Strong Chemical Interaction and Self-Demetalation of Zinc-Phthalocyanine on Al(100)

We investigate the early stages of the growth of zinc-phthalocyanine on Al(100) using X-ray photoemission spectroscopy (XPS) and low-energy electron diffraction (LEED). Diffraction patterns show a (5 x 5) reconstruction, characteristic of flat-lying molecules forming a long-range-ordered structure with a square unit cell. The degree of ordering (i.e., the average domain size) is increased when the substrate is kept above 100 degrees C during the deposition. At low coverage (<= 1 ML), a sizeable charge transfer from the substrate to the molecules is observed, indicating a strong interaction at the organic-inorganic interface. As a consequence of charge filling of ZnPc LUMO, a self-demetalation of the molecule occurs while the structure of the ligand remains mostly unaffected.