AMADEus Seminar - Kirsten M. Ø. Jensen - July 2, 2019 - 3:00 pm - ICMCB (Amphi)le 02/07 de 15h à 16h
Department of Chemistry and Nanoscience Center
University of Copenhagen
"New nanostructures from x-ray total scattering and PDF analysis"
Nanomaterials have come to play a huge role in modern materials chemistry: By nanosizing the functional materials used in a range of different applications, the properties of the materials can be improved, and new applications can arise. This development has challenged the conventional techniques for material characterization. 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. Here, I will present recent work illustrating how we use x-ray total scattering to study atomic structure in advanced nanomaterials, with special focus on metal and metal oxide nanoparticles.  We observe that new structural motifs, unstable in the bulk form, become dominant in nanoscale materials. In molybdenum oxides, for example, we use PDF analysis coupled with HR-STEM to determine the structure of 3 nm MoO2 particles, where rutile-based shear planes appear, changing the material properties.
Apart from studying the synthesized nanoparticles, I will also show how in situ x-ray total scattering allows following the formation of materials. Despite decades of research into nucleation processes, very little is known on how nanoparticle formation during solvothermal synthesis takes places on the atomic scale. We have developed methods which allows using in situ synchrotron X-ray Total Scattering and Pair Distribution Function analysis to follow nanoparticle nucleation and growth in situ. In contrast to conventional crystallographic studies, PDF analysis gives structural information from non-crystalline species, allowing obtaining structural information on the atomic scale, all the way from precursor to the final nanoclusters during synthesis. Using x-ray total scattering, we deduce the atomic structure of prenucleation clusters, present in the processes just before the crystalline nanoparticles have formed. We show that the solvent and synthesis conditions have large influence on the nucleation pathway and the structure of the nano-scale clusters in the synthetic pathway.
 S. J. L. Billinge, I. Levin, Science 316, 561-565, (2007).
 K. M. Ø. Jensen, P. Juhas, M. A. Tofanelli, C, K, Heinecke, G. Vaughan, C. Ackerson, S. J. L. Billinge, Nature
Communications 7, 11859, (2016).
 K. M. Ø. Jensen, C. Tyrsted, M. Bremholm, B. B. Iversen, ChemSusChem 7, 1594-1611, (2014).