Two-Step Nucleation and Growth of InP Quantum Dots via Magic-Sized Cluster Intermediates

Abstract

We report on the role of magic-sized clusters (MSCs) as key intermediates in the synthesis of indium phosphide quantum dots (InP QDs) from molecular precursors. Heterogeneous growth from the MSCs directly to InP QDs was observed without intermediate sized particles. These observations suggest that previous efforts to control nucleation and growth by tuning precursor reactivity have been undermined by formation of these kinetically persistent MSCs prior to QD formation. The thermal stability of InP MSCs is influenced by the presence of exogenous bases as well as choice of the anionic ligand set. Addition of a primary amine, a common additive in previous InP QD syntheses, to carboxylate terminated MSCs was found to bypass the formation of MSCs, allowing for homogeneous growth of InP QDs through a continuum of isolable sizes. Substitution of the carboxylate ligand set for a phosphonate ligand set increased the thermal stability of one particular InP MSC to 400 °C. The structure and optical properties of the MSCs with both carboxylate and phosphonate ligand sets were studied by UV-Vis absorption spectroscopy, powder XRD analysis, and solution 31 P{ 1 H} and 1 H NMR spectroscopy. Finally, the carboxylate terminated MSCs were identified as effective single source precursors (SSPs) for the synthesis of high quality InP QDs. Employing InP MSCs as SSPs for QDs effectively decouples the formation of MSCs from the subsequent second nucleation event and growth of InP QDs. The concentration dependence of this SSP reaction, as well as the shape uniformity of particles observed by TEM suggests that the stepwise growth from MSCs directly to QDs proceeds via a second nucleation event rather than an aggregative growth mechanism.

Discovering Amorphous Indium Phosphide Nanostructures with High-Temperature ab Initio Molecular Dynamics

“…for crystalline InP 66 , but it is above the typical temperature for InP quantum dot synthesis (450 K) 14,[16][17][18] . Since our simulation only includes indium and phosphorus atoms, rearrangements of the InP(111) model in the AIMD trajectory are completely defined by average instantaneous In-P, In-In, and P-P distances ( Figure 2).…”

“…These larger P-P distances do not necessarily mean that phosphorus atoms aggregate on the surface. In and P atoms have comparable probabilities in the distance to the cluster center of mass (see Supporting Information Figure In order to identify whether features of RDFs are size-dependent, we group clusters as "small" (3-7 pairs), "intermediate" (8)(9)(10)(11)(12)(13)(14), and "large" (15)(16)(17)(18)(19)(20)(21)(22), based in part on energetic trends ( Figure 5). A comparison of RDFs for these three groups (see Supporting Information Figure S8) reveals that small clusters have a shorter distance for the first-minimum in the In-P RDF, which is below 3.1 Å.…”

“…InP QDs have since been identified as one of the most promising alternatives to CdSe both because of their broader emission color range and lack of intrinsic toxicity [13][14][15] . Nevertheless, preparation of highquality InP QDs has remained challenging, despite ongoing efforts to understand and direct the nucleation and growth mechanisms during synthesis [14][15][16][17][18] .…”

A compact dispersive refocusing Rowland circle X-ray emission spectrometer for laboratory, synchrotron, and XFEL applications

“…The InP quantum dots (QDs) were prepared by a procedure from Gary and Cossairt. 58 One sample consisted of the pure as-synthesized InP QDs, while the second sample consisted of Zn-passivated InP QDs, which were post-synthetically modified with zinc oleate as described in the work of Stein et al 59 The third sample measured was InP magic-sized clusters with the initial carboxylate ligand environment replaced with phosphonates, prepared following a procedure from the work of Gary et al 60 …”

The Effect of Fatty Amine Chain Length on Synthesis Process of Inp/Zns Quantum Dots

“…It has been confirmed that when primary fatty amines were used as ligand in InP quantum dots synthesis, heterogeneous growth of quantum dots from intermediate magic-sized clusters is switched to homogeneous growth from molecular precursors, resulting in narrower size distribution 28 .…”