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1
Min, Byoung Koun. « Scanning tunneling microscopic studies of SiO2 thin film supported metal nano-clusters ». Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/2737.
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This dissertation is focused on understanding heterogeneous metal catalysts supported on oxides using a model catalyst system of SiO2 thin film supported metal nano-clusters. The primary technique applied to this study is scanning tunneling microscopy (STM). The most important constituent of this model catalyst system is the SiO2 thin film, as it must be thin and homogeneous enough to apply electron or ion based surface science techniques as well as STM. Ultra-thin SiO2 films were successfully synthesized on a Mo(112) single crystal. The electronic and geometric structure of the SiO2 thin film was investigated by STM combined with LEED, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The relationship between defects on the SiO2 thin film and the nucleation and growth of metal nano-clusters was also investigated. By monitoring morphology changes during thermal annealing, it was found that the metal-support interaction is strongly dependent on the type of metal as well as on the defect density of the SiO2 thin film. Especially, it was found that oxygen vacancies and Si impurities play an important role in the formation of Pd-silicide. By substituting Ti atoms into the SiO2 thin film network, an atomically mixed TiO2-SiO2 thin film was synthesized. Furthermore, these Ti atoms play a role as heterogeneous defects, resulting in the creation of nucleation sites for Au nano-clusters. A marked increase in Au cluster density due to Ti defects was observed in STM. A TiO2-SiO2 thin film consisting of atomic Ti as well as TiOx islands was also synthesized by using higher amounts of Ti (17 %). More importantly, this oxide surface was found to have sinter resistant properties for Au nano-clusters, which are desirable in order to make highly active Au nano-clusters more stable under reaction conditions.
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SCHLEXER, PHILOMENA DENIZ. « Nanostructures in Catalysis - Support Effects on Metal Clusters and Oxide Thin Films ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/158187.
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La catalisi ha profondamento modificato la nostra società e giocherà un ruolo chiave nella risoluzione della crisi energetica ed ambientale che stiamo affrontando in questo secolo. Il grande vantaggio nello sviluppo dei nanomateriali nel regno della nanotecnologia ha portato a possibilità impreviste anche per la progettazione di nuovi catalizzatori. La produzione e la comprensione del funzionamento di catalizzatori ad alta efficienza basati su materiali nanostrutturati è lo sforzo del campo emergente della nanocatalisi. Negli ultimi anni, i nanocatalizzatori sono stati ampiamente studiati e si è registrato un costante progresso nella loro produzione su larga scala. La tecnologia è tuttora in evoluzione ed ulteriore ricerca è necessaria per capitalizzare appieno il suo potenziale.
I metodi computazionali sono molto adatti a studiare il funzionamento dei nanocatalizzatori e a fornire importanti informazioni da un punto di vista atomistico. Un accurato ed efficiente metodo è rappresentato dalla teoria del funzionale della densità (DFT). In questa tesi, abbiamo esplorato le caratteristiche chimiche e fisiche di clusters metallici supportati e di film sottili di ossidi utilizzando principalmente il metodo basato su DFT. Questi materiali sono di particolare interesse nella catalisi e in molte altre applicazioni, a causa delle loro caratteristiche uniche che derivano dalla nanostrutturazione. In particolare, abbiamo studiato la geometria, lo stato di carica, l’interazione cluster-supporto, e la reattività di clusters metallici sub-nanometrici supportati su ossidi. In un caso particolare abbiamo inoltre affrontato il ruolo della dimensione in nanoparticelle metalliche più grandi. Per quanto riguarda i clusters supportati, abbiamo verificato che le forze di dispersione di van-der-Waals sono molto importanti per la corretta descrizione dell’interazione cluster-supporto. Inoltre, abbiamo stabilito che difetti e dopanti presenti sulla superfice del supporto ossido hanno un'influenza determinante sui cluster, determinandone intrinsecamente la reattività. Anche la modifica dei cluster attraverso la formazione di leghe altera l’interazione metallo-supporto, e può essere sfruttata per evitare l’agglomerazione dei clusters. La nanostrutturazione del supporto a base di ossido può generare nuove proprietà del materiale e in questo contesto abbiamo esaminato le caratteristiche di un film ultrasottile di ossido supportato su metallo. Infine, abbiamo eseguito studi meccanicistici che hanno contribuito a chiarire il meccanismo di reazione dell’ossidazione di CO su catalizzatori a base di Au/TiO2 e dell’idrogenazione di CO2 su catalizzatori a base di Ru/TiO2 and Cu/TiO2.Catalysis has largely shaped society and will play a key part in the resolution of the energy and environment crisis we are facing in this century. The great advancements in the development of nanomaterials in the realm of nanotechnology have brought forth unforeseen possibilities also for the design of novel catalysts. The production and understanding of highly efficient catalysts based on nanostructured materials is the endeavor of the emerging field of nanocatalysis. In the last years, nanocatalysts have been studied extensively and progress in their large-scale fabrication has been demonstrated. Still, the technology is immature and further research is necessary to capitalize its full potential. Computational approaches are well suited to investigate the functioning of nanocatalysts and provide valuable atomistic insights. An accurate and efficient method is density functional theory (DFT). In this thesis, we explored the physical and chemical characteristics of supported metal clusters and oxide thin films using mainly DFT. These materials are of special interest in catalysis and many other applications, because of their unique features emerging from the nanostructuring. In particular, we investigated the geometry, the charge state, the cluster-support interaction, and the reactivity of sub-nanometer metal clusters supported on oxides. In a case study, we also addressed size-effects on larger metal nanoparticles. Regarding the supported clusters, we find that van-der-Waals dispersion forces are important for the correct description of the cluster-support interaction. Furthermore, we establish that defects and dopants present on the supporting oxide surface have a determining influence on the clusters, inherently affecting their reactivity. Also the modification of the clusters via alloying alters the metal-support interaction which can be exploited against cluster agglomeration. Nanostructuring of the oxide support engenders new material properties and in this context we examined the features of metal-supported oxide ultrathin films. Finally, we performed mechanistic studies contributing to elucidate the reaction mechanism of CO oxidation on Au/TiO2, as well as CO2 hydrogenation on Ru/TiO2 and Cu/TiO2.
3
Carew, Alexander Jon. « Fundamental studies into the catalytic properties of metal-oxide supported gold and copper nanoparticles ». Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367710.
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Jerratsch, Jan-Frederik Karl [Verfasser]. « Investigation and manipulation of thin oxide films supported on metal single crystals : a scanning tunneling microscopy study / Jan-Frederik Karl Jerratsch ». Berlin : Freie Universität Berlin, 2011. http://d-nb.info/1025355822/34.
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PRADA, STEFANO. « Enhancing oxide surface reactivity by doping or nano-structuring ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/50011.
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Wide band-gap simple oxides are rather inert materials, which found applications in heterogeneous catalysis mainly as supports for active metal nanoparticles. This thesis investigates tailored modifications of the oxide characteristics aimed at making these substrates more reactive in catalytic processes. In particular we are interested in engineering the charge transfer with supported metal catalysts in order to enhance their activity and selectivity. By using first principles calculations in the framework of the density functional theory, we have explored two main routes in this field: 1) nanostructuring, in particular nanothick oxide films supported on metals, and 2) doping of oxides with substitutional metal ions. After addressing methodological aspects related to the theoretical simulations of these materials, we have considered the role of oxide doping in optimizing the structural and electronic properties of supported gold adparticles; we have shown that depending on the dopant and the nature of the oxide it is possible to finely tune the shape and the charge state of adsorbed metal particle. Moreover we have combined oxide doping and nanostructuring in modifying the work function of metal substrates. By varying parameters like nature, position, and concentration of dopants within the metal-supported oxide films, it is possible in principle to modify the work function of the metallic support in a desired way.
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Benia, Hadj Mohamed. « Spatially resolved optical measurements on supported metal particles and oxide surfaces with the STM ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15862.
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In der vorliegenden Arbeit wurde mit Hilfe eines Photon-STM die Korrelation zwischen optischen Eigenschaften und der lokalen Morphologie an zwei unterschiedlichen Systemen untersucht. Hierfür wurden zum einem oxidgetragene Ensemble von Silber-Partikeln präpariert, wobei sowohl die Partikelform (Kuppel- und Scheibenform) als auch die deponierte Partikeldichte variiert werden konnte. Neben der Präparation solcher Partikel auf Al10O13/NiAl, konnten sphärische Silber-Kolloide geordnet, als auch ungeordnet auf HOPG aufgebracht und untersucht werden. Dabei zeigte sich, dass das Verhältnis von Höhen zu Breiten nicht nur einen signifikanten Einfluss auf die Mie-Resonanz des einzelnen Partikels hat, sondern auch die elektromagnetische Kopplung der Partikel in einem Ensemble stark kontrolliert. Die energetische Lage der Mie-Resonanz zeigt im Fall der kuppelförmigen Ag-Partikel eine starke Abhängigkeit vom Intepartikel-Abstand, was sich in einer Verschiebung zu höheren Energien für eine steigende Partikeldichte äußert. Eine solche Abhängigkeit konnte bei den Ensembles der scheibenförmigen Partikel nicht beobachtet werden. Des weiteren zeigte sich, dass, verglichen mit den ungeordneten Ensembles, die selbstorganisierte langreichweitige Ordnung der Silber-Kolloide auf HOPG nur einen schwachen Einfluss auf die energetische Position der Mie Resonanz hat.Das zweite hier untersuchte System sind dünne MgO Filme unterschiedlicher Dicken auf einem Mo(001) Substrat. Diese zeigen ein reichhaltiges Wachstumsverhalten, welches durch eine Differenz in den Gitterkonstanten von 5.3% begründet ist und erst ab etwa 25 ML zu einem flachen und defektarmen Film führt. Die so induzierte Spannung relaxiert bis zu einer Dicke von etwa 7 ML in einer periodischen Überstruktur die aus abwechselnd flachen und verkippten Ebenen an der MgO-Mo Grenzschicht hervorgeht. Für MgO Filme mit einer Dicke von etwa 12 ML werden dann Schraubenversetzungen, ausgedehnte verkippte Ebenen und Stufenkanten mit einer Orientierung entlang der Richtung beobachtet. Die optische Charakterisierung durch Feldemission von Elektronen aus der STM-Spitze in den MgO-Film wird dominiert von zwei Emissionsmaxima bei Energien von 3.1 eV und 4.4 eV. Die kontrollierte Nukleation von Gold Partikeln und die Erzeugung von Farbzentren im MgO Film erlaubten eine Zuordnung dieser Emissionen zu strahlenden Zerfällen von Exitonen an Ecken, Kinken bzw. Stufen des Magnesiumoxids. Solche Emissionsprozesse konnten allerdings nur unter Einstellungen beobachtet werden, bei denen ein gleichzeitiges Rastern der Oberfläche unmöglich ist. Bei moderaten Einstellungen war auch eine ortsaufgelösten Spektroskopie möglich, wobei dann neue Emissionsmechanismen beobachtet wurden. Dabei sind zwei Prozesse wesentlich; zum einen die Ausbildung von sog. Spitzen-induzierten Plasmonen im Bereich zwischen Spitze und dem Mo-Substrat, zum anderen strahlende Elektronenübergänge zwischen sog. Feldemissionsresonanzen, die sich im Spitze/MgO-Film System ausbilden.In this thesis, the correlation between the optical properties and the local morphology of supported silver nanoparticle ensembles and MgO thin films deposited on Mo(001) systems is explored by means of Photon-STM. In the first section, dome and disk shaped Ag nanoparticle ensembles with increasing density on an alumina film on NiAl(110) were analyzed as well as ordered and disordered ensembles of Ag nanocolloids on HOPG. The aspect ratio of the Ag nanoparticles was found to have a significant influence not only on the Mie plasmon resonance of a single particle, but also on the electromagnetic coupling within the nanoparticle ensembles. The Mie resonance in the ensemble of dome shaped Ag nanoparticles shows a strong dependence on the interparticle distance, where it shifts to higher energies with increasing particle density, due to destructive interference effects. In the disk-like Ag ensembles, however, the plasmon energy is independent of particle-particle separation. The long-range lateral ordering of size-selected Ag nanocolloids is found to induce a high dipole-dipole coupling within the ensemble. This is mainly reflected by the enhancement of the spectral intensity of the in-plane Mie mode, due to constructive coupling. However, ensembles with either well-ordered or disordered arrangements reveal no important difference in their optical properties, reflecting the weak influence of the long-range order in the particle ensemble. Thin MgO films with different thicknesses were grown on a Mo(001) surface. The stress resulting from the 5.3% lattice mismatch between the MgO(001) and the Mo(001) lattice parameters is found to control the surface morphology of the MgO film until thicknesses of around 25ML at which flat and defect-poor films are obtained. The relaxation of the stress induces a periodic network in the first 7ML of the MgO film, consisting of alternated flat and tilted mosaics. The presence of screw dislocations, steps oriented along the MgO directions, and tilted planes is observed when the MgO films are approximately 12ML thick. In addition, an increase of the MgO work function around these new surface features is revealed from STM spectroscopy. The photon emission induced by field-emitted electron injection from the STM tip into the MgO films is dominated by two emission bands located at 3.1eV and 4.4eV. To check the origin of these bands, further experiments, namely, nucleation of Au particles and creation of F-centers on the MgO surface, have been performed. The nucleation of Au particles at the low coordinated sites is found to quench the MgO optical signal, while the creation or annihilation of F-centers does not alter the MgO emission bands. The 3.1eV and the 4.4eV bands are therefore assigned to the radiative decay of MgO excitons at corner and kink sites, and step sites, respectively. Besides, spatially resolved optical measurements in the tunneling mode of the STM revealed different light emission mechanisms. These radiative processes are mainly related to tip-induced plasmons that form between the tip and the Mo support and to electron transitions between field-emission-resonance states in the STM tip-MgO film junction. The signal from exciton decays at corners and kinks of the MgO surface is however only observed at excitation conditions where the spatial resolution is already strongly reduced.
7
Kiisk, Valter. « Optical investigation of metal-oxide thin films / ». Online version, 2006. http://dspace.utlib.ee/dspace/bitstream/10062/115/1/kiiskvalter.pdf.
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Ponja, Sapna D. « Metal oxide thin films for optoelectronic applications ». Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10045545/.
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This thesis details the use of aerosol assisted chemical vapour deposition to deposit transparent conducting oxide thin films. Transparent conducting oxides are a special class of materials that exhibit high optical transparency as well as good electrical conductivity, two properties usually in contradiction with each other. The combination of these properties in one material has established an essential role for transparent conducting oxides in a range of applications such as flat screen displays, photovoltaic cells, gas sensors, low-emissive coatings and light emitting diodes. Aerosol assisted chemical vapour deposition is increasingly becoming recognised as a simple, low-cost and reliable technique for depositing thin films. It involves generating an aerosol mist from a solution containing the precursors that is transported with the aid of an inert or reactive carrier gas into the reaction chamber where deposition takes place on a heated substrate. Two of the attractive features of this method are its versatility in allowing the use of precursors that are not suitable for conventional chemical vapour deposition methods as the method depends on solubility rather than volatility and the facility to use multiple precursors simultaneously within a single vessel. The focus of this work is on doping and co-doping of metal oxide thin films, namely ZnO and SnO2, to enhance their optoelectronic properties. The ZnO films were doped with group III elements aluminium or gallium, and the SnO2 films were doped with multivalent elements antimony or tungsten. All four systems were co-doped by introducing fluorine to replace the oxygen ion in the lattice. Fluorine was used as the co-dopant because of its established use in fluorine doped tin(IV) oxide transparent conducting oxides, a commercially available product. Co-doping has received less attention compared with single cation doping largely because of the limitations of other deposition methods. The rationale for co-doping is that it would allow greater tuning of the optoelectronic properties of the transparent conducting oxides to suit specific applications. All films synthesised in this investigation were characterised using a wide range of techniques including X-ray diffraction, energy and/or wavelength dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible-near infrared spectroscopy and Hall effect measurements.
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Snyder, Mark Q. « Modification of Semi-metal Oxide and Metal Oxide Powders by Atomic Layer Deposition of Thin Films ». Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/SnyderMQ2007.pdf.
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Han, Sanggil. « Cu2O thin films for p-type metal oxide thin film transistors ». Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/285099.
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The rapid progress of n-type metal oxide thin film transistors (TFTs) has motivated research on p-type metal oxide TFTs in order to realise metal oxide-based CMOS circuits which enable low power consumption large-area electronics. Cuprous oxide (Cu2O) has previously been proposed as a suitable active layer for p-type metal oxide TFTs. The two most significant challenges for achieving good quality Cu2O TFTs are to overcome the low field-effect mobility and an unacceptably high off-state current that are a feature of devices that have been reported to date. This dissertation focuses on improving the carrier mobility, and identifying the main origins of the low field-effect mobility and high off-state current in Cu2O TFTs. This work has three major findings. The first major outcome is a demonstration that vacuum annealing can be used to improve the carrier mobility in Cu2O without phase conversion, such as oxidation (CuO) or oxide reduction (Cu). In order to allow an in-depth discussion on the main origins of the very low carrier mobility in as-deposited films and the mobility enhancement by annealing, a quantitative analysis of the relative dominance of the main conduction mechanisms (i.e. trap-limited and grain-boundary-limited conduction) is performed. This shows that the low carrier mobility of as-deposited Cu2O is due to significant grain-boundary-limited conduction. In contrast, after annealing, grain-boundary-limited conduction becomes insignificant due to a considerable reduction in the energy barrier height at grain boundaries, and therefore trap-limited conduction dominates. A further mobility improvement by an increase in annealing temperature is explained by a reduction in the effect of trap-limited conduction resulting from a decrease in tail state density. The second major outcome of this work is the observation that grain orientation ([111] or [100] direction) of sputter-deposited Cu2O can be varied by control of the incident ion-to-Cu flux ratio. Using this technique, a systematic investigation on the effect of grain orientation on carrier mobility in Cu2O thin films is presented, which shows that the [100] Cu2O grain orientation is more favourable for realising a high carrier mobility. In the third and final outcome of this thesis, the temperature dependence of the drain current as a function of gate voltage along with the C-V characteristics reveals that minority carriers (electrons) cause the high off-state current in Cu2O TFTs. In addition, it is observed that an abrupt lowering of the activation energy and pinning of the Fermi energy occur in the off-state, which is attributed to subgap states at 0.38 eV below the conduction band minimum. These findings provide readers with the understanding of the main origins of the low carrier mobility and high off-state current in Cu2O TFTs, and the future research direction for resolving these problems.
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Besharat, Zahra. « Adsorption of molecular thin films on metal and metal oxide surfaces ». Doctoral thesis, KTH, Materialfysik, MF, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-195613.
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Metal and metal oxides are widely used in industry, and to optimize their performance their surfaces are commonly functionalized by the formation of thin films. Self-assembled monolayers (SAMs) are deposited on metals or metal oxides either from solution or by gas deposition. Thiols with polar terminal groups are utilized for creating the responsive surfaces which can interact electrostatically with other adsorbates. Surface charge effects wetting and adhesion, and many other surface properties. Polar terminal groups in thiols could be used to modify these factors. Mixed SAMs can provide more flexible surfaces, and could change the resulting surface properties under the influence of factors such as pH, temperature, and photo-illumination. Therefore, in order to control these phenomena by mixed polar-terminated thiols, it is necessary to understand the composition and conformation of the mixed SAMs and their response to these factors. In this work, mixtures of thiols with carboxylic and amino terminal groups were studied. Carboxylic and amino terminal groups of thiol interact with each other via hydrogen bonding in solution and form a complex. Complexes adsorb to the surface in non-conventional orientations. Unmixed SAMs from each type, either carboxylic terminated thiols or amino terminated thiols are in standing up orientation while SAMs from complexes are in an axially in-plane orientation. Selenol is an alternative to replace thiols for particular applications such as contact with biological matter which has a better compatibility with selenol than sulfur. However, the Se-C bond is weaker than the S-C bond which limits the application of selenol. Understanding the selenol adsorption mechanism on gold surfaces could shed some light on Se-C cleavage and so is investigated in this work. Se-C cleavage happens in the low coverage areas on the step since atoms at steps have lower coordination making them more reactive than atoms on the terraces. Another area where the self-assembly of molecules is of importance is for dye sensitized solar cells, which are based on the adsorption of the dye onto metal oxides surfaces such as TiO2.The interface between the SAM of dye and the substrate is an important factor to consider when designing dyes and surfaces in dye sensitized solar cells (DSSCs). The quality of the self-assembled monolayers of the dye on the TiO2 surface has a critical influence on the efficiency of the DSSCs. Creation of just a monolayer of dye on the surface could lead to an efficient current of photo-excited electrons to the TiO2 and degeneration of the dye by redox. This work, T-PAC dye showed island growth with some ad-layer that is not in contact with the surface, whereas the MP13 dye adsorption is laminar growth. Cuprite (Cu2O) is the initial and most common corrosion product for copper under atmospheric conditions. Copper could be a good replacement for noble metal as catalysts for methanol dehydrogenation. Knowledge about the structure of Cu2O(100) and Cu2O(111) surfaces could be used to obtain a deeper understanding of methanol dehydrogenation mechanisms with respect to adsorption sites on the surfaces. In this work, a detailed study was done of Cu2O(100) surface which revealed the possible surface structures as the result of different preparation conditions. Studies of the structure of Cu2O(100) and Cu2O(111) surfaces show that Cu2O(100) has a comparatively stable surface and reduces surface reactivity. As a consequence, dehydrogenation of methanol is more efficient on the Cu2O(111) surface. The hydrogen produced from methanol dehydrogenation is stored in oxygen adatom sites on both surfaces.QC 20161107
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Della, Gaspera Enrico. « Noble Metal / Metal Oxide nanocomposite thin films for optical gas sensors ». Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3427450.
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In the last decades, the research field known as nanotechnology has been deeply investigated since it helps to understand the properties of the materials, and provides a useful tool to design materials with tailored properties, that can be exploited for many applications across the whole field of science. Nanomaterials exhibit distinctive size-dependent properties, and a high surface to volume ratio, extremely useful in applications like sensing and catalysis.
In this doctoral project, different combinations of noble metals and transition metal oxides have been used to prepare inorganic thin films to be used as reducing gases sensors through an optical interface: while the semiconductive metal oxide is usually responsible for the detection mechanism, metal nanoparticles play the role of optical probes, enhancing the optical response, and/or catalysts, improving the sensor performances. The main work presented here was focused on the synthesis of these nanocomposite materials through different strategies, according to the desired quality of the final material, the easiness of the procedure, the control on key aspects like size and shape of the particles, their size distribution, the crystallinity of the different components, the porosity.
In the first part, noble metal (Au, Ag, Pt) ions have been embedded inside oxide matrixes by means of sol-gel or impregnation processes, and reduced to metal nanoparticles through high temperature annealing, which is necessary also to promote the oxides crystallization: remarkable gas sensing properties have been observed for NiTiO3-TiO2-Au films for hydrogen sulfide detection, with extremely good sensitivity and selectivity towards interfering gases like CO and H2. The experimental results suggest a catalytic oxidation of H2S to sulfur oxides promoted by NiTiO3 crystals, while Au nanoparticles are not involved directly in the reaction mechanism, but act as probes providing an easily detectable optical signal. Quite good sensing properties for CO and hydrogen detection have been presented for other nanocrystalline thin films like SiO2-NiO-Ag prepared combining sol-gel and impregnation processes, sol-gel ZnO-NiO-Au nanocomposites, and microstructured WO3-Au-Pt films synthesized with the sputtering technique and a subsequent impregnation process.
The second part is based on the colloidal synthesis of metal (Au, Pt, Au@Pt core@shell) and oxide (TiO2, ZnO pure and doped with transition metal ions) nanoparticles with desired size and distribution: purification and concentration protocols have been developed and the final colloidal solutions have been directly used for films deposition, obtaining nanocrystalline coatings at low temperatures. TiO2-based films show good sensitivity for CO and H2, with a detection threshold of about 2 ppm, quite remarkable considering that films are only 40-60 nm thick. These materials were also able to detect ethanol vapors at room temperature. Moreover samples containing both Au and Pt NPs are able to reversibly detect hydrogen at room temperature, thanks to the synergetic effect occurring between the optical properties of Au and the catalytic properties of Pt. ZnO-based samples have been tested as CO sensors with a detection limit down to 1-2 ppm, and a relationship between type of dopant (Ni, Co, Mn) and response intensity has been presented.
The third part is focused on the deposition of Au nanoparticles layers on properly functionalized substrates, and their subsequent coating with sol-gel films: when Au nanoparticles are in close contact with each other, a coupling of the plasmon frequencies is found to occur, and this effect can be used to enhance sensing, SERS and catalytic performances. Au nanoparticles layers covered with NiO or TiO2 films showed promising gas sensing properties for CO and hydrogen detection at high temperatures, and for ethanol sensing at low temperatures. More complex structures composed of an Au nanoparticles layer sandwiched between two different oxide layers (NiO, TiO2, ZnO) are also prepared, trying to enhance the selectivity towards interfering gases by providing two different noble metal / metal oxide interfaces.Negli ultimi decenni, il campo delle nanotecnologie è stato largamente studiato, poiché tramite esso si è in grado di comprendere le proprietà dei materiali, ed esso stesso fornisce un mezzo per progettare materiali aventi le proprietà desiderate, che possono essere utilizzati in diverse applicazioni nell’intero campo della scienza. I nanomateriali presentano interessanti proprietà dipendenti dalla dimensione delle particelle, e inoltre il rapporto superficie-volume in questi materiali è estremamente alto, il che li rende utili per applicazioni in sensoristica e catalisi. In questo progetto di dottorato, diverse combinazioni di metalli nobili e ossidi di metalli di transizione sono state sfruttate per preparare film sottili inorganici, utilizzati come sensori ottici di gas riducenti: solitamente l’ossido semiconduttivo è responsabile per il meccanismo di rilevazione, mentre le nanoparticelle metalliche agiscono da sonde ottiche, aumentando la sensibilità, e/o da catalizzatori, migliorando le prestazioni del sensore. Il principale lavoro presentato in questa tesi è stato focalizzato sulla sintesi di questi materiali attraverso diverse strategie, a seconda della qualità desiderata per il materiale finale, della semplicità operativa, del controllo su parametri chiave come forma e dimensione delle particelle, la loro distribuzione dimensionale, la cristallinità dei diversi costituenti, la porosità. Nella prima parte, ioni di metalli nobili (Ag, Au, Pt) sono stati inseriti all’interno di matrici di ossidi attraverso sintesi sol-gel o processi di impregnazione, e successivamente ridotti a particelle metalliche attraverso trattamenti termici ad alta temperatura, che sono necessari anche per la cristallizzazione degli ossidi: i sistemi NiTiO3-TiO2-Au hanno dimostrato notevoli proprietà sensoristiche nella rilevazione di acido solfidrico, con elevata sensibilità e selettività nei confronti di gas interferenti quali H2 e CO. I risultati sperimentali suggeriscono un effetto dei cristalli di NiTiO3 nel promuovere l’ossidazione catalitica dell’H2S a ossidi di zolfo, mentre le nanoparticelle di oro non sono coinvolte direttamente nella reazione, ma agiscono come sonde ottiche, producendo un segnale ottico facilmente rilevabile. Discreti risultati per la rilevazione di CO e idrogeno sono stati presentati per altri film sottili nanocristallini, come SiO2-NiO-Ag, preparati combinando la tecnica sol-gel e il processo di impregnazione, film sol-gel a base di una matrice di ZnO e NiO contenenti nanoparticelle di Au, e film microstrutturati di WO3 contenenti nanoparticelle di Au e Pt sintetizzati combinando sputtering e impregnazione. La seconda parte di questa tesi è basata sulla sintesi colloidale di nanoparticelle di metalli (Au, Pt, Au@Pt core@shell) e di ossidi (TiO2, ZnO puro e drogato con ioni di metalli di transizione), aventi la desiderata dimensione e distribuzione dimensionale: protocolli di purificazione e concentrazione sono stati sviluppati, e le soluzioni ottenute sono state direttamente utilizzate per la deposizione di film sottili, ottenendo così rivestimenti nanocristallini a bassa temperatura. I film a base di TiO2 hanno mostrato buona sensibilità per idrogeno e CO, con un limite di rilevazione di circa 2 ppm, notevole se considerato che i film sono spessi solo 40-60 nm. Inoltre questi materiali si sono dimostrati capaci di rilevare vapori di etanolo a temperatura ambiente. Infine, campioni contenenti nanoparticelle di oro e platino sono in grado di rilevare idrogeno a temperatura ambiente, grazie all’effetto sinergico che avviene tra le proprietà ottiche dell’oro e quelle catalitiche del platino. I film a base di ZnO sono stati testati come sensori di CO, dimostrando una soglia di rilevazione di circa 1-2 ppm, e una relazione fra il tipo di dopante utilizzato (Ni, Co, Mn) e l’intensità della risposta è stata presentata. La terza parte è focalizzata sulla deposizione di strati di nanoparticelle di oro su substrati opportunamente funzionalizzati, e il loro successivo ricoprimento con film sol-gel: quando le particelle di oro sono molto vicine le une alle altre, le risonanze plasmoniche si accoppiano, e questo effetto può essere sfruttato per migliorare le prestazioni in ambiti quali sensoristica, SERS e catalisi. Strati di particelle di Au ricoperti da film di NiO o TiO2 hanno mostrato promettenti proprietà per la rilevazione di CO e idrogeno ad alte temperature, e di vapori di etanolo a basse temperature. Inoltre, strutture più complesse a base di uno strato di particelle di oro immobilizzato fra due film di ossidi diversi (NiO, TiO2, ZnO) sono state preparate, con lo scopo di migliorare la selettività verso gas interferenti, fornendo due diverse interfacce metallo/ossido.
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Rooth, Mårten. « Metal Oxide Thin Films and Nanostructures Made by ALD ». Doctoral thesis, Uppsala University, Department of Materials Chemistry, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8898.
Texte intégralRésumé :
Thin films of cobalt oxide, iron oxide and niobium oxide, and nanostructured thin films of iron oxide, titanium oxide and multilayered iron oxide/titanium oxide have been deposited by Atomic Layer Deposition (ALD). The metal oxides were grown using the precursor combinations CoI2/O2, Fe(Cp)2/O2, NbI5/O2 and TiI4/H2O. The samples were analysed primarily with respect to phase content, morphology and growth characteristics.
Thin films deposited on Si (100) were found to be amorphous or polycrystalline, depending on deposition temperature and the oxide deposited; cobalt oxide was also deposited on MgO (100), where it was found to grow epitaxially with orientation (001)[100]Co3O4||(001)[100]MgO. As expected, the polycrystalline films were rougher than the amorphous or the epitaxial films. The deposition processes showed properties characteristic of self-limiting ALD growth; all processes were found to have a deposition temperature independent growth region. The deposited films contained zero or only small amounts of precursor residues.
The nanostructured films were grown using anodic aluminium oxide (AAO) or carbon nanosheets as templates. Nanotubes could be manufactured by depositing a thin film which covers the pore walls of the AAO template uniformly; free-standing nanotubes retaining the structure of the template could be fabricated by removing the template. Multilayered nanotubes could be obtained by depositing multiple layers of titanium dioxide and iron oxide in the pores of the AAO template. Carbon nanosheets were used to make titanium dioxide nanosheets with a conducting graphite backbone. The nucleation of the deposited titanium dioxide could be controlled by acid treatment of the carbon nanosheets.
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Söderlind, Fredrik. « Colloidal synthesis of metal oxide nanocrystals and thin films ». Doctoral thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11831.
Texte intégralRésumé :
A main driving force behind the recent years’ immense interest in nanoscience and nanotechnology is the possibility of achieving new material properties and functionalities within, e.g., material physics, biomedicine, sensor technology, chemical catalysis, energy storing systems, and so on. New (theoretical) possibilities represent, in turn, a challenging task for chemists and physicists. An important feature of the present nanoscience surge is its strongly interdisciplinary character, which is reflected in the present work. In this thesis, nanocrystals and thin films of magnetic and ferroelectric metal oxides, e.g. RE2O3 (RE = Y, Gd, Dy), GdFeO3, Gd3Fe5O12, Na0.5K0.5NbO3, have been prepared by colloidal and sol-gel methods. The sizes of the nanocrystals were in the range 3-15 nm and different carboxylic acids, e.g. oleic or citric acid, were chemisorbed onto the surface of the nanoparticles. From FT-IR measurements it is concluded that the bonding to the surface takes place via the carboxylate group in a bidentate or bridging fashion, with some preference for the latter coordination mode. The magnetic properties of nanocrystalline Gd2O3 and GdFeO3 were measured, both with respect to magnetic resonance relaxivity and magnetic susceptibility. Both types of materials exhibit promising relaxivity properties, and may have the potential for use as positive contrast enhancing agents in magnetic resonance imaging (MRI). The nanocrystalline samples were also characterised by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and quantum chemical calculations. Thin films of Na0.5K0.5NbO3, GdFeO3 and Gd3Fe5O12 were prepared by sol-gel methods and characterized by x-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). Under appropriate synthesis conditions, rather pure phase materials could be obtained with grain sizes ranging from 50 to 300 nm. Magnetic measurements in the temperature range 2-350 K indicated that the magnetization of the perovskite phase GdFeO3 can be described as the sum of two contributing terms. One term (mainly) due to the spontaneous magnetic ordering of the iron containing sublattice, and the other a susceptibility term, attributable to the paramagnetic gadolinium sublattice. The two terms yield the relationship M(T)=M0(T)+χ(T)*H for the magnetization. The garnet phase Gd3Fe5O12 is ferrimagnetic and showed a compensation temperature Tcomp ≈ 295 K.
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Yagoubi, Benabdella. « A study of some thin transition metal oxide films ». Thesis, Brunel University, 1989. http://bura.brunel.ac.uk/handle/2438/5348.
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This thesis analyses the effect of varying the compositions of co-evaporated V205/TeO2, W03/CeO2, SiO/TeO2 and W03/TeO2 amorphous thin films on their electrical and optical properties. Some information about the electronic properties of these oxides may be obtained by comparison of the results. In the oxide systems containing transition metal ions the expression for hopping energy at low temperatures contains a term due to the hopping energy of polarons in addition to that due to the disorder. In the dielectric SiO/TeO2 thin films the distortion of 'the molecule is thought to be quite weak and thus the carriers do not form polarons. They would move by hopping at the band edge at low temperatures and by excitation to a mobility edge at high temperatures. The electrical conductivity of V205/TeO2 amorphous thin films is discussed in the light of the Mott(1968) theory. The optical absorption edge was found to obey the direct forbidden transitions equation cc ico=B(fiw-EOP)3'2. The frequency-squared dependence of the conductivity of W03/CeO2 thin films (high content of CeO2) in the frequency region where the capacitance is constant is associated with the lead resistance according to Street et al (1971). The optical energy gap of the films varies with the composition in same way as in doped crystalline semiconductors. The value of the, optical W03/Ce02 was calculated using the Davis and Mott (1970) formula for non-direct optical transitions. The capacitance of SiO/TeO2 thin films is found to be almost independent of frequency as well as of temperature. This is due to a strong ionic bonding which characterises a good insulator. The optical absorption edge of SiO/TeO2 is found to be sharper than that of W03/ CeO2 and very similar to that found in most crystalline solids. The value of the optical energy gap is calculated using the same formula as in W03/CeO2. The systematic change of the optical gap with composition is observed only in a limited range of compositions. The a. c electrical properties of W03/Te02 amorphous thin films are described using the Springett(1974) and Elliott(1977) models. The optical absorption edge of WO3/TeO2 is found to lead to new arguments about the origin of the Urbach edges.The a. c electrical conductivity shows a frequency dependence of the form as ca wS in all samples studied in the present work. The mechanism of conduction at low temperatures with the index varying from 0.5 to I is thought to be due to hopping of electrons between localized states in the gap. At high fields the d. c current shows a non-linear dependence on the applied electric field. This is thought to be due to either space charge or Schottky effects in the oxides containing transition metal ions. In SiO/TeO2 dielectric films, the non-linear dependence of current on the electric field is thought to be due to either the Poole-Frenkel effect or at slightly lower fields it could be due to impurities.
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Bhachu, D. « The synthesis and characterisation of metal oxide thin films ». Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1392591/.
Texte intégralRésumé :
This thesis details the use of chemical vapour deposition to deposit transparent conducting oxide (TCO) thin films for potential use in a wide range of applications ranging from electrodes in photovoltaic devices to low-ε-coatings in architectural glazing. TCO materials exhibit optical transparency along with electrical conductivity. The nature of electrical conductivity arises from either excess electrons in the conduction band or holes in the valence band. FTO thin films were deposited by use of an aerosol delivery system from methanolic solutions of monobutyltin trichloride. The deposition temperature was varied from 350-550 °C. The as-synthesised films displayed enhanced functional properties compared to commercial standards in terms of film microstructure i.e. pyramidal particle microstructure ideal for enhanced light scattering required for amorphous based silicon solar cells and also sheet resistances comparable to commercial standards. The natural progression from tin dioxide films was to explore zinc oxide thin films with respect to their opto-electronic properties. Highly conductive and transparent ZnO films were synthesized by the reaction of diethyl zinc (in toluene) with methanol by dual source aerosol assisted chemical vapour deposition. The scope of this thesis then moves away from TCO materials and concentrates on microporous oxide films produced by combining chemical vapour deposition (CVD) and hydrothermal methods. Dense, adhesive zeolitic films were synthesised from this method by using a CVD process to deposit a dense amorphous silica or titanium doped silica which was then converted to a crystalline nanoporous zeolite by a hydrothermal process using an organic structure directing agent. To demonstrate the capability of the method, silicalite (S-1) and titanium silicalite (TS-1) zeolites were prepared. In order to assess the generality of this method metal organic framework films were also synthesised by reacting zinc oxide films, deposited by chemical vapour deposition (CVD), with the appropriate linker in a conventional solvothermal process.
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Ren, Huilin. « Current Voltage Characteristics of a Semiconductor Metal Oxide Sensor ». Fogler Library, University of Maine, 2001. http://www.library.umaine.edu/theses/pdf/RenH2001.pdf.
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Sankar, Jayasree. « Chemical vapor deposition (CVD) of transition metal and metal oxide thin films ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0018/NQ58161.pdf.
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Beach, Geoffrey S. D. « The COxFe₁₀₀₋x metal/native oxide multilayer / ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3090452.
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Vemuri, Venkata Rama Sesha Ravi Kumar. « Fabrication and characterization of zirconium oxide thin films ». To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Martynova, Yulia [Verfasser], et Reinhard [Akademischer Betreuer] Schomäcker. « CO oxidation on metal supported ultrathin oxide films / Yulia Martynova. Betreuer : Reinhard Schomäcker ». Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2013. http://d-nb.info/1035767384/34.
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De, Los Santos Valladares Luis. « Study of thin metal films and oxide materials for nanoelectronics applications ». Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/244598.
Texte intégralRésumé :
Different types of thin metal films and oxide materials are studied for their potential application in nanoelectronics: gold and copper films, nickel nanoelectrodes, oxide nanograin superconductors, carboxyl ferromagnetic microspheres and graphene oxide flakes. The crystallization and surface morphology of gold and copper films on SiO2/Si substrates is investigated as a function of annealing temperature. Annealing arranges the Au crystallites in the [111] direction and changes the morphology of the surface. Relaxation of the Au layer at high temperatures is responsible for the initial stages of cluster formation. These may form at disordered points on the surface and become islands when the temperature is increased. In the case of Cu/SiO2/Si films, oxides are formed after thermal oxidation at different temperatures up to 1000 °C. The phase evolution Cu -> Cu + Cu2O -> Cu2O -> Cu2O + CuO -> CuO is detected. Pure Cu2O films are obtained at 200 °C, whereas uniform CuO films without structural surface defects are obtained in the temperature range 300 - 550 °C. A resistivity phase diagram, which is obtained from the current-voltage response of the copper oxides, is presented. In the case of thin nickel films, the necessary reagents, conditions and processes required to obtain nano and atomic gaps between soft and clean nickel electrodes are described by using a conventional electrochemical cell. Current-voltage characteristics are also presented to evaluate possible applications of the nanogap electrodes in electronic nanodevices. In addition to the metal surfaces, oxides materials such as the superconductor LaCaBaCu3O7 (La1113), carboxyl ferromagnetic microparticles and graphene oxide flakes are studied. La1113 is a high critical temperature superconductor with TC(onset) = 80 K and its structure is similar to the tetragonal YBCO. This thesis explores the attachment of La1113 nanograins on Au(111) surfaces through selfassembled monolayers of HS-C8H16-HS [octane (di)thiol] for their potential application in nanotransistors. It is found that La1113 particles (100 nm mean diameter) can be functionalized by octane (di)thiol without affecting their superconducting critical temperature (TC = 80 K). A design for a superconducting transistor fabricated by immobilized La1113 nanograins in between two gold electrodes which could be controlled by an external magnetic field gate is suggested. Furthermore, the mechanical reorientation of thiolated ferromagnetic microspheres bridging a pair of gold electrodes under an external magnetic field is studied. Finally, a flexible film made of graphene oxide flakes is prepared and characterized by X ray diffraction. It is achieved by the chemical oxidation of commercial graphite and the subsequent reaction with NaOH. It is found that the interlayer distance between graphene increases upon oxidation due to the formation of chemical groups and results in the delamination and flexibility of the flakes.
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Efremenko, Alina Yurievna. « Theoretical and Experimental Spectroscopic studies of Conducting Metal Oxide Thin Films ». NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-04212009-144306/.
Texte intégralRésumé :
In order to expand on the growing field on Surface Plasmon Resonance Spectroscopy (SPRS) the application of SPRS to Conducting Metal Oxides (CMO) was studied. Through experimental and theoretical studies it was concluded that CMOâs are capable of sustaining Surface Plasmon Polaritons (SPP) like those in noble metals. Specifically, we have used indium tin oxide (ITO) as a test case to demonstrate the interplay of experiment and theory. Theoretical studies provided an excellent basis for comparison to experimental data. Furthermore, Near Edge X-Ray Absorption Fine Structure Spectroscopy (NEXAFS) was applied in order to examine the ITO as a substrate for self assembled monolayers (SAMs). It was found that hexadecanethiol and phosphonic acid form ordered monolayers on ITO.
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Jonsson, AnnaKarin. « Charge Transport in Transition Metal Oxide Thin Films and Electrochromic Devices ». Doctoral thesis, Uppsala universitet, Materialvetenskap, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3030.
Texte intégralRésumé :
Thin film devices for windows, mirrors, space applications and other purposes, have become an essential part of modern technology. A great advantage with a thin film device is the small amount of material used and the compact volume of the device. Dynamic control of thin film device properties is usually obtained by the application of a potential with a resulting charge transport. To understand this charge transport, thus become of great importance to improve, develop, and invent new thin film devices. Charge transport in transition metal oxide thin films and electrochromic devices have been studied in this thesis using dielectric and electrochemical methods. The dielectric methods used are impedance spectroscopy, the isothermal transient ionic current technique and current-voltage measurements. The electrochemical methods include the galvanostatic intermittent titration technique and electrochemical impedance spectroscopy. Ion intercalation parameters have been obtained for sputtered and ALD ZrO2 and sputtered TiO2, and the ion conduction processes have been analysed. The dielectric permittivity of as-deposited as well as intercalated thin films of ZrO2 and TiO2 have been studied and electron conduction mechanisms in as-deposited films deduced. From the impedance spectroscopy it is found that the dielectric response changes drastically upon ion intercalation. The complex dielectric response suggests different relaxation processes being important at different levels of intercalation and an explanation built on defect induced dipoles is proposed. Moreover, ion transport in electrochromic devices has been studied. The transient ionic current has been analysed to extract transport parameters both in single layers and whole devices and a deeper understanding of the ionic motion has been achieved.
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Wilson, Rachel Lyndsey. « Deposition of ultra-thin metal oxide films for gas sensing applications ». Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/10040158/.
Texte intégralRésumé :
The aim of this research project was to investigate the use of Atomic Layer Deposition (ALD) and Chemical Vapour Deposition (CVD) to deposit n- and p-type metal oxide thin films for use in gas sensing applications, with the long term goal to identify the materials which provide maximum sensitivity and selectivity. Two ALD reactors have been designed and constructed specifically for this project. N-type TiO2 thin films have been deposited by ALD of titanium(IV) isopropoxide and water, where film growth was shown to proceed via a self-limiting mechanism. Films were characterised using AFM, XRD, XPS and Raman, which confirmed anatase phase on the film surfaces. TiO2 films of various thickness were deposited onto gas sensor substrates and exposed to a range of test gases in order to evaluate their gas sensitivity at operating temperatures of 350 °C and 480 °C at several different relative humidity’s. Electrical resistance changes were observed for a 50 nm TiO2-coated sensor in response to NH3, where the sensor response was found to decrease with increasing relative humidity. However for a 10 nm film, whose thickness was most consistent with reported literature values of the Debye length for TiO2 was the not the most sensitive. Attempts to deposit p-type NiO films via ALD were less successful. However two novel nickel complexes were synthesised: [Ni(dmamp)2] and [Ni{(NiPr2)2CNEt2}2], whose volatility was greater than some of the other commonly used nickel precursors for ALD and CVD applications. These precursors, along with [Ni(thd)2] and [Ni(Cp)2], have been screened for their use in the deposition of NiO thin films via ALD with water. However, XPS analysis confirmed nickel metal and/or Ni(OH)2 on the film surfaces, which has been attributed to both a lack of reactivity between the nickel precursors and water and issues with the reactor design. Separate CVD experiments performed with [Ni(dmamp)2] and [Ni{(NiPr2)2CNEt2}2] resulted in the deposition of NiO films, as confirmed by XRD and XPS. Under the CVD conditions used, film growth could be controlled relatively easily, as compared to other conventional CVD methods.
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Cross, A. J. « The synthesis, characterisation and functional testing of metal oxide thin films ». Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1450011/.
Texte intégralRésumé :
This thesis is concerned with the deposition of titanium dioxide thin films using chemical vapour deposition (CVD). The work emphasises the influence of deposition parameters on the properties of the resultant film. The materials have been designed with a wide range of potential applications in mind, from air and water purification to energy production and medical implant devices. Where possible, tests have been conducted to assess the efficacy of the material for these applications. The first chapter highlights a number of technologically important applications of titanium dioxide in order to demonstrate the motivation for research in this area. Some theoretical concepts are presented which are fundamental to understanding the behaviour of titanium dioxide. The principles behind chemical vapour deposition and the photocatalytic tests used in this work are discussed. The second chapter focusses on the use of three different metal substrates in TiO2 CVD. Firstly, the phase of TiO2 deposited on steel substrates was investigated. It was shown that the grade of steel had little influence with predominantly anatase films being formed in the vast majority of areas analysed. Since each grade of steel has different mechanical properties and is used in different applications, this work demonstrates that the photocatalytic properties of anatase films can be endowed to a large range of products. Secondly, TiO2 was shown to be adherent to a flexible substrate, namely aluminium foil. It was demonstrated from XPS analysis that aluminium ions did not diffuse into the TiO2, which remained photocatalytically active. A photocatalyst on a lightweight, flexible substrate offers several advantages over glass which has been the most frequently employed substrate to date. Thirdly, titanium dioxide was coated onto an alloy of cobalt, chromium and molybdenum, CoCrMo. The alloy is of interest for biomedical implants but suffers from poor biocompatability. By coating its surface with TiO2, it was shown to enhance osteogenic differentiation. Chapter three investigates nitrogen doped titanium dioxide for its potential as a visible light photocatalyst. A novel synthetic strategy was employed in which the amount of oxygen precursor was varied to determine if this would affect the position of the nitrogen in the titanium dioxide crystal structure. Differences were observed in the nitrogen XPS signal, the absorption profile, surface morphology and photocatalytic activity under both UV and visible irradiation. Visible light activity was observed for a sample made with lower amounts of oxygen precursor under UV and visible light. Finally, brookite, a rare, metastable form of titanium dioxide, was formed by atmospheric pressure chemical vapour deposition, APCVD. A brief literature review discusses the potential applications and some of the previously employed synthetic routes to brookite formation. Three sets of conditions are reported for the first known synthesis of brookite by atmospheric pressure chemical vapour deposition. A possible mechanism for brookite formation is hypothesised. This work concludes with a summary of the key findings from the experimental work and possible avenues for further research.
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Trapatseli, Maria. « Doping controlled resistive switching dynamics in transition metal oxide thin films ». Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/423702/.
Texte intégralRésumé :
Transition metal oxide thin films have attracted increasing attention due to their potential in non-volatile resistive random access memory (RRAM) devices, where such thin films are used as active layers in metal-insulator-metal (MIM) configurations. Titanium dioxide is one of the most celebrated oxides among the ones that exhibit resistive switching behaviour due to its wide band gap, high thermal stability, and high dielectric constant. RRAM devices with various materials as active layers, have demonstrated very fast switching performance but also huge potential for miniaturisation, which is the bottleneck of FLASH memory. Nevertheless, these devices very often suffer poor endurance, physical degradation, large variability of switching parameters and low yields. In most cases, the physical degradation stems from high electroforming and switching voltages. Doping of the active layer has been often employed to enhance the performance of RRAM devices, like endurance, OFF/ON ratio, forming voltages, etc. In this work, doping in TiO2-x RRAM devices was used to engineer the electroforming and switching thresholds so that device degradation and failure can be delayed or prevented. Al and Nb were selected with basic criteria the ionic radius and the oxidation state. The doped RRAM devices, showed improved switching performance compared to their undoped counterparts. Alternative approaches to doping were also investigated, like multilayer stacks comprising Al2O3-y and TiO2-x thin films. Furthermore, Al:TiO2-x/Nb:TiO2-x bilayer RRAM devices were fabricated, to prove whether a diode behaviour of the p-n interface inside the RRAM was feasible. The latest would be a particularly interesting finding towards active electronics.
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Le, Thi Ly. « Preparation of transition metal oxide thin films used as solar absorbers ». Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30120/document.
Texte intégralRésumé :
Ce travail de thèse a porté sur l'élaboration de nanoparticules et de couches minces d'oxydes spinelles mixtes de MxCo2-xMnO4 (M = Ni, Cu, Zn ; x = 0, 0,15, 0,30, 0,60) semi-conducteurs, absorbants de lumière avec d'intéressantes applications potentielles pour la photo-catalyse et le photovoltaïque. Le premier chapitre présente tout d'abord une vue globale du contexte énergétique à l'échelle mondiale et des ressources d'énergie renouvelables, alternatives aux énergies fossiles les plus répandues. Une revue détaillée est ensuite faite des différents matériaux et systèmes employés dans la fabrication de cellules solaires, en portant une attention plus particulière à un nouveau type de cellules photovoltaïques en couches minces, dites " Tout-oxyde ", basées notamment sur l'utilisation d'oxydes de type spinelle utilisés comme absorbeurs solaires. Le deuxième chapitre présente les techniques expérimentales de synthèse et de caractérisation utilisées lors de ce travail de thèse. Le procédé de polycondensation inorganique, optimisé au laboratoire, utilisé pour synthétiser les poudres d'oxydes à basse température (T < 120 °C) sans agent organique complexe est décrit. Ensuite, les méthodes de préparation de dispersions colloïdales à l'ambiante dans l'éthanol et de films minces homogènes d'oxydes par trempage-retrait sont explicitées. Le troisième chapitre présente les résultats détaillés des structures atomiques et électroniques des matériaux de base à l'étude, issus de calculs par la méthode Density Functional Theory (DFT), réalisés en collaboration avec le laboratoire CEMES de Toulouse. Les résultats des calculs de densités électroniques et détermination de structures de bandes, réalisés pour la première fois à notre connaissance, sur l'ensemble de la solution solide MnxCo3-xO4 (0 = x = 3), sont comparés à nos données expérimentales, obtenues notamment sur les largeurs de bande interdite (gap) à partir de mesures optiques faites sur couches minces. Un gap de 0,8 eV est calculé, qui serait dû à des transitions inter-métalliques en sites B. Deux gaps à 1,5 et 2,2 eV, obtenus expérimentalement dans l'UV-VIS, qui augmentent avec la quantité de manganèse, correspondraient à des transitions respectives B-A et O-B, respectivement. Les propriétés magnétiques de ces matériaux sont également discutées. Le quatrième chapitre présente l'élaboration et la caractérisation (micro-)structurale des poudres et des couches minces d'oxydes de type spinelle. Toutes les compositions (Co2MnO4 dopé au Ni, Cu ou Zn) cristallisent dans une phase cubique. Les nanoparticules sont sphériques avec la taille variant entre 20 et 50 nm. Les couches minces homogènes ont été déposées sur quartz, alumine, nitrure de titane et platine afin de mesurer leurs propriétés électriques et optiques. Une température de frittage environ de 1000 °C sous air a été déterminée par dilatométrie et les couches sont stables jusqu'à 900 °C quel que soit le substrat. En revanche, seules les couches déposées sur platine permettent d'atteindre la température de frittage sous air (et d'accroitre la compacité donc la conductivité des couches) sans réaction avec le substrat. Le chapitre cinq présente les variations des propriétés optiques et électriques des couches minces avec le frittage. Les propriétés d'absorbance de lumière des couches minces ainsi préparées, mesurées sur une gamme de longueurs d'ondes du domaine spectral UV-visible, montrent deux bandes d'absorbance, correspondantes à deux valeurs de gap pour chaque composition. La propriété d'absorbance des couches minces augmente dans la gamme du visible après frittage et les gaps diminuent. Les couches minces sont plus compactées. La résistivité des couches minces diminue de 105 à 102 Omega.cm avec l'augmentation de la température de 20 à 300 ºC. Une étude parallèle, basée sur la préparation de films minces absorbants de lumière de Co2MnO4 et Cu2O par la technique de Pulsed Laser Deposition (PLD) est également présentéeThe present thesis deals with the synthesis and structural characterization of transition metals doped cobalt and manganese based spinel oxides MxCo2-xMnO4 (with M = Ni, Cu, Zn and x = 0, 0.15, 0.30, 0.60), in relationships with their conduction and optical properties. These materials are good p-type semiconductors and light absorbers in the UV and visible regions, therefore interesting for photo-catalysis and photovoltaics. The first chapter is a brief overview of the energy context and nature of global warming, renewable energy resources and a literature review of materials used for solar cells including the newly studied system type based on all-oxide photovoltaics. Chapter two presents all the experimental methods and characterization techniques used for this research work. The inorganic polycondensation method optimized in our laboratory and used for synthesizing spinel oxide powders at low temperature (T < 120 °C) without complex organic agents is described. Then, the preparation of colloidal dispersions stabilized at room temperature using an azeotrope solution based on absolute ethanol and water only is described, in order to obtain homogenous oxide thin films by the dip-coating technique. The third chapter presents detailed results on the atomic and electronic structures of the materials under study performed by using a full density functional theory investigation thanks to a collaboration with the CEMES. First principles electronic structure calculations were performed for the first time to our knowledge over the whole spinel oxide solid solution range MnxCo3-xO4 (0 = x = 3), and compared with our experimental data. A small band gap of ~ 0.8 eV is calculated, due to metal-metal transitions in B sites. The experimental band gaps observed at 1.5 and 2.2 eV, which increase with the amount of manganese, would correspond to B-A and O-B transitions, respectively. The magnetic properties of these materials are also discussed. Chapter four shows the experimental details of the preparation and characterization of the spinel oxide powders, colloidal dispersions and thin films. All samples (Ni, Cu or Zn-doped Co2MnO4) are well crystallized with a single cubic spinel oxide phase. Nanoparticles are spherical and their diameters vary from 20 to 50 nm, doping with Zn, Ni to Cu, mainly due to steric effects. Homogenous oxide thin films were deposited on quartz, alumina, titanium nitride and platinum in order to measure their optical and electrical properties, and to increase the film compactness (thus electrical conductivity and light absorbance) after thermal treatment. Thin films are well preserved up to 900 °C in air and can handle higher temperatures (up to 1000 ºC) on platinum without reaction with the substrate. Chapter five deals with the optical and electrical properties of thin films before and after sintering. The optical properties were measured over a wide range of wavelengths (UV-VIS). The optical properties of spinel oxide thin films show two strong absorption band gaps for each composition at the UV front and close to 700 nm in wavelength. These band gaps are direct and mostly lower than 2 eV for the first band. Both band gaps increase with further doping and decrease after annealing. Thin film resistivity is about 105 .cm at room temperature and decreases with increasing temperature (a few tens of 20cm at 300 ºC). In parallel to the soft chemistry method and dip-coating technique used to prepare our spinel oxide thin layers, Pulsed Laser Deposition technique was used to prepare pure Co2MnO4 and Cu2O dense thin films. Their structural and optical main features are discussed
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Lipowsky, Peter. « Deposition of metal oxide thin films from solutions containing organic additives ». [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-33262.
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Sohi, A. M. « Metal oxide films on glass and steel substrates ». Thesis, Teesside University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391529.
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Farkas, Natalia. « SCANNING PROBE MICROSCOPE OXIDATION AND HIGH-VOLTAGE PARALLEL WRITING ON METAL AND METAL NITRIDE THIN FILMS ». University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1152948068.
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Gao, Xiang. « Carboxylate Precursor Effects on MOD Derived Metal Oxide (Ni/NiO) Thin Films ». University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1331300391.
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Wang, Chao-Hsiung. « The growth of thin film epitaxial oxide-metal heterostructures ». Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368667.
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Huggins, Chris. « Growth & ; surface characterisation of metal oxide thin films under UHV conditions ». Thesis, Queen Mary, University of London, 2005. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1755.
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Thin films of a variety of technologically important oxide systems (chromium oxide, barium oxide, titanium oxide and iron oxide) have been grown under ultra-high vacuum conditions by vapour deposition techniques. The surface structure and chemistry of these oxide films have been characterised by x-ray photoelectron spectroscopy( XPS), low energy electron diffraction (LEED), reflection absorption infrareds pectroscopy(R AIRS) and temperaturep rogrammedd esorptions pectroscopy (T'PD). These studies have included investigation of both the clean oxide surface and their interaction with small molecules. Well-defined chromium oxide films were produced and the surface structure of these films was found to be consistent with the (0001) surface Of C17203T- he studies of barium oxide have revealed a complicated oxygen chemistry with transformation between different forms being brought about by different preparation conditions and post-treatments including heating and exposure to 02, C02 and CO. Well-defined iron oxide films have been generated and in addition to their characterisation such films have been used as a support for the deposition of silver metal nanoparticles. The surface chemistry of this mixed metal/oxide Ag/FeO., system has been probed in particular by the adsorption of propene at sub-ambient temperatures. The ultimate aim of this researchw as to studyt hesem etal oxide thin films as a means to elucidatinga deeperf undamentalu nderstandingo f the surfacec hemistryo f these systemsw, hich is of both academica nd industriali nterest.
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Mpofu, Pamburayi. « Homebuilt reactor design and atomic layer deposition of metal oxide thin films ». Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-176609.
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This research thesis covers work done on building an atomic layer deposition (ALD) reactor followed by the development and optimization of an ALD process for indium oxide thin films on crystalline silicon substrates from new precursors using this new homebuilt cost-effective tool. This work describes the design, building and testing of the ALD system using an indium triazenide precursor and water in a novel precursor combination. The reactor was built to be capable of depositing films with comparable results to commercially built systems.Indium oxide thin films were deposited as the deposition temperature was varied from 154 to 517 0C to study the effects of deposition temperature on the obtained film thicknesses and ascertain the ALD temperature window between 269-384 0C. The presence of indium oxide films was confirmed with X-ray diffraction analysis, which was also used to study their crystallinity. The films were found to have a polycrystalline structure with a cubic phase. Measurement of film thickness was performed using X-ray reflectivity which determined a growth rate of approximately 1 Å/cycle. Elemental composition was determined by X-ray photoelectron spectroscopy which confirmed contamination-free indium rich films. Scanning electron microscope imaging was used to examine the surface morphology of the films as well as thick cross-sectional thicknesses.Since indium oxide films are potentially useful in various electronic, optical, and catalytic applications, emphasis is also placed on the accurate characterization of the chemical and physical properties of the obtained thin films. Optical and electrical properties of the produced transparent conducting oxide films were measured for transparency (and optical band gap) and electrical characterization by resistivity measurements, from UV-Vis spectrophotometry and 4-point probe data respectively. A high optical transmission >70 %, a wide band gap 3.99-4.24 eV, and low resistivity values ∼0.2 mΩcm, showed that In2O3 films have interesting properties for various applications confirming indium oxide a key material in transparent electronics.
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Kim, Se Jin. « Pulsed laser deposited metal oxide thin films mediated controlled adsorption of proteins ». [Gainesville, Fla.] : University of Florida, 2008. http://purl.fcla.edu/fcla/etd/UFE0022878.
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Patel, Shyam Bharatkumar. « Structural and Mechanical Study of CeO2/TiO2 Mixed Metal Oxide Thin Films ». Thesis, Patel, Shyam Bharatkumar (2018) Structural and Mechanical Study of CeO2/TiO2 Mixed Metal Oxide Thin Films. Honours thesis, Murdoch University, 2018. https://researchrepository.murdoch.edu.au/id/eprint/41543/.
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Thin films are well researched in the field of materials science and engineering. Modern thin films have proven to be versatile as they have been developed and modified to attain films with special properties such as high hardness values, improved photovoltaic and photocatalytic properties to name a few. Thin films that exhibit a wide range of exceptional properties are sought after as they could be the solution to a wide range of global challenges.
CeO2/TiO2 mixed metal oxide (MMO) films are capable of showing a wide range of excellent properties and relevant applications such as photovoltaic and photocatalytic capabilities. However, the mechanical properties of these films are not well researched. This study intends to link the Ce-Ti percentage to the mechanical and structural properties of MMO films by studying them at the fundamental atomic level.
The Magnetron sputtered CeO2/TiO2 MMO films were studied using advanced characterization techniques. High temperature in-situ X-ray diffraction (XRD) was conducted to identify and investigate the stability of the oxides present in the films whilst X-ray photoelectron spectroscopy (XPS) was used to find the bonding states within the film. The surface morphology was investigated using a field emission scanning electron microscope (FESEM). The mechanical properties such as hardness and Young’s modulus were determined using nanoindentation tests, whilst the stresses within the film were visualized with the aid of finite element modeling (FEM).
The material characterization indicates the presence of a primary α-Ce2O3 phase in samples containing cerium, whilst a rutile form of TiO2 was found for samples containing TiO2. The mechanical test results of the pure CeOx film show a hardness value as high as 20.1 GPa. The FEM results indicate the stress distribution and is implemented to obtain models of several thin film and substrate combinations.
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Nyman, May. « Synthesis and characterization of precursors for chemical vapor deposition of metal oxide thin films ». Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07112009-040219/.
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Wu, Qingliu. « SYNTHESIS AND ENERGY APPLICATIONS OF ORIENTED METAL OXIDE NANOPOROUS FILMS ». UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/206.
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This dissertation mainly addresses the synthesis of well-ordered mesoporous titania thin films by dip coating with PEO-PPO-PEO triblock copolymer surfactant template P123. Because P123 is composed of poly(ethylene oxide) [PEO] and poly(propylene oxide) [PPO] blocks, concentrations of ingredients are adjusted to tune the films’ wall thickness, pore size and mesophase. Structural changes are consistent with partitioning of species among PEO blocks, PPO blocks, and the PEO/PPO interface. Titanates localize near PEO and increase wall thickness (by 5 nm to 7 nm). Depending on aging temperature, PPG either swells the PPO cores (when it is hydrophobic) or introduces large (>200 nm) voids (when it is hydrophilic but phase separates during heating). 1-butanol localizes at the PEO/PPO interface to favor a 3D hexagonal mesostructure.
In another approach, anodizing Ti foils yields vertically aligned titania nanotubes arrays with exceptional stabilities as anodes in lithium ion batteries; they maintain capacities of 130-230 mAhg-1 over 200 cycles. No microstructural changes are induced by battery cycling and good electrical contact is maintained. A diffusion induced stress model suggests that thin-walled nanotubes arrays should be stable under testing conditions, and that ordered hexagonal columnar pore arrays should have both high charge/discharge rates and low stress development.
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Chun, Yoonsoo. « Domain coupling and resistance in perpendicularly magnetized metal-oxide bilayers / ». Thesis, Connect to this title online ; UW restricted, 2007. http://hdl.handle.net/1773/10570.
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Hill, Matthew Roland Chemistry Faculty of Science UNSW. « The single source chemical vapour deposition of alkaline earth metal oxide thin films ». Awarded by:University of New South Wales. School of Chemistry, 2006. http://handle.unsw.edu.au/1959.4/32903.
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Metal oxide thin films are dynamic materials that have revolutionised the nature of semiconductor and electronic thin film devices. Recently, progress has stagnated in some aspects due to the increasingly complex deposition apparatus required, and the dearth of suitable precursor complexes of certain ???difficult??? metals. This thesis seeks to address both of these issues. The application of a precursor complex, Mg6(O2CNEt2)12 to the SSCVD of MgO thin films delivered the highest quality films ever reported with this technique. The resultant films were found to be of purely (111) orientation. Due to the nature of the precursor, the chemical reactions occurring at the surface during SSCVD growth result in a high growth rate, low flux environment and films of (111) orientation have been achieved without the amorphous underlayer. This finding has important implications for buffer layers in perovskite thin film devices. The unprecedented precursor chemistry has been used as a basis for the extremely high quality material produced, along with the unusual, yet beneficial structural morphology it possesses. A new range of barium complexes with single encapsulating ligands have been prepared for use in chemical vapour deposition (CVD) of BaTiO3 thin films. A novel pathway to an unprecedented class of barium carbamates is reported, and also new dianionic bis ??-ketoesterates and their barium, strontium, and calcium analogues were synthesised. High resolution mass spectrometry showed the barium bis ??-ketoesterate derivatives to be monomeric, and preliminary testing indicated some volatility in these species. Insights were gained into the likely successful pathways to building a volatile heterobimetallic precursor complex containing an alkaline earth metal. The knowledge of intimate mixing in heterobimetallic precursor complexes was extended by some novel chemistry to develop the first mixed Zn/Mg carbamato cluster complexes. These complexes were found to be excellent SSCVD precursors for ZnxMg1-xO thin films. Thin films were deposited with these precursors and exhibited a single preferred orientation, with a constant amount of magnesium throughout the bulk of the films. Investigation of the light emission properties of the films revealed significant improvements in the structural order commensurate with the incorporation of magnesium, and the formation of the ZnxMg1-xO alloy.
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Wen, Rui-Tao. « Electrochromism in Metal Oxide Thin Films : Towards long-term durability and materials rejuvenation ». Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267111.
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Electrochromic thin films can effectively regulate the visible and infrared light passing through a window, demonstrating great potential to save energy and offer a comfortable indoor environment in buildings. However, long-term durability is a big issue and the physics behind this is far from clear. This dissertation work concerns two important parts of an electrochromic window: the anodic and cathodic layers. In particular, work focusing on the anodic side develop a new Ni oxide based layers and uncover degradation dynamics in Ni oxide thin films; and work focusing on the cathodic side addresses materials rejuvenation with the aim to eliminate degradation. In the first part of this dissertation work, iridium oxide is found to be compatible with acids, bases and Li+-containing electrolytes, and an anodic layer with very superior long-term durability was developed by incorporating of small amount (7.6 at. %) of Ir into Ni oxide. This film demonstrated sustained cycle-dependent growth of charge density and electrochromic modulation even after 10,000 CV cycles. The (111) and (100) crystal facets in Ni oxide are found to possess different abilities to absorb cation and/or anion, which yields different degrees of coloration and this is very significant for the electrochromic properties. The degradation of charge capacity in Ni oxide has an inevitable rapid decay in the first hundreds of cycles, subsequently combined with a more gradual decay, which is independent of applied potential and film composition. The consistent phenomenon can be very well modeled by power-law or stretched exponential decay; however the two models are indistinguishable in the current stage. Interestingly, in both models, the power-law exponent is 0.2 ≤ p ≤ 0.8, with most of the values around 0.5, in line with normal or anomalous diffusion models. The second part of dissertation work deals with cathodic WO3 and TiO2. WO3 suffers from ion trapping induced degradation of charge capacity and optical modulation upon electrochemical cycling. This speculation is strongly supported by direct evidence from Time-of-Flight Elastic Recoil Detection Analysis (ToF-ERDA). Most importantly, this ion trapping induced degradation can be eliminated by a galvanostatic de-trapping process. Significant ion-trapping takes place when x exceeds ~0.65 in LixWO3. The trapped ions are stable in the host structure, meaning that the ions cannot de-trap without external stimuli. The similar work done on TiO2 significantly complements and extends the work on the recuperation of WO3; the difference is that the trapped ions in host TiO2 seem to be less stable compared with the trapped ions in WO3. Overall, this dissertation presents a refined conceptual framework for developing superior electrochromic windows in energy efficient buildings.
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Bowers, Norman Mark. « Metal oxide nanocrystalline thin films as buffer layers in organic/ hybrid solar cells ». University of Western Cape, 2019. http://hdl.handle.net/11394/7698.
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>Magister Scientiae - MScWithout reverting to encapsulation, organic bulk - heterojunction solar cells can be protected from the oxidation of the highly reactive low work function cathode metal electrode, by the deposition of metal oxide buffer layers onto an indium-tin oxide (ITO) substrate. The zinc-oxide (ZnO) or titanium dioxide (TiO2) layer can serve as an electron collecting contact. In such a case the ordering of layer deposition is inverted from the traditional layer sequencing, using an additional effect of the metal oxide layer acting as a hole blocking contact
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Miller, Paul. « Zinc Oxide : A spectroscopic investigation of bulk crystals and thin films ». Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/3618.
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The optical properties of zinc oxide crystals and thin films prepared by different methods are investigated. Single crystal zinc oxide samples prepared by melt and hydrothermal growth techniques were obtained. The influence of polarity and growth method on the optical properties were studied and correlated with their electronic properties. Thin films prepared by molecular beam epitaxy (MBE) and sputtering were studied and the influence of growth conditions and post growth treatment on the optical properties of the films was investigated. The photo-luminescence (PL) of bulk zinc oxide was examined at high resolution. Line widths of less than 0.1 meV were observed. More than a dozen different transitions in the near band edge region (NBE 360-380 nm) were noted, several of which displayed a separation of <0.5 meV which goes some way to illustrating the complexity of the system. Attempts were made, with some success, to reconcile the two main competing identification systems of the NBE transitions and explanations for some of the discrepancies are provided. The controversial deep level transitions in the visible part of the spectrum are fit with 3 Gaussians and their identities discussed with relation to the available literature. The presence of copper impurities was detected in annealed films and a model to explain their behaviour under annealing conditions is hypothesised. Films grown by MBE here at the University of Canterbury are shown to have PL line widths of as little as 2.2 meV, the ratio of active oxygen species in the growth chamber during deposition is shown to effect the optical quality of the films. It is shown that annealing can improve the optical quality of the films and various other methods of influencing the films properties are discussed. Reactive, magnetron, direct current sputtering is shown to be the optimal method of growth for maximising both optical and piezo-electric properties. Optimum annealing temperatures were found at 900 and 1100 ℃ with a local minimum at 1000 ℃. X-ray diffraction, atomic force and scanning electron microscopy measurements in addition to optical PL measurements show the influence of annealing on the polycrystalline sputtered ZnO films. Films grown on glass, silicon, sapphire and quartz were shown to display similar behaviour under annealing conditions. It was found that zinc oxide based devices were liable to be chemically unstable at temperatures above 1100 ℃. The piezo electric properties of the films were examined and attempts were made to prepare a zinc oxide film optimised for both optical quality and piezoelectric properties for possible future applications of a hybrid opto-mechanical coupled devices.
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Garza, Michelle. « Reactivity of Oxide Surfaces and Metal-Oxide Interfaces : Effects of Water Vapor Pressure on Ultrathin Aluminum Oxide Films, and Studies of Platinum Growth Modes on Ultrathin Oxide Films and Their Effects on Adhesion ». Thesis, University of North Texas, 2004. https://digital.library.unt.edu/ark:/67531/metadc4517/.
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The reactivity of oxide surfaces and metal-oxide interfaces play an important role in many technological applications such as corrosion, heterogeneous catalysis, and microelectronics. The focus of this research was (1) understanding the effects of water vapor exposure of ultrathin aluminum oxide films under non-ultrahigh vacuum conditions (>10-9 Torr) and (2) characterization of Pt growth modes on ultrathin Ta silicate and silicon dioxide films and the effects of growth modes on adhesion of a Cu overlayer. These studies were conducted with X-ray photoelectron spectroscopy (XPS). Ni3Al(110) was oxidized (10-6 Torr O2, 800K) followed by annealing (1100K). The data indicate that the annealed oxide film is composed of NiO, Al2O3 and an intermediate phase denoted here as "AlOx". Upon exposure of the oxide film at ambient temperature to increasing water vapor pressure (10-6 - 5 Torr), a shift in both the O(1s) and Al(2p)oxide peak maxima to lower binding energies is observed. In contrast, exposure of Al2O3/Al(polycrystalline) to water vapor under the same conditions results in a high binding energy shoulder in the O(1s) spectra which indicates hydroxylation. Spectral decomposition provides further insight into the difference in reactivity between the two oxide films. The corresponding trends of the O(1s)/Ni0(2p3/2) and Al(2p)/Ni0(2p3/2) spectral intensity ratios suggest conformal changes of the oxide film on Ni3Al(110). The growth behavior of sputter deposited Pt at ~300K on Ta silicate and SiO2 ultrathin films formed on Si(100) was investigated. The XPS data show that Pt deposition results in uniform growth or "wetting" on Ta silicate and 2-D cluster growth on SiO2. Electroless Cu deposition on ~11 monolayers (ML) Pt/Ta silicate film results in an adherent Cu film which passed the Scotch tape test. In contrast, electroless Cu deposition on ~11ML Pt/SiO2 results in a non-adherent Cu film due to weak Pt/SiO2 interaction.
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Dolci, Mathias. « Design of magnetic iron oxide nanoparticle assemblies supported onto gold thin films for SPR biosensor applications ». Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAE001/document.
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La bio-détection de molécules reposant sur le phénomène de résonnance plasmon permet de détecter des espèces en utilisant les propriétés optiques de films métalliques. L’utilisation de ce type de capteurs nécessite néanmoins l’augmentation de leurs performances afin de détecter des concentrations faibles d’analyte dans des milieux complexes. L’assemblage de nanoparticules d’oxyde de fer sur des substrats d’or, en utilisant des groupements complémentaires spécifiques via la méthode de chimie « click », permet de contrôler leur distribution spatiale à la surface du substrat. Les propriétés magnétiques portées par les nanoparticules sont ainsi étudiées en fonction de leurs distances inter-particules ainsi que de leurs tailles. Par ailleurs, le plasmon de surface du substrat étant directement influencé par l’assemblage des nanoparticules, il sera possible de contrôler la sensibilité du capteur pour étudier la détection de différentes biomolécules impliquées dans des processus biologiques. La présence des nanoparticules augmente les propriétés optiques intrinsèques de la surface du substrat et la géométrie de l’assemblage permet d’augmenter la quantité de biomolécules détectéesBiomolecular detection based on the surface plasmon resonance phenomenon allow detecting species by using the optics properties of metallic thin films. This kind of biosensors require the increase of their performances in order to detect low concentration analyte in complex medium. The assembly of iron oxide nanoparticles on gold substrates by using specific complementary groups via the “click” chemistry technique allows controlling their spatial distribution on the substrate surface. The magnetic properties carried by the nanoparticles are studied as function of their inter-particle distances and their sizes. Moreover, the surface plasmon of the substrate is directly influenced by the nanoparticle assembly and the control of the sensor sensitivity will be possible in order to study the detection of different biomolecules implies in biological processes. The presence of nanoparticles increases the intrinsic optical properties at the substrate surface and the geometry of the assembly allow increasing the number of biomolecules detected
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Sporar, Daniel. « Sputter Deposition of Iron Oxide and Tin Oxide Based Films and the Fabrication of Metal Alloy Based Electrodes for Solar Hydrogen Production ». Connect to Online Resource-OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1183481021.
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Thesis (M.S.Ch.E.)--University of Toledo, 2007.Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science degree in Chemical Engineering." Bibliography: leaves 72-77.
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Liu, Zhihong. « A study of thermally nitrided silicon dioxide thin films for metal-oxide-silicon VLSI techology / ». [Hong Kong : University of Hong Kong], 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12718488.
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Matoba, Tomohiko. « Fabrication of transition-metal oxide thin films with atomically smooth surface for spintronics application ». 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174948.
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Phillips, Monifa Louise. « Spectroscopic investigation of resistive switching mechanisms in pulsed laser deposited metal-oxide thin films ». Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/38989/.
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Today, CMOS-compatible Flash memory technology dominates the non-volatile memory storage market due to high density and low fabrication costs. However, with CMOS approaching fundamental scaling limits, research into novel emerging non-volatile memory storage technologies that exploit materials properties including resistance, spin and polarisation, has significantly progressed. The ideal non-volatile memory technology would compete with Flash, offering high-density memory storage at low costs, however it would outperform Flash due to its faster operating speeds, lower energy requirements, greater endurance and greater potential for scaling. Of all the emerging technologies, resistive RAM (RRAM) elements, in which reproducible (switchable) and distinct high and low resistance states are the basis of memory storage, are considered most advantageous due to their superior potential for scaling, fastest exhibited operating speeds and extremely low energy requirements. Despite progress in the field of RRAM research, the underlying mechanisms that allow a device to switch between high and low resistance states remains unclear in many materials systems and is the key motivation behind this work. Here, Pulsed Laser Deposited (PLD) RRAM devices that incorporate resistive switching transition metal oxide thin films were studied using Electron Energy Loss Spectroscopy (EELS). Basic metal/oxide/metal RRAM heterostructures that incorporated strongly oxidising titanium electrodes and polycrystalline ZnO and manganese-doped ZnO were investigated in Chapter 3. These devices were designed for direct comparison to a device in presented the literature which displayed the simultaneous co-switching of resistance and magnetisation states. In the devices fabricated here, EELS analysis revealed Mn-phase segregation both at grain boundaries both above and below the top and bottom electrodes, which supported the proposed co-switching mechanism. In Chapter 4, epitaxial single crystal perovskite oxide Pr0.48Ca0.52MnO3 was incorporated into a novel metal/oxide/tunnel-oxide/metal RRAM structure, where the thickness of the interfacial Yttria-stabilised Zirconia tunnel oxide varied the output current density. In both the ZnO and Pr0.48Ca0.52MnO3 devices, EELS analysis revealed that the observed resistive switching was mediated by the field-induced exchange of oxygen vacancies between the bulk oxide and an interfacial oxide. Despite this similarity, the overall device resistance was governed by different effects: for the polycrystalline ZnO-based devices, this was the oxygen-vacancy induced formation and dissolution of a highly resistive TiO2 interfacial layer; in contrast, for the epitaxial Pr0.48Ca0.52MnO3 device, this was the oxygen-vacancy induced charge accumulation and dissipation in the tunnel oxide, which modulated the tunnel barrier height.