Influence of α-Al2O3 (0001) surface reconstruction on wettability of Al/Al2O3 interface: A first-principle study

Influence of alpha-Al2O3 (0001) surface reconstructions on the wettability of Al/alpha-Al2O3 system was theoretically examined by employing density functional theory (DFT). The (root 31 x root 31) R9 degrees reconstructed surface was modeled by removing two outmost oxygen layers from the (1 x 1) stoichiometric alpha-Al2O3 (0001) surface while the unreconstructed surface with Al termination was simulated for contrast. Interface structure, electronic analysis, work of adhesion (W-ad) and deduced contact angle theta of the interface systems were presented. We found that though the (1 x 1) stoichiometric alpha-Al2O3 (0001) surface is most stable, agreeing with other theoretical studies and experimental evidence, interfacial systems of Al/alpha-Al2O3 with (root 31 x root 31) R9 degrees reconstruction has the largest work of adhesion (2.05 J/m(2)), far larger than that of the Al/alpha-Al2O3 system with (1 x 1) stoichiometric alpha-Al2O3 (0001) surface (1.03 J/m(2)). For unoxidized condition at 1073 K, the contact angle theta deduced from the calculated W-ad for the interface system with (1 x 1) stoichiometric alpha-Al2O3 (0001) surface was around 95 degrees, while that of the interfacial system with (root 31 x root 31) R9 degrees reconstruction was only about 38 degrees. If oxidation of liquid Al occurs, the contact angle for both systems will be further decreased. The significant wettability improvement occurs with surface reconstructions of alpha-Al2O3 results from the formation of a metallic Al layer on the reconstructed alpha-Al2O3 surface. Our calculation results provide theoretical verifications for the improved wettability observed experimentally in Al/alpha-Al2O3 systems with surface reconstructions. (C) 2014 Elsevier B.V. All rights reserved.