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Optical resonators, which confine light by resonant recirculation, serve as the basis for a wide variety of optical components. Though they appear in many geometric forms, the most effective of optical resonators show axial symmetry in at least one dimension. A popular variation that finds broad application is the dielectric sphere. Acclaimed for their high quality (Q) factor and small modal volume, spheres owe credit of these attractive features to their support of whispering gallery mode (WGM) resonances. The sensitivity of a resonance's frequency and Q to strain, temperature, and other parameters of the surrounding medium can be the basis for ultracompact modulators and sensors. Physically, WGMs are special optical modes which can be understood as light rays that orbit the equator of the sphere guided by total internal reflection. Like a smooth stone can be skipped along the surface of a pond, light can be confined to the inside of a sphere by successive reflections. To best excite WGMs, the source light should initially trace a line tangent to the sphere's circumference. But incorporating a tiny sphere with such nanometric tolerances into a practical sensor structure has its challenges and the prospects for microsphere applications have suffered because of the plight of this problem. The work in this dissertation details the fabrication and function of three new "press fit" spherical resonators. These etched fiber micro-devices were developed to meet the demand for a robust, self-integrated means of coupling light between an optical fiber and WGMs in a microsphere resonator. The etching processes have been tuned to enable secure storage of a microsphere while also providing efficient excitation and interrogation of WGMs. Furthermore, the methods have been designed to be staightforward, quick, and repeatable. Using standard etchants on common polarization-maintaining fiber with readily purchased microspheres, the press fit resonators demonstrated here can be batch-fabricated and assembled. The press fit spherical resonator offers an alignment-free and conveniently pigtailed WGM coupler that has great potential for bio-science sensing applications and studies of resonant bispheres. / Ph. D.

The considerable interest in nanomaterials and nanotechnology over the last decade is attributed to Industry's desire for lower cost, more sophisticated devices and the opportunity that nanotechnology presents for scientists to explore the fundamental properties of nature at near atomic levels. In pursuit of these goals, researchers around the world have worked to both perfect existing technologies and also develop new nano-fabrication methods; however, no technique exists that is capable of producing complex, 2D and 3D nano-sized features of arbitrary shape, with smooth walls, and at low cost. This in part is due to two important limitations of current nanofabrication methods. First, 3D geometry is difficult if not impossible to fabricate, often requiring multiple lithography steps that are both expensive and do not scale well to industrial level fabrication requirements. Second, as feature sizes shrink into the nano-domain, it becomes increasingly difficult to accurately maintain those features over large depths and heights. The ability to produce these structures affordably and with high precision is critically important to a number of existing and emerging technologies such as metamaterials, nano-fluidics, nano-imprint lithography, and more. Summary To overcome these limitations, this study developed a novel and efficient method to etch complex 2D and 3D geometry in silicon with controllable sub-micron to nano-sized features with aspect ratios in excess of 500:1. This study utilized Metal-assisted Chemical Etching (MaCE) of silicon in conjunction with shape-controlled catalysts to fabricate structures such as 3D cycloids, spirals, sloping channels, and out-of-plane rotational structures. This study focused on taking MaCE from a method to fabricate small pores and silicon nanowires using metal catalyst nanoparticles and discontinuous thin films, to a powerful etching technology that utilizes shaped catalysts to fabricate complex, 3D geometry using a single lithography/etch cycle. The effect of catalyst geometry, etchant composition, and external pinning structures was examined to establish how etching path can be controlled through catalyst shape. The ability to control the rotation angle for out-of-plane rotational structures was established to show a linear dependence on catalyst arm length and an inverse relationship with arm width. A plastic deformation model of these structures established a minimum pressure gradient across the catalyst of 0.4 - 0.6 MPa. To establish the cause of catalyst motion in MaCE, the pressure gradient data was combined with force-displacement curves and results from specialized EBL patterns to show that DVLO encompassed forces are the most likely cause of catalyst motion. Lastly, MaCE fabricated templates were combined with electroless deposition of Pd to demonstrate the bottom-up filling of MaCE with sub-20 nm feature resolution. These structures were also used to establish the relationship between rotation angle of spiraling star-shaped catalysts and their center core diameter. Summary In summary, a new method to fabricate 3D nanostructures by top-down etching and bottom-up filling was established along with control over etching path, rotation angle, and etch depth. Out-of-plane rotational catalysts were designed and a new model for catalyst motion proposed. This research is expected to further the advancement of MaCE as platform for 3D nanofabrication with potential applications in thru-silicon-vias, photonics, nano-imprint lithography, and more.

Revealing the prior austenite grain boundaries from a martensitic structure is well known to be very difficult and dependent on the chemical composition and the thermomechanical processing of the steel. In the present study, four different chemical etching reagents and additional thermal etching have been conducted for thermomechanical simulated tool steels Orvar Supreme and Stavax ESR. The etching results have been characterized using light optical microscopy and electron backscattered diffraction. The obtained results show that saturated aqueous picric acid, oxalic and sodium bisulfite based acid reveals prior austenite grain boundaries well for Orvar Supreme. For Stavax ESR, only aqueous CrO3-NaOH-picric acid provides good results in revealing the prior austenite grain boundaries. Thermal etching shows good potential and if conducted properly, thermal etching is a good alternative to the chemical reagents from a health- and environmental perspective.

No description available.

Nous étudions la possibilité de réaliser des cellules à base de diséléniure de cuivre, indium et gallium (CIGSe) à absorbeur ultra-mince, en réduisant l’épaisseur de la couche de CIGSe de 2500 nm jusqu’à 100 nm, tout en conservant un haut rendement de conversion.Grâce à l’utilisation d’outils de simulation numérique, nous étudions l’influence de la réduction d’épaisseur de l’absorbeur sur les paramètres photovoltaïques de la cellule. Une importante dégradation du rendement est observée, principalement attribuée à une réduction de la fraction de lumière absorbée par le CIGSe ainsi qu’à une collecte des porteurs de charge réduite dans les dispositifs ultraminces. Des solutions permettant de surmonter ces problèmes sont proposées et leur influence potentielle est numériquement simulée ; nous démontrons qu’une ingénierie de face avant (couche tampon alternative, couche anti-réfléchissante…) et de face arrière (contact arrière réfléchissant, diffusion de la lumière) sur une cellule CIGSe à absorbeur ultramince permet de potentiellement améliorer le rendement de la cellule solaire au niveau de celui d’une cellule à absorbeur référence (2.5 μm).Grâce à l’utilisation de techniques de gravure chimique sur des échantillons standards de CIGSe épais, nous réalisons des cellules solaires avec différentes épaisseurs d’absorbeurs, et nous étudions l’influence de l’épaisseur du CIGSe sur les paramètres photovoltaïques des cellules. Le comportement similaire aux simulations numériques.Une ingénierie du contact avant sur des cellules CIGSe à différentes épaisseurs est réalisée pour spécifiquement améliorer l’absorption dans la couche de CIGSe. Nous étudions l’influence d’une couche tampon alternative de ZnS, de la texturation de la fenêtre avant de ZnO:Al, et d’une couche anti-reflet sur la cellule solaire. D’importantes améliorations sont observées quelque soit l’épaisseur de la couche de CIGSe, ce qui permet d’obtenir des rendements de conversions supérieurs à ceux obtenus dans la configuration standard des dispositifs.Une ingénierie du contact arrière à basse température est également réalisée avec l’utilisation d’un procédé novateur combinant la gravure chimique du CIGSe avec un « lift-off » mécanique de la couche de CIGSe afin de la séparer du substrat de Molybdène. De nouveaux matériaux fortement réflecteur de lumière et précédemment incompatible avec le procédé de croissance du CIGSe sont utilisés comme contact arrière pour des cellules CIGSe ultra-minces. Une étude comparative en fonction de l’épaisseur de CIGSe entre des cellules avec contact arrière réfléchissant en Or (Au) et cellules solaires avec contact arrière standard Mo est effectuée. Le contact Au permet d’augmenter significativement le rendement de conversion des cellules solaires à absorbeur sub-microniques comparé au contact standard Mo avec un rendement de conversion supérieur à 10% obtenu sur une cellule CIGSe de 400 nm (comparé à 7.9% avec Mo).Afin de réduire encore plus l’épaisseur de la couche de CIGSe, jusque 100-200 nm, les modèles numériques montrent qu’il est nécessaire d’utiliser un réflecteur lambertien sur la face arrière de la cellule afin de maximiser l’absorption de la lumière. Un dispositif preuve de concept expérimental est réalisé avec une épaisseur de CIGSe de 200 nm et un réflecteur arrière lambertien, et ce dispositif est caractérisé par spectroscopie de transmission/réflexion. La réponse spectrale est déterminée en combinant des valeurs issues de simulation numérique et la mesure expérimental de l’absorption du dispositif. Nous calculons un courant de court circuit de 26 mA.cm-2 pour ce dispositif avec réflecteur lambertien, bien supérieur à ce qui est calculé pour la même structure sans réflecteur (15 mA.cm-2), et comparable au courant mesuré sur une cellule de référence de 2500 nm (28 mA.cm-2). L’utilisation de réflecteur lambertien pour des cellules CIGSe ultraminces est donc particulièrement adaptée pour maintenir de hauts rendements. / In this thesis, we investigate on the possibility to realize ultrathin absorber Copper Indium Gallium Di-Selenide (CIGSe) solar cells, by reducing the CIGSe thickness from 2500 nm down to 100 nm, while conserving a high conversion efficiency.Using numerical modeling, we first study the evolution of the photovoltaic parameters when reducing the absorber thickness. A strong decrease of the efficiency of the solar cell is observed, mainly related to a reduced light absorption and carrier collection for thin and ultrathin CIGSe solar cells. Solutions to overcome these problems are proposed and the potential improvements are modeled; we show that front side (buffer layer, antireflection coating) and back side (reflective back contact, light scattering) engineering of an ultrathin device can potentially increase the conversion efficiency up to the level of a standard thick CIGSe solar cell.By using chemical bromine etching on a standard thick CIGSe layer, we realize solar cells with different absorber thicknesses and experimentally study the influence of the absorber thickness on the photovoltaic parameters of the devices. Experiments show a similar trends to that observed in numerical modeling.Front contact engineering on thin CIGSe solar cell is realized to increase the specific absorption in CIGSe, including alternative ZnS buffer, front ZnO:Al window texturation and anti-reflection coating. Substantial improvements are observed whatever the CIGSe thickness, with efficiencies higher that the default configuration.A back contact engineering at low temperature is realized by using an innovative approach combining chemical etching of the CIGSe and mechanical lift-off of the CIGSe from the original Molybdenum (Mo) substrate. New highly reflective materials previously incompatible with the standard solar cell process are used as back contact for thin and ultrathin CIGSe solar cells, and a comparative study between standard Mo back contact and alternative reflective Au back contact solar cells is performed. The Au back reflector significantly enhance the efficiency of solar cell with sub-micrometer absorbers compared to the standard Mo back reflector; an efficiency higher than 10 % on a 400 nm CIGSe is obtained with Au back contact (7.9% with standard Mo back contact). For further reduction of the absorber thickness down to 100-200 nm, numerical modeling show that a lambertian back reflector is needed to fully absorb the incident light in the CIGSe. An experimental proof of concept device with a CIGSe thickness of 200 nm and a lambertian back reflector is realized and characterized by reflection/transmission spectroscopy, and the experimental spectral response is determined by combining simulation and experimentally measured absorption. A short circuit current of 26 mA.cm-2 is determined with the lambertian back reflector, which is much higher than what is obtained for the same device with no reflector (15 mA.cm-2), and comparable to the short circuit current measured on a reference 2500 nm thick CIGSe solar cell (28 mA.cm-2). Lambertian back reflectors are therefore found to be the most effective way to enhance the efficiency of an ultrathin CIGSe solar cell up to the level of a reference thick CIGSe solar cell.

L’objectif de ce travail est d’utiliser les nanoparticules (NPs) de nanosondes fluorescentes de température en particulier dans les films lubrifiants. Le développement de ces nanosondes nécessite la détermination de leurs sensibilités thermiques afin de pouvoir sélectionner les NPs les plus prometteuses. Pour atteindre cet objectif, nous avons présenté deux méthodes d’élaboration utilisées pour la synthèse des nanostructures à base de SiC-3C, la méthode d’anodisation électrochimique et la méthode d’attaque chimique. Dans le premier cas, les analyses FTIR,RAMAN et MET des NPs finales ont montré que la nature chimique de ces NPs est majoritairement formée de carbone graphitique. L’étude détaillée de la photoluminescence de ces NPs a montré que le processus d’émission dépend de la chimie de surface des NPs, du milieu de dispersion et de sa viscosité, de la concentration des suspensions et de la température du milieu. Pour la deuxième famille de NP de SiC, les analyses cohérentes MET, DLS et PL ont montrées une taille moyenne de 1.8 nm de diamètre avec une dispersion de ±0.5nm. Le rendement quantique externe de ces NPs est de l’ordre de 4%. Les NPs dispersées dans l’éthanol, n’ont pas montré une dépendance à la température exploitable pour notre application. Par contre, les NPs de SiC produites par cette voie, étant donné la distribution en taille resserrée et le rendement quantique « honorable » pour un matériau à gap indirect, sont prometteuses pour des applications comme luminophores en particulier pour la biologie grâce à la non toxicité du SiC. Dans le cas des NPs de Si, nous avons également étudié deux types différents de NPs. Il s’agit de : (i) NPs obtenues par anodisation électrochimique et fonctionnalisées par des groupements alkyls (décène, 1-octadécène). Nous avons mis en évidence pour la première fois une très importante variation de l’énergie d’émission dEg/dT avec la température de type red-shift entre 300 et 400K. Les mesures de(T) conduisent à une sensibilité thermique de 0.75%/°C tout à fait intéressante par rapport aux NPs II-VI. De plus il a été montré que la durée de vie mesurée n’est pas fonction de la concentration. (ii) NPs obtenue par voie humide et fonctionnalisées par le n-butyl. Pour ce type de NPs nous avons mis pour la première fois en évidence un comportement de type blue-shift pour dEg/dT de l’ordre de -0.75 meV/K dans le squalane. Pour ces NPs, la sensibilité thermique pour la durée de vie de 0.2%°C est inférieure à celle des NPs de type (i) mais largement supérieure à celle des NPs de CdSe de 4 nm (0.08%/°C). La quantification de cette la sensibilité à la température par la position du pic d’émission dEg/dT et de la durée de vie nous permet d’envisager la conception de nanosondes de température basée sur les NPs de Si avec comme recommandations l’utilisation de NPs obtenues par anodisation électrochimique et de la durée de vie comme indicateur des variations en température. / The goal of this study is the use of Si and SiC nanoparticles (NPs) as fluorescent temperature nanoprobes particularly in lubricating films. The development of these nanoprobes requires the determination of their thermal sensitivity in order to select the best prospects NPs. To achieve this goal, we presented two preparation methods used for the synthesis of 3C-SiC based nanostructures : (i) anodic etching method and (ii) chemical etching method. In the first case, the FTIR, Raman and TEM analysis of final NPs showed that the chemical nature of these NPs is formed predominantly of graphitic carbon. The detailed photoluminescence study of these NPs showed that the emission process depends on the surface chemistry of the NPs, the dispersion medium and its viscosity, the suspension concentration and temperature of the environment.. In the second case, coherent TEM, DLS and PL analyzes showed an average size of 1.8 nm in diameter with a dispersion of ±0.5 nm. The external quantum efficiency of these NPs is 4%. NPs dispersed in ethanol, did not show an exploitable fluorescence dependence on temperature for our application. On the other hand, 3C-SiC NPs produced by this way, given the narrow size distribution and the reasonably high quantum yield for an indirect bandgap material, are promising for applications such as luminophores in particular in the biology field thanks to nontoxicity of SiC. In the case of Si we studied also two different types of NPs. (i) NPs obtained by anodic etching and functionalized by alkyl groups (decene, octadecene). We have demonstrated for the first time an important red-shift in the emission energy dEg/dT with temperature from 300 to 400K. The PL lifetime measurement(T) lead to a thermal sensitivity of 0.75% /°C very interesting compared to II-VI NPs. Furthermore it has been shown that t is not depending on the concentration. (ii) NPs obtained by wet-chemical process and functionalized with n-butyl. For this type of NPs we have identified for the first time a blue-shift behavior of dEg dT in the order of -0.75 meV/K in squalane. The thermal sensitivity for the PL lifetime of these NPs is 0.2%/°C, which is lower than that of NPs obtained by anodic etching method, but much greater than that of CdSe NPs with 4 nm of diameter (0.08%/°C). Quantification of the temperature sensitivity by the position of emission peak dEg/dT and the PL lifetime dτ/dT allows us to consider the realization of temperature nanoprobes based on Si NPs with recommendations to use Si NPs obtained by anodic etching method and PL lifetime as an indicator of temperature changes.

Surface roughness exists at many length scales-from atomic dimensions to meters. At sub-micron scale, the distribution of roughness is largely dependent on the process that generates the surface through the mechanisms of material removal/addition involved and the process parameters. The focus of the research is to quantitatively characterize the evolution of sub-micron scale surface roughness in the mechanical, chemical and electrochemical material removal techniques and study the influence of roughness on the mechanical behavior of surfaces. High purity aluminum surfaces are subjected to surface dissolution techniques such as electropolishing, chemical etching and anodization. Owing to the lack of sufficient lateral resolution in conventional roughness measurement techniques and appropriate scale independent roughness characterization techniques, the effect sub-micron scale electrochemical inhomogeneities present on the surfaces have on the roughness evolution at various length scales has not been understood. In this work, the power spectral density method of roughness characterization is used to quantitatively evaluate the roughness length scales affected in the surface generation processes as a function of time. Results indicate that in the case of electropolishing, roughness is not uniformly reduced at all length scales. Further, cut-off frequencies are suggested to optimize the electropolishing process. In chemical etching, the nature of roughness produced is found to be dependent on the nature of the starting surface. The nature of surface and sub-surface structures produced in the initial stage of the anodization process, and the transition from a disordered to an ordered structure are studied. In order to study the mechanical behavior of surfaces as a function of surface roughness, a single asperity indentation is modeled using nanoindentation of micropillar produced by focused ion beam machining of aluminum surfaces. Load-displacement curves are constructed to show the transition from a single asperity deformation to bulk deformation as function of indentation depth. Additionally, indentation responses of polymer coated surfaces with varying degree of roughness that were produced by the aforementioned surface generation processes are studied. it is shown how high interface roughness gives rise to high scatter both in loading and unloading portions of the load-displacement curves. Finally, porous alumina surface generated by the anodization process discussed above is indented to simulate a multi-asperity interaction.

In the initial stage, the sample preparation was done by using the techniques of Anodic etching and anodic forming processes where a repeated trial and error method of sample preparation headed towards making out a suitable sample set for characterization. After this step, the set of 2 different industrial samples were introduced and anodic oxide forming process was carried out in different electrolytes.    In the sample preparations, 4 different electrolytes were used 15% wt. Ammonium Adiphate, 1.5% wt. Ammonium Phosphate, 7% wt. Boric acid and 15% Penta Borate at different stages for performing the anodic oxide forming process. Minimum forming voltages of 20V to a maximum of 100V was employed in the sample preparation and to overcome the waiting time in forming the etched samples a higher current of 0.5A was used.   After the samples preparation, Electrochemical Impedance spectroscopy was used as a tool for characterising the various groups of samples and for observing the micro structures of various samples, they were fractured and the observed on the cross section by SEM.   After the analysis of the etched samples was made, an attempt to compare the results of the data of these samples to that of the 2 set of industrial samples was made and found that the resultant data wasn’t stable enough to characterize since huge scattering were occurring and whereby the simulation of the CPE circuit for the chosen circuit in the analysis was not possible.   Under the analysis, a randomly chosen industrial sample was also used and the resultant data was utilised in understanding the response of the system to different electrolytes. / Sammanfattning   Avhandlingsarbetet har genomförts på KEMET AB i samarbete med yttekniklaboratoriet vid JTH i syfte att karakterisera den etsade anodiska aluminiumfolien som grundprov med anodisering och etsning för ytbehandling.   I inledningsskedet gjordes provberedningen med användning av teknikerna för anodisk etsning och anodbildande processer där en upprepad provnings- och felmetod för provberedning ledde ut mot att utarbeta en lämplig provuppsättning med avseende på karakterisering. Efter detta steg infördes uppsättningen av 2 olika industriella prover och anodoxidbildande process utfördes i olika elektrolyter.   I provpreparaten användes 4 olika elektrolyter 15 % vikt Ammoniumadiphat, 1,5 vikt% Ammoniumfosfat, 7 vikt% Borsyra och 15 % Penta-borat vid olika steg för utförande av anodoxidbildningsförfarandet. Minimala formningsspänningar på 20V till ett maximum av 100V användes i provframställningen och för att övervinna väntetiden vid bildning av de etsade proven användes en högre ström av 0,5A.   Efter provberedningen användes elektrokemisk impedansspektroskopi som ett verktyg för att karakterisera de olika grupperna av prover och för att observera mikrostrukturerna i olika prover, de bröts och de observerades i tvärsnittet av SEM.   Efter att analysen av de etsade proverna gjordes ett försök att jämföra resultaten av data från dessa prover till den för de två uppsättningarna av industriella prover. Det är konstaterat att de resulterande data inte var stabila nog att karakterisera eftersom stor spridning inträffade och varigenom simuleringen av CPE-kretsen för den valda kretsen i analysen inte var möjlig.   Under analysen användes också ett slumpmässigt valt industriellt prov och de resulterande data användes för att förstå systemets respons till olika elektrolyter.

Ces travaux de doctorat proposent d’apporter une contribution à l’identification et à la compréhension des phénomènes limitant les performances de détecteurs de rayon X à base de CdTe:Cl développés pour des applications en radiographie. En effet, des inhomogénéités spatiales non-stables dans le temps sont observées dans la réponse de ces capteurs. Les défauts des cristaux utilisés pour la détection ont été caractérisés. Notamment, les dislocations révélées par attaque chimique et par topographie X présentent des arrangements en mur à la surface des échantillons, ces défauts sont majoritairement traversant dans toute l’épaisseur du cristal. Il a ensuite été montré que ces murs de dislocations sont responsables des inhomogénéités de photo-courant sous irradiation par des rayons X et de courant de fuite d’un détecteur à base de CdTe:Cl. De plus, les niveaux pièges dans le gap du CdTe ont été investigués par des méthodes de spectroscopie optique à basse température : les images de cathodoluminescence mettent en évidence le caractère non-radiatif des murs de dislocations, mais ne montrent pas l’apparition de la luminescence Y au niveau de ces défauts, normalement attribuée aux dislocations dans la littérature. Enfin, l’influence des murs de dislocations sur les propriétés de transport des porteurs de charge a été étudiée par la méthode « Ion Beam Induced Current » (IBIC) montrant qu’ils entraînent une diminution de la valeur du produit mobilité-temps de vie des électrons et des trous / In the present Ph.D. thesis, we investigate microstructural defects in a chlorine-doped cadmium telluride crystal (CdTe:Cl), to understand the relationship between defects and performance of CdTe-based radiation detectors. Characterization tools, such as diffraction topography and chemical etching, are used for bulk and surface investigations of the distribution of dislocations. Dislocations are arranged into walls. Most of them appear to cross the whole thickness of the sample. Very good correlation is observed between areas with variations of dark-current and photo-current, and positions of the dislocation walls revealed at the surface of the sample. Then spectroscopic analysis of these defects was performed at low temperatures. It highlighted that dislocation walls induce non-radiative recombination, but it didn’t show any Y luminescence usually attributed to dislocations in the literature. Ion Beam Induced Current (IBIC) measurements were used to evaluate the influence of dislocation walls on charge carrier transport properties. This experiment shows that they reduce the mobility-Iifetime product of the charge carriers. A very clear correlation was, in fact, established between the distribution of the dislocation network and the linear defects revealed by their lower CIE on the device