Energy‐Dependent Nucleation and Hierarchical Aggregation of Gold Nanoparticles During Synchrotron X‐Ray Radiolysis Revealed by in Situ Transmission Imaging and SAXS

ABSTRACT

Controlling the hierarchical aggregation of functional nanomaterials during nonequilibrium synthesis remains a fundamental challenge in materials chemistry, as the underlying structural kinetics are rarely captured in real time. Here, we elucidate the energy‐dependent nucleation and hierarchical aggregation pathways of gold nanoparticles synthesized via synchrotron x‐ray radiolysis of an aqueous precursor, utilizing a complementary suite of in situ x‐ray transmission imaging, dynamic light scattering (DLS), and time‐resolved small‐angle x‐ray scattering (SAXS). In situ transmission imaging under attenuated white x‐rays reveals a monotonic decay in transmittance, which, when mapped onto an effective Finke–Watzky nucleation/autocatalytic‐growth model, demonstrates dose‐rate‐controlled radiolytic reduction. Crucially, post‐irradiation DLS and time‐resolved SAXS quantitatively uncover how the primary x‐ray interaction probability governs the physical assembly pathways. Multi‐level Beaucage unified fitting of the SAXS profiles resolves two distinct power‐law regimes evolving simultaneously: a low‐ q exponent reflecting mass‐fractal cluster aggregation, and an intermediate‐ q exponent transitioning toward compact, Porod‐like scattering. This dual behavior provides direct, real‐time evidence of localized densification and structural compactification within the expanding agglomerates. These findings establish that precise tuning of incident photon energy controls not only the radiolytic yield but the entire hierarchical aggregation trajectory, offering a sophisticated blueprint for the rational design of functional nanostructures under radiation fields.