Revealing the Origin and Nature of the Buried Metal‐Substrate Interface Layer in Ta/Sapphire Superconducting Films

Journal Article · Tue Feb 18 23:00:00 EST 2025 · Advanced Science

DOI:https://doi.org/10.1002/advs.202413058· OSTI ID:2519713

Anbalagan, Aswin k. ^[1]; Cummings, Rebecca ^[2]; Zhou, Chenyu ^[3]; Mun, Junsik ^[4]; Stanic, Vesna ^[5]; Jordan‐Sweet, Jean ^[5]; Yao, Juntao ^[6]; Kisslinger, Kim ^[3]; Weiland, Conan ^[7]; Nykypanchuk, Dmytro ^[3]; Hulbert, Steven L. ^[1]; Li, Qiang ^[8]; Zhu, Yimei ^[2]; Liu, Mingzhao ^[3]; Sushko, Peter V. ^[9]; Walter, Andrew L. ^[1]; Barbour, Andi M. ^[1]

---

1. National Synchrotron Light Source II Brookhaven National Laboratory Upton New York 11973 USA
2. The Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA
3. Center for Functional Nanomaterials Brookhaven National Laboratory Upton New York 11973 USA
4. The Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA, Center for Functional Nanomaterials Brookhaven National Laboratory Upton New York 11973 USA
5. IBM T. J. Watson Research Center 1101 Kitchawan Road Yorktown Heights New York 10598 USA
6. The Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA, Department of Materials Science and Chemical Engineering Stony Brook University Stony Brook New York 11794 USA
7. Material Measurement Laboratory National Institute of Standard and Technology Gaithersburg Maryland 20899 USA
8. The Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA, Department of Physics and Astronomy Stony Brook University Stony Brook New York 11794 USA
9. Physical and Computational Sciences Directorate Pacific Northwest National Laboratory Richland Washington 99354 USA

Abstract

Despite constituting a smaller fraction of the qubit's electromagnetic mode, surfaces and interfaces can exert significant influence as sources of high‐loss tangents, which brings forward the need to reveal properties of these extended defects and identify routes to their control. Here, we examine the structure and composition of the metal‐substrate interfacial layer that exists in Ta/sapphire‐based superconducting films. Synchrotron‐based X‐ray reflectivity measurements of Ta films, commonly used in these qubits, reveal an unexplored interface layer at the metal‐substrate interface. Scanning transmission electron microscopy and core‐level electron energy loss spectroscopy identified an intermixing layer (≈0.65 ± 0.05 nm) at the metal‐substrate interface containing Al, O, and Ta atoms. Density functional theory modeling reveals that the structure and properties of the Ta/sapphire heterojunctions are determined by the oxygen content on the sapphire surface prior to Ta deposition for two atomic terminations of sapphire. Using a multimodal approach, we gained deeper insights into the interface layer between the metal and substrate, which suggests that the orientation of deposited Ta films depend on the surface termination of sapphire. The observed elemental intermixing at the metal‐substrate interface influences the thermodynamic stability and electronic behavior of the film, which may also affect qubit performance.

• Sponsoring Organization: USDOE
• Grant/Contract Number: NONE; SC0012704; AC02-05CH11231
• OSTI ID: 2519713
• Alternate ID(s): OSTI ID: 2519714; OSTI ID: 2529401
• Journal Information: Advanced Science, Journal Name: Advanced Science; ISSN 2198-3844
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: Germany
• Language: English