Interfacial interaction and wetting in the Ta₂O ₅/Cu-Al system

Wettability and interfacial interaction of the Ta₂O ₅/Cu-Al system were studied. Pure Cu does not wet the Ta ₂O₅ substrate, and improved spreading is achieved when relatively a high fraction of the active element (∼40 at.% Al) was added. The Al₂O₃ and AlTaO₄ phases were observed at the Ta₂O₅/Cu-Al interface. A thermodynamic evaluation allowed us to suggest that the lack of wetting bellow 40 at.% Al is due to the presence of a native oxide, which covers the drop. The conditions of the native oxide decomposition and the formation of the volatile Al₂O suboxide strongly depend on the vacuum level during sessile drop experiments and the composition of the Cu-Al alloy. In our case, Al contents greater than 40% provides thermodynamic conditions for the formation of Al₂O (as a result of Al reaction with Al₂O₃) and the drop spreading. It was suggested that the final contact angle in the Ta₂O ₅/Cu-Al system (50°) is determined by Ta adsorption on the newly formed alumina interlayer.