Surface studies of niobium chemically polished under conditions for superconducting radio frequency (SRF) cavity production

The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed tr...

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Bibliographic Details
Published in:Applied surface science 2006-11, Vol.253 (3), p.1236-1242
Main Authors: Tian, Hui, Reece, Charles E., Kelley, Michael J., Wang, Shancai, Plucinski, Lukasz, Smith, Kevin E., Nowell, Matthew M.
Format: Article
Language:English
Subjects:
Accelerator cavities
ACCELERATORS
ATOMIC FORCE MICROSCOPY
CAVITIES
Chemical etching
CHEMICAL POLISHING
DIFFRACTION
ELECTRONS
ENERGY
EXHIBITS
FLOW RATE
LAYERS
national synchrotron light source
NIOBIUM
Niobium RF cavities
ORIENTATION
PARTICLE ACCELERATORS
PHOTONS
PRODUCTION
RANGE
ROUGHNESS
SHEETS
SOLUTIONS
Surface analysis
SURFACES
SYNCHROTRONS
THICKNESS
X-RAY PHOTOELECTRON SPECTROSCOPY
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Summary:The performance of niobium superconducting radiofrequency (SRF) accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially as influenced by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant datasets. We found that the predominant general surface orientation is (1 0 0), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3–1.4 times that resulting from static solution. The standard deviation of the roughness measurements is ±30% and that of the surface composition is ±5%.
ISSN:0169-4332
1873-5584
DOI:10.1016/j.apsusc.2006.01.083