(a) Angularly averaged, incoherently summed diffraction patterns from 512 polydisperse individual Co@SiO<sub>2</sub> NPs

<p><strong>Figure 6.</strong> (a) Angularly averaged, incoherently summed diffraction patterns from 512 polydisperse individual Co@SiO<sub>2</sub> 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 SiO<sub>2</sub>. (b) Angularly averaged, incoherently summed simulated diffraction patterns from a 512-NP cluster (figure <a href="http://iopscience.iop.org/0953-4075/46/16/164033/article#jpb465322f5" target="_blank">5</a>(d)) at ten random orientations with 1200 eV (thick line) and 777 eV (thin line) photons. The experimental average in figure <a href="http://iopscience.iop.org/0953-4075/46/16/164033/article#jpb465322f4" target="_blank">4</a>(d) for 1200 eV from 20 random clusters has been scaled and superimposed (dashed) to show qualitative agreement.</p> <p><strong>Abstract</strong></p> <p>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@SiO<sub>2</sub> 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@SiO<sub>2</sub> 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.</p>