Role of interfacial crystallites in the crystallization of α-Fe2O3/α-Al2O3(0001) thin films

In situ crystallization of α-Fe 2 O 3 /α-Al 2 O 3 (0 0 0 1) thin films was studied in real-time synchrotron X-ray scattering experiments. We find the coexistence of α-Fe 2 O 3 (hexagonal) and Fe 3 O 4 (cubic) interfacial crystallites (∼50-A-thick), well aligned [0.02° full-width at half-maximum (FWHM)] to the α-Al 2 O 3 [0 0 0 1] direction, in the sputter-grown amorphous films. As the annealing temperature increases up to 750°C, the cubic stacking of the Fe 3 O 4 crystallites gradually changes to the hexagonal α-Fe 2 O 3 stacking, together with the growth of the well-aligned (WA) (0.02° FWHM) grains from the α-Fe 2 O 3 crystallites. In the meanwhile, heterogeneous nucleation starts to occur on the substrate at ∼600°C, resulting in the formation of misaligned (1.39° FWHM) α-Fe 2 O 3 grains. Our study reveals that the interfacial crystallites act as a template for the growth of the WA α-Fe 2 O 3 grains.