Fracture toughness evaluated by indentation methods and its relation to surface energy in silicon single crystals

Fracture toughness of silicon crystals has been investigated by indentation methods, and their surface energy has been calculated using molecular dynamics (MD). When a conical indenter was forced into a (001) silicon wafer at room temperature, {110} cracks were mainly introduced from the indent, indicating that fracture occurs most easily along the {110} plane among the crystallographic planes of the <001> zone. To confirm this orientation dependence, surface energies for those planes were computed using molecular dynamics. The surface energy calculated exhibits the minimum value of 1.50 J·m^-2 at the {110} plane, and it increases up to 2.26 J·m^-2 at the {100} plane. Fracture toughness was derived from these computed surface energies, and it was shown that K_IC value for the {110} crack plane was the minimum among those for the planes of the <001> zone. This result is in good agreement with that obtained by indentation fracture (IF) methods, although the absolute K_IC values evaluated by the IF method were larger than those obtained by the calculation.