<p>In a society aiming to be carbon neutral, hydrogen is expected to be a clean energy source, but it also has problems, such as its susceptibility to explosion and hydrogen embrittlement of metals. The questions “where is hydrogen trapped in materials and where does it cause embrittlement?” and “Where is the location of the hydrogen leak from the gas line?" can be answered by measuring the location of hydrogen. However, as is well known, that it is difficult to specify the location of hydrogen. Operando hydrogen microscope (OHM) is a hydrogen visualization equipment using electron stimulated desorption (ESD) method [1,2]. In the equipment, permeated hydrogen atoms through the sample membrane are ionized by incident electron on the sample surface, desorbed into UHV environment and detected. By using the electron source of a scanning electron microscope (SEM) as the excitation source for the ESD, we visualize the surface hydrogen distribution from the hydrogen desorption position.</p><p></p><p>By OHM, we measured the diffusion coefficients of austenite-dominant regions and martensite-dominant regions in stainless steel, cold-worked dual-phase SUS304, based on changes in the amounts of hydrogen permeating time from the backside of the sample [3]. We used electron backscattering diffraction (EBSD) to determine the martensite/austenite ratio and compare the structure distribution and hydrogen distribution measured in OHM. Then, we were able to create a model of hydrogen diffusion through a dual-phase region [4]. We also observed the effect of surface film to reduce hydrogen desorption. We have created a chromium oxide film on the surface of SUS316 steel and confirmed that the release of hydrogen inside the material was suppressed to less than half. We also found that there was hydrogen release from hole-like-defects where the chromium oxide was incomplete [5]. This study found that the outgassing from the chromium oxide surfaces was not uniform, but from specific locations. In this way, OHM measurements can also be used to identify the location of gas leaks, not averaged outgassing.</p><p></p><p>The standard conductance element (SCE) is a filter of open type standard leak, and it uses sintered stainless steel as a leak medium [6]. We attempted to visualize where the gas flows in SCE, regarding the pores of the sintered body as the gas leakage points of the SCE. The figure shows SEM picture of the surface of the SCE (SCE-ICF34-04-S1, Puaron Japan co.,ltd) (left) and hydrogen distribution at the same position with the SEM (right), at the conditions of hydrogen supplying pressure of 100 Pa, SCE temperature of 373 K and ESD signals integrated 3024 maps in 168 hours. High concentration of hydrogen was measured on the pore edge area of the micro particle surface of sintered body that constitutes the SCE. We assume that the hydrogen as the adsorption source is only from the hydrogen gas flowed through the filter pores and it adsorbs with the same adsorption ratio on the SCE surface and inner surface of the pores. The hydrogen pressure inside the pore and near the exhaust port of the pore is higher than the hydrogen pressure in the measurement chamber. It is considered that the hydrogen adsorbed on the way through the pore and desorbed by ESD around the SCE pores. This is a reason why the signal is increasing at around the SCE pore. It will be possible to confirm with OHM how hydrogen flowed through the leak pores.</p><p></p><p>[1] N. Miyauchi, et al., Scripta Materialia 144 (2018) 69</p><p>[2] A. Nakamura, et al., J.P. Patent 06796275, 2020</p><p>[3] N. Miyauchi, et al., Applied Surface Science 527 (2020) 146710</p><p>[4] A. N. Itakura, et al., Scientific Reports 11 (2021) 8553</p><p>[5] N. Miyauchi, et al., Applied Surface Science 492 (2019) 280</p><p>[6] H. Yoshida, et al., Vacuum, 86 (2012) 838</p>