Orientation selection in functional oxide thin films

Mechanisms for orientation selection in complex oxide thin films are discussed, focusing on two examples: (1) development of a preferential texture in sol-gel prepared polycrystalline PZT films on Pt electrode layers and (2) selection of oxides for epitaxial growth on Si (111) and (100). In sol-gel PZT, a direct link was found between the formation of a well crystallized transient fluorite phase, promoted by reducing pyrolysis conditions, and the emergence of a strongly preferred (111) texture after crystallization. Meanwhile, in the MBE growth of epitaxial oxides on silicon, matching of silicon and oxide surface lattices is not a sufficient condition to achieve layer-by-layer growth, needed for planar films. In fact, for planar growth on Si(111), fluorite-structure compounds are required, while rocksalt and perovskite structure oxides are suited for the growth of low-roughness films on Si(100). These examples illustrate the important role played by surface energy in orientation selection.