Surface activation of colloidal indium phosphide nanocrystals

Abstract

Against general wisdom in crystallization, the nucleation of InP and III-V quantum dots (QDs) often dominates their growth. Systematic studies on InP QDs identified the key reason for this: the dense and tight alkanoate-ligand shell around each nanocrystal. Different strategies were explored to enable necessary ligand dynamics—i.e., ligands rapidly switching between being bonded to and detached from a nanocrystal upon thermal agitation—on nanocrystals to simultaneously retain colloidal stability and allow appreciable growth. Among all the surface-activation reagents tested, 2,4-diketones (such as acetylacetone) allowed the full growth of InP QDs with indium alkanoates and trimethylsilylphosphine as precursors. While small fatty acids (such as acetic acid) were partially active, common neutral ligands (such as fatty amines, organophosphines, and phosphine oxides) showed limited activation effects. The existing amine-based synthesis of InP QDs was activated by acetic acid formed in situ. Surface activation with common precursors enabled the growth of InP QDs with a distinguishable absorption peak between ~450 and 650 nm at mild temperatures (140–180 °C). Furthermore, surface activation was generally applicable for InAs and III-V based core/shell QDs.