Fracture toughness of silicon crystals has been investigated using indentation methods and their surface energies have been calculated by molecular dynamics (MD). In order to determine the most preferable fracture plane at room temperature, a conical indenter was forced into a (001) silicon wafer at room temperature. Dominant {110} cracks were 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 of fracture toughness, 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 KIC value for the {110} crack plane was the minimum among those for the planes of the ‹001› zone. Fracture toughness of {110} plane and the other planes of ‹001› zone were measured by the indentation fracture (IF) method. The result is qualitatively in a good agreement with those obtained from the MD, although the absolute KIC values estimated by the IF method were larger than those obtained by the calculation.
