Peters, Emily Sarah; (2004) Precursor synthesis and chemical vapour deposition of transition metal sulfides. Doctoral thesis , University College London.

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Abstract

This thesis investigates the formation of thin films of early transition metal sulfides via a range of chemical vapour deposition (CVD) processes. Three different CVD routes were used; low pressure (LP)CVD, aerosol assisted (AA)CVD and atmospheric pressure (AP)CVD. Both single-source and dual-source precursor systems were employed. The synthesis of transition metal thiolates of titanium, zirconium, niobium and tantalum were investigated in order to produce single-source precursors to metal disulfide films. The primary synthetic methodologies used include substitution reactions of transition metal amides with thiols or via salt metathetical reactions of transition metal chlorides with thiols in the presence of a base. A range of transition metal thiolate compounds were made and [Me2NH2][Ti(SCH2CF3)6], [TiCl(SC5H4N)3], [TiCl(SC4H3N2)], [Me2NH2][Zr2(u2-StBu)3(StBu)6] and [Ta(StBu)2(NMe2)3] were crystallographically characterised; their suitability for use as single-source precursors being assessed by thermal gravimetric analysis and differential scanning calorimetry. Titanium disulfide (TiS2) thin films were deposited from the titanium thiolate precursors via LPCVD at 500 or 600°C. Films were analysed using Raman microscopy, X-ray diffraction, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy. The morphology of the films was studied by scanning electron microscopy. The optical properties of the films have been investigated and their band gaps calculated. The first reported growth of transition metal (Ti, Nb, Ta) disulfide films via AACVD is described. A novel pseudo dual source route involving the in situ generation of the transition metal thiolate was used; this has been compared with the traditional route from the isolated single source precursor. The effect of solvent on films produced is reported. TiS2 films have been deposited from the APCVD reaction of TiCl4 and tBu2S2, HS(CH2)2SH or S(SiMe3)2 over a range of temperatures. The APCVD reaction of TiCl4 and tBU2S2 gave TiS2 films above 400 °C and below this TiS3 films were formed. The deposition of WS2 films from the APCVD reaction of WCl6, W(CO)6 or WOCl4 and either tBuSH or HS(CH2)2SH over a range of temperatures is reported. The APCVD reaction of NbCl5 and sulfides (tBu2S2 or S(SiMe3)2) has been investigated and the formation of a new lT-NbS2 polytype is described. The APCVD reaction of thiols (tBuSH or HS(CH2)2SH) with NbCl5 resulted in 3R-NbS2 thin films.

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