FRIEDLEIN laboratory
<Major Research Areas>Supramolecular Science, Interface Physics and Chemistry, Photoelectron Spectroscopy

Electronic structure of supramolecular nanostructures, surfaces and interfaces

Research activity

　　In a rapidly changing information-based society, major technological breakthroughs can be achieved in multidisciplinary fields combining physics, chemistry, biochemistry and electrical engineering. The laboratory aims to establish a research program based on the ultraviolet photoelectron spectroscopy (UPS) of nanostructured, preferentially self-assembled molecular thin film. Electronic processes in such nanostructures can be fundamentally new and might be highly relevant for novel types of organic electronic devices. Insight into both the dynamic properties of charge carriers, and into the electronic structure of the material itself shall be obtained using advanced photoelectron spectroscopic techniques bridging the gap between the molecular chemical design and the functioning of devices.

1Organic supramolecular nanostructures

　　Electronic properties of highly-ordered, thin films of nanostructured, preferentially self-assembled molecular multilayer on inorganic and flexible organic surfaces shall be investigated by high-resolution and angle-resolved UPS. Molecules are selected due to their relevance for organic or organic/semiconductor hybrid electronic device applications, because newly synthesized (aromatic) molecules might have potentially special electronic functions or provide a unique aggregation state (e.g. liquid crystalline), or because model systems for the study of fundamental properties can be realized.

2Dynamic properties and screening at organic-inorganic interfaces

　　The charge-vibrational coupling, charge de-localization processes and the dynamic screening of charge carriers in well-defined mono- and multilayer films of polyaromatic molecules is studied using UPS and synchrotron-based resonant photoelectron spectroscopic techniques. These parameters shall be related to the charge transport across the interface.

3Charge-transfer states

　　The energetics of the static charge transfer in acceptor-donor complexes and in intercalation compounds of aromatic and conjugated organic materials is studied. These systems are used as stable, self-doped, possibly conducting layers (donor-acceptor systems) or as energy storage media in Li ion batteries.

Equipment

High-resolution ultraviolet photoelectron spectrometer (VG Scienta SES-100 electron analyzer) with integrated sample preparation system, synchrotron-based photoelectron spectroscopies.

The main research achievements in the past five years

1. R. Friedlein, S. Braun, M. P. de Jong, W. Osikowicz, M. Fahlman, W. R. Salaneck, Ultrafast charge transfer in organic electronic materials and at hybrid interfaces studied using the core-hole clock technique, J. Electr. Spectr. Relat. Phenom., in print.
2. R. Friedlein, Y. Wang, A. Fleurence, F. Bussolotti, Y. Ogata, Y. Yamada-Takamura, Stacks of nucleic acids as molecular wires: Direct measurement of the intermolecular band dispersion in multilayer guanine assemblies, J. Am. Chem. Soc. (Commun.) 132, 12808 (2010).
3. F. Bussolotti, R. Friedlein, Hybrid interfaces of biological molecules and metals: The prototypical case of adenine on Cu (110), J. Chem. Phys. 132, 184705 (2010).
4. F. Bussolotti, R. Friedlein, Hybridization and charge transfer at the anthracene/Cu(110) interface: Comparison to pentacene, Phys. Rev. B 81, 115457 (2010).
5. F. Bussolotti, Y. Yamada-Takamura, R. Friedlein, Intermolecular band dispersion in single-crystalline anthracene multilayer films, Phys. Rev. B 80, 153402 (2009).