Spring constant calibration

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Ben Ohler Posted: Wed, Apr 28 2010 6:22 PM

Spring constant calibration is a very important topic for anyone desiring to measure quantitative material properties or any other kind of quantitative force measurements using AFM. It is also often a confusing topic for those just getting started. So I just want to gather together here what I believe to be good starting resources for those who want to learn more about the various methods for spring constant calibration.

Please feel free to add to the discussion. What are your favorite references?

Veeco Application Note: Practical Advice on the Determination of Cantilever Spring Constants  http://nanoscaleworld.bruker-axs.com/nanoscaleworld/media/p/143.aspx

This is a review that I wrote several years back that should serve as a good starting point. It reviews all of the most common methods for calibrating cantilever spring constants, discusses anticipated uncertainty in these methods, makes recommendations for various circumstances, and finally gives step by step procedures for a few of the most common methods. Note that this review also contains references to many of the most commonly cited articles.

Jeffrey Hutter's website (University of Western Ontario): Calibration of AFM Cantilevers

This is another nice review of common methods. Maybe of particular interest is some specific information on implementing the thermal tune method using third-party hardware if your current AFM doesn't have that function built-in.

John Sader's website (University of Melbourne): Atomic Force Microscope Cantilevers (Calibration method of Sader)

Sader developed one of the common calibration methods, most often simply called the "Sader method." His website reviews the background theory and contains a very useful java applet for performing the final calculation of the method.

My publication in RSI: Cantilever spring constant calibration using laser Doppler vibrometry

This study looks at the uncertainty associated with two of the most common calibration methods, thermal tune and the Sader method. It also discusses a bit some of the main limitations and pitfalls of the techniques.

Regards,

-Ben

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Sarah replied on Thu, May 6 2010 2:28 AM

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"It is also often a confusing topic for those just getting started. "

I really agree with that. I still don't know how to choose a suitable calibration method for different cantilevers. How do I know if my results are accurate?

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Ben Ohler replied on Thu, May 6 2010 1:41 PM

If you haven't downloaded the App Note linked above then I suggest you start there. It gives a good starting point to selecting a method, considering both technical and practical issues. It includes a brief description of the uncertainty of the methods too.

The RSI publication linked at the bottom of my post provides some idea of the best case uncertainty of the thermal tune and Sader methods. But of course the accuracy of any of the methods mostly depends on implementation. Often times errors will cause huge mistakes in the calibration, which will be obvious when the calibrated value is an order of magnitude or more off from the nominal spring constant. But implementation errors can cause smaller errors too. The best way to guard against those is to use more than one method and compare results.

-Ben

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Polis Tyrol replied on Wed, Aug 28 2013 2:15 AM

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Just in case somebody else desperately tries to open the first link from above - you can find it here now: http://nanoscaleworld.bruker-axs.com/nanoscaleworld/media/p/143.aspx

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Stephen Minne replied on Wed, Aug 28 2013 4:22 PM

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Thanks Polis! I just corrected the original post.

Steve