Influence of electron irradiation and heating on secondary electron yields from non-evaporable getter films observed within situx-ray photoelectron spectroscopy

Abstract

Nonevaporable getter (NEG) film has been used for the beam ducts of particle accelerators as a pump having a large area. NEG film has been considered to have a low outgas rate induced by energetic particle irradiation and a low secondary electron yield (SEY). In this article, we focused on SEY measurements and in situ surface characterization of four NEG film samples using x-ray photoelectron spectroscopy (XPS). The NEG samples were TiZrV thin films deposited by magnetron sputtering at 100 or 300°C on stainless steel. In addition, NEG samples saturated by CO gas exposure were prepared. SEY and XPS measurements of the surfaces of NEG samples were carried out under the conditions of as received, after electron beam irradiation, and after heating at 200°C for 24h. The maximum SEY values of the primary electron energy dependence, δmax, of all NEG samples decreased to around 1 by electron beam irradiation owing to a change in the carbon impurities, such as carbon oxide, carbon hydroxide, and hydrocarbon, to graphite state (graphitization) during the irradiation. After heating, δmax values of the NEG samples without CO gas exposure were also around 1 owing to the carbonization of Ti, Zr, and V. The δmax≈1 was remarkably lower than that of copper baked under the same conditions. However, in saturated NEG samples, metal carbides were not produced to a significant extent by heating, and the δmax values did not decrease, showing values of 1.5–1.7.