The New Science of Atomic Force Microscopy AFM

One of the key problems in the AFM is the fact that the movonait of the piezotube and tip must be added together. Qearly it is desirable to have as stiff a cantilever as possible so that most of the displacement is governed by the piezotube. Then the jumping of the tip onto the surface of the sample can be studied. It is important to ronove all moisture in such experiments otherwise, ccmdaised capillary films obscure the results. 

One of the issues is to provide a realistic theory for the summing of London forces over the geometry of a probe tip. This has been carried out by various groups, and found to differ from the standard Hamaker expressions for sphere approaching flat, especially when the probe was very fine, e.g. less than lOnm diameter at the tip. The results obtained for the force on the tip as a function of separation could then be explained, and the Hamaker constant determined. Alternatively, a small sphere could be glued to the cantilever, in which case the 

Standard equation applied. The results shown in Fig. 4.16 were obtained by 

All experiments in the AFM gave attractive jumping behavior in vacuum or air. In watCT and other liquids, jumping behavior could be observed as in Fig. 4.16, but could be stopped by stiffening the cantilever. The other question to be asked relates to the effect of surface roughness on such tests. Ultimately, the AFM probe can sense the diffeent force curves across a surface, which then appears bumpy in force toms, even though it is pCTfectly flat in moleeular terms. 

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