FT-IR,XPS,and AES Studies on Surface Films of W-S-Cu Cluster Compounds on Copper

Abstract

Conversion films of W-S-Cu cluster compounds with a metallic luster of various shades and colors have been applied to a copper surface by the interface reaction between WS^2–₄ and the Cu₂O layer due to the formation of W-S-Cu bonds; their colors have been changed by heating treatment. FT-IR, XPS, and AES determinations were carried out, and the results show that W-S-Cu, terminal W-S, and terminal W-O bonds exist in the cluster films. The films are composed of the elements W, S, Cu, and O, the valences of those elements being +6, −2, +1, and −2, respectively. The films are all multimolecular layers and can be described as an overlapping double-layer structure. The outer (upper) layer has been oxidized to some extent. WS₂ clusters remain in the inner (lower) layer. As for the heated films, they are also composed of W, S, Cu, and O, but the content, distribution, and valence state of each element and the structure of the films change. The first layer of the heated films is largely composed of CuO. The second is a mixture of CuO and Cu₂O. The third is an intermediate layer. The fourth is composed of W, S, Cu, and O; the valence of W remains ambiguous, while the other three are −2, +1, and −2, respectively. WS₂ units survive the heating in this layer. There is still another intermediate layer between the whole film and the copper surface confirming the penetration of tungsten and sulfur. The colors of the unheated and the heated films are probably caused by W-S-Cu bonds and a statistical distribution and overlapping of various molecular layers since the films are complicated multicomponent and multilayer systems. The disparity of colors before and after heating treatment is caused by the change of composition and structure of the films.