Titanium nitride TiNx (0.1 <= x <= 1) thin films were deposited onto Al2O3(0001) substrates using reactive magnetron sputtering at substrate temperatures (T-s) ranging from 800 to 1000 degrees C and N-2 partial pressures (pN(2)) between 13.3 and 133 mPa. It is found that Al and O from the substrates diffuse into the substoichiometric TiNx films during deposition. Solid-state reactions between the film and substrate result in the formation of Ti2O and Ti3Al domains at low N-2 partial pressures, while for increasing pN(2), the Ti2AlN MAX phase nucleates and grows together with TiNx. Depositions at increasingly stoichiometric conditions result in a decreasing incorporation of substrate species into the growing film. Eventually, a stoichiometric deposition gives a stable TiN(111) parallel to Al2O3(0001) structure without the incorporation of substrate species. Growth at T-s 1000 degrees C yields Ti2AlN(0001), leading to a reduced incorporation of substrate species compared to films grown at 900 degrees C, which contain also Ti2AlN(10 (1) over bar3) grains. Finally, the Ti2AlN domains incorporate 0, likely on the N site, such that a MAX phase oxynitride Ti2Al(O,N) is formed. The results were obtained by a combination of structural methods, including X-ray diffraction and (scanning) transmission electron microscopy, together with spectroscopy methods, which comprise elastic recoil detection analysis, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy. (C) 2010 Elsevier Ky. All rights reserved.