Environmental effects of H2O on fracture initiation in silicon: A hybrid electronic-density-functionalÕmolecular-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 K50.4 MPa•Am, 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 •Am, an H2O molecule either oxidizes or breaks a Si–Si bond. © 2004 American Institute of Physics. @DOI: 10.1063/1.1689004#