Indium nitride has many applications as a semiconductor. High quality films of indium nitride can be grown using Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD), but the availability of precursors and knowledge of the underlaying chemical reactions is limited. In this study the gas phase decomposition of a new indium precursor, N,N-dimethyl-N',N''-diisopropylguanidinate, has been investigated by quantum chemical methods for use in both CVD and ALD of indium nitride. The computations showed significant decomposition at around 250°C, 3 mbar indicating that the precursor is unstable at ALD conditions. A computational study of the surface chemical mechanism of the adsorption of trimethylindium and ammonia on indium nitride was also performed as a method development for other precursor surface mechanism studies. The results show, in accordance with experimental data, that the low reactivity of ammonia is a limiting factor in thermal ALD growth of indium nitride with trimethylindium and ammonia.

Philosophiae Doctor - PhD / When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity. / South Africa

Philosophiae Doctor - PhD / When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell.A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon.In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity.The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped.A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.

Magister Scientiae - MSc / In this study SBA-15 mesoporous silica template was synthesized and used as a sacrificial template in the preparation of ordered mesoporous carbon material. A chemical vapour deposition (CVD) technique using LPG or alternatively sucrose, pyrolyzed upon a mesoporous Si matrix were used to produce nanostructured ordered mesoporous carbon (OMC) with graphitic character after removing the Si template. The sucrose method was found to be a suitable route for preparing OMC. The OMC was used as a conductive three dimensional porous support for depositing catalytic nanophase Pt metal. Deposition of Pt nanoparticles on OMC was accomplished using a CVD method with Pt(acac)2 as a precursor. The synthesized nano-composite materials were characterized by several techniques such as, HRTEM, HRSEM, EDS, XRD, BET, TGA, FT-IR and CV. / South Africa

>Magister Scientiae - MSc / Organic-inorganic lead-based perovskite has exhibited great performance in the past few years. However, the lead (Pb) embedded in those compounds is a significant drawback to further progress, due to its environmental toxicity. As an alternative, tin (Sn) based-perovskites have demonstrated promising results in terms of electrical and optical properties for photovoltaic devices, but the oxidation of tin ion- from stannous ion (Sn2+) to stannic ion (Sn4+) presents a problem in terms of performance and stability when exposed to ambient conditions. A more feasible approach may be in a Pb-Sn binary metal perovskite in pursuit of efficient, stable perovskite solar cells (PSCs) with reduced Pb-content, as compared to pure Pb- or Sn-based PSCs. Here, we report on the deposition of a Pb-Sn binary perovskite by sequential chemical vapor deposition.

Surface treatments are often used in the manufacturing industry to change the surface of a product, including its related properties and functions. The occurrence of degradation and corrosion in surface treatment processes can lead to critical breakdowns over time. Critical breakdowns may impair the properties of the products and shorten their service life, which causes increased lead times or additional costs in the form of rework or scrapping.  Prevention of critical breakdowns due to machine component failure requires a carefully selected maintenance policy. Predictive maintenance is used to anticipate equipment failures to allow for maintenance scheduling before component failure. Developing predictive maintenance policies for surface treatment processes is problematic due to the vast number of attributes to consider in modern surface treatment processes. The emergence of smart sensors and big data has led companies to pursue predictive maintenance. A company that strives for predictive maintenance of its surface treatment processes is Seco Tools in Fagersta. The purpose of this master's thesis has been to investigate the occurrence of critical breakdowns and failures in the machine components of the chemical vapor deposition and post-treatment wet blasting processes by mapping the interaction between its respective process variables and their impact on critical breakdowns. The work has been conducted as a Six Sigma project utilizing the problem-solving methodology DMAIC.  Critical breakdowns were investigated combining principal component analysis (PCA), computational fluid dynamics (CFD), and statistical process control (SPC) to create an understanding of the failures in both processes. For both processes, two predictive solutions were created: one short-term solution utilizing existing dashboards and one long-term solution utilizing a PCA model and an Orthogonal Partial Least Squares (OPLS) regression model for batch statistical process control (BSPC). The short-term solutions were verified and implemented during the master's thesis at Seco Tools. Recommendations were given for future implementation of the long-term solutions. In this thesis, insights are shared regarding the applicability of OPLS and Partial Least Squares (PLS) regression models for batch monitoring of the CVD process. We also demonstrate that the prediction of a certain critical breakdown, clogging of the aluminum generator in the CVD process, can be accomplished through the use of SPC. For the wet blasting process, a PCA methodology is suggested to be effective for visualizing breakdowns.

Graphene has unrivalled properties and is heralded as a revolutionary material for the 21^st century. Chemical vapour deposition (CVD) on metals is a promising method to produce large-area graphene. Controlling the properties of CVD graphene is vital for its integration in a wide-range of future applications. Many factors can influence the CVD growth of graphene and its properties, therefore further investigations will be beneficial to fully understand and control this technique. In this thesis I expand the knowledge about the growth of pure and heteroatom-doped graphene by low pressure chemical vapour deposition (LPCVD) and atmospheric pressure chemical vapour deposition (APCVD) on commercially available Cu and Pt foils. Using a range of characterisation techniques, I investigate the influence of the substrate’s properties and the synthesis conditions on the growth of graphene, in pursuit of improved, controlled or optimised production, which can promote high quality, large-area, single-layer graphene, or other as desired. By characterising the topography, surface roughness, crystallographic orientations, and chemical composition of six Cu foils, I find that their properties vary greatly and this influences the growth of CVD graphene. I elucidate that the commonly used 99.8 % Alfa Aesar Cu foil has a surface coating composed of calcium, chromium, and phosphorus, which detrimentally influences graphene growth. Cleaning Cu foils with CH₃COOH is shown to reduce the concentration of surface contaminants, consequently reducing the nucleation density and increasing the growth rate of CVD graphene. I also demonstrate that the shape, orientation, edge-geometry and thickness of CVD graphene domains can be controlled by the Cu crystallographic orientations. Single layer LPCVD graphene domains align with zigzag edges parallel to a single <101> direction on Cu{111} and Cu{101}, while bilayer domains align to two directions on Cu{001}. Hexagonal APCVD domains also preferentially align with edges parallel to the <101> direction(s). This discovery resolves a key challenge of controlling the orientation of individual graphene domains and opens a new avenue for tailored production of large-area CVD graphene with improved properties. By controlling the synthesis conditions of APCVD graphene on Pt foils I optimise production of ~0.5 mm single layer graphene domains with reduced nucleation density and increased growth rate of ~100 &mu;m/min by synthesis at 1150°C, a higher temperature than previously reported. The absence of large, hexagonal, single-crystal domains on pristine Pt foil, and observation of a reaction between quartz and Pt that promotes hexagonal domains, suggests that a silicon or platinum silicide surface layer may be advantageous for improved growth of graphene. Finally, I demonstrate that the dopant concentration of nitrogen-doped graphene is increased at lower synthesis temperatures and higher NH₃ concentration, up to 1.3 %, but with an associated decrease in the growth rate. Direct visualisation, elemental confirmation, and electronic characterisation of individual nitrogen atoms is shown for the first time using aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy. Boron-doped graphene is also synthesised. The implications of these findings, and many additional minor contributions, are wide-ranging and of considerable importance for the future understanding of CVD growth of graphene on metals, and more generally for the advancement of scientific knowledge for manufacturing large-area graphene. Collectively, these discoveries represent a significant body of work that can improve the efficiency of production and assist with controlling the properties of large-area CVD graphene.

This thesis reports on the chemical vapour deposition (CVD) growth of carbon nanostructures (mainly carbon nanotubes (CNTs)) on perovskite oxide surfaces with the aid of various catalysts. Two types of perovskite oxide, single crystal SrTiO3 (001) and polycrystalline BaSrTiO₃, have been used as catalyst supports (in metal-catalyst-involved CVD routes) or as catalysts (via metal-catalyst-free CVD routes) for the growth of carbon nanostructures. In metal-catalyst-involved cases, SrTiO₃ (001) single crystal has been proven, for the first time, to serve as a substrate for the growth of CNTs. Fe and Ni catalysts can be tailored in a controllable manner on SrTiO3 (001) surfaces prior to the CNT synthesis, forming truncated pyramid shaped nanocrystals with uniform size distributions. The growth of vertically aligned CNT carpets was realised with the aid of Fe on SrTiO₃ (001) surfaces, and it was further found that the CNTs grow via a base growth model. Furthermore, it is possible to grow helical carbon nanostructures on BaSrTiO3 substrates by introducing a Sn catalyst into the system. The synthesised helical carbon nanostructures follow a tip growth mode, where the structural and chemical aspects of catalyst particles gave rise to a wide range of carbon morphologies. CNTs were also grown on single crystal SrTiO₃ (001) and polycrystalline BaSrTiO3 substrates via metal-catalyst-free routes. The surface-roughness-tailored growth of CNTs was surprisingly achieved on a series of engineered SrTiO₃ (001) surfaces, where a correlation between the surface roughness/morphology of the substrates and the relevant catalytic activity was revealed. The growth of CNTs arises because the catalyst fabrication methods lead to the formation of SrTiO₃ asperities with nanoscale curvatures, over which the CNTs are generated throughout a lift-off process. Facet-selective growth of CNTs was observed on polycrystalline BaSrTiO₃ surfaces, where BaSrTiO₃ (110) facets lead to the growth of CNTs on them, whereas the (001) facets result in no growth at all. This observation was further analysed in the content of the adsorption and diffusion of carbon species on distinct BaSrTiO₃ facets, before reaching the conclusion that the formation of CNTs occurs through a metal-free, stack-up process driven by the assembly of the carbon fragments.

This thesis discusses the growth of thin-film silicon layers suitable for solar cells using liquid phase epitaxy and the behaviour of oxide LPCVD silicon nitride stacks on silicon in a high temperature ambient.¶ The work on thin film cells is focussed on the characteristics of layers grown using liquid phase epitaxy. The morphology resulting from different seeding patterns, the transfer of dislocations to the epitaxial layer and the lifetime of layers grown using oxide compared with carbonised photoresist barrier layers are discussed. The second half of this work discusses boron doping of epitaxial layers. Simultaneous layer growth and boron doping is demonstrated, and shown to produce a 35um thick layer with a back surface field approximately 3.5um thick.¶ If an oxide/nitride stack is formed in the early stages of cell processing, then characteristics of the nitride may enable increased processing flexibility and hence the realisation of novel cell structures. An oxide/nitride stack on silicon also behaves as a good anti- reflection coating. The effects of a nitride deposited using low pressure chemical vapour deposition on the underlying wafer are discussed. With a thin oxide layer between the silicon and the silicon nitride, deposition is shown not to significantly alter effective life-times.¶ Heating an oxide/nitride stack on silicon is shown to result in a large drop in effective Lifetimes. As long as at least a thin oxide is present, it is shown that a high temperature nitrogen anneal results in a reduction in surface passivation, but does not significantly affect bulk lifetime. The reduction in surface passivation is shown to be due to a loss of hydrogen from the silicon/silicon oxide interface and is characterised by an increase in Joe. Higher temperatures, thinner oxides, thinner nitrides and longer anneal times are all shown to result in high Joe values. A hydrogen loss model is introduced to explain the observations.¶ Various methods of hydrogen re-introduction and hence Joe recovery are then discussed with an emphasis on high temperature forming gas anneals. The time necessary for successful Joe recovery is shown to be primarily dependent on the nitride thickness and on the temperature of the nitrogen anneal. With a high temperature forming gas anneal, Joe recovery after nitrogen anneals at both 900 and 1000oC and with an optimised anti-reflection coating is demonstrated for chemically polished wafers.¶ Finally the effects of oxide/nitride stacks and high temperature anneals in both nitrogen and forming gas are discussed for a variety of wafers. The optimal emitter sheet resistance is shown to be independent of nitrogen anneal temperature. With textured wafers, recovery of Joe values after a high temperature nitrogen anneal is demonstrated for wafers with a thick oxide, but not for wafers with a thin oxide. This is shown to be due to a lack of surface passivation at the silicon/oxide interface.

<p>In the history of Chemistry, materials chemists have developed their ideas mainly by doing experiments in laboratories. The underlying motivation for this laboratory work has generally been pure curiosity or the ambition to find a solution to a specific problem. Minor changes in the composition or structure of a material can cause major changes in its properties. The development of powerful computers has now opened up the possibility to calculate properties of new materials using quantum mechanical methods.</p><p>The Chemistry of different boron-related materials has been evaluated in this thesis by Density Functional Theory (DFT). Cubic boron nitride (c-BN) is a most interesting material for the microelectronics and tool industry. During thin film deposition of c-BN, several problems arise which most often result in unwanted BN isomorphs. Chemical processes at the (110) and (111) surface of c-BN have been investigated in order to shed light upon some of these complex processes. Typically adsorption energies and surface reconstruction were found to differ significantly between the two surfaces. </p><p>Other materials investigated are layered transition-metal diborides (MeB₂). Incorporation of transition-metal atoms into elemental boron in its most fundamental structure, ά-boron, has also been investigated. The calculations on MeB₂ focused on the stability of the planar compared to the puckered structure of MeB₂. Stability was investigated by calculating Density of States (DOS) and bond populations. Deviations in the cell parameters from their ideal values were also considered. </p><p>A separate project concerned reactivity of the TiB₂(001) surface. Molecular and dissociated adsorption energies and adsorption geometries were calculated for H₂, H₂O and O₂. It was concluded that the titanium surface was more reactive than the boron surface and that the adsorption energies were comparable to or stronger than other well known surface-active compounds like TiO₂.</p>