HVEM/AFM Studies on Crack Tip Plasticity in Si Crystals

Abstract

Crack tip plasticity in silicon crystals has been studied by both high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into silicon wafers at mom temperature by Vickers indentation method. Specimens indented were annealed at temperatures higher than 773K to activate dislocation sources around a crack tip under the residual stress due to the indentation. In the present study, two types of plastic zones were examined: the 45° -shear-type in |001} wafers and hinge-type in |011} wafers. In AFM observations, very fine and sharp slip bands were found around crack tips in both types of plastic zones, where the step heights in the slip bands we around a few nanometers. In HVEM study, characteristic dislocation configurations have been observed in each type of plastic zone. Contrast simulations for the dislocations revealed not only their slip systems but also the signs of their Burgers vectors. The dislocation structures characterized by HVEM correspond well with the slip bands found by AFM. Those dislocations were shielding-type, which contributes to the increase of facture toughness to cause the sharp brittle-to-ductile transition of silicon crystals.