Dissertations / Theses on the topic 'Nano structure materials'

The integration of sensors, actuators, and control systems is an ongoing process in a wide range of applications covering automotive, medical, military, and consumer electronic markets. Four major families of ceramic and metallic actuators are under development: piezoelectrics, electrostrictors, magnetostrictors, and shape-memory alloys. All of these materials undergo at least two phase transformations with coupled thermodynamic order parameters. These transformations lead to complex domain wall behaviors, which are driven by electric fields (ferroelectrics), magnetic fields (ferromagnetics), or mechanical stress (ferroelastics) as they transform from nonferroic to ferroic states, contributing to the sensing and actuating capabilities. This research focuses on two multiferroic crystals, Pb(Mg1/3Nb2/3)O3-PbTiO3 and Fe-Ga, which are characterized by the co-existence and coupling of ferroelectric polarization and ferroelastic strain, or ferro-magnetization and ferroelastic strain. These materials break the conventional boundary between piezoelectric and electrostrictors, or magnetostrictors and shape-memory alloys. Upon applying field or in a poled condition, they yield not only a large strain but also a large strain over field ratio, which is desired and much benefits for advanced actuator and sensor applications. In this thesis, particular attention has been given to understand the structure-property relationships of these two types of materials from atomic to the nano/macro scale. X-ray and neutron diffraction were used to obtain the lattice structure and phase transformation characteristics. Piezoresponse and magnetic force microscopy were performed to establish the dependence of domain configurations on composition, thermal history and applied fields. It has been found that polar nano regions (PNRs) make significant contributions to the enhanced electromechanical properties of PMN-x%PT crystals via assisting intermediate phase transformation. With increasing PT concentration, an evolution of PNRï  PND (polar nano domains)-> micron-domains-> macro-domains was found. In addition, a domain hierarchy was observed for the compositions near a morphotropic phase boundary (MPB) on various length scales ranging from nanometer to millimeter. The existence of a domain hierarchy down to the nm scale fulfills the requirement of low domain wall energy, which is necessary for polarization rotation. Thus, upon applying an E-field along <001> direction(s) in a composition near the MPB, low symmetry phase transitions (monoclinic or orthorhombic) can easily be induced. For PMN-30%PT, a complete E-T (electric field vs temperature) diagram has been established. As for Fe-x at.% Ga alloys, short-range Ga-pairs serve as both magnetic and magnetoelastic defects, coupling magnetic domains with bulk elastic strain, and contributing to enhanced magnetostriction. Such short-range ordering was evidenced by a clear 2theta peak broadening on neutron scattering profiles near A2-DO3 phase boundary. In addition, a strong degree of preferred [100] orientation was found in the magnetic domains of Fe-12 at.%Ga and Fe-20 at.%Ga alloys with the A2 or A2+DO3 structures, which clearly indicates a deviation from cubic symmetry; however, no domain alignment was found in Fe-25 at.%Ga with the DO3 structure. Furthermore, an increasing degree of domain fluctuations was found during magnetization rotation, which may be related to short-range Ga-pairs cluster with a large local anisotropy constant, due to a lower-symmetry structure.
Ph. D.

The mixing of polymers and nanoparticles makes it possible to give advantageous macroscopic material performance by tailoring the microstructure of composites. In this thesis, five combinations of nano inclusion and polymer matrix have been investigated. The first type of composites is titanium dioxide/ polyaniline combination. The effects of 4 different doping-acids on the microstructure, morphology, thermal stability and thermoelectric properties were discussed, showing that the sample with HCl and sulfosalicylic dual acids gave a better thermoelectric property. The second combination is titanium dioxide/polystyrene composite. Avrami equation was used to investigate the crystallization process. The best fit of the mass derivative dependence on temperature has been obtained using the double Gaussian dependence. The third combination is titanium dioxide/polyaniline/ polystyrene. In the titanium dioxide/polyaniline/ polystyrene ternary system, polystyrene provides the mechanical strength supporting the whole structure; TiO2 nanoparticles are the thermoelectric component; Polyaniline (PANI) gives the additional boost to the electrical conductivity. We also did some investigations on Polyethylene odide-TiO2 composite. The cubic anatase TiO2 with an average size of 13nm was mixed with Polyethylene-oxide using Nano Debee equipment from BEE international; Single wall carbon nanotubes were introduced into the vinyl acetate-ethylene copolymer (VAE) to form a connecting network, using high pressure homogenizer (HPH). The processing time has been reduced to 1/60 of sonication for HPH to give better sample quality. Theoretical percolation was derived according to the excluded volume theory in the expression of the threshold as a function of aspect ratio.

This thesis is devoted to first-principles simulations of bio- and nano-materials,focusing on various soft x-ray spectra, ground-state energies and structures of isolated largemolecules, bulk materials, and small molecules in ambient solutions. K-edge near-edge x-ray absorption fine structure (NEXAFS) spectra, x-ray emission spectra, andresonant inelastic x-ray scattering spectra of DNA duplexes have been studied by means oftheoretical calculations at the density functional theory level. By comparing a sequence of DNAduplexes with increasing length, we have found that the stacking effect of base pairs has verysmall influence on all kinds of spectra, and suggested that the spectra of a general DNA can bewell reproduced by linear combinations of composed base pairs weighted by their ratio. The NEXAFS spectra study has been extended to other realistic systems. We have used cluster modelswith increasing sizes to represent the infinite crystals of nucleobases and nucleosides, infinitegraphene sheet, as well as a short peptide in water solution. And the equivalent core holeapproximation has been extensively adopted, which provides an efficient access to these largesystems. We have investigated the influence of external perturbations on the nitrogen NEXAFSspectra of guanine, cytosine, and guanosine crystals, and clarified early discrepancies betweenexperimental and calculated spectra. The effects of size, stacking, edge, and defects to theabsorption spectra of graphene have been systematically analyzed, and the debate on theinterpretation of the new feature has been resolved. We have illustrated the influence of watersolvent to a blocked alanine molecule by using the snapshots generated from molecular dynamics. Multi-scale computational study on four short peptides in a self-assembled cage is presented. It isshown that the conformation of a peptide within the cage does not corresponds to its lowest-energyconformation in vacuum, due to the Zn-O bond formed between the peptide and the cage, and theconfinement effect of the cage. Special emphasis has been paid on a linear-scaling method, the generalized energy basedfragmentation energy (GEBF) approach. We have derived the GEBF energy equation at the Hartree-Focklevel with the Born approximation of the electrostatic potential. Numerical calculations for amodel system have explained the accuracy of the GEBF equation and provides a starting point forfurther refinements. We have also presented an automatic and efficient implementation of the GEBFapproach which is applicable for general large molecules.
QC 20110404

In the past decade the interest in molecular electronic devices has escalated. The synthesis of molecular crystals has improved, providing single crystals or thin films with mobility comparable with or even higher than amorphous silicon. Their mechanical flexibility admits new types of applications and usage of electronic devices. Some of these organic crystals also display magnetic effects. Furthermore, the fullerene and carbon nanotube allotropes of carbon are prominent candidates for various types of applications. The carbon nanotubes, in particular, are suitable for molecular wire applications with their robust, hollow and almost one-dimensional structure and diverse band structure. In this thesis, we have theoretically investigated carbon based materials, such as carbon nanotubes, pentacene and spiro-biphenalenyl neutral radical molecular crystals. The work mainly deals with the electron structure and the transport properties thereof. The first studies concerns effects and defects in devices of finite carbon nanotubes. The transport properties, that is, conductance, are calculated with the Landauer approach. The device setup contains two metallic leads attached to the carbon nanotubes. Structural defects as vacancies and bending are considered for single-walled carbon nanotubes. For the multi-walled carbon nanotubes the focus is on inter-shell interaction and telescopic junctions. The current voltage characteristics of these systems show clear marks of quantum dot behaviour. The influence of defects as vacancies and geometrical deformations are significant for infinite systems, but in these devices they play a minor role. The rest of the studies concern molecular crystals, treated with density-functional theory (DFT). Inspired by the enhance of the electrical conductivity obtained experimentally by doping similar materials with alkali metals, calculations were performed on bundles of single-walled carbon nanotubes and pentacene crystals doped with potassium. The most prominent effect of the potassium intercalation is the shift of Fermi level in the nanotube bands. A sign of charge transfer of the valence electrons of the potassium atoms. Semi-conducting bundles become metallic and metallic bundles gain density of states at the Fermi level. In the semi-conducting pristine pentacene crystals structural transitions occur upon doping. The herringbone arrangement of the pristine pentacene molecules relaxes to a more π-stacked structure causing more dispersive bands. The charge transfer shifts the Fermi level into the lowest unoccupied molecular orbital band and turns the crystal metallic. Finally, we have studied molecular crystals of spiro-biphenalenyl neutral radicals. According to experimental studies, some of these materials show simultaneous electrical, optical and magnetical bistability. The electronic properties of these crystals are investigated by means of DFT with a focus on the possible intermolecular interactions of radical spins.

In this thesis electron microscopy was employed to characterise the nanoscale and atomic scale structure and chemistry of organic and inorganic materials. In chapter 4, the thin film morphology of the organic blend of [poly(9,9-dioctylfluorene- co-benzothiadiazole)] (commonly referred as F8BT) and poly[9,9-dioctyfluorene-co- N-(4-butylphenyl)-diphenylamine] (abbreviated as TFB) was investigated, mainly by bright field transmission electron microscopy (BF-TEM). F8BT and TFB are conjugated polymers, which are candidates to replace inorganic semiconductors in many applications because of their simple preparation and processing procedures. The phase separation of the F8BT:TFB blend was investigated at different compositions. Polymer domains were found in the thin film, with sub- micrometer size which varies with concentration. The 1:1 weight ratio sample showed sub-micrometer TFB rich areas in a F8BT matrix, while the 1:4 weight ratio thin film presented F8BT phases, whose areas are mostly below 0.02 μm2, in a TFB layer. Since some electronic applications, especially in optoelectronics, show increased efficiency after addition of quantum dots in the polymer blend, the effect of CdSe quantum dots on the phase separation of the organic blend was investigated together with their effect on the nanoscale morphology. The CdSe quantum dots were found to aggregate in clusters with limited dispersion within the polymer domains, which did not present significantly morphology changes as a consequence of quantum dots (QDs) addition. The atomic structure and chemistry of the inorganic Ba6−3xNd8+2xTi18O54 microwave ceramic was quantitatively investigated in chapter 4, using high resolution scanning transmission electron microscopy (HR-STEM) and electron energy loss spectroscopy (EELS). These materials are an essential part of telecommunication systems, they can be found in components such as resonators and antennas, on account of their high permittivity, temperature stability and the very low dielectric loss at microwave frequencies. The unit cell was refined with sub-Å precision based on extensive data analysis of HR-STEM images and the unit cell structure showed no significant changes as a consequence of changes in composition or cooling rate after annealing. Ba was found to substitute preferentially to specific Nd atomic columns in the structure, and these trends apply across the whole composition range. These results were confirmed by comparisons with image simulations and provided a starting point for improved refinements of X-ray data.

The present thesis is focused on various methods of controlling electronic and geometrical structure of two-dimensional overlayers adsorbed on metal surfaces exemplified by graphene and hexagonal boron nitride (h-BN) grown on transition metal (TM) substrates. Combining synchrotron-radiation-based spectroscopic and various microscopic techniques with in situ sample preparation, we are able to trace the evolution of overlayer electronic and geometrical properties in overlayer/substrate systems, as well as changes of interfacial interaction in the latter.It is shown that hydrogen uptake by graphene/TM substrate strongly depends on the interfacial interaction between substrate and graphene, and on the geometrical structure of graphene. An energy gap opening in the electronic structure of graphene on TM substrates upon patterned adsorption of atomic species is demonstrated for the case of atomic oxygen adsorption on graphene/TM’s (≥0.35 eV for graphene/Ir(111)). A non-uniform character of adsorption in this case – patterned adsorption of atomic oxygen on graphene/Ir(111) due to the graphene height modulation is verified. A moderate oxidation of graphene/Ir(111) is found largely reversible. Contrary, oxidation of h-BN/Ir(111) results in replacing nitrogen atoms in the h-BN lattice with oxygen and irreversible formation of the B2O3 oxide-like structure.      Pronounced hole doping (p-doping) of graphene upon intercalation with active agents – halogens or halides – is demonstrated, the level of the doping is dependent on the agent electronegativity. Hole concentration in graphene on Ir(111) intercalated with Cl and Br/AlBr3 is as high as ~2×1013 cm-2 and ~9×1012 cm-2, respectively.     Unusual periodic wavy structures are reported for h-BN and graphene grown on Fe(110) surface. The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of ~0.8 Å. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [11 ̅1] or [111 ̅] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110).     Chemical vapor deposition (CVD) formation of graphene on iron is a formidable task because of high carbon solubility in iron and pronounced reactivity of the latter, favoring iron carbide formation. However, growth of graphene on epitaxial iron films can be realized by CVD at relatively low temperatures, and the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a periodically corrugated pattern on Fe(110): it is modulated in one dimension forming long waves with a period of ~4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The novel 1D templates based on h-BN and graphene adsorbed on iron can possibly find an application in 1D nanopatterning. The possibility for growing high-quality graphene on iron substrate can be useful for the low-cost industrial-scale graphene production.

The thesis focuses on exploring the sub-grain structure in stainless steel 316L prepared by additive manufacturing (AM). Two powder-bed based AM methods are involved: selective laser melting (SLM) and electron beam melting (EBM). It is already known that AM 316L has heterogeneous property and hierarchy structure: micro-sized melt pools, micro-sized grains, nano-sized sub-grain structure and nano-sized inclusions. Yet, the relation among these structures and their influence on mechanical properties have not been clearly revealed so far. Melt pool boundaries having lower amount of sub-grain segregated network structures (Cellular structure) are weaker compared to the base material. Compared with cell boundaries, grain boundaries have less influence on strength but are still important for ductility. Cell boundaries strengthen the material without losing ductility as revealed by mechanical tests. Cellular structure can be continuous across the melt pool boundaries, low angle sub-grain boundaries, but not grain boundaries. Based on the above understanding, AM process parameters were adjusted to achieve customized mechanical properties. Comprehensive characterization were carried out to investigate the density, composition, microstructure, phase, magnetic permeability, tensile property, Charpy impact property, and fatigue property of both SLM and EBM SS316L at room temperature and at elevated temperatures (250°C and 400°C). In general, SLM SS316L has better strength while EBM SS316L has better ductility due to the different process conditions. Improved cell connection between melt pools were achieved by rotating 45° scanning direction between each layer compared to rotating 90°. Superior mechanical properties (yield strength 552 MPa and elongation 83%) were achieved in SLM SS316L fabricated with 20 µm layer thickness and tested in the building direction. Y2O3 added oxide dispersed strengthening steel (ODSS) were also prepared by SLM to further improve its performance at elevated temperatures. Slightly improved strength and ductility (yield strength 574 MPa and elongation 90%) were obtained on 0.3%Y2O3-ODSS with evenly dispersed nanoparticles (20 nm). The strength drops slightly  but ductility drops dramatically at elevated temperatures. Fractographic analysis results revealed that the coalescence of nano-voids is hindered at room temperature but not at elevated temperatures. The achieved promising properties in large AM specimens assure its potential application in nuclear fusion. For the first time, ITER first wall panel parts with complex inner pipe structure were successfully fabricated by both SLM and EBM which gives great confidence to application of AM in nuclear industry.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Canada produces about one-third of the global supply of medical radioisotopes. The nuclear power reactors in Ontario, Quebec and New Brunswick have generated about 17 percent of the electricity in the country every year (NWMO, 2010; Noorden; 2013). Since the 1960s, more than 2 million used (or spent) fuel bundles (high-level radioactivity) and 75,000 m³ of low- and intermediate-level radioactive waste have been produced, which is increasing by 2000 to 3000 m³ every year after reducing the processed volume (Jensen et al., 2009). More than 30 countries around the world, including Canada, have proposed construction of very deep geological repositories (DGRs) to store this nuclear waste for design periods 1,000,000 years. DGR concepts under development in Canada (the DGR is likely to be constructed in Ontario) are based on a multi-barrier system (NWMO, 2012). A crucial component of the multi-barrier system is the engineered barrier system (EBS), which includes a buffer, backfill, and tunnel sealing materials to physically, chemically, hydraulically and biologically isolate the nuclear waste. Bentonite-based material has been chosen for this critical use because of its high swelling capacity, low hydraulic conductivity, and for its good ability to retain radionuclides in the case of failed canisters. However, the presence of bentonite-based material in DGRs, surrounded by an aggressive environment of underground saline water, nuclear waste heat decay, and corrosion products under confining stress, may lead to mineralogical changes. Consequently, the physical and physiochemical properties of bentonite-based materials may change, which could influence the performance of bentonite in an EBS as well as the overall safety of DGRs. The objective of this research is to investigate the impact of the underground water salinity, heat generated by nuclear waste, and corrosion products of nuclear waste containers in Ontario on the engineering and micro-/nano-structural properties of bentonite-sand engineered barrier materials. Free-swelling, swelling pressure and hydraulic conductivity tests have been performed on bentonite-sand mixtures subjected to various chemical (groundwater chemistry; corrosion water with iron as a corrosion product) and thermal (heat generated) conditions. Several techniques of micro- and nano-structural analyses, such as x-ray diffraction (XRD), X-Ray microanalysis (DES), surface area and pore size distribution analyses (BET, BJH) and differential gravimetric (TGA and DTG) analyses have also been conducted on the bentonite-sand materials. Valuable results have been obtained for better understanding the durability and performance of the bentonite-sand barrier for the DGR which may be located in Ontario. The obtained results have shown that the groundwater chemistry and corrosion products of the nuclear containers significantly deteriorate the swelling and permeability properties of the tested bentonite-sand barrier materials, while temperature has little or no effect.

An aqueous droplet in a solution of lipids in oil acquires a lipid monolayer coat, and two such droplets adhere to form a bilayer at their interface. Networks of droplets have been constructed in this way that function as light sensors, batteries and electrical circuits by using membrane proteins incorporated into the bilayers. However, the droplets have been confined to a bulk oil phase, which precludes direct communication with physiological environments. Further, the networks typically have been assembled manually, which limits their scale and complexity. This thesis addresses these limitations, and thereby enables prospective medical and technological applications for droplet networks. In the first part of the work, defined droplet networks are encapsulated within mm-scale drops of oil in water to form structures called multisomes. The encapsulated droplets adhere to one another and to the surface of the oil drop to form interface bilayers that allow them to communicate with each other and with the surrounding aqueous environment through membrane pores. The contents of the droplets can be released by changing the pH or temperature of the surrounding solution. Multisomes have potential applications in synthetic biology and medicine. In the second part of the work, a three-dimensional printing technique is developed that allows the construction of complex networks of tens of thousands of heterologous droplets ~50 µm in diameter. The droplets form a self-supporting material in bulk oil or water analogous to biological tissue. The mechanical properties of the material are calculated to be similar to those of soft tissues. Membrane proteins can be printed in specific droplets, for example to establish a conductive pathway through an otherwise insulating network. Further, the networks can be programmed by osmolarity gradients to fold into designed shapes. Printed droplet networks can serve as platforms for soft devices, and might be interfaced with living tissues for medical applications.

The structural analysis serves as a bridge to link the structure of materials to their properties. Revealing the structure details allows a better understanding on the growth mechanisms and properties of materials, and a further designed synthesis of functional materials. The widely used methods based on X-ray diffraction have certain limitations for the structural analysis when crystals are small, poorly crystallized or contain many defects. As electrons interact strongly with matter and can be focused by electromagnetic lenses to form an image, electron crystallography (EC) approaches become prime candidates for the structural analysis of a wide range of materials that cannot be done using X-rays, particularly nanomaterials with poor crystallinity. Three-dimensional electron diffraction tomography (3D EDT) is a recently developed method to automatically collect 3D electron diffraction data. By combining mechanical specimen tilt and electronic e-beam tilt, a large volume of reciprocal space can be swept at a fine step size to ensure the completeness and accuracy of the diffraction data with respect to both position and intensity. Effects of the dynamical scattering are enormously reduced as most of the patterns are collected at conditions off the zone axes. In this thesis, 3D EDT has been used for unit cell determination (COF-505), phase identifications and structure solutions (ZnO, Ba-Ta3N5, Zn-Sc, and V4O9), and the study of layer stacking faults (ETS-10 and SAPO-34 nanosheets). High-resolution transmission electron microscope (HRTEM) imaging shows its particular advantages over diffraction by allowing observations of crystal structure projections and the 3D potential map reconstruction. HRTEM imaging has been used to visualize fine structures of different materials (hierarchical zeolites, ETS-10, and SAPO-34). Reconstructed 3D potential maps have been used to locate the positions of metal ions in a woven framework (COF-505) and elucidate the pore shape and connectivity in a silica mesoporous crystal. The last part of this thesis explores the combination with X-ray crystallography to obtain more structure details.

In this thesis, advanced characterisation methods, including atom probe tomography (APT) and transmission Kikuchi diffraction (TKD) were employed to study surface and interfaces in a range of nano-scale and nano-structured materials. These techniques were used to measure solute segregation towards grain boundaries and to explore the relationship between grain boundary segregation and grain boundary mobility. APT was also used to characterise the structure of nanoparticles used as catalysts, and the adsorption behaviour of sulphur on catalytic surfaces, to gain more information about the structure-activity relationships, and deactivation processes. This research included the development and improvement of new and existing APT sample preparation techniques, conducting the experiments, and data analysis. The first part of this thesis is concerned with nanocrystalline alloys processed by severe plastic deformation. In the second part the exceptional hardening of an 316L austenitic steel during annealing was also investigated using APT. This thesis also concentrated on the study of nanoparticles for catalysis via APT. Systematic investigations of different APT sample preparation techniques were performed in order to find a way of producing reproducible and reliable specimens. Different acquisition parameters, substrates and coatings were tested to improve the APT data quality. Experiments were conducted in which needles were dipped in thiophene. Here the aim was to investigate the phenomenon of sulphur poisoning by using APT to investigate how thiophene bonds with different metal substrates. A glovebag setup was designed for the transfer of APT samples in a controlled environment, to avoid oxidation of the samples. This allowed the comparison of oxidised and un-oxidised specimen states. In the last part of this thesis, the accuracy of crystallographic information contained within APT datasets was verified for the first time by comparing the datasets to TKD measurements.

This research reveals a catalyst development towards achieving catalysts with hierarchical porous structures with enhanced mechanical properties by using nano-structured macro-porous PolyHIPE polymer. This work can be divided into two parts: the fabrication and its characterisation of hierarchical metal structure using PHP and other fibre materials; and the fabrication and characterisation of PHP with silica particles and glass wool, further coated with silane material as templates. A catalyst system was successfully fabricated forming a 3D-interconnecting network of pore size, ranging from tens of micrometers and gradually reducing finally to nanometer scale. An electroless deposition flow through method using Ni-B bath solution was performed on the templates and was subsequently heat treated to obtain porous metallic structures, thus providing accessibility for reactants to the surface and for products away from the surface. Meanwhile, silanated templates were produced by surface treatment. This was performed by submerging templates directly into the silanes solution at room temperature (24°C) using a water-ethanol based solution of the silanes. The polymer-metal/alloy or silica functionalized based composite demonstrated a high impact strength. The results showed that not only hierarchical pore structure was formed, but it was also demonstrated that silica particles were totally and uniformly covered/coated by metal deposit and had good adhesion. When used on glass wool, silanation had greatly improved the bond strengths of metal deposits to the templates. SEM micrographs revealed that the formation of cracks were tremendously reduced and exhibited higher bond strengths due to silanated glass surface. It is expected to be more efficient and robust in the case of an enhanced surface area, and most desirable in catalyst applications.

Palladium, being impermeable to all gases except hydrogen, has been widely studied for hydrogen extraction in recent years. The specific surface area of the membrane is an important factor affecting the hydrogen permeation rate. How to obtain a palladium membrane with a high specific surface area is a great challenge for material scientists. In this study, a novel template-assisted technique was used to prepare nano-structured palladium membranes with a greatly increased hydrogen contacting surface. First, the anodic aluminum oxide (AAO) template was fabricated by anodizing electro-deposited aluminum film and commercially available aluminum foil. The template was then filled with palladium using the electrochemical and the sputter deposition techniques. Various factors affecting the preparation of the palladium membrane were analyzed and optimized. The preliminary hydrogen-permeation experiments clearly showed that the nano-structured palladium membrane is a promising candidate for the application of hydrogen separation.
Le palladium, étant imperméable à tous les gaz à l’exception de l'hydrogène, a été largement étudié pour l'extraction d'hydrogène dans les dernières années. La surface spécifique de la membrane est un facteur important qui affecte le taux de perméabilité d'hydrogène. Un grand défi pour la communauté scientifique est d’obtenir une membrane en palladium avec une surface spécifique élevée. Dans cette étude, une nouvelle technique utilisant une matrice ordonnée a été employée pour préparer des membranes de palladium nano-structurées avec une surface de contact avec l’hydrogène considérablement accrue.Tout d’abord, l'oxyde d'aluminium anodique (OAA) a été fabriqué en anodisant une couche d’aluminium électro-déposée et un papier d'aluminium commercial. Puis, la matrice d'OAA a été remplie de palladium utilisant la technique électrochimique et la technique par pulvérisation. De divers facteurs affectant la préparation de la membrane de palladium ont été analysés et optimisés. Les expériences préliminaires de la perméabilité d’hydrogène ont clairement prouvé que de telles membranes de palladium sont un candidat prometteur pour l'application de la séparation d'hydrogène.

Organic photovoltaic (OPV) technology has emerged as a potential cost-effective solution to produce electrical energy. The foreseen low manufacturing costs combined with features as semi-transparency or mechanical flexibility give to OPV devices a strong potential for industrial applicability. However, the commercial implementation of this technology faces the challenge of increasing the relatively low power conversion efficiency of the current state-of-the-art OPV devices. This thesis presents an optical based approach to enhance the performance of OPV devices by effectively controlling sunlight photons. Such control is possible because of the coherent interaction between light and the multilayered structure constituting the OPV device. Accordingly, we studied the dependence of the optical field distribution inside the solar cell relative to the optical properties of the different layers including their refractive index , extinction coefficient , and thickness. This optical study led to the prediction of optimal OPV device structures. The first implementation of a photon control was done by changing the relative thicknesses of the different layers in the device. An optimal combination of thicknesses was found and confirmed experimentally. A significant reduction of the energy lost in the device was demonstrated. As a consequence, the photon harvesting improved, which led to a close matching between the external and internal quantum efficiencies in a broad wavelength range. A second photon control strategy to enhance the performance of OPV cells was implemented by modifying the complex refractive index of the nonactive device layers. Both and were changed in specific layers by considering new materials. Three different cases were considered: in the first example a BCP layer was used to replace calcium as electron transporting layer. The parasitic absorption induced by the highly absorptive calcium layer was diminished almost to zero after replacing this layer with BCP, a material whose extinction coefficient is null for a broad wavelength range. A 19% performance enhancement was demonstrated. In the second example, an ultrathin nickel oxide layer was used to replace the commonly used PEDOT layer as hole transporting layer. Very thin layers of nickel oxide could be used for a better photon distribution and harvesting in the photoactive layer. In the last case, a metallic cupper/nickel semi-transparent electrode was used to replace an ITO electrode. This new metallic electrode in combination with the back aluminum electrode enabled the formation of an optical cavity which resulted in a stronger localization of the field in the active layer. Finally, several of the concepts considered above to effectively localize the field in the active layer were used in conjunction with a photonic structure integrated in the OPV architecture to achieve an optically optimized semi-transparent OPV device. In particular, a one-dimensional non-periodic photonic crystal was designed and added to a semi-transparent OPV device in order to re-harvest UV and IR photons while keeping a high transmission for the visible photons. A power conversion efficiency enhancement larger than 56% was achieved while maintaining the device luminosity around 30%. An additional feature of the integration of such photonic crystal was the possibility of tuning the color transmitted by the device which was also demonstrated. In summary, in this thesis we demonstrate experimentally and theoretically that optics plays a very relevant role for enhancing the power conversion efficiency of OPV devices. The methods presented are perfectly compatible with a more oriented material science approach to achieve the final objective of obtaining a performance-competitive OPV technology.
La tecnología fotovoltaica orgánica (OPV) ha surgido como una solución potencial rentable para producir energía eléctrica. Los bajos costos de manufactura previstos combinados con propiedades como semi-transparencia o flexibilidad mecánica le dan a los dispositivos OPV un gran potencial de ser aplicados industrialmente. Sin embargo, la implementación comercial de esta tecnología se enfrenta al reto de incrementar la relativamente baja eficiencia de los dispositivos OPV del estado del arte. Esta tesis presenta una aproximación óptica para aumentar la eficiencia de los dispositivos OPV mediante un control efectivo de los fotones de la radiación solar. Tal control es posible debido a la interacción coherente entre la luz y la estructura de multi-capas que constituye el dispositivo OPV. Consecuentemente, en esta tesis se estudia la dependencia de la distribución del campo óptico dentro de la celda solar con las propiedades ópticas de las diferentes capas. Entre esas propiedades se incluyen el índice de refracción , el coeficiente de extinción y espesor de cada una de las capas. Este estudio óptico ha permitido predecir estructuras óptimas para los dispositivos OPV. La primera implementación del control de fotones fue hecha al cambiar los espesores relativos de las diferentes capas en el dispositivo. Una combinación óptima fue encontrada y confirmada experimentalmente. Una reducción significativa de la energía perdida por reflexión especular fue demostrada y como consecuencia, la recolección de fotones fue mejorada lo cual condujo a la concordancia entre las eficiencias cuánticas externa e internas en un amplio rango de longitudes de onda. Una segunda estrategia de control de fotones para mejorar el desempeño de los dispositivos OPV fue implementada tras modificar las propiedades ópticas de las capas en el dispositivo distintas a la capa activa. Tanto como fueron cambiados en capas específicas tras considerar nuevos materiales. Tres casos diferentes fueron considerados: en el primer caso, una capa de BCP fue usada para reemplazar el calcio como capa transportadora de electrones. La absorción parásita inducida por el elvevado coeficiente de extinción de la capa de calcio fue reducida casi hasta cero tras reemplazar esta capa con una de BCP, un material cuyo coeficiente de absorción es prácticamente cero para un amplio rango de longitudes de onda. Se demostró un aumento en el desempeño de los dispositivos de hasta el 19%. En el segundo ejemplo, una capa ultra-delgada de óxido de níquel fue usada para reemplazar la comúnmente empelada capa de PEDOT como capa transportadora de huecos. Estas capas de óxido de níquel permitieron una mejor distribución y recolección de fotones en la capa foto-activa. En el último caso, un electrodo semi-transparente hecho de cobre/níquel fue usado para reemplazar un electrodo de ITO. Este nuevo electrodo metálico en combinación con el electrodo de aluminio posterior del dispositivo permitió la formación de una cavidad óptica la cual resultó en una mayor localización del campo en la capa activa. Finalmente, varios de los conceptos considerados anteriormente para localizar efectivamente el campo en la capa activa fueron usados en combinación con una estructura fotónica integrada en la estructura para obtener un dispositivo OPV semitransparente ópticamente optimizado. Concretamente, un cristal fotónico unodimensional no-periódico fue diseñado y añadido al dispositivo OPV semi-trasparente con la intención de recolectar fotones UV e IR y al tiempo manteniendo una alta transmisión de los fotones visibles. Una mejora en el desempeño de los dispositivos superior al 56% fue obtenida preservando la luminosidad del dispositivo alrededor del 30%. Una propiedad adicional aportada por la integración de tales cristales fotónicos fue la posibilidad de modular el color transmitido por el dispositivo lo cual fue también demostrado. En síntesis, en esta tesis se demostró experimental y teóricamente que la óptica juega un papel relevante para aumentar la eficiencia de los dispositivos OPV. Los métodos presentados son perfectamente compatibles con la aproximación que se realiza desde la perspectiva de la ciencia de los materiales al objetivo final de obtener una tecnología OPV competitiva.

The spread of bacteria and infections, initially associated with an increased number of hospital-acquired infections, has now extended into the community causing severe and difficult to treat diseases. Additionally, many of those diseases are evoked by bacteria that have become resistant to antibiotics. Overcoming the ability of bacteria to develop resistance will potentially reduce the burden of these infections on the healthcare systems worldwide and prevent thousands of deaths each year. The nano-scale particles are promising candidates to fight bacteria, since developing of resistance to their action is less likely to occur. Nanoparticles (NPs) can be incorporated into polymeric matrices to design a wide variety of nanocomposites. Such nano-structures consisting of inorganic and inorganic/organic NPs represent a novel class of materials with a broad range of applications. This thesis is about the development of antibacterial nano-structured materials aimed at preventing the spread of bacteria. To achieve this, two versatile physicochemical and biotechnological tools, namely sonochemistry and biocatalysis were innovatively combined. Ultrasound irradiation used for the generation of various nano-structures and its combination with biocatalysts (enzymes) opens new perspectives in materials processing, here illustrated by the production of NPs coated medical textiles, water treatment membranes and chronic wound dressings. The first part of the thesis aims at the development of antibacterial medical textiles to prevent the bacteria transmission and proliferation using two single step approaches for antibacterial NPs coating of textiles. In the first approach antibacterial zinc oxide NPs (ZnO NPs) and chitosan (CS) were deposited simultaneously on cotton fabric by ultrasound irradiation. The obtained hybrid NPs coatings demonstrated durable antibacterial properties after multiple washing cycles. Moreover, the presence of biopolymer in the NP hybrids improved the biocompatibility of the material in comparison with ZnO NPs coating alone. In the second approach, a simultaneous sonochemical/enzymatic process for durable antibacterial coating of cotton with ZnO NPs was carried out. The enzymatic treatment provides better adhesion of the ZnO NPs and, as a consequence, enhanced coating stability during exploitation. Likewise to the antibacterial coatings obtained in the first approach, the antibacterial efficiency of these textiles was maintained after multiple intensive laundry regimes used in hospitals. The NPs-coated cotton fabrics inhibited the growth of the most medically relevant bacteria species. In the second part of the thesis, hybrid antibacterial biopolymer/silver NPs and cork matrices, were enzymatically assembled into an antimicrobial material with potential for water remediation. Intrinsically antibacterial amino-functional biopolymers, namely CS and aminocellulose were used as doping agents to stabilize colloidal dispersions of silver NPs (AgNPs), additionally providing the particles with functionalities for covalent immobilization on cork to impart durable antibacterial effect. The biopolymers promoted the antibacterial efficacy of the obtained nanocomposites in conditions simulating a real situation in constructed wetlands. In the last, third part of the thesis, a bioactive nanocomposite hydrogel for wound treatment was developed. Sonochemically synthesized epigallocatechin gallate nanospheres (EGCG NSs) were incorporated and simultaneously crosslinked enzymatically into a thiolated chitosan hydrogel. The potential of the generated material for chronic wound treatment was evaluated by assessing its antibacterial properties and inhibitory effect on myeloperoxidase and collagenase biomarkers of chronic wound infection. Sustained release of the EGCG NSs from the biopolymer matrix was achieved. The latter, coupled with the good biocompatibility of the hydrogel, suggested its potential for chronic wound management.
La propagación de bacterias e infecciones, inicialmente limitada a infecciones adquiridas en el hospital, se ha extendido al resto de la sociedad causando enfermedades muy graves y más difíciles de tratar. Además, muchas de estas enfermedades son provocadas por bacterias que se han hecho resistentes a los antibióticos convencionales. Por lo tanto, limitar la capacidad de estas bacterias para desarrollar resistencia puede potencialmente reducir la alta incidencia de estas infecciones y evitar miles de muertes cada año. Las partículas de escala nanométrica son unas candidatas prometedoras para combatir las bacterias, ya que su mecanismo de acción las hace disminuir las probabilidades en el desarrollo de resistencia. Las nanopartículas (NPs) se pueden incorporar en matrices poliméricas para diseñar una amplia variedad de materiales nanocompuestos. Estas nanoestructuras consisten en NPs orgánicas/inorgánicas e inorgánicas representando una nueva clase de materiales con una amplia gama de aplicaciones. Esta tesis trata sobre el desarrollo de materiales antibacterianos con estructura nanométrica dirigidos a prevenir la propagación de bacterias. Para lograr esto, dos herramientas fisicoquímicas y biotecnológicas versátiles tales como sonoquímica y biocatálisis, se combinaron de manera innovadora. La irradiación por ultrasonido se ha utilizado para la generación de nanoestructuras diversas y su combinación con biocatalizadores (enzimas) abre nuevas perspectivas en el tratamiento de materiales, aquí ilustrados por la producción de textiles médicos recubiertos con NPs, membranas de tratamiento de agua y apósitos para heridas crónicas. La primera parte de la tesis tiene como objetivo el desarrollo de textiles médicos antibacterianos para prevenir la transmisión y proliferación de bacterias utilizando dos estrategias "de un solo paso" para el recubrimiento antibacteriano de estos textiles con NPs. En el primer enfoque NPs antibacterianas de óxido de zinc (ZnO NPs) y quitosano (CS) fueron depositadas simultáneamente sobre tejido de algodón por irradiación de ultrasonido. Los recubrimientos híbridos de NPs obtenidos demostraron propiedades antibacterianas duraderas después de varios lavados exhaustivos. Por otra parte, la presencia de biopolímeros en las NPs híbridas mejoraba la biocompatibilidad del material en comparación con el recubrimiento de solamente de ZnO NPs. En la segunda parte de la tesis, híbridos antibacterianos hechos de biopolímeros y NPs de plata y matrices de corcho, fueron ensamblados enzimáticamente en un material antimicrobiano para su utilización en la remediación de aguas. Biopolímeros antibacterianos aminofuncionalizados (CS y aminocelulosa) se utilizaron como agentes dopantes para estabilizar las dispersiones coloidales de plata (Ag NPs). Además, estas partículas presentan todas las funciones necesarias para su inmovilización covalente en el corcho proporcionando un efecto antibacteriano duradero. Estos biopolímeros aumentaron la eficacia antibacteriana de estos nanocompuestos en condiciones que simulan una situación real en humedales construidos. En la tercera parte de la tesis, se desarrolló un hidrogel nanocompuesto bioactivo para el tratamiento de heridas crónicas. Nanoesferas de galato de epigalocatequina (EGCG NSs) fueron sintetizadas a través de sonoquimica y se incorporaron y simultáneamente reticularon enzimáticamente en un hidrogel de quitosano tiolado. El potencial del material generado para el tratamiento de heridas crónicas fue evaluado por sus propiedades antibacterianas y su efecto inhibidor sobre biomarcadores producidos en heridas crónicas infectadas (mieloperoxidasa y colagenasa). También se consiguió la liberación sostenida de EGCG NSs por parte de la matriz generada, que junto con su buena biocompatibilidad, demostraba su potencial para el tratamiento de heridas crónicas.

The first part of the project focused on the optimization of processes for the preparation of enzyme-containing silicagel nanoparticles and for their coating and stabilization with a polycationic layer. A procedure for coating surfaces with polymer layers was established. Atom transfer radical polymerization was used for the synthesis of a cationic macroinitiator adsorbed on the anionic surface of near-monodisperse silica nanoparticles, used as model for enzyme-containing silicagel nanoparticles. The latter were easily purified via gel filtration, while enzymatic activity was substantially retained during both macroinitiator adsorption and gel filtration. The subsequent growth of water soluble poly (glycerol monomethacrylate) (pGMMA) via ATRP onto coated enzyme-containing silicagel nanoparticles was achieved in a living fashion and with a substantial retention of the activity of encapsulated enzymes. The decoration of the surface with hydrophilic and protein-repellent polymers can provide 'stealth' properties to the supported enzymes, which can be eventually functionalized to obtain more sophisticated biologically responsive nanoparticles.In the second part of the project characterization of nano-structured materials at sub-nanometer resolution was achieved by Atomic Force Spectroscopy (AFM) to probe simultaneously the structure and specific chemical and physical parameters of the system. At the same time, the force-deformation behavior of nano-structured materials subjected to concentrated loads (nanoindentation) yield detailed information and insight about their local mechanical and adhesion properties. In particular, we have focused on the characterization of nanoparticles, surface layers and self-assembled fibrillar materials, combining imaging with a local mechanical (Young's modulus) and physical (adhesion force and surface energy) analysis of the materials.

This thesis describes the design, manufacture and characterisation of thick vacuum plasma sprayed tungsten (W) coatings on steel substrates. Fusion is a potentially clean, sustainable, energy source in which nuclear energy is generated via the release of internal energy from nuclei. In order to fuse nuclei the Coulomb barrier must be breached - requiring extreme temperatures or pressures – akin to creating a ‘star in a box’. Tungsten is a promising candidate material for future fusion reactors due to a high sputtering threshold and melting temperature. However, the large coefficient of thermal expansion mismatch with reactor structural steels such as the low activation steel Eurofer’97 is a major manufacturing and in-service problem. A vacuum plasma spraying approach for the manufacture of tungsten and tungsten/steel graded coatings has been developed successfully. The use of graded coatings and highly textured 3D interface surfi-sculpt substrates has been investigated to allow the deposition of thick plasma sprayed tungsten coatings on steel substrates. Finite element models have been developed to understand the residual stresses that develop in W/steel systems and made use of experimental measurements of coating thermal history during manufacture and elastic moduli measured by nano-indentation. For both the graded and surfi-sculpt coating, the models have been used to understand the mechanism of residual stress redistribution and relief in comparison with simple W on steel coatings, particularly by consideration of stored strain energy. In the case of surfi-sculpt W coatings, the patterned substrate gave rise to regular stress concentrating features, and allowed 2mm thick W coatings to be produced reproducibly without delamination. Preliminary through thickness residual stress measurements were compared to model predictions and provided tentative evidence of significant W coating stress relief by regulated coating segmentation.

Bulk nanostructured silver components were fabricated from nano-sized powder using a shockwave consolidation technique. The grain size evolution during compaction, the mechanical properties of the bulk components, and the effect of surface finish on the mechanical behavior were studied. X-Ray diffraction, transmission electron microscopy (TEM), atomic force microscopy (AFM), microhardness, compression testing and shear punch testing at room temperature were used to characterize the materials. Upon consolidation, the average grain size calculated from image analysis of the TEM micrographs was 49+/-22 nm, showing the feasibility of maintaining a nanostructure upon dynamic consolidation. The hardness of the bulk nanostructured components was constant across the diameter with an average of 83+/-1 HV. Compression results showed strength about 390+/-10 MPa and ductility of 23+/-2%, which is well above strength level obtainable from strain hardened Ag components. The AFM results show that samples possessing a surface roughness of 267 nm exhibited a brittle behavior and a reduction in strength of 35% when compared to the smoother surfaces. Dimples were observed for the samples exhibiting plasticity, while an intergranular pattern was identified for the brittle materials. Fracture toughness of 0.2 MPa m was calculated, which confirms the strong relationship between fracture toughness and defects observed in nanomaterials.

A nano-structured carbon material referred to as Graphene-Carbon Nanotube hybrid is developed for electrochemical energy conversion and storage devices. The hybrid is obtained by catalyst-free growth of free-standing graphene on CNT scaffolds. The hybrid combines the advantageous properties of constituent materials, including an ultra-high density of graphitic edges of graphene and a porous structure of CNTs. As a catalyst support for platinum in PEM fuel cells, the hybrid shows both enhanced catalytic activity and superior stability compared to a commercial carbon black-supported platinum catalyst. The hybrid is also used as a support material for amorphous molybdenum sulfide in supercapacitor and hydrogen evolution reaction catalyst applications. As a supercapacitor electrode material, the hybrid shows high specific capacitance and good stability. As a hydrogen evolution reaction catalyst, the hybrid is one of the most active non-precious catalysts ever reported. FIB-SEM tomography is used to reconstruct the porous 3D structure of carbon electrodes.

This thesis addresses two of the main materials for solar cells, namely silicon and the family of halide perovskites. For silicon, light trapping structures are investigated for solar cell applications while perovskite materials are investigated as a gain material for optoelectronic applications. Light trapping allows the capture of photons that might otherwise be lost, especially at the red end of the spectrum where silicon is less absorptive. The key is to enhance the efficiency of silicon cells by thinning down the wafer and reducing the bulk recombination losses and to achieve a higher Voc while maintaining strong light absorption (represented by a high short circuit current, Jsc) by applying efficient light trapping schemes. It is still an open question whether nanostructures are beneficial for real devices, especially since highly efficient solar cells employ >100 μm thick absorber materials and use wet etched micron-sized pyramids for light trapping. In this thesis, I conduct a study which compares nanostructures and pyramid microstructures on wafer-based silicon solar cells. This study is important because (1) most light trapping nanostructures are investigated only in the optical regime, while I realize them on silicon devices to analyze both their optical and their electrical character; (2) nanostructures perform better than microstructures in wafer based silicon solar cells, highlighting the effectivity of nanostructures even in wafer-based silicon. Here, the nanostructures comprise wet and dry-etched quasi-random structres and they are compared with pyramidal microstructures. A photocurrent as high as 38 mA/cm2 for a dry etched quasirandom nanostructure is attained experimentally, which is 3.2 mA/cm2 higher than wet etched pyramids fabricated in the same batch. The other material which is now becoming very popular in the solar cell community is the family of metal halide perovskite materials that are increasingly attracting the attention of optoelectronics researchers, both for solar cell and for light emission applications. The ultimate is in simplicity, however, is to observe lasing from a continuous thin film, which has not been aimed before. Here, I show perovskite random lasers; they are deposited at room temperature on unpatterned glass substrates and they exhibit a minimum threshold value of 10 μJ/cm2. A rather special feature is that some of the films exhibit single and dual mode lasing action, which is rarely observed in random lasers. This work fully exploits the simplicity of the solution-based process and thereby adds an important capability to the emerging field of perovskite-based light emitters.

Doutoramento em Ciência e Engenharia de Materiais
This work is about the combination of functional ferroelectric oxides with Multiwall Carbon Nanotubes for microelectronic applications, as for example potential 3 Dimensional (3D) Non Volatile Ferroelectric Random Access Memories (NVFeRAM). Miniaturized electronics are ubiquitous now. The drive to downsize electronics has been spurred by needs of more performance into smaller packages at lower costs. But the trend of electronics miniaturization challenges board assembly materials, processes, and reliability. Semiconductor device and integrated circuit technology, coupled with its associated electronic packaging, forms the backbone of high-performance miniaturized electronic systems. However, as size decreases and functionalization increases in the modern electronics further size reduction is getting difficult; below a size limit the signal reliability and device performance deteriorate. Hence miniaturization of siliconbased electronics has limitations. On this background the Road Map for Semiconductor Industry (ITRS) suggests since 2011 alternative technologies, designated as More than Moore; being one of them based on carbon (carbon nanotubes (CNTs) and graphene) [1]. CNTs with their unique performance and three dimensionality at the nano-scale have been regarded as promising elements for miniaturized electronics [2]. CNTs are tubular in geometry and possess a unique set of properties, including ballistic electron transportation and a huge current caring capacity, which make them of great interest for future microelectronics [2]. Indeed CNTs might have a key role in the miniaturization of Non Volatile Ferroelectric Random Access Memories (NVFeRAM). Moving from a traditional two dimensional (2D) design (as is the case of thin films) to a 3D structure (based on a tridimensional arrangement of unidimensional structures) will result in the high reliability and sensing of the signals due to the large contribution from the bottom electrode. One way to achieve this 3D design is by using CNTs. Ferroelectrics (FE) are spontaneously polarized and can have high dielectric constants and interesting pyroelectric, piezoelectric, and electrooptic properties, being a key application of FE electronic memories. However, combining CNTs with FE functional oxides is challenging. It starts with materials compatibility, since crystallization temperature of FE and oxidation temperature of CNTs may overlap. In this case low temperature processing of FE is fundamental. Within this context in this work a systematic study on the fabrication of CNTs - FE structures using low cost low temperature methods was carried out. The FE under study are comprised of lead zirconate titanate (Pb1-xZrxTiO3, PZT), barium titanate (BaTiO3, BT) and bismuth ferrite (BiFeO3, BFO). The various aspects related to the fabrication, such as effect on thermal stability of MWCNTs, FE phase formation in presence of MWCNTs and interfaces between the CNTs/FE are addressed in this work. The ferroelectric response locally measured by Piezoresponse Force Microscopy (PFM) clearly evidenced that even at low processing temperatures FE on CNTs retain its ferroelectric nature. The work started by verifying the thermal decomposition behavior under different conditions of the multiwall CNTs (MWCNTs) used in this work. It was verified that purified MWCNTs are stable up to 420 ºC in air, as no weight loss occurs under non isothermal conditions, but morphology changes were observed for isothermal conditions at 400 ºC by Raman spectroscopy and Transmission Electron Microscopy (TEM). In oxygen-rich atmosphere MWCNTs started to oxidized at 200 ºC. However in argon-rich one and under a high heating rate MWCNTs remain stable up to 1300 ºC with a minimum sublimation. The activation energy for the decomposition of MWCNTs in air was calculated to lie between 80 and 108 kJ/mol. These results are relevant for the fabrication of MWCNTs – FE structures. Indeed we demonstrate that PZT can be deposited by sol gel at low temperatures on MWCNTs. And particularly interesting we prove that MWCNTs decrease the temperature and time for formation of PZT by ~100 ºC commensurate with a decrease in activation energy from 68±15 kJ/mol to 27±2 kJ/mol. As a consequence, monophasic PZT was obtained at 575 ºC for MWCNTs - PZT whereas for pure PZT traces of pyrochlore were still present at 650 ºC, where PZT phase formed due to homogeneous nucleation. The piezoelectric nature of MWCNTs - PZT synthesised at 500 ºC for 1 h was proved by PFM. In the continuation of this work we developed a low cost methodology of coating MWCNTs using a hybrid sol-gel / hydrothermal method. In this case the FE used as a proof of concept was BT. BT is a well-known lead free perovskite used in many microelectronic applications. However, synthesis by solid state reaction is typically performed around 1100 to 1300 ºC what jeopardizes the combination with MWCNTs. We also illustrate the ineffectiveness of conventional hydrothermal synthesis in this process due the formation of carbonates, namely BaCO3. The grown MWCNTs - BT structures are ferroelectric and exhibit an electromechanical response (15 pm/V). These results have broad implications since this strategy can also be extended to other compounds of materials with high crystallization temperatures. In addition the coverage of MWCNTs with FE can be optimized, in this case with non covalent functionalization of the tubes, namely with sodium dodecyl sulfate (SDS). MWCNTs were used as templates to grow, in this case single phase multiferroic BFO nanorods. This work shows that the use of nitric solvent results in severe damages of the MWCNTs layers that results in the early oxidation of the tubes during the annealing treatment. It was also observed that the use of nitric solvent results in the partial filling of MWCNTs with BFO due to the low surface tension (<119 mN/m) of the nitric solution. The opening of the caps and filling of the tubes occurs simultaneously during the refluxing step. Furthermore we verified that MWCNTs have a critical role in the fabrication of monophasic BFO; i.e. the oxidation of CNTs during the annealing process causes an oxygen deficient atmosphere that restrains the formation of Bi2O3 and monophasic BFO can be obtained. The morphology of the obtained BFO nano structures indicates that MWCNTs act as template to grow 1D structure of BFO. Magnetic measurements on these BFO nanostructures revealed a week ferromagnetic hysteresis loop with a coercive field of 956 Oe at 5 K. We also exploited the possible use of vertically-aligned multiwall carbon nanotubes (VA-MWCNTs) as bottom electrodes for microelectronics, for example for memory applications. As a proof of concept BiFeO3 (BFO) films were in-situ deposited on the surface of VA-MWCNTs by RF (Radio Frequency) magnetron sputtering. For in situ deposition temperature of 400 ºC and deposition time up to 2 h, BFO films cover the VA-MWCNTs and no damage occurs either in the film or MWCNTs. In spite of the macroscopic lossy polarization behaviour, the ferroelectric nature, domain structure and switching of these conformal BFO films was verified by PFM. A week ferromagnetic ordering loop was proved for BFO films on VA-MWCNTs having a coercive field of 700 Oe. Our systematic work is a significant step forward in the development of 3D memory cells; it clearly demonstrates that CNTs can be combined with FE oxides and can be used, for example, as the next 3D generation of FERAMs, not excluding however other different applications in microelectronics.
Este trabalho é sobre a combinação de óxidos ferroelétricos funcionais com nanotubos de carbono (CNTs) para aplicações na microeletrónica, como por exemplo em potenciais memórias ferroelétricas não voláteis (Non Volatile Ferroelectric Random Access Memories (NV-FeRAM)) de estrutura tridimensional (3D). A eletrónica miniaturizada é nos dias de hoje omnipresente. A necessidade de reduzir o tamanho dos componentes eletrónicos tem sido estimulada por necessidades de maior desempenho em dispositivos de menores dimensões e a custos cada vez mais baixos. Mas esta tendência de miniaturização da eletrónica desafia consideravelmente os processos de fabrico, os materiais a serem utilizados nas montagens das placas e a fiabilidade, entre outros aspetos. Dispositivos semicondutores e tecnologia de circuitos integrados, juntamente com a embalagem eletrónica associada, constituem a espinha dorsal dos sistemas eletrónicos miniaturizados de alto desempenho. No entanto, à medida que o tamanho diminui e a funcionalização aumenta, a redução das dimensões destes dipositivos é cada vez mais difícil; é bem conhecido que abaixo de um tamanho limite o desempenho do dispositivo deteriora-se. Assim, a miniaturização da eletrónica à base de silício tem limitações. É precisamente neste contexto que desde 2011 o Road Map for Semiconductor Industry (ITRS) sugere tecnologias alternativas às atualmente em uso, designadas por Mais de Moore (More than Moore); sendo uma delas com base em carbono (CNTs e grafeno) [1]. Os CNTs com o seu desempenho único e tridimensionalidade à escala nanométrica, foram considerados como elementos muito promissores para a eletrónica miniaturizada [2]. Nanotubos de carbono possuem uma geometria tubular e um conjunto único de propriedades, incluindo o transporte balístico de eletrões e uma capacidade enorme de transportar a corrente elétrica, o que os tornou de grande interesse para o futuro da microeletrónica [2]. Na verdade, os CNTs podem ter um papel fundamental na miniaturização das memórias ferroelétricas não voláteis (NV-FeRAM). A mudança de uma construção tradicional bidimensional (2D) (ou seja, a duas dimensões, como são os filmes finos) para uma construção tridimensional 3D, com base num arranjo tridimensional de estruturas unidimensionais (1D), como são as estruturas nanotubulares, resultará num desempenho melhorado com deteção de sinal elétrico optimizada, devido à grande contribuição do elétrodo inferior. Uma maneira de conseguir esta configuração 3D é usando nanotubos de carbono. Os materiais ferroelétricos (FE) são polarizados espontaneamente e possuem constantes dielétricas altas e as suas propriedades piroelétricas, piezoelétricas e eletroópticas tornam-nos materiais funcionais importantes na eletrónica, sendo uma das suas aplicações chave em memórias eletrónicas. No entanto, combinar os nanotubos de carbono com óxidos FE funcionais é um desafio. Começa logo com a compatibilidade entre os materiais e o seu processamento, já que as temperaturas de cristalização do FE e as temperaturas de oxidação dos CNTs se sobrepõem. Neste caso, o processamento a baixa temperatura dos óxidos FE é absolutamente fundamental. Dentro deste contexto, neste trabalho foi realizado um estudo sistemático sobre a fabricação e caracterização estruturas combinadas de CNTs – FE, usando métodos de baixa temperatura e de baixo custo. Os FE em estudo foram compostos de titanato zirconato de chumbo (Pb1-xZrxTiO3, PZT), titanato de bário (BaTiO3, BT) e ferrite de bismuto (BiFeO3, BFO). Os diversos aspetos relacionados com a síntese e fabricação, como efeito sobre a estabilidade térmica dos nanotubos de carbono multiparede (multiwall CNTs, MWCNTs), formação da fase FE na presença de MWCNTs e interfaces entre CNTs / FE foram abordados neste trabalho. A resposta ferroelétrica medida localmente através de microscopia de ponta de prova piezoelétrica (Piezoresponse Force Microscopy (PFM)), evidenciou claramente que, mesmo para baixas temperaturas de processamento óxidos FE sobre CNTs mantém a sua natureza ferroelétrica. O trabalho começou pela identificação do comportamento de decomposição térmica em diferentes condições dos nanotubos utilizados neste trabalho. Verificou-se que os MWCNTs purificados são estáveis até 420 ºC no ar, já que não ocorre perda de peso sob condições não isotérmicas, mas foram observadas, por espectroscopia Raman e microscopia eletrónica de transmissão (TEM), alterações na morfologia dos tubos para condições isotérmicas a 400 ºC. Em atmosfera rica em oxigénio os MWCNTs começam a oxidar-se a 200 ºC. No entanto, em atmosfera rica em árgon e sob uma taxa de aquecimento elevada os MWCNTs permanecem estáveis até 1300 ºC com uma sublimação mínima. A energia de ativação para a decomposição destes MWCNTs em ar foi calculada situar-se entre 80 e 108 kJ / mol. Estes resultados são relevantes para a fabricação de estruturas MWCNTs - FE. De facto, demonstramos que o PZT pode ser depositado por sol-gel a baixas temperaturas sobre MWCNTs. E, particularmente interessante foi provar que a presença de MWCNTs diminui a temperatura e tempo para a formação de PZT, em cerca de ~ 100 ºC comensuráveis com uma diminuição na energia de ativação de 68 ± 15 kJ / mol a 27 ± 2 kJ / mol. Como consequência, foi obtido PZT monofásico a 575 ºC para as estruturas MWCNTs – PZT, enquanto que para PZT (na ausência de MWCNTs) a presença da fase de pirocloro era ainda notória a 650 ºC e onde a fase de PZT foi formada por nucleação homogénea. A natureza piezoelétrica das estruturas de MWCNTs - PZT sintetizadas a 500 ºC por 1 h foi provada por PFM. Na continuação deste trabalho foi desenvolvida uma metodologia de baixo custo para revestimento de MWCNTs usando uma combinação entre o processamento sol – gel e o processamento hidrotermal. Neste caso o FE usado como prova de conceito foi o BT. BT é uma perovesquita sem chumbo bem conhecida e utilizada em muitas aplicações microeletrónicas. No entanto, a síntese por reação no estado sólido é normalmente realizada entre 1100 - 1300 ºC o que coloca seriamente em risco a combinação com MWCNTs. Neste âmbito, também se ilustrou claramente a ineficácia da síntese hidrotérmica convencional, devido à formação de carbonatos, nomeadamente BaCO3. As estruturas MWCNTs - BT aqui preparadas são ferroelétricas e exibem resposta electromecânica (15 pm / V). Considera-se que estes resultados têm impacto elevado, uma vez que esta estratégia também pode ser estendida a outros compostos de materiais com elevadas temperaturas de cristalização. Além disso, foi também verificado no decurso deste trabalho que a cobertura de MWCNTs com FE pode ser optimizada, neste caso com funcionalização não covalente dos tubos, ou seja, por exemplo com sodium dodecyl sulfate (SDS).

Nowadays, the ability to pattern surfaces on the micro- and nano- scale is the basis for a wide range of research fields. Over last few decades, a lot of processing technologies offer the possibility to fabricate complex 2D and 3D polymeric designs which are mostly static in nature since they cannot be physically and chemically modified once fabricated. The aim of the present thesis is to overcome such a limitation, exploiting stimuli-responsive materials (Chapter I). We allow to engineer polymeric architectures adding interesting functionalities, by providing an active manipulation of pre-structured systems, which could be helpfully in a wide variety of applications, such as biosensing and cell conditioning. In the first part of the present dissertation (Chapter II), a thermos-sensitive material is employed. We investigate the thermo-responsive behavior of Poly(N-isopropylacrylamide) (pNIPAAm)-based crosslinkable hydrogel as active binding matrix in optical biosensors. In this study, we propose an extension of surface plasmon resonance (SPR) and optical waveguide mode (OWS) spectroscopy, for in situ observation of nano-patterned hydrogel film that are allowed to swell and collapse by varying the external temperature of the aqueous environment. Weak refractive index contrast of hydrogel structures arranged in periodic pattern, is generally associated with intrinsically low diffraction efficiency. In order to enhance the intensity of diffracted light, the surface is probed by resonantly excited optical waveguide modes, taking advantage of the fact that the hydrogel can serve as optical waveguide (HOW) enabling the excitation of additional modes besides surface plasmons. Thus, we provide a hydrogel optical waveguide-enhanced diffraction measurements, taking advantage of strong electromagnetic field intensity enhancements that amplifies the weak diffracted light intensity. The main part of the thesis is focused in the study of azopolymer-containing materials, a specific class of light-responsive materials. Upon photon absorption, azobenzene undergo reversible trans-cis photoisomerization, which induces a substantial geometrical change of its molecular structure, that can be translated into larger-scale movements of the material below the glass transition temperature (Tg) of the polymer. In Chapter III, by exploiting the light-induced mass migration phenomenon, we demonstrate that an azopolymeric film patterned by soft imprinting technique, can be anisotropically deformed and consequent restored in its initial shape via single irradiation just by controlling the polarization state of the incident laser beam. We also propose that the light-driven morphological manipulation can induce anisotropic wettability changes. Lastly, a polarization driven birefringence effect on flat and structured surfaces is discussed. Chapter IV focuses in the design of novel azopolymeric systems, where the optical response is provided by azobenzene molecules, which doped two different host materials. The photo-responsive behavior and potential applications of azo compounds incorporated into either a soft elastomeric and in rigid matrix is discussed. Azo-embedded poly(dimethylsiloxane) (PDMS) is studied as tunable optical lens and an azo-doped photocurable commercial polymeric resin is developed to study the photo-mechanical transduction of a 3D suspended membrane fabricated by two photon lithography technique. In Chapter V, we propose a light-deformable azopolymeric micro-pillars patterned substrate as a biocompatible and “smart” platform for dynamic material-cell observation in 2D environment, modified by a holographic optical conditioning. The aim is to observe by time-lapse acquisitions, how an in situ deformation of a pre-patterned structure can influence cell functions and fate. Finally, in Chapter VI, general remarks of the present work are discussed, and directions for future perspective are summarized.

Light manipulation is an important method to enhance the light-matter interactions in micro and nano photonic materials and structures by generating usefulelectric field components and increasing time and pathways of light propagationthrough the micro and nano materials and structures. For example, quantum wellinfrared photodetector (QWIP) cannot absorb normal incident radiation so thatthe generation of an electric field component which is parallel to the original incident direction is a necessity for the function of QWIP. Furthermore, the increaseof time and pathways of light propagation in the light-absorbing quantum wellregion will increase the chance of absorbing the photons.The thesis presents the theoretical studies of light manipulation and light-matter interaction in micro and nano photonic materials and structures, aiming atimproving the performance of optical communication devices, photonic integrateddevices and photovoltaic devices.To design efficient micro and nano photonic devices, it is essential to knowthe time evolution of the electromagnetic (EM) field. Two-dimensional and three-dimensional finite-difference time-domain (FDTD) methods have been adopted inthe thesis to numerically solve the Maxwell equations in micro and nano photonicmaterials and structures.Light manipulation in micro and nano material and structures studied in thisthesis includes: (1) light transport in the photonic crystal (PhC) waveguide, (2)light diffraction by the micro-scale dielectric PhC and metallic PhC structures(gratings); and (3) exciton-polaritons of semiconductor quantum dots, (4) surfaceplasmon polaritons at semiconductor-metallic material interface for subwavelengthlight control. All these aspects are found to be useful in optical devices of multiplebeam splitter, quantum well/dot infrared photodetectors, and solar cells.
QC 20120507

Nanostructured materials have attracted a broad interest for applications in scientific and engineering fields due to their extraordinary properties stemming from the nanoscale dimensions. This dissertation presents the development of nanomaterials used for different applications, namely biomedicine and dye lasing. Various inorganic nanoparticles have been developed as contrast agents for non-invasive medical imaging, such as magnetic resonance imaging (MRI) and X-ray computed tomography (CT), owing to their unique properties for efficient contrasting effect. Superparamagnetic iron oxide nanoparticles (SPIONs) are synthesized by thermo-decomposition method and phase-transferred to be hydrophilic used as MRI T2 (negative) contrast agents. Effects of surface modification of SPIONs by mesoporous silica (mSiO2) coating have been examined on the magnetic relaxivities. These contrast agents (Fe3O4@mSiO2) were found to have a coating-thickness dependent relaxation behavior and exhibit much higher contrast efficiency than that for the commercial ones. By growing thermo-sensitive poly(N-isopropylacrylamide -co-acrylamide) (P(NIPAAm-co-AAm)) as the outermost layer on Fe3O4@mSiO2 through free radical polymerization, a multifunctional core-shell nano-composite has been built up. Responding to the temperature change, these particles demonstrate phase transition behavior and were used for thermo-triggered magnetic separation. Their lower critical solution temperature (LCST) can be subtly tuned from ca. 34 to ca. 42 ˚C, suitable for further in vivo applications. An all-in-one contrast agent for MRI, CT and fluorescence imaging has been synthesized by depositing gadolinium oxide carbonate hydrate [Gd2O(CO3)2·H2O] shell on mSiO2-coated gold nanorod (Au NR), and then the particles were grafted with antibiofouling copolymer which can further link with the fluorescent dye. It shows both a higher CT and MRI contrast than the clinical iodine and gadolinium chelate contrast agent, respectively. Apart from the imaging application, owing to the morphology of Au NR, the particle has a plasmonic property of absorbing near-infrared (NIR) irradiation and suitable for future photothermal therapy. Cytotoxicity and biocompatibility of aforementioned nanoparticles have been evaluated and minor negative effects were found, which support their further development for medical applications. Gold nanoparticles embedded in the optical gain material, water solution of Rhodamine 6G (Rh6G) in particular, used in dye lasers can both increase and damp the dye fluorescence, thus, changing the laser output intensity. The studies of size effect and coating of gold nanoparticles on photostability of the gain media reveal that small sized (ca. 5.5 nm) gold nanoparticles are found detrimental to the photostability, while for the larger ones (ca. 25 nm) fluorescence enhancement rather than quenching is likely to occur. And a noticeable improvement of the photostability for the gain material is achieved when gold is coated with SiO2.
QC 20120605

L'accroissement des fonctionnalités dans les appareils électroniques portables a pour conséquence des besoins de plus en plus importants en énergie et en puissance dans un espace limité. Les micro-batteries Li-ion sont les sources d'énergie les plus utilisées de nos jours. Mais ses inconvénients sont une faible tenue en puissance, une durée de vie limitée et une gamme de température restreinte. Micro-supercapacités à base de carbone, d'autre part, sont capables de fournir de l'énergie en peu de temps, offrant ainsi une forte puissance, de travailler à basse température avec une durée de vie illimitée. Cette thèse propose plusieurs micro-supercondensateurs à base de carbone, d'être intégrés sur un substrat de silicium avec d'autres composants de l'électronique ou des capteurs. Ils ont suscités beaucoup d'intérêt comme un remplacement potentiel ou effectif de micro-batteries, ou comme complément de ces mêmes micro-batteries permettant l'amélioration globale des performances du système d'alimentation. Le travail de thèse se concentre principalement sur les matériaux et les technologies adaptées pour permettre à la réalisation des micro-supercondensateurs. Deux types de micro-supercondensateurs sur puce avec motifs interdigitées ont été développés: l'un préparé par dépôt électrophorétique (EPD) de poudres de carbone ou nous étudierons la combinaison entre des matériaux de carbone de différentes natures et différents types d'électrolytes, l'autre par la chloration de carbure film en carbone (TiC-CDC ou SiC-CDC) sur la puce en silicium avec différentes techniques de microfabrication. Micro-supercondensateur à base de oignons de carbone par EPD montre une excellente capacité en puissance (vitesse de balayage allant jusqu'à 100 V / s) dans l'électrolyte organique, et une large gamme de température (50 ° C - 80 ° C) dans un mélange eutectique liquide ionique. Différentes techniques pour structurer les films de carbure ont été développées pour fabriquer un micro-supercondensateur à base de CDC: gravure ionique réactive (RIE) ou faisceau d'ions focalisé (FIB). Micro-supercondensateurs à base de films TiC-CDC montrent des résultats préliminaires prometteurs. Les technologies développées ouvrent la voie à une intégration pleine et effective des dispositifs de stockage d'énergie micro-taille sur-puce
The increasing number of functions in portable electronic devices requires more and more energy and power within a limited space. Li-ion thin film or so-called micro-batteries are the current solution for power supply. Drawbacks of these storage elements are poor power performance with limited life-span and temperature range. Carbon-based micro- supercapacitors, on the other hand, are able to deliver energy in short time, thus offering high power capability, to work at low temperature and they present an unlimited life-span. This thesis proposes several carbon-based micro-supercapacitors, to be integrated on a silicon substrate together with other electronics components or sensors. They are foreseen as a potential replacement or complement of Li-ion micro-batteries to enhance the total performance of the whole power source system. The thesis work is mainly focused on adapted materials and technologies for enabling micro-supercapacitors realization. Two types of on-chip micro-supercapacitors with planar interdigitated electrodes configuration were developed: one prepared from Electrophoretic deposition (EPD) and its combination of different carbon materials and different types of electrolytes, the other from patterned titanium or silicon carbide derived carbon film (TiC-CDC or SiC-CDC) on Si chip with different microfabrication techniques. Onion like carbon-based micro-supercapacitor by EPD shows high power delivery (scan rate up to 100V/s) in organic electrolyte, and high temperature range (-50 °C - 80 °C) in a eutectic mixture of ionic liquids. Different techniques for patterning carbide films have been developed to fabricate a CDC based micro- supercapacitor: reactive ion etching (RIE) or focused ion beam (FIB). TiC-CDC film based micro-supercapacitors show promising preliminary results. The developed technologies pave the way to a full and effective integration of micro-size energy storage devices on-chip

In this dissertation, simulation techniques are used to understand the role of surfaces, interfaces, and capillary forces on the deformation response of bicontinuous metallic composites and porous materials. This research utilizes atomistic scale modeling to study nanoscale deformation phenomena with time and spatial resolution not available in experimental testing. Molecular dynamics techniques are used to understand plastic deformation of metallic bicontinuous lattices with varying solid volume fraction, connectivity, size, surface stress, loading procedures, and solid density. Strain localization and yield response on nanoporous gold lattices as a function of their solid volume fraction are investigated in axially strained periodic samples with constant average ligament diameter. Simulation stress results revealed that yield response was significantly lower than what can be expected form the Gibson-Ashby formalism for predicting the yield response of macro scale foams. It was found that the number of fully connected ligaments contributing to the overall load bearing structure decreased as a function of solid volume fraction. Correcting for this with a scaling factor that corrects the total volume fraction to "connected, load bearing" solid fraction makes the predictions from the scaling equations more realistic. The effects of ligament diameter in nanoporous lattices on yield and elastic response in both compressive and tensile loading states are reported. Yield response in compression and tension is found to converge for the two deformation modes with increasing ligament diameter, with the samples consistently being stronger in tension, but weaker in compression. The plastic response results are fit to a predictive model that depends on ligament size and surface parameter (f). A modification is made to the model to be in terms of surface area to volume ratio (S/V) rather than ligament diameter (1/d) and the response from capillary forces seems to be more closely modeled with the full surface stress parameter rather than surface energy. Fracture response of a nanoporous gold structure is also studied, using the stress intensity-controlled equations for deformation from linear elastic fracture mechanics in combination with a box of atoms, whose interior is governed by the molecular dynamics formalism. Mechanisms of failure and propagation, propagation rate, and ligament-by-ligament deformation mechanisms such as dislocations and twin boundaries are studied and compared to a corresponding experimental nanoporous gold sample investigated via HRTEM microscopy. Stress state and deformation behavior of individual ligaments are compared to tensile tests of cylinder and hyperboloid nanowires with varying orientations. The information gathered here is used to successfully predict when and how ligaments ahead of the crack tip will fracture. The effects of the addition of silver on the mechanical response of a nanoporous lattice in uniaxial tension and compression is also reported. Samples with identical morphology to the study of the effects of ligament diameter are used, with varying random placement concentrations of silver atoms. A Monte Carlo scheme is used to study the degree of surface segregation after equilibration in a mixed lattice. Dislocation behavior and deformation response for all samples in compression and tension are studied, and yield response specifically is put in the context of a surface effect model. Finally, a novel bicontiuous fully phase separated Cu-Mo structure is investigated, and compared to a morphologically similar experimental sample. Composite interfacial energy and interface orientation structure are studied and compared to corresponding experimental results. The effect of ligament diameter on mechanical response in compressive stress is investigated for a singular morphology, stress distribution by phase is investigated in the context of elastic moduli calculated from the full elastic tensor and pure elemental deformation tests. Dislocation evolution and its effects on strain hardening are put in the context of elastic strain, and plastic response is investigated in the context of a confined layer slip model for emission of a glide loop. The structure is shown to be an excellent, low interface energy model that can arrest slip plane formation while maintaining strength close to the theoretical prediction. Dislocation content in all samples was quantified via the dislocation extraction algorithm. All visualization, phase dependent stress analysis, and structural/property analysis was conducted with the OVITO software package, and its included python editor. All simulations were conducted using the LAMMPS molecular dynamics simulation package. Overall, this dissertation presents insights into plastic deformation phenomena for nano-scale bicontinuous metallic lattices using a combination of experimentation and simulation. A more holistic understanding of the mechanical response of these materials is obtained and an addition to the theory concerning their mechanical response is presented.
Doctor of Philosophy
Crystalline metals can be synthesized to have a sponge-like structure of interconnected ligaments and pores which can drastically change the way that the material chemically interacts with its environment, such as how readily it can absorb oxygen and hydrogen ions. This makes it attractive as a catalyst material for speeding up or altering chemical reactions. The change in structure can also drastically change how the material responds when deformed by pressing, pulling, tearing or shearing, which are important phenomena to understand when engineering new technology. High surface or interface area to volume ratios can cause a massive surface-governed capillary force (the same force that causes droplets of water to bead up on rain coat) and lead to a higher pressure within the material. The effect that both structure and capillary forces have on the way these materials react when deformed has not been established in the context of capillary force theory or crystalline material plasticity theory. For this reason, we investigate these materials using simulation methods at the atomic level, which can give accurate and detailed data on the stress and forces felt atom-by-atom in a material, as well as defects in the material, such as dislocations and vacancies, which are the primary mechanisms that cause the crystal lattice to permanently deform and ultimately break. A series of parameters are varied for multiple model systems to understand the effects of various scenarios, and the understanding provided by these tests is presented.

Nous avons développé une nouvelle méthode de microscopie par effet électro-optique linéaire (effet Pockels), dite PLEOM, permettant de cartographier la susceptibilité du deuxième ordre Chi(2) d'un matériau non-centrosymétrique [1, 2]. Cette méthode est complémentaire de la microscopie de génération de seconde harmonique, et s’en distingue par différents aspects physiques et pratiques. Grâce à une détection interférométrique stabilisée, le retard de phase provoqué par une variation d'indice locale du matériau non-linéaire sous l'effet d'un champ électrique est détecté à 10-6 radians près, ouvrant la voie à l'imagerie d'échantillons biologiques ou au suivi du mouvement de nano-sondes [3]. PLEOM apporte un type de données nouveau, la "réponse en phase" du matériau, porteuse d'information physiques plus difficilement accessibles en microscopie biphotonique.Ce manuscrit décrit de nouveaux domaines de développement et d’application de PLEOM, qui a évolué vers une plateforme aux applications variées et multi-échelles, allant du nanométrique au millimétrique.Nous avons tout d’abord montré comment déterminer le vecteur de polarisation attaché à des nano-cristaux ferroélectriques uniques, en vue de leur utilisation comme nano-sondes. Cette nouvelle méthode permet, à notre connaissance de façon unique, de distinguer deux nano-cristaux mono-domaines d'orientations exactement opposées, dont les réponses en SHG ne peuvent pas être distinguées. Une image de phase électro-optique, combinée à un diagramme de polarisation, donne accès à l'orientation vectorielle d'un nano-cristal orienté aléatoirement dans le référentiel du laboratoire. Un verrou est ainsi levé pour des applications comme l'imagerie de nano-domaines ferroélectriques, celle de potentiels électrochimiques membranaires, où l'étude de la dynamique de rotation de molécules. Deux spécificités remarquables de PLEOM en font une méthode d'avenir : la faible intensité de pompage qui assure une bien meilleure biocompatibilité ainsi que la simplicité de la source laser continue utilisée.Nous avons ainsi pu utiliser PLEOM pour caractériser les domaines ferroélectriques d'un cristal de KTiOPO4 périodiquement réorienté en vue d’un quasi-accord de phase, ainsi que ceux d'un cristal bidimensionnel quasi-périodique de LiNbO3. Un retournement clair de la phase de 180 degree est observé au travers des parois de domaines, dont les coefficients électro-optiques apparaissent opposés dans le référentiel du laboratoire. PLEOM se présente ainsi comme un outil de caractérisation non destructif des propriétés de ces cristaux artificiels dont les motifs et les défauts (tels qu'une orientation localement incomplète) ont été caractérisés spatialement, et permet de mesurer localement leurs propriétés non-linéaires, dont le caractère tensoriel permet d’aller au-delà des informations acquises en microscopie classique.En outre, nous avons fait la preuve de principe d'une nouvelle expérience biomimétique, visant à étudier les potentiels membranaires cellulaires, en utilisant PLEOM sur des membranes phospholipidiques créées sur puce micro-fluidique et dopées en colorants
Complementing Second-Harmonic Generation (SHG) microscopy, a new home-made nonlinear microscope named Pockels Linear Electro-Optical Microscopy (PLEOM) based on the linear electrooptic (Pockels) effect, has been developed and used to map the second-order susceptibility Chi(2) of non-centrosymmetric materials with high sensitivity due to a stabilized interferometric homodyne detection scheme [1, 2]. This enables PLEOM to detect the electrooptic phase retardation of light resulting from the variation of the refractive index of nonlinear materials down to 10-6 radian and to investigate nonlinear materials at the nano-scale [3] towards applications in imaging of biological samples and tracking of labels therein. With PLEOM, a new imaging method allows to access, besides the aplitude, the no less crucial phase response, which is not readily amenable to classical SHG microscopy. In the frame of this dissertation, we have further extended the range of applications of PLEOM to investigate nonlinear materials and structures from nano- to millimeter-scale.Firstly, we have proposed and demonstrated a new approach towards the full vector determination of the spontaneous polarization of single ferroelectric nano-crystals used as SHG nano-probes. This method allows to remove the ambiguity inherent to earlier polarization-resolved SHG microscopy experiments, and has permitted full determination of the orientation of single domain ferroelectric nano-crystals. The electrooptic phase response obtained in the form of phase images and polarization diagrams yields the full orientation in the laboratory frame of randomly dispersed single nano-crystals, together with their electric polarization dipole. The complete vector determination of the dipole orientation is a prerequisite to important applications including ferroelectric nano-domain orientation, membrane potential imaging and rotation dynamics of single biomolecules, especially by using a new low-cost non-invasive imaging method with a low intensity illumination beam.The ferroelectric domain pattern of periodically poled KTiOPO4 and of a two-dimensional decagonal quasi-periodic LiNbO3 nonlinear crystal was determined by local measurement of their electro-optically induced phase retardation. Owing to the sign reversal of the electrooptic coefficients upon domain inversion, a 180 degree (pi) phase shift is observed across domain barriers between domains with opposed orientations. PLEOM allows to reveal the nonlinear and electrooptic spatially modulated patterns in ferroelectric crystals in a non-destructive manner and to determine their poling period, duty cycle and short-range order as well as to detect local defects in the domain structure, such due to incomplete poling.In addition, we have also proposed and demonstrated a new method, based on the voltage dependence of the electrooptic dephasing, to mimic the membrane potential in cells, working at this stage on nonlinear dye containing phospholipidic membranes, grown in a microfluidic set-up

In this project, nano powder of CoSb3 thermoelectric material was synthesized using chemical alloying novel co-precipitation method. This method involved co-precipitation of TE precursor compounds in controlled pH aqueous solutions followed by thermo-chemical treatments including calcination and reduction to produce nano-particulates of CoSb3. The nano powder was consolidated using rapid solid state spark plasma sintering (SPS) and the processing time was of the order of few minutes. On a result very high densities were achieved and grain growth was almost negligible. Various batches of the CoSb3 nano powder were produced to achieve high purity, minimum particle size and compensate Sb evaporation during thermo-chemical reduction. For de-agglomeration, powder was grinded before and after calcination. Samples were characterized at each stage during synthesis using XRD and SEM (with EDX). Thermal gravimetric analysis (TGA) was done before thermochemical treatments to observe weight losses with heating the powder at high temperatures and other physiochemical changes. Thermal diffusivity of the samples was measured at room temperature using Laser Flash Apparatus (LFA) and heat capacity was measured using Differential Scanning Calorimetry (DSC).   Thermal conductivities are calculated using these thermal diffusivities, heat capacities and densities of the sintered pellets. Average grain size is measure using image size J software. It was observed that powder purity and size is affected by batch size, reduction conditions like holding temperature and time.  During sintering with SPS; heating and cooling rates, sintering temperature, holding pressure and time were the main variables. Grain size and morphology was analyzed using SEM. It was observed that larger the grain size higher will be the thermal diffusivity, which leads to increase in thermal conductivity. Hence, grain size has affected on thermal conductivity and also on TE performance.
QC 20100708

The optical properties of planar semiconductor microstructures and three-dimensional nanostructures containing narrow linewidth In₀.₀₄Ga₀.₉₆As quantum wells are studied in this dissertation. The interaction of quantum-well excitons with light in environments different from free space gives a pronounced effect on the optical response. N periodically arranged quantum wells are coupled to each other by light leading to N exciton-polariton eigenmodes. Each eigenmode is characterized by a distinct energy and radiative lifetime depending on the periodicity of the quantum wells. For a period of about half the excitonic transition wavelength, linear measurements of reflection, transmission, and absorption show significant features of the light-coupled eigenmodes. At Bragg periodicity, the oscillator strengths of all quantum well excitons are concentrated into one superradiant mode resulting in an N times increased radiative decay rate. The slope of the reflectivity linewidths versus N gives the radiative linewidth of the quantum well exciton. For off-Bragg periodicity, however, other eigenmodes become optically active and show their features in reflection and absorption spectra. Oxide-aperture three-dimensional nanocavities containing a single quantum well are investigated. The discrete transverse modes due to the lateral confinement of the optical field are observed in empty cavities with various aperture sizes. The linewidth measurements of the cavity modes show quality-factor values around 2000 for aperture diameters down to 2 μm. This is high enough to give a strong light-coupling effect in the nonperturbative regime, named normal mode coupling or vacuum Rabi splitting. The anti-crossing behavior of exciton and cavity modes for a 2 μm diameter aperture cavity is measured in transmission by temperature tuning of the exciton resonance through the lowest transverse cavity mode. A minimum splitting value of 3.9 meV and a splitting-to-linewidth ratio of 4.9 are obtained. Then, nonlinear pump-probe measurements on nanocavities with several aperture sizes are performed. The transition from the nonperturbative regime to the weak coupling regime is observed as the pump power increases. From the measured saturation powers for various aperture diameters, a photon density of 90 photons/μm² is found necessary to saturate the normal-mode peaks. The effect of quantum fluctuations of the light field in the nonperturbative regime of planar semiconductor microcavities containing quantum wells is studied. A pronounced third transmission peak lying spectrally between the two normal modes is observed in resonant single-beam-transmission and pump-probe measurements. Measurements on three-dimensional nanocavities confirm the important role of guided modes for this intriguing effect.

Research studies on systems with reduced size and dimensionality have attracted great attention for the past two decades. This is mainly driven by industrial development, which demands the fabrication of new, small, well-controlled devices as well as the desire to understand quantum effects which manifest in these small structures.
In this thesis we theoretically investigate quantum coherent transport properties of nano structures in the form of molecular electronic systems. Our approach is based on Landauer-Buttiker transport theory. However, the details of the method depend on the interaction complexity.
We have carried out detailed analysis on finite length carbon nanotubes based magnetic tunnel junction using tight binding atomic model and Green's function approach. This device shows clear spin valve effect even when contacted with the same ferro-magnetic material with a long spin scattering length. In addition to this, transport at the atomic level is highly affected by the molecular states resulting in conductance oscillation of finite size arm-chair carbon nanotube as a function of its length.
When short carbon nanotubes are weakly contacted to external leads, they act as quantum dots with strong interaction at the molecular scale. To analyse these systems, we have developed a many-body wave function formalism which include spin degeneracy. This approach clearly shows the strong dependence of the device electronic response on the number of electrons already inside the tube.
Finally, we have carried out ab initio analysis based on Density Functional Theory within Local Density Approximations to investigate the current-voltage (I-V) characteristics of various gold nanowires. Our results demonstrate that transport properties of these systems crucially depend on the electronic properties of the scattering region, the leads, and most importantly the interaction of the scattering region with the leads. For ideal, clean Au contacts, the theoretical results indicate a linear I-V behavior. However, when sulfur impurities exist at the contact junction, nonlinear I-V curves emerge due to a tunnelling barrier established in the presence of the S atom. The most striking observation is that even a single S atom can cause a qualitative change of the I-V curve from linear to nonlinear.
Our theoretical results were compared to experimental data, qualitative and sometimes quantitative understanding of the experiments are obtained.

UV-LIGA is a microfabrication process realzed by material deposition through microfabricated molds. UV photolithography is conducted to pattern precise thick micro molds using UV light sensitive materials, mostly SU-8, and electroforming is performed to fabricate micro metallic structures defined by the micro molds. Therefore, UV-LIGA is a bottom-up in situ material-addition process. UV-LIGA has received broad attention recently than LIGA – a micro molding fabrication process using X-ray to pattern the micro molds. LIGA is an expansive and is limited in access. In comparing to LIGA, the UV-LIGA is a cost effective process, and is widely accessible and safe. Therefore, it has been extensively used for the fabrication of metallic micro-electro-mechanical-systems (MEMS). The motivation of this research was to study micro mechanical systems fabricated with nano-structured metallic materials via UV-LIGA process. Various micro mechanical systems with high-aspect-ratio and thick metallic structures have been developed and are presented in this desertation. A novel micro mechanical valve has been developed with nano-structured nickel realized with UV-LIGA fabrication technique. Robust compact valves are crucial for space applications where payload and rubstaness are critically concerned. Two types of large flow rate robust passive micro check valve arrays have been designed, fabricated and tested for robust hydraulic actuators. The first such micro valve developed employs nanostructured nickel as the valve flap and single-crystal silicon as the substrates to house inlet and outlet channels. The Nano-structured nickel valve flap was fabricated using the UV-LIGA process developed and the microchannels were fabricated by deep reactive etching (DRIE) method. The valves were designed to operate under a high pressure (>10MPa), able to operate at high frequencies (>10kHz) in cooperating with the PZT actuator to produce large flow rates (>10 cc/s). The fabricated microvalves weigh 0.2 gram, after packing with a novel designated valve stopper. The tested results showed that the micro valve was able to operate at up to 14kHz. This is a great difference in comparison to traditional mechanical valves whose operations are limited to 500 Hz or less. The advantages of micro machined valves attribute to the scaling laws. The second type of micro mechanical valves developed is a in situ assembled solid metallic (nickel) valves. Both the valve substrates for inlet and outlet channels and the valve flap, as well as the valve stopper were made by nickel through a UV-LIGA fabrication process developed. Continuous multiple micro molds fabrication and molding processes were performed. Final micro mechanical valves were received after removing the micro molds used to define the strutures. There is no any additional machining process, such as cutting or packaging. The alignment for laminated fabrication was realized under microscope, therefore it is a highly precise in situ fabrication process. Testing results show the valve has a forward flow rate of19 cc/s under a pressure difference of 90 psi. The backward flow rate of 0.023 cc/s, which is negligible (0.13%). Nano-structured nickel has also been used to develop laminated (sandwiched) micro cryogenic heater exchanger with the UV-LIGA process. Even though nickel is apparently not a good thermal conductor at room temperature, it is a good conductor at cryogentic temerpature since its thermal conductivity increases to 1250 W/k·m at 77K. Micro patterned SU-8 molds and electroformed nickel have been developed to realize the sandwiched heat exchanger. The SU-8 mold (200mm x 200mm x50mm) array was successfully removed after completing the nickel electroforming. The second layer of patterned SU-8 layer (200mm x 200mm x50mm, as a thermal insulating layer) was patterned and aligned on the top of the electroformed nickel structure to form the laminated (sandwiched) micro heat exchanger. The fabricated sandwiched structure can withstand cryogenic temperature (77K) without any damages (cracks or delaminations). A study on nanocomposite for micro mechanical systems using UV-LIGA compatible electroforming process has been performed. Single-walled carbon nanotubes (SWNTs) have been proven excellent mechanical properties and thermal conductive properties, such as high strength and elastic modulus, negative coefficient of thermal expansion (CTE) and a high thermal conductivity. These properties make SWNT an excellent reinforcement in nanocomposite for various applications. However, there has been a challenge of utilizing SWNTs for engineering applications due to difficulties in quality control and handling – too small (1-2nm in diameter). A novel copper/SWNT nanocomposite has been developed during this dissertational research. The goal of this research was to develop a heat spreader for high power electronics (HPE). Semiconductors for HPE, such as AlGaN/GaN high electron mobility transistors grown on SiC dies have a typical CTE about 4~6x10-6/k while most metallic heat spreaders such as copper have a CTE of more than 10x10-6/k. The SWNTs were successfully dispersed in the copper matrix to form the SWNT/Cu nano composite. The tested composite density is about 7.54 g/cm3, which indicating the SWNT volumetric fraction of 18%. SEM pictures show copper univformly coated on SWNT (worm-shaped structure). The measured CTE of the nanocomposite is 4.7 x 10-6/°C, perfectly matching that of SiC die (3.8 x 10-6/°C). The thermal conductivity derived by Wiedemann-Franz law after measuring composit's electrical conductivity, is 588 W/m-K, which is 40% better than that of pure copper. These properties are extremely important for the heat spreader/exchanger to remove the heat from HPE devices (SiC dies). Meanwhile, the matched CTE will reduce the resulted stress in the interface to prevent delaminations. Therefore, the naocomposite developed will be an excellent replacement material for the CuMo currently used in high power radar, and other HPE devices under developing. The mechanical performance and reliability of micro mechanical devices are critical for their application. In order to validate the design & simulation results, a direct (tensile) test method was developed to test the mechanical properties of the materials involved in this research, including nickel and SU-8. Micro machined specimens were fabricated and tested on a MTS Tytron Micro Force Tester with specially designed gripers. The tested fracture strength of nanostructured nickel is 900±70 MPa and of 50MPa for SU-8, resepctively which are much higher than published values.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering

Conjugated polymers are novel organic electronic materials highly important for organic photovoltaic applications. Charge transport is one of the key properties which defines the performance of conjugated polymers in electronic devices. This work aims to explore the charge transport anisotropy in thin films of P3HT, one of the most common conjugated polymers. Using X-ray diffraction techniques and charge transport measurements, the relation between vertical charge transport through thin P3HT films and structure of the films was established. It was shown that particular orientations of crystalline domains of P3HT, namely face-on and chain-on, are beneficial for vertical charge transport. These orientations provide the efficient pathways for the charges to be transported vertically, either via π-π stacking interaction between the adjacent conjugated chains, or via the conjugated chain backbones. It was also demonstrated that particular orientations of crystallites are favourable for the formation of interconnected percolated pathways providing enhanced vertical charge transport across the film. Deposition of P3HT on most commonly used silicon substrates typically results in the formation of mostly edge-on orientation of crystallites which is unfavourable for vertical charge transport. Nanoimprint lithography was demonstrated as a powerful processing method for reorienting the edge-on crystalline domains of P3HT into chain-on (vertical) orientation. It is also shown that thin P3HT films with preferentially face-on orientations of crystallites can be deposited on graphene surface by spin coating. Using patterning of thin P3HT films by nanoimprint lithography, unprecedentedly high average vertical mobilities in the range of 3.1-10.6 cm2 V-1 s-1 were achieved in undoped P3HT. These results demonstrate that charge transport in thin films of a relatively simple and well-known conjugated polymer P3HT can be significantly improved using optimization of crystallinity,orientation of crystallites, polymer chain orientation and alignment in the films.

With the semiconductor industry racing toward a historic transition, nano chips with less than 45 nm features demand I/Os in excess of 20,000 with multi-core processors aggregately providing highest bandwidth at lowest power. On the other hand, emerging mixed signal systems are driving the need for 3D packaging with embedded active components and ultra-short interconnections. Being able to provide several fold increase in the chip-to-package vertical interconnect density is essential for garnering the true benefits of nanotechnology that will utilize nano-scale devices. Electrical interconnections are multi-functional materials that must also be able to withstand complex, sustained and cyclic thermo-mechanical loads. Device- to- system board interconnections are typically accomplished today with either wire bonding or solders. Both of these are incremental and run into either electrical or mechanical barriers as they are extended to higher interconnections densities. Downscaling traditional solder bump interconnect will not satisfy the thermo-mechanical reliability requirements at very fine pitches. Other approaches such as compliant interconnects require lengthy connections and are limited in terms of electrical properties. A novel chip-package interconnection technology is developed to address the IC packaging requirements and to introduce innovative design and fabrication concepts that will further advance the performance of the chip, the package, and the system board. The nano-structured interconnect technology simultaneously packages all the ICs intact in wafer form with quantum jump in the number of interconnections with the lowest electrical parasitics. The intrinsic properties of nano materials also enable several orders of magnitude higher interconnect densities with the best mechanical properties for the highest reliability and yet provide higher current and heat transfer densities. This thesis investigates the electrical and mechanical performance of nano-structured interconnections through modeling and test vehicle fabrication. Test vehicles with nano-interconnections were fabricated using low cost electro-deposition techniques and assembled with various bonding interfaces. Interconnections were fabricated at 200 micron pitch to compare with the existing solder joints and at 50 micron pitch to demonstrate fabrication processes at fine pitches. Experimental and modeling results show that the proposed nano-interconnections could enhance the reliability and potentially meet all the system performance requirements for the emerging micro/nano-systems.