Lateral Force Microscopy

A number of publications have appeared on how to calibrate atomic force microscopes for lateral force measurements since Ogletree, et al. published the wedge method [D. F. Ogletree, R. W. Carpick, and M. Salmeron, Rev. Sci. Instrum. 67,3298 (1996)]. Some of them are indirect methods of calibration, that require theoretical model analyses with a lot of uncertainties in their modeling variables. Some of them are inadequate for bio experiments (i.e. they are primarily applicable for very sharp tips, not for colloidal probes), and some of them are even wrong in principle.
 
If you are interested in principles and an overview of various calibration methods, you may look up a paper [Li, Q., Kim, K.-S., Rydberg, A., 2006. Lateral Force Calibration of an AFM with a Diamagnetic-Levitation Spring System. Review of Scientific instruments 77(6), 065105 ]. If you are interested in learning practical use of the diamagnetic lateral force calibrator (D-LFC) method, you may like to visit http://www.engin.brown.edu/facilities/nanomicro/calibrator/dlfcindex.html.

I haven't used this method myself but here is another possibility from Rev. Sci. Instrum.: Direct force balance method for atomic force microscopy lateral force calibration. the DOI is 10.1063/1.2190210

Hi Will.

I have not used the method of Li et al mentioned above, but I have read their paper carefully and discussed it with Prof. Kim, and I believe this to be a robust method. Furthermore, this is the only method that allows you to fully deal with the issue of cross-talk between the normal and lateral channels. It appears to be a very elegant method.

If you wish to use the wedge technique, indeed our paper mentioned above (Ogletree et al) is the original reference. However, I have clarified some of the discussion, fixed an error in one of the figures, and included error analysis in a chapter in my thesis, which can be downloaded from here:
http://mandm.engr.wisc.edu/faculty_pages/carpick/publications.htm (scroll down to “Calibration of frictional forces in atomic force microscopy” and click on the link marked “Click here for additional, updated information”).

We have MatLab scripts available on the web for assisting in the analysis of the data from this method:

http://mandm.engr.wisc.edu/faculty_pages/carpick/toolbox.htm

Furthermore, the wedge method was improved by Varenberg et al, in the following paper, and I recommend you consult it:

M. Varenberg, I. Etsion & G. Halperin. "An improved wedge calibration method for lateral force in atomic force microscopy". Rev. Sci. Instrum. 74, 3362-7 (2003)

We recently published another method of lateral calibration that we call the “test probe” method. This method has the advantage that you do not need to place the tip in contact with a sample to calibrate it. This is useful if you have a sensitive tip, e.g. functionalized with biomolecules, and you are concerned about fouling it. The disadvantage, as we discuss in the paper, is that it is not as accurate as the wedge method, and somewhat more difficult to carry out experimentally. That being said, it is entirely feasible to implement. The reference is:

R. J. Cannara, M. Eglin & R. W. Carpick. "Lateral force calibration in atomic force microscopy: a new lateral force calibration method and general guidelines for optimization". Rev. Sci. Instrum. 77, 53701/1-11 (2006) http://dx.doi.org/10.1063/1.2198768

Finally, the paper that Andre Brown cites, “Direct force balance method for atomic force microscopy lateral force calibration,” is erroneous. If you take a look you can see that the free-body diagrams are simply wrong. I strongly recommend you do not use this method; it is completely incorrect.

Regarding which cantilevers to use, I recommend silicon nitride over silicon, but both can wear out. You'll want to check for tip wear and contamination. Go for the lowest force constant probes you can get, but check that the in-plane bending is not too significant (this issue is discussed in the paper above by Cannara et al, and the original detailed reference is here: J. E. Sader & C. P. Green. "In-plane deformation of cantilever plates with applications to lateral force microscopy". Rev. Sci. Instrum. 75, 878 (2004) http://dx.doi.org/10.1063/1.1667252)

Calibration is challenging, but it is important to do, and it is an excellent learning experience for the student, who will be much more familiar with the AFM after going through it. Good luck,

Rob