iMechanica - polymer - Comments

Sorry for the late reply.

Ying Li — Tue, 24 Jun 2008 04:56:10 -0400

Sorry for the late reply. EBSD is a good method to monitor the texture of the film. By the EBSD, the grain size of the Cu could be clearly investigated. Especially, the in-situ SEM loading with the EBSD could check the grain growth when the Cu film is under tension. Such a in-situ SEM with EBSD method has been successfully applied to investigate the equal channel angular extruded Mg-3Al-Zn magnesium alloy. However, as you say, the indexing rate is very low for nano grains.

Ying Li Department of Engineering Mechanics Tsinghua University Beijing, 100084, P. R. CHINA

The size effect on failure modes of metal thin films

Nanshu Lu — Thu, 12 Jun 2008 13:26:26 -0400

Hi, Teng,

Thanks for pointing this out. Actually it is what I am doing now.

Basically the film failure mode exhibits a ductile-brittle transition as film thickness reduces. But we found that neither the thickness nor the grain size alone will be sufficient to understand the phenomenon. I am trying to take both factors into consideration to give better explanations now.

I'll send you some preliminary results through email.

Nanshu

Difficulty with grain size distribution

Nanshu Lu — Thu, 12 Jun 2008 13:10:00 -0400

Ying, thanks for your interest and comment.

We haven't found any efficient way to determine the statistical distribution of nano grains so that we are trying to show straightforward micrographs at this point.

TEM is not suitable because the film microstructure is very unstable and easy to change during sample preparation.

EBSD works well for annealed films with micron-sized grains but the indexing rate is very low for nano grains.

XRD does not show much broadening because our grain size is not small enough.

I will try AFM to see if it can give reasonable results.

Manually sketching grain boundaries will always work but I will keep it as the last choice.

Do you have any experience or suggestions on this to share with us? Many thanks.

Nanshu

Effect of film thickness

Teng Li — Thu, 12 Jun 2008 11:08:49 -0400

Nanshu,

Neat experiments! The paper reveals another critical mechanism governing the failure of metal films on polymer substrates.

The films reported in paper are about 1 micron thick. I'm curious about the effect of film thickness on the deformation-induced grain growth. For example, does similar phenomenon occur in a thinner film (say, a few hundred nm thick) on a polymer substrate.

Interesting work!

Ying Li — Thu, 12 Jun 2008 08:26:24 -0400

Have you done the detailed work on the grain size distribution according to your SEM or FBI imagines? I think the statistical data may be more helpful to understanding the deformation-induced grain growth.

Ying Li Department of Engineering Mechanics Tsinghua University Beijing, 100084, P. R. CHINA

That's good news indeed.

Albert F Yee — Sun, 27 Apr 2008 18:01:42 -0400

That's good news indeed. I've been looking for such a book for reference and teaching.

Thanks! Unfortunately, we

cbrinson — Sun, 27 Apr 2008 11:58:56 -0400

Thanks! Unfortunately, we did not go into shape memory polymers. A topic saved for the second edition!

Great!

Xiang Chen — Sat, 26 Apr 2008 15:22:36 -0400

I'm just in need of such a book. Is there specific discussion on shape memory polymers?

No debonding observed in undeformed specimens

Nanshu Lu — Tue, 09 Oct 2007 22:25:18 -0400

To answer your question in another point of view we used FIB to cut undeformed specimens as well and observed no debonding at all. Hence we believe that FIB will not cause metal film debonding from the substrate.

Initial stress

Nanshu Lu — Tue, 09 Oct 2007 16:18:30 -0400

This is what we are working on actually. We did not deal with stress-strain in this submitted paper. You must already know that an ordinary way to determine the residual stress is to do curvature measurment of the specimen.

thanks

Rongmei niu — Mon, 08 Oct 2007 21:56:43 -0400

Hi, Nanshu, thanks for your telling me the method. hehe, comparing with your advanced method, my method is too backward. At the beginning, I kept eye on the Keithley source meter and recorded the value at once, and when one test finish, my hand is already too tired to raise.

Resistance measurement

Nanshu Lu — Mon, 08 Oct 2007 13:34:08 -0400

Hi, Rongmei,

Thanks for your interests on our work. To determine the initial resistance we measured the sample with a Keithley multimeter and then subtracted the system resistance which was obtained by contacting the two probes of the multimeter. We recorded in-situ resistance during tension by connecting the multimeter to the computer with a well-known software named LabView . Of course there's a little programing to do.

Regards,

Nanshu

thank you

Rongmei niu — Sun, 07 Oct 2007 10:44:32 -0400

Dear Xi , thanks. I want to make cross-section specimen of Cu films on PI all the time, but failed due to PI substrates. so I will learn from you, thanks again.

Re: FIB induced damage

Xi Wang — Sat, 06 Oct 2007 17:05:27 -0400

Hi Rongmei, thanks for being interested in our work. The milling process from the ion impact can cause some damages to the sample, including surface amorphization and contamination. MRS bulletin May 2007 actually has a very good review article about FIB milling process. The cut in Fig.5(b) was made by several steps, including fine polish steps with very low beam current. It is unlikely the feature is due to the FIB process.

Another question

Rongmei niu — Fri, 05 Oct 2007 19:27:05 -0400

Nan shu, I have another question want to consult you.

How about the initial stress before your tension?

Thank!

Best Regards

Rongmei