Interface Formation between Diethynyl-Zn-porphyrin and C60 Investigated by SR-induced Photoemission Spectroscopy

C60 doping of multilayer 2,8,12,18-tetraethyl-5,15-diethynyl-3,7,13,17-tetramethylporphyrinato-Zn(II) (Zn-Pf) has been accomplished. The sublimed Zn-Pf molecules initially lay flat on the Cu(111) substrate and progressively tilt their arrangement in order to be oriented with the molecular plane nearly perpendicular to the Cu(111) substrate surface, at both monolayer and multilayer coverage, as detected by NEXAFS spectroscopy at the N K-edge. It is noteworthy that C60 interacts with the Zn-Pf sample film producing a perturbation of the electronic structure reflected in the spectral changes at the C1s core level, at the N1s and shake-up satellites of Zn-Pf and in the VB region. By the strong spectral modification that occurs at the Zn-Pf multilayer sample C60 diffusion into the substrate is also argued, giving rise most probably to an intercalated composite assembly with C60 spheres in between two Zn-Pf planes. The observed changes are interpreted in terms of charge transfer taking place from C60 to Zn-Pf with a lowering of the band gap and presence of occupied states closer to EF.