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 deg. C. X-ray diffraction ω-2θ scans, ω-rocking curves, and pole figures show that layers grown at T s = 40 and 100 deg. 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 deg. C leads to polycrystalline Cu layers with 001, 203, and 1-bar75-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 x 7 Cu unit cells occupying 6 x 6 MgO cells. In addition, for T s ≥ 200 deg. C, the 001-oriented grains relax by tilting by 4o or 15o about <110> or <100> axes, respectively, while the 203 and 1-bar75-oriented grains exhibit complex epitaxial relationships with the substrate: (203)Cu||(001)MgO with [010]Cu||[110]MgO and [302-bar]Cu||[11-bar0]MgO; and (1-bar75)Cu||(001)MgO with [211-bar]Cu||[100]MgO and [43-bar5]Cu||[010]MgO. The surface roughness, as determined by X-ray reflectivity, increases with growth temperature. The smoothest layers are grown at 40 deg. C and exhibit an rms surface and buried interface roughness of 0.7 and 1.4 nm, respectively