PhD student in Chemistry of materials

Synthesis and characterization of chiral Twited 2D II-VI semiconductor nanoparticles

Semiconductor colloidal nanocrystals present optical properties tunable with their size and compositions, and it’s been 7 years that these nanocrystals are introduced in displays as a source of light. Among them, 2D nanoparticles (called nanoplatelets NPLs)1 , present enhanced optical properties due to their thickness control at the atomic scale without roughness. In a colloidal dispersion of NPLs, all the nanoparticles have exactly the same thickness. The NPLs are stabilized by organic molecules called ligands and due to the large lateral extension of the NPLs, they can be seen as flexible substrate for the self-assembly of molecules. In reaction to these ligands which bring stress, the NPLs fold as helices or twists2 .

Recently we have shown that a mechanical model taking into account the nature of the inorganic core nanocrystals, the anchoring group of the ligands and the aliphatic chain of the ligands, we could predict the folding of NPLs.3 However at the end of a synthesis, there is a racemic mixture of NPLs left and right handed. The goal of the PhD student will then be to get nanoplatelets with all the same direction of rotation. Several strategies will be explored either by bottom up techniques through the direct synthesis of one enantiomer of helix or by top down techniques through the sorting of NPLs. The NPLs will be further characterized by circular dichroism spectrocopies both in absorption and emission. A new set-up for the Circular photoluminescence spectroscopy will be built in collaboration with other team members.

References

1. Ithurria, S. et al. Colloidal nanoplatelets with two-dimensional electronic structure. Nat. Mater. 10, 936–941 (2011).

2. Dufour, M. et al. Halide Ligands to Release Strain in Cadmium Chalcogenide Nanoplatelets and Achieve High Brightness, ACS Nano 13, 5326–5334 (2019).

3. Po, H. et al. Chiral Helices Formation by Self-Assembled Molecules on Semiconductor Flexible Substrates, ACS Nano 16, 2901-2909 (2022)