Дисертації з теми "2D oxides"
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1
SCALISE, EMILIO. "Vibrational Properties of Defective Oxides and 2D Nanolattices." Doctoral thesis, KuLeuven, 2013. http://hdl.handle.net/10281/181816.
Анотація:
The nanoelectronic evolution, which was driven for many years by the ‘‘aggressive scaling’’ of the complementary metal-oxide-semiconductor (CMOS) devices,
needs new approaches in order to face the demands for smaller, more performing, and less power-consuming integrated circuits.
A few years ago, high-mobility semiconductors, e.g., germanium and III–V semiconductors, started to be investigated as possible substitutes of silicon as
materials for the CMOS channel. On the other hand, dielectric materials with a higher dielectric constant (j) than the native silicon dioxide, such as HfO2, were
introduced into CMOS devices a couple of years ago, in order to obtain a larger oxide capacitance, improving the performance of the devices while keeping their
power consumption as low as possible. To take effective advantage of the introduction of high-mobility semiconductors and high-j dielectrics in the next generations of CMOS devices, high quality interfaces are required.
In the first part of this thesis, we investigate the vibrational properties of defective HfO2 by first-principles simulations, and we compare them with experimental results from inelastic electron tunneling spectroscopy (IETS). This spectroscopic technique is very powerful for the investigation of nanoscale junctions. We also model amorphous defective GeO2, likely present at the interface of Ge/HfO2 gate stacks. Different defects, including three-folded oxygen atoms and divalent germanium centers are investigated. We show how the calculated vibrational spectra of the defective oxides, correlated to IETS measurements, can be successfully used for the investigation of high-mobility/high-j gate stacks interfaces.
Recently, the interest of the physics and electronic engineering community in 2D materials, such as graphene, increased exponentially. These materials, made up of one single atomic layer, can be used to exploit quantum confinement effects, resulting in unique electronic and magnetic properties.
The linear electronic dispersion observed in graphene, linked to the presence of massless Dirac fermions, was recently predicted also for its silicon and germanium counterparts, the so-called silicene and germane. This is very appealing for nanoelectronic and energy applications, in which materials with an extremely high conductivity are highly demanded. Recent experiments showed that silicene grown on metallic substrates has different structural configurations and presents a characteristic puckering of the silicon atoms, which are in contrast to graphene.In the second part of this thesis, the structural and vibrational properties of silicene on Ag(111) surfaces are calculated. Their comparison with experimental measurements, such as scanning tunneling microscopy and Raman spectroscopy, allows us to investigate the structural but also the electronic properties of different silicene reconstructions on Ag(111).
Finally, the possible growth of silicene on nonmetallic templates is theoretically investigated. We show that different layered chalcogenide compounds (i.e., MoX2 and GaX, X=S, Se, Te) can be used as templates for the silicene layer. The van der Waals interaction between the silicene layer and the templates is important for avoiding strong interactions (hybridization) between the silicon atoms and the substrates. The different in-plane lattice parameters of the chalcogenide compounds can be exploited to tune the electronic properties of the silicene layer, preserving in some cases its massless Dirac fermions.
2
Odziomek, Mateusz Janusz. "Colloidal Synthesis and Controlled 2D/3D Assemblies of Oxide Nanoparticles." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN092/document.
Анотація:
La nanotechnologie est devenue un domaine clé de la technologie du XXIe siècle. L’important développement des approches pour la synthèse des nanoparticules (NPs) avec une composition, une taille et une forme désirées rend compte du potentiel de leur utilisation comme « blocs de construction » pour des structures de plus grande échelle. Cela permet d’envisager à la fois la fabrication de matériaux fonctionnels et de dispositifs directement à partir de colloïdes par approche ascendante et la conception de matériaux sur plusieurs échelles de grandeur. Le procédé utilise l'assemblage ou l'auto-assemblage de NPs et conduit à des matériaux avec des architectures différentes notamment 1D (bâtonnets), 2D (films) ou 3D (super-réseaux ou gels). Cependant, la plupart des assemblages 3D sont limités à l'échelle micrométrique et sont difficiles à contrôler. Pratiquement, la seule voie permettant la préparation de structures 3D macroscopiques à partir de NPs est la gélification et la préparation d'aérogels. Une voie alternative consiste à disperser les NPs dans une matrice, conduisant ainsi à un matériau composite massif, avec des NPs non agrégées distribuées de manière homogène.Le présent travail est consacré au développement de matériaux à partir de NPs d'oxydes métalliques (principalement Y3Al5O12: Ce et Li4Ti5O12) de différentes dimensions et pour diverses applications. La première partie de ce travail décrit la synthèse de NPs de YAG: Ce et de LTO par approche glycothermale. Dans le cas du YAG: Ce, les conditions de réaction ont été ajustées de façon appropriée pour obtenir des nanocristaux (NCs) non agrégés de quelques nanomètres. Des solutions colloïdales de différentes concentrations contenant de tels NCs ont été utilisées, pour la fabrication par la technique de « spin-coating », de films minces avec une épaisseur contrôlable. A l’inverse, la synthèse de LTO conduit à des NPs agrégées dans une structure hiérarchique très bénéfique pour les batteries au lithium. La grande surface spécifique et la porosité du matériau obtenu assurent en effet un échange efficace des ions lithium entre l'électrolyte et le matériau d'anode.Par ailleurs, les NCs de YAG: Ce ont été utilisés pour la préparation de matériaux monolithiques de grande taille avec une porosité et une transparence élevées. Pour cela, la solution colloïdale de NCs a été gélifiée par le changement brusque de la constante diélectrique du solvant de dispersion des NCs. Les gels ainsi obtenus ont été par la suite séchés de manière supercritique, donnant ainsi des aérogels à base de NPs de YAG:Ce, avec une porosité et une transparence élevées. La même approche s'est avérée appropriée pour d'autres systèmes à base de NPs de GdF3 ou de mélanges de NPS de YAG: Ce et de GdF3.Alternativement, les NPs de YAG: Ce ont été incorporées dans des aérogels de silice formant ainsi des aérogels macroscopiques robustes et hautement transparents présentant les propriétés des NPs incorporées. Ces aérogels composites ont été utilisés en tant que nouveaux types de capteurs pour les rayonnements ionisants de basse énergie dans les liquides ou les gaz. Leur porosité élevée permet un contact optimal entre l'émetteur radioactif et le scintillateur assurant ainsi une bonne récupération de l'énergie radioactiveNanotechnology 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
3
Paerschke, Ekaterina. "Interplay of Strong Correlation, Spin-Orbit Coupling and Electron-Phonon Interactions in Quasi-2D Iridium Oxides." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-235245.
Анотація:
In the last decade, a large number of studies have been devoted to the peculiarities of correlated physics found in the quasi-two-dimensional square lattice iridium oxides. It was shown that this 5d family of transition metal oxides has strong structural and electronic similarities to the famous 3d family of copper oxides. Moreover, a delicate interplay of on-site spin-orbit coupling, Coulomb repulsion and crystalline electric field interactions is expected to drive various exotic quantum states. Many theoretical proposals were made in the last decade including the prediction of possible superconductivity in square-lattice iridates emerging as a sister system to high-Tc cuprates, which however met only limited experimental confirmation. One can, therefore, raise a general question: To what extent is the low-energy physics of the quasi-two-dimensional square-lattice iridium oxides different from other transition metal oxides including cuprates? In this thesis we investigate some of the effects which are usually neglected in studies on iridates, focusing on quasi-two-dimensional square-lattice iridates such as Sr2IrO4 or Ba2IrO4. In particular, we discuss the role of the electron-phonon coupling in the form of Jahn-Teller interaction, electron-hole asymmetry introduced by the strong correlations and some effects of coupling scheme chosen to calculate multiplet structure for materials with strong on-site spin-orbit coupling.
Thus, firstly, we study the role of phonons, which is almost always neglected in Sr2IrO4, and discuss the manifestation of Jahn-Teller effect in the recent data obtained on Sr2IrO4 with the help of resonant inelastic x-ray scattering. When strong spin-orbit coupling removes orbital degeneracy, it would at the same time appear to render the Jahn-Teller mechanism ineffective. We show that, while the Jahn-Teller effect does indeed not affect the antiferromagnetically ordered ground state, it leads to distinctive signatures in the spin-orbit exciton.
Second, we focus on charge excitations and determine the motion of a charge (hole or electron) added to the Mott insulating, antiferromagnetic ground-state of square-lattice iridates. We show that correlation effects, calculated within the self-consistent Born approximation, render the hole and electron case very different. An added electron forms a spin-polaron, which closely resembles the well-known cuprates, but the situation of a removed electron is far more complex. Many-body configurations form that can be either singlets and triplets, which strongly affects the hole motion. This not only has important ramifications for the interpretation of angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy experiments of square lattice iridates, but also demonstrates that the correlation physics in electron- and hole-doped iridates is fundamentally different.
We then discuss the application of this model to the calculation of scanning tunneling spectroscopy data. We show that using scanning tunneling spectroscopy one can directly probe the quasiparticle excitations in Sr2IrO4: ladder spectrum on the positive bias side and multiplet structure of the polaron on the negative bias side. We discuss in detail the ladder spectrum and show its relevance for Sr2IrO4 which is in general described by more complicated extended t-J -like model. Theoretical calculation reveals that on the negative bias side the internal degree of freedom of the charge excitation introduces strong dispersive hopping channels encaving ladder-like features.
Finally, we discuss how the choice of the coupling scheme to calculate multiplet structure can affect the theoretical calculation of angle-resolved photoemission spectroscopy and scanning tunnelling spectroscopy spectral functions.
4
Asel, Thaddeus J. "Nanoscale Characterization of Defects in Complex Oxides and Germanane." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523982077791833.
5
Treske, Uwe. "Valence changes at interfaces and surfaces investigated by X-ray spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-162589.
Анотація:
In this thesis valence changes at interfaces and surfaces of 3d and 4f systems are investigated by X-ray spectroscopy, in particular X-ray photoemission (XPS), X-ray absorption (XAS) and resonant photoemission spectroscopy (ResPES). The first part addresses the electronic properties of the oxides LaAlO3, LaGaO3 and NdGaO3 grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals along (001)-direction. These polar/non-polar oxide interfaces share an insulator to metal phase transition as a function of overlayer thickness including the formation of an interfacial two dimensional electron gas. The nature of the charge carriers, their concentration and spatial distribution, and the band alignment near the interface are studied in a comparative manner and evaluated quantitatively. Irrespective of the different overlayer lattice constants and bandgaps, all the heterostructures behave similarly. Rising Ti3+ concentration is monitored by Ti 2p XPS, Ti L-edge XAS and by resonantly enhanced Ti 3d excitations in the vicinity of EF (ResPES) when the layer number n increases. This indicates that the active material is in all cases a near interface SrTiO3 layer of 4nm thickness. Band bending in SrTiO3 occurs but no electric field is detected inside the polar overlayers. Essential aspects of the findings are captured by scenarios where the polar forces are alleviated by surface defect creation or the separation of photon generated electron-hole pairs in addition to the electronic reconstruction at n = 4 unit cells layer thickness. Furthermore, deviations from an abrupt interface are found by soft X-ray photoemission spectroscopy which may affect the interface properties. The surface sensitivity of the measurements has been tuned by varying photon energy and emission angle. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From a quantitative analysis it is concluded that during the growth process a small amount of Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide. In the second part of this thesis the heavy fermion superconductors CeMIn5 (M = Co, Rh, Ir) are investigated by temperature- and angle-dependent XPS. In this material class the subtle interplay between localized Ce 4f and itinerant valence electrons dominate the electronic properties. The Ce 3d core level has a very similar shape for all three materials and is indicative of weak f-hybridization. The spectra are analyzed using a simplified version of the Anderson impurity model, which yields a Ce 4f occupancy that is larger than 0.9. The temperature dependence shows a continuous, irreversible and exclusive broadening of the Ce 3d peaks, due to oxidation of Ce at the surfaceIn der vorliegenden Dissertation werden Valenzänderungen an Grenzflächen und Oberflächen mittels Verfahren der Röntgenspektroskopie untersucht, zu denen die Röntgenphotoelektronen- (XPS), die Röntgenabsorptions- (XAS) und die resonante Photoelektronenspektroskopie (ResPES) gehören. Kapitel 3 behandelt die elektronischen Eigenschaften der Oxide LaAlO3, LaGaO3 und NdGaO3, welche mittels Laserdeposition (PLD) auf TiO2-terminierte SrTiO3 Einkristalle entlang (001)-Richtung gewachsen wurden. Diese polaren/nicht-polaren Oxidgrenzflächen weisen einen Isolator-Metall Phasenübergang als Funktion der Schichtdicke auf, bei dem sich ein zwei dimensionales Elektronengas an der Grenzfläche bildet. Die Eigenschaften dieser Ladungsträger, deren Konzentration und räumliche Ausdehnung, sowie der Verlauf der Energiebänder an der Grenzfläche werden vergleichend untersucht und quantitativ bestimmt. Es wird gezeigt, dass sich die drei untersuchten Grenzflächen, trotz unterschiedlicher Gitterkonstanten und Energiebandlücken, ähnlich verhalten. Das mit der Schichtdicke ansteigende Ti3+ Signal wird im Ti 2p XPS, Ti L-Kante XAS und durch die resonant verstärkten Ti 3d Anregungen nahe EF (ResPES) nachgewiesen. Daraus lässt sich schlussfolgern, dass in allen Fällen eine SrTiO3 Schicht mit einer Dicke von 4nm der eigentlich aktive Bereich ist. Im SrTiO3 tritt eine Bandverbiegung auf, ein elektrisches Feld in der polaren Deckschicht kann jedoch nicht nachgewiesen werden. Grundlegende Aspekte dieser Ergebnisse sind in einem Szenario vereinbar, bei dem die polaren Kräfte durch die Entstehung von Oberflächendefekten, durch die Trennung von photoneninduzierten Elektronen-Lochpaaren und durch eine elektronische Umordnung bei 4 uc Schichtdicke eliminiert werden. Des Weiteren werden Abweichungen von einer abrupten Grenzfläche mittels weich-Röntgenphotoelektronenspektroskopie festgestellt, die die Grenzflächeneigenschaften beeinflussen können. Für oberflächenempfindlichere Messbedingungen zeigt die Sr 3d Anregung, im Gegensatz zu Rumpfniveaus anderer Elemente, eine unerwartete Aufspaltung, was nur durch das Vorhandensein einer zweiten chemischen Strontiumkomponente zu erklären ist. Aus quantitativen Betrachtungen lässt sich schließen, dass einige Strontiumatome während des Wachstums an die Oberfläche diffundieren und möglicherweise Strontiumoxid gebildet wird. Der zweite Schwerpunkt der vorliegenden Arbeit ist die Untersuchung von Schwer-Fermionen Supraleitern CeMIn5 (M = Co, Rh, Ir) mittels temperatur- und winkelabhängiger XPS. Bei dieser Materialklasse dominiert das feine Zusammenspiel zwischen lokalisierten Ce 4f und frei beweglichen Leitungselektronen die elektronischen Eigenschaften. Das Ce 3d Rumpfniveauspektrum besitzt für die drei Materialien eine sehr ähnliche Form, die auf eine schwache f-Hybridisierung schließen lässt. Die Spektren werden mittels einer vereinfachten Version des Anderson-Impurity Modells analysiert, wobei sich eine Ce 4f Besetzung von mehr als 0,9 ergibt. Die Temperaturabhängigkeit zeigt eine kontinuierliche und irreversible Verbreiterung ausschließlich für die Ce 3d Anregung, dieser Umstand kann einer Oxidation der reaktiven Ceratome an der Oberfläche zugeordnet werden
6
Crowley, Kyle McKinley. "Electrical Characterization, Transport, and Doping Effects in Two-Dimensional Transition Metal Oxides." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1597327584506971.
7
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.
Анотація:
La formation d’oxydes quasicristallins dodécagonaux 2D (OQC), ainsi que celle de phases approximantes associées ont été récemment rapportées dans des films minces dérivés des pérovskites BaTiO₃ ou SrTiO₃, déposés sur des monocristaux de Pt orientés (111). Ces structures 2D ajoutent de nouvelles fonctionnalités aux films ultra-minces d’oxydes ternaires supportés sur des métaux à l’approche de la limite 2D. Ici, nous utilisons une approche d’empilement de couches minces dans laquelle le monocristal est remplacé par une couche tampon de Pt(111), déposée par MBE sur un substrat d’Al₂O₃(0001). Un film ultra-mince de SrTiO₃ a ensuite été déposé par PLD. L’empilement de films est entièrement caractérisé par des techniques de diffraction (LEED, RHEED, XRD), de microscopie (STM, Nano-SAM,TEM) et de spectroscopie (XPS, AES). Nous rapportons la découverte de trois nouveaux approximants obtenus par réduction de ce système par recuit à haute température dans des conditions de vide poussé. Ces phases peuvent être décrites par trois pavages différents construits avec des éléments du pavage NGT. Un modèle atomique déterminé par DFT, en accord avec les observations expérimentales, est proposé pour chaque approximant. Cette approche en couche mince peut être utile pour explorer la formation de phases d’oxyde 2D complexes dans d’autres combinaisons métal-oxydeThe 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
8
Paerschke, Ekaterina [Verfasser], Jeroen van den [Akademischer Betreuer] Brink, Jeroen/van den [Gutachter] Brink, and Krzysztof [Gutachter] Wohlfeld. "Interplay of Strong Correlation, Spin-Orbit Coupling and Electron-Phonon Interactions in Quasi-2D Iridium Oxides / Ekaterina Paerschke ; Gutachter: Jeroen van den Brink, Krzysztof Wohlfeld ; Betreuer: Jeroen van den Brink." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://d-nb.info/1160875170/34.
9
Pärschke, Ekaterina [Verfasser], Jeroen van den [Akademischer Betreuer] Brink, Jeroen/van den [Gutachter] Brink, and Krzysztof [Gutachter] Wohlfeld. "Interplay of Strong Correlation, Spin-Orbit Coupling and Electron-Phonon Interactions in Quasi-2D Iridium Oxides / Ekaterina Paerschke ; Gutachter: Jeroen van den Brink, Krzysztof Wohlfeld ; Betreuer: Jeroen van den Brink." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://d-nb.info/1160875170/34.
10
Mayer-Uhma, Tobias. "Von molekularen Precursoren zu Oxidphasen im System V2O5 / Nb2O5. Darstellung, Eigenschaften, katalytische Aktivität." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1107505327269-01068.
Анотація:
In this work, mixed alkoxides of general formula [V(O)Nbx(OR)(3+5x)] (R = n-C3H7 and C2H5, x = 1, 4.5 and 9) are obtained. They are used to prepare complex (V/Nb)-pentoxides. Different spectroscopic methods, for example UV/VIS, resonance raman, infrared, temperature dependant 51V NMR and two dimensional 1H or 13C NMR, are used to elucidate structural details. It can be shown that the alkoxide precursor is a mixture of monomers and dimers which exchange very quickly. 2 % [V(O)Nb(OPr)8] (Pr = propyl) exists in a 0.1 molar solution. This complex is in equilibrium with V(O)(OPr)3 and Nb(OPr)5. Nb(OPr)5 itself exchanges with [Nb(OPr)5]2. For nuclear magnetic resonance experiments the exchange has to be slowed down using low temperatures.Controlled hydrolysis at 5 °C of a mixture of V(O)(OPr)3 and [Nb(OEt)5]2 in propanol leads to a clear transparent gel. The ratio of V : Nb is 1 : 1, 1 : 4.5 or 1 : 9, and oxalic acid is used as a chelating agent. Moreover, a dried product of a frozen solution of ammonium vanadate and ammonium oxyoxalatoniobate in water is found to be an appropriate precursor for the fore-mentioned oxides. Thermal decomposition of the gels and of the freeze dried products is monitored thermoanalytically and mass spectrometrically.The compositions of the resulting phases are examined and compared with the composition obtained via conventional synthesis (sintering of powder mixtures). Phases VNbxO(2.5+2.5x) (x = 1, 4.5 and 9) are obtained through the sol-gel technique and freeze drying at distinctly lower temperatures. VNbO5 crystallizes between 400 and 650 °C and V4Nb18O55 between 550 and 750 °C. A clean, non-reduced phase, VNb9O25, crystallizes above 1100 °C in oxygen. Below this temperature, solid solutions of V2O5 in TT- or M-Nb2O5 exist. Conventionally, pure VNbO5 is not obtainable. Some sol-gel synthesized products have the advantage of a more complete phase formation. In this way, a new phase of composition VNb9O25 can be found. The phase is homöotypic to M-Nb2O5.An additional advantage of the sol-gel synthesis lies in relatively high surface areas. Adversely, carbon remaining from the alcohol groups favours the thermodynamically stable phase VNb9O25 over the phase V4Nb18O55. Consequently, the freeze drying method seems to be the best way to get metastable phases in the system V2O5/x·Nb2O5.The formation of the complex oxides is controlled through the thermodynamics at phase boundaries. Therefore, to get mixed phases, structurally similar starting materials are preferred. In other words, using V2O5 and TT-Nb2O5 as starting materials the mixed phase similar to TT-Nb2O5 can be obtained. B-Nb2O5 as precursor yields another mixed phase similar to B-Nb2O5. In this work, this effect is called the "structure directing effect". It is explained through the consumption of free enthalpy at the phase boundaries.As an additional point, catalytic activities of the complex oxides are examined. Because of a synergism of the known good activity of V2O5 and the good selectivity of Nb2O5, a strongly enhanced activity of the mixed oxides is found. Large surface areas further improve the activity. Connections between oxygen partial pressure, band gap and catalytic activity are found. A dilution of V2O5 in Nb2O5 down to 10 mol-% also causes an enhancement of catalytic activityIn der Arbeit werden durch die Synthese gemischter Alkoxide der Gesamtzusammensetzung [V(O)Nbx(OR)(3+5x)] (R = n-C3H7 und C2H5, x = 1, 4,5 und 9) sowie gefriergetrockneter Pulver Ausgangssubstanzen für gemischte, komplexe Vanadium- und Nioboxide erhalten. Untersuchungen mittels UV/VIS-, Resonanz-Raman- und IR-Spektroskopie sowie temperaturabhängiger 51V- und zweidimensionaler 1H-/13C NMR-Spektroskopie zeigen, dass es sich bei der Alkoxid-Vorstufe um ein Gemisch aus monomeren und dimeren Einheiten handelt, die in schnellem Gleichgewicht miteinander stehen. So liegt [V(O)Nb(OPr)8] als Donorkomplex vor, der im Gleichgewicht mit VO(OPr)3 und Nb(OPr)5 steht. Nb(OPr)5 steht wiederum im Gleichgewicht mit [Nb(OPr)5]2. Die Bildung und der Zerfall des Donorkomplexes erfolgen bei Raumtemperatur so schnell, dass er nur durch UV/VIS- und Resonanz-Raman-Spektroskopie sichtbar wird; bei der Kernresonanzspektroskopie muss der Austausch durch tiefe Temperaturen verlangsamt werden.Mittels kontrollierter Hydrolyse einer Mischung aus VO(OPr)3 und [Nb(OEt)5]2 in Propanol mit Oxalsäure als Chelatbildner und der Verlangsamung der Kondensation über die Erniedrigung der Temperatur wird ein homogenes, transparentes Gel aus V2O5 und Nb2O5 hergestellt. Daneben wird durch eine Lösung aus Ammoniumvanadat und Ammoniumoxyoxalatoniobat ein für die Gefriertrocknung geeigneter Precursor zur Synthese der Oxidphasen gefunden. Die Zersetzung des Gels und der gefriergetrockneten Pulver werden mittels DTA, TG und Massenspektrometrie untersucht und die Phasenausbildung mit der Reaktion von konventionellen Festkörpergemengen verglichen.Die dabei entstehenden metastabilen und thermodynamisch stabilen Phasen VNbxO(2,5+2,5x) (x = 1, 4,5 und 9) sind durch das Sol-Gel-Verfahren sowie durch die Gefriertrocknung bei deutlich niedrigeren Temperaturen und mit geringerem Fremdphasenanteil als bei der konventionellen Synthese erhältlich. VNbO5 existiert bis 650 °C, V4Nb18O55 bis 750 °C, darüber wandelt sich jede Zusammensetzung in VNb9O25 bzw. in verschiedene Nb2O5-Modifikationen und V2O5 um. Die Sol-Gel-Methode liefert im Vergleich zur Gefriertrocknung bei 900-1100 °C den Vorteil der schnelleren Phasenausbildung durch die größere Homogenität der Vorstufe. So erhält man Zwischenstufen, die sonst nur mit Beimengungen zu synthetisieren sind. In diesem Zusammenhang kann erstmalig eine zu M-Nb2O5 homöotype Verbindung der Zusammensetzung VNb9O25 erhalten werden. Ein weiterer Vorteil der Sol-Gel-Synthese ist der Erhalt größerer Oberflächen nach der Zersetzung. Nachteilig erscheinen jedoch bei einer Synthese bei tiefen Temperaturen (500-800 °C) die Alkoholatreste. So entstehen wesentlich eher die thermodynamisch begünstigten Phasen, z. B. VNb9O25 vor V4Nb18O55 und V4Nb18O55 vor VNbO5. Weiterhin macht sich die komplizierte Präparation der Gele bemerkbar; daher stellt im Allgemeinen die Gefriertrockung die Methode der Wahl dar.Die Ausbildung der komplexen Oxide erfolgt stark geprägt durch die Thermodynamik an den Phasengrenzen. Daher erfolgt eine bevorzugte Ausbildung strukturähnlicher Mischphasen. Diese erstmalig in diesem Ausmaß festgestellte Tatsache wird in der Arbeit der Strukturdirigierende Effekt genannt. Eine Erklärung dieses Effektes erfolgt anhand des Verbrauchs der Freien Enthalpie an den Phasengrenzen.Aufgrund eines Synergismus der Eigenschaften von V2O5 und Nb2O5 bei der oxidativen Dehydrierung von Propan zu Propen (relativ hohe katalytische Aktivität von V2O5 und hohe Selektivität von Nb2O5) wird eine überproportional hohe katalytische Aktivität bei den Mischoxiden erhalten. Die durch die unkonventionellen Methoden erhaltenen großen Oberflächen verbessern die Aktivität weiter. Es können Zusammenhänge festgestellt werden zwischen der Sauerstoffabgabetendenz, der Redoxkraft, der Bandlücke der Mischoxide und der katalytischen Aktivität. Die Einzigartigkeit des Nb2O5-Wirtsgitters bewirkt bei der Verdünnung von V2O5 darin eine hohe katalytische Leistungssteigerung
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Thébaud, Simon. "Electron and phonon transport in disordered thermoelectric materials : dimensional confinement, resonant scattering and localization." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1168/document.
Анотація:
Ces dernières décennies, l'urgence croissante de la crise énergétique et la prise de conscience qu'une grande partie de l'énergie utilisée dans le monde est dissipée sous forme de chaleur ont provoqué un engouement pour le développement de modules thermoélectriques performants. Ces dispositifs pourraient récupérer la chaleur provenant de procédés industriels ou d'autres sources, transformant un gradient de température en voltage grâce à l'effet Seebeck. Les matériaux thermoélectriques performants doivent posséder une faible conductivité thermique, une haute conductivité électrique et un grand coefficient Seebeck. L'optimisation simultanée de ces paramètres est un défi majeur pour la physique de la matière condensée et la science des matériaux. Dans l'optique d'améliorer les propriétés thermoélectriques de plusieurs matériaux prometteurs, nous explorons plusieurs stratégies dans lesquelles les défauts (substitutions atomiques, lacunes…), le désordre et le confinement dimensionnel jouent un rôle central. Nous réalisons des calculs en théorie de la fonctionnelle densité et des projections sur des orbitales de Wannier afin de construire des Hamiltoniens et des matrices dynamiques réalistes décrivant leur structure électronique et vibrationnelle dans l'espace réel. Ces paramètres sont ensuite utilisés pour calculer les propriétés de transport thermoélectrique en utilisant le formalisme de Kubo, l'équation de Boltzmann, le formalisme de Landauer et la méthode Chebyshev polynomial Green's function, qui permet un traitement exact du désordre. Nous étudions les propriétés de transport électronique et les performances thermoélectriques de deux matériaux prometteurs pour la production d'énergie à hautes températures, le titanate de strontium et l'oxyde de titane rutile. Nous obtenons un très bon accord entre nos prédictions et un grand nombre de données expérimentales. Nous montrons que l'augmentation du coefficient Seebeck observée dans les superlayers de titanate de strontium, jusque-là attribuée à des effets de confinement quantique, est en réalité très bien expliquée par l'hypothèse d'électrons délocalisés. Nous explorons les effets généraux des états résonant sur le transport électronique dans le cadre d'une étude modèle, et nous trouvons une augmentation d'un facteur six des performances thermoélectriques. Nous examinons ensuite le cas particulier du titanate de strontium, et nous montrons que les performances sont détruites par des effets de localisation si des atomes de Vanadium sont introduits comme impuretés résonantes. Nous étudions l'influence des défauts dans les matériaux bidimensionnels. Contrairement aux adatomes, nous montrons que les substitutions dans les dichalcogénures de métaux de transition ont pour effet de localiser les porteurs de charge. Nous étudions l'effet des lacunes sur le transport de phonons dans le graphène, et nous déterminons les taux de diffusion phonon-lacune. Nous obtenons un très bon accord entre notre théorie et des mesures de conductivité thermique dans des échantillons de graphène irradiés et de tailles finiesOver 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
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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.
Анотація:
L’émergence d’une grande variété de structures photoniques, au cours des dernières décennies, a permis le développement de composants intégrés sur puce réalisant des fonctions optiques en espace libre de plus en plus complexes. Parmi elles, les structures diélectriques membranaires ont permis d’implémenter une large panoplie de composants optiques planaires, allant du filtrage spectral résonant à la mise en forme de faisceau avec de faibles pertes. Toutefois, si ces structures permettent d’obtenir un contrôle quasi-total du champ électromagnétique rayonné, ce contrôle est généralement statique et déterminé par la fabrication. Un nombre croissant d’applications – telles que les télécommunications en espace libre, les capteurs pour systèmes autonomes ou encore l’imagerie – nécessitent pourtant des composants photoniques agiles, motivant ainsi la recherche de moyens de contrôle actifs de la réponse optique à implémenter au sein des structures diélectriques. À cette fin, différentes propriétés du graphène s’avèrent prometteuses. En particulier, la possibilité de moduler dynamiquement son absorption ouvre de nombreuses perspectives pour le contrôle électrique et optique des structures photoniques intégrant du graphène. Des modulateurs électro-optiques et tout-optique ont ainsi pu être réalisés, s’appuyant sur le développement récent de procédés de transfert des matériaux 2D qui permettent aujourd’hui d’obtenir des structures hybrides graphène/diélectrique de grande qualité. Dans ce contexte, les travaux présentés dans cette thèse cherchent à exploiter l’absorption modulable du graphène pour obtenir une accordabilité dynamique de la réponse optique des composants adressables par la surface, dans le cas particulier de structures photoniques diélectriques travaillant dans le proche infrarouge. Un modèle générique de composant hybride diélectrique/ graphène est tout d’abord développé en théorie des modes couplés afin d’identifier les paramètres d’intérêt pour maximiser le contrôle permis par l’absorption du graphène. Dans le cas à une résonance, le comportement du système est principalement déterminé par la condition de couplage critique classiquement définie pour l’étude de l’absorption du graphène. Dans le cas à deux résonances en revanche, un nouveau paramètre de contrôle – associé à la différence d’absorption induite sur les résonances – permet d’obtenir un levier d’accordabilité supplémentaire. Différentes stratégies de maximisation de ce paramètre sont proposées et les procédés technologiques nécessaires à leur implémentation sont étudiés expérimentalement afin d’évaluer – par le biais de la spectroscopie Raman et de la spectroscopie de photoélectrons – leur effet sur la qualité structurelle et chimique du graphène, intégré dans de telles structures. La modulation spatiale de l’absorption du graphène – proposée pour différencier l’absorption induite sur différents modes optiques – est ensuite étudiée expérimentalement à l’aide de structures exploitant le transfert de charges entre le graphène et un oxyde à grand travail de sortie, à savoir l’oxyde de tungstène. Les dispositifs réalisés permettent d’obtenir une modulation du potentiel chimique du graphène de 0.1eV – caractérisée par nano-XPS (ligne ANTARES du synchrotron SOLEIL) et spectroscopie Raman – pouvant aboutir à une modulation de l’absorption supérieure à 70% pour certaines longueurs d’onde. Finalement, une architecture de composant hybride actif permettant d’obtenir un contrôle dynamique de l’émission laser est proposée. Cette architecture repose sur l’utilisation d’une membrane à brisure de symétrie verticale et permet, en principe, d’obtenir une commutation entre deux angles d’émission par la modulation de l’absorption du graphène. L’intérêt de ces structures pour parvenir à une accordabilité continue de l’angle d’émission est également exposéThe 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
13
Zhang, Yubai. "Electrochemical synthesis of 2D materials and their applications in energy storage." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/410071.
Анотація:
2D materials have inspired the intrigue of researchers and industries for its potential to improve the performance of existing materials in energy storage field. However, wide application of 2D material such as graphene and transition metal dichalcogenides in batteries is not implemented since the tremendous challenges and issues, the quality, quantity, and cost concerns impede its commercialization. Electrochemical approach performs as a controllable and scalable method for exfoliating, expanding, and functionalizing the pristine bulk materials on-demand. Sodium ion batteries, a promising candidate for lithium ion batteries, and aqueous zinc ion batteries, a safe energy storage system have received considerable attention in recent decades. The research herein focuses on the electrochemical exfoliation of graphite for its application in sodium ion battery anode, adopting the electrochemical graphene oxide (EGO) as functional agent combining with vanadium oxide for aqueous zinc ion battery cathode, and electrochemical production of molybdenum disulfide in a packed bed reactor.
The PhD thesis generally is composed of three parts. In the first part, graphite is exfoliated and oxidized in a packed bed reactor. The effects of boron doping and oxidation on the graphene-based material were studied for high performance sodium ion battery anode respectively in Chapter 2 and Chapter 3. The electrochemical route from natural graphite to graphene oxide is investigated in terms of concentration of acid electrolyte (sulfuric acid). It was found that 12 M sulfuric acid reacted graphene oxide could deliver higher capacity of sodium ion battery than other concentrations. Boron doped graphene was synthesized by a twostep reaction, electrochemical fabrication of the tetraborate anions intercalated graphite oxide followed by reduction by annealing at 900 °C for 3 h under Ar gas. It was found that the boron doped graphene containing 0.21 at. % of boron was highly defective delivers a good capacity of 129.59 mAh g-1 at the current density of 100 mA g-1 and a long-term cyclic stability under current density of 500 mA g-1 retaining 100.20 mA g-1 after 800 cycles. The battery performance of boron doped graphene is better than that without boron doping.
To further improve the sodium ion battery anode performance, mildly reduced graphite oxide with layered structure was synthesized by a simple electrochemical oxidation of expanded graphite followed by mildly heating reduction as reported in Chapter 3. The irrigated pipe in the expanded graphite packed bed assists with diffusion of electrolyte. A fast thermal reduction at 150 °C for 20 min on the electrochemical graphite oxide achieves a controlled deoxygenation and maintaining of the large interlayer gap of the product for high sodium storage capacity. The thermally processed electrochemically produced graphite oxide could deliver a high reversible capacity of 268 mAh g-1 at a current density of 100 mA g-1, and 163 mAh g-1 at a high current density of 500 mA g-1 and a good capacity retaining capability (in average 0.0198% loss per cycle) over 2000 cycles.
In the second part, the EGO was integrated with vanadium oxide as cathode material for aqueous zinc ion battery. A simple spray dry method is applied to generate electrode materials, which is catering to industrial production. The aqueous mixture for spray drying is formed by quenching the molten V2O5. The products received after spray drying is vanadium oxide hydrate of amorphous structure. The zinc ion storage performance is investigated in terms of content of graphene oxide in the composite. The fabricated amorphous V2O5-EGO composite xerogel with 2D heterostructure possesses high zinc ion storage capability, high rate performance and stable cycling stability due to the functionality of graphene embedded in the composite material.
In the third part, inspired by the common intercalation electrochemistry of graphite and transition metal dichalcogenide, exfoliation for 2D MoS2 from its bulk crystal powder is investigated by using the packed bed set up. Organic solvent is found to be a critical factor in the electrochemical activation and the mechanical exfoliation process. The MoS2 bulk crystal can be exfoliated to few-layer nanosheets with stable solution dispersibility. This finding further broadens the horizon of electrochemical production of transition metal dichalcogenides through a scalable approach of electrochemical reaction in packed bed.
To sum up, this PhD thesis represents a huge step forward for EGO applications in sodium ion battery anode and aqueous zinc ion battery cathode. In addition, it develops a scalable production of vanadium oxide/graphene material by the spray dry method. The utility of the packed bed electrochemical reactor is extended to transition metal dichalcogenide MoS2. This work will be a valuable guidance for adoption of graphene, vanadium oxide, and MoS2 in the market of energy storage materials.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Science
Science, Environment, Engineering and Technology
Full Text
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Wu, Ziyang. "Rational design of two-dimensional architectures for efficient electrocatalysis." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235888/1/ziyang%2Bwu%2Bthesis%284%29.pdf.
Анотація:
In this thesis, the principal focus is the rational design and fabrication of two-dimensional (2D) nanoarchitectures, e.g., low-cost metal oxide nanosheets and earth-abundant transition metal layered double hydroxides (LDHs) for enhanced electrocatalysis. The related hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance not only demonstrated the advances of 2D nanomaterials, such as unique physical and mechanical properties, unprecedented electronic features, and ultrahigh surface areas but also indicated the possible mechanisms behind boosted activity and stability, e.g., phase engineering function and oxygen vacancies influence.
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Kang, Seungyeon. "Femtosecond laser direct writing of 3D metallic structures and 2D graphite." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11495.
Анотація:
This thesis explores a novel methodology to fabricate three dimensional (3D) metal-dielectric structures, and two dimensional (2D) graphite layers for emerging metamaterials and graphene applications. The investigations we report here go beyond the limitations of conventional fabrication techniques that require multiple post-processing steps and/or are restricted to fabrication in two dimensions. Our method combines photoreduction mechanism with an ultrafast laser direct writing process in innovative ways. This study aims to open the doors to new ways of manufacturing nanoelectronic and nanophotonic devices. With an introductory analysis on how the various laser and chemical components affect the fabrication mechanism, this dissertation is divided into three sections.Engineering and Applied Sciences
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Tararan, 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.
Анотація:
La spectroscopie de perte d’énergie des électrons (EELS) et la cathodoluminescence (CL) dans un microscope électronique en transmission à balayage (STEM) sont des techniques puissantes pour l’étude des nanostructures isolées. Cependant, des électrons rapides peuvent endommager fortement des échantillons minces et fragiles, ce qui limite la résolution spatiale et l’intensité des signaux spectroscopiques. Pendant cette thèse, nous avons dépassé cette restriction par le développement de protocoles d’acquisition spécifiques pour l’étude de certains archétypes de nanosystèmes fragiles. Dans la première partie de cette thèse, nous avons caractérisé des flocons minces de graphène oxydé (GO) et GO réduit (RGO) par EELS dans le STEM. Grâce aux spécificités techniques de notre microscope et à la définition des conditions d’illumination optimales, nous avons dérivé des cartes du contenu d’oxygène dans le (R)GO à une résolution spatiale inédite. Aussi, par l’analyse des pics EELS de structure fine, nous avons révisé les modèles atomiques proposés dans la littérature. Des molécules isolées constituent une autre classe de nanomatériaux fortement sensibles à l’irradiation et aussi à l’environnement chimique et physique. Nous avons conduit des expériences de CL sur des molécules individuelles, grâce à un choix avisé du substrat. Le nitrure de bore hexagonal (h-BN) est un matériaux bidimensionnel chimiquement inerte, qui participe activement au processus de CL en absorbant l’énergie incidente. Le transfert de l’excitation aux molécules et l’utilisation d’une routine innovante d’acquisition par balayage aléatoire ont permis de réduire les effets d’illumination. Ensuite, l’intérêt porté aux propriétés optiques du h-BN ont inspiré l’étude de sa phase cubique (c-BN), qui a été peu caractérisé auparavant à cause d’impuretés dans les cristaux. Nous avons analysé des cristaux de c-BN de haute pureté par EELS, en identifiant une bande interdite d’énergie plus grande que précédemment rapportée et plus proche des calculs les plus récents. Dans des cristaux moins purs, nous avons identifié et analysé plusieurs émissions associées à des défauts, en termes d’énergie caractéristique, distribution spatiale et temps de vie, par CL et interférométrie en intensité de Hanbury-Brown et TwissElectron 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
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Hu, Xiao. "Ultra-thin oxide films." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:d7373376-84f1-459e-bffb-f16ce43f02b7.
Анотація:
Oxide ultra-thin film surfaces have properties and structures that are significantly different from the terminations of the corresponding bulk crystals. For example, surface structures of epitaxial ultra-thin oxide films are highly influenced by the crystallinity and electronegativity of the metal substrates they grown on. Some enhanced properties of the novel reconstructions are related to catalysis, sensing and microelectronics, which has resulted in an increasing interest in this field. Ultra-thin TiOx films were grown on Au(111) substrates in this work. Two well-ordered structures within monolayer coverage - honeycomb (HC) and pinwheel - were generated and investigated. Special attention has been paid to the uniform (2 x 2) Ti2O3 HC phase including its regular structure and imperfections such as domain boundaries (DBs) and point defects. Linear DBs with long-range repeating units have been observed; density functional theory (DFT) modelling has been used to simulate their atomic structures and calculate their formation energies. Rotational DBs/defects show up less frequently, however a six-fold symmetrical 'snowflake' DB loop stands out. Two types of point defects have been discovered and assigned to Ti vacancies and oxygen vacancies/hydroxyl groups. Their diffusion manners and pairing habits have been discussed within an experimental context. The results of growing NbOx ultra-thin films on Au(111) are also presented in this thesis. An identical looking (2 x 2) HC structure to the Ti2O3 ultra-thin film has been formed; a stoichiometry of Nb2O3 is suggested. Another interesting reconstruction is a hollow triangle structure. Various sizes have been found, and sides of these equilateral triangles all show a double-line feature aligned along the { 1 ₁⁻ } directions of the Au(111) lattice. Chemical composition characterisations of NbOx thin films are still required as is DFT modelling. Experimental techniques used in this thesis include scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), and X-ray photoelectron spectroscopy (XPS). Ultra-thin oxide films were created by physical vapour deposition (PVD) in ultra-high vacuum (UHV) systems.
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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.
Анотація:
De nos jours, les émulsions stabilisées par adsorption de particules colloïdales à l'interface liquide-liquide (émulsions de Pickering) présentent un intérêt pour une grande variété d'applications allant des produits pharmaceutiques ou alimentaires aux modèles pour la préparation de nouveaux matériaux. Dans cette thèse, des émulsions huile-dans-eau (H/E) et eau-dans-huile (E/H) ont été efficacement stabilisées grâce à des particules inorganiques colloïdales (oxyde de graphène (GO) et nanofeuillets de nitrure de bore (h-BNNS)). L'adsorption de particules à l'interface huile-eau est induite par l'ajustement de la mouillabilité des particules dans les milieux liquides. Deux types d'émulsions, H/E et E/H, sont formées en utilisant des matériaux bidimensionnels qui possèdent des comportements hydrophiles différents. Les conditions requises pour atteindre l'émulsion la plus stable sont étudiées en variant la formulation de l’émulsion pour chaque type de particules. Les microstructures finales des émulsions peuvent être modifiées en ajustant leur composition initiale. L'utilisation d'une concentration élevée de particules améliore la stabilité des émulsions. Des émulsions à base de h-BNNS ont été rapportées dans ce travail pour la première fois et leur comportement a été profondément étudié. De plus, une nouvelle approche verte pour obtenir des membranes poreuses à base d'alcool polyvinylique (PVA) a été rapportée. Dans ce cas, l'ajout de PVA à l'émulsion augmente sa stabilité à long terme et permet sa mise en forme à l'aide de technologies conventionnelles telles que l’étalement. Les composites polymères obtenus à partir d'émulsions Pickering présentent une microporosité de 0,19 ± 0,03 µm ou 1,1 ± 0,3 µm en fonction du temps de séchage. Les membranes poreuses obtenues présentent de bonnes performances en matière de perméabilité à l'eau et de rejet des particules. Pour des membranes ayant une taille de pores d'environ 1,1 µm et une perméabilité à l'eau d'environ 2000 L / h / m2, un taux de rejection de 86% a été mesuré avec des particules de la même taille que les poresEmulsions 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
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Dedigamuwa, Gayan S. "Formation of nanocoatings by laser-assisted spray pyrolysis and laser ablation on 2d gold nanotemplates." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001205.
20
Muchharla, Baleeswaraiah. "Low Temperature Electrical Transport in 2D Layers of Graphene, Graphitic Carbon Nitride, Graphene Oxide and Boron-Nitrogen-Carbon." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/1132.
Анотація:
In this work, we have investigated temperature dependent electrical transport properties of carbon based two-dimensional (2D) nanomaterials. Various techniques were employed to synthesize the samples. For instance, high quality large area graphene and boron, nitrogen doped graphene (BNC) were grown using thermal catalytic chemical vapor deposition (CVD) method. Liquid phase exfoliation technique was utilized to exfoliate graphene and graphitic carbon nitride samples in isopropyl alcohol. Chemical reduction technique was used to reduce graphene oxide (rGO) by utilizing ascorbic acid (a green chemical) as a reducing agent. Detailed structural and morphology characterization of these samples was performed using state of the art microscopy as well as spectroscopic techniques (for example; Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), UV-Visible spectroscopy as well as Raman Spectroscopy). The low temperature (5 K< T <400 K) electrical transport properties of these materials show substantial difference from sample to sample studied. For instance, CVD grown graphene film has displayed metallic behavior over a wide range of temperature (5 K < T <300 K). At higher temperatures, resistivity followed linearly with the temperature (ρ(T) ~T). A power law dependence (ρ(T) ~ T4) observed at lower temperatures. Where as liquid phase exfoliated graphene and graphitic carbon nitride samples displayed nonmetallic nature: increasing resistance with decrease in temperature over a wide range (8 K < T < 270 K) of temperature. Electrical transport behavior in these samples was governed by two different Arrhenius behaviors in the studied temperature range. In the case of rGO and BNC layers, electrical conduction show two different transport mechanisms in two different temperature regimes. At higher temperatures, Arrhenius-like temperature dependence of resistance was observed indicating a band gap dominating transport behavior. At lower temperatures, Mott's two dimensional-Variable Range Hopping (2D-VRH) behavior was observed.
21
Pakulski, Dawid. "Graphene based materials and their potential applications." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF060.
Анотація:
Cette thèse de doctorat a pour objectif scientifique la synthèse de matériaux bidimensionnels fonctionnalisés (graphène et oxyde de graphène) et leur caractérisation physicochimique complète, avec un accent particulier apporté sur les propriétés d'adsorption et de stockage d'énergie. Nous avons démontré que la modification covalente de l'oxyde de graphène (GO) avec un polymère organique (BPEI) affecte très favorablement l'efficacité du processus d'adsorption. Les valeurs de la capacité maximale d'adsorption (qmax) des ions de métaux lourds favorisent de manière significative ce matériau par rapport à la majorité des adsorbants connus à base de carbone. En outre la fonctionnalisation de GO avec l'aminosilicate mésoporeuse (SiO2NH2) conduit à l'obtention d'un adsorbant efficace et rapide des colorants organiques cationiques (MB, RhB, MV). En plus nous avons prouvé que la fonctionnalisation du graphène (EEG), en utilisant les sous-unités de surfactant POM, a montré que ce type de matériau hybride organique-inorganique est très stable et présente des propriétés électriques intéressantes pouvant être utilisées dans la production de supercondensateursScientific 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
22
Ciornii, Dmitri. "Performance-oriented strategies for integration and wiring of the photosystem I inside 2D and 3D architectures and coupling photocatalysis with enzymatic catalysis." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21813.
Анотація:
In der vorliegenden Arbeit sind unterschiedliche Kopplungsstrategien des natürlichen Photosystems I (PSI) aus Cyanobakterium Thermosynechococcus elongatus mit verschiedenen Elektrodenoberflächen sowie Interaktion mit Nanomaterialien und Enzymen bearbeitet worden. Zum einen wurde gezeigt, dass die Immobilisierung des PSI auf modifizierten mehr-wandigen Kohlenstoffnanoröhrchen zur funktionalen Photobiohybridelektrode führt. Dabei wurde das PSI mit der Elektrode elektrisch mit Hilfe eines Redoxproteins, Cytochrom c (cyt c), verknüpft. Das System (PSI-cyt c) wurde auch auf eine dreidimensionale Elektrodenoberfläche des Metaloxids Indiumzinnoxid (eng. ITO) übertragen. Hierbei wurde zusätzlich die TransparenzEigenschaft solcher Oberflächen ausgenutzt. Die Präparation solcher transparenter Elektroden wurde optimiert, um höhere Photoströme zu generieren. Weiterhin wurde eine neue Methode der elektrischen Kontaktierung des PSI mit der Elektrode etabliert. Hierfür wurden Fullerene eingesetzt. Durch erhöhte molekulare Effizienz wurde gezeigt, dass Fullerene effektivere Elektronvermittler zwischen PSI und der Elektrode sind als das cyt c. Zusätzlich wurden im Rahmen dieser Doktorarbeit die photokatalytischen Eigenschaften von PSI mit den biokatalytischen Eigenschaften des Enzyms humane Sulphit Oxidase (hSOx) kombiniert. Hierbei wurde das Enzym als ein alternativer und effizienter Elektronzulieferer für PSI eingesetzt. Ein drittes Protein, das cyt c, fungierte als elektrisches Bindeglied und sicherte die elektrische Kommunikation zwischen den katalytischen Proteinen im System und der Elektrode. Die Komplexität des PSI sowie seine Kommunikation mit anorganischen Nanomaterialien und anderen komplexen Biomolekülen, wie z.B. Enzymen, zeigt ein großes Potential des Einsatzes von PSI-basierter Biohybriden in den Biotechnologien der Zukunft.In this thesis, different strategies for coupling of the natural complex photosystem I from the cyanobacterium Thermosynechococcus elongatus with different electrode surfaces, and the interaction of PSI with nanomaterials and enzymes has been investigated. First, it was shown that immobilization of PSI on modified multi-walled carbon nanotubes (MWNT) leads to a functional photobiohybrid electrode. Here, PSI has been electrically wired to the electrode via a redox-active protein, cytochrome c (cyt c). The system (PSI-cyt c) has been scaled up to the three-dimensional surface of a metal-oxide, indium tin oxide (ITO). Here, additionally the high transparency property of this material has been exploited. The new preparation procedure of such transparent electrodes has been optimized in order to achieve high pohotocurrents. Furthermore, a new method of electric wiring of the PSI with the electrode has been established. Here, fullerenes have been employed. The high molecular efficiency of such a system proves that fullerenes are more effective wiring agents between the PSI and the electrode as compared to the cyt c. Additionally, in this thesis the photocatalytic property of the PSI has been combined with the biocatalytic property of the enzyme human sulphite oxidase, hSOx. Here, the enzyme has been employed as an alternative electron supplier for PSI. The third protein, cyt c, acted as an electric wiring agent and ensured electric communication between both catalytic proteins of the system and the electrode. The versatility of the PSI as well as its communication with anorganic nanomaterials and biological molecules, e.g. such as enzymes, shows a great potential for use of PSI-based biohybrids in the future biotechnological applications.
23
Akrobetu, Richard K. "The Interplay of Surface Adsorbates and Cationic Intermixing in the 2D Electron Gas Properties of LAO-STO Heterointerfaces." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1491575404930072.
24
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.
Анотація:
Les piles à combustible à membrane échangeuse de protons sont des dispositifs de conversion de l’énergie propre et efficace. Les gammes de puissance accessibles permettent leur utilisation dans le domaine de transport et des applications stationnaires. Il existe deux verrous technologiques à lever pour le déploiement de la cathode:i) Diminution de la quantité de platine dans le catalyseur.ii) l'amélioration de la stabilité du support de catalyseur à haut potentiel. Dans ce travail, nous présentons deux stratégies qui permettent de faire face à ces problématiques et améliorer les performances et la durabilité des cathodes: développer de nouveaux électrocatalyseurs à très faible quantité de platine et des supports à base de matériaux résistants à la corrosion.Afin de réduire la quantité de platine dans le catalyseur, nous avons développé des nanostructures fines de platine, qui permettent une exploitation électrocatalytique maximale et une quantité minimale de métal noble. Pour atteindre cet objectif, nous avons utilisé une méthode électrochimique basée sur le dépôt sous potentiel et le déplacement galvanique. Les nanostructures fines déposées sur le substrat modèle ont été caractérisées électrochimiquement ainsi que par des techniques microscopiques et d'analyse élémentaire.Pour réaliser un support résistant à la corrosion, notre approche a consisté en le remplacement du carbone noir conventionnel par un matériau conducteur d’oxyde d'étain dopé. Les matériaux à base de SnO2 ont démontré leur efficacité comme support électrochimique stable mais également efficace pour la réaction de réduction de l'oxygène. Dans cette étude, l’oxyde d’étain dopé au tantale a été préparé par électrofilage suivi d'une étape de calcination, permettent ainsi d’obtenir des fibres de morphologie tubulaires. Ces fibres ont été utilisées comme support de nanoparticules de platine préparées par la méthode de polyol assistée par micro-ondes, puis caractérisées pour leurs propriétés physico-chimiques et électrocatalytiques. En particulier, la stabilité aux cyclage en potentiel a été évaluée par analyse électrochimique ex situ. La possibilité d’associer l'électrocatalyseur à surface étendue avec les supports résistants à la corrosion pour obtenir des cathodes actives et durables est en coursProton 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
25
Huang, Yinjuan, Rui Yuan, Fugui Xu, Yiyong Mai, Xinliang Feng, and Deyue Yan. "Ultra-large sheet formation by 1D to 2D hierarchical self-assembly of a “rod–coil” graft copolymer with a polyphenylene backbone." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-225638.
Анотація:
This communication reports a unique ultra-large sheet formation through hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone and flexible poly(ethylene oxide) (PEO) side chains. The hierarchical self-assembly process involved a distinctive morphological transition of 1D helical to 2D superstructures. The graft copolymer offers a new chance for the challenging bottom-up fabrication of ultra-large self-assembled nanosheets in solution, as well as a novel system for fundamental studies on 2D self-assembly of polymers.
26
Huang, Yinjuan, Rui Yuan, Fugui Xu, Yiyong Mai, Xinliang Feng, and Deyue Yan. "Ultra-large sheet formation by 1D to 2D hierarchical self-assembly of a “rod–coil” graft copolymer with a polyphenylene backbone." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A30347.
Анотація:
This communication reports a unique ultra-large sheet formation through hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone and flexible poly(ethylene oxide) (PEO) side chains. The hierarchical self-assembly process involved a distinctive morphological transition of 1D helical to 2D superstructures. The graft copolymer offers a new chance for the challenging bottom-up fabrication of ultra-large self-assembled nanosheets in solution, as well as a novel system for fundamental studies on 2D self-assembly of polymers.
27
Gut, Stephan [Verfasser], Christoph [Akademischer Betreuer] Alexiou, Christoph [Gutachter] Alexiou, and Diana [Gutachter] Dudziak. "Cellular effects of paclitaxel-loaded iron oxide nanoparticles on breast cancer using different 2D and 3D cell culture models / Stephan Gut ; Gutachter: Christoph Alexiou, Diana Dudziak ; Betreuer: Christoph Alexiou." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2021. http://d-nb.info/1241827273/34.
28
Lee, Veronica. "A Combined Theoretical and Experimental Study on Deposition of Solid State Materials." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1707299/.
Анотація:
Deposition of solid state materials span a wide variety of methods and often utilize high energy sources such as plasmas and ultra-violet light resulting in a wide variety of characteristics and applications. A fundamental understanding is essential for furthering the applications of these materials which include catalysis, molecular filtration, electronics, sensing devices, and energy storage among others. A combination of experimental and theoretical work is presented here on several materials including 2D silicates on Pd, boron oxide, and vanadium oxynitride. Silicate formation under low energy electron microscopy demonstrate film permeability to oxygen, while ab initio molecular dynamics simulations reveal the possible initial mechanisms associated with the formation of boron oxide films during atomic layer deposition. Lastly, vanadium oxynitrides have shown preferential sputtering of N over O sites and theoretical binding energies serve as a guide for assigning experimental x-ray photoelectron spectra.
29
Chicot, Gauthier. "Effet de champs dans le diamant dopé au bore." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-01062250.
Анотація:
Alors que la demande en électronique haute puissance et haute fréquence ne fait qu'augmenter, les semi-conducteurs classiques montrent leurs limites. Des approches basées soit sur des nouvelles architectures ou sur des matériaux à large bande interdite devraient permettre de les dépasser. Le diamant, avec ses propriétés exceptionnelles, semble être le semi-conducteur ultime pour répondre à ces attentes. Néanmoins, il souffre aussi de certaines limitations, en particulier d'une forte énergie d'ionisation du dopant de type p (bore) qui se traduit par une faible concentration de porteurs libres à la température ambiante. Des solutions innovantes s'appuyant sur un gaz 2D et /ou l'effet de champ ont été imaginées pour résoudre ce problème. Ce travail est axé sur deux de ces solutions : i) le diamant delta dopé au bore qui consiste en une couche fortement dopée entre deux couches intrinsèques, afin d'obtenir une conduction combinant une grande mobilité avec une grande concentration de porteurs et ii) le transistor à effet de champ métal oxide semiconducteur( MOSFET ), où l'état " on " et l'état " off " du canal sont obtenus grâce au contrôle électrostatique de la courbure de bandes à l' interface de diamant/oxyde. Pour ces deux structures, beaucoup de défis technologiques doivent être surmontés avant de pouvoir fabriquer un transistor. La dépendance en température de la densité surfacique de trous et de la mobilité de plusieurs couche de diamant delta dopées au bore a été étudiée expérimentalement et théoriquement sur une large gamme de température (6 K
30
Pezzotti, Simone. "DFT-MD simulations and theoretical SFG spectroscopy to characterize H-Bonded networks at aqueous interfaces : from hydrophobic to hydrophilic environments Structural definition of the BIL and DL: a new universal methodology to rationalize non-linear χ(2)(ω) SFG signals at charged interfaces, including χ(3)(ω) contributions What the Diffuse Layer (DL) Reveals in Non-Linear SFG Spectroscopy 2D H-Bond Network as the Topmost Skin to the Air-Water Interface Combining ab-initio and classical molecular dynamics simulations to unravel the structure of the 2D-HB-network at the air-water interface 2D-HB-Network at the air-water interface: A structural and dynamical characterization by means of ab initio and classical molecular dynamics simulations Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface Molecular hydrophobicity at a macroscopically hydrophilic surface Graph theory for automatic structural recognition in molecular dynamics simulations DFT-MD of the (110)-Co3O4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLE008.
Анотація:
Améliorer notre connaissance de la structure de l'eau dans l'environnement spécial offert par une interface est essentiel pour la compréhension de nombreux phénomènes naturels et applications technologiques. Pour révéler cette structure interfaciale de l'eau, des techniques capables de fournir des informations microscopiques, de manière sélective, pour cette couche interfaciale (BIL) sont nécessaires. Dans le présent travail de thèse, nous avons donc étudié les interfaces aqueuses au niveau moléculaire, en couplant la modélisation théorique à partir de simulations DFT-MD avec les spectroscopies SFG et THz-IR. En développant de nouveaux protocoles/outils d'investigation associant simulations DFT-MD et spectroscopie SFG, en particulier pour la rationalisation plus complexe des interfaces chargées, nous avons fourni une compréhension globale de l'effet des conditions interfaciales d'hydrophilicité, de pH, de force ionique sur le réseau des liaisons-H formé dans la couche interfaciale BIL, sur ses signatures spectroscopiques et sur son impact sur les propriétés physico-chimiques. Nous avons montré pour la première fois que, dans des conditions suffisamment hydrophobes, l'eau interfaciale crée des réseaux des liaisons-H bidimensionnels, révélé expérimentalement par les spectres THz-IR. Le réseau-2D dicte la dynamique de l'eau interfaciale, le potentiel de surface, l'acidité de surface, la tension superficielle et la thermodynamique d'hydratation des solutés hydrophobes. Cet "ordre horizontal" aux interfaces hydrophobes est opposé à "l'ordre verticale" obtenu aux interfaces hydrophiles. Nous avons aussi révélé comment les ions et les conditions de pH modifient ces arrangements structurauxImproving our knowledge on water H-Bonded networks formed in the special environment offered by an interface is pivotal for our understanding of many natural phenomena and technological applications. To reveal the interfacial water arrangement, techniques able to provide detailed microscopic information selectively for the interfacial layer are required. In the present thesis work, we have hence investigated aqueous interfaces at the molecular level, by coupling theoretical modeling from DFT-MD simulations with SFG & THz-IR spectroscopies. By developing new investigation protocols/tools, coupling DFT-MD simulations and SFG spectroscopy, in particular for the more complex rationalization of charged interfaces, we have provided a global comprehension of the effect of various interfacial conditions (hydrophilicity, pH, ionic strength) on the HB-Network formed in the interfacial layer (BIL), on its spectroscopic signatures and on its impact on physico-chemical properties. We have shown for the first time that, in sufficiently hydrophobic conditions, BIL interfacial water creates special 2-Dimensional HB-Networks, experimentally revealed by one specific THz-IR marker band. Such 2D-network dictates HBs and orientational dynamics of interfacial water, surface potential, surface acidity, water surface tension and thermodynamics of hydration of hydrophobic solutes. Such "horizontal ordering” of water at hydrophobic interfaces is found opposite to the “vertical ordering” of water at hydrophilic interfaces, while coexistence of the two orders leads to disordered interfacial water in intermediate hydrophilic/hydrophobic conditions. Both DFT-MD and SFG further revealed how ions & pH conditions alter these BIL-water orders
31
Das, Ranjan. "Optoelectronic and Magnetic Properties of 2D Layered Organic-Inorganic Hybrids and Selected Transition Metal Oxides." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/6164.
Анотація:
Perovskites with the general chemical formula ABX3 can be categorized into oxides and halides depending on the nature of the X anion. 3D organic-inorganic halide perovskites are extensively studied in the context of solar cell and photo- and electro-luminescence applications due to their outstanding optoelectronic properties, while oxide perovskites have attracted a great deal of attention for their many interesting physical properties such as structural, electrical, magnetic, and magnetocaloric effects. More recently, 2D layered organic-inorganic hybrid (OIH) materials have emerged as a new class of materials with rich optoelectronic properties. They exhibit proven advantages over their 3D counterparts due to their large structural diversity and improved environmental stability against heat and moisture.
2D OIH materials have exhibited many interesting physical properties such as high exciton binding energies, intense photoluminescence, ferroelectricity, and chiro-optical properties. While the Lead-based hybrid perovskites have been very well studied for their spectacular optoelectronic properties, lately there have been attempts to design new materials such as Cd2+, Cu2+, Sn2+ -based hybrid halide materials which offer a new playground in the field of photovoltaic research. The work reported in this thesis explores the ferroelectric properties of Cd2+ - and Cu2+ -based halide materials and discusses the possible microscopic mechanisms for the origin of ferroelectricity in these materials. Further, using experimental and theoretical inputs, it is shown that the Cu2+ -based hybrid materials have outstanding chiro-optical properties. In addition, we also explore the interesting magnetic properties of a few transition metal compounds, exhibiting inverse magnetocaloric effect as well as Griffiths phase in some temperature ranges.
Chapter 1 briefly introduces various concepts relevant to the investigations reported in subsequent chapters of this thesis. The present status of the research in the field of 2D organic- inorganic hybrid materials with an emphasis on various exciting properties such as ferroelectricity, bandgap modulation, and chiro-optical properties has been discussed. This chapter also presents discussions relevant to the family of oxide perovskites with reference to
magnetic properties from fundamental and technological standpoints.
Chapter 2 describes different experimental and theoretical methods that were employed to carry out the studies presented in this thesis.
Chapter 3 presents a detailed study of the successive structural phase transitions of BA2CdCl4. These results establish that these structural phase transitions are associated with intrinsic ferroelectric transitions, from room temperature paraelectric to intermediate temperature ferroelectric, followed by another low-temperature ferroelectric phase. It was widely believed that ferroelectricity in these 2D organic-inorganic hybrid materials originated due to the order-disorder transition of molecular dipoles associated with the organic spacer cations. However, results in this thesis show that there are dipoles also associated with the inorganic components due to local structural distortions. The thesis presents a combination of experimental and theoretical results suggesting that the dipoles associated with the organic spacers and the dipoles originating from these local structural distortions within the inorganic units both play significant roles in the observed ferroelectricity of BA2CdCl4.
Chapter 4 deals with the chiro-optical properties of quasi 2D (R-/S-MBA)2CuBr4 hybrid material. We discussed the role of chiral organic amine cations on the optical properties of these hybrid materials. Few Lead based compounds and one copper-based sample show giant chiro-optical properties but these are chirally active only for wavelengths < 490nm, limited by their large bandgaps. (R-/S-MBA)2CuBr4 shows a relatively large chiro-optical property in the orange-red part of the visible spectrum. Structural analyses of these compounds show that these are made of alternating layers of the chiral organic units and an inorganic layer of isolated CuBr4 units. Such isolated inorganic units distinguish this class of compounds from the more intensely investigated hybrid lead halide systems where the basic PbX6 (X = Cl, Br, or I) units
are linked together by corner sharing of the halide ions, making them intrinsically 2D systems. The present Cu-based system would have qualified as a 0D system but for the Cu-Br….Br-Cu interactions that allow the separated CuBr4 units to interact, making the system a quasi-2D system. This subtle structural aspect plays an important role in giving this system remarkable chiro-optical properties. The semi-isolation of the CuBr4 units allows them to be rotated along
the 21 screw-axis by the chiral organic units via strong hydrogen bonding, thereby imparting the giant chirality to the entire hybrid system. Simultaneously, the connectivity of the CuBr4 units via Br…Br interactions imparts a quasi-2D character helping to achieve a broadband absorption, thereby extending the chiro-optical properties to longer wavelengths.
Chapter 5 discusses tuning of the bandgap while retaining ferroelectricity through halide substitution in Cu2+ -based chiral 2D hybrid materials to obtain small bandgap ferroelectric materials. Search for such small bandgap ferroelectric materials has been popular in the literature, not only because most ferroelectrics tend to have large bandgaps but also because of their obvious applications in solar photovoltaics. The ferroelectric Lead-based hybrid perovskites have been very well studied for their rich optoelectronic properties that are relevant in photovoltaic applications, but all are having a relatively higher bandgap. We have lowered the ligand to metal charge transfer bandgap from ~2.53 to 2.09 eV while retaining ferroelectricity in a copper chloride based low-dimensional hybrid material through partial substitution of chlorine with bromine. Our results show that a complete substitution of Cl- by Br- leads to a bandgap of ~1.62 eV with a loss of the ferroelectric state in the pure bromide material.
Chapter 6 discusses the low temperature magnetic state along with the main ferromagnetic ordering at ~200 K and the magnetocaloric effect of double perovskite, Nd2NiMnO6. An earlier study on this compound established that for any applied magnetic field lower than 3 T, these samples show a downturn in M(T), and any field higher than 3 T, shows an upturn in M(T) for the temperature range below 100 K. This has been interpreted as Nd moments experience an effective ~3 T internal magnetic field due to the presence of the ordered Ni-Mn ferromagnetic sublattices. This indicates that the low temperature magnetic state of this compound is easily influenced by an externally applied magnetic field in the tune of 3 T, suggesting possible interesting magnetocaloric effects in this material. This chapter presents a detailed study of the magnetocaloric properties of Nd2NiMnO6. Interestingly, it shows a significant inverse magnetocaloric effect (IMCE) at low temperatures (T < 50 K) together with a significant conventional magnetocaloric effect (CMCE) at the ferromagnetic ordering temperature (Tc ~200 K). IMCE and CMCE correspond to the antiferromagnetic arrangement of Nd and Ni–Mn sublattices and ferromagnetic ordering of Ni–Mn sublattices, respectively. Nd2NiMnO6 with its second order phase transition follows the universal behavior of magnetic entropy change, ΔSM(T); it also shows a power law dependency on the magnetic field as ΔSM ∝ 𝐻𝜂.
Chapter 7 deals with Griffiths phase-like magnetic anomalies in disordered La0.85Sr0.15CoO3 induced by chemical doping. In earlier studies on doped LaCoO3 with doping concentration higher than the percolation threshold (18%) shows non-Griffiths phase-like behavior. But no reports are available for the composition just below the percolation limit in this context. So, we chose the 15% doping concentration and explored its magnetic properties carefully. Our results
establish that this composition shows typical Griffiths phase-like behavior in the intermediate temperature range and followed by spin glass behavior below 60 K. The existence of nanoscale ferromagnetic clusters below 240 K contributes to the total magnetization of the system for low applied magnetic fields resulting in a downturn of the χ-1 vs. T plot. The extent of this downturn is strongly suppressed by increasing the dc applied magnetic field, a typical signature of
Griffiths phase.
In the appendix, we present results of investigating Cs- and Na-doped WO3 exhibiting strong absorption in the near-infrared (NIR) and transmittivity in the visible range. Despite several publications, there is a lack of agreement in the community on the origin of this strong optical absorption with competing claims of polaronic and plasmonic origins. We address this controversy by first investigating bulk samples that are relatively free of complications arising from any shape anisotropy; we show by combining experimental and theoretical results that all spectral features in both bulk and nanoparticle samples are consistent with plasmonic excitations, without any need to invoke a polaronic mechanism. Doped WO3 exhibits strong optical absorption primarily due to surface plasmon resonances in colloidal nanoparticles,
while their bulk counterparts are dominated by bulk plasmonic features. Investigating systems with different crystal structures and charge doping levels, we established that the complex spectral features of these plasmonic absorption bands for both bulk and nano samples are dominated by the underlying structure-dependent anisotropic electronic properties that determine the plasmonic features
32
Pärschke, Ekaterina. "Interplay of Strong Correlation, Spin-Orbit Coupling and Electron-Phonon Interactions in Quasi-2D Iridium Oxides." Doctoral thesis, 2017. https://tud.qucosa.de/id/qucosa%3A30957.
Анотація:
In the last decade, a large number of studies have been devoted to the peculiarities of correlated physics found in the quasi-two-dimensional square lattice iridium oxides. It was shown that this 5d family of transition metal oxides has strong structural and electronic similarities to the famous 3d family of copper oxides. Moreover, a delicate interplay of on-site spin-orbit coupling, Coulomb repulsion and crystalline electric field interactions is expected to drive various exotic quantum states. Many theoretical proposals were made in the last decade including the prediction of possible superconductivity in square-lattice iridates emerging as a sister system to high-Tc cuprates, which however met only limited experimental confirmation. One can, therefore, raise a general question: To what extent is the low-energy physics of the quasi-two-dimensional square-lattice iridium oxides different from other transition metal oxides including cuprates? In this thesis we investigate some of the effects which are usually neglected in studies on iridates, focusing on quasi-two-dimensional square-lattice iridates such as Sr2IrO4 or Ba2IrO4. In particular, we discuss the role of the electron-phonon coupling in the form of Jahn-Teller interaction, electron-hole asymmetry introduced by the strong correlations and some effects of coupling scheme chosen to calculate multiplet structure for materials with strong on-site spin-orbit coupling.
Thus, firstly, we study the role of phonons, which is almost always neglected in Sr2IrO4, and discuss the manifestation of Jahn-Teller effect in the recent data obtained on Sr2IrO4 with the help of resonant inelastic x-ray scattering. When strong spin-orbit coupling removes orbital degeneracy, it would at the same time appear to render the Jahn-Teller mechanism ineffective. We show that, while the Jahn-Teller effect does indeed not affect the antiferromagnetically ordered ground state, it leads to distinctive signatures in the spin-orbit exciton.
Second, we focus on charge excitations and determine the motion of a charge (hole or electron) added to the Mott insulating, antiferromagnetic ground-state of square-lattice iridates. We show that correlation effects, calculated within the self-consistent Born approximation, render the hole and electron case very different. An added electron forms a spin-polaron, which closely resembles the well-known cuprates, but the situation of a removed electron is far more complex. Many-body configurations form that can be either singlets and triplets, which strongly affects the hole motion. This not only has important ramifications for the interpretation of angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy experiments of square lattice iridates, but also demonstrates that the correlation physics in electron- and hole-doped iridates is fundamentally different.
We then discuss the application of this model to the calculation of scanning tunneling spectroscopy data. We show that using scanning tunneling spectroscopy one can directly probe the quasiparticle excitations in Sr2IrO4: ladder spectrum on the positive bias side and multiplet structure of the polaron on the negative bias side. We discuss in detail the ladder spectrum and show its relevance for Sr2IrO4 which is in general described by more complicated extended t-J -like model. Theoretical calculation reveals that on the negative bias side the internal degree of freedom of the charge excitation introduces strong dispersive hopping channels encaving ladder-like features.
Finally, we discuss how the choice of the coupling scheme to calculate multiplet structure can affect the theoretical calculation of angle-resolved photoemission spectroscopy and scanning tunnelling spectroscopy spectral functions.
33
Treske, Uwe. "Valence changes at interfaces and surfaces investigated by X-ray spectroscopy." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A28574.
Анотація:
In this thesis valence changes at interfaces and surfaces of 3d and 4f systems are investigated by X-ray spectroscopy, in particular X-ray photoemission (XPS), X-ray absorption (XAS) and resonant photoemission spectroscopy (ResPES). The first part addresses the electronic properties of the oxides LaAlO3, LaGaO3 and NdGaO3 grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals along (001)-direction. These polar/non-polar oxide interfaces share an insulator to metal phase transition as a function of overlayer thickness including the formation of an interfacial two dimensional electron gas. The nature of the charge carriers, their concentration and spatial distribution, and the band alignment near the interface are studied in a comparative manner and evaluated quantitatively. Irrespective of the different overlayer lattice constants and bandgaps, all the heterostructures behave similarly. Rising Ti3+ concentration is monitored by Ti 2p XPS, Ti L-edge XAS and by resonantly enhanced Ti 3d excitations in the vicinity of EF (ResPES) when the layer number n increases. This indicates that the active material is in all cases a near interface SrTiO3 layer of 4nm thickness.
Band bending in SrTiO3 occurs but no electric field is detected inside the polar overlayers. Essential aspects of the findings are captured by scenarios where the polar forces are alleviated by surface defect creation or the separation of photon generated electron-hole pairs in addition to the electronic reconstruction at n = 4 unit cells layer thickness.
Furthermore, deviations from an abrupt interface are found by soft X-ray photoemission spectroscopy which may affect the interface properties. The surface sensitivity of the measurements has been tuned by varying photon energy and emission angle. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From a quantitative analysis it is concluded that during the growth process a small amount of Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.
In the second part of this thesis the heavy fermion superconductors CeMIn5 (M = Co, Rh, Ir) are investigated by temperature- and angle-dependent XPS. In this material class the subtle interplay between localized Ce 4f and itinerant valence electrons dominate the electronic properties. The Ce 3d core level has a very similar shape for all three materials and is indicative of weak f-hybridization. The spectra are analyzed using a simplified version of the Anderson impurity model, which yields a Ce 4f occupancy that is larger than 0.9. The temperature dependence shows a continuous, irreversible and exclusive broadening of the Ce 3d peaks, due to oxidation of Ce at the surface.In der vorliegenden Dissertation werden Valenzänderungen an Grenzflächen und Oberflächen mittels Verfahren der Röntgenspektroskopie untersucht, zu denen die Röntgenphotoelektronen- (XPS), die Röntgenabsorptions- (XAS) und die resonante Photoelektronenspektroskopie (ResPES) gehören. Kapitel 3 behandelt die elektronischen Eigenschaften der Oxide LaAlO3, LaGaO3 und NdGaO3, welche mittels Laserdeposition (PLD) auf TiO2-terminierte SrTiO3 Einkristalle entlang (001)-Richtung gewachsen wurden. Diese polaren/nicht-polaren Oxidgrenzflächen weisen einen Isolator-Metall Phasenübergang als Funktion der Schichtdicke auf, bei dem sich ein zwei dimensionales Elektronengas an der Grenzfläche bildet. Die Eigenschaften dieser Ladungsträger, deren Konzentration und räumliche Ausdehnung, sowie der Verlauf der Energiebänder an der Grenzfläche werden vergleichend untersucht und quantitativ bestimmt. Es wird gezeigt, dass sich die drei untersuchten Grenzflächen, trotz unterschiedlicher Gitterkonstanten und Energiebandlücken, ähnlich verhalten. Das mit der Schichtdicke ansteigende Ti3+ Signal wird im Ti 2p XPS, Ti L-Kante XAS und durch die resonant verstärkten Ti 3d Anregungen nahe EF (ResPES) nachgewiesen. Daraus lässt sich schlussfolgern, dass in allen Fällen eine SrTiO3 Schicht mit einer Dicke von 4nm der eigentlich aktive Bereich ist. Im SrTiO3 tritt eine Bandverbiegung auf, ein elektrisches Feld in der polaren Deckschicht kann jedoch nicht nachgewiesen werden. Grundlegende Aspekte dieser Ergebnisse sind in einem Szenario vereinbar, bei dem die polaren Kräfte durch die Entstehung von Oberflächendefekten, durch die Trennung von photoneninduzierten Elektronen-Lochpaaren und durch eine elektronische Umordnung bei 4 uc Schichtdicke eliminiert werden. Des Weiteren werden Abweichungen von einer abrupten Grenzfläche mittels weich-Röntgenphotoelektronenspektroskopie festgestellt, die die Grenzflächeneigenschaften beeinflussen können. Für oberflächenempfindlichere Messbedingungen zeigt die Sr 3d Anregung, im Gegensatz zu Rumpfniveaus anderer Elemente, eine unerwartete Aufspaltung, was nur durch das Vorhandensein einer zweiten chemischen Strontiumkomponente zu erklären ist. Aus quantitativen Betrachtungen lässt sich schließen, dass einige Strontiumatome während des Wachstums an die Oberfläche diffundieren und möglicherweise Strontiumoxid gebildet wird. Der zweite Schwerpunkt der vorliegenden Arbeit ist die Untersuchung von Schwer-Fermionen Supraleitern CeMIn5 (M = Co, Rh, Ir) mittels temperatur- und winkelabhängiger XPS. Bei dieser Materialklasse dominiert das feine Zusammenspiel zwischen lokalisierten Ce 4f und frei beweglichen Leitungselektronen die elektronischen Eigenschaften. Das Ce 3d Rumpfniveauspektrum besitzt für die drei Materialien eine sehr ähnliche Form, die auf eine schwache f-Hybridisierung schließen lässt. Die Spektren werden mittels einer vereinfachten Version des Anderson-Impurity Modells analysiert, wobei sich eine Ce 4f Besetzung von mehr als 0,9 ergibt. Die Temperaturabhängigkeit zeigt eine kontinuierliche und irreversible Verbreiterung ausschließlich für die Ce 3d Anregung, dieser Umstand kann einer Oxidation der reaktiven Ceratome an der Oberfläche zugeordnet werden.
34
Sahoo, Anindita. "Electrical Transport in the Hybrid Structures of 2D Van Der Waals Materials and Perovskite Oxide." Thesis, 2016. http://etd.iisc.ac.in/handle/2005/2948.
Анотація:
Perovskite oxides have provided a wide variety of exotic functionalities based on their unique physical and chemical properties. By combining different perovskite oxides, interesting physical phenomena have been observed at the interfaces of perovskite heterostructures. The most interesting among these phenomena is the formation of two dimensional electron gas at the interface of two perovskite materials SrTiO3 and LaAlO3 which led to a number of fascinating physical properties such as metal-insulator transition, super-conductivity, large negative magnetoresistance and so on. This has raised the interest in exploiting the interface of various hybrids structures built on the perovskite oxide backbone. On the other hand, the two dimensional (2D) van der Waals materials such as graphene, MoS2, boron nitride etc. represent a new paradigm in the 2D electron-ics. The functionalities of these individual materials have been combined to obtain new enriched functionalities by stacking different materials together forming van der Waals heterostructures. In this work, we present a detailed study of the interface in hybrid structures made of vander Waals materials (graphene and MoS2) and their hybrids with a perovskite material namely, SrTiO3 which is known as the building block of complex oxide heterostructures.
In graphene-MoS2 vertical heterostructure, we have carried out a detailed set of investigations on the modulation of the Schottky barrier at the graphene-MoS2 interface with varying external electric field. By using different stacking sequences and device structures, we obtained high mobility at large current on-off ratio at room temperature along with a tunable Schottky barrier which can be varied as high as ∼ 0.4 eV by applying electric field. We also explored the interface of graphene and SrTiO3 as well as MoS2 and SrTiO3 by electrical transport and low frequency 1/f noise measurements. We observed a hysteretic feature in the transfer characteristics of dual gated graphene and MoS2 field effect transistors on SrTiO3. The dual gated geometry enabled us to measure the effective capacitance of SrTiO3 interface which showed an enhancement indicating the possible existence of negative capacitance developed by the surface dipoles at the interface of SrTiO3 and the graphene or MoS2 channel. Our 1/f noise study and the analysis of higher order statistics of noise also support the possibility of electric field-driven reorient able surface dipoles at the interface.
35
Sahoo, Anindita. "Electrical Transport in the Hybrid Structures of 2D Van Der Waals Materials and Perovskite Oxide." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2948.
Анотація:
Perovskite oxides have provided a wide variety of exotic functionalities based on their unique physical and chemical properties. By combining different perovskite oxides, interesting physical phenomena have been observed at the interfaces of perovskite heterostructures. The most interesting among these phenomena is the formation of two dimensional electron gas at the interface of two perovskite materials SrTiO3 and LaAlO3 which led to a number of fascinating physical properties such as metal-insulator transition, super-conductivity, large negative magnetoresistance and so on. This has raised the interest in exploiting the interface of various hybrids structures built on the perovskite oxide backbone. On the other hand, the two dimensional (2D) van der Waals materials such as graphene, MoS2, boron nitride etc. represent a new paradigm in the 2D electron-ics. The functionalities of these individual materials have been combined to obtain new enriched functionalities by stacking different materials together forming van der Waals heterostructures. In this work, we present a detailed study of the interface in hybrid structures made of vander Waals materials (graphene and MoS2) and their hybrids with a perovskite material namely, SrTiO3 which is known as the building block of complex oxide heterostructures.
In graphene-MoS2 vertical heterostructure, we have carried out a detailed set of investigations on the modulation of the Schottky barrier at the graphene-MoS2 interface with varying external electric field. By using different stacking sequences and device structures, we obtained high mobility at large current on-off ratio at room temperature along with a tunable Schottky barrier which can be varied as high as ∼ 0.4 eV by applying electric field. We also explored the interface of graphene and SrTiO3 as well as MoS2 and SrTiO3 by electrical transport and low frequency 1/f noise measurements. We observed a hysteretic feature in the transfer characteristics of dual gated graphene and MoS2 field effect transistors on SrTiO3. The dual gated geometry enabled us to measure the effective capacitance of SrTiO3 interface which showed an enhancement indicating the possible existence of negative capacitance developed by the surface dipoles at the interface of SrTiO3 and the graphene or MoS2 channel. Our 1/f noise study and the analysis of higher order statistics of noise also support the possibility of electric field-driven reorient able surface dipoles at the interface.
36
PAN, JIAN-ZONG, and 潘建宗. "Preparation of 2D Surfactant with Graphene Oxide (GO)." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/33254787113617713250.
37
Chen, Ruei-Shiang, and 陳瑞祥. "2D/3D CFD Simulation of Metal Oxide Chemical Vapor Deposition (MOCVD) of GaN." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/18622910568436707550.
Анотація:
碩士國立交通大學
機械工程學系
99
Metal organic chemical vapor deposition (MOCVD) process of GaN in the vertical reactor is studied by various computational fluid dynamics (CFD) simulations under 2D condition. First, with different pressure, figuring out that flow distribution at 100 Torr is stable. Second, we use CFD to analyze temperature distribution inside gap between wafer carrier and substrate, then adding metal film below substrate to process with different temperature. Third, discussing flow distribution stability on substrate with different rotation speed (100rpm-800rpm). Meanwhile, comparing flow influence for temperature at different height from inlet to substrate (16mm–31mm). Trough simulation, if Gr/Re2 number is below 0.5 under 100 Torr, 800 rpm, 1323K and 30,000 sccm condition, the flow distribution is stable. Finally, temperature difference for different height is 0.5K. After 2D simulation, I use 3D CFD simulations implement gas phase chemical reactions and surface chemical reactions for GaN growth from trimethylgallium, nitrogen and ammonia. By fixing condition of total flow rate 30,000 sccm, high speed rotation causes high nonuniformity and high growth rate. Growth Rates for 1,600 rpm rotation plane is twice than 100 rpm. With nonuniformity viewpoint, between 400 rpm and 1,500 rpm plane decreases below 5%. However, low rotation speed as 100 rpm will cause 16% high nonuniformity due to buoyancy influence. On the other hand, through study of flow rate control (7,500sccm–90,000sccm), it will cause different flow distribution and nonuniformity. Especially for ratio of buoyancy influence to plane inertia of momentum and inlet inertia of momentum (Gr/RewRe) discussion, high Gr/RewRe (0.64) will form Rotation–induced flow or vorticity on substrate. As a result, vorticity will caused 6%。In other word, low (Gr/RewRe) between 0.032 to 0.008 will keep stability flow distribution and control below 5%.
38
Wei, Joy, and 魏巧依. "Crystal orientation of conjugated polymer in the 2D confined space templated by anodic aluminum oxide nanochannels." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/51020599910853326882.
Анотація:
碩士國立清華大學
化學工程學系
104
The effect of spatial confinement on the structure and phase transition behavior of polymer has been a subject of extensive interest. This study is centered on resolving the preferred orientation of poly(3-hexylthiophene) (P3HT) crystallites formed within the 2D nanoconfined space of Anodic Aluminum Oxide Template (AAO) nanochannels. P3HT is a crystalline semiconduting polymer which has attracted significant attention due to its potential in the application as the active material for bulk heterojunction solar cell and organic field-effect transistors (OFETS). The opto-electronic properties of P3HT are expected to strongly depend on its degree of crystallinity and the gobal arrangement of the crystallites; therefore, controlling these two morphological paraemeters is important for tailoring the photophysical properties of the material. In this work, we incorporated P3HT into AAO nanochannels with the diameter of 20 and 100 nm and examined the crystal orientation within the channels as a function of the post treatment condition Tc by means of 2D wide angle X-ray diffraction patterns collected at BL01C2 and BL17A1 at the National Synchrotron Radiation Research Center (NSRRC). The P3HT crystallites predominantly adopted the edge-on orientation with the crystalline backbone aligning perpendicularly to the long axis of the cylindrical pores since this type of orientation was kinetically favored for the long range crystal growth along the channel axis. However, using AAO nanochannels with smaller diameter and an annealing or recrystallization treatment at 160˚C induced the formation of a small fraction of the face-on orientation. It was also found that the as-cast P3HT in the confined space with smaller pore size exhibited higher degree of crystallinity and better orientation. The samples prepared from the xylene solution generally possessed better orientation and higher crystallinity than those prepared from the THF solution. However, we found that melt recrystallization removed the nucleus in the samples, which hindered the crystal growth, resulting in a decrease in the degree of crystallinity.
39
Sousa, Ana Rita Lima de. "Development of graphene oxide based nanomaterials for cancer therapy." Master's thesis, 2018. http://hdl.handle.net/10400.6/9771.
Анотація:
Breast cancer is one of the leading causes of death in the world, affecting mostly women. The most common treatments for this disease include radio- and chemo-therapies. However, these therapeutic approaches have a sub-optimal efficacy and can induce adverse side effects to patients. In this way, there is an urgent demand for the development of novel breast cancer treatments.
To improve the breast cancer treatment, researchers are developing new therapeutic approaches. In particular, photothermal therapy (PTT) mediated by nanomaterials has captured the attention of researchers and clinicians. This type of therapy takes advantage from the physicochemical and optical properties of some light-responsive nanostructures. These can accumulate preferentially in the tumor zone, and induce, after external irradiation with near infrared (NIR) light, a temperature increase that can damage cancer cells.
In this thesis, reduced graphene oxide (rGO) was produced by using an environmentally-friendly method. Then rGO was functionalized with a novel hyaluronic acid (HA)-based amphiphilic polymer to be applied in targeted breast cancer PTT. HA was selected due to its hydrophilic character and targeting capacity to the CD44 receptors, which are overexpressed on breast cancer cells’ membrane. The obtained results revealed that the treatment of graphene oxide with L-ascorbic acid (3 mM) for 60 minutes at 80 °C is ideal considering the NIR absorption and the size distribution of the obtained materials. Then, rGO was functionalized with the HA-based amphiphilic polymer through non-covalent interactions. The functionalization of rGO improved its stability, cytocompatibility, and internalization by CD44 overexpressed by breast cancer cells, which indicates the targeting capacity of this nanoformulation. Furthermore, the on-demand PTT mediated by HA functionalized rGO induced cancer cells’ death, thereby confirming the potential of this nanoformulation for targeted breast cancer therapy.O cancro da mama é uma das principais causas de morte em todo o mundo, afetando principalmente as mulheres. Os tratamentos mais comuns para esta doença incluem a radioterapia e a quimioterapia. No entanto, estas abordagens terapêuticas apresentam uma baixa eficácia e podem, também, induzir efeitos secundários adversos nos pacientes. Desta forma, existe uma enorme necessidade em desenvolver novos tratamentos mais eficazes para o cancro da mama. Neste contexto, diferentes investigadores estão a desenvolver novas abordagens terapêuticas. Em particular, a terapia fototérmica mediada por nanomateriais tem recebido um interesse crescente por parte dos investigadores e profissionais de saúde. Esta abordagem tira partido das propriedades físico-químicas e óticas de alguns tipos de nanomateriais. Estas nanoestruturas responsivas à luz conseguem acumular-se preferencialmente na zona tumoral e posteriormente induzir, após irradiação com luz com um comprimento de onda na região do infravermelho próximo (NIR), um aumento de temperatura que pode danificar as células cancerígenas. Nesta dissertação, materiais à base de óxido de grafeno reduzido (rGO) foram produzidos através de um método de redução ecológico e funcionalizados com um novo polímero anfifílico à base de ácido hialurónico (HA) para aplicação na terapia fototérmica do cancro da mama. O HA foi escolhido devido ao seu carácter hidrofílico e por possuir capacidade de direcionamento para os recetores CD44, que são sobreexpressos na membrana citoplasmática das células do cancro da mama. Os resultados obtidos revelaram que o tratamento do óxido de grafeno com ácido L-ascórbico (3 mM), durante 60 minutos, a 80 ºC, constituem as condições ideais de redução tendo em conta a absorção no NIR apresentada pelo rGO e a distribuição de tamanhos dos materiais obtidos. Posteriormente, a funcionalização do rGO com o polímero anfifílico à base de HA foi efetuada através de interações não-covalentes. A funcionalização melhorou a estabilidade, citocompatibilidade e internalização dos nanomateriais pelas células do cancro da mama que sobreexpressam o recetor CD44, o que confirma a capacidade de direcionamento desta nanoformulação. Adicionalmente, a terapia fototérmica mediada pelo rGO funcionalizado induziu a morte das células cancerígenas, confirmando assim o potencial desta nanoformulação para aplicação na terapia direcionada do cancro da mama.
40
Yu, Shang-Yu, and 游尚祐. "2D & 3D structuration of solution-based metal oxide precursor via photolithography and its optical/electrical application." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/u5f674.
41
Brahma, Madhuchhanda. "Multiscale Modeling of Quantum Transport in 2D Material Based MoS Transistors." Thesis, 2019. https://etd.iisc.ac.in/handle/2005/5133.
Анотація:
Atomically thin 2D materials have ushered in a new era in the fi eld of nano-science and tech-
nology and have been translated to notable advancements in the design of sensors, optoelectronic
devices, exible electronics. These atomically thin materials are predicted to replace conven-
tional bulk materials, Si and Ge, for transistor channels and extend the complementary metal
oxide semiconductor technology road-map beyond the deca-nanometer regime. Constant efforts
are being made to fabricate devices based on some of the recently discovered van der Waal's
materials such as graphene, hexagonal boron nitride, MoS2, phosphorene. Apart from these, a
large number of novel 2D materials and their derivatives are being constantly explored through
both experiments and density functional theory analysis. In order to narrow down the mate-
rial and design selection space for time- and cost-heavy experimental device fabrication, atomic
level density functional theory (DFT) calculations need to be coupled with device-level physics
models. Thus, we propose a multiscale computational framework bridging first principles based
DFT calculations with device physics simulations. Under this framework, we start with crys-
tallographic information of a 2D material and perform DFT simulations to extract important
electronic parameters, such as effective mass, band gap, real and complex band dispersion, and
phonon spectrum. This is followed by construction of the material hamiltonian based on the
DFT extracted parameters. Next, the hamiltonian is used to perform self-consistent solution
of the Schrodinger and the Poisson's equations through the non-equilibrium Green's function
approach in order to describe the complex, spatially heterogeneous intrinsic carrier transport
and resulting device performance in both ballistic and dissipative regimes. Modeling studies
on three devices: (i) monolayer germanane metal oxide semiconductor fi eld effect transistors
(MOSFETs), (ii) monolayer GeSe based tunneling field effect transistor (TFET), and (iii)
phosphorene based MOSFET and TFET, will be presented in the thesis and their design and
performance limits will be evaluated to guide future material selection and device fabrication.
42
Gaddam, Venkateswarlu. "Synthesis and Characterization of 1D & 2D Nanostructures : Performance Study for Nanogenerators and Sensors." Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3886.
Анотація:
Recently, efforts have been made for self-powering the batteries and portable electronic devices by piezoelectric nanogenerators. The piezoelectric nanogenerators can work as a power source for nano-systems and also as an active sensor. The piezoelectric nanogenerator is a device that converts random mechanical energy into electrical energy by utilizing the semiconducting and piezoelectric properties. Also, the mechanical energy is always available in and around us for powering these nano devices.
The aim of the present thesis work is to explore 1D and 2D ZnO nanostructures (nanorods and nanosheets) on metal alloy substrates for the development of piezoelectric nanogenerators in energy harvesting and sensors applications. Hydrothermal synthesis method was adopted for the growth of ZnO nanostructures. The nanogenerators were fabricated by using the optimized synthesis parameters and subsequently studied their performance for power generation and as an active speed sensor. These 1D and 2D nanostructures based nanogenerators have opened up a new window for the energy harvesting applications and sensors development. The thesis is divided into following six chapters.
Chapter 1:
This chapter gives a general introduction about energy harvesting devices such as nanogenerators, available energy sources, mechanical energy harvesting, ZnO material and the details on hydrothermal synthesis process. A brief literature survey on different applications of piezoelectric nanogenerators is also included.
Chapter 2:
A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. Details on the synthesis of 1D ZnO nanorods on Phynox alloy substrate by hydrothermal method are presented. Further, the optimization of parameters such as growth temperature, seed layer annealing and substrate temperature effects on the synthesis of ZnO nanorods are discussed in detail. As-synthesized ZnO nanorods have been characterized using XRD, FE-SEM, TEM and XPS.
Chapter 3:
It reports on the fabrication of piezoelectric nanogenerator on Phynox alloy substrate as power generating device by harvesting the mechanical energy. Initially, the performance of the nanogenerator for power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the output voltage response of the nanogenerator was studied for its use as an active speed sensor.
Chapter 4:
Synthesis of Al doped 2D ZnO nanorsheets on Aluminum alloy (AA-6061) substrate by hydrothermal method is reported in this chapter. The optimized parameters such as growth temperature and growth time effects on the synthesis of ZnO nanosheets are discussed. As-synthesized ZnO nanosheets were characterized using XRD, FE-SEM, TEM and XPS. The Al doping in ZnO is confirmed by EDXS and XPS analysis.
Chapter 5:
Cost effective fabrication of Al doped 2D ZnO nanosheets based nanogenerator for direct current (DC) power generation is reported in this chapter. The performance of the nanogenerator for DC power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the DC output voltage response of the nanogenerator was studied for its use as an active speed sensor.
Chapter 6:
The first section summarizes the significant features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.
43
Gaddam, Venkateswarlu. "Synthesis and Characterization of 1D & 2D Nanostructures : Performance Study for Nanogenerators and Sensors." Thesis, 2015. http://etd.iisc.ernet.in/2005/3885.
Анотація:
Recently, efforts have been made for self-powering the batteries and portable electronic devices by piezoelectric nanogenerators. The piezoelectric nanogenerators can work as a power source for nano-systems and also as an active sensor. The piezoelectric nanogenerator is a device that converts random mechanical energy into electrical energy by utilizing the semiconducting and piezoelectric properties. Also, the mechanical energy is always available in and around us for powering these nano devices.
The aim of the present thesis work is to explore 1D and 2D ZnO nanostructures (nanorods and nanosheets) on metal alloy substrates for the development of piezoelectric nanogenerators in energy harvesting and sensors applications. Hydrothermal synthesis method was adopted for the growth of ZnO nanostructures. The nanogenerators were fabricated by using the optimized synthesis parameters and subsequently studied their performance for power generation and as an active speed sensor. These 1D and 2D nanostructures based nanogenerators have opened up a new window for the energy harvesting applications and sensors development. The thesis is divided into following six chapters.
Chapter 1:
This chapter gives a general introduction about energy harvesting devices such as nanogenerators, available energy sources, mechanical energy harvesting, ZnO material and the details on hydrothermal synthesis process. A brief literature survey on different applications of piezoelectric nanogenerators is also included.
Chapter 2:
A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. Details on the synthesis of 1D ZnO nanorods on Phynox alloy substrate by hydrothermal method are presented. Further, the optimization of parameters such as growth temperature, seed layer annealing and substrate temperature effects on the synthesis of ZnO nanorods are discussed in detail. As-synthesized ZnO nanorods have been characterized using XRD, FE-SEM, TEM and XPS.
Chapter 3:
It reports on the fabrication of piezoelectric nanogenerator on Phynox alloy substrate as power generating device by harvesting the mechanical energy. Initially, the performance of the nanogenerator for power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the output voltage response of the nanogenerator was studied for its use as an active speed sensor.
Chapter 4:
Synthesis of Al doped 2D ZnO nanorsheets on Aluminum alloy (AA-6061) substrate by hydrothermal method is reported in this chapter. The optimized parameters such as growth temperature and growth time effects on the synthesis of ZnO nanosheets are discussed. As-synthesized ZnO nanosheets were characterized using XRD, FE-SEM, TEM and XPS. The Al doping in ZnO is confirmed by EDXS and XPS analysis.
Chapter 5:
Cost effective fabrication of Al doped 2D ZnO nanosheets based nanogenerator for direct current (DC) power generation is reported in this chapter. The performance of the nanogenerator for DC power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the DC output voltage response of the nanogenerator was studied for its use as an active speed sensor.
Chapter 6:
The first section summarizes the significant features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.
44
Gaddam, Venkateswarlu. "Synthesis and Characterization of 1D & 2D Nanostructures : Performance Study for Nanogenerators and Sensors." Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3885.
Анотація:
Recently, efforts have been made for self-powering the batteries and portable electronic devices by piezoelectric nanogenerators. The piezoelectric nanogenerators can work as a power source for nano-systems and also as an active sensor. The piezoelectric nanogenerator is a device that converts random mechanical energy into electrical energy by utilizing the semiconducting and piezoelectric properties. Also, the mechanical energy is always available in and around us for powering these nano devices.
The aim of the present thesis work is to explore 1D and 2D ZnO nanostructures (nanorods and nanosheets) on metal alloy substrates for the development of piezoelectric nanogenerators in energy harvesting and sensors applications. Hydrothermal synthesis method was adopted for the growth of ZnO nanostructures. The nanogenerators were fabricated by using the optimized synthesis parameters and subsequently studied their performance for power generation and as an active speed sensor. These 1D and 2D nanostructures based nanogenerators have opened up a new window for the energy harvesting applications and sensors development. The thesis is divided into following six chapters.
Chapter 1:
This chapter gives a general introduction about energy harvesting devices such as nanogenerators, available energy sources, mechanical energy harvesting, ZnO material and the details on hydrothermal synthesis process. A brief literature survey on different applications of piezoelectric nanogenerators is also included.
Chapter 2:
A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. Details on the synthesis of 1D ZnO nanorods on Phynox alloy substrate by hydrothermal method are presented. Further, the optimization of parameters such as growth temperature, seed layer annealing and substrate temperature effects on the synthesis of ZnO nanorods are discussed in detail. As-synthesized ZnO nanorods have been characterized using XRD, FE-SEM, TEM and XPS.
Chapter 3:
It reports on the fabrication of piezoelectric nanogenerator on Phynox alloy substrate as power generating device by harvesting the mechanical energy. Initially, the performance of the nanogenerator for power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the output voltage response of the nanogenerator was studied for its use as an active speed sensor.
Chapter 4:
Synthesis of Al doped 2D ZnO nanorsheets on Aluminum alloy (AA-6061) substrate by hydrothermal method is reported in this chapter. The optimized parameters such as growth temperature and growth time effects on the synthesis of ZnO nanosheets are discussed. As-synthesized ZnO nanosheets were characterized using XRD, FE-SEM, TEM and XPS. The Al doping in ZnO is confirmed by EDXS and XPS analysis.
Chapter 5:
Cost effective fabrication of Al doped 2D ZnO nanosheets based nanogenerator for direct current (DC) power generation is reported in this chapter. The performance of the nanogenerator for DC power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the DC output voltage response of the nanogenerator was studied for its use as an active speed sensor.
Chapter 6:
The first section summarizes the significant features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.
45
Pan, Jia-Chyi, and 潘嘉琪. "Design and Fabrication of an Inkjet Printed Flexible Tungsten Oxide-Based pH Sensor Array for 2D pH Monitoring of Chronic Wound." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/52066641576789051963.
Анотація:
碩士國立交通大學
生醫工程研究所
104
In this work, nanoparticle silver ink is printed on kapton, patterned by SU-8, as wire and reference electrode after chlorination. Pre-treated by Tollen’s reagent can not only reduce electrical resistivity of the printed Ag interconnects but also strengthen printed microstructures for sensor fabrication because of mirror reaction. Then, tungsten oxide is printed and sinter in 120oC as working electrode of a pH sensor. After fabrication, we connect the sensor to Jiehan 5600 Electrochemical Workstation to obtain the open circuit potential and the sensitivity of the pH sensor is -23.7 mV/pH.
46
Chieh-LunWu and 吳頡倫. "Fabrication and sulfidation/carbonization of 2D MOF nanoflakes-graphene oxide hybrid films as the electrode materials for all-solid-state supercapacitors." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/86qb78.
47
Huang, Pei-Chen, and 黃北辰. "Analysis and Investigation of Strain Engineering Utilized in 2D/3D Nano-scaled Germanium-based Metal Oxide Semiconductor Field Transistors Enabled by Column IV Semiconductor alloys." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/69394912930853497123.
Анотація:
碩士中原大學
機械工程研究所
104
Currently, strain-engineering techniques are well established in Si-based metal–oxide semiconductor field-effect transistor (MOSFET)technology. To compensate for the drawback of device-size reduc-tion, germanium-substituted silicon is chosen as a channel material.Ge exhibits highly enhanced carrier mobility and it is regarded to be apromising channel material in a nano-scale MOSFET beyond the sub-22 nm technology node. This element has attracted considerable at-tention because of its potential to enhance the drive current of MOSFETsby replacing traditional strained Si-channel technology. Implanting Siatoms in the source/drain (S/D) region on the Ge substrate is a con-ventional method. Si and Ge atoms generate lattice mismatching,which improves device efficiency. Thus, this study adjusts the layout pattern of the device and usea 3D finite element model to simulate channel stress and mobility. Bycombining appropriate S/D stressors composed of Ge1 − x Six alloyswith the CESL at the considered intrinsic stress points, a significant en-hancement in the performance of tensile strained Ge-based nMOSFET can be acquired. Moreover, the strained GeSn alloy embedded into a Ge-based device is considered as a promising solution of next generation advanced devices. In contrast with Si, Ge, C in group IV semiconductor devices, GeSn alloy is indeed a novel material adopted in strained engineering. On the other hand, the arrangement of device layout also plays an important rule to influence device performance as S/D stressors are exerted. However, the analysis regarding comprehensive effects integrated GeSn stressors with the layout of that salient gate width extends across a dummy active diffused region (Dummy OD) is little. For this reason, a reliable device stress simulation is proposed and performed to explore the above-mentioned concerns under the vehicle consideration of a 20 nm Ge-based pMOSFET with a 100 nm gate width and a 100 nm dummy gate width. For the FinFETs layout design, the larger S/D region length and narrow channel length was suggested to enhance the longtidual stress of concerned channel.