Abstract
The oxides of platinum group metals are promising for future electronics and spintronics due to the delicate interplay of spin-orbit coupling and electron correlation energies. However, their synthesis as thin films remains challenging due to their low vapour pressures and low oxidation potentials. Here we show how epitaxial strain can be used as a control knob to enhance metal oxidation. Using Ir as an example, we demonstrate the use of epitaxial strain in engineering its oxidation chemistry, enabling phase-pure Ir or IrO2 films despite using identical growth conditions. The observations are explained using a density-functional-theory-based modified formation enthalpy framework, which highlights the important role of metal-substrate epitaxial strain in governing the oxide formation enthalpy. We also validate the generality of this principle by demonstrating epitaxial strain effect on Ru oxidation. The IrO2 films studied in our work further revealed quantum oscillations, attesting to the excellent film quality. The epitaxial strain approach we present could enable growth of oxide films of hard-to-oxidize elements using strain engineering.
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The source data for the results of this work can be accessed using the given link: https://doi.org/10.13020/9wm7-x981. Any additional data related to this paper may be requested from the corresponding authors.
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Acknowledgements
We thank N. Seaton for help with SEM, EDX and EBSD. Funding for film growth and characterization (S.N., D.L. and B.J.) was supported by the US Department of Energy through DE-SC0020211. S.N. and D.L. acknowledge support from the Air Force Office of Scientific Research (AFOSR) through grant numbers FA9550-21-1-0025 and FA9550-21-0460. S.G., Z.Y. and K.A.M. were supported partially by the UMN MRSEC program under award number DMR-2011401. S.G. and K.A.M. were also supported by SMART, one of seven centres of nCORE, a Semiconductor Research Corporation program, sponsored by the National Institute of Standards and Technology (NIST). Parts of this work were carried out at the Characterization Facility, University of Minnesota, which receives partial support from the National Science Foundation (NSF) through the MRSEC program under award number DMR-2011401. S.J. acknowledges support from the NSF under award number DMR-2129879. W.J. acknowledges support from the US Department of Energy (DOE) Office of Science under DE-SC0023478. R.B.C. acknowledges support from the AFOSR Young Investigator Program under FA9550-20-1-0034. A.J. and A.S. acknowledge support from the NSF through the UD-CHARM University of Delaware Materials Research Science and Engineering Center (number DMR-2011824). The first-principles calculations used Bridges-2 at PSC through allocation DMR150099 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by NSF grant numbers 2138259, 2138286, 2138307, 2137603 and 2138296, and the DARWIN computing system at the University of Delaware, which is supported by NSF grant number 1919839. This research used resources of the Center for Functional Nanomaterials and National Synchrotron Light Source II, which are US DOE Office of Science Facilities, at Brookhaven National Laboratory under contract number DE-SC0012704. This research used resources of the Advanced Photon Source, a DOE Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under contract number DE-AC02-06CH11357.
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S.N. and B.J. conceived the idea and established proof of concept. S.N. grew films and characterized them using XRD, AFM, optical microscopy, SEM and electrical transport measurements. S.N. and B.J. analysed the data. Z.Y. performed magneto-transport measurements and data analysis. D.L. performed XPS measurements. S.G. performed STEM analysis under the supervision of K.A.M. LEEM, LEED and XPS were performed by J.T.S. and analysed by S.J., W.J. and R.B.C. Y.L. and H.Z. carried out synchrotron X-ray diffraction measurements and data analysis. DFT calculations were performed by A.S. under the supervision of A.J. S.N. and B.J. wrote the manuscript. All authors contributed to the discussion and preparation of the manuscript. B.J. directed and organized the different aspects of the project.
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Nair, S., Yang, Z., Lee, D. et al. Engineering metal oxidation using epitaxial strain. Nat. Nanotechnol. 18, 1005–1011 (2023). https://doi.org/10.1038/s41565-023-01397-0
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DOI: https://doi.org/10.1038/s41565-023-01397-0
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