Growth of epitaxial Cu on MgO(001) by magnetron sputter deposition

100-nm-thick Cu layers were grown on MgO(001) substrates by ultra-high vacuum magnetron sputter deposition at substrate temperatures T_s ranging from 40 to 300 °C. X-ray diffraction ω−2θ scans, ω-rocking curves, and pole figures show that layers grown at T_s = 40 and 100 °C are complete single crystals with a cube-on-cube epitaxial relationship with the substrate: (001)_Cu||(001)_MgO with 100]_Cu||100]_MgO. In contrast, T_s ≥ 200 °C leads to polycrystalline Cu layers with 001, 203, and 1¯75-oriented grains. The transition from a single- to a polycrystalline microstructure with increasing T_s is attributed to temperature-induced mass transport that allows Cu nuclei to sample a larger orientational space and find lower energy (and/or lower lattice mismatch) configurations. The large Cu- to-MgO lattice mismatch of 14% is relieved by 7 × 7 Cu unit cells occupying 6 × 6 MgO cells. In addition, for T_s ≥ 200 °C, the 001-oriented grains relax by tilting by 4° or 15° about 〈110〉 or 〈100〉 axes, respectively, while the 203 and 1¯75-oriented grains exhibit complex epitaxial relationships with the substrate: (203)_Cu||(001)_MgO with 010]_Cu||110]_MgO and 302¯]_Cu||11¯0]_MgO; and (1¯75)_Cu||(001)_MgO with 211¯]_Cu||100]_MgO and 43¯5]_Cu||010]_MgO. The surface roughness, as determined by X-ray reflectivity, increases with growth temperature. The smoothest layers are grown at 40 °C and exhibit an rms surface and buried interface roughness of 0.7 and 1.4 nm, respectively.