Electrochemical Synthesis of Oriented CuO Coatings on Stainless Steel Substrates: Solution-Mediated Control over Orientation

Anodic oxidation of an alkaline (pH>13) copper tartrate bath results in the deposition of an adherent CuO coating. The orientation of the coating depends on the pH of the bath and thickness of the deposit. At pH 13, deposits are unoriented, whereas at pH 13.2 the deposits are oriented along the [020] direction. At pH 13.3, the orientation switches to [110] and at pH 13.5 to [100]. The switch in orientation takes place over a very narrow range of pH values. Scanning electron micrography reveals that the particles have an ellipsoidal morphology. This is a consequence of twinning combined with rapid crystal growth normal to the 010 plane. Different orientations are obtained by the rotation of the ellipsoidal particles about the minor axis through different angles. The minor axis of the ellipsoids is parallel to the c-crystallographic axis.