Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014)
    Thin Films Tuesday Sessions
       Session TF-TuE

Paper TF-TuE4
Well-Ordered Monolayers of Alkali-doped Coronene and Picene

Tuesday, December 9, 2014, 6:40 pm, Room Makai

Session: Thin Film Synthesis & Characterization I
Presenter: Yoichi Yamada, University of Tsukuba, Japan
Authors: Y. Yamada, University of Tsukuba, Japan
M. Yano, University of Tsukuba, Japan
M. Endo, University of Tsukuba, Japan
E. Shimizu, University of Tsukuba, Japan
Y. Hasegawa, University of Tsukuba, Japan
M. Sasaki, University of Tsukuba, Japan
Correspondent: Click to Email
Although the electronic modifications of the organic thin films by means of the chemical doping have been widely investigated, the structural properties of the doped organic materials have been poorly understood. This is generally due to an inhomogeneity of the doped materials, hindering the detailed understanding of the structure. However, structural information is inevitable for understanding the mechanism of the doping. For the basic investigation on the doping of the organic materials, we utilize well-defined monolayers of organic materials. We model the doping by depositing the dopant onto the monolayer. When the substrate is inert enough, self-organization of the dopants and host materials will be facilitated and well-ordered doped monolayer will be obtained. We focus mainly on so-called "metal-intercalated aromatic superconductors" discovered in 2010 in K-doped picene [1]. Since its discovery, electronic properties of these materials have been investigated by means of the photoemission spectroscopy. However, contradicting results, deviating from a metallic to an insulating ground state, have been obtained. It is speculated that there exists notable variation of the structures in the thin films used in the photoemission studies. The theoretical reports have also reached contradicting results and have suggested that the electronic states are quite sensitive to the molecular arrangements. Therefore it is demanded to realize the well-ordered samples of these materials. Here we demonstrated the fabrication of the well-defined monolayer of the metal-intercalated aromatic superconductors, such as K-doped picene and coronene. These systems enable us the systematic investigations of the relation between structure and electronic properties. It is found that the alkali-doping causes a rearrangement of the host monolayers, based on the scanning tunneling microscopy and the X-ray absorption spectroscopy. Upon the reconstruction, electronic states of the host molecules also change drastically, suggesting the charge transfer from alkali metals to the molecule, revealed by means of the photoelectron spectroscopy. These observations confirm that the well-ordered monolayer, as realized in this study, can properly model the doping process [2,3].

[1] R. Mitsuhashi, et al., Nature 464, 76 (2010)

[2] M. Yano, et al., J. Chem. Phys. 141, 034708 (2014)

[3] Y. Hasegawa, et al., J. Phys. Chem. C (in press)