Differential conductance measurements of single test molecules on various supports by lowtemperature STM to quantify the influence of molecule-support and inter-molecular interactions on a molecular electronic system

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The major objective of this project will be a study of the evolution of electronic and conductance properties of single molecules, investigated as a function of (i) coupling strength to a support and (ii) inter-molecular interactions. For this purpose, simple alkanes and pconjugated molecules are deposited on surfaces exerting different binding strengths towards molecules, such as inert oxide, semiconductor and metal surfaces. The molecular density of states (DOS) is probed by conductance spectroscopy with a low-temperature STM. The experiments will provide information on the energy levels of nearly decoupled molecules as well as strongly bound molecule-substrate units, thus reflecting the influence of bond formation on the molecular electronic system. The results can serve as input parameters for a theoretical modelling of the respective systems, performed by participating groups of this Schwerpunktprogramm. In a second step, well-defined molecular assemblies are formed by manipulation of individual molecules with the STM tip. These experiments focus on the influence of inter-molecular interactions on the DOS and on the possibility to form coupled molecular systems. Conductance measurements are complemented by vibrational and optical spectroscopy of single molecules with the STM, generating additional data on binding strength and level positions in the molecules. The project aims to provide information, how the transport properties of a molecular junction can be controlled by a systematic modifications of molecule-support and inter-molecular interactions.