Dissertations / Theses on the topic 'Silica films'
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1
Campbell-Rance, Debbie. "Electrodeposited Silica Thin Films." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2123.
Abstract:
Sol-gel derived silica thin film synthesis has gained prominence because of the mild processing conditions and widespread understanding of the chemistry of the process. Traditionally, silicate films are prepared by spin- and dip-coating but these materials lack the desired porosity for sensing, separations and catalysis applications. Electrochemical deposition was proposed to improve the porosity of silicate films. The main aims of this work were threefold. First we wanted to elucidate what parameters influenced film formation during electrodeposition. Then we wanted to understand how these parameters affected the morphology of the materials prepared. These films were characterized by profilometry, AFM, and SEM-EDX. Films electrodeposited via cathodic potentials are particle-like, thicker and rougher than spin-coated films. The final goal was to pattern a substrate with silica using photolithography, sol-gel process and electrodeposition. Successful patterning was hindered by the deposition of silica on glass, especially when the gap between ITO bands was smaller than the diffusion layer thickness of the electroactive species.
2
Spaargaren, Susan Marianne Rosemary. "Radiation effects on silica based waveguides." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267942.
3
Klichko, Yaroslav Vladimirovich. "Functional mesoporous silica films for nanosystems applications." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1998520791&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
4
Kokan, Julie Runyan. "Processing of low permittivity silica thin films." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/20032.
5
Geite, Patrik. "Medical Implant Applications of Mesoporous Silica Films." Thesis, Linköpings universitet, Nanostrukturerade material, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-154463.
Abstract:
A literature review of medical implant applications of mesoporous silica films was written, highlighting the advantages and limitations of different film synthesis methods. Both films synthesized through the EISA sol-gel method and particulate films, including those synthesized through the direct growth method, were reviewed and discussed. All films were found to have their strengths and weaknesses, however, the films synthesized through the direct growth method was found to be the most promising type for coating implants. In addition to the literature review, copper-doped mesoporous silica films were synthesized on titanium grade 2 substrates. SEM shows that particles grown on all the films and EDX elemental analysis confirms the presence of copper in the material. Nitrogen physisorption measurements show that particles with incorporated copper have a higher specific surface area, and pore volume compared to un-doped particles. No copper content could be confirmed through FTIR. The particles grown on titanium substrates were more rod-like compared to the ones grown on the silicon substrates as control.
6
Wooten, Mary K. "NANOFILTRATION MEMBRANES FROM ORIENTED MESOPOROUS SILICA THIN FILMS." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/28.
Abstract:
The synthesis of mesoporous silica thin films using surfactant templating typically leads to an inaccessible pore orientation, making these films not suitable for membrane applications. Recent advances in thin film synthesis provide for the alignment of hexagonal pores in a direction orthogonal to the surface when templated on chemically neutral surfaces. In this work, orthogonal thin film silica membranes are synthesized on alumina supports using block copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as the template. The orthogonal pore structure is achieved by sandwiching membranes between two chemically neutral surfaces, resulting in 90 nm thick films. Solvent flux of ethanol through the membrane demonstrates pore accessibility and suggests a silica pore size of approximately 10 nm. The permeability of ions and fluorescently tagged solutes (ranging from 4,000 to 70,000 Da) is used to demonstrate the membrane’s size selectivity characteristics. A size cut off occurs at 69,000 Da for the model protein BSA. By functionalizing the silica surface with a long chained alkyl group using n-decyltriethoxysilane (D-TEOS), the transport properties of the membranes can be altered. Contact angle measurements and FTIR results show the surface to be very hydrophobic after functionalization. Solvent flux of ethanol through the silica thin film membrane is similar before and after functionalization, but water flux decreases. Thin film silica membranes show much promise for applications in catalysis, bio-sensing, and affinity separations.
7
Bragg, Donald. "Photocatalytic Oxidation of Carbon Monoxide Using Sputter Deposited Molybdenum Oxide Thin Films on a Silicon Dioxide Substrate." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/BraggD2007.pdf.
8
Basnig, Deomila. "Élaboration de films minces de silice pour des applications en chimie analytique." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0102.
Abstract:
Un film orienté à base de silice mésoporeuse sur une électrode FTO a été préparé par une approche d'auto-assemblage assistée par électrochimie (EASA). Un potentiel de -1,5 V a été appliqué à l'électrode FTO contenant un précurseur de silice préhydrolysée (par exemple, l'orthosilicate de tétraéthyle), en présence d'un modèle (par exemple, le bromure de cétrimonium) et d'un électrolyte. Cette approche permet de générer des nanocanaux de silice alignés verticalement avec des tailles de pores ajustables entre 2 et 3 nm, selon le modèle. Ce travail a montré le comportement voltammétrique et la sélectivité du film de silice mésoporeuse vis-à-vis de divers cations chargés positivement de nature, de taille et de charge différentes. Les résultats ont montré une accumulation et une sélectivité favorisant l'ion le moins chargé positivement : MB⁺ > PQ²⁺ > DQ²⁺ > Ru(bpy)₃²⁺ > Ru(NH₃)₆³⁺. L'augmentation des signaux voltamétriques par rapport à l'électrode FTO nue dépendait fortement du type de sonde. L'accumulation des différentes sondes redox est attribuée à l'orientation verticale du nanocanal qui favorise le transport rapide et la diffusion à la surface de l'électrode. Une caractérisation électrochimique plus poussée a montré une interaction entre le processus contrôlé par la surface et le processus contrôlé par la diffusion, où les espèces adsorbées sont plus importantes dans les milieux dilués. Les résultats ont montré que la modification de la longueur debye et du rayon électrocinétique du nanocanal de silice en raison de la force ionique ou du diamètre du nanocanal affecte également le transport et la détection électrochimique de l'analyte paraquat. Les films de silice mésoporeuse ayant des tailles de pores différentes, préparés en utilisant différents bromure d'alkylammonium comme modèle, donnent des sensibilités différentes, qui pourraient être dues à la différence de charge électrochimique de la surface de la silice, ainsi qu'à la distribution des ions dans le nanocanal. Enfin, une tentative de modification de la surface de la paroi de silice en utilisant de la zircone a également été faite pour étudier le transport des cations, ce qui pourrait ouvrir la voie à une meilleure stabilité du film mésoporeuxOriented mesoporous silica-based film on FTO electrode was prepared via electrochemically-assisted self-assembly approach (EASA). A potential of -1.5V was applied to the FTO electrode containing a prehydrolyzed silica precursor, (e.g. tetraethyl orthosilicate), in the presence of a template (e.g. cetrimonium bromide) and electrolyte. This approach could generate vertically-aligned silica nanochannels with pore sizes adjustable between 2 and 3 nm, depending on the template. This work showed the voltammetric behavior and the selectivity of the mesoporous silica film towards various positively-charged cations of different nature, size, and charge. Results showed an accumulation and selectivity favoring the least positive charged ion: MB⁺ > PQ²⁺ > DQ²⁺ > Ru(bpy)₃²⁺ > Ru(NH₃)₆³⁺. The enhancement of the voltammetric signals relative to the bare FTO electrode was strongly dependent on the probe type. The accumulation of the different redox probe is attributed to the due to the vertical orientation of the nanochannel favoring fast transport and diffusion unto the electrode surface. Further electrochemical characterization showed an interplay of the suface-controlled and diffusion-controlled process, wherein adsorbed species is more prominent in diluted media. Results showed that changing the debye length and electrokinetic radius of the silica nanochannel due to the ionic strength or nanochannel diameter also affects the transport and electrochemical detection of the paraquat analyte. Mesoporous silica films having different pore size, prepared using different alkyl ammonium bromide as template, yield different sensitivities, which could be due to the difference in electrochemical charge of the silica surface, as well as the distribution of ions in the nanochannel. Finally, an attempt to modify the surface of silica wall using zirconia was also made to study the transport of cations, which could pave a way for an improved stability of the mesoporous film
9
CHAKRAVARTY, SRINIVAS L. N. "DEVELOPMENT OF SCRATCH RESISTANT PECVD SILICA-LIKE FILMS." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin973542599.
10
Moskowitz, Steven. "Atomic force miscroscopy [sic] study of SiO₂/Si(111)--(7x7) grown via atomic oxygen plasma /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/11556.
11
Sawtell, David Arthur Gregory. "Plasma enhanced chemical vapour deposition of silica thin films." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/plasma-enhanced-chemical-vapour-deposition-of-silica-thin-films(2c75bbd8-8d89-42f2-b926-b464e619b4aa).html.
Abstract:
Atmospheric pressure chemical vapour deposition is an industrially significant process for forming functional thin films. There is a great opportunity for increased scientific understanding with the aim of improving current processes and helping to formulate new ones. This work is concerned with developing a methodology to assist this ongoing concern. A combination of spectroscopic and chemometric techniques are used to investigate several chemical vapour deposition processes. The first investigation concerns the spatial concentration mapping of key by-products during the thermal chemical vapour deposition of tin oxide films through the use of near infra red laser diode spectroscopy. This novel two dimensional characterisation of the process has identified reaction hotspots within the process, and has identified the redundancy of part of the exhaust mechanism. Subsequently, there has been improvements to the head design, and the operation of the process.The main thrust of the investigations are focussed towards the use of chemometric methods, such as experimental design and principal components analysis, in conjunction with a suite of spectroscopic measurement techniques, to analyse the plasma enhanced chemical vapour deposition of silica films. This work has shown the importance of active oxygen species on the chemistry. It has also been shown that the film properties are highly dependant on oxygen concentration in the reactor, and hence active oxygen species forming in the plasma. The identification of by-products in the silica deposition process has also been carried out for the first time. Finally, this work also presents the first rigorous studies of a new precursor for silica deposition, dichlorodimethylsilane.
12
Steinthal, Michael Gregory 1964. "Laser densification of sol-gel-derived silica coatings." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277183.
Abstract:
Sol-gel derived silica coatings were deposited on soda-lime-silica by dip-coating. An absorbing metallic layer was sputtered onto the surface of the gel to couple near-infrared radiation from a Nd:YAG laser into the transparent coating. Laser energy was utilized to heat the ceramic coating on a substrate which has a lower glass transition temperature than the coating. Scanning the sample across the beam's path resulted in the formation of a 50 mum wide channel. The characteristics of a channel were altered by varying laser power, sol-gel coating thickness, and scanning speeds. Profilometry and SEM analysis verified that the coating can be heated to high temperatures without damaging the substrate.
13
Yang, Hong. "Forms of mesoporous silica, fibers, films, curved shapes and patterns." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0006/NQ41535.pdf.
14
MaCarthy, Orla. "Selective area doping of porous silica films for optical applications." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299318.
15
Abbas, Bassam. "Linear and nonlinear optical phenomena in thin sol-gel organic-inorganic films." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298744.
16
De, Witt Joanna Christine. "Switching the reflection in chiral nematic mesoporous silica and organosilica films." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43781.
17
Robertson, Joseph William F. "Fabrication, analysis and patterning of sol-gel based silica ultrathin films." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280795.
Abstract:
A novel approach to sol-gel thin film fabrication has been developed which leads to the production of ultrathin ∼2 nm to 100 nm thick silica and conductively-doped silica films on metal and semiconductor substrates. The research described herein focuses on the development, characterization and potential application of these thin films in current technology. These ultrathin films were fabricated by a sol-gel procedure, which utilized highly diluted silica precursor compounds. The [H₂O]:[Si] ratio ranged from 50 to 1000, far above the typical values (4-10) used in sol-gel film preparation. This dilution leads to highly densified silica when spin-cast onto an appropriately compatible surface. The surface examined included Si(111)/SiO₂; ITO; and 3-(mercaptopropyl)trimethoxysilane (3MPT) modified Au and Ag. These surfaces must act as wetting control agents for the sol-gel precursor, while simultaneously providing adhesion to the nm sized sol-gel aggregates. The 3MPT-Ag monolayer was examined in detail by Tl, Pb and Cd underpotential deposition electrochemistry, to understand the interfacial structure of the molecule. These results show that the 3MPT monolayer is very stable to outside influences (i.e. Tl and Pb reversibly deposit monolayers at the metal surface). The UPD of metal ions is highly size dependent with Tl depositing with fewer kinetic limitations than Pb and Cd not depositing at all. Raman spectral characterization shows that 3MPT undergoes some reversible rearrangement during the UPD process. The electronic properties of the pure silica films were examined in great detail. The results suggested that in solution, a solvated gel layer at the film-solution interface gives rise to an anomalously low capacitance <100 pF/cm², which has no comparison in the current literature. In the dry state, these silica films have a dielectric constant of ε = 3.5, which is close to that of thermally-grown silica on silicon (3.9). These films were doped with 1,1'-bistriethoxysilylferrocene, an electrochemically-active sol-gel material. The results suggest that under the proper precursor solution conditions, thin ( <10 nm), uniform films can be fabricated. By simply adjusting the ratio of the ferrocene moiety in solution, the film composition can be adjusted. XPS verifies that the atom ratio in solution is near to the observed atom ratio in the films, with some indication of surface segregation of the ferrocene moiety. Electrochemical analysis of these films suggests that electron hopping between the ferrocene centers drives the electrochemical response only when there are pinhole defects, to support counterion conduction to the surface. (Abstract shortened by UMI.)
18
Ghaffari, Kasra. "Optical interferometric measurement of in-plane residual stresses in SiO₂ films on silicon substrates." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/16815.
19
De, Paz-Simon Héloise. "Sol-gel photopolymerization of inorganic precursors and application for mesoporous silica films elaboration." Thesis, Mulhouse, 2013. http://www.theses.fr/2013MULH6112/document.
Abstract:
Alors que le procédé sol-gel a été fortement étudié il existe peu d’études concernant le procédé sol-gel photoinduit. Le principe repose sur la libération in situ d’espèces acides ou basiques photogénérées capables d’amorcer les réactions d’hydrolyse et de condensation caractéristiques du procédé sol-gel. L’alternative photoinduite est particulièrement adaptée pour préparer des films minces et possède de nombreux avantages tel qu’une formulation de départ stable, sans solvant et photolatente ainsi que des vitesses de réactions plus importantes. À partir de précurseurs inorganiques simples, nous avons dans un premier temps réalisé une étude mécanistique et cinétique de ce procédé en catalyse acide. Puis l’influence de différents paramètres physiques, chimiques et photochimiques sur les vitesses de réactions a été évaluée. Une comparaison avec un système similaire en catalyse basique a aussi été réalisée.Dans un second temps, nous nous sommes intéressés à appliquer ce procédé photoinduit pour la préparation de films de silice mésoporeuse. Un tensioactif de type copolymère tribloc a été ajouté au précurseur inorganique de départ. La faisabilité d’une approche photochimique à partir de formulation sans eau ni solvant a d’abord été étudiée, des films mésoporeux ont été obtenus. Puis, nous nous sommes intéressés à la compréhension des 2 mécanismes interdépendants : le mécanisme d’assemblage du tensioactif et la condensation du réseau inorganique. Par la suite, le système a été optimisé pour aboutir à un contrôle précis de la structure et de la taille des pores. Enfin, une dernière étape a consisté à éliminer la partie organique (pour libérer la porosité) grâce à l’UVWhereas sol-gel process has been extensively studied almost no papers concerning photoinduced sol-gel process subsists. This later is based on in situ generation of acids or basics species able of initiating hydrolysis and condensation reactions happening on sol-gel process. This photoinduced alternative is particularly adapted for preparation of thin films and has lots of advantages such as photolatent, stable, solvent and water free initial formulation along with faster reaction rates. In one hand, from simple inorganic precursors, a kinetic and mechanistic study of the photoacid-catalyzed sol-gel reactions was realized. Then, we attempt to define what chemical, physical and photochemical parameters determine the precise sequence, kinetics and advancement of these reactions under different processing conditions Furthermore, an equivalent photobase-catalyzed sol-gel process has been also studied thoroughly. In a second hand, we focus on application of this photoinduced process for the preparation of mesoporous silica films. A triblock copolymer surfactant was added to the initial inorganic precursor. Feasibility of this photochemical approach from water and solvent free formulation was first investigated and mesoporous films were obtained. Then, we work on understanding the two interdependent mechanisms: surfactant self-assembly and inorganic network condensation. The system was after that optimized in order to have a precise control of pore size and structure. Finally, the last point involves organic photodegradation in order to liberate porosity
20
Mårtensson, Niklas. "Optical Properties of Silica-Copper Oxide Thin Films Prepared by Spin Coating." Thesis, Linköpings universitet, Tillämpad optik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-71188.
Abstract:
Optical properties of copper oxide nanoparticles in a silica matrix thin film have been investigated. Films were prepared on Si substrates from a sol-gel by spin coating. Four samples with different thicknesses, from 14,5-109 nm, were fabricated. Optical properties were measured with Variable Angle Spectroscopic Ellipsometry. The aim of the project was to gain further understanding of these films that are interesting in applications for solar absorbers as solar selective coatings. Ellipsometricangles Ψ and Δ were measured in the wavelength range from 250-1700 nm. A dispersion model was developed and fitted to experimental data with acceptable results.
21
Björk, Emma M. "Mesoporous Building Blocks : Synthesis and Characterization of Mesoporous Silica Particles and Films." Doctoral thesis, Linköpings universitet, Nanostrukturerade material, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-99858.
Abstract:
Catalyst supports, drug delivery systems, hosts for nanoparticles, and solar cells are just some examples of the wide range of exciting applications for mesoporous silica. In order to optimize the performance of a specific application, controlling the material’s morphology and pore size is crucial. For example, short and separated particles are beneficial for drug delivery systems, while for molecular sieves, the pore size is the key parameter. In this thesis, mesoporous silica building blocks, crystallites, with hexagonally ordered cylindrical pores were synthesized, with the aim to understand how the synthesis parameters affect the particle morphology and pore size. The synthesis of the particles is performed using a sol-gel process, and in order to increase the pore size, a combination of low temperature, and additions of heptane and NH4F was used. By variations in the amounts of reagents, as well as other synthesis conditions, the particle morphology and pore size could be altered. Separated particles were also grown on or attached to substrates to form films. Also, a material with spherical pore structure was synthesized, for the first time using this method. It was found that a variation in the heptane concentration, in combination with a long stirring time, yields a transition between fiber and sheet morphologies. Both morphologies consist of crystallites, which for the fibers are joined end to end, while for the sheets they are attached side by side such that the pores are accessible from the sheet surface. The crystallites can be separated to a rod morphology by decreasing the stirring time and tuning the HCl concentration, and it was seen that these rods are formed within 5 min of static time, even though the pore size and unit cell parameters were evolving for another 30 min. Further studies of the effects of heptane showed that the shape and mesoscopic parameters of the rods are affected by the heptane concentration, up to a value where the micelles are fully saturated with heptane. It was also observed that the particle width increases with decreasing NH4F concentration, independent of heptane amount, and a platelet morphology can be formed. The formation time of the particles decrease with decreasing NH4F, and the growth mechanism for platelets was further studied. The pore sizes for various morphologies were altered by e.g. variations in the hydrothermal treatment conditions, or the method for removing the surfactants. The separated particles can be attached to substrates, either during the particle synthesis or by post grafting prior to calcination. The film formation during the one-pot-synthesis was studied and a formation mechanism including nucleation of elongated micelles on the substrate was suggested. During the post grafting film synthesis, the medium in which the particles are dispersed, as well as functionalization of both particle and substrate are crucial for the post grafting process. The pores are easily accessible independent of the method, even though they are aligned parallel to the substrate when the one-pot-method is used, while post grafting gives a perpendicular pore orientation. In summary, this work aims to give an understanding for the formation of the synthesized material, and how to tune the material properties by alterations in parameter space. Successful syntheses of four different particle morphologies and two new types of films were performed, and the pore size could easily be tuned by various methods.
22
WAGH, VIJAY HEMANT. "VAPOR PHASE SILANATION OF PLASMA-POLYMERIZED SILICA-LIKE FILMS BY 3-AMINOPROPYLTRIETHOXYSILANE." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1121884987.
23
TURNER, ROBERT HAINES. "MOLECULAR STRUCTURE OF INTERFACES FORMED WITH PLASMA POLYMERIZED SILICA-LIKE PRIMER FILMS." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin997298644.
24
Ye, Fangmao. "Single molecule studies of meso/macro porous silica materials and gradient films." Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1699.
25
Leuty, Gary Martin. "Structure and Dynamics of Fluoromethane Films Adsorbed on Graphite and Silica Substrates." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/402.
Abstract:
Molecular Dynamics (MD) simulation methods were used to perform simulations of the adsorption of multilayer films of three fluoromethane compounds -- nonpolar CF4 and its polar relatives, CF3Cl and CF3Br -- onto two chemically and structurally different substrates: graphite and hydroxylated α-quartz (a form of silica). The purpose of the simulations was to determine how differences in polarity and substrate type affect the structure of film layers at the adsorption surface, as well as to compare how these factors affect the mobility of molecules near the surface as they move along or away from the surface, to see how each of these factors affects the substrate affinity for the adsorbed compound. Simulations were performed for pure fluoromethane films as well as films created from binary mixtures of the above fluoromethanes adsorbed on each substrate over a range of temperatures from 80 K to 280 K. Analysis suggests a strong influence of substrate characteristics on both the structure and mobility of molecules in adsorbed layers, an effect that is partially temperature dependent but only weakly suggestive of effects due to the differences in polarity of the adsorbed molecules.
26
Motos, Blanca. "Silices fonctionnalisées contenant des espèces ioniques pour la catalyse hétérogène." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2011. http://www.theses.fr/2011ENCM0015.
Abstract:
La catalyse hétérogène est en plein développement pour des raisons économiques, de santé et de protection environnementale. Les travaux de cette thèse s'intéressent à la préparation des silices fonctionnalisées par des sous-structures ioniques pour leur application en catalyse hétérogène. D'abord, des matériaux mésoporeux fonctionnalisés par des entités di-aryl imidazoliums ont été préparés par des réactions de post-greffage. En plus, films de type PMO contenant des entités di-aryl imidazoliums ont été synthétisés en présence d'un surfactant anionique. Ensuite, complexes carbéniques N-hétérocycliques du cuivre et du palladium supportés ont été préparés et appliqués en tant que catalyseurs organométalliques dans des réactions A3 (Cu-NHC) et de couplage de Suzuki (Pd-NHC). Les silices fonctionnalisées avec des entités imidazoliums ont également été utilisées en tant qu'organocatalyseurs des réactions de Henry et dans de cycloaddition du dioxyde de carbone aux époxydes. Des matériaux de type ‘PMO' contenant des entités amines/ammoniums ainsi que des sous-structures zwitterioniques ont été utilisés en réactions organocatalysées de Henry et BiginelliHeterogenous catalysis is an area in continuous development due to economical, health and environmental issues. This thesis deals with the preparation of i-silica materials for the posterior application in heterogeneous catalysis. First, di-aryl imidazolium containing silica materials were synthesized by post-grafting reactions on mesoporous SBA-15. Moreover, di-alkyl imidazolium containing PMO films were prepared in presence of an anionic surfactant. Then, supported copper and palladium N-heterocyclic carbenes were synthesized from di-aryl imidazolium silica and applied to A3 reactions (Cu-NHC) and Suzuki cross-coupling reactions (Pd-NHC). Imidazolium functionalized silicas were also utilized as heterogeneous organocatalysts in Henry reactions and in reactions of cycloaddition of carbon dioxide to epoxides. Finally, PMO type materials containing amine/ammonium and zwitterionic substructures were applied to Henry and Biginelli organocatalysed reactions, respectively
27
Kang, Laeugu. "Study of HFO₂ as a future gate dielectric and implementation of polysilicon electrodes for HFO₂ films /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004301.
28
Cao, Yuanmei. "Antireflective Polyimide Based Films." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1335501090.
29
LORENZI, ROBERTO. "Silica based functional materials: - Charge transport in nanostructured SnO2: SiO2 thin films. - Second harmonic generation in niobium potassium silicate glasses. - Tapered silica optical microfibres for gas sensors." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/10933.
Abstract:
"Charge transport in nanostructured
SnO2:SiO2 thin films":
Silica based nanostructured thin films grown on silicon substrates are promising materials for novel light emitter devices. In particular, tin dioxide is a wide band gap n-type semiconductor (Eg=3.6 eV) with an expected band-to-band emission centered in the ultraviolet (344 nm) region of the electromagnetic spectrum. Our group succesfully demonstrated UV emission from such systems, but at the beginning of my work many issues in charge transport processes needed to be explained.
Aim of this project was to clarify electric transport and charge trapping mechanisms. As a result of a materials science approach we can now interpret the experimental data through specific relationships between synthesis conditions, clustering morphology (nanoparticle (NP) size distribution and volumic concetration, interphase substoichiometry, film thickness), and electric response.
The observed phenomena have been analyzed within the percolation theory. Main results concern: electric transport of both holes and electrons is sustained by NP-to-NP hopping events and dielectric enhancement results from oscillating charges (holes) on NPs. "Second Harmonic Generation in potassium niobium silicate glasses": Second harmonic generation (SHG) is a non linear optical process largely employed in current laser technology and photonics. However in almost every application the material employed for these purposes are single crystals. Therefore the possibility to achieve large SHG in amorphous systems may lead to devices with innovative configurations. SHG may occur only if the system is non-centrosymmetric, therefore for glasses it is forbidden due to intrinsic isotropy. The inversion symmetry can be broken up with poling treatments. They consist in applying strong electrostatic field while the sample is stressed by external perturbation (typically heat, electron beam or laser light).
We have explored the effect of thermal poling treatment on potassium niobium silicate glasses on inducing non linear optical properties. The results have revealed a strong SHG associated with structural modifications.
The proposed mechanism involves a rearrangement of niobium oxide groups mediated by non bridging oxygen and potassium ion transport across the glass. These new charge arrangements form a non-centrosymmetric region underneath the anodic contact responsible of the detected SH signal. "Tapered silica optical microfibres for gas sensors": In the last years, tapered silica fibres have attracted much interest in photonic research, because of peculiar properties emerging in waveguides with lateral dimensions of the same order of the guided modes. In particular, in these structures the large evanescent field enables some interesting properties, such as microfluidic sensors and high Q optical resonators (coiling the tapered fibre), non-linear effects and supercontinuum generation. In this project, carried out at the University of Southampton (UK) in the group of Dr. Gilberto Brambilla, we have explored the feasibility of an innovative optical absorption device, based on ring down spectroscopy.
In this case we are interested in a sensor for in-line application: a fluidic channel wrapped with tapered fibre in which the analyte can flow. The large power fraction outside the fibre interacts with the flowing medium and any change in the surrounding optical properties (refractive index or absorption coefficient) leads to a modification of the recorded light intensity propagating in the fibre.
The idea is to exploit ring down time of a silica tapered microcoil resonator as an indicator of the absorption coefficient of a gas (or a liquid) flowing in the channel.
30
Yilmaz, Emre. "Sensitization Of Sol-gel Derived Titania-silica Photocatalytic Thin Films With Ascorbic Acid." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614226/index.pdf.
Abstract:
The photocatalytic activity of semiconductor metal oxides can be improved by the addition of sensitizer which enhances the band gap by considerable red shift of the absorption edge of semiconductor. In the present study, the effect of ascorbic acid as sensitizer on the photocatalytic activity of titania-silica binary mixtures was studied. The SiO2-TiO2 mixtures having 50wt%Ti:Si composition were prepared with sol-gel method. The surface area and porosity of the samples were modified by using various amounts of polyethylene glycol (PEG) as template. The thin films of the samples were obtained by dip coating of glass plates to colloidal solutions. The samples were characterized by methylene blue adsorption method and UV-Vis spectrophotometry. The photocatalytic activities of the samples were measured with methylene blue degradation, methyl orange degradation and direct water splitting in the presence and absence of ascorbic acid. Increase in the surface area and reaction rate with increasing PEG addition until a threshold value was observed. Highest methylene blue degradation activity was observed for 27g PEG added sol-gel derived film and surface area of this film is measured as 44m2/m2. Ascorbic acid presence shows a significant increase in the photocatalytic degradation activity of methyl orange. The sensitization effect of ascorbic acid was also compared with the effect of EDTA. It was found that the effect of ascorbic acid on the methyl orange degradation rate is significantly higher than the effect of EDTA. However, the effect of EDTA is more pronounced in water splitting reaction.
31
Korkmaz, Erdural Beril. "Photocatalytic Antimicrobial And Self-cleaning Properties Of Titania-silica Mixed Oxide Thin Films." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615137/index.pdf.
Abstract:
In this study photocatalytic antibacterial and self-cleaning activities of TiO2-SiO2 thin films as a function of TiO2/SiO2 ratios were investigated. TiO2-SiO2 mixed oxides were synthesized by sol-gel method and coated over soda-lime glass plates by dip coating technique. Escherichia coli was used as a model microorganism for the photocatalytic antibacterial tests. Degradation rate of methylene blue (MB) molecules was used to characterize photocatalytic self-cleaning activities of thin film surfaces.
The maximum antibacterial activity was achieved over 92 wt% SiO2 containing thin films. However, when the SiO2 content exceeds 92 wt%, photocatalytic antibacterial activity decreased considerably, which was explained by the dilution of TiO2 phase and inaccessibility of TiO2. Increase in photocatalytic antibacterial activity was attributed to increases in the relative surface area, roughness, hydroxyl (OH-) groups and bacterial adhesion. The favored bacterial adhesion enhanced direct contact of bacteria with TiO2 particles and surface reactive oxygen species.
The highest initial decomposition rate of MB was obtained for 60 wt% SiO2 and the activity decreases as SiO2 concentration increases. The increase in photocatalytic activity by the SiO2 addition can be explained by the increase of the amount of MB per unit area of TiO2-SiO2 thin films.
Different adsorption capability of thin films against MB molecule and E. coli cell was explained as the first reason why the antibacterial and self-cleaning activities reached their maximum values at different SiO2 ratios. The second reason could be related with the different control mechanisms of self-cleaning and antibacterial activities by different textural and surface properties.
32
Taylor, Mark Philip. "Studies of the reaction of silane and hydrogen peroxide forming silica thin films." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337161.
33
Moloney, John, Thomas McDermott, Taslima Akter, Michael McCann, J. M. Donal MacElroy, Damian A. Mooney, and Denis P. Dowling. "Molecular simulation of the fabrication and permselective characterisation of thin nanoporous silica films." Diffusion fundamentals 16 (2011) 21, S. 1-3, 2011. https://ul.qucosa.de/id/qucosa%3A13753.
34
Hudgins, Robert Anthony. "Photonic Applications of Rare Earth Doped TEOS Based Silica Thin Films and Waveguides." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054758007.
35
Moloney, John, Thomas McDermott, Taslima Akter, Michael McCann, J. M. Donal MacElroy, Damian A. Mooney, and Denis P. Dowling. "Molecular simulation of the fabrication and permselective characterisation of thin nanoporous silica films." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184768.
36
Syme, Derric Benjamin. "Microfabrication and Characterization of Freestanding and Integrated Carbon Nanotube Thin Films." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7376.
Abstract:
This work chronicles the fabrication of two unique thin films using carbon nanotubes. The first is a carbon film made primarily from vertically grown carbon nanotubes (CNTs) and rolled into lateral alignment. The second is an insulating film created by CNTs as a scaffolding to create a porous silica layer. Each topic represents a different method of utilizing CNTs for thin-film fabrication.Investigation of an entirely carbon thin film, comprised of aligned and laterally oriented carbon nanotubes was performed. The thin film was strengthened by deposition of amorphous carbon for a total thickness of <<> 5 µm. This thickness is thinner than many previous films fabricated entirely out of carbon. Vertically aligned CNT arrays were manually rolled into a thin sheet and released from the growth substrate. Infiltration with amorphous carbon (as carbon coating) on the rolled CNTs was used to improve adhesion between neighboring CNTs after lateral alignment and to improve the mechanical integrity of the film. Mechanical property characterization indicated the ability to sustain a pressure differential across the film of up to 82.7 kPa for a suspended film of 4 mm in diameter. Peak stress, Young<'>s modulus and biaxial modulus were obtained as a characterization of the strength of the thin film.Fabrication and examination of a porous silica thin film, potentially for use as an insulating thermal barrier, was investigated. A vertically aligned CNT forest, created by chemical vapor deposition (CVD), was used as a scaffolding for the porous film. Silicon was deposited on the CNT forest using low pressure CVD (LPCVD), then oxidized to remove the CNTs and convert the silicon to silica <&hyphen>“ a material often used for electrical or thermal passivation. This fabrication method introduces hollow pores where the CNTs once occupied, further increasing the material<'>s insulating properties. Thermal testing was performed by equating radiative and conductive heat transfer in a vacuum chamber and comparing the temperature difference between the film and a reference sample of comparable thermal resistance. For films approximately 50 µm thick, the thermal conductivity was found to be 0.054 - 0.071 W/mK.
37
Heineman, Dawn Laurel. "Optimization of ALD grown titania thin films for the infiltration of silica photonic crystals." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-05142004-143254/unrestricted/heineman%5Fdawn%5Fl%5F200407%5Fms.pdf.
Abstract:
Thesis (M.S.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2005. Directed by Christopher Summers.Summers, Christopher, Committee Chair ; Snyder, Robert, Committee Member ; Wang, Zhong Lin, Committee Member. Includes bibliographical references.
38
Fuhrich, Alexander Benedikt [Verfasser]. "Ultra-thin Germania and Germania-Silica films : Growth, structure and reactivity / Alexander Benedikt Fuhrich." Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1199937002/34.
39
Oblitas, Torrico Ruben Felipe Arturo [UNESP]. "Preparação e caracterização de híbridos orgânico-inorgânicos à base de epoxí-silica." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/139461.
Abstract:
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Este projeto visa a investigar a relação entre a estrutura e as propriedades dos materiais epoxi-silica preparados pelo método sol-gel. Os híbridos foram preparados pela reação de cura entre o poly(Bisphenol A-co-epichlorohydrin) (DGBEA) , e o dietil triamina (DETA) assim como pelo processo Sol-Gel de hidrolise e condensação entre GPTMS (3-Glycidoxypropyl)methyldiethoxysilane) e TEOS. Ressonância magnética nuclear (RMN), espectroscopia de fotoelétrons de raios X (XPS), espalhamento de raios X a baixo ângulo (SAXS), espectroscopia de Infravermelho e RAMAN, microscopia de força atômica (AFM) assim como termogravimétria foram utilizadas com o proposito de investigar a morfologia e as propriedades estruturais do material. Finalmente as propriedades anticorrosivas dos filmes foram testadas em uma solução salina por meio de espectroscopia de impedância eletroquímica (EIS). Durante a fase inicial do projeto diferentes amostras com diferentes concentrações de TEOS foram preparadas. A estabilidade térmica como as propriedades anticorrosivas foram testadas. Os resultados mostraram que para maiores concentrações de TEOS, as propriedades anticorrosivas e térmicas dos híbridos melhoram significativamente. Vários resultados interessantes foram obtidos, para híbridos com razoes molares de TEOS : GPTMS : DGBEA = 1 : 1: 1, tendo módulos de impedância de até 1010 Ω cm-2. Durante a segunda fase do projeto, duas series de amostras com concentrações diferentes de GPTMS a TEOS foram preparadas. As propriedades estruturais foram obtidas por meio de Espectroscopia Infravermelho, Raman, RMN e XPS e espalhamento de raios X a baixo ângulo. A hidrofobicidade assim como as propriedades térmicas foram avaliadas por meio de testes de molhabilidade e análise termogravimétrica. Finalmente as propriedades anticorrosivas dos filmes em contato com solução salina foram testadas por meio de espectroscopia de impedância electroquímica.
This work aims to investigate the relationship between the structure and the properties of the sol-gel prepared epoxy-silica materials. The organic-inorganic hybrids were prepared from the curing reaction of poly(Bisphenol A-co-epichlorohydrin) (DGBEA), with Diethyltriamine (DETA) and (3-Glycidoxypropyl)methyltriethoxysilane) (GPTMS) combined with the sol-gel hydrolysis and condensation reactions between Tetraethoxysilane (TEOS) and GPTMS. Nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), Infrared and Raman spectroscopy (IR), Atomic force microscopy, as well as thermogravimetry (TG) have been used with the purpose to investigate the morphological and structural properties of the material. Finally the anticorrosive properties of the hybrid coated carbon steel were evaluated in saline solution using electrochemical impedance spectroscopy (EIS). During the initial phase of the project different samples with increasing concentrations of TEOS have been prepared and their thermal stability as well as their anticorrosive properties were tested. It was found, that for increasing TEOS concentration, the hybrid’s anticorrosive and thermal properties can be improved. Several interesting results were obtained for hybrid coatings at a TEOS : GPTMS : DGBEA = 1 : 1 : 1 ratio, having an impedance modulus of up to 1010 Ω cm-2. During the second phase of the work, a series of epoxy-silica hybrids were synthetized varying the concentrations of GPTMS and TEOS. Their structural properties were characterized by means of Infrared, Raman, solid NMR and XPS spectroscopy. Their hydrophobicity as well as their thermal resistance were evaluated using the drop shape analysis and thermogravimetry. Finally the anticorrosive properties of the coatings in saline solution were tested using electrochemical impedance spectroscopy.
40
Eker, Zeynep. "Preparation And Characterization Of Titania-silica-gold Thin Films Over Ito Substrates For Laccase Immobilization." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12611022/index.pdf.
Abstract:
The aim of this study was to immobilize the redox enzyme laccase over TiO2-SiO2-Au thin film coated ITO glass substrates in order to prepare electrochemically active surfaces for biosensor applications. Colloidal TiO2-SiO2-Au solution was synthesized by sol-gel route and thin film was deposited onto the substrates by dipcoating method. The cysteamine was utilized as a linker for immobilization of enzyme covalently through gold active sites. Preliminary studies were conducted by using invertase as model enzyme and Pyrex glasses as substrates.
The effect of immobilization parameters such as immobilization temperature, concentration of enzyme deposition solution, immobilization time for laccase were examined. Leakage studies were conducted and storage stability of immobilized laccase was determined. Highest laccase activity was achieved when immobilization was performed with 50 µg/ml solution at 4°
C for 2 hours. Laccase activity decreased after 4 hours of impregnation in enzyme solution. Laccase leakage was observed in the first usage of substrates and 55% activity decrease was determined in the subsequent use which might be attributed to the presence of uncovalently adsorbed enzyme on the fresh samples. In air and in buffer storage stabilities were also tested. It was found that the activity of samples almost vanished after 6 days regardless of storage conditions. Both enzymes had more activity on ITO substrate.
41
BENGU, BASAK. "THE MOLECULAR STRUCTURE OF INTERFACES FORMED BETWEEN PLASMA POLYMERIZED SILICA-LIKE FILMS AND EPOXY ADHESIVES." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1195657609.
42
Li, Xin. "MULTISCALE DYNAMIC MONTE CARLO / CONTINUUM MODELING OF DRYING AND CURING IN SOL-GEL SILICA FILMS." Lexington, Ky. : [University of Kentucky Libraries], 2008. http://hdl.handle.net/10225/950.
Abstract:
Thesis (Ph. D.)--University of Kentucky, 2008.Title from document title page (viewed on December 11, 2008). Document formatted into pages; contains: xii, 143 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 137-142).
43
Boffelli, Marco <1987>. "Defects related cathodoluminescence of N-doped silica thin films prepared by radio frequency magnetron sputtering." Master's Degree Thesis, Università Ca' Foscari Venezia, 2012. http://hdl.handle.net/10579/1703.
Abstract:
Lo scopo principale di questo lavoro è lo studio dettagliato di film sottili di N-SiO2, depositati mediante RF magnetron sputtering. Per studiare la natura della popolazione dei difetti nei film di SiO2 è stata utilizzata la spettroscopia da catodoluminescenza, mentre la caratterizzazione fisica è stata ottenuta attraverso misure RBS, XPS e IBIL. Allo scopo di studiare l’evoluzione termica dei film depositati, i campioni ottenuti sono trattati termicamente in un range di temperature da 50°C a 1200°C, con step di 50°C.
44
Lewandowski, Adrián Leandro. "The Atomic Structure of Ultrathin Germania Films." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20874.
Abstract:
Die Herstellung von ultradünnen Germaniumdioxidfilmen auf Metallsubstraten ist erstmals erfolgreich gelungen. Die Filmstruktur konnte mittels oberflächensensitiven Techniken mit atomarer Präzision und chemischer Sensitivität aufgelöst werden. Zur Untersuchung werden STM-Bilder analysiert und durch niederenergetische Elektronenbeugung (LEED), eine dynamischen LEED-Studie und extern ausgeführte Dichtefunktionaltheorieberechnungen (DFT) ergänzt.
In dieser Arbeit werden atomar aufgelöste Rastertunnelmikroskopiebilder (STM) von ultradünnen Germaniumdioxid- und Siliziumdioxidfilmen direkt verglichen. Ziel der Analyse ist es, den Einfluss des Metallsubstrats auf die Struktur von Oxidfilmen zu untersuchen. Zu diesem Zweck werden ultradünne Germaniumdioxid-Filme auf Ru(0001), Pt(111) und Au(111) abgeschieden und mit Siliziumdioxid-Filmen auf verschiedenen Substraten verglichen, die in früheren Studien untersucht wurden. Germaniumdioxid und Siliziumdioxid sind eng miteinader verknüpft. Hierbei sind Struktur und chemische Eigenschaften als äquivalent anzusehen.
Es wurden drei verschiedene Netzwerkstrukturen aufgeklärt: Monolagen-, Zickzack- und Bilagenfilme. Die einzelnen Bausteine in diesen Filmsystemen bestehen aus verzerrten Tetraedern, in denen ein Germaniumatom von vier Sauerstoffatomen umgeben ist. Benachbarte Tetraeder sind durch Ge-O-Ge-Bindungen miteinander verknüpft und binden im Fall der Monolagenfilme an das darunterliegende Metallsubstrat. In Bilagenfilmen hingegen gibt es keine chemischen Bindungen zum Substrat, wodurch die Filmstruktur flexibler wird. Durch Variation der Herstellungsbedingungen kann man rein kristalline, amorphe oder Phasen mittlerer Ordnung erhalten. Es ist wichtig hervorzuheben, dass der amorphe Germaniumdioxid-Bilagenfilm ein neues amorphes zweidimensionales Material darstellt.The preparation of metal-supported ultrathin films of germanium dioxide, termed also germania, has been successfully achieved for the first time. The structure of the films is elucidated with atomic precision and chemical sensitivity using surface science techniques. The investigation is performed by analyzing STM images and is complemented by low-energy electron diffraction (LEED) patterns, a dynamical LEED study, and external support from density functional theory (DFT) calculations. In this work, we compare side-by-side atomically-resolved scanning tunneling microscopy (STM) images of ultrathin films of germania and silica. The analysis aims to investigate the impact of the metal support on the structure of oxide films. For that purpose, ultrathin germania films are grown on Ru(0001), Pt(111) and Au(111), and compared with previously reported silica ultrathin films supported on different substrates. Germania has been widely associated with silica since they are considered to be structural and chemical equivalent materials. Three main network structures have been characterized: monolayer, zigzag and bilayer films. In all systems, the building block consists of a distorted tetrahedron with a germanium atom surrounded by four oxygen atoms. Adjacent tetrahedra connect to each other through Ge-O-Ge bonds and, in the case of the monolayer films, they also bind to the metal support. Conversely, in bilayer films there are no chemical bonds to the metal substrate, thus providing more flexibility to the film structure. Through a meticulous control of the preparation conditions one can obtain a purely crystalline phase, an amorphous one, or one with intermediate order. It is important to highlight that the amorphous germania bilayer film represents a new 2-dimensional amorphous material.
45
Foster, Evan Wayne. "Self-assembly of extended, high-density gold nanoparticle monolayers on silicon dioxide /." view abstract or download file of text, 2006. http://proquest.umi.com/pqdweb?did=1188875831&sid=1&Fmt=2&clientId=11238&RQT=309&VName=PQD.
Abstract:
Thesis (Ph. D.)--University of Oregon, 2006.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 173-182). Also available for download via the World Wide Web; free to University of Oregon users.
46
Del, Campo Menoyo Javier. "Compatibilisation of polyimide-silica ceramers and interfacial interactions with carbon fibres in high-temperature matrix composites." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/27080.
Abstract:
When the inorganic domain sizes in a composite are reduced to a level such that a "molecular composite" is formed, the hybrid materials are commonly referred to as "ceramers". Hybrid materials span from inorganically modified organic polymers to inorganic g1asses slightly modified by organic polymers. The incorporation of an inorganic phase into an organic polymer is done almost exclusively by the "sol-gel" process.
47
Kaya, Sarp. "Structural and catalytic investigations on vanadium oxide nanoparticles supported on silica films grown an a Mo(112) substrate." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2007. http://dx.doi.org/10.18452/15639.
Abstract:
Die breite Anwendung von Modellsystemen, um heterogene katalytische Prozesse zu verstehen, basiert darauf, die Lücke der strukturellen Komplexität zu überbrücken zwischen heutigen technischen Katalysatoren, bestehend aus einem Metalloxid sowie einem darauf geträgerten Metall, sowie kristallinen Metallen und planaren Metall/Oxid-Systemen, welche dazu benutzt werden, Struktur-Reaktivitäts-Beziehungen mittels einer Fülle von Surface Science-Methoden zu untersuchen. In der vorliegenden Arbeit liegt das Hauptaugenmerk auf so genannten Vanadiumoxid-‚Monolagen’-Katalysatoren, die insbesondere für Oxidationsreaktionen von Methanol eingeführt wurden. Mittels eines ‚bottom-up’-Ansatzes wurden Silica-geträgerte Vanadiumoxid-Modellkatalysatoren untersucht. Durch Kombination einer Reihe experimenteller Techniken wurde die Oberfläche von Mo(112), die als Substrat für den Silica-Film diente, im Detail untersucht und die atomare Struktur des Silica-Films wurde ermittelt. Adsorption von Wasser und das Wachstum von Vanadiumoxid-Nanopartikeln auf dem Silica-Film und schließlich die Reaktivität von Vanadiumoxid/Silica-Systemen gegenüber Methanol wurden untersucht. Im Gegensatz zu früher vorgeschlagenen Modellen sollte eine Sauerstoff-induzierte p(2×3)-Überstruktur, die sich auf einer Mo(112)-Oberfläche ausbilded, angenommen werden als ein eindimensionales Oberflächenoxid, bei dem sich Mo=O-Gruppen bevorzugt entlang der [-1-11]-Richtung der Mo(112)-Oberfläche ausbilden. Monolagen-Silica-Filme, die auf Mo(112) gewachsen wurden, bestehen aus einem zweidimensionalen Netz von SiO4-Tetraedern. In Abhängigkeit der Bedingungen, unter denen der Film präpariert wurde, kann die Struktur durch zusätzlich auf dem Mo-Substrat adsorbierte Sauerstoff-Atome verändert werden. Die Defekt-Struktur schließt Antiphasen-Domänengrenzen ein, die durch eine Verschiebung um die halbe Gitterkonstante entlang der [-110]-Richtung gebildet werden, und eine geringe Dichte von Punkt-Defekten, die höchstwahrscheinlich Silizium-Fehlstellen darstellen. Wasser dissoziiert nicht auf dem Monolagen-Silica-Film. Eine Wasser-Struktur, die geordnet bezüglich des Silica-Films ist, wurde bei 140 K beobachtet, was der guten Übereinstimmung der Gitterkonstanten von Silica-Film und hexagonalem Eis geschuldet ist. Amorphe Lagen festen Wassers, die die Oberfläche bei 100 K homogen bedecken, wurden als reaktive Lagen für Vanadiumoxid-Partikel benutzt, um die ‚Nasschemie’ nachzubilden, wie sie in der Präparation technischer Katalysatoren zum Einsatz kommt. Die Ergebnisse verdeutlichen, dass die Eis-Lagen die Bildung von hydratisierten Vanadiumoxid-Nanopartikeln, welche teilweise von V=O und V-OH-Gruppen terminiert werden, begünstigen. Die Dehydratisierung geschieht oberhalb 500 K, wobei eine V-terminierte Oberfläche entsteht. Methanol dissoziiert auf dehydratisierten Vanadiumoxid-Partikeln, und Methoxy-Spezies sind auf der Oberfläche stabil bis 500 K, allerdings nur in der Gegenwart von V-Plätzen. Die Produktion von Formaldehyd, die bei etwa 550 K stattfindet, ist stark abhängig von der Struktur der Oberfläche der Vanadiumoxid-Partikel und weist ein Maximum bei einem spezifischen Verhältnis zwischen V- und V=O-Oberflächenplätzen auf. Die hier vorgestellten Ergebnisse könnten unser Verständnis von katalytischen Reaktionen auf molekularer Ebene bedeutend vorantreiben.The widespread use of model systems for understanding the heterogeneous catalytic processes is based on bridging the structural complexity gap between present generation of supported metal and metal oxide technical catalysts and crystalline metal and planar metal/oxide systems, which are utilized to investigate structure-reactivity relationships by a large variety of surface science techniques. In this thesis, we focused on a concept of so-called ''monolayer'' vanadium oxide catalysts, which have been introduced particularly for methanol oxidation reactions. Following a bottom-up approach, silica supported vanadium oxide model catalysts were investigated. Combining a number of experimental techniques, the surface of Mo(112) used as a substrate for the silica films was characterized in detail and the atomic structure of the silica film was determined. Adsorption of water and growth of vanadium oxide nanoparticles on the silica films, and finally the reactivity of vanadium oxide/silica systems towards methanol were studied. In contrast to the previously suggested models, an oxygen induced p(2×3) superstructure formed on a Mo(112) surface should be considered as one dimensional surface oxide where Mo=O groups are formed preferentially along the [-1-11] direction of the Mo(112) surface. Monolayer silica films grown on Mo(112) surfaces are composed of two-dimensional network of SiO4 tetrahedra. Depending on the film preparation conditions, the structure can be altered by additional oxygen atoms adsorbed on the Mo substrate. The defect structure includes antiphase domain boundaries which form by a half-lattice shift along the [-110] direction and a low density of point defects, most probably silicon vacancies. Water does not dissociate on the monolayer silica film. An ordered structure of water with respect to silica film was observed at 140 K owing to good lattice matching between the silica film and hexagonal ice. Amorphous solid water layers homogenously covering the surface at 100 K were used as reactive layers for vanadium oxide particles in order to mimic ''wet chemistry'' used in preparation of technical catalysts. The results revealed that ice layer assisted the formation of hydrated vanadium oxide nanoparticles partially terminated by V=O and V-OH groups. The dehydration takes place above 500 K, thus exposing V-terminated surface. Methanol dissociates on dehydrated vanadium oxide particles and methoxy species are stable on the surface up to 500 K only in the presence of vanadium terminated surface sites. Formaldehyde production which takes place at ~550 K is strongly affected by the surface structure of the vanadium oxide particles and exhibits a maximum at specific ratio between V- and V=O sites on the surface. The results presented may have a strong impact on our understanding of the catalytic reactions at the molecular level.
48
Guillemin, Yann. "Électrogénération sol-gel de films minces siliceux mésostructurés : méthylation, variations structurales, contrôle morphologique et microlithographie." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0249/document.
Abstract:
Grâce à un mécanisme coopératif d'auto-assemblage électro-assisté ("Electro-Assisted Self-Assembly" : EASA), l'électrogénération de couches minces sol-gel à partir d'un sol constitué d'alcoxysilanes et d'un tensioactif cationique (bromure de cétyltriméthylammonium : CTAB) permet l'accès à des films mésostructurés présentant des mésopores orientés perpendiculairement au support. Des films mésostructurés à base de silice méthylée présentant une porosité organisée et "verticalement" orientée ont été électrogénérés en réalisant la co-condensation en une étape d'un alcoxysilane et d'un organo-alcoxysilane en présence de CTAB. Une étude des transferts de matière au sein de ces couches minces démontre que leur perméabilité peut être modulée par la teneur en groupements -CH3. Le procédé EASA a ensuite été étendu à l'utilisation de sols principalement aqueux. Ceci permet l'accès à de nouvelles structures, au contrôle de l'orientation du réseau poreux et à la possibilité de moduler la morphologie du matériau déposé en faisant varier les contre-anions associés aux édifices micellaires. Différentes stratégies de synthèse visant à augmenter la porosité de films électrogénérés ont été évaluées (utilisation d'agents gonflants et d'un copolymère triblocs). Des résultats probants concernant l'électrogénération de couches minces à porosité hiérarchisée (interconnexion de mésopores et de macropores) sont aussi présentés. Enfin, la dernière partie s'attache à étendre le concept EASA à l'échelle locale (micrométrique) par l'utilisation d'un microscope électrochimique à balayage en tant que moyen de synthèse, ceci ouvrant la voie à l'électromicrolithographie sol-gelThanks to an Electro-Assisted Self-Assembly (EASA) cooperative process, the sol-gel electrogeneration of silica thin films from sols containing alkoxysilanes and cationic surfactant molecules (cetyltrimethylammonium: CTAB) allows to obtain mesostructured films exhibiting mesopore channels orthogonal to the substrate. Organized methylated silica thin films with "vertically"-aligned mesopores were electrogenerated by performing a one-step co-condensation between alkoxysilanes and organo-alkoxysilanes in the presence of CTAB. Monitoring mass transport issues inside these thin layers demonstrates that their permeability can be modulated by the -CH3 moieties ratio. The EASA process was then extended to the use of mainly aqueous sols. This permits the electrogeneration of new structures, the control of the porous network orientation and a modulation of the deposited material morphology by changing the CTA+ counter-anion. Various synthesis strategies aiming at increasing the porosity of electrogenerated films were evaluated (use of swelling agents and a triblock copolymer). Some convincing results dealing with the electrogeneration of silica films exhibiting a hierarchical porosity (combination of mesopores with macropores) are also presented. Finally, the last part of this work demonstrates how the EASA process can be applied at the local scale (micrometric) by using a scanning electrochemical microscope as a synthesis tool, thus opening the way to the sol-gel electromicrolithography
49
hung, chien chi, and 簡吉鴻. "Silica、Zirconia and Zirconium Silicate Thin Films Prepared by Magnetron Sputtering." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/85817605148903407982.
Abstract:
碩士國立東華大學
材料科學與工程研究所
89
The developments of future gate oxide of MOS device for ULSI technology and next-generation capacitor of DRAM devices for memory storage require new dielectric materials. There is significant interest in using ZrO2 for the fabrication of charge storage insulators in the next generation memories. In this study, thin films of zirconia, silica, and zirconium silicate were deposited on Si(100) and glass substrates by R.F. magnetron sputtering from zirconia, silica and zirconium silicate composite ceramic targets instead of metal targets. This research was focused on the evaluations of film growth kinetics, microstructure, mechanical properties, optical properties, and electrical properties. The results showed the films were structurally amorphous, besides 90 ZrO2-10 SiO2 system. The surface morphology of all films were smooth and dense. Their growth rates increased as the silica content and R.F. power increased. The maximum growth rate was nearly 10 nm/min. Regarding to mechanical properties, residual stress was compressive for all films, the hardness of thin films was in the range of 2~12 GPa, and there was a good adhesion to glass substrates with a the maximum critical load of 21.2 N. The refraction index showed a maximum value of 2.17 for pure ZrO2 system. The transmittance with a maximum value of 90 % for pure SiO2 system was influenced by ZrO2 content in targets. In respect of electric properties, the dielectric constant which varied with target composition had a highest of 32. The resistivity was higher than 109 ohm-cm, with a higher value after annealing. The breakdown fields were meassured with values higher than 3 MV/cm.
50
WANG, CHEN-JUI, and 王貞芮. "The study of copper-silica nanocomposite films." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/54097224380372810920.
Abstract:
碩士國立臺灣科技大學
材料科技研究所
93
This thesis uses the magnetron co-sputter to deposit Cu-SiO2 composite films, and probe electricity in the composite films of different copper content. The first part of experiment studies composition and structure of the as-deposited and annealed Cu-SiO2 films, using XPS. The second part of experiment studies the change of crystallite size in the Cu-SiO2 films, using XRD, TEM, and UV-Visible spectroscopy. The third part of experiment studies electrical properties of the Cu-SiO2 films using Ti/ Cu-SiO2/Ti sandwich structure. Both Cu and Cu2O crystallite appear in the Cu-SiO2 nano-composite films. Crystallite size increases with Cu content, annealing temperatures and time. However, some Cu segregate to surface of the nano-composite films with high concentration Cu. Electrical properties of the Cu-SiO2 films are affected by both the Cu concentration and the annealing conditions. Breakdown voltages of the Cu-SiO2 films decrease but the leakage currents increase while Cu content increases. The Cu-SiO2 films become conductive after the breakdown.