Investigation of Cation‐Transport Processes during Anodic Oxidation of Duplex Layers of Tantalum on Niobium by the Use of Rutherford Backscattering and Nuclear Microanalysis

Abstract

It has been shown that, during anodic oxidation of superimposed metallic films of tantalum on niobium, a regime exists in which the growth laws of niobium substrate oxidation are the same as those found during pure niobium oxidation. Using ⁴He Rutherford backscattering techniques we have shown that the order of cations is partially inverted in the oxide films. A pure niobium oxide region near the metal is covered by a layer in which both cations (Ta and Nb) are present. The fraction of niobium atoms present in this last region was measured as a function of oxidation potential, tantalum deposit thickness, current density, and temperature. It was found that, for sufficiently high oxidation potentials, is voltage independent and lies around 25%. increases with increasing current density or decreasing temperature, while is independent of tantalum layer thickness for thicknesses above 6 nm. Possible cation transport mechanisms corresponding to these observations are proposed and discussed.