The role of dislocation activities in the brittle-ductile transition in silicon single crystals

Abstract

To determine the controlling mechanisms in the brittle-ductile transition (BDT) in silicon single crystals, one must identify the conditions for dislocation nucleation at crack tips. In the present study, dislocation nucleation in $\{110\}$$$ oriented silicon is determined experimentally. The specimens are first statically loaded at high temperatures, and then fractured at room temperature. It is found that an increase in fracture toughness is associated with crack-tip dislocation activity during the high-temperature static loading. The loading condition at the onset of fracture-toughness increase corresponds to the one for dislocation nucleation at the high temperatute. The results indicate that dislocations can nucleate at temperatures well below the commonly observed BDT temperature, indicating that the BDT in silicon is governed by dislocation mobility rather than dislocation nucleation.

Room-temperature fracture surfaces after the static loading exhibit periodic waviness, which is attributed to inhomogeneous dislocation emission. Confocal microscopy is employed to quantify the fracture surface roughness. The results show that the increase of fracture toughness is directly associated with the increased area of the rough surface, which can be characterized by roughness number or fractal dimension increment.

A numerical model is developed to capture the physical processes in the BDT. The model predictions are consistent with experimental observations. The numerical results indicate that the number of active slip systems at the crack tip plays a significant role in determining the behavior of the BDT.