Fatigue and debris generation at indentation-induced cracks in silicon

The nature of fatigue in bulk silicon subjected to cyclic loading is considered. Indentation tests with hard spheres of millimeter-scale radius are used to generate fractures principally in {1 0 0} silicon surfaces, but also in selected {1 1 1} silicon, polycrystalline silicon and {1 0 0} monocrystalline germanium surfaces. Pronounced damage accumulation is observed with progressive indenter cycling, as ejection of slabs and particles onto the specimen surfaces. It is argued that the fatigue arises from sliding at friction points within the crack interfaces, with consequent production of debris outside and (ultimately) within the contact. Section views through the indentation sites provide clues as to the material ejection process, involving coalescence of secondary cracks into a primary ring crack to create the slabs. Ejection is facilitated by linkage between adjacent ring cracks, leading ultimately to mass removal.