A peek behind the behaviour of nanomaterials
Fundamental studies of nanoscale physicochemical phenomena in functional materials by in situ electron microscopy methodologies
Parallel beam of electrons
A deeper understanding of the fundamental behaviour of materials can help scientists identify ways in which their performance and functionality can be enhanced. We spoke to Dr Vasiliki Tileli about her work in using Transmission Electron Microscopy (TEM) techniques to investigate physico-chemical phenomena in nanomaterials.
Project Objectives
Structural and chemical phase transformation of catalytic surfaces.
A technique with its roots in research conducted during the 1930s, transmission electron microscopy (TEM) allows researchers to image and analyse the properties of materials in great depth, right down to the sub-nanometre scale. Based at the Institute of Materials at Ecole Polytechnique Federale de Lausanne (EPFL), Dr Vasiliki Tileli is using electron microscopy techniques to probe the physico-chemical behaviour of certain nanomaterials and gain deeper insights into the factors that may lead them to degrade. “In my research group we’re looking at functionality at different scales, but we’re focusing particularly on the nanoscale,” she says. The nanoscale is between 1-100 nanometres (10-9 of a metre), and Dr Tileli says imaging materials on this scale can lead to important insights. “It is important to understand how the properties of a material change at the nanoscale – because this is where certain effects originate, which then affect behaviour at higher scales,” she explains. “If you can understand interactions at the nanoscale, you could control the overall performance of the material.” Functional materials The primary focus of Dr Tileli’s research is the issue of how nanomaterials interact with different media. For example, the catalyst in a fuel cell typically works with either gases or liquids while an electrical process is taking place. “These are the kinds of interactions that we’re trying to image,” outlines Dr Tileli. By using site-specific in situ TEM techniques, Dr Tileli and her colleagues hope to gain a fuller picture of the functionality of nanomaterials, specifically ABO3-type perovskite nanostructures. “In the TEM, our materials are held within specialized microdevices and irradiated with an electron beam, which is then transmitted through the sample. This electron beam can interact with our material in many ways. TEM techniques allow us to measure and analyse these beamspecimen interactions to learn about different aspects of that material. One signal can allow us to form images that show crystallographic and orientational information, where another
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Convergent beam of electrons
Liquid cell configuration (TEM)
By developing and applying in situ nanoanalytical transmission electron microscopy techniques (TEM), this project aims to address fundamental questions governing the functionality of ABO3-type perovskite nanostructures. More specifically, the project is centered in linking their exceptional properties with respect to site specific reaction mechanisms for catalytic applications and local phase-induced structural transformations for computing devices.
Project Funding
The project received funding from the Swiss National Research Foundation under award no. 200021_175711.
Contact Details
Biasing Chip
Parallel beam of electrons
Dynamic domain wall movement of ferroelectric materials.
Convergent beam of electrons relates to composition – what elements do we have and where are they located,” she continues. “We can also run a dynamic process by applying different stimuli and then seeing what happens. Typically we just see the changes in morphology when we are in a transmission imaging mode, but we can also use electron diffraction and chemical analysis for structural and elemental identification.”
By using specialized techniques, one can also probe the chemical state of different elements. “For example, if you have a metal that is connected to four oxygen atoms, then it has a different chemical state than a metal that is connected to five. That suggests that the material has reconstructed,” says Dr Tileli. “This proposal is about two different categories of functionalities; catalysts and
Using real-life operating conditions while performing
transmission electron microscopy experiments of functional materials provides valuable insights on their properties. This enables researchers to gain a fuller picture of the modifications that specific materials undergo while in operation. “By performing both chemical analysis and structural analysis, we can understand what is happening to the material. What is changing?” outlines Dr Tileli. A lot of information can be gathered using these in situ techniques, such as elemental or atomic rearrangement.
ferroelectrics. We’ve made a lot of progress in understanding their dynamic behaviour under relevant operating conditions.” The operating conditions here relate primarily to the application of an external potential which is very important to the functionality of catalysts and, in general, energy-based materials. Traditionally, electron microscopy experiments are conducted in a
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vacuum environment and in a static state, with no real connection to the environment of the material in a device, but now Dr Tileli and her colleagues are taking a different approach. “We are trying to image the materials in their native environment,” she explains. This will enable researchers to build a deeper understanding of nanoscale physicochemical phenomena in these materials, which opens up the possibility of controlling them more precisely in future. “When you understand what is happening in a material, you can then identify what you need to change in order to enhance their performance,” says Dr Tileli. “For example, you can understand what separates a good catalyst from a bad catalyst, and from that what needs to be improved in the design of the next generation of functional materials.”
Next generation materials This research holds important implications for industry, with companies across the commercial sector seeking improved materials, while also addressing wider concerns around sustainability. The results of these in situ experiments are not expected to lead immediately to the production of new materials, but Dr Tileli says they are still of interest to industry. “Our results will help describe the changes that materials undergo during operation that leads to their failure. With this knowledge we can then point the way towards methodologies to enhance their properties,” she outlines. One important aspect of the next generation of energy materials is the ability to self-heal; this is an issue that Dr Tileli plans to explore further in future, alongside research into improving the TEM techniques
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used for in situ experiments. “We plan to probe self-healing mechanisms in different kinds of functional energy-based materials,” she says. A further dimension of Dr Tileli’s research centres around investigating how the nanoscale properties of a system affect its overall behaviour. It is not clear at this stage how phenomena observed on the nanoscale translate to the micro or macro-scales. “Using TEM, we can image the degradation mechanisms of materials in a very localized area, but will the full device degrade in the same way? At the same time or at the same rate? That’s something we want to look at,” continues Dr Tileli. “The way the experiment is performed in a TEM is different to that in the actual device, for example inside a fuel cell or a battery. We can see many interesting, fundamental phenomena, but there’s still a question mark over how these relate to the processes taking place in a device. We are trying to further develop in situ techniques so that the experiments match real-life device operation conditions. We also complement the knowledge gained on the nanoscale with similar experiments on the mesoscale using other methods.” This is something Dr Tileli plans to probe further over the coming years, alongside her many other research interests. Advanced in situ studies will continue to play an important role in research, as Dr Tileli says they bring several important advantages over other methods. “With in situ TEM techniques you are site-specific, you know where things are happening, and you know exactly when things are changing,” she stresses. “The visual aspect is not matched by any other technique.”
Project Coordinator, Dr Tileli Vasiliki EPFL STI IMX INE Station 12 1015 Lausanne Switzerland T: +41 21 693 67 39 E: vasiliki.tileli@epfl.ch W: http://ine.epfl.ch R. Ignatans, D. Damjanovic and V. Tileli, “Local hard and soft pinning of 180º domain walls in BaTiO3 probed by in situ transmission electron microscopy” Physical Review Materials (2020) 4, 104403 T. -H. Shen, L. Spillane, J. Vavra, T. H. M. Pham, J. Peng, Y. Shao-Horn, and V. Tileli, “Oxygen evolution reaction in Ba0.5Sr0.5Co0.8Fe0.2O3-δ aided by intrinsic Co/Fe spinel-like surface”, Journal of the American Chemical Society (2020) 142, 15876
Dr Vasiliki Tileli
Vasiliki Tileli is currently Assistant Professor at the Institute of Materials at Ecole Polytechnique Federale de Lausanne (EPFL). Her research uses in situ electron microscopy techniques to probe how the nanomaterials properties are affected by changes in temperature, electric field, and gaseous and/or liquid environment. Her group develops the techniques in order to dynamically observe the changes as they happen during real-time operation of their bulk counterparts.
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