The performance of catalyst nanoparticles is generally dependent on their size, shape, strain, composition and support. However, the relationship between these parameters and the catalyst performance is not well understood. In most instances, the catalyst design process involves several design and testing iterations until the desired performance is attained, and identifying the structure-property relationships would enable rational catalyst design. In order to relate the nanoparticle properties to catalytic activity, it is necessary to characterise them at atomic resolution.
With aberration corrected STEM it is now possible to image and perform spectroscopy on nanocatalysts at high resolution to obtain detailed structural and compositional information. Here we show how experiment design including detailed calibration of imaging and spectroscopy parameters can reveal the required information, using Ru, Pt and alloyed Pt-Co catalyst nanoparticles as examples.
As a first example, structural studies of Ru nanoparticles, using methods recently developed–, indicated the formation of thin Ru rafts (Figure 1). The formation of Ru rafts has been controversial since their hypothesis. These results demonstrate how quantitative ADF imaging can be used to resolve this question.
Using a new detector mapping technique developed at Oxford University, a range of Pt nanoparticles were characterised for their three dimensional structure (Figure 2). The models, created using an energy minimisation approach previously described in ref , indicate a Wulff-like structure. We will show how these models can be used as input for density functional theory simulations, thus unlocking the possibility to study the electronic structure of experimental catalyst nanoparticles.
It is important to increase analysis throughput by software automation  in order to gain statistically meaningful results. In Figure 3 a rapid particle size measuring algorithm was used to measure the size distribution of Pt and Pt-alloy nanoparticle systems. The size distribution can then be used as a guide for the microscopist to selectively choose nanoparticles which represent the particle ensemble.
Finally, experiment design and preliminary EDX and EELS results at high resolution will be presented. This approach aims to decouple composition and thickness effects in order to obtain structural information of alloyed nanoparticles.
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To cite this abstract:Aakash Varambhia, Lewys Jones, Annick De Backer, Vidar Fauske, Sandra Van Aert, Dogan Ozkaya, Sergio Lozano-Perez, Peter Nellist; Experiment design for quantitative dark field imaging and spectroscopy of catalyst nanoparticles using Scanning Transmission Electron Microscopy (STEM). The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/experiment-design-for-quantitative-dark-field-imaging-and-spectroscopy-of-catalyst-nanoparticles-using-scanning-transmission-electron-microscopy-stem/. Accessed: September 19, 2018
EMC Abstracts - https://emc-proceedings.com/abstract/experiment-design-for-quantitative-dark-field-imaging-and-spectroscopy-of-catalyst-nanoparticles-using-scanning-transmission-electron-microscopy-stem/