Photopatterning of Metal Oxide Catalyst in Porous Glass
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PHOTOPATTERNING OF METAL OXIDE CATALYST IN POROUS GLASS John C. Luong, Nick F. Borrelli Jan W.H. Schreurs and Dave L. Morse Corning Glass Works R&D Laboratory Corning, N.Y. 14831 - USA INTRODUCTION It
is well recognized that Vycor brand porous glass impregnated with a
photosensitive organometallic compound can be used to produce refractive index patterns upon photolysis [1-31. For instance, a metal carbonyl such as Mn2 (CO) 1 0 adsorbed into the porous glass matrix has been used to photopattern high resolution phase gratings albeit with low diffraction efficiencies due to the low refractive index change (an) so produced [1]. The use of photochemical methods to alter locally the kinetic barrier for area-selective deposition of thin films is emerging as a new class of light-induced chemical processes on surfaces [4]. We wish to describe an approach whereby the surface chemistry is photochemically modified for subsequent reactions which would lead to a dramatic enhancement of the refractive index pattern in porous glass. This technique is deemed useful for recording of phase information where the variation of index profile with thickness due to lensing effect may lead to distortion and ultimately decrease of diffraction efficiency (5]. A somewhat related latent imaging technique has been reported by Chandross et al., [6], to alleviate the problem mentioned above for recording volume holograms in porous glass. In their process, a pattern of an initiator was photochemically produced by selectively destroying some of the initiators adsorbed in porous glass and subsequent development of the latent image was achieved by a uniform light exposure of the porous glass backfilled with a monomer. In our technique, the catalyst pattern initially produced by photolysis is a metal oxide, hence, its dimensional stability offers high
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spatial resolution capability. The subsequent catalytic surface reaction also leads to a metal oxide derivative allowing significant index enhancement with no loss of resolution. EXPERMENTAL METHODS The procedure for photopatterning of the metal oxide was substantially the same as that in [1]. Vycor brand porous glass (Corning Code 7920), a leached borosilcate glass with a narrow distribution of pore sizes centered near 50 A and a pore volume of the order of 30% (See Fig. 1) was used as the porous glass matrix for impregnating organometallic compounds. These organometallic compounds which include carbonyls and cylclopentadienyl complexes of transition metals, and organotin were used as received without further purification. They were introduced into 0.5 mm or 1 mm thick glass samples (2.5cm X 2.5 cm) either by vapor diffusion or as diluted CH2 CI2 solutions. Either direct patterning with a broad band Ar ion laser, a Liconix single mode He-Cd laser (325 and 442nm) or conventional UV exposure through photomasks were used for photopatterning.
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