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Impact of thermal annealing on stress, morphology, and field emission of NbTiN thin films

Frederic Braun, Florian Brockner, and Dirk Lützenkirchen-Hecht

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Phys. Rev. Accel. Beams 29, 084302 – Published 24 August, 2026

DOI: https://doi.org/10.1103/hznn-ftkg

Abstract

NbTiN thin films are promising candidates for superconducting multilayer structures aimed at surpassing the intrinsic field limits of bulk Nb in superconducting radio-frequency (SRF) cavities. In this work, Nb0.75Ti0.25N films grown by plasma-enhanced atomic layer deposition were systematically investigated with respect to their crystalline structure, surface morphology, and field emission behavior in their as-deposited state, as well as after annealing in vacuum at 900 °C and 1000 °C, respectively. X-ray diffraction reveals that annealing induces significant grain growth, a pronounced (111)-texture, and a strong reduction of residual stress, with the 1000 °C samples exhibiting the most uniform and relaxed microstructure. Optical profilometry shows a clear decrease in macroscopic roughness by approximately 20%–25% after annealing, while atomic force microscopy measurements confirm that the nanoscale roughness remains low and largely unaffected by the heat treatments. Field emission scanning microscopy demonstrates that annealing substantially increases the onset field for electron field emission from values below 60  MV/m in the as-deposited state to 180–220  MV/m for annealed films, correlating with improved crystallinity, reduced stress, and enhanced film-substrate adhesion. Complementary ultraviolet photoelectronspectroscopy measurements yield a work function of ΦNbTiN=(4.32±0.07)  eV, supporting the interpretation of the field emission scanning microscope data. The combined results show that high-temperature annealing, particularly at 1000 °C, significantly enhances the structural and functional performance of NbTiN films, underscoring their potential for application in superconducting multilayer coatings for next-generation SRF cavities.

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Phys. Rev. Accel. Beams 29, 084302– Published 24 August, 2026
  • Received 18 December 2025
  • Accepted 30 June 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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