Effect of Amine-Based Organic Compounds on the Work-Function Decrease of Graphene

We have demonstrated that amine and alkyl groups, applied by a simple spin-coating method, can provide an n-type doping effect on graphene sheets. The organic compounds used in this work are based on amine, phenyl amine, butylphenyl amine, benzoylphenyl amine, and tolylvinylphenyl amine groups. The increases in sheet resistance, decreases in transmittance and work function, and shifts of the G peak to higher wavenumbers and the 2D peak to lower wavenumbers in the Raman spectra indicate that graphene was doped to n-type after the graphene sheets were spin-coated by the amine-based compounds. In particular, graphene doped with butylphenyl amine showed the strongest n-type effect among all of the samples because butylphenyl amine has the strongest binding energy with graphene sheets and disperses in nonpolar solvents, suggesting that the binding energy with graphene sheets and the degree of dispersion in solvents are important factors in the doping process. Molecular calculations based on density functional theory confirmed the n-type properties of graphene doped with amine-based compounds. These results suggest that amine and alkyl groups play a crucial role in the n-type doping of graphene.