Université Pierre et Marie Curie (UPMC), France
Abstract / Thesis download
In this thesis work I studied the structure and reacvity of Luteum bis-phthalocyanine (LuPc2) thin
films deposited on metallic surfaces. The knowledge of the structure of epitaxial organic thin films is
extremely important to design the next generaon of devices based on organic electronics, because
crucial parameters as carrier mobility, and to an extent charge recombinaon, crically depend on the
molecular configuraon and thin film ordering. The second part of the work deals with the reacvity
of molecular thin films towards atmospheric gases. This is parcularly important when considering the
lifeme of the device, as at the moment this is one of the greatest hindrance to the extensive use of
organic electronic devices in everyday life. Phthalocyanine were chosen due to their already wide use
in devices and their ease of process. In parcular we chose LuPc2 because, due to the double decker
molecular geometry (see Figure 1) they should present a different reacvity respect to single decker
phthalocyanine, as the second macrocycle should hinder the reacvity on the metallic caon.
The work was carried out with a surface science approach, the thin films were prepared by thermal
evaporaon under ultra-high vacuum condions and analysed by means of Scanning Tunnelling
Microscopy (STM) and X-ray Diffracon (XRD) to achieve a complete characterizaon of the structure
and the morphology. Than the chemical changes aer reacon towards gases were studied by means
of X-ray Photoemission Spectroscopy (XPS) and Near Edge X-ray Absorpon Fine Structure
Spectroscopy (NEXAFS) to study.
We resolved the structure of a LuPc2 thin film deposited on Au(111), showing that the molecules adopt
a β structure, the interacon with the substrate via the relaxaon of the surface reconstrucon, and
demonstrated the templang effect of the substrate via the epitaxial relaons with the overlayer. We
then present the surface morphology at the molecular scale, showing the formaon of large (tens of
nm) islands composed by a double layer of molecules. From a careful analysis of the STM images we
are able to show the stacking geometry, as well as the relave orientaon of the different domains
and compare this results with the one obtained by XRD.
We tested the reacvity of these thin films towards atmospheric gases, in parcular oxygen and water,
showing a low reacvity and managing to demonstrate the adsorpon sites, which indeed are not the
central caon, but rather on the macrocycle. We also showed how molecular oxygen is a greater threat
to the molecular stability than water.
Figure 1 Left: β structure of LuPc2; right: proposed absorption geometry for O2 molecule
See a recent presentation.