Insights into Large Thiolate-protected Gold Clusters and Nanoparticles




Vergara Perez, Sandra Milena

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Metallic clusters and nanoparticles display unique optical, electronic, and chemical properties compared to their bulk counterparts. These properties are influenced by its internal structure. Therefore, atomic structural characterization of clusters and nanoparticles is of paramount importance in nanotechnology. The use of thiols as surface-protecting ligands has provided numerous stable clusters with atomically well-defined composition as well as small quasi-monodisperse nanoparticles. In this dissertation, I present the structural analysis of two of these systems: ~29 kDa pMBA- protected gold cluster and ~400 kDa hexanethiol-protected gold nanoparticles. In the former case, the structure of the cluster Au146(p-MBA)57 (~29 kDa gold core) was solved by electron diffraction to subatomic resolution (0.85 Å) and by X-ray diffraction at atomic resolution (1.3 Å). The core atoms are organized in a twinned FCC structure whereas the surface protecting motifs follow a C2 rotational symmetry about an axis bisecting the twinning plane. Au146(p-MBA)57 is the largest aqueous gold cluster solved to date as well as the smallest gold particle exhibiting a twinning plane. I also applied Pair distribution function (PDF) analysis to compare the new twinned FCC-structure with previous proposed icosahedral and decahedral models. Au146(p-MBA)57 structure was the most consistent structure with experimental X-ray PDF data for ~29 kDa p-MBA protected gold cluster. For the case of thiolate protected nanoparticles, I present the structural characterization of ultra-small, highly monodisperse ~400 kDa (~3.8 nm) gold nanoparticles using scanning transmission electron microscopy. The high resolution images clearly showed the sample was composed of ~30% of asymmetric decahedral particles and ~70% of FCC structures with multiple planar defects. Remarkably, some FCC nanoparticles displayed two crystalline domains with a high angle misorientation. This high energy configuration is not favorable for such small systems. To my knowledge, this would be the first report of sub-10nm nanoparticles displaying stable high energy grain boundaries.


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Electron microscopy, gold clusters, MicroED, nanoparticles



Physics and Astronomy