1. J. Bardeen, Phys. Rev. 71, 717 (1947).
2. W. Shockley and G. L. Pearson, Phys. Rev. 74, 232 (1948).
3. J. W. Gibbs, “Collected Works,” Yale University Press, 1948, Vol. 1.
4. See for example W. W. Mullin in “Metal Surfaces,” ASM, 1963, p. 17.
5. For a review see A. D. Adamson “Physical Chemistry of Surfaces,” Interscience Publishers, Inc. 1960.