Hole or Electron Doped C 60 Polymer Using Free Electron Laser Irradiation
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Hole or Electron Doped C60 Polymer Using Free Electron Laser Irradiation Nobuyuki Iwata, Daiki Koide, Syouta Katou, Eri Ikeda, and Hiroshi Yamamoto CST, Nihon Univ., 7-24-1 Narashinodai, Funabashi-shi, Chiba 274-8501, Japan ABSTRACT Polymerized C60 crystals were grown using the free electron laser (FEL) irradiation. In order to promote the polymerization degree, hole or electron was doped in the C60 crystals grown by the liquid-liquid interfacial precipitation (LLIP) method to eliminate the degradation by oxidation. The specimen grown with the I2 dissolved butylalcohol (BTA, CH3(CH2)3OH) and the C60 saturation o-xylene solution, subsequently pressed at 7GPa, showed only Ag(2)-derived mode at 1456 cm-1 after the FEL irradiation. The specimen belonged to so-called F phase, which is not obtained by the typical photo-induced polymerization process. It was noted that the FEL irradiation for polymerization of C60 was quite useful. INTRODUCTION The three dimensional (3D) C60 polymer can be obtained by high-presure and hightemperature (HPHT) method [1]. The sub-mm 3D crystalline C60 polymer is prepared by HPHT from single crystal of two dimensinal (2D) C60 polymers [2]. In the 3D-C60, C60 moleculres are polymerized via [3+3] cycloadition in addition to the [2+2] one [3]. For example, otrhorhombic 2D-C60 polymaer is converted to orthorhombic 3D-C60 polymer under 15GPa at 500-700ºC, however, the 30% 2D-C60 remains and a graphite-like amorphous phase is obtained at temperatures higher than 700ºC. The aim of our study is to develop a novel photopolymerization process for C60 molecules and synthesize an amorphous 3D C60 polymer at the bulk scale for various application fields. The C60 polymer is expected to have features of stiffness, low-density as well as flexibility like organic material owing to the amorphous phase of C60 polymer, and the density lower than that of metal alloys [4]. We chose the FEL as a light source, which has unique features: a tunable wavelength in the infrared range, and a micropulses with a pulse width less than one ps [5]. H. Nakayama et al. demonstrated that a hole doping in graphite induces the same effect as applying pressure [6]. Whereareas, the polymerization is carried out by doping an electron and a hole using a sccaning tunnneling microscope (STM) tip, meaning that both of the doping is effective to promote the polymerization, where the polymerization degrree depends on the molecules distance [7-9]. In our previous report, in the specimen with shorter molecular distance under 7GPa, the polymerization degree is also promoted, and we found the hole doping is effective for polymerization. However, the preparation of the specimen of mixed C60 and iodine was done in air, where a degradation of molecules is expected by oxidation [10,11]. Futhermore the polymerization area is limited to approximately 5ȝm in diameter when the FEL is irradiated to the pressed C60 powder. The reason is probably the limited directions for polymerization. The directionality is expected to be reduced inserting some molecule
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