Scanning transmission electron microscopy of atomic structure of nanoparticle

[摘要] This thesis presents the researches on the size and atomic structure of the nanoclusters including ligand protected monometallic clusters, ligand protected bimetallic clusters and biological metallic clusters, by using aberration corrected HAADF -STEM. The atom counting method with size selected clusters as mass balance was utilized to "fractionate" the relative broad distributed sample and make the structure study focus on the certain size range. The atomic structures of Auss Schmid clusters were investigated. Nearly half of these clusters were found to have a hybrid structure. A combination of geometric size analysis and atom counting method was performed to determine both the size and composition of the AuAg alloy clusters. We found that Ag-rich clusters tend to have an icosahedral structure while the Au-rich clusters prefer the fcc structure. For the biological nanoparticles, the ferritins' iron loadings were obtained. Different morphologies of the ferritin iron cores were observed as a function of iron loading, suggesting the iron core growth process in the protein shell. The HAADF -STEM was also successfully employed to characterize the ultra-small Au and Pd catalysts supported on the Ti02, which are helpful to understand the catalytic performance of these catalysts. A multilayer deposition method was developed to accommodate and process the large abundance of clusters from the new high-flux cluster source. With the similar experimental setup, size-selected colloidal clusters were produced by dissolving the multilayer cluster-PVP stacks. The colloidal clusters were observed by the STEM and their sizes were found to be conserved during the dissolving process.

[发布机构] University:University of Birmingham;Department:School of Physics and Astronomy

[关键词] Q Science;QC Physics