Interface formation between C60 and diethynyl-Zn-porphyrinato investigated by SR-induced photoelectron and near-edge X-ray absorption (NEXAFS) spectroscopies

Abstract

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(1 1 1) substrate and progressively tilt their arrangement in order to be oriented with the molecular plane nearly perpendicular to the Cu(1 1 1) 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.