In situ XPS analysis of surface transformations in activated Ti-Zr-V thin films by nitrogen venting

Abstract

Non-evaporable getter (NEG) films have become critical for fourth-generation diffraction-limited storage ring vacuum systems. Repeated venting-activation cycles lead to reduced pumping performance and saturation of the film's absorptive capacity; therefore, it is necessary to minimize the number of activations by protecting or storing the film. In this study, NEG films were deposited on oxygen-free copper substrates using pulsed magnetron sputtering. The microstructure, surface morphology, and phase composition were analyzed. The X-ray photoelectron spectroscopy was employed to investigate the activation characteristics and the evolution of the chemical valence states of the NEG film's surface before and after nitrogen venting. The results indicate that the activated films form oxides and nitrides following initial nitrogen venting at room temperature. Compared to oxygen molecules, the reaction of the film with nitrogen molecules is insufficient, resulting in the formation of only a small quantity of nitrides. After nitrogen venting, the surface of the activated films retains a high proportion of zero-valent metals, exhibiting numerous active surface sites. An extended nitrogen venting period did not lead to a significant increase in oxide and nitride content, indicating that the film had not deteriorated further. These findings suggest the potential use of nitrogen for film protection and storage.