Solvent controlled 2D structures of bottom-up fabricated nanoparticle superlattices

We demonstrate that oleyl phosphate ligand-stabilized iron oxide nanocubes as building blocks can be assembled into 2D supercrystalline mono- and multilayers on flat YSZ substrates within a few minutes using a simple spin-coating process. As a bottom-up process, the growth takes place in a layer-by-layer mode and therefore by tuning the spin-coating parameters, the exact number of deposited monolayers can be controlled. Furthermore, ex situ scanning electron and atomic force microscopy as well as X-ray reflectivity measurements give evidence that the choice of solvent allows the control of the lattice type of the final supercrystalline monolayers. This observation can be assigned to the different Hansen solubilities of the solvents used for the nanoparticle dispersion because it determines the size and morphology of the ligand shell surrounding the nanoparticle core. Here, by using toluene and chloroform as solvents, it can be controlled whether the resulting monolayers are ordered in a square or hexagonal supercrystalline lattice.

Automated summary

In this study, it is demonstrated that oleyl phosphate ligand-stabilized iron oxide nanocubes can be assembled into 2D supercrystalline mono- and multilayers on YSZ substrates using a spin-coating process. The growth occurs layer-by-layer, allowing control of the number of deposited monolayers by adjusting the spin-coating parameters. The choice of solvent is found to influence the lattice type of the final supercrystalline monolayers.