The Origin of Fracture Surface Instabilities in (111) silicon crystal
Liron Ben Bashat Bergman (Technion), Dov Sherman (Technion)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium A
Tue 10:45 - 12:15
CIT 165
Fracture surface instabilities is a term used to describe disturbances on the fracture surface scales from nanometric undulations to macroscopic deflection. Previous investigations showed micron scale height corrugations instabilities on the fracture surface of the (111) low energy cleavage plane of silicon, when the crack was propagated in the [11 ] direction at speed below 1100 m/sec. These corrugations were evident in three point bending and tensile experiments, and resemble fluctuations on the (111) and (110) low energy cleavage planes, propagating along the intersection line of both planes. Recently, the density of these surface corrugations on the same crack system under bending was investigated in specimens having two distinct boron concentrations. Experiments showed that the corrugations density reduced significantly in specimens with low boron concentration. Experiments under ultra-high vacuum were conducted in STM microscope revealed that atomistc steps instabilities initiated during collision of the crack with a single boron dopants, which pile-up to initiate the larger surface corrugations. Quantum mechanical hybrid multi scale calculations with and without a single boron interstitial verified the latter experimental results. The fundamental query is whether surface instabilities are formed due to interactions of the crack front with crystal defects or, alternatively, is crack surface in ideal, defects free crystal, is always stable. We will present the experimental finding and the origin of the low speed crack surface instabilities and discuss the stability of the fracture surfaces in ideal brittle crystals.