1. For an introductory survey, see “Physics Today”, April, 1975
2. For surveys of the theory of the electronic structure of clean surfaces see: N.D. Lang, Solid State Physics 28, 225 (1973)
3. J.A. Appelbaum, in “Surface Physics of Crystalline Materials”, ed. by J.M. Blakely (Academic, N.Y., 1975)
4. Surveys of chemisorption theory have been given by: T.B. Grimley, J. Vac. Sci. Technol. 8, 31 (1971)
5. J.R. Schrieffer, J. Vac. Sci. Technol. 9, 561 (1972)