Indium phosphide (InP) quantum dots have attracted attention in recent years as viable, cadmium-free, chromophores with tunable absorbance across the visible region of the electromagnetic spectrum. The inherent difficulty in synthesizing this covalent material is the main impediment to their introduction to bio-imaging and device applications. Efforts to improve the synthesis have focused almost entirely on aspects of the precursor conversion chemistry. Conventional syntheses employ highly reactive phosphorus precursors such as tris(trimethylsilyl)phosphine (P(SiMe3)3). This species is completely consumed to give InP within seconds of addition to the In3+ source at the elevated temperatures necessary to form InP. Our group has recently synthesized novel P3- sources that persist at elevated temperatures to act as an in situ reservoir of InP. Using these precursors and P(SiMe3)3 in tandem, we have been able to show that nucleation and growth are temporally distinct in systems that incorporate two P3-sources with radically different precursor conversion rates.Although previous efforts have been successful in separating nucleation and growth for InP, the synthesis remains inferior relative to cadmium selenide in terms of control of size distribution and shape uniformity. While investigating new P3- sources and capping ligands for InP syntheses we have discovered a new class of magic-sized InP clusters. These clusters can exhibit extreme thermodynamic stability depending on their coordination environment. These particles also exhibit heterogeneous growth in situ in a process that can be conceptualized as a second nucleation event, resulting in growth from clusters of roughly 1 nm diameter to quantum dots with a 4 nm particle diameter. The existence of these particles within the growth profile of InP calls for closer inspection of the growth process of these materials. The impact of additives, capping ligands, In3+ source, and even P3- source on crystal growth should be considered when designing future syntheses.

Charting the growth profile of indium phosphide quantum dots using magic-sized clusters

248th National Meeting (2014)

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