Although the doping of graphene grown by chemical vapor deposition is crucial in graphene-based electronics, noninvasive methods of n-type doping have not been widely investigated in comparison with p-type doping methods. We developed a convenient and robust method for the noninvasive n-type doping of graphene, wherein electrons are directly injected from sodium anions into the graphene. This method involves immersing the graphene in solutions of [K(15-crown-5)2]Na prepared by dissolving a sodium-potassium (NaK) alloy in a 15-crown-5 solution. The n-type doping of the graphene was confirmed by downshifted G and 2D bands in Raman spectra and by the Dirac point shifting to a negative voltage. The electron-injected graphene showed no sign of structural damage, exhibited higher carrier mobilities than that of pristine graphene, and remained n-doped for over a month of storage in air. In addition, we demonstrated that electron injection enhances noncovalent interactions between graphene and metallomacrocycle molecules without requiring a linker, as used in previous studies, suggesting several potential applications of the method in modifying graphene with various functionalities.
Keywords: electron injection; graphene; metallomacrocycle; n-type doping; noncovalent interaction; sodium anion.