Highlights of the Effect of Superlattice Organisation on the Plasmonic Properties of Metallic Nanocrystals

Metallic nanocrystals (M-NCs) are of great interest due to the possibility of controlling the plasmonic band through three-dimensional self-assembly arising from the interactions between neighbouring NCs, which can result in new properties non-present in the original constituents of the superlattice. That is because the Localized Surface Plasmon Resonance (LSPR) is highly affected by the surface-surface distance between the NCs, so the right engineering of this kind of system can lead to the discovery of an uncountable number of potential applications. Recently we obtained highly monodisperse Au-NCs and Ag-NCs perfectly suitable to be used as building blocks of such superlattices. So through a microemulsion method using oleic acid as a functionalizing agent, we were able to induce the self-assembly of such NCs into ordered superlattices. To relate the effect of the organization of the NCs into superlattices onto the LSPR it is necessary to combine structural and optical analysis. SAXS experiments are crucial for the determination of the specifically obtained superlattice. Single species systems tend to organize themselves into pseudo-hexagonal superlattices, meanwhile, hybrid systems organize themselves into aggregates of NCs aligned in rows. The pseudo-hexagonal organization causes a shift in the maximum absorption wavelength and the rise of a new absorption peak to the monodisperse NCs. Then, the hybrid systems show the presence of both plasmonic bands of Ag- and Au-NCs. Therefore, we were able to modulate the plasmonic properties of the metallic NCs inducing a different superlattice organization.