Magnetite, goethite, and lepidocrocite thin films have been electrochemically grown on titanium substrates by the anodic oxidation of ferrous ions in a 0.01 M FeSO 4 ͑NH 4 ͒ 2 SO 4 •6H 2 O + 0.04 M CH 3 COOK, pH 6.0, aqueous solution. It is demonstrated that the deposition potential can be used as a tool to tune the obtainment of the different pure phases of the iron oxide-oxyhydroxides thin films. Results of an exhaustive structural characterization, a morphological study, and X-ray photoelectron spectroscopy characterization are presented.
The optical properties of nanoporous alumina (Al 2 O 3 ) prepared by electrochemical anodization of aluminum foils are studied. The samples show an ordered array of nanometric sized pores. Their reflectance spectra show an absorption edge in the UV that shifts into the visible with anodization temperature. A strong photoluminescence (PL) in the blue-green spectral range is also shown. The PL spectra shift in the same direction as the reflectance. The PL spectra were also measured at low temperatures. The results are best interpreted assigning the PL to oxygen vacancies. [6,7]. The knowledge of the optical properties of PAA, and their dependence with the preparation method, is important for the study of the previously mentioned composite structures [3,8]. This is the main objective of the present work. The relation between the optical and structural properties of PAA has been studied by spectroscopic ellipsometry [9]. Similar ellipsometric studies have recently identified resonant transitions in the IR and UV regions [10]. It has been also shown that PAA PL depends on the preparation conditions, like annealing [6] or substrate [11,12]. In this work reflectance and absorption of PAA samples are investigated and correlated with the PL variations. They depend on the preparation (anodization) temperature (T A ), and more weakly on the measuring (sample) temperature (T s ). This behaviour is expected for single ionized oxygen vacancies which predominates for lower T A .
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