Atomic-scale insights into oxygen adsorption pathways on Ti-V-Nb ternary alloy NEG surfaces

Maintaining ultra-high vacuum (UHV) conditions is necessary for particle accelerators yet challenges like outgassing degrade vacuum quality over time. Our novel Ti-V-Nb alloy non evaporable getter (NEG) coatings provide effective solutions by adsorbing residual gases, including H₂and CO. It is important to note that oxygen adsorption inevitably occurs on the getter surface during critical stages including material preparation, sample transfer and activation procedures. This surface oxygen can potentially occupy active sites or alter surface chemistry, thereby impacting the material's subsequent adsorption efficiency for dominant residual vacuum gases, particularly hydrogen. Using density functional theory (DFT), this study analyzed oxygen adsorption on the Ti-V-Nb surface. The adsorption was spontaneous across all sites, with the Ti-Ti bridge site (B1) exhibiting the strongest adsorption energy of -5.838 eV. The results reveal that oxygen molecules, for the studied adsorption sites, preferentially adsorb at the bridge site > hollow site > top site, as indicated by adsorption energies and O-O bond lengths. Titanium atoms played a dominant role, exhibiting high reactivity and significant charge transfer during adsorption. Partial density of states (PDOS) and Mulliken charge population analysis revealed strong covalent Ti-O bonding driven by orbital hybridization in the valence band. The relevant research findings provide certain reference value for the component optimization design and performance enhancement of novel NEG films. It has also laid a solid theoretical foundation for further studying the adsorption mechanism of residual gases such as hydrogen and carbon monoxide on the surface oxidation of getters.