Title:	Influence of Oxygen Plasma on the Growth and Stability of Epitaxial NiCo2O4 Ultrathin Films on Various Substrates
Authors:	Ruwisch, Kevin Alexander, Andreas Pollenske, Tobias Küpper, Karsten Wollschläger, Joachim
ORCID of the author:	https://orcid.org/0000-0001-5551-7240 https://orcid.org/0000-0003-4047-7092 https://orcid.org/0000-0003-0364-9385 https://orcid.org/0000-0002-3043-3718
Abstract:	In this work, we investigated the influence of oxygen plasma on the growth of nickel cobaltite (NiCo2O4) thin films compared to growth in a molecular oxygen atmosphere. The films were grown on MgO(001), MgAl2O4(001) and SrTiO3(001) substrates by oxygen plasma (atmosphere of activated oxygen)-assisted and reactive molecular beam epitaxy (molecular oxygen atmosphere). Soft X-ray photoelectron spectroscopy showed that only the use of oxygen plasma led to a spectrum characteristic of (NiCo2O4). Low energy electron diffraction measurements were conducted to obtain information on the structure of the film surfaces. The results proved the formation of a spinel surface structure for films grown with oxygen plasma, while the formation of a rock salt structure was observed for growth with molecular oxygen. To determine the film thickness, X-ray reflectivity measurements were performed. If oxygen plasma were used to grow (NiCo2O4) films, this would result in lower film thicknesses compared to growth using molecular oxygen although the cation flux was kept constant during deposition. Additional X-ray diffraction experiments delivered structural information about the bulk structure of the film. All films had a rock salt bulk structure after exposure to ambient conditions. Angle-resolved hard X-ray photoelectron spectroscopy revealed a homogeneous depth distribution of cations of the grown film, but no typical (NiCo2O4) spectrum anymore. Thus, on the one hand, (NiCo2O4) films with a spinel structure prepared using activated oxygen were not stable under ambient conditions. The structure of these films was transformed into NiCo oxide with a rock salt structure. On the other hand, it was not possible to form (NiCo2O4) films using molecular oxygen. These films had a rock salt structure that was stable under ambient conditions.
Citations:	Ruwisch K, Alexander A, Pollenske T, Küpper K, Wollschläger J.: Influence of Oxygen Plasma on the Growth and Stability of Epitaxial NiCo2O4 Ultrathin Films on Various Substrates. Materials. 2022; 15(19):6911.
URL:	https://doi.org/10.48693/297 https://osnadocs.ub.uni-osnabrueck.de/handle/ds-202305028725
Subject Keywords:	nickel cobaltite; ultrathin films; RMBE; OPA-MBE; LEED; XPS; XRD; growth study; HAXPES
Issue Date:	5-Oct-2022
License name:	Attribution 4.0 International
License url:	http://creativecommons.org/licenses/by/4.0/
Type of publication:	Einzelbeitrag in einer wissenschaftlichen Zeitschrift [Article]
Appears in Collections:	FB06 - Hochschulschriften Open-Access-Publikationsfonds

This item is licensed under a Creative Commons License