Trace Level Impurity Quantitation and the Reduction of Calibration Uncertainty for Secondary Ion Mass Spectrometry Analysis of Niobium Superconducting Radio Frequency Materials

Over the last decade, the interstitial alloying of niobium has proven to be essential for enabling superconducting radiofrequency (SRF) cavities to operate more efficiently at high accelerating gradients. The discovery of "nitrogen doping" was the first readily accessible avenue of interstitial alloying in which researchers saw an increase in cavity performance. However, the serendipitous nature of the discovery led to additional research to fundamentally understand the physics behind the increase in cavity performance. This knowledge gap is bridged by materials characterization. Secondary ion mass spectrometry (SIMS) is a characterization technique which has become a staple of SRF cavity characterization that details elemental concentration profiles as a function of depth into the niobium surface with submicron resolution. SIMS has been widely used by the semiconductor industry for decades but has found less application in other fields due to the difficulty to produce reproducible data for polycrystalline materials. Much effort has been given to reduce the uncertainty of SIMS results to as low as 1% - 2% for single crystals. However, less attention has been given to polycrystalline materials with uncertainty values reported between 40% - 50% The sources of uncertainty were found to be deterministic in nature and therefore could be mitigated to produce reliable results. This dissertation documents the efforts to reduce SIMS method uncertainty which has been further used to solve mysteries regarding the characterization of SRF cavities which include predictive modeling of oxygen diffusion as well as the identification of contaminants resulting from cavity furnace treatments.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Materials Science and Engineering

Department dc:contributor.department

Materials Science and Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2022

Author dc:creator

• Angle, Jonathan Willis

Chair dc:contributor.committeechair

• Kelley, Michael J.

Committee members dc:contributor.committeemember

• Stevie, Fred A.
• Murayama, Mitsuhiro
• Reece, Charles E.
• Reynolds, William T. Jr.

• Materials Characterization
• SIMS
• SRF
• Nitrogen Doping
• Oxygen Alloying

Statement dc:rights

• Creative Commons Attribution 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:34252

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/109615