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.

Synthesis of hexagonal boron carbonitride without nitrogen void defects

Mannan, M. A.*; Baba, Yuji; Kida, Tetsuya*; Nagano, Masamitsu*; Noguchi, Hideyuki*

Materials Sciences and Applications, 6(5), p.353 - 359, 2015/05

https://doi.org/10.4236/msa.2015.65041

The synthesis and structure of hexagonal boron carbonitride (h-BCN) film on polycrystalline diamond surface were reported. Polycrystalline diamond and/or diamond-like carbon were first fabricated on Si (100) and then it was used as substrate. The deposition was performed by radio frequency plasma enhanced chemical vapor deposition. In order to reduce the content of nitrogen void defects, the deposition was performed at the high temperature of 950C under the working pressure of 2.6 Pa. The typical sample with atomic composition of BCNO in the h-BCN lattice was characterized by X-ray photoelectron spectroscopy. The fine structure of the film was studied by near-edge X-ray absorption fine structure (NEXAFS) measurements. The B K-edge and N K-edge of NEXAFS spectra revealed that the synthesized h-BCN film has the ideal honeycomb-like BN configuration without nitrogen void defects.

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.

Analysis of molecular orientation for organic semiconductor using photo electron emission microscope with excitation sources of linear-polarized X-rays and ultraviolet light

Sekiguchi, Tetsuhiro; Honda, Mitsunori; Hirao, Norie; Ikeura, Hiromi*

no journal, , 

High degrees of molecular orientation play a crucial role in the improvement of electronic properties in organic semiconductors. Thus, it is essential to selectively characterize materials with different orientation direction in microscopic domains. So far, we have strived to observe orientation of organic-semiconductors in microscopic domains using the photoelectron emission microscopy (PEEM) system with excitation by linearly polarized ultraviolet (UV) light from mercury lamp and synchrotron X-rays.

Electronic structures of sulfur-containing organic electronic materials probed by X-ray absorption spectroscopy

Ikeura, Hiromi*; Sekiguchi, Tetsuhiro

no journal, , 

Many peaks are observed in X-ray absorption fine structure near the inner-shall edges. Such fine structures are called near-edge X-rays absorption fine structure or abbreviated as NEXAFS. NEXAFS spectra provide us with information on property of electronic states concerning partial density of states of unoccupied conduction band for materials. In this work, we have investigated several sulfur-containing thiophene derivative polymers using NEXAFS spectroscopy. We have recorded the S K-edge NEXAFS spectra of film samples of these electronic materials and tried to interpret the origin of electronic transition seen in NEXAFS on the basis of molecular orbital theory. Furthermore, we discuss whether there is a potential relation between the observed spectra and charge-transfer property of the materials.