Price, Louise Susan; (2001) Atmospheric pressure chemical vapour deposition of tin sulfide films on glass. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis investigates the formation of films of tin sulfides on glass by the chemical vapour deposition process. Two methods were used. These were atmospheric pressure chemical vapour deposition with either thermal delivery or aerosol delivery. The primary system investigated was the reaction of tin tetrahalides with hydrogen sulfide. This was found to form all three binary phases of tin sulfide, in high purity. The factor which had highest influence on the phase deposited was the deposition temperature. In general, it was found that below 450 °C tin(IV) sulfide was formed, above 550 °C tin(II) sulfide was formed and at intermediate temperatures mixed valent tin(II) tin(IV) trisulfide was formed. Single source precursors to tin sulfides were also investigated. These included tin thiolates and tin dithiocarbamates. The tin thiolates studied were tin(IV) thiolate, tin(IV) η2-ethane 1,2-dithiolate and tin(IV) 2,2,2-trifluoroethane thiolate. The tin(II) thiolate [Sn(SCPh3)2] was also studied, but no film could be formed. The only homoleptic dithiocarbamate studied was [Sn(S2CNEt2)4], although a large number of alkyl tin dithiocarbamates were investigated. These were [R3Sn(S2CNR'2)] R=Me, nBu; R'=Me, Et and asymmetric dithiocarbamate precursors [Me3SnS2CNMeBu] and [BuSn(S2CNMeBu)3], In almost all cases addition of hydrogen sulfide was necessary to make tin sulfide films. This was because, as mass spectrometry showed to be the case for [Sn(SPh)4], two thiolate groups may be lost as an RSSR moiety. A small number of reactions were successful in forming tin sulfide without H2S. Tin(IV) η2-ethane 1,2-dithiolate was the most successful single source precursor, and this was attributed to the inability to lose an RSSR entity. Some precursors were investigated with a view to forming tin oxide sulfide and tin sulfide selenide. To make tin oxide sulfide, tin tetrachloride, hydrogen sulfide and water were reacted together. Subsequently, single source precursors [Cl2Sn(SCH2C(O)OMe)2] and [tBu2Sn(O-OCH2CH2S)] were investigated. To form tin sulfide selenides [Sn(SPh)4] and [Sn(SePh)4] were reacted together. Ligand exchange formed [Sn(SPh)n(SePh)4-n] (n=0-4) with all compounds in the statistical ratio. This was then investigated by CVD. Visual inspection, Raman microscopy and EDAX were used to investigate all films produced. The morphology of each film was observed by SEM, and particles were of the order 0.5 - 5 μm in dimension. A number were also examined by X-ray diffraction and X- ray Photoelectron Spectroscopy. Band gaps were measured for some of the films.

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