Journal of the Electrochemical Society, Vol.144, No.5, 1604-1609, 1997
Surface-Enhanced Raman-Spectroscopy of Iron-Oxide Thin-Films - Comparison with the Passive Film on Iron
Thin films (33 nm to 1.4 mu m) of iron oxides were deposited onto roughened silver substrates by laser ablation of Fe3O4 and gamma-Fe2O3, targets. Surface enhanced Raman (SER) spectra from the 33 to 37 nm thick films, both in air and in aqueous berate buffer (pH 8.4), were identical to SER spectra of the passive film formed on iron in the same solution that is, all were characterized by a strong broad peak centered at approximately 530 to 580 cm(-1). The 33 to 37 nm thick films were potentiodynamically reduced in berate buffer. Electrochemical reduction of the ablated iron oxide films initiated at a more cathodic potential than that found for the passive film on iron. Thicker 178 nm films formed by laser ablation of Fe3O4 exhibited spectra partially resembling the iron passive film and partially resembling the normal Raman spectrum of bulk Fe3O4. The 153 nm and 1.4 mu m thick films formed from Fe2O3 and 1.3 mu m thick films formed from Fe3O4 gave very weak Raman spectra that were characteristic of the hulk oxides. and did not resemble the iron passive film. The observation that the SER spectra from passive films on iron, as measured in this and previous studies, are identical to the SER spectra from thin films laser ablated from targets of Fe3O4 and Fe2O3 (in both cases, resulting in iron oxides most probably hydrated and of small par-tide size) permits the more accurate assignment of spectral features in future, as well as past SERS studies.
Keywords:IN-SITU XANES;ALKALINE-SOLUTIONS;CORROSION FILMS;BORATE BUFFER;SPECTRA;CHROMIUM;SCATTERING;MOSSBAUER;NICKEL;ALLOYS