Teses / dissertações sobre o tema "Oxydes 2D"
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Odziomek, Mateusz Janusz. "Colloidal Synthesis and Controlled 2D/3D Assemblies of Oxide Nanoparticles". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN092/document.
Texto completo da fonteNanotechnology has become a key domain of technology in XXI century. The great development of the synthetic approaches toward nanoparticles (NPs) with desired composition, size and shape expose the potential of their use as building blocks for larger scale structures. It allows fabrication of functional materials and devices directly from colloids by bottom-up approach, thus involving possibility of material design over several length scales. The process is referred to NPs assembly or self-assembly and leads to materials with varying architectures as for instance 1D (rods), 2D (films) or 3D (superlattices or gels). However most of 3D assemblies are limited to the micrometric scale and are difficult to control. Practically the only route allowing preparation of macroscopic 3D structures from NPs is their gelation and preparation of aerogels. As an alternative, NPs can be embedded in some matrix creating bulk composite material, with homogenously distributed non-aggregated NPs.Therefore, this work is devoted to development of materials with different dimensionalities for various applications from metal oxides NPs (mainly Y3Al5O12:Ce and Li4Ti5O12). The first part describes the syntheses of YAG:Ce and LTO NPs by glycothermal approach. In the case of YAG:Ce, the reactions conditions were appropriately adjusted in order to obtain non-aggregated nanocrystals (NCs) of few nanometers. The colloidal solution containing such NCs with different concentration was used for fabrication of thin films with controllable thickness by spin-coating method. Contrary, the synthesis of LTO led to aggregated NPs with hierarchical structuration which was highly beneficial for Li-ion batteries. The large surface area and porosity ensured efficient exchange of Li ions between electrolyte and anode material. Furthermore, the YAG:Ce NCs were used for preparation of macroscopic monoliths with high porosity and transparency. For that reason, colloidal solution of NCs was gelled by the abrupt change of solvent dielectric constant. The gels were further supercritically dried yielding YAG:Ce NPs-based aerogels with high porosity and transparency. The same approach turned o be appropriate for other systems like GdF3 or hybrid aerogels of YAG:Ce and GdF3.Alternatively, YAG:Ce NPs were incorporated into silica aerogels forming robust macroscopic and highly transparent aerogels exhibiting properties of incorporated NPs. They served for novel type of sensors for low-energy ionizing radiation in liquids and gases. Their high porosity assured well-developed contact between radioactive emitter and the scintillator ensuring good harvesting of radioactive energy
Souza, dos Santos Edgar Gonzaga. "Etude théorique et expérimentale des propriétés magnétiques des oxydes de métaux de transition quasi-bidimensionnels du type AB2O6". Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY047/document.
Texto completo da fonteThis work aims to contribute to the study of magnetism in insulating oxides of the type AB_2O _6 (A = Fe, Co, Ni, Ta = B, Sb). These compounds crystallize in a trirutile structure and present a rich variety of magnetic phases. All the observed orderings can be classified as antiferromagnetic, but they differ from a simple Néel type order. Moreover, substitutions such as Fe_xCo_{1-x}Ta_2O_6, Fe_xNi_{1-x}Ta_2O_6 and Co_xNi_{1-x}Ta_2O_6 produce several regions of phase coexistence and bicritical points in the phase diagram T vs. x. A particularly interesting characteristic of these compounds is the quasi-two-dimensional nature of their magnetism, since the transition-metal ions A appear in layers separated by two planes of the non-magnetic ions B. They also show strong crystal-field anisotropy on the magnetic sites due to axial distortion of the oxygen octahedra surrounding the A ions. Our approach involves two complementary aspects: theoretical and experimental. From the theoretical point of view, a reformulation of the two-dimensional model used until now to describe the paramagnetic susceptibility allows us to obtain exchange parameters compatible with the observed planar magnetic orderings. Considering that the three-dimensional character the magnetic structures revealed by neutron diffraction indicates that the coupling between planes, although weak, plays an important role to low temperatures, we propose a three-dimensional model consistent with the observed orderings both in the ab plane and along the c axis. From the experimental point of view, we make substitutions on the non-magnetic sites, in order to systematically modify the spacing between planes and, consequently, the coupling between them. In particular, we have synthesized compounds of type ANb_xTa_{2-x}O_6 with A = Fe, Ni and Co, remaining in the stability region of tetragonal phase, since the presence of Nb favors an orthorhombic phase. The structural and magnetic characterization of the systems is done via the X-ray and neutron diffraction as well as measurements of magnetic susceptibility, specific heat, and magnetization as a function of the applied field. We also study series with Sb in place of Nb where we additionally include substitutions in the magnetic site
Ruano, Merchán Catalina. "Synthesis and characterization of 2D complex oxide films in the SrTiO₃/Pt(111)/Al₂O₃(0001) system". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0039.
Texto completo da fonteThe formation of 2D dodecagonal quasicrystalline oxides (OQC), as related approximant phases were recently reported in thin films derived from BaTiO₃ or SrTiO₃ perovskites deposited on (111)-oriented Pt single crystal. These 2D structures add novel functionalities to the ultra-thin films of ternary oxides supported on metals when approaching the 2D limit. Here, we use a thin film stacking approach in which the single crystal is replaced by a Pt (111) buffer layer, deposited by MBE on an Al₂O₃(0001) substrate. An ultra-thin film of SrTiO₃ was subsequently deposited by PLD. The film stacking is fully characterized by diffraction (LEED, RHEED, XRD),microscopy (STM, TEM, Nano-SAM) and spectroscopy (XPS, AES) techniques. We report the discovery of three OQC approximants obtained by reducing this system by annealing at high temperature under vacuum conditions. These phases can be described by three different tilings constructed with NGT elements. An atomic model determined by DFT, in agreement with the experimental observations, is proposed for each approximant. This thin-film approach can be useful for exploring the formation of complex 2D oxide phases in other metal-oxide combinations
Souza, dos Santos Edgar Gonzaga. "Etude théorique et expérimentale des propriétés magnétiques des oxydes de métaux de transition quasi-bidimensionnels du type ABúO¦". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00771466.
Texto completo da fonteSantos, Edg. "Étude théorique et expérimentale des propriétés magnétiques des oxydes de métaux de transition quasi-bidimensionnels du type $\bm{AB_2}{\bf O}_{\bm 6}$". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00764155.
Texto completo da fonteMeziane, Mohamed. "Modélisation 2D et 3D d'un écoulement gazeux instationnaire activé par décharges couronne dans un réacteur multi-pointes plan dédié à la décontamination des gaz". Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00652493.
Texto completo da fonteThébaud, Simon. "Electron and phonon transport in disordered thermoelectric materials : dimensional confinement, resonant scattering and localization". Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1168/document.
Texto completo da fonteOver the past decades, the increasingly pressing need for clean energy sources and the realization that a huge proportion of the world energy consumption is wasted in heat have prompted great interest in developing efficient thermoelectric generation modules. These devices could harvest waste heat from industrial processes or other sources, turning a temperature gradient into a voltage through the Seebeck effect. Efficient thermoelectric materials should exhibit a low thermal conductivity, a high electrical conductivity and a high Seebeck coefficient. Simultaneously optimizing these parameters is a great challenge of condensed matter physics and materials science. With a view to enhance the thermoelectric properties of several promising materials, we explore several strategies in which defects (atomic substitutions, vacancies…), disorder and dimensional confinement play a crucial role. We perform density functional theory calculations and projections on Wannier orbitals to construct realistic Hamiltonians and dynamical matrices describing their electronic and vibrational structure in real space. These parameters are then used to compute the thermoelectric transport properties using the Kubo formalism, the Boltzmann transport equation, the Landauer formalism, and the Chebyshev polynomial Green's function method that allows for an exact treatment of disorder. We investigate the electronic transport properties and thermoelectric performances of two promising materials for high-temperature power generation, strontium titanate and rutile titanium dioxide. Comparison of our predictions with a wealth of experimental data yields a very good agreement. We show that the increase of the Seebeck coefficient observed in strontium titanate superlayers, until now attributed to quantum confinement effects, is in fact well explained assuming delocalized electrons. The general effects of resonant states on electronic transport are explored in a model study, showing a sixfold increase of the thermoelectric performances. The particular case of strontium titanate is then examined, and localization effects are shown to destroy the performances if Vanadium atoms are introduced as resonant impurities. The influence of defects in two-dimensional materials is investigated. Contrary to adatoms, substitutions in transition metal dichalcogenides are shown to localize the charge carriers. We study the effect of vacancies on phonon transport in graphene, and determine the phonon-vacancy scattering rate. Comparison with thermal conductivity data for irradiated and finite-size graphene samples yields a very good agreement between theory and experiments
Lhuillier, Jérémy. "Accordabilité des composants photoniques à base de structures hybrides graphène/diélectrique adressables par la surface". Electronic Thesis or Diss., Lyon, 2022. https://bibli.ec-lyon.fr/exl-doc/TH_2022LYSEC008.pdf.
Texto completo da fonteThe emergence of a wide variety of photonic structures over the past decades has enabled the realization of on-chip devices performing increasingly complex free-space optical functions. Among them, dielectric membrane structures have made it possible to implement a wide range of planar optical devices, ranging from resonant spectral filtering to beam shaping, with negligible losses. While these structures provide almost a full control of the radiated electromagnetic field, this control is usually static and determined by manufacturing. An increasing number of applications - such as free-space telecommunications, sensors for autonomous systems or imaging - require agile photonic devices, thus motivating the search for means of active control of the optical response to be implemented within the dielectric structures. To this purpose, various properties of graphene are proving promising. In particular, the capability to modulate its absorption opens up numerous prospects for the electrical and optical control of photonic structures that integrate graphene. This has led to the demonstration of various electro-optic and all-optical modulators, by leveraging the recently developed 2D material transfer processes, which have made it possible to obtain high-quality hybrid graphene/dielectric structures. In this context, the work presented in this thesis seeks to exploit graphene’s tunable absorption to achieve dynamic control of surface-addressable device’s optical response, in the special case of dielectric photonic structures operating in the near infrared. A generic coupled mode theory model is first developed and adapted to hybrid dielectric/ graphene structures in order to identify the key parameters for maximising the control allowed by graphene absorption. In the single resonance case, the system’s response is mainly determined by the critical coupling condition classically defined for the study of graphene’s absorption. In the two-resonance case however, a new control parameter – associated with the absorption difference between the resonances – provides an additional tunability factor. Different strategies for maximising this parameter are therefore proposed and the technological processes underlying their implementation are studied experimentally in order to assess - by means of Raman spectroscopy and photoelectron spectroscopy - their effect on the structural and chemical quality of graphene. The spatial modulation of graphene’s absorption – here proposed to differentiate the absorption induced on different optical modes – is then studied experimentally using structures exploiting the charge transfer effect at the interface between graphene and an oxide with high workfunction, namely tungsten oxide. The devices developed here allow to obtain a graphene’s chemical potential modulation of 0.1eV - characterized by nano-XPS (ANTARES beamline of the SOLEIL synchrotron) and Raman spectroscopy - which can lead to an absorption modulation higher than 70% for certain wavelengths. Ultimately, an active hybrid device architecture enabling dynamic control of the laser emission is proposed. This architecture is based on a vertical symmetry breaking membrane and allows us, in principle, to switch between two emission angles by modulating graphene’s absorption. The interest of these structures in achieving continuous tunability of the emission angle is also presented
Gonzalez, Ortiz Dánae. "DEVELOPMENT OF POROUS MEMBRANES FROM EMULSIONS STABILIZED BY 2D NANOPARTICLES (h-BNNS)". Thesis, Montpellier, Ecole nationale supérieure de chimie, 2018. http://www.theses.fr/2018ENCM0006/document.
Texto completo da fonteEmulsions stabilized through the adsorption of colloidal particles at the liquid-liquid interface have been of interest in a wide variety of applications, ranging from pharmaceutical or food products to templates for the preparation of new materials. In this thesis, oil-in-water (O/W) and water-in-oil (W/O) emulsions are efficiently stabilized using colloidal inorganic particles (graphene oxide (GO) and hexagonal boron nitride nanosheets (h-BNNS)). The adsorption of particles to the oil-water interface is induced by adjusting the particle wetting behavior in the liquid media. Two types of emulsions, O/W and W/O are formed by using two-dimensional materials possessing different hydrophilic behaviors. The conditions required to reach the most stable emulsion using two different types of particles at different formulations are investigated. The final microstructures of the mixtures are tailored by adjusting the initial composition of emulsion. The use of high concentration of particles leads to enhanced stability of particles-stabilized emulsions. h-BNNS based emulsions were reported in this work for the first time and their behavior was deeply investigated. Furthermore, a novel green approach to obtain polyvinyl alcohol (PVA)-based porous membranes was reported. In this case, the addition of PVA to the emulsion increases its long term stability and allows its shaping using conventional technologies such as casting. The polymer composites obtained from emulsions stabilized with inorganic particles exhibit microporosity, showing typical pore dimensions of 0.19 ± 0.03 µm or 1.1 ± 0.3 µm depending on the curing time. These obtained porous membranes display good performance in water permeability and particle rejection. Membranes displaying a pore size about 1.1 µm showed water permeability about 2000 L/h m2 bar, and a rejection rate of 86 % with particles of the same size than the pores
Sutrisno, Hari. "Synthèse et caractérisation d'oxyde de titane (TiO2) micro-mésostructuré à dimensionnalité contrôlée (0D, 1D, 2D et 3D)". Nantes, 2001. http://www.theses.fr/2001NANT2098.
Texto completo da fontePakulski, Dawid. "Graphene based materials and their potential applications". Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF060.
Texto completo da fonteScientific purpose of this doctoral dissertation is synthesis of functionalized two-dimensional materials (graphene and graphene oxide) and their comprehensive physicochemical characterization, with particular emphasis on adsorption and energy storage properties. We could demonstrate that covalent modification of graphene oxide (GO) with an organic polymer (BPEI) very favorably affects the efficiency of the adsorption process. The maximum adsorption capacity (qmax) values for heavy metal ions significantly favour this material in comparison to the majority of known carbon adsorbents. Moreover, functionalization of GO with mesoporous aminosilica (SiO2NH2) leads to obtaining an efficient and rapid adsorbent of organic cationic dyes (MB, RhB, MV). ln addition we proved that the functionalization of graphene (EEG) using the POM-surfactant su bu nits proved that this type of organic-inorganic hybrids material is very stable and have interesting electrical properties with potential application in the production of supercapacitors
Liu, Liyuan. "Les matériaux 2D pour le stockage de l'énergie". Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30204.
Texto completo da fonteThe aim of this thesis is to study the electrochemical properties of 2D materials used as electrode in batteries and supercapacitor. The first part starts with using reduced graphene oxide (rGO) aerogel as a negative electrode material for potassium-ion batteries (PIBs). The influence of the nature of the electrolyte and the drying methods used were investigated in order to optimize the electrochemical performance of freeze-dried rGO in PIBs. Electrochemical impedance spectroscopy (EIS) were used to assess the performance of our rGO material in PIBs. rGO can deliver a high capacity of 267 mAh g-1 at C/3 rate together with 78% capacity retention during 100 cycles, combined with high rate capability (92 mAh g-1 at 6.7 C). This set of results makes rGO aerogel a promising electrode material for PIBs. Afterwards, we focused on molten salt method (MSM) to design materials with enhanced electrochemical properties for energy storage applications. With MSM, 2D K0.27MnO2·0.54H2O (KMO) and 1D CaV6O16·7H2O (CVO) have successfully prepared. KMO nanosheet has been used as cathode for aqueous Zn-ion batteries, with high specific capacities (288 mAh g-1) and long-term cyclability (91% capacity retention after 1000 cycles at 10 C). Electrochemical quartz crystal admittance (EQCM) technique was firstly performed to confirm the consequent H3O+ and Zn2+ intercalation charge storage mechanism. Additionally, CVO was further used as cathode material in aqueous Ca-ion batteries. As a result, excellent electrochemical performance was achieved, with a capacity of 205 mA h g-1, long cycle life (>97% capacity retention after 200 cycles at 3C rate) and high rate performance (117 mAh g-1 at 12 C) during Ca-ion (de)intercalation reactions. Differently from the previous flash molten salt method achieved in air, we designed another molten salt method under argon atmosphere to prepare 2D metal carbides (MXene) materials such as Ti3C2 (M=Ti, X=C). By playing with the chemistry of the MAX precursor and the Lewis acid melt composition, we generalize this synthesis route to a wide chemical range of MAX precursors (A=Zn, Al, Si, Ga). The obtained MXene materials (termed as MS-MXenes) exhibits enhanced electrochemical performance in Li+ containing non-aqueous electrolyte, with a capacity of 205 mAh g-1 at 1.1 C, making these materials highly promising as negative electrodes for high power Li batteries or hybrid devices such as Li-ion capacitors. Besides APS, another etchant (FeCl3) has been used to dissolve Cu. Furthermore, high conductive ACN-based electrolyte has been applied to improve the power performance of multi-layered MS-MXene. To sum up, this method allows producing new types of MXene that are difficult or even impossible to be prepared by using previously reported synthesis methods like HF etching. As a result, it expands further the range of MAX phase precursors that can be used and offer important opportunities for tuning the surface chemistry and make MS-MXene as high rate electrode in non-aqueous system
Dolet, Aneline. "2D and 3D multispectral photoacoustic imaging - Application to the evaluation of blood oxygen concentration". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI070/document.
Texto completo da fontePhotoacoustic imaging is a functional technique based on the creation of acoustic waves from tissues excited by an optical source (laser pulses). The illumination of a region of interest, with a range of optical wavelengths, allows the discrimination of the imaged media. This modality is promising for various medical applications in which growth, aging and evolution of tissue vascularization have to be studied. Thereby, photoacoustic imaging provides access to blood oxygenation in biological tissues and also allows the discrimination of benign or malignant tumors and the dating of tissue death (necrosis). The present thesis aims at developing a multispectral photoacoustic image processing chain for the calculation of blood oxygenation in biological tissues. The main steps are, first, the data discrimination (clustering), to extract the regions of interest, and second, the quantification of the different media in these regions (unmixing). Several unsupervised clustering and unmixing methods have been developed and their performance compared on experimental multispectral photoacoustic data. They were acquired on the experimental photoacoustic platform of the laboratory, during collaborations with other laboratories and also on a commercial system. For the validation of the developed methods, many phantoms containing different optical absorbers have been produced. During the co-supervision stay in Italy, specific imaging modes for 2D and 3D real-time photoacoustic imaging were developed on a research scanner. Finally, in vivo acquisitions using a commercial system were conducted on animal model (mouse) to validate these developments
Haidar, Fatima. "Nanostructures 2D et supports d’oxydes métalliques pour des cathodes de piles à combustible à faible teneur en platine". Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS121.
Texto completo da fonteProton exchange membrane fuel cells are clean and efficient energy converters. Their accessible power ranges allow their use in the field of transport or stationary applications. Two main challenges concern the cathode deployment:i) The reduction of the amount of low abundant platinum group metal in the catalyst.ii) The enhancement of stability of the catalyst support at high voltage.In this work we present two strategies to address these challenges and improve performance and durability of the cathodes: developing novel ultra-low loaded platinum electrocatalysts and corrosion resistant support materials.To reduce noble metal amount in the catalyst, we developed platinum thin films, which allow maximal electrocatalytic exploitation thus minimal loading. For that, we have used electrochemical methods based on under-potential deposition and galvanic displacement. The thin structures deposited on model substrates were characterized by electrochemical, elemental analysis and microscopy techniques.To prepare corrosion resistant supports, our strategy was the replacement of conventional carbon black with a doped conducting tin oxide. SnO2-based materials have been demonstrated as electrochemical stable supports also promoting platinum activity for the oxygen reduction reaction. In this work, tantalum-doped tin oxide was prepared by electrospinning followed by calcination, leading to a fiber-in-tube morphology. This support was catalyzed with platinum nanoparticles prepared by a microwave-assisted polyol method, and characterized for their physico-chemical and electrocatalytic properties. In particular, stability to voltage cycling was evaluated by ex situ electrochemical analysis.The possibility to associate the extended surface electrocatalyst with the corrosion resistant supports to obtain active and durable cathodes is in progress
Ries, Lucie. "Functionalized two-dimensional (2D) MoS2 nanosheets as building blocks for water purification membranes". Thesis, Montpellier, Ecole nationale supérieure de chimie, 2019. http://www.theses.fr/2019ENCM0009.
Texto completo da fonteMembrane separation technology plays an important role in various fields including water treatment, chemicals and gas separation for numerous industrial fields, and food processing. There has been a renewed focus on two-dimensional(2D) materials for membrane application since their atomic thicknessand confined interlayer spacing could theoretically lead to enhanced separative performances. Either the single nanosheets themselves, or the stackingof multiple sheets can form selective membranes. The multilayer assembly of single nanosheets – forming nanolaminate membranes – creates 2D capillaries(or nanochannels) that can efficiently sieve chemical species depending ontheir size.Recent examples have been reported in the literature demonstrating the potential of 2D materials as multi- or single-layer membranes for molecular sieving(222; 260; 466; 204), gas separation (219; 246; 190), energy harvesting (467)and water desalination (198; 194).Among the different building blocks of nanolaminate membranes made of two-dimensional materials (2D), graphene oxide (GO) has been studied as a candidate for molecular sieving via size-limited diffusion in the 2D capillaries (222). Unfortunately the high hydrophilicity of GO nanosheets makes GO membranes unstable in water, while the poor control of the capillary width between the nanosheets limits the water permeance of the membranes. Other 2D materials such as exfoliated nanosheets of transition metal dichalcogenides (TMDs)constitute attractive platforms for the realization of nanolaminate membranes.Recent works carried out on nanolaminate membranes made of molybdenum disulfide (MoS2) have demonstrated improved stability (3). Within this thesis we have studied the performance of a novel type of MoS2 nanolaminate membranes with well-controlled surface chemistry of the nanosheets (14). Inorder to assess the role of surface chemistry, we explored the impact of covalent functionalization on molecular sieving toward water purification (i.e. desalination and micropollutant removal) (14). Our results open novel directions to finely tune the sieving behavior of membranes based on 2D materials
Leriche, Raphaël. "Unconventional superconductivity in quasi-2D materials with strong spin-orbit coupling". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS577.
Texto completo da fonteThe realization of topological superconductors is one of the main current goals of condensed matter physics. It was indeed predicted that such systems should host Majorana fermions. These Majorana fermions possess both a non-Abelian statistics and, because of their topological origin, a certain robustness against local disorder, which makes them attractive for quantum computing applications. One approach likely to lead to topological superconductivity consists in considering superconducting systems with strong spin-orbit coupling and with broken inversion symmetry. It is in this framework that, during this thesis, I performed scanning tunneling microscopy and spectroscopy measurements on quasi-2D materials : (LaSe)1,14(NbSe2)2 and Sr2IrO4. I first studied the electronic properties of misfit compound LaNb2Se5, which is a parent of transition metal dichalcogenide 2H-NbSe2. (LaSe)1,14(NbSe2)2 is a heterostructure made out of alternations of NbSe2 bilayers with trigonal prismatic geometry and LaSe bilayers with rocksalt structure. (LaSe)1,14(NbSe2)2 is a potential candidate for topological superconductivity because of the presence of both a strong spin-orbit coupling and of broken inversion symmetry in NbSe2 planes. Here, I present spectroscopic results showing that the electronic structure of(LaSe)1,14(NbSe2)2 is very similar to the one of electron-doped monolayer NbSe2 with a shift of the chemical potential of 0,3 eV, priorly never reached. I could also demonstrate the quasi- 2D nature of (LaSe)1,14(NbSe2)2 and more particularly the presence of a strong Ising spinorbit coupling. Moreover, the observed weakness of superconductivity against non-magnetic disorder combined with quasiparticle interferences measurements allowed me to exhibit the unconventional nature of (LaSe)1,14(NbSe2)2 superconducting order parameter. This study opens the possibility to use misfit heterostructures such as (LaSe)1,14(NbSe2)2 to study thephysics of transition metal dichalcogenides in the 2D limit, for which many theoretical studies predict topological superconductivity. In this thesis, I also present a study on the effects of doping on the electronic properties of iridate compound Sr2IrO4. Sr2IrO4 is a spin-orbit induced Mott insulator. Because inversion symmetry is locally broken in Sr2IrO4, some theoretical predictions suggest that Sr2IrO4 should turn into a topological superconductor once doped. Here, I exhibit a nanometer-scaleinhomogeneous doping-driven Mott insulator to pseudo-metallic phase transition. This work further justifies the importance of using a local probe such as scanning tunnelling microscopy in order to complete results on Mott physics obtained by integrative methods like angle-resolved photoemission spectroscopy
Schmittlein, Carina [Verfasser], e Joachim [Akademischer Betreuer] Wegener. "Sensors and Actuators for 2D and 3D Cell Culture Models based on Oxygen Sensitive Culture Substrates / Carina Schmittlein ; Betreuer: Joachim Wegener". Regensburg : Universitätsbibliothek Regensburg, 2018. http://d-nb.info/1170955738/34.
Texto completo da fonteTararan, Anna. "Spectroscopy in fragile 2D materials : from Graphene Oxide to single molecules at hexagonal Boron Nitride". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS441/document.
Texto completo da fonteElectron energy loss spectroscopy (EELS) and cathodoluminescence(CL) in a scanning transmission electron microscope (STEM) are extremely powerful techniques for the study of individual nanostructures. Nevertheless, fast electrons damage extremely sensitive thin specimens, imposing strong limitations on the spatial resolution and the intensity of spectroscopic measurements. During this thesis we have overcome this restriction by developing material-specific acquisition protocols for the study of some archetypical fragile nanosystems. In the first part of this thesis we have characterized graphene oxide (GO) and reduced graphene oxide (RGO) thin flakes by EELS spectroscopy in the STEM. Thanks to the particular setup of our microscope and by experimentally defining the optimal illumination conditions, we have derived oxygen quantification maps of (R)GO at an unprecedented spatial resolution. On the basis also of EELS fine structures analysis, we have revised the existing proposed atomic models for these materials. Another class of exceedingly sensitive nanometric systems is represented by individual molecules, which are strongly affected by both illumination and chemical/physical environment. We have performed the first CL-STEM investigation on the luminescence of isolated molecules, thanks to a watchful choice of the substrate. Hexagonal boron nitride (h-BN) is a flat, chemically inert 2D material, that actively takes part in the CL process by absorbing the incident energy. Excitation transfer from h-BN to molecules and the use of an innovative random scan acquisition routine in the STEM have allowed to considerably lower illumination effects and improve CL intensity. Afterwards, the attractive optical properties of h-BN have led to the study of its cubic phase (c-BN), which has been up to now hindered by the poor quality of the crystals. By EELS in the STEM we have analysed c-BN crystals of the highest available purity, identifying a wider optical band-gap with respect to previous experimental studies and in better agreement with recent calculations. In commercial crystals, several defect-related emissions have been identified and analysed in terms of characteristic energy, spatial distribution and lifetime using CL and Hanbury-Brown and Twiss intensity interferometry
Feizbakhsh, Bazargani Mona [Verfasser], Christian [Gutachter] Robl e Kurt [Gutachter] Merzweiler. "Synthesis and characterization of ten new 1D, 2D and 3D-coordination polymers with oxygen or nitrogen containing ligands by using different metal cations / Mona Feizbakhsh Bazargani ; Gutachter: Christian Robl, Kurt Merzweiler". Jena : Friedrich-Schiller-Universität Jena, 2019. http://d-nb.info/1205885226/34.
Texto completo da fonteBenchakar, Mohamed. "Synthèse et caractérisation de nouveaux composés bidimensionnels, les MXènes, pour le stockage et la conversion de l'énergie". Thesis, Poitiers, 2020. http://www.theses.fr/2020POIT2271.
Texto completo da fonteHydrogen is the most promising energy vector for the future energy grid implementation. It can be obtained from different methods of production. However, an eco-friendly hydrogen with a high purity can only be produced using water electrolysis. Furthermore, the design of low cost, active and stable electrodes is required for the development of large scale electrolysis systems. In this context, 2D materials are of upmost interest for the development of catalysts in reason of their high surface to volume ratio, conferring them unique properties far from those of their bulk counterparts. In this way, MXene family (discovered in 2011) is a good candidate. Their intrinsic properties (high electronic conductivity, hydrophilicity, versatile chemistry) reinforces the passion they arouse and make these materials as promising candidates for the design of efficient catalysts. In this work, several Ti3C2Tx MXenes were first synthesized using different etching agents and characterized in order to elucidate the hydration chemistry, composition, structure, surface chemistry and macroscopic properties. This MXene, which nevertheless exhibits a low catalytic performance toward hydrogen and oxygen evolution reactions, has been used as a support for cobalt-based layered double hydroxides. The presence of numerous terminal groups on the MXene surface allows obtaining a good dispersion of the active phase. In addition, MXene ensures the good electronic conductivity of the electrode which promotes the charge transfer. The structural properties of the resulting material (Co-LDH@ Ti3C2Tx) were studied and correlated to its good catalytic activity toward oxygen evolution reaction in alkaline medium. This performance could be associated to the electronic interaction occurring between the active phase and the MXene. Further, Mo2CTx MXenes were also synthesized, characterized and used as a precursor for the synthesis of a MoS2/Mo2CTx two-dimensional heterostructure. This innovative material was obtained by topotactic transformation (sulfurization) of Mo2CTx. This composite has proven to be an excellent catalyst toward hydrogen evolution reaction in alkaline medium. This high activity could be attributed to the intimate contact existing between the MoS2 and Mo2CTx phases on one hand, allowing an activation of the 2D sulfide basal plane and to the presence of weakly coordinated atoms on the other hand, allowing the water activation at low overpotentials.Thus, efficient and stable MXene-based catalysts have been developed for oxygen and hydrogen evolution reaction. The prospects for this work are numerous considering the chemistry richness of these new 2D materials in order to obtain more efficient electrodes
Chicot, Gauthier. "Effet de champs dans le diamant dopé au bore". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-01062250.
Texto completo da fonteLee, Zhe-Yu, e 李哲裕. "Enhanced Photoelectrochemical Efficiency by 2D Material-Silicon Heterojunction for Oxygen Evolution Reaction". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/9wcz8e.
Texto completo da fonte國立臺灣大學
材料科學與工程學研究所
107
Developing the alternative energy is imperative due to the energy crisis and exponential growth of energy demand in the decades. Among new energy sources, photoelectrochemical (PEC) water splitting into hydrogen and oxygen, which is renewable, environment-friendly, and sustainable, has been seen as one of the most promising way to solve the challenge. In addition, two dimensional materials also attract a lot of attention of scientists all over the world due to their peculiar physical properties since the first discovery of mechanically exfoliated graphene in 2004. In this study, application of 2D material-silicon heterojunction has been first time applied to the PEC water splitting for oxygen evolution reaction. Herein, 2D materials, graphene and MoS_2, coupled with n-type silicon have been used as water splitting photoanode for oxygen evolution reaction (OER). In the first part, graphene-silicon Schottky junction photoanode is synthesized by conventional PMMA graphene transfer method and thermal evaporation of nickel thin film. Compared to the Si-Ni structure, the Si-Gr-Ni photoanode shows enhanced OER efficiency from linear sweep voltammetry (LSV) measurement and reduced charge transfer resistance from electrochemical impedance microscopy(EIS). To further improve it, metallic p-type doping is adopted to tune the work function of graphene and the enhanced built-in potential is demonstrated by the Mott-Schottky plot. In the second part, Si-MoS_2-Ni photoanode is synthesized also by PMMA transfer method and thermal evaporation. Due to the special band bending in the photoanode, two carrier transporting paths have been observed from the LSV measurement and the reduced charge recombination of MoS_2-Si heterojunction, compared to pure MoS_2, has been proved by quenching of PL and longer life time of TRPL. Most importantly, the OER efficiency of Si-MoS_2-Ni photoanode is comparable to those in the literatures. In brief, the application of graphene and MoS_2 in this study has provided a 2D material-silicon heterojunction paradigm for PEC water splitting photoanode. Many modification strategies are worth expecting to optimize the efficiency.
Chappel, Eric. "Magnétisme de quelques composés bidimensionnels de la famille AMO2 (A=Li, Na: M=Ni, Fe, Co)". Phd thesis, 2000. http://tel.archives-ouvertes.fr/tel-00008226.
Texto completo da fonte