Hybrid Oleate-Iodide Ligand Shell for Air-Stable PbSe Nanocrystals and Superstructures

A postsynthetic treatment is presented to improve the air stability of PbSe nanocrystals (NCs) and PbSe square superstructures. The addition of z-type Pb(oleate)2 ligands together with x-type iodide ligands creates a hybrid ligand shell containing both ligands. The air stability of the PbSe NCs is checked by enduring absorption spectroscopy under ambient conditions. With a combined NaI + Pb(oleate)2 treatment, the absorption spectrum remains unchanged for several days under ambient conditions. Fourier transform infrared spectroscopy shows that the surface coordination of the oleate ligands changes by the chemical treatment: from mixed chelating bidentate + bridging to Pb for the pristine nanocrystals to almost exclusive chelating bidentate coordination after chemical passivation. The shift of the C-H stretching vibration shows that the oleate hydrocarbon layer is in a more liquidlike state after the chemical treatment, suggesting that oleate and iodide ligands are often present on adjacent surface positions.