Photon Factory Activity Report 2018 #36 (2019)

BL-13B/2016T002

Oxygen-Free Palladium/Titanium Coating, a Novel Nonevaporable Getter Coatingwith an Activation Temperature of 133 °C
Tetsuya Miyazawa1, Masashi Kurihara2, Shinya Ohno2, Naoya Terashima3, Yuto Natsui3,Hiroo Kato3, Yoshihiro Kato4, Ayako Hashimoto5,6, Takashi Kikuchi7, and Kazuhiko Mase1,7,*1
SOKENDAI, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
2
Yokohama National University, Yokohama, Kanagawa 240-8501, Japan
3
Hirosaki University, Hirosaki, Aomori 036-8561, Japan
4
Irie Koken Co., Ltd., 740-5 Shimoakasaka, Kawagoe, Saitama 350-1155, Japan
5National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
6
University of Tsukuba, 1-2-1 Sengen, Tsukuba 305-0047, Japan
7
Photon Factory, Institute of Materials Structure Science, High Energy Research Organization(KEK), 1-1 Oho, Tsukuba, 305-0801, Japan
1 Introduction
Nonevaporable getter (NEG) pumps are ideal formaintaining an ultra-high vacuum (UHV) owing to theirhigh pumping speed for active residual gases (particularlyhydrogen). NEG coating is a technique to coat the innerwalls of vacuum chambers with NEG thin films that can beactivated through baking under UHV [1, 2]. We recently
developed a new NEG coating with an activation
temperature of 185 °C using Ti vacuum sublimation
followed by Pd vacuum sublimation (low-oxygen-content
Pd/Ti coating) [3]. In the present paper, we report Pd/Ti
coating with extremely low oxygen concentration(oxygen-free Pd/Ti coating) with an activation temperature
as low as 133 °C [4].
2 Experiment
The apparatus used for the preparation of oxygen-freePd/Ti samples for scanning transmission electronmicroscope (STEM), scanning electron microscope (SEM),
and transmission electron microscope (TEM), and X-ray
photoelectron spectroscopy (XPS) measurements is shownin Fig. 1. The apparatus used for the oxygen-free Pd/Ti
coating for SS316L formed bellows is shown in Fig. 2. The
oxygen-free Pd/Ti film was deposited on the SS304L
substrates or inner walls of the formed bellows under clean
UHV conditions. The concentration of oxygen in the Pd/Ti
film was estimated to be less than 0.05%.
The apparatus used to measure pressure curves ofoxygen-free-Pd/Ti-coated formed bellows is shown in Fig.
3. The UHV chamber is pumped with a TMP through amanual UHV gate valve. A B-A gauge is installed tomeasure the pressure in the UHV chamber. The oxygenfree-Pd/Ti-coated bellows, a nipple made of 0.2%-BeCu
alloy, and a B-A gauge are connected to the UHV chamber
via an all-metal valve. This system was pumped, and thensuccessively baked at 133 °C for 12 h, 176 °C for 3.5 h,
and 200 °C for 3.5 h. After each baking the pressure curves
are measured with the B-A gauge.
3 Results and Discussion
STEM, SEM, and TEM images of oxygen-free Pd/Ti areshown in Figs. 4, 5, and 6, respectively. The Ti and the Pd

films were almost uniform, and the Ti film was completely
overcoated by the Pd film. The thicknesses of the Pd andTi thin films were approximately 50 nm and 1.3 μm,respectively. The Pd/Ti surface had an uneven structurewith irregularities of several tens to several hundreds ofnanometers. XPS spectra of oxygen-free Ti and Pd/Ti films
are shown in Fig. 7. Ti and oxygen were negligible on thePd/Ti surface.
Figure 8 shows the summarized pressure curves afterbaking at 133 °C for 12 h, 176 °C for 3.5 h, and 200 °C for
3.5 h. After closing the all-metal valve, the pressure in thesystem reached values of 4.6 × 10−6 Pa, 1.7 × 10−7 Pa, and6.1 × 10−8 Pa, respectively. The pumping speeds of thecoated bellows after baking at a maximum temperature of
133 °C for 12 h, 176 °C for 3.5 h, and 200 °C for 3.5 h
were estimated to be 0.028, 0.23, and 0.23 L s −1,respectively. The pumping speed did not decrease evenafter the oxygen-free-Pd/Ti-coated bellows were vented.
The results indicated that the Pd film prevented theoxidation of the Ti film during venting.

Fig. 1: Schematic of oxygen-free Pd/Ti and Ti coating
apparatus for STEM, SEM, TEM, and XPS samples.
Reproduced from Ref. 4, with the permission of AIP
Publishing.

Photon Factory Activity Report 2018 #36 (2019)

Fig. 2: Schematic of oxygen-free Pd/Ti coating apparatus
for formed bellows. Reproduced from Ref. 4, with thepermission of AIP Publishing.

Fig. 3: Schematic of apparatus used to measure pressure
curves of oxygen-free-Pd/Ti-coated bellows. Reproducedfrom Ref. 4, with the permission of AIP Publishing.

Fig. 4: STEM dark-field image of cross section of oxygenfree Pd/Ti film. Reproduced from Ref. 4, with thepermission of AIP Publishing.

Fig. 5: SEM image of surface of oxygen-free Pd/Ti film.
Reproduced from Ref. 4, with the permission of AIP
Publishing.

Fig. 6: TEM bright-field image of interface between Ti andPd films of oxygen-free Pd/Ti. Reproduced from Ref. 4,with the permission of AIP Publishing.

Fig. 7: XPS spectra of oxygen-free Ti and Pd/Ti films.
Reproduced from Ref. 4, with the permission of AIPPublishing.

Photon Factory Activity Report 2018 #36 (2019)

Fig. 8: Pressure curves of uncoated bellows and oxygenfree-Pd/Ti-coated bellows. Reproduced from Ref. 4, withthe permission of AIP Publishing.
The advantages of the oxygen-free Pd/Ti coating are as
follows: 1) it can be activated by baking at a maximum
temperature of 133 °C for 12 h, 2) it is durable against
repeated venting-baking cycles in principle, 3) it iseconomical, 4) it does not require skilled technicians, and5) it can be applied to large chambers with a complicatedstructure. Therefore, the targets of this oxygen-free Pd/Ti
coating will be expanded to include vacuum systems withViton® O-rings.
Acknowledgement
The authors are grateful to Mr. Norihiro Irie, Ms. Miyuki
Okada, Mr. Ryosuke Tachi, Mr. Hiroshi Minamoto, Mr.
Katsushi Nishioka, Mr. Kazunari Aoki (Irie Koken Co.,Ltd.), Ms. Misao Yamanaka (NIMS), Prof. Yasunori
Tanimoto (KEK-ACCL), Mr. Akio Toyoshima (KEKIMSS), Mr. Hirokazu Tanaka (KEK-IMSS), Mr. Hiromu
Nishiguchi (Baroque International Inc.), and Ms. Eriko
Kazama (Baroque International Inc.) for their invaluableadvice and support. A part of this work was carried out by
using the facility of NIMS TEM station. This research wasconducted through collaboration with Irie Koken Co., Ltd.,and was partly supported by a Grant-in-Aid for scientificresearch (JSPS KAKENHI Grant Number JP17K05067)
and by TIA-Kakehashi grants (TK17-013 and TK18-014).
This work was partially supported by the Global ResearchCenter for Environment and Energy based on
Nanomaterials Science.
References[1] C. Benvenuti et al., J. Vac. Sci. Technol. A 16, 148(1998).
[2] C. Benvenuti et al., Vacuum 50, 57 (1998).
[3] T. Miyazawa et al., Vac. Surf. Sci. 61, 227 (2018).
[4] T. Miyazawa et al., J. Vac. Sci. Technol. A 36, 051601(2018).
* mase@post.kek.jp