(a) Angularly averaged, incoherently summed diffraction patterns from 512 polydisperse individual Co@SiO₂ NPs

Figure 6. (a) Angularly averaged, incoherently summed diffraction patterns from 512 polydisperse individual Co@SiO₂ NPs. Both NP shell and core radii, 14 nm and 4 nm, respectively, have coefficients of variation 0.1. The red curve represents the diffraction intensities at 1200 eV from these particles with their Co core replaced by SiO₂. (b) Angularly averaged, incoherently summed simulated diffraction patterns from a 512-NP cluster (figure 5(d)) at ten random orientations with 1200 eV (thick line) and 777 eV (thin line) photons. The experimental average in figure 4(d) for 1200 eV from 20 random clusters has been scaled and superimposed (dashed) to show qualitative agreement.

Abstract

Unraveling the complex morphology of functional materials like core–shell nanoparticles and its evolution in different environments is still a challenge. Only recently has the single-particle coherent diffraction imaging (CDI), enabled by the ultrabright femtosecond free-electron laser pulses, provided breakthroughs in understanding mesoscopic morphology of nanoparticulate matter. Here, we report the first CDI results for Co@SiO₂ core–shell nanoparticles randomly clustered in large airborne aggregates, obtained using the x-ray free-electron laser at the Linac Coherent Light Source. Our experimental results compare favourably with simulated diffraction patterns for clustered Co@SiO₂ nanoparticles with ~10 nm core diameter and ~30 nm shell outer diameter, which confirms the ability to resolve the mesoscale morphology of complex metastable structures. The findings in this first morphological study of core–shell nanomaterials are a solid base for future time-resolved studies of dynamic phenomena in complex nanoparticulate matter using x-ray lasers.