Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 16: Scanning probe methods II

O 16.4: Talk

Monday, March 26, 2012, 16:45–17:00, MA 043

Revealing the angular symmetry of chemical bonds by atomic force microscopy — •Joachim Welker and Franz J. Giessibl — Faculty of Experimental and Applied Physics, University of Regensburg, Universitätsstraße 31, 93053 Regensburg

The angular symmetry of chemical bonds determines the structure of condensed matter from the atomic to the macroscopic scale. Angular dependence is characteristic of covalent bonding, which occurs in organic molecules aswell as bulk solids. Here, we have measured the angular dependence of chemical bonding forces between two atomic bonding partners: a carbon monoxide molecule that is adsorbed to a copper surface and the front atom of the metallic tip of a combined scanning tunneling microscope (STM) and atomic force microscope (AFM). We present tomographic maps of force and current as a function of distance that reveal the emergence of strongly directional chemical bonds and a conductive channel as tip and sample approach. The force maps show pronounced single, dual or triple minima depending on the directional preferences of the bonds that develop, while tunneling currents maps show a single dip for all three tip conditions.