A SURFACE ANALYTICAL STUDY OF THE FORMATION AND ADHESION OF CHROMIUM FILMS ON ALUMINA

Chromium-alumina bonding was characterized by using surface analysis techniques. The metal-ceramic interface was produced by vapour deposition of the metal at room temperature in an ultra-high vacuum chamber equipped with AES (Auger electron spectroscopy), EELS (electron energy loss spectroscopy), and XPS (X-ray photoelectron spectroscopy) facilities. Two kinds of alumina surface were used as the support for Cr condensation: a stoichiometric (1 x 1) alpha-Al2O3 surface (called the perfect surface or class a) and an oxygen-deficient surface giving rise to LEED patterns (called the reduced surface or class b). It is shown that on perfect surfaces the Cr film grows layer by layer but on reduced surfaces a three-dimensional (3D) growth process is observed. These results are explained by a strong chemical interaction between Cr and the class a surface, and by 3D nucleation on defect sites on the class b surface. After ageing for a few days under vacuum, the thick Cr film deposited on the reduced surface delaminates. This behaviour can be interpreted as competition between Cr atoms and Al ions to form an interfacial oxide layer.