Raman Enhancement of a Dipolar Molecule on Graphene

We show a large enhancement in the Raman signal from a highly polarizable molecule attached to single layer graphene. Through spatial mapping of the Raman signal and wavelength-dependent Raman measurements from a dipolar chromophore latched to a graphene/SiO2 substrate and to a bare SiO2 substrate, we show that strong electronic coupling in the hybrid structure contributes to the enhancement. The dipolar molecule is a pyrene tethered Disperse Red 1 (DR1P) that noncovalently binds to graphene. Upon comparison of the Raman signal of DR1P on single layer graphene with that on a bare SiO2/Si substrate, we found that the enhancement factor is in the range 29–69 at 532 nm excitation. As the surface coverage of DR1P on graphene increases, Raman intensity also increases and saturates at a certain concentration. The saturation of the Raman signal intensity at higher DR1P concentrations were accompanied by shifts in the G band and the 2D band of graphene due to p-doping. We further show that the Raman enhancement t...