Y2O3 thin films: internal stress and microstructure

Thin films of yttrium oxide, Y2O3, were deposited on Si (1 0 0), MgO and SrTiO3 substrates by ion beam sputtering. The as-deposited samples are under a strong compressive stress whatever the substrates are. Furthermore the in-plane (2 2 2) or (4 0 0) Bragg peaks are shifted and non-symmetric. The high-resolution transmission electron microscopy investigations on the epitaxially grown Y2O3 thin films lead to the conclusion that the ion beam deposition process promotes a strong disorder on the oxygen network. The crystallographic symmetry of the Y2O3 structure which is Th7 becomes a fluorite related symmetry which is Fm3m. Annealing treatments or deposition involving a secondary ion beam assisted deposition process re-orders the Fm3m structure which comes back to the equilibrium Th7 symmetry.