1. L. Holland, “The Properties of Glass Surfaces” (Chapman and Hall, London, 1964).
2. P. M. Sutton, in “Progress in Dielectrics”, Vol. 2 (Heywood and Co., 1960).
3. D. K. Davies, Electrical Research Association, Leatherhead;K. A. Hughes, University College of North Wales Bangor.
4. G. Carter andJ. S. Colligon, “Ion Bombardment of Solids” (Heinemann, London, 1968) p. 358.
5. T. M. Elmer, Proc. 7th Inter. Cong. Glass, Brussels, (1965) paper 30.