Relationship between crystalline orientations of gold and surface-enhanced Raman scattering spectroscopy of polypyrrole and mechanism of roughening procedure on gold via cyclic voltammetry

The polypyrrole (PPy) films were electrochemically deposited on roughened gold substrates with different predominant crystalline orientations of (111) and (220), respectively. Gold was roughened via a cyclic voltammetry procedure. The result indicates that the (220) crystalline orientation of gold was partially changed into (111) one after gold was roughened with oxidation-reduction cycles (ORC) treatment. The surface-enhanced Raman scattering (SERS) spectroscopy of PPy deposited on gold with predominant (111) orientation exhibits higher intensity and more excellent resolution. Meanwhile, the redox behavior of gold and the resulting complex in ORC were strongly sensitive to the crystalline orientation. A mechanism of the roughening procedure on gold was also proposed to illustrate the resulting complex and its effect on the SERS enhancement.