Дисертації з теми "Films nanocomposite"

This thesis describes technical and scientific aspects of new types of composite films/coatings for corrosion protection of carbon steel, composite films with nanometer thickness consisting of mussel adhesive protein (Mefp‐1) and ceria nanoparticles, and polymeric composite coatings with micrometre thickness consisting of conducting polymer and ceria nanoparticles in a UV‐curing polyester acrylate (PEA) resin. The influence of microstructure on corrosion behaviour was studied for a Fe‐Cr‐V‐N alloy containing micro‐sized nitrides with different chemical composition spread in martensitic alloy matrix. The Volta potential mapping suggested higher relative nobility for the nitride particles than the alloy matrix, and the nitrides with higher amounts of nitrogen and vanadium exhibited higher nobility. Potentiodynamic polarization measurements in a 0.1 M NaCl solution at neutral pH and ambient temperature showed passivity breakdown with initiation of localized corrosion which started in the boundary region surrounding the nitride particles, especially the ones enriched in Cr and Mo. Mefp‐1/ceria nanocomposite films were formed on silica and metal substrates by layer‐by‐layer immersion deposition. The film formation process was studied in situ using a Quartz Crystal Microbalance with Dissipation (QCM‐D). The film grows linearly with increasing number of immersions. Increasing Mefp‐1 concentration or using Mefp‐1 with larger size leads to more Mefp‐1 being deposited. Peak Force Quantitative Nanomechanical Mapping (Peak Force QNM) of the composite films in air indicated that the elastic modulus of the film increased when the film deposited had a higher Mefp‐1 concentration. It was also noted that the nature of the outermost layer can affect bulk morphology and surface mechanical properties of the film. The QCM‐D study of Mefp‐1 on an iron substrate showed that Mefp‐1 adsorbs at a high rate and changes its conformation with increasing adsorption time. The QCM‐D and in situ Peak Force QNM measurements showed that the addition of Fe3+ ions causes a transition in the single Mefp‐1 layer from an extended and soft layer to a denser and stiffer layer. In situ ATR‐FTIR and Confocal Raman Microscopy (CRM) analyses revealed complex formation between Fe3+ and catechol groups in Mefp‐1. Moreover, optical microscopy, SEM and AFM characterization of the Mefp‐1/ceria composite film formed on carbon steel showed micron‐size aggregates rich in Mefp‐1 and ceria, and a nanostructure of well dispersed ceria particles in the film. The CRM analysis confirmed the presence of Mefp‐1/Fe complexes in the film. Electrochemical impedance microscopy and potentiodynamic polarization measurements showed that the Mefp‐1/ceria composite film can provide corrosion protection for carbon steel, and that the protection efficiency increases with exposure time. Composite coatings of 10 μm thickness composed of a UV‐curing PEA resin and a small amount of conductive polymer and ceria nanoparticles were coated on carbon steel. The conductive polymer (PAni) was synthesized with phosphoric acid (PA) as the dopant by chemical oxidative polymerization. The ATR‐FTIR and SEM analyses confirmed that the added particles were well dispersed in the coatings. Electrochemical measurements during long exposure in 0.1 M NaCl solution, including open circuit potential (OCP) and EIS, were performed to investigate the protective performance of the coatings. The results showed that adding ceria nanoparticles can improve the barrier properties of the coating, and adding PAni‐PA can lead to active protection of the coating. Adding PAni‐PA and ceria nanoparticles simultaneously in the coating can improve the protection and stability of the composite coating, providing excellent corrosion protection for carbon steel.

QC 20131024

This thesis consists of three main investigations. The first of these is a study of the magnetic properties of Fe nanoparticles embedded in an Al matrix, with different volume fraction. Both Fe nanoparticles, with a diameter of ̴ 2 nm, and the Al matrix were deposited from the gas phase. The atomic Fe moment of the Fe nanoparticles in Al is much less than the bulk Fe value because of considerable alloying at the Fe nanoparticle and Al matrix interface. Two important parameters, the exchange field (Hex) and random anisotropy field (Hᵣ), were investigated using the Random Anisotropy Model (RAM). Fitting the data to this model reveals that with increasing volume filling fraction (VFF) of Fe nanoparticles in Al, both Hex and Hr show an increase, with Hr showing a more significant increase than for Hₑₓ. The second main investigation in this thesis is a study of structure and magnetism in Co nanoparticles embedded in antiferromagnetic Cr. Co K edge and Cr K edge extended x-ray absorption fine structure (EXAFS) experiments were performed in order to investigate atomic structure in the Cr-embedded Co nanoparticles and Cr matrix respectively, whereas magnetism was investigated using a vibrating sample magnetometer (VSM). The atomic structure of the Co nanoparticles is same as the host Cr matrix (bcc), although with a degree of disorder, rather than the bulk Co hcp structure. The net Co moment per atom in the Co/Cr nanocomposite films is significantly lower than bulk Co value, and decreases as the proportion of Co nanoparticles in the film is decreased; for the sample with the most dilute concentration of Co nanoparticles (4.9% by volume), the net Co moment was 0.18 μB/atom. Both the structural and magnetic results show that there is a degree of alloying at the nanoparticle/matrix interface, leading to a core/shell structure in the embedded nanoparticles consisting of an antiferromagnetic CoCr alloy shell surrounding a reduced ferromagnetic Co core. The final part of this work is an investigation into the structure and magnetism of Fe nanoparticles embedded in a Cu1-ₓAlₓ alloy matrix, where the structure of the matrix could be controlled by control over its composition. Cu K edge EXAFS measurements show that there is a slight stretch in the Cu-Cu interatomic distances in the alloy matrix, while the face centred structure in the Cu1-ₓAlₓ matrix is maintained, as the Al-content is increased. Fe K edge EXAFS measurements reveal that for low Al-content in the Cu1-ₓAlₓ matrix, Fe nanoparticles have both fcc and bcc structures, but for higher Al-content the structure of Fe nanoparticles is consistent with bcc. The magnetism measurements, obtained from VSM and SQUID magnetometers, show that the Fe atomic moment increases sharply due to the increasing proportion of bcc Fe nanoparticles. However for Al-content higher than 0.13, the net atomic moment value of Fe decreases slightly, which is consistent with a high degree of alloying between Fe and Al atoms.

Els materials superconductors d’alta temperatura tenen propietats úniques, objecte d’investigació des de fa molts anys, especialment les propietats relacionades amb la conductivitat sense resistència a temperatures relativament altes o sota camps magnètics alts. Existeix un gran esforç a nivell internacional per optimitzar les propietats d’aquests materials i desenvolupar metodologies pel seu creixement que siguin compatibles amb la producció a gran escala i baix cost. En aquest context, els resultats inclosos en aquesta tesi són un important pas endavant, ja que demostren per primera vegada la possibilitat d’utilitzar la millora de propietats superconductores aconseguida amb tecnologia de nanocompòsits combinada amb una metodologia de creixement basada en la deposició de solucions químiques i intermedis líquids que presenta un baix cost i alt rendiment. El creixement de l’YBa2Cu3O(7-x) s’ha dut a terme mitjançant una nova metodologia anomenada “creixement assistit per líquid transitori” (TLAG per les seves sigles en anglès), la qual combina el baix cost  de la deposició de solucions químiques amb la presència d’un líquid transitori que proveeix velocitats de creixement ultra-ràpides. Hem aconseguit combinar aquest creixement a través de fases líquides amb la presència de nanopartícules a través de l’estudi de la nucleació, la micro-estructura i la disposició de defectes en les nostres capes primes. Pels estudis de capes nanocompòsites vam triar nanopartícules  de BaZrO3, BaHfO3 i LaF3, estabilitzades en medis alcohòlics. Els resultats presentats estan dividits segons les diferents rutes de creixement.En la ruta de temperatura, varis paràmetres han estat optimitzats amb l’objectiu d’aconseguir capes nanocompòsites epitaxials, tals com la rampa d’escalfament i el gruix de capes tampó d’YBCO sintetitzades a través de PLD. També presentem resultats amb diferents estequiometries de la fase líquida, elucidant la importància de controlar la sobresaturació per aconseguir capes epitaxials. La densitat de corrent crítica a 77K és 1MA/cm2. Hem demostrat que introduir nanopartícules al creixement d’YBCO per TLAG crea una estructura de defectes amb un gran potencial per millorar la fixació de vòrtexs sota camps magnètics. Hem investigat el creixement de capes nanocompòsites d’YBCO a través de la ruta de PO2 amb quantitats de BaZrO3 o BaHfO3 entre el 6% i el 32%. Hem descrit l’ús d’una capa prima precursora sense nanopartícules per tal d’aconseguir una bona reproductibilitat i capes nanocompòsites completament orientades en l’eix c en el cas de nanocompòsits amb 6% i 12% de nanopartícules. Hem demostrat una Jc de 2.2MA/cm2 a 77K, el qual és un resultat molt prometedor que ens ha portat a avaluar la Jc respecte camps magnètics aplicats. Hem pogut demostrar com les propietats dels nanocompòsits sota camp magnètic són millors que en les mostres estàndard, característica necessària per aplicacions de les cintes recobertes superconductores sota alts camps magnètics. Aquesta dissertació també inclou un estudi preliminar sobre el creixement de capes gruixudes d’YBCO (1um) i sobre la compatibilitat de capes tampó amb TLAG. Hem pogut demostrar la completa eliminació del carbonat de bari en capes de 1um de gruix, i hem aconseguit capes gruixudes completament epitaxials a través de la ruta de PO2. Hem fet servir el mètode de deposició de solucions químiques per créixer capes de Ba2342, Nd2CuO4, LaMnO3 (LMO), la reactivitat de les quals ha estat avaluada durant el creixement amb fases líquides. També s’ha estudiat la nucleació de YBCO a sobre d’aquestes capes tampó. El material més prometedor ha estat LMO, per tant hem utilizat substrats metàl·lics comercials amb LMO com a l’última de les capes tampó de la seva arquitectura. Hem aconseguit el creixement epitaxial de capes d’YBCO amb bona temperatura crítica a sobre d’aquestes capes, demostrant que la metodologia TLAG és compatible amb arquitectures comercial de capes recobertes superconductores.
Los materiales superconductores de alta temperatura tienen propiedades únicas, que han sido objeto de investigación des de hace muchos años, especialmente las propiedades relacionadas con la conductividad sin resistencia a temperaturas relativamente altas o bajo campos magnéticos. Existe un gran esfuerzo a nivel internacional para optimizar las propiedades de estos materiales y desarrollar metodologías para su crecimiento que sean compatibles con la producción a gran escala y bajo coste. En este contexto, los resultados incluidos en esta tesis son un importante paso adelante ya que demuestran por primera vez la posibilidad de utilizar la mejora de propiedades superconductoras conseguida con tecnología de nanocompuestos combinada con una metodología de crecimiento basada en la deposición de soluciones químicas e intermedios líquidos que presenta un bajo coste y alto rendimiento. El crecimiento de YBa2Cu3O(7-x) se ha hecho mediante una nueva metodología llamada “crecimiento asistido por líquido transitorio” (TLAG por sus siglas en inglés), la cual combina el bajo coste de la deposición de soluciones químicas con la presencia de un líquido transitorio que da velocidades de crecimiento ultra-rápidas. Hemos conseguido combinar este crecimiento a través de fases líquidas con la presencia de nanopartículas a través del estudio de la nucleación, la microestructura y la disposición de los defectos en nuestras capas delgadas. Para los estudios de capas nanocompuestas hemos elegido nanopartículas de BaZrO3, BaHfO3 y LaF3, estabilizadas en medios alcohólicos. Los resultados están divididos según las diferentes rutas de crecimiento. En la ruta de temperatura, varios parámetros han sido optimizados con el objetivo de conseguir capas nanocompuestas epitaxiales, tales como la rampa de calentamiento y el grosor de capas tampón de YBCO sintetizadas a través de PLD. También presentamos resultados con diferentes estequiometrias de la fase líquida, elucidando la importancia de controlar la sobresaturación para conseguir capas epitaxiales. La densidad de corriente crítica a 77K es 1MA/cm2. Hemos demostrado que introducir nanopartículas al crecimiento de YBCO a través de TLAG crea una estructura de defectos con un gran potencial para mejorar la fixación de vórtices bajo campos magnéticos. Hemos investigado el crecimiento de capas nanocompuestas de YBCO a través de la ruta de PO2 con cantidades de BaZrO3 o BaHfO3 entre el 6% y el 32%. Hemos descrito el uso de una capa delgada precursora sin nanopartículas con tal de conseguir una buena reproductibilidad y capas nanocompuestas completamente orientadas en el eje c en el caso de nanocompuestos con el 6% y el 12% de nanopartículas. Hemos demostrado una Jc de 2.2MA/cm2 a 77K, lo cual es un resultado muy prometedor que nos ha llevado a evaluar la Jc respeto campos magnéticos aplicados. Hemos podido demostrar como las propiedades de las capas nanocompuestas bajo campos magnéticos son mejores que en las muestras estándar, característica necesaria para aplicaciones de las cintas recubiertas superconductoras bajo altos campos magnéticos. Esta disertación también incluye un estudio preliminar sobre el crecimiento de capas gruesas de YBCO (1um) y sobre la compatibilidad de capas tampón con TLAG. Hemos podido demostrar la completa eliminación del carbonato de bario en capas de 1um de grosor. Hemos utilizado el método de CSD para crecer capas de Ba2342, Nd2CuO4, y LaMnO3 (LMO), la reactividad de las cuales ha sido evaluada durante el crecimiento con fases líquidas. El material más prometedor ha sido LMO, y por lo tanto hemos usado sustratos metálicos comerciales con LMO como última capa de su arquitectura. Hemos conseguido el crecimiento epitaxial de capas YBCO con buena temperatura crítica encima de estas capas, demostrando que la metodología TLAG es compatible con la arquitectura comercial de capas recubiertas superconductoras.
High temperature superconducting materials have unique properties which have been under investigation for many years, mainly involved with their zero resistance properties at high temperatures or at high magnetic fields. Currently, one of the main interest in the superconducting community is to demonstrate the applicability of these materials, in order to achieve the widespread use of their applications. As such, there is a big international effort on optimizing performances and developing growth methodologies compatible with big-scale production at low cost. In this context, the results presented in this thesis are an important step forward, reporting for the first time the possibility to use the increased superconducting properties of nanocomposite technology together with a low-cost and high throughput liquid-based methodology based on chemical solution deposition. The growth of YBa2Cu3O(7-x) } is performed by the newly reported method of transient liquid assisted growth (TLAG), which combines the inexpensive chemical solution deposition with the presence of a transient liquid that provides ultra-high growth rates. We have been successful in combining this liquid-based growth with the presence of nanoparticles through the understanding of nucleation, microstructure and defect landscape of our films. We have chosen BaZrO3, BaHfO3 and LaF3 pre-formed nanoparticles stabilized in alcoholic media for these studies. The results are divided by the different processing routes, presenting the efforts on optimizing the nucleation, growth and superconducting properties of nanocomposites in two chapters. The two different paths consist of the temperature route (heating at constant PO2), and PO2-route (heating at very low PO2 and then increasing PO2 to reach growth conditions). In the T-route, several parameters were optimized in order to achieve epitaxial nanocomposite films, such as heating ramp and the thickness of a PLD-YBCO buffer layer. Also different liquid stoichiometries were tested, revealing the importance of supersaturation control to achieve epitaxy. Jc is 1MA/cm2, and we demonstrated that introducing pre-formed nanoparticles to TLAG-YBCO creates a defect structure with a lot of potential towards improved vortex pinning. The growth of YBCO nanocomposites through the PO2-route with BaZrO3 and BaHfO3 molar percentages ranging from 6% to 32% was studied through XRD techniques which allow the quantification of different YBCO crystalline orientations. Introduction of a seed layer accomplished a better reproducibility and fully c-axis oriented epitaxial films for 6% and 12% nanocomposites. We demonstrated Jc self-field up to 2.2MA/cm2 at 77K, a very promising result, which led to the evaluation of Jc under applied magnetic fields through dc-SQUID and electrical transport measurements. Thus, we could show the increased performance of nanocomposites with magnetic field in comparison with pristine samples, necessary for high magnetic field applications of coated conductors. This dissertation also includes a preliminary study on the growth of YBCO thick films (1um) and buffer layer compatibility with TLAG. We demonstrated the successful elimination of barium carbonate in films up to 1um thick and fully epitaxial YBCO layers could be processed by the PO2-route. CSD methodologies were used to grow thin films of Ba2342, Nd2CuO4, LaMnO3 and La0.8Sr0.2MnO3, in order to evaluate the reactivity of the transient liquid with these materials as well as the nucleation of YBCO on top. LaMnO_3 (LMO) was found to be a very promising material and was further investigated by using PLD-grown LMO and SuNAM commercial tape with LMO as the last layer of their architecture. We achieved epitaxial YBCO films with good Tc on top of these buffers layers, demonstrating that TLAG is compatible with commercial coated conductors architecture.

Clay platelets and silica nanoparticles are used as Pickering stabilizers in the fabrication of hybrid armored polymer particles through a Pickering emulsion polymerization process. A variety of hydrophobic comonomers (i.e., styrene-co- (n-butyl acrylate) (Sty:BA), methyl methacrylate-co-(n-butyl acrylate) (MMA:BA)), styrene-co-(2-ethyl hexyl acrylate) (Sty:2-EHA), vinyl acetate (VAc) and vinyl pivalate (VPiv) are used as organic film forming components. Polymerization kinetics and particle size distributions were examined as a function of monomer conversion. Additionally, key mechanistic features of the polymerization process by quantitatively analyzing the concentration of silica nanoparticles in the water phase during monomer conversion by disc centrifugation are unraveled. It is also showed the crucial role of Laponite clay discs in the particle formation (nucleation) of the Pickering emulsion polymerization process. Increasing amounts of clay nanodiscs leads to smaller average particles sizes, but broader particle size distributions. Polymer films of poly(styrene-co-n-butyl acrylate) armored with Laponite clay were studied as a function of clay amount. Improvements in mechanical, thermal and surface topography provided by clay platelets are reported. In addition, advantages are shown in use of hybrid polymer particles in comparison with simple blend mixtures of polymer particles plus inorganic particles. Humidity properties of poly(styrene-co-n-butyl acrylate) films as a function of clay content are investigated. It is demonstrated that the presence of Laponite clay improves the water storage capacity of polymer films. Also water barrier properties are improved when clay platelets are applied. Finally, a versatile two step Pickering emulsion polymerization for the fabrication of core-shell particles armored with Laponite clay XLS is developed. The obtained particles contain a "hard" core and a "soft" shell armored with clay. The different in the refractive indexes between the core and shell makes these core-shell particles interesting for possible use as colloidal crystals.

Electronic technology is moving towards flexible, durable, and smaller devices with multifunctional capability. To accelerate this movement, creating materials with outstanding properties is critical. Nanocomposites based on single wall carbon nanotubes (SWCNTs) have received considerable attention because of their unique mechanical and electrical properties. When SWCNTs are formed as a sheet, they provide large contact area and ease of control, especially when incorporated into a flexible format. However, when SWCNT films are adhered to an elastic substrate, there are challenges with their use in flexible electronics, such as a reduction Young?s modulus under deformation. SWCNT films can undergo plastic behavior at even a small strain because individual SWCNTs slide past each other in response to deformation. To address these challenges, a strain-induced elastic buckling instability for mechanical measurements (SIEBIMM) method was used to query SWCNT film mechanics. The buckling wavelength and the film thickness are two main factors that influence the mechanics of nanocomposite thin films adhered to elastomeric substrates. SWCNT films coated with a second nanomaterial, such as a polymer thin film or nanocrystals (NCs), have shown a significant enhancement in elasticity. The studies described in this dissertation demonstrate that polymer thin film can reduce the strain softening of SWCNT films, where both yield strain and Young?s modulus increase with the introduction of SWCNT-polymer layers. Specifically, the films started to exhibit a strong synergy between SWCNT and polymer at a film thickness of around 20 nm, which is attributed to the thickness approaching the characteristic interfacial width between the two materials. Both a ?passive? polymer thin film (for example, polystyrene-PS) and an ?active? polymer thin film, the conducting polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS), were investigated, spanning a bilayer to the bulk limit of SWCNT-polymer multilayers. In addition, ultrathin SWCNT films coated with colloidal NCs have also been investigated. We have utilized two approaches to coat SWCNT films with NCs: Langmuir-Blodgett (LB) and spray coating. Both Si and CdSe nanocrystals showed a roughly two-fold enhancement in film elasticity, which was attributed to an excluded volume effect that prevents the SWCNT rearrangement under an applied strain.

The structural evolution of carbon:transition metal (C:TM) nanocomposite thin films is investigated in two regimes: (i) surface diffusion governed regime occurring during the film growth and (ii) bulk diffusion dominated regime occurring during the post-deposition thermal annealing. C:V, C:Co, and C:Cu nanocomposite films were grown by ion beam co-sputtering. The influence of the metal type, metal content (15-40 at.%), substrate temperature (RT-500°C), and annealing temperature (300-700°C) on the structure and morphology of the composite is studied by the means of elastic recoil detection analysis, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Vanadium (copper) is in carbidic (metallic) state in the whole temperature range of the study. In contrast, cobalt is in carbidic state up to 300°C and becomes metallic at higher growth temperatures. The nanoparticles in C:V films exhibit a globular shape at RT-500°C, whereas in C:Co and C:Cu films a growth transition from globular to elongated nanoparticles occurs around 300°C. The comparison of the Raman spectroscopy results from carbon reference and C:TM thin films shows that the presence of the metal during growth significantly enhances the formation of sixfold ring carbon clusters at temperatures as low as RT. The enhancement occurs independently of the nanoparticle size, shape, and phase, and metal content, and is related to processes taking place on the nanoparticle surface of the growing film rather than in the bulk. The degree of enhancement depends on the TM type and content. Post-deposition annealing of C:Co and C:Cu films at 700°C causes the metal segregation at the film surface, while no changes upon annealing occur in C:V films. In addition, cobalt brings about the carbon graphitization by a dissolution-diffusion-precipitation mechanism, similar to the metal-mediated crystallization of amorphous silicon or germanium. No graphitization upon annealing occurs in C:V, C:Cu, and carbon reference films
Die Strukturentwicklung in Kohlenstoff-Übergangsmetall-Nanokompositschichten wird in zwei Bereichen untersucht: (i) im oberflächendiffusionsgesteuerten Bereich während des Schichtwachstums und (ii) im bulkdiffusionsdominierten Bereich während des nachträglichen Temperns. C:V, C:Co und C:Cu Nanokompositschichten wurden durch Ionenstrahl Co-Sputtern hergestellt. Der Einfluss des Metalltyps, des Metallgehalts (15-40 at.%), der Substrattemperatur (RT-500°C) und der Temperatur beim Tempern (300-700°C) auf die Struktur und Morphologie des Komposits wird mittels elastischer Rückstoßteilchen-Analyse, Röntgenbeugung, Transmissionselektronenmikroskopie und Ramanspektroskopie untersucht. Vanadium (Kupfer) ist im gesamten Temperaturbereich der Studie in karbidischem (metallischen) Zustand. Im Gegensatz dazu befindet sich Kobalt bis zu einer Temperatur von 300°C in karbidischem Zustand und wird bei höheren Abscheidetemperaturen metallisch. Die Nanopartikel in C:V Filmen besitzen eine runde Form im Temperaturbereich von RT bis 500°C wohingegen bei den C:Co und C:Cu Filmen ein Übergang von runden zu länglichen Partikeln bei etwa 300°C zu beobachten ist. Der Vergleich der Ramanspektroskopieresultate der Kohlenstoffreferenzproben und der Nanokompositschichten zeigt, dass die Anwesenheit des Metalls während des Schichtwachstums die Bildung von sechsatomigen Kohlenstoffringclustern bei Temperaturen so niedrig wie Raumtemperatur deutlich fördert. Die Erhöhung tritt unabhängig von der Partikelgröße, -form und phase und unabhängig vom Metallgehalt auf, und betrifft eher Prozesse, die auf der Oberfläche der Nanopartikel während des Schichtwachstums stattfinden als im Bulk. Der Grad der Erhöhung hängt vom Metalltyp und -gehalt ab. Nachträgliches Tempern der C:Co und C:Cu Filme bei 700°C führt zur Segregation des Metalls an der Schichtoberfläche während in den C:V Filmen keine Veränderungen durch das Tempern auftreten. Des weiteren kommt es in den C:Co Filmen zur Graphitisierung des Kohlenstoffs durch einen „Lösungs-Diffusions-Ablagerungs“ Mechanismus ähnlich der metallvermittelten Kristallisierung in amorphem Silizium und Germanium. In den C:V, C:Cu und Kohlenstoffreferenzfilmen findet keine Graphitisierung während des Temperns statt

This thesis explores thin films of binary and ternary transition metal carbides, in the Nb-C, Ti-Si-C, Nb-Si-C, Zr-Si-C, and Nb-Ge-C systems. The electrical and mechanical properties of these systems are affected by their structure and here both nanocomposite and amorphous thin films are thus investigated. By appropriate choice of transition metal and composition the films can be designed to be multifunctional with a combination of properties, such as low electric resistivity, low contact resistance and high mechanical strength. Electrical contacts are one example of application that has been of special interest in this thesis. Since some industrially important substrates used in electrical contacts soften at higher temperature, all films were deposited with dc magnetron sputtering at a low substrate temperature (200-350 °C). I show that the electrical resistivity and mechanical properties of composites consisting of nanocrystalline NbC grains (nc-NbC) in a matrix of amorphous C (a-C) depend strongly on the amount of amorphous C. The best combination of hardness (23 GPa) and electrical resistivity (260 μΩ*cm) are found in films with ~15 at.% a-C phase. This is a higher hardness and lower resistivity than measured for the more well studied Ti-C system if deposited under similar conditions. The better results can be explained by a thinner matrix of amorphous C phase in the case of NbC. The nc-NbC/a-C is therefore interesting as a material in electrical contacts. Si can be added to further control the structure and thereby the properties of binary Me-C systems. There are however, different opinions in the literature of whether Si is incorporated on the Ti or C site in the cubic NaCl (B1) structure of TiC. In order to understand how Si is incorporated in a Me-Si-C material I use a model system of epitaxial TiCx (x ~0.7). In this model system a few atomic percent of Si can be incorporated in the cubic TiC structure. The experimental results together with theoretical stability calculations suggest that the Si is positioned at the C sites forming Ti(Si,C)x. The calculation further shows a strong tendency for Si segregation, which is seen at higher Si contents in the experiments, where Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy. If Si is added to an Nb-C nanocomposite, it hinders the grain growth and thus a reduced size of the NbC grains is observed. The Si segregates to the amorphous matrix forming a-SiC. At the same time the resistivity increases and the hardness is reduced. With even higher amounts of Si (>25 at.%) into the Nb-Si-C material, grain growth is no longer possible and the material becomes amorphous. In order to separate between effects from the addition of Si and the choice of transition metal I compare the Nb-Si-C system to already published results for the Zr-Si-C system. I find that the hardness of the material depends on the amount of strong Si-C bonds rather than the type of transition metal. The reduced elastic modulus is, however, dependent on the choice of transition metal. I therefore suggest that it is possible to make Me-Si-C films with high wear resistance by an appropriate choice of transition metal and composition. Electron microscopy was of importance for determining amorphous structures of Nb-Si-C and Zr-Si-C at high Si contents. However, the investigations were obstructed by electron beam induced crystallization. Further investigations show that the energy transferred from the beam electrons to C and Si atoms in the material is enough to cause atomic displacements. The displacements cause volume fluctuations and thereby enhance the mobility of all the atoms in the material. The result is formation of MeC grains, which are stable to further irradiation. Finally, I have studied substitution of Ge for Si in a ternary system looking at Nb-Ge-C thin films. I show that the films consist of nc-NbC/a-C/a-Ge and that Ge in a similar way to Si decreases the size of the crystalline NbC grains. However, a transition to a completely amorphous material is not seen even at high Ge contents (~30 at.%). Another dissimilarity is that while Si bonds to C and forms a matrix of a-SiC, Ge tends to bond to Ge.

The development of efficient, high-performance materials for electrical energy storage and conversion applications has become a must to meet an ever-increasing need for electrical energy. Among devices developed for this purpose, capacitors have been used for pulsed power applications that require large power density with millisecond-scale charge and discharge. However, conventional polymeric films, which possess high breakdown strength, are limited due to low permittivity and hence compromise the energy storage capability of capacitors. In order to develop high energy density dielectric materials for pulsed power applications, two hurdles must be overcome: 1) the appropriate selection of materials that possess not only large permittivity but also high breakdown strength, 2) the optimization of material processing to improve morphology of dielectric films to minimize loss during energy extraction process. This thesis will present the development of novel dielectric material, with emphasis on the optimization of material and thin film processing toward improved morphology as ways to achieve high energy density at the material level. After first two chapters of introduction and experimental details, Chapter 3 will demonstrate the improvement of nanocomposite morphology via processing optimization and study its effect on the energy storage characteristics of nanocomposites thereof. Chapter 4 will investigate dielectric sol-gel materials containing dipolar cyano side groups, which are relatively a new class of material for pulsed power applications. Finally, Chapter 5 will discuss the effect of tunneling barrier layer on sol-gel films to mitigate charge carrier injection and associated conduction and breakdown phenomena, which would be significantly detrimental to the energy storage performance of dielectric sol-gel films.

Gold nanoparticle and gold / semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapour deposition. Two gold precursors have been investigated which would be unsuitable for use with conventional atmospheric pressure chemical vapour deposition. HAuCU was used in methanol solution to deposit films at substrate temperatures of 350 - 500 °C. Powder X-ray diffraction and X-ray photoelectron spectroscopy revealed that these films consisted of metallic gold. The optical properties of these films corresponded to nanoscale gold particles, specifically displaying surface plasmon resonance (SPR) absorption. The wavelength of the SPR absorption maximum varied with precursor concentration and substrate temperature from 1000 - 600 nm. Scanning electron microscopy revealed particles a wide variety of sizes and shapes, as well as regions of island growth morphology. Depositions carried out from solutions of HAuCU and a range of quaternary ammonium ion surfactants led to films of particles with narrow size distributions. The use of tetraoctylammonium bromide (TOAB) led to films of spherical particles, the mean diameter of which could be altered by changing HAuCU : TOAB ratio, deposition temperature and solvent volume. Films with mean particle diameters ranging from 65 nm to 120 nm and arithmetic standard deviations of less than 20% of the mean could be deposited in this way. Toluene solutions of pre-formed gold particles were used to deposit films. These films showed similar optical properties to the original precursor solution. Nanocomposite films were deposited by combining HAuCU or pre-formed gold particles with a conventional CVD precursor in a single precursor solution. W(CO)6 , Mo(CO)6 , W(OPh)6 , TiPrU were combined with a gold precursor to deposit metal oxide films with incorporated gold particles. The concentration of gold within the films could be varied by changing the precursor ratios. These films showed SPR peaks that were redshifted compared to gold particles alone.

A series of exfoliated and intercalated polyurethane (PU) organoclay nanocomposites, polyurethane-graphite oxide (GO) and polyurethane carbon nanotubes (single-walled (SWNT) and multi-walled carbon nanotubes (MWNT)) were prepared by in situ polymerization. It is believed that the preparation of polymer/clay or polymer/CNTs nanocomposites with homogeneous dispersion of nanofillers in the matrices is a crucial step to developing high-performance polymer nanocomposites. The effects of various organoclays and carbon nanotubes (CNTs), polyol types and dispersion situation i.e. intercalation or exfoliation on viscosity were investigated. The interactions between the polyol and nanofillers and the mixing temperature play an important role in the occurrence of exfoliation and intercalation in polyurethane nanocomposite. The mechanism of exfoliation of clay was proposed based on the rheological data. The surface mechanical properties of the polyurethane nanocomposite films were investigated by means of nanoindentation. The results showed that the hardness and elastic modulus of the nanocomposites dramatically increased with the incorporation of nanofillers. This improvement was dependent on the content of nanofillers as well as the formation structure of organoclay in the polyurethane matrix. At 3wt% clay content, the hardness and elastic modulus of intercalated nanocomposites increased by approximately 16% and 44%, respectively, compared to the pure PU. For the exfoliated clay/PU nanocomposites, the improvement in these properties was about 3.5 (hardness) and 1.6 (modulus) times higher than the intercalated ones. For the polyurethane graphite oxide (GO) nanocomposites both the hardness and the elastic modulus were enhanced as a function of GO concentration. With incorporation of 4wt% GO, the hardness and modulus increased nearly ~400% and ~350%, respectively. Upon incorporation of only 1wt% SWNT, the hardness of polyurethane was greatly improved by about 150% from 3 MPa to 7.8 MPa and the modulus was improved by about 50% from 12MPa to 18.5 MPa. For only 1wt% MWNT, the hardness of polyurethane was improved by about 50% and the modulus is just slightly improved by about ~5%. The creep behaviour of bulk and sub-surface of the polyurethane nanocomposites were investigated by means of uniaxial conventional creep testing and nanoindentation, respectively. The results showed that the creep resistance of the PU was significantly improved by incorporation of nanofillers. The enhancement of creep resistance was dependent on the filler. With 1wt% clay, the creep resistance increased by approximately 50% for the intercalated system and 67% for the exfoliated system, respectively, compared to the pure PU. The elastic-viscoelastic (EVE) model was employed to examine the effect of organoclay loadings on the creep performance of PU nanocomposites. Results showed the model was in good agreement with the experimental data. A similar results were also noticed in polyurethane with GO and CNTs. The creep deformation decreases when the GO content increases, as expected from the addition of a rigid reinforcement of GO and CNTs into a polyurethane matrix. In scratch test, the results pronounced that with incorporation of nanofillers the scratch depth of polyurethane matrix was dramatically reduced.

In this work, I start by introducing a relatively recently innovated thin film architecture which offers a new direction in strain control, the vertically aligned nanocomposite (VAN). I first present the literature in the field, explaining the advantages and unique novel properties stemming from VAN structures. Next, I introduce the work I did to examine the unique strain states of Ba0.6Sr0.4TiO3–Sm2O3 VAN structures. It was found that the strain states in the functional Ba0.6Sr0.4TiO3 phase are unconventional compared to those in planar thin films. 3-dimensional strain was found to be acting on the Ba0.6Sr0.4TiO3 phase in the VAN structure. The origin of the strain was explained using a simple model which takes into account thermal expansion mismatch as well as lattice mismatch and elastic coefficients. The ferroelectric properties of the films were presented in relation to the observed strain states. I next present the work I did on the influence of strain on the magnetic properties in VAN film of Sm0.34Sr0.66MnO3–Sm2O3. Ferromagnetism was achieved in an otherwise antiferromagnetic Sm0.34Sr0.66MnO3. The effect was explained by a strain induced transition from super-exchange to double exchange coupling in the material. Last but not least, the potential of scalability of VAN films was explored by using sputtering to grow VAN structures instead of the commonly-used PLD growth. BaTiO3–Sm2O3 was used as a primary study material due to its well reported VAN properties. Preliminary results showing indications of a VAN structure. Some basic physical property characterization is also presented and compared to the properties of PLD-grown films in the literature. Limitations and challenges that arise due to the fundamental differences between sputtering and PLD are also described.

Mechanical property and thermal stability of Zr-Si-N films of varying silicon contents deposited on Al₂O₃ (0001) substrates are characterized. All films provided for characterization were deposited by reactive DC magnetron sputter deposition technique from elemental Zr and Si targets in a N₂/Ar plasma at 800 ^oC. The hardness and microstructures of the as deposited films and post-annealed films up to 1100 ^oC are evaluated by means of nanoindentation, X-ray diffractometry and transmission electron microscopy. The Zr-Si-N films with 9.4 at.% Si exhibit hardness as high as 34 GPa and a strong (002) texture within which vertically elongated ZrN crystallites are embedded in a Si₃N₄ matrix. The hardness of these two dimensional nanocomposite films remains stable up to 1000 ^oC annealing temperatures which is in contrast to ZrN films where hardness degradation occurs already above 800 ^oC. The enhanced thermal stability is attributed to the presence of Si₃N₄ grain boundaries which act as efficient barriers to hinder the oxygen diffusion. X-ray amorphous or nanocrystalline structures are observed in Zr-Si-N films with silicon contents > 13.4 at.%. After the annealing treatments, crystalline phases such as ZrSi₂, ZrO₂ and Zr₂O are formed above 1000 ^oC in the Si-containing films while only zirconia crystallites are observed at 800 ^oC in pure ZrN films because oxygen acts as artifacts in the vacuum furnace. The structural, compositional and hardness comparison of as-deposited and annealed films reveal that the addition of silicon enhances the thermal stability compared to pure ZrN films and the hardness degradation stems from the formation of oxides at elevated temperatures.

The potentially most important challenges today are related to energy and the environment. New materials and methods are needed in order to, in a sustainable way, convert and store energy, reduce pollution, and clean the air and water from contaminations. In this, nanomaterials and nanocomposites play a key role, and hence knowledge about the relation between synthesis, structure, and properties of nanosystems is paramount. This thesis demonstrates that solution-chemical synthesis, using amine-modified acetates and nitrates, can be used to prepare widely different nanostructured films. By adjusting the synthesis parameters, metals, oxides, and metal–oxide or oxide–oxide nanocomposites were prepared for two systems based on Co and Zn:Fe, respectively, and the films were characterised using diffraction, spectroscopy, and microscopy techniques, and SQUID magnetometry. A variety of crystalline cobalt films—Co metal, CoO, Co3O4, and composites with different metal:oxide ratios—were synthesised. Heat-treatment parameters and control of the film thickness enabled tuning of the phase ratios. Random and layered Co–CoO composites were prepared by utilising different heating rates and gas flow rates together with a morphology effect associated with the furnace tube. The Co–CoO films exhibited exchange bias due to the ferromagnetic–antiferromagnetic interaction between the Co and CoO, whereas variations in e.g. coercivity and exchange bias field were attributed to differences in the structure and phase distribution. Ordered structures of wurtzite ZnO surrounded by amorphous ZnxFeyO were prepared through controlled phase segregation during the heating, which after multiple coating and heating cycles yielded ZnO–ZnxFeyO superlattices. The amorphous ZnxFeyO was a prerequisite for superlattice formation, and it profoundly affected the ZnO phase, inhibiting grain growth and texture, already from 1% Fe. In addition, ZnO–ZnxFeyO exhibited a photocatalytic activity for the oxidation of water that was higher than results reported for pure ZnO, and comparable to recent results reported for graphene-modified ZnO.

Mestrado em Ciência e Engenharia de Materiais
Os efeitos resultantes da hidrofilicidade de compósitos TiO2-SiO2 com diferente reatividade e composição química em processos sol-gel têm sido descritos na literatura. Esses resultados mostram que formulações sol-gel menos reativas originam super-hidrofilicidade, isto é, um ângulo de contacto inferior a 10° após envelhecimento superior a 8 semanas (envelhecimento em condições ambiente). Tendo em conta a morfologia de derivados de filmes compósitos e diferentes modelos termodinâmicos de superficie, sugere-se que um filme compósito com uma textura mais porosa poderá levar a um efeito de super-hidrofilicidade superior. Para verificar esta hipótese, neste projeto optou-se por estudar em detalhe compósitos TiO2-SiO2 mais reativos com diferentes composições (0, 20, 60 e 100 mol% de SiO2), em que a uma maior reatividade sol-gel é esperada uma redução da super-hidrofilicidade dos filmes compósitos. Com o objetivo de criar artificialmente uma morfologia rugosa/porosa, utilizaram-se neste caso camadas de esferas de poliestireno (PS) com um diâmetro médio de 0.6 μm. Com o objetivo de definir as melhores condições para obter camadas compactas 2D de esferas de PS foram estudados diferentes parâmetros no método de revestimento spin-coating. Realizaram-se experiências com diferentes velocidades de rotação (1000rpm e 500rpm). Outros parâmetros de deposição por spin-coating ajustados foram a rotação a 5000rpm/s, tempo de rotação de 1s, concentração de esferas de PS a 1wt% em EtOH, e um volume de 100μL para a solução de PS. As camadas 2D de PS foram posteriormente impregnadas em sóis de TiO2-SiO2. A utilização de esferas de PS permitiu obter filmes compósitos de TiO2-SiO2 com rugosidade aproximadamente cem vezes superior aos filmes compósitos obtidos na ausência das esferas de PS. Estas características morfológicas foram confirmadas por microscopia ótica, microcopia eletrónica (SEM) e microscopia de força atómica (AFM). Por sua vez, medições do ângulo de contacto mostraram que a hidrofilicidade aumenta após as modificações morfológicas efetuadas e, nos melhores casos (amostras com 20-60 mol% de SiO2), os ângulos de contacto de água obtidos foram inferiores a 5o, após 6 semanas de envelhecimento (sob condições ambiente). Este estudo mostrou igualmente que nestes casos existe uma relação entre: 1) o revestimento da superfície das esferas de PS, 2) a rugosidade/porosidade da superfície dos filmes S1-X+PS, e 3) a persistência da super-hidrofilicidade.
Enhanced hydrophilicity effects arising from TiO2-SiO2 granular interfaces in composite films deposited via sol-gel routes have been studied before. Results obtained so far have shown that sol-gel formulations yielding less reactive sols lead to enhanced super-hydrophilicity persistence of composite films, i.e. a water contact angle less than 10o after aging for more than 8 weeks (aging under ambient conditions without UV radiation). Taking into account the morphology of derived composite films and different surface thermodynamics models, we have suggested that a more rough/porous structure of the composite film might even increase this enhanced hydrophilicity effect. To verify this hypothesis, we have chosen to study more reactive TiO2-SiO2 composite sols with different compositions (0, 20, 60 and 100mol% of SiO2). This greater sol-gel reactivity is expected to reduce the natural super-hydrophilicity of composite films in order to better assess eventual effects of the morphology. Then, in order to artificially create rough/porous morphologies, we have used polystyrene (PS) beads with average diameter of 0.6μm. Different parameters of spin-coating deposition method were tested to define the best conditions to obtain 2D layers of closely packed PS beads. Further, two experiments with different rotation speeds (1000rpm and 500rpm) were performed. Other spin-coating conditions were fixed as follows: acceleration of 5000rpm/s, rotation time of 1s, concentration of PS beads 1wt% in EtOH, volume of PS solution 100μL. Such 2D PS layers were then impregnated with TiO2-SiO2 composite sols. Using PS beads, we have obtained TiO2-SiO2 composite films with a roughness that is almost 100 times higher than composite films without PS beads. These morphology features are confirmed by optical microscopy, AFM and FEG-SEM measurements. Water contact angle measurements show in turn that the hydrophilicity effects are increased by morphologic modifications, and in the best cases (samples with 20-60mol% of SiO2) water contact angles are close to 5o after 6 weeks of aging under ambient conditions without UV radiation. This study also shows that, in these cases, there is some relation between: 1) the surface coverage of PS beads, 2) the surface roughness/porosity of S1-X+PS films, and 3) their super-hydrophilicity persistence.

Mimicking nature gives rise to many important facets of biomaterials. This study is inspired by nature and reports on the fabrication of an intercalated polymer-NiTi nanocomposite that mimics the structural order of urethral tissue performing micturition. PTFE is chosen due to its hydrophobicity, low surface energy, and thermal and chemical stability. NiTi has been selected as a prime candidate for this research due to its excellent mechanical stability, corrosion resistance, energy absorbance, shape memory and biocompatibility. Nanoscale engineering of intercalated nanocomposites is done by PVD sputtering PTFE and NiTi. FTIR spectroscopy confirms that PTFE reforms as polymer chains after sputtering. Suitable PVD sputtering parameters were selected by investigating their influence on deposition rates, microstructure and properties of PTFE and NiTi thin films. PTFE forms stable nanocomposite coatings with NiTi and displays favourable surface interactions, known as ‘intercalation’. Intercalated PTFE-NiTi films were fabricated as layered and co-sputtered thin films. Co-sputtered nanocomposites contained nearly one-third vacant sites within its internal microstructure because of intercalation while intercalation introduced minute pits in fibrous NiTi columns of layered nanocomposites. These pits allow PTFE to extend their chains and crosslinks, resulting in microstructural and functional changes in the thin films. Intercalated PTFE-NiTi nanocomposites offer a close match to the natural tissue in terms of responding to the fluid contact (wetting angle modifications), and allow the soft and hard matter to incorporate in one framework without any chemical reactions (intercalation). An intercalated microstructure in co-sputtered and layered nanocomposites was verified by EDS-SEM and EDS-TEM techniques. The functional responses were witnessed by changes in water contact angle (WCA) and coefficient of friction (CoF) values measured on the film surface. The WCA (99°) and CoF (0.1 – 0.2) of the intercalated nanocomposite (sample PNT12) were different to the NiTi (top layer). WCA and CoF indicate the internal microstructural interactions because of intercalation. Although the pseudoelastic behaviour of NiTi can provide additional fluid response but the difficulty is an absence of crystallinity in as-deposited NiTi, and the heat treatment that melts PTFE. However, DSC and XRD techniques were employed to find the optimum NiTi composition and transition temperatures for phase transformation related to pseudoelasticity. This study provides the basis to incorporate the shape memory (pseudoelasticity or thermal shape memory effect (shape memory effect)) features of NiTi into the intercalated nanocomposite in future. The intercalated PTFE-NiTi nanocomposite reveals a fascinating research precinct, having the response generating characteristics similar to that of natural tissue.

The focus of this study was to explore process-structure-property relationships in biodegradable polymer nanocomposite films in order to eliminate the commonly used trial and error approach to materials design and to enable manufacturing of composites with tailored properties for targeted applications. The nanofiller type and concentration, manufacturing method and compounding technique, as well as processing conditions were systematically altered in order to study the process-structure-property relationships. Polylactic acid (PLA) was used as the polymer and exfoliated graphite nanoplatelets (GNP), carbon nanotubes (CNT), and cellulose nanocrystals (CNC) were used as reinforcement. The nanocomposite films were fabricated using three different methods: 1) melt compounding and melt fiber spinning followed by compression molding, 2) solution mixing and solvent casting, and 3) solution mixing and electrospinning followed by compression molding. Furthermore, the physical properties of the polymer, namely the crystallization characteristics were altered by using two different cooling rates during compression molding. The electrical response of the composite films was examined using impedance spectroscopy and it was shown that by altering the physical properties of the insulating polymer matrix, increasing degree of crystallinity, the percolation threshold of the GNP/PLA films is significantly reduced. Additionally, design of experiments was used to examine the influence of nanofiller type (CNT versus GNP), nanofiller content, and processing conditions (cooling rate during compression molding) on the elastic modulus of the composite films and it was concluded that the cooling rate is the primary factor influencing the elastic modulus of both melt compounded CNT/PLA and GNP/PLA films. Furthermore, the effect of nanofiller geometry and compounding method was examined and it was shown that the high nanofiller aspect ratio in the CNT/PLA films led to decreased percolation threshold compared to the GNP/PLA films. The melt compounded GNP/PLA films displayed a lower percolation threshold than the solution cast GNP/PLA films most likely due to the more homogeneous distribution and dispersion of GNP in the solution cast films. Fully biodegradable and biorenewable nanocomposite films were fabricated and examined through the incorporation of CNC in PLA. Through the addition of CNC, the degree of crystallinity of the matrix was significantly increased. Focusing the design space through investigation of process-structure-property relationships in PLA nanocomposites, can help facilitate nanocomposites with tailored properties for targeted applications.

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.

À travers l’histoire, la lumière a suscité le plus vif intérêt chez de nombreuses personnes curieuses, qu’il s’agisse de philosophes questionnant sa nature ou de scientifiques cherchant à interpréter les phénomènes qui lui sont associés. L’optique joue un rôle essentiel dans nombre de nos applications quotidiennes. L’indice de réfraction est l’un des facteurs les plus importants en photonique. Il est possible d’améliorer l’efficacité des dispositifs photoniques, comme les diodes électroluminescentes, les cellules photovoltaïques, etc., en réduisant la disparité des indices de réfraction des matériaux utilisés dans les dispositifs optiques. Cette thèse apporte quelques éclaircissements sur l’adaptation de l’indice de réfraction des matériaux, détaillant des aspects de l’indice de réfraction et de son ingénierie à l’aide de nanocomposites de polymère. Ce chapitre d’introduction évolue vers une discussion plus large sur l’indice de réfraction, ses différentes valeurs, et les avantages potentiels que son ingénierie pourrait générer. De minces films polymères ont été préparés et les nanoparticules ont été introduites de façon à modifier l’indice de réfraction. De la même manière, des films épais ont été préparés en utilisant du PMMA et du polystyrène, ceux-ci ayant été utilisés pour caractériser optiquement et morphologiquement les échantillons préparés. De nombreuses méthodes ont été employées pour préparer les films polymères. Des films polymères ultraminces ont également été préparés en utilisant la technique de revêtement par centrifugation, puis l’épaisseur du film de polystyrène a été modifiée afin d’étudier son impact sur l’indice de réfraction. Il a fallu surmonter plusieurs obstacles lors des recherches, comme la préparation d’un substrat ultra pur, l’uniformité du film polymère mince préparé, l’adhérence du film polymère mince sur les substrats après le coulage au solvant, etc. Tous ces défis ont été relevés grâce aux innovations détaillées dans cette thèse
Historically, light was a centre of interest for numerous inquisitive people: the philosophers who were interested in its nature and the scientists who wanted to interpret its associated phenomena. Optics is playing a pivotal role in many of our day to day applications.The refractive index is one of the most significant parameters in photonics. An increase in the efficiency of the photonic devices, like Light Emitting Diodes, Solar Cells, etc., can be achieved by reducing the refractive index mismatch of materials used in the optical devices.This thesis throws some light into the tailoring the refractive index of materials, by giving detailed aspects of refractive index and engineering of the refractive index using polymer nanocomposite. This introductory chapter evolves into a wider discussion on the refractive index and the types of refractive index and the potential leverage that can be obtained by engineering the refractive index. Polymer thin films were prepared and the nanoparticles were introduced so as to modify the refractive index. Similarly, thick polymer films were prepared using PMMA and Polystyrene and these were utilized to optically and morphologically characterize the prepared samples. Multiple methods have been utilized to prepare the polymer films. Ultra thin polymer films were also prepared using the spin coating technique and later the thickness of the polystyrene film was changed so as to understand its impact on the refractive index. There were multiple challenges to overcome while carrying out the research like the preparation of ultra pure substrate, uniformity in the prepared polymer thin film, adherence of the polymer thin film on to the substrates after solvent casting etc. All the challenges were overcome using the innovations, which are detailed in the thesis

La fabricació de capes superconductores nanocomposite d’YBa2Cu3O7-x (YBCO) mitjançant la incorporació de nanopartícules a la matriu ha demostrat haver realçat el rendiment d’ancoratge de vòrtexs sota camps magnètics aplicats i haver reduït l’anisotropia efectiva, garantint un gran potencial pel seu ús en nombroses aplicacions. Diferents concentracions, mides i processos de creixement de les nanopartícules condueixen a una rica varietat de defectes en les capes, llur efectivitat en ancoratge i relaxació de vòrtexs depèn de la temperatura i la magnitud i orientació del camp magnètic. En aquesta tesi, es presenta una amplia investigació en nanocomposites d’YBCO crescuts mitjançant la tècnica escalable i de baix cost “depòsit de solucions químiques” (CSD), en la que la incorporació de nanopartícules s’obté seguint dues estratègies diferents: nanopartícules de segregació espontània i nanopartícules prèviament formades. Mitjançant la combinació de mesures de transport elèctric amb l’anàlisi micro-estructural efectuat amb XRD o STEM, ha estat possible establir correlacions entre les propietats superconductores i el paisatge de defectes, la qual cosa ens ha permès separar contribucions d’ancoratge i relaxació de vòrtexs en les regions del diagrama camp-magnètic—temperatura i així preveure el millor paisatge per funcionar a certes condicions fins a camps magnètics molt intensos (35 T). S’ha demostrat que la incorporació de nanopartícules indueix altes densitats de falles d’apilament que afecten les contribucions d’ancoratge i relaxació de vòrtexs a qualsevol orientació. Grans forces d’ancoratge isotròpic sorgeixen a camps magnètics baixos i intermedis i a temperatures baixes i intermèdies. Per altra banda, les contribucions d’ancoratge anisotròpic es veuen altament alterades, especialment a camps magnètics intensos i temperatures altes. L’arranjament i la tipologia de les falles d’apilament induïdes per la incorporació de nanopartícules és determinant per la ponderació final de contribucions d’ancoratge. Aquí demostrem que l’ús de nanopartícules petites prèviament formades (7 nm) habilita el bon control d’una microestructura rica en falles d’apilament. S’ha identificat que un paisatge de defectes caracteritzat per una gran densitat de falles curtes i homogèniament distribuïdes és el millor dels paisatges possibles per promoure contribucions d’ancoratge isotròpic enormes atribuïdes al nanostrain localitzat a les vores de les falles d’apilament i a defectes atòmics que poden ser vacants de Cu-O situades en l'interior de les falles d’apilament. A més a més, la gran densitat de falles d’apilament és concomitant a una gran densitat de plans de macla, ambdós defectes beneficiosos per l’ancoratge anisotròpic quan el camp magnètic és paral·lel als plans-ab (H||ab) i a l’eix-c (H||c), respectivament. No obstant, la coherència dels plans de macla es trenca més sovint, cosa que fa que disminueixi la temperatura en la qual l’ancoratge anisotròpic és efectiu per H||c. Els nanocomposites gruixuts de nanopartícules prèviament formades han mostrat evitar significativament aquest trencament de la coherència i ser capaços d’assolir corrents crítiques altes a camps magnètics intensos i altes temperatures. Els falles d’apilament també han mostrat jugar un paper decisiu en l’impediment d’excitacions double-kink, que estimulen la relaxació de flux magnètic per H||c i especialment H||ab. A més a més, la contribució isotròpica de relaxació associada a les regions de nanostrain també es minimitza en el cas dels nanocomposites. En aquest treball es mostra que els nanocomposites proveeixen al mateix temps ancoratge més fort i relaxació més lenta de flux magnètic, especialment a camps magnètics baixos i intermedis i a temperatures baixes i intermèdies. La regió d’aquestes bones propietats es pot eixamplar més a camps i temperatures més alts mitjançant nano-enginyeria addicional, comptant amb que s’ha vist que diferents paisatges de defectes poden ser particularment interessants per diferents condicions donades.
The fabrication of superconducting YBa2Cu3O7-x (YBCO) nanocomposite films by the incorporation of nanoparticles in the matrix has demonstrated to strongly enhance the vortex pinning performances under applied magnetic fields and to reduce the effective anisotropy, ensuring great potential for their use in a broad number of applications. Different nanoparticle concentrations, sizes and growth process conditions lead to a rich variety of defects in the films, whose vortex pinning and vortex creep effectiveness depends on temperature and the magnitude and orientation of the magnetic field. In this thesis, it is presented an extensive research of YBCO nanocomposites grown by the scalable and low-cost chemical solution deposition (CSD) technique, where the incorporation of nanoparticles is obtained following two different approaches: spontaneous segregated nanoparticles and preformed nanoparticles. By the combination of electrical transport measurements with XRD and STEM microstructural analysis, correlation between superconducting performance and the defect landscape has been possible, allowing us to separate pinning and creep contributions in the regions of the magnetic-field--temperature diagram and therefore foresee the best landscape to operate at certain conditions up to very high magnetic fields (35 T). It has been demonstrated that the incorporation of nanoparticles induces large densities of stacking faults which strongly affect the pinning and creep contributions in all orientations. Large isotropic pinning forces arise at low-intermediate magnetic fields and at low-intermediate temperatures and anisotropic pinning contributions are strongly altered, especially at high magnetic fields and temperatures. The arrangement and the typology of the stacking faults induced by the incorporation of nanoparticles is determinant for the final balance of vortex pinning contributions. We demonstrate that the use of preformed small nanoparticles (7 nm) enables a very good control of the stacking-fault-rich microstructure. A defect landscape characterized by a large density of homogeneously distributed short stacking faults has been identified as the best one to promote huge isotropic pinning contributions, which are ascribed to the nanostrain located at the edges of stacking faults and to atomic defects which may be Cu-O vacancies hosted by stacking faults. Furthermore, the large density of stacking faults is concomitant with a large density of twin boundaries, both beneficial for the anisotropic pinning when the magnetic field orientation is parallel to the ab-planes (H||ab) and the c-axis (H||c) respectively. However, the coherence of twin boundaries is commonly broken, which reduces the temperature where anisotropic pinning is effective for H||c. Thick nanocomposites from preformed nanoparticles have shown to significantly avoid this coherence segmentation and be able to afford large critical currents at high magnetic fields and high temperatures. Stacking faults have been also found to play a decisive role for the preclusion of double kink excitations, which boost magnetic flux creep for H||c and especially H||ab. Furthermore, the isotropic flux creep contribution associated to the nanostrained regions is also reduced in nanocomposites. In this work, it is shown that nanocomposites provide simultaneously higher flux pinning and lower flux creep especially at low-intermediate temperatures and at low-intermediate magnetic fields. The region of this outstanding performance can be enlarged to larger fields and temperatures by further nanoengineering, where it has been shown that different defect landscapes can be particularly interesting for given operating conditions.

In this tribological study, a temperature dependent inquiry of the changes in chemistry and crystal structure of two selected double metal oxides is undertaken. It is known that chameleon coatings of Mo2N/Ag/MoS2 produce a friction coefficient of 0.1 from wear testing at 600 °C for 300,000 cycles. The low friction is attributed to the formation of silver molybdates layers, a lubricious double-metal oxide, in the coating. Double-metal oxides consisting of a group 6 transitional metal and silver (silver molybdate (Ag2Mo2O7) and silver tungstate (Ag2WO4)) were used for this investigation. Thin films and powders were investigated using high temperature x-ray diffraction, high-temperature Raman spectroscopy and differential scanning calorimetry in tandem with sliding tests from 25 to 600 °C. Our results were compared to external ab-initio molecular dynamic simulations performed elsewhere to qualify experimental results. The layered atomic structure of silver molybdate facilitates sliding, resulting in a low coefficient of friction (<0.2) from 300-500 °C. Unlike Ag2Mo2O7, however, Ag2WO4 does not possess a layered atomic structure and produced coefficients of friction (>0.4) in all temperature ranges between room temperature and 500 °C. Applying the knowledge gained from prior studies of the intrinsic properties of double metal oxides of group 6, chameleon coatings consisting of group 5 transitional metal nitrides (vanadium nitride, niobium nitride, and tantalum nitride) with silver inclusions were created using unbalanced magnetron sputtering to investigate their potential application as adaptive, friction reducing coatings. The coatings were tribotested against a Si3N4 counterface in the 22 to 1000 °C temperature range. In-situ Raman Spectroscopy measurements were taken during heating and wear testing at 700 °C to identify the evolution of phases in the coatings' surfaces and in the wear track. The chemical and structural properties of the coatings were also characterized before and after wear testing using x-ray diffraction. At higher temperatures, oxygen, silver and the transition metals react on the surface to form potentially lubricious double oxide phases (silver vanadate, silver niobate and silver tantalate). All coatings performed similarly up to 750 °C. The VN/Ag coating, however, had a lower coefficient of friction at 750 °C comparatively to TaN/Ag and NbN/Ag, likely due to its reported lower melting temperature (450 °C) and its layered crystal structure.

This thesis investigates thin films of the transition metal carbide systems Ti-Si-C, Nb-Si-C, and Zr-Si-C, deposited at a low substrate temperature (350 °C) with dc magnetron sputtering in an Ar discharge. Both the electrical and mechanical properties of these systems are highly affected by their structure. For Nb-Si-C, both the ternary Nb-Si-C and the binary Nb-C are studied. I show pure NbC films to consist of crystalline NbC grains embedded in a matrix of amorphous carbon. The best combination of hardness and electrical resistivity are for ~15 at.% a-C phase. The properties of nc-NbC/a-C are similar to films consisting of nc-TiC/a-C. I further show that in a model system of epitaxial TiCx (x ~0.7) up to 5 at.% Si can be incorporated. At higher Si content, Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy. Higher amounts of Si into the Nb-Si-C and Zr-Si-C systems make them become amorphous. These amorphous structures are unstable under electron irradiation were they crystallize. I show that the cause of crystallization is driven by atomic displacement events.

Two sets of nanocomposite films consisting of different atomic concentrations of Au dispersed in a TiO2 dielectric matrix were deposited by DC reactive magnetron sputtering, and subjected to several annealing trataments in vacuum, for temperatures ranging from 300 to 800 0C. The obtained results show that the structure and the size of Au clusters, together with the matrix crystallinity, changed as a result of the annealing As a result of these structural variations the film optical properties were modified too. The optical changes, and the correspondent Surface Plasmon Resonance effect were confirmed by reflectivity and CIELab colour measurements. XRD analysis confirmed the presence of gold in all the samples, and the crystallization of the TiO2 matrix for the samples annealed at temperatures above 4000C. With further increase of the annealing temperature, there is a change from the TiO2 anatase phase into rutile-type structure. Simultaneously, the Au atoms are organized in crystalline nanoparticles (revealing an fcc-type structure, with the (111) preferential growth orientation). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34916

Progress in the burgeoning field of organic electronics is enabling the development of novel technologies such as low-cost, printable solar cells and flexible, high-resolution displays. One exciting avenue of research in this field is nanostructured hybrid organics such as quantum dot (QD)-polymer devices. The incorporation of QDs can greatly improve a device’s efficiency and gives one the ability to tune its electrical and optical characteristics. In order for such technologies to be commercially viable, it is important to classify their mechanical integrity and reliability. Surprisingly little is known about the mechanical properties of QD-polymer thin films (<100 nm). This is in part due to challenges of: (1) isolating the mechanical response of a thin film from the underlying substrate, (2) obtaining a homogeneous dispersion of QDs in the film, and (3) the sensitivity of mechanical properties to the inherent rate dependence of polymer deformation (i.e., viscoelasticity). All of these challenges can introduce significant errors in the measurement of mechanical properties. Furthermore, the deformation mechanisms in nanocomposites are not well understood, so it is difficult to predict the effect of adding QDs on the mechanical behavior of films. In this thesis, these challenges are addressed for characterizing the mechanical properties of thin films of CdSe QD-poly[2-methoxy-5-2(2΄-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) nanocomposites using quasi-static nanoindentation testing. Elastic modulus, hardness, and creep are measured as a function of QD concentration and loading and unloading rates. The QDs' ligands are removed by pyridine treatment prior to mixing with MEH-PPV to improve dispersion. The films are prepared via spin-coating onto glass substrates and subsequent annealing in air. Efforts are taken in the mechanical testing to minimize errors due to viscoelastic creep and interference from the substrate. Transmission electron microscopy reveals that the QDs are relatively well-dispersed in the polymer matrix. It is observed that adding QDs increases the elastic modulus (E) and hardness (H) of the films, while reducing the viscoelastic creep. Both E and H increase linearly with the volume percent of QDs. E ranges from 14.5 GPa to 52.7 GPa for pure MEH-PPV (0% QDs) and 100% QD films, respectively, while H ranges from 220 MPa to 1430 MPa for the same films, respectively. The films behave viscoelastically at lower QD loading, but assume a more granular character as the loading approaches 100%.

Vertically aligned nanocomposite (VAN) thin films have recently stimulated significant research interest to achieve better material functionality or multifunctionalities. In VAN thin films, both phases grow epitaxially in parallel on given substrates and form a unique nano-checkerboard structure. Multiple strains, including the vertical strain which along the vertical interface and the substrate induced strain which along the film and substrate interface, exist in VAN thin films. The competition of these strains gives a promise to tune the material lattice structure and future more the nanocomposite film physical properties. Those two phases in the VAN thin films are selected based on their growth kinetics, thermodynamic stability and epitaxial growth ability on given substrates. In the present work, we investigated unique epitaxial two-phase VAN (BiFeO3)x:(Sm2O3)1-x and (La0.7Sr0.3MnO3)x:(Mn3O4)1-x thin film systems by pulsed laser deposition. These VAN thin films exhibit a highly ordered vertical columnar structure with good epitaxial quality. The strain of the two phases can be tuned by deposition parameters, e.g. deposition frequency and film composition. Their strain tunability is found to be related directly to the systematic variation of the column widths and domain structures. Their physical properties, such as dielectric loss and ferromagnetisms can be tuned systematically by this variation. The growth morphology, microstructure and material functionalities of VAN thin films can be varied by modifying the phase ratio, substrate orientation or deposition conditions. Systematic study has been done on growing (SrTiO3)0.5:(MgO)0.5 VAN thin films on SrTiO3 and MgO substrates, respectively. The variation of column width demonstrates the substrate induced strain plays another important role in the VAN thin film growth. The VAN thin films also hold promise in achieving porous thin films with ordered nanopores by thermal treatment. We selected (BiFeO3)0.5:(Sm2O3)0.5 VAN thin films as a template and get uniformly distributed bi-layered nanopores. Controllable porosity can be achieved by adjusting the microstructure of VAN (BiFeO3):(Sm2O3) thin films and the annealing parameters. In situ heating experiments within a transmission electron microscope column provide direct observations into the phases transformation, evaporation and structure reconstruction during the annealing. Systematic study in this dissertation demonstrate that the vertically aligned nanocomposite microstructure is a brand new architecture in thin films and an exciting approach that promises tunable material functionalities as well as novel nanostructures.

博士
國立成功大學
化學工程學系碩博士班
93
Multifunctional diamond-like carbon (DLC) nanocomposite films containing a high concentration of TiO2 nanoparticles are to be synthesized for optical, tribological and MEMS applications. The nanocomposite films had good hydrophilic property under ultraviolet (UV) radiation and hardness of 14 GPa. The XRD, XPS, Raman, and TEM analysis revealed that the films were incorporated TiO2 and TiC nanoparticles in the DLC matrix. The nanocomposite films were highly abrasion-resistant and had long-life hydrophilic surface. 　DLC films were deposited using benzene or acetylene with or without nitrogen doping at elevated temperatures by capacitive RF plasma chemical vapor deposition (CVD). The method for preparing DLC films with a high hardness and a good electrical conductivity was simultaneously achieved by combining the effects of nitrogen doping and raising deposition temperature. The film resistivity could reach 0.10 Wcm with hardness of 25 GPa. The film resistivity decreased with increasing N2 concentration or deposition temperature. At a lower deposition temperature, the hardness of films decreased with increasing the nitrogen content. Appropriate nitrogen content enhanced the hardness at a higher deposition temperature. However, a nitrogen concentration too high induced the formation of CºN bonds which obstructed the carbon-carbon cross-linking structure of DLC films. The formation of fullerene-like structure was observed in the DLC films using benzene as carbon source. According to TEM images, the microstructure of DLC films is significantly varied with the deposition temperature. By FT-IR, Raman, and residual stress analysis, we concluded that the formation of fullerene-like nanoparticles was attributed to the benzene structure and the induced local thermal spike at a high substrate bias of –1500 V. The growth mechanism was studied and will be discussed. 　To improve thermal resistance of DLC films, we incorporated a high concentration of silicon in the films. Acetylene was employed as the carbon source, and argon was used to sputter Si target for low temperature depositions. Low stress and thermally stable silicon-containing DLC films were deposited on the silicon wafer substrates. We found that the hardness decreased with increasing the concentration of silicon. When the atomic percent of silicon was higher than 50 %, the DLC films stress was only 0.48 GPa, and the films was stable up to 600℃, in comparison to the conventional undoped DLC films with a high stress of 2.13 GPa and thermal stability only below 400℃. However, the hardness was decreased from 18.6 GPa to 10.9 GPa when the atomic percent of silicon was increased from 0 % to 50 %. 　A new method in preparing carbon-based molecular sieve (CMS) membranes for gas separation has been proposed. Carbon-based films are deposited on porous Al2O3 disks using hexamethyldisiloxane (HMDSO) by remote inductively-coupled-plasma (ICP) CVD. After treating the film with ion bombardment and subsequent pyrolysis at a high temperature, carbon-based molecule sieve membranes can be obtained, exhibiting a very high H2/N2 selectivity around 100 and an extremely high permeance of H2 around 1.5x10-6 mol·m-2·s-1·Pa-1 at 298 K. The O2/N2 selectivity could reach 5.4 with the O2 permeance of 2x10-7 mol·m-2·s-1·Pa-1 at 423 K. 　During surface treatments, HMDSO ions were found to be more effective than CH4, Ar, O2 and N2 ions to improve the selectivity and permeance. Short and optimized surface treatment periods were required for high efficiency. Without pyrolysis, surface treatments alone greatly reduced the H2 and N2 permeances and had no effect on the selectivity. Besides, without any surface treatment, pyrolysis alone greatly increased the H2 and N2 permeances, but had no improvement on the selectivity, owing to the creation of large pores by desorption of carbon. A combination of surface treatment and pyrolysis is necessary for simultaneously enhancing the permeance and the selectivity of CMS membranes, very different from the conventional pore-plugging mechanism in typical CVD.

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.

Vertically aligned nanocomposite (VAN) oxide thin films are unique nanostructures with two-phase self-assembled, heteroepitaxially grown on single-crystal substrates. Both phases tend to grow vertically and simultaneously on a given substrate with lattice matching in the system. The nanostructured thin film system could form different in-plane morphologies including nano-checkerboard, nanopillar in matrix and nanomaze structures. The VAN thin films with tunable vertical lattice strain and novel microstructures provide fascinating approaches to achieve enhanced functionalities. In this dissertation, the microstructure and vertical strain effect on low-field magnetoresistance (LFMR) have been investigated in heteroepitaxial La0.7Sr0.3MnO3 (LSMO):CeO2 and LSMO:ZnO VAN thin films with a vertical strain of 0.13 % and 0.5 %, respectively. We demonstrate that LFMR can be tuned by column width and vertical strain in these VAN systems, i.e., smaller column width and larger vertical strain could result in a larger LFMR in the vertical nanocomposite heteroepitaxial thin films. The physical mechanism of enhanced LFMR in LSMO-based VAN has been explored. Single-phase LSMO and LSMO-based VANs have been grown on different substrates with different secondary phase compositions. Substrate effect in single-phase LSMO films shows that LFMR tends to increase with grain misorientation factor because the cross-section of electron conduction paths reduces as grain misorientation factor increases. (LSMO)1-x:(ZnO)x VAN heteroepitaxial films without large angle grain boundary (GB) have been used to study the pure phase boundary (PB) effect on the LFMR. It shows that increased PBs tends to reduce the cross-section of the conducting path and thus favor the spin-dependent tunneling in nanomaze structures with ferromagnetic/insulating/ferromagnetic vertical sandwiches. Tilted aligned LSMO nanostructured films with artificial GBs have been designed to investigate pure GBs influence on LFMR. The results indicate that decoupling of neighboring ferromagnetic (FM) domains by artificial GBs is necessary to achieve enhanced LFMR properties; and the strength of the GBs can be controlled by post-annealing to tune the LFMR effect. The VAN heteroepitaxial films display excellent microstructure compatibility and strain tuning. Perovskite oxides can be combined with many other oxide materials to form VAN architectures. The microstructure and lattice strain in the unique heteroepitaxial VANs can be used to engineer and tune the existing/new functionalities.

碩士
明道大學
材料科學與工程學系碩士班
97
The high temperature oxidation behavior of CrTiAlSiN coatings was studied. These coating were deposited on silicon substrates by us cathodic-arc deposition system with lateral rotating arc cathodes. Titanium, Chromium and Al88Si12 cathodes were used for the deposition of CrTiAlSiN coatings. For the high temperature oxidation test, the coated samples were annealed at high temperature ranging from 700℃-1000℃ in air for 2 hours. In addition, structure characterization was conducted using a Scanning Electron Microscope (SEM), and an X-ray diffraction (XRD) instrument. Mechanical properties including Young’s modulus and hardness were measured by nano-indentation. The chemical variation and bonding structures of the oxidized coatings were identified by a high- resolution X-ray photoelectron spectrometer (XPS). It indicated that CrTiAlSiN with higher Cr, Al, and Si contents possessed superior oxidation resistance than TiAlN, due to the amorphous SiNx phase existed. The different oxidation mechanisms of the deposited CrTiAlSiN at high temperature are developed in this study.

The structural evolution of carbon:transition metal (C:TM) nanocomposite thin films is investigated in two regimes: (i) surface diffusion governed regime occurring during the film growth and (ii) bulk diffusion dominated regime occurring during the post-deposition thermal annealing. C:V, C:Co, and C:Cu nanocomposite films were grown by ion beam co-sputtering. The influence of the metal type, metal content (15-40 at.%), substrate temperature (RT-500°C), and annealing temperature (300-700°C) on the structure and morphology of the composite is studied by the means of elastic recoil detection analysis, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Vanadium (copper) is in carbidic (metallic) state in the whole temperature range of the study. In contrast, cobalt is in carbidic state up to 300°C and becomes metallic at higher growth temperatures. The nanoparticles in C:V films exhibit a globular shape at RT-500°C, whereas in C:Co and C:Cu films a growth transition from globular to elongated nanoparticles occurs around 300°C. The comparison of the Raman spectroscopy results from carbon reference and C:TM thin films shows that the presence of the metal during growth significantly enhances the formation of sixfold ring carbon clusters at temperatures as low as RT. The enhancement occurs independently of the nanoparticle size, shape, and phase, and metal content, and is related to processes taking place on the nanoparticle surface of the growing film rather than in the bulk. The degree of enhancement depends on the TM type and content. Post-deposition annealing of C:Co and C:Cu films at 700°C causes the metal segregation at the film surface, while no changes upon annealing occur in C:V films. In addition, cobalt brings about the carbon graphitization by a dissolution-diffusion-precipitation mechanism, similar to the metal-mediated crystallization of amorphous silicon or germanium. No graphitization upon annealing occurs in C:V, C:Cu, and carbon reference films.
Die Strukturentwicklung in Kohlenstoff-Übergangsmetall-Nanokompositschichten wird in zwei Bereichen untersucht: (i) im oberflächendiffusionsgesteuerten Bereich während des Schichtwachstums und (ii) im bulkdiffusionsdominierten Bereich während des nachträglichen Temperns. C:V, C:Co und C:Cu Nanokompositschichten wurden durch Ionenstrahl Co-Sputtern hergestellt. Der Einfluss des Metalltyps, des Metallgehalts (15-40 at.%), der Substrattemperatur (RT-500°C) und der Temperatur beim Tempern (300-700°C) auf die Struktur und Morphologie des Komposits wird mittels elastischer Rückstoßteilchen-Analyse, Röntgenbeugung, Transmissionselektronenmikroskopie und Ramanspektroskopie untersucht. Vanadium (Kupfer) ist im gesamten Temperaturbereich der Studie in karbidischem (metallischen) Zustand. Im Gegensatz dazu befindet sich Kobalt bis zu einer Temperatur von 300°C in karbidischem Zustand und wird bei höheren Abscheidetemperaturen metallisch. Die Nanopartikel in C:V Filmen besitzen eine runde Form im Temperaturbereich von RT bis 500°C wohingegen bei den C:Co und C:Cu Filmen ein Übergang von runden zu länglichen Partikeln bei etwa 300°C zu beobachten ist. Der Vergleich der Ramanspektroskopieresultate der Kohlenstoffreferenzproben und der Nanokompositschichten zeigt, dass die Anwesenheit des Metalls während des Schichtwachstums die Bildung von sechsatomigen Kohlenstoffringclustern bei Temperaturen so niedrig wie Raumtemperatur deutlich fördert. Die Erhöhung tritt unabhängig von der Partikelgröße, -form und phase und unabhängig vom Metallgehalt auf, und betrifft eher Prozesse, die auf der Oberfläche der Nanopartikel während des Schichtwachstums stattfinden als im Bulk. Der Grad der Erhöhung hängt vom Metalltyp und -gehalt ab. Nachträgliches Tempern der C:Co und C:Cu Filme bei 700°C führt zur Segregation des Metalls an der Schichtoberfläche während in den C:V Filmen keine Veränderungen durch das Tempern auftreten. Des weiteren kommt es in den C:Co Filmen zur Graphitisierung des Kohlenstoffs durch einen „Lösungs-Diffusions-Ablagerungs“ Mechanismus ähnlich der metallvermittelten Kristallisierung in amorphem Silizium und Germanium. In den C:V, C:Cu und Kohlenstoffreferenzfilmen findet keine Graphitisierung während des Temperns statt.

碩士
元智大學
機械工程學系
104
Graphene nanoplatelets (GNP) with excellent mechanical and thermal properties have been considered as ideal reinforcements. In this investigation, various contents of graphene nanoplatelets (MWCNT) ranging from 0.3 % ~1.0 % wt. were added to the epoxy to fabricate the nanocomposites. Nanocomposite films with thickness of 0.3 mm were deposited on the aluminum substrate using the spin coating. The Young’s modulus of the nanocomposite film was determined by the three-point bending test and nanoindentation test. The stress distribution and load carrying capability of the nanocomposite film subjected to tensile and bending loads were derived basing on the shear lag model and Bernoulli beam theory. Three-point and four-point bending tests were conducted to determine the interfacial fracture toughness of mode I and II, respectively. Experimental test results show that the Young’s modulus, load carrying capability and fracture toughness of the nanocomposite film are increasing with the increase of the content of GNPs In the case of nanocomposite film with 1.0 % wt. GNPs, the Young’s modulus, load carrying capability and fracture toughness are increased by 39%, 34% and 44% compared with neat epoxy, respectively. In addition, the dispersion of GNPs in the epoxy based matrix was examined using the scanning electronic microscope (SEM). The SEM images depict that GNPs are well dispersed resulting in the enhancement of the mechanical properties of the nanocomposite films.

博士
國立成功大學
化學工程學系碩博士班
100
Diamond-like carbon (DLC) nanocomposite films containing nanostructures were synthesized by various deposition techniques, including inductively-coupled plasma chemical vapor deposition (ICP-CVD), sputtering-assisted CVD, capacitive-coupled plasma CVD, plasma jet CVD etc. By incorporating high densities of ceramic nanoparticles (SiC, Si3N4, ZrO2, TiC, TiO2, ZnO, etc.) and nano-carbons, DLC nanocomposites can present the increase of film hardness and the reduction of film stress, as well as the enhancement of toughness, increase of film adhesion, and decrease of friction coefficients with novel function of light-induced hydrophilicity. SiCxNy nanocrystallites-containing DLC nanocomposite films were prepared by ICP-CVD using a hexamethyldisilazane (HMDSN) precursor. The substrate was biased by a pulsed-DC power supply to provide the necessary energy of deposited ions. The effects of substrate bias on the surface morphology, roughness, and the mechanical properties of nanocomposite film were well investigated. The results revealed the film has maximum hardness of 15 GPa at a relative low stress of 0.5 GPa at an ICP power of 100W, and a substrate bias of -200V. The films exhibited a lower coefficient of friction in the range of 0.06 to 0.09 via nano-scratch technique, and had lower wear depth with a good wear performance using nano-wear test. The fracture toughness of the film was greatly enhanced by the incorporation of SiCxNy nanoparticles in the DLC matrix, measured from its resistance to crack propagation by the indentation method of Vickers indenter. Zirconia-containing DLC nanocomposite films were prepared by sputtering-assisted plasma CVD. ZrO2-DLC films were deposited using acetylene as the carbon source, and argon was used to sputter ZrO2 target. AFM results show that the surface of the films is very smooth. The tribological properties of the films could be controlled by adjusting the substrate biases during depositions. A higher energy of ion bombardment in this system biasing by pulsed-DC, induces the formation of sp2 carbon bonding in the film and makes the films’ hardness and Young’s modulus drop. The fractured toughness of DLC nanocomposite films measured by Vickers indenter were in the range from 14 to 22 MPa•m1/2, revealing the enhancement of film toughness. Nano-carbons embedded in DLC nanocomposite films were synthesized by plasma jet CVD in the mixed gases of benzene and nitrogen. Transmission electron microscopy images of the films indicate the existence of nanostructured carbon. A high degree of dissociation and reaction in plasma jet reactor and appropriate nitrogen contents in the gas phase are important for the growth of nanostructured carbon embedded in the DLC matrix. Synthesis of TiO2-DLC nanocomposite films with novel functions were studied by sputtering-assisted plasma CVD. With titanium-oxygen species sputtered from titania (TiO2) target by argon using a radio-frequency (RF) power, DLC films were simultaneously grown on the negatively-biased substrate by plasma CVD of acetylene gas using a pulsed direct-current (DC) power. By adjusting the sputtering power, both TiO2 and TiC nanoparticles could be incorporated in the DLC films. The TiO2-DLC nanocomposite films deposited at 80.7 % Ar exhibited a high hardness of around 14 GPa at a relatively low stress and, particularly, a fast rate of turning super-hydrophilic by reaching zero degree of water contact angle under 40 minutes of ultraviolet irradiation. Synthesis of amorphous boron nitride films (a-BN) at low temperature were studied by hollow cathode discharge CVD. Borazine and N2 gases were employed as the precursors to deposit a-BN films. The as-deposited films were amorphous phase with a transparent and smooth surface. Fourier transform infrared spectroscopy (FTIR) revealed that with a high nitrogen concentration and a high hollow cathode power, high content of sp3-bonded BN can be obtained. Hollow cathode plasma was essential in forming the sp3-bonded BN in the film.

The present study focuses on the preparation and characterization of bioactive nanocomposite sericin/ polyvinyl alcohol (PVA) blend films. Films were prepared by blending sericin and PVA by solvent casting method. Different blends were created by varying the concentrations of glutraldehyde (GA), glycerol as plasticizer, closite 30B as bioactive nanoclay and silver nitrate as antimicrobial bioactive material. Films were characterised for mechanical, structural, morphological, thermal, biodegradable and antimicrobial properties. Fourier Transform Infrared Spectroscopy (FTIR) of films revealed that GA chemically cross linked with sericin and PVA. Scanning electron microscopic (SEM) revealed that no phase separation in prepared films. These films show the antimicrobial activity against gram negative bacteria Neisseria. Such biodegradable blended films can be used for smart food packaging material.

Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.

First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃ (BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.

Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂ thin film system, which has an insulating CeO₂ in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂ increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.

Third, the transition metal element in Bi₃MoM_TO₉ (M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved.

The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.