping of 0.003 – 0.004 e/molecules is calculated using the GGA functional.
Finally for NH3 both donor and acceptor behaviour (0.03 – 0.05 e/molecule) is calculated. In all cases the origin of the doping is related to the relative position of the HOMO and LUMO molecular orbitals with respect to the Dirac point of graphene and low energy density of states.