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

借助于扫描隧道显微镜(STM)，在准确了解和控制原子结构(包括与引线的耦合)的同时，可以从多个方面研究电子在吸附和吸附结构中的传输。因此，扫描隧道显微镜在分子电子学领域得到了非常成功的应用。然而，扫描隧道显微镜的研究仅限于导电衬底，实验数据由样品的几何结构和电子结构以一种复杂且往往含糊不清的方式确定。为了克服这两个限制，预计将试验性地实施力检测，作为分子电子学中的一种额外措施，即在通过单个分子的电子传输测量中。为此，在正在进行的供资期间，建造了一台在尖端装有力探测器的扫描隧道显微镜。计划测量与单个分子接触形成时作用于尖端的力，以提供一套更完整的实验数据，可用于模拟和理解接触形成。其次，我们想利用力检测来明确区分成像和任何电子传输测量中电流信号中的电子和几何效应。第三，探索了通过静电力检测来量化分子和分子结构中电荷再分布的可能性。最后，力检测将允许研究样品完全绝缘区域上的导电分子结构。总之，该项目将在电子通过分子和工程分子结构的实验中建立作用力的检测，从而以原子尺度的精度更好地控制分子电子学中的几何图形。

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.