Visando compreender os fluxos na fase líquida do crescimento de silício pelo método Czochralski, é feita a Simulação Numérica do silício fundido, resolvendo-se as equações que governam o fenômeno da convecção forçada no fluido: Balanço de Quantidade de Movimento e Balanço de Massa. A técnica numérica escolhida é a de Elementos Finitos, onde é utilizada a formulação de Galerkin, com aproximações quadráticas nas componentes da velocidade e linear na pressão. A partir de várias combinações de rotações cadinho-cristal, os perfis de velocidade obtidos são analisados com relação aos efeitos de incorporação de impurezas e/ou dopantes no cristal em crescimento. / In order to visualise the flow conditions during crystal growth of Silicon by the Czochralski technique, a numerical simulation is done. It is used the Finite Element Method with the Galerkin Formulation , and with quadratic approximations on the components of the velocity and linear approximations on the pressure. Many combinations of crystal and crucible rotations are analised and discussed considering optimal growth conditions.

Graphene, a single layer of graphite, owing to its excellent mechanical, electrical, and thermal properties, has evolved as an exceptional nanomaterial in the past decade. It holds great promise in developing various novel applications from biomedical to structural composites. However, several challenges remain in realising the great potential of this material; one being the bulk scale production of graphene. This thesis has been concerned with production of pristine few-layer graphene (FLG) using liquid phase exfoliation (LPE) of graphite in various solvent media and exploring the applications of graphene-based composite coatings as optical Raman-strain sensors. LPE of natural graphite using bath sonication was used to produce highly stable pristine FLG in 1-methyl-2-pyrrolidinone (NMP) and N,N-dimethylformamide (DMF). Atomic force microscope (AFM) was used to analyse the exfoliation efficiency and lateral dimensions, while Raman spectroscopy provided an insight about the quality of the graphene flakes. Moreover, the potential for dynamic light scattering (DLS) as an efficient in situ characterisation technique for estimating the lateral dimensions of graphene flakes in dispersions was demonstrated. LPE was also employed to explore various routes to produce pristine graphene in aqueous media which can be used for toxicity studies. Aqueous dispersions were prepared by a solvent exchange method of graphene originally in organic solvents (NMP and DMF) using dialysis, achieving 0.1 v/v% organic solvent levels. Pristine aqueous graphene dispersions were also prepared by directly exfoliating graphite in biocompatible surfactant (TDOC- Sodium taurodeoxycholate) and biomolecules (Phosphatidylcholine and human serum albumin) solutions. Cell culture studies by collaborators revealed that solvent-exchanged and TDOC-exfoliated pristine FLG displayed minimal toxicity and albumin-exfoliated FLG hardly any cytotoxicity, whereas phosphatidylcholine-exfoliated FLG was cytotoxic. Raman spectroscopy is a well-established technique used to study the local deformation of carbon-based composites by following the shift rates of the Raman 2D band with strain. Raman active strain coatings were produced from epoxy composites made with the FLG produced by LPE in organic solvents and by electrochemical exfoliation method. The deformation experiments on these coatings revealed little or no strain sensitivity, due to several factors such as length of flakes, processing history, graphene loading, defects in graphene and alignment of flakes within the composites. As an alternative, composite coatings made from chemical vapour deposition (CVD) graphene were investigated. Excellent strain sensitivity was observed upon various cyclic deformational sequences and Raman mapping over 100 × 100 µm area. In comparison to the commercially available wide area strain sensors, CVD graphene composite coatings with a calculated absolute accuracy of ~ ± 0.01 % strain and absolute resolution of ~ 27 microstrains show promise for wide area Raman-based strains sensors.

The microcantilever (MC) has become a common transducer for chemical and biological sensing in gas phase and liquid phase during recent years. MC sensors provide superior mass sensitivity by converting weak chemical and biological stimuli into high mechanical response. Moreover, other advantages such as small size, low cost and array format have made MCs more attractive than other comparable sensors. Selectivity in MC sensors can be enhanced by creating a differentially functionalized MC array (MCA) with responsive phases (RPs). A well-designed array should incorporate RPs exhibiting a variety of possible interactions with the analytes, and a specific analyte should induce a distinctive response pattern demonstrated by the array. The first major division of the dissertation research work focused on enhancing selectivity of MC sensor by creating a differentiating MCA. The MCs within the array were nanostructured in a previously developed manner. A self-designed capillary array was set up to chemically functionalize different ligands onto individual MCs in an array for metal ion sensing in liquid phase. Another array was prepared by selectively vapor depositing different organic RPs onto nanostructured MCs and applied to landfill siloxane sensing in gas phase. Both of the arrays demonstrated response diversity to the target analytes. The second major division of the dissertation research work focused on developing a new method to modify MC surfaces with a function nanostructure. Aluminium oxide nanoparticles (AONP) were uniformly dispersed onto MC and a roughened surface with high surface area was achieved as stable sensor platform. Alkoxysilyl compounds were then grafted onto this platform as RPs. For demonstration, a MCA functionalized with three different alkoxysilanes was prepared for volatile organic compound sensing in gas phase. Additionally, another MCA was functionalized with anti-human immunoglobulin G and anti-biotin for bio-sensing in liquid phase. Both of the arrays were prepared with the aforementioned capillary array setup. Selective responses of specific analytes, as well as good sensitivity, were obtained from each type of AONP MCA.

In this study, the characteristics of Nickel-doped LPD-TiO2 films on silicon substrate were investigated. In our experiment, we do some measurement about physical, chemical and electrical properties for undoped and Nickel-doped LPD-TiO2 films and discussed with them. The TiO2 film thickness was characterized by field emission scanning electron microscopy ( FE-SEM ), structure was characterized by X-ray diffraction (XRD), chemical properties was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and electrical properties was characterized by leakage current: current-voltage (B1500A) and dielectric constant: capacitance-voltage (4980A). For the electrical property improvements, we investigated the Ni-doped LPD-TiO2 films by the post-anneal treatments in nitrogen, oxygen and nitrous oxide ambient. For nickel doping, the nickel chloride was used as the doping solution and the electrical characteristics were improved. After thermal annealing in nitrous oxide at 700 oC, the dielectric constant of polycrystalline titanium oxide film is 29 and can be improved to 94 with nickel doping.

An uniform titanium oxide film was grown on indium tin oxide/glass substrate with the aqueous solutions of ammonium hexafluoro-titanate and boric acid. The as-deposition titanium oxide film shows good electrochromic property because of fluorine passivation on defects and dangling bonds. The transmittance of as-grown titanium oxide on indium tin oxide/glass with a thickness of 270 nm is about 85% at the wavelength of 550 nm. By 50 times electrochromic cycling test, the transparency ratio of TiO2 film is kept at 45% between fully colored state and fully bleached state at the wavelength of 550 nm. Under ultraviolet illumination, the growth of titanium oxide film grown is enhanced. The root mean squared value of surface roughness is improved from 3.723 to 0.523 nm. Higher fluorine concentration from (NH4)2TiF6 passivate defects and dangling bonds of titanium oxide during the growth. After 50 times electrochromic cycling test, the transparency ratio UV-TiO2 is improved from 37.5% to 42.4% at the wavelength of 550 nm. The electrical characteristics of nickel-doped titanium oxide films on p-type (100) silicon substrate by liquid phase deposition were investigated. For nickel doping, the nickel chloride was used as the doping solution and the electrical characteristics were improved. After thermal annealing in nitrous oxide at 700 oC, the dielectric constant of polycrystalline titanium oxide film is 29 and can be improved to 94 with nickel doping. Uniform nickel oxide film was grown on a conducting glass substrate with the aqueous solution of saturated NiF2¡E4H2O solution and H3BO3. The quality of NiO is improved after thermal annealing at 300 oC in air from the decrease of oxygen vacancy and better F ion passivation on defects and dangling bonds. The transmittance of as-deposited NiO/ITO/glass with a thickness of 100 nm is about 78% and improved to 88% after annealing at the wavelength of 550 nm. By the electrochromic cycling test 50 times on annealed NiO film, the transparency ratio is kept at 48% between fully colored state and fully bleached state at the wavelength of 550 nm. By the memory time test, the annealed LPD-NiO film has shorter memory time. The growth of nickel oxide film grown on indium-tin oxide/glass substrate by liquid phase deposition is enhanced under ultraviolet photo-irradiation was studied. a-Ni(OH)2 dominates the composition of as-grown NiO film. After thermal treatment at 300 oC,a-Ni(OH)2 is transformed into NiO. For thermally treated NiO under ultraviolet photo-irradiation, the recrystallization and the colored and bleached transmittance after 50 times electrochromic test were improved. Both improvements come from fluorine passivation. Transparent and conductive thin films consisting of p-type nickel oxide (NiO) semiconductors were prepared by liquid phase deposition. A resistivity of 8 x 10-1 -cm was obtained for NiO films prepared at liquid phase deposition. The transmittance of NiO is almost 70 % in the 550 nm wavelength was obtained for a 384.3 nm thick NiO film.

In this study, the characteristics of LPD-NiO, and lithium-doped LPD-NiO filmson glass substrate were investigated. In our experiment, we do some measurement about physical, chemical, electrical and optical properties for LPD-NiO and lithium-doped LPD-NiO films and discussed with them. The NiO film thickness was characterized by field emission scanning electron microscopy (FE-SEM), structure was characterized by X-ray diffraction (XRD), chemical properties were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). Electrical properties were characterized by four-point probe, and optical properties were characterized by a reflecting spectrograph. The thermal annealing was used to improve the characteristics of LPD-NiO and lithium-doped LPD-NiO films in nitrogen, air and nitrous oxide ambient. For lithium doping, the lithium chloride was used as the doping solution and the electrical characteristics were enhanced. After thermal annealing in air at 400 oC, the resistivity of NiO films is 7.5 ¡Ñ 10-1 ohm-cm and can be lowed to 7.2 ¡Ñ 10-3 ohm-cm with lithium doping.

High dielectric constant barium doped titanium silicon oxide films with equivalent oxide thickness below 1 nm can be prepared by liquid phase deposition. We learn from this research that the deposition rate of titanium silicon oxide films can be much enhanced by nitric acid incorporation, and the dielectric constant of materials can be increased by the dipole polarization from barium. The key parameter for the deposition rate, refractive index, and the dielectric constant of barium doped titanium silicon oxide is the molarity of barium nitrate. The electrical properties can be improved effectively by thermal annealing treatments. The optimum equivalent oxide thickness of barium doped titanium silicon oxide thin film is 0.9 nm with the optical thickness of 7.4 nm. The high dielectric constant can reach 31.9 and the leakage current density is 5 ¡Ñ 10-6 A/cm2 at the electrical field intensity of 5 MV/cm, which has high potential application for the next generation MOSFET.

In the present study / the effects of the powder metallurgical parameters such as the mixing method, compaction pressure, initial tungsten (W) particle size, composition, sintering temperature and sintering time on the sintering behavior of selected high density W-Ni-Cu alloys were investigated. The alloys were produced through conventional powder metallurgy route of mixing, cold compaction and sintering. The total solute (Ni-Cu) content in the produced alloys was kept constant at 10 wt%, while the copper concentration of the solutes was varied from 2.5 wt% to 10 wt%. Mainly liquid phase sintering method was applied in the production of the alloys. The results of the study were based on the density measurements, microstructural characterizations including optical and scanning electron microscopy and mechanical characterizations including hardness measurements. The results showed that the nature of the mixing method applied in the preparation of the powder mixtures has a considerable effect on the final sintered state of W-Ni-Cu alloys. Within the experimental limits of the study, the compaction v pressure and initial W particle size did not seem to affect the densification behavior. It was found that the sintering behavior of W-Ni-Cu alloys investigated in this study was essentially dominated by the Ni content in the alloy and the sintering temperature. A high degree of densification was observed in these alloys with an increase in the Ni content and sintering temperature which was suggested to be due to an increase in the solubility and diffusivity of W in the binder matrix phase with an increase in these parameters, leading to an increase in the overall sintering kinetics. Based on the results obtained in the present study, a model explaining the kinetics of the diffusional processes governing the densification and coarsening behavior of W-Ni-Cu alloys was proposed.

Recently, the evolutions of wireless communication systems are growing rapidly to satisfy the personal communication requirements. Compact, small size, low cost, and multi-function are the major developing trends among these modern wireless communication devices. The use of ceramic materials with high permittivity can effectively reduce the sizes of microwave devices. This thesis consists of two parts: the research of microwave dielectric materials and the implementation of microstrip ceramic antennas. In the first part of the dissertation, the systematic investigations of the microstructure and microwave dielectric properties in respect of BiNbO4-based ceramics and MCAS glass-added Al2O3-TiO2 ceramics have presented. By the addition of CuO, V2O5, or CuO-V2O5 mixture, the BiNbO4 ceramics can be densified at lower sintering temperatures less than 940¢J. The excellent microwave dielectric properties are obtained as 0.5 wt% CuO or V2O5 are added as sintering aids. The exceeded additive amount or sintering temperatures will result in the appearance of abnormal grain growth and the increase of grain boundary inclusions, which will decrease the microwave dielectric properties including the quality factor (Q) and the temperature coefficient of resonant frequency (£nf). The CuO-added BiNbO4 ceramics reveal a negative £nf value and V2O5-added BiNbO4 ceramics reveal a positive one. The £nf values can be reduced to near 0 ppm/¢J by controlling the weight ratio of CuO/V2O5. Another method to reduce the £nf values to near 0 ppm/¢J is the substitution of Sm for Bi. For the (Bi1-xSmx)NbO4 ceramics, the presence of the £]-form of (Bi1-xSmx)NbO4 ceramics will affect the grain growth, density, Q¡Ñf values and £nf values, but that has no apparent effect on £`r values. On the whole, a high permittivity, an acceptable quality factor, and the temperature stable BiNbO4-based ceramic can be obtained. As for (1-x)Al2O3-xTiO2 ceramics, the addition of MCAS glass can lower the sintering temperatures of (1-x)Al2O3-xTiO2 ceramics from 1500¢J to 1300¢J. And the £nf value can be adjusted to near zero by controlling the TiO2 content and sintering temperature. The appearance of Al2TiO5 phase, resulted from the consumption of TiO2, exhibits intense effect on the microwave dielectric properties of (1-x)Al2O3 -xTiO2 ceramics. The major contributions in this research would be the lower sintering temperatures and the near 0 ppm/¢J of £nf value. The 2wt%- MCAS-added (1-x)Al2O3-xTiO2 ceramics sintered at 1300¢J and x = 0.12 has a minimum £nf value of ¡V0.6 ppm/¢J. In the second part of the dissertation, the microstrip antennas with high permittivity BiNbO4 ceramics (£`r = 43) substrate are fabricated. The bandwidths obtained are narrow and insufficient for the WLAN application. The techniques of U-slots patch and stacked structure are used to enhance the bandwidth of the microstrip ceramic antennas by combining the two adjacent resonant modes. The results indicate that the impedance bandwidth can be enhanced from 2.3% to 5.3% by embedding double U-shaped slots in the rectangular patch, or to 4.5% by using stacked patches.

The purpose of this work is the development of MEMS-based resonant sensors for liquid-phase biochemical sensing applications. Specifically, the sensors developed here are aimed at embedded or point-of-sampling applications: (1) when there is not enough time to send a sample to a lab for analysis, (2) in resource-poor settings, (3) when collecting analyte and shipping it to a lab would damage the sample, or (4) for in-situ monitoring. To this end, a bulk micromachined resonant cantilever sensor and a surface micromachined sensor based on the spring-softening effect are investigated as transducer elements. The developed cantilever resonators are operated in an in-plane vibration mode to reduce fluid damping and mass loading by the surrounding fluid. The surface of the resonator is either coated with a chemically sensitive polymer film for chemical sensing or with a layer of protein or antibody for biosensor testing. Chemical tests for sensing volatile organic compounds using polymer-coated in-plane resonators in the liquid-phase give estimated limits of detection below 100 ppb. In addition, biosensor tests for the detection of anti-IgG yield estimated limits of detection around 100 ng/ml. In an attempt to further improve sensor reliability and to further lower the limits of detection, a second sensing concept has been investigated. The presented sensing scheme is capacitive with a resonator acting as an analog-to-digital converter. The resonator and the sensing capacitors are coupled via the spring softening effect. Through this mechanism a change in capacitance causes a shift in resonant frequency. Extensive device modeling has been performed and a process has been developed allowing for fabrication and on-chip packaging of these sensor structures. Initial mechanical characterization data show that the resonators do in fact vibrate.