(a)–(c) Simulated cluster with 128 Co@SiO<sub>2</sub> particles and its simulated diffraction intensities with 1200 and 777 eV incident energies

<p><strong>Figure 5.</strong> (a)–(c) Simulated cluster with 128 Co@SiO<sub>2</sub> particles and its simulated diffraction intensities with 1200 and 777 eV incident energies. (d)–(f) Simulated cluster with 512 Co@SiO<sub>2</sub> particles and its simulated diffraction intensities. Pink cores of the particles in (a) and (d) denote elemental Co, while their white shells represent SiO<sub>2</sub>. Projection images of either cluster, randomly rotated, at the two resolutions are inset in the corresponding diffraction patterns. These projections are the real part of the Fourier transforms of their phased complex valued diffraction patterns.</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>