Screening of charge impurities: an alternative mechanism for the detection of gases on graphene and nanotubes

by Jorge O. Sofo (The Pennsylvania State University)

Monday 19 Jan 2015, 16:00 → 18:00 Europe/Rome

Sala Direzione INFN (Dip. di Fisica - Edificio G. Marconi)

In gas detection with carbon nanotubes or graphene, the change in conductivity due to molecular adsorption has been generally attributed to a change in carrier density due to charge transfer. However, these explanation does not take into account several important physical effects. 1) The counter-ions left after the charge transfer process lower the mobility and might compensate the effect of extra carriers. 2) The experimental results are not consistent with variations in the ionization potential or electron affinities of the adsorbates. We proposed an alternative explanation based on the screening produced by the molecules on the charge impurities of the substrate. Given that the scattering with these impurities is the main limiting factor of the conductivity, the change in screening produced by the mol! ecules has a substantial effect on the conductivity. Our model is based on the dielectric function of graphene at the RPA level and the impurity scattering in the first Born approximation. With this model we explain the increase in conductivity and we determine optimum parameters to increase the sensitivity of the devices.