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Zhigang Suo's picture

Rongmei: Could you please add a description to this image? You may also want to make hyperlinks to existing discussions.

 This image show a clearly intergranular fracture of 100nm-thick Cu films at strain about 15%. And could it be enough to indicate a decreasing local thinning? From many images of deformed Cu films, it seems the decreasing of through-thick deformation(thinning) with reducing films thickness.   

 

Teng Li's picture

Rongmei, is this one of your Cu films on polyimide substrate?  It seems to me that the grain size is about 40-60nm, close to that of the Cu films in our APL paper.  The dark part of this image seems intergranular fracture to me. I'm wondering how thick this film is and how large the applied strain is. Thanks.

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Prof. Li, thanks for your replies. yes it is an image of Cu films on PI substrate. the strain is 15% and film thicknesss is 100nm. Why you ask such a question?

Thanks.

Rongmei 

Teng Li's picture

The grain size in this image is similar to that of Cu film in our APL paper, which showed both intergranular cracking and local thinning. The thickness of that Cu film in our paper is 170nm and the strain is 30%. So my observation here is that film thickness also plays its role in the failure mode of the film, with local thinning more likely occurs in thicker film. Of course, this needs further systematic experiments to verify.

-Teng

Prof.Li, does the presence of Pi substrate suppess the local elongation, and also assist multiple thinning on films surfaces? I was puzzled by it.

Could you please clarify my mind and guide me? Thanks!

Rongmei

Teng Li's picture

Rongmei,

The polymer substrate can delocalize the deformation of the thin metal film, carrying the film to large strain. Depending on the relative stiffness and thickness of the polymer and the metal, different numbers of necks (local thinnings) may form in the film, instead of forming one single neck that leads to the failure of the film if it is freestanding.  Hope this is helpful.

-Teng 

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