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.

Physical vapour deposition (PVD) techniques used for the application of advanced surface engineering materials have been developed over many years, but only in about the last 10 years has the unbalanced magnetron sputtering (UBMS) PVD technique been developed and emerged as one of the most promising techniques for depositing reliable and high quality films used in industrial production. Hard coatings have been studied for many years for the purpose of improving the performance of various tools, mechanical parts, and engineering components. The most studied binary hard coatings (such as stoichiometric titanium nitrides and titanium carbides) and the ternary hard coating (such as titanium carbonitride) have been developed for wear resistance for many years. Although many investigations have been made into the production of coatings with stoichiometric phases, it is both scientifically and commercially interesting to investigate the production and reproducibility of the pure titanium sub-nitride Ti2N films. The first results in chapter 5 describe work carried out to investigate the effect of nitrogen and carbon concentration within the films and was a prelude to the main activity of the development of Ti2N films using commercial conditions. The work for Ti2N was carried out without substrate rotation in the UBMS coating process. The static deposition processes were studied to give a better understanding of the effect of partial pressures on the compositions of the Ti-N films. The phase development as a function of the composition of the films was investigated. The main contribution during this procedure was to achieve a suitable range of nitrogen partial pressure by which the films containing pure Ti2N phase were produced using a UBMS deposition technique. The nitrogen content of the film was very sensitive to variation in nitrogen partial pressure and the nitrogen concentration influenced the phases developed in the films. The reproducibility of the pure Ti2N phase was also discussed in this initial work. A series of extensive experiments were conducted to investigate the formation of Ti2N phase in the UBMS deposition processes using one to three fold rotations. The nitrogen partial pressure of the deposition process was basically determined from the results of the initial work. The effect of substrate rotation on the film composition during processing was studied. In general the film deposited using substrate rotation consisted of different composition using the same chamber condition in one process in which the nitrogen content of the coating increased from one fold rotation to three fold rotation. The film containing dominant eTi2N phase could be produced on a sample using three fold rotation in a process whilst the multiphase compositions (aTiN0.3 + eTi2N) were developed on the sample using the one and two fold rotations in the same process. Characteristics of the eTi2N films and the films containing multiphase compositions were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), glow discharge optical emission spectrometer (GDOES), X-ray diffraction (XRD), and a variety of mechanical testing instruments. The eTi2N films have very smooth surface, very dense and fine columnar structure, relatively high hardness, and excellent adhesion with the substrate. The drilling tests using coated high speed steel drills compared the coatings containing eTi2N phase with those containing a single TiN phase and showed excellent wear resistant results.6.

The Physical Vapour Deposition (PVD) magnetron sputtering process is one of the widely used techniques for depositing thin film coatings on substrates for various applications such as integrated circuit fabrication, decorative coatings, and hard coatings for tooling. In the area of coatings on cutting tools, tool life can be improved drastically with the application of hard coatings. Application of coatings on cutting tools for various machining techniques, such as continuous and interrupted cutting, requires different coating characteristics, these being highly dependent on the process parameters under which they were formed. To efficiently optimise and customise the deposited coating characteristics, PVD process modelling using RSM methodology was proposed. The aim of this research is to develop a PVD magnetron sputtering process model which can predict the relationship between the process input parameters and resultant coating characteristics and performance. Response Surface Methodology (RSM) was used, this being one of the most practical and cost effective techniques to develop a process model. Even though RSM has been used for the optimisation of the sputtering process, published RSM modelling work on the application of hard coating process on cutting tool is lacking. This research investigated the deposition of TiAlN coatings onto tungsten carbide cutting tool inserts using PVD magnetron sputtering process. The input parameters evaluated were substrate temperature, substrate bias voltage, and sputtering power; the out put responses being coating hardness, coating roughness, and flank wear (coating performance). In addition to that, coating microstructures were investigated to explain the behaviour of the developed model. Coating microstructural phenomena assessed were; crystallite grain size, XRD peak intensity ratio I111/I200 and atomic number percentage ratio of Al/Ti. Design Expert 7.0.3 software was used for the RSM analysis. Three process models (hardness, roughness, performance) were successfully developed and validated. The modelling validation runs were within the 90% prediction interval of the developed models and their residual errors compared to the predicted values were less than 10%. The models were also qualitatively validated by justifying the behaviour of the output responses (hardness, roughness, and flank wear) and microstructures (Al/Ti ratio, crystallographic peak ratio I111/1200, and grain size) with respect to the variation of the input variables based on the published work by researchers and practitioners in this field. The significant parameters that influenced the coating hardness, roughness, and performance (flank wear) were also identified. Coating hardness was influenced by the substrate bias voltage, sputtering power, and substrate temperature; coating roughness was influenced by sputtering power and substrate bias; and coating performance was influenced by substrate bias. The analysis also discovered that there was a significant interaction between the substrate temperature and the sputtering power which significantly influenced coating hardness, roughness, and performance; this interaction phenomenon has not been reported in previously published literature. The correlation study between coating characteristics, microstructures and the coating performance (flank wear) suggested that the coating performance correlated most significantly to the coating hardness with Pearson coefficient of determination value (R2) of 0.7311. The study also suggested some correlation between coating performance with atomic percentage ratio of Al/Ti and grain size with R2 value of 0.4762 and 0.4109 respectively.

Solid state synthesis of layered, rotationally disordered intergrowths consisting of rock salt (MX) and hexagonal (TX2) constituents in various sequences [(MX)1+δ]m[TX2]n is carried out by developing structural and compositional prototypes of the desired product, using fine control of the elemental reactants and then annealing at low temperature to facilitate self-assembly. (M = Sn, La, Eu; T = V, Mo.) The remarkable rotational disorder in these systems - in contrast to traditional misfits - and their proven applications in thermal, electrical and thermoelectric disciplines make them a useful group of materials for demonstrating control of reaction pathways of solid state reactions using low temperatures and short times. The synthesized materials are structurally characterized using X-ray diffraction (XRD), X-ray reflectivity (XRR), and Scanning Transmission Electron Microscopy (STEM). Electrical characterization is carried out on patterned samples using the Van der Pauw method of resistivity and the Hall effect method. Composition of the samples is determined using wavelength dispersive electron probe microanalysis (EPMA). Time domain thermoreflectance is used to determine the cross plane thermal conductivity. The family of [(SnSe)1.05]m(MoSe2)n (m = n = 1, 2, 3, 4), which possess the same composition but different unit cell thicknesses, shows that there is no correlation between c-axis unit cell thickness and cross plane thermal conductivity. The family of structural isomers [(SnSe)1.05]4[MoSe2]4, [(SnSe)1.05]3[MoSe2]3[(SnSe)1.05]1[MoSe2]1, [(SnSe)1.05]3[MoSe2]2[(SnSe)1.05]1[MoSe2]2, [(SnSe)1.05]2[MoSe2]3[(SnSe)1.05]2[MoSe2]1,[(SnSe)1.05]2[MoSe2]1[(SnSe)1.05]1[MoSe2]2[(SnSe)1.05]1[MoSe2]1 and [(SnSe)1.05]2[MoSe2]2[(SnSe)1.05]1[MoSe2]1[(SnSe)1.05]1[MoSe2]1 have the same c-axis lattice thickness and absolute composition but have different numbers of [(SnSe)1.05]/[MoSe2] interfaces. Thermal conductivity studies carried out on these showed no correlation with the interface density. (LaSe1-x)1.17(VSe2-y)n (n = 2, 3, 4) feature a family of compounds that self-assemble at higher than usual temperatures. They form non-stoichiometric moieties with unique structural proclivities including La vacancies and V interstitials compared to other ferecrystals or previous misfits. The designable electrical properties show evidence of charge transfer. (EuSe)1+δ(VSe2)n (n = 1, 2, 3) is a family of materials that complements the investigation of Ln-based ferecrystals. They show evidence of multiple M oxidation states. These compounds highlight the use of rational design of structure and composition to tune properties. This dissertation includes previously published and unpublished co-authored material. / 10000-01-01

Evaluation of the wet etching properties of several different thin film oxidesgrown by physical vapour deposition was performed in this work. MgO, Al2O3,SiO2, TiO2, HfO2 ZrO2 and Y2O3 were coated on two types of substrates; Si andborosilicate glass and etching tests were performed in different etchingsolutions. MgF2 thin films have also been evaluated. Important aspects of the choice of the thin films was taken into account in orderto match to good optical properties such as refractive index (n), extinction coefficient (k) and optical thickness (TP) as well as good chemical properties in the wet etching process. A description is made of the physics of optical filters and how a combination of different oxides stacked onto each other can create interference filters. A description of the manufacturing process of the thin films where physical vapour deposition (PVD) was used is presented. Thermal shift of the optical spectra caused by porous coatings was investigated and analyses of the thin films by ellipsometry, surface profilometry and transmission spectrophotometry have been performed. The wet etching properties were evaluated by monitoring the transmission insituon transparent borosilicate glass substrates. A method of how to measure the wet etching rate for different thin films is described. A computer software was used to calculate the Pourbaix diagrams in order to understand the chemical behaviour of the etching solutions. The pH can have a significant impact on the etching behaviour. In case of TiO2, it can be dissolved in an alkaline solution of H2O2. The catalytically process behind this is evaluated. Etching rate for both Y2O3 andSiO2 were matched by adjusting the etchant concentration as a case example. The group IVB oxides are difficult to etch. The catalytic etching of TiO2 with peroxide is slow but detectable. Al2O3, Y2O3 and MgO are reasonably easy to etch but have too low refractive indices to be useful in multilayer optical filters. The In-situ etching instrument was found to be very useful for measuring etching rates. / Utvärdering av våtkemiska egenskaper för flera olika oxidtunnfilmer utfördes idetta arbete på tunnfilmer av MgO, Al2O3, SiO2, TiO2, HfO2 ZrO2 and Y2O3 vakuumdeponerade på både kiselwafers och borosilikatglas. Etstester gjordes med ett flertal etslösningar. Även MgF2-tunnfilmer utvärderades. Både optiska och kemiska egenskaper togs i beaktande vid utvärderingen av tunnfilmerna. De optiska lagar som gäller för tunnfilmer redovisas, bl a hur kombinationer av olika oxider kan skapa interferrensfilter. En beskrivning av tillverkningsprocessen varvid PVD användes presenteras. Termiskt skift av det optiska transmissionsspektrat orsakat av porositet undersöktes. Analyser av tunnfilmerna med ellipsometri, profilometri och transmissions spektroskopi utfördes. Våtetsningsegenskaperna utvärderades genom att mäta in-situ vid etsprocessen på transparenta borosilikatglassubstrat. Metoden för att mäta etshastigheten för olika oxider är beskriven. Datorberäkningar av pourbaixdiagram användes för att skapa en förståelse av de kemiska egenskaperna för etslösningarna. Etsegenskaperna påverkas till stordel av lösningens pH. TiO2 kan etsas i basisk lösning av peroxid. Denna process utvärderades, likaså utvärderades etshasigheten för Y2O3 och SiO2 för att erhålla matchande par avoxider som en fallstudie. Grupp IVB oxiderna är mycket svåra att etsa. Katalytisk etsning av TiO2 med peroxid är detekterbar men långsam. Al2O3, Y2O3 och MgO är förhållandevis enkla att etsa men har för låga brytningsindex för att var praktiskt använbara i optiska multilagerfilter. In-situ etsinstrumentet befanns vara ett utmärkt verktyg för att mäta etshastigheten för tunnfilmer.

In this thesis, we have developed a reproducible, safe, and scalable sequential thermal vapour deposition (STVD) method for the growth of quality 3D halide perovskite (HaP) thin films. High-quality methylammonium lead tri-bromide (MAPbBr3), methylammonium lead tri-iodide (MAPbI3), and methylammonium lead bromide-iodide (MAPb(I1-xBrx)3) thin films have been optimised using the STVD technique. The structural, optical, morphological, and electrical properties were tuned by varying the thicknesses of the organic (MAI, MABr) and inorganic (PbI2, PbBr2) precursor thin films and post-annealing times of the HaP. X-ray diffractograms confirmed the cubic MAPbBr3 structure with the Pm¯3 m space group, tetragonal MAPbI3 crystal structure with I4/mcm space group, and the tetragonal MAPbI3 structure being transformed to cubic MAPbBr3 system as MAPb(I1-xBrx)3 (x=0.89-0.95) forms. UV-Vis spectra revealed broad absorption bands with a redshift in absorption onset from 540 to 550 nm for MAPbBr3 and 750 to 780 nm for MAPbI3 as the thickness of respective organic precursors increased from 300 to 500 nm. The bandgap of MAPb(I1-xBrx)3 decreased from 2.21 to 2.14 eV as the thicknesses of MABr precursors increased from 300 to 500 nm. The crystallisation of the HaP started within the chamber, and prolonged post-annealing times exceeding 10 min caused the transformation of MAPbI3 to PbI2. Scanning Electron Micrographs show pin-hole-free and densely packed grains with an average size that increases as thicknesses increase. The charge carrier mobility increases while trap density decreases as the thickness of organic precursors increased. Besides, the thesis investigated the growth and stability of thin MAPbBr3 films at metal/MAPbBr3 interfaces. We studied the structure, morphology, and stability of the optimised MAPbBr3 perovskite on aluminium (Al), tin (Sn), silver (Ag), gold-zinc (Au-Zn) and gold (Au) electrodes, immediately and 60 days later. FE-SEM images show an average grain size that increased linearly with the work function from 294 nm for Al to 850 nm for Au. The MAPbBr3 grains remain glued to Sn, Ag, Au-Zn but delaminate quickly on Al. X-ray analysis of MAPbBr3 reveals variable crystallographic texturing for various metals and loss in intensity of prominent peaks at different rates over time. We found that the best thicknesses of 100 nm PbI2 and 500 nm MAI, and 100 nm PbBr2 and 500 nm MABr are needed for the preparation of quality MAPbI3 and MAPbBr3 thin films for solar cells, respectively. Quality thin MAPb(I0.11Br0.89)3 film is formed by inter-diffusion and halide exchange processes when optimised MAPbBr3 is grown on optimised MAPbI3 as a bottom layer. Al speeds up the degradation of MAPbBr3 at Al/MAPbBr3 while MAPbBr3 is relatively stable at Au-Zn/MAPbBr3 interfaces. / Thesis (PhD (Physics))--University of Pretoria, 2020. / University of Pretoria, the National Research Foundation/The World Academy of Sciences (NRF-TWAS), and NRF grant no N0115/115463 of the SARChI / Physics / PhD (Physics) / Restricted

Silicon phthalocyanines (R₂-SiPcs) are an emerging class of high-performance n-type or ambipolar organic semiconductors which have found application in organic electronic devices, including organic thin-film transistors (OTFTs), organic photovoltaics (OPVs) and organic light-emitting diodes (OLEDs). Owing to their tetravalent silicon metal centre, R₂-SiPcs can be substituted with a range of axial ligands including phenols, carboxylic acids, and silanes to tune their intermolecular interactions, optical properties, electronic properties and solubility. While early reports of R₂-SiPcs have demonstrated promising results, the relationship between their structure and performance in OTFTs is poorly understood. Additionally, many OTFTs with R₂-SiPcs as semiconductor only demonstrate n-type behaviour under inert atmospheres due to their shallow lowest unoccupied orbital level below -4.1 eV making them susceptible to electron trapping by moisture and oxygen. This thesis presents developments in both the understanding of how R₂-SiPc structure influences performance, device engineering and exploration of these materials in ammonia sensors. First, I develop of structure-property relationships for a catalogue of fifteen R₂-SiPcs integrated into OTFTs including eleven materials used in OTFTs for the first time. I then explore the influence of dielectric surface chemistry on the texture of R₂-SiPc films and their resulting performance in OTFTs using silane self-assembled monolayers and para-sexiphenyl to understand the weak epitaxial growth behaviour of this class of materials. Next, I report eight novel peripherally fluorinated and axially substituted silicon phthalocyanines (R₂-FₓSiPcs) to investigate the influence of peripheral and axial fluorination on air-stable electron transport and determine the threshold for achieving air-stable n-type OTFTs. Finally, I integrate R₂-FₓSiPcs into organic heterojunction ammonia gas sensors to understand the influence of peripheral fluorination on the majority charge carrier in this device architecture.

The present thesis is concerned with solid solutions of organic dyes. The organic molecules are incorporated in both optically inert or active and in rigid or flexible matrices, respectively. Exclusively thin films prepared by physical vapor deposition are studied. The optical response of the systems, in dependence on their structure and on the matrix nature, is investigated by means of absorption and luminescence spectroscopy. In the first part, perylene and 2,2-difluoro-1,3,2-dioxaborine derivatives, and Alq3 (tris(8-hydroxyquinoline) aluminium) embedded in the optically inactive SiO2 and polyimide hosts are studied. For the system dye molecules/SiO2 matrix, two sample preparation approaches, co-deposition and layer-by-layer, are compared. It is demonstrated that the luminescence properties of the mixed layers are affected by dye distribution and thin film composition. The photoluminescence quantum efficiency is strongly influenced by dye aggregation and Föster transfer. Therefore, effective separation and isolation of dye molecules in the matrix results in increased PL efficiency. Furthermore, it is established that layer-by-layer growth mode assures more homogeneous dye distribution. The spectroscopic studies also show that, since dye and matrix condense successively in time, luminescence losses due to thermal degradation of molecules are reduced. Hence, the film structure can be optimized with regard to high absorption and luminescence quantum efficiency. The experimental findings suggest that the luminescent properties of the embedded dyes are influenced by the nature of the host environment as well. In the rigid SiO2 matrix, it is possible to observe isolated facial Alq3 molecules with distinctive blue luminescence. In contrast, in the "soft" organic polyimide matrix Alq3 exhibits ordinary green luminescence. Thus, the structural properties of the host, rigidity and density, are found to be crucial for preservation of the facial Alq3 molecules. It is further demonstrated that the immobilization of molecules in the rigid SiO2 matrix in combination with layer-by-layer growth results in improved photostability. In polyimide matrix, the behavior of incorporated molecules is governed by the morphological changes of the host. These changes are defined by the curing procedure, needed for imidization, and give rise to a certain film structure. In the second part, special attention is paid on the luminescence response of dispersed DCM (4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyril)-4H-pyran) and rubrene (5,6,11,12-tetraphenyl-naphthacene) molecules in the optically active Alq3 matrix. The observed enhancement of luminescence intensity and alteration of emitted color are favorable for application of the doped Alq3 films as converter layers in combination with commercial blue light emitting diodes in luminescence conversion devices. It is demonstrated that by optimization of the conversion layer parameters white light generation can be achieved. The devices are characterized by high conversion efficiency and Lambertian distribution of the emitted light. However, they lack sufficient stability with regard to practical applications.

Mit dünnen Schichten, die mittels der PVD-Dünnschichttechnik auf Textilien aufgebracht werden, wird eine neue Möglichkeit zur Veredlung von Textilien eröffnet. Die Plasmabehandlung bewirkt eine Veränderung der Substratoberfläche in zwei Richtungen. Einerseits werden die Oberflächenspannung und die Adhäsion beeinflusst und andererseits kommt es zum Aufrauhen der Oberfläche. Die Zunahme der Oberflächenrauheit, hat drei Auswirkungen. Erstens bietet die größere Fläche mehrere molekulare Aufstellungsorte für die Wechselwirkung zwischen dem Adhärens und dem Adhäsiv an. Zweitens wird das mechanische Ineinandergreifen (Interlocking) zwischen dem Adhäsiv und Adhärens stärker und drittens kommt es zum Entfernen der schwachen Grenzschichten auf der Proben-Oberfläche. Die Vorbehandlung mittels Fluorierung führt ebenso wie die Niederdruckplasmabehandlung mit Sauerstoff bei Gewebe aus synthetische Fasern grundsätzlich zu einer Verbesserung der Festigkeit im Verbund. Beide Vorbehandlungsmethoden stellen alternative, notwendige Verfahren zur Haftungsverbesserung dar. Im Allgemeinen haften die Schichten bei besputterten Proben gegenüber bedampften Proben besser. Eine wesentlich geringere Haftung weisen die Schichten auf den unbehandelten Substraten auf. Neben Untersuchungen zur Haftbeständigkeit der Schichten erfolgen Untersuchungen zur Leitfähigkeit und zur elektromagnetischen Schirmdämpfung der Substrate. Die Oberflächenwiderstände werden sowohl von der Konstruktion der textilen Fläche als auch von den Beschichtungszeiten beeinflusst. Erwartungsgemäß führen längere Beschichtungszeiten zu sinkenden Oberflächenwiderständen.