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For next-generation superconducting radiofrequency (SRF) cavities, the interior walls of existing Nb SRF cavities are coated with a thin Nb3Sn film to improve the superconducting properties for more efficient, powerful accelerators. The superconducting properties of these Nb3Sn coatings are limited due to inhomogeneous growth resulting from poor nucleation during the Sn vapor diffusion procedure. To develop a predictive growth model for Nb3Sn grown via Sn vapor diffusion, we aim to understand the interplay between the underlying Nb oxide morphology, Sn coverage, and Nb substrate heating conditions on Sn wettability, intermediate surface phases, and eventual Nb3Sn nucleation. In this work, Nb-Sn intermetallic species are grown on a single crystal Nb(100) in an ultrahigh vacuum chamber equipped with in situ surface characterization techniques including scanning tunneling microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Sn adsorbate behavior on oxidized Nb was examined by depositing Sn with submonolayer precision on a Nb substrate held at varying deposition temperatures (Tdep). Experimental data of annealed intermetallic adlayers provide evidence of how Nb substrate oxidization and Tdep impact Nb-Sn intermetallic coordination. The presented experimental data contextualize how vapor and substrate conditions, such as the Sn flux and Nb surface oxidation, drive homogeneous Nb3Sn film growth during the Sn vapor diffusion procedure on Nb SRF cavity surfaces. This work, as well as concurrent growth studies of Nb3Sn formation that focus on the initial Sn nucleation events on Nb surfaces, will contribute to the future experimental realization of optimal, homogeneous Nb3Sn SRF films.
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In situ anisotropic NiO nanostructure growth at high temperature and under water vapor
Abstract Anisotropic growth of nanostructures from individual nickel nanoparticles was observed during in situ heating experiments in an environmental scanning electron microscope (ESEM) at 800°C under water vapor atmosphere. The morphology of nanostructures exhibited one directional growth with rates ranging below 1.8 nm/s. Energy dispersive X‐ray spectroscopy and selected area electron diffraction confirmed NiO stoichiometry of the growing nanostructures. Variations of the oxygen partial pressure during ex situ annealing and in situ ESEM heating experiments elucidate that anisotropic NiO growth is energetically favored in areas where the local surface energy density is relatively high. Growth of NiO nanostructures was absent in dry air and dry nitrogen environments and required the presence of water vapor. The results of this study suggest that the manipulation of surface energy prior to exposure to water vapor at elevated temperatures can prevent unwanted oxide nanostructure growth.
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- Award ID(s):
- 1836571
- PAR ID:
- 10448390
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 105
- Issue:
- 4
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 2454-2464
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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