Phase stability of epitaxially grown Ti2AlN thin films

The preferred orientation and thermal stability of MAX phase (M: early transition metal; A: A group element; X: C and/or N) Ti2AlN thin films sputtered onto MgO(111) and Al2O3(0001) substrates have been investigated by in situ x-ray diffraction and Rutherford backscattering (RBS). Low-temperature deposition results in epitaxial growth with inclined basal planes. An increased substrate temperature changes the preferred orientation to a parallel basal plane growth. In contrast to high bulk thermal stability, thin films decompose in vacuum already at 800°C by outward Al diffusion, followed by de-twinning of the remaining Ti2N slabs and concurrent TiN and Ti4AlN3 formation.