Estimating the lower bound of the average core–shell particle radius from the individual experimental diffraction patterns of single clusters of Co@SiO₂ particles and their average pattern

Figure 4. Estimating the lower bound of the average core–shell particle radius from the individual experimental diffraction patterns of single clusters of Co@SiO₂ particles and their average pattern. (a), (b) Example fits of ideal uniform sphere diffraction intensities (red) to the experimental diffraction patterns of clusters of various sizes within the range q = 0.25–0.31 nm⁻¹ (demarcated by thin vertical lines). Diffraction intensities in this q-range are expected to be most sensitive to the form factor of our individual particles. (c) Histogram of average particle radii from 159 fits similar to (a), (b). (d) Difference between the average of 20 brightest diffraction intensities from single clusters illuminated on resonance (777 eV, thick, black line) and off-resonance (1200 eV, thin, black line). The averaged intensities at 1200 eV fit the form factor of sphere of radius 12.5 nm (red, dashed line).

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.