Reactive spulter deposition of ceramic oxide nanolaminates: ZrO 2 –Al 2 O 3 and ZrO 2 –Y 2 O 3 model systems

Abstract

The growth of ceramic nanolaminate films by reactive sputter deposition is reviewed. Phase formation in nanolaminates with the same nominal architecture but with different chemical constituents is investigated. Two model systems, zirconia–alumina and zirconiayttria, allow comparison of the effects of chemical reactivity between constituents at the interface. In zirconia–alumina nanolaminates, each component is a separate entity and the interface is incoherent. Phase evolution in zirconia layers of decreasing thickness is predicted by the finite crystal size effect. Tetragonal zirconia is produced in layers whose thickness is less than the critical thickness for stabilisation of monoclinic zirconia (the STP phase). The amorphous structure of alumina is a consequence of its structural flexibility. Overall morphological roughness of the film arises from the polycrystalline nature of the zirconia layers. In zirconia–yttria nanolaminates, an interfacial reaction between components completely obliterates yttria as a separate entity. The reaction product, cubic zirconiayttria, forms needlelike crystallites and accentuates the overall morphological roughness resulting from the polycrystalline nature of the deposit. As zirconia layer thickness increases, monoclinic zirconia is produced along with interfacial cubic zirconia–yttria. This research clearly demonstrates the ability to forminterfacial oxide solid solutions at low temperature in a system in which the bulk equilibrium phase diagram predicts reaction between oxide components. Thus, thin films consisting entirely of interface reaction products can be fabricated if the bilayer spacing is small enough.