Epitaxy and bonding of Cu films on oxygen-terminated α-Al2O3(0001) surfaces

Transmission electron microscopy studies of oxygen-terminated Cu(111)/alpha-Al2O3(0001) interfaces possessing two different orientation relationships are reported. The oxygen-terminated alpha-Al2O3(0001) surfaces were generated by utilizing an oxygen plasma at different temperatures in ultrahigh vacuum, and then Cu thin films were grown by molecular beam epitaxy on these surfaces. A clean hydroxylated alpha-Al2O3(0001) surface could be obtained by room temperature oxygen plasma cleaning. On this surface Cu films grew following the conventional face-centered cubic/hexagonal close-packed orientation relationship at room temperature, i.e., (111)Cu parallel to(0001)(alpha) and +/-[1 (1) over bar0]Cu parallel to[10 (1) over bar0](alpha), and were nearly incoherent to the substrate lattice. The high-temperature (similar to 750 degrees C) oxygen plasma treatment after a dehydroxylation process of alpha-Al2O3(001) generated an oxygen-rich surface. On this surface, the Cu films showed a thermally activated wetting by forming Cu2O-like bonding at the interface in an orientation relationship rotated by 30 degrees from the conventional orientation relationship around the interface normal: (111)Cu parallel to(0001)(alpha), and +/- [2 (1) over bar(1) over bar ]Cu parallel to[10 (1) over bar0](alpha). (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.