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Description
Non-evaporable getter (NEG) thin films are essential for achieving ultra-high vacuum in the narrow-bore chambers. Pd/Ti bilayer NEG thin films were deposited on oxygen-free copper and silicon substrates by DC magnetron sputtering. The microstructure and elemental distribution were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The films exhibit a cauliflower-like surface morphology and a columnar cross-sectional structure, providing a high specific surface area and effective pathways for gas diffusion. The pumping speed for H$_2$ was evaluated using the constant-pressure dynamic flow method after activation at 150 °C for 12 h. The pumping speed decreases from 0.13 to 0.02 L s$^{-1}$ within a pumped quantity range of $1 \times 10^{-5}$ - $6.5 \times 10^{-3}$ Pa L. A non-monotonic variation in pumping speed was observed, which is attributed to hydrogen adsorption, dissociation on the Pd surface, and subsequent diffusion into the Ti layer for hydride formation. The results demonstrate that the Pd overlayer effectively enables low-temperature activation and enhances hydrogen sorption behavior, indicating that Pd/Ti NEG thin films are promising candidates for ultra-high vacuum applications in accelerator systems.
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