Overview

The performance of organic light emitting devices (OLED) suffers from low extraction efficiencies of photons generated inside a thin-film multilayer stack. Possible non-radiative pathways are coupling of light to wave-guided modes inside the substrate and the organic layers, to surface plasmon polaritons (SPP) and to charge oscillations not capable of propagation at the electrodes. In this project we investigate the mechanism of energy transfer from radiant organic dyes to different channels and develop methods to utilize them for light-emission and spectroscopy.

Magneto-optical active materials turn the polarization direction of linear polarized light when a magnetic field is present. Typically, these materials are represented by iron garnets. Bi₃Fe₅O₁₂ represents the alloy having the highest degree of Faraday rotation at room temperature. Presently, the magneto-optical active garnets are merely deposited on substrates which likewise have a garnet structure (e.g. Gd₃Ga₅O₁₂). To make their properties accessible as a new function to microelectro mechanical systems or to integrated optics it is required to integrate them on Si or SiO₂ , which is the intention of this project. Combining those different materials poses a particular challenge. The integration of Bi₃Fe₅O₁₂ on Si/SiO₂ can only be realized via a Y₃Fe₅O₁₂ buffer layer, which leads to interference effects and thus to an enhanced Faraday rotation during light transmission.

With the aid of combinatorics double layers of garnet materials with different degrees of doping will be integrated on Si or SiO₂ for the first time. Further, the interference effect will be examined. Another objective of this project is to elucidate the integration process of the garnet double layers on Si or SiO₂ by means of extensive structural examinations. By manipulating the Faraday effect occurring in the garnets a magneto-optical switching element could be realized. For this purpose, the influence of acoustic surface waves on the Faraday rotation is to be examined.

In the recent past substantial efforts have been devoted to define mechanisms that lead to self-assembly of regular nanostructures at surfaces, including the exploitation of regular arrays of misfit dislocations, long-range adsorbate-adsorbate interactions mediated by metallic surface states, or short-range adsorbate-adsorbate interactions based on hydrogen bonds. Very recently, a new type of self-assembly mechanism has been found in a purely inorganic system. It leads to a surprising new nanostructured material based on a bilayer of hexagonal boron nitride (h-BN) on a Rh(111) surface [M. Corso et al., Science 303, 217 (2004)]. A highly regular mesh forms by self-assembly, with a 3.2 nm periodicity and a 2 nm hole size. Two layers of mesh cover the surface uniformly after high-temperature exposure of the clean rhodium surface to borazine (HBNH)3. The two layers are offset in such a way as to expose a minimum metal surface area. Hole formation is likely driven by the lattice mismatch of the film and the rhodium substrate. This regular nanostructure has remarkable properties and can serve as a template to organize molecules, as is exemplified by the decoration of the mesh by C60 molecules.
The main objectives of the NanoMesh project are to understand the self-assembly processes leading to this highly interesting and non-trivial nanostructure, to find routes for controlling the mesh parameters and for mass production, and to demonstrate its prospects for future applications as a sturdy oxygen- and carbon-free template for the production of nanocatalysts, nanomagnets and functionalized surfaces. Rather than taking a broad approach on self-assembly in general, the NanoMeshproject thus focuses on this particular h-BN material. The NanoMesh project brings together leading specialists in Europe with unique expertise in synthetic chemistry as well as novel experimental and theoretical techniques to investigate the processes leading to the selfassembly of the nanomesh in situ, and to explore new combinations of chemical precursors and substrates in order to control the mesh size and shape. It also includes the expertise for fabricating self-assembling hydrogen-bonded molecular networks in order to try to achieve higher hierarchies of self-assembly on top of the nanomesh, leading to regular structures that bridge the nanoscopic and the mesoscopic scale, and to demonstrate the design of functionalized surfaces for sensing and biological applications. An industrial partner will investigate the nanomeshes as potential substrates for electronic devices, specifically for spintronic and quantum computing applications. The results will enable the application specific tailoring of regular nanostructures and the prediction of their physical, chemical and maybe also biological properties.

For the optical properties of metallic nanoparticles, a collective electronic excitation plays a prominent role: the so-called surface plasmon. In this project, properties of the surface plasmon like its frequency and width are studied. Of particular interest is the relaxation dynamics on the femtosecond scale accessible to modern pump-probe experiments.

In silicon technology as well as in polymer electronics the development of complementary logic is considered a milestone for the design of robust low-loss digital circuits. The use of ambipolar materials as compared to discrete p- and n-channel transistors represents an alternative concept for the realisation of a complementary logic involving organic field-effect transistors, which is to be examined in this project.

This project aims to elucidate the connection between the molecular structure, the structure in solid bodies and the optoelectronic properties of OLEDs. A special emphasis is placed on the energetics and dynamics of the triplet state in Alq3 and materials derived therefrom. A better understanding of the photophysical processes is expected to permit a more efficient doping with phosphorescent colour pigments to increase the efficiency of OLEDs.