Self-assembly of Pbs Quantum Dots in Ordered Superstructures

NIR-emitting colloidal quantum dots (QDs) attract much attention due to their unique properties in order to utilize in diverse areas of applications: from bio-sensing to solar cells fabrication. The self-assembly of QDs in a periodically ordered superstructures, such as superlattices and supercrystals, enables a formation of a new class of functional materials with remarkable optical, electronic, and vibrational properties. In this study we investigated the structures, obtained by self-assembly of lead sulfide (PbS) QDs of different sizes deposited on a mica substrate. The test samples were prepared by a method based on the evaporation of a saturated solution. The methods of X-ray structural analysis were used to describe the morphology of obtained ordered structures. It was found that the self-assembly of smaller QDs leads to formation of the superlattices, while the assembly of larger dots results in formation of three-dimensional structures. These superstructures possess the set of narrow peaks in the SAXS patterns similar to that obtained for conventional crystals. The positions of the scattering peaks were used for calculation of the crystal structure of the samples. It was shown that these structures have a primitive orthorhombic lattice with size of tens of micrometers. This work is of considerable interest for the development of photonic devices based on QDs superstructures, absorbing light in NIR-region.