Atomically Coherent Nanocrystal Superlattices
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Many applications have been envisioned for supercrystals of quantum dots (QDs), ranging from solar cells to LEDs. The properties of such systems depend on the properties of the constituent particles, but also on the structure of the supercrystal. Especially the novel effects related to the formation of a superstructure remain to be addressed experimentally. Here we present a combined scanning tunneling microscopy (STM), electron microscopy (EM) and electron tomography study on the two-dimensional oriented attachment of PbSe QDs. Several different atomically coherent nanocrystal superlattices are formed with linear, cubic and honeycomb symmetry depending on the synthesis conditions. We show that the interpretation of STM and TEM data is not straightforward, hence we used electron-tomography to prove that the honeycomb crystal is actually buckled into a silicene like structure. Moreover, initial scanning tunneling spectroscopy results are presented and, combined with atomistic tight binding calculations, a first interpretation is given to the acquired spectra.