Materials properties controlled by microstructure and external fields
Prof. Dr. Horst Hahn (Institute for Nanotechnology and Helmholtz Institute Ulm / Karlsruhe Institute of Technology (KIT) )
The mechanical, physical and chemical properties of materials are determined by their microstructure. Modern materials science uses the complex interplay of defects, such as impurities, phases, point and line defects and interfaces, to tailor properties and obtain high-performance metallic alloys and ceramics.In this approach of materials design, properties can only be changed by modifying their microstructure, for example by initiating grain growth during annealing at elevated temperatures. Such a behavior, that fixes the properties irreversibly to the microstructure, is advantageous for many applications of materials, where long-term stability of the properties is required.
Metallic glasses offer interesting properties due to their disordered atomic structure. Due to the fact that they are prepared predominantly by rapid quenching, only a certain range of microstructural parameters has yet been explored. As an example for materials that exhibit novel effects by tailoring the microstructure, nanoglasses will be discussed. Nanoglasses consist of two distinct structural components, which differ in their free volume and elemental constitution, and have been shown to exhibit drastic property changes.
In contrast, tuning using external fields, i.e., electric, offers completely new opportunities for the fully reversible control of materials properties. Such tuning of physical properties will be demonstrated for several nanostructures, i.e. (epitaxial) thin films, nanoporous, nanoparticulate structures and nanowires. Tuning can be either achieved using dielectric/ferroelectric gating, well known from semiconductor physics, or by electrolyte gating using liquid or solid electrolytes. Furthermore, using electrochemical ion intercalation, fully reversible properties can be achieved.
Finally, the concepts employed for tuning properties of nanostructures can be employed in applications as well. As an example, field-effect transistors based on inorganic nanoparticles as the channel material and solid electrolyte for the gating will be described.