Le réchauffement climatique dû à l’augmentation des émissions de gaz à effet de serre constitue l’une des problématiques majeures actuelles. Dans ce contexte, le stockage du CO2 dans des réservoirs géologiques se présente comme un moyen susceptible de limiter les conséquences de ces émissions sur l’environnement. Pour des raisons sécuritaires, cette méthode de gestion nécessite une surveillance continue des réservoirs de stockage à l’aide de capteur IR pouvant descendre dans les puits. L’application de cette technologie nécessite également de connaître le comportement du CO2 lors des différentes étapes de stockage, notamment lorsqu’il est dans son état supercritique. C’est pourquoi la microfluidique est actuellement utilisée afin de simuler et comprendre les phénomènes liés à l’injection et au stockage du CO2 sous forme supercritique. La mise en œuvre d’une telle approche requiert : (i) le développement de nouvelles solutions compactes pour la surveillance in situ des réservoirs en continu pour sécuriser les sites de stockage et; (ii) la bonne compréhension du comportement du CO2 lors des différentes étapes de stockage.Le premier axe de recherche consiste à synthétiser des matériaux vitreux afin d’optimiser l’efficacité d’un capteur optique de CO2 pour la surveillance des sites de stockage en aquifère salin et susceptible de détecter d’autres gaz, tels le méthane ou le monoxyde de carbone. Le capteur doit pouvoir être déployé en profondeur et capable de détecter des concentrations inférieures à 1000 ppmv pour repérer rapidement d’éventuelles fuites. Les verres de chalcogénures dopés avec des ions de terres rares spécifiques, peuvent produire une luminescence qui peut ensuite être utilisée pour détecter les signatures infrarouges de toutes les molécules possédant des bandes d'absorption dans la région spectrale 3-5 µm. Les compositions vitreuses Ga5Ge20Sb10(Se,S)65 (%mol.) dopées Pr3+ et Dy3+ ont été développées en vue de réaliser un capteur environnemental de CO2. Le potentiel de ces matériaux pour la multidétection de gaz (CO2, CH4 et CO) a également été exploré.Les systèmes microfluidiques HP/HT actuels ne permettent pas de coupler simultanément la spectroscopie infrarouge et Raman à ces dispositifs. Ce problème est dû à l’utilisation du verre Pyrex associé au wafer de silicium pour la fabrication des microréacteurs. C’est pourquoi le deuxième axe de recherche développé au cours de cette thèse vise à explorer différents systèmes vitreux pour trouver une alternative au Pyrex. Le verre en question doit présenter le meilleur compromis entre les propriétés optiques, thermomécaniques et électriques visées. Ainsi, des verres à base de GeO2 ont été développés pour répondre aux spécifications attendues, telle que le procédé de collage anodique utilisé pour fixer le verre au wafer de silicium. La composition vitreuse retenue pour les tests est 70GeO2-15Al2O3-10La2O3-5Na2O (%mol.). / Global warming due to the increase of greenhouse gas emissions is one of the main current challenges. In this context, the CO2 storage in geological reservoirs appears as a likely way to limit the consequences of these emissions on the environment. For safety reasons, this management method requires continuous monitoring of the storage tanks by using IR sensors who can go down into the wells. The application of this technology also requires to know the CO2 behavior during various storage steps, in particular when it is in its supercritical state. This is why microfluidics is currently used to simulate and understand the phenomena related to the injection and storage of CO2 in supercritical form. The implementation of such approach requires: (i) the development of novel compact solutions for in situ continuous gas monitoring to secure the storage site and; (ii) a better understanding of the CO2 behavior during the different storage steps.The first research axis of this thesis has consisted in developing vitreous active materials to increase the efficiency of optical CO2 sensor (and eventually other gas like CH4 or CO) for their continuous monitoring in saline aquifer storage sites. This sensor must be able to be deployed in depth and be sensitive to CO2 concentrations below 1000 ppmv to quickly identify any leak. Chalcogenide glasses doped with specific rare earth ions may provide broadband luminescence that can be used to detect infrared signatures of all molecules whose absorption bands are located in the 3-5 µm spectral region. Glass compositions Ga5Ge20Sb10(Se,S)65 (mol.%) doped Pr3+ and Dy3+ have been developed in order to be integrated into a functional environmental CO2 sensor. The multi-sensing gas (CO2, CH4 and CO) potential of these materials has also been investigated.Current HP/HT microfluidic systems do not allow coupling FTIR and Raman spectroscopies. This problem is due to the using of Pyrex glass for the manufacture of these microreactors. That is why the second research axis developed during this thesis has consisted in exploring various vitreous systems to propose an alternative to the Pyrex glass. The target glass had to demonstrate the best compromise between the desired optical, thermomechanical and electrical properties. In this way, glasses based on GeO2 have been developed to meet these specifications, such as the anodic bonding process used to attach the glass on the silicon wafer. The glass composition selected after the completed studies is 70GeO2-15Al2O3-10La2O3-5Na2O (mol.%)

A new approach to the discovery of high absorbing semiconductors for solar cells was taken by working under a set of design principles and taking a systemic methodology. Three transition metal chalcogenides at varying states of development were evaluated within this framework. Iron pyrite (FeS���) is well known to demonstrate excellent absorption, but the coexistence with metallic iron sulfides was found to disrupt its semiconducting properties. Manganese diselenide (MnSe���), a material heavily researched for its magnetic properties, is proposed as a high absorbing alternative to iron pyrite that lacks destructive impurity phases. For the first time, a MnSe��� thin film was synthesized and the optical properties were characterized. Finally, CuTaS���, a known but never characterized material, is also proposed as a high absorbing semiconductor based on the design principles and experimental results. / Graduation date: 2013

The thesis consists of eight chapters of which the first chapter presents a brief overview of inorganic nanostructures. Synthesis and magnetic properties of MnO and NiO nanocrystals are described in Chapter 2, with emphasis on the low-temperature ferromagnetic interactions in these antiferromagnetic oxides. Chapter 3 deals with the synthesis and characterizations of nanocrystals of ReO3, RuO2 and IrO2 which are oxides with metallic properties. Pressure-induced phase transitions of ReO3 nanocrystals and the use of the nanocrystals for carrying out surface-enhanced Raman spectroscopy of the molecules form Chapter 4. Use of ionic liquids to synthesize different nanostructures of semiconducting metal sulfides and selenides is described in Chapter 5. Synthesis of Mn-doped GaN nanocrystals and their magnetic properties are described in Chapter 6. A detailed investigation has been carried out on the growth kinetics of nanostructures of a few inorganic materials by using small-angle X-ray scattering and other techniques (Chapter 7). The study includes the growth kinetics of nanocrystals of Au, CdS and CdSe as well as of nanorods of ZnO. Results of a synchrotron X-ray study of the formation of nanocrystalline gold films at the organic-aqueous interface are also included in this chapter. Chapter 8 discuses the use of the organic-aqueous interface to generate Janus nanocrystalline films of inorganic materials where one side of the film is hydrophobic and other side is hydrophilic. This chapter also includes the formation of nanostructured peptide fibrils at the organic-aqueous interface and their use as templates to prepare inorganic nanotubes.

Ce travail est dédié à la compréhension de phénomènes photoinduits dansles verres de chalcogénure. Ces phénomènes, bien que connus depuis des années,ne sont pas encore bien compris. Travailler sur des couches minces, fabriquées icipar co-pulvérisation cathodique, ajoute une diffculté supplémentaire : il y a peude matière qui interagit avec la lumière et il faut composer avec la présence dusubstrat. Afin d'étudier les phénomènes photoinduits, il a été nécessaire d'adapterdes techniques expérimentales déjà existantes telles que la spectroscopie pompe-sonde, qui permet d'étudier la dynamique électronique ultra-rapide (inférieure à lananoseconde) et les capteurs au quartz piezoélectrique qui permettent de mesurerla masse volumique et les modules mécaniques du matériau déposé à leurs surface.Des essais préliminaires de résonance en transmission ont été également réalisés etsont prometteurs. Une machine de DMA (Dynamical Mechanical Analysis) a étéspécialement conçue au laboratoire afin de réaliser une étude dynamique des verres de chalcogénures sous formes de fibres et de films minces. Toutes ces techniquesexpérimentales permettent d'étudier les effets photoinduits à différentes échelles detemps et de mieux les expliquer. / This work aims to understand photoinduced phenomena in chalcogenide glasses. These phenomena are known for years but yet not fully understood. Studying thin films, deposited by co-sputtering here, adds an other difficulty : the light-matter interaction takes place in a small amount of matter and it is inevitable to deal with the substrate. To study these photoinduced effects, it was necessary to adapt some already existing methods such as pump-probe spectroscopy which measures ultrafast electronic dynamics (less than a nanosecond), piezoelectric quartz sensors which gives density and mechanical modulus of the materials deposited on. Preliminary tests were run to investigate optical transmission resonance and are promising. A DMA machine (Dynamical Mechanical Analysis) was especially designed in the laboratory to study the behaviour of fibers and films. All these experimental setups allow to study photoinduced phenomena at various timescale and to better understand them.

Technology scaling beyond Moore’s law demands cutting-edge solutions of the gate length scaling in sub-10 nm regime for low power high speed operations. Recently SOI technology has received considerable attention, however manufacturable solutions in sub-10 nm technologies are not yet known for future nanoelectronics. Therefore, to continue scalinginsub-10 nm region, new one(1D) and two dimensional(2D) “nano-materials” and engineering are expected to keep its pace. However, significant challenges must be overcome for nano-material properties in carrier transport to be useful in future silicon nanotechnology. Thus, it is very important to understand and modulate their electronic band structure and transport properties for low power nanoelectronics applications. This thesis tries to provide solutions for some problems in this area. In recent times, one dimensional Silicon nanowire has emerged as a building block for the next generation nano-electronic devices as it can accommodate multiple gate transistor architecture with excellent electrostatic integrity. However as the experimental study of various energy band parameters at the nanoscale regime is extremely challenging, usually one relies on the atomic level simulations, the results of which are at par with the experimental observations. Two such parameters are the band gap and effective mass, which are of pioneer importance for the understanding of the current transport mechanism. Although there exists a large number of empirical relations of the band gap in relaxed Silicon nanowire, however there is a growing demand for the development of a physics based analytical model to standardize different energy band parameters which particularly demands its application in TCAD software for predicting different electrical characteristics of novel devices and its strained counterpart to increase the device characteristics significantly without changing the device architecture. In the first part of this work reports the analytical modeling of energy band gap and electron transport effective mass of relaxed and strained Silicon nanowires in various crystallographic directions for future nanoelectronics. The technology scaling of gate length in beyond Moore’s law devices also demands the SOI body thickness, TSi0 which is essentially very challenging task in nano-device engineering. To overcome this circumstance, two dimensional crystals in atomically thin layered materials have found great attention for future nanolectronics device applications. Graphene, one layer of Graphite, is such 2D materials which have found potentiality in high speed nanoelectronics applications due to its several unique electronic properties. However, the zero band gap in pure Graphene makes it limited in switching device or transistor applications. Thus, opening and tailoring a band gap has become a highly pursued topic in recent graphene research. The second part of this work reports atomistic simulation based real and complex band structure properties Graphene-Boron nitride heterobilayer and Boron Nitride embedded Graphene nanoribbons which can improve the grapheme and its nanoribbon band structure properties without changing their originality. This part also reports the direct band-to-band tunneling phenomena through the complex band structures and their applications in tunnel field effect transistors(TFETs) which has emerged as a strong candidate for next generation low-stand by power(LSTP) applications due to its sub-60mV/dec Sub threshold slope(SS). As the direct band-to-band tunneling(BTBT) is improbable in Silicon(either its bulk or nanowire form), it is difficult to achieve superior TFET characteristics(i.e., very low SS and high ON cur-rent) from the Silicon TFETs. Whereas, it is explored that much high ON current and very low subthreshold slope in hybrid Graphene based TFET characteristics open a new prospect in future TFETs. The investigations on ultrathin body materials also call for a need to explore new 2D materials with finite band gap and their various nanostructures for future nanoelectronic applications in order to replace conventional Silicon. In the third part of this report, we have investigated the electronic and dielectric properties of semiconducting layered Transition metal dichalcogenide materials (MX2)(M=Mo, W;X =S, Se, Te) which has recently emerged as a promising alternative to Si as channel materials for CMOS devices. Five layered MX2 materials(exceptWTe2)in their 2D sheet and 1D nanoribbon forms are considered to study the real and imaginary band structure of thoseMX2 materials by atomistic simulations. Studying the complex dispersion properties, it is shown that all the five MX2 support direct BTBT in their monolayer sheet forms and offer an average ON current and subthresholdslopeof150 A/mand4 mV/dec, respectively. However, onlytheMoTe2 support direct BTBT in its nanoribbon form, whereas the direct BTBT possibility in MoS2 and MoSe2 depends on the number of layers or applied uniaxial strain. WX2 nanoribbons are shown to be non-suitable for efficient TFET operation. Reasonably high tunneling current in these MX2 shows that these can take advantage over conventional Silicon in future tunnel field effect transistor applications.

Technology scaling beyond Moore’s law demands cutting-edge solutions of the gate length scaling in sub-10 nm regime for low power high speed operations. Recently SOI technology has received considerable attention, however manufacturable solutions in sub-10 nm technologies are not yet known for future nanoelectronics. Therefore, to continue scalinginsub-10 nm region, new one(1D) and two dimensional(2D) “nano-materials” and engineering are expected to keep its pace. However, significant challenges must be overcome for nano-material properties in carrier transport to be useful in future silicon nanotechnology. Thus, it is very important to understand and modulate their electronic band structure and transport properties for low power nanoelectronics applications. This thesis tries to provide solutions for some problems in this area. In recent times, one dimensional Silicon nanowire has emerged as a building block for the next generation nano-electronic devices as it can accommodate multiple gate transistor architecture with excellent electrostatic integrity. However as the experimental study of various energy band parameters at the nanoscale regime is extremely challenging, usually one relies on the atomic level simulations, the results of which are at par with the experimental observations. Two such parameters are the band gap and effective mass, which are of pioneer importance for the understanding of the current transport mechanism. Although there exists a large number of empirical relations of the band gap in relaxed Silicon nanowire, however there is a growing demand for the development of a physics based analytical model to standardize different energy band parameters which particularly demands its application in TCAD software for predicting different electrical characteristics of novel devices and its strained counterpart to increase the device characteristics significantly without changing the device architecture. In the first part of this work reports the analytical modeling of energy band gap and electron transport effective mass of relaxed and strained Silicon nanowires in various crystallographic directions for future nanoelectronics. The technology scaling of gate length in beyond Moore’s law devices also demands the SOI body thickness, TSi0 which is essentially very challenging task in nano-device engineering. To overcome this circumstance, two dimensional crystals in atomically thin layered materials have found great attention for future nanolectronics device applications. Graphene, one layer of Graphite, is such 2D materials which have found potentiality in high speed nanoelectronics applications due to its several unique electronic properties. However, the zero band gap in pure Graphene makes it limited in switching device or transistor applications. Thus, opening and tailoring a band gap has become a highly pursued topic in recent graphene research. The second part of this work reports atomistic simulation based real and complex band structure properties Graphene-Boron nitride heterobilayer and Boron Nitride embedded Graphene nanoribbons which can improve the grapheme and its nanoribbon band structure properties without changing their originality. This part also reports the direct band-to-band tunneling phenomena through the complex band structures and their applications in tunnel field effect transistors(TFETs) which has emerged as a strong candidate for next generation low-stand by power(LSTP) applications due to its sub-60mV/dec Sub threshold slope(SS). As the direct band-to-band tunneling(BTBT) is improbable in Silicon(either its bulk or nanowire form), it is difficult to achieve superior TFET characteristics(i.e., very low SS and high ON cur-rent) from the Silicon TFETs. Whereas, it is explored that much high ON current and very low subthreshold slope in hybrid Graphene based TFET characteristics open a new prospect in future TFETs. The investigations on ultrathin body materials also call for a need to explore new 2D materials with finite band gap and their various nanostructures for future nanoelectronic applications in order to replace conventional Silicon. In the third part of this report, we have investigated the electronic and dielectric properties of semiconducting layered Transition metal dichalcogenide materials (MX2)(M=Mo, W;X =S, Se, Te) which has recently emerged as a promising alternative to Si as channel materials for CMOS devices. Five layered MX2 materials(exceptWTe2)in their 2D sheet and 1D nanoribbon forms are considered to study the real and imaginary band structure of thoseMX2 materials by atomistic simulations. Studying the complex dispersion properties, it is shown that all the five MX2 support direct BTBT in their monolayer sheet forms and offer an average ON current and subthresholdslopeof150 A/mand4 mV/dec, respectively. However, onlytheMoTe2 support direct BTBT in its nanoribbon form, whereas the direct BTBT possibility in MoS2 and MoSe2 depends on the number of layers or applied uniaxial strain. WX2 nanoribbons are shown to be non-suitable for efficient TFET operation. Reasonably high tunneling current in these MX2 shows that these can take advantage over conventional Silicon in future tunnel field effect transistor applications.

Ce mémoire de thèse s'inscrit dans le contexte du projet FUTUR financé par l'ANR et concernant le développement de Fonctions optiques pour les Transmissions à très haut débit dans le Réseau coeur et porte sur la génération de sources optiques fibrées très hautes cadences et la caractérisation de fibres optiques microstructurées en verre de Chalcogénure. A cet effet, nous étudions les caractéristiques linéaires et non-linéaires au sein de fibres microstructurées en verre de chalcogénures conçue et réaliser via différentes collaborations dans le cadre du projet de l'ANR FUTUR. Pour cela un grand nombre de méthodes de caractérisations ont été mises au point donnant une comparaison entre une fibre SMF standard et ces fibres microstructurées chalcogénures. Par exemple, un montage interférométrique pour la mesure de la dispersion chromatique pour échantillon court, ou encore de nombreux banc expérimentaux permettant la caractérisation des propriétés non-linéaires de ces fibres (diffusion Raman, diffusion Brillouin, Coefficient non linéaire Kerr...). La seconde partie de ce mémoire présente la mise au point de méthode de conversion d'un battement sinusoïdal en un train d'impulsions hautement cadencé. Il est montré dans ce manuscrit que cette technique a été exploitée au plus prêt de ses limites, par l'obtention d'impulsions extrêmement courtes et par des débits très élevés. Les trains d'impulsions à très hautes cadences ont été caractérisés par un dispositif expérimental SHG-FROG. Une démonstration de la multiplication du débit par deux a été démontrée par l'effet Talbot. / This memory of thesis s' registered voter in the context of the FUTUR project financed by l'ANR and concerning the development of optical finctions fot the high bit-rate transmissions in the Network heart and carries on very high rates optical fibers sources generation and the optical chalcogenide microstructured fiber charaterization. For this purpose, we study the linear and non-linear characteristics of microstructured chalcogenide fibers conceived and realized in various collaborations within the framework of the ANR FUTUR project. For that a great number of characterizations methods were developed giving a comparison between a standard single mode fiber and there microstructured chalcogenide fibers. For exemple, an interferometric setup for the chromatic dispersion measurement for short sample, or many experimental setup allowing the nonlinear properties characterizations as of these fibers (Raman scattering, nonlinear Kerr Coefficient). The second part of this memory presents the settling of sinusoidal beat conversion into a high bit rate generation method. It is shown in this manuscript that this technique was exploited with readiest of its limits, by obtaining extremely short pulses and by very high bit-rate. The pulses train at very high rates were characterized by an experimental device SHG-FROG. A demonstration of the multiplication of the bit-rate by two at summer shown by Talbot effect.

Les verres de chalcogénures sont utilisés en tant qu'optiques pour les caméras IR grâce à leur transparence dans les deux fenêtres atmosphériques [3 – 5 µm] et [8 – 12 µm]. Afin de diminuer leur prix et d'augmenter la gamme des compositions qui pourraient être produites, une nouvelle méthode de synthèse a été élaborée au laboratoire Verres et Céramiques. Les travaux présentés dans ce manuscrit ont ainsi porté sur le développement de la technique de synthèse des verres et vitrocéramiques de chalcogénures par mécanosynthèse et frittage flash, ainsi que sur l'étude de la structure et des propriétés mécaniques des vitrocéramiques. Les différents paramètres de broyage et frittage ont été étudiés et la possibilité de produire des matériaux massifs, avec une structure et des propriétés similaires à celles des verres obtenus par voie classique de fusion-trempe, a été démontrée. Egalement, il a été constaté que la génération des particules cristallines dans la matrice vitreuse permet d'améliorer les propriétés mécaniques sans altérer la transmission optique des échantillons. Finalement, une étude théorique, basée sur la méthode DFT, a été initié pour accéder à des informations plus précises concernant la structure et les propriétés mécaniques des verres et vitrocéramiques de chalcogénures. / Chalcogenide glasses are used as optics for the IR cameras thanks to their transparence in the two atmospheric windows [3 – 5 µm] and [8 – 12 µm]. In order to reduce their price and to increase the panel of compositions which may be produced, a new method of synthesis has been elaborated in the Glass and Ceramics group. Thus, this manuscript presents the development of the new way of synthesis of chalcogenide glasses and glass-ceramics by mechanical milling and SPS sintering, and the study of the structure and mechanical properties of glass-ceramics. The different milling and sintering parameters have been studied and the possibility to produce bulk samples with a structure and properties similar to those of glasses synthesized by melt-quenching method has been demonstrated. Also, it has been shown that the generation of crystalline particles in the glassy matrix increases mechanical properties of the samples without spoiling their optical transmission. Finally, a theoretical study, based on the DFT method, has been initiated in order to access more precise information concerning glass and glass-ceramic structure and mechanical properties.

<p>Predmet istraživanja ove doktorske disertacije su bila halkogenidna stakla iz sistema Ag_x(As₄₀S₃₀Se₃₀)_100&ndash;x (x = 0, 0.5, 1, 2, 3, 4, 5, 10, 12, 13, 15 at. % Ag) &ndash; 3D forma i tanki filmovi preparirani iz prethodno sintetisanih stakala (x &le; 5 at. % Ag) &ndash; 2D forma.<br />Utvrđena je oblasti amorfnosti u faznom dijagramu po odabranom preseku.&nbsp; Ispitivan je uticaj procentualnog udela srebra&nbsp; na&nbsp; fizičke&nbsp; karakteristike sintetisanih stakala i prepariranih tankih filmova koje su&nbsp; od&nbsp; značaja&nbsp; za&nbsp; primenu&nbsp; ovakvih&nbsp; materijala.<br />Izvr&scaron;ena je karakterizacija električnih,&nbsp; optičkih, strukturnih&nbsp; i&nbsp; termičkih&nbsp; osobina&nbsp; na&nbsp; osnovu&nbsp; kojih&nbsp; su izvedeni&nbsp; zaključci&nbsp; o&nbsp; uticaju&nbsp; i&nbsp; modifikaciji&nbsp; strukture As₄₀S₃₀Se₃₀halkogenidne matrice usled inkorporacije atoma srebra. Strukturna analiza ispitivanih sastava je potvrdila homogenost uzoraka sa manjom koncentracijom srebra (x &le; 5 at. %&nbsp; Ag), dok je&nbsp; kod uzoraka sa većim procentualnim udelom ovog metala (x = 10, 13, 15 at. % Ag) pokazano da postoji fazna separacija. Kod sastava sa x = 13 i 15 at. % Ag potvrđena&nbsp; je&nbsp; prisutnost kristalnih centara AgAsSe_2. Na osnovu rezultata dobijenih DSC tehnikom, pokazano je da pri zagrevanju balk uzoraka dolazi do delimične kristalizacije koja se odvija zapreminski sa dvodimenzionalnim&nbsp; i&nbsp; trodimenzionalnim rastomkristalnih centara. Optička i spektralna ispitivanja su pokazala&nbsp; da uvođenje&nbsp; Ag&nbsp; u&nbsp; matricu&nbsp; stakla As₄₀S₃₀Se₃₀&nbsp; dovodi&nbsp; do&nbsp; smanjenja&nbsp; &scaron;irine&nbsp; optički zabranjene zone i kod 3D i 2D uzoraka, kao i da svi sastavi ispoljavaju normalan oblik disperzije indeksa prelamanja. Takođe, rezultati Raman&nbsp; spektroskopije su ukazali&nbsp; na&nbsp; činjenicu&nbsp; da&nbsp; inkorporacija&nbsp; srebra&nbsp; u strukturnu&nbsp; mrežu&nbsp; ispitivanih&nbsp; stakala&nbsp; utiče&nbsp; na formiranje Ag&ndash;(S,Se)&ndash;As veza, odnosno uzrokuje formiranje novih strukturnih jedinica koje bi mogle uticati na provodljivost ovih sastava.&nbsp; Merenja električnih karakteristika 3D uzoraka izvr&scaron;ena su u jednosmernom i naizmeničnom režimu i pokazano je da&nbsp; koncentracija&nbsp; srebra&nbsp; ima&nbsp; značajan&nbsp; uticaj&nbsp; na električne&nbsp; osobine.&nbsp; Utvrđeni&nbsp; su&nbsp; različiti&nbsp; mehanizmi odgovorni za transport&nbsp; nosilaca naelektrisanja zavisno od&nbsp; koncentracije dopanta.&nbsp; Kompleksni impedansni spektri svih sastava&nbsp; su&nbsp; ukazali&nbsp; na prisustvo temperaturske zavisnosti procesa relaksacije, na ne idealan Debye&ndash;vski tip relaksacije, kao i negativni temperaturski koeficijent otpornosti koji je karakterističan za poluprovodnike.</p> / <p>The subject of this dissertation are chalcogenide&nbsp; glasses from the system Agx(As₄₀S₃₀Se₃₀)_100&ndash;x (x = 0, 0.5, 1, 2, 3, 4, 5, 10, 12, 13, 15 at. % Ag) &ndash; 3D form and thin films prepared from previously synthesised&nbsp; glasses (x &le; 5 at. % Ag) &ndash; 2D form. The amorphous&nbsp; area in the phase diagram was determined by the&nbsp; selected&nbsp;&nbsp;&nbsp; tie&ndash; line. The influence of the silver&nbsp; percentage on the physical characteristics of the&nbsp; synthesized glasses and prepared thin films was&nbsp; investigated due to the importance of such materials&nbsp; for the application. Characterization of electrical, optical, structural and thermal properties has been performed, based on which conclusions on theinfluence and structure modification of the As₄₀S₃₀Se₃₀&nbsp; chalcogenide&nbsp; matrix due to the&nbsp; incorporation of silver atoms have been derived. Structural analysis of the investigated samples confirmed the homogeneity of samples with a lower silver concentration (x&nbsp; &le;&nbsp; 5&nbsp; at.%&nbsp; Ag),&nbsp; while&nbsp; in samples with a higher percentage content of&nbsp; this metal (x = 10, 13, 15 at.% Ag) it was shown that&nbsp; there was a phase separation. The presence of crystal&nbsp; centers AgAsSe₂ was confirmed in the samples with x = 13 and 15 at. % Ag. Based on the results obtained with the DSC technique, it has been shown that by heating the samples, partial crystallization takes place voluminously, with two&ndash;dimensional and three&ndash;dimensional growth of crystalline centers.&nbsp; Opticaland spectral investigations have shown that the introduction of Ag into the glass matrix As₄₀S₃₀Se₃₀ leads to a reduction in the optical band gap in both 3D and 2D samples, and that all compositions exhibit a normal dispersion of index of&nbsp; refraction. Also, the Raman spectroscopy results pointed to the fact that the incorporation of silver into the structural network of the investigated samples influences the formation of&nbsp; Ag&ndash;(S,Se)&ndash;As structures that is, causes the formation of new structural units that could affect the conductivity of these compositions. Measurements of the electrical characteristics of the 3D samples were performed in&nbsp; DC and AC regime and it was shown that silver concentration has a significant effect on electrical properties. Different mechanisms that are responsible for the transport of charge carriers depending on dopant concentration were determined. The complex&nbsp; impedance spectra of all compositions indicated the presence of the temperature dependence of the relaxation process, the non&ndash;Debye relaxation and the negative temperature coefficient of resistance which is characteristic of the semiconductors.</p>

In the last few years a renewed interest has reappeared in materials that were highly investigated in the 50s-70s, like manganese perovskites, spinel chalcogenides and vanadium oxides. The first two classes of materials are nowadays intensively studied due to the colossal magnetoresistance effect, which is the magnetoresistance associated with a ferromagnetic-paramagnetic transition. Vanadium oxides are known to form many compounds and most of them undergo metal-to-insulator phase transitions, with a high increase in the electrical conductivity (MIT). Many technological applications derive from the variation of the physical properties around the phase transition temperature. Although many efforts have been done in order to understand their electronic structures and to elucidate the MIT mechanisms, the vanadium oxides are still matter of debate in science.The present study has been performed in order to understand the electronic structure of these very intriguing materials. The role of different dopants that induce strong changes in the electronic and magnetic properties has been investigated making use of two spectroscopic techniques, namely X-ray photoelectron and X-ray emission spectroscopy.