Low damage pre-doping on CVD graphene/Cu using a chlorine inductively coupled plasma

This study reports a novel approach for chlorine doping of graphene using low-energy plasma in a low damage inductively coupled plasma (ICP) system, which results in significant reduction (∼60%) of the sheet resistance while maintaining high optical transparency. The chemical vapor deposited graphene on Cu (graphene/Cu foil) was directly doped with low-damage chlorine plasma before transferring to the substrate, i.e. pre-doped, in addition to the normal doping conducted after the transfer. Some of the pre-doped chlorine remained on the graphene surface even after the wet transfer to the substrate due to strong C-Cl bonds formed at the graphene defect site. This technique allowed us to achieve the highest chlorine doping ever reported, 47.2%, through combination of pre-doping with conventional doping. By this additional pre-doping on graphene/copper foil (that is, 90 s pre-doping + 90 s normal doping), a monolayer of graphene with very low sheet resistance of 240 Ω/sq could be obtained without sacrificing the optical transmittance (>97.7% at 550 nm wavelength).