A usable concept for the indentation of thin porous films

Abstract

Abstract The paper deals with the application of Pharr’s concept of the effectively shaped indenter as well as an extension of that concept – referred to as extrapolation method – on the determination of the yield strength of porous thin films. As an example, a 1066 nm thick porous SiO2 xerogel film having a porosity of about 50% and an average pore size in the range 3 – 4 nm was investigated. Three different spherical indenters with radii of 1.4, 3.11 and 110 lm were used in this investigation. Depending on the indenter radius and the applied load the physical nature of the sample deformation was different making the one or the other of the two methods more suitable for analysis. We found that the data received with the large indenter could be well analysed using Pharr’s concept, while for the two smaller indenters the extrapolation method had to be used. The yield strength values obtained with the two methods were in remarkable agreement (109 vs. 99 MPa).