To obtain functional nanomaterials and integrate them into technical devices, nanocrystals (NCs) must be aligned into ordered superstructures, similar to the arrangement of atoms in a crystalline solid material. Thereby, the electronic properties of the single NCs are enhanced, so they can further be applied in devices such as heat sensors and solar cells. To what extent these properties can be magnified depends on the positional and orientational order of the NCs within the supercrystal. In this work, the self-assembly of semiconducting core-shell PbTe/PbS NCs to supercrystals was investigated. These particles are thermoelectric, and their ability to convert heat to electricity makes them an important candidate e.g. for waste heat recovery and active cooling . The NCs were provided by M. Ibáñez at the Institute of Science and Technology in Austria (ISTA), dispersed in a solvent. The crystal structure of the particles was determined using X-ray diffraction (XRD). Then, self-assembly through two mechanisms: solvent evaporation and diffusion of a non-solvent into a solvent were investigated in-situ, as well as ex-situ, using small-angle X-ray scattering (SAXS). The resulting superstructures were later observed under the optical microscope and compared to the results from the SAXS measurements. Then, the impact of the NCs' shape on the superstructure was investigated to recreate their positional and orientational order within the supercrystals. The main resulting structure during both mechanisms was determined to be body-centered cubic (bcc). During evaporation of the solvent a much denser, but less ordered structure, than during diffusion, was obtained. During the diffusion process, hexagonal close-packed (hcp) stacking faults were found in between the bcc lattice at certain positions. The ex-situ measurements, which were performed a few weeks later, revealed large supercrystals with a mostly hexagonal structure. Apparently, the supercrystals rearranged themselves during this period. In the microscopy images taken afterwards, large crystals can be seen, which correlate with the results from the SAXS measurements. In this work it has been shown, that through the diffusion of a non-solvent into the solvent, as well as through evaporation of the solvent, ordered crystalline structures can be built from PbTe/PbS core-shell nanoparticles. This information is essential for further studies of the electronic properties of the supercrystals, as they highly depend on their internal structure.
|Translated title of the contribution||Growth and characterization of colloidal supercrystals formed by PbTe/PbS core-shell nanocrystals|
|Award date||21 Oct 2022|
|Publication status||Published - 2022|
Bibliographical noteno embargo