Trilayer-cubic core-shell structure of PbS/EuS nanocrystals revealed by the combination of the synchrotron small-angle X-ray scattering method and energy-dispersive X-ray spectroscopy

Multilayer nanostructure analysis has been carried out for core-shell PbS/EuS nanocrystals by the combination of the synchrotron small-angle X-ray scattering (SAXS) method and energy-dispersive X-ray spectroscopy (EDS). SAXS patterns of a dilute hexane solution of the PbS/EuS nanocrystals were measured at a high signal-to-noise ratio by using synchrotron radiation. Initial structure models used for SAXS data analyses were obtained from EDS images of the particle where Eu and O atoms are localized only in the shell part of a quasi-cubic particle and, on the other hand, Pb and S atoms in the core. By simulating the intensity of SAXS using multilayer-cubic models with various core-shell electron density distributions, it was found that the particle structure was explained approximately as a trilayer-cubic model having the PbS core and the EuS/Eu₂O₃ shell. The diagonal length of the cubic particle was ca. 9.4 nm and the estimated thicknesses of EuS and Eu ₂O₃ layers in the shell were ca. 1.9 and 2.9 nm at maximum, respectively.