1. J. J. Thomson, in “Rays of positive electricity and their application to chemical analyses”, Longmans Green and Co., London (1921) 2nd edition.
2. J.Vac.Soc.Jpn. 24(1981)456 (in japanese).
3. P.Sigmund in Sputtering by Particle Bombardment I, R.Behrisch ed., Top.Appl.Phys. 47(Springer, 1981).
4. R.Kelly, private communication.
5. Physics Abstracts, Subject Index 1965–68. 1969–72. 1973–76. 1977–80. 1981–84.