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Hi,
I am new to QNM and am trying to measure the modulus of films (100's of nm thick on Si substrate) in the 5-10GPa range.
(1) What kind of precision is expected for measurements calibrated to a reference and what procedure is recommend for comparing multiple samples? I have been using the TAP525A tip, and noticed I am either getting tip contamination and/or wear. I am leaning towards contamination from SEM inspection.
My procedure has been: calibrate sensitivity, thermal tune,
measure beginning RS-15m (for tip monitor),
measure ref (QNM cal PS film), measure sample #1, measure sample #2
measure ref (QNM cal PS film), measure sample #3, measure sample #4, and so on
measure final ref (QNM cal PS film)
measure final RS-15m (for tip monitor).
On one day the tip radius didn't change throughout the measurements and the PS-film was +- 0.1 GPA. The other day I wasn't so lucky.
(2) I just discovered the Indentation Analysis feature. Can I use this function instead of QNM (just collecting several force curves) to minimize tip wear/contamination? Also, for the analysis, I don't know what radius to use (at height of max indentation or extracted tip radius or just to match reference?).
Any advice greatly appreciated!
Jeff
Dear Jeff,
I spend most of my time working on biological samples with QNM but I also have experience with QNM on much stiffer samples (up to 100 GPa). I noticed that whatever the sample, the tips often get contaminated and/or dulled after even just one scan. Of course this severely impacts on the measured Young's modulus.
If you start from a tip having a large tip radius (more than 20 nm), the risk of seeing the tip radius get increased after one scan is much lower than when starting from a very sharp probe (2, 5 or 10 nm).
So the ony trick I found so far is to work with larger probes (when I work on live cells, I even use to wear the tip on purpose on a stiff surface, prior to the experiment).
Now in reagards of the debris and comtaminants, you can use a perfusion systems to drag most of the contaminants away while imaging.
Good luck,
Alex.
Thanks for the advice. I had more time to analyze our tips (TAP525A) comparing before and after measurements. I am significantly wearing the tips (radius 8nm->~100nm) and also building up sample debris. I do have DDESP (DLC coated) tips that are less sharp to also try but am not sure if they are suitable for my sample hardness. Any suggestion on other tips for 5-10GPa range. I may try your suggestion of pre-wearing a tip (TAP525A).
Wow... 100nm; that's a lot!
For 5-10 Gpa, the TAP525 are really the best. The RTESPA are slightly too soft and the DNISP slightly too stiff.
Best,