The influence of thermal annealing to remove polymeric residue on the electronic doping and morphological characteristics of graphene

The impact of polymer removal by forming gas and vacuum annealing on the doping, strain, and morphology of chemical vapor deposited (CVD) and mechanically exfoliated (ME) graphene is investigated using Raman spectroscopy and atomic force microscopy (AFM). The behavior of graphene exposed and unexposed to polymer is compared. It is found that the well-known doping effect after forming gas annealing is induced in CVD–ME graphene by polymeric residue/hydrogen-functionalization. Further, forming gas annealing of ME graphene is shown to induce strain via pinning of the graphene layer to the substrate. It is found that vacuum annealing removes most polymeric residue, with minor doping and strain effects. Finally, a study of AFM step height and roughness measurements provides a comprehensive understanding of those annealing-based processes which create morphological changes and directly influence doping and strain in the graphene layer, such as removal of polymer, removal of the interfacial graphene–substrate water layer, environmental doping effects and deformation of the graphene layer.