Detailed Infromation on Hybrid Structures

Hybrid structures combine organic and inorganic as well as soft and hard materials, and thus provide a natural link between Functional Polymers and hard Correlated Matter. These structures can combine properties and advantages of organic and inorganic components in one structured material. Compared to purely organic materials studied in the research area Functional Polymers, hybrid structures can extend the range of accessible physical phenomena, applications and material properties. Hybrid structures benefit from the complementary properties of their organic and inorganic components. Organic materials provide features such as processibility, flexibility, biological compatibility, stabilization, and specific functions. Inorganic, usually crystalline, components offer properties such as mechanical strength, catalytic activity, or special optical, electronic, or magnetic properties. We define hybrid structures in a broad sense, including hybrid structures formed from natural and artificial materials. This provides strong links to the research area Bio-Related Materials, where we investigate the class of bio-hybrid structures.

Many biological building materials are natural organic and inorganic hybrids with structural features in the nanometer regime. Prominent examples include hard materials like dental enamel or seashells, where organic fibers organize and connect inorganic nanocrystals. Artificial hybrid structures can also have features on the nanoscale that determine their properties. One well-known basis for the commercial success of composite materials is that embedded particles can significantly improve the mechanical properties of the surrounding matrix, which is, e.g., realized in low-frictioncar tires.

Our research includes hybrid structures that can play a very important role in optoelectronics (e.g. light-emitting diodes) and energy production (e.g. solar cells). Dye-sensitized or hybrid solar cells rely for example on a large interface between inorganic and organic semiconducting materials. Hybrid solar cells offer the promise to harvest electricity from robust, flexible and solvent free modules. The interface can be controlled by designing small organic molecules or polymers to especially bind to the inorganic surface (Butt, Heinze, Müllen,Tremel, Zentel). Within MAINZ, most of this energy-related research regarding photovoltaics is integrated in the IRTG1404. Tethering polymers to inorganic nanoparticles makes hybrids both soluble in organic solvents and dispersible in polymers. Furthermore, this improves the electrical connectivity between the inorganic and organic semiconducting materials for instance to increase the energy harvesting efficiency. The group of assistant professor Sulpizi performs first-principles computer simulations of hybrid structures for energy conversion, designed to support and direct the experimental efforts.

Since the length scales of many nanoparticles are similar to or smaller than the wavelength of light, their interaction with light is strongly affected and often fundamentally different from that of the corresponding bulk material. Tuning the size thus allows for tuning functionality for a broad range of applications. We prepare helical super-structures of fluorescent semiconductor nanocrystals using organic molecules to force the nanocrystals into a liquid crystal super-structure (Sönnichsen,Zentel). The organic liquid crystal not only orients the inorganic optically active nanocrystals but also serves as a photonic crystal. This arrangement drastically enhances the optical coupling between fluorescent inorganic nanocrystals and is therefore an excellent example for the scientific objective Rational Design of tailored Materials. Related projects address the objective to organize inorganic nanocrystals into superstructures using organic materials and to stabilize inorganic nanocrystals in biological environments for medical applications (Tremel, Zentel). Magnetic nanoparticles are especially interesting in this respect because they show an enormous potential as contrast agents for magnetic resonance imaging (MRI). Their magnetic interaction is orders of magnitude stronger compared to purely organic materials. Furthermore, the surface of nanoparticles can be decorated with special molecules providing molecular recognition for advanced diagnostics. These projects are closely related to activities in the research area Bio-Related Materials and constitute good examples of our the scientific objective Function-through-Structure.

Further projects address surface modifications for super-hydrophobicity (Butt), projects for materials for optical applications (Elmers, Kläui), materials for spintronics (Kläui) and molecular electronics (Müllen, Schönhense, Elmers, Kühnle). Many of those projects have originated from MAINZ activities and through CRC625.

New research activities

Based on these previous research and activities at MAINZ, several projects have been launched to study or prepare hybrid structures for optical, optoelectronic and energy-related applications, which rely on polymers synthesized within the research area Functional Polymers. Supramolecular structures are prepared from semiconductor nanocrystals, organic dyes, and biological light harvesting complexes within the area of Bio-Related Materials (Müllen, Paulsen).

In projects closely linked to efforts in the research area Correlated Matter and Model Systems, hybrid organic-inorganic interfaces are used to create novel spintronics devices. Organic semiconductors can form interfaces with ferromagnetic metals showing high spin-injection efficiency and particularly long spin lifetimes in the organic material. By exploiting the extreme flexibility and tunability of organics, it is expected that hybrid interfaces will constitute a fundamental building block for advanced spintronics devices. Here, a fine-tuning of the physical and chemical properties of the interface controls the spin injection, in line with the scientific objective Engineering Correlations and Interaction Strengths. MAINZ PIs further attempt to tune the interaction strength to manipulate spins at the hybrid interface by using electron doping to modify the electronic properties of cobalt-copper phthalocyanine interfaces.

Teaching, learning and training opportunities

The preparation and synthesis, characterization and theoretical description of hybrid structures allows training in these areas to include soft matter and solid state physics, organic synthesis, inorganic crystal preparation, biochemical methods and x-ray crystallography. These are central elements of the technical training areas Synthesis and Characterization. Furthermore, organic-inorganic hybrid structures require a specialized set of analysis tools providing ample opportunity for Method Development. PhD students working on hybrid systems benefit from the interdisciplinary approach of MAINZ as well as the opportunity to work with colleagues specialized in the organic or inorganic components of hybrid structures, respectively.

Connection to the other MAINZ research areas

Research performed within the field of Hybrid Structures provides several links to the other research areas of MAINZ. Research in Hybrid Structures depends on tailor-made Functional Polymers. Therefore, mastering both synthesis and functionality of polymers constitutes a prerequisite for successful fabrication of hybrid organic/inorganic structures. Moreover, a close link also exists towards Bio-Related Materials. Here, nanoscopic hybrid structures can be used as contrast agents, sensors, and for therapeutic purposes. Many concepts from nature are either directly or indirectly relevant for tailoring hybrid structures. They can even serve as Model Systems for complex hybrid systems, such as electrolyte and ionic liquid-gated devices. These devices have recently attracted the interest of the Correlated Matter community because the correlations and interaction strengths can easily be tuned, providing a path to in efficient switching of devices.