Deformation mechanisms at multiple pop-ins under spherical nanoindentation of (1 1 1) Si

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The pop-in events and the deformation mechanisms of (1 1 1) Si under spherical nanoindentation were investigated using molecular dynamics simulations. The simulations result successfully reproduced the plastic deformation mediated by high-pressure phase transformations and dislocation burst, and the highly desirable brittle fracture of silicon. Quadruple occurrences of the pop-ins were observed in loading curves. The one-to-one relationship between the multiple pop-ins and the deformation mechanisms was established. Two fundamental processes, the asynchronous occurrences of high-pressure phase transformation and extrusion of α-Si, were identified from several deformation modes to be responsible for the multiple pop-ins. Moreover, the dislocation burst also contributes to the plastic deformation, and the cracks were observed to contribute to the brittle deformation, but contribute nothing to the pop-ins.