Crack tip dislocations observed by TEM-tomography in silicon single crystals

Abstract

3D observations of dislocations at a crack tip were attempted by transmission electron microscopy and computed tomography in order to reveal the 3D structure of dislocations emitted around a crack tip. {011} cracks were introduced into a (001) silicon single crystal wafer by using an indentation method at room temperature. The specimens indented were heated and kept at high temperatures to introduce dislocations from the crack tip. The specimen holder was tilted ±31° by 2° step and dislocation images were taken at every step. The diffraction vector was kept nearly 220 during the tilting operation. The Burgers vectors of the dislocation segments were determined, which included the signs of Burgers vectors. The dislocations observed here were those which accommodate mode II stress intensity around the crack tip. 3D observations using electron tomography reveal these complex crucial processes around the crack tip, which should contribute to understanding the dislocation process improving fracture toughness of crystalline materials.