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The thesis examines ion-assisted physical-vapour deposition (PVD) of thin coatings on non-flat three-dimensional samples, concentrating on the case of free-standing edges and comers. Changes in the electric field in the vicinity of sharp edges lead to local changes in the ion bombardment (ion flux and angle of incidence) which can significantly affect the ion-surface interaction and thus the properties and the performance of the coatings growing in the edge region. This work presents a detailed electron microscopy study of the edge-related changes in the coating properties and develops a physical model to explain and quantify the effects. The problem is studied on a system typical for industrial coating of cutting tools used in dry high speed cutting: TiAlN-type coatings (TiAlN/VN and TiAlCrYN) deposited on wedge-shaped samples by closed-field unbalanced magnetron sputtering (UBM), using high-flux, low-energy Ar+ ion irradiation (J[i]/J[me]~4, E[i] = 75-150 eV). The morphology and composition of the coatings in the edge region, as a function of the edge geometry (angle and radius of curvature) and the deposition conditions (substrate bias), is studied using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM+EDX). The internal structure of the coatings growing on sharp edges is examined by transmission electron microscopy (TEM). A detailed theoretical analysis of the effects, based on the simulations of the plasma sheath around the samples and the resulting ion bombardment distribution, is presented. A direct relationship between the experimentally observed magnitude and spatial extent of the changes in the edge region and the simulated characteristics of the plasma sheath around the edges is shown.

A critical stage of the combined steered arc and unbalanced magnetron process is the metal ion pre-treatment which improves the adhesion of the TiN coating. In this study, Conversion Electron Mossbauer Spectroscopy (CEMS) has been used to investigate surface interactions in a commercial Arc Bond Sputtering (ABS) coating system. A novel application of the Liljequist theory of CEMS has been used to determine ion etch rates for deposited natural iron on stainless steel substrates, for various Ti ion pre¬treatment processes. The approach has estimated an etch rate of 60 nm min.'1 for samples positioned without substrate rotation at a cathode-sample distance of 250 mm. This has been calculated to correspond to a bias current density of 6.68 Amps m-2. Similar experiments involving modes of rotation yield an average etch rate of approximately 40 nm min.-1 To detect small quantities of iron containing phases formed during a pre-treatment process it has been necessary to enrich substrates with the Mossbauer isotope, 57Fe to achieve greater surface sensitivity. The enrichment used the technique of the deposition of an estimated 25 nm of 57Fe on polished mild steel substrates followed by annealing to generate an 57Fe diffusion profile into the near surface region. A diffusion model has been used to predict the 57Fe depth profile due to the adopted annealing process parameters. Verification of the estimated thickness of the deposited 57Fe overlayer and the diffusion profile has been provided by SIMS and SNMS. Using the 57Fe enriched mild steel samples, CEMS has investigated the formation of iron- titanium phases after a typical industrial ten minute pre-treatment process using substrate rotation, at a substrate bias voltage of -1200 V. Significant phase formation of both crystalline Fe[x]Ti[1-x] and amorphous Fe[x]Ti[1-x] have been identified. The formation of the crystalline phase has been confirmed by XRD. Using a model of the 57Fe isomer shift dependence of x, in amorphous alloys yielded x=0.31 +/-0.08 for Fe[x]Ti[1-x] Further experiments using an estimated 25 nm of 57Fe deposited on mild steel without annealing, showed the presence of magnetite and a small quantity of crystalline FeTi for a 25 s pre¬treatment process. After a 300 s pre-treatment time the oxide layer is removed and significant quantities of both crystalline and amorphous FeTi are formed. CEMS has also showed increased 57Fe removal at a 6 x 10-5 mbar Ar operating pressure within the coating chamber compared with a pre-treatment performed at a higher Ar pressure of 3 x 10-3 mbar, showing the greater effect of the Ti ion etching under these conditions. During the experiments performed at different Ar pressures, CEMS also identified iron carbonitride phases. Similar phases have also been identified in the early growth stages of a compound layer in a process performed using a modified Balzers coating system. CEMS has proved to be a powerful technique, enabling the investigation of surface interaction phenomena occurring in the near surface region of 57Fe enriched substrates treated by Physical Vapour Deposition (PVD) processes. The information provided by the technique makes it strategically important in the future research of interface regions generated by PVD processes.

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Metal-containing polymer thin films are known to possess interesting electrical, magnetic, optical or barrier properties. Such coatings can be deposited by plasma assisted chemical vapour deposition (PACVD). This technique comprises the fragmentation and rearrangement of metallorganic precursors within a low pressure non-equilibrium electrical discharge. In this work, the deposition of titanium containing species embedded into a polymeric network from titanium tetraisopropoxide (TiTP), Ti[OCH(CH(_3))(_2)](_4), and tetrakis (dimethylamido) titanium (TMT), Ti[N(CH(_3))(_2)](_4), precursors has been investigated as a function of glow discharge power and substrate location. In addition these precursors have been mixed with hydrogen and ammonia gases during PACVD. These metal-containing plasma polymers layers have been characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and atomic force microscopy (AFM).It has been demonstrated that Ti02/polymer composite layers can be produced using the TiTP precursor with a wide range of stoichiometries. The mixing of hydrogen gas with TiTP create films which are stable towards oxidation and aging. TiTP/ammonia mixtures produced Ti(0,N)/polymer films which contained Ti-N bonds. Injection of TMT into a glow discharge has been found to result in a non-thermally assisted intramolecular alkyl (3-hydrogen activation mechanism to produce Ti(0,C,N)/polymer composite films. The film composition is found to be independent of glow discharge power beyond 5 W. Mixing with hydrogen gas lowers the carbon content due to recombination reactions competing with plasma polymerization. TMT/ammonia mixtures result in a gas phase transamination reaction prior to and during plasma activation causing a drop in the total carbon content due to replacement of the -N(CH(_3))(_2) ligand by –NH(_x).

Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the Faculty of science Department of Chemistry University of the Witwatersrand. November 2016. / An overview of the evolution of synthesis and applications of indium nitride and gallium nitride in modern science and technology is provided. The working principles and parameters of chemical vapour deposition (CVD) synthesis technique are explored in this study. In this study indium oxide, indium phosphate, indium nitride and gallium nitride materials are prepared by CVD. The versatility of CVD on the fabrication of one-dimensional (1D) structures is portrayed. Both change in dimensionality and change in size are achieved by a CVD technique. 1D indium oxide (In2O3) nanowires, nanonails and nanotrees are synthesised from vapour deposition of three-dimensional In2O3 microparticles. While 1D structures of the novel indium phosphate known as triindium bisphosphate In3(PO4)2 were obtained from reactions of In2O3 with ammonium phosphate. The effect of temperature, activated carbon and the type of indium precursor on dimensionality of the synthesized materials is studied. The inter-dependency between temperature and precursors is observed. The presence of activated carbon at high temperatures encouraged growth of secondary structures via production of excess indium droplets that act as catalysts. The combination of activated carbon and high temperature was found responsible for the novel necklace, nanonail, nanotree and nanocomb structures of In2O3. Indium nitride (InN) has for the first time been made by a combined thermal/UV photoassisted process. In2O3 was reacted with ammonia using two different procedures in which either the ammonia was photolysed or both In2O3 and ammonia were photolysed. A wide range of InN structures were made that was determined by the reaction conditions (time, temperature). Thus, the reaction of In2O3 with photolysed NH3 gave InN rod like structures that were made of cones (6 h/ 750 oC) or discs (6 h/ 800 oC) and that contained some In2O3 residue. Photolysis of In2O3 and NH3 by contrast gave InN nanobelts, InN tubes and pure InN tubes filled with In metal (> 60 %). The transformation of the 3D In2O3 particles to the tubular 1D InN was monitored as a function of time (1-6 h) and temperature (700-800 oC); the product formed was very sensitive to temperature. The band gap of the InN tubes was found to be 2.19 eV and of the In filled InN tubes to be 1.89 eV. Gallium nitride (GaN) and indium gallium nitride (InGaN) nanostructures were synthesized from thermal ammonification of gallium oxide (Ga2O3) as well ammonification of a mixture of In2O3 and Ga2O3 respectively. The effect of temperature on preparation of high purity GaN was studied. The GaN materials synthesized at 800 °C showed a mixture of the gallium oxide and the gallium nitride phases from the XRD analysis. However at temperatures ≥ 900 °C high quality GaN nanorods were obtained. The band-to-band ultraviolet optical emission value of 3.21 eV was observed from the GaN nanorods. However, the preparation of InGaN was complicated by the thermally stable In2O3. At lower temperatures inhomogeneous materials consisting of GaN nanorods and In2O3 were obtained. While at high temperatures (≥ 1050 °C) InGaN was obtained. However because indium has a high vapour pressure and a low melting point only a minute amount of it was incorporated in the crystal lattice. Hexagonally shaped nanoplates of In0.01Ga0.99N were successfully obtained. A shift in optical emission to longer wavelengths was observed for the InGaN alloy. A blue optical emission with the energy value of 2.86 eV was observed for the InGaN nanoplates. The two n-type group III-nitrides (InN, GaN) prepared in this study were used for the detection of CO, NH3, CH4 and NO2 gases in the temperature range between 250 and 350 °C. The InN sensor and GaN sensor responses were compared to the response of the wellestablished n-type SnO2 sensor under the same conditions. All the three sensors responded to all the four gases. However, InN and GaN were much more selective in comparison to SnO2. InN sensitivity to CO at 250 °C surpassed its sensitivity to any other gas at the studied temperature range. Its response towards CO at 250 °C was about five times more than that of SnO2 towards CO at the same temperature. While, GaN was the best CH4 sensor at 300 °C in comparison to InN and SnO2 sensors at all temperatures. Meanwhile SnO2 responded remarkably to both NH3 and CO across the studied temperature range with its performance improving with increasing temperature. The ability for InN to respond to both NH3 and NO2 at 250 °C opens up the possibility for an application of InN as an ammonia sensor in diesel engines. InN and SnO2 sensors were found susceptible to humidity interference in a real environmental situation. On the contrary, GaN sensor presented itself as an ideal candidate for indoor and outdoor environments as well as in bio-sensors because it showed robustness and inertness towards humidity. InN and GaN by showing activity at high temperatures only, presented themselves as good candidates for in-situ high temperate gas sensing applications. Response and recovery times for all sensors showed improvement with increasing temperature. / MT2017