Research Area B: Structure formation and self organisation on the nm scale, nano-electrochemistry

The controlled structuring of materials on the nanometer scale is of fundamental importance for nanotechnology. Modern preparation methods allow the controlled and directed preparation and manipulation of materials and individual structures with atomic scale precision (size, form and composition). A particularly elegant strategy for the controlled generation of nanostructures with specific properties is based on so called bottom-up approaches. According to this principle, the functional structures are produced via self-organisation processes, exploiting non-covalent intermolecular interactions. These (supra-) molecular structures are particularly attractive because of their various advantages such as their highly parallel production and the extreme variation in physical, chemical and biological properties that can be realized.

Of particular interest are hierarchically organized structures, since they allow us to realize direct correlations between function and structural complexity. This is impressively demonstrated by appropriate systems in nature. In molecular biology, numerous functions are reached by hierarchical organisation, with individual functional units, which by themselves consist of well defined groups of sub-units, forming a more complex system. This way, the high level of complexity of such a system, with its generic properties, can be reduced to the control of a few well defined parameters, i.e., to the controlled use of intermolecular interactions.

Building on the know how on the generation of various nanostructured materials accumulated in the competence network functional nanostructures so far, from metal clusters of a few atoms in size to complex biomolecular hybrid systems, the work in the next funding period will focus on the use of these self organized nanostructures for various applications, primarily in the areas of energy conversion (B1) and molecular information technology (B3, B5).

On the search for renewable and sustainable energy carriers, fuel cell technology has, together with other forms for energy storage, once again attracted enormous scientific interest. Fuel cells are one of the most efficient methods for the direct conversion of chemical energy into electrical energy. In contrast to thermal power engines, their efficiency is not limited by the Carnot cycle. However, important and long standing problems regarding durability and practical efficiency are still unresolved. These are directly related to the electrochemical processes at the electrode surface. In addition, there is a need for efficient catalysts for the generation of H₂ as chemical energy carrier and fuel for fuel cells. Self organization processes are ideally suited to generate surfaces with chemical heterogeneities, with structures from the atomic scale up to the nanometer and micrometer range. Structures on the nanoscale allow us to achieve novel catalytic properties. In particular bimetallic systems (B1) can be highly active and can be tuned in a controlled way via their nanoscale structure. Such systems are investigated both experimentally and theoretically in project B1. This aims at developing novel concepts and materials for energy relevant nano-electrochemistry, in particular for electrocatalysis.

In addition to the efficient conversion of chemical energy into electrical energy, the sustainable generation of hydrogen as clean chemical energy carrier is a demanding task. Central aspect herein are efficient procedures for the direct conversion of solar energy into hydrogen. The catalytic nanostructures developed in B1 offer interesting new approaches, e.g., for the photocatalytic water splitting.

Nanoscopically structured materials consisting of biologic macromolecules (e.g., proteins and polysaccharides) and inorganic materials have outstanding physical properties, as demonstrated by the biominerals nacre and bone. The projects B3 and B5 aim at developing hybrid nanomaterials with controlled optical, magnetic and electronic properties via hierarchical self organization processes and the characterization of these materials. In B3, proteins with defined structure and structural modifications, and the information encoded in the sequence shall be used to fabricate systems with defined geometry and mutual orientation of inorganic nanoparticles via self organization and non-classical crystallization of these nanoparticles. In this case, a ring shaped fibril building protein is used as framework, and an elastic protein for controlling the formation of nanoparticle and their fixation at the organic framework. This way, new routes for building elastic, switchable nanoscale magnets shall be developed, which offer a wide spectrum of applications, including electronic data storage, in medical diagnostics, e.g., as contrast medium in magnetic resonance tomography, in sensorics or finally in electronics.

In B5, the use of functionalized polymer nanocrystals as pre-formed building blocks allows us to control the order also in extremely thin insulator / semiconductor layers. Ordered systems, which are aimed at in this concept, are interesting not only for fundamental studies of their transport properties, but in the long term also for applications in electronic devices such as organic field effect transistors. Ordered hybrid structures can be produced in a bottom-up approach, without the need of high temperatures, which is attractive for the fabrication of inexpensive high power electronics for flexible and mobile applications.

Connecting aspect of the projects B1 – B5 are fundamental studies of processes for hierarchical nanostructuring via self organization. We aim both at a qualitative understanding of the structure determining processes and, for simple model systems, at a quantitative determination and control of the relevant (intermolecular) interactions.