The cleavage energy at initiation of (110) silicon

We evaluated the cleavage energy at initiation of the (110)[10] low energy cleavage system of silicon crystal under pure Mode I, at room conditions and under inert argon gas at atmospheric pressure. The results revealed significant reduction of the room cleavage energy, presumably due to the effect of environmental molecules at the crack front. We also show that misalignment between the precrack and the maximum plane yields large variations in the cleavage energy, which may explain the large discrepancy appearing in the literature. Comparison of our results with those existing in the literature, enabled conclusion regarding the lower limit of the cleavage energy at initiation of brittle crystals and comments on other physical effects associated with crack initiation in these materials. We describe in details the experimental method that was used to evaluate the cleavage energy at initiation. This method is aimed at cleaving brittle materials in a controllable and noiseless manner and to generate high resolution fracture experiments. It consists in gluing a thin, precracked, rectangular brittle specimen in a rectangular aluminum frame, using thin layers of epoxy resin. Being very complaint, these layers enable to reduce the energy flow to the crack tip and to manipulate crack speed for accurate evaluation of materials properties. Crack initiation, propagation, and arrest, when needed, occur upon heating the assembly by only a few , due to the coefficients of thermal expansion mismatch between the specimen and the aluminum frame. Among other advantages, it facilitates accurate evaluation of fracture properties of brittle crystals, through utilizing the assembly as a boundary value problem appropriate for finite element analysis without requiring any assumptions regarding boundary conditions.