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 roug hened silver substrates by laser ablation of Fe3O4 and gamma-Fe2O3, ta rgets. 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 identi cal to SER spectra of the passive film formed on iron in the same solu tion that is, all were characterized by a strong broad peak centered a t approximately 530 to 580 cm(-1). The 33 to 37 nm thick films were po tentiodynamically 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 fo rmed by laser ablation of Fe3O4 exhibited spectra partially resembling the iron passive film and partially resembling the normal Raman spect rum of bulk Fe3O4. The 153 nm and 1.4 mu m thick films formed from Fe2 O3 and 1.3 mu m thick films formed from Fe3O4 gave very weak Raman spe ctra that were characteristic of the hulk oxides. and did not resemble the iron passive film. The observation that the SER spectra from pass ive films on iron, as measured in this and previous studies, are ident ical 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 assign ment of spectral features in future, as well as past SERS studies.