Probing Volumetric Effects in Suspended Binary Superlattices of Infrared Colloidal Nanocrystals using Transmission Electron Microscopy and Optical Characterization

By combining two types of infrared colloidal nanocrystals (NCs) into binary superlattices, a type of ‘artificial solid’ can be created where the NCs would be ‘atoms’ and NC-to-NC interactions are ‘bonds.’ These binary superlattices then allow for control of desired optoelectronic properties and offer the technological advantage of scalable solution-based synthesis for low-cost infrared optoelectronics. One roadblock in these engineered systems is the small size of individual ordered domains (analogous to grain size in polycrystalline materials), which prohibits detailed understanding of structure-property relationships. Expanding on our previous work [1, 2], we manipulate the surface chemistry in these artificial solids to create enlarged (&gt;1 μm) domains of binary components comprised of infrared plasmonic Cu_2-xS/PbS core/shell and excitonic PbS nanocrystals. These superlattices are suspended across holes, proving both their ability to be self-supporting as well as allowing for transmission electron microscopy and optical characterization without need to account for substrate effects. However, as structured solids with a three-dimensional extent, we then face a challenge in determining volumes of superlattice domains when suspended in this fashion. Here, we determine both thickness and spatial extent of the superlattice to define the local volume in individual superlattice domains, and then compare these to correlated photoluminescence from the same domains. Combined with time-resolved photoluminescence spectroscopy, these results suggest that energy transfer occurs between the excitonic emitters and plasmonic nanocrystals.<br/><br/><br/><b>References</b><br/><br/>[1] S. Brittman, N. A. Mahadik, S. B. Qadri, P. Y. Yee, J. G. Tischler, and J. E. Boercker, <i>ACS Appl. Mater. Interfaces</i> <b>12</b>, 24271 (2020).<br/>[2] P. Y. Yee, S. Brittman, N. A. Mahadik, J. G. Tischler, R. M. Stroud, Al. L. Efros, P. C. Sercel, and J. E. Boercker, <i>Chem. Mater.</i> <b>33</b>, 6685 (2021).