Sol-gel preparation of silicon nitride materials

Abstract

Sol-gel techniques are mainly used for oxides but are of growing interest for non-oxide materials. They allow formation of solid materials through gelation of precursor solutions and can be used to control composition and to produce a large number of useful morphologies such as films, monoliths, aerogels, foams and materials with ordered pores on various length scales. Often the synthesis of non-oxide materials using sol-gel methods has focused on producing powders for applications such as catalysis, where controlled porosity and basic catalytic sites are the point of interest.
In this thesis, formation of silicon nitride based materials as thin films, aerogels, inverse opal films and phosphor powders have been synthesised using non-oxide sol-gel methods. For thin films formation of amorphous silicon nitride, [Si(NHMe)4] solution in tetrahydrofuran (THF) with ammonia in the presence of a triflic acid catalyst was used. The sols formed from this mixture were used to make films using a simple dip coating technique. A number of coating and pyrolysis regimes have been compared. Aerogels were prepared through a small change in the sol preparation conditions leading to bulk gelation, supercritical drying was then applied to these gels. For templated films, the precursor was dissolved in hexane and polystyrene array tiles were coated with that solution using dip, drop or capillary techniques. The effects of several coating techniques and different pyrolysis temperatures on film morphologies have been studied.
In addition, the sol-gel process offers an effective and controllable means of adding elements into Si-N matrix with the aim of combining the low reactivity of silicon nitride materials with other functional properties. Co-ammonolysis of a rare-earth amide with a silicon amide is shown to be an effective route to phosphor materials. Amorphous Tb:SiNx composition show strong photoluminescence and the variation in PL intensity with composition has been probed.

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ORCID for Andrew Hector: orcid.org/0000-0002-9964-2163

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