Yokohama National University, Graduate School of Engineering Science, Yokohama, Japan
NIMS, Tsukuba, Ibaraki, Japan
KEK, Tsukuba, Japan
Sokendai, The Graduate University for Advanced Studies, Tsukuba, Japan
Yokohama National University, Yokohama, Japan
We have developed a zero-length conflat fin-type nonevaporable getter (NEG) pump that uses oxygen-free palladium/titanium (Pd/Ti)*. After baking at 150 degrees centigrade for 12 h, the pumping speeds of the NEG pump for H2 and CO were 2350~800 L/s and 1560~20 L/s, respectively, in the pumped-quantity range 0.01~30 Pa L. The morphologies of oxygen-free Pd/Ti films on the partition plates and the base plate were examined by scanning electron microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The Ti was completely coated with Pd on the bottom, whereas the partition plates were covered by Pd/Ti nanostructures. Our new NEG pump is ideal for maintaining ultrahigh vacuums in the range 10-8 to 10-9 Pa, because (a) its pumping speeds for H2 and CO are quite large, (b) it can evacuate H2O and CO2 when an ionization gauge is used in the vacuum system, (3) it can be activated by baking at 150 degrees centigrade for 12 h, (c) its pumping speed does not decrease even after 9 cycles of pumping, baking, cooling to room temperature, and exposure to air**, (5) it requires neither a dedicated power supply nor electric feedthroughs, and (6) it is space saving and lightweight.
*T. Miyazawa et al., J. Vac. Sci. Technol. A 36, 051601 (2018).
**T. Kikuchi et al., AIP Conf. Proc. 2054, 060046 (2019).
University of Tokyo, Kashiwa, Japan
KEK, Tsukuba, Japan
Sokendai, The Graduate University for Advanced Studies, Tsukuba, Japan
Tokyo University of Science, Noda, Japan
Yokohama National University, Yokohama, Japan
TIT, Tokyo, Japan
Yokohama National University, Graduate School of Engineering Science, Yokohama, Japan
Although nonevaporable getter (NEG) pumps are widely used in synchrotron radiation facilities, pure metal Titanium (Ti) has not been used as a NEG because the activation temperature of a Ti thin film deposited by DC magnetron sputtering was reported to be 350-400 °C*. Recently Miyazawa et al. found that high-purity Ti deposited under ultra-high vacuum (UHV) followed by N2 introduction works as a NEG with an activation temperature of 185 °C**,***. Since the concentration of impurities such as O, C, and N in the Ti thin film prepared by this method is 0.05% or less, we named this as oxygen-free Ti. In this study, we evaluated the pumping properties of oxygen-free Ti thin films after high-purity N2 introduction by total and partial pressure measurements. A vacuum vessel with oxygen-free Ti deposited on the inner walls was found to pump H2, H2O, O2, CO and CO2 even after 30 cycles of high purity N2 introduction, air exposure, pumping, and baking at 185 °C. Furthermore, we analyzed the oxygen-free Ti thin films after high-purity N2 or air introduction by synchrotron radiation X-ray photoelectron spectroscopy. The results show that more TiN was formed when high-purity N2 was introduced after oxygen-free Ti deposition. High purity of the Ti thin film and TiN formation on the surface seem to be responsible for the reduced activation temperature as low as 185 °C.
*C. Benvenuti et al., J. Vac. Sci. Technol. A 16, 148 (1998).
**T. Miyazawa et al., Vac. Surf. Sci. 61, 227 (2018).
***KEK, patent pending, WO2018097325 (Nov. 28, 2017).