Characterization of anodic oxide films

Vita.Anodic oxide films are used extensively in a variety of applications. This study focuses on characterization of anodic oxide films grown on valve-type metals (Ti, Zr, Nb and Hf) under a variety of experimental conditions. Physical and growth characteristics of the anodic films were compared for the systems studied. Surface characterization of the film surface was accomplished through the use of X-ray photoelectron spectroscopy (XPS). Information provided by this technique included identification of the surface species, the oxidation state of the surface species, and trends in relative surface species concentrations. Bulk characteristic were determined through depth profiling in conjunction with XPS of select samples, and through the use of Rutherford backscattering spectroscopy (RBS). The depth profiling provided information regarding ion-induced reduction, identification of species below the surface and trends in relative concentration. Information provided by RBS included oxide layer thickness, stoichiometric composition of the oxide layer and concentration of the incorporated species. Of particular interest in this study is the incorporation of foreign species from the electrolytic solution during the growth process. This project examined oxides of selected valve metals grown in a variety of forming solutions, under varying conditions. The growth time for niobium, zirconium and hafnium was unaffected by changing the growth temperatures, and increased with increasing applied voltages. Titanium oxide displayed two growth regimes for all systems studied, supporting evidence that a structure change occurs during the growth process. Surface characterization showed that anion incorporation was observed for all systems studied. A close association of the sodium and anionic species from the forming solution was noted. Depth profiling used with XPS showed a continued association below the surface between the sodium and anion species. Evidence of ion-induced reduction is shown for niobium and titanium, but zirconium appeared to be unaffected. RBS data support earlier work that led to the proposal that anions are incorporated in a periodic fashion. This was observed for all metals grown in the presence of sodium tungstate. A film growth model is suggested based on periodic precipitation reactions