[Raman Enhancement of a Dipolar Molecule on CVD Graphene]

The CVD graphene was chosen as the Raman enhancement substrate, graphene-enhanced Raman scattering(GERS) of dipolar molecule DREP were explored with a laser wavelength λ = 532 nm of micro-Raman spectroscopy. Upon comparison of the raman signal of DREP molecular latched to a graphene/SiO₂ substrate and to a bare SiO₂substrate, we found that the Raman signal of pure DREP molecule basically does not exist at low concentrations, until it reaches a certain concentration of 1 x 10⁻⁵ mol · L⁻¹, its Raman signal emerging and as the increasing of the concentration, Raman signal and fluorescence signal all increase. However, the raman signal of DREP molecular on the grapheme occur at the concentration of 1 x 10⁻⁷ mol · L⁻¹ and as the increasing of concentration, the raman signal increasing quickly but the fluorescence signal is not obvious. The studies were shown that graphene can achieve the Raman signal of DREP molecule enhancement, and can quench fluorescent backing off, increase the ratio of Raman signal and fluorescence signals. Comparing the GERS of DREP and DR1P molecules with different molecular dipole moment, indicating that the greater the dipole moment, the greater the enhancement factor, the degree of enhancement is stronger. Finally, we analyze the mechanism of Raman enhancement about DREP molecule on the grapheme. The dipole molecular is a pyrene terminal tethered a azobenzene molecular that was modified. There will happen the electron transfer of the pyrene terminal on the graphene interface through π-π interactions, changing the energy level of grapheme and leading to a p-doping. The mechanism of Raman enhancement are chemical mechanisms. The study of GERS of DREP molecular can help the comprehension of grapheme and the mechanism of grapheme enhanced raman scattering, for example the transfer of grapheme electron, the theory of chemical enhancement mechanism and how to separate the chemical enhancement mechanism from electromagnetic enhancement mechanism.