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Chemical-state evolution and phase stability of epitaxial PtCoO2 thin films probed by XPS, HAXPES, and in situ XRD

Kerry Hazeldine1,*, Jean-Philippe Soulié1, Robin Petit2, Christophe Detavernier2, Silvia Armini1, and Christoph Adelmann1

  • 1Imec, Kapeldreef 75, 3001 Leuven, Belgium
  • 2Department of Solid State Sciences, Krijgslaan 281-S1, Ghent University, 9000 Gent, Belgium

  • *Contact author: Kerry.hazeldine@imec.be
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Phys. Rev. Materials 10, 105003 – Published 19 October, 2026

DOI: https://doi.org/10.1103/n9ds-9x2h

Abstract

Epitaxial PtCoO2 thin films were grown on Al2O3(0001) substrates by physical vapor deposition under back-end-of-line compatible conditions, followed by postdeposition annealing to induce crystallization. While annealing-driven structural evolution in delafossite oxides has been reported, the corresponding chemical-state evolution across crystallization and decomposition boundaries remains insufficiently understood. Here, x-ray photoelectron spectroscopy, hard x-ray photoelectron spectroscopy (HAXPES), and in situ x-ray diffraction are combined to track chemical states and phase stability in PtCoO2 thin films as a function of thermal processing. This multimodal approach resolves the spectroscopic fingerprints of the metallic delafossite phase, unambiguously identifying formal Pt1+ and Co3+ valence states. Bulk-sensitive HAXPES, reported here for PtCoO2, mitigates surface artifacts and enables direct correlation between bulk chemistry and structural order. Annealing at 800∘C yields phase-pure, epitaxial PtCoO2, whereas higher temperatures induce decomposition into metallic Pt and cobalt oxide phases, defining a narrow thermal stability window. Highly crystalline films down to 4.5 nm thickness exhibit low in-plane resistivities consistent with the metallic delafossite phase. These results establish a chemically specific framework for assessing phase formation and stability in PtCoO2 thin films and demonstrate the utility of combined photoelectron spectroscopy and in situ diffraction for complex oxide metals.

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Phys. Rev. Materials 10, 105003– Published 19 October, 2026
  • Received 24 April 2026
  • Accepted 9 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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