GROWTH AND STRUCTURE OF COPPER THIN-FILMS DEPOSITED ON (0001) SAPPHIRE BY MOLECULAR-BEAM EPITAXY

The structure of copper films grown on (0001) sapphire by molecular beam epitaxy at 200 degrees C and 600 degrees 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 degrees C, but {111}(Cu) textured at 600 degrees C. However, in both instances growth occurs with the copper (111) plane parallel-to the interface. In the case of the 200 degrees 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 degrees C and near single crystal growth at 200 degrees C are explained in terms of entropy contributions to the free energy of the Cu/Al2O3 interface.