HRTEM characterization of atomic structures in Cu/α-Al₂O₃ (0001) interface

Thin Cu film was deposited on the (0001) surface of α-Al₂O₃ by a pulsed-laser deposition technique at substrate temperature of 800°C. The atomic structure of Cu/Al₂O₃ (0001) interface was characterized by high-resolution transmission electron microscopy (HRTEM). It was found that the interface was atomically sharp and the following orientation relationship (OR) was existed; (111)_Cu//(0001)_Al(2)O(3), [11̄0]_Cu//[11̄00]_Al(2)O(3). In contrast, the OR with geometrically high coherency across the interface was evaluated by the coincidence of reciprocal lattice points method, and the result showed that the preferred OR was (111)_Cu//(0001)_Al(2)O(3), [112̄]_Cu//[11̄00]_Al(2)O(3). This OR is not consistent with the experimental results, and suggests that interfacial chemical bonding plays an important role to form the actual OR. In order to understand the nature of the chemical bonding at the interface, HRTEM image simulations were performed and their results were compared with the experimental images. It was found that the Cu(111)/Al₂O₃(0001) interface terminated at oxygen-layer, which indicates that Cu-O bonds determine the stability of the interface.