Abstract
Prediction and optimization of the chemical interactions between reactive hydrogen and transition metal (TM) compounds−including nitrides, oxides, and carbides (collectively referred to as TMX)−are crucial for a wide range of advanced technological applications. These applications range from energy production systems, such as fusion reactors, to semiconductor fabrication processes, including extreme ultraviolet
lithography machines. In such systems, TMX coatings are exposed to reactive hydrogen, leading to their chemical degradation. This degradation primarily occurs through reduction reactions, resulting in the loss of X−atoms. Consequently, this undermines system performance and poses significant operational risks. This thesis, therefore, focuses on identifying the key material parameters that govern the reduction reaction of TMX thin films in hydrogen radicals (H*) and low−energy hydrogen plasma (H−plasma).
The thesis demonstrates that the work function serves as a predictive and tunable parameter governing the hydrogen−induced reduction of TMX. Group 3–5 TMX thin films exposed to H* and H−plasma show that the TMX reduction reaction effectively stops once they reach a specific chemical composition. At this stage, the TMX work function consistently measures 4.3 ± 0.5 eV. It is proposed that the TMX reduction reaction stops at this threshold due to the preferential binding of H* to TM—atoms rather than X—atoms, thus preventing the formation of volatile (XHy) species.
Further, the thesis shows that the work function of TMX can be modulated through alloying. Increasing the fraction of a low−work function TM decreases the work function of the TMX alloy, thereby decreasing its reducibility in hydrogen. This, in turn, stabilizes the higher oxidation states of a high−work function TM, which would otherwise readily reduce.
The insights presented in the thesis offer a comprehensive framework for the strategic selection and development of TMX coatings, tailored to meet the specific needs of hydrogen−based systems.
lithography machines. In such systems, TMX coatings are exposed to reactive hydrogen, leading to their chemical degradation. This degradation primarily occurs through reduction reactions, resulting in the loss of X−atoms. Consequently, this undermines system performance and poses significant operational risks. This thesis, therefore, focuses on identifying the key material parameters that govern the reduction reaction of TMX thin films in hydrogen radicals (H*) and low−energy hydrogen plasma (H−plasma).
The thesis demonstrates that the work function serves as a predictive and tunable parameter governing the hydrogen−induced reduction of TMX. Group 3–5 TMX thin films exposed to H* and H−plasma show that the TMX reduction reaction effectively stops once they reach a specific chemical composition. At this stage, the TMX work function consistently measures 4.3 ± 0.5 eV. It is proposed that the TMX reduction reaction stops at this threshold due to the preferential binding of H* to TM—atoms rather than X—atoms, thus preventing the formation of volatile (XHy) species.
Further, the thesis shows that the work function of TMX can be modulated through alloying. Increasing the fraction of a low−work function TM decreases the work function of the TMX alloy, thereby decreasing its reducibility in hydrogen. This, in turn, stabilizes the higher oxidation states of a high−work function TM, which would otherwise readily reduce.
The insights presented in the thesis offer a comprehensive framework for the strategic selection and development of TMX coatings, tailored to meet the specific needs of hydrogen−based systems.
| Original language | English |
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| Qualification | Doctor of Philosophy |
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| Supervisors/Advisors |
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| Award date | 1 Apr 2025 |
| Place of Publication | Enschede |
| Publisher | |
| Print ISBNs | 978-90-365-6527-1 |
| Electronic ISBNs | 978-90-365-6528-8 |
| DOIs | |
| Publication status | Published - 1 Apr 2025 |