From particles to materials_

From particles to materials – from colloidal to material science
When animals form inorganic biomaterials, they start from nanoparticles. Specialized cells synthesize amorphous, sub‐micron spheres and add them at defined positions of the growing beak, bone or shell, where they are converted into crystals and become functional elements. In my group, we start from nanoparticles and follow the same route to create engineering materials: silicon nanowires for microelectronics, metal arrays for surface‐enhanced Raman scattering and hybrid x‐ray detectors for diagnostics, for example. To this end, particles are chemically synthesized with narrow distributions in size and shape. Their interactions are tuned through ligands and their mobility is adjusted until the particles spontaneously arrange – “self‐assemble” – into regular superstructures. The superstructures are functional materials or templates for functional materials.
In this Seminar, I will discuss which arrangements are desirable for different materials and how particles can be arranged accordingly. We find that controlled assembly invariably requires:
• mobility, so that particles can find free energy minima,
• interaction, so that the minima are clearly defined, and, possibly,
• confinement to determine the overall shape of the arrangement.
Processes that balance the above allow us to arrange particles into
• dense packings for electrically conductive layers,
• percolating fibrils with a large interface to a polymer matrix,
• spaced arrays for analytics and microelectronics, for example.

Tobias Kraus studied Chemical Engineering at the Technical University in Munich, with detours to  MIT in Boston and Neuchâtel in Switzerland. He then stayed in Switzerland to pursue a PhD under Prof. Nicholas D.  Spencer at ETH ZurichCls Department of Materials. His goal was to arrange and print various objects  (including, but not limited to, nano) in close collaboration with IBMCls Zurich Research  Laboratory. Tobias remained at IBM for a brief PostDoc and then accepted a position at the Leibniz‐Institute for New Materials in Saarbrücken,  Germany, where he now heads a Junior Research Group that synthesizes, assembles and analyzes  nanoparticles.

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