Nanoindentation is a relatively new technique designed to probe material behaviour on the nanoscale. Experimentally, proximal probe tips such as the scanning force microscope (SFM), are used both to perform the indentations and to image the sample surface afterwards. The force acting on the tip is measured as a function of the indentation depth, and this relationship allows mechanical properties, such as hardness and Young's modulus, to be determined. The indenter is generally made from diamond and has an axisymmetric or pyramidal geometry with a small radius of curvature at the apex, since the indenter blunts with continued operation.

In this work, complementary parallel molecular dynamics simulations have been performed to gain further insight into the mechanisms governing deformation behaviour at the nanoscale. Indentations are performed in a quasi-static fashion using a diamond cube-cornered pyramidal tip with curvature applied at the apex, as shown below.

A range of materials have been studied, including carbon based materials and both bcc and fcc metals, showing a diverse range of behaviour. Million atom simulations with metals show the materials deform plastically, characterised by a large permanent impression in the surface and tip-induced pile-up around the sides of the indent. The simulations have also revealed that plastic deformation of metals is strongly influenced by both crystal and indenter geometry. Complex dislocation mechanisms and tip-induced pile-up is found to occur along preferred crystallographic directions. The images below show the tip-induced surface topography and dislocation loops for indentation of Fe {110}.