Microfabrication of ceramic features has become a critical issue in realizing the miniaturization of devices. Micromolding and sintering play critical roles in fabricating micron- and submicron-sized ceramic features using nanoparticles. Developed from soft lithography, replica molding has been proven a good method to prepare micron- and submicron-sized features. However, the fidelity of the features can be compromised by incomplete feature cavity filling and feature shrinkage during the forming process. In this study, centrifuge-aided micromolding is developed to prepare micron- and submicron-sized ZnO features. By introducing a centrifugal force, the shear-thinning behavior of the suspensions is utilized, and the cavity filling process and the diffusion of trapped air out of the features are accelerated. The drying shrinkage is decreased by increasing the density of the wet nanoparticle packing from the centrifugal process. The centrifugal force improves the fidelity of all the designed features. ZnO ridges from 0.4 μm to 2 μm size and rods of 1.6 μm size are prepared successfully. The wide applicability of this strategy has been demonstrated by preparing ZrO2 features via the same method. Sintering process has a significant influence on the morphology and microstructural evolution of micron-sized ceramic features. When ceramic features decrease to much smaller sizes, such as in the micron range, the dominating sintering mechanism(s) can be different from those of the bulk at large scales. However, limited effort has been devoted to understanding the sintering behaviors. In this study, the as-prepared micron-sized ZnO ridges and rods were sintered at 950oC for different time in air atmosphere. The sintering process destructs the ZnO features via abnormal grain growth and surface roughening. Destruction prediction of features using sintering time is established based on grain growth. Feature surface roughening is further analyzed with respect to thermodynamic fundamentals. Because of the evaporation tendency during zinc oxide sintering, sintering atmosphere has a significant influence on the sintering behavior and feature fidelity. In this study, micron-sized ZnO ridge features were sintered under air and argon atmospheres. Ridge size, line edge roughness, and grain size were characterized. Quantitative calculation of sintering behaviors was performed in order to obtain fundamental understating of the micron-sized ZnO feature sintering. It is found that oxygen partial pressure is the deciding factor for the ridge feature evolution. ZnO evaporation and defects diffusion are responsible for the ZnO bulk and ridge sintering behavior differences. / Master of Science / In order to produce portable devices with small sizes, novel techniques are required to make small components, which is called microfabrication. Since ceramic materials are widely used in various electronic devices, microfabrication of small ceramic features has become an important issue. When ceramic nanoparticles are used as the raw material, the fabrication of ceramic features mainly consists of two processes: micromolding and sintering, which are the problems that this thesis focuses on. In the micromolding process, the loose nanoparticles are packed to form features with specific shapes. In the sintering process, the nanoparticles in as-prepared features are bonded into a coherent and dense feature. For the micromolding process, a suspension made from the nanoparticles is poured into a mold with as-designed feature shape, and the dry feature is obtained after a drying process. In this study, the factors that will affect the shape of the features are studied. It is found that the major factors include completeness of the filling process and shrinkage during the drying process. By completing the micromolding process in a centrifugal machine, the micromolding process is accelerated, and the shrinkage during the drying process is decreased. Both the two aspects will benefit the feature quality. By using this technique, zinc oxide ridges from 0.4 μm to 2 μm size and rods of 1.6 μm size are fabricated successfully. It is also demonstrated that this technique can be applied to other ceramic materials. Sintering process can convert packed nanoparticles into a coherent object, which can help us to obtain dense ceramic features. However, the sintering process will cause the change in feature shape. For large size ceramic bulks, the sintering theory has been well established to explain these changes. When the size of ceramic materials decreases to very small scale, such as micron size, new sintering theory is needed to explain the change of ceramic features in the sintering process. In this study, micron-sized zinc oxide ridges and rods were sintered at 950oC for different time. It was found that the sintering process will distort the shape of the zinc oxide features. Based on thermodynamic views, the corresponding new theory was established. Because zinc oxide is relatively easy to evaporate during sintering, sintering atmosphere will also affect the shape of the features. In this study, micron-sized zinc oxide ridge features were sintered under air and argon atmospheres. It was found that oxygen content was the major factor that will affect the shape change. The corresponding theory was established to explain the effect of the sintering atmosphere based on thermodynamic views.

No / Zinc oxide (ZnO) nanoparticles are widely used in cosmetics and sunscreens. Human epidermal keratinocytes may serve as the first portal of entry for these nanoparticles either directly through topically applied cosmetics or indirectly through any breaches in the skin integrity. Therefore, the objective of the present study was to assess the biological interactions of ZnO nanoparticles in primary human epidermal keratinocytes (HEK) as they are the most abundant cell type in the human epidermis. Cellular uptake of nanoparticles was investigated by scanning electron microscopy using back scattered electrons imaging as well as transmission electron microscopy. The electron microscopy revealed the internalization of ZnO nanoparticles in primary HEK after 6 h exposure at 14 microg/ml concentration. ZnO nanoparticles exhibited a time (6-24 h) as well as concentration (8-20 microg/ml) dependent inhibition of mitochondrial activity as evident by the MTT assay. A significant (p < 0.05) induction in DNA damage was observed in cells exposed to ZnO nanoparticles for 6 h at 8 and 14 microg/ml concentrations compared to control as evident in the Comet assay. This is the first study providing information on biological interactions of ZnO nanoparticles with primary human epidermal keratinocytes. Our findings demonstrate that ZnO nanoparticles are internalized by the human epidermal keratinocytes and elicit a cytotoxic and genotoxic response. Therefore, caution should be taken while using consumer products containing nanoparticles as any perturbation in the skin barrier could expose the underlying cells to nanoparticles.

The goal of this work is to investigate the piezoelectricity of composite laminates embedded with layers of zinc oxide (ZnO) nanowires. ZnO nanowire embedded composites have the potential to sense and actuate giving the potential for these smart composites to serve the function of being load bearing structures and monitoring the integrity of the structure. This work examines the piezoelectric characteristics of composite beams by investigating their electromechanical coupling in the form of vibration under the presence of electrical excitation. With the help of a mathematical model, piezoelectric constants are estimated for these samples. A layer of ZnO nanowires were grown on plane woven fiberglass fabric that was incorporated into a carbon fiber epoxy composite. The beam deflection velocity was measured as a varying voltage was applied to the composite. Using Hamilton's Principle and Galerkin's method of weighted residuals, a mathematical model was derived to estimate piezoelectric constants for the composites from the experimental data. Piezoelectric properties were determined using vibrational testing and a mathematical model. Piezoelectric constants h31, g31, and d31 were estimated to be 9.138 E7 V/m, 6.092 E-4 Vm/N, and 2.46 E-14 respectively. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M. / Master of Science / A major problem facing both commercial and military aircraft fleets is aircraft grounded time due to inspection. Inspection times tend to be lengthy since visual inspection cannot detect all types of incurred damage an aircraft may face. In the case of composite aircraft structures, a special type of damage known as delamination (when layers of the composite structure become un-bonded) can occur. Since delamination is not always visible from the surface, and composite structures cannot be taken apart since they are made in one piece; additional damage detection methods are necessary. Impedance-based structural health monitoring (IBSHM) is one technique of nondestructive evaluation (NDE) that examines changes in vibrational response of the structure in order to detect damage. A novel approach to IBSHM is incorporating zinc oxide, a type of piezoelectric material, inside the composites due to its ability to deform in the presence of an electric field or generate a voltage when stressed. The goal of this research is to determine piezoelectric properties of composites with ZnO nanowires grown on inner layers of the laminates. Piezoelectric properties were determined using vibrational testing and a mathematical model. To demonstrate the electromechanical coupling, ZnO nanowire composites were bonded to Al beams that were progressively damaged to determine if a change in electrical impedance could be observed to correspond to the change in structural impedance of the host beam. Changes in impedance were detected by a change in root mean squared deviation damage metric M. A significant correlation was shown between increasing damage in the host beam and an increase in damage metric M.

This dissertation focuses on two aspects of integrating near-infrared plasmonics with electronics with the intent of developing the platform for future photonics. The first aspect focuses on fabrication by introducing and developing a simple, single reflective optical element capable of high–throughput, large scale fabrication of micro- and nano-sized structure templates using holographic lithography. This reflective optical element is then utilized to show proof of concept in fabricating three dimensional structures in negative photoresists as well as tuning subwavelength features in two dimensional compound lattices for the fabrication of dimer and trimer antenna templates. The second aspect focuses on the study of aluminum zinc oxide (AZO), which belongs to recently popularized material class of transparent conducting oxides, capable of tunable plasmonic capabilities in the near-IR regime. Holographic lithography is used to pattern an AZO film with a square lattice array that are shown to form standing wave resonances at the interface of the AZO and the substrate. To demonstrate device level integration the final experiment utilizes AZO patterned gratings and measures the variation of diffraction efficiency as a negative bias is applied to change the AZO optical properties. Additionally efforts to understand the behavior of these structures through optical measurements is complemented with finite difference time domain simulations.

No / To summarise the clinical and economic literature relating to the effect of Cavilon No Sting Barrier Film on the incidence of incontinence-associated dermatitis, which is a risk factor for pressure ulceration and exudate-related peri-wound skin damage. Method: A systematic literature search was performed using available computerised databases for publications on Cavilon barrier film and other relevant terms. Six clinical studies were identified providing data on 1,563 patients treated with the barrier film or a comparator. The publications comprised prospective studies, randomised and non-randomised studies, multicentre trials, single-centre reports and a volunteer study. Due to the nature of the comparators, five studies were open-label. Differences in methodology and outcomes made a qualitative review the most appropriate analysis. Results: The barrier film was at least as effective as petroleum ointments and more effective than zinc oxide formulations in preventing incontinence-associated dermatitis. The barrier film was also effective in peri-wound skin protection, although its clinical efficacy was not significantly different to that of petroleum ointments and zinc oxide formulations. Nevertheless, the barrier film was more cost-effective than either petroleum ointments or zinc oxide formulations in managing incontinence-associated dermatitis and peri-wound skin protection, largely due to savings in nursing time. Conclusion: The barrier film is at least as clinically effective and potentially more cost-effective in incontinence-associated dermatitis prophylaxis and peri-wound skin protection than petroleum ointments or zinc oxide formulations, releasing health care resources for alternative use. Further studies are required to quantify the relative efficacy and cost-effectiveness of the barrier film and other barrier formulations in different clinical settings and enhance the quality of the evidence base.

One-dimensional (1D) nanostructures have gained tremendous attention over the last decade due to their wide range of potential applications. Particularly, ZnO 1D nanostructures have been investigated with great interest due to their versatility in synthesis with potential applications in electronics, optics, optoelectronics, sensors, photocatalysts and nanogenerators. The thesis deals with the challenges and the answer to grow ZnO 1D nanostructure by vapor phase transport (VPT) continuously without any length limitation. The conventional VPT technique has been modified for the non-catalytic growth of ultralong ZnO 1D nanostructures and branched structures in large area with controllable aspect ratio. It has been shown that the aspect ratio can be controlled both by thermodynamically (temperature) and kinetically (vapour flux). The thesis also deals with the fabrication of carbon nanotube (CNT) -ZnO based multifunctional devices and the field emission performance of ZnO nanowires by employing various strategies. The entire thesis has been organised as follows: Chapter 1 deals with Introduction. In this chapter, importance of ultralong nanowires and significance of ultralong ZnO nanowires has been discussed. Various efforts to grow ultralong ZnO nanowire with their advantages and disadvantages have been summarised. Lastly the significance of forming ZnO nanowires based nano hybrid structures and importance of doping in ZnO nanowires and has also been discussed. Chapter 2 deals with experimental procedure and characterization. In this chapter, a single step VPT method for the growth of ultralong ZnO nanowires that incorporates local oxidation barrier for the source has been described. The synthesized nanowires were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman & photoluminescence. Chapter 3 deals with growth of ZnO nanowires, controlling the aspect ratio of ZnO nanowires, and role of other experimental aspects. In this chapter, a way to grow nanowires continuously without any apparent length limitation, a way to control the diameter of the nanowires kinetically without catalyst particle or seed layer and obtaining smaller diameter of the nanowires by non-catalytic growth as compared to that set by the thermodynamic limit has been discussed. Furthermore, the significance and importance of local oxidation barrier on source for protecting them from degradation, ensuring the continuous supply of vapour and enabling the thermodynamically and kinetically controlled growth of nanowires has been discussed. Lastly, the scheme for large area deposition and a method to use same source material for several depositions has been presented. Chapter 4 deals with multifunctional device based on CNT -ZnO Nanowire Hybrid Architectures same device can be used as a rectifier, a transistor and a photodetector. In this chapter, the fabrication of CNT arrays-ZnO nanowires based hybrid architectures that exhibit excellent high current Schottky like behavior with p-type conductivity of ZnO has been discussed. CNT-ZnO hybrid structures that can be used as high current p-type field effect transistors (FETs) and deliver currents of the order of milliamperes has been presented. Furthermore, the p-type nature of ZnO and possible mechanism for the rectifying characteristics of CNT-ZnO has been discussed. Lastly, the use of hybrid structures as ultraviolet detectors where the current on-off ratio and the response time can be controlled by the gate voltage has been presented and also an explanation for photoresponse behaviour has been provided. Chapter 5 deals with the substrate-assisted doping of ZnO nanowires grown by this technique. In this chapter, the non-catalytic growth of ZnO nanowires on multiwalled carbon nanotubes (MWCNTs) and soda lime glass (SLG) with controlled aspect ratio has been presented. The elemental mapping to confirm the presence and distribution of carbon and sodium in ZnO nanowires and the transport studies on both carbon and sodium doped ZnO has also been presented. Furthermore the stability of carbon doped ZnO has also been presented. Lastly, the advantage of growing ZnO nanowires on MWCNTs and overall advantage associated with this technique has been discussed. Chapter 6 deals with formation of ZnO nanowire branched structures. In this chapter, a possibility to grow ZnO nanowires on already grown ZnO nanowires has been demonstrated. The formation of branched structure during multiple growth of ZnO nanowire on ZnO nanowire has been presented and evolution of aspect ratio in these branched structures has been discussed. Furthermore, the advantage of using ZnO branched structures and also the ZnO nanoneedles on MWCNT mat for field emission has been presented. Chapter 7 summarizes all the findings of the thesis.

The atmosphere we live in contains various kinds of chemical species, natural and artificial, some of which are vital to our life, while many others are more or less harmful. The vital gases like oxygen, humidity have to be kept at adequate levels in the living atmosphere, whereas the hazardous and toxic gases like hydrocarbons, H2, volatile organic compounds, CO2, CO, NOx, SO2, NH3, O3 etc should be controlled to be under the designated levels. The measurement technology necessary for monitoring these gases has emerged, particularly as organic fuels and other chemicals have become essential in domestic and industrial life. In addition to other applications, environmental pollution monitoring and control has become a fundamental need in the recent years. Therefore, there has been an extensive effort to develop high-performance chemical sensors of small size, rugged construction, light weight, true portability, and with better sensing characteristics such as high sensitivity, fast response and recovery times, low drift, and high degree of specificity. Among the various types of gas sensors studied, solid state gas sensors based on semiconducting metal oxides are well established, due to their advantages over the other types, and hence cover a wide range of applications. However, the widespread application of these sensors has been hindered by limited sensitivity and selectivity. Various strategies have been employed in order to improved the performance parameters of these sensors. This thesis work has two major investigations, which form two parts of the thesis. The first part of this thesis describes the efforts to improve the sensing behaviour of one of the extensively studied metal oxide gas sensors, namely, ZnO, through a novel, ultrasonic-nebulised spray pyrolyis synthesis method, employing an aqueous combustion mixture (NSPACM). The second part of the thesis deals with the ideal of gas detection by optical means through the reversible phase transformation between V2O5 and V6O13 deposited by metalorganic chemical vapor deposition(MOCVD). The introductory chapter I deals with basics of chemical sensors and the characteristic sensing parameters. Different types of gas sensors based on the phenomena employed for sensing are discussed, with an emphasis on semiconducting metal oxide gas sensors. The importance of material selection for solid state gas sensors, depending on the purpose, location, and conditions of operation are discussed, supporting the assertion that semiconducting metal oxides are better suited to fulfill all the requirements of modern gas sensors. Some of the effective methods to improve performance parameters including the influence of grain size, microstructure, and surface doping are described., followed by the motivation of the present thesis. The part I of the thesis is based on the resistive semiconducting metal oxide, where the system investigated was ZnO. Part one comprises Chapters 2, 3 and 4. In Chapter 2, a brief introduction to the material properties of ZnO, followed by various synthesis techniques are discussed. An overview of spray pyrolysis and combustion synthesis is followed by the details of the method employed in the present study, namely NSPACM, which is based on the above two methods, for the formation of ZnO films. A detailed description of the film deposition system built in house is presented, followed by the deposition procedure and the parameters used. Thermal study of the combustion mixture and non-combustion precursor shows the importance of the fuel, along with oxidizer, in forming the film. The films formed using combustion mixture are found to be polycrystalline, whereas films formed without combustion were found to have preferred crystallographic orientation even on an amorphous substrate, which is explained on the basis of minimization of surface energy. The observed unique microstructure with fine crystallite size and porous morphology is attributed to the combustion method employed, which is interesting from the point of view of gas sensing. Chapter 3 concerns the gas sensing study of these ZnO films. The design of the home made gas sensing system is explained in detail. The study of electrode characteristics is followed by the important steps in gas sensing measurements. ZnO gas sensors were mainly studied for their selectivity between aliphatic and aromatic hydrocarbons. The results show two regions of temperature where the sensitivity peaks for aliphatic hydrocarbons, whereas aromatic hydrocarbons show a single sensitive region. This observation can pave the way for imparting selectivity. Possible reasons for the observed behavior are mentioned. Chapter 4 describes the chemical and physical modifications done to ZnO thin films by doping with catalysts, and through the use of x-y translational stage for large-area deposition.. Homogenous distribution of catalysts achieved by the NSPACM synthesis procedure, determined by the x-ray elemental mapping, is discussed. The addition of catalysts improved the sensing both because of catalytic effects and by promoting preferred crystallographic orientation, with Ni addition showing the better effects. The use of the x-y stage in producing the films with high orientation, which improved the gas sensing behavior, is explained. Part II of the thesis comprises Chapters 5,6 and 7, and describes a detailed study of V2O5 and V6O13 thin films deposited by MOCVD for optical sensing of chemical species. In Chapter 5, a brief introduction to chemical vapor deposition is given, followed by the importance of the characteristics of CVD precursors – in particular, the importance of their thermal behavior in film formation. This is followed by the importance of vapor pressure and partial pressure studies in the MOCVD of oxides of a multivalent metal such as vanadium. Various techniques of measuring vapor pressure are listed, followed by the details of the method used in the present study employing rising temperature thermogravimetry, based on the Langmuir equation. Thermogravimetric analysis performed, both at atmospheric as well as at low pressure, using commercial and home made apparatus, respectively is discussed. A detailed description of the home made setup is also presented. Chapter 6 describes the application of the vapor pressure and partial pressure studies to the deposition of films using MOCVD. Here, a detailed description of the vanadium oxide phase diagram and the stability of various phases is presented, which points the importance of precise parameter control during the deposition to obtain pure phases. The details of the CVD setup, followed by the procedure and parameters of deposition, are presented. The films deposited at various deposition temperatures, analyzed using XRD and SEM, are discussed. The effect of temperature on the growth is explained. The effect of vapor pressure is studied by varying the precursor vaporizer temperature, with a growth temperature maintained invariant. The influence of the amount of precursor on film growth, with a particular crystalline orientation and phase content, is explained followed by the description of the deposition of pure phases of V2O5 and V6O13 through the optimization of CVD parameters. Chapter 7 deals with the optical study of the films deposited by the above method. Here, the importance of two phases of vanadium oxide, V2O5 and V6O13, to the proposed gas sensing action, is presented. Their structural similarity in terms of polyhedral arrangement in the ab plane can be the basis of a reversible phase change. The difference in the optical transmittance in two phases forms the basis for the optical method for chemical sensing. The details of the laser-based optical sensing setup, its, design and the detection method, are explained. Studies on hydrocarbon sensing with vanadium, pentoxide films are also presented. The novelty in using reversible chemical transformation of a material system for detection of reducing and oxidizing gases in the ambient gases is discussed. Chapter 8 provides a summary of the present thesis, together with the main conclusions. The work reported in this thesis has been carried out by the candidate as part of the Ph.d training programme. She hopes that this would constitute a worthwhile contribution towards the understanding and subsequent application of ZnO and oxides of vanadium(V2O5 and V6O13) as novel gas sensors which will be useful for environmental protection, as well as for safety in industrial an domestic sectors.

<p>Renewable energy technologies and the development of cleaner and more environmentally friendly power have been at the forefront of research for the past few decades. Photovoltaic systems – systems that convert photon energy to electrical energy – are at the center of these research efforts. Decreasing the cost of energy production, through increasing the power conversion efficiency or decreasing the device cost, is a key factor in widespread use of these energy production systems. To increase the energy conversion efficiency, ideally, all useful photons should be absorbed by the solar cell; however, due to the large discontinuity in the refractive index at the solar cell/air interface, a large fraction of incidence light is lost due to reflection (30% loss in crystalline silicon cells). The currently used single and double layer anti-reflection coatings reduce the reflection losses, but their optimal performance is limited to a narrow range of wavelengths and angles of incidence. Moth-eye anti-reflection coatings are composed of patterned single layer films having a gradual decrease in refractive index from the solar cell surface to air. This study is focused on developing an inexpensive method for direct deposition of patterned films – in the form of moth-eye anti-reflection coatings – on solar cell surface.</p> <p>In this research, the creation of moth-eye anti-reflection coatings has been attempted through the process of electrodeposition. ZnO was chosen for the thin film material, and the ability to develop the required moth-eye structure by changing the electrodeposition parameters including temperature, applied potential, type and concentration of solution-borne species, and type of substrate was investigated. Using this method, pyramidal and hemispherical structures with a 100-200 nm diameter and 100-200 nm height were created directly on ITO substrates. Similar structures were also developed on silicon substrates. The anti-reflection properties of ZnO-coated silicon substrates were investigated by comparing their broadband and broad angle reflection-mode UV-VIS spectrum with uncoated silicon. The optimized ZnO-coated silicon substrate showed a reflectance of at most 20% for wavelengths between 400-1500 nm at angles of incidence less than 50^O.</p> / Master of Applied Science (MASc)

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The initial charge transfer from dye molecules' excited states to the conduction band of a semiconductor, after absorption of visible light by the former, is critical to the performance of Dye sensitized Solar Cells (DSC). In a ZnO-based DSC sensitized by the organic indoline derivative D149, the dynamics associated with charge transfer are investigated with femtosecond transient absorption spectroscopy. The time-resolved measurement of the photo-initiated processes reveal electron transfer rates corresponding to excited state lifetimes of 100s of fs, consistent with previously measured high absorbed photon to current conversion efficiencies. The photo-electrode measured as an isolated system shows decay times of bound electrons in excited states of the dye to be ~150 fs and shows the subsequent emergence of absorption bands of the oxidized molecules. When the I-/I-3 redox couple is added to the system, these excited state lifetimes change and are found to be dependent on the cation in the electrolytic solution. Small cations like Li+ reduce the excited state lifetime to sub-100 fs, whilst larger cations like the organic tetrabutylammonium result in longer lifetimes of 240 fs. The action of the electrolyte can be observed by the reduced lifetime of the oxidized dye molecules' absorption bands. The effect of operating parameters and changes in the production protocol of the DSC on the primary charge injection are also investigated and reported on. / AFRIKAANSE OPSOMMING: Die aanvanklike ladingsoordrag vanuit kleurstofmolekules' opgewekte toestande tot in die leidingsband van 'n halfgeleier, na absorpsie van sigbare lig deur eersgenoemde, is van kritiese belang vir die uitset van halfgeleier-gebaseerde sonkragselle wat met kleurstowwe vir absorpsie verhoging, gebind is. In hierdie werk word hierdie proses en verwante fotodinamika in die geval van 'n ZnO sonkragsel gekleur met indolien D149 ondersoek d.m.v femtosekonde-tydopgelosde absorpsiespektroskopie. Hierdie metings onthul elektron-oordragstempos wat ooreenstem met lewenstye van opgewekte toestande in die orde van 100 fs. Hierdie is met voorheen-bepaalde hoë foton-tot-stroom omskakelingsdoeltreffendheid ooreenkomstig. Die foto-elektrode, as geïsoleerde sisteem beskou, toon afvalstye van gebonde elektrone in opgewekte toestande van ~150 fs, en die gevolglike opkoms van absorpsie deur geoksideerde molekules word waargeneem. As die I-/I-3 redoks oplossing tot die sisteem bygevoeg word, verander die opgewekte toestande se afvalstye en toon 'n katioon-afhanklikheid. Klein katioone soos Li+ verkort die afvalstye tot onder 100 fs, terwyl groter katioone soos die organiese tetra-butielammonium langer afvalstye (240 fs) tot gevolg het. Die werking van die elektrolitiese oplossing kan waargeneem word deur die verkorte lewenstyd van die absorpsiebande wat aan die geoksideerde molekules toegeken is. Die uitwerking van operasionele parameter asook veranderinge in die produksie protokol op die primêre ladingsoordrag word ondersoek en verslag daarop word gelewer.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This study developed and optimised zinc oxide (ZnO) nanowire-based nanogenerator. The nanogenerator works on the piezoelectric effect that is, a mechanical force is converted to an electrical voltage. The ZnO nanowires are piezoelectric and when any force is applied to the nanowires an output voltage is generated. This ZnO nanowire-based nanogenerator can be used to power small electronic devices, such as pacemakers. The nanogenerator can also be incorporated into clothes and shoes to generate electricity to charge a cell phone for example. The problem experienced currently is that the nanogenerator does not generate enough electricity to be of practical use and needs to be further optimised. Simulations and mathematical models were used to identify areas where the nanogenerator could be optimised in order to increase the output voltage. It is shown that the morphology of the nanowires can have a considerable effect on the output voltage. For this reason the growth of the nanowires was investigated first. Different methods were used to propagate the nanowires in order to select the method that, on average, has the highest output voltage. Accordingly, one parameter at a time and design of experiments were used to optimise the nanowire growth. Consequently, these two methods were used to optimise the growth parameters with the respect to the output voltage. The aqueous solution method was found to yield nanowires that give the highest generated output voltage. After growing over 600 nanowire samples, optimal growth parameters for this method were found. These optimal growth parameters were subsequently used to grow nanowires that were used to manufacture the nanogenerator. The nanowires were grown on a solid substrate and hence the nanogenerator was also manufactured on the solid substrate. Through various optimisations of the manufacturing process the maximum output voltage achieved was about 500 mV. However, this output voltage is too low to be of practical use, even though the output has been raised considerably. The main problem was found to be the fact that the contact between the nanowires and the electrode was weak due to contamination. A new method was therefore required where the electrode and the nanowires would be in proper contact to ensure that higher output voltages were achieved. Subsequently, a flexible nanogenerator was manufactured in order to solve this problem. Accordingly, the nanowires were grown on the flexible polyimide film and a buffer layer was then spun onto the flexible substrate, leaving only the nanowire tips exposed. The electrode was then sputtered on top of this buffer layer, covering the nanowire tips. This ensured proper contact between the nanowires and the electrode. The nanogenerator, which was manufactured with non-optimal growth parameters, gives a maximum voltage output of 1 V, double the maximum achieved with the solid nanogenerator. When the optimal growth parameters were used the output voltage was raised to 2 V. Various optimisation techniques were performed on the nanogenerator, including plasma treatment and annealing and the use of various materials in the buffer layer. Combining these optimisation methods subsequently led to an optimised nanogenerator that can generate an output voltage of over 5 V. This was achieved after over 1200 nanogenerators had been manufactured. However, the output voltage was not in a usable form. Circuitry was therefore developed to transform the voltage generated by the nanogenerator to a useable form. The best circuit, the LTC3588, was used to power an LED for 10 seconds. The completed device was found to achieve a power output of 0.3 mW, enough for small electronic devices. / AFRIKAANSE OPSOMMING: ‘n Sink-oksied (ZnO) nanodraad gebaseerde nanogenerator is ontwikkeld en geöptimeer. Die nanogenerator werk met behulp van die piezoelektriese effek - meganiese krag work omgesit in ‘n elektriese spanning. Die ZnO nanodrade is piezoelektries en wanneer ‘n krag op die drade aangewend word, word ‘n uittree spanning gegenereer. Die nanogenerator kan gebruik word om klein elektroniese toestelle, soos ‘n pasaangeër, van krag te voorsien. Die nanogenerator kan in klere en skoene geïnkorporeer word om elektrisiteit op te wek vir die laai van ‘n selfoon. Die probleem is egter dat die nanogenerator tans nie genoeg krag opwek om prakties van nut te wees nie en verdere optimasie word benodig. Simulasies en wikundige modelle work gebruik om areas te identifiseer waar die nanogenerator geöptimeer kan word, met die doel om die uittreespanning te verhoog. Dit word bewys dat die morfologie van die nanodrade ‘n groot effek het op die uittreespanning. Dus word die groei van die nanodrade eerste ondersoek. Verskillende metodes word gebruik om die nanodrade te groei en die beste metode, wat die hoogste uittreespanning op gemiddeld verskaf, word gekies. Een parameter op ‘n slag en ontwerp van eksperimente word gebruik om die nanodraad groei te optimeer. Die groei parameters word geöptimeer deur van die twee metodes gebruik te maak, en die optimeering word gedoen in terme van die uittreespanning. Die oplossing groei metode lei tot nanodrade wat die hoogste uittreespanning verskaf. Na oor die 600 nanodraad monsters gegroei is, is die optimale parameters gevind. Hierdie optimale parameters word uitsluitlik gebruik om die nanogenerator te vervaardig. Die nanodrade word op ‘n soliede substraat gegroei en dus word die nanogenerator op dieselfde soliede substraat vervaardig. Verskeie metodes is gebruik om die vervaardiging te optimeer en die hoogste uittreespanning wat bereik is, is 500 mV. Die uittreespanning is te laag om van praktiese nut te wees alhoewel dit heelwat verhoog is. Die grootste probleem is die swak kontak tussen die nanodrade en die elektrode, wat veroorsaak word deur kontaminasie. ‘n Nuwe metode word verlang wat beter kontak tussen die nanodrade en elektrode sal verseker. ‘n Buigbare nanogenerator is vervaardig om die probleem op te los. Die nanodrade word nou op ‘n buigbare film gegroei. ‘n Bufferlaag word tussen die nanodrade in gedraai, tot net die punte van die nanodrade nog sigbaar is. Die elektrode word bo-op die bufferlaag gedeponeer, wat behoorlike kontak tussen die nanodrade en elektrode verseker. Die nanogenerator wat met nie-optimale groei parameters vervaardig is, bereik ‘n uittreespanning van 1 V, dubbel die soliede nanogenerator. Met optimale groei parameters word die uittreespanning tot 2 V verhoog. Verskeie optimasie tegnieke word op die nanogenerator toegepas. Die metodes sluit in suurstof plasma behandeling, verhitting en die inkorporasie van verskillende materiale in die bufferlaag. ‘n Kombinasie van die metodes geïnkorporeer in een nanogenerator lei tot ‘n uittreespanning van 5 V. Die uittreespanning is bereik na oor die 1200 nanogenerators vervaardig is. The uittreespanning is nog nie in ‘n bruikbare vorm nie. Spesiale stroombane is ontwikkel wat die nanogenerator spanning omskakel na ‘n bruikbare vorm. Die beste stroombaan, die LTC3588, kan ‘n LED aanskakel vir 10 sekondes. The toestel kan ook 0.3mWuittreekrag voorsien, genoeg vir klein elektroniese toestelle om te werk.