Hydrogen adsorption mechanism on non-evaporable getter ternary alloy Ti-V-Nb surface

Non evaporable getter coatings are essential for achieving ultra-high vacuum (UHV) and extremely high vacuum (XHV) conditions in high-energy particle accelerators, with hydrogen (H₂) being a major residual gas of concern. This research uses Density Functional Theory (DFT) to investigate the adsorption of H₂ molecules on the Ti-V-Nb (110) surface, maintaining a 1:1:1 elemental ratio of Ti-V-Nb. The analysis prioritizes adsorption sites based on factors such as adsorption energy, H-H bond length, and charge redistribution. The results show that hydrogen molecules preferentially adsorb at the Hollow site > Bridge site > Top site, with corresponding variations in adsorption energies and bond lengths. The partial density of states (PDOS) calculations reveals significant hybridization between the H₂ molecule and the Ti-V-Nb (110) surface at each adsorption site, confirming the formation of strong chemical bonds. Mulliken charge population analysis results highlight significant charge redistribution upon adsorption, indicative of chemisorption phenomena. Bond population analysis confirms covalent bonding between H atoms and surface metals. The H-H bond length indicates nondissociation at the V top site (0.97Å) and dissociation at the Ti-V bridge (2.28 Å) and Ti-V-Nb hollow (2.73 Å) sites. Electron density difference calculations further confirm the activation mechanism of H₂ molecules on the Ti-V-Nb (110) surface by showing the accumulation and depletion of charges on H₂ at the selected sites. These insights contribute to understanding the hydrogen adsorption mechanism on Ti-V-Nb surfaces, which can enhance the efficiency of NEG coatings for achieving UHV and XHV conditions in high-energy particle accelerators.