Dissertations / Theses on the topic 'Functional thin films'

Thin film technology is of great significance for a variety of products, such as electronics, anti-reflective or hard coatings, sensors, solar cells, etc. This thesis concerns the synthesis of thin functional films, reactive magnetron sputter deposition process as such and the physical and functional characterization of the thin films synthesized. Characteristic for reactive sputtering processes is the hysteresis due to the target poisoning. One particular finding in this work is the elimination of the hysteresis by means of a mixed nitrogen/oxygen processing environment for dual sputtering of Alumina-Zirconia thin films. For a constant moderate flow of nitrogen, the hysteresis could be eliminated without significant incorporation of nitrogen in the films. It is concluded that optimum processing conditions for films of a desired composition can readily be estimated by modeling. The work on reactively sputtered SiO2–TiO2 thin films provides guidelines as to the choice of process parameters in view of the application in mind, by demonstrating that it is possible to tune the refractive index by using single composite Six/TiO2 targets with the right composition and operating in a suitable oxygen flow range. The influence of the target composition on the sputter yield is studied for reactively sputtered titanium oxide films. It is shown that by using sub-stoichiometric targets with the right composition and operating in the proper oxygen flow range, it is possible to increase the sputter rate and still obtain stoichiometric coatings. Wurtzite aluminum nitride (w-AlN) thin films are of great interest for electro-acoustic applications and their properties have in recent years been extensively studied. One way to tailor material properties is to vary the composition by adding other elements. Within this thesis (Al,B)N films of the wurtzite structure and a strong c-axis texture have been grown by reactive sputter deposition. Nanoindentation experiments show that the films have nanoindentation hardness in excess of 30 GPa, which is as hard as commercially available hard coatings such as TiN. Electrical properties of w-(Al,B)N thin films were investigated. W-(Al,B)N thin films are found to have a dielectric strength of ~3×106 V/cm, a relatively high k-value around 12 and conduction mechanisms similar to those of AlN. These results serve as basis for further research and applications of w-(Al,B)N thin films. An AlN thin film bulk acoustic resonator (FBAR) and a solidly mounted resonator (SMR) together with a microfluidic transport system have been fabricated. The fabrication process is IC compatible and uses reactive sputtering to deposit piezoelectric AlN thin films with a non-zero mean inclination of the c-axis, which allows in-liquid operation through the excitation of the shear mode. The results on IC-compatibility, Q-values, operation frequency and resolution illustrate the potential of this technology for highly sensitive low-cost micro-biosensor systems for applications in, e.g. point-of-care testing.

Polycrystalline tin-doped indium oxide (ITO) thin films were prepared by Pulsed Laser Deposition (PLD) with an ITO (In\(_2\)O\(_3\)-10 wt.% SnO\(_2\)) target and deposited on borosilicate glass substrates. By changing independently the thickness, the deposition temperature and the oxygen pressure, a variety of microstructures were deposited. The impact on thin film physical properties of different gas dynamics is stressed and explained. Films deposited at room temperature (RT) show poorer opto-electrical properties. The same is true for films deposited at low or high oxygen pressure. It is shown that films grown with 1 to 10 mT Oxygen pressure at 200 °C show the best compromise in terms of transmittance and resistivity. The influence of the thickness, the substrate temperature and the oxygen pressure on the microstructure and ITO film properties is discussed. A practical application (a Dye Sensitized Solar Cell) is proposed.

The functionalization of surfaces has received attention because the process allows the design and tailoring of substrate surfaces with a new or improved function. â Host-guestâ thin film complexes are composed of â hostâ molecules attached the substrate surface, either through physisorption or covalent bonds, with cavities for the inclusion of desired â guestâ molecules for the functionalization of the surface. Two methods for fabricating functional â host-guestâ thin films were investigated: Langmuir-Blodgett (LB) deposition and self-assembly monolayer (SAM). Langmuir films were created at the air-water interface using octadecanesulfonic acid (C18S) as the amphiphilic â hostâ molecules separated by hydrophilic guanidinium (G) spacer molecules, which created a cavity allowing the inclusion of desired â guestâ molecules. Surface pressure-area isotherms of the (G)C18S, with and without guests, are characterized by the lift-off molecular areas and are use to determine the proper deposition surface pressure. â Host-guestâ Langmuir films are deposited onto silicon substrates using the LB deposition technique. The LB films were then subjected to stability testing using different solvents over increasing periods of time. Grazing-angle incidence X-ray diffraction (GIXD), specular X-ray reflectivity (XRR) and transfer ratio measurements were used to characterize the crystallinity, film thickness, overall film stability and film coverage. The GIXD data revealed that the crystallinity of the deposited film varies with the â guestâ molecules and can be disrupted by the functional group on the â guestâ molecule through hydrogen bonding. After modeling the XRR data using StochFit, it was discovered that the more polar solvent, tetrahydrofuran (THF), removed the film completely while the nonpolar solvent, hexane, compacted the thin film and increased the electron density. With transfer ratios around 0.95 to 1.05, the deposited films were homogenous. The second method used was self-assembly monolayers, which differs from Langmuir films in that they are created by a spontaneous chemical synthesis from immersing a substrate into a solution containing an active surfactant. Octadecyltrichlorosilane (OTS) was used initially as a molecule to study the self-assembled monolayer procedure. To study a â host-guestâ self-assembled monolayer system, a compound is being synthesized from 9-bromoanthracene. This compound would already contain the cavity necessary for the inclusion of â guestâ molecules. The solution that contained OTS was composed of a 4:1 mixture of anhydrous octadecane: chloroform. Silicon substrates with a deposited oxide layer were hydroxylated for the surfactant binding chemical reaction to occur. The OTS SAMs were exposed to the same stability tests as the LB films. Surface contact angle measurements were taken of the OTS SAMs before and after the stability tests. The contact angle prior to the stability tests was 110° (±2°). The contact angle after immersion in THF was 101° (±2°) while the contact angle resulting from immersion in hexane was 105° (±2°). From the contact angle measurements, the degradation of the OTS SAMs was less extensive than that of the (G)C18S LB films.
Master of Science

Functional polymeric scaffolds have been employed in biological applications as several utilities, from nano-sized drug delivery systems to concrete implants. The progression in biological fields essentially relies on finding an appropriate material to fulfil the critical requirements for various types of applications with great potential for tuning functionality and mechanical properties. Therefore, the generation of new materials in extensive libraries is desirable for researchers. In this thesis, two main varieties of functional scaffolds have been constructed; these include i) periodic structure isoporous membranes and ii) three dimension (3D) crosslinked networks with programmable functionalities and mechanical properties. In the first case, a library of linear dendritic (LD) block copolymers was synthesised from biocompatible 2,2-bis(methylol)propionic acid (bis-MPA) dendrons and 2- hydroxyethyl methacrylate (HEMA) derivatives. These materials were successfully employed for the fabrication of isoporous membranes via the facile Breath Figure (BF) method. The dendritic periphery end groups control the manipulation of film morphology, as well as introduction of desired functionalities, either pre- or post- film formation. The introduction of azide functional group along the polymer backbone allows crosslinking reaction, which enhances the stability of the isoporous films. The stability towards temperature was improved from around its glass transition temperature (Tg) to 400 °C after crosslinking; simultaneously the porosity is maintained after immersion in the whole range of pH (1-14). These materials show great potential use as high performance isoporous membranes in futuristic applications such as micro-reactors, sensors and cell patterning platforms. In the second case, the facile fabrication of functional networks employs off-stoichiometric crosslinking, which resulted in residual reactive functional groups after film formation and networks with different crosslinking density. This straightforward off-stoichiometric concept is applied with commercially available materials and well-controlled dendritic-linear-dendritic (DLD) hybrid polymers, generating functional networks with different properties from high stiffness film to soft hydrogels. The network post-modification can be performed topologically and throughout the scaffold. Several crosslinking chemistries were employed for construction of hydrogels from DLD hybrid polymers. The Copper(I) Catalysed Azide-Alkyne Cycloaddition (CuAAC) click reaction results in hydrogels with higher compressive modulus compared to other hydrogels constructed from thiol-ene, thiol-yne and amine-N-hydroxysuccinimide (NHS) esters coupling methods with similar building blocks. These functional crosslinked networks are suitable for numerous applications including fabrication of microfluidic devices, cell culture platforms and bone adhesives.

QC 20150520

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.
Includes bibliographical references.
Initiated chemical vapor deposition (iCVD) was explored as a novel method for synthesis of functional polyacrylic thin films. The process introduces a peroxide initiator, which can be decomposed at low temperatures (<200⁰C) and initialize addition reaction of monomer species. The use of low temperatures limits the decomposition chemistry to the bond scission of initiator, while retaining functional groups of monomers, which has been confirmed in the infrared spectroscopy, nuclear magnetic resonance, and x-ray photoelectron spectroscopy of iCVD poly(glycidyl methacrylate) (PGMA) thin films. Studies of PGMA iCVD deposition kinetics and molecular weights indicate a free radical polymerization mechanism and provide guide for vapor-phase synthesis of other vinyl monomers. The retained epoxy groups can crosslink under e-beam irradiation, resulting in e-beam patterning of iCVD PGMA thin films with 80 nm negative-tone features achieved. iCVD copolymerization was also investigated to further tune film composition and properties. A surface propagation mechanism was proposed based on the study of the monomer reactivity ratios and the copolymer molecular weights during iCVD copolymerization.
(cont.) The synthesized acrylic copolymers have been investigated in applications as positive-tone e- beam resists, CO₂-developable resists, and low surface energy coatings with improved mechanical properties. The process of iCVD polymerization is extendable to vapor-phase polymerization of other vinyl monomers and creates new opportunities for the application of functional polymer thin films.
by Yu Mao.
Ph.D.

The bio-enabled syntheses of functional nano-structured metal oxide thin films is of importance for a range of applications, in photonics, electronics, sensing, cell engineering, and biochemical devices. This type of novel syntheses method can overcome problems common in conventional oxide processing. In general, conventional oxide processes often require thermal treatment, caustic chemicals, and mechanical processing when producing shape-controlled inorganic materials. In contrast, biological processes are usually carried out under mild conditions (low temperature, neutral pH, and atmospheric pressure) and are therefore promising for the development of benign processes. Functional materials synthesized at room temperature using biomolecules are promising due to their expediency. During recent years, significant discoveries and progress have been made in discovering, and finding new applications for such biomimetic oxide-based minerals. However, much of the research has focused on SiO- and TiO-bearing organic-inorganic hybrid materials, of which a significant limitation is that, there are relatively few water-soluble inorganic oxide precursors commercially available for such biological syntheses. Two common compounds that are used in the biomimetic syntheses of SiO₂ and TiO₂ are tetramethoxisilane (TMOS) and Ti(IV) -bis(ammonium lactato) dihydroxide ( TiBALDH ). As a result, approaches to synthesize new water-soluble transitional metal complexes for use as precursors in the biomineralization of the corresponding functional metal oxide thin films were explored in this work, in order to expand the range of functional oxide chemistries formed via bio-enabled methods. A Ti-containing compound was synthesized to compare the behavior of commercially-available and as-synthesized TiBALDH. Another titanium-containing complex with citrate ligands, instead of lactate, was also synthesized to investigate the influence of the ligand type on the deposition behavior of the precursors. Zirconium- and hafnium-containing complexes were also synthesized to demonstrate the feasibility and versatility of the idea of applying bio-enabled syntheses to the fabrication of functional mineral oxides other than the reported SiO₂ and TiO₂. The second part of this thesis focuses on developing a novel way to fabricate porous functional mineral oxide thin films with controlled pore size, which can be used in a variety of applications, such as dye loading for optical, photochemical, or electrochemical purposes. Commercially-available, carboxyl-group-terminated polystyrene spheres of different sizes were utilized as pore-size controllers in the bio-enabled syntheses of TiO₂ by protamine. This approach has been found to be an effective means of creating uniform pores in inorganic mineral oxide coatings. The accomplishments of this work have the potential to be integrated so as to expand the boundaries of biomineralization in materials science and engineering fields.

Plasma Polymerization is a novel technique for the preparation of polymer-like thin film coatings at low temperatures onto almost any type of substrates: plastic, metal, semiconductors, wood, textile fibers or membranes, to cite just a few. The films can be grown directly from liquid monomers that are introduced in the vapor phase into a vacuum chamber equipped with one or more electrodes that generate the plasma after a high voltage in continuous current mode (DC), low-frequency (AC) or high frequency (RF) is applied. The plasma state is a high-energy gas state in which the density of electrons, ions, excited species and radical fragments is abundant. The introduction of an organic monomer vapor into the plasma triggers the formation of molecular fragments capable of initiating multiple reactions: in the gas phase, recombination of radicals, oligomerization of high-weight molecules and aggregation into nanoscopic dust can occur, whereas adsorption and reaction onto any solid surface will result in the growth of highly adherent thin films. The structural, chemical and functional properties of these coatings are determined by the composition of the precursor gas mixture and the type of monomer, and also by several technological parameters that can be fine-tuned, such as the pressure, plasma power, frequency of change of electrode polarization, substrate location, flux of gas, etc... By controlling these technological parameters it is possible to modulate the value of the magnitudes that govern the physico-chemical mechanisms which are responsible for film growth: residence time of molecules, available energy per molecule, degree of monomer fragmentation, density and energy of ion bombardment on the substrates, and gas transport in the reactor, among others. Plasma polymerization allows to grow films from virtually any kind of organic molecule which can be evaporated at low temperatures (<80 °C) and introduced in the reactor at sufficient flow rates (> lsccm), even when that molecule would not be the characteristic repeating unit of any conventional polymer synthesized by other physical or chemical means. The technique is also applicable to other types of monomers (non-carbon based), such as organosilicon or organometallic molecules. The use of organosilicon monomers allows to obtain films with a wide spectrum of properties, from those frequently attributed to an elastomeric polymer such as silicone (polydimethylsiloxane, PDMS) to those associated to a hard inorganic material, such as glass (amorphous silicon dioxide, silica). Regardless of their apparently opposed nature, these two materials share an extremely similar chemical backbone based on silicon-oxygen chemical bonds. During the investigations conducted in our study, different organosilicon monomers have been employed for plasma polymerization: hexamethyldisiloxane (HMDSO), hexamethyldisilazane (HMDSN) and tetraethoxysilane (TEOS), but the only results presented within the scope of this Thesis are those obtained for ppHMDSO films. This is due to the fact that HMDSO is the only monomer allowing the growth of polymer-like films, inorganic-like films, intermediate stoichiometry films and even graded films with properties varying with depth in a single plasma process. With respect to power sources for plasma generation, most published works choose high frequency electrical power sources, such as radiofrequency (RF) or microwaves (MW), although plasma polymerization can also be carried on with direct-current high-voltage sources (HV-DC), from 500 V to 3000 V. In our investigations, these three types of sources have been employed, as can be found in our related publications, but again only results with the DC plasma source will be presented due to their simple design and use in industrial applications. A main objective of this Thesis is to establish its limitations, such as the limited film thickness attainable or the excessive heating of substrates, depending on the reactor configuration and the operating parameters. As a consequence, the scope of this Thesis covers two main objectives: first, the study of DC plasma polymerization of hexamethyldisiloxane (DC ppHMDSO) with and without addition of carrier gases in the precursor mixture, in order to obtain polymer-like or inorganic silica-like coatings with specific mechanical, optical and corrosion protective functional properties, for further application to solving some practical problems of industrial interest; secondly, the study of modifications produced by a different non-additive post-treatments in a polymer-like ppHMDSO film, in order to obtain a film with graded properties varying with depth.
La polimerització assistida per plasma és una tècnica novedosa per a la obtenció de recobriments polimèrics a baixa temperatura sobre qualsevol tipus de substrat: plàstic, metall, semiconductors, fusta, fibra tèxtil o membranes, per citar-ne només alguns. Els recobriments són obtinguts directament a partir de monòmers líquids que s'introdueixen controladament en fase vapor dins una cambra de buit equipada amb un o més elèctrodes que, en aplicació d'una tensió elèctrica constant (DC), alterna (AC) o d'alta freqüència (RF, MW), generen el plasma. Les propietats estructurals, químiques i funcionals d'aquests recobriments venen determinades per la composició de la mescla gasosa precursora i la naturalesa del monòmer, i per diferents paràmetres tecnològics controlables, com ara la pressió, la potència acoplada al plasma, la freqüència d'oscil•lació de la polarització, la posició dels substrats, el flux circulant de gas, etc. L'ús de monòmers orgànics de base silici permet obtenir propietats amb característiques molt amples, des de les més pròpies d'un polímer elastomèric com la silicona (polidimetilsiloxà, PDMS) a les d'un material inorgànic dur, com el vidre (òxid de silici amorf, Si02. Aquests dos materials comparteixen una base química extraordinàriament similar fonamentada en un esquelet d'enllaços Silici-Oxigen. Durant el treball de desenvolupament d'aquest estudi s'han emprat diferents monòmers de base silici: l'hexametildisiloxà (HMDSO), l'hexametildisilazana (HMDSN) i el tetraetoxisilà (TEOS), però només es presentaran els resultats obtinguts en els dipòsits de polimerització plasma del primer, HMDSO, degut a ser l'únic amb capacitat de generar recobriments de caire polimèric, inorgànic, intermedi o fins i tot amb propietats variables amb la profunditat en un únic recobriment. L’objectiu principal d’aquesta tesi és l’estudi de la polimerització assistida per plasma en corrent contínua de l’hexametildisiloxà (DC ppHMDSO) amb i sense addició de gasos portadors, per a l’obtenció de recobriments polimèrics o inorgànics de base silici amb especials propietats funcionals mecàniques, òptiques i protectores contra la corrosió, i l’aplicació pràctica d’aquests recobriments a la solució d’alguns problemes d’interès industrial. El segon objectiu és l’estudi de les modificacions de les capes de naturalesa polimèrica ja dipositades mitjançant un segon plasma o post-tractament sense contingut de monòmer per tal de modificar la superfície del recobriment i aconseguir un gradient en profunditat de les propietats del material.

Le contrôle de la microstructure et de la morphologie de surface est essentiel pour que les couches minces soient appliquées dans des dispositifs optiques et acoustiques. Des couches minces de TiO2, LaNiO3 et ZnO et leurs hétérostructures ont été obtenues par des techniques de pulvérisation cathodique à radio fréquence et de dépôt chimique en phase vapeur (CVD). L'optimisation des paramètres de dépôt, tels que la température, la pression totale de la chambre, la pression partielle d'O2 et la vitesse de croissance, a conduit à une amélioration de la qualité structurelle et fonctionnels des films minces et de leurs hétérostructures. L'orientation des couches minces épitaxiales de ZnO et TiO2 a été ajustée non seulement par le lien épitaxial avec divers substrats, mais également par les conditions de dépôt. La qualité optique des films de TiO2 a été principalement optimisée par l'élimination des défauts de microstructure et l'augmentation de la non-stoechiométrie en oxygène. Il a été démontré que les défauts ponctuels et microstructuraux dans les films polycristallins et épitaxiaux jouent un rôle clé dans les pertes de propagation optique. L'effet de la polarité du substrat sur les propriétés structurelles, optiques et acoustiques des films minces à base de ZnO a également été étudié. Les couches sacrificielles et / ou d'initiation de croissance ont été identifiées pour l'intégration hétérogène de films acoustiques et optiques fonctionnels sur substrats semi-conducteurs
The control of microstructure and surface morphology is essential for the thin films to be applied in optical and acoustic devices. Thin films of TiO2, LaNiO3 and ZnO and their heterostructures in this work were obtained by radio frequency (RF) magnetron sputtering and metalorganic chemical vapor deposition (MOCVD) techniques. The optimization of deposition parameters, such as temperature, total chamber pressure, O2 partial pressure and growth rate, led to high structural quality of functional thin films and their heterostructures. The orientation of epitaxial ZnO and TiO2 thin films was tuned not only through lattice matching with various substrates, but as well through deposition conditions. The optical quality of TiO2 films was mostly optimized through elimination of microstructural defects and increasing oxygen non-stoichiometry. It was shown that microstructural and lattice defects in polycrystalline and epitaxial films played a key role in optical propagation losses. Effect of substrate polarity on the structural, optical and acoustic properties of ZnO-based thin films was studied, as well. The sacrificial and/or seed layers were identified for heterogeneous intégration of functional acoustical and optical films with semiconductor substrates

This thesis is concerned with the deposition of titanium dioxide thin films using chemical vapour deposition (CVD). The work emphasises the influence of deposition parameters on the properties of the resultant film. The materials have been designed with a wide range of potential applications in mind, from air and water purification to energy production and medical implant devices. Where possible, tests have been conducted to assess the efficacy of the material for these applications. The first chapter highlights a number of technologically important applications of titanium dioxide in order to demonstrate the motivation for research in this area. Some theoretical concepts are presented which are fundamental to understanding the behaviour of titanium dioxide. The principles behind chemical vapour deposition and the photocatalytic tests used in this work are discussed. The second chapter focusses on the use of three different metal substrates in TiO2 CVD. Firstly, the phase of TiO2 deposited on steel substrates was investigated. It was shown that the grade of steel had little influence with predominantly anatase films being formed in the vast majority of areas analysed. Since each grade of steel has different mechanical properties and is used in different applications, this work demonstrates that the photocatalytic properties of anatase films can be endowed to a large range of products. Secondly, TiO2 was shown to be adherent to a flexible substrate, namely aluminium foil. It was demonstrated from XPS analysis that aluminium ions did not diffuse into the TiO2, which remained photocatalytically active. A photocatalyst on a lightweight, flexible substrate offers several advantages over glass which has been the most frequently employed substrate to date. Thirdly, titanium dioxide was coated onto an alloy of cobalt, chromium and molybdenum, CoCrMo. The alloy is of interest for biomedical implants but suffers from poor biocompatability. By coating its surface with TiO2, it was shown to enhance osteogenic differentiation. Chapter three investigates nitrogen doped titanium dioxide for its potential as a visible light photocatalyst. A novel synthetic strategy was employed in which the amount of oxygen precursor was varied to determine if this would affect the position of the nitrogen in the titanium dioxide crystal structure. Differences were observed in the nitrogen XPS signal, the absorption profile, surface morphology and photocatalytic activity under both UV and visible irradiation. Visible light activity was observed for a sample made with lower amounts of oxygen precursor under UV and visible light. Finally, brookite, a rare, metastable form of titanium dioxide, was formed by atmospheric pressure chemical vapour deposition, APCVD. A brief literature review discusses the potential applications and some of the previously employed synthetic routes to brookite formation. Three sets of conditions are reported for the first known synthesis of brookite by atmospheric pressure chemical vapour deposition. A possible mechanism for brookite formation is hypothesised. This work concludes with a summary of the key findings from the experimental work and possible avenues for further research.

It has been hypothesized that increasing the number of active sites on a cochlear implant electrode array will enable the recipient to distinguish a higher number of pitch precepts, thus creating a more natural sound. While DSP processing strategies for cochlear implants have evolved significantly to address this, technology for the actual electrode array has remained relatively constant and limits the number of physical electrodes possible. Previous work introduced the concept of using Thin-Film Array (TFA) technology to allow for much higher site densities, although the original devices proved unreliable during surgical insertion tests. This work presents a new method of combining polyimide-based TFA's with supporting silicone insertion platforms to create assembled electrode arrays that are a more viable option for surgical insertion. The electrical and mechanical properties of these assemblies are investigated with physical deformation tests and finite element analysis in COMSOL to quantify how they will perform upon insertion into the cochlea, and the preliminary results of a surgical insertion study into human cadaveric temporal bones will be discussed.

Fe-chalcogenides are of great interest because they have the simplest structure in the Fe-based superconductors, and show low anisotropies, high critical fields and high current densities all of which make these compounds useful for understanding Fe-based superconductors, a new class of superconductors with unusual properties, both for fundamental physics and potential high-field applications. The main part of this thesis concentrates on the fabrication and characterization of FeySe1-xTex (Fe-11) thin films in order to link superconductivity and microstructure in this system. Since sputtering has been rarely used for the deposition of Fe(Se,Te) films, we used sputtering to study the feasibility of this technique for this purpose and to optimize the processing conditions. Phase evolution and texture development as a function of processing conditions are studied, and the optimum conditions for the best quality film are found. Crystallization temperature of the 11-phase was found to be 250°C, and texture is shown to be dependent on substrate, substrate temperature and film thickness which strongly control in-plane alignment. The best texture is obtained at 315°C for films thinner than 50nm on the MgO. Texture of the films becomes poorer on the substrates in the order MgO > LAO > STO > CaF2 > LiF > LSAT, and the relationship between texture and substrate is shown to be more related to the growth mechanism rather than lattice misfit. 2D layer-by-layer growth is found for the LSAT, while the films on the LAO and MgO show 3D island growth, and a combination of both growths is found for the film on the STO. The films grown by in-situ sputtering are shown to have better quality than those grown by the ex-situ. A sharp TC of about 10.2K is obtained for a single crystal Fe1.01Se0.56Te0.44.film with a thickness of 58nm. Most of the deposited films are Fe-rich (y > 1) due to compositional variation in the target and the volatility of Se and Te. Extra Fe is the main detrimental parameter for the suppression of superconductivity in these films showing the necessity of using multiple sources in sputtering. Nano-scale inhomogeneities are also observed in the majority of the films possibly as a result of different Se/Te ratios and Fe3O4 impurity. Substitution of 2% Mn for Fe in the FeySe1-xTex structure leads to the stabilization of tetragonal 11 phase and improvement of crystallographic texture. Mn atoms are shown to occupy interstitial Fe sites in the tetragonal unit cell. I also applied TEM technique to functional materials from external collaborators including Bi2Te3 and CaFe2As2. Studies of Mn-doped Bi2Te3 single crystals reveal that at doping concentrations, Mn incorporates with the Bi2Te3 structure differently. At low doping concentrations (9%Mn), Mn atoms are randomly substituted onto the Bi sites resulting in the variation in both composition and lattice parameter. At high doping concentrations (15%Mn), supersaturation occurs and the extra Mn atoms occupy the interstitial sites in addition to forming nano-scale Mn-rich precipitates. CaFe2As2 single crystals grown by the FeAs-flux method are unstable FeAs-supersaturated crystals containing a high concentration of stacking faults. Annealing at high temperature (700°C) causes the extra FeAs to form needle-shaped precipitates perpendicular to the c-axis by Ca diffusion, and the matrix develops dislocations. Annealing at lower temperature (400°C) results in a number of stacking faults and similar precipitates with low Ca. As a result, the microstructure of the CaFe2As2 single crystals, especially the amount of strain, can be controlled by the annealing temperature resulting in similar effects to applying external pressure.

We try to explain the mathematical theory of thin liquid film evolution. We start with introducing physical processes in which thin film evolution plays an important role. Derivation of the classical thin film equation and existing mathematical theory in the literature are also introduced. To explain the thin film evolution we derive a new family of degenerate parabolic equations. We prove results on existence, uniqueness, long time behavior, regularity and support properties of solutions for this equation. At the end of the thesis we consider the classical thin film Cauchy problem on the whole real line for which we use asymptotic equipartition to show H^1(R) convergence of solutions to the unique self-similar solution.

This study is focused on the fabrication of plasma polymerized ultrathin films and the elucidation of their unique properties with an emphasis on the solvent-less, dry polymerization process to introduce post-deposition functionality, robustness, and shape preservation. Two major classes of materials are the subject of this study: biological monomers, specifically the amino acids tyrosine and histidine and synthetic organic and inorganic monomers including acrylonitrile, 2-hydroxyethyl methacrylate, N-isopropylacrylamide, titanium isopropoxide and ferrocene. The unique chemical and physical properties of highly cross-linked ultrathin plasma polymerized amino acid and synthetic polymer films are demonstrated along with their functional response and robustness on both planar and complex surface structures. The work emphasizes the facile ability of plasma polymerization to create unique, tailored ultrathin coatings. Chemical functionality retention (OH, NH₂) of the tyrosine and histidine amino acids is demonstrated by the subsequent mineralization of gold or titania nanoparticles on the plasma polymerized ultrathin films using a wet chemical approach. Inorganic nanoparticle mineralization is further investigated as a method to modify the optical properties of composite nanocoatings. Plasma co-polymerization of tyrosine and synthetic monomers is used to create nanocomposite coatings with unique surface functionalities, responsive behavior, optical characteristics and a high level of integration between monomers. The fabrication of novel plasma polymerized Janus microspheres, micropatterned substrates and free-standing films also demonstrate numerous plasma polymerized materials which exhibit unique structural properties. Overall, facile plasma polymerization of novel, functional ultrathin films and complex topological coatings having potential biocompatible and optical applications is established.

The scope of this work is to fathom different possibilities to create functional coatings with polymer brushes. The immobilization of nanoparticles and enzymes is investigated, as well as the affection of their properties by the stimuli-responsiveness of the brushes. Another aspect is the coating of 3D-nanostructures by polymer brushes and the investigation of the resulting functional properties of the hybrid material. The polymer brush coatings are characterized by a variety of microscopic and spectroscopic techniques, with a special emphasis on the establishment of the combinatorial quartz crystal microbalance/spectroscopic ellipsometry technique as a tool to characterize the functional properties of the polymer brush systems insitu. The pH-responsive swelling of the polyelectrolyte brushes poly(acrylic acid) and poly(2-vinylpyridine), as well as the thermoresponsive swelling of poly(N-isopropylacryl amide) is studied in detail by this technique. Poly(2-vinylpyridine) and binary poly(N-isopropylacryl amide)-poly (2-vinylpyridine) brushes are used as templates for the insitu-synthesis of palladium and platinum nanoparticles with catalytic activity. As an example for the use of polymer brushes to immobilize enzymes, the model enzyme glucose oxidase is physically adsorbed to poly (2-vinylpyridine) and poly (acrylic acid) brushes and also covalently bound to poly (acrylic acid) brushes. In the last part of this thesis, sculptured thin films are coated with poly (acrylic acid) and poly (N-isopropylacryl amide) brushes and the swelling characteristics as well as the adsorption behavior of the model protein bovine serum albumin are investigated.

For decades, Metallic Glass, with its isotropic featureless structure while exhibiting outstanding mechanical properties was possible only at a high rate of quenching and with at least one dimension in the submicron regime.  This limitation was overcome with the discovery of Bulk Metallic glasses, BMGs, containing three or more elements following the additional two empirical rules of optimum geometric size differences and negative energy of mixing among the constituent elements. Since then thousands of Fe-, Ni-, Al-, Mg-, Ti- based BMGs have been discovered and comprehensively investigated mainly by groups in Japan and USA. Yet the discovery of new combinations of elements for BMGs is alchemy. We do not know with certainty which element when added will make possible a transition from being a ribbon to a bulk rod.    In this thesis we report a discovery of castable BMGs rods on substitution of Fe by nickel in an alloy of FeBNb which could otherwise have been only melt-spun into ribbons.  For example, we find that substitution of just 6 at.% of Fe raises the glass forming range, GFA, to as much as ∆Tx =40K while the other parameters for GFA like Trg, γ, and δ reach enhanced values 0.57, 0.38, and 1.40 respectively.  Furthermore, the electrical conductivity is found to increase by almost a factor of two.  Magnetically it becomes softer with coercivity 260mOe which further reduces to much lower values on stress relaxation.  Ni does not seem to carry a magnetic moment while it enhances the magnetic transition temperature linearly with Ni concentration. We have investigated the role of Ni in another more stable BMGs based FeBNbY system in which case ∆Tx becomes as large as 94K with comparable enhancement in the other GFA parameters. Due to the exceptional soft magnetic properties, Fe-based bulk metallic glasses are considered potential candidate for their use in energy transferring devices. Thus the effect of Ni substitution on bulk forming ability, magnetic and electrical transport properties have been studied for FeBNb and FeBNbY alloy systems. The role of Ni in these systems is densification of the atomic structure and its consequence. We have exploited the superior mechanical properties of BMGs by fabricating structures that are thin and sustainable.  We have therefore investigated studies on the thin films of these materials retaining their excellent mechanical properties. Magnetic properties of FeBNb alloy were investigated in thin films form (~200-400nm) in the temperature range of 5-300K. These Pulsed Laser deposited amorphous films exhibit soft magnetism at room temperature, a characteristic of amorphous metals, while they reveal a shift in hysteresis loop (exchange anisotropy, HEB=18-25Oe), at liquid helium temperature. When thickness of films is reduced to few nanometers (~8-11nm), they exhibit high transparency (>60%) in optical spectrum and show appreciably high saturation Faraday rotation (12o/μm, λ= 611nm). Thin films (~200-400nm) of Ni substituted alloy (FeNiBNb) reveal spontaneous perpendicular magnetization at room temperature. Spin-reorientation transition was observed as a function of film thickness (25-400nm) and temperature (200-300K), and correlated to the order/disorder of ferromagnetic amorphous matrix as a function of temperature. These two phase films exhibits increased value of coercivity, magnetic hardening, below 25K and attributed to the spin glass state of the system.    Using the bulk and thin films we have developed prototypes of sensors, current meters and such simple devices although not discussed in this Thesis.                                         Ti-based bulk metallic glasses have been attracting significant attention due to their lower density and high specific strength from structural application point of view. High mechanical strength, lower values of young’s modulus, high yield strength along with excellent chemical behaviors of toxic free (Ni, Al, Be) Ti-based glassy metals make them attractive for biomedical applications. In the present work, toxic free Ti-Zr-Cu-Pd-Sn alloys were studied to optimize their bulk forming ability and we successfully developed glassy rods of at least 14mm diameter by Cu-mold casting. Along with high glass forming ability, as-casted BMGs exhibit excellent plasticity. One of the studied alloy (Ti41.5Zr10Cu35Pd11Sn2.5) exhibits distinct plasticity under uniaxial compression tests (12.63%) with strain hardening before failure which is not commonly seen in monolithic bulk metallic glasses.

QC 20120906

Hero-m

Ink-jet printing offers an ideal answer to the emerging trends and demands of depositing at ambient temperatures picoliter droplets of oxide solutions into functional thin films and device components with a high degree of pixel precision. It is a direct single-step mask-free patterning technique that enables multi-layer and 3D patterning. This method is fast, simple, easily scalable, precise, inexpensive and cost effective compared to any of other methods available for the realization of the promise of flexible, and/or stretchable electronics of the future on virtually any type of substrate. Because low temperatures are used and no aggressive chemicals are required for ink preparation, ink-jet technique is compatible with a very broad range of functional materials like polymers, proteins and even live cells, which can be used to fabricate inorganic/organic/bio hybrids, bio-sensors and lab-on-chip architectures. After a discussion of the essentials of ink-jet technology, this thesis focuses particularly on the art of designing long term stable inks for fabricating thin films and devices especially oxide functional components for electronics, solar energy conversion, opto-electronics and spintronics. We have investigated three classes of inks: nanoparticle suspension based, surface modified nanoparticles based, and direct precursor solution based. Examples of the films produced using these inks and their functional properties are: 1) In order to obtain magnetite nanoparticles with high magnetic moment and narrow size distribution in suspensions for medical diagnostics, we have developed a rapid mixing technique and produced nanoparticles with moments close to theoretical values (APL 2011 and Nanotechnology 2012). The suspensions produced have been tailored to be stable over a long period of time. 2)In order to design photonic band gaps, suspensions of spherical SiO2 particles were produced by chemical hydrolysis (JAP 2010 and JNP 2011 - not discussed in the thesis). 3) Using suspension inks, (ZnO)1-x(TiO2)x composite films have been printed and used to fabricate dye sensitized solar cells (JMR 2012). The thickness and the composition of the films can be easily tailored in the inkjet printing process. Consequently, the solar cell performance is optimized. We find that adding Ag nanoparticles improves the ‘metal-bridge’ between the TiO2 grains while maintaining the desired porous structure in the films. The photoluminescence spectra show that adding Ag reduces the emission intensity by a factor of two. This indicates that Ag atoms act as traps to capture electrons and inhibit recombination of electron-hole pairs, which is desirable for photo-voltaic applications. 4) To obtain and study room temperature contamination free ferromagnetic spintronic materials, defect induced and Fe doped MgO and ZnO were synthesized ‘in-situ’ by precursor solution technique (preprints). It is found that the origin of magnetism in these materials (APL 2012 and MRS 2012) is intrinsic and probably due to charge transfer hole doping. 5) ITO thin films were fabricated via inkjet printing directly from liquid precursors. The films are highly transparent (transparency >90% both in the visible and IR range, which is rather unique as compared to any other film growth technique) and conductive (resistivity can be ~0.03 Ω•cm). The films have nano-porous structure, which is an added bonus from ink jetting that makes such films applicable for a broad range of applications. One example is in implantable biomedical components and lab-on-chip architectures where high transparency of the well conductive ITO electrodes makes them easily compatible with the use of quantum dots and fluorescent dyes. In summary, the inkjet patterning technique is incredibly versatile and applicable for a multitude of metal and oxide deposition and patterning. Especially in the case of using acetate solutions as inks (a method demonstrated for the first time by our group), the oxide films can be prepared ‘in-situ’ by direct patterning on the substrate without any prior synthesis stages, and the fabricated films are stoichiometric, uniform and smooth. This technique will most certainly continue to be a versatile tool in industrial manufacturing processes for material deposition in the future, as well as a unique fabrication tool for tailorable functional components and devices.

QC 20120907

Els òxids basats en manganites de lantà formen una extensa família de compostos derivats del LaMnO3: una perovskita de la forma general ABO3. Les propietats físiques d’aquesta es poden modi car substancialment per substitució catiònica. En aquesta tesi estudiem dos compostos obtinguts per substitució dels cations A i B. D’una banda, el La2Co0.8Mn1.2O6 (LCMO), obtingut per substitució del Mn per Co (catió B), que conforma una estructura doble perovkita amb propietats aïllants i ferromagnètiques. D’altra banda, el La0.7Sr0.3MnO3 (LSMO) format per substitució parcial de La per Sr (catió A) i que resulta en un material metàl.lic i ferromagnètic. El desenvolupament de tècniques de creixement de materials òxids en forma de capes primes els dóna un gran potencial per ser integrats en la tecnologia de semiconductors i per dissenyar dispositius micro i nanomètrics per a aplicacions en spintrònica i memòries no-volàtils. Actualment hi ha gran interès en l’estudi de capes primes de perovskites dobles amb propietats ferromagnètiques i aïllants, ja que tenen una temperatura de transició relativament alta i són fàcils d’integrar sobre altres òxids. La implementació d’aïllants ferromagnètics com a substituts dels dispositius ferromagnètics basats en metalls pot conduir a una e ciència de commutació molt més gran i un transport de corrent menys dissipatiu. Assolir capes ultra primes d’aquests materials permetria obtenir una barrera túnel activa que selecciona l’espín, per tant actua com a ltre d’aquest. Així, l’objectiu principal de la primera part d’aquesta tesi és comprendre les propietats físiques del LCMO i obrir una via per futures aplicacions potencials. En primer lloc, es presenta un estudi detallat del creixement i la caracterització estructural i magnètica de capes primes de LCMO. Demostrem que podem obtenir capes d’alta qualitat, amb temperatures de transició de ns a 230 K i amb un bon ordre catiònic tot i petites desviacions de l’estequiometria. A continuació, analitzem els efectes d’anisotropia magnètica centrats en els aspectes següents: 1) l’estudi de l’aparició d’una forta anisotropia magnètica perpendicular (PMA) amb un alt camp coercitiu i d’anisotropia, i 2) la relació del signe i la força de l’anisotropia magnètica amb els desajustos estructurals amb el substrat. En particular, la PMA apareix en el cas que la tensió sigui expansiva mentre que la tensió compressiva produeix un eix fàcil d’imantació dins el pla. Per trobar una explicació a l’origen de l’anisotropia magnètica desenvolupem un model atòmic simple basat en càlculs de primer ordre de teoria de pertorbacions. A més, relacionem les prediccions extretes amb experiments de dicroisme magnètic circular de raigs X (XMCD tot demostrant que l’anisotropia magnètica en l’LCMO té un origen magnetocristal.lí a causa del fort acoblament d’espín-òrbita del Co2+. Amb l’objectiu d’integrar les propietats aïllants ferromagnètiques i la PMA en un dispositiu, hem fabricat unions túnel utilitzant el LCMO com a barrera magnèticament activa i hem explorat les seves funcionalitats d’espín. Hem trobat que el dispositiu proporciona una alta e ciència de ltratge d’espín (gairebé el 100% de polarització) i funcionalitats de sensor i memòria anisotròpica. És a dir, que la forta PMA induïa per la tensió epitaxial provoca una gran diferència entre les corbes de magnetoresistència mesurades amb el camp magnètic aplicat perpendicular o parallelament; aquesta és l’anomenada magnetoresistència túnel anisotròpica (TAMR). S’han trobat valors de TAMR de 20-30%. Finalment, s’ha provat que el dispositiu pot funcionar com una memòria magnètica ja que podem detectar dos estat no volàtils de resistència ben diferenciats que s’escriuen canviant la direcció del camp magnètic aplicat. En la darrera part de la tesi, s’han presentat resultats basats en l’altre sistema de manganita, el LSMO. Mostrem que les inestabilitats del creixement poden conduir a la formació de superfícies de doble terminació. Allunyar-se del comportament ideal de creixement constitueix una forma d’obtenir nanoestructures formades espontàniament amb propietats funcionals locals en superfícies. Les propietats de transport i la composició d’aquestes superfícies s’analitzen utilitzant tècniques de sonda d’escaneig i microscopia electrònica de fotoemissió amb resolució lateral. Aquestes tècniques sensibles a la superfície són adequades per caracteritzar les propietats a la nanoescala d’aquest tipus de sistemes.
Lanthanum manganite-based oxides conform an extensive family of compounds deriving from LaMnO3: a perovskite with general formula ABO3. Its physical properties can be drastically modified by cation substitution. In this thesis we explore two compounds obtained by A-site and B-site substitutions. On the one hand, La2Co0.8Mn1.2O6 (LCMO), obtained by substitution of Mn by Co (B-site substitution), leads to a double perovskite structure with ferromagnetic insulating properties. On the other side, the La0.7Sr0.3MnO3 (LSMO) compound resulting from the partial substitution of La by Sr (A-site substitution) turns the material into a ferromagnetic half-metal. The development of techniques for the growth of oxide materials in the form of thin films ease their integration in semiconductors technology and enable the design of micro and nanoscale devices with potential in spintronics and non-volatile memory applications. Nowadays, there is an increasing interest in the study of double perovskite thin films combining ferromagnetic and insulating properties due to their relatively high transition temperature and their integration on top of other perovskite oxides. The implementation of ferromagnetic insulators (FM-I) as substitutes of ferromagnetic metal-based devices can lead to much higher switching eficiency and less dissipative current transport. For instance, ultrathin films of (FM-I) might be used as spin-selective active tunneling barriers acting as spin-filters. Therefore, the main objective of the first part of this thesis has been to give a comprehensive understanding of LCMO physical properties and propose a guide to potential applications. Firstly, we present a detailed study of the growth of the LCMO films as well as their structural and magnetic characterization. We demonstrate that we can obtain high quality thin films, with transition temperatures up to 230 K and with good cationic order despite a certain degree of off-stoichiometry. Then, we analyze magnetic anisotropy effects, focusing on the following aspects: i) the study of the appearance of strong perpendicular magnetic anisotropy (PMA) with large coercive and anisotropy fields, and ii) the relation of magnetic anisotropy strength and sign with lattice mismatches. In particular, we show that PMA appears for the tensile strain case while compressive strain produces in-plane easy axis. We also give a more detailed understanding of the origin of magnetic anisotropy using a simple atomistic model based on first-order perturbation theory calculations.We relate our predictions with X-ray magnetic circular dichroism (XMCD) experiments and evidence that magnetic anisotropy in LCMO has a magnetocrystalline origin due to the strong spin-orbit coupling of Co2+ ions. With the aim of integrating ferromagnetic insulating properties and PMA in a device, we have fabricated tunnel junctions using LCMO as a magnetically active barrier and have explored its spin-derived functionalities. We have found that the device provides high spin-filtering effciency (of almost 100% of spin-polarization) as well as anisotropic sensing and memory functionalities. This is, the strong straininduced PMA provokes a large difference between magnetoresistance curves measured with the magnetic field applied in the perpendicular or parallel directions, this phenomenon is the so called tunneling anisotropic magnetoresistance (TAMR). TAMR values as high as 20-30% have been found. Finally, we have proven that the device can be used as a magnetic memory as we can detect the existence of two nonvolatile resistive state that switches depending on the direction of the magnetic field used to write it. The last part of thesis presents results focused on the A-substituted manganite, LSMO, thin films. We show that growth instabilities can lead to the formation of double-terminated surfaces. Indeed, deviations from the ideal growth behaviour constitute a way to obtain spontaneously formed nanostructures with modulated local functional properties at the surface. The transport properties and the composition of these films have been analyzed by making use of scanning probe techniques and space-resolved photoemission electron microscopy, which are surface-sensitive techniques suitable to characterize properties at the nanoscale of this type of systems.

Els òxids amb estructura perovskita són molt interessants causa del seu ampli rang de possibles en aplicacions en espintrònica, dispositius magneto-òptics o catàlisi. La majoria d'aquestes aplicacions requereixen de la utilització de capes primes o heteroestructures. Les propietats electròniques de les perovskita estan determinades per les propietats físiques associades amb els metalls de transició i amb els anions oxigen dels vèrtexs dels octahedres BO6. Les tècniques de creixement a partir de dissolucions químiques són molt prometedores per a la consecució de capes epitaxials d'òxids, degut al seu elevat rendiment, fàcil escalat, baix cost i al fet que poden ser més respectuoses amb el medi ambient. Primerament, presentem els conceptes bàsics relatives als òxids metàl·lics tipus perovskita, incloent la seva estructura i propietats magnètiques, i els mètodes utilitzats en general per al seu creixement. Seguidament presentem els detalls del mètode de creixement per deposició assistida per polímers (DAP), i les tècniques de caracterització de les propietats estructurals i físiques de les capes crescudes. La tercera part consisteix en la compilació dels articles ja publicats sobre capes epitaxials de La0.92MnO3, La2CoMnO6 i La2NiMnO6 crescudes per DAP. El comportament tèrmic de les solucions precursores s'ha analitzat per mitjà de mesures combinades d'anàlisi termogravimètrica i calorimetria diferencial. La propietats estructurals es van analitzar a partir de la difracció de raigs-x. El gruix de les capes es estajo a partir de mesures de reflectivitat de raigs-x. La microscòpia de forces atòmiques va servir per estudiar la rugositat de les capes. Les propietats magnètiques estàtiques es van estudiar utilitzant un magnetòmetre SQUID. Mesures de microscòpia electrònica de rastreig combinades espectrocopia de pèrdua d'energia d'electrons van confirmar l'ordenament catiònic Co / Mn en capes de La2CoMnO6, i mesures amb radiació de sincrotró (sincrotró ALBA) es van utilitzar per determinar el grau de desordre en capes de La2NiMnO6. Les propietats de dinàmica de magnetisme en capes de La0.92MnO3 i en bicapes de La0.92MnO3/Pt en funció de la temperatura, van ser estudiades per mesures de ressonància ferromagnètica. Els resultats mostren que les condicions de creixement pròpies de de la DAP (condicions de creixement lentes i pròximes a l'equilibri termodinàmic) promouen la formació de capes d'alta qualitat amb una elevada cristal·linitat, a el mateix temps que afavoreixen l'ordenament catiònic. D'aquesta manera, s'han obtingut capes de La2CoMnO6 completament ordenades, i capes de La2NiMnO6 amb un ordre proper al 80%. D'altra banda, les mesures de ressonància ferromagnètica en capes de La0.92MnO3 i en bicapes de La0.92MnO3 / Pt, indiquen un clar augment de l'eixamplament ferromagnètic a les bicapes, la qual cosa indica una transferència de el moment d'espín de la capa d'La0 .92MnO3 a la cap de Pt per bombament d'espines. Aquest fet demostra que la tècnica DAP permet l'obtenció de capes d'òxids complexos d'una qualitat microestuctural elevada i adequades per a aplicacions en espintrònica. Els resultats obtinguts demostren que la DAP és competitiva comparada amb els mètodes físics de creixement de capes, i permet obtenir capes epitaxials d'òxids complexos de gran qualitat. En particular, les condicions de creixement pròpies de la DAP són propícies a facilitar l'ordenament catiònic en CAAPS d'òxids amb estructura doble perovskita.
Los óxidos con estructura perovskita son muy interesantes debido a su amplio rango de posibles aplicaciones en espintrónica, dispositivos magneto-ópticos o catálisis. La mayoría de estas aplicaciones requieren de la utilización de capas delgadas o heterostructuras. Las propiedades electrónicas de las perovskitas están determinadas por las propiedades físicas asociadas con los metales de transición y con los aniones oxígeno de los vértices de los octaehdros BO6. Las técnicas de crecimiento a partir de disoluciones químicas son muy prometedoras para la consecución de capas epitaxiales de óxidos, debido a su elevado rendimiento, fácil escalado, bajo coste y a que pueden ser más respetuosas con el medio ambiente. En esta Tesis, se ha utilizado la deposición asistida por polímeros (DAP), utilizando disoluciones acuosas para preparar capas de compuestos derivados de las manganitas de lantano, como son La0.92MnO3, La0.7Sr0.3MnO3, La2CoMnO6 y La2NiMnO6 sobre substratos de SrTiO3 y LaAlO3. El La0.92MnO3 y el La0.7Sr0.3MnO3 son ferromagnéticos y metálicos a bajas temperaturas, mientras que el La2CoMnO6 y el La2NiMnO6 son ferromagnéticos y aislantes. Todos estos compuestos poseen una temperatura de Curie cercana a temperatura ambiente. Primeramente, presentamos los conceptos básicos relativas a los óxidos metálicos tipo perovskita, incluyendo su estructura y propiedades magnéticas, y los métodos utilizados en general para su crecimiento. Seguidamente presentamos los detalles del método de crecimiento por DAP, y las técnicas de caracterización de las propiedades estructurales y físicas de las capas crecidas. La tercera parte consiste en la compilación de los artículos ya publicados sobre capas epitaxiales de La0.92MnO3, La2CoMnO6 y La2NiMnO6 crecidas por DAP. El comportamiento térmico de las soluciones precursoras se ha analizado por medio de medidas combinadas de análisis termogravimétrico y calorimetría diferencial. La propiedades estructurales se analizaron a partir de la difracción de rayos-x. El espesor de las capas se estajo a partir de medidas de reflectividad de rayos-x. La microscopia de fuerzas atómicas sirvió para estudiar la rugosidad de las capas. Las propiedades magnéticas estáticas se estudiaron utilizando un magnetómetro SQUID. Medidas de microscopia electrónica de rastreo combinadas espectrocopía de pérdida de energía de electrones confirmaron el ordenamiento catiónico Co/Mn en capas de La2CoMnO6, y medidas con radiación de sincrotrón (ALBA) se utilizaron para determinar el grado de desorden en capas de La2NiMnO6. Las propiedades de dinámica de magnetismo en capas de La0.92MnO3 y en bicapas de La0.92MnO3/Pt en función de la temperatura, fueron estudiadas por medidas de resonancia ferromagnética. Los resultados muestran que las condiciones de crecimiento propias de la DAP (condiciones de crecimiento lentas y próximas al equilibrio termodinámico) promueven la formación de capas de alta calidad con una elevada cristalinidad, al mismo tiempo que favorecen el ordenamiento catiónico. De esta forma, se han obtenido capas de La2CoMnO6 completamente ordenadas, y capas de La2NiMnO6 ordeadas 80%. Por otra parte, las medidas de resonancia ferromagnética en capas de La0.92MnO3 y en bicapas de La0.92MnO3/Pt, indican un claro aumento del ensanchamiento ferromagnético en las bicapas, lo cual indica una trasferencia del momento de espín de la capa de La0.92MnO3 a la cap de Pt por bombeo de espines. Este hecho demuestra que la técnica DAP permite la obtención de capas de óxidos complejos de una calidad microestuctural elevada y adecuadas para aplicaciones espintrónicas. Los resultados obtenidos demuestran que la DAP es competitiva comparada con los métodos físicos de crecimiento de capas, y permite obtener capas epitaxiales de óxidos complejos de gran calidad. En particular, las condiciones de crecimiento propias de la DAP son propicias a facilitar el ordenamiento catiónico en capas de óxidos con estructura doble perovskita.
Perovskites oxides are of strong interest due the huge potential range of applications they offer with a particularly simple structure, such as spintronics, magneto-optic devices, or catalysis, and most of these applications require the use of thin films and heterostructures. Most of the electronic properties of perovskites are determined by the physics associated with the transition metal and the corner-sharing oxygen anions of the BO6 octahedra therefore, in double perovskite structures, the ordered arrangement of cations in the B-site position is of major relevance. Chemical solution deposition (CSD) techniques are promising methodologies to achieve epitaxial oxide thin films combining high performance with high easy scalability, environment friendly fabrication and low cost. In this thesis, the polymer-assisted deposition (PAD), an aqueous CSD method, is used to prepare derivatives of lanthanum manganite perovskite films, including La0.92MnO3, La0.7Sr0.3MnO3, La2CoMnO6 and La2NiMnO6 films on SrTiO3 and LaAlO3 substrates. La0.92MnO3 and La0.7Sr0.3MnO3 display ferromagnetic metallic conducting properties, La2CoMnO6 and La2NiMnO6 are ferromagnetic insulating. All these films have Curie temperatures near room temperature. Firstly, we introduced the basic concepts related to perovskite oxides, including the structure and the magnetic properties, and the methods to grow oxide thin films. Secondly, more detailed processes of PAD method and characterizations will be presented. The third part is a compilation of articles of the La0.92MnO3, La2CoMnO6 and La2NiMnO6 films. All the films were prepared by PAD method. The thermal behavior of the mixed metal polymer precursor solution was traced by combining differential scanning calorimetry and thermogravimetric analysis. The structural features were studied by X-ray diffraction. The thickness was measured with X-ray reflectivity. The surface topography of the films was measured by AFM. Static magnetic properties were measured using a SQUID magnetometer. The scanning transmission electron microscopy (STEM) measurements together with electron energy loss spectroscopy (EELS) was used to confirm the full Co/Mn cationic ordering in La2CoMnO6 films, and ALBA synchrotron radiation facilities were used to investigate the disordering in La2NiMnO6 films. The dynamic magnetic properties of La0.92MnO3 thin films and La0.92MnO3/Pt bilayers as a function of temperature were studied by using a ferromagnetic resonance spectrometer. The results show that the particular crystallization and growth process conditions of PAD (very slow rate, close to thermodynamic equilibrium conditions) promote high crystallinity and quality of the films, as well as favors spontaneous B-site cationic ordering, almost full B-site cationic ordering can be achieved in La2CoMnO6 while the ordering factor in La2NiMnO6 films is around 80%. The La2CoMnO6 and La2NiMnO6 samples prepared by rapid thermal annealing (RTA) have similar magnetic properties to the counterpart films prepared by using conventional annealing processes, showing only slight differences in the microstructure. On the other hand, ferromagnetic resonance (FMR) measurements in La0.92MnO3 films and La0.92MnO3/Pt bilayers indicate a clear increase of the magnetic damping in the later, which may be indicative of the transfer of spin momentum from La0.92MnO3 to the Pt layer by spin pumping. This fact demonstrates that PAD technique allows obtaining complex oxide thin films of high microstructural quality suitable for spintronics applications. Our results make evident the CSD-PAD method can be competitive with physical methods allowing obtaining complex oxide epitaxial thin films of high quality. In particular, the growth conditions of PAD are prone to promote spontaneous B-site cationic ordering in double perovskite oxide.

Titanium dioxide (TiO2) is the leading material for self-cleaning applications due to its chemical inertness, mechanical robustness, durability to extended photocatalytic cycling, low cost and high photocatalytic activity. There has been a concerted effort to try and improve the material’s functional properties through impurity doping; altering the band structure and electronic transport properties. However, any improvements are difficult to optimise using traditional methods. Thin-film combinatorial methods have heralded the discovery of more than 20 new families of materials since their resurgence in the mid-90’s. Such methods enable a high diversity of states to be produced in a single deposition and are now being used more prominently to optimise the functional properties of existing materials. Atmospheric pressure chemical vapour deposition (APCVD) has been applied in a combinatorial fashion to deposit thin-films containing compositional gradients and is also the native method in which thin-films of TiO2 are mass-produced. Utilising combinatorial APCVD, we investigated N, Nb and W doped TiO2 thin-film systems. The Ndoped TiO2 system has been studied most prominently for improved visible light photocatalysis. Nitrogen can either substitute oxygen sites (substitutional doping - Ns) or enter within the TiO2 framework (interstitial doping - Ni), yet there is little consensus on which type of doping or dopant concentration yields the more active photocatalyst. Using the combinatorial APCVD approach, TiCl4 and ethyl acetate precursors were used to form the host TiO2 matrix with either NH3 or t-butylamine used as the N-sources. From three separate investigations we were able to produce combinatorial films with transitional composition/ phase gradients of (i) Ns/ Ni-doped to pure Ni-doped anatase TiO2 (0 ≤ Ns: Ti ≤ 8.4 %, 0.57 ≤ Ni: Ti ≤ 3.3 %), (ii) Ns-doped anatase TiO2 and rutile TiO2 phase mixtures (0 ≤ Ns: Ti ≤ 11 %, 0 ≤ anatase TiO2 ≤ 100 %, 0 ≤ rutile TiO2 ≤ 41 %) and (iii) pure pseudo-brookite Ti3-δO4N to pure Ni-doped anatase TiO2 phase mixtures. In tailoring high-throughput screening methods to these systems we were able to characterise large numbers of unique states across each combinatorial system and inter-relate their physical and functional properties. It was found that (i) pure Ni-doped anatase TiO2 is a more photocatalytically active material than Ns-doped anatase TiO2 under UVA and visible light (> 420 nm), (ii) un-doped anatase TiO2 is more photocatalytically active than Ns-doped anatase TiO2 under UVA light and (iii) pseudo-brookite Ti3-δO4N is a more active photocatalyst than Ni-doped anatase TiO2 under UVA light. The photocatalytic activity of Nb and W doped TiO2 solid solutions had not previously been investigated; however, their film resistivities for potential applications as more durable transparent conducting oxide materials had been. Using combinatorial APCVD we were able to produce NbxTi1-xO2 (0.0004 ≤ x ≤ 0.0194) and WxTi1-xO2 (0.0038 ≤ x ≤ 0.1380) anatase TiO2 thin-film solid solutions with transitional composition gradients. The Nbdoped system was formed from combining TiCl4, ethyl acetate and NbCl5 precursors. By characterising the film with our screening methods were we able to determine the strong functional inter-relationship between the material’s bandgap, photocatalytic activity and film resistivity in three dimensions; where an increased photocatalytic activity was associated with a lower bandgap energy and electrical resistance. The importance of oxygen vacancies on increasing charge carrier mobility presided over the number of charge carriers in the system (Nb-doping level). The W-doped system was formed from combining TiCl4, ethyl acetate and WCl6 precursors. Using high-throughput screening methods once more, the strong physical inter-relationship between the material’s Raman shift, unit cell volume and W-doping level were determined; where increased W-doping increasingly expanded the unit cell in the a/b axis and caused the prominent Raman active Eg vibrational mode of (144 cm-1) to shift to higher energies. Increased W-doping increasingly disrupted crystallisation, yielding less active photocatalysts. More interestingly however, increased preferred orientation in the (211) plane induced a greater degree of photo-induced surface wetting. Given the mechanism for the photo-induced wetting process in anatase TiO2 is, to our knowledge, yet to be studied, the trends highlighted the importance of the (211) plane in this process. Films synthesized by the combinatorial APCVD route, analysed in conjunction with high-throughput characterisation methods, provide a shortcut to understanding and optimising the functional properties of composition/ phase space.

The work presented in this thesis deals with experimental and theoretical studies related to alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. However, controlling thin film growth of this material, in particular at low substrate temperatures, is not straightforward. The aim of this work is to increase the understanding of the basic mechanisms governing alumina growth and to investigate novel ways of synthesizing alumina coatings. The thesis can be divided into two main parts, where the first part deals with fundamental studies of mechanisms affecting alumina growth and the second part with more application-oriented studies of high power impulse magnetron sputter (HiPIMS) deposition of the material. In the first part, it was shown that the thermodynamically stable α phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of merely 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α-alumina (in addition to the effect of the chromia nucleation layer). Moreover, the effects of residual water on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1*10-5 Torr was introduced, the columnar α-alumina growth was disrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the γ-alumina content was found to increase with increasing film thickness. To gain a better understanding of the atomistic processes occurring on the surface, density functional theory based computational studies of adsorption and diffusion of Al, O, AlO, and O2 on different α-alumina (0001) surfaces were also performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites and also show how adsorbed hydrogen might inhibit further growth of α-alumina crystallites. In addition, it was shown that the Al surface diffusion activation energies are unexpectedly low, suggesting that limited surface diffusivity is not the main obstacle for low-temperature α-alumina growth. Instead, it is suggested to be more important to find ways of reducing the amount of impurities, especially hydrogen, in the process and to facilitate α-alumina nucleation when designing new processes for low-temperature deposition of α-alumina. In the second part of the thesis, reactive HiPIMS deposition of alumina was studied. In HiPIMS, a high-density plasma is created by applying very high power to the sputtering magnetron at a low duty cycle. It was found, both from experiments and modeling, that the use of HiPIMS drastically influences the characteristics of the reactive sputtering process, causing reduced target poisoning and thereby reduced or eliminated hysteresis effects and relatively high deposition rates of stoichiometric alumina films. This is not only of importance for alumina growth, but for reactive sputter deposition in general, where hysteresis effects and loss of deposition rate pose a substantial problem. Moreover, it was found that the energetic and ionized deposition flux in the HiPIMS discharge can be used to lower the deposition temperature of α-alumina. Coatings predominantly consisting of the α phase were grown at temperatures as low as 650 °C directly onto cemented carbide substrates without the use of nucleation layers. Such coatings were also deposited onto cutting inserts and were tested in a steel turning application. The coatings were found to increase the crater wear resistance compared to a benchmark TiAlN coating, and the process consequently shows great potential for further development towards industrial applications.

La tesis aborda la integración monolítica de óxidos funcionales sobre silicio y la exploración de intercaras entre SrTiO3(110), SrTiO3(111) y otros óxidos En primer lugar la tesis detalla la integración monolítica del BaTiO3 en silicio, la plataforma actual en microelectrónica. Para ello se ha usado la heteroestructura LaNiO3/CeO2/YSZ como capa de barrera química y acomodación estructural. Se han investigado las propiedades estructurales y funcionales. Las capas son epitaxiales y orientadas con el eje c perpendicular al substrato, y presentan rugosidad superficial muy baja y alta polarización ferroeléctrica en remanencia. El óxido ferrimagnético CoFe2O4 fue integrado seguidamente en la estructura. La estructura multifuncional obtenida presenta alta calidad estructural, con excelentes propiedades ferromagnéticas y ferroeléctricas a temperatura ambiente. Asimismo presentamos la integración de BaTiO3 epitaxial sobre Si usando SrTiO3 como capa de barrera. También en este caso los ciclos de polarización ferroeléctrica medidos señalan las buenas propiedades funcionales de la estructura. Se presenta una comparación de las propiedades estructurales y funcionales de BaTiO3 crecido sobre SrTiO3/Si(001) y sobre CeO2/YSZ/Si(001). La segunda parte de la tesis se centra en las propiedades estructurales y de transporte de intercaras de LaAlO3/SrTiO3, con un especial énfasis en el estudio de la formación de un gas bidimensional de electrones en la intercara LaAlO3/SrTiO3(110). El análisis de la estructura y química de la intercara, de su jerarquía orbital electrónica, y de sus propiedades superconductoras amplían el conocimiento existente de los gases bidimensionales de electrones en intercaras de óxidos. Se han estudiado también las intercaras conductoras entre SrTiO3(110) y óxidos amorfos. El estudio ha permitido determinar la importancia relativa de la afinidad con el oxígeno de los metales depositados y la dependencia con la orientación de la energía de formación y difusión de vacantes de oxígeno. Además la tesis detalla el crecimiento monocapa a monocapa de Y:ZrO2 sobre SrTiO3(110), dando lugar a la relación epitaxial [110]YSZ(001) //[001]SrTiO3(110). Representa una nueva intercara presentando discontinuidad de simetría sin presentar variantes cristalinas gracias a usar la superficie de menor simetría como substrato, y abre paso al desarrollo de otras intercaras originales entre óxidos.
In this thesis the focus was aimed to the monolithic integration of functional oxides on silicon and to the exploration of interfaces between different oxides and the SrTiO3(110) and SrTiO3 (111) surfaces. Herein we report the monolithic integration of ferroelectric BaTiO3 on silicon, the current platform for microelectronics. This was done using the LNO/CeO2/YSZ buffer layer. The structural and functional properties are investigated. The films are epitaxial an c-oriented. Very low surface roughness and high ferroelectric remanent polarization are reported. High crystal quality ferrimagnetic CoFe2O4 was subsequently integrated in the structure. Thus obtained multifunctional structure shows high structural quality, robust ferromagnetism and superior ferroelectric properties, all at room temperature. Moreover, we report the integration of epitaxial BaTiO3 on Si using SrTiO3 buffer layer. Also in this case the recorded ferroelectric loops point to the good functional properties of this structure. A structural and functional comparison is given between BTO grown on the thin SrTiO3 and CeO2/YSZ buffer layers on silicon. We also report on the structural and transport properties of LaAlO3/SrTiO3 interfaces, with special emphasis on the LaAlO3/SrTiO3(110) interface featuring two-dimensional electron gas (2DEG). Further analysis of the interface structure and chemistry, electronic orbital hierarchy and superconductivity enriched our knowledge of the 2DEG electronic properties. Special focus also was given to the conductive interfaces comprising SrTiO3(110) and amorphous oxides. This study enables us to disentangle the relative importance of the oxygen affinity of the deposited metals and the orientation-dependent energy of vacancy formation and diffusion on the creation of oxygen vacancies. In addition we report the layer by layer growth of Y:ZrO2 on SrTiO3(110), leading to the epitaxial relationship [110]YSZ(001) //[001]SrTiO3(110). This novel idea of an interface featuring a symmetry discontinuity with the substrate being the lower symmetry material paves the way towards development of other innovative oxide interfaces.

Ferroelectric oxides are a group of advanced electronic materials with a wide variety of properties useful in applications such as memory devices, resonators and filters, infrared sensors, microelectromechanical systems, and optical waveguides and modulators. Among the oxide perovskite-structured ferroelectric thin film materials, sodium potassium niobate or Na0.5K0.5NbO3 (NKN) has recently emerged as one of the most promising materials in radio frequency (rf) and microwave applications due to high dielectric tenability and low dielectric loss. This thesis presents results on growth and structural, optical, and electrical characterization of NKN thin films. The films were deposited by rf-magnetron sputtering of a stoichiometric, high density, ceramic Na0.5K0.5NbO3 target onto single crystal LaAlO3 (LAO), Al2O3 (sapphire), SrTiO3, and Nd:YAlO3, and polycrystalline Pt80Ir20 substrates. By x-ray diffractometry, NKN films on c-axis oriented LaAlO3, SrTiO3 and Nd:YAlO3 substrates were found to grow epitaxially, whereas films on r-cut sapphire and polycrystalline Pt80Ir20 substrates were found to be preferentially (00l) oriented. The surface morphology was explored using atomic force microscopy. Optical and waveguiding properties of the Na0.5K0.5NbO3/substrate heterostructures were characterized using prism-coupling technique. Sharp and distinguishable transverse magnetic and electric propagation modes were observed for NKN thicknesses up to 2.0 μm. The extraordinary and ordinary refractive indices were calculated together with the birefringence of the NKN material. The electro-optic effect in transverse geometry was measured in transmission, where the effective linear electro-optic response was determined to reff = 28 pm/V for NKN/Al2O3 with an applied dc field up to 18 kV/cm. The ferroelectric state in NKN films on Pt80Ir20 at room temperature was indicated by a polarization loop with saturated polarization as high as 33.4 μC/cm2 at 700 kV/cm, remnant polarization of 10 μC/cm2, and coercive field of 90 kV/cm. Current-voltage characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties, with the leakage current density for an NKN IDC on the order of 30 nA/cm2 at 400 kV/cm. Rf dielectric spectroscopy demonstrated low loss, low frequency dispersion, and high voltage tunability. At 1 MHz, NKN/LAO showed a dissipation factor tan δ = 0.010 and a tunability of 16.5 % at 200 kV/cm. For the same structure the frequency dispersion was Δεr = 8.5 % between 1 kHz and 1 MHz.
QC 20100928

An investigation was made into the effect of rf magnetron deposition parameters on the resulting properties of chromium oxide thin films. The films were sputtered in an argon/ oxygen plasma environment with the main deposition parameters being the argon and oxygen flow rate, chamber pressure, deposition-time and the deposition power (forward and back). Tire effect of the sputter deposition regime which is controlled by the sputtering hysteresis phenomenon i.e. the reactive and metallic regimes, are expected to have a significant effect on the properties of the sputtered films and will have to be taken into account. The films were deposited on a range of substrates such as silicon, glass micro-slides and stainless steel 304 and the composition of the mainly amorphous sputtered films was determined through XPS, EDX and XRD. Optical characterisation and determination of optical constants was undertaken by transmission/reflection spectrophotometry, ellipsometry and Raman and FTIR analysis. Two designs of a solar thermal absorber (multilayer interference and tandem absorber) were designed and fabricated based on the optical constants measured by the methods previously stated and their performance analysed. The surface energy was calculated through measurement of the contact angle with three different liquids and the corrosion resistance of the films measured by OCP, linear sweep and EIS analysis in 3.5wt% NaCI solution. The mechanical properties were measured by nanoindentation, from which the hardness and elastic modulus of the samples could be obtained. The electrical properties were measured using a four point probe to calculate the thin film resistivity and the Kelvin probe analysis was used to measure the work function of the samples.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Autonomous mini- and microscale devices require the miniaturization of component devices such as on board integrated circuits (ICs) and electrochemical power sources. A paradigm shift to micro/nanostructured 3D geometries can enable high device performance within a small areal footprint. Fabrication of such devices requires processes to form structures in a material of interest and subsequently modify the structure with additional functional materials. This thesis explores the chemical vapor deposition (CVD) of polymer thin films to enable both the formation and modification of nanostructures. The CVD method allows for simultaneous polymer synthesis and thin film formation. The broad range of applications studied in this thesis all benefit from the single-step, in-situ control of the final polymer functionality and thin film properties enabled by the CVD of polymers. The first portion of this thesis studies the formation of nanostructures for ICs via the directed self-assembly (DSA) of block copolymers (BCPs). Initiated CVD (iCVD) is used to form cross-linked poly(divinyl benzene) (pDVB) films that control the orientation of self-assembled BCPs. The cross-linking mechanism of pDVB is first ascertained to form durable films. In-situ chemical modification of iCVD pDVB is then used to tune the final orientation of the selfassembled BCP film. A conformal iCVD pDVB film is then integrated into existing DSA processes to yield a nano-template that could be used to fabricate nanostructured ICs. The second portion of this thesis studies the modification of nanostructures by active and supporting materials used in electrochemical power systems. The iCVD process is used to develop conformal, solid polymer electrolytes, a supporting material for solid state lithium ion batteries. Out of several multi-vinyl cyclic chemistries, poly(tetravinyltetramethylcyclotetrasiloxane) (pV4D4) films displayed the highest ionic conductivity (10-⁷ S cm-¹) and high conformality. Active materials for supercapacitors were developed using the oxidative chemical vapor deposition (oCVD) of conductive polymers. The oCVD process was used to control the crystallographic texture of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. Edge-on texture maximized the pseudocapacitive charge storage of this material. Conformal PEDOT thin films on micro-structured current collectors enabled higher energy densities in a high power, asymmetric supercapacitor.
by Priya Moni.
Ph. D.

El desenvolupament de nous dispositius, cada cop més complexes, que s’adeqüin a les necessitats del mercat s’està convertint en una tasca cada cop més complicada deguda a la gairebé completa explotació de les propietats ofertes pels materials actuals. No obstant, és possible desenvolupar dispositius que ofereixin noves funcionalitats a través de la fabricació d’heteroestructures epitaxials (a l’escala nano-mètrica) compostes per diferents materials, on les propietats de cadascun dels compostos emprats són alterades degut a la seva interacció mútua. Quan aquestes estructures estan formades per òxids del tipus “perovskita”, existeix una forta interacció entre els diferents graus de llibertat dels electrons (xarxa cristal·lina, espín, òrbita i càrrega) donant lloc a un gran ventall de propietats físiques fascinants, que, a més, poden ser modificades a mida mitjançant la subtil alteració de les seves propietats estructurals a través de la tensions. Per tal d’entendre els fenòmens físics que donen lloc a aquest tipus d’efectes, és necessari conèixer l’estructura real dels defectes i/o distorsions que apareixen en aquestes estructures. Per aquesta raó, és indispensable l’ús de noves tècniques de caracterització capaces d’analitzar en l’espai real i amb resolució atòmica aquests sistemes. El desenvolupament de la tècnica de la microscòpia electrònica de transmissió d’escaneig corregida d’aberracions, combinada amb la espectroscòpia EELS (STEM-EELS), va significar un avanç notable ja que aquesta tècnica permet la observació directe d’estructures complexes i no periòdiques (així com defectes o interfases) en l’espai real i amb resolució subatòmica, sense la necessitat d’emprar simulacions numèriques. En aquest treball, s’aborden tres casos paradigmàtics de distorsions estructurals derivades de les tensions en capes fines epitaxials d’òxids tipus perovskita. En primer lloc, s’ investiga la forta interacció entre la microestructura, els tipus de defectes i les propietats superconductores de les capes fines de YBa2Cu3O7 del tipus nanocompost, on nanopartícules orientades aleatòriament resten atrapades dins de la pròpia matriu del YBCO. A més, s’ estudia en detall totes les distorsions que apareixen al voltant d’un dels defectes més comuns observats en aquest tipus de capes, que també tenen una influencia rellevant en les seves propietats superconductores. En segon lloc, s’ estudien els mecanismes estructurals que ajuden en l’acomodació de la tensió epitaxial, tan compressiva con expansiva, en les capes fines de LaNiO3 (LNO) i NdNiO3 (NNO), crescudes sobre monocristalls de LAO i LSAT, respectivament. S’observa la formació de dos tipus diferents de defectes en funció del compostos emprats, tant en la capa com en el substrat. Les propietats de transport elèctric de les capes són també investigades per tal de correlacionar els defectes generats i les propietats macroscòpiques de les capes. Finalment s’ investiguen els efectes de disminuir el gruix de les capes de La0.7Sr0.3MnO3 fins a l’ordre d’uns pocs nanòmetres. S’observa l’aparició d’una transició des d’un estat ferromagnètic i metàl·lic cap a un altre ferromagnètic i aïllant quan el gruix de les capes és reduït per sota d’un gruix crític, fet que contradiu el mecanisme de transport elèctric esperat en aquest compost: el conegut com a intercanvi doble o “double-exchange mechanism”. S’aporta una nova visió d’aquest fenomen a través de la caracterització de les modificacions estructurals que tenen lloc en aquestes capes, que apareixen degut a la tensió epitaxial i al confinament espacial. Es creu que les propietats estructurals mostrades poden ajudar en l’entesa de les alteracions de les propietats físiques observades en les capes de LSMO quan aquestes són reduïdes a uns pocs nanòmetres.
The continuous development of novel and complex devices for fulfilling the market demands is becoming more complex over time because of the wholly exploitation of the available bulk materials. One possibility to accomplish novel devices possessing new functionalities is by engineering epitaxial heterostrucutres, in the nanometric scale, where the properties of the used compounds can be modified because of their mutual interaction. When these heterostructures are made of perovskite oxides, the strong interplay between the lattice, spin, orbit and charge degrees of freedom lead to a huge range of fascinating properties that can be tailored by the subtle structural modifications induced by strains. In order to understand the underlying physics behind these phenomena, it is crucial to know the real structure of the emerging lattice defects or distortions within these kind of structures. For this reason, new techniques capable of analyzing these systems in the real space with atomic resolution are required. The development of the aberration-corrected scanning transmission electron microscopy, combined with the electron energy loss spectroscopy, technique (STEM-EELS) marked a notable breakthrough as it permits to directly see, without the need of simulations, the real structure of complex non-periodical structures, such as defects or interfaces, in real space and with sub-atomic resolution. In this work, we address three paradigmatic examples of strain-driven structural distortions appearing in one of the most studied family of functional oxides materials, this is, the case of perovskite oxides. First, we investigate the strong interplay between the microstructure, the defect landscape and the superconducting properties of YBa2Cu3O7 nanocomposite films, where randomly oriented nanoparticles are trapped within the YBCO host matrix. Besides, we analyze in detail all the emerging distortions around one of the most common defect found in YBCO nanocomposite films, which will also ultimately impinge on its superconducting properties. Second, we study in detail the structural mechanisms that help on the accommodation of the epitaxial strain, either compressive or tensile, in LaNiO3 (LNO) and NdNiO3 (NNO) thin films grown onto LAO and LSAT single crystal substrates, respectively. Two different kind of defects are identified in the studied heterostructures, which are observed to appear depending on the used compound and substrate. The electrical transport properties are also under investigation in order to find out the implications of the generated defect landscapes in the macroscopic properties of the films. Finally, we investigate the effect of reducing the film thickness of La0.7Sr0.3MnO3 thin films down to few nanometers. A transition from a ferromagnetic-metallic to a ferromagnetic-insulating phase is identified when films are reduced below a critical thickness, which contradicts the electrical transport mechanism expected for this compound. We provide new insights on the structural modifications generated by the epitaxial strain and the spatial confinement effects in these ultrathin films, which might help to understand the observed modifications on the LSMO physical properties.

Les deux systèmes de création d’une contrainte dans les films polymériques ont été développés, chacun répondant à un gradient de gonflement du polymère dans la direction normale au film. Ce gonflement peut être provoqué soit par la présence d’un gradient de densité de réticulation dans la direction normale à la surface (films de poly(4-vinylpyridine) réticulés par UV ou dans les films de chitosan réticulés thermiquement et ioniquement ; ou soit par une pénétration asymétrique de vapeur de solvant dans le film (ici le polydiméthylsiloxane oxydé en surface). Un troisième système polymérique auto-enroulant a également été réalisé par la création d’une contrainte permanente au sein du film de polydiméthylsiloxane, grâce à l’extraction sélective d’un additif non-réticulé, l’huile de silicone. Un modèle théorique du processus d’auto-enroulement, basé sur la théorie linéaire d’élasticité a ainsi pu être proposé
Two systems of stress creation in the polymer films were developed, each based on the swelling gradient in the direction normal to the film. This swelling may be caused either by the presence of a crosslinking density gradient in the direction normal to the surface (poly (4-vinylpyridine film) crosslinked by UV or in the thermally or ionically crosslinked chitosan films; or by asymmetric penetration of solvent vapor in the film (here polydimethylsiloxane surface-oxidized). A third self-rolling polymeric system has also been realized by the creation of a permanent strain in the polydimethylsiloxane film by selective extraction of a non-cross-linked additive, silicone oil. A theoretical model of self-rolling process based on the linear theory of elasticity has been proposed

Anatase, a form of titanium dioxide (TiO2), is arguably the most studied wide band gap semiconducting photocatalyst. TiO2 has many other applications, including water and air purification, self-cleaning surfaces and photovoltaic. However, for many applications, as well as for safety concerns related to the handling of nanoparticles, the simultaneous synthesis and deposition of photocatalytic TiO2 thin films is highly desirable. Numerous routes towards the simultaneous synthesis and deposition of anatase TiO2 thin films have already been reported. Chemical vapour deposition (CVD) methods have successfully been implemented for the industrial production of photocatalytic TiO2 thin films. Nevertheless, the rather high temperature required in CVD does not allow the coating of heat sensitive substrates. Similarly, other photocatalytic TiO2 deposition processes all possess significant drawbacks, such as the lowpressure environment required by physical vapour deposition (PVD) and the post-heating treatment or the large number of steps required by sol-gel approaches. In addition, most of the methods remain difficult to implement on complex shape substrates and/or non-conformal. The following research thesis reports on new functional coatings, based on boron-doped TiO2, which were deposited by APCVD and AP-PECVD on different matrices and substrates. Boron, as a dopant for TiO2 systems, has been used and reported to enhanced TiO2 photocatalytic performance under UV light, as well as numerous scientific papers reported on the visible light response of borondoped TiO2. However, in most of the cases the successful B-TiO2 was synthesised in the form of powders, not thin films. Also, when B-TiO2 thin films were synthesised, only substitutional boron-doped TiO2 was previously reported, whereas, the higher stability and long-term life of interstitial boron vs substitutional has been proven and reported theoretically and experimentally.

This thesis describes the synthesis and characterisation of molecular, single-source precursors for the deposition of group 13 metal oxides and pnictides and their subsequent application in the formation of thin films of those materials by Aerosol Assisted Chemical Vapour Deposition (AACVD). A range of tetradentate β-ketoimine ligands have been developed and subsequently employed in the formation and isolation of complexes of group 13 metals aluminium, gallium and indium through a variety of synthetic routes. In particular, the ligand systems have been successfully employed in the stabilisation of rare gallium mono-hydride species, which exhibit considerable thermal stability. The thermal decomposition of the group 13 β-ketoiminate complexes was investigated by thermogravimetric analysis and subsequently the deposition of gallium oxide was carried out on glass substrates in an AACVD process. The resulting films were amorphous as-deposited, however crystalline gallium oxide was obtained in some cases through the addition of a post-deposition annealing step. The single-source deposition of InAs by AACVD has been investigated, including an investigation of the alkane elimination reaction between trimethyl indium and tert-butyl arsine in the formation of InAs cluster complexes. InAs was successfully deposited, representing the first report of the deposition of this material by AACVD. Thin films were analysed and characterised by multiple common techniques, including glancing angle powder X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy and scanning electron microscopy, confirming the formation of InAs, though film quality was hampered by varying degrees of indium oxide formation within the films, in particular at the surface. Hall effect measurements provided an initial investigation of the electrical properties of the films, showing the formation of conductive, n-type InAs. However, electron mobility was poor by comparison to literature suggesting that optimisation of the deposition conditions is required in order to yield device-quality materials.

There are a number of “smart” coatings that can be applied to glass. These include self-cleaning coatings based on titanium dioxide, and low-E coatings based on fluorine-doped tin oxide. Products are often more desirable with colour options such as Pilkington Activ BlueTM. There are currently no alternatives to body tinting glass to achieve colour, which is a time-consuming and expensive procedure. The work in this project details a number of coloured coatings via the AACVD or combustion processing of metal nitrate/urea precursors.

Les matériaux multiferroïques et/ou magnétoélectriques sont riches en promesses de nouvelles applications, comme par exemple des mémoires quatre états à densité accrue ou des mémoires magnétoélectriques à faible consommation d’énergie. Ces promesses restent cependant pour l’instant lettres mortes en raison du très faible nombre de matériaux présentant ces propriétés à température ambiante, et des forts courants de fuite qu’ils présentent en couches minces. Cette thèse porte sur un matériau prometteur en termes d’applications, car magnétoélectrique et ferrimagnétique à température ambiante, le ferrite de gallium de composition Ga0.6Fe1.4O3 (GFO).Nous avons démontré la possibilité de réduire les courants de fuite et moduler à volonté le type de conduction n ou p dans les couches minces de cet oxyde transparent, semi-conducteur, et magnétique, par dopage par des ions Ni2+. Une optimisation de la croissance de GFO par pulvérisation cathodique a par ailleurs montré qu’il était possible de le déposer sous champ électrique, ce qui ouvre d’intéressantes perspectives pour l’optimisation de la polarisation électrique des couches minces
The multiferroic and/or magnetoelectric materials are full of promises in terms of new applications, such as for example higher density four state memories or lower power consuming magnetoelectric memories. These promises are however actually put off because too few materials present these properties at room temperature and because their thin films present too high leakage currents. This thesis focusses on a room temperature magnetoelectric and ferrimagnetic material promising in terms of applications, the gallium ferrite Ga0.6Fe1.4O3 (GFO).We have demonstrated the possibility to strongly reduce the leakage currents and perfectly tune from n to p the conduction type in transparent, semi-conducting, and magnetic thin films of GFO through Ni2+ doping. The optimization of the growth of GFO thin films by sputtering has moreover shown the possibility of deposition under an electric field, which opens ways to control of the electric polarization of the films