10th International Workshop on Thin Films and New Ideas for Pushing the Limits of RF Superconductivity

Stress-induced omega (ω) phase transition in Nb thin films

Sep 22, 2022, 10:00 AM

30m

CEBAF Center auditorium

SRF Thin Films Characterization: Materials, Surfaces & Structures SRF Thin Film Characterization

Speaker

Jaeyel Lee (Fermilab)

Description

We analyzed omega (ω) phase transition in Nb thin film deposited by high power impulse magnetron sputtering (HiPIMS) using transmission electron microscopy (TEM) [1]. ~170 nm Nb thin film is deposited on Si (100) substrate and it showed a typical columnar structure with (110) texture on the surface. TEM analysis revealed that the Nb thin films contain ~1 vol.% of hexagonal structured omega (ω) phase Nb in bcc Nb and the size of the omega phase varies from 10-100 nm, which is comparable to the coherence length of Nb (~40 nm). The current finding indicates that Nb thin films are prone to structural change such as omega phase transition due to the internal stresses in the films owing to the low yield strength and critical resolved shear stresses of Nb. We conclude by discussing the superconducting properties of the ω-phase and their possible roles in the Nb thin film SRF cavities.

[1] J. Lee et al, arXiv 2207.12495 (2022)

Presentation materials

thin film SRF workshop_omega phase transition in Nb thin films.pdf