Single-Particle X-ray Scattering Reveals a High Local Supersaturation of Precursors as the Origin of CoO Assembly Formation

Sani Y. Harouna-Mayer; Lars Klemeyer; Cecilia A. Zito; Johan Bielecki; Xuemei Cheng; Davide Derelli; Armando D. Estillore; Tjark L. R. Groene; Lukas V. Haas; Romain Letrun; Chan Kim; Jayanath C. P. Koliyadu; Abhishek Mall; Parichita Mazumder; Diogo V. M. Melo; Adam R. Round; Amit K. Samanta; Abhisakh Sarma; Zhou Shen; Xiao Sun; Patrik Vagovic; Tamme Wollweber; Richard Bean; Jochen Küpper; Henry N. Chapman; Dorota Koziej; Kartik Ayyer

arXiv · 2512.08488

Single-Particle X-ray Scattering Reveals a High Local Supersaturation of Precursors as the Origin of CoO Assembly Formation

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Abstract

Single-particle small-angle X-ray scattering (SP-SAXS) enables quantitative morphological analysis by recording diffraction snapshots from isolated particles using X-ray free-electron laser (XFEL) pulses. Unlike conventional X-ray techniques, which average over the entire illuminated sample volume, SP-SAXS resolves low-contrast, less abundant, or transient species within heterogeneous particle populations that would otherwise remain hidden. Here, we apply SP-SAXS to investigate the solvothermal formation of CoO nanocrystal assemblies from a Co(acac)$_3$ precursor in benzyl alcohol. The single-particle data reveal amorphous, uniform-density Co(acac)$_2$ spheres as transient intermediates that directly crystallize into cavernous CoO nanocrystal assemblies, which explains why CoO forms as hierarchical aggregates rather than as isolated nanocrystals. These results demonstrate that SP-SAXS provides a powerful framework for disentangling morphological heterogeneity in nanoparticle formation processes.

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Sani Y. Harouna-Mayer, Lars Klemeyer, Cecilia A. Zito, Johan Bielecki, Xuemei Cheng, Davide Derelli, Armando D. Estillore, Tjark L. R. Groene, Lukas V. Haas, Romain Letrun, Chan Kim, Jayanath C. P. Koliyadu, Abhishek Mall, Parichita Mazumder, Diogo V. M. Melo, Adam R. Round, Amit K. Samanta, Abhisakh Sarma, Zhou Shen, Xiao Sun, Patrik Vagovic, Tamme Wollweber, Richard Bean, Jochen Küpper, Henry N. Chapman, Dorota Koziej, Kartik Ayyer. 2025-12-09. Single-Particle X-ray Scattering Reveals a High Local Supersaturation of Precursors as the Origin of CoO Assembly Formation. https://arxiv.org/abs/2512.08488

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