Pop-in phenomenon in MgO and LiF: observation of dislocation structures

This letter is based on recent progress in the observation of dislocation distributions around nanoindentations by chemical etching. This so-called nanoetching technique is used to determine the dislocation mechanisms associated with the pop-in phenomenon in MgO and LiF. Successive stages of highly controlled chemomechanical polishing have revealed that these dislocations are half-loops lying in the classical slip systems of MgO or LiF. However, they do not extend on the surface in the classical rosette-arms pattern but stay concentrated around the imprint. A mechanism of dislocation interactions, enhanced by the fact that the dislocations are suddenly nucleated in a small volume, is proposed to explain this specific distribution.