  Scanning quantum dot microscopy is a recently developed high-resolution
microscopy technique that is based on atomic force microscopy and is capable of
imaging the electrostatic potential of nanostructures like molecules or single
atoms. Recently, it could be shown that it not only yields qualitatively but
also quantitatively cutting edge images even on an atomic level. In this paper
we present how control is a key enabling element to this. The developed control
approach consists of a two-degree-of-freedom control framework that comprises a
feedforward and a feedback part. For the latter we design two tailored feedback
controllers. The feedforward part generates a reference for the current scanned
line based on the previously scanned one. We discuss in detail various aspects
of the presented control approach and its implications for scanning quantum dot
microscopy. We evaluate the influence of the feedforward part and compare the
two proposed feedback controllers. The proposed control algorithms speed up
scanning quantum dot microscopy by more than a magnitude and enable to scan
large sample areas.
