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STEM with Atomic Resolution


planes of ordered Pt3


In the second experiment, the alternating Pt and Co (100) Co particle provided an internal marker


for observation of surface reconstruction in oxygen. Tis allowed atomic-level compositional imaging at the surface. Te details of this observed oxygen-driven Pt surface enrich- ment may pave a way for designing and tailoring the structure and performance of the Pt-Co ORR catalyst. Tis case study highlights the capability of Z-contrast HAADF-STEM imag- ing combined with image simulation for analysis of chemical composition changes at nanoparticle surfaces under realistic catalytic conditions. Tus, a MEMs-based window gas cell enables an in situ


atmospheric STEM study at atomic resolution to explore novel and interesting phenomena occurring during gas-solid inter- actions. However, some limitations still exist in the current form of the windowed gas cell for more general analyses on a wider range of materials. Tese limitations include a lower contrast for light-element materials (for example, graphene, boron nitride) because of the dimension of the SiNx


windows


and the single-tilting function of the current design. But it may only be a matter of time before these constraints are removed. We believe that atomic-resolution in situ STEM under atmo- spheric pressure will be an essential tool for advanced research of gas-solid interactions, and numerous exciting findings can be expected.


Conclusion In summary, the windowed gas cell now allows atomic-


resolution STEM observation of dynamic structure evolution of catalytic nanomaterials under realistic gaseous conditions, providing information that is beneficial to understanding their structure-properties relationship. Te two application exam- ples presented here clearly demonstrate the advantages and capability of this in situ technique, particularly the high spatial resolution and high stability under atmospheric gas pressure.


Acknowledgments Te authors thank Protochips Inc. for the technical sup-


port of the Atmosphere windowed gas cell facility. Additional support was provided by the University of California – Irvine Materials Research Institute (IMRI) for use of the state-of-the- art TEMs.


References [1] R Sharma, J Mater Res 20 (2005) 1695–1707. [2] ED Boyes , Ultramicroscopy 67 (1997) 219–32. [3] Y Li , Nat Commun 6 (2015) 7583. [4] JR Jinschek, Chem Commun 50 (2014) 2696–06. [5] N de Jonge , Nano Lett 10 (2010) 1028–32. [6] T Alan , Appl Phys Lett 100 (2012) 081903. [7] LF Allard , Microsc Microanal 18 (2012) 656–66. [8] T Avanesian , J Am Chem Soc 139 (2017) 4551–58. [9] J Gu , Chem Soc Rev 41 (2012) 8050–65.


[10] SR Longwitz , J Phys Chem B 108 (2004) 14497–14502. [11] J Enkovaara , J Phys Condens Matter 22 (2010) 253202. [12] MJ Kale , ACS Catal 6 (2016) 5599–5609. [13] S Dai , Nat Commun 8 (2017) 204. [14] CT Koch. Ph.D. Tesis, Arizona State University, 2002.


2019 May • www.microscopy-today.com


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