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sem graph

 a 175nm-thick cu films well bonded to polyimide substrate, and strained to 20% using the micro-force testing system( MTS tytron 250)

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Zhigang Suo's picture

This image looks very good. It does look like necking to me. Could you please write a description of this image? Simply click the tab "edit" at the top of your post, and add a body of text. Thank you very much!

Note added on 1 January 2007.  See a related forum topic

 dear professor suo, thanks your answer.i am very encouraged to see what you said --my image looks like necks! is it the multiple necks as simulated in professor Li's papers? i think it would be necks ,while other  do not think so. they advice me to focus on the necks and give a further magnified microstructure. how about you? and your advice?

dear professor suo, can i have another request?

I am reading a doctor instructed by professor Jun Sun, your friend, and these research is  parts of the his 973 project. Considering the copyright, i wish the image just for our communication in private, and not be copied without permission. About this  research part, i am  writing the manuscript.

Zhigang Suo's picture

Dear Rongmei:

Here are a few points that might help to address your concern.

Your own your post, but everyone can use it, with proper attribution. If you scroll down to the very bottom of iMechanica, you will see a description of the copyright of materials posted on iMechanica. Basically, each author owns the copyright, and anyone can use the materials for free, provided the user gives proper attribution.

Most journals permit authors to post preprints. Also at the bottom of iMechanica you will find a link to a post on how to cite a journal article. The post gives you details about how copyright works for journals. Basically, most journals permit authors to post their own PREPRINT (not reprint) online, before or after a paper is published in a journal.

Each post in iMechanica is a publication, with a distinct timestamp. So, you can consider this image published. People can cite the post by giving the URL. Since you own its copyright, you can use the image any way you want it, including publishing it again in a journal article.

I think as a creator of content, you got absolutely nothing to lose to post all your work online. Let me know if you have further thoughts on this.

Dear all, i have another question. How to creep copper films bonded on PI substrate? Could you please give me some advice? many thanks!

Zhigang Suo's picture

You must know this paper:

Lu L, Sui ML, Lu K, Superplastic extensibility of nanocrystalline copper at room temperature, SCIENCE 287, 1463-1466 (2000)

I recall the authors caused huge deformation by rolling.  They argued that the deformation is due to diffusion along the grain boundaries.  Correct me if I'm wrong.  It has been a long time since I last read this paper.

Dear Prof. Suo, thanks for your replies.  yes, i have read the paper and you are right.  

Rongmei

chris's picture

Hi Rongmei,

I guess there are two ways to see if there is necking in your film:

 

- Use a Focussed Ion Beam (FIB) microscope, deposit Pt or W on the surface, prepare a cross section with the FIB and use an SEM to image since the Ion beam will destroy your sample. You will need to use a Field Emission Gun SEM to get high enough resolution. This solution is tough because the polymere underneeth will charge and will make it awfully hard even with a FEG SEM to get a good resolution.

 

- Use a TEM to study the deformed region. This is the better solution since a TEM will have definitely enough resolution. It will be probably also possible to study the dislocation structure at the crack tip or at least in the necked region if it is necked. The sample preparation is much harder but definitely worth it. Either you use a FIB/SEM dual beam to prepare the sample or you use the traditional path. Therefore you have to deposit a metal on top of your damaged film (e.g. Ni by electrodepositing), cut a cross section and thin it down to a couple of microns and use a ion beam milling step to form a thin wedge. The dual beam way is the more expensive but easier way. furthermore it is possible to prepare the sample from a location you choose with the SEM.

 

Chris.

 

 

Johns Hopkins University

Tel.: 410 516 6108 

Dear Chris,

         Nice to meet you very much!

       Thanks a lot for your advice! I am sorry for reply so later!

         I have tried and found that both FIB and TEM are unfeasible! it is very difficult to prepare a cross-section samples: by FIB, the ion beam destroy the sample surface, and  to image also is difficulty. In addition, the sample is too thin to constraint dislocations, and dislocations completely escape and i could not capture even a dislocation!

      Just as you said, it really is expensive both in time and money.

    Regards

Rongmei

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