| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Poster Session |
| Presenter: | Masahiro Yano, University of Tsukuba, Japan |
| Authors: | M. Yano, University of Tsukuba, Japan M. Endo, University of Tsukuba, Japan R. Shimizu, University of Tsukuba, Japan Y. Hasegawa, University of Tsukuba, Japan Y. Yamada, University of Tsukuba, Japan M. Sasaki, University of Tsukuba, Japan |
| Correspondent: | Click to Email |
In this paper, we demonstrate that K-doped coronene and picene monolayers form well-defined structures and they are model systems suitable to clarify the mechanism of electronic and structural modifications of aromatic hydrocarbon crystals due to alkali doping. It can be a basis to control the electronic properties of organic materials by foreign metal-doping.
Modification of the electronic properties of organic materials by doping with foreign metals is one of the key technologies used in next-generation organic electronics. In general, microscopic structural information is essential for understanding the underlying mechanisms. However quite few number of investigations have addressed the microscopic structural features with respect to doping, mainly due to difficulties in the measurement of inhomogeneous samples. Therefore, basic investigation into the microscopic structural nature of metal-doped organic systems utilizing well-defined models is necessary.
In the present study, we have investigated molecular-scale structure and electronic state of K-doped coronene and picene monolayer. For the substrate, we employ inert surfaces, such as Au(111) and highly oriented pyrolytic graphite (HOPG), to minimize the effect of the substrate on the reaction between K and molecules.
After the coronene and picene monolayers were prepared on Au(111) or HOPG using vacuum deposition, K was deposited on the monolayer from alkali dispensers.
The structures were observed by means of scanning tunneling microscope (STM). STM images show significant structural changes of coronene and picene monolayers upon K deposition. Both the K-doped monolayers exhibit well-defined herringbone-like molecular arrangement. In this phase, while the surface reconstruction of Au(111) is still visible, individual K atoms are not observed. We speculate that K atoms intercalate between molecular planes and directly interact with the molecules.
The electronic states were investigated by means of photoemission spectroscopy on a HOPG substrate. In both the monolayers, with increasing doping, a new state appears more clearly just below the Fermi level. The formation of this state is very sensitive to the molecular arrangement [1].
Moreover, it should be noted that a very similar photoemission spectrum has been reported in K-doped thick picene film on HOPG [1]. This similarity ensures the perspective that the well-defined K-doped monolayer can be a model for the doped aromatic hydrocarbons crystals.
[1] H. Okazaki et al., Phys. Rev. B 88, 245414 (2013).