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Surface smoothing of glass substrate by irradiation of ionic liquid ion beams Mitsuaki Takeuchi, Takuya Hamaguchi, Hiromichi Ryuto, Gikan H Takaoka Photonics and Electronics Science and Engineering Center, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8510, Japan ABSTRACT Surface smoothing of a barium borosilicate glass substrate by irradiation of ionic liquid ion beams were investigated. 1-ethyl-3-methylimidaolium tetrafluoroborate (EMIM-BF4) and 1butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) were used for the source liquid. Surface roughness represented as the arithmetic mean value decreased from 0.17 nm to 0.13 nm by the BMIM-PF6 negative ion beam. Secondary electron microscope (SEM) observation for the glass surface irradiated with the BMIM-PF6 negative ion beam showed a clear image without an electrical charge-up, though the EMIM-BF4 negative ion beam irradiated glass yielded a charged up image. X-ray photoelectron spectroscopy (XPS) analysis implied that the surface layer including cation-anion pair of BMIM-PF6 was deposited by the BMIM-PF6 negative ion beam irradiation, while an insulated surface with barium fluoride was formed by the EMIM-BF4 negative ion beam irradiation. INTRODUCTION Ionic liquid ion sources (ILIS) have attracted considerable attention because of their unique characteristics such as easy negative ion beam generation and numerous molecular combinations. The ionic liquids (ILs) that are molten salts at room temperature typically exhibit moderate electrical conductivity of 1-100 S/m, high thermal stability and extremely low vapor pressure. Since the typical ILs includes halogens in its anion, reactive etching for silicon wafer have been reported [1]. Moreover, ILIS have been studied as the ion source for focused ion beam processing (FIB) [1], ion thrusters [2], and secondary ion mass spectroscopy (SIMS) probes [3]. A borosilicate glass composed of silicon oxide, barium oxide, boron oxide and aluminum oxide, is an essential material for electronics devices such as flat panel displays and touch screens. For the applications, the surface smoothness is very important property to suppress fracture because submicrometer-order cracks on the surface could be often origin to propagate fracture. Irradiation of ILs ion beam are expected to be effective for surface smoothing or sputtering because they encompass many types of molecules, especially boron, phosphorus and halogens, that considerably affect chemical reactions on glass. Moreover, the ILs ion beam has a potential to yield a charge-up less irradiation onto the glasses that are electrical insulators because the ILs ion beams includes high mass/charge ratio molecule as reported elsewhere [4]. We reported that surface roughness on a barium borosilicate glass decreased by 1-butyl-3methyimidazolium hexafluorophosphate (BMIIM-PF6) ion beam irradiation at acceleration voltage of 4 kV [4]. However, dependences on ion species and ion fluence are not clear. In this study, IL ion beams generated from two types of IL were irradia