POTENTIAL-DEPENDENT AND PH-DEPENDENT SURFACE-ENHANCED RAMAN-SCATTERING OF P-MERCAPTOANILINE ON SILVER AND GOLD SUBSTRATES

The reaction of p-mercaptoaniline (p-MA) with rough silver or gold surfaces delivers robust organically modified surfaces exhibiting intense surface-enhanced Raman scattering (SERS). The SERS spectra strongly depend on the pH of a surrounding solution as well as on the electrostatic potential applied. We investigated these effects on the SERS spectra of the immobilized p-MA. Two states of the adsorbate can be distinguished by their spectra: the aromatic state existing in acidic solutions and at negative electrochemical potentials and a quinonoidic one being present in neutral and alkaline solutions or at more positive potentials. The transition between these states is related to pH- and potential-induced protonations and deprotonations of the amino group. The SERS signals are easily observable using low-power diode laser excitation.