Optical quality controllable wet chemical doping of graphene through a uniform, transparent and low roughness F4 TCNQ/MEK layer
Controllable chemical doping of graphene has already proven very useful for electronic applications, but when turning to optical and photonic applications, the additional requirement of having both a high transparency and a low surface roughness has, to our knowledge, not yet been fulfilled by any chemical dopant system reported so far. In this work, a new method that meets for the first time this optical quality requirement while also providing efficient, controllable doping is presented. The method relies on F4 TCNQ dissolved in methyl ethyl ketone (MEK) yielding a uniform deposition after spin coating because of an extraordinary charge transfer interaction between the F4 TCNQ and MEK molecules. The formed F4 TCNQ/MEK layer exhibits a very high surface quality and optical transparency over the visible infrared wavelength range between 550 and 1900 nm. By varying the dopant concentration of F4 TCNQ from 2.5 to 40 mg ml 1 MEK, the doping effect can be controlled between Dn +5.73 x 1012 cm 2 and +1.09 x 1013 cm 2 for initially strongly p type hydrogen intercalated graphene grown on 6H silicon carbide substrates, and between Dn +5.56 x 1012 cm 2 and +1.04 x 1013 cm 2 for initially weakly p type graphene transferred on silicon samples. This is the first time that truly optical quality chemical doping of graphene is demonstrated, and the obtained doping values exceed those reported before for F4 TCNQ based graphene doping by as much as 50%