Trouble Scanning Tungsten Tips, Any Ideas?
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Hello,
I am a undergraduate research assistant and I have been trying to find the surface roughness of Tungsten IFM tips in the AFM. I am a TermoMicroscopes Autoprobe M5 in Tapping Mode. I am placing the Tungsten tip vertically and approaching the apex. I can visually see the tip with the microscope, so I am sure the cantilever is in the correct area. The problem I face is that it seems I get a lot of noise and sometimes the cantilever will "fall off" the tip and I must re-position the cantilever. The radius of curvature of the tip ranges; the smallest radius I have so far (verified by SEM) is 1.63 microns, and the biggest thus far is 20.85 microns. I am able to get readings on tips with radii larger than 14 microns with some time, anything smaller is extremely difficult. Any suggestions? -
Hi - we use two techniques in our group:
1. TEM. This gives you a transverse image (i.e., a 2-d projected profile) of the tip along one axis (transverse to the long axis of the lever). You can tilt a bit to get profiles from somewhat different angles, but this is rather limited in most TEMs. It required adapting a standard TEM holder in which you mount the cantilever, but once that is done, one can have pretty decent throughput. In our group, we machined a new TEM holder that holds 3 cantilevers and a calibration grid all at once, for better throughput. We are happy to share the info on this device. Advantages: works for tips down to even 10 nm or less, if you have a good TEM; you can do analytical work (diffraction, EELS, EDX) on the tip to determine the structure and composition, and can even get atomic lattice resolution if desired. Disadvantages: Requires dismounting the cantilever from your AFM each time you want to image it, which can be risky; exposes tip to possible e-beam induced damage or contamination buildup in TEM (TEM must have good vacuum, and/or use short imaging times and not-to-high beam intensity); a bit time-consuming (mounting the cantilever in the holder, TEM wand has to pump down each time, etc.).
2. Blind tip reconstruction - scan the tip over samples with sharp features and reconstruct the tip shape. Commercial samples like TipCheck and NioProbe from Aurora Nanodevices, or the TGT-01 from NT-MDT, are good for this. Advantages: no TEM needed, it's in-situ and relatively fast. Disadvantages: you need software (you can buy SPIP which is expensive; I believe the free softwares like Gwyddion and WSXM can do it too but I'm not sure; we are working on a free MatLab version but its not ready yet); software is sensitive to algorithm parameters so you need to be careful; tip can be accidentally damaged during the imaging process, but a good AFM person can avoid this.
Method #2 is much easier to start with, especially if you are not trained on using a TEM!
This paper discusses details on both methods, with references to further background on them:
Preventing nanoscale wear of atomic force microscopy tips through the use of monolithic ultrananocrystalline diamond probes. J. Liu, D. S. Grierson, N. Moldovan, J. Notbohm, S. Li, P. Jaroenapibal, S. D. O’Connor, A. V. Sumant, N. Neelakantan, J. A. Carlisle, K. T. Turner, R. W. Carpick. Small, 6, 1140-9 (2010).
Good luck! Please let us know here how it works out.