Self-assembly of very-low height/width aspect-ratio Li₃Ni₂NbO₆ disks embedded in Li₃NbO₄ epitaxial films

We here report the self-assembly of Li₃Ni₂NbO₆ (LNNO) epitaxial disks with very low height/width aspect ratios. An epitaxial LNNO thin film is obtained at a substrate temperature (T_s) of 400 °C, using a pulsed laser deposition technique, and by increasing the T_s to 600 °C, Li₃NbO₄ epitaxial domains are formed inside the LNNO epitaxial film. Further increasing the T_s to 700 °C leads to the formation of LNNO disks (with diameters of a few micrometers and a typical height of ~ 100 nm) embedded in a Li₃NbO₄ film. Interestingly, transmission electron microscopy observations reveal that the LNNO disks are separated from the Li₃NbO₄ films by amorphous compounds, indicating the formation of a planar core-shell structure. Understanding of the growth processes of these unique nanostructures pave the way to fabrication of higher hierarchical structures embedded in thin film matrices.