The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti–Al–N thin films


The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti–Al–N thin films

Beckers, M.; Höglund, C.; Baehtz, C.; Martins, R. M. S.; Persson, P. O. Å.; Hultman, L.; Möller, W.

Ternary Ti–Al–N films were deposited onto Al2O3 0001 substrates by reactive cosputtering from elemental Ti and Al targets and analyzed by in situ and ex situ x-ray scattering, Rutherford backscattering spectroscopy, transmission electron microscopy, and x-ray photoemission spectroscopy. The deposition parameters were set to values that yield Ti:Al:N ratios of 2:1:1 and 4:1:3 at room temperature. 2TiAlN depositions at 675 °C result in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. Nominal 4TiAl3N depositions at 675 °C and above, however, yield domain growth of TiN and Ti2AlN due to Al loss to the vacuum. Depositions at a lower temperature of 600 °C yield films with correct 4:1:3 stoichiometry, but Ti4AlN3 formation is prevented, supposedly by insufficient adatom mobility. Instead, an incoherent Tin+1AlNn structure with random twinned stacking sequences n is obtained that exhibits both basal plane orientations parallel and nearly perpendicular to the substrate interface. X-ray photoemission spectroscopy shows that in contrast to stoichiometric nitrides the Al is metallically bonded and hence acts as twinning plane within the Tin+1AlNn stackings. Domains with perpendicular basal plane orientation overgrow those with parallel orientation in a competitive growth mode. The resulting morphology is a combination of smooth-surface parallel-basal-plane-oriented domains interrupted by repeated facetted hillocklike features with perpendicular basal plane orientation.

Keywords: in-situ magnetron sputtering; MAX phases

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Publ.-Id: 13641