Environmental effects of H2O on fracture initiation in silicon: A hybrid electronic-density-functional/molecular-dynamics study.

A hybrid quantum-mechanical/molecular-dynamics simulation is performed to study the effects of environmental molecules on fracture initiation in silicon. A (110) crack under tension (mode-I opening) is simulated with multiple H 2 O molecules around the crack front. To accurately model the long-range stress field, the quantum-mechanical description is embedded in a large classical molecular-dynamics simulation. The hybrid simulation results show that the reaction of H 2 O molecules at a silicon crack tip is sensitive to the stress intensity factor K. For K 0.4 MPa. √ m, an H 2 O molecule either decomposes and adheres to dangling-bond sites on the crack surface or oxidizes Si, resulting in the formation of a Si-O-Si structure. For a higher K value of 0.5 MPa· m, an H 2 O molecule either oxidizes or breaks a Si-Si bond. [ABSTRACT FROM AUTHOR]