Nanomechanics emerged as chemists and physicists began fabricating nanoscale objects. However, there are some materials that have neither been fabricated nor mechanical investigated at the nanoscale, such as rhodium. Rhodium is used in many applications, especially in coatings and catalysis. To contribute to the understanding the nano-properties of this important material, rhodium was fabricated and mechanically investigated at the nanoscale. The nanopillars approach was employed to study size effects on mechanical properties. Nanopillars with different diameters were fabricated using electroplating followed by uniaxial compression tests. SEM was used as a quality control technique by imaging the pillars before and after compression to assure the absence of buckling, barrelling, or any other problems. Transmission electron microscopy (TEM) and SEM were used as microstructural characterization techniques, and the energy-dispersive X-ray spectroscopy (EDX) was used as the chemical characterization technique. Due to substrate induced effects, only the plastic region of the stress-strain curves were investigated, and it was revealed that rhodium softens with decreased nanopillar diameter. This softening/weakening effect was due to the nanocrystallinity of the fabricated pillars. This effect is consistent with the literature that demonstrates the reversed size effect of nanocrystalline metals, i.e., smaller is weaker. Further studies should focus on eliminating the substrate effect that was due to the adhesion layers between Rh and the silicon substrate being softer than Rh, consequently, causing Rh to sink into the adhesion layer when compressed and thus perturbing the stress-strain curve. Moreover, further investigation of other properties of Rh is required to achieve a comprehensive understanding of Rh at the nanoscale, and to render it suitable for specific, multivariable applications.

One-dimensional and hierarchical nanostructures have acquired tremendous attention in the past decades due to their possible application. In spite of the rapid emergence of new morphologies, the underlying growth mechanism is still not well understood. The lack of effective p-type or n-type doping is another obstacle for many semiconducting nanomaterials. A deeper investigation into these structures and new methods to fabricate devices are of significant impact for nanoscience and nanotechnology. Motivated by a desire to understand the growth mechanism of nanostructures and investigate novel device fabrication method, the research described in this thesis carried out on the synthesis, characterization, and device fabrication of semiconducting nanostructures. The main focus of the research was on ZnO, SnO2, and Zn3P2 for their great capability for fundamental phenomena studying, promising applications in sensors and optoelectronics, and the potential generalization of results to other materials. Within this study the following goals have been achieved: 1) Improved understanding of polar-surface-induced growth mechanism in wurtzite-structured ZnO and generalization of this growth mechanism with the discovery and analysis of rutile ¨Cstructured SnO2, 2) observation of the significance of the transversal growth, which is usually ignored, in interpenetrative ZnO nanowires, 3) rational design and growth control over versatile nanostructures of ZnO and Zn3P2, and 4) conjunction of p-type Zn3P2 and n-type ZnO semiconducting nanostructures for device fabrications. The framework for the research is reviewed first in chapter 1. Chapter 2 gives the detailed experimental setup, synthesis procedure, and common growth mechanism for nanostructure growth. A detailed discussion on the growth of ZnO nanostructures in chapter 3 provides more insight into the polar-surface-induced growth, transversal growth, vapor-solid growth, and vapor-liquid-solid growth during the formation of nanostructures. Polar-surface-induced growth is also confirmed in the growth of SnO2 nanostructures, which is also included in chapter 2. Chapter 3 presents Zn3P2 nanostructures from the newly designed experiment setup and the device fabrication from ZnO and Zn3P2 crossed nanowires.

In this work, the use of theoretical tools of molecular modeling for tailoring 1D novel nanomaterials is demonstrated. There are four selected nano-structures as examples, each tailored for a specic demand of nano-technology that is yet to be fullled. For the purpose of modeling/calculating the electronic and structural properties, various methods of dening the interatomic interaction, such as empirical potential energy functions, semi-empirical methods and density functional theory, are used. Each of these methods have a dierent level of approximations leading to limitations in their use. Furthermore, each method needs to be calibrated carefully in order to obtain physically meaningful results. Examples being novel nano-structures, there does not exist any experimental observations directly studying the material at hand. Thus, in order to obtain a parameter set that best describes the system, a series of pre-existing structures that are physically and/or chemically related are used. Among the methods employed, the density functional theory (DFT) is certainly the most popular one, due to its accuracy and more importantly the framework it provides for perturbative extensions otherwise nearly impossible to calculate in Hartree-Fock level.

The UV-Visible spectra of a-C composites and nano composites have provided a very useful information about the electronic states and band structure. The UV-Visible spectra of a-C as well as nanoparticle are qualitatively similar. They do not show any absorption cutoff in wavelength (_max). In fact they are good absorbers of UV-Visible light in whole range. Composites show some absorptions which could be the combined effect of filler as we as host matrix. Since there is no _max, hence it is very unlikely to define any optical band gap. The nanoparticle is a good absorber in midinfrared compared to a-C. That may be due to presence of complicated kind of vibrational modes of carbon cased nanoparticle.Besides Fe3C also produces some additional modes. With kind of spectrum we have it is difficult to identify the different modes unambiguously for nanoparticle. The combined effects of filler as well as host polymer are reflected in both sets of composites. A new absorption is observed in a-C as well as in nanoparticle composites at 2370 cm−1 and 3462 cm−1 respectively. This peak may arise in composites due to interaction between filler and host matrix. The thermo gravimetric analysis is a useful characterization techniques for polymer and composites. It gives the information about the stability, phase change, degradation, chemical reaction and many more. The a-C composites as well as nano composites are stable up to 200_ C. These composites can be safely used for any practical purpose below this temperature. During the synthesis of composites the filler does not take part in any reaction. This fact is reflected in the DTG curve. The composites degrade in the way host polymer degrades.

Nanocomposite thin films with gold nanoparticles embedded in a host metal oxide prepared by spray pyrolysis deposition have been investigated. A single-step process has been developed using a one-pot solution containing precursors for both gold nanoparticles and host metal oxides. The films obtained display combined features of colouration, electrical conductivity and solar control. In this study two precursors for gold nanoparticles were used: preformed gold colloids and HAuCl₄. Three metal oxide host materials, TiO₂, SnO₂ and ZnO, were investigated. These films were deposited at a substrate temperature of 200-600 °C. Powder X-ray diffraction analysis reveals the presence of metallic gold. SEM inspection typically showed particulate gold of 5-20 nm in diameter, distributed at the surface or within the host matrix. Optical spectroscopy showed an intense absorption in the visible region due to the characteristic surface plasmon resonance (SPR) effects of gold nanoparticles. The wavelength of the SPR peaks varies depending on the refractive index of surrounding host material which is significantly influenced by the substrate deposition temperature. On the other hand, SnO₂ and ZnO, together with the introduction of dopants, were further investigated as suitable materials for transparent conducting oxides (TCO). SnO₂:F films were found to attain very low electrical resistivity, while ZnO films exhibit higher transparency in the visible. A double layered structure with a TCO layer of SnO₂:F on top of a layer embedded with gold nanoparticles has been employed to achieve the combined functionalities of conductivity and colouration. The electrical conductivity is significantly enhanced compared to a nanocomposite single layer film due to the introduction of the TCO top layer. In this thesis, spray pyrolysis deposition has demonstrated a simple and rapid approach to the production of a variety of thin films. It can be immediately integrated with current industrial coating equipment and scaled up for large-scale production process.

As silicon-based transistor technology continues to scale ever downward, anticipation of the fundamental limitations of ultimately-scaled devices has driven research into alternative device technologies as well as new materials for interconnects and packaging. Additionally, as power dissipation becomes an increasingly important challenge in highly miniaturized devices, both the implementation and verification of high mobility, high thermal conductivity materials, such as low dimensional carbon nanomaterials, and the experimental investigation of heat transfer in the nanoscale regime are requisite to continued progress. This work furthers the current understanding of structure-property relationships in low dimensional carbon nanomaterials, specifically carbon nanotubes (CNTs) and graphene, through use of combined thermal conductance and transmission electron microscopy (TEM) measurements on the same individual nanomaterials suspended between two micro-resistance thermometers. Through the development of a method to measure thermal contact resistance, the intrinsic thermal conductivity, [kappa], of multi-walled (MW) CNTs is found to correlate with TEM observed defect density, linking phonon-defect scattering to the low [kappa] in these chemical vapor deposition (CVD) synthesized nanomaterials. For single- (S) and double- (D) walled (W) CNTs, the [kappa] is found to be limited by thermal contact resistance for the as-grown samples but still four times higher than that for bulk Si. Additionally, through the use of a combined thermal transport-TEM study, the [kappa] of bi-layer graphene is correlated with both crystal structure and surface conditions. Theoretical modeling of the [kappa] temperature dependence allows for the determination that phonon scattering mechanisms in suspended bi-layer graphene with a thin polymeric coating are similar to those for the case of graphene supported on SiO₂. Furthermore, a method is developed to investigate heat transfer through a nanoscale point contact formed between a sharp silicon tip and a silicon substrate in an ultra high vacuum (UHV) atomic force microscope (AFM). A contact mechanics model of the interface, combined with a heat transport model considering solid-solid conduction and near-field thermal radiation leads to the conclusion that the thermal resistance of the nanoscale point contact is dominated by solid-solid conduction. / text

Nanotechnology is an increasing market. Engineered nanoparticles (NPs), materials with at least one dimension between 1 and 100 nm, are produced on a large scale. NPs are vastly used in industrial processes and consumer products and they are most likely discharged into wastewater treatment plants after being used. Activated Sludge is one of the most applied biological wastewater treatment processes for the degradation of organic matter in sewage. Activated sludge produces an excess of sludge that is commonly treated and stabilized by anaerobic digestion. Recent studies have found that NPs accumulate in the activated sludge; thus, there is a potential for the concentrations of NPs to magnify as concentrated waste sludge is fed into the anaerobic digestion process. For this reason, it is important to study the possible toxic effects of NPs on the microorganisms involved in the anaerobic digestion process and the approaches to overcome toxicity if necessary. The present work evaluates the toxic effect of NPs on anaerobic wastewater treatment processes and also presents approaches for toxicity attenuation. The first objective of this dissertation (Chapter III) was to evaluate the toxicity of high concentrations (1, 500 mg L⁻¹) of Ag⁰, Al₂O₃, CeO₂, Cu⁰, CuO, Fe⁰, Fe₂O₃, Mn₂O₃, SiO₂, TiO₂, and ZnO NPs to acetoclastic and hydrogenotrophic methanogens and the effect of a dispersant on the NPs toxicity to methanogens. The findings indicated that only Cu⁰ and ZnO NPs caused severe toxicity to hydrogenotrophic methanogens and Cu⁰, CuO, and ZnO NPs to acetoclastic methanogens. The dispersant did not impact the NPs toxicity. The concentrations of Cu⁰ and ZnO causing 50% of inhibition (IC₅₀) to hydrogenotrophic methanogens were 68 and 250 mg L⁻¹, respectively. Whereas the IC₅₀ values for acetoclastic methanogens were 62, 68, and 179 for Cu⁰, ZnO, and CuO-Cu NPs respectively. These findings indicate that acetoclastic methanogens are more sensitive to NP toxicity compared to hydrogenotrophic methanogens and that Cu⁰ and ZnO NPs are highly toxic to both. Additionally, it was observed that the toxicity of any given metal was highly correlated with its final dissolved concentration in the assay irrespective of whether it was initially added as a NP or chloride salt, indicating that corrosion and dissolution of metals from NPs may have been responsible for the toxicity. The second objective of this dissertation (Chapter IV) was to evaluate the Cu⁰ NP toxicity to anaerobic microorganisms of wastewater treatment processes. Cu⁰ is known to be toxic to methanogens; nonetheless, little is known about its toxic effects on microorganisms of upper trophic levels of anaerobic digestion or other anaerobic process used for nitrogen removal. This specific objective evaluated Cu⁰ NP toxicity to glucose fermentation, syntrophic propionic oxidation, methanogenesis, denitrification and anaerobic ammonium oxidation (anammox). Chapter IV showed that anammox and glucose fermentation were the least and most inhibited processes with inhibition constants (K(i)) values of 0.324 and 0.004 mM of added Cu⁰ NPs, respectively. The Ki values obtained from the residual soluble concentration of the parallel experiments using CuCl₂ indicated that Cu⁰ NP toxicity is most likely caused by the release of soluble ions for each one of the microorganisms tested. The results taken as a whole demonstrate that Cu⁰ NPs are toxic to a variety of anaerobic microorganisms of wastewater treatment processes. The third objective of this document (Chapter V) was to study the role of biogenic sulfide in attenuating Cu⁰ and ZnO NP toxicity to acetoclastic methanogens. Previous literature results and research presented in this dissertation indicated that the release of soluble ions from Cu and ZnO NPs cause toxicity to methanogens. In the past, the application of sulfide to precipitate heavy metals as inert non-soluble sulfides was used to attenuate the toxicity of Cu and Zn salts. Building on this principle, Chapter V evaluated the toxicity of Cu⁰ and ZnO NPs in sulfate-containing (0.4 mM) and sulfate-free conditions. The results show that Cu⁰ and ZnO were 7 and 14x less toxic in sulfate-containing than in sulfate-free assays as indicated by the differences in K(i) values. The K(i) values obtained based on the residual metal concentration of the sulfate-free and sulfate-containing assays were very similar, indicating that the toxicity is well correlated with the release of soluble ions. Overall, this study demonstrated that biogenic sulfide is an effective attenuator of Cu⁰ and ZnO NP toxicity to acetoclastic methanogens. Finally, the last objective (Chapter VI) of this dissertation was to evaluate the effect of iron sulfide (FeS) on the attenuation of Cu⁰ and ZnO toxicity to acetoclastic methanogens. FeS is formed by the reaction of iron(II) and sulfide. This reaction is common in anaerobic sediments where the reduction of iron(III) to iron(II) and sulfate to sulfide occurs. FeS plays a key role controlling the soluble concentrations of heavy metals and thus their toxic effects in aquatic sediments. This study evaluated the application of FeS as an approach to attenuate Cu⁰ and ZnO NP toxicity and their salt analogs to acetoclastic methanogens. Two particle sizes, coarse FeS (FeS-c, 500-1200 µm) and fine FeS (FeS-f, 25-75 µm) were synthesized and used in this study. The results showed 2.5x less FeS-f than FeS-c was required to recover the methanogenic activity to the same extent from the exposure to highly inhibitory concentrations of CuCl₂ and ZnCl₂ (0.2 mM). The results also showed that a molar ratio of FeS-f/Cu⁰, FeS-f/ZnO, FeS-f/Zn Cl₂, and FeS-f/CuCl₂ of 3, 3, 6, and 12 respectively, was necessary to provide a high recovery of methanogenic activity (>75%). The excess of FeS needed to overcome the toxicity indicates that not all the sulfide in FeS was readily available to attenuate the toxicity. Overall, Chapter VI demonstrated that FeS is an effective attenuator of the toxicity of Cu⁰ NP and ZnO NPs and their salt analogs to methanogens, albeit molar excesses of FeS were required.

<p>Nano-structures were investigated for the advancement of energy conversion technology because of their enhanced catalytic, thermal, and physiochemical interfacial properties and increased solar absorption. Hydrogen is a widely investigated and proven fuel and energy carrier for promising "green" technologies such as fuel cells. Difficulties involving storage, transport, and availability remain challenges that inhibit the widespread use of hydrogen fuel. For these reasons, in-situ hydrogen production has been at the forefront of research in the renewable and sustainable energy field. A common approach for hydrogen generation is the reforming of alcoholic and hydrocarbon fuels from fossil and renewable sources to a hydrogen-rich gas mixture.</p><p>Unfortunately, an intrinsic byproduct of any fuel reforming reaction is toxic and highly reactive CO, which has to be removed before the hydrogen gas can be used in fuel cells or delicate chemical processes. In this work, Au/alpha-Fe2O3 catalyst was synthesized using a modified co-precipitation method to generate an inverse catalyst model. The effects of introducing CO2 and H2O during preferential oxidation (PROX) of CO were investigated. For realistic conditions of (bio-)fuel reforming, 24% CO2 and 10% water the highest document conversion, 99.85% was achieved. The mechanism for PROX is not known definitively, however, current literature believes the gold particle size is the key. In contrast, we emphasize the tremendous role of the support particle size. A particle size study was performed to have in depth analysis of the catalysts morphology during synthesis. With this study we were also able to modify how the catalyst was made to further reduce the particle size of the support material leading to ~99.9% conversion. We also showed that the resulting PROX output gas could power a PEM fuel cell with only a 4% drop in power without poisoning the membrane electrode assembly.</p><p> The second major aim of this study is to develop an energy-efficient technology that fuses photothermal catalysis and plasmonic phenomena. Although current literature has claimed that the coupling of these technologies is impossible, here we demonstrate the fabrication of reaction cells for plasmon-induced photo-catalytic hydrogen production. The localized nature of the plasmon resonance allows the entire system to remain at ambient temperatures while a high-temperature methanol reformation reaction occurs at the plasmonic sites. Employing a nanostructured plasmonic substrate, we have successfully achieved sufficient thermal excitement (via localized surface plasmon resonance (LSPR)) to facilitate a heterogeneous chemical reaction. The experimental tests demonstrate that hydrogen gas can indeed be generated in a cold reactor, which has never been done before. Additionally, the proposed method has the highest solar absorption out of several variations and significantly reduces the cost, while increasing the efficiency of solar fuels.</p> / Dissertation

Au nanoparticles are increasingly being used in biological applications. Their use is of interest based upon their unique properties that are achieved at the nanoscale, which includes strong optical absorbances that are size and aggregation state dependent. Such absorbances can be used in sensitive chemical/biological detection schemes where bioligands can be directly attached to the nanoparticle surface using facile methods. Unfortunately, a number of complications persist that prevent their wide-scale use. These limitations include minimal nanoparticle stability in biological-based media of high ionic strength, unknown surface functionalization effects using simple biomolecules, and determining the binding motifs of the ligands to the nanoparticle surface. This situation can be further complicated when employing shaped materials where crystallographic facets can alter the binding potential of the bioligands. We have attempted to address these issues using traditional nanoparticle functionalization techniques that are able to be characterized using readily available analytical methods. By exploiting the optical properties of Au nanomaterials, we have been able to determine the solution stability of Au nanorods in a buffered medium and site-specifically functionalized Au nanomaterials of two different shapes: spheres and rods. Such abilities are hypothesized to be intrinsic to the bioligand once bound to the surface of the materials. Our studies have focused mainly on simple amino acids that have demonstrated unique assembly abilities for the materials in solution, resulting in the formation of specific patterns. The applications for such capabilities can range from the use of the materials as sensitive biochemical sensors to their directed assembly for use as device components.

Pour répondre aux nouvelles contraintes économiques et environnementales auxquelles l'industrie doit faire face aujourd'hui, des techniques de frittage rapide se développent pour la fabrication des céramiques. Parmi elles, une technique prometteuse est le frittage par micro-ondes dans laquelle le champ électromagnétique à l'origine du chauffage pourrait permettre d'obtenir des microstructures innovantes, tout en réduisant la température, le temps de cycle et la consommation énergétique. Pour expliquer le comportement particulier des poudres en présence des micro-ondes, différentes théories prévoyant des effets thermiques ou non-thermiques ont été proposées. L'existence même de ces effets n'a cependant toujours pas été démontrée de façon sûre, notamment à cause des limites des dispositifs expérimentaux qui ne permettent pas une comparaison pertinente du frittage micro-ondes avec le frittage conventionnel. Dans ce contexte, les travaux réalisés pendant cette thèse, dans le cadre du projet ANR Fµrnace, ont été consacrés à la mise en évidence et à la compréhension de l'influence du champ électromagnétique sur les mécanismes responsables de la densification et de l'évolution microstructurale de poudres céramiques. Une forte attention a été portée au développement technologique de la cavité de chauffage micro-ondes monomode utilisée dans nos recherches. Le procédé a été entièrement automatisé et équipé de divers systèmes de contrôle de la température et du retrait des échantillons pour que les résultats obtenus puissent être comparés de façon incontestable avec ceux issus d'essais de frittage conventionnel. Des simulations numériques ont été réalisées pour améliorer la compréhension de la propagation du champ électromagnétique et de son interaction avec les éléments introduits au sein de la cavité micro-ondes. Un matériau de référence, l'alumine, a été choisi et l'influence de certaines caractéristiques des poudres (surface spécifique, présence de dopants, transformation de phase) sur les cinétiques de densification et l'évolution microstructurale a été étudiée. Les résultats obtenus ont permis d'identifier des effets spécifiques des micro-ondes sur les mécanismes de diffusion responsables de la densification et de la croissance granulaire. Ces effets se produisent principalement pendant les stades initial et intermédiaire du frittage, ainsi que pendant la transformation de phase de poudres de transition et ont été attribués à une force de type pondéromotrice déjà proposée dans la littérature. L'utilisation de cette technique de frittage n'a cependant pas permis d'obtenir des alumines avec des microstructures plus performantes que celles issues du frittage conventionnel. / To meet the new economic and environmental constraints that the industry faces today, fast sintering processes are developed for the fabrication of ceramics. Among them, a promising technique is microwave sintering, in which the electromagnetic field at the origin of heating could be used to obtain innovative microstructures, while reducing sintering temperature, cycle time and energy consumption. To explain the particular behavior of powders under microwaves, different hypotheses related with thermal or non-thermal effects have been proposed in the literature. These effects, however, has not really been demonstrated for the moment, especially because of the limits of experimental devices that do not allow for a meaningful comparison of microwave sintering with conventional sintering. In this context, the work performed during this thesis in the framework of FμRNACE ANR project has been dedicated to identifying and understanding the influence of the electromagnetic field on the mechanisms of densification and microstructure changes in ceramic powders. High attention has been paid to the technological development of the single-mode microwave cavity used in our research. The heating process has been fully automated and instrumented with various equipments allowing for temperature and sample shrinkage measurement. The aim was to ensure direct and reliable comparison of microwave sintering data with those resulting from conventional sintering. Numerical simulation has been conducted to improve our understanding of the propagation of the electromagnetic field and its interaction with the components introduced in the microwave cavity. Alumina has been chosen as a reference material and the influence of several features of the powders (specific surface area, doping elements, phase transformation) on densification kinetics and microstructure changes has been studied. The results have identified specific effects of microwaves on the mechanisms controlling densification and grain growth. These effects occur essentially during the initial and intermediate stages of sintering and during the phase transformation of transition powders. They have been attributed to the ponderomotive force as already proposed in the literature. However the use of microwaves as a heating mode does not permit obtaining alumina with better microstructures than those resulting from conventional sintering.