Studies of the low temperature oxidation of alloys by X-ray photoelectron spectroscopy: CuZn

Abstract

X-ray photoelectron spectroscopy (ESCA) has been employed to study the oxidation of α-CuZn alloys in the range, 65% <Cu <80%. The process was conducted in air at room temperature, with moderate humidity, producing what has been previously labeled “natural” passivation. A combination of sputter etching and controlled growth studies have been employed to document the entire passivation process from inception to termination. The layering features have been described with emphasis on the resulting physical chemistry. The initial oxide layer formed, ZnO, seems to produce a depletion of Zn 0 in the outer surface of the alloy. Cu 0 appears trapped in this relatively thick (50–100 Ȧ) ZnO layer. After the ZnO growth has extensively formed, an overlayer of copper oxides begins to grow, first with Cu 2O formation, then followed by a terminal Cu(II) layer, composed of CuO and Cu(OH) 2. The latter layers are noticeably thinner than the corresponding oxide growth on pure Cu, perhaps due to the relatively small amount of Cu 0 in the ZnO sublayer. A discussion of the Cabrera-Mott growth characteristics and their connection to the semiconductor status of the resulting oxides is included.