Using advanced depth-sensitive hardness measurements, the homogenous nucleation of dislocations was observed in dislocation-free single crystals. This process was related to a sudden displacement jump in the force-displacement curve. The mechanical stress for the set-in of this pop-in effect was estimated with the Hertzian elastic contact theory. Experimental results of dislocation loop nucleation showed good agreement with the continuum theory of dislocations. Electron microscopy provided a direct proof of dislocation nucleation during nano-indentation.

Pop-In Effect as Homogeneous Nucleation of Dislocations during Nano-Indentation. D.Lorenz, A.Zeckzer, U.Hilpert, P.Grau, H.Johansen, H.S.Leipner: Physical Review B, 2003, 67[17], 172101 (4pp)