Surface analysis and vacuum performance of BeCu material

Abstract

1. Introduction

It is necessary to reduce the outgassing from the materials for achieving the extreme high vacuum, and research on surface treatment and other methods. The component of temperature rises due to heat source such as the filament of the vacuum gauge and the mass spectrometer become to increase the outgassing [1]. BeCu material has characteristics high thermal conductivity (13 times more than stainless steel) and low thermal emissivity (1/7 of stainless steel). The special heat treatment is able to reduce the diffusion of gases from BeCu material. Furthermore, an oxide film (BeO) is formed on the surface of BeCu material to prevent gas permeation. Due to these characteristics, the use of BeCu material made it possible to reduce the outgassing [2]. So BeCu material with the special heat treatment used for extreme high vacuum equipment such as vacuum gauge, mass spectrometers, and vacuum piping [3]. The performance was confirmed by the build-up method.

2. X-ray Photoelectron Spectroscopy (XPS)

Mr. Watanabe reported that the BeO film thickness on the surface is about 10 nm, but no verification data remains. Therefore, the surface condition with and without heat treatment was observed by XPS analysis. The result of analysis shows Be (0%), C (49.9%), O (24.5%) and Cu (14.5%) without heat treatment, and Be (34.5%), C (9.8%), O (52.9%) and Cu (2.5%) with the heat treatment. The thickness of the surface oxide film was 1 nm (CuO) without the heat treatment and 7.4 nm (BeO) with heat treatment. The type of each oxide film was different. Details will be reported on the day.

3. Build up test

The build-up evaluation method is 25 hours baking at 200 degrees C. The chamber is isolated after the chamber pressure is stabilized after baking. The chamber pressure measures during 120 minutes after isolated. After the measurement was completed, the baking is restarted without purge to the atmosphere, and the same measurement was performed 5 times. For performance comparison, we also measured SUS304 chamber was pretreated by vacuum firing (10 hours baking at 850 degrees C) [4]. Both of the ultimate pressure and the buildup pressure without the baking were lower for SUS304 than for BeCu. This is because the BeCu chamber before test was stored in the atmosphere, and the SUS304 chamber before test was stored in a vacuum pack after vacuum firing. BeCu was lower in both the ultimate pressure and the buildup pressure in the first baking. As the number of baking times increased, both the ultimate pressure and the build-up pressure of BeCu decreased. For SUS304, the ultimate pressure remained almost unchanged, but the buildup pressure decreased. Details will be reported on the day.

Reference

[1] F. Watanabe: J. Vac. Soc. Jpn. Vol. 49, No.6, 2006

[2] F.Watanabe: J. Vac. Sci. Technol. A, Vol. 22, No. 1, Jan/Feb 2004

[3] F. Watanabe: J. Vac. Soc. Jpn. Vol. 56, No.6, 2013

[4] J. Kamiya: e-j Surf. Sci. Nanotechnol. 21, 144-153 (2023)