From Single Molecules to Two-Dimensional Systems

Germar Hoffmann^1*

¹Dept. of Physics, NTHU, Hsinchu, Taiwan

* Presenter:Germar Hoffmann, email:germar.hoffmann@googlemail.com

Technology truly entered the era of two dimensional systems, in chemistry, application, and devices. The next step is the exploration of the further reduction in dimensionality, i.e., linear structures, laterally restricted as well as introduction of inhomogeneities into two dimensional systems. The gained knowledge in physical and chemical properties as well as the tailored design will impact the design of batteries, energy efficiency of nm-scale electronic devices, pave the way to organic electronics, and improve catalysts’ performances.

The research of our group is dedicated to this approach and my talk will cover some of its aspects. Central objective is the creation of one- and restricted two-dimensional products by the design of molecular precursors. In simple words, we aim for an improved understanding of the ongoing, local chemical processes and physical properties in on-surface synthesis for the formation of covalently coupled networks of predefined structure, composition, and functionality. This is realized within an interdisciplinary working network in chemistry, material science, complementary methods, with us employing Scanning Tunneling Microscopy and Spectroscopy. Major part of the presentation will focus on a simple, substituted precursor molecule, a Phenacene, studied on metallic substrates. We will present different coupling mechanisms towards building up larger, coupled molecular systems. Thereby, (1) an unexpected coupling mechanism, a de-hydrogenative cyclization was observed – (2) the intermediate stage of Wurtz-type coupling occurs at room-temperature on a time scale of hours. With the surface analysis performed at low temperature, we obtain access to the halted process at different times otherwise not trivially accessible. Our approach and results will be discussed within the framework of the known challenges and questions in this field, which evolved in the last decade since its very first principal realization.

This will guide us to the second part of the talk. Solving the challenges of on-surface synthesis for applications requires the transfer of chemical reactions onto two-dimensional substrates or even insulating materials in the future. Related to our experimental methods, we studied preparative aspects of and characterized defects in two-dimensional materials, i.e., specifically of a topological insulator and a transition metal dichalcogenide, for the next scientific steps, which will conclude the presentation.

Keywords: Scanning Tunneling Microscopy, Surface Science, On-Surface Synthesis, Low Dimensional Structures, Molecular Adsorption