Nanomaterials research is interested in colloidal semiconductor nanocrystals for their optoelectronic properties that strongly depend on their composition, size and morphology. In particular, colloidal nanoplatelets have recently emerged as a new class of quantum well nanomaterials with novel optical properties when compared to quantum dots. However, the difficulty of synthesis and structural control of these nanocrystals remains a challenge.

In collaboration with the Institute of Physical Chemistry of the Polish Academy of Sciences at Warsaw, Poland, researchers at IRIG present a new approach to produce ZnO nanoplatelets with controlled thickness (from 3.2 to 7.5 nm) and durable colloidal stability. These Zn-based nanoplatelets are an attractive alternative, free of toxic heavy metals, to conventional cadmium chalcogenide-based colloidal 2D semiconductor nanostructures.
Beyond an original synthetic procedure, based on the controlled hydrolysis of organometallic complexes by H₂O, this work reveals the particular role of the chosen benzamidine ligands. Using dynamic nuclear polarization-enhanced solid-state NMR, the researchers increased the intensity of the ¹⁵N NMR signals of the surface ligands without resorting to ¹⁵N isotopic enrichment. This approach allowed them to reveal the original role of the benzamidine ligands in stabilizing the surface of these nanomaterials, since they can bind to both polar (basal planes) and non-polar (lateral surfaces) facets of the nanocrystals. This bimodal stabilization, where the synthetic ligands behave as both X- and L-type ligands, allows obtaining hexagonal nanoplatelets.
Further study of the interactions and arrangement of surface ligands is underway. This fundamental information on the organic-inorganic interfaces of ZnO nanoplatelets will facilitate the design of new stable and size-controlled colloidal suspensions.


ZnO nanoplatelets and its organic–inorganic interfaces. Credit CEA​