Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 44: Focussed session: Functional molecules at surfaces II
O 44.1: Topical Talk
Mittwoch, 28. März 2012, 10:30–11:00, A 053
Scanning Tunneling Spectroscopy and Atomic Force Microscopy of Functional Molecules on Thin Insulating Films — •Jascha Repp — Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany
Ultrathin insulating films on metal substrates facilitate the use of the scanning tunneling microscope (STM) to study the electronic properties of single atoms and molecules, which are electronically decoupled from the metallic substrate. The ionic relaxations in a polar insulator lead to a charge bistability of some adsorbed atoms and molecules. It is shown that control over the charge-state of individual molecules in such systems can be obtained by choosing a substrate system with an appropriate work function. The distribution of the additional charge is studied using difference images. These images show marked intra-molecular contrast. In addition, we investigated C20S2H12 molecules adsorbed on ultrathin layers of NaCl using a combined low-temperature scanning tunneling and atomic force microscope. These non-planar molecules exist in two stable conformations. By means of excitations from inelastic tunneling electrons we can switch between both conformations. We present atomic force microscopy (AFM) measurements with sub-molecular resolution directly revealing the conformational changes. From AFM data and taking the chirality of the molecules into account, we could unambiguously determine the pathway of the conformational change. Hence, the AFM channel reveals additional information that is truly complementary to the STM data set.