Photon Factory Activity Report 2018 #36 (2019)

BL-3B/2016T002

XPS Study on the Thermal Stability of Oxygen-Free Pd/Ti Thin Film,a New Nonevaporable Getter (NEG) Coating
Tetsuya Miyazawa1, Masashi Kurihara2,Shinya Ohno2, Takashi Kikuchi3, and Kazuhiko Mase1,3,*
1
SOKENDAI, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
2
Yokohama National University, Yokohama, Kanagawa 240-8501, Japan3
Photon Factory, Institute of Materials Structure Science, High Energy Research Organization(KEK), 1-1 Oho, Tsukuba, 305-0801, JapanTi 3p
Ti 3s

Pd 4p1/2, 4p3/2ValenceO 2p

Intensity (a.u.)

1 Introduction
Nonevaporable getter (NEG) coating is a technique tocoat the inner walls of vacuum chambers with NEG thinfilms that can be activated through baking under ultrahighvacuum (UHV). The activated NEG films suppress
outgassing from the chambers and evacuate residual gasses,
and consequently maintain UHV in the range 10–8 Pa withsmall ion pumps. The most widely-used NEG coating isdeposited TiZrV films that can be fully activated afterbaking at 180 °C for 24 h [1, 2]. However, NEG coatingshave rarely been applied to beamlines and endstations insynchrotron radiation facilities. To expand the scope ofNEG coating applications, we developed a new NEG
coating using oxygen-free Pd/Ti film deposition [3,4]. In
this paper we report thermal stability of oxygen-free Pd/Ti
investigated by using X-ray photoelectron spectroscopy(XPS) [5].

65 60 55 50 45 40 35 30 25 20 15 105360 C
340 C320 C300 C280 C260 C240 C
220 C200 C180 C160 C140 C
120 C
100 C
RT0Binding energy (eV)Fig. 1: Wide-scan XPS spectra of the oxygen-free Pd/Tifilm. Reproduced from Ref. 5, with the permission of AIP
Publishing.

2 Experiment
The oxygen-free-Pd/Ti was deposited on SS304L
substrates under clean UHV conditions. XPS
measurements were carried out using p-polarized SR witha photon energy (hν) of 110 eV and ARPES II (VSW, withHA54) at BL-3B of Photon Factory. The sample wasirradiated at an incidence angle of 45° from the surface
normal, and photoelectrons emitted in the surface normal
direction were detected. The sample was annealed at 100,120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340,
or 360 °C for 5–10 min by electron bombardment.
3 Results and Discussion
Figure 1 shows wide-scan XPS spectra of the oxygenfree Pd/Ti film as a function of annealing temperature in
the range 100–360 °C. The Fermi level was taken as theorigin of the binding energy (BE) axis. At room
temperature, the Pd 4p1/2 and 4p3/2 peaks were observed at
BEs of 51.1 and 49.4 eV, respectively, as shown in Fig. 2a.
The Ti 3s and 3p peaks were not observed, as shown inFigs. 2a and 2b. This result indicates that the Pd film
completely overcoated the Ti film. The Ti 3p peak
appeared at BE of 33.9 eV when the sample was annealed
at 280 °C, as shown in Fig. 2b. We assigned this Ti 3p peakto Ti1+, because BE of Ti (Ti0) was reported as 32.5 eV [6],while BEs of Ti2O3 (Ti3+) and TiO2 (Ti4+) were reported as36.2 eV [7] and 37.5 eV [8], respectively. The O 2p peak
was not clear at 280 °C, but clearly appeared at BE of 9.3

Fig. 2: Enlarged XPS spectra in the region of (a) Pd 4p1/2(BE = 51.1 eV) and Pd 4p3/2 (BE = 49.4 eV), (b) Ti 3p (BE= 33.9 eV), and (c) O 2p (BE = 9.3–11.1 eV) peaks of theoxygen-free Pd/Ti film. Reproduced from Ref. 5, with thepermission of AIP Publishing.

Photon Factory Activity Report 2018 #36 (2019)eV at 300 °C as shown in Fig. 2c. Because the vapor
pressure of Pd is negligible in this temperature region [9],the results indicate that Ti segregates to the surface at 280–
300 °C and forms Ti1+ such as Ti–OH and Ti2O. On theother hand, the intensities of the Pd 4p1/2 and 4p3/2 peaks
decreased at 300 °C and became negligible at temperatures
greater than 320 °C, as shown in Fig. 2a. The Ti 3p and O
2p peaks grew at above 300 °C, as shown in Figs. 2b and2c. These results indicate that Ti segregates to the surface
and oxidizes forming Ti1+ at above 280–300 °C. Therefore,
the maximum allowable temperature of oxygen-free Pd/Tifilms is approximately 260 °C. This temperature has
almost no limitations in its use in SR facilities because themaximum allowable temperature of beamlines andendstations is usually less than 260 °C.
Acknowledgement
The authors are grateful to Dr. Kenichi Ozawa (TokyoInstitute of Technology), Mr. Hiromu Nishiguchi (BaroqueInternational Inc.), and Ms. Eriko Kazama (BaroqueInternational Inc.) for their invaluable advice and support.
This research was partly supported by a Grant-in-Aid forscientific research (JSPS KAKENHI Grant Number
JP17K05067), TIA-Kakehashi grants (TK17-013 andTK18-014), and the Matching Planner Program from Japan
Science and Technology Agency, JST.
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).
[5] T. Miyazawa et al., AIP Conf. Proc. 2054, 060045(2019)[6] A. Lebugle et al., Physica Scripta 23, 825 (1981).
[7] F. Werfel and O. Brümmer, Physica Scripta 28, 92(1983).
[8] F. Lange et al., J. Electron Spectrosc. Relat. Phenom.
57, 307 (1991).
[9] R. E. Honig and D. A. Kramer, RCA Rev. 30, 285–305(1969).
* mase@post.kek.jp