Etude des propriétés optiques de nanofils individuels de Si, de Ge, et d'alliages et hétérostructures SiGe pour le contrôle de l'absorption et de la diffusion de la lumière

Cette thèse porte sur l'étude de la réponse optique de nanofils semiconducteurs individuels afin de déterminer les paramètres clefs contrôlant l'interaction de la lumière avec un nanofil. L'objectif est d'exalter l'absorption pour des applications photovoltaïques ou la diffusion pour le contrôle de l'émission de lumière. Dans un premier temps, des calculs de la réponse optique de nanofils individuels d'alliages Si_{1-x}Ge_{x} effectués dans le cadre de la théorie analytique de Lorenz-Mie, montrent des résonances optiques ajustables dans la gamme du spectre solaire en fonction de la composition x en germanium et du diamètre du nanofil. Ces calculs sont confrontés aux spectres de diffusion élastique obtenus par microscopie optique confocale en champ sombre sur des nanofils isolés de différents diamètres et compositions. Dans un deuxième temps, l'étude théorique de la réponse optique est élargie à des structures complexes de type cœur/gaine Ge/Si et Si/Ge pour optimiser l'efficacité d'absorption par rapport à des nanofils simples, les hétérostructures radiales étant intéressantes dans une cellule solaire à base de nanofils. Enfin, l'optimisation de la diffusion de la lumière et l'exaltation du champ électromagnétique au voisinage du nanofil sont mis en évidence par l'exaltation de la photoluminescence d'un plan de nanocristaux de Si placé dans le champ proche d'un nanofil de Si qui se comporte comme une antenne, par analogie avec les nanostructures plasmoniques. De plus, nous établissons une corrélation entre l'augmentation de l'intensité du champ électrique local induite par la présence du nanofil, calculée par simulations numériques, et l'exaltation de la photoluminescence des nanocristaux.In this thesis is presented a study of the optical response of individual semiconductor nanowires in order to determine the key parameters controlling the interaction of light with a nanowire. The main objective is to enhance either the absorption efficiency for photovoltaic applications or the scattering efficiency for the control of light emission. In a first step, calculations of the optical response of single Si_{1-x}Ge_{x} nanowires performed using the analytical Mie theory, show that optical resonances occur in the solar sun wavelength range. Such resonances can be tuned by changing the nanowire diameter and Ge composition. The calculations are compared to light scattering experiments performed using dark field confocal optical microscopy on single nanowires of different diameter and Ge composition. In a second step, the theoretical study is extended to complex structures such as core-sheath Ge/Si structures to optimize the absorption efficiency compared to simple nanowires. At last, the nanowire-light emitter interaction is evidenced by the polarization dependent photoluminescence enhancement of a Si nanocrystal plane positioned in the near field of a Si nanowire, which one behaves as an optical antenna by analogy with plasmonic nanostructures. Furthermore, we show a correlation between the increase of the local electromagnetic field intensity, obtained by numerical simulations, and the Si nanocrystal photoluminescence enhancement

Effets de la concentration des défauts sur la surface d'énergie potentielle du silicium amorphe

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Thermal emission from a single glass fiber

In this article, we study the thermal light emission from individual fibers of an industrial glass material, which are elementary building blocks of glass wool boards used for thermal insulation. Thermal emission spectra of single fibers of various diameters partially suspended on air are measured in the far-field by means of infrared spatial modulation spectroscopy.These experimental spectra are compared with the theoretical absorption efficiency spectra of cylindrical shaped fibers calculated analytically in the framework of Mie theory taking as an input the measured permittivity of the industrial glass material. An excellent qualitative agreement is found between the measured thermal radiation spectra and the theoretical absorption efficiency spectra.Comment: 25 pages, 5 figures, JQSRT, 201

Evolution of the potential-energy surface of amorphous silicon

The link between the energy surface of bulk systems and their dynamical properties is generally difficult to establish. Using the activation-relaxation technique (ART nouveau), we follow the change in the barrier distribution of a model of amorphous silicon as a function of the degree of relaxation. We find that while the barrier-height distribution, calculated from the initial minimum, is a unique function that depends only on the level of distribution, the reverse-barrier height distribution, calculated from the final state, is independent of the relaxation, following a different function. Moreover, the resulting gained or released energy distribution is a simple convolution of these two distributions indicating that the activation and relaxation parts of a the elementary relaxation mechanism are completely independent. This characterized energy landscape can be used to explain nano-calorimetry measurements.Comment: 5 pages, 4 figure

Thermal emission from a single glass fiber

International audienceIn this article, we study the thermal light emission from individual fibers of an industrial glass material, which are elementary building blocks of glass wool boards used for thermal insulation. Thermal emission spectra of single fibers of various diameters partially suspended on air are measured in the far field by means of infrared spatial modulation spectroscopy. These experimental spectra are compared with the theoretical absorption efficiency spectra of cylindrical shaped fibers calculated analytically in the framework of Mie theory taking as an input the measured permittivity of the industrial glass material. An excellent qualitative agreement is found between the measured thermal radiation spectra and the theoretical absorption efficiency spectra

Design and thermal conductivity of 3D artificial cross-linked random fiber networks

We propose a novel procedure to design three-dimensional (3D) printable cross-linked random fiber networks. Our procedure describes how to implement, in a novel way, a modified version of random-walk based algorithm using a combination of different free and open-source software programs. Second, we describe in detail a method based on an open-source finite-element software, to analyse the steady-state heat conduction and to compute the effective thermal conductivity for cross-linked fibrous structures immersed in vacuum. We apply this method to examine how the orientations of the fibers and the fiber volume fraction influence the effective thermal conductivity of 3D artificial cross-linked random glass fiber networks. Our numerical results show explicitly the direct link between the effective thermal conductivity and the percolating conduction paths through a 3D cross-linked fiber network. The proposed procedure for creating the 3D drawing and the one for volume meshing as well as the method for solving the steady-state heat conduction problem described in this paper can be extended to other 3D complex structures with closed surfaces

Comparison of various culture modes for the production of rabies virus by Vero cells grown on microcarriers in a 2-l bioreactor

International audienceWe studied Vero cell growth on Cytodex 1 (3 g/l) and MEM supplemented with foetal calf serum (FCS) in a 2-l bioreactor using continuous (recirculation and perfusion) and batch culture modes. We achieved a cell density level equal to 4.35 × 106 cells/ml using the recirculation culture mode while perfused cultures yielded a higher cell density level equal to 4.73 × 106 cells/ml. However, as compared to the recirculation culture mode, the specific medium consumption rate was two-fold higher. Batch culture of Vero cells resulted in 2.2 × 106 cells/ml with a specific medium consumption rate similar to recirculation culture.Rabies virus production (LP 2061/Vero strain) by Vero cells was also investigated. We analysed in spinner flasks, the effects on virus multiplication of multiplicity of infection (MOI), regulation of glucose level to 1 g/l and type of medium. The highest virus titer was reached when cells were infected at an MOI of 0.3 in M199 medium supplemented with 0.2% of bovine serum albumin (BSA) and without regulating glucose level. In these conditions, virus titer was equal to 1.5 × 106 fluorescent focus units (FFU)/ml.We then evaluated rabies virus production by Vero cells grown on 3 g/l of Cytodex 1 using recirculation culture mode during the growth phase. Cells were infected at the optimal conditions previously determined. The maximal virus titer was equal to 2 × 107 FFU/ml. The activity of the experimental vaccine prepared showed a protective activity that meets WHO requirements