McMaster University DOCTOR OF PHILOSOPHY (2017) Hamilton, Ontario (Engineering Physics) TITLE: Luminescent Silicon Carbonitride Thin Films Grown using ECR PECVD: Fabrication and Characterization AUTHOR: Zahra Khatami , M.A.Sc. (Shahid Behehsti University) SUPERVISOR: Professor Peter Mascher NUMBER OF PAGES: xx, 268 / Silicon, the cornerstone semiconductor of microelectronics, has seen growing interest as a low-cost material in photonics. Nanoscience has employed various strategies to overcome its fundamentally inefficient visible light emission such as developing new silicon-based nanostructures and materials. Each of the proposed materials has its own advantages and disadvantages in attempting to reach commercialization. Silicon carbonitride (SiCxNy) is a less-studied and multi-functional material with tunable optical features. Despite reports on promising mechanical properties of SiCxNy thin films, they have not yet been well explored optically. This thesis presents the first in-depth analysis of the luminescent properties of SiCxNy thin films at a broad range of compositions and temperatures. To better understand this ternary structure, the reported data of the two fairly well studied binary structures was used as a reference. Therefore, three classes of silicon-based materials were produced and explored; SiCxNy, SiNx, and SiCx. Samples were fabricated using one of the common methods in the semiconductor industry; electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR PECVD). A multitude of characterization techniques were utilized including; optical methods (ultraviolet-visible spectroscopy (UVVIS), variable angle spectroscopic ellipsometry (VASE), photoluminescence (PL)) and structural techniques (elastic recoil detection (ERD), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM)). In view of the exploring of emission properties of SiCxNy materials, our approach was towards the enhancement of the visible emission by adjusting the film composition and subsequent thermal treatment. First, a systematic study of the influence of carbon on the optical, compositional, and structural properties of SiCxNy was carried out. This investigation was followed by an exploration of influence of growth conditions on the visible emission and its connection with the other film properties including hydrogen concentration, microstructure, and composition. In addition, hydrogen diffusion was explored and associated with two featured annealing temperatures. The key element of this thesis is the comprehensive report on the interdependency of the visible light emission and all optical, structural, and compositional features of SiCxNy structures. Unlocking the potential of this ternary and less studied material can appeal to the silicon photonics community to implement it in anti-reflection, solar cell, and sensing applications, and in particular as a substitution of SiNx used in existing microelectronic devices. / Thesis / Doctor of Philosophy (PhD)

The global energy market is continuously changing due to changes in demand and fuel availability. Amongst the technologies considered as capable of fulfilling these future energy requirements, Photovoltaics (PV) are one of the most promising. Currently the majority of the PV market is fulfilled by crystalline Silicon (c-Si) solar cell technology, the so called 1st generation PV. Although c-Si technology is well established there is still a lot to be done to fully exploit its potential. The cost of the devices, and their efficiencies, must be improved to allow PV to become the energy source of the future. The surface of the c-Si device is one of the most important parts of the solar cell as the surface defines the electrical and the optical properties of the device. The surface is responsible for light reflection and charge carrier recombination. The standard surface finish is a thin film layer of silicon nitride deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). In this thesis an alternative technique of coating preparation is presented. The HiTUS sputtering tool, utilising a remote plasma source, was used to deposit the surface coating. The remote plasma source is unique for solar cells application. Sputtering is a versatile process allowing growth of different films by simply changing the target and/or the deposition atmosphere. Apart from silicon nitride, alternative materials to it were also investigated including: aluminium nitride (this was the first use of the material in solar cells) silicon carbide, and silicon carbonitride. All the materials were successfully used to prepare solar cells apart from the silicon carbide, which was not used due to too high a refractive index. Screen printed solar cells with a silicon nitride coating deposited in HiTUS were prepared with an efficiency of 15.14%. The coating was deposited without the use of silane, a hazardous precursor used in the PECVD process, and without substrate heating. The elimination of both offers potential processing advantages. By applying substrate heating it was found possible to improve the surface passivation and thus improve the spectral response of the solar cell for short wavelengths. These results show that HiTUS can deposit good quality ARC for silicon solar cells. It offers optical improvement of the ARC s properties, compared to an industrial standard, by using the DL-ARC high/low refractive index coating. This coating, unlike the silicon nitride silica stack, is applicable to encapsulated cells. The surface passivation levels obtained allowed a good blue current response.

O desenvolvimento de eletrocatalisadores eletricamente condutores com alta atividade para a reação de redução de oxigênio (ORR - Oxygen Reduction Reaction) e desprendimento de oxigênio (OER - Oxygen Evolution Reaction) é de extrema importância e interesse para dispositivos de eletro-conversão de energia, como as células a combustível e eletrolisadores, que operam tanto em meio alcalino quanto ácido. Em meio alcalino, é possível o uso de metais não nobres e, assim, são viáveis para o uso em larga escala. Em meio ácido, é necessário o uso de materiais estáveis, uma vez que eles são expostos a um ambiente extremamente corrosivo e à altos potenciais, principalmente durante o processo de liga/desliga do dispositivo. Diante disso, este trabalho foi dividido em três linhas de pesquisa: Parte I - estudos de eletrocatalisadores bifuncionais para a ORR e OER em meio alcalino, sendo eles compostos por espinélios de manganês-cobalto em combinação com nanopartículas de ouro (MnCo2O4/Au). Parte II - estudos de eletrocatalisadores alternativos para a ORR em eletrólito ácido, onde foram considerados carbetos e nitretos de molibdênio (Mo2C-MoN) e, oxinitretos de tântalo (Ta-ON). Parte III - estudo de suportes alternativos ao carbono para a ORR em eletrólito ácido, sendo eles compostos por carbonitretos de tântalo e titânio (Ta-CN e Ti-CN). Os resultados da Parte I para MnCo2O4/Au mostraram que houve um aumento significativo na atividade de MnCo2O4 com a adição de ouro para ambas as reações. Foi possível observar que a combinação de nanopartículas condutoras (ouro) com nanopartículas ativas, mas não condutoras (MnCo2O4), é promissora para o desenvolvimento de eletrocatalisadores ativos para uso como eletrodos de oxigênio. Quanto a Parte II, os materiais compostos por Mo2C-MoN foram obtidos por meio da inserção de carbono e nitrogênio com tratamento térmico, na presença de carbono Vulcan e NH3, em alta temperatura. O material nomeado como MoN + Mo2C (molibdato) foi o que apresentou maior atividade catalítica, o que pôde ser atribuído ao menor tamanho de cristalito, maior quantidade da sua fase MoN e ao efeito sinérgico entre MoN e Mo2C, facilitando a ORR em comparação ao nitreto e carbeto de molibdênio puros. Nesta mesma linha de pesquisa, oxinitretos de tântalo foram sintetizados utilizando ureia como fonte de nitrogênio. Foi observado que Ti-Ta-ON apresentou maior atividade catalítica quando comparado aos demais eletrocatalisadores. Já na Parte III, os resultados para carbonitreto de titânio como suporte para a platina (Pt/Ti-CN) mostraram que, além da sua atividade para a ORR ser semelhante à platina suportada em carbono (Pt/C), ele também se mostrou mais estável que Pt/C após a realização de testes de estabilidade. / The development of conductive electrocatalysts with high activity for the oxygen reduction and evolution reactions (ORR and OER) is of extremely importance for devices that electroconvert energy, such as fuel cells and electrolizers, which work in alkaline and acid media. A substantial amount of metals can be employed in alkaline electrolytes once the latter do not require the use of noble metals. The acid medium asks for stable materials, since they are exposed to a high oxidative environment and potentials during the start-up/shutdown events of the device. On the base of these facts, this research work has been divided into three parts: Part I - bifunctional electrocatalysts studies for the ORR and OER in alkaline electrolyte, the materials were composed of spinel manganese-cobalt oxide combined with gold nanoparticles (MnCo2O4/Au). Part II - studies of alternative electrocatalysts for the ORR in acid electrolyte, which included molybdenum carbides and nitrides (Mo2C-MoN), and tantalum oxynitrides (Ta-ON). Part III - alternative supports to the carbon for the ORR in acid electrolyte, which included tantalum and titanium carbonitrides (Ta-CN and Ti-CN). The results for MnCo2O4/Au, in Part I, showed that the addition of gold on the surface of the oxide improved the latter activity for both reactions. The combination of conductive nanoparticles (gold) with active, but non-conductive, nanoparticles (MnCo2O4) seems promising for the development of active electrocatalysts for the ORR and OER. In Part II, the materials composed of Mo2C-MoN were synthesized through carbon and nitrogen insertion, in a high temperature heat treatment, in the presence of Vulcan carbon and NH3. Among the gotten materials, the so called MoN + Mo2C (molybdate) showed the better electrocatalytic activity for the ORR, which could be attributed to its smaller crystallite size and the greater amount of its MoN phase, along with the synergistic effect between MoN and Mo2C. In this way, tantalum oxynitrides materials were obtained via a urea synthesis. The catalyst referred to as Ti-Ta-ON showed the better ORR activity among all the others studied oxynitrides materials. In Part III, besides the activity for the ORR of platinum supported on titanium carbonitride (Pt/Ti-CN) was similar to the activity of platinum supported on carbon (Pt/C), Pt/Ti-CN was also more stable than the latter, after the stability tests.

O desenvolvimento de eletrocatalisadores eletricamente condutores com alta atividade para a reação de redução de oxigênio (ORR - Oxygen Reduction Reaction) e desprendimento de oxigênio (OER - Oxygen Evolution Reaction) é de extrema importância e interesse para dispositivos de eletro-conversão de energia, como as células a combustível e eletrolisadores, que operam tanto em meio alcalino quanto ácido. Em meio alcalino, é possível o uso de metais não nobres e, assim, são viáveis para o uso em larga escala. Em meio ácido, é necessário o uso de materiais estáveis, uma vez que eles são expostos a um ambiente extremamente corrosivo e à altos potenciais, principalmente durante o processo de liga/desliga do dispositivo. Diante disso, este trabalho foi dividido em três linhas de pesquisa: Parte I - estudos de eletrocatalisadores bifuncionais para a ORR e OER em meio alcalino, sendo eles compostos por espinélios de manganês-cobalto em combinação com nanopartículas de ouro (MnCo2O4/Au). Parte II - estudos de eletrocatalisadores alternativos para a ORR em eletrólito ácido, onde foram considerados carbetos e nitretos de molibdênio (Mo2C-MoN) e, oxinitretos de tântalo (Ta-ON). Parte III - estudo de suportes alternativos ao carbono para a ORR em eletrólito ácido, sendo eles compostos por carbonitretos de tântalo e titânio (Ta-CN e Ti-CN). Os resultados da Parte I para MnCo2O4/Au mostraram que houve um aumento significativo na atividade de MnCo2O4 com a adição de ouro para ambas as reações. Foi possível observar que a combinação de nanopartículas condutoras (ouro) com nanopartículas ativas, mas não condutoras (MnCo2O4), é promissora para o desenvolvimento de eletrocatalisadores ativos para uso como eletrodos de oxigênio. Quanto a Parte II, os materiais compostos por Mo2C-MoN foram obtidos por meio da inserção de carbono e nitrogênio com tratamento térmico, na presença de carbono Vulcan e NH3, em alta temperatura. O material nomeado como MoN + Mo2C (molibdato) foi o que apresentou maior atividade catalítica, o que pôde ser atribuído ao menor tamanho de cristalito, maior quantidade da sua fase MoN e ao efeito sinérgico entre MoN e Mo2C, facilitando a ORR em comparação ao nitreto e carbeto de molibdênio puros. Nesta mesma linha de pesquisa, oxinitretos de tântalo foram sintetizados utilizando ureia como fonte de nitrogênio. Foi observado que Ti-Ta-ON apresentou maior atividade catalítica quando comparado aos demais eletrocatalisadores. Já na Parte III, os resultados para carbonitreto de titânio como suporte para a platina (Pt/Ti-CN) mostraram que, além da sua atividade para a ORR ser semelhante à platina suportada em carbono (Pt/C), ele também se mostrou mais estável que Pt/C após a realização de testes de estabilidade. / The development of conductive electrocatalysts with high activity for the oxygen reduction and evolution reactions (ORR and OER) is of extremely importance for devices that electroconvert energy, such as fuel cells and electrolizers, which work in alkaline and acid media. A substantial amount of metals can be employed in alkaline electrolytes once the latter do not require the use of noble metals. The acid medium asks for stable materials, since they are exposed to a high oxidative environment and potentials during the start-up/shutdown events of the device. On the base of these facts, this research work has been divided into three parts: Part I - bifunctional electrocatalysts studies for the ORR and OER in alkaline electrolyte, the materials were composed of spinel manganese-cobalt oxide combined with gold nanoparticles (MnCo2O4/Au). Part II - studies of alternative electrocatalysts for the ORR in acid electrolyte, which included molybdenum carbides and nitrides (Mo2C-MoN), and tantalum oxynitrides (Ta-ON). Part III - alternative supports to the carbon for the ORR in acid electrolyte, which included tantalum and titanium carbonitrides (Ta-CN and Ti-CN). The results for MnCo2O4/Au, in Part I, showed that the addition of gold on the surface of the oxide improved the latter activity for both reactions. The combination of conductive nanoparticles (gold) with active, but non-conductive, nanoparticles (MnCo2O4) seems promising for the development of active electrocatalysts for the ORR and OER. In Part II, the materials composed of Mo2C-MoN were synthesized through carbon and nitrogen insertion, in a high temperature heat treatment, in the presence of Vulcan carbon and NH3. Among the gotten materials, the so called MoN + Mo2C (molybdate) showed the better electrocatalytic activity for the ORR, which could be attributed to its smaller crystallite size and the greater amount of its MoN phase, along with the synergistic effect between MoN and Mo2C. In this way, tantalum oxynitrides materials were obtained via a urea synthesis. The catalyst referred to as Ti-Ta-ON showed the better ORR activity among all the others studied oxynitrides materials. In Part III, besides the activity for the ORR of platinum supported on titanium carbonitride (Pt/Ti-CN) was similar to the activity of platinum supported on carbon (Pt/C), Pt/Ti-CN was also more stable than the latter, after the stability tests.

Orientadores: Maria Helena Robert, Elisa Maria Ruiz Navas / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-19T00:27:43Z (GMT). No. of bitstreams: 1 BravoSalazar_JaimeAlejandro_D.pdf: 9695376 bytes, checksum: d35ebfbcaf1dac8c6665392b7d784d23 (MD5) Previous issue date: 2007 / Resumo: Este trabalho estuda o processo de fabricação de compósitos de matriz de alumínio AA6061 reforçado com TiCN por metalurgia do pó, envolvendo as etapas de mistura de pós, compactação uniaxial e sinterização com fase líquida. Para efeitos de comparação foram produzidos e caracterizados compactados da liga AA6061 sem adição de reforços. Foram investigados os parâmetros de processo: teores de reforço (5% e 10% massa), teor de aditivos Pb e Sn (0,1, 0,15, 0,2 e 0,4% massa), pressão de compactação (400, 600 e 800 MPa), tempos (15, 30, 45 e 60 min) e temperatura de sinterização (590, 600, 610 e 620 ºC). Em cada etapa do processo foram caracterizados os produtos (mistura de pós e compactados); o produto final obtido, após sinterização, foi caracterizado com relação à sua microestrutura, propriedades físicas (densificação e variação dimensional) e mecânicas (resistência à flexão e dureza). Os resultados obtidos mostraram uma grande eficiência do processo na obtenção de compósitos; a adição do teor de reforço de 5%TiCN foi eficiente na promoção de rupturas das camadas de óxidos do pó da liga de alumínio compactado à pressão de 400 MPa, auxiliando a sinterização por difusão da fase líquida formada a partir da fusão de Al+Mg2Si, melhorando a densificação e diminuindo a variação dimensional dos produtos sinterizados. Do ponto de vista metalúrgico, os materiais compósitos obtidos apresentaram microestruturas homogêneas, com uma boa distribuição dos reforços na matriz e relativa diminuição de poros. A adição de Pb e Sn promovem maior eficiência de ativação de mecanismos de sinterização; para compactados produzidos à pressão de 800 MPa, a adição de 0,1% desses elementos já apresentou significativa influência na sinterização. Com relação às propriedades mecânicas e físicas observou-se que a adição de TiCN aumentou quase no dobro de seus valores obtidos quando são comparados com a liga AA6061 / Abstract: This work investigates the process of production of composites of the alloy AA6061 reinforced with TiCN particles, by powder metallurgy involving the steps: conventional mixture of powders, compaction by uniaxial cold pressing and sintering with formation of a liquid phase. For comparative analysis it was also produced sintered AA6061 without addition of reinforcements. The following processing parameters were studied: reinforcing particles content (5 and 10 wt%); content of trace elements Pb and Sn (0.1, 0.15, 0.2 0.4 wt%); compaction pressure (from 400, 600 and 800 MPa); time and temperature of sintering (15, 30, 45, 60 min and 590, 600, 610, 620 oC). In each step products were characterized (powder mixture and green compacts); the final sintered product was characterized related to microstructure, physical (densification and dimensional changes) and mechanical (hardness and bending strength) properties. Obtained results showed high efficiency of the applied process to produce reliable composite products; the addition of 5 wt% TiCN was efficient to promote fracture of the oxide layer in the aluminum particles surface during pressing. At sintering temperatures liquid phase is formed by Al+Mg2Si melting and is distributed among particles through the fractures of the oxide layer, improving the material densification and its mechanical properties. Microstructures obtained showed homogeneous distribution of TiCN and reduced porosity, whereas AA6061 alloy microstructure showed higher porosity. Addition of Pb and Sn promoted higher efficiency of sintering mechanisms in compacts submitted to high pressures, leading to enhanced physical and mechanical properties in those materials. / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Es werden die physikalischen Grundlagen zur inelastischen Streuung mittelschneller Elektronen im Hinblick auf die Untersuchung des Energieverlustes beschrieben. Die instrumentellen Grundlagen der Energieverlust-Spektroskopie unter besonderer Berücksichtigung des Einsatzes in Transmissionselektronenmikroskopen werden erläutert. Der Einfluß des erfaßsten Streuwinkelbereichs wird diskutiert. Es werden Möglichkeiten zur Auswertung von Energieverlustmessungen im Bereich der Interbandübergangs- und Plasmonanregungen sowie im Bereich der Anregung von tieferliegenden (Rumpf-)Zuständen angegeben. Zur Anwendung der Elektronen-Energieverlust-Spektroskopie werden einige Beispiele angeführt. Von Messungen an ionengestützt abgeschiedenen Kohlenstoff- und Kohlenstoff-Stickstoff-Schichten werden Aussagen zur elektronischen und atomaren Struktur abgeleitet. Diese Ergebnisse werden unter Berücksichtigung relevanter Strukturmodelle und Abscheideparameter diskutiert. Aus Untersuchungen von Bornitridschichten wird eine vertikale Schichtung von kubischem Bornitrid über hexagonal koordiniertem verifiziert. Die Streuphase des bei der Ionisation des Al-1s-Zustandes entstehenden Sekundärelektrons bei der Rückstreuung an den nächsten Nachbarn wird durch Untersuchung der kantenfernen Feinstruktur bestimmt. Weitere Untersuchungen kantennaher Feinstrukturen an einer amorphen SiCrAl-Schicht sowie an Kohlenstoffschichten werden vorgestellt. Mögliche Einflüsse kovalenter Bindungen auf die Ergebnisse werden dabei diskutiert. Schließlich werden räumlich hochauflösende Energieverlustmessungen vorgestellt, die zum Nachweis etwa 2 nm dicker Vanadiumoxidschichten auf Rutilkristalliten führten.

Lower k and low-leakage silicon carbonitride (SiCxNy ) films were fabricated using single precursor by using radio-frequency (RF) plasma-enhanced chemical vapor deposition (PECVD). We explored precursors with (1) cyclic-carbon-containing structures, (2) higher C/Si ratio, (3) multiple vinyl groups, as well as (4) the incorporation of porogen for developing low-k SiCxNy films as etch-stop/diffusion barrier (ES/DB) layer for copper interconnects in this study. SiCxNy films with k values between 3.0 and 3.5 were fabricated at T≦ 200 o C, and k~4.0-4.5 at 300-400 °C. Precursors with vinyl groups yielded SiCxNy films with low leakage, excellent optical transmittance and high mechanical strength due to the formation of cross-linked Si-(CH2)n-Si linkages.

Silicon was selectively removed from a silicon carbonitride (SiCN) aerogel by hot chlorine gas treatment, leading to a N-doped carbon aerogel (N-CDC aerogel). The combined effects of pyrolysis and etching temperature were studied with regard to the change in the composition of the material after etching as well as the microstructure of the produced hierarchically porous material. Upon removal of Si from amorphous SiCN, carbon and nitrogen, which are not bonded together in the starting material, react, creating new C–N bonds. The removal of silicon also gives rise to a high amount of micropores and hence a high specific surface area, which can be beneficial for the functionality of the carbonaceous material produced. The mesoporous structure of the aerogel allows us to complete the etching at low temperature, which was found to be a crucial parameter to maintain a high amount of nitrogen in the material. The combination of a high amount of micropores and the mesopore transport system is beneficial for adsorption processes due to the combination of a high amount of adsorption sites and effective transport properties of the material. The N-CDC aerogels were characterized by nitrogen physisorption, X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG/DTA), and infrared spectroscopy (DRIFT) and they were evaluated as CO2 absorbers and as electrodes for electric double-layer capacitors (EDLCs).

Silicon was selectively removed from a silicon carbonitride (SiCN) aerogel by hot chlorine gas treatment, leading to a N-doped carbon aerogel (N-CDC aerogel). The combined effects of pyrolysis and etching temperature were studied with regard to the change in the composition of the material after etching as well as the microstructure of the produced hierarchically porous material. Upon removal of Si from amorphous SiCN, carbon and nitrogen, which are not bonded together in the starting material, react, creating new C–N bonds. The removal of silicon also gives rise to a high amount of micropores and hence a high specific surface area, which can be beneficial for the functionality of the carbonaceous material produced. The mesoporous structure of the aerogel allows us to complete the etching at low temperature, which was found to be a crucial parameter to maintain a high amount of nitrogen in the material. The combination of a high amount of micropores and the mesopore transport system is beneficial for adsorption processes due to the combination of a high amount of adsorption sites and effective transport properties of the material. The N-CDC aerogels were characterized by nitrogen physisorption, X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG/DTA), and infrared spectroscopy (DRIFT) and they were evaluated as CO2 absorbers and as electrodes for electric double-layer capacitors (EDLCs).

Global warming and depletion in fossil fuels have forced the society to search for alternate, clean sustainable energy sources. An obvious solution to the aforesaid problem lies in electrochemical energy storage systems like fuel cells and batteries. The desirable properties attributed to these devices like quick response, long life cycle, high round trip efficiency, clean source, low maintenance etc. have made them very attractive as energy storage devices. Compared to many advanced battery chemistries like nickel-metal hydride and lithium - ion batteries, metal-air batteries show several advantages like high energy density, ease of operation etc. The notable characteristics of metal - air batteries are the open structure with oxygen gas accessed from ambient air in the cathode compartment. These batteries rely on oxygen reduction and oxygen evolution reactions during discharging and charging processes. The efficiency of these systems is determined by the kinetics of oxygen reduction reaction. Platinum is the most preferred catalyst for many electrochemical reactions. However, high cost and stability issues restrict the use of Pt and hence there is quest for the development of stable, durable and active electrocatalysts for various redox reactions. The present thesis is directed towards exploring the electrocatalytic aspects of titanium carbonitride. TiCN, a fascinating material, possesses many favorable properties such as extreme hardness, high melting point, good thermal and electrical conductivity. Its metal-like conductivity and extreme corrosion resistance prompted us to use this material for various electrochemical studies. The work function as well as the bonding in the material can be tuned by varying the composition of carbon and nitrogen in the crystal lattice. The current study explores the versatility of TiCN as electrocatalyst in aqueous and non-aqueous media. One dimensional TiC0.7N0.3 nanowires are prepared by simple one step solvothermal method without use of any template and are characterized using various physicochemical techniques. The 1D nanostructures are of several µm size length and 40 ± 15 nm diameter (figure 1). Orientation followed by attachment of the primary particles results in the growth along a particular plane (figure 2). (a) (b) (c) Figure 1. (a) SEM images of TiC0.7N0.3 nanowires (b) TEM image and (c) High resolution TEM image showing the lattice fringes. (a) (b) (d) Figure 2. Bright field TEM images obtained at different time scales of reaction. (a) 0 h; (b) 12 h; (c) 72 h and (d) 144 h. The next aspect of the thesis discusses the electrochemical performance of TiC0.7N0.3 especially for oxygen reduction. Electrochemical oxygen reduction reaction (ORR) reveals that the nanowires possess high activity for ORR and involves four electron process leading to water as the product. The catalyst effectively converts oxygen to water with an efficiency of 85%. A comparison of the activity of different (C/N) compositions of TiCN is shown in figure 3. The composition TiC0.7N0.3 shows the maximum activity for the reaction. The catalyst is also very selective for ORR in presence of methanol and thus cross-over issue in fuel cells can be effectively addressed. Density functional theory (DFT) calculations also lead to the same composition as the best for electrocatalysis, supporting the experimental observations. Figure 3. Linear sweep voltammetric curves observed for different compositions of titanium carbonitride towards ORR. The next chapter deals with the use of TiC0.7N0.3 as air cathode for aqueous metal - air batteries. The batteries show remarkable performance in the gel- and in liquid- based electrolytes for zinc - air and magnesium - air batteries. A partial potassium salt of polyacrylic acid (PAAK) is used as the polymer to form a gel electrolyte. The cell is found to perform very well even at very high current densities in the gel electrolyte (figures 4 and 5). Figure 4 Photographs of different components of the gel - based zinc - air battery. (a) (b) Figure 5. a) Discharge curves at different current densities of 5, 20, 50 and 100 mA/cm2 for zinc-air system with TiC0.7N0.3 cathode b) Charge – discharge cycles at 50 mA/cm2 for the three electrode configuration with TiC0.7N0.3 nanowire for ORR and IrO2 for OER and Zn electrode (2h. cycle period). Similarly, the catalytic activity of TiC0.7N0.3 has also been explored in non-aqueous electrolyte. The material acts as a bifunctional catalyst for oxygen in non- aqueous medium as well. It shows a stable performance for more than 100 cycles with high reversibility for ORR and OER (figure 6). Li-O2 battery fabricated with a non-aqueous gel- based electrolyte yields very good output. (a) (b) (c) Figure 6. Galvanostatic charge –discharge cycles. (a) at 1 mA/cm2 (b) specific capacity as a function of no. of cycles (c) photographs of PAN-based gel polymer electrolyte. Another reaction of interest in non –aqueous medium is I-/I3-. redox couple. TiC0.7N0.3 nanowires show small peak to peak separation, low charge transfer resistance and hence high activity. The catalyst is used as a counter electrode in dye sensitized a solar cell that shows efficiencies similar to that of Pt, state of the art catalyst (figure 7). (a) (b) (c) Figure 7 (a) Cyclic voltammograms for I-/I3 - redox species on TiC0.7N0.3 nanowires (red), TiC0.7N0.3 particle (black) and Pt (blue). (b) Photocurrent density - voltage characteristics for DSSCs with different counter electrodes. TiC0.7N0.3 nanowire (black), TiC0.7N0.3 particle (blue), Pt (red). (c) Photograph of a sample cell. (a) (b) (c) (d) Figure 8 a) Comparison ORR activity for (i) NiTiO3(black), (ii) N-rGO (red), (iii) NiTiO3 – N-rGO (green) and (iv) Pt/C (blue) (b) Linear sweep voltammograms for OER observed on NiTiO3 – N-rGO composite (black), NiTiO3 (brown), N-rGO (blue), glassy carbon (red) in 0.5 M KOH. (c) Galvanostatic discharge curves of NiTiO3 – N-rGO as air electrode (d) Charge – discharge cycle at 5 mA/cm2 for the rechargeable battery with 10 min. cycle period. The last part of the thesis discusses about a ceramic oxide, nickel titanate. The electrocatalytic studies of the material towards ORR and OER reveal that the catalyst shows remarkable performance as a bifunctional electrode. A gel - based zinc - air battery fabricated with nickel titanate – reduced graphene oxide composite shows exceptional performance of 1000 charge-discharge cycles in the rechargeable mode (figure 8). Of course, the primary battery configuration works very well too The thesis contains seven chapters on the aspects mentioned above with summary and future perspectives given as the last chapter. An appendix based on TiN nanotubes and supercapacitor studies is given at the end.