Microplasmas são plasmas gerados em espaços com dimensões reduzidas, tipicamente, de dezenas a centenas de micrômetros. Apresentam como principal vantagem a possibilidade de se obter plasmas frios com densidades elevadas com baixo consumo de energia em pressões maiores do que em reatores convencionais, reduzindo sensivelmente o custo do equipamento. Um gerador de microplasma inédito foi desenvolvido neste trabalho, utilizando a tecnologia LTCC. O dispositivo é constituído por dois eletrodos paralelos de prata-paládio perfurados por centenas de microfuros, formando microcanais. O microplasma é gerado na região entre os eletrodos e é conduzido para fora do gerador através dos microcanais, constituindo um plasma remoto que pode interagir com a superfície de um material a ser processado. Os microfuros formam a estrutura de um microcatodo oco. Na fabricação, as camadas de cerâmica verde foram usinadas com uma máquina de CNC e os eletrodos foram obtidos por serigrafia. O método de pós-sinterização utilizando a cerâmica de transferência mostrou ser bastante reprodutível e produziu eletrodos totalmente planos, sem arqueamento. O gerador de microplasma foi instalado dentro de um reator RIE convencional e o microplasma foi gerado em DC e RF. A caracterização dos microplasmas de Ar, O2, N2 e He foi realizada por meio de curvas VxI, sonda dupla de Langmuir e espectroscopia de emissão óptica. Para descargas DC, em condições de baixa vazão de gás e elevada pressão, as curvas VxI mostraram três modos de descarga: catodo oco, normal e anormal. O efeito catodo oco foi evidenciado também pelos espectros de emissão óptica que mostraram raias na faixa de 300 a 450 nm, que indicam a presença de elétrons de alta energia. Essas raias foram mais fortemente evidenciadas em descargas RF. Temperaturas de elétrons elevadas, na faixa de 10 a 30 eV, foram obtidas através de medidas com a sonda dupla de Langmuir, nas condições em que o efeito catodo oco foi observado. A aplicabilidade do gerador de microplasma foi testada com foco no tratamento de superfície de polietileno e os resultados mostraram alta capacidade de redução do ângulo de contato e aumento da molhabilidade superficial, demonstrando, conseqüentemente, substancial modificação da energia de superfície do material, através desse processo a microplasma. / Microplasmas are plasmas generated in spaces with reduced dimensions, typically ranging from tens to hundreds of microns. The major advantage of a microplasma generator is the possibility of glow discharge generation with high plasma density and low power consumption at pressures higher than usually observed in conventional plasma reactors, reducing considerably the equipment cost. A novel structure of microplasma generator was developed in this work, using the LTCC technology. The device is composed of two silver-palladium parallel electrodes perforated by hundreds of microholes, constituting microchannels. The microplasma itself is formed between the electrodes and the plasma species are carried through the microchannels to reach the processing chamber, where they can interact with the samples to be treated. The presence of microholes can promote microhollow cathode effect. In the fabrication process, green tapes were micromachined by using a CNC and the electrodes were obtained by screen printing. The post-fire method using transfer tapes has demonstrated to be very reproducible and produced very flat electrodes. The microplasma generator was mounted into a conventional homemade reactive ion etching (RIE) reactor and driven by DC and RF power supply. Characterization of Ar, O2, N2 and He microplasmas was performed by means of VxI characteristics, double Langmuir probe and optical emission spectroscopy. For DC discharges, the VxI characteristics revealed three distinct regions: microhollow cathode mode, normal glow and abnormal glow, for low gas flow rate and high pressure conditions. The microhollow cathode effect was evidenced by optical emission that presented lines in wavelengths between 300 and 450 nm, indicating the presence of high energy electrons. These emission lines have shown to be more intense in RF discharges. Double Langmuir probe diagnostic showed high electron temperatures ranging from 10 and 30 eV, under the microhollow cathode effect conditions. The microplasma generator applicability was tested focusing on the surface treatment of polyethylene film. The results showed high efficiency of this process in reducing water contact angle and thus substantially increasing the polyethylene wettability, thus demonstrating effective modification of surface energy of the material. One can conclude that among other potential applications for material processing, the microplasma generator has already shown to be a reliable tool to modify the surface energy of materials.

Microplasmas são plasmas gerados em espaços com dimensões reduzidas, tipicamente, de dezenas a centenas de micrômetros. Apresentam como principal vantagem a possibilidade de se obter plasmas frios com densidades elevadas com baixo consumo de energia em pressões maiores do que em reatores convencionais, reduzindo sensivelmente o custo do equipamento. Um gerador de microplasma inédito foi desenvolvido neste trabalho, utilizando a tecnologia LTCC. O dispositivo é constituído por dois eletrodos paralelos de prata-paládio perfurados por centenas de microfuros, formando microcanais. O microplasma é gerado na região entre os eletrodos e é conduzido para fora do gerador através dos microcanais, constituindo um plasma remoto que pode interagir com a superfície de um material a ser processado. Os microfuros formam a estrutura de um microcatodo oco. Na fabricação, as camadas de cerâmica verde foram usinadas com uma máquina de CNC e os eletrodos foram obtidos por serigrafia. O método de pós-sinterização utilizando a cerâmica de transferência mostrou ser bastante reprodutível e produziu eletrodos totalmente planos, sem arqueamento. O gerador de microplasma foi instalado dentro de um reator RIE convencional e o microplasma foi gerado em DC e RF. A caracterização dos microplasmas de Ar, O2, N2 e He foi realizada por meio de curvas VxI, sonda dupla de Langmuir e espectroscopia de emissão óptica. Para descargas DC, em condições de baixa vazão de gás e elevada pressão, as curvas VxI mostraram três modos de descarga: catodo oco, normal e anormal. O efeito catodo oco foi evidenciado também pelos espectros de emissão óptica que mostraram raias na faixa de 300 a 450 nm, que indicam a presença de elétrons de alta energia. Essas raias foram mais fortemente evidenciadas em descargas RF. Temperaturas de elétrons elevadas, na faixa de 10 a 30 eV, foram obtidas através de medidas com a sonda dupla de Langmuir, nas condições em que o efeito catodo oco foi observado. A aplicabilidade do gerador de microplasma foi testada com foco no tratamento de superfície de polietileno e os resultados mostraram alta capacidade de redução do ângulo de contato e aumento da molhabilidade superficial, demonstrando, conseqüentemente, substancial modificação da energia de superfície do material, através desse processo a microplasma. / Microplasmas are plasmas generated in spaces with reduced dimensions, typically ranging from tens to hundreds of microns. The major advantage of a microplasma generator is the possibility of glow discharge generation with high plasma density and low power consumption at pressures higher than usually observed in conventional plasma reactors, reducing considerably the equipment cost. A novel structure of microplasma generator was developed in this work, using the LTCC technology. The device is composed of two silver-palladium parallel electrodes perforated by hundreds of microholes, constituting microchannels. The microplasma itself is formed between the electrodes and the plasma species are carried through the microchannels to reach the processing chamber, where they can interact with the samples to be treated. The presence of microholes can promote microhollow cathode effect. In the fabrication process, green tapes were micromachined by using a CNC and the electrodes were obtained by screen printing. The post-fire method using transfer tapes has demonstrated to be very reproducible and produced very flat electrodes. The microplasma generator was mounted into a conventional homemade reactive ion etching (RIE) reactor and driven by DC and RF power supply. Characterization of Ar, O2, N2 and He microplasmas was performed by means of VxI characteristics, double Langmuir probe and optical emission spectroscopy. For DC discharges, the VxI characteristics revealed three distinct regions: microhollow cathode mode, normal glow and abnormal glow, for low gas flow rate and high pressure conditions. The microhollow cathode effect was evidenced by optical emission that presented lines in wavelengths between 300 and 450 nm, indicating the presence of high energy electrons. These emission lines have shown to be more intense in RF discharges. Double Langmuir probe diagnostic showed high electron temperatures ranging from 10 and 30 eV, under the microhollow cathode effect conditions. The microplasma generator applicability was tested focusing on the surface treatment of polyethylene film. The results showed high efficiency of this process in reducing water contact angle and thus substantially increasing the polyethylene wettability, thus demonstrating effective modification of surface energy of the material. One can conclude that among other potential applications for material processing, the microplasma generator has already shown to be a reliable tool to modify the surface energy of materials.

The aim of this thesis is the characterization of electrical properties of solar cell using CCD camera. Diagnostic methods are based on electroluminescence and microplasma emitted from the surface of the solar cell. The results are then compared with the method LBIC (Light Beam Induced Current) and described the various defects in industrial production.

No description available.

Nous étudions la génération de rayonnement TeraHertz (THz) dans des microplasmas produits par des lasers femtosecondes. Cette technique est prometteuse pour créer efficacement des sources THz compactes et étendue spectralement (0.3-30 THz), qui intéressent de nombreuses applications, comme l’identification spectroscopique de substances dangereuses ou encore l’imagerie en biologie et médecine. Contrairement aux sources conventionnelles, comme les interrupteurs photo-conducteur, les sources THz basées sur des plasmas ne sont pas limitées par la tenue au flux et couvrent l’ensemble du spectre THz. Afin de modéliser des microplasmas générés par des faisceaux laser fortement focalisés, nous présentons un nouvel algorithme qui permet d’injecter tout type de laser dans des codes électromagnétiques. Nous dérivons aussi un modèle compatible avec les équations de Maxwell qui inclut les deux mécanismes générateurs de THz: le courant d’ionisation (IC) et le mécanisme “Transition-Cherenkov” (TC). Ce dernier mécanisme domine la production de THz pour des lasers à plusieurs cycles optiques, où l’émission est produite par les courants d’électron longitudinaux. Dans le cas des microplasmas où un champ électrostatique externe est ajouté, le taux de conversion énergétique laser/THz peut être augmenté de deux ordres de grandeur via le mécanisme IC lorsque le champs statique ou la pression du gaz sont accrus. De plus, les simulations 3D montrent que pour un faisceau laser à deux couleurs et dans des conditions optimales de focalisation, une énergie laser de 10 micro-Joule est suffisante pour atteindre des taux de conversion bien au-dessus de 10−4. Dans ce cas, la nature transverse du courant IC est cruciale pour accroitre l’efficacité avec la longueur du plasma. En considérant un faisceau laser à deux couleurs de forme elliptique, nous proposons de contrôler les spectres d’émission en exploitant les effets plasmoniques résonants. / We investigate terahertz (THz) generation in fs-laser-induced microplasmas, which are promising candidates for compact and efficient broadband THz sources (0.3-30 THz). Such sources have various applications as spectroscopic identification of hazardous substances or THz imaging in biology and medicine. Unlike conventional THz sources as photoconductive switches, gas-plasma-based THz sources do not suffer from irreversible material damage and can cover the whole THz range at once. To simulate tightly-focused-laser-induced microplasmas, we propose an efficient numerical algorithm that can introduce any arbitrarily shaped laser pulses into electromagnetic codes. We derive a Maxwell-consistent model that includes two major THz generation mechanisms, the ionization current (IC) and transition-Cherenkov mechanisms (TC). The latter mechanism is shown to dominate for single-color multi-cycle lasers pulses where the emission is driven by longitudinal electron currents. For microplasmas a constant electric field can boost the laser-to-THz converison efficiency by two orders of magnitude via the IC mechanism when increasing the gas-pressure and bias-voltage. Moreover for two-color-driving laser pulses, Maxwell-consistent 3D simulations show, that only 10 μJ laser pulse energy are sufficient to reach conversion efficiencies well above 10−4 when optimizing the focusing conditions. Here, the transverse nature of the IC currents is crucial for the up-scaling of the efficiency with the plasma length. By using elliptically-shaped two-color-driving laser beams, we propose to control the emission spectra by exploiting resonant plasmonic effects.

No description available.

Atmospheric pressure microplasmas are uniquely characterized by their very high energy densities and also by their small discharge sizes. These properties allow for unique applications in plasma processing technologies. We have investigated the operational characteristics of microplasmas at higher energy densities and smaller sizes by operating microplasma configurations at high pressure conditions. We studied the discharge and analyzed its variation with changes in current and pressure. The discharge was analyzed by microscopic visualization and data from the images and was processed to measure the current density and estimate charged particle density. By increasing the pressure beyond 200 psi and by minimizing the discharge current required for sustaining the plasma, we have been able to achieve discharge sizes of 7 mu m in nitrogen and as small as 20 μm in helium. Optical emission spectroscopic studies were carried out to measure gas temperature and vibrational temperature using the nitrogen 2nd positive system. With increase in pressure, the transition from non-equilibrium plasma to equilibrium plasma was also studied using the OES temperature measurements. iv Temperature measurements are also used to estimate normalized current densities. Normalized current density results obtained after introducing the corrected effective pressure based on the increased gas temperature are close to the value of 400 mu A /cm^2*Torr^2 obtained for low pressure normal glow discharges in nitrogen. This research presents further validation of the general operational characteristics of microplasmas being pressure scaled versions of normal glow discharges. Attained energy densities are ten to twenty times higher than in atmospheric pressure microplasmas. Discharge sizes are also significantly smaller, decreasing with increasing pressure, but the scaling is with density ‘nd’ rather than pressure ‘Pd’ due to the increase in gas temperature with pressure, indicating a dependence on collisional processes. We can infer that at higher pressures, the operational characteristics of more complex plasma discharges like dielectric barrier discharges, RF plasmas, etc. follow scaling patterns, transitions and limits similar to the microplasma discharge studied in this thesis.

The prospect of finding life outside Earth has fascinated mankind for ages, and new technology continuously pushes the boundary of how remote and how obscure evidence we can find. Employing smaller, or completely new, types of landers and robots, and equipping them with miniature instruments would indeed revolutionize exploration of other planets and moons. In this thesis, microsystems technology is used to create a miniature high-precision isotope-resolving molecular spectrometer utilizing the optogalvanic effect. The heart of the instrument, as well as this thesis, is a microplasma source. The plasma source is a split-ring resonator, chosen for its simplicity, pressure range and easily accessible plasma, and modified to fit the challenging application, e.g., by the adding of an additional ground plane for improved electromagnetic shielding, and the integration of microscopic plasma probes to extract the pristine optogalvanic signal. Plasma sources of this kind have been manufactured in both printed circuit board and alumina, the latter for its chemical inertness and for compatibility with other devices in a total analysis system. From previous studies, classical optogalvanic spectroscopy (OGS), although being very sensitive, is known to suffer from stability and reproducibility issues. In this thesis several studies were conducted to investigate and improve these shortcomings, and to improve the signal-to-noise ratio. Moreover, extensive work was put into understanding the underlying physics of the technique. The plasma sources developed here, are the first ever miniature devices to be used in OGS, and exhibits several benefits compared to traditional solutions. Furthermore, it has been confirmed that OGS scales well with miniaturization. For example, the signal strength does not decrease as the volume is reduced like in regular absorption spectroscopy. Moreover, the stability and reproducibility are greatly increased, in some cases as much as by two orders of magnitude, compared with recent studies made on a classical OGS setup. The signal-to-noise ratio has also been greatly improved, e.g., by enclosing the sample cell and by biasing the plasma. Another benefit of a miniature sample cell is the miniscule amount of sample it requires, which can be important in many applications where only small amounts of sample are available. To conclude: With this work, an important step toward a miniature, yet highly performing, instrument for detection of extraterrestrial life, has been taken.

Th.--Sci., électronique--Toulouse--I.N.P., 1977. N°: 28.

The thesis deals with detailed theoretical and experimental investigation of noise and transport characteristics of selected photovoltaic cells in both forward and reversed directions focusing on the area of local PN junction instability (within the microplasma regions). It will be studied the correlation among different characteristics.