Materials Colloquium 2020 – May, 13th, 16:30

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Shovon Pal (Multifunctional Ferroic Materials)

The goal of observing electrons in motion in real time took a leap forward with the use of short laser pulses. First we use a laser pulse to knock or perturb electrons from their equilibrium position in their respective energy landscape, say for example with optical or infrared energies. This pump pulse will then be followed quickly by a terahertz laser probe that reveals the status of the hole that electron leaves behind or even the various scattering routes that the electrons take while relaxing back. If we do this repeatedly for a couple of times, we can find out exactly how the electron is moving and what it is getting up to. In my talk, I will use this simple ideology on materials with fundamentally different band structures and show what we can learn.

Overview Materials Colloquium 2020

 

Materials Colloquium 2020 – April, 22nd, 16:30

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Sandra Skjærvø (Mesoscopic Systems)

Artificial spin systems are arrays of nanomagnets that are fabricated through state-of-the-art lithography techniques. The nanomagnets interact through dipolar coupling and, depending on the arrangement of the nanomagnets, the system can order magnetically. With X-ray Photon Correlation Spectroscopy, we aim to understand the evolution of the magnetic order in an artificial spin system with square geometry through the known antiferromagnetic phase transition. Below the phase transition at T_N, the system is in a single-domain antiferromagnetic ground state. Upon heating, slow fluctuations in the system lead to striking speckle patterns with distinct features and long life times. The small size and rectangular shape of the array of nanomagnets provides a possible explanation for the distinctness of the speckle patterns, with stripe-like domains nucleating at and propagating from the edges of the array, in line with previous observations.

Overview Materials Colloquium 2020

Materials Colloquium 2020 – April, 1st, 16:30

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Yaroslav Romanyuk (EMPA Dübendorf)

Thin-film solar cells belong to the so-called second generation of solar cells, whereby a thin semiconductor absorber layer of 1…5 microns is used to fully absorb incoming sunlight. The talk will describe current status and research challenges for three thin-film technologies based on Cu(InGa)Se2, CdTe and organometal lead halide perovskites, which have demonstrated power conversion efficiencies in the 22-25% range. All technologies are being actively investigated at the Laboratory for Thin Films and Photovoltaics at Empa: https://www.empa.ch/web/s207

Overview Materials Colloquium 2020

Yinyin Bao (D-CHAB)

Additive manufacturing (commonly called 3D printing) has attracted great attention due to its powerful ability to create complex 3D geometries with precise microarchitectures. In combination with medical imaging techniques, it might provide enormous opportunities to design customized drug formulations and biomedical devices.1 Among the existing 3D printing techniques, digital light processing (DLP) emerged with high resolution and surface quality, desktop size, designable materials and relatively low cost, which is based on a localized light-initiated photopolymerization process, taking place in a bath containing liquid (macro)monomers and photoinitiators. However, the lack of biocompatible and biodegradable materials suitable for DLP limits their application in the biomedical area, especially for the manufacture of elastic personalized devices.2 As a typical elastic implant, airway stents are designed to simulate the airway anatomy providing palliation of symptoms in patients suffering from central airway obstruction.3 However, the clinical use of commercial one-size-fits-all stents is often constrained by the geometrical mismatching to the complex tracheabronchial anatomy of individual patients,4 this could be changed by personalized 3D printing. We aim at the development of biodegradable polymeric materials for DLP 3D printing with highly tunable mechanical properties, towards the manufacture of personalized airway stents. This work opens new perspectives for developing precise personalized medical devices with biodegradability as well as high mechanical properties by 3D printing.
References
1. Zhao, H.; Yang, F.; Fu J.; Gao, Q.; Liu, A.; Sun, M.; He, Y. ACS Biomater. Sci. Eng. 2017, 3, 3083.
2. Zhang, J.; Xiao, P. Polym. Chem., 2018, 9, 1530.
3. Lee P.; Kupeli E.; Mehta A. C. Clin. Chest Med. 2010, 31, 141.
4. Dutau, H.; Musani, A. I.; Laroumagne, S.; Darwiche, K.; Freitag L.; Astoul P. Respiration 2015, 90, 512.

Overview Materials Colloquium 2020

Guido Panzarasa (Soft and Living Materials)

Living systems can grow bottom-up a huge variety of materials with the highest degree of sophistication and an overall efficiency that remains largely unparalleled by artificial fabrication techniques. Moreover, living materials are adaptive i.e. are able to exist and perform autonomously under dissipative conditions. These features are possible thanks to the ability to control complex reactions networks, carefully organized in spatio-temporal sequences. Filling the gap between state-of-the-art stimuli-responsive materials and living materials requires to combine materials science with systems chemistry. In this way, chemical curiosities such as clock and oscillating reactions become versatile tools to program in time the autonomous and transient self-assembly of organic as well as inorganic building blocks. The design of such ad hoc reaction networks is at the core of my current research efforts. I will show how to “clock” molecules, polymers and metal cations into different structures (from nanoparticles to gels), without the need for external control, and how this approach can pave the way to the development of (almost) living artificial materials.

References:

1. Panzarasa*, A. Osypova, A. Sicher, A. Bruinink, E. R. Dufresne, Controlled formation of chitosan particles by a clock reaction Soft Matter 2018, 14, 6415–6418 DOI: 10.1039/C8SM01060A
2. Panzarasa*, Eric R. Dufresne, Impact of in situ acid generation and iodine sequestration on the chlorite-iodide clock reaction Chaos 2019, 29, 071102 (5 pp) DOI: 10.1063/1.5108791
3. Panzarasa*, T. Sai, A. L. Torzynski, K. Smith-Mannschott, E. R. Dufresne, Supramolecular assembly by time-programmed acid autocatalysis Mol. Syst. Des. Eng. 2020 DOI: 10.1039/c9me00139e
4. Panzarasa*, A. L. Torzynski, T. Sai, K. Smith-Mannschott, E. R. Dufresne, Transient supramolecular assembly of a functional perylene diimide controlled by a programmable pH cycle Soft Matter 2020, 16, 591-594 DOI: 10.1039/C9SM02026H
5. C. C. M. Sproncken, B. Gumí-Audenis, G. Panzarasa, I. K. Voets, Two-stage polyelectrolyte assembly orchestrated by a clock reaction ChemSystemsChem 2020 (accepted)

Overview Materials Colloquium 2020

Arkadiy Simonov (D-MATL, Multifunctional Ferroic Materials)

Prussian blue analogues (PBAs) are a broad and important family of microporous inorganic solids, famous for their gas storage, metal-ion immobilisation, proton conduction, and stimuli-dependent magnetic, electronic and optical properties, The family also includes widely investigated hexacyanoferrate/hexacyanomanganate (HCF/HCM) battery materials. Central to the various physical properties of PBAs is the ability to transport mass reversibly, a process made possible by structural vacancies. In the absence of a better model the distribution of such vacancies was assumed random.

In this talk I would like to present the latest results of analysis of the diffuse scattering from PBA single crystals which show that vacancy show surprisingly strong local ordering. Moreover, the distribution of these vacancies is influenced by crystallization conditions. Our results establish a clear foundation for correlated defect engineering in PBAs as a means of controlling storage capacity, anisotropy, and transport efficiency.

Overview Materials Colloquium 2020

Marc Willinger (ScopeM)

Modern analytical transmission electron microscopes are capable of delivering picometer resolved information about the geometric arrangement of atoms. It is possible to simultaneously obtain quantitative information about the elemental composition of a material and even to measure the local electronic structure or electric and magnetic fields. One of the side-effects of using strongly interacting electrons for the imaging process is the requirement of a good vacuum near the sample and throughout the optical system. Obtaining detailed information about the state of an isolated material in vacuum is not sufficient if we are interested in processes such as material growth- and decomposition, corrosion or (electro)catalysis. With the availability of MEMS- (micro electro mechanic systems) technology based TEM holders for in situ experiments, it is now possible to study the response of a material to a physical or chemical stimuli and study gas-phase, temperature and electrochemically induced processes. Since atomic motions can be fast and the temporal resolution of conventional microscopes is limited and furthermore, processes are often related to collective dynamics of many atomic species, a combination of high-resolution imaging with context embedded observation at lower magnification is required.

In my presentation I will show how the combination of in situ scanning and transmission electron microscopy enables a multi-scale approach for the study of functional materials in their relevant state. Examples range from CVD growth of 2D materials [1] to corrosion processes and catalysed surface reactions (see Figure1) [2]. It will be shown how in situ microscopy reveals the beauty of complex dynamics in systems that are operated far from thermodynamic equilibrium. The field is still relatively new and with the development of more sensitive and faster detectors as well as further improvement of tools for in situ electron microscopy, we are looking towards an exciting expansion of our possibilities to study complex processes related to atomistic dynamics. Figure 1: A shows an overview image recorded during NO₂ hydrogenation on Pt at T = 172 °C; _NO2:_H2  ≈ 1:10; p_tot = 3.6 × 10⁻² Pa. Propagating chemical waves give rise to beautiful dissipative structures. B shows the variation in contrast between subsequent light-off events and 3D plots of the secondary electron intensity.

References:

1. J. Wang et al., ACS Nano, 2015, 9, 1506–1519, Z.-J. Wang et al., Nature Communications, 2016, 7:13256, Z.-J. Wang et al., Adv. Mater. Interfaces, 2018, 1800255, M. Huang et al. Nature Nanotechnology, 2020, doi:10.1038/s41565-019-0622-8
2. Barroo, Z.-J. Wang, R. Schlögl, M.-G. Willinger, Nature Catalysis, 2019, doi:10.1038/s41929-019-0395-3

Overview Materials Colloquium 2020

Guillaume Habert (Sustainable Construction, D-BAUG)

Construction industry consumes 40% of all material extracted, but one can also turn this challenge into opportunities. New buildings can be an opportunity to mitigate environmental pressures and generate economic growth. Future construction can store carbon emissions, be used as depositories of materials to be later mined. Building renovation can be a catalyst to re-activate social and economic networks in a neighborhood. Buildings rather than degrading the air quality can help to reduce harmful effect of transportation through noise and pollution absorption. To do so, we need to reconsider the global carbon cycle integrating biological, geological and anthropogenic flows. 

Overview Materials Colloquium 2019

Nick Jaensson (Soft Materials, D-MATL)

Emulsions and foams play an important role in many technological and biological applications. Some everyday examples include foods, cosmetics and pharmaceuticals, but they also found uses in, for example, additive manufacturing, lightweight materials and biomedical scaffolding. A crucial determining factor for the successful use of emulsions and foams is their stability, which is strongly related to the rheological properties of the gas-liquid or liquid-liquid interface, for foams and emulsions respectively. In this talk, we study the role of complex interfacial rheology in drop and bubble coalescence, which is one of the main destabilizing mechanisms. First, we use a range of experimental techniques to characterize the rheology of complex interfaces, i.e. their mechanical response to well-defined deformations. We then go one step up in complexity, and use “simple complex” flows to study the coalescence process in an accurate and controlled manner. The experimental results are compared to simulations in order to come to a complete picture of the role of complex interfacial rheology in drop and bubble coalescence, and with that the stability of foams and emulsions.  

Overview Materials Colloquium 2019

Sebastian Huber (D-PHYS)

The elastic properties of materials are determined by a few material constants such as the Young’s modulus. Using super-​structures one can effectively change these “constants”. In this way we obtain functionalities such as wave-​guiding, acoustic lensing or programmable failure. I will show how topological band theory, known from the description of electrons in solids, provides us with a powerful design-​principle for such mechanical metamaterials.

Overview Materials Colloquium 2019