Characterization of porous oxide antimony films

O. E. LINAREZ PÉREZ; M. LÓPEZ TEIJELO

Simposio; 10th Symposium on the passivation of metals and semi-conductors and the properties of thin oxide layers; 2011

The electrochemistry of ?valve metals? (Al, Ti, Zr, Ta, Bi, etc.) has been extensively studied due to their applications in optical films, microelectronics, capacitor manufacturing as well as corrosion protection. Recently, the formation of self-organized nanostructures and patterns of metal oxides, mainly porous alumina and titania, has attracted also a great interest. Despite considerable work has been carried out, no universally accepted model in the case of the ?valve? metals has been devised to explain the mechanism of anodic oxide growth. On typical valve metals the growth has been described in terms of the high field model (HFM) as proposed by Verwey and Cabrera and Mott, the point defect model (PDM) developed by Macdonald1 and by the model proposed by Bojinov2, based on a surface charge approach. Furthermore, depending on formation conditions, the existence of pores or pits can modify the film properties. Usually, the analysis based on electrochemical impedance spectroscopy (EIS) measurements, may provide valuable information on electrical properties and structure. Nevertheless, in most cases the films are considered homogeneous in thickness and the effect of the formation of pores and/or pits has not been considered in detail. In this work, the growth of antimony oxide films on Sb in chloride solutions in a wide range of conditions for oxide growth is analyzed. Electrochemical impedance spectroscopy (EIS) as well as ellipsometric results for the anodic films are correlated with the morphology obtained by AFM. As opposite to results obtained in phosphate solutions where anodic films are essentially homogeneous in thickness, porous films are obtained in chloride solutions. Impedance results are compared with predictions of models in terms of passive electronic elements in electrical equivalent circuits. Impedance results are interpreted in terms of the Surface Charge Assisted High-Field Migration Model2 (SCAHFMM) for anodic film growth. Porous structure is also incorporated in the impedance analysis and equivalent circuits for taking into account the formation of pits (?active pit model?3,4) are proposed. The dependence of the values obtained for the different circuit elements with film formation potential and electrolyte concentration is also discussed. Film porous nature and its dependence with formation conditions are corroborated by AFM. References 1 D.D. Macdonald, J. Electrochem. Soc. 139 (1992) 3434. 2 M. Bojinov, Electrochim. Acta 42 (1997) 3489. 3 J. Hitzig, K. Juttner, W. Lorentz, W. Paatsch, J. Electrochem. Soc. 133 (1986) 887. 4 K. Juttner, Electrochim. Acta 35 (1990) 1111.