AVS 47th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeM

Paper VT-WeM5
Study of Desorption of Carbonaceous Gas Molecules from Copper Surfaces under Electron Bombardment

Wednesday, October 4, 2000, 9:40 am, Room 201

Session: Sorption Processes and Leak Detection
Presenter: M. Nishiwaki, The Graduate University for Advanced Studies, Japan
Authors: M. Nishiwaki, The Graduate University for Advanced Studies, Japan
S. Kato, KEK, Japan
Correspondent: Click to Email
Adoption of oxygen free copper has been recently begun to vacuum chambers of particle accelerators such as the KEKB accelerator that is a two ring electron-positron collider. Due to irradiation of the energetic particles and/or exposure to residual gas, however, the copper surface composition should be easily altered and consequently would give instable vacuum property because the passive surface cannot form on copper material which is different from other materials with passive surface such as stainless steel and aluminum. In this study, we aim to make clear about the mechanism about the adsorption and desorption on the copper surface using some isotope gas species. The copper surfaces to which some surface treatments were carried out were exposed to isotope gas species of @super 13@C with a known quantity in an ultra high vacuum. Afterwards, electron stimulated gas desorption (ESD) rates from these sample surfaces were measured using throughput method with a calibrated residual gas analyzer quantitatively. By using the isotope gas, desorbed gas under electron bombardment from the surface on which @super 13@C related gas molecules adsorb can be distinguished from desorbed @super 12@C related gas molecules which consist of diffused carbon atoms from the bulk since @super 13@C atoms do not exist in the bulk. Preliminary experimental results showed that enhancement of carbon diffusion to the surface under the electron bombardment occurred at a high sample temperature. This might suggest that the origin of carbon in the carbonaceous desorbed gas molecules such as CO and CH4 is not the top surface but the bulk possibly in a electron penetoration depth. Surface characterization of the copper materials will be also done using x-ray photoelectron spectroscopy in the adsorption and desorption processes of the isotope gas.