Tuning the Molecule-Substrate Interaction: Porphyrins on Ultrathin Insulators
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Date: 12-01-2005
Start Time:
11:00am
End Time: 12:00pm
Speaker: Dr. Luca Ramoino
From:
University of Basel, Switzerland
Location: 414 Schapiro/CEPSR
Hosted by:
Center for Integrated Science
Abstract:
The adsorption and self-organization of copper(II) octaethyl porphyrin (CuOEP) has been studied in detail on heterogeneous surfaces by STM, LEED and UPS. Ultrathin NaCl films have been grown on Cu(111), Ag(111) and Ag(001) and for submonolayer coverage the formation of NaCl islands 1 to 3 ML thick coexisting with clean metal regions is observed. CuOEP molecules have been deposited on the so prepared heterogeneous salt-metal surfaces. STM reveals that the molecules self organize in ordered monolayers on the bare metal areas as well as on the NaCl islands. Series of STM observations performed by increasing the CuOEP coverage reveal that the molecule-substrate interaction can be tuned in a discrete manner by controlling the number of NaCl layers. In particular the adsorption energy of CuOEP decreases by introducing an insulator layer and by increasing its thickness. Such a dependence of the adsorption energy on the NaCl thickness can be explained in the frame of van der Waals theory. On the other hand, for CuOEP directly adsorbed on metals, UPS measurements show that a charge transfer from the adsorbate to the substrate occurs. The comparison of UPS and STM measurements with DFT calculations shows that on all the three metal substrates the CuOEP-metal binding is mainly of ionic nature and no chemisorption occurs.