Incorporation of Zinc in Electroless Deposited Nickel-Phosphorus Alloys II. Compositional Variations Through Alloy Coating Thickness

The zinc state in Ni-Zn-P coatings electrolessly plated from alkaline solution with citrate as the main complexing agent was examined by combining X-ray photoelectron spectroscopy (XPS) and scanning Auger electron spectroscopy (SAES). It was demonstrated that zinc at the surface of Ni-Zn-P films was in an oxidized state. The SAES sputter-etch depth profiling showed that zinc incorporated within the coating was always accompanied by oxygen with an almost parallel profile, independent of the substrate. Analyzing the observed chemical shift of the LMM peaks in SAES and XPS spectra, it seems reasonable to assume that zinc is incorporated in the coating in a partially oxidized state. The parallel profiles of all components of the alloy indicated their actual codeposition and suggested almost homogeneous distribution through the film thickness in this type of Ni-Zn-P coatings. The elemental profiles in specially designed two-layer samples (Ni-Zn-P over Ni-P) demonstrated the significant reduction in phosphorus content caused by zinc codeposition, which started at the interface between Ni-P and Ni-Zn-P. © 2001 The Electrochemical Society. All rights reserved.