Journal
ACS MATERIALS LETTERS
Volume 1, Issue 2, Pages 209-216Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsmaterialslett.9b00200
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Funding
- National Institute of Standards and Technology [DMR-1508249]
- National Science Foundation [DMR-1508249]
- MIT Portugal Seed Fund
- Camille and Henry Dreyfus Foundation
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Differences between the properties of PbS nanocrystals prepared using a large excess of PbCl2 and those prepared using other Pb sources have led to speculation that a thin PbClx shell may be present on the surface of PbCl2-derived PbS nanocrystals. However, characterization of this chloride layer has proven to be challenging because of the poor contrast provided by electron and X-ray scattering probes. Here, we show that small-angle neutron scattering (SANS) provides the compositional sensitivity needed to unambiguously quantify the PbClx shell that is present on the surface of PbCl2-derived PbS nanocrystals. Using a charge-balanced structural model, the scattering contribution of a similar to 0.3 nm thick surface PbClx layer is parsed separately from ligand carboxylate head groups and PbS in the core. Global fitting of the SANS data across a solvent deuteration series enables unique determination of the spatial distribution of each material. These results are corroborated by quantitative nuclear magnetic resonance (NMR) and energy-dispersive X-ray spectroscopy (EDS). This work resolves a discrepancy in reported sizing curves for PbS nanocrystals prepared by different syntheses and further demonstrates the power of SANS in resolving molecular structure in soft and hybrid nanomaterials.
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