Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-3×3.

C Emanuelsson,H M Zhang,L S O Johansson

doi:10.1063/1.5038721

Abstract

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-3×3 surface and studied using photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS). All core levels related to the imide group of the molecules showed a partial shift to lower binding energies at low coverages. In NEXAFS spectra, the first transitions to the unoccupied states were weaker at low coverages compared to thicker films. Also, extra states in the valence band between the regular highest occupied molecular orbital and the Fermi level were found at low coverages. These changes were explained by two types of molecules. Due to charge transfer from the surface, these two types have different interactions between the imide group and the substrate. As a result, one type has a partially filled lowest unoccupied molecular orbital while the other type does not.

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

Introduction

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]

Results

Discussion

Conclusion