Abstract:

Electron tomography has evolved into a powerful tool to investigate a broad variety of nanomaterials. Most of these results have been obtained with a resolution at the nanometer scale but different approaches have recently pushed the resolution to the atomic level.

One possibilitiy to perform electron tomography with atomic resolution is by applying reconstruction algorithms based on compressive sensing. The methodology was applied to HAADF-STEM images acquired from defect-free Au nanorods and core-shell Au@Ag nanorods [1,2]. Another challenge is to measure defects and lattice strain in 3D. Nanodecahedra consist of five segments bound by {111} twin boundaries, yielding a strained structure. A continuous tilt series of HAADF-STEM was acquired and a dedicated alignment and reconstruction procedure was applied. In this example, the coordinates of the atoms are a direct outcome of the reconstruction. As such, it becomes straightforward to calculate the 3D displacement map [3].

An emerging challenge is to fully understand the connection between the 3D structure and properties under realistic conditions. Therefore, innovative methodologies are required to track the fast 3D changes of nanomaterials that occur in different thermal and gaseous environments. For example, to investigate the thermal stability of Au nanoparticles, a combination of a tomographic heating holder with fast tilt series acquisition has been used. We investigated the morphological evolution of a Au nanostar at elevated temperatures and quantified local volume changes [4]. To quantify nanoparticle shape dynamics in a gaseous environment in 3D, HAADF-STEM images served as an input for atom counting procedures followed by 3D relaxation of the structure. In this manner, we characterized shape changes of a Pt nanoparticle in a gaseous environment (Figure 1). The conditions have been varied from vacuum (Figure 1.a) to a 1 bar H2 flow (Figure 1.b), followed by a 1 bar O2 environment (Figure 1.c). To investigate the behaviour during cycling, we repeated the experiment several times using the same particle (Figure 1.d&e). We clearly observe morphology changes and we were even able to quantify the occurrence of the different surface facets [5].

 

Figure 1. Morphology of a Pt nanoparticle in different gaseous environments. The atoms are shown using different colours, according to the type of facet: blue={100}, pink={110}, purple={111}, grey=higher index.

[1] B. Goris, S. Bals, W. Van den Broek, E. Carbo-Argibay, S. Gomez-Grana, L. M. Liz-Marzan, G. Van Tendeloo, Nature Materials 11 (2012) 930
[2] B. Goris, A. De Backer, S. Van Aert, S. Gómez-Graña, L. M. Liz-Marzán, G. Van Tendeloo, S. Bals, Nano Letters 13 (2013) 4236
[3] B. Goris, J. De Beenhouwer, A. De Backer, D. Zanaga, K. J. Batenburg, A. Sánchez-Iglesias, L.M. Liz-Marzán, S. Van Aert,  S. Bals, J. Sijbers, G. Van Tendeloo Nano Letters 15 (2015) 6996
[4] H. Vanrompay, E. Bladt, W. Albrecht, A. Béché, M. Zakhozheva, A. Sánchez-Iglesias, L. M. Liz-Marzán, S. Bals, Nanoscale 10 (2018) 22792
[5] T. Altantzis, I. Lobato, A. De Backer, A. Béché, Y. Zhang, S. Basak, M. Porcu, Q. Xu, A. Sánchez-Iglesias, L. M. Liz-Marzán, G. Van Tendeloo, S. Van Aert, S.Bals, Nano Letters 19 (2019) 477

Bio:

The research of Sara Bals focuses on electron tomography of nanostructures, even with atomic resolution. She is a Full Professor at the University of Antwerp and she received her PhD degree (2003) from the same University. She did post-doctoral work at the National Centre for Electron Microscopy at the Lawrence Berkeley National Laboratory in California. She is the author of more than 300 ISI contributions, including Nature or Science type contributions. Her work has been cited more than 7500 times and she has an h-index of 46 (web of science). She gave more than 40 invited presentations at international conferences and workshops.

She has organized several workshops and symposia and chaired several sessions at international microscopy conferences. In 2013, she received an ERC Starting Grant concerning 3D characterisation of nanostructures (Colouratom). In 2016, she became "Laureate of the Academy for Natural Sciences" awarded by the Royal Flemish Academy of Science. In 2017, she received the title of “Francqui Research Professor”. Her ERC Consolidator Grant “Realnano” started in 2019.

Hosted by Francesc Teixidor, LMI group