Investigation Of The Electronic And Geometric Structure Of Fullerene (C₆₀, PC₆₁BM)/Metal Interface

Energy level alignment at the interface between organic semiconductor and metal electrode plays crucial role in the performance of organic electronic devices. In this thesis, I have investigated the electronic structures and geometric structures of C60 and PC61 BM on some metal surfaces. The organic materials under study, C60 and PC61 BM,are n-type semiconductors and have exhibited extensive applications in organic electronic devices. The research methods adopted in the thesis include synchrotron photoemission spectroscopy (SRPES) measurements, density functional theory (DFT)calculations and scanning tunneling microscopy (STM) measurements.According to the PES data of C60 film with different thickness on Ag(100), we found that the Ag atoms of the substrate diffused far into the C60 film and act as n-type dopants in the organic film. On the basis of the energy levels diagram across the C60/Ag(100) interface, we proposed that the interface between a C60 thick film and a metal substrate should be described by the two sub-interfaces (TSI) model together with the Integer Charge-Transfer (ICT) model. The sub-interface between the C60 bottom monolayer (BML) and the substrate is Fermi level alignment, and another sub-interface between the BML and the C60 multilayer is vacuum level alignment following the ICT model. The TSI + ICT model is supported by our further studies of the electronic structures of C6o film on the surfaces of Au(111), Ag(111), Al(111) and Al(100). According to the TSI + ICT model, the performance of organic electronic devices is directly related to the work function of the C60 BML and HOMO, LUMO of the second C60 molecular layer.We have studied some 1 ML C60/metal systems with DFT calculations. The focus is on the effects of the substrate reconstruction on the electronic structure of the C60 overlayer. Here the substrate reconstruction means the pits of the metal substrate dug by the C60 molecules. Some metal atoms are dug out during the formation of the pits;these atoms are referred to as metal adatoms. We found that the pits and adatoms can alter the work functions of the 1 ML C60/metal systems and increase the amount of charge transfer from the metals to C60.At last, we studied the geometric structures of PC6iBM/Au(111) system with STM measurements. It was found that PC61BM can form three types of phase-pure monolayer, namely, the compact straight molecular double-row (CSMDR) monolayer,the glassy monolayer and the hexagonal-packing monolayer. In addition to Van de Waals interaction and hydrogen bond, the steric effect of the side tail plays conspicuous role in the molecular self-assembly at high coverages. The molecular orientations differ between different types of monolayer. Considering the intrinsic dipole moment of PC61BM, we can predict that different packing manners of PC61BM on metal surface lead to drastic variation of the interface dipole.