Macro to atomistic examination of dynamic cleavage in single crystal silicon

A set of cleavage experiments with strip-shaped single-crystal silicon specimens subjected to three-point bending will be presented. The experiments enabled examination of the relationships between crack velocity, the crystallographic orientation, and the cleavage plane of propagation. Dynamic crack propagation experiments show that when a [001] silicon single crystal is fractured under three-point bending at measured velocity of up to 1500 m/sec, it prefers to cleave along the vertical (110) plane, while when the specimen is fractured under the same conditions but at a velocity higher than 2900 m/sec, it cleaves along the inclined (111) plane. At intermediate velocities, the crack will deflect from the (110) plane to the (111) plane. The deflection phenomenon presents an excellent opportunity to examine the upper crack tip's velocity limit. Analysis of the experimental results showed that the normalized crack tip velocity in the (110) plane with the Rayleigh surface wave speed yields ratio of up to 0.65 (in the [1 1 0] direction), which reduces to as low as 0.01 (in the [001] direction). It is suggested that the cause of the deflection phenomenon and the reasoning for the low limiting crack tip velocity is the anisotropic, velocity dependent, irreversible cleavage energy, resulted phonon radiation caused by anisotropic, velocity dependent lattice vibrations.