A device for scanning the surface of a sample which is covered with a liquid, comprising a probe which has a tip at one end, means for moving the probe and the sample relative to one another a light source focussing device which focuses light from the light source onto a location in the area of the tip located in the liquid and a detector for detecting light which was scattered by the tip, wherein a boundary surface at which the light enters the liquid is located on the light path between the light source and the tip, wherein the boundary surface is positionally fixed with respect to the probe.