Indium Coordination as a Handle for Controlling Indium Phosphide Quantum Dot and Nanowire Nucleation and Growth

Indium phosphide (InP) is a less toxic semiconductor with exciting nanoscale applications in LED displays, bioimaging, and single-nanowire transistors and optoelectronics. However, colloidal InP synthesis lacks mechanisms for precursor reactivity-based size control, and standard synthesis methods rely on hazardous precursors that require high energetic input. To address these challenges, we have taken inspiration from natural biomineralization to expand control over nucleation and growth, focusing on modulating the indium coordination environment. We examined the effect of a strongly chelating anion on the nucleation and growth of InP QDs synthesized using aminophosphine chemistry. Increasing the equivalents of metal-chelating aminopolycarboxylic acid EDTA ([CH₂N(CH₂CO₂H)₂]₂) (0–0.75 equivalents per indium) was found to decrease the final diameter of InP QDs from 4.5 to 2.3 nm by lowering the initial InP growth rate. This size trend was rationalized by invoking a continuous nucleation model in which the suppressed initial growth rates are attributed to a competitive decrease in reactivity caused by indium EDTA complexation and a lower effective concentration. In opposition to strong indium chelation by EDTA, the weak indium-binding ligands trifluoroacetate and trifluoromethanesulfonate allow the aminophosphine-based InP chemistry to access nanowires through a solution-liquid-solid mechanism. Slow phosphorus reactivity is identified by ³¹P NMR spectroscopy which, along with the weak indium-ligand interactions and the overall reducing environment, are proposed to allow access to the indium metal necessary for nanowire growth. Transmission Electron Microscopy identifies unusual nanoribbon morphologies of zinc-blende InP. Altogether, we identify that controlling indium coordination provides a versatile handle and access to new chemistries for the nucleation and growth of InP nanocrystals.