(a)–(c), (g)–(i) Selection of diffraction patterns and (d)–(f), (j)–(l) respective iterative phase-retrieval reconstruction of the real space image of clusters of Co@SiO<sub>2</sub> NPs irradiated with x-rays pulses of 1200 eV photon energy

<p><strong>Figure 2.</strong> (a)–(c), (g)–(i) Selection of diffraction patterns and (d)–(f), (j)–(l) respective iterative phase-retrieval reconstruction of the real space image of clusters of Co@SiO<sub>2</sub> NPs irradiated with x-rays pulses of 1200 eV photon energy.</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>