IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Applied Surface Analysis Monday Sessions
       Session AS-MoP

Paper AS-MoP2
Thermal and Electron-beam Irradiation Effects on the Surfaces of Niobium@footnote 1@

Monday, October 29, 2001, 5:30 pm, Room 134/135

Session: Student Poster Competition/Aspects of Applied Surface Analysis I Poster Session
Presenter: Q. Ma, Argonne National Laboratory
Authors: Q. Ma, Argonne National Laboratory
R.A. Rosenberg, Argonne National Laboratory
Correspondent: Click to Email
Superconducting radio frequency (SCRF) cavities represent the future for producing high acceleration gradients. Many problems encountered during the course of rf cavity production, such as the field emission of impurity particulate, have largely been solved, and nowadays gradients as high as 25 MV/m are readily achievable. However, new issues are emerging that limit further increases of the accelerating gradient. It has become increasingly apparent that further advances in cavity performance will be linked to scientifically understanding the nature of the surface oxide layer. Preliminary results of a study of the surfaces of Nb samples for SCRF cavities are presented. The samples were prepared by chemical etching or electro-polishing, the processes used in cavity production. The surfaces of such prepared samples are covered typically by a layer of oxides and some hydrocarbons. The study is focused on thermal effect on the surfaces of as-prepared samples and on electron-beam interaction with these surfaces. At temperatures from 200 C to 300 C, the surface oxide reduction occurs. The native Nb@sub 2@O@sub 5@ oxide reduces to Nb@sub 2@O@sub x@ (x @<=@ 1). Some niobium carbide also forms on the surfaces. As a result, the secondary electron yield (SEY) decreases dramatically. At these temperatures, oxygen migration into Nb is evidenced, for which the diffusion coefficient is estimated. It is also found that the SEYs of as-prepared samples decrease significantly under electron-beam irradiation, which can be accounted for by the electron-beam-induced changes in surface chemistry. These changes will be discussed in terms of the effect of the cross section of electron/matter interaction. @FootnoteText@ @footnote 1@ Work supported by U. S. Department of Energy, Office of Basic Energy Sciences, under contract no. W-31-109-ENG-38.