Role of surface instabilities in mixing and oxidation mechanisms of bilayered Y/Zr films at elevated temperature

Two-layered Y/Zr films (0.1 mm thick of Y film on 1.0 mm thick of Zr film) have been deposited on silicon substrate and oxidized in three different ways: (i) thermal annealing in air; (ii) oxidation under high-flux low-energy ion irradiation, and (iii) oxidation under high-flux solar energy irradiation in air. The characterization of coating structure was carried out by X-ray diffraction. Secondary ion mass spectrometry was used for recording depth profiles of the most important elements in films and at interface. The surface topography was monitored by atomic force microscopy and scanning electron microscopy. The oxidation kinetics were studied in the temperature range 350–800 8C. It is shown that oxidation kinetics significantly depends on the way of surface treatment. Homogeneous nanocrystalline YSZ films have been obtained after 180 min at 600 8C oxidation in air, after 30 min at 450 8C treatment in low-pressure oxygen plasma and after 20 s irradiation at 800 8C by flux of solar energy in air. The atomic mixing and oxidation mechanisms are discussed. Emphasis is given on the analysis of surface instabilities acting as possible driving force for the intermixing and restructuring of Y/Zr layers with continuous supply of oxygen through the surface. # 2003 Elsevier B.V. All rights reserved