Abstract text (incl. figure legends and references)

The properties of metallic nanoparticles (NPs) are linked to their three-dimensional (3D) structure. However, these particles exhibit structural and morphological transformations under the conditions relevant to their applications, and subtle changes in the structure may significantly modify their performance. Hence, an atomic-scale understanding of the transformations under realistic conditions has a vital importance in preserving the functionalities of metal NPs. In situ transmission electron microscopy is a valuable technique to observe the dynamics of NPs. Combining the in situ experiments with fast electron tomography even enables 3D in situ measurements. [1] Despite the progress in this field, atomic-scale transformations cannot always be understood by experimental techniques alone as these measurements do not provide the necessary time or spatial resolution. In this study, we have demonstrated that such limitations can be overcome by linking 3D characterization techniques with atomistic simulations.

A first example is the in situ 3D investigation of the thermal stability of Au@Pt NPs, which is important to understand their behavior during catalytic reactions. However, since the heating cycles were interrupted during the experiments to acquire tomography tilt series, the ongoing transformations could not be fully monitored by experimental observations. We therefore used experimentally determined 3D reconstructions of Au@Pt NPs as realistic input models (Fig 1) for molecular dynamics (MD) simulations. In this manner, it has been possible to unravel atomic-scale dynamics at elevated temperatures, and to systematically investigate the parameters that influence the thermal stability of these NPs. [2]

This approach becomes even more important when the environmental triggers cannot be applied in situ. For example, in many optical and photothermal applications, Au NPs are excited by laser irradiation. However, due to the ultrafast time scales, laser-induced restructuring of NPs cannot be monitored by experiments. To do so, tomography tilt series of the same NP was acquired before and after laser excitation (ex situ) and the laser heating regime was modelled to mimic the experiments. By performing MD simulations based on the 3D reconstructions and the heating regime, laser-induced complex atomistic rearrangements causing shape and structural deformations have been unraveled (Fig 2). [3]

The approach presented in this study is of great potential as it enables performing simulations based on the experimentally measured surface structure. Moreover, it enables us to capture the ongoing processes at the atomic scale, as well as to understand the driving mechanisms behind the complex transformations that possibly occur during applications.

References

[1] W. Albrecht, S. Bals, J. Phys. Chem. C 124 (2020), 50, 27276–27286.

[2] A. Pedrazo-Tardajos, E. Arslan Irmak et al., ACS Nano 16 (2022), 6, 9608–9619.

[3] W. Albrecht, E. Arslan Irmak et al., Adv. Mater. 33 (2021), 2100972.

[4] This work was supported by the European Research Council (770887 PICOMETRICS to SVA and 815128 REALNANO to SB, 823717 ESTEEM3), Marie Sklodowska-Curie Actions (797153 SOPMEN to WA), and Research Foundation Flanders (G.0267.18N, G.0502.18N, G.0346.21N).

Fig 1. 3D reconstructions and corresponding 3D models of a Au (a,b) and Au@Pt (c,d) NP. [2]

Fig 2. 3D reconstructions of a Au NP before (a) and after (b) laser excitation. c) The results of MD simulations. [3]