Surface Chemistry of InP Quantum Dots: A Comprehensive Study

Abstract

Advanced (1)H, (13)C, and (31)P solution and solid-state NMR studies combined with IR spectroscopy were used to probe, at the molecular scale, the composition and the surface chemistry of indium phosphide (InP) quantum dots (QDs) prepared via a non-coordinating solvent strategy. This nanomaterial can be described as a core-multishell object: an InP core, with a zinc blende bulk structure, is surrounded first by a partially oxidized surface shell, which is itself surrounded by an organic coating. This organic passivating layer is composed, in the first coordination sphere, of tightly bound palmitate ligands which display two different bonding modes. A second coordination sphere includes an unexpected dialkyl ketone and residual long-chain non-coordinating solvents (ODE and its isomers) which interact through weak intermolecular bonds with the alkyl chains of the carboxylate ligands. We show that this ketone is formed during the synthesis process via a decarboxylative coupling route and provides oxidative conditions which are responsible for the oxidation of the InP core surface. This phenomenon has a significant impact on the photoluminescence properties of the as-synthesized QDs and probably accounts for the failure of further growth of the InP core.

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.…”

Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

“…The resulting colloidal CdS nanocrystals are highly to moderately soluble in chloroform, toluene and hexane. After careful purification by cold acetone-or methanol-induced precipitation ("crashing") and centrifugation to remove excess ligands, we observe NMR resonances predominantly from surface-bound ligands and not from free ligands, 44 along with a few weak NMR resonances from trace amount of synthesis solvent (Ph 2 O, Figure 3). As predicted, the relative population of the different surface ligands is proportional to the relative ligand concentrations used during nanocrystal synthesis (Figure 3 diffusion rates that are about 1 order of magnitude slower (onetenth) compared to resonances from free ligands and trace solvent, unambiguously demonstrating that after two washes and centrifugation we completely or nearly completely (>99%) removed free or excess ligands.…”

Room‐Temperature Synthesis of Air‐Stable and Size‐Tunable Luminescent ZnS‐Coated Cd3P2 Nanocrystals with High Quantum Yields

“…Then, strenuous purification procedures are required and residual solvent cannot be totally removed, resulting in high carbon contents. [12] In addition, Cd 3 P 2 NCs, being oxygen sensitive, precludes any application in open air in the absence of a protective shell around the NCs.…”