Exploring the metallo-organic interface of archetype molecules (specifically CuPc and PTCDA) on Cu(111)
Friday November 6, 12:00, IFAE: Dr. Hatice Karacuban, Fachbereich Physik, Universität Duisburg-Essen
When molecules are adsorbed on a surface the interaction may have an enormous effect the properties of both, the substrates and the adsorbates. The growth and interface properties of the archetype molecules CuPc (Copper Phthalocyanine) and PTCDA (3,4,9,10 perylentetracarboxylicacid-dianhydride) were investigated on a Cu(111) substrate. The experiments were carried out with a low temperature scanning tunneling microscope, at about 10 K, under ultra high vacuum conditions.
Upon adsorption of CuPc on Cu(111), a reduction of the symmetry of the molecules is observed. Furthermore, when the occupied states of the molecules are imaged, a switching of the tunneling current between two distinct levels is found. Based on high resolution data, an on-top adsorption geometry of the CuPc molecules on Cu(111) can be deduced.
For PTCDA on Cu(111) two new superstructures are observed at low temperatures. Within these superstructures the molecules are tilted with respect to the substrate. Scanning tunnelling spectroscopy measurements reveal a local variation of the electronic states of PTCDA molecules within the herringbone pattern. A sharp resonance is observed at about 300 meV below the Shockley surface state of the Cu(111)-surface. The latter is found for the free Cu(111) surface, but there is no indication within the molecular spectra. This suggests a strong interaction with the molecular states leading to the formation of a metal-organic interface state. If both molecules PTCDA and CuPc are present on the sample, local spectroscopy enables a direct comparison. Where the CuPc molecules are in ‘contact' to the PTCDA molecules they also show this interface state.