Microstructure of plastic zones around crack tips in silicon revealed by HVEM and AFM

In order to understand the dislocation process for the sharp brittle-to-ductile transition in silicon crystals, microstructures of plastic zones around crack tips have been investigated using high-voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were introduced into {1 1 0} silicon wafers at room temperature by Vickers indentation method. The temperature of specimens indented was raised to higher than 823 K to activate dislocation sources around a crack tip under the presence of residual stress due to the indentation. The crack observed was extending along the 〈1 1 0〉 direction from the edge of the indent. AFM study has revealed two types of fine slip bands around the crack tip: one type of slip bands is those parallel to 〈1 1 2〉, and another type is those parallel to the 〈1 1 0〉 direction. The former is corresponding to so-called hinge-type plastic zone, and the latter is 45°-shear-type. HVEM study has revealed the characteristics of dislocation structures corresponding to the both types of plastic zones. Detailed analyses of each dislocation, including the determination of the sign of Burgers vector, have been made to characterize those plastic zones.