Phase Control in Thin Films of Layered Cuprates

Perovskite-related layered cuprates are considered the basis of all high-<i>T</i>_c superconductors. Considerable effort has been put into understanding these materials. Deposition of phase-pure and oriented thin films can help shed light on the unusual interplay between the structure and properties, as the copper layers will be oriented in the same direction throughout the sample. Chemical deposition routes have been considered difficult, because of detrimental decomposition of metalorganic precursors, catalyzed by deposited copper species. In the current paper, we present a route for atomic layer deposition (ALD) of layered lanthanum cuprates. The system exhibits remarkable stoichiometric control, enabling deposition of a variety of lanthanum cuprate species. La₂CuO₄ films is shown to be tetragonal and (001) oriented on LaAlO₃ (100)_pc, with the copper planes parallel to the film surface. We go on to demonstrate that the oxygen-stoichiometry of LaCuO_3–<i>x</i> films can be tuned by post-treatment, resulting in phase control of the complex perovskite lanthanum cuprate system. Epitaxial films have been obtained for oxygen annealed monoclinic and air annealed orthorhombic variants of LaCuO_3–<i>x</i> on LaAlO₃ (100)_pc substrates with a LaCuO_3–<i>x</i>(100)|[640]||LaAlO₃(100)_pc|[310]_pc and LaCuO_3–<i>x</i>(100)_pc|[110]_pc||LaAlO₃(100)_pc|[110]_pc epitaxial relationship, respectively