Photochemical Bonding of Fluorocarbon and Fused Silica Glass for Ultraviolet Ray Transmitting
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Photochemical Bonding of Fluorocarbon and Fused Silica Glass for Ultraviolet Ray Transmitting Kenji Asano and Masataka Murahara Department of Electrical Engineering, Tokai University 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-1292, Japan ABSTRACT Fluorocarbon was photo-chemically combined to a fused silica glass with the silicon oil used as a bonding agent. Balsam, unsaturated polyester resins and UV hardening adhesives have been generally used for joining two optical glasses together. They, however, have a strong absorption band in the UV region. Therefore, a new bonding method was developed for optical materials to allow UV rays to pass through using silicone oil and excimer- lamp. This new method requires the fluorocarbon-polishing pad employed in our PCP (Photo-Chemical Polishing) method in hydrofluoric acid ambience, which is bonded with the silica glass. The silicone oil was put between the fused silica glass and the fluorocarbon (FEP), and an excimer- lamp was irradiated. When the excimer lamplight was irradiated vertically, the silicon oil ((-O-Si(CH3 )-O-)n) was photo-dissociated and reacted with the oxygen adsorbed on the silica glass surface to produce a SiO 2 . On the other hand, the H atoms photo-dissociated from the silicon oil pulled out the F atoms of the FEP. As a result, the FEP and the silica glass were combined. The tensile strength of the sample bonded by the photo -chemical reaction was evaluated. The tensile strength of 5.4 [kgf/cm2 ] was obtained, whereas that of the non-treatment sample was nil. Moreover, the transmittance of the vitrified silicone oil was measured at the 193 nm of ArF laser wavelength. It increased by 90.6% from 29.2% without the UV photon irradiation. The results showed that the silicon oil changed to silica glass by the excited oxygen, which improved the UV rays under 200nm transmittance. INTRODUCTION We have developed the photochemical polishing (PCP) method of synthetic fused silica glass, using the photochemical reactions and pulse of ArF excimer laser [1]. This method required a polishing optical material such as a fused silica glass that transmits ultraviolet rays in practical application. There are, however, many polishing optical materials such as silicon wafer, silicon carbide and BK7 glass that do not transmit UV rays. So, we considered not penetrating such materials but a bonding agent that is a polishing pad. An UV light transmitting polisher must be made to achieve it; therefore, the transparent fluorocarbon (FEP) was adhered on the fused silica glass. Balsam, unsaturated polyester resins and UV-curing adhesives have been generally employed for bonding optical glasses together. But, such UV-curing adhesives deteriorate materia ls used and cannot obtain high adhesive strength [2,3]. In order to solve the problems, J.Rayss had mixed two UV-curing adhesives to bond the fused silica glass to PTFE strongly [4]. Moreover, Iida had tried to improve the adhesive strength by UV-ozone surface treatment or lower
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temperature plasma treatment [5]. With
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