Effect of thermal cycling on microstructure and adhesion properties of Ti-Zr-V thin films

Non-evaporable getter films are essential to obtain the ultra-high vacuum environments for the modern accelerators. However, regular thermal activation of the NEG films is required to maintain their pumping capacity. The thermal activation rises the risk of deteriorating the film/substrate adhesion, which, unfortunately, has been overlooked. In the present work, ternary Ti-Zr-V films were deposited by DC magnetron sputtering on oxygen free copper (OFC) and Si substrates. The effect of thermal cycling on the microstructure and adhesion strength of the thin films were characterized. The results indicate that thermal cycling induce an increased surface roughness due to coarsening of the particle size. Contrary effect is imposed on the adhesion strength of the NEG film deposited on the OFC substrate as compared with that on the Si substrate. After thermal cycling, the scratching critical load of the Ti-Zr-V film on OFC decreases from 0.14 N to 0.06 N while those on Si substrate increased by tenfold from 0.56 N to 5.79 N. The current work is insightful on long-term maintenance of the NEG coated chambers from an angle different from the commonly emphasized pumping capabilities.