A ReaxFF Molecular Dynamics Study of Hydrogen Diffusion in Ruthenium-The Role of Grain Boundaries

Chidozie Onwudinanti, Mike Pols, Geert Brocks, Vianney Koelman, Adri C.T. van Duin, Thomas Morgan, Shuxia Tao (Corresponding author)

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Ruthenium (Ru) thin films are used as protective caps for the multilayer mirrors in extreme ultraviolet lithography machines. When these mirrors are exposed to atomic hydrogen (H), it can permeate through Ru, leading to the formation of hydrogen-filled blisters on the mirrors. H has been shown to exhibit low solubility in bulk Ru, but the nature of H diffusion through Ru and its contribution to the mechanisms of blistering remain unknown. This work makes use of reactive molecular dynamics simulations to study the influence of imperfections in a Ru film on the behavior of H. For the Ru/H system, a ReaxFF force field which reproduces structures and energies obtained from quantum-mechanical calculations was parametrized. Molecular dynamics simulations have been performed with the newly developed force field to study the effect of tilt and twist grain boundaries on the overall diffusion behavior of H in Ru. Our simulations show that the tilt and twist grain boundaries provide energetically favorable sites for hydrogen atoms and act as sinks and highways for H. They therefore block H transport across their planes and favor diffusion along their planes. This results in the accumulation of hydrogen at the grain boundaries. The strong effect of the grain boundaries on hydrogen diffusion suggests tailoring the morphology of ruthenium thin films as a means to curb the rate of hydrogen permeation.

Original languageEnglish
Pages (from-to)5950–5959
Number of pages10
JournalJournal of Physical Chemistry C
Issue number13
Publication statusPublished - 7 Apr 2022

Bibliographical note

Funding Information:
This research was carried out under project number T16010a in the framework of the Partnership Program of the Materials Innovation Institute M2i ( www.m2i.nl ) and the Technology Foundation TTW ( www.stw.nl ), which is part of The Netherlands Organization for Scientific Research ( www.nwo.nl ). Some of the material in this article was published in C. Onwudinanti’s doctoral dissertation.


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