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3D Structure of Nanomaterials under Realistic Conditions

Periodic Reporting for period 3 - REALNANO (3D Structure of Nanomaterials under Realistic Conditions)

Okres sprawozdawczy: 2022-05-01 do 2023-10-31

The properties of nanomaterials are essentially determined by their 3D structure. Electron tomography enables one to measure the morphology and composition of nanostructures in 3D, even at atomic resolution. Unfortunately, all these measurements are performed at room temperature and in ultra-high vacuum, which are conditions that are completely irrelevant for the use of nanoparticles in real applications! Moreover, nanoparticles often have ligands at their surface, which form the interface to the environment. These ligands are mostly neglected in imaging, although they strongly influence the growth, thermal stability and drive self-assembly.

I will develop innovative and quantitative 3D characterisation tools, compatible with the fast changes of nanomaterials that occur in a realistic thermal and gaseous environment. To visualise surface ligands, I will combine direct electron detection with novel exit wave reconstruction techniques.

Tracking the 3D structure of nanomaterials in a relevant environment is extremely challenging and ambitious. However, our preliminary experiments demonstrate the enormous impact. We will be able to perform a dynamic characterisation of shape changes of nanoparticles. This is important to improve thermal stability during drug delivery, sensing, data storage or hyperthermic cancer treatment. We will provide quantitative 3D measurements of the coordination numbers of the surface atoms of catalytic nanoparticles and follow the motion of individual atoms live during catalysis. By visualising surface ligands, we will understand their fundamental influence on particle shape and during self-assembly.

This program will be the start of a completely new research line in the field of 3D imaging at the atomic scale. The outcome will certainly boost the design and performance of nanomaterials. This is not only of importance at a fundamental level, but is a prerequisite for the incorporation of nanomaterials in our future technology.
To combine the principles of in situ transmission electron microscopy (TEM) with 3D characterisation, we developed fast high angle annular dark field scanning TEM (HAADF STEM) electron tomography (ET). We hereby reduced the acquisition time of a tilt series for ET from 1 hour to less than 5 minutes [1-3]. We combined our methodology with a dedicated heating ET holder and were able to investigate morphological transformations of Au and AuPd octapods at high temperatures [4]. Next, we measured 3D changes in composition for AuAg nanoparticles and could reveal the importance of grain boundaries, present in pentatwinned nanorods [5,6]. We realised that surface ligands might have an influence on the interpretation of heating studies and we investigated different procedures to eliminate the effect of ligands during such experiments [7]. In order to combine ET with energy dispersive X-ray spectroscopy (EDXS), it is necessary to overcome the need for long acquisition times. We therefore developed a dose-minimizing technique based upon deep learning [8]. Since gas cell holders do not enable conventional ET, we exploited a methodology based on atom counting [9]. The counting results are used to build a 3D starting model for molecular dynamics simulations. Such simulations may easily result in a closest local minimum in the potential energy landscape where the reconstructed structure deviates from the experiments. Therefore, we proposed an iterative local minima search algorithm which is also taking high temperature into account [10]. We applied this methodology to investigate the behaviour of CeO2 supported Au nanoparticles at high temperature [11].

References:

[1] Vanrompay H, Skorikov A, Bladt E, Béché A, Freitag B, Verbeeck J, Bals S, Ultramicroscopy 221, 113191 (2021).
[2] Albrecht W, Bals S, The Journal of Physical Chemistry C 124, 27276 (2020).
[3] Esteban DA, Vanrompay H, Skorikov A, Béché A, Verbeeck J, Freitag B, Bals S, Microscopy And Microanalysis 27, 2116 (2021).
[4] Albrecht W, Bladt E, Vanrompay H, Smith JD, Skrabalak SE, Bals S, Acs Nano 13, 6522 (2019).
[5] Skorikov A, Albrecht W, Bladt E, Xie X, van der Hoeven JES, van Blaaderen A, Van Aert S, Bals S, Acs Nano 13, 13421 (2019).
[6] Mychinko M, Skorikov A, Albrecht W, Sánchez‐Iglesias A, Zhuo X, Kumar V, Liz‐Marzán LM, Bals S, Small , 2102348 (2021).
[7] De Meyer R, Albrecht W, Bals S, Micron 144, 103036 (2021).
[8] Skorikov A, Heyvaert W, Albecht W, Pelt DM, Bals S, Nanoscale 13, 12242 (2021).
[9] Van Aert S, de Backer A, Martinez GT, Goris B, Bals S, Van Tendeloo G, Rosenauer A, Physical Review B 87, 064107 (2013).
[10] Arslan Irmak E, Liu P, Bals S, Van Aert S, Small Methods , 2101150 (2021).
[11] Liu P, Arslan Irmak E, De Backer A, De wael A, Lobato I, Béché A, Van Aert S, Bals S, Nanoscale 13 (2021).
In this program, 3D characterisation of nanomaterials will be taken to the next level by tracking 3D changes of the structure and composition of nanoparticles and their surface ligands in a realistic environment. Such experiments are very challenging and much more demanding than a simple combination of electron tomography and in situ TEM. So far, fast scanning techniques have been combined with advanced 3D reconstruction algorithms and 3D modelling approaches. In this manner, we have been able to track 3D changes of the structure and composition of nanomaterials under different thermal environments.It is of great importance to note that our innovative methodology also enables the characterisation of nanomaterials that are very sensitive to the electron beam and for which fast measurements are the only possibility to reveal their real 3D structure. Currently, experiments under gaseous environment are performed, which will enable a better understanding of the 3D structure-property connection and will therefore lead to a boost of the characterisation of nanocatalysts. To visualise surface ligands in 3D, we will combine exit wave reconstruction with a direct electron detector and the optimisation of the sample support is hereby crucial. This program will enable the necessary understanding to improve the properties and stability of nanomaterials at work and may even trigger the synthesis of novel nanostructures.
3D visualization of a Au/Pd octopod before (25 °C) and after heating at different temperatures