Effect of Surface Adsorbates on Carrier Transport in Graphene

摘要

Interaction of graphene with adsorbates on its surface was investigated by analyzing two important electrical parameters - graphenes carrier density and mobility, recorded simultaneously. NH₃ and NO₂ molecules were exposed to the graphene separately as ionized donor and acceptor, respectively. With the exposure of NO₂ on the graphene, graphenes carrier density was observed to be increasing monotonically, and NH₃ exposure showed an opposite behavior as expected. Even though gas molecules attached on the graphene supposed to be working as ionized impurity scattering centers, graphenes mobility did not drop for both cases - the mobility dropped with NO₂ exposure while it increased with NH₃ exposure. To understand the mechanism, we proposed a theoretical model here which includes ionized impurities both from substrate and external adsorbates influencing the graphenes mobility change as one system. A strong donor C₉H₂₂N₂ molecules effect on the graphene was also examined. Its high electron donating effect transformed graphene from p-type to n-type, while the mobility change during the whole transformation still followed the proposed model which further verified the model's reliability.