Nano electronics: IUB researchers find evidence for effective electron transport in hybrid semiconductors

Stefan Tautz, IUB Professor of Physics, and his group for the first time managed to detect a much larger delocalization of electrons in an organic monolayer semiconductor deposited on a metallic substrate than ever detected in an insulated organic semiconductor. The results, which were published in Nature 444, p. 350 – 353, on November 16, 2006, allow insights into basic mechanisms of electron transport within organic materials and their interfaces with metallic surfaces. Moreover, the results may be of relevance for the development of new hybrid materials with interesting new electronic properties regarding future application.

[ Nov 16, 2006]  The IUB researchers employed a special model system consisting of monomolecular layers of the organic semiconductor material PTCDA (3,4,9,10-perylenetetracarboxylicacid-dianhydride), deposited as nanometer sized molecule islands on the metallic Ag(111)substrate. The experiments were performed using of a state of the art low temperature, ultra high vacuum scanning tunnelling microscope at IUB, which allows the visualization of single molecules and molecule clusters as well as the spectroscopic study of the nano-scale structures of the semiconductor.

The origin for the observed unusually strong electron delocalization is a complex chemical interaction between the two components of the hybrid material, which causes a spatial deformation of the organic molecules and the formation of a thin interface layer with completely new electronic properties. Electron delocalization, that is the dissociation of electrons from their firm attachment to molecules, is an important prerequisite for the transport of electrons or electricity within materials. The large degree of delocalization measured in the PTCDA/Ag(111) model system suggests that the electrons move along the interface layer in a highly efficient wave-like manner instead of slowly „hopping“ from molecule to molecule as they often do in disordered organic materials. The IUB experiments give clear evidence to such a specific chemical interaction between metal and organic molecules in semiconductors.

Organic semiconductor electronics, in contrast to conventional silicon based electronics, is regarded as a future field for highly cost efficient, miniaturized and performance efficient electronic applications. „Our findings on organic-metallic interfaces are an important step in understanding basic molecular mechanisms of electron transport. Furthermore, they have the potential of leading to the optimization of electronic processes, which is a necessary developmental step for making organic electronics fit for application,“ comments Stefan Tautz on the results of his research group.

„For me it was an exciting experience to be part of such basic research already during my undergraduate studies,“ says Adina Luican, co-author of the Nature paper. The 22-year old Romanian, now a physics graduate student at Rutgers University in New Jersey, contributed to the data evaluation, especially to the calculation of the electron delocalization in the context of her third-year „guided research project“.