  Electron transparent TEM lamella with unaltered microstructure and chemistry
is the prerequisite for successful TEM explorations. Currently, TEM specimen
preparation of quantum nanostructures, such as quantum dots (QDs), remains a
challenge. In this work, we optimize the sample-preparation routine for
achieving high-quality TEM specimens consisting of SrRuO3 (SRO) QDs grown on
SrTiO3 (STO) substrates. We demonstrate that a combination of ion-beam-milling
techniques can produce higher-quality specimens of quantum nanostructures
compared to TEM specimens prepared by a combination of tripod polishing
followed by Ar+ ion milling. In the proposed method, simultaneous imaging in a
focused ion-beam device enables accurate positioning of the QD regions and
assures the presence of dots in the thin lamella by cutting the sample inclined
by 5{\deg} relative to the dots array. Furthermore, the preparation of TEM
lamellae with several large electron-transparent regions that are separated by
thicker walls effectively reduces the bending of the specimen and offers broad
thin areas. The final use of a NanoMill efficiently removes the amorphous layer
without introducing any additional damage.
