Reversible Facet Reconstruction of CdSe/CdS Core/Shell Nanocrystals by Facet-Ligand Pairing

Synthesis of colloidal semiconductor nanocrystals with defined facet structures is challenging, though such nanocrystals are essential for fully realizing their size-dependent optical and optoelectronic properties. Here, for the mostly developed colloidal wurtzite CdSe/CdS core/shell nanocrystals, facet reconstruction is investigated under typical synthetic conditions, excluding nucleation, growth, and interparticle ripening. Within the reaction time window, two reproducible sets of facets -each with a specific group of low-index facets -can be reversibly reconstructed by switching the ligand system, indicating thermodynamic stability of each set. With a unique < 0001 > axis, atomic structures of the low-index facets of wurtzite nanocrystals are diverse. Experimental and theoretical studies reveal that each facet in a given set is paired with a common ligand in the solution, namely, either fatty amine and/or cadmium alkanoate. The robust bonding modes of ligands are found to be strongly facet-dependent and often unconventional, instead of following Green's classification. Results suggest that facet-controlled nanocrystals can be synthesized by optimal facet-ligand pairing either in synthesis or after-synthesis reconstruction, implying semiconductor nanocrystal formation with size-dependent properties down to an atomic level.

Automated summary

This study investigates facet reconstruction of colloidal wurtzite CdSe/CdS core/shell nanocrystals under typical synthetic conditions and reveals that two sets of facets with specific low-index facets can be reversibly reconstructed by switching the ligand system, indicating their thermodynamic stability. The atomic structures of the low-index facets of wurtzite nanocrystals are diverse, and each facet is paired with a common ligand in the solution. The results suggest that facet-controlled nanocrystals can be synthesized by optimal facet-ligand pairing, enabling the formation of semiconductor nanocrystals with size-dependent properties at an atomic level.