Low Temperature Epitaxial Oxide Ultrathin Films and Nanostructures by Atomic Layer Deposition

Highly epitaxial and pure (001) CeO2 ultrathin films have been prepared by atomic layer deposition (ALD) at 275 degrees C on Y-stabilized ZrO2 cubic fluorite single crystal substrate using cerium beta-diketonate (Ce(thd)(4)) and ozone (O-3) as precursors. Substrate temperature and precursor pulses have been optimized to set the ALD window obtaining a growth per cycle of approximate to 0.2 angstrom/cycle. This extremely low growth rate has been identified as a key parameter to ensure epitaxial growth at these low temperatures. Post-thermal treatments at 900 degrees C in oxygen further improve ALD-CeO2 film texture while maintaining film stoichiometry and ultrasmooth surface, rms < 0.4 nm. ALD-CeO2 thin film growth has also been tested on perovskite single crystal substrates, SrTiO3 and LaAlO3, exhibiting CeO2 epitaxial growth and thus validating ALD as an outstanding method for low temperature epitaxial growth. Furthermore, we demonstrate that by combining e-beam lithography and ALD it is feasible to obtain size-controlled CeO2 nanostructures.