Estimate of theoretical shear strength of C60 single crystal by nanoindentation

The onset of plasticity in a single crystal C-60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems ⟨011 over bar ⟩111supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C-60 theoretical shear strength was about 1/11 of the shear modulus on {111} planes.