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Surface energy is one of the most fundamental parameters of a solid since it depends directly on the binding forces of the material. Indeed, it is a measure of the work necessary to separate a material into two parts along a plane. Very few measurements have been made of this quantity and these by indirect means, because of difficulties of measurement and interpretation. This report deals with a direct measurement of specific surface energy of Ge and Si made by the cleavage technique. By measuring the force just necessary to move a crack "in reversible fashion" the surface energy can be obtained. The measured value for the 111 planes of Ge and Si are 1060 ergs/cm2 and 1230 ergs/cm2. From these measured values the energy of the planes 100 and 110can be estimated. They are:
R. J. Jaccodine (Tue,) studied this question.