Comparative research on the secondary electron yields and photon-stimulated desorption of Ti and Pd/Ti bilayer thin films

Particle accelerators operate in an ultrahigh vacuum (UHV) environment to reduce interactions between the particle beam and residual gas molecules, which helps to decrease beam losses and extend beam lifetimes. Non-evaporable getter films, owing to the uniform pumping speeds and minimal outgassing characteristics, are extensively employed to sustain UHV conditions in particle accelerators. The deposition of a palladium (Pd) layer on the surface of titanium (Ti) film enhances oxidation resistance and lowers the activation temperature. A single-layer Ti film and a double-layer Pd/Ti film were deposited using the direct current (DC) magnetron sputtering method. The microstructures, cross-sectional elemental distributions, surface elemental compositions, secondary electron yields (SEYs), and photon-stimulated desorption (PSD) yields of these two types of films were tested and analyzed, respectively. The results show that the introduction of the Pd layer leads to a morphological transformation of the film surface from a stonelike structure to a cauliflowerlike structure. In SEY tests, the maximum SEY value of the Pd/Ti film was lower than that of oxygen-free copper but higher than that of the pure Ti film, whereas the PSD of H2, CO, and CO2 for the Pd/Ti film was lower than that for the Ti film.