The implementation of force detection in experiments on electron transport through single molecules

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By means of scanning tunneling microscopy (STM) it is possible to investigate electron transport through adsorbates and adsorbate structures in a large variety of aspects, while having exact knowledge and control of the atomistic structure including the coupling to the leads. Therefore, STM has been very successfully applied in the field of molecular electronics. However, STM investigations are limited to conducting substrates and the experimental data is determined by both the geometry and the electronic structure of the sample in a complex and often ambiguous manner. To overcome these two limitations, it is projected to experimentally implement force detection as an additional measure in molecular electronics, that is, in electron transport measurements through a single molecule. To this end, a scanning tunneling microscope equipped with a force detector at the tip was built in the ongoing funding period. It is planned to measure the forces that act on the tip upon contact formation to a single molecule, to provide a more complete set of experimental data that can be used to model and understand the contact formation. Second, we would like to exploit the force detection to unambiguously discriminate between electronic and geometric effects in the current signal in imaging as well as in any electron-transport measurement. Third, the possibilities in quantifying charge redistribution in molecules and molecular structures by electrostatic force detection will be explored. Finally, force detection will allow the investigation of conducting molecular structures on completely insulating areas of a sample. Altogether this project shall establish the detection of forces in experiments on electron transport through molecules and engineered molecular structures and thereby provide a better control of the geometry in molecular electronics with atomic-scale precision.