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Materials Colloquium 2020 - December, 2nd, 16:30

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Laura Alvarez (Laboratory for Soft Materials and Interfaces, D-MATL, ETHZ)

Programming the dynamics of artificial microswimmers provides a benchmark towards the realization of smart microscale devices. Motile microorganisms, such as bacteria, have developed sophisticated mechanisms to regulate their dynamics based on environmental changes [1]. The creation of artificial programmable microswimmers capable of reproducing such complex performance using much simpler structures remains an open challenge [2]. Here we present two strategies to create artificial microscale active agents that are able to move, sense and respond to external stimuli [3-5]. In both cases, a real time feedback with the environment dictates the swimming behavior of artificial microswimmers. This new generation of adaptive active colloids constitutes an important step in the pursuit of autonomous microsystems with potential applications in microrobotics.

[1] K. Son, et.al. Nature Reviews, 13, 761-775 (2015).
[2] C. Bechinger, et.al., Revi. Mod. Phys, 88, 045006-045056 (2016).
[3] M. A Fernandez-Rodriguez et.al, Nature Communications, 11, 4223 (2020).
[4] A. R. Sprenger et.al., Langmuir, 36, 25 (2020).
[5] L. Alvarez et.al, submitted (2020).

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Materials Colloquium 2020 - December, 2nd, 16:30

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Marta Gibert (Physik-Institut, University of Zurich)

The large variety of functionalities exhibited by transition metal oxides places them as highly attractive materials both from a fundamental and applied point of view. Furthermore, the possibility to assemble oxides in epitaxial heterostructures allows us to further tune their properties and even access novel electronic behaviours not displayed by the parent compounds. Here, we will use atomically-controlled NdNiO3/SmNiO3 superlattices to show that the length scale of the interfacial coupling between metal and insulator phases is determined by balancing the energy cost of the boundary between a metal and an insulator and the bulk phase energies [1]. The structure-property relation of ferromagnetic La2NiMnO6 thin films as their thickness is reduced to just few unit cells will also be presented.

[1] Dominguez et al., Nature Materials 19, 1182 (2020)

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Materials Colloquium 2020 - November, 4th, 16:30

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Sebastian Stepanow (Magnetism and Interface Physics, D-MATL, ETHZ)

Magnetic resonance techniques are widely employed for probing the electronic and magnetic properties of solids, liquids, and molecules as well as for their elemental and structural characterization. These techniques probe with high precision the excitation of the magnetic states of an atom, or of a nucleus, and provide information on their chemical environment. For instance, electron paramagnetic resonance (EPR) is routinely used for non-invasive spin detection in materials science and chemistry research. However, conventional magnetic resonance techniques can only detect a macroscopic number of spins (~107 electron spins, ~1012 nuclear spins) and have poor spatial resolution. Scanning tunneling microscopy (STM), on the other hand, is a unique technique to achieve subatomic spatial resolution with simultaneous local spectroscopic information of single atoms and molecules on conductive surfaces.  Recently, the two techniques were combined to probe magnetic interactions and properties of single spins on surfaces. In this presentation, I will introduce the EPR-STM technique and highlight recent advances. 

Overview Materials Colloquium 2020

Materials Colloquium 2020 - November, 4th, 16:30

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Anna Fontcuberta i Morral (Laboratory of Semiconductor Materials, EPFL)

Solar energy harvesting constitutes of the technological paths to replace production of electrical power by burning fossil fuels. Some compound semiconductors such as GaAs and InGaAsP exhibit a high absorption coefficient in the photon energy of interest for solar energy conversion. Their commercial potential in terrestrial applications is reduced due to the scarcity (and thus high cost) of group III elements such as In and Ga. In this talk we present two approaches to render the use of this kind of materials sustainable: a strong reduction in material use through nanostructures and the replacement of group III by group II such as zinc. We find nanostructures also provide a path to increase light collection [1]. We show how II-V compounds such as Zn3P2 exhibit one magnitude higher absorption coefficient than GaAs [2]. We explain how these materials can be fabricated with high crystal quality, opening the path for the creation of alternative and sustainable compound semiconductor solar cells [3,4].

[1] P. Krogstrup et al Nature Photon 7, 306 (2013)
[2] M.Y. Swinkels et al Phys. Rev. Appl. 14, 024045 (2020)
[3] S. Escobar Steinvall et al Nanoscale Horizons 5, 274-282 (2020)
[4] R. Paul et al, Crys. Growth. Des. 20, 3816–3825 (2020)

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Materials Colloquium 2020 - October, 7th, 16:30

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Ahmad Rafsanjani (SDU Biorobotics, University of Southern Denmark)

Soft robotics surged a bioinspired evolution in robot design through their highly deformable structure by enabling robots to interact adaptively with complex environments and cooperate safely with humans. Flexible mechanical metamaterials are compliant structures with exotic mechanical properties and complex deformation behavior associated with their unique architecture rather than their chemical makeup. Integrating the complex behavior of highly deformable metamaterials into the function of soft robots allows us to embody intelligent behavior into their structure and substantially enhance their performance. In this talk, I will present several examples in which flexible metamaterials can enable us to assign primitive forms of intelligent behavior to the body of soft robots and perform simple tasks.

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Materials Colloquium 2020 - October, 7th, 16:30

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Brendan Bulfin (Professorship of Renewable Energy Carriers, D-MAVT, ETH Zürich)

Metal oxide redox cycles offer a pathway for converting heat into chemical energy via the thermal reduction of a metal oxide. The reduced metal oxide can then be used in a number of applications by re-oxidized it in a second step, utilizing the stored chemical energy and returning the oxide to its original state. Applications include; thermochemical fuel production via water or carbon dioxide splitting, thermal energy storage, and oxygen storage and separation. Here we discuss these applications, with a focus on the redox materials and their requirements. The crucial limiting factors for these applications are the thermodynamics of the reactions, which depend strongly on the choice of oxide. These limitations will be discussed along with developments in the field. Finally, a large material screening study of perovskite oxides will be presented.

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Materials Colloquium 2020 - September, 9th, 16:30

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Roland Logé (Laboratory of Thermomechanical Metallurgy, Institute of Materials, EPFL)

Laser Powder Bed Fusion (LPBF, also known as SLM, Selective Laser Melting) is a well known Additive Manufacturing technology, among the most studied in literature for metals and alloys. A number of drawbacks however still limit its range of applications, among which : (i) the high level of residual stresses; (ii) the often narrow safe processing window, which does not leave much space for microstructure optimization; (iii) the time consuming search for optimum laser parameters, which is material and machine dependent, and also relates to the part size and shape. To solve some of these issues, we introduce a new hybrid “3D LSP” manufacturing process, combining Laser Shock Peening (LSP) with LPBF. 3D LSP can efficiently strain harden a metal and convert LPBF induced Tensile Residual Stresses into CRS. It opens a range of new possibilities such as increased fatigue life or geometrical accuracy, 3D design of grain structures, and improved processability. We also present a new “translation rule”, which is able to predict optimum LPBF parameters for one material, based on those found for another material, using the concept of normalized enthalpy.

Overview Materials Colloquium 2020

Materials Colloquium 2020 - September, 9th, 16:30

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Chiara Gattinoni (Materials Theory, D-MATL, ETH Zürich)

A precise understanding of the surface and interface behavior of ferroelectric materials is necessary towards their use in promising applications such as memory storage or catalysis. In this seminar I will focus on the example of lead titanate and bismuth ferrite to describe how structural and electronic properties affect ferroelectricity at the nanoscale. I will show that surfaces and interfaces play a pivotal role in (de)stabilizing the ferroelectric polarization in thin films and nanoparticles. I will then investigate how the special properties of ferroelectric surfaces can be used to create efficient catalytic devices.

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Special Edition of the Materials Colloquium 2020

July, 23rd, 15:00

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Elsa Olivetti (MIT, Department of Materials Science and Engineering)

Materials have long played a role in transitioning between eras. Now the materials community’s most pressing task is to decarbonize society. For the past several decades, materials science has played a key role in lowering carbon dioxide emissions from the electricity sector through development of renewable energy generation and high performing energy storage technologies. However, outside of the energy sector there remain significant greenhouse gas emissions linked to materials production, particularly in the form of infrastructure and chemicals production. This presentation focuses on the significant challenge of reducing the burden of materials production itself. I will review recent progress in understanding the potential for decarbonization in the materials production sector and describe where and how the material science community can have significant impact.

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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