Imperfections of the crystal structure, such as partial ordering, formation of core-shell and Pt rich skin improve the electro-catalytic activity of Pt-based intermetallic nanoparticles used as a catalyst material in low-temperature fuel cells [1, 2]. Impact on the surface reactivity by the core–shell nanostructures could be explained with the induced lattice strain [3, 4]. In the case of twinned structure, the lattice strain significantly influences the interatomic distances and consequently the energy levels of bonding electrons, which determines the catalytic, electrical and optical properties .
In this work we studied the local structure and chemistry near the lamellar (111) twin boundaries in sol-gel prepared intermetallic Cu3Pt nanoparticles, specially tailored  to exhibit high amount of polysynthetic twins. Using HAADF-STEM (Jeol ARM 200 CF) imaging in conjunction with image simulations we extracted the information about chemical composition and strain on the level of individual atom columns. Experimental Cu-Pt column intensities were measured using modified approach by LeBeau and Stemmer . Experimental intensities were compared to the intensities from simulated images where chemical composition and thickness of individual Cu-Pt columns were varied.
In Fig. 1a a LAADF micrograph (20 – 80 mrad) of (111) twin boundaries in 60 nm sized Cu3Pt nanoparticle is displayed. Enlarged image of lamellar twins is shown in Fig. 1b. The bright contrast around planar defect indicates strain. From HAADF (70 – 180 mrad) images (Fig. 2a) the intensity ratios were extracted and correlated to the average chemical composition of individual columns. Fig. 2b is the distribution of normalized intensities of atomic columns around the twin boundary where a significant decrease in the intensity near the boundary indicating depletion in Pt content. For conversion of intensities to Pt/Cu ratio HAADF images were simulated using a multislice method with frozen phonon approximation (QSTEM software). Using DFT calculations the energy and lattice relaxation were calculated as a function of local chemical composition near the twin boundaries. Taking into account the local strain and chemical composition variation the influence of twin boundaries on electrocatalytic properties will be discussed in details.
The authors acknowledge funding from the Slovenian Research Agency (J2-6754 and P2-0393)
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To cite this abstract:Goran Drazic, Francisco Ruiz Zepeda, Anja Lautar, Primoz Jovanovic, Marjan Bele, Miran Gaberscek; Quantitative approach to twin boundaries in Cu3Pt nanoparticles. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/quantitative-approach-to-twin-boundaries-in-cu3pt-nanoparticles/. Accessed: January 21, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/quantitative-approach-to-twin-boundaries-in-cu3pt-nanoparticles/