Materials Day 2013 – Today, Tomorrow and Beyond

Abstracts

(in order of appearance)

From Materials to Cosmology: Studying the early universe under the microscope

Prof. Nicola Spaldin
What happened in the early universe just after the Big Bang? This is one of the most intriguing basic questions in all of science, but it is extraordinarily difficult to answer because of insurmountable issues associated with replaying the Big Bang in the laboratory.  One route to the answer -- which lies at the intersection between cosmology and materials physics -- is to use laboratory materials to test the so-called "Kibble-Zurek" scaling laws proposed for the formation of defects such as cosmic strings in the early universe. Here I will show that a popular multiferroic material -- with its coexisting magnetic, ferroelectric and structural phase transitions -- generates the crystallographic equivalent of cosmic strings. I will describe how straightforward solution of the Schroedinger equation for the material allows the important features of its behavior to be identified and quantified, and present experimental results of the first unambiguous demonstration of Kibble-Zurek scaling in real materials.
Materials Theory

Advanced characterization of magnetoelectric functionalities

Prof. Manfred Fiebig
Coupling effects between magnetic and electric properties are the focus of our institute. Such magnetoelectric interaction becomes particularly large in compounds with a coexistence of magnetic and electric order, the so-called multiferroics, which are grown and investigated in our lab by "advanced characterization techniques". These include nonlinear optics, ultrafast time-resolved laser spectroscopy, and a broad range of force microscopy techniques. The magnetoelectric functionalities include photoenhanced magnetism, ferrotoroidicity as a novel type of ferroic magnetic vortex order, or ferroelectric domain walls as building block in oxide electronics. In going beyond application the topology of multiferroics is investigated and reveals universal properties that are also relevant on the cosmological scale.
Multifunctional Ferroic Materials

Why are quasicrystals quasiperiodic?

Prof. Walter Steurer
In the past two decades significant progress has been made in the search for stable quasicrystals, the determination of their structures and the understanding of their physical properties. Now, quasiperiodic ordering states are not only known for intermetallic compounds, but also for mesoscopic systems such as ABC-star terpolymers, liquid crystals, thin BaTiO3 layers or different kinds of colloids. However, in spite of all these achievements fundamental questions concerning quasicrystal formation, growth and stability are still not fully answered yet. This talk addresses some of the open questions concerning the origin of quasiperiodicity.
Crystallography

Synthetic 2D polymers

Prof. A. Dieter Schlüter
The present interest in graphene, a naturally occurring two-dimensional polymer, makes clear that there is no synthetic method available that would allow accessing a covalently bonded molecular sheet with internal periodicity and a thickness of one monomer unit only. After a brief overview of "organic" and "polymer" approaches performed so far, our concepts will be presented which rest upon carefully designed monomers, interfacial as well as single crystalline ordering, and both metal-complexation and light-induced polymerizations. The lecture will provide a state-of-the-art picture including the first solutions to the problem.
Polymer Chemistry

The challenges for self-assembly at liquid interfaces

Prof. Lucio Isa
Self-assembly of micro and nanoparticles has the potential to offer innovative solutions for the fabrication of functional materials. In particular, confining micro and nanoscale building blocks at the interface between two fluids can be used to produce “quasi” two-dimensional materials, which find use, for instance, in sensing, photonics and bio-applications. Often, the results of the self-assembly process are different from the ones expected solely from equilibrium considerations.  Heterogeneity in the particle properties, crowding and trapping into metastable states have a strong impact on the structures that can be attained experimentally. In this talk, I will illustrate several examples of nanoscale characterization that highlight the effect of non-equilibrium phenomena in the self-assembly of micro and nanoparticles at liquid interfaces, and the potential consequences in materials fabrication.
Interfaces, Soft matter and Assembly

Watching electrons at the nanoscale

Prof. Joost VandeVondele
The flow of electrons in transistors has enabled our information society, the flow of electrons in solar cells might once power our world. However, can one compute how electrons look like in devices that are just a few nanometers in size? Our group enables such calculations by developing software and new algorithms that allow for electronic structure calculations on systems containing millions of atoms. Whereas the world's largest supercomputers are still needed to do these calculations today, sustained exponential growth of computer power paves the road for broad applicability. Results on the electronic structure of Titanium dioxide nanoparticles will be presented.
Nanoscale Simulations

With a little help from entropy...

Prof. Hans Christian Öttinger
Entropy is supposed to make our life easier. Dynamic systems possessing an entropy function behave better in the sense of having robust solutions with controlled qualitative behavior (most importantly, smoothness). In the context of rarefied gas dynamics, which is relevant to aerodynamics of satellites and space stations in the outer limits of our atmosphere as well as to microfluidics, we demonstrate that the effort of introducing an entropy is rewarded by superb numerical algorithms. Even shock simulation, which is usually considered as a seriously challenging problem, works amazingly well.
Polymer Physics

Imitating nature on a surface: polymer brushes and gels

Prof. Nicholas Spencer
Nature lubricates in ways that often have no direct counterparts in man-made, machine-element lubrication. One aspect is the lubricant, which in nature is invariably water-based, but contains additives such as glycoproteins. Furthermore, by using soft, liquid-filled porous materials that slowly deform upon loading, nature uses the liquid phase to share the load, and thus to protect the delicate porous structure from damage. A further aspect is the use of layered and gradient systems, where outer, more rigid, layers can afford protection, while the softer underlayers lead to greater compliance of the system, with potential benefits for lubrication.
We have mimicked all three aspects in our laboratory, using a variety of polymer brushes to lubricate in aqueous media, applying oil-compatible, ATRP-synthesized methacrylate polymer brushes to lubricate in oils, and creating layered brush-gel systems that are reminiscent of the structure of skin.
Surface Science and Technology

From nano to macro: Materials synthesis over several length scales

Prof. Markus Niederberger
Nanoparticles with their size and shape-dependent properties are the ideal building blocks for the fabrication of new materials with tailor-made functionalities. However, the assembly of such nanoscale constituents to macroscopic materials requires subtle control over their arrangement in three dimensions and over several orders of length scales.
The talk will present two examples of macroscopic materials, which were prepared by liquid-phase chemistry using preformed metal oxide particles as building blocks. In one case, titanium dioxide nanoparticles are connected by oriented attachment into a three-dimensional, highly porous and nanocrystalline aerogel monoliths. The macroscopic size of the final material is the result of a self-assembly process from the nm to the cm range. The modularity of the approach makes it possible to prepare multicomponent aerogels not accessible by any other technique. The second example includes the preparation of metal foams by wet-chemical deposition of copper onto ZnO spheres, removal of the template particles, and processing into macroscopic bodies.
The aerogels as well as the metal foams represent illustrative examples, how the controlled assembly of preformed inorganic building blocks gives access to unique and complex materials with a broad variety of chemical and physical properties.
Multifunctional Materials

Designer microcapsules made by microfluidics

Prof. André R. Studart

Microcapsules are used to uptake, store, transport and release chemicals in a wide number of applications, ranging from materials and pharmaceuticals to food and agricultural products. Increasing the level of complexity of such carriers has enabled control of the release kinetics of chemicals, the incorporation of multiple functionalities and the encapsulation of the other types of cargo such as particles and living cells. Because it allows for unprecedented control over the size, structure and chemistry of microcapsules, emulsion templates made in microfluidic devices are particularly attractive for the assembly of such complex carrier systems. In this talk, I will describe two processing routes that we have explored to create colloidosomes and polymer-based microcapsules from double emulsions made by microfluidics. In the first part of the talk, I will present our tools to obtain polymer-based capsules with predictable, well-defined size and shell thickness, as well as tunable mechanical behavior and shell microstructure. In the second part, I will describe a general strategy to create multifunctional colloidosomes that can release cargo on-demand and multiple times in response to an external chemical trigger. These approaches provide a general platform for the design and assembly of advanced carrier systems that respond to mechanical or chemical external stimuli and that feature tunable spatio-temporal control over the release of cargo for several established or emerging applications.
Complex Materials

Control of spin flips in artificial ferroic systems

Prof. Laura Heyderman
In artificial ferroic systems, interacting ferroic components, which could be for example ferromagnetic and/or ferroelectric, can be combined to give novel functionality. One important goal here is to be able to control the reversal of the magnetic moments in nanoscale magnets by careful choice of geometries and materials, and applying magnetic or electric fields, or heat. In this presentation, some routes to such control are demonstrated in two systems; artificial spin ice consisting of specific arrangements of dipolar interacting nanomagnets, and artificial multiferroics, combining a magnetic material with a ferroelectric. The observations are performed using photoemission electron microscopy, which provides unique possibilities for probing magnetic behaviour.
Mesoscopic Systems

New metallic materials for medical applications

Prof. Jörg F. Löffler
Medical implants used in osteosynthesis and vascular intervention are usually made of metallic materials designed either to remain in the body or to be removed in a second surgery. They often generate problems, such as prolonged physical irritation and chronic inflammation, and can only be applied in pediatric surgery to a limited extent. A new class of biodegradable metallic alloys, developed in our laboratory, overcomes the limitations of such permanent devices because they degrade in the body after performing their task. I will describe our efforts in the development of amorphous and crystalline Mg-alloys, based on metal physical design rules. MgZnCa alloys, in particular, are suitable for use as biodegradable implants, as they are biocompatible, show good osteoconductivity and osteoinductivity, and reveal adjustable degradation rates.
Metal Physics and Technology

Colors in thin materials: From interference in insulators to interstitials in intermetallics

Prof. Ralph Spolenak
Colors are the first thing we appreciate about a material, usually before we even touch it or in a more sophisticated manner investigate it microscopically. This talk will investigate how the microstructure, the architecture and the chemistry of a thin film material influences its interaction with photons in the visible energy range. Examples will be given from all materials classes and the phenomena of interference (strong and "weak"), inference, as well as band structure induced colors will be described. Applications will be given in the biomedical field, microelectronics and jewellry. Briefly, other application-driven properties of coatings will be addressed, which range from fracture strength over wear resistance, to electrochemical stability.
Nanometallurgy