Organometallic Metallorganic Chemical Vapor Deposition MOCVD

2 Organometallic (Metallorganic) Chemical Vapor Deposition (MOCVD) 

MOCVD is traditionally a planar surface technique used for the deposition of very thin layers of materials from the vapor phase. This technique offers a wide versatility in the synthesis of dusters in zeolites. The advantage of this technique, in comparison with the ion exchange technique, is that the location of the clusters in the zeolites can be easily controlled by the choice of organometallic precursors e.g. a metal carbonyl or metal alkyl), such that they can be sterically restricted to large channels or cages. For example, with zeolite Y, one can select 

Intrazeolitic MOCVD chemistry is relatively new. A synthetic chemistry for the preparation of encaged clusters from metd alkyl precursors (alkyl is often methyl) has been suggested by a few researchers. [220, 221] In the first step, a vapor phase precursor is introduced into the zeolite supercages. One of the methyl groups can then react with a Brpnsted add site, thereby produdng CH4 and a concurrent anchoring of the organometallic precursor to the zeolite internal surface (Eq. 4.16, Z represents the zeolite framework). 

The semiconductor clusters can then be formed in the zeolite by a ship-in-a-bottle synthesis (Eqs. 4.17 and 4.18). Here, the precursor anchored in the supercages of zeolite is allowed to react with an appropriate reagent e.g. H2S, H2Se, or PH3) at a slightly elevated temperature whereby the remaining methyl groups of the anchored precursor are released as CH4 and a labile spedes is formed (Eq. 4.17, X = S, Se, or P). Condensation reactions then follow (Eq. 4.18). 

The reaction is driven to com]detion when excess H2S or H2Se is removed, leaving the semiconductor dusters in the cages. 

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