An investigation was made, of the atomic-scale details of atomic force microscopy, by performing quasi-static molecular dynamics simulations using a density-functional based tight-binding method. Changes in the atomic force microscope tip-shape and the size of the tip/sample contact area were studied for {111}, {110} and {100} surfaces. The contact area was found to depend upon the indentation depth in a manner which implied a jump from a non-contact to a contact mode. This was suggested by a sudden increase in the contact area over a short distance, and by the presence of a small attractive force during the pre-loading phase. Simulated atomic force microscopic measurements could be used to identify atomic rearrangements during indentation. The atomic force microscopy could detect impurities on the surface, and defects beneath the surface; at least under zero-temperature conditions. Sub-surface vacancies, or a H-coverage of the surface, decreased the hardness and the Young’s modulus.

Nanoindentation of Silicon Surfaces – Molecular Dynamics Simulations of Atomic Force Microscopy R.Astala, M.Kaukonen, R.M.Nieminen, T.Heine: Physical Review B, 2000, 61[4], 2973-80