Observation of oriented organic semiconductor using Photo-Electron Emission Microscope (PEEM) with polarized synchrotron

Sekiguchi, Tetsuhiro; Baba, Yuji; Hirao, Norie; Honda, Mitsunori; Izumi, Toshinori; Ikeura, Hiromi*

Molecular Crystals and Liquid Crystals, 622(1), p.44 - 49, 2015/12

BB2014-1632.pdf:0.71MB

https://doi.org/10.1080/15421406.2015.1096989

The molecular orientation is one of the important factors for controlling various properties in organic semiconductor materials. Films are usually heterogeneous. Thus they exist as a mixture of microscopic domains which have a variety of orientation directions. Therefore, it is essential to observe selectively microscopic domains with different orientation direction. In this work, we have developed the photoelectron emission microscopy (PEEM) system combined with the linearly polarized vacuum ultraviolet (VUV) light or synchrotron radiation (SR) X-rays. PEEM images (FOV = ca.50 micro m) for poly(3-hexylthiophene), P3HT thin films were observed under the UV irradiation with various polarization angles, including in-plain and out-of-plain polarization. Morphologies at some bright parts are different each other. The resultant observation suggests that it enables us to distinguish oriented micro-domains with specific directions of polymer chain axis from other amorphous parts.

Molecular orientation of pentacene derivative

Ikeura, Hiromi*; Sekiguchi, Tetsuhiro

Photon Factory Activity Report 2013, Part B, P. 518, 2014/00

Organic electrically conducting -stacked small molecules are widely regarded as promising materials for future application of low-cost and flexible nanoelectronics. Pentacene is one of the most promising organic semiconductors because of its excellent device performance. Direct measurements of electronic structures of unoccupied states of organic semiconductors lead to better understanding of mechanism of electron conduction. For probing unoccupied partial density of states (DOS), X-ray absorption spectroscopy (XAS) is commonly used, where selective excitation of the 1s core electron to the unoccupied conduction band is possible. The molecular orientation of pentacene derivative has been investigated by angle dependent XAS measurements. Electronic states were calculated by DVX method.

Analysis of the structure of -sexithiophene thin films grown on layered materials

Kodama, Hiraku*; Hiraga, Kenta*; Ono, Shinya*; Sekiguchi, Tetsuhiro; Baba, Yuji; Tanaka, Masatoshi*

no journal, , 

Orientation of organic semiconductor has been important issue because of its strong anisotropy of the electronic property. We have investigated the orientation effect of -sexithiphene (6T) molecule deposited on WSe or GaSe substrate, which is layered semiconductor material. Thickness was controlled by regulating deposition rate and time. Orientation angle was analyzed by angle-resolved NEXAFS spectroscopy. The results show that molecular orientation angle depend not only on the substrate but also the thickness. Tilt angle is thought to be determined by the energy stability due to the commensurate at the interface as well as the molecule-substrate interaction.