Quantification of a PbCl_x Shell on the Surface of PbS Nanocrystals

Abstract

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 PbCl x 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 PbCl x shell that is present on the surface of PbCl2-derived PbS nanocrystals. Using a charge-balanced structural model, the scattering contribution of a ∼0.3 nm thick surface PbCl x 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.

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures

“… 82 , 83 Furthermore, recent work has demonstrated that PbS NCs synthesized from PbCl 2 have a PbCl 2 -rich surface, leading to improved photoluminescence quantum yield and chemical stability, which might be related to the passivation by a layer of the hereby reported Pb 3 S 2 Cl 2 phase. 84 − 86 This hypothesis may stimulate further studies aiming at a more detailed characterization of those systems.…”

Combining HR-TEM and XPS to elucidate the core–shell structure of ultrabright CdSe/CdS semiconductor quantum dots

“…2-12, 10587 Berlin, Germany. * email: joerg.radnik@bam.de; ute.resch@bam.de electron microscopy ((HR-)TEM), scattering techniques like small and wide angle X-ray scattering (SAXS and WAXS), and wavelength dispersive X-ray spectroscopy (WDX), as well as dynamic light scattering (DLS) and small-angle neutron scattering (SANS) 22 . Very small inorganic NP like QD with sizes below 10 nm are mainly analyzed with TEM, measuring dried samples on a substrate in vacuum 23 .…”

Optimal loading for injection

“…and the minimal injection duration, t * , depends on the model parameters through its linear proportionality with the derivative of the viscosity: be scaled up by two orders of magnitude while maintaining low size dispersity in the batch. 26 The size dispersity is strongly influenced by the duration of injection for the sulfur precursor solution. In order to successfully scale up the synthesis, it was essential to minimize the duration of injection.…”

“…Our original synthetic procedure would yield ∼75 mg of nanocrystals. In order to perform neutron scattering experiments on concentrated solutions of PbS nanocrystals, the yield of the synthetic procedure would need to be scaled up by two orders of magnitude while maintaining low size dispersity in the batch 26 . The size dispersity is strongly influenced by the duration of injection for the sulfur precursor solution.…”