Optical Characteristics Of Silica-Poly(Ethylene Oxide) Hybrid Thin Films
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445 Mat. Res. Soc. Symp. Proc. Vol. 576 © 1999 Materials Research Society
material is silica-poly (ethylene oxide) (PEO) hybrid material prepared by using yglycidoxypropyl-trimethoxysilane (GPTS) as a precursor. The silica network is formed through hydrolysis and condensation in the presence of water, and PEO polymeric network is made by epoxide polymerization with addition of polymerization initiator. However, in the presence of water and catalyst, the epoxy group could react with water to form glycol by opening epoxy rings to terminate the polymerization [1]. In the previous work[5], we prepared silica-PEO hybrid materials by thermal curing and examined their optical properties. However, the UV curing is more desirable for the application of integrated technology. Thus, in the present study, the silica-PEO hybrid material is prepared by sol-gel reaction of GPTS, followed by epoxide polymerization by UV curing using UV polymerization initiator. The structural evolution by UV curing is examined and the epoxide polymerization is confirmed. Concurrently, the variation in the optical properties of the silica-PEO hybrid thin films is investigated. EXPERIMENT Synthesis of the Silica-PEO Hybrid Solution The silica-PEO
hybrid solutions were prepared by using
72-glycidoxypropyl-
trimethoxysilane (GPTS, Aldrich) as the starting precursor. The water for hydrolysis was added to the GPTS solution, and the solution was stirred for 16 hours. The molar ratio of water to GPTS was 1.5:1 and the pH of the solution was adjusted at 5.5 by bubbling CO 2 through it (prehydrolyzed GPTS). The prehydrolyzed GPTS was refluxed at 801C for 12 hours to form the silica network because the cationic polymerization initiator could not work in base contamination. Mixed triarylsulfonium hexafluorophosphate salt(UVI-6990, Union Carbide) was used as a cationic polymerization initiator. The prepared solution was mixed with UVI-6990 before the coating process. Then the solution was deposited on Si(1 00) wafers and fused silica substrates by the spin-coating method. Structure Analysis and Optical Characterization The structural evolution with the hydrolysis and condensation of the solution was examined by using 1H & 13C nuclear magnetic resonance (NMR) spectroscopy (Bruker AM 300). The epoxide polymerization of silica-PEO hybrid materials was examined through the changes of epoxy groups as UV doses. The change of epoxy group was investigated by Fourier-transformed infrared spectroscopy (FT-IR, Bruker EQUINOX55). The optical absorbance was examined using a UV/VIS/NIR spectrophotometer (Shimadzu UV-
446
3101 PC). Also, the refractive index of the films deposited on fused silica was measured by using prism coupling method. RESULTS AND DISCUSSION Preparation of Silica-PEO Hybrid Materials GPTS was hydrolyzed with water by bubbling CO 2 through it, and then the solution was
refluxed at 80 °C for 12hours(refluxed GPTS
OCH 3
H3CCO--Si "iO'•."ý-
0
OCH3
solution). The structural changes with refluxing to the prehydrolyzed GPTS solution was investiga
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