image with the desired resolution. This may occur if the tip is too blunt or if the probe has more than one apex, which can lead to doubled or ghost images. For some probes, in situ modification of the tip apex is possible, this is usually done by either crashing the tip into the surface or by applying a large electric field. The latter is achieved by applying a bias voltage (of order 10V) between the tip and the sample, as this distance is usually 1-3 Angstroms, a very large field is generated.

The additional