Kirsten Jensen1 Troels Christiansen1 Mikkel Juelsholt1

1, Department of Chemistry, University of Copenhagen, Copenhagen Ø, , Denmark

Ultrasmall nanoparticles have come to play a huge role in modern materials chemistry. This development has challenged the conventional techniques for material characterization, which break down for structures on the nanoscale. However, total scattering combined with Pair Distribution Function analysis allows us to look further into nanostructure and establish the structure-property relation for advanced functional materials.[1]
We have applied X-ray total scattering with Pair Distribution Function analysis to elucidate the existence of polymorphism in the 29kDa gold nanocluster, Au144(SR)60.[2] We have shown that apart from the well-known icosahedral cluster type, another decahedral polymorph, closer in structure to a twinned fcc structure also exist. Our data showed that for some thiol ligands, the two structures can coexist, illustrating their closeness in energy. The existence of polymorphism on the nanoscale opens for a new aspect in nanostructure engineering. In order to understand the relation between synthesis and structure, it is important to get further insight into the nucleation processes dictating the outcome of a reaction. We have recently shown that X-ray total scattering can be applied for in situ studies of particle formation, giving atomic scale insight into nucleation processes.[3, 4] Since structural information can be extracted from X-ray total scattering even for structures without long range order, in situ studies of particles nucleation allow deducing structures from precursor clusters over pre-nucleation clusters to the final nanoparticles. Here, we will present new results regarding the formation of monodisperse metal and metal oxide colloidal nanoparticles, getting closer to an understanding of the atomic scale processes in particle nucleation. In studies of several different nanoparticle systems, including colloidal iron oxide nanoparticles, we see that the structure of the clusters seen immediately after nucleation can be directly connected to the structural motifs present in the final nanoparticles, explaining the formation of defects in nanostructured particles.

1. Billinge, S. J. L.; Levin, I. Science 2007, 316, (5824), 561-565.
2. Jensen, K. M. O.; Juhas, P.; Tofanelli, M. A.; Heinecke, C. L.; Vaughan, G.; Ackerson, C. J.; Billinge, S. J. L. Nat Commun 2016, 7.
3. Jensen, K. M. O.; Andersen, H. L.; Tyrsted, C.; Bojesen, E. D.; Dippel, A. C.; Lock, N.; Billinge, S. J. L.; Iversen, B. B.; Christensen, M. ACS Nano 2014, 8, (10), 10704-10714.
4. Jensen, K. M. Ø.; Tyrsted, C.; Bremholm, M.; Iversen, B. B. ChemSusChem 2014, 7, (6), 1594-1611.