EXAFS provides the capability to interrogate nanoparticle (NP) structure in atomistic detail without relying on long-range crystallinity. There is a limitation in that EXAFS provides averaged structural information, making it difficult to separate a small amount of heterogeneous structure from bulk. In this work, models were developed to extract surface-specific information from conventional EXAFS measurements collected on UO 2 NPs of varying size. Specifically, the surface terminating species of UO 2 NPs was determined from comparison of coordination numbers with geometric models while the origin of static disorder was interrogated from user-defined simulations. Results show that the degree of oxygenation on the NP surface does not significantly deviate from bulk surface and that static disorder is highly enhanced in NP surface layers but cannot be attributed to surface relaxation effects alone. The approach described herein has the potential to be adapted to a range of inorganic NP systems to interrogate surface structure.[a] S. Bang, A.

The Front Cover shows UO2 nanoparticles with a pictorial representation of the atoms (uranium in blue and oxygen in red). In this work, user‐defined X‐ray absorption spectroscopy models informed by surface relaxation effects and inherent surface disorder were generated and preferentially fit to experimentally derived data. The developed method enables representative local surface structure attributes to be extracted from bulk X‐ray absorption spectroscopy data. Results show that the UO2 surface is highly disordered compared with the bulk structure, and this cannot be explained through surface relaxation effects alone. Additionally, this trend is notably not observed in 8 nm nanoparticles (which resemble the bulk), as it is in 1.4 and 4.7 nm particles. This suggests that there may be a critical domain size for ordering within UO2 nanoparticle surfaces. More information can be found in the Research Article by L. M. Moreau and co‐workers.