Analysis of Several-keV Electron Stimulated Desorption Gases from Oxygen-free Copper Electrode with a Directional Quadrupole Mass Spectrometer

Gases desorption from an electrode by electron irradiation are regarded as one of causes leading to vacuum breakdown. Desorbed gases stimulated by several-keV electrons from oxygen-free copper were analyzed by using a quadrupole mass spectrometer (QMS). In order to measure gases desorbed from the sample electrode with QMS directionally, a cooling shroud was surrounded with the QMS. The cooled shroud with cooling medium can adsorb not only background gases but also the gases desorbed from the wall of the vacuum chamber by the impacts of reflected or scattered electrons, and prevent them from entering the QMS detector directly. In this experiment, two types of cooling medium were used. When a liquid nitrogen was used into the shroud as cooling medium, gas analysis showed that desorbed gas components from the sample electrode were H2, H2O and CO, and in particular desorption of H2 was significant. Using liquid helium as cooling medium, it was confirmed that gases including H2 gas were condensed on the shroud. However in this experimental condition the desorbed gases from the sample electrode was not confirmed