Abstract: Iridescent chromium films prepared by cathode electrodeposition on Ni substrate are studied by XPS and UPS. The mechanism of the film formation is also studied by electrochemical method. The results show that the films consist of three layers: (1) Surface layer, about 30 nm thick, containing Cr(Ⅵ) and Cr(Ⅲ)[Cr(OH)₃, CrOOH and Cr₂O₃], which were formed by adsorption of chemical compounds near the elecctrode; (2) Intermediate layer, about 200 nm thick, mainly composed of Cr₂O₃produced by electroreduction of CrO₃; (3) Interfacial layer connected with the substrate, about 150 nm thick, comprised of Cr₂O₃, Cr and Ni. The third was formed by reduction of the oxide films on the electrode. The colour of the films arises from the absorption of light of the unpaired 3d electrons under the influence of O₂-distorted octahedral iigand field and from the light interference in the thin films.

Key words: Iridescent chromium films, CrO₃, Cathode films, XPS, UPS