Dresden 2006 – scientific programme
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DS: Dünne Schichten
DS 7: Mechanical properties of thin films
DS 7.4: Talk
Monday, March 27, 2006, 16:45–17:00, GER 38
Yield strength of soft and brittle porous materials by nanoindentation — •Matthias Herrmann1, Norbert Schwarzer2, and Frank Richter1 — 1Solid State Physics, Institute of Physics, TU Chemnitz, Germany — 2Saxonian Institute of Advanced Surface Mechanics, Eilenburg, Germany
Yield stress and Young’s modulus of the above mentioned materials have been investigated in order to understand the material behaviour under typical loading conditions for instance during the chemical-mechanical polishing process.
For the characterization of such soft and brittle layers, no adequate method exists. Two usable methods for the determination of yield stress of porous materials will be demonstrated which are based on Pharr’s concept of the effectively shaped indenter. It assumes the plastically/elastically deformed zone beneath the indenter as an equivalent indenter and enables one to evaluate the complete elastic stress field during nanoindentation. One of us (N.S.) has proposed an extension of Pharr’s concept which allows the evaluation of the yield stress for the case of higher amounts of inelastic deformation even at low applied loads.
Our investigations were done on mesoporous SiO2 xerogel as well as MSQ-based films on silicon with porosities of 30 up to 57 volume percent. The film thickness was in the range of 600 nm. The yield strength was in the range of 75 - 150 MPa and the Young’s modulus between 1 and 4 GPa, depending on material (xerogel or MSQ) and porosity.