Seminario di Dipartimento: Understanding the adsorption of shuttle-cock shaped subphthalocyanine molecule on Cu(111) surface di Shashank S. Harivyasi
7 luglio 2017, ore 10, nell'aula riunioni della sezione Struttura della materia
Dipartimento di Fisica di Via Celoria 16
Speaker: Shashank S. Harivyasi, Graz University of Technology (Graz, Austria)
We know that the structure of an organic molecule plays a determining role in its adsorption on metal surface and on the subsequent interaction with it. For example, large planar molecules typically lie completely flat on most metal surfaces. However, the situation becomes more complex in case of non-planar molecules which show a varying tendency in planarization upon adsorption, depending mainly on the metal-molecule combination. Here, we try to understand these phenomena in a system that shows extreme behavior: adsorption of shuttle-cock shaped three-fold symmetric Chloroboron subphthalocyanine molecule on Cu (111) surface results in an almost complete planarization and considerable hybridization of molecular orbitals with metal electronic states, making this interface an interesting test-case for links between the two phenomena. Moreover, at sub-monolayer coverage, the adsorbed molecules aggregate into two separate phases that have different contrasts in the scanning tunneling microscopy (STM) and show different growth behavior.
In this talk, S. S. Harivyasi combines results from density-functional theory and from ultraviolet photospectroscopy & low-temperature STM to analyze the adsorption process as well as the interfacial geometry and electronic structure of the molecule onCu(111). Using DFT, we study the steps of the adsorption process by gradually increasing the van der Waals interaction (between the adsorbate and the substrate) and following the evolution of the molecule’s electronic and geometrical structure. We identify that the bonding of the molecule is a two-stage process involving Fermi-level pinning followed by a rehybridization of the molecule’s frontier orbitals. Especially the observed evolution of charge rearrangements help us to explain why we see an almost complete planarization. Further, by investigating different possible conformations and their energy costs and by comparing simulations and experiments, we deduce that the molecule on Cu(111) is susceptible to dechlorination. Since a majority but not all molecules undergo dechlorination, the overall result is a formation of the two different species that in turn lead to the formation of the two phases.
The results thus highlight the need to carefully consider what surface-mediated chemical processes might happen as well as how they happen.
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