Fracture experiments to evaluate the cleavage energy of the ð110Þ½11 0 and ð111Þ½1 12 cleavage systems in silicon at room temperature and humidity give 2:7 AE 0.3 and 2.2 AE 0.2 J=m 2 , respectively, lower than any previous measurement and inconsistent with density functional theory (DFT) surface energy calculations of 3.46 and 2.88 J=m 2 . However, in an inert gas environment, we measure values of 3.5 AE 0.2 and 2.9 AE 0.2 J=m 2 , consistent with DFT, that suggest a previously undetected stress corrosion cracking scenario for Si crack initiation in room conditions. This is fully confirmed by hybrid quantum-mechanicsmolecular-mechanics calculations.

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