Konomi, T. Kako, E. Michizono, S. Nagata, T. Nojima, T. Sakai, H. Umemori, K. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-194-6 10.18429/JACoW-LINAC2018-TUPO073 English 506-509 TUPO073 cavity niobium vacuum injection ECR Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-LINAC2018-TUPO073 http://jacow.org/linac2018/papers/tupo073.pdf KEK has been investigating the better conditions of the heat treatment in nitrogen, which are called as nitrogen doping and nitrogen infusion. We have tried to understand the high gradient performance of the cavity from the analyses of samples which were prepared in the same conditions for the cavity. The main tools are D-SIMS for the depth profile of the elemental concentration, XPS for composition analysis and SQUID magnetometry for the critical DC magnetic field measurement. The difference in the depth profiles of the nitrogen, carbon and oxygen between the heat treatment conditions was observed in vacuum and furnace temperature of nitrogen infusion by D-SIMS and XPS. Such a difference correlates with the vortex penetration field measured by SQUID. In particular, that of nitrogen doping sample was greatly degraded, while that of nitrogen infusion sample was slightly improved. The tendency is similar to the RF high gradient test results. Details of the sample analysis are shown in this presentation.