Elwin, Gareth Steven; (1999) Atmospheric pressure chemical vapour deposition of the nitrides and oxynitrides of vanadium, titanium and chromium. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A study has been made into the atmospheric pressure chemical vapour deposition of nitrides and oxynitrides of vanadium, titanium and chromium. Vanadium tetrachloride, vanadium oxychloride, chromyl chloride and titanium tetrachloride have been used as precursors with ammonia, at different flow conditions and temperatures. Vanadium nitride, vanadium oxynitride, chromium oxynitride, titanium/vanadium nitride and titanium/chromium oxynitride have been deposited as thin films on glass. The APCVD reaction of VCl4 and ammonia leads to films with general composition VNxOy. By raising the ammonia concentration so that it is in excess (0.42 dm3 min-1 VCl4 with 1.0 dm3 min-1 NH3 at 500 °C) a film has been deposited with the composition VN0.8O0.2. Further investigation discovered similar elemental compositions could be reached by deposition at 350 °C (0.42 dm3 min-1 VCl4 with 0.5 dm3 min-1 NH3, followed by annealing at 650 °C, and cooled under a flow of ammonia. Only films formed below 400 °C were found to contain carbon or chlorine (<5 %). The reaction of VOCl3 and ammonia also lead to films of composition VNxOy the oxygen to nitrogen ratios depending on the deposition conditions. The reaction of VOCl3 (0.42 dm3 min1) and ammonia (0.2 dm3 min-1) at 500 °C lead to a film of composition VN0.47O1.06. The reaction of VOCl3 (0.42 dm3 min-1) and ammonia (0.5 dm3 min-1) at 650 °C lead to a film of composition VN0.63O0.41. The reaction of chromyl chloride with excess ammonia led to the formation of chromium oxide (Cr2O3) films. Mixed metal films were prepared from the reactions of vanadium tetrachloride, titanium tetrachloride and ammonia to prepare VxTiyNz and chromyl chloride, titanium tetrachloride and ammonia to form TiCrxOyNz. Both reactions produced the intended mixed coating but it was found that the vanadium / titanium nitride contained around 10 % vanadium whatever the conditions used. Oxygen contamination affected the films to a lesser extent than the single metal films. The reaction of VCl4 (0.33 dm3 min-1) and TiCl4 (0.1 dm3 min-1) with NH3 (0.5 dm3 min-1), at 550 °C lead to a film of composition Ti0.75V0.1NO0.15 Chromium / titanium oxynitride films contained minimal titanium (<10 %), but in contrast to the chromyl chloride / ammonia reaction nitrogen incorporation was good. The reaction of CrO2Cl2 (0.25 dm3 min-1) and TiCl4 (0.1 dm3 min-1) with NH3 (0.5 dm3 min-1), at 600 °C lead to a film of composition CrTi0.1N0.5O0.75. All films have been investigated for their use as heat control mirrors, with vanadium / titanium nitride films and vanadium oxynitride films providing results of interest to the solar control industry. A film prepared by the reaction of VOCl3 (0.42 dm3 min-1) and NH3 (0.8 dm3 min-1) at 500 °C for 30 seconds resulted in a film with nearly 657c IR reflectance, good visual transmission and an attractive lustre. A film deposited from VCl4 (0.33 dm3 min-1), TiCl4 (0.1 dm3 min-1) and NH3 (0.6 dm3 min-1) at 550 °C for 30 seconds produced a film of equivalent heat mirror quality. Films deposited from CrO2Cl2 and NH3 were found not to confer heat control mirror qualities.

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