Evidence of chemical effect on surface-enhanced Raman scattering of polypyrrole films electrodeposited on roughened gold substrates

In this study, polypyrrole (PPy) films were electrochemically deposited on gold substrates roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 N KCl. The results indicate that the intensity of surface-enhanced Raman scattering (SERS) of PPy significantly depends on the ORC scans. Correspondingly, the superficial complex formed on the roughened gold has a strong influence on the SERS effect. The optimum Raman signal of PPy deposited on Au roughened with 25 scans in ORC is ca. 300 times larger than that of PPy deposited on Au without ORC treatment. Meanwhile, the (220) face of Au partly changes into the (111) face with the lowest surface energy after ORC roughening. Toward higher frequency, a shift of C=C backbone stretching of PPy situated at ca. 1575 cm^-1 in the SERS spectrum was found which is attributed to interfacial charge transfer from electrodeposited pyrrolylium nitrogen to the roughened gold. Furthermore, this study shows that the SERS enhancement of PPy electropolymerized on roughened Au mainly arises from the chemical effect between PPy and the Au-containing complex.