Abstract
Nominally uniform and amorphous sputter‐deposited binary alloys (Al‐Ta, Al‐Nb, Al‐Zr, Al‐Ti) prepared by conventional magnetron sputtering of valve metals are shown in reality to comprise fine scale, multilayered alloy films for particular conditions of deposition. The layers, each about 1 nm thick, are the result of a periodic modulation of the composition of the alloy film during the deposition process, leading to layers relatively enriched and depleted in the alloying element compared with the mean composition of the alloy. During subsequent anodizing at high Faradaic efficiency, amorphous anodic films, that are mainly uniform in thickness, composition and structure, are formed on the sputter‐deposited alloys indicating that the heterogeneity of the substrate is not imparted to the bulk of the anodic film material. This is apparently due to the smoothing effect of the ionic transport processes during anodic film growth. However, near to the alloy film/anodic film interface, significant variations in the composition of the anodic film, associated with the heterogeneity of the substrate, are evident, suggesting that the variation in substrate composition is of importance to the formation and subsequent composition of relatively thin anodic films and the inner regions of thick ones. Consideration is given to the use of multilayered alloy films as investigative probes of anodic film growth, in particular of the migration of Al3+ ions and cations of the alloying element under the electric field, and the formation of anodic film material at the alloy film/anodic film interface. Of wider relevance, the heterogeneity of the substrate would be of critical importance to the use of sputter‐deposited alloys in studies of dealloying, passivation and pitting as well as in the practical use of such sputter‐deposited materials.