Abstract
3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Sn/ Si(111)-23×23 surface and studied using photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS). We found evidences of a strong interaction between the PTCDI molecules and the substrate. The interactions cause changes in the Sn 4d, C 1s, and N 1s core level spectra. These interactions also cause a complete absence of transitions to the lowest unoccupied molecular orbital (LUMO) in the NEXAFS spectra, in combination with a new state between the regular highest occupied molecular orbital (HOMO) and the Fermi level at low coverages. These changes are explained to be due to the charge transfer from the top Sn atoms to the PTCDI molecules, resulting in a split of the HOMO, and lowering of the LUMO levels. The interactions are shown to heavily involve the carbonyl carbon and partly nitrogen atoms of the imide group.
Highlights
The last few decades, thin films of organic semiconductors have received growing attention from the scientific community since they show promising properties for use in electronic devices
In this paper we have studied the same system, perylene tetracarboxylic dii mide (PTCDI) on Sn/Si (111)-2 3 × 2 3, using ultraviolet photoelectron spectroscopy (UPS), X-ray photoelec tron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) to further investigate the electronic structures and clarify the interactions involved in this interface
There was no apparent change in the lineshape or energy position of the peaks in the Si 2p core level spectra when PTCDI was deposited onto the surface
Summary
The last few decades, thin films of organic semiconductors have received growing attention from the scientific community since they show promising properties for use in electronic devices. To understand the interface it is important to characterize the molecule/substrate interactions and the intermolecular interac tions, and their relative strength, since they determine the morphology and electronic structure of the interface. The perylene derivative 3,4,9,10-perylene tetra carboxylic dianhydrid (PTCDA) has been used as a model molecule for self-assembled molecular films. To further understand the interactions involved in the growth of large -conjugated molecules on substrates, it is important to study similar molecules as PTCDA but with different endgroups. One such molecule, 3,4,9,10-perylene tetracarboxylic dii mide (PTCDI), has recently attracted attention since it can be functio nalized through its endgroups to tune its properties [1]. The electronic structure of thin PTCDI films has previosuly been studied using ultraviolet photoelectron spectroscopy (UPS), X-ray photoelec tron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) on Si(111) [2], Ni(111) [2], Au(111) [3,4], Ag(111) [4], Cu (111) [4], TiO2 [5,6] and Ag/Si(111)- 3 × 3 [7]
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