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In this study, the carbon electrode of supercapacitor was fabricated by using mesocarbon microbeads. For finding the optimal processing parameters of carbon electrode, the effects of specific surface area of activated carbon, the amount of carbon black and binder, and various electrolytes on the capacitative properties of supercapacitor are investigated. To fabricate the composite electrode of supercapacitor, NiO and WO3 thin films were deposited respectively on the carbon electrode by electron beam evaporation. The influences of various scan rates of cyclic voltammograms (CV) on the characteristic of capacitance are studied. The charge-discharge efficiency and life time of the composite electrode are also discussed. Experimental results reveal that the optimum carbon electrode can be obtained using mesocarbon microbeads with high specific surface area (2685 m2/g) and larger pore volume (0.6 cm3/g) and adding 10 wt.% carbon black and 2wt.% binder. The specific capacitances of carbon electrodes in 1 M KOH and 1 M Et4NBF4 are 230.8 F/g and 221.5 F/g, respectively. Besides, the XRD and SEM results showed that NiO and WO3 thin films on composite electrode are sheet-liked crystal structure and stone-liked amorphous structure, respectively. The composite electrode exhibits better capacitance properties than those of carbon electrode at high scan rate by CV analysis. It reveals the promotion of the capacitative property of supercapacitor at higher power density and the improving of the decay property in capacitance at high scan rate. Finally, in the test of charge-discharge efficiency and life time, the charge-discharge efficiency is near 100% after 5000 cycles and it still retains good adhesion between electrode material and substrate.

The microstructural, electrochemical and optical properties of sol-gel derived tungsten oxide electrochromic coatings have been investigated. Coatings were formed by spinning of tungsten metal based aqueous sol on glass with native ITO layer. Three sol formulations / acetylated peroxotungstic acid (APTA), peroxotungstic acid (PTA) and titanium-doped peroxotungstic acid (Ti-PTA) were employed to obtain 200-300 nm thick multi-layered coatings. Material and electrochromic characterization of the coatings have been performed by DSC, XRD, SEM, cyclic voltammetry and UV-Vis spectroscopy. The electrochromic performance of the WO3 coatings was influenced by calcination temperature, by sol chemistry and by the adsorbed water content. For all sol formulations the coatings calcined at 250 &deg / C were amorphous and have shown better performance compared to crystalline counterparts calcined at 400 &deg / C. High calcination temperature also leads to formation of WO3 nanocrystals for APTA and PTA derived coatings, titanium doping retards crystallization. Presence of acetic acid as in APTA sol improved the electrochromic and electrochemical performance. This was related to removal of organics- acetic acid and peroxo ligands- during calcination, which results in an open W-O network providing more ion insertion sites. The water adsorption affected the electrochromic performance in different ways for the coatings calcined at 250 &deg / C and 400 &ordm / C. The amorphous coatings with limited structural water removal and excessive hydroxyl groups tend to crystallize by condensation of W-OH groups upon storage in open atmosphere, therefore exhibiting degrading electrochromic activity with aging. Conversely, hydroxyl groups enhanced Li+ ion insertion for the stable crystalline coatings calcined at 400 &deg / C.

En esta tesis doctoral, se ha investigado y desarrollado un nuevo método de CVD asistido por aerosol (AACVD), que permite el crecimiento de nanoestructuras de WO3 intrínsecas y funcionalizadas con Au. Así mismo se han depositado capas policristalinas de SnO2 para aplicaciones de detección de gases. La síntesis de materiales nanoestructurados, la fabricación de dispositivos y sus propiedades de detección de gases, han sido estudiadas. El método AACVD fue utilizado para la síntesis y la deposición directa de capas activas encima de sustratos de alúmina y también sobre substratos micromecanizados (microhotplates), lo que demuestra la compatibilidad entre la tecnología de silicio y la deposición de la capas activas nanoestructuradas. En la tesis se ha demostrado que las capas nanoestructuradas de WO3 funcionalizadas con oro tienen una sensibilidad mejor que las intrínsecas frente a algunos gases relevantes y al mismo tiempo se ha producido un cambio de selectividad. / In this doctoral thesis, it has been investigated and developed the Aerosol Assisted Chemical Vapour Deposition (AACVD) method for direct in-situ growth of intrinsic and Au-functionalised nanostructured WO3, as well as SnO2-based devices for gas sensing applications. The nanostructured material synthesis, device fabrication and their gas sensing properties have been studied. AACVD method was used for synthesis and direct deposition of sensing films onto classical alumina and microhotplate gas sensor substrates, demonstrating the compatibility between the microhotplate fabrication process and the sensing nanostructured layer deposition. The effect of Au nanoparticles on the gas sensor’s response was measured and presented in this thesis. The test results revealed that the addition of Au nanoparticles to the WO3 nanoneedles has increased the sensor’s response towards the tested gases (i.e. EtOH). It was therefore demonstrated that the Au-functionalisation has an enhancing effect on the gas sensing properties of WO3 nanoneedles

In the present thesis structure, morphology, chemical and electronic properties of the Pt - Au/tungsten oxide model system were investigated by means of RHEED, AFM and PES. The epitaxial tungsten oxide thin films were prepared by oxidation of W(110) single-crystal surface using a RF oxygen plasma source followed by thermal annealing. Gold and Platinum were deposited "in-situ" by evaporation. Gold or platinum deposition led to the growth of oriented particles having (111) epitaxial plane as well as to the growth of polycrystalline phase. Platinum encapsulation was proved by CO adsorption observed by SRPES. Deposition of the second metal led to the formation of core - shell bimetallic clusters. Detail structure of the bimetallic system depends on the order of deposited metals and the substrate temperature. Thermal stability of the system was investigated by heating up to 600 řC.

Tungsten oxide thin films were prepared by vacuum evaporation on surfaces of Pd(111), Cu(111), Cu(110) and Cu(100) single crystals and studied by RHEED, XPS and AFM methods. The tungsten oxide deposition was done at temperatures from 300 řC to 400 řC in UHV or in oxygen atmosphere. The best deposition conditions - substrate temperature of 400 řC and oxygen atmosphere - were found resulting in growth of epitaxial and only partially reduced thin films. Thin films grown on the Pd(111) and Cu(111) surfaces consisted of two phases: a nearly atomically flat phase with (100) epitaxial plane and a phase formed by three dimensional particles with (111) epitaxial plane. Thin film deposited on Cu(100) also consisted of two phases: a flat film with (100) epitaxial plane and self-organised 1D structures parallel to Cu[010] and Cu[001] directions. Thin film prepared on the Cu(110) surface contained solely 1D structures parallel to Cu[1-10] surface direction. Capability of the partially reduced thin films for oxidation was studied. We applied oxidation using RF oxygen plasma, O2 exposure at elevated temperature and exposure to atmosphere. Thermal stability of the WO3/Cu(110) system was also investigated by heating up to 620 řC.

Tungsten oxide (WO3) is a semiconducting transition metal oxide with interesting electronic, structural, and chemical properties that have been exploited in applications including catalysis, gas sensing, electrochromic displays, and solar energy conversion. Nanocrystalline WO3 can absorb visible light to catalyze heterogeneous photooxidation reactions. Also, the acidity of the WO3 surface makes this oxide a good thermal catalyst in the dehydration of alcohols to various industrially relevant chemicals. This dissertation explores the photocatalytic and thermal catalytic reactivity of nanocrystalline porous WO3 microparticles. Furthermore, investigations into the changes in WO3 reactivity are carried out after modifying the porous WO3 particles with gold nanoparticles (Au NPs). On their own, Au NPs are an important class of materials that have had a large impact in many fields such as catalysis, biomedical imaging, and drug delivery. When combined with WO3, however, their influence as part of a composite Au/WO3 catalyst has not been widely studied. Porous WO3 microparticles were first prepared using mesoporous silica (SiO2) spheres as hard templates and the physical properties of these materials were fully characterized. A facile sonochemical method was used to deposit Au NPs on the WO3 surface. Using methylene blue (MB) as a photocatalytic probe, the reaction products and the catalytic activity of WO3 and Au/WO3 catalysts were compared. Composite Au/WO3 photocatalysts exhibited significantly greater rates of MB degradation compared to pure WO3. Interestingly, the observed mechanism of MB degradation was not vastly different between the two types of catalysts. The gas-phase photocatalytic oxidation of methanol (MeOH) was studied to further understand the role of WO3 and Au NPs in these photocatalysts. Porous WO3 showed greater photooxidation rates compared to bulk WO3 because of its increased active surface area. Pure WO3 and Au NPs on porous SiO2 (SiO2-Au) were both active MeOH photooxidation catalysts and were highly selective to formaldehyde (HCHO) and methyl formate (MF), respectively. Two different mechanisms, namely band gap excitation of WO3 and surface plasmon resonance (SPR) on Au NPs, were responsible for this result. Again, the Au/WO3 composite catalysts showed greater photocatalytic activity than WO3, which increased with Au loading. This high activity led to the complete photooxidation of MeOH to carbon dioxide (CO2) over Au/WO3 catalysts. Finally, the thermal catalytic transformation of MeOH under aerobic conditions was carried out to further characterize the acid and redox active sites of WO3 and Au/WO3 catalysts. Pure WO3 was highly selective for MeOH dehydration to dimethyl ether (DME), whereas Au/WO3 showed increased oxidation selectivity to products such as HCHO, FM, and COx. The Au NPs increased the reducibility of the WO3 species, which made surface oxygen atoms more labile and reactive towards MeOH. Also, the WO3 facilitated the formation of cationic Au (Au δ+) species. This combination of effects created through a strong Au/WO3 interaction increased the activity of WO3 species, but it decreased the activity of the Au NPs.

<p>Nanoparticles of iron, cobalt and tungsten oxide were synthesised by photolytic laser assisted chemical vapour deposition (LCVD). An excimer laser (operating at 193 nm) was used as an excitation source. The LCVD process, was monitored <i>in situ</i> by optical emission spectroscopy (OES). The synthesised particles were further analysed using transmission electron spectroscopy (TEM), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.</p><p>Iron and cobalt single crystalline nanoparticles were synthesized using ferrocene and cobaltocene precursors. The diameter of the particles could be tailored by the experimental parameters (e.g., partial pressure and laser power) and were in the range 1 - 50 nm in diameter. In both cases, the particles were covered by a carbon shell, typically 7 nm thick. A thin graphitic layer was observed at the interface metal-carbon. Amorphous carbon was deposited on top of the graphitic carbon. Particle temperature, reaching the boiling point of the respective metal, was observed by OES of the thermal emission during the laser-induced particle formation process (and subsequent heating). Both bcc and fcc Fe phases were formed, both hcp and fcc for the Co phases. Size dependent magnetic properties were observed using superconducting quantum interference device (SQUID) measurements, where super-paramagnetic magnetic domains dominated for <i>d</i> < 10 nm. The iron particles were further processed, whereby the amorphous shell was removed by refluxing in nitric acid. In a subsequent step, the graphitic surface was functionalized by attaching an octyl ester, rendering the particles hydrophobic.</p><p>Tungsten oxides were synthesized from combinations of WF₆/H₂/O₂ as precursors. No particles could be deposited if H₂ was removed from the gas-mixture. The as-deposited oxide nanoparticle film was amorphous. A monoclinic WO₃ particle film could be achieved by annealing the amorphous oxide. Above 400°C, the oxide particles increased in size from ca. 20 nm to 60 nm through coalescence. The gas-sensing properties of the tungsten oxide were tested by conductance measurements using H₂S as analyte. The sensitivity of the amorphous oxide nanoparticle film was found to be superior to that of a crystalline oxide nanoparticle film. </p>

The ability to detect and quantify presence and concentration of unknown gasses is sought for applications ranging from environmental monitoring to medical analysis. Metal oxide based chemical sensing technology currently exists but the ability to provide a compositional gas breakdown reliably within a short time frame is not readily available. A very small sensor that can differentially identify the type and concentration of a gas is required. Novel methods of creating low cost and easily tuned one and two-dimensional gas sensing elements are explored. Tungsten trioxide has been thoroughly documented as an electrochromic coating, but highly sensitive WO3 elements with beam and nanowire structures have yet to be explored. Research of WO3 as a gas sensor encompasses three major components: A suitable sensing chamber with accurate analyte gas flow control and temperature control, a reliable method for WO3 deposition, and a high yield fabrication process. This thesis explores all three of these technologies. Chapter two starts with a summary of existing tungsten trioxide fabrication methods. An overview of WO3 processing follows. A comprehensive setup was designed and created to test the gas sensing response of a series of metal oxide based resistive elements through conductimetric analysis. Chapter three provides an in depth account of gas sensor test chamber design and testing. Critical test chamber aspects such as temperature control, precise gas flow control, highly efficient analyte gas switching and ease of use are presented. Chapter four outlines WO3 electrodeposition and the fabrication of beam structures for testing, while chapter five explores the templated electrodeposition of WO3 segments intercalated between gold nanowire segments. Finally, chapter six provides a summary of the research presented in this thesis as well as future directions and options available for further exploration of WO3 gas sensing elements. / Micro-Electro-Mechanical Systems (MEMS) and Nanosystems

Nanoparticles of iron, cobalt and tungsten oxide were synthesised by photolytic laser assisted chemical vapour deposition (LCVD). An excimer laser (operating at 193 nm) was used as an excitation source. The LCVD process, was monitored in situ by optical emission spectroscopy (OES). The synthesised particles were further analysed using transmission electron spectroscopy (TEM), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Iron and cobalt single crystalline nanoparticles were synthesized using ferrocene and cobaltocene precursors. The diameter of the particles could be tailored by the experimental parameters (e.g., partial pressure and laser power) and were in the range 1 - 50 nm in diameter. In both cases, the particles were covered by a carbon shell, typically 7 nm thick. A thin graphitic layer was observed at the interface metal-carbon. Amorphous carbon was deposited on top of the graphitic carbon. Particle temperature, reaching the boiling point of the respective metal, was observed by OES of the thermal emission during the laser-induced particle formation process (and subsequent heating). Both bcc and fcc Fe phases were formed, both hcp and fcc for the Co phases. Size dependent magnetic properties were observed using superconducting quantum interference device (SQUID) measurements, where super-paramagnetic magnetic domains dominated for d &lt; 10 nm. The iron particles were further processed, whereby the amorphous shell was removed by refluxing in nitric acid. In a subsequent step, the graphitic surface was functionalized by attaching an octyl ester, rendering the particles hydrophobic. Tungsten oxides were synthesized from combinations of WF6/H2/O2 as precursors. No particles could be deposited if H2 was removed from the gas-mixture. The as-deposited oxide nanoparticle film was amorphous. A monoclinic WO3 particle film could be achieved by annealing the amorphous oxide. Above 400°C, the oxide particles increased in size from ca. 20 nm to 60 nm through coalescence. The gas-sensing properties of the tungsten oxide were tested by conductance measurements using H2S as analyte. The sensitivity of the amorphous oxide nanoparticle film was found to be superior to that of a crystalline oxide nanoparticle film.