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Description
So far, the most common practice for measuring H at microstructural features in APT is using the heavier isotope deuterium in combination with voltage pulses. For metals with a high evaporation field, including steels, the formation of H2+ ions is inhibited. Hence, the peak at 2 Da can solely be attributed to D, which was introduced via electrochemical or gas charging, or implantation. But what about samples, that fracture easily in voltage mode? Usually, laser-assisted evaporation is employed for these materials, which incurs a higher concentration of H and the formation of H2+. The amount of artificial H from the vacuum chamber can be estimated by the evaporation rate method, i.e. varying the time between pulses.
In this work, commonly used measurement parameters like constant detection rate or frequency are compared with measurements with constant flux of ions and varying frequencies. The newest generation of LEAP instruments is equipped to run simultaneous voltage and laser pulses. This feature allows the use of low laser energy while keeping a low field between pulses to limit background noise. In this way, H2+ formation is mitigated, while ensuring smooth evaporation of the samples. The concentration of H is tracked throughout the experiments and visualized as a function of time between pulses. Measurement parameters to distinguish artificial H2+ from introduced D+ at the 2 Da peak are investigated.
