Epitaxial Ti2AlN(0Â 0Â 0Â 1) thin film deposition by dual-target reactive magnetron sputtering

Ultrahigh-vacuum dual-target reactive magnetron sputtering, in a mixed Ar/N2 discharge was used to deposit epitaxial single-crystal MAX phase Ti2AlN(0 0 0 1) thin films, without seed layers, onto Al2O3(0 0 0 1) substrates kept at 1050 °C. By varying the N2 partial pressure a narrow process window was identified for the growth of single-crystal Ti2AlN. The film microstructure was characterized by a combination of X-ray diffraction, spherical aberration (Cs) corrected transmission electron microscopy (TEM), high-resolution image simulation and high-resolution scanning TEM. Nitrogen-depleted deposition conditions resulted in the concurrent formation of N-free Ti-Al intermetallics at the film/substrate interface and a steady-state growth of Ti2AlN together with N-free intermetallic phases. At higher N2 partial pressures the growth assumes a columnar epitaxial nature. 1 Å resolution of the lattice enabling location of all elements in the Ti2AlN unit cell is demonstrated.