*Article* **Atomic Layer Deposition of GdCoO3 and Gd0.9Ca0.1CoO3**

#### **Marion Duparc, Henrik Hovde Sønsteby, Ola Nilsen, Anja Olafsen Sjåstad and Helmer Fjellvåg \***

Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, 0315 Oslo, Norway; m.j.l.duparc@smn.uio.no (M.D.); h.h.sonsteby@kjemi.uio.no (H.H.S.); ola.nilsen@kjemi.uio.no (O.N.); a.o.sjastad@kjemi.uio.no (A.O.S.)

**\*** Correspondence: helmer.fjellvag@kjemi.uio.no

Received: 16 November 2019; Accepted: 16 December 2019; Published: 19 December 2019

**Abstract:** Thin films of the catalytically interesting ternary and quaternary perovskites GdCoO3 and Gd0.9Ca0.1CoO3 are fabricated by atomic layer deposition using metal β-diketonates and ozone as precursors. The resulting thin films are amorphous as deposited and become single-oriented crystalline on LaAlO3(100) and YAlO3(100/010) after post-annealing at 650 ◦C in air. The crystal orientations of the films are tunable by choice and the orientation of the substrate, mitigated through the interface via solid face epitaxy upon annealing. The films exhibit no sign of Co2+. Additionally, high-aspect-ratio Si(100) substrates were used to document the suitability of the developed process for the preparation of coatings on more complex, high-surface-area structures. We believe that coatings of GdCoO3 and Gd1−*<sup>x</sup>*Ca*x*CoO3 may find applications within oxidation catalysis.

**Keywords:** gadolinium cobaltites; atomic layer deposition; β-diketonates; ozone; preferential crystal growth orientation; high-aspect-ratio substrate
