Results recently published by Ito et al. showed that "furnace baking" Nb SRF cavities after electropolishing yields high quality factors and anti-Q-slopes resembling that of N doped cavities. Small Nb samples were prepared following the recipe outlined by Ito. These samples were measured by SIMS to examine impurity contributions to the RF penetration layer. These diffusion profiles are modeled, and their consequences on RF properties discussed.

Historically, niobium has been used as the superconducting material in SRF cavities. Due the high operational costs, other materials are currently being considered. Nb3Sn coatings have been investigated over the past several decades, motivated by potentially higher operating temperatures. More recently niobium has been doped with nitrogen to improve the quality factor (Q) [1]. Currently, a need for better understanding still exists for both mechanisms. Electron backscatter diffraction (EBSD) has been shown to be a viable technique to determine the crystallographic orientation and the size of the NB3Sn grains [2]. The EBSD maps obtained show a bimodal distribution of grain sizes with smaller Nb3Sn grains found present near the Nb3Sn/Nb interface. In addition to the Nb3Sn coatings, N-doped niobium coupons were analyzed by EBSD and found that the coupon had preferred surface orientation. The EBSD analysis was found to be vital as specific grains could be targeted in secondary ion mass spectrometer (SIMS) to better understand the diffusion of nitrogen with respect to crystal orientation.

Understanding of Nb3Sn nucleation and growth is essential to the progress with Nb3Sn vapor diffusion coatings of SRF cavities. Samples representing different stages of Nb3Sn formation have been produced and examined to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb3Sn films from few hundreds of nm up to ~15 μm were grown and characterized using AFM, SEM/EDS, XPS, EBSD, SIMS, and SAM. Microscopic examinations of samples suggest the mechanisms behind Nb3Sn thin film nucleation and growth. RF measurements of coated cavities were combined with material characterization of witness samples to adapt the coating process in "Siemens" coating configuration. Understanding obtained from sample studies, applied to cavities, resulted in Nb3Sn cavity with quality factor 2 ×1010 at 15 MV/m accelerating gradient at 4 K, without "Wuppertal" Q-slope. We discuss the genesis of the Nb3Sn thin film in a typical tin vapor diffusion process, and its consequences to the coating of SRF cavities.