HETEROEPITAXIAL GROWTH OF ZIRCONIA FILMS OBTAINED BY WET CHEMICAL ROUTE

René Guinebretiere, Alain Dauger, Claire Mary, Cyril Delage and Bernard Soulestin

Laboratoire de Matériaux Céramiques et Traitements de Surfaces - UPRES_A CNRS 6015, ENSCI - 47 Avenue Albert Thomas - 87065 LIMOGES - France
r.guinebretiere@ensci.fr

Heteroepitaxial single crystal thin films of pure zirconia have been deposited on single crystalline ceramic substrates using alcoholic precursor solution of zirconium n-propoxide.

Annealing dip-coated substrates at 600°C results in the formation of 50 nm thick films made of tetragonal polycrystalline zirconia. Film nanocrystals, about 5 nm in size, are randomly oriented even at the film substrate interface.

Thermal treatments at higher temperatures induce film breakup and substrate uncovering through the formation of single crystalline isolated islands displaying specific crystallographic relationships with the single crystalline substrates The solid state epitaxy mechanism is not related to the primary crystallization step, but results from abnormal growth process, an instability causes the film to break into isolated islands.

Controlled incidence x-ray diffraction and cross sectional transmission electron microscopy were employed to investigate islands structure, orientation, morphology and growth process. Different cases were studied since zirconia films were deposited as well on magnesia (00l) as on sapphire (112^-0) or (000l) substrates.

On magnesia substrates, MgO-ZrO₂ solid solution single crystalline islands display cube on cube epitaxy : {hkl}_ZrO2 // {hkl}_MgO. On the other hand, whatever the sapphire surface orientation, the formation of two families of zirconia islands, with different normal orientations, is observed. The two island families are randomly distributed on the substrate, the first one having the ZrO₂ {00l} planes and the other the ZrO₂ {hhh} planes parallel to the sapphire substrate surface planes.

Moreover, the two types of oriented islands display different morphologies. The (00l) oriented islands are thin plate shaped and grow in the substrate plane with a large interface area, whereas the {hhh} oriented islands hemispheric in shape and seem to minimize the interface area. By choosing the initial film thickness we show that {00l} oriented island can be favored, and quasi-single crystalline continuous zirconia thin films can be formed on sapphire substrates.