1. A. Arnau, F. Aumayr, P. Echenique, M. Grether, W. Heiland, J Limburg, R. Morgenstern, P. Roncin, S. Schippers, R. Schuch, N. Stolterfoht, P. Varga, T. Zouros, and H. Winter, Surf. Sci. Reports 27, 113 (1997)
2. J. Burgdörfer, Review of Fundamental Processes and Applications of Atoms and Ions, p. 517, World Scientific, Singapore, 1993.
3. H. Winter and F Aumayr, J. Phys. B 32, R39 (1999)
4. H. Hagstrum, Phys. Rev. 96, 325 (1954)
5. U. Arifov, E. Mukhamadiev, E. Parilis, and A. Pasyuk, Zh. Tekh. Fiz. 43 375 (1973), [Soy. Phys.-Tech. Phys. 18, 240 (1973)]