Many-pass techniques

Fig. 1 Line scans across a single magnetic domainfor various initial tip-sample spacings are presented [1].

In general many-pass techniques are used in tasks where other than topography data are to be obtained at that topography unwanted side effects must be eliminated. As example on left side picture line scans across a single magnetic domain for various initial tip-sample spacing are presented [1]. Analogous measurements can be carried out for determining thickness of the liquid film on the solid substrate [2], nanomanipulations (e.g. positioning single atoms [3]), nanolithographies [4].
First pass can be carried out in Contact or Fmplitude modulation (Intermittent-Contact, Semicontact) modes. On the second pass one can measure electric forces and potentials, magnetic fields, dissipations, surface capacitance distributions. In some cases third pass can be necessary particularly to eliminate not only topography but surface electric fields influence. 

    References

1. Appl. Phys. Lett. 52, 244 (1988). 
2. J. Chem. Phys. 90, 7550 (1989). 
3. Nature 344, 524 (1990). 
4. Nature 347, 748 (1989).

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