AVS 49th International Symposium
    Vacuum Technology Wednesday Sessions
       Session VT-WeM

Paper VT-WeM6
Study on Desorption of Carbonaceous Gas Molecules from Copper Surfaces under Electron Bombardment and the Surface Characterization

Wednesday, November 6, 2002, 10:00 am, Room C-104

Session: Outgassing
Presenter: M. Nishiwaki, KEK, Japan
Authors: M. Nishiwaki, KEK, Japan
S. Kato, KEK & The Graduate University for Advanced Studies, Japan
Correspondent: Click to Email
In particle accelerators, the carbonaceous gas desorption is generally observed as a result of the energetic particle stimulation at ducts and r.f. component surfaces during the operation and would deteriorate the beam performance. Therefore we aim to understand origin of the desorbed carbonaceous gas from the copper surface using carbon isotope. The passive layer cannot be formed at the surface of the oxygen free copper adopted to the beam duct. Since the surface should be easily altered due to irradiation of energetic particles and/or exposure to residual gas, the carbonaceous gas desorption mechanism from the surface is of high interest. In this study, we focused on the electron stimulated desorption (ESD) from the copper surface and its in-site surface characterization by x-ray photoelectron spectroscopy and Auger electron spectroscopy. For the surface cleaning and initializing, the copper samples were sputtered with Ar@super +@ ion beam and annealed. Exposure of @super 13@C isotope gas and @super 13@C ion implantation were done to the samples with the known quantities respectively. Afterwards, ESD rates from the samples were measured using throughput method with a calibrated residual gas analyzer quantitatively. By using the isotope, influences of @super 12@C in the residual gas and the bulk of copper can be eliminated during observation of desorbed gas from the sample under electron bombardment. The ESD of @super 13@C related gas species from the surface exposed to @super 13@CO@sub 2@ were not observed. In the experiments of @super 13@C implanted samples, the ESD of @super 13@C related gas species with a low current density were not observed either at the room temperature. However the ESD rates of @super 13@C related gas species from the heated @super 13@C implanted sample around 65 degrees C were as high as the thermal desorption rates at around 250 degrees C. These results showed that the diffusion of implanted @super 13@C from the bulk was enhanced by heating and/or electron bombardment depending on the beam current density and might suggest that origin of the desorbed carbonaceous gas is not the top surface but the bulk possibly in a range of the electron penetration depth.