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How to get the young's modulus from one peak force curve?

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zhihengzuo posted on Thu, Mar 27 2014 5:06 PM


I have some problems about getting young's modulus from a single force curve.

We use peakforce QNM to get a lots of force curve for our sample and use nanoscope analysis to do the offline analysis.

When I choose a single peak force and do the indentation analysis, I get results: R^2 Young's Modulus and reduced Modulus in exact number. However, if I changed the max force fit boundary and min force fit boundary, the young's modulus changes a lot. Besides, if I change fit method and model the value changes too.

I can understand that different models will get different results, but I don't understand what is the function of those max and min fit boundary? should I keep them above baseline or is there any restrictions about boundary chosen?

I just want to know, how exactly the young's modulus for one force curve is calculated out by the software.

I know the equations but if we use either hertian or sneddon equations, we would get a young's modulus from one signal point of a force curve. If we use curve fitting by least square method, which part of the force curve should we use? Like the retrace curve above the baseline or curve from the peak force point to the contact points or something else?

Another question, if my curve shows a great adhesion force which is about two times larger than the peak force, can I use those models to calculate the young's modulus?


Thank you so much for everyone

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Ang Li replied on Wed, May 21 2014 2:50 AM

Hi, in ideal case, if the sample is purely elastic and the experiment condition follow exactly the contact geometry of Hertzian or Sneddon models, the fitting boundary shouldn't affect the results. but this is not the case for most of the samples and different fitting range would give different results. generally speaking, we would like to include the most likely elastic deformation regime for best fitting and best calculation of the modulus and also try to avoid high adhesion from the fitting.  

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