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

Güven Kurtuldu (Metal Physics and Technology, D-MATL)

During the past 20 years, the availability of Micro Electro Mechanical Systems (MEMS)-based sensor technology leads to the development of Fast Differential Scanning Calorimetry (FDSC) with a focus on fast measurement capabilities for small scale material physics. Heating and cooling rates are typically between 1 and 50,000 K/s for a sample size between 10 ng and 10 µg. With such fast scan rates and high sensitivity, FDSC reveals new material behaviors that were previously inaccessible using conventional techniques. It gives the ability to study the relationships between the kinetics of processes in millisecond timescales and the expectations based on thermodynamics occurring in metallic systems, polymers, biological solutions, and pharmaceutical substances. In this talk, I will demonstrate how our novel experimental strategies for which FDSC has been used as a processing and phase identification technique, reveal the hidden competition between several stable and metastable crystals (including quasicrystals) in undercooled liquid metals. I will also discuss that the temperature and enthalpy calibrations of FDSC still remain a challenge that a material-specific calibration methodology must be developed and followed for each FDSC sample and scan rate.

Overview Materials Colloquium 2019

Rowena Crockett (EMPA Dübendorf)

The sculptures of the Swiss artist Jean Tinguely are rusty, steel constructions that generate a high-pitched squeal during motion. While the sculptures are visually remarkable, an essential component of the work is the noise. Unfortunately, the sliding parts have been wearing out over the years, and as a result the amount of time that the sculptures can be in motion has been reduced significantly. In order to protect these works of art, we would like to develop a system that protects the sliding parts against wear but, at the same time, allows the high-pitched squeal to be maintained. In this presentation, the noise emissions will be described and possible solution strategies will be discussed.

Overview Materials Colloquium 2019

Petr Novák (D-CHAB/PSI)

Li-ion batteries are to dominate the high-end rechargeable energy storage market for a foreseeable future. Research and development of commercially relevant electrode/electrolyte systems focus today strongly on extending the lifetime of the cells. Progress is however hampered by the lack of fundamental understanding of the underlying lifetime-limiting processes which will be the key to further im­provements in energy density, safety, and life time of batteries. Our approach to answer the related scientific questions starts with the development of various advanced analytical methods. Then, the physi­cal and electro­chemical proper­ties of battery materials and their electrochemical interfaces are investigated under in situ or operando conditions. Wherever possible, the combina­tion of two methods in a single electrochemical cell is a highly promising approach.

In the talk, the basics of energy storage in batteries will be discussed first. Then an overview of the most promising characterization methods for battery materials and electrodes will be given. The techniques include Differential/Online Electrochemical Mass Spectrometry (DEMS/OEMS) which can detect qualitatively and quantitatively volatile reaction products that are evolved during cycling of an electrochemical cell. Spectroscopic techniques are established for investigations of surface related electrochemical processes. Operando Raman spectroscopy allows following the intercalation and deintercalation of lithium and other ions into/from battery active materials. For the bulk investigations, in contrast to XRD, neutrons are sensitive to lithium. Therefore, the combination of results from synchrotron based operando X-ray diffraction methods and operando neutron diffraction is essential for understanding the reactions of battery materials’ bulk.

Overview Materials Colloquium 2019

Maksym Yarema (D-ITET)

Colloidal chalcogenide nanocrystals are convenient building blocks of various solution-processed devices, such as displays, photovoltaics, thermoelectrics, and phase-change memory. Likewise, chalcogenide colloids are handy materials for the fundamental and use-inspired research, featuring size-dependent optical and electronic properties in addition to composition dependences and structure diversity. In this talk, we will summarize the state-of-the-art for the colloidal chalcogenide nanocrystals, outline challenges and future directions in the field. In particular, we will focus on multicomponent nanocrystals, for which composition-dependent effects are superimposed on size dependences. We will also discuss opportunities for chalcogenide colloids with metastable and amorphous structures.

Overview Materials Colloquium 2019