L'énergie photovoltaïque est promise à une forte croissance dans les prochaines années. Propre et renouvelable, elle possède en effet de sérieux atouts pour répondre aux grands enjeux posés par le réchauffement climatique et l'appauvrissement des ressources en énergie fossile. Elle reste néanmoins une énergie chère en comparaison des autres formes de production électrique. D'importants efforts de R&D doivent être mis en œuvre pour abaisser son coût et la rendre plus compétitive. Il existe d'ores et déjà dans les laboratoires des technologies permettant d'augmenter significativement le rendement des cellules solaires en silicium (qui représentent aujourd’hui l'essentiel du marché). Mais elles font appel le plus souvent à des procédés, comme la photolithographie, qui restent chères pour l'industrie photovoltaïque. Les technologies laser sont une voie envisagée pour répondre à ce problème. Sélectifs, sans contact et autorisant de hautes cadences, les procédés laser permettent de réaliser des structures avancées de cellules à moindre coût. Il existe ainsi une forte dynamique de recherche autour de ces procédés. Les traitements laser permettent d’usiner ou de modifier la matière, de façon rapide et fiable. Il est ainsi possible d’ablater sélectivement certains matériaux, de réaliser des tranchées ou des trous, ou encore de modifier des profils de dopage. Des architectures complexes deviennent ainsi accessibles sans recourir aux couteuses technologies de la microélectronique. C'est dans ce contexte que se déroule ce travail de thèse, financé par l'ADEME et la société SEMCO Eng., et s'inscrivant également dans le projet de l'Agence National pour la Recherche PROTERRA. Deux objectifs principaux ont motivé sa mise en place : développer un savoir-faire au laboratoire INL sur les technologies laser avec l'ambition de rejoindre les instituts leaders sur ces thématiques et transférer les procédés développés à l'équipementier SEMCO Eng. pour lui donner accès à une technologie aujourd'hui inédite dans l'industrie photovoltaïque française. Ces recherches ont porté sur les cellules photovoltaïques en silicium, dites de première génération, et se sont articulées autour de trois axes principaux : la modélisation de l'interaction laser matière, l'ablation sélective de diélectriques (notamment de la couche antireflet afin de permettre de nouvelles techniques de métallisation) et la réalisation de dopages localisés. Des cellules de grandes dimensions fabriquées en collaboration avec SEMCO Eng. et tirant parti de ces procédés ont permis d’obtenir des rendements en accord avec l’état de l’art (proche de 18 %). / Silicon solar cells still require cost reduction and improved efficiency to become more competitive. New architectures can provide a significant increase in efficiency, but today most of the approaches need additional fabrication steps. In this context, laser processing offers a unique way to replace technological steps like photolithography that is not compatible with the requirements of the photovoltaic industry. This PhD thesis will present two promising laser processes for silicon solar cells: selective laser doping and selective laser ablation. Laser-assisted diffusion of dopants is a promising way to produce at low cost advanced silicon solar cells with high efficiency. Indeed, selective emitters, which rely on high dopant concentration localized under the front electrical contacts are an effective way to reduce power losses at the front surface of silicon solar cells. Several laser-based techniques are competing to optimise the emitter geometry. One of the main approaches is to take advantage of the doping glass (usually P2O5 for p-type silicon solar cells) that is formed during the standard diffusion process. Selective laser ablation is an effective way to open the antireflection layer (SiNx) in order to perform alternative front side metallization. Indeed, in the industrial production of standard silicon solar cells, the front side metallization is made by screen printing of metal paste. This process scheme is very cost efficient but it leads to serious limitations of the solar cell efficiency. Electrochemical metallization avoids these issues but requires a selective opening of SiNx, which is usually done by photolithography. Direct laser ablation allows to consider this approach at an industrial level. These processes are presented illustrated by research conducted during this PhD at INL in laser technologies for photovoltaics. An innovative and potentially self-aligned process is also discussed, where the laser is used to open locally the antireflection and passivation coating, and at the same time, achieve local phosphorus diffusion. Moreover solar cells results above 18% have been obtained thanks to a selective emitter structure achieved with selective laser doping.

Das Problem des Missbrauchs von Erythropoietin (EPO) als Dopingsubstanz zur Steigerung der Ausdauerleistung wurde schlagartig weltweit durch den Skandal zur Tour de France 1998 bekannt. Das Internationale Olympische Komitee (IOC) führte ab 1992 Erythropoietin explizit auf der Liste der verbotenen Wirkstoffe auf, ohne des es möglich war zwischen den rekombinantem und dem körpereigene Erythropoietin zu unterscheiden. Bei der im Institut für Dopinganalytik und Sportbiochemie Kreischa durchgeführten Arbeit wurden zwei generelle Strategien verfolgt: zum einen ein indirekter Nachweis des rhEPO, basisierend auf dessen Auswirkungen auf die Erythropoese, und zum anderen der direkte Nachweis des Unterschieds zwischen rekombinantem und humanem Erythropoietin. In der ersten durchgeführten Populationsuntersuchung von 229 Leistungssportlern konnte bei der Auswertung der Daten lediglich eine signifikante Erhöhung des löslichen Transferrinrezeptors (sTfR) bei den Ausdauerathleten gefunden werden, während sich die hämatologischen Parameter nicht unterschieden. In der anschließenden Verlaufsuntersuchung von Ausdauerathleten des Deutschen Leichtathletikverbandes wurden zusätzlich zu den bereits in der Populationsstudie untersuchten Parametern erstmalig von Hochleistungs-athleten Retikulozyten und deren Reifeparameter untersucht. Bei den Hochleistungs-sportlern konnten, insbesondere für die Retikulozyten-parameter, über den Zeitraum der Studie konstante Werte gefunden werden. Die Untersuchung der zirkadianen Rhythmik zeigte lediglich für den Parameter Erythropoietin einen signifikante Veränderung mit einem Maximum in den späten Abendstunden (20:00 bis 23:00 Uhr) erreichte. Die Untersuchung der Variation der indirekten Parameter über den Zeitraum eines Jahres zeigte, dass im Gegensatz zu der Verlaufsuntersuchung der DLV-Athleten, bei der der längste Untersuchungs-zeitraum sechs Monate betrug, eine Veränderung aller Parameter, mit Ausnahme von Erythropoietin, bestand. Bei der Auswertung der Belastungsstudien wurde für die gut trainierten Athleten nur ein geringer Einfluss auf die hämatologischen Parameter gefunden, während bei einigen Retikulozytenparametern signifikante Erhöhungen durch die Belastung festgestellt werden konnten. Mit der Etablierung der direkten Nachweismethode für EPO im Urin und der Anpassung der ursprünglichen Methode an das neue Präparat ARANESP, ein modifiziertes EPO, änderte sich die Aufgabenstellung für die indirekten Parameter, da es ab sofort möglich war eine große Anzahl Proben unter Verwendung von niedrigeren Grenzwerten zu screenen. Anhand der Werte der weltbesten Ausdauerathleten wurden allgemein gültige Grenzwerte und eine globale Strategie für ein Screening aufgestellt. Bei einem auffälligen Befund würde in jedem Fall die korrespondierende Urinprobe mittels der direkten Methode untersucht und erst mit dem Nachweis des rekombinanten Erythropoietins als positiv bewertet werden. Zusätzlich zu den indirekten Parametern wurden Untersuchungen hinsichtlich des direkten Nachweis, d. h. der Anreicherung von Erythropoietin und einer massenspektrometrischen Analyse einzelner Glykanketten, durchgeführt, bei denen mit der Kombination Nanospray und TOF-MS die notwendigen Nachweisgrenzen erreicht werden konnten. Die Ergebnisse der Arbeit zeigen, dass ausgewählter Blutparameter sehr gut geeignet sind, um als Screeningmethode für erythropoesesteigernde Substanzen zu dienen. Im Gegensatz zur Methode des direkten Nachweises von EPO im Urin, die durch die Verfügbarkeit der Referenzsubstanzen limitiert ist, bietet der indirekte Nachweis über Blutparameter den Vorteil, Veränderungen des erythropoetischen Systems, verursacht durch neue Substanzen oder Methoden, erfassen zu können.

Title: ​Proportionality of a four-year ineligibility for the first intentional anti-doping rule violations and its impact on professional athletes' careers Objectives: ​The aim of this thesis is to ascertain whether the four-year ineligibility for the first intentional anti-doping rule violations has liquidation impact on professional athletes' careers. Methods: ​For quantitative research, I have used the electronic interrogation method and for qualitative research the in-depth semi-structured interview. Results: ​I have found that most athletes really do perceive a four-year ineligibility for the first intentional anti-doping rule violations as disproportionate. Only 24 % of surveyed athletes said that a four-year ineligibility is an appropriate punishment. 82 % of surveyed athletes would end their careers after receiving a four-year ineligibility, and just 30 % of them think that It's realistic to go back to an active career after a four-year break. Moreover, athletes have consistently said that the most crucial obstacles to their return are financial distress, loss of motivation and lack of racing mode. On the basis of these results, I have also developed my own solution to ineligibility for the first intentional anti-doping rule violations. Keywords: ​proportionality, sanction, ineligibility,...

Das Problem des Missbrauchs von Erythropoietin (EPO) als Dopingsubstanz zur Steigerung der Ausdauerleistung wurde schlagartig weltweit durch den Skandal zur Tour de France 1998 bekannt. Das Internationale Olympische Komitee (IOC) führte ab 1992 Erythropoietin explizit auf der Liste der verbotenen Wirkstoffe auf, ohne des es möglich war zwischen den rekombinantem und dem körpereigene Erythropoietin zu unterscheiden. Bei der im Institut für Dopinganalytik und Sportbiochemie Kreischa durchgeführten Arbeit wurden zwei generelle Strategien verfolgt: zum einen ein indirekter Nachweis des rhEPO, basisierend auf dessen Auswirkungen auf die Erythropoese, und zum anderen der direkte Nachweis des Unterschieds zwischen rekombinantem und humanem Erythropoietin. In der ersten durchgeführten Populationsuntersuchung von 229 Leistungssportlern konnte bei der Auswertung der Daten lediglich eine signifikante Erhöhung des löslichen Transferrinrezeptors (sTfR) bei den Ausdauerathleten gefunden werden, während sich die hämatologischen Parameter nicht unterschieden. In der anschließenden Verlaufsuntersuchung von Ausdauerathleten des Deutschen Leichtathletikverbandes wurden zusätzlich zu den bereits in der Populationsstudie untersuchten Parametern erstmalig von Hochleistungs-athleten Retikulozyten und deren Reifeparameter untersucht. Bei den Hochleistungs-sportlern konnten, insbesondere für die Retikulozyten-parameter, über den Zeitraum der Studie konstante Werte gefunden werden. Die Untersuchung der zirkadianen Rhythmik zeigte lediglich für den Parameter Erythropoietin einen signifikante Veränderung mit einem Maximum in den späten Abendstunden (20:00 bis 23:00 Uhr) erreichte. Die Untersuchung der Variation der indirekten Parameter über den Zeitraum eines Jahres zeigte, dass im Gegensatz zu der Verlaufsuntersuchung der DLV-Athleten, bei der der längste Untersuchungs-zeitraum sechs Monate betrug, eine Veränderung aller Parameter, mit Ausnahme von Erythropoietin, bestand. Bei der Auswertung der Belastungsstudien wurde für die gut trainierten Athleten nur ein geringer Einfluss auf die hämatologischen Parameter gefunden, während bei einigen Retikulozytenparametern signifikante Erhöhungen durch die Belastung festgestellt werden konnten. Mit der Etablierung der direkten Nachweismethode für EPO im Urin und der Anpassung der ursprünglichen Methode an das neue Präparat ARANESP, ein modifiziertes EPO, änderte sich die Aufgabenstellung für die indirekten Parameter, da es ab sofort möglich war eine große Anzahl Proben unter Verwendung von niedrigeren Grenzwerten zu screenen. Anhand der Werte der weltbesten Ausdauerathleten wurden allgemein gültige Grenzwerte und eine globale Strategie für ein Screening aufgestellt. Bei einem auffälligen Befund würde in jedem Fall die korrespondierende Urinprobe mittels der direkten Methode untersucht und erst mit dem Nachweis des rekombinanten Erythropoietins als positiv bewertet werden. Zusätzlich zu den indirekten Parametern wurden Untersuchungen hinsichtlich des direkten Nachweis, d. h. der Anreicherung von Erythropoietin und einer massenspektrometrischen Analyse einzelner Glykanketten, durchgeführt, bei denen mit der Kombination Nanospray und TOF-MS die notwendigen Nachweisgrenzen erreicht werden konnten. Die Ergebnisse der Arbeit zeigen, dass ausgewählter Blutparameter sehr gut geeignet sind, um als Screeningmethode für erythropoesesteigernde Substanzen zu dienen. Im Gegensatz zur Methode des direkten Nachweises von EPO im Urin, die durch die Verfügbarkeit der Referenzsubstanzen limitiert ist, bietet der indirekte Nachweis über Blutparameter den Vorteil, Veränderungen des erythropoetischen Systems, verursacht durch neue Substanzen oder Methoden, erfassen zu können.

Title: Doping Cases in Czech Sport Objectives: The main goal of this work is to analyze doping cases in the Czech Republic by doping findings in terms of doping substances and methods, other doping offense, sport, nature of sampling, sanctions, and gender. Then compare the results with the statistics of doping cases in the world. The purpose is to collect, compare, then process and clarify the current statistics doping cases. Methods: To create work were used document analysis, text interpretation, comparison, collection of data, information and subsequent processing. Results: Among the athletes were punished the most abused group of anabolic substances. The largest representation of all groups detected substances were marijuana and testosterone. Among many other anti-doping rule violations included failing to submit to doping control. Most of doping cases were detected in bodybuilding. Individual athletes were compared with the collective prone to doping. In team sports doping was most widespread among volleyball players, football players and hockey players. Athletes were tested more than the competition out of the competition. The most common punishment for violation of anti-doping rules was two years Ineligibility. The highest rate was granted a lifetime Ineligibility. The men were compared with...

Title: Doping Cases in Czech Sport Objectives: The main goal of this work is to analyze doping cases in the Czech Republic by doping findings in terms of doping substances and methods, other doping offense, sport, nature of sampling, sanctions, and gender. Then compare the results with the statistics of doping cases in the world. The purpose is to collect, compare, then process and clarify the current statistics doping cases. Methods: To create work were used document analysis, text interpretation, comparison, collection of data, information and subsequent processing. Results: Among the athletes were punished the most abused group of anabolic substances. The largest representation of all groups detected substances were marijuana and testosterone. Among many other anti-doping rule violations included failing to submit to doping control. Most of doping cases were detected in bodybuilding. Individual athletes were compared with the collective prone to doping. In team sports doping was most widespread among volleyball players, football players and hockey players. Athletes were tested more than the competition out of the competition. The most common punishment for violation of anti-doping rules was two years Ineligibility. The highest rate was granted a lifetime Ineligibility. The men were compared with...

Le silicium (Si) et le germanium (Ge) sont les matériaux de base utilisés dans les circuits intégrés. Cependant, à cause de leur gap indirect, ces matériaux ne sont pas adaptés à la fabrication de dispositifs d'émission de lumière, comme les lasers ou diodes électroluminescentes. Comparé au Si, le Ge pur possède des propriétés optiques uniques, à température ambiante son gap direct est de seulement 140 meV au-delà du gap indirect tandis qu'il est supérieur à 2 eV dans le cas du Si. Compte tenu du coefficient de dilatation thermique du Ge, deux fois plus grand que celui du Si, une croissance de Ge sur Si à hautes températures suivie d'un refroidissement à température ambiante permet de générer une contrainte en tension dans le Ge. Cependant, l'existence d'un désaccord de maille de 4,2% entre deux matériaux conduit à une croissance Stranski-Krastanov avec la formation des films rugueux et contenant de forte densité des dislocations. Nous avons mis en évidence l'existence d'une fenêtre de température de croissance, permettant de supprimer la croissance tridimensionnelle de Ge/Si. En combinant la croissance à haute température à des recuits thermiques par cycles, une contrainte de 0,30% a pu être obtenue. Le dopage de type n a été effectué en utilisant la décomposition de GaP, ce qui produit des molécules P2 ayant un coefficient de collage plus grand par rapport à celui des molécules P4. En particulier, en mettant en oeuvre la technique du co-dopage en utilisant le phosphore et l'antimoine, nous avons mis en évidence une augmentation de l'émission du gap direct du Ge à environ 150 fois, ce qui constitue l'un des meilleurs résultats obtenus jusqu'à présent. / Silicon (Si) and germanium (Ge) are the main materials used as active layers in microelectronic devices. However, due to their indirect band gap, they are not suitable for the fabrication of light emitting devices, such as lasers or electroluminescent diodes. Compared to Si, pure Ge displays unique optical properties, its direct bandgap is only 140 meV above the indirect one. As Ge has a thermal expansion coefficient twice larger than that of Si, tensile strain can be induced in the Ge layers when growing Ge on Si at high temperatures and subsequent cooling down to room temperature. However, due to the existence of a misfit as high as 4.2 % between two materials, the Ge growth on Si proceeds via the Stranski-Krastanov mode and the epitaxial Ge films exhibits a rough surface and a high density of dislocations. We have evidenced the existence of a narrow substrate temperature window, allowing suppressing the three-dimensional growth of Ge on Si. By combining high-temperature growth with cyclic annealing, we obtained a tensile strain up to 0.30 %. The n-doping in Ge was carried out using the decomposition of GaP to produce the P2 molecules, which have a higher sticking coefficient than the P4 molecules. In particular, by implementing a co-doping technique using phosphorus and antimony, we have evidenced an intensity enhancement of about 150 times of the Ge direct band gap emission. This result represents as one of the best results obtained up to now.

O aprimoramento cognitivo farmacológico refere-se ao uso de medicamentos por pessoas saudáveis para melhorar o funcionamento do cérebro e aprimorar o desempenho cognitivo. Um dos medicamentos mais utilizados no Brasil com esta finalidade é o cloridrato de metilfenidato, comercializado com o nome de Ritalina ou Concerta. Ele tem sido utilizado por universitários, empresários e profissionais da saúde que visam aumentar a capacidade produtiva para cumprir prazos e metas. Considerando que esta prática está se disseminando na sociedade e chegando aos alunos do ensino médio, optou-se por fazer um estudo cujo objetivo foi caracterizar a percepção de alunos do 3º ano do ensino médio de escolas públicas, privadas e profissionalizantes e de cursinhos públicos e privados das cidades de Juazeiro do Norte (CE), Fortaleza (CE) e São Paulo (SP), sobre o uso de medicamentos para aprimoramento cognitivo, buscando identificar condições preditoras ao uso dessas substâncias. Para atingir tal objetivo o procedimento de coleta de dados foi composto de duas etapas: a primeira desenvolveu-se por meio de um estudo quali-quantitativo, com aplicação de questionários, que buscou evidenciar um panorama geral sobre o tema, sendo realizada com 534 sujeitos oriundos do 3º ano do ensino médio de escolas públicas, privadas e profissionalizantes e de cursinhos públicos e privados das cidades de Juazeiro do Norte (CE), Fortaleza (CE) e São Paulo (SP). A partir dos dados colhidos foi realizada uma segunda etapa com 13 alunos da escola profissionalizante da cidade de Juazeiro do Norte (CE), com abordagem qualitativa e realização de grupo focal, que buscou aprofundar o entendimento dessas questões. No tratamento de dados da primeira etapa utilizou-se o teste não paramétrico Qui-quadrado, e na segunda etapa a Análise de Conteúdo. Os resultados apontaram que os alunos querem ingressar no ensino superior, mais do que outras opções, consideram esta a principal função da escola e se consideram preparados para tal. Trabalhar não é seu desejo imediato e por isso não consideram importante que a escola os prepare para tanto. A compreensão de fundamentos científico-tecnológicos e o aprimoramento como pessoa humana foram considerados aspectos importantes. Medicamentos para aprimoramento foram vistos como algo positivo que poderia ser usado às vésperas do vestibular; para ajudar nos momentos de pressão por parte dos pais e da escola, em que se sentem sobrecarregados pelas suas obrigações; para conseguir realizar múltiplas atividades; para garantir energia e concentração. Verificou-se ainda que dispor de informações sobre medicamentos e conhecer usuários predispõe a um possível uso. A possibilidade de consumir os medicamentos está presente em todas as cidades analisadas e em todas as instituições. Quando tiveram a oportunidade de pensar melhor sobre o tema e falar sobre ele nos grupos focais, os alunos conseguiram perceber os fatores envolvidos na adesão ao uso de substâncias, e o que leva os estudantes a consumi-las. Os dados levantados evidenciaram que os participantes se mostraram curiosos em relação a uma substância ainda desconhecida para muitos, mas que em suas fantasias pode ser interessante para ajudar a atingir seus objetivos. Conclui-se que este é um tema relevante e preocupante; por isso, sua discussão em diferentes meios deve ser aprofundada / Pharmacological cognitive enhancement refers to the use of drugs by healthy individuals aiming at brain functioning improvement and cognitive performance enhancement. One of the widely used drugs in Brazil with these aims is methylphenidate hydrochloride, marketed under the name of Ritalina or Concerta. It has been used by college students, businessmen and health professionals aiming at enhancing their productive capacity to meet deadlines and goals. Considering the dissemination of this practice reaching high school students, this study was held aiming at characterizing the perception of high-school final-year students from public, private and vocational schools and public and private pre-college preparatory courses in the cities of Juazeiro do Norte (CE), Fortaleza (CE) and São Paulo (SP) on the use of drugs for cognitive enhancement, searching to identify predictive conditions to the use of such substances. For such, the procedure for data collection comprised two stages: the first was developed through a quali-quantitative study, searching to demonstrate a general panorama on the theme, with questionnaires applied to 534 individuals in the final year of high school in public, private and vocational schools and public and private pre-college preparatory courses in the cities of Juazeiro do Norte (CE), Fortaleza (CE) and São Paulo (SP). A second stage was held using the collected data for a qualitative approach and focus group with thirteen students from the vocational school in Juazeiro do Norte (CE), searching to deeply comprehend such issues. For data processing, non-parametric chi-square test was used in the first stage, and Content Analysis in the second one. Results indicated that the students wish to apply for university education, more than other options, consider this the main function of the school, and consider themselves prepared for this goal. Working is not their immediate wish and, for this reason, they do not deem important that the schools provide them with training for it. Comprehension of scientific-technological fundamentals and their enhancement as human beings were considered as important aspects. Enhancement drugs were deemed something positive that could be used on the eve of entrance examinations; to help in moments of pressure from parents and school when they feel overwhelmed by their duties; to be able to perform multiple activities; to ensure energy and focus. It was verified that they are predisposed to a possible use when provided with information and acquainted to other users. The possibility to consume such medicines is present in all analyzed cities and institutions. When faced with the opportunity to think more on the theme and talk about it in focus groups, students could perceive the factors involved in the adhesion to the use of substances and what drives them to its consumption. Collected data revealed that the participants were curious about a substance yet unknown to many of them, but imagined that it might be interesting to use it to reach their goals. It is concluded that the theme is relevant and worrisome; for this reason, the discussion about it in different backgrounds must be deepened

Silver containing chalcogenide glasses have been extensively studied during the last few decades; the main interest in these materials being their electrical conductivity which changes by several orders of magnitude upon silver doping. Glassy chalcogenides doped with silver have applications in optical elements, gratings, micro-lenses, waveguides, bio & chemical sensors, solid electrolytes, batteries, etc. Chalcohalide glasses have become important in the recent times, from both scientific & technological points of view, due to the interesting properties exhibited by these glasses such as the transparency in the infrared region, the stability against devitrification, solubility of rare earth elements, etc. In this thesis work, the thermal properties and electrical switching behavior of certain silver and iodine doped chalcogenide glasses have been investigated The thesis contains five chapters: Chapter 1: This chapter is an introduction to the fundamental aspects of amorphous semiconductors with a particular reference to chalcogenide glasses. The advantages and applications of chalcogenide glasses are also described. Chapter 2: The methods of preparation and characterization of the glasses investigated are described in this chapter. Also, the details of the experiments undertaken, namely temperature modulated Alternating Differential Scanning Calorimetry (ADSC), electrical switching analysis, Photo-thermal Deflection Spectroscopy (PDS), etc, are outlined. Chapter 3: In this chapter, the thermal behavior and electrical switching of silver doped Ge-Se and As-Se chalcogenide glasses are described. Bulk, melt-quenched Se-rich Ge0.15Se0.85-xAgx glasses have been found to be microscopically phase separated and composed of Ag2Se clusters and GeSe2-Se network. When the silver concentration exceeds 10 atom %, the Ag2Se clusters embedded in the GeSe2-Se network percolate. The signature of this percolation threshold is clearly observed as the sudden appearance of two exothermic crystallization peaks in ADSC runs. Density, molar volume and micro hardness studies also strongly support the view of a percolation transition. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be connected with the silver phase percolation. It has been found that Ge0.15Se0.85-xAgx glasses of lower silver concentration (x = 0.07 and 0.08) do not exhibit electrical switching at voltages up to 1100 V. A negative resistance behavior and threshold type electrical switching is seen in Ge0.15Se0.85-xAgx samples with x 0.09. Also, fluctuations are observed in the I-V characteristics of these samples, which have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the Ge-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 0.10, is related to silver phase percolation in these glasses. Bulk As20Se80-xAgx glasses (0 x 15) have been found to exhibit two endothermic glass transitions and two exothermic crystallization reactions on heating. Based on which it is suggested that As20Se80-xAgx glasses are also microscopically phase separated, containing Ag2Se phases embedded in an As-Se backbone. The occurrence of microscopic phase separation in As20Se80-xAgx glasses is also confirmed by SEM studies. With increasing silver concentration, the Ag2Se phase percolates in the As-Se matrix, with a well-defined percolation threshold at x = 8. This silver phase percolation is exemplified by sudden jumps in the composition dependence of the second crystallization peak and non-reversible heat-flow, Hnr obtained at the second glass transition reaction of As20Se80-xAgx glasses. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be associated with the observed silver phase percolation. Like Ge0.15Se0.85-xAgx glasses, As20Se80-xAgx glasses also exhibit threshold type electrical switching with fluctuations in the I-V characteristics; these fluctuations have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the As-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 8, is found to be related to silver phase percolation in these glasses, which has been proposed on the basis of ADSC experiments. Chapter 4: The chapter 4 deals with thermal studies, electrical switching investigations and Photo-thermal Deflection Spectroscopic (PDS) measurements on certain Ge-Te-I and As-Te-I chalcohalide glasses. It has been found that the compositional variation of the glass transition temperature of Ge22Te78-xIx glasses, obtained by Alternating Differential Scanning Calorimetry (ADSC), exhibits a broad hump around 5 atom % of iodine. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy (Hnr) of Ge22Te78-xIx glasses at x = 5, which is suggestive of a thermally reversing window at this composition. Electrical switching studies on Ge22Te78-xIx glasses indicate that these glasses exhibit memory type electrical switching. At lower iodine concentrations, a decrease is seen in switching voltages with an increase in iodine content (in comparison with the base Ge22Te78 glass), which is due to the decrease in network connectivity. The increase seen in switching voltages of Ge22Te78-xIx glasses at higher iodine contents, suggests that the influence of the metallicity is stronger at higher iodine proportions. It is also interesting to note that the composition dependence of the threshold voltages shows a slope change at x = 5, the inverse rigidity percolation threshold of the Ge22Te78-xIx system. . Further, it is found that the thermal diffusivities ( D) of Ge22Te78-xIx glasses decrease with the increase in iodine content, which has been understood on the basis of fragmentation of the Ge-Te network with the addition of iodine. Also, a cusp is seen in the composition dependence of thermal diffusivity at the composition x = 5 (average coordination number, r = 2.39), which has been identified to be the inverse rigidity percolation threshold of the system at which the network connectivity is lost. ADSC studies on As45Te55-xIx chalcohalide glasses (3 x 10) reveal that there is not much variation in the glass transition temperature of As45Te55-xIx glasses, even though there is a wide variation in r . Based on this observation we suggest that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than the average coordination number. Further, the non-reversing enthalpy Hnr of As45Te55-xIx glasses is found to exhibit a sharp minimum at the composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 x 7. These results indicate a narrow thermally reversing window in As45Te55-xIx glasses around the composition x = 6. As45Te55-xIx glasses have been found to exhibit a memory to threshold type change in switching behavior with iodine content (x 6), which has been understood on the basis of the sharp increase in thermal diffusivity above x = 6. It is also observed that the switching voltages do not change appreciably with composition/average coordination number. Though no pronounced signature of a stiffness transition is seen in the variation with composition of VT, fluctuations are seen in the switching voltages around x = 6, the composition corresponding to the sharp thermally revering window. PDS studies indicate that the thermal diffusivities () of As45Te55-xIx chalcohalide exhibit a sharp minimum at the composition x = 6. This result reasserts the presence of a sharp thermally reversing window in As45Te55-xIx glasses around the composition x = 6. Chapter 5: The significant results obtained in the present thesis work have been summarized in this chapter. Further, the scope for future work is also presented.

The history of silicon technology showed that controlled doping was a key step for the realization of e®ective, stable and reproducible devices. When the conduction type was no longer determined by impurities but could be controlled by doping, the breakthrough of classical microelectronics became possible. Unlike inorganic semiconductors, organic dyes are up to now usually prepared in a nominally undoped form. However, controlled and stable doping is desirable in many organic-based devices as well. If we succeed in shifting the Fermi level towards the transport states, this could reduce ohmic losses, ease carrier injection from contacts and increase the built-in potential of Schottky- or pn-junctions.