An electrochemical and X-ray photoelectron spectroscopic study into the mechanism of Ti + W alloy etching in H 2O 2 solutions

Abstract

One of the most striking aspects of etching Ti + W alloys in aqueous H 2O 2 solutions is the decrease in etch rate under improved mass transport conditions. This aspect was studied by X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. XPS results showed that Ti dissolves preferentially and that a W oxide film (WO x) is formed at the surface during etching. The valence of W in this oxide is between IV and VI. The WO x film is thicker for a rotating Ti + W sample than for a stationary one. The electrochemical experiments showed that H 2O 2 is reduced at the WO x covered surface. Intermediates of this reduction reaction (most probably OH . radicals) interact with WO x and enhance further oxidation into the soluble WO 5 2− ion. Removal of these intermediates by improved mass transport conditions and/or better supply of the stabilizing agent in H 2O 2 solutions results in lower etch rates.