Highly sensitive detection of net hydrogen charged into austenitic stainless steel with secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) is used to detect local distributions of hydrogen in various materials. However, it has been well-known that it is extremely difficult to analyze net hydrogen (H_N) in metals with SIMS. This was because hydrogen, which is originated from moisture (H ₂O), hydrocarbon (C_xH_y) or other organic materials (C_xH_yO_z) existing on a sample surface or in the SIMS chamber, is simultaneously detected in the SIMS measurement of the H_N, and the H_N and the background-originated hydrogen (H_BG) cannot be distinguished in a SIMS profile. The effective method for reductions and determinations of the H_BG in hydrogen measurements of metallic materials with the SIMS method has not been established. The present paper shows an effective method for reduction and estimation of H_BG in SIMS analyses of hydrogen charged into type 316 L austenitic stainless steel, and an accurate estimation method of the net charged hydrogen. In this research, a silicon wafer is sputtered by a primary ion beam of a SIMS near an analyzed area (silicon sputtering method) to reduce H_BG. An uncharged type 316 L sample was prepared for estimation of H_BG in SIMS measurements of the hydrogen-charged sample. The gross intensities of hydrogen between the hydrogen-charged sample and the uncharged sample were compared. The gross intensities of hydrogen of the uncharged sample (26.8-74.5cps) were much lower than the minimal gross intensities of hydrogen of the hydrogen-charged sample (462-1140 cps). Thus, we could reduce the H _BG enough to estimate the hydrogen charged into the type 316 L sample. Moreover, we developed a method to determine intensities of H _BG in the measurement of the hydrogen-charged sample by estimating the time-variation of hydrogen intensities in the measurements of the uncharged sample. The intensities of the charged hydrogen can be obtained by subtracting the estimated intensities of the H_BG from the gross intensities of hydrogen of the hydrogen-charged sample. The silicon sputtering method used to reduce H_BG and the determination method for H_BG in this research can be applied to the accurate hydrogen analysis for other various metallic materials.