INTERFACE CHEMISTRY, WETTING BEHAVIOR AND ADHESION ENERGY IN METAL-OXIDE SYSTEMS

Pure non-reactive metals develop weak interactions with iono-covalent oxides (insulators) which can be both physical (Van der Waals) and che mical (low density interfacial electronic states). As a result, the in terface is weak and non-wetting is generally observed, the contact ang le theta being larger than 90 degrees. Reactivity can promote wettabil ity and adhesion by two different mechanisms depending on the strength of the interactions between the metal and dissolved oxygen. For moder ate O-metal interactions, the liquid-side of the interface can be modi fied by adsorption of O-metal clusters, the oxygen coming from the dis solution of the oxide substrate. This mechanism can lead to a decrease of theta down to approximate to 60 degrees and to energetically moder ate interfaces. For strong O-metal interactions precipitation at the s olid-side of the interface of a new phase can occur. When this new pha se features metallic bonding, wetting can be strongly improved and nea rly perfect wetting and strong interfaces can be obtained.