Surface enhanced Raman spectroscopy study of the galvanostatic reduction of the passive film on iron

Surface enhanced Raman (SER) spectra were acquired continuously with time during the galvanostatic reductive dissolution of the passive film grown on iron in borate buffer (pH 8.4) by anodic polarization at one of three different potentials, + 1000, + 600, and 0 mV (SCE). Complementary measurements of the SER spectra of the passive film were made during the formation of the film by galvanostatic anodic polarization. The results indicate that the passive film consists of a layered structure with at least two components. The inner layer is most likely Fe3O4 and the outer layer is primarily an Fe(III) species with an SER spectrum that is characterized by an intense, broad peak centered in the range 570-524 cm(-1). The outer layer may also contain gamma-Fe2O3 that is associated with an SER spectroscopy peak at 690 +/- 5 cm(-1). (C) 1999 The Electrochemical Society. S0013-4651(99)03-052-9. All rights reserved.