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

Qin Xu (Soft and Living Materials, D-MATL)

Wetting of liquid droplets on soft gels deforms gel interface significantly: a wetting ridge grows under the balance between liquid surface tension and solid surface stress near contact line. Using interference microscopy and fast camera imaging, we directly observe the recovery of gel surface from this wetting-induced deformation after removing liquid droplet. We show experimentally that surface relaxation of soft gels cannot be simply modelled by their viscoelastic rheology. Instead, the internal flow of free chains through elastic network is very rather important. Our results extend the current understanding of elastocapillarity with the effect of bulk porosity, and bring new insight into the study of wetting dynamics on soft materials.

Overview Materials Colloquium 2019

David Schilter (Editor of Nature Reviews Chemistry)

This century has seen increasing pressure on academics to not only conduct novel and relevant research, but also to publish it in journals of international repute. Thus, even with exciting results in hand, academics still face the challenge of finding the appropriate venue for their research and effectively communicating the significance of their results, particularly to broad readerships. Nature-branded journals are among the highest-visibility venues for original research and review articles.

I will describe how clear writing skills and a knowledge of the publication process can help give you the best possible chance of disseminating your work in the most prestigious journals. Indeed, by familiarising yourself with the content, policies and readership of your target journal, you are well-placed to begin depicting your research in the most effective and interesting way.

Overview Materials Colloquium 2019

Christoforos Moutafis (University of Manchester)

Magnetic skyrmions are quasi-particle nanoscale magnetic spin configurations with a whirling vortex-like spin structure (Fig. 1a) with distinct topological properties [1,2] and intriguing dynamics [3,4]. The recent demonstrations from various groups of room temperature chiral skyrmions and their dynamical response are a first step for controlling their behaviour. Their ultra-small size, ability to move with low electrical current densities and robustness makes them excellent candidates for integration in next generation spintronics devices. In practice, chiral skyrmions can arise due to the interplay between the anisotropy and long-range dipolar energy with the short-range symmetric Heisenberg and antisymmetric Dzyaloshinskii-Moriya (DMi) exchange interactions [1,2].

They can span from tens of nanometers in diameter, behaving as classical quasi-particles exhibiting large inertia [4], down to the ~1 nanometer size. They are endowed with topological protection that can, practically, make them robust with enhanced tolerance to material defects present in devices. Recently, chiral skyrmions (sub-100nm) have been observed at room temperature in technologically relevant multilayers, confined in nanostructures, e.g. [5,6]. In fact, nanomagnets, can host a plethora of skyrmionics spin configurations that can also behave as quasi-particles (e.g. Fig. 2b)). Any possible integration in skyrmionic devices will necessarily involve controlled nucleation/generation and propagation of skyrmions, which is an active research topic e.g. [7,8].  A next step towards the development of skyrmionic devices is to shed light on the mechanisms of creation/destruction of topological charge in defects, which are present in realistic systems [9]. Such objects, like the prominent magnetic skyrmions, are promising candidates for future next generation skyrmion-based devices with diverse functionality such as memory [2], Boolean computing [10], stochastic computing [11], reservoir computing [12], biomimetic and artificial neuronal behavior [13-15].

Figure 1 A (a) Néel type skyrmion and (b) an antiskyrmion spin configuration.

References

[1] N. Nagaosa and Y. Tokura, Nat. Nanotech. 8, 899 (2013).
[2] A. Fert, V. Cros, and J. Sampaio, Nature Nanotechnology 8, 152 (2013).
[3] C. Moutafis, S. Komineas, J.A.C. Bland, Physical Review B 79, 224429 (2009).
[4] F. Büttner, C. Moutafis, et al., Nature Physics 11, 225 (2015).
[5] C. Moreau-Luchaire, C. Moutafis, et al., Nature Nanotechnology 11, 444 (2016).
[6] O. Boulle, J. Vogel, et al., Nature Nanotechnology 11, 449 (2016).
[7] S. Woo, K. Litzius, et al.,  Nature Materials, 15, 501 (2016).
[8] W. Legrand,…, C. Moutafis, et al., Nano Letters, 17 (4), 2703 (2017).
[9] L. Pierobon, C. Moutafis, Y. Li, J. F. Löffler, M. Charilaou, Scientific Reports, 8, 16675 (2018).
[10] M. Chauwin, …, C. Moutafis, J. S. Friedman https://arxiv.org/abs/1806.10337 (2018).
[11] D. Pinna, F.A. Araujo, et al., Phys. Rev. Appl. 9, 064018 (2018).
[12] D. Prychynenko, M. Sitte, et al., Phys. Rev. Appl. 9, 014034 (2018).
[13] S. Li, W. Kang, et al., Nanotechnology 28, 31LT01 (2017).
[14] Y. Huang, W. Kang, et al., Nanotechnology 28, 1 (2017).
[15] T. Bhattacharya, S. Li, Y. Huang, W. Kang, W. Zhao and M. Suri, IEEE Access, 7, 5034 (2019).

Overview Materials Colloquium 2019

Johann Michler (EMPA Thun)

We developed recently techniques to probe mechanical properties at small length scales under extreme conditions of temperature, at high strain rates and under control of humidity. I combination with in-situ observation techniques such as electron backscatter diffraction (EBSD) during micro-mechanical testing strain/stress fields or dislocation distributions can be mapped at several steps during progressive loading, which allows to reveal nanoscale deformation mechanisms for the first time under these conditions.

The talk will cover a number of application examples of these techniques ranging from a) model materials synthesised on purpose to understand longstanding problems in materials mechanics such as fracture mechanisms of monocrystalline Tungsten, plastic deformation of nanostructured metal thin films or failure mechanisms of 3D printed microlattices to b) medical applications such as fracture of bone and to c) current industrial applications of Swiss companies such as creep of watch components, toughness of hard coatings or fatigue of MEMS.

Overview Materials Colloquium 2019

Kunal Masania (Complex Materials, D-MATL)

Nature utilises hierarchy at multiple length scales to structure relatively weak building blocks into complex shapes with outstanding mechanical performance. Despite successful research aimed at implementing biological design principles in synthetic materials, man-made manufacturing technologies remain limited compared to the elegant directed self-assembly of living organisms to grow materials. We will share our work on combining bottom up self-assembly with top-down shaping during 3D printing of crystal polymers to generate recyclable lightweight structures with hierarchical architectures and unprecedented stiffness and toughness.

Overview Materials Colloquium 2019

Rachel Grange (D-PHYS)

Nonlinear optics is present in our daily life with many applications, e.g. light sources for microsurgery or green laser pointer. All of them use bulk materials such as glass fibres or crystals. Generating nonlinear effects from materials at the nanoscale can expand the applications to biology as imaging markers or sensors, and to optoelectronic integrated devices. However, nonlinear signals scale with the volume of a material. Therefore, finding nanostructured materials with high nonlinearities to avoid using high power and large interaction length is challenging. Here I will show several strategies to maximize nonlinear optical signals in nano-oxides with noncentrosymmetric crystalline structure and semiconductors. I will demonstrate how we enhance second-harmonic generation (SHG) by using the scattering properties of individual barium titanate (BaTiO₃) nanoparticles, and AlGaAs standing nanodisks. Our results suggest that a strong increase of the SHG signal can be obtained without using plasmonics or hybrid nanostructures.

Then, I will present innovative fabrication approaches of metal-oxides materials that are very different from standard semiconductors or metals. First, solution-processing of nano-oxides may solve, at the same time, the low nonlinear signal and the low throughput of photonic crystal cavity fabrication to obtain cost-effective disposable devices. Our recent results show that the easy fabrication of nonlinear 3D woodpile photonic crystal is possible with solutions of BaTiO₃ nanoparticles. Besides chemically synthesized nanostructures, we developed lithography processes to obtain lithium niobate (LiNbO₃) nanowaveguides, or BaTiO₃ metasurfaces.

Overview Materials Colloquium 2019