Published online by Cambridge University Press: 15 February 2011
A model has been developed to determine the hardness of thin films from the measured change in hardness with indenter displacement using a depth-sensing indentation instrument. The model is developed by dividing the measured hardness into film and substrate contributions based on the projected areas of both the film and substrate under the indenter. The model incorporates constraints on the deformation of the film by the surrounding material in the film, the substrate, and friction at the indenter/film and film/substrate interfaces. These constraints increase the pressure that the film can withstand and account for the increase in measured hardness as the indenter approaches the substrate.
The model is evaluated by fitting the predicted hardness versus depth curves to data obtained from titanium and Ta2O5 films of varying thicknesses on sapphire substrates. The model predicts a lower interfacial strength for Ta2O5 films on sapphire with a carbon layer between the film and the substrate than that obtained for a film without an interfacial carbon layer.
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