Effect of oxygen plasma treatment on the structural and superconducting properties of atomic-layer-deposited NbN thin films
Abstract
Surface oxidation is a common concern for ultrathin NbN superconducting devices, yet which superconducting properties it affects has not been established for films grown by plasma-enhanced atomic layer deposition. We expose NbN films about 11.4 nm thick to an O2 plasma for 0 to 60 s, which oxidizes the surface without etching the film, and characterize the same sample series by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and transport measurements on 500 nm wide nanowires. XPS of the surface and the underlying layer shows that the plasma converts the surface to Nb2O5, whereas the bulk of the treated film is chemically identical to that of the untreated film. Crystalline δ-NbN remains intact. During exposure, the total film thickness rises and saturates between 40 and 60 s, indicating self-limiting surface oxide growth. The normal-state resistivity rises by 21% (dc) and 25% (optical) with the plasma dose, while the critical temperature and transition width are unchanged. The switching current densities of 4.9-6.2 MA/cm2 at 4.2 K show no systematic dependence on the plasma dose. Their temperature dependence follows the dirty-limit depairing current of Kupriyanov and Lukichev, and the extrapolated switching currents reach 39-46% of the depairing current calculated from the optical resistivity and diffusion coefficient, in agreement with the width dependence reported for nanowires from the same process. The oxygen signature is confined to temperatures near Tc, where the supercurrent of the treated wires vanishes at least 0.5 K earlier than that of the untreated wire, consistent with a partially oxidized surface layer that acts on the film by the proximity effect. At these doses, oxygen narrows the temperature range of the supercurrent from above but does not systematically reduce the low-temperature current-carrying capacity of the wires.
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BibTeX
@misc{yerra2026effect,
title = {{Effect of oxygen plasma treatment on the structural and superconducting properties of atomic-layer-deposited NbN thin films}},
author = {Nitesh Yerra and Mustafa Teke and Felix Otto and Marco Diegel and Detlef Born and Uwe Hübner and Nan Du and Mario Ziegler and Sahitya Varma Vegesna and Heidemarie Krüger},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32529},
eprint = {2610.32529},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32529},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Effect of oxygen plasma treatment on the structural and superconducting properties of atomic-layer-deposited NbN thin films
AU - Nitesh Yerra
AU - Mustafa Teke
AU - Felix Otto
AU - Marco Diegel
AU - Detlef Born
AU - Uwe Hübner
AU - Nan Du
AU - Mario Ziegler
AU - Sahitya Varma Vegesna
AU - Heidemarie Krüger
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32529
UR - https://arxiv.org/abs/2610.32529
AB - Surface oxidation is a common concern for ultrathin NbN superconducting devices, yet which superconducting properties it affects has not been established for films grown by plasma-enhanced atomic layer deposition. We expose NbN films about 11.4 nm thick to an O_2 plasma for 0 to 60 s, which oxidizes the surface without etching the film, and characterize the same sample series by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and transport measurements on 500 nm wide nanowires. XPS of the surface and the underlying layer shows that the plasma converts the surface to Nb_2O_5, whereas the bulk of the treated film is chemically identical to that of the untreated film. Crystalline δ-NbN remains intact. During exposure, the total film thickness rises and saturates between 40 and 60 s, indicating self-limiting surface oxide growth. The normal-state resistivity rises by 21% (dc) and 25% (optical) with the plasma dose, while the critical temperature and transition width are unchanged. The switching current densities of 4.9-6.2 MA/cm^2 at 4.2 K show no systematic dependence on the plasma dose. Their temperature dependence follows the dirty-limit depairing current of Kupriyanov and Lukichev, and the extrapolated switching currents reach 39-46% of the depairing current calculated from the optical resistivity and diffusion coefficient, in agreement with the width dependence reported for nanowires from the same process. The oxygen signature is confined to temperatures near T_c, where the supercurrent of the treated wires vanishes at least 0.5 K earlier than that of the untreated wire, consistent with a partially oxidized surface layer that acts on the film by the proximity effect. At these doses, oxygen narrows the temperature range of the supercurrent from above but does not systematically reduce the low-temperature current-carrying capacity of the wires.
ER -