HVEM observation of crack tip dislocations in silicon crystals

Dislocation configurations near the tip of a crack in Si crystals has been investigated by using a high voltage electron microscope (HVEM). A (1̄10) crack was introduced into a (001) silicon wafer by using indentation method at room temperature, and the specimen was annealed at 823 K to emit dislocations from the tip of the crack under the presence of residual stress due to the indentation. An array of dislocations was seen not only in front of the crack tip but also in the crack wake. The dislocations were emitted on the (11̄1) plane which is oblique to the (1̄10) crack. The effect of crack tip shielding due to the dislocations is analyzed to be mainly mode I. Dense dislocation region is also found near the tip, suggesting the occurrence of dislocation multiplication around the crack tip.