Investigation of ultra thin coatings using nanoindentation

Abstract Recently, one of us (N.S.) has applied his extended Hertzian theory for the elastic deformation of layered materials to Pharr's concept of the effectively shaped indenter, thus being able to determine completely the elastic field for indentation experiments in the moment of beginning unloading. This opens up a wide range of new possibilities to extract information from nanoindentation experiments. The aim of this paper is to investigate further the capabilities of this novel approach taking a series of tetrahedral amorphous carbon ( ta -C) films ranging from 4.3 to 125 nm as well as a 44 nm TiN film (both on single crystal silicon) as examples. It is demonstrated that the yield strength of the TiN film as well as that of the ta -C films down to 31.4 nm thickness can be determined in good agreement with other information. In case of the thinner ta -C films a transition from pure coating failure over inelastic behaviour occurring at the interface to pure substrate failure for the thinnest coatings can be observed. The latter results indicate that the method allows to investigate relatively complex failure mechanisms like phase transitions or plastic deformation in the vicinity of the interface.