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Atomic-Scale Science on Insulating Films

Workgroup Repp, Faculty of Physics, University of Regensburg

Research

The primary objective of our team is to study the physical and chemical properties of single adsorbates and adsorbate structures on the atomic length scale. The technique of choice is low-temperature scanning probe microscopy, namely scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). The strength of these scanning probe techniques lies in their ability to analyze the structural environment of one particular defect or adsorbate on the atomic length scale and to probe the local properties of this individual, well-characterized structure.

Recently we have been mainly interested in STM experiments on individual adsorbates on ultrathin insulating films. Ultrathin insulating films on metal substrates facilitate the use of the scanning tunneling microscope to study the electronic properties of single atoms and molecules, which are electronically decoupled from the metallic substrate. Most importantly, many physical and chemical properties are not only quantitatively but also qualitatively different on an insulating surface compared with a (semi-)conducting surface. Therefore, it has become of supreme importance to study insulating materials, as science advances to the atomic length scale. New experimental possibilities which are to be examined comprise (meta-)stable charging processes of individual adsorbates and STM-induced chemistry of single molecules on insulators. Furthermore, these investigations shall open new research avenues in molecular electronics, as they combine the following two elements: the electronic decoupling of an adsorbate provided by the insulator and the ability of STM and AFM to analyze the structural environment of an adsorbed molecule.

Our research is carried out using two hybrid scanning tunneling / non-contact atomic force microscopes operated at a temperature of 5K under ultra-high vacuum conditions. Further, the capability is being built up to perform measurements in strong magnetic fields to additionally study spin and magnetic properties, as well as combined with terahertz-frequency pump-probe laser experiments.

The group was established in March 2007 by the hiring of Jascha Repp on a Lichtenberg Professorship. We gratefully acknowledge funding from the Volkswagen Foundation (Lichtenberg Professorship), the Deutsche Forschungsgemeinschaft (through SFB 689, GRK 1570, and the research project RE 2669/4-1) and the European Union (through "MOLESCO" project # 606728).