Quantitative High-Resolution Atomic Force Microscopy of Organic Compounds with Copper-Oxide Functionalized Tips

Basic data for this project

Description

Noncontact atomic force microscopy (NC-AFM) with functionalized probe tips has become a powerful approach to achieve sub-molecular resolution of organic molecules on surfaces. In particular, probe particles like CO or Xe are co-adsorbed on the surface under study and subsequently picked up by the tip. This allows chemically passivating the tip termi-nation and thus facilitating imaging at significantly reduced tip-sample distances, revealing the internal bond structure of organic compounds in NC-AFM experiments. In fact, this methodology has pushed investigations in surface chemistry and molecular self-assembly to a completely new level. However, despite these tremendous advancements, a major drawback of the involved tip-functionalization is the lateral deflection of the probe particle during scanning. The related tip flexibility leads to image distortions, a systematic bond elon-gation, and the appearance of virtual bonds. Seeking for alternative ways of tip functional-ization, we have made substantial progress particularly involving metal-oxide surfaces, where we used various oxygen-induced reconstructions on different copper surfaces as model systems. We were able to introduce an oxygen-terminated copper tip (CuO tip) for sub-molecular NC-AFM imaging as a complementary probe and potential alternative to the established tip-functionalization approaches. Therefore, one focus of the project is to sys-tematically explore the capabilities of the structurally rigid CuO tip in high-resolution NC-AFM experiments in terms of quantitative bond length determination and intermolecular bonding. Due to the high technological relevance of the interface formation between functional organic layers and metal oxides (e.g. for organic optoelectronic semiconductor devices), we will take advantage of these model systems as substrates. We will study the interface formation of organic compounds in a comparative way for pure metallic and oxidized surfaces. Here, mol-ecule-substrate interactions and surface diffusion properties of organic molecules will be studied by controlled NC-AFM manipulations with CuO-functionalized tips. The resulting quantitative manipulation forces from these experiments will be correlated with photoelectron spectroscopy (PES). Furthermore, we will investigate different molecules with inherent dipole moments perpendicular to the surface with sub-molecular resolution at various distances (3D NC-AFM) to cover the whole short-range interaction regime. Our results will be highly rele-vant for the fundamental understanding of the imaging mechanisms in NC-AFM in the repul-sive force regime and will establish the CuO tip as a benchmark probe for experiments with ultra-high resolution.