Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O2 atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al2O3 formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO2 at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotr...