Speaker
Description
The investigation of hydrogen in Atom Probe Tomography remains a relevant challenge. Its low mass, high diffusion coefficient, and presence as a residual gas in vacuum chambers generate multiple complications for APT investigations. Different solutions were proposed in the literature to charge our sample, such as ex-situ charging coupled with cryotransfer [1], or hydrogen charging at high temperatures in a separate chamber [2]. Nevertheless, these solutions often faced challenges due to the complex control of specimen temperature during hydrogen charging and subsequent analysis.
In this paper, we propose an alternative route for in-situ H charging in atom probe derived from a method developed in field ion microscopy to study He implantation damage. By applying negative voltage nanosecond pulse on the specimen in an atom probe chamber under low pressure of H2, it is demonstrated that high dose of H (~100,000 at) can be implanted in the range 2-20 nm beneath the specimen surface. An atom probe chamber was modified to enable direct negative pulse application with controlled gas pressure, pulse repetition rate and pulse amplitude. Through electrodynamical simulations, we show that the implantation energy falls within the range 100 - 1,000 eV. A theoretical depth of implantation was predicted and compared to results.
To investigate the hydrogen embrittlement, our objective is to understand the impact of hydrogen implanted within the sample by examining the evaporation electric field. A comparison is made between hydrogen coming from the analysis chamber and from the materials. The result indicates that hydrogen from the sample significantly reduces the evaporation electric field (~6%).
References:
[1] Yi-Sheng Chen et al. Cryo Atom Probe: Freezing atoms in place for 3D mapping. Nano Today 37 (2021).
[2] J. Takahashi et al. Origin of hydrogen trapping site in vanadium carbide precipitation strengthening steel. Acta Materialia 153, p 193-204 (2018).
