The concepts of self-assembly and self-organization provide interesting routes towards surface patterning (from a few nanometers to micrometer in size) via bottom-up approaches. The patterning processes and the properties of the patterns formed (shape, size, function, etc.) can be adjusted by tailoring the properties of building blocks. We are particularly interested here in the possibilities to construct monolayer system with controlled lateral structures, which can be realized by adjusting the balance of the different phases (with one or more chemical components) thermodynamically and kinetically by means of Langmuir Blodgett (LB) technique. The goal is the development of new surface patterning methods based on bottom-up strategies. The ordered molecules with active end groups can be further used for the specific adsorption of molecules, proteins and nanoparticles. We demonstrated recently that the method established here could be applied to two-component systems. Further works will be focused on the organization of functional organic molecules such light emitting molecules, organic semiconductor as well as nanosized materials such as clusters and tubes. On the other side, combining with wet and dry etching methods, the structures can be converted into topographic patterns, which offer a platform for the investigation of cell-surface interaction. Furthermore, in cooperation with theoretical groups, we are going to achieve a quantitative description of the spatial-temporal pattern formation during the LB transfer process thus to lay the basis for the development of strategies for the self-organized formation of more complex patterns.
Template directed self-assembly of nanomaterials and molecular complexes into functional systems can be realized by using heterogeneous patterned surfaces. The heterogeneous surface structures may be composed of different materials, different tailored molecules, but can also be composed of single component but with different molecular packing. We are on one side working on the heterogeneous surface functionalization by means of LB patterning, soft lithography and photo/e-beam lithography techniques; on the other side, we are interested in the mechanisms of molecular interactions - from liquid phase or gas phase - with such structured surfaces. Specific (e.g. chemical binding) and unspecific (e.g. electrostatic force) interactions need to be taken into consideration, together with molecular diffusion and nucleation.
Uniformly patterned organic molecules over large areas will meet the demands for e.g. microdisplays at micrometer scale and photonic devices for light emissive organic molecules. The latter provides the possibility to increase the extraction efficiency of organic light emitting diodes (OLEDs) and photovoltaic devices in a way analogous to inorganic semiconducting diodes. Besides nucleation control, the orientation of molecules in the aggregate state may be controlled by pre-designed patterns, thus providing the possibility to control the polarization by light emissive molecules and improving the charge transport behaviour of organic conductive/semiconductive materials. In the future works, we are going to concentrate the P- and n-type organic semiconductors for organic field emission transistor (OFET).
Connection of functional molecular complexes and nanomaterials with addressable microscopic structures is an important issue for applications in e.g. nanoelectronics. We started in the last three years to combine surface modification with SAMs, e-beam lithography, soft-lithography and template directed self-assembly for connecting nanoclusters, functional molecules or molecular aggregates with addressable microelectrodes. On this base, we are going to study the size effect on conductive polymers and the related gas-sensing activity.
Scanning probe microscopes (SPMs) became powerful tool to characterize molecular assemblies on different surfaces. By applying SPM methods, one does not only obtain the information in topography and structure, but also measure the mechanical and electrostatic properties. Among these tools scanning force microscopes (SFM) in dynamic mode allow us to investigate soft molecular assemblies without mechanical damage. Using scanning tunneling microscopy (STM) we reveal molecular packing with high spatial resolution in monolayer and multilayer systems prepared under ambient conditions as well as in ultrahigh vacuum. One special focus in the future work will be study of "On-Surface" chemical reactions under well controlled conditions.