Atomic and electronic structures of Cu/a-Al2O3 interfaces prepared by pulsed-laser deposition

Interfacial atomic structures of Cu/Al2O3(0001) and Cu/Al2O3 systems prepared by a pulsed-laser deposition technique have been characterized by using high-resolution transmission electron microscopy (HRTEM). It was found that Cu metals were epitaxially oriented to the surface of Al2O3 substrates, and the following orientation relationships (ORs) were found to be formed: (111)Cu⁄⁄(0001)Al2O3, cu⁄⁄Al2O3 in the Cu/Al2O3(0001) interface and (001)Cu⁄⁄Al2O3, Cu⁄⁄[0001]Al2O3 in the Cu/Al2O3 interface. Geometrical coherency of the Cu/Al2O3 system has been evaluated by the coincidence of reciprocal lattice points method, and the result showed that the most coherent ORs were (111)Cu⁄⁄(0001)Al2O3, Cu⁄⁄[11Ī00]Al2O3 and Cu⁄⁄Al2O3, [111]Cu⁄⁄[0001]Al2O3, which are equivalent to each other. These ORs were not consistent with the experimentally observed ORs, and it was possible that crucial factors to determine the ORs between Cu and Al2O3 were not only geometrical coherency, but also other factors such as chemical bonding states. Therefore, to understand the nature of the interface atomic structures, the electronic structures of the Cu/Al2O3 interfaces have been investigated by electron energy-loss spectroscopy. It was found that the pre-edge at the lower energy part of the main peak appeared in the O-K edge spectra at the interface region in both the Cu/Al2O3(0001) and Cu/Al2O3 systems. This indicates the existence of Cu—O interactions at the interface. In fact, HRTEM simulation images based on O-terminated interface models agreed well with the experimental images, indicating that O-terminated interfaces were formed in both systems. Since the overlapped Cu atomic density in the experimental ORs were larger than that in the most coherent OR, it is considered that the on-top Cu—O bonds stabilize the O-terminated Cu/Al2O3 interfaces.