Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure Niobium samples using TOFSIMS technique

摘要

The performance of Superconducting radio frequency cavities (SRF) is stronglyinfluenced by various impurities within the penetration depth (~50nm) of Nb,which in turn depends on the applied surface treatments. The effect of thesesurface treatments on the impurities of Nb has been explored using varioussurface analytical treatments. But, the results are still inadequate in manyaspects and the effect of sequential SRF treatments on the impuritydistribution has not been explored. The present study analyses variousimpurities within the penetration depth of Nb samples, treated by SRF cavityprocessing techniques like colloidal silica polishing (simulating centrifugalbarrel polishing), buffer chemical polishing (BCP), high pressure rinsing (HPR)and degassing under high vacuum (HV) condition at 600{\deg}C for 10hrs. Static,dynamic and slow sputtering modes of Time of flight secondary ion massspectrometry (TOFSIMS) technique was employed to study the effect of the abovetreatments on interstitial impurities, hydrocarbons, oxides, acidic residuals,reaction products and metallic contaminations. The study confirms that theimpurity distribution in Nb is not only sensitive to the surface treatment, butalso to their sequence. Varying the treatment sequence prior to HV degassingtreatments affected the final impurity levels in HV degassed bulk Nb samples.BCP treated samples, exhibited minimum hydrocarbon and metallic contaminationbut, led to extensive contamination of the oxide layer with residuals andreaction products of acids used in BCP solution. HPR treatment, on the otherhand was effective in reducing the acidic impurities on the top surface. Thestudy also establishes the application of TOFSIMS technique to analyze andevolve SRF treatments.