Boscher, N.D.; (2006) Atmospheric pressure chemical vapour deposition of transition metal selenide thin films. Doctoral thesis , University of London.

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Abstract

This thesis investigates the formation of thin films of metal selenides via atmospheric pressure chemical vapour deposition (APCVD). The films and powders produced were characterised by SEM, EDAX/WDX, XPS, XRD, Raman, SQUID, reflectance and absorbance measurements. The APCVD reaction of TiCl4, V(NMe2)4 and NbCl5 with fBu2Se were respectively found to be a convenient route to stable and crystalline titanium, vanadium and niobium diselenide films. The use of VCI4 and VOCI3 showed that they were both found unsuitable for producing VSe2 from the APCVD reaction with 'Bu2Se. Molybdenum and tungsten diselenide films were respectively synthesised using M0CI5 and WC16 with Et2Se. The WSe2 films produced were highly hydrophobic with contact angles for water droplets in the range of 135 - 145 . Furthermore these surfaces were highly adherent for water droplets that did not roll or slide even at a tilt angle of 90 . The deposition of tin monoselenide and tin diselenide films was achieved by the reaction of SnCU with Et2Se. The deposition temperature, flow rates and position on the substrate determined whether mixed SnSe - SnSe2, pure SnSe or pure SnSe2 thin films could be obtained. The characterisation of the films and powders formed from the APCVD or gas phase reaction of Cr02Cl2 and Et2Se confirmed the formation of an unknown solid solution of Cr2Se3_xOx. Cr2Se3-xOx adopts the hexagonal Cr2C>3 structure for a stoichiometry between Cr2C>3 and Cr2Seo.202.g, and the rhombohedral Cr2Se3 structure for a stoichiometry varying from Cr2Seo.302.7 to Cr2Se2.15O0.85- Magnetic studies showed that all the Cr2Se3.xOx compounds formed with the rhombohedral Cr2Se3 structure had an antiferromagnetic ordering with a Neel temperature lower than the expected one for Cr2Se3.

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