I am about to check the possibilities offered by Gwyddion, WSxM and SPIP to derive the radius of AFM tips used in contact mode. I would be grateful if anybody with prior knowledge in this procedure could offer any insight. Thanks.
I usually use the 'NanoScope Analysis' software provided by Bruker Company. There is a function of tip qualification which can be used to obtain the 3D geometry of the tip. Then the radius of the AFM tip can be achieved.
Thanks Yanquan. Since I don't have a Bruker AFM, I guess I won't be able to access this software.
SPIP may also be a viable option which I used before. But some parameters (such as iterations and fit range) may have a large influence on the precision of the tip radius assessment.
I find that this is the main problem with the blind tip reconstruction approach. I tried the trial version of SPIP and the free Gwyddion software but the results vary greatly depending on the parameters used.
I suggest you can obtain a high magnification image of the side face of the tip by scanning electron microscope (SEM). And you can use a circle to fit the apex of the tip. The radius of the circle is roughly equal to the radius of the tip. Then you can cpmpare it with the different results obtained by the blind tip reconstruction approach with different parameters. The parameter of closest approximation can be used for the tip radius assessment. Simultaneously, you can chose several tips with different radii to verify the parameter you selected.
Thanks Yanquan, a few month ago, I have done what you suggested for one particular tip using SEM and Gwyddion. I found that the matching of both results is extremely sensitive to the noise parameter used during the blind tip reconstruction. I have not tried with additional tips because I am not convinced that the parameter used for one case would be the same for a second tip. Maybe you are right and I should try anyway. Thanks for taking the time to provide input to my question. Have a good day.
All the different softwares are based on the algorithm originally developped by a NIST researcher Villarubia in 1997 ([J. Res. Natl. Inst. Stand. Technol. 102, 425 (1997)] they should not give you too different results. But one thing you have to consider is the nature of the surface you are imaging. If you want a proper measurement of your tip shape you would need to image features with edges smaller than the AFM tip radius and face angles sharper than tip angles. The later needs to be randomly oriented. An other way and may be a more direct one would be to image needle etched silicon samples (tip radius and angle sharper than AFM ones). In this case you will directly have the 3D shape of the probe. Those samples can be easily purchased from AFM tip retailers.
All the best
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