This thesis addresses the design and use of suitable nanomaterials and surface acoustic wave sensors for hydrogen detection and sensing. Nanotechnology is aimed at design and synthesis of novel nanoscale materials. These materials could find uses in the design of optical, biomedical and electronic devices. One such example of a nanoscale biological system is a virus. Viruses have been given a lot of attention for assembly of nanoelectronic materials. The tobacco mosaic virus (TMV) used in this research represents an inexpensive and renewable biotemplate that can be easily functionalized for the synthesis of nanomaterials. Strains of this virus have been previously coated with metals, silica or semiconductor materials with potential applications in the assembly of nanostructures and nanoelectronic circuits. Carbon nanotubes are another set of well-characterized nanoscale materials which have been widely investigated to put their physical and chemical properties to use in design of transistors, gas sensors, hydrogen storage cells, etc. Palladium is a well-known material for detection of hydrogen. The processes of absorption and desorption are known to be reversible and are known to produce changes in density, elastic properties and conductivity of the film. Despite these advantages, palladium films are known to suffer from problems of peeling and cracking in hydrogen sensor applications. They are also required to be cycled for a few times with hydrogen before they give reproducible responses. The work presented in this thesis, takes concepts from previous hydrogen sensing techniques and applies them to two nanoengineered particles (Pd coated TMV and Pd coated SWNTs) as SAW resonator sensing materials. Possible sensing enhancements to be gained by using these nanomaterial sensing layers are investigated. SAW resonators were coated with these two different nano-structured sensing layers (Pd-TMV and Pd-SWNT) which produced differently useful hydrogen sensor responses. The Pd-TMV coated resonator responded to hydrogen with nearly constant increases in frequency as compared to the Pd-SWNT coated device, which responded with concentration-dependent decreases in frequency of greater magnitude upon hydrogen exposure. The former behavior is more associated with acousto-electric phenomena in SAW devices and the later with mass loading. The 99% response times were 30-40 seconds for the Pd-TMV sensing layer and approximately 150 seconds for the Pd-SWNT layer. Both the films showed high robustness and reversibility at room temperature. When the Pd film was exposed to hydrogen it was observed that it produced decreases in frequency to hydrogen challenges, conforming to mass loading effect. It was also observed that the Pd film started degrading with repeated exposure to hydrogen, with shifts after each exposure going smaller and smaller.

Face à la recrudescence de l'utilisation des nanotubes de carbone (NTCs) pour des applications de pointe, leur impact potentiel sur la santé et sur l'environnement est devenu une question centrale. Afin d'évaluer les risques liés à l'exposition accidentelle des êtres-vivants à ces nanoparticules de nombreuses études de toxicité ont été réalisées. Pour certaines, il est important de pouvoir déterminer précisément où et comment les NTCs s'accumulent dans les organismes aquatiques ou dans les cellules. Un des moyens habituel pour réaliser de telles expériences consiste à fonctionnaliser les NTCs avec des molécules fluorescentes, qui seront par la suite mises en évidence sous un rayonnement de longueur d'onde appropriée, permettant ainsi de localiser les nanotubes. Malgré le fait que cette technique soit bon marché et facilement mise en œuvre, elle souffre d'un défaut majeur: elle présuppose en effet que les molécules fluorescentes resteront attachées aux nanotubes de façon définitive. Cependant, cette supposition peut être sérieusement questionnée car les fluorophores possèdent généralement un ou plusieurs cycles aromatiques pouvant facilement conduire à l'adsorption de ces derniers sur les parois des NTCs. Dès lors, une fois que les NTCs atteignent l'environnement chimique complexe d'une cellule, on peut s'attendre à une désorption des molécules fluorescentes, pouvant de fait conduire à de mauvaises interprétations des résultats expérimentaux. Il est par conséquent essentiel d'évaluer l'efficacité du protocole de greffage et de déterminer les différentes proportions de molécules greffées de façon covalente et non-covalente (adsorbées). Bien entendu, la fonctionnalisation des NTCs étant une problématique clef dans le développement de leurs applications en science des matériaux, les questions soulevées ici dépassent le simple cadre de la santé et de l'environnement. Pour y répondre, nous avons décidé de nous intéresser à la fonctionnalisation de nanotubes de carbone double-parois (DWNTs) par deux molécules fluorescentes, l'Isothiocyanate de Fluorescéine (FITC) et la cyanine 5Me(Net2)2. Nous avons, pour ce faire, réaliser le greffage des fluorophores sur des DWNTs oxydés purifiés à l'aide d'un procédé de fonctionnalisation en 3 étapes. Enfin, nous avons caractérisé nos échantillons au moyen de deux techniques différentes de spectroscopie, la spectroscopie de photoélectron X (XPS) et la spectroscopie de diffusion inélastique de neutrons (INS). En complément de la spectroscopie de neutrons, nous nous sommes appuyés sur des simulations numériques, telle que la théorie de la fonctionnelle de la densité (DFT) pour les analyses de nos données expérimentales. Les résultats ainsi obtenus, ont permis de montrer que, contrairement à ce qui était communément attendu lors d'un greffage covalent, une part non négligeable des marqueurs fluorescent restait adsorbée à la surface des NTCs, et ce, en dépit de lavages consciencieux par des solvants appropriés. La présence de ces marqueurs fluorescents adsorbés montre, dans le cadre des études de toxicité, qu'il existe une certaine probabilité que ces derniers se détachent des NTCs lors de leur voyage dans un organisme ou dans une cellule, ce qui conduirait l'établissement de conclusions potentiellement erronées quant au destin de ces nanoparticules. / Facing the growing use of carbon nanotubes (CNTs) in state-of-the-art applications, the question of their potential impact on health and environment became a central one. In order to evaluate the risks related to living being exposure to those nanoparticles, several toxicity studies have been performed aiming at knowing the exact location of the CNTs accumulating inside organisms or cells. A very common way to track them in such conditions is to functionalize the CNTs with fluorescent molecules which would be highlighted afterwards under a light with appropriate exciting wavelength. Despite the fact that these fluorescence techniques are very cheap and easy to operate, they suffer from a major drawback: they assumes that the fluorescent molecule is permanently linked to the CNTs. It is however reasonable to question this assumption as the fluorescent molecules are usually constituted by one or more 6-carbon rings that can easily also simply adsorb on the surface of the CNTs. This non-covalent binding could lead to the desorption of the fluorophore once the CNTs reach the complex chemical environment of a living cell or organism. Therefore, the fluorescence data could lead to wrong information about the CNTs location. Therefore, it is fundamental to understand the grafting mechanisms in order to estimate the efficiency of the covalent functionalization of the CNTs as well as the amount of simply adsorbed fluorophores. Of course, the impact of such a question clearly exceeds the field of the health and the environment, because the functionalization of CNTs is a key for their application is Materials Science in general. In order to answer to these questions, we chose to study the functionalization of Double-Walled carbon Nanotubes (DWNTs) with two different fluorophores, the Fluorescein Isothiocyanate (FITC) and the STREPTOcyanine 5Me(Net2)2. We used a three-step functionalization process to graft the fluorophores on highly-purified oxidized DWNTs. Finally, both the surface and the bulk of the sample have been investigated using two different spectroscopic techniques, the X-ray photoelectron spectroscopy (XPS) and the inelastic neutron scattering spectroscopy (INS). In addition to neutron techniques we also used computational techniques such as Density Functional Theory (DFT) calculations for a better analysis of our results. The results obtained by means of this two powerful techniques highlighted that, although the fluorescent markers is always considered to be strongly bonded onto carbon nanotubes when using a covalent strategy, a non-negligible part may in fact be only adsorbed, even after thorough washings in appropriate solvents. This is likely, in the particular field of toxicology, to lead to a release of the fluorescent marker at some point along the journey of the nanoparticle throughout the cells or the whole organism, and thus to partially wrong conclusions in terms of their fate in terms of biodistribution, accumulation or excretion.

Casimir forces originating from vacuum fluctuations of the electromagnetic fields are of increasing importance in many scientific and technological areas. The manifestations of these long-range forces at the nanoscale have led to the need of better understanding of their contribution in relation to the stability of different physical systems as well as the operation of various technological components and devices. This dissertation presents mathematical and theoretical methods to calculate the Casimir interaction in various infinitely long cylindrical nanostructures. A dielectric-diamagnetic cylindrical layer immersed in a medium is first considered. The layer has a finite thickness characterized with specific dielectric and magnetic properties. Another system considered is that of perfectly conducting concentric cylindrical shells immersed in a medium. The electromagnetic energy between two infinitely long straight parallel dielectric-diamagnetic cylinders immersed in a medium is also considered. The mode summation method is used to calculate the Casimir energy of all these systems. The energy dependence on the cylindrical radial curvature and dielectric response of the cylinders is investigated. The fundamental effects of these long range interactions are studied in the form of exciton-plasmon interactions in carbon nanotubes and this is achieved by looking at the dielectric response of carbon nanotubes.

Carbon is a fascinating element which can be observed in a large variety of morphologies and atomic structures due to its chemical ability to form different hybridizations. The present PhD thesis proposes the synthesis of several carbon-based materials using a unique and quite simple technique: the oxy-acetylene combustion flame method. From crystalline sp3- diamond to planar sp2- graphite, from the unidirectional nanotubes, needles and rods to bidimensional petals, a large variety of carbon materials are synthesized under the atmospheric pressure. These various carbon forms have been produced using a set of different experimental parameters. Both the input gas ratio and the substrate temperature are found to play a key role in the synthesis of these new carbon materials. The high quality of the graphitic phases can be correlated to the large acetylene content in the gas and to the high temperature of the substrate. Some specific morphologies such as petal-like single graphite crystals have been synthesized. Their sizes reach up to 20 mm. These bidimensional carbon materials are of particular importance to investigate fundamental physics in ideal low-dimensional systems. Polyhedral graphite crystals, which exhibit a unidirectional morphology, have also been produced. Their crystal structure is found to be highly graphitic although they display a cylindrical/polyhedral shape. Preliminary measurements of their field emission properties reveal a huge emission current, which is higher than the emission current obtained for multi-wall carbon nanotubes. The latter have also been synthesized in large amount and high quality using our oxy-acetylene combustion flame technique. At last, using again the same experimental set-up, a crystalline carbon nitride phase has been synthesized for the first time using a specific molecule called “melamine” as an organic precursor. Several experimental techniques, such as Energy Dispersive X-ray (EDX), X-ray Photoelectron Spectroscopy (XPS), Electron Energy Loss Spectroscopy (EELS), X-ray diffraction and Raman and infra-red spectroscopies have been used to analyze both the chemical composition and the crystalline structure of this new material, revealing a graphitic-C3N4 phase.

This research is aimed at synthesizing millimeter-scale carbon nanotube arrays (CNTA) by conventional chemical vapor deposition (CCVD) and water-assisted chemical vapor deposition (WACVD) methods, and exploring their application as catalyst supports for electrochemical supercapacitors. The growth mechanism and growth kinetics of CNTA under different conditions were systematically investigated to understand the relationship among physical characteristics of catalyst particles, growth parameters, and carbon nanotube (CNT) structures within CNTAs. Multiwalled CNT (MWCNT) array growth demonstrates lengthening and thickening stages in CCVD and WACVD. In CCVD, the lengthening and thickening were found to be competitive. By investigating catalyst particles after different pretreatment conditions, it has been found that inter-particle spacing plays a significant role in influencing CNTA height, CNT diameter and wall number. In WACVD, a long linear lengthening stage has been found. CNT wall number remains constant and catalysts preserve the activity in this stage, while MWCNTs thicken substantially and catalysts deactivate following the previously proposed radioactive decay model in the thickening stage of WACVD. Water was also shown to preserve the catalyst activity by significantly inhibiting catalyst-induced and gas phase-induced thickening processes in WACVD. Mn3O4 nanoparticles were successfully deposited and uniformly distributed within millimeter-long CNTAs by dip-casting method from non-aqueous solutions. After modification with Mn3O4 nanoparticles, CNTAs have been changed from hydrophobic to hydrophilic without their alignment and integrity being destroyed. The hydrophilic Mn3O4/CNTA composite electrodes present ideal capacitive behavior with high reversibility. This opens up a new route of utilizing ultra-long CNTAs, based on which a scalable and cost-effective method was developed to fabricate composite electrodes using millimeter-long CNTAs. To improve the performance of the composites, -MnO2 nanorods were anodically pulse-electrodeposited within hydrophilic 0.5 mm-thick Mn3O4 decorated CNTAs. The maximum gravimetric capacitance for the MnO2 nanorods/CNTA composite electrode was found to be 185 F/g, and that for -MnO2 nanorods was determined to be 221 F/g. After electrodeposition, the area-normalized capacitance and volumetric capacitance values were increased by a factor of 3, and an extremely high area-normalized capacitance of 1.80 F/cm2 was also achieved for the MnO2 nanorods/CNTA composite. / Materials Engineering

Carbon nanotubes (CNTs) have been a major interest of study since 1991. A panel of properties and phenomena associated with carbon nanotubes due to their special combination of dimension, structure and topology have been investigated in the last years. Recently, it appears interesting to use carbon nanotubes at low loading content to obtain materials with enhanced mechanical and thermal properties. One of the major challenges is actually to disperse easily and individually these nanotubes in polymer matrices to obtain materials with increased properties for different application uses. Ethylene-vinyl acetate (EVA) copolymer is commonly used in cable industry. It is required to introduce high contents of alumina trihydrate (ATH) or magnesium dihydroxide (MDH) as fire retardant, to avoid fire hazards and reduce flammability. But this high mineral loading results in a decrease of the mechanical performances of the materials. This work aims at studying the influence of the incorporation of multiwall carbon nanotubes (MWNTs) on the tensile properties and the fire behavior of EVA nanocomposites. This work demonstrates, on one side, the significant effect of the previous nanotube coating by a thin layer of high density polyethylene (HDPE-coating) on the mechanical behavior of the so-obtained nanocomposites and explain, on the other side, the flame retardant efficiency of MWNTs in EVA nanocomposites. An original mechanism related to the action of the MWNTs during the combustion process is proposed and the effect of the HDE-coating on the cohesion of the residues is discussed.

Since their first observation in 1991, carbon nanotubes (CNTs) have attracted a lot of attention owing to their exceptional properties. Their excellent electrical and thermal conducting performances combined with their high toughness and transverse flexibility allow their use in a large range of varied applications. Offering at the same time a high aspect ratio (length-to-diameter) and a low density, carbon nanotubes show strong application potential in reinforced composite materials. Unfortunately, CNTs have the strong tendency to form bundles very difficult to dissociate and disperse in a majority of polymer matrices. Without efficient CNTs dispersion, nanocomposites can not present optimal mechanical, thermal and electrical properties. To overcome this drawback, one solution consists to graft polymer chains on the carbon nanotubes surface in order to disaggregate bundles and, in few cases, to improve interaction between the polymer matrix and nanotubes. The thesis work can be divided into three parts. The first is the one-step amination of multi-walled carbon nanotubes (MWNTs) via an original microwave plasma process. The MWNTs, placed in the post-discharge chamber in presence of H2, are subjected to a reactive flow of atomic nitrogen produced by the plasma. The results give evidence for efficient covalent grafting of primary amine groups along the sidewalls of MWNTs, avoiding any structural damage and alteration of properties. The so-grafted amine groups have been further consider as initiation sites for promoting the ring opening polymerization of lactone monomers yielding polyester-grafted MWNT nanohybrids. Finally, these nanohybrids have been used as highly filled masterbatches to be dispersed in the molten state within several polymer matrices, such as polycaprolactone (PCL) and high density polyethylene (HDPE), to obtain nanocomposites with largely improved properties. For instance, electrical measurements and morphological characterizations showed that the polyester surface-grafting allows for improving the dispersion state of the nanotubes in the different polymer matrices leading to enhanced electrical properties as well as thermal and mechanical performances.

Transparent electrodes made from metal oxides suffer from poor flexibility and durability. Highly transparent and electrically conductive thin films based on carbon nanotubes (CNTs) were assembled as a potential indium tin oxide (ITO) replacement using layer-by-layer (LbL) assembly. The ultimate objective of this dissertation work is to produce CNT-based assemblies with sheet resistance below 100 Omega/sq and visible light transmission greater than 85 percent. The alternate deposition of positively charged poly(diallyldimethylammonium chloride) [PDDA] and CNTs stabilized with negatively charged deoxycholate (DOC) exhibit linear film growth and thin film properties can be precisely tuned. Ellipsometry, quartz crystal microbalance, and UV-vis were used to measure the growth of these films as a function of PDDA-CNT bilayers deposited, while TEM, SEM, and AFM were used to visualize the nanostructure of these films. Following a literature review describing potential ITO substitutes and LbL technology, the influence of CNT type on optoelectronic performance of LbL assemblies is described. Three different types of nanotubes were investigated: (1) multiwalled carbon nanotubes (MWNTs), (2) few-walled carbon nanotubes (FWNT), and (3) purified single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (>85 percent visible light transmittance) and electrically conductive (148 S/cm, 1.62 kOmega/sq) 20-bilayer films with a 41.6 nm thickness, while MWNT-based films are much thicker and more opaque. A 20-bilayer PDDA/(MWNT DOC) film is approximately 103 nm thick, with a conductivity of 36 S/cm and a transmittance of 30 percent. In an effort to improve both transparency and electrical conductivity, heat and acid treatments were studied. Heating films to 300 degree C reduced sheet resistance to 701 Omega/sq (618 S/cm conductivity, 38.4 nm thickness), with no change in transparency, owing to the removal of insulating component in the film. Despite improving conductivity, heating is not compatible with most plastic substrates, so acid doping was investigated as an alternate means to enhance properties. Exposing SWNT-based assemblies to HNO3 vapor reduced sheet resistance of a 10 BL film to 227 Omega/sq. Replacing SWNTs with double walled carbon nanotubes (DWNTs) provided further reduction in sheet resistance due to the greater metallic of DWNT. A 5 BL DWNT film exhibited the lowest 104 Omega/sq sheet resistance (4200 S/cm conductivity, 22.9 nm thickness) with 84 percent transmittance after nitric acid treatment. DWNT-based assemblies maintained their low sheet resistance after repeated bending and also showed electrochemical stability relative to ITO. This work demonstrates the excellent optoelectronic performance, mechanical flexibility, and electrochemical stability of CNT-based assemblies, which are potentially useful as flexible transparent electrodes for a variety of flexible electronics.

An investigation was conducted towards the development and optimization of low electrical resistivity carbon nanotube (CNT) and thermoplastic composites as potential materials for future wire and cable applications in aerospace and energy exploration. Fundamental properties of the polymer, medium density polyethylene (MDPE), such as crystallinity were studied and improved for composite use. A parallel effort was undertaken on a broad selection of CNT, including single wall, double wall and multi wall carbon nanotubes, and included research of material aspects relevant to composite application and low resistivity such as purity, diameter and chirality. With an emphasis on scalability, manufacturing and purification methods were developed, and a solvent-based composite fabrication method was optimized. CNT MDPE composites were characterized via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Raman spectroscopy, and multiple routes of electron microscopy. Techniques including annealing and pressure treatments were used to further improve the composites' resulting electrical performance. Enhancement of conductivity was explored via exposure to a focused microwave beam. A novel doping method was developed using antimony pentafluoride (SbF 5 ) to reduce the resistivity of the bulk CNT. Flexible composites, malleable under heat and pressure, were produced with exceptional electrical resistivities reaching as low as 2*10 -6 Ω·m (5*10 5 S/m). A unique gas sensor application utilizing the unique electrical resistivities of the produced CNT-MDPE composites was developed. The materials proved suitable as a low weight and low energy sensing material for dimethyl methylphosphonate (DMMP), a nerve gas simulant.

Photophysical, electronic, and compositional properties of single-walled carbon nanotubes (SWCNTs) and bulk nanotube samples were investigated together with graphene oxide photoluminescence. First, we studied the effect of external electric fields on SWCNT photoluminescence. Fields of up to 10 7 V/m caused dramatic, reversible decreases in emission intensity. Quenching efficiency was proportional to the projection of the field on the SWCNT axis, and showed inverse correlation with optical band gap. The magnitude of the effect was experimentally related to exciton binding energy, as consistent with a proposed field-induced exciton dissociation model. Further, the electronic composition of various SWCNT samples was studied. A new method was developed to measure the fraction of semiconducting nanotubes in as- grown or processed samples. SWCNT number densities were compared in images from near-IR photoluminescence (semiconducting species) and AFM (all species) to compute the semiconducting fraction. The results provide important information about SWCNT sample compositions that can guide controlled growth methods and help calibrate bulk characterization techniques. The nature of absorption backgrounds in SWCNT samples was also studied. A number of extrinsic perturbations such as extensive ultrasonication, sidewall functionalization, amorphous carbon impurities, and SWCNT aggregation were applied and their background contributions quantified. Spectral congestion backgrounds from overlapping absorption bands were assessed with spectral modeling. Unlike semiconducting nanotubes, metallic SWCNTs gave broad intrinsic absorption backgrounds. The shape of the metallic background component and its absorptivity coefficient were determined. These results can be used to minimize and evaluate SWCNT absorption backgrounds. Length dependence of SWCNT optical properties was investigated. Samples were dispersed by ultrasonication or shear processing, and then length-fractionated by gel electrophoresis or controlled ultrasonication shortening. Fractions from both methods showed no significant absorbance variations with SWCNT length. The photoluminescence intensity increased linearly with length, and the relative quantum yield gradually increased, approaching a limiting value. Finally, a strong pH dependence of graphene oxide photoluminescence was observed. Sharp and structured excitation/emission features resembling the spectra of molecular fluorophores were obtained in basic conditions. Based on the observed pH-dependence and quantum calculations, these spectral features were assigned to quasi-molecular fluorophores formed by the electronic coupling of oxygen-containing addends with nearby graphene carbon atoms.