Growth and structure of copper thin films deposited on (0001) sapphire by molecular beam epitaxy

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Abstract
The structure of copper films grown on (0001) sapphire by molecular beam epitaxy at 200°C and 600°C was studied by in situ reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). Both RHEED and TEM confirm that growth is epitaxial at 200°C, but {111}Cu textured at 600°C. However, in both instances growth occurs with the copper (111) plane parallel to the interface. In the case of the 200°C films the close-packed directions of copper lie parallel to the close-packed directions of sapphire in the interfacial plane; these films contain low angle grain boundaries with the interface normal to the axis of rotation. High resolution and atomic resolution electron microscopy of the interface viewed in cross-section suggest that the atomic structure of the copper/sapphire interface is incoherent. The textured growth at 600°C and near single crystal growth at 200°C are explained in terms of entropy contributions to the free energy of the Cu/Al2O3 interface.