Dissertations / Theses on the topic 'Submicrometric'

Orientador: Lucila Helena Deliesposte Cescato
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo:Micropeneiras são dispositivos de microfiltração que se diferenciam das membranas filtrantes por apresentarem uma distribuição homogênea de poros e baixa rugosidade na sua superfície. Estas características as tornam uma melhor alternativa para processos de separação que requerem alta seletividade na indústria química, de fármacos e de biotecnologia. Neste trabalho desenvolvemos um processo de fabricação de Micropeneiras e Peneiras Submicrométricas utilizando a associação de técnicas de litografia convencional, litografia holográfica e eletroformação. As Micropeneiras eletroformadas em Níquel foram caracterizadas num sistema de microfiltração utilizando fluxo tangencial. Foram estudadas a seletividade da filtração e a resistência ao fluxo para peneiras com mesma área furada e diferentes geometrias de orifícios. Para as peneiras submicrométricas foi possível apenas realizar uma análise da capacidade de retenção de partículas e da pressão de ruptura. Os resultados das medidas de filtração apresentaram uma excelente seletividade na separação de partículas por tamanho, que demonstra a homogeneidade das dimensões dos orifícios das peneiras, fabricadas com esta técnica. O estudo experimental da resistência ao fluxo demonstrou que os modelos atualmente existentes (elaborados para a condição de fluxo frontal) não são adequados para descrever o comportamento das peneiras em regime de fluxo tangencial
Abstract:Microsieves are filtration devices that present a homogeneous distribution of pores, as well as smoother surface in comparison with filter membranes. Because of these characteristics they represent a better choice in processes of separation in the chemistry and biotechnology industries that require high selectivity. In this work we develop a process for fabrication of Microsieves and Submicrosieves. The process associates conventional litography, holographic litography and electroforming techniques. The fabricated Nickel Microsieves were characterized in a cross filtration system. The selectivity and the flow resistance of the microsieves, with the same perforated area and different geometries of the orifices, were analyzed. For the submicrosieves it was possible only to check the capability of retention of particles and the pressure of rupture. The results of the filtration measurements show high selectivity of particles by size, demonstrating the good homogeneity in the orifices of the microsieves. The analysis of the experimental results of the flow resistance measurements showed that the existing models are not appropriate for describing the behavior of microsieve in cross flow
Mestrado
Física
Mestre em Física

The uncertainty of the climate and health effects of aerosols is still large, one important reason being lack of knowledge of the primary emissions. This thesis combines laboratory and field experiments, and process modelling in an effort to better quantify the submicrometre aerosol emissions and to understand some of the processes in the atmosphere.

A parameterisation was derived for the source flux of sea salt particles (particles m^-2 s^-1) in the size range 0.02-2.8 µm dry diameter (D_p), it is the first parameterisation to almost cover two full decades of the submicrometre sea salt aerosol production, and to include the effect of water temperature. This sea salt parameterisation was validated for temperate water in the 0.1-1.1 μm D_p range using in situ size resolved emissions of marine aerosol particles, which were measured with the eddy covariance (EC) method. For periods sampled air was heated to 300ºC in order to evaporate semi-volatile organics and isolate the sea salt fraction. Comparisons with the total aerosol emissions suggest that in these emissions organic carbon and sea salt are internally mixed in the same particles. Finally an aerosol dynamics model was modified for marine conditions. In the model parameterised emissions of sea salt was included together with aerosol dynamics, chemistry and clouds representative for the marine boundary layer. The sea salt emissions are together with secondary sulphate, and cloud processing able to reproduce a typical marine aerosol size distribution and cloud condensation nuclei population.

Measurements with the EC method of the road traffic related aerosol source number flux for D_p>0.011 µm show that the major part of the aerosol fluxes is due to road traffic emissions. Both an emission factor for the whole fleet mix in Stockholm (1.4x10¹⁴ vehicle^-1 km^-1) and separate emission factors for light- and heavy-duty vehicles (HDV) were deduced. The result shows that during weekdays 70-80% of the emissions come from HDV.

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Polymer particles in the nanometer range are of fundamental interest today, especially when used as carrier systems in the controlled release of drugs, cosmetics and nutraceuticals, as well as in coating materials with magnetic properties. The main objective of the present study concerns the production of submicron particles of poly (methyl methacrylate) (PMMA) by crystallization of a polymer solution by thermally controlled cooling. In this work, PMMA solutions in ethanol and 1-propanol were prepared at different concentrations (1% to 5% by weight) and crystallized at different cooling rates (0.2 to 0.8 ? C / min) controlled linearly. Analysis of particle size distribution (DLS / CILAS) and scanning electron microscopy (SEM) were performed in order to evaluate the morphological characteristics of the produced particles. The results demonstrated that it is possible to obtain submicron polymer perfectly spherical particles using the technique discussed in this study. It was also observed that, depending on the cooling rate and the concentration of the polymer solution, it is possible to achieve high yield in the formation of submicron particles. In addition, preliminary tests were performed in order to verify the ability of this technique to form particulated carrier material with magnetic properties. The results showed that the developed technique can be an interesting alternative to obtain polymer particles with magnetic properties
Part?culas polim?ricas formadas em escala nanom?trica s?o de fundamental interesse atualmente, principalmente quando utilizadas como sistemas carreadores na libera??o controlada de f?rmacos, cosm?ticos e nutrac?uticos, al?m do interesse pr?tico no recobrimento de materiais com propriedades magn?ticas. O principal objetivo do presente estudo diz respeito ? produ??o de part?culas submicrom?tricas de poli(metacrilato de metila) (PMMA) atrav?s da t?cnica de cristaliza??o de uma solu??o polim?rica por resfriamento controlado termicamente, segundo um perfil de taxa linear de resfriamento. Neste trabalho, solu??es de PMMA em etanol e 1-propanol foram preparadas em diferentes concentra??es (1% a 5% em massa) e cristalizadas em diferentes taxas de resfriamento (0,2 a 0,8 ?C/min) controladas linearmente. An?lises de distribui??o de part?culas (DLS/CILAS) e microscopia eletr?nica de varredura (MEV) foram realizadas com o intuito de avaliar as caracter?sticas morfol?gicas das part?culas formadas. Os resultados demonstraram que ? poss?vel obter part?culas polim?ricas submicrom?tricas com morfologia perfeitamente esf?rica utilizando a t?cnica abordada no presente estudo. Observou-se tamb?m que, a depender da taxa de resfriamento e da concentra??o da solu??o polim?rica, ? poss?vel ter alto rendimento na forma??o de part?culas submicrom?tricas. Adicionalmente, foram realizados testes preliminares com o prop?sito de verificar a capacidade desta t?cnica em formar part?culas carreadoras de materiais com propriedades magn?ticas. Os resultados permitiram concluir que a t?cnica estudada pode ser uma alternativa interessante na obten??o de part?culas polim?ricas com propriedades magn?ticas

Les nanodiamants (NDs) font l'objet de recherches intenses dans les domaines biomédical, militaire et de la mécanique quantique. Pour produire ces NDs, le recours à la détonation d'un mélange RDX/TNT, aussi appelé hexolite, est souvent préféré. Cependant, pour produire des NDs aux propriétés physico-chimiques performantes, il est nécessaire d’avoir au préalable des particules fines d’hexolites, et des mélanges intimes et homogènes. Pour parvenir à cela, le laboratoire NS3E a développé le procédé de recristallisation par évaporation flash de spray (Spray Flash Evaporation, SFE). Cependant, l'influence des différentes conditions opératoires du procédé sur les caractéristiques physico-chimiques des particules est encore mal comprise. Améliorer cette compréhension permettrait une plus grande maîtrise des propriétés des particules recristallisées. Cette thèse vise donc, à l'aide d'analyses in situ telles que l'ombroscopie et le PDPA (Phase Doppler Particle Analyzer), à apporter des réponses. Les recherches se structurent en deux axes principaux. Le premier axe explore en profondeur les phénomènes physico-chimiques de l'évaporation flash d'un solvant (acétone) et l'impact du soluté (hexolite) sur le comportement du spray d'acétone. Le second axe porte quant à lui sur la caractérisation des particules d'hexolite, notamment en ce qui concerne leur sensibilité, leur taille et leur morphologie et les raisons qui ont conduit à de telles propriétés par rapport au comportement du spray
Nanodiamonds (NDs) are the subject of extensive research in biomedical, military, and quantum mechanics applications. To produce these NDs, the detonation of a RDX/TNT mixture, commonly referred to as hexolite, is frequently employed. However, to achieve NDs with high-performing physicochemical properties, it is essential to begin with finely divided hexolite particles and to ensure that the mixture is both intimate and homogeneous. In pursuit of this goal, the NS3E laboratory has developed a recrystallization process based on Spray Flash Evaporation (SFE). Despite this advancement, the influence of various operating conditions on the physicochemical characteristics of the resulting particles remains poorly understood. Gaining a deeper understanding of these influences would enable more precise control over the properties of the recrystallized particles. This thesis therefore aims to address these issues by employing in situ analytical techniques, such as shadowgraphy and Phase Doppler Particle Analysis (PDPA).The research is organized around two principal axes. The first focuses on an in-depth investigation of the physicochemical phenomena underlying the flash evaporation of a solvent (acetone) and examines how the presence of a solute (hexolite) affects the behavior of the acetone spray. The second axis centers on characterizing the resulting hexolite particles—specifically their sensitivity, size, and morphology—and elucidating the underlying reasons for these properties considering the spray’s behavior

L'etude des effets de porteurs chauds pouvant induire une degradation electrique des circuits integres est d'une grande importance pour les composants avances. Dans les transistors fortement submicroniques, la caracterisation et la modelisation a temperature ambiante et a basses temperatures de l'ionisation secondaire par impact et du courant de grille qui en resulte, completee par l'etude de l'emission lumineuse liee a ce mecanisme, ont ete menees a bien, apportant une meilleure comprehension de la generation de porteurs chauds dont l'energie est responsable de la creation d'etats d'interface et de la degradation des performances des composants. Tirant profit de l'acceleration du vieillissement electrique par l'intensification de l'ionisation secondaire, une nouvelle methode de prediction de la duree de vie des transistors dans leurs conditions nominales de polarisation est proposee. Enfin, l'impact du type de contrainte electrique et de l'architecture technologique sur la fiabilite des composants sont etudies.

The measurement of submicrometre (< 1.0 m) and ultrafine particles (diameter < 0.1 m) number concentration have attracted attention since the last decade because the potential health impacts associated with exposure to these particles can be more significant than those due to exposure to larger particles. At present, ultrafine particles are not regularly monitored and they are yet to be incorporated into air quality monitoring programs. As a result, very few studies have analysed their long-term and spatial variations in ultrafine particle concentration, and none have been in Australia. To address this gap in scientific knowledge, the aim of this research was to investigate the long-term trends and seasonal variations in particle number concentrations in Brisbane, Australia. Data collected over a five-year period were analysed using weighted regression models. Monthly mean concentrations in the morning (6:00-10:00) and the afternoon (16:00-19:00) were plotted against time in months, using the monthly variance as the weights. During the five-year period, submicrometre and ultrafine particle concentrations increased in the morning by 105.7% and 81.5% respectively whereas in the afternoon there was no significant trend. The morning concentrations were associated with fresh traffic emissions and the afternoon concentrations with the background. The statistical tests applied to the seasonal models, on the other hand, indicated that there was no seasonal component. The spatial variation in size distribution in a large urban area was investigated using particle number size distribution data collected at nine different locations during different campaigns. The size distributions were represented by the modal structures and cumulative size distributions. Particle number peaked at around 30 nm, except at an isolated site dominated by diesel trucks, where the particle number peaked at around 60 nm. It was found that ultrafine particles contributed to 82%-90% of the total particle number. At the sites dominated by petrol vehicles, nanoparticles (< 50 nm) contributed 60%-70% of the total particle number, and at the site dominated by diesel trucks they contributed 50%. Although the sampling campaigns took place during different seasons and were of varying duration these variations did not have an effect on the particle size distributions. The results suggested that the distributions were rather affected by differences in traffic composition and distance to the road. To investigate the occurrence of nucleation events, that is, secondary particle formation from gaseous precursors, particle size distribution data collected over a 13 month period during 5 different campaigns were analysed. The study area was a complex urban environment influenced by anthropogenic and natural sources. The study introduced a new application of time series differencing for the identification of nucleation events. To evaluate the conditions favourable to nucleation, the meteorological conditions and gaseous concentrations prior to and during nucleation events were recorded. Gaseous concentrations did not exhibit a clear pattern of change in concentration. It was also found that nucleation was associated with sea breeze and long-range transport. The implications of this finding are that whilst vehicles are the most important source of ultrafine particles, sea breeze and aged gaseous emissions play a more important role in secondary particle formation in the study area.

The measurement of submicrometre (< 1.0 m) and ultrafine particles (diameter < 0.1 m) number concentration have attracted attention since the last decade because the potential health impacts associated with exposure to these particles can be more significant than those due to exposure to larger particles. At present, ultrafine particles are not regularly monitored and they are yet to be incorporated into air quality monitoring programs. As a result, very few studies have analysed their long-term and spatial variations in ultrafine particle concentration, and none have been in Australia. To address this gap in scientific knowledge, the aim of this research was to investigate the long-term trends and seasonal variations in particle number concentrations in Brisbane, Australia. Data collected over a five-year period were analysed using weighted regression models. Monthly mean concentrations in the morning (6:00-10:00) and the afternoon (16:00-19:00) were plotted against time in months, using the monthly variance as the weights. During the five-year period, submicrometre and ultrafine particle concentrations increased in the morning by 105.7% and 81.5% respectively whereas in the afternoon there was no significant trend. The morning concentrations were associated with fresh traffic emissions and the afternoon concentrations with the background. The statistical tests applied to the seasonal models, on the other hand, indicated that there was no seasonal component. The spatial variation in size distribution in a large urban area was investigated using particle number size distribution data collected at nine different locations during different campaigns. The size distributions were represented by the modal structures and cumulative size distributions. Particle number peaked at around 30 nm, except at an isolated site dominated by diesel trucks, where the particle number peaked at around 60 nm. It was found that ultrafine particles contributed to 82%-90% of the total particle number. At the sites dominated by petrol vehicles, nanoparticles (< 50 nm) contributed 60%-70% of the total particle number, and at the site dominated by diesel trucks they contributed 50%. Although the sampling campaigns took place during different seasons and were of varying duration these variations did not have an effect on the particle size distributions. The results suggested that the distributions were rather affected by differences in traffic composition and distance to the road. To investigate the occurrence of nucleation events, that is, secondary particle formation from gaseous precursors, particle size distribution data collected over a 13 month period during 5 different campaigns were analysed. The study area was a complex urban environment influenced by anthropogenic and natural sources. The study introduced a new application of time series differencing for the identification of nucleation events. To evaluate the conditions favourable to nucleation, the meteorological conditions and gaseous concentrations prior to and during nucleation events were recorded. Gaseous concentrations did not exhibit a clear pattern of change in concentration. It was also found that nucleation was associated with sea breeze and long-range transport. The implications of this finding are that whilst vehicles are the most important source of ultrafine particles, sea breeze and aged gaseous emissions play a more important role in secondary particle formation in the study area.

Motor vehicles are a major source of gaseous and particulate matter pollution in urban areas, particularly of ultrafine sized particles (diameters < 0.1 µm). Exposure to particulate matter has been found to be associated with serious health effects, including respiratory and cardiovascular disease, and mortality. Particle emissions generated by motor vehicles span a very broad size range (from around 0.003-10 µm) and are measured as different subsets of particle mass concentrations or particle number count. However, there exist scientific challenges in analysing and interpreting the large data sets on motor vehicle emission factors, and no understanding is available of the application of different particle metrics as a basis for air quality regulation. To date a comprehensive inventory covering the broad size range of particles emitted by motor vehicles, and which includes particle number, does not exist anywhere in the world. This thesis covers research related to four important and interrelated aspects pertaining to particulate matter generated by motor vehicle fleets. These include the derivation of suitable particle emission factors for use in transport modelling and health impact assessments; quantification of motor vehicle particle emission inventories; investigation of the particle characteristic modality within particle size distributions as a potential for developing air quality regulation; and review and synthesis of current knowledge on ultrafine particles as it relates to motor vehicles; and the application of these aspects to the quantification, control and management of motor vehicle particle emissions. In order to quantify emissions in terms of a comprehensive inventory, which covers the full size range of particles emitted by motor vehicle fleets, it was necessary to derive a suitable set of particle emission factors for different vehicle and road type combinations for particle number, particle volume, PM1, PM2.5 and PM1 (mass concentration of particles with aerodynamic diameters < 1 µm, < 2.5 µm and < 10 µm respectively). The very large data set of emission factors analysed in this study were sourced from measurement studies conducted in developed countries, and hence the derived set of emission factors are suitable for preparing inventories in other urban regions of the developed world. These emission factors are particularly useful for regions with a lack of measurement data to derive emission factors, or where experimental data are available but are of insufficient scope. The comprehensive particle emissions inventory presented in this thesis is the first published inventory of tailpipe particle emissions prepared for a motor vehicle fleet, and included the quantification of particle emissions covering the full size range of particles emitted by vehicles, based on measurement data. The inventory quantified particle emissions measured in terms of particle number and different particle mass size fractions. It was developed for the urban South-East Queensland fleet in Australia, and included testing the particle emission implications of future scenarios for different passenger and freight travel demand. The thesis also presents evidence of the usefulness of examining modality within particle size distributions as a basis for developing air quality regulations; and finds evidence to support the relevance of introducing a new PM1 mass ambient air quality standard for the majority of environments worldwide. The study found that a combination of PM1 and PM10 standards are likely to be a more discerning and suitable set of ambient air quality standards for controlling particles emitted from combustion and mechanically-generated sources, such as motor vehicles, than the current mass standards of PM2.5 and PM10. The study also reviewed and synthesized existing knowledge on ultrafine particles, with a specific focus on those originating from motor vehicles. It found that motor vehicles are significant contributors to both air pollution and ultrafine particles in urban areas, and that a standardized measurement procedure is not currently available for ultrafine particles. The review found discrepancies exist between outcomes of instrumentation used to measure ultrafine particles; that few data is available on ultrafine particle chemistry and composition, long term monitoring; characterization of their spatial and temporal distribution in urban areas; and that no inventories for particle number are available for motor vehicle fleets. This knowledge is critical for epidemiological studies and exposure-response assessment. Conclusions from this review included the recommendation that ultrafine particles in populated urban areas be considered a likely target for future air quality regulation based on particle number, due to their potential impacts on the environment. The research in this PhD thesis successfully integrated the elements needed to quantify and manage motor vehicle fleet emissions, and its novelty relates to the combining of expertise from two distinctly separate disciplines - from aerosol science and transport modelling. The new knowledge and concepts developed in this PhD research provide never before available data and methods which can be used to develop comprehensive, size-resolved inventories of motor vehicle particle emissions, and air quality regulations to control particle emissions to protect the health and well-being of current and future generations.

Motor vehicles are a major source of gaseous and particulate matter pollution in urban areas, particularly of ultrafine sized particles (diameters < 0.1 µm). Exposure to particulate matter has been found to be associated with serious health effects, including respiratory and cardiovascular disease, and mortality. Particle emissions generated by motor vehicles span a very broad size range (from around 0.003-10 µm) and are measured as different subsets of particle mass concentrations or particle number count. However, there exist scientific challenges in analysing and interpreting the large data sets on motor vehicle emission factors, and no understanding is available of the application of different particle metrics as a basis for air quality regulation. To date a comprehensive inventory covering the broad size range of particles emitted by motor vehicles, and which includes particle number, does not exist anywhere in the world. This thesis covers research related to four important and interrelated aspects pertaining to particulate matter generated by motor vehicle fleets. These include the derivation of suitable particle emission factors for use in transport modelling and health impact assessments; quantification of motor vehicle particle emission inventories; investigation of the particle characteristic modality within particle size distributions as a potential for developing air quality regulation; and review and synthesis of current knowledge on ultrafine particles as it relates to motor vehicles; and the application of these aspects to the quantification, control and management of motor vehicle particle emissions. In order to quantify emissions in terms of a comprehensive inventory, which covers the full size range of particles emitted by motor vehicle fleets, it was necessary to derive a suitable set of particle emission factors for different vehicle and road type combinations for particle number, particle volume, PM1, PM2.5 and PM1 (mass concentration of particles with aerodynamic diameters < 1 µm, < 2.5 µm and < 10 µm respectively). The very large data set of emission factors analysed in this study were sourced from measurement studies conducted in developed countries, and hence the derived set of emission factors are suitable for preparing inventories in other urban regions of the developed world. These emission factors are particularly useful for regions with a lack of measurement data to derive emission factors, or where experimental data are available but are of insufficient scope. The comprehensive particle emissions inventory presented in this thesis is the first published inventory of tailpipe particle emissions prepared for a motor vehicle fleet, and included the quantification of particle emissions covering the full size range of particles emitted by vehicles, based on measurement data. The inventory quantified particle emissions measured in terms of particle number and different particle mass size fractions. It was developed for the urban South-East Queensland fleet in Australia, and included testing the particle emission implications of future scenarios for different passenger and freight travel demand. The thesis also presents evidence of the usefulness of examining modality within particle size distributions as a basis for developing air quality regulations; and finds evidence to support the relevance of introducing a new PM1 mass ambient air quality standard for the majority of environments worldwide. The study found that a combination of PM1 and PM10 standards are likely to be a more discerning and suitable set of ambient air quality standards for controlling particles emitted from combustion and mechanically-generated sources, such as motor vehicles, than the current mass standards of PM2.5 and PM10. The study also reviewed and synthesized existing knowledge on ultrafine particles, with a specific focus on those originating from motor vehicles. It found that motor vehicles are significant contributors to both air pollution and ultrafine particles in urban areas, and that a standardized measurement procedure is not currently available for ultrafine particles. The review found discrepancies exist between outcomes of instrumentation used to measure ultrafine particles; that few data is available on ultrafine particle chemistry and composition, long term monitoring; characterization of their spatial and temporal distribution in urban areas; and that no inventories for particle number are available for motor vehicle fleets. This knowledge is critical for epidemiological studies and exposure-response assessment. Conclusions from this review included the recommendation that ultrafine particles in populated urban areas be considered a likely target for future air quality regulation based on particle number, due to their potential impacts on the environment. The research in this PhD thesis successfully integrated the elements needed to quantify and manage motor vehicle fleet emissions, and its novelty relates to the combining of expertise from two distinctly separate disciplines - from aerosol science and transport modelling. The new knowledge and concepts developed in this PhD research provide never before available data and methods which can be used to develop comprehensive, size-resolved inventories of motor vehicle particle emissions, and air quality regulations to control particle emissions to protect the health and well-being of current and future generations.

Compte tenu de la reduction spectaculaire des dimensions critiques des dispositifs elementaires utilises dans la fabrication des circuits integres, les questions de fiabilite des dielectriques minces des technologies cmos submicroniques sont au cur des preoccupations de l'industrie des semiconducteurs. Dans ce contexte, l'objet de ce memoire est l'etude des phenomenes physiques responsables de la degradation des isolants intervenant dans les dispositifs mos. Apres des rappels generaux sur le systeme si-sio#2 et sur les methodes de caracterisation utilisees, nous presentons dans le deuxieme chapitre les caracteristiques de piegeage en volume des oxydes minces d'epaisseur entre 5,5 nm et 12 nm. Nous mettons clairement en evidence le caractere universel de la loi de degradation sur une large gamme d'epaisseurs et de conditions experimentales de contrainte et de temperature. Une tentative de modelisation de la loi universelle de piegeage est presentee sur la base d'un mecanisme de piegeage-depiegeage. Le troisieme chapitre est consacre aux problemes de claquage des dielectriques minces. Nous montrons de facon incontestable la relation existant entre les proprietes de piegeage et le phenomene de claquage. En particulier, nous demontrons l'existence d'une charge critique piegee en volume lors du claquage dont nous soulignons l'importance comme parametre determinant pour la comprehension et l'evaluation du claquage dans les oxydes compte tenu de son invariance avec les conditions experimentales (intensite de la contrainte et temperature). L'existence de cette charge permet de proposer un modele de claquage fonde sur les caracteristiques de piegeage des isolants qui autorise pour la premiere fois une comprehension quantitative des donnees de claquage obtenues en fonction du mode de contrainte (a tension constante ou a courant constant). Enfin, nous illustrons dans le quatrieme chapitre la pertinence de l'etude des proprietes de piegeage pour l'evaluation de la qualite du systeme si/sio#2 a travers l'etude des performances d'oxydes nitrures sous n#2o

碩士
國立成功大學
資源工程學系
102
Particle size effects of starting materials on mullite formation in the α-Al2O3/cristobalite powder systems was examined. α-Al2O3 and cristobalite powders with D50 values of 200, 300, and 400 nm were mixed in a stoichiometric composition of 3Al2O3∙2SiO2 (71.8 wt% α-Al2O3 and 28.2 wt% SiO2) as starting powder systems. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) techniques were used in this study. The results showed that mullite formation is related to the amorphization of silica. Cristobalite powder amorphized in advance during the thermal treatment, and then the Si component migrates to contact the α-Al2O3 particle to form mullite. A reduction in the size of α-Al2O3 particles resulted in a decrease in the amorphization temperatuer. Thus, the temperature of initiating mullite formation was lowered. A reduction in cristobalite particle sizes accelerated the amorphization reaction and resulted in higher rates of mullite formation. Thus it lowered the temperatures at which the powder system entirely converted into mullite. The activation energy calculated by isothermal experiments shows the reduction in particle sizes of cristobalite powders experienced more impact on the generation of the activation energy of mullite than that of α-Al2O3. As a result, in the α-Al2O3/cristobalite powder systems, size of cristobalite particles determined the rate of mullite formation.The crystal orientation of the mullite was controlled by the α-Al2O3 matrix, that is, [001] α-Al2O3 → [001] mullite. These results indicate that the amorphization of cristobalite may trigger the reaction of SiO2 with α-Al2O3, initiating the nucleation of mullite. The α-Al2O3 particles act as the hosts for mullite formation and determine the size of the mullite particles.

碩士
國立彰化師範大學
物理學系
96
Square pinning array of defects is fabricated on Nb superconducting films for the discussion of matching effect and vortices lattice. On the substrate coated with Si3N4, E-beam lithography and RIE(Reactive Ion Etching) have been employed to create periodic square array of holes. Then Nb films of 100nm thickness were deposited using DC sputtering. The film is wrinkled because of the holes on substrate and the wrinkles can act as pinning defects in the mixed state of superconductor. We have found matching effect in all of the samples. we can get maximum (minimum) of critical current (resistance) under the change of the magnetic field. But in our experiment, there would be a critical current peak disappear under a specific matching field. For understanding the detail, we discuss the possible vortex lattice by changing different parameter in simulation, and phase diagram is obtained. Fs-V curve reflects stability of vortex lattice under various magnetic field, we pick up the results which is agreeable to our experiment data, and try to explain the mechanism of the experiment result from the vortex lattice.

碩士
國立彰化師範大學
物理學系
92
In this study the periodic pinning of magnetic flux quanta in the Nb films with honeycomb array of submicrometer defects is investigated. Hole arrays with a spacing of about 400~700nm and a diameter close to 250~300nm were fabricated on Si3N4 substrate by the electron beam lithography and dry etching method. Then the superconducting Nb film was deposited using dc magnetic sputtering on top of the circular holes in the substrate. Consequently, the corrugations structure of the Nb thin film acts as flux pinning centers. Matching effect was observed in these samples. The vortices that penetrate into type-II superconductors in mixed state are movable due to three kinds of forces: Lorentz force, pinning force and vortex-vortex interaction. The minima of resistance and maxima of critical current appeared at certain values of magnetic field corresponding to the matching field of the lattice spacing of the defects. Many vortex configurations for the honeycomb arrays of pinning centers were suggested to form. When the magnetic field is equal to the matching field or fractional matching field, the vortices will be arranged in good order. We have found that the fractional matching fields for n=0.5 can be observed under three conditions: 1.smaller current, 2.lower temperature, 3.smaller lattice constant of defects. In the mixed state, the number of vortices in the pinning center would change with temperature. At low temperatures, more then one vortex can be pined by one defect. However when the temperature is close to critical Temperature Tc, the number of vortices at one pinning center become fewer. It indicates that vortex configurations should be changed, and magnetoresistance becomes larger markedly due to the vortex flow.

碩士
國立彰化師範大學
物理學系
99
The periodic pinning of magnetic flux quanta in the Nb film with composite array of submicrometer defects is investigated. We made two series of samples which have small holes and large holes. In series A, the large holes with a diameter of 300 nm form homeycomb arrays with a period of 400 nm, and the small holes with a diameter of 150, 200, 250 nm are located at the centers of honeycomb cell. In series B, the small holes with diameter of 150, 200, 250 nm form homeycomb arrays with a period of 400 nm, and the large holes with a diameter of 300 nm are located at the centers of every honeycomb cell. On the substrate coated with Si3N4, E-beam lithography and RIE (Reactive Ion Etching) have been employed to make periodic composite array of holes. Then Nb films of 100 nm thickness were deposited using DC sputtering. The film is corrugated because of the holes on substrate and the wrinkles can act as pinning defects in the mixed state of superconductor. The minima of resistance and maxima of critical current appeared at certain values of magnetic field, corresponding to the lattice spacing of the defects. From measurement of the critical current as a function of magnetic field for these samples, we can observe intervals of 50 Oe and 100 Oe between the peaks which are very different from the regular peaks for sample with triangular or honeycomb arrays. Comparing series A with series B ,we discover that the larger diameter of the defects , the earlier the vortices are caged in the defect. To understand the experimental phenomenon, we discuss the possible vortex lattice by changing different parameter in simulation, and the phase diagram is obtained.