Here we see some structures twice. The tip must have two atoms interacting with the sample.
The magnitude of the sample has to be enough little to fit into the microscope. To flee external influences the sample must build one system with the microscpe.
The expansion of the piezos can be well controlled (1 nm to 400 nm) which in contrast is a limitation on the scan range. Large depths of hights are thus a problem.
The torsion of the cantilever is not strictly linear. This deviation can be reduced by calculations.
The transformations of the piezos too is not strictly linear. As above calculations can reduce the bias.
The sharpnes of the tip is hardly to control. Usually the tips are drawn of a wire of copper. There is some presumption that one solely atom lies on the top. This one atom is the probe in the process of measuring. If there are two atoms which means two tips different characters are recorded twice. Or if the tip is too large some depths cannot be explored.
As we know the tip is drawn over the sample. Thus its altitude is modified with every change in topography. The magnitude modification and speed of the feedback process is given externally and can be changed. If we choose a modification that is too large the tip alters too much. While it moves down there is some probability of collision with the sample. Also the topography is measured too imprecisely. If we choose a modification which is too little the tip will, by moving too fast in x-direction, collide with the probe if the altidue is increasing – as an aircraft flying over a mountain but as the mountain gets higher the pilote is too slow in altering the planes altitude and is therefore risking a crash with the mountain. Therefore we usually choose a little too large modification. The result are some shadows (broad = higher) after every depth (dark = deeper).
