Дисертації з теми "Surface thermometry"

To effectively design systems of microchannels it is necessary for scientists and engineers to understand thermal transport characteristics of microchannels. To experimentally determine the convective heat transfer coefficient of microchannels it is necessary to measure both the bulk and surface temperature fields. This investigation aims to develop a technique, named Total Internal Reflection Fluorescent Micro-Thermometry (TIR-FMT), to measure the temperature of water within several hundred nanometers of a wall--effectively, the surface temperature of the wall. In TIR-FMT, an evanescent-wave is generated in the water near the wall. The intensity of this evanescent-wave decays exponentially with distance from the wall. A fluorophore if illuminated by the evanescent-wave can absorb a photon. Excited fluorophores subsequently emit red-shifted photons, which are called fluorescence. The probability of a fluorescent emission is temperature-dependent. Therefore, by monitoring the intensity of the fluorescence a correlation can be made to the temperature of the region of illumination. Using the TIR-FMT technique the temperature dependence of the fluorescence intensity from buffered fluorescein (pH=9.2) was determined to be 1.35%/C. TIR-FMT can be used to measure the temperature of a fluorophore solution within 600 nm of a wall across a temperature range of 12.5-55C. The average uncertainties (95% confidence) of the temperature measured was determined to be 2.3C and 1.5C for a single 1.5x1.5 and #956;m pixel and the entire 715x950 and #956;m viewfield. By spatial averaging, average uncertainties of 2.0C and 1.8C were attained with spatial resolutions of 16x16 and 100x100 and #956;m, respectively.

Thermal management challenges for microelectronics are a major issue for future integrated circuits, thanks to the continued exponential growth in component density described by Moore¡¯s Law. Current projections from the International Technology Roadmap for Semiconductors predict that local heat fluxes will exceed 1 kW/cm2 within a decade. There is thus an urgent need to develop new compact, high heat flux forced-liquid and evaporative cooling technologies. Thermometry techniques that can measure temperature fields with micron-scale resolution without disturbing the flow of coolant would be valuable in developing and evaluating new thermal management technologies. Specifically, the ability to estimate local convective heat transfer coefficients, which are proportional to the difference between the bulk coolant and wall surface temperatures, would be useful in developing computationally efficient reduced-order models of thermal transport in microscale heat exchangers. The objective of this doctoral thesis is therefore to develop and evaluate non-intrusive optical thermometry techniques to measure wall surface and bulk liquid temperatures with O(1-10 micronmeter) spatial resolution. Intensity-based fluorescence thermometry (FT), where the temperature distribution of an aqueous fluorescent dye solution is estimated from variations in the fluorescent emission intensity, was used to measure temperatures in steady Poiseuille flow at Reynolds numbers less than 10. The flow was driven through 1 mm square channels heated on one side to create temperature gradients exceeding 8 ¡ÆC/mm along both dimensions of the channel cross-section. In the evanescent-wave fluorescence thermometry (EFT) experiments, a solution of fluorescein was illuminated by evanescent waves to estimate the solution temperature within about 300 nm of the wall. In the dual-tracer FT (DFT) studies, a solution of two fluorophores with opposite temperature sensitivities was volumetrically illuminated over most of the `cross-section of the channel to determine solution temperatures in the bulk flow. The accuracy of both types of FT is determined by comparing the temperature data with numerical predictions obtained with commercial computational fluid dynamics software. The results indicate that EFT can measure wall surface temperatures with an average accuracy of about 0.3 ¡ÆC at a spatial resolution of 10 micronmeter, and that DFT can measure bulk water temperature fields with an average accuracy of about 0.3 ¡ÆC at a spatial resolution of 50 micronmeter in the image plane. The results also suggest that the spatial resolution of the DFT data along the optical axis (i.e., normal to the image plane) is at least an order of magnitude greater than the depth of focus of the imaging system.

The pursuit for improved engine efficiency is driving the demand for accurate temperature measurement inside turbine engines. Accurate measurement can allow engines to be operated closer to their design limits to improve thermal efficiency. It can enable engineers to verify mechanical integrity, provide better prediction of component life, validate CFD and other design tools and aid the development for leaner more efficient engines. Unfortunately, experimentally measuring surface temperatures under harsh rotating conditions is challenging. This EngD study conducted by Ashiq Hussain Khalid at the University of Manchester and Rolls-Royce plc, reviews the rationale of using phosphor thermometry over existing methods, including thermocouples, pyrometry and thermal paints/melts, which lack detail, accuracy, or are too expensive for continuous testing. Although phosphor thermometry exhibits desirable characteristics, the high temperature and fast rotating engine environment presents some challenges that would need to be addressed before a successful measurement system can be implemented. Examples of such issues include: rising blackbody radiation, restricted optical access, fibre optic constraints and limited time period to collect data. These factors will impose measurement limits and greatly influence the design philosophy of the system, including phosphor choice, phosphor lifetime characteristics, bonding technique, excitation/detection methodologies and probe design. Taking these into consideration, the research focuses on the development of phosphor thermometry systems for use in development gas turbine engines, with measurement solutions for specific engine components. The high pressure turbine blade was given research priority. A number of phosphors including YAG:Tb, YAG:Tm. Y2O3:Eu and Mg3F2GeO4:Mn were investigated and characterised in terms of intensity and lifetime decay, with increasing temperature up to 1500oC. Spectral analysis and absolute intensity measurements established emission peaks and permitted comparative quantitative analysis to optimise system setup. The intensity of phosphor emission relative to Planck's blackbody radiation was also performed. YAG:Tm under 355nm illumination was found to exhibit the highest emission intensity at high temperatures, and because its spectral emission peak at 458nm was the lowest, its advantage in terms of blackbody radiation was further amplified. For rotating components, an upper temperature limit is reached based on the emission intensity at rising blackbody radiation levels and the system's ability to detect fast decays. A lower limit is reached based on the quenching temperature, probe design and rotational velocity. There are different methods to correct the distorted decay waveform as it traverses through the acceptance cone of the fibre. A phosphor selection criterion, taking into consideration these limitations, was successfully applied for various rotating engine components. The optical layout was setup and tested on stationary and rotating cases under laboratory conditions using similar design constraints, including fibre choice, maximum permissible lens size and target distances. A series of tests validated design methodologies and assumptions to enable testing on full scale rotating engine components. Mg3F2GeO4:Mn, using 355nm illumination, was found to be the most suitable phosphor for the HP drive cone. The estimated performance under the expected rotational speeds was found to be 624-812°C with a standard uncertainty of ±0.99%. YAG:Tm, illuminated with 355nm, was found to be the most promising phosphor for high pressure turbine blade measurements. The performance under the expected rotational speeds was found to be 1117-1375°C with a standard uncertainty of ±0.97%. This is better than other competing technologies that are currently available for temperature measurement of rotating turbine blades.

Au cours de cette étude, nous mettons en évidence les différents problèmes qui se posent lorsque l'on désire mesurer la température d'une surface au moyen d'une sonde de contact. Nous proposons une étude théorique du comportement thermophysique d'une sonde active, thermorégulée destinée à la mesure fine, précise et instantanée des températures superficielles. Divers prototypes de transducteurs y sont décrits, aboutissant au modèle coplanaire retenu pour sa fonctionnalité. Nous exposons aussi les procédés qui ont permis la réalisation du transducteur en technologie couches minces. Nous décrivons enfin le système de gestion du transducteur ainsi que le logiciel associé permettant la régulation et la mesure en temps réel. Le mémoire s'achève par la présentation et l'analyse critique d'un ensemble de résultats de mesure sur diverses surfaces

Le géothermomètre Δ47 est basé sur la relation entre l’abondance des liaisons 13C–18O des carbonates et la température de calcification. Ce proxy contourne potentiellement les limites des autres thermomètres (δ18O, Mg/Ca) pour reconstruire les paléo-températures des océans, expliquant son développement exponentiel depuis dix ans. Cette thèse teste pour la première fois le potentiel et les limites de la thermométrie Δ47 sur les coccolithes, des nannofossiles calcaires produits par des organismes calcifiants dans la zone photique. Ces biominéraux calcitiques et ubiquistes constituent une part importante de l’archive sédimentaire. Des cultures in vitro nous ont permis d’établir que trois espèces de coccolithes actuelles enregistrent la même relation Δ47 – T que la calcite inorganique, alors qu'elles présentent de très larges effets vitaux en δ18O (±5‰). Nous concluons que ces espèces de coccolithes d'importance géologique ne présentent pas d’effets vitaux en Δ47. Nous avons ensuite appliqué le Δ47 à l’étude des sédiments enregistrant l’événement d’anoxie océanique du Toarcien (–183 Ma) au cours duquel les reconstructions de températures restent encore ambigües, notamment du fait de la méconnaissance de la composition isotopique en oxygène de l’eau de mer. Sur la base des données Δ47 acquises, nous proposons des températures élevées (de l’ordre de 36°C), mais restant relativement stables sur l'intervalle d'étude. En couplant ces températures aux données de δ18O des carbonates, nous suggérons une variation importante du δ18O de l'eau de mer dans le Bassin de Paris lors de la mise en place des faciès black shales. Enfin, sur des sédiments pélagiques subactuels, l’une des espèces étudiées présente des déséquilibres isotopiques en Δ47 non observés en culture et explicables par d’autres paramètres environnementaux comme l’intensité lumineuse. Cette thèse illustre le potentiel du thermomètre Δ47 des coccolithes en différents contextes, ouvrant un vaste champ d’application de reconstruction des paléo-environnements sur le Méso-Cénozoïque
The Δ47 geothermometer relies on the relationship between the 13C–18O abundance in carbonateand temperature of calcification. This proxy has the potential to overcome limitations of other thermometers(δ18O, Mg/Ca) to reconstruct oceanic paleotemperatures. This thesis evaluates for the first time the potentialand the limitations of the Δ47 thermometry of the coccoliths, the calcareous nannofossils produced byorganisms calcifying in the photic zone. These calcitic and ubiquitous biominerals represent an importantpart of the sedimentary archive. In vitro cultures allow us to establish that three modern coccoliths speciesrecord the same Δ47–T relation than inorganic calcite, although exhibiting substantial δ18O vital effects(±5‰). We conclude that these coccoliths species do not present any Δ47 vital effect. We subsequentlyapplied the Δ47 proxy to sediments from the Toarcian oceanic anoxic events (–183 Ma) during which thetemperatures reconstructions are still elusive, mainly due to the unknown oxygen isotopic composition ofseawater. On the basis of our Δ47 data, we infer relatively high, yet steady temperatures (around 36°C) duringthe examined interval. By combining these Δ47-derived temperatures to carbonate δ18O data, we can suggestdrastic change in the seawater δ18O composition in the Paris Basin at the onset of black shale deposition. Acore top calibration of Δ47 of coccoliths revealed that one of the studied cultured species exhibits Δ47disequilibrium that is accountable by other environmental parameters, such as light irradiance in the naturalenvironment. Thus, this thesis illustrates the potential of the coccolith Δ47 thermometer in different settings,opening a wide range of application to reconstruct the palaeoenvironments over the Meso-Cenozoic Eras

Utiliser le méthane comme carburant dans les moteurs fusées présente beaucoup d'avantages mais la combustion avec de l'oxygène pur à haute pression reste mal comprise. D'un point de vue thermodynamique, le méthane et l'oxygène partagent des valeurs de point critique très similaires, ce qui rend difficile la prédiction du mélange des ergols, l'accrochage, la stabilité et la structure de la flamme. De plus, quand le méthane est injecté en excès, des aérosols peuvent être produits, pouvant obstruer les lignes, endommager la turbine et réduire le rendement.Une mise à jour approfondie des connaissances sur la combustion LOX/CH4 est donc nécessaire. Ce défi est relevé au sein du consortium composé du laboratoire EM2C, de l'ONERA, du CNES et d'ArianeGroup. Deux campagnes d'essais sont menées sur le banc MASCOTTE de l'ONERA visant à étudier trois sujets centraux : la structure de la flamme, les transferts thermiques aux parois et la production d'aérosols. Dans ce but, divers diagnostics expérimentaux sont mis en œuvre simultanément pendant des essais à feu à haute pression.Différents diagnostics d'imagerie sont mis en place pour analyser la structure de la flamme et des jets liquides. Malgré les difficultés d'acquisition rencontrées dans ces conditions extrêmes, les analyses révèlent une structure de flamme complexe. En régime subcritique, les mécanismes d'atomisation et d'évaporation dominent. La flamme est alors bien plus ouverte et plus longue qu'à de plus hautes pressions, où les mécanismes de mélange diffusifs prévalent. Caractériser l'accrochage de la flamme reste un défi. En effet, un anneau de glace, probablement d'eau, entoure et masque le pied de la flamme. Des mécanismes de formation sont proposés et un cycle temporel de croissance/destruction est mis en avant. Sa présence affecte fortement la visualisation de la flamme, et peut conduire à des interprétations erronées de sa topologie.Pour la première fois à MASCOTTE, la phosphorescence induite par laser (LIP) est mise en place. Diverses méthodes LIP existent mais ne sont pas bien adaptées aux conditions de MASCOTTE : large gamme de températures, transitoires thermiques et environnement diphasique. C'est pourquoi une méthode spécifique a été mise au point (Full Spectrum Fitting method). Elle exploite la dépendance spectrale à la température, permettant des mesures instantanées de 100 à 900 K avec une précision de 17 K, sans dépendance à l'énergie d'excitation laser. Une analyse détaillée des données met en évidence les modes de transfert de chaleur prédominants, étudie l'influence des points de fonctionnement et compare les données expérimentales avec un modèle de transferts thermiques de paroi, particulièrement bien adapté pour déduire les caractéristiques convectives de l'écoulement à la paroi.Différents diagnostics sont mis en œuvre pour caractériser les aérosols. Une sonde intrusive prélève les particules et les gaz brûlés en aval de la flamme. Les particules sont prélevées sur des grilles adaptées à des analyses par microscopie électronique à transmission (TEM). Les images détaillées de leurs morphologies révèlent qu'il s'agit de suies. Les gaz sont analysés par chromatographie en phase gazeuse. Ceci permet d'identifier des molécules précurseurs des suies comme le benzène et l'acétylène. Les suies sont quantifiées temporellement par extinction laser. Des post-traitements dédiés sont développés et diverses hypothèses sont discutées pour expliquer les variations spatiales de production de suies
Using methane as a fuel in rocket engines would have many advantages but the combustion with pure oxygen at high pressure remains poorly understood. From a thermodynamic point of view, methane and oxygen share very similar critical point values, making it challenging to predict propellant mixing, flame anchoring, stability and structure. Moreover, when methane is injected in excess, aerosols can be produced, which can clog the lines, damage the turbine, and reduce the efficiency.Therefore, a thorough update of the knowledge of LOX/CH4 combustion is necessary. These challenges are tackled within the consortium composed of EM2C laboratory, ONERA, CNES, and ArianeGroup. Two test campaigns are carried out at the MASCOTTE facility from ONERA, aiming to study three central topics: the flame structure, wall heat transfers, and aerosol production. To this end, various experimental diagnostics are implemented simultaneously during high-pressure hot-fire tests.Various imaging diagnostics are implemented to analyze the flame structure and the dense liquid jets. Despite the acquisition difficulties encountered in these extreme conditions, the analyses reveal a complex flame structure. In the subcritical regime, atomization and evaporation mechanisms dominate. The flame is much more opened and longer than at higher pressures, where diffusive mixing mechanisms prevail. Characterizing flame anchoring remains a challenge. A water ice ring surrounding, and masking, the flame foot has been identified. Formation mechanisms are proposed, and a growth/destruction temporal cycle is highlighted. Its presence strongly affects flame visualizations, and may lead to misinterpretations of its topology.Laser-induced phosphorescence (LIP) is implemented for the first time at MASCOTTE. Various LIP methods exist, but they are not well suited to the MASCOTTE conditions: wide temperature range, thermal transients, and two-phase flow environment favoring laser absorption/diffusion. Therefore, a specific method, the Full Spectrum Fitting method (FSF method), has been developed. It exploits the spectral dependence on temperature, enabling instantaneous measurements from 100 to 900 K with a precision of 17 K, with no dependence on the laser excitation energy. A detailed data analysis highlights the predominant wall heat transfer modes, studies the influence of the operating points, and compares the experimental data with a wall heat transfer model, which is particularly well suited for deducing the convective properties of the flow.Three diagnostics are used to characterize aerosols. An intrusive probe samples particles and burnt gases downstream of the flame. The particles are sampled on TEM grids and analyzed by Transmission Electron Microscopy. Detailed images of the aerosol morphology reveal that the particles are soot. Combustion products are analyzed by gas chromatography. This makes it possible to identify soot precursor molecules such as benzene and acetylene. Soot are quantified temporally by laser extinction. A dedicated post-processing method is developed and various hypotheses are discussed to explain the spatial variations of the soot production downstream of the flame

Le developpement des cavites acceleratrices nb/cu elaborees par pulverisation magnetron est motive par leurs applications possibles dans les grands projets necessitant de hauts gradients. Neanmoins, afin de satisfaire aux criteres de fonctionnement imposes par les futurs collisionneurs lineaires, les performances hf de ces cavites doivent etre ameliorees. L'augmentation rapide de la resistance de surface avec l'amplitude du champ hf constitue la limitation principale de la technologie couche mince. Dans l'optique de comprendre et reduire ces dissipations energetiques, nous avons entrepris une serie d'etudes sur echantillons nb/cu. Nous avons optimise les conditions d'elaboration des films. L'augmentation de la temperature de depot et de la puissance appliquee au magnetron ainsi que la diminution de la pression de decharge ont conduit a une augmentation sensible du rrr des couches minces. Des analyses de la composition chimique des films par methodes nucleaires ont confirme une teneur reduite en impuretes legeres (o, c et h) ainsi que l'absence de pollution du niobium par diffusion du cuivre dans les joints de grains. Nous avons developpe et valide une nouvelle methode de mesure de la resistance de surface par thermometrie sous vide. Cette methode adaptee a la cavite te 0 1 1 deja utilisee au laboratoire a permis de determiner directement la resistance de surface d'echantillons nb/cu a 1,7k et a 4,2k. Nous avons etudie l'influence de l'etat de surface du substrat cuivre sur la resistance de surface du film de niobium en realisant des depots sur des substrats de rugosite tres variable. Les observations de la surface des films par microscopie electronique a balayage ont mis en evidence l'existence de defauts micrometriques de croissance, en particulier sur les echantillons rugueux. Les tests hf par thermometrie sous vide de ces echantillons ont permis d'etablir une correlation entre la forte densite de ces defauts et la degradation de la resistance de surface du depot, a bas champ comme a fort champ. Les resultats de ces recherches sur echantillons ont beneficie aux cavites 1,5 ghz. Les premiers tests hf sont encourageants (q o = 2 10 1 0 a bas champ et e a c c = 25 mv/m). Pour obtenir des resultats reproductibles et ameliorer encore les performances hf des cavites, il est primordial de poursuivre l'optimisation de la preparation de surface du cuivre avant le depot.

Recently, remarkable advances have been made in the understanding of micro/nanoscale energy transport, opening new opportunities in various areas such as thermal management, data storage, and energy conversion. This dissertation focuses on thermally-sensed nanotopography using a heated silicon microcantilever and near-field thermophotovoltaic (TPV) energy conversion system. A heated microcantilever is a functionalized atomic force microscope (AFM) cantilever that has a small resistive heater integrated at the free end. Besides its capability of increasing the heater temperature over 1,000 K, the resistance of a heated cantilever is a very sensitive function of temperature, suggesting that the heated cantilever can be used as a highly sensitive thermal metrology tool. The first part of the dissertation discusses the thermal characterization of the heated microcantilever for its usage as a thermal sensor in various conditions. Particularly, the use of heated cantilevers for tapping-mode topography imaging will be presented, along with the recent experimental results on the thermal interaction between the cantilever and substrate. In the second part of the dissertation, the so-called near-field TPV device is introduced. This new type of energy conversion system utilizes the significant enhancement of radiative energy transport due to photon tunneling and surface polaritons. Investigation of surface and bulk polaritons in a multilayered structure reveals that radiative properties are significantly affected by polariton excitations. The dissertation then addresses the rigorous performance analysis of the near-field TPV system and a novel design of a near-field TPV device.

碩士
國立成功大學
機械工程學系碩博士班
96
Experiments are conducted to investigate the surface emissivity characteristics for five different aluminum alloys, AL1100、AL2024、AL5083、AL6061、AL7005 at 600K, 700K and 800K. Six multispectral radiation thermometry (MRT) emissivity models, HRR, IST, IST* (another form of IST), IWS, WLT and WLT* (another form of WLT) are examined for the suitability of predicting aluminum alloy surface temperature. The goal of this study is to find the best MRT emissivity model which can well compensate the aluminum emissivity variations and accurately infer temperature. Wavelength range from 2.91μm to 4.13μm is chosen because of the high stability in emissivity measurement. For aluminum emissiveity behaviors, (1)overall, emissiveity decreases with increasing wavelength; (2)emissivity decreases between 600K and 700K, but increases between 700K and 800K. Increase in emissivity is contributed to the surface oxidation and discoloration which cause the surface color change from light gray to dark black; (3) at high temperature, aluminum alloys with more magnesium constituent cause the increase in emissivity which results in a much stronger alloy effect; (4)emissivity reaches steady state after the 2nd hour due to the surface oxidation becoming fully developed. For the examination of MRT emissivity models on aluminum, (1)most models achieve high accuracy in temperature prediction, except IWS and WLT emissivity models. HRR shows the best overall performance and stability; (2)for least-squares technique, the closer the inferred emissivity value and real one, the more accurate inferred temperature; (3)increasing wavelength number does not significantly improve measurement accuracy while applying MRT. However, compared with SRT and DWRT, MRT indeed provides better performance; (4)overall, constant emissivity value acquired with increasing heating time enhances temperature prediction; (5)results from the error analysis show good stability of experimental operation and MRT emissivity models predicting aluminum alloy surface temperature.

碩士
國立成功大學
機械工程學系碩博士班
97
In this study, experiments were conducted to examine the effect of surface oxidation on emissivity. The spectral emissivity were measured under an open-air heater system and a high-vacuum heater system for five different aluminum alloys (AL1100、AL2024、AL5083、AL6061、AL7005) at three temperatures (600 K、700 K、800 K). Eight emissivity models were used to examine the Multispectral Radiation Thermometry (MRT) for aluminum alloys in order to understand the effect of surface oxidation on temperature determination and find the best MRT emissivity model as well. For aluminum alloys emissivity behaviors, overall similar trends are found under oxidized and unoxidized conditions. (1) Emissivity decreases with increasing wavelength. (2) Emissivity increases with increasing temperature. The emissivity of oxidized sample is higher than that of unoxidized sample and this demonstrates that oxidation causes the increase in emissivity. (3) The emissivity of unoxidized sample doesn’t change with time. However, the emissivity of oxidized sample increases due to the growing oxide layer with time. For the examination of MRT emissivity models on aluminum alloys, (1) since the effect of oxidation changes the emissivity behaviors, different best models are found under conditions with and without oxidation. (2) Models having the percentage of average inferred temperature error under 4% are found for both oxidized and unoxidized samples. Therefore, MRT is suitable and applicable for aluminum alloy temperature determination. (3) For least-squares technique, the closer the inferred emissivity value and real one, the more accurate inferred temperature. (4) More accurate temperature measurement by MRT can be achieved in higher temperature. (5) Increasing number of wavelength doesn’t improve measurement accuracy while applying MRT. Therefore, it is sufficient to employ the required minimum number of wavelengths to save the time on computation. (6) Overall, three emissivity models, HRR、IST and WLT*, are able to achieve high accuracy in temperature prediction for both oxidized and unoxidized heating systems, especially HRR under oxidized condition and WLT* under unoxidized condition.

The understanding of the luminescence properties of silicon at nanoscale is a relevant subject for the development of new light emitting devices. In this work, the emission features of crystalline silicon nanoparticles is studied. To reveal the role of the surface termination on the photoluminescence properties of silicon nanoparticles with several terminations (hydrogen, silicon oxide or organic molecules) photoluminescence in steady-state and time-resolved modes and measurements of the emission quantum yield were performed. At room temperature, the emission spectra of silicon nanoparticles terminated with hydrogen and functionalized with organic molecules, with average mean diameter of ≈3.4 and ≈2.4 nm present an emission component peaking at ≈800 and ≈750 nm, respectively. This emission component is ascribed to recombination of photogenerated excitons in the silicon core of the nanoparticles. An additional emission component peaking at higher energy, ascribed to the donor-acceptor recombination within states associated with the oxide shell is also present in the spectra of the nanoparticles with an oxide shell. The emission lifetime and quantum yield values depend on the surface termination and are discussed the role of the surface termination int the inter- and intra-nanoparticle exciton transfer. The higher room temperature emission quantum yield was measured for silicon nanoparticles with organic functionalization processed as films (0.23±0.02). Another aspect studied was the homogeneous infilling of films of silicon nanoparticles with Al2O3 using atomic layer deposition. The infilling allows to protect the films against oxidation and also impacts on the photoluminescence emission spectrum of the nanoparticles. This work opens new questions about the role of the surface termination and separation between nanoparticles on the emission properties. Taking advantage from the dependence of the nanoparticles emission on temperature, an innovative primary thermometer was developed. It is shown that luminescent thermometers based on silicon nanoparticles films and solutions can operate in distinct environments with the thermometric parameter (emission peak position) described by a well-established equation. The thermometer has a reversibility and repeatability higher than 99.98% and the maximum relative thermal sensitivity is 0.04 %.K−1.
O entendimento das propriedades de luminescência do silício à escala nanométrica é uma questão relevante para o desenvolvimento de novos dispositivos emissores de luz. Neste âmbito, esta tese foca o estudo das propriedades de emissão de nanopartículas cristalinas de silício, com diferentes terminações da superfície (hidrogénio, óxido de silício ou moléculas orgânicas), utilizando espectroscopia de fotoluminescência em modo estacionário e resolvido no tempo e medidas de rendimento quântico de emissão. À temperatura ambiente, os espectros de emissão das nanopartículas terminadas com hidrogénio e funcionalizadas com moléculas orgânicas, com tamanhos médios de ≈3.4 e ≈2.4 nm, apresentam uma componente centrada, respetivamente em ≈800 e ≈750 nm. Esta componente é atribuída à recombinação de excitões fotogerados no núcleo de silício da nanopartícula. Uma componente adicional, a maiores energias, está presente no espectro de nanopartículas com óxido de silício à superfície, sendo atribuída à recombinação de pares dados-aceitador de estados associados ao óxido. Os valores medidos para os tempos de vida de emissão e para o rendimento quântico de emissão dependem da terminação da superfície e são discutidos, através da transferência de excitões intra- e inter-nanopartículas. O valor mais alto de rendimento quântico de emissão à temperatura ambiente para amostras em filme foi medido para nanopartículas com funcionalização orgânica (0.23±0.02). Uma outra vertente do trabalho, envolveu filmes de nanopartículas de silício infiltrados com Al2O3, utilizando deposição em camadas atómica. A camada depositada permite proteger os filmes contra a oxidação e observa-se uma alteração do espectro de emissão das nanopartículas, relativamente a nanopartículas análogas sem infiltração. Este trabalho abre novas questões sobre o papel da terminação e separação entre nanopartículas no que respeita às propriedades de emissão. Tirando partido da dependência da emissão com a temperatura foi desenvolvido um termómetro primário inovador. Em particular, é mostrado que termómetros luminescentes baseados em nanopartículas de silício processadas em filme e em solução podem operar em diversos ambientes com um parâmetro termométrico (energia do pico de emissão) descrito por uma equação de estado bem estabelecida. O termómetro apresenta uma reversibilidade e repetibilidade superior a 99.98%, e um valor máximo para a sensibilidade térmica relativa de 0.04 %.K−1.
Programa Doutoral em Física