Imaging

High-Resolution (S)TEM Imaging and Electron Diffraction Tomography

Details

Research Highlights

(Scanning) Transmission Electron Microscopy (S)TEM​ Imaging of Surface and Nanostructure of Catalysts
 
Combined (HR) X-ray Diffraction and Atomic-Resolution (S)TEM imaging of Nanoscale Structrual Ordering in a Complex Metal Oxide Catalyst
 
The determination of the atomic structure of a functional material is crucial to understanding its “structure-to-property” relationship (e.g., the active sites in a catalyst), which is however challenging if the structure possesses complex inhomogeneities. Here, we report an atomic structure study of an important MoVTeO complex metal oxide catalyst that is potentially useful for the industrially relevant propane-based BP/SOHIO process. We combined aberration-corrected scanning transmission electron microscopy with synchrotron powder X-ray crystallography to explore the structure at both nanoscopic and macroscopic scales. At the nanoscopic scale, this material exhibits structural and compositional order within nano-sized “domains”, while the domains show disordered distribution at the macroscopic scale. We proposed that the intra-domain compositional ordering and the inter-domain electric dipolar interaction synergistically induce the displacement of Te atoms in the Mo-V-O channels, which determines the geometry of the multifunctional metal oxo-active sites.  

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  •  Yihan Zhu, Qingxiao Wang, Lan Zhao, Baiyang Teng, Weimin Lu, Yu Han*, “ Atomic Resolution Imaging of Nanoscale Structural Ordering in a Complex Metal Oxide Catalyst”, Chemistry of Materials, 24 (2012), 3269–3278 ​​

       


Direct Observation of Surface Reconstruction and Termination on a Complex Metal Oxide Catalyst by Electron Microscopy ​

The surface reconstruction of an MoVTeO complex metal oxide catalyst was observed directly by various electron microscopic techniques and the results explain the puzzling catalytic behavior. ​

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  • Yihan Zhu, Qingxiao Wang, Lan Zhao, Yu Han*, “Direct Observation of Surface Reconstruction and Termination on a Complex Metal Oxide Catalyst by Electron Microscopy”, Angewandte Chemie International Edition51 (2012) 4176-4180​​ ​


(Scanning) Transmission Electron Microscopy (S)TEM​ Imaging of Upconversion Nanocrystals​

Characterizing the Core-Shell Upconversion Nanocrystals
 
We show that by rational design of a core-shell structure with a set of lanthanide ions doped into different layers at precisely defined concentrations, efficient upconversion emissions can be realized for lanthanide activators without ladder-like arranged energy levels.  Our mechanistic investigations suggest that the unusual upconversion phenomenon stems from energy migration through the gadolinium sublattice and subsequent trapping of the migrating energy by the activators.  This effect can also be harnessed to provide Förster resonance energy transfer for the first time to lanthanide-doped nanocrystal acceptors that typically feature narrow absorption bands and extremely low extinction coefficients. This work is mainly conducted at NUS, by Liu's group, while our contribution is the HR-STEM imaging with electron energy loss spectroscopy (EELS) analysis which explicitly verified the designed core-shell structure in the upconversion nanocrystals for the first time. 


  • Feng Wang, Renren Deng, Juan Wang, Qingxiao Wang, Yu Han, Haomiao Zhu, Xueyuan Chen, Xiaogang Liu*, “Tuning Upconversion through Energy Migration in Core-Shell Nanoparticles”, Nature Materials, Published online: 23 October 2011 | doi:10.1038/nmat3149
          Abstract | Full Text | PDF (654 KB) | Supplementary information​



Unveil the Complex Mesoporous ​Structures in Silica


Discovery of the first tri-continuous mesoporous silica IBN-9 by electron crystallography​

High resolution electron microscopy (HRTEM) has unique advantages for structural determination of nano-sized porous materials compared to X-ray diffraction, because it provides the important structure factor phase information which is lost in diffraction. We demonstrate the structure determination of the first tri-continuous mesoporous silica IBN-9 by electron crystallography. Similar procedures can also be applied for structure determination of other porous and nonporous crystalline materials. This work is in collaboration with Prof. Zou's group at Stockholm University.

  • ​Daliang Zhang, Junliang Sun, Yu Han and Xiaodong Zou*, Microporous & Mesoporous Materials 146 (2011), 88-96​
          Open Show preview  |   PDF (1853 K)   |  Supplementary content  |   



Electron Diffraction (ED) Tomography

Software package for ED tomography is under development (in collaboration with Daliang Zhang, Jilin University).