TEM/AFM observation of crack tip plasticity in silicon single crystals

Crack tip plasticity in silicon single crystals has been investigated using both high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into a (001) silicon wafer at room temperature by Vickers indentation method. The specimen temperature was increased to more than 873 K to activate dislocation generation around the crack tip under a residual stress due to the indentation. In specimens without the heat-treatment, no dislocations were observed around the crack, while in specimens with the heat-treatment, characteristic dislocation configurations were observed near the crack tip. AFM observations showed that slip bands were formed around the crack tip in the heat-treated specimens, and that the step heights of those slip bands were around one nanometer. Such crack tip plasticity is considered to be caused by mainly mode I tensile load, and contribute to increasing fracture toughness.