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 H2O molecules around the crack front. Electronic structure near the crack front is calculated with density functional theory. 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 H2O molecules at a silicon crack tip is sensitive to the stress intensity factor K. For K=0.4 MPa.rootm, an H2O 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.rootm, an H2O molecule either oxidizes or breaks a Si-Si bond. (C) 2004 American Institute of Physics.