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crack propagation in thin films
Tue, 2011-08-23 09:37 - bronger
I work in a thin-film photovoltaics institute. We deposit 1 µm silicon on glass substrate. This silicon has tensile stress.
Then, by etching through a tiny hole in the silicon with HF, we underetch the thin layer. This way, a circular area of the silicon is unattached to the glass. The circle grows with time. We observe spirals of cracks at these positions. Sometimes, there's only one spiral, sometimes we see two nested spirals.
Although we are experienced material scientists, nobody of us has competence in fracture mechanics. How do you think we should model this behaviour? Is there an analytical approach or will it only work with e.g. FEM? I'd be grateful for any keywords or literature that may help on this subject.
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crack patterns in thin films
Hi bronger,
Very interesting crack patterns. A couple of references may help you understand this problem:
Xia, Z.C., Hutchinson, J.W., 2000. Crack patterns in thin films. Journal of the Mechanics and Physics of Solids 48, 1107–1131.
H. Mei, Y. Pang, and R. Huang, Influence of interfacial delamination on channel cracking of elastic thin films. International Journal of Fracture 148, 331-342 (2007).
In the first paper, they considered crack patterns in an elastic thin film on substrate. In particular, they demonstrated a spiral crack path similar to your cracks. In the second paper, we showed the effect of interfacial delamination on the driving force for crack growth in thin films, which may explain why you only see cracks after underetching the Si film (detaching from the glass reduces the contraint against cracking of the film).
Regards,
RH